Browsing by Author "Ainooson, M.K."
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Item Effects of electrochemical properties of ferrocenylpyrazolylnickel( ii ) and palladium( ii ) compounds on their catalytic activities in ethylene oligomerisation reactions(RSC Advances, 2018-01) Obuah, C.; Ainooson, M.K.; Darkwa, J.Palladium complexes of ferrocenylpyrazolylpyridine and ferrocenylpyrazolylamine were synthesised and screened as pre-catalysts (1–4) for olefin polymerisation. The pre-catalysts 1–4 on activation with EtAlCl2 in the presence of ethylene with chlorobenzene or hexane as solvent were highly active with 1 being the most active, with an activity of 360 kg mol Pd⁻¹ h⁻¹. The major product from the reaction was 1-butene and high carbon content oligomers. The molecular weight (m/z) of the high carbon content oligomers is as high as 623.0. When toluene is used as solvent, the products obtained were ethyltoluene and butyltoluene and 1-butene. The electronic properties of the ligands (L1–L7) and complexes (1–10) were determined by cyclic voltammetry (CV) and molecular modelling. The CV results show that the ferrocenyl is easily oxidized upon the introduction of pyrazolyl derivatives, the process is quasi-reversible. However, complexation of the ligands with palladium or nickel results in difficulty in oxidizing the ferrocenyl moiety. This is an indication of the electrophilic nature of both the palladium and nickel centres. The mechanism of the oxidation was observed to be diffusion-controlled and is independent of scan rate. Molecular modelling experiments show that nickel and palladium complexes have lower HOMO–LUMO gaps and high global descriptors, an indication of a highly electrophilic metal centre. A plot of the electrophilicity indices of the pre-catalysts against yield of the oligomers show a linear correlation, an indication that the electrophilicity of the metal centre plays an important role in the activity of these pre-catalysts.Item In vitro activity of soybean extract on cocoa disease pathogens (Erythricium salmonicolor and Marasmiellus scandens) and termite pest (Microtermes subhyalinus)(Cogent Food & Agriculture, 2022) Bukari, Y.; Avicor, S.W.; Awudzi, G.; Ainooson, M.K.; Eric K. AsareThis study evaluated the antifungal and insecticidal properties of soybean extract on Marasmiellus scandens (causal pathogen of white thread blight disease on cocoa), Erythricium salmonicolor (causal pathogen of pink disease of cocoa) and termite (Microtermes subhyalinus). Agar plate test was used to determine the inhibitory activity of the extract on mycelial growth of the pathogens while a contact toxicity bioassay was conducted on the termites. Extract of the soybean reduced mycelial growth in a dose-dependent pattern, with 20% of the extract attaining the highest inhibition. Percentage inhibition of 80.4 and 86.8 were recorded for E. salmonicolor and M. scandens, respectively after 7 days of incuba tion. The IC50 values ranged between 0.64–2.44% and 0.12–0.45% for E. salmonicolor and M. scandens respectively. However, activity of the extract on the termite was low, with an LC50 of 15.42% after 24 hours of exposure. The effect of the extract on the fungal pathogens indicates that it could be further explored towards the development of a plant-based control method against white thread blight and pink diseases of cocoa in Ghana.Item A new sulfonamide-based chemosensor for potential fluorescent detection of Cu2þ and Zn2þ ions(Tetrahedron, 2023) Amoah, C.; Obuah, C.; Ainooson, M.K.; Oppong, A.; Muller, A.In recent times, there has been an increased demand in the search for probing materials for numerous substances in the environment such as the detection of metals ions. In this study, a new class of pyrazolyl-sulfonamide derivatives of para-nitroaniline were synthesized following a multistep approach. The ligands and complexes were characterized using NMR spectroscopy, IR spectroscopy, and mass spectrometry. All the compounds C1eC3 were synthesized in very good yields (85%e92%) and their photo-physical properties measured. All the compounds show fluorescence behaviour with emissions within the UV and far visible range with quantum yields between 7.7% and 25.7%. TD-DFT calculations predictions for the electronic transitions present are in good agreement with experimental observations. Fluorescent probing studies conducted on the compounds show that C1eC3 were analytically sensitive and possessed significant selectivity towards Cu2þ (for C3) and Zn2þ (for C1 and C2) ions with detection limits between 0.011 and 0.103 mg/L for Cu2þ ions and 0.002e0.135 mg/L for Zn2þ ions. Overall, C1 was found to be the most sensitive molecule for the metals studied, having good quantum yield and better selectivity for Zn2þ ion compared to Cu2þ.Item Quantum Mechanistic Studies of the Oxidation of Ethylene by Rhenium Oxo Complexes(Hindawi, 2021) Fosu, E.A.; Obuah, C.; Hamenu, L.; Aniagyei, A.; Ainooson, M.K.; Govender, K.K.Transition-metal-mediated oxygen transfer reactions are of importance in both industry and academia; thus, a series of rhenium oxo complexes of the type ReO3L (L = O− , Cl− , F− , OH− , Br− , I− ) and their effects as oxidation catalysts on ethylene have been studied. %e activation and reaction energies for the addition pathways involving multiple spin states (singlet and triplet) have been computed. In all cases, structures on the singlet potential energy surfaces showed higher stability compared to their counterparts on the triplet potential energy surfaces (PESs). Frontier Molecular Orbital calculations show electrons flow from the HOMO of ethylene to the LUMO of rhenium for all complexes studied except ReO4 − where the reverse case occurs. In the reaction between ReO3L (L = O− , Cl− , F− , OH− , Br− , and I− ) and ethylene, the concerted [3 + 2] addition pathway on the singlet PES leading to the formation of dioxylate intermediate is favored over the [2 + 2] addition pathway leading to the formation of a metal laoxetane intermediate and subsequent rearrangement to the dioxylate. %e activation and the reaction energies for the formation of the dioxylate on the singlet PES for the ligands studied followed the order O− > OH− > I − > F− > Br− >Cl− and O− > OH− > F− > I − > Br− > Cl− , respectively. Furthermore, the activation and the reaction energies for the formation of the metallaoxetane intermediate increase in the order O− > OH− > I − > Br− > Cl− > F− and O− > Br− > I − >Cl− > OH− > F− , respectively. %e subsequent rearrangement of the metallaoxetane intermediate to the dioxylate is only feasible in the case of ReO4 − . Of all the complexes studied, the best dioxylating catalyst is ReO3Cl (singlet surface) and the best epoxidation catalyst is ReO3F (singlet surface).Item Synthesis, characterization and fluorescent properties of ferrocenyl pyrazole and triazole ligands and their palladium complexes(Journal of Organometallic Chemistry, 2021) Amoah, C.; Obuah, C.; Ainooson, M.K.; Muller, A.The search for new fluorescent materials with high quantum yields has been the focus of research, con- sidering the diverse applications that fluorescent materials present. In this study, ferrocenyl pyrazolyl ( L1) and ferrocenyl triazolyl ( L2 ) ligands and their palladium metal complexes ( 1 and 2 ) were synthesized to investigate their fluorescence properties. While the pyrazolyl ligand was prepared through a ligand substitution reaction, synthesis of the triazolyl derivative involved the [3 + 2] azide-alkyne using click chemistry. All the prepared compounds have been characterized by NMR and IR spectroscopy, elemental analysis, mass spectrometry and single-crystal X-ray crystallography. These air-stable compounds were prepared in moderate to good yields (70% and 83%). The ferrocenyl-pyrazolyl L1 and ferrocenyl-triazolyl L2 ligands showed near-infrared (NIR) emission bands with quantum yields of 20% and 26% respectively. The addition of the Pd 2 + ions results in the reduction of fluorescence intensity and quantum yield. Such fluorescent properties demonstrate their potential use in bio-analysis and as fluorogenic probing.Item Theoretical studies on the reaction mechanisms of the oxidation of tetramethylethylene using MO3Cl (M=Mn, Tc and Re)(Journal of Molecular Graphics and Modelling, 2023) Fosu, E.A.; Obuah, C.; Hamenu, L.; Aniagyei, A.; Oppong, A.; Ainooson, M.K.; Muller, A.A theoretical study on the reaction mechanisms of the addition of transition metal oxo complexes of the type MO3Cl (M = Mn, Tc, and Re) to tetramethylethylene (TME) is presented. Theoretical calculations using B3LYP/ LACVP* and M06/LACVP* (LACVP* is a combination of the 6-31G(d) basis set along with LANL2DZ pseudo potentials on the metallic centres) were performed and the results are discussed within the framework of reaction energetics. The nature of the stability of the reaction mechanisms was equivalent for both theories. However, the M06/LACVP* simulations generally had slightly lower energies and shorter bond lengths compared to the B3LYP/LACVP* computations. Furthermore, it was observed that the reaction does not proceed via the stepwise reaction mechanism due to kinetic and thermodynamic instabilities. Epoxidation was also found to occur via the [2 + 2] concerted reaction mechanism for the MO3Cl (M = Tc and Re) whereas the permanganyl chloride complex epoxidizes TME via the [2 + 1] concerted reaction mechanism on the singlet potential energy surface (PES). Dioxylation was observed to proceed via the [3 + 2] route for the addition of MO3Cl (M = Tc and Re) and TME. Results indicate that all reaction surfaces were unselective except for the permanganyl chloride catalyzed surface which leads to the formation of epoxides exclusively. Changes in temperatures from 298.15 K to 373.15 K, resulted in kinetically and thermodynamically unstable reaction pathways as the activation and reaction energies increased generally. On the singlet PES, the rate constant calculations showed that the [3 + 2] catalyzed surface reaction mechanism leading to dioxylation was faster than the [2 + 2] mechanism in cases where plausible. Theoretical values from the global reactivity parameters, namely the chemical hardness, chemical potential, electrophilic and nucleophilic indices, are in good correlation with the DFT activation and reaction energies at both levels of theories. Thus, as the electrophilic nature of the metal decreases from Mn to Re, so do the activation and reaction energies increase from Mn to Re, indicating that the higher the electrophilicity of the metal centre, the more spontaneous the oxidation reaction.