Stephen F. Ralph

Synthesis, characterisation and ion transport studies on polypyrrole/polyvinylphosphate conducting polymer materials

A polypyrrole/polyvinylphosphate (PPy/PVP) polymer was prepared electrochemically from aqueous solutions of pyrrole and polyvinylphosphate. The polymer was found to have a ratio of 10:1 for nitrogen to phosphorous, a water content of 28±3%, and a conductivity of 0.28 S cm−1. The polymer, as shown by SEM and AFM, has a rough amorphous morphology. Electrochemical studies using electrodes with thin polymer films indicated that oxidation/reduction of the material varied depending on whether potassium, sodium, calcium, lithium, magnesium or hydrogen phosphate ion was present. Transport of each of these ions across membranes composed of the above polymer was achieved using pulsed potential waveforms.

A mass spectrometric investigation of the binding of gold antiarthritic agents and the metabolite [Au(CN)2]− to human serum albumin

Electrospray ionisation (ESI) mass spectrometry was used to examine the reactions of the clinically used antiarthritic agent [Au(S2O3)2]3−, and AuPEt3Cl, a derivative of another clinically used agent auranofin, with human serum albumin (HSA) obtained from a human volunteer. Both compounds reacted readily with HSA to form complexes containing one or more covalently attached gold fragments. In the case of AuPEt3Cl, binding was accompanied by the loss of the chloride ligand, while for [Au(S2O3)2]3− the mass spectral data indicated binding of Au(S2O3) groups. Experiments performed using HSA with Cys34 blocked by reaction with iodoacetamide were consistent with reaction of both gold compounds with this amino acid. Separate blocking experiments using diethylpyrocarbonate and AuPEt3Cl also provided evidence for histidine residues acting as lower-affinity binding sites for this gold compound. ESI mass spectra of solutions containing [Au(S2O3)2]3− or [Au(CN)2]−, and HSA, provided evidence for the formation of protein complexes in which intact gold molecules were non-covalently bound. In the case of [Au(S2O3)2]3−, these non-covalent complexes proved to be transitory in nature. However, for [Au(CN)2]− a non-covalent complex containing a single gold molecule bound to HSA was found to be stable, and constituted the main adduct formed in solutions containing low-to-medium Au-to-HSA ratios. Evidence was also obtained for the formation of a covalent adduct in which a single Au(CN) moiety was bonded to Cys34 of the protein. AuPEt3Cl reacted to a much lower extent with HSA that had Cys34 modified by formation of a disulfide bond to added cysteine, than with unmodified HSA. This suggests that the extent of modification of the protein in vivo may have an important influence on the transport and bioavailability of gold antiarthritic drugs.

Quadruplex DNA: A Promising Drug Target for the Medicinal Inorganic Chemist

Compounds that can bind to and stabilize quadruplex DNA structures in telomeres, or induce formation of such structures from ssDNA, represent an attractive general approach to the treatment of cancer. Until recently most effort in this area has been directed towards the synthesis of organic compounds for this purpose. More recently there has been growing recognition that metal complexes offer a number of potential advantages for the preparation of lead complexes that bind with high affinity and selectivity for quadruplex DNA. This review seeks to discuss the work that has been reported in this area to date. While most early studies focused on metal complexes of porphyrin ligands, during the past 4 years there has been a dramatic increase in the number of papers in the literature examining the potential of mononuclear complexes of a variety of other ligands, particularly Schiff base ligands and those based on phenanthroline, as quadruplex DNA binders and telomerase inhibitors. In addition, there has been growing interest in exploiting supramolecular chemistry to prepare novel multinuclear complexes that bind to this new drug target.

The effect of preparation conditions and biopolymer dispersants on the properties of SWNT buckypapers

The effect of varying preparation conditions on the properties of buckypapers made using single-walled carbon nanotubes (SWNTs) was systematically investigated. Changing the sonication time, final dispersion volume or membrane filter used to prepare SWNT–Triton X-100 buckypapers all generally had only a small influence on the density, thickness, contact angle and electrical conductivity of the resulting material. More significant changes were noted when the effects of variations in the above preparation conditions on the mechanical properties and surface morphology of SWNT–Triton X-100 buckypapers were investigated. However, the largest changes in properties were found when various biopolymers (bovine serum albumin, lysozyme, gellan gum and chitosan) were used instead of Triton X-100 to prepare dispersions from which the buckypapers were made. It was observed that the electrical conductivity of the buckypapers decreased as the molecular mass of the biopolymer dispersant used increased, whereas the mechanical properties of the materials showed significant improvements.

Electrochemically controlled transport of metal ions across polypyrrole membranes using a flow-through cell

Electrochemically facilitated transport of an aqueous mixture containing Na+, K+, Ca2+ and Mg2+ across two different conducting polymer composite membranes has been examined. The two membranes consisted of polypyrrole (PPy) doped with either polystyrenesulfonate/dodecylbenzenesulfonate (1%) (PPy/PSS/DBS) or polyvinylphosphate/dodecylbenzenesulfonate (1%) (PPy/PVP/DBS). In both cases the conducting polymer was deposited onto a platinum sputter-coated polyvinylidene fluoride filter. For both membranes, transport experiments were conducted using a flow-through cell with both pulsed potential and constant potential techniques. In addition, facilitated transport in a stirred solution cell with pulsed potential method was also investigated. The flux of Na+, K+ and Ca2+ ions was significantly higher when transport was examined using the flow-through cell and driven by application of a constant potential. In all the systems examined, the flux of metal ions followed the sequence Na+>K+>Ca2+>Mg2+. Transport of each metal ion was more facile under all conditions examined across composite membranes containing PPy/PSS/DBS. Atomic force microscopic examination of the surface of this membrane showed it to have a significantly smoother surface morphology compared to PPy/PVP/DBS.

15N and 195Pt N.M.R. Study of the Effect of Chain Length, n, on the Reactions of Amino Acids, + NH3(CH2)nCO2 -(n = 1, 2, 3), with Platinum(II) Ammine Complexes

15N and 195Pt n.m.r. have been used to study the reactions in solution of cis-Pt(15NH3)2(H20)22+ (1), cis-Pt(15NH3)2(OH)2 (2), cis-Pt(15NH3)2Cl2 (3), Pt(15NH3)3(H2O)2+ (4) and Pt(15NH3)3(OH)+ (5), with the amino acids +NH3(CH2)nCO2 - (LH) [n = 1 (glycine, glyH); n = 2 (β-alanine, βalaH), n = 3 (γ-aminobutyric acid, abaH)]. While glycine with (1) gives initially cis-Pt(NH3)2(glyH-O)(H2O)2+, with facile ring closure to Pt(NH3)2(gly- N, O) +, s-alanine and γ-aminobutyric acid with (1) give solutions containing a mixture of cis- Pt(NH3)2(LH-O)(H2O)2+, cis-Pt(NH3)2(LH-O)2 2+, and (Pt(NH3)2)2(µO,O.-LH)(µ-OH)3+, which are quite stable kinetically under mildly acid conditions. Ring closure to Pt(NH3)2(L- N, O)+ becomes increasingly difficult as n increases. At 37°C and initial pH 7, (3) with glycine gives Pt(NH3)2(gly-N, O)+, but s-alanine and γ-aminobutyric acid give predominantly cis-Pt(NH3)2Cl(LH-O)+. Compound (4) with glycine gives initially Pt(NH3)3(glyH-O)2+, which then isomerizes to Pt(NH3)3(glyH-N)2+. In corresponding reactions with /3-alanine and y-aminobutyric acid, Pt(NH3)3(LH-O)2+ is stable indefinitely under mildly acid conditions. Differences in reactivity of the amino acids with (2) and (5) in alkaline solutions may be correlated with decreasing nucleophilicity of the amine group of NH2(CH2)nCO2 -as n increases.

Synthesis and properties of a mechanically strong poly(bithiophene) composite polymer containing a polyelectrolyte dopant

Abstract Electrochemical polymerisation of 2,2′-bithiophene (BT) in the presence of a sulfated poly(β-hydroxyether) (S-PHE) yielded thin films that displayed excellent mechanical properties. Tensile strength measurements gave breaking strains ranging from 98 to 128 MPa for free standing poly(bithiophene)/sulfated poly(β-hydroxyether) (PBT/S-PHE) films, while scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies on this material revealed a uniform surface morphology, with an average distance between peaks and valleys on the surface of 1 μm. Four point probe measurements performed on free standing PBT/S-PHE indicated that they were semiconducting, with conductivities ranging from 0.2 to 0.8 S cm −1 . In propylene carbonate solution PBT/S-PHE was electroactive, with overoxidation commencing at approximately +1.35 V. Although electroinactive in aqueous solutions, PBT/S-PHE-coated electrodes were able to be used to examine the aqueous electrochemistry of electroactive solutes, such as cupric ion and ferrocyanide. All results indicate that PBT/S-PHE composite films and films are interesting candidates for a number of applications.

A new template encapsulation strategy for larger cavity metal ion cages

Stereospecific sequential condensation of paraformaldehyde and propionaldehyde with a tripodal bis(triamine)cobalt(III) template rapidly encapsulates the metal, and a subsequent facile reduction of imine functions gives an expanded cavity hexaazabicyclic cage system with unusual structural and chromophore electron properties, complemented by an exceptional stability and relatively fast CoII/III electron exchange rates.

Gold recovery using inherently conducting polymer coated textiles

The ability of inherently conducting polymer (ICP) coated textiles to recover gold metal from aqueous solutions containing [AuCl4]− was investigated. Nylon-lycra, nylon, acrylic, polyester and cotton were coated with a layer of polypyrrole (PPy) doped with 1,5-naphthalenedisulfonic acid (NDSA), 2-anthraquinonesulfonic acid (AQSA) orp-toluenesulfonic acid (pTS). Textiles coated with polyaniline (PAn) doped with chloride were also used. The highest gold capacity was displayed by PPy/NDSA/nylon-lycra, which exhibited a capacity of 115 mg Au/g coated textile, or 9700 mg Au/g polymer. Varying the underlying textile substrate or the ICP coating had a major effect on the gold capacity of the composites. Several ICP coated textiles recovered more than 90% of the gold initially present in solutions containing 10 ppm [AuCl4]− and 0.1 M HCl in less than 1 min. Both PPy/NDSA/nylon-lycra and PAn/Cl/nylon-lycra recovered approximately 60% of the gold and none of the iron present in a solution containing 1 ppm [AuCl4]−, 1000 ppm Fe3+ and 0.1 M HCl. The spontaneous and sustained recovery of gold metal from aqueous solutions containing [AuCl4]− using ICP coated textiles has good prospects as a potential future technology.

A novel enzymatic bioelectrode system combining a redox hydrogel with a carbon NanoWeb

A novel bioelectrode system has been prepared in which an enzyme and a conducting polymer hydrogel are combined in a nanostructured scaffold. The latter consists of fibres of carbon NanoWeb, grown by chemical vapour deposition onto reticulated vitreous carbon (RVC). The catalytic currents produced by this new bioelectrode system are significantly larger than those obtained using conventional electrodes.