Aquation

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

Theoretical exploration of the photophysical properties of two-component RuII-porphyrin dyes as promising assemblies for a combined antitumor effect.

Abstract: Due to the extraordinary success of porphyrins in photodynamic therapy (PDT) and Ru compounds as chemotherapeutics, a series of RuII-porphyrin complexes have recently been synthesized and proposed as promising dual-action therapeutic agents. The results of a careful DFT and TDDFT investigation on four mononuclear pyridyl triphenylporphyrin RuII-arene complexes are herein reported and compared with those obtained for the metal-free derivatives. The investigation aims at shedding light on the modulation of the photophysical properties of the light absorber upon metalation and exploring the hydrolysis process of the RuII-moiety in the presence of the bulky porphyrin unit. Type I and Type II photoreactions were analyzed computing absorption spectra, singlet-triplet energy gaps, spin orbit coupling constants and vertical electron affinity (VEA) along with ionization potentials (VIP) for all the investigated compounds, while the chloride/water exchange reaction kinetics were determined by exploring the first and second aquation reactions of the Ru-moiety. Despite the highly similar photophysical properties displayed by the members of this class of compounds, an analysis of the hydrolysis processes in the dark allows to point out an interesting difference related to the type of pyridylporphyrin isomer and could be a preliminary explanation of the greater phototoxicity experimentally found for 3'-pyridyl substituted compounds.

Kinetics and mechanism of tris-quinolinatochromium(III) aquation in HClO4 media

Abstract: The chromium(III)-quinolinato complexes, [Cr(quinH)3]0, [Cr(quinH)2(H2O)2]+ and [Cr(quinH)(H2O)4]2+ (where quinH = N,O-bonded quinolinic acid anion), were obtained and characterized in solution. The tris-quinolinato complex undergoes acid-catalyzed aquation to give the diaqua-product, whereas subsequent ligand liberation processes are exceptionally slow. Kinetics of the aquation were studied spectrophotometrically over the 0.1–1.0 M HClO4 range, at I = 1.0 M. The first aquation stage, the chelate-ring opening at the Cr-N bond, is much faster than the second one. The following rate laws were established: kobs = k1 + k−1/Q1[H+] and kobs = k2Q2[H+]/(1 + Q2[H+]), where k1 and k2 are the rate constants for the chelate-ring opening and the ligand liberation, respectively, k−1 is the rate constant of the chelate-ring closure, Q1 and Q2 are the protonation constants of the pyridine nitrogen and 3-carboxylate group in the one-end bonded intermediate, respectively. Kinetic parameters have been determined and the mechanism has been discussed.

Base hydrolysis of mono-alkylsubstituted chloropentaamminecobalt(III) complexes

Abstract: The preparation of the series ofcis- andtrans-[Co(NH3)4(RNH2)Cl]2+ complexes (withcis, R = Me orn-Pr andtrans, R = Me, Et,n-Pr,n-Bu ori-Bu) is described The uv-visible spectra indicate a decrease of the ligand field on increasing chain length Infrared spectra show an enhanced Co-Cl bond strength compared to the pentaammine Partial molar volumes of the complex cations do not reveal steric compression From proton exchange studies in D2O it follows that [Co(NH3)5Cl]2+ and thecis- andtrans-[Co(NH3)4-(CH3NH2)C1]2+ complexes exchange the amine protons on the grouptrans to the chloro faster than those on thecis A coordinated methylamine group exchanges its amine protons slower than a corresponding NH3 group in the parent pentaammine, but the methyl introduction accelerates the exchange of the other NH3 groups The aquation of thetrans-alkylamine complexes (studied at 52° C) is acceleratedca 10 times compared to the parent pentaammine, irrespective of the nature of the alkyl group Thecis complexes do not show this acceleration of aquation In base hydrolysis (studied at 25° C) thecis complexes are the most reactive (a factor 20 over the parent ion) Thecis/trans product ratio in base hydrolysis and the competition ratio in the presence of azide ions were calculated from the 500 MHz1H nmr spectra, which display distinctly different alkyl resonances for each individual complex Thecis ions react under stereochemical retention of configuration; thetrans compounds give 10±1%trans tocis rearrangement The ionic strength (⩽4 mol dm−3) and the pH do not affect this result The same product ratio is obtained in methanol-water and DMSO-water mixtures Ammoniation in liquid ammonia gives the same ratios as in base hydrolysis, base-catalyzed solvolysis in neat methylamine gives stereochemical retention for both thecis- andtrans-methylamine ion The product competition ratio (Co-N3)/(Co-OH2) for thecis compounds and the bulkier amines (R =n- andi-Bu), 15–25% at 1 mol dm−3N 3 − , isca twice that of thetrans compounds and the pentaammine The results are interpreted in the classical conjugate base mechanism, and discussed in the context of current ideas about stereochemistry of base hydrolysis

Stereospecific Formation of Pentaamine Complexes of Co(III) with Terdentate 2,6‐Bis(aminomethyl)pyridine

Abstract: Some pentaamine complexes of Co(III) with 2,6-bis(aminomethyl)pyridine (bamp), a diamine ligand (or two ammonia ligands) and one unidentate ligand have been prepared (Table 1). In all these species, bamp remains coordinated meridionally under a variety of conditions as shown by 1H- and 13C-NMR. spectroscopy and correlations by stereoretentive reaction cycles. The rates of amine proton exchange and of spontaneous aquation, Hg2+-induced aquation and base hydrolysis of some chloropentaamine complexes have been determined. They essentially follow the patterns observed for complexes with purely aliphatic amine ligands; the presence of a pyridine donor in these complexes does not suggest deviations from the mechanistic schemes usually proposed for the solvolytic reactions investigated.