Showing papers on "Aquation published in 1986"

Mechanism of cytotoxicity of anticancer platinum drugs: evidence that cis-diamminedichloroplatinum(II) and cis-diammine-(1,1-cyclobutanedicarboxylato)platinum(II) differ only in the kinetics of their interaction with DNA.

Abstract: The kinetics of the aquation reactions of cisplatin and carboplatin and their subsequent reactions with DNA, both in vitro and in vivo, have been measured. The results have been extrapolated to indicate the expected cytotoxicity of these compounds in cells obtained from human cancer patients. Rate constants for the aquation at 37 degrees C of cisplatin and carboplatin of 8 X 10(-5) and 7.2 X 10(-7) s-1, respectively, were calculated from the half-life of these compounds in phosphate buffer, pH 7. This difference in their rate of activation was matched by their rates of binding to DNA. By use of a 14C-labeled ligand, carboplatin was shown to bind monofunctionally to DNA, after which there was a time-dependent formation of difunctional interstrand cross-links, formed from some of these initially monofunctional adducts. A similar, although faster, accumulation of cross-links was seen when cisplatin was bound to DNA. The loss of the 14C-CBDCA ligand of carboplatin was calculated to occur with a rate constant of 1.3 X 10(-5) s-1 which was similar to that for the rate of formation of interstrand cross-links and faster than that for the monofunctional reaction with DNA. It was concluded therefore that the CBDCA ligand becomes a more labile leaving group once carboplatin has been monoaquated. In contrast, both chloro-ligands of cisplatin were shown to leave at similar rates. The fact that other difunctional lesions were formed to the same extent, by equal bound doses of cisplatin or carboplatin, was indicated by the unwinding of supercoiled plasmid DNA. The effects of cisplatin and carboplatin on this DNA were the same once bound to the same extent. About a 100-fold larger dose of carboplatin was, as predicted by their rates of aquation, required to produce equivalent binding to plasmid DNA. In vivo, equal binding of the two drugs to DNA of various cell systems resulted in equal cytotoxicity. Again a much larger dose (20- to 40-fold) of carboplatin was required to produce this equal binding. In general a DNA bound platinum level of about 20 nmol/g reduced cell survival by 90%, although certain cell lines were shown to be much more sensitive to DNA bound platinum. Similar binding values, to those above, were obtained in the DNA extracted from cells of human cancer patients treated with cisplatin. It was inferred that the cytotoxic effect of this level of platinum on DNA would be (unless the cells were of a sensitive phenotype) about 90%.(ABSTRACT TRUNCATED AT 400 WORDS)

Equilibrium and electrochemical studies on the ruthenium complexes formed by the interaction of K[Ru(EDTA-H)Cl].cntdot.2H2O with oxygen and hydrogen peroxide

Abstract: Etude en solution aqueuse. Le complexe subit une aquation rapide avec formation du complexe [Ru(EDTA-H)H 2 O] dont on calcule constantes de dissociation et d'hydrolyse. Avec H 2 O 2 on obtient [(EDTA-H)Ru III (H 2 O 2 )Ru III (EDTA-H)]

Photosubstitution reactions of the ruthenium(II) arene complexes Ru(.eta.6-arene)L32+ (L = ammonia or water) in aqueous solution

Abstract: Irradiation of the ruthenium(II) complexes Ru(eta/sup 6/-arene)L/sub 3//sup 2 +/ (arene = benzene, toluene, or isopropyltoluene; L = NH/sub 3/ or H/sub 2/O) in aqueous solution leads in each case to aquation of arene as the only observable photoreaction (Ru(eta/sup 6/-arene)L/sub 3//sup 2 +/ + 3H/sub 2/O ..-->.. Ru(H/sub 2/O)/sub 3/L/sub 3//sup 2 +/ + arene). Quantum yields phi/sub L/ for this process were a function of lambda/sub irr/, relatively low for the irradiation into the lowest energy absorption band but progressively higher at shorter wavelengths. The triammine ion Ru(eta/sup 6/-C/sub 6/H/sub 6/)(NH/sub 3/)/sub 3//sup 2 +/ showed no evidence for amine aquation or for photooxidation to Ru(III). The phi/sub L/ values were found to be nearly independent of whether L = NH/sub 3/ or H/sub 2/O although there are significant spectral differences between these complexes. In contrast, phi/sub L/ was found to be quite responsive to the nature of substituents on the arene ring. The spectral properties and potential mechanisms for arene photosubstitution are discussed.

Syntheses and acid aquation reactions of pentakis(methylamine)cobalt(III) complexes of the neutral ligands urea, dimethyl sulfoxide, dimethylformamide, trimethyl phosphate, and acetonitrile

Abstract: Preparation des cations [Co(NH 2 CH 3 ) 5 L] 3+ et cinetique d'aquation acide. Enthalpies d'activation

Micellar inhibition of the aquation of tris-(3,4,7,8-tetramethyl-1,10-phenanthroline)iron(II) by sodium dodecyl sulphate in aqueous acid medium

Abstract: The inhibition of the aquation of Fe(Me4phen)2+3 by sodium dodecyl sulphate (SDS) in aqueous acid media has been investigated and a mechanism which explains the pronounced inhibition and pre-micellar activity at low [SDS]T has been proposed. Inhibition is due to favourable thermodynamic-/hydrophobic/electrostatic binding between the FeII complex and SDS monomer aggregates. The bound FeII complex is stabilised with respect to dissociation and binding takes place between the ridges of the Stern layer. The partitioning of the substrate between the bulk-water phase and the micellar phase is in favour of the latter at low [H+]T and low [SDS]T. From the rate law obtained and the observed kinetic data, the micelle–complex binding constant (K1) and micelle–acid binding constant (K3) were calculated to be (2.81 ± 0.08)× 105 and (13.80 ± 0.16) dm3 mol–1, respectively, in acid media. Using the Scatchard method, K1 values of (3.95 ± 0.08)× 105 and (3.04 ± 0.16)× 105 dm3 mol–1 were calculated for the binding in neutral medium (distilled water) and 2 × 10–5 mol dm–3 H+, respectively. The decrease in K1 in acid media is attributed to competition between H+ and the complex ion for the binding sites on the micelle. The kψ–[SDS]T profiles are structured owing to the evolution (size, geometry, aggregation number, etc.) of the micelle. The inhibition of the aquation rate by HSO–4 and SO2–4 ions which form a negative field around the FeII complex is only significant at high acid concentrations. The micelle-bound complex and micelle-bound protons have opposing effects on the aquation rate. The degree of inhibition is therefore sensitive to the ratio of the concentration of these bound species.

Micellar effects on the kinetics of the aquation and the base hydrolysis of tris(1,10-phenanthroline)iron(II) and chloropentaamminecobalt(III) ions

Abstract: Les constantes de vitesse ne presentent pas de variations remarquables au-dessus de c.m.c. Pour Fe(phen) 3 2+ , au-dessous de c.m.c., les variations des constantes de vitesse sont liees a la formation d'agregats premicellaires. Effet de l'addition de NaCl

Hydrophobic and steric effects on the ion-pair formation of tris(1,10-phenanthroline)iron(II) and arenesulfonate ions. Kinetic determination of the formation constants of the ion pairs and a proton NMR study of their structures

Abstract: Ion-pair formation constants (K) for Fe(phen)/sub 3//sup 2 +/ and six kinds of arenesulfonate ions were obtained from kinetic studies of the aquation of the complex ion in aqueous sodium arenesulfonate solutions: K = 5 +/- 1, 13 +/- 2, 28 +/- 5, 19 +/- 3, 8 +/- 2, and 5 +/- 1 mol/sup -1/ dm/sup 3/ for benzene-, 4-methylbenzene-, 4-ethylbenzene-, 2,4-dimethylbenzene-, 1-naphthalene-, and 2-naphthalenesulfonate, respectively. An arenesulfonate of greater hydrophobicity showed a larger formation constant, except that small formation constants were shown by bulky naphthalenesulfonates. The formation constant was smaller for an arenesulfonate than for an alkanesulfonate with the same number of carbon atoms. The /sup 1/H NMR signal of arenesulfonate in the ion pair was found to shift upfield. Comparison of the observed shifts with those calculated on the basis of the current loop model supported a model of the ion pair in which the arenesulfonate ion lies in the hydrophobic cavity between two phenanthroline ligands of the complex ion with the sulfonate group directed outside the cavity.

Pulsed-laser photochemical study of tris(1,10-phenanthroline)chromium(III) ion in acidic and alkaline aqueous media

Abstract: The photochemistry and photophysics of tris(1,10-phenanthroline)chromium(III) ion, Cr(phen)/sub 3//sup 2 +/, following pulsed-laser excitation at 347 nm, have been studied in deaerated acidic and alkaline aqueous media (pH 3.0-11.1) at room temperature by using conductivity and visible optical detection methods. The lifetimes of the lowest doublet excited state(s) from which is derived the major portion of the photochemistry are little affected by changes in pH as monitored by emission and excited-state absorption nor are the initial intensity levels of these phenomena noticeably altered by pH changes. Alterations in pH do have significant effects on the conductivity signals, which correlate to photoaquation. Conductivity studies for natural pH (ca. pH 7.1) provide evidence for a ground-state intermediate with a pK/sub a/ value around 7. In basic media, an apparent single stage of conductivity occurs, and the values of the observed rate constant and the resulting overall change in conductance are dependent upon the concentration of hydroxide ion. The quantum yield for aquation at the highest pH of 11.1 is determined as 0.08 (+/-20%). By contrast, photochemical reaction in acidic media is found to be very much reduced relative to that occurring in alkaline solutions. A mechanism, incorporating a six-coordinate, monodentate phenathroline intermediate,more » is proposed, and it is used to discuss the occurrence of photoracemization and to compare the behavior of Cr(phen)/sub 3//sup 3 +/, where bpy designates the 2,2'-bipyridine ligand.« less

Syntheses and Acid Aquation Reactions of Pentakis(methylamine)cobalt(III) Complexes of the Neutral Ligands Urea, Dimethyl Sulfoxide, Dimethylformamide, Trimethyl Phosphate, and Acetonitrile.

Abstract: Reaction of the precursor complex (I) directly with coordinating solvent or neutral ligand yields the title compounds (II).

Volume profiles as mechanistic information for aquations of cis-acidotetraammineaquacobalt(2+) (cis-CoX(NH3)4(H2O)2+; X = Cl-, Br-, NO3-)

Abstract: Mesures des vitesses d'aquation dependant de l'acide, sous hautes pressions. On obtient les volumes de reaction par dilatometrie

The effect of ionic strength and pressure on the complex formation kinetics of the aquated iron(III)-thiocyanate system

Abstract: The kinetics of the complex formation and reverse aquation reactions in the aquated iron(III)-thiocyanate system were studied as a function of ionic strength (0.1 to 1.5 M) and pressure (up to 120 MPa) using a high-pressure temperature-jump technique. Volumes of activation for the various reaction steps were estimated from a combination of the kinetic data with the ionic strength and pressure dependencies of the overall equilibrium and acid dissociation constants determined before. The volume of activation for complexation of Fe(H2O)5OH2+ by SCN− exhibits a significant ionic strength dependence and possible explanations are offered. The results are compared and discussed in reference to earlier reported data, and mechanistic conclusions are drawn.

Synthesis and characterization of new di- and tri-nuclear cyano-bridged bis(dioximato)cobalt(III) complexes

Abstract: Several new neutral and cationic di- and tri-nuclear cyano-bridged bis(dioximato)cobalt(III) complexes have been synthesized and characterized (dioximato = dimethylglyoximato or diphenylglyoximato). These compounds are obtained through substitution of labile axial ligands by the nitrogen of the cyano-group in [Co(dioximato)2(CN)2]− or [LCo(dioximato)2(CN)] (L = H2O, NH3, or py). In the first case, the existence of only one band in the CN-stretching region of the i.r. spectrum at 2190–2200 cm−1 is indicative of a trinuclear compound, while the presence of a second band at 2140 cm−1 attributable to a terminal cyano-group indicates a dinuclear structure. In the presence of water, aquation of axial positions may take place at the same time as bridge formation, whereas the use of a non-aqueous solvent allows the preparation of complexes with pyridine or NH3.

E.M.F. and kinetic studies of the ion-pairing effects on the rate of aquation of chloropentamminechromium(III) perchlorate in different dicarboxylate medium

Abstract: Rate coefficients, k, for aquation of [Cr(NH3)5Cl]2+ in 10% ethanol solutions of some dicarboxylates have been determined by potentiometric titration methods The dissociation constants of ion-pairs so formed have been obtained from emfs of a cell comprising glass and calomel electrodes A wide range of k(ion) and k(ion-pair) values and dissociation constants has been obtained and a new correlation between k(ion-pair) and association constants among the dicarboxylate series studied has been established

A common dissociative interchange (Id) mechanism for the aquations of penta-aminechloro-cobalt(III) and -chromium(III) complexes

Abstract: The rate of aquation of [Cr(NH2Me)5Cl]2+ is slower than that of [Cr(NH3)5Cl]2+ because of a shorter Cr–Cl bond in the ground state of [Cr(NH2Me)5Cl]2+, which is consistent with an Id mechanism.

Reaction of chromium(II) with iodoacetamide and properties of (H2O)5CrCH2CO(NH2)2

Abstract: Cr(II) reagit avec l'iodoacetamide pour donner (H 2 O) 5 CrI 2+ , (H 2 O) 5 CrO(NH 2 )CCH 3 3+ et (H 2 O) 5 CrCH 2 CO(NH 2 ) 2+ . Mesures des vitesses d'equation

Kinetics of dissociation of the malonatobistrimethylenediamine cobalt (III) complex in acidic media

Abstract: The kinetics of dissociation of malonate from the malonatobistrimethylenediaminecobalt(III) complex have been investigated in aqueous perchloric acid media (0.1–1.0 mol dm−3 over a temperature range of 50–70°C at an ionic strength of 2.2 mol dm−3 adjusted with sodium perchlorate. The variation of observed pseudo-first-order rates on [acid] suggests the operation of two concurrent paths with kobs = ko + kH + [H+]. where ko and kH+ are the rate constants for uncatalysed and acid-catalysed pathways respectively. Under identical conditions the malonato complex was found to dissociate 103 times faster rate than that of corresponding oxalato complex. The influence of basicity and chelate ring size of the carboxylate and diamine groups on the aquation rate has been discussed. Analysis of rate data corresponding to kH+ suggests a dissociative mechanism involving the protonated complex.

Kinetics and mechanism of the thermal decomposition of the thiosulphatopentaamminecobalt(III) ion in dilute aqueous acid

Abstract: In acetic acid – sodium acetate buffer of pH 5.6 (25 °C) the Co(NH3)5S2O3+ ion undergoes redox decomposition rather than aquation. First-order kinetic are observed and the reaction products Co2+, N...

Specific effects of nucleophiles on the mercury(II)-assisted chloride aquation of the penta-amminechlorocobalt(III) cation and of the chloro[ethylenediaminetetra-acetato(3–)]cobaltate(III) anion

Abstract: Simple anions (X–) such as CH3CO2–, Cl–, N3–, Br– SCN–, and CN– influence the Hg2+-assisted chloride aquation of [CoCl(NH3)5]2+ and [Co(edta)Cl]2–(H4edta = ethylenediamine-NNN′N′-tetra-acetic acid) through the formation of HgX+. Observed rate changes reflect both the electrostatic and the inductive effects; the former predominates for CH3CO2–, Cl–, and N3–, while the latter does for CN–. Aminopolycarboxylates, such as edta4– and cdta4–(H4cdta = cyclopentane-1,2-diamine-NNN′N′-tetra-acetic acid) were specifically effective. A feature of the reactions with [CoCl(NH3)5]2+ is the production of [CoY(NH3)5]–(Y = edta or cdta) alongside [Co(NH3)5(OH2)]3+.

Micellar Effects on the Kinetics of the Aquation and the Base Hydrolysis of Tris(1,10-phenanthroline)iron(II) and Chloropentaamminecobalt(III) Ions.

Abstract: Les constantes de vitesse ne presentent pas de variations remarquables au-dessus de c.m.c. Pour Fe(phen) 3 2+ , au-dessous de c.m.c., les variations des constantes de vitesse sont liees a la formation d'agregats premicellaires. Effet de l'addition de NaCl