School of Pure and Applied Sciences
Permanent URI for this community
Browse
Browsing School of Pure and Applied Sciences by Subject "Aqua Ligand"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Publication Metadata only A kinetic study of aqua ligand substitution in dinuclear Pt(II) complexes containing four non-coplanar pyridine ligands(Springer link, 2014-09-30) Jaganyi, Deogratius; 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.Publication Metadata only Aqua substitution by biologically relevant nucleophiles in dinuclear platinum(II) complexes linked by diamino linkers with cyclohexyl groups(Springer link, 2014-11-02) Mambanda, Allen; Chipangura, Mathias; Jaganyi, Deogratius; Jaganyi, DeogratiusSubstitution of the aqua ligand from three platinum(II) complexes, namely [Pt(H2O)(N,N-bis(2-pyridylmethyl)cyclohexylamine](ClO4)2 (Pt1); [{Pt(H2O)}2(N,N,N′,N′-tetrakis(2-pyridylmethyl)-trans-1,4-cyclohexyldiamine)](ClO4)4 (Pt2); and [{Pt(H2O)}2(N,N,N′,N′-tetrakis(2-pyridylmethyl)-4,4′-ethylenedicyclohexyldiamine)](ClO4)4 (Pt3), by three biologically relevant nucleophiles [viz., glutathione (Glu); DL-penicillamine (Pen); and l-histidine (His)] was studied in aqueous 0.1 M perchloric acid medium. The substitutions were investigated under pseudo-first-order conditions as a function of nucleophile concentration and temperature using UV–visible spectrophotometry. The reactions of these complexes with the nucleophiles proceeded via a single step whose reactivity decreased in the order: Pt1 > Pt3 > Pt2 and was controlled by steric and electronic influences of the complexes. Sulfur donor nucleophiles (Glu and Pen) reacted much faster than the nitrogen bearing His, with Glu appearing to be more nucleophilic than Pen. The large and negative activation entropies and low but positive enthalpies of activation affirm an associative mode of activation.Publication Metadata only Detailed mechanistic study on ligand substitution reactions in dinuclear platinum(II) complexes: effect of alkanediamine linker(Springer link, 2014-03-14) Ongoma, Peter O.; Jaganyi, Deogratius; Jaganyi, DeogratiusSubstitution of the coordinated water ligands from the cis-[{Pt(NH3)2H2O}2-μ-NH2(CH2) n NH2]4+ (n = 2–4, 6, 8, 10) complexes: EnPt, PropPt, ButPt, HexPt, OctPt and DecPt with S-donor nucleophiles thiourea, N,N-dimethyl-2-thiourea and N,N,N,N-tetramethyl-2-thiourea was studied under pseudo-first-order conditions as a function of concentration and temperature, using stopped-flow and UV–Vis Spectrophotometric techniques. The substitution reaction proceeded in two steps: simultaneous substitution of the aqua ligands, followed by the displacement of the ammine ligands in the trans-position due to the strong trans-effect of the coordinated thiourea nucleophiles, with each of the steps being sensitive to steric and σ-electronic properties of the alkanediamine linker. A comparison of the second-order rate constants, k 2,1st and k 2,2nd, indicates that the rate constants of the first step are 1–2 orders larger than those of the second step in all cases. The large negative ΔS ≠ values support an associative mode of substitution mechanism for both reaction steps. 1H and 195Pt NMR spectroscopy established that the α,ω-alkanediamine linkers remained coordinated to the metal centres, possibly due to their cis geometry to the incoming thiourea nucleophilesPublication Metadata only Kinetic and mechanistic studies of cisplatin analogues bearing 2,2′-dipyridylalkylamine ligands(Springer link, 2015-12) 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.Publication Metadata only The role of substituents in a bidentate N,N-chelating ligand on the substitution of aqua ligands from mononuclear Pt(II) complexes(Springer link, 2015-12-01) Jaganyi, Deogratius; Khusi, Bongumusa B.; Mambanda, AllenThe rate of substitution of aqua ligands from three mononuclear platinum(II) complexes, namely [Pt{2-(pyrazol-1-ylmethyl)pyridine}(H2O)2](ClO4)2, [Pt(H 2 Py)]; [Pt{2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine}(H2O)2](ClO4)2, [Pt(dCH 3 Py)] and [Pt{2-[(3,5-bis(trifluoromethyl)pyrazoly-1-ylmethyl]pyridine}(H2O)2](ClO4)2, [Pt(dCF 3 Py)] by thiourea, N,N-dimethylthiourea and N,N,N′,N′-tetramethylthiourea, was studied in aqueous perchloric acid medium of constant ionic strength. The substitution reactions were investigated under pseudo-first-order conditions as a function of nucleophile concentration and temperature using UV/Visible and stopped-flow spectrophotometries. The observed pseudo-first-order rate constants, , for the stepwise substitution of the first and second aqua ligands obeyed the rate law: . The first substitution reaction takes place trans to the pyrazole ligand, while the second entering nucleophile is stabilised at the reaction site trans to the pyridine ligand. The rate of substitution of the first aqua ligand from the complexes followed the order: Pt(dCF 3 Py) > Pt(H 2 Py) > Pt(dCH 3 Py), while that of the second was Pt(H 2 Py) ≈ Pt(dCF 3 Py) > Pt(dCH 3 Py). Lower pK a values were found for the deprotonation of the aqua ligand cis to the pyrazole ring. Density functional theory calculations were performed to support the interpretation of the experimental results.