NMR techniques for the investigation of solvation phenomena and non-covalent interactions

Bagno, Alessandro; Rastrelli, Federico; Saielli, Giacomo

doi:10.1016/j.pnmrs.2005.08.001

Cited by 109 publications

(84 citation statements)

References 456 publications

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“…9 NMR quadrupolar relaxation originates in fluctuating electric-field gradients and the relaxation rate can be described by , where is the strength and c the correlation time of the electric-field-gradient fluctuations. 32 The quadrupolar relaxation of simple ions such as Mg 2+ and Cl -is in principle sensitive to all fluctuations of the dipole moments of local water molecules: rotations and translations. However, because the NMR lineshape is motionally narrowed, the slowest fluctuations have the greatest effect on the quadrupolar relaxation rate.…”

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confidence: 99%

Glasslike behavior in aqueous electrolyte solutions

Turton

Hunger

Hefter

et al. 2008

The Journal of Chemical Physics

109

162

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When salts are added to water, the viscosity generally increases suggesting the ions increase the strength of the water's hydrogen-bond network. However, infrared pump-probe measurements on electrolyte solutions have found that ions have no influence on the rotational dynamics of water molecules implying no enhancement or breakdown of the hydrogen-bond network. Here we report optical Kerr-effect and dielectric relaxation spectroscopic measurements, which have enabled us to separate the effects of rotational and transitional motions of the water molecules. These data show that electrolyte solutions behave like a supercooled liquid approaching a glass transition in which rotational and translational molecular motions are decoupled. It is now possible to understand previously conflicting viscosity data, nuclear magnetic resonance relaxation, and ultrafast infrared spectroscopy in a single unified picture.It is well known that when salts are added to water the viscosity typically increases, suggesting that the ions alter the hydrogen-bond network of the water, 1 which appears to be confirmed by, for example, neutron diffraction experiments. 2 However, recent ultrafast infrared pump-probe measurements on electrolyte solutions have found that ions do not influence the rotational dynamics of water molecules suggesting that there is no enhancement or breakdown of the hydrogen-bond network in liquid water. 3 As the effect of ions and ionic moieties on the structure of water is important for understanding protein stability, enzymatic reactions, and substrate binding, it is crucial to resolve this paradox. 4 Here we report ultrafast optical Kerr effect 5 (OKE) and dielectric relaxation 6 (DR) spectroscopy measurements, which show that salt solutions behave like a supercooled liquid approaching a glass transition, where rotational and translational molecular motions become decoupled. The rotational motions of bulk water molecules -observed as an -relaxation in DR -are essentially independent of concentration. The translational motions seen in OKE spectroscopy can be understood as a -relaxation 7 and their dynamics become increasingly inhomogeneous with increasing salt concentration. This insight reconciles previously conflicting viscosity data, 8 nuclear magnetic resonance relaxation, 9 and ultrafast infrared spectroscopy 3 data in a single unifying picture.When simple inorganic salts are added to water, the viscosity typically increases ( see FIG. 1). In the relatively low concentration range (up to ~0.5 M), this is described by the semi-empirical Jones-Dole equation, 1 , which expresses the shear viscosity in terms of the viscosity of pure water 0 , salt concentration c, and parameters A and B. For many salts additional terms have to be added to describe the rapid increase in viscosity at higher concentrations. The obvious conclusion to draw from this behavior is that ions alter the structure of water. Indeed, the empirical Jones-Dole B coefficient is often used to classify ions as either structure makers (kosmotropes...

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Section: Fig 1 (Color Online)mentioning

confidence: 99%

Glasslike behavior in aqueous electrolyte solutions

Turton

Hunger

Hefter

et al. 2008

The Journal of Chemical Physics

109

162

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“…In the large repertoire of physical methods used for ILs' characterization, NMR spectroscopy is still playing an important role, outlined in some recent review articles [1,2]. In turn, the nuclear Overhauser enhancement (NOE) is one of the most powerful NMR tool for the assessment of three dimensional structure of molecules [3] and for the detection of intermolecular interactions [4]. The first application of NOE to ILs dated back 1995 by the group of Osteyoung [5].…”

Section: Introductionmentioning

confidence: 99%

Multiple points of view of heteronuclear NOE: Long range vs short range contacts in pyrrolidinium based ionic liquids in the presence of Li salts

Castiglione

Appetecchi

Passerini

et al. 2015

Journal of Molecular Liquids

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The nuclear Overhauser enhancement (NOE) is a powerful tool of NMR Spectroscopy extensively used to gain structural information in ionic liquids (ILs). A general model for the distance dependence of intermolecular NOE in ILs was recently proposed showing that NOE spots beyond the first solvation shell and accounts for long-range effects. This conclusion prompted for a deep rethinking of the NOE data interpretation in ILs. In this paper we present an extensive and quantitative study of N-propyl-N-methyl pyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR 13 TFSI), the homologue with bis ( Li}NOE correlation experiments (HOESY). The former is mainly tuned on long-range interactions, the latter on short-range ones, due to the small and large Larmor frequency differences of the involved nuclei. The collected data are discussed in two different way: long-range { 1 H- 19F}NOEs spot on the polar/apolar domains within the ILs, whereas shortrange (e.g. regarding the first coordination shell) { 1 H-7 Li}NOEs describe the contacts between first neighbors, with interesting correlation with the distances' statistics derived by crystallographic data of related systems.

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“…The through-space character can be inferred, for example, from an unexpectedly large coupling between two atoms close in space but separated by several bonds. [5] TSC was observed for fluorine-fluorine, [6] fluorine-carbon, fluorine-nitrogen, [7] fluorine-hydrogen, [6d, 8] phosphorus-phosphorus, [9] carbonphosphorus, [10] and rarer metallic nuclear pairs. [11] Studies of TSC in van der Waals complexes without any covalent interaction are least frequent.…”

Section: Introductionmentioning

confidence: 99%

“…[22] The ring rotations are completely blocked at room temperature. In the benzophenanthrene derivatives 4 and 5 the hydrogen atom at the 12-position is close to the hydrogen atoms of the C-1 methyl group (4) or to the H-1 hydrogen atom (5). Compounds 6 and 7 were prepared as systems in which the TSC is supposed to be minimal.…”

Section: Introductionmentioning

confidence: 99%

Computational and Experimental Evidence of Through‐Space NMR Spectroscopic J Coupling of Hydrogen Atoms

Dračínský

Jansa

Bouř

2011

Chemistry A European J

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J coupling in NMR spectroscopy is conventionally associated with covalent bonds. A noncovalent contribution often called through-space coupling (TSC) has been observed for heavy atoms. In this study, the TSC was detected and analyzed for the more common (1)H-(1)H coupling as well. In synthesized model molecules the hydrogen positions could be well controlled. For several coupling constants the through-space mechanism was even found to be the predominant factor. The nature and magnitude of the phenomenon were also analyzed by density functional computations. Calculated carbon- and hydrogen-coupling maps and perturbed electronic densities suggest that the aromatic system strongly participates in the noncovalent contribution. Unlike covalent coupling, which is usually governed by the Fermi contact, TSC is dominated by the diamagnetic term comprising interactions of nuclei with the electron orbital angular momentum. The computations further revealed a strong distance and conformational dependence of TSC. This suggests that the through-space coupling can be explored in molecular structural studies in the same way as the covalent one.

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NMR techniques for the investigation of solvation phenomena and non-covalent interactions

Cited by 109 publications

References 456 publications

Glasslike behavior in aqueous electrolyte solutions

Glasslike behavior in aqueous electrolyte solutions

Multiple points of view of heteronuclear NOE: Long range vs short range contacts in pyrrolidinium based ionic liquids in the presence of Li salts

Computational and Experimental Evidence of Through‐Space NMR Spectroscopic J Coupling of Hydrogen Atoms

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