Glycans, polyglycans, and cross-linked polyglycans: An analytical study using solid state nuclear magnetic resonance, x-ray powder diffraction and other solid phase methods

Two polyglycans, chitin (CT) and chitosan (CS), were compared with their corresponding monomers, N-acetyl-D-glucosamine (GlcNAc) and D-glucosamine (GlcN) using solid state nuclear magnetic resonance (SSNMR) spectroscopy and x-ray powder diffraction (XRPD) in order to better understand structural changes during the commercial degradation of the natural polyglycans. A downfield 13C isotropic shift for the ring carbons in both polyglycans confirms structural differences from their monoglycans. Monoglycans were characterized according to their solution chemical shifts and the solid shifts were inadvertently misassigned in earlier literatures. The correct peak assignments for these monoglycans are proposed using shape factors from spinning sideband patterns for the first time.; Cross-linking chitosan with glutaraldehyde (CSGA) was thought to increase metal adsorption by increasing the surface area of CS, a highly desirable chemical engineering goal in the chelation industry to maximize chemical uptake. Experimental results indicate an increase of surface area to >200 m 2/g, but metal uptake is shown to be more likely due to absorption within the polymer lattice rather than adsorption on the surface. Seven metals (Cr, Mn, Fe, Co, Ni, Cu, and Zn) were selected to complex with CS and CSGA to allow for structural comparisons and understanding of the metal uptake properties of CS and CSGA. Cationic binding was found at the C2 position of each monomeric unit of the secondary amine in CS and at the imino linker in CSGA. Two portions of the amorphous XRPD pattern that were ignored in the past are demonstrated for the first time to have structural importance and to interact differently with different metals based on oxidation/electronic spin state, paramagnetic properties, and ligand configuration inside the hydrophilic pockets of the polymers. The former region was confirmed to correspond with the amine in CS by far-FTIR (far-Fourier transform infrared) spectrometry, whereas the latter region was proven to be stacking of intermolecular hydrogen bonding in a unique system between each helical turn. The imino linker in CSGA was calculated to have less negative charges than the amine in CS, which is unusual. Metal interaction in the amino-imino region was studied in detail. Torsion angles at C4 in the beta(1→4)glycosidic bond of several metal complexes were observed for the first time in SSNMR.