Anomalous Dehydration Behavior of a Short Collagen Model Polypeptide, (l-Prolyl-l-ProlylGlycyl)5, in Aqueous Solution

Abstract

High-frequency dielectric relaxation measurements from 1 MHz to 20 GHz were carried out on aqueous solutions of a short collagen model polypeptide, (l-prolyl-l-prolylglycyl)5 (PPG5), at several temperatures ranging from 10 to 40 °C. Experiments revealed that PPG5 behaved as a fully dissociated flexible zwitterionic polymer chain over a wide temperature range. However, its hydration number per PPG5 molecule was altered dramatically and stepwise at Tdh = 27 °C. This is close to the triple-helix-to-single-coil (TH−SC) transition temperature (Tt ∼ 30 °C) for PPG10, clearly showing a TH−SC transition like that of native collagens in aqueous media. Below the Tdh, PPG5 kept about 135 water molecules per molecule, while it retained less than 50 water molecules above Tdh. This anomalous hydration number change, observed at Tdh (∼Tt), should be a TH−SC transition trigger for the longer PPG10.