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Sample records for chloranil

  1. Triethylammonium hydrogen chloranilate

    Directory of Open Access Journals (Sweden)

    Kazuma Gotoh

    2010-12-01

    Full Text Available In the crystal structure of the title compound (systematic name: triethylammonium 2,5-dichloro-4-hydroxy-3,6-dioxocyclohexa-1,4-dien-1-olate, C6H16N+·C6HCl2O4−, two hydrogen chloranilate anions are connected by a pair of bifurcated O—H...O hydrogen bonds into a dimeric unit. The triethylammonium cations are linked on both sides of the dimer via bifurcated N—H...O hydrogen bonds into a centrosymmetric 2:2 aggregate. The 2:2 aggregates are further linked by intermolecular C—H...O hydrogen bonds.

  2. Imidazole-Chloranil Charge Transfer Complex

    Institute of Scientific and Technical Information of China (English)

    Hai-long Wang; Tong-tong Lu; Tian-jing He; Dong-ming Chen

    2008-01-01

    UV-Vis absorption spectra of the molecular complex formed by imidazole (Im) and chloranil (CA) were measured in chloroform. The stoichiometry of the imidazole-chloranil (Im-CA) complex was determined as 1:1 by applying Benesi-Hildebrand's equation and Job's continuous variation method. Density function theory (DFT) and MP2 calculations were performed to study the structures and the binding energies of the Im-CA complex. The calculations located four conformations (denoted as S1-S4) for the Im-CA complex, two edge(lm)-to-face(CA) linked and two edgc(Im)-to-edge(CA) linked. It was found that the edgc-to-face conformers are more stable than the edge-to-edge ones. The bonding characteristics of these conformers were investigated with natural population analysis (NPA), topological analysis of electron density, and natural bond orbital (NBO) analysis. It was revealed that the edge-to-face conformers are charge-transfer (CT) complexes whereas the edge-to-edge conformers are the hydrogen bond complexes. For the most stable conformation of the Im-CA comp]ex (S1), the charge transfer interaction of the imidazole n(N15) lone pair orbital with the chloranil π*(C1=O7) orbital plays a crucial role in the Im-CA binding, and the binding is further strengthened by the 07… H20 hydrogen bond. The electronic excitation energies of the complex (S1) were calculated with time-dependent DFT (TDDFT), and the observed UV-Visiblc spectrum of the complex was analyzed based on the computed results.

  3. Gabapentin-lactum–chloranilic acid (1/1

    Directory of Open Access Journals (Sweden)

    Jerry P. Jasinski

    2010-01-01

    Full Text Available In the title compound, C9H15NO·C6H2Cl2O4 [sytematic name: 2-azaspiro[4.5]decan-3-one–chloranilic acid (1/1], the cyclohexane ring of the lactam molecule adopts a slightly distorted normal chair conformation and the five-membered 3-azaspiro ring is in a slightly distorted chair conformation. The dihedral angle between the least-squares planes of the cyclohexane and 3-azaspiro rings is 84.0 (3°. In the crystal, the chloranilic acid molecule and the gabapentin-lactum molecules are held together by strong intermolecular N—H...O and O—H...O hydrogen bonds with two bifurcated O acceptor atoms on the chloranilic acid molecule and one on the gabapentin-lactum molecule, each bonding with an inter- and intramolecular hydrogen bond. The molecules are linked into chains parallel to (011 and propagating along the b axis.

  4. Electrical transport in ethyl cellulose–chloranil system

    Indian Academy of Sciences (India)

    P K Khare; R K Pandey; P L Jain

    2000-08-01

    The charge-transport behaviour in pure and chloranil (Chl) doped ethyl cellulose (EC) system has been studied by measuring the dependence of current on field, temperature, electrode material and dopant concentration. The role of doping molecular concentration in the polymer matrix and modification in the conduction characteristics are studied. Lowering of the activation energy due to doping was observed. The current was found to increase with an increase in the chloranil concentration. An explanation for this has been attempted on the basis of formation of molecular aggregates between chloranil molecules and ethoxy groups of ethyl cellulose. It is suggested that chloranil occupies interstitial positions between the polymer chains and assists in carrier transportation by reducing the hopping barriers. The current–voltage characteristics of different samples are analyzed using space charge limited current theory and quantitative information about the transport parameters is derived. The values of effective drift mobility and trapped charge carrier concentration which result in the build up of space charge have been calculated.

  5. Triplet exciplexes in reactions of electronically excited chloranil with unsatuated heterocyclic compounds

    Energy Technology Data Exchange (ETDEWEB)

    Petroshenko, K.B.; Frolov, Y.L.; Gorshkov, A.G.; Osipov, S.P.; Turchaninov, V.K.; Vokin, A.I.

    1985-08-10

    In the system indole + chloranil + dioxane the formation has been demonstrated of a triplet exciplex with complete charge transfer and a hydrogen bond between the components. The presence of a hydrogen bond in the dissociative state results in a decrease in the yield of free ion-radicals.

  6. Spectrophotometric Study on the Interaction of Water with Chloranilic Acid and its Analytical Application

    Institute of Scientific and Technical Information of China (English)

    Feng Lin ZHAO; Xi Lan FENG; Xue Jing LIU; Na LI; Ke An LI

    2005-01-01

    The reaction between chloranilic acid and water in alcohol was studied spectrophotometrically. The conditions of reaction were investigated in detail. The stable purple complex with an absorption wavelength at 530 nm was produced from the reaction between chloranilic acid and water. As a method for determination of H2O, Beer's law was obeyed in range of 0-6.0% or 0-8.0% (V/V) with the detection limit of 0.13%. The relative standard deviation (RSD) was less than 2%. The proposed method has been applied to determination of trace amount of water in ethanol, flour and food flavoring, respectively. The recoveries of water in samples were 97~102%.

  7. Redetermination of pyridine-4-carbonitrile–chloranilic acid (1/1 at 180 K

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    Hiroyuki Ishida

    2008-07-01

    Full Text Available In the crystal structure of the title compound, C6H4N2·C6H2Cl2O4, two chloranilic acid (systematic name: 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone molecules are connected by O—H...O hydrogen bonds to form a dimeric unit. The pyridine-4-carbonitrile molecules are linked on both sides of the dimer via N...H...O hydrogen bonds to give a centrosymmetric 2:2 complex of pyridine-4-carbonitrile and chloranilic acid. The H atom in the N...H...O hydrogen bond is disordered over two positions with approximately equal occupancies. The pyridine ring makes a dihedral angle of 61.54 (14° with the chloranilic acid plane. The 2:2 units are further linked by intermolecular C—H...O and C—H...Cl hydrogen bonds. This determination presents a siginficantly higher precision crystal structure than the previously published structure [Tomura & Yamasshita (2008. X-ray Struct. Anal. Online, 24, x31–x32].

  8. Spectrophotometric Determination of Various Drugs Using Chloranilic Acid as Chromogenic Reagent - II

    Directory of Open Access Journals (Sweden)

    V. Annapurna

    2010-01-01

    Full Text Available Simple, accurate and reproducible visible spectrophotometric method for the assay of drugs such as pyrilamine and fluvoxamine as maleates was established based on the formation of charge-transfer complex and redox reaction between the corresponding drug and substituted p-benzoquinone (chloranilic acid. The optical characteristics such as Beer’s law limits, molar absorptivity and Sandell’s sensitivity are reported. Regression analysis using the method of least squares was made to evaluate the slope (b, intercept (a and correlation coefficient (r and standard error of estimation (Se for each drug.

  9. Spectroscopic, thermal and structural studies of new L-leucine and D-leucine complexes with chloranilic acid

    Science.gov (United States)

    Pawlukojć, A.; Hetmańczyk, J.; Nowicka-Scheibe, J.; Maurin, Jan K.; Schilf, W.; Rozwadowski, Z.

    2017-04-01

    New molecular complexes of L-leucine and D-leucine with chloranilic acid have been synthesized. Crystal structures of these crystals have been solved; they crystallize in non-centrosymmetric monoclinic P21 space group. In the crystal, leucine molecules exist in protonated form (C6NO2H14+) and chloranilic acid molecules in deprotonated form (C6HCl2O4-). Electronic (UV-Vis) and vibrational absorption (VA) spectra for both materials were collected. Circular dichroism methods such as electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) were used to determine the absolute configuration of new complexes. In both methods a characteristic (-,+) Cotton patterns are observed. In ECD spectra absorption bands are observed at 212 nm for acetonitrile solution and at 202 nm for aqueous solution. VCD spectra (in DMSO-d6 solution) show (-,+) Cotton pattern with strong peaks at 1323 cm-1 (CH rocking mode). Differential scanning calorimetry (DSC) and thermogravimetric (TG) investigations were performed to explore thermal properties of new materials. In DSC curve the decomposition and combustion processes are observed in 220-227 °C. The decomposition process was described by use of TG method and quadruple mass spectrometer (QMS). NMR spectra of pure L-leucine and chloranilic acid as well as L-leucine - chloranilic acid complex in solutions (D2O and DMSO) and in solid state confirm the geometry of molecules in complex both in solution and in solid state.

  10. Correlation between proton transfer and (35)Cl NQR frequency as well as molecular geometry of chloranilic acid in co-crystals with some organic bases.

    Science.gov (United States)

    Asaji, Tetsuo; Seliger, Janez; Zagar, Veselko; Ishida, Hiroyuki

    2010-07-01

    Proton transfer in hydrogen-bonded organic co-crystals of chloranilic acid with some organic bases was investigated by nuclear quadrupole resonance (NQR) spectroscopy. The (35)Cl NQR frequencies of chloranilic acid molecule as well as (14)N NQR frequencies of the organic base molecule were measured with the conventional pulse methods as well as double-resonance methods, respectively. The extent of proton transfer in the O...H...N hydrogen bond was estimated from Townes-Dailey analysis of the (14)N NQR parameters. The (35)Cl NQR frequency and molecular geometry of chloranilic acid are correlated to the extent of proton transfer in the protonation process of the organic base molecule. It is shown that the hydrogen bond affects the pi-electron system of chloranilic acid. Geometry dependence of the O...H...N hydrogen bond, i.e. the H-N valence bond order versus the hydrogen-bond geometry correlation is also discussed.

  11. Phase transition and proton exchange in 1,3-diazinium hydrogen chloranilate monohydrate

    Energy Technology Data Exchange (ETDEWEB)

    Asaji, T., E-mail: asaji@chs.nihon-u.ac.jp; Hoshino, M. [Nihon University, Department of Chemistry, Graduate School of Integrated Basic Sciences (Japan); Ishida, H. [Okayama University, Department of Chemistry, Faculty of Science (Japan); Konnai, A. [National Maritime Research Institute, Navigation and System Engineering Department (Japan); Shinoda, Y. [Bruker AXS K. K. (Japan); Seliger, J. [University of Ljubljana, Faculty of Mathematics and Physics (Slovenia); Zagar, V. [Jozef Stefan Institute (Slovenia)

    2010-06-15

    In the hydrate crystal of 1:1 salt with 1,3-diazine and chloranilic acid (H{sub 2}ca), (1,3-diazineH){center_dot}H{sub 2}O{center_dot}Hca, an unique hydrogen-bonded molecular aggregate is formed. There exists proton disorder in the N-H...O hydrogen bond between 1,3-diazinium ion and water (H{sub 2}O) of crystallization. In order to reveal dynamic aspect of this disorder, {sup 35}Cl NQR measurements were conducted. Two resonance lines observed at 35.973 and 35.449 MHz at 321 K split into four lines below T{sub c} = 198 K clearly showing occurrence of a solid-solid phase transition; 36.565, 36.357, 36.011, 35.974 MHz at 77 K. Temperature dependence of spin-lattice relaxation time T{sub 1} in high-temperature phase was observed to obey an Arrhenius-type relation with the activation energy of 8.5 kJ mol{sup - 1}. This result leads to the conclusion that proton exchange in the N-H...O hydrogen bond takes place in the high-temperature phase. Specific heat measurements by DSC resulted in the transition entropy {Delta}S = 1.3 J K{sup - 1} per 1 mole [(1,3-diazineH){center_dot}H{sub 2}O{center_dot}Hca]{sub 2} which is far less than 2R ln2 = 11.5 J K{sup - 1} mol{sup - 1}. It is expected that proton exchange in the two hydrogen bonds within the aggregate does not occur independently but concertedly with strong correlation in the high-temperature phase.

  12. Spectroscopic characterization of charge transfer complexes of 2,3-diaminopyridine with chloranilic acid and dihydroxy-p-benzoquinone in polar solvent.

    Science.gov (United States)

    Al-Ahmary, Khairia M

    2014-01-03

    Charge transfer (CT) complexes formed between 2,3-aminopyridine (2,3-DAP) as electron donor with the π-electron acceptors chloranilic acid (CHA) and dihydroxy-p-benzoquinone (DHBQ) were investigated spectrophotometrically in ethanol. Minimum-maximum absorbance method has been used for estimating the formation constants of the charge transfer reactions (KCT). Job's method of continuous variation and photometric titration studies were used to detect the stoichiometric ratios of the formed complexes and they showed that 1:1 complexes were produced. The molar extinction coefficient (ε), oscillator strength (f), dipole moment (μ), charge transfer energy (ECT), ionization potential (IP) and the dissociation energy (W) of the formed complexes were estimated, they reached acceptable values suggesting the stability of the formed CT-complexes. The solid CT-complexes were synthesized and characterized by elemental analyses, (1)H NMR and FTIR spectroscopies where the formed complexes included proton and electron transfer.

  13. Spectrophotometric studies on the charge-transfer interaction between p-nitroaniline with chloranilic acid as π-acceptor in different polar solvents

    Science.gov (United States)

    Singh, Neeti; Ahmad, Afaq

    2017-01-01

    The charge transfer interaction between the donor p-nitroaniline with the acceptor chloranilic acid has been studied spectrophotometrically in various solvents such as chloroform, ethanol, and methanol at room temperature. The results indicate that formation of CTC in non-polar solvent is high. The stoichiometry of the complex was found to be 1:1 ratio by straight-line method between donor and acceptor with maximum absorption bands. The data are discussed in terms of formation constant (KCT), molar extinction coefficient (εCT), standard free energy (ΔG), oscillator strength (f), transition dipole moment (μN), resonance energy (RN) and ionization potential (ID). The results indicate that the formation constant (KCT) for the complex was shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents that were used. The formation of the complex has been confirmed by UV-visible, FT-IR, and 1H NMR techniques.

  14. Thermal degradation kinetics and solid state, temperature dependent, electrical conductivity of charge–transfer complex of phenothiazine with chloranil and picric acid

    Indian Academy of Sciences (India)

    M A Ashok; B N Achar

    2008-02-01

    Temperature dependent electrical conductivity and thermal degradation kinetics of charge–transfer (C–T) complexes of phenothiazine (PTZ) with -chloranil (CHL) and picric acid (PA), are reported. These C–T complexes exhibited semiconducting behaviour. The activation energies for PTZ–CHL and PTZ–PA complexes are calculated based on their electrical conductivities measured over the temperature ranges 30–110°C and 30–90°C, respectively. And these energies for PTZ–CHL and PTZ–PA are 0.54 eV and 0.75 eV, respectively. The complexes are analysed for the kinetic parameters like the activation energy for decomposition and the Arrhenius pre-exponential factors in their pyrolysis region using Broido’s, Coats–Redfern as well as Horowitz–Metzger methods. Using standard equations, thermodynamic parameters such as enthalpy, entropy and free energies, are calculated.

  15. Isotope ratio of Cl NQR spin-lattice relaxation times in 1D hydrogen-bonding system of tetramethylpyrazine-chloranilic acid at high temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Asaji, Tetsuo, E-mail: asaji@chs.nihon-u.ac.jp [Nihon University, Department of Chemistry, College of Humanities and Sciences (Japan)

    2013-05-15

    The temperature dependences of spin-lattice relaxation time T{sub 1} of {sup 35}Cl and {sup 37}Cl NQR were studied for the co-crystal of tetramethylpyrazine (TMP) with chloranilic acid (H{sub 2}ca), TMP-H{sub 2}ca, in which one-dimensional hydrogen bonding is formed by alternate arrangement of TMP and H{sub 2}ca. The isotope ratio {sup 37}Cl T{sub 1} / {sup 35}Cl T{sub 1} was determined to be 1.0 {+-} 0.1 above ca. 290 K where a steep decrease of spin-lattice relaxation time T{sub 1} with increasing temperature was observed. In this temperature range it is suggested that the relaxation is originated from the slow fluctuation of electric field gradient (EFG). Beside EFG fluctuation due to the external-charge-density fluctuation, the small angle reorientation of the quantization axis triggered by a proton transfer motion between N...H-O and N-H...O hydrogen bonding states is proposed.

  16. DFT calculations of 2,6-dimethylpyrazine (26DMP) and its complex with chloranilic acid (CLA): Comparison to INS, IR and Raman vibration spectra

    Science.gov (United States)

    Pawlukojć, A.; Sobczyk, L.; Prager, M.; Bator, G.; Grech, E.; Nowicka-Scheibe, J.

    2008-12-01

    The inelastic neutron scattering (INS), infrared and Raman spectra of crystalline 2,6-dimethylpyrazine (26DMP) and its complex with chloranilic acid (26DMP·CLA) were measured. Simultaneously the DFT calculations of the molecular structures and frequencies of the normal vibrations were performed by using various functionals. The INS spectra were simulated in the energy range up to 1200 cm -1, on the basis of the calculated frequencies. A very good conformity was obtained between experimental and calculated data with respect to the structure as well as to frequencies, with exception, however, of the CH 3 torsional modes. The structural analysis based on the deviation from the sum of the van der Waals radii showed that the packing of the methyl groups in the 26DMP·CLA complex was markedly stronger than that in the neat 26DMP. However, the DFT calculations overestimated the role of this effect that may be due to a limitation of the applied methods. In addition the anharmonicity of the rotational potential led to the librational energies different from those obtained using a harmonic potential.

  17. 阿苯达唑与氯冉酸的荷移反应与应用%Application of Charge Transfer Reaction BetweenAlbendazole and Chloranilic Acid

    Institute of Scientific and Technical Information of China (English)

    赵桂芝; 李华侃; 柳越; 王玉华

    2001-01-01

    The charge transfer reaction between albendazole and chloranilic acid in alcohol-acetone solution was studied spectrophotometrically. The apparent molar absorptivity is 8.03×103 L*mol-1*cm-1 at 525 nm. The Beer′s law was obeyed in the range of 0~280 mg/L of albendazode. The composition of complex is 1∶1. The proposed method was applied to the determination of albendazole tablets with satisfactory results.%摘要研究并确定了阿苯达唑与氯冉酸的荷移反应条件。在乙醇-丙酮介质中形成1∶1络合物,其λmax=525 nm,吸光度与阿苯达唑浓度在0~280 mg/L范围内呈线性关系;表观摩尔吸光系数为8.03×103L*mol-1*cm-1;桑德尔灵敏度为0.033 μg*cm-2;相对标准偏差小于1%(n=8),回收率符合要求。

  18. Electric response in the antiferroelectric crystal of 4,4‧-di-t-butyl-2,2‧-bipyridyl with chloranilic acid

    Science.gov (United States)

    Rok, M.; Piecha-Bisiorek, A.; Szklarz, P.; Bator, G.; Sobczyk, L.

    2015-05-01

    The electric response was analyzed in the vicinity of the structural phase transition at 412 K in the single crystals of 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (chloranilic acid, CLA) with 4,4‧-di-t-butyl-2,2‧-bipyridyl (dtBBP). The dielectric permittivity of the complex measured along the b direction between 300 and 440 K and at frequencies ranging from 500 Hz to 2 MHz indicates two phenomena. At low frequencies, dielectric losses are ascribed to the electric conductivity of the crystal, while at high frequencies, to the dielectric relaxation described by means of the Cole-Cole relationship. The parameters of the dielectric response: the relaxation time, τ, the dielectric increment, εο - ε∞, and the distribution parameter of the relaxation time, α, were estimated and analyzed. The low-temperature structure of the crystals indicates the antiferroelectric arrangement of the supramolecular hydrogen bonds. The dielectric results also presented for the deuterated crystals of dtBBP·CLA proved that the dynamics of protons in the hydrogen bonds are responsible for the mechanism of phase transition.

  19. Electric response in the antiferroelectric crystal of 4,4′-di-t-butyl-2,2′-bipyridyl with chloranilic acid

    Energy Technology Data Exchange (ETDEWEB)

    Rok, M., E-mail: magdalena.rok@chem.uni.wroc.pl; Piecha-Bisiorek, A.; Szklarz, P.; Bator, G.; Sobczyk, L.

    2015-05-01

    Highlights: • The semiconducting properties of the crystals were disclosed in the organic complex. • Dielectric relaxation and dc conductivity were investigated. • Activation energy for the thermally activated processes of the σ{sub dc} was estimated. • The effect of hydrogen bonds on the mechanism of the phase transition and the electric properties of the crystal was discussed. - Abstract: The electric response was analyzed in the vicinity of the structural phase transition at 412 K in the single crystals of 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (chloranilic acid, CLA) with 4,4′-di-t-butyl-2,2′-bipyridyl (dtBBP). The dielectric permittivity of the complex measured along the b direction between 300 and 440 K and at frequencies ranging from 500 Hz to 2 MHz indicates two phenomena. At low frequencies, dielectric losses are ascribed to the electric conductivity of the crystal, while at high frequencies, to the dielectric relaxation described by means of the Cole–Cole relationship. The parameters of the dielectric response: the relaxation time, τ, the dielectric increment, ε{sub ο} − ε{sub ∞}, and the distribution parameter of the relaxation time, α, were estimated and analyzed. The low-temperature structure of the crystals indicates the antiferroelectric arrangement of the supramolecular hydrogen bonds. The dielectric results also presented for the deuterated crystals of dtBBP·CLA proved that the dynamics of protons in the hydrogen bonds are responsible for the mechanism of phase transition.

  20. Desvenlafaxinium chloranilate ethyl acetate solvate

    Directory of Open Access Journals (Sweden)

    Manpreet Kaur

    2013-10-01

    Full Text Available In the cation of the title compound, C16H26NO2+·C6HCl2O4−·C4H8O2, the 1-hydroxy-cyclohexyl ring adopts a slightly distorted chair conformation. The dihedral angle between the mean planes of the 1-hydroxycyclohexyl and 4-hydroxyphenyl rings is 84.0 (8°. In the anion, the hydroxyl H atom is twisted slightly out of the ring plane with a C—C—O—H torsion angle of −171.9°. Disorder was modeled for the methyl group of the acetate group in the solvate with an occupancy ratio of 0.583 (15: 0.417 (15. In the crystal, O—H...O hydrogen bonds are observed between cations and between cations and anions, while bifuricated N—H...(O,O cation–anion hydrogen bonds are also present, forming chains along [010] and [100]. In addition weak cation–anion and cation–solvate C—H...O interactions occur.

  1. Hydrogen bonded NHO chains formed by chloranilic acid (CLA) with 4,4‧-di-t-butyl-2,2‧-bipyridyl (dtBBP) in the solid state

    Science.gov (United States)

    Bator, G.; Sawka-Dobrowolska, W.; Sobczyk, L.; Owczarek, M.; Pawlukojć, A.; Grech, E.; Nowicka-Scheibe, J.

    2012-01-01

    In crystalline state 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (chloranilic acid, CLA) forms with 4,4'-di-t-butyl-2,2'-bipyridyl (dtBBP) the hydrogen bonded chains along the b-axis. From one side of the CLA molecule the proton transfer takes place and the hydrogen bond length is very short (2.615 Å). A continuous infrared absorption is observed for dtBBP·CLA in the wavenumber range between 3100 and 800 cm -1 also indicating the strong hydrogen bonds. The DSC measurements show a weak, close to continuous, phase transition at 414 K. The complex dielectric permittivity for a single crystal sample was measured in the temperature range 100-440 K and at frequencies between 200 Hz and 2 MHz. The dielectric response is a combination of semiconducting properties and a relaxation process most probably connected with the proton dynamics in the hydrogen bonds. The mechanism of the structural phase transition is discussed.

  2. X-ray diffraction and inelastic neutron scattering study of 2,6-dimethylpyrazine (DMP) chloranilic acid (CLA) complex

    Science.gov (United States)

    Prager, M.; Sawka-Dobrowolska, W.; Sobczyk, L.; Pawlukojć, A.; Grech, E.; Wischnewski, A.; Zamponi, M.

    2007-01-01

    The DMP · CLA and DMP · CLA-d 2 crystals below 100 K are monoclinic, space group P2 1/c with four molecules in the unit cells. Infinite chains of hydrogen bonded counterparts are formed with O⋯N distances equal to 2.767(2) and 2.639(2) for non-deuterated DMP · CLA. Deuteration leads to the Ubbelohlde effect particularly well manifested in the second short O-H⋯N bridge (elongation by ca. 0.02 Å). In the IR spectra a Hadži's trio of the broad absorption is observed characteristic of strong hydrogen bonds. In the INS spectra the vibrational density of states and methyl rotational tunnel splittings were determined. The temperature dependence of tunneling bands enabled to make mode assignments and to determine the methyl rotational potentials. Comparison of the results to the pure electron donor DMP was made and the difference found can be almost completely assigned to the steric changes of the environment. A weak isotope effect with deuteration of the OH⋯N bridges of the DMP · CLA complex is assigned to a charge transfer of δe/ e = 0.006.

  3. Mechanochemical Synthesis of Two Polymorphs of the Tetrathiafulvalene-Chloranil Charge Transfer Salt: An Experiment for Organic Chemistry

    Science.gov (United States)

    Wixtrom, Alex; Buhler, Jessica; Abdel-Fattah, Tarek

    2014-01-01

    Mechanochemical syntheses avoid or considerably reduce the use of reaction solvents, thus providing green chemistry synthetic alternatives that are both environmentally friendly and economically advantageous. The increased solid-state reactivity generated by mechanical energy imparted to the reactants by grinding or milling can offer alternative…

  4. Spectrophotometric Determination of Quinine by Charge-Transfer Reaction Between Quinine and Chloranilic Acid with Micelle-Sensitized%奎宁与氯冉酸的胶束增敏荷移反应及其测定

    Institute of Scientific and Technical Information of China (English)

    王孝镕; 李桂华; 唐清华; 潘琳琳; 范淑云

    2004-01-01

    提出了一种基于胶束增敏荷移反应测定奎宁的光度分析法.研究了在阳离子表面活性剂氯化十六烷基吡啶(CPC)胶束体系中电子给体奎宁与电子受体氯冉酸之间的荷移反应产物的光谱性质.发现CPC对奎宁与氯冉酸的荷移反应络合物的光吸收有显著的增强作用,使络合物的表观摩尔吸光系数提高了2.5倍(λmax=520 nm,ε=3.64×103 L·mol-1·cm-1).奎宁浓度在20~800 mg/L范围内符合比耳定律,r =0.9991.本方法用于片剂中奎宁含量的测定,其回收率为97.3% ~99.2%;5次测定的相对标准偏差为1.6% ~2.5%.

  5. Emprego de reagente em suspensão em sistema de injeção em fluxo: determinação espectrofotométrica de sulfato em águas naturais

    Directory of Open Access Journals (Sweden)

    Crnkovic Paula Manoel

    2002-01-01

    Full Text Available This paper presents an automatic procedure employing a reagent in the form of a slurry in a flow-injection system. The feasibility of the proposal is demonstrated by sulphate determination in water using the Barium Chloranilate method, which is based on the precipitation of barium sulphate. The release of a stoichiometric amount of highly colored chloranilic ions is monitored at 528 nm. The reaction is carried out in alcoholic medium in order to reduce the solubility of the reagent. A considerable improvement in the sensitivity is attained by adding ferric ions to the released chloranilic ions. An on-line filtration step to separate the excess reagent from the released chloranilic ions was necessary. In addition, a column containing a cation exchange resin was included in the manifold to remove potentially interfering ions. The proposed procedure is suitable for 30 determinations per hour and the relative standard deviation is less than 2%. The analytical curve is linear between 0.0 and 40 mg L-1 and the determination limit is about 2.0 mg L-1SO4(2-. Accuracy was confirmed by running several samples already analysed by a standard turbidimetric procedure.

  6. Synthesis of ellagic acid and its 4,4'-di-Ο-alky derivatives from gallic acid

    OpenAIRE

    Alam, Ashraful; 高口, 豊; 坪井, 貞夫

    2005-01-01

    Synthesis of ellagic acid and its 4,4'-di-Ο-alkyl derivatives from gallic acid is described. Ellagic acid is prepared by oxidative coupling of gallic acid with ο-chloranil. Functionalized methyl bormogallate underwent Ullmann coupling to give the biphenyl that upon lactonization resulted in the ellagic acid and its alkoxy derivatives.

  7. Synthesis and electrochemical studies of charge-transfer complexes of thiazolidine-2,4-dione with σ and π acceptors

    Science.gov (United States)

    Singh, Prashant; Kumar, Pradeep; Katyal, Anju; Kalra, Rashmi; Dass, Sujata K.; Prakash, Satya; Chandra, Ramesh

    2010-03-01

    In the present work, we report the synthesis and characterization of novel charge-transfer complexes of thiazolidine-2,4-dione (TZD) with sigma acceptor (iodine) and pi acceptors (chloranil, dichlorodicyanoquinone, picric acid and duraquinone). We also evaluated their thermal and electrochemical properties and we conclude that these complexes are frequency dependent. Charge-transfer complex between thiazolidine-2,4-dione and iodine give best conductivity. In conclusion, complex with sigma acceptors are more conducting than with pi acceptors.

  8. A Selective Colorimetric Anion Sensor Based on Di(hydroxymethyl) Di-(2-pyrrolyl)methane -TCBQ System

    Institute of Scientific and Technical Information of China (English)

    Yong GUO; Shi Jun SHAO; Jian XU; Yan Pin SHI; Sheng Xiang JIANG

    2004-01-01

    A new class of non-covalent charge-transfer complex for anion sensing, consisting of di(hydroxymethyl) di-(2-pyrrolyl) methane and chloranil (TCBQ) is characterized. The new colorimetric anion sensors can generate visual color change against PO43- and HPO42- anions in EtOH/H2O (1:1 v/v) mixture solution. The dipyrromethane-quinone aggregations may be used for higher selective detection of PO43- than other inorganic anions in water solution.

  9. Review of the methods for determination of sulfur dioxide in the atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    Gentilizza, M.

    1974-01-01

    This literature survey describes and assesses assay methods based on determination of the atmospheric sulfate by oxidation (lead dioxide, turbidimetry, barium chloranilate, electrical conductivity analysis, acidimetry and thorine methods) or of the sulfite (determination in iodine or alkaline solution, with fuchsin, iodothiosulfate, by atomic absorption spectrophotometry, fluorimetry, etc.), based on measurement of sulfur dioxide (hydrogen flame emission spectrophotometry, gas chromatography), on adsorption on silica gel or in phenanthroline solution and on polarography.

  10. Spectrophotometric determination of nizatidine and ranitidine through charge transfer complex formation.

    Science.gov (United States)

    Walash, M; Sharaf-El Din, M; Metwalli, M E-S; RedaShabana, M

    2004-07-01

    Two Spectrophotometric procedures are presented for the determination of two commonly used H2-receptor antagonists, nizatidine (I) and ranitidine hydrochloride (II). The methods are based mainly on charge transfer complexation reaction of these drugs with either p-chloranilic acid (rho-CA) or 2, 3 dichloro-5, 6-dicyanoquinone (DDQ). The produced colored products are quantified spectrophotometrically at 515 and 467 nm in chloranilic acid and DDQ methods, respectively. The molar ratios for the reaction products and the optimum assay conditions were studied. The methods determine the cited drugs in concentration ranges of 20-200 and 20-160 microg/mL for nizatidine and ranges of 20-240 and 20-140 microg/mL for ranitidine with chloranilic acid and DDQ methods, respectively. A more detailed investigation of the complexes formed was made with respect to their composition, association constant, molar absorptivity and free energy change. The proposed procedures were successfully utilized in the determination of the drugs in pharmaceutical preparations. The standard addition method was applied by adding nizatidine and ranitidine to the previously analyzed tablets or capsules. The recovery of each drug was calculated by comparing the concentration obtained from the spiked mixtures with those of the pure drug. The results of analysis of commercial tablets and the recovery study (standard addition method) of the cited drugs suggested that there is no interference from any excipients, which are present in tablets or capsules. Statistical comparison of the results was performed with regard to accuracy and precision using student's t-test and F-ratio at 95% confidence level. There is no significant difference between the reported and proposed methods with regard to accuracy and precision.

  11. 35Cl NQR study of lattice dynamic and magnetic property of a crystalline coordination polymer {CuCA(phz)(H 2O) 2} n

    Science.gov (United States)

    Gotoh, Kazuma; Terao, Takeshi; Asaji, Tetsuo

    2007-01-01

    Copper(II) compounds {CuCA(phz)(H 2O) 2} n (H 2CA = chloranilic acid, phz = phenazine) having a layer structure of -CuCA(H 2O) 2- polymer chains and phenazine were studied by 35Cl nuclear quadrupole resonance (NQR). The single NQR line observed at 35.635 MHz at 261.5 K increased to 35.918 MHz at 4.2 K. The degree of reduction of electric field gradient due to lattice vibrations was similar to that of chloranilic acid crystal. Temperature dependence of spin-lattice relaxation time, T1, of the 35Cl NQR signal below 20 K, between 20 and 210 K, and above 210 K, was explained by (1) a decrease of effective electron-spin density caused by antiferromagnetic interaction, (2) a magnetic interaction between Cl nuclear-spin and electron-spins on paramagnetic Cu(II) ions, and (3) an increasing contribution from reorientation of ligand molecules, respectively. The electron spin-exchange parameter ∣ J∣ between the neighboring Cu(II) electrons was estimated to be 0.33 cm -1 from the T1 value of the range 20-210 K. Comparing this value with that of J = -1.84 cm -1 estimated from the magnetic susceptibility, it is suggested that the magnetic dipolar coupling with the electron spins on Cu(II) ions must be the principal mechanism for the 35Cl NQR spin-lattice relaxation of {CuCA(phz)(H 2O) 2} n but a delocalization of electron spin over the chloranilate ligand has to be taken into account.

  12. Spectroscopy of charge transfer complexes of four amino acids as organic two-dimensional conductors

    Energy Technology Data Exchange (ETDEWEB)

    Padhiyar, Ashvin; Patel, A J; Oza, A T [Department of Physics, Sardar Patel University, Vallabh Vidyanagar-388 120, Gujarat (India)

    2007-12-05

    It is found in this study that four amino acids, namely asparagine, arginine, histidine and glutamine form two-dimensional conducting systems which are charge transfer complexes (CTCs) with organic acceptors like TCNQ, TCNE, chloranil, DDQ, TNF and iodine. It is verified using optical absorption edges that these are 2d conductors like transition metal dichalcogenides obeying absorption functions different from 1d and 3d conductors. This 2d nature is related to the network of intermolecular H-bonding in these complexes, which leads to a global H-bonded network resulting in the absence of local deformation due to the relaxation of strain.

  13. Spectroscopy of charge transfer complexes of four amino acids as organic two-dimensional conductors

    Science.gov (United States)

    Padhiyar, Ashvin; Patel, A. J.; Oza, A. T.

    2007-12-01

    It is found in this study that four amino acids, namely asparagine, arginine, histidine and glutamine form two-dimensional conducting systems which are charge transfer complexes (CTCs) with organic acceptors like TCNQ, TCNE, chloranil, DDQ, TNF and iodine. It is verified using optical absorption edges that these are 2d conductors like transition metal dichalcogenides obeying absorption functions different from 1d and 3d conductors. This 2d nature is related to the network of intermolecular H-bonding in these complexes, which leads to a global H-bonded network resulting in the absence of local deformation due to the relaxation of strain.

  14. Utilization of charge-transfer complexation for the detection of carcinogenic substances in foods: Spectroscopic characterization of ethyl carbamate with some traditional π-acceptors

    Science.gov (United States)

    Adam, Abdel Majid A.; Refat, Moamen S.; Saad, Hosam A.

    2013-04-01

    The study of toxic and carcinogenic substances in foods represents one of the most demanding areas in food safety, due to their repercussions for public health. One potentially toxic compound for humans is ethyl carbamate (EC). EC is a multi-site genotoxic carcinogen of widespread occurrence in fermented foods and alcoholic beverages. Structural and thermal stability of charge-transfer complexes formed between EC as a donor with quinol (QL), picric acid (PA), chloranilic acid (CLA), p-chloranil (p-CHL) and 1,3-dinitrobenzene (DNB) as acceptors were reported. Elemental analysis (CHN), electronic absorption spectra, photometric titration, IR, and 1H NMR spectra show that the interaction between EC and acceptors was stabilized by hydrogen bonding, via a 1:1 stoichiometry. Thermogravimetric (TG) analysis indicates that the formation of molecular CT complexes was stable, exothermic and spontaneous. Finally, the CT complexes were screened for their antibacterial and antifungal activities. The results indicated that the [(EC)(QL)] complex exhibited strong antimicrobial activities against various bacterial and fungal strains compared with standard drugs.

  15. Utilization of Charge Transfer and Kinetic Methods for the Determination of Doripenem

    Directory of Open Access Journals (Sweden)

    Nora H. Al-Shaalan

    2012-01-01

    Full Text Available Problem statement: This study presents rapid, uncomplicated and sensitive spectrophotometric techniques for the analysis of doripenem in both its pure and pharmaceutical forms. Approach: The main principle of the approaches and procedures that have been developed is the reaction of doripenem as an n-electron donor to ninhydrin and π-acceptors, such as tetracyanoethylene, 7,7,8,8-tetracyanoquinodimethane, 2,3,5,6-tetrachloro-1,4-benzoquinone, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and chloranilic acid. The wavelengths 580, 264, 320, 357, 375 and 465 nm was used for measuring the resulting complexes for ninhydrin, chlorine, chloranilic acid, DDQ, TCNQ and TCNE respectively. Results: The suggested procedures for the determination of doripenem were successfully put into practice with good recovery; the percent recovery ranged from 99.31-100.55. Benes-Hildebrand plots were also used to study the association constants and the free energy changes. Conclusion: The results of the CT method agree with those of the kinetic method and there is no significant difference between them.

  16. An Exceptionally Facile Two-Step Structural Isomerization and Detoxication via a Water-Assisted Double Lossen Rearrangement

    Science.gov (United States)

    Li, Feng; Huang, Chun-Hua; Xie, Lin-Na; Qu, Na; Shao, Jie; Shao, Bo; Zhu, Ben-Zhan

    2016-12-01

    N-hydroxyphthalimide (NHPI), which is best known as an organocatalyst for efficient C-H activation, has been found to be oxidized by quinoid compounds to its corresponding catalytically active nitroxide-radical. Here, we found that NHPI can be isomerized into isatoic anhydride by an unusually facile two-step method using tetrachloro-1,4-benzoquinone (TCBQ, p-chloranil), accompanied by a two-step hydrolytic dechlorination of highly toxic TCBQ into the much less toxic dihydroxylation product, 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid). Interestingly, through the complementary application of oxygen-18 isotope-labeling, HPLC combined with electrospray ionization quadrupole time-of-flight and high resolution Fourier transform ion cyclotron resonance mass spectrometric studies, we determined that water was the source and origin of oxygen for isatoic anhydride. Based on these data, we proposed that nucleophilic attack with a subsequent water-assisted Lossen rearrangement coupled with rapid intramolecular addition and cyclization in two consecutive steps was responsible for this unusual structural isomerization of NHPI and concurrent hydroxylation/detoxication of TCBQ. This is the first report of an exceptionally facile double-isomerization of NHPI via an unprecedented water-assisted double-Lossen rearrangement under normal physiological conditions. Our findings may have broad implications for future research on hydroxamic acids and polyhalogenated quinoid carcinogens, two important classes of compounds of major chemical and biological interest.

  17. Textile dyes and pigments as a source of dioxins

    Energy Technology Data Exchange (ETDEWEB)

    Bostjan, K.; Marechal, A.M. le [Faculty of Mechanical Engineering, Maribor (Slovenia); Voncina, E. [Environmental Protection Institute, Maribor (Slovenia); Brodnjak-Voncina, D. [Faculty of Chemistry and Chemical Engineering, Maribor (Slovenia)

    2004-09-15

    Synthesis of colorants represents a relatively large group of chemicals with complex synthesis processes. Over 7 x 10 ton of dyestuff is produced annually worldwide with more than 100,000 types of dyes and pigments. During synthesis of some colorants polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) can be formed. Dioxins are related to halogens, especially chlorine and bromine homologues are most toxic and persistent. About 40% of worldwide used colorants contain organically bounded chlorine. Further formations of PCDD/Fs can occur via dyeing and textile finishing processes with conditions favoured for the generation of PCDD/Fs (high temperatures, alkaline conditions, UV radiations or other radical starters). Relative small number of data is available for PCDD/Fs presence and contents in textile dyes and pigments. Known sources of PCDD/Fs are dioxazine dyes and pigments, produced from chloranil1. Chloranil is produced from chlorinated phenols and during the synthesis PCDD/Fs as by products are formed. In a sample of Ni-phthalocyanine dye higher congeners of PCDD/Fs were found in {mu}g/kg concentration level. In our work six samples of disperse dyes were analysed for PCDD/Fs content. In two disperse black dyes, a mixture of anthraquinone and azo-disperse dye, considerable level ({mu}g/kg) of PCDD/Fs was determined. The OCDD was the dominant compound. Distribution of dioxins and their fate during textile processes were further investigated.

  18. Proton dynamics in one-dimensional hydrogen-bonding system in molecular co-crystals TMP-D{sub 2}ca and DMP-H{sub 2}ca

    Energy Technology Data Exchange (ETDEWEB)

    Asaji, T., E-mail: asaji@chs.nihon-u.ac.jp; Amino, D.; Tago, N. [Nihon University, Department of Chemistry, College of Humanities and Sciences (Japan); Mizuno, M. [Kanazawa University, Department of Chemistry, Graduate School of Natural Science and Technology (Japan)

    2010-04-15

    The proton dynamics in one-dimensional hydrogen-bonding system in molecular co-crystals of tetramethylpyrazine (TMP) with chloranilic acid (H{sub 2}ca), as well as 2,6-dimethylpyrazine (DMP) with H{sub 2}ca is studied by {sup 35}Cl NQR and {sup 2}H NMR spin-lattice relaxation measurements. No transfer motion of proton between the acid and base molecules is observed in DMP-H{sub 2}ca, while the motion of the acid proton is excited in TMP-H{sub 2}ca and the activation energy for the motion increases from 35 kJ mol{sup - 1} to 50 kJ mol{sup - 1} by the deuteration.

  19. New method for spectrophotometric determination of quinones and barbituric acid through their reaction. A kinetic study

    Science.gov (United States)

    Medien, H. A. A.

    1996-11-01

    A new and sensitive spectrophotometric method is described for the determination of p-benzoquinone, p-chloranil and 1.4-naphthoquinone. The method is based on the reaction between quinones and barbituric acid, by which a color is developed with maximum absorption between 485 and 555 nm in 50% methyl alcohol-water mixture. The absorption of the product obeys Beer's law within the concentration range 0.025-05 mM of orginal quinone. The kinetics of the reaction between p-benzoquinone and barbituric acid was studied in a range of methyl alcohol-water mixtures. The reaction follows overall second order kinetics, first order in each of the reactants. The rate increases with increasing dielectric constant. The method was applied for determination of barbituric acid with p-benzoquinone in the concentration range of 0.025-0.345 mM. Other barbiturates do not interfere.

  20. Electronic, infrared, mass, 1H NMR spectral studies of the charge-transfer complexes of sulphonamide drugs with π-acceptors in acetonitrile

    Science.gov (United States)

    Frag, Eman Y.; Mohamed, Gehad G.

    2010-08-01

    The rapid interaction between sulphonamides (sulphamethoxazole (SMZ), sulphaguanidine (SGD), sulphaquinoxaline sodium (SQX) and sulphadimidine sodium (SDD)) as n-electron donors with the 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid, p-CLA) as π-acceptors resulted in the formation of 1:1 charge-transfer complexes as the final products with the formula [(drug) (acceptor)]. The final products of the reactions have been isolated and characterized using FT-IR, 1H NMR, mass spectroscopy and elemental analyses as well as photometric measurements and thermogravimetric analysis (TG). The stoichiometry and apparent formation constants of the complexes formed were determined by applying the conventional spectrophotometric molar ratio method.

  1. Utility of Certain Π Acceptors for Spectrophotometric Determination of Sildenafil Citrate

    Directory of Open Access Journals (Sweden)

    Nora H. Al-Shaalan

    2007-01-01

    Full Text Available Sildenafil citrate was determined through charge transfer complexes (CTC formation with three electron acceptor reagents. The methods involve the reaction of Sildenafil citrate as n-donor with either Chloranil (tetrachloro 1,4-benzoquinone, tetracyanoethylene (TCNE or 7,7,8,8-tetracyanoquinodimethane (TCNQ as n-acceptors, to give a stable and highly colored radical anion. The colored products were quantified spectrophotometrically. The condition ranges adhering to Beer's law are 0.05-3.00 mg/ml. The molar ratios of the reactants were ascertained. The different parameters were carefully studied and optimized. Statistical analysis of the results revealed equal precision and accuracy to the results of the reported method. The methods were applied for determination of sildenafil citrate in pure form and in Viagra tablets.

  2. Light scattering from macromolecular systems: Molecular crystals and polymers

    Science.gov (United States)

    Bernstein, E. R.

    1981-11-01

    The research objectives were to: (1) characterize phase transitions theoretically and experimentally in molecular crystal systems; (2) use the above understanding gained by light scattering studies and theoretical interpretation to apply to the more complex system of lyotropic liquid crystals; and (3) then apply knowledge gained on the model systems of increasing complexity to polymer liquid crystals and solid polymers as observed by laser light scattering techniques. Systems experimentally and theoretically discussed are: trioxane, triazine, benzil, and chloranil. Studies of lyotropic liquid crystals (sodium decyl sulfate, sodium sulfate, decanol, water) have progressed. The major findings are: a number of phase transitions occur between 20 and 60 C; these transitions evidence strong critical behavior and long correlation times for fluctuations; and liquid crystals can be studied by light scattering. Spectra of solid powders, ribbons, and liquid crystals of PBT and solid PBO were obtained.

  3. Electron spectra of radical cations of heteroanalogs

    Energy Technology Data Exchange (ETDEWEB)

    Petrushenko, K.B.; Turchaninov, V.K.; Vokin, A.I.; Ermikov, A.F.; Frolov, Yu.L.

    1985-12-01

    Radical cation spectra of indazole and benzothiophene in the visible region were obtained by laser photolysis during the reaction of photoexcited quinones with these compounds in acetonitrile. The charge transfer bands of the complexes of the test compounds with p-chloranil and 7,7,8,8-tetracyanoquinodimethane in dioxane were recorded on a Specord M-40. Photoelectron spectra were obtained on a ES-3201 electron spectrometer. The He(I) resonance band (21.21 eV) was used for excitation. Measurements were carried out in the 60-120/sup 0/C range. The energy scale was calibrated form the first ionization potentials of Ar (15.76 eV) and chlorobenzene (9.06 eV). The error in the determination of the ionization potentials for the first four photoelectron bands was 0.05 eV.

  4. Synthesis and characterization of mibolerone

    Institute of Scientific and Technical Information of China (English)

    YANG Qing; FAN Bo-lin; TANG Rui-ren

    2007-01-01

    A simple and effective route for the synthesis of mibolerone was described starting from the estr-5(10)-en-3,17-dione in four steps with the overall yield of 47.0%. Thus, two methods for key intermediate methylnorandrost were investigated: one(method A) starting from estr-4-en-3,17-dione underwent 3-keto group protected with ethyl orthoformate to give 3-ethoxy-3,5-dien-estr-17-one, the other(method B) from estr-5(10)-en-3,17-dione and protected 3-keto group to give 3,3-dimethoxy-estr-5(10)-7-one in a mild acidic condition. Then, two intermediates were subsequently reacted with methyllithium followed by a mild hydrolytic procedure and gave methylnorandrost with total yield 25.0% and 86.0%, respectively. In the preparation of 6-dehydrogenation product of methylnorandrost, two procedures(method C and method D) were investigated: one was the protected 17α-methyl-17β-hydroxy △3,-5-enol ethers estrendiene brominated and the resulting 6-bromo-19-methylnortestosterone was then immediately dehydrohaloenated to give 6-dehydro-19-methylnortestosterone, the total yield only reaches 36.0%; the other was directly dehydrogenated with chloranil and the yield reaches 75.6% under the optimum conditions: in refluxing tetrahydrofuran,the molar ratio of methylnorandrost to chloranil is 0.66 and reaction time of 5 h. The titled compound and intermediates were characterized by 1H and 13C NMR, IRMS and elemental analysis.

  5. Spectral, thermal and kinetic studies of charge-transfer complexes formed between the highly effective antibiotic drug metronidazole and two types of acceptors: σ- and π-acceptors.

    Science.gov (United States)

    Refat, Moamen S; Saad, Hosam A; Adam, Abdel Majid A

    2015-04-15

    Understanding the interaction between drugs and small inorganic or organic molecules is critical in being able to interpret the drug-receptor interactions and acting mechanism of these drugs. A combined solution and solid state study was performed to describe the complexation chemistry of drug metronidazole (MZ) which has a broad-spectrum antibacterial activity with two types of acceptors. The acceptors include, σ-acceptor (i.e., iodine) and π-acceptors (i.e., dichlorodicyanobenzoquinone (DDQ), chloranil (CHL) and picric acid (PA)). The molecular structure, spectroscopic characteristics, the binding modes as well as the thermal stability were deduced from IR, UV-vis, (1)H NMR and thermal studies. The binding ratio of complexation (MZ: acceptor) was determined to be 1:2 for the iodine acceptor and 1:1 for the DDQ, CHL or PA acceptor, according to the CHN elemental analyses and spectrophotometric titrations. It has been found that the complexation with CHL and PA acceptors increases the values of enthalpy and entropy, while the complexation with DDQ and iodine acceptors decreases the values of these parameters compared with the free MZ donor.

  6. Ferroelectric phase transition, ionicity condensation, and multicriticality in charge-transfer organic complexes

    Science.gov (United States)

    Kishine, Jun-Ichiro; Luty, Tadeusz; Yonemitsu, Kenji

    2004-02-01

    To elucidate a pressure-temperature phase diagram of the quasi-one-dimensional mixed-stack charge-transfer complex tetrathiafulvalene-P-chloranil (TTF-CA), we study the quasi-one-dimensional spin-1 Blume-Emery-Griffiths model. In addition to the local charge-transfer energy (Δ) and the inter-stack polar (dipole-dipole) interaction (J⊥), we take account of the interstack electrostriction (Coulomb-lattice coupling). Using the self-consistent chain-mean-field theory, where the intra-stack degrees of freedom are exactly treated by the transfer-matrix method, we reproduce the gas-liquid-solid like phase diagram corresponding to the neutral (N), paraelectric ionic (Ipara), and ferroelectric ionic (Iferro) phases, respectively. Our classical model describes an essential point of the multicritical behavior of TTF-CA, i.e., the interchain electrostriction exclusively enhances the charge concentration (ionicity condensation), but does not affect the interchain ferroelectric coupling. This effect leads to appearance of the intermediate Ipara phase in between the N and Iferro phases on the Δ-T phase diagram.

  7. Spectrophotometric Determination of Mycophenolate Mofetil as Its Charge-Transfer Complexes with Two π-Acceptors

    Directory of Open Access Journals (Sweden)

    K. B. Vinay

    2012-01-01

    Full Text Available Two simple, selective, and rapid spectrophotometric methods are described for the determination of mycophenolate mofetil (MPM in pure form and in tablets. Both methods are based on charge-transfer complexation reaction of MPM with p-chloranilic acid (p-CA or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ in dioxane-acetonitrile medium resulting in coloured product measurable at 520 nm (p-CA or 580 nm (DDQ. Beer’s law is obeyed over the concentration ranges of 40–400 and 12–120 μg mL−1 MPM for p-CA and DDQ, respectively, with correlation coefficients (r of 0.9995 and 0.9947. The apparent molar absorptivity values are calculated to be 1.06×103 and 3.87×103 L mol−1 cm−1, respectively, and the corresponding Sandell’s sensitivities are 0.4106 and 0.1119 μg cm−1. The limits of detection (LOD and quantification (LOQ are also reported for both methods. The described methods were successfully applied to the determination of MPM in tablets. Statistical comparison of the results with those of the reference method showed excellent agreement. No interference was observed from the common excipients present in tablets. Both methods were validated statistically for accuracy and precision. The accuracy and reliability of the methods were further ascertained by recovery studies via standard addition procedure.

  8. Protonic motion in one-dimensional hydrogen-bonded molecular crystal [4,6-dmpH][Hca] as revealed by {sup 35}Cl NQR

    Energy Technology Data Exchange (ETDEWEB)

    Asaji, Tetsuo, E-mail: asaji@chs.nihon-u.ac.jp [Department of Chemistry, College of Humanities and Sciences, Nihon University, Sakurajosui 3-25-40, Setagaya-ku, Tokyo 156-8550 (Japan); Konnai, Akiko [Navigation and System Engineering Department, National Maritime Research Institute, Shinkawa 6-38-1, Mitaka, Tokyo 181-0004 (Japan); Oguni, Masaharu [Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, O-okayama 2-12-1, Meguro-ku, Tokyo 152-8551 (Japan)

    2012-03-20

    Highlights: Black-Right-Pointing-Pointer 1-D ferroelectric hydrogen-bonded chain. Black-Right-Pointing-Pointer The migration of a protonic soliton in the chain. Black-Right-Pointing-Pointer Protonic motion was detected by {sup 35}Cl NQR spin-lattice relaxation measurements. Black-Right-Pointing-Pointer Heat capacity revealed no phase transition in [4,6-dmpH][Hca]. - Abstract: A protonic motion in the 1-D hydrogen-bonded zigzag chain in 4,6-dimethylpyrimidinium hydrogen chloranilate, [4,6-dmpH][Hca], was studied from the measurements of {sup 35}Cl nuclear quadrupole resonance (NQR) spin-lattice relaxation time (T{sub 1}). The four NQR frequencies were observed at 36.846, 36.767, 35.945, and 35.905 MHz at 77 K. The temperature dependences of these frequencies were smooth and continuous in 77-360 K. The absence of solid-solid phase transition and the metastable phase was confirmed by heat capacity measurements. Temperature dependence of the NQR T{sub 1} suggests an excitation of a motion above ca. 200 K with the activation energy of 11.5 kJ mol{sup -1}. In the stable phase too, the excitation of proton transfer is expected to occur as suggested for the metastable phase of as-grown crystals. Such transfer motion may be possible at the kink structure of the 1-D ferroelectric zigzag chain, and the kink can migrate in the chain accordingly.

  9. Calculations of multipulse sequence in NQR of spins 32.

    Science.gov (United States)

    Odin, C

    1999-12-01

    The general formalism of the interaction representation with respect to an operator which is its own inverse is developed and applied to pure NQR of spins I = 32. Under the assumption of no relaxation and no dipolar coupling, it is shown that the calculation of the response to pure NQR multipulse sequences can be performed with the same concepts used in high field NMR, such as coherence pathways. All the tools and mathematical expressions to predict the time evolution of the signal created by a pure NQR multipulse sequence are presented explicitly. It takes into account the off-resonance irradiation as well as the angular dependence of the excitation and detection for every value of the electric field gradient asymmetry parameter. Particular attention is devoted to the powder average, which is performed via a probability function derived analytically for the first time, leading to a drastic reduction of simulation times. The theory is illustrated by the study of the optimization and excitation bandwidths of one- to three-pulse sequences and compared to experimental results on Chloranil. We show that the three-pulse "stimulated echo" sequence gives a more uniform excitation profile than the traditional two-pulse echo sequence for powder samples. Thus, the "stimulated echo" sequence could be useful to cover a large spectrum when the experiment duration, or the signal to noise ratio, are not critical parameters. Analytical expressions for the nutation spectra obtained by one or two-pulse sequences are also derived for the first time.

  10. Compatible validated spectrofluorimetric and spectrophotometric methods for determination of vildagliptin and saxagliptin by factorial design experiments

    Science.gov (United States)

    Abdel-Aziz, Omar; Ayad, Miriam F.; Tadros, Mariam M.

    2015-04-01

    Simple, selective and reproducible spectrofluorimetric and spectrophotometric methods have been developed for the determination of vildagliptin and saxagliptin in bulk and their pharmaceutical dosage forms. The first proposed spectrofluorimetric method is based on the dansylation reaction of the amino group of vildagliptin with dansyl chloride to form a highly fluorescent product. The formed product was measured spectrofluorimetrically at 455 nm after excitation at 345 nm. Beer's law was obeyed in a concentration range of 100-600 μg ml-1. The second proposed spectrophotometric method is based on the charge transfer complex of saxagliptin with tetrachloro-1,4-benzoquinone (p-chloranil). The formed charge transfer complex was measured spectrophotometrically at 530 nm. Beer's law was obeyed in a concentration range of 100-850 μg ml-1. The third proposed spectrophotometric method is based on the condensation reaction of the primary amino group of saxagliptin with formaldehyde and acetyl acetone to form a yellow colored product known as Hantzsch reaction, measured at 342.5 nm. Beer's law was obeyed in a concentration range of 50-300 μg ml-1. All the variables were studied to optimize the reactions' conditions using factorial design. The developed methods were validated and proved to be specific and accurate for quality control of vildagliptin and saxagliptin in their pharmaceutical dosage forms.

  11. Charge transfer complex studies between some non-steroidal anti-inflammatory drugs and π-electron acceptors

    Science.gov (United States)

    Duymus, Hulya; Arslan, Mustafa; Kucukislamoglu, Mustafa; Zengin, Mustafa

    2006-12-01

    Charge transfer (CT) complexes of some non-steroidal anti-inflammatory drugs, naproxen and etodolac which are electron donors with some π-acceptors, such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano- p-benzoquinone (DDQ), p-chloranil ( p-CHL), have been investigated spectrophotometrically in chloroform at 21 °C. The coloured products are measured spectrophotometrically at different wavelength depending on the electronic transition between donors and acceptors. Beer's law is obeyed and colours were produced in non-aqueous media. All complexes were stable at least 2 h except for etodolac with DDQ stable for 5 min. The equilibrium constants of the CT complexes were determined by the Benesi-Hildebrand equation. The thermodynamic parameters Δ H, Δ S, Δ G° were calculated by Van't Hoff equation. Stochiometries of the complexes formed between donors and acceptors were defined by the Job's method of the continuous variation and found in 1:1 complexation with donor and acceptor at the maximum absorption bands in all cases.

  12. Validated spectroflurimetric determination of some H1 receptor antagonist drugs in pharmaceutical preparations through charge transfer complexation.

    Science.gov (United States)

    el-Din, Mohie K Sharaf; Ibrahim, Fawzia; Eid, Manal I; Wahba, Mary E K

    2012-01-01

    A validated simple, rapid, and selective spectrofluorimetric method was developed for the determination of some antihistaminic H(1) receptor antagonist drugs namely ebastine (EBS), cetirizine dihydrochloride (CTZ), and fexofenadine hydrochloride (FXD). The method is based on the reaction of the cited drugs with some Π acceptors namely p-chloranilic acid (CLA), tetracyanoethylene (TCNE), and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) to give highly fluorescent derivatives. The fluorescence intensity-concentration plots were rectilinear over the concentration ranges of 0.2-3.0, 0.2-2.5 and 0.15-2.0 μg/ml for EBS with CLA, DDQ, and TCNE respectively; 0.5-7.0, 0.5-6.0, and 0.2-4.0 μg/ml for CTZ with the previously mentioned reagents, and 0.2-3.5, 0.5-6.0, and 0.2-3.5 μg/ml for FXD. The factors affecting the formation of the reaction products were carefully studied and optimized. The method was applied for the determination of the studied drugs in their dosage forms. The results obtained were in good agreement with those obtained by the comparison methods. Reactions Stoichiometries of the complexes formed between the studied drugs and Π acceptors were defined by the Job's method of the continuous variation and found in 1:1 in all cases.

  13. Phase Competition, Solitons, and Domain Walls in Neutral–Ionic Transition Systems

    Science.gov (United States)

    Tsuchiizu, Masahisa; Yoshioka, Hideo; Seo, Hitoshi

    2016-10-01

    Phase competition and excitations in the one-dimensional neutral-ionic transition systems are theoretically studied comprehensively. From the semiclassical treatment of the bosonized Hamiltonian, we examine the competition among the neutral (N), ferroelectric-ionic (I$_\\mathrm{ferro}$) and paraelectric-ionic (I$_\\mathrm{para}$) states. The phase transitions between them can become first-order when the fluctuation-induced higher-order commensurability potential is considered. In particular, the description of the first-order phase boundary between N and I$_\\mathrm{ferro}$ enables us to analyze N-I$_\\mathrm{ferro}$ domain walls. Soliton excitations in the three phases are described explicitly and their formation energies are evaluated across the phase boundaries. The characters of the soliton and domain-wall excitations are classified in terms of the topological charge and spin. The relevance to the experimental observations in the molecular neutral-ionic transition systems is discussed. We ascribe the pressure-induced crossover in tetrathiafulvalene-$p$-chloranil (TTF-CA) at a high-temperature region to that from the N to the I$_\\mathrm{para}$ state, and discuss its consequence.

  14. Development and Validation of Spectrophotometric Methods for the Determination of Rasagiline in Pharmaceutical Preparations

    Directory of Open Access Journals (Sweden)

    Serife Evrim Kepekci Tekkeli

    2013-01-01

    Full Text Available This study presents three simple, rapid, and accurate spectrophotometric methods for the determination of Rasagiline (RSG in pharmaceutical preparations. The determination procedures depend on the reaction of RSG with chloranilic acid for method A, tetrachloro-1,4-benzoquinone for method B, and 7,7,8,8-tetracyanoquinodimethane for method C. The colored products were quantitated spectrophotometrically at 524, 535, and 843 nm for methods A, B, and C, respectively. Different variables affecting the reaction were optimized. Linearity ranges of the methods with good correlation coefficients (0.9988–0.9996 were observed as 25–300 µg mL−1, 25–350 µg mL−1, and 50–500 µg mL−1 for methods A, B, and C, respectively. The formation of products takes place through different mechanisms. The sites of interaction were confirmed by elemental analysis using IR and 1H-NMR spectroscopy. The validation of the methods was carried out in terms of specificity, linearity, accuracy, precision, robustness, limit of detection, and limit of quantitation. No interference was observed from concomitants usually present in dosage forms. The methods were applied successfully to the determination of RSG in pharmaceutical preparations.

  15. Indirect flow-injection spectrophotometric determination of meloxicam, tenoxicam and piroxicam in pharmaceutical formulations.

    Science.gov (United States)

    Al-Momani, Idrees F

    2006-12-01

    A simple and sensitive indirect spectrophotometric method for the assay of meloxicam (MX), tenoxicam (TX) and piroxicam (PX) in pure and in pharmaceutical formulations by flow injection analysis (FIA) has been proposed. The method is based on the oxidation of these drugs by a known excess of N-bromosuccinimide (NBS) in an acidic medium, followed by a reaction of excess oxidant with chloranilic acid (CAA) to bleach its purple color. The absorbance values increased linearly with increasing concentrations of the drugs. Variables, such as the acidity, reagent concentrations, flow rate of reagents and other FI parameters were optimized to produce the most sensitive and reproducible results. The system obeyed Beer's low over concentration ranges of 10 - 160, 20 - 200 and 10 - 160 microg/ml for MX, TX and PX, respectively. The common excipients and additives did not interfere with their determinations. The method was successfully applied to the determinations of MX, TX and PX in various pharmaceutical preparations. The results obtained by the proposed method were found to be in good agreement with those found by the official HPLC methods.

  16. A microbial method using whole cells of Thiobacillus thiooxidans for measuring sulphate in waters

    Energy Technology Data Exchange (ETDEWEB)

    Nakamura, K.; Yudiarto, M.A.; Kaneko, N.; Kurosawa, H.; Amano, Y. [Dept. of Applied Chemistry and Biotechnology, Faculty of Engineering, Yamanashi Univ. (Japan)

    1997-12-31

    A microbial method to determine sulphate concentration in water was developed on the basis of sulphate-dependent acid phosphatase (APase) in whole cells of Thiobacillus thiooxidans. The activity of the APase was determined colorimetrically by using p-nitrophenylphosphate as substrate. The APase was activated by sulphate. A linear relationship was obtained between the activity of the APase and the concentration of sulphate in the range 0-0.06 mM. Therefore, the sulphate concentration was estimated from the APase activity, represented by the absorbance (A{sub 400}). The microbial method was applied to the determination sulphate in water. The lower limit of detection was 0.02 mM, the relative standard deviation being 2% for 10 measurements on a standard sample. As for practical samples, which were taken from rain, river and tap water, good agreement was obtained between the values measured by the microbial method and those given by a conventional barium chloranilate method. The relative standard deviation was 2.1% for 12 measurements of tap water. The activity of the APase was stable over a period of more than 100 days when the cells were stored in 0.1 M sodium acetate/acetic acid buffer (pH 5.0) at 4 C. (orig.)

  17. Geometry and quadratic nonlinearity of charge transfer complexes in solution: a theoretical study.

    Science.gov (United States)

    Mukhopadhyay, S; Pandey, Ravindra; Das, Puspendu K; Ramasesha, S

    2011-01-28

    In this paper, we have computed the quadratic nonlinear optical (NLO) properties of a class of weak charge transfer (CT) complexes. These weak complexes are formed when the methyl substituted benzenes (donors) are added to strong acceptors like chloranil (CHL) or di-chloro-di-cyano benzoquinone (DDQ) in chloroform or in dichloromethane. The formation of such complexes is manifested by the presence of a broad absorption maximum in the visible range of the spectrum where neither the donor nor the acceptor absorbs. The appearance of this visible band is due to CT interactions, which result in strong NLO responses. We have employed the semiempirical intermediate neglect of differential overlap (INDO∕S) Hamiltonian to calculate the energy levels of these CT complexes using single and double configuration interaction (SDCI). The solvent effects are taken into account by using the self-consistent reaction field (SCRF) scheme. The geometry of the complex is obtained by exploring different relative molecular geometries by rotating the acceptor with respect to the fixed donor about three different axes. The theoretical geometry that best fits the experimental energy gaps, β(HRS) and macroscopic depolarization ratios is taken to be the most probable geometry of the complex. Our studies show that the most probable geometry of these complexes in solution is the parallel displaced structure with a significant twist in some cases.

  18. Optimized and Validated Spectrophotometric Methods for the Determination of Enalapril Maleate in Commercial Dosage Forms

    Directory of Open Access Journals (Sweden)

    Sk Manirul Haque

    2008-01-01

    Full Text Available Four simple, rapid and sensitive spectrophotometric methods have been proposed for the determination of enalapril maleate in pharmaceutical formulations. The first method is based on the reaction of carboxylic acid group of enalapril maleate with a mixture of potassium iodate (KIO3 and iodide (KI to form yellow colored product in aqueous medium at 25 ± 1°C .The reaction is followed spectrophotometrically by measuring the absorbance at 352 nm. The second, third and fourth methods are based on the charge transfer complexation reaction of the drug with p-chloranilic acid (pCA in 1, 4-dioxan-methanol medium, 2, 3-dichloro 5, 6-dicyano 1, 4-benzoquinone (DDQ in acetonitrile-1,4 dioxane medium and iodine in acetonitrile-dichloromethane medium. Under optimized experimental conditions, Beer’s law is obeyed in the concentration ranges of 2.5–50, 20–560, 5–75 and 10–200 μg mL−1, respectively. All the methods have been applied to the determination of enalapril maleate in pharmaceutical dosage forms. Results of analysis are validated statistically.

  19. Quantitative analysis of total retronecine esters-type pyrrolizidine alkaloids in plant by high performance liquid chromatography

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Fang; Wang Changhong; Xiong Aizhen; Wang Wan; Yang Li [Key Laboratory of Standardization of Chinese Medicines of Ministry of Education, Shanghai University of Traditional Chinese Medicine, 1200 Cai Lun Road, Zhangjiang Hi-Tech Park, Shanghai 201203 (China); Branford-White, Christopher J. [Institute for Health Research and Policy, London Metropolitan University, 166-220 Holloway Road, London N7 8DB (United Kingdom); Wang Zhengtao [Key Laboratory of Standardization of Chinese Medicines of Ministry of Education, Shanghai University of Traditional Chinese Medicine, 1200 Cai Lun Road, Zhangjiang Hi-Tech Park, Shanghai 201203 (China); School of Chinese Pharmacy, China Pharmaceutical University, Nanjing 210038 (China)], E-mail: wangzt@shutcm.edu.cn; Bligh, S.W. Annie [Institute for Health Research and Policy, London Metropolitan University, 166-220 Holloway Road, London N7 8DB (United Kingdom)], E-mail: a.bligh@londonmet.ac.uk

    2007-12-12

    Pyrrolizidine alkaloids (PAs) are alkaloids which typically contain a necine (7-hydroxy-1-hydroxymethyl-6,7-dihydro-5H-pyrrolizidine) base unit, and they can be found in one third of the higher plants around the world. They are hepatotoxic, mutagenic and carcinogenic and pose a threat to human health and safety. A specific, quick and sensitive method is therefore needed to detect and quantify the PAs sometimes in trace amount in herbs, tea or food products. Based on high performance liquid chromatography with prior derivatization of the alkaloids using o-chloranil and Ehrlich's reagent, we report an improved method for quantitative analysis of the total amount of retronecine esters-type pyrrolizidine alkaloids (RET-PAs) in a plant extract. The total quantitation of RET-PAs is achieved because of a common colored retronecine marker, a 7-ethoxy-1-ethoxylmethyl retronecine derivative, is produced with all the different RET-PAs during the derivatization reaction. The chemical identity of the common retronecine marker was characterized on-line by positive mode electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy. The limit of detection using the improved method is 0.26 nmol mL{sup -1} and the limit of quantitation is 0.79 nmol mL{sup -1}. The advantages of this method are much enhanced sensitivity in detection and quantitation, and, no restriction on the choice of RET-PA as a calibration standard. Application of the developed method to the quantitation of total RET esters-type PAs in Senecio scandens from different regions of China is also reported.

  20. Development of a novel 96-microwell assay with high throughput for determination of olmesartan medoxomil in its tablets

    Directory of Open Access Journals (Sweden)

    Darwish Ibrahim A

    2012-01-01

    Full Text Available Abstract A novel 96-microwell-based spectrophotometric assay has been developed and validated for determination of olmesartan medoxomil (OLM in tablets. The formation of a colored charge-transfer (CT complex between OLM as a n-electron donor and 2, 5-dichloro-3, 6-dihydroxy-1, 4-benzoquinone (p-chloranilic acid, pCA as a π-electron acceptor was investigated, for the first time, and employed as a basis in the development of the proposed assay. The proposed assay was carried out in 96-microwell plates. The absorbance of the colored-CT complex was measured at 490 nm by microwell-plate absorbance reader. The optimum conditions of the reaction and the analytical procedures of the assay were established. Under the optimum conditions, linear relationship with good correlation coefficient was found between the absorbance and the concentration of OLM in the range of 1-200 μg ml-1. The limits of detection and quantitation were 0.3 and 1 μg ml-1, respectively. No interference was observed from the additives that are present in the pharmaceutical formulation or from hydrochlorothiazide and amlodipine that are co-formulated with OLM in some formulations. The assay was successfully applied to the analysis of OLM in tablets with good accuracy and precision. The assay described herein has great practical value in the routine analysis of OLM in quality control laboratories, as it has high throughput property, consumes minimum volume of organic solvent thus it offers the reduction in the exposures of the analysts to the toxic effects of organic solvents, and reduction in the analysis cost by 50-fold. Although the proposed assay was validated for OLM, however, the same methodology could be used for any electron-donating analyte for which a CT reaction can be performed.

  1. A novel strategy for spectrophotometric simultaneous determination of amitriptyline and nortriptyline based on derivation with a quinonoid compound in serum samples

    Science.gov (United States)

    Farnoudian-Habibi, Amir; Massoumi, Bakhshali; Jaymand, Mehdi

    2016-11-01

    A novel and efficient strategy for the simultaneous determination of two tricyclic antidepressant (TCA) drugs [amitriptyline (AT), and its main metabolite (nortriptyline; NT)] via a combination of magnetic solid phase extraction (MSPE), and spectrophotometric techniques in serum is suggested. For this purpose, the imidazolium ionic liquid (Imz)-modified Fe3O4@SiO2 nanoparticles (Fe3O4@SiO2-Imz) was employed as an adsorbent for the MSPE. Preconcentration (loading-desorption) studies were performed under optimized conditions including pH, adsorbent amount, contact time, eluent volume, and desorption time. Afterward, determination of each drug was carried out by specific strategy. Acetaldehyde (AC), and 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil; CL) were used as chemical reagents for reaction with NT, while AT did not react with these reagents. This method is based on the condensation reaction between secondary amine group of NT and AC to afford an enamine, and subsequently reaction with CL to produce a chlorinated quinone-substituted enamine. The final product exhibited maximum absorption at 556 nm, while the AT was determined at 240 nm. The limits of detections (LODs) for NT and AT in serum sample were obtained as 0.19 and 0.90 ng mL- 1, respectively. The limits of quantifications (LOQs) were obtained to be 0.63 and 2.93 ng mL- 1 for NT and AT, respectively. A linear range was obtained to be 1 to 5 ng mL- 1. Results indicated that the suggested method is applicable for simultaneous determination of NT and AT in serum samples.

  2. Analytical study for the charge-transfer complexes of losartan potassium

    Energy Technology Data Exchange (ETDEWEB)

    Darwish, Ibrahim A. [Department of Pharmaceutical Analytical Chemistry, Faculty of Pharmacy, Assiut University, Assiut 71526 (Egypt)]. E-mail: iadarwish@yahoo.com

    2005-09-06

    Studies were carried out, for the first time, to investigate the charge-transfer reactions of losartan potassium (LOS-K) as n-electron donor with the {sigma}-acceptor iodine and various {pi}-acceptors: 7,7,8,8-tetracyanoquinodimethane, 1,3,5-trinitrobenzene, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, p-chloranilic acid, tetracyanoethylene, 2,3,5,6-tetrabromo-1,4-benzoquinone, 2,3,5,6-tetrachloro-1,4-benzoquinone, and 2,4,7-trinitro-9-fluorenone. Different colored charge-transfer complexes and radical anions were obtained. Different variables affecting the reactions were studied and optimized. The formed complexes and the site of interaction were examined by UV-vis, IR, and {sup 1}H NMR techniques, and computational molecular modeling. The formation of the colored complexes were utilized in the development of simple, rapid and accurate spectrophotometric methods for the analysis of LOS-K in pure form as well as in its pharmaceutical tablets. Under the optimum reaction conditions, linear relationships with good correlation coefficients (0.9985-0.9998) were found between the absorbances and the concentrations of LOS-K in the range of 2-200 {mu}g ml{sup -1}. The limits of assays detection ranged from 0.61 to 19.65 {mu}g ml{sup -1}. No interference could be observed from the co-formulated hydrochlorothiazide (HCTZ), as well as from the additives commonly present in the tablets. The methods were successfully applied to the analysis of tablets from different manufacturers that contain LOS-K, alone or combined with HCTZ, with good accuracy and precision; the recovery percentages ranged from 98.96 {+-} 1.62% to 101.58 {+-} 1.29%. The results were compared favourably with the reported method.

  3. Analytical Study for the Charge-Transfer Complexes of Rosuvastatin Calcium with π-Acceptors

    Directory of Open Access Journals (Sweden)

    Nourah Z. Alzoman

    2013-07-01

    Full Text Available Studies were carried out to investigate the charge-transfer (CT reaction of ROS-Ca, as a n-electron donor with various p-acceptors: tetracyanoethylene, p-chloranilic acid, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, 2,3,5,6-tetrabromo-1,4-benzoquinone, 1,3,5-trinitrobenzene, 2,3,5,6-tetrachloro-1,4-benzoquinone, 7,7,8,8-tetracyano-quinodimethane, and 2,4,7-trinitro-9-fluorenone. Different colored CT complexes were obtained. The reaction mechanism and site of interaction were determined by ultraviolet-visible spectrophotometric techniques and computational molecular modeling. The formation of the colored complexes was utilized in the development of simple, rapid and accurate spectrophotometric methods for the determination of ROS-Ca. Under the optimum reaction conditions, linear relationships with good correlation coefficients (0.9984–0.9995 were found between the absorbances and the concentrations of ROS-Ca in the range of 2–200 mg mL−1. The limits of detection ranged from 0.41 to 12.24 mg mL−1. No interference could be observed from the additives commonly present in the tablets or from the drugs that are co-formulated with ROS-Ca in its combined formulations. The methods were successfully applied to the analysis of tablets with good accuracy and precision; the recovery percentages ranged from 99.54–100.46 ± 1.58–1.82%. The results were compared favorably with the reported method. The proposed methods are practical and valuable for routine application in quality control laboratories for determination of ROS-Ca in its bulk form and tablets.

  4. Spectrophotometric Determination of Some Fluoroquinolone Antibacterials through Charge-transfer and Ion-pair Complexation Reactions

    Energy Technology Data Exchange (ETDEWEB)

    El-Brashy, Amina Mohamed; El-Sayed Metwally Mohamed; El-Sepai, Fawzi Abdallah [University of Mansoura, Mansoura (Egypt)

    2004-03-15

    Two simple, rapid and sensitive spectrophotometric methods for the determination of three fluoroquinolones, namely levofloxacin, norfloxacin and ciprofloxacin have been performed either in pure form or in their tablets. In the first method, levofloxacin and norfloxacin are directly treated with bromocresol green (BCG) in dichloromethane while ciprofloxacin is allowed to react with the same dye in aqueous acidic buffer. Highly yellow colored complex species were formed instantaneously in case of levofloxacin and norfloxacin or after extraction into dichloromethane for ciprofloxacin. The formed complexes are quantified spectrophotometrically at their absorption maxima at 411 nm for levofloxacin and 412 nm for norfloxacin and ciprofloxacin. The second method involves the reaction of levofloxacin with {rho}-chloranilic acid ({rho}-CA) and norfloxacin with tetracyanoethylene (TCNE) in acetonitrile to give complexes with maximum absorbance at 521 and 333 nm for the two drugs, respectively. Adopting the first procedure, calibration graphs were linear over the range 1- 20 {mu}g mL{sup .1} with mean percentage recoveries of 100.41 {+-} 0.72, 99.99 {+-} 0.54 and 100.23 {+-} 0.91 for the three drugs, respectively. For the second procedure, the concentration ranges were 15-250 {mu}g mL{sup .1} for levofloxacin using {rho}-CA and 0.8-16 {mu}g mL{sup .1} for norfloxacin using TCNE with mean percentage recoveries of 99.88 {+-} 0.45 and 100.26 {+-} 0.68 for the two drugs, respectively. The proposed methods were successfully applied to determine these drugs in their tablet formulations and the results compared favorably to that of reference methods. The proposed methods are recommended for quality control and routine analysis

  5. 2-Hetaryl-1,3-tropolones based on five-membered nitrogen heterocycles: synthesis, structure and properties

    Directory of Open Access Journals (Sweden)

    Yury A. Sayapin

    2015-11-01

    Full Text Available A series of derivatives of 2-hetaryl-1,3-tropolone (β-tropolone was prepared by the acid-catalyzed reaction of 2-methylbenzoxazoles, 2-methylbenzothiazoles and 2,3,3-trimethylindoline with 3,4,5,6-tetrachloro-1,2-benzoquinone. The molecular structures of the three representative compounds were determined by X-ray crystallography. In crystal and (as shown by the DFT PBE0/6-311+G** calculations in solution, 2-hetaryl-4,5,6,7-tetrachloro- and 2-hetaryl-5,6,7-trichloro-1,3-tropolones exist in the NH-tautomeric form with a strong resonance-assisted intramolecular N–H···O hydrogen bond. The mechanism of the formation of 1,3-tropolones in the reaction of methylene-active five-membered heterocycles with o-chloranil in acetic acid solution has been studied using density functional theory (DFT methods. The reaction of 2-(2-benzoxa(thiazolyl-5,6,7-trichloro(4,5,6,7-tetrachloro-1,3-tropolones with alcohols leads to the contraction of the seven-membered tropone ring with the formation of 2-(2-benzoxa(thiazolyl-6-alkoxycarbonylphenols. The molecular structure of 2-(2-ethoxycarbonyl-6-hydroxy-3,4,5-trichlorophenylbenzoxazole has been determined by X-ray diffraction. 2-(2-Benzoxa(thiazolyl-6-alkoxycarbonylphenols display intense green fluorescence with anomalous Stokes shifts caused by the excited state intramolecular proton transfer (ESIPT effects.

  6. Timeresolved investigation of atomic order in tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) monocrystals after excitation with ultrashort light pulses; Zeitaufgeloeste Untersuchung atomarer Ordnung in Tetrathiafulvalen-Tetracyanochinodimethan (TTF-TCNQ)-Einkristallen nach Anregung mit ultrakurzen Lichtpulsen

    Energy Technology Data Exchange (ETDEWEB)

    Sager, Christian

    2011-02-15

    This thesis describes time-resolved investigations of the atomic structure of one-dimensional organic molecular crystals after laser excitation of the photo-induced phase transition. There is a neutral to ionic phase transition in tetrathiafulvalene-chloranil-crystals (TTF-CA-crystals). At this phase transition a Peierls distortion occurs. A new model is introduced, that can explain the photo-induced phase transition in TTF-CY-crystals. This model is called charge density wave model of photo induced structural phase transition. There is a structural phase transition in tetrathiafulvalene-tetracyanochinodimethane-crystals (TTF-TCNQ-crystals). At this phase transition the one-dimensional metal TTF-TCNQ is transformed to an insulator. The phase transition is driven by the Peierls distortion. The charge density wave model is appropriate for description of the processes in TTF-TCNQ-crystals after laser excitation. The results of time-resolved measurements of the structure of TTF-TCNQ-crystals after excitation of the photo-induced phase transition can be anticipated with the charge density wave model. In the basis of these anticipated results, a time-resolved measurement for investigation of the atomic structure of TTF-TCNQ after excitation of the photo-induced phase transition is proposed. The time-resolved measurement should be performed at a beamline of a third generation synchrotron by the optical pump X-ray probe technique. The time-resolved measurement is prepared by an optical characterization and by static X-ray diffraction measurements. The results of the optical characterization and the static X-ray diffraction measurements are presented and analyzed. (orig.)

  7. Phytochemical profiles and antioxidant activities in six species of ramie leaves.

    Directory of Open Access Journals (Sweden)

    Yongsheng Chen

    Full Text Available Increased consumption of vegetables or plant food has been associated with decreased risk of developing major chronic diseases, such as cancers, diabetes, cardiovascular diseases, and age-related functional decline. Ramie leaves are rich in phenolics and flavonoids, which have been suggested for human health benefits. Phenolic contents, flavonoid contents, phenolic compounds, and anti-cancer properties in six species of ramie leaves were analyzed by Folin-reagent method, sodium borohydride/chloranil-based assay (SBC, HPLC method and antiproliferation, cytoxicity, respectively. Antioxidant activities were measured through peroxyl radical scavenging capacity (PSC method, oxygen radical absorbance capacity (ORAC method, and cellular antioxidant activity (CAA. Research indicated that Boehmeria penduliflora contained the highest total phenolic content (2313.7±27.28 mg GAE/100 g FW, and flavonoid content (1682.4±27.70 mg CAE/100 g FW. Boehmeria tricuspis showed the highest PSC value (9574.8±117.63 µM vit. C equiv./100 g FW, while Boehmeria penduliflora indicated the highest ORAC value (330.44±16.88 µmol Trolox equiv./g FW. The antioxidant activities were correlated with phenolic contents and flavonoid contents. Boehmeria tricuspis had the highest antiproliferative capacity with the lowest EC₅₀ (4.11±0.19 mg/mL. The results for the analyzed ramie for CAA were significantly different from each other (p<0.05, Boehmeria tricuspis had the highest CAA value (133.63±7.10 µmol QE/100 g. Benzoic acid, 4-coumaric acid, caffeic acid, and ferulic acid were the dominant phenolic ingredients in the ramie leaves according to HPLC analysis. Our research is the first report to study the phytochemical profiles and antioxidant activities in different species of ramie leaves for their health benefit.

  8. 2-Hetaryl-1,3-tropolones based on five-membered nitrogen heterocycles: synthesis, structure and properties

    Science.gov (United States)

    Sayapin, Yury A; Tupaeva, Inna O; Kolodina, Alexandra A; Gusakov, Eugeny A; Komissarov, Vitaly N; Makarova, Nadezhda I; Metelitsa, Anatoly V; Tkachev, Valery V; Aldoshin, Sergey M; Minkin, Vladimir I

    2015-01-01

    Summary A series of derivatives of 2-hetaryl-1,3-tropolone (β-tropolone) was prepared by the acid-catalyzed reaction of 2-methylbenzoxazoles, 2-methylbenzothiazoles and 2,3,3-trimethylindoline with 3,4,5,6-tetrachloro-1,2-benzoquinone. The molecular structures of the three representative compounds were determined by X-ray crystallography. In crystal and (as shown by the DFT PBE0/6-311+G** calculations) in solution, 2-hetaryl-4,5,6,7-tetrachloro- and 2-hetaryl-5,6,7-trichloro-1,3-tropolones exist in the NH-tautomeric form with a strong resonance-assisted intramolecular N–H···O hydrogen bond. The mechanism of the formation of 1,3-tropolones in the reaction of methylene-active five-membered heterocycles with o-chloranil in acetic acid solution has been studied using density functional theory (DFT) methods. The reaction of 2-(2-benzoxa(thia)zolyl)-5,6,7-trichloro(4,5,6,7-tetrachloro)-1,3-tropolones with alcohols leads to the contraction of the seven-membered tropone ring with the formation of 2-(2-benzoxa(thia)zolyl)-6-alkoxycarbonylphenols. The molecular structure of 2-(2-ethoxycarbonyl-6-hydroxy-3,4,5-trichlorophenyl)benzoxazole has been determined by X-ray diffraction. 2-(2-Benzoxa(thia)zolyl)-6-alkoxycarbonylphenols display intense green fluorescence with anomalous Stokes shifts caused by the excited state intramolecular proton transfer (ESIPT) effects. PMID:26664640

  9. Spectrophotometric determination of quetiapine fumarate in pharmaceuticals and human urine by two charge-transfer complexation reactions

    Directory of Open Access Journals (Sweden)

    Vinay K.B.

    2012-01-01

    Full Text Available Two simple, rapid and accurate spectrophotometric procedures are proposed for the determination of quetiapine fumarate (QTF in pharmaceuticals and in spiked human urine. The methods are based on charge transfer complexation reactions of free base form of the drug (quetiapine, QTP, as n-electron donor (D, with either p-chloranilic acid (p-CAA (method A or 2,3-dichloro-5,6-dicyanoquinone (DDQ (method B as π-acceptors (A. The coloured charge transfer complexes produced exhibit absorption maxima at 520 and 540 nm, in method A and method B, respectively. The experimental conditions such as reagent concentration, reaction solvent and time have been carefully optimized to achieve the maximum sensitivity. Beer’s law is obeyed over the concentration ranges of 8.0 - 160 and 4.0 - 80.0 μg ml-1, for method A and method B, respectively. The calculated molar absorptivity values are 1.77 × 103 and 4.59 × 103 l mol-1cm-1, respectively, for method A and method B. The Sandell sensitivity values, limits of detection (LOD and quantification (LOQ have also been reported. The stoichiometry of the reaction in both cases was accomplished adopting the limiting logarithmic method and was found to be 1: 2 (D: A. The accuracy and precision of the methods were evaluated on intra-day and inter-day basis. The proposed methods were successfully applied for the determination of QTF in pharmaceutical formulations and spiked human urine.

  10. Validated spectrophotometric methods for determination of sodium valproate based on charge transfer complexation reactions

    Science.gov (United States)

    Belal, Tarek S.; El-Kafrawy, Dina S.; Mahrous, Mohamed S.; Abdel-Khalek, Magdi M.; Abo-Gharam, Amira H.

    2016-02-01

    This work presents the development, validation and application of four simple and direct spectrophotometric methods for determination of sodium valproate (VP) through charge transfer complexation reactions. The first method is based on the reaction of the drug with p-chloranilic acid (p-CA) in acetone to give a purple colored product with maximum absorbance at 524 nm. The second method depends on the reaction of VP with dichlone (DC) in dimethylformamide forming a reddish orange product measured at 490 nm. The third method is based upon the interaction of VP and picric acid (PA) in chloroform resulting in the formation of a yellow complex measured at 415 nm. The fourth method involves the formation of a yellow complex peaking at 361 nm upon the reaction of the drug with iodine in chloroform. Experimental conditions affecting the color development were studied and optimized. Stoichiometry of the reactions was determined. The proposed spectrophotometric procedures were effectively validated with respect to linearity, ranges, precision, accuracy, specificity, robustness, detection and quantification limits. Calibration curves of the formed color products with p-CA, DC, PA and iodine showed good linear relationships over the concentration ranges 24-144, 40-200, 2-20 and 1-8 μg/mL respectively. The proposed methods were successfully applied to the assay of sodium valproate in tablets and oral solution dosage forms with good accuracy and precision. Assay results were statistically compared to a reference pharmacopoeial HPLC method where no significant differences were observed between the proposed methods and reference method.

  11. Geometry and quadratic nonlinearity of charge transfer complexes in solution using depolarized hyper-Rayleigh scattering.

    Science.gov (United States)

    Pandey, Ravindra; Ghosh, Sampa; Mukhopadhyay, S; Ramasesha, S; Das, Puspendu K

    2011-01-28

    We report large quadratic nonlinearity in a series of 1:1 molecular complexes between methyl substituted benzene donors and quinone acceptors in solution. The first hyperpolarizability, β(HRS), which is very small for the individual components, becomes large by intermolecular charge transfer (CT) interaction between the donor and the acceptor in the complex. In addition, we have investigated the geometry of these CT complexes in solution using polarization resolved hyper-Rayleigh scattering (HRS). Using linearly (electric field vector along X direction) and circularly polarized incident light, respectively, we have measured two macroscopic depolarization ratios D=I(2ω,X,X)/I(2ω,Z,X) and D(')=I(2ω,X,C)/I(2ω,Z,C) in the laboratory fixed XYZ frame by detecting the second harmonic scattered light in a polarization resolved fashion. The experimentally obtained first hyperpolarizability, β(HRS), and the value of macroscopic depolarization ratios, D and D('), are then matched with the theoretically deduced values from single and double configuration interaction calculations performed using the Zerner's intermediate neglect of differential overlap self-consistent reaction field technique. In solution, since several geometries are possible, we have carried out calculations by rotating the acceptor moiety around three different axes keeping the donor molecule fixed at an optimized geometry. These rotations give us the theoretical β(HRS), D and D(') values as a function of the geometry of the complex. The calculated β(HRS), D, and D(') values that closely match with the experimental values, give the dominant equilibrium geometry in solution. All the CT complexes between methyl benzenes and chloranil or 1,2-dichloro-4,5-dicyano-p-benzoquinone investigated here are found to have a slipped parallel stacking of the donors and the acceptors. Furthermore, the geometries are staggered and in some pairs, a twist angle as high as 30° is observed. Thus, we have demonstrated in

  12. Chemical, pulse radiolysis and density functional studies of a new, labile 5,6-indolequinone and its semiquinone.

    Science.gov (United States)

    Pezzella, Alessandro; Crescenzi, Orlando; Natangelo, Anna; Panzella, Lucia; Napolitano, Alessandra; Navaratnam, Suppiah; Edge, Ruth; Land, Edward J; Barone, Vincenzo; d'Ischia, Marco

    2007-03-02

    The chemical and spectroscopic characterization of 5,6-indolequinones and their semiquinones, key transient intermediates in the oxidative conversion of 5,6-dihydroxyindoles to eumelanin biopolymers, is a most challenging task. In the present paper, we report the characterization of a novel, relatively long-lived 5,6-indolequinone along with its semiquinone using an integrated chemical, pulse radiolytic, and computational approach. The quinone was obtained by oxidation of 5,6-dihydroxy-3-iodoindole (1a) with o-chloranil in cold ethyl acetate or aqueous buffer: it displayed electronic absorption bands around 400 and 600 nm, was reduced to 1a with Na2S2O4, and reacted with o-phenylenediamine to give small amounts of 3-iodo-1H-pyrrolo[2,3-b]phenazine (2). The semiquinone exhibited absorption maxima at 380 nm (sh) and 520 nm and was detected as the initial species produced by pulse radiolytic oxidation of 1a at pH 7.0. DFT investigations indicated the 6-phenoxyl radical and the N-protonated radical anion as the most stable tautomers for the neutral and anion forms of the semiquinone, respectively. Calculated absorption spectra in water gave bands at 350 (sh) and 500 nm for the neutral form and at 310 and 360 (sh) nm for the anion. Disproportionation of the semiquinone with fast second-order kinetics (2k = 1.1 x 1010 M-1 s-1) gave a chromophore with absorption bands resembling those of chemically generated 1a quinone. Computational analysis predicted 1a quinone to exist in vacuo as the quinone-methide tautomer, displaying low energy transitions at 380 and 710 nm, and in water as the o-quinone, with calculated absorption bands around 400 and 820 nm. A strong participation of a p orbital on the iodine atom in the 360-380 nm electronic transitions of the o-quinone and quinone-methide was highlighted. The satisfactory agreement between computational and experimental electronic absorption data would suggest partitioning of 1a quinone between the o-quinone and quinone

  13. Influencing the coordination mode of tbta (tbta = tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine) in dicobalt complexes through changes in metal oxidation states.

    Science.gov (United States)

    Schweinfurth, David; Klein, Johannes; Hohloch, Stephan; Dechert, Sebastian; Demeshko, Serhiy; Meyer, Franc; Sarkar, Biprajit

    2013-05-21

    The complexes [(tbta)Co(μ-CA(-2H))Co(tbta)(CH3CN)](BF4)2 1 and [(tbta)Co(μ-OH)2Co(tbta)](BF4)4 2 (tbta = tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine and CA = chloranilic acid) were synthesized and characterized by X-ray crystallography, SQUID magnetometry and NMR spectroscopy. The reactions to form these complexes deliver 1 as a paramagnetic species containing two high spin Co(II) centers, and 2 as a diamagnetic compound with two low spin Co(III) centers. Structural analysis shows that in 1 the capped-octahedral environment around the Co(II) centers is highly distorted with rather long bonds between the metal and donor atoms. The tbta ligand binds to the Co(II) centers through the three triazole nitrogen donor atoms in a facial form, with the Co-N(amine) distance of 2.494(2) Å acting as a capping bond to the octahedron. In the crystal an unusual observation of one acetonitrile molecule statistically occupying the coordination sites at both Co(II) centers is made. 1 displays a series of intermolecular C-H···Cl and π-π interactions leading to extended three-dimensional structures in the solid state. These interactions lead to the formation of voids and explain why only one acetonitrile molecule can be bound to the dinuclear complexes. In contrast to 1, the cobalt centers in 2 display a more regular octahedral environment with shorter cobalt-donor atom distances, as would be expected for a low spin Co(III) situation. The tbta ligand acts as a perfect tetradentate ligand in this case with the cobalt-N(amine) distance of 2.012(3) Å falling in the range of a normal bond. Thus, we present the rare instances where the ligand tbta has been observed to bind in a perfectly tetradentate fashion in its metal complexes. The room temperature magnetic moment of 6.30 μB for 1 shows values typical of two high spin Co(II) centers, and this value decreases at temperatures lower than 30 K indicating a weak antiferromagnetic coupling and zero field splitting. Mass

  14. Determination of individual proton affinities of ofloxacin from its UV-Vis absorption, fluorescence and charge-transfer spectra: effect of inclusion in beta-cyclodextrin on the proton affinities.

    Science.gov (United States)

    Ghosh, Bankim Chandra; Deb, Nipamanjari; Mukherjee, Asok K

    2010-08-01

    Individual proton affinities of the four dissociable functional groups of (+/-)-9-fluoro-2,3-dihydro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-7H-pyrido[1,2,3-de]-1,4-benzoxazine-6-carboxylic acid (commonly called "ofloxacin" and to be denoted henceforth as OflH), have been determined from the pH-dependent variation of the UV-vis absorption and fluorescence spectra of the compound itself and of its charge transfer complexes (CT) with p-bromanil and p-chloranil (in aqueous medium containing 0.1% ethanol, v/v). To utilize the CT spectra for determination of the proton affinity of the anilinic N, the CT absorption band of the ofloxacin-p-bromanil complex has been studied by changing the pH of the medium. Further, the effect of inclusion on the proton affinities of the four dissociable groups of OflH has been studied in presence of beta-cyclodextrin (beta-CD). Two pK(a) values corresponding to anilinic and tertiary N atoms change, whereas those corresponding to phenolic -OH and aromatic -COOH groups remain unchanged by the addition of beta-CD, a fact that indicates partial inclusion of the ofloxacin molecule in beta-CD. Formation constant and related thermodynamic parameters for the OflH(2)(+).beta-CD inclusion complex in aqueous solution have been determined from absorption intensities. A general relation between pK(a) values of guests having proton-releasing functional groups and formation constants of the inclusion complexes of the protonated and deprotonated forms with a host molecule has been utilized for determination of the formation constant of the OflH(3)(+2).beta-CD complex from the pK(a) values of OflH(3)(+2) in the presence and absence of beta-CD, along with the formation constant of the OflH(2)(+).beta-CD complex. Results of the present study reveal that the N-methylpiperazinyl moiety of ofloxacin is included in beta-CD, and the remaining part of the guest molecule remains outside. Also, in molecular interaction with quinone-type electron acceptors

  15. Broadband echo sequence using a pi composite pulse for the pure NQR of a spin I = 32 powder sample

    Science.gov (United States)

    Odin

    2000-04-01

    other broadband echo sequences are also briefly discussed. We also study the effect of a small delay between the pulses of the composite pulse to take into account the experimental constraint imposed by the spectrometer. To be complete, we give an estimation of the performances of the Hahn echo, the stimulated echo, and the composite echo sequence optimized for a powder sample when applied to a monocrystal. Experiments performed on chloranil at ambient temperature confirm the predicted excitation profiles. Copyright 2000 Academic Press.

  16. Broadband Echo Sequence Using a π Composite Pulse for the Pure NQR of a Spin I = {3}/{2} Powder Sample

    Science.gov (United States)

    Odin, Christophe

    2000-04-01

    broadband echo sequences are also briefly discussed. We also study the effect of a small delay between the pulses of the composite pulse to take into account the experimental constraint imposed by the spectrometer. To be complete, we give an estimation of the performances of the Hahn echo, the stimulated echo, and the composite echo sequence optimized for a powder sample when applied to a monocrystal. Experiments performed on chloranil at ambient temperature confirm the predicted excitation profiles.