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1.
Langmuir ; 27(16): 10282-94, 2011 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-21728318

RESUMO

The utilization of proteins as nanodevices for solar cells, bioelectronics, and sensors generally necessitates the transfer of electrons to or from a conducting material. Here we report on efforts to maximize photocurrent generation by bacterial photosynthetic reaction center pigment-protein complexes (RCs) interfaced with a metal electrode. The possibility of adhering RCs to a bare gold electrode was investigated with a view to minimizing the distance for electron tunneling between the protein-embedded electron-transfer cofactors and the metal surface. Substantial photocurrents were achieved despite the absence of coating layers on the electrode or engineered linkers to achieve the oriented deposition of RCs on the surface. Comparison with SAM-covered gold electrodes indicating enhanced photocurrent densities was achieved because of the absence of an insulating layer between the photoactive pigments and the metal. Utilizing RCs surrounded by light-harvesting 1 complex resulted in higher photocurrents, surprisingly not due to enhanced photoabsorption but likely due to better surface coverage of uniformly oriented RC-LH1 complexes and the presence of a tetraheme cytochrome that could act as a connecting wire. The introduction of cytochrome-c (cyt-c) as a molecular relay also produced increases in current, probably by intercalating between the adhered RCs or RC-LH1 complexes and the electrode to mediate electron transfer. Varying the order in which components were introduced to the electrode indicated that dynamic rearrangements of RCs and cyt-c occurred at the bare metal surface. An upper limit for current generation could not be detected within the range of the illumination power available, with the maximum current density achieved by RC-LH1 complexes being on the order of 25 µA/cm(2). High currents could be generated consecutively for several hours or days under ambient conditions.


Assuntos
Eletrodos , Ouro/química , Complexos de Proteínas Captadores de Luz/química , Fotoquímica/métodos , Proteínas/química
2.
Biochim Biophys Acta ; 1798(3): 637-45, 2010 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-20036635

RESUMO

Photosynthetic membranes comprise a network of light harvesting and reaction center pigment-protein complexes responsible for the primary photoconversion reactions: light absorption, energy transfer and electron cycling. The structural organization of membranes of the purple bacterial species Rb. sphaeroides has been elucidated in most detail by means of polarized light spectroscopy and atomic force microscopy. Here we report a functional characterization of native and untreated membranes of the same species adsorbed onto a gold surface. Employing fluorescence confocal spectroscopy and light-induced electrochemistry we show that adsorbed membranes maintain their energy and electron transferring functionality. Gold-adsorbed membranes are shown to generate a steady high photocurrent of 10 microA/cm(2) for several minutes and to maintain activity for up to three days while continuously illuminated. The surface-adsorbed membranes exhibit a remarkable functionality under aerobic conditions, even when exposed to light intensities well above that of direct solar irradiation. The component at the interface of light harvesting and electron cycling, the LH1 complex, displays exceptional stability, likely contributing to the robustness of the membranes. Peripheral light harvesting LH2 complexes show a light intensity dependent decoupling from photoconversion. LH2 can act as a reversible switch at low-light, an increased emitter at medium light and photobleaches at high light.


Assuntos
Membrana Celular/efeitos da radiação , Transferência de Energia/efeitos da radiação , Ouro/química , Luz , Fotossíntese/fisiologia , Rhodobacter sphaeroides/citologia , Adsorção/efeitos da radiação , Membrana Celular/ultraestrutura , Eletrodos , Transporte de Elétrons/efeitos da radiação , Complexos de Proteínas Captadores de Luz/metabolismo , Microscopia de Força Atômica , Rhodobacter sphaeroides/efeitos da radiação , Soluções , Espectrometria de Fluorescência , Propriedades de Superfície/efeitos da radiação
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