[Aggregation of poly-L-proline in aqueous solution]

Infrared spectra were measured for both aqueous (D2O) solution and the solid state of form II poly-L-proline in the amide I region as a function of the temperature. The temperature range includes the region where a precipitation is known to occur. From the analysis of spectra of hydrated films and aqueous solutions at different temperatures one can see that there are some peptide C = O-groups which are bounded with water. From this study it has been concluded that poly-L-proline exists in aggregate form even at temperatures lower that required for precipitation. It is supposed that poly-L-proline forms the aggregates including at least 40--50 polypeptide chains with hexagonal packing. At heating crystallisation of such aggregates occurred and it causes precipitation of poly-L-proline II.