Rendering classical hydrophilic enantiopure Werner salts [M(en)3]n+nX- lipophilic (M/n = Cr/3, Co/3, Rh/3, Ir/3, Pt/4); new chiral hydrogen bond donor catalysts and enantioselectivities as a function of metal and charge.

Known hydrophilic halide salts of the title compounds are converted to new lipophilic BArf- (B(3,5-C6H3(CF3)2)4-) salts. These are isolated as hydrates (Λ- or Δ-[M(en)3]n+nBArf-·zH2O; z = 17-9) and characterized by NMR (acetone-d6) and microanalyses. Thermal stabilities are probed by capillary thermolyses and TGA and DSC measurements (onset of dehydration 71-151 °C). In the presence of tertiary amines, they are effective catalysts for enantioselective Michael type carbon-carbon or carbon-nitrogen bond forming additions of 1,3-dicarbonyl compounds (acceptors: trans-ß-nitrostyrene, di-tert-butylazodicarboxylate, 2-cyclopenten-1-one; average ee = 33%, 52%, 17%). Effects of the metal and charge upon enantioselectivities are analyzed. A number of properties appear to correlate to the NH Brønsted acidity order ([Pt(en)3]4+ > [Cr(en)3]3+ > [Co(en)3]3+ > [Rh(en)3]3+ > [Ir(en)3]3+).

Mechanical properties of DNA origami nanoassemblies are determined by Holliday junction mechanophores.

DNA nanoassemblies have demonstrated wide applications in various fields including nanomaterials, drug delivery and biosensing. In DNA origami, single-stranded DNA template is shaped into desired nanostructure by DNA staples that form Holliday junctions with the template. Limited by current methodologies, however, mechanical properties of DNA origami structures have not been adequately characterized, which hinders further applications of these materials. Using laser tweezers, here, we have described two mechanical properties of DNA nanoassemblies represented by DNA nanotubes, DNA nanopyramids and DNA nanotiles. First, mechanical stability of DNA origami structures is determined by the effective density of Holliday junctions along a particular stress direction. Second, mechanical isomerization observed between two conformations of DNA nanotubes at 10-35 pN has been ascribed to the collective actions of individual Holliday junctions, which are only possible in DNA origami with rotational symmetric arrangements of Holliday junctions, such as those in DNA nanotubes. Our results indicate that Holliday junctions control mechanical behaviors of DNA nanoassemblies. Therefore, they can be considered as 'mechanophores' that sustain mechanical properties of origami nanoassemblies. The mechanical properties observed here provide insights for designing better DNA nanostructures. In addition, the unprecedented mechanical isomerization process brings new strategies for the development of nano-sensors and actuators.