V.S. Fal’ko

Bio: V.S. Fal’ko is an academic researcher from Russian Academy of Sciences. The author has contributed to research in topics: Electron capture & Ion. The author has an hindex of 6, co-authored 9 publications receiving 106 citations.

Electron capture negative ion mass spectra of some typical matrix-assisted laser desorption/ionization matrices.

Abstract: A series of seven typical matrix-assisted laser desorption/ionization (MALDI) matrices has been investigated by means of electron capture negative ion mass spectrometry (ECNI-MS). It has been shown that the most effective matrices form deprotonated negative ions predominantly in the low-energy region. Relative dissociative cross sections have been measured for all molecules under investigation. The relative integrated abundance of [M − H]− ion formation in the series changes by four orders of magnitude. It has been shown that 2,5-DHB (gentisic acid), one of the most effective MALDI matrices, has maximal relative intensity of [M − H]− formation at the energy ∼0.8 eV. This result is in accordance with a finding of Frankevich and Zenobi [Book of Abstracts, Workshop-school “Mass spectrometry in chemical physics, bio-physics and environmental sciences”, Zvenigorod, Russia, April, 25–26, 2002, p. 40] that a probable origin of negative ions in MALDI is the process of low-energy (0.5–1 eV) dissociative electron capture by matrix molecules. Copyright © 2002 John Wiley & Sons, Ltd.

Temperature dependence of dissociative electron attachment to molecules of gentisic acid, hydroquinone and p-benzoquinone

Abstract: The temperature dependence of dissociative electron attachment to molecules of gentisic acid (2,5-dihydroxybenzoic acid) as well as to the products of its decomposition, namely molecules of hydroquinone and p-benzoquinone, has been investigated by means of electron capture negative ion mass spectrometry (ECNI-MS). We have obtained the negative ion yield as a function of incident electron energy for decay channels corresponding to m/z 108 which are [M−CO2−H2]− anion in the spectrum of gentisic acid, [M−H2]− anion in the spectrum of hydroquinone and [M]− parent long-lived anion in the spectrum of p-benzoquinone. It was shown that molecules of carbon dioxide may be formed at high temperature not only by decarboxylation of gentisic acid but also by capture of low-energy electrons (about 1 eV). Such a fact has a great importance for understanding of the problem of analyte desorption in matrix assisted laser desorption/ionization (MALDI) mass spectrometry in according to CO2-MALDI model where the desorption of large biomolecules is explained in terms of gas-bubbles formation by thermal decomposition of molecules of MALDI matrix.

Temperature dependencies of negative ions formation by capture of low-energy electrons for some typical MALDI matrices

Abstract: Some typical matrix assisted laser desorption/ionization (MALDI) matrices (gentisic, nicotinic, succinic, sinapinic, caffeic acids, urea and 6-aza-2-thiothymine) have been investigated by electron capture negative ions mass spectrometry (ECNI-MS) with purpose to find such decay channels of target molecule that may be important for processes of desorption and “primary” ions formation in MALDI. The temperature dependencies of the process of dissociative electron attachment to molecules of MALDI matrices were obtained for six different temperatures in the range of 70–300 °C. Also the relative dissociative attachment peak cross-sections for molecules under investigation were measured and ionization and desorption abilities of the MALDI matrices were calculated. The general conclusions are (1) a capture of low energy electrons by molecules of MALDI matrices leads to an appearance of anions CN − and [M−H] − that may take part in formation of analyte anions, (2) gas molecules in MALDI (CO 2 , H 2 , CH 3 CN and so on) are formed by a capture of low energy electrons that may leads to desorption of the analyte in according to CO 2 -MALDI model, (3) the dissociative attachment cross-section for molecules of matrix determines the ability to form both anions and gas bubbles as well as indicates how well a matrix preserves positive analyte ions from neutralization by the free low energy electrons.

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives.

Abstract: A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.

Violation of frozen shell approximation in dissociative electron capture by halogenated anthraquinones.

Abstract: A series of halogenated anthraquinone (AQ) derivatives has been studied by means of electron capture negative ion (NI) mass spectrometry (ECNI-MS). 1Cl-AQ and 2Br-AQ display dramatically steep positive temperature dependencies of Hal(-) ion abundance in the low electron energy region. Molecular NI intensity decreases rapidly with increasing temperature in the case of 1I-AQ. In the case of 2Br-AQ, a metastable NI peak (m/z 22.9) corresponding to the process BrAQ(-) --> Br(-) + AQ(0) was recorded. This means that the characteristic dissociation lifetime of the molecular NI Br-AQ(-) is at least approximately 25 micros at the energy approximately 0.67 eV in the low-temperature spectrum (T approximately 80 degrees C), and at the energy approximately 0.13 eV in the hot spectrum (T approximately 290 degrees C). Together with the observed temperature dependence of the 2Br-AQ curves of effective yield (CEY), this proves that this anion dissociates according to Coulson's model. The same halogen anion behavior is observed in the case of 1Cl-AQ. There are three consecutive stages in the process of molecular NI dissociation of Cl- and Br-substituted AQ, namely, electron capture into the empty pi-orbital by means of the shape resonance mechanism, followed by a radiationless transition into the ground electronic pi-state of the anion, as predicted by Compton in the case of the parabenzoquinone molecule, and, finally, a fluctuative dissociation of the molecular NI accompanied by the transition from the pi-term into the sigma-term, so-called predissociation. Calculations show reasonable agreement with the experimental data. In the case of 1I-AQ, an effect of inversion of empty levels in the process of electron capture by the molecule takes place, a violation of the so-called frozen shell approximation. The phenomenon found may be of significance not only in the case of ECNI-MS, but also in other experimental investigations using low-energy electron-molecule and ion-molecule collisions.

Ion formation mechanisms in UV-MALDI

Abstract: Matrix Assisted Laser Desorption/Ionization (MALDI) is a very widely used analytical method, but has been developed in a highly empirical manner. Deeper understanding of ionization mechanisms could help to design better methods and improve interpretation of mass spectra. This review summarizes current mechanistic thinking, with emphasis on the most common MALDI variant using ultraviolet laser excitation. A two-step framework is gaining acceptance as a useful model for many MALDI experiments. The steps are primary ionization during or shortly after the laser pulse, followed by secondary reactions in the expanding plume of desorbed material. Primary ionization in UV-MALDI remains somewhat controversial, the two main approaches are the cluster and pooling/photoionization models. Secondary events are less contentious, ion–molecule reaction thermodynamics and kinetics are often invoked, but details differ. To the extent that local thermal equilibrium is approached in the plume, the mass spectra may be straightforwardly interpreted in terms of charge transfer thermodynamics.

2,1,3‐Benzothiadiazole and Derivatives: Synthesis, Properties, Reactions, and Applications in Light Technology of Small Molecules

Abstract: 2,1,3-Benzothiadiazole (BTD) is one of the most important nuclei used in the chemistry of photoluminescent compounds and applicable for light technology. The understanding of its properties and reactions is fundamental for the design and application of these derivatives in molecular organic electronic devices and for other technologies. As a result of their potential as constituents of organic light-emitting diodes, solar cells, liquid crystals, dyes, photovoltaic cells, and many others, attention has been focused on BTD π-extended derivatives with potential use in this exciting area. Herein, we describe their syntheses, properties, reactions, and selected examples of applications in light technology using by BTD (small molecules) as the core.

Detection of pentazolate anion ( cyclo-N 5 - ) from laser ionization and decomposition of solid p-dimethylaminophenylpentazole

Abstract: Laser desorption ionization (LDI) time-of-flight (TOF) mass spectroscopy of solid p-dimethylaminophenylpentazole (1) gives strong peaks of m/z −42 and −70. The −70 peak was identified by 15N labeling of 1 to be the pentazolate anion (cyclo-N5−). The pentazolate anion is formed by an electron attachment to 1 forming the corresponding radical anion followed by a decomposition into 4-N(CH3)2-C6H4 and (cyclo-N5−). The LDI TOF experimental study also revealed that the (cyclo-N5−) is very stable. These conclusions are supported by QM calculations at the B3LYP/6-311+G(2df,p) level.

Role of electrons in laser desorption/ionization mass spectrometry.

Abstract: A nonmetallic sample support for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry enhances the positive ion yield by 2 orders of magnitude and generally affects the charge balance in the desorption plume. We interpret the effects of the target material and of the sample preparation on MALDI mass spectra as a result of photoelectrons emitted upon laser irradiation of a metal target covered by a thin sample layer. These electrons are shown to play an important role in MALDI and laser desorption/ionization because they decrease the yield of positive ions, reduce ions with higher oxidation states, and affect the ion velocity distribution as well as the mass resolution. Understanding the role of these photoelectrons helps to clarify previously obscure aspects of the ion formation mechanism in MALDI.