Search results for "13C"
showing 10 items of 194 documents
C4 plant isotopic composition (delta13C) evidence for urban CO2 pollution in the city of Cotonou, Benin (West Africa).
2006
9 pages; International audience; The carbon isotopic composition (delta13C) of plants can reveal the isotopic carbon content of the atmosphere in which they develop. The delta13C values of air and plants depend on the amount of atmospheric fossil fuel CO2, which is chiefly emitted in urban areas. A new indicator of CO2 pollution is tested using the delta13C variation in a C4 grass: Eleusine indica. A range of about 4 per thousand delta units was observed at different sites in Cotonou, the largest city in the Republic of Benin. The highest delta13C values, from -12 per thousand to -14 per thousand, were found in low traffic zones; low delta13C values, from -14 per thousand to -16 per thousan…
Impact of the ΔPhe configuration on the Boc-Gly-ΔPhe-NHMe conformation: experiment and theory
2019
Conformational propensities of N-t-butoxycarbonyl-glycine-(E/Z)-dehydrophenylalanine N′-methylamides (Boc-Gly-(E/Z)-ΔPhe-NHMe) in chloroform were investigated by NMR and IR techniques. The low-temperature crystal structure of the E isomer was determined by single crystal X-ray diffraction and the experimental data were elaborated by theoretical calculations using DFT (B3LYP, M06-2X) and MP2 approaches. The β-turn tendencies for both isomers were determined in the gas phase and in the presence of solvent. The obtained results reveal that the configuration of ΔPhe residue significantly affects the conformations of the studied dehydropeptides. The tendency to adopt β-turn conformations is sign…
Variation in the stable isotope trophic position of the bluefish Pomatomus saltatrix (Linnaeus, 1766) from two Mediterranean sites: insights from a g…
2022
A direct consequence of sea warming is the shift in the distribution range of thermo-tolerant species that have the potential to determine novel inter-specific interactions, ultimately altering food web structures and ecosystem processes. In this study, we investigated the trophic position of the bluefish Pomatomus saltatrix (Linnaeus, 1766), a pelagic predator that has recently expanded its distribution in the Mediterranean basin and for which scant information is available on its functional role in recently-colonised areas. Nitrogen and carbon stable isotopes were determined in muscle tissues of bluefish specimens collected in south-east Italy in the Gulf of Taranto (NW Ionian Sea) and in…
Life history, environment and extinction of the Scallop Carolinapecten Eboreus (Conrad) in the Plio-Pleistocene of the U.S. Eastern Seaboard
2019
Plio-Pleistocene mass extinction of marine bivalves on the U.S. eastern seaboard has been attributed to declines in temperature and primary production. We investigate the relationship of growth rate in the scallop Carolinapecten eboreus to variation in these parameters to determine which contributed to its extinction. We use ontogenetic profiles of shell δ18O to estimate growth rate and seasonal temperature, microgrowth-increment data to validate δ18O-based figures for growth rate, and shell δ13C to supplement assemblage evidence of production. Postlarval growth started in the spring/summer in individuals from the Middle Atlantic Coastal Plain but in the autumn/ winter in some from the Gulf…
Effect of RF Field Inhomogeneity and Sample Restriction on Spectral Resolution of CP/MAS-13C NMR Spectra of Natural Organic Matter
2010
It is well known that the induced B1 magnetic field in an NMR coil is inhomogeneously distributed. However, this issue has so far received little attention in the field of environmental NMR. As this research field often aims at quanti- tative results as well as relaxation phenomena, the repercussions of such inhomogeneity on peak integrals and relaxation times need to be taken into account. The objective of the present study was to test standard recording conditions on different sample positions in an NMR coil in order to determine the effect of the RF field inhomogeneity on the spectrum of a molecularly complex humic material and on some standard molecules of known structure and conformati…
Flavonoids in sbtribe Centaureinae (Cass.) Dumort (tribe Carduae, Asteraceae): distibution and 13C spectral data
2012
Asteraceae Bercht. & J. Presl is one of the biggest and most economically important plant families. The taxonomy and phylogeny of Asteraceae is rather complex and according to the latest and most reliable taxonomic classification of Panero & Funk, based on the analysis of nine chloroplast regions, the family is divided into 12 subfamilies and 35 tribes. One of the largest tribes of Asteraceae is Cardueae Cass. with four subtribes (Carlininae, Echinopinae, Carduinae and Centaureinae) and more than 2500 species. Susanna & Garcia-Jacas have organized the genera of Centaureinae (about 800 species) into seven informal groups, which recent molecular studies have confirmed: 1. Basal genera; 2. Vol…
Chemical and spectroscopic characteristics of the wood of Vitis vinifera cv. Sangiovese affected by esca disease.
2009
Chemical and spectroscopic analyses ((13)C cross-polarization-magic angle spinning NMR and attenuated total reflection Fourier transform infrared spectroscopies) were carried out on the wood of Vitis vinifera cv. Sangiovese with brown-red discoloration and black streaks caused by esca disease. The analyses of the brown-red wood revealed the destruction of hemicelluloses and noncrystalline cellulose as well as modifications in the pectic and ligninic wood fractions. The pectic fraction consisted of carbohydrates associated with polyphenols. The lignin fraction exhibited only a few changes in the aromatic systems and a partial demethylation, and it appeared to be associated with condensed phe…
Climate signals in stable carbon and hydrogen isotopes of lignin methoxy groups from southern German beech trees
2021
Stable hydrogen and carbon isotope ratios of wood lignin methoxy groups (δ13CLM and δ2HLM values) have been shown to be reliable proxies of past temperature variations. Previous studies showed that δ2HLM values even work in temperate environments where classical tree-ring width and maximum latewood density measurements are less successful for climate reconstructions. Here, we analyse the annually resolved δ13CLM values from 1916–2015 of four beech trees (Fagus sylvatica) from a temperate site near Hohenpeißenberg in southern Germany and compare these data with regional- to continental-scale climate observations. Initial δ13CLM values were corrected for the Suess effect (a decrease of δ13C i…
Rational normal curves and Hadamard products
2021
AbstractGiven $$r>n$$ r > n general hyperplanes in $$\mathbb P^n,$$ P n , a star configuration of points is the set of all the n-wise intersection of the hyperplanes. We introduce contact star configurations, which are star configurations where all the hyperplanes are osculating to the same rational normal curve. In this paper, we find a relation between this construction and Hadamard products of linear varieties. Moreover, we study the union of contact star configurations on a same conic in $$\mathbb P^2$$ P 2 , we prove that the union of two contact star configurations has a special h-vector and, in some cases, this is a complete intersection.
The 13C urea breath test in the diagnosis of Helicobacter pylori infection
1999
Summary The urea breath test (UBT) is one of the most important non-invasive methods for detecting Helicobacter pylori infection. The test exploits the hydrolysis of orally administered urea by the enzyme urease, which H pylori produces in large quantities. Urea is hydrolysed to ammonia and carbon dioxide, which diVuses into the blood and is excreted by the lungs. Isotopically labelled CO2 can be detected in breath using various methods. Labelling urea with 13 C is becoming increasingly popular because this non-radioactive isotope is innocuous and can be safely used in children and women of childbearing age. Breath samples can also be sent by post or courier to remote analysis centres. The …