Spectrophotometric stopped-flow apparatus suitable for high-pressure experiments to 200 MPa

Eldik, Rudi van; Gaede, Wolfgang; Wieland, S.; Kraft, Jochen; Spitzer, Markus; Palmer, Donald A.

doi:10.1063/1.1144466

Cited by 175 publications

(135 citation statements)

References 9 publications

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“…Experiments at elevated pressure were performed on a laboratory-made high pressure stopped-flow instrument for fast reactions. 44 Spectral changes of the reactions were first recorded over the wavelength range 190-600 nm to establish a suitable wavelength at which the kinetic trace could be followed. The ligand substitution reactions were studied under pseudo first order conditions.…”

Section: Kinetic Measurementsmentioning

confidence: 99%

Spectroscopic, thermodynamic, kinetic studies and oxidase/antioxidant biomimetic catalytic activities of tris(3,5-dimethylpyrazolyl)borate Cu(ii) complexes

et al. 2015

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A series of copper (II) ), have been synthesized and fully characterized. The substitution reaction of 1 with thiourea was studied under pseudofirst-order conditions as a function of concentration, temperature and pressure in methanol and acetonitrile as solvents. Two reaction steps that both depended on the nucleophile concentration were observed for both solvents. Substitution of coordinated methanol is about 40 times faster than the substitution of chloride. In acetonitrile, the rate constant for the displacement of coordinated acetonitrile was more than 20 times faster than the substitution of chloride. The reported activation parameters indicate that both reaction steps follow a dissociative mechanism in both solvents. On going from methanol to acetonitrile, the rate constant for the displacement of the solvent becomes more than 200 times faster due to the more labile acetonitrile, but the substitution mechanism remained to have a dissociative character. The antioxidant activities of 1-4 were evaluated for superoxide dismutase (SOD), glutathione-stransferase (GST0 and glutathione reduced (GSH-Rd) activity. 1 and 2 were found to show ( p < 0.05) the highest antioxidant activity in comparison to 3 and 4, which can be ascribed to the geometric configuration as well as the nature of the co-ligand. 1 showed catechol oxidase activity with turnover numbers of 20 min −1 and a coordination affinity for 3,5-DTBC of K 1 , = 31 mM −1 . K 1 is rather large and seems to be typical for faster biomimetic models, and also for the enzyme itself (25 mM −1). The reaction rate depended linearly on the complex concentration, indicating a first-order dependence on the catalyst concentration.

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Section: Kinetic Measurementsmentioning

confidence: 99%

Spectroscopic, thermodynamic, kinetic studies and oxidase/antioxidant biomimetic catalytic activities of tris(3,5-dimethylpyrazolyl)borate Cu(ii) complexes

et al. 2015

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“…The ligand tren in this complex (s,CH 3 ) ϩ 0.0627 P 2 ϩ 1.845 P] and P ϭ cell. [31] (F o 2 ϩ 2 F c 2 )/3. …”

Section: Methodsmentioning

confidence: 99%

Kinetics and Mechanism of Base Hydrolysis in Cobalt(III) Complexes – The Case of a Complex CoLCl2+ where L has the Novel Topology of a Square-Pyramidal NN4 Coordination Cap

Poth

Paulus

Elias³

et al. 1999

Eur. J. Inorg. Chem.

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Multi‐wavelength stopped‐flow spectrophotometry was used to study the kinetics of base hydrolysis of the octahedral cobalt(III) complex CoLCl2+ (2), in which the tetrapodal pentadentate ligand L has an NN4 donor set and forms a square‐pyramidal coordination cap [L = 2,6‐bis(1′,3′‐diamino‐2′‐methylprop‐2′‐yl)pyridine, 1]. The kinetic investigation, carried out at different temperatures, pressures and ionic strengths I, led to second‐order kinetics, rate = kOH [2][OH−], with kOH = 0.139 ± 0.001 M−1s−1 (I = 0.1 M) and kOH = 0.0570 ± 0.0004 M−1s−1 (I = 1.0 M) at 298 K. The temperature and pressure dependence of kOH resulted in ΔH‡ = 119 ± 3 kJmol−1 (I = 0.1 M) and ΔH‡ = 123 ± 3 kJmol−1 (I = 1.0 M), ΔS‡ = + 130 ± 13 Jmol−1K−1 (I = 0.1 M) and ΔS‡ = + 151 ± 15 Jmol−1K−1 (I = 1.0 M) and ΔV‡ = + 27.6 ± 0.6 cm3mol−1 (I = 1.0 M). The kinetic results support the operation of the conjugate base mechanism, Dcb, with intermediate deprotonation occuring cis to the leaving chloride ion. The observed inertness of complex 2 towards base hydrolysis is discussed on the basis of the special structural features of the ligand L. The pKa of the coordinated water in the aqua species CoL(H2O)3+(3) was determined to be pKa = 6.0 ± 0.1 at I = 0.1 M. The X‐ray crystal structure analysis of the hydroxo complex [CoL(OH)](ClO4)2 (4) shows a mononuclear terminal (hydroxo)CoIII complex, in which the ligand provides a regular square‐pyramidal NN4 donor cap for the octahedrally six‐coordinate CoIII ion [4, monoclinic, space group C2/m, a = 16.841(6) Å, b = 8.541(3) Å, c = 15.112(5) Å, β = 109.13(1)°, Z = 4]. Coordination of L is accompanied by the formation of 6 six‐membered chelate rings, all of which adopt a boat conformation. In the crystal lattice, pairs of cations are associated via four (hydroxo)O···H–N(primary amine) hydrogen bonds and related through an inversion center. Full spectroscopic data for 4 (1H‐, 13C‐NMR, IR, MS) are presented.

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“…Similar simulations have been performed for other copper complexes in the past. 68, 69 The key parameters which affect the form of the CV wave are the reduction potentials of species (1) and (4) and the rate constants k 41 , k 14 , k 23 and k 32 . ESP can in principle be used to calculate the parameters controlling the electrochemistry and our aim was to use this to resolve the couples which contribute to the overall process.…”

Section: Electrochemical Studiesmentioning

confidence: 99%

“…40, 41 The kinetic traces consisting of 1000 points per trace, were collected and stored on an IBM-compatible computer using Biologic (Claix, France) software. The rate constants were calculated using the OLIS KINFIT program (Olis, Bogart, Georgia, USA).…”

Section: Measurementsmentioning

confidence: 99%

Outer-sphere electron-transfer between horse heart cytochrome c and anionic Cu(ii/i) complexes. Evidence for precursor formation and coordination sphere reorganization for electron transfer

2003

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The outer-sphere electron-transfer reaction between anionic bis(5,6-bis(4-sulfonatophenyl)-3-(2-pyridyl)-1,2,4-triazine)Cu() and cytochrome c II was investigated as a function of pH, ionic strength, concentration, temperature and pressure. The plot of the observed pseudo-first-order rate constant as a function of the Cu() complex concentration showed saturation at higher Cu() concentrations, from which the precursor formation constant and the electron transfer rate constant could be separated (K = (7.7 ± 0.5) × 10 3 M Ϫ1 and k ET = 6.2 ± 0.4 s Ϫ1at I = 0.2 M, pH 7.4 and 288 K). The pseudo-first-order electron-transfer rate constant was measured as a function of temperature and pressure at (low and) high Cu() concentrations (∆H ‡ = (85 ± 4) 89 ± 4 kJ mol; ∆G ‡ (288 K) = (67.6) 66.1 kJ mol Ϫ1 ; ∆V ‡ = (ϩ8.8 ± 0.6) ϩ8.0 ± 0.7 cm 3 mol Ϫ1 ). Within the volume change for the overall reaction, the volume profile for the electron transfer step is almost symmetrical. The redox process and the change in coordination of the copper centre are proposed to be clearly separated. The back reaction between the Cu() complex and cytochrome c III was investigated as a function of Cu() concentration at pH 7.4 at 1 bar. The observed pseudo-first-order rate constant reaches a saturation at high Cu() concentrations from which the precursor formation constant and the electron-transfer rate constant were estimated (KЈ = (2.0 ± 0.2) × 10 3 M Ϫ1 and kЈ ET = 0.014 ± 0.001 s Ϫ1 at I = 0.2 M, pH 7.4 and 288 K). Simulations of the measured cyclovoltammogramms applying an EC mechanism with two redox systems and two homogeneous chemical reactions were performed. The results are discussed with reference to earlier studies involving Co, Ru and Cr complexes as redox partners for cytochrome c.

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Spectrophotometric stopped-flow apparatus suitable for high-pressure experiments to 200 MPa

Cited by 175 publications

References 9 publications

Spectroscopic, thermodynamic, kinetic studies and oxidase/antioxidant biomimetic catalytic activities of tris(3,5-dimethylpyrazolyl)borate Cu(ii) complexes

Spectroscopic, thermodynamic, kinetic studies and oxidase/antioxidant biomimetic catalytic activities of tris(3,5-dimethylpyrazolyl)borate Cu(ii) complexes

Kinetics and Mechanism of Base Hydrolysis in Cobalt(III) Complexes – The Case of a Complex CoLCl2+ where L has the Novel Topology of a Square-Pyramidal NN4 Coordination Cap

Outer-sphere electron-transfer between horse heart cytochrome c and anionic Cu(ii/i) complexes. Evidence for precursor formation and coordination sphere reorganization for electron transfer

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