Influence of pigment substitution on the electrochemical properties of Rhodobacter sphaeroides 601 reaction centers

With the help of pigment substitution, self-assembled monolayer film and sq uare wave voltammetry, the influence of pigment substitution on the electro chemical properties of Rhodobacter sphaeroides 601 reaction centers was inv estigated. Results showed that the charge separation could also be driven b y externally electric field, similar to the primary photochemical reaction in purple bacterial reaction center. On the surface of Au electrode, a self -assembled monolayer film (the RC-PDDA-DMSA film) was made up of 2,3-dimerc aptosuccinic acid (DMSA), poly-dimethyldiallylammonium chloride (PDDA) and reaction center (RC). When square wave voltammetry was used to study the RC -PDDA-DMSA film, four redox pairs in the photochemical reaction of RC were observed by changing frequency. With nonlinear fitting, the standard potent ial of P/P+ and the corresponding electrode reaction rate constant were det ermined to be 0.522 V and 13.04 S-1, respectively. It was found that the re dox peak at -0.02 V changed greatly when bacteriopheophytin was substituted by plant pheophytin in the reaction center. Further studies indicated that this change resulted from the decrease in electron transfer rate between B phe(-)/Bphe (Phe(-)/Phe) and Q(A)(-)/Q(A) after pigment substitution. After investigations of spectra and electrochemical properties of different RCs and comparisons of different function groups of pigments, it was indicated that the phytyl tail, similar to other substituted groups of pheophytin, af fected the efficiencies of pigment substitution.