Assembly of strongly phosphorescent hetero-bimetallic and -trimetallic [2]catenane structures based on a coinage metal alkynyl system.

Homo-metallic metal alkynyl complexes exhibit interesting catenane structures, but their hetero-metallic catenane counterparts are under-developed. In this work, we report rare examples of bimetallic Au-Cu (DtbpC[triple bond, length as m-dash]C- ligand; Dtbp = 3,5-di-tert-butylphenyl), Au-Ag ( t BuC[triple bond, length as m-dash]C- ligand), and Au-Cu, Au-Ag (C6-FluoC[triple bond, length as m-dash]C- ligand; C6-Fluo = 9,9-dihexyl-9H-fluoren-2-yl) complexes as well as a trimetallic Au-Ag-Cu (C6-FluoC[triple bond, length as m-dash]C- ligand) complex, which feature [2]catenane structures. The formation of the [2]catenane structure is significantly affected by the coinage metal ion(s) and change of the structure of the alkynyl ligand. These hetero-metallic [2]catenane structures are strongly luminescent with tunable emission λ max from 503 to 595 nm and Φ values up to 0.83.

From Cluster to Polymer: Ligand Cone Angle Controlled Syntheses and Structures of Copper(I) Alkynyl Complexes.

Copper(I) alkynyl complexes have attracted tremendous attention in structural studies, as luminescent materials, and in catalysis, and homoleptic complexes have been reported to form polymers or large clusters. Herein, six unprecedented structures of Cu(I) alkynyl complexes and a procedure to measure the cone angles of alkynyl ligands based on the crystal structures of these complexes are reported. An increase of the alkynyl cone angle in the complexes leads to a modulation of the structures from polymeric [((PhC≡CC≡C)Cu)2 (NH3 )]∞ , to a large cluster [(TripC≡CC≡C)Cu]20 (MeCN)4 , to a relatively small cluster [(TripC≡C)Cu]8 (Trip=2,4,6-iPr3 -C6 H2 ). The complexes exhibit yellow-to-red phosphorescence at ambient temperature in the solid state and the luminescence behavior of the Cu20 cluster is sensitive to acetonitrile.

Identification of "sarsasapogenin-aglyconed" timosaponins as novel Aß-lowering modulators of amyloid precursor protein processing.

The inhibition of amyloid ß (Aß) peptide production is a key approach in the development of therapeutics for the treatment of Alzheimer's disease (AD). We have identified that timosaponins consisting of sarsasapogenin (SSG) as the aglycone can effectively lower the production of Aß peptides and stimulate neurite outgrowth in neuronal cell cultures. Structure-activity relationship studies revealed that the cis-fused AB ring, 3ß-configuration, spiroketal F-ring and 25S-configuration of SSG are the essential structural features responsible for the Aß-lowering effects and neurite-stimulatory activity. New synthetic derivatives that retain the SSG scaffold also exhibited an Aß lowering effect. Treatment of cells with timosaponins led to modulation of amyloid precursor protein (APP) processing through the suppression of ß-cleavage and preferential lowering of the production of the 42-amino acid Aß species (Aß42) without affecting another γ-secretase substrate. The SSG and "SSG-aglyconed" timosaponins also penetrated brain tissue and lowered brain Aß42 levels in mice. Our studies demonstrate that timosaponins represent a unique class of steroidal saponins that may be useful for the development of AD therapeutics.