Kinetics of cyanate and imidazole binding to hemin in micelles

Simplicio, Jon; Schwenzer, Kathryn; Maenpa, Francis

doi:10.1021/ja00858a019

Cited by 39 publications

(39 citation statements)

References 5 publications

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“…1 and 6). In a surfactant micelle the hemin is located in the hydrophobic region near the micelle water interface, 8 where the effective relative permittivity 25 (ε = 32) is much lower than that in bulk water. Thus a change from an essentially aqueous to an essentially non-polar local heme environment in the micelles leads to a positive shift of the midpoint potential.…”

Section: Comparison With Proteinsmentioning

confidence: 99%

Electrochemical behaviour of (protoporphyrinato IX)iron(III) encapsulated in aqueous surfactant micelles

Das¹,

Bhattaray²,

Medhi³

1997

J. Chem. Soc., Dalton Trans.

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The electrochemical behaviour of iron protoporphyrinate IX (hemin) [(3,7,12,17-tetramethyl-8,13divinylporphyrin-2,18-dipropanoato)iron()] in aqueous sodium dodecyl sulfate (sds), hexadecyltrimethylammonium bromide or Triton X-100 surfactant micellar solution was investigated by cyclic voltammetry (CV) and Osteryoung square-wave voltammetry (OSWV) techniques. The dependence of the midpoint potential on the concentration and on the nature of the surfactant shows that the potentials shift anodically with respect to water or aqueous ethanol. The midpoint potentials of hemin at pH 7.0 vs. normal hydrogen electrode are Ϫ52 mV in NMe 3 (C 16 H 33 )Br, Ϫ112 mV in Triton X-100, Ϫ152 mV in sds and Ϫ190 mV in ethanol-water (1 : 1, v/v) solutions. Thus the hydrophobic effect of the micelle gives a positive shift of the midpoint potential. The maximum positive shift in surfactants (with respect to water) of ca. ϩ120 mV was found in the micelles. The trend in the anodic shift is EtOH-water < sds < Triton X-100 < NMe 3 (C 16 H 33 )Br. The diffusion coefficients of the hemin complex in the micelles are an order of magnitude smaller than that of monomeric hemin in aqueous ethanolic media. The rates of heterogeneous electron transfer at the glassy carbon electrode were found to be smaller in the micelles as compared to those in aqueous ethanolic media. The midpoint potential of hemin monomers encapsulated in aqueous surfactant micelles shows a pH dependence with ∆E/∆pH ca. Ϫ59 mV indicating that electron transfer at the iron site is influenced by the uptake of protons at the axial ligand.

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Section: Comparison With Proteinsmentioning

confidence: 99%

Electrochemical behaviour of (protoporphyrinato IX)iron(III) encapsulated in aqueous surfactant micelles

Das¹,

Bhattaray²,

Medhi³

1997

J. Chem. Soc., Dalton Trans.

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“…[14] Cyclodextrinss have been widely studied as host molecules for complexing porphyrin derivatives, [15] and many spectroscopic investigations on charged porphyrins interacting with neutral and charged micelles have been reported, [16] as well as equilibrium [17] and kinetic studies. [18] Here we report on a spectroscopic study on the heterotopic colloidal system formed by cationic heptakis-(2-w-amino-O-oligo(ethylene oxide)-6-hexylthio)-b-CD (SC6CDNH2; 2), (synthesized from the precursor heptakis(2-w-iodo-O-oligo(ethylene oxide)-6-hexylthio)-b-CD, [6,10] and water-soluble 5,10,15,20-tetrakis(4-sulfonatophenyl)-21H,23H-porphine (TPPS; 1). Preliminary results on the interaction of TPPS and other, water-insoluble porphyrins with cationic and neutral nanoaggregates of CDs were reported.…”

Section: Introductionmentioning

confidence: 99%

Novel Heterotopic Colloids of Anionic Porphyrins Entangled in Cationic Amphiphilic Cyclodextrins: Spectroscopic Investigation and Intracellular Delivery

Mazzaglia

Angelini

Darcy

et al. 2003

Chemistry A European J

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The entanglement process between water-soluble 5,10,15,20-tetrakis(4-sulfonatophenyl)-21H,23H-porphine and the amphiphilic cyclodextrin (CD) heptakis(2-omega-amino-O-oligo(ethylene oxide)-6-hexylthio)-beta-CD and the occurrence of various species at different porphyrin:CD ratios were studied by a combination of UV/Vis absorption, fluorescence anisotropy, time-resolved fluorescence, resonance light scattering, and circular dichroism. The effect of the entanglement process on the mean vesicle diameter was investigated over a wide concentration range by quasielastic light-scattering techniques. The experimental results indicate that the presence of porphyrins in this colloidal system promotes some structural rearrangements, essentially driven by charge interaction, which are responsible for a sensitive change of vesicle dimensions. In the range of porphyrin:CD molar ratios between 1:10 and 1:50, the porphyrin is solubilized in monomeric form (tau(1)=11.5 ns) and photosensitizes the production of singlet oxygen ((1)O(2)). At the same molar ratio the ability of this amphiphilic cyclodextrin to transport porphyrins into tumor cells indicates specificity at the nuclear-compartment level. These findings may be of potential interest for the of development agents for photodynamic therapy of tumors.

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“…The immediate microenvironment of hemes in aqueous micelles is predominantly apolar and the hydrophobic interactions of the heme with surfactants are found to be important to an understanding of interactions of the more complex hemoproteins. [20][21][22] The proton NMR and optical spectra of microperoxidase 11 are markedly dependent on pH and show equilibrium conversion of various axially ligated species and a high-to low-spin crossover in aqueous sds. 19 Thus, in aqueous surfactant solutions the heme undecapeptide provides an opportunity to study the effect of axial ligands, apolar nature of the local heme environment, spin crossover, and proton equilibria on the redox potential of the heme group over a wide range of pH.…”

mentioning

confidence: 99%

Effect of surfactant and pH on the redox potential of microperoxidase 11 in aqueous micellar solutions

Das¹,

Medhi²

1998

J. Chem. Soc., Dalton Trans.

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The redox potential of heme undecapeptide from cytochrome c (microperoxidase 11) in aqueous sodium dodecyl sulfate (sds), hexadecyltrimethylammonium bromide, and Triton X-100 surfactant micelles varied from ϩ2 mV at pH 3.0 to Ϫ222 mV at pH 9.0. The potentials at pH 7.0 were Ϫ114, Ϫ122, and Ϫ166 mV vs. the normal hydrogen electrode in the three surfactants. The nature of the axial ligands, spin state of iron, apolar nature of the local heme environment, and pH influence the potential in the micelles. Binding of histidine (HisH) of the peptide chain gave a negative shift of Ϫ60 mV, and deprotonation of co-ordinated HisH to histidinate gave a Ϫ100 mV shift of the potential in aqueous sds. At pH 5.0-6.0 the axial ligands to iron are H 2 O and HisH; deprotonation of coordinated H 2 O gave Ϫ65 mV shift of the potential. Interaction of hemin with surfactant gave a positive shift of the potential with respect to that in water. The diffusion coefficient of the undecapeptide (2.4 × 10 Ϫ7 cm 2 s Ϫ1 ) at pH 7.0 in the micelles is an order of magnitude smaller than that in water, indicating solubilisation of heme in surfactant solutions. The potential is strongly dependent on pH and is controlled by the uptake/release of protons at three sites: the unco-ordinated HisH of the peptide chain, the axially co-ordinated H 2 O and HisH ligands. The pK a values of these redox state-dependent ionisations in the iron() state are ca. 4.3, 6.3, and 8.3. The change in potential per unit change of pH (∆E/∆pH) was ca. Ϫ59 mV, which indicates proton-coupled electron transfer involving one electron and one proton.

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Kinetics of cyanate and imidazole binding to hemin in micelles

Cited by 39 publications

References 5 publications

Electrochemical behaviour of (protoporphyrinato IX)iron(III) encapsulated in aqueous surfactant micelles

Electrochemical behaviour of (protoporphyrinato IX)iron(III) encapsulated in aqueous surfactant micelles

Novel Heterotopic Colloids of Anionic Porphyrins Entangled in Cationic Amphiphilic Cyclodextrins: Spectroscopic Investigation and Intracellular Delivery

Effect of surfactant and pH on the redox potential of microperoxidase 11 in aqueous micellar solutions

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