Effect of microwave irradiation on the molecular and structural properties of hyaluronan.

Abstract Hyaluronan (Na + salt of hyaluronic acid, HA) was extensively depolymerised by HCl-catalyzed hydrolysis at pH 3 for up to 500 min under temperature-controlled microwave irradiation. The effects of microwave heating on the hydrodynamic properties of the polysaccharide were determined by SEC-MALLS and viscometry. The weight-average molecular mass ( M w ) of HA decreased from 1.44 × 10 6 to ∼5000, reaching the region of higher oligosaccharides. The scission of HA chains was found to proceed randomly during the whole degradation process. Treatment of the M w and intrinsic viscosity data according to the Mark–Houwink equation, [ η ] =  k  ×  M w α suggested three relationships with α 1  = 0.46 for M w  > 500,000, α 2  = 0.84 for M w between 500,000 and 50,000, and α 3  = 1.13 for M w M w  > 10,000 adopts a stiffish coil conformation in solution. As monitored by FT-IR and NMR spectroscopic techniques, the primary structure of the HA chains was maintained during the microwave-assisted hydrolysis at pH 3 at 105 °C. At reaction times larger than 240 min, uv spectroscopy suggested the depolymerisation of HA was accompanied by formation of by-products produced by side reaction.