Journal of the American Chemical Society, Vol.117, No.1, 368-374, 1995
Solution-Phase C-13 and H-1 Chemical-Shift Anisotropy of Sialic-Acid and Its Homopolymer (Colominic Acid) from Cross-Correlated
Sensitive pulse sequences were developed in order to determine geometry dependent H-1 and C-13 chemical shift anisotropy terms (CSAg) of simple carbohydrates and carbohydrate polymers in solution. The methods are capable of monitoring CSA/DD cross-correlated relaxation for ca. 1 M solutions at natural abundance. Measured spectral densities were quantitatively interpreted for sialic acid and its alpha-(2-->8) linked homopolymer, colominic acid. Although the geometric factors could not be separated from anisotropy terms, this is the first report of CSA data on a carbohydrate polymer, and its values differ substantially from those of monomeric sialic acid. The most pronounced differences were observed at C5, C6, and C7 for both H-1- and C-13-shift anisotropies. The differences may be attributed to conformational changes around the C6/C7 and C7/C8 bonds, and possible changes in hydrogen bonding interactions, and in OH rotamer populations. Application of these combined NMR methods provide a new parameter which may be sensitive to structural changes not detected with conventional NMR techniques.
Keywords:NUCLEAR-MAGNETIC-RESONANCE;MONTE-CARLO SIMULATIONS;COUPLED SPIN SYSTEMS;MODEL-FREE APPROACH;LONGITUDINAL RELAXATION;SOLUTION CONFORMATION;STRUCTURAL-ANALYSIS;NMR RELAXATION;DIPOLE-DIPOLE;DYNAMICS