The electronic behavior of a photosynthetic reaction center monitored by conductive atomic force microscopy.
The conductivity of a photosynthetic reaction center (RC) from Rhodobacter sphaeroides was measured with conductive atomic force microscopy (CAFM) on SAM-modified Au(111) substrates. 2-mercaptoethanol (2ME), 2-mercaptoacetic acid (MAC), 2-mercaptopyridine (2MP) and 4-mercaptopyridine (4MP) were prepared as SAM materials to investigate the stability and morphology of RCs on the substrate by using near-IR absorption spectroscopy and AFM, respectively. The clear presence of the three well known RC near-IR absorption peaks indicates that the RCs were native on the SAM-modified Au(111). Dense grains with various diameters of 5-20 nm, which corresponded to mixtures of single RCs up to aggregates of 10, were observed in topographs of RCs adsorbed on all the different SAM-modified Au(111) substrates. The size of currents obtained from the RC using a bare conductive cantilever were produced in the following order for SAM molecules: 2MP > 2ME > 4MP > MAC. A clear rectification of this current was observed for the modification of the Au(111) substrate with the pi-conjugated thiol, 2MP, indicating that 2MP was effective in both promoting the specific orientation of the RCs on the electrode and electron injection into the RC. Cyclic voltammetry measurements indicate that the 2MP is better mediator for the electron transfer between a quinone and substrate. The current with 2MP-modified cantilever was twice as high as that obtained with the Au-coated one alone, indicating that 2MP has an important role in lowering the electron injection barrier between special pair side of RC and gold electrode.
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan.
Takeshi
T
Mikayama
Kouji
K
Iida
Yoshiharu
Y
Suemori
Takehisa
T
Dewa
Tokuji
T
Miyashita
Mamoru
M
Nango
Alastair T
AT
Gardiner
Richard J
RJ
Cogdell
D004553:Electric Conductivity; D004563:Electrochemistry / Q000379:methods*; D018625:Microscopy, Atomic Force / Q000379:methods*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000502:physiology*; D012242:Rhodobacter sphaeroides / Q000737:chemistry* / Q000502:physiology*
D045322:Photosynthetic Reaction Center Complex Proteins