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1.
Summary The kinetics of the reaction of [Cu(bigH)2]2+ (bigH = biguanide) with an excess of amino acid (LH), namely glycine or -alanine, in aqueous solution in the 7.6–9.0 pH range at different temperatures (30–40° C) have been followed by stopped-flow spectrophotometry. The ligand replacement process has been found to pass through intermediate formation of a ternary complex, [Cu(bigH)L]+ at the slower step, followed by rapid transformation into the binary complex, [CuL2]. The overall ligand replacement process has a ligand dependent (k 1) path which is first order with respect to the incoming ligand (L-), and a ligand independent (k 0) path. Under pseudo-first order conditions containing excess amino acid, the experimental observations conform to the rate law k obs = k 0 + k 1 K a[L]T/([H=] + K a), where [L]T stands for the total concentration of amino acid and K a gives the deprotonation constant of LH. The solvent assisted dissociation (i.e. k 0 path) leads to a copper(II) mono-biguanide complex followed by rapid nucleophilic substitution; the k 1 path is in agreement with an associative mechanism. The activation parameters (H , S ) for each step have been determined.  相似文献   

2.
3.
Summary The kinetics of oxidation of ,-unsaturated alcohols (UA's), such as prop-2-ene-1-ol, but-2-ene-1-ol and 3-phenyl-prop-2-ene-1-ol, by manganese(III) acetate in aqueous H2SO4 at constant ionic strength and different acidities has been studied. The reaction was found to proceed through an outer sphere mechanism. The reactions were first order with respect to [MnIII] and fractional order in [UA]. The reaction showed first order dependence in [H+], and the rate decreased on addition of [MnII]. Added salts, such as Na2SO4, had a negligible effect on the rate. The data suggested that disproportionation of the MnIII-UA complex into free radicals was the rate determining step in the presence of [MnII]. A mechanism consistent with the experimental data is proposed. The activation parameters have been evaluated for the temperature range 298–313 K.  相似文献   

4.
Summary In aqueous solution [Cu(bigH)2]2+ (bigH=biguanide) reacts with 2,2-bipyridyl (bipy) and 1,10-phenanthroline (phen) through intermediate formation of ternary complexes [Cu(bigH)(L)]2+ and [Cu(bipy)(phen)]2+ and binary complexes [CuL2]2+ (L=bipy, phen). The rates of the different steps have been followed in borax buffer (pH 8.0±0.1) by stopped-flow spectrophotometry. For each step kobs=k0+kL[L] and the kL path appears to be associative. H and S values for the kL path conform to an isokinetic trend.  相似文献   

5.
The solubilization of an europium (III) β-diketonate chelate in aqueous medium and the changes in its photophysical properties upon its inclusion into an α-cyclodextrin hydrophobic cavity are described. The complex [Eu(tta)3·(H2O)2] (tta = 4,4,4-trifluoro-1-(thiophen-2-yl)butane-1,3-dione) was synthesized, characterized, and incorporated into the hydrophobic cavity by stirring in an α-cyclodextrin aqueous solution. The inclusion was confirmed by 1H NMR, and the stoichiometry of association was obtained by the Job method. The maximum in the excitation spectrum of the α-CD inclusion compound in aqueous solution was shifted 28 nm compared with the maximum of non α-CD complex. The emission spectrum of the association is similar to that of the free solid complex and displays the characteristic 5D0 → 7F0-4 Eu3+ transitions.  相似文献   

6.
The kinetics of ruthenium(III) catalyzed oxidation of chloramphenicol (CHP) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.1 mol l−1 was studied spectrophotometrically. The reaction between DPC and CHP in alkaline medium exhibits 1: 2 stoichiometry (CHP: DPC). The main oxidation products were identified by spot test, IR, NMR, and GC-MS spectral studies. The reaction is first order with respect to ruthenium(III) and DPC concentrations. The order with respect to chloramphenicol concentration varies from first order to zero order as the chloramphenicol concentration increases. As the alkali concentration increases the reaction rate increases with fractional order dependence on alkali concentration. Increase in periodate concentration decreases the rate. A mechanism adequately describing the observed regularities is proposed. The reaction constants involved in the different steps of the mechanism were calculated. The activation parameters with respect to limiting step of the mechanism are computed and discussed. Thermodynamic quantities are determined.  相似文献   

7.
Ibrahim  I.  Idris  S. O.  Abdulkadir  I.  Onu  A. D. 《Transition Metal Chemistry》2019,44(3):269-273
Transition Metal Chemistry - The kinetics of electron transfer between N,N′-phenylenebis-(salicylideneiminato)iron(III), hereafter referred to as [Fe(Salphen)]+, and oxalic acid was studied...  相似文献   

8.
The kinetics of the oxidation of tris(2,2′-bipyridyl)iron(II) and tris(1,10-phenanthroline)iron(II) complexes ([Fe(LL)3]2+, LL = bipy, phen) by nitropentacyanocobaltate(III) complex [Co(CN)5NO2]3? was investigated in acidic aqueous solutions at ionic strength of I = 0.1 mol dm?3 (HCl/NaCl). The reactions were carried out at fixed acid concentration ([H+] = 0.01 mol dm?3) and the temperature maintained at 35.0 ± 0.1 °C. Spectroscopic evidence is presented for the protonated oxidant. Protonation constants of 360.43 and 563.82 dm3 mol?1 were obtained for the monoprotonated and diprotonated Co(III) complexes respectively. Electron transfer rates were generally faster for [Fe(bipy)3]2+ than [Fe(phen)3]2+. The redox complexes formed ion-pairs with the oxidant with increasing concentration of the oxidant over that of the reductant. Ion-pair constants for these reaction were 160.31 and 131.9 dm3 mol?1 for [Fe(bipy)3]2+ and [Fe(phen)3]2+, respectively. The activation parameters measured for these systems have values as follows: ?H (kJ K?1 mol?1) = +113.4 ± 0.4 and +119 ± 0.3; ?S (J K?1) = +107.6 ± 1.3 and 125.0 ± 1.6; ?G (kJ K?1) = +81 ± 0.4 and +82.4 ± 0.4; and E a (kJ mol?1) = 115.9 ± 0.5 and 122.3 ± 0.6 for LL = bipy and phen, respectively. Effect of added anions (Cl?, $ {\text{SO}}_{4}^{2 - } $ and $ {\text{ClO}}_{4}^{ - } $ ) on the systems showed decrease in the electron transfer rate constant. An outer-sphere mechanism is proposed for the reaction.  相似文献   

9.
The kinetics of the oxidation of [Ni(II)(H2L1)](ClO4)2, (H2L1 = 3,8-dimethyl-4,7-diaza-3,7-decadiene-2,9-dione dioxime) and [Ni(II)(HL2)]ClO4, (H2L2 = 3,9-dimethyl-4,8-diaza-3,8-undecadiene-2,10-dione dioxime) by peroxodisulfate anion (PDS) in aqueous media at 298.0 K have been studied. The kinetics of oxidation of both Ni(II) complexes was found to be first order in the complex concentration. The dependence of the pseudo-first-order rate constant, k obs, for both complexes showed first-order dependence on PDS concentration. The kinetics of oxidation of [Ni(II)(H2L1)]2+ complex showed a complex dependence on [H+] over the pH range of 4.98–7.50, whereas that of [Ni(II)(HL2)]+ is independent of pH over the pH range of 5.02–7.76. The value of k obs, for both complexes, decreased with increasing ionic strength consistent with the involvement of oppositely charged ions in the rate-determining step. The effect of ionic strength is more pronounced for [Ni(II)(H2L1)]2+–PDS reaction than for [Ni(II)(HL2)]+–PDS reaction, confirming the higher charges of the latter.  相似文献   

10.
11.
The heats of formation of β-alanine complexes with the doubly charged copper(II) ion were determined calorimetrically. The heat effects of interaction of a solution of the amino acid with a solution of copper(II) were measured at 288.15, 298.15, and 308.15 K and ionic strengths of 0.50, 0.75, and 1.00 against the background of KNO3. The heats of dilution of a solution of copper nitrate with solutions of the background electrolyte were also determined for the introduction of the corresponding corrections. The standard thermodynamic characteristics of complex formation were calculated. The influence of temperature on the thermal effects of complex formation in the β-alanine-copper(II) ions system were considered. The standard enthalpies of formation of CuAla+ and CuAla2 complex particles in aqueous solution were calculated.  相似文献   

12.
Summary Complexes of empirical formulae [ML2Cl2(OH2)2], [CoL2Br2(OH2)2]L·4H2O, [NiL2Br2(OH2)2]L2·2H2O, [ML2(OH2)4]L2(NO3)2 and [ML4(OH2)2](ClO4)2·2H2O (M = CoII, NiII, L = 2,4-bipyridyl) were synthesized and characterized by elemental and spectral analyses. The thermal decomposition of the complexes was also investigated.Author to whom all correspondence should be directed.  相似文献   

13.
14.
The kinetics of the interaction of adenosine 5-monophosphate (5-AMP) with cis-[Pt(en)(H2O)2]2+ have been studied spectrophotometrically as a function of [Pt(en)(H2O)2]2+, [5-AMP] and temperature at pH 4.0, where the substrate complex exists predominantly as the diaqua species. Both N1 and N7 donor sites of 5-AMP are active for coordination to Pt at this pH. Base stacking and metal-induced macrochelate formation of 5-AMP plays a vital role in determining the concentration limit of 5-AMP during kinetics. Substitution occurs in two consecutive steps; both dependent on the 5-AMP concentration. Activation parameters for both steps have been calculated. The low H 1 (42.76 ± 1.64 kJ mol–1) and large negative values of S 1 (–112.1 ± 5.1 J K–1 mol–1) as well as H 2 (58.1 ± 1.4 kJ mol–1) and S 2 (–84.2 ± 4.4 J K–1 mol–1) indicate associative modes of activation for both ligand substitution processes in the two consecutive steps.  相似文献   

15.
Summary New potential tetradentate ligands, N-benzoyl-N-thiobenzohydrazide (H2BTBH) and N-salicyl-N-thiobenzohydrazide (H2SBTH) have been prepared and characterized. Their complexes with CoII, NiII and ZnII have been prepared and characterized on the basis of elemental analyses, magnetic susceptibility measurements, and u.v.-vis., i.r. and 1H-n.m.r. spectral studies. The bonding and stereochemistries of the complexes are discussed. H2BTBH, H2SBTH and the complexes have been screened towards a number of bacteria.  相似文献   

16.
The surfactantCo(III) complexes of the type cis-[Co(en)2AX]2+ (A?=?Tetradecylamine, X?=?Cl?,?Br?) were synthesised from corresponding dihalogeno complexes by the ligand substitution method. The critical micelle concentration (CMC) values of these surfactant complexes in aqueous solution were obtained from conductance measurements. The kinetics and mechanism of iron(II) reduction of surfactantCo(III) complexes, cis-[Co(en)2(C14H29NH2)Cl](ClO4)2 and cis-[Co(en)2(C14H29NH2)Br] (ClO4)2 ions were studied spectrophotometrically in an aqueous acid medium by following the disappearance of Co(III) using an excess of the reductant under pseudo-first-order conditions: [Fe(II)]?=?0.25?mol?dm?3, [H+]?=?0.1?mol?dm?3, [μ]?=?1.0?mol?dm?3 ionic strength in a nitrogen atmosphere at 303, 308 and 313?K. The reaction was found to be of second order and showed acid independence in the range [H+]?=?0.05–0.25?mol?dm?3. The second-order rate constant increased with surfactant–Co(III) concentration and the presence of aggregation of the complex itself altered the reaction rate. The effects of [Fe(II)], [H+] and [μ] on the rate were determined. Activation and thermodynamic parameters were computed. It is suggested that the reaction of [Fe(II)] with Co(III) complex proceeds by an inner-sphere mechanism.  相似文献   

17.
Summary The oxidation of -hydroxy acids (HA), viz. glycolic acid (GA), mandelic acid (MA) and lactic acid (LA), by pyridinium chlorochromate (PCC) in aqueous ethanoic acid solution was investigated in the presence and absence of RuIIICl3. The order in [HA] and [PCC] was found to be unity, with or without ruthenium(III) catalyst, and the order in [RuIII] was found also to be unity. The reaction was acid catalysed also in the presence and absence of ruthenium(III) catalyst, and hence the protonated form of PCC, was assumed to be the active species of oxidant. Added salts, and the change in dielectric constant of the medium, did not affect the oxidation rate. No induced polymerization occurred when acrylamide monomer was added to the reaction mixture. The pseudo-first order rate constants (k the formation constants (K f) of the substrate-catalyst complexes, activation and thermodynamic parameters have been evaluated. Suitable mechanisms in conformity with the experimental observations have been proposed for the uncatalysed and catalysed reactions.  相似文献   

18.
Oxalato(amine)(trien)cobalt(III) and salicylato(amine)(trien)cobalt(III) perchlorates have been synthesized and tentatively assigned a cis α configuration. The dissociation constants of the complexes have been determined. The base hydrolysis of the complexes have been investigated at 30, 35, 38.6°C and I = 1.0 mol dm−3. The rate laws for the oxalato and salicylato complexes are −dln[Complex]T/dt = k2[OH] and −dln[Complex]T = k1 + k2[OH] respectively. For the oxalato complex, k2(30°C) = (2.95 ± 0.05) × 10−2 dm3 mol−1 s−1, ΔH1 = (109 ± 4) KJ mol−1, ΔS1 = (85 ± 13) JK−1 mol−1 and for the salicylato complex, k1(30°C) = (1.58 ± 0.28) × 10−4 s−1, ΔH1 = (166 ± 7) KJ mol−1, ΔS1 = (229 ± 21) JK−1 mol−1 and k2(30°C) = (3.56 ± 0.10) × 10−3 dm3 mol−1 s−1, ΔH1 = (101 ± 6) KJ mol−1, ΔS1 = (42 ± 20) JK−1 mol−1. The base hydrolysis reactions of the complexes were followed in presence of imidazole and ethanolamine, in the presence of added anions and also in D2O medium. The results are discussed in terms of δ SN1CB mechanism involving rate limiting CoO bond fission for both k1 and k2 paths. However, the possibility of CO bond cleavage in the base hydrolysis of the oxalato complex is not ruled out.  相似文献   

19.
A series of new coordination compounds of cobalt(III) trans-dioximates with pyrazine [CoCl(DH)2Pz] · H2O (I), [CoBr(DH)2Pz] · H2O (II), [Co(DH)2Pz2]NO3 · H2O (III), [Co(DH)2Pz2][BF4] (IV), [Co(MgH)2Pz2][BF4] (V), and [Co(NioxH)2Pz2][BF4] (VI), where DH, MgH, and NioxH are dimethylglyoxime, methylglyoxime, and 1,2-cyclohexanedionedioxime monoanions, respectively, Pz is a pyrazine molecule were synthesized. The structures of compounds I, II, and VI were determined by X-ray diffraction. The Co(III) environment in these compounds is octahedral and the pseudomacrocyclic (DioxH)2 fragment occurs in the equatorial plane. This fragment is stabilized by O-H…O hydrogen bonds. The neutral Pz ligand is monodentate in all three compounds.  相似文献   

20.
The acid-catalysed hydrolysis of [Co(trpn)(CO3)]+ and [Co(trpn)(HCO3)]2+ ions (trpn = 3,3,3-triaminotripropylamine) have been studied spectrophotometrically in aqueous 1.0m HClO4/NaClO4. For the carbonato complex, [HClO4] = 0.02–0.25m and T = 20–35°C; for the bicarbonato complex, [HClO4] = 0.025–0.30m and T = 25°C. Both complexes hydrolyse to form the same cis-diaqua species. The rate law for the hydrolysis is d(ln[CoIII])/dt = k0+k1[H3O+]. The values of the rate constants (25°C), H (kJmol–1) and S (Jmol–1K–1)are:[Co(trpn)(CO3)]+,k0 = (1.7±0.6)× 10–4s–1, H 0 = 57±21, S 0 = –126±75; k1 = (1.0 ±0.1)×10–2m–1s–1, HDagger;1 = 62±8, S1 = –75 ±21, and for [Co(trpn)(HCO3)]2+, k0 = (2.9±0.7)× 10–4s–1, and k1 = (7.8±1.0)×10–2m–1s–1. The carbonato complex exhibits a deuterium isotope effect with k1D/k1H = 1.9, consistent with a rapid pre-equilibrium protonation, followed by rate-controlling ring-opening. The rate constants k0 and k1 (25°C and = 1.0m) for the ring-opening decarboxylation of the two systems studied lie within the experimental error. The results are compared with o ther related systems and the factors which influence the ring-opening decarboxylation (steric hindrance, ring strain, electron-donor ability of the amines) are discussed. The k1 path is interpreted in terms of concerted ring-opening and bond-making in the highly unstable aquabicarbonato intermediate.  相似文献   

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