Measurement of Association and Dissociation Rate Constants for Lead(II)/18-Crown-6 Using Square Wave Voltammetry at a Glassy Carbon Mercury Film Electrode

Highly Selective Fluorimetric Turn-Off Detection of Copper(II) by Two Different Mechanisms in Calix[4]arene-Based Chemosensors and Chemodosimeters

Isoxazolo-pyrene tethered calix[4]arenes selectively detect copper(II) ions without interference from related perchlorate ions. The fluorescence emission of the probes, synthesised by nitrile oxide alkyne cycloaddition, and characterised by spectroscopic and crystallographic data, is rapidly reduced by Cu(II) ions. Detection limits are in the micromolar or sub-micromolar range (0.3-3.6 μM) based on a 1 : 1 sensor:analyte interaction. Voltammetric behaviour and ¹ H NMR data provide new insights into the sensing mechanism which is dependent on the calixarene substitution pattern. When the calixarene lower rim is fully substituted, Cu(II) detection occurs through a traditional chelation mechanism. In contrast, for calixarenes 1,3-disubstituted on the lower rim, detection takes place through a chemodosimetric redox reaction. The isolation of a calix[4]diquinone from the reaction with excess Cu(ClO₄ )₂ provides confirmation that the sensor-analyte interaction culminates in irreversible sensor oxidation.

Synthesis, characterization, and x-ray crystal structures of cyclam derivatives. 8. Thermodynamic and kinetic appraisal of lead(II) chelation by octadentate carbamoyl-armed macrocycles

En route toward the development of hybrid organic-inorganic extracting materials incorporating lead-selective chelators and their implementation in water purification processes, the lead(II) binding properties of three N-carbamoylmethyl-substituted 1,4,8,11-tetraazacyclotetradecanes (cyclams) have been fully investigated by spectroscopic (IR, UV-vis, MALDI-TOF MS, (1)H and (13)C NMR), X-ray crystallographic, potentiometric, and kinetic methods. Solution NMR studies revealed that the Pb(2+) ion is entrapped in a molecular cage constituted by the four macrocyclic nitrogen and four amidic oxygen atoms. Protonation and lead binding constants determined in aqueous solution were shown to be linearly dependent, so that all three derivatives possess a similar affinity at any pH value. Thermodynamic and kinetic parameters revealed the crucial role played by the intramolecular hydrogen bonds also evidenced in the crystal structure of the tetraacetamide derivative L(1), which involve the lone pair of each macrocyclic tertiary amine and one amidic hydrogen atom belonging to the appended arm. In contrast to L(1), the absence of such intramolecular interactions for N-(dimethyl)carbamoylmethyl- and N-(diethyl)carbamoylmethyl-substituted cyclams (L(2) and L(3), respectively) accounts for the 2-3 orders of magnitude enhancement of their proton and lead binding affinities. Stopped-flow kinetic measurements enabled unraveling the formation process of the three lead(II) complexes that proceeds in a single rate-limiting step according to the Eigen-Winkler mechanism, while the apparent rate constants were found to increase in the order L(3) < L(2) << L(1) as a consequence of the more acidic character of L(1). A common proton-assisted dissociation mechanism has been found for the three lead(II) complexes, which involves the rapid formation of a protonated, six-coordinate intermediate followed by either a unimolecular decomposition or a bimolecular attack of a second hydronium ion.

Self-assembly of [60]fullerene-thiol derivatives on mercury surfaces

Herein we report the first self-assembly of fullerene-thiol conjugates (1 and 2) on thin mercury films (TMF) deposited on a glassy carbon electrode (GCE). The fullerene-containing SAMs were investigated by cyclic voltammetry and water contact angle measurements. Two reversible, surface-confined redox couples were obtained for the fullerene-containing SAMs on TMF/GCE in CH(2)Cl(2) solution. The surface coverage of both fullerene derivatives 1 and 2 on TMF/GCE was measured to be in the range of (1.7-1.8) x 10(-10) mol cm(-2). Both SAMs of 1 and 2 partially blocked the electron transfer across the electrode in aqueous solution. The contact angle measurements performed on TMFs clearly showed an enhancement of the surface hydrophobicity upon formation of the fullerene-containing monolayer.