Chiral tether-mediated stabilization and helix-sense control of complementary metallo-double helices. Issue 1 (1st October 2014) - Horie, Miki
Abstract : Control of the helical sense and stability enhancement of Pt II -linked double helices by interstrand cross-linking using chiral diphosphines and complete homochiral self-sorting is demonstrated. Abstract : A series of novel Pt II -linked double helices were prepared by inter- or intrastrand ligand-exchange reactions of the complementary duplexes composed of chiral or achiral amidine dimer and achiral carboxylic acid dimer strands joined by trans -Pt II –acetylide complexes with PPh3 ligands using chiral and achiral chelating diphosphines. The structure and stability of the Pt II -linked double helices were highly dependent on the diphosphine structures. An interstrand ligand exchange took place with chiral and achiral 1, 3-diphosphine-based ligands, resulting in trans -Pt II -bridged double helices, whose helical structures were quite stable even in dimethyl sulfoxide (DMSO) due to the interstrand cross-link, whereas a 1, 2-diphosphine-based ligand produced non-cross-linked cis -Pt II -linked duplexes, resulting from an intrastrand ligand-exchange that readily dissociated into single strands in DMSO. When enantiopure 1, 3-diphosphine-based ligands were used, the resulting trans -Pt II -bridged double helices adopted a preferred-handed helical sense biased by the chirality of the bridged diphosphines. Interestingly, the interstrand ligand exchange with racemic 1, 3-diphosphine toward an optically-active Pt II -linked duplex, composed of chiral amidine and achiral carboxylic acid strands, was found to proceed in a diastereoselective manner, thus forming complete homochiral trans -Pt II -bridged double helices via a unique chiral self-sorting.