Scielo RSS <![CDATA[Química Nova]]> http://www.scielo.br/rss.php?pid=0100-404220160007&lang=en vol. 39 num. 7 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[SYNTHESIS AND CHARACTERIZATION OF ALKYLPHENYL POLYGLYCOSIDIC SURFACTANTS FROM AMYLOSE AND ALKYL PHENOLS EXTRACTED FROM NATURAL CNSL]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700771&lng=en&nrm=iso&tlng=en The surfactants were synthesized by condensing the obtained oligosaccharides of amylose and alkyl phenols extracted from the natural cashew nut shell liquid (nCNSL). The Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared Spectroscopy (FTIR) data showed aromatic ring bands, glycosidic rings, olefins and paraffins. The Nuclear Overhauser Effect Spectroscopy (NOESY) experiments showed that the conformation of the glycosidic units is of the type 4C1 with an α anomeric configuration. The values of Gibbs free energy of micellization (ΔGºmic) indicate that the spontaneity of formed micelles are cardanyl oligoglycosides &gt; cardyl oligoglycosides &gt; anacardyl oligoglycosides. The surface tension (γ) measurements showed that critical micelle concentration (cmc) values were low for surfactants. The study γ versus lnc (g dm-3) indicated that the aggregation behavior of the surfactants is dependent on their structural characteristics, as well as their thermal behavior. The area per molecule (A) values indicates that cardyl oligoglycosides are likely to form aggregates smaller than cardanyl oligoglycosides and anacardyl oligoglycosides. The critical packing parameter (cpp) indicates that the aggregates are of the vesicles and bilayers. <![CDATA[POLIPHASIC SCREENING OF POLYHYDROXYALKANOATE-PRODUCING MICROORGANISMS]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700782&lng=en&nrm=iso&tlng=en Polyhydroxyalkanoates (PHAs) are fully biodegradable biopolyesters produced by many prokaryotes and accumulated as insoluble cytoplasmatic inclusions. The detection of these intracellular granule is usually provided using lipofilic azodyes, which are not specific. Another way to screen PHA-producing bacteria is through culture-independent molecular techniques such Polymerase Chain Reaction (PCR), and the search for new PHA-producer strains is essential to reduce the cost at industrial level. The application of these both methods is desirable. In the present study, 24 bacteria isolated from soil of the Atlantic forest in Maceió (AL, Brazil) and from agri-industrial sludge (Coruripe-AL, Brazil) were studied regarding to their capacity of growing in mineral salt medium, as indicative of PHA synthesis. All strains were submitted to biochemical characterization, whilst PCR has proved that isolates BMA-05, BMA-10, BMA-13 and BDL-07 has the gene phaC, which encodes a PHA synthase, the key for PHA synthesis. The amplification and sequencing of their 16S r-DNA region was able to identify these bacteria respectively as Pseudomonas fluorescens, Enterobacter aerogenes, Klebsiella oxytoca and Bacillus pumilus. The same minimal medium supplement with peptone demonstrated to induce growing of those strains. <![CDATA[CARCINOGENICITY OF POLYCYCLIC AROMATIC HYDROCARBONS]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700789&lng=en&nrm=iso&tlng=en The assessment of the carcinogenic potential of polycyclic aromatic hydrocarbons (PAH) is obtained by a principal component analysis (PCA) and quantitative structure-activity relationship (QSAR) using hydrophobic (LogP), stereo and electronic parameters (electron affinity, dipole moment and HOMO-LUMO gap) calculated from the AM1 method. The PAH-DNA interaction model is based on the unsynchronized resonating valence bond theory (RVB) developed by L. Pauling. The QSAR study reproduces the experimental values ​​of LD50 in rats with 95% confidence. The PCA analysis classify all the selected compounds as potential carcinogens, an important result since many of these PAH are not classified as carcinogens, indicating the need for an urgent revision of its classification. <![CDATA[SESQUITERPENES RECOVERY OF COPAIBA OIL-RESIN FROM MOLECULAR DISTILLATION]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700795&lng=en&nrm=iso&tlng=en Copaiba oil-resin has aromatic characteristics and pharmacological activities attributed to sesquiterpenes compounds. These purified compounds present application in perfume, pharmaceutical and cosmetic industries. Therefore, the objective of this work was to use molecular distillation to recover and purify sesquiterpenes of the copaiba oil-resin with purity high. The parameters evaporator temperature (TEV) from 45 to 100 ºC and feed flow rate (Q) between 15 and 30 ml min-1 were evaluated through design of experiments (22 with center points). The results showed that it was possible to recover sesquiterpenes with 98.12% purity in the distillate stream. Increased in TEV and reduction in Q were the effects observed experimentally and through the response surface. The best experimental condition was TEV of 100 °C and Q of 15 mL min-1. Collor differences were noticed between distillate streams (colorless) and residue (brown). These can be used as parameters for separation of sesquiterpenes and diterpenes. The molecular distillation proved to be an efficient processo to both recovery and purification of sesquiterpenes from the copaiba oil-resin. <![CDATA[SYNTHESES AND CHARACTERIZATION OF NOVEL ORGANOMETALLIC TIN (IV) COMPLEXES WITH DITHIOCARBIMATES AND THEIR ACTION AS ACCELERATORS IN THE NITRILE RUBBER VULCANIZATION]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700801&lng=en&nrm=iso&tlng=en This paper describes the synthesis of four new organotin compounds of general formula: (Ph4P)[Sn(Cy)3(RSO2N=CS2)] [Ph4P = tetraphenylphosphonium cation, Cy = cyclohexyl, R = C6H5 (1), 4-ClC6H4 (2), 4-BrC6H4 (3) and 4-IC6H4 (4)]. They were obtained by the reaction between four different potassium N-R-sulfonyldithiocarbimate salts and tricyclohexyltin chloride in methanol, and were isolated as tetraphenylphosphonium salts. The elemental analyses of C, H, N and the data of high-resolution mass spectrometry were consistent with the proposed formulae. The 119Sn NMR spectra and 119Sn Mössbauer spectroscopic data were consistent with the presence of tetracoordinated tin(IV) species in solution and in the solid state. The electrolytic molar conductance and the integration curves in the 1H NMR spectra are in accord with the 1:1 proportion between the tetraphenylphosphonium cations and the complex anions. The activity of the new compounds in the vulcanization of nitrile rubber was evaluated and the results were compared to those achieved with the commercial accelerators: N-tert-butyl-2-benzothiazolesulfenamide (TBBS), tetramethylthiuram disulfide (TMTD) and zinc diethyldithiocarbamate (ZEDC). <![CDATA[NONLINEAR OPTICAL PROPERTIES OF BC<sub>5</sub> CLUSTERS]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700807&lng=en&nrm=iso&tlng=en The first (β) and second (γ) hyperpolarizabilities of BC5 clusters were investigated through the PM6, PM3, and MNDO-d semiempirical Hamiltonians. The Im2, Imm2, P3m1, and P phases that are pointed out in literature as likely candidates of the BC5 superhard diamondlike real structure were investigated. In this way, the stability analysis of the BC5 clusters was performed. Moreover, insights into the nonlinear mechanisms were obtained via Resonating Valence Bond (RVB) theory. The semiempirical methodology was evaluated in relation to the β and γ hyperpolarizabilities by considering fully characterized nonlinear organic molecules reported in the literature. The high values of the dynamic β and γ hyperpolarizabilities exhibited by the BC5 phases demonstrate that these clusters present potential applications as nonlinear optical media. <![CDATA[DEVELOPMENT OF ELECTROPHILIC AND NUCLEOPHILIC POWER INDICES WITHIN THE CONCEPTUAL FRAMEWORK OF DENSITY FUNCTIONAL THEORY]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700817&lng=en&nrm=iso&tlng=en In this work, the electrophilic and nucleophilic power indices were developed in the basis of canonical and grand canonical ensembles respectively, also local versions of these indices has been derived in analogy to philicity concept by Chattaraj. It can be observed that local electrophilic power and local nucleophilic power contain a third order response function, namely the hyperhardness, which recently has been considered for its chemical relevance. Also, the reactivity indices proposed here were tested by predicting the relative reactivity of molecules within three series of compounds (butyl-lithium isomers, carbonyl compounds, and aromatic motifs). In general, the global reactivity indices were in agreement with the experimental observations, while local versions shown a good representation of the site reactivity of the majority of studied system giving better results in some of cases if matched with both the Fukui functions and dual descriptor. <![CDATA[FLUOROUS SUPPORTED SYNTHESIS OF PYRAZOLONE DERIVATIVES FROM ALLYLIC ALCOHOLS USING A PALLADIUM-CATALYZED STRATEGY]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700825&lng=en&nrm=iso&tlng=en Ten substituted pyrazolone derivatives were easily synthesized from perfluorinated allylic alcohols, via a straightforward two steps reaction involving a Heck-coupling/isomerization reaction and subsequent condensation of hydrazines. This fluorous supported methodology, that combines a cyclo-release approach and F-SPE purification allows for the obtaining of the final products with a good purity. <![CDATA[SPECTROSCOPIC STUDY OF EFFECTS OF TETRAALKYLAMMONIUM CATIONS ON F<sup>-</sup>-SENSING PROPERTIES OF CALIX[4]PYRROLE BORADIAZAINDACENE DYE]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700832&lng=en&nrm=iso&tlng=en A novel meso-tetracyclohexylcalix[4]pyrrole-based boradiazaindacene dye 3 was synthesized and characterized. F--binding properties of the dye in the presence of tetrabutylammonium (TBA+), tetraethylammonium (TEA+), and tetramethylammonium (TMA+) counter ions were investigated by UV-Vis, fluorescence, and NMR spectroscopies. Dye 3 displayed various degrees of absorption red shift, fluorescence quenching, and downfield shifts of NH signals for the three fluoride salts. The association constants of these salts mainly depend on cation size effects and ion-pairing effects and were in the order KTMA+ &gt; KTEA+ &gt; KTBA+. Thus, we speculate that both F- and tetraalkylammonium cations are concomitantly located above and below a bowl-shaped calix[4]pyrrole cup in an ion-paired complex, respectively. <![CDATA[IMMOBILIZED TITANIUM DIOXIDE (TIO<sub>2</sub>) IN DIFFERENT SUPPORT MATERIALS TO USE IN HETEROGENEOUS PHOTOCATALYSIS]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700836&lng=en&nrm=iso&tlng=en The technological bottleneck for the application of heterogeneous photocatalysis with titanium dioxide (TiO2) is the retention and reuse of the catalyst, which brings opportunities for studying techniques for its immobilization on solid supports. The main objective of this paper was to test different methods to effectively immobilize TiO2 on granular activated carbon (GAC), crushed ceramic material (CCM) and zeolite (ZEO) in order to use the catalyst for sulfamethoxazole (SMX) removal from aqueous solutions. For this, three TiO2 immobilization methods (1-immersion of the support in TiO2 slurry; 2-covering by sol-gel synthesis using titanium isopropoxide; 3- impregnating the support with white wall paint doped with TiO2) were tested and the resulting catalyst were characterized and evaluated for SMX removal. The results showed that GAC was the best support and that its immersion in a 50% (w/v) TiO2 suspension was the best immobilization method. Photodegradation assays with such catalyst carried out with 10 mg.L-1 of the antibiotic sulfamethoxazole (SMX) led to 90% of removal of this pharmaceutical after 3.5 hours, which was ~38% higher than the UV photolysis at the same contact time. <![CDATA[POLYMERIZATION OF ANILINE IN DIFFERENT SBA-16 SILICA HOSTS]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700845&lng=en&nrm=iso&tlng=en Polyaniline-silica composites made with mesoporous silica have been reported to improve the mechanical properties of the free polymer. However, there are not many studies about the effect of the chemical and physical properties of the inorganic material used as hosts over the final properties of polyaniline and the composites. Here, polyaniline-silica composites, exhibiting electrical conductivity, were synthesized using different types of SBA-16 mesoporous silica as hosts. The effects of the characteristics of the hosts in the polymerization kinetic, molecular weight and electrical conductivity of the final polymer were studied. The composites showed higher electrical conductivity in comparison with polyaniline synthesized under similar conditions of this work but in the absence of silica. The use of silica allowed to obtain composites with defined morphology, which did not occur in the absence of these hosts. From the results of this work, it can be concluded that SBA-16 mesoporous silica hosts have a bifunctional role in the formation of polyaniline-silica composites: the hosts behaved like nucleation sites, which favors polymerization of high molecular weight polyaniline and they catalyzed the polymerization reaction, especially when aluminum is present in the structure of the host. <![CDATA[THEORETICAL CHARACTERIZATION AND DESIGN OF EFFICIENT PHOTOACTIVE MATERIALS BASED ON NAPHTHOPYRROLE AND NAPHTHOTHIOPHENE DERIVATIVES AIMED TOWARDS ORGANIC SOLAR CELLS]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700853&lng=en&nrm=iso&tlng=en In this research we have designed electron donors D-π-A type containing two different π fragments to obtain naphthopyrrole (D-NPR-A) and naphthotiophene (D-NTP-A) derivatives, proposed for the use in organic bulk hetero-junction (BHJ) solar cells (OSCs). These derivatives were characterized by DFT and TD-DFT calculations. For all the electron donors the anchorage fragment was 2-methylenemalononitrile, while the chromophore fragment was spanned between diphenylamine, triphenylamine, thiophene. Properties affecting open-circuit photovoltage (VOC) and short-circuit photocurrent (JSC) from D-π-A type derivatives, such as geometric structure, frontier-molecular orbital energies, exciton driving force energy, natural bond orbital analysis, absorption spectra and light harvesting efficiency. Energy from HOMO and LUMO orbitals was discussed. Theoretical calculations from TD-DFT within Coulumb attenuation method CAM-B3LYP were able to predict excited state properties. The electron donors D-π-A type exhibit photoelectric conversion efficiency above 10%, being the naphthopyrrole derivatives (D-NPR-A) along with the [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) the complexes with higher photoelectric properties, these complexes are proposed as photoactive materials in the construction of organic bulk hetero-junction solar cells. <![CDATA[TOTAL SYNTHESIS IN BRAZIL EMPLOYING PALLADIUM CROSS-COUPLING AS KEY STEP]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700859&lng=en&nrm=iso&tlng=en This article aims to show the selected total syntheses of organic compounds conducted by Brazilian researchers, performed in Brazil, which have employed a palladium catalyzed cross-coupling reaction as key step. We intended to thus create an account, although restricted to the use of palladium, showing the evolution and current state of art of Synthetic Organic Chemistry in Brazil, which has advanced and accept the challenge of total synthesis of increasingly complex molecules, registering growth and maturity of this area among Brazilian researchers. <![CDATA[CLASSIFICATION OF MINERAL WATERS BASED ON DIGITAL IMAGES ACQUIRED BY SMARTPHONES]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700876&lng=en&nrm=iso&tlng=en This work describes a new procedure for classification of mineral waters based on digital images acquired by smartphones. Commercial waters from eight mineral springs plus distilled water and tap water were combined with eriochrome T black or murexide and transferred to a cuvette, which was positioned into a light controlled chamber. RGB (Red, Blue and Green) measurements of cuvette images were acquired in real time, using a free smartphone app, and employed as variables for the exploratory analysis. 2D data dispersion along component B for murexide (x axis) and component R for eriochrome T black (y axis) provides the clear visualization of clusters using the raw variables. Hierarchical cluster analysis (HCA) applied to this data confirmed the efficient discrimination of samples providing the characterization of nine clusters for the ten classes of water investigated. The classification of samples based on a k-nearest neighbors (k-NN) modelled to the efficiency rate of 100% for 8 classes and of 94.4% and 50% for the remaining classes, respectively, indicating the adequate performance of the proposed strategy. Considering the facilities to acquire the data, such as low cost instrumentation and reagents, and the rapidity of the procedures, this alternative may be applied for verification of commercial water adulteration. <![CDATA[TRANSMISSION AND REFLECTION COEFFICIENTS BY THE VARIABLE AMPLITUDE METHOD]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700882&lng=en&nrm=iso&tlng=en In this work, a simple derivation of the variable amplitude method using the variation of parameters to solve a differential equation is presented. The variable amplitude method was originally devised by Tikochinsky in 1977, using the quantum theory of scattering. The method is applied to two model potentials, the rectangular potential barrier and the Eckart potential, both with analytical solutions for the reflection coefficient. Numerical results will be compared with the exact values for several energies. The problem of calculating the reflection coefficient, usually involving extensive algebra as described in several textbooks, is reduced to solving a first order differential equation with initial condition. The method is very simple to apply, representing an attractive tool for teaching introductory quantum mechanics. A simple computer code is available from which reflection coefficients for the Eckart potential can be calculated. <![CDATA[ILL-POSED INVERSE PROBLEMS IN CHEMISTRY]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422016000700886&lng=en&nrm=iso&tlng=en What is an ill-posed inverse problem? The answer to this question is the main objective of the present paper and the pre-requisite to follow the material requires only elementary calculus. The first mathematical formulation of an inverse problem, due to N. H. Abel, together with the fundamental work by Jacques Hadamard, are explored at the beginning of the paper. A prototype system is used to consider the regularization concept. Three numerical methods, the Tikhonov regularization, the decomposition into singular values and the Hopfield neural networks, applied to remove the singularity are examined. General aspects of the ill-posed inverse problems in chemistry with emphasis in thermodynamics and a set of general rules for other areas of science are also analyzed.