Browsing by Author "Jaganyi, Deogratius"
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Item Kinetic and Mechanistic Studies of Cisplatin Analogues Bearing 2, 2′-Dipyridylalkylamine Ligands(Springer, 2016-03-01) Kinunda, Grace; Jaganyi, DeogratiusA series of mononuclear Pt(II) complexes of the type diaqua(2,2′-dipyridylalkylamine)platinum(II) (where the alkyl group = methyl, ethyl, propyl, butyl or hexyl) were synthesized to investigate their nucleophilic substitution behaviour and the influence of the alkyl chain bonded to the tertiary nitrogen atom joining the two pyridine rings on the reactivity of the chosen complexes. The trend in rate constant shows that introduction of the σ-donating alkyl chain on the tertiary nitrogen joining the two pyridine moieties reduces the π-acceptor ability of the cis coordinated pyridine rings resulting in a less reactive Pt(II) centre which causes a decrease in the reaction rate. This is well supported by data from DFT calculations. It is also evident that the alkyl chain also introduces a steric effect which blocks the approach of the nucleophile to the Pt(II) centre. The boat-like structure of the six-membered chelate ring also contributes to the steric effect. The study has also shown that two substitution processes going through an associative mode of activation are observed. The first is the simultaneous substitution of the two aqua ligands, and the second is due to the dechelation of the ligand, an indication of possible disintegration of the complex if used as a drug.Item A Kinetic Study of Aqua Ligand Substitution in Dinuclear Pt (II) Complexes Containing Four Non-Coplanar Pyridine Ligands(Springer, 2014-10-01) Kinunda, Grace; Jaganyi, DeogratiusSubstitution reactions of the aqua ligands from azine-bridged dinuclear platinum(II) complexes of the type [{cis-Pt(py)2(OH2)}2(μ-pzn)](ClO4)4 [pzn = pyrazine (Pt-PZN), 2,3-dimethylpyrazine (Pt-2,3PZN), 2,5-dimethylpyrazine (Pt-2,5PZN) or 2,6-dimethylpyrazine (Pt-2,6PZN)] by thiourea nucleophiles were investigated under pseudo first-order conditions as a function of concentration and temperature using the stopped-flow technique. The experimental results are discussed in reference to structures obtained by DFT calculations. The results are in good agreement with the pKa values of the complexes as well as DFT calculations. Compared to [{cis/trans-Pt(NH3)2(OH2)}2(μ-pzn)](ClO4)4, the complexes in this series react faster by a factor of 10 or 23 respectively due to the presence of pyridine rings, which forces the geometry to allow π-back bonding to take place such that the electrons from the metal centres are accepted to the empty π*-orbitals of the pyridine subunits. The reactivity of the nucleophile is sterically dependent, with N,N,N′,N′-tetramethylthiourea reacting three times slower than thiourea. In all complexes and for both substitution steps, the mode of activation remains associative in nature.Item Mechanistic study of the substitution reactions of [Pt(II)(bis(2-pyridylmethyl)amine)H2O](ClO4)2 and [Pt(II)(bis(2-pyridylmethyl)sulfide)H2O](ClO4)2 with azole Nucleophiles. Crystal structure of [Pt(II)(bis(2-pyridylmethyl)sulfide)Cl]ClO4(Elsevier, 2017) Nkabinde, Slindokuhle, V.; Kinunda, Grace; Jaganyi, DeogratiusThe substitution kinetics of the complexes [Pt(II)(bis(2-pyridylmethyl)amine)H2O](ClO4)2, Ptdpa and [Pt(II)(bis(2-pyridylmethyl)sulfide)H2O](ClO4)2, Ptdps, with a series of azole nucleophiles: Imidazole (Im), 1-methylimidazole (MIm), 1,2-Dimethylimidazole (DIm), 1,2,4-triazole (Trz) and pyrazole (Pyz), were studied in an aqueous medium at constant ionic strength (0.1 M NaClO4). The substitution of the coordinated water ligand on the Pt(II) complexes by the azoles was studied under pseudo-first order conditions as a function of the incoming nucleophiles concentration and temperature using either stopped-flow techniques or UV-Vis spectroscopy. Ptdps was found to be more reactive (three magnitude higher) than Ptdpa. The second-order rate constant, k2, for all the nucleophiles ranged between 0.087 ± 0.005 and 0.926 ± 0.05 M−1 s−1 for Ptdpa and between 146 ± 4 and 1458 ± 10 M−1 s−1 for Ptdps. The rate of substitution of the aqua ligand is dependent on the strength of the σ-donor character and the π-acceptability of the trans atom to the leaving group. The observed reactivity trend for the azoles followed the trend, MIm > Im > DIm > Trz > Pyz. This reactivity trend correlates with the basicity, steric and electrophilic effects of the nucleophiles. The X-ray crystal structure of Ptdps–Cl is reported.Item Understanding the Electronic and Π-Conjugation Roles of Quinoline on Ligand Substitution Reactions of Platinum (II) Complexes(Springer, 2014-05-01) Kinunda, Grace; Jaganyi, DeogratiusA kinetic and mechanistic study of chloride substitution by thiourea nucleophiles, namely thiourea, N-methylthiourea, N,N-dimethylthiourea and N,N,N′,N′-tetramethylthiourea in the complexes chlorobis-(2-pyridylmethyl)amineplatinum(II) (Pt1), chloro N-(2-pyridinylmethyl)-8-quinolinamineplatinum(II) (Pt2), chloro N-(2-pyridinylmethylene)-8-quinolinamineplatinum(II) (Pt3) and chlorobis(8-quinolinyl)amineplatinum(II) (Pt4) was undertaken under pseudo-first-order conditions using UV–visible spectrophotometry. The study showed that lability of the chloro leaving group is dependent on the strength of π-interactions between the filled dπ-orbitals of the metal and the empty π*-orbitals of the chelating ligand in the following manner: Pt1 > Pt3 > Pt2 > Pt4. Introduction of the quinoline moiety within the non-labile chelated framework of the Pt(II) complexes results in a more electron-rich metal centre which retards the approach of the nucleophile through repulsion. Moreover, the net σ-effect of the ligand moiety plays a significant role in controlling the reactivity of the complexes. The experimental results are interpreted with the aid of computational data obtained by density functional theory (B3LYP(CPCM)/LANL2DZp//B3LYP/-LANL2DZp) calculations. The mode of substitution remains associative as supported by negative entropies and the dependence of the second-order rate constants on the concentration of entering nucleophiles.