Estrutura e propriedades de elipticinas

The ellipticines constitute a broad class of molecules with antitumor activity. In the present work we analyzed the structure and properties of a series of ellipticine derivatives in the gas phase and in solution using quantum mechanical and Monte Carlo methods. The results showed a good correlation between the solvation energies in water obtained with the continuum model and the Monte Carlo simulation. Molecular descriptors were considered in the development of QSAR models using the DNA association constant (log Kapp) as biological data. The results showed that the DNA binding is dominated by electronic parameters, with small contributions from the molecular volume and area.

Estrutura e propriedades da difenil-4-amina sulfonato de sódio: um dopante de filmes condutores

This work contains the theoretical simulation of the conformation of diphenyl-4-amine sodium sulphonate (DASNa) and correlates its geometry with conductivity, showing that the conductivity increases as the molecule becomes more planar. The solvent effect was also evaluated, using water and dimethylsulfoxide. Some properties, such as bond distance, vibration al frequency and effective charge were calculated. The utilization of diphenyl-4-amine sodium sulphonate (DASNa) as dopant of aniline was investigated in view of the HOMO-LUMO energy gap.

Aplicação do ultra-som em sistemas eletroquímicos: considerações teóricas e experimentais

The aim of this review is to present and discuss the applications of ultrasound in electrochemical systems such as in sonoelectroanalysis and sonoelectrolysis for the electrochemical combustion of organic compounds. Initially, theoretical and experimental aspects are discussed, particularly those related to the enhancement of mass transport and the surface cleaning effects. Some results are included to illustrate alternative geometries for the experimental measurements and the working electrodes used in these systems. In the sequence, the available publications are presented and discussed to demonstrate that ultrasound combined with electrochemical techniques is a powerful set-up for the detection of analytes such as metals and/or organic compounds in hostile media and for the effective destruction of toxic organic substances. At the end, a table summarizes the results already published in the literature.

Avaliação da concentração de retinol em leite UHT ("Ultra High Temperature") comercializado em Natal, Rio Grande do Norte

Deficiency of micronutrients is a public health problem. Cow milk is a source of retinol. The objective of this study is to evaluate the retinol concentration in milk commercialized in Natal/RN. Ten samples were taken of each brand of UHT milk. Vitamin content was determined by HPLC using the Shimadzu LC-10 AD Chromatograph, coupled to the Shimadzu SPD 10 A UV-VIS Detector and the Shimadzu C-R6A Chromatopac Integrator with Shim-pack CLC-ODS (M) column, measuring 4.6 mm x 25 cm. The mobile phase was 100% methanol, with a flow of 1 mL/min. The mean retinol concentration varied between 22.7 ± 4.9 µg/100 mL and 44.1 ± 4.1 µg/100 mL, with the differences statistically significant (p<0.001). Only one of the 7 brands had retinol concentration below the normal requirements for human consumption.

Efeito de microondas na estrutura cristalina e na atividade catalítica de argilas

The effect of microwave (MW) irradiation on the crystalline structure of two natural clays and one commercial clay, Montmorillonite K10, was analyzed comparing the X-ray diffraction, N2 isotherms, NMR-MAS of 27Al and 29Si spectra of the clays before and after MW irradiation. The preparation of dioxolane ketals of isatin was used to analyze the MW effect on the catalyst activation. The yields achieved using catalysts activated by MW irradiation were lower (2 to 5%) than the yields achieved using catalysts activated by heat in a conventional oven.

Estrutura, reatividade e propriedades biológicas de hidantoínas

Hydantoin (imidazolidine-2,4-dione) is a 2,4-diketotetrahydroimidazole discovered by Baeyer in 1861. Thiohydantoins and derivatives were prepared, having chemical properties similar to the corresponding carbonyl compounds. Some biological activities (antimicrobial, anticonvulsant, schistosomicidal) are attributed to the chemical reactivity and consequent affinity of hydantoinic rings towards biomacromolecules. Therefore, knowledge about the chemistry of hydantoins has increased enormously. In this review, we present important aspects such as reactivity of hydantoins, acidity of hydantoins, spectroscopy and cristallographic properties, and biological activities of hydantoin and its derivatives.

O estado da arte da cromatografia líquida de ultra eficiência

Ultra Performance Liquid Chromatography (UPLC) retains the same principles as High Performance Liquid Chromatography (HPLC), but uses 1-2.1 mm i.d. columns with sub-2 µm particles. It is considered the newest advance in analytical separation science. The use of these small particles with mobile phases at high linear velocities increases resolution and detectability and decreases analysis time. Thus, the analyses are faster, the solvent volume is smaller, the efficiency is higher and the detectability is 2-3 times higher when compared with HPLC analysis.

Determinação de fósforo biodisponível em rações de peixes utilizando extração assistida por ultra-som e espectrofotometria no visível

The aim of the present work was to develop and optimize a method for determination of bioavailable phosphorus in samples of feces and fish feed using ultrasound extraction and subsequent quantification by visible spectrophotometry. Using as extractor solution HNO3 0.50 mol L-1, the great conditions of extraction established were: sample mass - 100 mg, samples granulometry - < 60 µm, sonification time - five cycles of 40 s and ultrasound potency - 136 W. The proposed method was applied in studies of digestibility of this nutrient in different feeds used in diets of juvenile of Nile tilapia.

Sistemas tampão: uma estrutura didática teórico-prática

Courses with practical and theoretical classes are potentially didactic structures for the development of motor and complex cognitive skills when operated in an integrated manner. When worked aligned, theory and practice enable a clearer view of the issue, opening scope for introducing concepts from other disciplines and for the development of lab skills. This paper presents a methodology for biochemistry labwork that promotes the teaching of the buffering systems contents together with to the development of scientific research practice concepts in an interdisciplinary perspective that integrates theory and practice.

Uma visão sobre a estrutura, composição e biodegradação da madeira

Wood is the main raw material used in the pulp and paper industry. It is a material that presents heterogeneous structure and complex composition, which results in a relatively resistant material to the biodegradation process. In the present review, we attempted to summarize the structural characteristics of wood and describe the chemical nature of its major components to, afterwards, comment about its biodegradation. The role of the enzyme manganese peroxidase in the lignin degradation by a selective white-rot fungus, Ceriporiopsis subvermispora, was highlighted.

Propriedades químico-quânticas empregadas em estudos das relações estrutura-atividade

In this work we show that structure-activity relationship studies are of great importance in modern chemistry and biochemistry. In order to obtain a significant correlation, it is crucial that appropriate descriptors be employed. Thus, quantum chemical calculations are an attractive source of new molecular descriptors which can, in principle, express all the electronic and geometric properties of molecules and their interactions with the biological receptor.

Efeitos da adição de átomos de Mn na rede do GaN via métodos de estrutura eletrônica

A computational method to simulate the changes in the electronic structure of Ga1-xMn xN was performed in order to improve the understanding of the indirect contribution of Mn atoms. This periodic quantum-mechanical method is based on density functional theory at B3LYP level. The electronic structures are compared with experimental data of the absorption edge of the GaMnN. It was observed that the indirect influence of Mn through the structural parameters can account for the main part of the band gap variation for materials in the diluted regime (x<0.08), and is still significant for higher compositions (x~0.18).

Análise cristalográfica da solução sólida com estrutura tipo Tungstênio Bronze de niobato de potássio e estrôncio dopado com ferro

Solid solution of iron doped potassium strontium niobate with KSr2(FeNb4)O15-Δ stoichiometry was prepared by high efficiency ball milling method. Structural characterization was carried out by X-ray diffraction. Crystalline structure was analyzed by the Rietveld refinements using the FullProf software. The results showed a tetragonal system with the tetragonal tungsten bronze structure - TTB (a = 12.4631 (2) Å and c = 3.9322 (6) Å, V = 610.78 (2) ų). In this work, the sites occupancy by the K+, Sr2+ and Fe3+ cations on the TTB structure were determined. NbO6 polihedra distortion and its correlation with the theoretical polarization are discussed.

Estudos de relações estrutura-atividade quantitativas (QSAR) de bis-benzamidinas com atividade antifúngica

This paper describes 2D-QSAR and 3D-QSAR studies against Candida albicans and Cryptococcus neofarmans for a set of 20 bisbenzamidines. In the studies of 2D-QSAR with C. albicans it was obtained a correlation between log MIC-1 and lipolo component-Z (r² = 0.68; Q² = 0.51). In the case of C. neofarmans a correlation between log MIC-1 and lipolo component-Z and of Balaban index (r² = 0.85; Q² = 0.6) was obtained. 3D-QSAR studies using CoMFA showed that the steric fields contributed more to the predicted activities for Candida albicans (94.9%) and Cryptococcus neofarmans (97.9%).

Glicoproteína-P, resistência a múltiplas drogas (MDR) e relação estrutura-atividade de moduladores

Multidrug resistance, MDR is a major obstacle for cancer chemotherapy. MDR can be reversed by drugs that vary in their chemical structure and main biological activity. Many efforts have been done to overcome MDR based on studies of structure-activity relationships and in this review we summarize some aspects of MDR mediated by P-glycoprotein (P-gp), as the most experimentally and clinically tested form of drug resistance. The most significant MDR mechanisms revealed until now are shortly discussed. Physicochemical and structural properties of MDR modulators, measures of the MDR reversal, and QSAR studies are included.