Regioselective oxidation catalysis in synthetic phospholipid vesicles. Membrane-spanning steroidal metalloporphyrins

John T. Groves, Ronny Neumann

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152 Citations (Scopus)

Abstract

A membrane-spanning porphyrin has been synthesized by attaching four 3β-hydroxy-5-cholenic acid moieties to α,β,α,β-meso-tetrakis(o-aminophenyl)porphyrin. The resulting steroidal porphyrin, H2ChP, and the corresponding metalloporphyrins, MChP, were shown by gel permeation chromatography, 31P NMR, and differential scanning calorimetry to intercalate into vesicle bilayers. The steroidal porphyrin was found to be in a well-defined and highly ordered microenvironment within the bilayer. The anisotropic ESR spectra of CuII(ChP) in orientated bilayer assemblies on Mylar film clearly indicated that the plane of the porphyrin ring was parallel to the plane defined by the bilayer-water interface. The porphyrin ring was also found to be in the middle of the bilayer with fluctuations of ±3-4 Å around the center. This was shown by use of tethered imidazole ligands of the general formula Im(CH2)nCOOH as molecular probes. Ligation to CoII(ChP) could be monitored by ESR as a function of the length of the tethered ligand and conclusively demonstrated that only ligands where n > 6 were able to coordinate to the metal. Iron(III) and manganese(III) steroidal porphyrins were then used as regioselective epoxidation and hydroxylation catalysts. Diolefinic sterols were epoxidized exclusively at the side chain. Epoxidation of polyunsaturated fatty acids was preferred by a ratio of 2/1 at the more hydrophobic terminus and it was found that by increasing the rigidity of the bilayer by the addition of cholesterol the selectivity could be raised to 9/1. Finally, it was shown that cholesterol could be selectively hydroxylated at the C25 tertiary carbon.

Original languageEnglish
Pages (from-to)2900-2909
Number of pages10
JournalJournal of the American Chemical Society
Volume111
Issue number8
Publication statusPublished - 1989

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Metalloporphyrins
Phospholipids
Porphyrins
Catalysis
Membranes
Oxidation
Ligands
Epoxidation
Cholesterol
Paramagnetic resonance
Molecular Probes
Polyunsaturated fatty acids
Differential Scanning Calorimetry
Sterols
Hydroxylation
Unsaturated Fatty Acids
Gel permeation chromatography
Gel Chromatography
Manganese
Ligation

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

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title = "Regioselective oxidation catalysis in synthetic phospholipid vesicles. Membrane-spanning steroidal metalloporphyrins",
abstract = "A membrane-spanning porphyrin has been synthesized by attaching four 3β-hydroxy-5-cholenic acid moieties to α,β,α,β-meso-tetrakis(o-aminophenyl)porphyrin. The resulting steroidal porphyrin, H2ChP, and the corresponding metalloporphyrins, MChP, were shown by gel permeation chromatography, 31P NMR, and differential scanning calorimetry to intercalate into vesicle bilayers. The steroidal porphyrin was found to be in a well-defined and highly ordered microenvironment within the bilayer. The anisotropic ESR spectra of CuII(ChP) in orientated bilayer assemblies on Mylar film clearly indicated that the plane of the porphyrin ring was parallel to the plane defined by the bilayer-water interface. The porphyrin ring was also found to be in the middle of the bilayer with fluctuations of ±3-4 {\AA} around the center. This was shown by use of tethered imidazole ligands of the general formula Im(CH2)nCOOH as molecular probes. Ligation to CoII(ChP) could be monitored by ESR as a function of the length of the tethered ligand and conclusively demonstrated that only ligands where n > 6 were able to coordinate to the metal. Iron(III) and manganese(III) steroidal porphyrins were then used as regioselective epoxidation and hydroxylation catalysts. Diolefinic sterols were epoxidized exclusively at the side chain. Epoxidation of polyunsaturated fatty acids was preferred by a ratio of 2/1 at the more hydrophobic terminus and it was found that by increasing the rigidity of the bilayer by the addition of cholesterol the selectivity could be raised to 9/1. Finally, it was shown that cholesterol could be selectively hydroxylated at the C25 tertiary carbon.",
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AU - Groves, John T.

AU - Neumann, Ronny

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N2 - A membrane-spanning porphyrin has been synthesized by attaching four 3β-hydroxy-5-cholenic acid moieties to α,β,α,β-meso-tetrakis(o-aminophenyl)porphyrin. The resulting steroidal porphyrin, H2ChP, and the corresponding metalloporphyrins, MChP, were shown by gel permeation chromatography, 31P NMR, and differential scanning calorimetry to intercalate into vesicle bilayers. The steroidal porphyrin was found to be in a well-defined and highly ordered microenvironment within the bilayer. The anisotropic ESR spectra of CuII(ChP) in orientated bilayer assemblies on Mylar film clearly indicated that the plane of the porphyrin ring was parallel to the plane defined by the bilayer-water interface. The porphyrin ring was also found to be in the middle of the bilayer with fluctuations of ±3-4 Å around the center. This was shown by use of tethered imidazole ligands of the general formula Im(CH2)nCOOH as molecular probes. Ligation to CoII(ChP) could be monitored by ESR as a function of the length of the tethered ligand and conclusively demonstrated that only ligands where n > 6 were able to coordinate to the metal. Iron(III) and manganese(III) steroidal porphyrins were then used as regioselective epoxidation and hydroxylation catalysts. Diolefinic sterols were epoxidized exclusively at the side chain. Epoxidation of polyunsaturated fatty acids was preferred by a ratio of 2/1 at the more hydrophobic terminus and it was found that by increasing the rigidity of the bilayer by the addition of cholesterol the selectivity could be raised to 9/1. Finally, it was shown that cholesterol could be selectively hydroxylated at the C25 tertiary carbon.

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