On the fundamentals of quantum rate theory and the long-range electron transport in respiratory chains.

It has been shown that both the electron-transfer rate constant of an electrochemical reaction and the conductance quantum are correlated with the concept of quantum capacitance. This simple association between the two separate concepts has an entirely quantum rate basis that encompasses the electron-transfer rate theory as originally proposed by Rudolph A. Marcus whether statistical mechanics is appropriately taken into account. I have prepared a concise review of the quantum mechanical rate theory principles focused on its quantum electrodynamics character to demonstrate that it can reconcile the conflicting views established on attempting to use the super-exchange (supported on electron transfer) or 'metallic-like' (supported on conductance quantum) mechanisms separately to explain the highly efficient long-range electron transport observed in the respiratory processes of living cells. The unresolved issues related to long-range electron transport are clarified in light of the quantum rate theory with a discussion focused on Geobacter sulfurreducens films as a reference standard of the respiration chain. Theoretical analyses supported by experimental data suggest that the efficiency of respiration within a long-range electron transport path is intrinsically a quantum mechanical event that follows relativistic quantum electrodynamics principles as addressed by quantum rate theory.

Quantum rate dynamics and charge screening at the nanoscale level.

It has been demonstrated that quantum-rate electrodynamics originate from charged quantum states within redox moieties coupled to electrodes. In this study, we demonstrate that this phenomenon is not restricted to redox reactions, and that it is applicable to certain charge screening conditions that depend on electron-ion pairing phenomena. Quantum-rate electrodynamics governs the dynamics of charged inorganic semiconductor states at the nanoscale level. This makes quantum-rate electrodynamics a crucial factor in the design of tailored interfaces within quantum charge transport, determining the efficiency of these interfaces. The applications of quantum-rate electrodynamics range from sensors to supercapacitors.

Ab Initio QM/MM Simulation of Ferrocene Homogeneous Electron-Transfer Reaction.

Here, we demonstrate the feasibility of hybrid computational methods to predict the homogeneous electron exchange between the ferrocene and its oxidized (ferrocenium) state. The free energy for ferrocene oxidation was determined from thermodynamic cycles and implicit solvation strategies within density functional theory (DFT) methods leading to no more than 15% of deviation (in the range of 0.1-0.2 eV) when compared to absolute redox free energies obtained experimentally. Reorganization energy, as defined according to the Marcus theory of electron-transfer rate, was obtained by sampling the vertical ionization/electron affinity energies using hybrid quantum/classical (QM/MM) Born-Oppenheimer molecular dynamics trajectories. Calculated reorganization energies show a subtle but noteworthy dependence with the nature and the localization of the compensating countercharge. We concluded that the adopted hybrid computational strategy, to simulate homogeneous redox reactions, was successfully demonstrated and it further permits applications in more complex systems (required in daily life applications), where the electron transfer occurs heterogeneously.

Electron transfer and conductance quantum.

The electron transfer rate constant of an electrochemical reaction and the conductance quantum are fundamental concepts that drive processes ranging from nanoscale electronic circuits to photosynthesis. In this paper, it is demonstrated that they are correlated with the concept of electrochemical capacitance. The relationship between electron transfer rate, quantum transport and electrochemical capacitance encompasses the theory of electron transfer rate proposed by Rudolph A. Marcus, and potentially unites electronics and electrochemistry.

Comparing glucose and urea enzymatic electrochemical and optical biosensors based on polyaniline thin films.

Analytical sensors that can detect chemical (including biological) analytes are becoming increasingly widespread within the field of analytical chemistry. More than this, in a world tending towards the 'internet-of-things', the miniaturization of such devices is becoming increasingly urgent. Accordingly, electrochemical methods that are simultaneously multiplexable and effective at a miniature scale are receiving much attention. In the present work, we compare the label-free electrochemical response of enzymatic biosensors with the response of their optical counterpart. As a proof-of-concept we compare the electrochemical impedimetric response and the first time described capacitive response of enzymatic biosensors to their optical reflectance response (measured in the visible region using a portable handset spectrophotometer). The target was the detection of glucose and urea. The chemical platform of the sensors was composed of enzymatically functionalized polyaniline thin films. Sensitivity, linearity, and the limit of detection were analyzed for both electrochemical and optical instrumental settings. We found that the impedimetric/capacitive electrochemical setup produced a response that was of a similar quality to the optical response (sensitivities of 10.7 ± 0.7, 7.4 ± 0.7 and 4.3 ± 0.2% per decade for impedimetric, capacitive and optical glucose biosensors, respectively) with a broader linear range (10-4 to 10-1 mol L-1 for both glucose and urea biosensors) and similar limit-of-detection in the range of 1 µmol L-1 within a relevant and practical diagnosis range for biomedical applications.

INSEL: an in silico method for optimizing and exploring biorecognition assays.

A practical in silico method for optimizing and exploring biointeraction-based events is developed.

Quartz crystal microbalance as a tool for kinetic enzymatic assays by variation of pH.

In this work, it is shown that the quartz crystal microbalance (QCM) can be a powerful and simple tool for quick and precise kinetic enzymatic assays. This is shown by measuring immobilized acetylcholinesterase (AChE) activity with variations of pH as a case study.

Changeover during in situ compositional modulation of hexacyanoferrate (Prussian Blue) material.

This paper describes the importance of (H2O)6 clusters in controlling the properties of hexacyanoferrate (Prussian Blue) materials. A careful in situ study of compositional changes by using electrogravimetric techniques (in ac and dc modes) in hexacyanoferrates containing K+ alkali metals reveals the existence of a changeover in the properties of these films in a narrow potential range. Control of the compositional variation of the changeover is dependent on the K+ stoichiometric number in the compound structure. However, a specific K+ occupation in the compound structure activates the occupation of the (H2O)6 cluster by H3O+ and/or H+, causing the changeover in the properties of hexacyanoferrate film. Thus, the information thus obtained is very useful for understanding the mechanisms involved in the electrochemical reversible switch between ferrimagnetism/paramagnetism, "semiconductor/metal" and electroluminescence/nonelectroluminescence properties of molecular cyanide materials.