Supramolecular Gold Nanoparticles for the Redox Recognition of Oxoanions:  Syntheses, Titrations, Stereoelectronic Effects, and Selectivity

Abstract

Stable, CH(2)Cl(2)-soluble mixed dodecanethiol/(amidoferrocenyl)alkanethiol (AFAT) gold colloids were synthesized by ligand substitution reactions from Brust's dodecanethiol gold colloids and the AFAT ligands to study the recognition and titration of oxoanions. Gold colloids were obtained with various chain lengths (C(11) and C(6) chains) of the AFAT ligand and different proportions of AFAT ligands in the colloids. Modification of the amidoferrocenyl structure [replacement of the free C(5)H(5) ferrocene ring by C(5)Me(5) (Cp) or C(5)H(4)COCH(3)] has been achieved to investigate the stereoelectronic effects on the recognition. The cyclic voltammetry of these colloids in CH(2)Cl(2) on Pt electrode shows a reversible Fe(II/III) wave with some adsorption. With AFAT ligands, a new, less electrochemically reversible wave (with some adsorption) at a potential 220 +/- 20 mV less positive than that of the initial wave appears upon titration of [n-Bu(4)N][H(2)PO(4)], and the initial wave completely disappears after addition of 1 equiv of anion, which allows its titration. The potential shift does not depend on the AFAT proportion nor on its chain length but is reduced with Cp and enhanced with C(5)H(4)COCH(3), showing the key role of the hydrogen bonding between the -NH-amido group and a terminal oxygen atom of the oxoanions. According to the Echegoyen-Kaifer model, the potential shift leads to the ratio K((+))/K((0)) of apparent association constants. In the presence of both [n-Bu(4)N][HSO(4)] and [n-Bu(4)N]Cl, a shift of the initial wave (rather than its replacement) allows an easy titration, ideally with 20-Fc. Upon addition of [n-Bu(4)N][HSO(4)] alone, a weak wave shift (30 mV) of the colloids is also observed, allowing the titration of the HSO(4)(-) anion by the colloids containing a low percentage of AFAT ligand. The Echegoyen-Kaifer model provides access to the apparent association constant K((+)) in this case for which the interaction between the anion and the neutral form of the host is not significant. With the C(5)H(4)COCH(3) modification of the amidoferrocenyl branch, a new wave appears at a potential 70 mV more positive than the initial wave, signifying a stronger interaction with this modified ligand than with the parent AFAT ligand. These colloids favorably compare with ferrocenyl dendrimers in terms of rapid synthesis and selectivity of H(2)PO(4-) over HSO(4-) and with gold surfaces for the recognition of HSO(4)(-).

Recent progress in synthesis of ferrocenyl dendrimers and their application in anion recognition

“…For example, Scheme 11. Hydrogen bonds between the amide H and the oxo-anion [9,36,37]. a selectivity trend that in consistent with the basicity order of the anions is usually observed when hydrogen bonding is the main interaction in the anion-binding process.…”

“…By forming a complex with the anions, the chemical shift (δ) of some protons of the FcDs changes, which can be detected by NMR technique [11,25,35,36]. The value of the NMR shift ( δ) reflects the binding strength with the anion and the association constants can be calculated through the EQNMR model [40].…”

Supramolekulare Chemie von Anionen: von der Erkennung zur chemischen Anwendung

“…[174] Dieselbe Gruppe baute außerdem gemischte Monoschichten aus dem ferrocenhaltigen Thiol und Dodecanthiol auf und verküpfte so Amidoferrocenylalkanthiole mit Goldnanopartikeln. [175] Beer und Mitarbeiter zeigten danach, dass eine Immobilisierung von ferrocenhaltigen Anionenrezeptoren an Goldoberflächen zu einer Verstärkung der elektrochemi- (Abbildung 65 a,b). [176] Beispielsweise erfolgt für die SAM eines Ferrocendiamids (Abbildung 65 a) bei Zugabe von Chlorid eine kathodische Verschiebung des Fc/Fc + -Redoxpaars um À100 mV im Vergleich zu einer kathodischen Verschiebung von À40 mV für den in der Elektrolytlç-sung (CH 2 Cl 2 /CH 3 CN 2:1) gelçsten Rezeptor.…”

Metal chalcogenide nanoclusters with ‘tailored’ surfaces via ‘designer’ silylated chalcogen reagents

“…Silylated ferrocenyl chalcogen reagents offer a controlled route to the formation of structurally characterized metal chalcogenolate and chalcogenide clusters and nanoclusters with multiple ferrocenyl moieties incorporated onto the surface. The assembly of ferrocenyl units onto the surface of both small and high-nuclearity clusters opens the door for a wide range of applications, including sensing and molecular electronic devices (Lebande et al 2002;Mulrooney et al 2009). …”