Sample records for ligands
from WorldWideScience.org

Sample records 1 - 20 shown. Select sample records:



1

Catalisadores contendo carbenos n-heterocíclicos como ligantes: propriedades, sínteses, aplicações e comparação com outros ligantes/ Catalysts containing n-heterocyclic carbenes as ligands: properties, syntheses, applications and comparison with other catalysts

Pastre, Julio Cezar; Correia, Carlos Roque Duarte
2008-01-01

Resumo em inglês N-heterocyclic carbenes (NHCs) have become of considerable importance in modern organometallic chemistry and homogeneous catalysis. There are several advantages in the use NHCs over their phosphorus analogues, which explains the enormous development of NHC ligands in the field of organometallic catalysis in the past few years. In this article, we present an overview of the importance of the catalysts containing NHC ligands, their synthesis, some pertinent synthetic applications, and a brief comparison with other catalysts.

Scientific Electronic Library Online (Portuguese)

2

Síntese e caracterização de novos compostos de coordenação de cobre (II) com ligantes não-simétricos N,O-doadores: contribuições para o sítio ativo da galactose oxidase/ Synthesis and characterization of new copper (II) coordination compounds with unsymmetrical N,O-donor ligands: contributions for the galactose oxidase active site

Romanowski, Stela Maris de Moraes; Mangrich, Antonio Sálvio; Neves, Ademir
2001-10-01

Resumo em inglês The reactions of four new unsymmetrical N,O-donor ligands, {H2BBPETEN= [N-(2-hydroxybenzyl) - N,N' - bis(2 methylpyridyl) -N'-(hydroxyethyl) ethylenodiamine], H3BPETEN=[N,N'- bis(2-hydroxybenzyl) -N- (2-methylpyridyl) -N'- (hydroxyethyl) ethylenodiamine], HTPETEN=[N,N,N'- tris(2-methylpyridyl) -N'- (hydroxyethyl) ethylenodiamine] and H3BIMETEN=[N,N'-(2-hydroxybenzyl)-N-(1-methylimidazol-2-il-methyl)-N'- (hydroxyethyl)ethylenodiamine]}, with Cu(II) salts afforded the follo (mais) wing mononuclear compounds: [CuII(HBBPETEN)]ClO4, [CuII(H2BPETEN)]ClO4 , [CuII(HTPETEN)](PF6)2 and [CuII(H2BIMETEN)]ClO4 . All were characterized by EPR, electronic spectroscopy and electrochemistry. The four copper (II) compounds showed interesting electrochemistry properties. All presented an anodic wave that can be attributed to the Cu (I) oxide formation at the electrode surface, or to a Cu0 sediment at the same surface or yet, to Cu(I) -> Cu(II) oxidation process with coupled chemistry reaction, due to their irreversibility. Two of the complexes are described as interesting synthetic models for the active site of the metalloenzyme galactose oxidase.

Scientific Electronic Library Online (Portuguese)

3

Monoterpenos di-hidroxilados e hidróxi-nitrogenados 1,2 e 1,3 como ligantes quirais em reação de reformatsky assimétrica/ 1,2- and 1,3-dihydroxylated and hydroxynitrogenated monoterpenes as chiral ligands in the asymmetric reformatsky reaction

Ribeiro, Carlos Magno R.; Morita, Cristina M.; Maia, Mônica P.
2008-01-01

Resumo em inglês This study describes the use of three (-)-alpha-pinene derivatives, one diol-1,2 [(-)-(1R, 2R, 3S, 5R)-2,6,6-trimethylbicyclo[3.1.1]heptane-2,3-diol 4] and two piridine-hydroxy derivatives [(+)-(1R,2S,3R,5S)-2,6,6-trimethyl-3-(2-pyridinylmethyl)bicyclo[3.1.1]heptan-3-ol 7 and (-)-(1R,2S,3R,5S)-2,6,6-trimethyl-3-[2-(2-pyridinyl) ethyl]bicyclo[3.1.1]heptan-3-ol 8]; one diol-1,3 [(-)-(1S,2R,5S)-2-(1-hydroxy-1-methylethyl)-5-methylcyclohexanol 5] derived from (+)-isopulegol 2 (mais) and one diol-1,3 [(+)-(1R,2R,5R)-2-(1-hydroxy-1-methylethyl)-5-methylcyclohexanol 6] derived from (+)-neo-isopulegol 3, as ligands in the asymmetric Reformatsky reaction. The best enantiomeric excess of beta-hydroxy ester obtained in the Reformatsky asymmetric reaction was 18% using ligand 6, and the chemical yield of the reactions was 65% on average.

Scientific Electronic Library Online (Portuguese)

4

Estudo espectroscópico de complexos de Eu3+, Tb3+ E Gd3+ com ligantes derivados de ácidos dicarboxílicos/ Spectroscopic study of the Eu3+, Tb3+ and Gd3+ complexes with ligands derived from dicarboxylic acids

Lima, Patrícia P.; Malta, Oscar L.; Alves Júnior, Severino
2005-10-01

Resumo em inglês Complexes of Eu3+, Tb3+ and Gd3+ with dipicolinic acid, chelidamic acid and chelidonic acid have been synthesized in order to study the effect of the substituent groups on the luminescence of the lanthanide complexes. The luminescence of the Eu3+ and Tb3+ complexes was quantified by quantum yield measurements. The complexes of Gd3+ have been used to determine the energies of the triplet states of the ligands. The Tb3+ complex synthesized with dipicolinic acid presented th (mais) e highest quantum yield due to the energy difference between the triplet state of the dipicolinic acid and the emitting level of the Tb3+ ion.

Scientific Electronic Library Online (Portuguese)

5

Síntese e caracterização de novos complexos de platina (II) com ligantes derivados do furano e nitrofurano/ Synthesis and characterization of new platinum (II) complexes containing furan and nitrofuran derived ligands

Guerra, Wendell; Fontes, Ana Paula Soares; Almeida, Mauro Vieira de; Silva, Heveline
2005-10-01

Resumo em inglês Platinum (II) complexes, for example, cisplatin and carboplatin, have been used as chemotherapeutic agents for the treatment of various types of cancer. Several other complexes of this metallic ion are also under clinical evaluation. This work describes the synthesis of five new platinum (II) complexes having furan and 5-nitrofuran derivatives and chloride as ligands. The compounds were characterized by NMR, IR and elemental analysis.

Scientific Electronic Library Online (Portuguese)

6

Síntese e caracterização estrutural de complexos mono e bimetálicos de paládio e platina com ligantes contendo nitrogênio e enxofre/ Synthesis and structural characterization of palladium and platinum mono- and bimetallic complexes with ligands containing nitrogen and sulfur

Knupp, Vagner Fernandes; Nicesio, Isa Carla; Queiroz, Fernanda de Magalhães; Matos, Robson Mendes; Passos, Bernadette de F. Trigo
1997-08-01

Resumo em inglês The synthesis of several mono- and bimetallic platinum and palladium complexes are reported. The monometallic complexes are of the type MCl2(PEt3)2L (L=2-aminothiazol; benzothiazol; 2-imidazolidithione; M=Pt; Pd), and the bimetallic complexes (M2Cl4(PEt3) 2L) are derived from them. Infrared spectroscopic characterization of the monometallic complexes shows that the metal centre are coordinated through the N-endocyclic (L=2-aminothiazol; benzothiazol) and through the sulph (mais) ur when L=2-imidazolidithione. Coordination of a second metal fragment occurs via the sulphur atom (L=2-aminothiazol; benzothiazol) according to infrared studies. 31P{¹H} NMR spectroscopy suggest that the complexes have a cis- configuration since the ¹J Pt-P are around the value found for this type of compound.

Scientific Electronic Library Online (Portuguese)

7

Um paradigma da química medicinal: a flexibilidade dos ligantes e receptores/ A medicinal chemistry paradigm: ligands and receptor flexibility

Verli, Hugo; Barreiro, Eliezer J.
2005-02-01

Resumo em inglês In general, molecular modeling techniques applied in medicinal chemistry have been static and drug based. However the active site geometry and the intrinsic flexibility of both receptor and ligand are fundamental properties for molecular recognition and drug action. As a consequence, the use of dynamic models to describe the ligand-receptor complex is becoming a more common procedure. In this work we discuss the relevance of considering the receptor structure in medicinal chemistry studies as well as the flexibility of the ligand-receptor complex.

Scientific Electronic Library Online (Portuguese)

8

O comportamento Fotoquímico dos Complexos Pentaaminas de Rutênio(II) com Ligantes π Insaturados/ The photochemical behaviour of pentaamineruthenium(ii) complexes with unsaturated π ligands

Carlos, Rose Maria; Tfouni, Elia; Neumann, Miguel G.
1997-06-01

Resumo em inglês A general overview on the photochemical behaviour of [Ru(NH3)5L]2+ complexes (where L is a p ligand) is presented. The proposed mechanisms and techniques employed for the study of these reactions are discussed. Emphasis is made on the mechanisms that allow the identification of the reactive excited state of the [Ru(NH3)5py]2+ complex.

Scientific Electronic Library Online (Portuguese)

9

Comportamento térmico de composto ciclopaladados binucleares contendo azo-ligantes aniônicos/ Thermal behaviour of binuclear cyclopalladated compounds containing anionic azo-ligands

ALMEIDA, Eduardo Tonon de; MAURO, Antonio Eduardo; SANTANA, Anderson Martinez
2002-01-01

Resumo em português No presente trabalho é descrita a investigação do comportamento térmico de uma nova série de complexos ciclopaladados, obtidos a partir de reações do azido-complexo [Pd(dmba)(mi-N3)]2 (1) (dmba = N,N-dimetilbenzilamina) com os azo-ligantes aniônicos pirazolato (pz), imidazolato (imz) e 3,5-dimetil-pirazolato (3,5-dmpz). Os compostos binucleares [Pd(dmba)(mi-pz)]2 (2), [Pd(dmba)(mi-imz)]2 (3) e [Pd(dmba)(mi-3,5-dmpz)]2 (4) foram caracterizados por análise elementa (mais) r, espectroscopia de absorção na região do infravermelho, espectroscopia de RMN de 13C{¹H} e ¹H e análise termogravimétrica. O produto final de decomposição térmica, paládio metálico, foi caracterizado pela difratometria de raios-X, método do pó. Resumo em inglês The present paper deals with the thermal behavior study of cyclopalladated complexes obtained from reactions of [Pd(dmba)N3]2 (1), dmba = N,N-dimethylbenzylamine, with azole-compunds, such as, the anionic ligands pyrazolate (pz), imidazolate(imz) and 3,5-dimethyl-pyrazolate (3,5-dmpz). The characterization of the binuclear complexes [Pd(dmba)(mu-pz)]2 (2), [Pd(dmba)(mu-imz)]2 (3) and [Pd(dmba)(mu-3,5-dmpz)]2 (4) was carried out by elemental analysis, IR and NMR spectrosco (mais) py. Their thermal behaviour has been investigated and the final product was identified by X-ray powder diffractometry which showed the formation of Pd(0) as final decomposition product.

Scientific Electronic Library Online (Portuguese)

10

Síntese e caracterização de complexos de platina (II) contendo iodeto e derivados do furano como ligantes/ Synthesis and characterization of platinum (II) complexes containing iodide and furan derivatives as ligands

Guerra, W.; Silva, H.; Almeida, M. V. de; Fontes, A. P. S.
2006-01-01

Resumo em português Alguns compostos de platina (II), como por exemplo, cisplatina, carboplatina e oxaloplatina, têm sido utilizados como agentes quimioterápicos no tratamento de vários tipos de câncer. Contudo, na tentativa de reduzir a toxicidade e ampliar o espectro de atividade da cisplatina e de seus análogos, milhares de complexos têm sido preparados variando a natureza dos ligantes. Este trabalho descreve a síntese e caracterização de novos complexos de platina, tendo iodeto e derivados do furano como ligantes. Os complexos foram caracterizados por RMN, IV e análise elementar. Resumo em inglês Platinum (II) compounds, for example, cisplatin, carboplatin and oxaloplatin, have been used as chemotherapeutic agents for the treatment of various types of cancer. However, in an attempt to reduce toxicity and widen the spectrum of activity of cisplatin and its analogous, thousands of platinum complexes have been prepared by varying the nature of the leaving groups and the carrier ligands. This work reports the synthesis and characterization of novel structural types of (mais) the platinum compounds, having iodide and furan derivatives as ligands. The compounds were characterized using NMR, IR and elemental analysis.

Scientific Electronic Library Online (Portuguese)

11

Mapeamento das interações proteína-ligante através de técnicas de RMN de ¹H utilizando detecção do ligante/ Screening protein-ligand interactions using ¹H NMR techniques for detecting the ligand

Figueiredo, Isis Martins; Marsaioli, Anita Jocelyne
2007-01-01

Resumo em inglês NMR is a valuable screening tool for the binding of ligands to proteins providing structural information on both protein and ligands and is thus largely applied to drug-discovery. Among the recent NMR techniques to probe weak binding protein-ligand complexes we have critically evaluated the advantages and disadvantages of STD (Saturation Transfer Difference), WaterLOGSY (Water Ligand Observation with Gradient Spectroscopy), NOE pumping and DOSY-NOESY (Diffusion-Ordered NO (mais) ESY) using a mixture of BSA (bovine serum albumin) plus salicylic acid, caffeine, citric acid, adipic acid and D-glucose.

Scientific Electronic Library Online (Portuguese)

12

Síntese e caracterização estrutural do ligante isatina-3-(N4-benziltiossemicarbazona) e do seu complexo de mercúrio(II)/ Synthesis and structural characterization of the ligand isatin-3-(N4-benzylthiosemicarbazone) and its mercury(II) complex

Fonseca, Alexandra de Souza; Peres, Gisele Louro; Storino, Tomás Garcia; Bresolin, Leandro; Carratu, Vanessa Santana; Giglio, Vinícius F.; Crespan, Estela dos Reis; Hörner, Manfredo
2010-01-01

Resumo em inglês The reaction of 4-(phenyl)thiosemicarbazide with isatin yielded a new ligand, isatin-3-(N4-benzylthiosemicarbazone). Isatin-3-(N4-benzylthiosemicarbazone) deprotonated in ethanol/KOH reacts with an ethanolic solution of Hg(NO3)2 to give a mercury complex. The compounds were characterized by IR and X-ray single crystal structure determination. The X-ray studies revealed that the complex possesses a tetrahedral geometry with two deprotonated thiosemicarbazone ligands coorde (mais) nated. The ligand and its mercury complex crystallize in the monoclinic (P2(1)/c) and triclinic (P-1) crystal system, respectively.

Scientific Electronic Library Online (Portuguese)

13

Aspectos recentes da absorção e biodisponibilidade do zinco e suas correlações com a fisiologia da isoforma testicular da Enzima Conversora de Angiotensina/ Recent aspects of zinc absorption and bioavailability and correlations with physiology of the testicular Angiotensin-Converting Enzyme

Henriques, Gilberto Simeone; Hirata, Mário Hiroiuki; Cozzolino, Sílvia Maria Franciscato
2003-09-01

Resumo em português A associação estável a macromoléculas e a flexibilidade da esfera de coordenação são propriedades intrínsecas do zinco e sua essencialidade encontra-se intimamente relacionada ao seu papel biológico, seja na ativação da função catalítica de enzimas, seja na estabilização das estruturas conformacionais de proteínas e ácidos nucléicos. O zinco é o segundo elemento traço essencial mais abundante no organismo humano e é necessário à atividade de mais d (mais) e 300 enzimas dos 6 tipos de classes existentes. Estas características tornaram o metal e seus ligantes fontes de grande interesse para a nutrição experimental, já que o seu estudo converge para a determinação da biodisponibilidade do metal. Dentre esses ligantes, a isoforma testicular da Enzima Conversora de Angiotensina, sintetizada pelas células germinais masculinas, pode ser considerada um exemplo marcante de regulação molecular a partir da ligação do zinco, influenciando tanto a atividade quanto a concentração desta enzima e conseqüentemente a função testicular. Resumo em inglês The stable association with macromolecules and the flexibility of the coordination geometry are particular properties of zinc and its essentiality has been associated with the biological functions assigned to the metal, either by participating directly in chemical catalysis or by helping to mantain protein and nucleic acid structures and stability. Zinc is the second most abundant essential trace element in the human organism and it is necessary to the activity of more th (mais) an 300 enzymes, covering all 6 classes of them. These properties make this metal and its ligands subjects of great interest for experimental nutrition, leading to the determination of zinc bioavailability. Among these ligands, the testicular Angiotensin- Converting Enzyme, synthesized by male germ cells, is an important example of the molecular regulation by zinc binding, determining both the activity and the concentrations of this enzyme, and affecting the testicular function.

Scientific Electronic Library Online (Portuguese)

14

Estudos de QSAR-3D em derivados 5-nitro-2-tiofilidênicos com atividade frente a Staphylococcus aureus multi-resistente/ 3D QSAR studies of 5-nitrothiophene derivatives with antimicrobial activity against multidrug-resistant Staphylococcus aureus

Masunari, Andrea; Tavares, Leoberto Costa
2007-06-01

Resumo em português Campos moleculares extraídos de aplicativos utilizados em estudos de QSAR-3D apresentam, em geral, grande número de informações, muitas vezes irrelevantes na expressão da atividade biológica. O programa Volsurf converte as informações presentes em mapas de energia de interação tridimensionais em número reduzido de descritores bidimensionais que se caracterizam como de fácil entendimento e interpretação. Assim, foram avaliados, neste estudo, dezoito derivados (mais) 5-nitro-2-tiofilidênicos com atividade antimicrobiana frente a Staphylococcus aureus multi-resistente, correlacionando as características tridimensionais destes ligantes com a referida atividade. Para o desenho e conversão tridimensional dos ligantes foram utilizados os aplicativos Sybyl (Tripos Inc) e CORINA (Molecular Networks GmbH Computerchemie), respectivamente. Os campos de interação molecular foram calculados no programa GRID (Molecular Discovery Ltd). A aplicação do programa Volsurf (Molecular Discovery Ltd) resultou em modelo estatisticamente robusto (r² = 0,93, q² = 0,87) com 48 descritores estruturais, mostrando ser a hidrofobicidade propriedade fundamental no condicionamento da atividade antimicrobiana. Resumo em inglês Studies in three-dimensional molecular fields generally contain a large amount of data, some of which are redundant or not relevant. The program Volsurf, a quite fast method, is able to compress the relevant information present in 3D molecular structures into a few easy bidimensional descriptors. This study correlates the antimicrobial activity of eighteen 5-nitro-2-thiophylidene derivatives against multidrug-resistant Staphylococcus aureus with three-dimensional molecula (mais) r fields of these ligands. For molecular structures sketching and 3D conversion, Sybyl and CORINA programs were used, respectively. The GRID force field was applied to generate the 3D interaction energies. The Volsurf characterization results on significant statistic model with 48 descriptors (r² = 0,93, q²= 0,87), observing a significant influence of hydrophobic properties on antimicrobial activity performance.

Scientific Electronic Library Online (Portuguese)

15

Catálise estereoespecífica de estireno por titanocenos alquil-substituídos do tipo (RCp)2TiCl2/ Styrene stereospecific catalysis by alkyl substituted titanocenes of the type (RCp)2TiCl2

PEREIRA, Brasílio Carvalho de Araújo; KLEIN, Stanlei Ivair; DIAS, Marcos Lopes
2000-01-01

Resumo em português Uma série de sete complexos alquil substituídos do tipo (RCp)2TiCl2 (R= H, etila, n-propila, iso-propila, n-butila, iso-amila, ciclo-hexila) foi preparada juntamente com o ainda inédito contendo R= sec-butila, e o efeito do substituinte na polimerização do estireno foi investigada à temperaturas de polimerização de 0 e 50 ºC. Foi encontrado que R = n-butila maximiza a produção de poliestireno sindiotático. Ligantes alquilas com R = RCH2- são superiores aos R = RR’CH- e ao precursor Cp2TiCl2 na produção de poliestireno sindiotático de alto peso molecular. Resumo em inglês A series of seven alkyl substituted complexes of the type (RCp)2TiCl2 (R= H, ethyl, n-propyl, iso-propyl, n-butyl, iso-amyl, ciclo-hexyl) was prepared, as well as the novel compound with R = sec-butyl, and the effects of the substituent on the polymerisation of styrene was investigated at the temperatures of 0 and 50 ºC. It was found that R = n-butyl maximises the production of syndiotactic polystyrene. Alkyl ligands with R = RCH2- are superior to those with R = RR’CH- and to the precursor Cp2TiCl2 in the production of high molecular weight syndiotactic polystyrene.

Scientific Electronic Library Online (Portuguese)

16

Dinâmica molecular: teoria e aplicações em planejamento de fármacos/ Molecular dynamics: theory and applications in drug design

Namba, A. M.; Silva, V. B. da; Silva, C. H. T. P. da
2008-12-01

Resumo em português Dinâmica Molecular (DM) é uma ferramenta computacional poderosa usada em Química Medicinal para o planejamento racional de fármacos. DM é uma extensão da Mecânica Molecular, onde o comportamento dinâmico de um sistema molecular é simulado através da integração numérica das equações de movimento. Esta técnica tem sido usada extensivamente para auxiliar e complementar o planejamento de novos ligantes de um alvo terapêutico, bem como estimar a sua potência. (mais) Este artigo enfoca a teoria básica da DM clássica e suas importantes aplicações no planejamento racional de potenciais compostos bioativos, particularmente compostos com atividade anti-HIV. Resumo em inglês Molecular dynamics (MD) is a powerful computational tool used for rational drug design in medicinal chemistry. MD is an extension of Molecular Mechanics, where the dynamic behavior of a molecular system is simulated through numerical integration of the equations of motion. This approach has been extensively used to aid and complement the design of novel ligands to a therapeutic target as well as to estimate their potency. Our review focuses on the basic theory of classica (mais) l MD and their important applications in rational drug design of potential bioactive compounds, particularly anti-HIV compounds.

Scientific Electronic Library Online (Portuguese)

17

Agentes antitumorais inibidores da angiogênese: modelos farmacofóricos para inibidores da integrina anb3/ Angiogenesis inhibitors antitumor agents: pharmacophore models to anb3 antagonists

Silva, Thais Horta Álvares da; Butera, Anna Paola; Leal, Daniel Henriques Soares; Alves, Ricardo José
2007-03-01

Resumo em português O câncer é, atualmente, uma das principais causas de morte no mundo. A angiogênese, formação de novos vasos capilares a partir de células endoteliais, é essencial para vários processos fisiopatológicos, tais como o desenvolvimento e a disseminação dos tumores. As integrinas são uma família de receptores de superfície que estão envolvidos na angiogênese, na qual a integrina anb3 exerce papel importante. Os antagonistas da integrina (mais) anb3 têm efeitos diretos na prevenção do crescimento, angiogênese e metástase tumorais. A avaliação in vitro frente à integrina anb3 de coleções de ciclopeptídeos levou a compostos muito ativos e seletivos. Antagonistas não-peptídicos da integrina anb3 também foram planejados e sintetizados. A partir da determinação da estrutura tridimensional da integrina anb3 complexada com um inibidor, tornou-se possível o planejamento racional de ligantes com alta afinidade. Além disto, estes estudos permitiram a validação e o refinamento de modelo farmacofórico para os inibidores da integrina anb3. Resumo em inglês Cancer is one of the leading causes of death. Angiogenesis, the growth of new blood vessels, is essential for tumor development and spreading. Integrins are a family of surface receptors that are involved in angiogenesis. The anb3 integrin plays an important role in tumor angiogenesis. anb3 inhibitors have direct effects to prevent tumor metastases, growth and angiogenesis. In vitro screening of cyclic peptide libraries le (mais) d to highly active and anb3-selective compounds. Non-peptidic anb3 antagonists were also designed and synthesized. The crystal structure of the anb3 integrin in complex with RGD ligant allowed structure-based rational design of ligands and validation of pharmacophore model to anb3 antagonists.

Scientific Electronic Library Online (Portuguese)

18

Cinética de solubilização de metais pesados por ácidos orgânicos em solos tratados com lodo de esgoto/ Kinetics of heavy metal solubilization by organic acids in sludge-treated soils

Pires, Adriana Marlene Moreno; Mattiazzo, Maria Emília
2007-02-01

Resumo em português A presença de ligantes orgânicos na rizosfera tem importante papel no processo de solubilização de metais pesados em solos tratados com lodo de esgoto. Ácidos orgânicos de baixo peso molecular exsudados por raízes e, ou, liberados por microrganismos são considerados agentes mobilizadores desses metais. No presente estudo, determinou-se a cinética de solubilização de Cu, Cr, Ni e Zn em solos tratados com lodo de esgoto, utilizando solução com mistura de quatro (mais) ácidos orgânicos (acético, cítrico, lático e oxálico) preparada para obter concentração final de 0,05 e 0,10 mol L-1. A extração foi feita segundo o método de "batch". A solução 0,10 mol L-1 de ácidos orgânicos extraiu maiores quantidades de Cu, Cr, Ni e Zn do que a solução 0,05 mol L¹. A cinética de solubilização apresentou duas fases: uma inicial, com rápida liberação dos metais, seguida de outra mais lenta, tendendo ao equilíbrio. As constantes de velocidade de solubilização mais altas foram observadas para Ni e Zn, seguidos de Cu e Cr. Os valores para o reservatório lábil variaram entre 2 e 15 % do total de cada metal pesado estudado. A porcentagem que este reservatório representou, em relação ao total, obedeceu à ordem: Zn > Cu @ Ni > Cr. Resumo em inglês The presence of organic ligands in the rhizosphere plays an important role in heavy metal solubilization in soils treated with sewage sludge. Low molecular weight organic acids exuded by roots and/or released by microorganisms are considered mobilizing agents of these metals. The present study determined Cd, Cu, Cr, Ni, and Zn solubilization kinetics in sewage sludge-treated soils using a mixture of four organic acids (acetic, citric, lactic, and oxalic) in 0.05 and 0.10 (mais) mol L-1 solutions. Based on the batch extraction method the 0.10 mol L-1 solution extracted greater quantities of Cu, Cr, Ni and Zn. Two phases of solubilization kinetics were observed: an initial one of fast metal release, followed by a slower one tending to equilibrium. The highest velocity constants were observed for Ni and Zn, followed by Cu and Cr. The values calculated for the labile pool varied from 2 to 15% of the total content of each metal under study. The percentage of this metal pool in relation to the total content followed the order: Zn > Cu @ Ni > Cr.

Scientific Electronic Library Online (Portuguese)

19

Controle da adipogênese por ácidos graxos/ Control of adipogenesis by fatty acids

Queiroz, Jean César Farias de; Alonso-Vale, Maria Isabel Cardoso; Curi, Rui; Lima, Fabio Bessa
2009-07-01

Resumo em português A obesidade é um dos principais problemas de saúde pública. Indivíduos obesos são mais suscetíveis a desenvolver doenças cardiovasculares e diabetes melito tipo 2. A obesidade resulta do aumento no tamanho e no número de adipócitos. O balanço entre adipogênese e adiposidade determina o grau de obesidade do indivíduo. Adipócitos maduros secretam adipocinas, tais como TNFα, IL-6, leptina e adiponectina, e lipocina, o ácido palmitoleico ω-7. A produç (mais) ão de adipocinas é maior na obesidade, o que contribui para o estabelecimento de resistência periférica à insulina. O conhecimento dos eventos moleculares que regulam a diferenciação dos pré-adipócitos e de células-tronco mesenquimais em adipócitos (adipogênese) é importante para o entendimento da gênese da obesidade. A ativação do fator de transcrição PPARγ é essencial na adipogênese. Certos ácidos graxos são ligantes de PPARγ e podem, assim, controlar a adipogênese. Além disso, alguns ácidos graxos atuam como moléculas sinalizadoras em adipócitos, regulando sua diferenciação ou morte. Dessa forma, a composição lipídica da dieta e os agonistas de PPARγ podem regular o balanço entre adipogênese e morte de adipócitos e, portanto, a obesidade. Resumo em inglês Obesity is one of the major Public Health problems. Obese individuals are more susceptible to develop cardiovascular diseases and type 2 diabetes mellitus. The obesity results from the increase in size and number of the adipocytes. The balance between adipogenesis and adiposity determines the degree of obesity. Mature adipocytes secrete adipokines, such as TNFα, IL-6, leptine and adiponectin, and lipokine, the palmitoleic acid ω-7. The production of adipokines i (mais) s increased in obesity, contributing to the onset of peripheral insulin resistance. The knowledge about the molecular events that regulate the differentiation of pre-adipocytes and mesenchymal stem cells into adipocytes (adipogenesis) is important for the comprehension of the genesis of obesity. Activation of transcription factor PPARγ plays an essential role in the adipogenesis. Certain fatty acids are PPARγ ligands and can control adipogenesis. Moreover, some fatty acids act as signaling molecules regulating their differentiation into adipocytes or death. Accordingly, the lipid composition of the diet and PPARγ agonists can regulate the balance between adipogenesis and death of adipocytes and, therefore, the obesity.

Scientific Electronic Library Online (Portuguese)

20

Exploração farmacológica do sistema endocanabinoide: novas perspectivas para o tratamento de transtornos de ansiedade e depressão?/ Pharmacological exploitation of the endocannabinoid system: new perspectives for the treatment of depression and anxiety disorders?

Saito, Viviane M.; Wotjak, Carsten T.; Moreira, Fabrício A.
2010-05-01

Resumo em português OBJETIVO: Este artigo revisa o sistema endocanabinoide e as respectivas estratégias de intervenções farmacológicas. MÉTODO: Realizou-se uma revisão da literatura sobre o sistema endocanabinoide e a sua farmacologia, considerando-se artigos originais ou de revisão escritos em inglês. DISCUSSÃO: Canabinoides são um grupo de compostos presentes na Cannabis Sativa (maconha), a exemplo do Δ9-tetraidrocanabinol e seus análogos sintéticos. Estudos sobre o seu pe (mais) rfil farmacológico levaram à descoberta do sistema endocanabinoide do cérebro de mamíferos. Este sistema é composto por pelo menos dois receptores acoplados a uma proteína G, CB1 e CB2, pelos seus ligantes endógenos (endocanabinoides; a exemplo da anandamida e do 2-araquidonoil glicerol) e pelas enzimas responsáveis por sintetizá-los e metabolizá-los. Os endocanabinoides representam uma classe de mensageiros neurais que são sintetizados sob demanda e liberados de neurônios pós-sinápticos para restringir a liberação de neurotransmissores clássicos de terminais pré-sinápticos. Esta sinalização retrógrada modula uma diversidade de funções cerebrais, incluindo ansiedade, medo e humor, em que a ativação de receptores CB1 pode exercer efeitos dos tipos ansiolítico e antidepressivo em estudos préclínicos. CONCLUSÃO: Experimentos com modelos animais sugerem que drogas que facilitam a ação dos endocanabinoides podem representar uma nova estratégia para o tratamento de transtornos de ansiedade e depressão. Resumo em inglês OBJECTIVE: The present review provides a brief introduction into the endocannabinoid system and discusses main strategies of pharmacological interventions. METHOD: We have reviewed the literature relating to the endocannabinoid system and its pharmacology; both original and review articles written in English were considered. DISCUSSION: Cannabinoids are a group of compounds present in Cannabis Sativa (hemp), such as Δ9-tetrahydrocannabinol, and their synthetic analog (mais) ues. Research on their pharmacological profile led to the discovery of the endocannabinoid system in the mammalian brain. This system comprises at least two G-protein coupled receptors, CB1 and CB2, their endogenous ligands (endocannabinoids; e.g. the fatty acid derivatives anandamide and 2-arachydonoyl glycerol), and the enzymes responsible for endocannabinoid synthesis and catabolism. Endocannabinoids represent a class of neuromessengers, which are synthesized on demand and released from post-synaptic neurons to restrain the release of classical neurotransmitters from pre-synaptic terminals.This retrograde signalling modulates a variety of brain functions, including anxiety, fear and mood, whereby activation of CB1 receptors was shown to exert anxiolytic-and antidepressant-like effects in preclinical studies. CONCLUSION: Animal experiments suggest that drugs promoting endocannabinoid action may represent a novel strategy for the treatment of depression and anxiety disorders.

Scientific Electronic Library Online (Portuguese)

21

Utilização do D-manitol em síntese orgânica/ D-Mannitol in Organic Synthesis

Oliveira, Pedro S. M. de; Ferreira, Vitor F.; Souza, Marcus Vinicius N. de
2009-01-01

Resumo em inglês D-mannitol is used in several fields including food, pharmaceuticals, cosmetics and textiles being an important carbohydrate found widespread in nature. Due to its chirality, it is largely used in organic synthesis with several applications, such as ligands, polymers, chiral pool, for preparation of small chiral building blocks, key intermediates in total synthesis. In this context, the aim of this review is to highlights recent applications of D-mannitol, especially in total synthesis.

Scientific Electronic Library Online (Portuguese)

22

Uma metodologia para o projeto teórico de conversores moleculares de luz/ A methodology for the theoretical design of light conversion molecular devices

Andrade, Antônio V. M. de; Costa Jr., Nivan B. da; Simas, Alfredo M.; Longo, Ricardo L.; Malta, Oscar L.; Sá, Gilberto F. de
1998-02-01

Resumo em inglês Recentlly, we have proposed the representation of lanthanides within AM1 as sparkles for the purpose of obtaing ground state geometries of their complexes. We tested our quantum chemical sparkle model (SMLC/AM1) for the prediction of the crystallographic structure of complexes with coordination number nine, eight and seven. A technique is introduced for the theoretical prediction of eletronic spectra of the organic part of lanthanide complexes by replacing the metal ion b (mais) y a point charge with the ligands held in their positions as determined by the SMLC/AM1, and by computing the theoretical spectra via the intermediate neglect of differential overlap/spectroscopic-configuration interaction (INDO/S-CI).

Scientific Electronic Library Online (Portuguese)

23

Síntese e reatividade de azaindóis: aplicações na preparação de moléculas de interesse biológico/ Synthesis and reactivity of azaindoles: applications in the preparation of bioactive molecules

Le Hyaric, Mireille; Almeida, Mauro Vieira de; Souza, Marcus Vinicius Nora de
2002-12-01

Resumo em inglês Synthetic methods used for the preparation of azaindoles are described in this article. Applications in the preparation of bioactive molecules are given: synthesis of substituted 6-azaindoles as benzodiazepines receptor ligands, substituted 7-azaindoles as dopamine D4 ligands and preparation of an olivacine analogue.

Scientific Electronic Library Online (Portuguese)

24

Síntese e caracterização de um novo complexo de platina (IV) a partir de seu análogo de platina (II) utilizando iodo molecular como agente oxidante: uma rota sintética interessante para obtenção de novos complexos de platina/ Synthesis and characterization of a novel platinum (IV) complex from its platinum (II) analogue using molecular iodine as an oxidizing agent: an interesting synthetic route for the preparation of new platinum complexes

Guerra, Wendell; Silva, Heveline; Almeida, Mauro Vieira de; Fontes, Ana Paula Soares
2007-02-01

Resumo em inglês In an attempt to reduce toxicity and widen the spectrum of activity of cisplatin and its analogues, much attention has been focused on designing new platinum complexes. This work reports the synthesis and characterization of novel compounds of the platinum (II) and platinum (IV) containing 2-furoic hydrazide acid and iodide as ligands. Although the prepared compounds do not present the classical structure of biologically active platinum analogues, they could be potentiall (mais) y active or useful as precursors to prepare antitumor platinum complexes. The reported compounds were characterized by ¹H NMR, 13C NMR, 195Pt NMR, IR and elemental analyses.

Scientific Electronic Library Online (Portuguese)

25

Síntese e caracterização de complexos de platina(IV) com derivados N-benzilados da 1,3-propanodiamina/ Synthesis and characterization of platinum(IV) complexes derived from N-benzyl-propanediamine

Fontes, Ana Paula Soares; Almeida, Mauro Vieira de; Faria, Bruno de Araújo; César, Eloi Teixeira
2010-01-01

Resumo em inglês The present work describes the synthesis of a series of platinum(IV) complexes with N-benzyl 1,3-propanediamine derivatives. Since substitution of the axial ligands in the platinum(IV) complexes may alter their pharmacological properties, we have prepared complexes with different groups, such as hydroxide, chloride and acetate using a sequence of substitution reactions. The resulting complexes were fully characterized by IR, ¹H, 13C and 195Pt NMR spectroscopies, and elemental analysis.

Scientific Electronic Library Online (Portuguese)

26

Síntese de aminoálcoois derivados do D-manitol/ Synthesis of aminoalcohols from D-mannitol

Oliveira, Pedro S. M. de; Ferreira, Vitor F.; Souza, Marcus Vinicius N. de; Carvalho, Erika Martins de
2008-01-01

Resumo em inglês Aminoalcohols have found important applications in synthetic and medicinal chemistry, being used as chiral building blocks for the synthesis of many biologically active compounds. This class of compounds has been also used as chiral auxiliaries and ligands in asymmetric synthesis. Due to the importance of aminoalcohols in the treatment of several diseases, such as tuberculosis, the aim of this article is the synthesis and preliminary evaluation against tuberculosis of six (mais) aminoalcohols in 5 or 6 steps using D-mannitol as starting material, which is a useful carbohydrate employed in many syntheses.

Scientific Electronic Library Online (Portuguese)

27

Feocromocitoma/ Pheochromocytoma

Costa, Liane; Gomes, António Taveira
2008-01-01

Resumo em português O feocromocitoma é uma neoplasia rara, produtora de catecolaminas, cuja origem mais frequente é a medula su-pra-renal. Tem um amplo espectro de apresentações clínicas mas a tríade sintomática de cefaleias, palpitações e hipersudorese, acompanhada de hipertensão arterial é muito característica. As crises hipertensivas e os eventos cardiovasculares potencialmente fatais causados por esta neoplasia decorrem do efeito potente da estimulação adrenérgica e justi& (mais) #64257;cam a importância de um diagnóstico célere e de uma abordagem terapêutica eficaz no controlo sintomático e na prevenção de complicações. O diagnóstico de feocromocitoma é obtido por testes bioquímicos sanguíneos ou urinários em que se evidencie excesso de catecolaminas ou dos seus metabolitos. Estes devem ser realizados em todos os doentes com clínica sugestiva, nos indivíduos assintomáticos que apresentem um incidentaloma supra-renal ou naqueles em que exista predisposição genética conhecida (p.e. síndrome de neoplasias endócrinas múltiplas tipo 2, doença de von Hippel Lindau, neurofibromatose tipo 1, síndrome de paragangliomas familiares). A avaliação imagiológica de um feocromocitoma - através de TC (tomografia computorizada), RMN (ressonância magnética) ou estudos com ligandos funcionais, como a cintigrafia com MIBG-I131 (metaiodobenzilguanidina marcada com iodo radioactivo) - deve ser efectuada após confirmação diagnóstica e é muito útil na determinação da localização e dimensões tumorais. O tratamento definitivo de qualquer feocromocitoma, especialmente se funcionante e sintomático, é cirúrgico e, actualmente, consiste quase sempre na adrenalectomia total laparoscópica. O potencial de cura desta neoplasia, se diagnosticada e tratada atempadamente, é enorme mas, nos casos em que se constata invasão tumoral ou metastização, o prognóstico é bastante mais reservado. Resumo em inglês Pheochromocytoma is a rare, catecholamine-producing tumour, usually arising from the adrenal medulla. It has a highly variable clinical presentation but headaches, palpitations, sweating and arterial hypertension are very characteristic. The paroxysmal hypertensive crisis and the potentially fatal cardiovascular events that can occur are due to the powerful effect of the catecholamine stimulation. Therefore, a prompt diagnosis and therapeutical approach are strongly justi (mais) fied, in order to assure the rapid control of the symptoms and the prevention of complications. The diagnosis of pheochromocytoma lies in the biochemical identification of excessive production of catecholamines or their metabolites, either in blood or urine. These biochemical tests should be performed in every patient with suggestive signs or symptoms, in the asymptomatic patients with an adrenal incidentaloma and in those with recognized genetic syndromes which predispose to the disease (multiple endocrine neoplasia type 2, von Hippel-Lindau syndrome, neurofibromatosis type 1 syndrome, paraganglioma syndromes, etc.). The imaging techniques used to locate biochemically proven tumours are CT (computerized tomography), MRI (magnetic resonance imaging) and techniques with functional ligands, such as scintigraphy with MIBG - I131 (radioactive Iodine metaidobenzoguanidine). The definitive treatment for any pheochromocytoma, especially if it is functional and symptomatic, is surgical. Laparoscopic adrenalectomy is now the preferred surgical technique for the removal of pheochromocytoma. Pheochromocytoma has a great potential for cure, after early diagnosis and treatment, but it is much poorer when there is evidence of tumoral invasion or metastases.

Scientific Electronic Library Online (Portuguese)

28

Estudos espectroscópicos e estruturais dos polímeros de coordenação 2D, ∞[Tb(DPA)(HDPA)] e ∞[Gd(DPA)(HDPA)]/ Structural and spectroscopic studies of the 2D coordination polymers, ∞[Tb(DPA)(HDPA)] and ∞[Gd(DPA)(HDPA)]

Rodrigues, Marcelo O.; Brito-Silva, Antonio M.; Alves Júnior, Severino; Simone, Carlos A. De; Araújo, Adriano Antunes S.; Carvalho, Pedro Henrique V. de; Santos, Sílvia Caroline G.; Aragão, Kennedy Alexandre S.; Freire, Ricardo O.; Mesquita, Maria Eliane
2009-01-01

Resumo em inglês This paper presents the synthesis of the coordination polymers ∞[Ln(DPA)(HDPA)] (DPA=2,6-pyridinedicarboxylate; Ln= Tb and Gd), their structural and spectroscopic properties. The structural study reveals that the ∞[Ln(DPA)(HDPA)] has a single Ln+3 ion coordinated with two H2DPA ligands in tridentade coordination mode, while two others H2DPA establish a syn-bridge with a symmetry-related Ln3+, forming a two-dimensional structure. The spectroscopic studies show (mais) that ∞[Tb(DPA)(HDPA)] compound has high quantum yield (q x≈ 50.0%), due to the large contribution of radiative decay rate. Moreover triplet level is localized sufficiently over the emitter level 5D4 of theTb3+ ion, avoiding a retrotransference process between these states.

Scientific Electronic Library Online (Portuguese)

29

Estimativa da entalpia reticular de adutos (DM Hm o ) utilizando-se formas modificadas da equação de Kapustinskii/ Estimating the value of lattice enthalpy (DM Hm o) for adducts by using modified forms of Kapustinskii equation

Farias, Robson Fernandes de
1999-04-01

Resumo em inglês In this work are presented two modified forms of Kapustinskii equation that could be used to estimate the values of the lattice enthalphies for adducts: DM Hm o=(-n.z+ .z- .10(2)/D).(1-d*/D) .K and DM Hm o=(-n.z+ .z-.10(2)/d).(1-d*/d).K.d. Two new parameters related with steric effects and donor power of the ligands, J anddare introduced. The proposed equations were tested for 49 adducts (mainly from the zinc group halides). The difference between experimental (calorimetric) and calculated values (using the proposed equations) values are less than 5% for 41 of the tested adducts.

Scientific Electronic Library Online (Portuguese)

30

Estimativa da entalpia reticular (Dm Hmº) de adutos através de termogravimetria: uso de uma equação empírica/ Lattice enthalpies (DMHmº) of adducts using an empirical equation supported in tg data

Farias, Robson Fernandes de
1997-10-01

Resumo em inglês An empirical equation: DMHmº = t i/b (where t i is the Kelvin temperature of the beginning of the thermal decomposition obtained from the thermogravimetry of the adducts; b is an empirical parameter wich depends on the metal halide and on the number of ligands) was obtained and tested for 53 adducts MX2.nL (where MX2 is a metal halide from the zinc group). The difference between experimental and calculated values was less than 6% for 22 adducts. To another 22 adducts, th (mais) at difference was less than 10%. Only for 4 compounds the difference between experimental and calculated values exceeds 15%.

Scientific Electronic Library Online (Portuguese)

31

Estimativa da entalpia de decomposição (deltaD Hmº) de adutos por termogravimetria/ Estimative of deltaD Hmº for adducts by thermogravimetry

Farias, Robson Fernandes de
1998-07-01

Resumo em inglês An empirical equation: deltaD HmO = t i/2.2(2-n) is obtained and tested for 102 adducts (mainly adducts with zinc group halides). In the equation, t i is the Kelvin temperature of the beginning of the thermal decomposition of the adduct, (obtained by thermogravimetry), and n is the number of ligands. For 1/3 of the tested adducts the difference between experimental and calculated values was less than 5%. For about 1/3 of the adducts that difference exceeds 15%.

Scientific Electronic Library Online (Portuguese)

32

Espectroscopia vibracional: sistemática para o cálculo dos estiramentos CO de complexos carbonílicos e determinação da sua atividade IV e Raman/ Vibrational spectroscopy: procedures for the calculation of the CO stretchings of carbonyl complexes and determination of their IR and Raman activity

Oliveira, Gelson Manzoni de
2002-07-01

Resumo em inglês IR bands related to M-C stretchings are not diagnostically significant for the identification of carbonyl groups in the spectra of carbonyl complexes. Otherwise, the frequency, intensity and number of bands for the CO stretchings provide very useful informations about the number of CO ligands and many others structural proprieties, like the presence of bridged CO groups. We report about a relatively simple and useful method for the determination of the CO stretchings of carbonyl complexes, which considers only the bond stretching internal coordinates of the CO groups.

Scientific Electronic Library Online (Portuguese)

33

Espectros eletrônicos de alguns complexos de geometria octaédrica de Ni2+: uma introdução prática à teoria do campo cristalino no curso de graduação/ Electronic spectra of some Ni2+ octahedral complexes: a practical introduction to the crystal field theory in the undergraduate course

Gushikem, Yoshitaka
2005-02-01

Resumo em inglês The experiment introduces the undergraduate students to the crystal field theory. The electronic spectra of the octahedral complexes of [Ni(L)n]2+ (L = H2O, dmso, NH3 and en) obtained in the experiment are used to calculate 10Dq and B parameters. The experiment shows how the parameters can be calculated and correlated with the nature of the ligands and the field intensities produced.

Scientific Electronic Library Online (Portuguese)

34

Emprego de catalisadores à base de níquel para homo- e copolimerização de estireno/ The use of nickel-based catalysts for homo-and copolymerization of styrene

Ferreira Jr., Luis Carlos; Costa, Marcos A. S.; Santa Maria, Luiz Claudio de; Coutinho, Fernanda M. B.; Guimarães, Pedro I. C.
2004-12-01

Resumo em inglês This review deals with the homo- and copolymerization of styrene with nickel catalysts. The catalytic activity, polymer stereoregularity, polymer molecular weight and polydispersity are dependent upon nickel ligands and reaction parameters. Catalysts supported on silica, treated with methylaluminoxane (MAO), have shown higher stereospecificity and activity compared to homogeneous ones. The influence of these parameters is discussed focusing on the elucidation of some aspects of the polymerization mechanism.

Scientific Electronic Library Online (Portuguese)

35

Dinâmica de íons em solo ácido lixiviado com extratos de resíduos de adubos verdes e soluções puras de ácidos orgânicos/ Dynamic of ions in acid soil leached with green manure residues extracts and pure solutions of organic acids

Franchini, Júlio Cezar; Miyazawa, Mario; Pavan, Marcos Antonio; Malavolta, Euripedes
1999-12-01

Resumo em português A influência da aplicação de resíduos vegetais na dinâmica de íons em solos ácidos é pouco conhecida. Neste estudo, a mobilidade de íons em amostra do horizonte Bw de um Latossolo Vermelho-Escuro álico lixiviado com soluções puras de ácidos cítrico e succínico e extratos aquosos de resíduos de nabo forrageiro (Raphanus sativus) e aveia-preta (Avena strigosa) foi avaliada em colunas de solo (5, 10, 20 e 40 cm de altura por 4 cm de diâmetro). Após a percol (mais) ação das soluções e extratos pelas colunas de solo determinaram-se, nas soluções efluentes, os teores de Ca (Ca s), Mg (Mg s), K (Ks), Al total (Al st), orgânico (Al so), monomérico (Al sm) e carbono orgânico dissolvido. No solo, foram determinados os teores trocáveis de Ca (Ca tr), Mg (Mg tr), K (Ktr) e Al (Al tr) e o pH (CaCl2). Os ácidos cítrico e succínico aumentaram os teores de Al st e Ca s, respectivamente, causando reduções nas frações trocáveis desses elementos no solo. O extrato de aveia-preta foi mais efetivo na remoção do Ca tr e o de nabo forrageiro na do Al tr. O decréscimo de Ca tr e Al tr foi seguido do aumento do Ktr. A formação de complexos entre Ca s e Al tr com compostos orgânicos de baixo peso molecular foi sugerida como o provável mecanismo responsável pela mobilidade dos íons polivalentes no subsolo de solos ácidos após a aplicação dos extratos de resíduos vegetais e das soluções puras de ácidos orgânicos. Resumo em inglês The influence of green manure residues addition in the dynamic of ions in acid soils is not well known. In this study, ion mobility in a sample of the Bw horizon of an Dark-Red Latosol (Oxisol), leached with citric and succinic acid pure solutions and with aqueous residue extracts of black oats (Avena strigosa) and oil seed radish (Raphanus sativus) were evaluated in soil columns (5, 10, 20, and 40 cm long by 4 cm diameter). After the solutions and extracts passed through (mais) the soil columns, the following parameters were determined: solubles contents of Ca s, Mg s, Ks, Al st (total), Al so (organic), Al sm (monomeric) and dissolved organic carbon. In soil, the parameters evaluated were the exchangeable contents of Ca ex, Mg ex, Kex, and Al ex and pH (CaCl2). Citric and succinic acids increased Al st and Ca s contents, respectively, resulting in decreasing exchangeable fractions of these elements in soil. Black oats extract was more effective to extract Ca ex and oil seed radish to extract Al ex. The decrease in Ca ex and Al ex was followed by an increase in Kex. Organic complexes formed with low molecular organic ligands and Ca s and Al ex were suggested to play a role in the mobility of ions in subsoils of acid soils after the addition of both crop residues extracts and pure organic acid solutions.

Scientific Electronic Library Online (Portuguese)

36

Digestão fotoquímica, assistida por microondas, de águas naturais: aplicação em estudos de partição e especiação do cobre/ Microwave-assisted photochemical digestion of natural waters: application in partition and speciation studies of copper

Sodré, Fernando F.; Peralta-Zamora, Patricio G.; Grassi, Marco T.
2004-10-01

Resumo em inglês The efficiency of a new procedure for the digestion of natural waters, based on a microwave-activated photochemical reactor was evaluated in this work. Fluorescence spectra showed a 99% reduction in the emission of a 40 mg L-1 humic acid solution after 15 min of UV irradiation. In the presence of H2O2, only 3 min were necessary to accomplish a reduction of almost 100% in the emission and 6 min to reduce the concentration of dissolved organic carbon by 95%. The copper reco (mais) very from synthetic samples containing commercial humic acid, from soil suspensions, as well as from natural waters varied between 91.5 and 106.6%. The digestion of dissolved and unfiltered samples was successfully accomplished in 6 and 12 min, respectively. No contaminations or sample losses were observed. Results of copper speciation in natural waters showed that this metal is predominantly bound to natural ligands. Only 3-6% of the total recoverable copper is present in the labile form.

Scientific Electronic Library Online (Portuguese)

37

Comparação da labilidade de metais empregando voltametria, difusão em filmes finos por gradiente de concentração (DGT) e modelo computacional/ Comparison of the speciation of trace metals in freshwater employing voltammetry, diffusive gradients in thin films (DGT) and a chemical equilibrium model

Anjos, Vanessa E. dos; Abate, Gilberto; Grassi, Marco T.
2010-01-01

Resumo em inglês Speciation of metals in a synthetic freshwater was comparatively evaluated using Anodic Stripping Voltammetry, Diffusive Gradients in Thin Films and a Chemical Equilibrium Model. The labile fractions of Cu and Zn quantified by DGT were similar to the ones measured by ASV. The labile species of Cd and Pb could not be determined by both experimental methods due to the formation of inert complexes with organic ligands in the sample. Despite the differences among the methods, (mais) the speciation results obtained by the use of DGT and ASV agreed well with predictions made by the chemical equilibrium model.

Scientific Electronic Library Online (Portuguese)