Maher Kalaji

Spectroelectrochemical and electrical characterization of low bandgap polymers

Abstract In situ FT-IR spectroscopy, and d.c. and a.c. electrical measurements were used to characterize an electronically conducting polymer prepared from the electropolymerization of a bridged dithienyl monomer. Electronic absorption bands were observed during both n- and p- doping processes. The solid state data showed that the metal|polymer|metal diodes displayed no rectification although capacitance and loss data showed a strong frequency dispersion characteristic of a Schottky diode.

Redox induced orientational changes in a series of short chain ferrocenyl alkyl thiols self-assembled on gold(111) electrodes

Abstract A series of short chain alkyl thiols (n=3–10) with a ferrocene terminal group were allowed to form organised monolayers at gold(111) surfaces. The redox activity of the monolayers was monitored using cyclic voltammetry and subtractively normalised interfacial Fourier transform infrared spectroscopy (SNIFTIRS). The in situ infrared spectra show that the oxidation of the ferrocene groups in the monolayers studied is accompanied by a rotation of the ferrocene groups towards a position where the plane of the cyclopentadienyl rings moves to a position normal to the surface of the electrode. Furthermore, electrochemical and spectroscopic data indicate that monolayers with longer alkyl chains are more ordered than the shorter analogues. A trend was observed in which the rate of adsorption and the surface coverage vary between the length of the alkyl chains.

Electrosynthesis and characterization of poly(1,3-dimethoxybenzene)

Abstract Poly(1,3-dimethoxybenzene) was synthesized via the electrochemical oxidation of the corresponding monomer (1,3-dimethoxybenzene) in an acetonitrile solution containing tetrabutylammonium tetrafluoroborate (Bu 4 NBF 4 ) and characterized spectroscopically. The resulting polymer is insoluble in all common solvents. Structural characterization using Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopies suggests that this material has a polymeric structure in which the methoxy groups are retained. Spectroscopic results are in good agreement with theoretical calculations based on a proposed structure. Electrical conductivity at room temperature is 2.5 × 10 −4 S cm −1 .

The study of conducting polymers for use as redox supercapacitors

Abstract Electronically conducting polymers have been prepared from bridged dithienyl derived monomers. These monomers have been designed in order to yield polymers that possess a low bandgap (c.a. 1 eV). Recently low bandgap polymers have been targeted for use as the active material in electrochemical capacitors, better known as Supercapacitors. We report the characterisation of these polymers using cyclic voltammetry, electrochemical impedance spectroscopy and discharge cycles.

Frequency resolved transmittance measurements on polyaniline films

Interest in electrochemically synthesised conducting polymers has increased enormously in recent years, and polyaniline (PANI) has received particular attention because it appears to be more stable than many other systems. One of the main objectives of the current research effort in this area is to obtain information about the structural and electronic properties of PANI by using in-situ techniques such as ESR [l-3], IR [4-61 and UV/visible [3,7] spectroscopy to supplement conventional electrochemical measurements. A key element of this approach should be the correlation between the electrical and optical response of polymer films under a variety of experimental conditions, but the application of spectroscopic methods to the PAN1 system has been restricted largely to steady-state or potentiodynamic conditions, with the main emphasis being placed on the relationship between spectroscopic properties and the potential or the state of charge of the film. The purpose of the present communication is to show that the application of UV/visible spectroscopy can be extended to consider the periodic response. It will be shown that comparison of the potential modulated transmittance or absorbance with the corresponding periodic electrical response (i.e. the impedance 2 or admittance p) of the film leads to resolution of the controversy concerning the role of so-called “charging current” contribution [8,9] to the voltammetric response of PANI. Further details of this study are presented elsewhere [lo].

Nickel dithiolenes containing pendant thiophene units: precursors to dithiolene-polythiophene hybrid materials{

The synthesis, electrochemical and spectroscopic properties of the new thiophene-substituted metal dithiolene complexes [Ni(b-3ted)2] (3) and [NBu4][Ni(b-3ted)2] ([NBu4][3]) are described [b-3ted = bis(3-thienyl)-1,2-ethylenedithiolene] and compared with new studies of the known compounds [Ni(b-2ted)2] (2) and [NBu4][Ni(b-2ted)2] ([NBu4][2]). X-Ray structures were determined for the neutral complexes 2 and 3 and both showed planar nickel dithiolene units with thiophene groups twisted out of the molecular plane, precluding close molecular π-stacking. Electrochemical investigations revealed two redox processes corresponding to interconversion between neutral, monoanionic and dianionic species for 3, analogous to 2. Oxidation of 0.1 mM [3]− in CH3CN was shown to give a green molecular film of 3 which, in contrast to as-prepared crystals of 3, showed significant conductivity. Electrochemical polymerisation of 3 carried out at different concentrations resulted in films; electrochemical, SNIFTIRS and UV-Vis results were consistent with incorporation of the intact metal dithiolene complex in these films. In contrast, electrochemical polymerisation of 2 gave a film charateristic of a polymerised thiophene but with no evidence of incorporation of the intact metal dithiolene complex. Copolymerisation of 3 with thiophene gave a gold-coloured electropolymerised film of significant conductivity that, upon dissolution in CH2Cl2, showed the characteristic low energy absorption of the Ni-dithiolene complex, confirming its incorporation. This copolymerisation approach offers a versatile route to the synthesis of metal dithiolene–polythiophene hybrid films.

The production of nanoparticulate ceria using reverse micelle sol gel techniques

Mesoporous ceria nanoparticles have, for the first time, been synthesized from cerium isopropoxide as precursor in a sol gel type process by controlled hydrolysis using reverse micelles. Water-filled reverse micelles have been facilitated by adding a non-ionic surfactant (TX-100) to an hydrophobic solvent (cyclohexane) above the critical micelle concentration. The detailed thermal chemistry of the gels has been studied at temperatures between 423 and 1123 K using XRD, SEM, TGA/DSC, elemental analysis and physical adsorption measurements. Calcination of gel in air produces porous nanoparticles of cerium dioxide with the fluorite structure at 823 K. Particle size and crystallinity increases with temperature along with loss of porosity indicating surface sintering and recrystallisation are taking place. Thermogravimetric analysis of ceria gel under air shows surfactant decomposition starts at ca. 500 K and is complete by ca. 700 K. Parallel calcination studies under nitrogen or argon show similar data to each other emphasising the importance of oxygen in the removal of carbonaceous material from the gels. Thus, in the absence of atmospheric O2, oxygen is instead removed from the fluorite ceria phase which is believed to result in the formation of non-stoichiometric CeO(2−x). This causes loss of crystallisation of the fluorite CeO2 phase producing glassy material rather than nanoparticles and prevents porosity developing. This also increases the diffusion limitations on carbon loss which results in C being retained in the gel until higher temperatures.

Colloidal gold modified with a genetically engineered nitroreductase: toward a novel enzyme delivery system for cancer prodrug therapy.

Directed enzyme prodrug therapy is an extensive area of research in cancer chemotherapy. Although very promising, the current directed approaches are still hampered by inefficient enzyme expression and tumor targeting. This work investigates the viability of using metal nanoparticles as a novel delivery vehicle for prodrug-activating enzymes. Using genetically incorporated amino acid sequences, a nitroreductase from E. coli was directly immobilized onto a 50 nm gold colloid, as confirmed by gel electrophoresis, DLS, and UV-vis spectroscopy. The resulting conjugates showed excellent stability in changing proton and sodium chloride environments, including PBS at 37 °C. Remarkably, the immobilized nitroreductase retained more than 99% activity to the CB1954 prodrug without the need for stabilizers. This work provides the foundation for attaching prodrug-activating enzymes to metal nanoparticles for future use in directed enzyme prodrug therapy.

Self-assembled monolayers of Vitamin B12 disulphide derivatives on gold

Using the self-assembly technique, novel monolayers on gold have been prepared from new cobyrinate dialkyl disulphide derivatives. The successful formation is proved by cyclic voltammetry and by in situ ellipsometry. The electrochemical characterisation by reductive desorption allows to estimate the surface coverage and reveals that the presence of two cobyrinates introduces some disorganisation in the monolayer. More packed and organised monolayers have been observed in systems containing only one terminal redox centre. From ellipsometric measurements a possible orientation of the cobyrinate centre in the adsorbed monolayer is modelled. The modified electrodes display electrocatalytic activity for the reduction of dissolved oxygen.

Synthesis, electrochemical properties and electropolymerization studies on 3-thienyl substituted tetrathiafulvalenes. Single-crystal X-ray structure of 4,4′,5,5′-tetrakis-(3-thienyl)-tetrathiafulvalene

Abstract The synthesis and solution electrochemical properties of two novel 3-thienyl substituted tetrathiafulvalene (TTF) donors 7 and 11 are described. The single-crystal X-ray structure of 7 is reported, which is characterized by the presence of short intermolecular SS contacts. Cyclic voltammetry of the derivatives indicates that two reversible redox waves, characteristic of TTF derivatives, are present. Attempts were made to electropolymerize the two derivatives at a platinum electrode in dichloromethane. Formation of a blue-coloured solid, characteristic of the thiophene radical cation species, was observed for one of the derivatives, but it was not possible to isolate a polymer on the working electrode. Preliminary electropolymerization studies on the TTF ‘half unit’ 6 are also reported.