Paul D. Hale

Electrical Communication Between Glucose Oxidase and Novel Ferrocene-Containing Siloxane-Ethylene Oxide Copolymers: Biosensor Applications

Abstract Electrical communication between the flavin adenine dinucleotide redox centers of glucose oxidase and a conventional electrode has been achieved using two electron transfer relay systems based on siloxane-ethylene oxide copolymers containing covalently attached ferrocene moieties. The results from stationary potential experiments show that carbon paste electrodes modified with these redox polymers and glucose oxidase respond rapidly to addition of glucose, with larger steady-state response currents than those measured in previous studies of glucose sensors based on ferrocene-modified siloxane polymers. The results also indicate that the mediating ability of the polymers is dependent upon the length of the ethylene oxide side chain onto which the ferrocene molecules are attached.

Conductivity mechanisms in phthalocyanine-based "molecular metals": Calculation of the temperature-dependent resistivity

The temperature dependence of the conductivity σ in the low‐dimensional material, NiPcI (Pc=phthalocyanine), is investigated using a transport theory for noninteracting electrons in a tight‐binding band scattered by one‐ and two‐phonon processes. The lattice motions found to be the dominant sources of resistivity along the chain are the longitudinal stretch and the interplanar twist (libron), with the former being a first‐order scattering process (σ1p ∝1/T) and the latter a second‐order mechanism (σ2l ∝1/T2). The resulting conductivity has a room‐temperature value of ∼400 Ω−1 cm−1 which increases to almost 4000 Ω−1 cm−1 at 50 K, with an overall temperature dependence of σ∼T−1.4, in good agreement with experiment. It is found that at low temperature, one‐phonon scattering is most important, while at room temperature one‐phonon and two‐libron scattering contribute nearly equally to the resistivity. The accuracy of the bandwidths and of the electron/phonon coupling constants, calculated using first‐principle...

Redox polymer-modified electrodes for the electrocatalytic regeneration of NAD

Abstract A new siloxane polymer containing covalently attached Meldola Blue has been synthesized and shown to mediate the oxidation of the reduced nicotinamide adenine dinucleotide cofactor (NADH). Cyclic voltammetry and stationary potential experiments demonstrate that spectrographic graphite electrodes coated with this polymer can electrocatalytically regenerate NAD+ at a substantially lower overvoltage (e.g., 0 mV vs. SCE) than can unmodified electrodes. These polymer-modified electrodes should be useful as transducers in dehydrogenase-based biosensors.

Electron correlation effects in reduced or oxidized mixed-valency molecules

Abstract The vibronic model ordinarily written for mixed-valence molecules predicts an intervalence transfer (IVT) frequency which, in the limit of delocalized states, is unchanged upon reduction by one further electron. This is in sharp disagreement with experiment, but can be remedied, qualitatively, by adding one-site Coulomb repulsion which shifts the analog of the IVT into the near ultraviolet, and an exchange term which produces the correct ordering of the energy levels, thus making a transition analogous to IVT spin-forbidden.