Photochemistry of Heparin‐acridine Orange Complexes in Solution: Photochemical Changes Occurring in the Dye and Polymer on Fluorescence Fading

Abstract

Photolysis of acridine-orange-heparin complexes in N2-and 0,-saturated solution results in permanent photooxidation of A 0 with little or no concomitant change in the heparin moiety. The major photoproduct is mono-N-demethylated acridine orange; in 0,-saturated solution an additional minor oxygenated product, most likely the 10-oxide (N-oxide) or the 9-acridanone (acridone) is also formed. The results suggest an intermolecular electron transfer between adjacently adsorbed dye molecules. The heparin moiety plays a significant role in the photochemistry by bringing dye molecules into favorable geometric orientation for biomolecular reaction and by means of specific dye-polymer interactions.

Structural basis for the anticoagulant activity of heparin. 2. Relationship of anticoagulant activity to the thermodynamics and fluorescence fading kinetics of acridine orange-heparin complexes

“…The photochemical fading of AO-heparin fluorescence involves a second-order photooxidation whereby two molecules of AO adjacently bound to the heparin framework react in the rate-determining step (Menter et al, 1978(Menter et al, , 1979b. The role of the heparin, or other GAGs, appears to be mainly to bring the AO molecules together for the photooxidation reaction without itself undergoing detectable chemical alteration in a manner similar to a heterogeneous catalyst.…”

“…Firstly, among the various GAGs, differences in the value of the cooperative binding constant, ATq, primarily reflect differences in the electrostatic properties of the polymer (Menter et al, 1977(Menter et al, , 1979a. Secondly, the photochemical fading of AO-GAG fluorescence under continuous irradiation with exciting light involves a second-order photooxidation of AO in which two adjacently bound AO molecules react in the rate-limiting step (Menter et al, 1978(Menter et al, , 1979b. Because of the involvement of two dye molecules in the slow step, the rate of fluorescence fading (r") depends critically on the geometry and conformation of the binding sites.…”