Structure Analysis of Sulfated Polysaccharides Extracted from Scinaia interrupta: A Experimental and Density Functional Theory Studies

In present report, a combined experimental and theoretical study has been performed to address theisolation procedure and spectroscopic structure elucidation of polysaccharides such as xylomannanisolated from marine red algal source Scinaia interrupta. The structure of the polysaccharides obtainedfrom the red algae of Scinaia interrupta has been studied from NMR, IR and GC-MS spectroscopy.The investigation revealed that red algae contained a backbone of α-(1→4)-linked D-mannopyranosylresidues substituted at 6-position with a single stub of β-D-xylopyranosyl residues. The majorpolysaccharide, which had 0.6 sulfate groups per monomer unit and an apparent molecular mass of120 KDa. The backbone structure was optimized at DFT/B3LYP/6-311G(d,p) level of theory andGIAO-NMR studies were performed at B3LYP/6-311++G(2d,p) level of theory followed by meanabsolute error calculations of the computed chemical shifts for two possible conformers resultingfrom the flipping of xylopyranosyl residue. The NMR calculations were in agreement with theexperimental findings. The experimental 1H NMR chemical shifts were then correlated with the NBO,Merz Kollman (MK), ChelpG and Mulliken charges of the predicted conformer. A reasonable correlationwith the experimental 1H NMR chemical shifts and the computed NBO charges with correlationcoefficient of 0.906.