Redução de amidas por boranos

Despite the fact that boranes are frequently used in amide reductions, the reaction mechanisms of the involved are note well known. This work presents the results of a bibliographic search on probable amide reduction mechanisms and an analysis of the existing literature. Steric and electronic effects were considered in light of reactivity since it could be concluded that the formation of intermediates and products depends mainly on the substitution patterns of both the boron and nitrogen atoms. Otherwise, results described in the literature for the reactions of boranes, sodium borohydride, lithium aluminum hydride, alkylboranes or haloboranes with others functional groups such as carboxylic acids, esters, ketones and alkenes were analysed with the aim to obtain something about the N-substituted amide reactions employing boranes.

Estudo do efeito do cloreto em catalisadores de paládio usando a análise no infravermelho e de fotoelétrons excitados por raios x

Chloride poisoning is known as having an inhibitor effect in the activity of metal catalysis. In this work in situ infrared spectroscopy (FTIR) of adsorbed carbon monoxide and x-ray photoelectron spectroscopy (XPS) were used to investigate the effect of chloride presence in the electronic metal density in the d subshell of palladium dispersed on alumina. The chloride poisoning effect was interpreted as an electronic effect since a weak back-bonded Pd-CO was formed due to the decrease in the electronic density of the d subshell of palladium, which could be also detected by the higher Pd 3d5/2 binding energy in the chloride presence. A similar poisoning effect was also observed for chloride free Pd/Al2O3 reduced at 500 ºC, and it was interpreted based on the interaction of metal with the alumina surface. The use of molybdena/alumina binary system as support, yield a contrary effect due to the metal-support interaction.

O impacto do crômio nos sistemas biológicos

The impact of biological chromium's activity may be beneficial or not. This review presents the most relevant chemical aspects of these "two faces" of chromium by covering first, the efforts toward a clearer understanding of the carcinogenic properties of chromium compounds. The biomimetic chemistry of Cr(V) complexes illustrates the interactions of the intermediates formed by Cr(VI) reduction with DNA or oligonucleotides. The importance of trivalent chromium as an essential element is also emphasized by summarizing the recent results of the investigations on trinuclear chromium complexes as models of the cofactor responsible for the insulin activity, as well as good candidates for new nutritional supplements.

Formação de multicamadas de polissacarídeos e proteína

In this work the formation of multilayers composed by carboxymethylcellulose (CMC), chitosane and bovine serum albumin (BSA) was studied by ellipsometry. First, the adsorption behavior of carboxymethylcellulose onto amino-terminated surfaces was investigated as a function of molecular weight and average degree of substitution of CMC. The influence of these parameters on the adsorbed amount of CMC onto amino-terminated substrates was absent. However, the interaction of CMC covered surfaces with chitosane and BSA was favored when the average degree of substitution of CMC was increased. The adsorption of BSA onto the polysaccharide systems was studied as a function of pH. At the isoelectric point of BSA a maximum in the adsorbed amount was found.

Formação de adutos exocíclicos com bases de DNA: implicações em mutagênese e carcinogênese

A number of ring-extended DNA adducts resulting from reaction of alpha,beta-unsaturated aldehydes, or their epoxides, with DNA bases have been characterized in recent years. These adducts can lead to miscoding during DNA replication which, if not repaired, result in mutations that can contribute to cancer development. Recently, the use of ultrasensitive methods allowed the detection of background levels of etheno DNA adducts in tissues of untreated animals and humans suggesting the existence of endogenous sources of reactive intermediates. In this review, we briefly summarize the recent advances in the chemistry of these DNA lesions.

Metodologias de síntese de 2-arilcicloexanonas

Several methodologies concerning the preparation of 2-aryl and 2-heteroarylcyclohexanones are presented. The use of these intermediates in the synthesis of chemically and biologically interesting organic compounds is also discussed.

Síntese dos analgésicos paracetamol e fenacetina e do adoçante dulcina: um projeto para química orgânica experimental

A synthesis of artificial sweetener dulcin starting from nitrobenzene was elaborated for undergraduate organic laboratory course. Paracetamol and phenacetin, both physiologically active analgesic compounds, were also prepared as intermediates. Besides a large scope of discussion subjects related with organic synthesis, interesting lectures about analgesics and sweeteners may also be performed in this project. The advantage of this project is the adaptability according to the conditions offered by the course, i.e., convenience and/or availability of time and reagents.

Estudo eletroanalítico do herbicida paraquat em soluções aquosas por voltametria de onda quadrada utilizando ultramicroeletrodos

The electrochemical behavior of paraquat on Pt, Au and carbon fiber ultramicroelectrodes were studied in laboratory samples by square wave voltammetry at high frequencies. The results showed two reversible peaks for paraquat reduction, in agreement to the literature data. The first peak was associated to the reduction of paraquat molecule in solution, with the further adsorption of the intermediate on the electrode surface. This adsorbed species undergoes to electroreduction in a reaction associated to the second voltammetric peak. The variation in pH and square wave parameters showed the best conditions to reduce paraquat as pH 5.0, frequency as high as 1000 s-1, scan increment of 2 mV and square wave amplitude of 50 mV. At such conditions, a variation of paraquat concentrations from 4.3 x 10-6 to 1.66 x 10-4 mol L-1 presented values for the detection limit equal to 3.9, 6.2 and 20.3 ppb on Pt, Au and carbon, respectively, at 1000 s-1. These values are quite below17 the allowed limit of paraquat in drinking water.

Análise teórica da interação de CO, CO2 e NH3 com ZnO

This paper presents a study of the interaction of small molecules with ZnO surfaces by means of theoretical methods. The AM1 semi-empirical method was used for optimizing the geometric parameters of adsorbed molecules. The optimized AM1 structures were used in the calculations of the ab initio RHF method with the 3-21G* basis set. The interaction of CO, CO2 and NH3 molecules were studied with (ZnO)22 and (ZnO)60 cluster models. We have analyzed the interaction energy, SCF orbital energies, Mulliken charges and the density of states (DOS).

Síntese e atividade antiedematogênica de derivados N-triptofil-5-benzilideno-2,4-tiazolidinadiona e N-triptofil-5-benzilideno-rodanina

Derivatives of N-tryptophyl-5-benzylidene-2,4-thiazolidinedione (7a-c) and N-tryptophyl-5-benzylidene-rhodanine (7d-f) were prepared by condensation of the intermediates 5 and 6 with different benzaldehydes, respectively. Their structural elucidation was carried through by IR, ¹H NMR and MS. The acute toxicity and antiedematogenic activity of the compounds 7b,c and 7e,f were evaluated. The data did not reveal any sign of toxicity, and no mortality was registered. As indomethacin (10 mg/kg; v.o.), the antiedematogenic activity of the compounds 7b (50 mg/kg; v.o.) and 7e, 7f (50 or 100 mg/kg; v.o.) against carrageenan-induced paw edema was verified at time intervals of 180 min.

Degradação de BTXs via processos oxidativos avançados

In this study the efficiency of advanced oxidative processes (AOPs) were investigated toward the degradation of aqueous solutions containing benzene, toluene and xylenes (BTX). The results indicated that BTX can be effectively oxidized by the UV-A-assisted photo-Fenton process. The treatment permits almost total degradation of BTX and removal of more than 80% of the phenolyc intermediates at reaction times of about 30 min. Preliminary investigations using solar light suggest a good potentiality of the process for the treatment of large volumes of aqueous samples containing these polluting species.

Factors affecting Hg (II) adsorption in soils from the Rio Negro basin (Amazon)

Mercury (II) adsorption studies in top soils (top 10 cm) from the Rio Negro basin show this process depends strongly on some selected parameters of the aqueous phase in contact with the soils. Maximum adsorption occurred in the pH range 3.0-5.0 (>90%). Dissolved organic matter shows an inhibitory effect on the availability of Hg (II) to be adsorbed by the soils, whereas a higher chloride content of the solution resulted in a lower adsorption of Hg (II) at pH 5.0. Soils with higher organic matter content were less affected by changes in the salinity. An increase in the initial Hg (II) concentration increased the amount of Hg (II) adsorbed by the soil and decreased the time needed to reach equilibrium. A Freundlich isotherm provided a good model for Hg (II) adsorption in the two types of soil studied. The kinetics of Hg (II) adsorption on Amazonian soils showed to be very fast and followed pseudo-second order kinetics. An environmental implication of these results is discussed under the real scenario present in the Negro River basin, where acidic waters are in contact with a soil naturally rich in mercury.

Tiossemicarbazonas: métodos de obtenção, aplicações sintéticas e importância biológica

Thiosemicarbazones are a class of compounds known by their chemical and biological properties, such as antitumor, antibacterial, antiviral and antiprotozoal activity. Their ability to form chelates with metals has great importance in their biological activities. Their synthesis is very simple, versatile and clean, usually giving high yields. They are largely employed as intermediates, in the synthesis of others compounds. This article is a survey of some of these characteristics showing their great importance to organic and medicinal chemistry.

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.

Quimioluminiscencia electrogenerada del luminol usando electrodos de bajo costo

The purpose of the study was to observe eletrogenerated chemiluminescence (ECL) of luminol using different materials as electrodes such as wires, nails, coins, razor blades, etc. Based on the experimental observations and the mechanisms proposed in the literature, students should be capable of analyzing their results in order to understand the phenomena studied. Students could then elaborate a mechanism of action consistent with the experimental results which could rationalize the formation of intermediates in the reaction and the dependence of ECL on solution pH in addition to other points of interest