Conformational analysis and helical preferences of normal and α,α‐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.