Vibrational coupling as diagnostic for intramolecular hydrogen bonds of carbohydrates in aqueous solution

Abstract

The coupling of nuC-O and deltaO-D vibrations in the 1200-900 cm(-1) IR range leads to band shifting in opposite directions, which provides information on intramolecular hydrogen bonding of carbohydrates in aqueous solution. The aqueous solution IR spectra of 2-acetamide-1,6-anhydro-2-deoxy-D-glucopyranose and cis-1,2-cyclopentanediol and tetrahydrofuran-ethanol mixtures are reported. Frequency upshifting upon deuteration is observed for the nuC-O bands of both a hydrogen bond acceptor and donor in ether-hydroxyl and hydroxyl-hydroxyl contacts. The 1200-900 cm(-1) range can be used to reveal the presence of intramolecular hydrogen bonds in aqueous carbohydrates, unlike the OH stretching region, which cannot be used in this sense due to carbohydrate band masking by the strong nuOH IR absorption of water.

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

“…This is mainly because (i) hydroxyl protons are difficult to detect via NMR spectroscopy 37,[109][110][111][112] (chemical exchange, mutual overlap, overlap with solvent signal); (ii) hydroxyl group vibrations are difficult to characterize via infrared (IR) spectroscopy 110,[113][114][115] (dual hydrogen-bond donoracceptor character, mutual overlap, overlap with solvent bands). Furthermore, X-ray crystallography provides limited reference information in the solid state, because the hydroxyl protons are invisible in these experiments (weak diffraction centers, orientational averaging).…”

“…124,132,133,135,137 Electrostatic effects: Electrostatic effects, mainly intramolecular hydrogen-bonding, are strongly sensitive to the nature and polarity of the solvent. Experimentally, intramolecular hydrogen-bonds in an aqueous environment can be detected only indirectly, for example, via NMR 37,[109][110][111][112]115,[124][125][126][138][139][140][141][142][143][144][145][146][147][148][149] or IR 110,[113][114][115]144,[149][150][151][152][153] spectroscopy. However, most studies to date have investigated model compounds (e.g., monosaccharide analogs) and only provided qualitative information on the existence or absence of a hydrogen-bond.…”

“…However, most studies to date have investigated model compounds (e.g., monosaccharide analogs) and only provided qualitative information on the existence or absence of a hydrogen-bond. Based on these studies, it appears that intramolecular hydrogen-bonds in aldohexopyranoses can be broadly classified into three groups in order of decreasing strength: 110,113,115,154 (i) six-membered hydrogenbonded 'rings' between 1,3-syn-diaxial hydroxyl groups; 101,102,110,114,121,122,125,126,141,[144][145][146][147][148]150,155,156 (ii) five-membered hydrogen-bonded 'rings' between cis-vicinal (axial-equatorial) hydroxyl groups; 121,150 and (iii) five-membered hydrogen-bonded 'rings' between transvicinal (diequatorial) hydroxyl groups. 121,150 Hydrogen-bonding interactions are strong in vacuum or in solvents of low polarity, 121,122,125,126,144,149,155 but probably represent rather weak conformational driving forces in aqueous environment.…”

“…121,150 Hydrogen-bonding interactions are strong in vacuum or in solvents of low polarity, 121,122,125,126,144,149,155 but probably represent rather weak conformational driving forces in aqueous environment. 84,142,146,150,157 For example, although hydrogen-bonds between 1,3-syndiaxial hydroxyl groups in fixed orientations are always observed in water, 110,114,141,148,156 they are not always present when this orientation is conformer-dependent (e.g., when the 'ring' involves one rotatable C-C bond 101,102,144,150 or can only be formed in one chair conformation of a flexible six-membered ring system 121,122,125,126,149,155 ). However, although sometimes questioned, 143 the existence of stable intramolecular hydrogen-bonds for monosaccharide analogs in aqueous solution has been unambiguously evidenced by NMR and IR techniques.…”

Investigation of the Hydrogen Bonding Properties of a Series of Monosaccharides in Aqueous Media by 1H NMR and IR Spectroscopy

“…In the case of ethanol in water (5% w/w), the ν(CϪO) upshift upon deuteration is about 2 cm Ϫ1 . [31] It is obvious that stronger ν(CϪO) upshifting is to be expected when carbohydrate intramolecular hydrogen bonds are present in water solution; otherwise these would be broken by water. We have used this infrared spectroscopic method to identify intramolecular hydrogen bonds in the carbohydrates studied here for the first time.…”