The molecular details of collagen hydration

Nuclear magnetic resonance and dielectric data on hydrated collagen are interpreted in terms of Ramachandran's hydration model. It is found that all data are compatible with this model, indicating two specific binding sites per three amino acids in the threefold collagen helix. Sorption data have been interpreted according to the multilayer theory of Guggenheim and used to derive the fraction of bound water in the primary sites. From magnetic resonance anisotropies structural details of the position of the water molecules can be derived under the assumption that both sites are equally occupied. The residence time of a water molecule in one of these sites in moderately hydrated collagen (45 g H 2 O/100 g collagen) is 1.2 × 10 −6 sec. The remainder of the water is weakly bound and consists of rapidly exchanging species with rotational correlation time shorter than 10 −10 sec. The sites are 50% occupied at a water content of 10 g/100 g collagen and may contribute significantly to the stability of the collagen threefold helix.