University of Botswana, Botswana
Daphne T Mapolelo has expertise in synthesis and spectroscopic characterization of ruthenium metal complexes. My current research interest lies in the synthesis, characterization and biological application of ruthenium polydentate pyridine and benzimidazole-based complexes. The characterization of these ruthenium complexes requires the use of a wide range of spectroscopic/magnetic techniques such as electron paramagnetic resonance (EPR), Nuclear Magnetic Resonance (NMR), MÖssbauer, resonance Raman, natural and magnetically induced circular dichroism (CD and MCD). In addition, in vitro and in vivo studies are employed to test the metal complexes for anticancer, anti HIV and antimicrobial activities.
We report herein the synthesis and characterization of Ru(II)-bis-benzimidazole-based complexes, Ru(III)- polydentate pyridine-based complexes and Ru(II)-bisbenzimidazole polydentate pyridine-based complexes respectively, being Ruthenium-aquo-1, 2-di(1Hbenzo[d]imidazole-2-yl) ethane trichloride [Ru(bbe)(H2O)Cl3], Ruthenium-tri-tert-butyl-2,2’,6,2’’- terpyridine-chloride-N,N,N’,N’-Tetrakis(pryidylmethyl)- 1,8 octanediamine perchlorate [Ru(terpy*)(1,8)Cl](ClO4)4 and Ruthenium-aquo-1, 2-di(1H-benzo[d]imidazole-2- yl)ethane chloride- N,N,N’,N’- Tetrakis- (pyridylmethyl)- 1,8-octanediamine perchlorate [Ru(bbe)(1,8)(H2O)Cl2](ClO4)4 respectively. Characterization of all the complexes was done by FTIR, 1 H-NMR, 13C-NMR spectroscopies, and Elemental Analysis. Cytotoxicity and antimicrobial activity studies against both gram negative and positive bacteria, as well as multi drug resistant bacterial isolates were tested for all the complexes. The CC50, EC50, MIC and possible mode of action for each metal complex were determined. Results showed that all metal complexes were not toxic to peripheral blood mononuclear cell (PBMCs), with calculated CC50 values ranging between 0.48 mg/mL to 1.0mg/mL. Antimicrobial properties of the complexes were determined by Kirby Bauer (KB) method and it was observed that both gram negative and positive bacteria, including multi drug resistant test microorganisms were susceptible. The calculated MICs ranged between 0.25- 2mg/L. The effective concentration (EC50) was between 0.18 mg/mL and 0.5mg/mL. Whereas the selective index (SI = CC50/EC50) was is 1.0 and 2.6 indicating low to high potential as microbial agent. The metal complexes were tested for possible mode of action and did not conform to known bactericidal activities suggesting a novel mechanism yet to be elucidated. !!!