Vadim V. Orlov

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.

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.

Mass-spectrometric study of the formation of silver nanoclusters in polyether media: 2. Fast atom bombardment and modeling

Within the problem of the synthesis of silver nanoclusters and nanoparticles in polyether media, systems containing silver nitrate AgNO3 and low-molecular-weight polyethers, poly(ethylene glycol) PEG-400 or oxyethylated glycerol OEG-5, were studied by fast atom bombardment (FAB) mass spectrometry. The formation of stable clusters of polyether oligomers (Mm) with silver cations Mm · Ag+ was shown, in agreement with the previous data of laser desorption/ionization. Quantum-chemical DFT calculations have shown that the Mm · Ag+ clusters are stabilized by wrapping of the polyether chain around the silver cation with the cation coordinating ether oxygen atoms. Silver nanoclusters were not found in the FAB mass spectra of liquid systems, but Agn+ clusters were detected for silver nanoparticles separated from the reaction medium. No products of chemical transformations of PEG-400 or OEG-5 were observed by FAB. A plausible mechanism of the reduction of silver cations involving nitrate anions is discussed.

Mass-spectrometric study of the formation of silver nanoclusters in polyethers: I. Laser desorption/ionization

Within the framework of a problem of the synthesis of silver nanoparticles and Agn nanoclusters in polyethers, the systems containing silver nitrate AgNO3 and the low-molecular-weight polyethers poly(ethylene glycol) PEG-400 and oxyethylated glycerol OEG-5, in which silver ions were reduced, were studied by laser desorption/ionization mass spectrometry. The occurrence of Agn silver nanoclusters with n up to 35 in the systems was detected. For n > 2, the presence of “magic numbers” was observed; that is, positively charged Agn+ clusters with predominantly odd values of n were detected. Negatively charged Agn clusters with n = 1–3 were also detected. It was shown that one of the expected processes, namely, the formation of the stable clusters of polyether oligomers (Mm) with the silver cation Mm · Ag+, took place in the test systems.