Interchain hydrogen bonds via bound water molecules in the collagen triple helix

If the collagen triple helix is so built as to have one set of NH ? O hydrogen bonds of the type N₃H₃(A) ? O₂(B), then it is possible to have a linkage between N₁H₁(B) and O₁(A) through the intermediary of a water molecule with an oxygen O leading to the formation of the hydrogen bonds N₁(B) ? O and O (A). In the same configuration, another water molecule with an oxygen O can link two earbonyl oxygens of chains A and B forming the hydrogen bonds O O₁(A) and O O₀ (B). The two water oxygens also become receptors at the same time for CH ? O hydrogen bonds. Thus, the neighboring chains in the triple helix are held together by secondary valence bond linkages occurring regularly sit intervals of about 3 Å along the length of the protofibril. The additional water molecules occur on the periphery of the proto-fibril and will contribute their full share towards stabilizing the structure in the solid state. In solution, they will be disturbed by the medium unless they are protected by long side groups. It appears that this type of two-bonded structure, in which one NH ? O bond is to a water molecule, can explain several observations on the stability and hydrogen exchange properties of collagen itself and related synthetic polypeptides. The nature of the water bonds and their strength are found to be better in the one-bonded structure proposed from Madras than in the one having the coordinates of Rich and Crick.