1,721,040 research outputs found
STRUCTURE ELUCIDATION AND PHYTOTOXICITY OF C13 NOR-ISOPRENOIDS FROM CESTRUM PARQUI
No full textTwelve C13 nor-isoprenoids have been isolated from the leaves of Cestrum parqui (Solanaceae). The structure (2R,6R,9R)-2,9-
dihydroxy-4-megastigmen-3-one has been assigned to the new compound. All the structures have been determined by spectroscopic
means and chemical correlations. The compounds showed phytotoxic effect on the germination and growth of Lactuca sativa L
Xenobiotics in the environment: an investigation on the transformation kinetics, the environmental metabolites and their formation mechanisms.
No full textWater-extractable organic matter and enzyme activity in three forest soils of the Mediterranean area
No full textSoil enzyme activities mediate key ecosystem functions of degradation, transformation and carbon mineralization. The study of microbial activity and its relations with water-extractable organic matter (WEOM) can be crucial to understand the dynamics of soil organic carbon pool. We investigated FDA-hydrolytic, β-glucosidase, cellulase, o-diphenol oxidase activities in soils under Fagus sylvatica (beech), Quercus ilex (holm-oak) and Quercus cerris (turkey-oak) stands. We investigated WEOM by liquid-state nuclear magnetic resonance (NMR) spectroscopy, useful to highlight the major functionalities in this fraction of soil organic matter. The highest enzyme activities, on mass basis, were recorded in soil under beech, with the highest organic carbon content. Reporting enzyme activities on organic carbon basis, it was possible to reveal enzyme enrichment for β-glucosidase and diphenol oxidase activities in soil under turkey-oak, with low organic matter. The 1H NMR spectra of WEOM highlighted a great richness of soluble organic compounds in soils with high organic carbon content, such as beech and holm-oak soils. All spectra are dominated by carbohydrate resonances. Spectra of WEOM from each stand exhibited specific signals. In WEOM from holm-oak, signals from substituted aliphatics account for up 28% of the total spectrum; in this sample signals from acetic and formic acids predominate, likely relating to the lower microbial utilization, according to the low heterotrophic (FDA-hydrolytic) activity. Only in WEOM from beech, signals from aromatics were detected probably related to the lower lignin degradation in soil, as expressed by the low phenol oxidase activity. However, the relationships among WEOM quality, tree species and microbial activity need further investigations
Photooxygenation of Heterocycles.
No full textThe photooxygenation of heterocycles represents a versatile and widely accepted tool for introducing
oxygenated functions in a mild, simple and selective way. The review evidences the synthetic potential of the
photooxygenation with particular attention to the reaction of Type II involving singlet oxygen in the first electronically
excited state (1Dg), which has been applied to the most studied heterocycles as furans, thiophenes, pyrroles, oxazoles,
imidazoles, indoles, nitrogen-containing six-membered systems. The singlet oxygenation of these systems occurs mainly
via [4+2] cycloaddition leading to unstable endoperoxides which, in addition to the classical transformations of peroxides
(reduction, hydrolysis, deoxygenation, generally performed at low temperature), afford characteristic rearranged products
depending on the heteroatom, substitution pattern and experimental conditions. 1,2-Oxygen addition can sometimes
compete with the Diels-Alder-type reaction, especially for pyrroles, imidazoles and indoles. The attention has been also
focused to the oxygenation of some biomolecules as histidine, triptophan and guanine which play a significant role in
biological processes as photodynamic effects or in the photoinduced deactivation of nucleic acids
Singlet Oxygen as Key Reagent for Novel C-Nucleosides and Glycosides of Pharmacological Interest
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