title: Vacuum-ultraviolet electronic circular dichroism study of methyl α-D-glucopyranoside in aqueous solution by time-dependent density functional theory.
abstract: The vacuum-ultraviolet (VUV) electronic circular dichroism (ECD) spectrum of methyl α-D-glucopyranoside (methyl α-D-Glc) was measured down to 163 nm in aqueous solution using a synchrotron-radiation VUV-ECD spectrophotometer. The spectrum exhibited two characteristic ECD peaks around 170 nm, which depend on the trans (T) and gauche (G) configurations of the hydroxymethyl group at C-5. To elucidate the influences of the T and G configurations on the spectrum, the ECD spectra of three rotamers (α-GT, α-GG, and α-TG) of methyl α-D-Glc were calculated using time-dependent density functional theory (TDDFT) combined with molecular dynamics simulation. A linear combination of the ECD spectra of these three rotamers, which differ markedly from each other, produced a methyl α-D-Glc spectrum similar to that observed experimentally. The spectrum was assignable to the n-σ* transitions of the ring oxygen and methoxy oxygen with minor contributions from the hydroxyl oxygen. The differences in α-GT, α-GG, and α-TG spectra were attributed to fluctuations of the configurations of the hydroxymethyl group at C-5 and the hydroxyl group at C-4, which strongly affected the orientations of intramolecular hydrogen bonds around the ring oxygen. These findings demonstrate that combining VUV-ECD and TDDFT is useful for structural characterization of saccharides in aqueous solution.
authors.affiliation: Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan. pika@hiroshima-u.ac.jp
authors.forename: Koichi
authors.initials: K
authors.lastname: Matsuo
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Namatame
authors.forename: Masaki
authors.initials: M
authors.lastname: Taniguchi
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Gekko
mesh_terms: D002942:Circular Dichroism; D004583:Electrons; D008757:Methylglucosides / Q000737:chemistry*; D011789:Quantum Theory; D012996:Solutions; D013997:Time Factors; D014466:Ultraviolet Rays; D014618:Vacuum; D014867:Water / Q000737:chemistry
chemical_list: D008757:Methylglucosides; D012996:Solutions; D014867:Water; C027020:methylglucoside