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561.
Spectral, redox and kinetic properties of the transient species formed by the reaction of 2- mercaptopyridine (2-MPy) with oxidants such as OH, Br¯2
.
; N
.
3 and Cl¯2
.
radicals and reductants such as e¯aq, H-atoms and (CH3)2
.
COH radicals have been studied by pulse radiolysis technique. Reaction of one-electron oxidants with 2-MPy at pH 11.5 led to the formation of 2-pyridyl thiyl radical. The reduction potential for the couple C5H4NS
.
/C5H4NS¯ was estimated to be 0.84 V vs NHE from the equilibrium studies with I¯2
.
/2I¯ couple. At pH 6.8, the reaction of N
.
3 radical with 2-MPy gave a cation radical derived from 2-MPy. At pH 6.8 and 11.5, OH radicals react with 2-MPy by addition pathway. Reaction of e¯aq with 2-MPy was found to give a reducing radical capable of transferring electron to methyl viologen. At acidic pH, the reaction of (CH3)2
.
COH radicals and H-atoms with 2-MPy gave transient species identical to those produced by the reaction of oxidising radicals, namely, OH radicals, Cl¯2
.
and Br¯2
.
radicals. 相似文献
562.
Ying Wei Meena Kishore Sakharkar Xia Wang Qin Liu Jiang Du 《Natural product research》2020,34(11):1607-1610
AbstractHepatitis C virus (HCV) infection is a global threat to human health with an estimated 1.75 million new cases in 2015. Our previous studies showed that the ethyl acetate extraction of Daphne papyracea exhibited an inhibitory effect towards the HCV NS3/4A protease and eight compounds were identified from the extract. In this study, we investigated which of the eight compounds was responsible for the inhibitory effect of the extract against the HCV NS3/4A protease. From both molecular docking and enzyme inhibition studies, (+)-usnic acid was shown to be the most active compound and could be used as a lead compound in developing novel anti-HCV agents. 相似文献
563.
The method of estimating the persulphate by direct titration using arsenious acid or sodium arsenite as a primary standard has been described.This method consists in taking a mixture of arsenious acid or sodium arsenite and an excess of potassium iodide in the titration mixture. The mixture is heated to 80°C and solid sodium bicarbonate is added. Persulphate solution is run in from a burette and the liberated iodine is instantaneously consumed by trivalent arsenic. At the end-point an excess drop of persulphate gives a yellow colour due to the liberated iodine remaining unreacted. The results are satisfactory and the error lies within permissible limits. 相似文献
564.
Enamul Karim Kaushal Kishore Jai N. Vishwakarma 《Journal of heterocyclic chemistry》2003,40(5):901-903
A facile one‐pot synthesis of 5‐benzoyl‐6‐methylthio‐1,2,3,4‐tetrahydropyrimidines in good yields is reported. 相似文献
565.
R. S. Misra S. S. Parmar V. Kishore B. Ali T. K. Gupta 《Journal of heterocyclic chemistry》1979,16(3):613-615
Several 1-(N-piperidinoacetyl)-4-arylthiosemicarbazides were synthesized from N-piperidinoacetyl hydrazide, which was obtained by the reaction of hydrazine hydrate with ethyl N-piperidinoacetate. The anticonvulsant activity of these substituted thiosemicarbazides was reflected by their ability to provide 10–50% protection against pentylenetetrazol-induced convulsions in mice. All substituted thiosemicarbazides (0.3 mM) inhibited in vitro monoamine oxidase activity of rat brain homogenates and provided 21–86% protection against hypoosmotic hemolysis at a final concentration of 0.1 mM. 相似文献
566.
Lipsitz RS Sharma Y Brooks BR Tjandra N 《Journal of the American Chemical Society》2002,124(35):10621-10626
An analysis of backbone hydrogen bonds has been performed on nine high-resolution protein X-ray crystal structures. Backbone hydrogen-bond geometry is compared in the context of X-ray crystal structure resolution. A strong correlation between the hydrogen-bond distance, R(HO), and the hydrogen-bond angle, theta(NHO), is observed when the X-ray crystal structure resolution is <1.00 A. Ab initio calculations were performed to substantiate these results. The angle and distance limits found in our correlation for the backbone hydrogen-bond geometry can be used to evaluate the quality of protein structures and for further NMR structure refinement. 相似文献
567.
Summary Some thorium(IV) complexes were synthesized with the tetradentate Schiff base ligands (N2O2 donor set) obtained by the condensation of ethylenediamine with salicylaldehyde (H2salen) or acetylacetone (H2 acacen). In all cases the neutral Schiff bases and not their anions are coordinated to the central thorium(IV) atom. The complexes have the general formula: ThL2Xa (L = H2 salen; X = Cl, Br, 1, NCS and L = lie acacen; X = Cl, 1, NCS, ClO4) or ThLX4 (L = H2 salen; X = NO3, ClO4 and L = H2 acacen; X = Br, NO3). The stoichiometry and coordination number of the complexes was determined on the basis of elemental analysis, conductivity measurements, i.r. spectra and t.g.a./d.t.a. data. The coordination number of the complexes is either 12 or 8 for the bisor monocomplexes respectively. 相似文献
568.
Yugal Sharma Oh Young Kwon Bernie Brooks Nico Tjandra 《Journal of the American Chemical Society》2002,124(2):327-335
Ab initio shielding tensor calculations were carried out on residues in human ubiquitin. Reported experimental data on isotropic and anisotropic components of the amide proton chemical shifts were used as benchmarks to test the validity of the chosen basis sets as well as methods in structure optimization and shielding calculations. The best agreement with the experimental values was observed when the 6-311**G and 6-311++G(2d,2p) basis sets were used to optimize the structure and to calculate the shielding tensor, respectively. The same method was employed in subsequent model calculations to characterize the dependence of amide proton shielding to the local structure. Both the isotropic and the anisotropic components of the symmetric tensor were found to depend very strongly on the hydrogen bond length. A weaker dependence can also be observed for the hydrogen bond angle. Antisymmetric tensor elements were found to be relatively small. This study permits separation of various local structure contributions to the amide proton shielding tensor that complements scarce experimental data. 相似文献
569.
Apparent molar volumes of a homologous series of amino acids in aqueous proline solutions have been obtained from densities
at 298.15 K, measured with a vibrating-tube digital densimeter. These data have been used to deduce the partial molar volumes
of transfer from water to aqueous proline solutions; these partial molar volumes of transfer are found to be positive for
glycine, alanine, α-amino-n-butyric acid and valine, whereas they are negative for leucine. The number of water molecules hydrated to the amino acids
was estimated from the partial molar volume data. In order to supplement this information, enthalpies of transfer of aqueous
amino acids from water to 0.1, 2.25 and 1 mol⋅dm−3 aqueous proline have been determined at 298.15 K using a VP-ITC titration calorimeter. The data on the partial molar volumes
and enthalpies of transfer are discussed in terms of various interactions operating in the ternary mixtures of amino acids,
water and proline. 相似文献
570.
Specific heat capacities and apparent molar heat capacities of aqueous nicotinamide have been determined from 25.0 to 55.0°C using microdifferential scanning calorimetry in the molality range of 0.07433 to 1.50124 mol-kg–1. Densities and apparent molar volumes have also been determined for aqueous nicotinamide from 10.30 to 34.98°C using a digital densimeter in the molality range 0.07804–2.02435 mol-kg–1. The results of these measurements have been used to calculate the following partial molar quantities and temperature derivatives for aqueous nicotinamide as a function of temperature: C
p,2,m
o, (C
p,2,m
o/T)p, (2Cp,2,m
o/T
2)p, V
2,m
o, ( V
2,m
o/T)p, and (2
V
2,m
2/T
2)p. The results are discussed in terms of the changes in the packing of nicotinamide molecules in the crystal, interactions in the aqueous form, and its structure-promoting ability with rise in temperature. 相似文献