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1.
Mycoses ; 67(2): e13699, 2024 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-38366288

RESUMEN

BACKGROUND: Superficial mycoses are fungal infections limited to the outermost layers of the skin and its appendages. The chief causative agents of these mycoses are dermatophytes and yeasts. The diagnosis of dermatophytosis can be made by direct mycological examination with potassium hydroxide (10%-30%) of biological material obtained from patients with suspected mycosis, providing results more rapid than fungal cultures, which may take days or weeks. This information, together with clinical history and laboratory diagnosis, ensures that the appropriate treatment is initiated promptly. However, false negative results are obtained in 5%-15%, by conventional methods of diagnosis of dermatophytosis. OBJECTIVES: To study the metabolic profiles of the commonly occurring dermatophytes by NMR spectroscopy. PATIENTS/MATERIALS: We have used 1D and 2D Nuclear Magnetic Resonance (NMR) experiments along with Human Metabolome Database (HMDB) and Chenomx database search for identification of primary metabolites in the methanol extract of two fungal species: Trichophyton mentagrophyte (T. mentagrophyte) and Trichophyton rubrum (T. rubrum). Both standard strains and representative number of clinical isolates of these two species were investigated. Further, metabolic profiles obtained were analysed using multivariate analysis. RESULTS: We have identified 23 metabolites in the T. mentagrophyte and another 23 metabolites in T. rubrum. Many important metabolites like trehalose, proline, mannitol, acetate, GABA and several other amino acids were detected, which provide the necessary components for fungal growth and metabolism. Altered metabolites were defined between Trichophyton mentagrophyte and T. rubrum strains. CONCLUSION: We have detected many metabolites in the two fungal species T. mentagrophyte and T. rubrum by using NMR spectroscopy. NMR spectroscopy provides a holistic snapshot of the metabolome of an organism. Key metabolic differences were identified between the two fungal strains. We need to perform more studies on metabolite profiling of the samples from these species for their rapid diagnosis and prompt treatment.


Asunto(s)
Arthrodermataceae , Dermatomicosis , Tiña , Humanos , Trichophyton , Dermatomicosis/microbiología , Tiña/diagnóstico , Tiña/microbiología , Espectroscopía de Resonancia Magnética
2.
Metab Brain Dis ; 37(3): 773-785, 2022 03.
Artículo en Inglés | MEDLINE | ID: mdl-35029797

RESUMEN

We report the potential role of 1H Nuclear Magnetic Resonance (NMR) based metabolomics in tuberculous meningitis (TBM). We also correlate the significant metabolites with clinical-radiological parameters. Forty-three patients with TBM were included, and their severity of meningitis was graded as stages I to III, and patients with positive Mycobacterium tuberculosis or its nucleic acid was considered as definite TBM. 1H NMR-based metabolomic study was performed on (CSF) samples, and the significant metabolites compared to healthy controls were identified. Outcome at three months was defined as death, poor and good based on the modified Rankin Scale. These metabolites were compared between definite and probable groups of TBM, and also correlated with MRI findings. About 11 metabolites were found to be significant for distinguishing TBM from the controls. In TBM, lactate, glutamate, alanine, arginine, 2-hydroxyisobutyrate, formate, and cis-aconitate were upregulated, and glucose, fructose, glutamine, and myo-inositol were downregulated compared to the controls. For differentiating TBM from the controls, the AUC of the ROC curve generated using these significant metabolites was 0.99, with a 95% confidence interval from 0.96 to 1, demonstrating that these metabolites were able to classify cases with good sensitivity and specificity. Lactate concentration in CSF correlated with hemoglobin, CSF glucose, and infarction. The outcome did not correlate with metabolomics parameters. NMR-based CSF metabolomics have a potential role in differentiating TBM from the controls.


Asunto(s)
Mycobacterium tuberculosis , Tuberculosis Meníngea , Humanos , Imagen por Resonancia Magnética , Espectroscopía de Resonancia Magnética , Metabolómica , Tuberculosis Meníngea/diagnóstico por imagen , Tuberculosis Meníngea/microbiología
3.
Analyst ; 146(21): 6582-6591, 2021 Oct 25.
Artículo en Inglés | MEDLINE | ID: mdl-34586127

RESUMEN

CDCl3 is the most frequently used solvent for the NMR investigation of organic compounds. Busy chemistry labs need to investigate hundreds of compounds daily. While 1H NMR investigation takes a couple of minutes, recording 13C NMR spectra necessitates hours of signal averaging due to the low abundance and low sensitivity of 13C nuclei. The longer acquisition time for 13C NMR results in a loss of precious spectrometer time in a shared multi-user environment. A regular 5 mm o.d. NMR tube is the most commonly used tube for NMR in organic chemistry labs and is also the cheapest option. We show that for analytes soluble in the CDCl3 solvent using a regular 5 mm o.d. NMR tube, the speed of 13C observation can be enhanced by a factor of two by resorting to a sample preparation method that employs a biphasic system made of H2O or D2O at the top of another layer of CDCl3. By using the biphasic system of two immiscible solvents, the analyte can be concentrated in the CDCl3 layer (within the more sensitive volume of the NMR coil), resulting in the improvement of the signal to noise ratio (SNR) by a factor of up to 1.8 for 13C and 2D 1H-13C HSQC spectra, which results in more than two-fold reduction in the experimental time. 1H NMR and other 2D NMR also get a sensitivity boost. The amount of CDCl3 required for sample preparation can also be reduced by 40% using this biphasic system (CDCl3/H2O). Sample preparation in such an immiscible biphasic system is effortless and straightforward. The performance of such biphasic samples is closer to that of Shigemi tubes and better than that of 3 mm o.d. tubes.


Asunto(s)
Imagen por Resonancia Magnética , Compuestos Orgánicos , Espectroscopía de Resonancia Magnética , Relación Señal-Ruido , Solventes
4.
J Proteome Res ; 19(9): 3668-3679, 2020 09 04.
Artículo en Inglés | MEDLINE | ID: mdl-32660248

RESUMEN

Hepatic encephalopathy (HE) is a debilitating neuropsychiatric complication associated with acute and chronic liver failure. It is characterized by diverse symptoms with variable severity that includes cognitive and motor deficits. The aim of the study is to assess metabolic alterations in the brain and liver using nuclear magnetic resonance (NMR) spectroscopy and subsequent multivariate analyses to characterize metabolic signatures associated with HE. HE was developed by bile duct ligation (BDL) that resulted in hepatic dysfunctions and cirrhosis as shown by liver function tests. Metabolic profiles from control and BDL rats indicated increased levels of lactate, branched-chain amino acids (BCAAs), glutamate, and choline in the liver, whereas levels of glucose, phenylalanine, and pyridoxine were decreased. In brain, the levels of lactate, acetate, succinate, citrate, and malate were increased, while glucose, creatine, isoleucine, leucine, and proline levels were decreased. Furthermore, neurotransmitters such as glutamate and GABA were increased, whereas choline and myo-inositol were decreased. The alterations in neurotransmitter levels resulted in cognitive and motor defects in BDL rats. A significant correlation was found among alterations in NAA/choline, choline/creatine, and NAA/creatine with behavioral deficits. Thus, the data suggests impairment in metabolic pathways such as the tricarboxylic acid (TCA) cycle, glycolysis, and ketogenesis in the liver and brain of animals with HE. The study highlights that metabolic signatures could be potential markers to monitor HE progression and to assess therapeutic interventions.


Asunto(s)
Encefalopatía Hepática , Animales , Encéfalo/diagnóstico por imagen , Encefalopatía Hepática/etiología , Espectroscopía de Resonancia Magnética , Espectroscopía de Protones por Resonancia Magnética , Ratas
5.
Magn Reson Chem ; 57(6): 304-316, 2019 06.
Artículo en Inglés | MEDLINE | ID: mdl-30762898

RESUMEN

NMR is a fast method for obtaining a holistic snapshot of the metabolome and also offers quantitative information without separating the compounds present in a complex mixture. Identification of the metabolites present in a plant extract sample is a crucial step for all plant metabolomics studies. In the present work, we used various two dimensional (2D) NMR methods such as J-resolved NMR, total correlation spectroscopy (TOCSY), and heteronuclear single quantum coherence sensitivity enhanced NMR spectroscopy for the identification of 36 common metabolites present in Coriandrum sativum L. seed extract. The identified metabolites belong to the following classes: organic acids, amino acids, and carbohydrates. 1 H NMR spectra of such complex mixtures in general display tremendous signal overlap due to the presence of a large number of metabolites with closely resonating multiplet signals. This signal overlapping leads to ambiguity in an assignment, and hence, identification of metabolites becomes tedious or impossible in many cases. Therefore, the utility of pure-shift proton spectrum along the indirect (F1 ) dimension of the F1 -PSYCHE-TOCSY spectrum is demonstrated for overcoming ambiguity in assignment of metabolites in crowded spectral regions from Coriandrum sativum L. seed extract sample. Because pure-shift NMR methods yield ultrahigh resolution spectrum (i.e., a singlet peak per chemical site) along one or more dimensions, such spectra provide better identification of metabolites compared with regular 2D TOCSY where signal overlap and peak distortions lead to ambiguity in the assignment. Nine metabolites were unambiguously assigned by pure-shift F1 -PSYCHE-TOCSY spectrum, which was unresolved in regular TOCSY spectrum.


Asunto(s)
Coriandrum/química , Espectroscopía de Resonancia Magnética/métodos , Metaboloma , Extractos Vegetales/química , Semillas/química , Coriandrum/metabolismo , Semillas/metabolismo
6.
Biochim Biophys Acta Gen Subj ; 1862(3): 485-494, 2018 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-29107813

RESUMEN

We report, based on biophysical studies and molecular mechanical calculations that curcumin binds DNA hairpin in the minor groove adjacent to the loop region forming a stable complex. UV-Vis and fluorescence spectroscopy indicated interaction of curcumin with DNA hairpin. In this novel binding motif, two É£ H of curcumin heptadiene chain are closely positioned to the A16-H8 and A17-H8, while G12-H8 is located in the close proximity of curcumin α H. Molecular dynamics (MD) simulations suggest, the complex is stabilized by noncovalent forces including; π-π stacking, H-bonding and hydrophobic interactions. Nuclear magnetic resonance (NMR) spectroscopy in combination with molecular dynamics simulations indicated curcumin is bound in the minor groove, while circular dichroism (CD) spectra suggested minute enhancement in base stacking and a little change in DNA helicity, without significant conformational change of DNA hairpin structure. The DNA:curcumin complex formed with FdU nucleotides rather than Thymidine, demonstrated enhanced cytotoxicity towards oral cancer cells relative to the only FdU substituted hairpin. Fluorescence co-localization demonstrated stability of the complex in biologically relevant conditions, including its cellular uptake. Acridine orange/EtBr staining further confirmed the enhanced cytotoxic effects of the complex, suggesting apoptosis as mode of cell death. Thus, curcumin can be noncovalently complexed to small DNA hairpin for cellular delivery and the complex showed increased cytotoxicity in combination with FdU nucleotides, demonstrating its potential for advanced cancer therapy.


Asunto(s)
Anticarcinógenos/farmacología , Antineoplásicos Fitogénicos/farmacología , Curcumina/farmacología , ADN/efectos de los fármacos , Floxuridina/farmacología , Anticarcinógenos/química , Antineoplásicos Fitogénicos/química , Apoptosis/efectos de los fármacos , Línea Celular Tumoral , Dicroismo Circular , Curcumina/química , Sinergismo Farmacológico , Floxuridina/metabolismo , Humanos , Modelos Moleculares , Simulación de Dinámica Molecular , Resonancia Magnética Nuclear Biomolecular , Conformación de Ácido Nucleico/efectos de los fármacos , Espectrometría de Fluorescencia , Espectrofotometría Ultravioleta
7.
Magn Reson Chem ; 56(10): 876-892, 2018 10.
Artículo en Inglés | MEDLINE | ID: mdl-29411898

RESUMEN

Enantiodiscrimination and their quantification using nuclear magnetic resonance (NMR) spectroscopy has always been a subject of great interest. Proton is the nucleus of choice for enantiodiscrimination due to its high sensitivity and ubiquitous presence in nature. Despite its advantages, enantiodiscrimination suffers from extensive signal splitting by the proton-proton scalar couplings, which give complex multiplets that spread over a frequency range of some tens of hertz. These multiplets often overlap, further complicating interpretation of the spectra and quantifications. In the present review, we discuss some of the recent developments in the pure shift 1 H NMR based methods for enantiomer resolution and enantiodiscrimination. We also compare various pure shift methods used for enantiodiscrimination and measurement of enantiomeric excess, considering the fact that conventional 1 H NMR fails to provide any detailed insight.

8.
NMR Biomed ; 30(10)2017 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-28759166

RESUMEN

Traumatic brain injury (TBI) has been shown to affect hippocampus-associated learning, memory and higher cognitive functions, which may be a consequence of metabolic alterations. Hippocampus-associated disorders may vary depending on the severity of injury [mild TBI (miTBI) and moderate TBI (moTBI)] and time since injury. The underlying hippocampal metabolic irregularities may provide an insight into the pathological process following TBI. In this study, in vivo and in vitro proton magnetic resonance spectroscopy (1 H-MRS) data were acquired from the hippocampus region of controls and TBI groups (miTBI and moTBI) at D0 (pre-injury), 4 h, Day 1 and Day 5 post-injury (PI). In vitro MRS results indicated trauma-induced changes in both miTBI and moTBI; however, in vivo MRS showed metabolic alterations in moTBI only. miTBI and moTBI showed elevated levels of osmolytes indicating injury-induced edema. Altered levels of citric acid cycle intermediates, glutamine/glutamate and amino acid metabolism indicated injury-induced aberrant bioenergetics, excitotoxicity and oxidative stress. An overall similar pattern of pathological process was observed in both miTBI and moTBI, with the distinction of depleted N-acetylaspartate levels (indicating neuronal loss) at 4 h and Day 1 and enhanced lactate production (indicating heightened energy depletion leading to the commencement of the anaerobic pathway) at Day 5 in moTBI. To the best of our knowledge, this is the first study to investigate the hippocampus metabolic profile in miTBI and moTBI simultaneously using in vivo and in vitro MRS.


Asunto(s)
Lesiones Traumáticas del Encéfalo/metabolismo , Hipocampo/metabolismo , Metaboloma , Animales , Análisis Discriminante , Hipocampo/patología , Análisis de los Mínimos Cuadrados , Espectroscopía de Resonancia Magnética , Masculino , Redes y Vías Metabólicas , Análisis de Componente Principal , Espectroscopía de Protones por Resonancia Magnética , Ratas Sprague-Dawley
9.
Chemphyschem ; 18(21): 3076-3082, 2017 Nov 03.
Artículo en Inglés | MEDLINE | ID: mdl-28833930

RESUMEN

A diagonal suppressed F1 decoupled total correlation spectroscopy(TOCSY) experiment is developed for analyses of complex mixtures. In 2D homonuclear correlation, assignment of the cross peaks is crucial for structure elucidation. However, when cross peaks are close to the diagonal peaks in overcrowded spectral regions, their assignment becomes tedious. In complex mixtures, the presence of multiple spectra along with broad and complex proton multiplets owing to homonuclear scalar couplings degrade the resolution to the extent that assignment of various cross peaks becomes tedious or impossible. Herein, a diagonal suppressed total correlation technique with F1 decoupling is presented to improve the resolution of the cross peaks. The resolution of the cross peaks is improved by both diagonal suppression as well as the collapse of the multiplets to singlets. Application of the method to a few mixtures of organic compounds reveals better identification of the cross peaks relative to other TOCSY variants.

10.
Magn Reson Chem ; 55(6): 553-558, 2017 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-27813168

RESUMEN

The small chemical shift dispersion and complex multiplicity pattern in proton NMR limit quantifications, for instance the determination of enantiomeric excess (ee) for an enantiomeric mixture. Herein, we present a simple proton-proton correlation experiment with band selective homonuclear (BASH) decoupling in both F1 and F2 dimensions, for the removal of scalar and residual dipolar couplings to provide collapsed singlet for each chemical site. The method has been demonstrated to separate the severely overlapped spectra of enantiomers using both chiral isotropic and anisotropic phases as well as a small biomolecule, particularly for the diastereotopic protons and also for the determination of ee. Copyright © 2016 John Wiley & Sons, Ltd.

11.
Chemphyschem ; 16(12): 2687-91, 2015 Aug 24.
Artículo en Inglés | MEDLINE | ID: mdl-26175136

RESUMEN

Real-time band-selective homonuclear (1) H decoupling during data acquisition of z-filtered J-resolved spectroscopy produces (1) H-decoupled (1) H NMR spectra and leads to sensitivity enhancement and improved resolution, and thus aids the measurement of J couplings and residual dipolar couplings in crowded regions of (1) H NMR spectrum. High quality spectra from peptides, organic molecules, and also from enantiomers dissolved in weakly aligned chiral media are reported.


Asunto(s)
Protones , Análisis Espectral/métodos
12.
Biophys Chem ; 313: 107306, 2024 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-39121649

RESUMEN

D-penicillamine (PA) is the primary chelator of choice to treat Wilson disease (WD). There are limitations in obtaining comprehensive data on PA metabolites in biological specimens by conventional approaches. Hence, the aim of the present was to identify the major hepatic PA metabolites and draw clear conclusions of the drug's xenobiotic in WD. Urine samples were collected from children with hepatic WD (n = 63, aged 14.8 ± 4 years) 5 h after PA administration (16.3 ± 3.8 mg/kg/day) and age-matched healthy volunteers comprised as controls (n = 30). High-resolution 800 MHz nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry was applied to reveal unambiguous appraisals of different excretory by-products of PA metabolism. Four new products comprising penicillamine disulphide (PD), penicillamine cysteine disulphide (PCD), S-methyl penicillamine (SMP), and N-acetyl penicillamine (NAP) of PA xenobiotic metabolites were identified using high-resolution NMR spectroscopy. Quantitative levels of PCD and SMP were approximately three-fold higher than those of PD and NAP, respectively. High-resolution NMR identifies the major PA metabolites with certainty. Reduction, sulfation, and methylation are the predominant pathways of PA metabolism. There is a potential application for assessing therapeutic monitoring of chelation in hepatic WD.


Asunto(s)
Degeneración Hepatolenticular , Penicilamina , Xenobióticos , Penicilamina/química , Penicilamina/uso terapéutico , Degeneración Hepatolenticular/tratamiento farmacológico , Degeneración Hepatolenticular/metabolismo , Humanos , Adolescente , Niño , Xenobióticos/metabolismo , Masculino , Femenino , Espectroscopía de Resonancia Magnética , Quelantes/química , Hígado/metabolismo , Hígado/efectos de los fármacos
13.
J Magn Reson ; 342: 107267, 2022 09.
Artículo en Inglés | MEDLINE | ID: mdl-35853368

RESUMEN

Limited chemical shift dispersion and broad multiplet patterns limit resolution in 1H NMR spectra. J-Resolved spectroscopy overcomes this problem to a great extent. However, the phase-twist line shape in J-Resolved spectroscopy allows only the magnitude mode of the experiment to be practical, which degrades resolution. Recently, various pure shift or broadband homonuclear decoupling approaches have been integrated with J-Resolved spectroscopy to eliminate the broad dispersive contribution. In the present work, we demonstrate a broadband 1H-1H J-Resolved spectrum with a greatly reduced dispersive contribution using the concept of slice selection. We show that slice selective excitation, t1 encoding, storage, and detection of the in-phase absorptive signals can be executed, while a gradient-based suppression of the dispersive antiphase signals can be performed during the storage period. In more than two spin systems, a small part of the doubly antiphase absorptive signal may also contribute to the spectrum in addition to the inphase absorptive signals. The overall effect is a reduced multiplet pattern similar to a regular J-Resolved case as the passive spins remain unflipped due to slice selective pulses. However, the effect is broadband for a fraction of the spins when all slices are considered analogous to Zangger-Sterk (ZS) broadband homo-decoupling. Further, the fresh magnetization from neighboring slices can be accessed in different scans by frequency shifting of the slice selective pulses without a recycle delay-an elegant aspect of the ZS pulse element. This allows faster signal averaging, improving sensitivity which depends on the T1 relaxation time of the signals. This method displays sensitivity up to 4-20 percent of the regular J-RES 1H signals.


Asunto(s)
Espectroscopía de Resonancia Magnética , Espectroscopía de Resonancia Magnética/métodos
14.
Chemphyschem ; 11(15): 3343-54, 2010 Oct 25.
Artículo en Inglés | MEDLINE | ID: mdl-20938997

RESUMEN

In a preliminary communication (B. Baishya, T. F. Segawa, G. Bodenhausen, J. Am. Chem. Soc. 2009, 131, 17538-17539), we recently demonstrated that it is possible to obtain clean echo decays of protons in biomolecules despite the presence of homonuclear scalar couplings. These unmodulated decays allow one to determine apparent transverse relaxation rates R(2) (app) of individual protons. Herein, we report the observation of R(2) (app) for three methyl protons, four amide H(N) protons, and all 11 backbone H(α) protons in cyclosporin A. If the proton resonances overlap, their R(2) (app) rates can be measured by transferring their magnetization to neighboring (13)C nuclei, which are less prone to overlap. The R(2) (app) rates of protons attached to (13)C are faster than those attached to (12)C because of (13)C-(1)H dipolar interactions. The differences of these rates allow the determination of local correlation functions. Backbone H(N) and H(α) protons that have fast decay rates R(2) (app) also feature fast longitudinal relaxation rates R(1) and intense NOESY cross peaks that are typical of crowded environments. Variations of R(2) (app) rates of backbone H(α) protons in similar amino acids reflect differences in local environments.


Asunto(s)
Protones , Isótopos de Carbono/química , Ciclosporina/química , Espectroscopía de Resonancia Magnética , Péptidos/química
15.
J Magn Reson ; 311: 106684, 2020 02.
Artículo en Inglés | MEDLINE | ID: mdl-31931343

RESUMEN

The heteronuclear multiple-quantum coherence in the indirect dimension of the two-dimensional HMQC experiment evolves under the passive 1H-1H J-couplings leading to multiplet structures in the F1 dimension. Besides, 1H-1H J-multiplets appear in the direct dimension as well. Thus, multiplets along both dimensions lower the resolution and sensitivity of this technique, when high resolution is required along both dimensions. An efficient broadband homodecoupling scheme along the F1 dimension of the HMQC experiment has not been realized to date. We have implemented broadband homonuclear decoupling using bilinear rotation decoupling (BIRD) by adding a 1H SQ evolution period followed by BIRD before the 1H-13C multiple-quantum evolution period in the HMQC. In the direct time domain, BIRD is implemented using a real-time or single-scan scheme, which further improves resolution and sensitivity of this technique. The resulting pure shift HMQC provides singlet peak per chemical site along F1 as well as F2 axes and, hence, better resolution and sensitivity than conventional HMQC spectrum for all peaks except diastereotopic methylene protons. Due to the incorporation of the BIRD, the indirect time domain becomes double in length compared to the conventional HMQC. However, slow relaxation of small molecules favors better sensitivity for ps-HMQC relative to conventional HMQC under all conditions. We also found that the sensitivity of ps-HMQC is only slightly less than ps-HSQC for small molecules.

16.
J Am Chem Soc ; 131(48): 17538-9, 2009 Dec 09.
Artículo en Inglés | MEDLINE | ID: mdl-19950988

RESUMEN

The modulation of spin echoes by homonuclear scalar couplings render the determination of transverse relaxation rates of individual spins difficult, in particular for molecules that are isotopically enriched in (13)C or (15)N, and for all molecules with scalar-coupled protons. To avoid echo modulations, most studies using refocusing pulses have so far been restricted to isolated (1)H, (13)C, or (15)N spins. We report measurements of apparent (1)H transverse relaxation rates of backbone and side-chain protons in Cyclosporin A (CsA) determined by quenching the echo modulations that arise from homonuclear scalar couplings between protons.

17.
J Magn Reson ; 301: 19-29, 2019 04.
Artículo en Inglés | MEDLINE | ID: mdl-30844690

RESUMEN

Two-dimensional J-RESolved spectroscopy (J-RES) finds routine use in metabolomics for reducing signal overlap as it separates chemical shift and multiplet information along two frequency axes. However, only magnitude mode of the experiment is practical which prevents exploitation of its full resolving power. Tailing from high-intensity metabolite peaks often obscure nearby low-intensity metabolite peaks which leads to ambiguity in assignment of metabolites. Absorptive mode J-RES spectroscopy offers better-resolving power but comes at the cost of either sensitivity or complicated post-processing. Quite often for certain complex mixtures such as bio-fluids some components of the mixture display intense singlet signals which dominate the whole spectrum resulting in less reliable detection of weaker metabolite signals. Multi-frequency presaturation could suppress these intense singlets but will also remove the useful weaker multiplet peaks which are either totally eclipsed with the intense singlets or very close in frequency. We show that by using a double quantum filter (DQF) in magnitude mode J-RES technique, the intensity of the strong singlet metabolite peaks can be reduced relative to the intensity of the sparsely present multiplet metabolite signals. This approach leads to the identification of many weak intensity multiplet peaks which are otherwise undetected due to their overlap with intense singlet peaks in regular J-RES as well as 1D 1H spectra. Although the improved intensity of most of the weaker peaks relative to the strong singlet peaks is observed, some multiplets can disappear due to the delay-dependent modulation of the signals by the DQF. A few DQF J-RES spectra recorded with different DQF delays, therefore, produce better assignment when analyzed together. The technique is demonstrated on a mixture of eight compounds, human urine, and plant extract samples.


Asunto(s)
Mezclas Complejas/química , Resonancia Magnética Nuclear Biomolecular/métodos , Algoritmos , Liofilización , Garcinia/química , Humanos , Metabolismo , Metabolómica , Extractos Vegetales/química , Teoría Cuántica , Orina/química
18.
J Magn Reson ; 192(1): 92-100, 2008 May.
Artículo en Inglés | MEDLINE | ID: mdl-18308598

RESUMEN

In the present work a novel methodology is developed for the unambiguous discrimination of enantiomers aligned in chiral liquid crystalline media and the simultaneous determination of 1H-1H and 13C-1H couplings in a single experiment. An INEPT transfer and back transfer of magnetization to protons retain the 13C edited 1H magnetization which is utilized to generate spin selective homonuclear triple quantum coherence of dipolar coupled methyl protons. Spin selective correlation of triple quantum to single quantum coherence results in spin state selective detection by 13C spin and the remaining passive protons. The difference between the successive transitions in the triple quantum dimension pertains to sum of the passive couplings and results in enhanced resolution by a factor of three. This results in unambiguous chiral visualization. The masked 13C satellite transitions in the single quantum spectrum are extracted for chiral discrimination. The technique retains all the passive homo- and heteronuclear couplings in the triple quantum dimension by the application of non-selective refocusing pulse on 1H as well as on 13C spins. This, however, refocuses the chemical shift evolution in the triple quantum dimension, and also overcomes the problem of field inhomogeneity. The method enables the determination of spectral information which is otherwise not possible to derive from the broad and featureless proton spectra. The elegant experimental technique has been demonstrated on different chiral molecules.

19.
J Magn Reson ; 192(1): 101-11, 2008 May.
Artículo en Inglés | MEDLINE | ID: mdl-18308600

RESUMEN

In general, the proton NMR spectra of chiral molecules aligned in the chiral liquid crystalline media are broad and featureless. The analyses of such intricate NMR spectra and their routine use for spectral discrimination of R and S optical enantiomers are hindered. A method is developed in the present study which involves spin state selective two dimensional correlation of higher quantum coherence to its single quantum coherence of a chemically isolated group of coupled protons. This enables the spin state selective detection of proton single quantum transitions based on the spin states of the passive nuclei. The technique provides the relative signs and magnitudes of the couplings by overcoming the problems of enantiomer discrimination, spectral complexity and poor resolution, permitting the complete analyses of the otherwise broad and featureless spectra. A non-selective 180 degrees pulse in the middle of MQ dimension retains all the remote passive couplings. This accompanied by spin selective MQ-SQ conversion leads to spin state selective coherence transfer. The removal of field inhomogeneity contributes to dramatically enhanced resolution. The difference in the cumulative additive values of chemical shift anisotropies and the passive couplings, between the enantiomers, achieved by detecting Nth quantum coherence of N magnetically equivalent spins provides enhanced separation of enantiomer peaks. The developed methodology has been demonstrated on four different chiral molecules with varied number of interacting spins, each having a chiral centre.

20.
J Magn Reson ; 191(2): 259-66, 2008 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-18226942

RESUMEN

The differential values of NMR spectral parameters like chemical shift anisotropies, dipolar couplings and quadrupolar couplings of enantiomers in chiral liquid crystalline media are employed not only for their visualization but also for their quantification. Large differences in chemical shift anisotropies and the quadrupolar couplings between the enantiomers enable the use of 13C and extensive 2H NMR detection for such a purpose. In spite of high magnetic moment, high sensitivity and abundant presence of protons in all the chiral molecules, 1H detection is not routinely employed due to severe overlap of unresolved transitions arising from short and long distance couplings. Furthermore, the doubling of the spectra from two enantiomers and their indistinguishable overlap due to negligible difference in chemical shift anisotropies hampers their discrimination. The present study demonstrates the use of proton chemical shift anisotropy as an exclusive parameter for such a discrimination. The method employs the non-selective excitation of homonuclear Nth quantum coherence of N coupled protons. The simultaneous flipping of all the coupled spins results in a single transition in the multiple quantum dimension at the cumulative sum of their anisotropic chemical shifts for each enantiomer, with the measurable difference between them, resulting in their complete unraveling.


Asunto(s)
Algoritmos , Anisotropía , Espectroscopía de Resonancia Magnética/métodos , Modelos Químicos , Modelos Moleculares , Protones , Estereoisomerismo , Simulación por Computador
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