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Dr Banothile Makhubela

Dr Banothile Makhubela
Department of Chemical Sciences (APK)
Senior Lecturer

Contact Details
C2-Lab 328
+27 (0) 11 559 3782
 
APK

BIOGRAPHY 

Banothile Makhubela is from Mzinti, Mpumalanga Province, South Africa. She obtained a BSc in Chemistry and Mathematics from the University of Zululand, and was awarded BSc. Honours and MSc. degrees in Chemistry by the University of Cape Town (UCT). Her research projects (supervised the late Prof John R. Moss and Prof Gregory Smith) focused on the synthesis and reactivity of platinum- and osmium-containing metallacycloalkanes - a class of organometallic compounds that are key intermediates in catalytic transformations such as oligomerization/polymerization and metathesis. This research also led to the development of a new synthetic route to osmium arene precursor complexes directly from potassium osmate – a result that has allowed easier access to osmium dimers through a less toxic and safer starting material such as potassium osmate instead of osmium tetroxide.
In 2012, she was awarded a Ph.D by UCT (supervised by Prof Gregory Smith and Dr. Anwar Jardine). Her research looked into the design and synthesis of novel platinum group metal (PGM) based organometallic complexes tethered onto macromolecules and biopolymers for applications in catalysis and green chemistry, with an emphasis on clean catalytic transformations in aqueous media, metal catalyst recycling and sustainability.
Banothile was awarded the UCT Science Faculty, Oppenheimer Memorial Trust and National Research Foundation (NRF) Innovation Postdoc Fellowships. Her postdoc study involved the development and evaluation of new PGM metal-containing polymers and metallodendrimers as anticancer agents. This work has revealed promising insights into the cytotoxic mechanism of ruthenium- and osmium–containing complexes/ macromolecules against cancerous cells, which will aid future rational design of metallodrugs.

In 2017, she was listed as one of the top 200 young and influential South Africans by the Mail and Guardian newspaper.  She is a SciFinder Future Leader in Chemistry, German Academic Exchange (DAAD) alumnus and a Japan Society for the Promotion of Science (JSPS) Hope Fellow. 

RESEARCH INTERESTS

Dr Makhubela's research interests include the preparation and study of new metal complexes for applications in catalysis and metallodrug discovery.

The focus in catalysis is on how to use renewable and scalable resources, like plant biomass and carbon dioxide, to make useful products such as chemicals, fuel(blends) and functional polymers.  The catalysis aspect of this research makes use of water-soluble homogeneous catalysts (to aid catalyst recycling and re-use) and heterogenized catalysts, with use of in situ spectroscopy and computational methods, for reaction pathway and kinetic studies. 

The research group also prepares novel metal complexes for investigation as potential biomedicines. Here, the approach is to prepare bio-active molecule conjugated metal complexes as anticancer agents and to further probe the cytotoxic mechanism of these agents experimentally and by in silico methods.

COLLABORATORS

  • Dr Gift Mehlana, Department of Chemical Technology, Midlands State University, Zimbabwe.
  • Dr Richard Tia, Computational and Theoretical Chemistry Centre, Kwame Nkrumah University of Science and Technology, Ghana.
  • Dr Lungile Sitole, University of Johannesburg, Biochemistry.
  • Prof Grace Mugumbate at the Dept. of Chemistry, Chinhoyi University of Technology, Zimbabwe.

PROFESSIONAL EXPERIENCE

  • 2015-present: Senior Lecturer, University of Johannesburg, Dept. of Chemistry.
  • 2014: Lecturer and Researcher Fellow, University of Cape Town, Dept. of Chemistry.
  • 2011-2015: (Online) Teaching Assistant, University of South Africa, Dept.of Chemistry.


TEACHING EXPERIENCE
  • 4th year BSc., Honours, Organometallic Chemistry
  • 3rd year BSc., Coordination Chemistry
  • 1st year General Chemistry

PROFESSIONAL ASSOCIATIONS/AFFILITIONS
  • Member- South African Chemical Institute (2007-present)
  • Member- Catalysis Society of South Africa (2007-present)
  • Member- American Chemical Society (2013-present)
  • African Academy of Sciences Young Affiliate (2015-present)
  • The World Academy of Science Young Affiliate (2015-present)

SELECTED PUBLICATIONS 
1. Novisi K. Oklu, Banothile C.E. Makhubela, Highly selective and efficient solvent-free transformation of bio-derived levulinic acid to γ-valerolactone by Ru(II) arene catalyst precursorsInorganica Chimica Acta, 2018, 482, 460-468. DOI: 10.1016/j.ica.2018.06.050.
                                                      Biomass.jpg
Highlights: A highly selective method of converting bio-based levulinic acid to γ-valerolactone using formic acid as a hydrogen carrier.Hydrogenation of levulinic acid resulted in 100% conversions and selectivity to γ-valerolactone, and in situ NMR characterization has aided the proposal of a plausible mechanism of the reaction.Ruthenium pre-catalysts catalyze the hydrogenation reactions without the need of a solvent and are also recyclable, thereby making the entire reaction conditions greener. 
2. Edward Ocansey, James Darkwa; Banothile C.E. Makhubela. Synthesis, characterization and evaluation of bulky bis(pyrazolyl)palladium complexes in Suzuki–Miyaura cross-coupling reactions.RSC Advances, 2018, 8, 13826–13834. DOI: 10.1039/c8ra01430b.
Suzuki-Miyaura.png

Highlights: Bulky bis(pyrazolyl) palladium complexes show remarkable catalytic activity in  Suzuki-Miyaura cross-coupling reactions.


3. Gershon Amenuvor; James Darkwa; Banothile C.E. Makhubela. Homogeneous polymetallic Ruthenium(II)^Zinc(II) complexes: Robust catalysts for the efficient hydrogenation of levulinic acid to γ-valerolactoneCatalysis Science and Technology, 2018, 8, 2370-2380. DOI: 10.1039/C8CY00265G.
              ruthenium(ii) zinc(ii) complexes.png

Highlights: Homogeneous polymetallic Ruthenium(II)^Zinc(II) complexes are incredibly robust and stable catalysts that can be recycled up to a record seven times, without significant loss in activity. A reaction mechanism was proposed based on in situ NMR spectra obtained during a typical reaction.  

 


​4. Alphonse Fiebor, Richard Tia, Banothile C. E. Makhubela and Henok H. Kinfe, Water-soluble SNS cationic palladium(II) complexes and their Suzuki–  Miyaura cross-coupling reactions in aqueous mediumBeilstein Journal of  Organic Chemistry. 2018, 14, 1859–1870. DOI: 10.3762/bjoc.14.160.       

Palladium Sulfur Pincers in Suzuki.png         
HighlightsUnlike their SCS analogues, SNS pincer complexes are poorly studied for their use in coupling reactions. Accordingly, a series of water soluble cationic Pd(II) SNS pincer complexes have been successfully synthesised and investigated in detail for their catalytic activity in Suzuki–Miyaura coupling reactions. By using only 0.5 mol % loading of the complexes, the coupling of inactivated aryl bromides and activated aryl chlorides with various boronic acids in water was achieved in excellent yields and the catalysts were found to be reusable for three cycles without a significant loss of activity. The investigation of the mechanism of the reaction revealed that a Pd(II) to Pd(IV) route is the more likely pathway which was further supported by computational studies.                             

5. Banothile C. E. Makhubela *; James Darkwa. The Role of Noble Metal Catalysts in Conversion of Biomass and Bio-derived Intermediates to Fuels and ChemicalsJohnson Matthey Technology Reviews, 2018, 62, 4-31. DOI: 10.1595/205651317x696261.                                                                Renewable.jpgHighlights: In the face of growing oil demand the use of renewable feedstocks for the potential to supply transportation fuels, electricity, chemicals and materials is increasingly attractive. This review covers novel technologies and pathways to produce liquid fuels and chemical intermediates in an efficient and cost-effective way. Several commercial and pilot scale projects by companies including Anellotech, USA; Johnson Matthey, UK; GFBiochemicals, Italy; Quaker Oats, USA; Changchun Dacheng Group, China; Avantium, The Netherlands; BASF, Germany and Rennovia, USA are highlighted. The review focuses on the use of non-food competing biomass, namely cellulose and hemicellulose biomass, and the use of precious metals to effect the key reaction steps: hydrolysis, dehydration, hydrodeoxygenation, hydrogenation and oxidation. The value added products achieved include fine chemicals and functional materials. Among these are dimethylfuran, methylfuran, 5-(ethoxymethyl)furfural, γ-valerolactone, ethyl levulinate and valeric biofuels suitable as fuels and fuel additives as well as renewable alkanes in the C5–C15 range for gasoline and diesel fuel applications.
6. Diteboho S. Ramarou, Banothile C. E. Makhubela, Gregory S. Smith*, Synthesis of Rh(I) alkylated-PTA complexes as catalyst precursors in the aqueous-biphasic hydroformylation of 1-octene. Journal of Organometallic Chemistry. 2018, 870, 23-31.  

                                                   1 Octene hydroformylation.jpg
Highlights: A series of mono- and multivalent phosphorus-based ligands was synthesised by the lower-rim benzylation of the water-soluble ligand, 1,3,5-triaza-7-phosphaadamantane (PTA). These ligands were used to prepare mono-, bi- and trinuclear Rh(I) complexes whose catalytic activity, product selectivity and recyclability were evaluated in the aqueous biphasic hydroformylation of 1-octene.

7. Asanda C. Matsheku , Marian Y-H. Chen , Sandra Jordaan , Sharon Prince , Gregory S. Smith, Banothile C. E. Makhubela. Acridine-containing RuII, OsII, RhIII and IrIII Half-Sandwich Complexes: Synthesis, Structure and Antiproliferative Activity. Applied Organometallic Chemistry, 2017, e3852. DOI: 10.1002/aoc.3852.

Ru Anti cancer half-sandwich complexes.pngRu Anti cancer half-sandwich complexes1.png
Highlights: New acridine-conjugated half-sandwich neutral and cationic complexes were synthesized and characterized. These complexes displayed promising cytotoxicity against human promyelocytic leukemia cells (HL60) and a notable selectivity to cancerous cells in comparison to non-tumorous cells (FG0). NMR studies show that the most active complex binds to DNA model guanosine-5'-monophosphate (5'-GMP), thus suggesting that the cytotoxic mechanism involves metal complex interaction with 5'-GMP found on DNA.
​8. Gershon. Amenuvor; Banothile C.E. Makhubela*; James Darkwa*. Efficient Solvent-Free Hydrogenation of Bio-Derived Levulinic Acid to γ-Valerolactone by Pyrazolyl-phosphite and Pyrazolyl-phosphinite Ruthenium(II) Complexes. ACS Sustainable Chem. Eng., 2016, 4, 6010-6018. DOI10.1021/acssuschemeng.6b01281.
Levulinic acid hydrogenation.png

Highlights: Solvent-free conversion of bio-derived levulinic acid (LA) to γ-valerolactone (GVL) has been achieved by new pyrazolylphosphite and pyrazolylphosphinite ruthenium(II) complexes as catalyst precursors, using both formic acid and molecular hydrogen as hydrogen sources. The reactions were very efficient at moderate temperatures of 100–120 °C. With a catalyst loading of 0.1%, 100% LA conversion (with hydrogen gas) was achieved with 100% GVL selectivity at 110 °C and 15 bar. The catalyst was recyclable up to three times without significant loss of activity and selectivity. The catalyst precursors are found to be more efficient when the hydrogen source was molecular hydrogen as compared to formic acid. NMR studies of reactions involving formic acid as a hydrogen source indicate that the initial step in the reaction involves the decomposition of formic acid to CO2 and H2.

9. Shepherd Siangwata, Nadia Baartzes, Banothile C. E. Makhubela and Gregory S. Smith. Synthesis, characterisation and reactivity of water-soluble ferrocenylimine-Rh(I) complexes as aqueous-biphasic hydroformylation catalyst precursorsJournal of Organometallic Chemistry, 2015, 796, 26-32. DOI: 10.1016/j.jorganchem.2015.04.029.
water-soluble ferrocenylimine-Rh(I) complexes.jpg








HighlightsA series of water-soluble sulfonatosalicylaldimine-ferrocenylimine complexes and their corresponding rhodium complexes of general formula: [Fc-Rh(sulfsal)(COD)] [Fc = ferrocenylimine, sulfsal = sulfonated salicylaldimine, COD = cyclooctadiene] were synthesised and characterised using standard spectroscopic and analytical techniques. The heterobimetalic complexes show moderate activity as hydroformylation catalyst precursors

10. Banothile C. E. Makhubela, Mervin Meyer, Gregory S. Smith. Evaluation of trimetallic Ru(II)- and Os(II)-Arene complexes as potential anti-cancer agentsJournal of Organometallic Chemistry, 2014, 772-773. 229-241. DOI: 
                                                Ru anticancer complexes.png
Highlights: Several new trimetallic Ru(II)- and Os(II)-arene complexes based on tris-2-(salicylaldimine ethyl)amine and tris-2-(2-pyridylimine ethyl)amine scaffolds were synthesized and characterized. These complexes display moderate to high cytotoxicity against human osteosarcoma (MG63) and ovarian cisplatin resistant (A2780cisR) cancer cells. Furthermore, the systems serve as inhibitors and/or poisons to DNA topoisomerase I (Topo I).

11. Emma B. Hager, Banothile C.E Makhubela and Gregory S. Smith. Sulfonate functionalised salicylaldimine dendritic cores: precursors to water soluble Rh(I) metallodendrimers for aqueous biphasic hydroformylation of 1-octene. Dalton Transactions, 2012, 41, 13927-13935. DOI: 10.1039/C2DT31471A.                                                        
Dendrematic hydroformylation of 1-octene.png
HighlightsWater-soluble dendritic ligands based on tris-2-(5-sulfonato salicylaldimine ethyl)amine (5) and DAB-(5-sulfonato salicylaldimine) (6) (DAB = diaminobutane) were synthesized by means of Schiff base condensation and sulfonation reactions. These dendritic ligands were fully characterized by 1H NMR, 13C NMR and FT-IR spectroscopy, elemental analysis and mass spectrometry. Dendritic ligands (5 and 6) in combination with [RhCl(COD)]2 (COD = 1,5-cyclooctadiene) were evaluated in aqueous biphasic hydroformylation of 1-octene. New water-soluble mononuclear 5-sulfonato propylsalicylaldimine Rh(I) complexes (7 and 8) were synthesized and characterized using 1H NMR, 13C NMR and FT-IR spectroscopy, elemental analysis as well as mass spectrometry. These complexes were applied as catalyst precursors in aqueous biphasic hydroformylation reactions. All the catalyst precursors were active in the hydroformylation of 1-octene under the investigated conditions. Optimal conditions were realized at 75 °C (40 bars), where the best selectivity for aldehydes was noticed. Catalyst recycling was achieved up to 5 times with minimal loss in conversion and consistent chemoselectivities and regioselectivities. Less Rh leaching was observed in the dendritic systems (5 and 6)/[RhCl(COD)]2 as compared to mononuclear catalyst precursors (7 and 8) as determined by inductively coupled plasma-mass spectrometry (ICP-MS)

12. Banothile C.E Makhubela, Anwar. Jardine, Gregory S. Smith. Rh(I) complexes supported on a biopolymer as recyclable and selective hydroformylation catalystsGreen Chemistry, 2012, 14, 338-347. DOI: 10.1039/C1GC15979H.
                                                      Rh(I) hydroformylation catalysts.png

Highlights: Chitosan has been used as a sustainable support for Rh catalysts, which are active and selective for the desired linear aldehyde under mild reaction conditions - catalyst recycling is also possible. 

13. Banothile C.E Makhubela, Anwar. Jardine, Gregory S. Smith. Pd nano-sized particles supported on chitosan and 6-deoxy-6-amino chitosan as recyclable catalysts for Suzuki–Miyaura and Heck cross-coupling reactionsApplied Catalysis: A General  393, 2011, 231-241. DOI: 10.1016/j.apcata.2010.12.002.

                                                                                   Chitosan Pd catalysts in suzuki coupling.jpg

HighlightsChitosan-supported Pd(II) catalysts were synthesized in good yield. The Pd(II) catalysts were characterized using various analytical techniques. High catalytic activity was exhibited in Suzuki–Miyaura and Heck coupling reactions. No Pd leaching was detected in the products as determined by ICP-MS. The catalysts could be recycled and reused up to five times with consistent activity.



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