Aquation

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

The chromium(II)-catalysed dissociation of monohalogenochromium(III) complexes and the effect of non-bridging ligands on electron-transfer reactions

Abstract: The reactions of chromium(II) with monobromochromium(III) and monoiodochromium(III) which result in a net dissociation of the bromide and iodide have been studied in aqueous perchloric acid solutions, ionic strength µ= 2·0M, by spectrophotometric techniques. In each case the kinetics conform to a rate equation of the type Rate =k3′[Cr2+][CrX2+][H+]–1 corrections being necessary for the chromium(II)-independent aquation of CrX2+. A rate equation of the same form has previously been reported for the reaction of CrCl2+. In each case the reactants are believed to be Cr2+ and Cr(X)OH+, and the activated complex [CrOHCrX]3+. In the reaction with CrF2+ there is in addition a hydrogen-ion-independent path which is believed to correspond to the activated complex [CrOHCrHF]4+. At 25° the non-bridging anions have a large (ca. 104) effect on rates, I–(2·13 × 10–2 sec.–1) > Br–(1·74 × 10–3 sec.–1) > Cl–(3·2 × 10–4 sec.–1) > F–(ca. 1·6 × 10–6 sec.–1). This order can be accounted for by considering the relative ligand-field strengths of the halide ions and the ease with which Cr–X bonds can be stretched, but other factors may be important. The effect is of about the same order of magnitude as that of bridging halide ions in the reactions of Cr2+ with CrX2+ and of Cr2+ with Cr(NH3)5X2+. Other data for the reactions of Cr(NH3)OH2+ and Cr(H2O)OH2+ with Cr2+ are considered.

Deprotonated ruthenium(III) hexa-ammine and its role in aquation and proton exchange reactions

Abstract: The deprotonated ruthenium(III) hexa-ammine complex is characterized by its absorption spectrum; its formation equilibrium constant is reported and its role in aquation and proton transfer reactions is discussed.

Competitive formation of DNA linkage isomers by a trinuclear platinum complex and the influence of pre-association

Abstract: 2D [1H, 15N] HSQC NMR spectroscopy has been used to monitor the reaction of fully 15N-labelled [{trans-PtCl(NH3)2}2(μ-trans-Pt(NH3)2{NH2(CH2)6NH2}2)]4+ (BBR3464 (15N-1)) with the 14-mer duplex (5′-{d(ATACATG(7)G(8)TACATA)}-3′·5′-{d(TATG(18)TACCATG(25)TAT)}-3′ or I) at pH 5.4 and 298 K, to examine the possible formation of 1,4 and 1,5-GG adducts in both 5′-5′ and 3′-3′ directions. In a previous study, the binding of the dinuclear 1,1/t,t to I showed specific formation of the 5′-5′ 1,4 G(8)G(18) cross-link, whereas in this case a mixture of adducts were formed. Initial 1H NMR spectra suggested the presence of two pre-associated states aligned in both directions along the DNA. The pre-association was studied in the absence of covalent binding, by use of the “non-covalent” analog [{trans-Pt(NH3)3}2(μ-trans-Pt(NH3)2{NH2(CH2)6NH2}2)]6+ (AH44, 0). Chemical shift changes of DNA protons combined with NOE connectivities between CH2 and NH3 protons of 0 and the adenine H2 protons on I show that two different molecules of 0 are bound in the minor groove. Molecular dynamic simulations were performed to study the interaction of 0 at the two pre-association sites using charges derived from density functional theory (DFT) calculations. Structures where the central platinum is located in the minor groove and the aliphatic linkers extend into the major groove, in opposite directions, often represent the lowest energy structures of the snapshots selected. In the reaction of 15N-1 and I, following the pre-association step, aquation occurs to give the mono aqua monochloro species 2, with a rate constant of 3.43 ± 0.03 × 10−5 s−1. There was evidence for two monofunctional adducts (3, 4) bound to the 3′ (G8) and 5′ (G7) residues and the asymmetry of the 1H,15N peak for 3 suggested two conformers of the 3′ adduct, aligned in different directions along the DNA. The rate constant for combined monofunctional adduct formation (0.6 ± 0.1 M−1) is ca. 2-fold lower for 1 compared to 1,1/t,t, whereas the rate constant for conversion of the combined monofunctional species to combined bifunctional adducts (5) (8.0 ± 0.2 × 10−5 s−1) is two-fold higher.

Kinetische Untersuchungen von Aquotisierung und Halogenid-Anation an gemischten Hexahalogenoosmaten(IV)

Abstract: Fur 13 System vom Typ [OsL4IX]2− + H2O ⇄ [OsL4I(H2O)]− + X− (X = F, Cl, Br, I; L4 = aquatoriale Gruppe von 4 Liganden Cl und I) werden die Geschwindigkeitskonstanten der Aquotisierung bzw. Anation durch spektrophotometrische Messungen in wasrig sauren Losungen bestimmt. Bei Ersatz jedes Cl-Liganden durch I in L4 beobachtet man einen labilisierenden cis-Effekt von etwa 1 kcal/mol. Die trans-Lockerung an der Achse ClOsI betragt demgegenuber 5–6 kcal/mol. Fur die Austauschreaktionen wird ein assoziativer Mechanismus angenommen. Die thermodynamische Stabilitat der Monaquokomplexe ist bei den chloridreichen Verbindungen um etwa 1 kcal/mol, bei den iodidreichen bis zu 2 kcal/mol geringer als fur die entsprechenden Hexahalogenokomplexe. Kinetic Studies on Aquation and Halide Anation of Mixed Hexahalo Osmates(IV) Rate constants of 13 aquation resp. anation reactions of type [OsL4IX]2− + H2O ⇄ [OsL4I(H2O)]− + X− (X = F, Cl, Br, I; L4 = 4 ligands Cl and I in the equatorial plain) are determined spectrophotometrically in acidic aqueous solutions. The replacement of each Cl ligand by I in L4 gives a labilization of about 1 kcal/mol by cis-effect. Against this the trans-labilization on the axis ClOsI is 5–6 kcal/mol. For the exchange reactions an associative mechanism is assumed. The thermodynamic stability of the monaquo complexes compaired to the corresponding hexahalo complexes is less by 1 kcal/mol for the compounds containing many Cl and by 2 kcal/mol for those containing many I ligands.