Relaxation spectra of molybdate-ethylenediaminetetraacetic acid complexes

Honig, Dan S.; Kustin, Kenneth

doi:10.1021/ja00798a017

Cited by 22 publications

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“…The procedure used was to find that set of rate constants leading to the best agreement between observed and calculated relaxation times by means of least-squares analysis. 24,30 The data for all systems is shown in Table I (supplementary material). Plots of the reciprocal relaxation time (r"1) against total stoichiometric concentration of metal ion show that r"1 increases as total metal increases.…”

Section: Resultsmentioning

confidence: 99%

Relaxation spectra of nickel(II) and cobalt(II) complexes of L-lysine and L-ornithine. The relative unreactivity of the .alpha.-amino acid zwitterion moiety

Kustin¹,

McClean²

1978

J. Phys. Chem.

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Reactions of nickel(II) and cobalt(II) with lysine and ornithine have been studied over a wide range of pH by the temperature-jump relaxation technique at 25 °C and µ = 0.1 M. The attacking and binding form of the ligand was found to be HL, where the proton is on the -nitrogen atom. Monoand bis-protonated complexes are formed according to the reactions M2+ + HL ^MHL2+ (kx, k-X), MHL2+ + HL ^M(HL)22+ (k2, &_2), where M = Ni or Co. Attempts to fit the data to other mechanisms, notably schemes with protonated complexes as minor species, failed. The rate constants (kx and k2 M"1 s-1, k-X and fc_2 s™1) are the following: for nickel and lysine kx = (4.2 ± 9.0%) X 103, k"x = 4.9 X 10"2, k2 = (4.7 ± 6.1%) X 103, fc_2 = 2.8 X 10-1; for nickel and ornithine kx = (2.2 ± 5.1%) X 10s, k.x = 4.1 X 10~2, k2 = (1.0 ± 9.3%) X 104, fc_2 = 9.8 X 10-1; for cobalt and lysine kx = (6.0 ± 18%) X 105, k.x = 8.8 X 101, k2 = (1.0 ± 5.0%) X 106, &_2 = 5.8 X 102; for cobalt and ornithine kx = (6.5 ± 5.1%) X 105, k_x = 1.5 X 102, k2 = (3.2 ± 2.2%) X 106, and fc_2 = 2.6 X 103. The rate-determining step is release of a coordinated water molecule. In each case k2 > kx, which indicates that the ligand labilizes the water molecules. For cobalt kx ~k0Kos (the water exchange rate times the ion-pair formation equilibrium constant). That the nickel kx < k(¡K0S is due to screening of ligand charge, i.e., a lowering of . Lysine and ornithine are reactive zwitterions, but the proton is not located at the binding site, and ring closure is not rate determining. The unreactivity of glycine-like, -amino acid zwitterions does not appear to be due to rate-limiting ring closure.

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Section: Resultsmentioning

confidence: 99%

Relaxation spectra of nickel(II) and cobalt(II) complexes of L-lysine and L-ornithine. The relative unreactivity of the .alpha.-amino acid zwitterion moiety

Kustin¹,

McClean²

1978

J. Phys. Chem.

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“…Although (Honig and Kustin, 1973) Lactate (lac) [MoO 2 (lac) 2 ] 2- (Cruywagen et al, 1993b) Azotochelin (azo) [MoO 2 (azo)] 3- (Bellenger et al, 2007;Bellenger et al, 2008) Cysteine (cys) [MoO 3 (cys)] 2- (Cavaleiro et al, 1990) Aspartate (asp) [MoO 3 (asp)] 2- (Cruywagen et al, 1993a) Mandelate (man) [MoO 2 (man) 2 ] 2- Oxalate (ox) [MoO 2 (ox) 2 ] 2- (Cruywagen et al, 1986) Malate (mal) [MoO 2 (mal) 2 ] 2- (Cruywagen et al, 1997) Citrate (cit) [MoO 2 (cit)] - Catecholate (cat) [MoO 2 (cat) 2 ] 2- (Kustin and Liu, 1973) Tannic acid (tan) [MoO 2 (tan) x ] 2- (Kiboku and Yoshimura, 1958;Wichard et al, 2009) Thiomalate (malS) [MoO 2 (malS) 2 ] 2- (Caldeira and Gil, 1986) Thiolactate (lacS) [MoO 2 (lacS) 2 ] 2- (Caldeira and Gil, 1986) Various o-hydroxy aromatic ligands (hydroxyAr) [MoO 2 (hydroxyAr)] 2- (Natansohn et al, 1980) a Multiple species are possible depending on reaction pH and relative concentrations of reactants. See references for more information.…”

Section: Discussionmentioning

confidence: 99%

Molybdenum speciation and burial pathway in weakly sulfidic environments: Insights from XAFS

Wagner

Chappaz

Lyons

2017

Geochimica et Cosmochimica Acta

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Sedimentary molybdenum (Mo) accumulation is a robust proxy for sulfidic conditions in both modern and ancient aquatic systems and has been used to infer changing marine redox chemistry throughout Earth's history. Accurate interpretation of any proxy requires a comprehensive understanding of its biogeochemical cycling, but knowledge gaps remain concerning the geochemical mechanism(s) leading to Mo burial in anoxic sediments. Better characterization of Mo speciation should provide mechanistic insight into sedimentary Mo accumulation, and therefore in this study we investigate Mo speciation from both modern (Castle Lake, USA) and ancient (Doushantuo Formation, China) environments using X-Ray Absorption Near Edge Structure (XANES) spectroscopy. By utilizing a series of laboratory-synthesized oxythiomolybdate complexes-many containing organic ligands-we expand the number of available standards to encompass a greater range of known Mo chemistry and test the linkage between Mo and total organic carbon (TOC). In weakly euxinic systems ([H 2 S (aq) ] < 11 µM), or where sulfide is restricted to pore waters, natural samples are best represented by a linear combination of MoO 3 , MoO x S 4-x 2-(intermediate thiomolybdates), and [MoO x (cat) 4-x ] 2-(cat = catechol, x = 2 or 3). These results suggest a revised model for how Mo accumulates in weakly sulfidic sediments, including a previously unrecognized role for organic matter in early sequestration of Mo and a de-emphasized importance for MoS 4 2-(tetrathiomolybdate).

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“…It must be remembered however that the EDTA complexes formed are sixand not four-coordinate. 18 It has been suggested that very rapid reactions of HM0O4' are due to a tendency of molybdate(VI) to increase its coordination number on protonation.8'19•22 Recent spectrophotometric studies by Cruywagen and Rohwer23 however suggest that only in the presence of a second proton are six-coordinate molybdate species detected. This observation is not in conflict with the results of kinetic studies in which only a single proton is required in the rate-determining step, since the first proton may promote the increase in coordination number while the second stabilizes the six-coordinate species which is formed.…”

Section: Discussionmentioning

confidence: 99%

An investigation of the rapid complexation of aquopentaamminecobalt(III) with molybdate in weakly basic solution

Taylor¹

1977

Inorg. Chem.

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The kinetics of equilibration of aquopentaamminecobalt(II1) with molybdate(V1) kf CO(NH,),OH,~+ + Co(NH,),MoO,+ + H,O have been studied at 25 OC and I = 1.0 M (NaC104) with 7.1 5 pH 5 8.0 by the stopped-flow method. The spectrophotometric equilibrium constant for (i), K I = kf/k,, is 475 f 15 M-I. The kinetics show a greater than first-order dependence on [Mood2-] and the second-order formation rate constant, kf, can be expressed as in k f = k , t kb[H+] t k,[M00,~'] t kd[H+][MOO,'-]Values of k, = 96 f 7 M-' SKI, kb = (1.1 f 0.2) X lo9 M-2 s-l, kc = (2.2 f 0.2) X lo3 M-2 s-l, and kd = (1.02 f 0.05) X loll M-) s-l are consistent with substitution at the Mo(V1) and not the Co(I1I) center. The paths k, and kb most probably correspond to the reaction of HM004-with Co(NH3)50H2+ (kl = 6.6 X lo4 M-I s-l) and Co(NH3)50H23+ (kz = 3.2 X 105 M-I SKI), respectively. These rate constants are much lower than those observed for addition of ligands to tetrahedral molybdate(V1) to give products of increased coordination number. The pathways involving two molybdate ions, k, and kd, correspond to reactions of dimolybdate(VI), a species which has not previously been detected in aqueous solution.The extreme inertness of the metal-oxygen bond in aquopentaamminecobalt(II1) results in very slow complex formation. With oxy anions which exhibit rapid oxygen exchange, complexation may be extremely rapid since the cobalt(III)-oxygen bond does not need to be broken. Studies on such reactions112 and those of other inert trivalent transition metal-aquo complexes3 have yielded valuable information on the nature of substitution mechanisms at oxy anion centers.Molybdate(V1) forms a series of stable octahedral complexes in weakly basic solution with bidentate ligands such as catech01,~ oxine,5 and oxinesulfonic acid,6 and kinetic studies of complex formation have been carried out. It is also known that molybdate(V1) complexes with C O ( N H~)~O H~~+ and that the product Co(NH3)5Mo04+ contains tetrahedrally coordinated molybdate(VI).' The fact that there is retention of tetrahedral geometry is of particular interest in this reaction. Conditions, [Mo(VI)] I 0.1 M and pH >7, were chosen so that isopolymolybdate species were not presentU8 Experimental Section Conditions. All measurements were carried out at 25 OC and I = 1.0 M (NaC104 or LiC104) in the presence of at least 0.1 M triethanolamine (TEA) buffer, unless otherwise stated.Materials. LiC104 was prepared and purified as described prev i o~s l y .~ NaC104 (Analar, Hopkin and Williams), triethanolamine (reagent grade, BDH), and Na2Mo04H20 (Analar, BDH) were not further purified. [Co(NH3)50H2](C104)3 was prepared by the standard method.I0J1 Measurement of pH. A Radiometer pHM4 meter fitted with G202C glass and K401 calomel (containing saturated NaCl instead of KCI) electrodes was used for pH measurement. The meter was calibrated at 1.0 M ionic strength with perchloric acid solutions (0.001-0.100 M) so that the measured pH corresponds to -log [H+], and pH used in this paper refers to such a quanti...

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Relaxation spectra of molybdate-ethylenediaminetetraacetic acid complexes

Cited by 22 publications

References 0 publications

Relaxation spectra of nickel(II) and cobalt(II) complexes of L-lysine and L-ornithine. The relative unreactivity of the .alpha.-amino acid zwitterion moiety

Relaxation spectra of nickel(II) and cobalt(II) complexes of L-lysine and L-ornithine. The relative unreactivity of the .alpha.-amino acid zwitterion moiety

Molybdenum speciation and burial pathway in weakly sulfidic environments: Insights from XAFS

An investigation of the rapid complexation of aquopentaamminecobalt(III) with molybdate in weakly basic solution

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