Papers by Sergio Paula Machado
Química Nova, 2013
Rich and Suter diagrams are a very useful tool to explain the electron configurations of all tran... more Rich and Suter diagrams are a very useful tool to explain the electron configurations of all transition elements, and in particular, the s 1 and s 0 configurations of the elements Cr, Cu, Nb, Mo, Ru, Rh, Pd, Ag, and Pt. The application of these diagrams to the inner transition elements also explains the electron configurations of lanthanoids and actinoids, except for Ce, Pa, U, Np, and Cm, whose electron configurations are indeed very special because they are a mixture of several configurations.
ABSTRACT Calculations were performed using density functional theory (DFT) in order to study the ... more ABSTRACT Calculations were performed using density functional theory (DFT) in order to study the interaction of light atoms (H, C, O, and S) model structures with nickel, iron and zinc of two different sizes. It was observed that for the adsorbed atoms, the site of adsorption involves the greatest possible number of neighbors. We evaluated the adsorption energies and distances between the adsorbed atoms and their nearest neighbors, as well as the influence of the cluster size on the phenomenon. The results explain the adsorption of light atoms on metals used as anodes for solid oxide type fuel cells (SOFC). These results agree with the experimental data, indicating that the theoretical model used is suitable for the interpretations presented.
Journal of biological inorganic chemistry : JBIC : a publication of the Society of Biological Inorganic Chemistry, Jan 3, 2018
The rational design of anti-cancer agents includes a new approach based on ruthenium complexes th... more The rational design of anti-cancer agents includes a new approach based on ruthenium complexes that can act as nitric oxide (NO) donor agents against specific cellular targets. One of the most studied classes of those compounds is based on bis(bipyridine) ruthenium fragment and its derivative species. In this work, we present the chemical and cytotoxicity properties against the liver hepatocellular carcinoma cell line HepG2 of cis-[Ru(NO)Cl(dcbpy)] conjugated to a polyclonal antibody IgG (anti-VDAC) recognizing a cell surface marker. UV-visible bands of the ruthenium complex were assigned with the aid of density functional theory, which also allowed estimation of the structures that explain the biological effects of the ruthenium complex-IgG conjugate. The interaction of cis-[Ru(NO)Cl(dcbpy)] with mitochondria was evaluated due to the potential of these organelles as anti-cancer targets, and considering they interact with the anti-VDAC antibody. The cytotoxicity of cis-[Ru(NO)Cl(dcb...
RESUMO Este trabalho descreve uma forma de classificar a Espectrometria de Fluorescência de Raios... more RESUMO Este trabalho descreve uma forma de classificar a Espectrometria de Fluorescência de Raios-X (FRX) como uma técnica analítica absoluta para determinação das dez ocorrências mais comuns em rochas de interesse para indústrias de petróleo. O tempo total de análise foi de doze minutos, no máximo, incluindo a preparação das amostras. BaO foi incluído neste método para avaliação dos fluidos de perfuração de poços de petróleo. As calibrações foram efetuadas com dois espectrômetros distintos, PW 1480 e PW 2400, disponíveis para comercialização em 1987 e 1994, respectivamente. Testes de exatidão foram efetuados com amostras referência da U. S. Geological Survey's (USGS) e do National Institute of Standards and Technology (NIST). Conclui-se que para um nível de 95% de confiança, os métodos são eficientes e equivalentes, quando aplicados aos tipos de amostras usadas e nas faixas analíticas dos elementos medidos. INTRODUÇÃO De acordo com as definições propostas pelo Comité Consultati...
Boletim Tecnico da PETROBRAS
Calculations were performed using density functional theory (DFT) in order to study the interacti... more Calculations were performed using density functional theory (DFT) in order to study the interaction of light atoms (H, C, O, and S) model structures with nickel, iron and zinc of two different sizes. It was observed that for the adsorbed atoms, the site of adsorption involves the greatest possible number of neighbors. We evaluated the adsorption energies and distances between the adsorbed atoms and their nearest neighbors, as well as the influence of the cluster size on the phenomenon. The results explain the adsorption of light atoms on metals used as anodes for solid oxide type fuel cells (SOFC). These results agree with the experimental data, indicating that the theoretical model used is suitable for the interpretations presented.
Química Nova, 2007
Recebido em 2/2/07; aceito em 18/5/07; publicado na web em 9/11/07 MEDICINAL BIOINORGANIC CHEMIST... more Recebido em 2/2/07; aceito em 18/5/07; publicado na web em 9/11/07 MEDICINAL BIOINORGANIC CHEMISTRY. Metals play a vital role in human and plant physiology and important research is directed towards exploring the interrelated mechanisms that govern their interactions with biomolecules. Bioinorganic medicinal chemistry studies the functions, processing, storage and applications of metal ions and their complexes in biological systems. This paper presents a brief discussion about on interactions of metals with biomolecules that determine their intracellular accumulation, where metal ions may fulfill essential functions in cellular metabolism or, in certain cases, exert toxic effects towards cells.
Química Nova, 2006
CONSTRUCTION OF THE EMPIRICAL FORCE FIELD FOR THE STUDY OF IRON (III) COMPLEXES WITH BIOINORGANIC... more CONSTRUCTION OF THE EMPIRICAL FORCE FIELD FOR THE STUDY OF IRON (III) COMPLEXES WITH BIOINORGANIC INTEREST. In this work we present a new parametrization in molecular mechanics for studying iron complexes. This force field was implemented in the FORCES 2000 program, developed in our group for studying in coordination compounds of interest in bioinorganic chemistry. Mononuclear and dinuclear iron complexes were studied using this program with good success.
Química Nova, 2005
Recebido em 14/6/04; aceito em 5/10/04; publicado na web em 28/2/05 COMBINATORIAL CHEMISTRY OF MA... more Recebido em 14/6/04; aceito em 5/10/04; publicado na web em 28/2/05 COMBINATORIAL CHEMISTRY OF MATERIALS WITH ANALYSIS BY X-RAY MICRODIFFRACTION. PART I: FUNDAMENTALS: Combinatorial chemistry refers to techniques to rapidly fabricate tens, hundreds or even thousands of different micro samples. The analysis of the large number of samples generated by combinatorial methods requires highly efficient analytical methods. In this case, the challenges are due not only to the large number of samples to be analyzed, but also to the small amount of sample available for analysis. This paper describes the fundamentals of combinatorial chemical methods applied to discover of materials and the development in x-ray diffraction to analyze micro samples.
Química Nova, 1999
Batista s/nº Valonguinho-24020-150-Niterói-RJ Recebido em 3/10/97; aceito em 2/12/98 MOLECULAR ME... more Batista s/nº Valonguinho-24020-150-Niterói-RJ Recebido em 3/10/97; aceito em 2/12/98 MOLECULAR MECHANICS APPLICATION IN INORGANIC CHEMISTRY. The present paper is a review about basic principles of the molecular mechanics that is the most important tool used in molecular modeling area, and their applications to the calculation of the relative stability and chemical reactivity of organometalic and coordination compounds. We show how molecular mechanics can be successfully applied to a wide variety of inorganic systems.
Química Nova, 2008
ON AN ACCIDENTAL DEGENERACY IN THE 31 P{ 1 H} NMR CHEMICAL SHIFTS IN RUTHENIUM DIPHOSPHINE COMPLE... more ON AN ACCIDENTAL DEGENERACY IN THE 31 P{ 1 H} NMR CHEMICAL SHIFTS IN RUTHENIUM DIPHOSPHINE COMPLEXES. The [RuCl(bipy)(dppb)(4-pic)]PF 6 complex was prepared and fully characterized. The X-ray crystal structure of this complex was determined in order to make an unambiguous distinction between the two possible positions of the 4-methylpyridine ligand (4-pic) in the compound: trans to phosphorus atom or trans to nitrogen atom. The [RuCl(bipy)(dppb)(4-pic)]PF 6 complex exhibits an unusual temperature-dependent accidental degeneracy of the 31 P chemical shifts in its solution NMR spectrum.
Química Nova, 2002
Recebido em 3/9/01; aceito em 27/2/02 METHODOLOGY TO OBTAIN MOLECULAR MECHANICS PARAMETERS APPLIE... more Recebido em 3/9/01; aceito em 27/2/02 METHODOLOGY TO OBTAIN MOLECULAR MECHANICS PARAMETERS APPLIED TO COORDINATION COMPOUNDS. A methodology is presented to obtain force field parameters to be used in molecular mechanics. The case of Ru(II) is investigated and the parameters obtained, specially its covalent radii, are employed to model Ru(II) coordination compound. The combined use of molecular mechanics with ab initio methods allowed us to predict the metal-ligand stretching force constant for Ru(II) coordination compounds.
Química Nova, 2011
INTERACTION OF SMALL ATOMS WITH TRANSITION METAL CLUSTERS. Density Functional Theory (DFT) calcul... more INTERACTION OF SMALL ATOMS WITH TRANSITION METAL CLUSTERS. Density Functional Theory (DFT) calculations on the interactions of small atoms (H, C, O, and S) on first-row transition metal clusters were performed. The results show that the adsorption site may vary between the metal surface and the edge of the cluster. The adsorption energies, adatom-nearest neighbor and adatom-metal plane distances were also determined. Finally, the authors present a discussion about the performance of these metals as anodes on solid oxide fuel cells. The results obtained agree with empirical data, indicating that the theoretical model used is adequate.
Journal of the Brazilian Chemical Society, 2006
A reação entre Fe(ClO 4) 3. nH 2 O e N,N'-bis[(2-hidroxibenzil)-N,N'-bis(1-metilimidazol-2-ilmeti... more A reação entre Fe(ClO 4) 3. nH 2 O e N,N'-bis[(2-hidroxibenzil)-N,N'-bis(1-metilimidazol-2-ilmetil)]etilenodiamina (H 2 bbimen) resulta na formação de dois isômeros geométricos, A e B, do cátion complexo [Fe(bbimen)] + , os quais foram isolados e caracterizados por espectroscopia na região do infravermelho e UV-visível, espectrometria de massas, medidas de condutividade molar, voltametria cíclica, espectroeletroquímica e espectroscopia de ressonância paramagnética eletrônica (RPE). A geometria de um desses isômeros foi claramente demonstrada por análise cristalográfica de raios X de monocristal. O composto cristaliza no sistema monoclínico, grupo espacial P2 1 /c, a = 14,104 (3), b = 15,626 (3), c = 13,291 (3) Å, β = 98,07 (3) o , Z = 4, R 1 = 6,35% e wR 2 = 20,57%. As propriedades eletroquímicas do cátion [Fe(bbimen)] + (-0,58 V versus NHE) são bastante similares às das transferrinas (-0,52 V versus NHE), indicando que o complexo é um bom modelo para as propriedades redox daquelas metaloenzimas. A espectroscopia de RPE foi a única técnica espectroscópica capaz de diferenciar os dois isômeros isolados (A e B). Os estudos de RPE revelaram que o isômero A trata-se de um complexo de Fe III spin alto distorcido rombicamente (E/D ≅ 0,33) e apresenta um espectro caracterizado por uma linha estreita em g 1 ≅ 4,1 e outra larga em g 2 ≅ 9,0. O espectro de RPE do isômero B apresenta, além das linhas em g 1 ≅ 4,2 e em g 2 ≅ 9,0, um conjunto de linhas em g 1 ≅ 3,0, g 2 ≅ 3,6 e g 3 ≅ 5,1, que têm sido atribuídas a complexos de Fe III com simetria tendendo à axial (E/ D ≅ 0,22). Estudos teóricos empregando cálculos semi-empíricos, combinados com os dados de RPE, foram essenciais para a atribuição das estruturas geométricas dos isômeros A e B. The reaction of Fe(ClO 4) 3. nH 2 O with N,N'-bis[(2-hydroxybenzyl)-N,N'-bis(1-methylimidazole-2-yl-methyl)]ethylenediamine (H 2 bbimen) affords two geometric isomers, A and B, of the complex cation [Fe(bbimen)] + , which were fully characterized by IR and UV-visible spectroscopies, ESI mass spectrometry, molar conductivity measurements, cyclic voltammetry, spectroelectrochemistry and EPR spectroscopy. The geometry of one of these isomers has been clearly demonstrated through X-ray crystallographic analysis. It crystallizes in the monoclinic system, space group P2 1 /c, a = 14.104 (3), b = 15.626 (3), c = 13.291 (3) Å, β = 98.07 (3) o , Z = 4, R 1 = 6.35% and wR 2 = 20.57%. The electrochemical properties of [Fe(bbimen)] + (-0.58 V versus NHE) are quite similar to those of transferrins (-0.52 V versus NHE) and indicate that it is a good model for the redox potential of these metalloenzymes. EPR spectroscopy was the only spectroscopic technique able to differentiate the isolated isomers A and B. EPR studies revealed that isomer A is better described as a rhombically distorted (E/D ≅ 0.33) highspin Fe III complex (g 1 ≅ 4.1 with a shoulder at g 2 ≅ 9.0), while the spectrum of B has a set of lines at g 1 ≅ 3.0, g 2 ≅ 3.6 and g 3 ≅ 5.1, in addition to the line at g 1 ≅ 4.2 and a shoulder at g 2 ≅ 9.0, which have been ascribed to Fe III complexes in axial symmetry (E/D ≅ 0.22). Semi-empirical theoretical studies, combined with EPR data, were essential to the proposition of the geometric structures of A and B.
Journal of the Brazilian Chemical Society, 2010
Dois ligantes tridentados, HL1, [(2-hidroxibenzil)(2-(imidazol-2-il)etil)]amina, e HL2, [(2-hidro... more Dois ligantes tridentados, HL1, [(2-hidroxibenzil)(2-(imidazol-2-il)etil)]amina, e HL2, [(2-hidroxibenzil)(2-(piridil-2-il)etil]amina, foram usados na síntese dos complexos binucleares [Cu 2 (L1) 2 ]Cl 2 • 2H 2 O, complexo 1, e [Cu 2 (L2) 2 ] (ClO 4) 2 • 1.5H 2 O, complexo 2, para serem empregados como catalisadores em processos de oxidação. Os complexos foram caracterizados por análise elementar e espectroscopias na região do infravermelho, ultravioleta-visível e ressonância paramagnética eletrônica. Foram também estudados por voltametria cíclica e titulação potenciométrica, a fim de caracterizar seus comportamentos em solução. A resolução da estrutura cristalina do complexo 1 mostrou um cátion binuclear contendo dois grupos fenóxido em ponte. Este arranjo possui uma distância Cu … Cu de 3.043(10) Å, similar à observada na catecol oxidase (2.90 Å). Os comportamentos catalíticos destes complexos foram investigados nas oxidações de cicloexano e de catecol. Na oxidação de cicloexano observou-se baixa atividade para ambos os complexos, que pode ser atribuída ao estereoimpedimento produzido pela falta de coplanaridade entre os anéis aromáticos do arcabouço dos ligantes, sugerindo que a aproximação entre o substrato e o centro ativo binuclear é uma etapa determinante no mecanismo da reação. Com relação à atividade de catecolase, foram observadas altas eficiências, com o complexo 2 sendo mais ativo que o complexo 1. Isto indica que o ligante piridina é capaz de estabilizar melhor o intermediário proposto para esse processo, que contém o centro Cu I Cu I. Isto é corroborado pela grande participação da piridina no LUMO (lowest unoccupied molecular orbital) do complexo 2, que pode ajudar a acomodar a carga negativa adicional quando o complexo é reduzido da forma Cu II Cu II para Cu I Cu I. The tridentate ligands HL1, [(2-hydroxybenzyl)(2-(imidazol-2-yl)ethyl)]amine, and HL2, [(2-hydroxybenzyl) (2-(pyridil-2-yl)ethyl]amine, were used to synthesize binuclear Cu II complexes, [Cu 2 (L1) 2 ]Cl 2 • 2H 2 O, complex 1, and [Cu 2 (L2) 2 ](ClO 4) 2 • 1.5H 2 O, complex 2, in order to obtain catalysts for oxidative processes. Both complexes were characterized by elemental analysis, IR, UV-Vis and EPR spectroscopies. In addition, they were studied by cyclic voltammetry and potentiometric titration in order to investigate their behavior in solution. The crystal structure of complex 1 revealed a binuclear cation where the metal centers are bridged by two phenoxo groups. This arrangement provides a Cu … Cu distance of 3.043(10) Å, which is similar to the observed for catechol oxidase (2.90 Å). The catalytic reactivities of both complexes were investigated for hydrocarbon and catechol oxidations. Complexes 1 and 2 led to low overall hydrocarbon oxidation conversion values of 6.34 % and 7.15 %, respectively. However, for complex 1, only cyclohexanol (Cy-OH) and cyclohexanone (Cy=O) were isolated as reaction products, with selectivities of 68.1% for Cy-OH. This low overall conversion is tentatively attributed to steric hindrance effects produced by the non-coplanar aromatic rings of the ligand scaffolds, which suggest that the access of the hydrocarbon molecule to the binuclear active center is a determinant step in the reaction mechanism. Investigation of catecholase activities has shown high efficiencies, with complex 2 being more active than complex 1. It indicates that the pyridine-containing ligand is able to stabilize the intermediate Cu I Cu I center which is proposed to be formed in this process. This is corroborated by the strong participation of pyridine in the LUMO (lowest unoccupied molecular orbital) of complex 2, which can help to accommodate the additional negative charge when the complex is reduced from Cu II Cu II to Cu I Cu I .
Journal of the Brazilian Chemical Society, 2010
Este trabalho relata a síntese e a caracterização dos complexos de manganês(II) [Mn II (Hbpeten)]... more Este trabalho relata a síntese e a caracterização dos complexos de manganês(II) [Mn II (Hbpeten)] e [Mn II (Hbnbpeten)], respectivamente [N,N'-bis-(2-hidroxibenzil)-N-(2-piridilmetil)-N'-(2hidroxietil)etano-1,2-diamine]manganês(II) e [N,N'-bis-(5-nitro-2-hidroxibenzil)-N'-(2-hidroxietil) etano-1,2-diamin]manganês(II), por análise elementar, voltametria cíclica, espectroscopias eletrônica (UV-Vis) e vibracional (FTIR), ressonância magnética nuclear de hidrogênio (1 H NMR) e espectroeletroquímica de ressonância paramagnética eletrônica (EPR). Os dados de espectroeletroquímica de EPR foram consistentes com a redução de um grupo nitro, tanto no H 3 bnbpeten livre quanto no complexo de manganês. Além disso, os cálculos teóricos foram consistentes com os resultados experimentais, mostrando que somente um grupo nitro contribui para a formação dos orbitais LUMO e sugerindo que os resultados teóricos são adequados para explicar as propriedades eletrônicas dos complexos. The synthesis and characterization of the manganese(II) complexes [Mn II (Hbpeten)] and [Mn II (Hbnbpeten)], where H 3 bpeten and H 3 bnbpeten are respectively [N,N'-bis-(2-hydroxybenzyl)-N-(2-pyridylmethyl)-N'-(2-hydroxyethyl)ethane-1,2-diamine] and [N,N'-bis-(5-nitro-2hydroxybenzyl)-N'-(2-hydroxyethyl)ethane-1,2-diamine], are reported. The characterization was carried out by elemental analyses, cyclic voltammetry, spectroscopic methods (UV-Vis, FTIR, 1 H NMR), electronic paramagnetic resonance spectroelectrochemistry (EPR) and theoretical DFT calculations. The electrochemistry and EPR espectroelectrochemistry data were consistent with the reduction of one of the nitro groups in free H 3 bnbpeten and in the respective manganese(II) complex. These results were supported by DFT calculations, which showed that only one nitro group contributes to the LUMO. The theoretical data appear to be suitable to describe the electronic properties of the compounds.
Química Nova, 2002
Recebido em 7/8/01; aceito em 2/4/02 SIDEROPHORES: "A MICROORGANISM'S ANSWER". Siderophores (from... more Recebido em 7/8/01; aceito em 2/4/02 SIDEROPHORES: "A MICROORGANISM'S ANSWER". Siderophores (from the Greek: "iron carriers") are defined as relatively low molecular weight, ferric ion specific chelating agents elaborated by microorganisms growing under low iron stress. The role of these compounds is to scavenge iron from the environment and to make this essential chemical element available to the microbial cell. The present paper is a brief presentation of siderophore coordination chemistry with emphasis on those aspects relevant to the transportation of iron (III) complexes across biological membranes. Finally, the role of siderophores in infection and their clinical potential as iron scavenging molecules are reviewed.
Boletim Tecnico da PETROBRAS
Calculations were performed using density functional theory (DFT) in order to study the interacti... more Calculations were performed using density functional theory (DFT) in order to study the interaction of light atoms (H, C, O, and S) model structures with nickel, iron and zinc of two different sizes. It was observed that for the adsorbed atoms, the site of adsorption involves the greatest possible number of neighbors. We evaluated the adsorption energies and distances between the adsorbed atoms and their nearest neighbors, as well as the influence of the cluster size on the phenomenon. The results explain the adsorption of light atoms on metals used as anodes for solid oxide type fuel cells (SOFC). These results agree with the experimental data, indicating that the theoretical model used is suitable for the interpretations presented.
Boletim Técnico da Petrobras, 2011
Calculations were performed using density functional theory (DFT) in order to study the interacti... more Calculations were performed using density functional theory (DFT) in order to study the interaction of light atoms (H, C, O,
and S) model structures with nickel, iron and zinc of two different sizes. It was observed that for the adsorbed atoms, the site of
adsorption involves the greatest possible number of neighbors. We evaluated the adsorption energies and distances between
the adsorbed atoms and their nearest neighbors, as well as the influence of the cluster size on the phenomenon. The results
explain the adsorption of light atoms on metals used as anodes for solid oxide type fuel cells (SOFC). These results agree with
the experimental data, indicating that the theoretical model used is suitable for the interpretations presented.
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Papers by Sergio Paula Machado
and S) model structures with nickel, iron and zinc of two different sizes. It was observed that for the adsorbed atoms, the site of
adsorption involves the greatest possible number of neighbors. We evaluated the adsorption energies and distances between
the adsorbed atoms and their nearest neighbors, as well as the influence of the cluster size on the phenomenon. The results
explain the adsorption of light atoms on metals used as anodes for solid oxide type fuel cells (SOFC). These results agree with
the experimental data, indicating that the theoretical model used is suitable for the interpretations presented.
and S) model structures with nickel, iron and zinc of two different sizes. It was observed that for the adsorbed atoms, the site of
adsorption involves the greatest possible number of neighbors. We evaluated the adsorption energies and distances between
the adsorbed atoms and their nearest neighbors, as well as the influence of the cluster size on the phenomenon. The results
explain the adsorption of light atoms on metals used as anodes for solid oxide type fuel cells (SOFC). These results agree with
the experimental data, indicating that the theoretical model used is suitable for the interpretations presented.