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Showing papers on "Aquation published in 1994"


Journal ArticleDOI
TL;DR: Aquation of the anticancer complex trans-[H2im][RuCl4(Him)2]1 (Him = imidazole) has been studied in D2O at a range of pH*(meter reading) values between 2.4 and 10 by observation of paramagnetically shifted 1H NMR resonances as discussed by the authors.
Abstract: Aquation of the anticancer complex trans-[H2im][RuCl4(Him)2]1(Him = imidazole) has been studied in D2O at a range of pH*(meter reading) values between 2.4 and 10 by observation of paramagnetically shifted 1H NMR resonances. At 310 K. pH* 5.6, the half-life was 3.4 h and three products were detected, assigned as mono- and di-aqua species. The rate was similar at low pH*, but the reaction followed a different course at high pH*. Aquation was also studied by separation of the products on a reversed-phase column using HPLC, by conductivity measurements, and by EPR spectroscopy. Slow oxidation of the complex to RuIV appeared to take place in perchlorate, phosphate or acetate solutions. Cyclic voltammetric studies showed that reduction of 1 to RuII(Em–0.14 V versus the normal hydrogen electrode, pH 7) was accompanied by the uptake of two protons with associated pKa values of 6.26 and 3.87. Both aquation and the more favourable reduction of 1 at low pH may play a role in the biological activity of the complex.

47 citations


Journal ArticleDOI
TL;DR: A detailed kinetic study of the substitution of aquacobalamin by a variety of substituted pyridine ligands was performed as function of entering ligand concentration, pH, temperature and pressure.
Abstract: A detailed kinetic study of the substitution of aquacobalamin by a variety of substituted pyridine ligands was performed as function of entering ligand concentration, pH, temperature and pressure. The kinetic data for the complex formation and reverse aquation reactions confirm previous findings on the operation of a dissociative interchange mechanism. Typical ΔV values for complex formation are between +4 and +4 cm 3 mol -1 . The thermodynamic data reflect significant precursor formation for this special class of ligands investigated, with formation constants that vary between 1 and 5 M -1

29 citations


Journal ArticleDOI
TL;DR: A mechanistic investigation of the aquation and anation reactions of substituted ethylenediamine platinum(I1) complexes was conducted in this article, where two ligands X and Y were shown to be kinetically equivalent for X = Y within the accuracy of 15N, 195Pt, 170 NMR.
Abstract: This paper reports a mechanistic investigation of the aquation and anation reactions of substituted ethylenediamine platinum(I1) complexes, which were shown to have very different in vivo antitumor activities. The general formula of the complexes is ruc-[Pt(R-en)XY]"' (X, Y = H20, C1-; n = 0, 1, 2), where the substituted ethylenediamine (R-en) is (1 R,2R,4S)-exo-2-(aminomethyl)-2-amino-7-oxabicyclo[2.2. llheptane (R1-en), (1 R,2S,4S)-endo-2-(aminomethyl)-2-amino-7-oxabicyclo[2.2. llheptane (R2-en), or (lS,2S,4S)-exo-2-(aminomethy1)-2-amino-7bicyclo[2.2.l]heptane (R3-en). The two ligands X and Y are shown to be kinetically equivalent for X = Y within the accuracy of 15N, 195Pt, 170 NMR, although the diamine is asymmetric. Using UV-vis spectrophotometry, it was possible to determine the rate constants (kl , k-1, k2, k-2) for the following two successive aquatiodanation reactions: [Pt(R-en)Cl,] + H 2 0 --L [Pt(R-en)(H,O)Cl]+ + C1( k I k l ) [Pt(R-en)(H,O)Cl]+ + H,O == [Pt(R-en)(H20)2]2+ f C1( k 2 k 2 ) K, = k, /k,

24 citations


Journal ArticleDOI
TL;DR: In this article, a review of mixed-ligand complexes is presented, with a focus on the photochemistry and photophysics of these compounds, as well as the solution reactivity (cyanide aquation and isomerization).

22 citations


Journal ArticleDOI
TL;DR: In this article, the activation entropies ΔS∗) for a series of thermal or Hg2+−assisted chloride release aquation rates from chloroam(m)ine complexes are ranked, orders for the effect of the non-replaced ligands are obtained.
Abstract: If the activation entropies ΔS∗) for a series of thermal or Hg2+−assisted chloride release aquation rates from chloroam(m)ine complexes are ranked, orders for the effect of the non-replaced ligands are obtained. These orders are within reasonable expectation for the extent of interchange that takes place as the reaction proceeds.

13 citations


Journal ArticleDOI
TL;DR: In this article, the geometry of the reactants and products was determined by molecular mechanics and the optimized structures were used to calculate by the extended Huckel method the charge distribution and relative electronic energies.

13 citations


Journal ArticleDOI
TL;DR: In this article, the kinetics of aquation of CoIII and CrIII complexes were investigated in aqueous mixtures of MeOH, EtOH, i-PrOH and t-BuOH.
Abstract: The kinetics of aquation of cis-[Co(en)2(H2O)Br]2+ and cis-[Cr(en)2(H2O)Br]2+ (en = ethylenediamine) were investigated in aqueous mixtures of MeOH, EtOH, i-PrOH and t-BuOH. The values of transfer functions corresponding to the transfer of reactants and activated complex from water to the solvent mixtures were evaluated from kinetic measurements and from solubilities of the complex salt. Analysis of the solvent effect confirmed a common Id mechanism for the aquation of the CoIII and CrIII complexes.

7 citations


Journal ArticleDOI
TL;DR: Reactions of chloro(diethylenetriamine)platinum(II) chloride with adenosine 5'-O-thiomonophosphate, adenosines 5-O-(2-thiodiphosphate), and adenosin 5- O-(3-thiotriphosphate) yielded exclusively (phosphothiorato)pl platinum(II), indicating that the aquated pathway contributes insignificantly toward complexation.

7 citations


Journal ArticleDOI
TL;DR: The reaction of Cr(NH 3 ) 5 (CN) 2+ with Hg 2+ was investigated in aqueous medium by various electrochemical techniques, as well as by absorption and emission spectrophotometry.

4 citations


Journal ArticleDOI
TL;DR: In this article, the authors report on the preparation and characterization of [Os(NH 3 ) 4 -(η 2,η 1 -(CH 2 =HCO 2 H) 2 ] 2 +(1) and [Os[NH 3 ] 4 (η2 -CH 2 (H 2 O)] 2+ (2) in aqueous solution.
Abstract: Herein we report on the preparation and characterization and on some aspects of the chemistry of [Os(NH 3 ) 4 -(η 2 ,η 1 -(CH 2 =HCO 2 H) 2 ] 2 +(1) and [Os(NH 3 ) 4 (η 2 -CH 2 =CHCO 2 H)(H 2 O)] 2+ (2) in aqueous solution. The pK a values, as determined by titration, for 1 are 3.20, 6.78, and 9.8 and for the corresponding Os(III) form are 1.76, 3.46, and 7.40. In each case they refer to deprotonation of η 1 -acrylic acid, η 2 -acrylic acid, and an ammonia, respectively. For 2, the values are 2.75, 5.27, and 8.57, and for the corresponding Os(III) form the values are 1.42, 3.65, and ≃8. Here they refer to deprotonation of the coordinated H 2 O, of the η 2 -acrylic acid, and of an ammonia, respectively

4 citations


Journal ArticleDOI
TL;DR: In this paper, a rate law for the anation of the pentacoordinate intermediate [Ru(tap)2(H2O)2] has been established at pH 5.6.
Abstract: Kinetic and mechanistic studies on the anation of cis-[Ru(tap)2(H2O)2]2+ (where tap = 2-(m-tolylazo)pyridine) by pyridine-2-aldoxime (LH) have been made spectrophotometrically at different temperatures (35–50° C) in aqueous medium and various EtOH-H2O mixtures. The following rate law has been established at pH 5.6: kobs = k1k2[LH]/(k−1 + k2[LH]) where k1 is the H2O dissociation rate constant of the substrate complex and k-1 and k2 are the aquation and ligand capturing rate constants of the pentacoordinate intermediate, [Ru(tap)2(H2O)]2+. The rate constants are independent of ionic strength. The reaction rate increases with increasing pH. Activation parameters (ΔH‡ and ΔS‡) have been calculated for media of four different dielectric constants and compared with other substitution reactions in aqueous medium. A dissociative mechanism is proposed.

Journal ArticleDOI
TL;DR: In this paper, a trans diastereoisomer of dichloro (meso-5,12-dimethyl-1,4,8,11 -tetraazacyclotetradecane)-cobalt(m) perchlorate has been prepared, and the electronic absorption and infrared spectral data studied.
Abstract: A new trans diastereoisomer of dichloro(meso-5,12-dimethyl-1,4,8,11 -tetraazacyclotetradecane)-cobalt(m) perchlorate has been prepared, and the electronic absorption and infrared spectral data studied. The assignments of the structure of the isomer have been accomplished by thorough stereochemical analysis combined with 1H and 13C NMR spectral data. Aquation kinetics have been studied at various temperatures and activation parameters determined. The results indicate a dissociative activation with retention of configuration and a distorted-square pyramidal activated complex.

Journal ArticleDOI
TL;DR: In this article, the quantum yield for photoaquation of trans-Ru(bipy) 2 Cl 2 ] +, where bipy2,2′-bipyridine, was found to be 1.5 × 10 −2 mol −1, when irradiated at its ligand field band.
Abstract: The quantum yield for photoaquation of trans -[Ru(bipy) 2 Cl 2 ] + , where bipy2,2′-bipyridine, is found to be 1.5 × 10 −2 mol Einstein −1 , when irradiated at its ligand field band. The estimated activation enthalpy for the thermoaquation of this complex is 20 kcal mol −1 . In comparison with trans -[Ru(en) 2 Cl 2 ] + , where enethylenediamine, the bipy complex has a higher quantum efficiency than the en complex. The difference between the reactivities in the ground state and excited state can be understood within the framework of the ligand field model. The electronic interaction between Ru(III) and ligands that stabilizes the ground state also stabilizes the intermediate in the photoaquation reaction. Hence the bipy complex is found to be less reactive toward aquation in the ground state than the en complex is but to be more reactive in the excited state.


Journal ArticleDOI
TL;DR: In this article, a review of mixed-ligand complexes is presented, with a focus on the photochemistry and photophysics of these compounds, as well as the solution reactivity (cyanide aquation and isomerization).
Abstract: The review deals with various aspects of a relatively young family of mixed-ligand complexes comprising mono- and polynuclear species, the latter cyano- or isocyano-bridged. Compared with other chromium(III) acido-am(m)ines, these exhibit atypical ground-state and excited-state properties arising from coordination of the CN− groups. A systematization is presented of the preparative procedures, followed by a collection of the most relevant structural results. The electronic absorption and emission spectra are then discussed, and the solution reactivity (cyanide aquation and isomerization) is reviewed. Particular attention is devoted to the photochemistry and photophysics of these compounds. The uncommon ligand-field state sequences give access to photolabilization patterns and photostereochemistries that are complementary to the usual occurrence, providing significant test cases for the photolysis models. In addition, the long-lived solution phosphorescence makes possible accurate studies of the possible doubletstate decay routes, as well as of energy transfer in supramolecular systems. The available data are summarized in 11 tables, and reference to the literature is made by 117 citations.