RESUMEN
Two simple chemosensors with urea (L1) and thiourea (L2) groups were synthesized and studied by different spectroscopic techniques. Both receptors can sense acetate (Ac-), dihydrogen phosphate (H2PO4 -), and fluoride (F-) anions, accompanied by changes in UV-vis and 1H NMR spectra, and an optical response is observed as a color change of the solutions due to deprotonation and hydrogen-bonding processes. Also, L1 and L2 were supported on TentaGel resins (R1 and R2), and their fluoride-sensing properties in DMSO and water solutions were studied. Interestingly, R2 can sense fluoride ions in sample solutions of 100% water.
RESUMEN
Through a simple proposal, the charge transfer obtained from the cornerstone theory of Parr and Pearson is partitioned, for each reactant, in two channels: an electrophilic, through which the species accepts electrons, and the other, a nucleophilic, where the species donates electrons. It is shown that this global model allows us to determine unambiguously the charge-transfer mechanism prevailing in a given reaction. The partitioning is extended to include local effects through the Fukui functions of the reactants. This local model is applied to several emblematic reactions in organic and inorganic chemistry, and we show that besides improving the correlations obtained with the global model it provides valuable information concerning the atoms in the reactants playing the most important roles in the reaction and thus improving our understanding of the reaction under study.
RESUMEN
Eleven oleanane-type saponins (1-11) have been isolated from Microsechium helleri and Sicyos bulbosus roots and were evaluated for their antifeedant, nematicidal and phytotoxic activities. Saponins {3-O-ß-D-glucopyranosyl (1â3)-ß-D-glucopyranosyl-2ß,3ß,16α,23-tetrahydroxyolean-12-en-28-oic acid 28-O-α-L-rhamnopyranosyl-(1â3)-ß-D-xylopyranosyl-(1â4)-[ß-D-xylopyranosyl-(1â3)]-α-L-rhamnopyranosyl-(1â2)-α-L-arabinopyranoside} (1), and {3-O-ß-D-glucopyranosyl-2ß,3ß,16α,23-tetrahydroxyolean-12-en-28-oic acid 28-O-α-L-rhamnopyranosyl-(1â3)-ß-D-xylopyranosyl-(1â4)-[ß-D-xylopyranosyl-(1â3)]-α-L-rhamnopyranosyl-(1â2)-α-L-arabinopyranoside} (2) were also isolated from M. helleri roots together with the two known compounds 3 and 4. Seven known structurally related saponins (5-11) were isolated from S. bulbosus roots. The structures of these compounds were established as bayogenin and polygalacic glycosides using one- and two-dimensional NMR spectroscopy and mass spectrometry. Compounds 7, 10, bayogenin (12) and polygalacic acid (13) showed significant (p<0.05) postingestive effects on Spodoptera littoralis larvae, compounds 5-11 and 12 showed variable nematicidal effects on Meloydogyne javanica and all tested saponins had variable phytotoxic effects on several plant species (Lycopersicum esculentum, Lolium perenne and Lactuca sativa). These are promising results in the search for natural pesticides from the Cucurbitaceae family.