Synthesis and conformational characterization of oligopeptide-cyclotriphosphazene hybrids

Abstract

Well-ordered and highly-oriented structures were constructed on a cyclotriphosphazene core by the ring-opening polymerization of N-carboxyanhydride of γ-methyl and γ-benzyl L-glutamates with hexakis(4-aminophenoxy)cyclotriphosphazene as an initiator. The polymers were found to form α-helix conformation from the positions of amide I and amide II in fourier transform infrared spectroscopy (FT-IR) spectra and negative Cotton effects in circular dichroizm (CD) spectra. Both the γ-methyl and γ-benzyl L-glutamate hybrids displayed conformational stability in their hexafluoro-2-propanol (HFIP) solutions under temperature changes between 5 and 60°C. The oligo(γ-benzyl L-glutamate) with short chain length (average 8 residue per each chain) showed extremely high α-helical content, which was determined to be almost 100%. These results demonstrate that the cyclotriphosphazene core exerts a strong secondary structure stabilizing effect.