Abstract The kinetics of the reaction of [Cu(bigH)2]2+ (bigH = biguanide) with an excess of different amino acids (LH) like ß-alanine, L-phenylalanine and L-valine in aqueous solution in the 7.60-9.00 pH range at different temperatures (30-40°C) have been studied by stopped-flow spectrophotometry and compared with those of different ligands reacting with the title copper(II) complex. The ligand replacement process has been suggested to pass through an intermediate formation of the ternary complex, [Cu(bigH)L]+ as the rate determining step, followed by the rapid transformation into the binary complex, [CuL2]. The overall ligand replacement process follows a two-term rate law, kobs = k0 + k1Ka[L]T/([H+] + Ka, where [L]T gives the total concentration of the entering ligand, i.e. amino acid, and Κa gives the deprotonation constant of the amino acid (LH). Thus the process experiences both the ligand independent path (i.e. k0) and ligand dependent path (i.e. k0). The solvent assisted k0 path leads to a copper(II) mono-biguanide complex followed by the rapid nucleophilic substitution; the k1 path is in agreement with an associative mechanism. The k0 path is independent of the structure and basicity of the entering amino acids while the k0 path is dependent on the basicity and steric crowding of the entering amino acid. The reactivity order is: glycine > α-alanine > ß-alanine > L-valine > L-phenylalanine. The activation parameters have been evaluated. An iso-kinetic trend for different amino acids and other nucleophiles reacting with the title copper(II) complex has been found to prevail.
{"title":"Kinetics and Mechanism of the Reactions of Bis(biguanide)copper(II) Ion with Different Amino Acids in Aqueous Media","authors":"A. Das","doi":"10.1515/irm-2000-0408","DOIUrl":"https://doi.org/10.1515/irm-2000-0408","url":null,"abstract":"Abstract The kinetics of the reaction of [Cu(bigH)2]2+ (bigH = biguanide) with an excess of different amino acids (LH) like ß-alanine, L-phenylalanine and L-valine in aqueous solution in the 7.60-9.00 pH range at different temperatures (30-40°C) have been studied by stopped-flow spectrophotometry and compared with those of different ligands reacting with the title copper(II) complex. The ligand replacement process has been suggested to pass through an intermediate formation of the ternary complex, [Cu(bigH)L]+ as the rate determining step, followed by the rapid transformation into the binary complex, [CuL2]. The overall ligand replacement process follows a two-term rate law, kobs = k0 + k1Ka[L]T/([H+] + Ka, where [L]T gives the total concentration of the entering ligand, i.e. amino acid, and Κa gives the deprotonation constant of the amino acid (LH). Thus the process experiences both the ligand independent path (i.e. k0) and ligand dependent path (i.e. k0). The solvent assisted k0 path leads to a copper(II) mono-biguanide complex followed by the rapid nucleophilic substitution; the k1 path is in agreement with an associative mechanism. The k0 path is independent of the structure and basicity of the entering amino acids while the k0 path is dependent on the basicity and steric crowding of the entering amino acid. The reactivity order is: glycine > α-alanine > ß-alanine > L-valine > L-phenylalanine. The activation parameters have been evaluated. An iso-kinetic trend for different amino acids and other nucleophiles reacting with the title copper(II) complex has been found to prevail.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"41 1","pages":"309 - 314"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86547020","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fabian Benzo, Alberto L. Capparelll, D. Mártire, B. Sienra
Abstract The kinetics of aquation and base hydrolysis reactions of fmns-[Co(NH3)4(NH2CH3)(OSO3)]+ have been studied. In acid solution the aquation rate, Raq, follows the equation Raq/[complex] = ks + kc[H+], at constant ionic strenght μ = 1.0Μ. The activation parameters are ΔΗ* = 88.8 kj mol-1, ΔS* = - 50.5 JK-1 mol-1 , ΔΗ* = 96.7 kj mol-1 and ΔS* =-23 JK-1 mol-1. The rate constants at 25°C are ks = 4.15 χ 10-6s-1 and kc = 4.52M -1s-1 . The rate of base hydrolysis, ROH, follows the equation ROH/complex] = k0H [OH-]. The activation parameters are ΔΗ*OH =74.9kJmol-1 and ΔS*OH = 2JK-1 mol-1 and the rate constant is kOH = 0.58M 1 s-1 at 25°C and μ, = 0.15 Μ. The stereochemistry of the hidroxo product has been determined (cis-[Co(NH3)4(NH2CH3)- (OH)]2+ =9%). The results are discussed in the light of the reaction mechanisms proposed so far.
{"title":"Aquation and Base Hydrolysis of trans-Tetraammine(methylamine)sulfatocobalt(III) Complex Ion","authors":"Fabian Benzo, Alberto L. Capparelll, D. Mártire, B. Sienra","doi":"10.1515/irm-2000-0410","DOIUrl":"https://doi.org/10.1515/irm-2000-0410","url":null,"abstract":"Abstract The kinetics of aquation and base hydrolysis reactions of fmns-[Co(NH3)4(NH2CH3)(OSO3)]+ have been studied. In acid solution the aquation rate, Raq, follows the equation Raq/[complex] = ks + kc[H+], at constant ionic strenght μ = 1.0Μ. The activation parameters are ΔΗ* = 88.8 kj mol-1, ΔS* = - 50.5 JK-1 mol-1 , ΔΗ* = 96.7 kj mol-1 and ΔS* =-23 JK-1 mol-1. The rate constants at 25°C are ks = 4.15 χ 10-6s-1 and kc = 4.52M -1s-1 . The rate of base hydrolysis, ROH, follows the equation ROH/complex] = k0H [OH-]. The activation parameters are ΔΗ*OH =74.9kJmol-1 and ΔS*OH = 2JK-1 mol-1 and the rate constant is kOH = 0.58M 1 s-1 at 25°C and μ, = 0.15 Μ. The stereochemistry of the hidroxo product has been determined (cis-[Co(NH3)4(NH2CH3)- (OH)]2+ =9%). The results are discussed in the light of the reaction mechanisms proposed so far.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"26 1","pages":"319 - 324"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90427285","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The reactions of [Pt(dipic)Cl] (where H2dipic = pyridine-2,6-dicarboxylic acid) with 1-methylimidazole, ethylenediamine and nicotinic acid were studied at 40°C in dimethylformamide medium spectrophotometrically. The successive entry of two 1- methylimidazole molecules through initial chloride ion replacement followed by carboxylate ring opening process was further verified through intermediate product isolation. Nicotinic acid shows only the chloride substitution reaction. Bidentate ethylenediamine ligand gets chelated with the platinum(II) complex through slow chloride replacement and rapid ring opening process. All the products have been isolated and characterised through 1H NMR spectra.
{"title":"Substitution Reactions of Platinum(II) Dipicolinate Complex with Some Mono- and Bidentate Ligands - Rates and Mechanism","authors":"M. Ray, Sukalpa Dey, P. Banerjee","doi":"10.1515/irm-2000-0405","DOIUrl":"https://doi.org/10.1515/irm-2000-0405","url":null,"abstract":"Abstract The reactions of [Pt(dipic)Cl] (where H2dipic = pyridine-2,6-dicarboxylic acid) with 1-methylimidazole, ethylenediamine and nicotinic acid were studied at 40°C in dimethylformamide medium spectrophotometrically. The successive entry of two 1- methylimidazole molecules through initial chloride ion replacement followed by carboxylate ring opening process was further verified through intermediate product isolation. Nicotinic acid shows only the chloride substitution reaction. Bidentate ethylenediamine ligand gets chelated with the platinum(II) complex through slow chloride replacement and rapid ring opening process. All the products have been isolated and characterised through 1H NMR spectra.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"399 1","pages":"281 - 288"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87410960","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1999-09-01DOI: 10.1515/IRM.2005.5.4.255
S. Mukhopadhyay, A. Ghosh
Kinetics of interacti on between uridine and [Rh(H10 )sOHf+ has been studied spectrophotometrically as a functi o n of [Rh(HzO)sOH 2 +] , [uridine] , pH and temperature. The reacti on has been monitored at 290 nm, the Amax of the substituted complex and where spectral difference between the reactant and product is maximum. The reaction rate increases with [uri dine] and reaches limiting value at higher ligand concentration. From the experimental findings an associative interchange mechanism for the substitution process is suggested. The activation parameters (t<.f{' = 46.5 ± 1.4 kJ mort, t<.S ~ =-181 ± 4 J K-'mor') support the proposition. The negative t<.C" (-15.1 kJ mort) for the first equilibrium step al so supports the sponta neous formation of an outersphere association complex. Platinum complexes, particularly cis-platin, a pure inorganic compound, exhibit powerful anticancer properties l . 2 . Because of it's toxicity the search for other alternatives continued in other 3d, 4d and 5d metal ions 3 - 6 . It is now established 7 that cis-platin is first hydro lysed in biological conditions and the aqua variety is the active species. Some of the products of hydrolysis are responsible for toxicity. Thus it is expected that the aqua complexes, if used directly, will be less toxic. ]n order to examine the bioactivity of rho dium(IIl) complexes we have already reported studies on the interaction of rhodium(lII) with pyridine-2Id . 8 dl h" 9 I . 10 d . II a oxtme, -met 10nIne, -cysteme , a enosme and cytidine l2 . Tn this paper the interaction of uridine with hydroxopentaaquarhodium(1J1) ion in aqueous medium is reported.
{"title":"Kinetic and Mechanistic Studies on the Interaction of Inosine with Hydroxopentaaquarhodium(III) Ion","authors":"S. Mukhopadhyay, A. Ghosh","doi":"10.1515/IRM.2005.5.4.255","DOIUrl":"https://doi.org/10.1515/IRM.2005.5.4.255","url":null,"abstract":"Kinetics of interacti on between uridine and [Rh(H10 )sOHf+ has been studied spectrophotometrically as a functi o n of [Rh(HzO)sOH 2 +] , [uridine] , pH and temperature. The reacti on has been monitored at 290 nm, the Amax of the substituted complex and where spectral difference between the reactant and product is maximum. The reaction rate increases with [uri dine] and reaches limiting value at higher ligand concentration. From the experimental findings an associative interchange mechanism for the substitution process is suggested. The activation parameters (t<.f{' = 46.5 ± 1.4 kJ mort, t<.S ~ =-181 ± 4 J K-'mor') support the proposition. The negative t<.C\" (-15.1 kJ mort) for the first equilibrium step al so supports the sponta neous formation of an outersphere association complex. Platinum complexes, particularly cis-platin, a pure inorganic compound, exhibit powerful anticancer properties l . 2 . Because of it's toxicity the search for other alternatives continued in other 3d, 4d and 5d metal ions 3 - 6 . It is now established 7 that cis-platin is first hydro lysed in biological conditions and the aqua variety is the active species. Some of the products of hydrolysis are responsible for toxicity. Thus it is expected that the aqua complexes, if used directly, will be less toxic. ]n order to examine the bioactivity of rho dium(IIl) complexes we have already reported studies on the interaction of rhodium(lII) with pyridine-2Id . 8 dl h\" 9 I . 10 d . II a oxtme, -met 10nIne, -cysteme , a enosme and cytidine l2 . Tn this paper the interaction of uridine with hydroxopentaaquarhodium(1J1) ion in aqueous medium is reported.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"57 1","pages":"255 - 263"},"PeriodicalIF":0.0,"publicationDate":"1999-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86220849","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The kinetics of oxidation of L-cystine by alkaline permanganate follows the rate law, where Κ is the formation constant for the complex between L-cystine and permanganate and k is the decomposition rate constant. The data suggest that the oxidation of L-cystine proceeds via the formation of a complex between L-cystine and permanganate which decomposes slowly, followed by a fast reaction between the free radical of L-cystine and another molecule of permanganate to give the products. The reaction constants involved in the mechanism are derived. There is good agreement between the observed and calculated rate constants under varying experimental conditions. The activation parameters are computed with respect to the slow step of the mechanism.
l -胱氨酸被碱性高锰酸盐氧化的动力学遵循速率定律，其中Κ为l -胱氨酸与高锰酸盐络合物的形成常数，k为分解速率常数。数据表明，l -胱氨酸的氧化是通过l -胱氨酸和高锰酸盐之间形成络合物进行的，该络合物缓慢分解，然后l -胱氨酸自由基与另一分子高锰酸盐发生快速反应生成产物。导出了反应机理中涉及的反应常数。在不同的实验条件下，速率常数的观测值与计算值吻合较好。根据机构的慢步，计算了激活参数。
{"title":"Free Radical Induced Oxidation of L-Cystine by Alkaline Permanganate - A Kinetic Study","authors":"M. R. Kembhavi, R. G. Panari, S. Nandibewoor","doi":"10.1515/irm-1999-0306","DOIUrl":"https://doi.org/10.1515/irm-1999-0306","url":null,"abstract":"Abstract The kinetics of oxidation of L-cystine by alkaline permanganate follows the rate law, where Κ is the formation constant for the complex between L-cystine and permanganate and k is the decomposition rate constant. The data suggest that the oxidation of L-cystine proceeds via the formation of a complex between L-cystine and permanganate which decomposes slowly, followed by a fast reaction between the free radical of L-cystine and another molecule of permanganate to give the products. The reaction constants involved in the mechanism are derived. There is good agreement between the observed and calculated rate constants under varying experimental conditions. The activation parameters are computed with respect to the slow step of the mechanism.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"42 1","pages":"225 - 232"},"PeriodicalIF":0.0,"publicationDate":"1999-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90208570","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract For the following equations relating to the aquation and anation processes of cisplatin and similar squareplanar platinum(II) diamine complexes: rate constant (k-2, Μ-1 s-1,25°C), activation enthalpy (ΔΗ#, kJ mol-1) , activation entropy (ΔS#, JΚ-1 mol-1) and activation volume (ΔV#, cm3 mol-1) data have been found for the bromide anation of cis- [Pt(N)2(OH2)2]2+ where (N)2 = tn, en, cis-(NH3)2, trans-(NH3)2, Me2tn, chxn; CJS-(NH3)2: k-2 = 0.45, ΔH# = 68, ΔS# = -25, trans-(NH3)2: 4.23,56, -44, chxn: 1.13, 70, -9, Me2tn: 1.53, 65, -24, en: 1.29, 71, -5, ΔV# = -5.3, tn: 1.86,68, -12, ΔV# = -7.4. Further activation volumes (ΔV#, cm3 mol-1) have been determined for selected k-1 and k-2 bromide or chloride anation data. k-1(cm3 mol-1, CI-): en -7.4. k-1(cm3 mol-1, Br-): cis-(NH3)2-11, en -9.4, tn -7.66. k-2(cm3 mol-1, CI-): cis-(NH3)2-5.1, en -5.7, tn -5.8. For all kx above where ΔV# has been measured, values lie in the range -4 to -11 cm3 mol-1 and apart from two exceptions ΔS# is negative in 36 cases implying an associative mechanism for the substitution process at square-planar platinum(II) centres.
{"title":"The Hydrolysis Kinetics of ds-diamminedichloroplatinum(II). 10. Activation Volumes for Halide Anation of Some czs-[Pt(N)2(OH2)2]2+ Systems","authors":"K. Hindmarsh, D. A. House, R. Eldik","doi":"10.1515/irm-1999-0204","DOIUrl":"https://doi.org/10.1515/irm-1999-0204","url":null,"abstract":"Abstract For the following equations relating to the aquation and anation processes of cisplatin and similar squareplanar platinum(II) diamine complexes: rate constant (k-2, Μ-1 s-1,25°C), activation enthalpy (ΔΗ#, kJ mol-1) , activation entropy (ΔS#, JΚ-1 mol-1) and activation volume (ΔV#, cm3 mol-1) data have been found for the bromide anation of cis- [Pt(N)2(OH2)2]2+ where (N)2 = tn, en, cis-(NH3)2, trans-(NH3)2, Me2tn, chxn; CJS-(NH3)2: k-2 = 0.45, ΔH# = 68, ΔS# = -25, trans-(NH3)2: 4.23,56, -44, chxn: 1.13, 70, -9, Me2tn: 1.53, 65, -24, en: 1.29, 71, -5, ΔV# = -5.3, tn: 1.86,68, -12, ΔV# = -7.4. Further activation volumes (ΔV#, cm3 mol-1) have been determined for selected k-1 and k-2 bromide or chloride anation data. k-1(cm3 mol-1, CI-): en -7.4. k-1(cm3 mol-1, Br-): cis-(NH3)2-11, en -9.4, tn -7.66. k-2(cm3 mol-1, CI-): cis-(NH3)2-5.1, en -5.7, tn -5.8. For all kx above where ΔV# has been measured, values lie in the range -4 to -11 cm3 mol-1 and apart from two exceptions ΔS# is negative in 36 cases implying an associative mechanism for the substitution process at square-planar platinum(II) centres.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"87 1","pages":"107 - 120"},"PeriodicalIF":0.0,"publicationDate":"1999-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81214998","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The complexation kinetics of fully deprotonated pendent arm macrocyclic ligands with Cu(II) hydroxo species had been investigated in aqueous solution at high pH. The pH dependence of the initial second order reaction is explained by the different reactivities for the tris- and tetra-hydroxo species of Cu(II). In some instances, the pendent arms accelerate the rates of the complex formation reaction. An intermediate complex is observed which reacts in a first order reaction to the final complex. The pH dependence of this reaction is the result of the existence of different numbers of aquo and hydroxo ligands additionally coordinated to the metal. Spectral changes for this second step are small, suggesting an isomerisation reaction is taking place.
{"title":"Complexation of Pendant Arm Macrocycles with Cu(II) Hydroxo Complexes in Strongly Alkaline Solutions. Investigation of pH Dependences","authors":"P. Lye, G. Lawrance, M. Maeder","doi":"10.1515/irm-1999-0209","DOIUrl":"https://doi.org/10.1515/irm-1999-0209","url":null,"abstract":"Abstract The complexation kinetics of fully deprotonated pendent arm macrocyclic ligands with Cu(II) hydroxo species had been investigated in aqueous solution at high pH. The pH dependence of the initial second order reaction is explained by the different reactivities for the tris- and tetra-hydroxo species of Cu(II). In some instances, the pendent arms accelerate the rates of the complex formation reaction. An intermediate complex is observed which reacts in a first order reaction to the final complex. The pH dependence of this reaction is the result of the existence of different numbers of aquo and hydroxo ligands additionally coordinated to the metal. Spectral changes for this second step are small, suggesting an isomerisation reaction is taking place.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"100 1","pages":"153 - 160"},"PeriodicalIF":0.0,"publicationDate":"1999-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80728004","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The stability constant of the complex formed between cobalt(II) and trimethyltren (Me3tren), 2,2′,2″-triaminotriethylamine monomethylated on each terminal amino group, in aqueous medium was determined (log Κ = 12.10 ± 0.01 at 25.0° C and ionic strength of 1.0 mol dm-3 (NaClO4)). The deprotonation constant of the aqua complex, [Co(Me3tren)(H2O)]2+, was also established (pKa = 9.31 ± 0.02 under the same conditions). It is concluded on the basis of these values and properties such as the UV/vis spectrum, that the complex possesses trigonal bipyramidal geometry, as does the corresponding copper(II) complex. Dissociation of both complexes, as a function of aqueous acid concentration, was monitored spectrophotometrically. For the copper(II) system there is a modest dependence on the acid concentration when [H+] < 0.4 mol dm-3 , and above this value the reaction is independent of acid concentration, with the firstorder rate constant reaching a limiting value of about 100 s-1 at 25.0°C. Dissociation of the cobalt(II) complex does not depend on the acid concentration and occurs at a rate of 34 s-1 . A mechanism accounting for these findings is proposed, and the rate and activation parameters are discussed in terms of the dissociation of other trigonal bipyramidal complexes.
{"title":"Kinetics of Dissociation of the Cobalt(II) and Copper(II) Complexes of 2,2′,2″-tris(monomethylamino)triethylamine in Aqueous Acidic Solution","authors":"F. Thaler, C. Hubbard, R. Eldik","doi":"10.1515/irm-1999-0202","DOIUrl":"https://doi.org/10.1515/irm-1999-0202","url":null,"abstract":"Abstract The stability constant of the complex formed between cobalt(II) and trimethyltren (Me3tren), 2,2′,2″-triaminotriethylamine monomethylated on each terminal amino group, in aqueous medium was determined (log Κ = 12.10 ± 0.01 at 25.0° C and ionic strength of 1.0 mol dm-3 (NaClO4)). The deprotonation constant of the aqua complex, [Co(Me3tren)(H2O)]2+, was also established (pKa = 9.31 ± 0.02 under the same conditions). It is concluded on the basis of these values and properties such as the UV/vis spectrum, that the complex possesses trigonal bipyramidal geometry, as does the corresponding copper(II) complex. Dissociation of both complexes, as a function of aqueous acid concentration, was monitored spectrophotometrically. For the copper(II) system there is a modest dependence on the acid concentration when [H+] < 0.4 mol dm-3 , and above this value the reaction is independent of acid concentration, with the firstorder rate constant reaching a limiting value of about 100 s-1 at 25.0°C. Dissociation of the cobalt(II) complex does not depend on the acid concentration and occurs at a rate of 34 s-1 . A mechanism accounting for these findings is proposed, and the rate and activation parameters are discussed in terms of the dissociation of other trigonal bipyramidal complexes.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"82 1","pages":"83 - 90"},"PeriodicalIF":0.0,"publicationDate":"1999-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84396245","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The kinetics and mechanisms of the reactions of aluminium(III) with ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) have been investigated in aqueous solution at 25°C and ionic strength 0.5 mol dm-3 NaClO4. Al3+ reacts with the H4DTPA- and H3DTPA2- with rate constants of 2.06(±0.35) and 19.3(±1.6) respectively while Al(OH)2+ reacts with H3DTPA2- with a rate constant of 1.34(±0.20) × 103 dm3 mol-1 s-1. The outersphere association constant for reaction of Al3+ with H3DTPA2- was found to be 175(±38) mol-1 dm3. Al3+ reacts with H3EDTA and H2EDTA2- with rate constants of 4.73(±1.25) and 21.5(±2.21) dm3 mol-1 s-1 respectively. The outer-sphere association constant for reaction of Al3+ with H2EDTA2- is 164(±52.9) mol-1 dm3.
{"title":"Kinetics and Mechanisms of the Reaction of Aluminium(III) with Polyaminocarboxylic Acids","authors":"Claire Τ. Tomany, M. Hynes","doi":"10.1515/irm-1999-0207","DOIUrl":"https://doi.org/10.1515/irm-1999-0207","url":null,"abstract":"Abstract The kinetics and mechanisms of the reactions of aluminium(III) with ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) have been investigated in aqueous solution at 25°C and ionic strength 0.5 mol dm-3 NaClO4. Al3+ reacts with the H4DTPA- and H3DTPA2- with rate constants of 2.06(±0.35) and 19.3(±1.6) respectively while Al(OH)2+ reacts with H3DTPA2- with a rate constant of 1.34(±0.20) × 103 dm3 mol-1 s-1. The outersphere association constant for reaction of Al3+ with H3DTPA2- was found to be 175(±38) mol-1 dm3. Al3+ reacts with H3EDTA and H2EDTA2- with rate constants of 4.73(±1.25) and 21.5(±2.21) dm3 mol-1 s-1 respectively. The outer-sphere association constant for reaction of Al3+ with H2EDTA2- is 164(±52.9) mol-1 dm3.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"128 1 1","pages":"137 - 144"},"PeriodicalIF":0.0,"publicationDate":"1999-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90012290","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The oxidation kinetics for the reaction of [FeII(1,2- pdta)] (1,2-pdta = 1,2-N,N′-1,2-propylenediaminetetraacetate) and [FeII(1,3-pdta)] (1,3-pdta = 1,2-N,Ν′- 1,3-propylenediaminetetraacetate) with molecular oxygen were studied as a function of [FeII], [O2], pH, temperature and pressure. It was observed that the reaction with [FeII(1,2-pdta)] is ca. 200 times faster than with the isomeric [FeII(1,3-pdta)] complex under comparable conditions. In the presence of an excess of [FeII(1,2-pdta)] three reaction steps could be identified for which the rate constants are = 3385 ± 607M-1 s-1, k2 = 226±9M-1s-1 and k3 = 111 ± 4M-1s-1 at pH = 6 and T = 25°C. Since [FeII(1,3-pdta)] is unstable during the reaction, only approximate rate constants for two of the electron-transfer steps could be determined, which are two orders of magnitude smaller than in the case of the [FeII(1,2-pdta)] complex. Rate and activation parameters for the 1,2-pdta system are reported and discussed in reference to our earlier work on related systems.
{"title":"The Influence of Steric Effects on the Oxidation Kinetics of [FeII(aminopolycarboxylato)] Complexes with Dioxygen","authors":"S. Seibig, R. Eldik","doi":"10.1515/irm-1999-0203","DOIUrl":"https://doi.org/10.1515/irm-1999-0203","url":null,"abstract":"Abstract The oxidation kinetics for the reaction of [FeII(1,2- pdta)] (1,2-pdta = 1,2-N,N′-1,2-propylenediaminetetraacetate) and [FeII(1,3-pdta)] (1,3-pdta = 1,2-N,Ν′- 1,3-propylenediaminetetraacetate) with molecular oxygen were studied as a function of [FeII], [O2], pH, temperature and pressure. It was observed that the reaction with [FeII(1,2-pdta)] is ca. 200 times faster than with the isomeric [FeII(1,3-pdta)] complex under comparable conditions. In the presence of an excess of [FeII(1,2-pdta)] three reaction steps could be identified for which the rate constants are = 3385 ± 607M-1 s-1, k2 = 226±9M-1s-1 and k3 = 111 ± 4M-1s-1 at pH = 6 and T = 25°C. Since [FeII(1,3-pdta)] is unstable during the reaction, only approximate rate constants for two of the electron-transfer steps could be determined, which are two orders of magnitude smaller than in the case of the [FeII(1,2-pdta)] complex. Rate and activation parameters for the 1,2-pdta system are reported and discussed in reference to our earlier work on related systems.","PeriodicalId":8996,"journal":{"name":"BioInorganic Reaction Mechanisms","volume":"2016 1","pages":"106 - 91"},"PeriodicalIF":0.0,"publicationDate":"1999-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82624859","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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