A mathematical model for interaction of spectroscopic probe with polysaccharides - The binding interaction between azure A and heparin

Heparin has a high anionic charge density and is known to interact with a large number of cationic dye through electrostatic interaction. To gain insight into the mechanism of interaction of the dye and heparin, we studied the cationic dye-azure A by a spectrophotometric method. The research was based on the fact that the absorption spectra of the free and bound dye are different. It is considered that the combination of heparin with azure A is due to the noncovalent binding forces. The Scatchard model is discussed from a new standpoint. The solution equilibrium of the reaction system was studied. A new linear regression equation has been developed. From this the binding ability of azure A on heparin can be estimated from the equilibrium constant K, and the maximum binding number N. The linear regression equation can determine these two parameters. The factors which influence the sensitivity of a dye binding heparin assay are discussed, and the Sandell index is used to express the sensitivity of heparin detection. It is found that the concentration of the azure A, sodium chloride solutions have significant effect on the interaction of heparin and azure A.