Electrochemical Properties of

A regenerable ruthenium tetraammine nitrosyl complex immobilized on a modified silica gel surface: preparation and studies of nitric oxide release and nitrite-to-NO conversion

Silica gel bearing isonicotinamide groups was prepared by further modification of 3-aminopropyl-functionalized silica by a reaction with isonicotinic acid and 1,3-dicyclohexylcarbodiimide to yield 3-isonicotinamidepropyl-functionalized silica gel (ISNPS). This support was characterized by means of infrared spectroscopy, elemental analysis, and specific surface area. The ISNPS was used to immobilize the [Ru(NH(3))(4)SO(3)] moiety by reaction with trans-[Ru(NH(3))(4)(SO(2))Cl]Cl, yielding [Si(CH(2))(3)(isn)Ru(NH(3))(4)(SO(3))]. The related immobilized [Si(CH(2))(3)(isn)Ru(NH(3))(4)(L)](3+/2+) (L=SO(2), SO(2-)(4), OH(2), and NO) complexes were prepared and characterized by means of UV-vis and IR spectroscopy, as well as by cyclic voltammetry. Syntheses of the nitrosyl complex were performed by reaction of the immobilized ruthenium ammine [Si(CH(2))(3)(isn)Ru(NH(3))(4)(OH(2))](2+) with nitrite in acid or neutral (pH 7.4) solution. The similar results obtained in both ways indicate that the aqua complex was able to convert nitrite into coordinated nitrosyl. The reactivity of [Si(CH(2))(3)(isn)Ru(NH(3))(4)(NO)](3+) was investigated in order to evaluate the nitric oxide (NO) release. It was found that, upon light irradiation or chemical reduction, the immobilized nitrosyl complex was able to release NO, generating the corresponding Ru(III) or Ru(II) aqua complexes, respectively. The NO material could be regenerated from these NO-depleted materials obtained photochemically or by reduction. Regeneration was done by reaction with nitrite in aqueous solution (pH 7.4). Reduction-regeneration cycles were performed up to three times with no significant leaching of the ruthenium complex.

Design of an NO photoinduced releaser xerogel based on the controlled nitric oxide donor trans-[Ru(NO)Cl(cyclam)](PF6)2 (cyclam=1,4,8,11-tetraazacyclotetradecane)

The immobilization and properties of the nitric oxide donor trans-[Ru(NO)Cl(cyclam)](PF(6))(2), RuNO, entrapped in a silica matrix by the sol-gel process is reported herein. The entrapped nitrosyl complex was characterized by spectroscopic (UV-vis, infrared (IR), X-ray photoelectron, and (13)C and (29)Si MAS NMR) and electrochemical techniques. The entrapped species exhibit one characteristic absorption band in the UV-vis region of the electronic spectrum at 354 nm and one IR nu(NO) stretching band at 1865 cm(-1), as does the RuNO species in aqueous solution. Our results show that trans-[Ru(NO)Cl(cyclam)](PF(6))(2) can be entrapped in a SiO(2) matrix with preservation of the molecular structure. However, in a SiO(2)/SiNH(2) matrix, the complex undergoes a nucleophilic attack by the amine group at the nitrosonium. Irradiation of the complex, entrapped in the SiO(2) matrix, with light of 334 nm, resulted in NO release. The material was regenerated to its initial nitrosyl form by reaction with nitric oxide.

Immobilization of the [RuII(edta)NO+] Ion on the surface of functionalized silica gel

The reaction of NO and the immobilized dimer complex (edta)(2)Ru(2)(III(1/2),III(1/2)) on silica gel chemically modified with [3-(2-aminoethyl)aminopropyl]trimethoxysilane (AEATS) produces the corresponding immobilized nitrosyl complex AEATS/Ru(II)NO(+). This compound, a monomer, was obtained by reducing the immobilized ruthenium dimer either electrochemically or with Eu(II) and reacting this species with NO(2)(-) ions. The properties of [Ru(edta)NO](-) in solution and anchored (AEATS/Ru(II)NO(+)) on silica were compared using electrochemical (DPV, CV) and spectroscopic (IR, UV-vis, and ESR) techniques. The results indicate that immobilization does not alter the reactivity of the ruthenium complex and confirm that [Ru(edta)(H(2)O)](2)(-) may be used, either in solution or immobilized, as a catalyst for the conversion of NO(2)(-) to NO(+). Both the anchored nitrosyl complex AEATS/Ru(II)NO(+) and the [Ru(edta)NO](-) species in solution, upon one-electron reduction, liberate NO at comparable rates.

Copper (II) adsorbed on SiO2/SnO2 obtained by the sol–gel processing method: application as electrochemical sensor for ascorbic acid

With the objective of producing a material showing better conductive properties to be used as a support for electroactive species, a SiO(2)/SnO(2) mixed oxide was prepared. The procedure for SiO(2)/SnO(2) mixed oxide preparation using the sol-gel processing method, starting from tetraethylorthosilicate and SnI(4) as precursor reagents, is described. SiO(2)/SnO(2) with composition Sn=15.6 wt% and S(BET) = 525 m(2)g(-1), V(p)=0.28 mlg(-1), and D(p)= 1.5 nm, where S(BET), V(p) and D(p) are the specific surface area, the average pore volume, and the average pore diameter, respectively, was obtained. The X-ray photoelectron spectroscopy showed that the mixed oxide was thermally very stable for samples heat-treated at up to 1073 K. The Brønsted acid sites, probed with pyridine molecules for samples heat-treated at various temperatures, were chemically stable up to 473 K. Segregation of SnO(2) crystalline phase was observed at 1473 K but no crystalline phase was verified for SiO(2) at this temperature. The porous SiO(2)/SnO(2) matrix was used as base for Cu(II) immobilization and an electrode was developed for application in electrochemical detection of vitamin C in tablets.

Electrochemical Properties of a Porphyrin-Cobalt (II) Adsorbed on Silica-Titania-Phosphate Composite Surface Prepared by the Sol-Gel Method

SiO(2)/TiO(2)/phosphate was obtained by the sol-gel processing method, having the following characteristics: specific surface area S(BET)=800 m(2) g(-1), Ti=14.8 wt% and P=1.5 wt%, and ion exchange capacity of 0.58 mmol g(-1). The tetrakis(1-methyl-4-pyridyl) porphyrin ion, H(2)TmPyP(4+), was immobilized on the matrix surface by an ion exchange reaction and then metallated in situ with Co(II), resulting in SiO(2)/TiO(2)/phosphate/CoTmPyP material. The amount of CoTmPyP incorporated to the matrix was 35.0 µmol g(-1). Cyclic voltammetry studies and rotating disk electrode experiments using a carbon paste electrode made with the material were carried out. The immobilized complex catalyzed O(2) reduction to H(2)O at -0.22 V in 1 mol L(-1) KCl solution at pH 6.8. The cathodic current intensities plotted against O(2) concentrations, between 1 and 11 ppm, showed a linear correlation. Copyright 2000 Academic Press.