Catalysis of Dioxygen Reduction by <i>Thermus thermophilus</i> Strain HB27 Laccase on Ketjen Black Electrodes

We present electrochemical analyses of the catalysis of dioxygen reduction by <i>Thermus thermophilus</i> strain HB27 laccase on ketjen black substrates. Our cathodes reliably produce 0.56 mA cm^–2 at 0.0 V vs Ag|AgCl reference at 30 °C in air-saturated buffer, under conditions of nonlimiting O₂ flux. We report the electrochemical activity of this laccase as a function of temperature, pH, time, and the efficiency of its conversion of dioxygen to water. We have measured the surface concentration of electrochemically active species, permitting the extraction of electron transfer rates at the enzyme-electrode interface: 1 s^–1 for this process at zero driving force at 30 °C and a limiting rate of 23 s^–1 at 240 mV overpotential at 50 °C

Modeling Dioxygen Reduction at Multicopper Oxidase Cathodes

We report a general kinetics model for catalytic dioxygen reduction on multicopper oxidase (MCO) cathodes. Our rate equation combines Butler–Volmer (BV) electrode kinetics and the Michaelis–Menten (MM) formalism for enzymatic catalysis, with the BV model accounting for interfacial electron transfer (ET) between the electrode surface and the MCO type 1 copper site. Extending the principles of MM kinetics to this system produced an analytical expression incorporating the effects of subsequent intramolecular ET and dioxygen binding to the trinuclear copper cluster into the cumulative model. We employed experimental electrochemical data on Thermus thermophilus laccase as benchmarks to validate our model, which we suggest will aid in the design of more efficient MCO cathodes. In addition, we demonstrate the model’s utility in determining estimates for both the electronic coupling and average distance between the laccase type-1 active site and the cathode substrate

Enhanced Ultraviolet Photon Capture in Ligand-Sensitized Nanocrystals

The small absorption cross sections (ε < 10 M^–1 cm^–1) characteristic of Laporte-forbidden transitions in the f-elements have limited the practical implementation of lanthanide nanoparticles in solar capture devices. While various strategies designed to circumvent the problems of low f–f oscillator strengths have been investigated, comparatively little work has explored the utility of organic ligands with high absorption coefficients (ε ≈ 10³–10⁵ M^–1 cm^–1) in sensitizing excited states in lanthanide nanocrystals. Here, we detail the photophysics of NaGd_1–<i>x</i>Eu_<i>x</i>F₄ nanoparticles featuring surface display of the ligand 3,4,3-LI­(1,2-HOPO), an aromatic antenna functioning as the terminal light absorber in this system. The result is a ligand–nanocrystal hybrid that converts UV (250–360 nm) light into red Eu­(III) luminescence with an external quantum yield of 3.3%. We analyze this sensitization process, responsible for a 10⁴-fold increase in luminescence relative to metal-centered excitation, through a quantitative treatment of energy transfer between ligand and metal states

Enhanced Ultraviolet Photon Capture in Ligand-Sensitized Nanocrystals

The small absorption cross sections (ε < 10 M^–1 cm^–1) characteristic of Laporte-forbidden transitions in the f-elements have limited the practical implementation of lanthanide nanoparticles in solar capture devices. While various strategies designed to circumvent the problems of low f–f oscillator strengths have been investigated, comparatively little work has explored the utility of organic ligands with high absorption coefficients (ε ≈ 10³–10⁵ M^–1 cm^–1) in sensitizing excited states in lanthanide nanocrystals. Here, we detail the photophysics of NaGd_1–<i>x</i>Eu_<i>x</i>F₄ nanoparticles featuring surface display of the ligand 3,4,3-LI­(1,2-HOPO), an aromatic antenna functioning as the terminal light absorber in this system. The result is a ligand–nanocrystal hybrid that converts UV (250–360 nm) light into red Eu­(III) luminescence with an external quantum yield of 3.3%. We analyze this sensitization process, responsible for a 10⁴-fold increase in luminescence relative to metal-centered excitation, through a quantitative treatment of energy transfer between ligand and metal states