Abstract
IT is well known that compounds which form strong hydrogen bonds can disrupt the intramolecular hydrogen bonds in synthetic and natural polypeptides. For example, urea in large amounts (about 20 per cent by weight of solution) causes the helix–coil transition in aqueous solutions of ribonuclease1. Various organic compounds, particularly acids, have also been reported to effect these transitions. Notably, trifluoroacetic acid (TFA)2 and dichloroacetic acid (DCA)3 have been used with success. For synthetic polypeptides, the evidence for helix–coil transitions has been obtained from measurements of intrinsic viscosity3 and, more conveniently, optical activity4.
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