Analysis and quantitation of rotenoids and flavonoids in Derris (Lonchocarpus urucu) by high-temperature high-resolution gas chromatography

A glass capillary column coated with PS-086 (15% phenyl-80% methylpolysiloxane, 15 m x 0.30-mm i.d., 0.1-microm film thickness) is used to analyze extracts from Lonchocarpus urucu (Derris urucu). Several secondary metabolites (8 flavonoids, 10 rotenoids) are characterized without derivatization, and the rotenoids are quantitated by high-temperature high-resolution gas chromatography (HTHRGC) and HTHRGC coupled with mass spectrometry (HTHRGC-MS). The limit of detection in flame ionization detection of rotenone is approximately 0.5 microg/mL, and the limit of quantitation was 2 microg/mL. Derris urucu bark is an excellent source of rotenone isomers (80 mg/g), deguelin (30 mg/g), and rotenolone (26 mg/g). Single solvent extractions (hexane, methylene dichloride, acetone, or methanol) are not able to fully extract the flavonoids and rotenoids. Complete extraction is achieved using a mixture of methanol-methylene dichloride (1:1), indicating a complex association of these compounds with the plant tissue. HTHRGC and HTHRGC-MS are shown to be quick and informative tools for the rapid analysis of crude extracts without the need for prior derivatization and fractionation.     

Perfect equilibria of a model of n-person noncooperative bargaining

We study the set of subgame perfect equilibria associated with then-person noncooperative bargaining mechanism proposed by Hart and Mas-Colell (1992). Our results pertain to transferable utility games. The set of perfect equilibria depends on the parameter representing the continuation probability, . For general TU games, we characterize the set of payoffs from perfect equilibria for (a) small values of and (b) large values of . For symmetric games a complete characterization for all values of is provided.We are grateful to Andreu Mas-Colell for help and encouragement and to two referees for every helpful comments.     

Dendromesogens: liquid crystal organizations of poly(amidoamine) dendrimers versus starburst structures

A new series of liquid crystalline poly(amidoamine) (PAMAM) dendrimers is described. These dendrimers are made by attaching to the 0-, 1-, 2-, 3-, and 4-generation of PAMAM-terminal promesogenic units that carry two decyloxy chains in the 3- and 4-positions of their peripheral aromatic ring. X-ray diffraction studies show that all the compounds display a hexagonal columnar mesophase. A high density of aliphatic chains imposes a curved interface with the promesogenic units that forces the molecules to adopt a radial conformation, and therefore, the columnar structure. A model for the supramolecular organization of the different generations within the columnar mesophase is proposed based on the variation of some of the structural parameters.     

Synthesis and properties of two new series of isomeric liquid crystalline polyesters with conjugated double bonds

Two homologous series of flexible main chain liquid crystalline polyesters with isomeric mesogenic groups containing conjugated double bonds, were synthesized and studied by differential scanning calorimetry and optical microscopy. One series (S1) has the p-phenylene-diacryloyloxydibenzoyl moiety as a mesogenic unit. The other (S2) has the terephtaloyl dioxydicinnamoyl moiety as a mesogenic unit. The reactivity of the conjugated double bonds of the p-phenylenediacryloxy unit, at the temperature of mesophase formation, impedes the stability of liquid crystalline mesophases of polymers of series (S1). Two low molecular weight analogues of polymers were also prepared and their properties compared with those of polymers of similar structure. The two model compounds form stable smectic mesophases over a wide range of temperatures, which shows the high mesomorphogenic ability of both mesogenic units.     

Columnar mesomorphic organizations in cyclotriphosphazenes

A synthetic strategy has been developed to prepare cyclotriphosphazenes that bear polycatenar aromatic esters as promesogenic units linked to phosphorus atoms. The microsegregation of the rigid and flexible parts of the system and the space-filling properties are the driving forces that determine the kind of mesomorphism exhibited by the organocyclotriphosphazenes. Mesogenic units that contain only one terminal alkyl chain give rise to calamitic mesomorphism, since the molecules are arranged to give a cylindrical superstructure with the aromatic promesogenic cores elongated in a manner approximately perpendicular to the cyclotriphosphazene ring. On the other hand, mesogenic units that contain three long terminal chains exhibit columnar mesophases. In this case, a discotic structure consisting of promesogenic cores arranged approximately parallel to the cyclotriphosphazene ring can explain the columnar organization. The X-ray diffraction patterns corresponding to the Col(h) mesophase of the cyclotriphosphazene with dodecyloxy chains (8) indicate the presence of helical ordering, which was confirmed for a homologous compound bearing stereogenic centers on two of the terminal chains (11). All of the synthesized phosphazenes show a high thermal stability.     

Photochemistry and Photobiological Properties of Dicloran, a Postharvest Fungicide with Photosensitizing Side Effects

Photochemical and laser flash photolysis studies on dicloran have shown that this fungicide undergoes photo-reactions such as photoreduction of the nitro group and homolytic rupture of the C-NH₂ bond. Dramatic changes in the dicloran photoreactivity by the influence of the solvents have been observed. More efficient photodegradation of this fungicide was observed in diethyl ether and chloroform than in methanol or acetonitrile. Photoreduction of the nitro group from the dicloran triplet state seems to be the most important photodegradation path-way in solvents of low polarity. Hydrogen abstraction by the triplet state or the intermediate radicals appears to be in the origin of linoleic acid peroxidations photosensitized by dicloran. The photohemolysis assay has been used, as an in vitro phototoxicity test, to demonstrate the involvement of radical-mediated cellular membrane damage in dicloran photosensitization.     

Zirconium removal from uranium/hydrogen carbonate solutions by adsorption on managanese dioxide

In order to determine the best conditions for removing⁹⁵Zr from uranium/hydrogen carbonate solutions, the adsorption behavior of fission product⁹⁵Zr on hydrated MnO₂ as a function of HCO ₃ ^– ion molarity has been studied both in the presence and absence of uranium. Batch experiments showed that the maximum⁹⁵Zr uptake occurred at low HCO ₃ ^– concentration, both in uranium-free and uranium (at a constant molarity of 0.02) containing solutions, the relative⁹⁵Zr uptake being lower when uranium was present in the solution. Conversely, when the HCO ₃ ^– concentration augmented beyond 0.10M, the⁹⁵Zr uptake was higher for the uranium containing solution. Concerning this last case, the maximum⁹⁵Zr uptake was found at a 0.06M HCO ₃ ^– concentration. However at this HCO ₃ ^– concentration, uranium was observed to precipitate and thus, a HCO ₃ ^– concentration of 0.12M was chosen to perform the dynamic⁹⁵Zr removal by MnO₂ from uranium/hydrogen carbonate solutions. Under these conditions, the⁹⁵Zr removal reached 99%.     

Analysis of (NH4)2SO4/(NH4)H2PO4 mixtures by thermogravimetry and X-ray diffraction

(NH₄)₂SO₄ and (NH₄)H₂PO₄ are the principal components in the powder material used in fire extinguishers. In this paper the mutual influence in their thermal decomposition is investigated by thermogravimetry. Two methods for the quantification of both salts in mixtures (NH₄)₂SO₄/(NH₄)H₂PO₄ are proposed. The first employs thermogravimetry and is based on the measurement of the mass fraction in the 500-550 °C interval, once (NH₄)₂SO₄ has totally decomposed to yield gaseous products. The second uses some selected peaks in the X-ray diffractogram.     

An improved outdoor calibration procedure for broadband ultraviolet radiometers

This article aims at improving the broadband ultraviolet radiometer's calibration methodology. For this goal, three broadband radiometers are calibrated against a spectrophotometer of reference. Three different one-step calibration models are tested: ratio, first order and second order. The latter is proposed in order to adequately reproduce the high dependence on the solar zenith angle shown by the other two models and, therefore, to improve the calibration performance at high solar elevations. The proposed new second-order model requires no additional information and, thus, keeps the operational character of the one-step methodology. The models are compared in terms of their root mean square error and the most qualified is subsequently validated by comparing its predictions with the spectrophotometer measurements within an independent validation data subset. Results show that the best calibration is achieved by the second-order model, with a mean bias error and mean absolute bias error lower than 2.2 and 6.7%, respectively.