The effect of protonation of cytosine and adenine on their interactions with carbon nanotubes.

Placing electrical charges on nanomaterials is a means to extend their functional capabilities in nanoelectronics and sensoring applications. This paper explores the effect of charging nitrogen bases cytosine (Cyt) and adenine (Ade) via protonation on their noncovalent interaction with carbon nanotubes (CNT) using quantum chemical calculations performed at the M05-2X/6-31++G** level of theory alongside with a molecular graphics method. It is shown that the protonation of the bases causes threefold increase of the interaction energy in the CNT·Cyt·H and СNT·Ade·H complexes as compared to the CNT complexes formed with neutral bases.

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.

Observation of poly(ethylene glycol) clusters with the chlorine anion in the gas phase under electrospray conditions.

It is demonstrated herein that poly(ethylene glycol) (PEG) oligomers can form stable complexes with the chlorine anion in the gas phase as evidenced by results from electrospray ionization mass spectrometry (ESI-MS) and molecular dynamics simulation. While the formation of crown-ether-like structures by acyclic polyethers in their complexes with alkali metal cations coordinated by the ether oxygen atoms has been extensively studied, the possibility of forming 'inversed' quasi-cyclic structures able to bind a monoatomic anion has not been proved till now. We have observed the formation of stable gas-phase complexes of oligomers of PEG-400 with the Cl(-) anion experimentally by ESI-MS for the first time.

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.

Evaluation of the reduction of imidazophenazine dye derivatives under fast-atom-bombardment mass-spectrometric conditions.

Satellite [M + 2](+*) and [M + 3](+) peaks accompanying the common peak of the protonated molecule [M + H](+) that are known to indicate the occurrence of a reduction process were observed in the fast atom bombardment (FAB) mass spectra of imidazophenazine dye derivatives in glycerol matrix. The distribution of the abundances in the [M + nH](+) peak group varied noticeably for different derivatives. This indicated different levels of the reduction depending on the different structure variations of the studied molecules.

On the stability of the organic dication of the bisquaternary ammonium salt decamethoxinum under liquid secondary ion mass spectrometry.

In the course of a liquid secondary ion mass spectrometric (SIMS) investigation on a bisquaternary ammonium antimicrobial agent, decamethoxinum, unusual pathways of fragmentation of the organic dication M2+ of this bisquaternary salt, with preservation of the doubly charged state of the fragments, were observed. To reveal the structural and electronic parameters of decamethoxinum, which are responsible for the stabilization of its organic dication in the gas phase, a comprehensive SIMS study using metastable decay, collision-induced dissociation and kinetic energy release techniques complemented by ab initio quantum chemical calculations was performed. Pathways of fragmentation of two main precursors originating from decamethoxinum-organic dication M2+ and its cluster with a Cl- counterion [M.

Characterization of noncovalent complexes of antimalarial agents of the artemisinin-type and FE(III)-heme by electrospray mass spectrometry and collisional activation tandem mass spectrometry.

In this study, we demonstrate, using electrospray ionization mass spectrometry (ESI-MS) and collision-induced dissociation tandem mass spectrometry (ESI-MS/CID/MS), that stable noncovalent complexes can be formed between Fe(III)-heme and antimalarial agents, i.e., quinine, artemisinin, and the artemisinin derivatives, dihydroartemisinin, alpha- and beta-artemether, and beta-arteether.

'Bubble chamber model' of fast atom bombardment induced processes.

A hypothesis concerning FAB mechanisms, referred to as a 'bubble chamber FAB model', is proposed. This model can provide an answer to the long-standing question as to how fragile biomolecules and weakly bound clusters can survive under high-energy particle impact on liquids. The basis of this model is a simple estimation of saturated vapour pressure over the surface of liquids, which shows that all liquids ever tested by fast atom bombardment (FAB) and liquid secondary ion mass spectrometry (SIMS) were in the superheated state under the experimental conditions applied.

Low-temperature SIMS mass spectra of diethyl ether.

For the first time a secondary ion mass spectrum of diethyl ether was obtained at low temperature. The spectrum recording became possible by carefully selecting the range of experimental conditions for the production of a cluster-type spectrum. This range is specified by the threshold for spectrum appearance above the melting temperature of the frozen sample and a fairly short time span of existence of the liquid estimated as only a few minutes.