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Sample records for intramolecular friedel-crafts cyclization

  1. An efficient and green synthesis of 1-indanone and 1-tetralone via intramolecular Friedel-Crafts acylation reaction

    DEFF Research Database (Denmark)

    Tran, Phuong Hoang; Huynh, Vy Hieu; Hansen, Poul Erik

    2015-01-01

    Metal-triflate-catalyzed intramolecular Friedel–Crafts acylation of 3-arylpropanoic and 4-arylbutanoic acids in triflate-anion ionic liquids under monomodal microwave irradiation is reported. The environmentally benign synthetic procedure allows the formation of cyclic ketones in good yields with...... a short reaction time. The catalytic metal triflate in triflate-anion ionic liquids can be easily recovered and reused several times without significant loss of the catalytic performance....

  2. Greener Friedel-Crafts Acylation using Microwave-enhanced reactivity of Bismuth Triflate in the Friedel-Crafts Benzoylation of Aromatic Compounds with Benzoic Anhydride

    DEFF Research Database (Denmark)

    Tran, Phuong Hoang; Nguyen, Hai Truong; Hansen, Poul Erik

    2017-01-01

    An efficient and facile bismuth trifluoromethanesulfonate-catalyzed benzoylation of aromatic compounds using benzoic anhydride under solvent-free microwave irradiation has been developed. The microwave-assisted Friedel-Crafts benzoylation results in good yields within short reaction times. Bismuth...

  3. Poly(vinyl chloride-grafted multi-walled carbon nanotubes via Friedel-Crafts alkylation

    Directory of Open Access Journals (Sweden)

    2010-11-01

    Full Text Available A novel approach was developed for the surface modification of the multi-walled carbon nanotubes (MWCNTs with high percentage of grafting (PG% by the grafting of polymer via the Friedel-Crafts alkylation. The graft reaction conditions, such as the amount of catalyst added, the reaction temperature, and the reaction time were optimized for the Friedel-Crafts alkylation of the MWCNTs with poly(vinyl chloride (PVC with anhydrous aluminum chloride (AlCl3 as catalyst in chloroform (CHCl3. The Fourier Transform Infrared (FT-IR, Raman, and thermogravimetric (TGA analysis showed that PVC had been successfully grafted onto MWCNTs both at the ends and on the sidewalls by the proposed Friedel-Crafts alkylation. The PVC grafted MWCNTs (PVC-MWCNTs could be dispersed well in organic solvent and the dispersion was more stable.

  4. Friedel-Crafts Alkylation Using Elemental Aluminum Catalyst: An Undergraduate Laboratory Experiment.

    Science.gov (United States)

    Meeks, B. Spencer; Lucas, Anita R.

    1989-01-01

    Provides methodology for carrying out the synthesis of sec-butyltoluene by the Friedel-Crafts alkylation of toluene. Suggests using simple elemental aluminum as the catalyst in place of AlCl3 or amalgamated aluminum. Notes satisfactory results for both macro- and microscale operations. (MVL)

  5. Pi-activated alcohols: an emerging class of alkylating agents for catalytic Friedel-Crafts reactions.

    Science.gov (United States)

    Bandini, Marco; Tragni, Michele

    2009-04-21

    The direct functionalization of aromatic compounds, via Friedel-Crafts alkylation reactions with alcohols, is one of the cornerstones in organic chemistry. The present emerging area deals with the recent advances in the use of pi-activated alcohols in the catalytic and stereoselective construction of benzylic stereocenters.

  6. Heterocycles by Transition Metals Catalyzed Intramolecular Cyclization of Acetylene Compounds

    International Nuclear Information System (INIS)

    Vizer, S.A.; Yerzhanov, K.B.; Dedeshko, E.C.

    2003-01-01

    Review shows the new strategies in the synthesis of heterocycles, having nitrogen, oxygen and sulfur atoms, via transition metals catalyzed intramolecular cyclization of acetylenic compounds on the data published at the last 30 years, Unsaturated heterocyclic compounds (pyrroles and pyrroline, furans, dihydro furans and benzofurans, indoles and iso-indoles, isoquinolines and isoquinolinones, aurones, iso coumarins and oxazolinone, lactams and lactones with various substitutes in heterocycles) are formed by transition metals, those salts [PdCl 2 , Pd(OAc) 2 , HgCl 2 , Hg(OAc) 2 , Hg(OCOCF 3 ) 2 , AuCl 3 ·2H 2 O, NaAuCl 4 ·2H 2 O, CuI, CuCl], oxides (HgO) and complexes [Pd(OAc) 2 (PPh 3 )2, Pd(PPh 3 ) 4 , PdCl 2 (MeCN) 2 , Pd(OAc ) 2 /TPPTS] catalyzed intramolecular cyclization of acetylenic amines, amides, ethers, alcohols, acids, ketones and βdiketones. More complex hetero polycyclic systems typical for natural alkaloids can to obtain similar. Proposed mechanisms of pyrroles, isoquinolines, iso indoles and indoles, benzofurans and iso coumarins, thiazolopyrimidinones formation are considered. (author)

  7. DNA-Accelerated Copper Catalysis of Friedel-Crafts Conjugate Addition/Enantioselective Protonation Reactions in Water

    NARCIS (Netherlands)

    García-Fernández, Almudena; Megens, Rik P.; Villarino, Lara; Roelfes, Gerard

    2016-01-01

    DNA-induced rate acceleration has been identified as one of the key elements for the success of the DNA-based catalysis concept. Here we report on a novel DNA-based catalytic Friedel-Crafts conjugate addition/enantioselective protonation reaction in water, which represents the first example of a

  8. Cu(I)-Catalyzed Enantioselective Friedel-Crafts Alkylation of Indoles with 2-Aryl-N-sulfonylaziridines as Alkylating Agents.

    Science.gov (United States)

    Ge, Chen; Liu, Ren-Rong; Gao, Jian-Rong; Jia, Yi-Xia

    2016-07-01

    A highly enantioselective Friedel-Crafts alkylation of indoles with N-sulfonylaziridines as alkylating agents has been developed by utilizing the complex of Cu(CH3CN)4BF4/(S)-Segphos as a catalyst. A range of optically active tryptamine derivatives are obtained in good to excellent yields and enantioselectivities (up to >99% ee) via a kinetic resolution process.

  9. Efficient intramolecular cyclizations of phenoxyethynyl diols into multisubstituted α,β-unsaturated lactones.

    Science.gov (United States)

    Egi, Masahiro; Ota, Yuya; Nishimura, Yuka; Shimizu, Kaori; Azechi, Kenji; Akai, Shuji

    2013-08-16

    AgOTf-catalyzed intramolecular cyclization of phenoxyethynyl diols proceeded under mild conditions to afford the multisubstituted α,β-unsaturated-γ-lactones in 55-98% yields. This method was also applicable to the synthesis of α,β-unsaturated-δ-lactones. A similar cyclization proceeded when AgOTf was replaced with a stoichiometric amount of N-bromosuccinimide to furnish the α-bromo-substituted α,β-unsaturated lactones.

  10. Potassium hydroxide/dimethyl sulfoxide promoted intramolecular cyclization for the synthesis of benzimidazol-2-ones.

    Science.gov (United States)

    Beyer, Astrid; Reucher, Christine M M; Bolm, Carsten

    2011-06-03

    A new protocol for intramolecular N-arylations of ureas to form benzimidazol-2-ones has been developed. The cyclization reaction occurs in the presence of KOH and DMSO at close to ambient temperature. Under these conditions the yields are high and a wide range of functional groups are tolerated.

  11. Double Friedel-Crafts acylation reactions on the same ring of a metallocene: synthesis of a 2,5-diacetylphospharuthenocene.

    Science.gov (United States)

    Carmichael, Duncan; Le Floch, Pascal; Le Goff, Xavier F; Piechaczyk, Olivier; Seeboth, Nicolas

    2010-12-27

    The synthetic outcome of the Friedel-Crafts acylation of 1',2',3,3',4,4',5'-heptamethylphospharuthenocene reflects the nature of the acylating agent, with alkanoyl anhydride/trifluoromethanesulfonic acid (TfOH) reagents giving monosubstitution at the phospholyl ring, whereas alkanoyl chloride/AlCl(3) gives 2,5-disubstitution. DFT calculations indicate that this unusual double acylation can be facilitated by the intervention of the phosphorus atom at an early stage in the reaction trajectory, with the acyl group being delivered from the phosphorus atom into the ring 2- or 2,5-positions.

  12. New amidines from intramolecular cyclization in triflic acid of ...

    Indian Academy of Sciences (India)

    TECS

    2007-05-22

    May 22, 2007 ... or the conversion of esters deriva- tives. 15 have also been reported. Recently, we reported the cyclization of 1-benzyl- amino-1-methylsulfanyl-2-nitroethenes in triflic acid leading to formation of the corresponding diazadi- hydroacenaphthylene derivatives with an isoxazo- line ring. 16. In the present paper ...

  13. A novel mesoporous sulfated zirconium solid acid catalyst for Friedel-Crafts benzylation reaction

    Energy Technology Data Exchange (ETDEWEB)

    Miao, Zhichao; Zhou, Jin; Zhao, Jinping; Liu, Dandan; Bi, Xu [School of Chemical Engineering, Shandong University of Technology, Zibo, 255049 (China); Chou, Lingjun, E-mail: ljchou@licp.cas.cn [State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000 (China); Zhuo, Shuping, E-mail: zhuosp_academic@yahoo.com [School of Chemical Engineering, Shandong University of Technology, Zibo, 255049 (China)

    2017-07-31

    Highlights: • A novel mesoporous ZrO{sub 2}/SO{sub 4}{sup 2−} has been prepared via a facile one-pot EISA strategy. • The M-ZrO{sub 2}/SO{sub 4}{sup 2−} exhibited excellent textural and acidic properties. • The introduced S species were homogeneously dispersed in mesoporous skeleton. • The M-ZrO{sub 2}/SO{sub 4}{sup 2−} exhibited excellent catalytic performance and reusability. - Abstract: In this paper, a novel mesoporous sulfated zirconium (M-ZrO{sub 2}/SO{sub 4}{sup 2−}) has been gotten by one-pot evaporation-induced self-assembly (one-pot EISA) strategy. The SXRD, N{sub 2}-physisorption and TEM characterization techniques indicated that M-ZrO{sub 2}/SO{sub 4}{sup 2−} possessed distinct mesostructure with big specific surface area (133.5 m{sup 2} g{sup −1}), large pore volume (0.18 cm{sup 3} g{sup −1}) and narrow pore size distribution (4.90 nm). Moreover, the existing states and the influence in mesostructure of introduced S species were detailedly investigated by the XRD, N{sub 2}-physisorption, TEM, TG-DSC, FT-IR and XPS techniques and the results showed that the S species, which existed as the type of SO{sub 4}{sup 2−}, improved the textural properties of prepared materials. In addition, the NH{sub 3}-TPD and IR spectra of adsorbed pyridine indicated the existence of strong Brønsted and Lewis acid sites in M-ZrO{sub 2}/SO{sub 4}{sup 2−} even evacuated at 400 °C. Furthermore, the M-ZrO{sub 2}/SO{sub 4}{sup 2−} was used as a promise solid acid catalyst and displayed excellent catalytic performance and reusability in Friedel-Crafts benzylation reaction.

  14. Facile approach to enantiomerically pure alpha-amino ketones by Friedel-Crafts aminoacylation and their conversion into peptidyl ketones.

    Science.gov (United States)

    Di Gioia, M L; Leggio, A; Liguori, A; Napoli, A; Siciliano, C; Sindona, G

    2001-10-19

    In this article we describe a versatile and straightforward preparative approach to chiral aryl alpha-amino ketones via a Friedel-Crafts-type reaction of stable and enantiomerically pure N-Fmoc protected L-amino acid chlorides with toluene in the presence of aluminum trichloride. The developed methodology provided aryl alpha-amino-p-methylphenyl ketones, which can be obtained and isolated as free bases or recovered as their N-acetyl derivatives, after treatment with acetic anhydride in chloroform at room temperature, subsequent to the Lewis acid induced removal of the 9-fluorenylmethoxycarbonyl protecting group. The Friedel-Crafts-like process and the cleavage of the amino function masking group can selectively be performed since, as verified in all cases, the alpha-aminoacylation step occurred with kinetics that were faster than those required to remove the N-protection. The presented approach was also explored as a facile and useful synthetic tool for the preparation of optically pure ketone di- and tripeptides. These compounds can be obtained in exceptionally overall yields without need of chromatographic purification. Moreover, either aryl alpha-amino ketones or modified di- and tripeptides, in all cases, can be isolated in very high chemical and optical purity without recourse to resolution of diastereomeric mixtures, since the chiralities of the asymmetric amino acid educts were completely conserved throughout the entire process.

  15. A Research-Based Undergraduate Organic Laboratory Project: Investigation of a One-Pot, Multicomponent, Environmentally Friendly Prins-Friedel-Crafts-Type Reaction

    Science.gov (United States)

    Dintzner, Matthew R.; Maresh, Justin J.; Kinzie, Charles R.; Arena, Anthony F.; Speltz, Thomas

    2012-01-01

    Students in the undergraduate organic laboratory synthesize tetrahydro-2-(4-nitrophenyl)-4-phenyl-2"H"-pyran via the Montmorillonite K10 clay-catalyzed reaction of p-nitrobenzaldehye with methanol, 3-buten-1-ol, and benzene. The synthesis comprises an environmentally friendly tandem Prins-Friedel-Crafts-type multicomponent reaction (MCR) and sets…

  16. Metal halide hydrates as lewis acid catalysts for the conjugated friedel-crafts reactions of indoles and activated olefins

    Energy Technology Data Exchange (ETDEWEB)

    Schwalm, Cristiane S.; Ceschi, Marco Antonio; Russowsky, Dennis, E-mail: dennis@iq.ufrgs.b [Universidade Federal do Rio Grande do Sul (IQ/UFRGS), Porto Alegre, RS (Brazil). Inst. de Quimica

    2011-07-01

    Metal halide hydrates such as SnCl{sub 2{center_dot}}2H{sub 2}O, MnCl{sub 2{center_dot}}4H{sub 2}O, SrCl{sub 2{center_dot}}6H{sub 2}O, CrCl{sub 2{center_dot}}6H{sub 2}O, CoCl{sub 2{center_dot}}6H{sub 2}O e CeCl{sub 3{center_dot}}7H{sub 2}O were investigated as mild Lewis acids catalysts for the conjugate Friedel-Crafts reaction between indoles and activated olefins. The reactions were carried out with aliphatic unsaturated ketones over a period of days at room temperature, while chalcones reacted only under reflux conditions. The reactions with nitrostyrene s were either performed in solvent or under solventless conditions. In all cases reasonable to good yields were obtained. (author)

  17. Methanetrisulfonic Acid: A Highly Efficient Strongly Acidic Catalyst for Wagner-Meerwein Rearrangement, Friedel-Crafts Alkylation and Acylation Reactions. Examples from Vitamin E Synthesis

    Directory of Open Access Journals (Sweden)

    Francesco Pace

    2009-04-01

    Full Text Available Methanetrisulfonic acid had been prepared for the first time over 140 years ago, but it was used only scarcely in chemical transformations. In the course of our activities dealing with key-steps of industrial syntheses of vitamins, e.g. economically important vitamin E (acetate, we found that methanetrisulfonic acid is an extremely effective catalyst in a variety of reactions. Examples of its applications are Wagner-Meerwein rearrangements, Friedel-Crafts alkylations and ring closures, as well as acylation reactions. Use of this catalyst in truly catalytic amounts (0.04-1.0 mol% resulted in highly selective transformations and yields over 95%. (Remark by the authors: We are describing only one example each for the various types of reactions. Therefore, it would be more appropriate to write (here and in the Introduction and in the Conclusion sections: “Wagner-Meerwein rearrangement, Friedel-Crafts alkylation and ring closure, as well as acylation reactions”

  18. AlCl₃·6H₂O-Catalyzed Friedel-Crafts Alkylation of Indoles by the para-Quinone Methide Moiety of Celastrol.

    Science.gov (United States)

    Zhu, Yi; Chen, Ziwen; Huang, Zhenfei; Yan, Siwei; Li, Zhuoer; Zhou, Hu; Zhang, Xiaokun; Su, Ying; Zeng, Zhiping

    2017-05-16

    A classical Friedel-Crafts alkylation of different indoles catalyzed by AlCl₃·6H₂O has been developed for a well-known important natural product, celastrol, resulting in a series of derivatives for further biological evaluation. The catalyst loading was reduced to 5 mol %, the reaction proceeds at ambient temperature and reaction time is only 3 h. The product yields range from 20% to 99%. A reaction mechanism is also proposed, based on our experiment results.

  19. Synthesis and Characterization of AlCl3 Impregnated Molybdenum Oxide as Heterogeneous Nano-Catalyst for the Friedel-Crafts Acylation Reaction in Ambient Condition.

    Science.gov (United States)

    Jadhav, Arvind H; Chinnappan, Amutha; Hiremath, Vishwanath; Seo, Jeong Gil

    2015-10-01

    Aluminum trichloride (AlCl3) impregnated molybdenum oxide heterogeneous nano-catalyst was prepared by using simple impregnation method. The prepared heterogeneous catalyst was characterized by powder X-ray diffraction, FT-IR spectroscopy, solid-state NMR spectroscopy, SEM imaging, and EDX mapping. The catalytic activity of this protocol was evaluated as heterogeneous catalyst for the Friedel-Crafts acylation reaction at room temperature. The impregnated MoO4(AlCl2)2 catalyst showed tremendous catalytic activity in Friedel-Crafts acylation reaction under solvent-free and mild reaction condition. As a result, 84.0% yield of acyl product with 100% consumption of reactants in 18 h reaction time at room temperature was achieved. The effects of different solvents system with MoO4(AlCl2)2 catalyst in acylation reaction was also investigated. By using optimized reaction condition various acylated derivatives were prepared. In addition, the catalyst was separated by simple filtration process after the reaction and reused several times. Therefore, heterogeneous MoO4(AlCl2)2 catalyst was found environmentally benign catalyst, very convenient, high yielding, and clean method for the Friedel-Crafts acylation reaction under solvent-free and ambient reaction condition.

  20. Synthesis of Chiral TFA-Protected α-Amino Aryl-Ketone Derivatives with Friedel-Crafts Acylation of α-Amino Acid N-Hydroxysuccinimide Ester.

    Science.gov (United States)

    Tachrim, Zetryana Puteri; Oida, Kazuhiro; Ikemoto, Haruka; Ohashi, Fumina; Kurokawa, Natsumi; Hayashi, Kento; Shikanai, Mami; Sakihama, Yasuko; Hashidoko, Yasuyuki; Hashimoto, Makoto

    2017-10-17

    Chiral N -protected α-amino aryl-ketones are one of the useful precursors used in the synthesis of various biologically active compounds and can be constructed via Friedel-Crafts acylation of N -protected α-amino acids. One of the drawbacks of this reaction is the utilization of toxic, corrosive and moisture-sensitive acylating reagents. In peptide construction via amide bond formation, N -hydroxysuccinimide ester (OSu), which has high storage stability, can react rapidly with amino components and produces fewer side reactions, including racemization. This study reports the first synthesis and utilization of N -trifluoroacetyl (TFA)-protected α-amino acid-OSu as a potential acyl donor for Friedel-Crafts acylation into various arenes. The TFA-protected isoleucine derivative and its diastereomer TFA-protected allo -isoleucine derivative were investigated to check the retention of α-proton chirality in the Friedel-Crafts reaction. Further utilization of OSu in other branched-chain and unbranched-chain amino acids results in an adequate yield of TFA-protected α-amino aryl-ketone without loss of optical purity.

  1. Friedel-Crafts Polyketones: Synthesis, Characterization and Antimicrobial Properties of Unsaturated Polyketones and Copolyketones Based on Difurfurylidene Cycloheptanone

    Directory of Open Access Journals (Sweden)

    Nayef S. Al-Muaikel

    2011-01-01

    Full Text Available A new type of unsaturated polyketones and copolyketones having cycloheptanone moiety in a p-conjugated main chain were synthesized via Friedel-Crafts reaction through the polymerization of the monomer: 2,7-bis furfurylidene cycloheptanone I with different diacid chlorides. The model compound was synthesized by reacting I with benzoyl chloride and characterized by 1H-NMR, IR, and elemental analyses. The polyketones and copolyketones were soluble easily in protic solvents like H2SO4 and trifluoroacetic acid. The thermal properties of these polyketones and copolyketones were evaluated and correlated to their structural units by TGA and DSC measurements. The crystallinity of some polymers was tested by X-ray analyses; also the morphological properties of selected examples of poly and copolyketones were detected by SEM. All the polyketones were tested for their biological activity against bacteria, fungi, and yeast. It was observed that the majority of the polyketones and its copolymers synthesized can be used as antibacterial and antifungal agents.

  2. Cu(3)(BTC)(2) as a viable heterogeneous solid catalyst for Friedel-Crafts alkylation of indoles with nitroalkenes.

    Science.gov (United States)

    Nagaraj, Anbu; Amarajothi, Dhakshinamoorthy

    2017-05-15

    In the present work, Friedel-Crafts alkylation reaction of indole with β-nitrostyrene is examined using a readily available copper based metal-organic frameworks (MOFs) namely, Cu 3 (BTC) 2 (BTC: 1,3,5-benzenetricarboxylic acid) as solid catalyst under mild reaction conditions. Among the various catalysts screened for this reaction, Cu 3 (BTC) 2 exhibits higher activity under the optimized reaction conditions. Besides the absence of leaching of active sites, it is also observed that the catalyst can be reused for four cycles with a minimal decrease in its activity. Cu 3 (BTC) 2 is used as a catalyst to synthesise a series of heterocyclic compounds with different indole and β-nitrostyrene derivatives in moderate to high yields. The present catalytic system shows comparable activity against to recent reports but the advantage of Cu 3 (BTC) 2 is that it does not require any post-functionalization and above all it can be readily synthesised, thus contributing to the synthesis of heterocyclic compounds with high biological interest. Copyright © 2017 Elsevier Inc. All rights reserved.

  3. Micro-Cu4I4-MOF: reversible iodine adsorption and catalytic properties for tandem reaction of Friedel-Crafts alkylation of indoles with acetals.

    Science.gov (United States)

    Zhu, Neng-Xiu; Zhao, Chao-Wei; Wang, Jian-Cheng; Li, Yan-An; Dong, Yu-Bin

    2016-10-20

    We report a convenient approach, the first of its kind, to construct a microscale non-metal@MOF composite catalytic host-guest system for an organic tandem reaction. The reported porous Cu 4 I 4 -MOF is able to reversibly adsorb molecular iodine at room temperature. The obtained I 2 @Cu 4 I 4 -MOF host-guest system can be a highly heterogeneous catalyst to promote the Friedel-Crafts alkylation of indoles with acetals in a one-pot two-step fashion under solvent-free conditions at room temperature.

  4. Intramolecular cyclization of diketopiperazine formation in solid-state enalapril maleate studied by thermal FT-IR microscopic system.

    Science.gov (United States)

    Lin, Shan-Yang; Wang, Shun-Li; Chen, Ting-Fang; Hu, Ting-Chou

    2002-09-01

    The pathway of diketopiperazine (DKP) formation of solid-state enalapril maleate has been studied by using a novel Fourier transform infrared microspectroscope equipped with a thermal analyzer (thermal FT-IR microscopic system). The thermogram of the conventional differential scanning calorimetry (DSC) method was also compared. The results show new evidence of IR peaks at 3250 cm(-1) (the broad O-H stretching mode of water), and at 1738 and 1672 cm(-1) (the carbonyl band of DKP), indicating DKP formation in enalapril maleate via intramolecular cyclization. Moreover, the disappearance of IR peaks from enalapril maleate at 3215 cm(-1) (the secondary amine), 1728 cm(-1) (the carbonyl group of carboxylic acid), and 1649 cm(-1) (the carbonyl stretching of tertiary amide) also confirmed the DKP formation. The thermal FT-IR microscopic system clearly evidenced that the DKP formation in enalapril maleate started from 129 degrees C, and reached a maximum at 137 degrees C. This result was also confirmed by the conventional DSC thermogram of the compressed mixture of KBr powder and enalapril maleate, in which an endothermic peak at 144 degrees C with an extrapolated onset temperature at 137 degrees C was observed. This strongly suggests that the thermal FT-IR microscopic system was able to qualitatively detect the formation of DKP derivatives in solid-state enalapril maleate via intramolecular cyclization.

  5. A Large Scale Formal Synthesis of CoQ{sub 10}: Highly Stereoselective Friedel-Crafts Allylation Reaction of Tetramethoxytoluene with (E)-4-Chloro-2-methyl-1-phenylsulfonyl-2-butene in the Presence of Montmorillonite K-10

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sang Who; Lee, Hee Bong; Kim, Bong Chan; Sadaiah, Kadivendi; Lee, Kyuwoong; Shin, Hyunik [LG Life Sciences, Ltd., Daejeon (Korea, Republic of)

    2013-04-15

    We disclosed that MK-10 is a highly effective catalyst for the Friedel-Crafts reaction of 6 and 7 in terms of yield and of stereoselectivity. Although there are numerous applications of clays in Friedel-Crafts reaction, there is very limited example which demonstrated its effect on the stereoselectivity. In that context, our result is significant and further expansion in this direction is highly envisioned. Ubiquinone, as its name represents, exists ubiquitously in human body, particularly in the heart. It mediates the electron transfer process in mitochondria and also exerts strong antioxidant effect in its reduced form. In clinical trial, it showed beneficial effect on heart-related diseases such as myocardial infarction, angina, and other related symptoms to cause decreased mortality compared to the placebo group.

  6. NMR spectroscopic characterization and DFT calculations of zirconium(IV)-3,3'-Br2-BINOLate and related complexes used in an enantioselective Friedel-Crafts alkylation of indoles with α,β-unsaturated ketones.

    Science.gov (United States)

    Blay, Gonzalo; Cano, Joan; Cardona, Luz; Fernández, Isabel; Muñoz, M Carmen; Pedro, José R; Vila, Carlos

    2012-12-07

    Experimental and theoretical studies on the structure of several complexes based on (R)-3,3'-Br(2)-BINOL ligand and group (IV) metals used as catalysts in an enantioselective Friedel-Crafts alkylation of indoles with α,β-unsaturated ketones have been carried out. NMR spectroscopic studies of these catalysts have been performed, which suggested that at room temperature the catalysts would form a monomeric structure in the case of Ti(IV) and a dimeric structure in the cases of Zr(IV) and Hf(IV). Density functional theory (DFT) calculations clearly corroborate the conclusions of these experimental spectroscopic studies. The dimeric structure with a doubly bridged motif [Zr(IV)(2)(μ-(R)-3,3'-Br(2)-BINOL)(2)] where each binaphthol ligand acts as bridge between the metal centers (Novak's model) is more stable than the dimeric structure with a doubly bridged motif [Zr(IV)(2)(μ-O(t)Bu)(2)] where the tert-butoxide groups act as bridging ligands (Kobayashi's model). The scope of the Friedel-Crafts alkylation with regard to the indole structure has been studied. Finally a plausible mechanism for the Friedel-Crafts reaction and a stereomodel for the mode of action of the catalyst that explain the observed stereochemistry of the reaction products have been proposed.

  7. Ready synthesis of free N-H 2-arylindoles via the copper-catalyzed amination of 2-bromo-arylacetylenes with aqueous ammonia and sequential intramolecular cyclization.

    Science.gov (United States)

    Wang, Huifeng; Li, Yaming; Jiang, Linlin; Zhang, Rong; Jin, Kun; Zhao, Defeng; Duan, Chunying

    2011-07-07

    A wide range of free N-H 2-arylindoles were synthesised via the copper(II)-catalyzed amination of 2-bromo-arylacetylenes with aqueous ammonia and sequential intramolecular cyclization. The convenience and atom economy of aqueous ammonia, and the low cost of the copper catalytic system make this protocol readily superior in practical application.

  8. Hg/Pt-catalyzed conversion of bromo alkynamines/alkynols to saturated and unsaturated γ-butyrolactams/lactones via intramolecular electrophilic cyclization.

    Science.gov (United States)

    Kiran Kumar, Yalla; Ranjith Kumar, Gadi; Sridhar Reddy, Maddi

    2016-01-28

    Convenient and general Hg(ii)/Pt(iv) catalyzed syntheses of γ-butyrolactams and α,β-unsaturated γ-butyrolactones/lactams are described via intramolecular electrophilic cyclizations of bromoalkynes with tosylamino and hydroxyl tethers. The reaction features the use of wet solvents, the exclusion of any base and additive, mild conditions and practical yields. We also synthesised few chiral lactams through this pathway. Additionally, it is shown that the NHTs group distanced further from the homopropargylic position assists regioselective bromoalkyne hydration to yield useful α-bromoketones. Furthermore, Boc protected bromo homo propargyl amines undergo 6-endo-dig cyclization through Boc oxygen to give bromomethylene substituted oxazinones.

  9. Palladium-catalyzed intramolecular asymmetric C-H functionalization/cyclization reaction of metallocenes: an efficient approach toward the synthesis of planar chiral metallocene compounds.

    Science.gov (United States)

    Deng, Ruixian; Huang, Yunze; Ma, Xinna; Li, Gencheng; Zhu, Rui; Wang, Bin; Kang, Yan-Biao; Gu, Zhenhua

    2014-03-26

    A palladium-catalyzed asymmetric synthesis of planar chiral metallocene compounds is reported. The reaction stereoselectively functionalized one of the ortho C-H bonds of Cp rings by intramolecular cyclization to form indenone derivatives in high yields with excellent enantioselectivity. The mild set of reaction conditions allowed a wide variety of chiral metallocene compounds to be synthesized with broad functional group tolerance. The influences of preinstalled chiralities on the other Cp-ring were also investigated.

  10. Intramolecular cyclization of aspartic acid residues assisted by three water molecules: a density functional theory study

    Science.gov (United States)

    Takahashi, Ohgi; Kirikoshi, Ryota

    2014-01-01

    Aspartic acid (Asp) residues in peptides and proteins (l-Asp) are known to undergo spontaneous nonenzymatic reactions to form l-β-Asp, d-Asp, and d-β-Asp residues. The formation of these abnormal Asp residues in proteins may affect their three-dimensional structures and hence their properties and functions. Indeed, the reactions have been thought to contribute to aging and pathologies. Most of the above reactions of the l-Asp residues proceed via a cyclic succinimide intermediate. In this paper, a novel three-water-assisted mechanism is proposed for cyclization of an Asp residue (forming a gem-diol precursor of the succinimide) by the B3LYP/6-31 + G(d,p) density functional theory calculations carried out for an Asp-containing model compound (Ace-Asp-Nme, where Ace = acetyl and Nme = NHCH3). The three water molecules act as catalysts by mediating ‘long-range’ proton transfers. In the proposed mechanism, the amide group on the C-terminal side of the Asp residue is first converted to the tautomeric iminol form (iminolization). Then, reorientation of a water molecule and a conformational change occur successively, followed by the nucleophilic attack of the iminol nitrogen on the carboxyl carbon of the Asp side chain to form the gem-diol species. A satisfactory agreement was obtained between the calculated and experimental energetics.

  11. Controlling the ambiphilic nature of σ-arylpalladium intermediates in intramolecular cyclization reactions.

    Science.gov (United States)

    Solé, Daniel; Fernández, Israel

    2014-01-21

    the metal center with the carbonyl group. Second, the additive phenol exchanges the iodide ligand to give an arylpalladium(II) phenoxide complex, which has a beneficial effect on the arylation. The formation of this transient intermediate not only stabilizes the arylpalladium moiety, thus preventing the nucleophilic attack at the carbonyl group, but also assists the enolization reaction, which takes place in a more favorable intramolecular manner. The azapalladacycle intermediate is, in the words of J. R. R. Tolkien, "the one ring to bring them all and in the darkness to bind them." With this intermediate, we can easily achieve the synthesis of a variety of heterocyclic systems by selectively promoting electrophilic α-arylation or nucleophilic addition reactions from the same precursors.

  12. Intramolecular hydroamination of alkynic sulfonamides catalyzed by a gold–triethynylphosphine complex: Construction of azepine frameworks by 7-exo-dig cyclization

    Directory of Open Access Journals (Sweden)

    Hideto Ito

    2011-07-01

    Full Text Available The gold-catalyzed, seven-membered ring forming, intramolecular hydroamination of alkynic sulfonamides has been investigated. The protocol, with a semihollow-shaped triethynylphosphine as a ligand for gold, allowed the synthesis of a variety of azepine derivatives, which are difficult to access by other methods. Both alkynic sulfoamides with a flexible linear chain and the benzene-fused substrates underwent 7-exo-dig cyclization to afford the nitrogen-containing heterocyclic seven-membered rings, such as tetrahydroazepine and dihydrobenzazepine, in good yields.

  13. Ciclização intramolecular: uma estratégia promissora no desenvolvimento de pró-fármacos Intramolecular cyclization: a promising strategy in the prodrug conception

    Directory of Open Access Journals (Sweden)

    Cledir Santos

    2008-09-01

    Full Text Available Muitos fármacos estão associados a vários efeitos adversos e limitada biodisponibilidade. A resolução destes problemas continua sendo um alvo importante para a comunidade científica. O desenvolvimento de pró-fármacos que conduzam a uma liberação controlada in vivo é um caminho atrativo para resolver estes problemas. Um pró-fármaco clássico é molécula inativa, em que o princípio ativo é ligado covalentemente a uma unidade transportadora, de modo que o fármaco pode ser liberado através de uma reação química ou enzimática. Um sistema novo e interessante de pró-fármaco, que tem sido apresentado para fármacos possuidores de grupos amino, álcool e tiol, é aquele no qual o princípio ativo é liberado através de uma ciclização intramolecular. Neste caso, o processo de ciclização, dependendo da cadeia da unidade transportadora e do próprio fármaco, pode controlar a velocidade de liberação do princípio ativo. Desta forma, este trabalho apresenta uma revisão do desenvolvimento de pró-fármacos baseados na liberação do princípio ativo através de uma ciclização intramolecular.Many drugs used for the treatment of common diseases are associated with various adverse effects and limited bioavailability. The suppression of such problems continues to be a very important target for scientists. The development of prodrugs for controlled release in vivo is an attractive way to overcome these problems. Classical in prodrug is an inactive molecule which the parent drug is covalently bonded to a carrier unit, and which can liberate the drug through chemical or enzymatic pathways. A new and interesting prodrug system for amine, alcohol, and thiol drugs takes advantage of several easy intramolecular cyclization reactions. So, the cyclization process can control the release rate of the parent drug. In this paper is a review about the prodrug strategies based on intramolecular cyclization reactions is presented.

  14. A highly selective turn-on fluorescent probe for hypochlorous acid based on hypochlorous acid-induced oxidative intramolecular cyclization of boron dipyrromethene-hydrazone

    International Nuclear Information System (INIS)

    Chen, Wei-Chieh; Venkatesan, Parthiban; Wu, Shu-Pao

    2015-01-01

    Highlights: • A BODIPY-based fluorescent probe for sensing HOCl was developed. • The probe utilizes the HOCl-promoted cyclization in response to the amount of HOCl. • The probe might have application in the investigation of HOCl in biological systems. - Abstract: A BODIPY-based fluorescent probe, HBP, was developed for the detection of hypochlorous acid based on the specific hypochlorous acid-promoted oxidative intramolecular cyclization of heterocyclic hydrazone in response to the amount of HOCl. The reaction is accompanied by a 41-fold increase in the fluorescent quantum yield (from 0.004 to 0.164). The fluorescence intensity of the reaction between HOCl and HBP is linear in the HOCl concentration range of 1–8 μM with a detection limit of 2.4 nM (S/N = 3). Confocal fluorescence microscopy imaging using RAW264.7 cells showed that the new probe HBP could be used as an effective fluorescent probe for detecting HOCl in living cells

  15. Synthesis of 2,3-dihydro-1H-pyrroles by intramolecular cyclization of N-(3-butynyl)-sulfonamides.

    Science.gov (United States)

    Chung, Min-Ching; Chan, Yung-Hsiang; Chang, Wen-Jung; Hou, Duen-Ren

    2017-05-03

    Hydroamination of 3-butynamine derivatives to give non-aromatic 2,3-dihydropyrroles was achieved by using PdCl 2 or AuCl as the catalyst. With microwave-assisted heating, up to 92% isolated yield was obtained from this intramolecular 5-endo-dig cyclisation. The cyclopentane- and cyclohexane-fused 2,3-dihydropyrroles were transformed into the corresponding N-tosyl-pyrrolidine-2-carboxylic acids.

  16. Tandem catalysis in domino olefin cross-metathesis/intramolecular oxa-conjugate cyclization: concise synthesis of 2,6-cis-substituted tetrahydropyran derivatives.

    Science.gov (United States)

    Fuwa, Haruhiko; Noguchi, Takuma; Noto, Kenkichi; Sasaki, Makoto

    2012-10-28

    Herein, we describe the concise synthesis of 2,6-cis-substituted tetrahydropyran derivatives based on a domino olefin cross-metathesis/intramolecular oxa-conjugate cyclization (CM/IOCC) reaction. We have found that the domino CM/IOCC of δ-hydroxy olefins with α,β-unsaturated carbonyl compounds (e.g., trans-crotonaldehyde or N-acryloyl-2,5-dimethylpyrrole) could be efficiently achieved in the presence of the second-generation Hoveyda-Grubbs catalyst under elevated temperature conditions, directly affording 2,6-cis-substituted tetrahydropyrans in excellent yields with synthetically useful diastereoselectivity ("auto-tandem catalysis"). In addition, we have found that the domino CM/IOCC of δ-hydroxy olefins with α,β-unsaturated carbonyl compounds could be achieved simply by performing CM in the presence of a Brønsted acid in CH(2)Cl(2) at 25-35 °C, which delivered 2,6-cis-substituted tetrahydropyrans in good yields with excellent diastereoselectivity ("orthogonal-tandem catalysis"). To understand the mechanism of auto-tandem catalysis in the domino CM/IOCC reaction, we have investigated the role of ruthenium hydride complexes in the IOCC of a ζ-hydroxy α,β-unsaturated ketone as a model case.

  17. Study of Meldrum's Acid Cyclization Reactions.

    Science.gov (United States)

    Trujillo, Cristina; Goya, Pilar; Rozas, Isabel

    2018-02-27

    On the basis of the cyclization reactions reported by Danishefsky et al. of Meldrum's acid hydroxylethyl and anilinoethyl derivatives, the cyclization of the sulfamidomethylene and ureidomethylene derivatives was attempted without success. To understand the lack of reactivity of these compounds versus the successful cyclization of the ethyl derivatives, the corresponding mechanisms of reaction for both processes have been explored by means of MP2/6-311+G(d,p) calculations in an aqueous environment. The conformational analysis of all of these structures revealed that, while for the ethyl derivatives the minimum energy conformation corresponds to that of the cyclization initiating structure, for the methylene analogues the entrance channel conformations are substantially less stable than the energy minimum. Intramolecular hydrogen bonds were found in all of the energy minima as well as in the cyclization initiating conformations as determined by analysis of their electron density. The potential energy surfaces for the successful and unsuccessful cyclization processes were obtained at room temperature and 100 °C. Comparison of both processes allows rationalization that the lack of reactivity of the methylene derivatives can be thermodynamically explained based not only on the strength of the intramolecular hydrogen bond formed in their energy minima but also by the energy penalty needed to reach the entrance channel conformation and by the calculated energy barriers.

  18. Cyclization-activated Prodrugs

    Directory of Open Access Journals (Sweden)

    Rui Moreira

    2007-11-01

    Full Text Available Many drugs suffer from an extensive first-pass metabolism leading to druginactivation and/or production of toxic metabolites, which makes them attractive targets forprodrug design. The classical prodrug approach, which involves enzyme-sensitive covalentlinkage between the parent drug and a carrier moiety, is a well established strategy toovercome bioavailability/toxicity issues. However, the development of prodrugs that canregenerate the parent drug through non-enzymatic pathways has emerged as an alternativeapproach in which prodrug activation is not influenced by inter- and intraindividualvariability that affects enzymatic activity. Cyclization-activated prodrugs have beencapturing the attention of medicinal chemists since the middle-1980s, and reached maturityin prodrug design in the late 1990s. Many different strategies have been exploited in recentyears concerning the development of intramoleculary-activated prodrugs spanning fromanalgesics to anti-HIV therapeutic agents. Intramolecular pathways have also a key role intwo-step prodrug activation, where an initial enzymatic cleavage step is followed by acyclization-elimination reaction that releases the active drug. This wor

  19. ELECTROPHILIC CYCLIZATION OF DITERPENOIDS

    Directory of Open Access Journals (Sweden)

    Veaceslav Kulciţki

    2006-06-01

    Full Text Available A review of diterpenoid cyclization initiated by electrophilic reagents is provided. Conventional protonic and Lewis acids are examined along with superacids as initiators of cyclization cascade. An emphasis is placed on the use of cyclization reactions as a tool for the synthesis of compounds with potential practical utility. The review contains 74 references.

  20. Synthesis of (--Indolizidine 167B based on domino hydroformylation/cyclization reactions

    Directory of Open Access Journals (Sweden)

    Settambolo Roberta

    2008-01-01

    Full Text Available Abstract The synthesis of (--Indolizidine 167B has been achieved from optically active (R-3-(pyrrol-1-ylhex-1-ene. The key step is a highly regioselective hydroformylation reaction and a one-pot intramolecular cyclization providing a general approach to the indolizine nucleus.

  1. New amidines from intramolecular cyclization in triflic acid of ...

    Indian Academy of Sciences (India)

    Marie2 Adima A Augustin1. Laboratoire des Procédés Industriels de Synthèse et d'Environnement, Institut National Polytechnique Félix Houphouët-Boigny, BP 991 Yamoussoukro, Côte d'Ivoire; Laboratoire `Synthèse et Réactivité des Substances ...

  2. The Cyclization of natural rubber

    International Nuclear Information System (INIS)

    Mirzataheri, M.

    2000-01-01

    The effect of solvent, temperature, time, weight percent of catalyst on the rate and mechanism of cyclization of natural rubber was studied in toluene and xylene solutions having tin tetra chloride catalyst (SnCl 4 ). Iodo metric titration show, with 8% SnCl 4 (based on polymer weight) cyclization occurs, leaving 27.4% of the total unsaturation. Infrared spectra of cyclized natural rubber show decreased absorption intensity at 840 and 780 cm -1 which are characteristic bands of the linear polymer and the appearance of absorption band at 890 cm -1 as cycles were formed. By using this chemical modification, natural rubber is transformed into a resinous thermoplastic, hard, non rubbery cyclized material with much less unsaturation than the original rubber, which could find commercial applications ad adhesives, printing inks, industrial and ship paints

  3. Synthesis and Electronic Properties of Fluoreno[2,1-a]fluorenedione and Fluoreno[1,2-a]fluorenedione.

    Science.gov (United States)

    Hacker, Allison S; Pavano, Mauricio; Wood, James E; Immoos, Chad E; Hashimoto, Hannah; Genis, Sam P; Frantz, Derik K

    2018-01-05

    The [2,1-a]- and [1,2-a]-isomers of fluorenofluorenedione have been synthesized via intramolecular Friedel-Crafts acylations. DFT calculations indicate that the [1,2-a]-isomer adopts a twisted, helical C 2 -symmetric structure and that its protonated form is the thermodynamic product of the Friedel-Crafts acylation in hot sulfuric acid. Absorption spectroscopy and cyclic voltammetry measurements provide experimental estimations of frontier molecular orbital energy levels, which are reported and discussed.

  4. Synthesis of Heterocycles through a Ruthenium‐Catalyzed Tandem Ring‐Closing Metathesis/Isomerization/N‐Acyliminium Cyclization Sequence

    DEFF Research Database (Denmark)

    Ascic, Erhad; Jensen, Jakob Feldthusen; Nielsen, Thomas Eiland

    2011-01-01

    Tandem bicycle: In the title reaction double bonds created during ring-closing metathesis isomerize to generate reactive iminium intermediates that undergo intramolecular cyclization reactions with tethered heteroatom and carbon nucleophiles. In this way, a series of biologically interesting hete...... heterocyclic compounds can be made, including a known precursor for the total synthesis of the antiparasitic natural product harmicine....

  5. Microwave-assisted facile and rapid Friedel-Crafts benzoylation of arenes catalysed by bismuth trifluoromethanesulfonate

    DEFF Research Database (Denmark)

    Tran, Phoung Hoang; Hansen, Poul Erik; Pham, Thuy Than

    2014-01-01

    The catalytic activity of metal triflates was investigated in Friedel–Crafts benzoylation under microwave irradiation. Friedel–Crafts benzoylation with benzoyl chloride of a variety of arenes containing electron-rich and electron-poor rings using bismuth triflate under microwave irradiation is de...... is described. This method allows the preparation of aryl ketones under solventless conditions in good to excellent yields and short reaction time. Bismuth triflate was easily recovered and reused five times without significant loss of the catalytic activity....

  6. Rationalizing Ring-Size Selectivity in Intramolecular Pd-Catalyzed Allylations of Resonance-Stabilized Carbanions

    DEFF Research Database (Denmark)

    Norrby, Per-Ola; Mader, Mary M.; Vitale, Maxime

    2003-01-01

    Computational methods were applied to the Pd-catalyzed intramolecular allylations of resonance-stabilized carbanions obtained from amide and ketone substrates, with the aim of rationalizing the endo- vs. exo-selectivity in the cyclizations. In addition, ester substrates were prepared and subjecte...

  7. Enantioselective Intramolecular Hydroarylation of Alkenes via Directed C-H Bond Activation

    Energy Technology Data Exchange (ETDEWEB)

    Harada, Hitoshi; Thalji, Reema; Bergman, Robert; Ellman, Jonathan

    2008-05-22

    Highly enantioselective catalytic intramolecular ortho-alkylation of aromatic imines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using [RhCl(coe){sub 2}]{sub 2} and chiral phosphoramidite ligands. Cyclization of substrates containing 1,1- and 1,2-disubstituted as well as trisubstituted alkenes were achieved with enantioselectivities >90% ee for each substrate class. Cyclization of substrates with Z-alkene isomers proceeded much more efficiently than substrates with E-alkene isomers. This further enabled the highly stereoselective intramolecular alkylation of certain substrates containing Z/E-alkene mixtures via a Rh-catalyzed alkene isomerization with preferential cyclization of the Z-isomer.

  8. Enantioselective intramolecular hydroarylation of alkenes via directed C-H bond activation.

    Science.gov (United States)

    Harada, Hitoshi; Thalji, Reema K; Bergman, Robert G; Ellman, Jonathan A

    2008-09-05

    Highly enantioselective catalytic intramolecular ortho-alkylation of aromatic imines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using [RhCl(coe)2]2 and chiral phosphoramidite ligands. Cyclization of substrates containing 1,1- and 1,2-disubstituted as well as trisubstituted alkenes were achieved with enantioselectivities >90% ee for each substrate class. Cyclization of substrates with Z-alkene isomers proceeded much more efficiently than substrates with E-alkene isomers. This further enabled the highly stereoselective intramolecular alkylation of certain substrates containing Z/E-alkene mixtures via a Rh-catalyzed alkene isomerization with preferential cyclization of the Z-isomer.

  9. Enantioselective Intramolecular Hydroarylation of Alkenes via Directed C–H Bond Activation

    Science.gov (United States)

    Harada, Hitoshi; Thalji, Reema K.; Bergman, Robert G.; Ellman, Jonathan A.

    2008-01-01

    Highly enantioselective catalytic intramolecular ortho-alkylation of aromatic imines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using [RhCl(coe)2]2 and chiral phosphoramidite ligands. Cyclization of substrates containing 1,1- and 1,2-disubstituted as well as trisubstituted alkenes were achieved with enantioselectivities >90% ee for each substrate class. Cyclization of substrates with Z-alkene isomers proceeded much more efficiently than substrates with E-alkene isomers. This further enabled the highly stereoselective intramolecular alkylation of certain substrates containing Z/E-alkene mixtures via a Rh-catalyzed alkene isomerization with preferential cyclization of the Z-isomer. PMID:18681407

  10. Enantioselective cyclizations and cyclization cascades of samarium ketyl radicals

    Science.gov (United States)

    Kern, Nicolas; Plesniak, Mateusz P.; McDouall, Joseph J. W.; Procter, David J.

    2017-12-01

    The rapid generation of molecular complexity from simple starting materials is a key challenge in synthesis. Enantioselective radical cyclization cascades have the potential to deliver complex, densely packed, polycyclic architectures, with control of three-dimensional shape, in one step. Unfortunately, carrying out reactions with radicals in an enantiocontrolled fashion remains challenging due to their high reactivity. This is particularly the case for reactions of radicals generated using the classical reagent, SmI2. Here, we demonstrate that enantioselective SmI2-mediated radical cyclizations and cascades that exploit a simple, recyclable chiral ligand can convert symmetrical ketoesters to complex carbocyclic products bearing multiple stereocentres with high enantio- and diastereocontrol. A computational study has been used to probe the origin of the enantioselectivity. Our studies suggest that many processes that rely on SmI2 can be rendered enantioselective by the design of suitable ligands.

  11. Gold versus silver catalyzed intramolecular hydroarylation reactions of [(3-arylprop-2-ynyl)oxy]benzene derivatives.

    Science.gov (United States)

    Arcadi, Antonio; Blesi, Federico; Cacchi, Sandro; Fabrizi, Giancarlo; Goggiamani, Antonella; Marinelli, Fabio

    2012-12-28

    The scope and the generality of gold versus silver catalyzed intramolecular hydroarylation reactions of 3-[(3-arylprop-2-ynyl)oxy]benzene derivatives in terms of rings substitution were investigated. Only products deriving from 6-endo cyclization were exclusively formed. The features of substituents had a considerable effect on the reaction outcome in the presence of silver catalysis, whereas gold catalysis revealed a unique blend of reactivity and selectivity and represented the only choice for the intramolecular hydroarylation reaction of the starting substrates bearing electron deficient arenes.

  12. Intramolecular and nonlinear dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Davis, M.J. [Argonne National Laboratory, IL (United States)

    1993-12-01

    Research in this program focuses on three interconnected areas. The first involves the study of intramolecular dynamics, particularly of highly excited systems. The second area involves the use of nonlinear dynamics as a tool for the study of molecular dynamics and complex kinetics. The third area is the study of the classical/quantum correspondence for highly excited systems, particularly systems exhibiting classical chaos.

  13. Highly efficient and enantioselective cyclization of aromatic imines via directed C-H bond activation.

    Science.gov (United States)

    Thalji, Reema K; Ellman, Jonathan A; Bergman, Robert G

    2004-06-16

    The first highly enantioselective catalytic reaction involving aromatic C-H bond activation is communicated. Enantioselective cyclization of aromatic ketimines containing alkenyl groups tethered at the meta position of an imine directing group has been achieved using 5 mol % [RhCl(coe)2]2 and 15 mol % of an (S)-binol-derived phosphoramidite ligand. Selectivities of up to 96% ee and up to quantitative yields were obtained. Moreover, the identified catalyst system enables the intramolecular alkylation reaction to be performed at temperatures 75 degrees C lower than our previously reported achiral system. The reaction can even be performed at room temperature for one of the optimal substrates.

  14. Germacrene D Cyclization: An Ab Initio Investigation

    OpenAIRE

    Setzer, William N.

    2008-01-01

    Essential oils that contain large concentrations of germacrene D are typically accompanied by cadinane sesquiterpenoids. The acid-catalyzed cyclization of germacrene D to give cadinane and selinane sesquiterpenes has been computationally investigated using both density functional (B3LYP/6-31G*) and post Hartree-Fock (MP2/6-31G* *) ab initio methods. The calculated energies are in general agreement with experimentally observed product distributions, both from acid-catalyzed cyclizations as wel...

  15. An Efficient Synthesis of Substituted Furans by Cupric Halide-Mediated Intramolecular Halocyclization of 2-(1-Alkynyl)-2-alken-1-ones

    International Nuclear Information System (INIS)

    Fu, Weijun; Guo, Wenbo; Zhu, Mei; Xu, Chen; Xu, Fengjuan

    2013-01-01

    An efficient synthesis of 3-halofurans by the intramolecular cyclization of 2-(1-alkynyl)-2-alken-1-ones with cupric halide has been developed. A broad range of 3-chloro- and 3-bromofuran derivatives could be obtained in the present method in moderate to good yields. The 3-halofuran derivatives are potential synthetic intermediates for amplification of molecular complexity

  16. Remarkable phosphine-effect on the intramolecular aldol reactions of unsaturated 1,5-diketones: highly regioselective synthesis of cross-conjugated dienones.

    Science.gov (United States)

    Thalji, Reema K; Roush, William R

    2005-12-07

    We report a phosphine-mediated intramolecular aldol cyclization of unsaturated diketones that proceeds with extremely high levels of regioselectivity for the cross-conjugated bicyclic dienone products. The sense of regioselectivity observed in this reaction is complementary to that obtained using traditional aldol conditions. Experimental evidence that supports the involvement of a phosphine Michael adduct is described.

  17. Synthesis of Some New 2-(3-Aryl-1-phenyl-4-pyrazolyl-benzoxazoles Using Hypervalent Iodine Mediated Oxidative Cyclization of Schiff’s Bases

    Directory of Open Access Journals (Sweden)

    Ajay Kumar

    2006-01-01

    Full Text Available Ten new 2-(3-aryl-1-phenyl-4-pyrazolylbenzoxazoles have been synthesized by oxidative intramolecular cyclization of the corresponding Schiff’s bases using iodobenzene diacetate in methanol as an oxidant.

  18. Indium triflate in 1-isobutyl-3-methylimidazolium dihydrogenphosphate: an efficient and green catalytic system for Friedel-Crafts acylation

    DEFF Research Database (Denmark)

    Tran, Phuong Hoang; Hoang, Huy Manh; Chau, Duy-Khiem Nguyen

    2015-01-01

    Indium triflate in the ionic liquid, 1-isobutyl-3-methylimidazolium dihydrogen phosphate ([i-BMIM]H2PO4), was found to show enhanced catalytic activity in the Friedel–Crafts acylation of various aromatic compounds with acid anhydrides. The catalytic system was easily recovered and reused without...

  19. Upward Trend in Catalytic Efficiency of Rare-Earth Triflate Catalysts in Friedel-Crafts Aromatic Sulfonylation Reactions

    DEFF Research Database (Denmark)

    Duus, Fritz; Le, Thach Ngoc; Nguyen, Vo Thu An

    2014-01-01

    90 % were achieved for short irradiation periods. This was the case especially for Tm(OTf)3, Yb(OTf)3, and Lu(OTf)3, of which Yb(OTf)3 was the most efficient. The upward trend in catalytic efficiency therefore correlates with the lanthanide sequence in the periodic table. The results can be explained...

  20. Friedel-Crafts Alkylation of o-xylene over V2O5/ZrO2 Catalysts

    CSIR Research Space (South Africa)

    Kesavan Pillai, Sreejarani

    2012-01-01

    Full Text Available and considerably more selective than the conventional homogeneous Lewis acid catalysts. The investigation of vanadia systems-catalyzed benzylation of o-xylene with benzyl chloride revealed that the catalytic activity and product selectivity are sensitive...

  1. Efficient Friedel-Crafts benzoylation of aniline derivatives with 4-fluorobenzoyl chloride using copper triflate in the synthesis of aminobenzophenones

    DEFF Research Database (Denmark)

    Tran, Phuong Hoang; Phung, Huy Quang; Hansen, Poul Erik

    2016-01-01

    An efficient pathway for the synthesis of the aminobenzophenone derivatives via Friedel–Crafts benzoylation using copper triflate as catalyst is proposed. New derivatives are synthesized. The copper triflate could be easily recovered and reused without loss of catalytic activity. Both the use...... of ionic liquids and microwave heating turned out to be fruitful....

  2. Stereoselective synthesis of 1,3-disubstituted isoindolines via Rh(III)-catalyzed tandem oxidative olefination-cyclization of 4-aryl cyclic sulfamidates.

    Science.gov (United States)

    Son, Se-Mi; Seo, Yeon Ji; Lee, Hyeon-Kyu

    2016-03-21

    Rh(III)-catalyzed tandem ortho C-H olefination of cyclic 4-aryl sulfamidates (1) and subsequent intramolecular cyclization are described. This reaction serves as a method for the direct and stereoselective synthesis of 1,3-disubstituted isoindolines (3) starting with enantiomerically enriched 4-aryl cyclic sulfamidates. In this process, the configurational integrity of the stereogenic center in the starting cyclic sulfamidate is completely retained. In addition, the process generates trans-1,3-disubstituted isoindolines exclusively.

  3. Tandem Rh-Catalyzed Oxidative C-H Olefination and Cyclization of Enantiomerically Enriched Benzo-1,3-Sulfamidates: Stereoselective Synthesis of trans-1,3-Disubstituted Isoindolines.

    Science.gov (United States)

    Achary, Raghavendra; Jung, In-A; Lee, Hyeon-Kyu

    2018-04-06

    A tandem process, involving Rh(III)-catalyzed oxidative C-H olefination of enantiomerically enriched 4-aryl-benzo-1,3-sulfamidates and subsequent intramolecular aza-Michael cyclization has been developed. The reaction produces trans-benzosulfamidate-fused-1,3-disubstituted isoindolines as major products, in which the configurational integrity of the stereogenic center in the starting material is preserved. Further transformations of the benzosulfamidate-fused-1,3-disubstituted isoindolines are described.

  4. Germacrene D cyclization: an Ab initio investigation.

    Science.gov (United States)

    Setzer, William N

    2008-01-01

    Essential oils that contain large concentrations of germacrene D are typically accompanied by cadinane sesquiterpenoids. The acid-catalyzed cyclization of germacrene D to give cadinane and selinane sesquiterpenes has been computationally investigated using both density functional (B3LYP/6-31G(*)) and post Hartree-Fock (MP2/6-31G(* *)) ab initio methods. The calculated energies are in general agreement with experimentally observed product distributions, both from acid-catalyzed cyclizations as well as distribution of the compounds in essential oils.

  5. Germacrene D Cyclization: An Ab Initio Investigation

    Directory of Open Access Journals (Sweden)

    William N. Setzer

    2008-01-01

    Full Text Available Essential oils that contain large concentrations of germacrene D are typically accompanied by cadinane sesquiterpenoids. The acid-catalyzed cyclization of germacrene D to give cadinane and selinane sesquiterpenes has been computationally investigated using both density functional (B3LYP/6-31G* and post Hartree-Fock (MP2/6-31G** ab initio methods. The calculated energies are in general agreement with experimentally observed product distributions, both from acid-catalyzed cyclizations as well as distribution of the compounds in essential oils.

  6. SOCl2 CATALYZED CYCLIZATION OF CHALCONES: SYNTHESIS ...

    African Journals Online (AJOL)

    Preferred Customer

    ABSTRACT. Some aryl-aryl 1H pyrazoles have been synthesised by cyclization of aryl chalcones and hydrazine hydrate in the presence of SOCl2. The yields of the pyrazoles are more than 85%. These pyrazoles are characterized by their physical constants and spectral data. The infrared,. NMR spectral group frequencies ...

  7. Non-Conventional Methodologies in the Synthesis of 1-Indanones

    Directory of Open Access Journals (Sweden)

    Manuela Oliverio

    2014-04-01

    Full Text Available 1-Indanones have been successfully prepared by means of three different non-conventional techniques, namely microwaves, high-intensity ultrasound and a Q-tube™ reactor. A library of differently substituted 1-indanones has been prepared via one-pot intramolecular Friedel-Crafts acylation and their efficiency and “greenness” have been compared.

  8. Solventless Lactam Synthesis by Intramolecular Cyclizations of α-Iminoester Derivatives under Microwave Irradiation

    Directory of Open Access Journals (Sweden)

    Aicha Derdour

    2007-03-01

    Full Text Available We have previously reported a new synthesis of amides from esters and amines under microwave irradiation, offering much higher yields than those achieved with conventional heating [1]. We have now extended these studies to the ring closure of neat iminoesters I2, I3 and I4-I6 to give five- and six-membered ring lactams L5, L6 and larger lactams L7-L9 (where I means imine and L means lactam, respectively, under both classical heating conditions and microwave irradiation.

  9. Stereoselective synthesis of 2,3-disubstituted indoline, pyrrolidine and cyclic ether-fused 1,2-dihydroquinoline derivatives using alkyne iminium ion cyclization of vinylogous carbamates: switch of regioselectivity using an internal hydroxy group as a nucleophile.

    Science.gov (United States)

    Gharpure, Santosh J; Prasath, V; Kumar, Vinod

    2015-09-14

    An intramolecular, alkyne iminium ion cyclization of vinylogous carbamates derived from o-alkynyl anilines and N-protected homopropargyl amines is developed for the stereoselective construction of trans-2,3-disubstituted indolines and pyrrolidine derivatives, respectively. The regioselectivity of the alkyne iminium ion cyclization could be switched using a hydroxy group as an internal nucleophile resulting in cyclic ether-fused 1,2-dihydroquinolines. The entire process of nitrogen heterocycle formation can also be carried out in a 'one-pot' manner starting from o-iodo aniline derivatives.

  10. Recombinant expression of backbone-cyclized polypeptides.

    Science.gov (United States)

    Borra, Radhika; Camarero, Julio A

    2013-09-01

    Here we review the different biochemical approaches available for the expression of backbone-cyclized polypeptides, including peptides and proteins. These methods allow for the production of circular polypeptides either in vitro or in vivo using standard recombinant DNA expression techniques. Polypeptide circularization provides a valuable tool to study the effects of topology on protein stability and folding kinetics. Furthermore, having biosynthetic access to backbone-cyclized polypeptides makes the production of genetically encoded libraries of cyclic polypeptides possible. The production of such libraries, which was previously restricted to the domain of synthetic chemistry, now offers biologists access to highly diverse and stable molecular libraries that can be screened using high-throughput methods for the rapid selection of novel cyclic polypeptide sequences with new biological activities. Copyright © 2013 Wiley Periodicals, Inc.

  11. The quantum-chemical investigation of N-cyclization reaction mechanism for epichlorohydrin aminolysis products

    Directory of Open Access Journals (Sweden)

    Andrey V. Tokar

    2014-12-01

    Full Text Available The mechanism of intramolecular cyclization for products of epichlorohydrin aminolysis by secondary amines has been investigated at ab initio level of theory. By comparative analysis of energetic characteristics, which obtained in vacuo as well as in acetonitrile solution with the trace quantities of water as an «active» solvation partner of reaction, it has been shown a decisive role of solvent, which occurs mainly at the expense of the polarizable effects for nonspecific solvation. Indeed, the addition to the substrate of one water molecule have decreased corresponding EACT values only 24.1 kJ/mol, while the appearance of acetonitrile surroundings have the same influence ~42.0 kJ/mol. The results of calculations are in good agreement with that data, which have been obtained for such type modeling previously.

  12. Fast and versatile microwave-assisted intramolecular Heck reaction in peptide macrocyclization using microwave energy.

    Science.gov (United States)

    Byk, Gerardo; Cohen-Ohana, Mirit; Raichman, Daniel

    2006-01-01

    We have revisited the intramolecular Heck reaction and investigated the microwave-assisted macrocyclization on preformed peptides using a model series of ring-varying peptides acryloyl-Gly-[Gly](n)-Phe(4-I)NHR; n = 0-4. The method was applied to both solution and solid supported cyclizations. We demonstrate that the intramolecular Heck reaction can be performed in peptides both in solution and solid support using a modified domestic microwave within 1 to 30 minutes in DMF under reflux with moderate yields ranging from 15 to 25% for a scale between 2-45 mg of linear precursors. The approach was applied to the synthesis of a constrained biologically relevant peptidomimetic bearing an Arg-Gly-Asp (RGD) sequence. These results make the microwave-assisted Heck reaction an attractive renovated approach for peptidomimetics. Copyright 2006 Wiley Periodicals, Inc.

  13. Knottin cyclization: impact on structure and dynamics

    Directory of Open Access Journals (Sweden)

    Gracy Jérôme

    2008-12-01

    Full Text Available Abstract Background Present in various species, the knottins (also referred to as inhibitor cystine knots constitute a group of extremely stable miniproteins with a plethora of biological activities. Owing to their small size and their high stability, knottins are considered as excellent leads or scaffolds in drug design. Two knottin families contain macrocyclic compounds, namely the cyclotides and the squash inhibitors. The cyclotide family nearly exclusively contains head-to-tail cyclized members. On the other hand, the squash family predominantly contains linear members. Head-to-tail cyclization is intuitively expected to improve bioactivities by increasing stability and lowering flexibility as well as sensitivity to proteolytic attack. Results In this paper, we report data on solution structure, thermal stability, and flexibility as inferred from NMR experiments and molecular dynamics simulations of a linear squash inhibitor EETI-II, a circular squash inhibitor MCoTI-II, and a linear analog lin-MCoTI. Strikingly, the head-to-tail linker in cyclic MCoTI-II is by far the most flexible region of all three compounds. Moreover, we show that cyclic and linear squash inhibitors do not display large differences in structure or flexibility in standard conditions, raising the question as to why few squash inhibitors have evolved into cyclic compounds. The simulations revealed however that the cyclization increases resistance to high temperatures by limiting structure unfolding. Conclusion In this work, we show that, in contrast to what could have been intuitively expected, cyclization of squash inhibitors does not provide clear stability or flexibility modification. Overall, our results suggest that, for squash inhibitors in standard conditions, the circularization impact might come from incorporation of an additional loop sequence, that can contribute to the miniprotein specificity and affinity, rather than from an increase in conformational rigidity

  14. Lactone radical cyclizations and cyclization cascades mediated by SmI2-H2O.

    Science.gov (United States)

    Parmar, Dixit; Matsubara, Hiroshi; Price, Kieran; Spain, Malcolm; Procter, David J

    2012-08-01

    Unsaturated lactones undergo reductive radical cyclizations upon treatment with SmI(2)-H(2)O to give decorated cycloheptanes in a single highly selective operation during which up to three contiguous stereocenters are generated. Furthermore, cascade processes involving lactones bearing two alkenes, an alkene and an alkyne, or an allene and an alkene allow "one-pot" access to biologically significant molecular scaffolds with the construction of up to four contiguous stereocenters. The cyclizations proceed by the trapping of radical anions formed by electron transfer reduction of the lactone carbonyl.

  15. Reaction kinetics of solid-state cyclization of enalapril maleate investigated by isothermal FT-IR microscopic system.

    Science.gov (United States)

    Wang, S L; Lin, S Y; Chen, T F

    2001-04-01

    To investigate the reaction kinetics of the solid-state degradation process of enalapril maleate, a Fourier transform infrared microspectroscope equipped with thermal analyzer (thermal FT-IR microscopic system) was used. The isothermal stability study was conducted at 120-130 degrees C for 1-2 h and changes in the three-dimensional plots of the IR spectra of enalapril maleate with respect to heating time were observed. The study indicates that the bands at 1649, 1728, and 1751 cm(-1) assigned to intact enalapril maleate gradually reduced in peak intensity with heating time. However, the peak intensities at 1672 and 1738 cm(-1) (due to enalapril diketopiperazine (DKP) formation) and at 3250 cm(-1) (corresponding to water formation) gradually increased with heating time. The solid-state diketopiperazine formation and the degradation process of enalapril maleate via intramolecular cyclization were found to be simultaneous. The isothermal decomposition curves were sigmoidal and were characterized by induction and acceleration periods, indicating the presence of autocatalytic solid-state decompositions. Moreover, the power-law equation (n = 1/4) was found to provide the best fit to the kinetics of decomposition. This isothermal FT-IR microscopic system was easily used to investigate the degradation of enalapril maleate and the concomitant formation of DKP. The solid-state reaction of enalapril maleate required an activation energy of 195+/-12 kJ/mol to undergo the processes of decomposition and intramolecular cyclization.

  16. Iodine - catalyzed prins cyclization of aliphatic and aromatic ketones

    Energy Technology Data Exchange (ETDEWEB)

    Kishore, K.R.; Reddy, K.; Silva Junior, Luiz F., E-mail: luizfsjr@iq.usp.br [Universidade de Sao Paulo (IQ/USP), SP (Brazil). Inst. de Quimica. Dept. de Quimica Fundamental

    2013-09-15

    Iodine-catalyzed Prins cyclization of homoallylic alcohols and ketones was investigated. Anhydrous conditions and inert atmosphere are not required in this metal-free protocol. The reaction of 2-(3,4-dihydronaphthalene-1-yl)propan-1-ol with six aliphatic symmetric ketones gave the desired products in 67-77% yield. Cyclization was performed with four aliphatic unsymmetric ketones, leading to corresponding pyrans in 66-76% yield. Prins cyclization was also accomplished with four aromatic ketones in 37-66% yield. Finally, Prins cyclization of the monoterpene isopulegol and acetone was successfully achieved. (author)

  17. Iodine - catalyzed prins cyclization of aliphatic and aromatic ketones

    International Nuclear Information System (INIS)

    Kishore, K.R.; Reddy, K.; Silva Junior, Luiz F.

    2013-01-01

    Iodine-catalyzed Prins cyclization of homoallylic alcohols and ketones was investigated. Anhydrous conditions and inert atmosphere are not required in this metal-free protocol. The reaction of 2-(3,4-dihydronaphthalene-1-yl)propan-1-ol with six aliphatic symmetric ketones gave the desired products in 67-77% yield. Cyclization was performed with four aliphatic unsymmetric ketones, leading to corresponding pyrans in 66-76% yield. Prins cyclization was also accomplished with four aromatic ketones in 37-66% yield. Finally, Prins cyclization of the monoterpene isopulegol and acetone was successfully achieved. (author)

  18. Solvent and electronic effects on kinetics of cyclization of thermolabile aryllithium reagents. A comparison between 1-bromo-2-(2-bromoethylbenzene and 4,5-dimethoxy-1-bromo-2-(2-bromoethylbenzene

    Directory of Open Access Journals (Sweden)

    David A. Hunt

    2009-05-01

    Full Text Available A dramatic solvent effect on the stability and kinetics of intramolecular cyclization is described for the aryllithium species generated from 2-bromo-4,5-dimethoxy-(2-bromoethylbenzene. The aryllithium generated by the halogen-metal exchange reaction with n-butyllithium, is stable for > 1h when generated at -95 to -100 oC in diethyl ether/hexane and can be trapped with electrophiles. However, when the reaction is conducted in a THF/hexane mixture, the intermediate undergoes instantaneous intramolecular cyclization to afford 4,5-dimethoxybenzocyclobutene. By comparison, the corresponding 1-lithio-2-(2-bromoethyl-benzene intermediate is stable for >1h in either THF/hexane or diethyl ether/hexane at -95 to -100 oC. These results indicate that substituent effects as well as the nature of aggregation of these intermediates play key roles in determining the reaction pathway of functionalized aryllithium intermediates when quenched with electrophiles.

  19. Sortase-mediated backbone cyclization of proteins and peptides

    NARCIS (Netherlands)

    van 't Hof, W.; Hansenová Maňásková, S.; Veerman, E.C.I.; Bolscher, J.G.M.

    2015-01-01

    Backbone cyclization has a profound impact on the biological activity and thermal and proteolytic stability of proteins and peptides. Chemical methods for cyclization are not always feasible, especially for large peptides or proteins. Recombinant Staphylococcus aureus sortase A shows potential as a

  20. Ring-size-selective construction of fluorine-containing carbocycles via intramolecular iodoarylation of 1,1-difluoro-1-alkenes

    Directory of Open Access Journals (Sweden)

    Takeshi Fujita

    2017-12-01

    Full Text Available 1,1-Difluoro-1-alkenes bearing a biaryl-2-yl group effectively underwent site-selective intramolecular iodoarylation by the appropriate cationic iodine species. Iodoarylation of 2-(2-aryl-3,3-difluoroallylbiaryls proceeded via regioselective carbon–carbon bond formation at the carbon atoms in β-position to the fluorine substituents, thereby constructing dibenzo-fused six-membered carbocycles bearing a difluoroiodomethyl group. In contrast, 2-(3,3-difluoroallylbiaryls underwent a similar cyclization at the α-carbon atoms to afford ring-difluorinated seven-membered carbocycles.

  1. Structural determinants of reductive terpene cyclization in iridoid biosynthesis

    DEFF Research Database (Denmark)

    Kries, Hajo; Caputi, Lorenzo; Stevenson, Clare E M

    2016-01-01

    The carbon skeleton of ecologically and pharmacologically important iridoid monoterpenes is formed in a reductive cyclization reaction unrelated to canonical terpene cyclization. Here we report the crystal structure of the recently discovered iridoid cyclase (from Catharanthus roseus) bound...... to a mechanism-inspired inhibitor that illuminates substrate binding and catalytic function of the enzyme. Key features that distinguish iridoid synthase from its close homolog progesterone 5β-reductase are highlighted....

  2. Symmetry of intramolecular quantum dynamics

    CERN Document Server

    Burenin, Alexander V

    2012-01-01

    The main goal of this book is to give a systematic description of intramolecular quantum dynamics on the basis of only the symmetry principles. In this respect, the book has no analogs in the world literature. The obtained models lead to a simple, purely algebraic, scheme of calculation and are rigorous in the sense that their correctness is limited only to the correct choice of symmetry of the internal dynamics. The book is basically intended for scientists working in the field of molecular spectroscopy, quantum and structural chemistry.

  3. Catalytic Enantioselective Synthesis of Tetrahydocarbazoles and Exocyclic Pictet-Spengler-Type Reactions

    DEFF Research Database (Denmark)

    Hansen, Casper Lykke; Ohm, Ragnhild Gaard; Olsen, Lasse Bohn

    2016-01-01

    A synthetic strategy for the synthesis of chiral tetrahydrocarbazoles (THCAs) has been developed. The strategy relies on two types of 6-exo-trig cyclization of 3-substituted indole substrates. Enantioselective domino Friedel-Crafts-type reactions leading to THCAs can be catalyzed by chiral phosph...... phosphoric acid derivatives (with up to >99% ee), and the first examples of exocyclic Pictet-Spengler reactions to form THCAs are reported....

  4. Cetalox and analogues: synthesis via acid-mediated polyene cyclizations.

    Science.gov (United States)

    Snowden, Roger L

    2008-06-01

    Using a novel, acid-mediated cyclization methodology, a direct access to Cetalox ((+/-)-1; a commercially important ambergris-type odorant) and various structurally related didehydro (i.e., 19, 26, and 30) and tetradehydro (i.e., 28 and 37/38) analogues is described. Treatment of either (E,E)-14 or (E)-15 with an excess of FSO(3)H in 2-nitropropane at -90 degrees stereospecifically afforded (+/-)-1 in 40 and 42% yield, respectively. Under similar conditions, cyclization of (E)-18 or 20 furnished 19 in 60 and 64% yield, respectively. Analogously, using an excess of ClSO(3)H in CH(2)Cl(2) at -80 degrees, 26 is formed with high stereoselectivity by cyclization of either (E)-24 or (Z)-25 (52 and 31% yield, resp.); in the same manner, 28 was prepared from 27 (22% yield). The same principle was applied to the synthesis of racemic Superambrox (30), via cyclization of 35, but only with poor selectivity (22%) and low yield (7%). Another approach via cyclization of (E)-40 under solvolysis conditions (excess TFA in CH(2)Cl(2) at -10 degrees) gave a higher yield (15%) with improved selectivity (43%). Finally, cyclization of 34 (1:1 diastereoisomer mixture) afforded 37/38 (10:1) in 27% yield. The qualitative organoleptic properties of 19, 26, 28, 30, and 37/38 (10:1) are briefly discussed.

  5. Inter- and intramolecular aldol reactions promiscuously catalyzed by a proline-based tautomerase.

    Science.gov (United States)

    Rahimi, Mehran; Geertsema, Edzard M; Miao, Yufeng; van der Meer, Jan-Ytzen; van den Bosch, Thea; de Haan, Pim; Zandvoort, Ellen; Poelarends, Gerrit J

    2017-03-28

    The enzyme 4-oxalocrotonate tautomerase (4-OT), which in nature catalyzes a tautomerization step as part of a catabolic pathway for aromatic hydrocarbons, was found to promiscuously catalyze different types of aldol reactions. These include the self-condensation of propanal, the cross-coupling of propanal and benzaldehyde, the cross-coupling of propanal and pyruvate, and the intramolecular cyclizations of hexanedial and heptanedial. Mutation of the catalytic amino-terminal proline (P1A) greatly reduces 4-OT's aldolase activities, whereas mutation of another active site residue (F50A) strongly enhances 4-OT's aldolase activities, indicating that aldolization is an active site process. This catalytic promiscuity of 4-OT could be exploited as starting point to create tailor-made, artificial aldolases for challenging self- and cross-aldolizations.

  6. Direct Lactamization of Azido Amides via Staudinger-Type Reductive Cyclization

    International Nuclear Information System (INIS)

    Heo, In Jung; Lee, Su Jeong; Cho, Chang Woo

    2012-01-01

    The direct lactamization of 1,3- and 1,4-azido amides has been achieved using triphenylphosphine and water, affording various γ- and δ-lactams in good to excellent yields. The direct lactamization of the azido amides was performed via the Staudinger-type reductive cyclization in which the amide group acts as the electrophile for lactam synthesis. This lactamization provides a mild, functional group tolerant and efficient route for the synthesis of various γ- and δ-lactams found in natural products and pharmaceuticals. Further studies will be conducted to develop new synthetic routes for the synthesis of various lactams. The lactam ring system is one of the most ubiquitous structural motifs found in natural products and pharmaceuticals. Owing to the prevalence of lactams, their synthesis has attracted considerable attention. Lactams are usually prepared by the coupling of activated carboxylic acid derivatives with amines. Alternative routes include the Beckmann rearrangement of oximes, the Schmidt reaction of cyclic ketones and hydrazoic acid, the Kinugasa reaction of nitrones and terminal acetylenes, the Diels-Alder reaction of cyclopentadiene and chlorosulfonyl isocyanate, transition metal catalyzed lactamization of amino alcohols, and iodolactamization of amides and alkenes. In particular, the intramolecular Staudinger ligation of azides and activated carboxy acids, including esters, is well known as an environmentally friendly and mild protocol for lactam synthesis

  7. Intramolecular Energy Transfer, Charge Transfer & Hydrogen Bond

    Indian Academy of Sciences (India)

    Ultrafast Dynamics of Chemical Reactions in Condensed Phase: Intramolecular Energy Transfer, Charge Transfer & Hydrogen Bond. Dipak K. Palit Radaition & Photochemistry Division Bhabha Atomic Research Centre Mumbai 400 085, India.

  8. Intramolecular Association within the SAFT Framework

    DEFF Research Database (Denmark)

    Avlund, Ane Søgaard; Kontogeorgis, Georgios; Chapman, Walter G.

    2011-01-01

    the contribution to the Helmholtz free energy from association (inter- as well as intramolecularly) at equilibrium. Sear and Jackson rederived the contribution to the Helmholtz free energy from association from the theory by Wertheim [J. Stat. Phys. 42 (3–4), 459 (1986)] with inclusion of intramolecular...... association, and using this approach we obtain an expression for the Helmholtz free energy that is valid also at non-equilibrium states (with respect to hydrogen bonds), which is very useful when calculating derivatives.......A general theory for modelling intramolecular association within the SAFT framework is proposed. Sear and Jackson [Phys. Rev. E. 50 (1), 386 (1994)] and Ghonasgi and Chapman [J. Chem. Phys. 102 (6), 2585 (1995)] have previously extended SAFT to include intramolecular association for chains with two...

  9. Preparation of Al-SBA-15 Pellets with Low Amount of Additives: Effect of Binder Content on Texture and Mechanical Properties. Application to Friedel-Crafts Alkylation

    Czech Academy of Sciences Publication Activity Database

    Topka, Pavel; Karban, Jindřich; Soukup, Karel; Jirátová, Květa; Šolcová, Olga

    2011-01-01

    Roč. 168, č. 1 (2011), s. 433-440 ISSN 1385-8947 R&D Projects: GA ČR GA104/09/0694; GA AV ČR KAN400720701 Institutional research plan: CEZ:AV0Z40720504 Keywords : mesoporous aluminosilicates * pellets * Al-SBA-15 Subject RIV: CI - Industrial Chemistry, Chemical Engineering Impact factor: 3.461, year: 2011

  10. An excited-state intramolecular photon transfer fluorescence probe for localizable live cell imaging of cysteine

    Science.gov (United States)

    Liu, Wei; Chen, Wen; Liu, Si-Jia; Jiang, Jian-Hui

    2017-03-01

    Small molecule probes suitable for selective and specific fluorescence imaging of some important but low-concentration intracellular reactive sulfur species such as cysteine (Cys) pose a challenge in chemical biology. We present a readily available, fast-response fluorescence probe CHCQ-Ac, with 2-(5‧-chloro-2-hydroxyl-phenyl)-6-chloro-4(3 H)-quinazolinone (CHCQ) as the fluorophore and acrylate group as the functional moiety, that enables high-selectivity and high-sensitivity for detecting Cys in both solution and biological system. After specifically reacted with Cys, the probe undergoes a seven-membered intramolecular cyclization and released the fluorophore CHCQ with excited-state intramolecular photon transfer effect. A highly fluorescent, insoluble aggregate was then formed to facilitate high-sensitivity and high-resolution imaging. The results showed that probe CHCQ-Ac affords a remarkably large Stokes shift and can detect Cys under physiological pH condition with no interference from other analytes. Moreover, this probe was proved to have excellent chemical stability, low cytotoxicity and good cell permeability. Our design of this probe provides a novel potential tool to visualize and localize cysteine in bioimaging of live cells that would greatly help to explore various Cys-related physiological and pathological cellular processes in cell biology and diagnostics.

  11. SOCl 2 catalyzed cyclization of chalcones: Synthesis and spectral ...

    African Journals Online (AJOL)

    Some aryl-aryl 1H pyrazoles have been synthesised by cyclization of aryl chalcones and hydrazine hydrate in the presence of SOCl2. The yields of the pyrazoles are more than 85%. These pyrazoles are characterized by their physical constants and spectral data. The infrared, NMR spectral group frequencies of these ...

  12. Diluent induced cyclization and phase separation in polymer networks

    Czech Academy of Sciences Publication Activity Database

    Dušková-Smrčková, Miroslava; Valentová, H.; Ďuračková, Andrea; Dušek, Karel

    306-307, č. 1 (2011), s. 67-76 ISSN 1022-1360. [Polymer Networks Group Meeting /20./. Goslar, 29.08.2010-02.09.2010] R&D Projects: GA ČR GA106/08/1409 Institutional research plan: CEZ:AV0Z40500505 Keywords : cyclization * elasticity * gelation Subject RIV: JI - Composite Materials

  13. Proline-catalysed asymmetric ketol cyclizations: The template ...

    Indian Academy of Sciences (India)

    Unknown

    Abstract. A modified template mechanism based on modelling studies of energy minimised complexes is presented for the asymmetric proline-catalysed cyclization of triketones 1, 2 and 3 to the 2S,3S-ketols. 1a, 2a and 3a respectively. The template model involves a three-point contact as favoured in enzyme– substrate ...

  14. Proline-catalysed asymmetric ketol cyclizations: The template ...

    Indian Academy of Sciences (India)

    A modified template mechanism based on modelling studies of energy minimised complexes is presented for the asymmetric proline-catalysed cyclization of triketones 1, 2 and 3 to the 2, 3-ketols 1a, 2a and 3a respectively. The template model involves a three-point contact as favoured in enzyme-substrate interactions.

  15. Divergence in Ynone Reactivity: Atypical Cyclization by 3,4-Difunctionalization versus Rare Bis(cyclization).

    Science.gov (United States)

    Almendros, Pedro; Alcaide, Benito; Lázaro-Milla, Carlos; Delgado-Martínez, Patricia

    2018-04-06

    Functionalized ynones can be activated by in situ generated Tf2C=CH2 to form zwitterionic species, which were trapped in an intramolecular fashion by several nucleophiles to generate in a divergent way two main types of triflones. Through fine-tuning the temperature, bis(triflyl)-6-membered- or (triflyl)-5-membered-fused-heterocycles were achieved in reasonable yields in a totally selective manner. In this way, bis(triflyl)flavones, bis(triflyl)thioflavones, bis(triflyl)selenoflavones, (triflyl)benzothienopyrans, (triflyl)benzoselenophenopyrans, (triflyl)vinyl aurones, and (triflyl)pyranoindoles were built. Conceivable mechanistic proposals were suggested based in the isolation of several intermediates and control experiments. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Rational reprogramming of fungal polyketide first-ring cyclization.

    Science.gov (United States)

    Xu, Yuquan; Zhou, Tong; Zhou, Zhengfu; Su, Shiyou; Roberts, Sue A; Montfort, William R; Zeng, Jia; Chen, Ming; Zhang, Wei; Lin, Min; Zhan, Jixun; Molnár, István

    2013-04-02

    Resorcylic acid lactones and dihydroxyphenylacetic acid lactones represent important pharmacophores with heat shock response and immune system modulatory activities. The biosynthesis of these fungal polyketides involves a pair of collaborating iterative polyketide synthases (iPKSs): a highly reducing iPKS with product that is further elaborated by a nonreducing iPKS (nrPKS) to yield a 1,3-benzenediol moiety bridged by a macrolactone. Biosynthesis of unreduced polyketides requires the sequestration and programmed cyclization of highly reactive poly-β-ketoacyl intermediates to channel these uncommitted, pluripotent substrates to defined subsets of the polyketide structural space. Catalyzed by product template (PT) domains of the fungal nrPKSs and discrete aromatase/cyclase enzymes in bacteria, regiospecific first-ring aldol cyclizations result in characteristically different polyketide folding modes. However, a few fungal polyketides, including the dihydroxyphenylacetic acid lactone dehydrocurvularin, derive from a folding event that is analogous to the bacterial folding mode. The structural basis of such a drastic difference in the way a PT domain acts has not been investigated until now. We report here that the fungal vs. bacterial folding mode difference is portable on creating hybrid enzymes, and we structurally characterize the resulting unnatural products. Using structure-guided active site engineering, we unravel structural contributions to regiospecific aldol condensations and show that reshaping the cyclization chamber of a PT domain by only three selected point mutations is sufficient to reprogram the dehydrocurvularin nrPKS to produce polyketides with a fungal fold. Such rational control of first-ring cyclizations will facilitate efforts to the engineered biosynthesis of novel chemical diversity from natural unreduced polyketides.

  17. Cobalt-Catalyzed Tandem C-H Activation/C-C Cleavage/C-H Cyclization of Aromatic Amides with Alkylidenecyclopropanes.

    Science.gov (United States)

    Li, Mingliang; Kwong, Fuk Yee

    2018-03-08

    A cobalt-catalyzed chelation-assisted tandem C-H activation/C-C cleavage/C-H cyclization of aromatic amides with alkylidenecyclopropanes (ACPs) is reported. This process allows the sequential formation of two C-C bonds, in which it is in sharp contrast to previous report of using Rh catalyst for the formation of C-N bond. Here the inexpensive catalyst system exhibits good functional group compatibility and relatively broad substrate scope. The desired products can be easily transformed into polycyclic lactones with m-CPBA. Mechanistic studies revealed that the tandem reaction proceeds through a sequential C-H cobaltation, β-carbon elimination and intramolecular C-H cobaltation pathway. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Double Intramolecular Transacetalization of Polyhydroxy Acetals: Synthesis of Conformationally-Restricted 1,3-Dioxanes with Axially-Oriented Phenyl Moiety

    Directory of Open Access Journals (Sweden)

    Samuel Asare-Nkansah

    2016-11-01

    Full Text Available The synthesis of conformationally-restricted 1,3-dioxanes with a phenyl moiety fixed in an axial orientation at the acetalic center is described. Starting with diethyl 3-hydroxyglutarate (15, benzaldehyde acetal 12a and acetophenone ketal 12b bearing a protected 1,3,5-trihydroxypentyl side chain in the o-position were prepared. The first acid-catalyzed intramolecular transacetalization gave a mixture of diastereomeric 2-benzofurans 18 (ratio of diastereomers 2:2:1:1. After OH group deprotection, the second intramolecular transacetalization afforded tricyclic alcohol 14a (2-(1,5-epoxy-1,3,4,5-tetrahydro-2-benzoxepin-3-yl]ethan-1-ol. Analogous cyclizations led to the corresponding silyl ether 22a (19% and azide 23a (13%. Whereas tricyclic alcohol 14a was obtained as a 1:1 mixture of diastereomers, the silyl ether 22a and the azide 23a afforded only one diastereomer. This observation indicates a faster cyclization of the minor diastereomers providing the thermodynamically-favored compounds with equatorially-oriented substituents in the 3-position of the tricyclic 1,5-epoxy-2-benzoxepine system. In general, acetophenone-derived ketalic compounds (b-series required very mild reaction conditions and gave lower yields than the corresponding acetalic compounds (a-series.

  19. Palladium-Catalyzed Intramolecular Trost-Oppolzer-Type Alder-Ene Reaction of Dienyl Acetates to Cyclopentadienes.

    Science.gov (United States)

    Bankar, Siddheshwar K; Singh, Bara; Tung, Pinku; Ramasastry, S S V

    2018-02-05

    A new approach to the synthesis of highly substituted cyclopentadienes, indenes, and cyclopentene-fused heteroarenes by means of the Pd-catalyzed Trost-Oppolzer-type intramolecular Alder-ene reaction of 2,4-pentadienyl acetates is described. This unprecedented transformation combines the electrophilic features of the Tsuji-Trost reaction with the nucleophilic features of the Alder-ene reaction. The overall outcome can be perceived as a hitherto unknown "acid-free" iso-Nazarov-type cyclization. The versatility of this strategy was further demonstrated by the formal synthesis of paucifloral F, a resveratrol-based natural product. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Structural, intramolecular hydrogen bonding and vibrational studies ...

    Indian Academy of Sciences (India)

    The harmonic oscillator model of aromaticity (HOMA) index elucidated the impact of hydrogen bond- ing in the ring. Intramolecular hydrogen bonding energy has been calculated from topological study. The low wavenumber vibrational modes obtained from experimental FT-Raman spectrum also supported the presence.

  1. Solvent control of intramolecular proton transfer

    DEFF Research Database (Denmark)

    Manolova, Y.; Marciniak, Heinz; Tschierlei, S.

    2017-01-01

    of molecules in the enol and zwitterionic proton transfer (PT) form exists in the ground state. However, the zwitterion is the energetically favored one in the electronically excited state. Optical excitation of the enol form results in intramolecular proton transfer and formation of the PT form within 1.4 ps...

  2. Structural, intramolecular hydrogen bonding and vibrational studies ...

    Indian Academy of Sciences (India)

    An extensive theoretical study on the molecular structure and vibrational analysis of 3-amino-4- methoxy benzamide (3A4MBA) was undertaken using density functional theoretical (DFT) method. The possibility of formation of intramolecular hydrogen bonding was identified from structural parameter analysis and confirmed ...

  3. Structural, intramolecular hydrogen bonding and vibrational studies

    Indian Academy of Sciences (India)

    An extensive theoretical study on the molecular structure and vibrational analysis of 3-amino-4- methoxy benzamide (3A4MBA) was undertaken using density functional theoretical (DFT) method. The possibility of formation of intramolecular hydrogen bonding was identified from structural parameter analysis and confirmed ...

  4. Photoswitchable Intramolecular H-Stacking of Perylenebisimide

    NARCIS (Netherlands)

    Wang, Jiaobing; Kulago, Artem; Browne, Wesley R.; Feringa, Ben L.

    2010-01-01

    Dynamic control over the formation of H- or J-type aggregates of chromophores is of fundamental importance for developing responsive organic optoelectronic materials. In this study, the first example of photoswitching between a nonstacked and an intramolecularly H-stacked arrangement of

  5. Structural, intramolecular hydrogen bonding and vibrational studies ...

    Indian Academy of Sciences (India)

    The harmonic oscillator model of aromaticity (HOMA) index elucidated the impact of hydrogen bond- ing in the ring. Intramolecular hydrogen ... (Figure 3). The total ener- gies obtained for these possible conformers are listed in Table 1. ..... Structure, Reactivity and Intermolecular Forces: An. Euristic Interpretation by Means of ...

  6. Proline-catalysed asymmetric ketol cyclizations: The template ...

    Indian Academy of Sciences (India)

    Unknown

    ted enantioselective aldol addition reactions of ace- tone and substituted acetones with aldehydes catalysed by proline. Conflicting kinetic evidence has been obtained by Agami et al9 for the participa- tion of two molecules of proline in the transition states of proline-catalysed intramolecular cycliza- tions and by Houk et al10 ...

  7. An optimized intein-mediated protein ligation approach for the efficient cyclization of cysteine-rich proteins.

    Science.gov (United States)

    Tarasava, Katsiaryna; Freisinger, Eva

    2014-12-01

    Head-to-tail backbone cyclization of proteins is a widely used approach for the improvement of protein stability. One way to obtain cyclic proteins via recombinant expression makes use of engineered Intein tags, which are self-cleaving protein domains. In this approach, pH-induced self-cleavage of the N-terminal Intein tag generates an N-terminal cysteine residue at the target protein, which then attacks in an intramolecular reaction the C-terminal thioester formed by the second C-terminal Intein tag resulting in the release of the cyclic target protein. In the current work we aimed to produce a cyclic analog of the small γ-Ec-1 domain of the wheat metallothionein, which contains six cysteine residues. During the purification process we faced several challenges, among them premature cleavage of one or the other Intein tag resulting in decreasing yields and contamination with linear species. To improve efficiency of the system we applied a number of optimizations such as the introduction of a Tobacco etch virus cleavage site and an additional poly-histidine tag. Our efforts resulted in the production of a cyclic protein in moderate yields without any contamination with linear protein species. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

  8. Intramolecular and Transannular Diels-Alder Reactions

    DEFF Research Database (Denmark)

    Tanner, David Ackland; Ascic, Erhad

    2014-01-01

    Few reactions can compete with the Diels-Alder (DA) [4+2] cycloaddition for the rapid and efficient generation of molecular complexity. The DA reaction is atom-economic and stereospecific, as well as diastereo- and regioselective. The intramolecular version (IMDA) of the DA cycloaddition and its...... and dienophile, methods for acceleration of IMDA reactions (such as use of high pressure) and catalysis (using oxophilic or carbophilic metal complexes, Brønsted acids, and enzymes). The use of furans as diene components (IMDAF), intramolecular hetero-DA (IMHDA) and IMDA reactions with inverse electron demand...... are also covered. Applications of IMDA to asymmetric synthesis (from substrate control through to enantioselective catalysis, including organocatalysis) are presented, along with tandem sequences involving IMDA cycloaddition. A theme pervading the whole chapter is the use of IMDA reactions for the total...

  9. Intramolecular Energy Transfer, Charge Transfer & Hydrogen Bond

    Indian Academy of Sciences (India)

    Ultrafast Dynamics of Chemical Reactions in Condensed Phase: Intramolecular Energy Transfer, Charge Transfer & Hydrogen Bond · PowerPoint Presentation · Slide 3 · Slide 4 · Slide 5 · Slide 6 · Slide 7 · Slide 8 · Slide 9 · Slide 10 · Slide 11 · Slide 12 · Slide 13 · Slide 14 · Slide 15 · Slide 16 · Slide 17 · Slide 18 · Slide 19.

  10. Intramolecular Energy Relaxation and Statistical Rate Theory

    OpenAIRE

    Okitsugu, KAJIMOTO; Department of Chemistry, Kyoto University

    1994-01-01

    Statistical rate theory is essentially based on the state counting without any restrictions other than the energy and the angular momentum conservation. In this work, two kinds of restrictions are introduced into the statistical theory. The first restriction is related to the intramolecular energy flow within the reacting molecular system. The excess energy of reaction is made distributed with some bias favoring a specific degree of freedom. That is, the statistical weight of each product sta...

  11. Cyclization cascade of allenyl azides: A dual mechanism

    Science.gov (United States)

    López, Carlos Silva; Faza, Olalla Nieto; Feldman, Ken S.; Iyer, Malliga R.; Hester, D. Keith

    2008-01-01

    A density functional theory based computational approach to describing the mechanistic course of the allene azide cycloaddition cascade sequence has been developed. The results of these calculations permit characterization of key reactive intermediates (diradicals and/or indolidenes), and explain the different behaviour observed in the experimental studies between conjugated and non-conjugated species. Furthermore, computational analysis of certain intermediates offer insight into issues of regioselectivity and stereoselectivity in cases where different reaction channels are in competition, suggesting suitable substitutions to achieve a single regioisomer in the indole synthesis via azide-allene cyclization. PMID:17530848

  12. Asymmetric, Stereodivergent Synthesis of (−)-Clusianone Utilizing a Biomimetic Cationic Cyclization **

    Science.gov (United States)

    Boyce, Jonathan H.

    2014-01-01

    We report a stereodivergent, asymmetric total synthesis of (−)-clusianone in six steps from commercial materials. We implement a challenging cationic cyclization forging a bond between two sterically encumbered quaternary carbons. Mechanistic studies point to the unique ability of formic acid to bring about successful cyclization to the clusianone framework. PMID:24916169

  13. Experimental and Quantum-mechanical Investigation of the Vinylsilane-Iminium Ion Cyclization

    DEFF Research Database (Denmark)

    Kværnø, Lisbet; Norrby, Per-Ola; Tanner, David Ackland

    2003-01-01

    A vinylsilane-ketiminium ion cyclization involving iminium species derived from amines 6 and 7 was investigated experimentally as a possible approach to some biologically interesting 1-azaspirocycles. However, even under conditions of microwave irradiation at high temperatures no such cyclization...

  14. Cyclization enhances function of linear anti-arthritic peptides.

    Science.gov (United States)

    Ali, Marina; Amon, Michael; Bender, Vera; Bolte, Andrea; Separovic, Frances; Benson, Heather; Manolios, Nicholas

    2014-01-01

    This study describes the biophysical and immunomodulatory features of a cyclic peptide termed C1 which consists of alternating d-, l-amino acids and is capable of inhibiting IL-2 production in vitro and reducing the induction and extent of T-cell mediated inflammation in animal models. Solid-state nuclear magnetic resonance demonstrates that the peptide orders the lipid bilayer, suggesting a transmembrane orientation, and this is supported by surface plasmon resonance indicating strong binding affinity of C1 to model membranes. In vitro cell viability and proliferation assays show that C1 does not disrupt the integrity of cell surface membranes. Permeation studies of C1 and analogs across human epidermis cells show that the stability and skin permeability are enhanced by cyclization. Treatment with C1 in an asthma and in an arthritis animal model resulted in a suppressed immune response. Cyclization may be a useful means of enhancing biological linear peptide activity and improving delivery. © 2013. Published by Elsevier Inc. All rights reserved.

  15. Vanadium haloperoxidase-catalyzed bromination and cyclization of terpenes.

    Science.gov (United States)

    Carter-Franklin, Jayme N; Parrish, Jon D; Tschirret-Guth, Richard A; Little, R Daniel; Butler, Alison

    2003-04-02

    Marine red algae (Rhodophyta) are a rich source of bioactive halogenated natural products, including cyclic terpenes. The biogenesis of certain cyclic halogenated marine natural products is thought to involve marine haloperoxidase enzymes. Evidence is presented that vanadium bromoperoxidase (V-BrPO) isolated and cloned from marine red algae that produce halogenated compounds (e.g., Plocamium cartilagineum, Laurencia pacifica, Corallina officinalis) can catalyze the bromination and cyclization of terpenes and terpene analogues. The V-BrPO-catalyzed reaction with the monoterpene nerol in the presence of bromide ion and hydrogen peroxide produces a monobromo eight-membered cyclic ether similar to laurencin, a brominated C15 acetogenin, from Laurencia glandulifera, along with noncyclic bromohydrin, epoxide, and dibromoproducts; however, reaction of aqueous bromine with nerol produced only noncyclic bromohydrin, epoxide, and dibromoproducts. The V-BrPO-catalyzed reaction with geraniol in the presence of bromide ion and hydrogen peroxide produces two singly brominated six-membered cyclic products, analogous to the ring structures of alpha and beta snyderols, brominated sesquiterpenes from Laurencia, spp., along with noncyclic bromohydrin, epoxide, and dibromoproducts; again, reaction of geraniol with aqueous bromine produces only noncyclic bromohydrin, epoxide, and dibromoproducts. Thus, V-BrPO can direct the electrophilic bromination and cyclization of terpenes.

  16. In vitro structure-activity relationship of Re-cyclized octreotide analogues

    Energy Technology Data Exchange (ETDEWEB)

    Dannoon, Shorouk F. [Department of Chemistry, University of Missouri, Columbia, MO 65211 (United States); Bigott-Hennkens, Heather M. [Department of Veterinary Medicine and Surgery, University of Missouri, Columbia, MO 65211 (United States); Ma Lixin [Department of Radiology, University of Missouri, Columbia, MO 65211 (United States); International Institute of Nano and Molecular Medicine, University of Missouri, Columbia, MO 65211 (United States); Nuclear Science and Engineering Institute, University of Missouri, Columbia, MO 65211 (United States); Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, MO 65201 (United States); Gallazzi, Fabio [Structural Biology Core, University of Missouri, Columbia, MO 65211 (United States); Lewis, Michael R., E-mail: lewismic@missouri.ed [Department of Veterinary Medicine and Surgery, University of Missouri, Columbia, MO 65211 (United States); Department of Radiology, University of Missouri, Columbia, MO 65211 (United States); Nuclear Science and Engineering Institute, University of Missouri, Columbia, MO 65211 (United States); Research Service, Harry S. Truman Memorial Veterans' Hospital, Columbia, MO 65201 (United States); Jurisson, Silvia S., E-mail: jurissons@missouri.ed [Department of Chemistry, University of Missouri, Columbia, MO 65211 (United States); Department of Radiology, University of Missouri, Columbia, MO 65211 (United States); Nuclear Science and Engineering Institute, University of Missouri, Columbia, MO 65211 (United States)

    2010-07-15

    Introduction: Development of radiolabeled octreotide analogues is of interest for targeting somatostatin receptor (SSTR)-positive tumors for diagnostic and therapeutic purposes. We are investigating a direct labeling approach for incorporation of a Re ion into octreotide analogues, where the peptide sequences are cyclized via coordination to Re rather than through a disulfide bridge. Methods: Various octreotide analogue sequences and coordination systems (e.g., S{sub 2}N{sub 2} and S{sub 3}N) were synthesized and cyclized with nonradioactive Re. In vitro competitive binding assays with {sup 111}In-DOTA-Tyr{sup 3}-octreotide in AR42J rat pancreatic tumor cells yielded IC{sub 50} values as a measure of SSTR affinity of the Re-cyclized analogues. Three-dimensional structures of Re-cyclized Tyr{sup 3}-octreotate and its disulfide-bridged analogue were calculated from two-dimensional NMR experiments to visualize the effect of metal cyclization on the analogue's pharmacophore. Results: Only two of the 11 Re-cyclized analogues investigated showed moderate in vitro binding affinity toward somatostatin subtype 2 receptors. Three-dimensional molecular structures of Re- and disulfide-cyclized Tyr{sup 3}-octreotate were calculated, and both of their pharmacophore turns appear to be very similar with minor differences due to metal coordination to the amide nitrogen of one of the pharmacophore amino acids. Conclusions: Various Re-cyclized analogues were developed and analogue 4 had moderate affinity toward somatostatin subtype 2 receptors. In vitro stable studies that are in progress showed stable radiometal cyclization of octreotide analogues via NS{sub 3} and N{sub 2}S{sub 2} coordination forming five- and six-membered chelate rings. In vivo biodistribution studies are underway of {sup 99m}Tc-cyclized analogue 4.

  17. Intramolecular Barbier reaction in water: cyclopentane and cyclohexane ring closure

    Directory of Open Access Journals (Sweden)

    RADOMIR N. SAICIC

    2002-03-01

    Full Text Available Zinc or indium promoted intramolecular Barbier reactions of aldehydes containing a suitably positioned allylic or propargylic halide unit afford unsaturated cyclic alcohols in moderate yields.

  18. Excited state Intramolecular Proton Transfer in Anthralin

    DEFF Research Database (Denmark)

    Møller, Søren; Andersen, Kristine B.; Spanget-Larsen, Jens

    1998-01-01

    Quantum chemical calculations performed on anthralin (1,8-dihydroxy-9(10H)-anthracenone) predict the possibility of an excited-state intramolecular proton transfer process. Fluorescence excitation and emission spectra of the compound dissolved in n-hexane at ambient temperature results...... in an unusually large fluorescence Stokes shift of 10500 cm−1. The emission appears as a broad band with a maximum at 17500 cm−1 and is characterized by a low and nearly temperature-independent quantum yield. The results are interpreted as an indication of a large equilibrium geometry change upon excitation...

  19. Femtosecond laser studies of ultrafast intramolecular processes

    Energy Technology Data Exchange (ETDEWEB)

    Hayden, C. [Sandia National Laboratories, Livermore, CA (United States)

    1993-12-01

    The goal of this research is to better understand the detailed mechanisms of chemical reactions by observing, directly in time, the dynamics of fundamental chemical processes. In this work femtosecond laser pulses are used to initiate chemical processes and follow the progress of these processes in time. The authors are currently studying ultrafast internal conversion and subsequent intramolecular relaxation in unsaturated hydrocarbons. In addition, the authors are developing nonlinear optical techniques to prepare and monitor the time evolution of specific vibrational motions in ground electronic state molecules.

  20. Intramolecular energy transfer reactions in polymetallic

    Energy Technology Data Exchange (ETDEWEB)

    Petersen, J.

    1990-11-01

    This report is concerned with intramolecular, energy-transfer reactions. The concept of preparing synthetically a complex molecular species, capable of absorbing a photon at one metal center (antenna fragment), transferring that energy to a second metal center (reactive fragment) via a bridging ligand was first reported by our group in 1979. It is now apparent that a major emphasis in inorganic chemistry in the future will involve these types of molecular ensembles. Complexes discussed include Rh, Ru, and Cu complexes. 23 refs., 14 tabs.

  1. Cyclization of ortho-hydroxycinnamates to coumarins under mild conditions: A nucleophilic organocatalysis approach

    Directory of Open Access Journals (Sweden)

    Florian Boeck

    2012-09-01

    Full Text Available (E-Alkyl ortho-hydroxycinnamates cyclize to coumarins at elevated temperatures of 140–250 °C. We find that the use of tri-n-butylphosphane (20 mol % as a nucleophilic organocatalyst in MeOH solution allows cyclization to take place under much milder conditions (60–70 °C. Several coumarins were prepared, starting from ortho-hydroxyarylaldehydes, by Wittig reaction with Ph3P=CHCO2Me to (E-methyl ortho-hydroxycinnamates, followed by the phosphane catalyzed cyclization.

  2. One-pot desymmetrizing hydroformylation/carbonyl ene cyclization process: straightforward access to highly functionalized cyclohexanols.

    Science.gov (United States)

    Bigot, Aurélien; Breuninger, Daniel; Breit, Bernhard

    2008-12-04

    Rapid access to highly functionalized alkylidene cyclohexanols through a one-pot desymmetrizing hydroformylation/carbonyl ene cyclization starting from simple bisalkenylcarbinols is reported. Mechanistic insight into the carbonyl ene reaction is given, highlighting the importance of hyperconjugative substituent effects.

  3. Double reductive cyclization: A facile synthesis of the indoloquinoline alkaloid cryptotackieine

    Digital Repository Service at National Institute of Oceanography (India)

    Parvatkar, P.T.; Parameswaran, P.S.; Tilve, S.G.

    A new synthesis of the indoloquinoline alkaloid cryptotackieine, isolated from Cryptolepis sanguinolenta, is described which involves a Perkin reaction, a tandem double reduction-double cyclization reaction followed by regioselective methylation...

  4. Syntheses of Gliocladin C and Related Alkaloids.

    Science.gov (United States)

    Hodges, Timothy R; Benjamin, Noah M; Martin, Stephen F

    2017-05-05

    A unique approach to gliocladin C and related alkaloids was developed that features an unprecedented nucleophilic addition of a diketopiperazine to an isatin derivative followed by a Friedel-Crafts alkylation of the resultant tertiary alcohol with indole to set the key quaternary center. Chemoselective oxindole reduction and cyclization delivered a pivotal hexahydropyrrolo[2,3-b]indole diketopiperazine intermediate that was readily converted into (±)-gliocladin C, (±)-T988C, and (±)-gliocladine C, culminating in the shortest approach to these alkaloids reported to date.

  5. SYNTHESIS 7-HYDROXY-3’,4’-DIMETHOXYISOFLAVON FROM EUGENOL

    Directory of Open Access Journals (Sweden)

    Andi Hairil Alimuddin

    2011-11-01

    Full Text Available Eugenol from the isolation of clove leaves oil had been utilized in the synthesis of 7-hydroxy-3',4'-dimethoxy-isoflavone based on deoxybenzoin intermediate. The raw material was firstly converted into methyleugenol using DMS (89.87%. Secondly, methyl eugenol was oxidized using KMnO4 to produce 3,4-dimethoxybenzyl carboxylic acid (21%. Friedel-Craft acylation of it with recorcinol produced 3,4-dimethoxybenzyl-2',4'-dihydroxyphenyl ketone (deoxybenzoin intermediate in 78% yield. Eventually, cyclization of the intermediate with reagents of BF3.OEt2/DMF/POCl3 yielded 7-hydroxy-3',4'-isoflavone in 85% yield.

  6. New Palladium-Catalyzed Domino Reaction with Intramolecular Ring Closure of an N-(2-Chloro-3-heteroaryl) arylamide: First Synthesis of Oxazolo[4,5-b] pyrazines

    DEFF Research Database (Denmark)

    Demmer, Charles S.; Hansen, Jacob C.; Kehler, Jan

    2014-01-01

    The synthesis of novel planar heterocycles is at the heart of basic research as such scaffolds constitute key building blocks in important diverse areas of research: drug discovery, material sciences, and pesticides. The well-known benzoxazole is often contained in drug candidates but tweaking its...... lipophilicity and target interaction points are often desired. In this respect, the oxazolo[4,5-b]pyrazine is an attractive heterocyclic scaffold as it possesses increased water solubility as well as two additional hydrogen bonding acceptors. We here report a new Pd(II)-catalyzed domino reaction comprising...... the first Pd(II)-assisted intramolecular cyclization of an N-(2-chloro-3-heteroaryl)arylamide and validate its value by application to the first synthesis of 2-substituted oxazolo[4,5-b]pyrazines. We demonstrate that a bidentate phosphorus ligand as well as the presence of an aromatic nitrogen atom...

  7. Influence of Intramolecular Charge Transfer and Nuclear Quantum Effects on Intramolecular Hydrogen Bonds in Azopyrimidines.

    Science.gov (United States)

    Bártová, Kateřina; Čechová, Lucie; Procházková, Eliška; Socha, Ondřej; Janeba, Zlatko; Dračínský, Martin

    2017-10-06

    Intramolecular hydrogen bonds (IMHBs) in 5-azopyrimidines are investigated by NMR spectroscopy and DFT computations that involve nuclear quantum effects. A series of substituted 5-phenylazopyrimidines with one or two hydrogen bond donors able to form IMHBs with the azo group is prepared by azo coupling. The barrier of interconversion between two rotamers of the compounds with two possible IMHBs is determined by variable temperature NMR spectroscopy and it is demonstrated that the barrier is significantly affected by intramolecular charge transfer. Through-hydrogen-bond scalar coupling is investigated in 15 N labeled compounds and the stability of the IMHBs is correlated with experimental NMR parameters and rationalized by path integral molecular dynamics simulations that involve nuclear quantum effects. Detailed information on the hydrogen bond geometry upon hydrogen-to-deuterium isotope exchange is obtained from a comparison of experimental and calculated NMR data.

  8. Oxidative cyclization of prodigiosin by an alkylglycerol monooxygenase-like enzyme

    DEFF Research Database (Denmark)

    de Rond, Tristan; Stow, Parker; Eigl, Ian

    2017-01-01

    Prodiginines, which are tripyrrole alkaloids displaying a wide array of bioactivities, occur as linear and cyclic congeners. Identification of an unclustered biosynthetic gene led to the discovery of the enzyme responsible for catalyzing the regiospecific C–H activation and cyclization of prodigi...... of prodigiosin to cycloprodigiosin in Pseudoalteromonas rubra. This enzyme is related to alkylglycerol monooxygenase and unrelated to RedG, the Rieske oxygenase that produces cyclized prodiginines in Streptomyces, implying convergent evolution....

  9. Mechanistic Study of Nickel-Catalyzed Ynal Reductive Cyclizations Through Kinetic Analysis

    OpenAIRE

    Baxter, Ryan D.; Montgomery, John

    2011-01-01

    The mechanism of nickel-catalyzed, silane-mediated reductive cyclization of ynals has been evaluated. The cyclizations are first-order in [Ni] and [ynal] and zeroth-order in [silane]. These results, in combination with the lack of rapid silane consumption upon reaction initiation are inconsistent with mechanisms involving reaction initiation by oxidative addition of Ni(0) to the silane. Silane consumption occurs only when both the alkyne and aldehyde and are present. Mechanisms involving rate...

  10. Biomimetic cyclization of epoxide precursors of indole mono-, sesqui- and diterpene alkaloids by Lewis acids.

    Science.gov (United States)

    Isaka, Tetsuya; Hasegawa, Morifumi; Toshima, Hiroaki

    2011-01-01

    Cyclization of the synthesized epoxide precursors of indole mono-, sesqui- and diterpene alkaloids was performed to elucidate the mechanism for biomimetic cationic cyclization to polycyclic structures. 3-(6,7-Epoxygeranyl)indole (11), 3-(10,11-epoxyfarnesyl)indole (2) and 3-(14,15-epoxygeranylgeranyl)indole (3) were respectively synthesized from geraniol, farnesol and geranylgeraniol in 6 or 7 steps. Four Lewis acids (MeAlCl(2), BF(3)·OEt(2), TiCl(4) and SnCl(4)) were applied for biomimetic cyclization of the synthesized epoxide precursors. The cyclization products (one product from 11, four products from 2, and three products from 3) were isolated after separation by chromatography. Their structures were determined by using NMR (COSY, HSQC, HMBC, NOESY, etc.) and HRMS analyses. The results show that biomimetic cyclization gave new polycyclic compounds similar to natural indole terpene alkaloids. We conclude that the stability of cation intermediates should determine the preference for product formation by biomimetic cyclization when using a Lewis acid.

  11. Gold-catalyzed cyclization reactions of allenol and alkynol derivatives.

    Science.gov (United States)

    Alcaide, Benito; Almendros, Pedro

    2014-03-18

    Although gold is chemically inert as a bulk metal, the landmark discovery that gold nanoparticles can be effective catalysts has opened up new and exciting research opportunities in the field. In recent years, there has been growth in the number of reactions catalyzed by gold complexes [gold(I) and gold(III)], usually as homogeneous catalysts, because they are soft Lewis acids. In addition, alkynes and allenes have interesting reactivities and selectivities, notably their ability to produce complex structures in very few steps. In this Account, we describe our work in gold catalysis with a focus on the formation of C-C and C-O bonds using allenes and alkynes as starting materials. Of these, oxa- and carbo-cyclizations are perhaps the best known and most frequently studied. We have divided those contributions into sections arranged according to the nature of the starting material (allene versus alkyne). Gold-catalyzed carbocyclizations in allenyl C2-linked indoles, allenyl-β-lactams, and allenyl sugars follow different mechanistic pathways. The cyclization of indole-tethered allenols results in the efficient synthesis of carbazole derivatives, for example. However, the compound produced from gold-catalyzed 9-endo carbocyclization of (aryloxy)allenyl-tethered 2-azetidinones is in noticeable contrast to the 5-exo hydroalkylation product that results from allenyl sugars. We have illustrated the unusual preference for the 4-exo-dig cyclization in allene chemistry, as well as the rare β-hydride elimination reaction, in gold catalysis from readily available α-allenols. We have also observed in γ-allenols that a (methoxymethyl)oxy protecting group not only masks a hydroxyl functionality but also exerts directing effects as a controlling unit in a gold-catalyzed regioselectivity reversal. Our recent work has also led to a combined experimental and computational study on regioselective gold-catalyzed synthetic routes to 1,3-oxazinan-2-ones (kinetically controlled

  12. Fluorescence and Intramolecular Energy Transfer in Polyphenylene Dendrimers

    NARCIS (Netherlands)

    Liu, Daojun; Feyter, Steven De; Cotlet, Mircea; Stefan, Alina; Wiesler, Uwe-Martin; Herrmann, Andreas; Grebel-Koehler, Dörthe; Qu, Jianqiang; Müllen, Klaus; Schryver, Frans C. De

    2003-01-01

    The fluorescence of polyphenylene dendrimers and the intramolecular energy transfer in polyphenylene dendrimers containing a perylenediimide core have been investigated in this paper. Polyphenylene dendrimers composed of tens or hundreds of out-of-plane twisted phenyl units exhibit strong

  13. Intramolecularly Hydrogen-Bonded Polypyrroles as Electro-Optical Sensors

    National Research Council Canada - National Science Library

    Nicholson, Jesse

    2001-01-01

    We have developed a new class of polypyrroles bearing both hydrogen-bond acceptor and hydrogen-donor groups such that the intramolecular hydrogen bonding holds the system planar enhancing conjugation...

  14. Structural basis for cyclization specificity of two Azotobacter type III polyketide synthases: a single amino acid substitution reverses their cyclization specificity.

    Science.gov (United States)

    Satou, Ryutaro; Miyanaga, Akimasa; Ozawa, Hiroki; Funa, Nobutaka; Katsuyama, Yohei; Miyazono, Ken-ichi; Tanokura, Masaru; Ohnishi, Yasuo; Horinouchi, Sueharu

    2013-11-22

    Type III polyketide synthases (PKSs) show diverse cyclization specificity. We previously characterized two Azotobacter type III PKSs (ArsB and ArsC) with different cyclization specificity. ArsB and ArsC, which share a high sequence identity (71%), produce alkylresorcinols and alkylpyrones through aldol condensation and lactonization of the same polyketomethylene intermediate, respectively. Here we identified a key amino acid residue for the cyclization specificity of each enzyme by site-directed mutagenesis. Trp-281 of ArsB corresponded to Gly-284 of ArsC in the amino acid sequence alignment. The ArsB W281G mutant synthesized alkylpyrone but not alkylresorcinol. In contrast, the ArsC G284W mutant synthesized alkylresorcinol with a small amount of alkylpyrone. These results indicate that this amino acid residue (Trp-281 of ArsB or Gly-284 of ArsC) should occupy a critical position for the cyclization specificity of each enzyme. We then determined crystal structures of the wild-type and G284W ArsC proteins at resolutions of 1.76 and 1.99 Å, respectively. Comparison of these two ArsC structures indicates that the G284W substitution brings a steric wall to the active site cavity, resulting in a significant reduction of the cavity volume. We postulate that the polyketomethylene intermediate can be folded to a suitable form for aldol condensation only in such a relatively narrow cavity of ArsC G284W (and presumably ArsB). This is the first report on the alteration of cyclization specificity from lactonization to aldol condensation for a type III PKS. The ArsC G284W structure is significant as it is the first reported structure of a microbial resorcinol synthase.

  15. Estudios sobre la síntesis del diterpeno de origen marino helioporina B

    OpenAIRE

    Esteban García, Gemma

    1998-01-01

    En el presente trabajo se ha elaborado un estudio encaminado a la síntesis del diterpeno de origen marino Helioporina B. Tras el planteamiento retrosintético se ha efectuado la síntesis del esqueleto tricíclico presente en el producto natural llevado a cabo sobre la misma a través de una secuencia constituida por un acoplamiento cruzado tipo Suzuki seguido de un proceso de acilación de Friedel-Crafts intramolecular. Esta metodología, nueva en su conjunto, se ha aplicado a la síntesis de difer...

  16. Intramolecular C(sp(3))H amination of arylsulfonyl azides with engineered and artificial myoglobin-based catalysts.

    Science.gov (United States)

    Bordeaux, Melanie; Singh, Ritesh; Fasan, Rudi

    2014-10-15

    The direct conversion of aliphatic CH bonds into CN bonds provides an attractive approach to the introduction of nitrogen-containing functionalities in organic molecules. Following the recent discovery that cytochrome P450 enzymes can catalyze the cyclization of arylsulfonyl azide compounds via an intramolecular C(sp(3))H amination reaction, we have explored here the CH amination reactivity of other hemoproteins. Various heme-containing proteins, and in particular myoglobin and horseradish peroxidase, were found to be capable of catalyzing this transformation. Based on this finding, a series of engineered and artificial myoglobin variants containing active site mutations and non-native Mn- and Co-protoporphyrin IX cofactors, respectively, were prepared to investigate the effect of these structural changes on the catalytic activity and selectivity of these catalysts. Our studies showed that metallo-substituted myoglobins constitute viable CH amination catalysts, revealing a distinctive reactivity trend as compared to synthetic metalloporphyrin counterparts. On the other hand, amino acid substitutions at the level of the heme pocket were found to be beneficial toward improving the stereo- and enantioselectivity of these Mb-catalyzed reactions. Mechanistic studies involving kinetic isotope effect experiments indicate that CH bond cleavage is implicated in the rate-limiting step of myoglobin-catalyzed amination of arylsulfonyl azides. Altogether, these studies indicate that myoglobin constitutes a promising scaffold for the design and development of CH amination catalysts. Copyright © 2014 Elsevier Ltd. All rights reserved.

  17. Intramolecular C(sp3)—H amination of arylsulfonyl azides with engineered and artificial myoglobin-based catalysts

    Science.gov (United States)

    Bordeaux, Melanie; Singh, Ritesh; Fasan, Rudi

    2014-01-01

    The direct conversion of aliphatic C—H bonds into C—N bonds provides an attractive approach to the introduction of nitrogen-containing functionalities in organic molecules. Following our recent discovery that cytochrome P450 enzymes can catalyze the cyclization of arylsulfonyl azide compounds via an intramolecular C(sp3)—H amination reaction, we have explored here the C—H amination reactivity of other hemoproteins. Various heme-containing proteins, and in particular myoglobin and horseradish peroxidase, were found to be capable of catalyzing this transformation. Based on this finding, a series of engineered and artificial myoglobin variants containing active site mutations and non-native Mn- and Co-protoporphyrin IX cofactors, respectively, were preparedWmvestigate the effect of these structural changes on the catalytic activity and selectivity of to these catalysts. Our studies showed that metallo-substituted myoglobins constitute viable C—H amination catalysts, revealing a distinctive reactivity trend as compared to synthetic metalloporphyrin counterparts. On the other hand, amino acid substitutions at the level of the heme pocket were found to be beneficial toward improving the stereo- and enantioselectivity of these Mb-catalyzed reactions. Mechanistic studies involving kinetic isotope effect experiments indicate that C—H bond cleavage is implicated in the rate-limiting step of myoglobin-catalyzed amination of arylsulfonyl azides. Altogether, these studies indicate that myoglobin constitutes a promising scaffold for the design and development of C— H amination catalysts. PMID:24890656

  18. Fates of imine intermediates in radical cyclizations of N-sulfonylindoles and ene-sulfonamides

    Directory of Open Access Journals (Sweden)

    Hanmo Zhang

    2015-09-01

    Full Text Available Two new fates of imine intermediates formed on radical cyclizations of ene-sulfonamides have been identified, reduction and hydration/fragmentation. Tin hydride-mediated cyclizations of 2-halo-N-(3-methyl-N-sulfonylindoleanilines provide spiro[indoline-3,3'-indolones] or spiro-3,3'-biindolines (derived from imine reduction, depending on the indole C2 substituent. Cyclizations of 2-haloanilide derivatives of 3-carboxy-N-sulfonyl-2,3-dihydropyrroles also presumably form spiro-imines as primary products. However, the lactam carbonyl group facilitates the ring-opening of these cyclic imines by a new pathway of hydration and retro-Claisen-type reaction, providing rearranged 2-(2'-formamidoethyloxindoles.

  19. Cyclization of the N-Terminal X-Asn-Gly Motif during Sample Preparation for Bottom-Up Proteomics

    DEFF Research Database (Denmark)

    Zhang, Xumin; Højrup, Peter

    2010-01-01

    We, herein, report a novel -17 Da peptide modification corresponding to an N-terminal cyclization of peptides possessing the N-terminal motif of X-Asn-Gly. The cyclization occurs spontaneously during sample preparation for bottom-up proteomics studies. Distinct from the two well-known N...

  20. Tandem Olefin Metathesis/Oxidative Cyclization: Synthesis of Tetrahydrofuran Diols from Simple Olefins.

    Science.gov (United States)

    Dornan, Peter K; Lee, Daniel; Grubbs, Robert H

    2016-05-25

    A tandem olefin metathesis/oxidative cyclization has been developed to synthesize 2,5-disubstituted tetrahydrofuran (THF) diols in a stereocontrolled fashion from simple olefin precursors. The ruthenium metathesis catalyst is converted into an oxidation catalyst in the second step and is thus responsible for both catalytic steps. The stereochemistry of the 1,5-diene intermediate can be controlled through the choice of catalyst and the type of metathesis conducted. This olefin stereochemistry then controls the THF diol stereochemistry through a highly stereospecific oxidative cyclization.

  1. Divergent Cyclization Reactions of Morita-Baylis-Hillman Carbonates of 2-Cyclohexenone and Isatylidene Malononitriles.

    Science.gov (United States)

    Peng, Jing; Ran, Guang-Yao; Du, Wei; Chen, Ying-Chun

    2015-09-18

    Zwitterionic dienolates generated from Morita-Baylis-Hillman carbonates of cyclohexen-2-one and a phenolic tertiary amine catalyst underwent divergent cyclization reactions with isatylidene malononitriles. A new [4 + 2] stepwise cyclization process was disclosed to deliver complex bridged spirooxindoles after the initial δ'-regioselective Rauhut-Currier-type reaction with N-methyl electrophiles by the catalysis of β-isocupreidine, while spirooxindoles incorporating an aromatic chromene motif were generated with N-MOM acceptors in the presence of α-isocupreine through different domino transformations.

  2. Tandem dinucleophilic cyclization of cyclohexane-1,3-diones with pyridinium salts

    Directory of Open Access Journals (Sweden)

    Mostafa Kiamehr

    2013-06-01

    Full Text Available The cyclization of cyclohexane-1,3-diones with various substituted pyridinium salts afforded functionalized 8-oxa-10-aza-tricyclo[7.3.1.02,7]trideca-2(7,11-dienes. The reaction proceeds by regioselective attack of the central carbon atom of the 1,3-dicarbonyl unit to 4-position of the pyridinium salt and subsequent cyclization by base-assisted proton migration and nucleophilic addition of the oxygen atom to the 2-position, as was elucidated by DFT computations. Fairly extensive screening of bases and additives revealed that the presence of potassium cations is essential for formation of the product.

  3. Multivariate data analysis as a tool to investigate the reaction kinetics of intramolecular cyclization of enalapril maleate studied by isothermal and non-isothermal FT-IR microscopy.

    Science.gov (United States)

    Widjaja, Effendi; Lim, Geok Hong; Chow, Pui Shan; Tan, Selvi

    2007-12-01

    In this paper, the use of multivariate data analysis approach to investigate the kinetics of solid-state reaction monitored via FT-IR thermal microscopy is discussed. The solid-state degradation of enalapril maleate was monitored non-isothermally at temperature range from 25 to 200 degrees C and isothermally at various temperatures (115, 120, 125, 130, and 135 degrees C) for a few hours. The collected FT-IR spectra were subjected to self-modeling curve resolution (SMCR) in order to elucidate the pure component spectral estimates. Subsequently, the relative contributions from the observed species could be obtained by projecting the pure component spectral estimates onto the collected FT-IR spectra. Accordingly, the conversion factors from enalapril maleate to diketopiperazine were calculated and were fitted to various solid-state reaction models. The activation energy values (E(a)) calculated from seven nucleation models were ranging from 176.4 to 193.9 kJ/mol. This multivariate data analysis approach proves to be an effective tool for analyzing the kinetic spectroscopic data having a high degree of overlap between original compound and its degradation product since the information from the whole spectral range is used.

  4. Asymmetric Synthesis of Substituted Tropinones using the Intramolecular Mannich Cyclization Reaction and Acyclic N-Sulfinyl β-Amino Ketone Ketals

    Science.gov (United States)

    Davis, Franklin A.; Theddu, Naresh; Gaspari, Paul M.

    2009-01-01

    Sulfinimine-derived, enantiopure N-sulfinyl β-amino ketone ketals on hydrolysis give dehydropyrrolidine ketones that on treatment with (Boc)2O/DMAP afford substituted tropinones in good yield. PMID:19278245

  5. Highly Functionalized Cyclopentane Derivatives by Tandem Michael Addition/Radical Cyclization/Oxygenation Reactions

    Czech Academy of Sciences Publication Activity Database

    Holan, Martin; Pohl, Radek; Císařová, I.; Klepetářová, Blanka; Jones, P. G.; Jahn, Ullrich

    2015-01-01

    Roč. 21, č. 27 (2015), s. 9877-9888 ISSN 0947-6539 R&D Projects: GA ČR GA13-40188S Institutional support: RVO:61388963 Keywords : cyclization * domino reactions * electron transfer * Michael addition * radical reactions Subject RIV: CC - Organic Chemistry Impact factor: 5.771, year: 2015

  6. Tandem Michael addition/radical cyclizations for the construction of highly functionalized cyclopentanes

    Czech Academy of Sciences Publication Activity Database

    Holan, Martin; Pohl, Radek; Císarová, I.; Jahn, Ullrich

    2012-01-01

    Roč. 106, - (2012), s1298-s1298 ISSN 0009-2770. [EuCheMS Chemistry Congress /4./. 26.08.2012-30.08.2012, Prague] Institutional research plan: CEZ:AV0Z40550506 Keywords : cyclization * diastereoselectivity * Michael addiction * radical reactions * domino reactions Subject RIV: CC - Organic Chemistry

  7. Solvent-free cyclization of linear dienes using olefin metathesis and the Thorpe-Ingold effect

    Energy Technology Data Exchange (ETDEWEB)

    Forbees, M.D.E.; Myers, T.L.; Maynard, H.D.; Schulz, G.R. (Univ. of North Carolina, Chapel Hill (United States)); Patton, J.T.; Smith, D.W. Jr.; Wagener, K.B. (Univ. of Florida, Gainesville (United States))

    1992-12-30

    The olefin metathesis reaction is of great synthetic utility in polymer chemistry. The recent development of ring-opening (ROMP) and acyclic diene (ADMET) metathesis polymerization reactions has opened new avenues for the synthesis of novel polymeric materials. Recently the authors used ADMET to synthesize several photochemically active poly(keto olefins) using the catalyst Mo(CHCMe[sub 2]Ph)(NAr)(OCMe(CF[sub 3])[sub 2])[sub 2] (Ar = 2,6-diisopropylphenyl) (1) developed by Schrock and co-workers in 1990. In the course of that work, they discovered that neat samples of highly substituted dienes will cyclize quantitatively via metathesis to give difunctional five- and seven-membered rings instead of the expected linear polymer. Examples of substituted diene cyclizations by metathesis even in the presence of a solvent are rare. Their systematic exploitation in organic synthesis has therefore been limited to two recent studies by Fu and Grubbs, who cyclized several substituted diene ethers, amines, and amides to unsaturated oxygen and nitrogen heterocycles. Cyclization of unsubstituted dienes in various solvents has been reported, but complete conversion occurred in only a few cases. Formation of cyclic alkene oligomers from back-biting during the ROMP reaction is also known. The reactions reported here are unusual in that they are intermolecular between catalyst and substrate, yet can give 100% yield of product solely from the monomer in the absence of solvent. 13 refs.

  8. Trifluoroacetic acid-promoted Michael addition-cyclization reactions of vinylogous carbamates.

    Science.gov (United States)

    Naganaboina, Ram Tilak; Nayak, Amrita; Peddinti, Rama Krishna

    2014-06-07

    A simple and efficient methodology has been developed for the synthesis of pyrrolobenzoxazine and 3-arylamino coumarin derivatives promoted by trifluoroacetic acid. The initial step in the current protocol involves a Michael addition of the 1,4-benzoxazinone derivatives, a novel class of vinylogous carbamates to the Michael acceptors and subsequent cyclization.

  9. Structural Basis for Cyclization Specificity of Two Azotobacter Type III Polyketide Synthases

    Science.gov (United States)

    Satou, Ryutaro; Miyanaga, Akimasa; Ozawa, Hiroki; Funa, Nobutaka; Katsuyama, Yohei; Miyazono, Ken-ichi; Tanokura, Masaru; Ohnishi, Yasuo; Horinouchi, Sueharu

    2013-01-01

    Type III polyketide synthases (PKSs) show diverse cyclization specificity. We previously characterized two Azotobacter type III PKSs (ArsB and ArsC) with different cyclization specificity. ArsB and ArsC, which share a high sequence identity (71%), produce alkylresorcinols and alkylpyrones through aldol condensation and lactonization of the same polyketomethylene intermediate, respectively. Here we identified a key amino acid residue for the cyclization specificity of each enzyme by site-directed mutagenesis. Trp-281 of ArsB corresponded to Gly-284 of ArsC in the amino acid sequence alignment. The ArsB W281G mutant synthesized alkylpyrone but not alkylresorcinol. In contrast, the ArsC G284W mutant synthesized alkylresorcinol with a small amount of alkylpyrone. These results indicate that this amino acid residue (Trp-281 of ArsB or Gly-284 of ArsC) should occupy a critical position for the cyclization specificity of each enzyme. We then determined crystal structures of the wild-type and G284W ArsC proteins at resolutions of 1.76 and 1.99 Å, respectively. Comparison of these two ArsC structures indicates that the G284W substitution brings a steric wall to the active site cavity, resulting in a significant reduction of the cavity volume. We postulate that the polyketomethylene intermediate can be folded to a suitable form for aldol condensation only in such a relatively narrow cavity of ArsC G284W (and presumably ArsB). This is the first report on the alteration of cyclization specificity from lactonization to aldol condensation for a type III PKS. The ArsC G284W structure is significant as it is the first reported structure of a microbial resorcinol synthase. PMID:24100027

  10. Evaluation of intramolecular charge transfer state of 4-N, N ...

    Indian Academy of Sciences (India)

    intermediate charge transfer (TICT) model.2 Evidence suggests that the intramolecular TICT process from a donor to an acceptor could be achieved by a twist- ing motion of the donor moiety that promotes initially generated locally excited (LE) state to an energeti- cally relaxed charge transfer state (CT).2–6,8,13 Besides.

  11. Excited state intramolecular charge transfer reaction in 4-(1 ...

    Indian Academy of Sciences (India)

    Administrator

    Abstract. Excited state intramolecular charge transfer reaction of 4-(1-azetidinyl) benzonitrile (P4C) in deuterated and normal methanol, ethanol and acetonitrile has been studied in order to investigate the solvent isotope effects on reaction rates and yields. These quantities (reaction rates and yields) along with several.

  12. Excited state intramolecular charge transfer reaction of 4 ...

    Indian Academy of Sciences (India)

    An intramolecular charge transfer (ICT) molecule with an extra hetero atom in its donor moiety has been synthesized in order to investigate how ICT reaction is affected by hetero atom replacement. Photo-physical and photo-dynamical properties of this molecule, 4-(morpholenyl)benzonitrile (M6C), have been studied in 20 ...

  13. Preparation of CN x /Carbon Nanotube Intramolecular Junctions by ...

    African Journals Online (AJOL)

    Preparation of CN x /Carbon Nanotube Intramolecular Junctions by Switching Gas Sources in Continuous Chemical Vapour Deposition. ... nanotubes were observed, and such different structures at both sides of the junctions indicated some interesting properties and offered potential applications for future nanodevices.

  14. and Di-hydration on the Intramolecular Proton Transfers and ...

    Indian Academy of Sciences (India)

    of the isomers did not change the stability trend, so that the tri-keto isomer was the most stable isomer among the hydrated and non-hydrated isomers. The activation energies (Ea) of the intramolecular proton transfers. (tautomerisms) and energy barriers of H-rotations around its C-O axis in enolic isomers were calculated.

  15. The intramolecular electron transfer between copper sites of nitrite reductase

    DEFF Research Database (Denmark)

    Farver, O; Eady, R R; Abraham, Z H

    1998-01-01

    The intramolecular electron transfer (ET) between the type 1 Cu(I) and the type 2 Cu(II) sites of Alcaligenes xylosoxidans dissimilatory nitrite reductase (AxNiR) has been studied in order to compare it with the analogous process taking place in ascorbate oxidase (AO). This internal process is in...

  16. Excited state intramolecular charge transfer reaction in 4-(1 ...

    Indian Academy of Sciences (India)

    Excited state intramolecular charge transfer reaction of 4-(1-azetidinyl) benzonitrile (P4C) in deuterated and normal methanol, ethanol and acetonitrile has been studied in order to investigate the solvent isotope effects on reaction rates and yields. These quantities (reaction rates and yields) along with several other ...

  17. Effects of acid concentration on intramolecular charge transfer ...

    Indian Academy of Sciences (India)

    of P4C molecule.7 Temperature-assisted aggregation of alcohol has also been observed by following the fluo- rescence response of the same solute.20 Electrolyte- induced modulation of intramolecular charge transfer rate of P4C molecule in pure solvent has been explored and a non-monotonic dependence observed.18.

  18. Excited state intramolecular proton transfer in some tautomeric azo dyes and Schiff bases containing an intramolecular hydrogen bond

    NARCIS (Netherlands)

    Joshi, H.C.; Kamounah, F.S.; Gooijer, C.; van der Zwan, G.; Antonov, L.

    2002-01-01

    Photophysical properties of several basically important aromatic azodyes (1-phenylazo-2-naphthol and 2-phenylazo-1-naphthol) and Schiff bases (N-(2-hydroxy-1-naphthylmethylidene) aniline and N-(1-hydroxy-2-naphthylmethylidene) aniline) all containing an intramolecular hydrogen bond were studied by

  19. Self-Cyclizing Antioxidants to Prevent DNA Damage Caused by Hydroxyl Radical.

    Science.gov (United States)

    AbdulSalam, Safnas F; Gurjar, Purujit N; Zhu, Haizhou; Liu, Jing; Johnson, Emma S; Kadekaro, Ana Luisa; Landero-Figueroa, Julio; Merino, Edward J

    2017-10-18

    Antioxidant therapy is a promising treatment strategy for protecting DNA from the damage caused by reactive oxygen species (ROS). Here, we report new self-cyclizing antioxidant reagents that are selective for the hydroxyl radical. Our mechanistic investigation revealed that the reagents react with three equivalents of oxidant in a cascade reaction to form a bicyclic final product. Among the reagents synthesized, 1 c showed favorable properties in vitro and in cellular studies. Using As 2 O 3 , which triggers ROS production, we showed that 1 c prevents formation of the guanine oxidation product 2,2,4-triamino-2H-oxazol-5-one-2'-deoxyribonucleoside and lowers cellular levels of reactive oxygen. The described self-cyclizing antioxidants are efficient, flexible, and tunable reagents with the potential to limit toxic oxidative stress. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Gold-Catalyzed Cyclizations of Alkynol-Based Compounds: Synthesis of Natural Products and Derivatives

    Directory of Open Access Journals (Sweden)

    Pedro Almendros

    2011-09-01

    Full Text Available The last decade has witnessed dramatic growth in the number of reactions catalyzed by gold complexes because of their powerful soft Lewis acid nature. In particular, the gold-catalyzed activation of propargylic compounds has progressively emerged in recent years. Some of these gold-catalyzed reactions in alkynes have been optimized and show significant utility in organic synthesis. Thus, apart from significant methodology work, in the meantime gold-catalyzed cyclizations in alkynol derivatives have become an efficient tool in total synthesis. However, there is a lack of specific review articles covering the joined importance of both gold salts and alkynol-based compounds for the synthesis of natural products and derivatives. The aim of this Review is to survey the chemistry of alkynol derivatives under gold-catalyzed cyclization conditions and its utility in total synthesis, concentrating on the advances that have been made in the last decade, and in particular in the last quinquennium.

  1. Reductive Cyclization and Petasis‐Like Reaction for the Synthesis of Functionalized γ‐Lactams

    DEFF Research Database (Denmark)

    Wu, Peng; Petersen, Michael Åxman; Cohrt, A. Emil

    2015-01-01

    An efficient reductive cyclization strategy was employed for the synthesis of N‐substituted β,γ‐dihydroxy‐γ‐lactams. A subsequent Petasis‐like reaction (PLR) through nucleophilic additions of boronic acids to intermediate N‐acyliminium ions produced substituted γ‐lactams. Overall, the application...... of this protocol provides β,γ‐dihydroxy‐γ‐lactams and functionalized γ‐lactams with potential interest for synthetic and bioorganic chemistry....

  2. Tandem Olefin Metathesis/Oxidative Cyclization: Synthesis of Tetrahydrofuran Diols from Simple Olefins

    OpenAIRE

    Dornan, Peter K.; Lee, Daniel; Grubbs, Robert H.

    2016-01-01

    A tandem olefin metathesis/oxidative cyclization has been developed to synthesize 2,5-disubstituted tetrahydrofuran (THF) diols in a stereocontrolled fashion from simple olefin precursors. The ruthenium metathesis catalyst is converted into an oxidation catalyst in the second step and is thus responsible for both catalytic steps. The stereochemistry of the 1,5-diene intermediate can be controlled through the choice of catalyst and the type of metathesis conducted. This olefin stereochemistry ...

  3. Methanococcus jannaschii Generates l-Proline by Cyclization of l-Ornithine

    Science.gov (United States)

    Graupner, Marion; White, Robert H.

    2001-01-01

    Cell extracts of Methanococcus jannaschii have been shown to readily convert l-ornithine to l-proline. This cyclization reaction proceeds with the loss of only the C-2 nitrogen, as has been documented for ornithine cyclodeaminase (EC 4.3.1.12). Since no gene homologous to that coding for ornithine cyclodeaminase is present in the genome of M. jannaschii, these results indicate that proline biosynthesis in M. jannaschii is accomplished by a previously unrecognized enzyme. PMID:11489875

  4. Gold(I-catalyzed domino cyclization for the synthesis of polyaromatic heterocycles

    Directory of Open Access Journals (Sweden)

    Mathieu Morin

    2013-11-01

    Full Text Available Gold(I complexes have emerged as powerful and useful catalysts for the formation of new C–C, C–O and C–N bonds. Taking advantage of the specificity of [IPrAuNCMe][SbF6] complexes to favor the 5-exo-dig cyclization over the 6-endo-dig pathway, we report a high yielding and efficient method to generate substituted polyaromatic heterocycles under remarkably mild reaction conditions.

  5. Green chemistry: solvent- and metal-free Prins cyclization. Application to sequential reactions.

    Science.gov (United States)

    Clarisse, Damien; Pelotier, Béatrice; Piva, Olivier; Fache, Fabienne

    2012-01-04

    Prins cyclization between a homoallylic alcohol and an aldehyde, promoted by trimethylsilyl halide, afforded 4-halo-tetrahydropyrans with good to excellent yields. Thanks to the absence of the solvent and metal, the THP thus obtained have been implicated without purification in several other reactions, in a sequential way, affording in particular new indole derivatives. This journal is © The Royal Society of Chemistry 2012

  6. Hydroxyl-substituted ladder polyethers via selective tandem epoxidation/cyclization sequence.

    Science.gov (United States)

    Czabaniuk, Lara C; Jamison, Timothy F

    2015-02-20

    A new and highly selective method for the synthesis of hydroxyl-substituted tetrahydropyrans is described. This method utilizes titanium(IV) isopropoxide and diethyl tartrate to perform a diastereoselective epoxidation followed by in situ epoxide activation and highly selective endo-cyclization to form the desired tetrahydropyran ring. The HIJ ring fragment of the marine ladder polyether yessotoxin was synthesized using this two-stage tactic that proceeds with high efficiency and excellent regioselectivity.

  7. Electrooxidative Tandem Cyclization of Activated Alkynes with Sulfinic Acids To Access Sulfonated Indenones

    Energy Technology Data Exchange (ETDEWEB)

    Wen, Jiangwei [The; Center; Shi, Wenyan [The; Zhang, Fan [The; Liu, Dong [The; Tang, Shan [The; Wang, Huamin [The; Lin, Xiao-Min [Center; Lei, Aiwen [The

    2017-05-25

    An,electrooxidative direct arylsulfonlylation of yones sulfintc acids via a radical tandem cyclization strategy has been developed for the construction of sulfonated ilicIenones:under oxidant, free conditions. This method provides a simple and efficient approach to prepare various sulfonylindenones in good to,excellent:Tyidds,, demonstrating the tremendous prospect of utilizing electrocatalysis in oxidative coupling, Notably, this reaction could Be easily scaled up with good, efficiency.

  8. Flow Pickering Emulsion Interfaces Enhance Catalysis Efficiency and Selectivity for Cyclization of Citronellal.

    Science.gov (United States)

    Chen, Huan; Zou, Houbing; Hao, Yajuan; Yang, Hengquan

    2017-05-09

    Cyclization of citronellal is a necessary intermediate step to produce the important flavor chemical (-)-menthol. Here, a continuous-flow Pickering emulsion (FPE) strategy for selective cyclization of citronellal to (-)-isopulegol by using water droplets hosting a heteropolyacid (HPA) catalyst to fill a column reactor is demonstrated. Owing to the large liquid-liquid interface and the excellent confinement ability of droplets toward HPA, the FPE system exhibited a much higher catalysis efficiency than its batch counterpart (2-5-fold) and an excellent durability (two months). Moreover, a remarkably enhanced selectivity was observed from 34.8 % for batch reactions to 64 % for the FPE reactions. It was found that the water droplet size and the flow rate significantly impact the catalysis selectivity and efficiency. This study not only represents an unprecedented and sustainable process for the selective cyclization of citronellal but also demonstrates a new flow-interface catalysis effect that can be useful for designing innovative catalysis systems in the future. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Mechanism of Intramolecular Rhodium- and Palladium-Catalyzed Alkene Alkoxyfunctionalizations

    KAUST Repository

    Vummaleti, Sai V. C.

    2015-11-13

    Density functional theory calculations have been used to investigate the reaction mechanism for the [Rh]-catalyzed intramolecular alkoxyacylation ([Rh] = [RhI(dppp)+] (dppp, 1,3-bis(diphenylphosphino)propane) and [Pd]/BPh3 dual catalytic system assisted intramolecular alkoxycyanation ([Pd] = Pd-Xantphos) using acylated and cyanated 2-allylphenol derivatives as substrates, respectively. Our results substantially confirm the proposed mechanism for both [Rh]- and [Pd]/ BPh3-mediated alkoxyfunctionalizations, offering a detailed geometrical and energetical understanding of all the elementary steps. Furthermore, for the [Rh]-mediated alkoxyacylation, our observations support the hypothesis that the quinoline group of the substrate is crucial to stabilize the acyl metal complex and prevent further decarbonylation. For [Pd]/BPh3-catalyzed alkoxycyanation, our findings clarify how the Lewis acid BPh3 cocatalyst accelerates the only slow step of the reaction, corresponding to the oxidative addition of the cyanate O-CN bond to the Pd center. © 2015 American Chemical Society.

  10. Structure and Intramolecular Proton Transfer of Alanine Radical Cations

    International Nuclear Information System (INIS)

    Lee, Gab Yong

    2012-01-01

    The structures of the four lowest alanine conformers, along with their radical cations and the effect of ionization on the intramolecular proton transfer process, are studied using the density functional theory and MP2 method. The energy order of the radical cations of alanine differs from that of the corresponding neutral conformers due to changes in the basicity of the NH 2 group upon ionization. Ionization favors the intramolecular proton transfer process, leading to a proton-transferred radical-cation structure, [NH 3 + -CHCH 3 -COO·], which contrasts with the fact that a proton-transferred zwitterionic conformer is not stable for a neutral alanine in the gas phase. The energy barrier during the proton transfer process is calculated to be about 6 kcal/mol

  11. Specific Features of Intramolecular Proton Transfer Reaction in Schiff Bases

    Directory of Open Access Journals (Sweden)

    Aleksander Koll

    2003-06-01

    Full Text Available Abstract: The differences between the intramolecular proton transfer in Mannich and Schiff bases are discussed. The tautomeric forms being in equilibrium in both types of molecules are seriously different. In Mannich bases there are in equilibrium the forms of phenols and phenolates. In Schiff bases each of tautomers is strongly influenced by resonance between zwitterionic and keto structures. Despite the common opinion that the proton transfer forms in compounds with internal π-electronic coupling are mainly keto forms it is shown in this work, that in Schiff bases the content of keto structure is slightly less than zwitterionic one. Almost equal participation of both forms leads to effective resonance between them and stabilization of intramolecular hydrogen bond in this way.

  12. Intramolecular interactions in dimedone and phenalen-1,3-dione adducts of 2(4)-pyridinecarboxaldehyde: Enol-enol and ring-chain tautomerism, strong hydrogen bonding, zwitterions

    Science.gov (United States)

    Sigalov, Mark; Shainyan, Bagrat; Krief, Pnina; Ushakov, Igor; Chipanina, Nina; Oznobikhina, Larisa

    2011-12-01

    The 2:1 adducts of dimedone and phenalen-1,3-dione with 2- and 4-pyridine carboxaldehyde, in spite of similar chemical behavior of their diketone precursors, have quite different tautomeric structure both in solid state and in solution. 2,2'-(Pyridin-2-ylmethanediyl)-bis(5,5-dimethyl-cyclohexane-1,3-dione) 5 exists as an equilibrium mixture of its dienol tautomer 5а' with two intramolecular H-bonds ОН⋯О dbnd С and OH ⋯N and the epimeric products of its reversible cyclization, that is, 4a-hydroxy-9-(pyridin-2-yl)-2,3,4,4a,6,7,9,9a-octahydro-5-H-xanthene-1,8-diones 5b (major) and 5c (minor), the latter appears only in polar media like DMSO. 2,2'-(Pyridin-4-ylmethanediyl)bis(5,5-dimethylcyclohexane-1,3-dione) 4, like other 2:1 dimedone-aldehyde adducts, both in solution and in solid state exists as dienol with two intramolecular H-bonds ОН ⋯О dbnd С. 4-[Bis(1H-phenalen-1,3(2H)-dione)methyl]pyridine 6 in nonpolar media like chloroform exists as dienol, but crystallizes from this solvent as zwitter-ion 6b with one very strong ionic hydrogen bond O sbnd H ⋯O sbnd and protonated pyridine nitrogen. The same zwitterion is formed in polar media (DMSO). For 2-[bis(1H-phenalen-1,3(2H)-dione)-methyl]-pyridine 7, fast exchange between its dienol tautomer 7a and zwitter-ion 7b occurs even in CD2Cl2, whereas in DMSO the equilibrium shifts towards zwitter-ion 7b.

  13. Intramolecular hydrogen bonding and tautomerism in Schiff bases ...

    Indian Academy of Sciences (India)

    N and keto-amine, O…H-N forms) in this series. The molecular structure of 8 has been determined crystallographically, and observed that the compound is in the form of phenol-imine, defined by the strong intramolecular [O-H…N = 1.72(3), 1.81(2) Å] hydrogen bonds. Compound 8 crystallizes in the monoclinic space group ...

  14. Utilizing redox-mediated Bergman cyclization toward the development of dual-action metalloenediyne therapeutics.

    Science.gov (United States)

    Lindahl, Sarah E; Park, Hyunsoo; Pink, Maren; Zaleski, Jeffrey M

    2013-03-13

    Reaction of 2 equiv of 1,2-bis((diphenylphosphino)ethynyl)benzene (dppeb, 1) with Pt(cod)Cl2 followed by treatment with N2H4 yields the reduced Pt(0) metalloenediyne, Pt(dppeb)2, 2. This complex is stable to both air oxidation and metal-mediated Bergman cyclization under ambient conditions due to the nearly idealized tetrahedral geometry. Reaction of 2 with 1 equiv of I2 in the presence of excess 1,4-cyclohexadiene (1,4-CHD) radical trap rapidly and near-quantitatively generates the cis-Bergman-cyclized, diiodo product 3 ((31)P: δ = 41 ppm, J(Pt-P) = 3346 Hz) with concomitant loss of 1 equiv of uncyclized phosphine chelate ((31)P: δ = -33 ppm). In contrast, addition of 2 equiv of I2 in the absence of additional radical trap instantaneously forms a metastable Pt(dppeb)2(2+) intermediate species, 4, that is characterized by δ = 51 ppm in the (31)P NMR (J(Pt-P) = 3171 Hz) and ν(C≡C) = 2169 cm(-1) in the Raman profile, indicating that it is an uncyclized, bis-ligated complex. Over 24 h, 4 undergoes ligand exchange to form a neutral, square planar complex that spontaneously Bergman cyclizes at ambient temperature to give the crystalline product Pt(dppnap-I2)I2 (dppnap-I2 = (1,4-diiodonaphthalene-2,3-diyl)bis(diphenylphosphine)), 5, in 52% isolated yield. Computational analysis of the oxidation reaction proposes two plausible flattened tetrahedral structures for intermediate 4: one where the phosphine core has migrated to a trans-spanning chelate geometry, and a second, higher energy structure (3.3 kcal/mol) with two cis-chelating phosphine ligands (41° dihedral angle) via a restricted alkyne-terminal starting point. While the energies are disparate, the common theme in both structures is the elongated Pt-P bond lengths (>2.4 Å), indicating that nucleophilic ligand substitution by I(-) is on the reaction trajectory to the cyclized product 5. The efficiency of the redox-mediated Bergman cyclization reaction of this stable Pt(0) metalloenediyne prodrug and

  15. Application to processing system using intra-molecular BRET

    Science.gov (United States)

    Otsuji, Tomomi; Okuda-Ashitaka, Emiko; Kojima, Satoshi; Akiyama, Hidehumi; Ito, Seiji; Ohmiya, Yoshihiro

    2003-07-01

    Luciferases are used as the reporter gene for promoter activity, whereas a green fluorescent protein (GFP) is used as marker for cellular function and localization. Recently, bioluminescence resonance energy transfer (BRET) between luciferase and YFP is used for analysis of inter-molecular reaction such as ligand-receptor in the living cells. The neuropeptides nocistatin (NST) and nociceptin/orphanin FQ (Noc/OFQ) are derived from the same precursor protein, while NST exhibits antagonism against Noc/OFQ-actions. In this study, we attempt an intra-molecular BRET system for monitoring dynamic biological process of the production of NST and Noc/OFQ in the living cells. At first, we constructed a fusion protein (Rluc-GFP) covalently linking luciferase (Renilla luciferase; Rluc) to Aequorea GFP as an intra-molecular BRET partner. Furthermore, we inserted constructs of mouse NST and Noc/OFQ (Rluc-m-GFP) or bovine NST and Noc/OFQ (Rluc-b-GFP) containing a proteolytic cleavage motif (Lys-Arg) within Rluc-GFP. When these constructions were transfected into Cos7 cells, all fusion proteins had luciferase activity and specific fluorescence. Luminescence spectra of Rluc-GFP, Rluc-m-GFP and Rluc-b-GFP fusion proteins with DeepBlueC as a substrate showed two peaks centered at 400 nm and 510 nm, whereas Rluc showed one peak centered at 400 nm. These results indicate that the proteolytic cleavage motif inserted fusion proteins between luciferase and GFP are available for intra-molecular BRET systems at first step.

  16. Total Syntheses of Polycyclic Polyprenylated Acylphloroglucinol Natural Products and Analogs Utilizing Alkylative Dearomatizations and Cationic Cyclizations

    Science.gov (United States)

    Boyce, Jonathan H.

    Polycyclic polyprenylated acylphloroglucinols (PPAPs) are structurally complex natural products with promising biological activities. These compounds have interesting anticancer and anti-HIV properties as well as other biological activities making them highly attractive synthetic targets. We report a stereodivergent, asymmetric total synthesis of (-)-clusianone in six steps from commercial materials. We have implemented a challenging cationic cyclization forging a bond between two sterically encumbered quaternary carbon atoms. Mechanistic studies point to the unique ability of formic acid to mediate the cyclization forming the clusianone framework. We also present a biosynthesis-inspired, diversity-oriented synthesis approach for rapid construction of PPAP analogs via palladium-catalyzed dearomative conjunctive allylic alkylation (DCAA). These efficient palladium-catalyzed protocols construct the [3.3.1]-bicyclic PPAP core in a single step from their stable aromatic precursors. The first syntheses of 13,14-didehydroxyisogarcinol and garcimultiflorone A stereoisomers are reported in six steps from a commercially available phloroglucinol. Lewis acid-controlled, diastereoselective cationic oxycyclizations enabled asymmetric syntheses of (-)-6-epi-13,14-didehydroxyisogarcinol and (+)-30-epi-13,14-didehydroxyisogarcinol. A similar strategy enabled production of the meso-derived isomers (+/-)-6,30- epi-13,14-didehydroxyisogarcinol and (+/-)-6,30-epi -garcmultiflorone A. A convenient strategy for gram scale synthesis of these stereoisomers was developed utilizing diastereomer separation at a later stage in the synthesis that minimized the number of necessary synthetic operations to access all possible stereoisomers. Finally, we report cationic rearrangements of dearomatized acylphloroglucinols leading to the formation of unprecedented PPAP scaffolds. A novel type A [3.3.1]-bicyclic PPAP was produced as a major product and the structure confirmed by X-ray crystallographic

  17. Intramolecular Hydrogen Bonding in (2-Hydroxybenzoyl)benzoylmethane Enol

    DEFF Research Database (Denmark)

    Hansen, Bjarke Knud Vilster; Winther, Morten; Spanget-Larsen, Jens

    2014-01-01

    , and the dienol form of 1,3-dibenzoylacetone. But in these examples the two H-bonds are equivalent, while in the case of OHDBM they are chemically different, involving one enolic and one phenolic hydroxy group. OHDBM is thus an interesting model compound with two competing H-bonds to the same carbonyl group......In the stable enol tautomer of the title compound (OHDBM), one carbonyl group is flanked by two β-hydroxy groups, giving rise to bifold intramolecular H-bonding. A similar situation is found in other β,β'-dihydroxy carbonyl compounds like chrysazin, anthralin, 2,2'-dihydroxybenzophenone...

  18. Recording Intramolecular Mechanics during the Manipulation of a Large Molecule

    Energy Technology Data Exchange (ETDEWEB)

    Moresco, Francesca; Meyer, Gerhard; Rieder, Karl-Heinz; Tang, Hao; Gourdon, Andre; Joachim, Christian

    2001-08-20

    The technique of single atom manipulation by means of the scanning tunneling microscope (STM) applies to the controlled displacement of large molecules. By a combined experimental and theoretical work, we show that in a constant height mode of manipulation the STM current intensity carries detailed information on the internal mechanics of the molecule when guided by the STM tip. Controlling and time following the intramolecular behavior of a large molecule on a surface is the first step towards the design of molecular tunnel-wired nanorobots.

  19. Human ceruloplasmin. Intramolecular electron transfer kinetics and equilibration

    DEFF Research Database (Denmark)

    Farver, O; Bendahl, L; Skov, L K

    1999-01-01

    Pulse radiolytic reduction of disulfide bridges in ceruloplasmin yielding RSSR(-) radicals induces a cascade of intramolecular electron transfer (ET) processes. Based on the three-dimensional structure of ceruloplasmin identification of individual kinetically active disulfide groups and type 1 (T1...... and indeed electron equilibration between T1A and the trinuclear copper center in the domain 1-6 interface takes place with a rate constant of 2.9 +/- 0.6 s(-1). The equilibrium constant is 0.17. Following reduction of T1A Cu(II), another ET process takes place between RSSR(-) and T1B copper(II) of domain 4...

  20. Cyclization reactions of bis(allenes) for the synthesis of polycarbo(hetero)cycles.

    Science.gov (United States)

    Alcaide, Benito; Almendros, Pedro; Aragoncillo, Cristina

    2014-05-07

    The chemistry of allenes is an appealing topic which fascinates chemists nowadays. Their reactivity and versatility makes this skeleton a useful moiety to create a great variety of structures depending on the functional groups attached and the reaction conditions used. Recently, there is a growing interest in the study of the reactivity of bis(allenes) inspired in the chemistry developed in simple allenes. In this review a collection of examples of cyclization reactions of bis(allenes) is presented as well as the future perspectives.

  1. Synthesis of New Phosphahelicene Scaffolds and Development of Gold(I)-Catalyzed Enantioselective Allenene Cyclizations.

    Science.gov (United States)

    Aillard, Paul; Retailleau, Pascal; Voituriez, Arnaud; Marinetti, Angela

    2015-08-17

    This paper reports on the development of an efficient synthesis of enantiopure phospha[6]helicenes through a [2+2+2] alkyne cyclotrimerization reaction. The corresponding gold complexes proved to be highly efficient both in terms of catalytic activity and enantioselectivity in [2+2] and [4+2] cycloaddition reactions. Furthermore, in the presence of an external nucleophile, such as water or alcohols, the tandem cyclization/addition reactions take place in high yields and excellent diastereo- and enantioselectivities. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Synthesis of 3,3'-spirocyclic oxindoles via phosphine catalyzed [4 + 2] cyclizations.

    Science.gov (United States)

    Gicquel, Maxime; Gomez, Catherine; Retailleau, Pascal; Voituriez, Arnaud; Marinetti, Angela

    2013-08-02

    Triphenylphosphine promoted reactions between 3-arylideneoxindoles and δ-aryl-substituted penta-2,3-dienoates afford an unprecedented access to spirocyclic oxindoles with functionalized six-membered rings. In these new [4 + 2] cyclization processes, the allenoates operate as the four-carbon synthons, thanks to the involvement of the substituted δ-carbons. These reactions give excellent control of the relative stereochemistry of the three stereogenic centers. The stereochemistry of the final product has been ascertained by X-ray diffraction studies.

  3. Improving the stability of alpha-conotoxin AuIB through N-to-C cyclization

    DEFF Research Database (Denmark)

    Armishaw, Christopher J; Jensen, Anders A; Balle, Lena D

    2011-01-01

    Modification of alpha-conotoxin frameworks through cyclization via an oligopeptide linker has previously been shown as an effective strategy for improving in vivo stability. We have extended this strategy by investigating cyclic analogs of alpha-conotoxin AuIB, a selective alpha3beta4 nicotinic a......-AuIB. As such, the cAuIB-2 globular isomer could constitute a useful probe for studying the role of the alpha3beta4 nicotinic acetylcholine receptor in a range of in vivo experimental paradigms....

  4. Modular Three-Component Synthesis of 4-Aminoquinolines via an Imidoylative Sonogashira/Cyclization Cascade.

    Science.gov (United States)

    Collet, Jurriën W; Ackermans, Kelly; Lambregts, Jeffrey; Maes, Bert U W; Orru, Romano V A; Ruijter, Eelco

    2018-01-19

    We developed a one-pot, two-stage synthetic route to substituted 4-aminoquinolines involving an imidoylative Sonogashira coupling followed by acid-mediated cyclization. This three-component reaction affords pharmaceutically valuable 4-aminoquinolines in a one-pot procedure from readily available starting materials. The reaction tolerates various substituents on the arene as well as the use of secondary and even primary isocyanides. Additionally, the wide tolerance for functionalized isocyanides allows for the one-pot synthesis of various substituted chloroquine analogues as well as other medicinally relevant products.

  5. Microwave-assisted rapid cyclization of lapachol, a main constituent of Heterophragma adenophyllum.

    Science.gov (United States)

    Singh, P; Natani, K; Jain, S; Arya, K; Dandia, A

    2006-02-01

    Cyclization reactions of lapachol (1) isolated from Heterophragma adenophyllum have been studied under microwave irradiation under different conditions using alumina (acidic, basic and neutral)/silica gel/montmorillonite (KSF and K-10) as solid support along with neat reaction using 2-3 drops of DMF giving naturally occurring dehydro-alpha-lapachone (2), alpha-lapachone (3), beta-lapachone (4) depending upon the nature of support and irradiation time. A novel naphthoquinone derivative adenophyllone (5) can be synthesized from lapachol using DMF under microwaves.

  6. Cyclization of lapachol induced by thallium salts; Ciclizacao do lapachol induzida por sais de talio III

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, Carlos Magno R.; Souza, Pablo P. de; Ferreira, Leticia L.D.M.; Pinto, Lia A.; Almeida, Leonardo S. de; Jesus, Janaina G. de [Universidade Federal Fluminense (UFF), Niteroi, RJ (Brazil). Inst. de Quimica. Dept. de Quimica Organica]. E-mail: gqocmrr@vm.uff.br

    2008-07-01

    This work describes the cyclization of lapachol (1) induced by thallium triacetate (TTA) and thallium trinitrate (TTN) in several solvents using magnetic stirring and under microwave irradiation. {alpha}-Xyloidone (2) - dehydro-a-lapachone - was obtained as the main product in these reactions in 20 - 75% yield. However, rhinacanthin-A (4) was isolated as main product in a 40% yield, using TTA and acetic anhydride:water (1:1) as solvent, and dehydroiso- a-lapachone (3) in 21% yield, using TTA and dichloromethane as solvent. The reaction time decreased drastically under microwave conditions, but the yields of these reactions were not the expected. (author)

  7. Synthesis of 2,1-benzisoxazole-3(1H-ones by base-mediated photochemical N–O bond-forming cyclization of 2-azidobenzoic acids

    Directory of Open Access Journals (Sweden)

    Daria Yu. Dzhons

    2016-05-01

    Full Text Available The base-mediated photochemical cyclization of 2-azidobenzoic acids with the formation of 2,1-benzisoxazole-3(1H-ones is reported. The optimization and scope of this cyclization reaction is discussed. It is shown that an essential step of the ring closure of 2-azidobenzoic acids is the formation and photolysis of 2-azidobenzoate anions.

  8. Intramolecularly coordinated azobenzene selenium derivatives: effect of strength of the Se···N intramolecular interaction on luminescence.

    Science.gov (United States)

    Srivastava, Kriti; Chakraborty, Tapash; Singh, Harkesh B; Butcher, Ray J

    2011-05-07

    A series of selenium derivatives (6-12) of 2-phenylazophenyl have been synthesized using o-lithiation route. The effect of the strength of the intramolecular Se···N interaction on the absorption spectra as well as emission spectra has been studied. The studies suggest that the secondary bonding Se···N interaction give rise to fluorescence, however, the strength of Se···N interaction cannot be directly correlated with the intensity of the fluorescence. TD-DFT calculations show that the main transition involved in the absorption spectra of the compound is the ligand based π-π* type.

  9. Excited state intramolecular proton transfer (ESIPT) in dihydroxyphenyl anthracenes.

    Science.gov (United States)

    Wang, Yu-Hsuan; Wan, Peter

    2011-12-01

    The photochemistry of three 9-(dihydroxyphenyl)anthracenes 6-8 was studied in neat CH(3)CN and selected organic solvents, to investigate excited state intramolecular proton transfer (ESIPT) from the phenol to the anthracene moiety. In D(2)O-CH(3)CN mixtures, the observed deuterium exchange of 6-8 is consistent with water-mediated (formal) ESIPT process from the ortho phenolic OH to the 10'-position of the anthracene ring, giving rise to quinone methide (QM) intermediates 12-14. There is no ESIPT for the corresponding methoxy-substituted compounds. Introduction of an extra hydroxyl group onto the phenol ring at different positions led to a range of deuterium exchange quantum yields (Φ = 0.03 to 0.15). In addition to the anticipated ESIPT process to the 10'-position, in neat CH(3)CN and other organic solvents, 6 (but not 7 or 8) undergoes a clean photocyclization to give bridged product 19 in quantitative yield. The mechanism of this unique photocyclization may involve a direct ESIPT or a 1,4-hydrogen transfer from the ortho phenolic OH to the 9'-position of the anthracene ring, generating a zwitterion (20) or diradical (21) intermediate, respectively, followed by ring closure. Fluorescence studies of 6 in various solvents show the existence of both local excited and intramolecular charge transfer states whereas only the former was present for 7 and 8, offering a possible rationalization for the photocyclization pathway.

  10. Enzyme-Like Catalysis of the Nazarov Cyclization by Supramolecular Encapsulation

    Energy Technology Data Exchange (ETDEWEB)

    Hastings, Courtney; Pluth, Michael; Bergman, Robert; Raymond, Kenneth

    2010-03-29

    A primary goal in the design and synthesis of molecular hosts has been the selective recognition and binding of a variety of guests using non-covalent interactions. Supramolecular catalysis, which is the application of such hosts towards catalysis, has much in common with many enzymatic reactions, chiefly the use of both spatially appropriate binding pockets and precisely oriented functional groups to recognize and activate specific substrate molecules. Although there are now many examples which demonstrate how selective encapsulation in a host cavity can enhance the reactivity of a bound guest, all have failed to reach the degree of increased reactivity typical of enzymes. We now report the catalysis of the Nazarov cyclization by a self-assembled coordination cage, a carbon-carbon bond-forming reaction which proceeds under mild, aqueous conditions. The acceleration in this system is over a million-fold, and represents the first example of supramolecular catalysis that achieves the level of rate enhancement comparable to that observed in several enzymes. We explain the unprecedented degree of rate increase as due to the combination of (a) preorganization of the encapsulated substrate molecule, (b) stabilization of the transition state of the cyclization by constrictive binding, and (c) increase in the basicity of the complexed alcohol functionality.

  11. Mechanism for cyclization reaction by clavaminic acid synthase. Insights from modeling studies.

    Science.gov (United States)

    Borowski, Tomasz; de Marothy, Sven; Broclawik, Ewa; Schofield, Christopher J; Siegbahn, Per E M

    2007-03-27

    The mechanism of the oxidative cyclization reaction catalyzed by clavaminic acid synthase (CAS) was studied in silico. First, a classical molecular dynamics (MD) simulation was performed to obtain a realistic structure of the CAS-Fe(IV)=O-succinate-substrate complex; then potential of mean force (PMF) was calculated to assess the feasibility of the beta-lactam ring, more specifically its C4' corner, approaching the oxo atom. Based on the MD structure, a relatively large model of the active site region was selected and used in the B3LYP investigation of the reaction mechanism. The computational results suggest that once the oxoferryl species is formed, the oxidative cyclization catalyzed by CAS most likely involves either a mechanism involving C4'(S)-H bond cleavage of the monocyclic beta-lactam ring, or a biosynthetically unprecedented mechanism comprising (1) oxidation of the hydroxyl group of PCA to an O-radical, (2) retro-aldol-like decomposition of the O-radical to an aldehyde and a C-centered radical, which is stabilized by the captodative effect, (3) abstraction of a hydrogen atom from the C4'(S) position of the C-centered radical by the Fe(III)-OH species yielding an azomethine ylide, and (4) 1,3-dipolar cycloaddition to the ylide with aldehyde acting as a dipolarophile. Precedent for the new proposed mechanism comes from the reported synthesis of oxapenams via 1,3-dipolar cycloaddition reactions of aldehydes and ketones.

  12. Diversity-oriented synthesis of dihydrobenzoxazepinones by coupling the Ugi multicomponent reaction with a Mitsunobu cyclization

    Directory of Open Access Journals (Sweden)

    Lisa Moni

    2014-01-01

    Full Text Available An operationally simple protocol for the synthesis of 2,3-dihydrobenzo[f][1,4]oxazepin-3-ones, based on an Ugi reaction of an ortho-(benzyloxybenzylamine, glycolic acid, an isocyanide and an aldehyde, followed by an intramolecular Mitsunobu substitution was developed. The required ortho-(benzyloxybenzylamines have been in situ generated from the corresponding azides, in turn prepared in high yields from salicylic derivatives.

  13. Reações intramoleculares como modelos não miméticos de catálise enzimática Intramolecular reactions as non mimetic models of enzyme catalysis

    Directory of Open Access Journals (Sweden)

    José Carlos Gesser

    1997-12-01

    Full Text Available This review gives a critical idea on the importance of intramolecular reactions as models for enzymatic catalysis. Intramolecular lactonizations, ester and amide hydrolysis studies result in theories which try to explain the difference between intermolecular, intramolecular and enzyme reactions and rationalize the enhancement promoted by these biological catalyst.

  14. Effect of dilution on structure and properties of polyurethane networks. Pregel and postgel cyclization and phase separation

    Czech Academy of Sciences Publication Activity Database

    Dušková-Smrčková, Miroslava; Valentová, H.; Ďuračková, Andrea; Dušek, Karel

    2010-01-01

    Roč. 43, č. 15 (2010), s. 6450-6462 ISSN 0024-9297 R&D Projects: GA ČR GA106/08/1409 Institutional research plan: CEZ:AV0Z40500505 Keywords : network formation * cyclization * gelation Subject RIV: JI - Composite Materials Impact factor: 4.838, year: 2010

  15. Nickel-catalyzed cyclization of alpha, omega-dienes: formation vs. cleavage of C-C bonds

    Czech Academy of Sciences Publication Activity Database

    Nečas, D.; Turský, M.; Tišlerová, I.; Kotora, Martin

    2006-01-01

    Roč. 30, č. 4 (2006), s. 671-674 ISSN 1144-0546 R&D Projects: GA MŠk 1M0508; GA ČR GD203/03/H140 Institutional research plan: CEZ:AV0Z40550506 Keywords : catalysis * nickel * cyclization * diene * cyclopentane Subject RIV: CC - Organic Chemistry Impact factor: 2.647, year: 2006

  16. N,2,3,4-Tetrasubstituted Pyrrolidines through Tandem Lithium Amide Conjugate Addition/Radical Cyclization/Oxygenation Reactions

    Czech Academy of Sciences Publication Activity Database

    Kafka, František; Pohl, Radek; Císařová, I.; Mackman, R.; Bahador, G.; Jahn, Ullrich

    2016-01-01

    Roč. 2016, č. 22 (2016), s. 3862-3871 ISSN 1434-193X R&D Projects: GA ČR GA13-40188S Grant - others:COST(XE) CM1201 Institutional support: RVO:61388963 Keywords : tandem reactions * nitrogen heterocycles * Michael addition * radical reactions * cyclization * enolates Subject RIV: CC - Organic Chemistry Impact factor: 2.834, year: 2016

  17. Ascorbic Acid-Initiated Tandem Radical Cyclization of N-Arylacrylamides to Give 3,3-Disubstituted Oxindoles

    Directory of Open Access Journals (Sweden)

    Sheng Liu

    2015-08-01

    Full Text Available An ascorbic acid-promoted and metal-free tandem room temperature cyclization of N-arylacrylamides with 4-nitrobenzenediazonium generated in situ was developed. This reaction proceeds smoothly through a radical mechanism and provides an environmentally friendly alternative approach to biologically active 3-alkyl-3-benzyloxindoles, avoiding the use of excess oxidants and light irradiation.

  18. Tandem electrophilic cyclization-[3+2] cycloaddition-rearrangement reactions of 2-alkynylbenzaldoxime, DMAD, and Br2.

    Science.gov (United States)

    Ding, Qiuping; Wang, Zhiyong; Wu, Jie

    2009-01-16

    Tandem electrophilic cyclization-[3+2] cycloaddition-rearrangement reactions of 2-alkynylbenzaldoximes, DMAD, and bromine are described, which afford the unexpected isoquinoline-based azomethine ylides in good to excellent yields. The products could be further elaborated via palladium-catalyzed cross-coupling reactions to generate highly functionalized isoquinoline-based stable azomethine ylides.

  19. Effect of Peptide Fragment Size on the Propensity of Cyclization in Collision-Induced Dissociation: Oligoglycine b(2)-b(8)

    NARCIS (Netherlands)

    Chen, X.; Yu, L.; Steill, J. D.; Oomens, J.; Polfer, N. C.

    2009-01-01

    The chemistry of peptide fragmentation by collision-induced dissociation (CID) is currently being reviewed, as a result of observations that the amino acid sequence of peptide fragments can change upon activation. This rearrangement mechanism is thought to be due to a head-to-tail cyclization

  20. Effect of peptide fragment size on the propensity of cyclization in collision-induced dissociation: Oligoglycine b2-b8

    NARCIS (Netherlands)

    Chen, X.; Yu, L.; Steill, J.D.; Oomens, J.; Polfer, N.C.

    2009-01-01

    The chemistry of peptide fragmentation by collision-induced dissociation (CID) is currently being reviewed, as a result of observations that the amino acid sequence of peptide fragments can change upon activation. This rearrangement mechanism is thought to be due to a head-to-tail cyclization

  1. Oxidative radical cyclizations of diketopiperazines bearing an amidomalonate unit. Heterointermediate reaction sequences toward the asperparalines and stephacidins

    Czech Academy of Sciences Publication Activity Database

    Amatov, Tynchtyk; Gebauer, Martin; Pohl, Radek; Císařová, I.; Jahn, Ullrich

    2016-01-01

    Roč. 50, Suppl 1 (2016), S6-S17 ISSN 1071-5762 Grant - others:COST(XE) CM1201 Institutional support: RVO:61388963 Keywords : alkaloids * diketopiperazines * radical cyclizations * single electron transfer * oxidation Subject RIV: CC - Organic Chemistry Impact factor: 3.188, year: 2016 http://www.tandfonline.com/doi/full/10.1080/10715762.2016.1223295

  2. Theoretical Study of Gold-Catalyzed Cyclization of 2-Alkynyl-N-propargylanilines and Rationalization of Kinetic Experimental Phenomena.

    Science.gov (United States)

    Duan, Yeqing; Liu, Yuxia; Bi, Siwei; Ling, Baoping; Jiang, Yuan-Ye; Liu, Peng

    2016-10-07

    Gold-catalyzed cyclization of 2-alkynyl-N-propargylanilines provides a step-economic method for the construction of three-dimensional indolines. In this article, the M06 functional of density functional theory was employed to gain deeper insights into the reaction mechanism and the associated intriguing experimental observations. The reaction was found to first undergo Au(I)-induced cyclization to form an indole intermediate, 1,3-propargyl migration, and substitution with the substrate 2-alkynyl-N-propargylaniline (R1) to generate the intermediate product P1, an allene species. Subsequently, Au(I)-catalyzed conversion of P1 into the final product P2, an indoline compound, occurs first through direct cyclization rather than via the previously proposed four-membered carbocycle intermediate. Thereafter, water-assisted oxygen heterocycle formation and proton transfer generate the final product. The calculated activation free energies indicate that P1 formation is 5.9 times slower than P2 formation, in accordance with the fact that P1 formation is rate-limiting. Futhermore, the intriguing experimental phenomenon that P2 can be accessed only after almost all the substrate R1 converts to P1 although P1 formation is rate-limiting was rationalized by employing an energetic span model. We found the initial facile cyclization to form a highly stable indole intermediate in the formation of P1 is the key to the intriguing experimental phenomenon.

  3. Synthesis of 1-(2-Ethynyl-6-methylphenyl)- and 1-(2-Ethynyl-6-methoxyphenyl)-Naphthalene and Their Cyclization

    Czech Academy of Sciences Publication Activity Database

    Storch, Jan; Čermák, Jan; Karban, Jindřich

    2007-01-01

    Roč. 48, č. 38 (2007), s. 6814-6816 ISSN 0040-4039 R&D Projects: GA MŠk(CZ) LC06070 Institutional research plan: CEZ:AV0Z40720504 Keywords : aromate * cyclization * cycloizomerization Subject RIV: CC - Organic Chemistry Impact factor: 2.615, year: 2007

  4. The Nature of the Intramolecular Charge Transfer State in Peridinin

    Science.gov (United States)

    Wagner, Nicole L.; Greco, Jordan A.; Enriquez, Miriam M.; Frank, Harry A.; Birge, Robert R.

    2013-01-01

    Experimental and theoretical evidence is presented that supports the theory that the intramolecular charge transfer (ICT) state of peridinin is an evolved state formed via excited-state bond-order reversal and solvent reorganization in polar media. The ICT state evolves in ICT state are generated via mixing of the “11Bu+” ionic state and the lowest-lying “21Ag–” covalent state. The resulting ICT state is primarily 1Bu+-like in character and exhibits not only a large oscillator strength but an unusually large doubly excited character. In most solvents, two populations exist in equilibrium, one with a lowest-lying ICT ionic state and a second with a lowest-lying “21Ag–” covalent state. The two populations are separated by a small barrier associated with solvent relaxation and cavity formation. PMID:23528091

  5. Intramolecular electron transfer in single-site-mutated azurins

    DEFF Research Database (Denmark)

    Farver, O; Skov, L K; Pascher, T

    1993-01-01

    . Natl. Acad. Sci. U.S.A. 86, 6968-6972]. The RSSR- radical produced in the above reaction was reoxidized in a slower intramolecular electron-transfer process (30-70 s-1 at 298 K) concomitant with a further reduction of the Cu(II) ion. The temperature dependence of the latter rates was determined...... and used to derive information on the possible effects of the mutations. The substitution of residue Phe114, situated on the opposite side of Cu relative to the disulfide, by Ala resulted in a rate increase by a factor of almost 2. By assuming that this effect is only due to an increase in driving force......Single-site mutants of the blue, single-copper protein, azurin, from Pseudomonas aeruginosa were reduced by CO2- radicals in pulse radiolysis experiments. The single disulfide group was reduced directly by CO2- with rates similar to those of the native protein [Farver, O., & Pecht, I. (1989) Proc...

  6. Intramolecular electron transfer in Pseudomonas aeruginosa cd(1) nitrite reductase

    DEFF Research Database (Denmark)

    Farver, Ole; Brunori, Maurizio; Cutruzzolà, Francesca

    2009-01-01

    The cd(1) nitrite reductases, which catalyze the reduction of nitrite to nitric oxide, are homodimers of 60 kDa subunits, each containing one heme-c and one heme-d(1). Heme-c is the electron entry site, whereas heme-d(1) constitutes the catalytic center. The 3D structure of Pseudomonas aeruginosa...... nitrite reductase has been determined in both fully oxidized and reduced states. Intramolecular electron transfer (ET), between c and d(1) hemes is an essential step in the catalytic cycle. In earlier studies of the Pseudomonas stutzeri enzyme, we observed that a marked negative cooperativity...... is controlling this internal ET step. In this study we have investigated the internal ET in the wild-type and His369Ala mutant of P. aeruginosa nitrite reductases and have observed similar cooperativity to that of the Pseudomonas stutzeri enzyme. Heme-c was initially reduced, in an essentially diffusion...

  7. Synthesis of fused azole-piperidionoses: A free radical cyclization approach

    Energy Technology Data Exchange (ETDEWEB)

    Marco-Contelles, Jose; Alhambra Jimenez, Carolina [Instituto de Quimica Organica General (CSIC), Madrid (Spain)

    1999-08-01

    A new strategy has been reported for the synthesis of fused azole-piperidinoses featuring and unprecedented and very efficient 6-exo-trig free radical cyclization onto heterocyclic sugar templates. These compounds are key intermediates for the synthesis of known or analogues of azole-glycosidase inhibitors. In this communication we describe our recent and successful results on the synthesis of fused triazole-piperidinoses. Radical precursors have been prepared by standard methodologies from 1, 2:5, 6-bis-O-isopropylidene-{alpha}-D-glucofuranose (4) via triazoles linked at C3 with {beta}-orientation, readily obtained by 1, 3-dipolar cycloaddition of azide 5 with diethyl acetylenedicarboxylate or methyl propiolate, and by S{sub N}2 displacement of the tosylate at C3 with 1, 2, 4-triazole in compound 20. The key 6-exp-trig free radical cyclizations proceeded in the usual conditions [tributyltin hydride or tris(trimethylsily)silane, AIBN, toluene] yielding the azaannulated sugars 9, 11, 19 and 23 in good or excellent yields. A mechanism for these cyclizations has been proposed. [Spanish] Se ha informado una nueva estrategia para la sintesis azol-piperidinosas fusionadas mediante una ciclizacion 6-exo-trig muy eficiente y sin precedentes, sobre plantillas de azucares heterociclicos. Estos compuestos son intermediarios claves para la sintesis de inhibidores de azol-glicosidasa conocidos analogos de ellos. En esta comunicacion describimos nuestros resultados recientes y exitosos sobre la sintesis de triazol-piperidinosas. Los precursores de radicales fueron preparados por la metodologia usual a partir de 1, 2:5, 6-bis-O-isopropiliden-{alpha}-D-glucofuranosa (4) via triazoles unidos en C3, con orientacion {beta}, los cuales se obtienen facilmente por cicloadicion 1, 3-dipolar de la azida 5 con acetilendicarboxilato de dietilo o propiolato de metilo y por desplazamiento S{sub N}2 del tosilato en C3 con 1, 2, 4-triazol en el compuesto 20. Las ciclizaciones 6-exo

  8. Asymmetric synthesis of multifunctional cyclopentanes and cyclohexanes via oxycarbenium ion cyclizations of 5-alkoxy- 2(3h)-dihydrofuranones

    NARCIS (Netherlands)

    Geertsema, Edzard M.; Leung, Chiu W.; Oeveren, Arjan van; Meetsma, Auke; Feringa, Bernard

    1995-01-01

    Intramolecular nucleophilic additions to oxycarbenium ions derived from 5-alkoxy-2(3)-dihydrofuranones gave substituted cyclopentanes or cyclohexanes in good yields. Stereoselectivity in these reactions was usually very high, while regioselectivity could be improved using silicon containing

  9. Dissociation or cyclization: options for a triad of radicals released from oxime carbamates.

    Science.gov (United States)

    McBurney, Roy T; Walton, John C

    2013-05-15

    A set of oxime carbamates having N-alkyl and N,N-dialkyl substituents were prepared via carbonyldiimidazole intermediates. It was shown by EPR spectroscopy that they underwent clean homolysis of their N-O bonds upon UV photolysis. During photolysis of acetophenone O-allylcarbamoyl oxime, the corresponding oxazolidin-2-onylmethyl radical was detected by EPR spectroscopy, providing the first evidence that N-monosubstituted carbamoyloxyl radicals can hold their structural integrity. N,N-Disubstituted carbamoyloxyl radicals dissociated rapidly at the lowest accessible temperatures. Above room temperature, both types of oxime carbamate acted as selective new precursors for aminyl and iminyl radicals. Rate parameters were measured for 5-exo cyclization of N-benzyl-N-pent-4-enylaminyl radicals; the rate constant was smaller than for C-centered and O-centered analogues. Oxime carbamates derived from the volatile diethylamine afforded aryliminyl radicals that proved convenient for phenanthridine preparations.

  10. Amorpha-4,11-diene synthase: mechanism and stereochemistry of the enzymatic cyclization of farnesyl diphosphate.

    Science.gov (United States)

    Picaud, Sarah; Mercke, Per; He, Xiaofei; Sterner, Olov; Brodelius, Maria; Cane, David E; Brodelius, Peter E

    2006-04-15

    Recombinant amorpha-4,11-diene synthase from Artemisia annua, expressed in Escherichia coli, was incubated with the deuterium-labeled farnesyl diphosphates, (1R)-[1-(2)H]FPP, (1S)-[1-(2)H]FPP, and [1,1-(2)H2]FPP. GC-MS analysis of amorpha-4,11-diene formed from the deuterated FPPs shows that the deuterium atoms are retained in the product. Furthermore, analysis of the MS-spectra obtained with the differently labeled substrate indicates that the H-1si-proton of FPP is transferred during the cyclization reaction to carbon 10 of amorphadiene while the H-1re-proton of FPP is retained on C-6 of the product. Proton NMR and COSY experiments proved that the original H-1si-proton of FPP is located at C-10 of amorpha-4,11-diene as a result of a 1,3-hydride shift following initial 1,6-ring closure. The results obtained support the previously suggested mechanism for the cyclization of farnesyl diphosphate by amorph-4,11-diene synthase involving isomerization of FPP to (R)-nerolidyl diphosphate (NPP), ionization of NPP, and C-1,C-6-ring closure to generate a bisabolyl cation, followed by a 1,3-hydride shift, 1,10-ring closure to generate the amorphane skeleton, and deprotonation at either C-12 or C-13 to afford the final product (1S,6R,7R,10R)-amorpha-4,11-diene.

  11. Metal-free cyclization of o-nitroaryl ynamides and ynamines towards spiropseudoindoxyls.

    Science.gov (United States)

    Marien, Niels; Bheemireddy, Narendraprasad Reddy; De Vleeschouwer, Freija; Goderis, Steven; Van Hecke, Kristof; Verniest, Guido

    2018-03-23

    An efficient metal-free cascade reaction between 1-dibromovinyl-2-nitro substituted aromatics and secondary amines is described, resulting in the formation of polycyclic pseudoindoxyls in a single step. The reaction mechanism leading to these fused ring systems was investigated and is believed to proceed via initial formation of nitroarylated ynami(d)(n)es. These intermediates cycloisomerize towards N-(alkenyl)-tethered 2-aminoisatogens via a carbene intermediate as demonstrated by QTAIM (Quantum Theory of Atoms in Molecules) and ELF (Electron Localization Function) analysis. A subsequent intramolecular dipolar cycloaddition afforded the title compounds. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Labeling, stability and biodistribution studies of {sup 99m}Tc-cyclized Tyr{sup 3}-octreotate derivatives

    Energy Technology Data Exchange (ETDEWEB)

    Bigott-Hennkens, Heather M. [Department of Veterinary Medicine and Surgery, University of Missouri, Columbia, MO 65211 (United States); Dannoon, Shorouk F.; Noll, Samantha M. [Department of Chemistry, University of Missouri, Columbia, MO 65211 (United States); Ruthengael, Varyanna C. [Research Service, Harry S Truman Memorial Veterans' Hospital, Columbia, MO 65201 (United States); Jurisson, Silvia S., E-mail: JurissonS@missouri.ed [Department of Chemistry, University of Missouri, Columbia, MO 65211 (United States); Lewis, Michael R., E-mail: LewisMic@missouri.ed [Department of Veterinary Medicine and Surgery, University of Missouri, Columbia, MO 65211 (United States); Research Service, Harry S Truman Memorial Veterans' Hospital, Columbia, MO 65201 (United States)

    2011-05-15

    Introduction: To probe the interplay between radiotracer stability and somatostatin receptor affinity, Tyr{sup 3}-octreotate and six variations of its peptide sequence, for which the Re-cyclized products were previously reported, were radiolabeled with {sup 99m}Tc and investigated for their in vitro stability. Methods: Radiolabeling of the peptides was effected by ligand exchange from {sup 99m}Tc-glucoheptonate, and the desired products were purified by radio-RP-HPLC. The in vitro stability in phosphate buffered saline, mouse serum and cysteine solutions at physiological temperature and pH for all seven {sup 99m}Tc-cyclized peptides was determined by radio-RP-HPLC and radio-TLC. Normal CF-1 mouse biodistribution studies were performed for three of the {sup 99m}Tc-cyclized peptides. Results: Based on the fully characterized Re-cyclized peptide analogues, four {sup 99m}Tc-coordination motifs were proposed for the {sup 99m}Tc-cyclized peptides. Technetium-99m-cyclized Tyr{sup 3}-octreotate derivatives with N{sub 2}S{sub 2} metal coordination modes and large metal ring sizes were susceptible to oxidation and loss of {sup 99m}Tc in the form of {sup 99m}TcO{sub 4}{sup -}, as evidenced by their instability in the various solutions under physiological conditions (15-58% intact at 24 h). As anticipated, the addition of a third cysteine to the sequence stabilized the {sup 99m}Tc metal coordination, and peptides with NS{sub 3} coordination modes remained >85% intact out to 24 h. No significant differences were observed in the biodistribution studies performed with three peptides of varying stabilities. Conclusions: Improvements in stability were not sufficient to outweigh the low somatostatin receptor affinity for the peptides in this study. Further improvements in the peptide sequence and/or metal coordination are needed to result in a radiodiagnostic/radiotherapeutic pair for targeting the somatostatin receptor.

  13. Detection of a transient intramolecular hydrogen bond using 1JNH scalar couplings

    Science.gov (United States)

    Xiang, ShengQi; Zweckstetter, Markus

    2014-06-01

    Hydrogen bonds are essential for the structure, stability and folding of proteins. The identification of intramolecular hydrogen bonds, however, is challenging, in particular in transiently folded states. Here we studied the presence of intramolecular hydrogen bonds in the folding nucleus of the coiled-coil structure of the GCN4 leucine zipper. Using one-bond 1JNH spin-spin coupling constants and hydrogen/deuterium exchange, we demonstrate that a transient intramolecular hydrogen bond is present in the partially helical folding nucleus of GCN(16-31). The data demonstrate that 1JNH couplings are a sensitive tool for the detection of transient intramolecular hydrogen bonds in challenging systems where the effective/useable protein concentration is low. This includes peptides at natural abundance but also uniformly labeled biomolecules that are limited to low concentrations because of precipitation or aggregation.

  14. Enantioselective synthesis of almorexant via iridium-catalysed intramolecular allylic amidation

    NARCIS (Netherlands)

    Fananas Mastral, Martin; Teichert, Johannes F.; Fernandez-Salas, Jose Antonio; Heijnen, Dorus; Feringa, Ben L.

    2013-01-01

    An enantioselective synthesis of almorexant, a potent antagonist of human orexin receptors, is presented. The chiral tetrahydroisoquinoline core structure was prepared via iridium-catalysed asymmetric intramolecular allylic amidation. Further key catalytic steps of the synthesis include an oxidative

  15. Dynamics of intramolecular spin exchange interaction of a nitronyl nitroxide diradical in solution and on surfaces

    OpenAIRE

    Lloveras Montserrat, Vega; Badetti, Elena; Veciana Miró, Jaume; Vidal-Gancedo, José

    2016-01-01

    In this paper we report the study of the dynamics of a thermally modulated intramolecular spin exchange interaction of a novel diradical nitronyl nitroxide-substituted disulfide in solution and when it is grafted on a gold surface. The structure of this diradical was designed to have flexible chains leading to intramolecular collisions and hence spin exchange interaction, and with an appropriate binding group to be grafted on the gold surface to study its behavior on the surface. In solution,...

  16. Intramolecular distribution of carbon isotopes in fatty acids

    International Nuclear Information System (INIS)

    von Unruh, G.E.; Hayes, J.M.

    1975-01-01

    It is well known that biochemical reactions fractionate the stable isotopes of carbon, distributing them unevenly among their products. For amino acids and biosynthesized acetate, it has been shown that the isotopes are fractionated on an intramolecular basis, with some carbon positions being enriched in 13 C relative to others. With the goal of eventually determining the extent to which the isotopic distribution pattern in acetate is carried over into alkyl chains, we are working to develop methods for determining isotopic distributions within fatty acids. Because there are no purely instrumental approaches with sufficient precision to allow isotopic measurements on the intact fatty acid, chemical degradation must be applied in order to prepare CO 2 from each position of interest. Kinetic isotope effects during the chemical reactions and vapor pressure isotope effects during sample preparation and handling can significantly affect the results, and must be very carefully controlled and investigated. Thus far, suitable methods have been developed for determination of the isotopic composition of the carboxyl carbon in fatty acids. The isotopic composition of the aliphatic portion of the molecule can then be determined by the difference after the overall 13 C content has been determined by combustion

  17. Intramolecular charge transfer effects on 3-aminobenzoic acid

    Energy Technology Data Exchange (ETDEWEB)

    Stalin, T. [Department of Chemistry, Annamalai University, Annamalainagar, Chidambaram 608 002, Tamil Nadu (India); Rajendiran, N. [Department of Chemistry, Annamalai University, Annamalainagar, Chidambaram 608 002, Tamil Nadu (India)], E-mail: drrajendiran@rediffmail.com

    2006-03-20

    Effect of solvents, buffer solutions of different pH and {beta}-cyclodextrin on the absorption and fluorescence spectra of 3-aminobenzoic acid (3ABA) have been investigated. The solid inclusion complex of 3ABA with {beta}-CD is discussed by UV-Vis, fluorimetry, semiempirical quantum calculations (AM1), FT-IR, {sup 1}H NMR and Scanning Electron Microscope (SEM). The thermodynamic parameters ({delta}H, {delta}G and {delta}S) of the inclusion process are also determined. The experimental results indicated that the inclusion processes is an exothermic and spontaneous. The large Stokes shift emission in solvents with 3ABA are correlated with different solvent polarity scales suggest that, 3ABA molecule is more polar in the S{sub 1} state. Solvent, {beta}-CD studies and excited state dipole moment values confirms that the presence of intramolecular charge transfer (ICT) in 3ABA. Acidity constants for different prototropic equilibria of 3ABA in the S{sub 0} and S{sub 1} states are calculated. {beta}-Cyclodextrin studies shows that 3ABA forms a 1:1 inclusion complex with {beta}-CD. {beta}-CD studies suggest COOH group present in non-polar part and amino group present in hydrophilic part of the {beta}-CD cavity. A mechanism is proposed to explain the inclusion process.

  18. Intramolecular Crosstalk between Catalytic Activities of Receptor Kinases

    KAUST Repository

    Kwezi, Lusisizwe

    2018-01-22

    Signal modulation is important for the growth and development of plants and this process is mediated by a number of factors including physiological growth regulators and their associated signal transduction pathways. Protein kinases play a central role in signaling, including those involving pathogen response mechanisms. We previously demonstrated an active guanylate cyclase (GC) catalytic center in the brassinosteroid insensitive receptor (AtBRI1) within an active intracellular kinase domain resulting in dual enzymatic activity. Here we propose a novel type of receptor architecture that is characterized by a functional GC catalytic center nested in the cytosolic kinase domain enabling intramolecular crosstalk. This may be through a cGMP-AtBRI1 complex forming that may induce a negative feedback mechanism leading to desensitisation of the receptor, regulated through the cGMP production pathway. We further argue that the comparatively low but highly localized cGMP generated by the GC in response to a ligand is sufficient to modulate the kinase activity. This type of receptor therefore provides a molecular switch that directly and/or indirectly affects ligand dependent phosphorylation of downstream signaling cascades and suggests that subsequent signal transduction and modulation works in conjunction with the kinase in downstream signaling.

  19. From dimerization, to cycloaddition, to atom transfer cyclization: the further chemistry of TMM diradicals.

    Science.gov (United States)

    Maiti, Arup; Gerken, James B; Masjedizadeh, Mohammad R; Mimieux, Yvette S; Little, R Daniel

    2004-12-10

    We describe [a] the first examples of intramolecular cycloaddition of a TMM diyl to a remotely tethered aldehyde, [b] the effect of a Lewis acid upon the course of TMM chemistry, [c] examples of exclusive intramolecular cycloaddition, competitive cycloaddition and ATC, and exclusive ATC, and [d] a set of predictive guidelines with which to assess whether cycloaddition or ATC will be the preferred path, and when the two processes will be competitive. Remarkably, a wide variety of structures can be obtained simply by varying the length of the tether within the diazenes investigated. DFT calculations were used to probe the energy surfaces for both atom transfer and cycloaddition. The transition structure for atom transfer involving the captodative system indicates that it occurs earlier along the reaction coordinate than for a system having only one radical stabilizing group. This is consistent with the existence of an exothermic process leading from the initial diyl to the captodatively stabilized distonic diyl. Gratifyingly, theory agrees with observation and provides substantial insight into the chemistry.

  20. Mechanism of radiation-induced addition reaction of carbon tetrachloride onto liquid 1,2-polybutadiene accompanied by cyclization

    Energy Technology Data Exchange (ETDEWEB)

    Okamoto, H.; Adachi, S.; Kakada, K.; Iwai, T.

    1979-05-01

    Effects of irradiation conditions were investgated in the ..gamma..-ray-induced addition reaction of carbon tetrachloride onto liquid 1,2-polybutadiene. The rate of addition reaction was proportional to the dose rate, and its apparent activation energy was 1.4 kcal/mole in the range of ca. 20 to 80/sup 0/C; the G values for the addition of carbon tetrachloride and vinyl consumption were high. The addition reactions of methyl isobutylate, isopropyl amine, and bromotrichloromethane to liquid 1,2-polybutadiene by ..gamma.. rays were studied to compare with carbon tetrachloride. Methyl isobutylate and isopropyl amine were added much more slowly. On the other hand, in bromotrichloromethane the rate of addition reacion was much faster but cyclization was less pronounced than in carbon tetrachloride. On the basis of these results a mechanism of a radical chain reaction which includes the addition of carbon tetrachloride, cyclization, and crosslinking, is proposed. 8 figures.

  1. Eosin Y-catalyzed visible-light-mediated aerobic oxidative cyclization of N,N-dimethylanilines with maleimides.

    Science.gov (United States)

    Liang, Zhongwei; Xu, Song; Tian, Wenyan; Zhang, Ronghua

    2015-01-01

    A novel and simple strategy for the efficient synthesis of the corresponding tetrahydroquinolines from N,N-dimethylanilines and maleimides using visible light in an air atmosphere in the presence of Eosin Y as a photocatalyst has been developed. The metal-free protocol involves aerobic oxidative cyclization via sp(3) C-H bond functionalization process to afford good yields in a one-pot procedure under mild conditions.

  2. A construction of 4,4-spirocyclic γ-lactams by tandem radical cyclization with carbon monoxide

    Directory of Open Access Journals (Sweden)

    Mitsuhiro Ueda

    2013-07-01

    Full Text Available A straightforward synthesis of 4,4-spirocyclic indol γ-lactams by tandem radical cyclization of iodoaryl allyl azides with CO was achieved. The reaction of iodoaryl allyl azides, TTMSS and AIBN under CO pressure (80 atm in THF at 80 °C gave the desired 4,4-spirocyclic indoline, benzofuran, and oxindole γ-lactams in moderate to good yields.

  3. Optimization of the Reaction Conditions for Synthesis of 3-(Aryloxy)quinoline Derivatives via Friedlander's Cyclization Reaction

    Energy Technology Data Exchange (ETDEWEB)

    Khan, Mohammad Ashrafuddin; Elgamal, Mohammed I.; Oh, Changhyun [Korea Institute of Science and Technology, Seoul (Korea, Republic of)

    2013-06-15

    6,7-Dimethoxy-2-methyl-3-(4-nitrophenoxy)quinoline was synthesized by Friedlaender's cyclization reaction. Different bases and solvents were tested in order to optimize the reaction conditions. The highest yields were obtained using piperidine in refluxing ethanol. Further reactions were carried out in order to prepare different diarylamide and diarylurea derivatives in moderate to high yields in order to examine their anticancer activities.

  4. Phosphahelicenes in asymmetric organocatalysis: [3+2] cyclizations of γ-substituted allenes and electron-poor olefins.

    Science.gov (United States)

    Gicquel, Maxime; Zhang, Yang; Aillard, Paul; Retailleau, Pascal; Voituriez, Arnaud; Marinetti, Angela

    2015-04-27

    The first use of phosphahelicene in enantioselective organocatalysis is reported. New chiral phosphahelicenes have been prepared and enable highly enantioselective [3+2] cyclization reactions between arylidene- or alkylidenemalononitriles and γ-substituted allenoates or cyanoallenes. These reactions afford cyclopentene derivatives in both high yields and diastereoselectivities, with enantiomeric excesses of up to 97 %. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Drug Delivery by an Enzyme-Mediated Cyclization of a Lipid Prodrug with Unique Bilayer-Formation Properties

    DEFF Research Database (Denmark)

    Linderoth, Lars; Peters, Günther H.j.; Madsen, Robert

    2009-01-01

    Special delivery: Liposomal drug-delivery systems in which prodrugs are activated specifically by disease-associated enzymes have great potential for the treatment of severe diseases, such as cancer. A new type of phospholipid-based prodrug has the ability to form stable small unilamellar vesicle...... (see picture). Activation of the prodrug vesicles by the enzyme sPLA2 initiates a cyclization reaction, which leads to the release of the drug....

  6. Rh(I)-catalyzed CO gas-free carbonylative cyclization reactions of alkynes with 2-bromophenylboronic acids using formaldehyde.

    Science.gov (United States)

    Morimoto, Tsumoru; Yamasaki, Kae; Hirano, Akihisa; Tsutsumi, Ken; Kagawa, Natsuko; Kakiuchi, Kiyomi; Harada, Yasuyuki; Fukumoto, Yoshiya; Chatani, Naoto; Nishioka, Takanori

    2009-04-16

    The rhodium(I)-catalyzed reaction of alkynes with 2-bromophenylboronic acids in the presence of paraformaldehyde resulted in a CO gas-free carbonylative cyclization, yielding indenone derivatives. [RhCl(BINAP)](2) and [RhCl(cod)](2) were responsible for the decarbonylation of formaldehyde and the subsequent carbonylation of alkynes with 2-haloboronic acids, respectively, leading to efficient whole carbonylation. Sterically bulky and electron-withdrawing groups on unsymmetrically substituted alkynes favored the alpha-position of indenones.

  7. Drawing Catalytic Power from Charge Separation: Stereoelectronic and Zwitterionic Assistance in the Au(I)-Catalyzed Bergman Cyclization.

    Science.gov (United States)

    Dos Passos Gomes, Gabriel; Alabugin, Igor V

    2017-03-08

    The synergy between bond formation and bond breaking that is typical for pericyclic reactions is lost in their mechanistic cousins, cycloaromatization reactions. In these reactions, exemplified by the Bergman cyclization (BC), two bonds are sacrificed to form a single bond, and the reaction progress is interrupted at the stage of a cyclic diradical intermediate. The catalytic power of Au(I) in BC stems from a combination of two sources: stereoelectronic assistance of C-C bond formation (i.e., "LUMO umpolung") and crossover from a diradical to a zwitterionic mechanism that takes advantage of the catalyst's dual ability to stabilize both negative and positive charges. Not only does the synergy between the bond-forming and charge-delocalizing interactions lead to a dramatic (>hundred-billion-fold) acceleration, but the evolution of the two effects results in continuous reinforcement of the substrate/catalyst interaction along the cyclization path. This cooperativity converts the BC into the first example of an aborted [3,3] sigmatropic shift where the pericyclic "transition state" becomes the most stable species on the reaction hypersurface. Aborting the pericyclic path facilitates trapping of cyclic intermediate by a variety of further reactions and provides a foundation for the discovery of new modes of reactivity of polyunsaturated substrates. The application of distortion/interaction analysis allows us to quantify the increased affinity of Au-catalysts to the Bergman cyclization transition state as one of the key components of the large catalytic effect.

  8. One-pot cascade michael.cyclization reactions of ο-hydroxycinnamaldehydes: Synthesis of functionalized 2,3-dihydrobenzofuranes

    Energy Technology Data Exchange (ETDEWEB)

    Gwon, Sung Hyuk; Kim, Sunggon [Kyonggi Univ., Suwon (Korea, Republic of)

    2012-04-15

    We described the cascade Michael.cyclization reaction of o-hydroxycinnamaldehydes with diethyl α-bromomalonate promoted by potassium carbonate. The reactions provided functionalized 2,3-dihydrobenzofurans in good yields for a variety of o-hydroxyaromatic α,β-unsaturated aldehydes. Current work focuses on expanding the scope of this reaction to other substrates such as sulfur yields, and on developing an efficient catalytic asymmetric variant. 2,3-Dihydrobenzofurans are found in numerous biologically active natural products and synthetic compounds. These are an attractive type of oxygenated compound because their basic core skeleton is present in neolignans, pterocarpans, and synthetic drugs used in the treatment of pulmonary hypertension, atherosclerotic peripheral arterial disease, and central nervous system trauma and ischemia. Owing to the importance of their structures, numerous synthetic methods for 2,3-dihydrobenzofurans have been developed, primarily: radical cyclizations, Lewis acid promoted reactions, anionic cyclizations, and transition-metal catalyzed processes. However, these methods cannot be generalized as much as is desirable, and they yielded poor chemo- and/or stereoselectivities. Hence, the development of an efficient enantioselective synthetic method for obtaining 2,3-dihydrobenzofuran scaffolds attracted our attention.

  9. One-pot cascade michael.cyclization reactions of ο-hydroxycinnamaldehydes: Synthesis of functionalized 2,3-dihydrobenzofuranes

    International Nuclear Information System (INIS)

    Gwon, Sung Hyuk; Kim, Sunggon

    2012-01-01

    We described the cascade Michael.cyclization reaction of o-hydroxycinnamaldehydes with diethyl α-bromomalonate promoted by potassium carbonate. The reactions provided functionalized 2,3-dihydrobenzofurans in good yields for a variety of o-hydroxyaromatic α,β-unsaturated aldehydes. Current work focuses on expanding the scope of this reaction to other substrates such as sulfur yields, and on developing an efficient catalytic asymmetric variant. 2,3-Dihydrobenzofurans are found in numerous biologically active natural products and synthetic compounds. These are an attractive type of oxygenated compound because their basic core skeleton is present in neolignans, pterocarpans, and synthetic drugs used in the treatment of pulmonary hypertension, atherosclerotic peripheral arterial disease, and central nervous system trauma and ischemia. Owing to the importance of their structures, numerous synthetic methods for 2,3-dihydrobenzofurans have been developed, primarily: radical cyclizations, Lewis acid promoted reactions, anionic cyclizations, and transition-metal catalyzed processes. However, these methods cannot be generalized as much as is desirable, and they yielded poor chemo- and/or stereoselectivities. Hence, the development of an efficient enantioselective synthetic method for obtaining 2,3-dihydrobenzofuran scaffolds attracted our attention

  10. Intramolecular Schmidt reaction of acyl chlorides with alkyl azides: preparation of pyrrolizine by intramolecular capture of intermediates with alkenes or alkynes.

    Science.gov (United States)

    Wang, Bao-Juan; Xue, Ping; Gu, Peiming

    2015-02-11

    The preparation of substituted pyrrolizines through the Schmidt reaction of acyl chlorides with alkyl azides has been realized. Intramolecular capture of the isocyanate ion and N-acyliminium ion intermediates from the Schmidt process with alkene or alkyne units was achieved, and the efficiency of the conversion with respect to ring construction and bond formation was demonstrated.

  11. Dynamics of the excited state intramolecular charge transfer

    International Nuclear Information System (INIS)

    Joo, T.; Kim, C.H.

    2006-01-01

    The 6-dodecanoyl-2-dimethylaminonaphtalene (laurdan), a derivative of 6-propanoyl- 2-dimethylaminonaphthalene (prodan), has been used as a fluorescent probe in cell imaging, especially in visualizing the lipid rafts by the generalized polarization (GP) images, where GP=(I 440 -I 490 )/(I 440 +I 490 ) with I being the fluorescence intensity. The fluorescence spectrum of laurdan is sensitive to its dipolar environment due to the intramolecular charge transfer (ICT) process in S 1 state, which results in a dual emission from the locally excited (LE) and the ICT states. The ICT process and the solvation of the ICT state are very sensitive to the dipolar nature of the environment. In this work, the ICT of laurdan in ethanol has been studied by femtosecond time resolved fluorescence (TRF), especially TRF spectra measurement without the conventional spectral reconstruction method. TRF probes the excited states exclusively, a unique advantage over the pump/probe transient absorption technique, although time resolution of the TRF is generally lower than transient absorption and the TRF spectra measurement was possible only though the spectral reconstruction. Over the years, critical advances in TRF technique have been made in our group to achieve <50 fs time resolution with direct full spectra measurement capability. Detailed ICT and the subsequent solvation processes can be visualized unambiguously from the TRF spectra. Fig. 1 shows the TRF spectra of laurdan in ethanol at several time delays. Surprisingly, two bands at 433 and 476 nm are clearly visible in the TRF spectra of laurdan even at T = 0 fs. As time increases, the band at 476 nm shifts to the red while its intensity increases. The band at 433 nm also shifts slightly to the red, but loses intensity as time increases. The intensity of the 476 nm band reaches maximum at around 5 ps, where it is roughly twice as intense as that at 0 fs, and stays constant until lifetime decay is noticeable. The spectra were fit by

  12. New fast organic scintillators using intramolecular bromine quenching

    Science.gov (United States)

    Berlman, I. B.; Lutz, S. S.; Flournoy, J. M.; Ashford, C. B.; Franks, L. A.; Lyons, P. B.

    1984-08-01

    Organic scintillator solutions with decay times as fast as 500 ps and with relatively high conversion efficiencies have been developed. The intramolecular quenching was achieved through the novel approach of adding a bromine atom to the 3- or 4-position of para-oligophenylenes, the fluorescent solutes in these binary solutions. The bromine serves to enhance singlet-to-triplet intersystem crossing in the chromophore, causing a reduction in the scintillation yield and a conconitant reduction in the decay time. The very fast value given above probably also involves some intermolecular self-quenching at high concentration. In addition, the bromine reduces the symmetry of the molecules, thereby increasing their solubility. Finally, an alkyl chain on the opposite para position further increases the solubility and also increases the immunity of the chromophore to quenching. The following solutes were studied in binary liquid solutions and to a limited extent in plastics: 4-bromo-4″-(5-hexadecyl)-p-terphenyl: (4-BHTP), 3-bromo-4″-(5-hexadecyl)-p-terphenyl: (3-BHTP), 4-bromo-p-terphenyl: (4-BTP), 3-bromo-p-terphenyl: (3-BTP), 4-bromo-4‴-(5-hexadecyl)-p-quaterphenyl: (4-BHQP). The decay times for binary liquid solutions in toluene (at the indicated concentrations) were 0.51 ns for 4-BHTP (0.14 M), 0.75 ns for 3-BHTP (0.14 M), 0.57 ns for 3-BTP (0.14 M), and 1.3 ns for 4-BHQP (0.06 M). Binary plastics with 4-BHTP as the solute in concentrations up to 0.14 M were cast in polystyrene. The shortest decay time, 0.40 ns, was measured for the 0.14 M concentration. A plastic scintillator containing 3-BTP (0.11 M in polystyrene) had a decay time of 0.85 ns. These results compare favorably with the plastic scintillator BC-422 whose decay time is about 1.4 ns.

  13. New fast organic scintillators using intramolecular bromine quenching

    International Nuclear Information System (INIS)

    Berlman, I.B.; Lutz, S.S.; Flournoy, J.M.; Ashford, C.B.; Franks, L.A.

    1984-01-01

    Organic scintillator solutions with decay times as fast as 500 ps and with relatively high conversion efficiencies have been developed. The intramolecular quenching was achieved through the novel approach of adding a bromine atom to the 3- or 4-position of para-oligophenylenes, the fluorescent solutes in these binary solutions. The bromine serves to enhance singlet-to-triplet intersystem crossing in the chromophore, causing a reduction in the scintillation yield and a concomitant reduction in the decay time. The very fast value given above probably also involves some intermolecular self-quenching at high concentration. In addition, the bromine reduces the symmetry of the molecules, thereby increasing their solubility. Finally, an alkyl chain on the opposite para position further increases the solubility and also increases the immunity of the chromophore to quenching. The decay times for binary liquid solutions in toluene (at the indicated concentrations) were 0.51 ns for 4-BHTP (0.14 M), 0.75 ns for 3-BHTP (0.14 M), 0.57 ns for 3-BTP (0.14 M), and 1.3 ns for 4-BHQP (0.06 M). Binary plastics with 4-BHTP as the solute in concentrations up to 0.14 M were cast in polystyrene. The shortest decay time, 0.40 ns, was measured for the 0.14 M concentration. A plastic scintillator containing 3-BTP (0.11 M in polystyrene) had a decay time of 0.85 ns. These results compare favorably with the plastic scintillator BC-422 whose decay time is about 1.4 ns. (orig./HSI)

  14. Cyclization of polyketides and non-ribosomal peptides on and off their assembly lines.

    Science.gov (United States)

    Pang, Bo; Wang, Min; Liu, Wen

    2016-02-01

    Modular polyketide synthases (PKSs) and non-ribosomal peptide synthetases (NRPSs) are multifunctional megaenzymes that serve as templates to program the assembly of short carboxylic acids and amino acids in a primarily co-linear manner. The variation, combination, permutation and evolution of their functional units (e.g., modules, domains and proteins) along with their association with external enzymes have resulted in the generation of numerous versions of templates, the roles of which have not been fully recognized in the structural diversification of polyketides, non-ribosomal peptides and their hybrids present in nature. In this Highlight, we focus on the assembly-line enzymology and associated chemistry by providing examples of some newly characterized cyclization reactions that occur on and off the assembly lines during and after chain elongation for the purpose of elucidating the template effects of PKSs and NRPSs. A fundamental understanding of the underlying biosynthetic logic would facilitate the elucidation of chemical information contained within the PKS or NRPS templates and benefit the development of strategies for genome mining, biosynthesis-inspired chemical synthesis and combinatorial biosynthesis.

  15. BF3 x Et2O-mediated cascade cyclizations: synthesis of schweinfurthins F and G.

    Science.gov (United States)

    Mente, Nolan R; Neighbors, Jeffrey D; Wiemer, David F

    2008-10-17

    The total synthesis of the natural stilbene (+)-schweinfurthin G (8) has been accomplished through a sequence based on an efficient cationic cascade cyclization. This cascade process is initiated by Lewis acid promoted ring opening of an epoxide and terminated through a novel reaction with a phenolic oxygen "protected" as its MOM ether. Several Lewis acids have been examined for their ability to induce this new reaction, and BF3 x Et2O was found to be the most effective. The only major byproduct under these conditions was one where the expected secondary alcohol was found as its MOM ether derivative (e.g., 30). While this byproduct could be converted to the original target compound through hydrolysis, it also could be employed as a protected alcohol to allow preparation of a benzylic phosphonate (43) without dehydration of the secondary alcohol. The resulting phosphonate was employed in a Horner-Wadsworth-Emmons condensation with an aldehyde representing the right half of the target compounds, an approach complementary to previous studies based on condensation of a right-half phosphonate and a left-half aldehyde.

  16. The Suzuki–Miyaura Cross-Coupling as a Versatile Tool for Peptide Diversification and Cyclization

    Directory of Open Access Journals (Sweden)

    Tom Willemse

    2017-02-01

    Full Text Available The (site-selective derivatization of amino acids and peptides represents an attractive field with potential applications in the establishment of structure–activity relationships and labeling of bioactive compounds. In this respect, bioorthogonal cross-coupling reactions provide valuable means for ready access to peptide analogues with diversified structure and function. Due to the complex and chiral nature of peptides, mild reaction conditions are preferred; hence, a suitable cross-coupling reaction is required for the chemical modification of these challenging substrates. The Suzuki reaction, involving organoboron species, is appropriate given the stability and environmentally benign nature of these reactants and their amenability to be applied in (partial aqueous reaction conditions, an expected requirement upon the derivatization of peptides. Concerning the halogenated reaction partner, residues bearing halogen moieties can either be introduced directly as halogenated amino acids during solid-phase peptide synthesis (SPPS or genetically encoded into larger proteins. A reversed approach building in boron in the peptidic backbone is also possible. Furthermore, based on this complementarity, cyclic peptides can be prepared by halogenation, and borylation of two amino acid side chains present within the same peptidic substrate. Here, the Suzuki–Miyaura reaction is a tool to induce the desired cyclization. In this review, we discuss diverse amino acid and peptide-based applications explored by means of this extremely versatile cross-coupling reaction. With the advent of peptide-based drugs, versatile bioorthogonal conversions on these substrates have become highly valuable.

  17. Solid-Phase Iminium Cyclization Reactions for the Synthesis of Natural Product-Like Diketopiperazines

    DEFF Research Database (Denmark)

    Petersen, Rico

    The development of methodology for the solid-phase synthesis of fused 2,5-diketopiperazines with an emphasis on structural and stereochemical control, has been accomplished through two different approaches. The first approach was based on a highly trans-stereoselective (82% d.e.) intramolecular N......-suited for the synthesis of diastereoisomeric mixtures of 2,5-diketopiperazino[6,1-a]tetrahydroisoquinolines in high purities (74 to 90%), allowing for the separation of the cis-diastereoisomers. The route based on glyoxylic acid was found to be cis-stereoselective (1:2) generating the 2,5-diketopiperazino[6,1-a...... inhibitors based on the 2,5-diketopiperazino[6,1-a]tetrahydroisoquinoline scaffold was prepared and subsequently evaluated for biologically activity. The compounds showed inhibitory activity against a nuclear extract of HeLa cells, on average 200-fold lower than the activity of SAHA. When screened towards...

  18. Kinetic evidence for the formation of discrete 1,4-dehydrobenzene intermediates. Trapping by inter- and intramolecular hydrogen atom transfer and observation of high-temperature CIDNP

    Energy Technology Data Exchange (ETDEWEB)

    Lockhart, Thomas P. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States); California Inst. of Technology (CalTech), Pasadena, CA (United States); Comita, Paul B. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States); California Inst. of Technology (CalTech), Pasadena, CA (United States); Bergman, Robert G. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States); California Inst. of Technology (CalTech), Pasadena, CA (United States)

    1981-07-01

    Upon heating, alkyl-substituted cis-1,2-diethynyl olefins undergo cyclization to yield reactive 1,4-dehydrobenzenes; the products isolated may be derived from either unimolecular or bimolecular reactions of the intermediate. (Z)-4,5-Diethynyl-4-octene (4) undergoes rearrangement to yield 2,3-di-n-propyl-1,4-dehydrobenzene (17). Solution pyrolysis of 4 in inert aromatic solvents produces three unimolecular products, (Z)-dodeca-4,8-diyn-6-ene (7), benzocyclooctene (9), and o-allyl-n-propylbenzene (10), in high yield. When 1,4-cyclohexadiene is added to the pyrolysis solution as a trapping agent, high yields of the reduced product o-di-n-propylbenzene (12) are obtained. The kinetics of solution pyrolysis of 4 in the presence and absence of trapping agent establish that 2,3-di-n-propyl-1,4-dehydrobenzene is a discrete intermediate on the pathway leading to products. When the reaction was run in the heated probe of an NMR spectrometer, CIDNP was observed in 10. This observation, along with kinetic and chemical trapping evidence, indicates the presence of two additional intermediates, formed from 17 by sequential intramolecular [1,5] hydrogen transfer, on the pathway to products. The observation of CIDNP, coupled with the reactivity exhibited by 17 and the other two intermediates, implicate a biradical description of these molecules. Biradical 17 has been estimated to have a lifetime of about 10-9 s at 200°C and to lie in a well of about 5 kcal/mol with respect to the lowest energy unimolecular pathway ([1,5] hydrogen transfer). Ring opening (expected to be the lowest energy process for 1,4-dehydrobenzenes in which intramolecular hydrogen transfer is unlikely) to the isomeric diethynyl olefin 7 appears to have an activation enthalpy of about 10 kcal/moL Upon thermal reaction in the gas phase (400°C) or in solution in inert solvents (Z)-hexa-2,3-diethyl-1,5-diyn-3-ene (5) rearranges in good yield to the isomeric diethynyl olefin (Z)-deca-3,7-diyn-5-ene (8

  19. Double Gold Activation of 1-Ethynyl-2-(Phenylethynyl)Benzene Toward 5-exo-dig and 6-endo-dig Cyclization Reactions.

    Science.gov (United States)

    Villegas-Escobar, Nery; Larsen Née Vilhelmsen, Mie Højer; Gutiérrez-Oliva, Soledad; Hashmi, A Stephen K; Toro-Labbé, Alejandro

    2017-09-27

    In this work, a detailed characterization was carried out of the ring-closure mechanism of EPB (1-ethynyl-2-(phenylethynyl)benzene) toward the 5-exo-dig and 6-endo-dig cyclization reactions, catalyzed by two Au-N-heterocyclic carbene (NHC) moieties. It was found that the 5-exo-dig cyclization takes place with a slightly lower activation barrier and larger exothermicity compared to that of the 6-endo-dig cyclization, in agreement with the available experimental data. A phenomenological partition (structural and electronic) for rate constants computed using transition-state theory and the reaction force analysis was used to shed light into the nature of the activation rate constant. It was found that rate constants are influenced by a strong structural component, which is larger for the 5-exo-dig cyclization due to the strain to form the five-membered ring. On the other hand, the gold activation mechanism is evidenced by a σ- and π-coordination of the Au-NHC moieties to the EPB substrate. It was found that differences in the σ-coordination arise on the reaction path for the 5-exo-dig and 6-endo-dig cyclizations. Thus, in the 6-endo-dig cyclization the σ gold-EPB interaction is weakened as a consequence of the formation of the cationic aryl intermediate, while for the 5-exo-dig cyclization this interaction was found to be favored. Furthermore, although minor changes in the Au-EPB coordination occur on the reaction path, these bonds are formally established in the TS vicinity. Results support the concerted nature of the dual gold activation mechanism. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Conductance and activation energy for electron transport in series and parallel intramolecular circuits.

    Science.gov (United States)

    Hsu, Liang-Yan; Wu, Ning; Rabitz, Herschel

    2016-11-30

    We investigate electron transport through series and parallel intramolecular circuits in the framework of the multi-level Redfield theory. Based on the assumption of weak monomer-bath couplings, the simulations depict the length and temperature dependence in six types of intramolecular circuits. In the tunneling regime, we find that the intramolecular circuit rule is only valid in the weak monomer coupling limit. In the thermally activated hopping regime, for circuits based on two different molecular units M a and M b with distinct activation energies E act,a > E act,b , the activation energies of M a and M b in series are nearly the same as E act,a while those in parallel are nearly the same as E act,b . This study gives a comprehensive description of electron transport through intramolecular circuits from tunneling to thermally activated hopping. We hope that this work can motivate additional studies to design intramolecular circuits based on different types of building blocks, and to explore the corresponding circuit laws and the length and temperature dependence of conductance.

  1. Accounting for intra-molecular vibrational modes in open quantum system description of molecular systems.

    Science.gov (United States)

    Roden, Jan; Strunz, Walter T; Whaley, K Birgitta; Eisfeld, Alexander

    2012-11-28

    Electronic-vibrational dynamics in molecular systems that interact with an environment involve a large number of degrees of freedom and are therefore often described by means of open quantum system approaches. A popular approach is to include only the electronic degrees of freedom into the system part and to couple these to a non-Markovian bath of harmonic vibrational modes that is characterized by a spectral density. Since this bath represents both intra-molecular and external vibrations, it is important to understand how to construct a spectral density that accounts for intra-molecular vibrational modes that couple further to other modes. Here, we address this problem by explicitly incorporating an intra-molecular vibrational mode together with the electronic degrees of freedom into the system part and using the Fano theory for a resonance coupled to a continuum to derive an "effective" bath spectral density, which describes the contribution of intra-molecular modes. We compare this effective model for the intra-molecular mode with the method of pseudomodes, a widely used approach in simulation of non-Markovian dynamics. We clarify the difference between these two approaches and demonstrate that the respective resulting dynamics and optical spectra can be very different.

  2. Nicholas reactions in the construction of cyclohepta[de]naphthalenes and cyclohepta[de]naphthalenones. The total synthesis of microstegiol.

    Science.gov (United States)

    Taj, Rafiq A; Green, James R

    2010-12-03

    The application of the Nicholas reaction chemistry of 2,7-dioxygenated naphthalenes in the synthesis of cyclohepta[de]napthalenes and in the synthesis of (±)-microstegiol (1) is presented. The substitution profile of Nicholas monosubstitution (predominantly C-1) and disubstitution reactions (predominantly 1,6-) on 2,7-dioxygenated napthalenes is reported. Application of a 1,8-dicondensation product and selected C-1 monocondensation products to the construction of cyclohepta[de]naphthalenes by way of ring closing metathesis and intramolecular Friedel-Crafts reactions, respectively, is described. Deprotection of the C-7 oxygen function to the corresponding naphthol allows tautomerization to cyclohepta[de]naphthalene-1-ones upon seven-membered-ring closure in most cases, and replacement of the C-2 oxygen function in the naphthalene by a methyl group ultimately allows the synthesis of (±)-microstegiol.

  3. A [2+2+2] cyclization strategy for the synthesis of phosphorus embedding [6]helicene-like structures.

    Science.gov (United States)

    Aillard, Paul; Retailleau, Pascal; Voituriez, Arnaud; Marinetti, Angela

    2014-02-28

    A Ni(0) promoted intramolecular [2+2+2] cyclotrimerization of triynes provides suitable access to a new series of phosphorus embedding helicenes. [6]Oxahelicenes in which the helical sequence terminates with a phosphole oxide unit have been prepared in both racemic and enantiopure forms and characterized by X-ray diffraction studies.

  4. Protein samples for NMR: expression and analysis without purification, and stabilization by covalent cyclization

    International Nuclear Information System (INIS)

    Otting, G.; Ozawa, K.; Prosselkov, P.; Williams, N.K.; Dixon, N.E.; Liepinsh, E.

    2002-01-01

    Full text: A modified cell-free in vitro expression system was established for the expression of milligram quantities of protein per mL reaction medium. Expression levels of the E coli cytoplasmic peptidyl-prolyl cis-trans isomerase, PpiB, in 0 6 mL reaction medium were sufficient for the direct recording of clean 15N-HSQC spectra without chromatographic purification or sample concentration steps, using a 600 MHz NMR spectrometer with cryoprobe. Besides providing a route to high-throughput sample preparation, in vitro expression systems are known to be highly economic in their utilization of selectively labelled ammo acids. Using dual-selective labelling with 15N- and 13C-labelled amino acids, the 15N-HSQC cross peaks of strategically selected ammo acids can readily be identified and monitored for their response to the presence of ligand molecules, again without sample purification. 2) The N-terminal domain of E coli DnaB is a protein of ca 110 residues with a structured core composed of 6 helices. Additional segments of 10 residues each at the N- and C-termini are highly mobile. Both ends are close in space and can be linked together in a covalent peptide bond using intern technology. The core structures of linear (lin-DnaB-N) and cyclized (cz-DnaB-N) protein are conserved, as evidenced by superimposable NOESY spectra and chemical shifts. The linker segment in cz-DnaB-N is mobile as shown by 1H-15N NOEs. Yet, the cyclic protein melts about 10 degrees higher than the linear version. A stabilization free energy of ca 2 kcal/mol is in agreement with predictions based on the reduced entropy in the unfolded state. Amide proton exchange rates are much slower in the cyclic protein and reveal cooperative exchange through total, global unfolding at a rate of once every 100 minutes in the linear protein

  5. A versatile synthesis of β-lactam-fused oxacycles through the palladium-catalyzed chemo-, regio-, and diastereoselective cyclization of allenic diols.

    Science.gov (United States)

    Alcaide, Benito; Almendros, Pedro; Carrascosa, Rocío; Casarrubios, Luis; Soriano, Elena

    2015-01-26

    Chemo-, regio- and stereocontrolled palladium-catalyzed preparations of enantiopure morpholines, oxocines, and dioxonines have been developed starting from 2-azetidinone-tethered γ,δ-, δ,ε-, and ε,ζ-allendiols. The palladium-catalyzed cyclizative coupling reaction of γ,δ-allendiols 2 with allyl bromide or lithium bromide was effective as 8-endo cyclization by attack of the primary hydroxy group to the terminal allene carbon to afford enantiopure functionalized oxocines; whereas the palladium-catalyzed cyclizative coupling reaction of 2-azetidinone-tethered ε,ζ-allendiols 4 furnished dioxonines 16 through a totally chemo- and regioselective 9-endo oxycyclization. By contrast, the palladium-catalyzed cyclizative coupling reaction of 2-azetidinone-tethered δ,ε-allendiols 3 with aryl and alkenyl halides exclusively generated six-membered-ring compounds 14 a and 15 a. These results could be explained through a 6-exo cyclization by chemo- and regiospecific attack of the secondary hydroxy group to the internal allene carbon. Chemo- and regiocontrol issues are mainly influenced by the length of the tether rather than by the nature of the metal catalysts and substituents. This reactivity can be rationalized by means of density functional theory calculations. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Surprisingly Mild Enolate-Counterion-Free Pd(0)-Catalyzed Intramolecular Allylic Alkylations

    DEFF Research Database (Denmark)

    Madec, David; Prestat, Guillaume; Martini, Elisabetta

    2005-01-01

    Palladium-catalyzed intramolecular allylic alkylations of unsaturated EWG-activated amides can take place under phase-transfer conditions or in the presence of a crown ether. These new reaction conditions are milder and higher yielding than those previously reported. A rationalization for such an......Palladium-catalyzed intramolecular allylic alkylations of unsaturated EWG-activated amides can take place under phase-transfer conditions or in the presence of a crown ether. These new reaction conditions are milder and higher yielding than those previously reported. A rationalization...

  7. The effect of intramolecular quantum modes on free energy relationships for electron transfer reactions

    DEFF Research Database (Denmark)

    Ulstrup, Jens; Jortner, Joshua

    1975-01-01

    -frequency intramolecular degrees of feedom on the free energy relationship for series of closely related reactions was investigated for various model systems involving displacement of potential energy surfaces, frequency shift, and anharmonicity effects. The free energy plots are generally found to pass through a maximum...... and to be asymmetric with a slower decrease in the transition probability with increasing energy of reaction. For high-frequency intramolecular modes this provides a rationalization of the experimental observation of ''activationless'' regions. Isotope effects are discussed as also are the oscillatory free energy...

  8. Influence of intramolecular and intermolecular hydrogen bonding on the fluorescence decay time of indigo derivatives

    International Nuclear Information System (INIS)

    Schneider, S.; Lill, E.; Hefferle, P.; Doerr, F.

    1981-01-01

    It is well known that both intramolecular and intermolecular hydrogen bonding can lead to drastic changes in the lifetime of the first excited singlet state. By employing a synchronously pumped, mode-locked dye-laser for excitation in connection with a continuously operated streak camera for detection, the solvent-dependent fluorescence decay times of several indigo derivatives were determined with high temporal resolution (approx. 5 ps with deconvolution). It is found that in indigo dyes intramolecular hydrogen bonding gives rise to a strong fluorescence quenching; intermolecular hydrogen bonding can also provide a channel for fast radiationless deactivation in those derivatives in which the former are not present. (author)

  9. Preparation of the Core Structure of Aspidosperma and Strychnos Alkaloids from Aryl Azides by a Cascade Radical Cyclization.

    Science.gov (United States)

    Wyler, Benjamin; Brucelle, François; Renaud, Philippe

    2016-03-18

    A novel approach to prepare the core structure of Aspidosperma and Strychnos alkaloids is described. The strategy is based on a cyclization cascade involving the formation of quaternary carbon center followed by trapping of the radical intermediate by an aryl azide to build the 5-membered ring of the pyrrolocarbazole system. This reaction is run with triethylborane without the need for any hydrogen atom donor such as a tin hydride or tris(trimethylsilyl)silane, and it furnishes the tetracyclic framework as a single diastereomer. The influence of different N-protecting groups on the starting iodoacetamide has been examined.

  10. Microwave-assisted cyclizations promoted by polyphosphoric acid esters: a general method for 1-aryl-2-iminoazacycloalkanes

    Directory of Open Access Journals (Sweden)

    Jimena E. Díaz

    2016-09-01

    Full Text Available The first general procedure for the synthesis of 5 to 7-membered 1-aryl-2-iminoazacycloalkanes is presented, by microwave-assisted ring closure of ω-arylaminonitriles promoted by polyphosphoric acid (PPA esters. 1-Aryl-2-iminopyrrolidines were easily prepared from the acyclic precursors employing a chloroformic solution of ethyl polyphosphate (PPE. The use of trimethylsilyl polyphosphate (PPSE in solvent-free conditions allowed for the synthesis of 1-aryl-2-iminopiperidines and hitherto unreported 1-aryl-2-iminoazepanes. The cyclization reaction involves good to high yields and short reaction times, and represents a novel application of PPA esters in heterocyclic synthesis.

  11. Radical cascade cyclization of 1,n-enynes and diynes for the synthesis of carbocycles and heterocycles.

    Science.gov (United States)

    Xuan, Jun; Studer, Armido

    2017-07-17

    Carbo- and heterocycles are widely found in natural products, biologically active structures, medicinally relevant compounds, and in many other fine chemicals. The development of novel, general and efficient methods for their construction has therefore gained great interest in synthetic organic chemistry. Recently, radical chemistry has become a heavily investigated research field (a renaissance!). Along these lines, radical cascade cyclization of 1,n-enynes and diynes has emerged as a powerful strategy for the preparation of carbo- and heterocycles. In this review, we highlight recent advances in this rapidly growing area also focusing on reaction mechanisms.

  12. Doped Si nanoparticles with conformal carbon coating and cyclized-polyacrylonitrile network as high-capacity and high-rate lithium-ion battery anodes

    Science.gov (United States)

    Xie, Ming; Molina Piper, Daniela; Tian, Miao; Clancey, Joel; George, Steven M.; Lee, Se-Hee; Zhou, Yun

    2015-09-01

    Doped Si nanoparticles (SiNPs) with conformal carbon coating and cyclized-polyacrylonitrile (PAN) network displayed capacities of 3500 and 3000 mAh g-1 at C/20 and C/10, respectively. At 1 C, the electrode preserves a specific discharge capacity of ˜1500 mAh g-1 for at least 60 cycles without decay. Al2O3 atomic layer deposition (ALD) helps improve the initial Coulombic efficiency (CE) to 85%. The dual coating of conformal carbon and cyclized-PAN help alleviate volume change and facilitate charge transfer. Ultra-thin Al2O3 ALD layers help form a stable solid electrolyte interphase interface.

  13. Microwave-assisted reductive cyclization: An easy entry to the indoloquinolines and spiro[2H-indole-2,30-oxindole].

    Digital Repository Service at National Institute of Oceanography (India)

    Parvatkar, P.T.; Majik, M.S.

    ., vol.4; 2014; 22481-22486 Microwave-assisted reductive cyclization: An easy entry to the indoloquinolines and spiro[2H-indole-2,3’-oxindole] Prakash T. Parvatkar* and Mahesh S. Majik Bio-organic Chemistry Laboratory, CSIR-National Institute... of this cyclization step under MW assisted condition delivered similar results indicating the reproducibility of this methodology. In case of entry 4 (Table 1), low yields of the two products (19 and 15) and no formation of compound 20 may be due to the temperature...

  14. Intramolecular Diels-Alder reactions of pyrimidines, a synthetic and computational study

    NARCIS (Netherlands)

    Stolle, W.A.W.

    1992-01-01

    This thesis deals with an investigation on the ringtransformation reactions of 2and 5-(ω-alkynyl)pyrimidine derivatives, which undergo upon heating an intramolecular Diels-Alder reaction and subsequently a spontaneous retro Diels- Alder reaction. To get a better insight into the

  15. Optimized measurements of separations and angles between intra-molecular fluorescent markers

    DEFF Research Database (Denmark)

    Mortensen, Kim; Sung, Jongmin; Flyvbjerg, Henrik

    2015-01-01

    We demonstrate a novel, yet simple tool for the study of structure and function of biomolecules by extending two-colour co-localization microscopy to fluorescent molecules with fixed orientations and in intra-molecular proximity. From each colour-separated microscope image in a time-lapse movie...

  16. Symmetry-breaking intramolecular charge transfer in the excited state of meso-linked BODIPY dyads

    KAUST Repository

    Whited, Matthew T.

    2012-01-01

    We report the synthesis and characterization of symmetric BODIPY dyads where the chromophores are attached at the meso position, using either a phenylene bridge or direct linkage. Both molecules undergo symmetry-breaking intramolecular charge transfer in the excited state, and the directly linked dyad serves as a visible-light-absorbing analogue of 9,9′-bianthryl.

  17. Intramolecular hydrogen bond: Can it be part of the basis set of ...

    Indian Academy of Sciences (India)

    IMHB appears in one of the equivalent complete VIC basis sets, its RFC could be used as a measure of bond strength parameter. Keywords. Hydrogen bond; intramolecular; relaxed force constant; normal mode analysis; bond strength parameter. 1. Introduction. The advantages of the compliance constants (the inverse.

  18. Neutral versus cationic Group 3 metal alkyl catalysts : performance in intramolecular hydroamination/cyclisation

    NARCIS (Netherlands)

    de Araujo Bambirra, Sergio; Tsurugi, H; van Leusen, D; Hessen, B

    2006-01-01

    The relative catalytic activity of neutral dialkyl versus cationic monoalkyl Group 3 metal catalysts in the intramolecular hydroamination/cyclisation of the 2,2-dimethyl-4-pentenylamine reference substrate was investigated. This was found to depend strongly on the nature of the monoanionic ancillary

  19. Isotope effects on chemical shifts in the study of intramolecular hydrogen bonds

    DEFF Research Database (Denmark)

    Hansen, Poul Erik

    2015-01-01

    The paper deals with the use of isotope effects on chemical shifts in characterizing intramolecular hydrogen bonds. Both so-called resonance-assisted (RAHB) and non-RAHB systems are treated. The importance of RAHB will be discussed. Another very important issue is the borderline between “static” ...

  20. Regio-Selective Intramolecular Hydrogen/Deuterium Exchange in Gas-Phase Electron Transfer Dissociation

    Science.gov (United States)

    Hamuro, Yoshitomo

    2017-05-01

    Protein backbone amide hydrogen/deuterium exchange mass spectrometry (HDX-MS) typically utilizes enzymatic digestion after the exchange reaction and before MS analysis to improve data resolution. Gas-phase fragmentation of a peptic fragment prior to MS analysis is a promising technique to further increase the resolution. The biggest technical challenge for this method is elimination of intramolecular hydrogen/deuterium exchange (scrambling) in the gas phase. The scrambling obscures the location of deuterium. Jørgensen's group pioneered a method to minimize the scrambling in gas-phase electron capture/transfer dissociation. Despite active investigation, the mechanism of hydrogen scrambling is not well-understood. The difficulty stems from the fact that the degree of hydrogen scrambling depends on instruments, various parameters of mass analysis, and peptide analyzed. In most hydrogen scrambling investigations, the hydrogen scrambling is measured by the percentage of scrambling in a whole molecule. This paper demonstrates that the degree of intramolecular hydrogen/deuterium exchange depends on the nature of exchangeable hydrogen sites. The deuterium on Tyr amide of neurotensin (9-13), Arg-Pro-Tyr-Ile-Leu, migrated significantly faster than that on Ile or Leu amides, indicating the loss of deuterium from the original sites is not mere randomization of hydrogen and deuterium but more site-specific phenomena. This more precise approach may help understand the mechanism of intramolecular hydrogen exchange and provide higher confidence for the parameter optimization to eliminate intramolecular hydrogen/deuterium exchange during gas-phase fragmentation.

  1. Intramolecular 13C analysis of tree rings provides multiple plant ecophysiology signals covering decades.

    Science.gov (United States)

    Wieloch, Thomas; Ehlers, Ina; Yu, Jun; Frank, David; Grabner, Michael; Gessler, Arthur; Schleucher, Jürgen

    2018-03-22

    Measurements of carbon isotope contents of plant organic matter provide important information in diverse fields such as plant breeding, ecophysiology, biogeochemistry and paleoclimatology. They are currently based on 13 C/ 12 C ratios of specific, whole metabolites, but we show here that intramolecular ratios provide higher resolution information. In the glucose units of tree-ring cellulose of 12 tree species, we detected large differences in 13 C/ 12 C ratios (>10‰) among carbon atoms, which provide isotopically distinct inputs to major global C pools, including wood and soil organic matter. Thus, considering position-specific differences can improve characterisation of soil-to-atmosphere carbon fluxes and soil metabolism. In a Pinus nigra tree-ring archive formed from 1961 to 1995, we found novel 13 C signals, and show that intramolecular analysis enables more comprehensive and precise signal extraction from tree rings, and thus higher resolution reconstruction of plants' responses to climate change. Moreover, we propose an ecophysiological mechanism for the introduction of a 13 C signal, which links an environmental shift to the triggered metabolic shift and its intramolecular 13 C signature. In conclusion, intramolecular 13 C analyses can provide valuable new information about long-term metabolic dynamics for numerous applications.

  2. Synthesis of benzannelated sultams by intramolecular Pd-catalyzed arylation of tertiary sulfonamides

    Directory of Open Access Journals (Sweden)

    Valentin A. Rassadin

    2017-09-01

    Full Text Available A new and efficient approach to five- and six-membered benzannelated sultams by intramolecular C-arylation of tertiary 1-(methoxycarbonylmethanesulfonamides under palladium catalysis is described. In case of the α-toluenesulfonamide derivative, an unexpected formation of a 2,3-diarylindole was observed under the same conditions.

  3. Synthesis of benzannelated sultams by intramolecular Pd-catalyzed arylation of tertiary sulfonamides.

    Science.gov (United States)

    Rassadin, Valentin A; Scholz, Mirko; Klochkova, Anastasiia A; de Meijere, Armin; Sokolov, Victor V

    2017-01-01

    A new and efficient approach to five- and six-membered benzannelated sultams by intramolecular C -arylation of tertiary 1-(methoxycarbonyl)methanesulfonamides under palladium catalysis is described. In case of the α-toluenesulfonamide derivative, an unexpected formation of a 2,3-diarylindole was observed under the same conditions.

  4. Intramolecular butenolide allene photocycloadditions and ensuing retro-ene reactions of some photoadducts

    NARCIS (Netherlands)

    Lutteke, G.; Kleinnijenhuis, R.A.; Jacobs, I.; Wrigstedt, P.J.; Correia, A.C.A.; Nieuwenhuizen, R.; Hue, B.T.B.; Goubitz, K.; Peschar, R.; van Maarseveen, J.H.; Hiemstra, H.

    2011-01-01

    This report describes intramolecular [2+2] photocycloadditions of several butenolides with an allenylmethyl substituent at the 5-position. These photosubstrates were prepared from 2-(silyloxy)furans through silver-mediated reactions with allenylmethyl bromides. Two cases were studied where the

  5. Intramolecular Morita-Baylis-Hillman reaction as a strategy for the construction of tricyclic sesquiterpene cores.

    Science.gov (United States)

    Peter, Clovis; Geoffroy, Philippe; Miesch, Michel

    2018-02-21

    Starting from a common polyfunctionalized bicyclo[3.2.1]octane-6,8-dione intermediate, a concise synthetic route to tricyclic cores found in quadrane, suberosane, cedrane and related sesquiterpenes was developed using a Morita-Baylis-Hillman intramolecular reaction as a key step.

  6. Synthesis of neplanocin A and its 3'-epimer via an intramolecular Baylis-Hillman reaction.

    Science.gov (United States)

    Tan, Yun Xuan; Santhanakrishnan, Sridhar; Yang, Hai Yan; Chai, Christina L L; Tam, Eric Kwok Wai

    2014-09-05

    The key cyclopentenyl intermediate 11b was synthesized in 4 steps from d-ribose in 41% overall yield via an efficient intramolecular Baylis-Hillman reaction. This novel key intermediate can be modified easily and transformed to neplanocin A (1a) and its 3'-epimer (1b).

  7. Recent applications of intramolecular Diels-Alder reactions to natural product synthesis

    DEFF Research Database (Denmark)

    Juhl, M.; Tanner, David Ackland

    2009-01-01

    This tutorial review presents some recent examples of intramolecular Diels-Alder (IMDA) reactions as key complexity-generating steps in the total synthesis of structurally intricate natural products. The opportunities afforded by transannular (TADA) versions of the IMDA reaction in complex molecule...

  8. Effect of intramolecular hydrogen bonding and electron donation on substituted anthrasemiquinone characteristics

    International Nuclear Information System (INIS)

    Pal, H.; Mukherjee, T.

    1994-01-01

    The acid-base and redox characteristics of the semiquinones of a number of hydroxy and amino-substituted anthraquinones have been investigated. Results are explained on the basis of electron-donating properties and intramolecular hydrogen bond forming capabilities of the substituents. (author). 4 refs., 1 tab., 1 fig

  9. 1 H NMR-Based Kinetic-Mechanistic Study of the Intramolecular ...

    African Journals Online (AJOL)

    A 1H NMR study of the acid-catalyzed, intramolecular trans-esterification between isomeric 2-exo-3-exo-dihydroxybornane monoacrylate esters has afforded insights into the reaction mechanism and permitted the determination of kinetic and thermodynamic parameters for the pseudo-first-order processes. KEYWORDS ...

  10. The first strand transfer during HIV-1 reverse transcription can occur either intramolecularly or intermolecularly

    NARCIS (Netherlands)

    van Wamel, J. L.; Berkhout, B.

    1998-01-01

    Reverse transcription is a complicated process that involves at least two cDNA transfer reactions to produce a full-length copy DNA of the retroviral RNA genome. Because one retrovirus particle contains two identical genomic RNA molecules, the transfers can occur in an intramolecular or

  11. Intramolecular Transannulation of Alkynyl Triazoles via Alkyne-Carbene Metathesis Step: Access to Fused Pyrroles

    Science.gov (United States)

    Shi, Yi; Gevorgyan, Vladimir

    2013-01-01

    An intramolecular Rh-catalyzed transannulation reaction of alkynyl triazoles has been developed. This method allows efficient construction of various 5,5-fused pyrroles, including tetrahydropyrrolo and spiro systems. The method demonstrates excellent functional group compatibility. A rhodium carbene-alkyne metathesis mechanism is proposed for this transformation. PMID:24093728

  12. On prediction of OH stretching frequencies in intramolecularly hydrogen bonded systems

    DEFF Research Database (Denmark)

    Hansen, Poul Erik; Spanget-Larsen, Jens

    2012-01-01

    OH stretching frequencies are investigated for a series of non-tautomerizing systems with intramolecular hydrogen bonds. Effective OH stretching wavenumbers are predicted by the application of empirical correlation procedures based on the results of B3LYP/6-31G(d) theoretical calculations in the ...

  13. Intramolecular Pnicogen Interactions in PHF(CH2)nPHF (n=26) Systems

    Czech Academy of Sciences Publication Activity Database

    Sanchez-Sanz, Goar; Alkorta, I.; Trujillo, Cristina; Elguero, J.

    2013-01-01

    Roč. 14, č. 8 (2013), s. 1656-1665 ISSN 1439-4235 Institutional support: RVO:61388963 Keywords : electron density shift * intramolecular interactions * ab initio calculations * pnicogens * electrostatic interactions Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.360, year: 2013

  14. Melanoma Therapy with Rhenium-Cyclized Alpha Melanocyte Stimulating Hormone Peptide Analogs

    Energy Technology Data Exchange (ETDEWEB)

    Thomas P Quinn

    2005-11-22

    Malignant melanoma is the 6th most commonly diagnosed cancer with increasing incidence in the United States. It is estimated that 54,200 cases of malignant melanoma will be newly diagnosed and 7,600 cases of death will occur in the United States in the year 2003 (1). At the present time, more than 1.3% of Americans will develop malignant melanoma during their lifetime (2). The average survival for patients with metastatic melanoma is about 6-9 months (3). Moreover, metastatic melanoma deposits are resistant to conventional chemotherapy and external beam radiation therapy (3). Systematic chemotherapy is the primary therapeutic approach to treat patients with metastatic melanoma. Dacarbazine is the only single chemotherapy agent approved by FDA for metastatic melanoma treatment (5). However, the response rate to Dacarbazine is only approximately 20% (6). Therefore, there is a great need to develop novel treatment approaches for metastatic melanoma. The global goal of this research program is the rational design, characterization and validation of melanoma imaging and therapeutic radiopharmaceuticals. Significant progress has been made in the design and characterization of metal-cyclized radiolabeled alpha-melanocyte stimulating hormone peptides. Therapy studies with {sup 188}Re-CCMSH demonstrated the therapeutic efficacy of the receptor-targeted treatment in murine and human melanoma bearing mice (previous progress report). Dosimetry calculations, based on biodistribution data, indicated that a significant dose was delivered to the tumor. However, {sup 188}Re is a very energetic beta-particle emitter. The longer-range beta-particles theoretically would be better for larger tumors. In the treatment of melanoma, the larger primary tumor is usually surgically removed leaving metastatic disease as the focus of targeted radiotherapy. Isotopes with lower beta-energies and/or shorter particle lengths should be better suited for targeting metastases. The {sup 177}Lu

  15. Melanome Therapy with Rhenium Cyclized Alpha Melanocyte Stimulating Hormone Peptide Analogs. Final report

    International Nuclear Information System (INIS)

    Quinn, Thomas P.

    2005-01-01

    Malignant melanoma is the 6th most commonly diagnosed cancer with increasing incidence in the United States. It is estimated that 54,200 cases of malignant melanoma will be newly diagnosed and 7,600 cases of death will occur in the United States in the year 2003 (1). At the present time, more than 1.3% of Americans will develop malignant melanoma during their lifetime (2). The average survival for patients with metastatic melanoma is about 6-9 months (3). Moreover, metastatic melanoma deposits are resistant to conventional chemotherapy and external beam radiation therapy (3). Systematic chemotherapy is the primary therapeutic approach to treat patients with metastatic melanoma. Dacarbazine is the only single chemotherapy agent approved by FDA for metastatic melanoma treatment (5). However, the response rate to Dacarbazine is only approximately 20% (6). Therefore, there is a great need to develop novel treatment approaches for metastatic melanoma. The global goal of this research program is the rational design, characterization and validation of melanoma imaging and therapeutic radiopharmaceuticals. Significant progress has been made in the design and characterization of metal-cyclized radiolabeled alpha-melanocyte stimulating hormone peptides. Therapy studies with 188 Re-CCMSH demonstrated the therapeutic efficacy of the receptor-targeted treatment in murine and human melanoma bearing mice (previous progress report). Dosimetry calculations, based on biodistribution data, indicated that a significant dose was delivered to the tumor. However, 188 Re is a very energetic beta-particle emitter. The longer-range beta-particles theoretically would be better for larger tumors. In the treatment of melanoma, the larger primary tumor is usually surgically removed leaving metastatic disease as the focus of targeted radiotherapy. Isotopes with lower beta-energies and/or shorter particle lengths should be better suited for targeting metastases. The 177 Lu-DOTA-Re(Arg11)CCMSH and

  16. Metal-Catalyzed Cyclization Reactions of 2,3,4-Trien-1-ols: A Joint Experimental-Computational Study.

    Science.gov (United States)

    Alcaide, Benito; Almendros, Pedro; Cembellín, Sara; Fernández, Israel; Martínez Del Campo, Teresa

    2016-08-08

    Controlled preparation of tri- and tetrasubstituted furans, as well as carbazoles has been achieved through chemo- and regioselective metal-catalyzed cyclization reactions of cumulenic alcohols. The gold- and palladium-catalyzed cycloisomerization reactions of cumulenols, including indole-tethered 2,3,4-trien-1-ols, to trisubstituted furans was effective, due to a 5-endo-dig oxycyclization by attack of the hydroxy group onto the central cumulene double bond. In contrast, palladium-catalyzed heterocyclization/coupling reactions with 3-bromoprop-1-enes furnished tetrasubstituted furans. Also studied was the palladium-catalyzed cyclization/coupling sequence involving protected indole-tethered 2,3,4-trien-1-ols and 3-bromoprop-1-enes that exclusively generated trisubstituted carbazole derivatives. These results could be explained through a selective 6-endo-dig cumulenic hydroarylation, followed by aromatization. DFT calculations were carried out to understand this difference in reactivity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Total Synthesis of 15-F2t-Isoprostane by Using a New Oxidative Cyclization of Distonic Radical Anions as the Key Step

    Czech Academy of Sciences Publication Activity Database

    Jahn, Ullrich; Dinca, E.

    2009-01-01

    Roč. 15, č. 1 (2009), s. 58-62 ISSN 0947-6539 Grant - others:DFG(DE) Ja896/3-1 Institutional research plan: CEZ:AV0Z40550506 Keywords : cyclization * electron transfer * prostanoids * radical ions Subject RIV: CC - Organic Chemistry Impact factor: 5.382, year: 2009

  18. Dibenzopentalenes from B(C6F5)3-induced cyclization reactions of 1,2-bis(phenylethynyl)benzenes.

    Science.gov (United States)

    Chen, Chao; Harhausen, Marcel; Liedtke, René; Bussmann, Kathrin; Fukazawa, Aiko; Yamaguchi, Shigehiro; Petersen, Jeffrey L; Daniliuc, Constantin G; Fröhlich, Roland; Kehr, Gerald; Erker, Gerhard

    2013-06-03

    'Lene' and mean: The strong Lewis acid B(C6F5)3 efficiently converts some bis(arylethynyl)benzenes into dibenzopentalenes through a series of Lewis acid induced cyclization reactions at room temperature. Thus the reaction has the potential to be useful in the synthesis of substituted dibenzopentalene derivatives which are difficult to make by conventional means.

  19. Palladium-Catalyzed Atom-Transfer Radical Cyclization at Remote Unactivated C(sp3 )-H Sites: Hydrogen-Atom Transfer of Hybrid Vinyl Palladium Radical Intermediates.

    Science.gov (United States)

    Ratushnyy, Maxim; Parasram, Marvin; Wang, Yang; Gevorgyan, Vladimir

    2018-03-01

    A novel mild, visible-light-induced palladium-catalyzed hydrogen atom translocation/atom-transfer radical cyclization (HAT/ATRC) cascade has been developed. This protocol involves a 1,5-HAT process of previously unknown hybrid vinyl palladium radical intermediates, thus leading to iodomethyl carbo- and heterocyclic structures. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. SHORT COMMUNICATION CHEMOSELECTIVE C-BENZOYLATION ...

    African Journals Online (AJOL)

    BCSE

    KEY WORDS: Chemoselective C-acylation, F-C reaction, Fries rearrangement. INTRODUCTION. Friedel-Crafts acylation and benzoylation reactions are of great important in both academic research and industrial processes to synthesize aromatic ketones [1, 2]. Traditional Friedel-. Crafts acylation or benzoylation reactions ...

  1. Intramolecular Hydroalkoxylation of Non-Activated C=C Bonds Catalysed by Zeolites: An Experimental and Theoretical Study

    Czech Academy of Sciences Publication Activity Database

    Pérez-Mayoral, E.; Matos, I.; Nachtigall, P.; Položij, M.; Fonseca, I.; Vitvarová, Dana; Čejka, Jiří

    2013-01-01

    Roč. 6, č. 6 (2013), s. 1021-1030 ISSN 1864-5631 R&D Projects: GA ČR GBP106/12/G015 Institutional support: RVO:61388955 Keywords : cyclization * density functional calculations * heterogeneous catalysis Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 7.117, year: 2013

  2. Evolution of a short route to strychnine by using the samarium-diiodide-induced cascade cyclization as a key step.

    Science.gov (United States)

    Beemelmanns, Christine; Reissig, Hans-Ulrich

    2015-06-01

    This comprehensive report accounts the development of a highly diastereoselective samarium diiodide-induced cascade reaction of substituted indolyl ketones. The complexity-generating transformation with SmI2 allows the diastereoselective generation of three stereogenic centers including one quaternary center in one step. The obtained tetra- or pentacyclic dihydroindole derivatives are structural motifs of many monoterpene indole alkaloids, and their subsequent transformations gave way to one of the shortest approaches towards strychnine (14 % overall yield in ten steps, or 10 % overall yield in eight steps). During the course of this report we discuss the influence of substituents on the cyclization step, plausible mechanistic scenarios for the SmI2 -induced cascade reaction, diastereoselective reductive amination, and regioselective dehydratization protocols towards the pentacyclic core structure of strychnos alkaloids. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. SOCl2 catalyzed cyclization of chalcones: Synthesis and spectral studies of some bio-potent 1H pyrazoles

    Directory of Open Access Journals (Sweden)

    K. Ranganathan

    2014-05-01

    Full Text Available Some aryl-aryl 1H pyrazoles have been synthesised by cyclization of aryl chalcones and hydrazine hydrate in the presence of SOCl2. The yields of the pyrazoles are more than 85%. These pyrazoles are characterized by their physical constants and spectral data. The infrared, NMR spectral group frequencies of these pyrazolines have been correlated with Hammett substituent constants, F and R parameters. From the results of statistical analyses the effects of substituent on the spectral frequencies have been studied. The antimicrobial activities of all synthesised pyrazolines have been studied using Bauer-Kirby method. DOI: http://dx.doi.org/10.4314/bcse.v28i2.11

  4. Theoretical Investigation of Intramolecular Hydrogen Shift Reactions in 3-Methyltetrahydrofuran (3-MTHF) Oxidation.

    Science.gov (United States)

    Parab, Prajakta R; Sakade, Naoki; Sakai, Yasuyuki; Fernandes, Ravi; Heufer, K Alexander

    2015-11-05

    3-Methyltetrahydrofuran (3-MTHF) is proposed to be a promising fuel component among the cyclic oxygenated species. To have detailed insight of its combustion kinetics, intramolecular hydrogen shift reactions for the ROO to QOOH reaction class are studied for eight ROO isomers of 3-MTHF. Rate constants of all possible reaction paths that involve formation of cyclic transition states are computed by employing the CBS-QB3 composite method. A Pitzer-Gwinn-like approximation has been applied for the internal rotations in reactants, products, and transition states for the accurate treatment of hindered rotors. Calculated relative barrier heights highlight that the most favorable reaction channel proceeds via a six membered transition state, which is consistent with the computed rate constants. Comparing total rate constants in ROO isomers of 3-MTHF with the corresponding isomers of methylcyclopentane depicts faster kinetics in 3-MTHF than methylcyclopentane reflecting the effect of ring oxygen on the intramolecular hydrogen shift reactions.

  5. Long-range intramolecular electron transfer in aromatic radical anions and binuclear transition metal complexes

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    1981-01-01

    radicals containing two aromatic end groups connected by a flexible polymethylene chain or a rigid cyclohexane frame is thus trapped on either aromatic end group, and ET between these groups can be detected by ESR techniques. Intramolecular ET also occurs in binuclear transition metal complexes in which......, and for intramolecular and inner sphere ET for transition metal complexes. The Journal of Chemical Physics is copyrighted by The American Institute of Physics....... the coupling between the metal centers [(Ru(II)/Ru(III) and Ru(II)/Co(III) couples] is sufficiently weak (class I or II mixed valence compounds). The ET mechanism can involve either direct transfer between the donor and acceptor groups or a higher order mechanism in which ET proceeds through intermediate...

  6. Communication: Practical intramolecular symmetry adapted perturbation theory via Hartree-Fock embedding.

    Science.gov (United States)

    Parrish, Robert M; Gonthier, Jérôme F; Corminbœuf, Clémence; Sherrill, C David

    2015-08-07

    We develop a simple methodology for the computation of symmetry-adapted perturbation theory (SAPT) interaction energy contributions for intramolecular noncovalent interactions. In this approach, the local occupied orbitals of the total Hartree-Fock (HF) wavefunction are used to partition the fully interacting system into three chemically identifiable units: the noncovalent fragments A and B and a covalent linker C. Once these units are identified, the noninteracting HF wavefunctions of the fragments A and B are separately optimized while embedded in the HF wavefunction of C, providing the dressed zeroth order wavefunctions for A and B in the presence of C. Standard two-body SAPT (particularly SAPT0) is then applied between the relaxed wavefunctions for A and B. This intramolecular SAPT procedure is found to be remarkably straightforward and efficient, as evidenced by example applications ranging from diols to hexaphenyl-ethane derivatives.

  7. Ciclização intramolecular de 2-(w-Bromoalquiloxi) anilinas /

    OpenAIRE

    Martendal, Adriano

    1999-01-01

    Dissertação (Mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas. Ciclizações intramoleculares podem ser estudadas como modelos miméticos de catálise enzimática. Esses modelos fundamentam-se no princípio de que os parâmetros físico-químicos que governam a reatividade entre dois grupamentos funcionais em uma reação intramolecular, estejam presentes também no mecanismo da ação enzimática. Os brometos de 2-(w-bromoalquiloxi)anilínio e 2-(w-bromoalquilo...

  8. EVAPORATION: a new vapour pressure estimation methodfor organic molecules including non-additivity and intramolecular interactions

    Science.gov (United States)

    Compernolle, S.; Ceulemans, K.; Müller, J.-F.

    2011-09-01

    We present EVAPORATION (Estimation of VApour Pressure of ORganics, Accounting for Temperature, Intramolecular, and Non-additivity effects), a method to predict (subcooled) liquid pure compound vapour pressure p0 of organic molecules that requires only molecular structure as input. The method is applicable to zero-, mono- and polyfunctional molecules. A simple formula to describe log10p0(T) is employed, that takes into account both a wide temperature dependence and the non-additivity of functional groups. In order to match the recent data on functionalised diacids an empirical modification to the method was introduced. Contributions due to carbon skeleton, functional groups, and intramolecular interaction between groups are included. Molecules typically originating from oxidation of biogenic molecules are within the scope of this method: aldehydes, ketones, alcohols, ethers, esters, nitrates, acids, peroxides, hydroperoxides, peroxy acyl nitrates and peracids. Therefore the method is especially suited to describe compounds forming secondary organic aerosol (SOA).

  9. A colorimetric and ratiometric fluorescent probe for sulfite based on an intramolecular cleavage mechanism.

    Science.gov (United States)

    Hou, Peng; Chen, Song; Voitchovsky, Kislon; Song, Xiangzhi

    2014-11-01

    A colorimetric and ratiometric fluorescent sulfite probe, the levulinate of 4-hydroxynaphthalimide, was successfully synthesized from 4-hydroxy-naphthalimide and levulinic acid. Through sulfite-mediated intramolecular cleavage, the probe was converted into 4-hydroxynaphthalimide, which when excited at 450 nm, displayed a large Stokes shift due to the intramolecular charge transfer process. The probe exhibited high selectivity and sensitivity towards sulfite over other typical anionic species (F(-), Cl(-), Br(-), I(-), HPO(4)(2-), SO(4)(2-), NO(3)(-), AcO(-), ClO(4)(-), HCO(3)(-)) in HEPES-buffered solution (25 mm, pH 7.4, 50% acetonitrile, v/v). Copyright © 2013 John Wiley & Sons, Ltd.

  10. Some kinetic and spectroscopic evidence on intramolecular relaxation processes in polyatomic molecules

    International Nuclear Information System (INIS)

    Quack, M.

    1983-01-01

    The description and definition of intramolecular vibrational relaxation processes is discussed within the framework of the quantum mechanical and statistical mechanical equations of motion. The evidence from quite different experimental sources is summarized under the common aspect of vibrational relaxation. Although much of the evidence remains ambiguous, there is good indication that a localized vibrational excitation relaxes typically in 0.1 to 10 picoseconds, which is long compared to many optical and reactive processes

  11. A Concomitant Allylic Azide Rearrangement/Intramolecular Azide–Alkyne Cycloaddition Sequence

    Science.gov (United States)

    2015-01-01

    An intramolecular Huisgen cycloaddition of an interconverting set of isomeric allylic azides with alkynes affords substituted triazoles in high yield. The stereoisomeric vinyl-substituted triazoloxazines formed depend on the rate of cycloaddition of the different allylic azide precursors when the reaction is carried out under thermal conditions. In contrast, dimerized macrocyclic products were obtained when the reaction was done using copper(I)-catalyzed conditions, demonstrating the ability to control the reaction products through changing conditions. PMID:24635056

  12. Intramolecular Azide to Alkene Cycloadditions for the Construction of Pyrrolobenzodiazepines and Azetidino-Benzodiazepines

    Directory of Open Access Journals (Sweden)

    Karl Hemming

    2014-10-01

    Full Text Available The coupling of proline- and azetidinone-substituted alkenes to 2-azidobenzoic and 2-azidobenzenesulfonic acid gives precursors that undergo intramolecular azide to alkene 1,3-dipolar cycloadditions to give imine-, triazoline- or aziridine-containing pyrrolo[1,4]benzodiazepines (PBDs, pyrrolo[1,2,5]benzothiadiazepines (PBTDs, and azetidino[1,4]benzodiazepines. The imines and aziridines are formed after loss of nitrogen from a triazoline cycloadduct. The PBDs are a potent class of antitumour antibiotics.

  13. An intramolecular inverse electron demand Diels–Alder approach to annulated α-carbolines

    Directory of Open Access Journals (Sweden)

    Zhiyuan Ma

    2012-06-01

    Full Text Available Intramolecular inverse electron demand cycloadditions of isatin-derived 1,2,4-triazines with acetylenic dienophiles tethered by amidations or transesterifications proceed in excellent yields to produce lactam- or lactone-fused α-carbolines. Beginning with various isatins and alkynyl dienophiles, a pilot-scale library of eighty-eight α-carbolines was prepared by using this robust methodology for biological evaluation.

  14. Intramolecular electron transfer through a bridging carboxylate group coordinated to two cobalt(III)-ions

    International Nuclear Information System (INIS)

    Wieghardt, K.

    1978-01-01

    Reduction of the binuclear μ-p-nitrobenzoato -di-μ-hydroxo -bis[triammine cobalt(III)] cation with (CH 3 ) 2 COH radicals yields a radical cation with the p-nitrobenzoato radical being coordinated to two cobalt(III) ions at the carboxylic group. The unprotonated form of this species undergoes intramolecular electron transfer producing Co(II) (k = (3.3 +- 0.3). x 10 3 s -1 ). The role of the carboxylate group in the intramolecular electron transfer process is tentatively assessed in terms of an intramolecular outer-sphere reaction because of lack of overlap of the donor orbitals (π) and the acceptor orbital (sigma). The protonated form of the radical cation (pKsub(a) = 2.5) disproportionates via a bimolecular process without production of Co(II). The effect of two coordinated Co(III) ions as compared to only one on the properties of the nitrobenzoate radical anion are discussed. (orig.) 891 HK 892 GM [de

  15. THE ROLE OF INTRAMOLECULAR TIES ENERGY IN THE PYROLYSIS PROCESS OF PET

    Directory of Open Access Journals (Sweden)

    P. Iu. Salikov

    2014-01-01

    Full Text Available Summary. Recycling plastic waste to focus on. The main type of used products made of polyethylene terephthalate (PET is a container from the various types of beverages. There was considered a possibility of waste of PET (bottles, bottles, packaging containers by pyrolysis. Most of the proposed methods are not suitable for recycling (recycling of waste consumption contamination. Purpose - to develop technological foundations and optimum modes waste PET to obtain useful secondary products, taking into account the energy of chemical intramolecular bonds. Applied scientific basis of recycling PET into useful forms of secondary products, in particular the establishment of the collapse of the intramolecular bonds, depending on the temperature of the pyrolysis method of mathematical processing - differentiation of polynomial equations change in the degree of pyrolysis temperature-dependent. The optimum modes of processing. The block diagram of apparatus for processing contaminated waste PET pyrolysis methods of control processing in accordance with the specified composition of secondary products. The possibility of controlling the amount and types of fuel components of secondary products due to measurable parameters of the pyrolysis process. The effective temperature pyrolysis of waste PET with the CCA-tures energy intramolecular bonds.

  16. Time-Resolved Signatures across the Intramolecular Response in Substituted Cyanine Dyes

    Science.gov (United States)

    Nairat, Muath; Webb, Morgan; Esch, Michael; Lozovoy, Vadim V.; Levine, Benjamin G.; Dantus, Marcos

    2017-06-01

    The optically populated excited state wave packet propagates along multidimensional intramolecular coordinates soon after photoexcitation. This action occurs alongside an intermolecular response from the surrounding solvent. Disentangling the multidimensional convoluted signal enables the possibility to separate and understand the initial intramolecular relaxation pathways over the excited state potential energy surface. Here we track the initial excited state dynamics by measuring the fluorescence yield from the first excited state as a function of time delay between two color femtosecond pulses for several cyanine dyes, having different electronic configurations. We find that when the high frequency pulse precedes the low frequency one and for timescales up to 200 fs, the excited state can be depleted through stimulated emission with efficiency that is dependent on the molecular electronic structure. A similar observation at even shorter times was made by scanning the chirp (frequencies ordering) of a femtosecond pulse. These changes reflect the rate at which the nuclear coordinates of the excited state leave the Franck-Condon (FC) region and progress towards achieving equilibrium. Through functional group substitution, we explore these dynamic changes as a function of dipolar change following photoexcitation. We show that with proper knowledge and control over the phase of the excitation pulses, we can extract the relative energy relaxation rates through which the early intramolecular modes are populated at the FC geometry soon after excitation

  17. Intramolecular stable isotope distributions detect plant metabolic responses on century time scales

    Science.gov (United States)

    Schleucher, Jürgen; Ehlers, Ina; Augusti, Angela; Betson, Tatiana

    2014-05-01

    Plants respond to environmental changes on a vast range of time scales, and plant gas exchanges constitute important feedback mechanisms in the global C cycle. Responses on time scales of decades to centuries are most important for climate models, for prediction of crop productivity, and for adaptation to climate change. Unfortunately, responses on these timescale are least understood. We argue that the knowledge gap on intermediate time scales is due to a lack of adequate methods that can bridge between short-term manipulative experiments (e.g. FACE) and paleo research. Manipulative experiments in plant ecophysiology give information on metabolism on time scales up to years. However, this information cannot be linked to results from retrospective studies in paleo research, because little metabolic information can be derived from paleo archives. Stable isotopes are prominent tools in plant ecophysiology, biogeochemistry and in paleo research, but in all applications to date, isotope ratios of whole molecules are measured. However, it is well established that stable isotope abundance varies among intramolecular groups of biochemical metabolites, that is each so-called "isotopomer" has a distinct abundance. This intramolecular variation carries information on metabolic regulation, which can even be traced to individual enzymes (Schleucher et al., Plant, Cell Environ 1999). Here, we apply intramolecular isotope distributions to study the metabolic response of plants to increasing atmospheric [CO2] during the past century. Greenhouse experiments show that the deuterium abundance among the two positions in the C6H2 group of photosynthetic glucose depends on [CO2] during growth. This is observed for all plants using C3 photosynthesis, and reflects the metabolic flux ratio between photorespiration and photosynthesis. Photorespiration is a major C flux that limits assimilation in C3 plants, which encompass the overwhelming fraction of terrestrial photosynthesis and the

  18. Catalytic Aldol-Cyclization Cascade of 3-Isothiocyanato Oxindoles with α-Ketophosphonates for the Enantioselective Synthesis of β-Amino-α-hydroxyphosphonates.

    Science.gov (United States)

    Kayal, Satavisha; Mukherjee, Santanu

    2015-11-06

    A cascade aldol-cyclization reaction between 3-isothiocyanato oxindoles and α-ketophosphonates has been developed for the synthesis of β-amino-α-hydroxyphosphonate derivatives. Catalyzed by a quinine-based tertiary amino-thiourea derivative, this reaction delivers 2-thioxooxazolidinyl phosphonates based on a spirooxindole scaffold bearing two contiguous quaternary stereogenic centers in high yields with excellent diastereo- (up to >20:1 dr) and enantioselectivities (up to >99:1 er).

  19. A Novel Synthesis of 1-Acetyl-4-Isopropenyl-1-Cyclopentene by Chemoselective Cyclization of 4-Methyl-3-(Oxobutyl-4-Pentenal: An Important Intermediate for Natural Product Synthesis

    Directory of Open Access Journals (Sweden)

    Castro Fernando de Lima

    1999-01-01

    Full Text Available This article presents the direct oxidation of limonene-oxide 1 with KIO4 in water, which is the best way to obtain the keto-aldehyde 3, an important intermediate in natural product synthesis. The cyclization of keto-aldehyde 3 with acidic Al2O3 proceeds chemoselectively to give ketone 4. These two reactions together increase the overall yield of ketone 4 to about 70% compared to 8% previously reported in the literature¹.

  20. Dual gold/photoredox-catalyzed bis-arylative cyclization of chiral homopropargyl sulfonamides with diazonium salts: rapid access to enantioenriched 2,3-dihydropyrroles.

    Science.gov (United States)

    Wang, Ze-Shu; Tan, Tong-De; Wang, Cai-Ming; Yuan, Ding-Qiang; Zhang, Te; Zhu, Pengfei; Zhu, Chunyin; Zhou, Jin-Mei; Ye, Long-Wu

    2017-06-22

    A novel dual gold/photoredox-catalyzed bis-arylative cyclization of chiral homopropargyl sulfonamides with diazonium salts has been developed, allowing the facile synthesis of various enantioenriched 2,3-dihydropyrroles in generally moderate to good yields with excellent enantioselectivities under very mild conditions without using any strong oxidants. The reaction is proposed to undergo an Au I /Au III redox cycle promoted by visible-light photoredox catalysis.

  1. Deconstructing selectivity in the gold-promoted cyclization of alkynyl benzothioamides to six-membered mesoionic carbene or acyclic carbene complexes

    KAUST Repository

    Vummaleti, Sai V. C.

    2014-05-02

    We demonstrate that the experimentally observed switch in selectivity from 5-exo-dig to 6-endo-dig cyclization of an alkynyl substrate, promoted by Au I and AuIII complexes, is connected to a switch from thermodynamic to kinetic reaction control. The AuIII center pushes alkyne coordination toward a single Au-C(alkyne) σ-bond, conferring carbocationic character (and reactivity) to the distal alkyne C atom. © 2014 American Chemical Society.

  2. K2CO3-Mediated Synthesis of Functionalised 4-Substituted-2-amino-3-cyano-4H-chromenes via Michael-Cyclization Reactions

    Directory of Open Access Journals (Sweden)

    Yanyang He

    2014-11-01

    Full Text Available An efficient approach for the synthesis of functionalized 4-substituted-2-amino-3-cyano-4H-chromenes moderate to high yields (up to 98% has been achieved via a tandem K2CO3 catalyzed conjugate addition-cyclization reaction of malononitrile and a range of Knoevenagel adducts previously formed from oxindole, pyrazolone, nitromethane, N,N-dimethylbarbituric acid or indanedione. This methodology differs from the previous classical methods in its simplicity and ready availability of the catalyst.

  3. Stereoselective synthesis of tricyclic compounds by intramolecular palladium-catalyzed addition of aryl iodides to carbonyl groups

    Directory of Open Access Journals (Sweden)

    Jakub Saadi

    2016-06-01

    Full Text Available Starting from γ-ketoesters with an o-iodobenzyl group we studied a palladium-catalyzed cyclization process that stereoselectively led to bi- and tricyclic compounds in moderate to excellent yields. Four X-ray crystal structure analyses unequivocally defined the structure of crucial cyclization products. The relative configuration of the precursor compounds is essentially transferred to that of the products and the formed hydroxy group in the newly generated cyclohexane ring is consistently in trans-arrangement with respect to the methoxycarbonyl group. A transition-state model is proposed to explain the observed stereochemical outcome. This palladium-catalyzed Barbier-type reaction requires a reduction of palladium(II back to palladium(0 which is apparently achieved by the present triethylamine.

  4. Syntheses of strychnine, norfluorocurarine, dehydrodesacetylretuline, and valparicine enabled by intramolecular cycloadditions of Zincke aldehydes.

    Science.gov (United States)

    Martin, David B C; Nguyen, Lucas Q; Vanderwal, Christopher D

    2012-01-06

    A full account of the development of the base-mediated intramolecular Diels-Alder cycloadditions of tryptamine-derived Zincke aldehydes is described. This important complexity-generating transformation provides the tetracyclic core of many indole monoterpene alkaloids in only three steps from commercially available starting materials and played a key role in short syntheses of norfluorocurarine (five steps), dehydrodesacetylretuline (six steps), valparicine (seven steps), and strychnine (six steps). Reasonable mechanistic possibilities for this reaction, a surprisingly facile dimerization of the products, and an unexpected cycloreversion to regenerate Zincke aldehydes under specific conditions are also discussed.

  5. Deuterium isotope effect on the intramolecular electron transfer in Pseudomonas aeruginosa azurin

    DEFF Research Database (Denmark)

    Farver, O.; Zhang, Jingdong; Chi, Qijin

    2001-01-01

    rather than negative. Isotope effects are, however, also inherent in the nuclear reorganization Gibbs free energy and in the tunneling factor for the electron transfer process. A slightly larger thermal protein expansion in H2O than in D2O (0.001 nm K-1) is sufficient both to account for the activation......Intramolecular electron transfer in azurin in water and deuterium oxide has been studied over a broad temperature range. The kinetic deuterium isotope effect, k(H)/k(D), is smaller than unity (0.7 at 298 K), primarily caused by the different activation entropies in water (-56.5 J K-1 mol(-1...

  6. A concise, efficient synthesis of sugar-based benzothiazoles through chemoselective intramolecular C-S coupling

    KAUST Repository

    Shen, Chao

    2012-01-01

    Sugar-based benzothiazoles are a new class of molecules promising for many biological applications. Here, we have synthesized a wide range of sugar-based benzothiazoles from readily accessible glycosyl thioureas by chemoselective, palladium-catalyzed C-S coupling reactions. Corroborated by theoretical calculations, a mechanistic investigation indicates that the coordination to the palladium by a pivaloyl carbonyl group and the presence of intramolecular hydrogen bonding play important roles in the efficiency and chemoselectivity of reaction. These fluorescent glycoconjugates can be observed to readily enter mammalian tumor cells and exhibit potential in vitro antitumor activity. This journal is © The Royal Society of Chemistry 2012.

  7. Path-integral calculation of the second virial coefficient including intramolecular flexibility effects

    Energy Technology Data Exchange (ETDEWEB)

    Garberoglio, Giovanni, E-mail: garberoglio@fbk.eu [Interdisciplinary Laboratory for Computational Science (LISC), FBK-CMM and University of Trento, via Sommarive 18, I-38123 Povo (Italy); Jankowski, Piotr [Department of Quantum Chemistry, Faculty of Chemistry, Nicolaus Copernicus University, Gagarina 7, PL-87-100 Toruń (Poland); Szalewicz, Krzysztof [Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States); Harvey, Allan H. [Applied Chemicals and Materials Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305-3337 (United States)

    2014-07-28

    We present a path-integral Monte Carlo procedure for the fully quantum calculation of the second molecular virial coefficient accounting for intramolecular flexibility. This method is applied to molecular hydrogen (H{sub 2}) and deuterium (D{sub 2}) in the temperature range 15–2000 K, showing that the effect of molecular flexibility is not negligible. Our results are in good agreement with experimental data, as well as with virials given by recent empirical equations of state, although some discrepancies are observed for H{sub 2} between 100 and 200 K.

  8. Dynamics of excited-state intramolecular proton transfer reactions in piroxicam. Role of triplet states

    Science.gov (United States)

    Cho, Dae Won; Kim, Yong Hee; Yoon, Minjoong; Jeoung, Sae Chae; Kim, Dongho

    1994-08-01

    The picosecond time-resolved fluorescence and transient absorption behavior of piroxicam at room temperature are reported. The keto tautomer in the excited singlet state ( 1K*) formed via the fast intramolecular proton transfer (≈ 20 ps) is observed. The short-lived (7.5 ns) triplet state of keto tauomer ( 3K*) is generated from 1K * in toluene whereas it is hardly observed in ethanol. Consequently, rapid reverse proton transfer takes place from 3K * to the enol triplet state ( 3E *.

  9. The Preparation and Intramolecular Radical Cyclisation Reactions of Chiral Oxime Ethers

    Directory of Open Access Journals (Sweden)

    Booth Susan E.

    1998-01-01

    Full Text Available Chiral oxime ether 2 and Oxime ester 4 have been prepared by alkylation and esterification of the oxime 1. Racemic hydroxylamine 6 and chiral hydroxylamine 10 have been synthesised from N-hydroxysuccinimide and the corresponding alcohol in the presence of diethylazodicarboxylate, the two products were converted into the oxime ethers 7 and 11 respectively. The intramolecular radical cyclisation reactions of these oxime ethers and esters has been studied, successful reaction was observed to produce alkyl hydroxylamines 3, 8 and 12.

  10. Some Brief Notes on Theoretical and Experimental Investigations of Intramolecular Hydrogen Bonding

    Directory of Open Access Journals (Sweden)

    Lucjan Sobczyk

    2016-12-01

    Full Text Available A review of selected literature data related to intramolecular hydrogen bonding in ortho-hydroxyaryl Schiff bases, ortho-hydroxyaryl ketones, ortho-hydroxyaryl amides, proton sponges and ortho-hydroxyaryl Mannich bases is presented. The paper reports on the application of experimental spectroscopic measurements (IR and NMR and quantum-mechanical calculations for investigations of the proton transfer processes, the potential energy curves, tautomeric equilibrium, aromaticity etc. Finally, the equilibrium between the intra- and inter-molecular hydrogen bonds in amides is discussed.

  11. Use of ionic model for analysis of intramolecular movement in alkali metal metaborate molecules

    International Nuclear Information System (INIS)

    Ezhov, Yu.S.; Vinogradov, V.S.

    1978-01-01

    To clear out the peculiarities of intramolecular movement in MBO 2 (where M=Li, Na, K, Rb, Cs) molecules the energy dependence of cation electrostatic interaction with BO 2 anion on the charge value of oxygen, values of the MOB valence angle and internuclear distance r(M-O) is calculated. The calculation results on the base of ionic model show that the minimum of potential energy function corresponds to angular configuration of the MBO 2 molecules. Parameters of potential function of deformation oscillation connected with the change of MOB angle, are evaluated

  12. Samarium(II) iodide-mediated intramolecular conjugate additions of alpha,beta-unsaturated lactones.

    Science.gov (United States)

    Molander, Gary A; St Jean, David J

    2002-05-31

    Samarium(II) iodide, in the presence of catalytic amounts of nickel(II) iodide, has been used to promote intramolecular conjugate additions of alkyl halides onto alpha,beta-unsaturated lactones. This process has been shown to be applicable to a number of alpha,beta-unsaturated lactones, including tetrasubstituted olefins, and has been demonstrated to be quite general for the formation of saturated bicyclic and tricyclic lactones. The method presented herein provides a mild, efficient process to form structurally complex lactones from simple precursors.

  13. Intramolecular hydrogen bond in molecular and proton-transfer forms of Schiff bases

    Energy Technology Data Exchange (ETDEWEB)

    Filarowski, A.; Koll, A.; Karpfen, A.; Wolschann, P

    2004-02-16

    The force field and structural parameters modifications upon the formation of intramolecular hydrogen bond and proton transfer reaction in N-methyl-2-hydroxybenzylidene amine (HBZA) are determined on the basis of ab initio and DFT calculations. Reliability of the calculations is verified by comparing of the theoretical vibrational spectra with those experimentally determined in the gas phase. A model of resonance interactions is applied and the quantitative contribution of ortho-quinoid structure in the particular conformers is estimated. A comparison is also made to the systems without {pi}-electron coupling (Mannich bases)

  14. Cooperative Metal–Ligand Catalyzed Intramolecular Hydroamination and Hydroalkoxylation of Allenes Using a Stable Iron Catalyst

    KAUST Repository

    El-Sepelgy, Osama

    2018-01-18

    A new iron-catalyzed chemoselective intramolecular hydroamination and hydroalkoxylation of the readily available α-allenic amines and alcohols to valuable unsaturated 5-membered heterocycles, 2,3-dihydropyrrole and 2,3-dihydrofuran, is reported. Effective selectivity control is achieved by a metal–ligand cooperative activation of the substrates. The mild reaction conditions and the use of low amounts of an air and moisture stable iron catalyst allow for the hydrofunctionalization of a wide range of allenes bearing different functional groups in good yields in the absence of base or any sensitive additives.

  15. Pulse radiolytic and electrochemical investigations of intramolecular electron transfer in carotenoporphyrins and carotenoporphyrin-quinone triads

    International Nuclear Information System (INIS)

    Land, E.J.; Lexa, D.; Bensasson, R.V.; Gust, D.; Moore, T.A.; Moore, A.L.; Liddell, P.A.; Nemeth, G.A.

    1987-01-01

    Thermodynamic and kinetic aspects of intramolecular electron-transfer reactions in carotenoporphyrin dyads and carotenoid-porphyrin-quinone triads have been studied by using pulse radiolysis and cyclic voltammetry. Rapid (<1 μs) electron transfer from carotenoid radical anions to attached porphyrins has been inferred. Carotenoid cations, on the other hand, do not readily accept electrons from attached porphyrins or pyropheophorbides. Electrochemical studies provide the thermodynamic basis for these observations and also allow estimation of the energetics of photoinitiated two-step electron transfer and two-step charge recombination in triad models for photosynthetic charge separation

  16. Synthesis and ion-binding properties of polymeric pseudocrown ethers II: Template ion induced cyclization of oligomeric ethylene glycol diacrylates

    Energy Technology Data Exchange (ETDEWEB)

    Mathur, A.M.; Scranton, A.B. [Michigan State Univ., East Lansing, MI (United States)

    1997-01-01

    Inexpensive polymeric pseudocrown ethers have been synthesized based upon a {open_quotes}template ion{close_quotes} effect in which oligomeric ethylene glycol diacrylates are induced to assume a circular conformation in which the unsaturated end-groups are in proximity. This synthetic scheme has considerable potential for the development of inexpensive materials for binding of target cations. In this contribution, the authors report a spectroscopic study of the induced cyclization caused by ion-dipole interactions between the templating cation and the electron lone pairs of the ethylene glycol ether linkages. Fluorescence spectroscopy was used to provide insight into the templatization process by examining excimer formation in pyrene end-labeled oligomeric ethylene glycol both in the absence and in the presence of the templating ion. Pyrene end-labeled tetraethylene glycol and pentaethylene glycol were synthesized and excimer fluorescence enhancement was studied with the introduction of cations such as nickel, chromium and tin in solvents such as tetrahydrofuran and chloroform. An increase in excimer fluorescence indicated enhanced excimer formation due to the templating effect of the cation which results in the end groups being close to each other. Molecular dynamics simulations of pyrene end-labeled ligands were performed to elucidate the effect of the large fluorescent chromophores on the chain conformations.

  17. Approach to Interfacial and Intramolecular Electron Transfer of the Diheme Protein Cytochrome c(4) Assembled on Au(111) Surfaces

    DEFF Research Database (Denmark)

    Chi, Qijin; Zhang, Jingdong; Taner, Arslan

    2010-01-01

    protein Pseudomonas stutzeri cytochrome c(4) has been a target for intramolecular, interheme ET. We report here voltammetric and in situ scanning tunneling microscopy (STM) data for P. stutzeri cyt c(4) at single-crystal, atomically planar Au(111)-electrode surfaces modified by variable-length omega...... direction and a single two-ET peak in the anodic direction. Intramolecular, interheme ET with high, 8,000-30,000 s(-1), rate constants is notably an essential part of this mechanism. The high rate constants are in striking contrast to ET reactions of P. stutzeri cyt c4 with small reaction partners...... in homogeneous solution for which kinetic analysis clearly testifies to electrostatic cooperative effects but no intramolecular, interheme ET higher than 0.1-10 s(-1). This difference suggests a strong gating feature of the process. On the basis of the three-dimensional structure of P. stutzeri cyt c(4), gating...

  18. Mechanistic Insights into the Post-Cyclization Isomerization in Gold-Catalyzed 7-exo-dig-Hydroarylations.

    Science.gov (United States)

    Pflästerer, Daniel; Schumacher, Sören; Rudolph, Matthias; Hashmi, A Stephen K

    2015-08-03

    The subsequent double-bond isomerization in the synthesis of dibenzocycloheptenes and their heteroaromatic analogues was investigated. In the case of biphenyls, a basic additive completely prevented an isomerization to the thermodynamic product. With electron-rich intramolecular heteroaromatic nucleophiles, the isomerization was still observed, but the kinetic product can be obtained by careful control of the reaction times in most cases. Mechanistic studies demonstrated that a slow isomerization is also possible with the gold catalyst at elevated temperatures, but much faster isomerization rates were observed with acidic additives. An observed initiation period for the gold-catalyzed isomerization indicates that not the homogenous catalyst, but a decomposition product of it may be the catalytically active species. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Intramolecular Hydrogen Bonding Involving Organic Fluorine: NMR Investigations Corroborated by DFT-Based Theoretical Calculations

    Directory of Open Access Journals (Sweden)

    Sandeep Kumar Mishra

    2017-03-01

    Full Text Available The combined utility of many one and two dimensional NMR methodologies and DFT-based theoretical calculations have been exploited to detect the intramolecular hydrogen bond (HB in number of different organic fluorine-containing derivatives of molecules, viz. benzanilides, hydrazides, imides, benzamides, and diphenyloxamides. The existence of two and three centered hydrogen bonds has been convincingly established in the investigated molecules. The NMR spectral parameters, viz., coupling mediated through hydrogen bond, one-bond NH scalar couplings, physical parameter dependent variation of chemical shifts of NH protons have paved the way for understanding the presence of hydrogen bond involving organic fluorine in all the investigated molecules. The experimental NMR findings are further corroborated by DFT-based theoretical calculations including NCI, QTAIM, MD simulations and NBO analysis. The monitoring of H/D exchange with NMR spectroscopy established the effect of intramolecular HB and the influence of electronegativity of various substituents on the chemical kinetics in the number of organic building blocks. The utility of DQ-SQ technique in determining the information about HB in various fluorine substituted molecules has been convincingly established.

  20. Organometallic copper I, II or III species in an intramolecular dechlorination reaction

    KAUST Repository

    Poater, Albert

    2013-03-15

    The present paper gives insight into an intramolecular dechlorination reaction involving Copper (I) and an ArCH2Cl moiety. The discussion of the presence of a CuIII organometallic intermediate becomes a challenge, and because of the lack of clear experimental detection of this proposed intermediate, and due to the computational evidence that it is less stable than other isomeric species, it can be ruled out for the complex studied here. Our calculations are completely consistent with the key hypothesis of Karlin et al. that TMPA-CuI is the substrate of intramolecular dechlorination reactions as well as the source to generate organometallic species. However the organometallic character of some intermediates has been refused because computationally these species are less stable than other isomers. Thus this study constitutes an additional piece towards the full understanding of a class of reaction of biological relevance. Further, the lack of high energy barriers and deep energy wells along the reaction pathway explains the experimental difficulties to trap other intermediates. © Springer-Verlag Berlin Heidelberg 2013.

  1. Effect of Hartree-Fock exact exchange on intramolecular magnetic coupling constants of organic diradicals.

    Science.gov (United States)

    Cho, Daeheum; Ko, Kyoung Chul; Ikabata, Yasuhiro; Wakayama, Kazufumi; Yoshikawa, Takeshi; Nakai, Hiromi; Lee, Jin Yong

    2015-01-14

    The intramolecular magnetic coupling constant (J) of diradical systems linked with five- or six-membered aromatic rings was calculated to obtain the scaling factor (experimental J/calculated J ratio) for various density functional theory (DFT) functionals. Scaling factors of group A (PBE, TPSSh, B3LYP, B97-1, X3LYP, PBE0, and BH&HLYP) and B (M06-L, M06, M06-2X, and M06-HF) were shown to decrease as the amount of Hartree-Fock exact exchange (HFx) increases, in other words, overestimation of calculated J becomes more severe as the HFx increases. We further investigated the effect of HFx fraction of DFT functional on J value, spin contamination, and spin density distributions by comparing the B3LYP analogues containing different amount of HFx. It was revealed that spin contamination and spin densities at each atom increases as the HFx increases. Above all, newly developed BLYP-5 functional, which has 5% of HFx, was found to have the scaling factor of 1.029, indicating that calculated J values are very close to that of experimental values without scaling. BLYP-5 has potential to be utilized for accurate evaluation of intramolecular magnetic coupling constant (J) of diradicals linked by five- or six-membered aromatic ring couplers.

  2. Discovery of intramolecular signal transduction network based on a new protein dynamics model of energy dissipation.

    Directory of Open Access Journals (Sweden)

    Cheng-Wei Ma

    Full Text Available A novel approach to reveal intramolecular signal transduction network is proposed in this work. To this end, a new algorithm of network construction is developed, which is based on a new protein dynamics model of energy dissipation. A key feature of this approach is that direction information is specified after inferring protein residue-residue interaction network involved in the process of signal transduction. This enables fundamental analysis of the regulation hierarchy and identification of regulation hubs of the signaling network. A well-studied allosteric enzyme, E. coli aspartokinase III, is used as a model system to demonstrate the new method. Comparison with experimental results shows that the new approach is able to predict all the sites that have been experimentally proved to desensitize allosteric regulation of the enzyme. In addition, the signal transduction network shows a clear preference for specific structural regions, secondary structural types and residue conservation. Occurrence of super-hubs in the network indicates that allosteric regulation tends to gather residues with high connection ability to collectively facilitate the signaling process. Furthermore, a new parameter of propagation coefficient is defined to determine the propagation capability of residues within a signal transduction network. In conclusion, the new approach is useful for fundamental understanding of the process of intramolecular signal transduction and thus has significant impact on rational design of novel allosteric proteins.

  3. Dynamic intramolecular regulation of the histone chaperone nucleoplasmin controls histone binding and release.

    Science.gov (United States)

    Warren, Christopher; Matsui, Tsutomu; Karp, Jerome M; Onikubo, Takashi; Cahill, Sean; Brenowitz, Michael; Cowburn, David; Girvin, Mark; Shechter, David

    2017-12-20

    Nucleoplasmin (Npm) is a highly conserved histone chaperone responsible for the maternal storage and zygotic release of histones H2A/H2B. Npm contains a pentameric N-terminal core domain and an intrinsically disordered C-terminal tail domain. Though intrinsically disordered regions are common among histone chaperones, their roles in histone binding and chaperoning remain unclear. Using an NMR-based approach, here we demonstrate that the Xenopus laevis Npm tail domain controls the binding of histones at its largest acidic stretch (A2) via direct competition with both the C-terminal basic stretch and basic nuclear localization signal. NMR and small-angle X-ray scattering (SAXS) structural analyses allowed us to construct models of both the tail domain and the pentameric complex. Functional analyses demonstrate that these competitive intramolecular interactions negatively regulate Npm histone chaperone activity in vitro. Together these data establish a potentially generalizable mechanism of histone chaperone regulation via dynamic and specific intramolecular shielding of histone interaction sites.

  4. EVAPORATION: a new vapour pressure estimation methodfor organic molecules including non-additivity and intramolecular interactions

    Directory of Open Access Journals (Sweden)

    S. Compernolle

    2011-09-01

    Full Text Available We present EVAPORATION (Estimation of VApour Pressure of ORganics, Accounting for Temperature, Intramolecular, and Non-additivity effects, a method to predict (subcooled liquid pure compound vapour pressure p0 of organic molecules that requires only molecular structure as input. The method is applicable to zero-, mono- and polyfunctional molecules. A simple formula to describe log10p0(T is employed, that takes into account both a wide temperature dependence and the non-additivity of functional groups. In order to match the recent data on functionalised diacids an empirical modification to the method was introduced. Contributions due to carbon skeleton, functional groups, and intramolecular interaction between groups are included. Molecules typically originating from oxidation of biogenic molecules are within the scope of this method: aldehydes, ketones, alcohols, ethers, esters, nitrates, acids, peroxides, hydroperoxides, peroxy acyl nitrates and peracids. Therefore the method is especially suited to describe compounds forming secondary organic aerosol (SOA.

  5. The role of hydrogen bonding in excited state intramolecular charge transfer.

    Science.gov (United States)

    Chipem, Francis A S; Mishra, Anasuya; Krishnamoorthy, G

    2012-07-07

    Intramolecular charge transfer (ICT) that occurs upon photoexcitation of molecules is a vital process in nature and it has ample applications in chemistry and biology. The ICT process of the excited molecules is affected by several environmental factors including polarity, viscosity and hydrogen bonding. The effect of polarity and viscosity on the ICT processes is well understood. But, despite the fact that hydrogen bonding significantly influences the ICT process, the specific role of hydrogen bonding in the formation and stabilization of the ICT state is not unambiguously established. Some literature reports predicted that the hydrogen bonding of the solvent with a donor promotes the formation of a twisted intramolecular charge transfer (TICT) state. Some other reports stated that it inhibits the formation of the TICT state. Alternatively, it was proposed that the hydrogen bonding of the solvent with an acceptor favors the TICT state. It is also observed that a dynamic equilibrium is established between the free and the hydrogen bonded ICT states. This perspective focuses on the specific role played by hydrogen bonding of the solvent with the donor and the acceptor, and by proton transfer in the ICT process. The utility of such influence in molecular recognition and anion sensing is discussed with a few recent literature examples in the end.

  6. Visible absorbing croconium dyes with intramolecular hydrogen bonding: A combined experimental and computational study

    Science.gov (United States)

    Prabhakar, Ch.; Promila; Tripathi, Anuj; Bhanuprakash, K.; Jayathirtharao, V.

    2017-10-01

    Croconium molecules CR1-CR4 with break-in conjugation (Csbnd N Bonding) was synthesized by condensation of croconic acid and arylamines. By using combined experimental and theoretical methods like UV-visible spectra, DFT and TDDFT studies, we have characterized electronic absorption properties. The reported molecules are having absorption in visible region ranging from 450 to 550 nm with large extinction coefficient (2.5-5.0 × 104 M-1 cm-1). We find that CR2 and CR4 are showing 50 to 100 nm red shifted absorption than CR1 and CR3. This red shift is possibly due to presence of intramolecular hydrogen bonding in CR2 and CR4. Further this is supported by DFT studies, in case of CR2 and CR4 shows strong intramolecular hydrogen bonding between oxygen of carboxylate group (at ortho position of phenyl ring) and hydrogen of nitrogen attached to the central croconate ring. It is also observed that, there is small diradicaloid character in these molecules. This study is helpful in design and synthesis of new croconium dyes which are useful in materials applications.

  7. Regioselective Synthesis of Procyanidin B6, A 4-6-Condensed (+-Catechin Dimer, by Intramolecular Condensation

    Directory of Open Access Journals (Sweden)

    Yusuke Higashino

    2018-01-01

    Full Text Available Proanthocyanidins, also known as condensed tannins or oligomeric flavonoids, are found in many edible plants and exhibit interesting biological activities. Herein, we report a new, simple method for the stereoselective synthesis of procyanidin B6, a (+-catechin-(4-6-(+-catechin dimer, by Lewis acid-catalyzed intramolecular condensation. The 5-O-t-butyldimethylsilyl (TBDMS group of 5,7,3′4′-tetra-O-TBDMS-(+-catechin was regioselectively removed using trifluoroacetic acid, leading to the “regio-controlled” synthesis of procyanidin B6. The 5-hydroxyl group of the 7,3′,4′-tri-O-TBDMS-(+-catechin nucleophile and the 3-hydroxyl group of 5,7,3′,4′-tetra-O-benzylated-(+-catechin electrophile were connected with an azelaic acid. The subsequent SnCl4-catalyzed intramolecular condensation proceeded smoothly to give the 4-6-condensed catechin dimer. This is the first report on the complete regioselective synthesis of a 4-6-connected oligomer without modifying the 8-position.

  8. Instantaneous normal mode analysis for intermolecular and intramolecular vibrations of water from atomic point of view

    Science.gov (United States)

    Chen, Yu-Chun; Tang, Ping-Han; Wu, Ten-Ming

    2013-11-01

    By exploiting the instantaneous normal mode (INM) analysis for models of flexible molecules, we investigate intermolecular and intramolecular vibrations of water from the atomic point of view. With two flexible SPC/E models, our investigations include three aspects about their INM spectra, which are separated into the unstable, intermolecular, bending, and stretching bands. First, the O- and H-atom contributions in the four INM bands are calculated and their stable INM spectra are compared with the power spectra of the atomic velocity autocorrelation functions. The unstable and intermolecular bands of the flexible models are also compared with those of the SPC/E model of rigid molecules. Second, we formulate the inverse participation ratio (IPR) of the INMs, respectively, for the O- and H-atom and molecule. With the IPRs, the numbers of the three species participated in the INMs are estimated so that the localization characters of the INMs in each band are studied. Further, by the ratio of the IPR of the H atom to that of the O atom, we explore the number of involved OH bond per molecule participated in the INMs. Third, by classifying simulated molecules into subensembles according to the geometry of their local environments or their H-bond configurations, we examine the local-structure effects on the bending and stretching INM bands. All of our results are verified to be insensible to the definition of H-bond. Our conclusions about the intermolecular and intramolecular vibrations in water are given.

  9. Redox-Tag Processes: Intramolecular Electron Transfer and Its Broad Relationship to Redox Reactions in General.

    Science.gov (United States)

    Okada, Yohei; Chiba, Kazuhiro

    2017-12-08

    Explosive growth in the use of open shell reactivity, including neutral radicals and radical ions, in the field of synthetic organic chemistry has been observed in the past decade, particularly since the advent of ruthenium complexes in 2008. These complexes generally induce single-electron transfer (SET) processes via visible-light absorption. Additionally, recent significant advancements in organic electrochemistry involving SET processes to provide open shell reactivity offer a complementary method to traditional polarity-driven reactions described by two-electron transfer processes. In this Review, we highlight the importance of intramolecular SET processes in the field of synthetic organic chemistry, which seem to be more elusive than the intermolecular versions, since they are net redox-neutral and thus cannot simply be regarded as oxidations or reductions. Such intramolecular SET processes can rationally be understood in combination with concomitant bond formations and/or cleavages, and are regulated by a structural motif that we call a "redox tag." In order to describe modern radical-driven reactions involving SET processes, we focus on a classical formalism in which electrons are treated as particles rather than waves, which offers a practical yet powerful approach to explain and/or predict synthetic outcomes.

  10. Instantaneous normal mode analysis for intermolecular and intramolecular vibrations of water from atomic point of view.

    Science.gov (United States)

    Chen, Yu-Chun; Tang, Ping-Han; Wu, Ten-Ming

    2013-11-28

    By exploiting the instantaneous normal mode (INM) analysis for models of flexible molecules, we investigate intermolecular and intramolecular vibrations of water from the atomic point of view. With two flexible SPC/E models, our investigations include three aspects about their INM spectra, which are separated into the unstable, intermolecular, bending, and stretching bands. First, the O- and H-atom contributions in the four INM bands are calculated and their stable INM spectra are compared with the power spectra of the atomic velocity autocorrelation functions. The unstable and intermolecular bands of the flexible models are also compared with those of the SPC/E model of rigid molecules. Second, we formulate the inverse participation ratio (IPR) of the INMs, respectively, for the O- and H-atom and molecule. With the IPRs, the numbers of the three species participated in the INMs are estimated so that the localization characters of the INMs in each band are studied. Further, by the ratio of the IPR of the H atom to that of the O atom, we explore the number of involved OH bond per molecule participated in the INMs. Third, by classifying simulated molecules into subensembles according to the geometry of their local environments or their H-bond configurations, we examine the local-structure effects on the bending and stretching INM bands. All of our results are verified to be insensible to the definition of H-bond. Our conclusions about the intermolecular and intramolecular vibrations in water are given.

  11. Vibrational Spectroscopy of Intramolecular Hydrogen Bonds in the Infrared and Near-Infrared Regions

    DEFF Research Database (Denmark)

    Schrøder, Sidsel Dahl

    and 1,4-diaminobutane). Experimentally, the hydrogen bonds have been studied with vibrational spectroscopy in the infrared and near-infrared regions. The focus is primarily on spectra recorded in the near-infrared regions, which in these studies are dominated by O-H and N-H stretching overtones....... Overtone spectra have been recorded with intracavity laser photoacoustic laser spectroscopy and conventional long path absorption spectroscopy. Theoretically, a combination of electronic structure calculations and local mode models have been employed to guide the assignment of bands in the vibrational......,4-diaminobutane, no sign of intramolecular N-H···N hydrogen bonds were identified in the overtone spectra. However, theoretical analyzes indicate that intramolecular N-H···N hydrogen bonds are present in all three diamines if two hydrogen atoms on one of the methylene groups are substituted with triuoromethyl...

  12. On the nature of intramolecular vibrational energy transfer in dense molecular environments

    Energy Technology Data Exchange (ETDEWEB)

    Benten, Rebekka S. von [Institut fuer Physikalische Chemie der Universitaet Goettingen, Tammannstrasse 6, D-37077 Goettingen (Germany); Abel, Bernd, E-mail: Bernd.Abel@uni-lepzig.de [Wilhelm-Ostwald-Institut fuer Physikalische und Theoretische Chemie, Universitaet Leipzig, Linne-Strasse 2, D-04103 Leipzig (Germany)

    2010-12-09

    Graphical abstract: Mechanisms of IVR in multi-tiers of intramolecular energy levels in different molecular environments are investigated. - Abstract: Transient femtosecond-IR-pump-UV-absorption probe-spectroscopy has been employed to shed light on the nature of intramolecular vibrational energy transfer (IVR) in dense molecular environments ranging from the diluted gas phase to the liquid. A general feature in our experiments and those of others is that IVR proceeds via multiple timescales if overtones or combination vibrations of high frequency modes are excited. It has been found that collisions enhance IVR if its (slower) timescales can compete with collisions. This enhancement is, however, much more weaker and rather inefficient as opposed to the effect of collisions on intermolecular energy transfer which is well known. In a series of experiments we found that IVR depends not significantly on the average energy transferred in a collision but rather on the number of collisions. The collisions are much less efficient in affecting IVR than VET. We conclude that collision induced broadening of vibrational energy levels reduces the energy gaps and enhances existing couplings between tiers. The present results are an important step forward to rationalize and understand apparently different and not consistent results from different groups on different molecular systems between gas and liquid phases.

  13. Multiwall nanotubes with intramolecular junctions (CNx/C): Preparation, rectification, logic gates, and application

    Science.gov (United States)

    Hu, Ping'an; Xiao, Kai; Liu, Yunqi; Yu, Gui; Wang, Xianbao; Fu, Lei; Cui, Guanglei; Zhu, Daoben

    2004-06-01

    We prepared a large quantity of multiwall nanotubes with intramolecular junctions (CNx/C) by pyrolysis of iron phthalocyanine with or without an inlet of ammonia gas. The nanotubes consist of two sections, one section made of carbon nitride featuring bamboo-like structure and the other one made of carbon featuring empty hollow cylinder structure, and thus the intramolecular junctions were formed in the middle as a result of being doped or undoped with nitrogen. Nanodiode based on a single CNx/C junction shows reproducible rectifying behavior with a rectification ratio of 1.3×103 at ±2 V. In addition, the nanodiode demonstrated as a half-wave rectifier worked at an input sine wave of 1 kHz. Two CNx/C junctions were configured together to exhibit functions of OR and AND logic gates. Moreover, after substituting the wave-detection silicon diode in common transistor radio set with our nanodiode, the radio set still worked normally, representing an important step toward the potential application for nano-scale devices.

  14. Estimating the energy of intramolecular hydrogen bonds from1H NMR and QTAIM calculations.

    Science.gov (United States)

    Afonin, Andrei V; Vashchenko, Alexander V; Sigalov, Mark V

    2016-11-29

    The values of the downfield chemical shift of the bridge hydrogen atom were estimated for a series of compounds containing an intramolecular hydrogen bond O-HO, O-HN, O-HHal, N-HO, N-HN, C-HO, C-HN and C-HHal. Based on these values, the empirical estimation of the hydrogen bond energy was obtained by using known relationships. For the compounds containing an intramolecular hydrogen bond, the DFT B3LYP/6-311++G(d,p) method was used both for geometry optimization and for QTAIM calculations of the topological parameters (electron density ρ BCP and the density of potential energy V in the critical point of the hydrogen bond). The calculated geometric and topological parameters of hydrogen bonds were also used to evaluate the energy of the hydrogen bond based on the equations from the literature. Comparison of calibrating energies from the 1 H NMR data with the energies predicted by calculations showed that the most reliable are the linear dependence on the topological ρ BCP and V parameters. However, the correct prediction of the hydrogen bond energy is determined by proper fitting of the linear regression coefficients. To obtain them, new linear relationships were found between the calculated ρ BCP and V parameters and the hydrogen bond energies obtained from empirical 1 H NMR data. These relationships allow the comparison of the energies of different types of hydrogen bonds for various molecules and biological ensembles.

  15. Characteristics of Intramolecular Charge Transfer by J-Aggregates in Merocyanine Dye LB Films.

    Science.gov (United States)

    Yang, Chang Heon; Kwon, Young-Soo; Shin, Hoon-Kyu

    2016-06-01

    In this study, for the development of future molecular electronic devices, we have investigated the characteristics of the aggregates of Langmuir-Blodgett films. The characteristics of intramolecular charge transfer by J-aggregates in merocyanine dye LB films have been studied experimentally by using UV irradiation and heat treatment. In addition to intramolecular charge transfer, we also studied the conjugation and energy changes of the molecules. In case a dye is thinned by LB method, the alkyl chain is often displaced in order to form a mono-molecular film with ease. Since the molecular association form is often made by self-organization of molecules themselves, in case the dye and the alkyl chain are strongly bonded by the covalent bond, it may be said that the properties of the LB film to be built up are almost determined at the time of synthesis of film-forming molecules. Meanwhile, since, in case LB film is fabricated by the diffusion absorption method, the cohesive force between the water-soluble dye and the surface-active mono-molecular film is electrostatic, the dye molecule can move relatively freely on the air/water interface, which may be regarded as a two-dimensional crystal growth process.

  16. Intramolecular proton transfer and tunnelling reactions of hydroxyphenylbenzoxazole derivatives in Xenon at 15 K

    Energy Technology Data Exchange (ETDEWEB)

    Walla, Peter J. [Max-Planck-Institute for Biophysical Chemistry, Department 010, Spectroscopy and Photochemical Kinetics, Am Fassberg 11, D-37077 Goettingen (Germany) and Department for Biophysical Chemistry, Technical University of Brunswick, Institute for Physical and Theoretical Chemistry, Hans-Sommerstr. 10, D-38106 Braunschweig (Germany)]. E-mail: pwalla@gwdg.de; Nickel, Bernhard [Max-Planck-Institute for Biophysical Chemistry, Department 010, Spectroscopy and Photochemical Kinetics, Am Fassberg 11, D-37077 Goettingen (Germany)

    2005-06-06

    We investigated the site dependence and the tunnelling processes of the intramolecular proton and deuteron transfer in the triplet state of the compounds 2-(2'-hydroxy-4'-methylphenyl)benzoxazole (m-MeHBO) and 2-(2'-hydroxy-3'-methylphenyl)benzoxazoles (o-MeHBO) and their deuterio-oxy analogues in a solid xenon matrix. After singlet excitation there occurs an ultrafast intramolecular enol {yields} keto proton transfer and subsequent intersystem crossing mainly to the keto triplet state. In the triplet state of m-MeHBO, the proton transfer back to the lower enol triplet state is governed by tunnelling processes. In o-MeHBO, however, the enol triplet state is higher and therefore normally no tunnel reaction can be observed. Because of the external heavy atom-effect in a xenon matrix, we were able to investigate the reverse enol-keto-tunnelling after exciting directly the enol triplet state of deuterated o-MeHBO. The time constants of the reverse enol-keto tautomerization are similar to those of the normal keto-enol tautomerization. In a xenon matrix, the observed site-selective phosphorescence spectra are very well-resolved vibrationally. This allowed the study of the tunnel rates in different well-defined sites. The vibrational energies obtained in the spectra are in good agreement with vibrational energies found in resonant Raman and IR spectra of 2-(2'-hydroxyphenyl)benzoxazole (HBO)

  17. Hydroxyalkoxy radicals: importance of intramolecular hydrogen bonding on chain branching reactions in the combustion and atmospheric decomposition of hydrocarbons.

    Science.gov (United States)

    Davis, Alexander C; Francisco, Joseph S

    2014-11-20

    During both the atmospheric oxidation and combustion of volatile organic compounds, sequential addition of oxygen can lead to compounds that contain multiple hydrogen-bonding sites. The presence of two or more of these sites on a hydrocarbon introduces the possibility of intramolecular H-bonding, which can have a stabilizing effect on the reactants, products, and transition states of subsequent reactions. The present work compares the absolute energies of two sets of conformations, those that contain intramolecular H-bonds and those that lack intramolecular H-bonds, for each reactant, product, and transition state species in the 1,2 through 1,7 H-migrations and Cα-Cβ, Cα-H, and Cα-OH-bond scission reactions in the n-hydroxyeth-1-oxy through n-hydroxyhex-1-oxy radicals, for n ranging from 1 to 6. The difference in energy between the two conformations represents the balance between the stabilizing effects of H-bonds and the steric cost of bringing the two H-bonding sites together. The effect of intramolecular H-bonding and the OH group is assessed by comparing the net intramolecular H-bond stabilization energies, the reaction enthalpies, and barrier heights of the n-hydroxyalkoxy radical reactions with the corresponding alkoxy radicals values. The results suggest that there is a complex dependence on the location of the two H-bonding groups, the location of the abstraction or bond scission, and the shape of the transition state that dictates the extent to which intramolecular H-bonding effects the relative importance of H-migration and bond scission reactions for each n-hydroxyalkoxy radical. These findings have important implications for future studies on hydrocarbons with multiple H-bonding sites.

  18. Modeling and computations of the intramolecular electron transfer process in the two-heme protein cytochrome c4

    DEFF Research Database (Denmark)

    Natzmutdinov, Renat R.; Bronshtein, Michael D.; Zinkicheva, Tamara T.

    2012-01-01

    ligands in both low- and high-spin states by structure-optimized DFT. The computations enable estimating the intramolecular reorganization energy of the ET process for different combinations of low- and high-spin heme couples. Environmental reorganization free energies, work terms (‘‘gating’’) and driving...... performed computational modeling of the intramolecular ET process by a combination of density functional theory (DFT) and quantum mechanical charge transfer theory to disclose reasons for this difference. We first address the electronic structures of the model heme core with histidine and methionine axial...

  19. Enantiodivergent synthesis of either enantiomer of ABCDE-ring analogue of antitumor antibiotic fredericamycin A via intramolecular [4 + 2] cycloaddition approach.

    Science.gov (United States)

    Akai, S; Tsujino, T; Fukuda, N; Iio, K; Takeda, Y; Kawaguchi Ki, K; Naka, T; Higuchi, K; Kita, Y

    2001-12-13

    [reaction: see text] An intramolecular enantiodivergent synthesis of both enantiomers of the ABCDE-ring analogue 22 of fredericamycin A is reported. Key steps involve an intramolecular [4 + 2] cycloaddition of 17 and an aromatic Pummerer-type reaction of 19. A lipase-catalyzed enantioselective desymmetrization of prochiral diol 2 using 1-ethoxyvinyl 2-furoate 3 led to the pivotal intermediate (R)-4.

  20. Structural effects on the electronic characteristics of intramolecularly intercalated alkali-rubrene complexes

    Energy Technology Data Exchange (ETDEWEB)

    Li, Tsung-Lung, E-mail: quantum@mail.ncyu.edu.tw [Department of Electrophysics, National Chia-Yi University, 300 Hsueh-Fu Road, Chiayi, 60004, Taiwan, ROC (China); Lu, Wen-Cai, E-mail: wencailu@jlu.edu.cn [Laboratory of Fiber Materials and Modern Textile, Growing Base for State Key Laboratory, College of Physics, Qingdao University, Qingdao, Shandong 266071 (China); State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun, Jilin 130021 (China)

    2016-11-01

    The geometric and electronic structures of neutral monolithium- and monosodium-rubrene (Li{sub 1} Rub and Na{sub 1} Rub) isomers are investigated and compared with monopotassium-rubrene (K{sub 1} Rub). Based on the alkali binding site, all isomers of these alkali-rubrene complexes can be subdivided into two types: intramolecularly intercalated and extramolecularly adsorbed. The minimum-energy Li{sub 1} Rub and Na{sub 1} Rub are intercalated structures, whereas the minimum-energy K{sub 1} Rub is adsorbed. The fact that the intercalated Li{sub 1} Rub and Na{sub 1} Rub structures are energetically favorable over the adsorbed ones can be explained by two energy rules. First, “double” proximity of the intercalating alkali element to a pair of phenyl side groups enormously reduces the total energy. Second, accommodation of a minuscule intercalant does not significantly deform the carbon frame and, thus, increases the energy only by a small amount. Additionally, the peculiar effects of intramolecular intercalation on the electronic structures of molecules are also studied in this simulation of monoalkali intercalation. In the monoalkali-intercalated rubrene complex, only one of the two pairs of phenyl groups of rubrene is intercalated, intentionally leaving another pair pristine, which facilitates the comparison of electronic structures between the intercalated and pristine pairs of phenyl side groups in a single molecule. The uniformity of chemical environments of the phenyl groups of the intercalated Li{sub 1} Rub/Na{sub 1} Rub is deteriorated by the incorporation of the intercalant, and leads to their spectral characteristics in contrast to K{sub 1} Rub. In particular, the introduction of the intercalant promotes the carbon 2p orbitals of the intercalated phenyl pair to take part in the electronic structures of the HOMO and LUMO peaks of Li{sub 1} Rub/Na{sub 1} Rub. The unpaired electron in the HOMO is delocalized over the backbone with higher probability of

  1. Structural effects on the electronic characteristics of intramolecularly intercalated alkali-rubrene complexes

    International Nuclear Information System (INIS)

    Li, Tsung-Lung; Lu, Wen-Cai

    2016-01-01

    The geometric and electronic structures of neutral monolithium- and monosodium-rubrene (Li 1 Rub and Na 1 Rub) isomers are investigated and compared with monopotassium-rubrene (K 1 Rub). Based on the alkali binding site, all isomers of these alkali-rubrene complexes can be subdivided into two types: intramolecularly intercalated and extramolecularly adsorbed. The minimum-energy Li 1 Rub and Na 1 Rub are intercalated structures, whereas the minimum-energy K 1 Rub is adsorbed. The fact that the intercalated Li 1 Rub and Na 1 Rub structures are energetically favorable over the adsorbed ones can be explained by two energy rules. First, “double” proximity of the intercalating alkali element to a pair of phenyl side groups enormously reduces the total energy. Second, accommodation of a minuscule intercalant does not significantly deform the carbon frame and, thus, increases the energy only by a small amount. Additionally, the peculiar effects of intramolecular intercalation on the electronic structures of molecules are also studied in this simulation of monoalkali intercalation. In the monoalkali-intercalated rubrene complex, only one of the two pairs of phenyl groups of rubrene is intercalated, intentionally leaving another pair pristine, which facilitates the comparison of electronic structures between the intercalated and pristine pairs of phenyl side groups in a single molecule. The uniformity of chemical environments of the phenyl groups of the intercalated Li 1 Rub/Na 1 Rub is deteriorated by the incorporation of the intercalant, and leads to their spectral characteristics in contrast to K 1 Rub. In particular, the introduction of the intercalant promotes the carbon 2p orbitals of the intercalated phenyl pair to take part in the electronic structures of the HOMO and LUMO peaks of Li 1 Rub/Na 1 Rub. The unpaired electron in the HOMO is delocalized over the backbone with higher probability of distributing over the central two fused rings than over the outer two

  2. Intramolecular Valence and Spin Interaction in meso and rac Diastereomers of a p-Quinonoid-Bridged Diruthenium Complex

    Czech Academy of Sciences Publication Activity Database

    Kumbhakar, D.; Sarkar, B.; Maji, S.; Mobin, S. M.; Fiedler, Jan; Urbanos, F. A.; Jimenez-Aparicio, R.; Kaim, W.; Lahiri, G. K.

    2008-01-01

    Roč. 130, č. 51 (2008), s. 17575-17583 ISSN 0002-7863 R&D Projects: GA MŠk OC 139; GA MŠk LC510 Institutional research plan: CEZ:AV0Z40400503 Keywords : intramolecular valence * spin interaction * diruthenium complex Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 8.091, year: 2008

  3. On Hydrogen Bonding in the Intramolecularly Chelated Taitomers of Enolic Malondialdehyde and its Mono- and Dithio-Analogues

    DEFF Research Database (Denmark)

    Carlsen, Lars; Duus, Fritz

    1980-01-01

    The intramolecular hydrogen bondings in enolic malondialdehyde and it mono- and dithio-analogues have been evaluated by a semiempricial SCF–MO–CNDO method. The calculations predict that the hydrogen bonds play an important part in the stabilities of malondialdehyde and monothiomalondialdehyde...

  4. Modeling and computations of the intramolecular electron transfer process in the two-heme protein cytochrome c4

    DEFF Research Database (Denmark)

    Natzmutdinov, Renat R.; Bronshtein, Michael D.; Zinkicheva, Tamara T.

    2012-01-01

    The di-heme protein Pseudomonas stutzeri cytochrome c4 (cyt c4) has emerged as a useful model for studying long-range protein electron transfer (ET). Recent experimental observations have shown a dramatically different pattern of intramolecular ET between the two heme groups in different local...

  5. Enantioselective synthesis of benzofurans and benzoxazines via an olefin cross-metathesis-intramolecular oxo-Michael reaction.

    Science.gov (United States)

    Zhang, Jun-Wei; Cai, Quan; Gu, Qing; Shi, Xiao-Xin; You, Shu-Li

    2013-09-11

    Chiral phosphoric acid and Hoveyda-Grubbs II were found to catalyze an olefin cross-metathesis-intramolecular oxo-Michael cascade reaction of the ortho-allylphenols and enones to provide a variety of benzofuran and benzoxazine derivatives in moderate to good yields and enantioselectivity.

  6. The effect of driving force on intramolecular electron transfer in proteins. Studies on single-site mutated azurins

    DEFF Research Database (Denmark)

    Farver, O; Skov, L K; van de Kamp, M

    1992-01-01

    An intramolecular electron-transfer process has previously been shown to take place between the Cys3--Cys26 radical-ion (RSSR-) produced pulse radiolytically and the Cu(II) ion in the blue single-copper protein, azurin [Farver, O. & Pecht, I. (1989) Proc. Natl Acad. Sci. USA 86, 6868-6972]. To fu...

  7. Asymmetric Synthesis of (-)-Incarvillateine Employing an Intramolecular Alkylation via Rh-Catalyzed Olefinic C-H Bond Activation

    Energy Technology Data Exchange (ETDEWEB)

    Tsai, Andy; Bergman, Robert; Ellman, Jonathan

    2008-02-18

    An asymmetric total synthesis of (-)-incarvillateine, a natural product having potent analgesic properties, has been achieved in 11 steps and 15.4% overall yield. The key step is a rhodium-catalyzed intramolecular alkylation of an olefinic C-H bond to set two stereocenters. Additionally, this transformation produces an exocyclic, tetrasubstituted alkene through which the bicyclic piperidine moiety can readily be accessed.

  8. Environment-sensitive quinolone demonstrating long-lived fluorescence and unusually slow excited-state intramolecular proton transfer kinetics

    Czech Academy of Sciences Publication Activity Database

    Zamotaiev, O. M.; Shvadchak, Volodymyr; Sych, T. P.; Melnychuk, N. A.; Yushchenko, Dmytro A.; Mely, Y.; Pivovarenko, V. G.

    2016-01-01

    Roč. 4, č. 3 (2016), č. článku 034004. ISSN 2050-6120 Institutional support: RVO:61388963 Keywords : quinolone * fluorescent probes * local polarity * hydration * excited-state intramolecular proton transfer * kinetics Subject RIV: CC - Organic Chemistry Impact factor: 2.656, year: 2016

  9. Bifunctional ferrocene-based squaramide-phosphine as an organocatalyst for highly enantioselective intramolecular Morita-Baylis-Hillman reaction.

    Science.gov (United States)

    Zhang, Xiaorui; Ma, Pengfei; Zhang, Dongxu; Lei, Yang; Zhang, Shengyong; Jiang, Ru; Chen, Weiping

    2014-04-21

    This work demonstrates that, in accord with metal catalysis, ferrocene could be an excellent scaffold for organocatalysts. The simple and easily accessible bifunctional ferrocene-based squaramide-phosphine shows high enantioselectivity in the intramolecular Morita-Baylis-Hillman reaction of 7-aryl-7-oxo-5-heptenals, giving a variety of 2-aroyl-2-cyclohexenols in up to 96% ee.

  10. Intramolecular TAT triplex in (dA).sub.58. (dT).sub.58. Influence of ions

    Czech Academy of Sciences Publication Activity Database

    Pečinka, Petr; Huertas, D.; Azorín, F.; Paleček, Emil

    1995-01-01

    Roč. 13, č. 1 (1995), s. 029-046 ISSN 0739-1102 R&D Projects: GA AV ČR IAA504402; GA ČR GA204/93/2336 Keywords : intramolecular triplex * H-DNA * chemical probing * osmium tetroxide complex * DEPC Impact factor: 1.528, year: 1995

  11. Deuterium isotope effect on the intramolecular electron transfer in Pseudomonas aeruginosa azurin

    DEFF Research Database (Denmark)

    Farver, O.; Zhang, Jingdong; Chi, Qijin

    2001-01-01

    -0' is also different, yielding entropy changes of -57 J K-1 mol-l in water and -84 J K-1 mol(-1) in deuterium oxide. The driving force difference of 10 mV is in keeping with the kinetic isotope effect, but the contribution to DeltaS(double dagger) from the temperature dependence of E-0' is positive......Intramolecular electron transfer in azurin in water and deuterium oxide has been studied over a broad temperature range. The kinetic deuterium isotope effect, k(H)/k(D), is smaller than unity (0.7 at 298 K), primarily caused by the different activation entropies in water (-56.5 J K-1 mol(-1...... entropy difference and to compensate for the different temperature dependencies of E-0'. Thus, differences in driving force and thermal expansion appear as the most straightforward rationale for the observed isotope effect....

  12. Cp*Rh(III)/Bicyclic Olefin Cocatalyzed C-H Bond Amidation by Intramolecular Amide Transfer.

    Science.gov (United States)

    Wang, Xiaoming; Gensch, Tobias; Lerchen, Andreas; Daniliuc, Constantin G; Glorius, Frank

    2017-05-10

    A bicyclic olefin was discovered as a cocatalyst in a Cp*Rh(III)-catalyzed C-H bond amidation proceeding by an intramolecular amide transfer in N-phenoxyacetamide derivatives. Combining experimental and theoretical studies, we propose that the olefin promotes a Rh(III) intermediate to undergo oxidative addition into the O-N bond to form a Rh(V) nitrenoid species and subsequently direct the nitrenoid to add to the ortho position. The amide directing group plays a dual role as a cleavable coordinating moiety as well as an essential coupling partner for the C-H amidation. This methodology was successfully applied to the late-stage diversification of natural products and a marketed drug under mild conditions.

  13. GTP binding to the ROC domain of DAP-kinase regulates its function through intramolecular signalling

    Science.gov (United States)

    Carlessi, Rodrigo; Levin-Salomon, Vered; Ciprut, Sara; Bialik, Shani; Berissi, Hanna; Albeck, Shira; Peleg, Yoav; Kimchi, Adi

    2011-01-01

    Death-associated protein kinase (DAPk) was recently suggested by sequence homology to be a member of the ROCO family of proteins. Here, we show that DAPk has a functional ROC (Ras of complex proteins) domain that mediates homo-oligomerization and GTP binding through a defined P-loop motif. Upon binding to GTP, the ROC domain negatively regulates the catalytic activity of DAPk and its cellular effects. Mechanistically, GTP binding enhances an inhibitory autophosphorylation at a distal site that suppresses kinase activity. This study presents a new mechanism of intramolecular signal transduction, by which GTP binding operates in cis to affect the catalytic activity of a distal domain in the protein. PMID:21738225

  14. Di- and sesquiterpenoids from Cystoseira genus: structure, intra-molecular transformations and biological activity.

    Science.gov (United States)

    Gouveia, Vera; Seca, Ana M L; Barreto, M Carmo; Pinto, Diana C G A

    2013-06-01

    Natural products have been the single most productive source of leads for the development of drugs, because of the great variety of their chemical structures. Previous chemical investigation of members of the genus Cystoseira resulted in the discovery of various bioactive secondary metabolites. The secondary metabolites isolated and characterized are very interesting, both from the biological activity and structural complexity points of view, which make this genus an attractive target for further investigations. The present review covers the research progress on natural products isolated from this genus since January 1995 until now, concerning the isolation and structural elucidation of the secondary metabolites from Cystoseira species. In this contribution significant biological properties are briefly discussed. Simultaneously, we gradually construct an intra-molecular pathway that logically interrelates the isolated compounds.

  15. Electron capture dissociation proceeds with a low degree of intramolecular migration of peptide amide hydrogens

    DEFF Research Database (Denmark)

    Rand, Kasper D; Adams, Christopher M; Zubarev, Roman A

    2008-01-01

    ECD using peptides with a unique selective deuterium incorporation. Our results show that only limited amide hydrogen migration occurs upon ECD, provided that vibrational excitation prior to the electron capture event is minimized. Peptide ions that are excessively vibrationally excited......Hydrogen (1H/2H) exchange combined with mass spectrometry (HX-MS) has become a recognized method for the analysis of protein structural dynamics. Presently, the incorporated deuterons are typically localized by enzymatic cleavage of the labeled proteins and single residue resolution is normally...... only obtained for a few residues. Determination of site-specific deuterium levels by gas-phase fragmentation in tandem mass spectrometers would greatly increase the applicability of the HX-MS method. The biggest obstacle in achieving this goal is the intramolecular hydrogen migration (i.e., hydrogen...

  16. Photophysical Model of 10-Hydroxybenzo[h]quinoline: Internal Conversion and Excited State Intramolecular Proton Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Junghwa; Joo, Taiha [Pohang Univ. of Science and Technology, Pohang (Korea, Republic of)

    2014-03-15

    Photophysics of 10-hydroxybenzo[h]quinoline (HBQ) has been in controversy, in particular, on the nature of the electronic states before and after the excited state intramolecular proton transfer (ESIPT), even though the dynamics and mechanism of the ESIPT have been well established. We report highly time resolved fluorescence spectra over the full emission frequency regions of the enol and keto isomers and the anisotropy in time domain to determine the accurate rates of the population decay, spectral relaxation and anisotropy decay of the keto isomer. We have shown that the ∼300 fs component observed frequently in ESIPT dynamics arises from the S{sub 2}→S{sub 1} internal conversion in the reaction product keto isomer and that the ESIPT occurs from the enol isomer in S{sub 1} state to the keto isomer in S{sub 2} state.

  17. Intramolecular synergistic effect of glutamic acid, cysteine and glycine against copper corrosion in hydrochloric acid solution

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Daquan, E-mail: zhdq@sh163.net [Department of Environmental Engineering, Shanghai University of Electric Power, Shanghai 200090 (China); Xie Bin; Gao Lixin; Cai Qirui [Department of Environmental Engineering, Shanghai University of Electric Power, Shanghai 200090 (China); Joo, Hyung Goun; Lee, Kang Yong [Stress Analysis and Failure Design Laboratory, School of Mechanical Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of)

    2011-10-31

    The corrosion protection of copper by glutamic acid, cysteine, glycine and their derivative (glutathione) in 0.5 M hydrochloric acid solution has been studied by the electrochemical impedance spectroscopy and cyclic voltammetry. The inhibition efficiency of the organic inhibitors on copper corrosion increases in the order: glutathione > cysteine > cysteine + glutamic acid + glycine > glutamic acid > glycine. Maximum inhibition efficiency for cysteine reaches about 92.9% at 15 mM concentration level. The glutathione can give 96.4% inhibition efficiency at a concentration of 10 mM. The molecular structure parameters were obtained by PM3 (Parametric Method 3) semi-empirical calculation. The intramolecular synergistic effect of glutamic acid, cysteine and glycine moieties in glutathione is attributed to the lower energy of the lowest unoccupied molecular orbital (E{sub LUMO}) level and to the excess hetero-atom adsorption centers and the bigger coverage on the copper surface.

  18. Intramolecular migration of amide hydrogens in protonated peptides upon collisional activation

    DEFF Research Database (Denmark)

    Jørgensen, Thomas J D; Gårdsvoll, Henrik; Ploug, Michael

    2005-01-01

    if collision-induced dissociation (CID) should provide reliable site-specific information from (1)H/(2)H exchange experiments. We have explored a series of unique, regioselectively deuterium-labeled peptides as model systems to probe for intramolecular amide hydrogen migration under low-energy collisional...... are protected against exchange with the solvent, while the amide hydrogens of the nonbinding sequences exchange rapidly with the solvent. We have utilized such long-lived complexes to generate peptides labeled with deuterium in either the binding or nonbinding region, and the expected regioselectivity...... of this labeling was confirmed after pepsin proteolysis. CID of such deuterated peptides, [M + 2H](2+), yielded fragment ions (b- and y-ions) having a deuterium content that resemble the theoretical values calculated for 100% scrambling. Thus, complete randomization of all hydrogen atoms attached to nitrogen...

  19. Unusual NHC-Iridium(I) Complexes and Their Use in the Intramolecular Hydroamination of Unactivated Aminoalkenes

    KAUST Repository

    Sipos, Gellért

    2016-04-10

    N-heterocyclic carbene (NHC) ligands with naphthyl side chains were employed for the synthesis of unsaturated, yet isolable [(NHC)Ir(cod)]+ (cod=1,5-cyclooctadiene) complexes. These compounds are stabilised by an interaction of the aromatic wingtip that leads to a sideways tilt of the NHC-Ir bond. Detailed studies show how the tilting of such N-heterocyclic carbenes affects the electronic shielding properties of the carbene carbon atom and how this is reflected by significant upfield shifts in the 13CNMR signals. When employed in the intramolecular hydroamination, these [(NHC)Ir(cod)]+ species show very high catalytic activity under mild reaction conditions. An enantiopure version of the catalyst system produces pyrrolidines with excellent enantioselectivities. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Controlling Long-Lived Triplet Generation from Intramolecular Singlet Fission in the Solid State

    KAUST Repository

    Pace, Natalie A.

    2017-11-30

    The conjugated polymer poly(benzothiophene dioxide) (PBTDO1) has recently been shown to exhibit efficient intramolecular singlet fission in solution. In this paper, we investigate the role of intermolecular interactions in triplet separation dynamics after singlet fission. We use transient absorption spectroscopy to determine the singlet fission rate and triplet yield in two polymers differing only by side chain motif in both solution and the solid state. Whereas solid-state films show singlet fission rates identical to those measured in solution, the average lifetime of the triplet population increases dramatically, and is strongly dependent on side-chain identity. These results show that it may be necessary to carefully engineer the solid-state microstructure of these “singlet fission polymers” in order to produce the long-lived triplets needed to realize efficient photovoltaic devices.

  1. Intramolecular stabilization of a catalytic [FeFe]-hydrogenase mimic investigated by experiment and theory.

    Science.gov (United States)

    Pandey, Indresh Kumar; Natarajan, Mookan; Faujdar, Hemlata; Hussain, Firasat; Stein, Matthias; Kaur-Ghumaan, Sandeep

    2018-04-03

    The mono-substituted complex [Fe2(CO)5(μ-naphthalene-2-thiolate)2(P(PhOMe-p)3)] was prepared taking after the structural principles from both [NiFe] and [FeFe]-hydrogenase enzymes. Crystal structures are reported for this complex and the all carbonyl analogue. The bridging naphthalene thiolates resemble μ-bridging cysteine amino acids. One of the naphthyl moieties forms π-π stacking interactions with the terminal bulky phosphine ligand in the crystal structure and in calculations. This interaction stabilizes the reduced and protonated forms during electrocatalytic proton reduction in the presence of acetic acid and hinders the rotation of the phosphine ligand. The intramolecular π-π stabilization, the electrochemistry and the mechanism of the hydrogen evolution reaction were investigated using computational approaches.

  2. Voltage Losses in Organic Solar Cells: Understanding the Contributions of Intramolecular Vibrations to Nonradiative Recombinations

    KAUST Repository

    Chen, Xiankai

    2017-12-18

    The large voltage losses usually encountered in organic solar cells significantly limit the power conversion efficiencies (PCEs) of these devices, with the result that the current highest PCE values in single-junction organic photovoltaic remain smaller than for other solar cell technologies, such as crystalline silicon or perovskite solar cells. In particular, the nonradiative recombinations to the electronic ground state from the lowest-energy charge-transfer (CT) states at the donor-acceptor interfaces in the active layer of organic devices, are responsible for a significant part of the voltage losses. Here, to better comprehend the nonradiative voltage loss mechanisms, a fully quantum-mechanical rate formula is employed within the framework of time-dependent perturbation theory, combined with density functional theory. The objective is to uncover the specific contributions of intramolecular vibrations to the CT-state nonradiative recombinations in several model systems, which include small-molecule and polymer donors as well as fullerene and nonfullerene acceptors.

  3. Intramolecular synergistic effect of glutamic acid, cysteine and glycine against copper corrosion in hydrochloric acid solution

    International Nuclear Information System (INIS)

    Zhang Daquan; Xie Bin; Gao Lixin; Cai Qirui; Joo, Hyung Goun; Lee, Kang Yong

    2011-01-01

    The corrosion protection of copper by glutamic acid, cysteine, glycine and their derivative (glutathione) in 0.5 M hydrochloric acid solution has been studied by the electrochemical impedance spectroscopy and cyclic voltammetry. The inhibition efficiency of the organic inhibitors on copper corrosion increases in the order: glutathione > cysteine > cysteine + glutamic acid + glycine > glutamic acid > glycine. Maximum inhibition efficiency for cysteine reaches about 92.9% at 15 mM concentration level. The glutathione can give 96.4% inhibition efficiency at a concentration of 10 mM. The molecular structure parameters were obtained by PM3 (Parametric Method 3) semi-empirical calculation. The intramolecular synergistic effect of glutamic acid, cysteine and glycine moieties in glutathione is attributed to the lower energy of the lowest unoccupied molecular orbital (E LUMO ) level and to the excess hetero-atom adsorption centers and the bigger coverage on the copper surface.

  4. Comparative analysis of intramolecular parameters of nitrocompounds: crystalline and gas phases

    Science.gov (United States)

    Arnautova, Elena A.; Pivina, Tatyana S.; Gladkikh, Olga P.; Vilkov, Lev V.

    1996-01-01

    The results of a study of intramolecular parameters for chemical classes of nitrocompounds in different states of aggregation are collected and analyzed: electron-diffraction experiments and microwave spectroscopy for the gas phase, and X-ray diffraction (from the Cambridge Bank of X-ray and neutron-diffraction data) for molecules in crystals. Systematic analysis of molecular structural parameters for valence bonds and angles of the nitrogroups in these compounds shows these properties to be conserved. This allows us to use the calculated geometrical molecular parameters of nitrocompounds (obtained theoretically by quantum-chemical schemes) when building models of base (rigid) molecules for constructing elementary cells within different structural classes, with the aim of a subsequent computer search for dense packing in the corresponding molecular crystals.

  5. TiO2/cyclized polyacrylonitrile hybridized nanocomposite: An efficient visible-light photocatalyst prepared by a facile “in situ” approach

    International Nuclear Information System (INIS)

    Luo, Qingzhi; Wang, Xiaojing; Wang, Desong; An, Jing; Li, Xueyan; Yin, Rong

    2015-01-01

    Highlights: • TiO 2 sol–gel was prepared in the presence of polyacrylonitrile. • Crystallization of TiO 2 and cyclization of PAN was simultaneously conducted. • CPAN chains around TiO 2 nanocrystals play a good role in partition to TiO 2 particles. • As-prepared nanocomposites possess good photocatalytic activity and stability. - Abstract: TiO 2 /cyclized polyacrylonitrile (CPAN) hybridized nanocomposites (h-TCP) were obtained via an “in situ” method. TiO 2 sol–gel was prepared initially in the presence of polyacrylonitrile (PAN). Then the prepared TiO 2 /PAN gel was heat-treated for simultaneous crystallization of TiO 2 and cyclization of PAN to obtain h-TCP nanocomposites. The as-prepared nanocomposites were characterized and compared with TiO 2 nanoparticles surface-modified by CPAN (sm-TCP) and neat TiO 2 . Results show that CPAN molecular chains existing around TiO 2 nanocrystals play a good role in partition to TiO 2 nanocrystals, which decreases the mean size of TiO 2 crystals in h-TCP, alleviates the aggregation of h-TCP nanocomposites, and increases their specific surface areas. The electron–hole pair separation efficiency and interface charge transfer efficiency are also improved compared with neat TiO 2 and sm-TCP. The h-TCP nanocomposites possess excellent visible-light photocatalytic activity and stability for photodegradation of methyl orange and phenol. The visible-light photocatalytic mechanism of h-TCP has been discussed

  6. TiO{sub 2}/cyclized polyacrylonitrile hybridized nanocomposite: An efficient visible-light photocatalyst prepared by a facile “in situ” approach

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Qingzhi; Wang, Xiaojing; Wang, Desong, E-mail: dswang06@126.com; An, Jing; Li, Xueyan; Yin, Rong

    2015-09-15

    Highlights: • TiO{sub 2} sol–gel was prepared in the presence of polyacrylonitrile. • Crystallization of TiO{sub 2} and cyclization of PAN was simultaneously conducted. • CPAN chains around TiO{sub 2} nanocrystals play a good role in partition to TiO{sub 2} particles. • As-prepared nanocomposites possess good photocatalytic activity and stability. - Abstract: TiO{sub 2}/cyclized polyacrylonitrile (CPAN) hybridized nanocomposites (h-TCP) were obtained via an “in situ” method. TiO{sub 2} sol–gel was prepared initially in the presence of polyacrylonitrile (PAN). Then the prepared TiO{sub 2}/PAN gel was heat-treated for simultaneous crystallization of TiO{sub 2} and cyclization of PAN to obtain h-TCP nanocomposites. The as-prepared nanocomposites were characterized and compared with TiO{sub 2} nanoparticles surface-modified by CPAN (sm-TCP) and neat TiO{sub 2}. Results show that CPAN molecular chains existing around TiO{sub 2} nanocrystals play a good role in partition to TiO{sub 2} nanocrystals, which decreases the mean size of TiO{sub 2} crystals in h-TCP, alleviates the aggregation of h-TCP nanocomposites, and increases their specific surface areas. The electron–hole pair separation efficiency and interface charge transfer efficiency are also improved compared with neat TiO{sub 2} and sm-TCP. The h-TCP nanocomposites possess excellent visible-light photocatalytic activity and stability for photodegradation of methyl orange and phenol. The visible-light photocatalytic mechanism of h-TCP has been discussed.

  7. Mechanisms of intramolecular communication in a hyperthermophilic acylaminoacyl peptidase: a molecular dynamics investigation.

    Science.gov (United States)

    Papaleo, Elena; Renzetti, Giulia; Tiberti, Matteo

    2012-01-01

    Protein dynamics and the underlying networks of intramolecular interactions and communicating residues within the three-dimensional (3D) structure are known to influence protein function and stability, as well as to modulate conformational changes and allostery. Acylaminoacyl peptidase (AAP) subfamily of enzymes belongs to a unique class of serine proteases, the prolyl oligopeptidase (POP) family, which has not been thoroughly investigated yet. POPs have a characteristic multidomain three-dimensional architecture with the active site at the interface of the C-terminal catalytic domain and a β-propeller domain, whose N-terminal region acts as a bridge to the hydrolase domain. In the present contribution, protein dynamics signatures of a hyperthermophilic acylaminoacyl peptidase (AAP) of the prolyl oligopeptidase (POP) family, as well as of a deletion variant and alanine mutants (I12A, V13A, V16A, L19A, I20A) are reported. In particular, we aimed at identifying crucial residues for long range communications to the catalytic site or promoting the conformational changes to switch from closed to open ApAAP conformations. Our investigation shows that the N-terminal α1-helix mediates structural intramolecular communication to the catalytic site, concurring to the maintenance of a proper functional architecture of the catalytic triad. Main determinants of the effects induced by α1-helix are a subset of hydrophobic residues (V16, L19 and I20). Moreover, a subset of residues characterized by relevant interaction networks or coupled motions have been identified, which are likely to modulate the conformational properties at the interdomain interface.

  8. Tether-directed synthesis of highly substituted oxasilacycles via an intramolecular allylation employing allylsilanes

    Directory of Open Access Journals (Sweden)

    Cox Liam R

    2007-02-01

    Full Text Available Abstract Background Using a silyl tether to unite an aldehyde electrophile and allylsilane nucleophile into a single molecule allows a subsequent Lewis-acid-mediated allylation to proceed in an intramolecular sense and therefore receive all the benefits associated with such processes. However, with the ability to cleave the tether post allylation, a product that is the result of a net intermolecular reaction can be obtained. In the present study, four diastereoisomeric β-silyloxy-α-methyl aldehydes, which contain an allylsilane tethered through the β-carbinol centre, have been prepared, in order to probe how the relative configuration of the two stereogenic centres affects the efficiency and selectivity of the intramolecular allylation. Results Syn-aldehydes, syn-4a and syn-4b, both react poorly, affording all four possible diastereoisomeric oxasilacycle products. In contrast, the anti aldehydes anti-4a and anti-4b react analogously to substrates that lack substitution at the α-site, affording only two of the four possible allylation products. Conclusion The outcome of the reaction with anti-aldehydes is in accord with reaction proceeding through a chair-like transition state (T.S.. In these systems, the sense of 1,3-stereoinduction can be rationalised by the aldehyde electrophile adopting a pseudoaxial orientation, which will minimise dipole-dipole interactions in the T.S. The 1,4-stereoinduction in these substrates is modest and seems to be modulated by the R substituent in the starting material. In the case of the syn-substrates, cyclisation through a chair T.S. is unlikely as this would require the methyl substituent α to the reacting carbonyl group to adopt an unfavourable pseudoaxial position. It is therefore proposed that these substrates react through poorly-defined T.S.s and consequently exhibit essentially no stereoselectivity.

  9. Reaction Coordinate, Free Energy, and Rate of Intramolecular Proton Transfer in Human Carbonic Anhydrase II.

    Science.gov (United States)

    Paul, Sanjib; Paul, Tanmoy Kumar; Taraphder, Srabani

    2018-03-22

    The role of structure and dynamics of an enzyme has been investigated at three different stages of its function including the chemical event it catalyzes. A one-pot computational method has been designed for each of these stages on the basis of classical and/or quantum mechanical-molecular mechanical molecular dynamics and transition path sampling simulations. For a pair of initial and final states A and B separated by a high free-energy barrier, using a two-stage selection process, several collective variables (CVs) are identified that can delineate A and B. However, these CVs are found to exhibit strong cross-coupling over the transition paths. A set of mutually orthogonal order parameters is then derived from these CVs and an optimal reaction coordinate, r, determined applying half-trajectory likelihood maximization along with a Bayesian information criterion. The transition paths are also used to project the multidimensional free energy surface and barrier crossing dynamics along r. The proposed scheme has been applied to the rate-determining intramolecular proton transfer reaction of the well-known enzyme human carbonic anhydrase II. The potential of mean force, F( r), in the absence of the chemical step is found to reproduce earlier results on the equilibrium population of two side-chain orientations of key residue His-64. Estimation of rate constants, k, from mean first passage times for the three different stages of catalysis shows that the rate-determining step of intramolecular proton transfer occurs with k ≃ 1.0 × 10 6 s -1 , in close agreement with known experimental results.

  10. Structural and biochemical characterizations of an intramolecular tandem coiled coil protein.

    Science.gov (United States)

    Shin, Donghyuk; Kim, Gwanho; Kim, Gyuhee; Zheng, Xu; Kim, Yang-Gyun; Lee, Sangho

    2014-12-12

    Coiled coil has served as an excellent model system for studying protein folding and developing protein-based biomaterials. Most designed coiled coils function as oligomers, namely intermolecular coiled coils. However, less is known about structural and biochemical behavior of intramolecular coiled coils where coiled coil domains are covalently linked in one polypeptide. Here we prepare a protein which harbors three coiled coil domains with two short linkers, termed intramolecular tandem coiled coil (ITCC) and characterize its structural and biochemical behavior in solution. ITCC consists of three coiled coil domains whose sequences are derived from Coil-Ser and its domain swapped dimer. Modifications include positioning E (Glu) residue at "e" and K (Lys) at "g" positions throughout heptad repeats to enhance ionic interaction among its constituent coiled coil domains. Molecular modeling of ITCC suggests a compact triple helical bundle structure with the second and the third coiled coil domains forming a canonical coiled coil. ITCC exists as a mixture of monomeric and dimeric species in solution. Small-angle X-ray scattering reveals ellipsoidal molecular envelopes for both dimeric and monomeric ITCC in solution. The theoretically modeled structures of ITCC dock well into the envelopes of both species. Higher ionic strength shifts the equilibrium into monomer with apparently more compact structure while secondary structure remains unchanged. Taken together, our results suggest that our designed ITCC is predominantly monomeric structure through the enhanced ionic interactions, and its conformation is affected by the concentration of ionic species in the buffer. Copyright © 2014 Elsevier Inc. All rights reserved.

  11. Stereospecific Syntheses of Enaminonitriles and β-Enaminoesters via Domino Ring-Opening Cyclization (DROC) of Activated Cyclopropanes with Pronucleophilic Malononitriles.

    Science.gov (United States)

    Saha, Amrita; Bhattacharyya, Aditya; Talukdar, Ranadeep; Ghorai, Manas K

    2018-02-16

    Two novel synthetic protocols for the syntheses of highly functionalized five-membered carbocyclic enaminonitriles and β-enaminoesters have been developed via domino ring-opening cyclization (DROC) and DROC/decarboxylative tautomerization of activated cyclopropanes with malononitrile pronucleophiles, respectively. Both of the efficient strategies (yield up to 93%) have been generalized with various donor-acceptor and acceptor cyclopropanes as well as with malononitrile derivatives. The stereospecific variants of the two S N 2-type DROC strategies have also been developed by employing enantiopure donor-acceptor (DA) cyclopropanes to synthesize the corresponding nonracemic products with excellent stereoselectivities (dr up to >99:1, ee up to >99%).

  12. Synthesis of 3-substituted 4-piperidinones via a one-pot tandem oxidation-cyclization-oxidation process: stereodivergent reduction to 3,4-disubstituted piperidines.

    Science.gov (United States)

    Bahia, Perdip S; Snaith, John S

    2004-04-30

    A novel approach to 3-substituted 4-piperidinones is described. The one-pot tandem oxidation-cyclization-oxidation of unsaturated alcohols 1a-e by PCC or PCC and trifluoromethanesulfonic acid affords piperidinones 2a-e in good yield. Reduction of 2a-e by L-Selectride gives the corresponding cis 3,4-disubstituted piperidines with diastereomeric ratios of >99:1. By contrast, reduction of 2a-e by Al-isopropoxydiisobutylalane gives the trans products with diastereomeric ratios of up to 99:1.

  13. Alternative Sm(II) Species-Mediated Cascade Coupling/Cyclization for the Synthesis of Oxobicyclo[3.1.0]hexane-1-ols.

    Science.gov (United States)

    You, Bingxin; Shen, Mengmeng; Xie, Guanqun; Mao, Hui; Lv, Xin; Wang, Xiaoxia

    2018-02-02

    The allylSmBr/HMPA/MsOH system has been found to be an efficient reagent for the "ester-alkene" coupling/cyclization cascade of readily available α-allyloxy esters. Oxobicyclo[3.1.0]hexane-1-ols were thus prepared in good to excellent yields and diastereoselectivities. Investigation on the mechanism suggested the possible existence of a new Sm(II) species, namely, CH 3 SO 3 SmBr, which resulted from the reaction between allylSmBr and MsOH and may be the actual SET reagent.

  14. Asymmetric Ring Opening/Cyclization/Retro-Mannich Reaction of Cyclopropyl Ketones with Aryl 1,2-Diamines for the Synthesis of Benzimidazole Derivatives.

    Science.gov (United States)

    Xia, Yong; Lin, Lili; Chang, Fenzhen; Liao, Yuting; Liu, Xiaohua; Feng, Xiaoming

    2016-09-26

    A highly efficient asymmetric ring-opening/cyclization/retro-Mannich reaction of cyclopropyl ketones with aryl 1,2-diamines has been realized using a chiral N,N'-dioxide/Sc(III) catalyst. Benzimidazoles containing chiral side chains were generated under mild reaction conditions in excellent outcomes (up to 99 % yield and 97 % ee). This method also provides efficient access to chiral benzimidazole-substituted amide and cycloheptene derivatives. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Synthesis of Poly-Substituted Benzene from Morita-Baylis-Hillman Adducts Via [3 + 1 + 2] Annulation Strategy: Palladium-catalyzed Domino Cyclization (5-exo/3-exo), Ring-Expansion by Palladium Rearrangement, and Aromatization

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ko Hoon; Kim, Su Yeon; Moon, Hye Ran; Kim, Jae Nyoung [Chonnam National University, Gwangju (Korea, Republic of)

    2016-02-15

    We reported the synthesis of nicotinates by palladium-catalyzed consecutive 5-exo/3-exo cyclization, ring-expansion, and subsequent aromatization process. As a continuous work, we envisaged that the synthesis of poly-substituted benzene ring could be achieved by using sulfonylacetate as an one-carbon linker. Poly-substituted benzene derivatives have been synthesized from MBH adducts by sequential introductions of sulfonylacetate and 2-bromoallyl bromides to MBH adducts, and a one-pot palladium catalyzed domino cyclization (5-exo/3-exo), ring-expansion by palladium rearrangement, and aromatization process.

  16. Metastatic melanoma imaging with an {sup 111}In-labeled lactam bridge-cyclized {alpha}-melanocyte-stimulating hormone peptide

    Energy Technology Data Exchange (ETDEWEB)

    Guo Haixun; Shenoy, Nalini; Gershman, Benjamin M.; Yang, Jianquan [College of Pharmacy, University of New Mexico, Albuquerque, NM 87131 (United States); Sklar, Larry A. [College of Pharmacy, University of New Mexico, Albuquerque, NM 87131 (United States); Cancer Research and Treatment Center, University of New Mexico, Albuquerque, NM 87131 (United States); Department of Pathology, University of New Mexico, Albuquerque, NM 87131 (United States); Miao Yubin [College of Pharmacy, University of New Mexico, Albuquerque, NM 87131 (United States); Cancer Research and Treatment Center, University of New Mexico, Albuquerque, NM 87131 (United States); Department of Dermatology, University of New Mexico, Albuquerque, NM 87131 (United States)], E-mail: ymiao@salud.unm.edu

    2009-04-15

    Introduction: The purpose of this study was to examine whether a novel lactam bridge-cyclized {sup 111}In-labeled 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-Gly-Glu-c[Lys-Nle-Glu-His-D-Phe-Arg-Trp-Gly-Arg-Pro-Val-Asp] {l_brace}DOTA-GlyGlu-CycMSH{r_brace} could be an effective imaging probe for metastatic melanoma detection. Methods: {sup 111}In-DOTA-GlyGlu-CycMSH was prepared and purified by reverse-phase high-performance liquid chromatography (RP-HPLC). The internalization and efflux of {sup 111}In-DOTA-GlyGlu-CycMSH were examined in B16/F10 melanoma cells. The biodistribution of {sup 111}In-DOTA-GlyGlu-CycMSH was determined in B16/F10 pulmonary metastatic melanoma-bearing and normal C57 mice. Pulmonary metastatic melanoma imaging was performed by small-animal single-photon emission computed tomography (SPECT)/CT (Nano-SPECT/CT) using {sup 111}In-DOTA-GlyGlu-CycMSH as an imaging probe and compared with 2-[{sup 18}F]fluoro-2-deoxy-D-glucose ([{sup 18}F]FDG) positron emission tomography (PET) imaging. Results: {sup 111}In-DOTA-GlyGlu-CycMSH was readily prepared with greater than 95% radiolabeling yield. {sup 111}In-DOTA-GlyGlu-CycMSH displayed rapid internalization and extended efflux in B16/F10 cells. {sup 111}In-DOTA-GlyGlu-CycMSH exhibited significantly (P<.05) higher uptakes (2.00{+-}0.74%ID/g at 2 h post-injection and 1.83{+-}0.12%ID/g at 4 h post-injection) in metastatic melanoma-bearing lung than that in normal lung (0.08{+-}0.08%ID/g and 0.05{+-}0.05%ID/g at 2 and 4 h post-injection, respectively). The activity accumulation in normal organs was low (<0.5%ID/g) except for the kidneys 2 and 4 h post-injection. B16/F10 pulmonary melanoma metastases were clearly visualized with {sup 111}In-DOTA-GlyGlu-CycMSH 2 h post-injection rather than with [{sup 18}F]FDG 1 h post-injection. Conclusions: {sup 111}In-DOTA-GlyGlu-CycMSH exhibited favorable metastatic melanoma-targeting and -imaging properties, highlighting its potential as an effective imaging

  17. Concise stereocontrolled formal synthesis of (+/-)-quinine and total synthesis of (+/-)-7- hydroxyquinine via merged Morita-Baylis-Hillman-Tsuji-Trost cyclization.

    Science.gov (United States)

    Webber, Peter; Krische, Michael J

    2008-12-05

    Concise stereoselective syntheses of (+/-)-quinine and (+/-)-7-hydroxyquinine are achieved using a catalytic enone cycloallylation that combines the nucleophilic features of the Morita-Baylis-Hillman reaction and the electrophilic features of the Tsuji-Trost reaction. Cyclization of enone-allyl carbonate 11 delivers the product of cycloallylation 13 in 68% yield. Diastereoselective conjugate reduction of the enone 13 (>20:1 dr) followed by exchange of the N-protecting group provides the saturated N-Boc-protected methyl ketone 19, which upon aldol dehydration provides quinoline containing enone 15, possessing all carbon atoms of quinine. Exposure of ketone 15 to L-selectride enables diastereoselective carbonyl reduction (>20:1 dr) to furnish the allylic alcohol 16. Stereoselective hydroxyl-directed epoxidation using an oxovanadium catalyst modified by N-hydroxy-N-Me-pivalamide delivers epoxide 17 (17:1 dr). Cyclization of the resulting amine-epoxide 17 provides (+/-)-7-hydroxyquinine in 13 steps and 11% overall yield from aminoacetaldehyde diethyl acetal. Notably, highly stereoselective formation of five contiguous stereocenters is achieved through a series of 1,2-asymmetric induction events. Deoxygenation of the N-Cbz-protected allylic acetate 22 provides olefin 23, which previously has been converted to quinine. Thus, (+/-)-quinine is accessible in 16 steps and 4% overall yield from commercial aminoacetaldehyde diethyl acetal.

  18. Concise Stereocontrolled Formal Synthesis of (±)-Quinine and Total Synthesis of (±)-7-Hydroxyquinine via Merged Morita-Baylis-Hillman-Tsuji-Trost Cyclization

    Science.gov (United States)

    Webber, Peter; Krische, Michael J.

    2010-01-01

    Concise stereoselective syntheses of (±)-quinine and (±)-7-hydroxyquinine are achieved using a catalytic enone cycloallylation that combines the nucleophilic features of the Morita-Baylis-Hillman reaction and the electrophilic features of the Tsuji-Trost reaction. Cyclization of enone-allyl carbonate 11 delivers the product of cycloallylation 13 in 68% yield. Diastereoselective conjugate reduction of the enone 13 (>20:1 dr) followed by exchange of N-protecting groups provides the saturated N-Boc-protected methyl ketone 19, which upon aldol dehydration provides quinoline containing enone 15, possessing all carbon atoms of quinine. Exposure of ketone 15 to L-selectride enables diastereoselective carbonyl reduction (>20:1 dr) to furnish the allylic alcohol 16. Stereoselective hydroxyl-directed epoxidation using an oxovanadium catalyst modified by N-hydroxy-N-Me-pivalamide delivers epoxide 17 (17:1 dr). Cyclization of the resulting amine-epoxide 17 provides (±)-7-hydroxyquinine in 13 steps and 11% overall yield from aminoacetaldehyde diethyl acetal. Notably, highly stereoselective formation of five contiguous stereocenters is achieved through a series of 1,2-asymmetric induction events. A formal synthesis of (±)-quinine is achieved upon deoxygenation of the N-Cbz-protected allylic acetate 22 to provide olefin 23, which previously has been converted to quinine. Thus, (±)-quinine is accessible in 16 steps and 4% overall yield from commercial aminoacetaldehyde diethyl acetal, making this route the most concise approach to quinine, to date. PMID:18989927

  19. Activation of electrophilicity of stable Y-delocalized carbamate cations in intramolecular aromatic substitution reaction: evidence for formation of diprotonated carbamates leading to generation of isocyanates.

    Science.gov (United States)

    Kurouchi, Hiroaki; Kawamoto, Kyoko; Sugimoto, Hiromichi; Nakamura, Satoshi; Otani, Yuko; Ohwada, Tomohiko

    2012-10-19

    Although cations with three heteroatoms, such as monoprotonated guanidine and urea, are stabilized by Y-shaped conjugation and such Y-conjugated cations are sufficiently basic to be further protonated (or protosolvated) to dications in strongly acid media, only O-monoprotonated species have been detected in the case of carbamates even in magic acid. We found that the trifluoromethanesulfonic acid-catalyzed cyclization of arylethylcarbamates proceeds to afford dihydroisoquinolones in high yield. In strong acids, methyl carbamates are fully O-monoprotonated, and these monocations do not undergo cyclization even under heating. But, as the acidity of the reaction medium is further increased, the cyclization reaction of methyl phenethylcarbamates starts to proceed as a first-order reaction, with a linear relationship between rate and acidity. The sign and magnitude of the entropy of activation ΔS(‡) were found to be similar to those of other A(Ac)1 reactions. These results strongly support the idea that further protonation of the O-protonated carbamates is involved in the cyclization, but the concentration of the dications is very low and suggests that the rate-determining step is dissociation of methanol from the diprotonated carbamate to generate protonated isocyanate, which reacts with the aromatic ring. Therefore, O-protonated carbamates are weak bases in sharp contrast to other Y-shaped monocations.

  20. Intra-molecular Charge Transfer and Electron Delocalization in Non-Fullerene Organic Solar Cells

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Qinghe; Zhao, Donglin; Goldey, Matthew B.; Filatov, Alexander S.; Sharapov, Valerii; Colon, Yamil; Cai, Zhengxu; Jiang, Xuanfeng; Wang, Junpeng; Chen, Wei; de Pablo, Juan; Galli, Giulia; Yu, Luping

    2018-03-28

    Two types of electron acceptors were synthesized by coupling two kinds of electron-rich cores with four equivalent perylene diimides (PDIs) at the a position. With fully aromatic cores, TPB and TPSe have pi-orbitals spread continuously over the whole aromatic conjugated backbone, unlike TPC and TPSi, which contain isolated PDI units due to the use of a tetrahedron carbon or silicon linker. Density functional theory calculations of the projected density of states showed that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for TPB are localized in separate regions of space. Further, the LUMO of TPB shows a greater contribution from the orbitals belonging to the connective core of the molecules than that of TPC. Overall, the properties of the HOMO and LUMO point at increased intra-molecular delocalization of negative charge carriers for TPB and TPSe than for TPC and TPSi and hence at a more facile intra-molecular charge transfer for the former. The film absorption and emission spectra showed evidences for the inter -molecular electron delocalization in TPB and TPSe, which is consistent with the network structure revealed by X-ray diffraction studies on single crystals of TPB. These features benefit the formation of charge transfer states and/or facilitate charge transport. Thus, higher electron mobility and higher charge dissociation probabilities under J(sc) condition were observed in blend films of TPB:PTB7-Th and TPSe:PTB7-Th than those in TPC:PTB7Th and TPSi:PTB7-Th blend films. As a result, the J(sc) and fill factor values of 15.02 mA/cm(2), 0.58 and 14.36 mA/cm(2), 0.55 for TPB- and TPSe-based solar cell are observed, whereas those for TPC and TPSi are 11.55 mA/cm2, 0.47 and 10.35 mA/cm(2), 0.42, respectively.

  1. An intramolecular bond at cluster of differentiation 81 ectodomain is important for hepatitis C virus entry.

    Science.gov (United States)

    Yang, Wei; Zhang, Meng; Chi, Xiaojing; Liu, Xiuying; Qin, Bo; Cui, Sheng

    2015-10-01

    Hepatitis C virus (HCV) infection is one of the leading causes of chronic liver diseases; however, HCV vaccine remains unavailable to date. One main obstacle is the lack of an efficient small animal model. Cluster of differentiation 81 (CD81) is an essential entry coreceptor for HCV species specificity to humans, though the underlying mechanisms are yet to be fully elucidated. We performed structural, biophysical, and virologic studies on HCV nonpermissive CD81s from mice and African green monkeys [mouse cluster of differentiation 81 (mCD81) and African green monkey cluster of differentiation 81 (agmCD81)] and compared with human cluster of differentiation 81 (hCD81). We discovered an intramolecular hydrogen bond (Gln188-Nε2-H: Glu196-Oε2, 2 Å, 124°) within the large extracellular loop (LEL) of mCD81 and a salt bridge (Lys188-Nζ: Asp196-Oδ2, 2.4 Å) within agmCD81-LEL between residues 188 and 196. This structural feature is missing in hCD81. We demonstrated that the introduction of a single 188-196 bond to hCD81 impaired its binding affinity to HCV envelope glycoprotein 2 (HCV E2) and significantly decreased HCV pseudoviral particle (HCVpp) entry efficiency (4.92- to 8.42-fold) and cell culture-grown HCV (HCVcc) infectivity (4.55-fold), despite the availability of Phe186. For HCV nonpermissive CD81s, the introduction of Phe186 by Leu186F substitution alone was insufficient to confer HCV permissiveness. The disruption of the original 188-196 bond and Leu186F substitution were both required for potent binding to HCV E2 HCVpp entry efficiency and HCVcc infectivity. Our structural and biophysical analyses suggest that the intramolecular 188-196 bond restricts the intrinsic conformational dynamics of D-helix of CD81-LEL, which is essential for HCV entry, thus impairs HCV permissiveness. Our findings reveal a novel molecular determinant for HCV entry in addition to the well-characterized Phe186 and provide further guideline for selecting an HCV small animal model

  2. Hydrogen bond strengthening induces fluorescence quenching of PRODAN derivative by turning on twisted intramolecular charge transfer

    Science.gov (United States)

    Yang, Yonggang; Li, Donglin; Li, Chaozheng; Liu, YuFang; Jiang, Kai

    2017-12-01

    Researchers have proposed different effective mechanisms of hydrogen bonding (HB) on the fluorescence of 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and its derivatives. Herein, excited state transition and dynamics analysis confirm that the fluorescence of PD (a derivative of PRODAN with ethyl replaced by 3-hydroxy-2,2-dimethylpropan) emits from the planar intramolecular charge transfer (PICT) state rather than twist ICT (TICT) state, because the fluorescence emission and surface hopping from the TICT state to the twist ground (T-S0) state is energy forbidden. Nevertheless, the strengthening of intramolecular-HB (intra-HB) and intermolecular-HB (inter-HB) of PD-(methanol)2 smooth the pathway of surface hopping from TICT to T-S0 state and the external conversion going to planar ground state by decreasing the energy difference of the two states. This smoothing changes the fluorescence state of PD-(methanol)2 to the TICT state in which fluorescence emission does not occur but surface hopping, leading to the partial fluorescence quenching of PD in methanol solvent. This conclusion is different from previous related reports. Moreover, the inter-HB strengthening of PD-methanol in PICT state induces the cleavage of intra-HB and a fluorescence red-shift of 54 nm compared to PD. This red-shift increases to 66 nm for PD-(methanol)2 for the strengthening of the one intra-HB and two inter-HBs. The dipole moments of PD-methanol and PD-(methanol)2 respectively increase about 10.3D and 8.1D in PICT state compared to PD. The synergistic effect of intra-HB and inter-HB induces partial quenching of PD in methanol solvent by turning on the TICT state and fluorescence red-shift. This work gives a reasonable description on the fluorescence red-shift and partial quenching of PD in methanol solvent, which will bring insight into the study of spectroscopic properties of molecules owning better spectral characteristics.

  3. Cyclization in concert

    NARCIS (Netherlands)

    Fraaije, Marco W.; Mattevi, Andrea

    2008-01-01

    The berberine bridge enzyme catalyzes the crucial step in the biosynthesis of an important class of alkaloids through a reaction that cannot be carried out using conventional organic chemistry tools. Characterization of the enzyme demonstrates a concerted mechanism that couples two distinct chemical

  4. Intramolecular charge separation in spirobifluorene-based donor–acceptor compounds adsorbed on Au and indium tin oxide electrodes

    International Nuclear Information System (INIS)

    Heredia, Daniel; Otero, Luis; Gervaldo, Miguel; Fungo, Fernando; Dittrich, Thomas; Lin, Chih-Yen; Chi, Liang-Chen; Fang, Fu-Chuan; Wong, Ken-Tsung

    2013-01-01

    Surface photovoltage (SPV) measurements were performed with a Kelvin-probe in spirobifluorene-based donor (diphenylamine)–acceptor (dicyano or cyanoacrylic acid moieties) compounds adsorbed from highly diluted solutions onto Au and indium tin oxide electrode surfaces. Strong intramolecular charge separation (negative SPV signals up to more than 0.1 V) due to directed molecule adsorption was observed only for spirobifluorene donor–acceptor compounds with carboxylic acid moiety. SPV signals and onset energies of electronic transitions depended on ambience conditions. - Highlights: ► Fluorene donor–acceptor derivatives were adsorbed at Au and indium tin oxide. ► Surface photovoltage measurements were performed with a Kelvin-probe. ► Strong intra-molecular charge separation was observed. ► SPV signals depended on ambience conditions

  5. EVAPORATION: a new vapor pressure estimation method for organic molecules including non-additivity and intramolecular interactions

    Science.gov (United States)

    Compernolle, S.; Ceulemans, K.; Müller, J.-F.

    2011-04-01

    We present EVAPORATION (Estimation of VApour Pressure of ORganics, Accounting for Temperature, Intramolecular, and Non-additivity effects), a method to predict vapour pressure p0 of organic molecules needing only molecular structure as input. The method is applicable to zero-, mono- and polyfunctional molecules. A simple formula to describe log10p0(T) is employed, that takes into account both a wide temperature dependence and the non-additivity of functional groups. In order to match the recent data on functionalised diacids an empirical modification to the method was introduced. Contributions due to carbon skeleton, functional groups, and intramolecular interaction between groups are included. Molecules typically originating from oxidation of biogenic molecules are within the scope of this method: carbonyls, alcohols, ethers, esters, nitrates, acids, peroxides, hydroperoxides, peroxy acyl nitrates and peracids. Therefore the method is especially suited to describe compounds forming secondary organic aerosol (SOA).

  6. Use of Alkyl Ethers as Traceless Hydride Donors in Brønsted Acid-Catalyzed Intramolecular Hydrogen Atom Transfer.

    Science.gov (United States)

    Gandamana, Dhika Aditya; Wang, Bin; Tejo, Ciputra; Bolte, Benoit; Gagosz, Fabien; Chiba, Shunsuke

    2018-03-25

    A new protocol for the deoxygenation of alcohols and the hydrogenation of alkenes under Brønsted acid catalysis has been developed. The method is based on the use of a benzyl or an isopropyl ether as a traceless hydrogen atom donor and involves an intramolecular hydride transfer as a key step that can be achieved in regio- and stereoselective manners. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Synthesis of Amidines from Amides Using a Nickel-Catalyzed Decarbonylative Amination through CO Extrusion Intramolecular Recombination Fragment Coupling.

    Science.gov (United States)

    Liu, Xiangqian; Yue, Huifeng; Jia, Jiaqi; Guo, Lin; Rueping, Magnus

    2017-09-04

    A catalytic synthesis of amidines from amides has been established for the first time. The newly developed CO extrusion recombination process takes advantage of an inexpensive nickel(II) catalyst and provides the corresponding amidines with high efficiency. The intramolecular fragment coupling shows excellent chemoselectivity, starts from readily available amides, and provides a valuable alternative amidine synthesis protocol. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. An enantioselective organocatalytic intramolecular Morita-Baylis-Hillman (IMBH) reaction of dienones, and elaboration of the IMBH adducts to fluorenones.

    Science.gov (United States)

    Satpathi, Bishnupada; Wagulde, Siddhant V; Ramasastry, S S V

    2017-07-13

    An enantioselective organocatalytic intramolecular Morita-Baylis-Hillman (IMBH) reaction of dienones is reported for the first time. This has been achieved by incorporating entropy and synergy considerations during the substrate design. The reaction conditions are thoroughly verified for an efficient synthesis of highly functionalised cyclopenta-fused arenes and heteroarenes in excellent yields and enantioselectivities. The synthetic utility of the IMBH-adducts has been demonstrated by transforming them into 3,4-disubstituted fluorenones in a serendipitous manner.

  9. On the Possibility of Uphill Intramolecular Electron Transfer in Multicopper Oxidases: Electrochemical and Quantum Chemical Study of Bilirubin Oxidase

    Czech Academy of Sciences Publication Activity Database

    Shleev, S.; Andoralov, V.; Falk, M.; Reimann, C. T.; Ruzgas, T.; Srnec, Martin; Ryde, U.; Rulíšek, Lubomír

    2012-01-01

    Roč. 24, č. 7 (2012), s. 1524-1540 ISSN 1040-0397 Grant - others:7th Framework Program(XE) NMP4-SL-2009-229255 Institutional research plan: CEZ:AV0Z40550506 Keywords : bilirubin oxidase * intramolecular electron transfer * rate-limiting catalytic step * reorganization energy * QM/MM calculations Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.817, year: 2012

  10. A Critical Check for the Role of Resonance in Intramolecular Hydrogen Bonding.

    Science.gov (United States)

    Jiang, Xiaoyu; Zhang, Huaiyu; Wu, Wei; Mo, Yirong

    2017-11-27

    Although resonance-assisted H-bonds (RAHBs) are well recognized, the role of π resonance in RAHBs is controversial, as the seemingly enhanced H-bonds in unsaturated compounds may result from the constraints imposed by the σ skeleton. Herein the block-localized wave function (BLW) method, which can derive optimal yet resonance-quenched structures with related physiochemical properties, was employed to examine the correlation between π resonance and the strength of intramolecular RAHBs. Examination of a series of paradigmatic molecules with RAHBs and their saturated analogues showed that it is inappropriate to compare a conjugated system with its saturated counterpart, as they may have quite different σ frameworks. Nevertheless, comparison between a conjugated system and its resonance-quenched (i.e., electron-localized) state, which have identical σ skeletons, shows that in all studied cases, π resonance unanimously reduces the bonding distance by 0.111-0.477 Å, strengthens the bonding by 40-56 %, and redshifts the D-H vibrational frequency by 104-628 cm -1 . Furthermore, there is an excellent correlation between hydrogen-bonding strength and the classical Coulomb attraction between the hydrogen-bond donor and the acceptor, which suggests that the dominant role of the electrostatic interaction in H-bonds and RAHBs originates from the charge flow from H-bond donors to acceptors through π conjugation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Mechanochemical Preparation of Cobalt Nanoparticles through a Novel Intramolecular Reaction in Cobalt(II Complexes

    Directory of Open Access Journals (Sweden)

    Seyed Abolghasem Kahani

    2015-01-01

    Full Text Available A novel solid state reaction involving a series of cobalt(II hydrazine-azides has been used to prepare metallic cobalt nanoparticles. The reactions of [Co(N2H4(N32], [Co(N2H42(N32], and [Co(N2H4(N3Cl]·H2O via NaOH, KOH as reactants were carried out in the solid state. These complexes undergo an intramolecular two-electron oxidation-reduction reaction at room temperature, producing metallic cobalt nanoparticles (Co1–Co6. The aforementioned complexes contain cobalt(II that is an oxidizing agent and also hydrazine ligand as a reducing agent. Other products produced include sodium azide and ammonia gas. The cobalt metal nanoparticles were characterized using X-ray powder diffraction (XRD, scanning electron microscopy (SEM, and vibrating sample magnetometer (VSM. The synthesized cobalt nanoparticles have similar morphologies; however, their particle size distributions are different.

  12. NMR investigation of intramolecular dynamics of heteroleptic triple-decker (porphyrinato)(phthalocyaninato) lanthanides.

    Science.gov (United States)

    Birin, Kirill P; Gorbunova, Yulia G; Tsivadze, Aslan Yu

    2011-11-21

    Intramolecular dynamics of meso-aryl substituents of porphyrin deck in the triple-decker lanthanide (porphyrinato)(phthalocyaninates) of symmetrical type [Br(4)TPP]Ln[(15C5)(4)Pc]Ln[Br(4)TPP] (Ln = La, Nd, Eu; [Br(4)TPP] = tetrakis-5,10,15,20-(4-bromophenyl)-porphyrinato-ligand; [(15C5)(4)Pc] = tetrakis-(15-crown-5)-phthalocyaninato-ligand) are investigated. Attempts to achieve coalescence were not successful, although the trend of exchanging protons to coalescence point was observed in the case of Nd and Eu complexes. The analysis of NOESY cross-peaks between exchanging protons allowed to evaluate the rotation rate constants at different temperatures. The activation barrier of the meso-aryl substituent rotation was calculated with Arrhenius equation based on determined rate constants. The rate constants are lower and activation barriers are higher than ones found previously for related compounds. This journal is © The Royal Society of Chemistry 2011

  13. Spectroscopic and theoretical investigations on intramolecular charge transfer phenomenon in 1-3-dioxolane derivative

    Science.gov (United States)

    Zhang, Zhiyong; Zhang, Zhongzhi; Luo, Yijing; Sun, Shanshan; Zhang, Guangqing

    2018-02-01

    High fluorescence quantum yield (FQY) and large Stokes shift (SS) cannot be easily achieved simultaneously by traditional PICT or TICT fluorescent probe. However, an 1-3-dioxolane derivative named 5-methyl-8,9-dihydro-5H-[1,3]dioxolo[4,5-b]carbazol-6(7H)-one (MDDCO) features both high FQY and large SS. The purpose of this study is to search the mechanism behind this phenomenon by theoretical method. Simulated structure changes and charge transfer suggest ICT process in MDDCO is similar to PLICT (Planarized Intramolecular Charge Transfer) process. Calculated UV-Vis spectra and fluorescence spectra show that PLICT-like state (S1 state) of MDDCO leads to large SS. Computed transient-absorption spectra and radiative decay rates indicate that PLICT-like state is key factor for high FQY of MDDCO. These findings suggest that PLICT-like state in 1,3-dioxolane derivatives can achieve both large SS and high FQY, which presents a new method for high-performance fluorescent probe design.

  14. Dynamics of intramolecular spin exchange interaction of a nitronyl nitroxide diradical in solution and on surfaces

    Science.gov (United States)

    Lloveras, V.; Badetti, E.; Veciana, J.; Vidal-Gancedo, J.

    2016-02-01

    In this paper we report the study of the dynamics of a thermally modulated intramolecular spin exchange interaction of a novel diradical nitronyl nitroxide-substituted disulfide in solution and when it is grafted on a gold surface. The structure of this diradical was designed to have flexible chains leading to intramolecular collisions and hence spin exchange interaction, and with an appropriate binding group to be grafted on the gold surface to study its behavior on the surface. In solution, this diradical shows a strong spin exchange interaction between both radicals which is modulated by temperature, but also gold nanoparticles (AuNPs) functionalized with this diradical permit investigation of such a phenomenon in surface-grafted radicals. The spin-labelled AuNP synthesis was optimized to obtain high coverage of spin labels to lead to high spin exchange interaction. The obtained AuNPs were studied by Electron Paramagnetic Resonance (EPR), UV-Vis, and IR spectroscopies, HR-TEM microscopy, Cyclic Voltammetry (CV), Energy Dispersive X-ray analysis (EDX) and Thermogravimetric Analysis (TGA). This inorganic-organic hybrid material also showed dipolar interactions between its radicals which were confirmed by the appearance in the EPR spectra of an |Δms| = 2 transition at half-field. This signal gives direct evidence of the presence of a high-spin state and permitted us to study the nature of the magnetic coupling between the spins which was found to be antiferromagnetic. Self-Assembled Monolayers (SAMs) of these radicals on the Au (111) substrate were also prepared and studied by contact angle, X-Ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), Cyclic Voltammetry and EPR. The magnetic as well as the electrochemical properties of the hybrid surfaces were studied and compared with the properties of this diradical in solution. Analogies between the properties of AuNPs with high coverage of radicals and those of SAM were

  15. Contribution of inter- and intramolecular energy transfers to heat conduction in liquids.

    Science.gov (United States)

    Torii, Daichi; Nakano, Takeo; Ohara, Taku

    2008-01-28

    The molecular dynamics expression of heat flux, originally derived by Irving and Kirkwood [J. Chem. Phys. 18, 817 (1950)] for pairwise potentials, is generalized in this paper for systems with many-body potentials. The original formula consists of a kinetic part and a potential part, and the latter term is found in the present study to be expressible as a summation of contributions from all the many-body potentials defined in the system. The energy transfer among a set of sites for which a many-body potential is defined is discussed and evaluated by the rate of increase in the kinetic energy of each site due to the potential, and its accumulation over all the potentials in the system is shown to make up the potential part of the generalized expression. A molecular dynamics simulation for liquid n-octane was performed to demonstrate the applicability of the new expression obtained in this study to measure the heat flux and to elucidate the contributions of inter- and intramolecular potentials to heat conduction.

  16. Discovery of intramolecular trans-sialidases in human gut microbiota suggests novel mechanisms of mucosal adaptation

    Science.gov (United States)

    Tailford, Louise E.; Owen, C. David; Walshaw, John; Crost, Emmanuelle H.; Hardy-Goddard, Jemma; Le Gall, Gwenaelle; de Vos, Willem M.; Taylor, Garry L.; Juge, Nathalie

    2015-07-01

    The gastrointestinal mucus layer is colonized by a dense community of microbes catabolizing dietary and host carbohydrates during their expansion in the gut. Alterations in mucosal carbohydrate availability impact on the composition of microbial species. Ruminococcus gnavus is a commensal anaerobe present in the gastrointestinal tract of >90% of humans and overrepresented in inflammatory bowel diseases (IBD). Using a combination of genomics, enzymology and crystallography, we show that the mucin-degrader R. gnavus ATCC 29149 strain produces an intramolecular trans-sialidase (IT-sialidase) that cleaves off terminal α2-3-linked sialic acid from glycoproteins, releasing 2,7-anhydro-Neu5Ac instead of sialic acid. Evidence of IT-sialidases in human metagenomes indicates that this enzyme occurs in healthy subjects but is more prevalent in IBD metagenomes. Our results uncover a previously unrecognized enzymatic activity in the gut microbiota, which may contribute to the adaptation of intestinal bacteria to the mucosal environment in health and disease.

  17. Polarization of emission from asymmetric rotors. II. Vector reorientation through intramolecular coupling and inelastic collisions

    Science.gov (United States)

    Truhins, Kaspars; McCaffery, Anthony J.; Alwahabi, Zeyad T.; Rawi, Zaid

    1997-07-01

    We report measurements of the linear and circular polarization ratios from fully resolved rotational levels of the asymmetric rotor NH2 populated by collisions with H atoms. The results compare well with a theoretical model that includes the depolarizing effects of intramolecular coupling of rotational angular momentum N to nuclear and to electron spin. These have a very significant influence on fluorescence polarization. The model also incorporates the tilting of the N vector in the molecule frame that occurs when inter-k stack transitions take place. Changes in N vector orientation are described with the aid of the angular momentum sphere, a classical representation of the motion of the N vector in a molecule fixed frame. The theoretical treatment assumes the classically impulsive limit for the collisional interaction with conservation of the m quantum number along the kinematic apse. This description of the fate of the N vector under the influence of intra- and intermolecular interactions allows stereodynamical conclusions to be drawn from experimental observations of fluorescence polarization.

  18. C—C bond formation in the intramolecular Diels-Alder reaction of triene amides

    Directory of Open Access Journals (Sweden)

    Abdelilah Benallou

    2018-02-01

    Full Text Available The mechanism nature of the intramolecular Diels–Alder reaction has been performed; and thus, the changes of C—C bond forming/breaking along IRC are characterized in this study. Conceptual DFT analyses of the most favorable adduct fused/exo shows that the flux electronic will take place from diene to dienophile moiety. Moreover, ELF topological analysis based on the electron density predicts that C—C bond is formed by the coupling of two pseudoradical centers generated at the most significant atoms of the molecules. However, C2 vs C3, also C1 and C4 interaction comes mainly from the global electron density transfer which takes place along the reaction. Two- stage one-step is the proposed mechanism of this reaction, the first stage aims for the formation of C2—C3 σ bond while the second stage aims for C1—C4 σ bond formation. Interestingly, the observed asynchronicity of this IMDA reaction due principally to the asymmetric reorganization of electron density at the most attractive centers.

  19. Absence of Intramolecular Singlet Fission in Pentacene-Perylenediimide Heterodimers: The Role of Charge Transfer State.

    Science.gov (United States)

    Wang, Long; Wu, Yishi; Chen, Jianwei; Wang, Lanfen; Liu, Yanping; Yu, Zhenyi; Yao, Jiannian; Fu, Hongbing

    2017-11-16

    A new class of donor-acceptor heterodimers based on two singlet fission (SF)-active chromophores, i.e., pentacene (Pc) and perylenediimide (PDI), was developed to investigate the role of charge transfer (CT) state on the excitonic dynamics. The CT state is efficiently generated upon photoexcitation. However, the resulting CT state decays to different energy states depending on the energy levels of the CT state. It undergoes extremely rapid deactivation to the ground state in polar CH 2 Cl 2 , whereas it undergoes transformation to a Pc triplet in nonpolar toluene. The efficient triplet generation in toluene is not due to SF but CT-mediated intersystem crossing. In light of the energy landscape, it is suggested that the deep energy level of the CT state relative to that of the triplet pair state makes the CT state actually serve as a trap state that cannot undergoes an intramolecular singlet fission process. These results provide guidance for the design of SF materials and highlight the requisite for more widely applicable design principles.

  20. Ruthenium-modified cytochrome c: temperature dependence of the rate of intramolecular electron transfer

    International Nuclear Information System (INIS)

    Isied, S.S.; Kuehn, C.; Worosila, G.

    1984-01-01

    The ruthenium-modified horse heart cytochrome c, Ru(III)-cyt c(III), where the ruthenium is bound to the histidines-33 residue has been synthesized and characterized by ruthenium analysis, UV-vis and CD spectra, and differential pulse polarography and cyclic voltammetry. The intermediate Ru(III)-cyt c(III) has been generated by pulse-radioanalysis with use of four different radicals, CO 2 -., (CH 3 )COH., (CH 2 OH) 3 CCHOH, and -OCCH(OH)C(OH)CO 2 -. The rate of intramolecular electron transfer within the Ru(III)-cyt c(III) complex and its temperature dependence were determined over a 40 0 C temperature range with the CO 2 -. radical. At 25 0 C, these values are k/sub u/=53 +/- s/sup -1/ (pH 7.01 M phosphate buffer, 0.1 M NaHCO 2 ), ΔH/sup +/=3.5 +/- 0.2 kcal mol/sup -1/, and ΔS/sup +/=-39 +/- 1 eu

  1. Structural factors influencing the intramolecular charge transfer and photoinduced electron transfer in tetrapyrazinoporphyrazines.

    Science.gov (United States)

    Novakova, Veronika; Hladík, Petr; Filandrová, Tereza; Zajícová, Ivana; Krepsová, Veronika; Miletin, Miroslav; Lenčo, Juraj; Zimcik, Petr

    2014-03-21

    A series of unsymmetrical tetrapyrazinoporphyrazines (TPyzPzs) from the group of azaphthalocyanines with one peripherally attached amino substituent (donor) were synthesized, and their photophysical properties (fluorescence quantum yield and singlet oxygen quantum yield) were determined. The synthesized TPyzPzs were expected to undergo intramolecular charge transfer (ICT) as the main pathway for deactivating their excited states. Several structural factors were found to play a critical role in ICT efficiency. The substituent in the ortho position to the donor center significantly influences the ICT, with tert-butylsulfanyl and butoxy substituents inducing the strongest ICTs, whereas chloro, methyl, phenyl, and hydrogen substituents in this position reduce the efficiency. The strength of the donor positively influences the ICT efficiency and correlates well with the oxidation potential of the amines used as the substituents on the TPyzPz as follows: n-butylamine ICT (with conjugated donors and acceptors) in the TPyzPz also proved to be much stronger than a photoinduced electron transfer in which the donor and the acceptor are connected through an aliphatic linker.

  2. Intramolecular Cooperativity in the Reaction of Diacyl Phosphates with Serine ß-Lactamases

    Science.gov (United States)

    Majumdar, Sudipta; Pratt, R.F.

    2010-01-01

    Asymmetric diaroyl phosphates (ArCOOPO2−OCOAr′, where Ar = Ph, Ar′ = 4-biphenyl, 2-benzothiophenyl and 2-benzofuranyl), have been prepared, evaluated as serine (classes A, C, D) β-lactamase inhibitors, and compared with respect to the latter with their symmetric “parents”, where Ar = Ar′. The asymmetric compounds, in general, were found to react with the β-lactamases in two modes, corresponding to different orientations with respect to the active site, whereby either of the two aroyl groups may acylate the enzyme to form two different inert acyl-enzymes, E-COAr and E-COAr′. In all cases, the asymmetric compounds, in one orientation, react more rapidly with the enzymes tested than one symmetrical “parent” but not both. From comparisons of activation free energy differences, it was found that the changes in free energy on changing from one aryl group to another, in either the acyl group or the leaving group, were not additive, i.e. that the effect of changing one aroyl group to another depended on the leaving group and vice versa. Thus, intramolecular cooperativity between the aroyl groups must exist, arising either from direct interaction between them or from protein-mediated interaction, or from a combination of both. Such cooperativity brings fresh opportunities and challenges to the search for novel ß-lactamase inhibitors. PMID:19678666

  3. Intramolecular hydrogen bonding in 5-nitrosalicylaldehyde: IR spectrum and quantum chemical calculations

    Science.gov (United States)

    Moosavi-Tekyeh, Zainab; Taherian, Fatemeh; Tayyari, Sayyed Faramarz

    2016-05-01

    The structural parameters, and vibrational frequencies of 5-nitrosalicylaldehyde (5NSA) were studied by the FT-IR and Raman spectra and the quantum chemical calculations carried out at the B3LYP/6-311++G(d,p) level of theory in order to investigate the intramolecular hydrogen bonding (IHB) present in its structure. The strength and nature of IHB in the optimized structure of 5NSA were studied in detail by means of the atoms in molecules (AIM) and the natural bond orbital (NBO) approaches. The results obtained were then compared with the corresponding data for its parent molecule, salicylaldehyde (SA). Comparisons made between the geometrical structures for 5NSA and SA, their OH/OD stretching and out-of-plane bending modes, their enthalpies for the hydrogen bond, and their AIM parameters demonstrated a stronger H-bonding in 5NSA compared with that in SA. The calculated binding enthalpy (ΔHbind) for 5NSA was -10.92 kcal mol-1. The observed νOH and γOH appeared at about 3120 cm-1 and 786 cm-1 respectively. The stretching frequency shift of H-bond formation was 426 cm-1 which is consistent with ΔHbind and the strength of H-bond in 5NSA. The delocalization energies and electron delocalization indices derived by the NBO and AIM approaches indicate that the resonance effects were responsible for the stronger IHB in 5NSA than in SA.

  4. Intramolecular interactions contributing for the conformational preference of bioactive diphenhydramine: Manifestation of the gauche effect

    Science.gov (United States)

    de Rezende, Fátima M. P.; Andrade, Laize A. F.; Freitas, Matheus P.

    2015-08-01

    Diphenhydramine is an antihistamine used to treat some symptoms of allergies and the common cold. It is usually marketed as the hydrochloride salt, and both the neutral and cation forms have the O-C-C-N fragment. The gauche effect is well known in fluorine-containing chains, because its main origin is hyperconjugative and the σ∗C-F is a low-lying acceptor orbital, allowing electron delocalization in the conformation where F and an adjacent electronegative substituent in an ethane fragment are in the gauche orientation. Our experimental (NMR) and theoretical findings indicate that diphenhydramine exhibits the gauche effect, since the preferential conformations have the O-C-C-N moiety in this orientation due especially to antiperiplanar σC-H → σ∗C-O and σC-H → σ∗C-N interactions. This conformational preference is strengthened in the protonated form due to an incremental electrostatic gauche effect. Because the gauche conformation matches the bioactive structure of diphenhydramine complexed with histamine methyltransferase, it is suggested that intramolecular interactions, and not only induced fit, rule its bioactive form.

  5. Hydrogen-deuterium exchange in spiro cyclic ketones: a search for intramolecular catalysis

    International Nuclear Information System (INIS)

    Hsu, R.C.L.

    1979-01-01

    The synthesis and characterization of 1'-hydroxy-3',3'-dimethylspiro[cyclohexane-1,2'-indan]-4-one (17b), 1'-amino-3',3'-dimethylspiro[cyclohexane-1,2'-indan]4-one (6a), 1'-N,N-dimethylamino-3',3'-dimethylspiro[cyclohexane-1,2'-indan]-4-one (6c) and 1'-[N-ethyl-α(d 2 )-amino]-3'-3'-dimethylspiro[cyclohexane-1,2'-indan]-4-one (6b) are described. The hydrogen-deuterium exchange reactions of aminoketones 6b and 6c with CH 3 OD are too fast to be followed by the mass spectrometric methodology. However, the H/D exchange between hydroxyketone 17b and CH 3 OD is shown to be intramolecularly catalyzed under both basic and neutral conditions. The rate constant for the exchange of C(3)-axial-H in 17b is 35 times greater than the rate constant for the exchange of an axial α-H in 4-t-butylcyclohexanone

  6. Constraints from protein structure and intra-molecular coevolution influence the fitness of HIV-1 recombinants.

    Science.gov (United States)

    Woo, Jeongmin; Robertson, David L; Lovell, Simon C

    2014-04-01

    A major challenge for developing effective treatments for HIV-1 is the viruses' ability to generate new variants. Inter-strain recombination is a major contributor to this high evolutionary rate, since at least 20% of viruses are observed to be recombinant. However, the patterns of recombination vary across the viral genome. A number of factors influence recombination, including sequence identity and secondary RNA structure. In addition the recombinant genome must code for a functional virus, and expressed proteins must fold to stable and functional structures. Any intragenic recombination that disrupts internal residue contacts may therefore produce an unfolded protein. Here we find that contact maps based on protein structures predict recombination breakpoints observed in the HIV-1 pandemic. Moreover, many pairs of contacting residues that are unlikely to be disrupted by recombination are coevolving. We conclude that purifying selection arising from protein structure and intramolecular coevolutionary changes shapes the observed patterns of recombination in HIV-1. Copyright © 2014 Elsevier Inc. All rights reserved.

  7. Intermolecular and very strong intramolecular C-SeO/N chalcogen bonds in nitrophenyl selenocyanate crystals.

    Science.gov (United States)

    Wang, Hui; Liu, Ju; Wang, Weizhou

    2018-02-14

    Single-crystal X-ray diffraction reveals that polymorphic ortho-nitrophenyl selenocyanate (o-NSC, crystals 1a and 1b) and monomorphic para-nitrophenyl selenocyanate (p-NSC, crystal 2) crystals are all stabilized mainly by intermolecular and very strong intramolecular C-SeO/N chalcogen bonds, as well as by other different interactions. Thermogravimetric (TG) and differential scanning calorimetry thermogram (DSC) analyses show that the starting decomposition temperatures and melting points of the three crystals are different, following the order 1b > 1a > 2, which is consistent with the structural characteristics of the crystals. In addition, atoms in molecules (AIM) and natural bond orbital (NBO) analyses indicate that the total strengths of the C-SeO and C-SeN chalcogen bonds decrease in the order 1b > 1a > 2. This study could be significant for engineering functional crystals based on robust C-SeO and C-SeN chalcogen bonds, and for designing drugs containing selenium as well as understanding their interaction in biosystems.

  8. Suppression of human immunodeficiency virus type 1 activity in vitro by oligonucleotides which form intramolecular tetrads.

    Science.gov (United States)

    Rando, R F; Ojwang, J; Elbaggari, A; Reyes, G R; Tinder, R; McGrath, M S; Hogan, M E

    1995-01-27

    An oligonucleotide (I100-15) composed of only deoxyguanosine and thymidine was able to inhibit human immunodeficiency virus type-1 (HIV-1) in culture assay systems. I100-15 did not block virus entry into cells but did reduce viral-specific transcripts. As assessed by NMR and polyacrylamide gel methods, I100-15 appears to form a structure in which two stacked guanosine tetrads are connected by three two-base long loops. Structure/activity experiments indicated that formation of intramolecular guanosine tetrads was necessary to achieve maximum antiviral activity. The single deoxyguanosine nucleotide present in each loop was found to be extremely important for the overall antiviral activity. The toxicity of I100-15 was determined to be well above the 50% effective dose (ED50) in culture which yielded a high therapeutic index (> 100). The addition of a cholesterol moiety to the 3' terminus of I100-15 (I100-23) reduced the ED50 value to less than 50 nM (from 0.12 microM for I100-15) and increased the duration of viral suppression to greater than 21 days (versus 7-10 days for I100-15) after removal of the drug from infected cell cultures. The favorable therapeutic index of such molecules coupled with the prolonged suppression of HIV-1, suggest that such compounds further warrant investigation as potential therapeutic agents.

  9. Intramolecular energy transfer at donor-acceptor interactions in model and biological membranes

    International Nuclear Information System (INIS)

    Umarova, Fatima T.

    2011-01-01

    Intramolecular triplet-triplet energy transfer between molecules of sensibilisator and photochrome for registration of protein interactions in the membrane preparation of Na,K-ATPase was investigated. Erythrosinithiocyanate (ERITC) was used as the triplet label of sensibilisator, and 4-acetoamido-4 -isothiocyanatostilbene-2,2 disullfonic acid (SITS) was used as the photochrome label. Na,K-ATPase preparations were covalently bound with ERITC in active centre of enzyme, and SITS molecules were covalently bound by NH2-groups. In model system, in chymotrypsinogene molecule, SITS and ERITC labels were used also. The cis-trans-isomerization of SITS was initiated by triplet-triplet energy transfer from light excited ERITC molecule to photochrome. The kinetics of isomerization was recorded by the SITS fluorescence measurements. The constant of rate of triplet-triplet energy transfer from ERITC to cis-isomers of SITS in Na,K-ATPase was determined as (3-7)x10 3 M -1 s -1 , and in model system it equals 1x 10 7 M 1 s -1 . The value of energy transfer between loos molecules of erythrosine and SITS in buffer solution equaled to 7x10 7 M -1 s -1 . This drop of R m y in the membrane preparation of Na,K-ATPase at 10 4 reflected the decrease in the frequency of label collisions caused by the increase in the media viscosity and steric hindrances. (author)

  10. Fluorescent sensors for selective detection of thiols: expanding the intramolecular displacement based mechanism to new chromophores.

    Science.gov (United States)

    Niu, Li-Ya; Zheng, Hai-Rong; Chen, Yu-Zhe; Wu, Li-Zhu; Tung, Chen-Ho; Yang, Qing-Zheng

    2014-03-21

    Biological thiols, including cysteine (Cys), homocystein (Hcy) and glutathione (GSH), play crucial roles in maintaining the appropriate redox status of biological systems. An abnormal level of biothiols is associated with different diseases, therefore, the discrimination between them is of great importance. Herein, we present two fluorescent sensors for selective detection of biothiols based on our recently reported intramolecular displacement mechanism. We expanded this mechanism to commercially available chromophores, 4-chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl) and heptamethine cyanine dye IR-780. The sensors operate by undergoing displacement of chloride by thiolate. The amino groups of Cys/Hcy further replace the thiolate to form amino-substituted products, which exhibit dramatically different photophysical properties compared to sulfur-substituted products from the reaction with GSH. NBD-Cl is highly selective towards Cys/Hcy and exhibits significant fluorescence enhancement. IR-780 showed a variation in its fluorescence ratio towards Cys over other thiols. Both of the sensors can be used for live-cell imaging of Cys. The wide applicability of the mechanism may provide a powerful tool for developing novel fluorescent sensors for selective detection of biothiols.

  11. NIR Phosphorescent Intramolecularly Bridged Benzoporphyrins and Their Application in Oxygen-Compensated Glucose Optode.

    Science.gov (United States)

    Zach, Peter W; Hofmann, Oliver T; Klimant, Ingo; Borisov, Sergey M

    2018-02-20

    A glucose optode measuring the internal oxygen gradient is presented. The multilayer biosensor is composed of (i) analyte-impermeable transparent support, (ii) first oxygen-sensing layer combined with an enzymatic layer, (iii) diffusion barrier, and (iv) second oxygen-sensing layer. To make this design suitable for measurement in subcutaneous tissue, a pair of NIR phosphorescent indicators with very different spectral properties is chosen. Combination of a conventional Pt(II) tetrabenzoporphyrin dye (absorption and emission maxima at 617 and 772 nm, respectively) used in the first layer and a new intramolecularly bridged Pt(II) complex (absorption and emission maxima at 673 and 872 nm, respectively) in the second layer enables efficient separation of both emission signals. This specially designed dye class is accessible via Scholl-reaction from tetraphenyltetrabenzoporphyrin complexes. For the first time, the new optode allows simultaneous glucose and oxygen measurement in a single spot and therefore accurate compensation of oxygen heterogeneities resulting from fluctuations in the tissue. The presented material covers the dynamic ranges from 0 to 150 hPa O 2 and from 0 to 360 mg/dL (20 mM) glucose (at 37 °C).

  12. Photoinduced symmetry-breaking intramolecular charge transfer in a quadrupolar pyridinium derivative.

    Science.gov (United States)

    Carlotti, Benedetta; Benassi, Enrico; Spalletti, Anna; Fortuna, Cosimo G; Elisei, Fausto; Barone, Vincenzo

    2014-07-21

    We report here a joint experimental and theoretical study of a quadrupolar, two-branched pyridinium derivative of interest as a potential non-linear optical material. The spectral and photophysical behaviour of this symmetric system is greatly affected by the polarity of the medium. A very efficient photoinduced intramolecular charge transfer, surprisingly more efficient than in the dipolar asymmetric analogue, is found to occur by femtosecond resolved transient absorption spectroscopy. TD-DFT calculations are in excellent agreement with these experimental findings and predict large charge displacements in the molecular orbitals describing the ground state and the lowest excited singlet state. The theoretical study also revealed that in highly polar media the symmetry of the excited state is broken giving a possible explanation to the fluorescence and transient absorption spectra resembling those of the one-branched analogous compound in the same solvents. The present study may give an important insight into the excited state deactivation mechanism of cationic (donor-π-acceptor-π-donor)(+) quadrupolar compounds characterised by negative solvatochromism, which are expected to show significant two-photon absorption (TPA). Moreover, the water solubility of the investigated quadrupolar system may represent an added value in view of the most promising applications of TPA materials in biology and medicine.

  13. The Intramolecular Hydrogen Bond N-H···S in 2,2'-Diaminodiphenyl Disulfide: Experimental and Computational Thermochemistry.

    Science.gov (United States)

    Ramos, Fernando; Flores, Henoc; Hernández-Pérez, Julio M; Sandoval-Lira, Jacinto; Camarillo, E Adriana

    2018-01-11

    The intramolecular hydrogen bond of the N-H···S type has been investigated sparingly by thermochemical and computational methods. In order to study this interaction, the standard molar enthalpies of formation in gaseous phase of diphenyl disulfide, 2,2'-diaminodiphenyl disulfide and 4,4'-diaminodiphenyl disulfide at T = 298.15 K were determined by experimental thermochemical methods and computational calculations. The experimental enthalpies of formation in gas-phase were obtained from enthalpies of formation in crystalline phase and enthalpies of sublimation. Enthalpies of formation in crystalline phase were obtained using rotatory bomb combustion calorimetry. By thermogravimetry, enthalpies of vaporization were obtained, and by combining them with enthalpies of fusion, the enthalpies of sublimation were calculated. The Gaussian-4 procedure and the atomization method were applied to obtain enthalpies of formation in gas-phase of the compounds under study. Theoretical and experimental values are in good agreement. Through natural bond orbital (NBO) analysis and a topological analysis of the electronic density, the intramolecular hydrogen bridge (N-H···S) in the 2,2'-diaminodiphenyl disulfide was confirmed. Finally, an enthalpic difference of 11.8 kJ·mol -1 between the 2,2'-diaminodiphenyl disulfide and 4,4'-diaminodiphenyl disulfide was found, which is attributed to the intramolecular N-H···S interaction.

  14. Emission Spectroscopy as a Probe into Photoinduced Intramolecular Electron Transfer in Polyazine Bridged Ru(II,Rh(III Supramolecular Complexes

    Directory of Open Access Journals (Sweden)

    Karen J. Brewer

    2010-08-01

    Full Text Available Steady-state and time-resolved emission spectroscopy are valuable tools to probe photochemical processes of metal-ligand, coordination complexes. Ru(II polyazine light absorbers are efficient light harvesters absorbing in the UV and visible with emissive 3MLCT excited states known to undergo excited state energy and electron transfer. Changes in emission intensity, energy or band-shape, as well as excited state lifetime, provide insight into excited state dynamics. Photophysical processes such as intramolecular electron transfer between electron donor and electron acceptor sub-units may be investigated using these methods. This review investigates the use of steady-state and time-resolved emission spectroscopy to measure excited state intramolecular electron transfer in polyazine bridged Ru(II,Rh(III supramolecular complexes. Intramolecular electron transfer in these systems provides for conversion of the emissive 3MLCT (metal-to-ligand charge transfer excited state to a non-emissive, but potentially photoreactive, 3MMCT (metal-to-metal charge transfer excited state. The details of the photophysics of Ru(II,Rh(III and Ru(II,Rh(III,Ru(II systems as probed by steady-state and time-resolved emission spectroscopy will be highlighted.

  15. Heat conduction in chain polymer liquids: molecular dynamics study on the contributions of inter- and intramolecular energy transfer.

    Science.gov (United States)

    Ohara, Taku; Yuan, Tan Chia; Torii, Daichi; Kikugawa, Gota; Kosugi, Naohiro

    2011-07-21

    In this paper, the molecular mechanisms which determine the thermal conductivity of long chain polymer liquids are discussed, based on the results observed in molecular dynamics simulations. Linear n-alkanes, which are typical polymer molecules, were chosen as the target of our studies. Non-equilibrium molecular dynamics simulations of bulk liquid n-alkanes under a constant temperature gradient were performed. Saturated liquids of n-alkanes with six different chain lengths were examined at the same reduced temperature (0.7T(c)), and the contributions of inter- and intramolecular energy transfer to heat conduction flux, which were identified as components of heat flux by the authors' previous study [J. Chem. Phys. 128, 044504 (2008)], were observed. The present study compared n-alkane liquids with various molecular lengths at the same reduced temperature and corresponding saturated densities, and found that the contribution of intramolecular energy transfer to the total heat flux, relative to that of intermolecular energy transfer, increased with the molecular length. The study revealed that in long chain polymer liquids, thermal energy is mainly transferred in the space along the stiff intramolecular bonds. This finding implies a connection between anisotropic thermal conductivity and the orientation of molecules in various organized structures with long polymer molecules aligned in a certain direction, which includes confined polymer liquids and self-organized structures such as membranes of amphiphilic molecules in water.

  16. FeCl3/ZnI2-catalyzed synthesis of benzo[d]imidazo[2,1-b]thiazole through aerobic oxidative cyclization between 2-aminobenzothiazole and ketone.

    Science.gov (United States)

    Mishra, Subhajit; Monir, Kamarul; Mitra, Shubhanjan; Hajra, Alakananda

    2014-12-05

    The FeCl3/ZnI2-catalyzed aerobic oxidative cyclization between 2-aminobenzothiazole and ketone/chalcone for the synthesis of benzo[d]imidazo[2,1-b]thiazole is described. A variety of fused benzoimidazothiazole derivatives are obtained by this protocol.

  17. An organocatalytic Michael-cyclization cascade of 4-oxa-α,β-unsaturated carboxylic acids with aldehydes: facile synthesis of chiral γ-lactols and trisubstituted γ-lactones.

    Science.gov (United States)

    Lin, Jun-Bing; Xu, Shi-Ming; Xie, Ji-Kang; Li, Hong-Yu; Xu, Peng-Fei

    2015-02-28

    An organocatalytic Michael-cyclization cascade of aldehydes with 4-oxa-α,β-unsaturated carboxylic acids has been developed, giving functionalized γ-lactols with high yields and enantioselectivities. The products could be easily transformed into complex trisubstituted γ-lactones and γ-lactams.

  18. Metal-Free α-C(sp3–H Functionalized Oxidative Cyclization of Tertiary N,N-Diaryl Amino Alcohols: Theoretical Approach for Mechanistic Pathway

    Directory of Open Access Journals (Sweden)

    Zakir Ullah

    2017-03-01

    Full Text Available The mechanistic pathway of TEMPO/I2-mediated oxidative cyclization of N,N-diaryl amino alcohols 1 was investigated. Based on direct empirical experiments, three key intermediates (aminium radical cation 3, α-aminoalkyl radical 4, and iminium 5, four types of reactive species (radical TEMPO, cationic TEMPO, TEMPO-I, and iodo radical, and three types of pathways ((1 SET/PCET mechanism; (2 HAT/1,6-H transfer mechanism; (3 ionic mechanism were assumed. Under the assumption, nine free energy diagrams were acquired through density functional theory calculations. From the comparison of solution-phase free energy, some possible mechanisms were excluded, and then the chosen plausible mechanisms were concretized using the more stable intermediate 7.

  19. Ruthenium Hydride/Brønsted Acid-Catalyzed Tandem Isomerization/N-Acyliminium Cyclization Sequence for the Synthesis of Tetrahydro-β-carbolines

    DEFF Research Database (Denmark)

    Hansen, Casper Lykke; Clausen, Janie Regitse Waël; Ohm, Ragnhild Gaard

    2013-01-01

    This paper describes an efficient tandem sequence for the synthesis of 1,2,3,4-tetrahydro-β-carbolines (THBCs) relying on a ruthenium hydride/Brønsted acid- catalyzed isomerization of allylic amides to N-acyliminium ion intermediates which are trapped by a tethered indolenucleophile. The methodol......This paper describes an efficient tandem sequence for the synthesis of 1,2,3,4-tetrahydro-β-carbolines (THBCs) relying on a ruthenium hydride/Brønsted acid- catalyzed isomerization of allylic amides to N-acyliminium ion intermediates which are trapped by a tethered indolenucleophile...... the Suzuki cross-coupling reaction to the isomerization/N-acyliminium cyclization sequence. Finally, diastereo- and enantioselective versions of the title reaction have been examined using substrate control (with dr >15: 1) and asymmetric catalysis (ee up to 57%), respectively...

  20. Synthesis of benzo[α]carbazole derivatives from β-(2-arylindolyl)nitroalkanes via Mn(OAc){sub 3}-mediated cyclization

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Su Yeon; Lim, Jin Woo; Min, Beom Kyu; Kim, Jae Nyoung [Dept. of Chemistry and Institute of Basic Science, Chonnam National University, Gwangju (Korea, Republic of)

    2016-11-15

    We also reported the synthesis of benzo[a]carbazoles from 2-arylindoles via sequential propargylation, propargyl–allenyl isomerization, and 6π-electrocyclization approach, as shown in Scheme. Various 5-benzyl- and 5-methylbenzo[a]carbazoles have been synthesized; however, 5-unsubstituted benzo[a]carbazoles could not be synthesized by the approach. In order to develop a synthetic method of 5-unsubstituted benzo[a]carbazoles, we decided to examine the reaction of a new synthetic method of benzo[a]carbazoles has been developed from β-(2-phenylindolyl)nitroalkanes via Mn(OAc){sub 3}-mediated cyclization protocol. Various 5-unsubstituted benzo[a]carbazoles could be synthesized, when compared with previous approach to 5-benzylbenzo [a]carbazoles involving 6π-electrocyclization reaction.

  1. Preparation of neuroprotective condensed 1,4-benzoxazepines by regio- and diastereoselective domino Knoevenagel–[1,5]-hydride shift cyclization reaction

    Directory of Open Access Journals (Sweden)

    László Tóth

    2014-11-01

    Full Text Available Condensed O,N-heterocycles containing tetrahydro-1,4-benzoxazepine and tetrahydroquinoline moieties were prepared by a regio- and diastereoselective domino Knoevenagel–[1,5]-hydride shift cyclization reaction of a 4-aryl-2-phenyl-1,4-benzoxazepine derivative obtained from flavanone. The relative configuration of products were determined by the correlation of 3JH,H coupling data with the geometry of major conformers accessed by DFT conformational analysis. Separated enantiomers of the products were characterized by HPLC-ECD data, which allowed their configurational assignment on the basis of TDDFT-ECD calculation of the solution conformers. Two compounds showed neuroprotective activities against hydrogen peroxide (H2O2 or β-amyloid25–35 (Aβ25–35-induced cellular injuries in human neuroblastoma SH-SY5Y cells in the range of those of positive controls.

  2. A computational mechanistic study of Pd(ii)-catalyzed γ-C(sp3)-H olefination/cyclization of amines: the roles of bicarbonate and ligand effect.

    Science.gov (United States)

    Liu, Jian-Biao; Tian, Ying-Ying; Zhang, Xin; Wang, Lu-Lin; Chen, De-Zhan

    2018-04-03

    The detailed mechanism of palladium-catalyzed γ-C(sp3)-H olefination/cyclization of triflyl-protected amines was investigated by density functional theory (DFT) calculations. The olefinated intermediate was initially formed in the first catalytic cycle involving ligand exchange, bicarbonate-assisted C(sp3)-H bond cleavage, alkene insertion and 'reductive β-hydride elimination'. The following syn-addition and reductive elimination furnish the aza-Wacker product. The first step of reductive elimination is the rate-determining step. The mechanism unveils the important roles of bicarbonate: aiding the C-H activation and abstracting the β-proton in the second step of reductive elimination. The parallel bridging mode in the metal-olefin intermediate facilitates the syn-addition, explaining the experimentally observed stereoselectivity. The effect of the monodentate pyridine-based ligands is also discussed.

  3. Stereoselective Synthesis of Functionalized 1,3-Disubstituted Isoindolines via Rh(III)-Catalyzed Tandem Oxidative Olefination-Cyclization of 4-Aryl-cyclic Sulfamidate-5-Carboxylates.

    Science.gov (United States)

    Achary, Raghavendra; Jung, In-A; Son, Se-Mi; Lee, Hyeon-Kyu

    2017-07-21

    A new method for the direct, stereoselective synthesis of highly functionalized 1,3-disubstituted isoindolines 6 from enantiomerically enriched cyclic 4-aryl-sulfamidate-5-carboxylates (5) is described. The process involves sulfamidate directed, Rh(III)-catalyzed tandem ortho C-H olefination of the 4-aryl-sulfamidate-5-carboxylates and subsequent cyclization by aza-Michael addition. In the reaction, which generates trans-1,3-disubstituted isoindolines exclusively, the configurational integrity of the stereogenic center in the starting cyclic sulfamidate is completely retained in the product. Examples are provided which show that the cyclic sulfamidate moiety not only serves as a chiral directing group but also as a versatile handle for further functionalization of the generated isoindoline ring system.

  4. Intramolecular energy transfer and the driving mechanisms for large-amplitude collective motions of clusters

    Science.gov (United States)

    Yanao, Tomohiro; Koon, Wang Sang; Marsden, Jerrold E.

    2009-04-01

    This paper uncovers novel and specific dynamical mechanisms that initiate large-amplitude collective motions in polyatomic molecules. These mechanisms are understood in terms of intramolecular energy transfer between modes and driving forces. Structural transition dynamics of a six-atom cluster between a symmetric and an elongated isomer is highlighted as an illustrative example of what is a general message. First, we introduce a general method of hyperspherical mode analysis to analyze the energy transfer among internal modes of polyatomic molecules. In this method, the (3n-6) internal modes of an n-atom molecule are classified generally into three coarse level gyration-radius modes, three fine level twisting modes, and (3n-12) fine level shearing modes. We show that a large amount of kinetic energy flows into the gyration-radius modes when the cluster undergoes structural transitions by changing its mass distribution. Based on this fact, we construct a reactive mode as a linear combination of the three gyration-radius modes. It is shown that before the reactive mode acquires a large amount of kinetic energy, activation or inactivation of the twisting modes, depending on the geometry of the isomer, plays crucial roles for the onset of a structural transition. Specifically, in a symmetric isomer with a spherical mass distribution, activation of specific twisting modes drives the structural transition into an elongated isomer by inducing a strong internal centrifugal force, which has the effect of elongating the mass distribution of the system. On the other hand, in an elongated isomer, inactivation of specific twisting modes initiates the structural transition into a symmetric isomer with lower potential energy by suppressing the elongation effect of the internal centrifugal force and making the effects of the potential force dominant. This driving mechanism for reactions as well as the present method of hyperspherical mode analysis should be widely applicable to

  5. Short Intramolecular N–H⋯C(carbonyl Interactions in Mixed-Ligand Molybdenum Hexacarbonyl Derivatives

    Directory of Open Access Journals (Sweden)

    Matthew G. Budge

    2011-06-01

    Full Text Available The syntheses and single-crystal structures of Mo(CO3(phen(dipy (1, Mo(CO3(biquin(dipy (2 and Mo(CO3(dpme(dipy (3, (phen = 1,10-phenanthroline, C12H8N2; dipy = 2,2'-dipyridylamine, C10H9N3; biquin = 2,2'-biquinoline, C18H12N2; dpme = 2,2'-dipyridylmethane, C11H10N2 are described. In each case, distorted fac-MoC3N3 octahedral coordination geometries arise for the metal atoms. Short intramolecular N–H…C interactions from the dipy N–H group to a carbonyl carbon atom occur in each structure. Crystal data: 1 (C25H17MoN5O3, Mr = 531.38, monoclinic, P21/n (No. 14, Z = 4, a = 11.0965 (5 Å, b = 13.0586 (6 Å, c = 16.6138 (8 Å, b = 108.324 (1°, V = 2285.31 (18 Å3, R(F = 0.035, wR(F2 = 0.070. 2 (C31H21MoN5O3, Mr = 607.47, monoclinic, P21/n (No. 14, Z = 4, a = 11.4788 (6 Å, b = 19.073 (1 Å, c = 11.9881 (6 Å, b = 95.179 (1°, V = 2613.9 (2 Å3, R(F = 0.030, wR(F2 = 0.076. 3 (C24H19MoN5O3, Mr = 521.38, monoclinic, P21/n (No. 14, Z = 4, a = 8.4222 (3 Å, b = 21.5966 (9 Å, c = 12.5011 (5 Å, b = 94.065 (1°, V = 2268.12 (15 Å3, R(F = 0.025, wR(F2 = 0.065.

  6. Euglena gracilis ascorbate peroxidase forms an intramolecular dimeric structure: its unique molecular characterization.

    Science.gov (United States)

    Ishikawa, Takahiro; Tajima, Naoko; Nishikawa, Hitoshi; Gao, Yongshun; Rapolu, Madhusudhan; Shibata, Hitoshi; Sawa, Yoshihiro; Shigeoka, Shigeru

    2010-02-09

    Euglena gracilis lacks a catalase and contains a single APX (ascorbate peroxidase) and enzymes related to the redox cycle of ascorbate in the cytosol. In the present study, a full-length cDNA clone encoding the Euglena APX was isolated and found to contain an open reading frame encoding a protein of 649 amino acids with a calculated molecular mass of 70.5 kDa. Interestingly, the enzyme consisted of two entirely homologous catalytic domains, designated APX-N and APX-C, and an 102 amino acid extension in the N-terminal region, which had a typical class II signal proposed for plastid targeting in Euglena. A computer-assisted analysis indicated a novel protein structure with an intramolecular dimeric structure. The analysis of cell fractionation showed that the APX protein is distributed in the cytosol, but not the plastids, suggesting that Euglena APX becomes mature in the cytosol after processing of the precursor. The kinetics of the recombinant mature FL (full-length)-APX and the APX-N and APX-C domains with ascorbate and H2O2 were almost the same as that of the native enzyme. However, the substrate specificity of the mature FL-APX and the native enzyme was different from that of APX-N and APX-C. The mature FL-APX, but not the truncated forms, could reduce alkyl hydroperoxides, suggesting that the dimeric structure is correlated with substrate recognition. In Euglena cells transfected with double-stranded RNA, the silencing of APX expression resulted in a significant increase in the cellular level of H2O2, indicating the physiological importance of APX to the metabolism of H2O2.

  7. Microsolvation and the Effects of Non-Covalent Interactions on Intramolecular Dynamics

    Science.gov (United States)

    Foguel, Lidor; Vealey, Zachary; Vaccaro, Patrick

    2017-06-01

    Physicochemical processes brought about by non-covalent interactions between neighboring molecules are undeniably of crucial importance in the world around us, being responsible for effects ranging from the subtle (yet precise) control of biomolecular recognition events to the very existence of condensed phases. Of particular interest is the differential ability of distinct non-covalent forces, such as those mediated by dispersion-dominated aryl (π-π) coupling and electrostatically-driven hydrogen bonding, to affect unimolecular transformations by altering potential surface topographies and the nature of reaction coordinates. A concerted experimental and computational investigation of "microsolvation" (solvation at the molecular level) has been undertaken to elucidate the site-specific coupling between solute and solvent degrees of freedom, as well as attendant consequences for the efficiency and pathway of intrinsic proton-transfer dynamics. Targeted species have been synthesized in situ under "cold" supersonic free-jet expansion conditions (T_{rot} ≈ 1-2K) by complexing an active (proton-transfer) substrate with various ligands (e.g., water isotopologs and benzene derivatives) for which competing interaction mechanisms can lead to unique binding motifs. A series of fluorescence-based spectroscopic measurements have been performed on binary adducts formed with the prototypical 6-hydroxy-2-formylfulvene (HFF) system, where a quasi-linear intramolecular O-H...O bond and a zero-point energy that straddles the proton-transfer barrier crest synergistically yield the largest tunneling-induced splitting ever reported for the ground electronic state of an isolated neutral molecule. Such characteristics afford a localized metric for unraveling incipient changes in unimolecular reactivity, with comparison of experimentally observed and quantum-chemical predicted rovibronic landscapes serving to discriminate complexes built upon electrostatic (hydrogen-bonding) and

  8. Excited state intramolecular charge transfer reaction in nonaqueous electrolyte solutions: temperature dependence.

    Science.gov (United States)

    Pradhan, Tuhin; Gazi, Harun Al Rasid; Biswas, Ranjit

    2009-08-07

    Temperature dependence of the excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) in ethyl acetate (EA), acetonitrile (ACN), and ethanol at several concentrations of lithium perchlorate (LiClO(4)) has been investigated by using the steady state and time resolved fluorescence spectroscopic techniques. The temperature range considered is 267-343 K. The temperature dependent spectral peak shifts and reaction driving force (-DeltaG(r)) in electrolyte solutions of these solvents can be explained qualitatively in terms of interaction between the reactant molecule and ion-atmosphere. Time resolved studies indicate that the decay kinetics of P4C is biexponential, regardless of solvents, LiClO(4) concentrations, and temperatures considered. Except at higher electrolyte concentrations in EA, reaction rates in solutions follow the Arrhenius-type temperature dependence where the estimated activation energy exhibits substantial electrolyte concentration dependence. The average of the experimentally measured activation energies in these three neat solvents is found to be in very good agreement with the predicted value based on data in room temperature solvents. While the rate constant in EA shows a electrolyte concentration induced parabolic dependence on reaction driving force (-DeltaG(r)), the former in ethanol and ACN increases only linearly with the increase in driving force (-DeltaG(r)). The data presented here also indicate that the step-wise increase in solvent reorganization energy via sequential addition of electrolyte induces the ICT reaction in weakly polar solvents to crossover from the Marcus inverted region to the normal region.

  9. Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

    Energy Technology Data Exchange (ETDEWEB)

    Barnes, J. C.; Fahrenbach, A. C.; Dyar, S. M.; Frasconi, M.; Giesener, M. A.; Zhu, Z.; Liu, Z.; Hartlieb, K. J.; Carmieli, R.; Wasielewski, M. R.; Stoddart, J. F.

    2012-06-08

    The kinetics and thermodynamics of intramolecular electron transfer (IET) can be subjected to redox control in a bistable [2]rotaxane comprised of a dumbbell component containing an electron-rich 1,5-dioxynaphthalene (DNP) unit and an electron-poor phenylene-bridged bipyridinium (P-BIPY2+) unit and a cyclobis (paraquat-p-phenylene) (CBPQT4+) ring component. The [2]rotaxane exists in the ground-state co-conformation (GSCC) wherein the CBPQT4+ ring encircles the DNP unit. Reduction of the CBPQT4+ leads to the CBPQT2(•+) diradical dication while the P-BIPY2+ unit is reduced to its P-BIPY•+ radical cation. A radical-state co-conformation (RSCC) results from movement of the CBPQT2(•+) ring along the dumbbell to surround the P-BIPY•+ unit. This shuttling event induces IET to occur between the pyridinium redox centers of the P-BIPY•+ unit, a property which is absent between these redox centers in the free dumbbell and in the 1:1 complex formed between the CBPQT2(•+) ring and the radical cation of methyl-phenylene-viologen (MPV•+). Using electron paramagnetic resonance (EPR) spectroscopy, the process of IET was investigated by monitoring the line broadening at varying temperatures and determining the rate constant (kET = 1.33 × 107 s-1) and activation energy (ΔG‡ = 1.01 kcal mol-1) for electron transfer. These values were compared to the corresponding values predicted, using the optical absorption spectra and Marcus–Hush theory.

  10. Weak intramolecular interaction effects on the torsional spectra of ethylene glycol, an astrophysical species

    Energy Technology Data Exchange (ETDEWEB)

    Boussessi, R., E-mail: rahma.boussesi@iem.cfmac.csic.es [Departamento de Química y Física Teóricas, I. Estructura de la Materia, IEM-CSIC, Serrano 121, Madrid 28006 (Spain); Laboratoire de Spectroscopie Atomique, Moléculaire et Applications-LSAMA LR01ES09, Faculté des sciences de Tunis, Université de Tunis El Manar, 2092 Tunis (Tunisia); Senent, M. L., E-mail: ml.senent@csic.es [Departamento de Química y Física Teóricas, I. Estructura de la Materia, IEM-CSIC, Serrano 121, Madrid 28006 (Spain); Jaïdane, N. [Laboratoire de Spectroscopie Atomique, Moléculaire et Applications-LSAMA LR01ES09, Faculté des sciences de Tunis, Université de Tunis El Manar, 2092 Tunis (Tunisia)

    2016-04-28

    An elaborate variational procedure of reduced dimensionality based on explicitly correlated coupled clusters calculations is applied to understand the far infrared spectrum of ethylene-glycol, an astrophysical species. This molecule can be classified in the double molecular symmetry group G{sub 8} and displays nine stable conformers, gauche and trans. In the gauche region, the effect of the potential energy surface anisotropy due to the formation of intramolecular hydrogen bonds is relevant. For the primary conformer, stabilized by a hydrogen bond, the ground vibrational state rotational constants are computed to be A{sub 0} = 15 369.57 MHz, B{sub 0} = 5579.87 MHz, and C{sub 0} = 4610.02 MHz corresponding to differences of 6.3 MHz, 7.2 MHz, and 3.5 MHz from the experimental parameters. Ethylene glycol displays very low torsional energy levels whose classification is not straightforward and requires a detailed analysis of the torsional wavefunctions. Tunneling splittings are significant and unpredictable due to the anisotropy of the potential energy surface PES. The ground vibrational state splits into 16 sublevels separated ∼142 cm{sup −1}. The splitting of the “G1 sublevels” was calculated to be ∼0.26 cm{sup −1} in very good agreement with the experimental data (0.2 cm{sup −1} = 6.95 MHz). Transitions corresponding to the three internal rotation modes allow assignment of previously observed Q branches. Band patterns, calculated between 362.3 cm{sup −1} and 375.2 cm{sup −1}, 504 cm{sup −1} and 517 cm{sup −1}, and 223.3 cm{sup −1} and 224.1 cm{sup −1}, that correspond to the tunnelling components of the v{sub 21} fundamental (v{sub 21} = OH-torsional mode), are assigned to the prominent experimental Q branches.

  11. Synthesis and characterization of cyclic polystyrene using copper-catalyzed alkyne-azide cycloaddition coupling - evaluation of physical properties and optimization of cyclization conditions

    Science.gov (United States)

    Elupula, Ravinder

    Polymers with a cyclic topology exhibit a range of unique and potentially useful physical properties, including reduced rates of degradation and increased rates of diffusion in bulk relative to linear analogs. However the synthesis of high purity cyclic polymers, and verification of their structural purity remains challenging. The copper-catalyzed azide-alkyne "click" cyclization route toward cyclic polymers has been used widely, due to its synthetic ease and its compatibility with diverse polymer backbones. Yet unoptimized click cyclization conditions have been observed to generate oligomeric byproducts. In order to optimize these cyclization conditions, and to better understand the structure of the higher molecular weight oligomers, these impurities have been isolated by size exclusion chromatography (SEC) and characterized by mass spectrometry (MS). Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-ToF) MS is a particularly valuable characterization tool and was used to determine that the high molecular weight impurities are predominantly cyclic oligomers. It should also be noted that the rapid analysis and small analyte requirements of this MS technique make it particularly attractive as a general tool for elucidating polymer architecture. Ability to tailor the physical properties of polymers by changing the architecture alone has garnered a lot of attention over the past few decades. Compared to their linear analogues, these novel polymer architectures behave completely different in nanoscale regime. Cyclic polymers are especially intriguing since we can compare the differences in the physical properties with that of the linear chains. One of the major physical property changes are T g-confinement effect. Using ATRP and "click chemistry" we have produced highly pure cyclic PS (c-PS) with number-average molecular weight (MW) of 3.4 kg/mol and 9.1 kg/mol. Bulk glass transition temperatures for c-PS were weakly depended on MWs

  12. An Efficient Synthesis of 1-Alkyl-2-phenyl-4-quinolones from 2-Halobenzoic Acids

    International Nuclear Information System (INIS)

    Song, Yoon Ju; Choi, Jin Sun; Lee, Jae In

    2013-01-01

    The present method offers an efficient synthesis of 1-alkyl-2-phenyl-4-quinolones from 2-haloben-zoic acids. It has the advantages with respect to (i) synthesis of 2 equiv of alkynones 5 from 1 equiv of 4,6-pyrimidyl di(2-halobenzoates) 3, (ii) synthesis of versatile 1-alkyl-2-phenyl-4-quinolones in high overall yields, and (iii) use of readily available and cheap starting materials. Therefore, this method could be utilized as a practical synthesis of 1-alkyl-2-phenyl-4-quinolones. Several methods have been developed to synthesize 1-alkyl-2-phenyl-4-quinolones from 2'-substituted acetophenones, anilines, and 2-halobenzoyl chlorides as starting materials. The reaction of N-methylisatoic anhydride with the lithium enolate of an 4'-methoxyacetophenone afforded the 1-methyl-2-phenyl-4-quinolone in a short sequence, but the yield was low. N-(2-Acetylphenyl)benzamides, prepared by Friedel-Crafts acylation of N-phenyl benzamides with acetyl chloride or benzoylation of 2'-aminoacetophenones with benzoyl chlorides,8 were cyclized with potassium t-butoxide to yield 2-aryl-4-quinolones, which were further alkylated with alkyl iodides to give 1-alkyl-2-aryl-4-quinolones

  13. Tunable excited-state intramolecular proton transfer reactions with Nsbnd H or Osbnd H as a proton donor: A theoretical investigation

    Science.gov (United States)

    Li, Yuanyuan; Wen, Keke; Feng, Songyan; Yuan, Huijuan; An, Beibei; Zhu, Qiuling; Guo, Xugeng; Zhang, Jinglai

    2017-12-01

    Excited-state intramolecular proton transfer (ESIPT) reactions occurring in the S1 state for five molecules, which possess five/six-membered ring intramolecular Nsbnd H···N or Osbnd H···N hydrogen bonds bearing quinoline or 2-phenylpyridine moiety, have been described in detail by the time-dependent density functional theory (TD-DFT) approach using the B3LYP hybrid functional. For the five molecules, the constrained potential energy profiles along the ESIPT reactions show that proton transfer is barrierless in molecules possessing six-membered ring intramolecular H-bonds, which is smoother than that with certain barriers in five-membered ring H-bonding systems. For the latter, chemical modification by a more strong acid group can lower the ESIPT barrier significantly, which harnesses the ESIPT reaction from a difficult type to a fast one. The energy barrier of the ESIPT reaction depends on the intensity of the intramolecular H-bond, which can be measured with the topological descriptors by topology analysis of the bond critical point (BCP) of the intramolecular H-bond. It is found that when the value of electron density ρ(r) at BCP is bigger than 0.025 a.u., the corresponding molecule might go through an ultrafast and barrierless ESIPT process, which opens a new scenario to explore the ESIPT reactions.

  14. EL APRENDIZAJE DE LOS CONCEPTOS DE FUERZAS INTERMOLECULARES E INTRAMOLECULARES MEDIANTE LA MODELIZACIÓN DIDÁCTICA

    OpenAIRE

    CHRISTIAN FERNNEY GIRALDO MACÍAS

    2013-01-01

    La modelización está siendo usada para la enseñanza y el aprendizaje en las Ciencias Naturales en diferentes contextos y para atender a diferentes problemáticas. En este caso será utilizada para explorar y analizar la relevancia que puede tener su uso en el aprendizaje de los conceptos Fuerzas Intramoleculares e Intermolecualres, partiendo de la aplicación de una serie de actividades basadas en el Ciclo Didáctico (Jorba y Sanmartí, 1996). Los datos se discuten mediante tres aspectos principal...

  15. Effect of structural changes in sesquifulvalene on the intramolecular charge transfer and nonlinear polarizations a theoretical study

    Science.gov (United States)

    Nandi, P. K.; Mandal, K.; Kar, T.

    2003-11-01

    Ab initio HF calculations of the ground state structural parameters, and the time dependent HF (TDHF) calculations of static nonlinear polarizabilities have been performed for a number of sesquifulvalene derivatives. The calculated NLO parameters show a good correlation with the hardness parameters. The nature of hetero-atoms and their positions can strongly influence the intramolecular charge transfer (ICT) interactions and the nonlinear polarizations of sesquifulvalene. Nonlinear polarizabilities in the twisted structures have been found to depend both on the energy barrier to twist and the transition energy corresponding to the twisted ICT (TICT) state characterized by the HOMO → LUMO transition.

  16. Tandem cross enyne metathesis (CEYM–intramolecular Diels–Alder reaction (IMDAR. An easy entry to linear bicyclic scaffolds

    Directory of Open Access Journals (Sweden)

    Javier Miró

    2015-08-01

    Full Text Available A new tandem cross enyne metathesis (CEYM–intramolecular Diels–Alder reaction (IMDAR has been carried out. It involves conjugated ketones, esters or amides bearing a remote olefin and aromatic alkynes as the starting materials. The overall process enables the preparation of a small family of linear bicyclic scaffolds in a very simple manner with moderate to good levels of diastereoselectivity. This methodology constitutes one of the few examples that employ olefins differently than ethylene in tandem CEYM–IMDAR protocols.

  17. Pd(II)-catalyzed ortho-hydroxylation and intramolecular oxidative C-C coupling of N- benzylbenzene sulfonamides

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, Eun Joo; Jo, Yoon Hyung; Jang, Min Jung; Youn, So Won [Dept. of Chemistry and Research Institute for Natural Sciences, Center for New Directions in Organic Synthesis, Hanyang University, Seoul (Korea, Republic of)

    2015-02-15

    We reported highly effective Pd-catalyzed C-C and/or C-N bond formations via C-H activation of aniline derivatives. Considering the lack of regioselective C(sp{sup 2}) H hydroxylation of benzylamines, our continued interest in Pd-catalyzed C-H bond functionalization prompted us to investigate the possibility of a Pd-catalyzed ortho-hydroxylation of NH-containing benzylamines. We have developed the Pd-catalyzed ortho-hydroxylation and/or intramolecular oxidative C-C coupling of N-benzyl sulfonamides, which operate through two different postulated mechanistic routes, as depicted in Scheme 2, depending on the reaction conditions.

  18. Unprecedented twofold intramolecular hydroamination in diam(m)ine-dicarboxylatodichloridoplatinum(IV) complexes - ethane-1,2-diamine vs. ammine ligands.

    Science.gov (United States)

    Reithofer, Michael R; Galanski, Markus; Arion, Vladimir B; Keppler, Bernhard K

    2008-03-07

    Reaction of (OC-6-13)-bis(2Z-3-carboxyacrylato)dichlorido(ethane-1,2-diamine)platinum(IV) and (OC-6-13)-diamminebis(2Z-3-carboxyacrylato)dichloridoplatinum(IV) with propylamine in the presence of 1,1'-carbonyl diimidazole afforded not the expected amides; instead, beside amide formation, a twofold intramolecular attack of the am(m)ine ligand at the C[double bond, length as m-dash]C bonds was observed involving either both (ethane-1,2-diamine) or only one (ammine) coordinated nitrogen atom(s).

  19. Probe development for detection of TERRA 1 intramolecular G-quadruplex formation using a fluorescent adenosine derivative.

    Science.gov (United States)

    Kim, In Sun; Seo, Young Jun

    2014-03-15

    We developed a probing system to detect the intramolecular G-quadruplex of telomeric repeat-containing RNA (TERRA 1). We used a fluorescent adenosine derivative rA(py) as a fluorophore and incorporated it into the dangling position of the parallel-type G-quadruplex sequence of TERRA 1. The rA(py)-modified G-quadruplex structure exhibited a strong fluorescence emission signal, while the emission signals of the single-strand and duplex structures were much lower. Copyright © 2014 Elsevier Ltd. All rights reserved.

  20. A classical trajectory study of the intramolecular dynamics, isomerization, and unimolecular dissociation of HO2.

    Science.gov (United States)

    Perry, Jamin W; Dawes, Richard; Wagner, Albert F; Thompson, Donald L

    2013-08-28

    The classical dynamics and rates of isomerization and dissociation of HO2 have been studied using two potential energy surfaces (PESs) based on interpolative fittings of ab initio data: An interpolative moving least-squares (IMLS) surface [A. Li, D. Xie, R. Dawes, A. W. Jasper, J. Ma, and H. Guo, J. Chem. Phys. 133, 144306 (2010)] and the cubic-spline-fitted PES reported by Xu, Xie, Zhang, Lin, and Guo (XXZLG) [J. Chem. Phys. 127, 024304 (2007)]. Both PESs are based on similar, though not identical, internally contracted multi-reference configuration interaction with Davidson correction (icMRCI+Q) electronic structure calculations; the IMLS PES includes complete basis set (CBS) extrapolation. The coordinate range of the IMLS PES is limited to non-reactive processes. Surfaces-of-section show similar generally regular phase space structures for the IMLS and XXZLG PESs with increasing energy. The intramolecular vibrational energy redistribution (IVR) at energies above and below the threshold of isomerization is slow, especially for O-O stretch excitations, consistent with the regularity in the surfaces-of-section. The slow IVR rates lead to mode-specific effects that are prominent for isomerization (on both the IMLS and XXZLG) and modest for unimolecular dissociation to H + O2 (accessible only on the XXZLG PES). Even with statistical distributions of initial energy, slow IVR rates result in double exponential decay for isomerization, with the slower rate correlated with slow IVR rates for O-O vibrational excitation. The IVR and isomerization rates computed for the IMLS and XXZLG PESs are quantitatively, but not qualitatively, different from one another with the largest differences ascribed to the ~2 kcal/mol difference in the isomerization barrier heights. The IMLS and XXZLG results are compared with those obtained using the global, semi-empirical double-many-body expansion DMBE-IV PES [M. R. Pastrana, L. A. M. Quintales, J. Brandão, and A. J. C. Varandas, J. Chem

  1. Relaxation dynamics in quantum dissipative systems: The microscopic effect of intramolecular vibrational energy redistribution

    Energy Technology Data Exchange (ETDEWEB)

    Uranga-Piña, L. [Facultad de Física, Universidad de la Habana, San Lázaro y L, Vedado, 10400 Havana (Cuba); Institute for Chemistry and Biochemistry, Freie Universität Berlin, Takustr. 3, D-14195 Berlin (Germany); Tremblay, J. C., E-mail: jean.c.tremblay@gmail.com [Institute for Chemistry and Biochemistry, Freie Universität Berlin, Takustr. 3, D-14195 Berlin (Germany)

    2014-08-21

    We investigate the effect of inter-mode coupling on the vibrational relaxation dynamics of molecules in weak dissipative environments. The simulations are performed within the reduced density matrix formalism in the Markovian regime, assuming a Lindblad form for the system-bath interaction. The prototypical two-dimensional model system representing two CO molecules approaching a Cu(100) surface is adapted from an ab initio potential, while the diatom-diatom vibrational coupling strength is systematically varied. In the weak system-bath coupling limit and at low temperatures, only first order non-adiabatic uni-modal coupling terms contribute to surface-mediated vibrational relaxation. Since dissipative dynamics is non-unitary, the choice of representation will affect the evolution of the reduced density matrix. Two alternative representations for computing the relaxation rates and the associated operators are thus compared: the fully coupled spectral basis, and a factorizable ansatz. The former is well-established and serves as a benchmark for the solution of Liouville-von Neumann equation. In the latter, a contracted grid basis of potential-optimized discrete variable representation is tailored to incorporate most of the inter-mode coupling, while the Lindblad operators are represented as tensor products of one-dimensional operators, for consistency. This procedure results in a marked reduction of the grid size and in a much more advantageous scaling of the computational cost with respect to the increase of the dimensionality of the system. The factorizable method is found to provide an accurate description of the dissipative quantum dynamics of the model system, specifically of the time evolution of the state populations and of the probability density distribution of the molecular wave packet. The influence of intra-molecular vibrational energy redistribution appears to be properly taken into account by the new model on the whole range of coupling strengths. It

  2. The effect of intramolecular donor–acceptor moieties with donor–π-bridge–acceptor structure on the solar photovoltaic performance

    Directory of Open Access Journals (Sweden)

    T. L. Wang

    2015-10-01

    Full Text Available A series of intramolecular donor–acceptor polymers containing different contents of (E-1-(2-ethylhexyl-6,9-dioctyl-2-(2-(thiophen-3-ylvinyl-1H-phenanthro[9,10-d]imidazole (thiophene-DOPI moiety and 4,4-diethylhexylcyclopenta[ 2,1-b:3,4-b']dithiophene (CPDT unit was synthesized via Grignard metathesis (GRIM polymerization. The synthesized random copolymers and homopolymer of thiophene-DOPI contain the donor–π-bridge–acceptor conjugated structure to tune the absorption spectra and energy levels of the resultant polymers. UV-vis spectra of the three polymer films exhibit panchromatic absorptions ranging from 300 to 1100 nm and low band gaps from 1.38 to 1.51 eV. It is found that more thiophene-DOPI moieties result in the decrease of band gap and lower the highest occupied molecular orbital (HOMO and lowest unoccupied molecular orbital (LUMO values of polymers. Photovoltaic performance results indicate that if the content of the intramolecular donor–acceptor moiety is high enough, the copolymer structure may be better than homopolymer due to more light-harvesting afforded by both monomer units.

  3. Intramolecular Immunological Signal Hypothesis Revived - Structural Background of Signalling Revealed by Using Congo Red as a Specific Tool

    Science.gov (United States)

    Jagusiak, A.; Konieczny, L.; Król, M.; Marszałek, P.; Piekarska, B.; Piwowar, P.; Roterman, I.; Rybarska, J.; Stopa, B.; Zemanek, G.

    2014-01-01

    Micellar structures formed by self-assembling Congo red molecules bind to proteins penetrating into functionrelated unstable packing areas. Here, we have used Congo red - a supramolecular protein ligand to investigate how the intramolecular structural changes that take place in antibodies following antigen binding lead to complement activation. According to our findings, Congo red binding significantly enhances the formation of antigen-antibody complexes. As a result, even low-affinity transiently binding antibodies can participate in immune complexes in the presence of Congo red, although immune complexes formed by these antibodies fail to trigger the complement cascade. This indicates that binding of antibodies to the antigen may not, by itself, fulfill the necessary conditions to generate the signal which triggers effector activity. These findings, together with the results of molecular dynamics simulation studies, enable us to conclude that, apart from the necessary assembling of antibodies, intramolecular structural changes generated by strains which associate high- affinity bivalent antibody fitting to antigen determinants are also required to cross the complement activation threshold. PMID:25429660

  4. Intramolecular immunological signal hypothesis revived--structural background of signalling revealed by using Congo Red as a specific tool.

    Science.gov (United States)

    Jagusiak, A; Konieczny, L; Krol, M; Marszalek, P; Piekarska, B; Piwowar, P; Roterman, I; Rybarska, J; Stopa, B; Zemanek, G

    2015-01-01

    Micellar structures formed by self-assembling Congo red molecules bind to proteins penetrating into function-related unstable packing areas. Here, we have used Congo red--a supramolecular protein ligand--to investigate how the intramolecular structural changes that take place in antibodies following antigen binding lead to complement activation. According to our findings, Congo red binding significantly enhances the formation of antigen-antibody complexes. As a result, even low-affinity transiently binding antibodies can participate in immune complexes in the presence of Congo red, although immune complexes formed by these antibodies fail to trigger the complement cascade. This indicates that binding of antibodies to the antigen may not, by itself, fulfill the necessary conditions to generate the signal which triggers effector activity. These findings, together with the results of molecular dynamics simulation studies, enable us to conclude that, apart from the necessary assembling of antibodies, intramolecular structural changes generated by strains which associate high- affinity bivalent antibody fitting to antigen determinants are also required to cross the complement activation threshold.

  5. Molecular simulation of caloric properties of fluids modelled by force fields with intramolecular contributions: Application to heat capacities

    Science.gov (United States)

    Smith, William R.; Jirsák, Jan; Nezbeda, Ivo; Qi, Weikai

    2017-07-01

    The calculation of caloric properties such as heat capacity, Joule-Thomson coefficients, and the speed of sound by classical force-field-based molecular simulation methodology has received scant attention in the literature, particularly for systems composed of complex molecules whose force fields (FFs) are characterized by a combination of intramolecular and intermolecular terms. The calculation of a thermodynamic property for a system whose molecules are described by such a FF involves the calculation of the residual property prior to its addition to the corresponding ideal-gas property, the latter of which is separately calculated, either using thermochemical compilations or nowadays accurate quantum mechanical calculations. Although the simulation of a volumetric residual property proceeds by simply replacing the intermolecular FF in the rigid molecule case by the total (intramolecular plus intermolecular) FF, this is not the case for a caloric property. We describe the correct methodology required to perform such calculations and illustrate it in this paper for the case of the internal energy and the enthalpy and their corresponding molar heat capacities. We provide numerical results for cP, one of the most important caloric properties. We also consider approximations to the correct calculation procedure previously used in the literature and illustrate their consequences for the examples of the relatively simple molecule 2-propanol, CH3CH(OH)CH3, and for the more complex molecule monoethanolamine, HO(CH2)2NH2, an important fluid used in carbon capture.

  6. TDDFT study on excited state intramolecular proton transfer mechanism in 2-amino-3-(2‧-benzazolyl)-quinolines

    Science.gov (United States)

    Jia, Xueli; Li, Chaozheng; Li, Donglin; Liu, Yufang

    2018-03-01

    The intramolecular proton transfer reaction of the 2-amino-3-(2‧-benzoxazolyl)-quinoline (ABO) and 2-amino-3-(2‧-benzothiazolyl)-quinoline (ABT) molecules in both S0 and S1 states at B3LYP/6-311 ++G(d,p) level in ethanol solvent have been studied to reveal the deactivation mechanism of the tautomers of the two molecules from the S1 state to the S0 state. The results show that the tautomers of ABO and ABT molecules may return to the S0 state by emitting fluorescence. In addition, the bond lengths, angles and infrared spectra are analyzed to confirm the hydrogen bonds strengthened upon photoexcitation, which can facilitate the proton transfer process. The frontier molecular orbitals (MOs) and natural bond orbital (NBO) are also calculated to indicate the intramolecular charge transfer which can be used to explore the tendency of ESIPT reaction. The potential energy surfaces of the ABO and ABT molecules in the S0 and S1 states have been constructed. According to the energy potential barrier of 9.12 kcal/mol for ABO molecule and 5.96 kcal/mol for ABT molecule, it can be indicated that the proton transfer may occur in the S1 state.

  7. Intramolecular photoinduced proton transfer in 2-(2′-hydroxyphenyl)benzazole family: A TD-DFT quantum chemical study

    Energy Technology Data Exchange (ETDEWEB)

    Roohi, Hossein, E-mail: hroohi@guilan.ac.ir; Mohtamedifar, Nafiseh; Hejazi, Fahemeh

    2014-11-24

    Highlights: • PBE1PBE/TD method was used to study the ESIPT process in the benzazole family. • Potential energy curves in ground and excited states were calculated. • Effect of substitution in benzazole ring on the ESIPT process was investigated. • In contrast to S{sub 0} state, keto form of the molecules can be formed at the S{sub 1} state. • The photophysical properties of the compounds were calculated. - Abstract: In this work, intramolecular photoinduced proton transfer in 2-(2′-hydroxyphenyl)benzazole family (HBO, HBI and HBT) was investigated using TD-DFT calculations at PBE1PBE/6-311++G(2d,2p) level of theory. The potential energy surfaces were employed to explore the proton transfer reactions in both states. In contrast to the ground state, photoexcitation from S{sub 0} state to S{sub 1} one encourages the operation of the excited-state intramolecular proton transfer process. Structural parameters, H-bonding energy, absorption and emission bands, vertical excitation and emission energies, oscillator strength, fluorescence rate constant, dipole moment, atomic charges and electron density at critical points were calculated. Molecular orbital analysis shows that vertical S{sub 0} → S{sub 1} transition in the studied molecules corresponds essentially to the excitation from HOMO (π) to LUMO (π{sup ∗}). Our calculated results are in good agreement with the experimental observations.

  8. Síntese de novas bases de tröger, fluorescentes via transferência protônica intramolecular no estado excitado (ESIPT)

    OpenAIRE

    Carlos Alberto Miranda Abella

    2003-01-01

    Neste trabalho, realizou-se a síntese e a caracterização de quatro novas bases de Tröger. Estes compostos pertencem à classe de heterociclos 2-hidroxifenibenzazóis, que caracterizam-se por apresentar uma forte emissão de fluorescência, devido à reação de transferência protônica intramolecular no estado excitado -ESIPT- por eles sofrrida quando excitados por luz ultravioleta. Os heterociclos sintetizadosapesentam ligações de hidrogênio intramolecular entrte o nitrogênio azólico e a hidroxila f...

  9. A ruthenium(II) complex as turn-on Cu(II) luminescent sensor based on oxidative cyclization mechanism and its application in vivo

    Science.gov (United States)

    Zhang, Yunfei; Liu, Zonglun; Yang, Kui; Zhang, Yi; Xu, Yongqian; Li, Hongjuan; Wang, Chaoxia; Lu, Aiping; Sun, Shiguo

    2015-02-01

    Copper ions play a vital role in a variety of fundamental physiological processes not only in human beings and plants, but also for extensive insects and microorganisms. In this paper, a novel water-soluble ruthenium(II) complex as a turn-on copper(II) ions luminescent sensor based on o-(phenylazo)aniline was designed and synthesized. The azo group would undergo a specific oxidative cyclization reaction with copper(II) ions and turn into high luminescent benzotriazole, triggering significant luminescent increasements which were linear to the concentrations of copper(II) ions. The sensor distinguished by its high sensitivity (over 80-fold luminescent switch-on response), good selectivity (the changes of the emission intensity in the presence of other metal ions or amino acids were negligible) and low detection limit (4.42 nM) in water. Moreover, the copper(II) luminescent sensor exhibited good photostability under light irradiation. Furthermore, the applicability of the proposed sensor in biological samples assay was also studied and imaged copper(II) ions in living pea aphids successfully.

  10. Linked production of pyroglutamate-modified proteins via self-cleavage of fusion tags with TEV protease and autonomous N-terminal cyclization with glutaminyl cyclase in vivo.

    Directory of Open Access Journals (Sweden)

    Yan-Ping Shih

    Full Text Available Overproduction of N-terminal pyroglutamate (pGlu-modified proteins utilizing Escherichia coli or eukaryotic cells is a challenging work owing to the fact that the recombinant proteins need to be recovered by proteolytic removal of fusion tags to expose the N-terminal glutaminyl or glutamyl residue, which is then converted into pGlu catalyzed by the enzyme glutaminyl cyclase. Herein we describe a new method for production of N-terminal pGlu-containing proteins in vivo via intracellular self-cleavage of fusion tags by tobacco etch virus (TEV protease and then immediate N-terminal cyclization of passenger target proteins by a bacterial glutaminyl cyclase. To combine with the sticky-end PCR cloning strategy, this design allows the gene of target proteins to be efficiently inserted into the expression vector using two unique cloning sites (i.e., SnaB I and Xho I, and the soluble and N-terminal pGlu-containing proteins are then produced in vivo. Our method has been successfully applied to the production of pGlu-modified enhanced green fluorescence protein and monocyte chemoattractant proteins. This design will facilitate the production of protein drugs and drug target proteins that possess an N-terminal pGlu residue required for their physiological activities.

  11. Experimental and theoretical characterization of organic salt: 2-((4-bromophenyl)amino) pyrido[1,2-a] quinoxalin-11-ium bromide monohydrate synthesized via oxidative cyclization

    Science.gov (United States)

    Faizi, Md. Serajul Haque; Alam, Mohammad Jane; Haque, Ashanul; Ahmad, Shabbir; Shahid, M.; Ahmad, Musheer

    2018-03-01

    Quinoxalines are nitrogen-embedded heterocyclic compounds that possess unique and versatile pharmacological applications. The present article describes synthesis and characterization of organic salt 2-((4-bromophenyl)amino)pyrido [1,2-a]quinoxalin-11-ium bromide (BAPQ), an oxidative cyclized product of N-phenyl-N-(pyridine-2-ylmethylene)benzene-1,4-diamine (PPMD). The structure of the synthesized product was extensively characterized by 1H NMR, 2D-COSY NMR, MS, IR, UV-vis, X-ray techniques and elemental analysis. The electronic and structural properties of BAPQ was well complemented by performing extensive computational studies (B3LYP/6-311G (d,p) basis sets). Metal-free, mild reaction condition, easy work-up and excellent yield with high purity are main features of this work and thus holds promise for the generation of new compounds of this class. Analytical results indicated ionic nature of the compound with bromide as counterion. DFT calculation showed low kinetic stability and high reactivity of the compound.

  12. Octazethrene and Its Isomer with Different Diradical Characters and Chemical Reactivity: The Role of the Bridge Structure

    KAUST Repository

    Hu, Pan

    2016-03-11

    The fundamental relationship between structure and diradical character is important for the development of open-shell diradicaloid-based materials. In this work, we synthesized two structural isomers bearing a 2,6-naphthoquinodimethane or a 1,5-naphthoquinodimethane bridge and demonstrated that their diradical characters and chemical reactivity are quite different. The mesityl or pentafluorophenyl substituted octazethrene derivatives OZ-M/OZ-F and their isomer OZI-M (with mesityl substituents) were synthesized via an intramolecular Friedel-Crafts alkylation followed by oxidative dehydrogenation strategy from the key building blocks 4 and 11. Our detailed experimental and theoretical studies showed that both isomers have an open-shell singlet ground state with a remarkable diradical character (y0 = 0.35 and 0.34 for OZ-M and OZ-F, and y0 = 0.58 for OZI-M). Compounds OZ-M and OZ-F have good stability under the ambient environment while OZI-M has high reactivity and can be easily oxidized to a dioxo-product 15, which can be correlated to their different diradical characters. Additionally, we investigated the physical properties of OZ-M, OZ-F and 15.

  13. Synthesis of Ene-ynamide Derivatives Starting from Baylis-Hillman Adducts: Isomerization with the Aid of π-Cation Interaction

    Energy Technology Data Exchange (ETDEWEB)

    Gowrisankar, Saravanan; Lee, Ka Young; Kim, Seung Chan; Kim, Jae Nyoung [Chonnam National University, Gwangju (Korea, Republic of)

    2005-09-15

    We prepared some ene-ynamides starting from the Baylis-Hillman adducts. During the investigations, we found that π-cation interactions could increase the acidity of the nearby protons of triple bond of non-conjugated ene-ynamide and could make come true the isomerization into a more stable conjugated ene-ynamide form. Recently, we have developed a facile synthetic method of 9-phenyl-7H-benzocycloheptene derivatives from the alkynyl moiety-containing Baylis-Hillman adducts, which involved intramolecular Friedel-Crafts alkenylation reaction of triple bond-tethered methyl cinnamates. We also reported the synthesis of iodoenol lactones from the same substrates via the typical iodolactonization protocol. During the investigation we envisaged that we could prepare the corresponding lactam derivatives from the acetates of the Baylis-Hillman adducts by using similar strategy as shown in Scheme 1. However, during the investigation for the synthesis of lactam derivatives from, we found the formation of isomerized conjugated ene-ynamide derivatives unexpectedly and wish to report herein the results.

  14. Photoreactivity, Optical Behavior and DFT Studies of 2,5-Bis[4-choloro-acetyl(thiophen-2-ylmethylene)]cyclopentanone BCTCP in Different Solvents.

    Science.gov (United States)

    Hussein, M A; Osman, O I; Asiri, A M; Rozman, H D; El-Daly, S A

    2017-05-01

    Diarylidenecyclopentanone compound namely, 2,5-bis[4-choloroacetyl-(thiophen-2-ylmethylene)]cyclopentanone (BCTCP) was firstly synthesized using the normal condition of Friedel-Crafts method by reacting 2,5-bis(thiophen-2-ylmethylene)cyclopentanone (BTCP) with chloroacetyl chloride in the presence of aluminum chloride anhydrous. The structure of this compound was confirmed by elemental and spectral analyses including FT-IR, 1 H-NMR, 13 C-NMR and mass spectrometry. The electronic absorption and emission properties of BCTCP were studied in different solvents. BCTCP displays a slight solvatochromic effect of the absorption and emission spectrum, indicating a small change in dipole moment of BCTCP upon excitation. BCTCP displayed photodecomposition in chlorinated solvents upon irradiating with 365 nm light. Ground and excited states electronic geometric optimizations were performed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively. A DFT natural bond orbital (NBO) analysis complemented the intramolecular charge transfer (ICT). The simulated maximum absorption and emission wavelengths are in line the observed ones in trend, and were proportionally red-shifted with the increase of the solvent polarity. The stability, hardness and electrophilicity of BCTCP in different solvents were correlated with the polarity of the elected solvents.

  15. Evolutionary importance of the intramolecular pathways of hydrolysis of phosphate ester mixed anhydrides with amino acids and peptides.

    Science.gov (United States)

    Liu, Ziwei; Beaufils, Damien; Rossi, Jean-Christophe; Pascal, Robert

    2014-12-11

    Aminoacyl adenylates (aa-AMPs) constitute essential intermediates of protein biosynthesis. Their polymerization in aqueous solution has often been claimed as a potential route to abiotic peptides in spite of a highly efficient CO2-promoted pathway of hydrolysis. Here we investigate the efficiency and relevance of this frequently overlooked pathway from model amino acid phosphate mixed anhydrides including aa-AMPs. Its predominance was demonstrated at CO2 concentrations matching that of physiological fluids or that of the present-day ocean, making a direct polymerization pathway unlikely. By contrast, the occurrence of the CO2-promoted pathway was observed to increase the efficiency of peptide bond formation owing to the high reactivity of the N-carboxyanhydride (NCA) intermediate. Even considering CO2 concentrations in early Earth liquid environments equivalent to present levels, mixed anhydrides would have polymerized predominantly through NCAs. The issue of a potential involvement of NCAs as biochemical metabolites could even be raised. The formation of peptide-phosphate mixed anhydrides from 5(4H)-oxazolones (transiently formed through prebiotically relevant peptide activation pathways) was also observed as well as the occurrence of the reverse cyclization process in the reactions of these mixed anhydrides. These processes constitute the core of a reaction network that could potentially have evolved towards the emergence of translation.

  16. Evolutionary Importance of the Intramolecular Pathways of Hydrolysis of Phosphate Ester Mixed Anhydrides with Amino Acids and Peptides

    Science.gov (United States)

    Liu, Ziwei; Beaufils, Damien; Rossi, Jean-Christophe; Pascal, Robert

    2014-12-01

    Aminoacyl adenylates (aa-AMPs) constitute essential intermediates of protein biosynthesis. Their polymerization in aqueous solution has often been claimed as a potential route to abiotic peptides in spite of a highly efficient CO2-promoted pathway of hydrolysis. Here we investigate the efficiency and relevance of this frequently overlooked pathway from model amino acid phosphate mixed anhydrides including aa-AMPs. Its predominance was demonstrated at CO2 concentrations matching that of physiological fluids or that of the present-day ocean, making a direct polymerization pathway unlikely. By contrast, the occurrence of the CO2-promoted pathway was observed to increase the efficiency of peptide bond formation owing to the high reactivity of the N-carboxyanhydride (NCA) intermediate. Even considering CO2 concentrations in early Earth liquid environments equivalent to present levels, mixed anhydrides would have polymerized predominantly through NCAs. The issue of a potential involvement of NCAs as biochemical metabolites could even be raised. The formation of peptide-phosphate mixed anhydrides from 5(4H)-oxazolones (transiently formed through prebiotically relevant peptide activation pathways) was also observed as well as the occurrence of the reverse cyclization process in the reactions of these mixed anhydrides. These processes constitute the core of a reaction network that could potentially have evolved towards the emergence of translation.

  17. Characterization by time-resolved UV/Vis and infrared absorption spectroscopy of an intramolecular charge-transfer state in an organic electron-donor-bridge-acceptor system

    NARCIS (Netherlands)

    Hviid, L.; Verhoeven, J.W.; Brouwer, A.M.; Paddon-Row, M.N.; Yang, J.

    2004-01-01

    A long-lived intramolecular charge-separated state in an electron-donor-acceptor molecule is characterized by time-resolved visible and infrared absorption spectroscopy. Bands that can be assigned to the negatively charged acceptor chromophore can be clearly observed in the time-resolved IR

  18. Cobalt-Porphyrin-Catalysed Intramolecular Ring-Closing C-H Amination of Aliphatic Azides: A Nitrene-Radical Approach to Saturated Heterocycles

    NARCIS (Netherlands)

    Kuijpers, P.F.; Tiekink, M.J.; Breukelaar, W.B.; Broere, D.L.J.; van Leest, N.P.; van der Vlugt, J.I.; Reek, J.N.H.; de Bruin, B.

    2017-01-01

    Cobalt-porphyrin-catalysed intramolecular ring-closing C−H bond amination enables direct synthesis of various N-heterocycles from aliphatic azides. Pyrrolidines, oxazolidines, imidazolidines, isoindolines and tetrahydroisoquinoline can be obtained in good to excellent yields in a single reaction

  19. Discovery of molluscicidal and cercaricidal activities of 3-substituted quinazolinone derivatives by a scaffold hopping approach using a pseudo-ring based on the intramolecular hydrogen bond formation.

    Science.gov (United States)

    Guo, Wei; Zheng, Lv-Yin; Li, Yong-Dong; Wu, Ren-Miao; Chen, Qiang; Yang, Ding-Qiao; Fan, Xiao-Lin

    2016-06-10

    Discovery of novel topological agents against Oncomelania hupensis snails and cercariae remains a significant challenge in current Schistosomiasis control. A pseudo-ring formed from salicylanilide by an intramolecular hydrogen bond led to the discovery of 3-substituted quinazolinone derivatives which showed a potent molluscicidal and cercaricidal activities. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

  20. Diastereoselective Synthesis of Novel Heterocyclic Scaffolds through Tandem Petasis 3-Component/Intramolecular Diels-Alder and ROM-RCM Reactions

    DEFF Research Database (Denmark)

    Ishøy, Mette; Petersen, Rico; Petersen, Michael Åxman

    2017-01-01

    A high-yielding, stereoselective and extraordinarily complexity generatingPetasis 3-component/intramolecular Diels-Alderreaction has been developed. In combination with ROM-RCM, rapid access to complex sp3-rich heterocyclic scaffolds amenableto subsequent functionalization and library synthesis...

  1. Photoinduced Ultrafast Intramolecular Excited-State Energy Transfer in the Silylene-Bridged Biphenyl and Stilbene (SBS) System: A Nonadiabatic Dynamics Point of View.

    Science.gov (United States)

    Wang, Jun; Huang, Jing; Du, Likai; Lan, Zhenggang

    2015-07-09

    The photoinduced intramolecular excited-state energy-transfer (EET) process in conjugated polymers has received a great deal of research interest because of its important role in the light harvesting and energy transport of organic photovoltaic materials in photoelectric devices. In this work, the silylene-bridged biphenyl and stilbene (SBS) system was chosen as a simplified model system to obtain physical insight into the photoinduced intramolecular energy transfer between the different building units of the SBS copolymer. In the SBS system, the vinylbiphenyl and vinylstilbene moieties serve as the donor (D) unit and the acceptor (A) unit, respectively. The ultrafast excited-state dynamics of the SBS system was investigated from the point of view of nonadiabatic dynamics with the surface-hopping method at the TDDFT level. The first two excited states (S1 and S2) are characterized by local excitations at the acceptor (vinylstilbene) and donor (vinylbiphenyl) units, respectively. Ultrafast S2-S1 decay is responsible for the intramolecular D-A excitonic energy transfer. The geometric distortion of the D moiety play an essential role in this EET process, whereas the A moiety remains unchanged during the nonadiabatic dynamics simulation. The present work provides a direct dynamical approach to understand the ultrafast intramolecular energy-transfer dynamics in SBS copolymers and other similar organic photovoltaic copolymers.

  2. Formal synthesis of solanoeclepin A: enantioselective allene diboration and intramolecular [2+2] photocycloaddition for the construction of the tricyclic core

    NARCIS (Netherlands)

    Kleinnijenhuis, R.A.; Timmer, B.J.J.; Lutteke, G.; Smits, J.M.M.; de Gelder, R.; van Maarseveen, J.H.; Hiemstra, H.

    2016-01-01

    An enantioselective synthesis of an intermediate in the Tanino total synthesis of solanoeclepin A has been developed. The key step was an intramolecular [2+2] photocycloaddition, which led to the tricyclo[5.2.1.0(1,6)]decane core in six steps. The first photosubstrate, prepared through an

  3. INFLUENCE OF SOLVENT ON INTRAMOLECULAR PROTON-TRANSFER IN HYDROGEN MALONATE - MOLECULAR-DYNAMICS SIMULATION STUDY OF TUNNELING BY DENSITY-MATRIX EVOLUTION AND NONEQUILIBRIUM SOLVATION

    NARCIS (Netherlands)

    MAVRI, J; BERENDSEN, HJC; VANGUNSTEREN, WF

    1993-01-01

    A density matrix evolution (DME) method (Berendsen, H. J. C.; Mavri, J. J. Phys. Chem. the preceding paper in this issue) in combination with classical molecular dynamics simulation was applied to calculate the rate of proton tunneling in the intramolecular double-well hydrogen bond of hydrogen

  4. γ‐ and δ-Lactams through Palladium-Catalyzed Intramolecular Allylic Alkylation: Enantioselective Synthesis, NMR Investigation, and DFT Rationalization

    DEFF Research Database (Denmark)

    Bantreil, Xavier; Prestat, Guillaume; Moreno, Aitor

    2011-01-01

    The Pd-catalyzed intramolecular allylic alkylation of unsaturated amides to give gamma- and delta-lactams has been studied in the presence of chiral ligands. Ligand (R)-3,5-tBu-MeOBIPHEP (MeOBIPHEP=6,6'-dimethoxybiphenyl-2,2-diyl)bis(diphenylphosphine)) afforded the best results and allowed the c...

  5. Approximate constants of motion for classically chaotic vibrational dynamics - Vague tori, semiclassical quantization, and classical intramolecular energy flow

    Science.gov (United States)

    Shirts, R. B.; Reinhardt, W. P.

    1982-01-01

    Substantial short time regularity, even in the chaotic regions of phase space, is found for what is seen as a large class of systems. This regularity manifests itself through the behavior of approximate constants of motion calculated by Pade summation of the Birkhoff-Gustavson normal form expansion; it is attributed to remnants of destroyed invariant tori in phase space. The remnant torus-like manifold structures are used to justify Einstein-Brillouin-Keller semiclassical quantization procedures for obtaining quantum energy levels, even in the absence of complete tori. They also provide a theoretical basis for the calculation of rate constants for intramolecular mode-mode energy transfer. These results are illustrated by means of a thorough analysis of the Henon-Heiles oscillator problem. Possible generality of the analysis is demonstrated by brief consideration of classical dynamics for the Barbanis Hamiltonian, Zeeman effect in hydrogen and recent results of Wolf and Hase (1980) for the H-C-C fragment.

  6. Collisional activation by MALDI tandem time-of-flight mass spectrometry induces intramolecular migration of amide hydrogens in protonated peptides

    DEFF Research Database (Denmark)

    Jørgensen, Thomas J D; Bache, Nicolai; Roepstorff, Peter

    2005-01-01

    -specific information about the incorporation of deuterium into peptides and proteins in solution. Using a unique set of peptides with their carboxyl-terminal half labeled with deuterium we have shown unambiguously that hydrogen (1H/2H) scrambling is such a dominating factor during low energy collisional activation...... of doubly protonated peptides that the original regioselective deuterium pattern of these peptides is completely erased (Jørgensen, T. J. D., Gårdsvoll, H., Ploug, M., and Roepstorff, P. (2005) Intramolecular migration of amide hydrogens in protonated peptides upon collisional activation. J. Am. Chem. Soc...... randomization among all exchangeable sites (i.e. all N- and O-linked hydrogens) also occurs upon high energy collisional activation of singly protonated peptides. This intense proton/deuteron traffic precludes the use of MALDI tandem time-of-flight mass spectrometry to obtain reliable information...

  7. Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses

    DEFF Research Database (Denmark)

    Canton, Sophie E.; Kjær, Kasper S.; Vankó, György

    2015-01-01

    Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectrosc...... states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined....... as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances. Experimental and theoretical results establish that mediation through electronically excited molecular...

  8. A non-adiabatic quantum-classical dynamics study of the intramolecular excited state hydrogen transfer in ortho-nitrobenzaldehyde.

    Science.gov (United States)

    Leyva, Verónica; Corral, Inés; Feixas, Ferran; Migani, Annapaola; Blancafort, Lluís; González-Vázquez, Jesús; González, Leticia

    2011-08-28

    Ab initio surface-hopping dynamics calculations have been performed to simulate the intramolecular excited state hydrogen transfer dynamics of ortho-nitrobenzaldehyde (o-NBA) in the gas phase from the electronic S(1) excited state. Upon UV excitation, the hydrogen is transferred from the aldehyde substituent to the nitro group, generating o-nitrosobenzoic acid through a ketene intermediate. The semiclassical propagations show that the deactivation from the S(1) is ultrafast, in agreement with the experimental measurements, which detect the ketene in less than 400 fs. The trajectories show that the deactivation mechanism involves two different conical intersections. The first one, a planar configuration with the hydrogen partially transferred, is responsible for the branching between the formation of a biradical intermediate and the regeneration of the starting material. The conversion of the biradical to the ketene corresponds to the passage through a second intersection region in which the ketene group is formed.

  9. Insights into the Intramolecular Properties of η6-Arene-Ru-Based Anticancer Complexes Using Quantum Calculations

    Directory of Open Access Journals (Sweden)

    Adebayo A. Adeniyi

    2013-01-01

    Full Text Available The factors that determine the stability and the effects of noncovalent interaction on the η6-arene ruthenium anticancer complexes are determined using DFT method. The intramolecular and intra-atomic properties were computed for two models of these half-sandwich ruthenium anticancer complexes and their respective hydrated forms. The results showed that the stability of these complexes depends largely on the network of hydrogen bonds (HB, strong nature of charge transfer, polarizability, and electrostatic energies that exist within the complexes. The hydrogen bonds strength was found to be related to the reported anticancer activities and the activation of the complexes by hydration. The metal–ligand bonds were found to be closed shell systems that are characterised by high positive Laplacian values of electron density. Two of the complexes are found to be predominantly characterised by LMCT while the other two are predominately characterised by MLCT.

  10. The Effect of Substituent Position on Excited State Intramolecular Proton Transfer in Benzoxazinone Derivatives: Experiment and DFT Calculation.

    Science.gov (United States)

    Bian, Gao-Feng; Guo, Yun; Lv, Xiao-Jing; Zhang, Cheng

    2017-01-01

    The preparation and the photophysical behaviour of two benzoxazinone derivatives isomers 2-(1-hydroxynaphthalen-2-yl)-4H-benzo[e][1, 3]oxazin-4-one(1) and 2-(3-hydroxynaphthalen-2-yl)-4H-benzo[e][1, 3]oxazin-4-one(2) designed for displaying were reported. The effect of substituent position and solvent effect on the excited state intramolecular proton transfer (ESIPT) dynamics and the spectroscopic properties were investigated using a combined theoretical (i.e., time-dependent density function theory (DFT)) and experimental (i.e., steady-state absorption and emission spectra and time-resolved fluorescence spectra) study. The results showed that compound 1 would facilitate ESIPT process and favored the keto tautomer emission, while compound 2 suppressed the ESIPT process and favored the enol emission.

  11. Intra-molecular electron communication, spectroscopic and conformational stability of the newly developed urethane modified polyetheramide coatings: Computational methods.

    Science.gov (United States)

    Adeniyi, Adebayo A; Akintayo, Cecilia O; Akintayo, Emmanuel T; Conradie, Jeanet

    2017-11-01

    There have been constant research efforts towards the development of new and thermally stable resins, containing properties to outdoor usage, such as high quality of adhesion, as well as resistance to water and acid, amongst others. In this computational study, the spectroscopic properties were calculated, also the intramolecular electronic communication, susceptibility, as well as conformational changes in two monomers of potential resins, namely Albiziabenth oil polyetheramide (ABOPEtA) and urethanated Albiziabenth oil polyetheramide (UABOPEtA), as well as their precursor, namely hydroxylethyl albiziabenth oil amide (HEABOA). Many of these computed properties clearly show that the urethane linkage group in UABOPEtA acts as a strong electron withdrawing group, consequently causing the rest of the molecule to be more nucleophilic. This leads to an increase in the stability of UABOPEtA, as compared the rest of the molecules, as evidenced by an increase in the intramolecular energy of interaction, as well as negative values of the polarizability exaltation index (Γ). Further UABOPEtA is also associated with higher non-linear optical properties, in terms of the hyperpolarizabilities (β) and increased aromaticity, than for molecules ABOPEtA and HEABOA. The conformational folding of molecule UABOPEtA is characterized by larger values of the bisphenol-A linkage bond angle C⋯C⋯C, contrary to the angle observed in molecule ABOPEtA. This is a direct effect of hiding the urethane unit in the cleft of the folded UABOPEtA, which clearly leads to an increase in the hydrophobicity of UABOPEtA. Copyright © 2017 Elsevier Inc. All rights reserved.

  12. In vivo distribution and elimination of hemoglobin modified by intramolecular cross-linking with 2-nor-2-formylpyridoxal 5'-phosphate

    International Nuclear Information System (INIS)

    Bleeker, W.K.; van der Plas, J.; Feitsma, R.I.; Agterberg, J.; Rigter, G.; de Vries-van Rossen, A.; Pauwels, E.K.; Bakker, J.C.

    1989-01-01

    Modified hemoglobin solutions have potential application as plasma expanders with oxygen-transporting capacity. In a previous study it was found that modification of hemoglobin by intramolecular cross-linking with 2-nor-2-formylpyridoxal 5'-phosphate (NFPLP) improves the vascular retention time by a factor of three, and it also improves the oxygen-transporting properties. In the present study we investigated in rats how, after exchange transfusion of a clinically relevant dose, the modified hemoglobin (HbNFPLP) was distributed in the body compared with how the unmodified hemoglobin was distributed. By using a new technetium 99m labeling technique, we found in a scintigraphic study that accumulation of hemoglobin in the kidneys was greatly diminished by the intramolecular cross-linking with NFPLP. These findings were confirmed by light-microscopic observations after diaminobenzidine staining. It was concluded that the impairment of kidney function caused by blockade of the tubuli is not to be expected from HbNFPLP. In the liver and spleen, where the free HbNFPLP is possibly eliminated, some accumulation of 99mTc label was observed, but the major part of the extravascular label was diffusely spread throughout the body. This led to the conclusion that important accumulation of undegraded HbNFPLP does not occur in the liver and spleen. Rapid appearance of both hemoglobin and HbNFPLP in the lymph showed that cross-linking with NFPLP does not prevent the distribution of hemoglobin over the interstitial space in the first hours after administration. However, pharmacokinetic analysis demonstrated that transcapillary transfer contributes only to a limited extent to the disappearance from the circulation. During 24-hour infusions of HbNFPLP, a steady state with a constant plasma concentration was easily reached

  13. Intramolecular telomeric G-quadruplexes dramatically inhibit DNA synthesis by replicative and translesion polymerases, revealing their potential to lead to genetic change.

    Directory of Open Access Journals (Sweden)

    Deanna N Edwards

    Full Text Available Recent research indicates that hundreds of thousands of G-rich sequences within the human genome have the potential to form secondary structures known as G-quadruplexes. Telomeric regions, consisting of long arrays of TTAGGG/AATCCC repeats, are among the most likely areas in which these structures might form. Since G-quadruplexes assemble from certain G-rich single-stranded sequences, they might arise when duplex DNA is unwound such as during replication. Coincidentally, these bulky structures when present in the DNA template might also hinder the action of DNA polymerases. In this study, single-stranded telomeric templates with the potential to form G-quadruplexes were examined for their effects on a variety of replicative and translesion DNA polymerases from humans and lower organisms. Our results demonstrate that single-stranded templates containing four telomeric GGG runs fold into intramolecular G-quadruplex structures. These intramolecular G quadruplexes are somewhat dynamic in nature and stabilized by increasing KCl concentrations and decreasing temperatures. Furthermore, the presence of these intramolecular G-quadruplexes in the template dramatically inhibits DNA synthesis by various DNA polymerases, including the human polymerase δ employed during lagging strand replication of G-rich telomeric strands and several human translesion DNA polymerases potentially recruited to sites of replication blockage. Notably, misincorporation of nucleotides is observed when certain translesion polymerases are employed on substrates containing intramolecular G-quadruplexes, as is extension of the resulting mismatched base pairs upon dynamic unfolding of this secondary structure. These findings reveal the potential for blockage of DNA replication and genetic changes related to sequences capable of forming intramolecular G-quadruplexes.

  14. Dependence of the cyclization of branched tetraethers (CBT) on soil moisture in the Chinese Loess Plateau and the adjacent areas: implications for palaeorainfall reconstructions

    Science.gov (United States)

    Wang, H.; Liu, W.; Zhang, C. L.

    2014-06-01

    Branched glycerol dialkyl glycerol tetraethers (bGDGTs) have been show promising for continental paleotemperature studies in loess-paleosol sequences (LPSs). Thus far, however, little is known about the effect of soil moisture on their distributions on the Chinese Loess Plateau (CLP). In this study, the relationships between environmental variables and the cyclization of bGDGTs (the so called CBT index) were investigated in a comprehensive set of surface soils in the CLP and its adjacent arid/semi-arid areas. We find that CBT correlates best with soil water content (SWC) or mean annual precipitation (MAP) for the total sample set. Particularly for the CLP soils, there is a significant positive relationship between CBT and MAP (CBT = -0.0021 · MAP + 1.7, n = 37, R2 = 0.87; MAP range: 210-680 mm). This indicates that CBT is mainly controlled by soil moisture in the alkalescent soils (pH > 7) in arid/semi-arid regions, where it is not sensitive to soil pH. Therefore, we suggest that CBT can potentially be used as a palaeorainfall proxy on the CLP. According to the preliminary CBT-MAP relationship for modern CLP soils, palaeorainfall history was reconstructed from three LPSs (Yuanbao, Lantian, and Mangshan) with published bGDGT data spanning the past 70 ka. The CBT-derived MAP records of the three sites consistently show precession-driven variations resembling the speleothem δ18O monsoon record, and are also in general accord with the fluctuations of the respective magnetic susceptibility (MS) record, supporting CBT as a reasonable proxy for palaeorainfall reconstruction in LPS studies. Moreover, the comparison of CBT-derived MAP and bGDGT-derived temperature may enable us to further assess the relative timing and magnitude of hydrological and thermal changes on the CLP, independent of chronology.

  15. Neuroprotection of a novel cyclopeptide C*HSDGIC* from the cyclization of PACAP (1-5 in cellular and rodent models of retinal ganglion cell apoptosis.

    Directory of Open Access Journals (Sweden)

    Huanhuan Cheng

    Full Text Available To investigate the protective effects of a novel cyclopeptide C*HSDGIC* (CHC from the cyclization of Pituitary adenylate cyclase-activating polypeptide (PACAP (1-5 in cellular and rodent models of retinal ganglion cell apoptosis.Double-labeling immunohistochemistry was used to detect the expression of Thy-1 and PACAP receptor type 1 in a retinal ganglion cell line RGC-5. The apoptosis of RGC-5 cells was induced by 0.02 J/cm(2 Ultraviolet B irradiation. MTT assay, flow cytometry, fluorescence microscopy were used to investigate the viability, the level of reactive oxygen species (ROS and apoptosis of RGC-5 cells respectively. CHC attenuated apoptotic cell death induced by Ultraviolet B irradiation and inhibited the excessive generation of ROS. Moreover, CHC treatment resulted in decreased expression of Bax and concomitant increase of Bcl-2, as was revealed by western-blot analysis. The in vivo apoptosis of retinal ganglion cells was induced by injecting 50 mM N-methyl-D-aspartate (NMDA (100 nmol in a 2 µL saline solution intravitreally, and different dosages of CHC were administered. At day 7, rats in CHC+ NMDA-treated groups showed obvious aversion to light when compared to NMDA rats. Electroretinogram recordings revealed a marked decrease in the amplitudes of a-wave, b-wave, and photopic negative response due to NMDA damage. In retina receiving intravitreal NMDA and CHC co-treatment, these values were significantly increased. CHC treatment also resulted in less NMDA-induced cell loss and a decrease in the proportion of dUTP end-labeling-positive cells in ganglion cell line.C*HSDGIC*, a novel cyclopeptide from PACAP (1-5 attenuates apoptosis in RGC-5 cells and inhibits NMDA-induced retinal neuronal death. The beneficial effects may occur via the mitochondria pathway. PACAP derivatives like CHC may serve as a promising candidate for neuroprotection in glaucoma.

  16. Cyclization of 1,6-enynes catalyzed by gold nanoparticles supported on TiO2: significant changes in selectivity and mechanism, as compared to homogeneous Au-catalysis.

    Science.gov (United States)

    Gryparis, Charis; Efe, Christina; Raptis, Christos; Lykakis, Ioannis N; Stratakis, Manolis

    2012-06-15

    Gold nanoparticles supported on TiO(2) (1.2 mol %) catalyze, for the first time under heterogeneous conditions, the cycloisomerization of a series of 1,6-enynes in high yields. In several cases, the product selectivity differs significantly as compared to homogeneous Au(I)-catalysis. Based on product analysis and stereoisotopic studies it is proposed that the major or exclusive pathway involves a 5-exo cyclization mode to form stereoselectively gold cyclopropyl carbenes that undergo a single cleavage pathway, in contrast to homogeneous Au-catalysis where the double cleavage pathway operates substantially.

  17. Organocatalytic Asymmetric Michael/Cyclization Cascade Reactions of 3-Hydroxyoxindoles/3-Aminooxindoles with α,β-Unsaturated Acyl Phosphonates for the Construction of Spirocyclic Oxindole-γ-lactones/lactams.

    Science.gov (United States)

    Chen, Lin; Wu, Zhi-Jun; Zhang, Ming-Liang; Yue, Deng-Feng; Zhang, Xiao-Mei; Xu, Xiao-Ying; Yuan, Wei-Cheng

    2015-12-18

    Enantioselective Michael/cyclization cascade reactions of 3-hydroxyoxindoles/3-aminooxindoles with α,β-unsaturated acyl phosphonates by using a cinchonine derived squaramide as the catalyst were developed. A broad range of spirocyclic oxindole-γ-lactones/lactams could be obtained in moderate to excellent yields (up to 98%) with good to excellent diastereo- and enantioselectivities (up to >99:1 dr and 97% ee) under mild conditions. This work represents the first example about the α,β-unsaturated acyl phosphonates for the asymmetric construction of spirocyclic oxindoles.

  18. Application of the generator coordinates method to the intra-molecular proton tunneling in the malonaldehyde molecule; Aplicacao do metodo das coordenadas geradoras ao processo de tunelamento do proton intramolecular na molecula de malonaldeido

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, Andre Campos Kersten

    1995-12-31

    The effects of different vibrational modes on the isomerization process of polyatomic molecules, or solvent`s effects on reaction rates are object of up-to-date interest. In general, such many body phenomena are, in principle, multidimensional, and they first require a reduction of relevant degrees of freedom. In order to investigated, some aspects of the intra-molecular proton tunneling on a malonaldehyde molecule, we use the Generator Coordinate Method. The model used to describe such a process is the so-called System-Bath model, where the system is the reaction coordinate and the bath are the intrinsic degrees of freedom (vibrational modes of the molecule), which are described by a harmonic oscillator set linearly coupled to the system. The reduction of the multidimensional problem to the effective unidimensional one is done using a energy related variational principle on the intrinsic degrees of freedom. we obtained analytically a effective Hamiltonian where the effects of the various degrees of freedom reveal themselves in the appearance of a effective mass and in changes of the shape of the potential barrier. The analyticity of the method was crucial on identifying clearly the roles played by the different physical parameters involved. (author) 17 refs., 29 figs.

  19. Excited-state intramolecular proton transfer in 3-hyroxyflavone isolated in solid argon: fluorescence and fluorescence-excitation spectra and tautomer fluorescence rise time

    Energy Technology Data Exchange (ETDEWEB)

    Dick, B.; Ernsting, N.P.

    1987-07-30

    The fluorescence properties of 3-hydroxyflavone isolated in solid argon at 15 K have been investigated. Upon electronic excitation the molecules undergo rapid intramolecular proton transfer. No fluorescence from the excited state of the normal form of the molecule could be detected. Perturbations due to hydrogen-bonding impurities which produce serious experimental problems in hydrocarbon glasses are largely suppressed in argon matrices. The rise of the green fluorescence of the tautomer was studied with excitation pulses of 230-fs duration and streak camera detection. An apparent tautomer fluorescence rise time of 2.7 ps was obtained by deconvolution. A comparative measurement of the dye coumarine 6 yielded an apparent fluorescence rise time of 2.5 ps, which can be entirely attributed to the group velocity dispersion of the streak camera optics. This indicates a rate constant for excited-state intramolecular proton transfer in 3-hydroxyflavone of greater than 10/sup 12/ s/sup -1/.

  20. Formation of an Intramolecular Periplasmic Disulfide Bond in TcpP Protects TcpP and TcpH from Degradation in Vibrio cholerae.

    Science.gov (United States)

    Morgan, Sarah J; French, Emily L; Thomson, Joshua J; Seaborn, Craig P; Shively, Christian A; Krukonis, Eric S

    2016-02-01

    TcpP and ToxR coordinately regulate transcription of toxT, the master regulator of numerous virulence factors in Vibrio cholerae. TcpP and ToxR are membrane-localized transcription factors, each with a periplasmic domain containing two cysteines. In ToxR, these cysteines form an intramolecular disulfide bond and a cysteine-to-serine substitution affects activity. We determined that the two periplasmic cysteines of TcpP also form an intramolecular disulfide bond. Disruption of this intramolecular disulfide bond by mutation of either cysteine resulted in formation of intermolecular disulfide bonds. Furthermore, disruption of the intramolecular disulfide bond in TcpP decreased the stability of TcpP. While the decreased stability of TcpP-C207S resulted in a nearly complete loss of toxT activation and cholera toxin (CT) production, the second cysteine mutant, TcpP-C218S, was partially resistant to proteolytic degradation and maintained ∼50% toxT activation capacity. TcpP-C218S was also TcpH independent, since deletion of tcpH did not affect the stability of TcpP-C218S, whereas wild-type TcpP was degraded in the absence of TcpH. Finally, TcpH was also unstable when intramolecular disulfides could not be formed in TcpP, suggesting that the single periplasmic cysteine in TcpH may assist with disulfide bond formation in TcpP by interacting with the periplasmic cysteines of TcpP. Consistent with this finding, a TcpH-C114S mutant was unable to stabilize TcpP and was itself unstable. Our findings demonstrate a periplasmic disulfide bond in TcpP is critical for TcpP stability and virulence gene expression. The Vibrio cholerae transcription factor TcpP, in conjunction with ToxR, regulates transcription of toxT, the master regulator of numerous virulence factors in Vibrio cholerae. TcpP is a membrane-localized transcription factor with a periplasmic domain containing two cysteines. We determined that the two periplasmic cysteines of TcpP form an intramolecular disulfide bond

  1. Highly asymmetric intramolecular cyclopropanation of acceptor-substituted diazoacetates by Co(II)-based metalloradical catalysis: iterative approach for development of new-generation catalysts.

    Science.gov (United States)

    Xu, Xue; Lu, Hongjian; Ruppel, Joshua V; Cui, Xin; Lopez de Mesa, Silke; Wojtas, Lukasz; Zhang, X Peter

    2011-10-05

    3,5-Di(t)Bu-QingPhyrin, a new D(2)-symmetric chiral porphyrin derived from a chiral cyclopropanecarboxamide containing two contiguous stereocenters, has been developed using an iterative approach based on Co(II)-catalyzed asymmetric cyclopropanation of alkenes. The Co(II) complex of 3,5-Di(t)Bu-QingPhyrin, [Co(P2)], has proved to be a general and effective catalyst for asymmetric intramolecular cyclopropanation of various allylic diazoacetates (especially including those with α-acceptor substituents) in high yields with excellent stereoselectivities. The [Co(P2)]-based intramolecular metalloradical cyclopropanation provides convenient access to densely functionalized 3-oxabicyclo[3.1.0]hexan-2-one derivatives bearing three contiguous quaternary and tertiary chiral centers with high enantiomeric purity.

  2. Intramolecular Rotation through Proton Transfer: [Fe(eta(5)-C5H4CO2-)(2)] Versus [(eta(5)-C5H4CO2-)Fe(eta(5)-C5H4CO2H)

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xue B.; Dai, Bing; Woo, Hin-koon; Wang, Lai S.

    2005-08-12

    We report a photoelectron spectroscopic study of doubly charged (?5C5H4CO2-)Fe(?5-C5H4CO2-) (1) and singly charged (?5C5H4CO2-)Fe(?5C5H4CO2H) (2). It is shown that strong intramolecular coulomb repulsion keeps 1 in the trans-form, in which the two ?CO2- groups on the cyclopentadienyl ligands are oriented opposite to each other, whereas 2 assumes the cis-form owing to a strong intramolecular H-bond. We estimate a rotational barrier of 1.4 eV for 1 and 0.6 eV for 2. A proton transfer to 1 would result in a 112? intramolecular rotation, whereas deportation of 2 would result in a similar intramolecular rotation. Thus 1 and 2 form a model molecular rotor system, controlled by a proton transfer.

  3. CMPO-calix[4]arenes with spacer containing intramolecular hydrogen bonding: effect of local rigidification on solvent extraction toward f-block elements.

    Science.gov (United States)

    Chu, Hongzhu; He, Lutao; Jiang, Qian; Fang, Yuyu; Jia, Yiming; Yuan, Xiangyang; Zou, Shuliang; Li, Xianghui; Feng, Wen; Yang, Yuanyou; Liu, Ning; Luo, Shunzhong; Yang, Yanqiu; Yang, Liang; Yuan, Lihua

    2014-01-15

    To understand intramolecular hydrogen bonding in effecting liquid-liquid extraction behavior of CMPO-calixarenes, three CMPO-modified calix[4]arenes (CMPO-CA) 5a-5c with hydrogen-bonded spacer were designed and synthesized. The impact of spacer rotation that is hindered by introduction of intramolecular hydrogen bonding upon extraction of La(3+), Eu(3+), Yb(3+), Th(4+), and UO2(2+) has been examined. The results show that 5b and 5c containing only one hydrogen bond with a less hindered rotation spacer extract La(3+) more efficiently than 5a containing two hydrogen bonds with a more hindered rotation spacer, demonstrating the importance of local rigidification of spacer in the design of extractants in influencing the coordination environment. The large difference in extractability between La(3+) and Yb(3+) (or Eu(3+)) by 5b (or 5c), and the small difference by 5a, suggests intramolecular hydrogen bonding do exert pronounced influence upon selective extraction of light and heavy lanthanides. Log-log plot analysis indicates a 1:1, 2:1 and 1:1 stoichiometry (ligand/metal) for the extracted complex formed between 5b and La(3+), Th(4+), UO2(2+), respectively. Additionally, their corresponding acyclic analogs 7a-7c exhibit negligible extraction toward these metal ions. These results reveal the possibility of selective extraction via tuning local chelating surroundings of CMPO-CA by aid of intramolecular hydrogen bonding. Copyright © 2013 Elsevier B.V. All rights reserved.

  4. Rh2(II)-catalyzed intramolecular aliphatic C-H bond amination reactions using aryl azides as the N-atom source.

    Science.gov (United States)

    Nguyen, Quyen; Sun, Ke; Driver, Tom G

    2012-05-02

    Rhodium(II) dicarboxylate complexes were discovered to catalyze the intramolecular amination of unactivated primary, secondary, or tertiary aliphatic C-H bonds using aryl azides as the N-atom precursor. While a strong electron-withdrawing group on the nitrogen atom is typically required to achieve this reaction, we found that both electron-rich and electron-poor aryl azides are efficient sources for the metal nitrene reactive intermediate. © 2012 American Chemical Society

  5. Rh2(II)-Catalyzed Intramolecular Aliphatic C–H Bond Amination Reactions Using Aryl Azides as the N-Atom Source

    Science.gov (United States)

    Nguyen, Quyen; Sun, Ke; Driver, Tom G.

    2012-01-01

    Rhodium(II) dicarboxylate complexes were discovered to catalyze the intramolecular amination of unactivated primary-, secondary-, or tertiary aliphatic C–H bonds using aryl azides as the N-atom precursor. While a strong electron-withdrawing group on the nitrogen atom is typically required to achieve this reaction, we found that both electron-rich- and electron-poor aryl azides are efficient sources for the metal nitrene reactive intermediate. PMID:22519742

  6. Tandem Cu-catalyzed ketenimine formation and intramolecular nucleophile capture: Synthesis of 1,2-dihydro-2-iminoquinolines from 1-(o-acetamidophenylpropargyl alcohols

    Directory of Open Access Journals (Sweden)

    Gadi Ranjith Kumar

    2014-05-01

    Full Text Available The copper-catalyzed ketenimine formation reaction of 1-(o-acetamidophenylpropargyl alcohols with various sulfonyl azides is found to undergo a concomitant intramolecular nucleophile attack to generate 1,2-dihydro-2-iminoquinolines after aromatization (via elimination of acetyl and hydroxy groups and tautomerization. The reaction produces 4-substituted and 3,4-unsubstituted title compounds in moderate to good yields under mild reaction conditions.

  7. New and concise syntheses of the bicyclic oxamazin core using an intramolecular nitroso Diels-Alder reaction and ring-closing olefin metathesis.

    Science.gov (United States)

    Watson, Kyle D; Carosso, Serena; Miller, Marvin J

    2013-01-18

    Herein two new and concise synthetic approaches for making an unsaturated bicyclic oxamazin core are reported. The first involves the use of an intramolecular Diels-Alder reaction to form both of the fused rings in one step. The second approach incorporates ring-closing olefin metathesis in the final step to form the second fused ring of the core. The scope of the second approach was also expanded further to afford larger ringed bicyclic systems.

  8. Intramolecular carbolithiation of N-allyl-ynamides: an efficient entry to 1,4-dihydropyridines and pyridines – application to a formal synthesis of sarizotan

    Directory of Open Access Journals (Sweden)

    Wafa Gati

    2012-12-01

    Full Text Available We have developed a general synthesis of polysubstituted 1,4-dihydropyridines and pyridines based on a highly regioselective lithiation/6-endo-dig intramolecular carbolithiation from readily available N-allyl-ynamides. This reaction, which has been successfully applied to the formal synthesis of the anti-dyskinesia agent sarizotan, further extends the use of ynamides in organic synthesis and further demonstrates the synthetic efficiency of carbometallation reactions.

  9. Magnesium-mediated intramolecular reductive coupling: a stereoselective synthesis of C(2)-symmetric 3,4-bis-silyl-substituted adipic acid derivatives.

    Science.gov (United States)

    Kundu, Pintu K; Ghosh, Sunil K

    2009-11-21

    Chiral C(2)-symmetric 3,4-bis-silyl-substituted adipic acid derivatives have been synthesised by a Mg/trimethylsilyl chloride-mediated intramolecular reductive coupling of symmetrical disiloxanes of beta-silylacrylic acid N-oxazolidinone derivatives. Efficient and short syntheses of enantiomerically pure enantiomers of 2,6-dioxabicyclo[3.3.0]octane-3,7-dione have been achieved from the bis-silylated adipic acid derivatives using Fleming-Tamao oxidation as the key step.

  10. Nickel-Catalyzed C-S Bond Formation via Decarbonylative Thioetherification of Esters, Amides and Intramolecular Recombination Fragment Coupling of Thioesters

    KAUST Repository

    Lee, Shao-Chi

    2018-01-15

    A nickel catalyzed cross-coupling protocol for the straightforward C-S bond formation has been developed. Various mercaptans and a wide range of ester and amide substrates bearing various substituents were tolerated in this process which afforded products in good to excellent yields. Furthermore, an intramolecular protocol for the synthesis of thioethers starting from thioesters has been developed. The utility of this protocol has been demonstrated in the synthesis of benzothiophene on the bench top.

  11. Iodine-Mediated Intramolecular Dehydrogenative Coupling: Synthesis of N-Alkylindolo[3,2-c]- and -[2,3-c]quinoline Iodides.

    Science.gov (United States)

    Volvoikar, Prajesh S; Tilve, Santosh G

    2016-03-04

    An I2/TBHP-mediated intramolecular dehydrogenative coupling reaction is developed for the synthesis of a library of medicinally important 5,11-dialkylindolo[3,2-c]quinoline salts and 5,7-dimethylindolo[2,3-c]quinoline salts. The annulation reaction is followed by aromatization to yield tetracycles in good yield. This protocol is also demonstrated for the synthesis of the naturally occurring isocryptolepine in salt form.

  12. EL APRENDIZAJE DE LOS CONCEPTOS DE FUERZAS INTERMOLECULARES E INTRAMOLECULARES MEDIANTE LA MODELIZACIÓN DIDÁCTICA

    Directory of Open Access Journals (Sweden)

    CHRISTIAN FERNNEY GIRALDO MACÍAS

    2013-07-01

    Full Text Available La modelización está siendo usada para la enseñanza y el aprendizaje en las Ciencias Naturales en diferentes contextos y para atender a diferentes problemáticas. En este caso será utilizada para explorar y analizar la relevancia que puede tener su uso en el aprendizaje de los conceptos Fuerzas Intramoleculares e Intermolecualres, partiendo de la aplicación de una serie de actividades basadas en el Ciclo Didáctico (Jorba y Sanmartí, 1996. Los datos se discuten mediante tres aspectos principales: las ideas previas de los estudiantes, el trabajo con nuevo material (nuevos conceptos, experimentos sencillos y uso de herramientas informáticas y los argumentos finales, mediante el uso de situaciones problemas. Los resultados muestran, como los estudiantes (14 y 16 años de edad evidencian un progreso conceptual al argumentar con mayor claridad las situaciones problema abordadas en el transcurso del trabajo y en la construcción de modelos más cercanos al campo científico.

  13. Rubrene: The interplay between intramolecular and intermolecular interactions determines the planarization of its tetracene core in the solid state

    KAUST Repository

    Sutton, Christopher

    2015-06-15

    Rubrene is one of the most studied molecular semiconductors; its chemical structure consists of a tetracene backbone with four phenyl rings appended to the two central fused rings. Derivatization of these phenyl rings can lead to two very different solid-state molecular conformations and packings: One in which the tetracene core is planar and there exists substantive overlap among neighboring π-conjugated backbones; and another where the tetracene core is twisted and the overlap of neighboring π-conjugated backbones is completely disrupted. State-of-the-art electronic-structure calculations show for all isolated rubrene derivatives that the twisted conformation is more favorable (by -1.7 to -4.1 kcal mol-1), which is a consequence of energetically unfavorable exchange-repulsion interactions among the phenyl side groups. Calculations based on available crystallographic structures reveal that planar conformations of the tetracene core in the solid state result from intermolecular interactions that can be tuned through well-chosen functionalization of the phenyl side groups, and lead to improved intermolecular electronic couplings. Understanding the interplay of these intramolecular and intermolecular interactions provides insight into how to chemically modify rubrene and similar molecular semiconductors to improve the intrinsic materials electronic properties.

  14. Tunable differentiation of tertiary C-H bonds in intramolecular transition metal-catalyzed nitrene transfer reactions.

    Science.gov (United States)

    Corbin, Joshua R; Schomaker, Jennifer M

    2017-04-13

    Metal-catalyzed nitrene transfer reactions are an appealing and efficient strategy for accessing tetrasubstituted amines through the direct amination of tertiary C-H bonds. Traditional catalysts for these reactions rely on substrate control to achieve site-selectivity in the C-H amination event; thus, tunability is challenging when competing C-H bonds have similar steric or electronic features. One consequence of this fact is that the impact of catalyst identity on the selectivity in the competitive amination of tertiary C-H bonds has not been well-explored, despite the potential for progress towards predictable and catalyst-controlled C-N bond formation. In this communication, we report investigations into tunable and site-selective nitrene transfers between tertiary C(sp 3 )-H bonds using a combination of transition metal catalysts, including complexes based on Ag, Mn, Rh and Ru. Particularly striking was the ability to reverse the selectivity of nitrene transfer by a simple change in the identity of the N-donor ligand supporting the Ag(i) complex. The combination of our Ag(i) catalysts with known Rh 2 (ii) complexes expands the scope of successful catalyst-controlled intramolecular nitrene transfer and represents a promising springboard for the future development of intermolecular C-H N-group transfer methods.

  15. Conformational properties of oxazole-amino acids: effect of the intramolecular N-H···N hydrogen bond.

    Science.gov (United States)

    Siodłak, Dawid; Staś, Monika; Broda, Małgorzata A; Bujak, Maciej; Lis, Tadeusz

    2014-03-06

    Oxazole ring occurs in numerous natural peptides, but conformational properties of the amino acid residue containing the oxazole ring in place of the C-terminal amide bond are poorly recognized. A series of model compounds constituted by the oxazole-amino acids occurring in nature, that is, oxazole-alanine (L-Ala-Ozl), oxazole-dehydroalanine (ΔAla-Ozl), and oxazole-dehydrobutyrine ((Z)-ΔAbu-Ozl), was investigated using theoretical calculations supported by FTIR and NMR spectra and single-crystal X-ray diffraction. It was found that the main feature of the studied oxazole-amino acids is the stable conformation β2 with the torsion angles φ and ψ of -150°, -10° for L-Ala-Ozl, -180°, 0° for ΔAla-Ozl, and -120°, 0° for (Z)-ΔAbu-Ozl, respectively. The conformation β2 is stabilized by the intramolecular N-H···N hydrogen bond and predominates in the low polar environment. In the case of the oxazole-dehydroamino acids, the π-electron conjugation that is spread on the oxazole ring and C(α)═C(β) double bond is an additional stabilizing interaction. The tendency to adopt the conformation β2 clearly decreases with increasing the polarity of environment, but still the oxazole-dehydroamino acids are considered to be more rigid and resistant to conformational changes.

  16. The effect of driving force on intramolecular electron transfer in proteins. Studies on single-site mutated azurins

    DEFF Research Database (Denmark)

    Farver, O; Skov, L K; van de Kamp, M

    1992-01-01

    these substitutions are not in the microenvironment separating the electron donor and acceptor, they were expected to affect the LRET rate because of their effect on the redox potential of the copper site and thus on the driving force of the reaction, as well as on the reorganization energies of the copper site....... The rate of intramolecular electron transfer from RSSR- to Cu(II) in the wild-type P. aeruginosa azurin (delta G degrees = -68.9 kJ/mol) has previously been determined to be 44 +/- 7 s-1 at 298 K, pH 7.0. The [M44K]azurin mutant (delta G degrees = -75.3 kJ/mol) was now found to react considerably faster (k...... = 134 +/- 12 s-1 at 298 K, pH 7.0) while the [H35Q]azurin mutant (delta G degrees = -65.4 kJ/mol) exhibits, within experimental error, the same specific rate (k = 52 +/- 11 s-1, 298 K, pH 7.0) as that of the wild-type azurin. From the temperature dependence of these LRET rates the following activation...

  17. Transition Metal Donor-Peptide-Acceptor Complexes: From Intramolecular Electron Transfer Reactions to the Study of Reactive Intermediates

    Energy Technology Data Exchange (ETDEWEB)

    Isied, Stephan S.

    2003-03-11

    The trans-polyproline (PII) oligomers (Figure 1) are unusually rigid peptide structures which have been extensively studied by our group for peptide mediated intramolecular electron transfer (ET) at long distances. We have previously studied ET across a series of metal ion donor (D) acceptor (A) oligoproline peptides with different distances, driving forces and reorganizational energies. The majority of these experiments involve generating the ET intermediate using pulse radiolysis methods, although more recently photochemical methods are also used. Results of these studies showed that ET across peptides can vary by more than twelve orders of magnitude. Using ruthenium bipyridine donors, ET reaction rate constants across several proline residues (n = 4 - 9) occurred in the millisecond (ms) to {micro}s timescale, thus limiting the proline peptide conformational motions to only minor changes (far smaller than the large changes that occur on the ms to sec timescale, such as trans to cis proline isomerization). The present report describes our large data base of experimental results for D-peptide-A complexes in terms of a model where the involvement of both superexchange and hopping (hole and electron) mechanisms account for the long range ET rate constants observed. Our data shows that the change from superexchange to hopping mechanisms occurs at different distances depending on the type of D and A and their interactions with the peptides. Our model is also consistent with generalized models for superexchange and hopping which have been put forward by a number of theoretical groups to account for long range ET phenomena.

  18. Intramolecular circularization increases efficiency of RNA sequencing and enables CLIP-Seq of nuclear RNA from human cells

    Science.gov (United States)

    Chu, Yongjun; Wang, Tao; Dodd, David; Xie, Yang; Janowski, Bethany A.; Corey, David R.

    2015-01-01

    RNA sequencing (RNA-Seq) is a powerful tool for analyzing the identity of cellular RNAs but is often limited by the amount of material available for analysis. In spite of extensive efforts employing existing protocols, we observed that it was not possible to obtain useful sequencing libraries from nuclear RNA derived from cultured human cells after crosslinking and immunoprecipitation (CLIP). Here, we report a method for obtaining strand-specific small RNA libraries for RNA sequencing that requires picograms of RNA. We employ an intramolecular circularization step that increases the efficiency of library preparation and avoids the need for intermolecular ligations of adaptor sequences. Other key features include random priming for full-length cDNA synthesis and gel-free library purification. Using our method, we generated CLIP-Seq libraries from nuclear RNA that had been UV-crosslinked and immunoprecipitated with anti-Argonaute 2 (Ago2) antibody. Computational protocols were developed to enable analysis of raw sequencing data and we observe substantial differences between recognition by Ago2 of RNA species in the nucleus relative to the cytoplasm. This RNA self-circularization approach to RNA sequencing (RC-Seq) allows data to be obtained using small amounts of input RNA that cannot be sequenced by standard methods. PMID:25813040

  19. Gel formation and low-temperature intramolecular conformation transition of a triple-helical polysaccharide lentinan in water.

    Science.gov (United States)

    Zhang, Yangyang; Xu, Xiaojuan; Zhang, Lina

    2008-10-01

    The gelation behavior of the triple-helical polysaccharide lentinan fractions having different molecular weights in water at 25 degrees C were studied by using a rheometer. The analysis of concentration and molecular weight dependence of shear stress and shear viscosity showed that aqueous lentinan is a typical shear-thinning fluid, possessing potential as a viscosity control agent, and that a weak gel with entangled network structure formed. The dynamic oscillatory behavior of lentinan in the temperature range of 1-15 degrees C was also investigated by rheologic method. The storage modulus G' and complex viscosity eta* increased first with decreasing temperature, and underwent a maximum centered at 7-9 degrees C, and then decreased with further decreasing temperature. This abnormal phenomenon was ascribed to formation of rigid structure in the gel state, which was confirmed by the experimental results from micro-DSC. The micro-DSC curves showed that an endothermic peak appeared at 7-9 degrees C for lentinan in water upon heating, which was attributable to the intramolecular order-disorder structure transition similar to triple-helical polysaccharide schizophyllan. Namely, at lower temperature, the side glucose residues of lentinan (triplix II) formed a well-organized triple-helical structure (triplix I) through hydrogen-bonding with the surrounding water molecules. Moreover, this conformation transition was proved to be thermally reversible. (c) 2008 Wiley Periodicals, Inc.

  20. Role of intramolecular interaction in connexin50: mediating the Ca2+-dependent binding of calmodulin to gap junction.

    Science.gov (United States)

    Zhang, Xianrong; Qi, Yipeng

    2005-08-15

    Gap junction channels formed by connexin50 (Cx50) are critical for maintenance of eye lens transparency. Cleavage of the carboxyl terminus (CT) of Cx50 to produce truncated Cx50 (Cx50trunc) occurred naturally during maturation of lens fiber cells. The mechanism of its altered properties is under confirmation. It has been suggested that calmodulin (CaM) participates in gating some kinds of gap junction. Here, we performed confocal colocalization and co-immunoprecipitation experiments to study the relationships between Cx50 and CaM. Results exhibited that the CaM could colocalize Ca2+ dependently with CT in the linear area of cell-to-cell contact formed by Cx50trunc, while it could not localize in the linear area without expression of CT. Further study indicated that the CT could interact Ca2+ independently with the cytoplasmic loop (CL) of Cx50. These data put forward the importance of Ca2+-independent intramolecular interaction between CT and CL of Cx50, which mediate the Ca2+-dependent binding of CaM to Cx50. These intra- and intermolecular interactions may further improve our understanding of biological significance of the Cx50 in the eye lens.