Chiral interaction of sequential lysine polypeptides with methyl orange. Effects of distance between lysine residues and hydrophobic side chains

Abstract

Two series of sequential poly(Lys-X) (X: Gly, βAla, and ɛAhx in series A; Gly, Ala, Leu and Phe in series B) have been synthesized. On the chiral interaction between cationic polypeptides and methyl orange (MO), the effects of the distance (series A) and of the hydrophobic side chains (series B) were examined by means of the absorption and induced circular dichroism (CD) spectroscopies. Dichroic bands associated with the blue shifted absorption peaks or shoulders of MO in the visible wavelength region were observed by complex formation between the polypeptides and the dye. The intensity of the induced CD was affected by the concentration of the complexes and time after preparing the complex solutions, suggesting the formation of the intermolecular aggregation in some instances. When MO molecules bound to lysine residues are apart from each other, the aggregation of the complexes is not marked. Roughly, the intensity of the induced CD decreases with increasing distance between the intramolecular lysine residues in series A polypeptides. When the hydrophobicity of the side chains is increased, the induced CD spectra of the series B polypeptide-MO complexes exhibits the inversion of the sign of the induced CD extrema.