N.M.R. studies of water proton relaxation in Sephadex bead suspensions

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Abstract
The effects of morphology and diffusive exchange on N.M.R. water proton transverse relaxation times in a model heterogeneous system consisting of packed Sephadex beads are interpreted within a unified theoretical framework based on the Bloch-Torrey equations. The relaxation depends on the radii of the Sephadex beads, the cross-linking density of the dextran and varies with the C.P.M.G. interpulse spacing. The larger beads show multiexponential relaxation with up to three components. Without recourse to concepts such as ‘bound-water’ or ‘multiple site occupancy’ we show how the data can be simply understood as arising from diffusive exchange between regions having different relaxation times and resonance frequencies.