Pr. Rajamohanan et al., CROSS-RELAXATION AND EXCHANGE IN POLY(ACRYLAMIDE) HYDROGEL STUDIED THROUGH H-1 MASS NMR AND 2D NUCLEAR OVERHAUSER ENHANCEMENT SPECTROSCOPY, Macromolecules, 28(7), 1995, pp. 2533-2536
A combination of two-dimensional (2D) NMR techniques, namely, (H-1-H-1
) NOESY, and ROESY, has been used for the first time to study cross-re
laxation and exchange phenomena in a poly(acrylamide) hydrogel. Intram
olecular cross-relaxation interactions are detected for the main-chain
protons and are seen to arise from polymer mobility occurring in the
long correlation regime (omega(0) tau(c) much greater than 1). Tempera
ture-dependent studies show chemical exchange, direct and relayed cros
s-relaxation pathways for the magnetization transfer. For amide proton
s, cross relaxation dominates over chemical exchange at room temperatu
re and below. Intermolecular exchange and cross-relaxation processes a
re identified for hydrated water, and evidence has been gathered for i
nteracting water molecules with a relatively long reorientational corr
elation time. The 2D data also point to the most probable location of
water close to the carbonyl group.