Ru- and Ir-complex decorated periodic mesoporous organosilicas as sensitizers for artificial photosynthesis

A versatile and facile strategy based on an inverse electron demand Diels-Alder reaction between 5-norbornen-2-yltriethoxysilane and a tetrazine derivative has been established for the synthesis of a new triethoxysilane precursor containing dipyridylpyridazine units. Such a precursor has been incorporated into the mesostructure of an ethylene-bridged periodic mesoporous organosilica (PMO) material through a one-pot synthesis via a co-condensation method. Upon attachment of Ru- and Ir-complexes to the pendant N-chelating heterocyclic ligands, the resulting decorated PMOs have acted as photosensitizers in artificial photosynthetic systems. The deposition of Pt on these PMOs has allowed us to obtain efficient photocatalytic materials for the hydrogen evolution reaction as a result of electron transfer from the light harvesting Ru- and Ir-complexes to the supported Pt nanoparticles through methyl viologen as an electron relay. They have exhibited total turnover number values of 573 and 846, respectively, under visible light irradiation. The role played by each component and the stability of the photocatalytic systems have been discussed. The present approach paves the way to the synthesis of different materials with coordination sites capable of forming surface complexes to be applied as sensitizers and catalysts.

Bioorthogonal tetrazine-mediated transfer reactions facilitate reaction turnover in nucleic acid-templated detection of microRNA

Tetrazine ligations have proven to be a powerful bioorthogonal technique for the detection of many labeled biomolecules, but the ligating nature of these reactions can limit reaction turnover in templated chemistry. We have developed a transfer reaction between 7-azabenzonorbornadiene derivatives and fluorogenic tetrazines that facilitates turnover amplification of the fluorogenic response in nucleic acid-templated reactions. Fluorogenic tetrazine-mediated transfer (TMT) reaction probes can be used to detect DNA and microRNA (miRNA) templates to 0.5 and 5 pM concentrations, respectively. The endogenous oncogenic miRNA target mir-21 could be detected in crude cell lysates and detected by imaging in live cells. Remarkably, the technique is also able to differentiate between miRNA templates bearing a single mismatch with high signal to background. We imagine that TMT reactions could find wide application for amplified fluorescent detection of clinically relevant nucleic acid templates.

Inverse electron demand Diels-Alder (iEDDA) functionalisation of macroporous poly(dicyclopentadiene) foams

Inverse electron demand Diels-Alder reactions performed on the double bonds in open cellular macroporous poly(dicyclopentadiene) monoliths yield a high degree of functionalisation (up to 2 mmol pyridazines per g or 8 mmol N per g) with grafted di(pyridyl)pyridazines in a single step.

Substituted pyridazines as ligands in homoleptic (fac and mer) and heteroleptic Ru(II) complexes

This article reports the preparation of a range of phenyl, pyridyl and pyrazinyl substituted pyridazines via the inverse electron demand [2 + 4] Diels-Alder reaction between 3,6-di(2-pyridyl)-1,2,4,5-tetrazines (bptz) and 3,6-di(2-pyrazinyl)-1,2,4,5-tetrazines (bpztz) and suitable dienophiles including acenaphthalene. The resulting polyaromatic compounds vary systematically in the number of aromatic substituents and the number and position of N-heteroatoms. For four of these compounds, the effect of the molecular changes on the solid-state structures were investigated using single crystal X-ray crystallography. The pyridazines were used as bidentate ligands in {M(II)(bipy)(2)} and tris(homoleptic) complexes (M = Fe, Ru). The optical and electrochemical properties of these complexes reflect the electron accepting character of the new ligands. The facial and meridional isomers of the tris complexes could be separated by column chromatography (on silica), thus allowing a spectral comparison of their absorption and emission properties. The solid-state structures of several of the metal complexes are discussed, including that of the facial isomer of the tris Ru(II) complex of 3,6-bis(2-pyridyl)-4,5-bis(4-pyridyl)pyridazine--a potential preformed geometric motif for the predirected construction of supramolecular assemblies.