Search results for "13C"
showing 10 items of 194 documents
Community structure and physiological characterization of microbial mats in Byers Peninsula, Livingston Island (South Shetland Islands, Antarctica)
2007
The community structure and physiological characteristics of three microbial mat communities in Byers Peninsula (Livingston Island, South Shetland Islands, Antarctica) were compared. One of the mats was located at the edge of a stream and was dominated by diatoms (with a thin basal layer of oscillatorian cyanobacteria), whereas the other two mats, located over moist soil and the bottom of a pond, respectively, were dominated by cyanobacteria throughout their vertical profiles. The predominant xanthophyll was fucoxanthin in the stream mat and myxoxanthophyll in the cyanobacteria-dominated mats. The sheath pigment scytonemin was absent in the stream mat but present in the soil and pond mats. …
Turnover and availability of soil organic carbon under different Mediterranean land-uses as estimated by 13C natural abundance
2013
Summary Soil organic matter (SOM) is an important factor in ecosystem stability and productivity. This is especially the case for Mediterranean soils suffering from the impact of humans and degradation as well as harsh climatic conditions. We used the carbon (C) exchange resulting from C3-C4 and C4-C3 vegetation change under field conditions combined with incubations under controlled conditions to evaluate the turnover and availability of soil organic C under different land-uses. The 40-year succession of Hyparrenia hirta L. (C4 photosynthesis) after more than 85 years of olive (Olea europaea L.) tree (C3 photosynthesis) growth led to the exchange of 54% of soil organic C from C3 to C4 form…
13C NMR of carbonyl compounds. 3. Structure and dynamics of protonated enones and dienones
1984
Abstract The unsaturated ketones 1 1 – 10 10 were protonated at low temperatures and studied by dynamic 13C NMR spectroscopy. Four interconverting stereoisomers were detected which differ in their conformation with respect to the CO and CC (enone) single bond.
Clerodane diterpenoids from Salvia splendens.
2006
Four new clerodane diterpenoids, salvisplendins A-D (1-4), have been isolated from an acetone extract of the flowers of SalVia splendens, together with an artifact (5), arising from salvisplendin D (4) by addition of diazomethane, and the already known clerodane olearin (6). The structures of the new compounds (1-5) were established mainly by 1D and 2D NMR spectroscopic studies and, in the case of salvisplendin A (1), by chemical correlation with splenolide B (7). Complete 1H and 13C NMR assignments for olearin (6), not published hitherto, are also reported.
13C-NMR Based Evaluation of the Electronic and Steric Interactions in Aromatic Amines
2005
Abstract: Chemical shifts of the para carbon atoms, δ(13C-4), in a series of aromatic amines were used to calculate the Ãp, ÃR and ÃOR substituent constants for different amino groups. 1-Pyrrolidino, N,N-di-n-butylamino and N,N-diethylamino groups were found to be the most strong electron-donors. ortho-Substitution decreases the donor properties of the amino group. The amino groups in 2,6-di-i-propylaniline and N,N-2,6-tetramethylaniline have very weak electron-donor properties. The nitrogen atom in benzoquinuclidine and N,N-dimethyl-2,6-di-i-propylaniline have an electron-acceptor character. The calculated substituent constants of the amino groups studied are consistent with the s…
Spectroscopic and conformational properties of size-fractions separated from a lignite humic acid
2007
Abstract A lignite humic acid (HA) was fractionated by preparative high performance size-exclusion chromatography (HPSEC) in seven different size-fractions. The size-fractions were characterized by cross polarization (CP) magic angle spinning (MAS) 13 C NMR spectroscopy and a further analytical HPSEC elution under UV and fluorescence detection. The alkyl hydrophobic components mainly distributed in the largest molecular-size-fraction, whereas the amount of oxidized carbons increased with decreasing size of fractions. Cross polarization time ( T CH ) and proton spin-lattice relaxation time in the rotating frame ( T 1 ρ (H)) were measured from variable contact time (VCT) experiments. The bulk…
Adsorption of dissolved organic matter on clay minerals as assessed by infra-red, CPMAS 13C NMR spectroscopy and low field T1 NMR relaxometry
2011
Abstract Dissolved organic matter (DOM) is a very important environmental constituent due to its role in controlling factors for soil formation, mineral weathering and pollutant transport in the environment. Prediction of DOM physical–chemical properties is achieved by studying its chemical structure and spatial conformation. In the present study, dissolved organic matter extracted from compost obtained from the organic fraction of urban wastes (DOM-P) has been analysed by FT-IR, CPMAS 13C NMR spectroscopy and 1H T1 NMR relaxometry with fast field cycling (FFC) setup. While the first two spectroscopic techniques revealed the chemical changes of dissolved organic matter after adsorption eith…
CHARACTERIZATION OF CHEMICAL AND PHYSICAL PROPERTIES OF BIOCHAR FOR ENERGY PURPOSES AND ENVIRONMENTAL RESTORATION
2014
Biochar production processes as well as its various applications provide numerous benefits to both environment and economy (Lehmann et al., 2006; Basu, 2010). However, understanding the physicochemical structure of this valuable product has to be improved in order to be able to obtain the aforementioned benefits and to avoid environmental costs. In this study, chicken or poultry manure (PM) was chosen as feedstock for biochar preparation. This biomass is traditionally used by farmers as an effective organic fertilizer (Chan et al., 2008). Indeed, it is considered a valuable source for readily available plant nutrients, such as N, P, K and other micronutrients (Huang et al., 2011). Notwithst…
Measurements of Collisional Line Widths in the Stimulated Raman Q-Branch of the v1 Band of Silane
1990
0377-0486; Self-broadened widths of 28SiH4 in the v1 Q-branch have been measured at room temperature (295 K) using high-resolution stimulated Raman spectroscopy. These collisional widths have been obtained by fitting a superposition of Voigt profiles to the experimental spectra in the pressure range 28-154 Torr. No evidence for line mixing within the tetrahedral components of a Q(J) line has been found. The line broadening coefficients for J up to 13 depend weakly on the rotational quantum number. The mean value is 103.7 x 10(-3) cm-1 atm-1.
A remark on hyperplane sections of rational normal scrolls
2017
We present algebraic and geometric arguments that give a complete classification of the rational normal scrolls that are hyperplane section of a given rational normal scrolls.