The heat capacity of water in hydrated collagen

✍ Scribed by B. M. Fung; J. A. Cox

• Publisher: Wiley (John Wiley & Sons)
• Year: 1979
• Tongue: English
• Weight: 202 KB
• Volume: 18
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1979.360180222

✦ Synopsis

Over the past 10 years calorimetric studies of collagen have been performed by several It is known that about 0.45-0.55 g H20 per collagen cannot be frozen,'^^-^ even at very low temperature.6 The freezable part of water has a melting point somewhat below 0°C.5,6 It was estimated that the enthalpy of the melting of collagen fiber (AH:, ca. 5OoC) is 18.0 f 0.8 cal/g or 5.4 kcal/mol per tripeptide unit.6 The AH: for acid-soluble collagen ranges from 0.8 to 1.6 kcal/mol per single peptide unit, increasing with the increasing content of imino acids and the associated heat stability.2

The heat capacity6 of collagen, dry or hydrated, has a fairly large temperature dependence below 0°C and very little temperature dependence above room t e m p e r a t ~r e . ~. ~ However, the interpretation of the heat capacity data of hydrated collagen above 2OoC is controversial. Haly and Snaith5 found the heat capacity of water in hydrated collagen a t 2OoC to be 1.00 cal deg-' g-' (18.0 cal deg-' mol-I), the same as that of bulk water. However, Hoeve and Kakivaya7 suggested that the C, of water in hydrated collagen at 3OoC was 1.24 cal deg-' g-' (23 cal deg-' mol-I), an amazingly high value. These authors interpret their results as indicating that "collagen acts, at least partly, as a nonpolar surface toward water chains." Since the interpretation of heat capacity data yields important implications for the understanding of the structure of hydrated collagen, we have undertaken a more detailed calorimetric study of the heat capacity of collagen hydrated with H2O and D20 in order to gain a better understanding of the nature of this system.