title: Anharmonic transitions in nearly dry L-cysteine I.
abstract: Two special dynamical transitions of universal character have recently been observed in macromolecules (lysozyme, myoglobin, bacteriorhodopsin, DNA and RNA) at T* ~100-150 K and T(D) ~180-220 K. The underlying mechanisms governing these transitions have been the subject of debate. In the present work, a survey is reported on the temperature dependence of structural, vibrational and thermodynamical properties of a nearly anhydrous amino acid (orthorhombic polymorph of the amino acid l-cysteine at a hydration level of 3.5%). The temperature dependence of x-ray powder diffraction patterns, Raman spectra and specific heat revealed these two transitions at T* = 70 K and T(D) = 230 K for this sample. The data were analyzed considering amino acid-amino acid, amino acid-water, water-water phonon-phonon interactions and molecular rotor activation. Our results indicated that the two referred temperatures define the triggering of very simple and particular events that govern all the interactions of the biomolecular: activation of CH(2) rigid rotors (T < T* ), phonon-phonon interactions between specific amino acid and water dimer vibrational modes (T* < T < T(D)), and water rotational barriers surpassing (T > T(D)).
authors.affiliation: Centro de Ciências Naturais e Humanas, UFABC, Rua Santa Adélia 166, Santo André, São Paulo, Brazil.
authors.forename: T A
authors.initials: TA
authors.lastname: Lima
authors.forename: E T
authors.initials: ET
authors.lastname: Sato
authors.forename: E T
authors.initials: ET
authors.lastname: Martins
authors.forename: P
authors.initials: P
authors.lastname: Homem-de-Mello
authors.forename: A F
authors.initials: AF
authors.lastname: Lago
authors.forename: M D
authors.initials: MD
authors.lastname: Coutinho-Neto
authors.forename: F F
authors.initials: FF
authors.lastname: Ferreira
authors.forename: C
authors.initials: C
authors.lastname: Giles
authors.forename: M O C
authors.initials: MO
authors.lastname: Pires
authors.forename: H
authors.initials: H
authors.lastname: Martinho
mesh_terms: D003545:Cysteine / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D044367:Phase Transition; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics; D014732:Vibration
chemical_list: D013438:Sulfhydryl Compounds; D003545:Cysteine