Overhauser-DNP-enhanced homonuclear 2D 19F correlation spectroscopy with diagonal suppression is presented for small molecules in the solution state at moderate fields. Multi-frequency, multi-radical studies demonstrate that these relatively low-field experiments may be operated with sensitivity rivalling that of standard 200-1000MHz NMR spectroscopy. Structural information is accessible without a sensitivity penalty, and diagonal suppressed 2D NMR correlations emerge despite the general lack of multiplet resolution in the 1D ODNP spectra. This powerful general approach avoids the rather stiff excitation, detection, and other special requirements of high-field 19FNMR spectroscopy. © 2014 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

N Chandrakumar

Department Of Chemistry

Chemical reactions

chemistry

CORRELATION SPECTROSCOPY

Dynamic nuclear polarization

High-field

Homonuclear

Multi frequency

OVERHAUSER DNP

Small molecules

Structural information

Nuclear magnetic resonance spectroscopy

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Angewandte Chemie - International Edition

Overhauser dynamic nuclear polarization (ODNP) is investigated at a moderately low field (1.2 T) for natural abundance 13C NMR of small molecules in solution state at room temperature. It is shown that ODNP transferred from 1H to 13C by NMR coherence transfer is in general significantly more efficient than direct ODNP of 13C. Compared to direct 13C ODNP, we demonstrate over 4-fold higher 13C sensitivity (signal-to-noise ratio, SNR), achieved in one-eighth of the measurement time by transferred ODNP (t-ODNP). Compared to the 13C signal arising from Boltzmann equilibrium in a fixed measurement time, this is equivalent to about 1500-fold enhancement of 13C signal by t-ODNP, as against a direct 13C 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 of 1H. 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 13C 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 2D 1H-13C HETCOR experiments at natural abundance, with decoupling in both dimensions. © 2017 American Chemical Society.

Journal of Physical Chemistry B

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

Solution-state Overhauser dynamic nuclear polarization (ODNP) at moderate fields, performed by saturating the electron spin resonance (ESR) of a free radical added to the sample of interest, is well known to lead to significant NMR signal enhancements in the steady state, owing to electron–nuclear cross-relaxation. Here it is shown that under conditions which limit radical access to the molecules of interest, the time course of establishment of ODNP can provide a unique window into internuclear cross-relaxation, and reflects relatively slow molecular motions. This behavior, modeled mathematically by a three-spin version of the Solomon equations (one unpaired electron and two nuclear spins), is demonstrated experimentally on the19F/1H system in ionic liquids. Bulky radicals in these viscous environments turn out to be just the right setting to exploit these effects. Compared to standard nuclear Overhauser effect (NOE) work, the present experiment offers significant improvement in dynamic range and sensitivity, retains usable chemical shift information, and reports on molecular motions in the sub-megahertz (MHz) to tens of MHz range—motions which are not accessed at high fields. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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

Two-dimensional nuclear magnetic resonance (2D NMR) correlation spectra help visualize inter- or intra-molecular spin connectivity through space or through bonds. This is accomplished by magnetization transfer between interacting (connected) spins located at different sites in molecules. In homonuclear 2D experiments, cross peaks which demonstrate spin connectivity and result from magnetization transfer between sites are unfortunately invariably accompanied by other peaks that result from magnetization that has not undergone any transfer, viz., diagonal peaks. The latter can often mask close-lying cross peaks. We report here the general principles that constitute a design strategy for diagonal suppression, relying on echo formation. Next, a novel experiment that effects diagonal suppression in the high-resolution mode is demonstrated. Pure phase capability is also introduced. Examples from both 2D exchange and high-resolution 2D correlation spectroscopy are included, and the proposed method is compared with other established as well as recent attempts to accomplish diagonal suppression. © 2014 American Chemical Society.

Journal of Physical Chemistry A

Two-dimensional nuclear magnetic resonance: Exploiting spin echoes to maximize information content by suppression of diagonal peaks in homonuclear experiments

We report a novel diagonal suppressed two-dimensional total correlation experiment in solution state and demonstrate its performance in 1H and 2H NMR. In DIagonal Suppressed spin echo TOtal Correlation SpectroscopY (DISTOCSY), diagonal peaks which occur around F1 = 0 in spin echo mode are removed by conversion to unobservable multiple quantum or longitudinal terms in each scan of a two scan procedure, on application of an appropriately phased 90° pulse at the time of the echo maximum. The limitation of this approach to short FID acquisition times is discussed, and an alternative two-scan version of DISTOCSY for high resolution situations is presented. © 2015 Elsevier B.V. All rights reserved.

Chemical Physics Letters

1H and 2H NMR: Diagonal suppressed total correlation spectroscopy in spin echo mode

Two dimensional homonuclear 1H correlation spectroscopy is of considerable interest for volume localized spectral studies, both in vivo and in vitro, of biological as well as material objects. The information principally sought from correlation spectra resides in the cross-peaks, which are often masked however by the presence of diagonal peaks in COSY, or 'pseudo-diagonal' peaks at F1 = 0 in SECSY. It has therefore been a concern to suppress these diagonal or 'pseudo-diagonal' peaks, in order to ensure that cross-peak information is fully discernible. We present here a report of our work on volume localized DIagonal Suppressed Spin Echo Correlation specTroscopy (LDISSECT) and demonstrate its performance in comparison to the standard volume localized SECSY experiment, employing brain metabolite phantoms in a gel. The sequence works in the inhomogeneous, multi-component environment by exploiting the short acquisition time to suppress undesired information by employing an additional rf pulse. A brief description of the pulse sequence, its theory, and simulations are also included, besides experimental benchmarking on two brain metabolite phantoms in gel phase. © 2013 Elsevier Inc. All rights reserved.

Journal of Magnetic Resonance

Volume localized spin echo correlation spectroscopy with suppression of 'diagonal' peaks

The Journal of Physical Chemistry B

DNP-Enhanced MAS NMR of Bovine Serum Albumin Sediments and Solutions

Angewandte Chemie

Towards Structure Determination of Self-Assembled Peptides Using Dynamic Nuclear Polarization Enhanced Solid-State NMR Spectroscopy

Angewandte Chemie International Edition

Physical Chemistry Chemical Physics

Liquid state DNP of water at 9.2 T: an experimental access to saturation

Chemical-shift-resolved 19FNMR spectroscopy between 13.5 and 135MHz: Overhauser-DNP-enhanced diagonal suppressed correlation spectroscopy

Journal	Data powered by TypesetAngewandte Chemie - International Edition
Publisher	Data powered by TypesetWiley-VCH Verlag
ISSN	14337851
Open Access	No