Oleg A. Boryak

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.

Interactions of oligomers of organic polyethers with histidine amino acid

RATIONALE Knowledge on noncovalent intermolecular interactions of organic polyethers with amino acids is essential to gain a better understanding on how polymers assemble in organic nanoparticles which are promising for drug delivery and cryoprotection. The main objective of the present study was to determine how polyethers assemble around ionizable amino acids such as histidine. METHODS Electrospray mass spectrometry was applied to probe the interactions in model systems consisting of polyethylene glycol PEG-400 or oxyethylated glycerol OEG-5 and amino acid histidine hydrochloride. Molecular dynamics simulation was utilized to visualize the structure of complexes of polyether oligomers with histidine in different charge states. RESULTS Stable gas-phase clusters composed of polyether oligomers (PEG(n), OEG(n)) with protonated histidine--PEG(n)•His•H(+), OEG(n)•His•H(+), OEG(n)•OEG(m)•His•H(+) and chlorine counterion--PEG(n)•Cl(-), OEG(n)•Cl(-), were observed under electrospray conditions. Molecular dynamics simulation of representative polyether-histidine complexes revealed the stabilization of oligomers by multiple hydrogen and coordination bonds whereby charged groups are wrapped by the polymeric chains. CONCLUSIONS The self-organization of polyether chains around the protonated imidazole group of histidine was revealed. This finding should be considered when modelling a pegylated protein structure and polyether-based organic nanoparticles.

About the plausible contribution of field ionization in the mechanism of the formation of dyes of ions under conditions of laser desorption/ionization from a nanostructurized graphite surface

An approach is proposed for the estimation of the contribution of field ionization (FI) to the mechanism of dye ion formation under the conditions of laser desorption/ionization (LDI) from a nanostructurized graphite surface. As test systems, rough graphite layers with dyes, e.g., imidazophenazine derivatives applied to them were chosen; these ensure FI in a strong electric field. The dyes form three neutral precursors upon reduction and various types of ions in different ionization methods. It was found that the mass distribution within the group of peaks formed by the initial dye molecule and the products of its reduction in the positive ion mode upon LDI from a rough graphite surface is shifted to lower masses by one atomic mass unit in comparison to the distribution recorded for LDI from a smooth metal support. The analysis of plausible pathways of ion formation has shown that such a shift may be due to the superposition of ions formed by the FI mechanism on a graphite substrate with a number of ions formed by protonation in LDI with no dependence on the support type. In the negative ion mode, the registration of LDI dye spectra succeeded only if the graphite substrates used favored negative FI and electron emission enhanced by the field.

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 fast atom bombardment mass spectra of HCl water solution

Abstract Low temperature fast atom bombardment mass spectra of the frozen water solution of HCl contain a set of clusters (H2O)n· H+, which is an order of magnitude more abundant and differs in intensity distribution from a simlar cluster set usually produced from pure water ice. The cluster pattern is discussed in the light of formation of phases of crystalline hydrates in the frozen solution.