Secondary structure of peptides

Summary

75.4 MHz ¹³C NMR CP/MAS spectra allowed the quantification of the secondary structure of (γOMe-L-Glu)_n and (γOBzl-L-Glu)_n. (OMe-L-Glu)_n contains α-helix and β-sheet structures the ratio of which varies considerably with the average degree of polymerization ($\overline {{\text{DP}}}$) of the samples and with the nature of the reaction medium. At $\overline {{\text{DP}}}$ ≥20 (γOBzl-L-Glu)_n contains more than 95% α-helix structure regardless of $\overline {{\text{DP}}}$ and reaction medium. The difference between both polyglutamates is explained by different molecular weight distributions resulting from aggregation and precipitation of oligo (γOMe-L-Glu)_n in the ß-sheet form.