Facial selectivity between carbohydrates and aromatic amino acids explained by a combination of NCI, NBO and EDA techniques with NMR spectroscopy

The influence of electrostatic and dispersion components of intermolecular interactions on the recognition of carbohydrates by aromatic protein residues is important for many biological processes. Interactions between glucose and galactose and aromatic moieties of tryptophan, phenylalanine and histidine were investigated through H-1 nuclear magnetic resonance (NMR) chemical shift perturbation and fully explained by molecular modelling at the density functional theory (DFT) level. According to NMR experiments, aromatic amino acids interact preferably with one face of the carbohydrate and the calculations showed how intermolecular interactions were determinant in explaining the selectivity. Non-covalent interaction surfaces revealed that a CH bond oriented toward the center of the aromatic ring maximized the attractive interaction while minimizing the steric repulsion. Energy decomposition analyses showed that the dispersion component was stronger than the electrostatic component and contributes more when hydrogen bonds are not present in the studied complexes. However, it was the electrostatic component that correlated with the facial preference, especially for the complexes with tryptophan305948967CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO ARAUCÁRIA DE APOIO AO DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO DO ESTADO DO PARANÁ - FAFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPsem informaçãosem informação211-14 - 201339712016/2410

The Conformational Analysis Of 2-halocyclooctanones.

The establishment of the most stable structures of eight membered rings is a challenging task to the field of conformational analysis. In this work, a series of 2-halocyclooctanones were synthesized (including fluorine, chlorine, bromine and iodine derivatives) and submitted to conformational studies using a combination of theoretical calculation and infrared spectroscopy. For each compound, four conformations were identified as the most important ones. These conformations are derived from the chair-boat conformation of cyclooctanone. The pseudo-equatorial (with respect to the halogen) conformer is preferred in vacuum and in low polarity solvents for chlorine, bromine and iodine derivatives. For 2-fluorocyclooctanone, the preferred conformation in vacuum is pseudo-axial. In acetonitrile, the pseudo-axial conformer becomes the most stable for the chlorine derivative. According to NBO calculations, the conformational preference is not dictated by electron delocalization, but by classical electrostatic repulsions.137176-8