Changes in Solution Properties of Poly(trans-5-methylproline) During Mutarotation

[摘要] Changes in CD, ORD and uv-spectra during the mutarotation of poly(trans-5-methyl-L-proline) (PTMP) were studied. The forward mutarotion of PTMP occurred in strong organic acids and trifluoroethanol, while the reverse mutarotation was observed by dilution of the trifluoroethanol solution with excess aliphatic alcohols. The changes in CD, ORD and uv-spectra during the forward and reverse mutarotation proceeded paralell to those found for the mutarotation of polyproline. The chemical shift of the ¥áCH-proton was shifted downfield about 0.3 ppm during the forward mutarotation. The reduced viscosity for the forward mutarotation increased from 0.15 to 0.26 (dl/g) during 5 days. The equilibrium between form ¥° and form ¥± was estabilished in an appropriate solvent mixture. All changes in solution properties mentioned above are similar to those found for polypoline. These results support that the two forms of PTMP are the same conformations as polyproline form ¥° and form ¥±, i. e., a right-handed helix with all cis amide bonds and a lefthanded helix with all trans amide bonds.

[学科分类] 化学（综合）