Molecular mechanisms of influence of slow electrons on biological structures

Abstract

Background: The article reviews investigations carried out by biophysicists of the Transcarpathian Branch of the Ukrainian Biophysical Society, dedicated to the memory of the prominent Ukrainian biophysicist, Professor Yuri Pavlovich Blagoi. Objectives: Study of the peculiarities of physical processes and structural changes in nucleic acid molecules initiated by low-energy electrons (10-1-102 eV). Materials and methods: Molecular components of nucleic acids – nucleobases, nucleosides – were chosen as objects of research. A complex of methods is applied: the spectral method for obtaining the luminescence spectra of molecules excited by an electron impact; the electric method in determining the complete cross-sections of the formation of positive and negative ions; the method of gas-phase mass spectrometry with electron impact ionization. A new approach is proposed, which is based on the development of the methods for obtaining biomolecules in an isolated (gas) state, the formation of molecular beams, and the implementation of a crossed electron and molecular beams method. Results: The processes of excitation, ionization and fragmentation of molecules of nucleic acid bases under electron impact are investigated. The radiation spectra of biomolecules in the wavelength region from 200 nm to 500 nm for different energies of incident electrons are obtained. For identification of spectral bands, the excitation functions of biomolecules are investigated, mass spectrometry analysis of the bases is performed, semi-empirical quantum-chemical calculations of structural parameters are carried out. It is established that the complex superpositional nature of the spectra reflects the simultaneous occurrence of various physical processes, including, in addition to the direct excitation of the singlet and triplet states of the base molecules, the dissociation excitation and excitation of ionized biomolecules and their fragments. The analysis of the excitation functions shows the presence of intersystem transitions with the formation of triplet metastable states of the nucleic acid bases molecules. It is shown that the processes of the appearance of negative ions are of resonant nature and are accompanied by the dissociation of molecules even at energies smaller than the thresholds for excitation and ionization.