ICEN - Instituto de Ciências Exatas e Naturais

URI Permanente desta comunidadehttps://repositorio.ufpa.br/handle/2011/2435

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Agora exibindo 1 - 20 de 157

Acesso aberto (Open Access)
A química na região Norte
(1997-12) ARRUDA, Alberto Cardoso
A historical overview of CHEMISTRY SCIENCE from the beginning of the ESCOLA DE QUÍMICA INDUSTRIAL DO PARÁ in the northern region of Brazil is given. Reports were conducted on graduate and under graduate coursework within research and teaching institutions in each State of the Amazon region. Data collection included teaching, research and industrial activities.
Acesso aberto (Open Access)
A statistical evaluation of the effects of process variables during catalytic hydrogenation of passion fruit (passiflora edulis) seed oil
(1998-03) ANDRADE, Géssie Maria Silva de; ROCHA FILHO, Geraldo Narciso da; TAQUEDA, Maria Elena Santos
Hydrogenation of passion fruit (passiflora edulis) seed oil was carried out with a commercial nickel/silica catalyst under different experimental conditions. The influence of reaction parameters (reaction temperature, hydrogen pressure, amount of catalyst, agitation rate and reaction time) on the response variable (iodine value) was studied using a central composite rotatable design and six center points for replication. Under the experimental conditions used, the model response equations for the iodine value showed good agreement with the experimental results.
Acesso aberto (Open Access)
Structure-activity relationship of compounds which are anti-schistosomiasis active
(1998-12) ALVES, Claudio Nahum; BARROSO, Lucia Pereira; SANTOS, Lourivaldo da Silva; JARDIM, Iselino Nogueira
The molecular orbital method AM1 was employed to calculate a set of molecular descriptors for twenty synthetic neolignan derivatives with anti-schistosomiasis activity. The pattern recognition method (principal component analysis PCA and cluster analysis CA and discriminant analysis methods) have been employed to obtain the relationship between the molecular descriptors and biological activity. The set of molecules was classified into two groups according to their degree of biological activity. These results allow us to rationally project new compounds, potential candidates for synthesis and biological evaluation.
Acesso aberto (Open Access)
Estudo da utilização do extrato aquoso de barbatimão (Stryphnodendron barbatimão, M.) no ensino de química
(1999) PINHEIRO, Marta Helena Tavares; LIMA, Waterloo Napoleão de
In the present work, the pH dependent colour change of the crude vegetal extracts is suggested in teaching chemical or acid-base equilibria, visual indicators and some aspects of spectrophotometric concepts its applications. The extraction methodology proposed is inexpensive and easy to perform in secondary schools and in general chemistry or instrumental undergraduate courses.
Acesso aberto (Open Access)
Coumarins and Alkaloids from the Stems of Metrodorea Flavida
(1999) GONÇALVES, Ana Cristina Baetas; ARRUDA, Mara Silvia Pinheiro; MÜLLER, Adolfo Henrique; ARRUDA, Alberto Cardoso
A new coumarin, 5,6-methylenedioxy-7,8-dimethoxycoumarin has been isolated from the stems of Metrodorea flavida, as well as known coumarins and alkaloids. The structures of the new and the known compounds were established by spectral data and by comparison with the literature data.
Acesso aberto (Open Access)
Two Dibenzylbutyrolactol derivatives and other chemical constituents from Aristolochia peltato-deltoidea
(1999-04) SILVA, Ana Paula Freitas da; PALMEIRA JUNIOR, Sebastião Ferreira; CONSERVA, Lucia Maria; GUILHON, Giselle Maria Skelding Pinheiro
The hexane extract from the aerial parts of Aristolochia peltato-deltoidea Hoehne (Aristolochiaceae) afforded two new epimeric lignans of the type dibenzylbutyrolactol, rel-(8R, 8 S, 9S)-3,4-dimethoxy-3 ,4 -methylenedioxy-9b-ethoxy- and rel-(8R, 8 S, 9R)-3,4-dimethoxy-3 ,4 -methylenedioxy-9a-ethoxy-lignans-8.8 ,9.O.9 , besides a benzofuran neolignan, known as eupomatenoid-7, a-tocopherylquinone, b-sitosterol and stigmasterol. From the chloroform extract were isolated two diastereomeric dibenzylbutyrolactone lignans: rel-(8R, 8 R)- and rel-(8R, 8 S)-3,4-dimethoxy-3 ,4 -methylenedioxy-9-oxo-lignans-8.8 ,9.O.9 . Chemical composition analysis by GC/MS of the non polar fractions from the hexane extract was also carried out and ten components were identified. The structures of the isolated compounds were elucidated utilizing spectrometric methods.
Acesso aberto (Open Access)
Investigação espectroscópica dos carbonilos heterobimetálicos cis-[Fe(CO)4(HgX)2], X = Cl, Br, I
(1999-12) ZAMIAN, José Roberto; MAURO, Antônio Eduardo; NOGUEIRA, Vânia Martins
Spectroscopic studies of heterobimetallic carbonyls cis-[Fe(CO)4(Hgx)2], X=Cl, Br, I.The series of compounds cis-[Fe(CO)4(HgX)2], X=Cl,Br, I shows an octahedral geometry around the iron atom with the two HgX groups cis to each other. In this paper the assignment for the carbonyl stretching modes and the calculation of their force constants were performed on the basis of the Cotton-Krainhanzel model. Taking into account all the data from the IR, 199Hg NMR and UV-vis spectra it is possible to verify the influence of X on the electronic densities at the metallic centers.
Acesso aberto (Open Access)
Thermal decomposition and stability in a series of heterobimetallic carbonyl compounds of the type [Fe(CO)4(HgX)2] (X=Cl, Br, I)
(2000) ZAMIAN, José Roberto; MAURO, Antônio Eduardo; NUNES, Carolina Coimbra; ALMEIDA, Eduardo Tonon de
Foram preparados compostos carbonílicos heterobimetálicos do tipo [Fe(CO)4(HgX)2] ( X= Cl, Br, I), contendo ligação metal-metal, objetivando investigar suas estabilidades térmicas em função do halogênio coordenado aos átomos de mercúrio. A caracterização destes complexos foi feita usando-se de técnicas espectroscópicas de infravermelho e ressonância magnética nuclear, além de análise elementar. O produto final das termodecomposições foi identificado através de espectroscopia no infravermelho e difratograma de raios-X, método de pó.
Acesso aberto (Open Access)
Determinação direta de selênio em água de coco e em leite de coco utilizando espectrometria de absorção atômica com atomização eletrotérmica em forno de grafite
(2000-06) ALEIXO, Poliana Carolina; NÓBREGA, Joaquim de Araújo; SANTOS JÚNIOR, Dário; MÜLLER, Regina Celi Sarkis
Selenium is both essential and toxic to man and animals, depending on the concentration and the ingested form. Most fruits and vegetables are poor sources of selenium, but coconut can be a good selenium source. Samples were suspended (1 + 4 v/v) in a mixture of tertiary amines soluble in water (10% v/v CFA-C). This simple sample treatment avoided contamination and decreased the analysis time. The standard additions method was adopted for quantification. The action of the autosampler was improved by the presence of the amines mixture in the suspension. A Varian model AA-800 atomic absorption spectrometer equipped with a graphite furnace and a GTA 100 autosampler was used for selenium determination in coconut water and coconut milk. Background correction was performed by means of the Zeeman effect. Pyrolytically coated graphite tubes were employed. Using Pd as chemical modifier, the pyrolysis and the atomization temperatures were set at 1400 and 2200oC, respectively. For six samples, the selenium concentration in coconut water varied from 6.5 to 21.0 mg L-1 and in coconut milk from 24.2 to 25.1 mg L-1. The accuracy of the proposed method was evaluated by an addition-recovery experiment and all recovered values are in the 99.5-102.3% range. The main advantage of the proposed method is that it can be directly applied without sample decomposition.
Acesso aberto (Open Access)
Flavones from the Leaves of Ficus gomelleira
(2001-08) AMARAL, Daniel Ferreira; ARRUDA, Mara Silvia Pinheiro; ARRUDA, Alberto Cardoso; MÜLLER, Adolfo Henrique; PANTOJA, Luna Luana de Jesus; LIMA, Tania Maria da Silva
Two new flavones, 5 -hydroxy -7,5' -dimethoxy -3',4' -methylenedioxyflavone and 5 -hydroxy -7,3',5' -trimethoxy -4' -(3,3 -dimethylallyloxy) flavone, as well as three known flavones: 5,6,7,3',4',5' -hexamethoxyflavone, 5 -hydroxy -8,3',4' -trimethoxy -2'',2'' -dimethylpyrano (5",6":6,7) -flavone and 5 -hydroxy -8,3',4',5' -tetramethoxy -2'',2'' -dimethylpyrano (5",6":6,7) -flavone were isolated from the leaves of Ficus gomelleira. Their structures were elucidated by spectroscopic methods and comparison with literature data.
Acesso aberto (Open Access)
Determinação espectrofotométrica do arsênio em cabelo usando o método do dietilditiocarbamato de prata (SDDC) e trietanolamina/CHCl3 como solvente
(2002) PEREIRA, Simone de Fátima Pinheiro; FERREIRA, Sérgio Luis Costa; COSTA, Antonio Celso Spínola; SARAIVA, Augusto Cesar Fonseca; SILVA, Antonia Kelen Frota
The silver diethyldithiocarbamate (SDDC) method, has been employed for the determination of arsenic in different materials. The disagreeable odor of the pyridine, the lower stability and reproducibility of the complex are justifications for many works related to the alternatives of the method. The SDDC/pyridine system was substituted for system using triethanolamine 5% v/v in chloroform with many advantages. The method was used for arsenic determination in hair samples with good recovery. Many kinds of digestions was studied.
Acesso aberto (Open Access)
A structure-activity relationship (SAR) study of neolignan compounds with anti-schistosomiasis activity
(2002-06) ALVES, Claudio Nahum; MACEDO, Luiz Guilherme Machado de; HONORIO, Kathia Maria; CAMARGO, Ademir João; SANTOS, Lourivaldo da Silva; JARDIM, Iselino Nogueira; BARATA, Lauro Euclides Soares; SILVA, Alberico Borges Ferreira da
A set of eighteen neolignan derivative compounds with anti-schistosomiasis activity was studied by using the quantum mechanical semi-empirical method PM3 and other theoretical methods in order to calculate selected molecular properties (variables or descriptors) to be correlated to their biological activities. Exploratory data analysis (principal component analysis, PCA, and hierarchical cluster analysis, HCA), discriminant analysis (DA) and the Kth nearest neighbor (KNN) method were employed for obtaining possible relationships between the calculated descriptors and the biological activities studied and predicting the anti-schistosomiasis activity of new compounds from a test set. The molecular descriptors responsible for the separation between active and inactive compounds were: hydration energy (HE), molecular refractivity (MR) and charge on the C19 carbon atom (Q19). These descriptors give information on the kind of interaction that can occur between the compounds and their respective biological receptor. The prediction study was done with a new set of ten derivative compounds by using the PCA, HCA, DA and KNN methods and only five of them were predicted as active against schistosomiasis.
Acesso aberto (Open Access)
Aprendizagem de eletromagnetismo via programação e computação simbólica
(2002-06) ALVES, Danilo Teixeira; AMARAL, Jair Vaz do; MEDEIROS NETO, João Felipe de; CHEB-TERRAB, Edgardo Salomon
We describe an experience in using programming in Maple as a student's tool for the learning of introductory electromagnetic theory. We believe that this paper can be of use for those interested in using computers as a pedagogical tool.
Acesso aberto (Open Access)
The Linear Potential Propagator via Wave Function Expansion
(2002-09) NASSAR, Antônio Boulhosa; BASSALO, José Maria Filardo; ALENCAR, Paulo de Tarso Santos; LOPES, José Luiz Magalhães; OLIVEIRA, José I. F. de; CATTANI, Mauro Sérgio Dorsa
We evaluate the quantum propagator for the motion of a particle in a linear potential via a recently developped formalism [A.B. Nassar et al., Phys. Rev. E56, 1230, (1997)]. In this formalism, the propagator comes about as a type of expansion of the wave function over the space of the initial velocities.
Acesso aberto (Open Access)
Approximate controllability for the semilinear heat equation in RN involving gradient terms
(2003) MENEZES, Silvano Dias Bezerra de
We prove the approximate controllability of the semilinear heat equation in RN, when the nonlinear term is globally Lipschitz and depends both on the state u and its spatial gradient Ñu. The approximate controllability is viewed as the limit of a sequence of optimal control problems. In order to avoid the difficulties related to the lack of compactness of the Sobolev embeddings, we work with the similarity variables and use weighted Sobolev spaces.
Acesso aberto (Open Access)
Seasonal variation in the essential oil of Pilocarpus microphyllus Stapf.
(2003-03) TAVEIRA, Francisca Socorro Nascimento; ANDRADE, Eloisa Helena de Aguiar; LIMA, Waterloo Napoleão de; MAIA, José Guilherme Soares
The essential oils of the leaves and fine stems of Pilocarpus microphyllus, collected on iron mineralized soil of the Serra de Carajás, Southeast of Pará State, Brazil, during the rainy and dry seasons, were obtained by hydrodistillation and analyzed by GC-MS. The main identified compounds were 2-tridecanone, b-caryophyllene, 2-pentadecanone, caryophyllene oxide and germacrene D. Their percentage contents varied with the season, the greater values having been detected mainly in the rainy season. For 2-tridecanone and b-caryophyllene the higher values were observed in the fine stem oils for the former, and in the leaf oils for the latter. For 2-pentadecanone, caryophyllene oxide and germacrene D they were also in the leaf oils. In general, the leaf oils were very distinguishable from those of fine stem oils, even in the same specimen.
Acesso aberto (Open Access)
Modeling of alkynes: synthesis and theoretical properties
(2003-06) ROSSETO, Renato; TORRES, José Celso; DEL NERO, Jordan
In this paper we present the synthesis and simulation of alkynes derivatives. Semiempirical calculations were carried out for the ground and first excited states, including the spectroscopic properties of the absorption and emission (fluorescence and phosphorescence) spectra by INDO/S-CI and DNdM-INDO/S-CI methods with geometries fully optimized by PM3/CI. The fact that the theoretical spectra are in accord with the experimental absorption spectra gives us a new possible approach on how structure modifications could affect the non-linear optical properties of alkynes.
Acesso aberto (Open Access)
Dye incorporation in polyphosphate gels: synthesis and theoretical calculations
(2003-06) DEL NERO, Jordan; GALEMBECK, André; SILVA, Sidicleia Bezerra Costa; SILVA, José Augusto Pereira da
In this work we described theoretical calculations on the electronic structure and optical properties of the dyes crystal violet and malachite green based in semiempirical methods (Parametric Method 3 and Intermediate Neglect of Differential Overlap / Spectroscopic - Configuration Interaction) and the synthesis of a new hybrid material based upon the incorporation of these dyes in an aluminum polyphosphate gel network. The samples are nearly transparent, free-standing thick films. The optical properties of the entrapped dyes are sensitive to chemical changes within the matrix caused either by gel aging or external stimulli such as exposition to acidic and basic vapors that can percolate within the matrix. Our theoretical modeling is in good agreement with the experimental results for the dyes.
Acesso aberto (Open Access)
A study of neolignan compounds with biological activity against Paracoccidioides brasiliensis by using quantum chemical and chemometric methods
(2003-10) CAMARGO, Ademir João; HONORIO, Kathia Maria; MERCADANTE, Ricardo; MOLFETTA, Fábio Alberto de; ALVES, Claudio Nahum; SILVA, Alberico Borges Ferreira da
Chemometric (statistical) methods are employed to classify a set of neolignan compounds with activity against Paracoccidioides brasiliensis. The AM1 (Austin Model 1) method was used to calculate a set of molecular descriptors (properties) of the neolignan compounds under study. The descriptors were further analyzed using Principal Components Analysis (PCA), Hierarchical Cluster Analysis (HCA) and K-Nearest Neighbor (KNN) chemometric methods. The PCA and HCA methods were quite efficient to classify the compounds into two groups (active and inactive) and three descriptors were found to be important in the classification: the highest occupied molecular orbital energy (EHOMO), the bond order between C1'-R7 atoms (L14) and the bond order between C5' -R6 atoms (L22). The three variables responsible for the separation between active and inactive compounds are all electronic descriptors, therefore we can conclude that electronic effects should have an important role when one is trying to understand the activity of neolignan compounds against Paracoccidioides brasiliensis.
Acesso aberto (Open Access)
Wheeler, Tiomno e a Física brasileira
(2003-12) BASSALO, José Maria Filardo; FREIRE JUNIOR, Olival
This paper analyzes the relationships between the American physicist, John Archibald Wheeler, and the Brazilian physicist Jayme Tiomno. It enlarges Tiomno's image as one of the most gifted theoretical physicist of his generation and it reveals that the losses of the Brazilian science, due to the military government (1964-1985), were more meaningful than what one usually admits.