engleski

Dynamic properties of stable radicals in gamma irradiated L- and D-alanine: A pulse EPR study

Alanine is one of the amino acids most commonly occurring in the nature. Both enantiomers of alanine, L- and D-alanine, are zwitterions, which favour good mechanical and thermal stability of alanine crystals. The number of experiments have reported indication of a parity violating phase transition, using a variety of methods including specific heat measurements, temperature dependent magnetic susceptibility, laser Raman spectra and solid state NMR experiments, but the physical- chemical basis is still not understood. Nevertheless, L-alanine, in contrast to D- alanine, is continually used as model for investigation on various types of intermolecular and intramolecular interactions [1, 2]. Furthermore, our research is focused on alanine in solid state, a hydrogen bonded crystal as a “model protein”. Considering that alanine is the simplest chiral amino acid with respect to molecular structure and the most widely used in the protein composition, the structural rearrangements are interesting from both biological and physical point of view. The role of hydrogen bonding is essential for understanding of more important biological processes and molecules such as proteins and peptides. Therefore, alanine crystals offer an ideal model system for studying the nature of hydrogen bonds in biochemical systems in more detail. It is well known, that upon irradiation of alanine in the solid state, stable radicals are produced within the lattice, which are ideally suited for EPR investigation as probes to obtain insight into microstructure. However, EPR investigations of D-alanine and L- alanine show different substructure and radical yield, but so far there is no explanation for such behaviour. In this communication, the temperature dependent relaxation measurements, focused on dynamics of the different parts of molecules obtained by pulsed EPR will be reported, as indication of possible changes in the static average of the structure of crystalline Land D-alanine and/or evidence of phase transitions or structural rearrangement related to thermally activated reorientation of the CH3 and NH3 moieties.

EPR; L- and D-alanine; radicals

nije evidentirano