Peter Ongoma’s research while affiliated with Egerton University and other places

Currently, researchers are seeking to reduce heavy metal contamination from the environment, using agricultural waste materials like rice husk, groundnuts shells among others. The study focused on the removal of Cu(II), Pb(II), Cd(II), Ni(II), and Cr(III) ions from aqueous solutions and Nakuru industrial wastewater using sugarcane bagasse (NSCB) and valorised bagasse ash (VSCB), as alternative low-cost agricultural waste bio-sorbents. To achieve this goal, sugarcane bagasse was collected from Nzoia sugar industry in western Kenya, while the valorised bagasse was obtained by heating sugarcane bagasse sample in a muffle furnace at 300°C for three hours. Furthermore, batch adsorption studies were performed, and the effects of several factors, i.e. adsorbent particle size, pH, contact time, initial heavy metal ions concentration and temperature were investigated to optimise the removal efficiency of Pb, Cu, Cd, Ni, and Cr. The optimal adsorption conditions were pH of 5.0, adsorbent dosage of 0.1 g and ≤ 150µm particle size, equilibrium time of 60 minutes and at 25 degrees Celcius. The removal kinetics of the metal ions onto both adsorbents fitted well with the pseudo-second-order model. The removal kinetics of the metal ions onto both adsorbents fitted well with the pseudo-second-order model. The adsorption of Pb2+ and Ni2+ onto NSCB fitted better with the Freundlich isotherm model, while Cd2+, Cu2+ and Cr3+ showed better fit for the Langmuir isotherm model. As for VSCB adsorbent, Cr3+ has a better fit with the Langmuir isotherm model whereas Pb2+, Ni2+, Cd2+, and Cu2+ fitted well on the Freundlich isotherm model. Freundlich constant’s (1/n) values and the separation factor (RL) from the Langmuir isotherm model indicate that the metal ions were favourably adsorbed onto the adsorbents. Langmuir isotherm model was used to estimate the maximum adsorption capacities (qmax) for Cu(II), Pb(II), Ni(II), Cd(II), and Cr(III). The negative free energy change (∆G) values revealed that adsorption process of the metal ions onto NSCB and VSCB was spontaneous. Fourier Transform Infrared Spectroscopy (FTIR) was used for characterization studies. Interactions with metal ions caused the frequencies of the active functional groups, –OH, C=O and C=C, on the bio-sorbent surfaces to shift to higher values. Therefore, sugarcane bagasse and valorised bagasse have demonstrated higher potential to remove relatively all selected heavy metals in the industrial wastewater at controlled pH.

Organometallic η6-arene ruthenium(II) complexes with 3-chloro-6-(1H-pyrazol-1-yl)pyridazine (Ru1, Ru2, and Ru5) and 3-chloro-6-(3,5-dimethyl-1H-pyrazol-1-yl)pyridazine (Ru3-4) N,N’ heterocyclic and η6-arene (cymene (Ru1-4) or toluene (Ru 5)) have been synthesized. The ruthenium(II) complexes have common “three-legged piano-stool” pseudo-octahedral structures known for half-sandwich complexes. Evolution of their UV–Visible absorption spectra in PBS buffer or DMSO over 24 h confirmed their good solvolysis stability. Titrations of the complexes with the calf thymus DNA (CT-DNA) were monitored using UV–Visible absorption and fluorescence spectroscopies. The complexes interact moderately with CT-DNA and their binding constants are in the order of 104 M−1. Competitive binding of the complexes to a DNA-Hoechst 33,258 depicted competitive displacement of Hoechst from DNA’s minor grooves. These complexes bind to glutathione forming GSH-adducts through S coordination by replacement of a halide, with the iodo-analogues having higher binding constants than the chloro-complexes. Cyclic voltammograms of the complexes exhibited one electron-transfer quasi-reversible process. Trends in the molecular docking data of Ru1-5/DNA were similar to those for DNA binding constants. Of the five, only Ru1, Ru3 and Ru5 showed some activity (moderate) against the MCF-7 breast cancer cells with IC50 values in the range of 59.2–39.9 for which Ru5 was the most active. However, the more difficult-to-treat cell line, MDA-MB 231 cell was recalcitrant to the treatment by these complexes. Molecular docking simulations visualized the interactions of arene Ru(II) complexes with CT-DNA via minor grooving. The trends were corroborated by electrochemical and cytotoxicity data.

Herein, we report the synthesis and single-crystal X-ray structures of three (η⁶-p-cymene)Ru(II) tetrafluoroborate salts, viz., [(η⁶-p-cymene)(3-chloro-6-(1H-pyrazol-1-yl)pyridazine)Ru(X)]BF4, (X = Cl, Br, I), Ru1-3. They were prepared by the reactions of [(η⁶-p-cymene)Ru(μ-X)(X)]2, (X = Cl, Br, I) with two-mole equivalents of 3-chloro-6-(1H-pyrazol-1-yl)pyridazine, under inert conditions at ambient temperatures, and subsequently precipitated by the addition of excess BF4⁻ ions. Orange crystalline precipitates were obtained in good yields, from which the respective single crystals for X-ray diffraction analysis were recrystallized by slow evaporation from their methanolic/diethyl ether solutions. The Ru(II) complexes were characterized by various spectroscopic techniques and chemical methods, which included FTIR, ¹H/¹³C NMR, UV-visible absorption, mass spectrometry, and elemental analysis. The molecular structures were solved by single-crystal X-ray crystal diffraction analysis. The complexes crystallized in the monoclinic crystal system in the P21/c (Ru1-2) and P21/n (Ru3) space groups. Density Functionals Theoretical (DFT) calculations were performed in methanol to gain an understanding of the electronic and structural properties of the complexes. Trends in the data metrics were established, and selected data were compared with the diffraction data. The electrophilicity indices of Ru1-3 follow the order Ru3 > Ru2 > Ru1, and the trend is in line with their anticipated order of reactivity towards nucleophiles.

The powder of the arene osmium(II) complex, [Os(II)(dpzm)(η⁶-p-cym)Cl]BF4 (dpzm = di(1H-pyrazol-1-yl)methane; η⁶-p-cym = para-cymene), with a formula of C17H22BClF4N4Os (referred to herein as 1) was isolated from the reaction of [(η⁶-p-cym)Os(μ-Cl)(Cl)]2 with dpzm dissolved in acetonitrile and under a flow of nitrogen gas. It was characterized by spectroscopic techniques (viz., FTIR, ¹H NMR, UV-Visible absorption). Yellow crystal blocks of 1 were grown by the slow evaporation from the methanolic solution of its powder. The single-crystal X-ray structure of 1 was solved by diffraction analysis on a Bruker APEX Duo CCD area detector diffractometer using the Cu(Kα), λ = 1.54178 Å as the radiation source, and 1 crystallizes in the monoclinic crystal system and the C2/c (no. 15) space group.