engleski

Dynamic Properties of the Stable Paramagnetic Centers in the L-alanine Crystal Lattice

Stable L-alanine paramagnetic centers (radicals ; • CHCH3COOH and • CNH3CH3COOH) denoted as, SAR1, and SAR2 respectively, have been studied over many years. Especially, SAR1 remains the most highly studied paramagnetic centers of a simple amino acid in the solid form. It has been examined by various electron paramagnetic resonance techniques (ESR, FT ESR, ENDOR, ELDOR). Despite of these investigations, molecular environment of the radical regarding the unusual large shift of the central carbon atom, Cα , containing 0.75 unpaired spin density as well as the dynamic processes associated with the radical motion are still not fully understood. Theoretical modelling of SAR1 was found restricted only on the center itself without any interaction with surrounding atoms. Moreover, internal rotations of the CH3 and NH3+ groups accompanied with molecular zwitterionic form in the crystalline state produce even more complex local environment of SAR1 for theoretical description at room temperature. Thus, for complete descriptions of the center one expects that additional improvement on more accurate estimation of the local position of the center and on more detailed evaluation of dynamical properties is essential. In this talk I would like to report on our latest work1, 2, 3 on CW-ESR (ENDOR and transfer saturation ESR) as well as Pulsed ESR (Relaxation rates and 2D-HYSCORE) spectroscopy measurements at different frequencies (X-band and W-band) which have been recently undertaken in order to bring new experimental parameters for additional more detailed description of centres dynamics. The obtained results clearly confirmed presence of additional dynamic properties of SAR1 center at room temperature besides earlier suggested shift of Cα and well known internal rotation of CH3 group.

alanine; radicals; EPR

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