CONFORMATIONAL-ANALYSIS AND HELICAL PREFERENCES OF NORMAL AND ALPHA,ALPHA-DIALKYL AMINO-ACIDS

Energy calculations have been performed on right‐handed helical structures of L‐alanine and α‐methylalanine oligomers. A new ′3.610′‐helix is described for α‐methylalanine peptides. The dependence of the relative stability of the α, 310, and 3.610 structural forms on helix length, dielectric, and force‐field, in the gas phase, has been studied. Potential energy surfaces for the interconversion of helices have been generated. The 310‐helix in α‐methylalanine oligomers exhibits a degree of enthalpic and entropic stabilization not observed for alanine. The relevance of the results to the formation of voltage‐sensitive ion channels is discussed. Copyright © 1990 John Wiley & Sons, Inc.