B3LYP/6-311++G* * study of structure and spin-spin coupling constant in heparin disaccharide.

Structures of heparin disaccharide have been analyzed by DFT using the B3LYP/6-311++G( * *) method. The optimized geometries of two forms of this disaccharide, differing in the conformation ((1)C(4) and (2)S(0)) of the IdoA2S residue, confirmed considerable influences of the sulfate and the carboxylate groups upon the pyranose ring geometries. The computed energies showed that disaccharide having the (1)C(4) form of the IdoA2S residue is more stable than that with the (2)S(0) form. Interatomic distances, bond and torsion angles showed that interconversion of the IdoA2S residue results in geometry changes in the GlcN,6S residue as well. Three-bond proton-proton and proton-carbon spin-spin coupling constants computed for both forms agree with the experimental data and indicate that only two chair forms contribute to the conformational equilibrium in disaccharide. Influences of the charged groups upon the magnitudes of spin-spin coupling constants are also discussed.

Modeling of nontraditional structures of carbon.

The present contribution deals with one of the possible structure types of nongraphitic carbon adsorbents. The proposed structure consists of infinite strips of condensed aromatic rings arranged into a hexagonal honeycomb-like structure with the edge formed only by sp2 carbon atoms. Quantum chemical calculations were performed at the UHF/STO-3G level using the CRYSTAL95 program package for periodical approach. The extremely high adsorption ability of some low-density paramagnetic carbon forms can be elucidated by the presence of the sp2 honeycomb carbon structure and the specific properties of its electronic structure.