Biomimetic Models of the Photosynthetic Reaction Center Based on Ruthenium−Polypyridine Complexes

Abstract

Mimicking the fundamental processes of the photosynthetic reaction center is a large field of research over the past decade. We present as biomimetic model systems for electron transfer the mono- and heteroleptic ruthenium complexes 2−9 containing differently substituted bipyridazine−glycol ligands. Depending on the number of glycol chains of the complexes 2−9, they are divided into three classes: A (2 branches, 2−4); B (3 branches, 5−6) and C (6 branches, 7−9). UV, fluorescence, single-photon counting, and laser flash photolysis were employed as techniques for photophysical characterization. Redox properties were determined using cyclic voltammetry. Detailed steady-state quenching studies of 2−9 with MV2+, OV2+, and MPVS have shown different supramolecular interactions between sensitizer and acceptor in the case of MV2+. These effects may be explained by π−π donor−acceptor attractions as well as hydrophobic interactions. Supporting molecular modeling studies have been done. The suitability as biomimetic model systems was shown by testing the ruthenium complexes 2−9 in artificial photosynthesis systems. Two typical reactions were selected: the sacrificial reduction of water and the reduction of CO2 to CH4. The use of 2−9 leads to satisfactory hydrogen production from the reduction of water. In the CH4/CO2 system, complexes 7−9 worked efficiently.

Ruthenium Polypyridine Complexes. On the Route to Biomimetic Assemblies as Models for the Photosynthetic Reaction Center

“…Future studies in the field of biomimetic artificial photosynthesis systems should be, as this Account shows, not in the domain of the often beautiful noncovalent assemblies but clearly on the covalently linked systems, which are clearly the superior systems. reaction center 100 ms (∼1) b bacterial photosynthetic 37 10 ns (∼1) a pentad c (Gust, Moore et al) 37 340 µs (0.15) tetrad d (Paddon-Row et al) 38 32 µs (0.23) C60 triad e (Gust, Moore et al) 39 170 ns (0.14) triad f (Sauvage et al) 40 33 ns (-) triad 9 + 16 (Seiler, Dü rr et al) 30,31,34,35 220 µs (∼0.4) diad 8a + 17 28 104 µs (∼0.05) diad 8b + 17 28 187 µs (∼0.05) diad 7 + 18 28 136 µs (∼0.1) [2]Catenane 6 26,27 242 ns (55%) 517 ns (45%) a Recombination of special pair + /bacteriopheophytin -. b Recombination of special pair + /quinone a -.…”

“…Therefore, model compounds of the types 8 and 9 [21][22][23][24][25]28,[30][31][32] were designed to be good models for such studies. A monobranched D-A-diad 7sin analogy to a …”

Structure and Lateral Electron Hopping in Osmium-tris-4,7-diphenylphenanthroline Perchlorate Monolayers at the Air/Water Interface

“…Investigations of electron transport concerned numerous supramolecular chemical systems created to model and reproduce functions of natural photosynthesis. [1][2][3][4][5] Much research in this area has been concerned with the kinetics of long-range electron tunneling. [6][7][8][9][10][11][12][13][14][15][16] Electron transport and related phenomena have also been a focus of substantial electrochemical investigations owing to the significance of these processes in electrocatalysis, in photoelectrochemical, electrochromic, and molecular electronic devices, and in electrochemical sensors.…”

“…Interest in this broad subject stems to a large extent from its relevance to biological electron transport processes. Investigations of electron transport concerned numerous supramolecular chemical systems created to model and reproduce functions of natural photosynthesis. − Much research in this area has been concerned with the kinetics of long-range electron tunneling. − Electron transport and related phenomena have also been a focus of substantial electrochemical investigations owing to the significance of these processes in electrocatalysis, in photoelectrochemical, electrochromic, and molecular electronic devices, and in electrochemical sensors. − Efficient electron transport over micrometer distances in multimolecular, microstructural media encountered in these systems is of crucial importance to their efficiency.…”

Phage Therapy and Photodynamic Therapy: Low Environmental Impact Approaches to Inactivate Microorganisms in Fish Farming Plants

“…Their natural occurrence and the important role in vital processes such as photosynthesis, oxygen transport and storage were responsible for decades of research devoted to the establishment of new and efficient synthetic methodologies to prepare them. New and highly efficient synthetic routes have generated many porphyrin-like compounds with unique characteristics for their uses in several other applications such as oxidative catalysis [ 209 , 210 ] and as biomimetic model systems of the primary processes of photosynthesis [ 211 , 212 ]. Presently, the interest also includes the supramolecular units, namely molecular recognition in chemical receptors and sensors [ 213 – 215 ], as light-harvesting devices [ 216 – 219 ] and as materials for advanced technologies, mainly in nanosciences [ 220 , 221 ].…”