925 resultados para ¹H and 13C-NMR
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Pós-graduação em Química - IQ
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Pós-graduação em Química - IQ
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The knowledge of the structure characteristic of the Organic Matter is important for the understanding of the natural process. In this context aquatic humic substances (principal fraction) were isolated from water sample collected from the two distinct rivers, using procedure recommended for International Humic Substances Society and characterized by elemental analysis, electron paramagnetic resonance and nuclear magnetic resonance (13C NMR). The results were interpreted using principal component analysis (PCA) and the statistical analyses showed different in the structural characteristics of the aquatic humic substances studied.
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
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The aqueous alcohol extract of the leaves of Alibertia macrophylla afforded two epimeric pairs of iridoid aglycones and one of them showed high inhibitory activity against Aspergillus niger, Cladosporium sphaerospermum, C. cladosporioides and Colletotrichum gloesporioides. Three of the compounds are reported for the first time from natural sources. Their structures were established on the basis of spectroscopic studies, mainly through 13C NMR analysis. © 1992.
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This work describes the creation of heuristics rules based on 13C-NMR spectroscopy that characterize several skeletal types of diterpenes. Using a collection of 2745 spectra we built a database linked to the expert system SISTEMAT. Several programs were applied to the database in order to discover characteristic signals that identify with a good performance, a large diversity of skeletal types. The heuristic approach used was able to differentiate groups of skeletons based firstly on the number of primary, secondary, tertiary and quaternary carbons, and secondly the program searches, for each group, if there are ranges of chemical shifts that identifies specific skeletal type. The program was checked with 100 new structures recently published and was able to identify the correct skeleton in 65 of the studied cases. When the skeleton has several hundreds of compounds, for example, the labdanes, the program employs the concept of subskeletal, and does not classify in the same group labdanes with double bounds at different positions. The chemical shift ranges for each subskeletal types and the structures of all skeletal types are given. The consultation program can be obtained from the authors. © 1997 - IOS Press. All rights reserved.
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Pós-graduação em Química - IQ
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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A phytochemical study of the ethyl acetate extract of the roots and adventitious roots of Spirotropis longifolia, a monodominant tree species of the Guianan rainforest, has allowed the isolation of three compounds: 2- hydroxy-8,9-methylenedioxy-2',2'-dimethylpyrano-[5',6':4,3]-6a-prenyl-[6aS,11aS]-pterocarpan (spirotropin A), 2-hydroxy-8,9-methylenedioxy-2',2'-dimethy1-3',4'-dihydropyrano-[5',6':4,3]-6a-prenyl-(6aS,11aS]-pterocarpan (spirotropin B), and 5,7-dihydroxy-6.8-dipreny1-2 ''''.2 ''''-dimethylpyrano[5 '''',6 '''': 3',4]-isoflavone (spirotropone). In addition, 10 known compounds, trans-oxyresveratrol, trans-resveratrol, piceatannol, daidzein, genistein, isoprunetin, lupeol, latifolol, gnetin D and gnetin E, were also isolated. These compounds were evaluated for their antifungal activity and their cytotoxicity, and their structures were established by 1D and 2D NMR, HRMS, CD and optical rotation measurements. (C) 2011 Elsevier Ltd. All rights reserved.