The effects of proteins on the proton N.M.R. transverse relaxation time of water

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Abstract
The changes in water proton transverse relaxation behaviour induced by aggregation of Bovine serum albumin are explained in terms of the simple molecular processes of diffusion and chemical exchange without recourse to invoking changes in ‘bound’ water or the ‘state’ of water in the system. It is proposed that the main effect of aggregation is to reduce the protein proton transverse relaxation time because dipole-dipole interactions between protein protons are no longer as efficiently averaged by rotational motions, this in turn causes a reduction in water proton transverse relaxation time since water protons are in fast chemical exchange with protein protons. Diffusive exchange between water molecules then spatially averages the water proton signal to an extent that depends on the morphology of the aggregate-water system. The diffusive averaging process can give rise to multi-exponential relaxation.