A few key theoretical issues of importance in modern molecular electrochemistry

International audienceThis opinion paper details three typical cases in which new theoretical concepts need to be implemented in molecular electrochemistry in order to rationalize experimental results obtained in nanoscale cells or performed in new electrolytic media such as RTILs

Electrochemical Monitoring of ROS/RNS Homeostasis Within Individual Phagolysosomes Inside Single Macrophages

International audienceReactive Oxygen/Nitrogen Species (ROS/RNS) produced by macrophages inside their phagolysosomes are closely related to immunity and inflammation by being involved in the removal of pathogens, altered cells, etc. The existence of a homeostatic mechanism regulating the ROS/RNS amounts inside phagolysosomes has been invoked to account for the efficiency of this crucial process but this could never be unambiguously documented. In this work, intracellular electrochemical analysis with platinized nanowires electrodes (Pt-NWEs) allowed monitoring ROS/RNS effluxes with sub-millisecond resolution from individual phagolysosomes randomly impacting onto the electrode inserted inside a living macrophage. This evidenced for the first time that the consumption of ROS/RNS by their oxidation at the nanoelectrode surface stimulates the production of significant ROS/RNS amounts inside phagolysosomes. These results established the existence of the long-time postulated ROS/RNS homeostasis and allowed quantifying its kinetics and efficiency. ROS/RNS concentrations may then be maintained at sufficiently high levels for sustaining proper pathogen digestion rates without endangering the macrophage internal structures

Simple and clear evidence for positive feedback limitation by bipolar behavior during scanning electrochemical microscopy of unbiased conductors

On the basis of an experimentally validated simple theoretical model, it is demonstrated unambiguously that when an unbiased conductor is probed by a scanning electrochemical tip (scanning electrochemical microscopy, SECM), it performs as a bipolar electrode. Though already envisioned in most recent SECM theories, this phenomenon is generally overlooked in SECM experimental investigations. However, as is shown here, this may alter significantly positive feedback measurements when the probed conductor is not much larger than the ti

Spatiotemporal Comparison of Drought Metrics over the Western United States

Thesis (Master's)--University of Washington, 2023Drought definitions and drought metrics come in many different forms and it is not always clear which definition or metric is most useful for describing or forecasting drought impacts. Drought metrics range from those which only incorporate precipitation anomalies to more comprehensive measures such as the United States Drought Monitor (USDM), which incorporates on-the-ground observations of drought impacts to arrive at a consensus-based drought status. Here, we develop a method to compare drought metrics, as reported in the Climate Toolbox (https://climatetoolbox.org/), and investigate their level of agreement in assessing drought conditions in the western continental United States. We compare two drought metrics and evaluate how they spatially evolve over the two decade period from 2000 to 2021. Our drought metrics are the USDM and Standardized Precipitation Index (SPI) at 30 day (SPI30d) and 180 day (SPI180d) intervals. We propose utilizing contiguous drought area (CDA) analysis to extract drought tracks from a larger network of drought characterizations. CDA blobs are organized through a directed graph that we can pull out individual paths called threads. Threads are aligned between different metric graphs through spatio-temporal intersection. USDM drought characterizations were found to move slowly and be more persistent than SPI characterizations. Meanwhile SPI30d drought characterizations were fragmented and moved quickly with dynamic changes in size. SPI180d drought characterizations moved faster than USDM drought characterizations, but not as dynamically as SPI30d drought characterizations. Contiguous areas between metrics were found to not necessarily result in the same drought evolution, yet we now have the means to compare evolutions. We found that the definition of drought used highly impacts the evolution observed

Reconstruction of Distributions of Nanoparticles or Electroactive Nano-Components in Electrochemical Arrays Based on Chronoamperometric Data

本文主要阐述和考察了一种简单的基于时间相关的电化学阵列计时电流响应数据来重构概率密度分布（f(ρ)）的数学和数值方法，并应用于表征平面导体电化学惰性表面存在的或沉积的电化学活性或电催化纳米组分的分布，建立了适用于三种阵列（一种周期性分散和两种随机分散）涉及近球形纳米组分在平滑表面分散的数学和数值有效方法. 而这三种阵列代表了大多数应用于分析或电催化的二维实验电化学纳米阵列.本文建立的重构步骤易于通过大多数商业数学程序来实现, 尽管方法简单，但允许恢复的概率密度精度很高, 即使是可利用的实验获得的时间范围太短时也能严格应用，因此，完全适合于大多数实验过程.The main scope of this work was to elaborate and test a simple mathematical and numerical procedure for reconstructing the probability density distributions f(ρ) characterizing the distribution of electroactive or electrocatalytic nano-components present or deposited on the electrochemically-inert surface of a planar conductor based on the time-dependent chronoamperometric responses of the corresponding electrochemical array. The mathematical and numerical validity of the procedure was established for three types of arrays (one periodical, two involving random dispersions) involving near-spherical nano-components dispersed on a flat surface. Indeed, altogether, these three types represent most 2D-experimental electrochemical nano-arrays used for analytical or electrocatalytic purposes. This reconstruction procedure is easily implementable using most commercial mathematical programs. Albeit the simplicity of its implementation, it allowed recovering probability densities with an excellent precision, even when the available time-range experimentally accessible was too short for its rigorous application, being thus perfectly adequate to most experimental purposes.This work was supported in parts by PSL, Ecole Normale Supérieure, CNRS, and the University Pierre and Marie Curie (UMR 8640). Support by the ANR-NSF bilateral (USA-France) program (ANR grant #ANR-AAP-CE06 “ChemCatNanoTech”) is also greatly acknowledged.This work was supported in parts by PSL, Ecole Normale Supérieure, CNRS, and the University Pierre and Marie Curie (UMR 8640). Support by the ANR-NSF bilateral (USA-France) program (ANR grant #ANR-AAP-CE06 “ChemCatNanoTech”) is also greatly acknowledged.作者联系地址：高等师范学院-巴黎文理研究大学联盟，化学系，索邦大学-巴黎第六大学，法国国家科学研究院混合研究单位8640巴斯德，洛蒙街24号，邮编75005，法国巴黎Author's Address: Ecole Normale Supérieure-PSL Research University, Département de Chimie, Sorbonne Universités-UPMC Paris 6, CNRS UMR 8640 PASTEUR, 24 rue Lhomond, 75005 Paris, France通讯作者E-mail：[email protected]