NMR studies of hydration in low water content biopolymer systems

The problem of characterising the behaviour of water and biopolymers by NMR in low water content biopolymer systems is discussed. A low water content system is defined, and the problems of characterising the relaxation behaviour of the water are analysed. In the case of protons, the types of protons contributing to the signal and the exchange mechanism between them cannot be systematised in terms of existing models that have been developed for high water content systems. It is suggested that any successful model must take account of at least three separate pools of water including water vapour. Experimental results indicate that although the motion of the biopolymer is radically affected by water, the reverse is not necessarily true. It is concluded that the use of nuclei such as (13)C and (15)N may be very effectively used to characterise biopolymer motion, but the use of both (1)H and (2)H for characterising water is still problematic. Despite the formidable experimental and theoretical difficulties, (17)O NMR may be the only way to finally to untangle the problem.