The molecular dynamic behavior of silkworm cocoons produced by a single Bombyx mori strain was investigated by means of high- and low-resolution solid-state NMR experiments. Cocoons with different moisture content were prepared to study the effects of physisorbed water on their molecular dynamics in the MHz regime, which was probed through the measurement of 1H T1 relaxation times at 25 MHz in the 25-95 °C temperature range. The water content of the different samples was determined from the analysis of 1H free-induction decays. In addition to the rotation of methyl groups, mostly from alanine, and to the reorientation of physisorbed water molecules, already identified in previous works as relaxation sinks, the reorientation of serine side-chains was here found to contribute to 1H T1 above room temperature. The analysis of the trends of 1H T1 versus temperature was carried out in terms of semiempirical models describing the three main motional processes, and indicated that methyl rotation, water reorientation and serine side-chain motions are the most efficient relaxation mechanisms below 0 °C, between 0 and 60 °C, and above 60 °C, respectively. The activation energies were found to decrease passing from serine to water to methyl motions.
|Autori:||Geppi M; Mollica G; Borsacchi S; Cappellozza S|
|Titolo:||Proton Spin-Lattice Relaxation in Silkworm Cocoons: Physisorbed Water and Serine Side-Chain Motions|
|Anno del prodotto:||2010|
|Digital Object Identifier (DOI):||10.1021/jp907843r|
|Appare nelle tipologie:||1.1 Articolo in rivista|