Aquation

About: Aquation is a research topic. Over the lifetime, 1443 publications have been published within this topic receiving 17507 citations.

Design, synthesis, characterisation and chemical reactivity of mixed-ligand platinum(II) oxadiazoline complexes with potential cytotoxic properties

Abstract: A series of mixed ligand platinum(II) oxadiazoline complexes bearing 7-nitro-1,3,5-triazaadamantane (7-NO2TAA) as a labile and reactive nitrogen ligand has been synthesised from easily accessible starting materials. [2+3] cycloaddition of nitrones R1R2C–N+(Me)O− to only one of the nitrile ligands in trans-[PtX2(PhCN)2] (X = Cl, Br) results in the selective formation of mono-oxadiazoline complexes trans-[PtX2(PhCN){NC(Ph)–O–N(Me)–CR1R2}] from which the remaining nitrile can be replaced by 7-NO2TAA. The resulting complexes trans-[PtX2(7-NO2TAA) {NC(Ph)–O–N(Me)–CR1R2}] and their precursors were characterised by elemental analysis, IR and multinuclear NMR spectroscopy.The suitability of the target complexes as anticancer agents was extrapolated from their general chemical reactivity. They are stable in DMSO, but react with thiols and undergo aquation of a chloro ligand. In the absence of a competing ligand, the coordinated 7-NO2TAA ligand slowly hydrolyses in an aqueous medium under release of formaldehyde, and this could induce bioactivity independent of the one typically found with platinum compounds. With nitrogen heterocycles such as pyridine a slow exchange of the 7-NO2TAA ligand occurs. A combined DFT/AIM study confirms the reaction observed in the experiment and predicts that other nitrogen heterocycles such as DNA nucleobases should react in the same way. Moreover, the 7-NO2TAA should be even more labile in an aqueous medium where protonation of the remaining amines can occur. A PM6 molecular modelling study suggests that the PtCl(oxadiazoline) fragment formed after release of one chloro and the labile 7-NO2TAA ligand fits well into the DNA groove and is able to form d(GpG) intrastrand crosslinks similar to the ones observed with cisplatin.

Octahedral {Ta6I12} Clusters.

Abstract: Ta powder reacts with I2 at 650 °C with the formation of Ta6I14, which belongs to the family of {M6(μ-X)12} clusters. It undergoes aquation with the formation of the intensely colored [Ta6I12(H2O)6]2+. The crystal structure was determined for [Ta6I12(H2O)6](BPh4)2·xH2O (Ta-Ta 2.9322(6) A, Ta-I 2.8104(7) A, Ta-O 2.3430(5) A). With DMF, [Ta6I12(DMF)6]I2·xDMF was isolated (Ta-Ta 2.9500(2) A, Ta-I 2.8310(4) A, Ta-O 2.2880(7) A). Cyclic voltammetry of [Ta6I12(H2O)6]2+ shows two consecutive quasi-reversible one-electron oxidations (E1/2 0.61 and 0.92 V vs Ag/AgCl). Reaction of Ta6I14 with Bu4NCN yields (Bu4N)4[Ta6I12(CN)6]·xCH3CN (Ta-Ta 2.9777(4) A, Ta-I 2.8165(6) A, Ta-C 2.2730(7) A). Quantum chemical calculations reproduce well the experimental geometry of the aqua complex and show the essentially Ta-centered nature of both the HOMO and LUMO. The long-term stability of [Ta6I12(H2O)6]2+ solutions can be greatly enhanced in the presence of polystyrenesulfonate (PSS), which forms nanoparticle associates with the aqua complex in water (ca. 1 cluster per 3 PSS monomeric units).

Reactivity, photolability, and computational studies of the ruthenium nitrosyl complex with a substituted cyclam fac-[Ru(NO)Cl2(κ3N4,N8,N11(1-carboxypropyl)cyclam)]Cl·H2O

Abstract: Chemical reactivity, photolability, and computational studies of the ruthenium nitrosyl complex with a substituted cyclam, fac-[Ru(NO)Cl2(κ3N4,N8,N11(1-carboxypropyl)cyclam)]Cl·H2O ((1-carboxypropyl)cyclam = 3-(1,4,8,11-tetraazacyclotetradecan-1-yl)propionic acid)), (I) are described. Chloride ligands do not undergo aquation reactions (at 25 °C, pH 3). The rate of nitric oxide (NO) dissociation (kobs-NO) upon reduction of I is 2.8 s−1 at 25 ± 1 °C (in 0.5 mol L−1HCl), which is close to the highest value found for related complexes. The uncoordinated carboxyl of I has a pKa of ∼3.3, which is close to that of the carboxyl of the non coordinated (1-carboxypropyl)cyclam (pKa = 3.4). Two additional pKa values were found for I at ∼8.0 and ∼11.5. Upon electrochemical reduction or under irradiation with light (λirr = 350 or 520 nm; pH 7.4), I releases NO in aqueous solution. The cyclam ring N bound to the carboxypropyl group is not coordinated, resulting in a fac configuration that affects the properties and chemical reactivities of I, especially as NO donor, compared with analogous trans complexes. Among the computational models tested, the B3LYP/ECP28MDF, cc-pVDZ resulted in smaller errors for the geometry of I. The computational data helped clarify the experimental acid-base equilibria and indicated the most favourable site for the second deprotonation, which follows that of the carboxyl group. Furthermore, it showed that by changing the pH it is possible to modulate the electron density of I with deprotonation. The calculated NO bond length and the Ru/NO charge ratio indicated that the predominant canonical structure is [RuIIINO], but the Ru–NO bond angles and bond index (b.i.) values were less clear; the angles suggested that [RuIINO+] could contribute to the electronic structure of I and b.i. values indicated a contribution from [RuIVNO−]. Considering that some experimental data are consistent with a [RuIINO+] description, while others are in agreement with [RuIIINO], the best description for I would be a linear combination of the three canonical forms, with a higher weight for [RuIINO+] and [RuIIINO].

Base-catalysed aquation of αβ-syn- and αβ-anti-chloro- and bromo-[1,9-bis(2′-pyridyl)-2,5,8-triazanonane]- and -[1,11-bis(2′-pyridyl)-2,6,10-triazaundecane]-cobalt(III) cations. An unusually base-sensitive halogenopentamine cobalt(III) system

Abstract: Complexes of the type [Co(picdien)X][ClO4]2 and [Co(picditn)X][ClO4]2[picdien = 1,9-bis(2′-pyridyl)-2,5,8-triazanonane, picditn = 1,11-bis(2′-pyridyl)-2,6,10-triazaundecane; X = Cl, Br, NO2, NCS, N3, MeCO2, or H2O] have been prepared. All complexes have the αβ configuration, those of picdien existing in either or both syn and anti forms, while only the anti forms of the picditn complexes have been isolated. Structures have been established by single-crystal X-ray diffraction and 1H n.m.r. spectroscopy in dimethyl sulphoxide and D2O. All complexes are unusually sensitive to base-catalysed hydrolysis over very wide ranges of pH. The pH-independent contribution to the solvolysis of the chloro- and bromo-picdien complexes is observed only at high temperatures and at high [H+] but there is a very important pH-independent contribution to the solvolysis of the corresponding picditn species, which are also somewhat more sensitive to base catalysis. Proton-exchange studies show that proton transfer is faster than substitution in even the most labile systems. The mechanism is discussed.