Thermodynamic Parameters Associated with the Binding of Adrenalin and Norephedrine to Heparin

Summary

Pulse radiolysis has been used to determine the thermodynamic parameters (ΔG′, ΔH′ and ΔS′) governing the binding of adrenalin and norephedrine to heparin. These complexes were completely dissociated by increasing concentrations of inorganic salts. Lower concentrations of divalent cations (e.g. Ca²⁺) than of monovalent cations (e.g. Na⁺) were necessary to effect dissociation of the complex. For each interaction an increase in drug binding occurred as the temperature was increased from ambient. However, a transition temperature was observed (48°C) above which the drug was progressively released as the temperature was increased. These observations are discussed in terms of conformational changes induced in the polymer below and above its melting temperature.