Avril Williams

First-row transition metal complexes of 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate)

Abstract Reaction of 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate) with M(NO 3 ) 2 · x H 2 O (M=Mn, Co, Ni, Zn) in acetonitrile solutions produced a linear polymer [Mn(μ-C 6 H 5 C 4 O 3 )(C 6 H 5 C 4 O 3 )(H 2 O) 3 ] n ( 1 ) and a series of isomorphous monomeric complexes [M(C 6 H 5 C 4 O 3 ) 2 (H 2 O) 4 ] [M=Co ( 2 ), Ni ( 3 ), Zn ( 4 )]. The complex 1 contains octahedral manganese with each metal centre being bridged μ-1,3 by a phenylsquarate ligand to two neighbouring metal atoms and further coordinated to a pendant phenylsquarate ligand group and three aqua ligands. The isomorphous monomeric complexes 2 – 4 all contain two phenylsquarate ligand groups oriented trans to each other, but with the substituent phenyl group on the ligand oriented cis to the ligating oxygen atom. The coordination polyhedron in each of these monomers is completed by four aqua ligands. The polymeric manganese complex shows no significant antiferromagnetic coupling and no semiconductivity.

Electrochemical Aptatoxisensor Responses on Nanocomposites containing electro-deposited silver nanoparticles on poly(propyleneimine) dendrimer for the detection of microcystin-lr in freshwater

A sensitive and reagentless electrochemical aptatoxisensor was developed on cobalt (II) salicylaldiimine metallodendrimer (SDD–Co(II)) doped with electro-synthesized silver nanoparticles (AgNPs) for microcystin-LR (L, l-leucine; R, l-arginine), or MC-LR, detection in the nanomolar range. The GCE|SDD–Co(II)|AgNPs aptatoxisensor was fabricated with 5’ thiolated aptamer through self-assembly on the modified surface of the glassy carbon electrode (GCE) and the electronic response was measured using cyclic voltammetry (CV). Specific binding of MC-LR with the aptamer on GCE|SDD–Co(II)|AgNPs aptatoxisensor caused the formation of a complex that resulted in steric hindrance and electrostatic repulsion culminating in variation of the corresponding peak current of the electrochemical probe. The aptatoxisensor showed a linear response for MC-LR between 0.1 and 1.1 µg·L−1 and the calculated limit of detection (LOD) was 0.04 µg·L−1. In the detection of MC-LR in water samples, the aptatoxisensor proved to be highly sensitive and stable, performed well in the presence of interfering analog and was comparable to the conventional analytical techniques. The results demonstrate that the constructed MC-LR aptatoxisensor is a suitable device for routine quantification of MC-LR in freshwater and environmental samples.

Label Free Poly(2,5-dimethoxyaniline)–Multi-Walled Carbon Nanotubes Impedimetric Immunosensor for Fumonisin B1 Detection

An impedimetric immunosensor for fumonisin B1 (FB1) was developed from a poly(2,5-dimethoxyaniline)-multi-walled carbon nanotube (PDMA-MWCNT) composite on the surface of glassy carbon electrode (GCE). The composite was prepared electrochemically and characterized using cyclic voltammetry. The preparation of the FB1 immunosensor involved the drop-coating of a bovine serum albumin mixture of the anti-fumonisin antibody (anti-Fms) onto the composite polymer-modified GCE. The electrochemical impedance spectroscopy (EIS) responses of the FB1 immunosensor (GCE/PDMA-MWCNT/anti-Fms) have a linear range of 7 to 49 ng·L−1, and the corresponding sensitivity and detection limits are 0.272 kΩ L·ng−1 and 3.8 pg·L−1, respectively. The limit of detection of the immunosensor for certified corn sample (i.e., certified reference material) is 0.014 ppm FB1, which is in excellent agreement with the value published by the vendors and significantly more accurate than that obtained with enzyme-linked immunosorbent assay (ELISA).

The complexing properties of the phenylsquarate ligand with Ru(II), Pt(II), Gd(III) and Tb(III) ions

Abstract Reaction of 3-phenyl-4-hydroxycyclobut-3-ene-1,2-dione (phenylsquarate) with Ru(dmso)4Cl2 in acetonitrile afforded crystals of the monomeric species Ru(dmso)3Cl(H2O)(C6H5C4O3)·H2O (1) in which the ruthenium is in a slightly distorted octahedral geometry with three fac S-bonded dmso ligands. No complexation occurs when Pt(NH3)4Cl2 is reacted with the same ligand in aqueous solution; instead, the hydrogen-bonded salt [Pt(NH3)4][C6H5C4O3]2·H2O (2) is produced. The isomorphous complexes {[M(μ-C6H5C4O3)(C6H5C4O3)2(H2O)4]·H2O}n [M=Tb (3), Gd (4)] formed by the reaction of the phenylsquarate ligand with the respective metal nitrate contain eight-coordinate metal centres surrounded by two μ-1,3-bridged and two pendant phenylsquarate ligands and four aqua ligands. In the solid state, 3 and 4 form interleaved π-stacked and hydrogen-bonded sheets with pronounced hydrophobic and hydrophilic surfaces. In compounds 1–4, the phenylsquarate ligands participate in π–π interactions and exhibit multiple bond localisation, the pattern of bonding being the same in each structure.