Study of the kinetics of reduction of an iron(III) porphyrin by hexaammineruthenium(II). Estimate of the self-exchange rate for a high-spin iron porphyrin complex

1978 ◽  
Vol 100 (3) ◽  
pp. 968-972 ◽  
Author(s):  
Robert F. Pasternack ◽  
Esther G. Spiro
Keyword(s):  
Exchange Rate ◽  
High Spin ◽  
The Self ◽  
Iron Porphyrin ◽  
Porphyrin Complex ◽  
Kinetics Of ◽  
Kinetics Of Reduction ◽  
High Spin Iron

Synthesis and characterization of the azido-bound five-coordinate high-spin iron(II) “picket fence” porphyrin complex

Polyhedron ◽  
2009 ◽  
Vol 28 (5) ◽  
pp. 954-958 ◽  
Author(s):  
Ibtissem Hachem ◽  
Mohamed Salah Belkhiria ◽  
Michel Giorgi ◽  
Charles E. Schulz ◽  
Habib Nasri
Keyword(s):  
High Spin ◽  
Synthesis And Characterization ◽  
Porphyrin Complex ◽  
Picket Fence ◽  
High Spin Iron

Electron transfer kinetics of cobaloxime complexes

1996 ◽  
Vol 74 (5) ◽  
pp. 658-665 ◽  
Author(s):  
Kefei Wang ◽  
R.B. Jordan
Keyword(s):  
Electron Transfer ◽  
Exchange Rate ◽  
Rate Constants ◽  
Ph Dependence ◽  
Outer Sphere ◽  
The Self ◽  
Oxidation Of Co ◽  
Reduction Potentials ◽  
Inner Sphere ◽  
Kinetics Of

The rates of oxidation of CoII(dmgBF2)2(OH2)2 by CoIII(NH3)5X2+ (X = Br−, Cl−, and N3−) have been studied at 25 °C in 0.10 M LiClO4. The rate constants are 50 ± 9, 2.6 ± 0.2, and 5.9 ± 1.0 M−1 s−1 for X = Br−, Cl−, and N3−, respectively, in 0.01 M acetate buffer at pH 4.7. The relative rates are consistent with the inner-sphere bridging mechanism established earlier by Adin and Espenson for the analogous reactions of CoII(dmgH)2(OH2)2. The rate constants with CoII(dmgBF2)2(OH2)2 typically are ~103 times smaller and this is attributed largely to the smaller driving force for the CoII(dmgBF2)2(OH2)2 complex. The outer-sphere oxidations of cobalt(II) sepulchrate by CoIII(dmgH)2(OH2)2+ (pH 4.76–7.35, acetate, MES, and PIPES buffers) and CoIII(dmgBF2)2(OH2)2+ (pH 3.3–7.42, chloroacetate, acetate, MES, and PIPES buffers) have been studied. The pH dependence gives the following rate constants (M−1 s−1) for the species indicated: (1.55 ± 0.09) × 105 (CoIII(dmgBF2)2(OH2)2+); (5.5 ± 0.3) × 103 (CoII(dmgH)2(OH2)2+); (3.1 ± 0.5) × 102 (CoIII(dmgH)2(OH2)(OH)); (2.5 ± 0.3) × 102 (CoIII(dmgBF2)2(OH2)(OH)). The known reduction potentials for cobalt(III) sepulchrate and the diaqua complexes, and the self-exchange rate for cobalt(II/III) sepulchrate, are used to estimate the self-exchange rate constants for the dioximate complexes. Comparisons to other reactions with cobalt sepulchrate indicates best estimates of the self-exchange rate constants are ~2.4 × 10−2 M−1 s−1 for CoII/III(dmgH)2(OH2)2and ~5.7 × 10−3 M−1 s−1 for CoII/III(dmgBF2)2(OH2)2. Key words: electron transfer, cobaloxime, inner sphere, outer sphere, self-exchange.

Outer-sphere electron transfer reactions of aqua(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetato) nickel(II) and (III).

2003 ◽  
Vol 81 (2) ◽  
pp. 186-192 ◽  
Author(s):  
Robert I Haines ◽  
Dean R Hutchings
Keyword(s):  
Electron Transfer ◽  
Exchange Rate ◽  
Outer Sphere ◽  
Second Order ◽  
Marcus Theory ◽  
Pendant Arm ◽  
Key Words Nickel ◽  
Kinetics Of ◽  
Kinetics Of Reduction ◽  
Sphere Mechanism

The outer-sphere oxidation of the nickel(II) complex of the deprotonated pendant-arm macrocycle, 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-1-acetate, [NiL1(OH2)]+ by bis-(1,4,7-triazacyclononane)nickel(III), [Ni(tacn)2]3+ has been studied in aqueous perchlorate media. The reaction displays reversible second-order behaviour and the kinetic study reveals the forward and reverse rate constants for the reaction: [Formula: see text] The kinetics show the forward reaction to be acid dependent, a feature that is attributed to protonation of the acetato group of the nickel(II) complex. Using Marcus theory, the self-exchange rate for the [NiL1(OH2)]+/2+ couple has been calculated. The nickel(II/III) electron transfer is a reversible one electron process with E° = 1.04 V (vs. S.H.E.). The formation of the authentic nickel(III) product has been confirmed by esr spectroscopy. The kinetics of reduction of the [NiL1(OH2)]2+ species by Fe2+(aq) exhibits a second-order rate law, the reaction being independent of acid. Using the calculated self-exchange rate for the nickel complex, its reaction with Fe2+(aq) has been examined in terms of an inner- versus outer-sphere mechanism. Key words: nickel(III), pendant-arm macrocycles, hexaaquairon(II), outer sphere, kinetics, Marcus theory.

Cobalt, Iron and Ruthenium Complexes of Picolinic and Dipicolinic Acids: Syntheses, Solution Properties and Kinetics of Electron Transfer Reactions With Cytochrome C(II) and Some Inorganic Reductants

1989 ◽  
Vol 42 (1) ◽  
pp. 1 ◽  
Author(s):  
RM Ellis ◽  
JD Quilligan ◽  
NH Williams ◽  
JK Yandell
Keyword(s):  
Exchange Rate ◽  
Cytochrome C ◽  
Rate Constant ◽  
Order Rate Constant ◽  
The Self ◽  
Transfer Reactions ◽  
Solution Properties ◽  
Cobalt Iron ◽  
Exchange Rate Constant ◽  
Kinetics Of

Tris picolinate complexes of CO111 and RU111 have been synthesized, and their standard potentials measured (432 �10, 403 �2 mV) at 25�C and ionic strength 0.1 mol dm-3. The self-exchange rate constant of Ru ( pic )3O/- was found to be (1 .4 �0.9)×108 dm3 mol-1 s-l, from reaction with cytochrome C(II), Co( bpy )32+ and ~Co( phen )32+. For the reaction between Fe( dipic )2- and cytochrome ~(II), at 2S260C, pH 5.5 and I 0.1 mol dm-3 (KNO3), the second-order rate constant was (3.2 �0.l)×105 dm3 mol-1 s-1,with ΔH+ 19.9 �0.9 kJ mol-1 and ΔS+ -72.8 �.7 J K-1 mol-l. The self-exchange rate constant of Fe( dipic )2-/2- was reevaluated as (5.8 �0.2)×106 dm3 mol-l s-1.

The Simplest Iron μ-oxo Species. The Molecular Structure of {[Fe(porphine)]2O}

2020 ◽  
Vol 24 (09) ◽  
pp. 1105-1112
Author(s):  
Ming Li ◽  
W. Robert Scheidt
Keyword(s):  
Molecular Structure ◽  
High Spin ◽  
Structure Determination ◽  
Twist Angle ◽  
Structural Features ◽  
Interplanar Angle ◽  
Porphyrin Complex ◽  
Porphyrin Ligand ◽  
New Formula ◽  
High Spin Iron

We have prepared a new [Formula: see text]-oxo iron(III) porphyrin complex based on the simplest possible porphyrin ligand, porphine. Our structure determination for {[Fe(porphine)]2O}shows that it has a decidedly different molecular structure compared to all other [Formula: see text]-oxo iron(III)porphyrin complexes with two independent porphyrin ligands. The Fe–O–Fe angle is 153.21 (16)[Formula: see text]which leads to a small interplanar angle of 22.7[Formula: see text]between the two porphine rings. This also leads to C[Formula: see text]C nonbonded contact as short as 3.35Å between the two rings. The twist angle of the two porphine rings is 16.8[Formula: see text]. Other structural features are in general accord with those expected for high-spin iron(III) porphyrinates.

scholarly journals Kinetics of cytochrome P450 3A4 inhibition by heterocyclic drugs defines a general sequential multi-step binding process

2020 ◽  
pp. jbc.RA120.016855
Author(s):  
F. Peter Guengerich ◽  
Kevin D McCarty ◽  
Jesse G Chapman
Keyword(s):  
Cytochrome P450 ◽  
High Spin ◽  
Enzyme Inhibitor ◽  
Spectral Shift ◽  
Slow Step ◽  
Multiple Structures ◽  
Kinetics Of ◽  
Pharmacokinetic Drug ◽  
Rapid Binding ◽  
High Spin Iron

Cytochrome P450 (P450, CYP) 3A4 is the enzyme most involved in the metabolism of drugs and can also oxidize numerous steroids. This enzyme is also involved in one-half of pharmacokinetic drug-drug interactions, but details of the exact mechanisms of P450 3A4 inhibition are still unclear in many cases. Ketoconazole, clotrimazole, ritonavir, indinavir, and itraconazole are strong inhibitors; analysis of the kinetics of reversal of inhibition with the model substrate 7-benzoyl (OBz) quinoline showed lag phases in several cases, consistent with multiple structures of P450 3A4 inhibitor complexes. Lags in the onset of inhibition were observed when inhibitors were added to P450 3A4 in 7-OBz quinoline O-debenzylation reactions, and similar patterns were observed for inhibition of testosterone 6β-hydroxylation by ritonavir and indinavir. Upon mixing with inhibitors, P450 3A4 showed rapid binding as judged by a spectral shift with at least partial high-spin iron character, followed by a slower conversion to a low-spin iron-nitrogen complex. The changes were best described by two intermediate complexes, one being a partial high-spin form and the second another intermediate, with half-lives of seconds. The kinetics could be modeled in a system involving initial loose binding of inhibitor, followed by a slow step leading to a tighter complex on a multi-second time scale. Although some more complex possibilities cannot be dismissed, these results describe a system in which conformationally distinct forms of P450 3A4 bind inhibitors rapidly and two distinct P450-inhibitor complexes exist enroute to the final enzyme-inhibitor complex with full inhibitory activity.

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