Browsing by Author "Robinson, Ross."

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    Role of a 2,3-bis(pyridyl)pyrazinyl chelate bridging ligand in the reactivity of Ru(ii)–Pt(ii) dinuclear complexes on the substitution of chlorides by thiourea nucleophiles – a kinetic study
    (New Journal of Chemistry, 2018-06-20) Bellam, Rajesh.; Jaganyi, Deogratius.; Mambanda, Allen.; Robinson, Ross.
    Chloride substitution from [(1,10-phenanthroline)2Ru(II)(μ-2,3-bis(2-pyridyl)pyrazine)Pt(II)dichloride]2+ (RuPt1), [(1,10-phenanthroline)2Ru(II)(μ-2,3-bis(2-pyridyl)quinoxaline)Pt(II)dichloride]2+ (RuPt2) and [(1,10-phenanthroline)2Ru(II)(μ-2,3-bis(2-pyridyl)benzo[g]quinoxaline)Pt(II)dichloride]2+ (RuPt3) by thiourea (TU), 1,3-dimethyl-2-thioura (DMTU) and 1,1,3,3-tetra methyl-2-thiourea (TMTU) was studied in a methanol medium (I = 0.10 M) under pseudo-first-order conditions. The rate of substitution was investigated as a function of concentration of nucleophile and temperature using the stopped-flow technique. Two consecutive substitution steps were observed. The first and fastest step was ascribed to the simultaneous substitution of the two chloride co-ligands by incoming nucleophiles according to the rate law: k1stobs = k1st2[Nu]. The subsequent step was assigned to the dechelation of the rigid 2,3-bis(pyridyl)pyrazinyl bridging ligand from the Pt(II) centres of the substituted intermediates to give Pt(Nu)42+ and (phen)2Ru(II)(2,3-bis(pyridyl)pyrazinyl) groups as products. The rate law for this step is k2ndobs = k2nd2[Nu] + k2nd−2. The second-order kinetics and large negative entropies for both steps support an associative mechanism of substitution. The rate of chloride substitution was RuPt1 ≪ RuPt2 < RuPt3. This is also the order of increase in the π-surface of the bridging ligand and an indication that π-back donation of electron density from the Pt-5dπ orbitals into the π*-acceptor bridging ligand is the dominant factor controlling the substitution of the chloride from the complexes. The nucleophiles’ order of reactivity was TU > DMTU > TMTU, in accordance with their steric bulk.
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    Seven membered chelate Pt(ii) complexes with 2,3-di(2-pyridyl)quinoxaline ligands: studies of substitution kinetics by sulfur donor nucleophiles, interactions with CT-DNA, BSA and in vitro cytotoxicity activities†
    (RSC Advances, 2019-10-01) Bellam, Rajesh.; Jaganyi, Deogratius.; Mambandam, Allen.; Robinson, Ross.; BalaKumarand, Manickam Dakshinamoorthi.
    Dichloro platinum(II) complexes coordinated with 2,3-di(2-pyridyl)quinoxaline ligands which form seven-membered chelates namely, bpqPtCl2, dmbpqPtCl2 and bbqPtCl2 (where bpq, dmbpq and bbq are 2,3-di(2-pyridyl)quinoxaline, 6,7-dimethyl-2,3-di(2-pyridyl)quinoxaline and 2,3-bis(2′pyriyl)benzo[g]quinoxaline, respectively) were synthesized, characterised and their respective hydrated product complexes namely, bpqPt(OH2)22+, dmbpqPt(OH2)22+ and bbqPt(OH2)22+ were prepared by chloride metathesis. The substitution kinetics of the aquated cations by thiourea nucleophiles indicated that the two aqua ligands are substituted simultaneously according to the rate law: kobs = k2[Nu]. This is followed by a forced dechelation of the ligands from the Pt (II) to form Pt(Nu)42+ species. The dechelation step is considerably slow to be monitored reliably. The rate of substitution is marginally enhanced by introducing two methyl groups and by extending the π-conjugation on the bpq core ligand. The reactivity order increased as bpqPt(OH2)22+ < dmbpqPt(OH2)22+ < bbqPt(OH2)22+. Reactivity trends were well supported by theoretical computed DFT electronic descriptors. The interactions of the Pt(II) complexes with CT-DNA and BSA were also examined spectroscopically in tris buffers at pH 7.2. Spectroscopic and viscosity measurements suggested strong associative interactions between the Pt(II) complexes and CT-DNA, most likely through groove binding. In silico theoretical binding studies showed energetically stable poses through associative non-covalent interactions. In vitro MTT cytotoxicity IC50 values of the Pt(II) complexes on human liver carcinoma cells (HepG2) cancer cell lines revealed bbqPtCl2 as the least active. The fluorescence staining assays revealed the morphological changes suggested early apoptotic induction as well as non-specific necrosis.