Showing papers in "Química Nova in 1998"
TL;DR: In this paper, the authors discuss some experimental procedures which may be employed for isolation of active compounds from medicinal plants based on their experience, and emphasize some insights about the way to obtain more active and selective compounds from natural products through structural modifications oriented for analysis of structure-activity relationships.
Abstract: In the present paper we discuss, based in our experience, some experimental procedures which may be employed for isolation of active compounds from medicinal plants. We have also emphasized some insights about the way to obtain more active and selective compounds from natural products through structural modifications oriented for analysis of structure-activity relationships.
285 citations
TL;DR: Basic concepts of two multivariate statistical techniques, principal component and hierarchical cluster analysis that have received broad acceptance for treating chemical data are discussed.
Abstract: The modern technological ability to handle large amounts of information confronts the chemist with the necessity to re-evaluate the statistical tools he routinely uses. Multivariate statistics furnishes theoretical bases for analyzing systems involving large numbers of variables. The mathematical calculations required for these systems are no longer an obstacle due to the existence of statistical packages that furnish multivariate analysis options. Here basic concepts of two multivariate statistical techniques, principal component and hierarchical cluster analysis that have received broad acceptance for treating chemical data are discussed.
169 citations
TL;DR: The layered double hydroxides, known as anionic clays and represented by the general formula [M2+1-x M3+x (OH) 2] x+ Am-x/m·nH 2O, are a group of materials which are of much interest currently as mentioned in this paper.
Abstract: The layered double hydroxides, known as anionic clays and represented by the general formula [M2+1-x M3+x (OH) 2] x+ Am-x/m·nH 2O, are a group of materials which are of much interest currently. They present a variety of potential applications as adsorbents, catalysts and catalyst support, ion-exchangers, antacids and as a polymer stabilizer. It is possible to obtain a broad variety of layered double hydroxides (LDHs), depending on the identity and ratio of the cations M2+ and M3+, as well as the interlamelar anion. The aim of this review is to give out some information about this class of materials, concerning to the synthesis, characterization, properties and applications.
105 citations
TL;DR: In this article, an overview of reaction mechanisms at the surface of semiconductors used as photocatalysts (specially TiO2), when heterogeneous photocatalysis is used to remove hazardous compounds from contaminated sites.
Abstract: Conventional technology used in the treatment of wastewater has been pointed as a major environmental problem for sustainable development, since minimization is not addressed accordingly. Advanced oxidation processes (AOP), based on the formation of hydroxyl radical (OH), a powerful oxidant agent, have been considered to be a potential technology for the destruction of many toxic compounds. Photocatalysis using solar light, an AOP, has been studied for nearly 20 years and recently attracted great interest as a clean-up technology. However, solar detoxification processes have not yet achieved commercial success. This article presents an overview of reaction mechanisms at the surface of semiconductors used as photocatalysts (specially TiO2), when heterogeneous photocatalysis is used to remove hazardous compounds from contaminated sites.
81 citations
TL;DR: Spectrophotometric determination of total protein is used in several areas such as clinical analysis, food science and technology, biochemistry, protein chemistry, physiology, etc. as mentioned in this paper.
Abstract: Spectrophotometric determination of total protein is used in several areas such as clinical analysis, food science and technology, biochemistry, protein chemistry, physiology. Five spectrophotometric methods are mostly used: biuret, Lowry, Bradford, Smith and UV absorption. In this review a general overview of these methods is presented (interferences, applications); other methodologies are also discussed.
72 citations
TL;DR: In this article, the input of heavy metals concentrations determinated by ICP-AES, in samples of the Cambe river basin, was evaluated by using the Principal Component Analysis.
Abstract: The input of heavy metals concentrations determinated by ICP-AES, in samples of the Cambe river basin, was evaluated by using the Principal Component Analysis. The results distinguishes clearly one site, which is strongly influenced by almost all elements studied. Special attention was given to Pb, because of the presence of one battery industry in this area. Some downstream samples were associated with the same characteristics of this site, showing residual action of contaminants along the basin. Other sites presented influence of soil elements, plus Cr near a tannery industry. This study allowed to distinguish different sites in the upper basin of the Cambe (Londrina-PR-BR), in accordance to elements input.
61 citations
TL;DR: In this paper, a review dealing with the use of screen-printing technology to manufacture disposable electrodes is presented, covering in details virtually all the publications in the area up to early 1997 and including 206 references.
Abstract: A review dealing with the use of screen-printing technology to manufacture disposable electrodes is presented, covering in details virtually all the publications in the area up to early 1997 and including 206 references. The elements and different strategies on constructing modified electrodes are highlighted. Commercial and Home-made ink recipes are discussed. Microelectrode arrays, built by the combination of photostructuring and screen-printing technologies to the mass production of advanced disposable sensors, are also discussed. Future research trends are predicted.
55 citations
TL;DR: Through bioassay-guided chromatographic fractionation, liriodenine, an oxoaporphine alkaloid, was isolated from the bark extracts as the bioactive compound.
Abstract: Extracts obtained from leaves, seeds and bark of Unonopsis lindmanii were evaluated by means of Brine Shrimp Lethality test (BSL). Through bioassay-guided chromatographic fractionation, liriodenine, an oxoaporphine alkaloid, was isolated from the bark extracts as the bioactive compound. Two additional inactive known alkaloids, unonopsine and lysicamine were also isolated from the bark extracts.
55 citations
TL;DR: The generation of chemical residues in both teaching and research laboratories is a serious problem in Brazil and a Chemical Residues Management Program is presented and discussed.
Abstract: The generation of chemical residues in both teaching and research laboratories is a serious problem in Brazil. In this article, a Chemical Residues Management Program is presented and discussed. The Program is centered in different hierarchic positions, but driven by minimization. A common ground for discussion and distribution of related information is also proposed as a mean to spread the program throughout Brazilian Universities.
50 citations
TL;DR: In this article, the main organic compounds: aldehydes, ketones, carboxylic acids, alcohols and esters, were determined through High Performance Liquid Chromatography (HPLC) and High Resolution Gas Cromatography (HRGC).
Abstract: This paper describes variations in the profile of the main volatile organic compounds present in Brazilian sugar cane spirits distilled in copper and stainless steel distillers. The main organic compounds: aldehydes, ketones, carboxylic acids, alcohols and esters, were determined through High Performance Liquid Chromatography (HPLC) and High Resolution Gas Cromatography (HRGC). The spirits produced in copper distillers exhibit higher contents of aldehydes with respect to the ones produced in stainless steel. The inverse is true with respect to the higher alcohol and ester contents. No significant variation has been observed for the carboxylic acids.
43 citations
TL;DR: Piqui (Caryocar brasiliense Camb) oil was transformed into a cocoa butter-like fat through an enzymatic interesterification reaction using Lipozyme in the presence of stearic acid that was incorporated in the sn 1,3-3,1 position into triglyceride as discussed by the authors.
Abstract: Piqui (Caryocar brasiliense Camb) oil was transformed into a cocoa butter-like fat through an enzymatic interesterification reaction using Lipozyme in the presence of stearic acid that was incorporated in the sn 1,3-3,1 position into triglyceride. Stearic acid incorporation was determined by HPLC, based on the quantification of the principal triglycerides (POP, POS e SOS) found in cocoa butter. The proposed process was feasible with a reaction time of 240 minutes with 10% of Lipozyme at 70oC and substract weight ratio of 0,33 (stearic acid:piqui oil).
TL;DR: In this article, the iridoids plumericin and isoplumericin were extracted from hexane extract of Himatanthus sucuuba barks utilizing Cladosporium sphaerospermum.
Abstract: Bioactivity-guided fractionation from hexane extract of Himatanthus sucuuba barks utilizing Cladosporium sphaerospermum led to the isolation of iridoids plumericin and isoplumericin, which showed higher inhibition against C. sphaerospermum than the antibiotic nistatin. Besides bioactive iridoids were isolated the inactive triterpenes lupeol cinnamate, a-amyrin cinnamate and lupeol acetate.
TL;DR: In this paper, the authors used the Enzefitte library of the more commonly used adsorption isotherm equations for obtaining tabular outuput suitable for plotting theoretical of fitted isotherms, has been used to estimate the advertisersorption parameters were used to calculate the amount adsorbed qcalc., a function of concentration (C).
Abstract: Adsorption of Cu(II), Ni(II), Pb(II) and Zn(II) ions from aqueous solutions by N-(3,4-dihydroxybenzyl) chitosan have been carried out. The Langmuir (L), Freundlich (F), Langmuir - Freundlich (LF), Redlich-Peterson (RP) and Toth (T) adsorption isotherms models have been applied to fit the experimental data. Nonlinear regression computational program "Enzefitte", which is a library of the more commonly used adsorption isotherm equations for obtaining tabular outuput suitable for plotting theoretical of fitted isotherms, has been used to estimate the adsorption parameters. These parameters were used to calculate the amount adsorbed qcalc., a function of concentration (C).
TL;DR: The phytochemical studies of Eschweilera longipes have led to the identification of ten triterpenoids, which were identified by analysis of IR, 1H and 13C NMR data and comparison with values of literature.
Abstract: The phytochemical studies of Eschweilera longipes have led to the identification of ten triterpenoids: fridelin, fridelinol, a-amirin, b-amirin, 3b-O-cinamoyl-a-amirin, 3b-O-cinamoyl-b-amirin, a-amirenone, b-amirenone, 3-a-hidroxi-lupeol, 3-a-hidroxi-taraxasterol, along with b-sitosterol, stigmasterol, a -tocopherol and tocotrienol. The structures of these compounds were identified by analysis of IR, 1H and 13C NMR data and comparison with values of literature.
TL;DR: In this paper, a commercial cellulase preparation was used for rice hull enzymatic hydrolysis using commercial cellulases and the results showed that the chlorite treatment produced the most significant change in the structure of rice hull.
Abstract: In the present work we reported the study of rice hull enzymatic hydrolysis using a commercial cellulase preparation The results showed that previous treatment with light and sodium chlorite inhibits the enzymatic process (314 and 118%, respectively) while hydrogen peroxide and ozone favoured the enzymatic production of reducing sugars (59 and 549%, respectively) Studies performed by quimiluminescence showed that the chlorite treatment produced the most significant change in the structure of rice hull Nevertheless, this treatment did not favour the subsequent enzymatic process Photomicrographs obtained from rice hull hydrolysates showed that pre-treatment changed mainly the inner epidermis and parenchyma cell and that they did not change cellular organization of the hull
TL;DR: In this paper, the selective hydrolysis of carboxyamide groups of asparagine and glutamine of collagen matrices for the preparation of negatively charged collagen biomaterials was performed in the presence of chloride and sulfate salts of alkaline and alkaline earth metals.
Abstract: This work describes the selective hydrolysis of carboxyamide groups of asparagine and glutamine of collagen matrices for the preparation of negatively charged collagen biomaterials. The reaction was performed in the presence of chloride and sulfate salts of alkaline and alkaline earth metals in aqueous dimethylsulfoxide solution and, selectively hydrolysis of carboxyamide groups of collagen matrices was promoted without cleavage of the peptide bond. The result is a new collagen material with controlled increase in negative charge content. Although triple helix secondary structure of tropocollagen was preserved, significative changes in thermal stabilities were observed in association with a new pattern of tropocollagen macromolecular association, particularly in respect microfibril assembly, thus providing at physiological pH a new type of collagen structure for biomaterial preparation, characterized by different charge and structural contents .
TL;DR: In this paper, a review has been conducted to collect and correlate all the various equations for the g matrix of strong field d5 systems obtained from different basis sets using full electron and hole formalism calculations.
Abstract: This review has tried to collect and correlate all the various equations for the g matrix of strong field d5 systems obtained from different basis sets using full electron and hole formalism calculations. It has corrected mistakes found in the literature and shown how the failure to properly take in symmetry boundary conditions has produced a variety of apparently inconsistent equations in the literature. The review has reexamined the problem of spin-orbit interaction with excited t4e states and finds that the earlier reports that it is zero in octahedral symmetry is not correct. It has shown how redefining what x, y, and z are in the principal coordinate system simplifies, compared to previous methods, the analysis of experimental g values with the equations.
TL;DR: The way new interactive computer technologies and the resources of the Internet could be used by teachers and students are explored and some of the internet resources in chemistry are described.
Abstract: The way new interactive computer technologies and the resources of the Internet could be used by teachers and students are explored. The possibilities of some of the Internet resources in chemistry are described.
TL;DR: In this paper, the authors present some characteristics related to slurry sampling in trace analysis in terms of its advantages, limitations and applications, as well as the latest advance in this area, such as mechanization, chemical modifiers, stabilization agents and others.
Abstract: This review presents some characteristics related to slurry sampling in trace analysis in terms of its advantages, limitations and applications, as well as the latest advance in this area, such as mechanization, chemical modifiers, stabilization agents and others. The reviewed applications include foods, biological and geological materials.
TL;DR: In this article, the pH dependent color change of the crude flower extracts is suggested as subject in teaching chemical or acid-base equilibria, visual indicators and some aspects of spectrophotometric concepts and applications.
Abstract: In the present work, the pH dependent colour change of the crude flower extracts is suggested as subject in teaching chemical or acid-base equilibria, visual indicators and some aspects of spectrophotometric concepts and applications. The vegetal species used are commonly found in Brazil, and the extraction methodology proposed is inexpensive and easy to perform in secondary schools and in general chemistry or instrumental undergraduate courses. A bibliographic review about the use of vegetal extracts in chemical education and a discussion of the flower colour are also presented.
TL;DR: In this article, a seasoning freeze-drying industry wastewater was electrolysed to increase its biodegradability, and conductivity, pH, biochemical (BOD) and chemical (COD) oxygen demands, Daphnia similis acute toxicity bioassays, and bacteria counting through the plate count agar method were determined after different times of electrolysis.
Abstract: Wastewater from a seasoning freeze-drying industry was electrolysed to increase its biodegradability. Stainless-steel electrodes were used at 9.09 A/m2, for up to 80 min. Conductivity, pH, biochemical (BOD) and chemical (COD) oxygen demands, Daphnia similis acute toxicity bioassays, and bacteria counting through the plate count agar method were determined after different times of electrolysis. The results (e.g. higher BOD and lower COD) showed that the biodegradability of the wastewater was significantly increased; furthermore, Fe2+ ions liberated by the electrodes cause microorganisms to die and, when oxidised to Fe3+, contribute for the flocculation and sedimentation of solid residues.
TL;DR: In this paper, the sulfate concentration in vinasse samples was determined by using ion exchange columns and the results obtained for some samples from Araraquara and Penapolis are presented.
Abstract: In this way it is very important to know the sulfate concentration in vinasse samples before to make the biodigestor design. A previous developed and indirect method (Anal. Chim. Acta. 1996, 329, 197), was used to determine sulfate in samples of vinasse, after previous treatments, done in order to eliminate organic matter with hydrogen peroxide 30% and concentrated nitric acid mixture (3:1), under heating. Interferent cationic ions were isolated by using ion exchange columns. The results obtained for some samples from Araraquara and Penapolis are here presented. The phosphate concentration was also determined.
TL;DR: In this paper, the authors identified and quantified several organic compounds in the atmosphere of a site into Amazon Basin with high impact of biomass burning emission and observed the formation of nitro-PAH from photochemical reactions.
Abstract: It was identified and quantified several organic compounds in the atmosphere of a site into Amazon Basin with high impact of biomass burning emission. It was important to know the particulate matter composition with respect to n-alkanes and PAH associated with the particulate matter because they provided indication on the main sources contributing to airborne particles, the contribution of natural vs. man-made emission and the aging of the particles. The main classes of compounds observed were n-alkanes, PAH and nitro-PAH. It was observed the formation of nitro-PAH from photochemical reactions. The aerosol mass concentration is mainly associated with fluoranthene, pyrene and benzo(ghi)perylene. Environmental and direct emissions samples (flaming and smoldering) were collected and analysed.
TL;DR: The physical and chemical characterization of vermicompost from bovine manure has been studied in this paper, where the pH and cation exchangeable capacity (CEC), organic matter content, electric conductivity and elementary and XRD analyses, among other characteristics, were examined.
Abstract: The physical and chemical characterization of vermicompost from bovine manure has been studied. It was examined the pH and cation exchangeable capacity (CEC), organic matter content, electric conductivity and elementary and XRD analyses, among other characteristics. The vermicompost was then applied to the retention and competition of metal micronutrients and pollutants (Cu and Zn) from metal nitrate solutions. The retention was affected by both the pH and adsorption time, while the competitive character of these metals for the substrate was relevant to each pH examined.
TL;DR: In this article, ent-16a,17-dihydroxykauran-19-oic acid and its derivatives were used to unambiguous 1H and 13C chemical shifts assignments and to indicate some mistake data described in the literature as consequence mainly of the chiral carbons C-4 and C-16.
Abstract: Phytochemical investigation of the leaves and branches of a specimen of Ouratea semiserrata led to the isolation and characterization of ent-16a,17-dihydroxykauran-19-oic acid, along with other natural products. This diterpenoid and its derivatives were used to unambiguous 1H and 13C chemical shifts assignments and to indicate some mistake data described in the literature as consequence mainly of the stereochemicals of the chiral carbons C-4 and C-16. The HRMS spectra were also analysed.
TL;DR: It is suggested that an intermediate, possibly a distorted trans-isomer of O=NOOH could be responsible for the harmful reactions of peroxynitrite, formed from the reaction of the superoxide anion with nitrogen monoxide near activated macrophages.
Abstract: Oxyradicals play a tole in several diseases While for several decades the hydroxyl radical - produced via the Fenton reaction - has been considered the species that initiates oxyradical damage, new findings suggest that much of this damage can be ascribed to peroxynitrite, O=NOO-, formed from the reaction of the superoxide anion with nitrogen monoxide near activated macrophages The rate constant for the reaction of this reaction has been investigated by flash photolysis and was found to be significantly higher than previously described in the literature, 19 x 1010 M-1s-1 Studies of the isomerization to nitrate resulted in the discovery of a complex between peroxynitrite and its protonated form with a stability constant of 1 x 104 M-1 Some of the harmful reaction of peroxynitrous acid have been ascribed to the hydroxyl radical as a product of homolysis of the O-O bond during the conversion to nitrate Kinetics of the isomerization reaction as a function of pressure show that the activation volume is only +15+10 ml mol-1, which is inconsistent with homolysis Instead, an intermediate, possibly a distorted trans-isomer of O=NOOH could be responsible for the harmful reactions of peroxynitrite
TL;DR: In this paper, the catalytic decomposition of soybean oil was studied in a fix bed reactor at 673 and 773 K and using amorphous silica-alumina and the zeolites USY, H-Mordenite and H-ZSM-5 as catalysts.
Abstract: The catalytic decomposition of soybean oil was studied in a fix bed reactor at 673 and 773 K and using amorphous silica-alumina and the zeolites USY, H-Mordenite and H-ZSM-5 as catalysts. Both the selectivity and the catalytic activity were determined by studying the product composition resulting from the chemical reactions. Physicochemical characteristics of the catalysts were obtained by X-ray fluorescence, Fourier Transform infrared spectroscopy, 29Si and 27Al Nuclear Magnetic Ressonance and textural analysis. The zeolites USY and H-ZSM-5, showing higher Bronsted acidity, yielded products with higher concentration in aromatic hydrocarbons, whereas with both H-Mordenite and amorphous silica-alumina the main products were paraffins.
TL;DR: In this paper, the optimal conditions for enzyme and biomass production and COD reduction were established under continuous agitation in order to establish optimal conditions (incubation period, incubation temperature, initial pH and nitrogen addition) for biomass and ribonuclease production, as well as biological depuration of the wastes.
Abstract: Penicillium citrinum grown in orange juice processing wastes medium under continuous agitation was studied in order to establish optimal conditions (incubation period, incubation temperature, initial pH and nitrogen addition) for biomass and ribonuclease production, as well as, biological depuration of the wastes. Nitrogen addition to wastes medium increased the biomass and ribonuclease production and provides COD reduction. The soy meal shows to be the best nitrogen source. The conditions for a more favorable enzyme and biomass production and COD reduction were initial pH 6.0 and temperature of 27°C. The maximum value obtained for these parameters on optimal conditions of cultivation was 11 U/mL of enzyme, 4 mg/mL of biomass (dry matter) and 55% of COD reduction, in 96 hours of incubation.
TL;DR: In this paper, the scientific career of Theodor Peckolt, naturalist and pharmacist, and his seminal contribution to the development of phytochemistry in Brazil are discussed in the light of the historical background of the Brazilian science and University at his time.
Abstract: In this paper we briefly describe the scientific career of Theodor Peckolt, naturalist and pharmacist, and his seminal contribution to the development of phytochemistry in Brazil. His achievements are discussed in the light of the historical background of the Brazilian science and University at his time.
TL;DR: The most active catalysts were those with the highest amount of copper as discussed by the authors and they had the highest surface areas under the reactional atmosphere and the greatest tendency to produce the active form; they also were poorly crystalline solids.
Abstract: Chromium and copper-doped hematites were prepared with the aim of studying the synergistic effect of these dopants on the textural and on the catalytic properties of the iron oxides towards the high temperature shift reaction. It was found that the most active catalysts were those with the highest amount of copper. They had the Fe(II)/Fe(III) ratio near the stoichiometric value of magnetite, the highest surface areas under the reactional atmosphere and the greatest tendency to produce the active form; they also were poorly crystalline solids. The best performance was shown by the catalyst with Fe/Cu=10, heated at 300oC. It can thus be concluded that copper acts both as textural and structural promoter in these catalysts.