Comparative electrocatalytic behavior of self-assembled monolayer of thiol derivatised Co (II) phthalocyanines on gold disk, ultramicro cylinder and fiber electrodes
- Nombona, Nolwazi, Geraldo, Daniela A, Hakuzimana, Jean, Schwarz, Anne, Westbroek, Philippe, Nyokong, Tebello
- Authors: Nombona, Nolwazi , Geraldo, Daniela A , Hakuzimana, Jean , Schwarz, Anne , Westbroek, Philippe , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263488 , vital:53632 , xlink:href="https://doi.org/10.1007/s10800-008-9716-y"
- Description: This paper reports on the use of thiol derivatised cobalt phthalocyanines as self assembled monolayers (SAMs) on gold disk electrode, gold ultramicro-cylinder electrode (UMCE) and on gold coated fiber for the detection of L-cysteine. The complexes are peripherally and non-peripherally substituted with phenylthio substituents. The SAM modified electrodes showed enhancement of catalytic currents and overpotential reduction occurred on the gold modified electrodes with different geometries. Electrocatalytic oxidation of L-cysteine on SAM modified gold coated fiber was reported for the first time. The gold coated fiber and ultramicro cylinder electrode were less stable towards the electrocatalytic oxidation of cysteine compared to its oxidation on the gold disk. The gold disk electrode gave better catalytic performance in terms of stability and reduction of overpotential.
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- Authors: Nombona, Nolwazi , Geraldo, Daniela A , Hakuzimana, Jean , Schwarz, Anne , Westbroek, Philippe , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263488 , vital:53632 , xlink:href="https://doi.org/10.1007/s10800-008-9716-y"
- Description: This paper reports on the use of thiol derivatised cobalt phthalocyanines as self assembled monolayers (SAMs) on gold disk electrode, gold ultramicro-cylinder electrode (UMCE) and on gold coated fiber for the detection of L-cysteine. The complexes are peripherally and non-peripherally substituted with phenylthio substituents. The SAM modified electrodes showed enhancement of catalytic currents and overpotential reduction occurred on the gold modified electrodes with different geometries. Electrocatalytic oxidation of L-cysteine on SAM modified gold coated fiber was reported for the first time. The gold coated fiber and ultramicro cylinder electrode were less stable towards the electrocatalytic oxidation of cysteine compared to its oxidation on the gold disk. The gold disk electrode gave better catalytic performance in terms of stability and reduction of overpotential.
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Electrochemical studies of titanium, manganese and cobalt phthalocyanines
- Authors: Nombona, Nolwazi
- Date: 2009
- Subjects: Titanium , Manganese , Cobalt , Phthalocyanines , Electrochemistry , Electrodes , Self-assembly (Chemistry)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4312 , http://hdl.handle.net/10962/d1004970 , Titanium , Manganese , Cobalt , Phthalocyanines , Electrochemistry , Electrodes , Self-assembly (Chemistry)
- Description: Syntheses, spectral, electrochemical and spectroelectrochemical studies of phenylthio and amino derivatised metallophthalocyanines complexes are reported. The complexes are immobilized onto a gold macro disk, gold ultramicroelectrode and gold coated fiber electrodes via self assembly with phenylthio MPc derivatives or onto a glassy carbon electrode via electropolymerisation with amino MPc derivatives. For the first time MPc SAMs were formed on gold coated fiber. The electrocatalytic behavior of the modified electrodes was studied for the detection of nitrite and L-cysteine, all modified electrodes showed improved electrocatalytic oxidation compared to the unmodified electrode. The MPc complexes catalyzed nitrite oxidation via a two-electron mechanism producing nitrate. Cobalt tetraaminophthalocyanine showed the best catalytic activity for nitrite oxidation in terms of overpotential lowering compared to other complexes and thus was used for nitrite detection in a food sample, the nitrite concentration was determined to be 59.13 ppm, well within the limit for cured meat products. Electrocatalytic oxidation of L-cysteine on SAM modified gold coated fiber was reported for the first time. The gold coated fiber and ultamicro cylinder electrode were less stable towards the electro-oxidation of cysteine compared to its oxidation on the gold disk. The gold disk electrode gave better catalytic performance in terms of stability and reduction of overpotential. The phenylthio cobalt phthalocyanine derivative gave the best catalytic activity for L-cysteine oxidation in terms of overpotential lowering compared to other phenylthio derivatized MPc complexes. The amount of L-cysteine in human urine was 2.4 mM, well within the urinary L-cysteine excretion range for a healthy human being.
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- Authors: Nombona, Nolwazi
- Date: 2009
- Subjects: Titanium , Manganese , Cobalt , Phthalocyanines , Electrochemistry , Electrodes , Self-assembly (Chemistry)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4312 , http://hdl.handle.net/10962/d1004970 , Titanium , Manganese , Cobalt , Phthalocyanines , Electrochemistry , Electrodes , Self-assembly (Chemistry)
- Description: Syntheses, spectral, electrochemical and spectroelectrochemical studies of phenylthio and amino derivatised metallophthalocyanines complexes are reported. The complexes are immobilized onto a gold macro disk, gold ultramicroelectrode and gold coated fiber electrodes via self assembly with phenylthio MPc derivatives or onto a glassy carbon electrode via electropolymerisation with amino MPc derivatives. For the first time MPc SAMs were formed on gold coated fiber. The electrocatalytic behavior of the modified electrodes was studied for the detection of nitrite and L-cysteine, all modified electrodes showed improved electrocatalytic oxidation compared to the unmodified electrode. The MPc complexes catalyzed nitrite oxidation via a two-electron mechanism producing nitrate. Cobalt tetraaminophthalocyanine showed the best catalytic activity for nitrite oxidation in terms of overpotential lowering compared to other complexes and thus was used for nitrite detection in a food sample, the nitrite concentration was determined to be 59.13 ppm, well within the limit for cured meat products. Electrocatalytic oxidation of L-cysteine on SAM modified gold coated fiber was reported for the first time. The gold coated fiber and ultamicro cylinder electrode were less stable towards the electro-oxidation of cysteine compared to its oxidation on the gold disk. The gold disk electrode gave better catalytic performance in terms of stability and reduction of overpotential. The phenylthio cobalt phthalocyanine derivative gave the best catalytic activity for L-cysteine oxidation in terms of overpotential lowering compared to other phenylthio derivatized MPc complexes. The amount of L-cysteine in human urine was 2.4 mM, well within the urinary L-cysteine excretion range for a healthy human being.
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The formation of self-assembled monolayers of thiophthalocyanine complexes of titanium, vanadium and manganese and their use in l-cysteine electrocatalysis
- Mbambisa, Gcineka, Nombona, Nolwazi, Nyokong, Tebello
- Authors: Mbambisa, Gcineka , Nombona, Nolwazi , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263375 , vital:53622 , xlink:href="https://doi.org/10.1016/j.microc.2009.04.009"
- Description: Self-assembled monolayers (SAMs) based on octapentylthiophthalocyanine complexes of oxovanadium (IV) (OVOPThPc), titanium(IV) (OTiOPThPc), and manganese (III) acetate (AcMnOPThPc), and of tetraphenylthiophthalocyanine complexes of hydroxo manganese(III) (OHMnTPPc) and oxotitanium(IV) (OTiTPPc) are described. The oxidation of l-cysteine was observed at potentials which ranged from 0.52 V to 0.67 V. The detection limits for l-cysteine analysis were of the order of 10− 7 to 10− 6 M.
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- Authors: Mbambisa, Gcineka , Nombona, Nolwazi , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263375 , vital:53622 , xlink:href="https://doi.org/10.1016/j.microc.2009.04.009"
- Description: Self-assembled monolayers (SAMs) based on octapentylthiophthalocyanine complexes of oxovanadium (IV) (OVOPThPc), titanium(IV) (OTiOPThPc), and manganese (III) acetate (AcMnOPThPc), and of tetraphenylthiophthalocyanine complexes of hydroxo manganese(III) (OHMnTPPc) and oxotitanium(IV) (OTiTPPc) are described. The oxidation of l-cysteine was observed at potentials which ranged from 0.52 V to 0.67 V. The detection limits for l-cysteine analysis were of the order of 10− 7 to 10− 6 M.
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The synthesis, cyclic voltammetry and spectroelectrochemical studies of Co (II) phthalocyanines tetra-substituted at the α and β positions with phenylthio groups
- Nombona, Nolwazi, Nyokong, Tebello
- Authors: Nombona, Nolwazi , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/264529 , vital:53742 , xlink:href="https://doi.org/10.1016/j.dyepig.2008.06.002"
- Description: Non-peripherally substituted cobalt 1,(4)-(tetraphenylthiophthalocyaninato) and peripherally substituted cobalt 2,(3)-(tetraphenylthiophthalocyaninato) complexes were synthesized. Redox processes were observed at E1/2 = −1.44 V (I), −0.39 V (II), +0.37 V (III), +0.78 V (IV) and 1.15 V (V) for the non-peripherally substituted and at E1/2 = −1.42 V (I), −0.57, −0.39 V (II), +0.27 V (III), +0.79 V (IV) and +1.10 V (V) for the peripherally substituted complexes, respectively. The couples were assigned to CoIPc−2/CoIPc−3 (I), CoIIPc−2/CoIPc−2 (II), CoIIIPc−2/CoIIPc−2 (III), and CoIIIPc−1/CoIIIPc−2 (IV) using spectroelectrochemistry. The last process (V) could not be ascertained by spectroelectrochemistry but is associated with ring oxidation. Upon reduction or oxidation, the Q band of the non-peripherally substituted complex became less red shifted compared to that of its peripherally substituted counterpart.
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- Authors: Nombona, Nolwazi , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/264529 , vital:53742 , xlink:href="https://doi.org/10.1016/j.dyepig.2008.06.002"
- Description: Non-peripherally substituted cobalt 1,(4)-(tetraphenylthiophthalocyaninato) and peripherally substituted cobalt 2,(3)-(tetraphenylthiophthalocyaninato) complexes were synthesized. Redox processes were observed at E1/2 = −1.44 V (I), −0.39 V (II), +0.37 V (III), +0.78 V (IV) and 1.15 V (V) for the non-peripherally substituted and at E1/2 = −1.42 V (I), −0.57, −0.39 V (II), +0.27 V (III), +0.79 V (IV) and +1.10 V (V) for the peripherally substituted complexes, respectively. The couples were assigned to CoIPc−2/CoIPc−3 (I), CoIIPc−2/CoIPc−2 (II), CoIIIPc−2/CoIIPc−2 (III), and CoIIIPc−1/CoIIIPc−2 (IV) using spectroelectrochemistry. The last process (V) could not be ascertained by spectroelectrochemistry but is associated with ring oxidation. Upon reduction or oxidation, the Q band of the non-peripherally substituted complex became less red shifted compared to that of its peripherally substituted counterpart.
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