Glassy carbon electrodes modified with single walled carbon nanotubes and cobalt phthalocyanine and nickel tetrasulfonated phthalocyanine: Highly stable new hybrids with enhanced electrocatalytic performances

The inorganic chemistry of the cobalt corrinoids - an update

The inorganic chemistry of the cobalt corrinoids, derivatives of vitamin B₁₂, is reviewed, with particular emphasis on equilibrium constants for, and kinetics of, their axial ligand substitution reactions. The role the corrin ligand plays in controlling and modifying the properties of the metal ion is emphasised. Other aspects of the chemistry of these compounds, including their structure, corrinoid complexes with metals other than cobalt, the redox chemistry of the cobalt corrinoids and their chemical redox reactions, and their photochemistry are discussed. Their role as catalysts in non-biological reactions and aspects of their organometallic chemistry are briefly mentioned. Particular mention is made of the role that computational methods - and especially DFT calculations - have played in developing our understanding of the inorganic chemistry of these compounds. A brief overview of the biological chemistry of the B₁₂-dependent enzymes is also given for the reader's convenience.

Electrocatalytic behavior of single walled carbon nanotubes with alkylthio-substituted cobalt binuclear phthalocyanines towards oxidation of 4-chlorophenols

This work describes the adsorption of synthesized cobalt mono (CoPc) and binuclear phthalocyanines (CoBiPc) with single walled carbon nanotubes (SWCNT) to form SWCNT-CoPc or SWCNT-CoBiPc as non-covalent conjugates onto glassy carbon electrodes (GCE). The cobalt complexes and their SWCNT-conjugate-modified electrodes were studied for their electrocatalytic oxidation towards 4-chlorophenol. All modified electrodes showed improved catalytic current and stability towards the detection of 4-chlorophenol. The best activity was observed for the SWCNT-CoBiPc2 system in terms of current response and the SWCNT-CoBiPc1 system in terms of resistance to electrode fouling.

Catalytic selectivity of metallophthalocyanines for electrochemical nitric oxide sensing

The catalytic properties of metallophthalocyanine (MPc) complexes have long been applied to electrochemical sensing of nitric oxide (NO) to amplify sensitivity and reduce the substantial overpotential required for NO oxidation. The latter point has significant ramifications for in situ amperometric detection, as large working potentials oxidize biological interferents (e.g., nitrite, L-ascorbate, and carbon monoxide). Herein, we sought to isolate and quantify, for the first time, the selectivity benefits of MPc modification of glassy carbon electrodes. A series of the most catalytically active MPc complexes towards NO, including Fe(II)Pc, Co(II)Pc, Ni(II)Pc, and Zn(II)Pc, was selected and probed for NO sensing ability under both differential pulse voltammetry (DPV) and constant potential amperometry (CPA). Data from DPV measurements provided information with respect to MPc signal sensitivity amplification (~1.5×) and peak shifting (100-200 mV). Iron-Pc exerted the most specific catalytic activity towards NO over nitrite. Catalyst-enabled reduction of the working potential under CPA was found to improve selectivity for NO over high potential interferents, regardless of MPc. However, impaired selectivity against low potential interferents was also noted.

Iron Phthalocyanine Decorated Nitrogen-Doped Graphene Biosensing Platform for Real-Time Detection of Nitric Oxide Released from Living Cells

Nitric oxide (NO) is a transcellular messenger involved in many physiological and pathological processes, but the real-time detection of NO in biological systems is still challenging due to its rapid diffusion, low concentration, and short half-life. A novel electrochemical sensing platform based on iron phthalocyanine (FePc) functionalized nitrogen-doped graphene (N-G) nanocomposites was constructed to achieve in situ monitoring of NO released from living cells on the sensing layer. By taking advantage of the synergetic effect of N-G and FePc nanocomposites, the N-G/FePc sensor displays excellent electrocatalytic activity toward NO with a high sensitivity of 0.21 μA μM^-1 cm^-2 and a low detection limit of 180 nmol L^-1. The following layer-by-layer assembly of poly-l-lysine (PLL) and Nafion further improved the capacity of resisting disturbance as well as the biocompatibility of the sensing interface. The flexible design of the ITO substrate based electrode provides a more controlled cellular biosensing system which could capture molecular signals immediately after NO released from human umbilical vein endothelial cells (HUVECs). The exhibited additional features of high sensitivity, rapid response, and ease of operation implies that the proposed N-G/FePc/Nafion/PLL ITO biosensor is a promising powerful platform in various complex biological systems.

Comparison of the catalytic activity for O2reduction of Fe and Co MN4 adsorbed on graphite electrodes and on carbon nanotubes

Metal phthalocyanines adsorbed on CNTs deliver much higher electrocatalytic currents for the ORR because of the high concentration of catalyst.

An effect of the substituent position and metal type on the electropolymerization properties of chalcone substituted metallophthalocyanines

Cobalt(ii) and manganese(iii) phthalocyanines bearing peripherally and non-peripherally tetra substituted {(2E)-3-[4-(dimethylamino)phenyl]prop-2-enoyl}phenoxy groups were synthesized by cyclotetramerization of the phthalonitrile derivatives and their electrochemical properties were examined using CV and SWV techniques for the first time.

Phthalocyanine-based hybrid materials for chemosensing

In the present review, we show how the chemical variability of phthalocyanines allowed to synthesize a broad range of hybrid materials. The combination of phthalocyanines or related derivatives with polymers or carbonaceous materials led to efficient chemical sensors. It is shown how the incorporation of macrocyclic molecules in hybrid materials highly modifies the structural and morphological characteristics of the materials. Rugosity, specific surface and porosity being key parameters in the analyte-sensing material interactions, these modifications highly improve the performance of chemical sensors. This is the reason why they are particularly promising materials for the development of new chemical sensors, associated with electrochemical, conductometric or optical transducers.

Self-assembly of tetrakis (3-trifluoromethylphenoxy) phthalocyaninato cobalt(II) on multiwalled carbon nanotubes and their amperometric sensing application for nitrite

In this work, the soluble cobalt phthalocyanine functionalized multiwalled carbon nanotubes (MWCNTs) are synthesized by π-π stacking interaction between tetrakis (3-trifluoromethylphenoxy) phthalocyaninato cobalt(II) (CoPcF) complex and MWCNTs. The physical properties of CoPcF-MWCNTs hybrids are evaluated using spectroscopy (UV-vis, XPS, and Raman) and electron microscopy (TEM and SEM). Subsequently, an amperometric nitrite electrochemical sensor is designed by immobilizing CoPcF-MWCNTs hybrids on the glassy carbon electrode. The immobilized CoPcF complex shows the fast electron transfer rate and excellent electrocatalytic activity for the oxidation of nitrite. Under optimum experimental conditions, the proposed nitrite electrochemical sensor shows the fast response (less than 2 s), wide linear range (9.6 × 10(-8) to 3.4 × 10(-4) M) and low detection limit (6.2 × 10(-8) M) because of the good mass transport, fast electron transfer rate, and excellent electrocatalytic activity.

Carbon nanotubes and metalloporphyrins and metallophthalocyanines-based materials for electroanalysis

We discuss here the state of the art on hybrid materials made from single (SWCNT) or multi (MWCNT) walled carbon nanotubes and MN4complexes such as metalloporphyrins and metallophthalocyanines. The hybrid materials have been characterized by several methods such as cyclic voltammetry (CV), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and scanning electrochemical microscropy (SECM). The materials are employed for electrocatalysis of reactions such as oxygen and hydrogen peroxide reduction, nitric oxide oxidation, oxidation of thiols and other pollutants.

Metallophthalocyanine/carbon nanotube hybrids: extending applications to microbial fuel cells

Pioneering work by Nyokong and others have highlighted the potential benefits for improved electron transfer processes and catalysis of hybrid configurations of metallophthalocyanines with carbon nanotubes. Here we examine the practical application of such hybrid configurations in an Enterobacter cloacae microbial fuel cell. Electrochemical investigations at glassy carbon electrodes (GCEs) showed that FePc and FePc :multiwalled carbon nanotube (MWCNT) hybrid surface modifications display significant oxygen reduction reaction electrocatalytic properties compared to either MWCNT-modified or bare GCE surfaces throughout acidic- to moderately-alkaline pHs. Significant stabilization of the current response at FePc :MWCNT surfaces are notable throughout the pH range, compared to GCE surfaces modified with FePc alone. Corresponding results were obtained for surface modifications of bare carbon paper (BCP) cathodes in a microbial fuel cell where power density increases were observed in the order: Pt > FePc :MWCNT > FePc > MWCNT > BCP. A synergistic combination of simple treatments such as increased ionic strength (300 mM NaCl ), temperature (35 °C), and agitation of the anode chamber in this MFC configuration increased the power density to 2.5 times greater than that achieved at platinised cathode configurations under non-optimised conditions, achieving peak power densities of 212 mW.m-2. The long-term stability of the MFC was assessed over 55 days. Surprisingly, the majority of signal loss over extended MFC operation was attributed, in this study, to fouling of the Nafion® PEM membrane rather than either leaching/fouling of the catalysts from the electrodes or nutrient depletion in the anode over the time periods examined.

Single walled carbon nanotubes functionalized with nickel phthalocyanines: effects of point of substitution and nature of functionalization on the electro-oxidation of 4-chlorophenol

In this work we report on electrochemical behavior of nickel phthalocyanine derivatives tetrasubstituted peripherally and non-peripherally with hydroxy and used to modify single walled carbon nanotubes. Nickel phthalocyanine complex octasubstituted at the peripheral positions with hydroxy groups was also used to modify single walled carbon nanotubes. Nickel phthalocyanine complex tetrasubstituted with amino groups at peripheral position was covalently and non-covalently linked to single walled carbon nanotubes. All the conjugates of nickel phthalocyanine derivatives with single walled carbon nanotubes were used for the electro oxidation of 4-chlorophenol. The nickel phthalocyanine octabsubstituted with hydroxy groups at the non-peripheral positions gave the best current response and the best resistance against electrode fouling for the oxidation of 4-chlorophenol.

CHARACTERIZATION OF QUANTUM DOTS, SINGLE WALLED CARBON NANOTUBES AND NICKEL OCTADECYLPHTHALOCYANINE CONJUGATES

In this work nickel octadecylphthalocyanine (NiPc(C10H21)8) and cadmium telluride quantum dots (QDs) capped with thioglycolic acid (TGA) are adsorbed on single walled carbon nanotubes (SWCNT) to form NiPc(C10H21)8 -SWCNT-QDs conjugate. X-ray photoelectron, ultra violet/visible and Raman spectroscopies are used to characterize the conjugate. SWCNT, poly- Ni(O)Pc(C10H21)8 , NiPc(C10H21)8 -SWCNT and NiPc(C10H21)8 -SWCNT-QDs complexes are used to modify glassy carbon electrode (GCE) and used for the electro-oxidation of pentachlorophenol as a test molecule. NiPc(C10H21)8 -SWCNT-QDs electrode gave the best detection current for pentachlorophenol.

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.

Nanostructured cobalt phthalocyanine single-walled carbon nanotube platform: electron transport and electrocatalytic activity on epinephrine

The fabrication, characterization and application of edge-plane pyrolytic graphite electrode modified with acid-functionalized single-walled carbon nanotubes, nanostructured cobalt phthalocyanine and a mixture of both, towards epinephrine detection and analysis are described. The morphological features of the films were evaluated using atomic force microscopy (AFM). Electrochemistry of these electrodes in [ Fe ( CN )6]3−/4− using cyclic voltammetry and electrochemical impedance spectroscopy showed higher peak current responses with accompanying low electron-transfer resistances in comparison to the bare electrode. The edge-plane pyrolytic graphite-single-walled carbon nanotubes-nanostructured cobalt phthalocyanine electrode exhibited good electrocatalytic activity towards epinephrine oxidation with enhanced peak currents. Analytical studies using edge-plane pyrolytic graphite-single-walled carbon nanotubes-nanostructured cobalt phthalocyanine electrode proved that the electrode is suitable for sensitivity determination of epinephrine in pH 5 conditions judging from the good sensitivity (8.71 ± 0.31 A.M−1), and limit of detection (0.04 µM) and quantification (1.31 µM) obtained. Determination of EP in the absence and presence of ascorbic acid in phosphate buffer pH 5 conditions was carried out and it was established that the presence of AA did not interfere in EP analysis. Rotating disk electrode experiments proved that the catalytic rate constant was 2.28 × 1016 mM−1.s−1.

Electrochemical nitric oxide sensors for physiological measurements

The important biological roles of nitric oxide (NO) have prompted the development of analytical techniques capable of sensitive and selective detection of NO. Electrochemical sensing, more than any other NO detection method, embodies the parameters necessary for quantifying NO in challenging physiological environments such as blood and the brain. In this tutorial review, we provide a broad overview of the field of electrochemical NO sensors, including design, fabrication, and analytical performance characteristics. Both electrochemical sensors and biological applications are detailed.

Amperometric biosensor based on tyrosinase immobilized onto multiwalled carbon nanotubes-cobalt phthalocyanine-silk fibroin film and its application to determine bisphenol A

An amperometric bisphenol A (BPA) biosensor was fabricated by immobilizing tyrosinase on multiwalled carbon nanotubes (MWNTs)-cobalt phthalocyanine (CoPc)-silk fibroin (SF) composite modified glassy carbon electrode (GCE). In MWNTs-CoPc-SF composite film, SF provided a biocompatible microenvironment for the tyrosinase to retain its bioactivity, MWNTs possessed excellent inherent conductivity to enhance the electron transfer rate and CoPc showed good electrocatalytic activity to electrooxidation of BPA. The cyclic voltammogram of BPA at this biosensor exhibited a well defined anodic peak at 0.625 V. Compared with bare GCE, the oxidation signal of BPA significantly increased; therefore, this oxidation signal was used to determine BPA. The effect factors were optimized and the electrochemical parameters were calculated. The possible oxidation mechanism was also discussed. Under optimum conditions, the oxidation current was proportional to BPA concentration in the range from 5.0 x 10(-8) to 3.0 x 10(-6) M with correlation coefficient of 0.9979 and detection limit of 3.0 x 10(-8) M (S/N=3). The proposed method was successfully applied to determine BPA in plastic products and the recovery was in the range from 95.36% to 104.39%.

Multi-walled carbon nanotubes with immobilised cobalt nanoparticle for modification of glassy carbon electrode: application to sensitive voltammetric determination of thioridazine

Multi-walled carbon nanotubes (MWCNTs) were immobilised with cobalt nanoparticles and analyzed by transmission electron microscopy. This modification procedure substantially improved colloidal dispersion of the immobilised MWCNTs in water and organic solvents, yielding uniform and stable thin films for modification of the glassy carbon electrode surface. The modified electrode showed an efficient catalytic role for the electrochemical oxidation of thioridazine (TR), leading to remarkable decrease in its oxidation overpotential of approximately 100 mV and enhancement of the kinetics of the electrode reaction, which can be confirmed by increasing in the peak current and sharpness of the peak. A remarkable enhancement in microscopic area of the electrode together with the catalytic role of the composite modifier resulted in a considerable increase of the peak current (approximately 55 times), and negative shift in the oxidation potential of TR. The effect of the thickness of the modifier on the GCE surface was optimized by monitoring its cyclic voltammetric responses toward TR. The mechanism of the electrocatalytic process on the surface of the modified electrode was analyzed by obtaining the cyclic voltammograms at various potential sweep rates and pHs of the buffer solutions. Differential pulse voltammetry was applied as a very sensitive analytical method for the determination of sub-micromolar amounts of TR. A linear dynamic range of 5.0 x 10(-7) to 1.0 x 10(-4)M with a detection limit of 5.0 x 10(-8)M TR was obtained. The prepared modified electrode shows several advantages such as simple preparation method, high stability and uniformity in the composite film, high sensitivity, and excellent catalytic activity in physiological conditions, long-term stability and remarkable voltammetric reproducibility. These excellent properties make the prepared sensor suitable for analysis in pharmaceutical and clinical preparations. The modified electrode was successfully applied for the accurate determination of minor amounts of TR in pharmaceutical and clinical preparations.

Electrocatalytic Detection of Amitrole on the Multi-Walled Carbon Nanotube - Iron (II) tetra-aminophthalocyanine Platform

It is shown that iron(II) tetra-aminophthalocyanine complex electropolymerized onto a multi-walled carbon nanotube-modified basal plane pyrolytic graphite electrode greatly enhanced the electrocatalytic detetion of amitrole (a toxic herbicide), resulting in a very low detection limit (0.5 nM) and excellent sensitivity of 8.80±0.44 μA/nM, compared to any known work reported so far. The electrocatalytic detection of amitrole at this electrode occurred at less positive potential (∼0.3 V vs Ag|ACl) and also revealed a typical coupled chemical reaction. The mechanism for this response is proposed. The electrode gave satisfactory selectivity to amitrole in the presence of other potential interfering pesticides in aqueous solutions.