Photosynthetic machineries in nano-systems

Abstract

Photosynthetic reaction centres are membrane-spanning proteins, found in several classes of autotroph organisms, where a photoinduced charge separation and stabilization takes place with a quantum efficiency close to unity. The protein remains stable and fully functional also when extracted and purified in detergents thereby biotechnological applications are possible, for example, assembling it in nano-structures or in optoelectronic systems. Several types of bionanocomposite materials have been assembled by using reaction centres and different carrier matrices for different purposes in the field of light energy conversion (e.g., photovoltaics) or biosensing (e.g., for specific detection of pesticides). In this review we will summarize the current status of knowledge, the kinds of applications available and the difficulties to be overcome in the different applications. We will also show possible research directions for the close future in this specific field.

Fig. (1)

A) The steady state absorption spectra of reaction centre proteins purified from three characteristic species of purple bacteria. 2.4.1.: Rhodobacter sphaeroides 2.4.1. carotenoid containing strain, usually referred as wild type. It contains BChl-a in the RC protein. R-26: Rhodobacter sphaeroides R-26 strain lacking the carotenoids. It, too, contains BChl-a in the RC protein. Rps. viridis: Rhodopseudomonas viridis. It contains BChl-b in the RC protein and a bound non-haem type cytochrome subunit. B) The reaction pathways of the electron transfer reaction within the reaction centre proteins of Rhodobacter sphaeroides species. The redox species and the forward (solid arrows) and recombination (dashed arrows) reactions, the corresponding lifetimes are also indicated.

Fig. (2)

Summary of the binding procedures of RCs to carbon nanotubes. The figure shows physical non-covalent hydrophobic binding to nonfunctionalized CNTs and to functionalized nanotubes through different functionalization procedures and with crosslinkers.

Fig. (3)

AFM amplitude image and height section of photosynthetic RCs sitting on MWNT after physical binding [62] (A) and after chemical crosslinking to amine functionalized SWNT by GTA (B, kindly provided by Ms. K. Nagy and Dr. Gy. Váró, MTA BRC, Szeged, Hungary).

Fig. (4)

The binding of atrazine and terbutryne (as indicated) to the reaction centre of Blastochloris (formerly Rhodopseudomonas) viridis according to the crystal structure. The figure was drawn by using the files downloaded from the Brookhaven Protein Data Bank. The pdb codes are: 2prc (RC/ubiquinone), 1dxr (RC/terbutryne), 5prc (RC/atrazine) complexes. The arrows show the possible hydrogen bonds (the distances shorter than 3 Å) and neighboring amino acid groups. The graph was realized by HyperChem 7.0.

Fig. (5)

Light induced photocurrent of the electrochemical cell using PTAA covered ITO electrode without (A) and with bound RC (B). UQ 0 mediator was added and light was switched on (↑) and off (↓) as indicated by the arrows [61].

Fig. (6)

Schematic representation of a nanosized optoelectronic device: the two electrodes are spaced by a few nanometers and the contact can be made by the insertion of a single protein molecule of either bacteriorhodopsin or RC. After small modification from [88].