Hydrated Sugars in the Gas Phase:  Spectroscopy and Conformation of Singly Hydrated Phenyl β-d-Glucopyranoside

Abstract

The structural investigation of a hydrated monosaccharide, phenyl β-D-glucopyranoside (PheβGlc), in the gas phase is presented. It is based upon ab initio computation coupled with the analysis of the resonant 2-photon ionization and IR ion-dip spectra of the singly hydrated clusters stabilized in a free jet expansion and follows an earlier investigation of the structure and conformations of the unhydrated sugar. 1 Despite the potentially large set of possible binding sites and conformations, only two singly hydrated complexes are formed in the free jet expansion. Tentative structural assignments are made on the basis of comparisons with those already established for related systems; comparisons between the observed O-H vibrational frequencies and those computed for structures optimized at the B3LYP/6-31+G(d) level of theory, and in light of the relative energies of these structures, calculated at the single-point MP2/6-311+G(d,p) level are made. A discrepancy between the latest revision of the Gaussian 98 package (revision A.11) and earlier revisions, which can lead to different computed structures when optimizing noncovalently bound molecular complexes, is discussed in an appendix.

Conformation, dynamics, solvation and relative stabilities of selected β-hexopyranoses in water: a molecular dynamics study with the gromos 45A4 force field

“…The present observations are also compatible with the results of IR ion-dip experiments on phenyl-b-D D-glucopyranoside in the gasphase, 162,163,338 suggesting a population ratio g + /t/g À of 25:68:7 (the inversion between g + and t may be related to the presence of the phenyl substituent 162,163,338,348 ), as well as with Raman optical activity measurements on methyl-b-D D-glucopyranoside in vacuum, 340 suggesting a corresponding approximate population ratio of 50:50:0. For Man, the few quantummechanical studies available suggest a ranking g À > t > g + .…”

“…162,348 A recent quantum-mechanical study of Glc monohydrates in vacuum 361 also suggested that the best water binding sites for Glc involved interactions with the O 5 and O 1 atoms, the 1-OH group systematically acting as donor for a strong sugar-water hydrogen-bond. The lowest-energy conformer not involving a direct interaction of the water molecule with the lactol group presented hydrogen-bonding interaction with the 4-OH group.…”

Density functional study of the infrared spectrum of glucose and glucose monohydrates in the OH stretch region

“…These experiments discriminate between the various possible glucoside and glucoside-water configurations, providing the infrared spectrum for individual conformations. Different glucoside conformations and glucoside-water complexes were reported [11][12][13] by those authors.…”

“…Recently, Simons and co-workers reported the in vacuo infrared gas-phase OH stretch region of a glucose derivative (1-phenyl-b-Dglucoside) [11], and complexes with one water molecule [12,13]. These experiments discriminate between the various possible glucoside and glucoside-water configurations, providing the infrared spectrum for individual conformations.…”

B3LYP/6-311++G** geometry-optimization study of pentahydrates of α- and β-d-glucopyranose

“…Some glucose-water heterodimer single state configuration calculations 20,21 have also taken water explicitly into account during geometry optimization. The semiempirical inclusion of solvent by use of solvent free-energy methods [5][6][7] is clearly not the same as the explicit inclusion of water molecules in the DFT calculations, where we obtain detailed structural and energetic information.…”