N.m.r. of agarose gels
Abstract
1 H spin lattice and spin-spin relaxation together with diffusion rates have been studied in agarose gels as functions of gel concentration and temperature in the ranges 0.9 to 18 % by weight, and from 273 to 323 K. Data have been interpreted in terms of a two phase model where rapid exchange occurs between bulk water molecules and those “bound” to macromolecules. The amount of bound water has been estimated from the amplitude of the signal due to unfrozen water at temperatures below the freezing point. The implications of this method of estimating hydration are discussed, and comparisons made with observations on frozen gels, and on water adsorbed on to agarose. This estimate, 0.59 g of water per g of agarose, is satisfactory for an explanation of spin lattice relaxation, but certain anomalies occur when applied to spin-spin relaxation. Interpretation of diffusion in terms of the Wang theory leads to a hydration value of 0.35. Previous estimates of hydration have been 0.1 and 3.5.