Recebido em 13/2/09; aceito em 9/9/09; publicado na web em 23/2/10 SUPRAMOLECULAR ORGANIZATION OF COBALT (II) PHTHALOCYANINE ON THE PATHWAY OF CYSTEINE OXIDATION. The interest in the chemistry of cobalt (II) tetrasulfonated phthalocyanine (PcTsCo) comes mainly from its macrocycle-ligand structure combined with their special chemical characteristics, such as high solubility, well-defined redox reactions and remarkable optical absorption in the visible region. In this work, we use layer-by-layer technique in order to assemble CoTsPc and poly(allylaminehydrochloride) (PAH) in hybrid supramolecular system. The electronic spectroscopy and cyclic voltammetry techniques were utilized to study PAH/CoTsPc multilayers growth and the cysteine catalytic oxidation. PAH/CoTsPc showed high electrochemical stability and worthwhile to mention is the remarkable influence of supramolecular arrangement on the final redox properties of the system. Keywords: cobalt phthalocyanine; cysteine; supramolecular. INTRODUÇÃODiversos tipos de materiais nanoestruturados podem ser estudados mediante técnicas de deposição de filmes ultrafinos, 1,2 principalmente as nanoarquiteturas híbridas.1-3 Pode-se citar a técnica Langmuir-Blodgett (LB), onde camadas moleculares são preparadas em ambientes com elevado controle molecular.1,4-6 Nos filmes LB, as estruturas são extremamente organizadas e podem interagir fortemente com um substrato sólido (vidro, quartzo, silício, ouro etc). Uma vez controlados os parâmetros de deposição, diversas estruturas podem ser idealizadas através da deposição de multicamadas de vários compostos, 1,4 como biomoléculas, complexos de coordenação, polímeros sintéticos e condutores, cristais líquidos poliméricos, entre outros. Em alternativa à técnica LB, Decher 20,25,28,[42][43][44] imobilizadas em filmes finos LbL apresentam processos redox bem definidos, elevada estabilidade química e um arranjo geométrico quadrado planar, onde os grupos pirrois, no plano equatorial, apresentam-se inertes em relação às reações de substituição.2,45-47 Além disso, as FtTsCo têm sido utilizadas para construção de sensores para moléculas biológicas e catalisadores de diversas espécies, como glutationa (GSH), 22,23,48 cisteína (CiSH), [23][24][25][26][27]48 histidina, 26 monóxido de nitrogênio, 21,28,31 pesticidas, 29 glucose 30 e hidrazina. 31Desta forma, este trabalho apresenta as propriedades supramoleculares de filmes multicamadas contendo FtTsCo(II) e polialilamina (PAH) (PAH/FtTsCo). Utilizou-se a voltametria cíclica e a espectroscopia eletrônica na região do visível como técnicas de investigação. Por fim, avaliaram-se as propriedades eletrocatalíticas do sistema PAH/FtTsCo para oxidar o aminoácido cisteína.
The search for natural, biocompatible and degradable materials amenable to be used in biomedical/analytical applications has attracted attention, either from the environmental or medical point of view. Examples are the polysaccharides extracted from natural gums, which have found applications in the food and pharmaceutical industries as stabilizers or thickening agent. In a previous paper, however, it was shown that a Brazilian natural gum, chicha (Sterculia striata), is suitable for application as building block for nanostructured film fabrication in conjunction with phthalocyanines. The films displayed electroactivity and could be used in sensing. In the present paper, we introduce the use of two different natural gums, viz., angico (Anadenanthera colubrina) and caraia (Sterculia urens), as active biomaterials to be used to modification layers, in the form of nanostructured thin films, including the study of dopamine detection. The multilayer films were assembled in conjunction with nickel tetrasulfonated phthalocyanines (NiTsPC) and displayed good chemical and electrochemical stability, allowing their use as transducer elements in sensors for detection of specific neurotransmitters. It is suggested here that nanoscale manipulation of new biodegradable natural polymers opens up a variety of new opportunities for the use of these materials in advanced biomedical and analytical devices.
The electrochemical behaviour of three redox couples, namely ferri/ferrocyanide, dopamine and 1,4-naphtoquinone is investigated at the surface of ITO substrates modified with layer-by-layer assembled poly(diallyl dimethylammonium) hydrochloride (PDAC) and reduced graphene oxide (RGO) films. The study with ITO modified with PDAC/RGO films is performed by cyclic voltammetry and electrochemical impedance spectroscopy. Regardless of the type of electrode (bare ITO and PDAC/RGO-modified), the electrochemical behaviour of all three redox couples is diffusion controlled. Despite that, modification of the ITO substrate with the PDAC/RGO film decreases the electron transfer rate constant and makes more irreversible the ferri/ ferrocyanide redox interconversion. In fact, it evidences that ferri/ferrocyanide is not a classical outer-sphere redox probe. On the other hand, the PDAC/RGO film has an inverse and positive effect on dopamine and 1,4naphtoquinone redox reactions. Further, impedance spectroscopy data reveal that the PDAC/RGO film reduces by about 9 orders of magnitude the charge transfer resistance with these organic redox couples. As a main conclusion of the study, it is found that the right matching between RGO energy levels and the reduction potential of the redox species is not enough to provide electrocatalytic activity. The surface chemistry of RGO-based electrode plays an equivalent role for the electrodes' response.
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