The role of the phonon-phonon interactions in systems with high anharmonicity: the case of the optical isomers L-cysteine and D-cysteine

• Grant number: 11/04896-3
• Support Opportunities: Scholarships in Brazil - Master
• Start date: March 01, 2012
• End date: January 31, 2013
• Field of knowledge: Physical Sciences and Mathematics - Physics - Condensed Matter Physics
• Principal Investigator: Herculano da Silva Martinho
• Grantee: Mariana Sayuri Ishikawa
• Host Institution: Centro de Ciências Naturais e Humanas (CCNH). Universidade Federal do ABC (UFABC). Ministério da Educação (Brasil). Santo André , SP, Brazil

Abstract

Two special dynamical transitions of universal character have been recently observed in macromolecules (lysozyme, myoglobine, bacteriorhodopsin, DNA, and RNA) at TD= 180 - 220 K and T*= 100 K. The first represents the threshold of biological activity and the transition from an anharmonic to harmonic dynamical regime of motion in hydrated biomolecules. The second represents the onset of a secondary harmonic characteristic behavior. Despite their relevance, a complete understanding of the nature of these transitions and their consequences for the bio-activity of the macromolecule is still lacking. Specifically one could cite as important open questions (i) the nature of the relaxation mechanisms evolved in the molecular interactions and their hydration dependence; (ii) the thermodynamic nature of the transitions; (iii) the dependence of TD and T* on the hydration level; (iv)role of the phonon-phonon interactions and relative contributions from intrinsic and extrinsic anharmonicites; (v) role of the local environment of the water site. The objective of the present project is contribute to elucidate the questions raised above choosing as system study the optical isomers (dextrogyre and levogyre) and the racemic mixture of the amino acid cysteine (C3H7NO2S) with several hydration levels. The relevance of this choice relies on the fact that dextrogyre forms does not display biological activity and we propose to verify whether the correlation absence of biological activity - harmonicity is valid. The employed methodology will consist in study the temperature dependence (10-300 K) of the thermodynamic (specific heat), structural (X-Ray difraction), and Raman-active phonon spectra aimed with computational simulations of the physical properties (DFT calculations).