Abstract
The molecular mobility of water in natural silk fibers is studied by 1H DQF NMR and single-pulse 1H NMR spectroscopy. It is found that water molecules slowly move and strongly interact with silk macromolecules. Using different functions for modeling the shape of the resonance signals in the 1H NMR spectra, the effect of the linewidth on the estimates of the relaxation times and the cross-relaxation parameters is considered. The detected 1H DQF NMR signal in Bombyx mori silk fibers with a water content of Cw = 0.065 gram H2O per gram dry weight suggests local order and anisotropic motion of water molecules; this leads to nonvanishing 1H-1H dipole interactions in natural silk fibers and is related to the creation of second-rank tensors 7 2,+1 and T2,-1. The DQF spectrum is described by the difference of two Lorentzian functions with different linewidths and analyzed on the basis of the theory of 1H DQF NMR spectroscopy and published data on the residual dipole interactions in systems with anisotropic mobility of water molecules. In the system studied, the residual dipole interactions are weak and, along with DQF signals, are not detected at higher water content (Cw = 0.18 gram H2O per gram dry weight). Copyright © 2004 by MAIK "Nauka/Interperiodica".