Issa Tapsoba

Electrochemical detection in a microfluidic device of oxidative stress generated by macrophage cells

The release of reactive oxygen species (ROS) or reactive nitrogen species (RNS), i.e., the initial phase of oxidative stress, by macrophage cells has been studied by electrochemistry within a microfluidic device. Macrophages were first cultured into a detection chamber containing the three electrodes system and were subsequently stimulated by the microinjection of a calcium ionophore (A23187). Their production of ROS and RNS was then measured by amperometry at the surface of a platinized microelectrode. The fabricated microfluidic device provides an accurate measurement of oxidative release kinetics with an excellent reproducibility. We believe that such a method is simple and versatile for a number of advanced applications based on the detection of biological processes of secretion by a few or even a single living cell.

Finding Out Egyptian Gods’ Secret Using Analytical Chemistry: Biomedical Properties of Egyptian Black Makeup Revealed by Amperometry at Single Cells

Lead-based compounds were used during antiquity as both pigments and medicines in the formulation of makeup materials. Chemical analysis of cosmetics samples found in Egyptians tombs and the reconstitution of ancient recipes as reported by Greco-Roman authors have shown that two non-natural lead chlorides (laurionite Pb(OH)Cl and phosgenite Pb(2)Cl(2)CO(3)) were purposely synthesized and were used as fine powders in makeup and eye lotions. According to ancient Egyptian manuscripts, these were essential remedies for treating eye illness and skin ailments. This conclusion seems amazing because today we focus only on the well-recognized toxicity of lead salts. Here, using ultramicroelectrodes, we obtain new insights into the biochemical interactions between lead(II) ions and cells, which support the ancient medical use of sparingly soluble lead compounds. Submicromolar concentrations of Pb(2+) ions are shown to be sufficient for eliciting specific oxidative stress responses of keratinocytes. These consist essentially of an overproduction of nitrogen monoxide (NO degrees ). Owing to the biological role of NO degrees in stimulating nonspecific immunological defenses, one may argue that these lead compounds were deliberately manufactured and used in ancient Egyptian formulations to prevent and treat eye illnesses by promoting the action of immune cells.

Angeli's Salt (Na2N2O3) is a Precursor of HNO and NO: a Voltammetric Study of the Reactive Intermediates Released by Angeli's Salt Decomposition

Under physiological conditions, it is usually accepted that the aerobic decomposition of Angelis salt produces nitrite (NO2−) and nitroxyl (HNO), which dimerizes and leads to N2O. No consensus has yet been established on the formation of nitric oxide (NO) and/or peroxynitrite (ONOO−) by Angelis salt. Because this salt has recently been shown to have pharmacological properties for the treatment of cardiovascular diseases, identification of its follow‐up reactive intermediates is of increasing importance. In this work, we investigated the decomposition mechanism of Angelis salt by voltammetry performed at platinized carbon fiber microelectrodes. By following the decomposition process of Angelis salt, we showed that the mechanism depends on the experimental conditions. Under aerobic neutral and slightly alkaline conditions, the formation of HNO, NO2−, but also of nitric oxide NO was demonstrated. In strongly alkaline buffer (pH>10), we observed the formation of peroxynitrite ONOO− in the presence of oxygen. These electrochemical results are supported by comparison with UV spectrophotometry data.

Ex vivo Activities of β‐Lapachone and α‐Lapachone on Macrophages: A Quantitative Pharmacological Analysis Based on Amperometric Monitoring of Oxidative Bursts by Single Cells

Artificial synapses for femtomolar detection: Amperometry at platinized carbon fibre electrodes has been used to unravel the complexity of β‐lapachones effects on cellular oxidative stress. α‐Lapachone, the pharmacologically inactive para‐quinone isomer, did not display such characteristics, but over longer incubation periods both quinones induced apoptosis. The observed effects were interpreted in terms of two mechanisms involving opposite reactivities of quinones in living cells.

Electrogenerated Base-Promoted Synthesis of Dithiocarbamate Acid Esters and 3-(N-Substituted-amino)-2-cyanodithiocrotonates from Primary or Secondary Amines and Carbon Disulfide

Electrogenerated cyanomethyl anion promotes the reaction between primary or secondary amines, carbon disulfide, and alkyl or benzyl halide. Secondary amines are converted to alkyl or benzyl dithiocarbamates, whereas primary amines give N-substituted alkyl or benzyl 3-amino-2-cyanodithiocrotonates. The mechanisms are discussed.

An organometallic derivative of a BAPTA ligand: towards electrochemically controlled cation release in biocompatible media

The combination of a ferrocenyl moiety with BAPTA provides a novel, water-soluble, redox-active chelator. This chelator behaving as a conformational sensor exhibits an unexpected electrochemical response with high affinity and selectivity for calcium.

Targeting structural motifs of flavonoid diglycosides using collision-induced dissociation experiments on flavonoid/Pb2+ complexes.

Differentiation of flavonoid congeners remains a challenging analytical problem and confirming the structures of the different isomers is difficult, even when they can be adequately separated from mixtures. In the present report, in order to overcome the limits of our recently proposed method that relies on the distinctive CID behaviors of [(flavonoid – H+) + Cu2+] complexes to obtain direct structural evidences, we decided to investigate the possibility of using Pb(II) complexation to generate significant differences upon CID. We selected five flavonoid diglycosides with targeted structural features to estimate the applicability of this methodology. Electrospray ionization from methanol—not acetonitrile—solutions was advantageously used for preparing the [(flavonoid diglycoside – H+) + Pb2+]+ complexes. Upon collisional activation, [(flavonoid diglycoside – H+) + Pb2+]+ ions mainly dissociate by glycosidic bond cleavage. Nevertheless, specific cross-ring cleavages are also induced and lead to a clear-cut determination of (i) the nature of the disaccharide group, i.e. rutinose or neohesperidose, (ii) the nature of the aglycone part, flavanone or flavone and (iii) the relative position of the disaccharide substituent on the aglycone part, i.e. 3–O– vs 7–O positions.

Solvent Effects on the Electrochemical Behavior of TAPD-Based Redox-Responsive Probes for Cadmium(II)

Two tetralkylated phenylenediamines (TAPD) 1 and 2 have been prepared by reductive alkylation of para-dimethylaminoaniline with furfural or thiophene 2-carboxaldehyde, respectively. Their chelation ability has been evaluated as electrochemical guest-responsive chemosensors for Cd(II) in acetonitrile (ACN), dimethylformamide (DMF), propylene carbonate (PC), and nitromethane (NM). The voltamperometric studies showed that these compounds are able to bind the Cd(II) cation with strong affinities except in DMF. The redox features of the chemosensors changed drastically when they are bounded to Cd(II) to undergo important anodic potential peak shifts comprised between ca. 500 and ca. 900 mV depending on the solvent. The addition of ∼4–10% molar triflic acid (TfOH) was found to be necessary to achieve rapidly the cation chelation which is slow without the acid. The electrochemical investigations suggested the formation of 1 : 2 stoichiometry complexes [Cd(L)2]2

Reactivity of N-thioamido amidines with halogenated alkyl derivatives: synthesis of 4,5-disubstituted 2-alkylaminothiazoles

2-Bromoacetate ethyl ester 4, 2-chloroacetonitrile 5, 2-bromo-1-(4-nitrophenyl)ethanone 6, and 2-chloroacetone 7 react with N-thioamido amidines 3 to yield the corresponding 4,5-disubstituted 2-alkylamino thiazoles 8, 9, 10, and 11 after the release of an amine molecule. The reaction of the amidines 3 with benzyl bromide 12, 4-chlorobutyronitrile 13, 3-bromopropionate ethyl ester 14, 3-chloropropionate ethyl ester 15, and 4-nitrobenzyl chloride 16 does not lead to the cyclic derivatives but gives opened-ring intermediates 17, 18, 19, 20, and 21. The cyclization mechanism is discussed on the basis of the study of the opened-ring intermediates which have been isolated in some cases and the AM1 and PM3 semi-empirical energetic calculations.

Electrochemical Study of Pharmacological Activity at Single Cells: Beta-lapachone Effect on Oxidative Stress of Macrophages

Beta-lapachone [1], a natural ortho-naphthoquinone, has been widely used for its large pharmacological activities, particularly against cancers. In the present study, amperometry at platinized carbon microelectrode was used to investigate the activity of [1], at different concentrations after various incubation times, on the oxidative bursts release of single macrophages. The results show that the presence of 0.1 to 100 μM of beta-lapachone, within one hour of incubation, leads to a decrease of reactive oxygen and nitrogen species release, comparatively to control. Conversely, when the incubation time increases (4 hours and more), the quantity of the species released in presence of 1 μM of [1] increases. Moreover, macrophage membranes became withered after 4 hours of incubation in presence of 10 μM of [1] and leading to cell death. These studies demonstrated the advantage of electrochemical methods for analyzing in real-time and quantitatively the effect of beta-lapachone on oxidative burst.