Surface-confined redox-active monolayers of a multifunctional anthraquinone derivative on nanoporous and single-crystal gold electrodes

We have investigated self-assembled molecular monolayers (SAMs) of a novel thiol-bearing anthraquinone derivative AQ(OMe) (1-amino-4-((3-mercapto-5-(methoxycarbonyl)phenyl)amino)-9,10-dioxo-9,10-dihydroanthracene-2-sulfonic acid) with multifarious protonation sites, on nanoporous gold (NPG) electrode surfaces. employ cyclic voltammetry, electrochemical impedance spectroscopy and X-ray photoelectron (XPS). Single-crystal Au(1 1 1)-electrode surfaces area used as reference. XPS exhibits S2p3/2 peaks at 161.1 162.1 eV, verifying well-defined Au-S bound SAMs. The mid-point potential (E1/2) the SAMs shifts negatively increasing pH slope ?55 mV pH?1, indicative 2e2H redox reaction. group quasi-reversible behavior over wide range values (from 2.8 to 9.0) sigmoidal electron transfer (ET) rate constant (kapp) maximum value 5.5, which is likely be close isoelectric point. electrochemically addressable surface coverage, determined from voltammetric peak areas, decreases pH. apparent coverage NPG more than 13 times higher that 1), attributed mainly larger different structural packing modes, possibly also favorable terrace edges NPG, but – somewhat unexpectedly little effect kapp. new offers perspectives for gentle immobilization efficient mediated interfacial ET proteins other complex biomolecules.