Effects of protonation state on a tyrosine-histidine bioinspired redox mediator

Gary F. Moore, Michael Hambourger, Gerdenis Kodis, Weston Michl, John Devens Gust, Thomas A Moore, Ana L Moore

Research output: Contribution to journalArticle

36 Citations (Scopus)

Abstract

The conversion of tyrosine to the corresponding tyrosyl radical in photosytem II (PSII) is an example of proton-coupled electron transfer. Although the tyrosine moiety (Tyrz) is known to function as a redox mediator between the photo-oxidized primary donor (P680"+) and the Mn-containing oxygen-evolving complex, the protonation states involved in the course of the reaction remain an active area of investigation. Herein, we report on the optical, structural, and electrochemical properties of tyrosine- histidine constructs, which model the function of their naturally occurring counterparts in PSII. Electrochemical studies show that the phenoxyl/ phenol couple of the model is chemically reversible and thermodynamically capable of water oxidation. Studies under acidic and basic conditions provide clear evidence that an ionizable proton controls the electrochemical potential of the tyrosine- histidine mimic and that an exogenous base or acid can be used to generate a low-potential or high-potential mediator, respectively. The phenoxyl/phenoxide couple associated with the low-potential mediator is thermodynamically incapable of water oxidation, whereas the relay associated with the high-potential mediator is thermodynamically incapable of reducing an attached photoexcited porphyrin. These studies provide insight regarding the mechanistic role of the tyrosine- histidine complex in water oxidation and strategies for making use of hydrogen bonds to affect the coupling between proton and electron transfer in artificial photosynthetic systems.

Original languageEnglish
Pages (from-to)14450-14457
Number of pages8
JournalJournal of Physical Chemistry B
Volume114
Issue number45
DOIs
Publication statusPublished - Dec 8 2010

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histidine
tyrosine
Protonation
Histidine
Tyrosine
Protons
Oxidation
Water
Electrons
oxidation
Porphyrins
protons
Electrochemical properties
electron transfer
Phenols
Structural properties
water
Hydrogen bonds
Optical properties
relay

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Materials Chemistry
  • Surfaces, Coatings and Films

Cite this

Effects of protonation state on a tyrosine-histidine bioinspired redox mediator. / Moore, Gary F.; Hambourger, Michael; Kodis, Gerdenis; Michl, Weston; Gust, John Devens; Moore, Thomas A; Moore, Ana L.

In: Journal of Physical Chemistry B, Vol. 114, No. 45, 08.12.2010, p. 14450-14457.

Research output: Contribution to journalArticle

Moore, Gary F. ; Hambourger, Michael ; Kodis, Gerdenis ; Michl, Weston ; Gust, John Devens ; Moore, Thomas A ; Moore, Ana L. / Effects of protonation state on a tyrosine-histidine bioinspired redox mediator. In: Journal of Physical Chemistry B. 2010 ; Vol. 114, No. 45. pp. 14450-14457.
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