Vadim S. Shelkovsky

On the production of an aqueous colloidal solution of fullerenes

The formation of a stable finely dispersed aqueous colloidal solution of fullerenes C60 and C70 with particle sizes ⩽0.22 µm is reported and hypotheses concerning the nature of the aqueous solutions are discussed.

Temperature dependences of ion currents of alcohol clusters under low-temperature secondary ion mass spectrometric conditions

The dependences of ion currents on temperature (ion thermograms) obtained by monitoring the abundance of different types of ions during the thawing of frozen samples of methanol and ethanol in low-temperature secondary ion mass spectrometry revealed special features in the temperature behaviour of the samples. Correlations between the changes in ion production and phase transitions (melting, boiling, evaporation) in the sample with temperature increase were revealed.

Comparison of Positive and Negative Ion Clusters of Methanol and Ethanol Observed by Low Temperature Secondary Ion Mass Spectrometry

Positively and negatively charged cluster ions were produced from methanol and ethanol samples under low temperature secondary ion mass spectrometric conditions. Neat alcohol clusters [Mn. H+], [Mn − H]− and mixed alcohol–water cluster sets [Mn. (H2O)m.H+] and [Mn.(H2O)m − H]− sets were recorded as the most prominent peaks in the spectra. Clusters composed of up to 30 molecules have been observed. Distributions of these cluster series, and also some satellite ion clusters observed with lower abundances, are discussed.

Sensitivity of redox reactions of dyes to variations of conditions created in mass spectrometric experiments

Redox behaviour of four imidazophenazine dye derivatives under mass spectrometric conditions of matrix-assisted laser desorption/ionization (MALDI), laser desorption/ionization (LDI) from metal and graphite surface, electrospray, low temperature secondary ion mass spectrometry (LT SIMS) and fast atom bombardment (FAB) was studied and distinctions in the reduction-dependent spectral patterns were analyzed from the point of view of different quantities of protons and electrons available for reduction in different techniques. The reduction products [M + 2H](+*), [M + 3H](+) and M(-*), [M + H](-) were observed in the positive and negative ion modes, respectively, which permitted to suggest independent occurrence of reduction and protonation/deprotonation processes. LDI from graphite substrate was the only technique that allowed us to obtain abundant negative ions of all dye derivatives. The yield of field ionization (FI) or field desorption (FD) mechanism to ion formation under LDI from rough graphite surface has been addressed. The sensitivity of reduction of the dyes to variation of reduction-initiating agents confirms high redox activity of the dyes essential for their functioning in natural and artificial systems.

Origin of clusters. II. Distinction of two different processes of formation of mixed metal/water clusters under low-temperature fast atom bombardment

The preparation of frozen samples, in which the heterogeneous structures differ on a scale comparable to the dimensions of the zone excited by a single bombarding particle, has permitted two different processes of formation of mixed metal/water clusters under fast atom bombardment conditions to be distinguished. Sandwich-like structures, in which sodium ions were located either above or beneath a thin layer of ice, produced different (H2O) n •Na+ cluster patterns. The formation of only the monohydrate (n = 1) in the first case was attributed to a direct sputtering process, while the appearance of clusters with n ≤ 6 in the second case was connected with the interactions in the deeper regions of the excited zone. Possible differences in desolvation of clusters, dependent on the depth of their origin, were also noted.

ON SOME PECULIARITIES OF THE LOW TEMPERATURE FAST ATOM BOMBARDMENT MASS SPECTRA OF ETHANOL

Frozen samples of distilled ethanol were studied under the conditions of low temperature fast atom bombardment mass spectrometry. The abundant production of ethanol clusters was observed in the −140° to −110°C temperature range. In addition to the earlier reported [Mn + H]+ (n=1−11) cluster set, several new less abundant sets of the type Mn+, [Mn-X]+ (X = 1−3, 13−19) and hydrates [Mn + H2O + H]+ were revealed. Suggestions as to the origin of these ions are made.

Origin of clusters. III. On the possibilities of production of mixed waterorganic solute clusters under fast-atom bombardment at subzero temperatures

The conditions necessary for formation of mixed water–organic solute clusters under fast-atom bombardment at low temperatures have been investigated by means of mass spectrometry. In the cases of water–ethanol and water–formaldehyde solutions it was concluded that mixed clusters originate from the liquid phase in which the samples exist at certain temperatures as predicted by the phase diagrams of these mixtures. It was found that the observed pattern of mixed clusters was independent of the initial ratio of water to ethanol. An explanation of this finding is suggested. In agreement with previous studies, clusters could not be produced from hydrogen-bonded organic solids. It was, however, found to be possible to sputter hydrate clusters from solid polyoxymethylene derivatives (formed during freezing of formaldehyde–water solutions), due, it is suggested, to a predominance of van-der-Waals type interactions among the oligomers in this solid. Results are discussed in relation to the biophysical and cryobiological problems of stable hydrates, strongly-bound water and mechanisms of action of cryoprotector compounds.

Observation of crystallization of amorphous solid water under the conditions of secondary emission mass spectrometric experiments

A phenomenon of termination of sputtering of protonated water clusters (H2O)nH+ in low-temperature secondary emission mass spectrometric studies of solid water is observed in the temperature range of crystallization of amorphous solid water (ASW). In this range the mass spectra contained only H3O+, H2O+•, and OH+ ions. The following explanation of the phenomenon revealed is suggested: the heat supplied to the ASW sample by the bombarding particles is spent on initiation of an amorphous–crystalline transition within the condensed sample but not for the transfer of the sample matter to the gas phase. At the same time heat released on crystallization causes a local rise in temperature of the crystallizing sample surface, which enhances the rate of sublimation of ice. The resulting increased concentration of subliming water molecules over the sample surface is reflected in a growth of the abundance of H2O+• molecular-ion radical, produced by gas-phase ionization mechanism. The appearance of a set of low-mass ...

Production of doubly charged clusters (H2O)n · Ba2+ and (H2O)n · Ca2+ under low temperature fast atom bombardment conditions

Abstract Production of doubly charged ions of alkaline earth metals Ba 2+ and Ca 2+ and their doubly charged clusters with water molecules (H 2 O) n · Ba 2+ , (H 2 O) n · Ca 2+ ( n = 1, 2, 3) by means of low temperature fast atom bombardment technique is observed in the case of crystalline hydrates of BaCl 2 and CaCl 2 salts, formed during freezing of water-salt solutions. Reasons for a possibility of production of the doubly charged species in the case of the two indicated salts and their absence in the case of chlorides of some other divalent metals (Mg, Mn, Co, Cu, Zn) are discussed. As to singly charged secondary ions Me + , MeCl + , MeOH + , [(H 2 O) n · MeCl] + , [(H 2 O) n · MeOH] + (where Me is metal), high efficiency of their production from crystalline hydrates was observed and possible explanation of the phenomenon is suggested.

Low-temperature experimental studies in molecular biophysics: a review

The enormous contribution of Academician Boris I. Verkin in laying the foundation of the biophysics research school in Kharkov are recalled in the Jubilee year commemorating his 80th birthday. This review describes the development and realization of his ideas during the last two decades at Molecular Biophysics Department of the Institute for Low Temperature Physics and Engineering (ILTPE) in Kharkov. Main results of the studies of physical and chemical properties of biopolymer fragments and biologically active compounds using methods of low-temperature electron–vibrational spectroscopy, low-temperature secondary-emission mass spectrometry, and low-temperature luminescence spectroscopy are presented.