Cross Adaptation - Heat and Cold Adaptation to Improve Physiological and Cellular Responses to Hypoxia

To prepare for extremes of heat, cold or low partial pressures of O2, humans can undertake a period of acclimation or acclimatization to induce environment specific adaptations e.g. heat acclimation (HA), cold acclimation (CA), or altitude training. Whilst these strategies are effective, they are not always feasible, due to logistical impracticalities. Cross adaptation is a term used to describe the phenomenon whereby alternative environmental interventions e.g. HA, or CA, may be a beneficial alternative to altitude interventions, providing physiological stress and inducing adaptations observable at altitude. HA can attenuate physiological strain at rest and during moderate intensity exercise at altitude via adaptations allied to improved oxygen delivery to metabolically active tissue, likely following increases in plasma volume and reductions in body temperature. CA appears to improve physiological responses to altitude by attenuating the autonomic response to altitude. While no cross acclimation-derived exercise performance/capacity data have been measured following CA, post-HA improvements in performance underpinned by aerobic metabolism, and therefore dependent on oxygen delivery at altitude, are likely. At a cellular level, heat shock protein responses to altitude are attenuated by prior HA suggesting that an attenuation of the cellular stress response and therefore a reduced disruption to homeostasis at altitude has occurred. This process is known as cross tolerance. The effects of CA on markers of cross tolerance is an area requiring further investigation. Because much of the evidence relating to cross adaptation to altitude has examined the benefits at moderate to high altitudes, future research examining responses at lower altitudes should be conducted given that these environments are more frequently visited by athletes and workers. Mechanistic work to identify the specific physiological and cellular pathways responsible for cross adaptation between heat and altitude, and between cold and altitude, is warranted, as is exploration of benefits across different populations and physical activity profiles

Direct extraction of kinetic parameters from experimental cyclic voltammetry

We introduce a novel method for the direct extraction of kinetic data from experimental cyclic voltammetry using numerical simulation. This method is not specific to a particular model of electrode kinetics, such as the Butler-Volmer or Marcus-Hush models, and is general to all electrode geometries for which the current density is uniform across the surface. The method is demonstrated using both theoretically simulated voltammetry and experimental data for the reduction of 2-methyl-2-nitropropane at a mercury hemisphere electrode. For the latter system, excellent agreement with previously reported kinetic parameters is obtained. © 2012 Elsevier B.V. All rights reserved

Mass transport to and within porous electrodes. Linear sweep voltammetry and the effects of pore size: The prediction of double peaks for a single electrode process

We simulate an electrode modified with a conducting porous film, where the electrolysis occurs both at the surface of the film and within it, in order to study the effect of pore size on the peak current in linear sweep voltammetry. For redox systems with reversible electrode kinetics we find that for both very large and very small pores the peak current is given by the Randles-Šev ik equation. For intermediate pore size, however, we observe a greatly enhanced peak current. When considering systems with irreversible electrode kinetics a very similar pattern is observed, except for the case of very small pores. In this case the peak current is actually smaller than expected from the Randles-Šev ik equation because the peak splits into two distinct peaks; one due to "thin layer" diffusion within the film and another caused by planar diffusion from bulk solution. The experimental implications of this observation are significant given the widespread use of modified electrodes for analysis. © Pleiades Publishing, Ltd., 2012

Giving physical insight into the Butler-Volmer model of electrode kinetics: Part 2-Nonlinear solvation effects on the voltammetry of heterogeneous electron transfer processes

Electrochemical and spectroscopic experiments have shown the weaknesses of the symmetric Marcus-Hush model to model electrode processes, which is likely related to "asymmetric" oxidation and reduction processes. In a previous paper (M.C. Henstridge, E. Laborda, Y. Wang, D. Suwatchara, N. Rees, A. Molina, F. Martínez-Ortiz, R.G. Compton, J. Electroanal. Chem. 672 (2012) 45) the effects arising from different vibrational force constants have been considered, and in the present work we focus on those associated with solvent reorganization. The effects of different solvent frequencies in the oxidized and reduced forms are analyzed for the Gibbs energy surface, the oxidation/reduction rate constants and the voltammetry of solution-phase and surface-bound redox systems. Criteria to assess these effects by electrochemical experiments are given based on the analysis of the value of the Butler-Volmer transfer coefficient. © 2012 Elsevier B.V. All rights reserved

The Marcus-Hush model of electrode kinetics at a single nanoparticle

We examine the effect of the Marcus-Hush model of electrode kinetics on electron transfer at the surface of a single nanoparticle impacting an electode. Using numerical simulation we demonstrate the possibility of observing a kinetically limited steady state current which is smaller than the mass transport limiting current for such a system. © 2013 Elsevier B.V. All rights reserved

Switching transition states with changing electrode potential: Zn(II)/Zn electrodeposition on glassy carbon in the N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid

The mechanisms for the electrodeposition and stripping of Zn 2+|Zn in the N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid are investigated via cyclic voltammetry. Analysis showed that the deposition of Zn onto a bulk Zn surface occurred via a two-electron process, with the first electron transfer being rate determining. The electrodissolution was found to occur via a potentialdependent mechanism with the first electron transfer being rate determining near the formal potential, while an intermediate chemical step became rate determining at more positive potentials. © Springer-Verlag 2012

Asymmetric Marcus theory: Application to electrode kinetics

The application of the simple Marcus-Hush (MH) formalism to fit the voltammetric experimental response of various solution-phase redox couples is unsuccessful. These and other experimental deviations have hitherto been tentatively attributed to differences of the force constants of the oxidized and reduced species. Accordingly, we report application of the asymmetric form of Marcus theory to the voltammetric study of the kinetics of electrode reactions. The resulting four-parameter model accounts for discrepancies in the values of the inner-shell force constants and offers deeper insight to the changes involved in electron transfer processes at electrodes. The variation of the electrochemical rate constant with the applied potential is examined, and seen to be in agreement with reported experimental deviations from the simple MH model. The application of the asymmetric model to cyclic and square wave voltammetries is further reported. © 2011 Elsevier B.V. All rights reserved

Asymmetric Marcus-Hush model of electron transfer kinetics: Application to the voltammetry of surface-bound redox systems

The asymmetric Marcus-Hush model (MH) is applied to the study of the voltammetric response of electroactive monolayers. While the well-documented symmetric MH model has been successful in modelling many aspects of surface-bound redox systems, it cannot account for the asymmetry evident in the Tafel plots for many experimental systems. The asymmetric model has previously been used to explain deviations from the symmetric MH model observed for solution-phase redox systems [E. Laborda, M.C. Henstridge, R.G. Compton, J. Electroanal. Chem. 667 (2012) 48-53] by taking into account inner-shell differences between the oxidised and reduced species. We extend the theory to the description of electron transfer reactions of surface-bound species and examine several experimental features for both cyclic and square wave voltammetry, as well as Tafel plots, using both symmetric and asymmetric Marcus-Hush models and the phenomenological Butler-Volmer model. The asymmetric MH model is seen to outperform the other models in terms of the quantitative description of the full voltammetric waveshape and is able to reproduce all of the experimental trends examined, as such its use for the analysis of surface-bound redox couples is highly recommended. © 2012 Elsevier B.V. All rights reserved