title: Facile synthesis of chlorophyll analog possessing a disulfide bond and formation of self-assembled monolayer on gold surface.
abstract: A chlorophyll analog forming self-assembled monolayers (SAMs) on a gold surface was synthesized for the first time. 13(2)-(Demethoxycarbonyl)pheophorbide-a, which was converted from naturally occurring chlorophyll-a, was condensed with 2-hydroxyethyl disulfide to give a chlorin dyad linked by a disulfide bond. The chlorin analog was spontaneously immobilized on a gold substrate by soaking in an acetone solution of the dyad for 24 h. The resulting gold plate exhibited a visible absorption spectrum with about 420- and 675-nm maxima as the Soret and Qy peaks, respectively, indicating that chlorin pi-conjugates were modified on the gold substrate through Au-S bonding. Both visible absorption and fluorescence emission bands of the chlorin chromophores on the gold substrate were red-shifted compared with those of the synthesized chlorin dyad in a homogeneous acetone solution. The measured absorbance at the Soret maximum suggests that the chlorin chromophores on the gold plate were densely packed on a gold surface to form a SAM. Cathodic photocurrents were generated from SAMs of the chlorins on a gold substrate with irradiation of visible-lights above 400 nm. Photoinduced electron transfer from chlorins on the gold substrate to oxygen molecules in an electrolyte solution were attributed to the cathodic photocurrent generation.
authors.affiliation: Department of Bioscience and Biotechnology, Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Saga
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tamiaki
mesh_terms: D002734:Chlorophyll / Q000031:analogs & derivatives / Q000138:chemical synthesis*; D004220:Disulfides / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular
chemical_list: D004220:Disulfides; D002734:Chlorophyll; D006046:Gold