Sample records for regioselective ring opening

  1. Regioselective Nucleophilic Ring Opening of Epoxides and Aziridines derived from Homoallylic Alcohols

    Tanner, David Ackland; Groth, Thomas


    The regioselectivity of nucleophilic ring opening of some 3,4-epoxy and 3,4-aziridino alcohols has been studied. The nucleophiles chosen were complex hydrides (LiAlH4, Red-Al and DIBAL) and Lipshutz- or Gilman-type organocuprate reagents. The C-4 substituent in the substrates was varied in order...... to study steric and electronic effects on the ring opening reactions. For alkyl substituents at C-4, most of the results can be explained on the basis of intramolecular delivery of the nucleophile to C-3 via a six-membered transition state, leading to 1,4-diols or 1,4-amino alcohol derivatives. In general...

  2. Synthesis of Human Milk Oligosaccharides and Regioselective Ring Opening of Oxabicycles

    Jennum, Camilla Arboe

    the fucose is also attached in the same pot. In addition, pNP-neuraminic acid was synthesized for the purpose to perform activity studies on enzymes. The enzymes were designed to perform sialyl transfer reactions in the synthesis human milk oligosaccharides containing neuraminic acid. OH O HO HO O OH O HO O...... HO OH HO O OH O NHAc OH O O HO HO O HOOH OH Lacto-N-fucopentaose OH O HO HO O OH O HO O HO OH O O OH HO NHAc Lacto-N-neofucopentaose OH O O HO HO O HOOH OH The second chapter describes the regioselective ring opening of enantiopure oxabicycles primarily by the use of rhodium catalysts and phosphine...... ligands. The ring opened iii products were similar to compounds, which had shown to be potential protein Bcl-XL antagonists, a target for future drugs in cancer treatment. The aim was to create a general asymmetric ring opening method of several enantiopure oxabicycles having different functional moieties...

  3. Mechanism, reactivity, and regioselectivity in rhodium-catalyzed asymmetric ring-opening reactions of oxabicyclic alkenes: a DFT Investigation

    Qi, Zheng-Hang; Zhang, Yi; Gao, Yun; Zhang, Ye; Wang, Xing-Wang; Wang, Yong


    The origin of the enantio- and regioselectivity of ring-opening reaction of oxabicyclic alkenes catalyzed by rhodium/Josiphos has been examined using M06-2X density functional theory(DFT). DFT calculations predict a 98% ee for the enantioselectivity and only the 1,2-trans product as one regio- and diastereomer, in excellent agreement with experimental results. The solvent tetrahydrofuran(THF) plays a key role in assisting nucleophilic attack. Orbital composition analysis of the LUMO and the NPA atomic charge calculations were conducted to probe the origins of the regioselectivity. The orbital composition analysis reveals two potential electrophilic sites of the Rh–π-allyl intermediate M3 and the NPA atomic charges demonstrate that Cα carries more positive charges than Cγ, which suggests that Cα is the electrophilic site. PMID:28074930

  4. Mechanism, reactivity, and regioselectivity in rhodium-catalyzed asymmetric ring-opening reactions of oxabicyclic alkenes: a DFT Investigation

    Qi, Zheng-Hang; Zhang, Yi; Gao, Yun; Zhang, Ye; Wang, Xing-Wang; Wang, Yong


    The origin of the enantio- and regioselectivity of ring-opening reaction of oxabicyclic alkenes catalyzed by rhodium/Josiphos has been examined using M06-2X density functional theory(DFT). DFT calculations predict a 98% ee for the enantioselectivity and only the 1,2-trans product as one regio- and diastereomer, in excellent agreement with experimental results. The solvent tetrahydrofuran(THF) plays a key role in assisting nucleophilic attack. Orbital composition analysis of the LUMO and the NPA atomic charge calculations were conducted to probe the origins of the regioselectivity. The orbital composition analysis reveals two potential electrophilic sites of the Rh-π-allyl intermediate M3 and the NPA atomic charges demonstrate that Cα carries more positive charges than Cγ, which suggests that Cα is the electrophilic site.

  5. Research Update: A hafnium-based metal-organic framework as a catalyst for regioselective ring-opening of epoxides with a mild hydride source

    Stephenson, Casey J.; Hassan Beyzavi, M.; Klet, Rachel C.; Hupp, Joseph T., E-mail:, E-mail: [Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208 (United States); Farha, Omar K., E-mail:, E-mail: [Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208 (United States); Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah (Saudi Arabia)


    Reaction of styrene oxide with sodium cyanoborohydride and a catalytic amount of Hf-NU-1000 yields the anti-Markovnikov product, 2-phenylethanol, with over 98% regioselectivity. On the other hand, propylene oxide is ring opened in a Markovnikov fashion to form 2-propanol with 95% regioselectivity. Both styrene oxide and propylene oxide failed to react with sodium cyanoborohydride without the addition of Hf-NU-1000 indicative of the crucial role of Hf-NU-1000 as a catalyst in this reaction. To the best of our knowledge, this is the first report of the use of a metal-organic framework material as a catalyst for ring-opening of epoxides with hydrides.

  6. Research Update: A hafnium-based metal-organic framework as a catalyst for regioselective ring-opening of epoxides with a mild hydride source

    Casey J. Stephenson


    Full Text Available Reaction of styrene oxide with sodium cyanoborohydride and a catalytic amount of Hf-NU-1000 yields the anti-Markovnikov product, 2-phenylethanol, with over 98% regioselectivity. On the other hand, propylene oxide is ring opened in a Markovnikov fashion to form 2-propanol with 95% regioselectivity. Both styrene oxide and propylene oxide failed to react with sodium cyanoborohydride without the addition of Hf-NU-1000 indicative of the crucial role of Hf-NU-1000 as a catalyst in this reaction. To the best of our knowledge, this is the first report of the use of a metal-organic framework material as a catalyst for ring-opening of epoxides with hydrides.

  7. Efficient, regioselective ring-opening of activated aziridine-2-carboxylates with [18F]fluoride

    Schjøth-Eskesen, Christina; Hansen, Paul Robert; Kjær, Andreas;


    Aziridines can undergo a range of ring-opening reactions with nucleophiles. The regio- and stereochemistry of the products depend on the substituents on the aziridine. Aziridine ring-opening reactions have rarely been used in radiosynthesis. Herein we report the ring opening of activated aziridin...

  8. Regioselective ring opening of epoxides using NH4SCN/silica sulfuric acid: An efficient approach for the synthesis of β-hydroxy thiocyanate under solvent-free conditions

    Ali R. Kiasat; Maryam Zayadi; Mehdi Fallah Mehrjardi


    Silica sulfuric acid was developed as a stable and efficient heterogeneous catalyst in organic synthesis. This solid acid catalyzed the regioselective ring opening of epoxides by thiocyanate anion to give thiocyanohydrins as key intermediates in agricultural and pharmaceutical chemistry in high yields under solvent-free conditions.

  9. 非对称环氧乙烷的区域选择性亲核开环反应%Regioselective Nucleophilic Ring Opening Reactions of Unsymmetric Oxiranes

    周婵; 许家喜


    本文总结了常用亲核试剂对非对称环氧乙烷的亲核开环反应及其区域选择性.强亲核性的亲核试剂通常只受空间效应影响,进攻非对称环氧乙烷位阻小的碳原子,对于烯基取代环氧乙烷还可以进攻烯基的β-碳原子发生Sn2'开环反应,其他亲核试剂同时受空间效应和电子效应的影响,对于烷基环氧乙烷通常进攻其取代少的碳原子,空间效应起主导作用,而对芳基和烯基取代环氧乙烷开环反应通常发生在环氧乙烷芳甲位和烯丙位的碳原子上,电子效应起主导作用.在质子酸或强Lewis酸存在下,虽然单烷基环氧乙烷的开环仍然发生在其取代少的碳原子上,但对于芳基、烯基和同碳双取代环氧乙烷,亲核开环反应将主要受电子效应控制,一般亲核试剂倾向于进攻环氧乙烷的芳甲位、烯丙位或多取代的碳原子.分子内的亲核开环反应主要受成环时环大小的控制,成环时的倾向是五元环>六元环>七元环.环氧乙烷亲核开环的区域选择性是环氧乙烷和亲核试剂空间效应和电子效应平衡的结果.%Nucleophilic ring opening reactions of unsymmetric oxiranes and their regioselectivity with widely used nucleophiles are reviewed. Strong nucleophiles attack the less substituted carbon atom of unsymmetric oxiranes, whatever alkyl, alkenyl, and aryloxiranes, controlled by the steric hindrance only. They can undergo an SN2' ring-opening reaction with alkenyloxiranes via the attack on the β-carbon atom of their alkenyl group. Other nucleophiles generally attack the less substituted carbon atom for alkyloxiranes, controlled by the steric hindrance,but attack the arylmethyl and allyl carbon atom for aryl and alkenyloxiranes, controlled by the electronic effect. In the presence of proton acids or strong Lewis acids, although monoalkyloxiranes are attacked on their less substituted carbon atom with nucleophiles (steric hindrance control), aryl, alkenyl

  10. Regioselective Nucleophilic Ring Opening Reactions of Unsymmetric Thiiranes%非对称环硫乙烷的区域选择性亲核开环反应

    周婵; 许家喜


    Thiiranes are a class of important intermediates in organic synthesis, as well in pharmaceutical and agrochemieal industries as their oxygen analogs oxiranes and nitrogen analogs aziridines. They have been widely applied in the preparation of sulfur-containing compounds, such as diverse thiols and thioethers and so on, via ring opening reaction and isomerization. Nucleophilic ring opening reactions of unsymmetric thiiranes and their regioseleetivity with various widely used nueleophiles are reviewed. Generally, nucleophilic ring opening reactions of unsymmetrie thiiranes occur on their less substituted carbon atom, controlled by the steric hindrance. 2- Alkenyhhiiranes can undergo an SN2' ring opening reaction in some cases via the attack on the β-carbon atom of their alkenyl group. Strong nucleophiles easily lead to desulfurization of thiiranes to afford the corresponding olefins, while the relatively weak nueleophiles readily result in polymerization of thiiranes, affording polythioethers. In the presence of Lewis acid, the electronic effect affects the regioselectivity in ring opening reactions, even as the prominent effect in the reactions. Although aliphatic thiiranes are still attacked predominantly on their less substituted carbon atom with nucleophiles (the steric hindrance control) , aromatic thiiranes and 2-alkenylthiiranes are attacked on their more substituted carbon atom with nucleophiles (the electronic effect control). The current review provides a general rule for the regioselectivity of the nucleophilic ring opening reaction of unsymmetric thiiranes.%环硫乙烷与它的氧类似物环氧乙烷和氮类似物氮杂环丙烷一样,是一类重要的有机合成中间体,在医药和农用化学品工业领域也得到广泛应用。通过开环和异构化反应,还广泛用于制备硫醇和硫醚等含硫化合物。本文总结了常用亲核试剂对非对称环硫乙烷的亲核开环反应及其区域选择性。环硫乙烷

  11. Synthesis of Azanucleosides through Regioselective Ring-Opening of Epoxides Catalyzed by Sulphated Zirconia under Microwave and Solvent-Free Conditions

    Guillermo E. Negrón-Silva


    Full Text Available New azanucleosides were obtained using sulphated zirconia (ZS as catalyst in the nucleophilic oxirane ring opening reaction of 1-allyl-3-(oxiran-2-ylmethyl pyrimidine-2,4(1H,3H-dione and 1-allyl-5-methyl-3-(oxiran-2-ylmethyl-pyrimidine-2,4(1H,3H-dione, with (S-prolinol. The new templates were obtained with good yields following a route which exploits the reactivity of epoxides in the presence of sulphated zirconia as catalyst. The key step was carried out using microwave and solvent-free conditions and proceeds with high selectivity.

  12. Conformation-induced regioselective and divergent opening of epoxides by fluoride: facile access to hydroxylated fluoro-piperidines.

    Yan, Nan; Fang, Zheng; Liu, Qing-Quan; Guo, Xiao-Hong; Hu, Xiang-Guo


    Utilizing molecular conformation as a controlling factor, epoxide-containing 2-aryl-piperidines can be ring-opened with the reagent combination of tetrabutylammonium fluoride (TBAF) and potassium bifluoride (KHF2) in a regioselective and divergent fashion. Four different types of hydroxylated fluoro-piperidines, valuable building blocks in drug development, were readily synthesized using this method. The basic nature of the reagent combination allowed a one-pot deprotection/ring opening process, which increased the efficacy of this transformation.

  13. Unusual Regioselectivity in the Opening of Epoxides by Carboxylic Acid Enediolates

    José Segura


    Full Text Available Addition of carboxylic acid dianions appears to be a potential alternative to the use of aluminium enolates for nucleophilic ring opening of epoxides. These conditions require the use of a sub-stoichiometric amount of amine (10% mol for dianion generation and the previous activation of the epoxide with LiCl. Yields are good, with high regioselectivity, but the use of styrene oxide led, unexpectedly, to a mixture resulting from the attack on both the primary and secondary carbon atoms. Generally, a low diastereoselectivity is seen on attack at the primary center, however only one diastereoisomer was obtained from attack to the secondary carbon of the styrene oxide.

  14. Platinum Catalyzed Ring-Opening of 1,2-Cyclopropanated Sugars with O-Nucleophiles

    Beyer, Jürgen; Skaanderup, Philip Robert; Madsen, Robert


    In the presence of a catalytic amount of Zeise's dimer 1,2-cyclopropanated sugars undergo regioselective ring-opening at C-1 with O-nucleophiles including alcohols, phenols and water to produce 2-C-branched carbohydrates.......In the presence of a catalytic amount of Zeise's dimer 1,2-cyclopropanated sugars undergo regioselective ring-opening at C-1 with O-nucleophiles including alcohols, phenols and water to produce 2-C-branched carbohydrates....

  15. Ring opening of a resin-bound chiral aziridine with phenol nucleophiles

    Ottesen, Lars Korsgaard; Jaroszewski, Jerzy W; Franzyk, Henrik


    An efficient and versatile solid-phase route for the preparation of aryl-alkyl ethers is described. Regioselective ring opening of a resin-bound chiral aziridine with phenolic nucleophiles constitutes the key feature of the present protocol that allows incorporation of fluorescent moieties...

  16. Regio- and Diasteroselectivity of Rhodium-catalyzed Ring Opening Reaction of Oxabenzonorbornadienes with Heteroatom Nucleophiles


    A new rhodium catalyzed ring opening reaction of oxabenzonorbornadienes and its derivatives was described. This reaction forms a new carbon-nitrogen bond via an intermolecular allylic displacement of the bridgehead oxygen with a piperazine's derivatives, which proceeds with very high regioselectivity.

  17. The Studies of Rhodium-catalyzed Ring Opening Reaction of N-Boc azabenzonorbornadiene with Heteroatom Nucleophiles

    Er Chang LIU; Ding Qiao YANG; Ying Feng HAN; Jian Xia DONG


    A rhodium-catalyzed ring opening reaction of N-Boc-azabenzonorbornadiene with heteroatom nucleophiles was described. Piperidine and piperazine's derivatives were nucleophiles in this reaction. The yields of the products 2a-f are good and the regioselectivity are excellent.

  18. Allyltin tribromide: A versatile reagent involved in the ring-opening of epoxides


    This paper presents a versatile reagent for epoxide cleavage.The allyltin tribromide could act as a novel and easily prepared allylation reagent and halide atom donor to convert epoxides to the corresponding homoallyl alcohols and halohydrins in high yields with excellent regioselectivities under mild reaction conditions,respectively.It could also act as a Lewis acid to catalyze the ring opening reactions of epoxides with alcohols.

  19. Ring-opening of N-Tosyl Aziridines with Hydroxyl Compounds Catalyzed by Acidic Ionic Liquid

    LI Yuling; GU Dagong; XU Xiaoping; JI Shunjun


    Ring-opening of two types of N-tosyl aziridines with hydroxyl compounds has been studied.The aziridines could react smoothly with alcohols in the presence of functional ionic liquid [hmim]HSO4 to afford the corresponding β-amino ethers in moderate to good yields with high regioselectivity.The recyclable property of [hmim]HSO4 was demonstrated in the process.

  20. A new approach to construct a fused 2-ylidene chromene ring: highly regioselective synthesis of novel chromeno quinoxalines.

    Kumar, K Shiva; Rambabu, D; Prasad, Bagineni; Mujahid, Mohammad; Krishna, G Rama; Rao, M V Basaveswara; Reddy, C Malla; Vanaja, G R; Kalle, Arunasree M; Pal, Manojit


    Regioselective construction of a fused 2-ylidene chromene ring was achieved for the first time by using AlCl(3)-induced C-C bond formation followed by Pd/C-Cu mediate coupling-cyclization strategy. A number of chromeno[4,3-b]quinoxaline derivatives were prepared by using this strategy. Single crystal X-ray diffraction study of a representative compound e.g. 6-(2,2-dimethylpropylidene)-4-methyl-6H-chromeno[4,3-b]quinoxalin-3-ol confirmed the presence of an exocyclic C-C double bond with Z-geometry. The crystal structure analysis and hydrogen bonding patterns of the same compound along with its structure elaboration via propargylation followed by Sonogashira coupling of the resulting terminal alkyne is presented. A probable mechanism for the formation of 2-ylidene chromene ring is discussed. Some of the compounds synthesized showed anticancer properties when tested in vitro.

  1. Flexible Twin Open Ring Metro WDM Network

    Susumu Kinoshita; Cechan Tian; Satoru Ohdate; Koji Takeguchi; Yasuhiko Aoki


    We have demonstrated a flexible twin open ring WDM network for metro applications. A pair of optical switches in the network keeps the fiber rings open to prevent signal circulation. Traffics are broadcast to every node and selected at the receiving side. Superior transmission and protection switching are proved.

  2. Regioselectivity and Tautomerism of Novel Five-Membered Ring Nitrogen Heterocycles Formed via Cyclocondensation of Acylthiosemicarbazides

    Karel D. Klika


    Full Text Available A series of 1-acyl-4-phenyl/(acridin-9-ylthiosemicarbazides 3, including fournew compounds, were prepared in order to study substituent effects on cyclizationreactions with oxalyl chloride (producing imidazolidine-4,5-diones 4, dimethylacetylenedicarboxylate (to give thiazolidin-4-ones 7 and 8 and autocondensation underalkaline conditions (to yield 1,2,4-triazoles 9. A positional isomer, 10 of compound 3f wasalso prepared. Altogether, twenty new compounds characterized and identified by IR, UV,1H, 13C and 2D NMR and quantum chemical calculations are described. The tautomerismof the products and regioselectivity of the reactions were evaluated. Compounds 3f−h,3h·2HCl, 7b,d and 10 were screened for cytotoxic activity against the L1210 leukemia cellline and all compounds, except for 3f, exhibited promising inhibitions of cell growth.

  3. SN2-type ring opening of substituted--tosylaziridines with zinc (II) halides: Control of racemization by quaternary ammonium salt

    Manas K Ghorai; Deo Prakash Tiwari; Amit Kumar; Kalpataru Das


    Quaternary ammonium salt mediated highly regioselective ring opening of aziridines with zinc(II) halides to racemic and non-racemic -halo amines in excellent yield and selectivity is described. The reaction proceeds via an SN2-type pathway and the partial racemization of the starting substrate and the product was effectively controlled by using quaternary ammonium salts to afford the enantioenriched products (er up to 95:5).

  4. Structural effects on the beta-scission reaction of alkoxyl radicals. Direct measurement of the absolute rate constants for ring opening of benzocycloalken-1-oxyl radicals.

    Bietti, Massimo; Lanzalunga, Osvaldo; Salamone, Michela


    [reaction: see text] The absolute rate constants for beta-scission of a series of benzocycloalken-1-oxyl radicals and of the 2-(4-methylphenyl)-2-butoxyl radical have been measured directly by laser flash photolysis. The benzocycloalken-1-oxyl radicals undergo ring opening with rates which parallel the ring strain of the corresponding cycloalkanes. In the 1-X-indan-1-oxyl radical series, ring opening is observed when X = H, Me, whereas exclusive C-X bond cleavage occurs when X = Et. The factors governing the fragmentation regioselectivity are discussed.

  5. Cu-catalyzed arylation of the amino group in the indazole ring: regioselective synthesis of pyrazolo-carbazoles.

    Anil Kumar, K; Kannaboina, Prakash; Dhaked, Devendra K; Vishwakarma, Ram A; Bharatam, Prasad V; Das, Parthasarathi


    Cu(II)-catalyzed cross-coupling of various aryl boronic acids with 5 and 6-amino indazoles has resulted in (arylamino)-indazoles. These (arylamino)-indazoles have been utilized in synthesizing medicinally important pyrazole-fused carbazoles via Pd(II)-catalyzed cross-dehydrogenative coupling (CDC). This combined N-arylation/C-H arylation strategy has been successfully applied to the regioselective synthesis of polyheterocycles 3,6-dihydropyrazolo[3,4-c]carbazoles and 1,6-dihydro pyrazolo[4,3-c]carbazoles. Quantum chemical analysis has been carried out to understand the regioselectivity and to trace the potential energy surface of the entire reaction upon 5-N-aryl-indazole conversion to the corresponding carbazole.

  6. The reduction ring-opening reaction of imidazoline

    史真; 李诤; 白银娟


    A new reduction ring-opening reaction of 2-imidazoline with sodium borohydride is reported, and the effect of reaction condition on the yield, reaction mechanism and the use of the new reaction in synthesis of ethylenediamine derivatives are discussed. A new method for the preparation of unsymmetrical substituted ethylenediamine via the reduction ring-opening reaction of imidazoline is provided.

  7. Ring-opening of gamma-valerolactone with amino compounds

    Chalid, Mochamad; Heeres, Hero J.; Broekhuis, Antonius A.


    Diols obtained by the ring-opening of biomass-based gamma-valerolactone (GVL) are potentially valuable building blocks that can be used as precursors in the manufacture of green polymers and resins. We report here a study on the ring-opening of GVL through adding amine compounds. The reactivity of

  8. Tandem Ring-Opening-Ring-Closing Metathesis for Functional Metathesis Catalysts.

    Nagarkar, Amit A; Yasir, Mohammad; Crochet, Aurelien; Fromm, Katharina M; Kilbinger, Andreas F M


    Use of a tandem ring-opening-ring-closing metathesis (RORCM) strategy for the synthesis of functional metathesis catalysts is reported. Ring opening of 7-substituted norbornenes and subsequent ring-closing metathesis forming a thermodynamically stable 6-membered ring lead to a very efficient synthesis of new catalysts from commercially available Grubbs' catalysts. Hydroxy functionalized Grubbs' first- as well as third-generation catalysts have been synthesized. Mechanistic studies have been performed to elucidate the order of attack of the olefinic bonds. This strategy was also used to synthesize the ruthenium methylidene complex.

  9. Photosonochemical catalytic ring opening of α-epoxyketones

    Saffar-Teluri Ali


    Full Text Available Abstract The combination of ultrasound and photochemical methods has been used for the catalytic ring opening of α-epoxyketones by 1-benzyl-2,4,6-triphenylpyridinium tetrafluoroborate (NBTPT as photocatalyst in methanol. Sonication of these compounds in the presence of NBTPT did not result in the opening of epoxide ring, but the use of ultrasound increased the rate of photoreaction.

  10. The base-free chemoselective ring opening of epoxides with carboxylic acids using [bmim]Br: a rapid entry into 1,2-diol mono-esters synthesis.

    Rad, Mohammad Navid Soltani; Behrouz, Somayeh


    A facile and highly convenient base-free protocol for the chemoselective preparation of 1,2-diol mono-esters is described. In this method, the regioselective ring opening of epoxides with carboxylic acids in the presence of [bmim]Br furnishes the corresponding 1,2-diol mono-esters in excellent yields. This method is efficient for various structurally diverse epoxides and carboxylic acids and it can be efficiently applied for the scale up synthesis of 1,2-diol mono-esters in reasonable to good yields. [bmim]Br remarkably influences the reaction progress and acts as both solvent and catalyst in this protocol.

  11. Ring opening of donor-acceptor cyclopropanes with the azide ion: a tool for construction of N-heterocycles.

    Ivanov, Konstantin L; Villemson, Elena V; Budynina, Ekaterina M; Ivanova, Olga A; Trushkov, Igor V; Melnikov, Mikhail Ya


    A general method for ring opening of various donor-acceptor cyclopropanes with the azide ion through an SN 2-like reaction has been developed. This highly regioselective and stereospecific process proceeds through nucleophilic attack on the more-substituted C2 atom of a cyclopropane with complete inversion of configuration at this center. Results of DFT calculations support the SN 2 mechanism and demonstrate good qualitative correlation between the relative experimental reactivity of cyclopropanes and the calculated energy barriers. The reaction provides a straightforward approach to a variety of polyfunctional azides in up to 91 % yield. The high synthetic utility of these azides and the possibilities of their involvement in diversity-oriented synthesis were demonstrated by the developed multipath strategy of their transformations into five-, six-, and seven-membered N-heterocycles, as well as complex annulated compounds, including natural products and medicines such as (-)-nicotine and atorvastatin.

  12. Nitrenes, diradicals, and ylides. Ring expansion and ring opening in 2-quinazolylnitrenes.

    Kvaskoff, David; Bednarek, Pawel; George, Lisa; Waich, Kerstin; Wentrup, Curt


    Tetrazolo[1,5-a]quinazoline (9) is converted to 2-azidoquinazoline (10) on sublimation at 200 degrees C and above, and the azide-tetrazole equilibrium is governed by entropy. 2-Quinazolylnitrenes 11 and 27 and/or their ring expansion products 14 and 29 can undergo type I (ylidic) and type II (diradicaloid) ring opening. Argon matrix photolysis of 9/10 affords 2-quinazolylnitrene (11), which has been characterized by ESR, UV, and IR spectroscopy. A minor amount of a second nitrene, formed by rearrangement or ring opening, is also observed. A diradical (19) is formed rapidly by type II ring opening and characterized by ESR spectroscopy; it decays thermally at 15 K with a half-life of ca. 47 min, in agreement with its calculated facile intersystem crossing (19T --> 19OSS) followed by facile cyclization/rearrangement to 1-cyanoindazole (21) (calculated activation barrier 1-2 kcal/mol) and N-cyanoanthranilonitrile (22). 21and 22 are the isolated end products of photolysis. 21 is also the end product of flash vacuum thermolysis. An excellent linear correlation between the zero-field splitting parameter D (cm(-1)) and the spin density rho on the nitrene N calculated at the B3LYP/EPRIII level is reported (R2 = 0.993 for over 100 nitrenes). Matrix photolysis of 3-phenyltetrazolo[1,5-a]quinazoline (25) affords the benzotriazacycloheptatetraene 29, which can be photochemically interconverted with the type I ring opening product 2-isocyano-alpha-diazo-alpha-phenyltoluene (33) as determined by IR and UV spectroscopy. The corresponding carbene 37, obtained by photolysis of 33, was detected by matrix ESR spectroscopy.

  13. Catalytic ring opening of cyclic hydrocarbons in diesel fuels

    Calemma, V.; Ferrari, M. [Eni S.p.A., San Donato Milanese (Italy). R and M Div.; Rabl, S.; Haas, A.; Santi, D.; Weitkamp, J. [Stuttgart Univ. (Germany). Inst. of Chemical Technology


    An approach for high-aromatic streams upgrading, allowing to meet future diesel quality standards, is saturation of the aromatic structures followed by the selective breaking of endocyclic C-C bonds of naphthenic structures so formed to produce alkanes with the same number of carbon atoms as the starting molecule ('selective ring opening, SRO'). Although theoretically, SRO is a promising route for upgrading low-value feeds to high-quality products, in practice, it continues to be a challenge owing to its complex chemistry. Product characteristics, do not only depend on the composition of the feed, but also on the operating conditions and the nature of the catalyst. Very recently, novel catalysts ('HIgh-PErformance Ring Opening Catalysts, HIPEROCs') were developed which allow a very selective ring opening of the model compound decalin to paraffins without degradation of the carbon number. The hydroconversion of dearomatized Light Cycle Oil (DeAr-LCO) over the abovementioned catalysts resulted in a remarkable change of the chemical structure of the feed with a strong decrease of naphthenic structures with two or more condensed rings and a concomitant increase of alkyl-substituted cyclohexanes and open-chain alkanes. The changes occurring in the chemical structures of feedstock during hydroconversion resulted in a remarkable increase of the Cetane Index of the products up to 11 units. In the present contribution, we examine the main factors affecting activity and selectivity of SRO catalysts in the light of the recent literature dealing with the subject and we report on the recent advances in hydroconversion of refinery cuts such as DeAr- LCO over HIPEROCs. (orig.)

  14. Synthesis of branched dithiotrisaccharides via ring-opening reaction of sugar thiiranes.

    Repetto, Evangelina; Manzano, Verónica E; Uhrig, María Laura; Varela, Oscar


    Satisfactory procedures are described for the synthesis of 5,6- and 3,4-thiirane derivatives from the respective hexofuranose or hexopyranose epoxide precursors. The controlled ring-opening reaction of thiiranes by 1-thioaldoses was successfully accomplished to afford, regio- and stereoselectively, β-S-(1→4)-3,4-dithiodisaccharides. For instance, the regioselective attack of per-O-acetyl-1-thioglucose (16) to C-4 of 2-propyl 2,6-di-O-acetyl-3,4-epithio-α-D-galactopyranoside (14) gave the derivative of Glcp-β-S-(1→4)-3,4-dithioGlcp-O-iPr (17). This thiodisaccharide was accompanied by the (1→3)-disulfide 18, formed between 16 and 17, and the symmetric (3→3)-disulfide 19, which resulted from the oxidative dimerization of 17. However, the S-acetyl derivative of 17 could be obtained in good yield (62%) by LiAlH(4) reduction of the crude mixture 17-19, followed by acetylation. The same sequence of reactions starting from 14 and the 1-thiolate of Galp afforded the per-O,S-acetyl derivative of Galp-β-S-(1→4)-3,4-dithio-α-D-Glcp-O-iPr (23), which was selectively S-deacetylated to give 25. The dithiosaccharides 17 and 25 are 3,4-di-S-analogues of derivatives of the natural disaccharides cellobiose and lactose, respectively. The ring-opening reaction of 5,6-epithiohexofuranoses of D-galacto (8) or L-altro (11) configuration with 1-thioaldoses was also regio- and stereoselective to give the respective β-S-(1→6)-linked 5,6-dithiodisaccharides 26 or 29 in excellent yields. Glycosylation of the free thiol group of 17, 25, or 26, using trichloroacetimidates as glycosyl donors, led to the corresponding branched dithiotrisaccharides. Some of them are sulfur analogues of derivatives of branched trisaccharides found in natural polysaccharides.

  15. 2-Pyridylnitrene and 3-pyridazylcarbene and their relationship via ring-expansion, ring-opening, ring-contraction, and fragmentation.

    Kvaskoff, David; Bednarek, Pawel; Wentrup, Curt


    Photolysis of triazolo[1,5-b]pyridazine 8 isolated in Ar matrix generates diazomethylpyridazines 9Z and 9E and diazopentenynes 11Z and 11E as detected by IR spectroscopy. ESR spectroscopy detected the 3-pydidazylcarbene 10 as well as pent-2-en-3-yn-1-ylidene 12 formed by loss of one and two molecules of N(2), respectively. Further photolysis caused rearrangement of the carbenes to 1,2-pentadien-4-yne 13 and 3-ethynylcyclopropene 14. Flash vacuum thermolysis (FVT) of 8 at 400-500 degrees C with Ar matrix isolation of the products yielded 13, 14, and 1,4-pentadiyne 15. At higher temperatures, glutacononitriles 27Z and 27E were formed as well together with minor amounts of 2- and 3-cyanopyrroles 28 and 29. Tetrazolo[1,5-a]pyridine/2-azidopyridine 22T/22A yields 2-pyridylnitrene 19 as well as the novel open-chain cyanodienylnitrene 23 and the ring-expanded 1,3-diazacyclohepta-1,2,4,6-tetraene 21 on short wavelength photolysis. Nitrenes 19 and 23 were detected by ESR spectroscopy, and cumulene 21 by IR and UV spectroscopy. FVT of 22T/22A also affords 2-pyridylnitrene 19 and diazacycloheptatetraene 21, as well as glutacononitriles 27Z,E and 2- and 3-cyanopyrroles 28 and 29. Photolysis of 21 above 300 nm yields the novel spiroazirene 25, identified by its matrix IR spectrum. The reaction pathways connecting the four carbenes (10Z,E and 12Z,E) and three nitrenes (19, 23EZ, and 23ZZ) in their open-shell singlet and triplet states are elucidated with the aid of theoretical calculations at DFT, CASSCF, and CASPT2 levels. Three possible mechanisms of ring-contraction in arylnitrenes are identified: (i) via ring-opening to dienylnitrenes, (ii) concerted ring-contraction, and (iii) via spiroazirenes 25, whereby (i) is the energetically most favorable.

  16. Block copolymer adhesion promoters via ring-opening metathesis polymerization

    Kent, M.S.; Saunders, R.


    Coupling agents are disclosed based on functionalized block copolymers for bonding thermoset polymers to solid materials. These are polymers which possess at least two types of functional groups, one which is able to attach to and react with solid surfaces, and another which can react with a thermoset resin, which are incorporated as pendant groups in monomers distributed in blocks (typically two) along the backbone of the chain. The block copolymers in this invention are synthesized by living ring-opening metathesis polymerization. 18 figs.


    Khadidja Benkenfoud; Amine Harrane; Mohammed Belbachir


    The cationic ring-opening polymerization of tetrahydrofuran using maghnite-H- is reported.Maghnite-H+,is a non-toxic solid catalyst issued from proton exchanged montmorillonite clay.Polytetrahydrofuran,also called "poly(butandiol) ether",with acetate and hydroxyl end groups was successfully synthesized.Effects of reaction temperature,weight ratio of initiator/monomer and reaction time on the conversion of monomer and on the molecular weight are investigated.A cationic mechanism of the reaction was proposed.This chemistry can be considered as a suitable route for preparing poly(THF) as a soft segment for thermoplastic elastomers.

  18. Tandem ring-opening/ring-closing metathesis polymerization: relationship between monomer structure and reactivity.

    Park, Hyeon; Lee, Ho-Keun; Choi, Tae-Lim


    Monomers containing either cycloalkenes with low ring strain or 1-alkynes are poor monomers for olefin metathesis polymerization. Ironically, keeping two inactive functional groups in proximity within one molecule can make it an excellent monomer for metathesis polymerization. Recently, we demonstrated that monomer 1 having cyclohexene and propargyl moieties underwent rapid tandem ring-opening/ring-closing metathesis (RO/RCM) polymerization via relay-type mechanism. Furthermore, living polymerization was achieved when a third-generation Grubbs catalyst was used. Here, we present a full account on this tandem polymerization by investigating how various structural modifications of the monomers affected the reactivity of the tandem polymerization. We observed that changing the ring size of the cycloalkene moieties, the length of the alkynes, and linker units influenced not only the polymerization rates but also the reactivities of Diels-Alder reaction, which is a post-modification reaction of the resulting polymers. Also, the mechanism of tandem polymerization was studied by conducting end-group analysis using (1)H NMR analysis, thereby concluding that the polymerization occurred by the alkyne-first pathway. With this mechanistic conclusion, factors responsible for the dramatic structure-reactivity relationship were proposed. Lastly, tandem RO/RCM polymerization of monomers containing sterically challenging trisubstituted cycloalkenes was successfully carried out to give polymer repeat units having tetrasubstituted cycloalkenes.

  19. Thermodynamic Presynthetic Considerations for Ring-Opening Polymerization.

    Olsén, Peter; Odelius, Karin; Albertsson, Ann-Christine


    The need for polymers for high-end applications, coupled with the desire to mimic nature's macromolecular machinery fuels the development of innovative synthetic strategies every year. The recently acquired macromolecular-synthetic tools increase the precision and enable the synthesis of polymers with high control and low dispersity. However, regardless of the specificity, the polymerization behavior is highly dependent on the monomeric structure. This is particularly true for the ring-opening polymerization of lactones, in which the ring size and degree of substitution highly influence the polymer formation properties. In other words, there are two important factors to contemplate when considering the particular polymerization behavior of a specific monomer: catalytic specificity and thermodynamic equilibrium behavior. This perspective focuses on the latter and undertakes a holistic approach among the different lactones with regard to the equilibrium thermodynamic polymerization behavior and its relation to polymer synthesis. This is summarized in a monomeric overview diagram that acts as a presynthetic directional cursor for synthesizing highly specific macromolecules; the means by which monomer equilibrium conversion relates to starting temperature, concentration, ring size, degree of substitution, and its implications for polymerization behavior are discussed. These discussions emphasize the importance of considering not only the catalytic system but also the monomer size and structure relations to thermodynamic equilibrium behavior. The thermodynamic equilibrium behavior relation with a monomer structure offers an additional layer of complexity to our molecular toolbox and, if it is harnessed accordingly, enables a powerful route to both monomer formation and intentional macromolecular design.

  20. Supported Catalysts Useful in Ring-Closing Metathesis, Cross Metathesis, and Ring-Opening Metathesis Polymerization

    Jakkrit Suriboot


    Full Text Available Ruthenium and molybdenum catalysts are widely used in synthesis of both small molecules and macromolecules. While major developments have led to new increasingly active catalysts that have high functional group compatibility and stereoselectivity, catalyst/product separation, catalyst recycling, and/or catalyst residue/product separation remain an issue in some applications of these catalysts. This review highlights some of the history of efforts to address these problems, first discussing the problem in the context of reactions like ring-closing metathesis and cross metathesis catalysis used in the synthesis of low molecular weight compounds. It then discusses in more detail progress in dealing with these issues in ring opening metathesis polymerization chemistry. Such approaches depend on a biphasic solid/liquid or liquid separation and can use either always biphasic or sometimes biphasic systems and approaches to this problem using insoluble inorganic supports, insoluble crosslinked polymeric organic supports, soluble polymeric supports, ionic liquids and fluorous phases are discussed.

  1. Ring opening polymerization of dilactide using salen complex as catalyst

    Idage, B.B., E-mail: bb.idage@ncl.res.i [Polymer Science and Engineering Division, National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008 (India); Idage, S.B.; Kasegaonkar, A.S.; Jadhav, R.V. [Polymer Science and Engineering Division, National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008 (India)


    The recent concerns about our environment have led to search for environmentally benign and sustainable materials that could substitute the more commonly used petroleum based materials. Biodegradable and sustainable polylactide (PLA) is becoming one of the most promising and practical materials as a partial replacement for the petroleum-based materials. The commercially available PLA is generally homochiral poly(L-lactide) (PLLA) at present because L-lactic acid with high optical purity can only be obtained in bulk by fermentation of carbohydrate. PLLA is mostly synthesized by ring opening polymerization (ROP) of homochiral L-lactide (LLA), which is a cyclic dimer of L-lactic acid. In the present work, poly(L-lactide)s were synthesized by the ring opening polymerization (ROP) of L-lactide using iron and manganese salen complexes as catalyst. The new iron and manganese salen complexes were synthesized, purified, characterized and used as catalyst for polymerization of L-lactide. The poly(L-lactide)s prepared were characterized by infrared, proton NMR spectroscopy, solution viscosity, gel permeation chromatography, thermal analysis and X-ray diffraction.

  2. Synthesis of stereotetrads by regioselective cleavage of diastereomeric MEM-protected 2-methyl-3,4-epoxy alcohols with diethylpropynyl aluminum.

    Torres, Wildeliz; Torres, Gerardo; Prieto, José A


    The regioselectivity of the epoxide ring opening of 2-methyl-3,4-epoxy alcohols with diethylpropynylalane has been studied as a function of the C1 alcohol protecting group. An efficient selective method was developed using MEM as the protecting group. The reaction proceeded in a highly regioselective manner providing the useful 1,3-diol motif. The undesired 1,4-diol product produced by some free alcohol diastereomers was not observed. This highly stereoselective method provides access to termini-differentiated stereotetrads, which are essential building bocks for polypropionate synthesis.

  3. Multiple Olefin Metathesis Polymerization That Combines All Three Olefin Metathesis Transformations: Ring-Opening, Ring-Closing, and Cross Metathesis.

    Lee, Ho-Keun; Bang, Ki-Taek; Hess, Andreas; Grubbs, Robert H; Choi, Tae-Lim


    We demonstrated tandem ring-opening/ring-closing metathesis (RO/RCM) polymerization of monomers containing two cyclopentene moieties and postmodification via insertion polymerization. In this system, well-defined polymers were efficiently formed by tandem cascade RO/RCM reaction pathway. Furthermore, these polymers could be transformed to new A,B-alternating copolymers via a sequential cross metathesis reaction with a diacrylate. Additionally, we demonstrated the concept of multiple olefin metathesis polymerization in which the dicyclopentene and diacrylate monomers underwent all three olefin metathesis transformations (ring-opening, ring-closing, and cross metathesis) in one shot to produce A,B-alternating copolymer.

  4. Regioselective Synthesis of Indanones

    van Leeuwen, Thomas; Neubauer, Thomas M.; Feringa, Ben L.


    The degree of hydrolysis of polyphosphoric acid (PPA) has a crucial effect on the regioselectivity of the PPA-mediated synthesis of indanones. It was found that the regioselectivity can be switched by employing PPA with either a high or low content of P2O5. This methodology was used for the regiosel

  5. Synthesis of 5-iodopyrrolo[1,2-a]quinolines and indolo[1,2-a]quinolines via iodine-mediated electrophilic and regioselective 6-endo-dig ring closure.

    Verma, Akhilesh Kumar; Shukla, Satya Prakash; Singh, Jaspal; Rustagi, Vineeta


    The endo-cyclic ring closure of 1-(2-(substituted ethynyl)phenyl)-1H-pyrroles 3a-t and 1-(2-(substituted ethynyl)phenyl)-H-indole 4a-o mediated by Lewis acid (I(2)) under mild conditions afforded substituted 5-iodopyrrolo[1,2-a]quinolines 5a-t and 5-iodoindolo[1,2-a]quinolines 6a-o in good to excellent yields. The reaction shows selective C-C bond formation on the more electrophilic alkynyl carbon, resulting in the regioselective 6-endo-dig-cyclized product. Iodo derivatives of pyrrolo- and indoloquinolines allow functional group diversification on the quinoline nucleus, which proves to be highly advantageous for structural and biological activity assessments.

  6. Piranti Lunak Pengujian Struktur Matematika Grup, Ring, Field Berbasis Osp (Open Source Program

    Ngarap Im Manik


    Full Text Available This design of a computer software is a development and continuation of the software made on the previous research (2009/2010. However, this further research developed and expanded the scopes of testing more on the Siclic Group, Isomorphism Group, Semi Group, Sub Group and Abelian Group, Factor Ring, Sub Ring and Polynomial Ring; developed on the OSP (Open Source Program-based. The software was developed using the OSP-based language programming, such Java, so it is open and free to use for its users. This research succeeded to develop an open source software of Java program that can be used for testing specific mathematical Groups, such Ciclic Group, Isomorphism Group, Semi Group, Sub Group and Abelian Group, and Rings, Commutative Ring, Division Ring, Ideal Sub Ring, Ring Homomorphism, Ring Epimorphism and Fields. By the results, the software developed was able to test as same as the results from manual testing.

  7. Phase transfer reagent promoted tandem ring-opening and ring-closing reactions of unique 3-(1-alkynyl) chromones.

    Liu, Yang; Jin, Shiyu; Huang, Liping; Hu, Youhong


    A phase transfer reagent promoted tandem ring-opening and ring-closing reaction of 3-(1-alkynyl) chromones has been developed. This process remarkably generates functionalized 3-acyl-2-substituted chromones. Interestingly, when 3-(hepta-1,6-diyn-1-yl)chromone derivatives are applied, a novel tetracyclic chromone scaffold can be obtained by a further intramolecular 4 + 2 cyclization.

  8. Organic and composite aerogels through ring opening metathesis polymerization (ROMP)

    Mohite, Dhairyashil P.

    Aerogels are open-cell nanoporous materials, unique in terms of low density, low thermal conductivity, low dielectric constants and high acoustic attenuation. Those exceptional properties stem from their complex hierarchical solid framework (agglomerates of porous, fractal secondary nanoparticles), but they also come at a cost: low mechanical strength. This issue has been resolved by crosslinking silica aerogels with organic polymers. The crosslinking polymer has been assumed to form a conformal coating on the surface of the skeletal framework by covalent bridging elementary building blocks. However, "assuming" is not enough: for correlating nanostructure with bulk material properties, it is important to know the exact location of the polymer on the aerogel backbone. For that investigation, we synthesized a new norbornene derivative of triethoxysilane (Si-NAD) that can be attached to skeletal silica nanoparticles. Those norbornene-modified silica aerogels were crosslinked with polynorbornene by ring opening metathesis polymerization (ROMP). The detailed correlation between nanostructure and mechanical strength was probed with a wide array of characterization methods ranging from molecular to bulk through nano. Subsequently, it was reasoned that since the polymer dominates the exceptional mechanical properties of polymer crosslinked aerogels, purely organic aerogels with the same nanostructure and interparticle connectivity should behave similarly. That was explored and confirmed by: (a) synthesis of a difunctional nadimide monomer (bis-NAD), and preparation of robust polyimide aerogels by ROMP of its norbornene end-caps; and, (b) synthesis of dimensionally stable ROMP-derived polydicyclopentadiene aerogels by grafting the nanostructure with polymethylmethacrylate (PMMA) via free radical chemistry.

  9. Green chemistry approaches to the regioselective synthesis of spiro heterobicyclic rings using iodine as a new and efficient catalyst under solvent-free conditions.

    Prajapati, Dipak; Bhuyan, Debajyoti; Gohain, Mukut; Hu, Wenhao


    Iodine catalyzes the pseudo four-component reaction of an aldehyde, a urea or thiourea, and cyclic 1,3-dicarbonyl compounds under microwave irradiation in a solvent-free condition to yield various σ symmetric spiro heterobicyclic rings in excellent yields.

  10. ElectronTransfer Induced Ring Opening of α-Epoxyketones: Spirodioxolane Formation

    Farzad Nikpour


    Full Text Available Stereospecific formation of spirodioxolanes has been observed on electron transfer induced ring opening of α-epoxyketones by 2,4,6-triphenylpyrylium tetrafluoroborate in the presence of cyclohexanone

  11. Computational study of hydrogen shifts and ring-opening mechanisms in α-pinene ozonolysis products

    Kurtén, Theo; Rissanen, Matti P.; Mackeprang, Kasper


    , sterically unhindered) H-shifts of all four peroxy radicals formed in the ozonolysis of α-pinene using density functional (ωB97XD) and coupled cluster [CCSD(T)-F12] theory. In contrast to the related but chemically simpler cyclohexene ozonolysis system, none of the calculated H-shifts have rate constants...... products in the α-pinene ozonolysis system, additional ring-opening reaction mechanisms breaking the cyclobutyl ring are therefore needed. We further investigate possible uni- and bimolecular pathways for opening the cyclobutyl ring in the α-pinene ozonolysis system....

  12. Conductance of closed and open long Aharonov-Bohm-Kondo rings

    Shi, Zheng; Komijani, Yashar


    We calculate the finite temperature linear dc conductance of a generic single-impurity Anderson model containing an arbitrary number of Fermi liquid leads, and apply the formalism to closed and open long Aharonov-Bohm-Kondo (ABK) rings. We show that, as with the short ABK ring, there is a contribution to the conductance from the connected four-point Green's function of the conduction electrons. At sufficiently low temperatures this contribution can be eliminated, and the conductance can be expressed as a linear function of the T matrix of the screening channel. For closed rings we show that at temperatures high compared to the Kondo temperature, the conductance behaves differently for temperatures above and below vF/L , where vF is the Fermi velocity and L is the circumference of the ring. For open rings, when the ring arms have both a small transmission and a small reflection, we show from the microscopic model that the ring behaves like a two-path interferometer, and that the Kondo temperature is unaffected by details of the ring. Our findings confirm that ABK rings are potentially useful in the detection of the size of the Kondo screening cloud, the π /2 scattering phase shift from the Kondo singlet, and the suppression of Aharonov-Bohm oscillations due to inelastic scattering.

  13. Thermoset polymers via ring opening metathesis polymerization of functionalized oils

    Larock, Richard C; Henna, Phillip H; Kessier, Michael R


    The invention provides a method for producing a thermosetting resin from renewable oils, the method comprising supplying renewable oil molecules containing strained ring alkene moieties; reacting the alkene moieties with cyclic alkenes to create a polymer; and repeating the above two steps until the resin having desired characteristics are obtained. Also provided is a thermoset resin comprising functionalized renewable oil polymerized with a co-monomer.

  14. A homologous series of regioselectively tetradeprotonated group 8 metallocenes: new inverse crown ring compounds synthesized via a mixed sodium-magnesium tris(diisopropylamide) synergic base.

    Andrikopoulos, Prokopis C; Armstrong, David R; Clegg, William; Gilfillan, Carly J; Hevia, Eva; Kennedy, Alan R; Mulvey, Robert E; O'Hara, Charles T; Parkinson, John A; Tooke, Duncan M


    Subjecting ferrocene, ruthenocene, or osmocene to the synergic amide base sodium-magnesium tris(diisopropylamido) affords a unique homologous series of metallocene derivatives of general formula [(M(C(5)H(3))(2))Na(4)Mg(4)(i-Pr(2)N)(8)] (where M = Fe (1), Ru (2), or Os (3)). X-ray crystallographic studies of 1-3 reveal a common molecular "inverse crown" structure comprising a 16-membered [(NaNMgN)(4)](4+) "host" ring and a metallocenetetraide [M(C(5)H(3))(2)](4-) "guest" core, the cleaved protons of which are lost selectively from the 1, 1', 3, and 3'-positions. Variable-temperature NMR spectroscopic studies indicate that 1, 2, and 3 each exist as two distinct interconverting conformers in arene solution, the rates of exchange of which have been calculated using coalescence and EXSY NMR measurements.

  15. 3-Pyridylnitrene, 2- and 4-pyrimidinylcarbenes, 3-quinolylnitrenes, and 4-quinazolinylcarbenes. Interconversion, ring expansion to diazacycloheptatetraenes, ring opening to nitrile ylides, and ring contraction to cyanopyrroles and cyanoindoles

    Curt Wentrup


    Full Text Available Precursors of 3-pyridylnitrene and 2- and 4-pyrimidinylcarbenes all afford mixtures of 2- and 3-cyanopyrroles on flash vacuum thermolysis, but 3-cyanopyrroles are the first-formed products. 3-Quinolylnitrenes and 4-quinazolinylcarbenes similarly afford 3-cyanoindoles. 2-Pyrimidinylcarbenes rearrange to 3-pyridylnitrenes, but 4-pyrimidinylcarbenes and 4-quinazolinylcarbenes do not necessarily rearrange to the corresponding 3-pyridylnitrenes or 3-quinolylnitrenes. The ring contraction reactions are interpreted in terms of ring opening of either the nitrenes or the diazacycloheptatetraenes to nitrile ylides.

  16. 3-Pyridylnitrene, 2- and 4-pyrimidinylcarbenes, 3-quinolylnitrenes, and 4-quinazolinylcarbenes. Interconversion, ring expansion to diazacycloheptatetraenes, ring opening to nitrile ylides, and ring contraction to cyanopyrroles and cyanoindoles

    Lan, Nguyen Mong; Lukosch, Adelheid; Bednarek, Pawel; Kvaskoff, David


    Summary Precursors of 3-pyridylnitrene and 2- and 4-pyrimidinylcarbenes all afford mixtures of 2- and 3-cyanopyrroles on flash vacuum thermolysis, but 3-cyanopyrroles are the first-formed products. 3-Quinolylnitrenes and 4-quinazolinylcarbenes similarly afford 3-cyanoindoles. 2-Pyrimidinylcarbenes rearrange to 3-pyridylnitrenes, but 4-pyrimidinylcarbenes and 4-quinazolinylcarbenes do not necessarily rearrange to the corresponding 3-pyridylnitrenes or 3-quinolylnitrenes. The ring contraction reactions are interpreted in terms of ring opening of either the nitrenes or the diazacycloheptatetraenes to nitrile ylides. PMID:23766786

  17. Ring opening of monocyclic dimethyl cyclopropene via metathesis by tungsten catalyst- A computational study

    Jay Singh Meena; Pompozhi Protasis Thankachan


    Metathesis reaction of 3,3-disubstituted cyclopropene mediated by the model catalyst tungsten alkylidene W(NH)(CH2)(OCH3)2 has been studied at the B3LYP/LANL2DZ level of theory. The stationary points on the potential energy surface for ring opening metathesis were calculated considering all stereochemically distinct approaches of the 3,3-disubstituted cyclopropene to the model tungsten catalyst. The ring opening of cyclopropene moiety proceeds in two steps i.e., cycloaddition and ring opening. Each step involves a twisted trigonal bipyramidal transition structure. The syn orientation of cyclopropene to the NH group of the tungsten alkylidene is more favourable for product formation. Cyclopropene addition to tungsten alkylidene takes place preferentially on the CNO face; which is favoured by 10.89 kcal/mol over the COO face. The energy barriers for the syn cycloaddition and syn ring opening steps are 8.47 and 10.94 kcal/mol, respectively. The ring opening step is the rate determining step for the reaction of cyclopropene with tungsten catalyst, in contrast with the case of the molybdenum catalyst.

  18. Fast and selective ring-opening polymerizations by alkoxides and thioureas

    Zhang, Xiangyi; Jones, Gavin O.; Hedrick, James L.; Waymouth, Robert M.


    Ring-opening polymerization of lactones is a versatile approach to generate well-defined functional polyesters. Typical ring-opening catalysts are subject to a trade-off between rate and selectivity. Here we describe an effective catalytic system combining alkoxides with thioureas that catalyses rapid and selective ring-opening polymerizations. Deprotonation of thioureas by sodium, potassium or imidazolium alkoxides generates a hydrogen-bonded alcohol adduct of the thiourea anion (thioimidate). The ring-opening polymerization of L-lactide mediated by these alcohol-bonded thioimidates yields highly isotactic polylactide with fast kinetics and living polymerization behaviour, as evidenced by narrow molecular weight distributions (Mw/Mn < 1.1), chain extension experiments and minimal transesterifications. Computational studies indicate a bifunctional catalytic mechanism whereby the thioimidate activates the carbonyl of the monomer and the alcohol initiator/chain end to effect the selective ring-opening of lactones and carbonates. The high selectivity of the catalyst towards monomer propagation over transesterification is attributed to a selective activation of monomer over polymer chains.

  19. Syntheses of 2- or 6-Substituted Chromones and Chromone Ring-opening Reaction in Polyphosphoric Acid

    HE Xun-gui; YOU Qi-dong; LI Zhi-yu


    In an attempt to find new antitumor agents, a novel class of chromone compounds with a benzimidazole or a benzoxazole ring in positions 2 or 6 were synthesized via condensation in polyphosphoric acid(PPA) by using chromone acids as the starting materials. During the preparation process, it was found that PPA could cleave the chromone ring to produce a ring-opening compound(6). The molar ratio of the chromone compound(5) to the ring-opening compound(6) varied with the change of reaction temperature and time. Based on MTT protocol, the antitumor activity of each of the compounds obtained was evaluated against three human cancer cell lines: KB(oral epidermal), A2780(ovary) and Bel7402(liver). The IC50 varied from 54.7 μmol/L to more than 180 μmol/L.

  20. Preparation of Bottlebrush Polymers via a One-Pot Ring-Opening Polymerization (ROP) and Ring-Opening Metathesis Polymerization (ROMP) Grafting-Through Strategy.

    Radzinski, Scott C; Foster, Jeffrey C; Matson, John B


    Bottlebrush polymers are synthesized using a tandem ring-opening polymerization (ROP) and ring-opening metathesis polymerization (ROMP) strategy. For the first time, ROP and ROMP are conducted sequentially in the same pot to yield well-defined bottlebrush polymers with molecular weights in excess of 10(6) Da. The first step of this process involves the synthesis of a polylactide macromonomer (MM) via ROP of d,l-lactide initiated by an alcohol-functionalized norbornene. ROMP grafting-through is then carried out in the same pot to produce the bottlebrush polymer. The applicability of this methodology is evaluated for different MM molecular weights and bottlebrush backbone degrees of polymerization. Size-exclusion chromatographic and (1)H NMR spectroscopic analyses confirm excellent control over both polymerization steps. In addition, bottlebrush polymers are imaged using atomic force microscopy and stain-free transmission electron microscopy on graphene oxide.

  1. The Cationic Ring-Opening Polymerization of Tetrahydrofuran with 12-Tungstophosphoric Acid

    Hassan Al-Shahri


    Full Text Available The cationic ring-opening polymerization reaction of tetrahydrofuran at 20 ºC was catalyzed by H3PW12O40·13H2O as solid acid catalyst. The effect of the proportions of acetic anhydride and catalyst, reaction time and support on the polymerization reaction was investigated. It has been found that the yield and the viscosity of the polymer depend on the proportion of acetic anhydride, the presence of the latter in the reactant mixture being required for the ring-opening. The catalytic activity of the alumina-supported heteropolyacid results showed that Brønsted acid sites are more effective than Lewis ones for the cationic ring-opening polymerization.

  2. Novel Platinum-Catalyzed Ring-Opening of 1,2-Cyclopropanated Sugars with Alcohols

    Beyer, Jürgen; Madsen, Robert


    Reaction of 1,2-cyclopropanated sugars with a catalytic amount ofZeise's dimer [Pt(C2H4)Cl2]2 and an alcohol gives 2-C-branched glycosides by a novel platinum catalyzed ring-opening. A wide variety of alcohols can participate in this ring-opening reaction giving 2-C-branched glycosides ranging from...... methyl glycosides to complex disaccharides (17 examples). Very high diastereoselectivity is obtained at the newly formed C-1 stereocenter strongly favoring the alfa-glycoside. The mechanism presumably involves the formation of an intermediate platinacyclobutane which undergoes ring-opening at C-1...... by the alcohol followed by reductive elimination of platinum....

  3. Selective Ring Opening of 1-Methylnaphthalene Over NiW-Supported Catalyst Using Dealuminated Beta Zeolite.

    Kim, Eun-Sang; Lee, You-Jin; Kim, Jeong-Rang; Kim, Joo-Wan; Kim, Tae-Wan; Chae, Ho-Jeong; Kim, Chul-Ung; Lee, Chang-Ha; Jeong, Soon-Yong


    Nanoporous Beta zeolite was dealuminated by weak acid treatment for reducing the acidity. Bi-functional catalysts were prepared using commercial Beta zeolites and the dealuminated zeolites for acidic function, NiW for metallic function. 1-Methylnaphthalene was selected as a model compound for multi-ring aromatics in heavy oil, and its selective ring opening reaction has been investigated using the prepared bi-functional catalysts with different acidity in fixed bed reaction system. The dealuminated Beta zeolites, which crystal structure and nanoporosity were maintained, showed the higher SiO2/Al2O3 ratio and smaller acidity than their original zeolite. NiW-supported catalyst using the dealuminated Beta zeolite with SiO2/Al203 mole ratio of 55 showed the highest performance for the selective ring opening. The acidity of catalyst seemed to play an important role as active sites for the selective ring opening of 1-methylnaphthalene but there should be some optimum catalyst acidity for the reaction. The acidity of Beta zeolite could be controlled by the acid treatment and the catalyst with the optimum acidity for the selective ring opening could be prepared.

  4. Synthesis of benzamides by microwave assisted ring opening of less reactive dimethylaminobenzylidene oxazolone

    Saurabh C. Khadse


    Full Text Available This paper presents the synthesis of some benzamide compounds (B1–B10 by microwave-assisted ring opening of 4-(4-dimethylaminobenzylidene-2-phenyl-5-oxazolone (AZ4. By conventional synthesis involving heating, it was found difficult to obtain ring-opened products, probably due to poor tendency of the carbonyl carbon (C5 of AZ4 to undergo nucleophilic attack by mono/or disubstituted anilines. Microwave assisted reactions were easy to perform, have reduced the reaction time and produced good yields.

  5. Catalytic ring opening of decalin. Biofunctional versus hydrogenolytic pathways

    Weitkamp, J.; Rabl, S.; Haas, A.; Santi, D. [Stuttgart Univ. (Germany). Inst. of Chemical Technology; Ferrari, M.; Calemma, V. [Eni R and M Div., San Donato Milanese (Italy)


    Ir/silica, Pt/La-X and Rh/H-Beta were prepared and tested in the hydroconversion of cisdecalin at different temperatures. The catalytic tests were carried out under hydrogen in a high-pressure flow-type apparatus at 5.2 MPa. On the three catalysts open-chain decane yields up to 20 % were achieved, which is much higher than the yields reported so far in the literature. Pt/La-X and Rh/H-Beta behave as bifunctional catalysts with a high tendency for skeletal isomerization. On these catalysts the so-called paring reaction via carbenium ions occurs, leading to iso-butane and methylcyclopentane as main hydrocracked products. On Ir/SiO{sub 2}, carbon-carbon bond cleavage occurs through hydrogenolysis on the noble metal without prior isomerization. As a consequence the product spectrum is less complex than on the bifunctional catalysts which makes the system particularly amenable to mechanistic studies. (orig.)

  6. Phenol-containing macrocyclic diamides as new catalysts in the highly regioselective conversion of epoxides to beta-hydroxy thiocyanates.

    Sharghi, H; Nasseri, M A; Niknam, K


    The regioselective ring-opening reactions of some epoxides with ammonium thiocyanate in the presence of a series of new phenol-containing macrocyclic diamides and also dibenzo-18-crown-6-, 18-crown-6-, benzo-15-crown-5-, and pyridine-containing macrocyclic diamide have been studied. The epoxides were subject to cleavage by NH(4)SCN in the presence of these catalysts under mild reaction conditions in various aprotic solvents. In this study, reagents and conditions have been discovered with which the individual beta-hydroxy thiocyanates can be synthesized in high yield and with more than 90% regioselectivity. The results can be discussed in terms of a four-step mechanism: (1) formation of complex between catalyst and NH(4)SCN, (2) release of SCN(-) nucleophile from the complex, (3) reaction of the active nucleophile at the less sterically hindered site in the epoxide, and (4) regeneration of catalyst. The major advantages of this method are as follows: (1) high regioselectivity, (2) simple regeneration of catalyst, (3) its reuse through several cycles without a decrease in activity, and (4) ease of workup of the reaction.

  7. Mass Spectral Profile for Rapid Differentiating Beta-Lactams from Their Ring-Opened Impurities

    Hecheng Wang


    Full Text Available High performance liquid chromatography tandem mass spectrometry (HPLC MS has been widely used for β-lactam antibiotics determination. However, its application to identify impurities of these frequently used drugs is not sufficient at present. In this job, characteristic profiles of the collision induced dissociation (CID spectra of both β-lactams and ring-opened β-lactams were extracted from the MS data of six β-lactam antibiotics and their forty-five impurities, and were confirmed by the MS data reported in the literature. These characteristics have been successfully applied to rapid differentiation of β-lactam and ring-opened β-lactam impurities in cefixime, cefdinir, and cefaclor. However, these characteristic profiles can only be obtained under low activating voltage. They did not display in the high energy activated CID spectra. Diagnostic fragmentations for determining the localization of double bond and substituents on the thiazine ring and the side chain were also observed. In addition, several characteristic fragmentations are hopeful to be used to differentiate the configurations of C-2 on the thiazine ring of ring-opened impurities, which is generally disadvantageous of mass spectrometry. Taken together, forty-five impurities were identified from the capsules of cefixime, cefdinir, and cefaclor.

  8. Mass Spectral Profile for Rapid Differentiating Beta-Lactams from Their Ring-Opened Impurities.

    Wang, Hecheng; Huang, Haiwei; Cao, Jin; Chui, Dehua; Xiao, Shengyuan


    High performance liquid chromatography tandem mass spectrometry (HPLC MS) has been widely used for β-lactam antibiotics determination. However, its application to identify impurities of these frequently used drugs is not sufficient at present. In this job, characteristic profiles of the collision induced dissociation (CID) spectra of both β-lactams and ring-opened β-lactams were extracted from the MS data of six β-lactam antibiotics and their forty-five impurities, and were confirmed by the MS data reported in the literature. These characteristics have been successfully applied to rapid differentiation of β-lactam and ring-opened β-lactam impurities in cefixime, cefdinir, and cefaclor. However, these characteristic profiles can only be obtained under low activating voltage. They did not display in the high energy activated CID spectra. Diagnostic fragmentations for determining the localization of double bond and substituents on the thiazine ring and the side chain were also observed. In addition, several characteristic fragmentations are hopeful to be used to differentiate the configurations of C-2 on the thiazine ring of ring-opened impurities, which is generally disadvantageous of mass spectrometry. Taken together, forty-five impurities were identified from the capsules of cefixime, cefdinir, and cefaclor.

  9. Ring-opening and Elimination Cooligomerization of Cyclic Carbonates and ε-Caprolactone

    Sándor Kéki; János T(o)r(o)k; Gy(o)rgy Deák; Miklós Zsuga


    @@ 1Introduction Cyclic carbonates e.g. ethylene- and propylene carbonate undergo ring-opening polymerization (ROP) at elevated temperatures (> 100 ℃ ) in the presence of initiators such as Lewis acids, bases, or transesterification catalysts to yield poly(ether carbonates) as outlined below. See Fig. 1.

  10. Sulfuric acid as a catalyst for ring-opening of biobased bis-epoxides

    Vegetable oils can be relatively and easily transformed into bio-based epoxides. Because of this, the acid-catalyzed epoxide ring-opening has been explored for the preparation of bio-based lubricants and polymers. Detailed model studies are carried out only with mono-epoxide made from methyl oleate,...

  11. Solvent-Free Microwave Synthesis of Aryloxypropanolamines by Ring Opening of Aryloxy Epoxides

    Rukhsana I. Kureshy


    Full Text Available The ring opening reaction of aryloxyepoxides with isopropylamine under solvent-free microwave irradiation produced therapeutically useful -blockers-aryloxypropanolamines in excellent yield (up to 98% in 10 minutes which is considerably less than the time taken in classical heating (∼16 hours.

  12. Clickable Polylactic Acids by Fast Organocatalytic Ring-Opening Polymerization in Continuous Flow

    Berg, van den Sebastiaan A.; Zuilhof, Han; Wennekes, Tom


    The use of microreactor technology for the ring-opening polymerization of l-lactide catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene allows for rapid optimization of reaction parameters (reaction temperature and residence time). At moderate catalyst loading, good control over the polymerization i

  13. Ring-Opening Polymerization of Lactide to Form a Biodegradable Polymer

    Robert, Jennifer L.; Aubrecht, Katherine B.


    In this laboratory activity for introductory organic chemistry, students carry out the tin(II) bis(2-ethylhexanoate)/benzyl alcohol mediated ring-opening polymerization of lactide to form the biodegradable polymer polylactide (PLA). As the mechanism of the polymerization is analogous to that of a transesterification reaction, the experiment can be…

  14. The photochemical ring opening reaction of chromene as seen by transient absorption and fluorescence spectroscopy

    Herzog, Teja T.; Ryseck, Gerald; Ploetz, Evelyn; Cordes, Thorben


    In this paper we investigate the photochromic ring-opening reaction of 2,2-diphenyl-5,6-benzo(2H)-chromene. In particular, we study the uncertainties and contradictions in various published reaction models using a combination of transient absorption and fluorescence spectroscopy with femtosecond

  15. Rhodium-catalyzed asymmetric ring opening of azabenzonorbornadiene with substituted piperazine nucleophiles

    Lei Xie; Ding Qiao Yang; Shuang Qi Zhao; Huan Wang; Li Hua Liang; Ren Shi Luo


    We have developed an asymmetric ring opening reaction of azabenzonorbornadiene with substituted piperazine. By increasing the amount of catalyst (from 2.5 to 5%) and ligands (5 to 10%) as well as addition of ammonium iodide, the products can be obtained in high yield and the reaction time shortened dramatically, but the ee values were rather low.

  16. Enzyme-catalyzed ring-opening polymerization of unsubstituted beta-lactam

    Schwab, Leendert W.; Kroon, Renee; Schouten, Arend Jan; Loos, Katja


    The synthesis of poly(beta-alanine) by Candida antarctica lipase B immobilized as novozyme 435 catalyzed ring-opening of 2-azetidinone is reported. After removal of cyclic side products and low molecular weight species pure linear poly(beta-alanine) is obtained. The formation of the polymer is confi

  17. An Introductory Organic Chemistry Review Homework Exercise: Deriving Potential Mechanisms for Glucose Ring Opening in Mutarotation

    Murdock, Margaret; Holman, R. W.; Slade, Tyler; Clark, Shelley L. D.; Rodnick, Kenneth J.


    A unique homework assignment has been designed as a review exercise to be implemented near the end of the one-year undergraduate organic chemistry sequence. Within the framework of the exercise, students derive potential mechanisms for glucose ring opening in the aqueous mutarotation process. In this endeavor, 21 general review principles are…

  18. Lewis Acid Catalyzed Ring-opening Polymerization of Epoxidized Soybean Oil in Liquid Carbon Dioxide

    Ring-opening polymerization of epoxidized soybean oil (ESO) catalyzed by boron trifluoride diethyl etherate (BF3•OEt2), in liquid carbon dioxide, was conducted in an effort to develop useful biobased biodegradable polymers. The resulting polymers (RPESO) were characterized by FTIR spectroscopy, diff...

  19. Ring-opening of cyclic ethers with carbon–carbon bond formation by Grignard reagents

    Christensen, Stig Holden; Holm, Torkil; Madsen, Robert


    The ring-opening of cyclic ethers with concomitant C–C bond formation was studied with a number of Grignard reagents. The transformation was performed in a sealed vial by heating to ∼160 °C in an aluminum block or at 180 °C in a microwave oven. Good yields of the product alcohols were obtained wi...

  20. Silica Chloride Nano Particle Catalyzed Ring Opening of Epoxides by Aromatic Amines

    Karimian Ramin; Piri Farideh; Karimi Babak; Moghimi Abolghasem


    Silica chloride nano particle (nano SiO2-Cl), has been found to be heterogeneous catalyst for facile, simple and mild ring opening of epoxides with aromatic amines to afford β-amino alcohols in dry CH2Cl2 at room temperature.

  1. Rhodium-catalyzed Asymmetric Ring Opening Reaction of Oxabenzo-norbornadiene with Substituted Phenolic Nucleophiles


    We have developed an asymmetric ring opening reaction of oxabenzonorbornadienes with substituted phenolic nucleophiles. Under the reaction conditions ( [Rh(COD)Cl]2 (1 mol%),(S)-(R)-PPF-ptBu2 (2 mol%), THF, reflux), the reaction products were obtained with high yield and enantiomeric excesses ( up to 99% ee).

  2. Organocatalytic Ring-Opening Polymerization of Trimethylene Carbonate to Yield a Biodegradable Polycarbonate

    Chan, Julian M. W.; Zhang, Xiangyi; Brennan, Megan K.; Sardon, Haritz; Engler, Amanda C.; Fox, Courtney H.; Frank, Curtis W.; Waymouth, Robert M.; Hedrick, James L.


    In this laboratory experiment, students work in pairs to synthesize a simple aliphatic polycarbonate via ring-opening polymerization of trimethylene carbonate using 1,8-diazabicyclo[5.4.0]undec-7-ene and thiourea as organocatalysts. Following polymer isolation, students cool the material in a dry ice/acetone bath to observe its glass-transition…

  3. Ring-Opening Polymerization of Lactide to Form a Biodegradable Polymer

    Robert, Jennifer L.; Aubrecht, Katherine B.


    In this laboratory activity for introductory organic chemistry, students carry out the tin(II) bis(2-ethylhexanoate)/benzyl alcohol mediated ring-opening polymerization of lactide to form the biodegradable polymer polylactide (PLA). As the mechanism of the polymerization is analogous to that of a transesterification reaction, the experiment can be…

  4. Microwave Power Transmission Using Electromagnetic Coupling of Open-Ring Resonators


    Ao, I. Awai and Y. Ohno, “Wireless Inter-Chip Signal Transmission by Electromagnetic Coupling of Open-Ring Resonators,” Japanese Journal of Applied Physics , vol...Y Hu, H. Kawai, N. Shinohara, N. Niwa, and Y. Ohno, : GaN Schottky Diodes for Microwave Power Rectification, Japanese Journal of Applied Physics , Vol

  5. Bifunctional Asymmetric Catalysis with Hydrogen Chloride: Enantioselective Ring-Opening of Aziridines Catalyzed by a Phosphinothiourea.

    Mita, Tsuyoshi; Jacobsen, Eric N


    Ring-opening of aziridines with hydrogen chloride to form β-chloroamine derivatives is catalyzed by a chiral phosphinothiourea derivative in high yields and with high enantioselectivities. On the basis of (31)P NMR studies, activation of HCl appears to proceed via quantitative protonation of the catalyst to afford a phosphonium chloride complex.

  6. Silver(I)-catalyzed dual activation of propargylic alcohol and aziridine/azetidine: triggering ring-opening and endo-selective ring-closing in a cascade.

    Bera, Milan; Roy, Sujit


    [Ag(COD)(2)]PF(6) catalyzes the reaction between propargyl alcohols and N-tosylaziridines/azetidines leading to a diverse range of N,O-heterocycles, namely, oxazines, oxazepines, and oxazocines via ring-opening and ring-closing in a cascade.

  7. Salicylaldimine Copper(II) complex catalyst: Pioneer for ring opening Polymerization of Lactide



    Salicylaldimine copper complex has been synthesized and its reactivity for the ring-opening polymerization(ROP) of lactide has been studied. This monomeric copper complex was prepared by the reaction ofcopper(II) solution with one molar equivalent of salicylaldimine Schiff-base ligand in methanol under nitrogenatmosphere. This copper complex has been characterized by different spectroscopic methods, which showedsquare planar geometry. The molecular structure of the salicylaldimine Schiff-base has been determined byX-ray diffraction studies. The complex was tested as the initiator for the ring-opening polymerization of lactide,with variation in diamine group in ligand. The rate of polymerization is dependent on the diamine groupin the following order: ethylene > propylene > phenyl. The salicylaldimine copper complex allows controlledring-opening polymerization as indicated by the linear relationship between the percentage conversion and thenumber-average molecular weight. On the basis of literature reports, a mechanism for ROP of lactide has beenproposed.

  8. Green chemistry: Efficient epoxides ring-opening with 1-butanol under microwave irradiation

    Garcia-Vidal, Jesus A. [Departamento de Quimica Inorganica, Facultad de Ciencias, Universidad de Extremadura, Campus Universitario, Avda. de Elvas, s/n, E-06071-Badajoz (Spain); Duran-Valle, Carlos J. [Departamento de Quimica Inorganica, Facultad de Ciencias, Universidad de Extremadura, Campus Universitario, Avda. de Elvas, s/n, E-06071-Badajoz (Spain)]. E-mail:; Ferrera-Escudero, Santiago [Departamento de Quimica Inorganica y Quimica Tecnica, Universidad Nacional de Educacion a Distancia, C/Senda del Rey, 9, E-28040 Madrid (Spain)


    Two activated carbons treated with mineral acids (HNO{sub 3} and sulfonitric mixture) have been tested as acid catalysts in the epoxides (1,2-epoxyhexane and styrene oxide) ring-opening reaction with 1-butanol under microwave (MW) irradiation. The mayor obtained product is that resulting of the alcohol addition to the most substituted carbon in the epoxide ring. The most active catalyst is that treated with sulfonitric mixture. The use of a MW oven allows achieving to the complete conversion of styrene oxide in only 2 min.

  9. Borane catalysed ring opening and closing cascades of furans leading to silicon functionalized synthetic intermediates

    Hazra, Chinmoy K.; Gandhamsetty, Narasimhulu; Park, Sehoon; Chang, Sukbok


    The conversion of renewable biomass resources to synthetically valuable chemicals is highly desirable, but remains a formidable challenge in regards to the substrate scope and reaction conditions. Here we present the development of tris(pentafluorophenyl)borane-catalysed conversion of furans via ring-opening and closing cascade processes to afford silicon-functionalized synthetic chemicals under transition metal-free conditions. The furan ring-opening with hydrosilanes is highly efficient (TON up to 2,000) and atom-economical without forming any byproduct to give rise to α-silyloxy-(Z)-alkenyl silanes. Additional equivalents of silane smoothly induce a subsequent B(C6F5)3-catalysed cyclization of initially formed olefinic silane compounds to produce anti-(2-alkyl)cyclopropyl silanes, another versatile synthon being potentially applicable in the synthesis of natural products and pharmacophores.

  10. Optimization of the oxirane ring opening reaction in biolubricant base oil production

    Jumat Salimon


    Full Text Available This study has successfully optimized the conversion of monoepoxide linoleic acid (MEOA into biolubricant via oxirane ring opening reaction using oleic acid (OA with p-toluene sulfonic acid (PTSA as a catalyst. The four main factors were studied according to a D-optimal design at three levels. These factors were OA/MEOA ratio, PTSA/MEOA ratio, temperature and reaction time. This analysis evidenced the best operating conditions of the oxirane ring opening reaction performed at the following condition; OA/MEOA ratio of 0.30:1 (w/w, PTSA/MEOA ratio of 0.50:1 (w/w, reaction temperature at 110 °C and reaction time at 4.5 h, an optimum yield of 84.61% and OOC of 0.05%. This model results showed a good agreement with the predict value, demonstrating that this methodology may be useful for industrial process optimization.

  11. Synthesis of first row transition metal carboxylate complexes by ring opening reactions of cyclic anhydrides

    Jubaraj Bikash Baruah


    Hydrolytic and solvolytic ring opening reactions of phthalic anhydride, pyromellitic dianhydride and 2,3-pyridine dicarboxylic anhydride in the presence of various transition metal salts with or without a ancillary ligands were studied. The reactions were found to be dependent on stoichiometry of ligand and types of anhydride used. In the case of pyromellitic dianhydride selective ring opening reaction by cobalt(II) ions gave 1,3-benzene dicarboxylate derivatives, whereas use of copper(II) ions gave 1,4-benzene dicarboxylate derivatives. Preference for methanolysis was seen in the case of copper (II) promoted reactions of pyromellitic dianhydride in the presence of 1:1 metal to 1,10-phenanthroline ratio.

  12. Ring Opening Metathesis Polymerization of Cyclopentene Using a Ruthenium Catalyst Confined by a Branched Polymer Architecture

    Mugemana, Clement


    Multi-arm polystyrene stars functionalized with Grubbs-type catalysts in their cores were synthesized and used for the ring-opening metathesis polymerization (ROMP) of cyclopentene. The spatial confinement of the catalytic sites and the nanoscale phase separation between polystyrene and the growing polypentenamer chains lead to a dramatic inhibition of the ROMP termination and chain transfer steps. Consequently, cyclopentene polymerizations proceeded fast and with a high degree of conversion even in air. The Grubbs second generation catalyst was oxidatively inactivated under the same conditions. In contrast to conventional small-molecule catalysts, the ultimate degree of conversion of cyclopentene monomer and the polydispersity of the product polypentenamer are not affected by the temperature. This indicates that spatial confinement of the catalyst resulted in a significant change in the activation parameters for the alkene metathesis ring-opening.

  13. Ring-Opening of Oxiranes using Taeniolite-Supported Tris(β-DiketonatoZirconium

    Yessi Permana


    Full Text Available A series of tris(β-diketonatozirconium(IV complexes were immobilized into a synthetic clay structure of Taeniolite by an ion-exchange method to generate organic/inorganic hybrid compounds. The hybrid compound served as a good catalyst for ring-opening reactions of methyl, ethyl, and dimethyl oxiranes with various alcohols to generate primary alkoxy alcohols in appreciable selectivity. This method described a technique to immobilize cationic zirconium complexes without losing selectivity.

  14. Improvement of Physicochemical Characteristics of Monoepoxide Linoleic Acid Ring Opening for Biolubricant Base Oil

    Jumat Salimon; Nadia Salih; Bashar Mudhaffar Abdullah


    For environmental reasons, a new class of environmentally acceptable and renewable biolubricant based on vegetable oils is available. In this study, oxirane ring opening reaction of monoepoxide linoleic acid (MEOA) was done by nucleophilic addition of oleic acid (OA) with using p-toluene sulfonic acid (PTSA) as a catalyst for synthesis of 9(12)-hydroxy-10(13)-oleoxy-12(9)-octadecanoic acid (HYOOA) and the physicochemical properties of the resulted HYOOA are reported to be used as biolubricant...

  15. Iridium-catalyzed asymmetric ring-opening reactions of oxabicyclic alkenes with secondary amine nucleophiles

    Dingqiao Yang


    Full Text Available Iridium-catalyzed asymmetric ring-opening reactions of oxabicyclic alkenes with various aliphatic and aromatic secondary amines are reported for the first time. The reaction gave the corresponding trans-1,2-dihydronaphthalenol derivatives in good yields with moderate enantioselectivities in the presence of 2.5 mol % [Ir(CODCl]2 and 5 mol % bisphosphine ligand (S-p-Tol-BINAP. The trans-configuration of 3f was confirmed by X-ray crystallography.

  16. Well-defined polyethylene molecular brushes by polyhomologation and ring opening metathesis polymerization

    Zhang, Hefeng


    A novel strategy using polyhomologation and ring opening metathesis polymerization (ROMP) has been developed for the synthesis of well-defined polyethylene (PE) molecular brushes. Polyhomologation was used to afford an OH-terminated PE, which after transformation to the norbornyl PE macromonomer was subjected to ROMP. Kinetics of ROMP of the PE macromonomer was studied by in situ1H NMR monitoring. The brush structure was proved from HT-GPC, 1H NMR and DSC results.

  17. Tri-n-butylphosphine Mediated Ring-Opening Reactions of Aziridines or Epoxides with Diphenyl Diselenide

    ZHANG Wan-Xuan; YE Kang; RUAN Shan; CHEN Zu-Xing; XIA Qing-Hua


    Aziridines and epoxides were reacted with diphenyl diselenide in the presence of a stoichiometric amount of (n-Bu)3P, respectively, giving β-amino-or β-hydroxy selenides in moderate to excellent yields under mild conditions. In the reactions the (n-Bu)3P might act as a reductant though it was a nucleophilic catalyst in other similar ring-opening reactions.

  18. Tri-n-butylphosphane catalyzed ring opening of aziridines with secondary amines

    Wan Xuan Zhang; Li Su; Wei Gang Hu; Jie Zhou


    Ring opening of aziridine with dialkyl amine took place readily in the presence of catalytic amounts of tri-n-butylphosphane (10 mol%) in the mixture of CH3CN/H2O (10:1),giving corresponding vicinal diamines in mediate to high yields (58-95%) with good regioselecfivifie,while aromatic secondary amine could not react under the same condifions.Tti-n-butylphosphane exhibited different catalytic selectivity to amines from Lewis acid catalysts.

  19. Lanthanum heterocyclic Schiff-base complex initiated ring-opening polymerization of ε-caprolactone

    Wen Lin; Wei Lin Sun; Zhi Quan Shen


    Lanthanum complex supported by the heterocyclic Schiff-base ligand of N-(2-pyridyl)-3,5-di-tert-butyl-salicylaldimine was prepared and employed for the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). The polymers obtained with this initiator showed a unimodal molecular weight distribution implied that only one active species was present. Mechanism study revealed that the polymerization proceeds via acyl-oxygen bond cleavage.

  20. Ring-opening Polymerization of 6-Caprolactone by Lanthanide Tris( 2,6- dimethylphenolate ) s

    张丽芳; 沈之荃; 于翠萍


    Lanthanide tris ( 2,6-dimethylphenolate ) s [ Ln ( ODMP)3 ] were used as iniliators for ring-opening polymerization of e-caprolac-tone (CL) for the first time. The influence of different rare earth elements and solvents was investigated. 1H NMR spectral data of polycaprolactone (PCL) obtained showed that the poly-merization mechanism is in agreement with the coordination-in-sertion mechanism and the selective cleavage of the acyl-oxygen bond of CL.

  1. Pyridine ring opening at room temperature at a rhenium tricarbonyl bipyridine complex.

    Huertos, Miguel A; Pérez, Julio; Riera, Lucía


    Pyridine ring opening occurs in the reaction of [Re(CO)3(MeIm)(bipy)]OTf with KN(SiMe3)2 followed by double methylation with methyl trifluoromethanesulfonate. Analogues of the neutral product of the initial deprotonation and of the product of the first methylation were isolated by using mesitylimidazole (MesIm) in place of methylimidazole (MeIm) and/or 1,10-phenanthroline (phen) instead of 2,2'-bipyridine (bipy).

  2. A new endocapsular open ring for prevention of anterior and posterior capsule opacification

    Pallikaris, Ioannis G; Stojanovic, Nela R; Ginis, Harilaos S


    Purpose The aim of this study is to demonstrate the functionality of a new design of a thick endocapsular open ring for prevention of anterior capsule opacification (ACO) and posterior capsule opacification (PCO). Setting The Institute of Vision and Optics, University of Crete and University Hospital of Heraklion, Crete, Greece. Design Prospective, interventional pilot study. Methods Fifteen patients (17 eyes) underwent cataract surgery with phacoemulsification. During surgery, a thick endocapsular open ring (peripheral capsule reconstructor) was inserted into the capsular bag, prior to intraocular lens (IOL) implantation. Six different models of IOL were implanted. Postoperatively, the degree of ACO and PCO was evaluated and described as none, mild, moderate, or severe. Results The mean follow-up period was 30±8.06 months (range: 12–36 months). At the last follow-up, mild PCO was observed in only three eyes and mild ACO in three patients. The centration of IOLs was good in all but one eye, which had a tilted IOL. Conclusion The results of this pilot study suggest that the implantation of a new design of thick endocapsular open ring is feasible and may contribute to the prevention of PCO and ACO after cataract surgery. PMID:27843291

  3. A new endocapsular open ring for prevention of anterior and posterior capsule opacification

    Pallikaris IG


    Full Text Available Ioannis G Pallikaris, Nela R Stojanovic, Harilaos S Ginis Institute of Vision and Optics, Department of Medicine, University of Crete, Heraklion, Crete, Greece Purpose: The aim of this study is to demonstrate the functionality of a new design of a thick endocapsular open ring for prevention of anterior capsule opacification (ACO and posterior capsule opacification (PCO. Setting: The Institute of Vision and Optics, University of Crete and University Hospital of Heraklion, Crete, Greece. Design: Prospective, interventional pilot study. Methods: Fifteen patients (17 eyes underwent cataract surgery with phacoemulsification. During surgery, a thick endocapsular open ring (peripheral capsule reconstructor was inserted into the capsular bag, prior to intraocular lens (IOL implantation. Six different models of IOL were implanted. Postoperatively, the degree of ACO and PCO was evaluated and described as none, mild, moderate, or severe. Results: The mean follow-up period was 30±8.06 months (range: 12–36 months. At the last follow-up, mild PCO was observed in only three eyes and mild ACO in three patients. The centration of IOLs was good in all but one eye, which had a tilted IOL. Conclusion: The results of this pilot study suggest that the implantation of a new design of thick endocapsular open ring is feasible and may contribute to the prevention of PCO and ACO after cataract surgery. Keywords: intraocular implant, cataract, phacoemulsification, silicone

  4. Open-Ring Enhancement in Pseudotumoral Multiple Sclerosis: Important Radiological Aspect

    Frederico Carvalho de Medeiros


    Full Text Available Introduction. Observation of open-ring enhancement in magnetic resonance imaging (MRI is considered a specificity marker for diagnosing pseudotumoral multiple sclerosis (MS. This finding is of great value in the differential diagnosis of tumefactive lesions. Case Report. We describe a 55-year-old white woman, with previous history of ovarian cancer and recent history of fatigue and bilateral retroorbital pain. Important bilateral visual impairment evolved over one month. Physical examination detected the presence of right homonymous hemianopia. Cranial MRI showed an expanding lesion with open-ring enhancement. Given the range of diagnostic possibilities, a stereotactic biopsy was performed, and histopathological examination was consistent with an active demyelinating disease. The patient was treated with 1 g of methylprednisolone and symptoms improved following a significant reduction in the lesion. Conclusions. We highlight the MRI results suggestive of pseudotumoral MS, especially open-ring enhancement, which is an important radiologic aspect to diagnosis and can assist in avoiding unnecessary biopsies.


    Hong-ming Zhang; Qing-zhong Guo; Tian-lu Chen


    A series of cyclic (arylene phosphonate) oligomers were prepared by reaction of phenylphosphonic dichloride (PPD) with various bisphenols under pseudo-high dilution conditions via interfacial polycondensation. The yield of cyclic (arylenc phosphonate) oligomers is over 85% by using hexadecyltrimethylammonium bromide as phase transfer catalyst (PTC) at 0 ℃. The structures of the cyclic oligomers were confirmed by a combination of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and IR analysis. These cyclic oligomers undergo facile ring-opening polymerization in the melt by using potassium 4,4'-biphenoxide as the initiator to give linear polyphosphonate. Free-radical ring-opening polymerization of cyclic(arylene phosphonate) oligomers containing sulfur linkages was also performed in the melt using 2,2'-dithiobis(benzothiazole) (DTB) as the initiator at 270℃ and the resulting polymer had a Mw of 8 × 103 with a molecular weight distribution of 4. Ring-opening copolymerization of these cyclic oligomers with cyclic carbonate oligomers was also achieved. The average molecular weight of the resulting copolymer is higher than the corresponding homopolymer and the thermal stability of the copolymer is better than the corresponding homopolymer.

  6. Liberation of methyl acrylate from metallalactone complexes via M-O ring opening (M = Ni, Pd) with methylation agents

    Lee, S. Y Tina


    Ring opening of various nickela- and palladalactones induced by the cleavage of the M-O bond by methyl trifluoromethanesulfonate (MeOTf) and methyl iodide (MeI) is examined. Experimental evidence supports the mechanism of ring opening by the alkylating agent followed by β-H elimination leading to methyl acrylate and a metal-hydride species. MeOTf shows by far higher efficiency in the lactone ring opening than any other methylating agent including the previously reported methyl iodide. © 2013 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

  7. Preparation of nucleoside-pyridine hybrids and pyridine attached acylureas from an unexpected uracil ring-opening and pyridine ring-forming sequence

    Xue Sen Fan; Xia Wang; Xin Ying Zhang; Dong Feng; Ying Ying Qu


    Novel pyrimidine nucleoside-3,5-dicyanopyridine hybrids (4) or pyridine attached acylureas (5) were selectively and efficiently prepared from the reaction of 2'-deoxyuridin-5-yl-methylene malonortitrile (1), malononitrile (2) and thiophenol (3) or from an unexpected uracil ring-opening and pyridine ring-forming sequence via the reaction of 1 and 3. It is the first time such a sequence has ever been reported.

  8. Synthesis of enantiomerically pure N-(S)-alpha-methylbenzyl-Beta-aminoalcohols by regio-and steroselective ring opening of epoxides

    Anaya de Parrodi, C. [Departamento de Quimica y Biologia. Universidad de las Americas-Puebla, Puebla (Mexico); Juaristi, E. [Departamento de Quimica Centro de Investigaciones y Estudios Avanzados. Instituto Politecnico Nacional, Mexico (Mexico)


    A high yield, stereoselective ring opening of symmetrically substituted epoxides with (S)-alpha-methylbenzylamine to produce enantiomerically pure N-(S)-alpha-methylbenzyl-Beta-aminoalcohols is described. In addition, the regio selective ring opening of (R)-styrene oxide with (S)-alpha -methylbenzylamine and enantiomerically pure secondary amines. (S)-N-benzyl-, (S)-N-isopropyl-. (S)-N-[(2-biphenyl) methyl]-alpha-methylbenzylamine is described. (Author) 16 refs.

  9. Synthesis of NLO polycarbonates via the ring-opening polymerization of macrocyclic prepolymers

    Kulig, Joseph B.; Moore, Collin G.; Brittain, William J.; Gilmour, Sandra; Perry, Joseph W.


    The synthesis and characterization of polycarbonates and polyformals is described. Copolymers of bisphenol A (BPA) and either a triphenyloxazole (1) or phenylquinoxaline (2) monomer were prepared. The polycarbonate copolymers were prepared by ring-opening polymerization of macrocyclic prepolymers using a solvent-free process. Preliminary electro- optic measurements have been performed on the polycarbonate copolymers of BPA and 1. Polyformals have also been prepared by a conventional polymerization process involving the reaction of dichloromethane with different feed ratios of BPA and either 1 or 2. The glass transition temperature of either the polyformals or polycarbonates is dramatically increased by increasing mole fractions of monomers 1 and 2.

  10. Ring Opening Reactions through C-O Bond Cleavage Uniquely Adding Chemical Functionality to Boron Subphthalocyanine

    Catherine Bonnier


    Full Text Available We are reporting the unexpected reaction between bromo-boron subphthalocyanine (Br-BsubPc and THF, 1,4-dioxane or γ-butyrolactone that results in the ring opening of the solvent and its addition into the BsubPc moiety. Under heating, the endocyclic C-O bond of the solvent is cleaved and the corresponding bromoalkoxy-BsubPc derivative is obtained. These novel alkoxy-BsubPc derivatives have remaining alkyl-bromides suitable for further functionalization. The alkoxy-BsubPcs maintain the characteristic strongly absorption in visible spectrum and their fluorescence quantum yields.

  11. Lactic Acid Yield Using Different Bacterial Strains, Its Purification, and Polymerization through Ring-Opening Reactions

    F. G. Orozco


    Full Text Available Laboratory-scale anaerobic fermentation was performed to obtain lactic acid from lactose, using five lactic acid bacteria: Lactococcus lactis, Lactobacillus bulgaricus, L. delbrueckii, L. plantarum, and L. delbrueckii lactis. A yield of 0.99 g lactic acid/g lactose was obtained with L. delbrueckii, from which a final concentration of 80.95 g/L aqueous solution was obtained through microfiltration, nanofiltration, and inverse osmosis membranes. The lactic acid was polymerized by means of ring-opening reactions (ROP to obtain poly-DL-lactic acid (PDLLA, with a viscosity average molecular weight (Mv of 19,264 g/mol.

  12. Ring-opening Polymerization of L-Lactide by an Anionic Cobalt(Ⅱ) Aryloxide

    袁春香; 徐小平; 张勇; 纪顺俊


    The reaction of anhydrous CoCl2 with NaOAr (ArO=2,4,6-tri-tert-butylphenoxo) in THF at room temperature in 1 : 3 molar ratio afforded anionic cobalt aryloxide [Na(THF)6][Co(OAr)3] (1). The definite structure of this com- plex was characterized by X-ray single crystal diffraction. It was found that this anionic aryloxo cobalt(Ⅱ) complex could effectively initiate the ring-opening polymerization of L-lactide both in solution and in bulk, leading to high molecular weight poly(L-lactide).

  13. Tetrahydrosalen backboned gadolinium complex as initiator for the ring-opening polymerization of ε-caprolactone

    Guang Ming Wu; Xu Feng Ni; Wei Lin Sun; Zhi Quan Shen


    Tetrahydrosalen ligand was employed in the synthesis of gadolinium complex. The ligand was deprotoned by LiBu, and the afforded lithium salt was reacted with anhydrous GdCl3 to produce the gadolinium complex through salt metathesis. This complex was successfully used to initiate the ring-opening polymerization of ε-caprolactone. The initiation conditions in different temperature, monomer-to-initiator ratio and time were investigated. Under the condition: [ε-caprolactone]: [catalyst]=600,56℃, toluene: 2ml, poly(ε-caprolactone) (PCL) with Mw=11,2782 and PDI=1.96 was achieved.

  14. Magnetite-polylactic acid nanoparticles by surface initiated organocatalysis ring opening polymerization

    Nan, Alexandrina [National Institute of R and D for Isotopic and Molecular Technologies (Romania); Leistner, Joachim [Humboldt-University Berlin, Institute of Chemistry (Germany); Turcu, Rodica, E-mail: [National Institute of R and D for Isotopic and Molecular Technologies (Romania)


    Organocatalysis by 4-N,N-dimethylaminopyridine was employed for ring opening polymerization of lactide initiated at magnetic nanoparticles covered by glycerol phosphate or ascorbic acid phosphate. The resulting magnetite-polylactic acid nanoparticles exhibit high colloidal stability in water and alcohol. Their morphology was investigated by transmission electron microscopy and the chemical structure was elucidated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The increase in mass after coating the nanoparticles was determined by thermogravimetric analysis, while dynamic light scattering revealed the increase in hydrodynamic size. Magnetic measurements revealed superparamagnetic behavior and high magnetization values. The magnetite-polylactic acid nanoparticles were further used for magnetic tagging of biotin.

  15. From N-alkylimidazole ligands at a rhenium center: ring opening or formation of NHC complexes.

    Huertos, Miguel A; Pérez, Julio; Riera, Lucía; Menéndez-Velázquez, Amador


    Cationic rhenium tricarbonyl complexes with three N-alkylimidazole ligands undergo deprotonation of the central CH group upon reaction with 1 equiv of KN(SiMe3)2. For the tris(N-methylimidazole) complex, the metal fragment shifts from N to C, leaving an NHC complex with a nonsubstituted N atom. For compounds with at least one N-mesitylimidazole ligand, the intramolecular attack of the deprotonated carbon onto the central carbon of an N-mesitylimidazole ligand results in ring opening of the latter.

  16. Spin polarized bound states in the continuum in open Aharonov-Bohm rings with the Rashba spin-orbit interaction

    Bulgakov, Evgeny N.; Sadreev, Almas F.


    We consider the trapping of electrons with a definite spin polarization by bound states in the continuum (BSC) in the open Aharonov-Bohm rings in the presence of the Rashba spin-orbit interaction (RSOI). Neglecting the Zeeman term we show the existence of BSCs in the one-dimensional ring when the eigenstates of the closed ring are doubly degenerate. With account of the Zeeman term BSCs occur only at the points of threefold degeneracy. The BSCs are found in the parametric space of flux and RSOI strength in close pairs with opposite spin polarization. Thereby the spin polarization of electrons transmitted through the ring can be altered by minor variation of magnetic or electric field at the vicinity of these pairs. Numerical simulations of the two-dimensional open ring show similar results for the BSCs. Encircling the BSC points in the parametric space of the flux and the RSOI constant gives rise to a geometric phase.

  17. 2-quinoxalinylnitrenes and 4-quinazolinylnitrenes: rearrangement to cyclic and acyclic carbodiimides and ring-opening to nitrile ylides.

    Kvaskoff, David; Vosswinkel, Michael; Wentrup, Curt


    This work was undertaken with the aim to obtain direct evidence for the interrelationships between hetarylnitrenes, their ring-expanded cyclic carbodiimide isomers, and ring-opened nitrile ylides. Tetrazolo[1,5-a]quinoxaline 11T and tetrazolo[5.1-c]quinazoline 13T undergo valence tautomerization to the corresponding azides 11A and 13A on mild flash vacuum thermolysis (FVT). Photolysis in Ar matrixes at ca. 15 K affords the triplet nitrenes 12 and 14, identified by ESR, UV, and IR spectroscopy. The nitrenes are converted photochemically to the seven-membered ring carbodiimide 15 followed by the open-chain carbodiimide 22. The 3-methoxy- and 3-chloro-2-quinoxalinylnitrenes 24 yield the ring-expanded carbodiimides 26 very cleanly on matrix photolysis, whereas FVT affords N-cyanobenzimidazoles 28. The ring-opened nitrile ylides 36 and 49 are identified as intermediates in the photolyses of 2-phenyl-4-quinazolinylnitrene 32 and 7-nitro-2-phenyl-4- quinazolinylnitrene 47. In these systems, a photochemically reversible interconversion of the seven-membered ring carbodiimides 35 and 48 and the nitrile ylides 36 and 49 is established. Recyclization of open-chain nitrile ylides is identified as an important mechanism of formation of ring contraction products (N-cyanobenzimidazoles). © 2011 American Chemical Society

  18. Synthesis of Polysiloxanes In Microemulsion Via ring opening of D4

    Liu Jiesheng


    Full Text Available Polydimethylsiloxane (PDMS has been synthesized by ring-opening polymerization of octamethylcyclotetrasiloxane (D4 in microemulsion with acidic catalyst. The structure and properties of microemulsion were characterized by Transmission Electron Microscopy (TEM, Fourier Transform Infrared Spectroscopy (FT-IR, Photo Correlation Spectroscopy (PCS. The effect of the variation in pH value, amount of catalyst, emulsifier and monomer dropping rate on the properties of microemulsion were investigated and discussed. The results showed that the particle size of the latex becomes smaller, and the distribution size becomes wider with increasing the content of catalyst and emulsifier. When pH value changed, the reaction rate of ring-opening of D4 was faster with strong acid than that under the weak acid condition. The emulsification of 2 % OP-10 (Alkylphenol polyoxyethylene ether and 3.0% DBSA (Dodecyl benzenesulfonic acid reached to equilibrium in microemulsion. As the amount of OP-10 increases, the size of particles lowered and their corresponding  distribution widened. It is observed that emulsifier (OP-10 does not affect the transparency of the microemulsion in the case of the application of DBSA. As the monomer dropping time increased, the grain size diminished and the size distribution widened. PCS results showed that the smallest particle size was around 20nm. Taking into account of the stability of the microemulsions, the dropping time of the monomer was around 30 min.

  19. The photochemical ring opening reaction of chromene as seen by transient absorption and fluorescence spectroscopy.

    Herzog, Teja T; Ryseck, Gerald; Ploetz, Evelyn; Cordes, Thorben


    In this paper we investigate the photochromic ring-opening reaction of 2,2-diphenyl-5,6-benzo(2H)chromene. In particular, we study the uncertainties and contradictions in various published reaction models using a combination of transient absorption and fluorescence spectroscopy with femtosecond time resolution. We propose a simplified reaction scheme which is in good agreement with theoretical studies. Here, photoexcitation populates a Franck-Condon state, whose fast vibrational wave packet motion, vibrational relaxation, bond-alternation and/or solvent rearrangement processes occur on the sub-picosecond timescale. Our data suggest that the resulting excited state minimum with picosecond lifetime still features structural characteristics of the closed form. Subsequently, the ring-opened photoproducts are formed in a concerted step from the excited state. The velocity of the photoreaction hence only depends on the time that the molecule needs to reach the transition region between the ground and excited states where the crucial bond breakage occurs.

  20. Cationic Ring Opening polymerization of ε-caprolactam by a Montmorillonite Clay Catalyst

    Djamal Eddine Kherroub


    Full Text Available The ring opening bulk polymerization of ε-caprolactam catalyzed by Maghnite-H+ was reported. Maghnite-H+ is a montmorillonite silicate sheet clay was prepared through a straight forward proton exchange process. The effect of the amount of catalyst, and temperature was studied. Increasing Maghnite-H+ proportion and temperature produced the increase in ε-caprolactam conversion. The kinetics indicated that the polymerization rate is first order with respect to monomer concentration. Mechanism studies showed that monomer inserted into the growing chains with the acyl–oxygen bond scission rather than the break of alkyl–oxygen bond. © 2014 BCREC UNDIP. All rights reservedSubmitted: 3rd October 2013; Revised: 28th February 2014; Accepted: 1st March 2014[How to Cite: Kherroub, D.E., Belbachir, M., Lamouri, S. (2014. Cationic Ring Opening Polymeriza-tion of ε-caprolactam by a Montmorillonite Clay Catalyst. Bulletin of Chemical Reaction Engineering & Catalysis, 9 (1: 74-79. (doi:10.9767/bcrec.9.1.5555.74-80][Permalink/DOI:

  1. In vitro eye irritation testing using the open source reconstructed hemicornea - a ring trial.

    Mewes, Karsten R; Engelke, Maria; Zorn-Kruppa, Michaela; Bartok, Melinda; Tandon, Rashmi; Brandner, Johanna M; Petersohn, Dirk


    The aim of the present ring trial was to test whether two new methodological approaches for the in vitro classification of eye irritating chemicals can be reliably transferred from the developers' laboratories to other sites. Both test methods are based on the well-established open source reconstructed 3D hemicornea models. In the first approach, the initial depth of injury after chemical treatment in the hemicornea model is derived from the quantitative analysis of histological sections. In the second approach, tissue viability, as a measure for corneal damage after chemical treatment, is analyzed separately for epithelium and stroma of the hemicornea model. The three independent laboratories that participated in the ring trial produced their own hemicornea models according to the test producer's instructions, thus supporting the open source concept. A total of 9 chemicals with different physicochemical and eye-irritating properties were tested to assess the between-laboratory reproducibility (BLR), the predictive performance, as well as possible limitations of the test systems. The BLR was 62.5% for the first and 100% for the second method. Both methods enabled to discriminate Cat. 1 chemicals from all non-Cat. 1 substances, which qualifies them to be used in a top-down approach. However, the selectivity between No Cat. and Cat. 2 chemicals still needs optimization.

  2. NATO Advanced Study Institute on Ring-opening Metathesis Polymerization of Olefins and Polymerization of Alkynes


    The first NATO Advanced Study Institute on Olefin Metathesis and Polymerization Catalysts was held on September 10-22, 1989 in Akcay, Turkey. Based on the fundamental research of RRSchrock, RGrubbs and K.B.Wagener in the field of ring opening metathesis polymerization (ROMP), acyclic diene metathesis (ADMET) and alkyne polymerization, these areas gained growing interest within the last years. Therefore the second NATO-ASI held on metathesis reactions was on Ring Opening Metathesis Po­ lymerization of Olefins and Polymerization of Alkynes on September 3-16, 1995 in Akcay, Turkey. The course joined inorganic, organic and polymer chemists to exchange their knowledge in this field. This volume contains the main and short lectures held in Akcay. To include ADMET reactions better into the title of this volume we changed it into: Metathesis Polymerization of Olefins and Alkyne Polymerization. This volume is addressed to research scientists, but also to those who start to work in the area of olefin metathesis and al...

  3. A quantum dynamics study of the benzopyran ring opening guided by laser pulses

    Saab, Mohamad, E-mail: [CTMM, Institut Charles Gerhardt Montpellier (UMR5253), CC 15001, Université Montpellier 2, F-34095 Montpellier (France); Doriol, Loïc Joubert, E-mail: [CTMM, Institut Charles Gerhardt Montpellier (UMR5253), CC 15001, Université Montpellier 2, F-34095 Montpellier (France); Lasorne, Benjamin, E-mail: [CTMM, Institut Charles Gerhardt Montpellier (UMR5253), CC 15001, Université Montpellier 2, F-34095 Montpellier (France); Guérin, Stéphane, E-mail: [Département Optique, Interaction Matière-Rayonnement (OMR) (UMR 6303), Université de Bourgogne, F-21078 Dijon (France); Gatti, Fabien, E-mail: [CTMM, Institut Charles Gerhardt Montpellier (UMR5253), CC 15001, Université Montpellier 2, F-34095 Montpellier (France)


    Highlights: • We perform quantum mechanical simulations for the ring-opening of benzopyran. • We develop strategies of control with laser pulses. • We focus on the physics involving the conical intersection. - Abstract: The ring-opening photoisomerization of benzopyran, which occurs via a photochemical route involving a conical intersection, has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method (MCTDH). We introduce a mechanistic strategy to control the conversion of benzopyran to merocyanine with laser pulses. We use a six-dimensional model developed in a previous work for the potential energy surfaces (PES) based on an extension of the vibronic-coupling Hamiltonian model (diabatization method by ansatz), which depends on the most active degrees of freedom. The main objective of these quantum dynamics simulations is to provide a set of strategies that could help experimentalists to control the photoreactivity vs. photostability ratio (selectivity). In this work we present: (i) a pump–dump technique used to control the photostability, (ii) a two-step strategy to enhance the reactivity of the system: first, a pure vibrational excitation in the electronic ground state that prepares the system and, second, an ultraviolet excitation that brings the system to the first adiabatic electronic state; (iii) finally the effect of a non-resonant pulse (Stark effect) on the dynamics.

  4. Ring opening reaction dynamics in the reaction of hydrogen atoms with ethylene oxide

    Shin, S. K.; Jarek, R. L.; Böhmer, E.; Wittig, C.


    Ethylene oxide, C2H4O, is a three-membered ring with a single oxygen atom bridging the two carbons. Reactions of H and D atoms with ethylene oxide have been studied in the gas phase to provide insight into the dynamics of three-membered ring opening. H atoms were produced by photolyzing HI in the wavelength range 240-266 nm. The channel leading to OH+C2H4 was monitored via laser-induced fluorescence (LIF) of the OH A 2Σ←X 2Π system. The D atom reaction yields OD with no hydrogen scrambling. With an available energy of 23 000 cm-1, the average OH D rotational energy is ˜350 cm-1 for OH(v=0) and OD(v=0) and ˜250 cm-1 for OD(v=1). OH(v=1) was not observed, while the OD(v=1) population was about one-tenth that of OD(v=0). There was no apparent bias in populations between Λ doublets in each of the spin-orbit states for both OH and OD. Doppler broadening of OH(v=0) rotational lines was measured to evaluate the average center-of-mass (c.m.) translational energy, which was found to be ˜2300 cm-1. On average, the ring opening process deposits ˜10% of the available energy into c.m. translation, ˜2% into OH rotation, and ˜88% into ethylene internal energy. Comparison with CH2CH2OH unimolecular dissociation dynamics and theoretical transition state calculations leads to a likely mechanism in which hydrogen abstracts oxygen via sequential C-O bond fission without involving a long-lived CH2CH2OH intermediate.

  5. Nonlinear optical signatures of ultraviolet light-induced ring opening in α-terpinene

    West, Brantley A.; Molesky, Brian P.; Montoni, Nicholas P.; Moran, Andrew M.


    Photoinduced electrocyclic ring opening reactions in conjugated cylcoalkenes are among the most elementary processes in organic chemistry. One prototypical ring opening reaction transforms cyclohexadiene into hexatriene. It is known that a sequence of sub-100 fs internal conversion transitions precedes bond breaking in cyclohexadiene and some of its derivatives. However, these excited state dynamics have never been directly monitored in solution because of insufficient time resolution. Here we aim to uncover the extraordinary photophysics behind related ultrafast internal conversion processes in a derivative of cyclohexadiene, α-terpinene (α-TP), solvated in cyclohexane. Transient absorption anisotropy experiments conducted with 20 fs laser pulses at 267 nm expose non-exponential depopulation kinetics for the ππ* electronic state of α-TP. Our data show that population transfer rapidly accelerates within the first 100 fs after photoexcitation. In addition, recurrences in two-dimensional photon echo (2DPE) line shapes reveal strong vibronic coupling in a normal mode near 523 cm-1, which involves torsions of the C=C bonds and hydrogen out-of-plane (HOOP) wagging on a vinyl group. With the support of several experiments, we hypothesize that the excited state wavepacket in α-TP undergoes several recurrences in the C=C stretching coordinate before displacement along the C=C torsion/vinyl HOOP coordinate finally sets it free from the Franck-Condon region of the potential energy surface. The unconfined wavepacket departs the ππ* electronic state by way of a conical intersection with a lower energy excited state. The present observations are made possible by recent improvements to both the time resolution and detection sensitivity of our experimental setup. This work demonstrates that it is now possible to acquire 2DPE signals in the deep ultraviolet, which are comparable with high-quality measurements in the visible spectral region. These technical developments

  6. Reactivity of NHC Alane Adducts towards N-Heterocyclic Carbenes and Cyclic (Alkyl)(amino)carbenes: Ring Expansion, Ring Opening, and Al-H Bond Activation.

    Schneider, Heidi; Hock, Andreas; Bertermann, Rüdiger; Radius, Udo


    The synthesis of mono-NHC alane adducts of the type (NHC)⋅AlH3 (NHC=Me2 Im (1), Me2 Im(Me) (2), iPr2 Im (3 and [D3 ]-3), iPr2 Im(Me) (4), Dipp2 Im (10); Im=imidazolin-2-ylidene, Dipp=2,6-diisopropylphenyl) and (NHC)⋅AliBu2 H (NHC=iPr2 Im (11), Dipp2 Im (12)) as well as their reactivity towards different types of carbenes is presented. Although the mono-NHC adducts remained stable at elevated temperatures, ring expansion occurred when (iPr2 Im)⋅AlH3 (3) was treated with a second equivalent of the carbene iPr2 Im to give (iPr2 Im)⋅AlH(RER-iPr2 ImH2 ) (6). In 6, {(iPr2 Im}AlH} is inserted into the NHC ring. In contrast, ring opening was observed with the sterically more demanding Dipp2 Im with the formation of (iPr2 Im)⋅AlH2 (ROR-Dipp2 ImH2 )H2 Al⋅(iPr2 Im) (9). In 9, two {(iPr2 Im)⋅AlH2 } moieties stabilize the ring-opened Dipp2 Im. If two hydridic sites are blocked, the adducts are stable with respect to further ring expansion or ring opening, as exemplified by the adducts (iPr2 Im)⋅AliBu2 H (11) and (Dipp2 Im)⋅AliBu2 H (12). The adducts (NHC)⋅AlH3 and (iPr2 Im)⋅AliBu2 H reacted with cAAC(Me) by insertion of the carbene carbon atom into the Al-H bond to give (NHC)⋅AlH2 /iBu2 (cAAC(Me) H) (13-18) instead of ligand substitution, ring-expansion, or ring-opened products. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Metal controlled regioselectivity in the cyclometallation of 2-(1-naphthyl)-pyridine.

    Kondrashov, Mikhail; Raman, Sudarkodi; Wendt, Ola F


    Cyclometallation of 2-(1-naphthyl)-pyridine is described. While cyclopalladation results in a five-membered metallacycle, cycloauration displays a completely orthogonal regioselectivity, resulting in the six-membered ring analogue. Bromination of the gold metallacycle results in the new C-H functionalisation product 2-(8-bromonaphth-1-yl)pyridine.

  8. The functional outcome of surgically treated unstable pelvic ring fractures by open reduction, internal fixation

    Kaykhosro Mardanpour


    Full Text Available Background:Unstable Pelvic fracture,a result of high energy antero-posterior compression injury, has been managed based on internal fixation and open reduction. The mode of fixation in Unstable Pelvic fracture has, however, been a subject of controversy and some authors have proposed a need to address the issue of partial breach of the pelvic ring elements in these injuries. This study was performed to evaluate the functional and radiological results of treatment of pelvic ring fractures by open reduction, internal fixation. Methods: Thirty eight patients with unstable pelvic fractures, treated from 2002 to2008 were retrospectively reviewed. The mean age of patients’ was 37 years old (range 20 to 67. Twenty six patients were men and 12 women. The most common cause was a road traffic accident (N=37, 97%. There were 11 type-C and 27 type-B fractures according to Tile’s classification. Thirty six patients sustained additional injuries. The most prevalent additional injuries were lower extremity fractures. Open reduction, internal fixation as a definite management was applied for all patients. Quality of reduction was graded according to the grades proposed by Matta and Majeed’s score was used to assess the clinical outcome. The mean period of follow-up was 25 months (ranged from 6 to 109 months. About 81.6% of patients had either good or excellent radiological reduction. Results: The functional outcome was excellent in 66%, good in 15%, fair in 11% and poor in 7% of the patients. There were 4 postoperative infections. No sexual function problem was reported. Nerve deficits recovered completely in 2 and partially in 3 of 11 patients with preoperative neurologic deficiency. There was no significant relation between functional outcome and the site of fracture Conclusion: Unstable pelvic ring fracture injuries should be managed surgically by rigid stabilization that must be carried out as soon as the general ndition of the patient permits, and

  9. Amidinate aluminium complexes: synthesis, characterization and ring-opening polymerization of rac-lactide.

    Qian, Feng; Liu, Keyin; Ma, Haiyan


    A series of aluminium alkyl complexes {PhC(NR')(NR'')}AlR(2) (4a-n, R' = 2,6-(i)Pr(2)C(6)H(3), 2,6-Me(2)C(6)H(3); R'' = aryl groups with various ortho-, para- or meta-substituents, tert-butyl; R = methyl, ethyl) bearing non-symmetrically N-substituted benzamidinate ligands were synthesized via the reaction of trialkylaluminium and the corresponding benzamidine proligands. Complex 5 bearing symmetric amidinate ligand was also obtained for comparison purposes. The X-ray diffraction studies of complexes 4b, 4c and 5 show in each case a distorted tetrahedral geometry around the aluminium center. All the amidinate aluminium complexes were found to catalyze the ring-opening polymerization (ROP) of rac-lactide with moderate activities. The steric and electronic characteristics of the ancillary ligands have a significant influence on the polymerization performance of the corresponding aluminium complexes. The introduction of electron-withdrawing substituents at the ortho-positions of N-phenyl ring of the ligands resulted in an obvious increase in catalytic activity. Complex 4b showed the highest activity among the investigated aluminium complexes due to the high electrophilicity of the metal center induced by the ortho-chloro substituents on the phenyl ring. The existence of ortho-substituents of small steric bulkiness is also beneficial for the increase of activity of these catalysts. However, further increase of steric hindrance of the ligands by introducing bulky ortho-substituents onto the phenyl moieties resulted in a decrease of activity and an increase in the isotactic bias of the obtained polylactides. The broad molecular weight distributions (PDI = 1.13-2.02) of the polymer samples indicated that the ROP of rac-lactide initiated by these complexes was not well-controlled.

  10. Detailed kinetic study of the ring opening of cycloalkanes by CBS-QB3 calculations.

    Sirjean, B; Glaude, P A; Ruiz-Lopez, M F; Fournet, R


    This work reports a theoretical study of the gas-phase unimolecular decomposition of cyclobutane, cyclopentane and cyclohexane by means of quantum chemical calculations. A biradical mechanism has been envisaged for each cycloalkane, and the main routes for the decomposition of the biradicals formed have been investigated at the CBS-QB3 level of theory. Thermochemical data(DeltaHf(o), S(o), Cp(o)) for all the involved species have been obtained by means of isodesmic reactions. The contribution of hindered rotors has also been included. Activation barriers of each reaction have been analyzed to assess the energetically most favorable pathways for the decomposition of biradicals. Rate constants have been derived for all elementary reactions using transition-state theory at 1 atm and temperatures ranging from 600 to 2000 K. Global rate constant for the decomposition of the cyclic alkanes in molecular products have been calculated. Comparison between calculated and experimental results allowed us to validate the theoretical approach. An important result is that the rotational barriers between the conformers, which are usually neglected, are of importance in decomposition rate of the largest biradicals. Ring strain energies (RSE) in transition states for ring opening have been estimated and show that the main part of RSE contained in the cyclic reactants is removed upon the activation process.

  11. Surface-plasmon-enhanced photoluminescence of quantum dots based on open-ring nanostructure array

    Kannegulla, Akash; Liu, Ye; Cheng, Li-Jing


    Enhanced photoluminescence (PL) of quantum dots (QD) in visible range using plasmonic nanostructures has potential to advance several photonic applications. The enhancement effect is, however, limited by the light coupling efficiency to the nanostructures. Here we demonstrate experimentally a new open-ring nanostructure (ORN) array 100 nm engraved into a 200 nm thick silver thin film to maximize light absorption and, hence, PL enhancement at a broadband spectral range. The structure is different from the traditional isolated or through-hole split-ring structures. Theoretical calculations based on FDTD method show that the absorption peak wavelength can be adjusted by their period and dimension. A broadband absorption of about 60% was measured at the peak wavelength of 550 nm. The emission spectrum of CdSe/ZnS core-shell quantum dots was chosen to match the absorption band of the ORN array to enhance its PL. The engraved silver ORN array was fabricated on a silver thin film deposited on a silicon substrate using focus ion beam (FIB) patterning. The device was characterized by using a thin layer of QD water dispersion formed between the ORN substrate and a cover glass. The experimental results show the enhanced PL for the QD with emission spectrum overlapping the absorption band of ORN substrate and quantum efficiency increases from 50% to 70%. The ORN silver substrate with high absorption over a broadband spectrum enables the PL enhancement and will benefit applications in biosensing, wavelength tunable filters, and imaging.

  12. DMSO molecule as ancillary ligand in Ru-based catalysts for ring opening metathesis polymerization

    Santana, Sirlane A.A.; Carvalho Junior, Valdemiro P.; Lima-Neto, Benedito S. [Universidade de Sao Paulo, Sao Carlos (USP), SP (Brazil). Inst. de Quimica


    The ring-opening metathesis polymerization (ROMP) of norbornene (NBE) occurs in the presence of the fac-[RuCl{sub 2}(S-DMSO){sub 3}(O-DMSO)] complex and ethyldiazoacetate (5 {mu}L), where DMSO is S- or O-bonded dimethylsulfoxide. The yield is 62% (PDI = 1.64) at room temperature for 5 min and 88% (PDI 1.93) at 50 deg C for 30 min, with [NBE]/[Ru] = 516 in CHCl{sub 3}. The yield is 90% (PDI = 1.64) in the presence of NBu{sub 4}ClO{sub 4} at room temperature for 5 min. The complex is practically inactive when one or two molecules of DMSO are replaced by pyridine, imidazole, 2-methyl-imidazole or benzimidazole. The in situ formation of the catalytic species and the behavior of the DMSO molecules as ancillary ligands in the reactivity of the RuII complexes are discussed. (author)

  13. Iridium-catalyzed asymmetric ring-opening of oxabenzonorbornadienes with phenols.

    Cheng, Hanchao; Yang, Dingqiao


    A novel iridium-catalyzed asymmetric ring-opening (ARO) reaction of oxabenzonorbornadienes with a variety of phenols was reported, which afforded the corresponding trans-2-phenoxy-1,2-dihydronaphthalen-1-ol products in high yields with moderate to excellent enantioselectivities (up to 98% ee) under mild conditions. The trans products are formed via the enantioselective cleavage of a bridgehead carbon-oxygen bond in 1 followed by S(N)2 nucleophilic attack by phenols. The effects of various bisphosphine ligands, Ag (I) salts, ammonium halides, bases, and solvents on the yield and enantioselectivity of the reaction were also investigated. The trans-configuration of the product 2a was confirmed by X-ray crystal structure analysis. A possible mechanism for the present catalytic reaction was proposed.


    Shu Xiao,


    Full Text Available Cellulose-graft-poly (L-lactide (cellulose-g-PLLA was prepared under homogeneous mild conditions. Ring-opening polymerization (ROP was carried out successfully using 4-dimethylaminopyridine (DMAP as an organic catalyst in an ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl. The structure of the polymer was characterized by GPC, 1H NMR, 13C NMR, FT-IR, TGA, WAXD, and AFM. The results indicated that the grafting rate of the polymer reached 4.44, which was higher than that reported in AmimCl with Sn(oct2 as a catalyst. In addition, AFM showed that the polymer in solution could aggregate and self-assemble into an approximately spherical structure, which was different from the rod-like structure of cellulose and round-like polylactic acid particles.

  15. Highly Defined Multiblock Copolypeptoids: Pushing the Limits of Living Nucleophilic Ring-Opening Polymerization

    Fetsch, Corinna


    Advanced macromolecular engineering requires excellent control over the polymerization reaction. Living polymerization methods are notoriously sensitive to impurities, which makes a practical realization of such control very challenging. Reversible-deactivation radical polymerization methods are typically more robust, but have other limitations. Here, we demonstrate by repeated (ge;10 times) chain extension the extraordinary robustness of the living nucleophilic ring-opening polymerization of N-substituted glycine N-carboxyanhydrides, which yields polypeptoids. We observe essentially quantitative end-group fidelity under experimental conditions that are comparatively easily managed. This is employed to synthesize a pentablock quinquiespolymer with high definition. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Ring-opening of cis-3-Substituted-2-vinylaziridines with Heteroatom Nucleophiles

    Lee, Gaeun; Shin, Miri; Kang, Hanyoung [Chungbuk National Univ., Cheongju (Korea, Republic of)


    The results of the ring opening reaction of N-protected-cis-2-vinyl-3-(benzyloxymethyl)aziridines as model compounds for cis-3-substituted-2-vinylaziridines with various heteroatom nucleophiles are summarized in Table 1. Methanol is a good nucleophile to provide the desired 1,2-amino-alcohol derivative as a single product in excellent yield. We analyzed briefly the effect of solvents with methanol. Although other solvents such as DMF and THF also gave the product, CH{sub 2}Cl{sub 2} was employed as a preferred solvent because of the high yield and ease of handling. All the reactions were, therefore, examined in CH{sub 2}Cl{sub 2} in the presence of BF{sub 3}·OEt{sub 2} as a Lewis acid unless mentioned otherwise. All alcohols behaved as good nucleophiles to exclusively give the desired products (entry 1-7)

  17. Enzymatic ring-opening copolymerization of trimethylene carbonate and ethylene ethyl phosphate

    FENG; Jun; (冯俊); ZHUO; Renxi; (卓仁禧); HE; Feng; (贺枫)


    Enzymatic ring-opening copolymerization of trimethylene carbonate (TMC) and ethylene ethyl phosphate (EEP) are performed in bulk at 100℃ using porcine pancreas lipase (PPL) or candida rugosa lipase (CL) as catalyst. The factors affecting the yield and molecular weights such as catalyst concentration, polymerization time and monomer feed ratio are investigated. The random copolymers obtained have molecular weight ranging from 3200 to 10200. The glass transition temperature (Tg) of the copolymers decreases from 28 to 41.7℃, with the increase of the EEP content in the feed from zero to 5∶10. Degradation tests show that the degradability of the copolymers is improved by introduction of the EEP unit into the copolymer chain.

  18. Statistical Ring Opening Metathesis Copolymerization of Norbornene and Cyclopentene by Grubbs’ 1st-Generation Catalyst

    Christiana Nikovia


    Full Text Available Statistical copolymers of norbornene (NBE with cyclopentene (CP were prepared by ring-opening metathesis polymerization, employing the 1st-generation Grubbs’ catalyst, in the presence or absence of triphenylphosphine, PPh3. The reactivity ratios were estimated using the Finemann-Ross, inverted Finemann-Ross, and Kelen-Tüdos graphical methods, along with the computer program COPOINT, which evaluates the parameters of binary copolymerizations from comonomer/copolymer composition data by integrating a given copolymerization equation in its differential form. Structural parameters of the copolymers were obtained by calculating the dyad sequence fractions and the mean sequence length, which were derived using the monomer reactivity ratios. The kinetics of thermal decomposition of the copolymers along with the respective homopolymers was studied by thermogravimetric analysis within the framework of the Ozawa-Flynn-Wall and Kissinger methodologies. Finally, the effect of triphenylphosphine on the kinetics of copolymerization, the reactivity ratios, and the kinetics of thermal decomposition were examined.

  19. Synthesis of novel anticancer agents through opening of spiroacetal ring of diosgenin.

    Hamid, A A; Hasanain, Mohammad; Singh, Arjun; Bhukya, Balakishan; Omprakash; Vasudev, Prema G; Sarkar, Jayanta; Chanda, Debabrata; Khan, Feroz; Aiyelaagbe, O O; Negi, Arvind S


    Diosgenin has been modified to furostane derivatives after opening the F-spiroacetal ring. The aldehyde group at C26 in derivative 8 was unexpectedly transformed to the ketone 9. The structure of ketone 9 was confirmed by spectroscopy and finally by X-ray crystallography. Five of the diosgenin derivatives showed significant anticancer activity against human cancer cell lines. The most potent molecule of this series i.e. compound 7, inhibited cellular growth by arresting the population at G0/G1 phase of cell division cycle. Cells undergo apoptosis after exposure to the derivative 7 which was evident by increase in sub G0 population in cell cycle analysis. Docking experiments showed caspase-3 and caspase-9 as possible molecular targets for these compounds. This was further validated by cleavage of PARP, a caspase target in apoptotic pathway. Compound 7 was found non-toxic up to 1000mg/kg dose in acute oral toxicity in Swiss albino mice.

  20. Highly conductive, transparent flexible films based on open rings of multi-walled carbon nanotubes

    Ko, Wen-Yin; Su, Jun-Wei; Guo, Chian-Hua; Fu, Shu-Juan; Hsu, Chuen-Yuan; Lin, Kuan-Jiuh, E-mail:


    Open rings of multi-walled carbon nanotubes were stacked to form porous networks on a poly(ethylene terephthalate) substrate to form a flexible conducting film (MWCNT-PET) with good electrical conductivity and transparency by a combination of ultrasonic atomization and spin-coating technique. To enhance the electric flexibility, we spin-coated a cast film of poly(vinyl alcohol) onto the MWCNT-PET substrate, which then underwent a thermo-compression process. Field-emission scanning electron microscopy of the cross-sectional morphology illustrates that the film has a robust network with a thickness of {approx} 175 nm, and it remarkably exhibits a sheet resistance of approximately 370 {Omega}/sq with {approx} 77% transmittance at 550 nm even after 500 bending cycles. This electrical conductivity is much superior to that of other MWCNT-based transparent flexible films.

  1. Creation of localized spins in graphene by ring-opening of epoxy derived hydroxyl.

    Chen, Jie; Zhang, Weili; Sun, Yuanyuan; Zheng, Yongping; Tang, Nujiang; Du, Youwei


    Creation of high-density localized spins in the basal plane of graphene sheet by introduction of sp(3)-type defects is considered to be a potential route for the realization of high-magnetization graphene. Theoretical and experimental studies confirmed that hydroxyl can be an effective sp(3)-type candidate for inducing robust magnetic moment. However, the artificial generation of hydroxyl groups for creating high-density spins on the basal plane of graphene sheet is very scarce. Here we demonstrate that high-content hydroxyl groups can be generated on the basal plane of graphene oxide (GO) sheet by ring opening of epoxy groups. We show that by introduction of 10.74 at.% hydroxyl groups, the density of localized spins of GO can be significantly increased from 0.4 to 5.17 μB/1000 C. Thus, this study provided an effective method to obtain graphene with high-density localized spins.

  2. Ring-opening polymerization of ω-pentadecalactone catalyzed by phosphazene superbases

    Ladelta, Viko


    A fast and living ring-opening polymerization (ROP) of ω-pentadecalactone (PDL), a representative monomer of macrolactones, was achieved using a primary alcohol as the initiator and t-BuP or t-octP as the catalyst. The use of t-BuP instead of the t-BuP superbase slows down the polymerization rate. The ROP of PDL proceeds to high conversion not only at 80 °C in bulk but also at room temperature and in dilute solution. The synthesized PDL homopolymers and block copolymers with poly(ethylene glycol) were characterized by high-temperature GPC (HT-GPC), H NMR and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Melting temperatures, determined by differential scanning calorimetry, are also reported.

  3. Cationic ring-opening polymerization of 3,3-bis(chloromethyl)oxacyclobutane in ionic liquids


    Cationic ring-opening polymerization of 3,3-bis(chloromethyl)oxacyclobutane catalyzed by BF3·OEt2 was carried out in ionic liquids [bmim]BF4 and [bmim]PF6. The influences of BCMO concentration and molar ratio of BCMO/BF3·OEt2 on the molecular weights and yield of PBCMO were investigated. The polymerization in ionic liquids proceed to high conversions, although molecular weights are limited, similar to polymerization in organic solvent such as CH2C12. Follow a viewpoint of green chemistry,we feel ionic liquid [bmim]BF4 is superior to [bmim]PF6. Extracting [bmim]PF6 from the product using organic solvent as extractant limits its advantage as a green reaction media.

  4. Preparation of polyamide 6/silica nanocomposites from silica surface initiated ring-opening anionic polymerization


    Full Text Available Polyamide 6/silica nanocomposites were synthesized by in situ ring-opening anionic polymerization of ε-caprolactam in the presence of sodium caprolactamate as a catalyst and caprolactam-functionalized silica as an initiator. The initiator precursor, isocyanate-functionalized silica, was prepared by directly reacting commercial silica with excess toluene 2,4-diisocyanate. This polymerization was found to occur in a highly efficient manner at relatively low reaction temperature (170°C and short reaction times (6 h. FTIR spectroscopy was utilized to follow the introduction and consumption of isocyanate groups on the silica surface. Thermogravimetric analysis indicated that the polyamide 6 was successfully grown from the silica surface. Transmission electron microscopy was utilized to image polymer-functionalized silica, showing fine dispersion of silica particles and their size ranging from 20 to 40 nm.


    Lei Zhang; Xu-feng Ni; Wei-lin Sun; Zhi-quan Shen


    An aromatic heterocyclic Schiff base neodymium complex bearing thizole was synthesized and its activity in the ring-opening polymerization of ε-caprolactone (CL) was examined. The conditions of the CL/Nd molar ratio, monomer concentration, polymerization time and temperature were investigated. Activities of ca.171 kg/Nd·h were obtained under the optimum condition (CL/Nd = 1600 (molar ratio), |CL] = 2.26 mol L-1, 1 h at 50℃), giving a poly(ε-caprolactone) (PCL) of number-average molecular weight Mn = 5.4 × 104 and molecular weight distribution MWD = 1.96. The conversion of CL monomer as high as 94% was observed after polymerized for one hour. The mechanism of coordination polymerization has also been illustrated.

  6. Zirconium(IV)-Catalyzed Ring Opening of on-DNA Epoxides in Water.

    Fan, Lijun; Davie, Christopher P


    DNA-encoded library technology (ELT) has spurred wide interest in the pharmaceutical industry as a powerful tool for hit and lead generation. In recent years a number of "DNA-compatible" chemical modifications have been published and used to synthesize vastly diverse screening libraries. Herein we report a newly developed, zirconium tetrakis(dodecyl sulfate) [Zr(DS)4 ] catalyzed ring-opening of on-DNA epoxides in water with amines, including anilines. Subsequent cyclization of the resulting on-DNA β-amino alcohols leads to a variety of biologically interesting, nonaromatic heterocycles. Under these conditions, a library of 137 million on-DNA β-amino alcohols and their cyclization products was assembled. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Immobilized Candida antarctica lipase B: Hydration, stripping off and application in ring opening polyester synthesis.

    Idris, Ani; Bukhari, Attaullah


    This work reviews the stripping off, role of water molecules in activity, and flexibility of immobilized Candida antarctica lipase B (CALB). Employment of CALB in ring opening polyester synthesis emphasizing on a polylactide is discussed in detail. Execution of enzymes in place of inorganic catalysts is the most green alternative for sustainable and environment friendly synthesis of products on an industrial scale. Robust immobilization and consequently performance of enzyme is the essential objective of enzyme application in industry. Water bound to the surface of an enzyme (contact class of water molecules) is inevitable for enzyme performance; it controls enzyme dynamics via flexibility changes and has intensive influence on enzyme activity. The value of pH during immobilization of CALB plays a critical role in fixing the active conformation of an enzyme. Comprehensive selection of support and protocol can develop a robust immobilized enzyme thus enhancing its performance. Organic solvents with a log P value higher than four are more suitable for enzymatic catalysis as these solvents tend to strip away very little of the enzyme surface bound water molecules. Alternatively ionic liquid can work as a more promising reaction media. Covalent immobilization is an exclusively reliable technique to circumvent the leaching of enzymes and to enhance stability. Activated polystyrene nanoparticles can prove to be a practical and economical support for chemical immobilization of CALB. In order to reduce the E-factor for the synthesis of biodegradable polymers; enzymatic ring opening polyester synthesis (eROPS) of cyclic monomers is a more sensible route for polyester synthesis. Synergies obtained from ionic liquids and immobilized enzyme can be much effective eROPS.

  8. Stereospecific Synthesis of 2-Iminothiazolidines via Domino Ring-Opening Cyclization of Activated Aziridines with Aryl- and Alkyl Isothiocyanates.

    Bhattacharyya, Aditya; Kavitha, C V; Ghorai, Manas K


    Lewis acid catalyzed domino ring-opening cyclization of activated aziridines with aryl and alkyl isothiocyanates has been accomplished leading to the formation of a wide variety of highly substituted and functionalized 2-iminothiazolidines with excellent diastereo- and enantiospecificity (de, ee up to >99%). The reaction proceeds via a Lewis acid catalyzed SN2-type ring-opening of the activated aziridine followed by a concomitant 5-exo-dig cyclization in a domino fashion to furnish the 2-iminothiazolidine derivative in excellent yields (up to 99%).

  9. (Salen)Ti(Ⅳ)-Catalyzed Asymmetric Ring-opening of meso Epoxides Using Dithiophosphorus Acid as the Nucleophile

    Zheng Hong ZHOU; Zhao Ming LI; Bing LIU; Kang Ying LI; Li Xin WANG; Guo Feng ZHAO; Qi Lin ZHOU; Chu Chi TANG


    The asymmetric ring-opening of epoxides with dithiophosphorus acids catalyzed by a (salen)Ti(Ⅳ) complex formed in situ from the reaction of Ti(OPr-i)4 and the chiral Schiff base derived from (1R,2R)-(+)-diaminocyclohexane was realized. The resulting products were obtained with low to good enantioselectivity (up to 73% ee).

  10. Metal-ligand binding affinity vs reactivity: qualitative studies in Rh(I)-catalyzed asymmetric ring-opening reactions.

    Tsui, Gavin Chit; Dougan, Patrick; Lautens, Mark


    Rh(I)-catalyzed asymmetric ring opening (ARO) of oxabenzonorbornadiene is used as a model system to qualitatively study reactions involving multiple metal-ligand interactions. The key feature of this approach is the use of product ee as an indicator to quickly gain important information such as the relative ligand binding affinity and relative reactivity of catalysts.

  11. Poly(dendrimers) with phosphorescent iridium(III) complex-based side chains prepared via ring-opening metathesis polymerization

    Lai, W.-Y.; Balfour, M.N.; Levell, J.W.; Bansal, A.K.; Burn, P.L.; Lo, S.-C.; Samuel, I.D.W.


    Phosphorescent poly(dendrimers) with a norbornene-derived backbone have been synthesized using ring-opening metathesis polymerization with the Grubbs III catalyst. The dendrimers are comprised of a heteroleptic iridium(III) complex core with two 2-phenylpyridyl ligands and a phenyltriazolyl ligand,


    Epoxidized soybean oil (ESO) was converted to a polysoap via a two-step synthetic procedure of catalytic ring-opening polymerization (PESO), followed by hydrolysis with a base (HPESO). Various molecular weights of PESO and HPESO were prepared by varying the reaction temperature and/or catalyst conc...

  13. Revisiting the Fully Automated Double-ring Infiltrometer using Open-source Electronics

    Ong, J.; Werkema, D., Jr.; Lane, J. W.


    The double-ring infiltrometer (DRI) is commonly used for measuring soil hydraulic conductivity. However, constant-head DRI tests typically involve the use of Mariotte tubes, which can be problematic to set-up, and time-consuming to maintain and monitor during infiltration tests. Maheshwari (1996, Australian Journal of Soil Research, v. 34, p. 709-714) developed a method for eliminating Mariotte tubes for constant-head tests using a computer-controlled combination of water-level indicators and solenoids to maintain a near-constant head in the DRI. A pressure transducer mounted on a depth-to-volume calibrated tank measures the water delivery rates during the test and data are saved on a hard drive or floppy disk. Here we use an inexpensive combination of pressure transducers, microcontroller, and open-source electronics that eliminate the need for Mariotte tubes. The system automates DRI water delivery and data recording for both constant- and falling-head infiltration tests. The user has the option of choosing water supplied to the DRI through a pressurized water system, pump, or gravity fed. An LCD screen enables user interface and observation of data for quality analysis in the field. The digital data are stored on a micro-SD card in standard column format for future retrieval and easy importing into conventional processing and plotting software. We show the results of infiltrometer tests using the automated system and a conventional Mariotte tube system conducted over test beds of uniform soils.

  14. Phosphazene-catalyzed ring-opening polymerization of ε-caprolactone: Influence of solvents and initiators

    Alamri, Haleema


    Phosphazene base (t-BuP2) catalysed metal-free ring-opening polymerization of ε-caprolactone (ε-CL) at room temperature with various protic initiators in different solvents was investigated. The polymerization proceeded, in most cases, in a controlled manner to afford poly(ε-caprolactone) with low dispersities and expected molecular weights. Kinetic studies showed that when a primary alcohol was used as an initiator the polymerization rate in different solvents followed the order of dichloromethane ≫ toluene > 1,4-dioxane ≈ tetrahydrofuran. Extremely fast polymerization of l-lactide (LLA), which was added as a second monomer, was observed in different solvents giving rise to poly(ε-caprolactone)-b- poly(l-lactide) diblock copolymers with neat PLLA blocks despite incomplete conversion of ε-CL. The dependence of polymerization rate on the concentrations of ε-CL and t-BuP2 was also revealed. In addition to primary alcohol, the feasibility of using other protic initiators, such as secondary alcohol (either on a small molecule or a polymer chain-end), (aliphatic/aromatic) amide, carboxylic acid, phenol and thiophenol, was also investigated. These studies provided important information for designing a metal-free route towards polyester-based (bio)materials. © 2014 the Partner Organisations.

  15. Improvement of Physicochemical Characteristics of Monoepoxide Linoleic Acid Ring Opening for Biolubricant Base Oil

    Jumat Salimon


    Full Text Available For environmental reasons, a new class of environmentally acceptable and renewable biolubricant based on vegetable oils is available. In this study, oxirane ring opening reaction of monoepoxide linoleic acid (MEOA was done by nucleophilic addition of oleic acid (OA with using p-toluene sulfonic acid (PTSA as a catalyst for synthesis of 9(12-hydroxy-10(13-oleoxy-12(9-octadecanoic acid (HYOOA and the physicochemical properties of the resulted HYOOA are reported to be used as biolubricant base oils. Optimum conditions of the experiment using D-optimal design to obtain high yield% of HYOOA and lowest OOC% were predicted at OA/MEOA ratio of 0.30 : 1 (w/w, PTSA/MEOA ratio of 0.50 : 1 (w/w, reaction temperature at 110∘C, and reaction time at 4.5 h. The results showed that an increase in the chain length of the midchain ester resulted in the decrease of pour point (PP −51∘C, increase of viscosity index (VI up to 153, and improvement in oxidative stability (OT to 180.94∘C.

  16. Improvement of physicochemical characteristics of monoepoxide linoleic acid ring opening for biolubricant base oil.

    Salimon, Jumat; Salih, Nadia; Abdullah, Bashar Mudhaffar


    For environmental reasons, a new class of environmentally acceptable and renewable biolubricant based on vegetable oils is available. In this study, oxirane ring opening reaction of monoepoxide linoleic acid (MEOA) was done by nucleophilic addition of oleic acid (OA) with using p-toluene sulfonic acid (PTSA) as a catalyst for synthesis of 9(12)-hydroxy-10(13)-oleoxy-12(9)-octadecanoic acid (HYOOA) and the physicochemical properties of the resulted HYOOA are reported to be used as biolubricant base oils. Optimum conditions of the experiment using D-optimal design to obtain high yield% of HYOOA and lowest OOC% were predicted at OA/MEOA ratio of 0.30 : 1 (w/w), PTSA/MEOA ratio of 0.50 : 1 (w/w), reaction temperature at 110°C, and reaction time at 4.5 h. The results showed that an increase in the chain length of the midchain ester resulted in the decrease of pour point (PP) -51°C, increase of viscosity index (VI) up to 153, and improvement in oxidative stability (OT) to 180.94°C.

  17. Novel Zinc-Catalytic Systems for Ring-Opening Polymerization of ε-Caprolactone

    Karolina Żółtowska


    Full Text Available Polycaprolactone (PCL is a biodegradable synthetic polymer that is currently widely used in many pharmaceutical and medical applications. In this paper we describe the coordination ring-opening polymerization of ε-caprolactone in the presence of two newly synthesized catalytic systems: diethylzinc/gallic acid and diethylzinc/propyl gallate. The chemical structures of the obtained PCLs were characterized by 1H- or 13C-NMR, FTIR spectroscopy and MALDI TOF mass spectrometry. The average molecular weight of the resulting polyesters was analysed by gel permeation chromatography and a viscosity method. The effects of temperature, reaction time and type of catalytic system on the polymerization process were examined. Linear PCLs with defined average molecular weight were successfully obtained. Importantly, in some cases the presence of macrocyclic products was not observed during the polymerization process. This study provides an effective method for the synthesis of biodegradable polyesters for medical and pharmaceutical applications due to the fact that gallic acid/propyl gallate are commonly used in the pharmaceutical industry.

  18. Cytotoxic activity of a synthetic deoxypodophyllotoxin derivative with an opened D-ring.

    Chen, Chuan; Wang, Cui-Cui; Wang, Zhong; Geng, Wen-Yue; Xu, Hui; Song, Xiao-Mei; Luo, Du-Qiang


    Podophyllotoxin and its synthetic derivatives are valuable medicinal agents that have antitumor, insecticidal, and antifungal properties. We previously synthesized a deoxypodophyllotoxin derivative with an opened D-ring (DPD) exhibiting potent insecticidal activity. This article was firstly performed to identify the cytotoxicity of DPD toward human cancer cell lines (SGC7901, HeLa, and A549) and normal cell line (HEK293T) using MTT assay. DPD showed potent cytotoxicity against human cancer lines (HeLa and A549) and less cytotoxicity against normal cell lines HEK293T. DPD could also induce the cell cycle arrest at G2/M phase in HeLa cells and significantly increase the phosphorylation (Tyr 15) of CDC2 leading to inactivation of CDC2. The effects of DPD on cellular microtubule networks were detected using immunofluorescence technique in HeLa cells. The immunofluorescence results showed DPD influenced the arrangement and organization of cellular microtubule networks in HeLa cells. Microtubules are long, hollow cylinders made up of polymerized tubulin dimers. Total microtubules were separated after DPD treatment. Western blot results showed that the free polymerized tubulin dimers were obviously increased after DPD treatment. DPD may be a good drug candidate with the therapeutic potential to human cancer by affecting microtubule polymerization.


    CHEN Xianhai; ZHANG Yifeng; SHEN Zhiquan


    Ring opening copolymerization of succinic anhydride (SA) with ethylene oxide (EO)was successfully carried out by using a series of aluminum-based catalyst in 1,4-dioxane at 62±2℃. The results showed that in-situ AlR3-H2O (R=ethyl, iso-butyl) catalysts gave higher molecular weight ((-M)w ~ 104), while Al(OR)3 catalysts gave the higher alternating copolymer structure with slightly lower molecular weight. The in-situ AlR3-H2O systems have been evaluated in more detail for the reaction which showed the optimum H2O/Al molar ratio to be 0.5. The copolymers with different composition (FSA/FEO = 36/64 to 45/55 mol/mol) were synthesized by using different monomer feed ratio. The melting point (Tm), glass transition temperature (Tg) and enthalpy of fusion (ΔHf) of these copolymers are depended on the copolymer composition and in the range of 87~ 102℃,-12 ~ -18℃, and 37 ~ 66J/g, respectively. The second heating scan of DSC also indicated that the higher alternating copolymer was more easily recrystallized. The onset decomposition temperature was more than 300℃ under nitrogen and influenced by the copolymer composition.

  20. Enantioselective Ring-Opening Polymerization of rac-Lactide Dictated by Densely Substituted Amino Acids.

    Sanchez-Sanchez, Ana; Rivilla, Ivan; Agirre, Maddalen; Basterretxea, Andere; Etxeberria, Agustin; Veloso, Antonio; Sardon, Haritz; Mecerreyes, David; Cossío, Fernando P


    Organocatalysis is becoming an important tool in polymer science because of its versatility and specificity. To date a limited number of organic catalysts have demonstrated the ability to promote stereocontrolled polymerizations. In this work we report one of the first examples of chirality transfer from a catalyst to a polymer in the organocatalyzed ring-opening polymerization (ROP) of rac-lactide (rac-LA). We have polymerized rac-LA using the diastereomeric densely substituted amino acids (2S,3R,4S,5S)-1-methyl-4-nitro-3,5-diphenylpyrrolidine-2-carboxylic acid (endo-6) and (2S,3S,4R,5S)-1-methyl-4-nitro-3,5-diphenylpyrrolidine-2-carboxylic acid (exo-6), combined with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a cocatalyst. Both diastereoisomers not only showed the ability to synthesize enriched isotactic polylactide with a Pm higher than 0.90 at room temperature but also were able to preferentially promote the polymerization of one of the isomers (l or d) with respect to the other. Thus, exo-6 preferentially polymerized l-lactide, whereas endo-6 preferred d-lactide as the substrate. Density functional theory calculations were conducted to investigate the origins of this unique stereocontrol in the polymerization, providing mechanistic insight and explaining why the chirality of the catalyst is able to define the stereochemistry of the monomer insertion.

  1. Dual Catalysis for Selective Ring-Opening Polymerization of Lactones: Evolution toward Simplicity.

    Naumann, Stefan; Scholten, Philip B V; Wilson, James A; Dove, Andrew P


    Much work has been directed to the design of complex single-site catalysts for ring-opening polymerization (ROP) to enhance both activity and selectivity. More simply, however, cooperative effects between Lewis acids and organocatalytic nucleophiles/Lewis bases provide a powerful alternative. In this study we demonstrate that the combination of N-heterocyclic carbenes, 1,8-diazabicycloundec-7-ene (DBU) and 4-dimethylaminopyridine (DMAP) with simple Lewis acids enables the ROP of the macrolactone pentadecalactone in a rapid and efficient manner. Remarkably, regardless of the nature of the nucleophile, the order of activity was observed to be MgX2 ≫ YCl3 ≫ AlCl3 and MgI2 > MgBr2 > MgCl2 in every case. The minimal influence of the organobase on polymerization activity allows for the use of simple and inexpensive precursors. Furthermore, extension of the study to other cyclic (di)ester monomers reveals the choice of Lewis acid to lead to monomer selective ROP activity and hence control over copolymer composition by choice of Lewis acid. This approach could lead to the realization of complex polymer structures with tunable physical properties from simple catalyst combinations.

  2. Bio-reducible polycations from ring-opening polymerization as potential gene delivery vehicles.

    Yu, Qing-Ying; Liu, Yan-Hong; Huang, Zheng; Zhang, Ji; Luan, Chao-Ran; Zhang, Qin-Fang; Yu, Xiao-Qi


    Synthetic polycations show great potential for the construction of ideal non-viral gene delivery systems. Several cationic polymers were synthesized by the epoxide ring-opening polymerization between diepoxide and various polyamines. Disulfide bonds were introduced to afford the polymers bio-reducibility, while the oxygen-rich structure might enhance the serum tolerance and biocompatibility. The polycations have much lower molecular weights than PEI 25 kDa, but still could well bind and condense DNA into nano-sized particles. DNA could be released from the polyplexes by addition of reductive DTT. Compared to PEI, the polycations have less cytotoxicity possibly due to their lower molecular weights and oxygen-rich structure. More significantly, these materials exhibit excellent serum tolerance than PEI, and up to 6 times higher transfection efficiency than PEI could be obtained in the presence of serum. The transfection mediated by was seldom affected even at a high concentration of serum. Much lower protein adsorption of polycations than PEI was proved by bovine serum albumin adsorption experiments. Flow cytometry also demonstrates their good serum resistance ability.

  3. Comparative Theoretical Study of the Ring-Opening Polymerization of Caprolactam vs Caprolactone Using QM/MM Methods

    Elsasser, Brigitta M.; Schoenen, Iris; Fels, Gregor


    Candida antarctica lipase B (CALB) efficiently catalyzes the ring-opening polymerization of lactones to high molecular weight products in good yield. In contrast, an efficient enzymatic synthesis of polyamides has so far not been described in the literature. This obvious difference in enzyme catalysis is the subject of our comparative study of the initial steps of a CALB catalyzed ring-opening polymerization of ε- caprolactone and ε-caprolactam. We have applied docking tools to generate the reactant state complex and performed quantum mechanical/molecular mechanical (QM/MM) calculations at the density functional theory (DFT) PBE0 level of theory to simulate the acylation of Ser105 by the lactone and the lactam, respectively, via the corresponding first tetrahedral intermediates. We could identify a decisive difference in the accessibility of the two substrates in the ring-opening to the respective acyl enzyme complex as the attack of ε-caprolactam is hindered because of an energetically disfavored proton transfer during this part of the catalytic reaction while ε-caprolactone is perfectly processed along the widely accepted pathway using the catalytic triade of Ser105, His224, and Asp187. Since the generation of an acylated Ser105 species is the crucial step of the polymerization procedure, our results give an explanation for the unsatisfactory enzymatic polyamide formation and opens up new possibilities for targeted rational catalyst redesign in hope of an experimentally useful CALB catalyzed polyamide synthesis.

  4. Evidence for concerted ring opening and C-Br bond breaking in UV-excited bromocyclopropane

    Pandit, Shubhrangshu; Preston, Thomas J.; King, Simon J.; Vallance, Claire; Orr-Ewing, Andrew J.


    Photodissociation of gaseous bromocyclopropane via its A-band continuum has been studied at excitation wavelengths ranging from 230 nm to 267 nm. Velocity-map images of ground-state bromine atoms (Br), spin-orbit excited bromine atoms (Br∗), and C3H5 hydrocarbon radicals reveal the kinetic energies of these various photofragments. Both Br and Br∗ atoms are predominantly generated via repulsive excited electronic states in a prompt photodissociation process in which the hydrocarbon co-fragment is a cyclopropyl radical. However, the images obtained at the mass of the hydrocarbon radical fragment identify a channel with total kinetic energy greater than that deduced from the Br and Br∗ images, and with a kinetic energy distribution that exceeds the energetic limit for Br + cyclopropyl radical products. The velocity-map images of these C3H5 fragments have lower angular anisotropies than measured for Br and Br∗, indicating molecular restructuring during dissociation. The high kinetic energy C3H5 signals are assigned to allyl radicals generated by a minor photochemical pathway which involves concerted C-Br bond dissociation and cyclopropyl ring-opening following single ultraviolet (UV)-photon absorption. Slow photofragments also contribute to the velocity map images obtained at the C3H5 radical mass, but the corresponding slow Br atoms are not observed. These features in the images are attributed to C3H5+ from the photodissociation of the C3H5Br+ molecular cation following two-photon ionization of the parent compound. This assignment is confirmed by 118-nm vacuum ultraviolet ionization studies that prepare the molecular cation in its ground electronic state prior to UV photodissociation.

  5. Control of Grafting Density and Distribution in Graft Polymers by Living Ring-Opening Metathesis Copolymerization.

    Lin, Tzu-Pin; Chang, Alice B; Chen, Hsiang-Yun; Liberman-Martin, Allegra L; Bates, Christopher M; Voegtle, Matthew J; Bauer, Christina A; Grubbs, Robert H


    Control over polymer sequence and architecture is crucial to both understanding structure-property relationships and designing functional materials. In pursuit of these goals, we developed a new synthetic approach that enables facile manipulation of the density and distribution of grafts in polymers via living ring-opening metathesis polymerization (ROMP). Discrete endo,exo-norbornenyl dialkylesters (dimethyl DME, diethyl DEE, di-n-butyl DBE) were strategically designed to copolymerize with a norbornene-functionalized polystyrene (PS), polylactide (PLA), or polydimethylsiloxane (PDMS) macromonomer mediated by the third-generation metathesis catalyst (G3). The small-molecule diesters act as diluents that increase the average distance between grafted side chains, generating polymers with variable grafting density. The grafting density (number of side chains/number of norbornene backbone repeats) could be straightforwardly controlled by the macromonomer/diluent feed ratio. To gain insight into the copolymer sequence and architecture, self-propagation and cross-propagation rate constants were determined according to a terminal copolymerization model. These kinetic analyses suggest that copolymerizing a macromonomer/diluent pair with evenly matched self-propagation rate constants favors randomly distributed side chains. As the disparity between macromonomer and diluent homopolymerization rates increases, the reactivity ratios depart from unity, leading to an increase in gradient tendency. To demonstrate the effectiveness of our method, an array of monodisperse polymers (PLA(x)-ran-DME(1-x))n bearing variable grafting densities (x = 1.0, 0.75, 0.5, 0.25) and total backbone degrees of polymerization (n = 167, 133, 100, 67, 33) were synthesized. The approach disclosed in this work therefore constitutes a powerful strategy for the synthesis of polymers spanning the linear-to-bottlebrush regimes with controlled grafting density and side chain distribution, molecular

  6. Fluoride-Triggered Ring-Opening of Photochromic Diarylpyrans into Merocyanine Dyes: Naked-Eye Sensing in Subppm Levels.

    Mukhopadhyay, Arindam; Maka, Vijay Kumar; Moorthy, Jarugu Narasimha


    The fluoride-mediated desilylation reaction has been exploited, for the first time, to trigger ring-opening of photochromic diarylbenzo-/naphthopyrans into highly colored anionic merocyanine dyes with high molar absorptivities to permit naked-eye sensing. The absorption spectral shifts, i.e., differences in the absorption maxima of colorless and colored forms, observed for a rationally designed set of silyloxy-substituted diarylpyrans subsequent to fluoride-induced ring opening are remarkably high (330-480 nm), and are unknown for any colorimetric probe. In particular, the disilyloxy-substituted diphenylnaphthopyran and its analog, in which the diphenyl groups are fused in the form of fluorene, allows "naked-eye" detection of fluoride in subppm levels (photochromic benzo-/naphthopyrans is heretofore unprecedented.


    Jin-ying Yuan; Cai-yuan Pana


    Polymerization of three cyclic ketene acetals: i.e., 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), 2-methylene-4-phenyl-1,3-dioxolane (MPDO) and 4,7-dimethyl-2-methylene-1,3-dioxepane (DMMDO) were carried out in the presence of ethyl α-bromobutyrate/CuBr/2,2'-bipyridine respectively. The structures ofpoly(BMDO), poly(MPDO) and poly(DMMDO)were characterized by 1H and 13C-NMR spectra. The effects of monomer structure on the behavior of atom transfer free radical ring-opening polymerization were investigated and the mechanism of controlled free radical ring-opening polymerization was discussed.

  8. Dendritic Macroinitiator for the Ring-Opening Polymerization of γ-Benzyl L-Glutamate N-Carboxyanhydride


    By using OH-terminated polyarylether dendrimer and N-Fmoc-glycine as raw materials, the dendritic polyarylether 2-aminoacetate (G3-NH2) was synthesized via two step reactions. G3-NH2 as a macroinitiator for the ring-opening polymerization of γ-benzyl L-glutamate N-carboxyanhydride was investigated. It is found that the resulting copolymers possessed relatively high molecular weight and narrow molecular weight distribution (1.12< Mw/Mn<1.28).

  9. Direct observation of ring-opening dynamics in strong-field ionized selenophene using femtosecond inner-shell absorption spectroscopy

    Lackner, Florian; Chatterley, Adam S.; Pemmaraju, C. D.; Closser, Kristina D.; Prendergast, David; Neumark, Daniel M.; Leone, Stephen R.; Gessner, Oliver


    Femtosecond extreme ultraviolet transient absorption spectroscopy is used to explore strong-field ionization induced dynamics in selenophene (C4H4Se). The dynamics are monitored in real-time from the viewpoint of the Se atom by recording the temporal evolution of element-specific spectral features near the Se 3d inner-shell absorption edge (˜58 eV). The interpretation of the experimental results is supported by first-principles time-dependent density functional theory calculations. The experiments simultaneously capture the instantaneous population of stable molecular ions, the emergence and decay of excited cation states, and the appearance of atomic fragments. The experiments reveal, in particular, insight into the strong-field induced ring-opening dynamics in the selenophene cation, which are traced by the emergence of non-cyclic molecules as well as the liberation of Se+ ions within an overall time scale of approximately 170 fs. We propose that both products may be associated with dynamics on the same electronic surfaces but with different degrees of vibrational excitation. The time-dependent inner-shell absorption features provide direct evidence for a complex relaxation mechanism that may be approximated by a two-step model, whereby the initially prepared, excited cyclic cation decays within τ1 = 80 ± 30 fs into a transient molecular species, which then gives rise to the emergence of bare Se+ and ring-open cations within an additional τ2 = 80 ± 30 fs. The combined experimental and theoretical results suggest a close relationship between σ* excited cation states and the observed ring-opening reactions. The findings demonstrate that the combination of femtosecond time-resolved core-level spectroscopy with ab initio estimates of spectroscopic signatures provide new insights into complex, ultrafast photochemical reactions such as ring-opening dynamics in organic molecules in real-time and with simultaneous sensitivity for electronic and structural

  10. Cationic Ring Opening Copolymerization of 1,3-Dioxolane with Styrene by Montmorillonite Maghnite-H+Catalyst

    Nabil Hamam; Mohammed Issam Ferrahi; Mohammed Belbachir


    In the present work, the copolymerization of 1,3-Dioxolane (DXL) with Styrene (St) catalyzed by Maghnite-H+ a montmorillonite sheet silicate clay exchanged with protons, was investigated. The cationic ring opening polymerization was initiated by Maghnite-H+ in bulk. The copolymer obtained was characterized by 1H-NMR, DSC and IR spectroscopy. The studies done, such as the effect of the amount of catalyser on the syntheses of poly (DXL -co- Styrene).

  11. Cationic Ring Opening Copolymerization of 1,3-Dioxolane with Styrene by Montmorillonite Maghnite-H+Catalyst

    Nabil Hamam


    Full Text Available In the present work, the copolymerization of 1,3-Dioxolane (DXL with Styrene (St catalyzed by Maghnite-H+ a montmorillonite sheet silicate clay exchanged with protons, was investigated. The cationic ring opening polymerization was initiated by Maghnite-H+ in bulk. The copolymer obtained was characterized by 1H-NMR, DSC and IR spectroscopy. The studies done, such as the effect of the amount of catalyser on the syntheses of poly (DXL -co- Styrene.

  12. Glycopolymers Prepared by Ring-Opening Metathesis Polymerization Followed by Glycoconjugation Using a Triazole-Forming "Click" Reaction.

    Okoth, Ronald; Basu, Amit


    We describe a protocol for the preparation of glycopolymers derived from the ring-opening polymerization of a norbornene carboxylic acid derivative. Polymerization is followed by attachment of a linker and subsequent glycoconjugation via a triazole-forming azide-alkyne click reaction. The use of a protected amine-terminating agent allows for the attachment of a probe molecule such as a fluorescein dye. The syntheses of a neutral galactopolymer as well a polyanionic poly-3-O-sulfo-galactopolymer are described.

  13. About Frequency Characteristics of Electric Fields of Cylindrical Piezoceramic Antenna with Screen in the Form of an Open Ring Layer

    Z.T. Gusak


    Full Text Available According to rigorous method of “related” fields the analytical expressions to describe electric fields of piezoceramic cylindrical antennas with screen in the form of an open ring layer of finite thickness was obtained. As a result of numerical analysis the quantity relations and the features of frequency characteristics of the electric current and the input impedance of the antenna with screen depending on the parameters of the antenna elements were found.

  14. Multi-photon ionization and fragmentation of uracil: Neutral excited-state ring opening and hydration effects

    Barc, B.; Ryszka, M.; Spurrell, J.; Dampc, M.; Limão-Vieira, P.; Parajuli, R.; Mason, N. J.; Eden, S. [Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom)


    Multi-photon ionization (MPI) of the RNA base uracil has been studied in the wavelength range 220–270 nm, coinciding with excitation to the S{sub 2}(ππ*) state. A fragment ion at m/z = 84 was produced by 2-photon absorption at wavelengths ≤232 nm and assigned to C{sub 3}H{sub 4}N{sub 2}O{sup +} following CO abstraction. This ion has not been observed in alternative dissociative ionization processes (notably electron impact) and its threshold is close to recent calculations of the minimum activation energy for a ring opening conical intersection to a σ(n-π)π* closed shell state. Moreover, the predicted ring opening transition leaves a CO group at one end of the isomer, apparently vulnerable to abstraction. An MPI mass spectrum of uracil-water clusters is presented for the first time and compared with an equivalent dry measurement. Hydration enhances certain fragment ion pathways (particularly C{sub 3}H{sub 3}NO{sup +}) but represses C{sub 3}H{sub 4}N{sub 2}O{sup +} production. This indicates that hydrogen bonding to water stabilizes uracil with respect to neutral excited-state ring opening.

  15. Adsorption and ring-opening of lactide on the chiral metal surface Pt(321){sup S} studied by density functional theory

    Franke, J.-H.; Kosov, D. S. [Department of Physics, Campus Plaine - CP 231, Universite Libre de Bruxelles, 1050 Brussels (Belgium)


    We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321){sup S}. Lactide is a precursor for polylactic acid ring-opening polymerization, and Pt is a well known catalyst surface. We study, here, the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using density functional theory with a functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures, and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.

  16. Direct valorisation of waste cocoa butter triglycerides via catalytic epoxidation, ring-opening and polymerisation.

    Plaza, Dorota D; Strobel, Vinzent; Heer, Parminder Kaur Ks; Sellars, Andrew B; Hoong, Seng-Soi; Clark, Andrew J; Lapkin, Alexei A


    Development of circular economy requires significant advances in the technologies for valorisation of waste, as waste becomes new feedstock. Food waste is a particularly important feedstock, containing large variation of complex chemical functionality. Although most food waste sources are complex mixtures, waste from food processing, no longer suitable for the human food chain, may also represent relatively clean materials. One such material requiring valorisation is cocoa butter. Epoxidation of a triglyceride from a food waste source, processing waste cocoa butter, into the corresponding triglyceride epoxide was carried out using a modified Ishii-Venturello catalyst in batch and continuous flow reactors. The batch reactor achieved higher yields due to the significant decomposition of hydrogen peroxide in the laminar flow tubular reactor. Integral and differential models describing the reaction and the phase transfer kinetics were developed for the epoxidation of cocoa butter and the model parameters were estimated. Ring-opening of the epoxidised cocoa butter was undertaken to provide polyols of varying molecular weight (Mw = 2000-84 000 Da), hydroxyl value (27-60 mg KOH g(-1)) and acid value (1-173 mg KOH g(-1)), using either aqueous ortho-phosphoric acid (H 3 PO 4) or boron trifluoride diethyl etherate (BF 3·OEt2)-mediated oligomerisation in bulk, using hexane or tetrahydrofuran (THF) as solvents. The thermal and tensile properties of the polyurethanes obtained from the reaction of these polyols with 4,4'-methylene diphenyl diisocyanate (MDI) are described. The paper presents a complete valorisation scheme for a food manufacturing industry waste stream, starting from the initial chemical transformation, developing a process model for the design of a scaled-up process, and leading to synthesis of the final product, in this case a polymer. This work describes aspects of optimisation of the conversion route, focusing on clean synthesis and also demonstrates the

  17. Chemical reactivity predictions: use of data mining techniques for analyzing regioselective azidolysis of epoxides.

    Borghini, Alice; Crotti, Paolo; Pietra, Daniele; Favero, Lucilla; Bianucci, Anna Maria


    Azidolysis of epoxides followed by reduction of the intermediate azido alcohols constitutes a valuable synthetic tool for the construction of beta-amino alcohols, an important chemical functionality occurring in many biologically active compounds of natural origin. However, depending on conditions under which the azidolysis is carried out, two regioisomeric products can be formed, as a consequence of the nucleophilic attack on both the oxirane carbon atoms. In this work, predictive models for quantitative structure-reactivity relationships were developed by means of multiple linear regression, k-nearest neighbor, locally weighted regression, and Gaussian Process regression algorithms. The specific nature of the problem at hand required the creation of appropriate new descriptors, able to properly reflect the most relevant features of molecular moieties directly involved in the opening process. The models so obtained are able to predict the regioselectivity of the azidolysis of epoxides promoted by sodium azide, in the presence of lithium perchlorate, on the basis of steric hindrance, and charge distribution of the substituents directly attached to the oxirane ring.

  18. Diels-Alder reactions using 4,7-dioxygenated indanones as dienophiles for regioselective construction of oxygenated 2,3-dihydrobenz[f]indenone skeleton


    Full Text Available Regioselective construction of 4,8,9-trioxygenated 2,3-dihydrobenz[f]indenones, key intermediates for the synthesis of kinamycin antibiotics, was achieved via Diels-Alder reactions (DAR using 4,7-dioxygenated indanone-type compounds as dienophiles. Reaction of indanetrione with 1-methoxybutadiene gave a 1 : 1 mixture of undesired 4,5,9-trioxygenated 2,3-dihydrobenz[f]indenone and [4.4.3]propellane. The addition of Lewis acid did not affect the product ratio, whereas the use of the 6-bromoindanetrione exclusively afforded the latter propellane. On the other hand, DAR of benzyne derived from bromoindan and furan gave 5,8-epoxy-2,3-dihydrobenz[f]indene, which was subjected to acid-induced ring opening to give 2,3-dihydrobenz[f]indenone with undesired 4,5,9-trioxy functions.


    Bo-yong Xue; Kenichi Ogata; Akinori Toyota


    Norbornene derivatives exo,endo-2-[2-(3,5-di-tert-butyl-4-hydroxyphenoxy)-acetoxy]methyl-5-norbornene(M1) and 3,3,5,5-tetramethyl-4-piperidinyl 5-norbornene-exo,endo-2-carboxylate(M2)were synthesized and polymerized by RuCl2(=CHPh)(PCy3)2 to prepare a novel kind of bi-functional polymer bearing sterically hindered phenol (SHP) and hindered amine(HLAS)groups via ring-opening metathesis polymerization(ROMP).The resulting copolymers were characterized by gel permeation chromatography(GPC),'H-NMR and differential scanning calorimetry (DSC).The number average molecular weight(Mn)and functional unit content of the resulting copolymer could be regulated by varying the concentration of catalyst and monomer feed.

  20. Regioselective monodeprotection of peracetylated carbohydrates.

    Filice, Marco; Guisan, Jose M; Terreni, Marco; Palomo, Jose M


    This protocol describes the regioselective deprotection of single hydroxyls in peracetylated monosaccharides and disaccharides by enzymatic or chemoenzymatic strategies. The introduction of a one-pot enzymatic step by using immobilized biocatalysts obviates the requirement to carry out tedious workups and time-consuming purifications. By using this straightforward protocol, different per-O-acetylated glycopyranosides (mono- or disaccharides, 1-substituted or glycals) can be transformed into a whole set of differentially monodeprotected 1-alcohols, 3-alcohols, 4-alcohols and 6-alcohols in high yields. These tailor-made glycosyl acceptors can then be used for stereoselective glycosylation for oligosaccharide and glycoderivative synthesis. They have been successfully used as building blocks to synthesize tailor-made di- and trisaccharides involved in the structure of lacto-N-neo-tetraose and precursors of the tumor-associated carbohydrate antigen T and the antitumoral drug peracetylated β-naphtyl-lactosamine. We are able to prepare a purified monoprotected carbohydrate in between 1 and 4 d. With this protocol, the small library of monodeprotected products can be synthesized in 1-2 weeks.

  1. Revisiting the Fully Automated Double-Ring Infiltrometer Using Open-Source Electronics

    The double-ring infiltrometer (DRI) is commonly used for measuring soil hydraulic conductivity. However, constant-head DRI tests typically involve the use of Mariotte tubes, which can be problematic to set-up, and time-consuming to maintain and monitor during infiltration tests....

  2. Revisiting the Fully Automated Double-Ring Infiltrometer Using Open-Source Electronics

    The double-ring infiltrometer (DRI) is commonly used for measuring soil hydraulic conductivity. However, constant-head DRI tests typically involve the use of Mariotte tubes, which can be problematic to set-up, and time-consuming to maintain and monitor during infiltration tests....

  3. Metal free synthesis of functionalized 1-aryl isoquinolines via iodine mediated oxidative dehydrogenation and ring opening of lactam in isoindoloisoquinolinones



    A facile and convenient method for the synthesis of substituted 2-(isoquinolin-1-yl)benzoic acids from isoindoloisoquinolinones in the presence of molecular iodine under sealed tube condition at 100◦C has been developed. This methodology involves the oxidative dehydrogenation and ring opening of hydroxylactam/methoxy lactam to furnish the 2-(isoquinolin-1-yl)benzoic acids. Some of these acids are successfully cyclized to furnish the azabenzanthrone derivatives, the potential precursors for the synthesis of menisporphine alkaloids and daurioxoisoaporphines.

  4. Enantioselectivity of recombinant Rhizomucor miehei lipase in the ring opening of oxazolin-5(4H)-ones.

    Turner, N A; Gaskin, D J; Yagnik, A T; Littlechild, J A; Vulfson, E N


    Enantioselectivity of enzyme catalysis is often rationalized via active site models. These models are constructed on the basis of comparing the enantiomeric excess of product observed in a series of reactions which are conducted with a range of homologous substrates, typically carrying various side chain substitutions. Surprisingly the practical application of these simple but informative 'pocket size' models has been rarely tested in genetic engineering experiments. In this paper we report the construction, purification and enantioselectivity of two recombinant Rhizomucor miehei lipases which were designed to check the validity of such a model in reactions of ring opening of oxazolin-5(4H)-ones.

  5. Synthesis of hyperbranched copolymers by combining enzymatic ring-opening polymerization and A TRP from a novel bifunctional initiator

    Al Peng; CHEN Liang; HU Dehua; CHEN Yanhua; LI Dongshuang; ZHANG Bao; SHA Ke; WANG Jingyuan


    The hyperbranched aliphatic polyester P(ε-CL) was synthesized by means of Novozyme435-catalyzed ring-opening polymerization (ROP) of BHB (2, 2-bis(hydroxymethyl) butyric acid). The chains ended with hydroxyl of P(ε-CL) were modified by the esterification of α-bromopropionyl bromide to obtain hyperbranched difunctional macroinitiator, which was used in the ATRP of St. CuCI/HMTETA was used as the catalyst system in the reaction of ATRP to acquire the hyperbranched copolymers polystyrene-blockpoly(2,2-bis(hydroxymethyl) butyric acid). The copolymer was confirmed by NMR and GPC.

  6. A water-soluble polycarbonate with dimethylamino pendant groups prepared by enzyme-catalyzed ring-opening polymerization.

    Zhang, Xiaojin; Cai, Mengmeng; Zhong, Zhenlin; Zhuo, Renxi


    A water-soluble polycarbonate with dimethylamino pendant groups, poly(2-dimethylaminotrimethylene carbonate) (PDMATC), is synthesized and characterized. First, the six-membered carbonate monomer, 2-dimethylaminotrimethylene carbonate (DMATC), is prepared via the cyclization reaction of 2-(dimethylamino)propane-1,3-diol with triphosgene in the presence of triethylamine. Although the attempted ring-opening polymerization (ROP) of DMATC with Sn(Oct)(2) as a catalyst fails, the ROP of DMATC is successfully carried out with Novozym-435 as a catalyst to give water-soluble aliphatic polycarbonate PDMATC with low cytotoxicity and good degradability.

  7. Synthesis and Ring-Opening Metathesis Polymerization of Second-Generation Dendronized Poly(ether Monomers Initiated by Ruthenium Carbenes

    Guzmán Pablo E.


    Full Text Available The Ring-Opening Metathesis Polymerization (ROMP of second-generation dendronized monomers is described. Using the highly active and fast-initiating third-generation ruthenium complex [(H2IMes(pyr2Cl2RuCHPh], moderate to high molecular weight polymers (430-2230 kDa are efficiently synthesized with low dispersities (Ð = 1.01-1.17. This study highlights the power of the metathesis approach toward polymer synthesis in a context where monomer structure can significantly impede polymerization.

  8. Persistent Spin and Charge Currents in Open Conducting Ring Subjected to Rashba Spin-Orbit Coupling

    ZHANG Xi-Sua; XIONG Shi-Jie


    We investigate persistent charge and spin currents of a one-dimensional ring with Rashba spin-orbit coupling and connected asymmetrically to two external leads spanned with angle (φ)0.Because of the asymmetry of the structure and the spin-reflection,the persistent charge and spin currents can be induced.The magnification of persistent currents can be obtained when tuning the energy of incident electron to the sharp zero and sharp resonance of transmission depending on the Aharonov-Casher (AC) phase due to the spin-orbit coupling and the angle spanned by two leads (φ)0.The general dependence of the charge and spin persistent currents on these parameters is obtained.This suggests a possible method of controlling the magnitude and direction of persistent currents by tuning the AC phase and (φ)0,without the electromagnetic flux though the ring.

  9. Ring Cleavage Reactions of Methyl α-D-Allopyranoside Derivatives with Phenylboron Dichloride and Triethylsilane

    Yuusuke Ito


    Full Text Available In the course of our studies on the regioselective carbon-oxygen bond cleavage of the benzylidene acetal group of hexopyranosides with a reducing agent, we found that a combination of a Lewis acid and a reducing agent triggered a ring-opening reaction of the pyranose ring of methyl α-D-allopyranosides. The formation of an acyclic boronate ester by the attachment of a hydride ion at C-1 indicated that the unexpected endocyclic cleavage of the bond between the anomeric carbon atom and the pyranose ring oxygen atom proceeded via an oxacarbenium ion intermediate produced by the chelation between O5/O6 of the pyranoside and the Lewis acid, followed by nucleophile substitution with a hydride ion at C1.

  10. Ring-Opening Polymerization of L-Lactide to Cyclic Poly(Lactide) by Zeolitic Imidazole Framework-8 Catalyst.

    Luo, Zhixiong; Chaemchuen, Somboon; Zhou, Kui; Verpoort, Francis


    The catalytic activity of ZIF-8 in the ring-opening polymerization of L-lactide without solvents or co-catalysts is presented for the first time. Two different synthetic strategies have been applied for synthesizing ZIF-8, either under solvothermal condition or by spray-drying procedure. Their catalytic activities are found to be correlating with the presence of open active sites in ZIF-8 structure. The structural defects which afford active acid and basic sites are supposed to cooperatively catalyze the reaction. ZIF-8 assembled by spray-drying technique, displays a superior catalytic activity at temperature of 160 °C, leading to the formation of high molecular weight cyclic polylactide. The ZIF-8 catalysts could be recycled and reused without any significant loss of catalytic activity. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Fe@Fe2O3 promoted electrochemical mineralization of atrazine via a triazinon ring opening mechanism.

    Ding, Xing; Wang, Shengyao; Shen, Wanqiu; Mu, Yi; Wang, Li; Chen, Hao; Zhang, Lizhi


    In this study, an electrochemical/electro-Fenton oxidation (EC/EF) system was designed to degrade atrazine, by utilizing boron-doped diamond (BDD) and Fe@Fe2O3 core-shell nanowires loaded active carbon fiber (Fe@Fe2O3/ACF) as the anode and the cathode, respectively. This EC/EF system exhibited much higher degradation rate, decholorination and mineralization efficiency of atrazine than the electrochemical (EC) and electrochemical/traditional electro-Fenton (EC/TEF) oxidation counterpart systems without Fe@Fe2O3 core-shell nanowires. Active species trapping experiment revealed that Fe@Fe2O3 could activate molecular oxygen to produce more OH through Fenton reaction, which favored the atrazine degradation. High performance liquid chromatography, high performance liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry were applied to probe the decomposition and mineralization of atrazine during this novel EC/EF process, which revealed that two intermediates of triazinons (the isomerization of hydroxylated atrazine) were generated during the electrochemical/electro-Fenton oxidation of atrazine in the presence of Fe@Fe2O3 core-shell nanowires. The experimental and theoretical calculation results suggested that atrazine might be degraded via a triazinon ring opening mechanism, while the presence of Fe@Fe2O3 notably accelerated the decholorination process, and produced more hydroxylated products to promote the generation of trazinons and the subsequent ring cleavage as well as the final complete mineralization. This work provides a deep insight into the triazine ring opening mechanism and the design of efficient electrochemical advanced oxidation technologies (EAOTs) for persistent organic pollutant removal. Copyright © 2017 Elsevier Ltd. All rights reserved.

  12. Competitive and Cooperative Torquoselectivity in the thermal ring opening of cyclobutene: A density functional insight

    Lakshminarayanan Akilandeswari; Chandrasekaran Prathipa


    The competition between the two electron donors (–OCH3 and –OSiH3) have been studied by positioning them at geminal and vicinal locations. We have also studied the cis and trans geometrical isomerism at the vicinal location. Thermodynamic and activation parameters such as free energies have been computed to understand the potential energy surface of the reaction. Our computed activation hardness supports the proposed torquoselectivity. Further, Nucleus Independent Chemical Shift (NICS) was calculated at the ring centre of the transition state (TS) which additionally supports the torquoselectivity. The delicate preferences for the pathways have been substantiated through NBO interactions.

  13. Upgrading of LCO by partial hydrogenation of aromatics and ring opening of naphthenes over bi-functional catalysts

    Calemma, Vincenzo; Giardino, Roberto; Ferrari, Marco [Eni R and M, Via Maritano 26, 20097 San Donato (Italy)


    Available options to upgrade LCO to diesel fuel are: i) aromatic saturation (ASAT) ii) mild hydrocracking and iii) aromatic saturation followed by selective ring opening (SRO) of naphthenic structures. Although the above mentioned routes lead to significant product quality enhancement, they suffer from several disadvantages. Hydrocracking leads to significant yields in gasoline-range products, ASAT is characterized by a relatively high consumption of hydrogen with only limited improvement of product quality in terms of density and cetane properties, ASAT + SRO route leads to higher improvements of product quality but it requires a very high hydrogen consumption which strongly affects the economics of the process. An alternative upgrading route consists in partial polyaromatic compound saturation and selective opening of both naphthenic and benzo-naphthenic structures to produce less condensed naphthenic structures and alkyl-benzenes respectively. In this case the hydrogen needed to improve product quality at the same level, of cetane properties and density, is lower in comparison with ASAT. This paper reports the results obtained during a research program aimed at upgrading LCO via selective ring opening. The hydroconversion of a low sulfur hydrotreated LCO has been studied over iridium and platinum loaded on different supports. The results of this study indicate that the properties of products heavily depend on the characteristics of the support and the metal used. The data obtained with the Ir/amorphous silica-alumina (MSA) show the possibility to get a clear increase of CN and decrease of density in comparison with the mere aromatic saturation. The practical consequence of this result is the possibility of producing products with CN and density similar to products obtained by complete dearomatization but still containing a significant percentage of aromatic structures so allowing a consistent saving of hydrogen. (author)

  14. Aluminum Alkyl Complexes Bearing Salicylaldiminato Ligands: Versatile Initiators in the Ring-Opening Polymerization of Cyclic Esters

    Tiziana Fuoco


    Full Text Available Linear aliphatic polyesters are degradable thermoplastic polymers, which can be obtained by ring-opening polymerization (ROP of cyclic esters through a coordination-insertion mechanism. Aluminum based organometallic complexes have a leading position as efficient catalysts for this polymerization process. Aluminumalkyl complexes bearing salicylaldiminato ligands, although less explored, have been shown to be efficient and versatile catalysts for the ROP of various cyclic esters. These species have the potential to function as active catalysts in the ROP because of their less coordinatively saturated nature with respect to analogous SALEN-type complexes. They have been used as efficient catalysts in the ROP of commercially available cyclic esters, such as ε-caprolactone, l-lactide, rac-lactide, and glycolide. Moreover, they resulted in efficient catalysts for the ROP of cyclic esters with large ring-size and for the ROP of functionalized lactide. Furthermore, they have been used in the co- and ter-polymerization of various cyclic esters affording well controlled polymerization and a plethora of microstructural architectures, ranging from random to block to multiblock.

  15. A Rectangular Ring, Open-Ended Monopole Antenna with Two Symmetric Strips for WLAN and WiMAX Applications

    Joong-Han Yoon


    Full Text Available A triple-band rectangular ring, open-ended monopole antenna with symmetric L strips for wireless local area network (WLAN/Worldwide Interoperability of Microwave Access (WiMAX applications is proposed. The proposed antenna consists of two symmetric folded arms and L strips. Based on the concept, a prototype of the proposed triple antenna has been designed, fabricated, and tested. The numerical and experimental results demonstrated that the proposed antenna satisfied the −10 dB impedance bandwidth requirement while simultaneously covering the WLAN and WiMAX bands. Furthermore, this paper presented and discussed the 2D radiation patterns and 3D gains according to the results of the experiment. The proposed antenna’s peak gain varied between 2.17 and 4.93 dBi, and its average gain varied between −2.97 and −0.53 dBi.

  16. Sulfated Carbon Quantum Dots as Efficient Visible-Light Switchable Acid Catalysts for Room-Temperature Ring-Opening Reactions.

    Li, Haitao; Sun, Chenghua; Ali, Muataz; Zhou, Fengling; Zhang, Xinyi; MacFarlane, Douglas R


    Acid catalytic processes play a classic and important role in modern organic synthesis. How well the acid can be controlled often plays the key role in the controllable synthesis of the products with high conversion yield and selectivity. The preparation of a novel, photo-switchable solid-acid catalyst based on carbon quantum dots is described. The carbon quantum dots are decorated with small amounts of hydrogensulfate groups and thus exhibit a photogenerated acidity that produces a highly efficient acid catalysis of the ring opening of epoxides with methanol and other primary alcohols. This reversible, light-switchable acidity is shown to be due to photoexcitation and charge separation in the carbon quantum dots, which create an electron withdrawing effect from the acidic groups. The catalyst is easily separated by filtration, and we demonstrate multiple cycles of its recovery and reuse.

  17. Synthesis, characterization and catalytic activity of Ag-acidfuchsin nanohybrid system towards the ring opening polymerization of ε-caprolactone.

    Meenarathi, B; Palanikumar, S; Kannammal, L; Anbarasan, R


    The acidfuchsin (AF) decorated Ag nanoparticle (NP) was synthesized and its ability towards the ring opening polymerization (ROP) of ε-caprolactone (CL) was studied under N2 atmosphere at 160 °C in the presence of stannous octoate (SO) as a catalyst. Both the nanohybrid and nanocomposites were characterized by various analytical tools like Fourier transform infrared (FTIR) spectroscopy, UV-visible spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, fluorescence spectroscopy, gel permeation chromatography (GPC), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The number of binding site from the fluorescence spectrum confirmed that all the functional groups present in AF might have been involved in the ROP of CL. Copyright © 2014 Elsevier B.V. All rights reserved.

  18. Phosphazene-promoted metal-free ring-opening polymerization of ethylene oxide initiated by carboxylic acid

    Zhao, Junpeng


    The effectiveness of carboxylic acid as initiator for the anionic ring-opening polymerization of ethylene oxide was investigated with a strong phosphazene base (t-BuP4) used as promoter. Kinetic study showed an induction period, i.e., transformation of carboxylic acid to hydroxyl ester, followed by slow chain growth together with simultaneous and fast end-group transesterification, which led to poly(ethylene oxide) (PEO) consisting of monoester (monohydroxyl), diester, and dihydroxyl species. An appropriate t-BuP4/acid ratio was proven to be essential to achieve better control over the polymerization and low dispersity of PEO. This work provides important information and enriches the toolbox for macromolecular and biomolecular engineering with protic initiating sites. © 2014 American Chemical Society.

  19. Synthesis and structural studies of copper(II) complex supported by -ONNO- tetradentate ligand:Efficient catalyst for the ring-opening polymerization of lactide

    Anita Routaray; Nibedita Nath; Somanath Mantri; Tungabidya Maharan; Alekha Kumar Sutar


    The –ONNO– tetradentate Schiff base ligandN,N’-bis(2-hydroxy-3-methoxybenzaldehyde)benzene-1,2-diamine (HMBBD) has been synthesized. The ligand was attached to copper (Cu-HMBBD) in methanol under N2 atmosphere to give a mononuclear complex. The reactivity of this complex in the ring-opening polymerization (ROP) of lactide has been studied. The complex has a square planner geometry, as determined by X-ray diffraction studies. The copper complex is highly active towards the ring-opening polymerization of lactide, and the rate of polymerization is heavily dependent on the initiator used. The copper complex allows controlled ring-opening polymerization, as shown by the linear relationship between the percentage conversion and the number average molecular weight. Based on the literature, a mechanism for the ROP of lactide has been proposed.

  20. Identification of 6-hydroxy-trans,trans-2,4-hexadienoic acid, a novel ring-opened urinary metabolite of benzene

    Kline, S.A.; Robertson, J.F.; Grotz, V.L.; Goldstein, B.D.; Witz, G. (Robert Wood Johnson Medical School, Piscataway, NJ (United States) Environmental and Occupational Health Sciences Institute, Piscataway, NJ (United States))


    The authors have studied the in vivo metabolism of benzene in mice to ring-opened compounds excreted in urine. Male CD-1 mice were treated intraperitoneally with benzene (110-440 mg/kg), [[sup 14]C] benzene (220 mg/kg) or trans,trans-muconaldehyde (MUC; 4 mg/kg), a microsomal, hematotoxic metabolite of benzene. Urine, collected over 24 hr, was extracted and analyzed by HPLC with a diode-array detector and by scintillation counting. In addition to trans,trans-muconic acid, previously the only known ring-opened urinary benzene metabolite, a new metabolite, 6-hydroxy-trans,trans-2,4-hexadienoic acid, was detected in urine of mice treated with either benzene or MUC. The authors identified the new metabolite based on coelution of metabolites and UV spectral comparison with authentic standards in unmethylated and methylated urine extracts. Results presented here are consistent with the intermediacy of the ring-opened metabolites.

  1. A 5 GHz high-temperature superconducting reaction-type transmitting filter based upon split open-ring resonators

    Futatsumori, S; Hikage, T; Nojima, T [Graduate School of Information Science and Technology, Hokkaido University, Kita 14, Nishi 9, Kita-ku, Sapporo, Hokkaido 060-0814 (Japan); Akasegawa, A; Nakanishi, T; Yamanaka, K [Fujitsu Limited, 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0197 (Japan)], E-mail:


    A new kind of high-temperature superconducting (HTS) transmitting filter based on a reaction-type resonator is presented. The purpose of an HTS reaction-type filter (HTS-RTF) is to eliminate the intermodulation distortion noise generated by microwave power amplifiers such as those employed in mobile base stations. An HTS-RTF enables both higher power handling capability and sharper cutoff characteristics compared to existing planar-type HTS transmitting filters, since a reaction-type resonator does not resonate with high power fundamental signals. To achieve steep skirt characteristics and high power handling capability simultaneously, a 5 GHz three-pole HTS-RTF using a split open-ring resonator is designed. This split open-ring resonator offers low maximum current densities and a high-unloaded Q factor with low radiation. The designed prototype filter has Chebyshev characteristics with a centre frequency of 4.95 GHz and a bandwidth of 1.5 MHz. The HTS-RTF is fabricated using a double-sided YBa{sub 2}C{sub 3}O{sub 7-{delta}} thin film deposited on a 0.5 mm thick MgO substrate. The measured filter shows an insertion loss of less than 0.1 dB and a third intermodulation distortion value of -56.7 dBc for a 40 dBm passband signal. In addition, adjacent channel leakage power ratio (ACLR) measurements using an actual wideband CDMA signal confirm an ACLR improvement of about 10 dB for a four-carrier signal with power up to 40 dBm.

  2. Synthesis and optimization ring opening of monoepoxide linoleic acid using p-toluenesulfonic acid.

    Salimon, Jumat; Abdullah, Bashar Mudhaffar; Yusop, Rahimi M; Salih, Nadia; Yousif, Emad


    Biolubricant base oils, 9,12-hydroxy-10,13-oleioxy-12-octadecanoic acid (HYOOA) was synthesized based on the esterification reaction of Monoepoxide linoleic acid 9(12)-10(13)-monoepoxy 12(9)-octadecanoic acid (MEOA) with oleic acid (OA) and catalyzed by p-Toluenesulfonic acid. The optimum conditions for the experiment using D-optimal design to obtain high yield% of 84.61, conversion% of 83.54 and lowest OOC% of 0.05 were predicted at OA/MEOA ratio of 0.2:1 (mol/mol), PTSA/MEOA ratio of 0.4:1 (mol/mol), reaction temperature at 110°C, and reaction time at 4.5 h. The FTIR peaks of HYOOA indicate the disappearance of the absorption band at 820 cm(-1), which belongs to the oxirane ring. (13)C and (1)H NMR spectra analyses confirmed the result of HYOOA with appearance carbon-ester (C = O) chemical shift at 174.1 ppm and at 4.06 ppm for (13)C and (1)H NMR respectively.

  3. Photoisomerization among ring-open merocyanines. I. Reaction dynamics and wave-packet oscillations induced by tunable femtosecond pulses

    Ruetzel, Stefan; Diekmann, Meike; Nuernberger, Patrick; Walter, Christof; Engels, Bernd; Brixner, Tobias


    Upon ultraviolet excitation, photochromic spiropyran compounds can be converted by a ring-opening reaction into merocyanine molecules, which in turn can form several isomers differing by cis and trans configurations in the methine bridge. Whereas the spiropyran-merocyanine conversion reaction of the nitro-substituted indolinobenzopyran 6-nitro-1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-indoline] (6-nitro BIPS) has been studied extensively in theory and experiments, little is known about photoisomerization among the merocyanine isomers. In this article, we employ femtosecond transient absorption spectroscopy with variable excitation wavelengths to investigate the excited-state dynamics of the merocyanine in acetonitrile at room temperature, where exclusively the trans-trans-cis (TTC) and trans-trans-trans (TTT) isomers contribute. No photochemical ring-closure pathways exist for the two isomers. Instead, we found that (18±4)% of excited TTC isomers undergo an ultrafast excited-state cis→trans photoisomerization to TTT within 200 fs, while the excited-state lifetime of TTC molecules that do not isomerize is 35 ps. No photoisomerization was detected for the TTT isomer, which relaxes to the ground state with a lifetime of roughly 160 ps. Moreover, signal oscillations at 170 cm-1 and 360 cm-1 were observed, which can be ascribed to excited-state wave-packet dynamics occurring in the course of the TTC→TTT isomerization. The results of high-level time-dependent density functional theory in conjunction with polarizable continuum models are presented in the subsequent article [C. Walter, S. Ruetzel, M. Diekmann, P. Nuernberger, T. Brixner, and B. Engels, J. Chem. Phys. 140, 224311 (2014)].

  4. Ruthenium(II)-Catalyzed Regioselective Ortho Amidation of Imidazo Heterocycles with Isocyanates.

    Shakoor, S M Abdul; Kumari, Santosh; Khullar, Sadhika; Mandal, Sanjay K; Kumar, Anil; Sakhuja, Rajeev


    Direct ortho amidation at the phenyl ring of 2-phenylimidazo heterocycles with aryl isocyanates has been achieved via a chelation-assisted cationic ruthenium(II) complex catalyzed mechanism. The methodology provides a straightforward, high-yielding regioselective approach toward the synthesis of an array of ortho-amidated phenylimidazo heterocycles without prior activation of C(sp(2))-H. This also reports the first method for coupling of aryl isocyanates with the imidazo[1,2-a]pyridine system via a pentacyclometalated intermediate. The methodology is found to be easily scalable and could be applied toward the selective ortho amidation of 2-heteroarylimidazo[1,2-a]pyridine frameworks.

  5. Regioselective, Transition Metal-Free C-O Coupling Reactions Involving Aryne Intermediates.

    Dong, Yuyang; Lipschutz, Michael I; Tilley, T Don


    A new transition-metal-free synthetic method for C-O coupling between various aryl halides and alkoxides is described. This type of transformation is typically accomplished using palladium catalysts containing a specialized phosphine ligand. The reactions reported here can be performed under mild, ambient conditions using certain potassium alkoxides and a range of aryl halides, with iodide and bromide derivatives giving the best results. A likely mechanistic pathway involves the in situ generation of an aryne intermediate, and directing groups on the aryl ring inductively control regioselectivity.

  6. A Prospective Randomized Trial to Assess Fixation Strategies for Severe Open Tibia Fractures: Modern Ring External Fixators Versus Internal Fixation (FIXIT Study).

    OʼToole, Robert V; Gary, Joshua L; Reider, Lisa; Bosse, Michael J; Gordon, Wade T; Hutson, James; Quinnan, Stephen M; Castillo, Renan C; Scharfstein, Daniel O; MacKenzie, Ellen J


    The treatment of high-energy open tibia fractures is challenging in both the military and civilian environments. Treatment with modern ring external fixation may reduce complications common in these patients. However, no study has rigorously compared outcomes of modern ring external fixation with commonly used internal fixation approaches. The FIXIT study is a prospective, multicenter randomized trial comparing 1-year outcomes after treatment of severe open tibial shaft fractures with modern external ring fixation versus internal fixation among men and women of ages 18-64. The primary outcome is rehospitalization for major limb complications. Secondary outcomes include infection, fracture healing, limb function, and patient-reported outcomes including physical function and pain. One-year treatment costs and patient satisfaction will be compared between the 2 groups, and the percentage of Gustilo IIIB fractures that can be salvaged without soft tissue flap among patients receiving external fixation will be estimated.

  7. A detailed kinetic study of the direct ring opening of cyclohexane and methylcyclohexane over monofunctional Ir/Al{sub 2}O{sub 3} catalysts

    Shi, Hui; Gutierrez, O.Y.; Lercher, J.A. [Technische Univ. Muenchen (Germany). Catalysis Research Center


    The present study analyses a series of Al{sub 2}O{sub 3}-supported iridium catalysts with different pretreatments and addresses the kinetic features and structural requirements of direct ring opening of cyclohexane and methylcyclohexane catalyzed by Ir in absence of acid-catalyzed ring contraction. Mild reaction conditions and high H{sub 2}/hydrocarbon ratios (200-1000) were used to improve accuracy of kinetic measurements and to negate deactivation. Isomerization and dehydrogenation pathways were suppressed to low extents (1-5%) over the weakly acidic catalysts under the reaction conditions applied. Three main observations are shown: 1) initial selectivity to ring opening products (ROPs) increases with iridium dispersion; 2) optimal H{sub 2} pressures differ not only between primary and secondary products, but also among ROPs and fragments; 3) the air-calcination step before catalyst reduction imposes a significant impact on both activity and product distribution. (orig.)

  8. Fast and Living Ring-Opening Polymerization of α-Amino Acid N-Carboxyanhydrides Triggered by an "Alliance" of Primary and Secondary Amines at Room Temperature

    Zhao, Wei


    A novel highly efficient strategy, based on an "alliance" of primary and secondary amine initiators, was successfully developed allowing the fast and living ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCAs) at room temperature. (Chemical Equation Presented). © 2015 American Chemical Society.

  9. Highly active and stereoselective zirconium and hafnium alkoxide initiators for solvent-free ring-opening polymerization of rac-lactide.

    Chmura, Amanda J; Davidson, Matthew G; Frankis, Catherine J; Jones, Matthew D; Lunn, Matthew D


    Under solvent-free conditions (at 130 degrees C), zirconium and hafnium amine tris(phenolate) alkoxides are extremely active, well-controlled, single-site initiators for the ring-opening polymerization of rac-lactide, yielding highly heterotactic polylactide.

  10. Fluoroantimonic acid hexahydrate (HSbF6-6H2O) catalysis: The ring-opening polymerization of epoxidized soybean oil

    Ring-opening polymerization of epoxidized soybean oil (ESO) catalyzed by a super acid, fluroantimonic acid hexahydrate (HSbF6-6H2O), in ethyl acetate was conducted in an effort to develop useful biodegradable polymers. The resulting polymerized ESO (SA-RPESO) were characterized by using infrared (IR...

  11. Calcium chloride doped zinc-cobalt metal-cyanide complex: Unexpected highly activity towards ring-opening polymerization of propylene oxide

    Yi Jun Huang; Xing Hong Zhang; Zheng Jiang Hua; Guo Rong Qi


    Highly active calcium chloride (CaCl2) doped Zn-CoⅢ double metal-cyanide (Ca-DMC) catalysts were firstly reported. Ca-DMCs presented a very higher polymer yield (54 kg polymer/g catalyst) at relative low temperature (80-115 ℃) toward ring-opening polymerization (ROP) of propylene oxide (PO) than did DMC catalysts without modification.

  12. Accuracy of a new ring-opening metathesis elastomeric dental impression material with spray and immersion disinfection.

    Kronström, Mats H; Johnson, Glen H; Hompesch, Richard W


    A new elastomeric impression material has been formulated with a ring-opening metathesis chemistry. In addition to other properties of clinical significance, the impression accuracy must be confirmed. The purpose of this study was to compare the accuracy of the new elastomeric impression material with vinyl polysiloxane and polyether following both spray and immersion disinfection. Impressions of a modified dentoform with a stainless steel crown preparation in the lower right quadrant were made, and type IV gypsum working casts and dies were formed. Anteroposterior (AP), cross-arch (CA), buccolingual (BL), mesiodistal (MD), occlusogingivobuccal (OGB), and occlusogingivolingual (OGL) dimensions were measured using a microscope. Working cast and die dimensions were compared to those of the master model. The impression materials were a newly formulated, ring-opening metathesis-polymerization impression material (ROMP Cartridge Tray and ROMP Volume Wash), vinyl polysiloxane (VPS, Aquasil Ultra Monophase/LV), and a polyether (PE, Impregum Penta Soft/Permadyne Garant L). Fifteen impressions with each material were made, of which 5 were disinfected by spray for 10 minutes (CaviCide), 5 were disinfected by immersion for 90 minutes (ProCide D), and 5 were not disinfected. There were significant cross-product interactions with a 2-way ANOVA, so a 1-way ANOVA and Dunnett's T3 multiple comparison test were used to compare the dimensional changes of the 3 impression materials, by disinfection status and for each location (alpha=.05). For ROMP, there were no significant differences from the master, for any dimension, when comparing the control and 2 disinfectant conditions. No significant differences were detected among the 3 impression materials for CA, BL, and MD. The working die dimensions of OGB and OGL for VPS with immersion disinfection were significantly shorter than with PE and ROMP (P<.05). Overall, the AP dimension was more accurate than CA, and the BL of working dies

  13. Regioselective oxidation of unprotected 1,4 linked glucans

    Eisink, Niek N.H.M.; Lohse, Jonas; Witte, Martin D.; Minnaard, Adriaan J.


    Palladium-catalyzed alcohol oxidation allows the chemo- and regioselective modification of unprotected 1,4 linked glucans. This is demonstrated in the two-step bisfunctionalization of 1,4 linked glucans up to the 7-mer. Introduction of an anomeric azide is followed by a highly regioselective mono-ox

  14. Bidirectional cross metathesis and ring-closing metathesis/ring opening of a C2-symmetric building block: a strategy for the synthesis of decanolide natural products

    Bernd Schmidt


    Full Text Available Starting from the conveniently available ex-chiral pool building block (R,R-hexa-1,5-diene-3,4-diol, the ten-membered ring lactones stagonolide E and curvulide A were synthesized using a bidirectional olefin-metathesis functionalization of the terminal double bonds. Key steps are (i a site-selective cross metathesis, (ii a highly diastereoselective extended tethered RCM to furnish a (Z,E-configured dienyl carboxylic acid and (iii a Ru–lipase-catalyzed dynamic kinetic resolution to establish the desired configuration at C9. Ring closure was accomplished by macrolactonization. Curvulide A was synthesized from stagonolide E through Sharpless epoxidation.

  15. Bidirectional cross metathesis and ring-closing metathesis/ring opening of a C 2-symmetric building block: a strategy for the synthesis of decanolide natural products.

    Schmidt, Bernd; Kunz, Oliver


    Starting from the conveniently available ex-chiral pool building block (R,R)-hexa-1,5-diene-3,4-diol, the ten-membered ring lactones stagonolide E and curvulide A were synthesized using a bidirectional olefin-metathesis functionalization of the terminal double bonds. Key steps are (i) a site-selective cross metathesis, (ii) a highly diastereoselective extended tethered RCM to furnish a (Z,E)-configured dienyl carboxylic acid and (iii) a Ru-lipase-catalyzed dynamic kinetic resolution to establish the desired configuration at C9. Ring closure was accomplished by macrolactonization. Curvulide A was synthesized from stagonolide E through Sharpless epoxidation.

  16. Synthesis of biodegradable amphiphilic Y-shaped block co-polymers via ring-opening polymerization for drug delivery.

    Jia, Lin; Yan, Lifeng; Li, Yang


    A series of novel Y-shaped biodegradable block co-polymers of poly(ε-caprolactone) (PCL) and poly(ethyl ethylene phosphate) (PEEP) (PCL-(PEEP)2) were synthesized via ring-opening polymerization (ROP) of EEP with bis-hydroxy-functional ROP initiator (init-PCL-(OH)2). The init-PCL-(OH)2 was synthesized by ROP of CL using 4-hydroxybutyl acrylate (HBA) as initiator and L-tartaric acid as catalyst in bulk, and subsequently the resulting vinyl-terminated PCL was end-capped by acetyl chloride, followed by Michael addition using excess diethanolamine. The Y-shaped co-polymers and their intermediates were characterized by (1)H-, (13)C-, (31)P-NMR, FT-IR and gel-permeation chromatography. The results indicated that the molecular weight of the Y-shaped co-polymers increased with the increasing of the molar ratios of EEP to init-PCL-(OH)2 in the feed, while the PCL chain length was kept constant. The amphiphilic block co-polymers could self-assemble into micelles in aqueous solution, which was demonstrated by dynamic light scattering, (1)H-NMR and atomic force microscopy. A study of controlled release of indomethacin indicated that the amphiphilic block co-polymers could potentially provide novel vehicles for drug delivery.

  17. Completely recyclable biopolymers with linear and cyclic topologies via ring-opening polymerization of γ-butyrolactone.

    Hong, Miao; Chen, Eugene Y-X


    Ring-opening polymerization (ROP) is a powerful synthetic methodology for the chemical synthesis of technologically important biodegradable aliphatic polyesters from cyclic esters or lactones. However, the bioderived five-membered γ-butyrolactone (γ-BL) is commonly referred as 'non-polymerizable' because of its low strain energy. The chemical synthesis of poly(γ-butyrolactone) (PγBL) through the ROP process has been realized only under ultrahigh pressure (20,000 atm, 160 °C) and only produces oligomers. Here we report that the ROP of γ-BL can, with a suitable catalyst, proceed smoothly to high conversions (90%) under ambient pressure to produce PγBL materials with a number-average molecular weight up to 30 kg mol(-1) and with controlled linear and/or cyclic topologies. Remarkably, both linear and cyclic PγBLs can be recycled back into the monomer in quantitative yield by simply heating the bulk materials at 220 °C (linear polymer) or 300 °C (cyclic polymer) for one hour, which thereby demonstrates the complete recyclability of PγBL.

  18. Application of ring-opening metathesis polymerization in study of polymer molecular weight-mediated catalytic properties of immobilized lipase

    DU Chuang; ZHANG Guo; WANG Zhi; LI Lei; TANG Jun; WANG Lei


    Recently, significant efforts have been devoted into the study of the effect of hydrophobic supports on the catalytic properties of immobilized lipases. It seems that immobilization lipases on hydrophobic supports is a simple and efficient method to improve the catalytic activity of lipases. In this study, the hydrophobic poly(N-propyl-norbornene-exo-2,3-dicarboximide)s with well-controlled molecular weight were synthesized by the living ring-opening metathesis polymerization, and the lipases from Pseudo-monas sp. were then immobilized on these hydrophobic polymer supports through the physical ad-sorption. The immobilized lipases exhibited higher activity and enantioselectivity for the transesterifi-cation of 2-octanol than those of free lipases. Furthermore, we investigated the polymer molecular weight-mediated catalytic properties of immobilized lipases. It was found that the catalytic activity and E value of the immobilized lipases increased with the increase of the polymer molecular weight. At the polymeric molecular weight of about 40kDa, the highest E value (58 at 54.2% of conversion, enanti-omeric excess = 99%) was reached. After the molecular weight of polymers getting higher than 40 kDa, catalytic activity end E value of the immobilized lipase decreased.

  19. Synthesis of High Performance Cyclic Olefin Polymers (COPs with Ester Group via Ring-Opening Metathesis Polymerization

    Jing Cui


    Full Text Available Novel ester group functionalized cyclic olefin polymers (COPs with high glass transition temperature, high transparency, good mechanical performance and excellent film forming ability have been achieved in this work via efficient ring-opening metathesis copolymerization of exo-1,4,4a,9,9a,10-hexahydro-9,10(1′,2′-benzeno-l,4-methanoanthracene (HBM and comonomers (5-norbornene-2-yl methylacetate (NMA, 5-norbornene-2-yl methyl 2-ethylhexanoate (NME or 5-norbornene-2-yl methyldodecanoate (NMD utilizing the Grubbs first generation catalyst, Ru(CHPh(Cl2(PCy32 (Cy = cyclohexyl, G1, followed by hydrogenation of double bonds in the main chain. The fully hydrogenated copolymers were characterized by nuclear magnetic resonance, FT-IR spectroscopy analysis, gel permeation chromatography, and thermo gravimetric analysis. Differential scanning calorimetry curves showed that the glass transition temperatures (Tg linearly decreased with the increasing of comonomers content, which was easily controlled by changing feed ratios of HBM and comonomers. Static water contact angles tests indicate that hydrophilicity of copolymers can also be modulated by changing the comonomers incorporation. Additionally, the mechanical performances of copolymers were also investigated.

  20. Immortal Ring-Opening Polymerization of rac-Lactide Using Polymeric Alcohol as Initiator to Prepare Graft Copolymer

    Na Liu


    Full Text Available In the presence of a small molecular protic initiator, immortal ring-opening polymerization (ROP of lactide (LA is a highly efficient strategy to synthesize polylactide in a controllable manner, while using polymeric alcohol as an initiator has been less investigated. A series of polymeric alcohols (PS–OH composed of styrene and 4.3%–18% hydroxyl functional styrene (diethyl(hydroxy(4-vinylphenylmethylphosphonate, St–OH were synthesized through reversible addition-fragmentation transfer (RAFT polymerization. Using PS–OH as an initiator, the immortal ROP of rac-LA was catalyzed by dibutylmagnesium (MgnBu2 under various ratios of monomer to hydroxyl group within PS–OH to generate polystyrene-g-polylactide (PS–g–PLA copolymers with different graft lengths. After thermal annealing at 115 °C, the PLA domain aggregated to nanospheres among the PS continuum. The size of the nanospheres, varying from 130.1 to 224.2 nm, was related to the graft density and length of PS–g–PLA. Nanoporous films were afforded through chemical etching of the PLA component.

  1. in situ ring-opening polymerization of hydroxyapatite/poly(ethylene adipate)--(ethylene terephthalate) biomimetic composites

    Punnama Siriphannon; Pathavuth Monvisade


    Hydroxyapatite/poly(ethylene adipate)--poly(ethylene terephthalate) biomaterials (HAp/PEA--PET) have been prepared by ring opening polymerization (ROP) of cyclic oligo(ethylene adipate)--oligo(ethylene terephthalate) (C-OEA--C-OET) in the porous hydroxyapatite (HAp) scaffolds at 250 °C for 24 h under vacuum. The content of ROP-PEA--PET in the HAp/PEA--PET composite was about 20 wt% with the values of number average molecular weight ($\\bar{M}$n) and weight average molecular weight ($\\bar{M}$W) of 3380 and 7160 g/mol, respectively. Compressive strength and modulus of the HAp/PEA--PET composites were about 29 and 246 MPa, respectively. These mechanical properties were higher than those of the porous HAp templates and natural cancellous bone. In vitro bioactivity of the HAp/PEA--PET composites was studied by soaking in simulated body fluid (SBF) under the flowing system at the rate of 130 mL/day for 7, 14, 21 and 28 days. The formation of hydroxyapatite nanocrystals was observed on the composite surfaces through the consumption of calcium and phosphorus from the SBF solution, indicating the bioactivity of these HAp/PEA--PET composites. These results indicated the competency of HAp/PEA--PET composites for biomedical applications.

  2. Sulfated Alkyl Glucopyranans with Potent Antiviral Activity Synthesized by Ring-Opening Copolymerization of Anhydroglucose and Alkyl Anhydroglucose Monomers

    Shiming Bai


    Full Text Available Sulfated glucopyranans having long alkyl groups were prepared by the ring-opening copolymerization of benzylated 1,6-anhydroglucopyranose with 3-O-octadecyl 1,6-anhydro-β-d-glucopyranose monomers, and subsequent deprotection and sulfation. Water-soluble sulfated glucopyranans with 2.8 and 4.7 mol% of 3-O-octadecyl group and lower molecular weights of M-n = 2.5 × 103–5.1 × 103 have potent anti-HIV activity at 0.05–1.25 μg/mL, even though sulfated polysaccharides with molecular weights below M-n = 6 × 103 had low anti-HIV activity. The interaction with poly-l-lysine as a model compound of proteins was analyzed by SPR, DSL, and zeta potential, indicating that the sulfated 3-O-octadecyl glucopyranans had high association and low dissociation rate constants, and the particle size increased after addition of poly-l-lysine. The anti-HIV activity was induced by electrostatic interaction between sulfate groups and amino groups of poly-l-lysine and by the synergistic effect of the hydrophobic long alkyl chain and hydrophilic sulfated group.

  3. Ring-opening copolymerization of (R,S-β-butyrolactone and ε-caprolactone using sodium hydride as initiator


    Full Text Available Copolymers of racemic β-butyrolactone ((R,S-BL and ε-caprolactone (CL, were synthesized by ring-opening polymerization initiated by sodium hydride (NaH. The initiator exhibited a satisfactory catalytic activity, producing copolymers whose yields are greatly influenced by the feed monomer ratio, CL/BL. All polymers obtained were characterized by nuclear magnetic resonance (NMR, gel permeation chromatography (GPC, thermogravimetric analysis (TGA, differential scanning calorimetry (DSC and wide angle X-rays scattering, WAXS. The molar composition of copolyesters determined by 1H-NMR spectra, showed that the incorporation of CL is favoured over the incorporation of (R,S-BL. Gel permeation chromatography and 13C-NMR spectra indicated that CL/BL copolymers had block sequence distribution. The TGA analysis of copolymers showed that these copolymers are stable up to temperatures near 200°C, followed by a decomposition process in two steps; the first one is attributed to the (R,S-BL block degradation and the second to the remaining PCL block. The crystallization process of these copolymers was studied by DSC and WAXS showing that the amorphous (R,S-BL segments chains did not affect the crystallinity of the PCL blocks.

  4. A low-cost dielectric spectroscopic system using metamaterial open horn-ring resonator-inspired BSF and detection circuitry

    Kumari, Ratnesh; Patel, Piyush N.


    The sensitivity in a lower microwave band dielectric spectroscopic system is relatively less compared to that of millimeter wave and terahertz system. This work reports modeling and development of an epsilon-negative metamaterial resonator-inspired microwave band-stop filter as a prototype device and its detection circuitry for the spectroscopic analysis of dielectric samples in S-band. The device structure consists of a diamond-shaped patch with a complementary open split horn-ring resonator, fabricated on a Neltech substrate of relative permittivity ( ɛ r = 3.2). The measured transmission coefficient at 2.2 GHz and simulated result at 2.24 GHz demonstrate an excellent accuracy in the device fabrication. A low-cost connector-type microwave signal detection system was assembled for the real-time transduction of device signal into an equivalent DC voltage. Further, a single channel cavity developed using polydimethylsiloxane was placed over the resonator gap for analyzing the perturbation effect of electric field intensity on the resonance and circuit output DC level for different dielectric samples under test. The performed calibrations show linearity up to 82.5 % in the device response.

  5. End-Group Evaluation of HEMA Initiated Poly(ε-caprolactone Macromonomers via Enzymatic Ring-Opening Polymerization

    N. Ugur Kaya


    Full Text Available Poly(ε-caprolactone (PCL macromonomers comprising acrylate end-functionality were synthesized via enzymatic ring-opening polymerization (eROP by utilizing commercially available Candida antarctica Lipase B (CALB, Novozyme-435. 2-Hydroxyethyl methacrylate (HEMA was purposed to be the nucleophilic initiator in eROP. The side reactions generated due to the cleavage of ester bonds in HEMA and the growing polymer chains were investigated through altering polymerization period, initiator concentration, temperature, and enzyme concentration. 1H NMR evaluations showed that minimum quantities of side reactions were in lower temperatures, initiator concentration, enzyme concentration, and lower monomer conversions. Gel permeation chromatography (GPC results revealed that lower polydispersity along with number-average molecular weight of end-functionalized PCL macromonomers was obtained depending on higher initiator/monomer ratios, lower temperature (60°C, enzyme concentration (100 mg, and/or polymerization time (2 h. Furthermore, 0.1 HEMA/ε-caprolactone (CL ratio had higher molecular weight than 0.5 HEMA/CL ratio, while keeping a close value of methacrylate transfer, total methacrylate end-groups, and lower polyester transfer.

  6. From interfacial ring-opening polymerization to melt processing of cellulose nanowhisker-filled polylactide-based nanocomposites.

    Goffin, Anne-Lise; Raquez, Jean-Marie; Duquesne, Emmanuel; Siqueira, Gilberto; Habibi, Youssef; Dufresne, Alain; Dubois, Philippe


    In the present work, cellulose nanowhiskers (CNWs), extracted from ramie fibers, were incorporated in polylactide (PLA)-based composites. Prior to the blending, PLA chains were chemically grafted on the surface of CNW to enhance the compatibilization between CNW and the hydrophobic polyester matrix. Ring-opening polymerization of l-lactide was initiated from the hydroxyl groups available at the CNW surface to yield CNW-g-PLA nanohybrids. PLA-based nanocomposites were prepared by melt blending to ensure a green concept of the study thereby limiting the use of organic solvents. The influence of PLA-grafted cellulose nanoparticles on the mechanical and thermal properties of the ensuing nanocomposites was deeply investigated. The thermal behavior and mechanical properties of the nanocomposites were determined using differential scanning calorimetry (DSC) and dynamical mechanical and thermal analysis (DMTA), respectively. It was clearly evidenced that the chemical grafting of CNW enhances their compatibility with the polymeric matrix and thus improves the final properties of the nanocomposites. Large modification of the crystalline properties such as the crystallization half-time was evidenced according to the nature of the PLA matrix and the content of nanofillers.

  7. The Effect of K and Acidity of NiW-Loaded HY Zeolite Catalyst for Selective Ring Opening of 1-Methylnaphthalene.

    Lee, You-Jin; Kim, Eun-Sang; Kim, Jeong-Rang; Kim, Joo-Wan; Kim, Tae-Wan; Chae, Ho-Jeong; Kim, Chul-Ung; Lee, Chang-Ha; Jeong, Soon-Yong


    Bi-functional catalysts were prepared using HY zeolites with various SiO2/Al2O3 ratios for acidic function, NiW for metallic function, and K for acidity control. 1-Methylnaphthalene was selected as a model compound for multi-ring aromatics in heavy oil, and its selective ring opening reaction was investigated using the prepared bi-functional catalysts with different levels of acidity in a fixed bed reactor system. In NiW/HY catalysts without K addition, the acidity decreased with the SiO2/Al2O3 mole ratio of the HY zeolite. Ni1.1W1.1/HY(12) catalyst showed the highest acidity but slightly lower yields for the selective ring opening than Ni1.1W1.1/HY(30) catalyst. The acidity of the catalyst seemed to play an important role as the active site for the selective ring opening of 1-methylnaphthalene but there should be some optimum catalyst acidity for the reaction. Catalyst acidity could be controlled between Ni1.1W1.1/HY(12) and Ni1.1W1.1/HY(30) by adding a moderate amount of K to Ni1.1W1.1/HY(12) catalyst. K0.3Ni1.1W1.1/HY(12) catalyst should have the optimum acidity for the selective ring opening. The addition of a moderate amount of K to the NiW/HY catalyst must improve the catalytic performance due to the optimization of catalyst acidity.

  8. Regioselective nitration of aromatic substrates in zeolite cages

    T Esakkidurai; M Kumarraja; K Pitchumani


    Phenol is nitrated regioselectively by fuming nitric acid inside the cages of faujasite zeolites (dependent on the loading level) and a remarkable orthoselectivity is observed in solid state nitration. Toluene and chlorobenzene also containing ortho-/para-orienting substituents, undergo faster nitration, though the regioselectivity is less significant in zeolite media. The results are explained on the basis of diffusion and binding of phenol inside zeolite, which facilitate regioselectivity (and which is absent in toluene and chlorobenzene). Other advantages of employing zeolites as media for mild and selective nitration are also highlighted.

  9. Regioselective enzymatic acylation of troxerutin in nonaqueous medium


    A series of monosubstituted troxerutin esters have been synthesized by enzyme-catalyzed regioselective acylation of troxerutin in nonaqueous medium.Using divinyl dicarboxylates(CH_2=CH-OOC-(CH_2)_n-COO-CH=CH_2,n = 2,3,4,7,8,11) featuring different chain length as acyl donors and alkaline protease from Bacillus subtilis as catalyst,troxerutin was regioselective acylated at B' ethoxyl group.The results indicated that the regioselectivity of the enzyme-catalyzed acylation was not affected by the chain lengt...

  10. Structural disorder and transformation in crystal growth: direct observation of ring-opening isomerization in a metal-organic solid solution.

    Jiang, Ji-Jun; He, Jian-Rong; Lü, Xing-Qiang; Wang, Da-Wei; Li, Guo-Bi; Su, Cheng-Yong


    A rare example is reported in which discrete Ag2 L 2 ring and (AgL)∞ chain motifs [L = N,N'-bis(3-imidazol-1-yl-propyl)-pyromellitic diimide] co-crystallize in the same crystal lattice with varying ratios and degrees of disorder. Crystal structures obtained from representative crystals reveal compatible packing arrangements of the cyclic and polymeric isomers within the crystal lattice, which enables them to co-exist within a crystalline solid solution. A feasible pathway for transformation between the isomers is suggested via facile rotation of the coordinating imidazolyl groups. This chemical system could provide a chance for direct observation of ring-opening isomerization at the crystal surface. Mass spectrometry and (1)H NMR titration show a dynamic equilibrium between cyclic and oligomeric species in solution, and a potential crystallization process is suggested involving alignment of precursors directed by aromatic stacking interactions between pyromellitic diimide units, followed by ring-opening isomerization at the interface between the solid and the solution. Both cyclic and oligomeric species can act as precursors, with interconversion between them being facile due to a low energy barrier for rotation of the imidazole rings. Thermogravimetric analysis and variable-temperature powder X-ray diffraction indicate a transition to a different crystalline phase around 120°C, which is associated with loss of solvent from the crystal lattice.


    Chi-fei Wu


    Porcine pancreas lipase (PPL) and PPL immobilized on narrow distributed micron-sized glass beads were employed successfully for the ring-opening polymerization of 5,5-dimethyl-1,3-dioxan-2-one (DTC) for the first time.Different polymerization conditions such as enzyme concentration and reaction temperature were studied. Immobilized PPL exhibits higher activity than native PPL. Along with the increasing enzyme concentration, the molecular weight of resulting PDTC decreases. PPL immobilized on narrow distributed micron-sized glass beads has outstanding recyclability. For the third recycle time, immobilized PPL exhibits the highest catalytic activity and with high activity even after the fifth recyle time for the synthesis of PDTC. The 1H-NMR spectra indicate that decarboxylation does not occur during the ring-opening polymerization.


    PAN Caiyuan; WANG Yin


    This paper describes the synthesis and free radical ring- opening polymerization of 2 - methyl-and2 - methyl - 9 - n - butyl ( - 7 - methylene - 1,4, 6 - trioxaspiro (4, 4 ) nonane ). The structures of the two polymers were verified by IR, 1H and 13C NMR spectra. The substituent on 9-position of 7-methylene- trioxaspiro (4, 4 ) nona ne affects the structure of polymer and polymerization activity. The polymerization mechanism is discussed .

  13. Salen complexes of zirconium and hafnium: synthesis, structural characterization, controlled hydrolysis, and solvent-free ring-opening polymerization of cyclic esters and lactides.

    Saha, Tanmoy Kumar; Ramkumar, Venkatachalam; Chakraborty, Debashis


    Dinuclear salen compounds of zirconium and hafnium are efficient initiators for the solvent-free ring-opening polymerization of cyclic ester monomers and lactides. There is a correlation between the theoretical and experimental number-average molecular weights (M(n)'s) in these polymerizations. Polymerization of β-butyrolactone gives poly(3-hydroxybutyrate) with a good M(n) and molecular weight distribution.

  14. Ring-Opening Metathesis Activity of Ruthenium-Based Olefin Metathesis Catalyst Coordinated with 1,3-Bis(2,6-Diisopropylphenyl)-4,5-Dihydroimidazoline

    Karabulut, Solmaz; Verpoort, Francis

    A 1,3-bis-(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene substituted ruthenium (Ru)-based complex (4) has been prepared starting from (PCy3)2(Cl)2Ru=CHPh (2). The catalytic performance of catalyst (4) is checked on ring-opening metathesis polymerization (ROMP) of the low strain monomer, cycloocta-1,5-diene (COD), and also compared with catalyst (2) and (3).

  15. A Synthetic Route to Chiral 1,4-Disubstituted Tetrahydro-β-Carbolines via Domino Ring-Opening Cyclization of Activated Aziridines with 2-Vinylindoles.

    Sayyad, Masthanvali; Wani, Imtiyaz Ahmad; Babu, Raja; Nanaji, Yerramsetti; Ghorai, Manas K


    A simple and efficient strategy for the synthesis of various 1,4-disubstituted tetrahydro-β-carbolines with excellent stereoselectivity (de, ee up to >99%) via domino ring opening cyclization (DROC) of activated aziridines with 2-vinylindoles is described. The reaction proceeds through LiClO4-catalyzed Friedel-Crafts-type alkylation of 2-vinylindoles with activated aziridines followed by an intramolecular aza-Michael reaction in a domino fashion.

  16. A Stereoselective Route to Tetrahydrobenzoxazepines and Tetrahydrobenzodiazepines via Ring-Opening and Aza-Michael Addition of Activated Aziridines with 2-Hydroxyphenyl and 2-Aminophenyl Acrylates.

    Shahi, Chandan Kumar; Bhattacharyya, Aditya; Nanaji, Yerramsetti; Ghorai, Manas K


    A simple and efficient synthetic route to 2,3,4,5-tetrahydrobenzoxazepines and -benzodiazepines bearing easily functionalizable appendages has been developed by ring-opening of activated aziridines with 2-hydroxyphenyl acrylates and 2-aminophenyl acrylate, respectively, and subsequent intramolecular C-N bond formation through palladium-catalyzed aza-Michael reaction. The straightforward synthetic approach delivers the desired molecular scaffolds in high yields (up to 82%) with excellent stereoselectivity (ee up to 94%).

  17. Recent Developments of Versatile Photoinitiating Systems for Cationic Ring Opening Polymerization Operating at Any Wavelengths and under Low Light Intensity Sources.

    Lalevée, Jacques; Mokbel, Haifaa; Fouassier, Jean-Pierre


    Photoinitiators (PI) or photoinitiating systems (PIS) usable in light induced cationic polymerization (CP) and free radical promoted cationic polymerization (FRPCP) reactions (more specifically for cationic ring opening polymerization (ROP)) together with the involved mechanisms are briefly reviewed. The recent developments of novel two- and three-component PISs for CP and FRPCP upon exposure to low intensity blue to red lights is emphasized in details. Examples of such reactions under various experimental conditions are provided.

  18. Gold-Catalyzed Regioselective Dimerization of Aliphatic Terminal Alkynes.

    Sun, Sheng; Kroll, Julien; Luo, Yingdong; Zhang, Liming


    A gold-catalyzed regioselective homodimerization of aliphatic terminal alkynes is described. Bulky and less Lewis acidic tBuXPhosAuNTf(2) is the preferred catalyst, and the additive, anhydrous NaOAc, substantially facilitates the reaction.

  19. Estimate of the parameters for a ring-shaped {open_quotes}myxine{close_quotes} for galatea thermonuclear reactors

    Morozov, A.I.; Khripunov, V.I.


    The parameters of an autonomous ring-shaped myxine are estimated in connection with the conditions for an energy-producing thermonuclear reactor operating with DT and D{sup 3}He reactions. 11 refs., 3 figs. 1 tab.

  20. Origins of Regioselectivity in Iridium Catalyzed Allylic Substitution

    Madrahimov, Sherzod T.; Li, Qian; Sharma, Ankit; Hartwig, John F.


    Detailed studies on the origin of the regioselectivity for formation of branched products over linear products have been conducted with complexes containing the achiral triphenylphosphite ligand. The combination of iridium and P(OPh)3 was the first catalytic system shown to give high regioselectivity for the branched product with iridium and among the most selective for forming branched products among any combination of metal and ligand. We have shown the active catalyst to be generated from ...

  1. Optimal Hydrophobicity in Ring-Opening Metathesis Polymerization-Based Protein Mimics Required for siRNA Internalization.

    deRonde, Brittany M; Posey, Nicholas D; Otter, Ronja; Caffrey, Leah M; Minter, Lisa M; Tew, Gregory N


    Exploring the role of polymer structure for the internalization of biologically relevant cargo, specifically siRNA, is of critical importance to the development of improved delivery reagents. Herein, we report guanidinium-rich protein transduction domain mimics (PTDMs) based on a ring-opening metathesis polymerization scaffold containing tunable hydrophobic moieties that promote siRNA internalization. Structure-activity relationships using Jurkat T cells and HeLa cells were explored to determine how the length of the hydrophobic block and the hydrophobic side chain compositions of these PTDMs impacted siRNA internalization. To explore the hydrophobic block length, two different series of diblock copolymers were synthesized: one series with symmetric block lengths and one with asymmetric block lengths. At similar cationic block lengths, asymmetric and symmetric PTDMs promoted siRNA internalization in the same percentages of the cell population regardless of the hydrophobic block length; however, with 20 repeat units of cationic charge, the asymmetric block length had greater siRNA internalization, highlighting the nontrivial relationships between hydrophobicity and overall cationic charge. To further probe how the hydrophobic side chains impacted siRNA internalization, an additional series of asymmetric PTDMs was synthesized that featured a fixed hydrophobic block length of five repeat units that contained either dimethyl (dMe), methyl phenyl (MePh), or diphenyl (dPh) side chains and varied cationic block lengths. This series was further expanded to incorporate hydrophobic blocks consisting of diethyl (dEt), diisobutyl (diBu), and dicyclohexyl (dCy) based repeat units to better define the hydrophobic window for which our PTDMs had optimal activity. High-performance liquid chromatography retention times quantified the relative hydrophobicities of the noncationic building blocks. PTDMs containing the MePh, diBu, and dPh hydrophobic blocks were shown to have superior

  2. Real-time propagation time-dependent density functional theory study on the ring-opening transformation of the photoexcited crystalline benzene

    Tateyama, Yoshitaka; Oyama, Norihisa; Ohno, Takahisa; Miyamoto, Yoshiyuki


    Mechanism of the ring-opening transformation in the photoexcited crystalline benzene is investigated on the femtosecond scale by a computational method based on the real-time propagation (RTP) time-dependent density functional theory (TDDFT). The excited-state dynamics of the benzene molecule is also examined not only for the distinction between the intrinsic properties of molecule and the intermolecular interaction but for the first validation using the vibration frequencies for the RTP-TDDFT approach. It is found that the vibration frequencies of the excited and ground states in the molecule are well reproduced. This demonstrates that the present method of time evolution using the Suzuki-Trotter-type split operator technique starting with the Franck-Condon state approximated by the occupation change of the Kohn-Sham orbitals is adequately accurate. For the crystalline benzene, we carried out the RTP-TDDFT simulations for two typical pressures. At both pressures, large swing of the C-H bonds and subsequent twist of the carbon ring occurs, leading to tetrahedral (sp3-like) C-H bonding. The ν4 and ν16 out-of-plane vibration modes of the benzene molecule are found mostly responsible for these motions, which is different from the mechanism proposed for the thermal ring-opening transformation occurring at higher pressure. Comparing the results between different pressures, we conclude that a certain increase of the intermolecular interaction is necessary to make seeds of the ring opening (e.g., radical site formation and breaking of the molecular character) even with the photoexcitation, while the hydrogen migration to fix them requires more free volume, which is consistent with the experimental observation that the transformation substantially proceeds on the decompression.

  3. Effect of Porphyrin Ligands on the Regioselective Dehydrogenation versus Epoxidation of Olefins by Oxoiron(IV) Mimics of Cytochrome P450

    Kumar, Devesh; Tahsini, Laleh; Visser, Sam P. De; Kang, Hye Yeon; Kim, Soo Jeong; Nam, Wonwoo


    The cytochromes P450 are versatile enzymes involved in various catalytic oxidation reactions, such as hydroxylation, epoxidation and dehydrogenation. In this work, we present combined experimental and theoretical studies on the change of regioselectivity in cyclohexadiene oxidation (i.e., epoxidation vs dehydrogenation) by oxoiron(IV) porphyrin complexes bearing different porphyrin ligands. Our experimental results show that meso-substitution of the porphyrin ring with electron-withdrawing substituents leads to a regioselectivity switch from dehydrogenation to epoxidation, affording the formation of epoxide as a major product. In contrast, electron-rich iron porphyrins are shown to produce benzene resulting from the dehydrogenation of cyclohexadiene. Density functional theory (DFT) calculations on the regioselectivity switch of epoxidation vs dehydrogenation have been performed using three oxoiron(IV) porphyrin oxidants with hydrogen atoms, phenyl groups, and pentachlorophenyl (ArCl5) groups on the meso-position. The DFT studies show that the epoxidation reaction by the latter catalyst is stabilized because of favorable interactions of the substrate with halogen atoms of the meso-ligand as well as with pyrrole nitrogen atoms of the porphyrin macrocycle. Hydrogen abstraction transition states, in contrast, have a substrate-binding orientation further away from the porphyrin pyrrole nitrogens, and they are much less stabilized. Finally, the regioselectivity of dehydrogenation versus hydroxylation is rationalized using thermodynamic cycles.

  4. Rapid Synthesis of a Lipocationic Polyester Library via Ring-Opening Polymerization of Functional Valerolactones for Efficacious siRNA Delivery.

    Hao, Jing; Kos, Petra; Zhou, Kejin; Miller, Jason B; Xue, Lian; Yan, Yunfeng; Xiong, Hu; Elkassih, Sussana; Siegwart, Daniel J


    The ability to control chemical functionality is an exciting feature of modern polymer science that enables precise design of drug delivery systems. Ring-opening polymerization of functional monomers has emerged as a versatile method to prepare clinically translatable degradable polyesters.1 A variety of functional groups have been introduced into lactones; however, the direct polymerization of tertiary amine functionalized cyclic esters has remained elusive. We report a strategy that enabled the rapid synthesis of >130 lipocationic polyesters directly from functional monomers without protecting groups. These polymers are highly effective for siRNA delivery at low doses in vitro and in vivo.

  5. Anion ring-opening polymerization of ethylene oxide by initiation of sodium 4-amino-N-(2-pyrimidinyl)benzene sulfonamide and influence of moisture on polymerization

    黄骏廉; 王海原


    Polyethylene oxide with sulfadiazine and hydroxyl end groups (PEOsf) were prepared by anion ring-opening polymerization of ethylene oxide initiated by sodium 4-amino-N-(2-pyrimidinyl)benzene sulfonamide (SF-Na). The product was characterized in detail by NMR, IR, GPC and DSC. Its molecular weight and molecular weight distribution are in the range of 1200-1 500 and 1.04-1.06 respectively, and the latter is nearly monodistribution. The trace of the moisture from air could accelerate the polymerization, and the mechanism is discussed.

  6. Al(HSO_4)_3/silica gel as a novel catalytic system for the ring opening of epoxides with thiocyanate anion under solvent-free conditions

    Ali; Reza; Kiasat; Arash; Mouradzadegun; Somayeh; Elahi; Mehdi; Fallah-Mehrjardi


    For the first time,metal hydrogen sulfates and phosphates/silica gel have been studied as efficient and powerful solid acid catalysts in the ring opening of epoxides with thiocyanate anion.The most significant result was obtained by Al(HSO_4)_3/SiO_2 which afforded the corresponding β-hydroxy thiocyanates under mild reaction conditions and in very short reaction times.The cheapness, availability of the catalyst,ease of procedure and work-up make this method attractive for the organic synthesis.

  7. Fe(OTf)3 versus Bi(OTf)3 as mild catalysts in epoxide oxidative ring-opening, urea α-diketone condensation, and glycoluril diether synthesis.

    Mandadapu, Vijaybabu; Wu, Feng; Day, Anthony I


    The salt Fe(OTf)3 has been shown to function as an effective catalyst in three different reactions, epoxide oxidative ring-opening to an α-hydroxy ketone, urea α-diketone condensation to form glycolurils, and glycoluril diether synthesis by formaldehyde condensation. In each of these reactions, Fe(OTf)3 was compared to Bi(OTf)3, a viable alternative catalyst with few or no prior examples of this type. Differences and advantages are highlighted but in most cases yields were generally high, and both catalysts outperformed conventional acid catalyzed methods.

  8. Halogen bonding controls the regioselectivity of the deiodination of thyroid hormones and their sulfate analogues.

    Manna, Debasish; Mondal, Santanu; Mugesh, Govindasamy


    The type 1 iodothyronine deiodinase (1D-1) in liver and kidney converts the L-thyroxine (T4), a prohormone, by outer-ring (5') deiodination to biologically active 3,3',5-triiodothyronine (T3) or by inner-ring (5) deiodination to inactive 3,3',5'-triiodothronine (rT3). Sulfate conjugation is an important step in the irreversible inactivation of thyroid hormones. While sulfate conjugation of the phenolic hydroxyl group stimulates the 5-deiodination of T4 and T3, it blocks the 5'-deiodination of T4. We show that thyroxine sulfate (T4S) undergoes faster deiodination as compared to the parent thyroid hormone T4 by synthetic selenium compounds. It is also shown that ID-3 mimics, which are remarkably selective to the inner-ring deiodination of T4 and T3, changes the selectivity completely when T4S is used as a substrate. From the theoretical investigations, it is observed that the strength of halogen bonding increases upon sulfate conjugation, which leads to a change in the regioselectivity of ID-3 mimics towards the deiodination of T4S. It has been shown that these mimics perform both the 5'- and 5-ring deiodinations by an identical mechanism. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Switchable regioselectivity in amine-catalysed asymmetric cycloadditions

    Zhou, Zhi; Wang, Zhou-Xiang; Zhou, Yuan-Chun; Xiao, Wei; Ouyang, Qin; Du, Wei; Chen, Ying-Chun


    Building small-molecule libraries with structural and stereogenic diversity plays an important role in drug discovery. The development of switchable intermolecular cycloaddition reactions from identical substrates in different regioselective fashions would provide an attractive protocol. However, this also represents a challenge in organic chemistry, because it is difficult to control regioselectivity to afford the products exclusively and at the same time achieve high levels of stereoselectivity. Here, we report the diversified cycloadditions of α‧-alkylidene-2-cyclopentenones catalysed by cinchona-derived primary amines. An asymmetric γ,β‧-regioselective intermolecular [6+2] cycloaddition reaction with 3-olefinic (7-aza)oxindoles is realized through the in situ generation of formal 4-aminofulvenes, while a different β,γ-regioselective [2+2] cycloaddition reaction with maleimides to access fused cyclobutanes is disclosed. In contrast, an intriguing α,γ-regioselective [4+2] cycloaddition reaction is uncovered with the same set of substrates, by employing an unprecedented dual small-molecule catalysis of amines and thiols. All of the cycloaddition reactions exhibit excellent regio- and stereoselectivity, producing a broad spectrum of chiral architectures with high structural diversity and molecular complexity.

  10. Nitrile anion cyclization with epoxysilanes followed by Brook rearrangement/ring-opening of cyclopropane nitriles/alkylation.

    Okugawa, Seigo; Masu, Hyuma; Yamaguchi, Kentaro; Takeda, Kei


    [reactions: see text] The reaction of delta-silyl-gamma,delta-epoxypentanenitrile derivatives 9-12 with a base and an alkylating agent affords (Z)-delta-siloxy-gamma,delta-unsaturated pentanenitrile derivatives via a tandem process that involves the formation of a cyclopropane derivative by epoxy nitrile cyclization followed by Brook rearrangement and an anion-induced cleavage of the cyclopropane ring. Exclusive formation of a (Z)-derivative from trans-epoxides is explained by the reaction pathway that involves a backside displacement of the epoxide by the alpha-nitrile carbanion and the O-Si bond formation followed by concerted processes involving Brook rearrangement and the anti-mode of eliminative ring fission of the cyclopropane from the rotamer 19. The fact that (E)-isomers are exclusively obtained from cis-epoxides and alpha-cyclopropyl-alpha-silylcarbinol derivative 26 provides experimental support for the proposed pathway.

  11. Multi-concentric-ring open-air ionization chamber for high-intensity X-ray beams

    Nariyama, Nobuteru


    An ionization chamber with four concentric ring electrodes was used to measure doses of white, 10, 15 and 20 keV synchrotron X-ray beams. The ring-shaped electrodes, which had diameters less than 11.8 mm, collected charges independently only around the beam, excluding strong in-beam charges when the beams passed through a small hole in the electrode centers. As a result, under low saturation voltages, the measured dose rates were confirmed to correlate with the beam intensity when conversion factors calculated with a Monte Carlo code were employed. The influence of the assumed beam sizes and incident positions on the current was almost negligible, with the exception of the incident position dependence at 10 keV.

  12. Hybrid scorpionate/cyclopentadienyl magnesium and zinc complexes: synthesis, coordination chemistry, and ring-opening polymerization studies on cyclic esters.

    Garcés, Andrés; Sánchez-Barba, Luis F; Alonso-Moreno, Carlos; Fajardo, Mariano; Fernández-Baeza, Juan; Otero, Antonio; Lara-Sánchez, Agustín; López-Solera, Isabel; Rodríguez, Ana María


    only accessible by protonolysis of the bis(amide) complexes [M{N(SiMe(3))(2)}(2)] (M = Mg, Zn) and the mixed ligand complex [EtZnOAr)] with the hybrid ligand bpzcpH to afford [Zn(R){kappa(2)-eta(1)(pi)-bpzcp}] (R = N(SiMe(3))(2) 13, R = 2,4,6-Me(3)C(6)H(2)O 14) and [Mg{N(SiMe(3))(2)}(kappa(2)-eta(5)-bpzcp)] (15). Finally, alkyl and alkoxide-containing complexes 1-10 and 14 can act as highly effective single-component living initiators for the ring-opening polymerization of epsilon-caprolactone and lactides over a wide range of temperatures. Epsilon-caprolactone is polymerized within minutes to give high molecular weight polymers with medium-broad polydispersities (M(n) > 10(5), M(w)/M(n) = 1.45). Lactide afforded poly(lactide) materials with medium molecular weights and polydispersities as narrow as M(w)/M(n) = 1.02. Additionally, polymerization of L-lactide occurred without racemization in the propagation process and offered highly crystalline, isotactic poly(L-lactides) with very high melting temperatures (T(m) = 165 degrees C). Microstructural analysis of poly(rac-lactide) by (1)H NMR spectroscopy revealed that propagations occur without appreciable levels of stereoselectivity. Polymer end group analysis showed that the polymerization process is initiated by alkyl transfer to the monomer.

  13. Developments in the use of rare earth metal complexes as efficient catalysts for ring-opening polymerization of cyclic esters used in biomedical applications

    Cota, Iuliana


    Biodegradable polymers represent a class of particularly useful materials for many biomedical and pharmaceutical applications. Among these types of polyesters, poly(ɛ-caprolactone) and polylactides are considered very promising for controlled drug delivery devices. These polymers are mainly produced by ring-opening polymerization of their respective cyclic esters, since this method allows a strict control of the molecular parameters (molecular weight and distribution) of the obtained polymers. The most widely used catalysts for ring-opening polymerization of cyclic esters are tin- and aluminium-based organometallic complexes; however since the contamination of the aliphatic polyesters by potentially toxic metallic residues is particularly of concern for biomedical applications, the possibility of replacing organometallic initiators by novel less toxic or more efficient organometallic complexes has been intensively studied. Thus, in the recent years, the use of highly reactive rare earth initiators/catalysts leading to lower polymer contamination has been developed. The use of rare earth complexes is considered a valuable strategy to decrease the polyester contamination by metallic residues and represents an attractive alternative to traditional organometallic complexes.

  14. Zirconium and hafnium complexes bearing pyrrolidine derived salalen-type {ONNO} ligands and their application for ring-opening polymerization of lactides.

    Duan, Yu-Lai; Hu, Zhi-Jian; Yang, Bo-Qun; Ding, Fei-Fei; Wang, Wei; Huang, Yong; Yang, Ying


    The reactions of pyrrolidine derived salalen-type {ONNO} ligands (S)-L(1-3)-H2 with 1 equiv. M(O(i)Pr)4(HO(i)Pr) (M = Zr or Hf) in diethyl ether yielded complexes [L(1-3)M(O(i)Pr)2] (L = L(1), M = Zr (1); L = L(2), M = Zr (2), Hf (3); L = L(3), M = Zr (4), Hf (5)). All of these complexes were well characterized by NMR spectroscopy, elemental analyses and single-crystal X-ray analysis in the case of complexes 1 and 3-5. X-ray structural determination revealed that these complexes were analogous mononuclear species and had a similar structure in which the metal centers were six-coordinated to two oxygen atoms and two nitrogen atoms of one ligand and two oxygen atoms of two isopropoxy groups. All of these complexes efficiently initialized the ring-opening polymerization of lactides to afford polymers with controlled molecular weight and narrow polydispersity. Furthermore, the ring-opening polymerization of rac-lactide catalyzed by complexes 1-5 afforded isotactic-enriched polymers in solution (Pm = 0.74-0.80) and under melt conditions (Pm = 0.63-0.72).

  15. Suicide Inhibition of Cytochrome P450 Enzymes by Cyclopropylamines via a Ring-opening Mechanism: Proton-Coupled Electron Transfer Makes a Difference

    Zhang, Xiaoqian; Li, Xiao-Xi; Liu, Yufang; Wang, Yong


    N-benzyl-N-cyclopropylamine (BCA) has been attracting great interests for decades for its partial suicide inactivation role to cytochrome P450 (P450) via a ring-opening mechanism besides acting as a role of normal substrates. Understanding the mechanism of such partial inactivation is vital to the clinical drug design. Thus, density functional theoretical (DFT) calculations were carried out on such P450-catalyzed reactions, not only on the metabolic pathway, but on the ring-opening inactivation one. Our theoretical results demonstrated that, in the metabolic pathway, besides the normal carbinolamine, an unexpected enamine was formed via the dual hydrogen abstraction (DHA) process, in which the competition between rotation of the H-abstracted substrate radical and the rotation of hydroxyl group of the protonated Cpd II moiety plays a significant role in product branch; In the inactivation pathway, the well-noted single electron transfer (SET) mechanism-involved process was invalidated for its high energy barrier, a proton-coupled electron transfer (PCET(ET)) mechanism plays a role. Our results are consistent with other related theoretical works on heteroatom-hydrogen (X-H, X = O, N) activation and revealed new features. The revealed mechanisms will play a positive role in relative drug design.

  16. Comparative Study of Aluminum Complexes Bearing N,O- and N,S-Schiff Base in Ring-Opening Polymerization of ε-Caprolactone and L-Lactide.

    Chang, Meng-Chih; Lu, Wei-Yi; Chang, Heng-Yi; Lai, Yi-Chun; Chiang, Michael Y; Chen, Hsing-Yin; Chen, Hsuan-Ying


    A series of Al complexes bearing Schiff base and thio-Schiff base ligands were synthesized, and their application for the ring-opening polymerization of ε-caprolactone (CL) and l-lactide (LA) was studied. It was found that steric effects of the ligands caused higher polymerization rate and most importantly the Al complexes with N,S-Schiff base showed significantly higher polymerization rate than Al complexes with N,O-Schiff base (5-12-fold for CL polymerization and 2-7-fold for LA polymerization). The reaction mechanism of CL polymerization was investigated by density functional theory (DFT). The calculations predicted a lower activation energy for a process involved with an Al complex bearing an N,S-Schiff base ligand (17.6 kcal/mol) than for that of an Al complex bearing an N,O-Schiff base ligand (19.0 kcal/mol), and this magnitude of activation energy reduction is comparable to the magnitude of rate enhancement observed in the experiment. The reduction of activation energy was attributed to the catalyst-substrate destabilization effect. Using a sulfur-containing ligand to decrease the activation energy in the ring-opening polymerization process may be a new strategy to design a new Al complex with high catalytic activity.

  17. Ring-Opening Polymerization of ε-Caprolactone Initiated by Ganciclovir (GCV for the Preparation of GCV-Tagged Polymeric Micelles

    Alicia J. Sawdon


    Full Text Available Ganciclovir (GCV is a nucleoside analogue with antiviral activity against herpes viral infections, and the most widely used antiviral to treat cytomegalovirus infections. However, the low bioavailability and short half-life of GCV necessitate the development of a carrier for sustained delivery. In this study, guanosine-based GCV was used as the initiator directly in ring-opening polymerization of ε-caprolactone (ε-CL to form hydrophobic GCV-poly(caprolactone (GCV-PCL which was then grafted with hydrophilic chitosan to form amphiphilic copolymers for the preparation of stable micellar nanoparticles. Successful synthesis of GCV-PCL and GCV-PCL-chitosan were verified by 1H-NMR analysis. Self-assembled micellar nanoparticles were characterized by dynamic light scattering and zetasizer with an average size of 117 nm and a positive charge of 24.2 mV. The drug release kinetics of GCV was investigated and cytotoxicity assay demonstrated that GCV-tagged polymeric micelles were non-toxic. Our results showed that GCV could be used directly in the initiation of ring-opening polymerization of ε-CL and non-toxic polymeric micelles for GCV delivery can be formed.

  18. Multi-level Quantum Mechanics and Molecular Mechanics Study of Ring Opening Process of Guanine Damage by Hydroxyl Radical in Aqueous Solution.

    Liu, Peng; Wang, Qiong; Niu, Meixing; Wang, Dunyou


    Combining multi-level quantum mechanics theories and molecular mechanics with an explicit water model, we investigated the ring opening process of guanine damage by hydroxyl radical in aqueous solution. The detailed, atomic-level ring-opening mechanism along the reaction pathway was revealed in aqueous solution at the CCSD(T)/MM levels of theory. The potentials of mean force in aqueous solution were calculated at both the DFT/MM and CCSD(T)/MM levels of the theory. Our study found that the aqueous solution has a significant effect on this reaction in solution. In particular, by comparing the geometries of the stationary points between in gas phase and in aqueous solution, we found that the aqueous solution has a tremendous impact on the torsion angles much more than on the bond lengths and bending angles. Our calculated free-energy barrier height 31.6 kcal/mol at the CCSD(T)/MM level of theory agrees well with the one obtained based on gas-phase reaction profile and free energies of solvation. In addition, the reaction path in gas phase was also mapped using multi-level quantum mechanics theories, which shows a reaction barrier at 19.2 kcal/mol at the CCSD(T) level of theory, agreeing very well with a recent ab initio calculation result at 20.8 kcal/mol.

  19. Suicide Inhibition of Cytochrome P450 Enzymes by Cyclopropylamines via a Ring-Opening Mechanism: Proton-Coupled Electron Transfer Makes a Difference

    Zhang, Xiaoqian; Li, Xiao-Xi; Liu, Yufang; Wang, Yong


    N-benzyl-N-cyclopropylamine (BCA) has been attracting great interests for decades for its partial suicide inactivation role to cytochrome P450 (P450) via a ring-opening mechanism besides acting as a role of normal substrates. Understanding the mechanism of such partial inactivation is vital to the clinical drug design. Thus, density functional theoretical (DFT) calculations were carried out on such P450-catalyzed reactions, not only on the metabolic pathway, but on the ring-opening inactivation one. Our theoretical results demonstrated that, in the metabolic pathway, besides the normal carbinolamine, an unexpected enamine was formed via the dual hydrogen abstraction (DHA) process, in which the competition between rotation of the H-abstracted substrate radical and the rotation of hydroxyl group of the protonated Cpd II moiety plays a significant role in product branch; In the inactivation pathway, the well-noted single electron transfer (SET) mechanism-involved process was invalidated for its high energy barrier, a proton-coupled electron transfer [PCET(ET)] mechanism plays a role. Our results are consistent with other related theoretical works on heteroatom-hydrogen (X-H, X = O, N) activation and revealed new features. The revealed mechanisms will play a positive role in relative drug design. PMID:28197402


    Cheng-pei Wu; Shi-jun Zheng; Cai-yuan Pan; Toshiyuki Uryu


    New highly stereoregular 2, 3-di-O-(p-azidobenzyl)-(1→5)-α-D-ribofuranan was synthesized by selective ring-opening polymerization of 1, 4-anhydro-2, 3-di-O-(p-azidobenzyl)-α-D-ribopyranose(ADABR) using phosphorus pentafluoride or tin tetrachloride as catalyst at low temperature in dichloromethane. The monomer was obtained by the reaction of p-bromomethyl-phenyleneazide with 1, 4-anhydro-α-D-ribose in DMF. The structure of poly(ADABR) was identified by specific rotation and 13CNMR spectroscopy. Acid chloride-AgCl4 complex catalyst such as CH2=C(CH3)C+OClO4- used in the polymerization resulted in polymers with mixed structures, i.e. (1→5)-α-D-ribofuranosidic and (1→4)-β-Dribopyranosidic units. However, with C6H5C+OClO4- as catalyst, pure (1→5)-α-D-ribofuranan was obtained.The effects of catalyst, polymerization temperature and time on polymer stereoregularity were examined, and the mechanism of the ring-opening polymerization was discussed.

  1. Pseudomonas aeruginosa Cif defines a distinct class of α/β epoxide hydrolases utilizing a His/Tyr ring-opening pair.

    Bahl, Christopher D; Madden, Dean R


    The Gram-negative bacterium Pseudomonas aeruginosa is an opportunistic pathogen that secretes a multitude of virulence factors during the course of infection. Among these is Cif, an epoxide hydrolase (EH) that reduces the functional localization of the cystic fibrosis transmembrane conductance regulator in epithelial cells. In addition to being the first reported EH virulence factor, Cif possesses unique sequence deviations from canonical EH motifs. Foremost among these is the substitution of a histidine for the first epoxide ring-opening tyrosine in the active site. To test the functional equivalence of Tyr and His side chains at this position, we have generated the mutant Cif-H177Y. Structural analysis confirms that both the WT His and mutant Tyr side chains can be accommodated without large-scale conformational changes. However, the Tyr mutant is functionally inactive. Based on a detailed analysis of the structure of the Tyr mutant, it appears that Cif's main-chain conformation imposes a functional requirement for a His at this position. Comparison with canonical EH structures reveals additional conformational differences, which are coupled to divergent sequence characteristics. When used to probe the genomes of other opportunistic pathogens, these sequence-structure criteria uncover candidate sequences that appear to form a distinct subfamily of Cif-like epoxide hydrolases characterized by a conserved His/Tyr ring-opening pair.

  2. Effect of the nature of the substituent in N-alkylimidazole ligands on the outcome of deprotonation: ring opening versus the formation of N-heterocyclic carbene complexes.

    Huertos, Miguel A; Pérez, Julio; Riera, Lucía; Díaz, Jesús; López, Ramón


    Complexes [Re(CO)(3)(N-RIm)(3)]OTf (N-RIm=N-alkylimidazole, OTf=trifluoromethanesulfonate; 1a-d) have been straightforwardly synthesised from [Re(OTf)(CO)(5)] and the appropriate N-alkylimidazole. The reaction of compounds 1a-d with the strong base KN(SiMe(3))(2) led to deprotonation of a central C-H group of an imidazole ligand, thus affording very highly reactive derivatives. The latter can evolve through two different pathways, depending on the nature of the substituents of the imidazole ligands. Compound 1a contains three N-MeIm ligands, and its product 2a features a C-bound imidazol-2-yl ligand. When 2a is treated with HOTf or MeOTf, rhenium N-heterocyclic carbenes (NHCs) 3a or 4a are afforded as a result of the protonation or methylation, respectively, of the non-coordinated N atom. The reaction of 2a with [AuCl(PPh(3))] led to the heterobimetallic compound 5, in which the N-heterocyclic ligand is once again N-bound to the Re atom and C-coordinated to the gold fragment. For compounds 1b-d, with at least one N-arylimidazole ligand, deprotonation led to an unprecedented reactivity pattern: the carbanion generated by the deprotonation of the C2-H group of an imidazole ligand attacks a central C-H group of a neighbouring N-RIm ligand, thus affording the product of C-C coupling and ring-opening of the imidazole moiety that has been attacked (2c, d). The new complexes featured an amido-type N atom that can be protonated or methylated, thus obtaining compounds 3c, d or 4c, d, respectively. The latter reaction forces a change in the disposition of the olefinic unit generated by the ring-opening of the N-RIm ligand from a cisoid to a transoid geometry. Theoretical calculations help to rationalise the experimental observation of ring-opening (when at least one of the substituents of the imidazole ligands is an aryl group) or tautomerisation of the N-heterocyclic ligand to afford the imidazol-2-yl product.

  3. Trichloromethylthiolation of N-Heterocycles: Practical and Completely Regioselective.

    Ernst, Johannes B; Rühling, Andreas; Wibbeling, Birgit; Glorius, Frank


    The first trichloromethylthiolation of a broad range of indoles and pyrroles is reported employing bench-stable N-trichloromethylthiosaccharin as reagent. This methodology is highly regioselective, exhibits high functional group tolerance, and provides access to two previously unknown classes of potentially bioactive compounds.

  4. Method Development in the Regioselective Glycosylation of Unprotected Carbohydrates

    Niedbal, Dominika Alina

    and the glycosylations were promoted by tetrabutylammonium bromide. The couplings were completely selective and gave rise to a number of 1,6-linked disaccharides with 1,2- cis-linked orientation. Project 2: Boron-mediated glycosylation of unprotected carbohydrates Boron-mediated regioselective Koenigs...

  5. The Quest for Converting Biorenewable Bifunctional α-Methylene-γ-butyrolactone into Degradable and Recyclable Polyester: Controlling Vinyl-Addition/Ring-Opening/Cross-Linking Pathways

    Tang, Xiaoyan


    α-Methylene-γ-butyrolactone (MBL), a naturally occurring and biomass-sourced bifunctional monomer, contains both a highly reactive exocyclic C═C bond and a highly stable five-membered γ-butyrolactone ring. Thus, all previous work led to exclusive vinyl-addition polymerization (VAP) product P(MBL)VAP. Now, this work reverses this conventional chemoselectivity to enable the first ring-opening polymerization (ROP) of MBL, thereby producing exclusively unsaturated polyester P(MBL)ROP with Mn up to 21.0 kg/mol. This elusive goal was achieved through uncovering the thermodynamic, catalytic, and processing conditions. A third reaction pathway has also been discovered, which is a crossover propagation between VAP and ROP processes, thus affording cross-linked polymer P(MBL)CLP. The formation of the three types of polymers, P(MBL)VAP, P(MBL)CLP, and P(MBL)ROP, can be readily controlled by adjusting the catalyst (La)/initiator (ROH) ratio, which is determined by the unique chemoselectivity of the La–X (X = OR, NR2, R) group. The resulting P(MBL)ROP is degradable and can be readily postfunctionalized into cross-linked or thiolated materials but, more remarkably, can also be fully recycled back to its monomer thermochemically. Computational studies provided the theoretical basis for, and a mechanistic understanding of, the three different polymerization processes and the origin of the chemoselectivity.

  6. Dual responsive polymeric nanoparticles prepared by direct functionalization of polylactic acid-based polymers via graft-from ring opening metathesis polymerization.

    Veccharelli, Kate M; Tong, Venus K; Young, Jennifer L; Yang, Jerry; Gianneschi, Nathan C


    Polylactic acid (PLA) has found widespread use in plastics and in biomedical applications due to its biodegradability into natural benign products. However, PLA-based materials remain limited in usefulness due to difficulty of incorporating functional groups into the polymer backbone. In this paper, we report a strategy for PLA functionalization that establishes the preparation of highly derivatized materials in which ring opening metathesis polymerization (ROMP) is employed as a graft-from polymerization technique utilizing a norbornene-modified handle incorporated into the PLA backbone. As a demonstration of this new synthetic methodology, a PLA-derived nanoparticle bearing imidazole units protected with a photolabile group was prepared. The morphology of this material could be controllably altered in response to exposure of UV light or acidic pH as a stimulus. We anticipate that this graft-from approach to derivatization of PLA could find broad use in the development of modified, biodegradable PLA-based materials.

  7. Cobaltocenium-containing block copolymers: ring-opening metathesis polymerization, self-assembly and precursors for template synthesis of inorganic nanoparticles.

    Ren, Lixia; Zhang, Jiuyang; Hardy, Christopher G; Ma, Shuguo; Tang, Chuanbing


    Side-chain cobaltocenium-containing block copolymers are prepared by ring-opening metathesis polymerization (ROMP). These block copolymers include one cobaltocenium-containing block, with the second block being either a nonmetal-containing segment or a cobaltocenium-containing segment with different counterions. These block copolymers are self-assembled into spherical core/shell micelles in solutions. A template strategy is used to prepare cobalt (II or III)-containing nanoparticles by treating the self-assembled micelles via UV/ozonolysis and pyrolysis. Characterization by X-ray photon spectroscopy and X-ray diffraction indicates that these nanoparticles consist of different oxidants of cobalt, depending on the chemical compositions of block copolymers. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Alternating Sequence Controlled Copolymer Synthesis of α-Hydroxy Acids via Syndioselective Ring-Opening Polymerization of O-Carboxyanhydrides Using Zirconium/Hafnium Alkoxide Initiators.

    Sun, Yangyang; Jia, Zhaowei; Chen, Changjuan; Cong, Yong; Mao, Xiaoyang; Wu, Jincai


    The ring-opening polymerization (ROP) of O-carboxyanhydrides (OCAs) can give diverse poly(α-hydroxy acid)s (PAHAs) with different functional groups because of easy modification of the side group of OCAs, which can extend applications of PAHAs widely. The stereoselective polymerization of O-carboxyanhydrides and further sequence controlled alternating copolymerization of OCAs were still big challenges until now for lack of suitable catalysts/initiators. In this work, a highly syndioselective ROP of OCAs system as the first stereoselective example in this area is reported using zirconium/hafnium alkoxides as initiators with the highest Pr value up to 0.95. Furthermore, these initiators were successfully applied in the precisely alternating sequence controlled copolymerization of PheOCA and Tyr(Bn)OCA, and alternating copolymerization of LacOCA and PheOCA was also achieved.

  9. Efficient Diethylzinc/Gallic Acid and Diethylzinc/Gallic Acid Ester Catalytic Systems for the Ring-Opening Polymerization of rac-Lactide

    Karolina Żółtowska


    Full Text Available Polylactide (PLA represents one of the most promising biomedical polymers due to its biodegradability, bioresorbability and good biocompatibility. This work highlights the synthesis and characterization of PLAs using novel diethylzinc/gallic acid (ZnEt2/GAc and diethylzinc/propyl gallate (ZnEt2/PGAc catalytic systems that are safe for human body. The results of the ring-opening polymerization (ROP of rac-lactide (rac-LA in the presence of zinc-based catalytic systems have shown that, depending on the reaction conditions, “predominantly isotactic”, disyndiotactic or atactic PLA can be obtained. Therefore, the controlled and stereoselective ROP of rac-LA is discussed in detail in this paper.

  10. Group 4 metal complexes of Trost's semi-crown ligand: synthesis, structural characterization and studies on the ring-opening polymerization of lactides and ε-caprolactone.

    Rajashekhar, Bijja; Roymuhury, Sagnik K; Chakraborty, Debashis; Ramkumar, Venkatachalam


    The synthesis of titanium(IV), zirconium(IV) and hafnium(IV) complexes of Trost's semi-crown ligand is described. All complexes were fully characterized by 1H and 13C NMR and mass spectroscopy. The molecular structures of the representative complexes 2, 3 and 4 were determined by single-crystal X-ray diffraction studies. The X-ray diffraction studies reveal that complexes 2, 3 and 4 crystallized in an orthorhombic crystal system. Complexes 2 and 3 have a monomeric structure in the solid state with distorted octahedral geometry around the metal center, whereas complex 4 was found to crystallize in a trimeric structure bridging with an oxygen atom, where the geometry around the titanium is distorted trigonal bipyramidal. The activities and stereoselectivities of these complexes toward the ring-opening polymerization (ROP) of lactides (L-LA and rac-LA) and ε-caprolactone (CL) have been investigated. Complexes 1–4 were found to be efficient single-component initiators for the ring-opening polymerization of cyclic esters and yielded high molecular weight polymers (Mn) with narrow molecular weight distributions (MWD).The microstructure of the resultant polylactides (PLAs) from rac-LA was determined. Complexes 2 and 3 afforded isotactic-enriched PLA (Pm = 0.78–0.71) with narrow MWD (1.07–1.04), on the other hand complexes 1 and 4 produced atactic PLA. Kinetic and post polymerization studies confirm that the polymerization proceeds through the coordination–insertion mechanism.

  11. Thiophene fused azacoronenes: regioselective synthesis, self organization, charge transport, and its incorporation in conjugated polymers

    Liu, Yi; He, Bo


    A regioselective synthesis of an azacoronene fused with two peripheral thiophene groups has been realized through a concise synthetic route. The resulting thienoazacoronene (TAC) derivatives show high degree of self-organization in solution, in single crystals, in the bulk, and in spuncast thin films. Spuncast thin film field-effect transistors of the TACs exhibited mobilities up to 0.028 cm.sup.2V.sup.-1 S.sup.-1, which is among the top field effect mobilities for solution processed discotic materials. Organic photovoltaic devices using TAC-containing conjugated polymers as the donor material exhibited a high open-circuit voltage of 0.89 V, which was ascribable to TAC's low-lying highest occupied molecular orbital energy level.

  12. Thiophene fused azacoronenes: regioselective synthesis, self organization, charge transport, and its incorporation in conjugated polymers

    Liu, Yi; He, Bo


    A regioselective synthesis of an azacoronene fused with two peripheral thiophene groups has been realized through a concise synthetic route. The resulting thienoazacoronene (TAC) derivatives show high degree of self-organization in solution, in single crystals, in the bulk, and in spuncast thin films. Spuncast thin film field-effect transistors of the TACs exhibited mobilities up to 0.028 cm.sup.2V.sup.-1 S.sup.-1, which is among the top field effect mobilities for solution processed discotic materials. Organic photovoltaic devices using TAC-containing conjugated polymers as the donor material exhibited a high open-circuit voltage of 0.89 V, which was ascribable to TAC's low-lying highest occupied molecular orbital energy level.

  13. Catalytic and regioselective oxidation of carbohydrates to synthesize keto-sugars under mild conditions.

    Muramatsu, Wataru


    A new catalytic and regioselective approach for the synthesis of keto-sugars is described. An organotin catalyst, Oc2SnCl2, in the presence of trimethylphenylammonium tribromide ([TMPhA](+)Br3(-)) accelerates the regioselective oxidation at the "axial"-OH group of 1,2-diol moieties in galactopyranosides. The reaction conditions can also be used for the regioselective oxidation of various carbohydrates.

  14. Reactive Species Involved in the Regioselective Photooxidation of Heptamethine Cyanines.

    Nani, Roger R; Kelley, James A; Ivanic, Joseph; Schnermann, Martin J


    Heptamethine cyanines are important near-IR fluorophores used in many fluorescence applications. Despite this utility, these molecules are susceptible to light-promoted reactions (photobleaching) involving photochemically generated reactive oxygen species (ROS). Here, we have sought to define key chemical aspects of this nearly inescapable process. Near-IR photolysis of a model heptamethine cyanine leads to the regioselective oxidative cleavage of the cyanine polyene. We report the first quantitative analysis of the major reaction pathway following either photolysis or exposure to candidate ROS. These studies clearly indicate that only singlet oxygen ((1)O2), and not other feasible ROS, recapitulates the direct photolysis pathway. Computational studies were employed to investigate the regioselectivity of the oxidative cleavage process, and the theoretical ratio is comparable to observed experimental values. These results provide a more complete picture of heptamethine cyanine photooxidation, and provide insight for design of improved compounds for future applications.

  15. Exploring Cooperative Effects in Oxidative NHC Catalysis: Regioselective Acylation of Carbohydrates.

    Cramer, David L; Bera, Srikrishna; Studer, Armido


    The utility of oxidative NHC catalysis for both the regioselective and chemoselective functionalization of carbohydrates is explored. Chiral NHCs allow for the highly regioselective oxidative esterification of various carbohydrates using aldehydes as acylation precursors. The transformation was also shown to be amenable to both cis/trans diol isomers, free amino groups, and selective for specific sugar epimers in competition experiments. Efficiency and regioselectivity of the acylation can be improved upon using two different NHC catalysts that act cooperatively. The potential of the method is documented by the regioselective acylation of an amino-linked neodisaccharide. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Copper-catalyzed regioselective allylic substitution reactions with indium organometallics.

    Rodríguez, David; Sestelo, José Pérez; Sarandeses, Luis A


    The first nucleophilic allylic substitution reactions of triorganoindium compounds with allylic halides and phosphates are reported. The reactions of trialkyl- and triarylindium reagents with cinnamyl and geranyl halides and phosphates, with the aid of copper catalysis [Cu(OTf)(2)/P(OEt)(3)], are described. In general, the reaction proceeds efficiently to give good yields and regioselectively to afford the S(N)2' product.

  17. Origins of Regioselectivity in Iridium Catalyzed Allylic Substitution.

    Madrahimov, Sherzod T; Li, Qian; Sharma, Ankit; Hartwig, John F


    Detailed studies on the origin of the regioselectivity for formation of branched products over linear products have been conducted with complexes containing the achiral triphenylphosphite ligand. The combination of iridium and P(OPh)3 was the first catalytic system shown to give high regioselectivity for the branched product with iridium and among the most selective for forming branched products among any combination of metal and ligand. We have shown the active catalyst to be generated from [Ir(COD)Cl]2 and P(OPh)3 by cyclometalation of the phenyl group on the ligand and have shown such species to be the resting state of the catalyst. A series of allyliridium complexes ligated by the resulting P,C ligand have been generated and shown to be competent intermediates in the catalytic system. We have assessed the potential impact of charge, metal-iridium bond length, and stability of terminal vs internal alkenes generated by attack at the branched and terminal positions of the allyl ligand, respectively. These factors do not distinguish the regioselectivity for attack on allyliridium complexes from that for attack on allylpalladium complexes. Instead, detailed computational studies suggest that a series of weak, attractive, noncovalent interactions, including interactions of H-bond acceptors with a vinyl C-H bond of the alkene ligand, favor formation of the branched product with the iridium catalyst. This conclusion underscores the importance of considering attractive interactions, as well as repulsive steric interactions, when seeking to rationalize selectivities.

  18. 有机小分子催化ε-己内酯开环聚合反应%Ring-Opening Polymerization of ε-Caprolactone Catalyzed by Organocatalyst

    许茸; 陈春霞


    聚己内酯(PCL)是一种生物可降解高分子材料,具有良好的环境、生物相容性,广泛应用于生物医学、包装等领域。有机小分子催化ε-己内酯单体开环聚合反应是制备聚己内酯的主要方式之一。与传统的金属催化相比,有机催化不仅反应条件温和、聚合可控,而且还可解决聚合物中金属残留问题,是目前高分子合成化学的研究热点。本文按照催化体系的不同活化方式,讨论了近年来有机催化在ε-己内酯开环聚合反应中的研究进展,归纳总结了不同催化体系的优缺点,并在此基础上展望了有机小分子催化剂在ε-己内酯开环聚合反应中的发展趋势和应用前景。%Poly(ε-caprolactone) (PCL) is an important class of biocompatible materials, which makes them interesting materials for a range of biomedical and commodity applications, including controlled drug release, tissue engineering, medical implants or environmentally friendly packaging materials. PCL can be prepared through the ring-opening polymerization of e-caprolactone catalyzed by organic molecules. Compared to traditional metal- catalyzed ROPs, organocatalysis processes can be performed under milder reaction conditions with controlled molar masses and narrow dispersities, furthermore the metal contaminants of the polymer products can be avoided to be removed prior to application as biomedical and pharmaceutical materials. Herein the progress of organocatalysts in the ring-opening polymerization of ε-eaprolactone is reviewed according to different means of the activation of the catalysts. The advantages and disadvantages of various catalytic systems are summarized, and development trends and application prospects of organocatalysis for polymerization of ε-caprolactone are also discussed.

  19. Regioselective intramolecular ring closure of 2-amino-6-bromo-2,6-dideoxyhexono-1,4-lactones to 5- or 6-membered iminuronic acid analogues:synthesis of 1-deoxymannojirimycin and 2,5-dideoxy-2,5-imino-D-glucitol

    Malle, Birgitte Mølholm; Lundt, Inge; Wrodnigg, Tanja M.


    the corresponding six-membered ring 1,5-iminuronic acid mimetics, namely (2R,3R,4S,5R)-3,4,5-trihydroxypipecolic acid (2,6-dideoxy-2,6- imino-D-galactonic acid, 16) and (2S,3R,4S,5R)-3,4,5-trihydroxypipecolic acid (2,6-dideoxy-2,6- imino-D-talonic acid, 17), were obtained. The corresponding enantiomers, L......-galacto- as well as L-talo-2-amino-6-bromo-2,6-dideoxy-1,4-lactones ent-14 and ent-15, reacted accordingly to give the D-galacto- and L-altro-1,5-iminuronic acid mimetics, (2S,3S,4R,5S)-3,4,5-trihydroxypipecolic acid (2,6-dideoxy-2,6-imino-L-galactonic acid, ent-16) and (2R,3S,4R,5S)-3,4,5-trihydroxypipecolic...

  20. Random Poly(Amino Acids Synthesized by Ring Opening Polymerization as Additives in the Biomimetic Mineralization of CaCO3

    Vladimir Dmitrovic


    Full Text Available Biominerals such as bones, teeth and seashells, very often have advanced material properties and are a source of inspiration for material chemists. As in biological systems acidic proteins play an important role in regulating the formation of CaCO3 biominerals, we employ poly(amino acids to mimic the processes involved in the laboratory. Here we report on the synthesis of random aminoacid copolymers of glutamic acid (Glu, lysine (Lys and alanine (Ala using the ring opening polymerization (ROP of their respective N-carboxy anhydrides (NCA. The synthetic approach yields a series of polymers with different monomer composition but with similar degrees of polymerization (DP 45–56 and comparable polydispersities (PDI 1.2–1.6. Using random copolymers we can investigate the influence of composition on the activity of the polymers without having to take into account the effects of secondary structure or specific sequences. We show that variation of the Glu content of the polymer chains affects the nucleation and thereby also the particle size. Moreover, it is shown that the polymers with the highest Glu content affect the kinetics of mineral formation such that the first precipitate is more soluble than in the case of the control.

  1. Surface-initiated ring-opening metathesis polymerization (SI-ROMP) to attach a tethered organic corona onto CdSe/ZnS core/shell quantum dots

    Vatansever, Fatma; Hamblin, Michael R.


    Core-shell CdSe/ZnS quantum dots (QDs) are useful as tunable photostable fluorophores for multiple applications in industry, biology, and medicine. However, to achieve the optimum optical properties, the surface of the QDs must be passivated to remove charged sites that might bind extraneous substances and allow aggregation. Here we describe a method of growing an organic polymer corona onto the QD surface using the bottom-up approach of surface-initiated ring-opening metathesis polymerization (SI-ROMP) with Grubbs catalyst. CdSe/ZnS QDs were first coated with mercaptopropionic acid by displacing the original tri-octylphosphine oxide layer, and then reacted with 7-octenyl dimethyl chlorosilane. The resulting octenyl double bonds allowed the attachment of ruthenium alkylidene groups as a catalyst. A subsequent metathesis reaction with strained bicyclic monomers (norbornene-dicarbonyl chloride (NDC), and a mixture of NDC and norbornenylethylisobutyl-polyhedral oligomeric silsesquioxane (norbornoPOSS)) allowed the construction of tethered organic homo-polymer or co-polymer layers onto the QD. Compounds were characterized by FT-IR, 1H-NMR, X-ray photoelectron spectroscopy, differential scanning calorimetry, and transmission electron microscopy. Atomic force microscopy showed that the coated QDs were separate and non-aggregated with a range of diameter of 48-53 nm.

  2. A facile glovebox-free strategy to significantly accelerate the syntheses of well-defined polypeptides by N-carboxyanhydride (NCA) ring opening polymerizations.

    Zou, Jiong; Fan, Jingwei; He, Xun; Zhang, Shiyi; Wang, Hai; Wooley, Karen L


    A facile N2 flow-accelerated N-carboxyanhydride ring opening polymerization (NCA ROP) is demonstrated, herein, with rigorous kinetic studies to evaluate the methodology in detail. By using n-hexylamine as initiator and γ-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) as monomer, the NCA ROP via a normal amine mechanism (NAM) reached 90% conversion in 2 h under N2 flow at room temperature in a fume hood, much shorter than the time required for the same polymerization conducted in a glove box (14 h). The efficient removal of CO2 from the reaction by N2 flow drove the carbamic acid-amine equilibrium toward the formation of active nucleophilic amino termini and promoted polymerization. The detailed kinetic studies of the polymerization with different feed ratios and N2 flow rates were conducted, demonstrating the living feature of the NCA ROP and the tuning of the polymerization rate by simply changing the flow rate of N2. Maintenance of the reactivity of the amino ω-chain terminus and control during a subsequent polymerization were confirmed by performing chain extension reactions. The N2 flow method provides a new straightforward strategy to synthesize well-defined polypeptides with predictable molecular weights and narrow molecular weight distributions (PDI < 1.19).

  3. Synthesis of Aluminum Complexes Bearing 8-Anilide-5,6,7-trihydroquinoline Ligands: Highly Active Catalyst Precursors for Ring-Opening Polymerization of Cyclic Esters

    Shaofeng Liu


    Full Text Available The stoichiometric reactions of 8-(2,6-R1-4-R2-anilide-5,6,7-trihydroquinoline (LH with AlR3 (R = Me or Et afforded the aluminum complexes LAlR2 (Al1–Al5,Al1: R1 = iPr, R2 = H, R = Me; Al2: R1 = Me, R2 = H, R = Me; Al3: R1 = H, R2 = H, R = Me; Al4: R1 = Me, R2 = Me, R = Me; Al5: R1 = Me, R2 = Me, R = Et in high yields. All aluminum complexes were characterized by NMR spectroscopy and elemental analysis. The molecular structures of complexes Al4 and Al5 were determined by single-crystal X-ray diffractions and revealed a distorted tetrahedral geometry at aluminum. In the presence of BnOH, complexes Al1–Al5 efficiently initiated the ring-opening homopolymerization of ε-caprolactone (ε-CL and rac-lactide (rac-LA, respectively, in a living/controlled manner.

  4. Green polymer chemistry: investigating the mechanism of radical ring-opening redox polymerization (R3P) of 3,6-dioxa-1,8-octanedithiol (DODT).

    Rosenthal-Kim, Emily Q; Puskas, Judit E


    The mechanism of the new Radical Ring-opening Redox Polymerization (R3P) of 3,6-dioxa-1,8-octanedithiol (DODT) by triethylamine (TEA) and dilute H2O2 was investigated. Scouting studies showed that the formation of high molecular weight polymers required a 1:2 molar ratio of DODT to TEA and of DODT to H2O2. Further investigation into the chemical composition of the organic and aqueous phases by 1H-NMR spectroscopy and mass spectrometry demonstrated that DODT is ionized by two TEA molecules (one for each thiol group) and thus transferred into the aqueous phase. The organic phase was found to have cyclic disulfide dimers, trimers and tetramers. Dissolving DODT and TEA in water before the addition of H2O2 yielded a polymer with Mn = 55,000 g/mol, in comparison with Mn = 92,000 g/mol when aqueous H2O2 was added to a DODT/TEA mixture. After polymer removal, MALDI-ToF MS analysis of the residual reaction mixtures showed only cyclic oligomers remaining. Below the LCST for TEA in water, 18.7 °C, the system yielded a stable emulsion, and only cyclic oligomers were found. Below DODT/TEA and H2O2 1:2 molar ratio mostly linear oligomers were formed, with <20% cyclic oligomers. The findings support the proposed mechanism of R3P.

  5. Mechanochemical Ring-Opening Polymerization of Lactide: Liquid-Assisted Grinding for the Green Synthesis of Poly(lactic acid) with High Molecular Weight.

    Ohn, Nuri; Shin, Jihoon; Kim, Sung Sik; Kim, Jeung Gon


    Mechanochemical polymerization of lactide is carried out by using ball milling. Mechanical energy from collisions between the balls and the vessel efficiently promotes an organic-base-mediated metal- and solvent-free solid-state polymerization. Investigation of the parameters of the ball-milling synthesis revealed that the degree of lactide ring-opening polymerization could be modulated by the ball-milling time, vibration frequency, mass of the ball media, and liquid-assisted grinding. Liquid-assisted grinding was found to be an especially important factor for achieving a high degree of mechanochemical polymerization. Although polymer-chain scission from the strong collision energy prevented mechanical-force-driven high-molecular-weight polymer synthesis, the addition of only a small amount of liquid enabled sufficient energy dissipation and poly(lactic acid) was thereby obtained with a molecular weight of over 1×10(5)  g mol(-1) . © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Synthesis and characterization of photoluminescent hybrids of poly( ɛ-caprolactone)-grafted-polyhedral oligosilsesquioxane by using a combination of ring-opening polymerization and click chemistry

    Cao, Xuan Thang; Showkat, Ali Md; Bach, Long Giang; Jeong, Yeon Tae; Kim, Jong Soo; Lim, Kwon Taek; Gal, Yeong-Soon


    Photoluminescent hybrids of poly( ɛ-caprolactone) (PCL), polyhedral oligosilsesquioxane (POSS) and terbium ions (Tb3+) were synthesized by using a combination of ring-opening polymerization (ROP), click chemistry and coordination chemistry. Initially, acetylene functionalized PCL (alkyne-PCL-COOH) was prepared by using ROP of ɛ-caprolactone with propargyl alcohol, and azide-substituted POSS (POSS-N3) was prepared by using the reaction of chloropropyl-heptaisobutyl-substituted POSS with NaN3. The click reaction between alkyne-PCL-COOH and POSS-N3 afforded POSS-g-PCL, which was subsequently coordinated with Tb3+ ions in the presence of 1,10-phenanthroline to produce POSS-g-PCL-Tb3+-Phen. The structures and compositions of the hybrids were investigated by using 1H nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FT-IR), Field emission scanning electron microscope (FE-SEM), Transmission electron microscopy (TEM), and Thermogravimetric analysis (TGA). The optical properties of POSS-g-PCL-Tb3+-Phen complexes were characterized by using photoluminescence spectroscopy, which showed four high emission bands centered at 489, 545, 584, and 620 nm with excitation at 330 nm. The emission spectra of the europium-ion-coordinated hybrids, POSS-g-PCL-Eu3+-Phen, had four high-intensity peaks, 594, 617, 652 and 686 nm, for an excitation wavelength of 352 nm.

  7. Green Polymer Chemistry: Investigating the Mechanism of Radical Ring-Opening Redox Polymerization (R3P of 3,6-Dioxa-1,8-octanedithiol (DODT

    Emily Q. Rosenthal-Kim


    Full Text Available The mechanism of the new Radical Ring-opening Redox Polymerization (R3P of 3,6-dioxa-1,8-octanedithiol (DODT by triethylamine (TEA and dilute H2O2 was investigated. Scouting studies showed that the formation of high molecular weight polymers required a 1:2 molar ratio of DODT to TEA and of DODT to H2O2. Further investigation into the chemical composition of the organic and aqueous phases by 1H-NMR spectroscopy and mass spectrometry demonstrated that DODT is ionized by two TEA molecules (one for each thiol group and thus transferred into the aqueous phase. The organic phase was found to have cyclic disulfide dimers, trimers and tetramers. Dissolving DODT and TEA in water before the addition of H2O2 yielded a polymer with Mn = 55,000 g/mol, in comparison with Mn = 92,000 g/mol when aqueous H2O2 was added to a DODT/TEA mixture. After polymer removal, MALDI-ToF MS analysis of the residual reaction mixtures showed only cyclic oligomers remaining. Below the LCST for TEA in water, 18.7 °C, the system yielded a stable emulsion, and only cyclic oligomers were found. Below DODT/TEA and H2O2 1:2 molar ratio mostly linear oligomers were formed, with <20% cyclic oligomers. The findings support the proposed mechanism of R3P.

  8. Ring-Opening Polymerization of N-Carboxyanhydrides for Preparation of Polypeptides and Polypeptide-Based Hybrid Materials with Various Molecular Architectures

    Pahovnik, David


    Different synthetic approaches utilizing ring-opening polymerization of N-carboxyanhydrides for preparation of polypeptide and polypeptide-based hybrid materials with various molecular architectures are described. An overview of polymerization mechanisms using conventional (various amines) as well as some recently developed initiators (hexamethyldisilazane, N-heterocyclic persistent carbenes, etc.) is presented, and their benefits and drawbacks for preparation of polypeptides with well-defined chain lengths and chain-end functionality are discussed. Recent examples from literature are used to illustrate different possibilities for synthesis of pure polypeptide materials with different molecular architectures bearing various functional groups, which are introduced either by modification of amino acids, before they are transformed into corresponding Ncarboxyanhydrides, or by post-polymerization modifications using protective groups and/or orthogonal functional groups. Different approaches for preparation of polypeptide-based hybrid materials are discussed as well using examples from recent literature. Syntheses of simple block copolymers or copolymers with more complex molecular architectures (graft and star copolymers) as well as modifications of nanoparticles and other surfaces with polypeptides are described.

  9. Controlled synthesis, optical properties and cytotoxicity studies of CdSe-poly(lactic acid) multifunctional nanocomposites by ring-opening polymerization.

    Islam, Md Rafiqul; Bach, Long Giang; Vo, Thanh-Sang; Lee, Doh C; Lim, Kwon Taek


    A facile synthetic route has been developed for the covalent grafting of biocompatible poly(lactic acid) (PLA) onto CdSe Quantum Dots (QDs) using surface initiated ring opening polymerization (ROP) to afford CdSe-g-PLA nanocomposites. At first, 2-mercaptoethanol (ME) capped CdSe QDs were synthesized through a wet chemical process. The surface initiated ROP of lactide was accomplished with Sn(Oct)2 to give CdSe-g-PLA nanocomposites having surface hydroxyl functionality. FT-IR data suggested that a robust covalent bond was formed between ME capped CdSe QDs and polymer moieties. The grafting density of PLA on CdSe QDs was found to be moderate as measured by TGA analysis. The CdSe QDs were well dispersed in CdSe-g-PLA nanocomposites matrices as captured by TEM. The cubic phase crystal structure of CdSe QDs in the nanocomposites was determined by XRD. The optical properties of the CdSe-g-PLA nanocomposites were investigated by UV-vis and photoluminescence spectroscopy which suggested their potentialities as optical materials in biomedical application. Cell viability studies revealed that the biocompatibility of CdSe QDs was improved upon PLA immobilization.

  10. Amino-Functionalized Multiwalled Carbon Nanotubes Lead to Successful Ring-Opening Polymerization of Poly(ε-caprolactone): Enhanced Interfacial Bonding and Optimized Mechanical Properties.

    Roumeli, Eleftheria; Papageorgiou, Dimitrios G; Tsanaktsis, Vasilios; Terzopoulou, Zoe; Chrissafis, Konstantinos; Avgeropoulos, Apostolos; Bikiaris, Dimitrios N


    In this work, the synthesis, structural characteristics, interfacial bonding, and mechanical properties of poly(ε-caprolactone) (PCL) nanocomposites with small amounts (0.5, 1.0, and 2.5 wt %) of amino-functionalized multiwalled carbon nanotubes (f-MWCNTs) prepared by ring-opening polymerization (ROP) are reported. This method allows the creation of a covalent-bonding zone on the surface of nanotubes, which leads to efficient debundling and therefore satisfactory dispersion and effective load transfer in the nanocomposites. The high covalent grafting extent combined with the higher crystallinity provide the basis for a significant enhancement of the mechanical properties, which was detected in the composites with up to 1 wt % f-MWCNTs. Increasing filler concentration encourages intrinsic aggregation forces, which allow only minor grafting efficiency and poorer dispersion and hence inferior mechanical performance. f-MWCNTs also cause a significant improvement on the polymerization reaction of PCL. Indeed, the in situ polymerization kinetics studies reveal a significant decrease in the reaction temperature, by a factor of 30-40 °C, combined with accelerated the reaction kinetics during initiation and propagation and a drastically reduced effective activation energy.

  11. Immobilization of Poly(1,1-dimethysilacyclobutane by Means of Anionic Ring-Opening Polymerization on Organic Nanoparticles and Reinvestigation of Crystallization

    Matthias Rehahn


    Full Text Available In the present study, the synthesis of poly(1,1-dimethylsilacyclobutane (PDMSB by anionic ring opening polymerization (ROP is reinvestigated, leading to narrowly distributed molar masses (polydispersities 1.04–1.15 in the range of 2.3 to 60 kg mol−1. Investigations of thermal behavior for low molar mass PDMSB revealed an untypical multiple peaks melting phenomenon, which at first glance, seems to be of the same origin as low molar mass poly(ethylene oxides. Small angle X-ray scattering (SAXS and X-ray diffraction (XRD measurements are done, proving the fast crystallization and subsequent recrystallization for investigated low molar mass samples. Synthetic attempts are expanded to the surface-initiated anionic ROP of 1,1-dimethylsilacyclobutane (DMSB monomer from the surface of cross-linked polystyrene (PS nanoparticles. Novel polycarbosilanes (PCS/organic core/shell particles are obtained, which are investigated by using transmission electron microscopy (TEM and dynamic light scattering (DLS experiments. First insights into the crystallization behavior of surface-attached PDMSB chains reveal that crystallization seems to be hindered.

  12. Vascular ring

    ... subclavian and left ligamentum ateriosus; Congenital heart defect - vascular ring; Birth defect heart - vascular ring ... Vascular ring is rare. It accounts for less than 1% of all congenital heart problems. The condition ...

  13. Gold-Catalyzed β-Regioselective Formal [3 + 2] Cycloaddition of Ynamides with Pyrido[1,2-b]indazoles: Reaction Development and Mechanistic Insights.

    Yu, Yinghua; Chen, Gui; Zhu, Lei; Liao, Yun; Wu, Yufeng; Huang, Xueliang


    Here, we report an unprecedented gold(I)-induced β-site regioselective formal [3 + 2] cycloaddition of ynamides with pyrido[1,2-b]indazoles, giving 3-amido-7-(pyrid-2'-yl)indoles in good to excellent yields. A complex of gold(I) catalyst with ynamide was isolated and characterized by X-ray diffraction analysis for the first time. Mechanistic investigations suggest the reaction pathway involves a gold-stabilized carbocation intermediate, which in turn participated in sequential C-H bond functionalization of the ortho-position of the phenyl ring.

  14. Organotin-catalyzed highly regioselective thiocarbonylation of nonprotected carbohydrates and synthesis of deoxy carbohydrates in a minimum number of steps.

    Muramatsu, Wataru; Tanigawa, Satoko; Takemoto, Yuki; Yoshimatsu, Hirofumi; Onomura, Osamu


    Nonprotected carbohydrates: The catalytic regioselective thiocarbonylation of carbohydrates by using organotin dichloride under mild conditions was demonstrated. The reaction afforded various deoxy saccharides in high yields and excellent regioselectivity in a minimum number of steps. The regioselectivity of the thiocarbonylation is attributed to the intrinsic character of the carbohydrates based on the stereorelationship of their hydroxy groups (see scheme).

  15. Extending the synthetic utilities of the tandem cyclic sulfate rearrangement-opening process: Synthesis of β-hydroxy-y-phenyl-γ-phenyl-γ-lactam

    Lee, Nagum; Yu, Min Lee; Jun, Hye Yeon; Ko, Soo Y. [Dept. of Chemistry, Ewha Womans University, Seoul (Korea, Republic of)


    Cinnamyl alcohol is an obvious choice of starting material that provides the carbon framework for the syntheses of these compounds. Stereoselective oxidations (epoxidation or dihydroxylation) pave the way for the introductions of O-/N-substituents. Issues of regioselections need to be dealt with in these transformation, which may be tackled either in the activation steps, in the substitution steps, or in the protection steps. In conclusion, we have incorporated a nitrile function at C-3 of the phenylpropyl skeleton in our tandem cyclic sulfate rearrangement-epoxide opening and epoxide ring closure-epoxide opening processes. The one-carbon extension broadens the synthetic utilities of our tandem processes, as exemplified in our synthesis of β-hydroxy-γ-phenyl-γ-lactam.

  16. Regio-selective Dehydrogenation on the D or E Rings of Oleanolic Acid by Pd-Promoted C-H Activation%钯促进的碳氢键活化在齐墩果酸D和E环脱氢烯化中的应用研究

    马玉勇; 李微; 俞飚


    Oleanane-type triterpenes and their glycosides are a structurally and biologically diverse class of metabolites that are widely distributed in terrestrial plants and some marine organisms. Many of these compounds bear functional groups and modifications on the D and/or E rings of the triterpenes. These triterpenes compounds are of growing interest for drug research as they are active constituents of folk medicines and provide valuable pharmacological profiles. For their limited availability and accessibility, chemical synthesis provides a realistic way to determine the availability of homogenous natural products and their derivatives. Here, we report the selective dehydrogenation on the D or E rings of oleanoic acid by palladium promoted C-H activation with 8-aminoquinoline amide (substrate 12) and 2-aminomethylpyridine amide (substrate 16) as the directing groups. Thus, upon treatment with thionyl chloride, the 28-COOH of oleanoic acid was converted into 28-COC1, which coupled with the corresponding amines to provide the substrates readily for dehydrogenation. Notably, treatment of 12 with optimized conditions (1.0 equiv. Pd(OAc)2, 1.5 equiv. Oxone?, 1,2-dichloroethane, 80 ℃, 24 h) led to the dehydrogenated products 13 [double bond at C(15)-C(16)] and 14 [double bond at C(20)-C(21)] in 55% and 2% yields respectively. Treatment of 16 with optimized conditions (1.0 equiv. Pd(Oac)2, 2.0 equiv. Oxone?, 1,2-dichloroethane, microwave 85 ℃, 50 min) provided 17 [double bond at C(20)-C(21)] and 18 [double bond at C(15)-C(16)] in 42% and 20% yields respectively. Moreover, the distribution of the products varied in different solvents. It is worth mentioning that the N,N-bidentate ligands (two nitrogen atoms as the coordination sites in 12 and 16) are crucial for the palladium promoted ole-fination.%齐墩果烷型的三萜及其糖苷化合物广泛分布于陆地植物和一些海洋生物中,是许多传统药物中的活性成分.这类五环三萜化合物的D和E

  17. Regioselective Allene Hydrosilylation Catalyzed by NHC Complexes of Nickel and Palladium

    Miller, Zachary D.; Li, Wei; Belderrain, Tomás R.; Montgomery, John


    Regioselective methods for allene hydrosilylation have been developed, with regioselectivity being governed primarily by choice of metal. Alkenylsilanes are produced via nickel catalysis with larger N-heterocyclic carbene ligands, and allylsilanes are produced via palladium catalysis with smaller N-heterocyclic carbene ligands. These complementary methods allow either regioisomeric product to be obtained with exceptional regiocontrol. PMID:24079389

  18. Hindered aryl bromides for regioselective palladium-catalysed direct arylation at less favourable C5-carbon of 3-substituted thiophenes

    Rongwei Jin


    Full Text Available The use of the congested aryl bromide 2-bromo-1,3-dichlorobenzene as coupling partner allows to modify the regioselectivity of the arylation of 3-substituted thiophene derivatives in favour of carbon C5. The coupling of this aryl bromide with a variety of 3-substituted thiophenes gave in all cases the desired 5-arylation products in moderate to good yields using only 0.5 mol % of a phosphine-free and air-stable palladium catalyst. Then, from these 5-arylthiophenes, a second palladium-catalysed C–H bond functionalization at C2 of the thiophene ring allows the synthesis of 2,5-diarylthiophenes with two different aryl units.

  19. Regioselective synthesis of 5- and 6-methoxybenzimidazole-1,3,5-triazines as inhibitors of phosphoinositide 3-kinase.

    Miller, Michelle S; Pinson, Jo-Anne; Zheng, Zhaohua; Jennings, Ian G; Thompson, Philip E


    Phosphoinositide 3-kinases (PI3K) hold significant therapeutic potential as novel targets for the treatment of cancer. ZSTK474 (4a) is a potent, pan-PI3K inhibitor currently under clinical evaluation for the treatment of cancer. Structural studies have shown that derivatisation at the 5- or 6-position of the benzimidazole ring may influence potency and isoform selectivity. However, synthesis of these derivatives by the traditional route results in a mixture of the two regioisomers. We have developed a straightforward regioselective synthesis that gave convenient access to 5- and 6-methoxysubstituted benzimidazole derivatives of ZSTK474. While 5-methoxy substitution abolished activity at all isoforms, the 6-methoxy substitution is consistently 10-fold more potent. This synthesis will allow convenient access to further 6-position derivatives, thus allowing the full scope of the structure-activity relationships of ZSTK474 to be probed.

  20. Ring blowers. Ring blower

    Nakahara, Y.; Okamura, T.; Takahashi, M. (Fuji Electric Co. Ltd., Tokyo (Japan))


    Features, structures and several products of ring blowers were outlined. The ring blower is featured by its medium characteristics because it is higher in air pressure than a turboblower and larger in airflow than a vane blower, and it is applicable flexibly to not only air blasting but various industrial fields such as suction transfer. As several products corresponding to various fields, the followings were outlined: the low noise type with optimum shapes of inlet, outlet and casing cover for reducing noises by 10 dB or more, the heat resistant, water-tight and explosion-proof types suitable for severe environmental conditions, the multi-voltage type for every country served at different voltages, the high air pressure type with two pressure rise stages, and the large airflow type with a wide impeller. In addition, as special use products, the glass fiber reinforced unsatulated polyester ring blower for respiration apparatus, and the variable speed blushless DC motor-driven one for medical beds were outlined. 2 refs., 9 figs., 1 tab.

  1. Aluminum Complexes Stabilized by Piperazidine-Bridged Bis(phenolate) Ligands: Syntheses, Structures, and Applica- tion in the Ring-Opening Polymerization of ε-Caprolactone

    李文艺; 姚英明; 张勇; 沈琪


    The synthesis and characterization of aluminum alkoxide and alkyl complexes stabilized by piperazidine- bridged bis(phenolate) ligands are described. Treatment of ligand precursors Hz[ONNO]^1 {Hz[ONNO]^1= 1,4-bis(2-hydroxy-3-tert-butyl-5-methylbenzyl)piperazidine} and Hz[ONNO]2 {H2[ONNO]2=1,4-bis(2-hydroxy3,5-di-tert-butylbenzyl)piperazidine} with A1Et2(OCH2Ph) and A1Etz(OPr-i), which were generated in situ by the reactions of AIEt3 with equivalent of the corresponding alcohols, in a 1: 1 molar ratio in THF gave the corresponding aluminum alkoxide complexes [ONNO]IAI(OCH2Ph) (1) and [ONNO]2Al(OPr-i) (2), respectively. The reaction of H2[ONNO]^1 with A1Etz(OCHzPh) in a 1 : 2 molar ratio in THF afforded a mixture of monometallic aluminum ethyl complex [ONNO] 1A1Et (3) and complex 1, which can be isolated by stepwise crystallization. Similarly, Hz[ONNO]2 reacted with A1Etz(OPr-0 in a 1: 2 molar ratio in THF to give a mixture of aluminum ethyl complex [ONNO]2AlEt (4) and complex 2. Complexes 1 and 2 were also available via treatment of complexes 3 and 4 with 1 equiv, of benzyl alcohol and isopropyl alcohol, respectively. All of these complexes were fully characterized including X-ray structural determination. It was found that complexes 1 to 4 can initiate the ring-opening polymerization of e-caprolactone, and complexes 1 and 2 showed higher catalytic activity in comparison with com- plexes 3 and 4.

  2. Scandium versus yttrium{amino-alkoxy-bis(phenolate)} complexes for the stereoselective ring-opening polymerization of racemic lactide and β-butyrolactone.

    Chapurina, Yulia; Klitzke, Joice; Casagrande, Osvaldo de L; Awada, Mouhamad; Dorcet, Vincent; Kirillov, Evgueni; Carpentier, Jean-François


    Scandium and yttrium amide complexes Ln{ONXO(R1,R2)}(N(SiHMe2)2)(THF)n (Ln = Sc, n = 0 or Y, n = 1; X = NMe2 or OMe; R(1) = Cumyl or p-Cl-Cumyl; R(2) = Me or Cumyl) were prepared by aminolysis of Ln[N(SiHMe2)2]3(THF) with the corresponding tetradentate diamino- or alkoxy-amino-bis(phenol) pro-ligands {ONXO(R1,R2)}H2. In the solid state and in toluene solution, the scandium complexes are monomeric and 5-coordinated, while the analogous yttrium complexes all bear an extra THF-coordinated molecule and are 6-coordinated. Sc{ONXO(R1,R2)}(N(SiHMe2)2) complexes are single-site initiators for the ring-opening polymerization (ROP) of racemic lactide but are less active than their yttrium analogues Y{ONXO(R1,R2)}(N(SiHMe2)2)(THF); also, in contrast to the latter ones, they are inactive in the ROP of the more demanding racemic β-butyrolactone. On the other hand, the scandium amide complexes feature a significantly improved control over the ROP of lactide, yielding PLAs with much narrower molecular weight distributions (Đ(M) < 1.1 for Sc vs. 1.5-2.0 for Y). The yttrium complex with the very bulky o,p-dicumyl-substituted ligand is more heteroselective than its scandium analogue (P(r) = 0.88 vs. 0.83), while the opposite is observed with complexes based on p-methyl-substituted ligands (P(r) = 0.50 in toluene or 0.72-0.75 in THF for Y vs. P(r) = 0.75-0.83 for Sc in toluene). These reactivity and selectivity trends are rationalized by a much more sterically crowded coordination sphere in scandium than in yttrium complexes.

  3. Effects of thermal history in the ring opening polymerization of CBT and its mixtures with montmorillonite on the crystallization of the resulting poly(butylene terephthalate)

    Lanciano, Giuseppina [Department of Innovation Engineering, University of Salento, Via per Arnesano, 73100 Lecce (Italy); Greco, Antonio, E-mail: [Department of Innovation Engineering, University of Salento, Via per Arnesano, 73100 Lecce (Italy); Maffezzoli, Alfonso [Department of Innovation Engineering, University of Salento, Via per Arnesano, 73100 Lecce (Italy); Mascia, Leno [Department of Materials, Loughborough University, Loughborough, LE 11 3TU (United Kingdom)


    Differential scanning calorimetry was used to study the thermal characteristics and morphological structure of species produced during the ring opening polymerization of cyclic butylene terephthalate (CBT). Thermal programs consisting of a first ramp heating scan and an isothermal step, followed by cooling and a second ramp heating step, were used to study the effects of thermal history, catalyst (butyl chlorotin dihydroxide) at concentrations between 0.1 and 1.3% (w/w), and the presence of a layered silicate nanofiller (montmorillonite at 4.0%, w/w) on the structure of the resulting polymer (poly(butylene terephthalate), pCBT). Wide angle X-ray diffraction was used to monitor the degree of exfoliation of the nanocomposites. It was found that pCBT is formed in the amorphous state, and crystallizes during the heating step or during the isothermal step at temperatures lower than the equilibrium melting temperature of the polymer (T{sub m}{sup 0}). When premixed with the nanofiller, irrespective of whether this was previously intercalated with a tallow surfactant or used in its pristine form, polymerization took place at higher temperatures and most of the crystallization was found to occur during the cooling stage. In those cases where crystallization took place during either the first heating scan, or during a prolonged isothermal step below the T{sub m}{sup 0} of the polymer, the resulting crystals were found to have a higher lamellar thickness, as compared with the same polymer crystallized from the melt during the cooling step from temperatures above the polymer T{sub m}{sup 0}.

  4. Preparation of polyhedral oligomeric silsesquioxane-based hybrid monolith by ring-opening polymerization and post-functionalization via thiol-ene click reaction.

    Liu, Zhongshan; Ou, Junjie; Lin, Hui; Wang, Hongwei; Dong, Jing; Zou, Hanfa


    A polyhedral oligomeric silsesquioxane (POSS) hybrid monolith was simply prepared by using octaglycidyldimethylsilyl POSS (POSS-epoxy) and cystamine dihydrochloride as monomers via ring-opening polymerization. The effects of composition of prepolymerization solution and polycondensation temperature on the morphology and permeability of monolithic column were investigated in detail. The obtained POSS hybrid monolithic column showed 3D skeleton morphology and exhibited high column efficiency of ∼71,000 plates per meter in reversed-phase mechanism. Owing to this POSS hybrid monolith essentially possessing a great number of disulfide bonds, the monolith surface would expose thiol groups after reduction with dithiothreitol (DTT), which supplied active sites to functionalize with various alkene monomers via thiol-ene click reaction. The results indicated that the reduction with DTT could not destroy the 3D skeleton of hybrid monolith. Both stearyl methylacrylate (SMA) and benzyl methacrylate (BMA) were selected to functionalize the hybrid monolithic columns for reversed-phase liquid chromatography (RPLC), while [2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl)-ammonium hydroxide (MSA) was used to modify the hybrid monolithic column in hydrophilic interaction chromatography (HILIC). These modified hybrid monolithic columns could be successfully applied for separation of small molecules with high efficiency. It is demonstrated that thiol-ene click reaction supplies a facile way to introduce various functional groups to the hybrid monolith possessing thiol groups. Furthermore, due to good permeability of the resulting hybrid monoliths, we also prepared long hybrid monolithic columns in narrow-bore capillaries. The highest column efficiency reached to ∼70,000 plates using a 1-m-long column of 75μm i.d. with a peak capacity of 147 for isocratic chromatography, indicating potential application in separation and analysis of complex biosamples. Copyright © 2014

  5. Regioselective deiodination of iodothyronamines, endogenous thyroid hormone derivatives, by deiodinase mimics.

    Mondal, Santanu; Mugesh, Govindasamy


    Iodothyronine deiodinases (IDs) are mammalian selenoenzymes that play an important role in the activation and inactivation£ of thyroid hormones. It is known that iodothyronamines (TnAMs), produced by the decarboxylation of thyroid hormones, act as substrates for deiodinases. To understand whether decarboxylation alters the rate and/or regioselectivity of deiodination by using synthetic deiodinase mimics, we studied the deiodination of different iodothyronamines. The triiodo derivative 3,3',5-triiodothyronamine (T3 AM) is deiodinated at the inner ring by naphthyl-based deiodinase mimics, which is similar to the deiodination of 3,3',5-triiodothyronine (T3). However, T3 AM undergoes much slower deiodination than T3. Detailed experimental and theoretical investigations suggest that T3 AM forms a weaker halogen bond with selenium donors than T3. Kinetic studies and single-crystal X-ray structures of T3 and T3 AM reveal that intermolecular I⋅⋅⋅I interactions may play an important role in deiodination. The formation of hydrogen- and halogen-bonding assemblies, which leads to the formation of a dimeric species of T3 in solution, facilitates the interactions between the selenium and iodine atoms. In contrast, T3 AM, which does not have I⋅⋅⋅I interactions, undergoes much slower deiodination. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Control of Reactivity and Regioselectivity for On-Surface Dehydrogenative Aryl-Aryl Bond Formation.

    Kocić, Nemanja; Liu, Xunshan; Chen, Songjie; Decurtins, Silvio; Krejčí, Ondřej; Jelínek, Pavel; Repp, Jascha; Liu, Shi-Xia


    Regioselectivity is of fundamental importance in chemical synthesis. Although many concepts for site-selective reactions are well established for solution chemistry, it is not a priori clear whether they can easily be transferred to reactions taking place on a metal surface. A metal will fix the chemical potential of the electrons and perturb the electronic states of the reactants because of hybridization. Additionally, techniques to characterize chemical reactions in solution are generally not applicable to on-surface reactions. Only recent developments in resolving chemical structures by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) paved the way for identifying individual reaction products on surfaces. Here we exploit a combined STM/AFM technique to demonstrate the on-surface formation of complex molecular architectures built up from a heteroaromatic precursor, the tetracyclic pyrazino[2,3-f][4,7]phenanthroline (pap) molecule. Selective intermolecular aryl-aryl coupling via dehydrogenative C-H activation occurs on Au(111) upon thermal annealing under ultrahigh vacuum (UHV) conditions. A full atomistic description of the different reaction products based on an unambiguous discrimination between pyrazine and pyridine moieties is presented. Our work not only elucidates that ortho-hydrogen atoms of the pyrazine rings are preferentially activated over their pyridine equivalents, but also sheds new light onto the participation of substrate atoms in metal-organic coordination bonding during covalent C-C bond formation.

  7. Regioselective alkane hydroxylation with a mutant AlkB enzyme

    Koch, Daniel J.; Arnold, Frances H.


    AlkB from Pseudomonas putida was engineered using in-vivo directed evolution to hydroxylate small chain alkanes. Mutant AlkB-BMO1 hydroxylates propane and butane at the terminal carbon at a rate greater than the wild-type to form 1-propanol and 1-butanol, respectively. Mutant AlkB-BMO2 similarly hydroxylates propane and butane at the terminal carbon at a rate greater than the wild-type to form 1-propanol and 1-butanol, respectively. These biocatalysts are highly active for small chain alkane substrates and their regioselectivity is retained in whole-cell biotransformations.

  8. Regioselective photoamination of 4-nitroveratrole upon cyclodextrin complexation

    M C Durai Manickam; K Pitchumani; C Srinivasan


    Photoamination of 4-nitroveratrole in cyclodextrins with the nucleophiles ammonia, methylamine and hexylamine provides a new route to regioselectivity. This method gives a displaced product para to the nitro group as the predominant product, in contrast to the solution reaction wherein the meta-displaced product predominates. This is due to the change in the mechanistic shift from S2Ar∗, wherein the nitro group is meta-directing, to a mechanism involving electron transfer from the nucleophile to the excited aromatic substrate (S (ET)Ar∗) to give the para-displaced product.

  9. Piperidine Promoted Regioselective Synthesis of α, β-unsaturated Aldehydes

    *A. H. Banday


    Full Text Available An efficient, facile and regioselective synthesis of α,β-unsaturated aldehydes from β-hydroxynitriles is reported. The reaction is carried out using DIBAL-H and promoted by piperidine under dry conditions at a temperature of -78 oC and can be described as a concomitant reduction-elimination reaction. The same reaction if carried out in the absence of piperidine gives mainly the uneliminated reduction product. The products formed are of immense importance as synthons in a large number of chemical reactions and biological processes.

  10. Analysis and Optimization of Locking Ring for Quick-opening Blind Plate Based on Ansys Workbench%基于Ansys Workbench的快开盲板锁环分析及优化

    周天旭; 陈平; 陈水莲; 罗聪


    Ansys Workbench was used to optimize tilt angle of the locking ring in quick-opening blind plate so as to work out an optimum angle; and the relation curve between the locking ring size and the blind plate' s supporting was plotted,and the influence of locking ring size and tilt angle on the ring' s strength and stiffness was considered to propose details needing attention in the locking ring design.%利用Ansys Workbench对快开盲板锁环的倾斜角度进行了参数化设计,并优化出最佳角度.绘制出锁环尺寸对盲板支承状况和锁环应力的影响曲线.综合研究了锁环尺寸和倾斜角对锁环强度、刚度的影响,并提出了锁环设计中需要注意的细节.

  11. The influence of water on visible-light initiated free-radical/cationic ring-opening hybrid polymerization of methacrylate/epoxy: Polymerization kinetics, crosslinking structure and dynamic mechanical properties


    The objective of this study was to determine the influence of water on the polymerization kinetics, crosslinking structure and dynamic mechanical properties of methacrylate/epoxy polymers cured by visible-light initiated free-radical/cationic ring-opening hybrid polymerization. Water-containing formulations were prepared by adding ~4–7 wt% D2O depending on the water miscibility of monomer resins. The water-containing adhesives were compared with the adhesives photo-cured in the absence of wat...

  12. A Mechanistic and Kinetic Study of the Photoinitiated Cationic Double Ring-opening Polymerization of 2-Methylene-7-phenyl-1,4,6,9-tetraoxa-spiro[4.4]nonane.

    Ge, Junhao; Trujillo-Lemon, Marianela; Stansbury, Jeffrey W


    Efficient photopolymerization of a potentially expandable monomer is of practical importance for a variety of polymeric applications demanding dimensional stability, particularly if the polymerization process is well controlled based on a detailed investigation of the reaction. In the current study, photoinitiated polymerization kinetics of 2-methylene-7-phenyl-1,4,6,9-tetraoxaspiro[4.4]nonane (MPN) either with cationic initiation alone or with combined cationic/free radical initiation was examined using real-time FT-IR. A proposed mechanism based on the simplified propagation steps of the cationic double ring-opening polymerization of MPN was confirmed by both computer modeling and NMR spectroscopic analysis of resulting polymers as well as the experimentally observed apparent activation energy. According to this mechanism, alpha-position attack is the predominant mode for the second ring opening during cationic polymerization of MPN. Further, cationic photopolymerization was performed along with a free radical co-initiator or with exposure to moisture to get an improved understanding of the complex cationic double ring-opening polymerization. As a result, free radical-promoted cationic polymerization helps increase the polymerization rate of MPN while even a trace amount of moisture was found to significantly impact both the reaction kinetics and the polymerization course.

  13. Regioselective synthesis of C3 alkylated and arylated benzothiophenes

    Shrives, Harry J.; Fernández-Salas, José A.; Hedtke, Christin; Pulis, Alexander P.; Procter, David J.


    Benzothiophenes are heterocyclic constituents of important molecules relevant to society, including those with the potential to meet modern medical challenges. The construction of molecules would be vastly more efficient if carbon-hydrogen bonds, found in all organic molecules, can be directly converted into carbon-carbon bonds. In the case of elaborating benzothiophenes, functionalization of carbon-hydrogen bonds at carbon-number 3 (C3) is markedly more demanding than at C2 due to issues of regioselectivity (C3 versus C2), and the requirement of high temperatures, precious metals and the installation of superfluous directing groups. Herein, we demonstrate that synthetically unexplored but readily accessible benzothiophene S-oxides serve as novel precursors for C3-functionalized benzothiophenes. Employing an interrupted Pummerer reaction to capture and then deliver phenol and silane coupling partners, we have discovered a directing group-free method that delivers C3-arylated and -alkylated benzothiophenes with complete regioselectivity, under metal-free and mild conditions.

  14. Regioselective Localization and Tracking of Biomolecules on Single Gold Nanoparticles.

    Rajeeva, Bharath Bangalore; Hernandez, Derek S; Wang, Mingsong; Perillo, Evan; Lin, Linhan; Scarabelli, Leonardo; Pingali, Bharadwaj; Liz-Marzán, Luis M; Dunn, Andrew K; Shear, Jason B; Zheng, Yuebing


    Selective localization of biomolecules at the hot spots of a plasmonic nanoparticle is an attractive strategy to exploit the light-matter interaction due to the high field concentration. Current approaches for hot spot targeting are time-consuming and involve prior knowledge of the hot spots. Multiphoton plasmonic lithography is employed to rapidly immobilize bovine serum albumin (BSA) hydrogel at the hot spot tips of a single gold nanotriangle (AuNT). Regioselectivity and quantity control by manipulating the polarization and intensity of the incident laser are also established. Single AuNTs are tracked using dark-field scattering spectroscopy and scanning electron microscopy to characterize the regioselective process. Fluorescence lifetime measurements further confirm BSA immobilization on the AuNTs. Here, the AuNT-BSA hydrogel complexes, in conjunction with single-particle optical monitoring, can act as a framework for understanding light-molecule interactions at the subnanoparticle level and has potential applications in biophotonics, nanomedicine, and life sciences.

  15. Saturn's Rings

    Cuzzi, J. N.


    The rings are changing before our eyes; structure varies on all timescales and unexpected things have been discovered. Many questions have been answered, but some answers remain elusive (see Cuzzi et al 2010 for a review). Here we highlight the major ring science progress over the mission to date, and describe new observations planned for Cassini's final three years. Ring Composition and particle sizes: The rings are nearly all water ice with no other ices - so why are they reddish? The C Ring and Cassini Division are "dirtier" than the more massive B and A Rings, as shown by near-IR and, recently, microwave observations. Particle sizes, from stellar and radio occultations, vary from place to place. Ring structure, micro and macro: numerous spiral density waves and ubiquitous "self-gravity wakes" reveal processes which fostered planet formation in the solar system and elsewhere. However, big puzzles remain regarding the main ring divisions, the C Ring plateau structures, and the B Ring irregular structure. Moonlets, inside and out, seen and unseen: Two gaps contain sizeable moonlets, but more gaps seem to contain none; even smaller embedded "propeller" objects wander, systematically or randomly, through the A ring. Rubble pile ringmoons just outside the rings may escaped from the rings, and the recently discovered "Peggy" may be trying this as we watch. Impact bombardment of the rings: Comet fragments set the rings to rippling on century-timescales, and boulders crash through hourly; meanwhile, the constant hail of infalling Kuiper belt material has a lower mass flux than previously thought. Origin and Age of the Rings: The ring mass and bombardment play key roles. The ring mass is well known everywhere but in the B Ring (where most of it is). New models suggest how tidal breakup of evolving moons may have formed massive ancient rings, of which the current ring is just a shadow. During its last three years, the Cassini tour profile will allow entirely new

  16. Zirconium and hafnium complexes containing N-alkyl substituted amine biphenolate ligands: coordination chemistry and living ring-opening polymerization catalysis.

    Liang, Lan-Chang; Lin, Sheng-Ta; Chien, Chia-Cheng; Chen, Ming-Tsz


    The coordination chemistry of zirconium and hafnium complexes containing the tridentate amine biphenolate ligands [RN(CH2-2-O-3,5-C6H2(tBu)2)2](2-) ([R-ONO](2-); R = tBu (1a), iPr (1b), nPr (1c)) featuring distinct N-alkyl substituents is described. Alcoholysis of Zr(OiPr)4(HOiPr) or Hf(OiPr)4(HOiPr) with H2[1a] in diethyl ether solutions at -35 °C generates the corresponding five-coordinate [1a]M(OiPr)2 (M = Zr (2a), Hf (3a)) in high isolated yield. Similar reactions employing H2[1b] produce six-coordinate [1b]M(OiPr)2(HOiPr) (M = Zr (2b·HOiPr), Hf (3b·HOiPr)) as an isopropanol adduct. Repetitive trituration of 2b·HOiPr and 3b·HOiPr with diethyl ether gives five-coordinate 2b and 3b, respectively. Treatment of M(OiPr)4(HOiPr) with H2[1c] under similar conditions affords six-coordinate [1c]M(OiPr)2(HOiPr) (M = Zr (2c·HOiPr), Hf (3c·HOiPr)), subsequent recrystallization of which from acetonitrile-diethyl ether solutions leads to acetonitrile adducts 2c·MeCN and 3c·MeCN. Reactivity studies of these zirconium and hafnium complexes revealed that they are all active catalysts for ring-opening polymerization of ε-caprolactone. Among them, the N-isopropyl derived complexes are most reactive. Polymerizations catalyzed by 2b, 3b and 3c·MeCN were proved to be living. The X-ray structures of 2a·HOiPr, 2a·MeCN, 2c·HOiPr, 2c·MeCN, and 3c·MeCN are presented.

  17. Synthesis of PNVP-Based Copolymers with Tunable Thermosensitivity by Sequential Reversible Addition–Fragmentation Chain Transfer Copolymerization and Ring-Opening Polymerization

    Yi-Shen Huang


    Full Text Available Through the reversible addition–fragmentation chain transfer (RAFT copolymerization of 3-ethyl-1-vinyl-2-pyrrolidone (C2NVP and N-vinylpyrrolidone (NVP, a series of well-defined P(C2NVP-co-NVP copolymers were synthesized (Mn = ca. 8000 to 16,000 and Mw/Mn <1.5 by using a difunctional chain transfer agent, S-(1-methyl-4-hydroxyethyl acetate O-ethyl xanthate (MHEX. Copolymerizing kinetics and different monomer ratio in feeds were conducted to study the apparent monomer reaction rate and reactivity ratios of NVP and C2NVP, which indicated similar reaction rates and predominantly ideal random copolymers for the two monomers. The Tgs of the obtaining P(C2NVP-co-NVP copolymers significantly corresponded to not only molecular weights MWs but also copolymer compositions. These copolymers presented characteristic lower critical solution temperatures (LCST behavior. We then studied the cloud points (CPs of the copolymers with varying MWs and compositions. With different MWs, the CPs were linearly decreased from ca. 51 to 45 °C. With different compositions, the CPs of the copolymers decreased from ca. 48 to 29 °C with C2NVP content (i.e., from 60.8 to 89.9 mol %. Fitting the CPs by the theoretical equation, the result illustrated that the introduction of more hydrophobic units of C2NVP suppressed the hydrophilic interaction between the polymer chain and water. We then successfully proceeded the chain extension through the ring-opening polymerization (ROP of ε-caprolactone (CL to the synthesis of a novel P(C2NVP-co-NVP-b-PCL amphiphilic block copolymer (Mn,NMR = 14,730 and Mw/Mn = 1.59. The critical micelle concentration (CMC of the block copolymer had a value of ca. 1.46 × 10−4 g/L. The block copolymer micelle was traced by dynamic light scattering (DLS, obtaining thermosensitive behaviors with a particle size of ca. 240 nm at 25 °C and ca. 140 nm at 55 °C, respectively.

  18. Vortex rings

    Akhmetov, D.G. [Lavrentiev Institute of Hydrodynamics, Novosibirsk (Russian Federation)


    This book presents a comprehensive coverage of the wide field of vortex rings. The book presents the results of systematic experimental investigations, theoretical foundation, as well as the practical applications of vortex rings, such as the extinction of fires at gushing gas and oil wells. All the basic properties of vortex rings as well as their hydrodynamic structures are presented. Special attention is paid to the formation and motion of turbulent vortex rings. (orig.)

  19. Ring theory

    Rowen, Louis H


    This is an abridged edition of the author's previous two-volume work, Ring Theory, which concentrates on essential material for a general ring theory course while ommitting much of the material intended for ring theory specialists. It has been praised by reviewers:**""As a textbook for graduate students, Ring Theory joins the best....The experts will find several attractive and pleasant features in Ring Theory. The most noteworthy is the inclusion, usually in supplements and appendices, of many useful constructions which are hard to locate outside of the original sources....The audience of non

  20. Novel and Highly Efficient Regioselective Route to Helicid Esters by Lipozyme TLL

    Yang, Rongling; Zhao, Xiangjie; Liu, Xueming


    Highly regioselective acylation of helicid with fatty acid vinyl esters catalyzed by the lipase from Thermomyces lanuginosus has been successfully performed for the first time. For the enzymatic caproylation of helicid, under the optimal conditions, initial reaction rate was 33.2 mM/h, and substrate conversion and regioselectivity were greater than 99%. In addition, the acyl recognition of the enzyme in the regioselective acylation of helicid was investigated. The results showed that although 6’-O-acyl derivatives of helicid were exclusively obtained with all the tested acyl donors, the enzymatic reaction rate varied widely with different acyl donors, presumably owing to their different interactions with the active site of the lipase. It is also interesting that the different configuration of only one hydroxyl group at C-3 in helicid couldn’t affect the lipase-catalyzed esterification and helicid has the same regioselectivity as that of D-glucose and arbutin. PMID:24278310

  1. A Novel Protocol for the Regioselective Bromination of Primary Alcohols in Unprotected Carbohydrates or Glycosides

    薛伟华; 张立芬


    The regioselective and efficient bromination of primary hydroxyl groups in unprotected carbohydrates or glycosides is successfully achieved by using (chloro-phenylthio-methylene)dimethylammoniumchloride (CPMA) in the presence of tetrabutylammonium bromide (TBAB) in dry DMF.

  2. Highly efficient and enzymatic regioselective undecylenoylation of gastrodin in 2-methyltetrahydrofuran-containing systems.

    Rongling Yang

    Full Text Available Highly efficient and regioselective acylation of pharmacologically interesting gastrodin with vinyl undecylenic acid has been firstly performed through an enzymatic approach. The highest catalytic activity and regioselectivity towards the acylation of 7'-hydroxyl of gastrodin was obtained with Pseudomonas cepacia lipase. In addition, it was observed the lipase displayed higher activity in the eco-friendly solvent 2-methyltetrahydrofuran-containing systems than in other organic solvents. In the co-solvent mixture of tetrahydrofuran and 2-methyltetrahydrofuran (3/1, v/v, the reaction rate was 60.6 mM/h, substrate conversion exceeded 99%, and 7'-regioselectivity was 93%. It was also interesting that the lipase-catalyzed acylation couldn't be influenced by the benzylic alcohol in gastrodin. However, pseudomonas cepacia lipase displayed different regioselectivity towards gastrodin and arbutin.

  3. Highly Regioselective Halogenation of Pyridine N-Oxide: Practical Access to 2-Halo-Substituted Pyridines.

    Chen, Ying; Huang, Jinkun; Hwang, Tsang-Lin; Chen, Maosheng J; Tedrow, Jason S; Farrell, Robert P; Bio, Matthew M; Cui, Sheng


    A highly efficient and regioselective halogenation reaction of unsymmetrical pyridine N-oxide under mild conditions is described. The methodology provides a practical access to various 2-halo-substituted pyridines, which are pharmaceutically important intermediates.

  4. Regioselective Palladium-Catalyzed Cross-Coupling Reactions of 2,4,7-Trichloroquinazoline.

    Wipf, Peter; George, Kara M


    The regioselective palladium-catalyzed cross-coupling reactions of 2,4,7-trichloroquinazoline with various aryl- and heteroarylboronic acids are reported. An efficient, sequential strategy was developed that provides access to novel, functionalized heterocycles.

  5. The Nitrilimine–Alkene Cycloaddition Regioselectivity Rationalized by Density Functional Theory Reactivity Indices

    Giorgio Molteni


    Full Text Available Conventional frontier molecular orbital theory is not able to satisfactorily explain the regioselectivity outcome of the nitrilimine–alkene cycloaddition. We considered that conceptual density functional theory (DFT could be an effective theoretical framework to rationalize the regioselectivity of the title reaction. Several nitrilimine–alkene cycloadditions were analyzed, for which we could find regioselectivity data in the literature. We computed DFT reactivity indices at the B3LYP/6-311G(2d,p//B3LYP/6-31G(d,p and employed the grand potential stabilization criterion to calculate the preferred regioisomer. Experimental and calculated regioselectivity agree in the vast majority of cases. It was concluded that predominance of a single regioisomer can be obtained by maximizing (i the chemical potential difference between nitrilimine and alkene and (ii the local softness difference between the reactive atomic sites within each reactant. Such maximization can be achieved by carefully selecting the substituents on both reactants.

  6. Regioselective Alcoholysis of Silychristin Acetates Catalyzed by Lipases

    Eva Vavříková


    Full Text Available A panel of lipases was screened for the selective acetylation and alcoholysis of silychristin and silychristin peracetate, respectively. Acetylation at primary alcoholic group (C-22 of silychristin was accomplished by lipase PS (Pseudomonas cepacia immobilized on diatomite using vinyl acetate as an acetyl donor, whereas selective deacetylation of 22-O-acetyl silychristin was accomplished by Novozym 435 in methyl tert-butyl ether/ n-butanol. Both of these reactions occurred without diastereomeric discrimination of silychristin A and B. Both of these enzymes were found to be capable to regioselective deacetylation of hexaacetyl silychristin to afford penta-, tetra- and tri-acetyl derivatives, which could be obtained as pure synthons for further selective modifications of the parent molecule.

  7. Regioselective reductive hydration of alkynes to form branched or linear alcohols.

    Li, Le; Herzon, Seth B


    The regioselective reductive hydration of terminal alkynes using two complementary dual catalytic systems is described. Branched or linear alcohols are obtained in 75-96% yield with ≥25:1 regioselectivity from the same starting materials. The method is compatible with terminal, di-, and trisubstituted alkenes. This reductive hydration constitutes a strategic surrogate to alkene oxyfunctionalization and may be of utility in multistep settings.

  8. Planetary Rings

    Tiscareno, Matthew S


    Planetary rings are the only nearby astrophysical disks, and the only disks that have been investigated by spacecraft. Although there are significant differences between rings and other disks, chiefly the large planet/ring mass ratio that greatly enhances the flatness of rings (aspect ratios as small as 1e-7), understanding of disks in general can be enhanced by understanding the dynamical processes observed at close-range and in real-time in planetary rings. We review the known ring systems of the four giant planets, as well as the prospects for ring systems yet to be discovered. We then review planetary rings by type. The main rings of Saturn comprise our system's only dense broad disk and host many phenomena of general application to disks including spiral waves, gap formation, self-gravity wakes, viscous overstability and normal modes, impact clouds, and orbital evolution of embedded moons. Dense narrow rings are the primary natural laboratory for understanding shepherding and self-stability. Narrow dusty...

  9. P,O-Phosphinophenolate zinc(II) species: synthesis, structure and use in the ring-opening polymerization (ROP) of lactide, ε-caprolactone and trimethylene carbonate.

    Fliedel, Christophe; Rosa, Vitor; Alves, Filipa M; Martins, Ana M; Avilés, Teresa; Dagorne, Samuel


    The P,O-type phosphinophenol proligands (1·H, 2-PPh2-4-Me-6-Me-C6H2OH; 2·H, 2-PPh2-4-Me-6-(t)Bu-C6H2OH) readily react with one equiv. of ZnEt2 to afford in high yields the corresponding Zn(II)-ethyl dimers of the type [(κ(2)-P,O)Zn-Et]2 (3 and 4) with two μ-OPh bridging oxygens connecting the two Zn(II) centers, as determined by X-ray diffraction (XRD) studies in the case of 3. Based on diffusion-ordered NMR spectroscopy (DOSY), both species 3 and 4 retain their dimeric structures in solution. The alcoholysis reaction of Zn(II) alkyls 3 and 4 with BnOH led to the high yield formation of the corresponding Zn(II) benzyloxide species [(κ(2)-P,O)Zn-OBn]2 (5 and 6), isolated in a pure form as colorless solids. The centrosymmetric and dimeric nature of Zn(II) alkoxides 5 and 6 in solution was deduced from DOSY NMR experiments and multinuclear NMR data. Though the heteroleptic species 5 is stable in solution, its analogue 6 is instable in CH2Cl2 solution at room temperature to slowly decompose to the corresponding homoleptic species 8via the transient formation of (κ(2)-P,O)2Zn2(μ-OBn)(μ–κ(1):κ(1)-P,O) (6′). Crystallization of compound 6 led to crystals of 6′, as established by XRD analysis. The reaction of ZnEt2 with two equiv. of 1·H and 2·H allowed access to the corresponding homoleptic species of the type [Zn(P,O)2] (7 and 8). All gathered data are consistent with compound 7 being a dinuclear species in the solid state and in solution. Data for species 8, which bears a sterically demanding P,O-ligand, are consistent with a mononuclear species in solution. The Zn(II) alkoxide species 5 and the [Zn(P,O)2]-type compounds 7 and 8 were evaluated as initiators of the ring-opening polymerization (ROP) of lactide (LA), ε-caprolactone (ε-CL) and trimethylene carbonate (TMC). Species 5 is a well-behaved ROP initiator for the homo-, co- and ter-polymerization of all three monomers with the production of narrow disperse materials under living and immortal

  10. Theoretical studies on the regioselectivity of iridium-catalyzed 1,3-dipolar azide-alkyne cycloaddition reactions.

    Luo, Qiong; Jia, Guochen; Sun, Jianwei; Lin, Zhenyang


    Iridium-catalyzed cycloaddition of thioalkynes and bromoalkynes with azides have been investigated with the aid of density functional theory (DFT) calculations at the M06 level of theory. Our investigation focused on the different regioselectivity observed for the reactions of the two classes of alkynes. The DFT results have shown that the mechanisms of cycloaddition reactions using thioalkynes and bromoalkynes as substrates are similar yet different. The reactions of thioalkynes occur via a metallabicyclic Ir-carbene intermediate formed through alkyne-azide oxidative coupling via attack of the azide terminal nitrogen toward the β alkyne carbon, whose carbene ligand is stabilized by an alkylthio/arylthio substituent. Reductive elimination from the intermediate leads to the formation of the experimentally observed 5-sulfenyltriazole. In the reactions of bromoalkynes RC≡CBr, the reaction mechanism involves the initial formation of a six-membered-ring metallacycle intermediate in the oxidative coupling step. The six-membered-ring intermediate then undergoes isomerization via migrating the terminal azide nitrogen from the β carbon to the α carbon to form a much less stable metallabicyclic Ir-carbene species from which reductive elimination gives 4-bromotriazole.

  11. Ligand Design for Rh(III)-Catalyzed C–H Activation: An Unsymmetrical Cyclopentadienyl Enables a Regioselective Synthesis of Dihydroisoquinolones

    Hyster, Todd K.; Dalton, Derek M.


    We report the regioselective synthesis of dihydroisoquinolones from aliphatic alkenes and O-pivaloyl benzhydroxamic acids mediated by a Rh(III) precatalyst bearing sterically bulky substituents. While the prototypical Cp* ligand provides product with low selectivity, sterically bulky Cpt affords product with excellent regioselectivity for a range of benzhydroxamic acids and alkenes. Crystallographic evidence offers insight as to the source of the increased regioselectivity. PMID:25489470

  12. Planetary Rings

    Cuzzi, Jeffrey N.


    Just over two decades ago, Jim Pollack made a critical contribution to our understanding of planetary ring particle properties, and resolved a major apparent paradox between radar reflection and radio emission observations. At the time, particle properties were about all there were to study about planetary rings, and the fundamental questions were, why is Saturn the only planet with rings, how big are the particles, and what are they made of? Since then, we have received an avalanche of observations of planetary ring systems, both from spacecraft and from Earth. Meanwhile, we have seen steady progress in our understanding of the myriad ways in which gravity, fluid and statistical mechanics, and electromagnetism can combine to shape the distribution of the submicron-to-several-meter size particles which comprise ring systems into the complex webs of structure that we now know them to display. Insights gained from studies of these giant dynamical analogs have carried over into improved understanding of the formation of the planets themselves from particle disks, a subject very close to Jim's heart. The now-complete reconnaissance of the gas giant planets by spacecraft has revealed that ring systems are invariably found in association with families of regular satellites, and there is ark emerging perspective that they are not only physically but causally linked. There is also mounting evidence that many features or aspects of all planetary ring systems, if not the ring systems themselves, are considerably younger than the solar system

  13. Theoretical investigation on regioselectivity of aromatic ketones in the addition with olefin catalyzed by RuH2(CO)(PPh3)3


    Ab initio method is employed to study the structures of twelve aromatic ketones at HF/3-21G, HF/6-31G and HF/6-31G* levels, respectively. A theoretical analysis is also carried out to study the regioselectivity and reactivity of aromatic ketones in the addition with olefin catalyzed by RuH2(CO)(PPh3)3. The results indicate that a U shape LUMO conjugation of aromatic ketones in a plane plays an important role in regioselectivity on the cleavage of --C-H bond and is a necessary factor to success of addition with olefin, and that steric effect is an indispensable factor in forming additional ortho-product. Meanwhile, electronic effect may influence the rate of addition for the structures alike which only have different replacements in the same site of aromatic ring, such as furan, thiophene and pyrole. A possible catalytic reaction mechanism is proposed that the addition of C-H bond may be carried out by a coordination of aromatic ketones with Ru complex.

  14. Theoretical investigation on regioselectivity of aromatic ketones in the addition with olefin catalyzed by RuH2(CO)(PPh3)3

    雷鸣; 冯文林; 杜洪光; 徐振峰


    Ab initio method is employed to study the structures of twelve aromatic ketones at HF/3-21G, HF/6-31G and HF/6-31G levels, respectively. A theoretical analysis is also carried out to study the regioselectivity and reactivity of aromatic ketones in the addition with olefin catalyzed by RuH2(CO)(PPh3)3. The results indicate that a U shape LUMO conjugation of aromatic ketones in a plane plays an important role in regioselectivity on the cleavage of p C-H bond and is a nec-essary factor to success of addition with olefin, and that sterle effect is an indispensable factor in forming additional ortho-product. Meanwhile, electronic effect may influence the rate of addition for the structures alike which only have different replacements in the same site of aromatic ring, such as furan, thiophene and pyrole. A possible catalytic reaction mechanism is proposed that the addition of C-H bond may be carried out by a coordination of aromatic ketones with Ru complex.

  15. Reactivity of Tp(Me2) -supported yttrium alkyl complexes toward aromatic N-heterocycles: ring-opening or C-C bond formation directed by C-H activation.

    Yi, Weiyin; Zhang, Jie; Huang, Shujian; Weng, Linhong; Zhou, Xigeng


    Unusual chemical transformations such as three-component combination and ring-opening of N-heterocycles or formation of a carbon-carbon double bond through multiple C-H activation were observed in the reactions of Tp(Me2) -supported yttrium alkyl complexes with aromatic N-heterocycles. The scorpionate-anchored yttrium dialkyl complex [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with 1-methylimidazole in 1:2 molar ratio to give a rare hexanuclear 24-membered rare-earth metallomacrocyclic compound [Tp(Me2) Y(μ-N,C-Im)(η(2) -N,C-Im)]6 (1; Im=1-methylimidazolyl) through two kinds of C-H activations at the C2- and C5-positions of the imidazole ring. However, [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with two equivalents of 1-methylbenzimidazole to afford a C-C coupling/ring-opening/C-C coupling product [Tp(Me2) Y{η(3) -(N,N,N)-N(CH3 )C6 H4 NHCHC(Ph)CN(CH3 )C6 H4 NH}] (2). Further investigations indicated that [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with benzothiazole in 1:1 or 1:2 molar ratio to produce a C-C coupling/ring-opening product {(Tp(Me2) )Y[μ-η(2) :η(1) -SC6 H4 N(CHCHPh)](THF)}2 (3). Moreover, the mixed Tp(Me2) /Cp yttrium monoalkyl complex [(Tp(Me2) )CpYCH2 Ph(THF)] reacted with two equivalents of 1-methylimidazole in THF at room temperature to afford a trinuclear yttrium complex [Tp(Me2) CpY(μ-N,C-Im)]3 (5), whereas when the above reaction was carried out at 55 °C for two days, two structurally characterized metal complexes [Tp(Me2) Y(Im-Tp(Me2) )] (7; Im-Tp(Me2) =1-methyl-imidazolyl-Tp(Me2) ) and [Cp3 Y(HIm)] (8; HIm=1-methylimidazole) were obtained in 26 and 17 % isolated yields, respectively, accompanied by some unidentified materials. The formation of 7 reveals an uncommon example of construction of a CC bond through multiple C-H activations.

  16. A computational insight into a metal mediated pathway for the ring-opening polymerization (ROP) of lactides by an ionic {(NHC)2Ag}(+)X(-) (X = halide) type N-heterocyclic carbene (NHC) complex.

    Stephen, Raji; Sunoj, Raghavan B; Ghosh, Prasenjit


    A metal mediated coordination-insertion pathway for the ring-opening polymerization (ROP) of L-lactide by an ionic {(NHC)(2)Ag}(+)X(-) (X = halide) type silver complex of N-heterocyclic carbene (NHC) has been investigated using the density functional theory (DFT) method. A clear insight into the lactide insertion process could be obtained by modeling two consecutive monomer addition steps with the first one mimicking chain initiation with the second representing a propagation step. In particular, in each of the cycles, the reaction initiates with the formation of a lactide coordinated species, [1+LL] and [2+LL] that transforms into a metal bound cyclic lactide intermediate, I([1+LL]→2) and I([2+LL]→3), which subsequently ring opens to give the lactide inserted products, 2 and 3. The estimated overall activation barrier for the initiation step is 42.0 kcal mol(-1) while the same for the propagation step is 31.5 kcal mol(-1). Studies on higher monomer insertions showed a decrease in the relative product energies as anticipated for an addition polymerization pathway.

  17. Azirinium ylides from α-diazoketones and 2H-azirines on the route to 2H-1,4-oxazines: three-membered ring opening vs 1,5-cyclization

    Nikolai V. Rostovskii


    Full Text Available Strained azirinium ylides derived from 2H-azirines and α-diazoketones under Rh(II-catalysis can undergo either irreversible ring opening across the N–C2 bond to 2-azabuta-1,3-dienes that further cyclize to 2H-1,4-oxazines or reversibly undergo a 1,5-cyclization to dihydroazireno[2,1-b]oxazoles. Dihydroazireno[2,1-b]oxazoles derived from 3-aryl-2H-azirines and 3-diazoacetylacetone or ethyl diazoacetoacetate are able to cycloadd to acetyl(methylketene generated from 3-diazoacetylacetone under Rh(II catalysis to give 4,6-dioxa-1-azabicyclo[3.2.1]oct-2-ene and/or 5,7-dioxa-1-azabicyclo[4.3.1]deca-3,8-diene-2-one derivatives. According to DFT calculations (B3LYP/6-31+G(d,p, the cycloaddition can involve two modes of nucleophilic attack of the dihydroazireno[2,1-b]oxazole intermediate on acetyl(methylketene followed by aziridine ring opening into atropoisomeric oxazolium betaines and cyclization. Azirinium ylides generated from 2,3-di- and 2,2,3-triaryl-substituted azirines give rise to only 2-azabuta-1,3-dienes and/or 2H-1,4-oxazines.

  18. N-heterocyclic carbene-induced zwitterionic ring-opening polymerization of ethylene oxide and direct synthesis of alpha,omega-difunctionalized poly(ethylene oxide)s and poly(ethylene oxide)-b-poly(epsilon-caprolactone) block copolymers.

    Raynaud, Jean; Absalon, Christelle; Gnanou, Yves; Taton, Daniel


    An N-heterocyclic carbene (NHC), namely, 1,3-bis-(diisopropyl)imidazol-2-ylidene (1), was demonstrated to bring about the metal-free ring-opening polymerization of ethylene oxide at 50 degrees C in dimethyl sulfoxide, in absence of any other reagents. Poly(ethylene oxide) (PEO) of polydispersities ethylene oxide to form a zwitterionic species, namely 1,3-bis-(diisopropyl)imidazol-2-ylidinium alkoxide, that further propagates by a zwitterionic ring-opening polymerization (ZROP) mechanism. Through an appropriate choice of terminating agent NuH or NuSiMe(3) at the completion of the polymerization, a variety of end-functionalized PEO chains could be generated. In particular, alpha,omega-bis(hydroxy)-telechelic PEO, alpha-benzyl,omega-hydroxy, and alpha-azido,omega-hydroxy-difunctionalized PEOs were synthesized by NHC (1)-initiated ZROP, using H(2)O, PhCH(2)OH, and N(3)SiMe(3) as terminating agent, respectively. Characterization of these alpha,omega-difunctionalized PEOs by techniques such as (1)H NMR spectroscopy, MALDI-TOF spectrometry, and size exclusion chromatography confirmed the quantitative introduction of functional groups at both alpha and omega positions of the PEO chains and the formation of very narrow molar mass polymers. Finally, the synthesis of a poly(ethylene oxide)-b-poly(epsilon-caprolactone) diblock copolymer by sequential ZROP of the corresponding monomers was successfully achieved using (1) as organic initiator without isolation of the PEO block intermediate.


    Rajesh G


    Full Text Available Supra mitral ring is a rare cause for congenital mitral valve obstr uction. The reported incidence of supramitral ring is 0.2-0.4% in general population and 8% in patients with congenital mitral valve disease. The condition is characterized by an abnormal ridge of connective tissue often circumferential in shape ,on the atrial side of the mitral valve encroaching on the orifice of the mitral valve. It may adhere to the leaflets of the valve and restrict their movements. Although a supramitral ring may be rarely nonobstructive, it often results in mitral valve inflow obstruction.

  20. Enzyme-Catalyzed Regioselective Modification of Starch Nanoparticles

    Chakraborty, Soma [Polytechnic Univ., Brooklyn, NY (United States). National Science Foundation (NSF) Center for Biocatalysis and Bioprocessing of Macromolecules, Othmer Dept. of Chemical and Biological Science and Engineering; Sahoo, Bishwabhusan [Polytechnic Univ., Brooklyn, NY (United States). National Science Foundation (NSF) Center for Biocatalysis and Bioprocessing of Macromolecules, Othmer Dept. of Chemical and Biological Science and Engineering; Teraoka, Iwao [Polytechnic Univ., Brooklyn, NY (United States). National Science Foundation (NSF) Center for Biocatalysis and Bioprocessing of Macromolecules, Othmer Dept. of Chemical and Biological Science and Engineering; Miller, Lisa M. [Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source (NSLS); Gross, Richard A. [Polytechnic Univ., Brooklyn, NY (United States). National Science Foundation (NSF) Center for Biocatalysis and Bioprocessing of Macromolecules, Othmer Dept. of Chemical and Biological Science and Engineering


    The selective esterification of starch nanoparticles was performed using as catalyst Candida antartica Lipase B (CAL-B) in its immobilized (Novozym 435) and free (SP-525) forms. The starch nanoparticles were made accessible for acylation reactions by formation of Aerosol-OT (AOT, bis(2-ethylhexyl)sodium sulfosuccinate) stabilized microemulsions. Starch nanoparticles in microemulsions were reacted with vinyl stearate, ε-caprolactone, and maleic anhydride at 40 °C for 48 h to give starch esters with degrees of substitution (DS) of 0.8, 0.6, and 0.4, respectively. Substitution occurred regioselectively at the C-6 position of the glucose repeat units. Infrared microspectroscopy (IRMS) revealed that AOT-coated starch nanoparticles diffuse into the outer 50 μm shell of catalyst beads. Thus, even though CAL-B is immobilized within a macroporous resin, CAL-B is sufficiently accessible to the starch nanoparticles. When free CAL-B was incorporated along with starch within AOT-coated reversed micelles, CAL-B was also active and catalyzed the acylation with vinyl stearate (24 h, 40 °C) to give DS = 0.5. After removal of surfactant from the modified starch nanoparticles, they were dispersed in DMSO or water and were shown to retain their nanodimensions.

  1. Regioselective trans-cis photoisomerization of m-styrylstilbenes

    Ito, Y.; Uozy, Y.; Dote, T.; Ueda, M.; Matsuura, T.


    Trans-cis photoisomerization of m-styrylstilbenes, i.e., 2,4,6-triisopropyl-3'-styrylstilbene (TISS), 2,4,6-trimethyl-3'-styrylstilbene (TMSS), and 3-styrylstilbene (SS), and of stilbenes, i.e., 2,4,6-triisopropylstilbene (TIS), 2,4,6-trimethylstilbene (TMS), and stilbene (S), are studied under direct of benzophenone-sensitized irradiation in hexane. Measurements of quantum yields of isomerization have revealed that although the styrylstilbene molecule bears two styryl groups, the reaction is highly regioselective, depending upon the excitation conditions and reactant structures. For example, isomerization of trans, trans-TISS and trans,cis-TISS occurred either at the 2,4,6-trisubstituted styryl side upon direct excitation or at the unstubstituted styryl side upon sensitized excitation. When the starting material carries an unsubstituted cis-styryl group, the major isomerization always occurred at this moiety by either direct or sensitized excitation, e.g., cis,trans-TISS ..-->.. trans,trans-TISS, cis,cis-TISS ..-->.. trans,cis-TISS, and cis,trans-SS ..-->.. trans,trans-SS. Furthermore, the photoisomerization of cis,cis-SS was found to be one-way. These results are interpreted in terms of the usual energy sink concept: the excited-state energies (E/sub S/ and E/sub T/) of the stilbene chromophores depend on molecular distortion in a subtle manner.

  2. Regioselective immobilization of short oligonucleotides to acrylic copolymer gels.

    Timofeev, E; Kochetkova, S V; Mirzabekov, A D; Florentiev, V L


    Four types of polyacrylamide or polydimethyl-acrylamide gels for regioselective (by immobilization at the 3' end) of short oligonucleotides have been designed for use in manufacturing oligonucleotide microchips. Two of these supports contain amino or aldehyde groups in the gel, allowing coupling with oligonucleotides bearing aldehyde or amino groups, respectively, in the presence of a reducing agent. The aldehyde gel support showed a higher immobilization efficiency relative to the amino gel. Of all reducing agents tested, the best results were obtained with a pyridine-borane complex. The other supports are based on an acrylamide gel activated with glutaraldehyde or a hydroxyalkyl-functionalized gel treated with mesyl chloride. The use of dimethylacrylamide instead of acrylamide allows subsequent gel modifications in organic solvents. All the immobilization methods are easy and simple to perform, give high and reproducible yields, allow long durations of storage of the activated support, and provide high stability of attachment and low non-specific binding. Although these gel supports have been developed for preparing oligonucleotide microchips, they may be used for other purposes as well. PMID:8774893

  3. Regioselective sulfation of Artemisia sphaerocephala polysaccharide: Characterization of chemical structure.

    Wang, Junlong; Yang, Wen; Wang, Jiancheng; Wang, Xia; Wu, Fang; Yao, Jian; Zhang, Ji; Lei, Ziqiang


    The biological activities of sulfated polysaccharides are related to the substitution positions of functional groups. In this study, regioselective sulfation of Artemisia sphaerocephala polysaccharides (SRSASP) was prepared by using triphenylchloromethane (TrCl) as protecting precursor. FT-IR spectra and X-ray photoelectron spectroscopy (XPS) showed that SO(3-) group (S(6+), high binding energy of 168.7eV) was widely present in sulfated polysaccharides. (13)C NMR spectroscopy showed that C-2 and C-3 substitution was occurred but not fully sulfation. Meanwhile, C-6 substituted signals near 65ppm were not observed. The degree of substitution varied from 0.44 to 0.63 in SRSASP which could be attributed to the low reactivity at secondary hydroxyl. Monosaccharide composition result showed a decrease in the ratio of mannose/glucose, indicating the change of chemical composition in sulfated polysaccharides. In size-exclusion chromatograph analysis, a decrease in molecular weight and broadening of molecular weight distribution of sulfated polysaccharides was also observed. It could be attributed to the hydrolysis of polysaccharide in the sulfated reaction.

  4. Interactive Visualization of Shadow Effects in the Planetary System of Saturn, its Rings and its Moons using an OpenGL Shader in IDL

    Fajardo Hernandez, E. M.; Pomarède, D.


    The planetary system of Saturn, its rings and its moons is a fantastic playground where physicists are confronting theories and observations. Since its insertion into orbit in 2004, the Cassini-Huygens spacecraft has returned a wealth of high-resolution images and data that calls for the development of dedicated interactive, immersive, three-dimensional, multi-purpose analysis and visualization tools. Alongside with observations, numerical simulations also provide new insights into the fundamental processes at stake in the formation of this system. The SDvision graphical interface, developed in the context of IDL Object Graphics and intended primarily for the visualization of complex and massive astrophysical plasma simulations, has been extended to provide an interactive visualization of both numerical simulations and observations of Saturn, its rings, and its moons. One major missing feature of IDL Object Graphics is the ability to render shadow effects at all. We have overcome this limitation by developing a custom GLSL Shader that is invoked by IDL objects. This Shader, based on purely geometrical computations, is fast and allows for seamless exploratory visualization of the planetary system.

  5. Determinantal rings

    Bruns, Winfried


    Determinantal rings and varieties have been a central topic of commutative algebra and algebraic geometry. Their study has attracted many prominent researchers and has motivated the creation of theories which may now be considered part of general commutative ring theory. The book gives a first coherent treatment of the structure of determinantal rings. The main approach is via the theory of algebras with straightening law. This approach suggest (and is simplified by) the simultaneous treatment of the Schubert subvarieties of Grassmannian. Other methods have not been neglected, however. Principal radical systems are discussed in detail, and one section is devoted to each of invariant and representation theory. While the book is primarily a research monograph, it serves also as a reference source and the reader requires only the basics of commutative algebra together with some supplementary material found in the appendix. The text may be useful for seminars following a course in commutative ring theory since a ...

  6. Cave Rings


    hypothesis, that cave rings are formed in the same manner as coffee rings[3], that is, due to the enhanced deposition at the edges of sessile drops ...ring’ is the deposit formed when a sessile drop of a solution containing dissolved particles, such as coffee or salt, dries. This was investigated by...who expanded on Deegan et al.[3] to find an exact form for the evaporation flux over a sessile drop . It turns out that solving 179 for the flux is

  7. Vascular rings.

    Backer, Carl L; Mongé, Michael C; Popescu, Andrada R; Eltayeb, Osama M; Rastatter, Jeffrey C; Rigsby, Cynthia K


    The term vascular ring refers to congenital vascular anomalies of the aortic arch system that compress the esophagus and trachea, causing symptoms related to those two structures. The most common vascular rings are double aortic arch and right aortic arch with left ligamentum. Pulmonary artery sling is rare and these patients need to be carefully evaluated for frequently associated tracheal stenosis. Another cause of tracheal compression occurring only in infants is the innominate artery compression syndrome. In the current era, the diagnosis of a vascular ring is best established by CT imaging that can accurately delineate the anatomy of the vascular ring and associated tracheal pathology. For patients with a right aortic arch there recently has been an increased recognition of a structure called a Kommerell diverticulum which may require resection and transfer of the left subclavian artery to the left carotid artery. A very rare vascular ring is the circumflex aorta that is now treated with the aortic uncrossing operation. Patients with vascular rings should all have an echocardiogram because of the incidence of associated congenital heart disease. We also recommend bronchoscopy to assess for additional tracheal pathology and provide an assessment of the degree of tracheomalacia and bronchomalacia. The outcomes of surgical intervention are excellent and most patients have complete resolution of symptoms over a period of time. Copyright © 2016 Elsevier Inc. All rights reserved.

  8. Regioselective one-pot protection and protection-glycosylation of carbohydrates.

    Wang, Cheng-Chung; Zulueta, Medel Manuel L; Hung, Shang-Cheng


    Deciphering the roles and structure-activity relationships of carbohydrates in biological processes requires access to sugar molecules of confirmed structure and high purity. Chemical synthesis is one of the best ways to obtain such access. However, the synthesis of carbohydrates has long been impeded by two major challenges--the regioselective protection of the polyol moiety of each monosaccharide building block and the stereoselective glycosylation to produce oligosaccharides of desired length. Here, we review the development of the first regioselective protection-glycosylation and a revolutionary regioselective combinatorial one-pot protection of monosaccharides that can be used to differentiate the various hydroxy groups of monosaccharides with a vast array of orthogonal protective groups in one-pot procedures.

  9. 六氟双酚A环状聚酯二聚体的开环聚合与表征%Characterization and ring- opening polymerization of cyclic aryl ester dimer containing hexafluoroisopropylidene unit

    郭庆中; 刘闯; 陆慧; 胡双锋


    采用界面缩聚反应,“假高稀”条件下,以六氟双酚A和邻苯二甲酰氯为单体,十六烷基三甲基溴化铵为相转移催化剂,合成了一种新型结构的芳香环状聚酯二聚体,利用MALDI-TOF-MS,NMR,FTIR,DSC等手段对其结构进行了表征.环状聚酯二聚体在阴离子引发剂苯甲酸钠的存在下,成功进行了熔融开环聚合,得到了线性高分子量的聚酯,其Tg为162.4℃,5%热失重温度为384℃.对环状聚酯熔融开环聚合过程的流变行为进行监测,结果表明,在开环聚合的引发阶段,熔融体的粘度低于10 Pa·S且增长缓慢,超过引发阶段,粘度快速增长.%Under pseudo -high dilution conditions, a kind of cyclic aryl ester dimer has been synthesized from phthaloyl dichloride and 4,4'-(hexafluoroisopropylidene) diphenol via interfacial polycondensation reaction. Detailed structural characterization of the cyclic dimer confirmed the cyclic nature by a combination of MALDI - TOF - MS, IR and 1 H NMR analyses. The cyclic dimer readily undergoes anionic ring - opening polymerization in the melt by using sodium benzoate as the initiator, producing linear, high molecular weight polyester with T, of 162. 4 ℃ and excellent thermal stability. Moreover, the isothermal chemorheology of the ring - opening polymerization of cyclic dimer is also investigated. The results show that the shear viscosity of the molten reactive mixture increases slowly and is lower than 10 Pa·S at a constant shear rate of 0. 05 S-1 in the initial stage of ring - opening polymerization and the viscosity increases dramatically after the initial stage.

  10. Cyclometallated ruthenium(II) carbonyl complexes with 1-pyrenaldehyde 4-R-3-thiosemicarbazones: Regioselective ruthenation of the 1-pyrenyl group

    Rupesh Narayana Prabhu; Samudranil Pal


    A facile method for the synthesis of a series of cyclometallated ruthenium(II) carbonyl complexes with 1-pyrenaldehyde 4-R-3-thiosemicarbazones (H2Ln where the two H’s represent the dissociable thioamide and pyrenyl protons; R = H, Me and Ph) has been described. The characterization of the complexes having the general molecular formula trans-[Ru(Ln)(CO)(EPh33)2] (where E = P or As) were accomplished by elemental (CHN) analysis, magnetic susceptibility and spectroscopic (ESI-MS, IR, UV-Vis, emission and 1H-NMR) measurements. Electronic spectra of the complexes display multiple strong absorptions in the range 440–224 nm due to intraligand transitions. All the complexes exhibit emission bands that are characteristic of ligand centred emissive states. X-ray diffraction studies with representative complexes reveal a pincer-like 5,5-membered fused chelate rings forming CNS coordination mode of the thiosemicarbazonate ligand (Ln)2− via regioselective activation of 1-pyrenyl ortho C–H and formation of a distorted octahedral C2NSE2 coordination sphere around the ruthenium(II) centre.

  11. Regioselective alkane hydroxylation with a mutant CYP153A6 enzyme

    Koch, Daniel J.; Arnold, Frances H.


    Cytochrome P450 CYP153A6 from Myobacterium sp. strain HXN1500 was engineered using in-vivo directed evolution to hydroxylate small-chain alkanes regioselectively. Mutant CYP153A6-BMO1 selectively hydroxylates butane and pentane at the terminal carbon to form 1-butanol and 1-pentanol, respectively, at rates greater than wild-type CYP153A6 enzymes. This biocatalyst is highly active for small-chain alkane substrates and the regioselectivity is retained in whole-cell biotransformations.

  12. Regioselective Benzoylation of Diols and Carbohydrates by Catalytic Amounts of Organobase

    Yuchao Lu


    Full Text Available A novel metal-free organobase-catalyzed regioselective benzoylation of diols and carbohydrates has been developed. Treatment of diol and carbohydrate substrates with 1.1 equiv. of 1-benzoylimidazole and 0.2 equiv. of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU in MeCN under mild conditions resulted in highly regioselective benzoylation for the primary hydroxyl group. Importantly, compared to most commonly used protecting bulky groups for primary hydroxyl groups, the benzoyl protective group offers a new protection strategy.

  13. Regioselective One-Pot Synthesis of Triptycenes via Triple-Cycloadditions of Arynes to Ynolates.

    Umezu, Satoshi; Dos Passos Gomes, Gabriel; Yoshinaga, Tatsuro; Sakae, Mikei; Matsumoto, Kenji; Iwata, Takayuki; Alabugin, Igor; Shindo, Mitsuru


    We developed the novel one-pot synthetic method of substituted triptycenes by the reaction of ynolates and arynes. This four-step process involves three cycloadditions and electrocyclic ring opening of the strained Dewar anthracene. Each of the three related but structurally distinct classes of nucleophiles (ynolate, enolate, and anthracenolate) reacts with o-benzyne in the same predictable manner controlled by chelation and negative hyperconjugation. The resulting functionalized C3 -symmetrical triptycenes hold promise in the design of functional materials.

  14. Effects of a One Year Reusable Contraceptive Vaginal Ring on Vaginal Microflora and the Risk of Vaginal Infection: An Open-Label Prospective Evaluation.

    Yongmei Huang

    Full Text Available A contraceptive vaginal ring (CVR containing Nestorone® (NES and ethinyl estradiol (EE that is reusable for 1- year (13 cycles is under development. This study assessed effects of this investigational CVR on the incidence of vaginal infections and change in vaginal microflora.There were 120 women enrolled into a NES/EE CVR Phase III trial and a microbiology sub-study for up to 1- year of cyclic product use. Gynecological examinations were conducted at baseline, the first week of cycle 6 and last week of cycle 13 (or during early discontinuation visits. Vaginal swabs were obtained for wet mount microscopy, Gram stain and culture. The CVR was removed from the vagina at the last study visit and cultured. Semi-quantitative cultures for Lactobacillus, Gardnerella vaginalis, Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, anaerobic gram negative rods (GNRs, Candida albicans and other yeasts were performed on vaginal and CVR samples. Vaginal infections were documented throughout the study.Over 1- year of use, 3.3% of subjects were clinically diagnosed with bacterial vaginosis, 15.0% with vulvovaginal candidiasis, and 0.8% with trichomoniasis. The detection rate of these three infections did not change significantly from baseline to either Cycle 6 or 13. Nugent scores remained stable. H2O2-positive Lactobacillus dominated vaginal flora with a non-significant prevalence increase from 76.7% at baseline to 82.7% at cycle 6 and 90.2% at cycle 13, and a median concentration of 107 colony forming units (cfu per gram. Although anaerobic GNRs prevalence increased significantly, the median concentration decreased slightly (104 to 103cfu per gram. There were no significant changes in frequency or concentrations of other pathogens. High levels of agreement between vaginal and ring surface microbiota were observed.Sustained use of the NES/EE CVR did not increase the risk of vaginal infection and was not disruptive to the vaginal ecosystem

  15. Synthesis,structure and catalytic activity of complexes [Ln(EDBP)2(DME)Na(DME)3](Ln=Er,Yb,Sm) for ring-opening polymerization of ε-caprolactone


    Discrete ion-pair complexes [Ln(EDBP)2(DME)Na(DME)3] [Ln=Er (1), Yb (2), Sm (3)] have been synthesized by the reaction between sodium salt of 2,2’-ethylidene-bis(4,6-di-tert-butylphenol)(EDBPH2) and Ln(BH4)3·3THF (Ln=Er, Yb, Sm) followed by centrifugation and recrystalization. The complexes were characterized by elemental analysis and FT-IR, and the bonding model of these compounds was confirmed by X-ray single crystal diffraction for complex 1. It was found that four O atoms in two biphenol ligands as well as two O atoms in one ethylene glycol dimethyl ether (DME) molecule connect to the center rare earth metal atom, while sodium exists as counterpart cation to balance the charge. Complexes 1―3 can all be used as single component initiators for the ring-opening polymerization of ε-caprolactone.

  16. 1-n-Butyl-3-methylimidazolium-2-carboxylate: a versatile precatalyst for the ring-opening polymerization of ε-caprolactone and rac-lactide under solvent-free conditions

    Astrid Hoppe


    Full Text Available The ring-opening polymerization of ε-caprolactone (ε-CL and rac-lactide (rac-LA under solvent-free conditions and using 1-n-butyl-3-methylimidazolium-2-carboxylate (BMIM-2-CO2 as precatalyst is described. Linear and star-branched polyesters were synthesized by successive use of benzyl alcohol, ethylene glycol, glycerol and pentaerythritol as initiator alcohols, and the products were fully characterized by 1H and 13C{1H} NMR spectroscopy, gel permeation chromatography (GPC, and differential scanning calorimetry (DSC. BMIM-2-CO2 acts as an N-heterocyclic carbene precursor, resulting from in situ decarboxylation, either by heating under vacuo (method A or by addition of NaBPh4 (method B. Possible catalytic and deactivation mechanisms are proposed.

  17. Synthesis of Novel μ-Star Copolymers with Poly(N-Octyl Benzamide) and Poly(ε-Caprolactone) Miktoarms through Chain-Growth Condensation Polymerization, Styrenics-Assisted Atom Transfer Radical Coupling, and Ring-Opening Polymerization.

    Huang, Chih-Feng; Aimi, Junko; Lai, Kuan-Yu


    Star copolymers are known to phase separate on the nanoscale, providing useful self-assembled morphologies. In this study, the authors investigate synthesis and assembly behavior of miktoarm star (μ-star) copolymers. The authors employ a new strategy for the synthesis of unprecedented μ-star copolymers presenting poly(N-octyl benzamide) (PBA) and poly(ε-caprolactone) (PCL) arms: a combination of chain-growth condensation polymerization, styrenics-assisted atom transfer radical coupling, and ring-opening polymerization. Gel permeation chromatography, mass-analyzed laser desorption/ionization mass spectrometry, and (1) H NMR spectroscopy reveal the successful synthesis of a well-defined (PBA11 )2 -(PCL15 )4 μ-star copolymer (Mn,NMR ≈ 12 620; Đ = 1.22). Preliminary examination of the PBA2 PCL4 μ-star copolymer reveals assembled nanofibers having a uniform diameter of ≈20 nm.

  18. Pd/C-mediated synthesis of α-pyrone fused with a five-membered nitrogen heteroaryl ring: A new route to pyrano[4,3-c]pyrazol-4(1H-ones

    Dhilli Rao Gorja


    Full Text Available Pd/C-mediated alkynylation of 5-iodo-pyrazole-4-carboxylic acid, involving the first regioselective construction of α-pyrone ring on a pyrazol moiety via tandem coupling–cyclization process, has been developed to afford pyrano[4,3-c]pyrazol-4(1H-one in a single pot.

  19. Topological rings

    Warner, S


    This text brings the reader to the frontiers of current research in topological rings. The exercises illustrate many results and theorems while a comprehensive bibliography is also included. The book is aimed at those readers acquainted with some very basic point-set topology and algebra, as normally presented in semester courses at the beginning graduate level or even at the advanced undergraduate level. Familiarity with Hausdorff, metric, compact and locally compact spaces and basic properties of continuous functions, also with groups, rings, fields, vector spaces and modules, and with Zorn''s Lemma, is also expected.

  20. The combined contraceptive vaginal ring (NuvaRing) and endometrial histology.

    Bulten, J.; Grefte, J.M.M.; Siebers, A.G.; Dieben, T.


    We investigated the effects of NuvaRing on endometrial histology in a 2-year open-label, multicenter trial in 103 premenopausal women aged 18-35 years. Subjects received 26 cycles of treatment, each comprising 3 weeks of ring use followed by a 1-week ring-free period. Endometrial biopsies were taken

  1. Active site substitution A82W improves the regioselectivity of steroid hydroxylation by cytochrome P450 BM3 mutants as rationalized by spin relaxation nuclear magnetic resonance studies.

    Rea, V; Kolkman, A J; Vottero, E; Stronks, E J; Ampt, K A M; Honing, M; Vermeulen, N P E; Wijmenga, S S; Commandeur, J N M


    Cytochrome P450 BM3 from Bacillus megaterium is a monooxygenase with great potential for biotechnological applications. In this paper, we present engineered drug-metabolizing P450 BM3 mutants as a novel tool for regioselective hydroxylation of steroids at position 16β. In particular, we show that by replacing alanine at position 82 with a tryptophan in P450 BM3 mutants M01 and M11, the selectivity toward 16β-hydroxylation for both testosterone and norethisterone was strongly increased. The A82W mutation led to a ≤42-fold increase in V(max) for 16β-hydroxylation of these steroids. Moreover, this mutation improves the coupling efficiency of the enzyme, which might be explained by a more efficient exclusion of water from the active site. The substrate affinity for testosterone increased at least 9-fold in M11 with tryptophan at position 82. A change in the orientation of testosterone in the M11 A82W mutant as compared to the orientation in M11 was observed by T(1) paramagnetic relaxation nuclear magnetic resonance. Testosterone is oriented in M11 with both the A- and D-ring protons closest to the heme iron. Substituting alanine at position 82 with tryptophan results in increased A-ring proton-iron distances, consistent with the relative decrease in the level of A-ring hydroxylation at position 2β.

  2. Ring interferometry

    Malykin, Grigorii B; Zhurov, Alexei


    This monograph is devoted to the creation of a comprehensive formalism for quantitative description of polarized modes' linear interaction in modern single-mode optic fibers. The theory of random connections between polarized modes, developed in the monograph, allows calculations of the zero shift deviations for a fiber ring interferometer. The monograph addresses also the

  3. 1,5-Anhydro-D-fructose: regioselective acylation with fatty acids

    Lundt, Inge; Andersen, Søren Møller; Marcussen, Jan;


    Regioselective acylation of 1,5-anhydro-D-fructose was performed with dodecanoic acid to give 1,5-anhydro-6-O-dodecanoyl-D-fructose, chemically in 50% yield and enzymatically in quantitative yield. Quantitative conversions were also obtained using hexadecanoic and octadecanoic acids as acyl donors...

  4. Silver(Ⅰ) Oxide Mediated Regioselective Monoacylation of 2,4-Dihydroxyls in L-Rhamnopyranosides

    Qian YANG; Xing Mei ZHU; Jin Song YANG


    A series of acyls (Ac, Bz and Ts) were introduced regioselectively to the 2-hydroxyl in methyl and ally 3-O-benzyl-α-L-rhamnopyranosides mediated by silver(Ⅰ) oxide in the presence of a catalytic amount of potassium iodide in 56-78% yields.

  5. Regioselective and Stereoselective Synthesis of the 3-Aryl-4-phosphoryl-1, 2, 4-triazoline-5-ones

    De Xin FENG; Ru Yu CHEN; You HUANG


    A novel and efficient route of synthesizing 1, 2, 4-triazoline-5-ones is reported. The title compounds can be prepared in high yield and purity by the one-pot oxidation and cyclization of 1-acylthiosemicarbazides. The reaction is regioselective and stereoselective. The reaction condition is mild.

  6. Solvent-dependent regioselective oxidation of trans-chalcones using aqueous hydrogen peroxide

    Peng, Wang; Jiabin, Yang; Lushen, Li, E-mail: [Southeast University, Nanjing (China). School of Biological Science and Medical Engineering; Jin, Cai; Chunlong, Sun; Min, Ji [Southeast University, Nanjing (China). School of Chemistry and Chemical Engineering


    A novel method for regioselective oxidation of trans-chalcones with hydrogen peroxide in acetonitrile to afford cinnamic acids is reported. Only trans-b-arylacrylic acids were observed. A wide range of functionalized products can be effectively produced from various chalcones in good to excellent yields. (author)

  7. Regioselective Protection of the 4-Hydroxyl of 3,4-Dihydroxy-benzaldehyde

    Randy R. Spaetzel


    Full Text Available The regioselective protection of the 4-hydroxyl group of 3,4-dihydroxy-benzaldehyde was accomplished with seven different protecting groups (benzyl, p-methoxybenzyl, o-nitrobenzyl, 2,6-dichlorobenzyl, 3,4-dichlorobenzyl, vinyl and propargyl in yields ranging between 67-75%.

  8. A simple, effective, green method for regioselective 3-acylation of unprotected indoles

    Tran, Phuong Huong; Tran, Hai N.; Hansen, Poul Erik;


    A fast and green method is developed for regioselective acylation of indoles in the 3-position without the need for protection of the NH position. The method is based on Friedel-Crafts acylation using acid anhydrides. The method has been optimized, and Y(OTf)3 in catalytic amounts is found...

  9. Regioselective desymmetrization of diaryltetrahydrofurans via directed ortho-lithiation: an unexpected help from green chemistry.

    Mallardo, Valentina; Rizzi, Ruggiero; Sassone, Francesca C; Mansueto, Rosmara; Perna, Filippo M; Salomone, Antonio; Capriati, Vito


    An efficient functionalization of diaryltetrahydrofurans via a regioselective THF-directed ortho-lithiation is first described. This reaction can be successfully carried out in cyclopentyl methyl ether as a "greener" alternative to Et2O, with better results in terms of yield and selectivity and, surprisingly, also in protic eutectic mixtures competitively with protonolysis.

  10. Regioselective Wacker Oxidation of Internal Alkenes: Rapid Access to Functionalized Ketones Facilitated by Cross-Metathesis

    Morandi, Bill


    Wacka wacka: The title reaction makes use of a wide range of directing groups (DG) to enable the highly regioselective oxidation of alkenes, and occurs predictably at the distal position. Both E and Z alkenes afford valuable functionalized ketones and cross-metathesis was shown to facilitate the preparation of the starting materials. BQ=benzoquinone.

  11. Palladium-catalyzed regioselective decarboxylative alkylation of arenes and heteroarenes with aliphatic carboxylic acids.

    Premi, Chanchal; Dixit, Ankit; Jain, Nidhi


    An unprecedented Pd(OAc)2-catalyzed decarboxylative alkylation of unactivated arenes, with aliphatic carboxylic acids as inexpensive alkyl sources, is reported. The alkylation, controlled by the directing group, is regioselective, shows high functional group tolerance, and provides mild access to alkylated indolines, 2-phenylpyridines, and azobenzenes under solvent-free conditions in moderate to high yields.

  12. Regioselective silylation of pyranosides using a boronic acid/Lewis base co-catalyst system.

    Lee, Doris; Taylor, Mark S


    The combination of a boronic acid and a Lewis base, both employed in substoichiometric amounts, enables the regioselective silylation of cis-diol groups in alkylpyranoside substrates. The proposed mode of activation involves the formation of a tetracoordinate adduct that displays enhanced nucleophilicity at the boron-bound alkoxide groups.

  13. The regioselectivity of glutathione adduct formation with flavonoid quinone methides is pH-dependent

    Awad, H.M.; Boersma, M.G.; Boeren, S.; Vervoort, J.; Bladeren, van P.J.; Rietjens, I.M.C.M.


    In the present study, the formation of glutathionyl adducts from a series of 3',4'-dihydroxy flavonoid o-quinone/p-quinone methides was investigated with special emphasis on the regioselectivity of the glutathione addition as a function of pH. The flavonoid o-quinones were generated using

  14. The Origin of Anti-Markovnikov Regioselectivity in Alkene Hydroamination Reactions Catalyzed by [Rh(DPEphos)](.).

    Couce-Rios, Almudena; Lledós, Agustí; Ujaque, Gregori


    The development of regioselective anti-Markovnikov alkene's hydroamination is a long-standing goal in catalysis. The [Rh(COD)(DPEphos)](+) complex is the most general and regioselective group 9 catalyst for such a process. The reaction mechanism for intermolecular hydroamination of alkenes catalyzed by [Rh(DPEphos)](+) complex is analyzed by means of DFT calculations. Hydroamination (alkene vs. amine activation routes) as well as oxidative amination pathways are analyzed. According to the computational results the operating mechanism can be generally described by alkene coordination, amine nucleophilic addition, proton transfer through the metal center and reductive elimination steps. The mechanism for the formation of the oxidative amination side product goes via a β-elimination after the nucleophilic addition and metal center protonation steps. The origin of the regioselectivity for the addition process (Markovnikov vs. anti-Markovnikov additions) is shown to be not charge but orbitally driven. Remarkably, η(2) to η(1) slippage degree on the alkene coordination mode is directly related to the regioselective outcome.

  15. The regioselectivity of glutathione adduct formation with flavonoid quinone methides is pH-dependent

    Awad, H.M.; Boersma, M.G.; Boeren, S.; Vervoort, J.; Bladeren, van P.J.; Rietjens, I.M.C.M.


    In the present study, the formation of glutathionyl adducts from a series of 3',4'-dihydroxy flavonoid o-quinone/p-quinone methides was investigated with special emphasis on the regioselectivity of the glutathione addition as a function of pH. The flavonoid o-quinones were generated using horseradis

  16. Stannylene‐Mediated Regioselective 6‐O‐Glycosylation of Unprotected Phenyl 1‐Thioglycopyranosides

    Maggi, Agnese; Madsen, Robert


    A straightforward procedure is described for the synthesis of (1→6)‐linked saccharides by regioselective glycosylation of unprotected glycosyl acceptors. Phenyl 1‐thioglycopyranosides derived from D‐glucose, D‐galactose and D‐mannose were treated with dibutyltin oxide to introduce a stannylene...

  17. Regioselective synthesis of heteroaryl triflones by LDA (lithium diisopropylamide)-mediated anionic thia-Fries rearrangement.

    Xu, Xiu-Hua; Wang, Xin; Liu, Guo-kai; Tokunaga, Etsuko; Shibata, Norio


    Novel heteroaryl triflones including oxindole, pyrazolone, pyridine, and quinoline derivatives have been regioselectively synthesized by LDA-mediated thia-Fries rearrangement for the first time. These reactions are also the first examples of the application of anionic thia-Fries rearrangement in heteroaromatic compounds.

  18. Solvent-dependent regioselective oxidation of trans-chalcones using aqueous hydrogen peroxide


    A novel method for regioselective oxidation of trans-chalcones with hydrogen peroxide in acetonitrile to afford cinnamic acids is reported. Only trans-b-arylacrylic acids were observed. A wide range of functionalized products can be effectively produced from various chalcones in good to excellent yields.

  19. On SAP-rings

    Zhixiang, Wu


    The rings whose simple right modules are absolutely pure are called right $SAP$-rings. We give a new characterization of right $SAP$ rings, right $V$ rings, and von Neumann regular rings. We also obtain a new decomposition theory of right selfinjective von Neumann regular rings. The relationships between $SAP$-rings, $V$-rings, and von Neumann regular rings are explored. Some recent results obtained by Faith are generalized and the results of Wu-Xia are strengthened.

  20. Cavity Ring Down Absorption of O2 in Air as a Temperature Sensor for an Open and a Cryogenic Optical Cavity.

    Nyaupane, Parashu R; Perez-Delgado, Yasnahir; Camejo, David; Wright, Lesley M; Manzanares, Carlos E


    The A-band of oxygen has been measured at low resolution at temperatures between 90 K and 373 K using the phase shift cavity ring down (PS-CRD) technique. For temperatures between 90 K and 295 K, the PS-CRD technique presented here involves an optical cavity attached to a cryostat. The static cell and mirrors of the optical cavity are all inside a vacuum chamber at the same temperature of the cryostat. The temperature of the cell can be changed between 77 K and 295 K. For temperatures above 295 K, a hollow glass cylindrical tube without windows has been inserted inside an optical cavity to measure the temperature of air flowing through the tube. The cavity consists of two highly reflective mirrors which are mounted parallel to each other and separated by a distance of 93 cm. In this experiment, air is passed through a heated tube. The temperature of the air flowing through the tube is determined by measuring the intensity of the oxygen absorption as a function of the wavenumber. The A-band of oxygen is measured between 298 K and 373 K, with several air flow rates. To obtain the temperature, the energy of the lower rotational state for seven selected rotational transitions is linearly fitted to a logarithmic function that contains the relative intensity of the rotational transition, the initial and final rotational quantum numbers, and the energy of the transition. Accuracy of the temperature measurement is determined by comparing the calculated temperature from the spectra with the temperature obtained from a calibrated thermocouple inserted at the center of the tube. This flowing air temperature sensor will be used to measure the temperatures of cooling air at the input (cold air) and output (hot air) after cooling the blades of a laboratory gas turbine. The results could contribute to improvements in turbine blade cooling design.

  1. Classification, prediction, and verification of the regioselectivity of fungal polyketide synthase product template domains.

    Li, Yanran; Image, Image Image; Xu, Wei; Image, Image; Tang, Yi; Image, Image


    The fungal iterative nonreducing polyketide synthases (NRPKSs) synthesize aromatic polyketides, many of which have important biological activities. The product template domains (PT) embedded in the multidomain NRPKSs mediate the regioselective cyclization of the highly reactive polyketide backbones and dictate the final structures of the products. Understanding the sequence-activity relationships of different PT domains is therefore an important step toward the prediction of polyketide structures from NRPKS sequences and can enable the genome mining of hundreds of cryptic NRPKSs uncovered via genome sequencing. In this work, we first performed phylogenetic analysis of PT domains from NRPKSs of known functions and showed that the PT domains can be classified into five groups, with each group corresponding to a unique product size or cyclization regioselectivity. Group V contains the formerly unverified PT domains that were identified as C6-C11 aldol cyclases. The regioselectivity of PTs from this group were verified by product-based assays using the PT domain excised from the asperthecin AptA NRPKS. When combined with dissociated PKS4 minimal PKS, or replaced the endogenous PKS4 C2-C7 PT domain in a hybrid NRPKS, AptA-PT directed the C6-C11 cyclization of the nonaketide backbone to yield a tetracyclic pyranoanthraquinone 4. Extensive NMR analysis verified that the backbone of 4 was indeed cyclized with the expected regioselectivity. The PT phylogenetic analysis was then expanded to include approximately 100 PT sequences from unverified NRPKSs. Using the assays developed for AptA-PT, the regioselectivities of additional PT domains were investigated and matched to those predicted by the phylogenetic classifications.

  2. Ab Initio MO study on the nucleophilic oxirane ring opening of exo and endo Aflatoxin B{sub 1} 8,9-Oxide; Ekiso oyobi endo Aflatoxin B{sub 1} 8,9-Oxide no kyukaku kaikan hanno ni taisuru Ab Initio ho ni yoru kaiseki

    Okajima, Toshiya; Hashikawa, Akane [Saga University, Saga (Japan). Department of Chemistry


    The difference of the reactivity for S{sub N}2 type oxirane ring opening of exo and endo Aflatoxin B{sub 1} (AFB{sub 1}) 8,9-oxide (exo-1 and endo-1, respectively) was analyzed with ab initio molecular orbital theory. All stationary points including transition-state structures were optimized with no geometry constraint at the RHF/3-21G basis set, and energies were evaluate at Becke3LYP/3-21G level based on the RHF/3-21G geometries. The calculation clarified the following three points: (1) the activation energy ({delta}E{sup {ne}}) for endo attacking of NH{sub 3} molecule (the reaction with exo derivatives containing exo-1) is considerably smaller than those for exo attacking (the reaction with endo ones containing endo-1), (2) the reactivity for nucleophilic oxirane ring opening is controlled by the distortion of LUMO{sub C-O} of oxirane ring, which is probably caused by exo/endo relationship between oxirane ring and five-membered dihydrofurano ring (B) with respect to A ring, and (3) the remaining part (inclusing coumarin skeleton) of AFB{sub 1} oxid has little influence on the geometry around the reaction center and the activation energy. (author)

  3. Unusual Example of Chelate Ring Opening upon Coordination of the 9-Ethylguanine Nucleobase to [Pt(di-(6-methyl-2-picolyl)amine)Cl]Cl.

    Andrepont, Chase; Pakhomova, Svetlana; Marzilli, Patricia A; Marzilli, Luigi G


    Anticancer-active monofunctional Pt(II) complexes have bulky carrier ligands and bind to G residues in DNA, causing structural distortions. To gain fundamental chemical information on such monofunctional adducts, we assessed the 9-ethylguanine (9-EtG) adducts formed by [Pt(N(H)6,6'-Me2dpa)Cl]Cl (N(H)6,6'-Me2dpa = di-(6-methyl-2-picolyl)amine). 9-EtG added to [Pt(N(H)6,6'-Me2dpa)Cl]Cl to form not only the expected [Pt(N(H)6,6'-Me2dpa)(9-EtG)](2+) monoadduct having syn and anti conformers but also a [Pt(N(H)6,6'-Me2dpa)(9-EtG)2](2+) bisadduct consisting of ΛHT and ΔHT conformers (HT = head-to-tail). For both adducts, the two conformers exist as a dynamic equilibrium mixture. Concomitant with formation of the bisadduct, the binding mode of the N(H)6,6'-Me2dpa ligand converts from tridentate to bidentate. A Pt(II)-bound 6-methyl-2-picolyl chain and the secondary amine constitute the bidentate chelate ring. The other 6-methyl-2-picolyl chain is dangling. The secondary nitrogen is an asymmetric center, and each conformer exists as a racemic mixture of two enantiomers. For a given configuration at the secondary amine of the [Pt(N(H)6,6'-Me2dpa)(9-EtG)2](2+) adduct, the more abundant HT conformer can form a hydrogen bond between the NH of the bidentate ligand and the cis 9-EtG O6. [Pt(N(H)6,6'-Me2dpa)Cl]Cl forms the monoadduct in ∼1/20 the time for its parent, [Pt(N(H)dpa)Cl]Cl (N(H)dpa = di(2-picolyl)amine), which exhibited typical behavior in forming only a monoadduct. We attribute the unusual new findings for [Pt(N(H)6,6'-Me2dpa)Cl]Cl to Pt-N bond weakening induced by the steric bulk of 6/6'-Me groups. We hypothesize that undetectable intermediates with a dangling 6-methyl-2-picolyl chain facilitate both rapid monoadduct formation and also bisadduct formation. Consistent with the intermediacy of such species with a dangling chain, addition of HCl to a [Pt(N(H)6,6'-Me2dpa)Cl]Cl solution readily produced a dichloro complex with the N(H)6,6'-Me2dpa chelate ligand in

  4. Regioselective chromatic orthogonality with light-activated metathesis catalysts.

    Levin, Efrat; Mavila, Sudheendran; Eivgi, Or; Tzur, Eyal; Lemcoff, N Gabriel


    The ability to selectively guide consecutive chemical processes towards a preferred pathway by using light of different frequencies is an appealing concept. Herein we describe the coupling of two photochemical reactions, one the photoisomerization and consequent activation of a sulfur-chelated latent olefin-metathesis catalyst at 350 nm, and the other the photocleavage of a silyl protecting group at 254 nm. Depending on the steric stress exerted by a photoremovable neighboring chemical substituent, we demonstrate the selective formation of either five- or six-membered-ring frameworks by light-triggered ring-closing metathesis. The orthogonality of these light-induced reactions allows the initiation of these processes independently and in interchangeable order, according to the wavelength of light used to promote them.

  5. Regioselective synthesis of chiral dimethyl-bis(ethylenedithiotetrathiafulvalene sulfones

    Flavia Pop


    Full Text Available Enantiopure (R,R and (S,S-dimethyl-bis(ethylenedithiotetrathiafulvalene monosulfones have been synthesized by the aerial oxidation of the chiral dithiolates generated from the propionitrile-protected precursors. Both enantiomers crystallize in the orthorhombic chiral space group P212121. They show a boat-type conformation of the TTF moiety, a rather rigid dithiin sulfone ring and the methyl groups in a bisequatorial conformation. Cyclic voltammetry measurements indicate fully reversible oxidation in radical cation and dication species.

  6. Paramagnetic nuclear magnetic resonance relaxation and molecular mechanics studies of the chloroperoxidase-indole complex: insights into the mechanism of chloroperoxidase-catalyzed regioselective oxidation of indole.

    Zhang, Rui; He, Qinghao; Chatfield, David; Wang, Xiaotang


    To unravel the mechanism of chloroperoxidase (CPO)-catalyzed regioselective oxidation of indole, we studied the structure of the CPO-indole complex using nuclear magnetic resonance (NMR) relaxation measurements and computational techniques. The dissociation constant (KD) of the CPO-indole complex was calculated to be approximately 21 mM. The distances (r) between protons of indole and the heme iron calculated via NMR relaxation measurements and molecular docking revealed that the pyrrole ring of indole is oriented toward the heme with its 2-H pointing directly at the heme iron. Both KD and r values are independent of pH in the range of 3.0-6.5. The stability and structure of the CPO-indole complex are also independent of the concentration of chloride or iodide ion. Molecular docking suggests the formation of a hydrogen bond between the NH group of indole and the carboxyl O of Glu 183 in the binding of indole to CPO. Simulated annealing of the CPO-indole complex using r values from NMR experiments as distance restraints reveals that the van der Waals interactions were much stronger than the Coulomb interactions in the binding of indole to CPO, indicating that the association of indole with CPO is primarily governed by hydrophobic rather than electrostatic interactions. This work provides the first experimental and theoretical evidence of the long-sought mechanism that leads to the "unexpected" regioselectivity of the CPO-catalyzed oxidation of indole. The structure of the CPO-indole complex will serve as a lighthouse in guiding the design of CPO mutants with tailor-made activities for biotechnological applications.

  7. Regioselective Ethanolamination and Ketalization of 3-Ph-2,4-diacetyl(diethoxycarbonyl-5-hydroxy-5-methylcyclohexanones

    Vitaly V. Sorokin


    Full Text Available The reaction of 3-phenyl-2,4-diacetyl(diethoxycarbonyl-5-hydroxy-5-methylcyclohexanones with ethanolamine and ethylene glycol proceeds regioselectively using the carbonyl group of the alicycle to produce the corresponding cyclohexenylethanolamines and dioxolanes.


    黄吉玲; 克莱伯特·多诺; 马海燕; 钱延龙


    @@ The ring opening metathesis polymerization of cyclic monomers is relatively a newcomer to the field of polymer chemistry. Depending on the monomer and the catalyst used, this type of reaction yields a wide range of products that have found important industrial applications.

  9. Swern Oxidation of Bicyclo[2.2.1]hept-5-ene-2,3-diol and Its Pyrazine-fused Derivatives: An Improved Synthesis of Bicyclo[2.2.1]hept-5-ene-2,3-dione and An Unexpected Ring-Opening Reaction

    Sayuri Kobayashi


    Full Text Available An improved synthesis of bicyclo[2.2.1]hept-5-ene-2,3-dione by Swern oxidation of bicyclo[2.2.1]hept-5-ene-2,3-diol, and an unexpected ring-opening reaction by the Swern oxidation of pyrazine-fused congeners are described.


    颜明发; 王涛; 黄永凯; 强娜; 全大萍


    In order to study the structure and the catalytic activity of aliphatic tertiary amines, the ring-opening polymerizations of trimethylene carbonate ( TMC ) and L-lactide ( L-LA) were catalyzed by aliphatic tertiary amines,including triethylamine ( TEA) , N, N, N', N'-tetramethylethylenediamine ( TMEDA ) , 1, 1,4,7, 7-pentamethyldiethylenetriamine (PMDTA) and 4-( dimethylamino) pyridine (DMAP) , using benzyl alcohol as initiator in THF at 551. Studies revealed the catalytic activity of these tertiary amines was increased according to the order; TEA < TMEDA ≈ PMDTA < DMAP. The relationships of polymer molecular weight with the conversion of monomer were linear, which were consistent with a living polymerization character. Finally, the plausible polymerization pathway was through an alcohol-activating mechanism. Aliphatic tertiary amines which were abundant in source and cheap in price were suitable for catalyzing the ring-opening bulk polymerization of lactone in low temperature because of their low boiling point, being liquid under ordinary conditions and being easy to get rid of.%为研究脂肪叔胺结构对内酯开环聚合规律的影响,以三乙胺( TEA)、N,N,N′,N′-四甲基乙二胺(TMEDA)、N,N,N′,N″,N″-五甲基二亚乙基三胺(PM DTA)3种不同结构的叔胺催化碳酸三亚甲基酯(TMC)和左旋丙交酯( L-LA)开环聚合.结果显示,在55℃的THF溶液中,以苄醇为引发剂,3种叔胺均能催化TMC和L-LA的开环聚合,聚合物的分子量与单体转化率成线性关系,表现出活性聚合特征.三者催化能力为TEA< TMEDA<PMDTA.对聚合物进行端基分析发现聚合反应可能是一个由醇活化机理引发的过程.

  11. Chromatographic assessment of two hybrid monoliths prepared via epoxy-amine ring-opening polymerization and methacrylate-based free radical polymerization using methacrylate epoxy cyclosiloxane as functional monomer.

    Wang, Hongwei; Ou, Junjie; Lin, Hui; Liu, Zhongshan; Huang, Guang; Dong, Jing; Zou, Hanfa


    Two kinds of hybrid monolithic columns were prepared by using methacrylate epoxy cyclosiloxane (epoxy-MA) as functional monomer, containing three epoxy moieties and one methacrylate group. One column was in situ fabricated by ring-opening polymerization of epoxy-MA and 1,10-diaminodecane (DAD) using a porogenic system consisting of isopropanol (IPA), H2O and ethanol at 65°C for 12h. The other was prepared by free radical polymerization of epoxy-MA and ethylene dimethacrylate (EDMA) using 1-propanol and 1,4-butanediol as the porogenic solvents at 60°C for 12h. Two hybrid monoliths were investigated on the morphology and chromatographic assessment. Although two kinds of monolithic columns were prepared with epoxy-MA, their morphologies looked rather different. It could be found that the epoxy-MA-DAD monolith possessed higher column efficiencies (25,000-34,000plates/m) for the separation of alkylbenzenes than the epoxy-MA-EDMA monolith (12,000-13,000plates/m) in reversed-phase nano-liquid chromatography (nano-LC). Depending on the remaining epoxy or methacrylate groups on the surface of two pristine monoliths, the epoxy-MA-EDMA monolith could be easily modified with 1-octadecylamine (ODA) via ring-opening reaction, while the epoxy-MA-DAD monolith could be modified with stearyl methacrylate (SMA) via free radical reaction. The chromatographic performance for the separation of alkylbenzenes on SMA-modified epoxy-MA-DAD monolith was remarkably improved (42,000-54,000 plates/m) when compared with that on pristine epoxy-MA-DAD monolith, while it was not obviously enhanced on ODA-modified epoxy-MA-EDMA monolith when compared with that on pristine epoxy-MA-EDMA monolith. The enhancement of the column efficiency of epoxy-MA-DAD monolith after modification might be ascribed to the decreased mass-transfer resistence. The two kinds of hybrid monoliths were also applied for separations of six phenols and seven basic compounds in nano-LC. Copyright © 2014 Elsevier B.V. All

  12. Regioselective carbon–carbon bond formation of 5,5,5-trifluoro-1-phenylpent-3-en-1-yne

    Motoki Naka


    Full Text Available The regioselective carbon–carbon bond formation was studied using 5,5,5-trifluoro-1-phenylpent-3-en-1-yne as a model substrate, and predominant acceptance of electrophiles β to a CF3 group as well as a deuterium trap experiment of the lithiated species led to the conclusion that the obtained regioselectivity is kinetically determined for the reactions with electrophiles, under equilibration of the possible two anionic species.

  13. Molecular determinants of the regioselectivity of toluene/o-xylene monooxygenase from Pseudomonas sp. strain OX1.

    Notomista, Eugenio; Cafaro, Valeria; Bozza, Giuseppe; Di Donato, Alberto


    Bacterial multicomponent monooxygenases (BMMs) are a heterogeneous family of di-iron monooxygenases which share the very interesting ability to hydroxylate aliphatic and/or aromatic hydrocarbons. Each BMM possesses defined substrate specificity and regioselectivity which match the metabolic requirements of the strain from which it has been isolated. Pseudomonas sp. strain OX1, a strain able to metabolize o-, m-, and p-cresols, produces the BMM toluene/o-xylene monooxygenase (ToMO), which converts toluene to a mixture of o-, m-, and p-cresol isomers. In order to investigate the molecular determinants of ToMO regioselectivity, we prepared and characterized 15 single-mutant and 3 double-mutant forms of the ToMO active site pocket. Using the Monte Carlo approach, we prepared models of ToMO-substrate and ToMO-reaction intermediate complexes which allowed us to provide a molecular explanation for the regioselectivities of wild-type and mutant ToMO enzymes. Furthermore, using binding energy values calculated by energy analyses of the complexes and a simple mathematical model of the hydroxylation reaction, we were able to predict quantitatively the regioselectivities of the majority of the variant proteins with good accuracy. The results show not only that the fine-tuning of ToMO regioselectivity can be achieved through a careful alteration of the shape of the active site but also that the effects of the mutations on regioselectivity can be quantitatively predicted a priori.

  14. Novel Platinum Catalyzed Glycosylation Using 1,2-Cyclopropanated Sugars as Glycosyl Donors

    Beyer, Jürgen; Madsen, Robert


    By treating 1,2-cyclopropanated sugars with Zeise's dimer and an alcohol a regioselective ring opening of the cyclopropane takes place to give 2-C-alkyl-2-deoxy-glycosides......By treating 1,2-cyclopropanated sugars with Zeise's dimer and an alcohol a regioselective ring opening of the cyclopropane takes place to give 2-C-alkyl-2-deoxy-glycosides...

  15. Origami rings

    Buhler, Joe; de Launey, Warwick; Graham, Ron


    Motivated by a question in origami, we consider sets of points in the complex plane constructed in the following way. Let $L_\\alpha(p)$ be the line in the complex plane through $p$ with angle $\\alpha$ (with respect to the real axis). Given a fixed collection $U$ of angles, let $\\RU$ be the points that can be obtained by starting with $0$ and $1$, and then recursively adding intersection points of the form $L_\\alpha(p) \\cap L_\\beta(q)$, where $p, q$ have been constructed already, and $\\alpha, \\beta$ are distinct angles in $U$. Our main result is that if $U$ is a group with at least three elements, then $\\RU$ is a subring of the complex plane, i.e., it is closed under complex addition and multiplication. This enables us to answer a specific question about origami folds: if $n \\ge 3$ and the allowable angles are the $n$ equally spaced angles $k\\pi/n$, $0 \\le k < n$, then $\\RU$ is the ring $\\Z[\\zeta_n]$ if $n$ is prime, and the ring $\\Z[1/n,\\zeta_{n}]$ if $n$ is not prime, where $\\zeta_n := \\exp(2\\pi i/n)$ is ...

  16. Introduction: Special issue on planetary rings

    Nicholson, Philip; Esposito, Larry


    This issue of Icarus is devoted largely to papers presented at an open conference held at the Univ. of Colorado on 13-15 August 2014. This Planetary Rings Workshop is the fourth in a series organized by the Rings Working Group of the Cassini-Huygens mission and most of the papers presented dealt with phenomena revealed

  17. Gold-Catalyzed Ring Expansion of Alkynyl Heterocycles through 1,2-Migration of an Endocyclic Carbon-Heteroatom Bond.

    Chen, Ming; Sun, Ning; Xu, Wei; Zhao, Jidong; Wang, Gaonan; Liu, Yuanhong


    A mild and efficient gold-catalyzed oxidative ring-expansion of a series of alkynyl heterocycles using pyridine-N-oxide as the oxidant has been developed, which affords highly valuable six- or seven-membered heterocycles with wide functional group toleration. The reaction consists of a regioselective oxidation and a chemoselective migration of an endocyclic carbon-heteroatom bond (favored over C-H migration) with the order of migratory aptitude for carbon-heteroatom bonds being C-S>C-N>C-O. In the absence of an oxidant, polycyclic products are readily constructed through a ring-expansion/Nazarov cyclization reaction sequence.

  18. Cationic Ring Opening Polymerization of Octamethylcyclotetrasiloxane Initiated by Acid Treated Bentonite%酸白土催化体系开环八甲基环四硅氧烷的研究及机理探讨

    陈碧; 詹晓力; 易玲敏; 陈丰秋


    Cationic ring opening polymerization of octamethylcyclotetrasiloxane (D4) initiated by acid treated bentonite was investigated. The experimental conditions were chosen on the basis of preliminary experiments.Higher temperature was found beneficial for the reaction process while stirring intensity beyond a certain level showed no obvious effect on the reaction rate. Polymers were characterized by Fourier transform infrared, proton nuclear magnetic resonance (1H-NMR) and gel permeation chromotography. The width of molecular mass distribution was found ranging between 1.2 and 1.4, which is extraordinarily narrow compared with that of cationic polymerizations reported elsewhere (>1.9). The results were believed due to the absence of free proton and counter ion which simplifies the polymerization process and the huge steric hindrance provided by bentonite particles which keeps the propagation of polysiloxane onto the surface of bentonite particles in a much more regular way. A feasible mechanism is proposed and seems to be supported well by experiments. Additionally, from the results of α,ω-dihydrogen terminated polysiloxanes prepared, the possibility of applying this potential environmentally friendly heterogeneous catalyst in industrial polymerization of cyclosiloxanes is anticipated.

  19. DYZ-2-90, a novel neo-tanshinlactone ring-opened compound, induces ERK-mediated mitotic arrest and subsequent apoptosis by activating JNK in human colorectal cancer cells.

    Wang, Li-Ting; Pan, Shiow-Lin; Chen, Tzu-Hsuan; Dong, Yizhou; Lee, Kuo-Hsiung; Teng, Che-Ming


    Over the past several decades, there has been a considerable and still growing interest in discovering natural products with anticancer potential from traditional Chinese medicine and increasing their anticancer selectivity by chemical modification. In addition, total synthesis of active compounds from natural products can overcome problems related to poor resource availability. DYZ-2-90 is a novel ring-opened compound modified from neo-tanshinlactone, which is isolated from Chinese medicinal herb tanshen. Both in vitro and in vivo tubulin polymerization assays showed that DYZ-2-90 directly bound to microtubules and rapidly induced tubulin depolymerization, inducing ERK-mediated mitotic arrest and subsequent apoptosis by JNK activation in cancer cells, respectively. These results suggest that the fate of cells that undergo mitotic arrest is dictated by two competing networks activated by DYZ-2-90: the cytoprotective ERK pathway and the stress-related JNK pathway. DYZ-2-90 is therefore a novel microtubule-destabilizing agent and a new drug candidate for cancer therapy. This paper provides a new insight into the model of mitotic cell death, which was proposed in order to elucidate how cancer cells respond to microtubule-interfering agents and prolonged cell cycle delay.

  20. Ring Opening Metathesis Polymerization of Norbornene and Derivatives by the Triply Bonded Ditungsten Complex Na[W2(µ-Cl3Cl4(THF2]·(THF3

    Georgios Floros


    Full Text Available In this study, the reactions of the bimetallic compound Na[W2(µ-Cl3Cl4(THF2]·(THF3 (1, (W 3 W6+, a'2e'4 with norbornene (NBE and some of its derivatives (5-X-2-NBE; X = COOH (NBE–COOH, OH (NBE–OH, CN (NBE–CN, COOMe (NBE–COOMe, CH=CH2 (VNBE; norbornadiene (NBD are described. Complex 1 contains a tungsten–tungsten triple bond, bearing three halide bridges and two labile THF ligands, in a cisoidal relationship along the metal–metal axis. The complex was found to be a highly efficient room temperature homogeneous and heterogeneous unicomponent initiator for the catalytic ring opening metathesis polymerization (ROMP of most substrates. NBE provides polynorbornene (PNBE of high molecular weight (Mw in high yields, soluble in organic solvents. The reaction proceeds with high cis-stereoselectivity (80%–86% cis, independently of the reaction conditions. Strongly coordinating pendant groups (–COOH, –OH, –CN deactivate 1, whereas substrates bearing softer ones (–COOMe, –CH=CH2 are quantitatively polymerized. NBD gives quantitatively insoluble PNBD. The polymers have been characterized by 1H, 13C NMR and Size Exclusion Chromatography (SEC. Monitoring the reactions in situ by 1H NMR (1/NBD or NBE provides direct evidence of the metathetical nature of the polymerization with the observation of the active tungsten alkylidene propagating polymeric chains. Mechanistic aspects of the reactions are discussed.

  1. A Novel and Highly Regioselective Synthesis of New Carbamoylcarboxylic Acids from Dianhydrides

    Ochoa-Terán, Adrián; Estrada-Manjarrez, Jesús; Martínez-Quiroz, Marisela; Landey-Álvarez, Marco A.; Alcántar Zavala, Eleazar; Pina-Luis, Georgina; Santacruz Ortega, Hisila; Gómez-Pineda, Luis Enrique; Ramírez, José-Zeferino; Chávez, Daniel; Montes Ávila, Julio; Labastida-Galván, Victoria; Ordoñez, Mario


    A regioselective synthesis has been developed for the preparation of a series of N,N′-disubstituted 4,4′-carbonylbis(carbamoylbenzoic) acids and N,N′-disubstituted bis(carbamoyl) terephthalic acids by treatment of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (1) and 1,2,4,5-benzenetetracarboxylic dianhydride (2) with arylalkyl primary amines (A-N). The carbamoylcarboxylic acid derivatives were synthesized with good yield and high purity. The specific reaction conditions were established to obtain carbamoyl and carboxylic acid functionalities over the thermodynamically most favored imide group. Products derived from both anhydrides 1 and 2 were isolated as pure regioisomeric compounds under innovative experimental conditions. The chemo- and regioselectivity of products derived from dianhydrides were determined by NMR spectroscopy and confirmed by density functional theory (DFT). All products were characterized by NMR, FTIR, and MS. PMID:24511299

  2. A Novel and Highly Regioselective Synthesis of New Carbamoylcarboxylic Acids from Dianhydrides

    Adrián Ochoa-Terán


    Full Text Available A regioselective synthesis has been developed for the preparation of a series of N,N′-disubstituted 4,4′-carbonylbis(carbamoylbenzoic acids and N,N′-disubstituted bis(carbamoyl terephthalic acids by treatment of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (1 and 1,2,4,5-benzenetetracarboxylic dianhydride (2 with arylalkyl primary amines (A-N. The carbamoylcarboxylic acid derivatives were synthesized with good yield and high purity. The specific reaction conditions were established to obtain carbamoyl and carboxylic acid functionalities over the thermodynamically most favored imide group. Products derived from both anhydrides 1 and 2 were isolated as pure regioisomeric compounds under innovative experimental conditions. The chemo- and regioselectivity of products derived from dianhydrides were determined by NMR spectroscopy and confirmed by density functional theory (DFT. All products were characterized by NMR, FTIR, and MS.

  3. Chemo- and Regioselective Organo-Photoredox Catalyzed Hydroformylation of Styrenes via a Radical Pathway.

    Huang, He; Yu, Chenguang; Zhang, Yueteng; Zhang, Yongqiang; Mariano, Patrick S; Wang, Wei


    An unprecedented, chemo- and regioselective, organo-photoredox catalyzed hydroformylation reaction of aryl olefins with diethoxyacetic acid as the formylation reagent is described. In contrast to traditional transition metal promoted ionic hydroformylation reactions, the new process follows a unique photoredox promoted, free radical pathway. In this process, a formyl radical equivalent, produced from diethoxacetic acid through a dye (4CzIPN) photocatalyzed, sequential oxidation-decarboxylation route, regio- and chemoselectively adds to a styrene substrate. Importantly, under the optimized reaction conditions the benzylic radical formed in this manner is reduced by SET from the anion radical of 4CzIPN to generate a benzylic anion. Finally, protonation produces the hydroformylation product. By using the new protocol, aldehydes can be generated regioselectively in up to 90% yield. A broad array of functional groups is tolerated in the process, which takes place under mild, metal-free conditions.

  4. A high-yielding, strictly regioselective prebiotic purine nucleoside formation pathway.

    Becker, Sidney; Thoma, Ines; Deutsch, Amrei; Gehrke, Tim; Mayer, Peter; Zipse, Hendrik; Carell, Thomas


    The origin of life is believed to have started with prebiotic molecules reacting along unidentified pathways to produce key molecules such as nucleosides. To date, a single prebiotic pathway to purine nucleosides had been proposed. It is considered to be inefficient due to missing regioselectivity and low yields. We report that the condensation of formamidopyrimidines (FaPys) with sugars provides the natural N-9 nucleosides with extreme regioselectivity and in good yields (60%). The FaPys are available from formic acid and aminopyrimidines, which are in turn available from prebiotic molecules that were also detected during the Rosetta comet mission. This nucleoside formation pathway can be fused to sugar-forming reactions to produce pentosides, providing a plausible scenario of how purine nucleosides may have formed under prebiotic conditions.

  5. Regioselective modification of a xyloglucan hemicellulose for high-performance biopolymer barrier films.

    Kochumalayil, Joby J; Zhou, Qi; Kasai, Wakako; Berglund, Lars A


    Biobased polymers such as starch and hemicelluloses from wood are of interest for packaging applications, but suffer from limitations in performance under moist conditions. Xyloglucan from industrial tamarind seed waste offers potential, but its Tg is too high for thermal processing applications. Regioselective modification is therefore performed using an approach involving periodate oxidation followed by reduction. The resulting polymer structures are characterized using MALDI-TOF-MS, size-exclusion chromatography, FTIR and carbohydrate analysis. Films are cast from water and characterized by thermogravimetry, dynamic mechanical thermal analysis, dynamic water vapor sorption, oxygen transmission and tensile tests. Property changes are interpreted from structural changes. These new polymers show much superior performance to current petroleum-based polymers in industrial use. Furthermore, this regioselective modification can be carefully controlled, and results in a new type of cellulose derivatives with preserved cellulose backbone without the need for harmful solvents.

  6. A facile regioselective synthesis of novel spiroacenaphthene pyrroloisoquinolines through 1,3-dipolar cycloaddition reactions

    Sarrafi, Yaghoub; Asghari, Asieh; Sadatshahabi, Marzieh, E-mail: [Department of Organic Chemistry, Faculty of Chemistry, University of Mazandaran (Iran, Islamic Republic of); Hamzehloueian, Mahshid [Department of Chemistry, Jouybar Branch, Islamic Azad University, Jouybar (Iran, Islamic Republic of); Alimohammadi, Kamal [Department of Chemistry, Dr. Shariati Branch, University of Farhangian, Sari (Iran, Islamic Republic of)


    An efficient one-pot three-component procedure for the synthesis of novel spiroacenaphthene pyrroloisoquinolines with high regioselectivity is described. These compounds were prepared from 1,3-dipolar cycloaddition of an azomethine ylide generated from acenaphthenequinone and 1,2,3,4-tetrahydroisoquinoline via [1,5]-H shift, with chalcone and nitrostyrene derivatives as dipolarophiles. The structure and stereochemistry of the cycloadducts have been established by single crystal X-ray structure and spectroscopic techniques. (author)

  7. Highly Regioselective Palladium-Catalyzed Carboxylation of Allylic Alcohols with CO2.

    Mita, Tsuyoshi; Higuchi, Yuki; Sato, Yoshihiro


    Various allylic alcohols were carboxylated in the presence of a catalytic amount of PdCl2 and PPh3 using ZnEt2 as a stoichiometric transmetalation agent under a CO2 atmosphere (1 atm). This carboxylation proceeded in a highly regioselective manner to afford branched carboxylic acids predominantly. The β,γ-unsaturated carboxylic acid thus obtained was successfully converted into an optically active γ-butyrolactone, a known intermediate of (R)-baclofen.

  8. Regioselective synthesis and initial evaluation of a folate receptor targeted rhaponticin prodrug

    Xu Hua Liang; Yang Sun; Lu Sha Liu; Ying Yong Zhao; Xiao Yun Hu; Jun Fan


    To improve the therapeutic effect of rhaponticin (RHA),a folate receptor (FR) targeted RHA prodrug was designed and regioselectively synthesized by utilizing a hydrophilic peptide spacer linked to folic acid (FA) via a releasable disulfide linker.A series of biological evaluation was investigated in vitro and in vivo.The positive results of biological investigations warrant further preclinical study before this novel targeted chemotherapeutic is considered for clinical investigation.

  9. Stereo- and regio-selectivity in the photosensitized dimerization of 1, 3-dimethylthymine in solution

    HEI Xiaoming; SONG Qinhua; TANG Wenjian; WANG Hongbo; GUO Qingxiang; YU Shuqin


    The effects of reaction pathway and temperature on stereo- and regio-selectivity of photocycloaddition of 1, 3-dimethylthymine (DMT) which gives four cyclobutane type dimers in solution using acetone as the photosensitizer, are investigated by measuring the product distribution. It is demonstrated that the ground-state aggregation between DMT molecules mainly leads to (h-t)dimers, and the diffusion-controlled triplet dimerization is favorable to the formation of (h-h) dimers.

  10. Regioselective Synthesis and Base Catalyzed Transacylation of Substituted 1H-Pyrazole-4-carboxamides

    REN,Jun(任军); ZHANG,Xiao-Hong(张晓弘); LIU,Ying(刘莹); CHEN,Wei-Qiang(陈卫强); JIN,Gui-Yu(金桂玉)


    New type of substituted 1H-pyrazole-4-carboxamides were obtained by regioselective synthesis under the catalysis of different bases. The structures of the title compounds were confirmed by elemental analysis, 1H NMR, IR, MS and X-ray crystallogaphy. Compounds 1 were transacylated into their corresponding amides 3 in the presence of sodium hydride.Preliminary bioassays indicated that some compounds showed fungicidal activities against Rhizoctonia solani and Sclerotinia sclerotiorum.

  11. Iron-Catalyzed Regioselective Transfer Hydrogenative Couplings of Unactivated Aldehydes with Simple Alkenes.

    Zheng, Yan-Long; Liu, Yan-Yao; Wu, Yi-Mei; Wang, Yin-Xia; Lin, Yu-Tong; Ye, Mengchun


    An FeBr3 -catalyzed reductive coupling of various aldehydes with alkenes that proceeds through a direct hydride transfer pathway has been developed. With (i) PrOH as the hydrogen donor under mild conditions, previously challenging coupling reactions of unactivated alkyl and aryl aldehydes with simple alkenes, such as styrene derivatives and α-olefins, proceeded smoothly to furnish a diverse range of functionalized alcohols with complete linear regioselectivity.

  12. Regioselective protection of 10-deacetylbaccatin Ⅲ and semi-synthesis of paclitaxel

    Zhang Hu; Li Li Ou; Guo Lin Zhang; Yong Ping Yu


    Semi-synthesis of paclitaxel was achieved in four steps from 10-deacetylbaccatin Ⅲ (10-DAB Ⅲ).The key steps are the regioselective protection at the hydroxyl group at C-7 of 10-DAB HI,using 1,1'-thiocarbonyldiimidazole as a selective reagent,and the deprotection of the protected paclitaxel with a mixture of p-toluenesulfonic acid and 0.1 mol/L aqueous hydrochloride.

  13. Highly Chemo- and Regioselective Reaction of Hydroxybenzenes in Acidic Ionic Liquid

    Guo, Hui; Zhuang, Yu Wei; Cao, Jian; Zhang, Guo Bao [High New Technology Research Center of Henan Academy of Sciences, Zhengzhou (China)


    Highly chemo- and regioselective reaction of hydroxybenzenes with α,β-unsaturated compounds in acidic ionic liquid l-butyl-3-methylimidazolium hydrogen sulphate ([BMIM]HSO{sub 4}) was reported for the first time. A series of oxa-Michael adducts and Friedel-Crafts alkylated products were synthesized with good yields. The acidic ionic liquid could be easily recycled for at least 5 times with only minor loss in activity.

  14. Rhodium-catalyzed intramolecular hydroarylation of 1-halo-1-alkynes: regioselective synthesis of semihydrogenated aromatic heterocycles.

    Murase, Hirohiko; Senda, Kousuke; Senoo, Masato; Hata, Takeshi; Urabe, Hirokazu


    The regioselective intramolecular hydroarylation of (3-halo-2-propynyl)anilines, (3-halo-2-propynyl) aryl ethers, or (4-halo-3-butynyl) aryl ethers was efficiently catalyzed by Rh2(OCOCF3)4 to give semihydrogenated aromatic heterocycles, such as 4-halo-1,2-dihydroquinolines, 4-halo-3-chromenes, or 4-(halomethylene)chromans, in good to excellent yields. Some synthetic applications taking advantage of the halo-substituents of the products are also illustrated.

  15. N-1 regioselective Michael-type addition of 5-substituted uracils to (2-hydroxyethyl acrylate

    Walczak Krzysztof Z


    Full Text Available Abstract N-1 regioselective Michael-type addition of 5-substituted uracils to (2-hydroxyethyl acrylate is presented. The reactions were performed in polar aprotic solvents and with avoidance of polymerization of acrylic substrate. The obtained adducts may serve as versatile substrates for further functionalization, e.g. into (3-uracil-1-ylpropanoic acids or transformations, with participation of hydroxyl group, into ester-conjugated acyclic nucleosides.

  16. A Scalable Method for Regioselective 3-Acylation of 2-Substituted Indoles under Basic Conditions

    Johansson, Karl Henrik; Urruticoechea, Andoni; Larsen, Inna


    Privileged structures such as 2-arylindoles are recurrent molecular scaffolds in bioactive molecules. We here present an operationally simple, high yielding and scalable method for regioselective 3-acylation of 2-substituted indoles under basic conditions using functionalized acid chlorides. The ....... The method shows good tolerance to both electron-withdrawing and donating substituents on the indole scaffold and gives ready access to a variety of functionalized 3-acylindole building blocks suited for further derivatization....

  17. Biphenyl metabolism by rat liver microsomes. Regioselective effects of inducers, inhibitors, and solvents

    Haugen, D.A.


    The effects of the inducers phenobarbital and 3-methylcholanthrene, the inhibitors 7,8-benzoflavone and 1-benzyl-imidazole, and the solvents methanol, acetone, and dimethyl sulfoxide on the 2-, 3-, and 4-hydroxylation of biphenyl and the O-de-ethylation of 7-ethoxycoumarin by rat liver microsomes were examined. Phenobarbital pretreatment primarily induced 2- and 3-hydroxylation, the latter most dramatically. 3-Methylcholanthrene pretreatment induced 2- and 3-hydroxylation to similar extents. The inhibitors and solvents had regioselective effects on biphenyl metabolism that were characteristic of the uninduced, phenobarbital-induced, and 3-methylcholanthrene-induced microsomes. The presence of multiple forms of cytochrome P-450 in uninduced microsomes is indicated by the regioselective effects of the solvents and the inhibitors. The 3-methylcholanthrene-dependent increases in 2- and 3-hydroxylation appear due to induction of a single form of cytochrome P-450, as indicated by similar dose-response relationships and similar changes in sensitivitty to the inhibitors. The phenobarbital-dependent increases in 2- and 3-hydroxylation appear due to the induction of two forms of cytochrome P-450, as indicated by different changes in sensitivity to the effects of dimethyl sulfoxide and 7,8-benzoflavone. The results indicate that examination of the regioselectivity of biphenyl metabolism is a useful approach for characterizing microsomal mono-oxygenases, and they suggest that the approach may also be useful in the characterization of purified mono-oxygenase systems. (JMT)

  18. Switching the Regioselectivity of a Cyclohexanone Monooxygenase toward (+)-trans-Dihydrocarvone by Rational Protein Design.

    Balke, Kathleen; Schmidt, Sandy; Genz, Maika; Bornscheuer, Uwe T


    The regioselectivity of the Baeyer-Villiger monooxygenase-catalyzed oxidation is governed mostly by electronic effects leading to the migration of the higher substituted residue. However, in some cases, substrate binding occurs in a way that the less substituted residue lies in an antiperiplanar orientation to the peroxy bond in the Criegee intermediate yielding in the formation of the "abnormal" lactone product. We are the first to demonstrate a complete switch in the regioselectivity of the BVMO from Arthrobacter sp. (CHMOArthro) as exemplified for (+)-trans-dihydrocarvone by redesigning the active site of the enzyme. In the designed triple mutant, the substrate binds in an inverted orientation leading to a ratio of 99:1 in favor of the normal lactone instead of exclusive formation of the abnormal lactone in case of the wild type enzyme. In order to validate our computational study, the beneficial mutations were successfully transferred to the CHMO from Acinetobacter sp. (CHMOAcineto), again yielding in a complete switch of regioselectivity.

  19. Regioselective oxidation of lauric acid by CYP119, an orphan cytochrome P450 from Sulfolobus acidocaldarius.

    Lim, Young-Ran; Eun, Chang-Yong; Park, Hyoung-Goo; Han, Songhee; Han, Jung-Soo; Cho, Kyoung Sang; Chun, Young-Jin; Kim, Donghak


    Archaebacteria Sulfolobus acidocaldarius contains the highly thermophilic cytochrome P450 enzyme (CYP119). CYP119 possesses stable enzymatic activity at up to 85 degrees C. However, this enzyme is still considered as an orphan P450 without known physiological function with endogenous or xenobiotic substrates. We characterized the regioselectivity of lauric acid by CYP119 using the auxiliary redox partner proteins putidaredoxin (Pd) and putidaredoxin reductase (PdR). Purified CYP119 protein showed a tight binding affinity to lauric acid (K(d)=1.1+/-0.1 microM) and dominantly hydroxylated (omega-1) position of lauric acid. We determined the steady-state kinetic parameters; k(cat) was 10.8 min(-1) and K(m) was 12 microM. The increased ratio to omega-hydroxylated production of lauric acid catalyzed by CYP119 was observed with increase in the reaction temperature. These studies suggested that the regioselectivity of CYP119 provide the critical clue for the physiological enzyme function in this thermophilic archaebacteria. In addition, regioselectivity control of CYP119 without altering its thermostability can lead to the development of novel CYP119-based catalysts through protein engineering.

  20. Transition metal-free intramolecular regioselective couplings of aliphatic and aromatic C-H bonds.

    Tian, Hua; Yang, Haijun; Zhu, Changjin; Fu, Hua


    Cross-dehydrogenative couplings of two different C-H bonds have emerged as an attractive goal in organic synthesis. However, achieving regioselective C-H activation is a great challenge because C-H bonds are ubiquitous in organic compounds. Actually, the regioselective couplings promoted by enzymes are a common occurrence in nature. Herein, we have developed simple, efficient and general transition metal-free intramolecular couplings of alphatic and aromatic C-H bonds. The protocol uses readily available aryl triazene as the radical initiator, cheap K2S2O8 as the oxidant, and the couplings were performed well with excellent tolerance of functional groups. Interestingly, α-carbon configuration of some amino acid residues in the substrates was kept after the reactions, and the couplings for substrates with substituted phenylalanine residues exhibited complete β-carbon diastereoselectivity for induction of the chiral α-carbon. Therefore, the present study should provide a novel strategy for regioselective cross-dehydrogenative couplings of two different C-H bonds.

  1. Regioselective acylation of pyridoxine catalyzed by immobilized lipase in ionic liquid

    Shu BAI; Mengyuan REN; Lele WANG; Yan SUN


    The regioselective acylation of pyridoxine cat-alyzed by immobilized lipase (Candida Antarctica) in 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) has been investigated,and compared with that in acetonitrile (ACN).The acetylation of pyridox-ine using acetic anhydride in [BMIM]PF6 gave compar-able conversion of pyridoxine to 5-monoacetyl pyridoxine with considerably higher regioselectivity (93%-95%) than that in ACN (70%-73%).Among the tested parameters,water activity (aw) and temperature have profound effects on the reaction performances in either [BMIM]PF6 or ACN.For the reaction in [BMIM] PF6,higher temperature (50℃-55℃) and lower aw (<0.01) are preferable conditions to obtain better con-version and regioselectivity.Mass transfer limitation and intrinsic kinetic from the ionic nature of ionic liquids (ILs) may account for a different rate-temper-ature profile and a lower velocity at lower temperature in [BMIM]PF6-mediated reaction.Moreover,consec-utive batch reactions for enzyme reuse also show that lipase exhibited a much higher thermal stability and bet-ter reusability in [BMIM]PF6 than in ACN,which repre-sents another advantage of ILs as an alternative to traditional solvents beyond green technology.

  2. Computational and Experimental Studies of Regioselective SNAr Halide Exchange (Halex) Reactions of Pentachloropyridine.

    Froese, Robert D J; Whiteker, Gregory T; Peterson, Thomas H; Arriola, Daniel J; Renga, James M; Shearer, Justin W


    The Halex reaction of pentachloropyridine with fluoride ion was studied experimentally and computationally with a modified ab initio G3MP2B3 method. The G3 procedure was altered, as the anionic transition state optimizations failed due to the lack of diffuse functions in the small 6-31G* basis set. Experimental Halex regioselectivities were consistent with kinetic control at the 4-position. The reverse Halex reaction of fluoropyridines with chloride sources was demonstrated using precipitation of LiF in DMSO as a driving force. Reverse Halex regioselectivity at the 4-position was predicted by computations and was consistent with kinetic control. Scrambling of halide ions between chlorofluoropyridines was catalyzed by n-Bu4PCl, and the products of these reactions were shown to result from a combination of kinetic and thermodynamic control. Comparison of the C-F and C-Cl homolytic bond dissociation energies suggests that an important thermodynamic factor which controls regioselectivity in this system is the weak C2-Cl bond. The differences between ΔH° values of chlorofluoropyridines can be explained by a combination of three factors: (1) the number of fluorine atoms in the molecule, (2) the number of fluorine atoms at the C2 and C6 positions, and (3) the number of pairs of fluorine atoms which are ortho to one another.

  3. Regioselectivity and Mechanism of Synthesizing N-Substituted 2-Pyridones and 2-Substituted Pyridines via Metal-Free C-O and C-N Bond-Cleaving of Oxazoline[3,2-a]pyridiniums

    Li, Bo; Xue, Susu; Yang, Yang; Feng, Jia; Liu, Peng; Zhang, Yong; Zhu, Jianming; Xu, Zhijian; Hall, Adrian; Zhao, Bo; Shi, Jiye; Zhu, Weiliang


    Novel intermediate oxazoline[3,2-a]pyridiniums were facilely prepared from 2-(2,2-dimethoxyethoxy)-pyridines via acid promoted intramolecular cyclization. Sequentially, the quaternary ammonium salts were treated with different nucleophiles for performing regioselective metal-free C-O and C-N bond-cleaving to afford prevalent heterocyclic structures of N-substituted pyridones and 2-substituted pyridines. The reaction mechanism and regioselectivity were then systematically explored by quantum chemistry calculations at B3LYP/6-31 g(d) level. The calculated free energy barrier of the reactions revealed that aniline and aliphatic amines (e.g., methylamine) prefer to attack C8 of intermediate 4a, affording N-substituted pyridones, while phenylmethanamine, 2-phenylethan-1-amine and 3-phenylpropan-1-amine favor to attack C2 of the intermediate to form 2-substituted pyridines. With the optimized geometries of the transition states, we found that the aromatic ring of the phenyl aliphatic amines may form cation-π interaction with the pyridinium of the intermediates, which could stabilize the transition states and facilitate the formation of 2-substituted pyridines. PMID:28120894

  4. Report of the eRHIC Ring-Ring Working Group

    Aschenauer, E. C. [Brookhaven National Lab. (BNL), Upton, NY (United States); Berg, S. [Brookhaven National Lab. (BNL), Upton, NY (United States); Blaskiewicz, M. [Brookhaven National Lab. (BNL), Upton, NY (United States); Brennan, M. [Brookhaven National Lab. (BNL), Upton, NY (United States); Fedotov, A. [Brookhaven National Lab. (BNL), Upton, NY (United States); Fischer, W. [Brookhaven National Lab. (BNL), Upton, NY (United States); Litvinenko, V. [Brookhaven National Lab. (BNL), Upton, NY (United States); Montag, C. [Brookhaven National Lab. (BNL), Upton, NY (United States); Palmer, R. [Brookhaven National Lab. (BNL), Upton, NY (United States); Parker, B. [Brookhaven National Lab. (BNL), Upton, NY (United States); Peggs, S. [Brookhaven National Lab. (BNL), Upton, NY (United States); Ptitsyn, V. [Brookhaven National Lab. (BNL), Upton, NY (United States); Ranjbar, V. [Brookhaven National Lab. (BNL), Upton, NY (United States); Tepikian, S. [Brookhaven National Lab. (BNL), Upton, NY (United States); Trbojevic, D. [Brookhaven National Lab. (BNL), Upton, NY (United States); Willeke, F. [Brookhaven National Lab. (BNL), Upton, NY (United States)


    This report evaluates the ring-ring option for eRHIC as a lower risk alternative to the linac-ring option. The reduced risk goes along with a reduced initial luminosity performance. However, a luminosity upgrade path is kept open. This upgrade path consists of two branches, with the ultimate upgrade being either a ring-ring or a linac-ring scheme. The linac-ring upgrade could be almost identical to the proposed linac-ring scheme, which is based on an ERL in the RHIC tunnel. This linac-ring version has been studied in great detail over the past ten years, and its significant risks are known. On the other hand, no detailed work on an ultimate performance ring-ring scenario has been performed yet, other than the development of a consistent parameter set. Pursuing the ring-ring upgrade path introduces high risks and requires significant design work that is beyond the scope of this report.

  5. 利用碳酸乙烯酯开环产物合成聚氨酯脲弹性体%Synthesis of Poly(urethane-urea)s Elastomers by Using Ring-opening Products of Ethylene Carbonate

    马彦龙; 朱晶心; 刘晓华


    二氧化碳的综合利用是关系人类生存环境的重大课题.采用二氧化碳的衍生物碳酸乙烯酯和1.6-己二胺开环反应合成脂肪族氨酯二醇,并将开环产物作为扩链剂与脂肪族聚碳酸酯二醇(PCDL)和异佛尔酮二异氰酸酯(IPDI)反应合成了脂肪族聚碳酸酯聚氨酯脲弹性体.研究表明,开环反应在38℃,反应10h后,可得到产率为89.9%(质量分数)的产物1.6-二(2-羟基-乙氧基羰基胺)已烷(DHDU).通过改变碳酸乙烯酯开环物(DHDU)在大分子链中形成的氨酯-脲硬段单元的比例,可以调节合成的聚氨酯脲弹性体的机械性能.当脂肪族聚碳酸酯二醇(PCDL)分子量相同时,随着PCDL/DHDU摩尔比的减小,合成的聚氨酯脲弹性体的拉伸强度和硬度增加,断裂伸长率减小.该合成产物在生物材料领域具有广泛的应用前景.%The comprehensive utilization of carbon dioxide is the major issue related to human and environment.In this paper,aliphatic urethane diols was firstly synthesized from ethylene carbonate,which is the derivative of carbon dioxide,and 1.6-diaminohexane.Then aliphatic polycarbonate poly(urethane-urea)s elastomers were synthesized from aliphatic polycarbonate diols (PCDL),isophoronodiisocyanate (IPDI),and the ring-oping product which was used as a chain extender.The results show that ring-opening product,1,6-bis(2-hydroxy-ethoxy carbonylaminohexane(DHDU),was obtained after reaction for 10 h at 38℃,with a yield of 89.9 wt%,and the mechanical propertie of poly(urethane-urea)s elastomers could be adjusted by changing the ratio of hard segments,which were the urethane and urea units formed by ring-oping product with IPDI,in polymer chains.As the molar ratio of PCDL to DHDU decreased,the tensile strength and hardness of elastomers increased and the elongation at break of elastomers decreased when the molecular weight of PCDL kept unchanged.The synthetic elastomer would have broad application prospects in the

  6. Prime rings with PI rings of constants

    Kharchenko, V K; Rodríguez-Romo, S


    It is shown that if the ring of constants of a restricted differential Lie algebra with a quasi-Frobenius inner part satisfies a polynomial identity (PI) then the original prime ring has a generalized polynomial identitiy (GPI). If additionally the ring of constants is semiprime then the original ring is PI. The case of a non-quasi-Frobenius inner part is also considered.

  7. Synthesis and structures of calcium and strontium 2,4-di-tert-butylphenolates and their reactivity towards the amine co-initiated ring-opening polymerisation of rac-lactide.

    Clark, Lawrence; Deacon, Glen B; Forsyth, Craig M; Junk, Peter C; Mountford, Philip; Townley, Josh P; Wang, Jun


    Calcium and strontium metals react with Hg(C6F5)2 and 2,4-di-tert-butylphenol (H-DBP) in tetrahydrofuran (THF) and 1,2-dimethoxyethane (DME) to give [Ca(DBP)2(THF)4] (1), [Ca2(DBP)4(DME)4(μ-DME)] (2), [Sr3(μ-DBP)6(THF)6] (3), and [Sr2(DBP)(μ-DBP)3(DME)3] (4). Compound 1 is a six coordinate trans-octahedral monomer, whereas in binuclear 2 two seven-coordinate Ca centres are bridged by a DME ligand. In 3 a central Sr is connected by three bridging DBP groups to each of two terminal Sr(THF)3 moieties, all metal atoms being six coordinate. Compound 4 has one six- and one seven-coordinate Sr, bridged by three DBP ligands, the former Sr also having a terminal DBP and a bidentate DME ligand and the latter two DME ligands. Complexes 2 and 4 act as ring-opening polymerisation (ROP) catalysts for the benzyl alcohol or benzylamine co-initiated ROP rac-lactide forming atactic alcohol- or amine-terminated polylactide H-[PLA]-XBn (X = O or NH) with reasonable control of molecular weight via an activated monomer propagation mechanism. Kinetic studies for BnNH2 found the unusual rate expression -d[LA]/dt = k(p(Ae))[2 or 4]0[rac-LA](2)[BnNH2]0(2.5) (k(p(Ca)) ≈ 1.7 ×k(p(Sr))). Preliminary studies suggest that [Y(DBP)3(THF)2] also catalyses amine or alcohol co-initiated ROP by an activated monomer mechanism without loss of a phenoxide ligand.

  8. Synthesis and structural determination of zinc complexes based on an anilido-aldimine ligand containing an O-donor pendant arm: zinc alkoxide derivative as an efficient initiator for ring-opening polymerization of cyclic esters.

    Wang, Chao-Hsiang; Li, Chen-Yu; Huang, Bor-Hunn; Lin, Chu-Chieh; Ko, Bao-Tsan


    Zinc complexes bearing the anilido-aldiminate AA(OMe) ligand (AA(OMe)-H = (E)-2,6-diisopropyl-N-(2-(((2-methoxyethyl)imino)methyl)phenyl)aniline) were synthesized in a stepwise method and were structurally characterized. The reaction of AA(OMe)-H (1) with one equivalent of diethyl zinc (ZnEt2) furnishes a three-coordinated and mononuclear zinc complex [(AA(OMe))ZnEt] (2). Further reaction of 2 with a stoichiometric amount of benzyl alcohol (BnOH) affords a four-coordinated and dinuclear zinc benzylalkoxide complex [(AA(OMe))Zn(μ-OBn)]2 (3). In the presence of two equivalents of AA(OMe)-H with ZnEt2, a homoleptic and four-coordinated zinc complex [(AA(OMe))2Zn] (4) is formed. The geometry around the zinc centres of 3 and 4 are both distorted tetrahedrals, while 2 adopts a different coordination mode with a slightly distorted trigonal planar geometry. The variable-temperature (1)H NMR studies of 3 illustrate that 3 exhibits a dinuclear structure in solution at low temperature as well as in the solid state. While raising the temperature, it drifts towards dissociation to form a mononuclear zinc benzylalkoxide species, which coexists in solution. The ring-opening polymerizations of ε-caprolactone (ε-CL) and β-butyrolactone (β-BL) catalyzed by complexes 3 and 4 are investigated. The ε-CL and β-BL polymerizations initiated by zinc alkoxide 3 were demonstrated to have living characteristics and to proceed in a controlled manner with narrow polydispersity indices (PDIs high monomer-to-initiator ratio (1200/1) initiated by 3 has also been reported.

  9. Radical theory of rings

    Gardner, JW


    Radical Theory of Rings distills the most noteworthy present-day theoretical topics, gives a unified account of the classical structure theorems for rings, and deepens understanding of key aspects of ring theory via ring and radical constructions. Assimilating radical theory's evolution in the decades since the last major work on rings and radicals was published, the authors deal with some distinctive features of the radical theory of nonassociative rings, associative rings with involution, and near-rings. Written in clear algebraic terms by globally acknowledged authorities, the presentation

  10. Regioselective Addition of Silyl Enolates to α,β-Unsaturated Aldehyde and its Acetal Catalyzed by MgI2 Etherate

    Xing Xian ZHANG; Wei Dong Z. LI


    Regioselective addition reactions of silyl enolates to α,β -unsaturated aldehyde and its acetal catalyzed by MgI2 etherate give aldol adducts (1, 2-addition) preferentially over Michael adducts (1, 4-addition). This unique regioselectivity is distinctly different with other Lewis acidic promoters and may be attributed to the high oxyphilicity of IMg+.

  11. Regioselectivity of the bromination of 1-oxo-1,2,3,4-tetrahydronaphthalene and 6,7-dimethyl-1-oxo-1,2,3,4-tetrahydronaphthalene, and thiabiscyclanones synthesis on their basis



    Full Text Available On the basis of quantum chemical (PM3 and RHF/6-31G* study, the regioselectivity of the bromination of 1-oxo-1,2,3,4-tetrahydronaphthalene (1 and 6,7-dimethyl-1-oxo-1,2,3,4-tetrahydronaphthalene (2 at their alicyclic and aromatic fragments was quantum chemically substantiated and confirmed experimentally. It was found that the above compounds undergo aromatic at the a-methylene position. The conditions for bromination at the positions 5, 8 of benzannelated ring were established. For the first time, non- and 2,2’-dibromosubstituted with respect to the oxo group bis(6,7-dimethyl-1-oxo-1,2,3,4-tetrahydronaphth-2-yl sulphides (7, 8a, b were obtained. The latter were found to show promise as stabilizing agents for the storage of cholera sera.

  12. Stirling engine piston ring

    Howarth, Roy B.


    A piston ring design for a Stirling engine wherein the contact pressure between the piston and the cylinder is maintained at a uniform level, independent of engine conditions through a balancing of the pressure exerted upon the ring's surface and thereby allowing the contact pressure on the ring to be predetermined through the use of a preloaded expander ring.

  13. Birth Control Ring

    ... Loss Surgery? A Week of Healthy Breakfasts Shyness Birth Control Ring KidsHealth > For Teens > Birth Control Ring A A A What's in this article? ... español Anillo vaginal anticonceptivo What Is It? The birth control ring is a soft, flexible, doughnut-shaped ring ...

  14. Actin Rings of Power.

    Schwayer, Cornelia; Sikora, Mateusz; Slováková, Jana; Kardos, Roland; Heisenberg, Carl-Philipp


    Circular or ring-like actin structures play important roles in various developmental and physiological processes. Commonly, these rings are composed of actin filaments and myosin motors (actomyosin) that, upon activation, trigger ring constriction. Actomyosin ring constriction, in turn, has been implicated in key cellular processes ranging from cytokinesis to wound closure. Non-constricting actin ring-like structures also form at cell-cell contacts, where they exert a stabilizing function. Here, we review recent studies on the formation and function of actin ring-like structures in various morphogenetic processes, shedding light on how those different rings have been adapted to fulfill their specific roles.

  15. Alternative loop rings

    Goodaire, EG; Polcino Milies, C


    For the past ten years, alternative loop rings have intrigued mathematicians from a wide cross-section of modern algebra. As a consequence, the theory of alternative loop rings has grown tremendously. One of the main developments is the complete characterization of loops which have an alternative but not associative, loop ring. Furthermore, there is a very close relationship between the algebraic structures of loop rings and of group rings over 2-groups. Another major topic of research is the study of the unit loop of the integral loop ring. Here the interaction between loop rings and group ri

  16. A Metal-Free Regioselective Multicomponent Approach for the Synthesis of Free Radical Scavenging Pyrimido-Fused Indazoles and Their Fluorescence Studies

    Jeyakannu Palaniraja


    Full Text Available This study deals with a new and efficient metal-free regioselective synthesis of pyrimido-fused indazoles with nitrogen ring junction motifs. We have developed a metal-free domino type reaction between 3-aminoindazole, aryl aldehydes and aceotophenones in the presence of KOH/DMF that leads to pyrimido[1,2-b]indazole analogues. Response Surface Methodology (RSM coupled with a Box-Behnken design (BBD were utilized for exploring the effect of base used (A, temperature of reaction (B and (C, reaction time. This approach can allow access to a variety of pyrimidoindazole fluorophores and related compounds. The compound N,N-dimethyl-4-(2-phenylpyrimido[1,2-b]indazol-4-ylaniline (4e displays the maximum fluorescence intensity at 518 nm and shows a fluorescence quantum yield of 0.068. The synthesized pyramido-fused indazoles have been evaluated for their free radical scavenging activity and compound 4f showed good antioxidant activity.

  17. A Metal-Free Regioselective Multicomponent Approach for the Synthesis of Free Radical Scavenging Pyrimido-Fused Indazoles and Their Fluorescence Studies.

    Palaniraja, Jeyakannu; Mohana Roopan, Selvaraj; Mokesh Rayalu, G; Abdullah Al-Dhabi, Naif; Valan Arasu, Mariadhas


    This study deals with a new and efficient metal-free regioselective synthesis of pyrimido-fused indazoles with nitrogen ring junction motifs. We have developed a metal-free domino type reaction between 3-aminoindazole, aryl aldehydes and aceotophenones in the presence of KOH/DMF that leads to pyrimido[1,2-b]indazole analogues. Response Surface Methodology (RSM) coupled with a Box-Behnken design (BBD) were utilized for exploring the effect of base used (A), temperature of reaction (B) and (C), reaction time. This approach can allow access to a variety of pyrimidoindazole fluorophores and related compounds. The compound N,N-dimethyl-4-(2-phenylpyrimido[1,2-b]indazol-4-yl)aniline (4e) displays the maximum fluorescence intensity at 518 nm and shows a fluorescence quantum yield of 0.068. The synthesized pyramido-fused indazoles have been evaluated for their free radical scavenging activity and compound 4f showed good antioxidant activity.

  18. Biphilic Organophosphorus Catalysis: Regioselective Reductive Transposition of Allylic Bromides via PIII/PV Redox Cycling

    Reichl, Kyle D.; Dunn, Nicole L.; Fastuca, Nicholas J.; Radosevich, Alexander T.


    We report that a regioselective reductive transposition of primary allylic bromides is catalyzed by a biphilic organophosphorus (phosphetane) catalyst. Spectroscopic evidence supports the formation of a pentacoordinate (σ5-P) hydridophosphorane as a key reactive intermediate. Kinetics experiments and computational modeling are consistent with a unimolecular decomposition of the σ5-P hydridophosphorane via a concerted cyclic transition structure that delivers the observed allylic transposition and completes a novel PIII/PV redox catalytic cycle. These results broaden the growing repertoire of reactions catalyzed within the PIII/PV redox couple and suggest additional opportunities for organophosphorus catalysis in a biphilic mode. PMID:25874950

  19. Regioselective enzymatic synthesis of non-steroidal anti-inflammatory drugs containing glucose in organic media.

    Wang, Na; Liu, Bo Kai; Wu, Qi; Wang, Jun Liang; Lin, Xian Fu


    Enzymatic transesterification of glucose with the vinyl ester of non-steroidal anti-inflammatory drugs (NSAIDs) was in organic media performed for synthesis of novel NSAIDs-glucose conjugates. Glucose was regioselectively acylated at the 6-hydroxyl group. The indomethacin-glucose conjugate and ketoprofen-glucose conjugate were produced by the catalysis of alkaline protease from Bacillus subtilis in the respective yields of 42% (over 48 h) and 63% (over 40 h). The etodolac-glucose conjugate was obtained in 26% yield (over 144 h) by lipase from Candida antarctica.

  20. Lewis Acid Triggered Regioselective Magnesiation and Zincation of Uracils, Uridines, and Cytidines.

    Klier, Lydia; Aranzamendi, Eider; Ziegler, Dorothée; Nickel, Johannes; Karaghiosoff, Konstantin; Carell, Thomas; Knochel, Paul


    The Lewis acid MgCl2 allows control of the metalation regioselectivity of uracils and uridines. In the absence of the Lewis acid, metalation of uracil and uridine derivatives with TMPMgCl·LiCl occurs at the position C(5). In the presence of MgCl2, zincation using TMP2Zn·2LiCl·2MgCl2 occurs at the position C(6). This metalation method provides easy access to functionalized uracils and uridines. Using TMP2Zn·2LiCl·2MgCl2 also allows to functionalize cytidine derivatives at the position C(6).

  1. FeCl3 catalysed regioselective allylation of phenolic substrates with (-hydroxy)allylphosphonates

    Mandala Anitha; Ramesh Kotikalapudi; K C Kumara Swamy


    Electrophilic allylation of phenolic substrates including salicylaldehydes with (-hydroxy) allylphosphonates is presented. It is observed that catalytic FeCl3 is sufficient to accomplish the allylation. Interestingly, the reaction led to the formation of allylphosphonates in addition to vinylphosphonates, depending upon the substituent. The vinylphosphonates obtained here are -isomers. More importantly, the reaction occurred regioselectively with respect to the phenolic substrates. Substituted allylphosphonates are formed when salicylaldehyde or (2-hydroxy-phenyl)arylmethanones are used. Conclusive proof for the formation of allylphosphontates as well as vinylphosphonates has been provided by single crystal X-ray crystallography.

  2. Microwave assisted regioselective synthesis of novel pyrazoles and pyrazolopyridazines via fluorine containing building blocks

    Althagafi, Ismail I.; Shaaban, Mohamed R.


    A facile regioselective synthesis of novel pyrazole derivatives containing a fluorophenyl moiety via the 1,3-dipolar cycloaddition of nitrileimines and enamines using conventional as well as microwave irradiation conditions have been achieved. Fluorine-containing building blocks methodology was used in order to access the targeted fluorinated compounds. The structures of the synthesized products were confirmed by 1H NMR, FT-IR, mass spectrometry, and elemental analyses. Furthermore, the synthesized pyrazoles have been used in the synthesis of some new pyrazolo pyidazines containing pendent to fluorophenyl moiety. An unambiguous structural assignment of the obtained pyrazole regioisomers was determined using the 1H NMR analysis as a valuable tool.

  3. Chemo-and regioselective hydroboration of △14,15 in certain cephalostatin analogue


    The symmetrical diketone II, which can be synthesized in gram scale using a well established method, was used as a starting material to prepare the 11a-methoxy ketomethylene VI. This is in continuation of our study aiming at the synthesis of multi-hydroxylated cephalostatin analogues, as for example cephalostatin 1 I, a potent anti-tumor natural product. Compound VI underwent chemo- and regioselective hydroboration reaction at only one of △14,15 double bonds furnishing compound IX as a major product in a fair yield.

  4. Polystyrene-supported organotin dichloride as a recyclable catalyst in lactone ring-opening polymerization: assessment and catalysis monitoring by high-resolution magic-angle-spinning NMR spectroscopy.

    Deshayes, Gaëlle; Poelmans, Kevin; Verbruggen, Ingrid; Camacho-Camacho, Carlos; Degée, Philippe; Pinoie, Vanja; Martins, José C; Piotto, Martial; Biesemans, Monique; Willem, Rudolph; Dubois, Philippe


    Dialkyltin dichloride grafted to a cross-linked polystyrene, with the formula [P-H]((1-t))[P-(CH2)nSnBuCl2]t (P=[CH2CH(pC6H4)], t=the degree of functionalization, and n=6 or 11), is investigated as a recyclable catalyst in the ring-opening polymerization (ROP) of epsilon-caprolactone (CL). It is demonstrated that high-resolution magic-angle-spinning (HR-MAS) NMR spectroscopy is an invaluable tool to characterize completely the supported catalyst. The 2D 1H-13C HSQC HR-MAS spectrum, in particular, allowed extensive assignment of the 1H and 13C resonances, as well as accurate measurement of the (n)J((1)H-(117/119)Sn) and (n)J((13)C-(117/119)Sn) coupling constants. 1H and 119Sn HR-MAS NMR spectroscopy is presented as a monitoring tool for catalytic processes based on organotin compounds, particularly for the investigation of the extent to which polymerization residues are observable in situ in the material pores and for the assessment of the chemical integrity and recycling conditions of the grafted catalyst. From polymerization experiments with CL, initiated by n-propanol and with [P-H]((1-t))[P-(CH2)nSnBuCl2]t of various compositions as the supported catalyst, it appears that a partial 'burst' of the polystyrene support occurs when the length of the alkyl spacer is limited to n=6, as a result of polymer chains growing within the pores of the support. However, extension of the length of the aliphatic polymethylene spacer from 6 to 11 carbon atoms preserves the support integrity and allows the production of catalyst-deprived poly(epsilon-caprolactone) (PCL) oligomers. A preliminary attempt to recycle the heterogeneous catalyst has shown that very good reproducibility can be obtained, in terms of both catalyst activity and molecular-weight parameters of the as-recovered PCL polyester chains.

  5. On JB-Rings

    Huanyin CHEN


    A ring R is a QB-ring provided that aR + bR = R with a, b ∈ R implies that there exists a y ∈ R such that a+by ∈ R-1q. It is said that a ring R is a JB-ring provided that R/J(R) is a QB-ring, where J(R) is the Jacobson radical of R. In this paper, various necessary and sufficient conditions, under which a ring is a JB-ring, are established. It is proved that JB-rings can be characterized by pseudo-similarity. Furthermore, the author proves that R is a J B-ring iff so is R/J(R)2.

  6. Bioactivation and Regioselectivity of Pig Cytochrome P450 3A29 towards Aflatoxin B1

    Jun Wu


    Full Text Available Due to unavoidable contaminations in feedstuff, pigs are easily exposed to aflatoxin B1 (AFB1 and suffer from poisoning, thus the poisoned products potentially affect human health. Heretofore, the metabolic process of AFB1 in pigs remains to be clarified, especially the principal cytochrome P450 oxidases responsible for its activation. In this study, we cloned CYP3A29 from pig liver and expressed it in Escherichia coli, and its activity has been confirmed with the typical P450 CO-reduced spectral characteristic and nifedipine-oxidizing activity. The reconstituted membrane incubation proved that the recombinant CYP3A29 was able to oxidize AFB1 to form AFB1-exo-8,9-epoxide in vitro. The structural basis for the regioselective epoxidation of AFB1 by CYP3A29 was further addressed. The T309A mutation significantly decreased the production of AFBO, whereas F304A exhibited an enhanced activation towards AFB1. In agreement with the mutagenesis study, the molecular docking simulation suggested that Thr309 played a significant role in stabilization of AFB1 binding in the active center through a hydrogen bond. In addition, the bulk phenyl group of Phe304 potentially imposed steric hindrance on the binding of AFB1. Our study demonstrates the bioactivation of pig CYP3A29 towards AFB1 in vitro, and provides the insight for understanding regioselectivity of CYP3A29 to AFB1.

  7. Bioactivation and Regioselectivity of Pig Cytochrome P450 3A29 towards Aflatoxin B1

    Wu, Jun; Chen, Ruohong; Zhang, Caihui; Li, Kangbai; Xu, Weiying; Wang, Lijuan; Chen, Qingmei; Mu, Peiqiang; Jiang, Jun; Wen, Jikai; Deng, Yiqun


    Due to unavoidable contaminations in feedstuff, pigs are easily exposed to aflatoxin B1 (AFB1) and suffer from poisoning, thus the poisoned products potentially affect human health. Heretofore, the metabolic process of AFB1 in pigs remains to be clarified, especially the principal cytochrome P450 oxidases responsible for its activation. In this study, we cloned CYP3A29 from pig liver and expressed it in Escherichia coli, and its activity has been confirmed with the typical P450 CO-reduced spectral characteristic and nifedipine-oxidizing activity. The reconstituted membrane incubation proved that the recombinant CYP3A29 was able to oxidize AFB1 to form AFB1-exo-8,9-epoxide in vitro. The structural basis for the regioselective epoxidation of AFB1 by CYP3A29 was further addressed. The T309A mutation significantly decreased the production of AFBO, whereas F304A exhibited an enhanced activation towards AFB1. In agreement with the mutagenesis study, the molecular docking simulation suggested that Thr309 played a significant role in stabilization of AFB1 binding in the active center through a hydrogen bond. In addition, the bulk phenyl group of Phe304 potentially imposed steric hindrance on the binding of AFB1. Our study demonstrates the bioactivation of pig CYP3A29 towards AFB1 in vitro, and provides the insight for understanding regioselectivity of CYP3A29 to AFB1. PMID:27626447

  8. Iridium-catalysed regioselective borylation of carboranes via direct B-H activation

    Cheng, Ruofei; Qiu, Zaozao; Xie, Zuowei


    Carboranes are carbon-boron molecular clusters, which can be viewed as three-dimensional analogues to benzene. They are finding many applications in medicine, materials and organometallic chemistry. On the other hand, their exceptional thermal and chemical stabilities, as well as 3D structures, make them very difficult to be functionalized, in particular the regioselective functionalization of BH vertex among ten similar B-H bonds. Here we report a very efficient iridium-catalysed borylation of cage B(3,6)-H bonds of o-carboranes with excellent yields and regioselectivity using bis(pinacolato)diboron (B2pin2) as a reagent. Selective cage B(4)-H borylation has also been achieved by introducing a bulky TBDMS (tert-butyldimethylsilyl) group to one cage carbon vertex. The resultant 3,6-(Bpin)2-o-carboranes are useful synthons for the synthesis of a wide variety of B(3,6)-difunctionalized o-carboranes bearing cage B-X (X=O, N, C, I and Br) bonds.

  9. Iridium-catalysed regioselective borylation of carboranes via direct B–H activation

    Cheng, Ruofei; Qiu, Zaozao; Xie, Zuowei


    Carboranes are carbon–boron molecular clusters, which can be viewed as three-dimensional analogues to benzene. They are finding many applications in medicine, materials and organometallic chemistry. On the other hand, their exceptional thermal and chemical stabilities, as well as 3D structures, make them very difficult to be functionalized, in particular the regioselective functionalization of BH vertex among ten similar B–H bonds. Here we report a very efficient iridium-catalysed borylation of cage B(3,6)–H bonds of o-carboranes with excellent yields and regioselectivity using bis(pinacolato)diboron (B2pin2) as a reagent. Selective cage B(4)–H borylation has also been achieved by introducing a bulky TBDMS (tert-butyldimethylsilyl) group to one cage carbon vertex. The resultant 3,6-(Bpin)2-o-carboranes are useful synthons for the synthesis of a wide variety of B(3,6)-difunctionalized o-carboranes bearing cage B–X (X=O, N, C, I and Br) bonds. PMID:28300061

  10. Regioselective enzymatic acylations of polyhydroxylated eudesmanes: semisynthesis, theoretical calculations, and biotransformation of cyclic sulfites.

    García-Granados, A; Melguizo, E; Parra, A; Simeó, Y; Viseras, B; Dobado, J A; Molina, J; Arias, J M


    Different lipase enzymes have been tested in order to perform regioselective acetylations on the eudesmane tetrol from vulgarin. High yields (95%) of 1,12-diacetoxy derivative (4) were achieved in 1 h with Candida antarctica lipase (CAL). However, only the 12-acetyl derivative (6) was obtained in similar yield with Mucor miehei (MML) or Candida cylindracea (CCL) lipases. The enzymatic protection at C-1 and C-12 has been used to form eudesmane cyclic-sulfites between C-6 and C-4 atoms. The R/S-sulfur configuration has been assigned by means of the experimental and theoretical (13)C and (1)H NMR chemical shifts. The theoretical shifts were calculated using the GIAO method, with a MM+ geometry optimization followed by a single-point calculation at the B3LYP/6-31G(*) level (B3LYP/6-31G(*)//MM+). Moreover, B3LYP/6-31G(*) geometry optimizations were carried out to test the B3LYP/6-31G(*)//MM+ results, for the deacetylated sulfites (12 and 15). In addition to the delta(C) and delta(H) shifts, the (3)J(HH) coupling constants were also calculated and compared with the experimental values when available. Finally, different reactivities have been checked in both sulfites by biotransformation with Rhizopus nigricans. While the R-sulfite gave 2 alpha- and 11 beta-hydroxylated metabolites, the S-sulfite yielded only regioselective deacetylations. Furthermore, both sulfites showed different reactivities in redox processes.

  11. Temperature-dependent regioselectivity of nucleophilic aromatic photosubstitution. Evidence that activation energy controls reactivity.

    Wubbels, Gene G; Tamura, Ryo; Gannon, Emmett J


    Irradiation (λ > 330 nm) of 2-chloro-4-nitroanisole (1) at 25 °C in aqueous NaOH forms three substitution photoproducts: 2-methoxy-5-nitrophenol (2), 2-chloro-4-nitrophenol (3), and 3-chloro-4-methoxyphenol (4), in chemical yields of 69.2%, 14.3%, and 16.5%. The activation energies for the elementary steps from the triplet state at 25 °C were determined to be 1.8, 2.4, and 2.7 kcal/mol, respectively. The chemical yields of each of the three products were determined for exhaustive irradiations at 0, 35, and 70 °C. The variation with temperature of the experimental yields is reproduced almost exactly by the yields calculated with the Arrhenius equation. This indicates that activation energy is the fundamental property related to regioselectivity in nucleophilic aromatic photosubstitution of the S(N)2 Ar* type. The many methods proposed for predicting regioselectivity in reactions of this type have had limited success and have not been related to activation energy.

  12. Regioselective patterning of multiple SAMs and applications in surface-guided smart microfluidics.

    Chen, Chuanzhao; Xu, Pengcheng; Li, Xinxin


    A top-down nanofabrication technology is developed to integrate multiple SAMs (self-assembled monolayers) into regioselective patterns. With ultraviolet light exposure through regioselectively hollowed hard mask, an existing SAM at designated microregions can be removed and a dissimilar kind of SAM can be regrown there. By repeating the photolithography-like process cycle, diverse kinds of SAM building blocks can be laid out as a desired pattern in one microfluidic channel. In order to ensure high quality of the surface modifications, the SAMs are vapor-phase deposited before the channel is closed by a bonding process. For the first time the technique makes it possible to integrate three or more kinds of SAMs in one microchannel. The technique is very useful for multiplex surface functionalization of microfluidic chips where different segments of a microfluidic channel need to be individually modified with different SAMs or into arrayed pattern for surface-guided fluidic properties like hydrophobicity/philicity and/or oleophobicity/philicity, etc. The technique has been well validated by experimental demonstration of various surface-directed flow-guiding functions. By modifying a microchannel surface into an arrayed pattern of multi-SAM "two-tone" stripe array, surface-guiding-induced 3D swirling flow is generated in a microfluidic channel that experimentally exhibits quick oil/water mixing and high-efficiency oil-to-water chemical extraction.

  13. Regioselective sulfation of Artemisia sphaerocephala polysaccharide: Solution conformation and antioxidant activities in vitro.

    Wang, Junlong; Yang, Wen; Tang, YinYing; Xu, Qing; Huang, Shengli; Yao, Jian; Zhang, Ji; Lei, Ziqiang


    Regioselective modification is an effective approach to synthesize polysaccharides with different structure features and improved properties. In this study, regioselective sulfation of Artemisia sphaerocephala polysaccharide (SRSASP) was prepared by using triphenylchloromethane (TrCl) as protecting precursor. The decrease in fractal dimension (df) values (1.56-2.04) of SRSASP was observed in size-exclusion chromatography combined with multi angle laser light scattering (SEC-MALLS) analysis. Compared to sample substituted at C-6, SRSASP showed a more expanded conformation of random coil, which was attributed to the breakup of hydrogen bonds and elastic contributions. Circular dichroism (CD), methylene blue (MB) and congo red (CR) spectrophotometric method and atomic force microscopy (AFM) results confirmed the conformational transition and stiffness of the chains after sulfation. SRSASP exhibited enhanced antioxidant activities in the DPPH, superoxide and hydroxyl radical scavenging assay. Sulfation at C-2 or C-3 was favorable for the chelation which might prevent the generation of hydroxyl radicals. It concluded that the degree of substitution and substitution position were the factors influencing biological activities of sulfated polysaccharides.

  14. On semi ring bornologies

    Imran, A. N.; Rakhimov, I. S.; Husain, Sh. K. Said


    Our main focus in this work is to introduce new structure bornological semi rings. This generalizes the theory of algebraic semi rings from the algebraic setting to the framework of bornological sets. We give basic properties for this new structure. As well as, We study the fundamental construction of bornological semi ring as product, inductive limits and projective limits and their extensions on bornological semi ring. Additionally, we introduce the category of bornological semi rings and study product and pullback (fiber product) in the category of bornological semi rings.

  15. Laparoscopic appendicectomy using endo-ring applicator and fallope rings

    Ali Iyoob


    Full Text Available Background/Aim: Wider adoption of laparoscopic appendicectomy (LA is limited by problems in securing the appendiceal base as well as the cost and the duration compared with the open procedure. The objective of this study was to assess the feasibility and efficacy of a new method for securing the appendiceal base in LA, so as to make the entire procedure simpler and cheaper, and hence, more popular. Methods: Twenty-five patients who were candidates for appendicectomy (emergency as well as elective and willing for the laparoscopic procedure were selected for this study. Ports used were 10 mm at the umbilicus, 5 mm at the lower right iliac fossa, and 10 mm at the left iliac fossa. Extremely friable, ruptured, or turgid organs of diameters larger than 8 mm were excluded from the study. The mesoappendix was divided close to the appendix by diathermy. Fallope rings were applied to the appendiceal base using a special ring applicator, and the appendix was divided and extracted through the lumen of the applicator. Results: The procedure was successful in 23 (92% cases, and the mean duration of the procedure was 20 minutes (15-32 minutes. There were no procedural complications seen during a median follow-up of two weeks. The equipment and rings were cheaper when compared with that of the standard methods of securing the base of the appendix. Conclusion: LA using fallope rings is a safe, simple, easy-to-learn, and economically viable method.

  16. Ring-strain-enabled reaction discovery: new heterocycles from bicyclo[1.1.0]butanes.

    Walczak, Maciej A A; Krainz, Tanja; Wipf, Peter


    Mechanistically as well as synthetically, bicyclo[1.1.0]butanes represent one of the most fascinating classes of organic compounds. They offer a unique blend of compact size (four carbon atoms), high reactivity (strain energy of 66 kcal/mol), and mechanistic pathway diversity that can be harvested for the rapid assembly of complex scaffolds. The C(1)-C(3) bond combines the electronic features of both σ and π bonds with facile homolytic and heterolytic bond dissociation properties and thereby readily engages pericyclic, transition-metal-mediated, nucleophilic, and electrophilic pathways as well as radical acceptor and donor substrates. Despite this multifaceted reaction profile and recent advances in the preparation of bicylo[1.1.0]butanes, the current portfolio of synthetic applications is still limited compared with those of cyclopropanes and cyclobutanes. In this Account, we describe our work over the past decade on the exploration of substituent effects on the ring strain and the reactivity of bicyclo[1.1.0]butanes, particularly in the context of metal-mediated processes. We first describe Rh(I)-catalyzed cycloisomerization reactions of N-allyl amines to give pyrrolidine and azepine heterocycles. The regioselectivity of the C,C-bond insertion/ring-opening step in these reactions is controlled by the phosphine ligand. After metal carbene formation, an intramolecular cyclopropanation adds a second fused ring system. A proposed mechanism rationalizes why rhodium(I) complexes with monodentate ligands favor five-membered heterocycles, as opposed to Rh(I)-bidentate ligand catalysts, which rearrange N-allyl amines to seven-membered heterocycles. The scope of Rh(I)-catalyzed cycloisomerization reactions was extended to allyl ethers, which provide a mixture of five- and seven-membered cyclic ethers regardless of the nature of the phosphine additive and Rh(I) precatalyst. The chemical diversity of these cycloisomerization products was further expanded by a consecutive

  17. Regioselective alkynylation followed by Suzuki coupling of 2,4-dichloroquinoline: Synthesis of 2-alkynyl-4-arylquinolines

    Ellanki A. Reddy


    Full Text Available A two step synthesis of 2-alkynyl-4-arylquinolines has been accomplished via Pd/C-mediated regioselective C-2 alkynylation of 2,4-dichloroquinoline in water followed by Suzuki coupling at C-4 of the resulting 4-chloro derivative.

  18. Chemo- and regioselective functionalization of nortrilobolide: application for semi-synthesis of the natural product 2-acetoxytrilobolide

    Doan, Thi Quynh Nhu; Crestey, François; Olsen, Carl Erik


    The difference of reactivity of the hexaoxygenated natural product thapsigargin (1) and the pentaoxygenated nortrilobolide (3) is compared in order to develop a chemo- and regioselective method for the conversion of nortrilobolide (3) into the natural product 2-acetoxytrilobolide (4). For the fir...... anticancer agents....

  19. Regioselective Hydration of an Alkene and Analysis of the Alcohol Product by Remote Access NMR: A Classroom Demonstration

    Smith, Maureen E.; Johnson, Sara L.; Masterson, Douglas S.


    A two-part demonstration was conducted in our first-semester organic chemistry course designed to introduce students to the formation of alcohols, regioselective reactions, and analysis of organic products by NMR analysis. This demonstration utilized the oxymercuration-demercuration sequence to prepare an alcohol from an alkene in a Markovnikov…

  20. Anhydrous ZnCl2: A Highly Efficient Reagent for Facile and Regioselective Conversion of Epoxides to β-Chlorohydrins

    Ronak Eisavi


    Full Text Available Facile conversion of structurally different epoxides to the corresponding β-chlorohydrins was carried out successfully with anhydrous ZnCl2 in CH3CN. The reactions were carried out within 10-50 min to give β-chlorohydrins with perfect regioselectivity and high yields (80-97%.

  1. Regioselective Glycosylation of Unprotected Phenyl 1‐Thioglycopyranosides with Phenylboronic Acid as a Transient Masking Group

    Fenger, Thomas Hauch; Madsen, Robert


    A useful protocol is described for the regioselective glycosylation of the secondary alcohols in unprotected glycosyl acceptors. Phenyl 1‐thioglycopyranosides derived from D‐glucose, D‐galactose, D‐glucosamine, L‐rhamnose, and L‐fucose were treated with phenylboronic acid to install a temporary...

  2. The halo-substituent effect on Pseudomonas cepacia lipase-mediated regioselective acylation of nucleosides: A comparative investigation.

    Wang, Zhao-Yu; Bi, Yan-Hong; Yang, Rong-Ling; Duan, Zhang-Qun; Nie, Ling-Hong; Li, Xiang-Qian; Zong, Min-Hua; Wu, Jie


    In this work, comparative experiments were explored to investigate the substrate specificity of Pseudomonas cepacia lipase in regioselective acylation of nucleosides carrying various substituents (such as the H, F, Cl, Br, I) at 2'- and 5-positions. Experimental data indicated that the catalytic performance of the enzyme depended very much on the halo-substituents in nucleosides. The increased bulk of 2'-substituents in ribose moiety of the nucleoside might contribute to the improved 3'-regioselectivity (90-98%, nucleosides a-d) in enzymatic decanoylation, while the enhancement of regioselectivity (93-99%) in 3'-O-acylated nucleosides e-h could be attributable to the increasing hydrophobicity of the halogen atoms at 5-positions. With regard to the chain-length selectivity, P. cepacia lipase displayed the highest 3'-regioselectivity toward the longer chain (C14) as compared to shorter (C6 and C10) ones. The position, orientation and property of the substituent, specific structure of the lipase's active site, and acyl structure could account for the diverse results.

  3. Regioselective Hydration of an Alkene and Analysis of the Alcohol Product by Remote Access NMR: A Classroom Demonstration

    Smith, Maureen E.; Johnson, Sara L.; Masterson, Douglas S.


    A two-part demonstration was conducted in our first-semester organic chemistry course designed to introduce students to the formation of alcohols, regioselective reactions, and analysis of organic products by NMR analysis. This demonstration utilized the oxymercuration-demercuration sequence to prepare an alcohol from an alkene in a Markovnikov…

  4. Stereo- and regio-selective one-pot synthesis of triazole-based unnatural amino acids and β- amino triazoles

    Synthesis of triazole based unnatural amino acids and β-amino triazole has been described via stereo and regioselective one-pot multi-component reaction of sulfamidates, sodium azide, and alkynes under MW conditions. The developed method is applicable to a broad substrate scope a...

  5. Palladium-catalyzed regioselective intramolecular coupling of o-carborane with aromatics via direct cage B-H activation.

    Quan, Yangjian; Xie, Zuowei


    Palladium-catalyzed intramolecular coupling of o-carborane with aromatics via direct cage B-H bond activation has been achieved, leading to the synthesis of a series of o-carborane-functionalized aromatics in high yields with excellent regioselectivity. In addition, the site selectivity can also be tuned by the substituents on cage carbon atom.

  6. A facile and regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles using click chemistry

    The reaction of α-tosyloxy ketones, sodium azide and terminal alkynes in presence of copper(I) in aqueous polyethylene glycol afforded regioselectively 1,4-disubstituted 1,2,3-triazoles in good yield at ambient temperature. The one-pot exclusive formation of 1,4-disubstituted 1,2...

  7. A facile and regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles using click chemistry

    The reaction of α-tosyloxy ketones, sodium azide and terminal alkynes in presence of copper(I) in aqueous polyethylene glycol afforded regioselectively 1,4-disubstituted 1,2,3-triazoles in good yield at ambient temperature. The one-pot exclusive formation of 1,4-disubstituted 1,2...

  8. Metal-Free Synthesis of 3-Arylquinolin-2-ones from Acrylic Amides via a Highly Regioselective 1,2-Aryl Migration: An Experimental and Computational Study.

    Liu, Le; Zhang, Tonghuan; Yang, Yun-Fang; Zhang-Negrerie, Daisy; Zhang, Xinhao; Du, Yunfei; Wu, Yun-Dong; Zhao, Kang


    Combined experimental and theoretical investigations into the phenyliodine bis(trifluoroacetate) (PIFA)-mediated reaction of N-arylcinnamamide to produce 3-arylquinolin-2-one derivatives have been conducted. High regioselectivity during the aryl migration process was observed in 3,3-disubstituted acrylamides. Density functional theory calculation was conducted in an attempt to understand the mechanism and the origin of the regioselectivity. On the basis of both the experimental and the theoretical results, a mechanism involving an oxidative annulation, followed by an aryl migration, has been proposed. The annulation is the regioselectivity determining step.

  9. Unveiling the physics of the Thomson jumping ring

    Ladera, Celso L.; Donoso, Guillermo


    We present a new theoretical model and validating experiments that unveil the rich physics behind the flight of the conductive ring in the Thomson experiment—physics that is hard to see because of the rapid motion. The electrodynamics of the flying ring exhibits interesting features, e.g., varying mutual inductance between the ring and the electromagnet. The dependences of the ring electrodynamics upon time and position as the ring travels upward are conveniently separated and determined to obtain a comprehensive view of the ring motion. We introduce a low-cost jumping ring setup that incorporates pickup coils connected in opposition, allowing us to scrutinize the ring electrodynamics and confirm our theoretical model with good accuracy. This work is within the reach of senior students of science or engineering, and it can be implemented either as a teaching laboratory experiment or as an open-ended project.

  10. Groups, rings, modules

    Auslander, Maurice


    This classic monograph is geared toward advanced undergraduates and graduate students. The treatment presupposes some familiarity with sets, groups, rings, and vector spaces. The four-part approach begins with examinations of sets and maps, monoids and groups, categories, and rings. The second part explores unique factorization domains, general module theory, semisimple rings and modules, and Artinian rings. Part three's topics include localization and tensor products, principal ideal domains, and applications of fundamental theorem. The fourth and final part covers algebraic field extensions

  11. Birth Control Ring

    ... Right Sport for You Healthy School Lunch Planner Birth Control Ring KidsHealth > For Teens > Birth Control Ring Print A A A What's in ... español Anillo vaginal anticonceptivo What Is It? The birth control ring is a soft, flexible, doughnut-shaped ...

  12. On Weakly Semicommutative Rings*



    A ring R is said to be weakly scmicommutative if for any a, b ∈ R,ab = 0 implies aRb C_ Nil(R), where Nil(R) is the set of all nilpotcnt elements in R.In this note, we clarify the relationship between weakly semicommutative rings and NI-rings by proving that the notion of a weakly semicommutative ring is a proper generalization of NI-rings. We say that a ring R is weakly 2-primal if the set of nilpotent elements in R coincides with its Levitzki radical, and prove that if R is a weakly 2-primal ring which satisfies oα-condition for an endomorphism α of R (that is, ab = 0 (←→) aα(b) = 0 where a, b ∈ R) then the skew polynomial ring R[π; αα]is a weakly 2-primal ring, and that if R is a ring and I is an ideal of R such that I and R/I are both weakly semicommutative then R is weakly semicommutative.Those extend the main results of Liang et al. 2007 (Taiwanese J. Math., 11(5)(2007),1359-1368) considerably. Moreover, several new results about weakly semicommutative rings and NI-rings are included.

  13. Physics of quantum rings

    Fomin, Vladimir M


    This book deals with a new class of materials, quantum rings. Innovative recent advances in experimental and theoretical physics of quantum rings are based on the most advanced state-of-the-art fabrication and characterization techniques as well as theoretical methods. The experimental efforts allow to obtain a new class of semiconductor quantum rings formed by capping self-organized quantum dots grown by molecular beam epitaxy. Novel optical and magnetic properties of quantum rings are associated with non-trivial topologies at the nanoscale. An adequate characterization of quantum rings is po

  14. Envelopes of Commutative Rings

    Rafael PARRA; Manuel SAOR(I)N


    Given a significative class F of commutative rings,we study the precise conditions under which a commutative ring R has an F-envelope.A full answer is obtained when.F is the class of fields,semisimple commutative rings or integral domains.When F is the class of Noetherian rings,we give a full answer when the Krull dimension of R is zero and when the envelope is required to be epimorphic.The general problem is reduced to identifying the class of non-Noetherian rings having a monomorphic Noetherian envelope,which we conjecture is the empty class.



    Proxy signatures have been used to enable the transfer of digital signing power within some context and ring signatures can be used to provide the anonymity of a signer. By combining the functionalities of proxy signatures and ring signatures, this paper introduces a new concept, named ring proxy signature, which is a proxy signature generated by an anonymous member from a set of potential signers. The paper also constructs the first concrete ring proxy signature scheme based on the provably secure Schnorr's signatures and two ID-based ring proxy signature schemes. The security analysis is provided as well.

  16. Saturn's largest ring.

    Verbiscer, Anne J; Skrutskie, Michael F; Hamilton, Douglas P


    Most planetary rings in the Solar System lie within a few radii of their host body, because at these distances gravitational accelerations inhibit satellite formation. The best known exceptions are Jupiter's gossamer rings and Saturn's E ring, broad sheets of dust that extend outward until they fade from view at five to ten planetary radii. Source satellites continuously supply the dust, which is subsequently lost in collisions or by radial transport. Here we report that Saturn has an enormous ring associated with its outer moon Phoebe, extending from at least 128R(S) to 207R(S) (Saturn's radius R(S) is 60,330 km). The ring's vertical thickness of 40R(S) matches the range of vertical motion of Phoebe along its orbit. Dynamical considerations argue that these ring particles span the Saturnian system from the main rings to the edges of interplanetary space. The ring's normal optical depth of approximately 2 x 10(-8) is comparable to that of Jupiter's faintest gossamer ring, although its particle number density is several hundred times smaller. Repeated impacts on Phoebe, from both interplanetary and circumplanetary particle populations, probably keep the ring populated with material. Ring particles smaller than centimetres in size slowly migrate inward and many of them ultimately strike the dark leading face of Iapetus.

  17. The contraceptive vaginal ring.

    Edwardson, Jill; Jamshidi, Roxanne


    The contraceptive vaginal ring offers effective contraception that is self-administered, requires less frequent dosing than many other forms of contraception, and provides low doses of hormones. NuvaRing (Organon, Oss, The Netherlands), the only contraceptive vaginal ring approved for use in the United States, contains etonogestrel and ethinyl estradiol. It is inserted into the vagina for 3 weeks, followed by a 1-week ring-free period, and works by inhibiting ovulation. Most women note a beneficial effect on bleeding profiles and are satisfied with NuvaRing. Commonly reported adverse events include vaginitis, leukorrhea, headaches, and device-related events such as discomfort. Serious adverse events are rare. In Chile and Peru, progesterone-only vaginal contraceptive rings are available for nursing women. Studies are ongoing examining new formulations of vaginal contraceptive rings.

  18. New Dust Belts of Uranus: One Ring, Two Ring, Red Ring, Blue Ring

    de Pater, I; Hammel, H B; Gibbard, S G; Showalter, M R


    We compare near-infrared observations of the recently discovered outer rings of Uranus with HST results. We find that the inner ring, R/2003 U 2, is red, whereas the outer ring, R/2003 U 1, is very blue. Blue is an unusual color for rings; Saturn's enigmatic E ring is the only other known example. By analogy to the E ring, R/2003 U 1 is probably produced via impacts into the embedded moon Mab, which apparently orbits at a location where non-gravitational perturbations favor the survival and spreading of sub-micron sized dust. R/2003 U 2 more closely resembles Saturn's G ring.

  19. Regioselective 5-exo-Trig Heterocyclization of 2-Allyl-1-naphthols under the Influence of N-Iodosuccinimide or Molecular Iodine in Aqueous Micelle

    Pradipta Kumar Basu


    Full Text Available Regioselective iodocyclization of a series of allylhydroxy naphthalene precursors involving N-iodosuccinimide and environment friendly green approach associated with surfactant-promoted molecular-iodine-mediated 5-exo-trig cyclization strategies has been explored.

  20. Efficient Regioselective Synthesis of 3-1odoindole N-Carboximidamides and N-Carboximidoates by a Sequential Aza-Wittig/Iodine Induced Cyclization

    聂熠博; 段专; 丁明武


    3-Iodoindole N-carboximidamides and N-carboximidoates 4 were prepared regioselectively via a sequential aza-Wittig/iodine induced cyclization, starting from easily accessible 2-alkynylphenyl iminophosphorane, isocyanates, various nucleophiles and iodine.

  1. Computational studies on the regioselectivity of metal-catalyzed synthesis of 1,2,3 triazoles via click reaction: a review.

    Hosseinnejad, Tayebeh; Fattahi, Bahareh; Heravi, Majid M


    Recently, the experimental and computational chemists have been attracted widely to the click synthesis of 1,2,3 triazoles and their derivatives, mainly due to the fact that they are interesting from structural and mechanistic points of view. Moreover, catalyzed click have been well established as a successful strategy showing high regioselectivity and high yield for the synthesis of 1,2,3-triazoles. In this review, we try to highlight the recently reported computational assessments on the origins and predection of regioselectivity in the catalyzed click synthesis of triazoles from the mechanistic and thermodynamical points of view. In this light, density functional theory (DFT) calculations on the free energy profiles of azide-alkyne cycloaddition reactions have been underscored. The stereoelectronic features for the role of copper, ruthenium, and iridium as catalyst on regioselectivity of click reactions have also be discussed. Graphical Abstract Computational origins for the regioselective behavior of 1,2,3 triazoles click synthesis.

  2. Certain near-rings are rings, II

    Howard E. Bell


    Full Text Available We investigate distributively-generated near-rings R which satisfy one of the following conditions: (i for each x,y∈R, there exist positive integers m, n for which xy=ymxn; (ii for each x,y∈R, there exists a positive integer n such that xy=(yxn. Under appropriate additional hypotheses, we prove that R must be a commutative ring.

  3. Reactivity and Regioselectivity in the Heck Reaction - A Hammett Study of 4-Substituted Styrenes

    Fristrup, Peter; Le Quement, Sebastian; Tanner, David Ackland


    The regioselectivity in the cationic Heck reaction of 4-substituted styrenes was addressed by a Hammett study. In this branching reaction, plots based on the substrate reactivity did not give meaningful data, whereas the product distribution was variable due to differing preferences for further...... substitution under the reaction conditions and, thus, unsuitable for Hammett plots. Mechanistically meaningful graphs were obtained by combination of the measured initial branching ratio with the approximately constant substrate reactivity. For the alpha-substitution a clear Hammett relation is observed......, whereas beta-substitution does not depend on electronic effects. This implies that, for alpha-substitution, the slow step of the addition is an electrophilic attack by Pd(II) on the double bond, followed by a rapid migratory insertion....

  4. Zwitterionic Cellulose Carbamate with Regioselective Substitution Pattern: A Coating Material Possessing Antimicrobial Activity.

    Elschner, Thomas; Lüdecke, Claudia; Kalden, Diana; Roth, Martin; Löffler, Bettina; Jandt, Klaus D; Heinze, Thomas


    A polyzwitterion is synthesized by regioselective functionalization of cellulose possessing a uniform charge distribution. The positively charged ammonium group is present at position 6, while the negative charge of carboxylate is located at positions 2 and 3 of the repeating unit. The molecular structure of the biopolymer derivative is proved by NMR spectroscopy. This cellulose-based zwitterion is applied to several support materials by spin-coating and characterized by means of atomic force microscope, contact angle measurements, ellipsometry, and X-ray photoelectron spectroscopy. The coatings possess antimicrobial activity depending on the support materials (glass, titanium, tissue culture poly(styrene)) as revealed by confocal laser scanning microscopy and live/dead staining.

  5. Regioselective synthesis of indazole N1- and N2-(beta-D-ribonucleosides).

    Seela, Frank; Peng, Xiaohua


    The regioselective synthesis of 4-nitroindazole N1- and N2-(beta-D-ribonucleosides) (8, 9, 1b and 2b) is described. The N1-regioisomers are formed under thermodynamic control of the glycosylation reaction [fusion reaction or Silyl Hilbert-Johnson glycosylation for 48 h (66%)], while the kinetic control (Silyl Hilbert-Johnson glycosylation for 5 h) afforded only the N2-isomer (64%). The structures of the nucleosides 1b and 2b were assigned by single crystal X-ray analyses. The 4-amino-N1-(beta-D-ribofuranosyl)-1H-indazole (3b) was obtained from the nitro nucleoside 1b by catalytic hydrogenation. Compound 3b shows fluorescence while the 4-nitroindazole nucleosides 1b and 2b do not possess this property.

  6. Bottlenecks in the prediction of regioselectivity of [4 + 2] cycloaddition reactions: An assessment of reactivity descriptors

    G Gayatri; G Narahari Sastry


    B3LYP/6-31G() calculations were performed to obtain all the transition states and products for the 128 distinct reaction channels of Diels-Alder reactions by taking all possible combinations from a series of dienes (1N-a, 1N-b, 2N, 1P-a, 1P-b, 2P, 1O, 1S) and dienophiles (NE, PE, OE, SE, AE, OHE, MeE, CNE). The predictive ability of the values to gauge the regioselectivity of the putative [4 + 2] cycloaddition reactions is analysed. No correlation is obtained between the reaction energies and activation energies. The extent of asynchronicity is measured based on the bond order analysis. DFT-based descriptors such as the local softness ($s^{+}_{k}$ and $s_{k}^{-}$), Fukui function indices ($f^{+}_{k}$ and $f_{k}^{-}$), global electrophilicity index () and local electrophilicity index () were found to be better than the conventional FMO predictions.

  7. Regioselective toluene nitration catalyzed with layered HNbMoO6

    Hu, Li-Fang; Tang, Yuan; He, Jie; Chen, Kai; Lv, Wei


    HNbMoO6 layered oxide was obtained by the ion-exchange from LiNbMoO6 prepared by solid state reaction (SSR). The micro-structure, textural characteristics and acidity of the as-prepared catalyst were characterized by powder X-ray diffraction (XRD), laser Raman spectroscopy (LRS) and ammonia temperature- programmed desorption (NH3-TPD). Catalytic performance was evaluated in the regioselective nitration of toluene with a novel nitration system containing acetic anhydride and CCl4. The optimal nitration conditions comprise the application of 95 wt % HNO3, HNO3-to-toluene molar ratio of 2.5, catalyst pretreatment temperature of 503 K, reaction temperature of 313 K, and reaction time of 2.5 h. The toluene conversion rate and para-selectivity were also attributable to the strong acidity and the appropriate interlayer distance of the studied catalyst.

  8. Efficient regioselective acylation of quercetin using Rhizopus oryzae lipase and its potential as antioxidant.

    Kumar, Vinod; Jahan, Firdaus; Mahajan, Richi V; Saxena, Rajendra Kumar


    The present investigation describes the regioselective enzymatic acylation of quercetin with ferulic acid using Rhizopus oryzae lipase. Optimization of reaction parameters resulted in 93.2% yield of the ester synthesized using 750IU of lipase in cyclo-octane at a temperature of 45°C. The reaction was successfully carried out upto 25g scale. The ester synthesized was analyzed by (1)H Nuclear magnetic resonance spectroscopy. The ester synthesized (quercetin ferulate) showed higher antiradical activity as compared to ascorbic acid using the 2,2-diphenyl-1-picrylhydrazyl radical method. These results on enzyme-catalyzed acylation of quercetin might be used to prepare and scale-up other flavonoids derivatives.

  9. Organocatalytic chemo- and regioselective oxyarylation of styrenes via a cascade reaction: remote activation of hydroxyl groups.

    Zhang, Yu-Chen; Jiang, Fei; Wang, Shu-Liang; Shi, Feng; Tu, Shu-Jiang


    The first organocatalytic oxyarylation of styrenes has been established through a cascade of vinylogous Michael addition/alkoxyl transfer reactions of o- or p-hydroxylstyrenes with quinone imine ketals. The process leads to a highly chemo- and regioselective oxyarylation of styrenes and provides access to m-alkylated anilines in generally high yields and excellent diastereoselectivity (up to 99% yield, >95:5 dr). An investigation of the reaction pathway revealed that the existence and position of the hydroxyl group of styrene played crucial roles in the cascade reaction, suggesting that the two reactants were simultaneously activated by binaphthyl-derived phosphoric acid via hydrogen bonding interactions and long-distance conjugative effects. In addition, the activating group of the hydroxyl functionality in the products can be easily removed or transformed, demonstrating the applicability and utility of this strategy in styrene oxyarylation and in the synthesis of styrene-based compounds.

  10. Feasibility of a ring FEL at low emittance storage rings

    Agapov, I., E-mail:


    A scheme for generating coherent radiation at latest generation low emittance storage rings such as PETRA III at DESY (Balewski et al., 2004 [1]) is proposed. The scheme is based on focusing and subsequent defocusing of the electron beam in the longitudinal phase space at the undulator location. The expected performance characteristics are estimated for radiation in the wavelength range of 500–1500 eV. It is shown that the average brightness is increased by several orders of magnitude compared to spontaneous undulator radiation, which can open new perspectives for photon-hungry soft X-ray spectroscopy techniques.

  11. On Exchange QB∞-Rings

    Huanyin Chen


    In this paper, we introduce a new class of rings, the QB∞-rings. We investigate necessary and sufficient conditions under which an exchange ring is a QB∞-ring. The modules over an exchange QB∞-ring are studied. Also, we prove that every regular square matrix over an exchange QB∞-ring admits a diagonal reduction by pseudo-invertible matrices.

  12. Neutrosophic LA-Semigroup Rings

    Mumtaz Ali


    Full Text Available Neutrosophic LA-semigroup is a midway structure between a neutrosophic groupoid and a commutative neutrosophic semigroup. Rings are the old concept in algebraic structures. We combine the neutrosophic LA-semigroup and ring together to form the notion of neutrosophic LA-semigroup ring. Neutrosophic LAsemigroup ring is defined analogously to neutrosophic group ring and neutrosophic semigroup ring.

  13. Numerical Simulation of Piston Ring Lubrication

    Felter, Christian Lotz


    This paper describes a numerical method that can be used to model the lubrication of piston rings. Classical lubrication theory is based on the Reynolds equation which is ap- plicable to confined geometries and open geometries where the flooding conditions are known. Lubrication of piston rings...... is extended to include also the oil film outside the piston rings. The numerical model consists of a 2D free surface code that solves the time dependent compressible Navier-Stokes equations. The equations are cast in Lagrangian form and discretized by a meshfree moving least squares method using the primitive......, however, fall outside this category of problems since the piston rings might suffer from starved running conditions. This means that the com- putational domain where Reynold equation is applicable (including a cavitation criteria) is unknown. In order to overcome this problem the computational domain...

  14. Recent applications of ring-rearrangement metathesis in organic synthesis

    Sambasivarao Kotha


    Full Text Available Ring-rearrangement metathesis (RRM involves multiple metathesis processes such as ring-opening metathesis (ROM/ring-closing metathesis (RCM in a one-pot operation to generate complex targets. RRM delivers complex frameworks that are difficult to assemble by conventional methods. The noteworthy point about this type of protocol is multi-bond formation and it is an atom economic process. In this review, we have covered literature that appeared during the last seven years (2008–2014.

  15. Magic Acts with the Cohesin Ring.

    Yu, Hongtao


    Recent studies, including two in this issue of Molecular Cell (Elbatsh et al., 2016; Beckouët et al., 2016), cast light on how cohesin regulators harness the energy of ATP hydrolysis to open the cohesin ring and enable dynamic, regulated entrapment of chromosomes.

  16. Cell Biology: Cohesin Rings Leave Loose Ends

    Skibbens, Robert V.


    Cohesins function in almost all aspects of chromosome biology. Two new studies confirm that a subset of cohesin subunits form a flexible but compressed ring that can be opened through degradation. X-ray crystallography supports potentially differing regulation of subunit associations. PMID:25649818

  17. Synthetic applications of gold-catalyzed ring expansions

    Cristina Nevado


    Full Text Available The development of new methodologies catalyzed by late transition metals involving cycloisomerizations of strained rings can open new venues for the synthesis of structurally complex molecules with interesting biological activities. Herein we summarize, from both a synthetic as well as a mechanistic point of view, the most recent developments in gold-catalyzed ring expansions.

  18. Gulf ring algae

    Although they rank among the tiniest of the microspcopic phytoplankton, coccolithophore algae aid oceanographers studying the Gulf Stream rings and the ring boundaries. The algal group could help to identify more precisely the boundary of the warm rings of water that spin off from the Gulf Stream and become independent pools of warm water in the colder waters along the northeastern U.S. coast.Coccolithophore populations in the Gulf Stream rings intrigue oceanographers for two reasons: The phytoplankton are subjected to an environment that changes every few days, and population explosions within one coccolithophore species seem to be associated with changes in the characteristics of ocean water, said Pat Blackwelder, an associate professor at the Nova Oceanographic Center in Dania, Fla. She is one of many studying the physics, chemistry, and biology of warm core rings. A special oceanography session on these rings was held at the recent AGU Fall Meeting/ASLO Winter Meeting.

  19. Token Ring Project

    Adela Ionescu


    Full Text Available Ring topology is a simple configuration used to connect processes that communicate among themselves. A number of network standards such as token ring, token bus, and FDDI are based on the ring connectivity. This article will develop an implementation of a ring of processes that communicate among themselves via pipe links. The processes are nodes in the ring. Each process reads from its standard input and writes in its standard output. N-1 process redirects the its standard output to a standard input of the process through a pipe. When the ring-structure is designed, the project can be extended to simulate networks or to implement algorithms for mutual exclusion

  20. Dusty plasma (Yukawa) rings

    Sheridan, T E


    One-dimensional and quasi-one-dimensional strongly-coupled dusty plasma rings have been created experimentally. Longitudinal (acoustic) and transverse (optical) dispersion relations for the 1-ring were measured and found to be in very good agreement with the theory for an unbounded straight chain of particles interacting through a Yukawa (i.e., screened Coulomb or Debye-H\\"uckel) potential. These rings provide a new system in which to study one-dimensional and quasi-one-dimensional physics.