Bibliografias temáticas / Isotopic 13C NMR

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Literatura científica selecionada sobre o tema "Isotopic 13C NMR"

Autor: Grafiati

Publicado: 29 de março de 2025

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Artigos de revistas sobre o assunto "Isotopic 13C NMR"

Kelleway, J. J., S. M. Trevathan-Tackett, J. Baldock e L. P. Critchley. "Plant litter composition and stable isotope signatures vary during decomposition in blue carbon ecosystems". Biogeochemistry 158, n.º 2 (1 de fevereiro de 2022): 147–65. http://dx.doi.org/10.1007/s10533-022-00890-3.

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AbstractThe ratio of isotopes of carbon (13C:12C or δ13C) and nitrogen (15N:14N or δ15N) are common indicators of the flow and storage of organic matter in coastal wetland research. Effective use of these indicators requires quantification and understanding of: (1) the variability of isotope signatures of potential organic matter source materials; and (2) the influence of organic matter decomposition on isotopic signatures. While it is well-established that organic matter characteristics change during the decomposition process, there has been little direct quantification of any concurrent shifts in isotope signatures for coastal detritus. In this study, we addressed this by quantifying: (1) shifts in sample composition using solid-state 13C Nuclear Magnetic Resonance (NMR) spectroscopy; and (2) shifts in δ13C and δ15N signatures of coastal plant tissues from field litterbag experiments. We observed significant shifts in 13C NMR spectra across the course of deployment for all four plant tissues assessed (leaves of mangrove Avicennia marina; branchlets of supratidal tree Casuarina glauca; leaf wrack and roots/rhizomes of the seagrass Zostera muelleri), driven largely by the preferential loss of labile constituents and concentration of more resistant macromolecules, such as lignin and leaf waxes. While there were shifts in isotope ratios for all species, these varied in direction and magnitude among species, tissue type and isotopes. This included δ13C enrichments of up to 3.1‰ and 2.4‰ in leaves of A. marina, and branchlets of C. glauca, respectively, but δ13C depletions of up to 4.0‰ for Z. muelleri. Shifts in δ15N varied among species and tissue types, with few clear temporal patterns. Partial least squares regression analyses showed that some tissue isotope signatures can be reliably predicted on the basis of sample composition (13C NMR spectra), however, multiple inter- and intra-species variations preclude a simple explanation of isotopic signature shifts on the basis of plant-material molecular shifts alone. Further, we cannot preclude the potential influence of microbe-associated organic matter on sample composition or isotopic signatures. Our findings emphasise the importance of considering decomposition effects on stable isotope signatures in blue carbon ecosystems. Isotope approaches will remain a valuable tool in coastal ecosystem research, but require robust experimental approaches (including appropriate use of decomposed end-members or fractionation correction factors; quantification of microbial organic matter) and quantification of decomposition dynamics for specific plant tissues and environmental settings.

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Bagga, Puneet, Kevin L. Behar, Graeme F. Mason, Henk M. De Feyter, Douglas L. Rothman e Anant B. Patel. "Characterization of Cerebral Glutamine Uptake from Blood in the Mouse Brain: Implications for Metabolic Modeling of 13C NMR Data". Journal of Cerebral Blood Flow & Metabolism 34, n.º 10 (30 de julho de 2014): 1666–72. http://dx.doi.org/10.1038/jcbfm.2014.129.

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13C Nuclear Magnetic Resonance (NMR) studies of rodent and human brain using [1-13C]/[1,6-13C2]glucose as labeled substrate have consistently found a lower enrichment (~25% to 30%) of glutamine-C4 compared with glutamate-C4 at isotopic steady state. The source of this isotope dilution has not been established experimentally but may potentially arise either from blood/brain exchange of glutamine or from metabolism of unlabeled substrates in astrocytes, where glutamine synthesis occurs. In this study, the contribution of the former was evaluated ex vivo using 1H-[13C]-NMR spectroscopy together with intravenous infusion of [U-13C5]glutamine for 3, 15, 30, and 60 minutes in mice. 13C labeling of brain glutamine was found to be saturated at plasma glutamine levels > 1.0 mmol/L. Fitting a blood–astrocyte–neuron metabolic model to the 13C enrichment time courses of glutamate and glutamine yielded the value of glutamine influx, VGln(in), 0.036 ± 0.002 μmol/g per minute for plasma glutamine of 1.8 mmol/L. For physiologic plasma glutamine level (~0.6 mmol/L), VGln(in) would be ~0.010 μmol/g per minute, which corresponds to ~6% of the glutamine synthesis rate and rises to ~11% for saturating blood glutamine concentrations. Thus, glutamine influx from blood contributes at most ~20% to the dilution of astroglial glutamine-C4 consistently seen in metabolic studies using [1-13C]glucose.

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Xie, Yimin, Xudong Chen, Kai Zhang, Sheng Cui e Gongxia Zhang. "Elucidation of lignin and polysaccharide linkages in wheat straw by 2H/13C isotopic tracer". BioResources 18, n.º 1 (17 de novembro de 2022): 550–69. http://dx.doi.org/10.15376/biores.18.1.550-569.

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To elucidate chemical linkages between lignin and polysaccharides, the aqueous mixed solutions of coniferin-[α-13C], syringin-[α-13C], D-glucose-[6-2H], and phenylalanine ammonia-lyase inhibitor were injected into a living wheat stalk. Internode tissues with high abundance of 2H-13C were collected. The milled wood lignin, lignin-carbohydrate complex (LCC), and residual LCC (R-LCC) with enrichment of 2H-13C were isolated. The 13C and 2H abundances showed that the lignin and polysaccharides of internode tissues were labeled by 13C and 2H, respectively. Analysis with carbon-13 nuclear magnetic resonance (13C-NMR) showed that ketal and benzyl ether bonds were formed between α-C of lignin and carbohydrates. The R-LCC and LCC were further treated with enzymes to obtain enzymatic degraded R-LCC (ED-R-LCC) and enzymatic degraded LCC (ED-LCC). 13C-NMR spectra of ED-LCC showed that the α-C of lignin side chain was combined with 6-C of carbohydrates by ether, ester, and ketal linkages. 1H-NMR differential spectra of ED-LCCs revealed an LC linkage of benzyl ether bond. Glucan-lignin (En-R-GL) and xylan-lignin (En-R-XL) complexes were separated from ED-R-LCC by ionic liquid. A part of lignin α-C was linked to cellulose 6-C by benzyl ether and α-ketal linkages. 13C-NMR spectra of En-R-XL showed there were α-benzyl ether and α-ketal bonds between lignin and xylan.

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Robinson, Alastair, Peter Richardson e Meghan Halse. "Hyperpolarised 1H–13C Benchtop NMR Spectroscopy". Applied Sciences 9, n.º 6 (20 de março de 2019): 1173. http://dx.doi.org/10.3390/app9061173.

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Benchtop NMR spectrometers with sub-ppm spectral resolution have opened up new opportunities for performing NMR outside of the standard laboratory environment. However, the relatively weak magnetic fields of these devices (1–2 T) results in low sensitivity and significant peak overlap in 1H NMR spectra. Here, we use hyperpolarised 13C{1H} NMR to overcome these challenges. Specifically, we demonstrate the use of the signal amplification by reversible exchange (SABRE) parahydrogen-based hyperpolarisation technique to enhance the sensitivity of natural abundance 1D and 2D 13C{1H} benchtop NMR spectra. We compare two detection methods for SABRE-enhanced 13C NMR and observe an optimal 13C{1H} signal-to-noise ratio (SNR) for a refocused INEPT approach, where hyperpolarisation is transferred from 1H to 13C. In addition, we exemplify SABRE-enhanced 2D 13C benchtop NMR through the acquisition of a 2D HETCOR spectrum of 260 mM of 4-methylpyridine at natural isotopic abundance in a total experiment time of 69 min. In theory, signal averaging for over 300 days would be required to achieve a comparable SNR for a thermally polarised benchtop NMR spectrum acquired of a sample of the same concentration at natural abundance.

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Smith, Alan J. R., Richard York, Dušan Uhrín e Nicholle G. A. Bell. "¹⁹F-centred NMR analysis of mono-fluorinated compounds". RSC Advances 12, n.º 16 (2022): 10062–70. http://dx.doi.org/10.1039/d1ra08046f.

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19F is the focal point of broadband, phase-sensitive 2D NMR experiments that provide 1H, 13C and 19F chemical shifts, values of JHF, JHH, and JFC coupling constants and 13C-induced 19F isotopic shifts to elucidate structures of fluorinated molecules.

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Giraudon, Sylvie, Marc Danzart e Marc H. Merle. "Deuterium Nuclear Magnetic Resonance Spectroscopy and Stable Carbon Isotope Ratio Analysis/Mass Spectrometry of Certain Monofloral Honeys". Journal of AOAC INTERNATIONAL 83, n.º 6 (1 de novembro de 2000): 1401–9. http://dx.doi.org/10.1093/jaoac/83.6.1401.

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Abstract Quantitative deuterium nuclear magnetic resonance spectroscopy (NMR) has been used in conjunction with stable carbon isotope ratio analysis/mass spectrometry to refine the detection of sugars that have been added to monofloral honeys. The 13C content of sugars indicates the type of photosynthetic metabolism of the plant that synthesized them; the deuterium content is more characteristic of secondary metabolism and of environmental factors. Consequently, determination of the 13C content of honeys and of proteins extracted from the honeys can be used to detect the addition of C4 plant sugars (cane or corn), but it does not reveal the addition of C3 plant sugars such as beet sugar. Deuterium NMR gives useful information for some monofloral honeys. NMR measurement is performed on ethanol obtained from fermentation of the honey and extracted by distillation. The isotopic composition of the ethanol indicates the nature of the sugars from which it was derived. Various types of monofloral honeys were studied, and the results obtained with commercially available honeys demonstrate the usefulness of isotopic analysis and the need to compile a database of authentic honeys to validate or affirm certain results.

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Bravin, F., R. Duca, N. Loiseau, M. Pean, O. Puel e M. Delaforge. "Production and use of mycotoxins uniformly enriched with stable isotopes for their dosage in biological samples". World Mycotoxin Journal 1, n.º 3 (1 de agosto de 2008): 275–81. http://dx.doi.org/10.3920/wmj2008.x037.

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Due to their low concentrations in biological matrices, mycotoxin analyses often encounter detection and quantification problems, especially for toxicokinetic studies. We have developed a strategy to produce in a single process, several fungi secondary metabolites uniformly enriched with 13C, 15N stable isotopes in their 'natural' composition. This includes: (1) a plant culture in the presence of 10%, 50% or 100% 13CO2 as the only source of carbon, and in the presence or not of 10% 15N-enriched nitrogen salts – as expected wheat or maize uniformlyincorporate enriched isotopes into their bioproducts; (2) a subsequent solid culture of different filamentous fungi on plant biomass led to the production of a 'natural' mixture of isotopes-enriched mycotoxins – these compounds exhibit a characteristic isotopic cluster, which can be easily detected by mass spectrometry. As an example, we achieved 10% uniformly 13C-enriched zearalenone, deoxynivalenol and mycophenolic acid by growing Fusarium graminearum or Penicillium brevicompactum on 10% 13C enriched wheat seeds and 3 to 10% 13C, 15N uniformly enriched fumonisins from Fusarium verticillioides cultures on maize seeds or straw. These compounds were used for metabolism and transport studies in mammals either in vitro or in vivo and analysed by MS and MSn spectra of the isotopic cluster but also by 13C, 15N NMR. Moreover, such isotopic pattern enrichment can be used for quantitative evaluations of mycotoxins transport across mammalian biological membranes, alone or in their 'natural' conditions in the presence of other fungi secondary metabolites. Finally, we used such enriched compounds with high reliabilityin order to study zearalenone metabolism but these enriched compounds would also be used as internal standards to quantify zearalenone or fumonisins in contaminated food samples.

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Matheron, Christelle, Anne-Marie Delort, Geneviève Gaudet, Evelyne Forano e Tibor Liptaj. "13C and 1H Nuclear Magnetic Resonance Study of Glycogen Futile Cycling in Strains of the Genus Fibrobacter". Applied and Environmental Microbiology 64, n.º 1 (1 de janeiro de 1998): 74–81. http://dx.doi.org/10.1128/aem.64.1.74-81.1998.

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ABSTRACT We investigated the carbon metabolism of three strains ofFibrobacter succinogenes and one strain ofFibrobacter intestinalis. The four strains produced the same amounts of the metabolites succinate, acetate, and formate in approximately the same ratio (3.7/1/0.3). The four strains similarly stored glycogen during all growth phases, and the glycogen-to-protein ratio was close to 0.6 during the exponential growth phase.13C nuclear magnetic resonance (NMR) analysis of [1-13C]glucose utilization by resting cells of the four strains revealed a reversal of glycolysis at the triose phosphate level and the same metabolic pathways. Glycogen futile cycling was demonstrated by 13C NMR by following the simultaneous metabolism of labeled [13C]glycogen and exogenous unlabeled glucose. The isotopic dilutions of the CH2 of succinate and the CH3 of acetate when the resting cells were metabolizing [1-13C]glucose and unlabeled glycogen were precisely quantified by using 13C-filtered spin-echo difference 1H NMR spectroscopy. The measured isotopic dilutions were not the same for succinate and acetate; in the case of succinate, the dilutions reflected only the contribution of glycogen futile cycling, while in the case of acetate, another mechanism was also involved. Results obtained in complementary experiments are consistent with reversal of the succinate synthesis pathway. Our results indicated that for all of the strains, from 12 to 16% of the glucose entering the metabolic pathway originated from prestored glycogen. Although genetically diverse, the four Fibrobacter strains studied had very similar carbon metabolism characteristics.

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Abadie, Cyril, e Guillaume Tcherkez. "13C Isotope Labelling to Follow the Flux of Photorespiratory Intermediates". Plants 10, n.º 3 (24 de fevereiro de 2021): 427. http://dx.doi.org/10.3390/plants10030427.

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Measuring the carbon flux through metabolic pathways in intact illuminated leaves remains challenging because of, e.g., isotopic dilution by endogenous metabolites, the impossibility to reach isotopic steady state, and the occurrence of multiple pools. In the case of photorespiratory intermediates, our knowledge of the partitioning between photorespiratory recycling, storage, and utilization by other pathways is thus rather limited. There has been some controversy as to whether photorespiratory glycine and serine may not be recycled, thus changing the apparent stoichiometric coefficient between photorespiratory O2 fixation and CO2 release. We describe here an isotopic method to trace the fates of glycine, serine and glycerate, taking advantage of positional 13C content with NMR and isotopic analyses by LC–MS. This technique is well-adapted to show that the proportion of glycerate, serine and glycine molecules escaping photorespiratory recycling is very small.

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Pironti, Concetta, Maria Ricciardi, Oriana Motta, Federica Camin, Luana Bontempo e Antonio Proto. "Application of 13C Quantitative NMR Spectroscopy to Isotopic Analyses for Vanillin Authentication Source". Foods 10, n.º 11 (30 de outubro de 2021): 2635. http://dx.doi.org/10.3390/foods10112635.

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The carbon stable isotope ratio (δ13C) is a valuable chemical parameter in the investigation of the geographic origin, quality, and authenticity of foods. The aim of this study is the evaluation of the feasibility of 13C-NMR (Nuclear Magnetic Resonance) spectroscopy to determine the carbon stable isotope ratio, at natural abundance, of small organic molecules, such as vanillin, without the use of IRMS (Isotope Ratio Mass Spectrometry). The determination of vanillin origin is an active task of research, and differentiating between its natural and artificial forms is important to guarantee the quality of food products. To reach our goal, nine vanillin samples were analyzed using both 13C quantitative NMR spectroscopy (under optimized experimental conditions) and IRMS, and the obtained δ13C values were compared using statistical analysis (linear regression, Bland–Altman plot, and ANOVA (analysis of variance)). The results of our study show that 13C-NMR spectroscopy can be used as a valuable alternative methodology to determine the bulk carbon isotope ratio and to identify the origin of vanillin. This makes it attractive for the analysis in the same experiment of site-specific and total isotope effects for testing authenticity, quality, and typicality of food samples. Moreover, the improvement of NMR spectroscopy makes it possible to avoid the influence of additives on carbon stable isotope ratio analysis and to clearly identify fraud and falsification in commercial samples.

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Mais fontes

Teses / dissertações sobre o assunto "Isotopic 13C NMR"

Olsson, Ulrika. "Structural Studies of O-antigen polysaccharides, Synthesis of 13C-labelled Oligosaccharides and Conformational Analysis thereof, using NMR Spectroscopy". Doctoral thesis, Stockholm University, Department of Organic Chemistry, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-7283.

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In order to understand biological processes, to treat and diagnose diseases, find appropriate vaccines and to prevent the outbreak of epidemics, it is essential to obtain more knowledge about carbohydrate structures. This thesis deals with structure and conformation of carbohydrates, analysed by NMR spectroscopy and MD simulations.In the first two papers, the structures of O-antigen polysaccharides (PS) from two different E. coli bacteria were determined using NMR spectroscopy. The O-antigenic PS from E. coli O152 (paper I) consists of branched pentasaccharide repeating units, built up of three different carbohydrate residues and a phosphodiester, whilst the repeating unit of the O-antigen from E. coli O176 (paper II) is built up of a linear tetrasaccharide consisting of two different monosaccharides.

In papers III and IV, the conformational analysis of different disaccharides is described. Conformational analysis was performed using NMR spectroscopy and MD simulations (paper IV). In paper III four different glucobiosides were studied using coupling constants and Karplus-type relationships. By use of specific ¹³C isotopically labelled derivatives, additional coupling constants were obtained and the number of possible torsion angles was reduced by half. In paper IV, we examine the conformations of two disaccharides that are part of an epitope of malignant cells. From NOE and T-ROE experiments, short proton-proton distances around the glycosidic linkage were estimated. Furthermore, interpretation of the extracted coupling constants using Kaplus relationships gave the values of the torsion angles. As in paper III, isotopically labelled compounds were synthesised in order to enhance the sensitivity of the analysis. Finally, MD simulations were performed and the results were compared with results from NMR data.

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Mhanna, Tania. "Biomarqueurs isotopomiques en 13C par RMN et GC-IRMS d’acides gras des produits laitiers : élucidation de voies métaboliques et applications alimentaires". Electronic Thesis or Diss., Nantes Université, 2024. http://www.theses.fr/2024NANU4054.

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Les triacylglycérols (TAG), principaux lipides de stockage énergétique, présentent une grande diversité structurelle due à la variété des acides gras les composant. Cette diversité s'étend à la distribution des isotopes lourds au sein de ces molécules, influencée par les fractionnements isotopiques lors de leur biosynthèse. Bien que les profils d'acides gras soient couramment utilisés comme biomarqueurs métaboliques, la composition isotopique 13C composé-spécifique ou positionnelle des acides gras individuels reste peu explorée. Au cours de la thèse, une nouvelle méthode par GC-IRMS a permis de mesurer avec précision les rapports isotopiques du 13C dans les acides gras séparés et en particulier les acides gras à courte chaîne (C4 à C12), non observés jusqu’à présent. Une méthodologie utilisant la RMN 13C quantitative a été mise en place pour déterminer la composition intramoléculaire des acides gras. Cette analyse demande un travail de préparation important concernant la séparation et purification des acides gras. Une nouvelle approche a été développée concernant l’expression des résultats de la composition isotopique sur une échelle « absolue » et non relative, en mettant en place le concept de référence isotopique intramoléculaire. À l'aide de ces méthodes analytiques avancées, l'étude a permis d’analyser systématiquement la composition isotopique des acides gras de divers produits laitiers, particulièrement sur différenciation des laits bio/conventionnels grâce à la teneur en 13C des acides butyrique et caprylique. D’une manière générale, les données isotopiques obtenues ont été soumises à des analyses chimiométriques pour étudier les corrélations isotopiques et décrypter les mécanismes de biosynthèse des acides gras. En développant ces méthodes analytiques avancées, cette thèse vise à fournir des outils novateurs pour la science alimentaire et la santé
Triacylglycerols (TAGs), the main energy storage lipids, exhibit a high structural diversity due to the variety of fatty acids composing them. This diversity extends to the distribution of heavy isotopes within these molecules, influenced by isotopic fractionations during their biosynthesis. Although fatty acid profiles are commonly used as metabolic biomarkers, the compound-specific or positional 13C isotopic composition of individual fatty acids remains poorly explored. During the thesis, a new GC-IRMS method allowed to accurately measure the 13C isotopic ratios in separated fatty acids and in particular short-chain fatty acids (C4 to C12), not observed until now. A methodology using quantitative 13C NMR was implemented to determine the intramolecular composition of fatty acids. This analysis requires significant preparation work concerning the separation and purification of Fatty acids. A new approach was developed concerning the expression of the results of the isotopic composition on an "absolute" and not relative scale, by setting up the concept of intramolecular isotopic reference. Using these advanced analytical methods, the study allowed to systematically analyze the isotopic composition of fatty acids of various dairy products particularly on the differentiation of organic/conventional milks thanks to the 13C content of butyric and caprylic acids. In general, the isotopic data obtained were subjected to chemometric analyses to study the isotopic correlations and decipher the mechanisms of fatty acid biosynthesis. By developing these advanced analytical methods, this thesis aims to provide innovative tools for food science and health

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Romek, Katarzyna. "Studies of isotope fractionation 13C during biotransformations and enzymatic reactions". Thesis, Nantes, 2016. http://www.theses.fr/2016NANT4034/document.

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La capacité de mesurer les rapports isotopiques par spectroscopie RMN du 13C (irm-13C NMR) donne un accès direct à la distribution d’isotopes possédant une position spécifique au sein de molécules. Dans cette thèse, cette approche a été développée dans le but d’élucider le fractionnement isotopique au cours de la biosynthèse dans des plantes de différents alcaloïdes (nicotine, tropine, tramadol) qui ont certaines caractéristiques communes lors de leurs biosynthèses. L’une des caractéristiques clés de ces composés est la présence de groupes O-méthyle et/ou N-méthyle. En général, le rapport 13C/12C dans les groupes O-méthyle et N-méthyle de produits naturels est exceptionnellement faible comparé aux autres carbones dans la molécule, ces travaux ont été axés sur l’explication de ce phénomène. La grande majorité de ces groupes méthyles dans les produits naturels proviennent du transfert d’un groupe Sméthyle de L-méthionine (L-Met) via la Sadénosylméthionine (AdoMet). Il a été prouvé par irm-13C NMR que, dans la molécule donneuse, L-Met, le groupe Sméthyle est appauvrit. La cause de ce phénomène a été explorée par le biais de l’étude de petit modèle théorique pour la cobalamin-independent méthionine synthase, l’enzyme responsable du transfert du groupement méthyle durant la biosynthèse de L-met. Ces calculs ont montré une barrière d’énergie élevée pour le transfert du groupe méthyle et un fort effet isotopique cinétique du 13C y associé. De plus, une méthodologie générique de l’étude du ratio 13C/12C dans les aminoacides a été développée, ce qui permet une meilleure compréhension du fractionnement isotopique intervenant durant la biosynthèse d’acides aminés. Une caractéristique supplémentaire de ces travaux est que les données permettent : (i) une comparaison entre les produits naturels et commerciaux, permettant de distinguer ces deux sources, et (ii) une interprétation du modèle isotopique en terme d’origine biosynthétique de composés naturels. Pour le tramadol, il a été possible de proposer un chemin hypothétique pour ce produit naturel récemment découvert
The ability to carry out isotope ratio monitoring by 13C NMR spectrometry (irm-13C NMR) gives direct access to position-specific isotope distributions in whole molecules. In this thesis this approach has been developed with the aim of elucidating isotopic fractionation during the biosynthetic pathways in plants of a number of alkaloids (nicotine, tropine and tramadol) that have certain features of their biosynthesis in common. One key common feature of these compounds is the presence of O-methyl and/or N–methyl groups. As it is generally found that the 13C/12C ratio in the O-methyl and N-methyl groups of natural products is exceptionally low relative to the other carbon positions in the molecule, the work focused on explaining this phenomenon. The vast majority of these methyl groups in natural products are derived by the transfer of the S-methyl group from L-methionine (L-Met) via S-adenosyl methionine (AdoMet). It is shown by irm-13C NMR that in the donor molecule, L-met, the S-methyl group is impoverished. The cause of this was investigated by the study of a small theoretical model for the cobalaminindependent methionine synthase, the enzyme responsible for methyl group transfer in L-met biosynthesis. These calculations showed a high energy barrier for methyl group transfer and an associated large 13C kinetic isotope effect. In addition, a generic methodology to study the 13C/12C ratios in amino acids has been developed, which allows insight into the isotopic fractionation occurring during amino acid biosynthesis. A further feature of the work is that the data allow: (i) a comparison of natural and commercial products, which enables distinguishing between sources, and (ii) an interpretation of the isotopic pattern in terms of the biosynthetic origin of natural compounds. For tramadol, this made it possible to propose a hypothetical pathway for this newly-discovered natural product

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Clouard, Mélanie. "Impact du lignite sur les caractéristiques physico-chimiques et microbiologiques des sols : application aux sols du bassin minier de Provence". Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4341.

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Les terrils du bassin minier de Provence sont implantés dans le paysage et demeurent à proximité des habitations de la métropole Aix-Marseille. Les terrils les plus anciens ont été naturellement colonisés par la végétation et des sols s’y sont développés avec une vitesse remarquable. Cette étude vise à comprendre les processus pédogénétiques en cours depuis 55 ans sur les terrils miniers. Nous avons étudié l’impact du lignite sur les caractéristiques physico-chimiques et microbiologiques d’un Rendosol naturel. Deux sols similaires, dont l’un est traversé par l’affleurement naturel d’une veine de lignite et l’autre pas, ont donc été comparés afin de caractériser les variables impactées par le lignite. L’étude du terril Armand a permis de comprendre les facteurs responsables de la formation et de la variabilité des caractéristiques des sols observés sur le terril. L’abondance de composés carbonés récalcitrants dans les sols enrichis en lignite affecte les niveaux d’activité des microorganismes responsables des processus biologiques dans les sols sans induire d’effets néfastes. Le lignite semble intervenir comme un facteur de dilution du carbone organique, diminuant ainsi la quantité de carbone disponible et donc la vitalité d’expression des fonctions microbiennes. Les activités biologiques sont diminuées en présence de lignite, mais les changements induits sur les propriétés physico-chimiques semblent améliorer la fertilité du sol. Les sols du terril Armand demeurent cependant encore à un stade d’évolution trop jeune pour préjuger de leur évolution future
Spoil heaps are scattered over the coal basin of Provence: they are inserted in the landscape and often located close to urban areas of the Aix-Marseille Metropole. The oldest spoil heaps have been naturally colonized by local vegetation and soils have simultaneously quickly developed. This study aims at understanding the processes involved in soil forming on undisturbed lignite-rich spoil heaps since 55 years. We studied the impact of lignite on the physico-chemical and microbiological characteristics of an undisturbed soil: we compared two similar Rendosols, except that one was developed in a natural lignite outcrop. Then we studied on the 55-year-old Armand spoil heap the factors responsible for soil genesis and variability of soil characteristics. Recalcitrant carbon compounds found in soils enriched with lignite modify microbial activity but do not induce negative effects. It seems that lignite acts as a diluting factor of the organic carbon that decreases the available carbon pool and consequently on the vitality of the expression of the microbial functions. Enzymatic activities and basal respiration decrease while changes observed on physico-chemical properties tend to improve soil fertility. Some characteristics of the soils developed on the spoil heap are similar to those of the soil developed from the lignite outcrop, while others are more related to the way the spoil heap was set up. Although these results have shed light on some of the processes involved in soil formation on spoil heaps in a carbonated environment, soils on Armand spoil heap are still at an early stage of development that precludes conclusion on their future evolution

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Zhou, Wenxuan. "Stoichiometry and Crystal Structure of Poly (Lactic Acid) (PLA) Stereocomplex (SC) in Cold-crystallization and Solution-grown Crystals as Studied by Solid-state NMR and 13C Isotope Labeling". University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1522239647112751.

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Silva, Luís André Perpétuo. "NMR Analysis of urinary acetaminophen-glucuronide enrichments from 2H and 13C metabolic tracers in mouse models". Master's thesis, 2020. http://hdl.handle.net/10316/90131.

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Dissertação de Mestrado em Bioquímica apresentada à Faculdade de Ciências e Tecnologia
A sociedade contemporânea está repleta de casos de obesidade e diabetes tipo 2, com maior incidência em países desenvolvidos, e a previsão para os próximos anos/décadas não é brilhante. Um dos principais componentes desta epidemia é o consumo de frutose que excede a base evolutiva em que os seres humanos estão inseridos, resultado no metabolismo desequilibrado de hidratos de carbono e lípidos.Aqui propomo-nos a estudar o impacto da frutose no metabolismo hepático, utilizando ratinhos C57BL/6, que são suscetíveis à obesidade induzida pela dieta e diabetes tipo 2. A abordagem baseia-se na utilização da marcação de isótopos estáveis, nomeadamente 2H (que permite o estudo dos fluxos metabólicos de todos os precursores de nutrientes) e 13C (para estudar o destino específico dos carbonos da glucose e da frutose, com base no perfil de marcação de isotopómeros).Este estudo foi realizado através da administração de paracetamol que se ligará ao precursor imediato do glicogénio (UDPG, glucose difosfato de uridina) via ligação glicosídica, originando um glucuronato (glucuronato-paracetamol). O glucuronato-paracetamol é excretado na urina como parte de um processo de destoxificação que ocorre no fígado, proporcionando um método de biópsia não invasiva que permite o estudo das vias metabólicas hepáticas.Para a análise de RMN do glucuronato-paracetamol, o processo mais comumente utilizado é a derivatização para MAGL (Lactona Glucurónica Monoacetonada). Como o foco deste estudo será em ratinhos e o protocolo de derivatização tem rendimentos reduzidos (rendimento aproximado de 30-50%), ele iria causar perdas significativas de material durante o processo de derivatização, invalidando a capacidade de progredir no estudo. Para resolver este problema, propomos também desenvolver e aperfeiçoar um processo de purificação com maior eficiência, nomeadamente utilizando colunas de SPE (rendimento aproximado de 80-92%).
Contemporary society abounds with cases of obesity and type 2 diabetes, with more incidence in developed countries, and the forecast for the upcoming years/decades is not bright. One of the key components of this epidemic is the consumption of fructose that exceeds the evolutionary basis in which humans exist, resulting in the unbalanced metabolism of carbohydrates and lipids.Here we propose to study the impact that fructose has on hepatic metabolism, using C57BL/6 mice: a strain that is susceptible to diet-induced obesity and type 2 diabetes. The approach is based on the use of stable isotope labelling, namely 2H (that allows metabolic fluxes from all nutrient precursors to be studied) and 13C (in order to study the specific destiny of the carbons of glucose and fructose, based on the isotopomer labelling profile).This study was realized by administrating acetaminophen (commonly known as paracetamol) that binds to the immediate precursor of glycogen (UDPG, uridine diphosphate glucose) via glycosidic bond, originating a glucuronide (AG, acetaminophen-glucuronide). AG is excreted in the urine as a part of a detoxification process that occurs in the liver, providing a non-invasive biopsy that allows the study of hepatic metabolic pathways.For NMR analysis of the AG, the most commonly used process is the derivatization to MAGL (Monoacetone Glucuronic Lactone). Because the focus of this study will be on mice and the derivatization protocol is characterized by having low yields (approximate yield 30-50%), it would cause significant material loses during the derivatization process, invalidating the ability to progress in the study. To solve this problem we also propose developing and perfecting a purification process with a higher efficiency, namely using SPE-columns process (approximate yield 80-92%).
Outro - Este projecto foi financiado por: FCT-FEDER (02/SAICT/2017/028147) “The Role of Visceral Fructose Metabolism in the Development of Non-alcoholic Fatty Liver Disease”

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Livros sobre o assunto "Isotopic 13C NMR"

Wehrli, F. W. Interpretation of carbon-13 NMR spectra. 2^a ed. Chichester: Wiley, 1988.

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Breitmaier, E. Carbon-13 NMR spectroscopy: High-resolution methods and applications in organic chemistry and biochemistry. 3^a ed. New York: VCH Publishers, 1987.

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Levy, George C. Carbon-13 nuclear magnetic resonance spectroscopy. Malabar, Fla: Krieger Pub. Co., 1992.

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Levy, George C. Carbon-13 nuclear magnetic resonance spectroscopy. 2^a ed. Malabar, Fla: Krieger, 1993.

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Tho, Pham Quang, ed. Proton and carbon NMR spectra of polymers. Penton Press, 1991.

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Capítulos de livros sobre o assunto "Isotopic 13C NMR"

Huang, Danting, Benjamin C. Hudson, Yuan Gao, Evan K. Roberts e Anant K. Paravastu. "Solid-State NMR Structural Characterization of Self-Assembled Peptides with Selective 13C and 15N Isotopic Labels". In Methods in Molecular Biology, 23–68. New York, NY: Springer New York, 2018. http://dx.doi.org/10.1007/978-1-4939-7811-3_2.

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Berger, S. "Chemical Models for Deuterium Isotope Effects in 13C- and 19F-NMR". In Isotope Effects in NMR Spectroscopy, 1–29. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-74835-6_1.

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Hanashima, Shinya, e Yoshiki Yamaguchi. "Indirect Detection of Hydroxy Proton Exchange Through Deuterium-Induced 13C-NMR 13C-NMR Isotope shift Isotope Shifts". In Glycoscience: Biology and Medicine, 129–35. Tokyo: Springer Japan, 2014. http://dx.doi.org/10.1007/978-4-431-54841-6_100.

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Risley, J. M., e R. L. van Etten. "Properties and Chemical Applications of 18O Isotope Shifts in 13C and 15N Nuclear Magnetic Resonance Spectroscopy". In Isotope Effects in NMR Spectroscopy, 81–168. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-74835-6_3.

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Mega, Tony L., e Robert L. Van Etten. "Oxygen Exchange and Bond Cleavage Reactions of Carbohydrates Studied Using the 180 Isotope Shift in 13C NMR Spectroscopy". In NMR Applications in Biopolymers, 85–93. Boston, MA: Springer US, 1990. http://dx.doi.org/10.1007/978-1-4684-5868-8_7.

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Gilbert, Alexis, Freddy Thomas e Serge Akoka. "Position-Specific 13C Isotope Analysis by NMR as a Tool for Authentication of Ethanol-Containing Beverages". In Handbook of Isotopologue Biogeochemistry, 1–27. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-10-7048-8_39-1.

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Remaud, Gerald S., Serge Akoka e Freddy Thomas. "Position-Specific 13C Isotope Analysis by NMR as a Tool for Characterizing the Manufacturing Process Used and for Fighting Pharmaceutics Counterfeiting". In Handbook of Isotopologue Biogeochemistry, 1–39. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-10-7048-8_41-1.

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Arbogast, Luke W., Robert G. Brinson e John P. Marino. "Application of Natural Isotopic Abundance 1H–13C- and 1H–15N-Correlated Two-Dimensional NMR for Evaluation of the Structure of Protein Therapeutics". In Methods in Enzymology, 3–34. Elsevier, 2016. http://dx.doi.org/10.1016/bs.mie.2015.09.037.

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Clayden, Jonathan, Nick Greeves e Stuart Warren. "1H NMR: Proton nuclear magnetic resonance". In Organic Chemistry. Oxford University Press, 2012. http://dx.doi.org/10.1093/hesc/9780199270293.003.0013.

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This chapter highlights proton (¹H) nuclear magnetic resonance (NMR). Proton NMR differs from ¹³C NMR in a number of ways. ¹H is the major isotope of hydrogen, while ¹³C is only a minor isotope. ¹H NMR is quantitative: the area under the peak shows the number of hydrogen nuclei, while ¹³C NMR may give strong or weak peaks from the same number of ¹³C nuclei. Moreover, protons interact magnetically (couple) to reveal the connectivity of the structure, while ¹³C is too rare for coupling between ¹³C nuclei to be seen. Finally, ¹H NMR shifts give a more reliable indication of the local chemistry than that given by ¹³C spectra. Nevertheless, proton NMR spectra are recorded in the same way as ¹³C NMR spectra: radio waves are used to study the energy level differences of nuclei in a magnetic field, but this time they are ¹H and not ¹³C nuclei.

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Wiechert, W., A. A. de Graaf e A. Marx. "IN VIVO STATIONARY FLUX DETERMINATION USING 13C NMR ISOTOPE LABELLING EXPERIMENTS". In Computer Applications in Biotechnology, 130–35. Elsevier, 1995. http://dx.doi.org/10.1016/b978-0-08-042377-7.50026-x.

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Trabalhos de conferências sobre o assunto "Isotopic 13C NMR"

Su, Haw-Lih, Rajeesha Rajan, Yousef Mohammad Hijji, Mohammad Ibrahim Ahmad Ibrahim e Mohammed Hussain S. A. Alsafran. "Detecting Organic Nitrogen with 1H-15N HMBC Spectra". In Qatar University Annual Research Forum & Exhibition. Qatar University Press, 2021. http://dx.doi.org/10.29117/quarfe.2021.0038.

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NMR spectroscopy has been the most important tool for organic chemistry research, providing detailed structure information. While 1H and 13C NMR spectra were frequently measured, 15N NMR spectra were relatively rare, even though nitrogen is commonly observed in organic molecules. This is due to the low gyromagnetic ratio and nature abundance. Usually 15N NMR spectra are observed when the sample is in very high concentration or the nitrogen is enriched with 15N isotope. HMBC is one of the 2D NMR techniques, measuring the through-bond correlations inside a molecule. 1H-15N HMBC actually collects a series of measurements of 1H NMR spectra with 15N information. Therefore, HMBC could get stronger signals than 15N signals and provide the opportunity for the indirect measurement of 15N signals.

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Jin, Cong, Steve I. Dworkin, William C. Hockaday e Todd L. Longbottom. "13C NMR CHARACTERIZATION AND STABLE ISOTOPE INVESTIGATION OF ORGANIC MATTER IN SILICIFIED WOOD, PETRIFIED FOREST NATIONAL PARK (ARIZONA, USA): EVIDENCE FOR LATE TRIASSIC CLIMATE CHANGE". In GSA Annual Meeting in Denver, Colorado, USA - 2016. Geological Society of America, 2016. http://dx.doi.org/10.1130/abs/2016am-285230.

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