Characterization of self-assembled monolayers of iron and cobalt octaalkylthiosubstituted phthalocyanines and their use in nitrite electrocatalytic oxidation

Cobalt and iron phenylthiosubstituted phthalocyanines have been deposited on Au electrode surfaces through the self-assembled monolayer (SAM) technique. The so formed layers were studied using voltammetric and impedance techniques. These SAMs blocked a number of Faradic processes and electrocatalyzed the oxidation of nitrite. The electrocatalytic parameters of the cobalt and iron phenylthiosubstituted phthalocyanines deposited on Au electrodes in nitrite solution were studied. Nitrite overpotentials which are lower than ever reported were obtained in this work for the iron phenylthiosubstituted phthalocyanines with very high stability.     

Characterization of manganese tetraarylthiosubstituted phthalocyanines self assembled monolayers

Manganese tetraarylthiosubstituted phthalocyanines (complexes 1-5) have been deposited on Au electrode surfaces through the self assembled monolayer (SAM) technique. SAM characteristics reported in this work are: ion barrier factor (∼1); interfacial capacitance (303-539 μF cm⁻²) and surface coverage (1.06 × 10⁻¹⁰-2.80 × 10⁻¹⁰ mol cm⁻²). Atomic force microscopy was employed in characterizing a SAM. SAMs of complexes 1-5 were employed to detect l-cysteine (with limit of detection ranging from 2.83 × 10⁻⁷ to 3.14 × 10⁻⁷ M at potentials of 0.68-0.75 V vs. Ag|AgCl) and nitrite (limit of detection ranging from 1.78 × 10⁻⁷ to 3.02 × 10⁻⁷ M at potentials of 0.69-0.76 V vs. Ag|AgCl).     

Electroanalysis of thiocyanate using a novel glassy carbon electrode modified by aryl radicals and cobalt tetracarboxyphthalocyanine

Electrochemical grafting of 4-nitrobenzenediazonium tetrafluoroborate onto a glassy carbon electrode (GCE) results in the formation of a nitrophenyl radical, which reacts with the surface to form a covalent bond (grafting) and results in a nitrophenyl modified electrode. The nitro group is electrochemically reduced to a NH₂ group. Cobalt tetracarboxyphthalocyanine (CoTCPc) complex is then attached to the NH₂ group using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and N-hydroxysuccinimide (NHS) as coupling agents. The new CoTCPc modified electrode was characterized using cyclic voltammetry and then employed for the catalytic oxidation of thiocyanate.     

Immobilization of tetra-amine substituted metallophthalocyanines at gold surfaces modified with mercaptopropionic acid or DTSP-SAMs

This paper shows that amine substituted cobalt phthalocyanine (CoTAPc) can be deposited on gold surfaces by using an interconnecting layer of a self-assembled monolayer (SAM) of mercaptopropionic acid or Lomant's reagent (dithiobis(N-succinimidyl propionate) (DTSP)). In both cases the new bond formed is obtained by the creation of an amide. The layers were characterized by electrochemistry and showed high coverage fractions (near 100%). Reductive and oxidative desorption of the SAMs limit the useful potential window from −0.6 to +0.5 V versus Ag|AgCl. The SAM-CoTAPc layers show electrocatalytic activities towards oxygen reduction through the Co(I) central metal ion. The amount of CoTAPc molecules deposited (obtained from the Co central metal ion activity in nitrogen purged solutions) revealed that the CoTAPc molecules are bonded in a perpendicular manner at the surface. Taking into account a surface of 200 Å² for a flatly bonded MPc, this should result in a four times less amount of deposited CoTAPc compared to the experimental value obtained. Both methods showed good results and promising long-term stability and will be interesting tools for further research in surface modification and sensor development.