Parâmetros termodinâmicos da reação de adsorção de boro em solos tropicais altamente intemperizados

The driving force of boron adsorption on some tropical soils was evaluated by means of thermodynamic parameters. The batch method was employed, and the reaction was monitored at different pH values. The Langmuir equation successfully fitted the experimental results and provided reasonable isotherm parameters. Boron adsorption increased as a function of the pH of the soil solution and the concentration of added boron. The reaction was favorable and proceeded spontaneously, being strongly exoergic, as indicated by a negative free energy (deltaG) and a separation factor (K R) < 1. The boron adsorption phenomenon and the soil-solution interface were thermodinamically described using a theoretical model.

Fotoquímica de alfa,alfa-dimetilvalerofenona adsorvida em celulose microcristalina

Irradiation of a,a-dimethylvalerophenone (1) adsorbed on microcrystalline cellulose employing methanol as the solvent shows a Norrish Type II/Type I ratio of 1.0±0.1. In solution, values of 2.3±0.3 in benzene and 8.7±2.0 in terc-butanol were obtained. The cyclization/elimination ratio for the Norrish Type II reaction of 1 shows values of 1.2±0.3 in cellulose, 17.9±2.7 in benzene and 3.2±03 in terc-butanol. When samples of 1/microcrystalline cellulose were prepared employing n-hexane, the Type II/Type I (29.5±2.9) and the cycl/elim (113.3±12.1) ratios were dramatically modified. These results demonstrate the difference in the behavior of 1 when entrapped in the cellulose chains or adsorbed on the cellulose surface.

Polímeros biodegradáveis - uma solução parcial para diminuir a quantidade dos resíduos plásticos

The large use of plastics has generated a waste deposit problem. Today plastic wastes represent 20% in volume of the total waste in the municipal landfills. To solve the disposal problem of plastics methods have been employed such as incineration, recycling, landfill disposal, biodegradation and the use of biodegradable polymers. Incineration of plastic wastes provokes pollution due to the production of poisonous gases. Recycling is important to reduce final costs of plastic materials, but is not enough in face of the amount of discarded plastic. In landfills plastic wastes remain undegraded for a long time, causing space and pollution problems. Biodegradation is a feasible method to treat some plastics, but intensive research is necessary to find conditions for the action of microorganisms. All of these methods are important and the practical application of each one depends on the type and amount of the plastic wastes and the environmental conditions. Therefore, a great deal of research has focused on developing biodegradable plastics and its application because it is an important way for minimizing the effect of the large volume of plastic waste discarded in the world.

Estratégias utilizadas no combate a resistência bacteriana

This article provides an overview on the recent achievements to combat Gram-positive bacteria and the mechanisms related to antimicrobial activity and bacterial resistance. Selected synthetic methodologies to access structurally diverse bioactive compounds are presented in order to emphasize the most important substances currently developed to overcome multiresistant strains. The main properties of vancomycin and related glycopeptide antibiotics are also discussed as a background to understanding the design of new chemotherapeutic agents.

Alquilbenzeno sulfonato linear: uma abordagem ambiental e analítica

The environmental impact of detergents and other consumer products is behind the continued interest in the chemistry of the surfactants used. Of these, linear alkylbenzene sulfonates (LASs) are most widely employed in detergent formulations. The precursors to LASs are linear alkylbenzenes (LABs). There is also interest in the chemistry of these hydrocarbons, because they are usually present in commercial LASs (due to incomplete sulfonation), or form as one of their degradation products. Additionally, they may be employed as molecular tracers of domestic waste in the aquatic environment. The following aspects are covered in the present review: The chemistry of surfactants, in particular LAS; environmental impact of the production of LAS; environmental and toxicological effects of LAS; mechanisms of removal of LAS in the environment, and methods for monitoring LAS and LAB, the latter in domestic wastes. Classical and novel analytical methods employed for the determination of LAS and LAB are discussed in detail, and a brief comment on detergents in Brazil is given.

A reatividade do estado excitado triplete de 1,3-indanodiona em benzeno

Rate constants for the quenching of 1,3-indandione (1) triplet by olefins and by hydrogen and electron donors were obtained employing the laser flash photolysis technique in benzene solution. These rate constants ranged from 2.5x10(5) Lmol-1s-1 (for 2-propanol) to 5.9x10(9) Lmol-1s-1 (for DABCO). From the quenching rate constants by 1,3-cyclohexadiene, trans- and cis-stilbene a value between 49.3 and 52.4 kcal/mol was estimated for the energy of the triplet state of 1,3-indandione. The npi* character of this triplet state was evidenced by the quenching rate constants obtained when typical hydrogen donors were employed as quenchers. For 2-phenyl-1,3-indandione (2, R=phenyl) a fast Norrish type I reaction is operating which prevents the determination of kinetic and spectroscopic data of its triplet state.

Métodos de extração para quantificação de manganês disponível em fertilizantes

The solubility of Mn in different fertilizers (MnSO4.H2O-p.a., MnO2-p.a.+MnO-Ind., MnO2-Ind.+MnO-Ind., MnO2-p.a., MnO2-Ind. and MnO-Ind.) was determined using different methodologies: total content and soluble contents in water, 10% H2SO4, citric acid at 20 g L-1, diluted neutral ammonium citrate, (1+9) and DTPA at 0.005 mol L-1. The Mn solubilities in the latter three extractors were assessed after agitation of the sample for one hour and after boiling for 5 minutes. The extraction procedure using neutral ammonium citrate (1+9), at 1:100, with agitation for one hour, was shown to be the most adequate to assess the availability of Mn in fertilizers.

Constituintes químicos das flores de Pterogyne nitens (Caesalpinioideae)

The phytochemical investigation of the flowers of Pterogyne nitens (Caesalpinioideae) resulted in the isolation and identification of nine phenolic derivatives, quercetin 3-O-sophoroside, taxifolin, astilbin, ourateacatechin, caffeic, ferulic, sinapic, chlorogenic and gallic acid, besides two guanidine alkaloids, pterogynine, pterogynidine. This is the first time these compounds have been reported in P. nitens flowers. As this is a monospecific genus, these secondary metabolites may have taxonomical significance. Their structures were assigned on the basis of spectroscopic analyses, including two-dimensional NMR techniques.

Estudo sobre a utilização da lama vermelha para a remoção de corantes em efluentes têxteis

Red mud is the principal residue of the alumina (Al2O3) industry. Generated during the Bayer process, it is characterized by strong alkalinity and ion exchange. Iron oxides are the principal component (30 to 60%). Annually millions of tons of red mud are generated in the world. Red mud disposal is responsible for a large part of the cost of alumina production. On the other hand, textile industry wastewaters containing dyes have a great impact on the environment and on human health. In this paper the possibility of applying red mud for the removal of dyes was investigated by two processes: adsorption and degradation by the Fenton reagent.

Chemical composition and antimicrobial activity of the essential oil of Hyptis pectinata (l.) Poit.

Essential oil was extracted from leaves of Hyptis pectinata using hydrodistillation, and its composition determined using GC-FID and GC-MS. Chemical analysis showed that there was a predominance of sesquiterpenes, of which β-caryophyllene (18.34%), caryophyllene oxide (18.00%) and calamusenone (24.68%) were measured for the first time in the genus Hyptis. Twenty-one compounds were identified, and calamusenone was isolated using preparative thin layer chromatography with a silica gel plate (60 PF254). The minimal inhibitory concentration (MIC) and minimal microbicidal concentration (MMC) were determined for various pathogenic microorganisms. H. pectinata oil was most effective against Gram (+) bacteria and yeasts.

Validação de métodos para determinação de fluoxetina em cápsulas

A UV spectrophotometric method was developed and validated and a chromatographic method was adapted from the American Pharmacopeia for the analysis of Fluoxetine Hydrochloride capsules. Ethanol was used as solvent for the spectrophotometric method, with detection and determination at 276 nm. The separation for the chromatographic method was carried out using the reversed-phase column LC-8, triethylamine buffer, stabilizer free tetrahydrofuran and methanol (5:3.5:1.5), pH 6.0 as mobile phase and detection at 227 nm. The results obtained for both methods showed to be accurate, precise, robust and linear over the concentration range 100.00 - 300.00 µg/mL and 40.00 - 80.00 µg/mL of fluoxetine hydrochloride for the spectrophotometric and chromatographic methods, respectively. The accuracy of the methods was evaluated by a recovery test and showed results between 98.89 and 101.10%.

Experimento didático sobre cromatografia gasosa: uma abordagem analítica e ambiental

This paper describes an experiment to teach the principles of gas chromatography exploring the boiling points and polarities to explain the elution order of a series of alcohols, benzene and n-propanone, as well as to teach the response factor concept and the internal standard addition method. Retention times and response factors are used for qualitative identification and quantitative analysis of a hypothetical contamination source in a simulated water sample. The internal standard n-propanol is further used for quantification of benzene and n-butanol in the water sample. This experiment has been taught in the instrumental analysis course offered to chemistry and oceanography students.