Vitaly K. Koltover

Endohedral metallofullerenes M@C82 (M=La, Y): synthesis and transport properties

Endohedral metallofullerenes M@C2n (M=La, Y) were synthesized by the arc-discharge method using optimum electric arc parameters. It was also shown that an organic solvent (N,N-dimethylformamide) is successfully used in selective extraction of M@C2n. We identified the resulting products by mass spectrometry, electron spectrophotometry, EPR and X-ray fluorescence spectroscopy. The resulting N,N-dimethylformamide extracts of La@C2n and Y@C2n are shown to be free of empty fullerenes and appear as a mixture of endometallofullerenes M@C2n whose main ingredient is M@C82 (∼80 wt%). Transport properties of the extracts of La@C82 and Y@C82 were studied using pressed pellets. It was found that oxygen and heat treatment affect conductivity of endometallofullerenes. Heat treatment results in a three-order increase of conductivity from 10−5 upto 10−2 Ohm−1 cm−1

Spin-transfer complexes of endohedral metallofullerenes: ENDOR and NMR evidences

The aim of this research was to answer the question whether the area of localization of unpaired electron in a paramagnetic endohedral metallofullerene is restricted by the fullerene shell or a “spin-leakage” beyond the fullerene cage is possible. Herein, we report an ENDOR investigation of La@C82 embedded into the polycarbonate films. The intensive 1H-ENDOR signal has been revealed. Since the La-EMF does not contain hydrogen atoms, this result testifies to the contact hyperfine interaction of the unpaired electron of La-EMF with the matrix hydrogen atoms, i.e. electron spin density on the polymer protons. We also report a NMR investigation of a liquid solution of the same La-EMF in hexamethylphosphoramide (HMPA), molecules of which contain the NMR active nucleus, phosphorus-31. The paramagnetic shift of the 31P NMR signal of bulk HMPA molecules in the presence of La-EMF has been revealed. Thus, much as the charge-transfer complexes, the paramagnetic EMF molecules can form the spin-transfer complexes in which the electron spin density partially localizes beyond the fullerene cage on atoms of the matrix in which the EMF molecules are embedded.

EPR Study of Reactivity of Endohedral Metallofullerenes La@C82 and Y@C82

Abstract Reactivity of La@C82 in the mixture with C60 and C70 vs L2pto, phosphoryl radical ∗P(O)(OR)2, and CF3COOH has been studied using EPR spectroscopy. Whereas two former reagents did not change EPR spectrum, treatment with CF3COOH in toluene caused the disappearance of minor octet and a new signal was observed. Similar behaviour was found upon treatment of Y@C82 with CF3COOH. It is interpreted as selective protonation of one isomer of endohedral metallofullerene.

Magnetic-isotope effect of magnesium in the living cell

12 1 There is a great variety of chemical elements which have both kinds of stable isotopes, nonmagnetic and magnetic ones. For example, among three stable iso topes of magnesium, 24Mg, 25Mg, and 26Mg with natu ral abundance of approximately 78.99, 10.00, and 11.01%, 25Mg is magnetic isotope (it has nuclear spin I = 5/2) while 24Mg and 26Mg are nonmagnetic iso topes (nuclear spin I = 0) [1]. In this work we studied the influence of different isotopes of magnesium on cells of Escherichia coli and found that the cells which were grown on magnetic isotope, 25Mg, essentially faster adapt to the new media by comparison with the cells which were grown on the nonmagnetic isotopes. Thus, we have experimentally revealed, for the first time, the magnetic isotope effect in vivo.

Bioantioxidants: the systems reliability standpoint.

The antioxidant power of the so-called antioxidants is negligible because their rate constants and concentrations are too small to compete with the specialized defense enzymes, like superoxide dismutase (SOD), for the reactive oxygen species. In this short review, we present a number of experimental data of our group, along with the relevant literature data, to show that in-vivo antioxidants increase the systems reliability in other tacks. For example, butylated hydroxytoluene can prevent production of O2 •– in mitochondria, whereas flavonoids can induce expression of antioxidant enzymes, SOD and catalase. We suggest that the timely introduction of antioxidants can provide the beneficial physiological effects through the prophylactic reliability maintenance against reactive forms of oxygen via the hormonal system.

EFFECTS OF ANTIOXIDANT BUTYLATED HYDROXYTOLUENE (BHT) ON HORMONAL REGULATION AND ESR SIGNALS IN ADULT AND OLD RATS

The effects of a single administration of BHT on the intensity of ESR signals in blood plasma, as well as on the plasma concentrations of ACTH, 11-OHCS, TSH and T3 hormones within 48 hours following the drug administration were studied in the experiments on adult (4–6 months) and old (24–26 months) male Wistar rats. Changes due to BHT took place in the intensity of ESR transferrin and ceruloplasmin signals in the blood. There were also significant BHT-induced changes in the plasma concentrations of ACTH, 11-OHCS, TSH and T3 hormones. The amplitude and the direction of the changes depended upon the type of hormones, the time period that had elapsed after BHT injection, and the animal’s age. Thus, the physiological effects of BHT in vivo seem to be mediated via the system of the organism’s neurohumoral regulation.

Free Radical Timer of Aging: from Chemistry of Free Radicals to Systems Theory of Reliability

There are two generally known concepts in biology of aging. Accordingly to the first one, there is a program of aging. The alternative concept advocates that aging proceeds stochastically. In this area of research, free radical-theory of aging, which was put forward by Denham Harman in fifties of XXth century, has determined the most heuristic line. The goal of this review is to demonstrate how the aging program and the aging stochastics are united on the basis of the systems theory of reliability. On this basis, universal features of aging, such as the exponential growth of mortality rate with time and correlation of longevity with the species-specific resting metabolism, are naturally explained. The stochastic malfunctions of the mitochondrial electron transport nanoreactors, which produce the oxygen anion-radicals (O2•-) as by-products of respiration, seem to be of first importance. As a reducing agent, O2•- affects the ratio of NAD(P)H/NAD(P)+ and, by changing the activity of sirtuins, slows down renewal of biomolecular constructs. As a consequence, the oxidative-stress products and other metabolic slag accumulate with the resulting impetus to autophagic or apoptotic cell death accompanied with age-associated clinical disorders. Based on this reliability-theory approach, one can estimate that the longevity of human brain could reach 250 years should the antioxidant defense against the free-radical failures be perfect. Thus, the free-radical redox timer serves as effective stochastic mechanism of realization of the programmed deficiency in reliability of biomolecular constructs.

Stable magnetic isotopes: from spin chemistry to biomedicine

Biomolecular nanoreactors, like other cell structures, are composed of atoms of chemical elements many of which have magnetic and non-magnetic stable isotopes. The so-called magnetic isotope effect well known in spin chemistry is a direct consequence of the law of conservation of the electron angular moment (spin) and manifests itself in the fact that chemical reactions with participation of free radical pairs or ion-radical pairs exhibit different reaction rates and different yields of products according to whether the reactants contain magnetic or nonmagnetic isotopes. The magnetic isotope effects in the enzymatic catalysis were first discovered in the pioneering works of Russian scientists, A. L. Buchachenko and his co-workers. Our team studied living cells enriched in different isotopes of magnesium and discovered for the first time the magnetic isotope effects (nuclear spin catalysis) in vivo. The magnetic isotope 25Mg was much more efficient than the non-magnetic isotope 24Mg in stimulating the recovery processes of the S. cerevisiae yeast cells after short-wavelength UV irradiation. The E. coli bacterial cells are adapted substantially faster to a new growth medium containing magnetic 25Mg than to a medium containing non-magnetic 24Mg or 26Mg. Furthermore, the effects of magnesium isotopes on the muscle protein myosin were investigated in cooperation with Ukrainian biochemists and stimulation of the ATPase activity of the enzyme by the magnetic 25Mg isotope 2–2.5 times exceeding the enzyme activity in the presence of non-magnetic magnesium isotopes was detected. Detailed physicochemical mechanisms of the magnetic isotope effects in the enzymatic catalysis and elucidation of the biological mechanisms of enhancement of these effects in living cells are the objectives of further research. Nevertheless, the experimental results obtained to date provide grounds for believing that pharmaceutical agents enriched in 25Mg and possibly in the magnetic isotopes of some other chemical elements will find use in biomedicine, for example, in cardiology for prevention and treatment of acute hypoxia, in oncology as cytostatics, and for the development of new antistress agents and radiation protectors.

Stability and mobility of the endohedral metallofullerene of La@C82 in polycarbonate polymer films

An La@C82-doped polymer (bisphenol-A polycarbonate) was prepared. EPR spectra of La@C82 in a solid polymer film and in a polycarbonate solution in o-dichlorobenzene were studied. The EPR spectrum shape of La@C82 was shown to be sensitive to the phase state of the polymer. La@C82 in the film was found to have a high chemical stability below the glass formation temperature, thus permitting one to use the polymer for the storage and study of endohedral metallofullerenes.

New EPR signals of endohedral metallofullerenes

The EPR spectra of endohedral metallofullerenes (EMF), La-EMF and Y-EMF, which were free of admixtures of C60 and of other empty fullerenes, were examined. Endohedral metallofullerenes were prepared by extraction of fullerene-containing soots with DMF. New signals withg factors close to those of fullerene radical anions were observed in the EPR spectra of solutions of EMF in DMF and DMSO. At −20 °C, these signals are observed as a doublet (ΔHpp≈0.04 mT) and singlet (ΔHpp≈0.01 mT) in solutions of La-EMF and Y-EMF, respectively. These EPR signals belong to solvated La@C82 and Y@C82 molecules and are characterized by small hyperfine interaction constantsaM due to a substantial decrease in the spin density of the unpaired electron at the metal atom.