On the stabilization of conducting pernigraniline salt by the synthesis and oxidation of polyaniline in hydrophobic ionic liquids

The electrochemical polymerization of aniline in a hydrophobic room-temperature ionic liquid and the spectroelectrochemical characterization of the formed film are presented. The polymerization occurs without the presence of acid in 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (BMMITFSI), leading to a very stable electroactive material where no degradation was observed even at high applied potentials. Both in situ UV-Vis and Raman spectroscopic studies provided evidence for the stabilization of pernigraniline salt at high oxidation potentials and that this polyaniline state is the conducting form, as was corroborated by in situ resistance measurements. These data are indicative that low conductivity is not an intrinsic property of pernigraniline salt and this point must be reconsidered.     

Mixture design optimization of extraction and mobile phase media for fingerprint analysis of Bauhinia variegata L

Two statistical mixture designs were used to optimize the proportions of solvents used in both the extraction medium and the reversed liquid chromatographic mobile phase to improve the quality of chromatographic fingerprints of Bauhinia variegata L extracts. For modeling, the number of peaks was used as a measure of fingerprint information. Three mobile phases, each with a chromatographic strength of two, gave good results. A methanol/water (77:23 v/v) mixture resulted in 17 peaks in the chromatographic fingerprint whereas acetonitrile/water (64.5:35.5 v/v) and methanol/acetonitrile/water (35:35:30 v/v/v) mixtures resulted in 18 and 20 peaks, respectively. The corresponding optimum solvent compositions to extract chemical substances for these three mobile phases were ethanol/acetone (25:75 v/v/v) and dichloromethane/acetone (70:30 v/v) mixtures, and pure dichloromethane, respectively. The mixture designs are useful for understanding the influence of different solvents on the strengths of the extraction medium and the mobile phase.     

On the molecular structure of uranium dicarbide: T-shape versus linear isomers

A theoretical study of the molecular structure of uranium dicarbide has been carried out employing DFT, coupled cluster, and multiconfigurational methods. A triangular species, corresponding to a (5)A(2) electronic state, has been found to be the most stable UC(2) species. A triplet linear CUC species, which has been observed in recent infrared spectroscopy experiments, lies much higher in energy. A topological analysis of the electronic density has also been carried out. The triangular species is shown to be in fact a T-shape structure with a U-C interaction which can be considered to be a closed-shell interaction.     

Enantioselective organo-SOMO cycloadditions: a catalytic approach to complex pyrrolidines from olefins and aldehydes

A new method to rapidly generate pyrrolidines via a SOMO-activated enantioselective (3 + 2) coupling of aldehydes and conjugated olefins has been accomplished. A radical-polar crossover mechanism is proposed wherein olefin addition to a transient enamine radical cation and oxidation of the resulting radical furnish a cationic intermediate which is vulnerable to nucleophilic addition of a tethered amine group. A range of olefins, including styrenes and dienes, are shown to provide stereochemically complex pyrrolidine products with high chemical efficiency and enantiocontrol.     

Application of thermal analysis to the study of anti-tuberculosis drug compatibility. Part 1

Worldwide Brazil is among one of the 22 countries with high rates of tuberculosis placing this disease as a priority for the Government Health Policies in this country. Studies with the main tuberculostatic drugs rifampicin, isoniazid, pyrazinamide, and ethambutol, aiming the development of fixed-dose combination formulations (FDCs) have been performed. The aim of this study was to evaluate the thermal behavior of these drugs by DSC, TG/DTG, and DTA in order to predict possible physical and chemical interactions between tuberculostatics. DSC and DTA curves suggested incompatibility and/or interactions among drug preparations resulting from new thermal events, as well as the disappearance and shift of the melting point of the drugs. TG/DTG curves of drug mixtures presented different profiles from those observed for the individually tested drugs, supporting the evidence of drug incompatibility and indicating that mixtures are less stable when compared to the drugs alone.     

Essential oil from the leaves of Annona vepretorum: chemical composition and bioactivity

The essential oil from the leaves of Annona vepretorun was obtained by hydrodistillation using a Clevenger-type apparatus and analyzed by GC-MS and GC-FID. Eighteen compounds representing 98.1% of the crude essential oil were identified. The major compounds identified were bicyclogermacrene (43.7%), spathulenol (11.4%), alpha-felandrene (10.0%), alpha-pinene (7.1%), (E)-beta-ocimene (6.8%), germacrene D (5.8%), and p-cymene (4.2%). The trypanocidal activity against Trypanosoma cruzi epimastigote forms, as well as, the antimicrobial and antioxidant proprieties was investigated. The essential oil showed a potent trypanocidal activity with IC50 value of 31.9 +/-1.3 microg x mL(-1). For antimicrobial activity, the best result was observed against Candida tropicalis with a MIC value of 100 microg x mL(-1). For antioxidant capacity the essential oil showed weak activity.     

Reactions of the tetrafluoroborate complex [Mo2Cp2(κ(2)-F2BF2)(μ-PPh2)2(CO)]BF4 with mono- and bidentate ligands having E-H bonds (E = O, S, Se, N, P)

The title compound reacted rapidly with CN(t)Bu at room temperature by displacing the BF(4)(-) ligand and incorporating three molecules of isocyanide to yield the electron-precise complex [Mo(2)Cp(2)(μ-PPh(2))(2)(CN(t)Bu)(3)(CO)](BF(4))(2), which was obtained as a mixture of cis and trans isomers. Reaction with several HER(n) molecules (HER(n) = HSPh, HSePh, H(2)PCy) took place with formal elimination of HBF(4) and spontaneous carbonylation to give the electron-precise cations [Mo(2)Cp(2)(μ-ER(n))(μ-PPh(2))(2)(CO)(2)](+). Reactions with several bidentate ligands (L(2)H) having acidic E-H bonds (2-hydroxypyridine, 2-mercaptopyridine, cathecol, 2-aminophenol, and 2-aminothiophenol) proceeded analogously with deprotonation of these bonds with the preference E = S > O > N. The N,O-donor ligands yielded 32-electron chelate derivatives of the type [Mo(2)Cp(2)(O,N-L(2))(μ-PPh(2))(2)(CO)]BF(4) (L(2) = OC(5)H(4)N, OC(6)H(4)NH(2)), whereas the S,N-donors yielded 34-electron, S-bridged complexes [Mo(2)Cp(2)(μ-S:S,N-L(2))(μ-PPh(2))(2)(CO)]BF(4) [L(2) = SC(5)H(4)N (Mo-Mo = 2.8895(8) ?), SC(6)H(4)NH(2)]. However, reaction with catechol gave a monodentate derivative [Mo(2)Cp(2)(O-OC(6)H(4)OH)(μ-PPh(2))(2)(CO)]BF(4). In contrast, reactions of the title complex with several carboxylic acids and related species (acetic, benzoic, and thioacetic acids, acetamide, thioacetamide, and sodium diethyldithiocarbamate) were insensitive to the nature of the donor atoms and gave in all cases 32-electron chelate derivatives of type [Mo(2)Cp(2)(κ(2)-L(2))(μ-PPh(2))(2)(CO)]BF(4). All of the above cations having Mo-bound OH, NH, or NH(2) groups were easily deprotonated upon reaction with 1,8-diazabicycloundec-7-ene (DBU) or other bases to give neutral complexes which exhibited different coordination motifs depending on the donor atoms, including chelate complexes of the type [Mo(2)Cp(2)(κ(2)-L(2)')(μ-PPh(2))(2)(CO)] (L(2)' = OC(6)H(4)O, OC(6)H(4)NH), the bridged complexes [Mo(2)Cp(2)(μ-S,N:S,N-SC(6)H(4)NH)(μ-PPh(2))(2)] and [Mo(2)Cp(2){μ-S,N-N(S)CMe}(μ-PPh(2))(2)], and the terminal acetylimido complex [Mo(2)Cp(2){N-N(O)CMe}(μ-PPh(2))(2)(CO)].     

Whistle variability in South Atlantic spinner dolphins from the Fernando de Noronha archipelago off Brazil

A series of quali- and quantitative analyses were conducted to evaluate the variability of spinner dolphin whistles from the Fernando de Noronha Archipelago off Brazil. Nine variables were extracted from each whistle contour, and the whistle contours shapes were classified into the seven categories described in Driscoll (1995). The analysis showed mean beginning and ending frequencies values of 10.78 and 12.74 kHz, respectively. On average, whistle duration was relatively short, with mean values around 0.495 s (N=702). Comparative analyses were also conducted to investigate the relationship between the obtained results and those presented in previous studies. When comparing averages, the results of the study of Oswald et al.(2003) in the Tropical Eastern Pacific (TEP) presented less significant differences in relation to this study; only whistle duration differed significantly between both works. The results of multivariate classification tests also pointed TEP population as the closest related to the population studied here. The similarities between such disjunct populations might be attributed to a more recent isolation event (the closing of the Panama Isthmus) than the divergence that has driven North and South Atlantic populations apart.     

An efficient approach toward the synthesis of the A/B rings of ouabain

The synthesis of the highly functionalized A/B ring related to ouabain has been accomplished efficiently from commercially available α-tetralone. A key Birch reductive alkylation allows the building of an angularly substituted decalone that was adequately functionalized to produce the intermediate 2c.     

Effects of DNA on the growth and optical properties of luminescent organic microcrystals

The reprecipitation method, which is a solvent-exchange process, was used to prepare free-standing microcrystals from an organic fluorescent dye, 4-n-octylamino-7-nitrobenz-2-oxa-1,3-diazole. Calf thymus DNA was introduced as an additive into the reprecipitation medium, strongly accelerating the process. The reprecipitation kinetics was monitored by UV/vis absorption spectroscopy, and the analysis of the rate constants allowed the role played by the additive to be clarified. DNA was also found to affect the shape and size of the dye microcrystals obtained. In particular, its presence induced the formation of a new type of microcrystal that displays original two-color fluorescence. The emission properties were first analyzed on the suspensions, using a traditional fluorimeter, and then on individual microcrystals by means of a space- and time-correlated photon-counting photomutiplier installed on a microscope. The study on single microcrystals suggests that the dual coloration observed originates from the reabsorption of the blue component of the emitted light, whereas the remaining red component propagates through the microcrystal body and is scattered by the edges. However, the color of the other types of microcrystals can be explained only by specific arrangements of molecules at the surface of the crystal.