Modeling the OEC with Two New Biomimetic Models: Preparations, Structural Characterization, and Water Photolysis Studies of a Ba–Mn Box Type Complex and a Mn4N6 Planar-Diamond Cluster

Abstract

The oxygen-evolving complex (OEC) is the native enzyme that catalyzes the oxidation of water in natural photosynthesis. Two new classes of manganese cluster complexes of formula Ba2Mn2L12(H3L1)2(CH3OH)4 1 and Mn4L26Cl2 2 were prepared (H4L1 = N,N′-(ethane-1,2-diyl)bis(2-hydroxybenzamide); L2 = methyl picolinimidate) and characterized by standard techniques including microanalysis, IR spectroscopy, ESI spectrometry, and magnetic susceptibility measurements. X-ray diffraction studies of these complexes revealed (i) a box-type structure for 1 formed by two redox-active manganese(III) ions and two barium(II) ions connected by two bridging bisamido-bisphenoxy ligand molecules; and (ii) a planar-diamond array for Mn4N6 cluster 2 where the picolinimidates act as chelating ligands through the two nitrogen atoms. The ability of 1 and 2 to split water has been studied by means of water photolysis experiments. In these experiments, the oxygen evolution was measured in aqueous media in the presence of p-benzoquinone (acting as the hydrogen acceptor), the reduction of which was followed by UV-spectroscopy. The relevant photolytic activity found for 1 is in contrast to the inactivity of 2 in the photolytic experiments. This different behavior is discussed on the basis of the structure of the biomimetic models and the proposed reaction mechanism for this process supported by DFT calculations.

Investigation on the photoinduced chemical reaction between p-benzoquinone and tryptophan in homogeneous solution

“…6 p-Benzoquinone (PBQ, Fig. 1) is a kind of representative bioquinone, which plays a significant role in biochemical reactions of biological photosynthesis, 11,12 and oxidative phosphorylation 13 and as an electron acceptor in mitochondria. 14 As one type of phenolic metabolite, PBQ has been proposed to initiate leukemic chromosomal translocations by acting as a topoisomerase II poison in humans.…”

Electrochemical Conversion of the Lignin Model Veratryl Alcohol to Veratryl Aldehyde Using Manganese(III)-Schiff Base Homogeneous Catalysts

“…We previously reported several homogeneous catalysts for the oxidation of lignin model compounds and these systems were inspired by examples of efficient catalyst systems capable of performing transformations that are already found in nature [17][18][19][20]. Manganese(III) Schiff base complexes have long been known to be effective catalysts for the oxygenation of both saturated and unsaturated hydrocarbons [21,22].…”