Nikos Psaroudakis

Development of an electrochemical chemosensor for the rapid detection of zinc based on air stable lipid films with incorporated calix4arene phosphoryl receptor

This work describes the preparation of a selective receptor for the rapid, selective, and sensitive electrochemical flow injection analysis of zinc using air stable lipid films supported on a methacrylate polymer on a glass fibre filter with incorporated artificial receptor. The selective receptor was synthesised by transformation of the –OH groups of resorcin4arene receptor into phosphoryl groups. These lipid films were supported on a methylacrylate polymer (i.e. methacrylic acid was the functional monomer for the polymerisation, ethylene glycol dimethacrylate was used as the crosslinker and 2,2′-azobis-2-methylpropionitrile as an initiator). A minisensor device was constructed for the electrochemical flow injection analysis of zinc based on air stabilised lipid films supported on a polymer. The device can sense the analyte in a drop (75 µL) of sample. Zinc was injected into flowing streams of a carrier electrolyte solution. A complex formation between the calix4arene phosphoryl receptor and zinc takes place. This enhances the pre-concentration of zinc at the lipid membrane surface which in turn causes dynamic alterations of the electrostatic fields and phase structure of membranes; as a result ion current transients were obtained and the magnitude of these signals was correlated to the substrate concentration. The response times were ca 5 s and zinc was determined at concentration levels of nanomolar. The analytical curve was linear in the concentration range 1.00 × 10−7 − 1.20 × 10−6 M with detection limit of 5.00 × 10−8 M and a relative standard deviation lower than 4%. The effect of potent interferences included a wide range of other metals. As an analytical demonstration, trace concentrations of Zn(II) were successfully detected in real samples of waters without any laborious and time-consuming treatment.

Homogeneous Catalytic Hydrogen Formation Using Dinuclear Multiply Bonded Complexes of Molybdenum (III) and Tungsten (III) and LowValency Metal Ions, M=Cr(II), V(II), in Aqueous Acidic Solutions

In the last twenty years intensive research has been done in the important field of multiply bonded dinuclear transition metal complexes. The chemistry of the (M-M)n+ containing compounds is extraordinarily rich and complex [1], and the factors governing the reactivity of metal-metal multiple bonds are now better understood. Additionally, some of the commonly observed reactions of these dimers are not found in mononuclear chemistry and point out to the importance of the (M-M)n+ unit as an inorganic functional group. In fact, the whole field of multiple bonds between metal atoms provides a distinct departure from classical coordination chemistry [2]. These species posses several attractive properties for their application as multielectron reagents or photoreagents. Firstly, their electronic structure is well defined, and often, the lowest energy excited states of many (M-M)n+ compounds are sufficiently long lived to permit their subsequent chemical reaction. Secondly, the binuclear metal core is an electron source or sink in oxidation-reduction processes. Addition of electrons to, or removal of, electrons from the metal-metal bond is accompanied by facile interconversion between (M-M)n+ dimers of different bond orders. Finally, substartes readily add to the coordinatively unsaturated metal-metal core. The ability to coordinate substrate molecules to redoxactive binuclear metal centers has important implications in the ultimate application of (M-M)n+ dimers as multi-electron catalysts or photocatalysts. Proton oxidative addition to mononuclear or cluster transition metal complexes leading to hydride formation [3] is a key step in many catalytic processes including chemical [4], photochemical [5], or biochemical [6], reactions in which dihydrogen is evolved.

Homogeneous catalytic hydrogen formation using a ditungsten cluster and low valency metal ions in aqueous acidic solutions

The formally triply-bonded nonachlorodimetallates [W2(μ-Cl)3Cl6]3- (6) and [Re2(μ-Cl)3Cl6]− (8) undergo a two-electron homogeneous reduction by the chromous or vanadous ions to give the quadruply-bonded species [W2Cl8]4- (4) and [Re2Cl8]2- (7). In aq. HCl solutions complex 6 is an effective catalyst for the anaerobic oxidation of CrII and VII to CrIII and VIII with simultaneous dihydrogen formation.

Redox chemistry of the[Re3(µ-Cl)3X9]3- halides (X = Cl or Br);isolation and structural characterization of the[{Re3(µ-Cl)3Br6(H2O)(µ-O)}2]2- cluster anion

The triangulo Re 3 9+ cluster [Re 3 (µ-Cl) 3 X 9 ] 3- (X = Cl 1a or Br 1b) in concentrated aqueous hydrohalogenic acid solutions underwent a facile one-electron reduction by various reducing agents (VCl 2 ·4H 2 O, Sn–SnCl 2 or Hg) to give the air-sensitive Re 3 8+ anion [Re 3 (µ-Cl) 3 X 9-n (H 2 O) n ] (4-n) - (X = Cl 2a or Br 2b), where n may be 1; the diamagnetism and EPR silence of this compound indicate that it may exist as a dimer with a direct or indirect rhenium–rhenium bond linking two Re 3 8+ trimetal cores. Oxidation of 2 by molecular oxygen in 6 mol dm -3 HX (X = Cl or Br) solutions yielded 1 quantitatively, whereas in the absence of acid and in aprotic solvents oxo-derivatives are formed; from 2b the hexanuclear anion [{Re 3 (µ-Cl) 3 Br 6 (H 2 O)(µ-O)} 2 ] 2- 3b was obtained whose structural characterization, as its [PPh 4 ] + salt 3c, shows that two µ-O ligands bridge two oxidized Re 3 10+ units. The structure of the Re 3 9+ cluster [Co(en) 3 ][Re 3 (µ-Cl) 3 Br 8 (H 2 O)]Br has been also determined by X-ray diffraction. The redox couple xRe 3 9+ –(Re 3 8 ) x , where x = 1 or 2, derived upon mixing 6 mol dm -3 HX (X = Cl or Br) solutions of 1 with an excess of mercury, catalyses efficiently the reduction of molecular oxygen to water.