Lieb D, Zahl A, Shubina T, Ivanovic-Burmazovic I (2010)
Publication Type: Journal article, Original article
Publication year: 2010
Original Authors: Lieb D., Zahl A., Shubina T., Ivanović-Burmazović I.
Publisher: American Chemical Society
Book Volume: 132
Pages Range: 7282-7284
Journal Issue: 21
DOI: 10.1021/ja1014585
In this work the rate constants (kex) and the activation parameters (ΔH, ΔS, and ΔV ) for the water exchange process on Mn centers have experimentally been determined using temperature and pressure dependent O NMR techniques. For the investigations the Mn porphyrin complexes [Mn(TPPS)S2] and [Mn (TMpyP)S2] (S = H2O and/or OH) have been selected due to their high solution stability in a wide pH range, enabling the measurements of water exchange in the case of both diaqua and aqua-hydroxo complexes. We have experimentally demonstrated that the water exchange on Mn porphyrins is a fast process (kex ≈ 10 s ) of an Id to I mechanism, strongly influenced by a Jahn-Teller effect and as such almost independent of a porphyrin charge and a trans ligand. This is also supported by our DFT calculations which show only a slight difference in an average Mn-OH2 bond found for a positively charged model porphyrin with protonated pyridine groups (2.446) and for a simple model without any substituents on the porphyrin ring (2.437). The calculated effective charge on the Mn center, which is significantly lower than its formal +3 charge (ca. +1.5 for diaqua; +1.4 for aqua-hydroxo), also contributes to its substitution lability. The herein presented results are discussed in connection to a possible fast exchanging substrate binding site in photosystem II and corresponding inorganic model complexes, as well as in the context of a possible inner-sphere catalytic pathway for superoxide dismutation on Mn centers.
APA:
Lieb, D., Zahl, A., Shubina, T., & Ivanovic-Burmazovic, I. (2010). Water exchange on manganese(III) porphyrins. Mechanistic insights relevant for oxygen evolving complex and superoxide dismutation catalysis. Journal of the American Chemical Society, 132(21), 7282-7284. https://dx.doi.org/10.1021/ja1014585
MLA:
Lieb, Dominik, et al. "Water exchange on manganese(III) porphyrins. Mechanistic insights relevant for oxygen evolving complex and superoxide dismutation catalysis." Journal of the American Chemical Society 132.21 (2010): 7282-7284.
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