Rotational isomers of N-alkylpyridylporphyrins and their metal complexes. HPLC separation, (1)H NMR and X-ray structural characterization, electrochemistry, and catalysis of O(2)(.-) disproportionation.
Rotational (atropo-) isomers of Mn(III) meso-tetrakis(N-alkylpyridinium-2-yl)porphyrins and corresponding metal-free porphyrin ligands (where alkyl is methyl, ethyl, n-butyl, n-hexyl) and Zn(II) meso-tetrakis(N-methyl(ethyl,n-hexyl)pyridinium-2-yl)porphyrins were separated and isolated by reverse-phase HPLC. The identity of the rotational isomers of metal-free meso-tetrakis(N-methylpyridinium-2-yl)porphyrin was established by (1)H NMR spectra and by the crystal structure of the fastest eluting fraction (R(f) = 7.7%, R(w) = 9.2%, P2(1)/c, Z = 8, a = 14.2846(15) A, b = 22.2158(24) A, c = 29.369(3) A, beta = 95.374(2) degrees ) which, in accordance with (1)H NMR interpretation, proved to be the alphabetaalphabeta isomer. This result, together with elution intensity patterns, was used to identify the fractions of other Mn(III)-porphyrins, Zn(II)-porphyrins, and corresponding metal-free ligands in the series. All of the atropoisomers were inert toward isomerization which was not observable for 30 days at room temperature and reached only 50% in 16 days at 90 degrees C in the case of the Mn(III)-ethyl analogue. However, a complete freeze-dry removal of the mobile phase from the HPLC fractions caused an almost 100% isomerization. The Mn(III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin, as a mixture of atropoisomers (AEOL-10113), has been shown to offer protection in oxidative stress injury ascribed to its high reactivity toward superoxide (k(cat) = 5.8 x 10(7) M(-1) s(-1)) as a consequence of its favorable redox potential (E(1/2) = +228 mV vs NHE). In this work, the atropoisomers were found to have similar redox potentials ranging from +240 to +220 mV, to be similarly potent catalysts of O(2)(.-) disproportionation (dismutation), with k(cat) ranging from 5.5 x 10(7) to 6.8 x 10(7) M(-1) s(-1), and not to preferentially bind to biological tissue.
Spasojević
Ivan
I
Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA. ivan@chem.duke.edu
Menzeleev
Ramil
R
White
Peter S
PS
Fridovich
Irwin
I
D000818:Animals; D001921:Brain / Q000378:metabolism; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D018360:Crystallography, X-Ray; D003574:Cytochrome c Group / Q000378:metabolism; D004563:Electrochemistry; D016166:Free Radical Scavengers / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008670:Metals / Q000737:chemistry*; D051379:Mice; D010100:Oxygen / Q000737:chemistry*; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D013482:Superoxide Dismutase / Q000378:metabolism; D014969:Xanthine Oxidase / Q000737:chemistry
D003574:Cytochrome c Group; D016166:Free Radical Scavengers; D008670:Metals; D011166:Porphyrins; D013482:Superoxide Dismutase; D014969:Xanthine Oxidase; D010100:Oxygen