Michael J. Bonné

Boronic acid dendrimer receptor modified nanofibrillar cellulose membranes

Cellulose nanofibrils from sisal of typically 4–5 nm diameter and ca. 250 ± 100 nm length are reconstituted into thin films of ca. 6 µm thickness (or thicker freestanding films). Pure cellulose and cellulose composite films are obtained in a solvent evaporation process. A boronic acid appended dendrimer is embedded as a receptor in the nanofibrillar cellulose membrane. The number of boronic acid binding sites is controlled by varying the dendrimer content. The electrochemical and spectrophotometric properties of the nanocomposite membrane are investigated using the probe molecule alizarin red S. Pure cellulose membranes inhibit access to the electrode. However, the presence of boronic acid receptor sites allows accumulation of alizarin red S with a Langmuirian binding constant of ca. 6000 ± 1000 M−1. The 2-electron 2-proton reduction of immobilized alizarin red S is shown to occur in a ca. 60 nm zone close to the electrode surface. With a boronic acid dendrimer modified nanofibrillar cellulose composition of 96 wt% cellulose and 4 wt% boronic acid dendrimer, the analytical range for alizarin red S in aqueous acetate buffer pH 3 is approximately 10 µM to 1 mM.

The electrochemical ion-transfer reactivity of porphyrinato metal complexes in 4-(3-phenylpropyl)pyridine | water systems

The transfer of ions between an aqueous and an organic phase is driven electrochemically at a triple phase junction graphite | 4-(3-phenylpropyl)pyridine | aqueous electrolyte. Tetraphenylporphyrinato (TPP) metal complexes (MnTPP+, FeTPP+, CoTPP) and hemin readily dissolve in the organic 4-(3-phenylpropyl)pyridine phase and undergo oxidation/reduction processes which are coupled to liquid | liquid ion transfer. In order to maintain charge neutrality, each one-electron oxidation (reduction) process is coupled to the transfer of one anion (here PF6−, ClO4−, SCN−, NO3−, OCN−, or CN−) from the aqueous (organic) into the organic (aqueous) phase. The range of anions studied allows effects of hydrophobicity and complex formation (association of the anion to the metal center) to be explored. A preliminary kinetic scheme is developed to quantify complex formation, facilitated anion transfer, and competing cation transfer processes. The effects of the organic solvent on the ion transfer processes are explored. Very strong binding and specific effects are observed for the reversible cyanide transfer process.

Binding site control in a layer-by-layer deposited chitosan–carbon nanoparticle film electrode

Thin chitosan–carbon nanoparticle films (ca. 2 nm average thickness increase per layer) are assembled onto tin-doped indium oxide (ITO) electrode substrates in a layer-by-layer deposition process employing carbon nanoparticles of ca. 8 nm average diameter and an aqueous solution of chitosan (poly-D-glucosamine, low molecular weight, 75–85% deacetylated). Chitosan introduces amine/ammonium functionalities which are employed for the immobilization of redox systems (i) via physisorption of indigo carmine and (ii) via chemisorption of 2-methyleneanthraquinone. The number of binding sites within the chitosan–carbon nanoparticle film is controlled by changing the thickness of the film deposit or by changing the chitosan content, which is varied by changing the chitosan concentration during layer-by-layer deposition. Voltammetric characteristics and stability of the chemisorbed and physisorbed redox systems are reported as a function of pH. The physisorbed redox system is expelled from the film at a pH consistent with the pKA of chitosan (approximately 6.5). However, the 2-methyleneanthraquinone redox system remains stable even in alkaline media and only a minor inflection in the plot of midpoint potentials vs. pH indicates the film deprotonation process at the pKA of chitosan.