Chemical Shifts Of Hydroxyl Protons Research Articles

Insights on the reactivity of chondroitin and hyaluronan toward 1,4-butanediol diglycidyl ether

Hyaluronic acid (HA) cross-linked with 1,4-butanediol diglycidyl ether (BDDE) are hydrogels with many biomedical applications. Degree of substitution, cross-linking and substitution position of the cross-linker might influence the properties of the hydrogels. We showed earlier that the most common substitution position of the cross-linker on the hyaluronan chain was the 4-hydroxyl of N-acetylglucosamine. This result has led us to investigate unsulfated chondroitin (CN) which only differ from HA in the primary structure by the configuration at C4 of the aminoglycan. In the present study, we have investigated (i) the substitution positions of the cross-linker in CN using NMR and LC-MS and compared the results to the data obtained for HA (ii) the effect of alkali on the 13C and 1H chemical shifts in CN and HA (iii) the temperature coefficients and chemical shifts of hydroxyl protons in CN and HA. In CN, the 2-hydroxyl of glucuronic acid and 6-hydroxyl of N-acetylgalactosamine were found to be the major sites of substitution by BDDE. Moreover, while chondroitinase was not able to cleave HA tetrasaccharide substituted at the 4-hydroxyl GlcNAc reducing end by BDDE, it is able to degrade CN-BDDE down to disaccharide units.

Correlation between 1H NMR chemical shifts of hydroxyl protons in n-hexanol/cyclohexane and molecular association properties investigated using density functional theory

Association of n-hexanol molecules in cyclohexane forming clusters is studied by DFT and 1H NMR. Geometry optimization, corrected binding energies, charge distributions, charge transfer energies, and 1H NMR chemical shifts have been obtained. The calculated chemical shifts of hydroxyl protons have been correlated to experimental data obtained in the range of n-hexanol molar fraction between 0.002 and 0.2, showing that n-hexanol molecules at a molar fraction around 0.1, where well-structured hydrogen bond networks are observed, tend to form linear pentamers and hexamers. The experimental data are consistent with the continuous linear association thermodynamic model, showing a dimensionless association constant of 284.

Interaction of phenol with NaX zeolite as studied by 1H MAS NMR, 29Si MAS NMR and 29Si CP MAS NMR spectroscopy

The interaction of phenol with zeolite NaX has been studied by 1H and 29Si MAS and 29Si-CP-MAS NMR spectroscopy. A large displacement of the chemical shift of hydroxyl protons from 1.2 ppm in the crystalline state to about 9 ppm occurs upon H-bonding of phenol to basic oxygen atoms of the zeolite. An enhancement of the 29Si-CP-MAS signal is observed for the phenol loaded NaX zeolite and interpreted in terms of an interaction of the aromatic ring with either Na + cations or oxygen atoms of the 12 member ring of the supercage. A small fraction of framework silicon atoms in four fold aluminum coordination, most likely Si atoms in four member ring positions of SIII or SIII’ sites, is electronically affected by interaction of phenol with Na + ions located in these sites. After thermal treatment to 320°C part of the phenol is deprotonated and rearranges to linear Na +… −OPh complexes.

Studies on Solute−Solvent Interactions in Gaseous and Supercritical Carbon Dioxide by High-Pressure 1H NMR Spectroscopy

A newly designed high-pressure NMR flow cell has been developed for studies of supercritical fluids. By using the high-pressure cell, 1H chemical shifts of nonpolar (n-hexane and benzene) and polar (dichloromethane, chloroform, acetonitrile, water, methanol, and ethanol) solute molecules in gaseous and supercritical carbon dioxide were measured in the wide pressure range between 2 and 30 MPa at 313.3 K. The chemical shifts of hydroxyl protons of water, methanol, and ethanol in carbon dioxide at 20.0 MPa were shifted to higher frequency due to intermolecular hydrogen bonding with increasing concentration. A comparison of the concentration dependence with relevant data in carbon tetrachloride indicated a specific interaction between alcohol and carbon dioxide molecules. The corrected 1H chemical shifts of nonpolar and polar solute molecules at infinite dilution, where the bulk magnetic susceptibility contribution was subtracted, were shifted to higher frequency with increasing density of carbon dioxide. The...

Conformational Flexibility of Carbohydrates: A Folded Conformer at the φ Dihedral Angle of a Glycosidic Linkage

The trisaccharide β-d-Glcp-(1→2)-β-d-Glcp-(1→3)-α-d-Glcp-OMe has been studied by Langevin dynamics (LD) simulations and NMR spectroscopy including measurement of transglycosidic 3JC,H coupling constants, 3JH,OH coupling constants, temperature dependence of the chemical shift of hydroxyl protons, and 2D NOESY and T-ROESY experiments as well as their 1D DPFGSE analogues. A folded conformer at the φH dihedral angle of the (1→2)-linkage observed in the LD simulation was corroborated by experimental NMR data, in particular spatial proximity of hydroxyl protons in nonadjacent sugar residues as deduced from a 2D T-ROESY experiment. The results from the present study with an “anti” φH conformer show that oligosaccharides exhibit large conformational flexibility under certain conditions and that this inherent property needs to be taken into account in the analysis of carbohydrate structure.

Chemical shifts of hydroxyl protons of various phenols in acetone-chromic anhydride systems

Chemical shifts of hydroxyl protons of various phenols in acetone-chromic anhydride systems