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Data on intermolecular noncovalent interactions of nitrogen base components of nucleic acid with organic polyethers are of interest both for fundamental molecular biophysics and for applications in the production of pharmaceutical organic nanoparticles. In the present work, systems composed of pyrimidine nitrogen base cytosine (Cyt) or its methyl derivatives and polyethylene glycol PEG-400 oligomers M have been examined by electrospray ionization ( ESI) and fast atom bombardment mass spectrometry. Detection of a set of associates of the M · Cyt · H type ( n = 3-17) in ESI mass spectra evidences the formation of protonated complexes of the base with oligomers of different chain lengths in all of the studied systems. Computer modeling by molecular dynamics gave answers to the questions concerning the stability and structure of these complexes under different conditions. It has been shown that M · Cyt · H clusters in the gas phase (vacuum) adopt a compact structure with a quasi-cyclic or quasi-helical self-organization of the polymer chain around the protonated base. It has been found that the compact structure of the M · Cyt · H complex characteristic for its state in the gas phase is preserved in a liquid medium of methanol (used as a solvent in ESI). The results of simulation of the evolution of a methanol droplet in vacuum, which mimics the droplet disintegration under ESI conditions, have shown that the M · Cyt · H complex initially present in the droplet does not disintegrate in the course of droplet evaporation. After the completion of desolvation, the complex returns to the conformation characteristic for the gas phase. Thus, the evidence has been found confirming that the M · Cyt · H clusters recorded in ESI mass spectra adequately reflect the presence of corresponding noncovalent complexes in the analyzed liquid solution. [ABSTRACT FROM AUTHOR]

Stable complexes of oligomers of polyether (oxyethylated glycerol derivatives) with a chlorine anion have first been registered in negative-ion electrospray ionization mass spectra. The results of molecular dynamics simulation demonstrate that the stabilization of such complexes in the gas phase can be due to the formation of a quasicyclic structure of the polymer chain around the chlorine anion and its coordination by CH- and OH- groups of the oligomer. This structure is inverted towards the known quasicyclic structure of polyethers, in which metal cations are coordinated by oxygen atoms of ether groups. [ABSTRACT FROM AUTHOR]

A problem of necessity of concentrating trace admixtures of metal ions required for ecological water analysis can be overcome by harnessing a physical phenomenon of phase separation in aqueous solutions during their freezing. It is shown that the accumulation of metal-containing solutes in the channels between ice crystallites in the frozen solids is sufficient for their successful detection by means of low-temperature secondary emission mass spectrometry. Sufficiency of microliters volumes of water is an advantage of such an approach. Observation of various types of metal ions in frozen water samples is demonstrated on the examples of tap water, sea water, snow and a medicinal preparation. Revisiting and summation of physical basics of mass spectrometric examining of frozen water-inorganic salt solutions and estimates of advancement of mass spectrometric instrumentation permit us to propose a workflow for accelerated and simplified mass spectrometric detection of metal pollutants in water. [ABSTRACT FROM AUTHOR]

Abstract: A paradoxical relation between the secondary emission mass spectra of Methylene Blue and its leuco form is revealed: in the mass spectrum of the dye cation Cat+ (oxidized form with the molecular weight 284), an intense product of its reduction with m/z 285 is recorded, while the mass spectrum of the leuco dye (reduced form with the molecular weight 285) corresponds to an oxidized form with a dominating peak at m/z 284. An explanation of this empirical fact is proposed: the redox reactions induced by ionizing factors under the conditions of secondary emission experiments pass in the direction permitted for the particular initial form of the redox-active compound. Namely, an oxidized form undergoes reduction, whereas the reduced form is oxidized. This effect should be taken into account for the correct identification of redox-active compounds by their secondary emission mass spectra and for simulating redox reactions in the systems containing redox-active dyes under mass spectrometric conditions. [ABSTRACT FROM AUTHOR]