Quantum chemical estimation of the possibility of the formation of chloro- and bromomethane radical anions and their fragmentation paths in the gas phase and in solution by MNDO and AM1 techniques

By semiempirical MNDO and AM1 methods it was shown that electron transfer on the chloro-and bromomethane molecules of the general formula CH_nHal_4–n (n=1–3) results either in a kinetically independent particle, i.e., a radical anion, or in C-Hal-bond cleavage with the formation of Hal^– and the respective radical. The enthalpy, activation energy of the reactions, and data on the geometry of the radical anion obtained show that the increasing the number of halogen atoms in the initial molecule and decreasing the solvent polarity favor radical anion stabilization. It was established that the cleavage of the C-H-bond in the radical anion is not favored energetically. Fragmentation at the C-H-bond can proceed according to the mechanism of dissociative electron capture by halomethane molecule only with additional factors favoring this reaction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1886–1892, November, 1993.     

Quantum-chemical study on electrode field effects in elementary stages in electrochemical methyl chloride reduction

MINDO/3 has been applied to the effects of field strength and direction on elementary stages in electroorganic reaction, the electrochemical reduction of methyl chloride: molecule and anion-radical orientation, electron transfer from electrode to molecule, anion radical dissociation, and methyl radical and anion inversion. The molecular electronic and stearic structures are affected by the field, as are those for the anion radical, the molecular and radical reorientation barriers, the direction and height in the radical dissociation barrier, and the radical and anion configuration stabilities. An explanation is given for the electrolysis data for alkyl halides and for the properties of chemically modified electrodes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. 4, pp. 412–420, July–August, 1989.     

A generation mechanism of triboelectricity due to the reaction of mechanoradicals with mechanoions which are produced by mechanical fracture of solid polymer

Mechanical fracture of solid polymer under vacuum at 77K can, in principle, produce both mechanoradicals and mechanoanions which are formed by homolytic and heterolytic scission of carbon-carbon bonds in the polymer main chain. The production of mechanoanions was claimed by a detection of tetracyanoethylene (TCNE) anion radical (TCNE^–), which was observed by electron spin resonance (ESR) spectroscopy using the electron trapping method with TCNE.A novel mechanism for generating triboelectricity is proposed. The charge carrer is an electron. The electron donor is the mechanoanion A^–, which is produced by heterolytic carbon-carbon bond scission of the main chain of polymer A. The electron acceptor is the mechanoradical B·, which is produced by homolytic carbon-carbon bond scission of the main chain of polymer B. Charge separation is due to an electron transfer from the mechanoanion to the mechanoradical when in contact. It is possible to speculate the sign of the charge induced by friction from the electron release potential of A^–, Pr(A^–), and the molecular electron affinity of B·, Ea(B·). The triboelectric series deduced from our mechanism is PMMA-PP-PE-PVDF-PTFE, in which polymers having a relatively low Pr(A^–) to high Pr(A^–) or polymers having a relatively low Ea(B·) to high Ea(B·) are arranged. This order is identical with well-known triboelectric series.Dedicated to Professor Hans-Henning Kausch on the occasion of his 60th birthday     

Dibromine radical anion reactions with heme enzymes

Reactions of Br ₂ ^– radical anion with heme enzymes, catalase and horseradish peroxidase, have been studied by pulse radiolysis. It has been found that Br ₂ ^– does not react with the heme centre of investigated enzymes. Dibromine radical anion reacts with tryptophan residues of catalase without any influence on the activity of catalase. It is suggested that in pulse radiolysis studies, where horseradish peroxidase is at about tenfold excess towards Br ₂ ^– , the enzyme is modified rather by Br₂, than by Br ₂ ^– .     

Enzymatic oxidation of lignin and compounds modeling it. III. Formation of singlet oxygen in the peroxidase oxidation of lignin

The main emitters of radiation in the aerobic oxidation of lignin are the carbonyl groups in an excited state and singlet oxygen. It has been shown that the main source of O₂(¹) may be the radical anion O^–·₂. Singlet oxygen and the radical anion are by-products of the radical oxidation of lignin.Siberian Scientific-Research Institute of Cellulose and Board, Bratsk. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 510–514, July–August, 1984.     

Reaction of derivatives of 1,4-dihydropyridine with the peroxynitrite anion

The reaction of derivatives of 1,4-dihydropyridine (1,4-DHP) with peroxynitrite anion is an oxidation reaction; no products of nitration were detected. It was found that some 1,4-DHP increase the lifetime of the peroxynitrite anion and the yield of hydroxyl radical in decomposition of the peroxynitrite anion.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 355–357, March, 1998.     

Determination of a flame retardant hydrolysis product in human urine by SPE and LC–MS. Comparison of molecularly imprinted solid-phase extraction with a mixed-mode anion exchanger

Diphenyl phosphate is a hydrolysis product and possible metabolite of the flame retardant and plasticiser additive triphenyl phosphate. A molecularly imprinted polymer solid-phase extraction (MISPE) method for extracting diphenyl phosphate from aqueous solutions has been developed and compared with SPE using a commercially available mixed-mode anion exchanger. The imprinted polymer was prepared using 2-vinylpyridine (2-Vpy) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker, and a structural analogue of the analyte as the template molecule. The imprinted polymer was evaluated for use as a SPE sorbent, in tests with both aqueous standards and spiked urine samples, by comparing recovery and breakthrough data obtained using the imprinted form of the polymer and a non-imprinted form (NIP). Extraction from aqueous solutions resulted in more than 80% recovery. Adsorption by the molecularly imprinted polymer (MIP) was non-selective , but selectivity was achieved by selective desorption in the wash steps. Diphenyl phosphate could also be selectively extracted from urine samples, although the urine matrix reduced the capacity of the MISPE cartridges. Recoveries from urine extraction were higher than 70%. It was important to control pH during sample loading. The MISPE method was found to yield a less complex LC–ESI–MS chromatogram of the urine extracts compared with the mixed-mode anion-exchanger method. An LC–ESI–MS method using a Hypercarb LC column with a graphitised carbon stationary phase was also evaluated for organophosphate diesters. LC–ESI–MS using negative-ion detection in selected ion monitoring (SIM) mode was shown to be linear for diphenyl phosphate in the range 0.08–20 ng L^–1.     

Anion-radical mechanism of bromine exchange by iodine in furan derivatives

The kinetics of bromine exchange by iodine in furan derivatives were studied; it is shown that the reaction is reversible and inhibited by oxidizing agents. Chloro derivatives of furan do not undergo this reaction. A cryptoreductive mechanism is proposed; the first stepof this mechanism consists of electron transfer to the halofuran molecule with subsequent reversible dissociation of the anion radical — inclusion of the iodide anion in the dissociation equilibrium leads to the substitution product.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1601–1606, December, 1976.     

One-electron transfer in the vinylation of 4,5,6,7-tetrahydroindole with acetylenes in the system KOH-DMSO

It has been shown by EPR, using 2-methyl-2-nitrosopropane as a radical trap, that vinylation of 4,5,6,7-tetrahydroindole with phenylacetylene in the system KOH-DMSO involves the formation of the 4,5,6,7-tetrahydroindolyl radical by transfer of an electron from the 4,5,6,7-tetrahydroindole anion to the acetylene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 142–144, January, 1990.     

Cyclization of isoprene compounds

Conclusions Reaction of geranic ester with cationic initiators of the type RCOMX_n+1, depending on the nature of the R radical and the anion MX _n+1 ^– , leads to the formation of cyclic or acyclic products containing the radical RCO, or of their mixtures. The factors which determine the trend of the reaction are examined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 866–874, April, 1968.     

Removal of185W,99Mo and125Sb radioisotopes from aqueous solutions using polyamine incorporated polysaccharides

Polyamino group-containing resins act both as chelating ion exchangers and weakly basic anion exchangers depending upon the species in contact in the solution. In the present work, ion exchangers based on polyamine incorporated polysaccharides (cellulose and galactomannan or guaran) have been used for removal of radioisotopes of¹⁸⁵W as WO ₄ ^2– ,⁹⁹Mo as MoO ₄ ^2– and¹²⁵Sb as Sb³⁺ from their separate aqueous solutions. These chelating anion exchangers have been synthesized by reaction of polysaccharides with epichlorohydrin followed by the respective polyamines as nucleophiles in a strongly alkaline medium. WO ₄ ^2– and MoO ₄ ^2– are adsorbed from their aqueous solutions through anion exchange process by chloride form of cellulose-triethylenetetraamine (cellulose-trien), cellulose-tetraethylenepentaamine (cellulose-tetren), guaran-triethylenetetraamine (guar-trien) and guar-tetraethylenepentaamine (guar-tetren) weakly basic anion exchangers. Guar-tetren chelating polymer has been found to be highly selective for¹²⁵Sb isotopes presumably due to the presence of chelating cis-hydroxy and tetren groups in the galactomannan matrix.     

Biomimetic Ketone Reduction by Disulfide Radical Anion

The conversion of ribonucleosides to 2′-deoxyribonucleosides is catalyzed by ribonucleoside reductase enzymes in nature. One of the key steps in this complex radical mechanism is the reduction of the 3′-ketodeoxynucleotide by a pair of cysteine residues, providing the electrons via a disulfide radical anion (RSSR^•−) in the active site of the enzyme. In the present study, the bioinspired conversion of ketones to corresponding alcohols was achieved by the intermediacy of disulfide radical anion of cysteine (CysSSCys)^•− in water. High concentration of cysteine and pH 10.6 are necessary for high-yielding reactions. The photoinitiated radical chain reaction includes the one-electron reduction of carbonyl moiety by disulfide radical anion, protonation of the resulting ketyl radical anion by water, and H-atom abstraction from CysSH. The (CysSSCys)^•− transient species generated by ionizing radiation in aqueous solutions allowed the measurement of kinetic data with ketones by pulse radiolysis. By measuring the rate of the decay of (CysSSCys)^•− at λ_max = 420 nm at various concentrations of ketones, we found the rate constants of three cyclic ketones to be in the range of 10⁴–10⁵ M⁻¹s⁻¹ at ~22 °C.     

On the mechanism of the photoinduced reduction of an adduct of ferricytochrome C with a poly(4-vinylpyridine) polymer containing –Re (CO)3(3,4,7,8-tetramethyl-1,10-phenanthroline) pendants

Changes in the UV–vis absorption spectrum revealed the formation of adducts between the Re^I polymer and ferricytochrome C, Fe^III-Cyt c. Different morphologies for the Re^I polymer and the adducts formed between the Re^I polymer and Fe^III-Cyt c were observed by TEM. The reduction of the Re^I chromophores in the polymer, achieved by the reductive quenching of the MLCT excited state of the Re^I polymer by triethylamine (TEA) and/or by the reaction between e⁻_solv and {[(vpy)₂vpyRe^I(CO)₃(tmphen)⁺]}_n200 in pulse radiolysis experiments, produces –Re^I(CO)₃(tmphen) and –Re^I(CO)₃(tmphenH)⁺ as the main species. The reductive quenching of the MLCT of the Re^I polymer by TEA was followed by a rapid electron transfer from the –Re^I(CO)₃(tmphen) to the Fe^III center in the heme to produce ferrocytochrome C, Fe^II-Cyt c.     

Reaction mechanism and chemical polarization of phosphorus nuclei when diethyl phenylazophosphonate is reacted with sodium ethylate

Conclusions The action of ethoxide anion on diethyl phenylazophosphonate leads to nucleophilic substitution of the phenyldiazenyl anion, the cleavage of nitrogen from it, and subsequent electron transfer from the formed phenyl anion to the starting phosphonate molecule. Singlet-triplet evolution in the singlet radical pair that is formed here and its recombination give diethyl diphenylhydrazophosphates, which exhibit the³¹P CPN effect.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2796–2799, December, 1976.     

Chemistry of the intekaction of a peroxy radical with manganese stearate

Conclusions A ketone and a basic salt of trivalent manganese have been identified as the final products of the reaction between a peroxy radical and bivalent manganese. During the reaction the change in the valence of the manganese is accompanied by the conversion of the peroxy radical into an anion.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 1217–1218, December, 1966.     

Nitroazines. 4. Polarographic behavior of 5-nitropyrazolo[3,4-b]pyridines and the esr spectra of their electrochemically generated free radicals

1-Methyl- and 1-phenyl-substituted derivatives of 5-nitropyrazolo[3,4-b]pyridines are reduced at a dropping mercury electrode in a single one-electron wave with the formation of radical anions in interval of potentials from –0.94 to –1.06 V. Compounds unsubstituted at the N(₁) nitrogen atom give an additional polarographic wave at E_1/2 = –1.4 V due to the reduction of the deprotonated form (anion). The potentials and HFS constants of the ESR spectra of the corresponding electrochemically generated free radicals are given.For Communication 3, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 689–693, May, 1985.     

Reaction of the 3-nitrotriazole anion with xenon difluoride

Conclusions Xenon difluoride in acetonitrile is capable of oxidizing the anion of 3-nitro-1,2,4-triazole to form the corresponding radical.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 736–738, March, 1989.     

Mechanism of halogen substitution in the electrochemical reduction of halonitrofurans in dimet hylformamide

The polarographic reduction of 2-halo-5-nitrofurans in dimethylformamide, which leads ultimately to replacement of the halogen by hydrogen to give a nitrofuran, was studied. The ESR spectra of halonitrofuran anion radicals (Hal=Cl, Br) were recorded. Only the spectrum of the nitrofuran anion radical can be observed in the reduction of 2-I-5-nitrofuran. It is shown that the stabilities of the anion radicals of the halonitrofurans and the mechanism of their subsequent transformations depend to a considerable degree on the nature of the halogen.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 23–26, January, 1977.     

Interpreting the solvent dependence for the rate of electron exchange between tetracyanoquinodimethane and its anion radical

An approach previously devised is used in interpreting the observed solvent dependence of the rate of electron exchange between tetracyanoquinodimethane and its anion radical, as it incorporates effects from strong interaction in electrontransfer reactions involving intramolecular rearrangement. The kinetic characteristics have been derived, for which satisfactory values have not been obtained in the interpretation based on the traditional approach.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 3, pp. 353–357, May–June, 1987.I am indebted to L. D. Zusman for directing attention to [4].     

Polyfluorinated cyclohexadienones

Conclusions In strong acids, polyfluorinated nitrocyclohexadienones undergo both radical decomposition with the formation of polyfluorinated aroxyl radicals and also nucleophilic replacement of the nitro-group by the anion of the acid.For Communication 1, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1594–1602, July, 1970.