Infrared absorption and raman scattering of sulfate groups of heparin and related glycosaminoglycans in aqueous solution

Abstract

The i.r. spectra for aqueous solutions of sulfated glycosaminoglycans and model compounds in the transmittance “window” region of the solvent (1400-950 cm −1) are dominated by the strong and complex absorption centered at ∼1230 cm −1 and associated with the antisymmetric stretching vibrations of the SO groups. Primary and secondary O-sulfate groups absorb at somewhat higher frequencies (1260-1200 cm −1) than N-sulfates (∼1185 cm −1). Each sulfate band lends itself to quantitative applications, especially within a given class of sulfated polysaccharide. Laser-Raman spectra of heparin and model compounds have been obtained in aqueous solution and in the solid state. The most-prominent Raman peak (at ∼1060 cm −1) is attributable to the symmetrical vibration of the SO groups, with N-sulfates emitting at somewhat lower frequencies (∼1040 cm −1) than O-sulfates. The Raman pattern in the 950-800 cm −1 region (currently used in the i.r. for distinguishing between types of sulfate groups) also involves vibrations that are not localized only in the COS bonds.