Gas phase polyalanine: Assessment of i → i + 3 and i → i + 4 helical turns in [Alan + 4H]4+ (n = 29-49) ion

摘要: The structures of a series quadruply protonated polyalanine peptides ([Ala n + 4H] 4 , = 29-49) have been examined in the gas phase using high-pressure drift tube/mass spectrometry and molecular modeling techniques.The results indicate that [Ala ions favor stretched helices; i → 3 hydrogen-bonding interactions are significant stabilizing extended structures. Experiment theory fraction increases with increasing polymer length. It appears stabilize smaller polymers, where repulsive Coulombic greater. For 6 ∼35% associated contacts, while ∼65% correspond to associations. In larger 8 polymer, ∼85% residues involved interactions.