Amphoteric behavior of di-2-pyridyl ketone benzoylhydrazone in ethanol-water mixtures

The ligand di-2-pyridyl ketone benzoylhydrazone (DPKBH) is widely used for the determination of transition metal ions in environmental samples. Due to its low solubility in water it is used in aqueous-ethanol (1:1) solvent and for higher sensitivity the pH must be properly adjusted. The properties of DPKBH solutions must be known at different ethanol-water percentages in order to achieve higher sensitivity and/or selectivity for metal analysis. The acid-base behavior of this reagent in aqueous-ethanol solvent and the dissociation/ionization constants (pK1 and pK2) of DPKBH have been determined in different aqueous-ethanol solvent mixtures (10, 20, 30 and 50 % V/V of ethanol) from potentiometric titrations at 25.0 ± 0.1° C. As the amount of ethanol increases from 10 to 30% the pK1 and pK2 values increased, but they decreased in 50% of the organic solvent. The results are correlated with the medium composition and its effects.

Profile of organic acid concentrations in the digestive gland and hemolymph of Biomphalaria glabrata under estivation

Using high performance liquid chromatography (HPLC) analysis it was possible to determine simultaneously the concentration of organic acids (pyruvate, lactate, succinate, fumarate, malate, acetate, propionate, acetoacetate, and ß-hydroxybutyrate) in the digestive gland and the extracellular concentration of these same acids in the hemolymph of estivating Biomphalaria glabrata, the intermediate host of Schistosoma mansoni. After a 7 day period of estivation, there was a significant increase in the tissue levels of lactate, succinate, malate and acetate compared to non-estivating snails. After 14 days of estivation, the levels of lactate and acetate were also significantly elevated. The hemolymph concentrations of pyruvate and acetate increased significantly after 7 days and acetate concentrations continued to be significantly increased up to 14 days of estivation. The other organic acids studied, such as ketone body acetoacetate and ß-hydroxybutyrate or the volatile acid propionate, did not accumulate. Their tissue concentrations, however, increased on the 7th day of estivation and reached normal levels within two weeks of estivation for some of them. One should take into consideration how the reduction in metabolism can be handled under aerobic conditions, and what role anaerobic pathways may play in both energy formation and redox balance processes.

Serine protease activities in Oxysarcodexia thornax (Walker) (Diptera: Sarcophagidae) first instar larva

We report for the first time the expression of multiple protease activities in the first instar larva (L1) of the flesh fly Oxysarcodexia thornax (Walker). Zymographic analysis of homogenates from freshly obtained L1 revealed a complex proteolytic profile ranging from 21.5 to 136 kDa. Although some activities were detected at pH 3.5 and 5.5, the optimum pH for most of the proteolytic activities was between pH 7.5 and 9.5. Seven of 10 proteases were completely inactivated by phenyl-methyl sulfonyl-fluoride, suggesting that main proteases expressed by L1 belong to serine proteases class. Complete inactivation of all enzymatic activities was obtained using N-p-Tosyl-L-phenylalanine chloromethyl ketone (100 µM), a specific inhibitor of chymotrypsin-like serine proteases.

Higher glandular trichome density in tomato leaflets and repellence to spider mites

The objective of this work was to evaluate the feasibility of selection for higher glandular trichome densities, as an indirect criterion of selection for increasing repellence to spider mites Tetranychus urticae, in tomato populations derived from an interspecific cross between Lycopersicon esculentum x L. hirsutum var. glabratum PI 134417. Trichome densities were evaluated in 19 genotypes, including 12 from advanced backcross populations, derived from the original cross L. esculentum x L. hirsutum var. glabratum PI 134417. Counts were made both on the adaxial and abaxial leaf surfaces, and trichomes were classified into glandular types IV and VI, other glandular types (types I+VII), and nonglandular types. Mite repellence was measured by distances walked by mites onto the tomato leaf surface after 20, 40 and 60 min. Spider mite repellence biotests indicated that higher densities of glandular trichomes (especially type VI) decreased the distances walked by the mites onto the tomato leaf surface. Selection of plants with higher densities of glandular trichomes can be an efficient criterion to obtain tomato genotypes with higher resistance (repellence) to spider mites.

Transformações químicas do (+)-10b,14-diol-allo-aromadendrano, isolado de duguetia glabriuscula r. e. fries (r. e. fries) (annonaceae) e avaliações biológicas de alguns derivados obtidos

The sesquiterpene (+)-allo-aromadendrane-10b-14-diol 1 was the lead compound to the preparation of several derivatives in order to test their biological activity against A. salina, C. sphaerospermum, E. coli and S. aureus. In this way the monoalcohols (+)-viridiflorol 4, 9 and 11 were synthesized from 1 together with the acetal 6, the ketal 7, and the ketone 8. The oxirane 3 and nitrile 5 were also prepared using as an intermediate the tosylate derivative 2.

Fotólise no estado estacionário e com pulso de laser de 1-benzociclanonas e de seus derivados a,a -dimetilados

Laser excitation of 0.01 M solutions of 1-indanone (Ia), 1-tetralone (Ib), 1-benzosuberone (Ic), and their a,a -dimethyl derivatives IIa-c, respectively, in benzene, produced transients with maximum absorption at 425 nm, and lifetimes ranging from 62 ns (IIa) to 5.5ms (Ic). Quenching studies using well known triplet quenchers such as 1,3-cyclohexadiene and oxygen demonstrated the triplet nature of these transients. In the presence of hydrogen donors, such as 2-propanol, the triplet state decay of the ketones Ia-c leads to the formation of the corresponding ketyl radicals, i.e. IIIa-c, which show absorption spectra very similar to the parent ketone, with lmax at 430 nm and lifetime in excess of 20 ms. Steady state irradiations show that the a,a -dimethyl ketones IIa and IIc form ortho-alkyl benzaldehydes probably derived from an initial a-cleavage of the corresponding triplet excited states.

Wilhelm Michler, uma aventura científica nos trópicos

Wilhelm Michler lived in Brazil for seven years from 1882 to 1889, when he died. Here, he published several articles on natural products, and became a professor of Industrial Chemistry at the Escola Politécnica, in Rio de Janeiro. He was respected by colleagues and students. This article addresses this poorly known period of the life of a scientist, world-famous by the aromatic ketone that carries his name.

Efeito da substituição por átomos de flúor no equilíbrio conformacional de chalcona

Chalcone (1) and its fluorinated derivatives 2-4, as well as their cyclic analogues 5-10, were synthesized through an aldol condensation reaction between the corresponding ketone and aldehyde. These compounds were characterized by IR, EIMS and ¹H and 13C NMR spectral data. Modern NMR techniques allowed us to conclude that the compounds obtained show E configuration. These techniques were also employed to investigate the equilibrium involving the s-cis and s-trans conformations of 1-4, with this equilibrium being dependent on the fluorine substitution on both aromatic rings, A or B. IR studies indicated that the yield of the s-cis conformation in the fluorinated derivatives is 57.4±1.4; 88.1±0.4 and 66.4±0.7%, for 2, 3 and 4, respectively, based on previous ¹H NMR calculations for chalcone. Theoretical calculations, using the MMX method, were employed to justify the variation of chemical shifts for the fluorinated derivatives and cyclic analogues. These chemical shifts are consequence of the anisotropic effect showed by the carbonyl group on these compounds.

Análise de glicocorticosteróides por CG-EM: uma nova abordagem de derivatização para o controle de dopagem no esporte

Glucocorticosteroids (CT) show a powerful anti-inflammatory effect. In view of this, they are extensively used in sports medicine, but their misuse (systemic administration) can lead to severe injuries on athletes and has been restricted by the IOC in recent years. For GC-MS analysis, a derivatization step is necessary in order to convert them to a stable form, thus preventing thermal breakdown with the loss of the ketone side chain. Derivatization of CT is reviewed and a new approach of silylation is presented for screening of CT in urine.

Uma proposta de síntese para o ensino integrado das disciplinas experimentais de química orgânica e inorgânica nos cursos de graduação

The synthesis of the layered compound VO(PO4)(H2O)2 and its use to oxidize 2-butanol to the ketone 2-butanone, is proposed as an experiment to integrate the organic and inorganic experimental undergraduate chemistry courses, in an atempt to overcome the observed disrupture between organic and inorganic chemistry.

Recuperação de metais de catalisadores de hidrorrefino usados via fusão com KHSO4

This work describes a process for metal recovery from spent NiMo and CoMo/Al2O3 commercial hydrorefining catalysts. The samples were treated by fusion with potassium hydrogen sulfate (5 h, 600 ºC) with a KHSO4/catalyst mass ratio of 10:1. After fusion the solid was solubilized in water (100 ºC), leaving silicon compounds as residue. Losses of nickel and cobalt may reach 16 wt% of the amount present in the sample, depending on the silicon content. Soluble metals were isolated by selective precipitation techniques (nickel, cobalt, aluminum) or by solvent extraction with methyl-isobutyl ketone (molybdenum) in a hydrochloric acid medium. All metals were recovered in very good yields except for nickel and cobalt in the presence of considerable amounts of silicon. Soluble wastes consist of potassium/sodium sulfates/chlorides. Solid wastes correspond to about 4 wt% of the catalyst and can be discarded in industrial dumps.

Determinação de metil-etil-cetona em amostras de urina com amostragem por micro extração em fase sólida (MEFS) em headspace associada à cromatografia gasosa com detector de ionização de chama (CG-DIC)

Methyl ethyl ketone (MEK) is a solvent commonly used in chemical, paint and shoe industry. The aim of this study was to develop and validate a method for urinary quantification of MEK, employing headspace solid phase micro extraction sampling (SPME) coupled to gas chromatography with flame ionization detection (GC-FID). The calibration curve (y=4.6851x-0.0011) presented good linearity with r²=0.9993. Accuracy (94-109%), intra-assay precision (4.07-5.91%) and inter-assay precision (3.03-5.62%) were acceptable. The quantification limit was 0.19 mg/L. This low cost method can be used routinely in the biological monitoring of occupational exposure to MEK, according to the requirements of the Brazilian legislation.

Estudo da reatividade do estado excitado triplete de 1,4-diaza-9-fluorenonas frente a doadores de hidrogênio e de elétron

The effect of the introduction of nitrogen atoms upon the triplet excited state reactivity of 1,4-diaza-9-fluorenone (1) and 1,4-diaza-9-benz[b]fluorenone (2), in acetonitrile, was investigated employing the nanosecond laser flash photolysis technique. The intersystem crossing quantum yield (Φces) for 1 and 2 was determined using 9-fluorenone as a secondary standard (Φces= 0.48, in acetonitrile) and for both diazafluorenones a value of Φces= 0.28 was found. Quenching rate constants ranged from 8.17x10(4) L mol-1 s-1 (2-propanol) to 1.02x10(10) L mol-1 s-1 (DABCO) for 1,4-diaza-9-fluorenone and from 6.95x10(5) L mol-1 s-1 (2-propanol) to 5.94x10(9) L mol-1 s-1 (DABCO) for 1,4-diaza-9-benz[b]fluorenone, depending if the quenching process involves energy, hydrogen or electron transfer. A comparison between quenching rate constants for both diazaflurenones and the parent compound, i.e. 9-fluorenone, a ketone with lowest triple state of ππ* configuration, lead to the conclusion that the reactive triplet excited state for 1,4-diaza-9-fluorenone and 1,4-diaza-9-benz[b]fluorenone has ππ* configuration.

Otimização da etapa de extração do ácido clavulânico presente no caldo de fermentação utilizando misturas de solventes

The purpose of this work was to study four different solvent mixtures intended to increase the yield of the extraction stage of clavulanic acid (CA), which is one of the steps in the purification process. Four central composite rotatable designs (CCRD) were utilized to optimize the solvent mixtures. The variables selected for the factorial design were solvent mixture ratio (mL/mL) and temperature (ºC). The results showed that the yield of CA extracted from fermentation broth with the solvent mixtures of methyl-ethyl-ketone and ethyl acetate, and methyl-isobutyl-ketone and ethyl acetate (44.7 and 50.0%, respectively) was higher than that of the individual ethyl acetate alone (36.5%).

ENZYMATIC RESOLUTION OF ANTIDEPRESSANT DRUG PRECURSORS IN AN UNDERGRADUATE LABORATORY

The use of biocatalysts in synthetic chemistry is a conventional methodology for preparing enantiomerically enriched compounds. Despite this fact, the number of experiments in chemical teaching laboratories that demonstrate the potential of enzymes in synthetic organic chemistry is limited. We describe a laboratory experiment in which students synthesized a chiral secondary alcohol that can be used in the preparation of antidepressant drugs. This experiment was conducted by individual students as part of a Drug Synthesis course held at the Pharmacy Faculty, Lisbon University. This laboratory experiment requires six laboratory periods, each lasting four hours. During the first four laboratory periods, students synthesized and characterized a racemic ester using nuclear magnetic resonance spectroscopy and gas chromatography. During the last two laboratory periods, they performed enzymatic hydrolysis resolution of the racemic ester using Candida antarctica lipase B to yield enantiomerically enriched secondary alcohol. Students successfully prepared the racemic ester with a 70%-81% overall yield in three steps. The enzymatic hydrolysis afforded (R)- secondary alcohol with good enantioselectivity (90%-95%) and reasonable yields (10%-19%). In these experiments, students were exposed to theoretical and practical concepts of aromatic acylation, ketone reduction, esterification, and enzymatic hydrolysis.