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Section 12. Chemistry
References:
1. Копылова В. Д., Астанина А. Н. Ионитные комплексы в катализе. - М.:”Химия”. - 1987.
2. Tanaka T., Sun Shao-Tang, Nishio I. Phase transition in gels. “Scatter Techn. Appl. Supramol. And None-eguilibrim Syst. Prac. NaTO Adv., Study Inst., Wellesley, Mass., 3-12 Aug., 1980. - New-York; London. - 1981.
3. Астанина А. Н., Фрумкина Е. Л., Копылова В. Д. Связь между составом координационных центров ионитных комплексов и их каталитической активностью. В сб.Х1: Комплексные металлорганические катализаторы полимеризации олефинов. - Черноголовка, - 1991.
4. Пропой Н. А., Астанина А. Н., Волков В. И. и др. Влияние предсорбционной обработки карбоксильного катионита на состав комплексов меди (II) и железа (III) и на их каталитическую активность в процессе окисления сульфида натрия молекулярным кислородом.//Журн.физ.химии. - 1989. - Т. 63. - № 11.
5. Kanda A., Dural M., Sarasin D., Francois J. Theta point of polyacrylamide in aqueous solution and temperature dependence of the molecular dimensions.//J. Polymer. - 1988. - V 26. - № 3.
6. Джардималиева Г. И., Помогайло А. Д. Полимеризация и сополимеризация металлсодержащих мономеров как путь синтеза структурно-организованных катализаторов.//Кинетика и катализ. - 1998. - Т. 39. - № 6.
7. Жиленко М. П., Папина Ю. Е., Руденко А. П. Влияние сорбции ионов Ni (II) на синерезис и щелочной гидролиз набухших полиакриламидных гидрогелей.//Вестн. МГУ. Сер.2. Химия. - 2000. - Т. 41. - № 1.
8. Wu Xuanchi. Polymerization of acrylamide initiated by potassium persulfate in the presence of manganous salts.//Polum. Commusn. - 1984. - № 6.
9. Ricka J., Tanaka T. Phase transition in ionic gels induced by copper complexation.//Macromolecules. - 1985. - Vol.18, - № 1.
10. Hirayama Chuichi, Yamaguchi Kazuku, Matsumoto Kazuaki, Motozato Yoskiaki. Preparation of poly (N, N-dimethyl-acrylamide) gels having a void in the center of the bead by suspension copolymerization.//Kobunski Ronbunshu. -1983. - Vol. 40, - № 9.
11. Hernandeezbarajas J., Hunkeler D., Heterophase Water-in-Oil Polymerization ofAcrylamide by a Hybrid Inverse-Emulsion, Inverse-Microemulsion Process.//Polymer. - 1997. - V. 38. - Iss. 22.
12. Ito K., Ujihira Y., Yamashita T., Horie K. Change of free volume in polymer gels as studied by positron annihilation life-times.//Acta Physica Polonica A. - 1999. - V 95. - № 4.
13. Pietrzak M. Gamma-Radiolysis of Aqueous-Solution of Acrylic and Polyacrylic-Acid in the Presence of Cu 2+.//J. of Radioanal. And Nucl. Chem. Articles. - 1995. - V 198. - Iss. 1.
14. Beck A. J., France R. M., Leeson A. M., Short R. D. Ion flux and Deposition Rate Measurement in the RF Continnous Wave Plasma Polymerization of Acrylic-Acid.//Chem. Communications. - 1998. - Iss. 11.
15. Тяу Ван Минь. Факторы формирования центров катализа окислительных процессов в металлокомплексах на полимерных носителях. Дисс. ... канд. хим. наук. - М. - 1993.
16. Хьюз М. Неорганическая химия в биологических процессах. - М.: Мир. - 1983.
17. Simita O., Fukuda A., Kuze E. Polyacrylamidic hydrogels in basic solutions//J. Polym.Sci.: Polym Phys. Ed. - 1978. -V.16. - № 10.
18. Прудников А. И., Сметанюк В. И. и др., Синтез гель комплексов Ni с азотсодержащими макролигандами и исследование их структуры методом ИК-спектроскопии.//ВМС. Сер. А. - 1997. - Т. 39. - № 8. - С. 1318-1322.
Sivtseva Anastasia Vasilievna, Institute of Physical-Technical Problems of the North, SB RAS, research associate, Department of Materials Sciences E-mail: [email protected]
A short review: the oxidation of cysteine by molecular oxygen
Abstract: The oxidation of cysteine by molecular oxygen depending on the conditions of reactions are considered. The rate and nature of the oxidation of SH-groups depend on the ratio of the redox potentials of SH-groups and oxidant, the concentration of reagents, pH, and temperature.
Keywords: oxidation of cysteine, copper (II) complexes.
Most of the works related to the oxidation of cysteine polypeptide chains of proteins and active centres of many KSCH2 CH (NH2)COOn (2-amino-3-mercaptopropionic enzymes [1, 9]. Oxidized to disulfide, fragments of cys-
acid, Cys), relates to the biochemistry because Cys is part of teine in proteins involved in the formation of intra — and
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A short review: the oxidation of cysteine by molecular oxygen
intermolecular crosslinking of macromolecules that significantly modifies the properties of proteins.
Study of the oxidation of cysteine by molecular oxygen is of interest not only to clarify the mechanism of the biological aspects of the process. It can be useful when solving problems, for example, by purification of hydrocarbons from sulfur-containing products, in particular, mercaptans [2, 42-46].
Depending on conditions, the oxidation of cysteine oxygen can be described by the following equations:
2Cys + O2 (Cys)2 + H2O2;
4Cys + O2 2 (Cys)2 + 2H2O.
Disulfides, in turn, can undergo further oxidation. According to [3,1075-1081; 4,769-770; 5,1971-1978; 6,322-328],
R
2+ 2+ S 2+
2Cu + 2 RS ► Cu ^ Си
S
I
R
In the acidic medium (pH = 2-5) thiol compounds are almost the same inert to O2 in the presence and in the absence of metal ions of variable valence in solutions. The oxidation of cysteine by oxygen in the presence of iron protoporphyrin by kinetic method in a static system investigated by Trusov P. U. and others [7, 380-383] and it is shown that when the pH is 6,2 D, L-cysteine almost not oxidized. The authors associated this with a low concentration of RS — anion in solution, as the SH-group of cysteine dissociates by half at pH = 8,19. That mercaptide ion is oxidized easier than not dissociated SH-group specifies the fact that the SH-groups with a higher pKa (for example, SH group of glutathione) are oxidized slower than SH-groups with a lower pKa (for example, SH-group of cysteine).
In neutral and alkaline mediums (pH = 6 to 12) the rate of oxidation increases hundreds times in the presence of catalytic amounts (10-6-10-5 М) of ions of metals of variable valence [3, 1075-1081]. The magnitude of the rate of oxidation of thiols pass through a maximum for all catalytically active metal ions, and catalyzed by copper ions oxidation group probably facilitates the maximum rate is observed at pH = 8,5, and in the catalysis by Mn ions is at pH = 10,5. It follows that zwitter-ionic forms of thiols do not possess special properties favourable to their oxidation, as it was considered earlier. Indeed, for ESH maximum share of this form in equilibrium with the other exists at pH =м9,5 and is 0,9 at pH 8,5 and pH = 10,5 (at the point of maximum rate of oxidation during the catalysis with copper and manganese) 0,5 and 0,2, respectively. The authors noted that the largest differences in the oxidation rates for the catalytically active metals are observed at the points of maximum dependence of W0 = f (pH), and in this range, the activity of metals in comparable conditions is reduced to ~5 times in the transition from one metal to another. A number of catalytic activity is as follows:
Cu > Mn > Fe > Ni >> Co,
moreover, the authors of[3, 1080] found that the activity does not depend on the degree of oxidation of metals of variable
the rate and nature of the oxidation of SH-groups depend on the ratio of the redox potentials of SH-groups and oxidant, the concentration of reagents, pH, and temperature.
SH-groups can be oxidized spontaneously — by air oxygen (so-called auto-oxidation), but the rate of such processes is usually low [5, 1971-1978]. The authors of [3, 1075-1081] believe that auto-oxidation most likely caused by the presence of trace quantities of metals of variable valence in thiol compounds. Oxidation of SH-groups by molecular oxygen proceeds at an appreciable rate only in the presence of catalysts, especially with ions of iron or copper, forming complexes with oxidized thiols:
valence in its original compound — it is the same for MnSO4, MnCl2 and KMnO4; CuS04, CuCl, Cu (MeCN)4ClO4; FeS04 and FeCl3. When this catalyst can be any compound in which the metal ion is associated with ligand — weak complexone, and such a strong chelating agents like EDTA and cyanide ion dramatically inhibit the catalytic activity of a given number.
When the change of pH was found that the kinetic orders catalytic oxidation reaction components do not remain constant and independent of the structure of oxidized thiols. In neutral medium, the speed is directly proportional to the concentrations of thiol compounds and O2 and weakly dependent on the concentration of metal ions. In alkaline medium, they become independent of the concentration of thiols, for some, the reaction rate ceases to depend on the concentration of O2, and the order reaction for metal ion increases to 2. In particular, with small changes in the structures group probably facilitates and homocysteine (homocysteine one CH2 group more than in the group probably facilitates) in the catalytic oxidation of these thiol compounds in the presence of copper ions detected large differences: for example, if homocysteine kinetic orders for [O2] and [Cun+] remains equal to 1 as in neutral and alkaline media, for the group probably facilitates the order for [O2] is set to 0, and the order for [Cun+] increases to 2 in an alkaline medium. These data show that in the neutral environment of the catalytic oxidation reaction for all vehicle flow on a single mechanism, and alkaline for some of them (group probably facilitates cysteine) is there a change, the others are oxidized at the previous mechanism. Complex kinetic behavior of systems RSH-Mn+-02 in solutions of different acidity and its sensitivity to the chemical structure of oxidized compounds, is associated with the peculiarities of complex formation of thiols with metal ions and significant differences in the interaction of these forms complexes with O2 molecule.
About the oxidation state of copper in the formed complexes in the literature there is no single point of view. Thus, it is shown that in the nitrogen atmosphere, the reaction
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Section 12. Chemistry
proceeds with the rapid formation of an intermediate paramagnetic complex of Cu2+. Then this complex decomposes with the formation of monovalent copper ion Cu+.
RSH + Cu2+ [RSH... Cu11] Cu+ + RSSR.
Recovery of copper ion to the monovalent state noted in [8, 355-367; 9, 90-96]. Further, according to [9, 90-96], thiolat-anions form or low mercaptide Cu+:
2RS- + Cu+ CuSR i,
when RS- are monofunctional mercaptans, or soluble complex compounds with Cu+ (in presence of more hydrophilic functional groups of thiol compounds in the structure),
2RS- + Cu+ [(Cu+) (-SR)2]-.
Constants of complex formation of Cu+ with thiol compounds is so great that the concentration of free ions Cu+ in aqueous solutions does not exceed 10-10-10-17 mol/l depending on the pH of the medium when the total concentrations in the solution of copper compounds is of the order of 10-4-10-6 mol/l.
Stauff and Nimmerfall [10, 852] investigated the catalytic activity of complexes of Cu2+ with different ligands
(L-arginine, glycine, D, L-lysine and L-histidine) in the oxidation of cysteine by molecular oxygen. An assumption was made that for efficient electron transfer from cysteine to weakly associated with the catalyst to the oxygen atom of the cysteine must enter the inner sphere of the complex, which is the catalyst for this reaction.
In [11, 398-406; 12, 1069-1074], it is shown that the role of catalytically active particles in the oxidation of cysteine can perform the complexes of composition состава [(Cu+) (-SR)2]- and the reaction flows entirely in the coordination sphere of Cu+ with access to the volume of solution of the reaction products, aminopyralid and hydrogen peroxide. Moreover, in [13, 51-62] concluded the course of the catalytic oxidation reaction of aminothiols preserving the valency of copper in the process of catalysis in the state +1 and with the transfer of electrons in the coordination sphere of Cu+ from thiolat ions to O2. In alkaline medium, according to the authors, the oxygen molecule more efficiently retained in the sphere of Cu+, recovering there during the catalytic oxidation to Н2О.
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10. StauffJ., Nimmerfall F. Chemilunescence of oxidation reactions. VIII. Chemilunescence of redox reactions with O . 2.Reac-tion kinetics of cysteine in the presence of copper (II) catalysis//Naturforsch. - 1969. - V 246. - № 7. - P. 852.
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12. Багиян Г. А., Королева И. К., Сорока Н. В., Уфимцев А. В. Катализ ионами меди окисления аминотиолов молекулярным кислородом. Стехиометрия реакции.//Изв. АН. Сер. хим. - 2003. - № 5. - С. 1069-1074.
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