Pulsed-accelerated-flow spectrometer with integrating observation for measurement of rapid rates of reaction

Jacobs, Stephen A.; Nemeth, Mark T.; Kramer, Gary W.; Ridley, Thomas Y.; Margerum, Dale W.

doi:10.1021/ac00271a004

Cited by 21 publications

(34 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This has been accomplished by the use of pulsed-accelerated-flow (PAF) instruments where variable flow velocities permit the resolution of mixing rate constants and reaction rate constants during the mixing process. [2][3][4][5][6] The range of quantifiable reaction rate constants has been pushed to values as large as 500,000 s Ϫ1 (t 1/2 = 1.4 µs) for pseudo-first-order reactions. 6 The Margerum research group has made extensive use of several PAF instruments for the determination of many rate constants 7-9 that could not be obtained with stopped-flow or relaxation techniques.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Pulsed-accelerated-flow studies of the temperature dependence of fast reactionsBased on the presentation given at Dalton Discussion No. 4, 10–13th January 2002, Kloster Banz, Germany.

Becker

Bartlett

Urbansky

et al. 2002

J. Chem. Soc., Dalton Trans.

Self Cite

View full text Add to dashboard Cite

A pulsed-accelerated-flow (PAF) spectrometer (model V) capable of non-ambient temperature studies of fast reaction kinetics is described. The PAF method uses accelerated flow mixing of reactants during short time periods to enable the resolution of mixing and reaction rate constants. A new mixing/observation cell and cell supports are designed to permit measurement of reaction kinetics from 40 ЊC to below 0 ЊC. The cell consists of two machined PEEK [(-OC 6 H 4 OC 6 H 4 COC 6 H 4 -) n ] pieces joined together to give an internal solution distribution system, which greatly reduces the number of connections needed compared to previous instruments to bring the reactants together. The reaction between W(CN) 8 4Ϫ and IrCl 6 2Ϫ in 0.50 M H 2 SO 4 is studied at 0.0, 25.0, and 40.0 ЊC. Second-order rate constants of 0.650 × 10 8 M Ϫ1 s Ϫ1 , 1.05 × 10 8 M Ϫ1 s Ϫ1 , and 1.29 × 10 8 M Ϫ1 s Ϫ1 are obtained, respectively. These data give activation parameters of ∆H ‡ = 10.0 ± 0.8 kJ mol Ϫ1 and ∆S ‡ = Ϫ58 ± 3 J mol Ϫ1 K Ϫ1 . Activation parameters for reverse bromine hydrolysis (HOBr ϩ Br Ϫ ϩ H ϩ Br 2 ϩ H 2 O) were determined from rate constants measured from 0.0 to 40.0 ЊC. These were used to calculate the activation parameters for the forward bromine hydrolysis (∆H ‡ = 66 ± 1 kJ mol Ϫ1 and ∆S ‡ = 10 ± 20 J mol Ϫ1 K Ϫ1 ). The temperature dependence of the extremely rapid BrCl hydrolysis reaction (in equilibrium with BrCl 2 Ϫ) is determined as well. For reactions at temperatures of 25.0 ЊC, 10.0 ЊC, and 0.0 ЊC the values are 3.3 × 10 6 s Ϫ1 , 2.06 × 10 6 s Ϫ1 , and 1.75 × 10 6 s Ϫ1 , respectively. These values correspond to activation parameters of ∆H ‡ = 15 ± 7 kJ mol Ϫ1 and ∆S ± = Ϫ71 ± 24 J mol Ϫ1 K Ϫ1 for BrCl hydrolysis.

show abstract

Section: Introductionmentioning

confidence: 99%

“…The mixing rate constant is equal to a mixing proportionality constant (k m ) times the velocity at which the mixing takes place (k mix = k m v). 4,11,12 These two constants are resolved by use of eqn. (3), which takes into account the velocity dependence of k mix .…”

Section: Introductionmentioning

confidence: 99%

Pulsed-accelerated-flow studies of the temperature dependence of fast reactionsBased on the presentation given at Dalton Discussion No. 4, 10–13th January 2002, Kloster Banz, Germany.

Becker

Bartlett

Urbansky

et al. 2002

J. Chem. Soc., Dalton Trans.

Self Cite

View full text Add to dashboard Cite

show abstract

“…Under second-order reaction conditions, when reactant concentrations were low enough to measure with the stopped-flow spectrophotometer, small absorbance changes caused the rate data to be unreliable. Therefore, the Ni(III) tripeptide redox reactions were studied by using the pulsed-accelerated-flow (PAF) method. − The PAF method is a continuous-flow method with integrated observation in which the reaction is observed along the direction of flow in the observation tube. The instrument was interfaced to a Hewlett-Packard 2100A general-purpose computer for mathematical treatment to resolve the apparent (measured) first-order reaction rate constant ( k app ) into its two components, namely, the actual reaction first-order rate constant, k reaction , and the mixing rate constant, k m . − The computer was programmed to do this, and the rate constants reported in Table are the resolved k reaction values.…”

Section: Methodsmentioning

confidence: 99%

“…Values of k 12 obsd are from the linear plots of Figure , which were forced through the intercept. b Ox = oxidant, Red = reductant. Reactant concentrations was chosen following published guidelines which describe the development and use of the PAF instrument. − c The reverse rate constant for Ni III + Ir III is calculated from the equilibrium constant to be (6.5 ± 0.1) × 10 6 M –1 s –1 d pH = 1 (HClO 4 ). …”

Section: Methodsmentioning

confidence: 99%

A Kinetic Study of the Electron-Transfer Reactions of Nickel(III,II) Tripeptide Complexes with Cyano Complexes of Molybdenum, Tungsten, and Iron

et al. 2020

Self Cite

View full text Add to dashboard Cite

Experimentally measured rate constants, k 12 obsd, for the reductions of [Ni(III)tripeptides(H2O)2] with Fe(CN)6 4–, Mo(CN)8 4–, and W(CN)8 4– are 102 to 105 times faster than the calculated rate constants with the Marcus theory for outer-sphere electron-transfer processes, k 12 calc, even when work terms are considered. This gives rise to a kinetic advantage of k 12 obsd/k 12 calc = 102–105, which is consistent with an inner-sphere electron-transfer mechanism via a bridged intermediate. In addition, k 12 obsd values are nearly independent of the electrochemical driving force of the reactions. This is consistent with one of the two axial water ligands coordinated to [Ni(III)tripeptides(H2O)2] being substituted in the rate-limiting step to form bridged intermediates of the type [(CN)5or7M-(CN)-NiIII(tripeptide)(H2O)]4– with M = FeII, MoIV, or WIV. A limiting rate constant of H2O replacement from [Ni(III)tripeptides(H2O)2] of (5 ± 2) × 107 M–1 s–1 at 25.0 °C is observed. Electron paramagnetic resonance spectra of Ni(III) peptide complexes in the presence of Fe(CN)6 3–, Mo(CN)8 3–, or IrCl6 3– provide evidence for the cyanide-bridged intermediates. Substitution-limited electron-transfer reactions could serve as an additional criterion for inner-sphere pathways when atom or group transfer does not occur during electron-transfer and when precursor and successor complexes cannot be observed directly.

show abstract

“…With the introduction of eq and subsequent progress in technology, − it has become possible to measure k Ψ values up to about 1500 s –1 in well-maintained stopped-flow instruments. However, the concept of micromixing and the use of eq had to be retained even when further attempts were made to achieve faster mixing in the pulsed accelerated flow technique. − The performance of pulsed accelerated flow was only marginally better than that of stopped-flow, so the former technique did not become popular.…”

Section: Introductionmentioning

confidence: 99%

Minimal Reaction–Diffusion Model of Micromixing during Stopped-Flow Experiments

Ditrói

Lente

2018

J. Phys. Chem. A

View full text Add to dashboard Cite

The reaction-diffusion equation was used to simulate kinetic curves measured in a stopped-flow instrument in order to understand the origin of micromixing effects. The partial differential equations were solved both by numeric means and by a more analytical approach using Fourier series. A fully analytical solution was obtained for the diffusion only case (when no reaction occurs). Comparisons with the results of numerical calculations showed that very reasonable analytical approximations were obtained for the diffusion-reaction case. The simulations could readily reproduce the saturation of the pseudo-first-order rate constants with an increase in the concentration of excess reagent, a phenomenon first observed about 30 years ago. From the results, it can be concluded that further improvement of the performance of stopped-flow instruments is not possible by simply reducing the dead time; the efficiency of the mixing is the primary limiting factor.

show abstract

Pulsed-accelerated-flow spectrometer with integrating observation for measurement of rapid rates of reaction

Cited by 21 publications

References 24 publications

Pulsed-accelerated-flow studies of the temperature dependence of fast reactionsBased on the presentation given at Dalton Discussion No. 4, 10–13th January 2002, Kloster Banz, Germany.

Pulsed-accelerated-flow studies of the temperature dependence of fast reactionsBased on the presentation given at Dalton Discussion No. 4, 10–13th January 2002, Kloster Banz, Germany.

A Kinetic Study of the Electron-Transfer Reactions of Nickel(III,II) Tripeptide Complexes with Cyano Complexes of Molybdenum, Tungsten, and Iron

Minimal Reaction–Diffusion Model of Micromixing during Stopped-Flow Experiments

Contact Info

Product

Resources

About