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Section 12. Chemistry
Section 12. Chemistry
Sivtseva Anastasia Vasilievna, Institute of Physical-Technical Problems of the North, SB RAS, research associate, Department of Materials Sciences E-mail: sianva@yandex.ru
A short review: specific properties of the gel — carrier of the active phase in metal-polymer catalysts
Abstract: Preparations of the gels, these be used on carrier of the active phase of catalyst and its chemical characteristic are rewiewed. To investigate of non-additivity effects possible when applying two joint catalytic reactions, may be used metal-complex catalyst based on polyacrylamide gel, believing that the catalyst of this type described above has a number of advantages in comparison with catalysts on the hard drives.
Keywords: metal-polymer catalysts, gels, carrier of active phase of catalyst.
Interest in the creation of a new type of polymers (based on gels) in working condition swell, but not dissolve in the reaction medium, due to the fact that these structures combine the advantages of crosslinked and soluble macroligands. They have a higher permeability to the solvent and the substrate, and a relatively higher degree of use of functional groups other than high-molecular organic (or inorganic) polymer compound three-dimensional structure [1, 44]. The presence of functional groups capable of coordinating interaction with ions of transition metals, makes it easy to prepare metal complex catalysts in a gel base.
According to [2, 321], the gel is a structural grid of the polymer, disperses in the liquid, and has a number of specific
The specific properties of the gels are their ability to hold a lot of liquid, repeatedly (up to thousands times) greater than their own weight, and high conformational mobility of mesh structures, which can be adjusted by changing the degree of crosslinking of polymer chains. The consequence of this mobility of three-dimensional polymer network with the functional groups may be able to kind of “settings” of the catalyst on the substrate that is referenced by a number of researchers discussing properties of organic ion-exchangers metal-containing catalysts [3, 36-50; 4, 54-57].
In [3, 36-50] studied the effect of the degree of crosslinking copper (Il)-containing ion-exchangers with pyridine groups AN-40 AN-25 on the decomposition of Н2 О2 and it is shown that in both cases, increasing the degree of crosslinking of 4 to 8 % of their catalytic activity is reduced in 3 times.
The decrease of catalytic activity of sulfonic cation exchanger KU-2 with ions of iron (III) more than 2-times was observed also in the process of interaction of acetic acid with hydrogen peroxide by increasing the degree of crosslinking of 2 to 12 % [4, 54-57]. This effect the authors explain the decrease in the mobility of the active centers of the catalyst due to the formation of more rigid and ordered structure of the polymer. Such effects, which testify to interdiffuse braking reactions in phase of ionite catalysts, in case of catalysts based on high-swollen gel structures, apparently, should be less. In this regard, an important role is played the method of preparation of the polymer matrix of the catalyst.
Common methods of producing swelling of gels is a method of radical polymerization [5, 406-412; 6, 893-899; 7, 48-52; 8, 446-456; 9, 83-85], which can be performed in various conditions. The suspension [10, 547-553], emulsion [11, 5623-5641], precipitation [12, 551-556] polymerization also describe in literature. The ammonium (potassium, sodium) persulfate may be used like initiators of radical polymerization [8, 446-456]. Sometimes polymerization using a redox system is carried out in the presence of transition metal ions [9, 83-85] or in the presence of compounds with transition metals [5, 406-412].
There are various methods of crosslinking of linear polymer chains during polymerization or after it to obtain insoluble cross-linked structures. These include radiation method [13, 191-202], polymerization under the action of plasma [14, 1221-1222], thermal treatment of dry monomers or their mixtures, using cross-linking agents.
In [15, 120-146] described the preparation of metal-containing polyacrylamide hydrogels (PAAH), which consists the heating of solutions of acrylamide and of ammonium persulfate with or without added into the reaction mixture of ions Ni (II), Co (II), Cu (II), Fe (II, III) to 333-363 K and subsequent treatment of the polymer mass of solution of
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A short review: specific properties of the gel — carrier of the active phase in metal-polymer catalysts
potassium hydroxide (5-15 %). In this case, the formation of three-dimensional polymer structure due to intermolecular imidization amide groups, occurring simultaneously with the polymerization reaction of acrylamide, and the variation amount of the swelling of the samples is due to partial hydrolysis of the crosslinks in the subsequent processing of the obtained gels alkaline solutions. The disadvantages of these methods include thermal acceleration of decomposition of the polymerization initiator is ammonium persulfate, uncontrolled number of intramolecular and intermolecular crosslinking due to local overheating of the volume of the reaction medium and the partial hydrolysis of intermolecular crosslinks, flowing along with the saponification of amide groups of the polymer chains during the alkaline treatment of the samples. Because of this, there are certain difficulties with reproducibility of the properties of the catalysts.
More appropriate is the preparation of the gels using a crosslinking agent. This method allows to obtain three-dimensional structure at low temperatures and controlled to vary the degree of crosslinking gels by changing the amount of crosslinking agent in the reaction mixture when carrying out the polymerization.
X X
4c=0 + M2+-----------^ NC-0fiVM2+
Ft/ Ft/
So, in the case of the preparation of polyacrylamide gels (PAAH) as a crosslinking agent is usually used N, N’-methy-lene-bis-acrylamide [2], which comprises two hydrolytically unstable peptide bond.
In acidic and alkaline environments amide group of PAAH hydrolyzed to carboxyl group, which leads to the partial destruction of the cross-pieces and makes a major contribution to the growth of swelling hydrolyzed PAAH, since it leads to increase in cell size in the grid of the polymer and to increase the mobility of the polymer chains. This can significantly change interdiffuse characteristics of the catalysts in the reaction. The presence of transition metal ions in phase of gel can affects the hydrolysis [7, 48-52].
The catalytic hydrolysis of amides, esters, simple peptides and model compounds with peptide bonds, with the participation of transition metal ions [16; 17, 1801-1815] were mainly concerned with their accelerating effect on this process. This assumes the coordination of the metal ion on the carbonyl oxygen of the peptide bond or chelation with his participation. Such coordination helps to increase the excess positive charge and facilitates nucleophilic attack, resulting in the rupture of the C-Xbond.
where X = RNH or EtO.
When the carbonyl group is not activated, the hydrolysis of C-X bond can be significantly slowed down.
In [7, 48-52; 18, 1318-1322] noted that Nickel ions increase the hydrolytic stability of polyacrylamide gel due to
the inhibition of alkaline hydrolysis of the polymer network of PAAH and the more Ni (II) in the gel phase, the more pronounced inhibitory effect. The authors suggested that the inhibition may be caused by coordination of the metal ion through nitrogen atoms linking the fragments of the gel:
I ci ci I
CH2 О ,N| о CH2 1 II / 'x II I
CH—c—l\L .N—C—CH
I I I I
CH2 H UM2 H CH2
+2QH~
-2H20
I Xv Y I сн2 о /n/ о ch2 I и /V II I си—c—n. ":n-c-ch
CH2 UH2 CH2,
A
В
where X, Y = Cl-, OH-.
This coordination is likely to considerably reduce the magnitude of the excess positive charge on the carbonyl carbon, making it difficult nucleophilic attack of the hydroxyl anion. It has been found that for each fixed Ni (II) ions on PAAH is a threshold concentration of alkali, which is Ni (II)/PAAH withstand without failure. So, for [NiCl2] = 0.01 mol/l this threshold is observed of [NaOH] = 0.1 mol/l.
Increased swelling associated with hydrolysis of PAAH is totally removed after the interaction of hydrolyzed gel with 0.1 mol/l solution of Nickel chloride. The swelling property of the gel reaches the value characteristic for the original (non-hy-drolyzed) sample of PAAH, i. e. the phenomenon of syneresis.
The syneresis is called spontaneous reduction of jellies or gels, followed by liquid separation. It occurs as a result of compaction spatial structural grid formed in jellies macromolecules in the gel — particles of the dispersed phase. The
syneresis can be caused by different reasons, including the influence of electrolytes on the external environment.
As shown in [7, 48-52], the original (non-hydrolyzed) PAAH is not subject to syneresis. This means that swollen PAG holds so much water that the electrolyte NiCl2 solutions in the lab in the investigated range of concentrations does not lead to its displacement, but can only equilibrium to be distributed in the hydration sphere of the swollen gel.
For the detection and investigation of non-additivity effects possible when applying two joint catalytic reactions, may be used metal-complex catalyst based on polyacrylamide gel, believing that the catalyst of this type described above has a number of advantages in comparison with catalysts on the hard drives. Namely, a higher permeability for the reactants and products of reactions, higher conformational mobility of the polymer matrix, contributing to the optimization of catalytic processes.
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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: sianva@yandex.ru
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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