Evidence of Coexistence of Change of Caged Dynamics at Tg and the Dynamic Transition at Td in Solvated Proteins
Articolo
Data di Pubblicazione:
2012
Abstract:
Moessbauer spectroscopy and neutron scattering measurements
on proteins embedded in solvents including water and aqueous mixtures have
emphasized the observation of the distinctive temperature dependence of the
atomic mean square displacements,, commonly referred to as the dynamic
transition at some temperature Td. At low temperatures, increases slowly,
but it assumes stronger temperature dependence after crossing Td, which
depends on the time/frequency resolution of the spectrometer. Various
authors have made connection of the dynamics of solvated proteins, including
the dynamic transition to that of glass-forming substances. Notwithstanding, no
connection is made to the similar change of temperature dependence of
obtained by quasielastic neutron scattering when crossing the glass transition
temperature Tg, generally observed in inorganic, organic, and polymeric glassformers.
Evidences are presented here to show that such a change of the
temperature dependence of from neutron scattering at Tg is present in hydrated or solvated proteins, as well as in the solvent
used, unsurprisingly since the latter is just another organic glass-former. If unaware of the existence of such a crossover of at
Tg, and if present, it can be mistaken as the dynamic transition at Td with the ill consequences of underestimating Td by the lower
value Tg and confusing the identification of the origin of the dynamic transition. The obtained by neutron scattering at not
so low temperatures has contributions from the dissipation of molecules while caged by the anharmonic intermolecular potential
at times before dissolution of cages by the onset of the Johari-Goldstein beta-relaxation or of the merged alpha-beta relaxation. The
universal change of at Tg of glass-formers, independent of the spectrometer resolution, had been rationalized by sensitivity to
change in volume and entropy of the dissipation of the caged molecules and its contribution to. The same rationalization
applies to hydrated and solvated proteins for the observed change of at Tg.
on proteins embedded in solvents including water and aqueous mixtures have
emphasized the observation of the distinctive temperature dependence of the
atomic mean square displacements,
transition at some temperature Td. At low temperatures,
but it assumes stronger temperature dependence after crossing Td, which
depends on the time/frequency resolution of the spectrometer. Various
authors have made connection of the dynamics of solvated proteins, including
the dynamic transition to that of glass-forming substances. Notwithstanding, no
connection is made to the similar change of temperature dependence of
obtained by quasielastic neutron scattering when crossing the glass transition
temperature Tg, generally observed in inorganic, organic, and polymeric glassformers.
Evidences are presented here to show that such a change of the
temperature dependence of
used, unsurprisingly since the latter is just another organic glass-former. If unaware of the existence of such a crossover of
Tg, and if present, it can be mistaken as the dynamic transition at Td with the ill consequences of underestimating Td by the lower
value Tg and confusing the identification of the origin of the dynamic transition. The
so low temperatures has contributions from the dissipation of molecules while caged by the anharmonic intermolecular potential
at times before dissolution of cages by the onset of the Johari-Goldstein beta-relaxation or of the merged alpha-beta relaxation. The
universal change of
change in volume and entropy of the dissipation of the caged molecules and its contribution to
applies to hydrated and solvated proteins for the observed change of
Tipologia CRIS:
01.01 Articolo in rivista
Keywords:
neutron scattering; protein dynamics; dynamic transition
Elenco autori:
Paciaroni, Alessandro; Capaccioli, Simone
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