Associate Professor, Department of Chemical Sciences, University of Johannesburg - South Africa Phone: +27 11 559 6335 Address: University of Johannesburg, Doornfontein Campus John Orr building, Room 4116
ABSTRACT Triphenylphosphine-linkedmultiwalledcarbonnanotubes (Tpp-MWCNT) were prepared in aprotic... more ABSTRACT Triphenylphosphine-linkedmultiwalledcarbonnanotubes (Tpp-MWCNT) were prepared in aprotic media and under anhydrous conditions by treating bromo-arylated-MWCNT with potassium diphenylphosphine (Tpp-MWCNT (1)), or with chlorodiphenylphosphine and butyllithium (Tpp-MWCNT (2)). Tpp-MWCNT were characterised by various techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The presence of the expected elements (C and P) is evident in the XPS spectra. Furthermore XPS results showed the presence of phosphorus with average concentrations of 0.7% and 2.6% in Tpp-MWCNT (1) and Tpp-MWCNT (2), respectively. TGA results revealed the following thermaldecomposition order: Tpp-MWCNT (2) < Tpp-MWCNT (1) < purified MWCNT, thus suggesting that the thermal stability of the MWCNT decreases with increasing amount of triphenylphosphine moieties attached to their surface. Moreover TGA results demonstrate that Tpp-MWCNTs have improved flame retardant behaviour since they produce 4–5 times more char than purified MWCNT
Abstract: The aim of this project was to synthesize novel bisphosphonic acid derivatives, study t... more Abstract: The aim of this project was to synthesize novel bisphosphonic acid derivatives, study their reactivity and test them for antibacterial, antimalarial and antitrypanosomal activity. The first step towards the target compounds was the synthesis of substituted vinylgembisphosphonates by Knoevenagel condensation between aromatic aldehydes and tetraethylmethylenebisphosphonate. The vinyl bisphosphonates were then oxidized using hydrogen peroxide to give aryl substituted epoxygembisphosphonates. 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) catalysed and microwave assisted reactions of the epoxy bisphosphonates gave mixtures of phosphinyl phosphonate diastereomers due to phosphonate phosphate rearrangement of bisphosphonates under basic conditions and high temperatures. A new class of compounds analogous to the pyrophosphate, 1,4-azaphosphinane-3-phosphonates, were synthesized by phospha-Dieckmann condensation of amino diphosphonate. The vinylgembisphosphonates were deprotected by reacting with bromotrimethylsilane followed by methanolysis to give bisphosphonic acids. Epoxygembisphosphonates were dealkylated with dibutylamine to give novel aryl substituted dibutylammonium diethyl epoxygembisphosphonates salts. The compounds synthesized were characterised by nuclear magnetic resonance (NMR) spectroscopy, Fourier transformed infrared spectroscopy (FT-IR) and mass spectrometry...Ph.D. (Chemistry
Journal of Environmental Chemical Engineering, 2019
Abstract In this research, insoluble nanosponge β-cyclodextrin (β-CD) polyurethane was modified w... more Abstract In this research, insoluble nanosponge β-cyclodextrin (β-CD) polyurethane was modified with phosphorylated multiwalled carbon nanotubes (pMWCNTs) and further decorated with titanium dioxide and silver nanoparticles. This modification of β-CD polyurethane was achieved through subsequent reactions of amidation, cross polymerization, using a functional linker such as diisocyanate, and sol-gel. The new polymeric nanobiosorbent obtained was characterized by Fourier-transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM); for surface area analysis, the Brunauer-Emmett-Teller (BET) method was employed. The developed nanobiosorbent, with a high surface area (352.5 m2 g−1), favors the adsorption of trichloroethylene (TCE) and Congo red (CR) dye from wastewater samples using a batch method. The solution pH, adsorbent dosage effects, isotherm, kinetic, thermodynamic as well as regeneration and desorption studies on the adsorption mechanism were also explored. The nanobiosorbent maximum capacities of removal from the Langmuir model were respectively, 27507 mg g−1 (TCE) and 146.96 mg − (CR dye). The adsorption mechanisms of TCE and CR dye were well-established and taking place via an endothermic process.
Environmental Science and Pollution Research, 2014
Gadolinium oxide nanoparticles of diameters <5 nm were uniformly d... more Gadolinium oxide nanoparticles of diameters <5 nm were uniformly decorated on the surfaces of multiwalled carbon nanotubes which were subsequently used as templates to fabricate gadolinium oxide nanoparticle-decorated multiwalled carbon nanotube/titania nanocomposites. The prepared nanocomposites were evaluated for the photocatalytic degradation of methylene blue under simulated solar light irradiation. Higher photocatalytic activity was observed for the gadolinium oxide-decorated multiwalled carbon nanotube-based nanocomposites compared to the neat multiwalled carbon nanotube/titania nanocomposite and commercial titania. This improvement in photocatalytic activity was ascribed to the gadolinium oxide nanoparticles supported at the interface of the carbon nanotubes and titania resulting in efficient electron transfer between the two components of the composite. Total organic carbon (TOC) analysis revealed a higher degree of complete mineralisation of methylene blue (80.0 % TOC removal) which minimise the possible formation of toxic by-products. The photocatalyst could be re-used for five times, reaching a maximum degradation efficiency of 85.9 % after the five cycles. The proposed photocatalytic degradation mechanism is outlined herein.
In this paper we report a convenient and environmentally friendly method for the synthesis of sub... more In this paper we report a convenient and environmentally friendly method for the synthesis of substituted 1,2-epoxy ethylgembisphosphonates using hydrogen peroxide in methanol-water solvent system. This reaction allows easy access to the desired epoxy bisphosphonates in good to excellent yields. It can also be scaled up easily since it requires small amounts of solvents and there are no by-products. The epoxy bisphosphonates were dealkylated with dibutylamine under solvent-free conditions to give novel symmetrical dibutylammonium diethyl (oxirane-2,2-diyl)bisphosphonate salts.
Hybrid molecule approach of drug design has become popular due to advantages such as delayed resi... more Hybrid molecule approach of drug design has become popular due to advantages such as delayed resistance, reduced toxicity, ease of treatment of co-infection and lower cost of preclinical evaluation. Antifungal drugs currently available for the treatment of fungal diseases suffer a major side effect of drug resistance. Hybrid drugs development is one of the approaches that has been employed to control microbial resistance. Their antifungal activity is influenced by their design. This review is focused on hybrid molecules exhibiting antifungal properties to guide scientists in search of more efficient drugs for the treatment of fungal diseases.
Hybrid molecule approach of drug design has become popular due to advantages such as delayed resi... more Hybrid molecule approach of drug design has become popular due to advantages such as delayed resistance, reduced toxicity, ease of treatment of co-infection and lower cost of preclinical evaluation. Antifungal drugs currently available for the treatment of fungal diseases suffer a major side effect of drug resistance. Hybrid drugs development is one of the approaches that has been employed to control microbial resistance. Their antifungal activity is influenced by their design. This review is focused on hybrid molecules exhibiting antifungal properties to guide scientists in search of more efficient drugs for the treatment of fungal diseases.
This study reports the synthesis and characterization of a novel bio nanosponge filter for applic... more This study reports the synthesis and characterization of a novel bio nanosponge filter for applications in water treatment. Firstly the oxidized multiwalled carbon nanotubes (MWCNTs) were chlorinated using oxalyl chloride and then phosphorylated via an amidation reaction. The phosphorylated carbon nanotube (pMWCNT) obtained was polymerized with β-cyclodextrin (βCD) using hexamethylene diisocyanate (HMDI) as a linker. The resulting polymer (pMWCNT-βCD) was decorated by a sol-gel method with TiO2 and Ag nanoparticles to obtain a biopolymer nanocomposite, pMWCNT-βCD/TiO2-Ag. For a better evaluation of the target material, CD polymer and pMWCNT-CD polymer were also synthesized for comparison purposes. Fourier-transform infrared (FTIR) spectroscopy was used to confirm the presence of functional groups on the surface of modified MWCNTs and the polymerization reaction. Laser Raman spectroscopy analysis showed the presence of MWCNT, CD and the anatase crystalline form of TiO2 in the nanocomposite. Preliminary adsorption studies were also conducted in order to test the capability of the new bio nanosponge filter to remove metal ions pollutants from synthetic wastewater solutions.
This study reports the synthesis and characterization of a novel bio nanosponge filter for applic... more This study reports the synthesis and characterization of a novel bio nanosponge filter for applications in water treatment. Firstly the oxidized multiwalled carbon nanotubes (MWCNTs) were chlorinated using oxalyl chloride and then phosphorylated via an amidation reaction. The phosphorylated carbon nanotube (pMWCNT) obtained was polymerized with β-cyclodextrin (βCD) using hexamethylene diisocyanate (HMDI) as a linker. The resulting polymer (pMWCNT-βCD) was decorated by a sol-gel method with TiO2 and Ag nanoparticles to obtain a biopolymer nanocomposite, pMWCNT-βCD/TiO2-Ag. For a better evaluation of the target material, CD polymer and pMWCNT-CD polymer were also synthesized for comparison purposes. Fourier-transform infrared (FTIR) spectroscopy was used to confirm the presence of functional groups on the surface of modified MWCNTs and the polymerization reaction. Laser Raman spectroscopy analysis showed the presence of MWCNT, CD and the anatase crystalline form of TiO2 in the nanocomposite. Preliminary adsorption studies were also conducted in order to test the capability of the new bio nanosponge filter to remove metal ions pollutants from synthetic wastewater solutions.
Abstract γ-Cyclodextrin-graphene oxide nanocomposite was synthesized and characterized for sorpti... more Abstract γ-Cyclodextrin-graphene oxide nanocomposite was synthesized and characterized for sorption, kinetics, thermodynamics, and simulation studies of tetracycline and chlortetracycline antibiotics removal from water. The optimized sorption parameters were 400 mg/L concentration, 30 min contact time, pH 8.0, dose 1.0 g/L and 25 °C temperature. The sorption followed Langmuir, Temkin, and D-Rs models. The maximum removals of tetracycline and chlortetracycline were 91.25 and 93.75% respectively, with a variation of percentage removal at different pHs ranges [355.0 (88.75%), 360.0 (90.0%) and 365.0 mg/g (91.25%) for tetracycline and 365.0 (91.25%), 370.0 (92.5%) and 375.0 mg/g (93.75%) chlortetracycline]. The sorption followed pseudo-second kinetic order reaction and liquid film diffusion kinetic model. The positive values of entropy (12.043 & 12.842 kJ/mol.K) and negative values of enthalpy (-0.944 & −1.113 kJ/mol) and free energy (-14.60 to −13.55 kJ/mol) confirmed the spontaneous sorption at all temperatures. The simulation results agreed with the sorption results. Also, the modeling was used to ascertain the supramolecular mechanism, which involved hydrogen bonding and π-π interactions.
Phosphorus, Sulfur, and Silicon and the Related Elements, 2020
Abstract A series of 2-substituted vinylidene-1,1-bisphosphonate esters and their acids were synt... more Abstract A series of 2-substituted vinylidene-1,1-bisphosphonate esters and their acids were synthesized and tested in vitro for activity against Plasmodium falciparum and Trypanosoma brucei. For each compound, % parasite viability in treated wells was calculated relative to untreated controls for both P. falciparum and T. brucei. Fifty percentage inhibitory concentration (IC50) was also determined for the compounds. Chloroquine and pentamidine were used as positive control drug standards for activity against P. falciparum and T. brucei, respectively. The esters had better antiparasitic activity compared to their corresponding acids. Some of the compounds reduced % parasite viability to as low as 24.3% for P. falciparum and down to 0.602% for T. brucei. Tetraethyl-2-(o-tolyl)-ethene-1,1-bisphosphonate (3b) recorded the best IC50 against T. brucei which was 0.0345 µmol/mL. GRAPHICAL ABSTRACT
ABSTRACT Triphenylphosphine-linkedmultiwalledcarbonnanotubes (Tpp-MWCNT) were prepared in aprotic... more ABSTRACT Triphenylphosphine-linkedmultiwalledcarbonnanotubes (Tpp-MWCNT) were prepared in aprotic media and under anhydrous conditions by treating bromo-arylated-MWCNT with potassium diphenylphosphine (Tpp-MWCNT (1)), or with chlorodiphenylphosphine and butyllithium (Tpp-MWCNT (2)). Tpp-MWCNT were characterised by various techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The presence of the expected elements (C and P) is evident in the XPS spectra. Furthermore XPS results showed the presence of phosphorus with average concentrations of 0.7% and 2.6% in Tpp-MWCNT (1) and Tpp-MWCNT (2), respectively. TGA results revealed the following thermaldecomposition order: Tpp-MWCNT (2) < Tpp-MWCNT (1) < purified MWCNT, thus suggesting that the thermal stability of the MWCNT decreases with increasing amount of triphenylphosphine moieties attached to their surface. Moreover TGA results demonstrate that Tpp-MWCNTs have improved flame retardant behaviour since they produce 4–5 times more char than purified MWCNT
Abstract: The aim of this project was to synthesize novel bisphosphonic acid derivatives, study t... more Abstract: The aim of this project was to synthesize novel bisphosphonic acid derivatives, study their reactivity and test them for antibacterial, antimalarial and antitrypanosomal activity. The first step towards the target compounds was the synthesis of substituted vinylgembisphosphonates by Knoevenagel condensation between aromatic aldehydes and tetraethylmethylenebisphosphonate. The vinyl bisphosphonates were then oxidized using hydrogen peroxide to give aryl substituted epoxygembisphosphonates. 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) catalysed and microwave assisted reactions of the epoxy bisphosphonates gave mixtures of phosphinyl phosphonate diastereomers due to phosphonate phosphate rearrangement of bisphosphonates under basic conditions and high temperatures. A new class of compounds analogous to the pyrophosphate, 1,4-azaphosphinane-3-phosphonates, were synthesized by phospha-Dieckmann condensation of amino diphosphonate. The vinylgembisphosphonates were deprotected by reacting with bromotrimethylsilane followed by methanolysis to give bisphosphonic acids. Epoxygembisphosphonates were dealkylated with dibutylamine to give novel aryl substituted dibutylammonium diethyl epoxygembisphosphonates salts. The compounds synthesized were characterised by nuclear magnetic resonance (NMR) spectroscopy, Fourier transformed infrared spectroscopy (FT-IR) and mass spectrometry...Ph.D. (Chemistry
Journal of Environmental Chemical Engineering, 2019
Abstract In this research, insoluble nanosponge β-cyclodextrin (β-CD) polyurethane was modified w... more Abstract In this research, insoluble nanosponge β-cyclodextrin (β-CD) polyurethane was modified with phosphorylated multiwalled carbon nanotubes (pMWCNTs) and further decorated with titanium dioxide and silver nanoparticles. This modification of β-CD polyurethane was achieved through subsequent reactions of amidation, cross polymerization, using a functional linker such as diisocyanate, and sol-gel. The new polymeric nanobiosorbent obtained was characterized by Fourier-transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM); for surface area analysis, the Brunauer-Emmett-Teller (BET) method was employed. The developed nanobiosorbent, with a high surface area (352.5 m2 g−1), favors the adsorption of trichloroethylene (TCE) and Congo red (CR) dye from wastewater samples using a batch method. The solution pH, adsorbent dosage effects, isotherm, kinetic, thermodynamic as well as regeneration and desorption studies on the adsorption mechanism were also explored. The nanobiosorbent maximum capacities of removal from the Langmuir model were respectively, 27507 mg g−1 (TCE) and 146.96 mg − (CR dye). The adsorption mechanisms of TCE and CR dye were well-established and taking place via an endothermic process.
Environmental Science and Pollution Research, 2014
Gadolinium oxide nanoparticles of diameters <5 nm were uniformly d... more Gadolinium oxide nanoparticles of diameters <5 nm were uniformly decorated on the surfaces of multiwalled carbon nanotubes which were subsequently used as templates to fabricate gadolinium oxide nanoparticle-decorated multiwalled carbon nanotube/titania nanocomposites. The prepared nanocomposites were evaluated for the photocatalytic degradation of methylene blue under simulated solar light irradiation. Higher photocatalytic activity was observed for the gadolinium oxide-decorated multiwalled carbon nanotube-based nanocomposites compared to the neat multiwalled carbon nanotube/titania nanocomposite and commercial titania. This improvement in photocatalytic activity was ascribed to the gadolinium oxide nanoparticles supported at the interface of the carbon nanotubes and titania resulting in efficient electron transfer between the two components of the composite. Total organic carbon (TOC) analysis revealed a higher degree of complete mineralisation of methylene blue (80.0 % TOC removal) which minimise the possible formation of toxic by-products. The photocatalyst could be re-used for five times, reaching a maximum degradation efficiency of 85.9 % after the five cycles. The proposed photocatalytic degradation mechanism is outlined herein.
In this paper we report a convenient and environmentally friendly method for the synthesis of sub... more In this paper we report a convenient and environmentally friendly method for the synthesis of substituted 1,2-epoxy ethylgembisphosphonates using hydrogen peroxide in methanol-water solvent system. This reaction allows easy access to the desired epoxy bisphosphonates in good to excellent yields. It can also be scaled up easily since it requires small amounts of solvents and there are no by-products. The epoxy bisphosphonates were dealkylated with dibutylamine under solvent-free conditions to give novel symmetrical dibutylammonium diethyl (oxirane-2,2-diyl)bisphosphonate salts.
Hybrid molecule approach of drug design has become popular due to advantages such as delayed resi... more Hybrid molecule approach of drug design has become popular due to advantages such as delayed resistance, reduced toxicity, ease of treatment of co-infection and lower cost of preclinical evaluation. Antifungal drugs currently available for the treatment of fungal diseases suffer a major side effect of drug resistance. Hybrid drugs development is one of the approaches that has been employed to control microbial resistance. Their antifungal activity is influenced by their design. This review is focused on hybrid molecules exhibiting antifungal properties to guide scientists in search of more efficient drugs for the treatment of fungal diseases.
Hybrid molecule approach of drug design has become popular due to advantages such as delayed resi... more Hybrid molecule approach of drug design has become popular due to advantages such as delayed resistance, reduced toxicity, ease of treatment of co-infection and lower cost of preclinical evaluation. Antifungal drugs currently available for the treatment of fungal diseases suffer a major side effect of drug resistance. Hybrid drugs development is one of the approaches that has been employed to control microbial resistance. Their antifungal activity is influenced by their design. This review is focused on hybrid molecules exhibiting antifungal properties to guide scientists in search of more efficient drugs for the treatment of fungal diseases.
This study reports the synthesis and characterization of a novel bio nanosponge filter for applic... more This study reports the synthesis and characterization of a novel bio nanosponge filter for applications in water treatment. Firstly the oxidized multiwalled carbon nanotubes (MWCNTs) were chlorinated using oxalyl chloride and then phosphorylated via an amidation reaction. The phosphorylated carbon nanotube (pMWCNT) obtained was polymerized with β-cyclodextrin (βCD) using hexamethylene diisocyanate (HMDI) as a linker. The resulting polymer (pMWCNT-βCD) was decorated by a sol-gel method with TiO2 and Ag nanoparticles to obtain a biopolymer nanocomposite, pMWCNT-βCD/TiO2-Ag. For a better evaluation of the target material, CD polymer and pMWCNT-CD polymer were also synthesized for comparison purposes. Fourier-transform infrared (FTIR) spectroscopy was used to confirm the presence of functional groups on the surface of modified MWCNTs and the polymerization reaction. Laser Raman spectroscopy analysis showed the presence of MWCNT, CD and the anatase crystalline form of TiO2 in the nanocomposite. Preliminary adsorption studies were also conducted in order to test the capability of the new bio nanosponge filter to remove metal ions pollutants from synthetic wastewater solutions.
This study reports the synthesis and characterization of a novel bio nanosponge filter for applic... more This study reports the synthesis and characterization of a novel bio nanosponge filter for applications in water treatment. Firstly the oxidized multiwalled carbon nanotubes (MWCNTs) were chlorinated using oxalyl chloride and then phosphorylated via an amidation reaction. The phosphorylated carbon nanotube (pMWCNT) obtained was polymerized with β-cyclodextrin (βCD) using hexamethylene diisocyanate (HMDI) as a linker. The resulting polymer (pMWCNT-βCD) was decorated by a sol-gel method with TiO2 and Ag nanoparticles to obtain a biopolymer nanocomposite, pMWCNT-βCD/TiO2-Ag. For a better evaluation of the target material, CD polymer and pMWCNT-CD polymer were also synthesized for comparison purposes. Fourier-transform infrared (FTIR) spectroscopy was used to confirm the presence of functional groups on the surface of modified MWCNTs and the polymerization reaction. Laser Raman spectroscopy analysis showed the presence of MWCNT, CD and the anatase crystalline form of TiO2 in the nanocomposite. Preliminary adsorption studies were also conducted in order to test the capability of the new bio nanosponge filter to remove metal ions pollutants from synthetic wastewater solutions.
Abstract γ-Cyclodextrin-graphene oxide nanocomposite was synthesized and characterized for sorpti... more Abstract γ-Cyclodextrin-graphene oxide nanocomposite was synthesized and characterized for sorption, kinetics, thermodynamics, and simulation studies of tetracycline and chlortetracycline antibiotics removal from water. The optimized sorption parameters were 400 mg/L concentration, 30 min contact time, pH 8.0, dose 1.0 g/L and 25 °C temperature. The sorption followed Langmuir, Temkin, and D-Rs models. The maximum removals of tetracycline and chlortetracycline were 91.25 and 93.75% respectively, with a variation of percentage removal at different pHs ranges [355.0 (88.75%), 360.0 (90.0%) and 365.0 mg/g (91.25%) for tetracycline and 365.0 (91.25%), 370.0 (92.5%) and 375.0 mg/g (93.75%) chlortetracycline]. The sorption followed pseudo-second kinetic order reaction and liquid film diffusion kinetic model. The positive values of entropy (12.043 & 12.842 kJ/mol.K) and negative values of enthalpy (-0.944 & −1.113 kJ/mol) and free energy (-14.60 to −13.55 kJ/mol) confirmed the spontaneous sorption at all temperatures. The simulation results agreed with the sorption results. Also, the modeling was used to ascertain the supramolecular mechanism, which involved hydrogen bonding and π-π interactions.
Phosphorus, Sulfur, and Silicon and the Related Elements, 2020
Abstract A series of 2-substituted vinylidene-1,1-bisphosphonate esters and their acids were synt... more Abstract A series of 2-substituted vinylidene-1,1-bisphosphonate esters and their acids were synthesized and tested in vitro for activity against Plasmodium falciparum and Trypanosoma brucei. For each compound, % parasite viability in treated wells was calculated relative to untreated controls for both P. falciparum and T. brucei. Fifty percentage inhibitory concentration (IC50) was also determined for the compounds. Chloroquine and pentamidine were used as positive control drug standards for activity against P. falciparum and T. brucei, respectively. The esters had better antiparasitic activity compared to their corresponding acids. Some of the compounds reduced % parasite viability to as low as 24.3% for P. falciparum and down to 0.602% for T. brucei. Tetraethyl-2-(o-tolyl)-ethene-1,1-bisphosphonate (3b) recorded the best IC50 against T. brucei which was 0.0345 µmol/mL. GRAPHICAL ABSTRACT
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