Right-handed α-Helix and Conformational Changes in Poly-β-benzyl-L-aspartate

Abstract

THE need to use non-aqueous solvents has limited the biological value of experimental work on many synthetic polypeptides. Considerable interest has therefore been shown in their surface chemistry, because, quite apart from the importance of understanding the conformation of polypeptides at interfaces, the properties of the polymer when exposed to water can also be investigated. From a combination of the classical methods of surface chemistry with the normal methods of structural investigation, there is at present good evidence to show that the α-helix is present in molecular monolayers of a number of synthetic polypeptides at the air/water interface¹. This work has been extended to poly-β-benzyl-L-aspartate, and in this communication I consider chiefly the properties of the polymer after removal from the water surface; full details of the surface chemistry will be given elsewhere. In contrast to most synthetic polypeptides composed of L-residues, this polymer normally exists in solution and in the solid state as a left-handed rather than a right-handed α-helix^2,3. If a specimen is heated to 160° C it undergoes a transition to the ω-helix, containing four residues per turn, which also appears to be left-handed⁴. Orientated specimens have characteristic infrared absorption frequencies and dichroism enabling the two conformations to be clearly recognized and distinguished from the right-handed α-helix⁴.