Solution conformation of the ferrichromes. VI. Charge relay at the peptide bond. Proton magnetic resonance study of solvation effects on the amide electron density distribution

摘要: The proton magnetic resonance (/sup 1/H NMR) manifestations of amide solvation in polypeptides have been studied using alumichrome and C as model compounds. extreme structural rigidity the alumichromes allowed investigation to center on chemical shifts amides conformational drifts are precluded. data analyzed primarily terms two main events: H bonding nitrogen basic solvents (Me/sub 2/SO, DMF, pyridine), protonation carbonyl by Bronsted acids (chloroform, TFE, TFA). solvent types cause a low-field shift which first case arises from direct effect, while second case, consistent with an earlier suggestion Schwyzer Ludescher, deshielding would result electronic lability peptide link permits electron density flow carbonyl. solvent-induced is shown depend extent exposure pertinent hydrogen oxygen atoms so that magnitude direction effect reflect features molecule at sites. (auth)