Balázs Nyerges and Attila Kovács

Density Functional study of the conformational space of ⁴C₁ d-glucuronic acid

The Journal of Physical Chemistry A, 109 (2005) 892-897

The conformational space of ⁴C₁ a- and b-D-glucuronic acid was scanned by HF/3-21G(p) calculations followed by optimization of the 15 most stable structures for each, using the B3LYP density functional theory method in conjunction with a diffuse polarized valence triple-zeta basis set. We found a general preference of the a anomers in the isolated molecules in agreement with the large endo-anomeric hyperconjugation effects in these structures. From the other intramolecular interactions (exo-anomeric hyperconjugation, hydrogen bonding, dipole-dipole, and steric interactions) the effect of the hydrogen bonding is the most pronounced and plays a major role in determining the stability order within the a and b series. The most stable conformer of both a and b ⁴C₁ D-glucuronic acid is the structure with the maximum number (5) of intramolecular hydrogen bonds. Introduction of solvent (water) effects by the SCI-PCM model resulted in two characteristic changes of the energetic properties: the gas-phase stability order changed considerably and the energy range of the 15 most stable conformers decreased from 30 kJ/mol to 15 kJ/mol. The geometrical parameters reflect well the superimposed effects of hyperconjugation and hydrogen bonding interactions. Most characteristic are the variations of the C–O bond distances (within a range of 0.04 Å) upon the combined intramolecular effects.

Selected conformers of a-d-glucuronic acid