Temperature jump kinetics of the binding of imidazole to ferriprotoporphyrin IX

1969 ◽  
Vol 47 (17) ◽  
pp. 3225-3232 ◽  
Author(s):  
Brian B. Hasinoff ◽  
H. Brian Dunford ◽  
Dale G. Horne
Keyword(s):  
Dissociation Constant ◽  
Rate Constant ◽  
Temperature Jump ◽  
Spectrophotometric Titration ◽  
Specific Rate ◽  
Specific Rate Constant ◽  
Solvent Systems ◽  
Ph Scale ◽  
Kinetics Of ◽  
Imidazolium Ion

The kinetics of binding of imidazole to ferriprotoporphyrin IX (hemin) in aqueous ethanol has been studied at 25° using the temperature jump technique. The reaction was studied quantitatively as a function of acid concentration using the pH scale developed by Bates et al. for mixed solvent systems. The results can be explained by a mechanism in which the imidazolium ion binds to hemin with a specific rate constant of (4 ± 2) × 106 M−1 s−1 and imidazole binds with a rate constant of (3 ± 0.3) × 104 M−1 s−1. The dissociation constant for the imidazolium ion was determined by acid–base titration to be 1.8 × 10−7 M, and a dissociation constant for the hemin of 2.3 × 10−7 M was determined by spectrophotometric titration in a solvent containing 44.5 weight % of ethanol. The latter dissociation involves the proton on a solvent ligand.

Effect of variable specific rate constant in non uniform catalysts

1977 ◽  
Vol 32 (2) ◽  
pp. 155-159 ◽  
Author(s):  
J. Cervelló ◽  
J.F.J. Melendo ◽  
E. Hermana
Keyword(s):  
Rate Constant ◽  
Specific Rate ◽  
Specific Rate Constant

A Raman Spectral Study of the Kinetics of Hydrolysis of Acetonitrile Catalyzed by Hg(II)

1975 ◽  
Vol 53 (3) ◽  
pp. 427-436 ◽  
Author(s):  
Yu-Keung Sze ◽  
Donald E. Irish
Keyword(s):  
Time Span ◽  
Water Molecules ◽  
Specific Rate ◽  
Ammine Complexes ◽  
Kinetics Of Hydrolysis ◽  
Specific Rate Constant ◽  
Rate Of Hydrolysis ◽  
Raman Spectral ◽  
Kinetics Of ◽  
Hydrolysis Of

Raman spectroscopy has been employed to follow the relatively slow rate of hydrolysis of acetonitrile, catalyzed by mercury(II). Raman lines at 2275 and 2305 cm−1 are characteristic of CH3CN bound to Hg2+, and are distinct from lines of bulk solvent. The intensities of these new lines decrease with time. From the intensities, concentrations of bound acetonitrile, [CH3CN]B were calculated for a time span of 400 min. The data fit a second order rate law: Rate = k[CH3CN]B[H2O]. The specific rate constant, k, obtained from four sets of data for the system Hg(ClO4)2–CH3CN–H2O equals 1.05 ± 0.06 × 10−4 mol−1 1 min−1 at 25 °C. The energy of activation is 18.9 kcal mol−1. In the proposed mechanism water molecules attack acetonitrile molecules which are bound to Hg2+ and form a mercury(II)–acetamide complex. Raman lines characteristic of this species are observed. This species slowly converts to mercury(II) ammine complexes and acetic acid. Anions which coordinate with Hg2+ more strongly than CH3CN, such as nitrate or acetate, slow or prevent the hydrolysis reaction.

scholarly journals Facet-dependent performance of BiOBr for photocatalytic reduction of Cr(vi)

RSC Advances ◽  
2016 ◽  
Vol 6 (3) ◽  
pp. 2028-2031 ◽  
Author(s):  
Zao Fan ◽  
Yubao Zhao ◽  
Wei Zhai ◽  
Liang Qiu ◽  
Hui Li ◽  
...  
Keyword(s):  
Electric Field ◽  
Rate Constant ◽  
Photocatalytic Reduction ◽  
Specific Rate ◽  
Internal Electric Field ◽  
Specific Rate Constant

BiOBr dominated with {110} facets giving a specific rate constant 3 times as high as BiOBr with {001} facets, and its much stronger internal electric field was believed to be the main reason.

A STUDY OF SOME REACTIONS OF THE CYCLOPENTYL RADICAL

1965 ◽  
Vol 43 (3) ◽  
pp. 570-581 ◽  
Author(s):  
Alvin S. Gordon
Keyword(s):  
Hydrogen Atom ◽  
Kinetic Parameters ◽  
Rate Constant ◽  
Energy Of Activation ◽  
Radical Reactions ◽  
Specific Rate ◽  
Exponential Factor ◽  
Allyl Radical ◽  
Specific Rate Constant ◽  
Activated Complex

The specific rate constant for opening the cyclopentyl radical has been determined to be 1014.5 exp –37 700/RT s−1. The energy of activation indicates that any eclipsed pairs of H atoms in the cyclic radical are not de-eclipsed in the activated complex. No evidence for the resulting five-membered linear radical can be found, only evidence for its breakdown products, allyl radical and ethylene.The disproportionation/combination ratio for methyl and cyclopentyl radicals is about 0.3. The energy of activation for methyl abstracting a hydrogen atom from cyclopentane has been confirmed as about 9.5 kcal/mole.Cyclopentyl radical also loses a hydrogen atom to form cyclopentene. The kinetic parameters are difficult to obtain because of radical–radical reactions which form cyclopentene. An analysis of the results indicates an energy of activation at least equal to that for opening the cyclopentyl ring.Evidence is presented to support the view that the cyclopentyl radical loses a molecule of hydrogen to form the resonance-stablized cyclopentenyl radical with an energy of activation close to that for opening the ring, and a pre-exponential factor about 1/10 of that for the opening of the ring.

SPECIFIC RATE CONSTANT FOR URETHAN CLEAVAGE

1963 ◽  
Vol 67 (4) ◽  
pp. 930-931 ◽  
Author(s):  
A. V. Tobolsky ◽  
E. Peterson
Keyword(s):  
Rate Constant ◽  
Specific Rate ◽  
Specific Rate Constant

Kinetics of zinc ion incorporation in base into a centrally aprotic beta-octabrominated cationic water-soluble porphyrin and its monolithium complex

2001 ◽  
Vol 05 (12) ◽  
pp. 829-834 ◽  
Author(s):  
SABRINA L. BAILEY ◽  
P. HAMBRIGHT
Keyword(s):  
Formation Constant ◽  
Zinc Ion ◽  
Water Soluble ◽  
Specific Rate ◽  
First Order ◽  
Specific Rate Constant ◽  
Zinc Concentrations ◽  
Water Soluble Porphyrin ◽  
Ion Incorporation ◽  
Kinetics Of

The kinetics of zinc incorporation from pH 12 to 13 into the centrally aprotic BrP (4)2+ form of beta-octabromo-meso-tetrakis(N-methyl-4-pyridyl)porphyrin and its monolithium complex were studied at 25.0 °C, ionic strength (I) = 0.10. The reactions were first order in porphyrin and total zinc concentrations. For BrP (4)2+, the specific rate constant was 5.1 × 105 M -1 s -1 for Zn ( OH )2 aq , 9.9 × 104 M -1 s -1 for [Formula: see text] and [Formula: see text] was unreactive. The Li - BrP (4)3+ complex had a formation constant with BrP (4)2+ of 1.1 × 103 M -1 from both kinetic and equilibrium measurements. In solutions containing both BrP (4)2+ and Li - BrP (4)3+, zinc incorporation proceeded only through BrP (4)2+.

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