Rapid elucidation of chemical shift correlations in complex NMR spectra of organic molecules: Two-dimensional Hadamard pure shift NMR spectroscopy

Kakita, Veera Mohana Rao; Kupče, Ēriks; Jagadeesh, B.; Hosur, Ramakrishna V.

doi:10.1016/j.jmr.2018.06.006

Cited by 6 publications

(12 citation statements)

References 51 publications

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“…Currently, nonconventional NMR strategies have been employed for the assignment of complex molecules and mixtures, such as pure shift-based NMR experiments, in which pulse sequences collapse scalar coupling into singlets resulting in higher resolution NMR spectra. Distinct pure shift pulse sequences, such as TOCSY (total correlated spectroscopy) and HSQC (heteronuclear single quantum coherence spectroscopy) experiments, are effective alternatives for traditional 2D NMR experiments . However, these experiments require careful discernment of pulse sequences because of the sensitivity to misoptimization, and consequently, production of strong coupling artifacts.…”

Section: Results and Discussionmentioning

confidence: 99%

“…Distinct pure shift pulse sequences, such as TOCSY (total correlated spectroscopy) and HSQC (heteronuclear single quantum coherence spectroscopy) experiments, are effective alternatives for traditional 2D NMR experiments. 36 However, these experiments require careful discernment of pulse sequences because of the sensitivity to misoptimization, and consequently, production of strong coupling artifacts. An alternative NMR experiment to improve resolution, with a more robust and simpler NMR protocol, is 2D J-resolved spectroscopy, which separates chemical shifts and couplings.…”

Section: Mw Heating and 1 H Nmr Evaluationmentioning

confidence: 99%

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Introduction Biodiesel Course: Evaluating the Quality of Waste Cooking Oil by ¹H NMR Spectroscopy

Anjos

Silva

2020

J. Chem. Educ.

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Biodiesel is an important biomass, largely employed in the transport sector and produced from vegetable oils. Additionally, waste cooking oils may be reused to produce biodiesel fuel, minimizing environmental pollution. A laboratory experiment that affords a widespread way to discuss degradation concepts and tools for used vegetable oil characterization is presented. Through evaluation of the edible oil composition from distinct origins (oilseeds, heating types, and local community), an analytic evaluation of the composition and byproducts and a discussion about handling and storage of used vegetable oils was completed. For this purpose, nuclear magnetic resonance analysis was employed as an analytical method to access the waste cooking oil profile and explore the advantages of this versatile and practical spectroscopic technique.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Mw Heating and 1 H Nmr Evaluationmentioning

confidence: 99%

Introduction Biodiesel Course: Evaluating the Quality of Waste Cooking Oil by ¹H NMR Spectroscopy

Anjos

Silva

2020

J. Chem. Educ.

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“…Previously, NMR data of its acetyl derivative or NMR data of chemically synthesized cleistanthoside A have been reported. 19−23 The 1 H and 13 C NMR spectra of cleistanthoside A recorded in dimethyl sulfoxide (DMSO)-d 6 displayed duplicated signals for anomeric and aromatic protons and carbons due to hindered rotation. Even at slightly higher and lower temperature (data not shown), only a small change in the intensities of the two sets of signals could be observed.…”

Section: Isolation and Quantification Of Cleistanthoside Amentioning

confidence: 99%

“…One cost-intensive possibility relies on hardware improvements, for example, use of higher magnetic fields, N 2 /He cryo-cooled NMR probes, multi receivers, and so on. A second approach lies in the development of time-saving fast NMR methods such as Hadamard encoding, computer-optimized folding, covariance processing, projection reconstruction, ultrafast NMR spectroscopy, and non-uniform sampling (NUS) with or without the above hardware. − Only recent developments combine different 2D techniques like heteronuclear multiple bond correlation (HMBC), heteronuclear single quantum coherence (HSQC), correlation spectroscopy (COSY), and nuclear Overhauser enhancement spectroscopy (NOESY) in nested super sequences (NOAH-4) to accelerate data collection. , …”

Section: Introductionmentioning

confidence: 99%

Elusive Toxin in Cleistanthus collinus Causing Vasoconstriction and Myocardial Depression: Detailed NMR Analyses and Biological Studies of Cleistanthoside A

et al. 2021

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Cleistanthus collinus leaf extracts are consumed for suicidal purposes in southern India. The boiled decoction is known to be more toxic than the fresh leaf juice. Although several compounds have been isolated and their toxicity tested, controversy remains as to which compounds are responsible for the high level of toxicity of C. collinus. We report herein that cleistanthoside A is the major toxin in the boiled aqueous extract of fresh leaves and causes death in rats in small doses. The toxicity of the boiled extract prepared in the manner described can be attributed entirely to cleistanthoside A. Cleistanthin A could also be isolated from the boiled extract, albeit in trace amounts. As hypotension not responding to vasoconstrictors is the cause of death in patients who have consumed the boiled extract, effects of cleistanthoside A on the determinants of blood pressure, namely, force of cardiac contraction and vascular resistance, were tested in isolated organ experiments. Cleistanthoside A has a direct vasoconstrictor effect; however, it inhibits ventricular contractility. Therefore, the notion that the shock in C. collinus poisoning is of vascular origin must be considered carefully, and the possibility of cardiogenic shock must be studied. We present the crystal structure of cleistanthin A and show the potency of fast NMR methods (NOAH4-BSCN-NUS) in the full spectral assignment of cleistanthoside A as a real-world sample of a natural product. We also compare the results of the NOAH4-BSCN-NUS NMR experiments with conventional NMR methods.

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“…Recently, a two‐dimensional BIRD‐HSQC method has been demonstrated to identify the unambiguous chemical shifts of metabolites, and it provides a very high chemical shift dispersion . Even so, to identify the constituents at very low concentrations, spectra need to be acquired for rather long instrumental times; it is possible, however, to reduce this time by invoking the ideas of non‐uniform sampling schedules and Hadamard schemes along the indirect dimension . BIRD‐HSQC has another limitation that this method cannot decouple the diastereotopic protons.…”

Section: Figurementioning

confidence: 99%

Ultraclean Pure Shift NMR Spectroscopy with Adiabatic Composite Refocusing Pulses: Application to Metabolite Samples

2019

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In Pure shift NMR (pure shift yielded by chirp pulse excitation (PSYCHE)) Sideband Averaging by Periodic PHase Incrementation of Residual J Evolution (SAPPHIRE) has proved to be a very useful technique for obtaining clean high-resolution NMR spectra; SAPPHIRE suppresses homo-decoupling sidebands resulting in high-quality pure shift spectra. As a consequence, it enables circumventing dynamic range problems for complex mixtures having wide range of concentrations of constituents; in conventional PSYCHE spectra, the signals of low concentration constituents may get masked by the sidebands. However, the SAPPHIRE-PSYCHE scheme is very sensitive to pulse/power calibrations and does not perform well for miscalibrations. In this background we propose here an improvement employing adiabatic composite refocusing pulses (ad-SAPPHIRE-PSYCHE) which has enabled us to obtain ultraclean pure shift NMR spectra with high resolution. The resulting improvements with the new scheme have been demonstrated on metabolite samples, honey and peppermint oil, and we believe that this will become routinely usable in commercial environments using autosamplers and with technically not-sowell trained researchers.The recent development of homo-decoupled (pure shift) [1] nuclear magnetic resonance methods, namely, Zangger-Sterk (ZS), [2] bilinear rotational decoupling (BIRD), [3] pure shift yielded by chirp excitation (PSYCHE), [4] band-selective homodecoupling, [5] and several of their variants [6] have proved very useful for simplifying complex NMR spectra. These methods remove homonuclear scalar couplings which results in dramatic improvement in the spectral resolution. The versatility of pure shift NMR methods has been demonstrated in different applications: enantiomeric determination, [7] diastereomeric determination, 8 NOE/ROE measurement, [5b,9] chemical shift assignments, [2b,d,3d,4b,5a] diffusion measurements, [10] scalar coupling determination, [11] and identification of different chem-ical constituents in the mixtures [12] and metabolite samples. [13] Nevertheless, identifying chemical constituents in metabolite mixtures is a rather difficult task due to a number of issues: (i) spectral sensitivity of the pure shift NMR methods is quite poor; (ii) some pulse schemes decouple only -CH and CH 3 protons, and they do not work for the -CH 2 spins; (iii) in most of the cases, homo-decoupling sidebands appear due to improper Jrefocusing, and this renders analysis, especially of constituents at very low concentrations, ambiguous since their signals may get masked by the sidebands (dynamic range problem). Recently, a two-dimensional BIRD-HSQC method has been demonstrated to identify the unambiguous chemical shifts of metabolites, and it provides a very high chemical shift dispersion. [13a] Even so, to identify the constituents at very low concentrations, spectra need to be acquired for rather long instrumental times; it is possible, however, to reduce this time by invoking the ideas of non-uniform sampling schedules [12a] and Hadama...

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Rapid elucidation of chemical shift correlations in complex NMR spectra of organic molecules: Two-dimensional Hadamard pure shift NMR spectroscopy

Cited by 6 publications

References 51 publications

Introduction Biodiesel Course: Evaluating the Quality of Waste Cooking Oil by ¹H NMR Spectroscopy

Introduction Biodiesel Course: Evaluating the Quality of Waste Cooking Oil by ¹H NMR Spectroscopy

Elusive Toxin in Cleistanthus collinus Causing Vasoconstriction and Myocardial Depression: Detailed NMR Analyses and Biological Studies of Cleistanthoside A

Ultraclean Pure Shift NMR Spectroscopy with Adiabatic Composite Refocusing Pulses: Application to Metabolite Samples

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Rapid elucidation of chemical shift correlations in complex NMR spectra of organic molecules: Two-dimensional Hadamard pure shift NMR spectroscopy

Cited by 6 publications

References 51 publications

Introduction Biodiesel Course: Evaluating the Quality of Waste Cooking Oil by 1H NMR Spectroscopy

Introduction Biodiesel Course: Evaluating the Quality of Waste Cooking Oil by 1H NMR Spectroscopy

Elusive Toxin in Cleistanthus collinus Causing Vasoconstriction and Myocardial Depression: Detailed NMR Analyses and Biological Studies of Cleistanthoside A

Ultraclean Pure Shift NMR Spectroscopy with Adiabatic Composite Refocusing Pulses: Application to Metabolite Samples

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Product

Resources

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Introduction Biodiesel Course: Evaluating the Quality of Waste Cooking Oil by ¹H NMR Spectroscopy

Introduction Biodiesel Course: Evaluating the Quality of Waste Cooking Oil by ¹H NMR Spectroscopy