scholarly journals The Heteronuclear Multiple-Quantum Correlation Experiment: Perspective from Classical Vectors, Nonclassical Vectors, and Product Operators

2016 ◽  
Vol 2016 ◽  
pp. 1-9
Author(s):  
Karen de la Vega-Hernández ◽  
Manuel Antuch
Keyword(s):  
Quantum Correlation ◽  
Quantum Coherence ◽  
Pulse Sequence ◽  
Building Blocks ◽  
2D Nmr ◽  
Vector Model ◽  
Comparative Approach ◽  
Multiple Quantum ◽  
Spin Evolution ◽  
Starting Point

It is usually accepted that most 2D-NMR experiments cannot be approached using classical models. Instructors argue that Product Operators (PO) or density matrix formalisms are the only alternative to get insights into complex spin evolution for experiments involving Multiple-Quantum Coherence, such as the Heteronuclear Multiple-Quantum Correlation (HMQC) technique. Nevertheless, in recent years, several contributions have been published to provide vectorial descriptions for the HMQC taking PO formalism as the starting point. In this work we provide a graphical representation of the HMQC experiment, taking the basic elements of Bloch’s vector model as building blocks. This description bears an intuitive and comfortable understanding of spin evolution during the pulse sequence, for those who are novice in 2D-NMR. Finally, this classical vectorial depiction is tested against the PO formalism and nonclassical vectors, conveying the didactic advantage of shedding light on a single phenomenon from different perspectives. This comparative approach could be useful to introduce PO and nonclassical vectors for advanced upper-division undergraduate and graduate education.

scholarly journals t1-Noise eliminated dipolar heteronuclear multiple-quantum coherence solid-state NMR spectroscopy

2020 ◽  
Vol 22 (36) ◽  
pp. 20815-20828 ◽  
Author(s):  
Amrit Venkatesh ◽  
Xuechen Luan ◽  
Frédéric A. Perras ◽  
Ivan Hung ◽  
Wenyu Huang ◽  
...  
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Quantum Correlation ◽  
Quantum Coherence ◽  
Pulse Sequences ◽  
Multiple Quantum ◽  
Heteronuclear Correlation ◽  
Heteronuclear Multiple Quantum Coherence ◽  
Multiple Quantum Coherence ◽  
Nuclear Magnetic Resonance Pulse

t1-Noise eliminated (TONE) heteronuclear multiple quantum correlation (HMQC) solid-state nuclear magnetic resonance pulse sequences improve the sensitivity of 2D 1H{X} heteronuclear correlation experiments with X = 17O, 25Mg, 27Al and 35Cl.

scholarly journals One New Royleanumoate fromTeucrium royleanumWall. ex Benth

2014 ◽  
Vol 2014 ◽  
pp. 1-3
Author(s):  
Shabir Ahmad ◽  
Riaz Ullah ◽  
Naser M. AbdElsalam ◽  
Hassan Fouad ◽  
Ahtaram Bibi ◽  
...  
Keyword(s):  
Structure Elucidation ◽  
Quantum Coherence ◽  
Multiple Bond ◽  
2D Nmr ◽  
Correlation Spectroscopy ◽  
Multiple Quantum ◽  
Heteronuclear Multiple Bond Correlation ◽  
Heteronuclear Multiple Quantum Coherence ◽  
Nmr Techniques ◽  
Multiple Quantum Coherence

One new royleanumoate, a benzene ester (1), has been isolated fromT. royleanumWall. ex Benth along with two known compounds, namely, 3,4-dihydroxymethyl benzoate (2) and oleanolic acid (3). The structure elucidation of the isolated compounds was established on two-dimensional (2D) NMR techniques including heteronuclear multiple bond correlation (HMBC), heteronuclear multiple quantum Coherence (HMQC), and correlation spectroscopy (COSY) experiment.

scholarly journals t1-Noise Eliminated Dipolar Heteronuclear Multiple-Quantum Coherence Solid-State NMR Spectroscopy

2020 ◽  
Author(s):  
Amrit Venkatesh ◽  
Xuechen Luan ◽  
Frédéric Perras ◽  
Ivan Hung ◽  
Wenyu Huang ◽  
...  
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Quantum Coherence ◽  
Pulse Sequence ◽  
Signal Amplitude ◽  
Spatial Proximity ◽  
Multiple Quantum ◽  
Heteronuclear Multiple Quantum Coherence ◽  
Frequency Fluctuations ◽  
Multiple Quantum Coherence

<p>Heteronuclear correlation (HETCOR) spectroscopy is one of the key tools in the arsenal of the solid-state NMR spectroscopist to probe spatial proximity between two different nuclei and enhance spectral resolution. Dipolar heteronuclear multiple-quantum coherence (D-HMQC) is a powerful technique that can be potentially utilized to obtain <sup>1</sup>H detected 2D HETCOR solid-state NMR spectra of any NMR active nucleus. A long-standing problem in <sup>1</sup>H detected D-HMQC solid-state NMR experiments is the presence of <i>t</i><sub>1</sub>-noise which reduces sensitivity and impedes spectral interpretation. In this contribution, we describe novel pulse sequences, termed <i>t</i><sub>1</sub>-noise eliminated (TONE) D-HMQC, that suppress <i>t</i><sub>1</sub>-noise and can provide higher sensitivity and resolution than conventional D-HMQC. Monte-Carlo and numerical simulations confirm that <i>t</i><sub>1</sub>-noise in conventional D-HMQC primarily occurs because random MAS frequency fluctuations cause variations in the NMR signal amplitude from scan to scan, leading to imperfect cancellation of uncorrelated signals by phase cycling. The TONE D-HMQC sequence uses <sup>1</sup>H p-pulses to refocus the evolution of <sup>1</sup>H CSA across each recoupling block, improving the stability of the pulse sequence to random MAS frequency fluctuations. The <sup>1</sup>H refocusing pulses also restore the orthogonality of in-phase and anti-phase magnetization for all crystallite orientations, enabling the use of 90° flip-back or LG spin-lock trim pulses to reduce the intensity of uncorrelated signals. We demonstrate the application of these methods to acquire detected 2D <sup>1</sup>H-<sup>35</sup>Cl and <sup>1</sup>H-<sup>13</sup>C HETCOR spectra of histidine•HCl•H<sub>2</sub>O with reduced <i>t</i><sub>1</sub>-noise. To show generality, we also apply these methods to obtain 2D <sup>1</sup>H-<sup>17</sup>O spectra of 20%-<sup>17</sup>O fmoc-alanine and for the first time at natural abundance, 2D <sup>1</sup>H-<sup>25</sup>Mg HETCOR spectra of magnesium hydroxide. The TONE D-HMQC sequences are also used to probe <sup>1</sup>H-<sup>25</sup>Mg and <sup>1</sup>H-<sup>27</sup>Al proximities in Mg-Al layered double hydroxides and confirm the even mixing of Mg and Al in these materials.</p>

scholarly journals t1-Noise Eliminated Dipolar Heteronuclear Multiple-Quantum Coherence Solid-State NMR Spectroscopy

2020 ◽  
Author(s):  
Amrit Venkatesh ◽  
Xuechen Luan ◽  
Frédéric Perras ◽  
Ivan Hung ◽  
Wenyu Huang ◽  
...  
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Quantum Coherence ◽  
Pulse Sequence ◽  
Signal Amplitude ◽  
Spatial Proximity ◽  
Multiple Quantum ◽  
Heteronuclear Multiple Quantum Coherence ◽  
Frequency Fluctuations ◽  
Multiple Quantum Coherence

<p>Heteronuclear correlation (HETCOR) spectroscopy is one of the key tools in the arsenal of the solid-state NMR spectroscopist to probe spatial proximity between two different nuclei and enhance spectral resolution. Dipolar heteronuclear multiple-quantum coherence (D-HMQC) is a powerful technique that can be potentially utilized to obtain <sup>1</sup>H detected 2D HETCOR solid-state NMR spectra of any NMR active nucleus. A long-standing problem in <sup>1</sup>H detected D-HMQC solid-state NMR experiments is the presence of <i>t</i><sub>1</sub>-noise which reduces sensitivity and impedes spectral interpretation. In this contribution, we describe novel pulse sequences, termed <i>t</i><sub>1</sub>-noise eliminated (TONE) D-HMQC, that suppress <i>t</i><sub>1</sub>-noise and can provide higher sensitivity and resolution than conventional D-HMQC. Monte-Carlo and numerical simulations confirm that <i>t</i><sub>1</sub>-noise in conventional D-HMQC primarily occurs because random MAS frequency fluctuations cause variations in the NMR signal amplitude from scan to scan, leading to imperfect cancellation of uncorrelated signals by phase cycling. The TONE D-HMQC sequence uses <sup>1</sup>H p-pulses to refocus the evolution of <sup>1</sup>H CSA across each recoupling block, improving the stability of the pulse sequence to random MAS frequency fluctuations. The <sup>1</sup>H refocusing pulses also restore the orthogonality of in-phase and anti-phase magnetization for all crystallite orientations, enabling the use of 90° flip-back or LG spin-lock trim pulses to reduce the intensity of uncorrelated signals. We demonstrate the application of these methods to acquire detected 2D <sup>1</sup>H-<sup>35</sup>Cl and <sup>1</sup>H-<sup>13</sup>C HETCOR spectra of histidine•HCl•H<sub>2</sub>O with reduced <i>t</i><sub>1</sub>-noise. To show generality, we also apply these methods to obtain 2D <sup>1</sup>H-<sup>17</sup>O spectra of 20%-<sup>17</sup>O fmoc-alanine and for the first time at natural abundance, 2D <sup>1</sup>H-<sup>25</sup>Mg HETCOR spectra of magnesium hydroxide. The TONE D-HMQC sequences are also used to probe <sup>1</sup>H-<sup>25</sup>Mg and <sup>1</sup>H-<sup>27</sup>Al proximities in Mg-Al layered double hydroxides and confirm the even mixing of Mg and Al in these materials.</p>

Nepetolide: A New Diterpene from Nepeta suavis

2008 ◽  
Vol 63 (5) ◽  
pp. 591-594 ◽  
Author(s):  
Javid Hussain ◽  
Farman Ullah ◽  
Hidayat Hussain ◽  
Tasleem Hussain ◽  
M. Raza Shah
Keyword(s):  
Structure Elucidation ◽  
Quantum Coherence ◽  
Multiple Bond ◽  
2D Nmr ◽  
Correlation Spectroscopy ◽  
Multiple Quantum ◽  
Heteronuclear Multiple Bond Correlation ◽  
Heteronuclear Multiple Quantum Coherence ◽  
Nmr Techniques ◽  
Multiple Quantum Coherence

A new tricyclic clerodane-type diterpene, nepetolide (1), has been isolated from Nepeta suavis along with three known compounds namely β -sitosterol, stigmasterol, and ursolic acid. The structure elucidation of the isolated compounds was based primarily on two-dimensional (2D)-NMR techniques including correlation spectroscopy (COSY), heteronuclear multiple quantum coherence (HMQC), and heteronuclear multiple bond correlation (HMBC) experiments.

Unusual pyranosyl cembranoid diterpene from Sarcophyton trocheliophorum

2016 ◽  
Vol 71 (12) ◽  
pp. 1211-1217 ◽  
Author(s):  
Mohamed Shaaban ◽  
Mohamed A. Ghani ◽  
Khaled A. Shaaban
Keyword(s):  
Quantum Coherence ◽  
Soft Coral ◽  
High Resolution Mass Spectrometry ◽  
Nuclear Overhauser Effect ◽  
Multiple Bond ◽  
2D Nmr ◽  
Correlation Spectroscopy ◽  
Multiple Quantum ◽  
Chemical Structures ◽  
Sarcophyton Trocheliophorum

Abstract9-Hydroxy-10,11-dehydro-sarcotrocheliol (1), a new pyrane-based cembranoid diterpene, has been isolated along with three other known compounds, namely, sarcotrocheliol acetate (2), (+)-sarcophytol A (3), and (−)-sarcophytonin A (4), from the organic extract of the soft coral Sarcophyton trocheliophorum. The chemical structures of compounds 1–4 were determined on the basis of their 1D and 2D NMR [1H, 13C, 1H–1H correlation spectroscopy, heteronuclear multiple-quantum coherence, heteronuclear multiple-bond correlation, and nuclear Overhauser effect (NOE)] and mass spectra [electron ionization (EI), electrospray ionization, and high resolution mass spectrometry (HRMS)], and by comparison with related structures. The compounds 1–4 showed neither antimicrobial activity against 11 diverse tested microorganisms, nor cytotoxicity against brine shrimp, whereas the soft coral extract showed low cytotoxicity with a mortality rate of 1.7%.

NMR studies on Fraser fir Abies fraseri (Pursh) Poir. lignins

Holzforschung ◽  
2005 ◽  
Vol 59 (5) ◽  
pp. 488-496 ◽  
Author(s):  
Mikhail Yu. Balakshin ◽  
Ewellyn A. Capanema ◽  
Barry Goldfarb ◽  
John Frampton ◽  
John F. Kadla
Keyword(s):  
Quantum Coherence ◽  
Lignin Content ◽  
Lower Amount ◽  
Multiple Quantum ◽  
Normal Wood ◽  
Nmr Studies ◽  
Oh Groups ◽  
Fraser Fir ◽  
Heteronuclear Multiple Quantum Coherence ◽  
Balsam Woolly Adelgid

Abstract The composition of mature, juvenile uninfested and juvenile infested Fraser fir wood (Rotholz) and the structures of lignins isolated from these woods were elucidated to verify differences between juvenile and mature wood and the effect of balsam woolly adelgid (BWA) infestation. Milled wood lignin (MWL) isolated from mature, juvenile and Rotholz wood were comprehensively characterized using heteronuclear multiple quantum coherence (HMQC) and quantitative 13C NMR techniques. The Rotholz wood was found to have ∼13% higher lignin content and more than five-fold the amount of galactans than that of the uninfested wood. Rotholz lignin possesses higher amounts of p-hydroxyphenyl units and aliphatic OH groups and a lower amount of alkyl-O-alkyl linkages and dibenzodioxocin moieties. The degree of condensation of the Rotholz lignin was rather similar to that of normal wood. Only small differences in the structure of mature and juvenile wood components were found.

scholarly journals Structural characteristics of plant cell wall elucidated by solution-state 2D NMR spectroscopy with an optimized procedure

2020 ◽  
Vol 9 (1) ◽  
pp. 650-663
Author(s):  
Wanwan Wang ◽  
Jibao Cai ◽  
Zhenyu Xu ◽  
Yi Zhang ◽  
Fanchao Niu ◽  
...  
Keyword(s):  
Cell Wall ◽  
Quantum Coherence ◽  
Nmr Spectra ◽  
Plant Cell Wall ◽  
Milling Time ◽  
Structural Characteristics ◽  
2D Nmr ◽  
2D Nmr Spectroscopy ◽  
Complete Representation

AbstractA method was developed for rapid qualitative determination of lignocellulose in the tobacco cell wall by utilizing 2D heteronuclear single quantum coherence NMR spectra (2D HSQC NMR). Traditional methods for analyzing the structure of lignocellulose involve many steps of separation and extraction, which is labor-intensive. In this work, the whole cell wall was milled and dissolved in deuterium solvent. The solvent dimethylsulfoxide (DMSO-d6) containing hexamethylphosphoramide (HMPA-d18) enhanced swelling of the sample and gave high-resolution spectra. The tobacco samples are ball milled at different ball milling times, and the state of the particles is observed through an electron microscope, and then the probability of the particles being less than 5 µm is counted. Through the comparison of the abundance and integration of the peak signals in the spectra under different transmittances, it was determined that when the milling time was 6 h, the quality of the NMR spectra was the best. The optimum conditions of characterizing tobacco structure were DMSO-d6/HMPA-d18 solution and 6 h milling time. Under these conditions, complete representation of the structure of lignocellulose and simplified process could be achieved.

Two-dimensional NMR studies of acrylate copolymers

2009 ◽  
Vol 81 (3) ◽  
pp. 389-415 ◽  
Author(s):  
A. S. Brar ◽  
Ashok Kumar Goyal ◽  
Sunita Hooda
Keyword(s):  
Methyl Methacrylate ◽  
Methyl Acrylate ◽  
Quantum Coherence ◽  
Multiple Bond ◽  
Microstructural Analysis ◽  
2D Nmr ◽  
Correlation Spectroscopy ◽  
Nmr Studies ◽  
Poly Methyl Methacrylate ◽  
Nmr Study

High-resolution NMR spectroscopy is the most versatile, reliable, and generally acceptable technique for the determination of the microstructure of polymers. 2D NMR techniques, along with 1D NMR, have more potential to study absolute configurational assignments and sequence distribution of copolymers. Physical and chemical properties of polymers are influenced fundamentally by their microstructure. We discuss the detailed microstructure analysis of a large number of homopolymers, copolymers, and terpolymers. 2D NMR study of poly(methyl methacrylate) (PMMA), poly(methyl acrylate) (PMA), and poly(methacrylonitrile) (PMAN) is discussed in this article. In addition to homopolymers, 2D heteronuclear single-quantum coherence (HSQC), total correlation spectroscopy (TOCSY), and heteronuclear multiple-bond correlation (HMBC) study of different copolymers such as poly(methyl methacrylate-co-methyl acrylate), poly(styrene-co-methyl methacrylate), and poly(methyl methacrylate-co-methacrylonitrile) have also been reported here. This in turn helps in microstructural analysis of terpolymers such as poly(methacrylonitrile-co-styrene-co-methyl methacrylate), poly(acrylonitrile-co-methyl methacrylate-co-methyl acrylate), and poly(ethylene-co-vinyl acetate-co-carbon monoxide).

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