Contribution of capillary electrophoresis to an integrated vision of humic substances size and charge characterizations

International audienceThe physicochemical properties of three different humic substances (HS) are probed using capillary zone electrophoresis in alkaline carbonate buffers, pH 10. Special attention is drawn to the impact of the electrolyte ionic strength and counter-ion nature, chosen within the alkali-metal series, on HS electrophoretic mobility. Taylor-Aris dispersion analysis provides insights into the hydrodynamic radius (R$_H$) distributions of HS. The smallest characterized entities are of nanometric dimensions, showing neither ionic strength- nor alkali-metal-induced aggregation. These results are compared with the entities evidenced in dynamic light scattering measurements, the size of which is two order of magnitude higher, $ca$. 100 nm. The extended Onsager model provides a reasonable description of measured electrophoretic mobilities in the ionic strength range 1-50 mM, thus allowing the estimation of limiting mobilities and ionic charge numbers for the different HS samples. An unexpected HS electrophoretic mobility increase (in absolute value) is observed in the order Li$^+$ < Na$^+$ < K$^+$ < Cs$^+$ and discussed either in terms of retarding forces or in terms of ion-ion interactions

Caractérisation physicochimique par électrophorèse capillaire de nanoparticules magnétiques, anioniques et cationiques : distribution de taille, densité de charge et coefficient de diffusion collectif

Au cours de ce travail nous nous sommes intéressés à la caractérisation de nanoparticules magnétiques anioniques et cationiques en électrophorèse capillaire (CE). Dans le cadre de l'analyse de particules cationiques, différentes stratégies de modification du capillaire ont été envisagées de sorte à supprimer les phénomènes d'adsorption et ainsi permettre une mesure précise de la mobilité électrophorétique de ces particules. Il a été montré l'influence de différents paramètres inhérents au choix de l'électrolyte de séparation, dont la force ionique, la nature et la concentration des co-ions et contre-ions ainsi que le pH, sur la mobilité et la dispersion électrophorétique des particules. Une séparation en taille a été obtenue pour des populations de particules de maghémite dont les diamètres moyens (< 10 nm) diffèrent de seulement 2 nm et expliquée à la lumière des théories d'Overbeek-Booth qui tiennent compte de l'effet de relaxation. Une caractérisation précise de la charge de surface de particules cœur/coquille bifonctionnalisées amino-PEG a également été réalisée sur des populations de particules de taille uniforme (~ 40 nm), et corrélée à un taux de greffage effectif. Enfin un protocole de mesure du coefficient de diffusion collectif des particules a été développé, basé sur la théorie de la dispersion de Taylor, permettant de (i) distinguer des populations de particules dont les diamètres moyens (< 10 nm) diffèrent de seulement 2 nm, (ii) mettre en évidence l'existence d'interactions répulsives de nature électrostatique entre particules de même signe de charge, (iii) quantifier ces interactions en fonction de la force ionique du milieu de dispersion. Ces nouvelles méthodes de caractérisation à la fois simples et rapides devraient s'avérer cruciales pour l'optimisation de la conception de nanoparticules fonctionnalisées destinées à des applications biomédicales

Electromigration separation methodologies for the characterization of nanoparticles and the evaluation of their behaviour in biological systems

International audienc

Electrokinetic elucidation of the interactions between persistent luminescent nanoprobes and the binary apolipoprotein-E/albumin protein system

International audienceThe affinity between functional nanoparticles (NPs) and proteins could determine the efficacy of nanoprobes, nanosensors, nanocarriers, and many other devices for biomedical applications. Therefore, it is necessary to develop analytical strategies to accurately evaluate the magnitude of these protein corona interactions in physiological media. In this work, different electrokinetic strategies were implemented to accurately determine the interactions between PEGylated ZnGa1.995Cr0.005O4 persistent luminescent NPs (ZGO-PEG) and two important serum proteins: human serum albumin (HSA), the most abundant serum protein, and apolipoprotein-E (ApoE), associated with the active transport of NPs through the blood–brain barrier. Firstly, the injection of ZGO-PEG in a background electrolyte (BGE) containing individual proteins allowed an affinity study to separately characterize each NP–protein system. Then, the same procedure was applied in a buffer containing a mixture of the two proteins at different molar ratios. Finally, the NPs were pre-incubated with one protein and thereafter electrokinetically separated in a BGE containing the second protein. These analytical strategies revealed the mechanisms (comparative, cooperative or competitive systems) and the magnitude of their interactions, resulting in all cases in notably higher affinity and stability between ZGO-PEG and ApoE (Ka = 1.96 ± 0.25 × 1010 M−M) compared to HSA (Ka = 4.60 ± 0.41 × 106 M−M). For the first time, the inter-protein ApoE/HSA interactions with ZGO-PEG were also demonstrated, highlighting the formation of a ternary ZGO-PEG/ApoE/HSA nanocomplex. These results open the way for a deeper understanding of the protein corona formation, and the development of versatile optical imaging applications for ZGO-PEG and other systemically delivered nanoprobes ideally vectorized to the brain

Speciation and quantitation of precious metals in model acidic leach liquors, theoretical and practical aspects of recycling

International audienceWaste printed circuits boards are a major source of strategic materials such as platinum group metals since they are used for the fabrication of technological devices, such as hard drive discs, capacitors, diodes, etc. Because of the high cost of platinum, palladium and gold (> 25k€ / kg), an economic and environmental challenge is their recycling from printed circuit boards, that represent around 2% weight of electronic equipment. Hydrometallurgical treatments allow to recover these metals in solution, with a high recovery rate for a leaching liquor made of thiourea in hydrochloric acid. So as to develop an efficient recycling process from this leach liquor, one requires the speciation of these strategic metals, as well as their extraction and quantitation in the mixture. For this purpose, platinum, palladium and gold were dissolved in model leach liquors made of hydrochloric acid and thiourea at low concentration. The identification of metal complexes was determined in function of thiourea concentration (between 10 µmol/L and 10 mmol/L) by the combination of UV-Visible spectrometry, cyclic voltammetry and for the first time capillary electrophoresis. The electrokinetic method was then applied for the quantitation of trace metal analyses in leach samples from waste printed circuit boards reprocessing, demonstrating its applicability for industrializable recycling applications

Capillary electrophoresis with mass spectrometric detection for separation of S-nitrosoglutathione and its decomposition products: a deeper insight into the decomposition pathways

International audienceS-Nitrosoglutathione (GSNO) is a very important biomolecule that has crucial functions in many physiological and physiopathological processes. GSNO acts as NO donor and is a candidate for future medicines. This work describes, for the first time, the separation and the detection of GSNO and its decomposition products using capillary electrophoresis coupled to mass spectrometry (CE–MS). The separation was performed in slightly alkaline medium (pH 8.5) under positive-ionization MS detection. The identification of three byproducts of GSNO was formally performed for the first time: oxidized glutathione (GSSG), glutathione sulfinic acid (GSO2H), and glutathione sulfonic acid (GSO3H). GSO2H and GSO3H are known to have important biological activity, including inhibition of the glutathione transferase family of enzymes which are responsible for the elimination of many mutagenic, carcinogenic, and pharmacologically active molecules. We observed, after the ageing of GSNO in the solid state, that the proportion of both GSSG and GSO3H increases whereas that of GSO2H decreases. These results enabled us to propose an oxidation scheme explaining the formation of such products

Capillary electrophoresis coupled to contactless conductivity detection for the analysis of S-nitrosothiols decomposition and reactivity

International audienceS-Nitrosothiols (RSNO) are composed of a NO group bound to the sulfhydryl group of a peptide or protein. RSNO are very important biological molecules, since they have many effects on human health. RSNO are easily naturally decomposed by metal ions, light, and heat, with different kinetics. They can furthermore undergo transnitrosation (NO moieties exchange), which is a crucial point in physiological conditions since the concentration ratios between the different nitrosothiols is a key factor in many physiopathological processes. There is therefore a great need for their quantitation. Many S-nitrosothiol detection and quantitation methods need their previous decomposition, leading thus to some limitations. We propose a direct quantitation method employing the coupling of capillary electrophoresis with a homemade capacitively coupled contactless conductivity (C4D) detector in order to separate and quantify S-nitrosoglutathione and its decomposition products. After optimization of the method, we have studied the kinetics of decomposition using light and heat. Our results show that the decomposition by light is first order (kobs = (3.40 ± 0.15) × 10−3 s−1) while that using heat (at 80°C) is zeroth order (kobs,80°C = (4.34 ± 0.14) × 10−6 mol L−1 s−1). Transnitrosation reaction between S-nitrosoglutathione and cysteine was also studied, showing the possibility of separation and detection of all the products of this reaction in less than 2.5 min

Surface functionalization of cyclic olefin copolymer by plasma‐enhanced chemical vapor deposition using atmospheric pressure plasma jet for microfluidic applications

International audienceLab‐On‐A‐Chips promise solutions for high throughput and specific analysis for environmental and health applications, with the challenge to develop materials allowing fast, easy, and cheap microfabrication and efficient surface treatment. Cyclic olefin copolymer (COC) is a promising thermoplastic, easily microfabricated for both rapid prototyping and low‐cost mass production of microfluidic devices but still needing efficient surface modification strategies. This study reports for the first time the optimization of an easy COC silica coating process by plasma‐enhanced chemical vapor deposition at atmospheric pressure with plasma jet and tetraethylorthosilicate as precursor, leading to a 158 ± 7 nm thickness and a 14‐day‐stability of hydrophilic properties for a COC‐embedded microchannel (100 µm), paving the way for a simplified and controlled COC surface modification

Capillary electrophoresis coupled to contactless conductivity detection for the analysis of S‐nitrosothiols decomposition and reactivity

S‐Nitrosothiols (RSNO) are composed of a NO group bound to the sulfhydryl group of a peptide or protein. RSNO are very important biological molecules, since they have many effects on human health. RSNO are easily naturally decomposed by metal ions, light, and heat, with different kinetics. They can furthermore undergo transnitrosation (NO moieties exchange), which is a crucial point in physiological conditions since the concentration ratios between the different nitrosothiols is a key factor in many physiopathological processes. There is therefore a great need for their quantitation. Many S‐nitrosothiol detection and quantitation methods need their previous decomposition, leading thus to some limitations. We propose a direct quantitation method employing the coupling of capillary electrophoresis with a homemade capacitively coupled contactless conductivity (C4D) detector in order to separate and quantify S‐nitrosoglutathione and its decomposition products. After optimization of the method, we have studied the kinetics of decomposition using light and heat. Our results show that the decomposition by light is first order (kobs = (3.40 ± 0.15) × 10−3 s−1) while that using heat (at 80°C) is zeroth order (kobs,80°C = (4.34 ± 0.14) × 10−6 mol L−1 s−1). Transnitrosation reaction between S‐nitrosoglutathione and cysteine was also studied, showing the possibility of separation and detection of all the products of this reaction in less than 2.5 min.361619821988COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESSem informaçã

Electrografting of aryl diazonium on thin layer platinum microbands: Towards customized surface functionalization within microsystems

International audienc