Low temperature circular dichroism of poly (glycyl- l-prolyl- l-alanine)

The circular dichroism of poly(glycyl- l-prolyl- l-alanine) ‡ ‡ Abbreviation used in the text for this compound is (Gly-Pro-Ala) n. , a synthetic polytripeptide analogue of the non-polar regions of collagen, was investigated in ethylene glycol-water solution (2:1, v v ) over the temperature range of −112 °C to + 24 °C. Lowering of the temperature results in an increased optical activity of (Gly-Pro-Ala) n . At −112 dgC (Gly-Pro-Ala) n exhibits circular dichroism maxima and minima similar in position, but not as large as those observed for guinea pig skin collagen. A comparison of the low-temperature circular dichroism of (Gly-Pro-Ala) n with that of poly- l-proline II and collagen (in the same solvent and at the same temperature) indicates that the observed increase in optical activity of (Gly-Pro-Ala) n is not the result of temperature-dependent solvent effects. Thus the observed increase in optical activity of (Gly-Pro-Ala) n with decreasing temperature is the result of an increase in the amount of periodic structure present in the polymer. Although it is not possible to specify the structure formed in (Gly-Pro-Ala) n at low temperatures in solution, the far ultraviolet circular dichroism is consistent with the structure being a triple helix of the type present in collagen and suggested for (Gly-Pro-Ala) n in the solid state.