Viscoelastic Studies of the Structure of Collagen; Dependence on Temperature and PH

Abstract

Dynamic mechanical properties of bovine Achilles tendon were measured at 11 Hz over a range of values of pH and temperature.Heating at 0.4°C/min produced a first-order transition (melting) evidenced by decreases in the length and Young's modulus (E*) and by a peak in the damping (tan δ) at constant tensile stress. The transition temperature decreased from about 62°C at pH 7 to 40°C at pH 2; the co-operativity was simultaneously reduced, the transition half-width increasing by a factor of 5.The damping measurements revealed the existence of a minor transition at a lower temperature than the main melting transition. At low pH the temperature of this minor transition approached the molecular melting temperature in solution.An explanation for the observed phenomena is given in terms of the spatial distribution of basic amino acid residues throughout the collagen fibrils.