Solid state NMR and X-ray diffraction studies of α-d-galacturonic acid monohydrate

Abstract

Crystalline a-D-galacturonic acid monohydrate has been studied by 13 C CPMAS NMR and X-ray crystallography. The molecular dynamics were investigated by evaluating 13 C spin-lattice relaxation in the rotating frame (T 1r ) and chemical-shift-anisotropy properties of each carbon. Only limited molecular motions can be detected in the low frequency (B 10 4 Hz) range by 13 C relaxation time measurements (T 1r ) and changes of chemical shift anisotropy properties as a function of temperature. X-ray analysis (at both ambient temperature and 150 K) shows that the acid has the usual chair-shaped, pyranose ring conformation, and that the acid and water molecules are linked, through all their O H groups, in an extensively hydrogen-bonded lattice.

Molecular Dynamics of Polycrystalline Cellobiose Studied by Solid-State NMR

“…Similar effects were also observed for methyl a-d-glucopyranoside [31], glycosylated a-tocopherols [32], galacturonic acid [16,17] and its methylated derivatives [17]. Such differences probably result from the differences in the H-bond patterns in the solution and solid state.…”

“…Using galacturonic acid and its methyl derivatives as model systems for pectin, we found that the proton relaxation pathways in galacturonic acid, the monomer of pectin backbone, were mainly motions of hydroxyl groups and water of crystallisation [16,17]. No significant pyran ring motion was detected [17] in the crystalline form.…”

“…state, (2) inter-and intra-molecular interactions such as hydrogen bonding patterns and (3) crystal packing [16,31].…”

Phenyl galactopyranosides – 13 C CPMAS NMR and conformational analysis using genetic algorithm

“…The difference D provides an information about conformational flexibility of molecules. It can also reflect changes in intra-or intermolecular interactions such as hydrogen bonding involving hydroxyl groups or water of crystallization [47]. For the flexible fragments, like O-C6 0 -C5 0 , high D values are observed (up to 4.4 ppm), and for the rigid parts (pyranose skeleton, aromatic ring) D does not exceed 0.5 ppm.…”

Hg(II)-coordination by sugar-acids: Role of the hydroxy groups

“…The IR spectra of the free acids show very strong bands in the 3450-3200 cm À1 range assigned to strongly hydrogen bonded OH groups [32] that are present in the crystal structure of galacturonic acid [33]. The shift of OH stretching vibrations toward higher frequencies is due to the general weakening of strong sugar hydrogen bonding system upon acid metalation, as observed in Mg(II) and Ba(II) complexes of D-glucuronic acid [34].…”