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Fingerprints of hydrogen bonds revealed by mid- and far-infrared spectroscopy

Date of news: 14 August 2017

Fingerprints of hydrogen bonds revealed by mid- and far-infrared spectroscopy


Researchers at the FELIX laboratory have identified systematic shifts the frequencies of three hydrogen bond vibrational modes, representing the inter- and intramolecular hydrogen bond strength. These hydrogen bond (H-bond) deforming modes are measured via the infrared spectra of isolated clusters of saligenin with water molecules, which exhibit intra- and intermolecular hydrogen bonds. In cooperation with groups at the University of Wisconsin-Madison (USA) and the Université d'Evry val d'Esonne (France), advanced, anharmonic calculations were applied to identify the three dimensional structures of the clusters, and the spectral signatures of the hydrogen bonds.PCCP2017_Rijs_cover

Saligenin (2-(hydroxymethyl)phenol) exhibits both strong and weak intramolecular electrostatic interactions. The bonds that result from these interactions compete with intermolecular hydrogen bonds once saligenin binds to one or more water molecules. Infrared (IR) ultraviolet (UV) ion-dip spectroscopy was used to study isolated saligenin–(H2O)n clusters (n = 1–3) in the far- and mid-IR regions of the spectrum. Both harmonic and anharmonic (coupled local modes and Born–Oppenheimer molecular dynamics) quantum chemical calculations were applied to assign cluster geometries to the measured spectra. The hydrated clusters with n = 1 and 2 have geometries that are quite similar to benzyl alcohol–water clusters, whereas the larger clusters with n = 3 show structures equivalent to the isolated water pentamer.

Systematic shifts in the frequencies of three hydrogen bond (H-bond) deforming modes, namely OH stretching, OH torsion and H-bond stretching, were studied as a function of the hydrogen bond strength represented by either the OH bond length or the H-bond length. The shifts of the frequencies of these three modes correlate linearly to the OH length, despite both intra- and intermolecular H-bonds being included in this analysis. The OH torsion vibration displays the largest frequency shift when H-bonded, followed by the OH stretching vibrations and finally the H-bond stretching frequency. The frequency shifts of these H-bond deforming modes behave non-linearly as a function of the H-bond length, asymptotically approaching the frequency expected for the non H-bonded modes.



Fingerprints of inter- and intramolecular hydrogen bonding in saligenin-water clusters revealed by mid- and far-infrared spectroscopy

D. J. Bakker, A. Dey, D. P. Tabor, Q. Ong, J. Mahé, M. P. Gaigeot, E. L. Sibert III and A. M. Rijs, Physical Chemistry Chemical Physics 19, 20343-20356 (2017). DOI: 10.1039/C7CP01951C

More Information?
Dr.  A. Rijs, Radboud University, a.rijs@science.ru.nl