Conformations of oligoprolines with different configurational sequences and their association complexes with alkali and alkali-earth ions.

To clarify the possible molecular mechanism of cation unit conductance of poly(D,L-proline) across lipidic membranes, the structure and conformation of tetraproline derivatives with different configurational sequences in solid state, as well as in solution and in the presence of alkali and alkali-earth ions, were investigated using x-ray analysis, CD, and nmr spectroscopy. The tetraproline derivatives Boc(D-Pro-L-Pro-L-Pro-D-Pro)OBg and Boc(L-Pro)(4)OBg show very different conformational versatilities in solutions as well as different propensities to form complexes with Ca2+ ion. This is interpreted, based on previous evidence, as dice to different abilities to form ion complexing cavities