Maryvonne L. Martin

Deuterium labelling at the natural abundance level as studied by high field quantitative 2H NMR

Abstract It is shown that very large differences exist in the internal distribution of natural deuterium and the 2H quantitative NMR method is proposed as an efficient tool for characterizing the chemical and geographical origin of a molecule and for investigating chemical and biochemical mechanisms.

Deuterium NMR in the Study of Site-Specific Natural Isotope Fractionation (SNIF-NMR)

The isotope content and in particular the ratio of deuterium and hydrogen atoms in a given molecular species, D/H, are not constant on Earth. On the basis of the overall molecular isotope contents accessible by mass spectrometry techniques, important information has been obtained on biochemical and physiological aspects of biosyntheses under natural conditions. The original approaches provided by the NMR study of Site-Specc Natural Isotope Fractionation of hydrogen must be seen in this context.

Complete assignments of the 1H, 13C and 15N NMR spectra of caffeine

Abstract Complete assignments of the 1 H, 13 C and 15 N NMR spectra of caffeine are given using a combination of modern instrumental techniques. A combination of proton coupled, decoupled, HETCOR and NH-COLOC spectra are employed to provide an unambiguous set of assignments.

A Site-Specific and Multi-Element Isotopic Approach to Origin Inference of Sugars in Foods and Beverages

A strategy is presented for the characterization of sugars according to their botanical origin. The samples fermented in standardized conditions can be described in the multi-dimensional space of the overall carbon isotope ratio of ethanol measured by isotope ratio mass spectrometry (IRMS) and of the specific hydrogen isotope parameters of the methyl and methylene sites derived from nuclear magnetic resonance investigation of site-specific natural isotope fractionation (SNIF-NMR method). In the comparison of natural juices, the deuterium and oxygen-18 parameters of water extracted from the juice and from the end fermentation medium also contain information on the origin of the product. The isotopic effects of the concentration processes leading to concentrated juices, musts and syrups can be estimated and taken into account in interpreting the data.The classification power of this multi-element and multi-site approach is illustrated by discriminant analyses involving selected isotopic variables associated with pineapple, apple and barley sugars, compared to beet and cane sugars which are common sources of enrichment. The ability of the method to detect adulteration by exogeneous sugars is improved when environmental conditions can be taken into account.

Natural chirality of methylene sites applied to the recognition of origin and to the study of biochemical mechanisms

Naturel abundance deuterium NMR has been applied to the quantitative determination of natural methylene chirality in amino acids of different configurations and in ethanols of different origins. An enantiomeric enrichment is detected for aspartic acid of the L series obtained from fermentation and the technique therefore provides an absolute method for identifying the natural origin of a given substance. In ethanols of different origins the pro‐R and pro‐S positions appear as naturally equally populated at the present level of precision of the experiments. These results provide a new source of information about reaction mechanisms in the natural conditions.

New isotopic criteria for the short-term dating of brandies and spirits

As a result of the atmospheric atomic experiments carried out in the 1960s a method for short-term dating of wines and spirits could be based on the determination of the 14 C radioactivity of ethanol. However, due to the turnover of atmospheric 14 CO 2 this method is no longer applicable to the most recent samples. The aptitude of stable isotopes of carbon and hydrogen to provide new probes for dating brandies such as cognacs and armagnacs is evaluated. The overall carbon isotope ratio of ethanol is measured by isotope ratio mass spectrometry and the site-specific hydrogen parameters of the methyl, (D/H) 1 , and methylene, (D/H) II , sites are determined by the SNIF-NMR method. The isotopic results can be interpreted in terms of fractionation phenomena associated with thermo-kinetic evaporation undergone in the casks during the ageing period. A theoretical estimation of the vintage founded on this isotopic evolution requires the knowledge of the isotope ratios of the starting product. In principle, these values can be estimated on the basis of the meteorological parameters associated with the growing period of the corresponding vine. However, although the combined contributions of climatic effects and of evaporation phenomena conveniently explain the general isotopic behaviour, the influence of oenological practices such as ullage (replacement of the amount of a liquid lost in a cask by evaporation) must also be considered. Further progress towards an unequivocal dating procedure using stable isotope ratios is expected from the access to isotope databanks of the wine precursors.

Etude par RMN 1H et 13C des ferrocenophanes-cage. Mono- et bis-(1,3-cyclopentylene) ferrocene et de leurs derives acyles et alkyles

Abstract The asymmetry of the bridge in (1,1′)(1,3-cyclopentylene)ferrocenophane (I) affords a route for synthesizing a series of ferrocenophane cage compounds. Their detailed study in 1 H (100 and 250 MHz) and 13 C NMR establishes the nature and the position of the substituents. The anisotropic effects of each substituent on the various ferrocene ring sites is shown. The NMR data also allow us to discuss the conformation of the cyclopentylene bridge and correlate the results with the X-ray data in the solid state. In particular, the asymmetry of the bridge in I in relation to the plane passing through the iron, C(7) and the middle of C(9)-C(10) does not appear in solution because of the rapid exchange between two equally populated conformations, but is well-characterized by NMR when one conformer is sterically favored by a substituent in the α-position.

The search for d-glucose derivatives suitable for the study of natural hydrogen isotope fractionation

Abstract In order to apply Site-specific Natural Isotope Fractionation (SNIF) to chemical, biochemical, and environmental studies of d -glucose, there is a need for readily prepared compounds which give 2 H NMR spectra with all or most signals resolved. Changing substituents of C-1 and/or C-6 of α- d -glucopyranose pentaacetate improved the dispersion of deuterium signals, the best results being achieved with 1,2,3,4-tetra- O -acetyl-6-deoxy-6-thiocyanato-α- d -glucopyranose, for which only the 2 H-2 and 2 H-4 signals were not resolved, and with 2,3,4-tri- O -acetyl-6-bromo-6-deoxy-α- d -glucopyranosyl bromide, for which only the 2 H-6a and 2 H-6b signals were not resolved. Periodate oxidation of methyl 4,6- O -benzylidene-α- d -glucopyranoside and 4,6-dichloro-4,6-dideoxy- d -galactose was also examined as a possible source of useful compounds. Products obtained from the benzylideneglucoside gave inadequate resolution and broad deuterium signals. The oxidation of 4,6-dichloro-4,6-dideoxy- d -galactose was not straightforward. The α anomer was oxidised more rapidly than the β anomer. The oxidation product, 2,4-dichloro-2,4-dideoxy-3- O -formyl- d -threose, was too labile to be isolated pure and its hydrolysis to 2,4-dichloro-2,4-dideoxy- d -threose was accompanied by a slow elimination to form 2,4-dichlorobut-2-enal.

Thirty Years of Flavor NMR

Nuclear Magnetic Resonance is a very flexible spectroscopic tool, with a great diversity of applications in the field of flavor chemistry. In this domain, as in many others, the spectacular development in instrumentation over the last thirty years have not only been accompanied by a significant improvement in the performance of the method but have also provided access to new types of information. However before examining the different paths of evolution of flavor NMR it should be emphasized honestly that practical applications in flavor industry have remained, until recently, rather limited. NMR, which requires sophisticated and relatively costly instruments, is certainly not a traditional equipment of analytical laboratories. Nevertheless it has largely contributed to a better understanding of the composition, the structure, the elaboration, and the properties of aroma compounds. Moreover, in its SNIF-NMR version, it occupies an increasing place in quality control.

15N Chemical Shifts

Compilation until 1979 of the literature on 15N parameters, namely chemical shifts and coupling constants, has provided a large amount of data. Examination of Fig. 1.1 shows that most 15N resonances lie in a 500 ppm range, although some compounds, such as nitroso derivatives, extend the field of δ 15N to 800 ppm.