Electrocatalytic oxidation of nitrite by tetra-substituted oxotitanium(IV) phthalocyanines adsorbed or polymerised on glassy carbon electrode

Multiple Pulse Amperometry-An Antifouling Approach for Nitrite Determination Using Carbon Fiber Microelectrodes

Nitrite is a ubiquitous pollutant in modern society. Developing new strategies for its determination is very important, and electroanalytical methods present outstanding performance on this task. However, the use of bare electrodes is not recommended because of their predisposition to poisoning and passivation. We herein report a procedure to overcome these limitations on carbon fiber microelectrodes through pulsed amperometry. A three-pulse amperometry approach was used to reduce the current decay from 47% (after 20 min under constant potential) to virtually 0%. Repeatability and reproducibility were found to have an RSD lower than 0.5% and 7%, respectively. Tap water and synthetic inorganic saliva samples were fortified with nitrite, and the results obtained with the proposed sensor were in good agreement with the amount added.

Four Dibutylamino Substituents Are Better Than Eight in Modulating the Electronic Structure and Third-Order Nonlinear-Optical Properties of Phthalocyanines

2(3),9(10),16(17),23(24)-Tetrakis(dibutylamino)phthalocyanine compounds M{Pc[N(C4H9)2]4} (1-5; M = 2H, Mg, Ni, Cu, Zn) were prepared and characterized by a range of spectroscopic methods in addition to elemental analysis. Electrochemical and electronic absorption spectroscopic studies revealed the more effective conjugation of the nitrogen lone pair of electrons in the dibutylamino side chains with the central phthalocyanine π system in M{Pc[N(C4H9)2]4} than in M{Pc[N(C4H9)2]8}, which, in turn, results in superior third-order nonlinear-optical (NLO) properties of H2{Pc[N(C4H9)2]4} (1) over H2{Pc[N(C4H9)2]8}, as revealed by the obviously larger effective imaginary third-order molecular hyperpolarizability (Im{χ((3))}) of 6.5 × 10(-11) esu for the former species than for the latter one with a value of 3.4 × 10(-11) esu. This is well rationalized on the basis of both structural and theoretical calculation results. The present result seems to represent the first effort toward directly connecting the peripheral functional substituents, electronic structures, and NLO functionality together for phthalocyanine molecular materials, which will be helpful for the development of functional phthalocyanine materials via molecular design and synthesis even through only tuning of the peripheral functional groups.

Effects of the number of ring substituents of cobalt carboxyphthalocyanines on the electrocatalytic detection of nitrite, cysteine and melatonin

Cobalt phthalocyanine (CoPc), cobalt tetracarboxy phthalocyanine (CoTCPc) and cobalt octacarboxy phthalocyanine (CoOCPc), adsorbed onto glassy carbon electrodes, have been used for the electrocatalytic detection of nitrite, L-cysteine and melatonin. The modified electrodes electrocatalytically detected nitrite around 800 mV vs. Ag|AgCl , a value less positive compared to that of an unmodified glassy carbon electrode (at 950 mV vs. Ag|AgCl ) and also gave detection limits in the 10-7 M range for nitrite detection. L-cysteine was detected by the modified electrodes at potentials between 0.50 to 0.65 V vs. Ag|AgCl , with L-cysteine detection limits also in the 10-7 M range. The detection limits for melatonin ranged from 10-7 to 10-6 M. CoPc-modified electrodes displayed good separation of interferents (tryptophan and ascorbic acid) in the presence of melatonin. Analyses of commercial melatonin tablets using modified electrodes gave excellent agreement with manufacturer's value for all modified electrodes of this work.

Electrocatalytic and photosensitizing behavior of metallophthalocyanine complexes

Electrocatalytic or photosensitizing (photocatalytic) properties of metallophthalocyanine (MPc) complexes are dependent on the central metal. Electrocatalytic behavior is observed for electroactive central metals such as Co , Mn and Fe , whereas photosensitizing behavior is observed for diamagnetic metals such as Al , Zn and Si . In the presence of nanoparticles such as quantum dots, the photosensitizing behavior of MPc complexes is improved. Carbon nanotubes enhance the electrocatalytic behavior of MPc complexes.

The key role of peripheral substituents in the chemistry of phthalocyanines and their analogs

The preparation and optical properties of peripherally substituted phthalocyanines and their analogs (i.e. naphthalocyanines, anthracyanines, aza-analogs of phthalocyanines, and tetraazaporphyrins) have been widely discussed. This review highlights methodologies that have been published in poorly known and mostly unavailable Russian journals.

Voltammetric and spectroelectrochemical characterization and electrocatalytic application of metallophthalocyanines carrying pendant bulky units

In this work, voltammetric, spectroelectrochemical, and electrocatalytic properties of the metallophthalocyanines bearing four chloro and four biphenyl-malonic ester bulky groups were investigated. Voltammetric and spectroelectrochemical measurements of the metallophthalocyanines show that while cobalt phthalocyanine presents both metal-based and ring-based redox processes, all other complexes give only ring-based reduction and oxidation processes. The redox processes have generally diffusion-controlled, reversible and one-electron transferred mechanisms. Cobalt phthalocyanine electrocoated easily on the glassy carbon working electrode during the repeating cycles, a very useful feature for application in fabrication of thin films. Electrocatalytic activity of cobalt phthalocyanine to hydrogen evolution reaction was studied in solution titrated with perchloric acid and on glassy carbon electrode modified with cobalt phthalocyanine in aqueous solution. Electrocatalytic measurements show that cobalt phthalocyanine has significant catalytic activities towards hydrogen evolution reaction. Moreover, the catalytic activity of the complex enhanced significantly when the complex was incorporated into the cation exchange Nafion polymeric matrix.

Edge plane pyrolytic graphite electrode covalently modified with 2-anthraquinonyl groups: theory and experiment

An edge plane pyrolitic graphite (EPPG) electrode was modified by electrochemical reduction of anthraquinone-2-diazonium tetrafluoroborate (AQ2-N(2)(+)BF(4)(-)), giving an EPPG-AQ2-modified electrode of a surface coverage below a monolayer. Cyclic voltammograms simulated using Marcus-Hush theory for 2e(-) process assuming a uniform surface gave unrealistically low values of reorganisation energies, λ, for both electron transfer steps. Subsequently, two models of surface inhomogeneity based on Marcus-Hush theory were investigated: a distribution of formal potentials, E', and a distribution of electron tunneling distances, r(0). The simulation of cyclic voltammograms involving the distribution of formal potentials showed a better fit than the simulation with the distribution of tunneling distances. Importantly the reorganization energies used for the simulation of E' distribution were similar to the literature values for adsorbed species.