The (NH3)5CoOC(NH2)23+ ion is consumed in water according to the rate law k(obs.) = k1 + k2[OH−], where k1 = 4.0 × 10−5 s−1 and k2 = 14.2 M−1 s−1 (0–0.1 M [OH−];μ = 1.1 M, NaClO4, 25 °C). A hitherto unrecognized intramolecular O- to N- linkage isomerization reaction has been detected. In strongly acid solution only aquation to (NH3)5CoOH23+ is observed, but in 0.1–1.0 M [OH−], 7% of the directly formed products is the urea-N complex (NH3)5CoNHCONH22+ which has been isolated. In the neutral pH region a much greater proportion (25%) of the products is the urea-N species. These results are interpreted in terms of an urea-O to urea-N linkage isomerization reaction competing with hydrolysis for both spontaneous (k1) and base-catalyzed (k2) pathways; the rearrangement is not observed in strongly acidic solution (pH ⩽ 1) because the protonated N-bonded isomer (pK′a ≈ 3) is unstable with respect to the O-bonded form. The appearance of the isomerization pathway as the pH is raised in the 0–6 region is commensurate with a rate increase which cannot be attributed to a contribution from the base catalysis term k2[OH−]. It is argued that this observation establishes, for the spontaneous pathway, that hydrolysis and linkage isomerization are separate reaction pathways — there is no common intermediate. The product distribution and rate data lead to the complete rate law, k(obs.) = k1 + k2[OH−] = (ks + kON) + (kOH + k′ON) [OH−] for the reactions of the O-bonded isomers, where ks, kOH are the specific rates for hydrolysis, and kON, k′ON are the specific rates for O- to N-linkage isomerization, by spontaneous and base-catalyzed pathways respectively; kON = 1.3 × 10−5 s−1 and k′ON = 1.1 M−1 s−1 (μ = 1.0 M, NaClO4, 25 °C). The O- to N- linkage isomerization has been observed also for complexes of N-methylurea, N,N-dimethylurea and N-phenylurea, but not for the N,N′-dimethylurea species. There is an approximately statistical relationship among the data for −NH2 capture (versus H2O), while −NHR and −NR2 do not compete with water as nucleophiles for Co(III) in either the spontaneous or base-catalyzed hydrolysis processes. For each urea-O complex, O- to N-isomerization is a more significant parallel reaction in the spontaneous as opposed to the base-catalyzed pathway. This is interpreted as being indicative of more associative character in the spontaneous route to products, a conclusion supported by other evidence. Some activation parameter data have been recorded and the effect of the N-substitution on the rates of solvolysis (H2O, Me2SO) is discussed. The urea-N complexes have been isolated as their deprotonated forms, [(NH3)5CoNHCONRR′](ClO4)2·xH2O (R,R′ = H, CH3). They are kinetically inert in neutral to basic solution but in acid they protonate (H2O, pK′a 2–3; μ = 1.0 M, 25 °C) and then isomerize rapidly back to their O-bonded forms. Some solvolysis accompanies this N- to O-rearrangement in H2O and Me2SO. Specific rates and activation parameters are reported. The kinetic data follow a rate law of the form kNO(obs.) = (k + kNO)[H+]/(K′a + [H+]) and the active species in the reaction is the protonated form; k, kNO are the specific rates for hydrolysis and isomerization, respectively. Proton NMR data establish that the site of protonation (in Me2SO) is the cobalt-bound nitrogen atom. For the unsubstituted urea species (NH3)5CoNH2CONH23+, diastereotopic exo-NH2 protons arising from restricted rotation about the CN bond are observed. The relevance to the mechanism of the linkage isomerization process is considered. 13C and 1H NMR and electronic absorption spectral data are presented, and distinctions between linkage isomers and the solution structures (electronic and conformational) are discussed. The urea-N/urea-O complex equilibrium is governed by the relation K′NO(obs.) = K′NO[H+]/[H+](K′a), where K′NO is the equilibrium constant = [(NH35Co(urea-O)3+]/[(NH3)5Co(urea-N)3+]. Values for K′NO(=kNO/kON = 260 and pK′a ≈ 3 for the NH2CONH2 system are consistent with the stability of the N-isomer in feebly acidic to basic solution (e.g. pH 6, K′NO(obs.) = 2.6 × 10−2) and instability in acid solution (e.g. pH 1, K′NO(obs.) = 240). The equilibrium data for this and other urea complexes of (NH3)5Co(III) are contrasted with the result for the analogous Rh(III)NH2CONH2 system K′NO ≈ 1). 相似文献
Complex formation between Pd(II), Pt(II) and iodide has been studied at 25 °C for an aqueous 1.00 M perchloric acid medium. Measurements of the solubility of PdI2(s) in aqueous mercury(II) perchlorate and of AgI(s) and PdI2(s) in aqueous solutions of Pd2+(aq) and Ag+(aq) gave the solubility product of PdI2(s) as Kso=(7±3) × 10−32 M3, which is much smaller than previous literature values.The stability constants β1=[MI(H2O)3+]/([M(H2O)42+][I−]) for the two systems were obtained as the ratio between rate constants for the forward and reverse reactions of (i). The following values of k1 (s−1 M−1), k−1 (s−1) and β1 (M−1) were obtained at 25 °C: (1.14±0.11) × 106, (0.92±0.18), (12±4) × 105 for MPd, and (7.7±0.4), (8.0±0.7) × 10−5, (9.6±1.3) × 104 for MPt. Combination with previous literature data gives the following values of log(β1 (M−1)) to log(β4 (M−4)): 6.08, ∼22, 25.8 and 28.3 for MPd, and 4.98, ∼25, ∼28, and ∼30 for MPt. The present results show that the large overall stability constants β4 observed for the M2+I− systems are most likely due to a very large stability of the second complex MI2(H2O)2, which is probably a cis-isomer. A distinct plateau in the formation curve for mean ligand number 2 is obtained both for MPd and Pt. The other iodo complexes are not especially stable compared to those of chloride and bromide.ΔH≠ (kJ mol−1) and ΔS≠ (JK−1 mol−1) for the forward reaction of (i), MPd, are (17.3±1.7) and (−71±5), and for the reverse reaction of (i) MPd, (45±3) and (−95±6), respectively. The kinetics are compatible with associative activation (Ia). The contribution from bond-breaking in the formation of the transition state seems to be less important for Pd than for Pt. 相似文献
trans-[Ru(NH3)4P(OR)3(H2O)]2+ (R = Me, Pr, iPr, and Bu) reacts with isonicotinamide at second-order- specific rates k1 of 1.2, 2.3, 7.4 and 8.1 M−1 s−(25 °C, μ = 0.10 NaCF3COO/CH3COOH), respectively, for R = Me, Pr, iPr and Bu. The products trans- [Ru(NH3)4P(OR)3isn](PF6)2 have been isolated and characterized by micro analysis, cyclic voltammetry, and electronic spectral data. The aquation rates k−1 for the isonicotinamide (isn) derivatives are 5.2 × 10−2, 5.9 × 10−2, 2.0 × 10−1 and 3.4 × 10−1 s−1 for R= Me, Pf, Bu and iPr, respectively. The activation parameters for the forward and backward reactions indicate the same mechanism for all of them. The substitution proceeds by a dissociative mechanism with a significant outer-sphere association of trans-[Ru(NH3)4P(OR)3(H2O)]2+ complexes with isn. Assuming k1 as indicative of the lability of the coordinated water molecule on the monophosphite complexes, the following sequence of increasing trans-effect mav be proposed: P(OMe)3 <P(OEt)3 <P(OPr)3 <P(OiPr)3 <P(OBu)3. The affinity of the monophosphite complexes for isn increases according to P(OMe)3 ⋍ P(OiPr)3 < P(OEt)3 < P(OPr)3 ⋍ P(OBu)3. 相似文献
Oxidation of the title complexes with ozone takes place by hydrogen atom, hydride, and electron transfer mechanisms. The reaction with (NH3)4(H2O)RhH2+ is a two electron process, believed to involve hydride transfer with a rate constant k = (2.2 ± 0.2) × 105 M−1 s−1 and an isotope effect kH/kD = 2. The oxidation of (NH3)4(H2O)RhOOH2+ to (NH3)4(H2O)RhOO2+ by an apparent hydrogen atom transfer is quantitative and fast, k = (6.9 ± 0.3) × 103 M−1 s−1, and constitutes a useful route for the preparation of the superoxo complex. The latter is also oxidized by ozone, but more slowly, k = 480 ± 50 M−1 s−1. 相似文献
The reaction of 2,3-tri with CrCl3·6H2O1, dehydrated in boiling DMF, results in the formation of mer-CrCl3(2,3-tri) and anation of hydrolysed solutions of mer-MCl3(2,3,-tri) (M=Co, Cr) with 6 M HCl containing HClO4, forms trans-dichloro- mer-[MCl2(2,3-tri)(OH2)]ClO4·H2O (M=Cr, Co; I, II). trans-Dinitro-mer-[Co(NO2)2(NH3)(2,3-tri)] ClO4 crystallises from the reaction between mer-Co(NO2)3(2,3-tri) and aqueous 7 M ammonia, on addition of NaClO4·H2O, and trans-dichloro-mer-[CoCl2(NH3)(2,3-tri)]ClO4 (III) can be isolated by treatment of the dinitro with 12 M HCl. Reaction of mer-CoCl3(2,3-tri) with C2O42−, followed by addition of aqueous NH3 and NaClO4·H2O results in the isolation of racemic mer-[Co(ox)(NH3)(2,3-tri)]ClO4· H2O. This complex was resolved into its enantiomeric forms and treatment of these with SOCl2/MeOH/ HClO4 gave the chiral forms of trans-dichloro-mer- [CoCl2(NH3)(2,3-tri)]ClO4 (R or S at the see-NH center). The rates of loss of the first chloro ligand from these dichloro complexes have been measured spectrophotometrically in 0.1 M HNO3 over a 15 K temperature range to give the following kinetic parameters; (I) kH(298)=7.25 × 10−5 s−1, Ea=78.5 kJ mol−1, δS298#=−69 J K−1 mol−1; (II) kH(298)=4.00 × 10−3 s−1, Ea=89.9, δS298#= +87.5; (III) kH(298)=3.09 × 10−4 s−1, Ea=103, δS298#=+27. Treatment of the dichloro cations with Hg2+/HNO3 results in the generation of mer- M(2,3-tri)(OH2)33+ (M=Cr, Co; IV, V) and trans- diaqua-mer-Co(NH3)(2,3-tri)(OH2)23+ (VI). The Co(III) cations isomerise to the fac configuration with (V) Kisom(298) μ=1.0 M)=2.97 × 10−5 s−1, Ea=115, δS298#=+46. (VI) Kisom(298) (μ=1.0 M)=4.13 × 10−5 s−1, Ea=113, δS298#=+52. 相似文献
The kinetics of rapid CO substitution by PPh3 in Co4(CO)12 and Rh4(CO)12 have been examined by stopped-flow and low temperature FT-IR methods. In Co4(CO)12 rapid (kobs ∼ 1.8 s−1) substitution of CO occurs after a 1–15 s induction period at 28 °C in C6H5Cl solvent by a catalytic process. Addition of PPh3 to Rh4(CO)12 yields Rh4(CO)11(PPh3) according to a predominantly second order rate law k1[Rh4- (CO)12] + k2[Rh4(CO)12][PPh3] with k1 = 25 ± 11 s−1 and k2 = 2.97 ± 0.27 X 104 M−1 s−1 at 28 °C. Substitution of a second CO ligand also occurs rapidly with k1 = 0.15 ± 0.09 s−1 and k2 = 6.54 ± 0.07 X 102 M−1 s−1 at 28 °C. The reactivity of Rh4(CO)12 toward associative substitution is 104– 1011 faster than for the Co and Ir analogues, In Rh4(CO)11(PPh3) the increase in CO substitution rates over Co and Rh analogues is 102–107. The ordering of associative substitution rates Co << Rh >>> Ir in these clusters exaggerates the trend seen in mononuclear metal complexes. 相似文献
The reaction of CrCl3 · 6H2O (dehydrated in DMSO) with 1,5,9-triazanonane (3,3-tri) gives mer- CrCl3(3,3-tri), the configuration being established by isomorphism with the corresponding Co(III) complex. This non-electrolyte is hydrolyzed in aqueous acidic solution and mer-[CrCl2(3,3-tri)- (OH2)]ClO4 can be isolated by anation with HCl in the presence of HClO4. Reaction of mer-CrCl3- (3,3-tri) in DMF with diamines produces complexes of the type [CrCl(diamine)(3,3-tri)] Cl2 [diamine= 1,2-diaminoethane (en), 1.2-diaminopropane (pn), 1,3-diaminopropane (tn), 2,2-dimethyl-1,3-diaminopropane (Me2tn) and cyclohexanediamine (chxn, cis plus trans mixture; two isomers A and B)] and these have been characterized as the ZnCl42− salts. The configuration of the triamine ligand in these complexes has been established as mer-(H↓)- by a single crystal X-ray analysis of [CrCl(en)(3,3-tri)]- ZnCl4, monoclinic, P21, a=7.932, b= 14.711, c= 8.312 Å, β=104.6° and Z=2, refined to a conventional R factor of 0.034. The kinetics of the Hg2+- assisted chloride release from [CrCl(diamine)(3,3- tri)]ZnCl4 salts were measured spectrophotometrically (μ=1.0 M HClO4 or HNO3) over 15 K temperature ranges to give, in order, 104kHg (298.2 K) (M−1 s−1), Ea(kJ mol−1), ΔS# (J K−1 mol−1): en- (HClO4): 5.95, 78.1, -53; pn(HClO4); 5.24, 81.2; -44; tn(HClO4): 26.7, 85.6, -15; Me2tn(HClO4): 21.8, 78.6, -40; A-chxn(HNO3): 7.60, 81.0,-41; B-chxn(HNO3): 18.3, 56.8, -115. A ‘non-replaced ligand effect’ on the rate is observed for the first time in this series of homologous Cr(III) complexes. The kinetics of the thermal aquation (kH, 0.1 M HClO4) were measured titrimetrically for CrCl(diamine) (3,3-tri)2+ to give the following kinetic parameters: diamine=en: 107kH (298.2)=5.34 s−1, Ea=99.2 kJ mol−1, ΔS#=-40 J K−1 mol-1; diamine =tn: 107kH (298.2)=5.04 s−1, Ea= 82.8, ΔS#= -96. 相似文献
A kinetic study of the oxidation of (hydroxyethyl)ferrocene (HEF) by [2-pyridylmethylbis(2-ethyl-thioethyl)ainine]copper(II) (Cu(pmas)2+) is reported, with the objective of documenting the influence of the two thioether sulfur ligands on the electron transfer rate. Both reactants exhibit a first-order dependence at pH 6, I = 0.1 M(NaNO3); k(25°C) = 1.3 × 104M−1sec−1, ΔH3 = 10.1 kcal/mole, ΔS3 = −6 eu. The apparent Cu(pmas)2+/+ self-exchange electron transfer rate constant calculated from this reaction on the basis of relative Marcus theory (4.7 × 101M−1 sec−1) agrees well with previous findings on ferrocytochrome c, Fe(CN)64−, and Ru(NH3)5py2+ oxidations. Spectrophotometric titrations of Cu(pmas)2+ and Cu(tmpa)2+ (tmpa = tris(2-pyridylmethyl)amine) with azide ion showed that both Cu(pmas)N3)+ (Kf1 = 3.1 × 103M−1) and Cu(pmas)(N3)2 (Kf2 = 3.5 × 101M−1) but Cu(tmpa)(N3)+ (Kf = 6.6 × 102M−1) are formed up to 0.15 M N3− (25°C, pH 6, I = 0.2 M), suggesting that a thioether sulfur atom is displaced in the uptake of a second N3− ion by Cu(pmas)(N3)+. The effect of thioether sulfur displacement by azide ion on the HEF-Cu(pmas)2+ reaction rate may be understood entirely through the tendency of N3− to shift the position of the redox equilibrium towards the reactant side, without invoking any special role for the sulfur ligand in promoting electron transfer reactivity. 相似文献
cis,cis,trans-[PtIV(NH3)2Cl2(OH)2] reacts reversibly with ascorbic acid to give dehydroascorbic acid and mainly cis-[PtII(NH2Pri)2Cl2]. The parameters for the forward reaction are: kf = 0.584 M− s− at 37.0 °C, ΔH≠f = 108.6 −+ 6.4 kJ mol−1 andΔS≠f = 101 −+ 22 J K−1 mol−1. 相似文献
Kinetic studies of the reduction of ferrioxamine B (Fe(Hdesf)+) by Cr(H2O)62+, V(H2O)62+, and dithionite have been performed. For Cr(H2O)62+ and V(H2O)62+, the rate is ?d[Fe(Hdesf)+]/dt = k[Fe(Hdesf)+][M2+]. For Cr(H2O)62+, k = 1.19 × 104 M?1 sec?1 at 25°C and μ = 0.4 M, and k is independent of pH from 2.6 to 3.5. For V(H2O)62+, k = 6.30 × 102 M?1 sec?1 at 25°C, μ = 1.0 M, and pH = 2.2. The rate is nearly independent of pH from 2.2 to 4.0. For Cr(H2O)62+ and V(H2O)62+, the activation parameters are ΔH≠ = 8.2 kcal mol?1, ΔS≠ ?12 eu and ΔH≠ = 1.7 kcal mol?1, ΔS≠ = ?40 eu (at pH 2.2) respectively. Reduction by Cr(H2O)62+ is inner-sphere, while reduction by V(H2O)62+ is outer-sphere. Reduction by dithionite follows the rate law ?d[Fe(Hdesf)+]/dt =kK[Fe(Hdesf)+][S2O42?] where K is the equilibrium constant for dissociation of S2O42? into SO2? radicals. The value of k at 25°C and μ = 0.5 is 2.7 × 103 M?1 sec?1 at pH 5.8, 3.5 × 103 M?1 sec?1 at pH 6.8, and 4.6 × 103 M?1 sec?1 at pH 7.8, and ΔH≠ = 6.8 kcal mol?1 and ΔS≠ = ?19 eu at pH 7.8. 相似文献
The rate of phosphate hydrolysis of ATP in the substitution-inert complex Co(NH3)4ATP-has been examined in the presence and absence of [Co(cyclen)(H2O)2]3+. The rate of hydrolysis of Co(NH3)4ATP- in the absence of [Co(cyclen)(H2O)2]3+ is essentially independent of pH in the range 6.0 to 9.0, and the rate constant is 2.6 × 10?5 sec ?1 at pH 9.0, 40°C, and 1.0 M ionic strength Rate constants for the hydrolysis of Co(NH3)4ATP- in the presence of [Co(cyclen)(H2O)2]3+ are sharply dependent upon pH in the same range. The rate constants at pH 8.0, 8.6, and 9.0 are 8, 63, and 95 times larger than the rate constant at pH 7.0. At pH 9 the rate constant is 1.2 × 10?3 sec?1 for 16 mM Co(NH3)4ATP- in the presence of 10 mM [Co(cyclen)(H2O)2]3+. The proposed mechanism for hydrolysis involves the coordination of a phosphate group of Co(NH3)4ATP- by [Co(cyclen)(H2O)2]3+ to form a dinuclear species, followed by internal attack of coordinated hydroxide on the phosphate chain. 相似文献
Chloride anation of trans-Pt(CN)4ClOH2− has been studied with and without Pt(CN)42− present at 25.0°C by use of stopped-flow and conventional spectrophotometry and a 1.00 M perchlorate medium. The rate law in the absence of Pt(CN)42− is Rate=(p1 + p2 [H+] ) [Cl−]2 [complex]/(1 + q [Cl−]) with p1=(3.0 ± 0.1) × 10−5 M−2s−1, p2=(3.6 ± 0.1) × 10−5 M−3 s−1 and q=(0.62 ± 0.02) M−1. It is compatible with a chloride assistance via an intermediate of the type Cl-Cl-Pt(CN)4···OH22−, in which the reactivity of the aqua ligand is enhanced due to a partial reduction of the platinum. This mechanism of halide assistance is in principle the same as the modified reductive elimination oxidative addition (REOA) mechanism proposed by Poë, in which the intermediate is not split into free halogen, platinum(II) and water, and in which electron transfer not necessarily involves complete reduction to platinum(II). To avoid confusion with complete reductive eliminations, reactions without split of the intermediates are here termed halide-assisted reactions. The pH-dependence indicates acid catalysis via a protonated intermediate ClClPt(CN)4···OH3−.The Pt(CN)42−accelerated path has the rate law Rate= [Cl-] [Pt(CN)42−] [complex] where k=(39.9±0.5) M−2 s−1 and Ka=(4.0±0.2)10−2 M is the protolysis constant of trans-Pt(CN)4ClOH2−.Reaction between PtCl5OH2− and chloride is accelerated by Pt(CN)42− and gives PtCl62− as the reaction product. The rate law is Rate=k [Cl−] [Pt(CN)42−] [PtCl5OH2−] with k=(5.6 ± 0.2)10−3 M−2 s−1 at 35.0°C and for a 1.50 M perchlorate acid medium. The reaction takes place without central ion exchange. Alternative mechanisms with two consecutive central ion exchanges can be excluded. The role of Pt(CN)42− in this reaction is very similar to that of the assisting halide in the halide assisted anations. [p ]Reaction between trans-Pt(CN)4ClOH2− and PtCl42− gives Pt(CN)42− and PtCl5OH2− as products and has the rate law Rate=k[PtCl42−] [trans-Pt(CN)4ClOH2−] with k=(3.32 ± 0.02) M−1 s−1 at 25 °C for a 1.00 M perchloric acid medium. The formation of an aqua complex as the primary reaction product and the rate independent of [Cl−] shows that formation of a bridged intermediate of the type Pt(II)Cl4ClPt(IV)(CN)4OH23− is formed in the initial reaction step, not five-coordinated PtCl53−. 相似文献
Energy-transfer rate-constants from photo-excited [Ru(N–N)3]2+ (N–N = 2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (4dmb), 5,5′-dimethyl-2,2′-bipyridine (5dmb)) to [Cr(O–O)3]3− (O–O2− = ox2− ((COO−)2), mal2− (CH2(COO−)2)) and [Cr(CN)6]3− in encounter complexes were evaluated in aqueous solutions containing alkali metal ion. The rate constant depends on the molecular size of the ruthenium(II) complex: 1.8 × 108 s−1 for [Ru(bpy)3]2+ (molecular radius, r = 5.8 Å), 1.4 × 108 s−1 for [Ru(5dmb)3]2+ (r = 6.1 Å) and 0.96 × 108 s−1 for [Ru(4dmb)3]2+ (r = 6.7 Å) in the system of [Ru(N–N)3]2+–[Cr(ox)3]3− in aqueous solution. However, the rate constant is much more sensitive to the chromate(III) complex than to ruthenium(II) complex; 1.8 × 108 s−1 and 0.43 × 108 s−1 for [Cr(ox)3]3− (r = 4.0 Å) and [Cr(mal)3]3− (r = 4.2 Å) in the [Ru(bpy)3]2+–[Cr(O–O)3]3− systems, respectively. We conclude that the congeniality between the donor’s and acceptor’s ligands in encounter complex plays an important role in energy transfer in aqueous solution. 相似文献
In the present study we examine the effects of Al on the uptake of Ca2+ and H2PO-4 in beech (Fagus sylvatica L.) grown in inorganic nutrient solutions and nutrient solutions supplied with natural fulvic acids (FA). All the solutions used were chemically well characterized. The uptake of Al by roots of intact plants exposed to solutions containing 0, 0.15 or 0.3 mM AlCl3 for 24 h, was significantly less if FA (300 mg l−1) were also present in the solutions. The Ca2+(45Ca2+) uptake was less affected by Al in solutions supplied with FA than in solutions without FA. There was a strong negative correlation between the Al and Ca2+ uptake (r2=0.98). When the Al and Ca2+ (45Ca2+) uptake were plotted as a function of the Al3+ activity (or concentration of inorganic mononuclear Al), almost the same response curves were obtained for the -FA and +FA treatments. We conclude that FA-complexed Al was not available for root uptake and therefore could not affect the Ca2+ uptake. The competitive effect of Al on the Ca2+ uptake was also shown in a 5-week cultivation experiment, where the Ca concentration in shoots decreased at an AlCl3 concentration of 0.3 mM. The effect of Al on H2PO−4 uptake was more complex. The P content in roots and shoots was not significantly affected, compared with the control, by cultivation for 5 weeks in a solution supplied with 0.3 mM AlCl3, despite a reduction of the H2PO−4 concentration in the nutrient solution to about one-tenth. At this concentration Al obviously had a positive effect on H2PO−4 uptake. The presence of FA decreased 32P-phosphate uptake by more than 60% during 24 h, and the addition of 0.15 or 0.3 mM AlCl3 to these solutions did not alter the uptake of 32P-phosphate. 相似文献
The preparation of the planar yellow [Ni([8]aneN2)2](ClO4)2 is described. The complex dissociates in basic solution, with rate = kOH[NiL][OH?] (L = 1,5-diazacyclo-octane). At 25 °C, kOH = 4.5 x 10?2 M?1 s?1 and the corresponding activation parameters are ΔH≠ = 69.2 kJ mol?1 and ΔS298≠ = ?38.6 J K?1 mol?1. Acid catalysed dissociation in quite slow even in strongly acidic solutions. The kinetic data in this case can be fitted to the expression Kobs = ko + KH[H+], where ko relates to a solvolytic pathway and kH to the acid catalysed pathway. At 60 °C, Ko = 2 x 10?5 s?1 and kH is 2 x 10?5 M?1 s?1. Possible mechanisms for these reactions are considered.The Ni(II)/Ni(III) redox couple for NiLn+ is irreversible on Pt using MeCN as solvent. 相似文献
Efforts to delineate the interactions of neurotoxic Al(III) with low molecular mass substrates relevant to neurodegenerative processes, led to the investigation of the pH-specific synthetic chemistry of the binary Al(III)-[N-(phosphonomethyl) iminodiacetic acid] (Al-NTAP), Al(III)-[nitrilo-tris(methylene-phosphonic acid)] (Al-NTA3P), and Al(III)-[1-hydroxy ethylidene-1,1-diphosphonic acid] (Al-HEDP) systems, in correlation with solution speciation studies. Reaction of Al(NO3)3·9H2O with NTAP at pH 7.0 and 4.0 afforded the new species (CH6N3)4[Al2(C5H6NPO7)2(OH)2]·8H2O (1) and (NH4)2[Al2(C5H6NPO7)2(H2O)2]·4H2O (2), while reaction of Al(NO3)3·9H2O with NTA3P led to K8[Al2(C3H6NP3O9)2(OH)2]·20H2O (3). Complexes 1–3 were characterized by elemental analysis, FT-IR, 13C, 31P, 1H NMR (for 1–2 solid state and solution NMR where feasible), and X-ray crystallography. The structures of 1–3 reveal the presence of uniquely defined dinuclear complexes of octahedral Al(III) bound to fully deprotonated phosphonate ligands, water and hydroxo moieties. The aqueous solution speciation studies on the aforementioned binary systems project a clear picture of the binary Al(III)–(carboxy)phosphonate interactions and species under variable pH-conditions and specific Al(III):ligand stoichiometry. The concurrent solid state and solution work (a) exemplifies essential structural and chemical attributes of soluble aqueous species, reflecting well-defined interactions of Al(III) with phosphosubstrates and (b) strengthens the potential linkage of neurotoxic Al(III) chemical reactivity toward O,N-containing (carboxy)phosphate-rich cellular targets. 相似文献
The complexes CodptX3 and [Codpt(H2O)X2]ClO4 (X = Cl, Br; dpt = dipropylenetriamine = NH(CH2CH2CH2NH2)2) have been prepared and characterized. Rate constants (s−1) for aqueous solution at 25 °C and μ = 0.5 M (NaClO4), for the acid-independent sequential ractions. have been measured spectrophotometrically. For X = Cl: k1 ⋍ 2 × 10−2, k2 = 1.7 × 10−4 and k3 = 4.8 × 10−6, and for X = Br: k1 ⋍ 2 × 10−2, k2 = 5.25 × 10−4 and k3 = 2.5 × 10−5 The primary equation was found to be acid independent, while the secondary and tertiary aquations were acid-inhibited reactions. For the second step, the rate of the reaction was given by the rate equation where Ct is the complex concentration in the aqua-and hydroxodihalo species, k′2 is the rate constant for the acid-dependent pathway and Ka is the equilibrium constant between the hydroxo and aqua complex ions. The activation parameters were evaluated, for X = Cl: ΔH≠2 = 106.3 ± 0.4 kJ mol−1 and ΔS≠2 = 40.2 ± 1.7 J K−1 mol−, and for X = Br: ΔH≠2 = 91.6 ± 0.4 kJ mol−1 and ΔS≠2 = 0.4 ± 1.7 J K−1 mol−1. The results are discussed and detailed comparisons of the reactivities of these complexes with other haloaminecobalt(III) species are presented. 相似文献
One isomer of [CrCl(N-Me-tn)(dien)]ZnCl4 has been isolated from the reaction of CrCl3·6H2O, dehydrated in DMF, with the polyamines N-methyl- 1,3-diaminopropane and diethylenetriamine. This complex is isomorphous with δλ-(R,S)usft-[CoCl(N-Me-tn)(dien)] ZnCl4 and thus has the unsym-fac- configuration with the N-Me group trans to the sec-NH group of the coordinated triamine. The Cr(III) complex has been resolved with NH4BCS and the chiroptical parameters of (-)488-[CrCl(N-Me-tn)(dien)]- ZnCl4, derived from the less soluble diastereoisomeride by metathesis, are similar to those obtained for the less soluble (-)534-λ-(S)-a,cb,edf-Co(III) analogue, of known absolute configuration. Kinetic parameters for the rates of thermal aquation (μ= 1.0 M, HClO4) and Hg2+-assisted chloride release (μ= 1.0 M) for usft-[CrCl(N-Me-tn)(dien)]ZnCl4 are kH= 3.7 × 10−6 s−1, Ea=93 ± 8 kJ mol−1, ΔS2984t#= −45 ± 16 J K−1 mol−1 and kHg=2.01 × 10−3 M−1 s−1, Ea=64.2 ± 3.3, ΔS298#=−89.5 ± 7, respectively at 298 K. 相似文献
Activated white cells use oxidants generated by the heme enzyme myeloperoxidase to kill invading pathogens. This enzyme utilizes H2O2 and Cl−, Br−, or SCN− to generate the oxidants HOCl, HOBr, and HOSCN, respectively. Whereas controlled production of these species is vital in maintaining good health, their uncontrolled or inappropriate formation (as occurs at sites of inflammation) can cause host tissue damage that has been associated with multiple inflammatory pathologies including cardiovascular diseases and cancer. Previous studies have reported that sulfur-containing species are major targets for HOCl but as the reactions are fast the only physiologically relevant kinetic data available have been extrapolated from data measured at high pH (>10). In this study these values have been determined at pH 7.4 using a newly developed competition kinetic approach that employs a fluorescently tagged methionine derivative as the competitive substrate (k(HOCl + Fmoc-Met), 1.5×108 M−1 s−1). This assay was validated using the known k(HOCl + NADH) value and has allowed revised k values for the reactions of HOCl with Cys, N-acetylcysteine, and glutathione to be determined as 3.6×108, 2.9×107, and 1.24×108 M−1 s−1, respectively. Similar experiments with methionine derivatives yielded k values of 3.4×107 M−1 s−1 for Met and 1.7×108 M−1 s−1 for N-acetylmethionine. The k values determined here for the reaction of HOCl with thiols are up to 10-fold higher than those previously determined and further emphasize the critical importance of reactions of HOCl with thiol targets in biological systems. 相似文献
The equilibrium, kinetics and mechanism of the reaction of chromium(III) with pentane-2,4-dione (Hpd) have been investigated in aqueous solution at 55°C and ionic strength 0.5 mol dm−3 NaClO4. The equilibrium constant (log β1) is 10.08(±0.01) while the pK of Hpd is 8.69(±0.01). The kinetics are consistent with a mechanism in which [Cr(H20)6]3+ and [Cr(H20)5(OH)]2+ react with the enol tautomer of Hpd with rate constants of 1.05(±0.26) × 10−2 and 2.78(±0.08) × 10−1 dm3 mol−1 s−1 respectively. These rate constants are considerably more rapid than those predicted by the Eigen-Wilkins mechanism. These data are compared with literature values. 相似文献