Methylene heparin complex

The property of polyanions to give metachromatic reactions with basic dyes80 (see Section XI) has been widely exploited for the titration of glycosaminoglycans. Because of its high charge-density, heparin displays large shifts in the visible spectrum of the dye upon complex-formation, and can conveniently be titrated (most commonly, with Methylene Blue or Azure A), even in the presence of minor proportions of other glycosaminoglycans. It should be realized that quantitative responses with metachromatic dyes are different for different pure heparin... 

The ability of heparin and heparinoids to complex with organic bases and proteins results in many significant biological effects. An interesting model for the biological effects of heparin as an ion exchange and adsorption agent is indicated by the data of Palos and Kocsan and others. Leuco-methylene blue imdei oes oxidation more quickly in an anaerobic system in the presence of heparin, as the dye is adsorbed onto the surface of the heparin and then becomes more sensitive to oxidative influences. 

Numerous publications, particularly by Stone [38, 39], describe the induced Cotton effects in dye complexes with acidic polysaccharides such as heparin, chondroitin sulfate, carboxy me thy 1-cellulose, pectic acid and hyaluronic acid [40—42]. Methylene blue is usually used for these investigations, as its metachromasy depends to a high degree on the polysaccharide structure, As an example of a 4-1 linked amino sugar, heparin with methylene blue has a metachromatic absorption maximum of X = 565 nm. It its ORD a trough appears at 587 nm ( 3), and the CD also shows an exciton split with a zero crossover at 578 nm. These observations indicate dipole coupling and a helical arrangement of the bound dye molecules. 

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