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Substituted catechols as complexing agents for the determination of bismuth, lead, copper and cadmium by adsorptive stripping voltammetry

  • Authors: Limson, Janice L , Nyokong, Tebello
  • Date: 1997
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293311 , vital:57074 , xlink:href="https://doi.org/10.1016/S0003-2670(96)00585-5"
  • Description: Copper, cadmium, lead and bismuth (> 5 μg ml−1) are determined by adsorptive cathodic stripping voltammetry (AdCSV) on a mercury film glassy carbon electrode, using catechol, 4-methylcatechol, 4-t-butylcatechol and resorcinol as complexing ligands. Complexes of lead, copper and bismuth with resorcinol showed the largest increase in current with increase in metal concentration, whereas complexes of these metals with 4-t-butylcatechol showed the lowest current response. Cadmium showed a different behaviour from the other three metals in that the highest current response was observed with 4-methylcatechol. The four metals could be determined simultaneously in the presence of resorcinol, although considerable interference was observed between bismuth and copper.
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The study of the interactions of cobalt (II) tetrasulfophthalocyanine with cysteine and histidine

  • Authors: Sekota, Mantoa , Nyokong, Tebello
  • Date: 1997
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293458 , vital:57087 , xlink:href="https://doi.org/10.1016/S0277-5387(97)00096-X"
  • Description: Kinetics for the interaction of cobalt(II) tetrasulfophthalocyanine ([CoIITSPc]4−, Pc(−2) = phthalocyanine dianion) with the amino acids, histidine and cysteine, in pH 7.2 phosphate buffer were studied. The rates were found to be first order in both the [CoIITSPc]4− and the amino acid. The formation of the [CoIIITSPc]3− species in the presence of histidine occurred with a rate constant of 0.16 dm3 mol−s−1, whereas the formation of the [CoITSPc]5− species in the presence of cysteine gave a rate constant of 2.2 dm3 mol−1.
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Use of cobalt (II) phthalocyanine to improve the sensitivity and stability of glassy carbon electrodes for the detection of cresols, chlorophenols and phenol

  • Authors: Mafatle, Tsukutlane J , Nyokong, Tebello
  • Date: 1997
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293335 , vital:57076 , xlink:href="https://doi.org/10.1016/S0003-2670(97)00464-9"
  • Description: A cobalt(II) phthalocyanine-modified glassy carbon electrode (CoPc-GCE) was used for the detection of o-, m- and p-cresols, and of 2-chlorophenol, 4-chlorophenol and phenol. Modification of the glassy carbon electrode with CoPc increases the oxidation currents of these species and increases the stability of the electrode. CoPc-GCE showed less fouling by the oxidation products of these compounds than the unmodified GCE. Comparison of some first row transition metal phthalocyanines showed the following trend for the enhancement of the currents for the oxidation of cresols and phenols: Co(II)Pc > Mn(II)Pc > Fe(II)Pc > Ni(II)Pc > Cu(II)Pc > H2Pc > Zn(II)Pc > GCE. When [Co(II)TSPc]4− (TSPc=tetrasulfo Pc) was added to aqueous solutions containing the cresols and phenols, an enhancement of the oxidation currents was also observed.
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Voltammetric behavior of cysteine and metallothionein on cobalt (II) tetrasulfonated phthalocyanine modified glassy carbon electrodes

  • Authors: Limson, Janice L , Nyokong, Tebello
  • Date: 1997
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293346 , vital:57077 , xlink:href="https://doi.org/10.1002/elan.1140090314"
  • Description: Cysteine, and rat Cd, Zn-metallothionein (Cd, Zn-MT) have been studied electrochemically at glassy carbon electrodes modified with cobalt(II) tetrasulfonated phthalocyanine, [CoIITSPc]4−, where Pc(2-) = phthalocyanine dianion. The electrode was modified by electrodeposition of [CoIITSPc]4−. The anodic currents for the oxidation of cysteine on these electrodes are observed at 0.82 V (vs. Ag/AgCl) in acidic media. The anodic currents for the oxidation of Cd, Zn-MT are observed at 0.90 V at pH 8.4 (Tris buffer).
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Cyclic voltammetry and spectroelectrochemistry of osmium phthalocyanines in aqueous and non-aqueous solvents

  • Authors: Sekota, Mantoa , Nyokong, Tebello
  • Date: 1996
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293358 , vital:57078 , xlink:href="https://doi.org/10.1016/0277-5387(95)00581-1"
  • Description: Cyclic voltammetry of osmium phthalocyanine complexes, [(CN)2OsIIPc]2− and (py)2OSIIPc (PC = phthalocyanine dianion), show two oxidation couples and two reduction couples in acetonitrile and dimethy1formamide. Oxidation and reduction in these complexes occur at the ring to form cation and anion radical species, respectively. The [(CN)2OsIIPC]2− complexes show a remarkable ease of ring oxidation with oxidation potentials that are much lower than is typical for metallophthalocyanines. Half-wave potentials of 0.25 and 0.67 V (versus saturated calomel electrode, SCE) were obtained for the first and second ring oxidations, respectively. The [(CN)2OSIIPc]2− complex is soluble in water at pHs greater than 4. This complex shows one oxidation couple in pH 9 buffer at −0.11 V versus SCE.
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Electrocatalytic oxidation of cysteine by molybdenum (V) phthalocyanine complexes

  • Authors: Mafatle, Tsukutlane J , Nyokong, Tebello
  • Date: 1996
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293369 , vital:57079 , xlink:href="https://doi.org/10.1016/0022-0728(95)04519-8"
  • Description: Chemically modified electrodes, constructed by incorporating oxomolybdenum(V) phthalocyanine (OMo(V)(OH)Pc, Pc = phthalocyanine dianion) into graphite powder were used to catalyse the oxidation of cysteine. Solution catalysis of cysteine by oxomolybdenum(V) tetrasulfophthalocyanine, [OMo(V)(OH)TSPc]4−, was also investigated. A considerable reduction in overpotential for cysteine oxidation was observed. Cysteine oxidation occurred at 0.26 and 0.28 V vs. Ag/vbAgCl for catalysis by Omo(V)(OH)Pc and [OMo(V)(OH)TSPc]4− respectively as opposed to 0.77 V vs. Ag/vbAgCl observed on CoPc chemically modified electrodes. The anodic peak currents vary linearly with cysteine concentration in the range 0.02 to 0.08 mol dm−3 and 0.008 to 0.02 mol dm−3 for [OMo(V)(OH)TSPc]4− and OMo(V)Pc respectively.
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Photochemically induced electron transfer between sulfur dioxide and tin (IV) mono-and di-phthalocyanines

  • Authors: Nensala, Ngudiankama , Nzimande, Ayanda , Nyokong, Tebello
  • Date: 1996
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293402 , vital:57082 , xlink:href="https://doi.org/10.1016/1010-6030(96)04344-4"
  • Description: Photolysis, using radiation from a tungsten lamp, of tin diphthalocyanine (Pc2Sn(IV)) in dichloromethane containing SO2 results in the one-electron oxidation of this species to [Pc(−2)Sn(IV)Pc(−1)]+. The relative quantum yields for the formation of the oxidized species were in the order of 10−3. The one-electron oxidized complex was also formed when Pc2Sn was photolysed in an acetonitrile/dichloromethane solvent mixture. Photolysis of the monomeric (L)2Sn(IV)Pc(LOH−, Cl−, Br− and F−) in pyridine and in the presence of SO2 resulted in the reduction of these species to (L)2Sn(IV)Pc(−3)]− with quantum yields in the order of 10−2.
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Spectroelectrochemical studies of tin (IV) diphthalocyanine

  • Authors: Nensala, Ngudiankama , Nyokong, Tebello
  • Date: 1996
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293436 , vital:57085 , xlink:href="https://doi.org/10.1016/0277-5387(95)00325-1"
  • Description: Cyclic voltammetry of tin(IV) diphthalocyanine (Pc2Sn) in dichloromethane containing TEAP shows two reduction couples at −0.56 and −0.89 versus saturated calomel electrode (SCE) and one oxidation couple at 0.35 V versus SCE; all were quasireversible one-electron couples. The oxidation couple corresponds to [Pc(−1)SnIVPc(−2)+/Pc(−2)SnIVPc(−2) and the reduction couples to Pc(−2)SnIVPc(−2)/[Pc(−3)SnIVPc(−2)]− and [Pc(−3)SnIVPc(−2)]−/[Pc(−3)SnIVPc(−3)]2−, respectively. The electronic absorption spectra of the various reduced or oxidized tin(IV) diphthalocyanine species are reported.
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Equilibrium and kinetic studies of the reaction between pyridine and cobalt (II) phthalocyanine in DMSO

  • Authors: Nyokong, Tebello
  • Date: 1995
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293380 , vital:57080 , xlink:href="https://doi.org/10.1016/0277-5387(95)00090-F"
  • Description: Kinetics and equilibria for the reaction between pyridine and cobalt(II) phthalocyanine [CoPc] (H2Pc = phthalocyanine) in dimethyl sulphoxide (DMSO) were studied at 25°C. The complex, CoPc(py)2, is formed in two consecutive steps. The formation of the mono-substituted CoPc(py)(DMSO) occurs first with a pseudo-first-order rate constant of k1f = 7.7 ± 0.3 × 10−3 dm3 mol−1 s−1. The final disubstituted CoPc(py)2 complex is formed with k2f= 1.1 ± 0.1 × 10−4dm3mol−1−1. The equilibrium constants were found to be K1 = 160 ± 20dm3 mol−1 and K2 = 15 ± 3 dm3mol−1 for the formation of CoPc(py)(DMSO) and CoPc(py)2, respectively.
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The reaction of cyanide with iron (II) hexadecachlorophthalocyanine

  • Authors: Nyokong, Tebello
  • Date: 1995
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293447 , vital:57086 , xlink:href="https://doi.org/10.1016/0277-5387(94)00291-L"
  • Description: Kinetics and equilibria for the reaction between cyanide and iron(II) hexadecachlorophthalocyanine ((Cl)16PcFe(DMSO)2, where Pc(−2) = phthalocyanine dianion) in dimethyl sulphoxide (DMSO) are reported. Only the spectrophotometric changes due to the formation of the dicyano, [(Cl)16PcFe(CN)2]2−, complex were observed. This complex is formed with the equilibrium constant, K3 = 1.6 × 103 dm3 mol−1 and a rate constant of k3f = 4.2 × 10−3 dm3 mol−1 s−1. The K2[(Cl)16PcFe(CN)2] complex dissolves in DMSO and dimethyl formamide (DMF) with ϵ = 110 000 and 92 000 dm3 mol−1 cm−1, respectively.
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Cyclic voltammetry and photooxidation of molybdenum (V) phthalocyanine

  • Authors: Nyokong, Tebello
  • Date: 1994
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/295475 , vital:57344 , xlink:href="https://doi.org/10.1016/S0277-5387(00)86594-8"
  • Description: Cyclic voltammetry of OMoV(OH)Pc in chloronaphthalene shows two quasi-reversible oxidation couples at 0.38 and 1.22 V and three quasi-reversible reduction couples at −0.74, −1.15 and −1.85 V vs S.C.E. Bulk electrolysis of OMoV(OH)Pc (Pc2 = phthalocyanine dianion) shows that the first oxidation couple is due to the oxidation of the central MoV metal to MoVI and the first reduction couple due to reduction to OMoIVPc. Cyclic voltammetry and spectroelectrochemistry in DMSO also showed redox activity at the metal. Further reductions or oxidations in OMoVPc complexes occur at the phthalocyanine ring. OMoV(OH)Pc is readily photooxidized at the metal in the presence dichloromethane or dichlorobenzene, with the formation of OMoVIPc species.
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Cyclic voltammetry and spectroelectrochemistry of rhodium phthalocyanines

  • Authors: Nyokong, Tebello
  • Date: 1994
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/295486 , vital:57346 , xlink:href="https://doi.org/10.1039/DT9940001359"
  • Description: The electrochemistry of RhIII(pc)(pc = phthalocyanine dianion) complexes containing chloride, pyridine, dimethyl sulfoxide (dmso) and cyanide as axial ligands was investigated by cyclic voltammetry and UV/VIS spectroelectrochemistry. The compounds were K[Rh(pc)(CN)2], [Rh(pc)(Cl)(py)] and [Rh(pc)Cl(dmso)]. For all of these the first oxidation occurs at the phthalocyanine ligand with the formation of a π-cation radical species. The addition of one electron to the complexes leads to one of two different reduction products depending on the nature of the axial ligands. The first reduction of [Rh(pc)Cl(py)] and [Rh(pc)Cl(dmso)] occurs at the metal, followed by rapid dimerization of the reduced species. The first and subsequent reductions of K[Rh(pc)(CN)2] occur at the ring.
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Photoassisted electron transfer between sulfur dioxide and tin (IV) phthalocyanines

  • Authors: Nyokong, Tebello
  • Date: 1994
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/295520 , vital:57349 , xlink:href="https://doi.org/10.1039/C39940001983"
  • Description: Photolysis of tin(IV) phthalocyanine complexes in the presence of sulfur dioxide shows a first-order kinetic dependence on sulfur dioxide, and a one-electron reduction of SnPc to an anion radical species.
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Photoreduction of tin (IV) phthalocyanines

  • Authors: Nyokong, Tebello
  • Date: 1994
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293413 , vital:57083 , xlink:href="https://doi.org/10.1016/S0277-5387(00)83491-9"
  • Description: Photolysis of Sn(IV)Pc(OH)2 (Pc = phthalocyanine dianion) and Sn(IV)Pc(Cl)2 using a tungsten lamp, and in the presence of SnCl2·2H2O as an electron donor results in the reduction of these complexes of π anion radical species. The reduction shows second order dependence on the concentration of the Sn(IV)Pc complexes and a first order dependence on SnCl2·H2O.
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Redox reactions of an Mo (V) tetrasulfophthalocyanine

  • Authors: Ferraudi, Guillermo , Nyokong, Tebello , Feliz, Mario , Perkovic, Marc , Rillema, D Paul
  • Date: 1994
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/295530 , vital:57351 , xlink:href="https://doi.org/10.1016/0020-1693(93)03664-V"
  • Description: The preparation of an Mo(V) tetrasulfophthalocyanine and some of its thermal and photochemical reactions have been investigated in this work. Electrochemical processes have been followed by means of the UVVis spectral changes and compared with those observed in flash photolysis. Mo(IV) and Mo(V)-ligand-radical species are common intermediates of the electrochemical and photochemical reactions. In 254 nm irradiations of the Mo(V) tetrasulfophthalocyanine in aqueous solutions of 2-propanol, the macrocycle can be photohydrogenated and the product of the photolysis can be reoxidized with O2 back to the parent complex.
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Interaction of cyanide with iron (II) phthalocyanine

  • Authors: Nyokong, Tebello
  • Date: 1993
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/295497 , vital:57347 , xlink:href="https://doi.org/10.1039/DT9930003601"
  • Description: The kinetics and equilibria for the reaction between cyanide and iron (II) phthalocyanine [Fe(pc)](H2pc = phthalocyanine) in dimethyl sulfoxide (dmso) were studied at 25 °C. The complex [Fe(pc)(CN)2]2– is formed in two consecutive pseudo-first-order processes with k2f= 17.5 ± 0.8 dm3 mol–1 s–1 and k3f= 0.20 ± 0.05 dm3 mol–1 s–1, where k2f and k3f are the rate constants for the binding of the first and second cyanide ligands, respectively. The equilbrium constants were fund to be K2= 3.0 × 103 dm3 mol–1 and K3= 5.7 × 102 dm3 mol–1, for the formation of [Fe(pc)(CN)(dmso)]– and [Fe(pc)(CN)2]2–, respectively.
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Kinetics of the reaction of cyanide with ruthenium phthalocyanine complexes

  • Authors: Nyokong, Tebello , Guthrie-Strachan, Jeffry
  • Date: 1993
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/295509 , vital:57348 , xlink:href="https://doi.org/10.1016/S0020-1693(00)85128-2"
  • Description: Kinetic studies of the reaction of cyanide with (CO)(DMF)RuPc and (DMSO)2RuPc in DMF are reported. In the presence of a large excess of cyanide, the (CN)2RuPc complex is formed by pseudo first order kinetics. The reaction is first order in both cyanide and phthalocyanine, with specific rate constants of 5.2×10−2 and 7.2×10−2 M−1 s−1 for reactions of cyanide with (CO)(DMF)RuPc and (DMSO)2RuPc, respectively. The rate constants correspond to the coordination of the second cyanide ligand to the ruthenium phthalocyanine species.
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The nature of the oxidation products of dicyanoruthenium phthalocyanine in aqueous and non-aqueous solvents

  • Authors: Nyokong, Tebello
  • Date: 1993
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/295543 , vital:57352 , xlink:href="https://doi.org/10.1016/S0277-5387(00)81741-6"
  • Description: The cyclic voltammetry of [(CN)2RuIIPc]2− in acetonitrile or dichloromethane shows two oxidation couples at E12 = 0.31 and 0.85 V (vs S.C.E.) in CH2Cl2 and E12 = 0.45 and 1.15 V (vs S.C.E.) in acetonitrile. The spectroelectrochemistry of [(CN)2RuIIPc]2− in these solvents showed that oxidations occur at the phthalocyanine ligand. K2[(CN)2RuIIPc] dissolves in water at pHs greater than 5. The cyclic voltammetry of this complex showed oxidation couples at 0.32 and 0.29 V (vs S.C.E.) for aqueous solutions containing sodium sulphate (0.1M) and for buffered solutions (pH = 9), respectively. Both cyclic voltammetry and controlled potential coulometry gave evidence of electrocrystallization of the oxidation product. Chemical oxidations of [(CN)2RuIIPc]2− in water also showed phthalocyanine ligand oxidation.
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