Kinetic study of peroxidase-catalyzed oxidation of 1-hydroxypyrene. Development of a nanomolar hydrogen peroxide detection system

Integrated Experimental and Theoretical Studies on an Electrochemical Immunosensor

Electrochemical immunosensors (EIs) integrate biorecognition molecules (e.g., antibodies) with redox enzymes (e.g., horseradish peroxidase) to combine the advantages of immunoassays (high sensitivity and selectivity) with those of electrochemical biosensors (quantitative electrical signal). However, the complex network of mass-transfer, catalysis, and electrochemical reaction steps that produce the electrical signal makes the design and optimization of EI systems challenging. This paper presents an integrated experimental and modeling framework to address this challenge. The framework includes (1) a mechanistic mathematical model that describes the rate of key mass-transfer and reaction steps; (2) a statistical-design-of-experiments study to optimize operating conditions and validate the mechanistic model; and (3) a novel dimensional analysis to assess the degree to which individual mass-transfer and reaction steps limit the EI's signal amplitude and sensitivity. The validated mechanistic model was able to predict the effect of four independent variables (working electrode overpotential, pH, and concentrations of catechol and hydrogen peroxide) on the EI's signal magnitude. The model was then used to calculate dimensionless groups, including Damkohler numbers, novel current-control coefficients, and sensitivity-control coefficients that indicated the extent to which the individual mass-transfer or reaction steps limited the EI's signal amplitude and sensitivity.

Excited state intramolecular proton transfer in 1-hydroxypyrene

1-Hydroxypyrene (1) shows unusual acid–base chemistry in its singlet excited state. Whereas most hydroxyarenes experience a marked enhancement in their acidity when excited, and rapidly deprotonate to give the corresponding phenolate anion, this is not an important pathway for 1, despite theoretical predictions that 1 should experience enhanced acidity as well. In this work, we demonstrate that 1 undergoes a competing excited state intramolecular proton transfer from the OH to carbon atoms at the 3, 6, and 8 positions of the pyrene ring to give quinone methide intermediates. When the reaction is carried out in D2O, reversion of these quinone methides to starting material results in replacement of the ring hydrogens with deuterium, providing a convenient handle to follow the reaction with NMR spectroscopy and mass spectrometry. The quantum yield for the reaction is 0.025 and appears to not be strongly dependent on the water content when aqueous acetonitrile solutions are used. 1-(2-Hydroxyphenyl)pyrene (19) was prepared and studied and shows similar reactivity to 1.