Simultaneous diffusion and chemical activation control of the kinetics of the binding of carbon monoxide to ferroprotoporphyrin IX in glycerol–water mixtures of high viscosity

Abstract

BRIAN B . HASINOFF. Can. J. Chem. 55,3955 (1977).The kinetics of the reaction of ferroprotoporphyrin IX with CO have been studied in mixed glycerol-water solvents of high viscosity in order that the simultaneous influence of chemical activation and diffusion control of the reaction might be observed. Analyses of curved Arrhenius plots indicated that in the low temperature high viscosity limits the reaction is largely diffusion controlled. The deviation of the second order diffusion rate constants, from that predicted by simple theory for reaction between uniformly reactive spheres of equal radii, is a factor of 0.3 to 0.9, depending upon the solvent composition. A couple of other models for diffusion controlled reaction, ascribing these deviations to changes of steric requirements, were also examined. BRIAN B . HASINOFF. Can. J. Chem. 55,3955 (1977) On a etudie la cinetique de la reaction de la ferroprotoporphyrine IX avec le CO dans des solvants mixtes de g l y c e r o l~a u de grande viscosite de f a~o n a pouvoir observer simultankment l'influence de l'aclivation chimique et du contrale de la diffusion sur la reaction. L'analyse des courbes d'Arrhenius indique qu'aux limites de basse temperature et de haute viscosite la reaction est grandement contralee par la diffusion. La dkviation des constantes de vitesse de diffusion du deuxieme ordre par rapport a celles qui sont prtdites par la theorie simple de la reaction entre des spheres reactives uniformes qui ont un rayon &gal est d'un facteur de 0.3 a 0.9 dkpendant de la composition du solvant. Une couple d'autres modeles pour une reaction contralee par la diffusion et attribuant ces deviations a des changements dans les facteurs steriques ont aussi kt6 examines.[Traduit par le journal]In a previous study (1) the reaction of ferroprotoporphyriil IX (heme) with carbon monoxide was studied by laser flash photolysis as a function of temperature and pressure in 100% glycerol and 80% vv/ ethylene glycol -water. A comparison of the activation enthalpies and activation volumes with the viscosity activation parameters indicated that in 100% glycerol the kinetics are almost totally controlled by diffusion. From a consideration of AV* (I), obtained in 80% vv/ ethylene glycol -water, a dissociative mechanism was indicated.This study extends the range of viscosities studied by using mixtures of glycerol and water, such that both chemical activation and diffusion control contribute to the kinetics. It is of interest to measure the kinetics in this region as a test of the applicability of the theory of diffusion controlled reactions. Glycerol-water solvent mixtures exhibit a wide range of viscosities (2) with large temperature coefficients so that the Can. J. Chem. Downloaded from www.nrcresearchpress.com by 52.36.4.81 on 05/10/18For personal use only.

Kinetics of Intercluster Reactions between Atomically Precise Noble Metal Clusters [Ag25(DMBT)18]− and [Au25(PET)18]− in Room Temperature Solutions

“…where k B is the Boltzmann constant, T is the temperature, N A is the Avogadro constant, and η is the dynamic viscosity of the solvent (DMF). 48 With η = 0.799 × 10 −3 Pa•s 49 and T = 298 K, k D amounts to 8.3 L nmol −1 s −1 , which is approximately 3 orders of magnitude larger than typical dimerization rate constants from our simulations. In the case of charged molecules the diffusion limited rate constant of eq 4 must be multiplied by the Debye factor f Debye which accounts for the Coulomb interaction between the ions.…”

“…The physical upper limit for the dimerization rate constant of near-spherical, neutral molecules in solution is the diffusion limited case for which the rate constant is given by where k B is the Boltzmann constant, T is the temperature, N A is the Avogadro constant, and η is the dynamic viscosity of the solvent (DMF) . With η = 0.799 × 10 –3 Pa·s and T = 298 K, k D amounts to 8.3 L nmol –1 s –1 , which is approximately 3 orders of magnitude larger than typical dimerization rate constants from our simulations.…”

Determination of Binding Strengths of Host‐Guest Complexes in Deep Eutectic Solvents Using Spin Probe Methodology

“…Very fast rates for CD complex formation can be observed in water, but diffusion limit is not generally reached [18] . On the other hand, in highly viscous solvent like DES, diffusion control for the association process cannot be excluded and simultaneous chemical activation and diffusion could contribute to the observed kinetic as already observed, for example, in the binding of carbon monoxide by ferroprotoporphyrin IX in glycerol‐water mixtures [19] . In this regime, 1/ k =1/ k 0 +1/ k D where k is the observed second order rate constant and k 0 is the rate constant that would be measured if diffusion effects were absent [19] .…”

“…On the other hand, in highly viscous solvent like DES, diffusion control for the association process cannot be excluded and simultaneous chemical activation and diffusion could contribute to the observed kinetic as already observed, for example, in the binding of carbon monoxide by ferroprotoporphyrin IX in glycerol‐water mixtures [19] . In this regime, 1/ k =1/ k 0 +1/ k D where k is the observed second order rate constant and k 0 is the rate constant that would be measured if diffusion effects were absent [19] . If this holds, plots of Log( k ) vs. T −1 should show increasing deviations from linearity when moving to lower temperature limit as a consequence of the increasing weight of viscosity term.…”

Diffusion effects in initiator decomposition in highly viscous and macromolecular solutions

“…Literature review indicates that diffusivity in such systems varies inversely with viscosity raised to an exponent which is close to 213. In fact, the assumption of validity of Stokes-Einstein equation in such systems has at times led to irrational conclusions (Hasinoff, 1977). The exponent 2/3 has been recently justified on the basis of Eyring rate theory (Hiss and Cussler, 1973).…”