THE SOLUTION STRUCTURE OF SMALL PEPTIDES - AN IR CD STUDY OF AQUEOUS-SOLUTIONS OF (L-ALA)(N) [N = 3, 4, 5, 6] AT DIFFERENT TEMPERATURES ANDIONIC STRENGTHS

The solution conformation of a number of small, linear alanine oligome rs was investigated via ir (or vibrational) CD (VCD). We find that the se oligopeptides assume distinct solution conformations that depend pr imarily on chain lengths, and to a lesser degree on temperature, ionic strength, and pH. As expected, the longer chain oligomers exhibit mor e distinct VCD features and, presumably, more stable solution structur es. Al the level of the hexamer, however, aggregation of the peptide o ccurs. The fast time scale of VCD allows solution structures to be det ected that may not be observable using slower techniques such as vario us forms of nmr spectroscopy. The VCD results reported here confirm th at it is generally possible to obtain conformational information for s mall, linear homo- and heterooligopeptides via VCD spectroscopy. In th is respect, the sensitivity of VCD is similar to that of electronic CD . Furthermore, the temperature dependence of the VCD results indicate that at elevated temperatures, the increasing number of conformational states results in a loss of discernible conformers, and consequently, a broadening and weakening of the VCD features. (C) 1998 John Wiley & Sons, Inc.