Photodamage of a Mn(III/IV)-oxo mixed-valence compound and photosystem II: evidence that a high-valent manganese species is responsible for UV-induced photodamage of the oxygen-evolving complex in photosystem II.

The Mn cluster in photosystem II (PS II) is believed to play an important role in the UV photoinhibition of green plants, but the mechanism is still not clear at a molecular level. In this work, the photochemical stability of [Mn(III)(O)(2)Mn(IV)(H(2)O)(2)(Terpy)(2)](NO(3))(3) (Terpy=2,2':6',2''-terpyridine), designated as Mn-oxo mixed-valence dimer, a well characterized functional model of the oxygen-evolving complex in PS II, was examined in aqueous solution by exposing the complex to excess light irradiation at six different wavelengths in the range of 250 to 700 nm. The photodamage of the Mn-oxo mixed-valence dimer was confirmed by the decrease of its oxygen-evolution activity measured in the presence of the chemical oxidant oxone.

[(H2O)(terpy)Mn(mu-O)2Mn(terpy)(OH2)](NO3)3 (terpy = 2,2':6,2''-terpyridine) and its relevance to the oxygen-evolving complex of photosystem II examined through pH dependent cyclic voltammetry.

Photosynthetic water oxidation occurs naturally at a tetranuclear manganese center in the photosystem II protein complex. Synthetically mimicking this tetramanganese center, known as the oxygen-evolving complex (OEC), has been an ongoing challenge of bioinorganic chemistry. Most past efforts have centered on water-oxidation catalysis using chemical oxidants.

Acetylacetonate anchors for robust functionalization of TiO2 nanoparticles with Mn(II)-terpyridine complexes.

A novel class of derivatized acetylacetonate (acac) linkers for robust functionalization of TiO2 nanoparticles (NPs) under aqueous and oxidative conditions is reported. The resulting surface adsorbate anchors are particularly relevant to engineering photocatalytic and photovoltaic devices since they can be applied to attach a broad range of photosensitizers and photocatalytic complexes and are not affected by humidity. Acac is easily modified by CuI-mediated coupling reactions to provide a variety of scaffolds, including substituted terpy complexes (terpy = 2,2':6,2''-terpyridine), assembled with ligands coordinated to transition-metal ions.

Functional Models for the Oxygen-Evolving Complex of Photosystem II.

In the last ten years, a number of advances have been made in the study of the oxygen-evolving complex (OEC) of photosystem II (PSII). Along with this new understanding of the natural system has come rapid advance in chemical models of this system. The advance of PSII model chemistry is seen most strikingly in the area of functional models where the few known systems available when this topic was last reviewed has grown into two families of model systems.

Role of carboxylate bridges in modulating nonheme diiron(II)/O(2) reactivity.

A series of diiron(II) complexes of the dinucleating ligand HPTP (N,N,N',N'-tetrakis(2-pyridylmethyl)-2-hydroxy-1,3-diaminopropane) with one or two supporting carboxylate bridges has been synthesized and characterized. The crystal structure of one member of each subset has been obtained to reveal for subset A a (micro-alkoxo)(micro-carboxylato)diiron(II) center with one five- and one six-coordinate metal ion and for subset B a coordinatively saturated (micro-alkoxo)bis(micro-carboxylato)diiron(II) center. These complexes react with O(2) in second-order processes to form adducts characterized as (micro-1,2-peroxo)diiron(III) complexes.