The effects of nuclear signal quenching induced by the presence of a paramagnetic polarizing agent are documented for conditions used in magic angle spinning (MAS)-dynamic nuclear polarization (DNP) experiments on homogeneous solutions. In particular, we present a detailed analysis of three time constants: (1) the longitudinal build-up time constant TB for 1H; (2) the rotating frame relaxation time constant T1? for 1H and 13C and (3) T2 of 13C, the transverse relaxation time constant in the laboratory frame. These relaxation times were measured during microwave irradiation at a magnetic field of 5 T (140 GHz) as a function of the concentration of four polarizing agents: TOTAPOL, 4-amino-TEMPO, trityl (OX063), and Gd-DOTA and are compared to those obtained for a sample lacking paramagnetic doping. We also report the EPR relaxation time constants T1S and T2S, the DNP enhancements, ?, and the parameter E, defined below, which measures the sensitivity enhancement for the four polarizing agents as a function of the electron concentration. We observe substantial intensity losses (paramagnetic quenching) with all of the polarizing agents due to broadening mechanisms and cross relaxation during MAS. In particular, the monoradical trityl and biradical TOTAPOL induce ~40 and 50% loss of signal intensity. In contrast there is little suppression of signal intensity in static samples containing these paramagnetic species. Despite the losses due to quenching, we find that all of the polarizing agents provide substantial gains in signal intensity, and in particular that the net enhancement is optimal for biradicals that operate with the cross effect. We discuss the possibility that much of this polarization loss can be regained with the development of instrumentation and methods to perform electron decoupling.
Level anti-crossings in ParaHydrogen Induced Polarization experiments with Cs-symmetric molecules
From The DNP-NMR Blog:
Level anti-crossings in ParaHydrogen Induced Polarization experiments with Cs-symmetric molecules
Buljubasich, L., et al., Level anti-crossings in ParaHydrogen Induced Polarization experiments with Cs-symmetric molecules. J Magn Reson, 2012. 219(0): p. 33-40.
http://www.ncbi.nlm.nih.gov/pubmed/22595295
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11-21-2013 01:14 AM
Population transfer for signal enhancement in pulsed EPR experiments on half integer high spin systems
From The DNP-NMR Blog:
Population transfer for signal enhancement in pulsed EPR experiments on half integer high spin systems
Kaminker, I., et al., Population transfer for signal enhancement in pulsed EPR experiments on half integer high spin systems. Phys Chem Chem Phys, 2009. 11(31): p. 6799-806.
http://www.ncbi.nlm.nih.gov/pubmed/19639154
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09-23-2013 09:41 PM
Low concentration of a Gd-chelate increases the signal-to-noise ratio in fast pulsing BEST experiments
Low concentration of a Gd-chelate increases the signal-to-noise ratio in fast pulsing BEST experiments
Publication year: 2012
Source:Journal of Magnetic Resonance</br>
Nathalie Sibille, Gaëtan Bellot, Jing Wang, Hélène Déméné</br>
Despite numerous developments in the past few years that aim to increase the sensitivity of NMR multidimensional experiments, NMR spectroscopy still suffers from intrinsic low sensitivity. In this report, we show that the combination of two developments in the field, the Band-selective Excitation Short-Transient (BEST) experiment and the...
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08-08-2012 07:16 PM
Covariance spectroscopy with a non-uniform and consecutive acquisition scheme for signal enhancement of the NMR experiments
Covariance spectroscopy with a non-uniform and consecutive acquisition scheme for signal enhancement of the NMR experiments
Publication year: 2012
Source:Journal of Magnetic Resonance</br>
Yixuan Li, Qiang Wang, Zhengfeng Zhang, Jun Yang, Bingwen Hu, Qun Chen, Isao Noda, Feng Deng</br>
Two-dimensional covariance (COV2D) spectroscopy with non-uniform and consecutive acquisition (NUCA) scheme is introduced. This NUCA-COV2D method allows the number of t1 points to be reduced by a factor of 1.5~3 without any broadening of the linewidth. Furthermore, the...
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03-09-2012 09:16 AM
Covariance spectroscopy with a non-uniform and consecutive acquisition scheme for signal enhancement of the NMR experiments
Covariance spectroscopy with a non-uniform and consecutive acquisition scheme for signal enhancement of the NMR experiments
Publication year: 2012
Source: Journal of Magnetic Resonance, Available online 6 March 2012</br>
Yixuan*Li, Qiang*Wang, Zhengfeng*Zhang, Jun*Yang, Bingwen*Hu, ...</br>
Two-dimensional covariance (COV2D) spectroscopy with non-uniform and consecutive acquisition (NUCA) scheme is introduced. This NUCA-COV2D method allows the number of t1points to be reduced by a factor of 1.5~3 without any broadening of the linewidth. Furthermore, the signal-to-noise ratio (S/N) can...
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03-08-2012 08:46 AM
Signal enhancement for the sensitivity-limited solid state NMR experiments using a continuous, non-uniform acquisition scheme.
Signal enhancement for the sensitivity-limited solid state NMR experiments using a continuous, non-uniform acquisition scheme.
Signal enhancement for the sensitivity-limited solid state NMR experiments using a continuous, non-uniform acquisition scheme.
J Magn Reson. 2011 Aug 30;
Authors: Qiang W
Abstract
We describe a sampling scheme for the two-dimensional (2D) solid state NMR experiments, which can be readily applied to the sensitivity-limited samples. The sampling scheme utilizes continuous, non-uniform sampling profile for the...
5D 13C-detected experiments for backbone assignment of unstructured proteins with a very low signal dispersion
5D 13C-detected experiments for backbone assignment of unstructured proteins with a very low signal dispersion
Abstract Two novel 5D NMR experiments (CACONCACO, NCOCANCO) for backbone assignment of disordered proteins are presented. The pulse sequences exploit relaxation properties of the unstructured proteins and combine the advantages of 13C-direct detection, non-uniform sampling, and longitudinal relaxation optimization to maximize the achievable resolution and minimize the experimental time. The pulse sequences were successfully tested on the sample of partially disordered delta...
Paramagnet Induced Signal Quenching in MAS-DNP Experiments in Homogeneous Solutions
Linear Mode
