Site-specific natural isotope fractionation measured by deuterium NMR (SNIF-NMR) was used for investigating the deuterium transfers occurring in the fermentation of sugars into ethanol. In contrast to carbon-13, which is usually assumed to be randomly distributed within the glucose skeleton, very large deviations with respect to a statistical repartition are determined for deuterium. By transforming glucose samples from different origins into acetates and nitrates, the absolute values of the D/H ratios in the nonexchangeable sites were obtained. The hydroxyl sites were considered to contribute to the isotope content of the starting water medium. The site-specific isotope parameters were determined for more than 50 ethanol samples obtained by fermenting glucose samples issued from different starches and sucroses in water media with different isotope ratios. Several concentrations of sugar, several strains of the same yeast, and different temperatures of fermentation were considered. The whole set of isotope parameters characterizing the nonexchangeable sites of glucose, the starting and end water media, and the methyl and methylene sites of ethanol was submitted to factor analysis. The results are satisfactorily reproduced on the basis of two main factors which may be associated with the independent contributions of the isotope ratios of glucose and water. The isotope parameters of the end products and of the starting materials were then considered to be related by a set of linear equations and the coefficients of the redistribution matrix were calculated by multidimensional analysis. Thus the isotope ratio of the methyl site of ethanol exhibits a strong sensitivity toward the nonexchangeable sites of glucose and depends to a lesser extent on the isotope content of the starting water medium. By contrast, no direct connection is found between glucose and the methylene site which is only sensitive, with a strong discriminating effect against deuterium, to the isotope content of water. A redistribution coefficient slightly less than unity (0.96 for a concentration of sugar of 100 g L-I) is found between the isotope ratio of the end and starting water media. Although the bioconversion of glucose into ethanol occurs with high fractionation effects which are the source of high deuterium depletions in the methyl and methylene sites of ethanol as compared to glucose, constant redistribution parameters can be obtained in appropriate conditions and the isotope parameters measured in alcohols may be used as a fingerprint for characterizing the sugar and aqueous juice from which they have been produced. The site-specific natural isotope-parameters of ethanol therefore constitute a faithful and powerful probe for investigating the physiological biochemical and climatological effects which have governed the photosynthesis of sugars in natural conditions.The first issue of this journal, which appeared in 1879, began with a paper by D. P. Ricketts' which was devoted to the characterization of sugars from different origins. More t...
Objectives Osteoarthritis (OA) is a common degenerative joint disease with the pathological features of the reduced cartilage cellularity. Celastrol, a compound from Tripterygium wilfordii, exerted therapeutic effects on arthritis, but the potential mechanism remains unclear. Methods Tunicamycin was used to establish a model of OA in vitro, and ACLT surgery model in rats was applied to verify the mechanism. Chondrocytes were isolated from the knee articular cartilage of rabbit. MTT and flow cytometry assay were used to detect cell viability and apoptosis rate. Haematoxylin-eosin staining was used to assess for the histopathological changes. The activity and expression of apoptosis-related factors and ERs (endoplasmic reticulum stress)related factors were detected by ELISA, WB, PCR and IHC, respectively. Key findings Celastrol exhibited significant enhancement on cell viability and reduced the rate of apoptosis in Tm-exposed chondrocytes. Celastrol reduced enzyme activity and protein expression of caspase-3, caspase-6 and caspase-9, decreased Bip, Atf6, Chop and Xbp-1 expression both at protein and mRNA levels. Celastrol showed a more significant effect on cell apoptosis rate and mRNA expression in the combination with 4-PBA.Conclusions This study reveals that celastrol may prevent OA by inhibiting the ERs-mediated apoptosis. All these might supply beneficial hints for celastrol on OA treatment.
NMR determination of site‐specific hydrogen isotope ratios at natural deuterium abundance (SNIF‐NMR) provides the basis for simultaneous access to primary and secondary thermodynamic fractionation factors in exchange reactions and avoids the need for selective isotope labelling of the reagents. The method was applied to the measurement of fractionation parameters involving OH, CH2, CH3 and =CH groups in keto–enol tautomeric equilibria. The fractionation factors relating the =CH and OH sites of the enol species are simply derived from 2H NMR spectra whereas the determination of isotope parameters which relate keto and enol positions exploits a combination of 2H and 1H NMR experiments. Since only monolabelled isotopomers have to be considered at natural abundance, the method also offers the advantage of avoiding the occurrence of complex equilibria associated with multi‐labelled species possibly introduced by deuterium enrichment. The primary equilibrium isotope effects illustrate a preference of deuterium for the methylene fragment of the keto form with respect to the ethylenic position of the enol tautomer. Since the enol species is itself engaged in a fast tautomeric equilibrium associated with a symmetric or unsymmetric double minimum potential, the thermodynamic parameters are averaged over the exchanging partners. It is shown that the average thermodynamic fractionation factor relating the OH and =CH hydrogens of the enol are significantly influenced by the nature of the substituents at both carbonyl positions of the β‐diketones. Moreover, methyl and chlorine substitution increases by a factor of about 1·1 the thermodynamic isotopic fractionation factor relating the –COCHCO– position of the keto form to the hydroxyl position of the enol.
<p style="text-align: justify;">Stable isotope and elemental analyses were applied to the study of wines produced from the Cabernet Franc vine variety cultivated during several years (1982 to 1990) on specific parts of the Saumur-Champigny vineyard dedicated to the « terroir » experiment of INRA. The purpose of this work was to describe the behaviour or <sup>2</sup>H, <sup>13</sup>C and <sup>18</sup>O isotopes in the water and ethanol of wines in terms of the meteorological conditions (temperature, precipitation and insolation) which govern vine growing. Since the « terroir » concept involves a synergy between the c1imate and the soil, the distribution of typical metallic elements was also determined by flame and electrothermal ionization atomic absorption. About twenty parcels, carefully described from the geological and pedological point of view were considered in this study which demonstrated the ability of Sr, Al and Rb to discriminate between wines from the same year but grown on adjacent parcels. The content in trace elements of the wines was also shown to be correlated with the geological nature of the soil. As far as stable isotopes are considered, it appears that the climate of the year of production of a given region has a drastic influence on the isotope ratios of water and ethanol of wines and good correlations way be computed between these parameters and temperature and precipitations. From a more basic aspect, it is also shown that the nature of the soil which governs, at least in a part, the water use efficiency of vine, induces typical variations in the isotopic composition of wines. The results of this study demonstrate also the ability of stable isotope and elemental analyses to determine the geographical origin of a wine, and when the region of production is known, to infer the year of production from meteorological data. This method might prove to be an alternative method to radio carbon analysis for the next vintages.</p>
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.