meso-Substituted octabromoporphyrins: synthesis, spectroscopy, electrochemistry and electronic structure

Gali, Hariprasad; Dahal, Sanjay; Maiya, Bhaskar G.

doi:10.1039/dt9960003429

Cited by 65 publications

(45 citation statements)

References 24 publications

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“…1). Our finding is in agreement with available literature on the effect of ␤-bromination on the E1 ⁄2 of metalloporphyrins (41)(42)(43)(44)(45)(46)(47)). An almost identical increase in E1 ⁄2 (508 mV) was achieved by placing four quaternized ortho-pyridyls in the meso positions of the Mn III T-2-PyP ϩ .…”

Section: Electrostatics Versus Redox Potential In the Catalysis Of Osupporting

confidence: 83%

“…The electron-withdrawing effect of the ␤-pyrrolic bromines on the redox properties of the metal center of the porphyrins (50 -70 mV/bromine) has been previously established (41)(42)(43)(44)(45)(46)(47). The effect of eight ␤-pyrrolic bromines was expected to be similar in magnitude to the effect of the four quaternized pyridyl nitrogens on the redox properties of the starting unsubstituted Mn III T-2-PyP ϩ porphyrin molecule.…”

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confidence: 88%

“…Thus it was possible to determine the halfwave potentials, E1 ⁄2 , given in Table I. The two compounds have almost identical Mn II /Mn III metal-centered E1 ⁄2 values at pH 7.8, as predicted from the number and the nature of the electron-withdrawing substituents on the meso positions of the porphyrin ring (41)(42)(43)(44)(45)(46)(47). Moreover, their voltammetric behavior in terms of electrochemical reversibility (peak-to-peak potential separation, ⌬E pp ( Fig.…”

Section: Electrochemistrymentioning

confidence: 99%

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Electrostatic Contribution in the Catalysis of O 2·_Dismutation by Superoxide Dismutase Mimics

Spasojević

Batinić‐Haberle

Rebouças

et al. 2003

Journal of Biological Chemistry

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The Mn(III) meso-tetrakis(N-ethylpyridinium-2-yl)-porphyrin (Mn III TE-2-PyP 5؉ ) is a potent superoxide dismutase (SOD) mimic in vitro and was beneficial in rodent models of oxidative stress pathologies. Its high activity has been ascribed to both the favorable redox potential of its metal center and to the electrostatic facilitation assured by the four positive charges encircling the metal center. (ϩ890 mV versus NHE). Thus it allows equal driving force (hence k ox ϭ k red ϭ ϳ2 ϫ 10 9 M Ϫ1 s Ϫ1 ) for both half-reactions of the catalytic cycles (Reactions 1 and 2) (18 -20). For Escherichia coli Fe-SOD,the E1 ⁄2 is ϩ223 mV versus NHE at pH 7.4, and for Mn-SOD from the Bacillus stearothermophilus and E. coli the E1 ⁄2 were ϩ260 and ϩ310 mV versus NHE at pH 7 (1, 21, 22). However, when manganese was replaced by iron in the active site of Mn-SOD the enzymatic activity was lost (18), which has been attributed to the decrease of the redox potential below that required for the oxidation of superoxide ion (3, 18). Such metal ion specificity (2) has been recently explained by the higher affinity of Fe 3ϩ than Mn 3ϩ for hydroxide (6, 8).The crystal structures of different SODs reveal a highly conserved electrostatic "funnel" (13,14,16) that is believed to guide the negatively charged superoxide toward the active site of the enzyme. In the past there have been considerable efforts to evaluate the extent of electrostatic facilitation, but a major difficulty lies in the inability to specifically modify the positively charged residues without affecting the structural integrity of the active site (9).The Mn(III) porphyrin, Mn III TE-2-PyP 5ϩ (AEOL-10113) has been shown (23-27) to possess high SOD-like activity in vitro * This work was supported in part by Grant BA1-0103-1 from the Christopher Reeve Paralysis Foundation and by Aeolus/Incara Pharmaceuticals, Research Triangle Park, NC. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.§ To whom correspondence should be addressed. 1 The abbreviations used are: NHE, normal hydrogen electrode; SOD, superoxide dismutase; meso, refers to the substituents at the 5, 10, 15, and 20 (meso carbon) position of the porphyrin core; ␤, refers to the substituents at ␤-pyrrolic carbons; Mn III T-2-PyP ϩ , Mn(III) 5,10,-15,20-tetrakis(2-pyridyl)porphyrin; Mn III TE-2-PyP 5ϩ (Mn-2E 5ϩ ) (AEOL-10113), manganese(III) 5,10,15,20-tetrakis(N-ethylpyridinium-2-yl)porphyrin; Mn III TM-2(3,4)-PyP 5ϩ (Mn-2(3,4)M 5ϩ ), manganese(III) 5,10,15,20-tetrakis(N-methylpyridinium-2(3,4)-yl)porphyrin, where 2 (AEOL-10112), 3, and 4 refer to ortho, meta, and para isomers, respectively; Mn III Br 8 T-2-PyP ϩ (Mn-Br 8 ϩ ), Mn(III) 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(2-pyridyl)porphyrin; Mn II Br 8 TM-4-PyP 4ϩ , Mn(II) 2,3,7,8,12,13,17,10,15,porphyrin; Mn II Cl 5 TE-2-PyP 4ϩ , Mn(II) ␤-pentachloro-5,10,15,20-tetrakis(N-ethylpyridi...

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Section: Electrostatics Versus Redox Potential In the Catalysis Of Osupporting

confidence: 83%

mentioning

confidence: 88%

Section: Electrochemistrymentioning

confidence: 99%

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Electrostatic Contribution in the Catalysis of O 2·_Dismutation by Superoxide Dismutase Mimics

Spasojević

Batinić‐Haberle

Rebouças

et al. 2003

Journal of Biological Chemistry

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“…Introducing ␤-electron-withdrawing substituents and modifying meso substituents of water soluble porphyrins can have a major impact on the redox and electrostatic properties of manganese porphyrins (1)(2)(3)(4)(5)(6)(7). Such substitution allows the redox potential to approach the potential of SOD itself, E1 ⁄2 ϳ ϩ0.…”

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confidence: 99%

The Ortho Effect Makes Manganese(III)Meso-Tetrakis(N-Methylpyridinium-2-yl)Porphyrin a Powerful and Potentially Useful Superoxide Dismutase Mimic

Batinić‐Haberle¹,

Benov²,

Spasojević³

et al. 1998

Journal of Biological Chemistry

254

300

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The ortho, meta, and para isomers of manganese(III) 5,10,15,20-tetrakis(N-methylpyridyl)porphyrin, MnTM-2-PyP 5؉ , MnTM-3-PyP 5؉, and MnTM-4-PyP 5؉ , respectively, were analyzed in terms of their superoxide dismutase (SOD) activity in vitro and in vivo. The impact of their interaction with DNA and RNA on the SOD activity in vivo and in vitro has also been analyzed. Differences in their behavior are due to the combined steric and electrostatic factors. In vitro catalytic activities are closely related to their redox potentials. The half-wave potentials (E1 ⁄2 ) are ؉0.220 mV, ؉0.052 mV, and ؉0.060 V versus normal hydrogen electrode, whereas the rates of dismutation (k cat ) are 6.0 ؋ 10 7 , 4.1 ؋ 10 6 , and 3.8 ؋ 10 6 M ؊1 s ؊1 for the ortho, meta, and para isomers, respectively. However, the in vitro activity is not a sufficient predictor of in vivo efficacy. The ortho and meta isomers, although of significantly different in vitro SOD activities, have fairly close in vivo SOD efficacy due to their similarly weak interactions with DNA. In contrast, due to a higher degree of interaction with DNA, the para isomer inhibited growth of SOD-deficient Escherichia coli.Due to their high stability and chemical versatility, manganese porphyrins are a promising group of compounds for development as SOD 1 mimics. Introducing ␤-electron-withdrawing substituents and modifying meso substituents of water soluble porphyrins can have a major impact on the redox and electrostatic properties of manganese porphyrins (1-7). Such substitution allows the redox potential to approach the potential of SOD itself, E1 ⁄2 ϳ ϩ0.26 V (8). This is approximately midway between the redox potentials of the two half-reactions of the dismutation process (9, 10). While maintaining the redox potential at a value close to that of SOD, it is important to also ensure electrostatic facilitation. We have already shown that ␤-bromination (11, 12) of the manganese(III) 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (13) and of manganese(III) 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin increases their SOD-like activities (13).2 However, the large positive redox potential of the former, E1 ⁄2 ϭ ϩ0.480 mV versus NHE, (13) stabilizes manganese in its 2ϩ state and diminishes stability, and the latter compound had only modest activity, probably due to lack of electrostatic facilitation (13).It has been shown that ortho substitution on the meso phenyl ring exhibits an ortho effect that is as strong as if the same substituent were placed directly on the meso position (14). Thus, meso-tetrakis(2-methylphenyl)porphyrin behaves similar to the meso tetramethylporphyrin (14). The same was found for other porphyrins in which meso phenyl groups have different ortho substituents, as well as when meso groups are ortho pyridyls, such as 5,10,15,20-tetrakis-(N-methylpyridinium-2-yl) (H 2 TM-2-PyP 4ϩ ) and its zinc complex, ZnTMP-2-PyP 4ϩ (15)(16)(17)(18)(19). Such a profound impact on the properties of the ortho isomers, known as the ortho effect, is due to the combi...

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“…Intensive fundamental and applied researches in this direction are conducted in many countries. [3,6,[9][10][11][12][13][14][15][16] As in the case of chemical heterogeneous catalysis, main effects of electrocatalysis are associated with the adsorption interaction between substrate and active site, which determines the initial structure of the activated complex and the nature of the activation energy of the considered process. And, electrocatalytic processes are implemented at the phase boundary since those accompany the heterogeneous electron transfer between the conducting phase and the reactant being located at the interface with electrolyte.…”

Section: Introductionmentioning

confidence: 99%

Influence of Molecular Isomerism of Monopyridylporphyrin on Electrochemical and Electrocatalytic Properties in Alkaline Solution

Minh¹,

Berezina²,

Базанов³

et al. 2014

MHC

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The comparative investigation of the electrochemical reduction of a number of pyridylporphyrin derivatives with alkyl substituents and their cobalt(II) complexes in 0.1 M KOH is carried out by cyclic voltammetry (CV). The influence of isomerism of the porphyrin molecule and the nature of metal on the oxidative capacity of the tetrapyrrole macrocycle and on the electrocatalytic activity of compounds studied for the oxygen electroreduction reaction is established.

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meso-Substituted octabromoporphyrins: synthesis, spectroscopy, electrochemistry and electronic structure

Cited by 65 publications

References 24 publications

Electrostatic Contribution in the Catalysis of O 2·_Dismutation by Superoxide Dismutase Mimics

Electrostatic Contribution in the Catalysis of O 2·_Dismutation by Superoxide Dismutase Mimics

The Ortho Effect Makes Manganese(III)Meso-Tetrakis(N-Methylpyridinium-2-yl)Porphyrin a Powerful and Potentially Useful Superoxide Dismutase Mimic

Influence of Molecular Isomerism of Monopyridylporphyrin on Electrochemical and Electrocatalytic Properties in Alkaline Solution

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