Spectroscopic Evidence of Nanodomains in THF/RTIL Mixtures: Spectroelectrochemical and Voltammetric Study of Nickel Porphyrins

The presence and effect of RTIL nanodomains in molecular solvent/RTIL mixture were investigated by studying the spectroelectrochemistry and voltammetry of nickel octaethylporphyrin (Ni(OEP)) and nickel octaethylporphinone (Ni(OEPone)). Two oxidation and 2–3 reduction redox couples were observed, and the UV–visible spectra of all stable products in THF and RTIL mixtures were obtained. The E° values for the reduction couples that were studied were linearly correlated with the Gutmann acceptor number, as well as the difference in the E° values between the first two waves (ΔE12° = |E1° – E2°|). The ΔE12° for the reduction was much more sensitive to the %RTIL in the mixture than the oxidation, indicating a strong interaction between the RTIL and the anion or dianion. The shifts in the E° values were significantly different between Ni(OEP) and Ni(OEPone). For Ni(OEP), the E1° values were less sensitive to the %RTIL than were observed for Ni(OEPone). Variations in the diffusion coefficients of Ni(OEP) and Ni(OEPone) as a function of %RTIL were also investigated, and the results were interpreted in terms of RTIL nanodomains. To observe the effect of solvation on the metalloporphyrin, Ni(OEPone) was chosen because it contains a carbonyl group that can be easily observed in infrared spectroelectrochemistry. It was found that the νCO band was very sensitive to the solvent environment, and two carbonyl bands were observed for Ni(OEPone)− in mixed THF/RTIL solutions. The higher energy band was attributed to the reduced product in THF, and the lower energy band attributed to the reduced product in the RTIL nanophase. The second band could be observed with as little as 5% of the RTIL. No partitioning of Ni(OEPone)+ into the RTIL nanodomain was observed. DFT calculations were carried out to characterize the product of the first reduction. These results provide strong direct evidence of the presence of nanodomains in molecular solvent/RTIL mixtures

Electrochemistry and Spectroelectrochemistry of 1,4-Dinitrobenzene in Acetonitrile and Room-Temperature Ionic Liquids: Ion-Pairing Effects in Mixed Solvents

Room-temperature ionic liquids (RTILs) have been shown to have a significant effect on the redox potentials of compounds such as 1,4-dinitrobenzene (DNB), which can be reduced in two one-electron steps. The most noticeable effect is that the two one-electron waves in acetonitrile collapsed to a single two-electron wave in a RTIL such as butylmethyl imidazolium-BF4 (BMImBF4). In order to probe this effect over a wider range of mixed-molecular-solvent/RTIL solutions, the reduction process was studied using UV–vis spectroelectrochemistry. With the use of spectroelectrochemistry, it was possible to calculate readily the difference in E°’s between the first and second electron transfer (ΔE12° = E1° – E2°) even when the two one-electron waves collapsed into a single two-electron wave. The spectra of the radical anion and dianion in BMImPF6 were obtained using evolving factor analysis (EFA). Using these spectra, the concentrations of DNB, DNB–•, and DNB2– were calculated, and from these concentrations, the ΔE12° values were calculated. Significant differences were observed when the bis(trifluoromethylsulfonyl)imide (NTf2) anion replaced the PF6– anion, leading to an irreversible reduction of DNB in BMImNTf2. The results were consistent with the protonation of DNB2–, most likely by an ion pair between DNB2– and BMIm+, which has been proposed by Minami and Fry. The differences in reactivity between the PF6– and NTf2– ionic liquids were interpreted in terms of the tight versus loose ion pairing in RTILs. The results indicated that nanostructural domains of RTILs were present in a mixed-solvent system

Influence of RTIL Nanodomains on the Voltammetry and Spectroelectrochemistry Of Fullerene C\u3csub\u3e60\u3c/sub\u3e in Benzonitrile/Room Temperature Ionic Liquids Mixtures

The cyclic voltammetry of fullerene C60 was examined in mixed benzonitrile/RTIL solvents in order to probe the effect of nanodomains in the mixed RTIL/benzonitrile solutions and their effect upon the voltammetry. In probing the interactions of the fullerides (up to C603−) with RTILs, BMIm+ (1-butyl-3-methylimidazolium, mostly planar) and tetraalkylammonium (more spherical/flexible) salts were used. In order to investigate these shifts in more detail, the ΔE12° (=E°1–E°2) and ΔE23° (=E°2–E°3) values, which were independent of the reference potential, were used. At higher concentrations of the RTILs, greater stabilization of the more highly charged fullerides were observed. These shifts were attributed to the interaction of the fullerides with nanodomains of the RTIL. This was further confirmed by examining the shifts in the E1/2 values of non-RTIL and RTIL salts at constant ionic strength and the changes in diffusion coefficient with %RTIL. The observed shifts in the E1/2 values with increased concentration of the RTIL salts could not be explained by ion pairing equilibria alone. Changes in the visible and near infrared spectra between benzonitrile and mixed benzonitrile/RTIL spectra were most significant for C603−, where voltammetric evidence indicates the strongest interaction between the fullerides and the RTIL. Among the RTILs studied, preliminary DFT calculations showed that the more flexible tetraalkylammonium ion was able to stabilize the C60-anionic species better than the planar BMIm+ species, under similar solution conditions

Visible and Infrared Spectroelectrochemistry of Zinc and Manganese Porphinones: Metal vs. Porphyrin Reduction

The visible and infrared spectroelectrochemistry of zinc and manganese porphinones and porphinediones was carried out in THF solutions. The aim of this work was to use FTIR spectroelectrochemistry and DFT calculation to determine whether the reduction was centered predominantly on the metal or the macrocycle. For zinc(II), the first one-electron reduction must occur on the macrocyclic ring because the metal’s d-orbitals are filled (d10). The carbonyl bands on the macrocyclic ring were used to probe the electronic structure because they can be readily observed in the infrared spectra. The results of this study are complementary to previous spectroelectrochemical studies that have been reported for the iron and cobalt complexes of the same macrocycles. As expected for the formation of a π-radical anion species, significant downshifts in the carbonyl bands were observed. DFT calculations showed that the behavior of the porphinedione complexes were most sensitive to the electronic structure of the M(OEPdione)− species. If a MI species is formed, the two carbonyl groups will be downshifted by similar energies. For MII-radical anions, one carbonyl will be downshifted significantly, and the second one will be downshifted by a small amount. On the basis of this criterion, it was determined that cobalt(I) and iron(I) complexes were formed, while zinc and manganese formed π-radical anion species. The visible spectroelectrochemistry was also consistent with these electronic structures

In Situ Study of the Photodegradation of Carbofuran Deposited on TiO\u3csub\u3e2\u3c/sub\u3e Film under UV Light, Using ATR-FTIR Coupled to HS-MCR-ALS

The in situ study of the photodegradation of carbofuran deposited on a TiO2 catalyst film under UV light was carried out using the ATR-FTIR technique. The data were analyzed using a Hard–Soft Multivariate Curve Resolution-Alternating Least Squares (HS-MCR-ALS) methodology. Using S-MCR-ALS, four factors were deduced from the evolving factor analysis of the data, and their concentrations and spectra were determined. These results were used to draw qualitative and quantitative analyses of the major products of carbofuran photodegradation. The results of this analysis were in good agreement with GC-MS results and with reported mechanisms. Hard-MCR-ALS was then used to refine the spectra and concentrations, using a multistep kinetic model. The rate constant for the first step in the photodegradation of carbofuran was found to be 2.9 × 10–3 min–1. The higher magnitude of the correlation (96.87%), the explained variance (99.87%) and LOF (3.01), are good indicators of the reliability of the outcome of this approach. This method has been shown to be an efficient approach to study in situ photodegradation of pesticides on a solid surface

Blow-up, concentration phenomenon and global existence for the Keller-Segel model in high dimension

This paper is devoted to the analysis of the classical Keller-Segel system over $\mathbb{R}^d$, $d\geq 3$. We describe as much as possible the dynamics of the system characterized by various criteria, both in the parabolic-elliptic case and in the fully parabolic case. The main results when dealing with the parabolic-elliptic case are: local existence without smallness assumption on the initial density, global existence under an improved smallness condition and comparison of blow-up criteria. A new concentration phenomenon criteria for the fully parabolic case is also given. The analysis is completed by a visualization tool based on the reduction of the parabolic-elliptic system to a finite-dimensional dynamical system of gradient flow type, sharing features similar to the infinite-dimensional system.Comment: 44 pages, 2 figure

Direct Observation of Photoinduced Charge Separation in Ruthenium Complex/Ni(OH)\u3csub\u3e2\u3c/sub\u3e Nanoparticle Hybrid

Ni(OH)2 have emerged as important functional materials for solar fuel conversion because of their potential as cost-effective bifunctional catalysts for both hydrogen and oxygen evolution reactions. However, their roles as photocatalysts in the photoinduced charge separation (CS) reactions remain unexplored. In this paper, we investigate the CS dynamics of a newly designed hybrid catalyst by integrating a Ru complex with Ni(OH)2 nanoparticles (NPs). Using time resolved X-ray absorption spectroscopy (XTA), we directly observed the formation of the reduced Ni metal site (~60 ps), unambiguously demonstrating CS process in the hybrid through ultrafast electron transfer from Ru complex to Ni(OH)2 NPs. Compared to the ultrafast CS process, the charge recombination in the hybrid is ultraslow (≫50 ns). These results not only suggest the possibility of developing Ni(OH)2 as solar fuel catalysts, but also represent the first time direct observation of efficient CS in a hybrid catalyst using XTA

Mathematical modelling of the atherosclerotic plaque formation

International audienceThis article is devoted to the construction of a mathematical model describing the early formation of atherosclerotic lesions. Following the work of El Khatib, Genieys and Volpert, we model atherosclerosis as an inflammatory disease. We consider that the inflammatory process starts with the penetration of Low Density Lipoproteins cholesterol in the intima. This phenomenon is related to the local blood flow dynamics. Using a system of reaction-diffusion equations, we first provide a one-dimensional model of lesion growth. Then we perform numerical simulations on a two-dimensional geometry mimicking the carotid artery. We couple the previous mathematical model with blood flow and we provide a model in which the lesion appears in the area of lower shear stress