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941.
Protocatechuic acid esters (= 3,4‐dihydroxybenzoates) scavenge ca. 5 equiv. of radical in alcoholic solvents, whereas they consume only 2 equiv. of radical in nonalcoholic solvents. While the high radical‐scavenging activity of protocatechuic acid esters in alcoholic solvents as compared to that in nonalcoholic solvents is due to a nucleophilic addition of an alcohol molecule at C(2) of an intermediate o‐quinone structure, thus regenerating a catechol (= benzene‐1,2‐diol) structure, it is still unclear why protocatechuic acid esters scavenge more than 4 equiv. of radical (C(2) refers to the protocatechuic acid numbering). Therefore, to elucidate the oxidation mechanism beyond the formation of the C(2) alcohol adduct, 3,4‐dihydroxy‐2‐methoxybenzoic acid methyl ester ( 4 ), the C(2) MeOH adduct, which is an oxidation product of methyl protocatechuate ( 1 ) in MeOH, was oxidized by the DPPH radical (= 2,2‐diphenyl‐1‐picrylhydrazyl) or o‐chloranil (= 3,4,5,6‐tetrachlorocyclohexa‐3,5‐diene‐1,2‐dione) in CD3OD/(D6)acetone 3 : 1). The oxidation mixtures were directly analyzed by NMR. Oxidation with both the DPPH radical and o‐chloranil produced a C(2),C(6) bis‐methanol adduct ( 7 ), which could scavenge additional 2 equiv. of radical. Calculations of LUMO electron densities of o‐quinones corroborated the regioselective nucleophilic addition of alcohol molecules with o‐quinones. Our results strongly suggest that the regeneration of a catechol structure via a nucleophilic addition of an alcohol molecule with a o‐quinone is a key reaction for the high radical‐scavenging activity of protocatechuic acid esters in alcoholic solvents. 相似文献
942.
Marie-Hélène Paclet Cécile F. Rousseau Campion Yannick Françoise Morel Anthony W. Coleman 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(3-4):353-357
The effects of para-Sulphonato-calix[4]arene, para-Sulphonato-calix[6]arene and para-Sulphonato-calix[8]arene on the activation of NADPH oxidase in neutrophils has been studied. All three molecules do not induce NADPH oxidase activation, and hence do not stimulate neutrophils. Measurement of cell viability demonstrates that these three water-soluble calix[n]arene derivatives are not cytotoxic. 相似文献
943.
Gengliang Yang Zhiwei Li Dexian Wang Zhefeng Zhang Erdong Liu Yi Chen 《Chromatographia》2002,56(7-8):515-518
Summary A high-performance liquid chromatographic method was developed for the chiral separation of a new anti-diabetic agent, N-(trans-4-isopropylcyclohexylcarbonyl)-D-phenylalanine,
and its L-enantiomer. The separation was performed on a Sumichiral OA-3300 column. Optimized mobile phase was 0.025 mol.L−1 ammonium acetate in methanol solution. UV detection was at 210 nm. Baseline chiral separation was obtained within 12 minutes.
The detection limits are 80 pg for the D-enantiomer and 120 pg for the L-enantiomer. RSD of the method was below 1% (n=5). 相似文献
944.
C. Etzlstorfer H. Falk E. Mayr S. Schwarzinger 《Monatshefte für Chemie / Chemical Monthly》1996,127(12):1229-1237
Summary The strongly enhanced acidity of the bay hydroxyl group as compared to the respectiveperi hydroxyl groups of fringelite D, hypericin, and stentorin could be rationalized on the basis of a vinylogous carboxylic acid and was nicely corroborated by semiempirical calculations of the AM1 type. Experimental data obtained from several independent experimental methods, like polarized absorption spectroscopy, hole burning, and isotope effects, as well as from semiempirical AM1 and 6–31G levelab initio calculations conclusively pointed to dissymmetrical hydrogen bonding systems in both theperi andbay regions of the correspondingbay phenolate ions.
Zu Acidität und Wasserstoffbrückenbindung von Hydroxyphenanthroperylenchinonen wie Fringelit D, Hypericin und Stentorin
Zusammenfassung Die stark erhöhte Acidität der bay-Hydroxylgruppen gegenüber jener derperi-Hydroxylgruppen von Fringelit D, Hypericin und Stentorin läßt sich auf der Basis einer vinylogen Carbonsäure verstehen und wurde auch durch semiempirische Rechnungen vom AM1-Typ erhärtet. Daten aus unabhängigen Experimenten wie Polarisationsspektroskopie, Lochbrennen und Isotopeneffekte sowie semiempirische AM1- undab initio-Rechnungen auf 6–31G Niveau belegen ein unsymmetrisches Wasserstoffbrückenbindungssystem sowohl für denperi-als auch denbay-Bereich der entsprechendenbay-Phenolationen.相似文献
945.
The effect of an electron attracting substituent in the Lewis acid catalyzed oligomerization of flavanols was investigated. The results showed that the presence of a COCF3, at the 8 position of a (+)-catechin unit strongly influenced the attack of the 6 free nucleophile flavanol position by the electrophile generated from a 4-O-alkyloxy protected catechin unit. This was observed either with TiCl4 or TMSOTf as Lewis acids in which the carbon-carbon bond formation was inhibited and the corresponding dimer was detected in small amount. On the contrary, the formation of a carbon-oxygen bond was observed and the corresponding C-4→O→C-3 ether linked procyanidin dimer was isolated in a good yield. In order to avoid the participation of the C-3 hydroxyl group in the dimerization reaction, the two flavanol units were forced into C-4→C-8 coupling by use of an internal link. The structural elucidation of the isolated compounds was achieved through MS and NMR spectroscopy. 相似文献
946.
三元配合物钯(Ⅱ)-2,2''-联吡啶-L-天冬氨酸与DNA作用研究 总被引:1,自引:0,他引:1
The ternary complex Pd(Ⅱ)-2,2‘-bipyridine-L-asparagic acid was synthesized and characterized by elemental analysis, IR-spectra and molar conductance. The formula of the complex is Pd(bipy)(L-asp). The interaction of the complex with DNA has been studied by UV-spectra, fluorescence spectra, CD-spectra and gel electrophoresis. The results showed that the interaction of the complex with DNA performed mainly in intercalative mode and the extent of interaction was dependent on the concentration of the complex. 相似文献
947.
V. I. Terenin E. A. Sumtsova S. Z. Vatsadze E. V. Kabanova I. F. Leshcheva A. P. Pleshkova N. V. Zyk 《Chemistry of Heterocyclic Compounds》2003,39(7):943-952
We have studied the behavior of asymmetrically substituted dipyrrolo[1,2-a;2',1'-c]pyrazines and their 5,6-dihydro analogs under phosphorylation reaction conditions. 相似文献
948.
K. P. Butin A. A. Moiseeva T. V. Magdesieva E. V. Sergeeva V. I. Rozenberg V. G. Kharitonov 《Russian Chemical Bulletin》1994,43(5):783-789
The potentials of electrochemical oxidation (
) and reduction (
) of monobromo- and isomeric di- and tribromo[2.2]paracyclophanes as well as
of mono-, di-, and tribromobenzenes were measured in acetonitrile. The similarity between the properties ofpseudo-para-disubstituted cyclophanes andmeta-disubstituted benzenes, on the one hand, andpseudo-meta-disubstituted cyclophanes andpara-disubstituted benzenes, on the other hand, was confirmed by the existence of a linear relationship between
of bromo-substituted [2.2]paracyclophanes and
of the corresponding bromo-substituted benzenes. The results were explained in terms of the qualitative theory of molecular orbitals, taking into account a through space interaction between the -systems of the benzene rings.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 839–845, May, 1994.The authors wish to express their gratitude to Professor R. Hoffmann (Cornell University, USA) for a useful discussion and criticisms of the text of this paper.This work was financially supported by the Russian Foundation for Basic Research (Project 93-03-5246). 相似文献
949.
Interactions between divalent alkali earth metal (DAEM) ions M (M?Be, Mg, Ca, Sr, Ba) and the second stable glycine conformer in the gas phase, which can transfer into the ground‐state glycine‐M2+ (except the glycine–Be2+) among each corresponding isomers when these divalent metal ions are bound, are studied at the hybrid three‐parameter B3LYP level with three different basis sets. Proton transfers from the hydroxyl to the amino nitrogen of the glycine without energy barriers have been first observed in the gas phase in these glycine–M2+ systems. The interaction between the glycine and these DAEM ions except beryllium and magnesium ion only create an amino hydrogen pointing to the original hydroxyl due to their weaker interaction relative to those divalent transition metal (DTM) ion‐bound glycine derivatives, being obviously different from that between the glycine and DTM ions, in which two amino hydrogens point to the original hydroxyl oxygen when these metal‐chelated glycine derivatives are produced. The interaction energy between the glycine and divalent magnesium would be the boundary of one or two amino hydrogens pointing to the hydrogyl oxygen, i.e., the ?170.3 kcal/mol of binding energy is a critical point. Similar intramolecular proton transfer has also been predicted for those DTM ion‐chelated glycine systems; however, that in the gas state has not been observed in the monovalent metal ion‐coordinated glycine systems. The binding energy between some monovalent TM ion and the glycine is similar to that of the glycine–Ba2+, which has the lowest binding strength among these DAEM–ion chelated glycine complexes. The difference among them only lies in the larger electrostatic and polarized effects in the latter, which favor the stability of the zwitterionic glycine form in the gas phase. According to these observations, we predict that the zwitterionic glycine would exist in the field of two positive charges in the gas phase. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 205–214, 2003 相似文献
950.
In this paper we have presented the results of acoustic emission (AE) during non-isothemal crystallization of polypropylene (PP) melt with mean cooling rate 4℃/min, and discussed the effects of molecular weight (MW) on AE activity. It is shown that the amount of AE ring-down counts during whole crystallization of PP depends on the MW strongly.The copious AE bursts have been observed at the late stage of PPcrystallization. AE bursts are caused by cracking, crazing and cavitation between spherulites and inside spherulites. 相似文献