Abstract
The nuclear magnetic spin‐lattice and transverse relaxation processes for the ^1^H and ^2^D nuclei in purified elastin (ligamentum nuchae), exchanged and hydrated with excess D~2~O, have been studied in the temperature range 276°–340°K. The ^2^D relaxation results clearly show the presence of D^2^O (1) external to the bulk elastin sample, (2) in spaces within the bulk elastin, and (3) as an integral part of the protein on a molecular level. It is shown from these measurements that the protein on a molecular level. It is shown from these measurements that the water content of the protein itself changes from ∼0.8 g D~2~O/g dry elastin at ∼280°K to ∼0.2 g D~2~O/g dry elastin at ∼335°K, a decrease of 400%. The D~2~O content of the interfiber spaces decreases by less than 20% over the same temperature range. This fact throws considerable doubt on the validity of the values of β, the thermal expansion coefficient of elastin, used by other workers in discussion of the elastic mechanism in elastin. The elastin proton transverse relaxation shows the presence of three regions in elastin having different degrees of molecular mobility. These are assigned to protons associated with the crosslinks, a fairly mobile, hydrophobic, and low‐water‐content region, and a more mobile higher water‐content region. The temperature variation of the relative proportions of these three regions is explained in terms of a hypothetical temperature‐composition phase diagram in which the two mobile regions are represented as two partially miscible phases with different negative temperature coefficients of ‘solubility’ in water. The implications of these observations for current views of the nature of elastin are assessed. It is concluded that the spin‐relaxation results are consistent with a multiphase structural model for elastin.
An approximate sorption isotherm for the water/elastin system is reported and shows the relatively weak nature of the water/elastin interaction.