Electro-oxidation of phenol and its derivatives on poly-Ni (OH) TPhPyPc modified vitreous carbon electrodes
- Obirai, Joseph, Bedioui, Fethi, Nyokong, Tebello
- Authors: Obirai, Joseph , Bedioui, Fethi , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289353 , vital:56625 , xlink:href="https://doi.org/10.1016/j.jelechem.2004.11.006"
- Description: The electrochemical oxidation of phenol and its derivatives using poly-nickel hydroxy tetraphenoxypyrrolephthalocyanine (poly-Ni(OH)TPhPyPc) modified vitreous carbon electrodes are described. The films were formed by the electro-transformation of the electropolymerized pyrrole-substituted phenoxyphthalocyanine poly-NiTPhPyPc modified electrode in aqueous 0.1 M NaOH solution. The poly-Ni(OH)TPhPyPc films showed better stability and resistance to electrode fouling compared to poly-NiTPhPyPc and unmodified electrodes. The resistance to surface fouling and stability can be attributed to the structure of the ring substituent on the phthalocyanine macrocycle and to the particular O–Ni–O bridged architecture of the nickel phthalocyanine film.
- Full Text:
- Date Issued: 2005
- Authors: Obirai, Joseph , Bedioui, Fethi , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289353 , vital:56625 , xlink:href="https://doi.org/10.1016/j.jelechem.2004.11.006"
- Description: The electrochemical oxidation of phenol and its derivatives using poly-nickel hydroxy tetraphenoxypyrrolephthalocyanine (poly-Ni(OH)TPhPyPc) modified vitreous carbon electrodes are described. The films were formed by the electro-transformation of the electropolymerized pyrrole-substituted phenoxyphthalocyanine poly-NiTPhPyPc modified electrode in aqueous 0.1 M NaOH solution. The poly-Ni(OH)TPhPyPc films showed better stability and resistance to electrode fouling compared to poly-NiTPhPyPc and unmodified electrodes. The resistance to surface fouling and stability can be attributed to the structure of the ring substituent on the phthalocyanine macrocycle and to the particular O–Ni–O bridged architecture of the nickel phthalocyanine film.
- Full Text:
- Date Issued: 2005
Electrocatalytic oxidation and detection of hydrazine at gold electrode modified with iron phthalocyanine complex linked to mercaptopyridine self-assembled monolayer
- Ozoemena, Kenneth I, Nyokong, Tebello
- Authors: Ozoemena, Kenneth I , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/286065 , vital:56235 , xlink:href="https://doi.org/10.1016/j.talanta.2005.02.030"
- Description: Electrocatalytic oxidation and detection of hydrazine in pH 7.0 conditions were studied by using gold electrode modified with self-assembled monolayer (SAM) films of iron phthalocyanine (FePc) complex axially ligated to a preformed 4-mercaptopyridine SAMs. The anodic oxidation of hydrazine in neutral pH conditions with FePc-linked-mercaptopyridine-SAM-modified gold electrode occurred at low overpotential (0.35 V versus Ag|AgCl) and the treatment of the voltammetric data showed that it was a pure diffusion-controlled reaction with the involvement of one electron in the rate-determining step. The mechanism for the interaction of hydrazine with the FePc-SAM is proposed to involve the Fe(III)Pc/Fe(II)Pc redox process. Using cyclic voltammetry (CV) and Osteryoung square wave voltammetry (OSWV), hydrazine was detected over a linear concentration range of 1.3 × 10−5 to 9.2 × 10−5 mol/L with low limits of detection (ca. 5 and 11 μM for OSWV and CV, respectively). At concentrations higher than 1.2 × 10−4 mol/L the anodic peak potential shifted to 0.40 V (versus Ag|AgCl), and this was interpreted to be due to kinetic limitations resulting from the saturation of hydrazine and its oxidation products onto the redox-active monolayer film. This type of metallophthalocyanine-SAM-based electrode is a highly promising electrochemical sensor given its ease of fabrication, good catalytic activity, stability, sensitivity and simplicity.
- Full Text:
- Date Issued: 2005
- Authors: Ozoemena, Kenneth I , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/286065 , vital:56235 , xlink:href="https://doi.org/10.1016/j.talanta.2005.02.030"
- Description: Electrocatalytic oxidation and detection of hydrazine in pH 7.0 conditions were studied by using gold electrode modified with self-assembled monolayer (SAM) films of iron phthalocyanine (FePc) complex axially ligated to a preformed 4-mercaptopyridine SAMs. The anodic oxidation of hydrazine in neutral pH conditions with FePc-linked-mercaptopyridine-SAM-modified gold electrode occurred at low overpotential (0.35 V versus Ag|AgCl) and the treatment of the voltammetric data showed that it was a pure diffusion-controlled reaction with the involvement of one electron in the rate-determining step. The mechanism for the interaction of hydrazine with the FePc-SAM is proposed to involve the Fe(III)Pc/Fe(II)Pc redox process. Using cyclic voltammetry (CV) and Osteryoung square wave voltammetry (OSWV), hydrazine was detected over a linear concentration range of 1.3 × 10−5 to 9.2 × 10−5 mol/L with low limits of detection (ca. 5 and 11 μM for OSWV and CV, respectively). At concentrations higher than 1.2 × 10−4 mol/L the anodic peak potential shifted to 0.40 V (versus Ag|AgCl), and this was interpreted to be due to kinetic limitations resulting from the saturation of hydrazine and its oxidation products onto the redox-active monolayer film. This type of metallophthalocyanine-SAM-based electrode is a highly promising electrochemical sensor given its ease of fabrication, good catalytic activity, stability, sensitivity and simplicity.
- Full Text:
- Date Issued: 2005
Synthesis, electrochemical and electrocatalytic behaviour of thiophene-appended cobalt, manganese and zinc phthalocyanine complexes
- Obirai, Joseph, Nyokong, Tebello
- Authors: Obirai, Joseph , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/286103 , vital:56238 , xlink:href="https://doi.org/10.1016/j.electacta.2005.03.024"
- Description: This work reports on the syntheses of new thiophene tetra substituted cobalt, manganese and zinc phthalocyanine (CoTETPc, (Cl)MnTETPc and ZnTETPc) complexes. The redox processes due to the thiophene substituent on the ring of the metallophthalocyanines (MPcs) were observed, in addition to Pc ring and metal (for Co and Mn complexes) based redox activity. The electrocatalytic activity of the CoTETPc complex adsorbed on glassy carbon electrode (GCE) by drop/dry-thermal annealing was investigated using L-cysteine. The modified electrode was stable to repetitive use without any signs of deactivation by oxidation products and was used to determine L-cysteine at concentrations between 0.0015 and 1 mM in pH 4 aqueous conditions.
- Full Text:
- Date Issued: 2005
- Authors: Obirai, Joseph , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/286103 , vital:56238 , xlink:href="https://doi.org/10.1016/j.electacta.2005.03.024"
- Description: This work reports on the syntheses of new thiophene tetra substituted cobalt, manganese and zinc phthalocyanine (CoTETPc, (Cl)MnTETPc and ZnTETPc) complexes. The redox processes due to the thiophene substituent on the ring of the metallophthalocyanines (MPcs) were observed, in addition to Pc ring and metal (for Co and Mn complexes) based redox activity. The electrocatalytic activity of the CoTETPc complex adsorbed on glassy carbon electrode (GCE) by drop/dry-thermal annealing was investigated using L-cysteine. The modified electrode was stable to repetitive use without any signs of deactivation by oxidation products and was used to determine L-cysteine at concentrations between 0.0015 and 1 mM in pH 4 aqueous conditions.
- Full Text:
- Date Issued: 2005
Hydrogen peroxide oxidation of 2-chlorophenol and 2, 4, 5-trichlorophenol catalyzed by monomeric and aggregated cobalt tetrasulfophthalocyanine
- Agboola, Bolade, Ozoemena, Kenneth I, Nyokong, Tebello
- Authors: Agboola, Bolade , Ozoemena, Kenneth I , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289249 , vital:56612 , xlink:href="https://doi.org/10.1016/j.molcata.2004.10.041"
- Description: Cobalt tetrasulfophthalocyanine (CoTSPc) was used to catalyze the oxidation of 2-chlorophenol (2-CP) and 2,4,5-trichlorophenol (TCP) using hydrogen peroxide (H2O2) as the oxidant. This CoTSPc catalyzed hydrogen peroxide oxidation of chlorophenols resulted in the formation of different types of oxidation products depending on the solvent conditions. In water/methanol conditions (where CoTSPc is mainly monomeric, and unionized forms of the phenols), phenol and hydroquinone were the main oxidation products, while in phosphate buffer solutions (pH 7 and 10 for TCP and 2-CP, respectively, where CoTSPc is mainly aggregated, and ionized forms of the phenols), benzoquinone was the main product. In contrast to CoTSPc, other MTSPc complexes studied (AlTSPc, CuTSPc and NiTSPc) exhibited no detectable catalytic effect on the oxidation of chlorophenols under the experimental conditions employed, thus proving the effect of the central metal ions on efficient catalysis of chlorophenol. Reaction pathways are proposed based on the relative time of oxidation products formation.
- Full Text:
- Date Issued: 2005
- Authors: Agboola, Bolade , Ozoemena, Kenneth I , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289249 , vital:56612 , xlink:href="https://doi.org/10.1016/j.molcata.2004.10.041"
- Description: Cobalt tetrasulfophthalocyanine (CoTSPc) was used to catalyze the oxidation of 2-chlorophenol (2-CP) and 2,4,5-trichlorophenol (TCP) using hydrogen peroxide (H2O2) as the oxidant. This CoTSPc catalyzed hydrogen peroxide oxidation of chlorophenols resulted in the formation of different types of oxidation products depending on the solvent conditions. In water/methanol conditions (where CoTSPc is mainly monomeric, and unionized forms of the phenols), phenol and hydroquinone were the main oxidation products, while in phosphate buffer solutions (pH 7 and 10 for TCP and 2-CP, respectively, where CoTSPc is mainly aggregated, and ionized forms of the phenols), benzoquinone was the main product. In contrast to CoTSPc, other MTSPc complexes studied (AlTSPc, CuTSPc and NiTSPc) exhibited no detectable catalytic effect on the oxidation of chlorophenols under the experimental conditions employed, thus proving the effect of the central metal ions on efficient catalysis of chlorophenol. Reaction pathways are proposed based on the relative time of oxidation products formation.
- Full Text:
- Date Issued: 2005
Surface electrochemistry of iron phthalocyanine axially ligated to 4-mercaptopyridine self-assembled monolayers at gold electrode
- Ozoemena, Kenneth I, Nyokong, Tebello
- Authors: Ozoemena, Kenneth I , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289282 , vital:56615 , xlink:href="https://doi.org/10.1016/j.jelechem.2005.02.018"
- Description: Surface electrochemical behaviour of a self-immobilised iron phthalocyanine (FePc) ultrathin film, via axial ligation reaction, onto a preformed 4-mercaptopyridine self-assembled monolayer on gold electrode has been described. Electrochemical evidence for the sensor clearly suggested surface-confined, flat “umbrella”-oriented and densely-packed monolayer film structure. The proposed electrochemical sensor exhibited good catalytic activity towards the oxidation of thiocyanate in pH 4.0 medium over a linear range of three decades of concentration (ca. 10−6–10−3 mol dm−3) with a detection limit in the order of ∼10−7 mol dm−3. The sensor exhibited useful potential for the analysis of thiocyanate in human urine and saliva samples. The advantageous properties of this type of electrode as a sensor for thiocyanate lie in its ease of fabrication, excellent catalytic activity, stability, sensitivity and simplicity.
- Full Text:
- Date Issued: 2005
- Authors: Ozoemena, Kenneth I , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289282 , vital:56615 , xlink:href="https://doi.org/10.1016/j.jelechem.2005.02.018"
- Description: Surface electrochemical behaviour of a self-immobilised iron phthalocyanine (FePc) ultrathin film, via axial ligation reaction, onto a preformed 4-mercaptopyridine self-assembled monolayer on gold electrode has been described. Electrochemical evidence for the sensor clearly suggested surface-confined, flat “umbrella”-oriented and densely-packed monolayer film structure. The proposed electrochemical sensor exhibited good catalytic activity towards the oxidation of thiocyanate in pH 4.0 medium over a linear range of three decades of concentration (ca. 10−6–10−3 mol dm−3) with a detection limit in the order of ∼10−7 mol dm−3. The sensor exhibited useful potential for the analysis of thiocyanate in human urine and saliva samples. The advantageous properties of this type of electrode as a sensor for thiocyanate lie in its ease of fabrication, excellent catalytic activity, stability, sensitivity and simplicity.
- Full Text:
- Date Issued: 2005
Synthesis, spectral and electrochemical characterization of mercaptopyrimidine-substituted cobalt, manganese and Zn (II) phthalocyanine complexes
- Authors: Obirai, J , Nyokong, Tebello
- Date: 2005
- Language: English
- Type: Article
- Identifier: vital:6973 , http://hdl.handle.net/10962/d1018958
- Description: A new family of thiol-derivatized metallophthalocyanine has been synthesized. The electrochemical behaviors of the complexes have been investigated. The modified glassy carbon electrode using the electropolymerized manganese complex (poly-MnTMPyrPc) was characterized in aqueous solution. The result indicates that the complexes are easier to electropolymerize in dichloromethane (DCM) than in dimethylformamide (DMF). The poly-MnTPyrPc-modified electrode showed pH dependence within the pH range studied (2–8). The cathodic wave of the electrode showed more pH dependence than the anodic wave. Poly-MnTPyrPc could catalyse the reduction of oxygen. , Original publication is available at http://doi:10.1016/j.electacta.2004.12.003
- Full Text: false
- Date Issued: 2005
- Authors: Obirai, J , Nyokong, Tebello
- Date: 2005
- Language: English
- Type: Article
- Identifier: vital:6973 , http://hdl.handle.net/10962/d1018958
- Description: A new family of thiol-derivatized metallophthalocyanine has been synthesized. The electrochemical behaviors of the complexes have been investigated. The modified glassy carbon electrode using the electropolymerized manganese complex (poly-MnTMPyrPc) was characterized in aqueous solution. The result indicates that the complexes are easier to electropolymerize in dichloromethane (DCM) than in dimethylformamide (DMF). The poly-MnTPyrPc-modified electrode showed pH dependence within the pH range studied (2–8). The cathodic wave of the electrode showed more pH dependence than the anodic wave. Poly-MnTPyrPc could catalyse the reduction of oxygen. , Original publication is available at http://doi:10.1016/j.electacta.2004.12.003
- Full Text: false
- Date Issued: 2005
Synthesis, photophysicochemical studies of adjacently tetrasubstituted binaphthalo-phthalocyanines
- Seotsanyana-Mokhosi, Itumeleng, Chen, Ji-Yao, Nyokong, Tebello
- Authors: Seotsanyana-Mokhosi, Itumeleng , Chen, Ji-Yao , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289294 , vital:56616 , xlink:href="https://doi.org/10.1142/S108842460500040X"
- Description: Adjacent binaphthalo-phthalocyanines tetra-substituted with phenoxy (4a), 4-carboxyphenoxy (4b) and 4-t-butylphenoxy (4c) groups, as well as the di-substituted 4-carboxyphenoxy (5b) have been synthesized and characterized. The photophysical and photochemical behavior of 4a-c, were compared with those of the corresponding di-substituted derivatives, (5a-c). The secondary substituents on the phenoxy ring have an influence on the aggregation of the molecules and hence on their photophysical properties. All of the complexes exhibit a relatively good conversion of energy from the triplet-excited state to the singlet oxygen. The less aggregated molecule (4c), has the highest singlet oxygen quantum yield. For all the molecules, fluorescence yields are low and they all have relatively shorter triplet lifetimes compared with the unsubstituted zinc phthalocyanine. Increasing the number of ring substituents on these rigid MPc complexes (from complexes 5 to 4) showed a general increase in the triplet state lifetimes and singlet oxygen quantum yields, and a decrease in stability.
- Full Text:
- Date Issued: 2005
- Authors: Seotsanyana-Mokhosi, Itumeleng , Chen, Ji-Yao , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289294 , vital:56616 , xlink:href="https://doi.org/10.1142/S108842460500040X"
- Description: Adjacent binaphthalo-phthalocyanines tetra-substituted with phenoxy (4a), 4-carboxyphenoxy (4b) and 4-t-butylphenoxy (4c) groups, as well as the di-substituted 4-carboxyphenoxy (5b) have been synthesized and characterized. The photophysical and photochemical behavior of 4a-c, were compared with those of the corresponding di-substituted derivatives, (5a-c). The secondary substituents on the phenoxy ring have an influence on the aggregation of the molecules and hence on their photophysical properties. All of the complexes exhibit a relatively good conversion of energy from the triplet-excited state to the singlet oxygen. The less aggregated molecule (4c), has the highest singlet oxygen quantum yield. For all the molecules, fluorescence yields are low and they all have relatively shorter triplet lifetimes compared with the unsubstituted zinc phthalocyanine. Increasing the number of ring substituents on these rigid MPc complexes (from complexes 5 to 4) showed a general increase in the triplet state lifetimes and singlet oxygen quantum yields, and a decrease in stability.
- Full Text:
- Date Issued: 2005
Immobilized cobalt (II) phthalocyanine–cobalt (II) porphyrin pentamer at a glassy carbon electrode
- Ozoemena, Kenneth I, Zhao, Zhixin, Nyokong, Tebello
- Authors: Ozoemena, Kenneth I , Zhao, Zhixin , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/300322 , vital:57916 , xlink:href="https://doi.org/10.1016/j.elecom.2005.04.019"
- Description: This communication describes the electrochemistry of a novel cobalt phthalocyanine–cobalt porphyrin (cobalt(II)phthalocyanine–cobalt(II)tetra(5-phenoxy-10,15,20-triphenylporphyrin)) (CoPc-(CoTPP)4) immobilised onto a glassy carbon electrode (GCE). The GCE-CoPc-(CoTPP)4 displayed high efficiency as a potential amperometric sensor for hydrogen peroxide (H2O2) in neutral and alkaline pH conditions. Electrochemical and electrocatalytic properties of the pentamer seem to depend mostly on the central CoPc, and partly, on the synergistic effect of the CoPc/CoPP units. The GCE-CoPc-(CoTPP)4 showed very fast amperometric response (∼1 s), with linearities up to ⩾1.50 mM, low detection limits (μM range) and stability (8 weeks) towards the amperometric determination of laboratory and medical solutions of H2O2.
- Full Text:
- Date Issued: 2005
- Authors: Ozoemena, Kenneth I , Zhao, Zhixin , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/300322 , vital:57916 , xlink:href="https://doi.org/10.1016/j.elecom.2005.04.019"
- Description: This communication describes the electrochemistry of a novel cobalt phthalocyanine–cobalt porphyrin (cobalt(II)phthalocyanine–cobalt(II)tetra(5-phenoxy-10,15,20-triphenylporphyrin)) (CoPc-(CoTPP)4) immobilised onto a glassy carbon electrode (GCE). The GCE-CoPc-(CoTPP)4 displayed high efficiency as a potential amperometric sensor for hydrogen peroxide (H2O2) in neutral and alkaline pH conditions. Electrochemical and electrocatalytic properties of the pentamer seem to depend mostly on the central CoPc, and partly, on the synergistic effect of the CoPc/CoPP units. The GCE-CoPc-(CoTPP)4 showed very fast amperometric response (∼1 s), with linearities up to ⩾1.50 mM, low detection limits (μM range) and stability (8 weeks) towards the amperometric determination of laboratory and medical solutions of H2O2.
- Full Text:
- Date Issued: 2005
Photophysical and photochemical studies of sulphonated non-transition metal phthalocyanines in aqueous and non-aqueous media
- Ogunsipe, Abimbola, Nyokong, Tebello
- Authors: Ogunsipe, Abimbola , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289271 , vital:56614 , xlink:href="https://doi.org/10.1016/j.jphotochem.2005.03.001"
- Description: The photophysical and photochemical parameters for mixed sulphonated metallophthalocyanine complexes (AlPcSmix, SiPcSmix, GePcSmix, SnPcSmix, and ZnPcSmix) are reported in phosphate buffer saline (PBS, pH 7.4), PBS containing the surfactant Triton X-100, and in dimethylsulphoxide (DMSO). The ground state spectra of SiPcSmix, GePcSmix and SnPcSmix show splitting of the Q-band in DMSO, but the fluorescence spectra have only one band, suggesting that only some components of the mixed complexes fluoresce. In general the quantum yields of fluorescence (ΦF) were smaller in DMSO compared to the aqueous solvents, while quantum yields of triplet state (ΦT) were larger in DMSO. Triplet lifetimes were much lower in aqueous solutions (compared to DMSO) due to the fact that water absorbs strongly around 1108 nm, which corresponds to the triplet energy of a metallophthalocyanine complex. The MPcSmix complexes quenched hydroquinone, and the Stern–Volmer constants follow the order: AlPcSmix > SiPcSmix > GePcSmix > ZnPcSmix > SnPcSmix which is the order of the extinction coefficients (of the low energy band for complexes with split Q-band) of these molecules. The rate constants for fluorescence, intersystem crossing, internal conversion, and photodegradation were determined from the hydroquinone quenching data.
- Full Text:
- Date Issued: 2005
- Authors: Ogunsipe, Abimbola , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289271 , vital:56614 , xlink:href="https://doi.org/10.1016/j.jphotochem.2005.03.001"
- Description: The photophysical and photochemical parameters for mixed sulphonated metallophthalocyanine complexes (AlPcSmix, SiPcSmix, GePcSmix, SnPcSmix, and ZnPcSmix) are reported in phosphate buffer saline (PBS, pH 7.4), PBS containing the surfactant Triton X-100, and in dimethylsulphoxide (DMSO). The ground state spectra of SiPcSmix, GePcSmix and SnPcSmix show splitting of the Q-band in DMSO, but the fluorescence spectra have only one band, suggesting that only some components of the mixed complexes fluoresce. In general the quantum yields of fluorescence (ΦF) were smaller in DMSO compared to the aqueous solvents, while quantum yields of triplet state (ΦT) were larger in DMSO. Triplet lifetimes were much lower in aqueous solutions (compared to DMSO) due to the fact that water absorbs strongly around 1108 nm, which corresponds to the triplet energy of a metallophthalocyanine complex. The MPcSmix complexes quenched hydroquinone, and the Stern–Volmer constants follow the order: AlPcSmix > SiPcSmix > GePcSmix > ZnPcSmix > SnPcSmix which is the order of the extinction coefficients (of the low energy band for complexes with split Q-band) of these molecules. The rate constants for fluorescence, intersystem crossing, internal conversion, and photodegradation were determined from the hydroquinone quenching data.
- Full Text:
- Date Issued: 2005
Modelling the sustainable harvest of Sclerocarya birrea subsp. caffra fruits in the South African lowveld
- Emanuel, P L, Shackleton, Charlie M, Baxter, Jeremy
- Authors: Emanuel, P L , Shackleton, Charlie M , Baxter, Jeremy
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/181312 , vital:43718 , xlink:href="https://doi.org/10.1016/j.foreco.2005.03.066"
- Description: Levels of commercialization, size class profile and fruit production of Sclerocarya birrea (marula) trees were studied in the Bushbuckridge region of South Africa. A stage-based population matrix model was used to estimate the sustainable yield for S. birrea fruit. The trees begin to bear fruit at an average size of 42.8 cm in circumference and this relates to an approximate age of 19 years. For a stable size class profile, the population growth rate, λ, was 1.1828758. The observed size class profile did not conform to the stable stage size class profile, obtained from the model. Thus, it was not possible to predict the state of the observed population. Using the model, it was estimated that 92% of fruit could be removed without impacting the current population profile. The management of other more destructive forms of S. birrea resource use (such as bark or firewood harvesting), however, do need to be monitored to limit negative impacts on the population that may reduce fruit availability for regeneration or cropping.
- Full Text:
- Date Issued: 2005
- Authors: Emanuel, P L , Shackleton, Charlie M , Baxter, Jeremy
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/181312 , vital:43718 , xlink:href="https://doi.org/10.1016/j.foreco.2005.03.066"
- Description: Levels of commercialization, size class profile and fruit production of Sclerocarya birrea (marula) trees were studied in the Bushbuckridge region of South Africa. A stage-based population matrix model was used to estimate the sustainable yield for S. birrea fruit. The trees begin to bear fruit at an average size of 42.8 cm in circumference and this relates to an approximate age of 19 years. For a stable size class profile, the population growth rate, λ, was 1.1828758. The observed size class profile did not conform to the stable stage size class profile, obtained from the model. Thus, it was not possible to predict the state of the observed population. Using the model, it was estimated that 92% of fruit could be removed without impacting the current population profile. The management of other more destructive forms of S. birrea resource use (such as bark or firewood harvesting), however, do need to be monitored to limit negative impacts on the population that may reduce fruit availability for regeneration or cropping.
- Full Text:
- Date Issued: 2005
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