Studies in polymerization - XX. On free-radical formation by oxidation of molybdenum carbonyl with carbon tetrahalides: carbon tetrachloride

The interaction of molybdenum carbonyl and carbon tetrachloride in a suitable medium gives rise to paramagnetic molybdenum products which can be studied by electron spin resonance (e. s. r.) spectroscopy. Most of the observations described in this paper have been made with ethyl acetate at 80 °C as solvent; in many respects methyl methacrylate gives similar results, but the rapid increase in viscosity accompanying polymerization limits investigation to short reaction times. E. s. r. spectra are consistent with the formation of Mo v species with one unpaired spin per Mo atom as the final oxidation state. Mo I and Mo III derivatives are not stable in the presence of carbon tetrachloride, but are rapidly oxidized to Mo v compounds. Kinetic investigations show that the signal-intensity versus reaction-time curve is sigmoid, the initial rate of growth of the signal being much lower than the rate of free-radical generation. It is concluded that there are at least two rate-determining processes in the reaction, the first being displacement of a CO ligand by solvent and the second the oxidation of an intermediate Mo species to a Mo v derivative. The first rate-determining reaction is followed rapidly by primary oxidation, producing one radical per Mo(CO) 6 consumed; this is essentially the only radical-generating step observed at short reaction times. The secondary oxidation, leading to Mo v , yields two radicals. Clearly some of the individual oxidation steps occur without radical formation; suggestions about the nature of the secondary oxidations are advanced. Measurements of carbon monoxide evolution indicate that all the CO ligands are ultimately released, and lead to the tentative conclusion that, in ethyl acetate, evolution of 5 molecules of CO per Mo(CO) 6 consumed accompanies formation of the primary radical. In methyl methacrylate CO evolution is slower, with a greater contribution from processes involved in secondary oxidation. The paramagnetic products of the reaction decompose to a diamagnetic black solid containing Mo IV on removal of volatile materials.

1967 ◽  
Vol 22 (6) ◽  
pp. 580-586 ◽  
Author(s):  
C. H. Bamford ◽  
R. Denyer ◽  
G. C. Eastmond

In a series of publications we have described the kinetics of free-radical formation from molybdenum carbonyl in association with organic halides in a number of electron-donating solvents. Radical formation involves the displacement of carbon monoxide from the carbonyl by the solvent or vinyl monomer in a rate-determining process giving rise to complexes of the type Mo (CO)5L (where L represents the solvent or monomer) which then react directly with the halide. This paper describes a study of the behaviour of Mo (CO)5Py in association with organic halides in methyl methacrylate solution. The results show that Mo (CO)5Py does not react directly with the halide but first undergoes activation by reaction with monomer, mainly with displacement of pyridine. The relative reactivities of complexes of the type Mo (CO)5L are discussed.The mechanism previously proposed to account for the inhibition processes observed in Mo (CO) 6-organic halide systems satisfactorily explains the extensive inhibition observed in the present work.


Determination of the conversion as a function of reaction time in the polymerization of methyl methacrylate initiated by Mo(CO) 6 + CBr 4 a t 80 °C indicates that the rate constant for carbonyl consumption is the same as in the CCI 4 system and corresponds to displacement of a CO ligand by monomer; further, each Mo(CO) 6 consumed gives rise to three free radicals. The limiting initial rate of polymerization at high [CBr 4 ] is consistent with the rapid formation of three radicals per Mo(CO) 6 . It is concluded that primary and secondary oxidation steps occur as with CCI 4 , but that on account of the relatively high reactivity of CBr 4 the two stages occur effectively simultaneously and cannot readily be separated. Tracer investigations with 14 CBr 4 reveal that both stages yield CBr 3 radicals. The electron spin resonance (e. s. r.) spectra of the paramagnetic products formed in ethyl acetate solution at 80 °C are shown to arise from Mo v species. The signal intensity grows at a remarkably high rate, corresponding to a half-life of 0.25 h; the rate is markedly reduced by the presence of free radical scavengers such as methyl methacrylate or cyclohexane. These observations are thought to indicate the occurrence of a chain process involving CBr 3 and Mo I , which react with Mo(CO) 6 and CBr 4 , respectively. Experiments in which CBr 3 radicals were produced photochemically from Mn 2 (CO) 10 + CBr 4 in the presence of Mo(CO) 6 support the proposed mechanism. Although the carbonyls of chromium and tungsten, in association with halides, initiate polymerization, the products do not give observable e. s. r. spectra. It is suggested that these reactions lead to oxidation states III and VI respectively, rather than V, which is particularly stable in the case of molybdenum.


Author(s):  
Yusuf Rabbani ◽  
Claude Mona Airin ◽  
Sugeng Riyanto

Degenerative diseases are mostly caused by high free radical concentrations in the body. Kepel fruit(Stelechocarpus burahol) is known to contain flavonoid compounds, a class of compounds that has free radicalscavenging activity in the body and could affect the activity of antioxidant enzymes. There have been reportsthat methanolic extract and ethyl acetate fractions of Kepel fruit have the lowest IC50 values, compared toextracts or fractions which are made using other organic solvents, on in vitro assays so that flavonoids aresuspected as responsible compounds to the free radical scavenging activity. This study aimed to identify thepresence of flavonoid content in methanolic extract and the fraction of ethyl acetate of Kepel fruit and also itseffect on rat alpha Glutathione S-Transferase (α-GST) enzyme concentration for the function to prevent hepaticcell damage due to carbon tetrachloride exposure. The identification of flavonoids content used a series ofcolor chemical reaction tests and thin layer chromatography that used silica gel 60F254 as the solid phase andmixture of ethyl acetate, formic acid, glacial acetic acid, and water (100: 11 : 11: 20 v/v) as the mobile phase.This study used 30 Sprague-Dawley female rats (age 2-3 months) that were grouped into 5 groups as solventcontrol (CMC-Na) group, negative control (CCl4) group, positive control (vitamin C) group, methanolic extractgroup, and ethyl acetate fraction group. All groups were induced with carbon tetrachloride (CCl4) compoundsexcept for the CMC-Na solvent control group. Blood sampling at 0 h, 24 h, and 72 h, while liver sampling at 24h and 72 h, with 3 samples each group. The analysis of rat α-GST enzyme concentrations used theEnzyme-linked Immunosorbent Assay (ELISA) method. Based on the phytochemical test, the methanolicextract and the ethyl acetate fraction of Kepel fruit have been identified contains flavonoids compound. Basedon the in vivo study, the positive control group's α-GST enzyme concentration was decreased, while thenegative control group's α-GST enzyme concentration was increased. Administration of methanolic extractand ethyl acetate fraction also decreased both liver and blood rat α-GST enzyme concentrations, althoughwithout significant correlation, and still could prevent the hepatic cell damage due to carbon tetrachlorideexposure.


Author(s):  
И.Д. Габдрахманова ◽  
В.А. Мышкин ◽  
Д.А. Еникеев ◽  
А.Р. Гимадиева

Цель исследования: изучение влияния сукцината 1,3,6-триметил-5-гидроксиурацила на антиоксидантную систему и свободнорадикальные процессы в печени взрослых и старых крыс при воздействии тетрахлорметана. Методика. В эксперименте использованы половозрелые животные 12-месячного возраста со средней массой 250 г и старые животные 24-месячного возраста, средней массой 395 г по 30 особей в каждой возрастной группе. Токсическое поражение печени вызывали подкожным введением 50%-ного масляного раствора тетрахлорметана (ТХМ, 2 г/кг) в течение 4 сут. Одновременно с токсикантом опытным животным внутрибрюшинно вводили водный раствор коплексного соединения сукцинат-1,3,6-триметил-5-гидроксиурацила (2,5 мг/100 г) 3 раза в сут. в течение первых 4 сут. и в течение последующих 3 сут. 1 раз в сут. Контролем служили опытные животные, которым вводили физиологический раствор в том же объеме. Изучали окислительную модификацию белков, перекисное окисление липидов (по содержанию ТБК-реагирующих продуктов, уровню гидроперекисей липидов и содержанию диеновых конъюгатов). Состояние антиоксидантной системы оценивали по активности ферментов супероксиддисмутазы, каталазы и глутатионпероксидазы, определяемых биохимическими методами. Антирадикальную активность комплексного соединения и его составляющих субстанций исследовали в модельной системе «этилбензол-ледяная уксусная кислота» с вычислением константы К - скорости взаимодействия перекисных радикалов с молекулами изучаемого соединения в сравнении с эталонным антиоксидантом-ионолом с витамином Е. Результаты. Сукцинат + 1,3,6-триметил-5-гидрокси-урацила существенно снижает токсическое действие ТХМ на печень взрослых и старых крыс, устраняет дисбаланс в системах свободнорадикального окисления белков у старых крыс, статистически значимо улучшает показатели свободнорадикального окисления (СРО) липидов в печени взрослых и старых крыс: снижает уровень продуктов ПОЛ - гидроперекисей, диеновых конъюгатов, ТБК-реагирующих продуктов, а также улучшает работу антиоксидантной системы (АОС), повышая активность каталазы, супероксиддисмутазы и глутатионпероксидазы. Установлена высокая антирадикальная активность изучаемого препарата сопоставимая с активностью эталонного антиоксиданта ионола. Заключение. Сукцинат и его производные способны выступать как индивидуальные вещества с непосредственным антирадикальным механизмом действия, а не только как стимуляторы ферментативных систем антиоксидантной защиты. Aim. To study the effect of a complex compound, 1,3,6-trimethyl-5-hydroxyuracil succinate, on the antioxidant system and free radical processes induced by carbon tetrachloride in the liver of adult and old rats. Methods. The study used sexually mature animals aged 12 months and weighing 250 g and old animals aged 24 months weighing 395 g (total n= 60, 30 rats in each age group). Toxic damage of liver was induced by subcutaneous injections of a 50% oil solution of carbon tetrachloride (CTC) at 2 g/kg for 4 days. Together with the toxicant, experimental animals were injected with a water solution of a complex compound, succinate 1,3,6-trimethyl-5-hydroxyuracil, at a dose of 2.5 mg/100 g, i.p., 3 times per day for the first 4 days and once daily for the following 3 days. Experimental animals were used as controls, which were administered saline in the same volume. Oxidative modifications of proteins, lipid peroxidation (by levels of thiobarbituric acid reactive substances (TBARS), lipid hydroperoxides, and conjugated dienes) were studied. Condition of the antioxidant system was evaluated by activities of superoxide dismutase, catalase, and glutathione peroxidase using biochemical methods. Antiradical activity of the complex compound and its components was studied in a model system of ethylbenzene-glacial acetic acid; the K7 constant of the rate of peroxide radical interaction with molecules of the studied compound was compared with the reference antioxidant ionol with vitamin E. Results. Succinate +1.3.6-trimethyl-5-hydroxyuracil, considerably reduced TXM hepatotoxicity in adult and old rats; removed the disbalance in free radical systems of protein oxidation in old rats; significantly improved indexes of free-radical oxidation (FRO) of hepatic lipids in adult and old rats; decreased levels of LP products, hydroperoxides, conjugated dienes, and TBARS, and enhanced performance of the antioxidant system (AOS) by increasing activities of catalase, superoxide dismutase, and glutathione peroxidase. The study demonstrated a high antiradical activity of the study drug comparable with the activity of the reference antioxidant, ionol. Сonclusion. Succinate and its derivatives can perform as individual substances with a direct antiradical mechanism of action rather than as stimulators of enzymic systems of antioxidant defence.


1990 ◽  
Vol 277 (2) ◽  
pp. 402-409 ◽  
Author(s):  
Kirk R. Maples ◽  
Christopher H. Kennedy ◽  
Sandra J. Jordan ◽  
Ronald P. Mason

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