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Preparacão e caracterização de hidrogéis para aplicações biomédicas

Almeida, José Filipe da Silva Lapas
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Tese de Doutorado
POR
Relevância na Pesquisa
26.04%
Presentemente, o estudo da libertação controlada de fármacos, tem recebido bastante atenção por parte da comunidade científica, devido às suas aplicações biomédicas. A maneira de controlar a libertação passa pela formulação dos sistemas, sendo que a maioria deles se baseia em polímeros, copolímeros e misturas de polímeros com outros materiais. Atendendo às suas propriedades, nomeadamente biocompatibilidade e biodegradação, os polissacarídeos, como o Dextrano ou Quitosano apresentam-se como materiais poliméricos promissores para a sua aplicação, nomeadamente em géis – veículos de drogas de aplicação tópica muito utilizados em farmacologia. Actualmente existem diversos estudos envolvendo este tipo de materiais e respectiva aplicabilidade como biomaterial focando-se a maioria deles na necessária modificação para a obtenção de velocidades de libertação de fármacos desejáveis. Todavia, e apesar dessa quantidade de trabalhos, ainda existem poucos estudos sobre a influência do tempo de reacção e dos métodos reaccionais nas características finais dos géis. O objectivo deste trabalho centrou-se na síntese de copolímeros de enxerto (“graft”) de bases Dextrano e Quitosano, usando, como comonómero a NIsopropilacrilamida (NIPAAm)...

Influence of cerium (IV) ions on the mechanism of organosilane polymerization and on the improvement of its barrier properties

SUEGAMA, P. H.; MELO, H. G. de; BENEDETTI, A. V.; AOKI, I. V.
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
106.54%
In this work, the effect of cerium (IV) ammonium nitrate (CAN) addition on the polymerization of bis-[triethoxysilyl]ethane (BTSE) film applied on carbon steel was studied. The electrochemical characterization of the films was carried out in 0.1 mol L(-1) NaCl solution by open-circuit potential measurements, anodic and cathodic polarization curves and electrochemical impedance spectroscopy (EIS). Morphological and chemical characterization were performed by atomic force microscopy (AFM), contact angle measurements, infrared-spectroscopy, nuclear magnetic resonance and thermogravimetric analysis. The results have clearly shown the improvement on the protective properties of the Ce(4+) modified film as a consequence of the formation of a more uniform and densely reticulated silane film. A mechanism is proposed to explain the accelerating role of Ce(4+) ions on the cross-linking of the silane layer. (C) 2008 Elsevier Ltd. All rights reserved.

Modificação da superfície de aço eletrozincado para proteção contra a corrosão por revestimentos isentos de cromo; Surface modification of electrogalvanized steel for protection against corrosion for coatings free chrome

Ferreira Júnior, José Mario
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 15/01/2014 PT
Relevância na Pesquisa
26.33%
Os revestimentos eletrozincados empregados como proteção galvânica ativa sobre os aços são utilizados industrialmente há longo tempo. Entretanto, como o zinco é um elemento muito reativo, o tratamento da sua superfície é necessário para aumentar sua vida útil. O tratamento mais utilizado consiste em imersão em solução de conversão contendo cromo hexavalente, o qual vem sendo banido por gerar substâncias tóxicas e carcinogênicas, tendo sua utilização proibida pelas normas europeias. Neste trabalho, foram estudados tratamentos alternativos ao cromato para o aço eletrozincado que não geram resíduos tóxicos. O tratamento escolhido foi desenvolvido em etapas. A primeira etapa envolveu o uso de um composto orgânico, o 2 butino-1,4 diol propoxilato, em solução com sais oxidantes e com nitrato de cério como aditivo. A etapa seguinte consistiu em imersão da superfície tratada pela etapa anterior, em um agente oxidante, o peróxido de hidrogênio. A terceira etapa consistiu na imersão em solução com 2 butino-1,4 diol propoxilato e oxalato de nióbio amoniacal (ANO). As superfícies tratadas, após cada uma das etapas, foram caracterizadas por microscopia óptica e eletrônica de varredura (MEV), difração de raios X (DRX)...

Influence of cerium (IV) ions on the mechanism of organosilane polymerization and on the improvement of its barrier properties

Suegama, P. H.; de Melo, H. G.; Benedetti, A. V.; Aoki, I. V.
Fonte: Pergamon-Elsevier B.V. Ltd Publicador: Pergamon-Elsevier B.V. Ltd
Tipo: Artigo de Revista Científica Formato: 2655-2662
ENG
Relevância na Pesquisa
106.45%
In this work, the effect of cerium (IV) ammonium nitrate (CAN) addition on the polymerization of bis-[triethoxysilyl]ethane (BTSE) film applied on carbon steel was studied. The electrochemical characterization of the films was carried out in 0.1 mol L(-1) NaCl solution by open-circuit potential measurements, anodic and cathodic polarization curves and electrochemical impedance spectroscopy (EIS). Morphological and chemical characterization were performed by atomic force microscopy (AFM), contact angle measurements, infrared-spectroscopy, nuclear magnetic resonance and thermogravimetric analysis. The results have clearly shown the improvement on the protective properties of the Ce(4+) modified film as a consequence of the formation of a more uniform and densely reticulated silane film. A mechanism is proposed to explain the accelerating role of Ce(4+) ions on the cross-linking of the silane layer. (C) 2008 Elsevier Ltd. All rights reserved.

Properties of Chitosan-Genipin Films Grafted with Phenolic Compounds from Red Wine

Gonçalves, Fernando Jorge
Fonte: P.L. Soni Publicador: P.L. Soni
Tipo: Artigo de Revista Científica
Publicado em 20/02/2015 ENG
Relevância na Pesquisa
25.98%
Chitosan has been studied as a renewable biopolymer to form edible films and coatings to improve the shelf life of food products. Chemical modification of chitosan is a strategy to prepare chitosan films with enhanced properties to be used as food preservatives. Wine, particularly red wine, is a rich natural source of phenolic compounds, namely anthocyanins, proanthocyanidins, monomeric catechins, and phenolic acids. Phenolic compounds, in general, present strong antioxidant properties. The aim of this work was to develop chitosan-based films with higher antioxidant activity by grafting wine phenolic compounds. Fractions of red wine phenolic compounds, rich in phenolic acids, anthocyanins, and total phenolic compounds, were grafted to the glucosamine residues of chitosan by a radical mechanism using ammonium cerium (IV) nitrate. In order to increase the stability of the films in aqueous acidic medium, genipin, a natural compound with capacity of cross-linking chitosan, was also used in film preparation. The grafting of all phenolic compounds-rich fractions obtained from wine provided films with antioxidant activity more than 100% than those films prepared only with chitosan-genipin. Moreover, the use of genipin allowed obtaining stable films in a large range of pH. The chitosan-genipin film grafted with anthocyanins and total phenolic compounds lost less than 3% of their mass in acidic media after an exhaustive stirring during 7 days...

Mode of action and active site of an extracellular peroxidase from Pleurotus ostreatus.

Han, Y H; Shin, K S; Youn, H D; Hah, Y C; Kang, S O
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/03/1996 EN
Relevância na Pesquisa
25.98%
The properties of the haem environment of an extracellular peroxidase from Pleurotus ostreatus were studied by electronic absorption spectroscopy. A high-spin ferric form was predominant in the native enzyme and a high-spin ferrous form in the reduced enzyme. Cyanide was readily bound to the haem iron in the native form, thereby changing the enzyme to a low-spin cyano adduct. The electronic absorption spectra of the enzyme were similar to those of lignin peroxidase from Phanerochaete chrysosporium. Compound III of the enzyme was formed after the addition of an excess of H2O2 to the native enzyme, and thereafter spontaneously reverted to the native form. The enzyme oxidized 1-(3,5-dimethoxy-4-hydroxyphenyl)-2-(2-methoxyphenoxy)-1,3-dihydroxyp ropane in the presence of H2O2 to produce 1-(3,5-dimethoxy-4-hydroxyphenyl)-2-(2-methoxyphenoxy)-1-oxo-3-hydroxypr opane , 2,6-dimethoxyhydroquinone, 2-(2-methoxyphenoxy)-3-hydroxypropanal, 2-(2-methoxyphenoxy)-3-hydroxypropanoic acid, 2,6-dimethoxy-1,4-benzoquinone and guaiacol. A similar oxidation pattern was demonstrated with a one-electron oxidant, ammonium cerium(IV)nitrate. Free radicals were detected as intermediates of the enzyme-mediated oxidation of 1-(3,5-dimethoxy-5-hydroxyphenyl)-2-(2-methoxyphenoxy)-1...

(E)-3,3′-(Diazene-1,2-di­yl)bis­(1-methyl-1,4,5,6-tetra­hydro­pyrrolo­[3,4-c]pyrazol-5-ium) dinitrate dihydrate

Chen, Jin-Mei; Zhao, Hong
Fonte: International Union of Crystallography Publicador: International Union of Crystallography
Tipo: Artigo de Revista Científica
Publicado em 17/12/2011 EN
Relevância na Pesquisa
45.98%
The title compound, C12H18N8 2+·2NO3 −·2H2O, was synthesized unexpectedly from 3-amino-1-methyl-1,4,5,6-tetra­hydro­pyrrolo­[3,4-c]pyrazol-5-ium chloride and cerium(IV) ammonium nitrate. The cation has a crystallographically imposed centre of symmetry. In the crystal, the ions and water mol­ecules are linked via O—H⋯N, N—H⋯O and O—H⋯O hydrogen bonds into a three-dimensional network.

Oxidative modification of native protein residues using cerium(IV) ammonium nitrate

Seim, Kristen L.; Obermeyer, Allie C.; Francis, Matthew B.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
86.35%
A new protein modification strategy has been developed based on an oxidative coupling reaction that targets electron-rich amino acids. This strategy relies on cerium(IV) ammonium nitrate (CAN) as an oxidation reagent and results in the coupling of tyrosine and tryptophan residues to phenylene diamine and anisidine derivatives. The methodology was first identified and characterized on peptides and small molecules, and was subsequently adapted for protein modification by determining appropriate buffer conditions. Using the optimized procedure, native and introduced solvent accessible residues on proteins were selectively modified with polyethylene glycol (PEG) and small peptides. This unprecedented bioconjugation strategy targets these underutilized amino acids with excellent chemoselectivity and affords good-to-high yields using low concentrations of the oxidant and coupling partners, short reaction times, and mild conditions.

B-Ring-Aryl Substituted Luotonin A Analogues with a New Binding Mode to the Topoisomerase 1-DNA Complex Show Enhanced Cytotoxic Activity

González-Ruiz, Víctor; Pascua, Irene; Fernández-Marcelo, Tamara; Ribelles, Pascual; Bianchini, Giulia; Sridharan, Vellaisamy; Iniesta, Pilar; Ramos, M. Teresa; Olives, Ana I.; Martín, M. Antonia; Menéndez, J. Carlos
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 15/05/2014 EN
Relevância na Pesquisa
45.98%
Topoisomerase 1 inhibition is an important strategy in targeted cancer chemotherapy. The drugs currently in use acting on this enzyme belong to the family of the camptothecins, and suffer severe limitations because of their low stability, which is associated with the hydrolysis of the δ-lactone moiety in their E ring. Luotonin A is a natural camptothecin analogue that lacks this functional group and therefore shows a much-improved stability, but at the cost of a lower activity. Therefore, the development of luotonin A analogues with an increased potency is important for progress in this area. In the present paper, a small library of luotonin A analogues modified at their A and B rings was generated by cerium(IV) ammonium nitrate-catalyzed Friedländer reactions. All analogues showed an activity similar or higher than the natural luotonin A in terms of topoisomerase 1 inhibition and some compounds had an activity comparable to that of camptothecin. Furthermore, most compounds showed a better activity than luotonin A in cell cytotoxicity assays. In order to rationalize these results, the first docking studies of luotonin-topoisomerase 1-DNA ternary complexes were undertaken. Most compounds bound in a manner similar to luotonin A and to standard topoisomerase poisons such as topotecan but...

Acyclic N-halamine-immobilized polyurethane: Preparation and antimicrobial and biofilm-controlling functions

Luo, Jie; Porteous, Nuala; Lin, Jiajin; Sun, Yuyu
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
45.98%
Hydroxyl groups were introduced onto polyurethane surfaces through 1,6-hexamethylene diisocyanate activation, followed by diethanolamine hydroxylation. Polymethacrylamide was covalently attached to the hydroxylated polyurethane through surface grafting polymerization of methacrylamide using cerium (IV) ammonium nitrate as an initiator. After bleach treatment, the amide groups of the covalently bound polymethacrylamide chains were transformed into N-halamines. The new N-halamine-immobilized polyurethane provided a total sacrifice of 107–108 colony forming units per milliliter of Staphylococcus aureus (Gram-positive bacteria), Escherichia coli (Gram-negative bacteria), and Candida albicans (fungi) within 10 min and successfully prevented bacterial and fungal biofilm formation. The antimicrobial and biofilm-controlling effects were both durable and rechargeable, pointing to great potentials of the new acyclic N-halamine-immobilized polyurethane for a broad range of related applications.

NSC4313; Ammonium ceric nitrate; Ammonium cerium nitrate (VAN); Ammonium hexanitratocerate; Ammonium hexanitratocerate(IV); Cerate(2-), hexakis(nitrato-O)-, diammonium, (OC-6-11)- (9CI); Cerate(2-), hexanitrato-, diammonium (8CI); Ceric ammonium nitrate (VAN); Ceric(IV) ammonium nitrate; Cerium ammonium nitrate (VAN); Diammonium cerium hexanitrate; Diammonium hexanitratocerate; Diammonium hexanitratocerate(2-)

US National Cancer Institute
Fonte: Unilever Center for Molecular Informatics, Cambridge University Publicador: Unilever Center for Molecular Informatics, Cambridge University
Tipo: Outros Formato: 4601 bytes; chemical/x-cml
EN_GB
Relevância na Pesquisa
36.63%