(Pyridyl)benzoazole ruthenium(III) complexes: Kinetics of ligand substitution reaction and potential cytotoxic properties

The present work investigates the kinetics of ligand substitution reaction and anticancer activities of the complexes, [{2-(2-pyridyl) benzimidazole} RuCl3] (C1), [{2-(2-pyridyl) benzoxazole} RuCl3] (C2), [{2-(2-pyridyl) benzothiazole} RuCl3] (C3) and [{1-propyl-2- (pyridin-2-yl)-H-benzoimidazole} RuCl3] (C4). The substitution kinetics reaction of the complexes with the three bio-relevant nucleophiles, viz.: thiourea (TU), 1, 3-dimethyl-2-thiourea (DMTU) and 1, 1, 3, 3-tetramethyl-2-thiourea (TMTU) was investigated under pseudo first-order conditions as a function of concentration and temperature using UV–Visible spectrophotometer. The substitution of the coordinated chloride was controlled by the electronic effect. The order of reactivity of the complexes with the nucleophiles is in the form C1 > C2 > C3 > C4 which is in line with the density functional theory (DFT) studies. The complexes showed minimal anticancer activity against the HeLa cell line, which is in contrast to the molecular docking experiments that exhibited stronger DNA binding affinities. © 2018 Elsevier B.V

Understanding the role of flexible 4′-functionalized polyethylene glycoxy chains on the behavior of platinum(II) (4′-(ethylene glycoxy)-2,2′:6′,2′′-terpyridine: a kinetic and a mechanistic study

<div><p>The ligand substitution kinetics of 4′-functionalized mononuclear Pt(II) (4′-(ethylene glycoxy)-2,2′:6′,2′′-terpyridine complexes, [Pt(nY-tpy)Cl)Cl] (where Y = ethylene glycoxy, <i>n</i> = number of ethylene, glycoxy units = 1, 2, 3, and 4, and tpy = 2,2′:6′,2′′-terpyridine), with thiourea, 1,3-dimethyl-2-thiourea, 1,1,3,3-tetramethyl-2-thiourea, and iodide were investigated under <i>pseudo</i>-first-order conditions as a function of concentration and temperature by conventional stopped-flow technique. The observed first-order rate constants followed the simple rate law <i>k</i>_obs = <i>k</i>₂[Nu]. The data obtained show that the ethylene glycoxy pendant, <i>trans</i> to the leaving group, acts as a <i>σ</i>-donor into the terpyridine ligand and is effective only up to <i>n</i> = 1, beyond which the substitution reactivity of the complexes are controlled by the steric influence of the appended ethylene glycoxy pendant units, which decreases with increase in the number of ethylene glycoxy units. The activation parameters obtained support an associative mechanism, where bond formation in the transition state is favored. The observed reactivity trends were supported by density functional theory calculations.</p></div

A kinetic and mechanistic study of dinuclear Pt(II) 2,2′:6′,2″-terpyridine compounds bridged with polyethyleneglycol ether flexible linkers

<div><p>A series of dinuclear Pt(II) complexes bridged with polyethyleneglycol ether of the type [ClPt(tpy)O(CH₂CH₂O)_n(tpy)PtCl]Cl₂ where <i>n</i> = 1 <b>(Ptdteg)</b>, 2 <b>(Ptdtdeg)</b>, 3 <b>(Ptdtteg)</b>, 4 <b>(Ptdttteg),</b> and linker-free complex, <b>(Ptdt)</b> (where tpy = 2,2′:6′,2″-terpyridine), were synthesized and characterized to investigate the role of bridging polyethyleneglycol ether linker on the substitution reactivity of dinuclear Pt(II) complexes. Substitution reactions were studied using thiourea nucleophiles, <i>viz</i>. thiourea (TU), 1,3-dimethyl-2-thiourea (DMTU), 1,1,3,3-tetramethyl-2-thiourea (TMTU) under <i>pseudo</i>-first-order conditions as a function of concentration and temperature by conventional stopped-flow reaction analyzer. The reactions gave single exponential fits following the rate law <i>k</i>_obs = <i>k</i>₂[Nu]. Introduction of polyethyleneglycol ether linker decreases the electrophilicity of the platinum center and the whole complex. The results obtained indicate that the rate of substitution is controlled by both electronic and steric hindrance which increases with the length of the linker. Experimental results are supported by density functional theory calculations and structures obtained at B3LYP/LANL2DZ level. The order of the reactivity of the nucleophiles is TU > DMTU > TMTU. The magnitude and the size of the enthalpy of activation and entropy of activation support an associative mode of mechanism, where bond formation in the transition state is favored.</p></div

Determination of inorganic pollutants and assessment of the current South African guidelines on permissible utilisation of sewage sludges

A total of 71 sludge samples originating from 61 sewage treatment works in South Africa were used in this investigation. Moisture, pH and total mineral ion content were determined. Moisture values were found to vary between 2.7% and 88.5% with the pH of the majority of the samples falling between 5.1 and 6.5. Mineral ion determinations showed that P was the most abundant in most of the sludges whereas, of the heavy metals, Zn had the highest concentrations and Cd the lowest. The current results (for 10 elements) were compared with the current South African maximum limits as stipulated in the permissible utilisation and disposal of sewage sludge for unrestricted use. The amounts of Cu, Se, Pb and Zn were found to be above the limit in more than 90% of the samples. No sewage works met the required limits for all the elements of interest. The results were also compared with the USA and EU limits, according to which all the elements were within the acceptable range and over 50% of the sludge samples met the required limits. These results suggest that the current South African limit is too conservative. Water SA Vol.31 (3) 2005: pp.359-36