[Effect of chain length on formation of a double-layer structure of Z-(Gly-Pro-Gly)n-OMe oligotripeptides]

Effect of chain length on the formation of the double-layered sheet in synthetic oligotripeptides Z-(Gly-Pro-Gly)n-OMe (n = 1,2,3,4) in the solid state has been studied by the IR-spectroscopy method. The major spectral features characteristic for the polymer structure was found in the oligomer spectra beginning with that of hexapeptide (n = 2). So a minimum peptide length when peptide chains are still able to adopt the double-layered sheet conformation in the solid state includes two triplets. The result is similar to that we have revealed early by investigation of the collagen-like triple helix formation in the oligomer series Z-(Gly-Pro-Pro)n-OMe. The double-layered sheet structure of the hexapeptide was found completely regular as that of the polymer. So the formation of the double-layered sheet structure unlike the formation of the triple-helical structure occurs at once without gradual ordering of interpeptide bonds and molecular packing by further increasing of the triplet number in oligomer chains. Additional information concerning specific incorporation of bound water in the double-layered sheet and water influence on peptide packing has been derived from analyses of hydration effect on the oligotripeptide IR-spectra especially on the components of the amide I band.