Slow Molecular Motions in Ionic Liquids Probed by Cross‐Relaxation of Nuclear Spins During Overhauser Dynamic Nuclear Polarization

Banerjee, Abhishek; Dey, Arnab; Chandrakumar, N.

doi:10.1002/ange.201607308

Cited by 3 publications

(2 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For example, relaxation measurements can be used to extract rotational correlation times over a wide range of frequencies, 17,18 pulsed field gradient (PFG) NMR can provide direct measurement of self-diffusion coefficients, 19,20 electrophoretic NMR can probe ion clustering, 21−23 and dynamic nuclear polarization (DNP) methods can be used to study both structure and dynamics. 24,25 The HOESY (heteronuclear Overhauser effect spectroscopy) NMR experiment in particular has been used by a number of research groups to probe ionic interactions in ILs and IL electrolytes. 26−36 This method involves a transfer of spin polarization between nuclear isotopes (e.g., from 7 Li to 1 H) via a process known as the nuclear Overhauser effect (NOE).…”

mentioning

confidence: 99%

Correlating Intermolecular Cross-Relaxation Rates with Distances and Coordination Numbers in Ionic Liquids

Martin

Chen

Forsyth

et al. 2018

J. Phys. Chem. Lett.

View full text Add to dashboard Cite

The HOESY NMR experiment is commonly used to probe ion associations in ionic liquids and their mixtures. The parameter measured in this experiment is the heteronuclear cross-relaxation rate σ, which has dimensions of s–1. For intramolecular NOEs this scales as r –6 where r is the internuclear distance, but in the intermolecular case (as typically probed in studies of ionic liquids), theory predicts a more complex behavior including a distance dependence that is affected by the relative frequencies of the nuclei involved. Specifically, for nuclei with similar resonance frequencies such as 1H and 19F, it has been predicted that intermolecular NOEs will be sensitive to longer range distances than for nuclei with very different frequencies such as 1H and 7Li. In this contribution, we test this theory using a combination of quantitative HOESY analysis and molecular dynamics simulations carried out on two different ionic liquid electrolyte systems. In agreement with theoretical predictions, we find excellent correlations between the experimentally measured 1H–7Li NOEs and carbon–lithium distances below 4 Å, while longer distances (>6 Å) must be considered in order to obtain good correlations between 1H–19F NOEs and carbon–fluorine coordination numbers. This demonstrates the utility of HOESY NMR in understanding structure and interactions in ionic liquids while also illustrating that care must be taken in interpreting the measured cross-relaxation rates.

show abstract

mentioning

confidence: 99%

Correlating Intermolecular Cross-Relaxation Rates with Distances and Coordination Numbers in Ionic Liquids

Martin

Chen

Forsyth

et al. 2018

J. Phys. Chem. Lett.

View full text Add to dashboard Cite

show abstract

“…While direct ODNP of 13 C in solution state is well-known since long as stated earlier, it suffers in general from the requirement of rather long polarization times (tens of seconds), and further results in differential enhancements, i.e., site specific positive or negative enhancements in the same molecule. Direct 13 C enhancements are also influenced by three-spin effects, 29,33,34 especially at low radical concentrations. Differential enhancements and three-spin effects could both be of interest if the purpose were investigation of molecular dynamics or spin interaction dynamics.…”

Section: ■ Principlesmentioning

confidence: 99%

Transferred Overhauser DNP: A Fast, Efficient Approach for Room Temperature ¹³C ODNP at Moderately Low Fields and Natural Abundance

2017

Self Cite

View full text Add to dashboard Cite

Overhauser dynamic nuclear polarization (ODNP) is investigated at a moderately low field (1.2 T) for natural abundance C NMR of small molecules in solution state at room temperature. It is shown that ODNP transferred fromH to C by NMR coherence transfer is in general significantly more efficient than direct ODNP ofC. Compared to direct C ODNP, we demonstrate over 4-fold higherC sensitivity (signal-to-noise ratio, SNR), achieved in one-eighth of the measurement time by transferred ODNP (t-ODNP). Compared to the C signal arising from Boltzmann equilibrium in a fixed measurement time, this is equivalent to about 1500-fold enhancement ofC signal by t-ODNP, as against a direct C ODNP signal enhancement of about 45-fold, both at a moderate ESR saturation factor of about 0.25. This owes in part to the short polarization times characteristic ofH. Typically, t-ODNP reflects the essentially uniform ODNP enhancements of all protons in a molecule. Although the purpose of this work is to establish the superiority of t-ODNP vis-à-vis direct C ODNP, a comparison is also made of the SNR in t-ODNP experiments with standard high resolution NMR as well. Finally, the potential of t-ODNP experiments for 2D heteronuclear correlation spectroscopy of small molecules is demonstrated in 2DH-C HETCOR experiments at natural abundance, with decoupling in both dimensions.

show abstract

Motional Dynamics of Halogen‐Bonded Complexes Probed by Low‐Field NMR Relaxometry and Overhauser Dynamic Nuclear Polarization

Banerjee

Dey

Chandrakumar

2019

Chemistry An Asian Journal

Self Cite

View full text Add to dashboard Cite

Halogen bonding is asubject of considerable interest owing to wide-ranging chemical, materials and biological applications. The motional dynamics of halogenbonded complexes play ap ivotalr ole in comprehending the nature of the halogen-bonding interaction. However, not many attempts appear to have been made to shed light on the dynamical characteristics of halogen-bonded species. For the first time, we demonstrateh ere that the combination of low-field NMR relaxometry andO verhauser dynamic nuclear polarization (ODNP) makes it possible to obtain ac ogentp icture of the motional dynamics of halogen-bonded species. We discussh ere the advantages of this combined approach. Low-field relaxometry allows us to infer the hydrodynamic radius and rotational correlation time, whereas ODNP probest he molecular translational correlation times (involving the substrate as well as the organic radical) with high sensitivity at low field. Noncovalent interactions are among the most discussed and debated areas in contemporaryc hemistry and biology.S everal experimentala nd theoretical efforts have been made to characterizea nd classify these interactions.A mong several such interactions H-bonding, halogenb onding, etc. play an important role in chemistry. [1] Halogen bonding (XB) has been defined as an attractive interaction between an electrophilicr egion aroundahalogen atom (X) in am olecule or moiety,a nd an ucleophilic region (B) in another molecule or moiety.S tructurally,t he electrophilic region at the halogen atom has been associated with a" s hole". In recent times, halogen bondingh as impacted diverse fields including supramolecular chemistry,o rganic synthesis, catalysis, separation chemistry,b iology,e tc. [2] In adducing evidencef or halogen bonding av arietyo ft heoretical studies have been reported, besidese xperimental structural studies in solution and solid state. [3] NMR [4a-m] andE SR [5] investigations are among major experimentalt echniques employed in recent times. In particular, one may mention NMR chemicals hift titration, [4a] heteronuclear Overhauser effect (NOE) measurements, [4g] as well as NMR self-diffusion measurements [4h] on halogen bondedc omplexes. ESR studies have typically involved an itroxide free radicalt hat doubles up as the nucleophile. [5] In our view,m ost such studies reported thus far do not directly establish the motional dynamics of "halogen bonded" species, but principally infer the presence of some form of interaction, for example, either by NMR chemical shift changes or by changes in self-diffusion coefficients measured by NMR. The NMR chemical shift( 1 H/ 19 F) titrationa pproach runs into difficulties when small or negligible chemical shift change is observed, and the stoichiometry of the adduct is unknown.Interpretations of NOE 4g measurements are often vitiated by employing at wo-spin model well beyond its region of approximate validity in am ultispin system, i.e.,b eyond the initial build-up rate regime. NOE'sa lso becomev ery weak on the rotational model if the s...

show abstract

Slow Molecular Motions in Ionic Liquids Probed by Cross‐Relaxation of Nuclear Spins During Overhauser Dynamic Nuclear Polarization

Cited by 3 publications

References 37 publications

Correlating Intermolecular Cross-Relaxation Rates with Distances and Coordination Numbers in Ionic Liquids

Correlating Intermolecular Cross-Relaxation Rates with Distances and Coordination Numbers in Ionic Liquids

Transferred Overhauser DNP: A Fast, Efficient Approach for Room Temperature ¹³C ODNP at Moderately Low Fields and Natural Abundance

Motional Dynamics of Halogen‐Bonded Complexes Probed by Low‐Field NMR Relaxometry and Overhauser Dynamic Nuclear Polarization

Contact Info

Product

Resources

About

Slow Molecular Motions in Ionic Liquids Probed by Cross‐Relaxation of Nuclear Spins During Overhauser Dynamic Nuclear Polarization

Cited by 3 publications

References 37 publications

Correlating Intermolecular Cross-Relaxation Rates with Distances and Coordination Numbers in Ionic Liquids

Correlating Intermolecular Cross-Relaxation Rates with Distances and Coordination Numbers in Ionic Liquids

Transferred Overhauser DNP: A Fast, Efficient Approach for Room Temperature 13C ODNP at Moderately Low Fields and Natural Abundance

Motional Dynamics of Halogen‐Bonded Complexes Probed by Low‐Field NMR Relaxometry and Overhauser Dynamic Nuclear Polarization

Contact Info

Product

Resources

About

Transferred Overhauser DNP: A Fast, Efficient Approach for Room Temperature ¹³C ODNP at Moderately Low Fields and Natural Abundance