[The molecular mobility of water in natural polymers: silk Bombyx mori with a low water content as studied by 1H DQF NMR].

The molecular mobility of water in fibres of natural silk (Bombyx mori) was studied by the double-quantum-filtered (DQF) and single-pulse 1H NMR techniques. The results obtained showed a slow motion of water molecules and their strong interaction with silk macromolecules. At different model functions for resonance lineshape in 1H NMR spectra, the influence of signal linewidth on the estimation of relaxation times and cross-relaxation parameters was considered. The observed 1H DQF NMR signal in B. mori silk fibres (BC = 0.065) indicated a local order and anisotropic motion of water molecules, which leads to 1H-1H dipolar interactions in natural silk fibers due to the creation of the second-rank tensors (T(2,+1), T(2,-1)). DQF spectra were the difference of two Lorentzians with different linewidths and were analyzed using the theory of 1H DQF NMR and the data on residual dipolar interactions in systems with the anisotropic mobility of water molecules. The residual dipolar interactions was insignificant and, as the humidity increased (0.18), no DQF-signals and residual dipolar interactions were observed.