Ruthenium Complexes Bearing Axially Chiral Bipyridyls: The Mismatched Diastereomer Showed Red Circularly Polarized Phosphorescence

Ruthenium^II complexes bearing three axially chiral bipyridyl ligands were synthesized as a new family of chiral complex dyes, and Δ-(S)- and Λ-(S)-diastereomers were obtained. The X-ray crystal structure analyses, spectroscopy, and DFT calculations suggested that all the bipyridyls maintained chirality in both the ground and excited states, and the Δ-(S)- and Λ-(S)-isomers are the matched (more relaxed) and mismatched (more constrained) pairs, respectively. The mismatched Λ-(S)-isomer exhibited red circularly polarized phosphorescence (CPP) both in solution and in the solid state. The solution state CPP is the most intense of ruthenium complexes, while the solid state CPP is the first example of them. It is supposed that, for the Λ-(S)-isomer, the six cumulative CH/π interactions suppress further distortion in the T₁ state.

Spontaneous Assembly of an Organic-Inorganic Nucleic Acid Z-DNA Double-Helix Structure

Herein, we report a hybrid polyoxometalate organic-inorganic compound, Na₂ [(HGMP)₂ Mo₅ O₁₅ ]⋅7 H₂ O (1; where GMP=guanosine monophosphate), which spontaneously assembles into a structure with dimensions that are strikingly similar to those of the naturally occurring left-handed Z-form of DNA. The helical parameters in the crystal structure of the new compound, such as rise per turn and helical twist per dimer, are nearly identical to this DNA conformation, allowing a close comparison of the two structures. Solution circular dichroism studies show that compound 1 also forms extended secondary structures in solution. Gel electrophoresis studies demonstrate the formation of non-covalent adducts with natural plasmids. Thus we show a route by which simple hybrid inorganic-organic monomers, such as compound 1, can spontaneously assemble into a double helix without the need for a covalently connected linear sequence of nucleic acid base pairs.