PubMed Health⌕ Search

Biomedical subjects

Fethi Bedioui

Publications and source records attributed to Fethi Bedioui.

13 recordsLinked to original sources
PubMed2006

Conformationally gated photoinduced processes within photosensitizer-acceptor dyads based on osmium(II) complexes with triarylpyridinio-functionalized terpyridyl ligands: insights from experimental study.

[(ttpy)Os(tpy-ph-TPH(3)(+))](3+) (2), [(ttpy)Os(tpy-xy-TPH(3)(+))](3+) (3), [(ttpy)Os(tpy-ph-TPH(2)(NO(2))(+))](3+) (4), and [(ttpy)Os(tpy-xy-TPH(2)(NO(2))(+))](3+) (5) are a series of dyads made of an Os(II) bis-tpy complex (tpy = 2,2':6',2"-terpyridine) as the photosensitizer (P) and 2,4,6-triarylpyridinium group (TP(+)) as the electron acceptor (A). These dyads were designed to form charge-separated states (CSS) upon light excitation. Together with analogous Ru(II) complexes (7-10), they have been synthesized and fully characterized. We describe herein how intramolecular photoinduced processes are affected when the electron-accepting strength of A (by nitro-derivatization of TP(+)) and/or the steric hindrance about intercomponent linkage (by replacing a phenyl spacer by a xylyl one) are changed. Electronic absorption and electrochemical behavior revealed that (i) chemical substitution of TP(+) (i.e., TP(+)-NO(2)) has no sizable influence on P-centered electronic features, (ii) reduction processes located on TP(+) depend on the intercomponent tilt angle. Concerning excited-state properties, photophysical investigation evidenced that phosphorescence of P is actually quenched in dyads 4 and 5 only. Ultrafast transient absorption (TA) experiments allowed attributing the quenching in conformationally locked dyad 5 to oxidative electron transfer (ET) from the (3)MLCT level to the TP(+)-NO(2) acceptor (k(el) = 1.1 x 10(9) s(-)(1)). For 4, geometrically unlocked, the (3)MLCT state was shown to first rapidly equilibrate (reversible energy transfer; k(eq) approximately 2 x 10(9) s(-)(1)) with a ligand centered triplet state before undergoing CSS formation. Thus, the pivotal role of conformation in driving excited-state decay pathways is demonstrated. Also, inner P structural planarization as a relaxation mode of the (3)MLCT states has been inferred from TA experiments.

Electrons↗
PubMed2006

Electrocatalytic activity of cobalt phthalocyanine CoPc adsorbed on a graphite electrode for the oxidation of reduced L-glutathione (GSH) and the reduction of its disulfide (GSSG) at physiological pH.

Modified electrodes coated by adsorbed cobalt phthalocyanines are known to show substantial electrocatalytic activity for the electro-oxidation of several thiols in alkaline aqueous solution. In this context, we explore in this study the electrocatalytic activity of adsorbed cobalt phthalocyanine (CoPc) on ordinary pyrolytic graphite electrode for the oxidation of reduced L-glutathione GSH and the reduction of its disulfide GSSG at physiological pH. To do so, cyclic and rotating disk voltammetries were performed and the amperometric results show that a stable electrochemical sensing material, with good reproducibility and sensitivity (in accordance with the concentrations of GSH expected in biological media), can be easily achieved. This opens the way for the design of an electrochemical sensor able to detect these two analytes in biologically relevant experimental conditions (in terms of pH).

Catalysis↗
PubMed2006

Spectroscopic and electrochemical study of the adsorption of [Co(en)2Cl2]Cl on gamma-alumina: influence of the alumina ligand on Co(III)/(II) redox potential.

UV-visible and Raman spectroscopies as well as electrochemical techniques have been used to characterize cis- and trans-[Co(III)(en)2Cl2]Cl (en=ethylenediamine) complexes and the gamma-alumina-supported cis-Co((III)) complex. It is shown that the electrochemical reduction of these complexes occurs according to a multistage mechanism involving two electrochemical steps, with the formation of a dimer that was characterized by UV-visible spectroscopy (intervalence band at 670 nm). The apparent standard redox potential for each step has been determined, and experimental results reveal that cis and trans complexes present similar electrochemical characteristics. It is also shown that the deposition of trans-[Co(III)(en)2Cl2]+ on gamma-alumina leads to an inner-sphere complex (ISC) in a cis configuration in which Cl- ligands are substituted by OH or O- surface groups of alumina. These changes in the coordination sphere of the complex induce a substantial decrease of its apparent redox potential since it is -0.63 V/SCE (saturated calomel electrode) for the gamma-alumina-supported cis-Co(III) complex, whereas values of -0.17 and -0.35 V/SCE were determined in dimethyl sulfoxide (DMSO) for the trans and cis precursor complexes, respectively.

Journal Article↗
PubMed2005

An electrochemical sensor array system for the direct, simultaneous in vitro monitoring of nitric oxide and superoxide production by cultured cells.

A new approach for an amperometric array sensor platform employing arrays of sensors in a 24-well cell culture plate format has been developed for simultaneous in vitro determination of nitric oxide (NO) and superoxide free radicals (O(2)(-)) produced by stimulated cells. The work reported focuses on the direct, real-time monitoring of extracellular production of these two analytes, as well as the effects of their interaction. The sensor platform was manufactured by a combination of sputtering gold electrodes and screen-printing carbon electrodes. The O(2)(-) sensor uses covalent immobilization of cytochrome c via a binder, DTSSP (3,3'-dithio-bis(sulphosuccinimidylpropionate) onto the surface of the Au electrodes, whereas the NO sensor system involves an NiTSPc (nickel tetrasulfonated phthalocyanine) film electrodeposited onto the surface of the carbon electrodes and subsequently covered with an external layer of Nafion. For in vitro demonstration of the platforms as a potential drug-screening system, A172 glioblastoma cells were cultured and transferred into the 24-well arrays. Simultaneous and direct monitoring of NO and O(2)(-) production as a response to chemicals of biomedical relevance was carried out. The results obtained demonstrated that it would be possible to envisage a drug screening platform for compounds designed to be inhibitors of nitric oxide synthase or to have an inhibitory effect on superoxide free radical production. By suitable modification of the electrodes employed it would also be possible to extend the platform to measure alternative species.

Biosensing Techniques↗
PubMed2005

Photoinduced processes within compact dyads based on triphenylpyridinium-functionalized bipyridyl complexes of ruthenium(II).

As an alternative to conventional charge-separation functional molecular models based on long-range ET within redox cascades, a "compact approach" has been examined. To this end, spacer elements usually inserted between main redox-active units within polyad systems have been removed, allowing extended rigidity but at the expense of enhanced intercomponent electronic communication. The molecular assemblies investigated here are of the P-(theta (1))-A type, where the theta (1) twist angle is related to the degree of conjugation between the photosensitizer (P, of {Ru(bpy)(3)}(2+) type) and the electron-acceptor (A). 4-N- and 4-N-,4'-N-(2,4,6-triphenylpyridinio)-2,2'-bipyridine ligands (A(1)-bpy and A(2)-bpy, respectively) have been synthesized to give complexes with Ru(II), 1-bpy and 2-bpy, respectively. Combined solid-state analysis (X-ray crystallography), solution studies ((1)H NMR, cyclic voltammetry) and computational structural optimization allowed verifying that theta (1) angle approaches 90 degrees within 1-bpy and 2-bpy in solution. Also, anticipated existence of strong intercomponent electronic coupling has been confirmed by investigating electronic absorption properties and electrochemical behavior of the compounds. The capability of 1-bpy and 2-bpy to undergo PET process was evaluated by carrying out their photophysical study (steady state emission and time-resolved spectroscopy at both 293 and 77 K). The conformational dependence of photoinduced processes within P-(theta (1))-A systems has been established by comparing the photophysical properties of 1-bpy (and 2-bpy) with those of an affiliated species reported in the literature, 1-phen. A complementary theoretical analysis (DFT) of the change of spin density distribution within model [1-bpy(theta (1))](-) mono-reduced species as a function of theta (1) has been undertaken and the possibility of conformationally switching emission properties of P was derived.

2,2'-Dipyridyl↗
PubMed2005

Combined system for the simultaneous optical and electrochemical monitoring of intra- and extracellular NO produced by glioblastoma cells.

A combined, optospectroscopic and electrochemical assay system for the simultaneous monitoring of intra- and extracellular production of biologically important species has been developed and assessed. The present model system evaluates intra- and extracellular nitric oxide produced by stimulated glioblastoma multiform cell line (A172). The production of endogenous NO was induced by phorbol-12-myristate-13-acetate and inhibited by N(omega)-nitro-l-arginine methyl ester. Intracellular production of NO was monitored via fluorescence image analysis using a 4,5-diaminofluorescein probe, while extracellular NO release was monitored via a chemically modified electrode, which was incorporated into an optically transparent cell chip. The results indicated that there was no mutual interference between the optical and electrochemical measurement systems. The response time of the combined optical/electrochemical system was found to be in the range of a few tens of seconds.

Cell Line, Tumor↗
PubMed2005

Simultaneous intra- and extracellular superoxide monitoring using an integrated optical and electrochemical sensor system.

A new integrated optical and electrochemical sensor system for simultaneous monitoring of intra- and extracellular superoxide (O(2)(-)) was developed using an array-based cell chip. For in vitro assays, A172 human glioblastoma cells were transferred into the cell chip and stimulated by phorbol 12-myristate 13-acetate (PMA). Intracellular O(2)(-) generation was detected via fluorescence image analysis with a dye probe, dihydrorhodamine 123 (DHR 123). Extracellular O(2)(-) was detected using an amperometric sensor constructed by immobilisation of cytochrome c using a binder, 3,3'-dithiobis(sulphosuccinimidylpropionate), to attach the redox protein onto the surface of electrodeposited Au electrodes incorporated into the optically transparent cell chip. The simultaneous intra- and extracellular production of O(2)(-) was successfully observed from PMA-stimulated A172 cells and inhibited by superoxide dismutase (SOD). The quantification of O(2)(-) concentration based on a mathematical model study and possible applications using the sensor system developed were discussed. The results confirm that there was no detectable interference or crosstalk between the optical and electrochemical assays. Feasibility of the integration of the two methods, optical and electrochemical, and the neutralisation of the intra- and extracellular O(2)(-) levels by SOD have been demonstrated.

Cell Line↗
PubMed2005

Simultaneous detection of the release of glutamate and nitric oxide from adherently growing cells using an array of glutamate and nitric oxide selective electrodes.

The simultaneous detection of nitric oxide and glutamate using an array of individually addressable electrodes, in which the individual electrodes in the array were suitably modified with a highly sensitive nitric oxide sensing chemistry or a glutamate oxidase/redox hydrogel-based glutamate biosensor is presented. In a sequence of modification steps one of the electrodes was covered first with a positively charged Ni porphyrin entrapped into a negatively charged electrodeposition paint followed by the manual modification of the second working electrode by a bienzyme sensor architecture based on crosslinked redox hydrogels with entrapped peroxidase and glutamate oxidase. Adherently growing C6-glioma cells were grown on membrane inserts and placed in close distance to the modified sensor surfaces. The current responses recorded at each electrode after stimulation of glutamate and NO release by means of K+ and bradykinin clearly demonstrate the ability of the individual electrode in the array to detect the analyte towards which its sensitivity and selectivity was targeted without interference from the neighbouring electrode or other analytes present in the test mixture.

Animals↗
PubMed2004

Photoinduced intramolecular electron transfer in ruthenium and osmium polyads: insights from theory.

Ru(II) and Os(II) complexes (P) of [4'-(p-phenyl)]terpyridyl ligand (ptpy) derivatized with an electron acceptor (A) of the triphenylpyridinium (H3TP+) type have been recently proposed as functional models for electron-transfer (ET) processes in the context of artificial photosynthesis. These inorganic dyads, P-A, are expected to undergo intramolecular photoinduced ET to form a charge separated (CS) state of pivotal interest. To draw a complete picture of possible ET processes, the ground- and excited-state properties of these complexes, both in their native and monoreduced forms, have been studied by the means of density functional theory (DFT). A time-dependent-DFT approach (TDDFT) was used to interpret the electronic spectra, while additional spectroscopic measurements have been carried out in order to complete the available experimental information and to further confirm the theoretical issues. Besides the noticeable quantitative agreement between computed and experimental absorption spectra, our results allow us to clarify, by first principles, the actual nature and interplay of the electronic and geometrical coupling between the acceptor moiety and the photosensitizer. The possibility of a direct (optical) ET from the ground state to the targeted *[P+-A-] CS state is theoretically postulated and found to be consistent with available photophysical data (transient absorption spectroscopy). Concerning backward ET (from the CS state), the occurrence of a quinoidal-like electronic redistribution inherent to the photoreduced acceptor-ligand is proposed to favor efficient charge recombination.

Journal Article↗
PubMed2004

Functionalised electrode array for the detection of nitric oxide released by endothelial cells using different NO-sensing chemistries.

In a preliminary study aimed at developing strategies for the simultaneous detection of various biologically important molecules, a procedure is described that allows the electrochemical detection of nitric oxide (NO) released by a population of human umbilical vein endothelial cells (HUVEC) by using an array of electrodes comprising three individually addressable electrodes. Each electrode in the array was modified with a different NO-sensitive electrocatalyst, thereby demonstrating the possibility of modifying the individual electrodes in an array with different sensing chemistries. This study opens a doorway to the development of arrays of electrodes for the simultaneous detection of multiple analytes in a complex environment by suitably tailoring the sensitivity and selectivity of each electrode in the array to a specific analyte in the test medium.

Biosensing Techniques↗
PubMed2002

Triarylpyridinium-functionalized terpyridyl ligand for photosensitized supramolecular architectures: intercomponent coupling and photoinduced processes.

The electronic (absorption spectra) and electrochemical properties of a novel series of triphenylpyridinium (H(3)TP(+)=A) electron-acceptor-based polyad species have been correlated with their steady-state (emission spectra) and time-resolved (ns and ps laser flash photolysis) photophysical behavior (at both 293 and 77 K). These d(6) transition metal complexes (M=Ru(II), Os(II)) of 2,2':6',2"-terpyridines (tpy) are denoted as P0 and P1, depending on whether they incorporate H(3)TP(+)-tpy or H(3)TP(+)-ptpy ligands (ptpy=4'-phenyl-substituted tpy), respectively. For the P0/Ru-based compounds, the luminescence quantum yield and excited-state lifetime of the "[Ru(tpy)(2)](2+)" chromophore have been found to be considerably enhanced at 293 K (e.g., tau=0.56 ns for isolated P0/Ru in acetonitrile vs tau=55 and 27 ns for P0/Ru within P0 A/Ru and P0 A(2)/Ru (A=electron acceptor), respectively). In spite of the lack of conjugation between P0 and A, this behavior has been ascribed to a through-bond mediated electronic substituent effect originating from the directly connected H(3)TP(+) electron-withdrawing group. For the P1-based compounds, the possibility of photoinduced electron-transfer (PET) processes with the formation of charge-separated (CS) states is discussed, and the main results may be summarized as follows: 1) when involved, the electron-donor D (D=Me(2)N of Me(2)N-ptpy) is strongly electronically coupled to P1 but cannot facilitate a reductive quenching of *P1 to give the *[D(+)-P1(-)]-type of CS state for thermodynamic reasons, irrespective of whether M is Ru(II) or Os(II); 2) the P1 and A components have been shown to be very weakly electronically coupled; 3) at 293 K, P1/Ru- and P1/Os-based polyad systems display distinct photophysical behavior with respect to A, with only the latter exhibiting a noticeable quenching of luminescence (up to 50 % for P1 A/Os with respect to P1/Os); 4) for assemblies made up of P1/Os and A components only, comparison between their room-temperature (RT) and low-temperature (LT; 77 K, frozen matrix) photophysical properties, together with information gleaned from combined transient absorption experiments and spectroelectrochemical studies of P1/Os and P1 A/Os, further supported by thermodynamic considerations, allowed us to conclude that a PET process does take place within the P1 A/Os dyad leading to the *[P1(+)-A(-)] CS state. For the DP1 A/Os triad, the formation of such a CS state followed by an enhanced electron-releasing inductive effect from D is postulated.

Electrochemistry↗
PubMed2002

A new class of functionalized terpyridyl ligands as building blocks for photosensitized supramolecular architectures. Synthesis, structural, and electronic characterizations.

A new class of triarylpyridinio-derivatized [4'-(p-phenyl)(n)]terpyridyl ligands, R(1)(2)R(2)TP(+)-(p)(n)tpy, was designed as a novel category of electron-acceptor (A)-substituted proto-photosensitizing molecules. The first elements of this versatile family of ligands (i.e., n = 0, 1 and R(1) = R(2) = H), H(3)TP(+)-tpy and H(3)TP(+)-ptpy, were synthesized as well as their Ru(II) and Os(II) complexes to form the related acceptor-functionalized M(tpy)(2)(2+) and M(ptpy)(2)(2+) photosensitizer components denoted P0 and P1, respectively. Within the P1 series of compounds, an electron-donor (D)-substituted ligand, Me(2)N-ptpy, was also involved and associated with H(3)TP(+)-ptpy, giving rise to various combinations (up to 10 polyad systems). The two resulting series of nanometer-scale rigid rod-like photosensitized supramolecular architectures are of potential interest for long-range photoinduced electron transfer purposes. The main structural features of such supermolecules were determined by comparing the results obtained from (i) single-crystal X-ray analysis of the two free ligands together with that of the P0A/Ru and P1A(2)/Ru complexes and (ii) a detailed solution (1)H NMR study of the P0 series and, more specifically, of the P0A/Ru dyad (ROESY experiment). It is shown that the pseudoperpendicular conformation of the covalently linked A and P subunits found in the solid state is persistent in fluid medium; i.e., A is not conjugated with P (P0 and P1). The first insights regarding the consequences upon intercomponent couplings of combined substituent effects and conjugation (case of D-based polyads)-or absence of conjugation-are discussed in the light of ground-state electronic properties of the compounds.

Journal Article↗