Relationship between photosensitizing activities and chemical structure of hypocrellin A and B.

Hypocrellins A (HA) and B (HB) are two main pigments isolated from the parasitic fungi Hypocrella bambusae (B. et Br) Sacc. and Shiraia bambusicola P. Heen found in China. These pigments have a long history as traditional medicinal agents. Although HA and HB have the same perylene quinonoid structure, there are different side rings. The different photosensitizing activities of HA and HB due to their different side rings were studied by electron paramagnetic resonance (EPR), spin trapping and spin counteraction techniques. It is demonstrated that the ability to generate active oxygen (1O2, O2.- and .OH) is stronger during HA photosensitization than during HB photosensitization. Under anaerobic conditions, the ability to generate HA.- during HA photosensitization is stronger than the ability to generate HB.- during HB photosensitization. There is a relationship between photosensitizing ability and chemical structure.     

Regiochemical observations on the lithiation of 1,2,4-trichlorobenzene and reaction with DMF and oxamide electrophiles in THF

Unusual regiochemistry is observed in the products arising from the reaction of lithiated 1,2,4-trichlorobenzene with N,N-dimethylformamide and tetraalkyloxamides.     

Relationship between structure and CO oxidation activity of ceria-supported gold catalysts

Gold catalysts supported on cerium oxide were prepared by solvated metal atom dispersion (SMAD), by deposition-precipitation (DP), and by coprecipitation (CP) methods and were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS). The catalytic activity was tested in the CO oxidation reaction. The structural and surface analyses evidenced the presence of a modified ceria phase in the case of the DP sample and the presence of pure ceria and gold metal crystallites in the case of the SMAD and CP samples. The DP sample, after a mild treatment in air at 393 K, exhibited only ionic gold, and it was very active below 273 K. By comparing the activities of the different catalysts, it is suggested that the presence of small gold particles, as obtained by the SMAD technique, is not the main requisite for the achievement of the highest CO conversion. The strong interaction between ionic gold and ceria, by enhancing the ceria surface oxygen reducibility, may determine the particularly high activity.     

Chemistry and biochemistry of hemicelluloses: Relationship between hemicellulose structure and enzymes required for hydrolysis

The lignified plant cell wall is a composite material in which cellulose, hemicelluloses and lignin are in tight association. Xylans constitute the predominant hemicellulose of hardwoods and straw, wherease galactomannans represent the largest hemicellulose fraction in softwoods. Naturally occuring hemicelluloses, commercially available hemicelluloses and xylans and mannans from technical processes have distinct differences with respect to degree of polymerization and extent of branching. In principle, naturally occuring hemicelluloses carry more side chains compared to those which have been extracted with alkali or under pressure and heat. The presence or absence of substituents is also reflected by the enzymes required for complete hydrolysis. The action of the depolymerizing xylanases and mannanases may be partly dependent on debranching enzymes. Special empasis is therefore given on the substrate requirements of the so-called accessory enzymes (i.e. α-glucuronidase, α-arabinosidase, α-galactosidase, acetyl- and phenolic acid esterase) as well as on synergy effects with the depolymerizing enzymes.     

Relationship between structure,fluxionality and racemization activity in organometallic derivatives of polyoxometalates

The catalytic activity of several organometallic derivatives of polyoxometalates, especially those of general formula [M₄O₁₆{M′(η⁶-arene)}₄] (M = Mo, W; M′ = Ru, Os), was evaluated in the racemization of secondary alcohols. A link between composition, fluxionality and catalytic activity was established.     

Relationship of electrochemical oxidation of catechins on their antioxidant activity in microsomal lipid peroxidation.

The oxidation potentials of catechins were measured by employing flow-through column electrolysis. The oxidation potentials of catechins were shown to depend on their structures. At the same time, the antioxidant activity of catechins on NADPH-dependent lipid peroxidation in rat liver microsomes was evaluated. Catechins showed a 50% inhibition of lipid peroxidation in the concentration range of 10-51 microM. Among those studied, galloylated catechins exhibited stronger antioxidant activities than those of nongalloylated catechins. A quantitative relationship has been obtained to describe the antioxidant activity of catechins: log IC50 (microM)= 1.56+2.49E1/2 (V)-0.29 logP (r=0.907), where IC50 represents the concentration for 50% inhibition of lipid peroxidation, E1/2 represents the half-wave potential of the first oxidation wave, and P represents the octanol/water partition coefficient. This relationship suggested two important characteristics determining catechin antioxidant activity, namely the ease of oxidation and the lipophilicity.     

Theoretical DFT study of the structure and chemical activity of small indium(III) oxide clusters

The B3LYP/Lanl2dz and B3LYP/SDD levels of DFT have been used to describe the structural properties of small stoichiometric indium(III) oxide clusters. It was shown that the most stable structures for the monomer and dimer are linear and cubic, respectively, in origin. The most stable trimer is due to the formation of three eight-membered and two six-membered rings with alternation of In and O atoms. Among neutral and monocation tetrameric structures, formation of an ??arrowhead?? isomer is energetically less favorable than the global minimum structure that has eight six-membered and six four-membered rings. In the pentamer and octamer, a few centers of higher coordination number and a variety of In?CO bond lengths are observed. The other centers cannot be fitted to the characteristic bixbyite structure, however, so the larger octamer cannot be a good model for mimicking the properties of the In₂O₃ crystal structure. An H-terminated cluster model consisting of In₁₃O₂₇H₁₅ is proposed that well describes basic features of indium oxide and tin-doped indium oxide (ITO) structures.     

苦参碱和氧化苦参碱电子结构与药性的关系

用量子化学从头算和半经验方法研究了苦参碱和氧化苦参碱的电子结构对药理活性的影响。结果表明：苦参碱与氧化苦参相比较，在最低能量的构象结构、分子轨道结构、电荷结构和原子间键序方面相近，而在分子轨道能级和原子电荷数值方面有明显差异。从立体作用、轨道作用和电性作用方面来看，氧化苦参碱比苦参碱具有更强的作用，由此预测，氧化苦参碱的药理活性高于苦参碱。     

Relationship between the chemical structure and pharmacological action of cardiac glycosides of the strophanthidin series

The possibility has been shown of finding and creating highly effective cardiotonic drugs for pediatric practice on the basis of cardenolides obtained by the chemical transformation of natural cardiac glycosides.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 581–585, July–August, 1995. Original article submitted November 21, 1994.     

Relationship between the helical structure and optical activity of some chiral cyclic esters

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催化臭氧氧化降解邻苯二甲酸二甲酯中催化剂构效关系

采用传统焙烧和微波辐射制备了不同活性炭 (AC) 负载 Ru 催化剂, 并用于催化臭氧氧化降解邻苯二甲酸二甲酯 (DMP) 反应中, 探讨了催化剂的构效关系. 结果表明, 所有 AC 和催化剂均能提高臭氧氧化 DMP 过程中 TOC (总有机碳) 去除率, 其活性顺序为 Ru/coal-AC > nutshell-AC > Ru/nutshell-AC > Ru/coconut-AC ≈ coal-AC > coconut-AC. 负载的 Ru 颗粒扩散到 AC 大孔中, 增加了反应的传质阻力, 使得反应物与 AC 内表面的活性位和金属 Ru 的接触机会减少, 这是 Ru/nutshell-AC 和 Ru/coconut-AC 活性低于 Ru/coal-AC 的一个原因; 催化剂表面 Ru 分散度也是导致其活性差别的原因之一. 微波加热引起 nutshell-AC 表面活性官能团发生变化, 从而导致其负载的 Ru 催化活性降低. 相对于传统焙烧, 微波辐射热处理能够提高 coal-AC 表面 Ru 的分散度, 从而提高催化剂活性.     

Relationship between the gas chromatographic behaviour and the molecular structure of hydrocarbon samples and various stationary phases Part I. Correlation of retention data and thermodynamic functions with chemical structure

Summary Retention parameters of different hydrocarbon classes were determined at 90–120°C on non-polar and medium-polar stationary phases. The specific retention volumes, and the thermodynamic functions of solution were calculated and the relationship between these data, the physicochemical properties and the chemical structure of the solutes (samples) and solvents (liquid phases) investigated.