A model for solvent contributions to polypeptide and protein circular dichroism

The possibility of bound solvent contributing directly to the circular dichroism of polypeptides and proteins is discussed. The model presented is based on the requirement of a breakdown in the planar symmetry of the amide environment. This symmetry breakdown is described in terms of the conformational states of the chain, and leads to necessary, but not sufficient, conditions for observable solvent contributions. Application of the model leads to the conclusion that, while some chain conformations are intrinsically incapable of roviding the required breakdown in the symmetry of solvent perturbations, other conformations force such a breakdown, notably poly-L -proline II and disordered chains.