The β conformation of polypeptides of valine, isoleucine, and threonine in solution and solid‐state: Optical and infrared studies

Water‐soluble polypeptides of L ‐valyl and L ‐isoleucyl residues flanked with DL ‐lysyl blocks [poly( DL Lys · HCl) x –poly( L Val) y –poly( DL Lys · HCl) x , poly( DL Lys · HCl) x –poly‐( L Ile) y –poly( DL Lys · HCl) x ] and homopoly( L ‐threonine) were prepared. The β conformation of these polymers in water, as well as in aqueous methanol, was confirmed by infrared spectroscopy and circular dichroism studies. The optical properties of these valyl and isoleucyl polypeptides were quite different from those of previously reported synthetic homopolypeptides in the β structure. Their differences could be explained by the presence of a “ single extended β chain ” without either intra ‐ or inter chain association.