Electrochemical properties of a 1-hydroxy-anthraquinone derivative (1-hydroxyAQ) self-assembled monolayer (SAM) were studied using reflectance infrared, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results of the electrochemical investigation into the proton-coupled electron transfer (PCET) reaction at various pHs and temperatures demonstrate a strong pH-charge transfer rate dependence. The charge transfer rates are faster in both acidic and basic solutions than near physiological pH. Interestingly, the activation enthalpy for the charge transfer reactions at physiological pH is low at 23 kJ mol(-1) compared to 67 kJ mol(-1) at pH 1.5. Variable temperature studies showed the entropic cost associated with the charge transfer reaction at pH 7.5 causes the slow charge transfer rate and suggests that pre-organizing proton donor solvents could lead to very fast charge transfer reactions at the hydrophobiclhydrophilic interface. (C) 2011 Elsevier B.V. All rights reserved.