1H-1H residual dipolar interactions in water molecules in oriented (along the
static magnetic field B0) and randomly oriented collagen fibers from two connective
tissues with different cross-linking level (fibers from adult steer and young calf) at
humidity level (HL) of 0.6 g water per g dry mass were investigated by 1H doublequantum-
filtered (DQF) NMR spectroscopy. It was observed that intensities of DQF
signal in fibers oriented along outer static magnetic field exceeded significantly the
DQF intensities in nonoriented fibers. The results were analysed on the basis of tensor
description of DQF signal formation at the action of special sequence of radio
frequency pulses with suitable phase cycling. The DQF signals dependencies upon
creation time forming the (T2,+1, T2,-1) tensors of the second rank were compared for
oriented and nonoriented collagen fibers with different cross-links. A role of exchange
has been clarified in an additional study of temperature influence on DQF signals. The
registered 1H DQF NMR signals were due to the residual dipolar interactions (RDIs)
between the protons of water molecules interacting with oriented collagen fibers.
Molecular mobility of water in the fibers of Bombyx mori natural silk has been studied
using the DQF NMR technique and single-pulse 1Н NMR. The observed 1Н DQF NMR
signal in the natural silk fibers with low water content testified about local order and
anisotropic motion of water molecules. DQF spectra in both collagens and silk fibers
were analysed within the theory of 1Н DQF NMR on RDIs in the systems with
anisotropic mobility. When a humidity level of natural silk fibers was increased to 0.18
g H2O per g dry mass, no DQF signals and RDIs were detected.
Keywords: Bombyx mori natural silk, Collagen fibers C15m and C8y, Creation
time, Double-quantum-filter (DQF) NMR, Evolution time, Free induction decay
(FID), Humidity level (HL), Natural biopolymers, Residual dipolar interaction
(RDI), Spin-lattice (longitudinal) relaxation time T1, Spin-spin (transverse)
relaxation time T2.
