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61.
《Analytical letters》2012,45(10):655-667
Abstract Radiometric and spectrophotometric procedures for selenium analysis have been developed which are based on the formation and separation of the mono-and di-piazseLenols of 3,3′-diaminobenzidine. Analysis of samples, reaction conditions, and sensitivity of the procedures are discussed. 相似文献
62.
For more than three decades the International Atomic Energy Agency (IAEA) has supported projects on food, nutrition and environment
for strengthening the analytical capabilities in developing countries (DCs). Over time, such efforts have led to the development
of proper study designs, harmonization of sampling protocols, adequate contamination control and evaluation of the suitability
of competing analytical techniques for the determination of specific analytes. Collectively, these consistent IAEA initiatives
have promoted harmonization of chemical measurements thus facilitating comparability of results of filed investigations. Importantly,
the Agency's efforts have infused a measure of metrological awareness in measurements carried out in field studies, including
physiological measurements. Nuclear and isotopic techniques have played an important role in reaching these goals by establishing
reliable measurement processes for application in health care studies. 相似文献
63.
64.
设G是一个简单图,在G上当且仅当两个顶点的距离为2时增加一条边,所得的图称为G的平方,记作G2;在G上每个顶点都增加一条悬挂边所得的图称为G的冠,记作I(G).设Pn是n个顶点的路,本文给出了I(Pn2)、I(Fn)、F2n徊和I(Fn2)的序列标号. 相似文献
65.
Nitric acid (HNO3) plays an important role in the Earth’s atmosphere as a reservoir molecule of NOx species. It has a strong infrared signature at 11 μm which is one of the most commonly used for the infrared retrieval of this species in the atmosphere since this spectral region coincides with an atmospheric window. It is therefore essential to have high quality spectral parameters in this spectral region. For the H14NO3 (main) isotopic species, the 11 μm bands were already the subject of numerous extensive studies which involve not only the ν5 and 2ν9 cold bands but also the first hot bands. The present work is the first high resolution Fourier transform analysis of the 11 μm bands for H15NO3, which is the second most abundant isotopomer of nitric acid [a ≅ 0.00365(7)]. In this way, the analysis of the ν5 and 2ν9 cold bands centered at 871.0955 and 893.4518 cm−1 was performed, and as for H14NO3, these bands are significantly perturbed since rather strong resonances couple the 51 and 92 rotational levels. The theoretical model that we used to compute the line positions and line intensities is directly issued from the one which we used recently for H14NO3 [A. Perrin, J. Orphal, J.-M. Flaud, S. Klee, G. Mellau, H. Mäder, D. Walbrodt, M. Winnewisser, J. Mol. Spectrosc. 228 (2004) 375-391]. Actually, for the H15NO3 line positions, the Hamiltonian matrix accounts for the rather strong Fermi and the weaker Coriolis interactions linking the 51⇔92 rotational levels. Using this model which accounts correctly for the strong mixing of the 51 and 92 upper state energy levels, the ν5 and 2ν9 line intensities for H15NO3 were satisfactorily computed using the ν5 and 2ν9 transition moment operators achieved previously for the 14N (main) isotopic species. In this way, the transfer of intensities from the ν5 fundamental (and presumably strong) band to the 2ν9 overtone (and presumably weak) band could be explained for H15NO3 as it was done previously for the 14N (main) isotopic species. Finally, the position of the H15NO3ν5 + ν9 − ν9 hot band was identified at 875.245 cm−1. 相似文献
66.
67.
The main result of this paper establishes that the irregularity strength of any tree with no vertices of degree two is its number of pendant vertices. 相似文献
68.
Structural Revision and Elucidation of the Biosynthesis of Hypodoratoxide by 13C,13C COSY NMR Spectroscopy
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Lena Barra Dr. Kerstin Ibrom Prof. Dr. Jeroen S. Dickschat 《Angewandte Chemie (International ed. in English)》2015,54(22):6637-6640
Feeding of (2,3,4,5,6‐13C5)mevalonolactone to the fungus Hypomyces odoratus resulted in a completely labeled sesquiterpene ether. The connectivity of the carbon atoms was easily deduced from a 13C,13C COSY spectrum, revealing a structure that was different from the previously reported structure of hypodoratoxide, even though the reported 13C NMR data matched. A structural revision of hypodoratoxide is thus presented. Its absolute configuration was tentatively assigned from its co‐metabolite cis‐dihydroagarofuran. Its biosynthesis was investigated by feeding of (3‐13C)‐ and (4,6‐13C2)mevalonolactone, which gave insights into the complex rearrangement of the carbon skeleton during terpene cyclization by analysis of the 13C,13C couplings. 相似文献
69.
Nicholle G. A. Bell Adam A. L. Michalchuk John W. T. Blackburn Dr. Margaret C. Graham Dr. Dušan Uhrín 《Angewandte Chemie (International ed. in English)》2015,54(29):8382-8385
Humic substances, the main component of soil organic matter, could form an integral part of green and sustainable solutions to the soil fertility problem. However, their global‐scale application is hindered from both scientific and regulatory perspectives by the lack of understanding of the molecular make‐up of these chromatographically inseparable mixtures containing thousands of molecules. Here we show how multidimensional NMR spectroscopy of isotopically tagged molecules enables structure characterization of humic compounds. We illustrate this approach by identifying major substitution patterns of phenolic aromatic moieties of a peat soil fulvic acid, an operational fraction of humic substances. Our methodology represents a paradigm shift in the use of NMR active tags in structure determination of small molecules in complex mixtures. Unlike previous tagging methodologies that focused on the signals of the tags, we utilize tags to directly probe the identity of the molecules they are attached to. 相似文献
70.
Dr. Ramona Riclea Prof. Dr. Jeroen S. Dickschat 《Angewandte Chemie (International ed. in English)》2015,54(41):12167-12170
The sesquiterpenoid 7‐epi‐neopetasone was synthesized via the Wieland–Miescher ketone. The compound was identical to a previously tentatively identified headspace constituent of Penicillium roqueforti. Feeding experiments with 13C‐labeled mevalonolactone isotopomers demonstrated that oxidation at C12 and an isomerization of the C11?C12 to a C7?C11 double bond must occur independently and not via a C7‐C11‐C12 allyl radical in one step. Feeding with (11,12,13‐13C3)‐7‐epi‐neopetasone resulted in labelling of the PR toxin, thus establishing this compound as a newly identified pathway intermediate. 相似文献