Showing papers on "Aquation published in 2014"

Multinuclear ruthenium( ii ) complexes as anticancer agents

Abstract: A series of dinuclear ruthenium(II) complexes that contain labile chlorido ligands, [{Ru(tpy)Cl}2{μ-bbn}]2+ {designated Cl-Rubbn; tpy = 2,2′:6′,2′′-terpyridine, bbn = bis[4(4′-methyl-2,2′-bipyridyl)]-1,n-alkane (n = 7, 10, 12, 14 or 16)} and derivatives containing nitro substituents on the tpy ligand and/or secondary amines within the bbn linking chain have been synthesised and their potential as anticancer agents examined. Some of the Cl-Rubbn species showed good anticancer activity against MCF-7 and MDA-MB-231 breast cancer cell lines, with the Cl-Rubb12 complex being four-times more active than cisplatin. Inclusion of nitro substituents on the tpy ligands of Cl-Rubb12 resulted in significantly decreased anticancer activity. The incorporation of amine groups into the linking ligand did not increase the anticancer activity of the Cl-Rubbn complexes. The Cl-Rubbn complexes and those containing amine groups in the linking chain aquated at approximately the same rate, with 50% aquation within 120 minutes. By comparison, the complexes containing nitro substituents on the tpy ligand aquated extremely slowly, with 60% of the chlorido complex remaining 24 hours after they were dissolved in water. Cyclic voltammetry with the model mononuclear complex [Ru{(NO2)3tpy}(Me2bpy)Cl]+ {(NO2)3tpy = 4,4′,4′′-trinitro-2,2′:6′,2′′-terpyridine} showed that the nitro substituents exerted a strong effect on the ruthenium centre, with the anodic peak corresponding to the Ru(III/II) couple shifted positively by 300 mV compared to that from the non-nitrated parent complex [Ru(tpy)(Me2bpy)Cl]+. 1H NMR studies of the reaction of the Cl-Rubbn complexes with GMP indicated that the ruthenium complexes covalently bound the nucleotide slowly, with 33% bound in 24 hours. However, the results of this study suggest that the cytotoxicity of the dinuclear ruthenium complexes is a combination of covalent and reversible binding with DNA.

Metal ion remediation by polyamidoamine dendrimers: a comparison of metal ion, oxidation state, and titania immobilization

Abstract: The exceptional ability of dendrimers to coor- dinate metal ions yields the potential for many applications including wastewater remediation, which is the focus of this study. Here, the comparison of metal ion removal rate from simulated wastewater by generation 4 dendrimers with external hydroxyl functional groups (G4-OH) is evaluated for Ni 2? ,F e 2? , and Fe 3? ions. Ni 2? to amine complexation occurred more rapidly than Fe 3? , which was more rapid than Fe 2? complexation. These results indicate that both charge density and d-electron configuration are important toward the chelation rate. The impact of both factors is discussed in light of existing models in which precursor aquation rates have been proposed as a key intermediate step. Additionally, the application of the dendrimers as chelation agents is further advanced by immobilizing the dendrimer to titania and re-evaluating its chelation ability for Ni 2? removal. The dendrimer immobilization decreased the pseudo-first-order rate coefficient for Ni 2? —amine complexation at a pH of 7 by a factor of 7.5. This result is significant as it suggests that mass transfer becomes important following immobilization of the dendrimer to titania.

Interactions of the aquated forms of ruthenium(III) anticancer drugs with protein: a detailed molecular docking and QM/MM investigation

Abstract: Interaction of monoaqua and diaqua ruthenium complexes such as [trans-RuCl3(H2O)(3H-imidazole)(dmso-S)] I, [trans-RuCl2(H2O)2(3H-imidazole)(dmso-S)]+1 II, [trans-RuCl3(H2O)(4-amino-1,2,4-triazole)(dmso-S)] III and trans-RuCl2(H2O)2(4-amino-1,2,4-triazole)(dmso-S)]+1 IV, which are formed after intracellular aquation of their respective complexes, with human serum albumin (HSA) has been computationally investigated by molecular docking and two layer QM/MM hybrid methods. The computed binding energy of monoaqua adduct I–HSA and III–HSA evaluated by docking simulation are found to be −4.52 kcal mol−1 and −4.58 kcal mol−1 whereas the binding energy of diaqua adducts II–HSA and IV–HSA are evaluated to be −4.74 kcal mol−1 and −4.91 kcal mol−1, respectively. Docking results also show that the ruthenium atoms of all the complexes are actively involved in coordination with histidyl nitrogen atoms in the active site of protein. In addition, in order to probe the stabilities of monoaqua and diaqua ruthenium complexes in the active site of protein, we have calculated their energetic by two layer QM/MM method. QM/MM study suggests higher stability of diaqua adduct, II–HSA. The stability of adducts varies in the order: II–HSA > IV–HSA > I–HSA > III–HSA. Binding energy values of all the complexes increase with the incorporation of solvent effect. Thus molecular docking and QM/MM results show that ruthenium complexes interact with the protein receptor more rapidly after their second hydrolysis. Hence, docking as well as ONIOM results will be highly beneficial for providing insight into the molecular mechanism of ruthenium complexes with protein receptor.

Synthesis, Spectroscopy and Electrochemistry of nitroso terpyridine-{1-(alkyl)-2-(arylazo) imidazole}ruthenium(II) Complexes

Abstract: Silver assisted aquation of blue [RuCl(tpy)(RaaiR ´ )](ClO 4 ) ( 1a-1i ) leads to the synthesis of solvento species, blue-violet [Ru(OH 2 )(tpy)(RaaiR ´ )](ClO 4 )( 2a-2i ), [RaaiR ´ =p-R-C 6 H 5 -N=N-C 3 H 2 -NN, abbreviated as N,N / -chelator, R = Me, Et, Bz, p-R=H Me, Cl] that have been reacted with NaNO 2 in warm EtOH resulting in violet nitro complexes of the type, [Ru(NO 2 )(tpy)(RaaiR)](ClO 4 )( 3a-3i ). The nitrite complexes are useful synthons of electrophilic nitrosyls, and on triturating the nitro compounds with conc. HClO 4 nitrosyl derivatives, [Ru(NO)(tpy)(RaaiR)](ClO 4 ) 3 are isolated. The diazotization of the primary aromatic amines with a strongly electrophilic mononitrosyl complex in acetonotrile and dichloromethane solution was thoroughly studied.

Kinetic studies on acid- and base-catalyzed aquation of bis-alaninatochromium(III) and on oxidation of tris- and bis-Aa–chromium(III) complexes (Aa = Gly, Ala, Asn) by H2O2

Abstract: Two aqua derivatives of [Cr(Ala)3] were characterized in solution. Acid-catalyzed aquation of cis-[Cr(Ala)2(H2O)2]+ leads to inert [Cr(Ala)(H2O)4]2+, whereas base hydrolysis of cis-Cr(Ala)2(OH)2]− causes dissociation of both the Ala ligands and formation of chromates(III). Kinetics of these processes have been studied spectrophotometrically in both 0.1–1.0 M HClO4 and 0.2–0.9 M NaOH under first-order conditions. A linear dependence of the kobs,H on [H+] and a small dependence of the (kobs)OH on [OH−] were established. In the proposed mechanism, the rate determining step is Cr–N bond breaking in the reactive form of the substrate, i.e., in the protonated aqua- or dihydroxo complex. The effect of pH on the complex reactivity is discussed. The kinetic results are compared with those determined previously for analogous glycine and asparagine complexes. Additionally, oxidation of tris- and bis-Aa–chromium(III) complexes, where Aa = Gly, Ala or Asn, by hydrogen peroxide in alkaline medium was studied. Two reaction products were detected: thermodynamically stable CrO42− and [Cr(O2)4]3− that under a large excess of hydrogen peroxide is metastable. The rate-limiting stage of this process is an inner sphere two-electron transfer within the peroxido intermediate.

Kinetic studies on H + - and OH − -catalysed aquation of bis -aspartatochromium(III)

Abstract: A potential synthetic biochromium source, bis-aspartatochromium(III) ion (where Asp is a tridentate N,O,O′-ligand, bonded via amine nitrogen and carboxylate oxygen atoms) has been obtained and characterized in aqueous solution. Kinetics of partial dechelation of the complex catalysed by H+ and OH− ions has been studied spectrophotometrically within 0.1–1.0 M HClO4 and 0.1–1.0 M NaOH ranges under first-order conditions. A linear dependence of the k obs,H on [H+] and independence of the k obs,OH on [OH−] were established. The derived rate expression and identification of components of the reaction mixture provide evidence for a reaction mechanism, where the key role in the overall process is the formation of an intermediate species with bidentate N,O-bonded Asp via both spontaneous and H+(OH−)-catalysed reaction paths. The intermediate is meta-stable and at pH 5–7 restores the substrate.

Kinetics of aquation of [Co(ODA)(H2O)3]induced by Fe(III)

Abstract: Abstract The aquation reaction of the oxydiacetate cobalt(II) complex, namely [Co(ODA)(H2O)2]•H2O (ODA = oxydiacetate), induced by the Fe(III) ions as the promoter has been studied spectrophotometrically (UV-Vis). Kinetic measurements were carried out in the 283.15 - 303.15 K temperature range and at a constant ionic strength of 1.0 M (NaNO3). The observed rate constants were computed by a program based on global analysis. Furthermore, the reaction activation parameters were determined using the Arrhenius and Eyring equations. The changes in the enthalpy, entropy as well as activation energy barriers were calculated in the range of 0.00125 M – 0.125 M of the Fe(III) ion concentration. Based on kinetic data a mechanism for the aquation of the [Co(ODA)(H2O)3] complex has been proposed. Graphical Abstract