Viscosity and optical studies of heparin

Abstract

Under conditions of low shear, the viscosity of heparin has been found to be shear dependent. This effect is most pronounced in water. Addition of neutral salt and acid decrease the viscosity markedly. In the case of neutral salt, the decrease seems to be related to the charge-shielding and the binding affinity between the cations and heparin. Hydrogen ions affect the viscosity due to the changing form of the molecule. The reduction in the reduced viscosity (ηSP/c) as a result of periodate oxidation is due to an increase in the flexibility of the polymer. Circular dichroism (CD) results indicate that the cations, Na+, K+, Cs+, Mg2+ and Ba2+, all bind in a similar way to the ionic sites on the polymer backbone. There is no evidence that the binding of these cations produces any major conformational change. However, the large hypsochromic shift observed in the negative CD band at 210 nm when Cu2+ (concentration 25x10-4M or greater) forms a complex with heparin, suggests that a change in the secondary structure is possible. The carboxyl groups may be intimately involved in this process, possibly through chelation with Cu2+. The pertubants, urea and guanidine hydrochloride (GuHCl) affect the structure of heparin significantly through the destruction of the intramolecular hydrogen bonds.