Structure-function analysis of the radioprotective and antioxidant activity of flavonoids

The recombination kinetics of a series of flavonoids with stable DPPH radicals are studied. Flavonols are the most reactive. Polarization of the carbonyl in flavones reduces the reactivity. Substitution on C-7 and the B ring has practically no effect on the reactivity. Glycosylation of C-3 reduces the reactivity if the sugar can form two intramolecular H-bonds. The reactivity of the flavonoid phenol hydroxyls, with the exception of the hydroxyl on C-5, is proportional to their number. The most promising antioxidants are lespedin, kaempferitrin, kaempferol, kaempferol-7-rhamnoside, kaempferol-3-robinobioside, and robinin.I. G. Kutateladze Institute of Pharmacochemistry, Georgian Academy of Sciences, Tbilisi, fax (99532)-25-00-26. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 42–46, January–February, 2000.     

Electrochemical oxidation of C4-vanillin- and C4-isovanillin-1,4-dihydropyridines in aprotic medium: Reactivity towards free radicals

This work reports the electrochemical oxidation of two new synthetic C4-vanillin and -isovanillin-1,4-dihydropyridines in aprotic medium. Its reactivity with alkylperoxyl radicals ABAP-derived at pH 7.4 is also studied. Voltammetry, coulometry, controlled-potential electrolysis, UV–visible spectroscopy and GC–MS techniques were employed to collect data that permitted us to study its oxidation. Effect of TBA-OH addition on the oxidation was electrochemically and spectroscopically followed. In aprotic medium, the oxidation mechanism involves the formation of the pyridine derivative, which was generated by controlled-potential electrolysis (CPE) at 1270 mV and identified by GC–MS technique as the final product of the electrolysis. Spectroelectrochemical experiments also support the formation of the pyridine derivative from the oxidation of both 1,4-dihydropyridines. Direct reactivity of synthesized compounds towards alkylperoxyl radicals ABAP-derived was determined. Results reveal that the inclusion of vanillin radical or its positional isomer, isovanillin in the 4-position of the dihydropyridine ring produced a significant positive effect on the reactivity towards alkylperoxyl radicals, even compared with commercial dihydropyridine drugs with a well-known antioxidant ability. Scavenging mechanism involves the electron-transfer and the formation of a pyridine derivative, which was identified by GC–MS.     

Liquid-phase oxidation of thiols with chlorine dioxide

The products and kinetics of the liquid-phase oxidation of 11 aliphatic and aromatic thiols with chlorine dioxide were studied at –10—+70 °C in organic media. The rate constants and activation parameters of the reaction were determined. The influence of the thiol structure on its reactivity was studied. A strong solvent effect on the reaction rate constant was found, and the reaction mechanism was proposed.     

The effect of Fe2O3 dopants on electrophysical and sorption properties of ZnO

The effect of Fe₂O₃ dopants (0–0.8 mol.%) on ZnO conductivity and its chlorine chemisorption ability has been studied in the temperature range of 20–250 °C. Introduction of dopants increases the activation energy of ZnO conductivity and decreases the conductivity. The effective charge of the chemisorbed chlorine species as well as the strength of their bonding to the surface in samples containing Fe₂O₃ are considerably lower than in initial ZnO, which leads to a decrease of reactivity of the doped catalysts in chlorination.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1196–1199, July, 1993.     

An X-ray and UV photoelectron spectroscopic study of CO chemisorption and dissociation on the stepped Co(10 2) surface

The chemisorption and surface dissociation of CO on cobalt are studied by X-ray and HeI/HeII photoemission. The nature of the high-temperature γ-CO state is elucidated and the usefulness of the Δ(1Π–4σ) parameter as a measure of chemical reactivity is tested.     

Study of the reactivity of ammonium carboxylates in the synthesis of amides under high-pressure deformation conditions

On deformation under pressures up to 10 GPa the ammonium salts of aliphatic and aromatic acids, as well as mixtures of a free carboxylic acid with the ammonium salts of strong mineral acids, are converted into the corresponding amides. The amide yields increase with pressure, the magnitude of shearing deformation, and temperature. The temperature and pressure coefficients for amide formation are low and have values of 2.5–4 kJ/mole and –1 to –2 cm³/mole, respectively. The reactivity of ammonium salts in the synthesis of amides alternates in the homologous series of aliphatic acids in a similar way to the shear stress of these salts. The reactivity of the ammonium salts of aliphatic acids increases when the reaction is conducted in a matrix of an ammonium salt which possesses plasticity and a high shear stress.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2289–2292, October, 1989.     

Reaction potential map analysis of chemical reactivity—III

Reaction potential maps (RPM) have been introduced as a new tool for the study of molecular reactivity. The equipotential energy maps, which are created on given planes around a molecule, define reaction contours towards specific counter-reagent models and are evaluated by perturbation theory. Since the calculated interaction energy involves electrostatic, polarization, exchange, and charge transfer energies, the RPM's can be used to predict site selectivity in a variety of chemical reactions. We found that the calculated RPM's of the SCN^– anion explained well the experimental observations that it reacts at the S atom with soft electrophiles and at the N atom with hard electrophiles. The difference in reactivity between SCN^– and OCN^– was clearly shown by the RPM's of these anions. The ambident nucleophilic nature of the NO ₂ ^– and the CH₂CHO^– anions was also well represented by their RPM's.     

The reaction of C-(N,N-dialkylamino)phosphaalkenes and their dimers with sulfur

The nature of the dialkylamino group has a significant effect on the reactivity of C-(N,N-di-alkylamino)phosphaalkenes upon their reaction with sulfur.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1169–1172, May, 1990.     

A study of the reactivity of copper nanopowders in their reaction with glacial acetic acid

The reactivity of copper nanopowders obtained by mechanical treatment or electric explosion of a conductor was studied in their reaction with glacial acetic acid. Two parameters were used to evaluate the reactivity: heat effect of the reaction and the maximum rate of heat release.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 12, 2004, pp. 1937–1941.Original Russian Text Copyright © 2004 by Mikubaeva, Kobotaeva, Sirotkina.     

Attenuation of substituent effects on reactivities of low-spin iron(II) complexes of Schiff base ligands

Substituent effects on reactivity are compared for base hydrolysis of tris-ligand-iron(II) complexes of Schiff base ligands derived from 2–acetylpyridine and substituted benzylamines and their aniline analogues. The methylene spacer in the former effectively isolates the iron from substituent effects in the phenyl ring, as indicated by the almost equal rate constants for base hydrolysis of the complexes derived from benzylamine and its 4–methyl, 4–fluoro, and 4– trifluoromethyl derivatives. Rate constants for base hydrolysis of the (substituted) benzylamine derivatives are also reported for some Me2CO-H2O and DMSO-H2O solvent mixtures. Reaction is faster in all these binary aqueous mixtures, mainly due to the higher chemical potentials of hydroxide ion.     

Some N-alkyl-naphthylazo pyridinium salts as new reagents for the spectrophotometric determination of anionic surfactants

Summary Eleven pyridinium azo dyes with straight-chain alkyl groups C_nH_2n+1–(n=6–18) and bromoalkyl groups BrC_mH_2m–(m=6–12) were synthesized with the intention of developing reagents for the determination of low levels of anionic surfactants in an aqueous medium. The effect of the alkyl chain length of these reagents on the reactivity with anionic surfactants such as sodium dodecylsulphate (SDS), sodium linear-dodecylbenzenesulphonate (DBS), sodium dodecylsulphonate (DS) and sodium laurate (SL) was studied. It was found that the alkyl chain length played an important role in the formation of ion associates and the composition of the ion associates formed. These reagents were classified into four groups with respect to the reactivity with anionic surfactants. The first group (n,m=6) reacts only with DBS. The second group (n,m=8) reacts with SDS, DBS and DS. The third group (n,m=10, 12) reacts with SDS, DBS and DS; however, the colour intensity of the DBS-ion associate was unstable. The fourth group (n=14, 16, 18) reacts with all anionic surfactants examined, and the composition of the ion associates with SDS and DS was 2:1 ([reagent]/[surfactant]) though that of the ion associates of the three reagent groups mentioned above was 1:1. The optimal conditions for the determination of anionic surfactants in river water with 1-octyl-4-(4-aminonaphthylazo)-pyridinium bromide was examined. The calibration graph was linear up to 3×10^–6 mol/l, and the apparent molar absorptivity of the ion associate was 3.8×10⁴ l mol^–1 cm^–1 (at 427 nm). The relative standard deviation for 2.4×10^–6 mol/l SDS was 4.9%. Recoveries of 88–107% were found for 8.0×10^–7 mol/l SDS in river water samples.     

Kinetic Regularities of Reactions of O,O-Diaryl Phosphorohydrazidothioates with Phenyl Isothiocyanate in Benzene

The effect of the temperature on the rate of reactions of O,O-diaryl phosphorohydrazidothioates with phenyl isothiocyanate in benzene is studied, and the activation parameters of the reactions are calculated. It is established that the reaction series under study obeys the isokinetic relationship with an enthalpy control and an isokinetic temperature of 690±24 K. The effect of electronically diverse substituents on phosphorus on the reactivity of O,O-diaryl phosphorohydrazidothioates is additive. It is described by the Hammett equation with σ^P constants.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 6, 2005, pp. 893–896.Original Russian Text Copyright © 2005 by Yanchuk, Ivanets.     

A quantum-chemical study of the effect of a solvent on the electron structure and reactivity of molecules

Conclusions The effect of the solvent on the electron structure and molecular reactivity has been discussed in terms of the quantum chemistry of proton transfer in a point-charge model of the NH₃+HF system.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No.1, pp.48–51, January, 1976.     

Effect of the nature of cross-linking acrylamides on structurization of gelatin by laser irradiation

We consider the characteristics of photochemical reactions in gelatin-cross-linking agent systems under the influence of emission from a helium-neon laser. We show that the degree of structural transformations is determined by the nature of the cross-linking agents and depends on their structure and reactivity.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 1, pp. 81–85, January–February, 1990.     

Study of some electrophilic reactions of 6-hydroxy (methoxy)-2-benzyl-3-hydroxypyridines

Conclusions A study was made of the effect of the benzyl group on the reactivity and the orientation of aromatic substitution in the 6-hydroxy(methoxy)-2-benzyl-3-hydroxypyridines and their N-oxides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 206–209, January, 1973.     

Reasons for increased selectivity of catalysts for partial oxidation of methane using N2O as oxidizing agent

It was found that the increase in the selectivity of catalysts of the partial oxidation of methane by nitrous oxide (compared with the oxidation by molecular oxygen) is due to the participation in the reaction of adsorbed oxygen anion radicals O^·–, with which the differences in the reactivity of methane and its mild oxidation products are leveled out. With O₂, the reactivity of methane is much lower than that of formaldehyde and methanol and, as a result, the selectivity is low, and a postoxidation of the partial oxidation products rapidly takes place. The formation of O^·– is promoted by low concentrations of metal ions in the catalyst. The influence of the geometrical factor is thus also manifested: at low concentrations of the metal ions (M), the surface postoxidation of the adsorbed formaldehyde (the nonlinear stage) is hindered, which favors increase in the selectivity with respect to HCHO.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 727–729, November–December, 1988.     

A force-field model and steric reactivity factor estimation

Steric reactivity factor estimation is considered on the basis of the energies of various substrate and intermediate conformations within the framework of a forcefield model. The example of alkali hydrolysis of ethyl esters of substituted acetic and malonic acids is taken to examine the relationship between the steric reactivity indices, the steric constants of the substituents, and the rate constants. It is found that the main contribution to the steric component of the free energy of activation comes from the van der Waals interaction in these systems.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. 3, pp. 366–370, May–June, 1986.     

Reactivity of propargylamines in complexation and polymerization reactions

Factors were determined which promote the formation of charge-transfer complexes of propargylamines with organic electron acceptors and a change of the activity of the triple bond in propargylamines under the effect of donor-acceptor interactions. On the basis of data from PMR spectroscopy and quantum-chemical calculations it was shown that the tendency of propargylamines to form charge-transfer complexes depends on the electron-donor properties of the substituents at the nitrogen atom. The values of the effective charges at the atoms and an analysis of the structure of the highest occupied molecular orbitals in the propargylamines and their radical cations indicate that mainly electrons localized on nitrogen atoms participate in the complexation reaction. An increase of the reactivity of the triple bond is related to an increase in its polarity under the effect of complexation.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 5, pp. 597–601, September–October, 1989.     

Reactivity and regioselectivity of the pyrrole,furan, and thiophene radical cations in polymerization reactions

Within the framework of the delocalization model, based on the perturbation theory, the rate constants of the reactions of the pyrrole, furan, and thiophene radical cations with the initial compounds were compared. It was estabished that attack of a cation in the 2-position of the heterocycle is more probable in comparison with the 3-position. The results of a comparison of the reactivity of the radical cations and the corresponding molecules in the triplet state in these reactions are discussed in connection with the experimental data.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, Nos. 5–6, pp. 483–487, September–December, 1992.     

Structure and reactivity of benzothiazole-2-thione polysulfides

A quantum-chemical study was made of the possibility of the formation of polysulfides from benzothiazole-2-thione and their structure. The reactivity indices of the benzothiazole-2-thione molecule and of the small sulfur fragments were calculated. It was shown that as the fragments approach each other the formation of polysulfide structures with increased reactivity becomes possible.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 1, pp. 73–78, January–February, 1990.