Theoretical Analysis of the Mackay Icosahedral Cluster Pd55(PiPr3)12(μ3-CO)20: An Open-Shell 20-Electron Superatom

The electronic structure of the spherical Mackay icosahedral nanosized cluster Pd₅₅(PiPr₃)₁₂(μ₃-CO)₂₀ is analyzed by using DFT calculations. Results reveal that it can be considered as a regular superatom with a “magic” electron count of 20, characterized by a 1S² 1P⁶ 1D¹⁰ 2S² jellium configuration. Its open shell nature is associated with partial occupation of non-jellium, 4d-type, levels located on the interior of the Pd₅₅ kernel. This shows that the superatom model can be used to rationalize the bonding and stability of spherical ligated group 10 clusters, despite their apparent 0-electron count.     

Normal and frictional forces between surfaces bearing polyelectrolyte brushes

Normal and shear forces were measured as a function of surface separation, D, between hydrophobized mica surfaces bearing layers of a hydrophobic-polyelectrolytic diblock copolymer, poly(methyl methacrylate)- block-poly(sodium sulfonated glycidyl methacrylate) copolymer (PMMA- b-PSGMA). The copolymers were attached to each hydrophobized surface by their hydrophobic PMMA moieties with the nonadsorbing polyelectrolytic PSGMA tails extending into the aqueous medium to form a polyelectrolyte brush. Following overnight incubation in 10 (-4) w/v aqueous solution of the copolymer, the strong hydrophobic attraction between the hydrophobized mica surfaces across water was replaced by strongly repulsive normal forces between them. These were attributed to the osmotic repulsion arising from the confined counterions at long-range, together with steric repulsion between the compressed brush layers at shorter range. The corresponding shear forces on sliding the surfaces were extremely low and below our detection limit (+/-20-30 nN), even when compressed down to a volume fraction close to unity. On further compression, very weak shear forces (130 +/- 30 nN) were measured due to the increase in the effective viscous drag experienced by the compressed, sliding layers. At separations corresponding to pressures of a few atmospheres, the shearing motion led to abrupt removal of most of the chains out of the gap, and the surfaces jumped into adhesive contact. The extremely low frictional forces between the charged brushes (prior to their removal) is attributed to the exceptional resistance to mutual interpenetration displayed by the compressed, counterion-swollen brushes, together with the fluidity of the hydration layers surrounding the charged, rubbing polymer segments.     

Controlled thermoreversible transfer of poly(oxazoline) micelles between an ionic liquid and water

Poly(2-nonyl-2-oxazoline-block-2-ethyl-2-oxazoline) block copolymer micelles were investigated as an alternative system to the approach proposed by He and Lodge (Y. He and T. P. Lodge, J. Am. Chem. Soc., 2006, 128, 12666) for the thermoreversible transfer of micelles between a hydrophobic ionic liquid phase and an aqueous phase; this work describes the possibility of thermally triggering and controlling this process.     

Diaroyl(methanato)boron difluoride compounds as medium-sensitive two-photon fluorescent probes

This paper evaluates the use of diaroyl(methanato)boron difluoride compounds for designing efficient fluorescent probes through two-photon absorption. Three different pathways allowing for the syntheses of symmetrical and dissymmetrical molecules are reported. The stable diaroyl(methanato)boron difluoride derivatives can be easily obtained in good yields. They exhibit a large one-photon absorption that is easily tuned in the near-UV range. Their strong fluorescence emission covers the whole visible domain. In addition to these attractive linear properties, several diaroyl(methanato)boron difluoride derivatives possess significant cross sections for two-photon absorption. The derived structure-property relationships are promising for designing new generations of molecules relying on the diaroyl(methanato)boron difluoride backbone.     

Enantioselective palladium-catalyzed addition of malonates to 3,3-difluoropropenes

Monofluoroalkenes bearing a malonate unit at the β position can be synthesized by the enantioselective addition of diesters to 3,3-difluoropropenes. The difference in reactivity regarding the geometry and the substituents of the alkene of the 3,3-difluoropropenes, as well as the alkyl groups of the malonates, was studied and limitations were identified. The reaction was also performed with different 3,3-difluoropropenes. Further synthetic transformations of a newly functionalized monofluoroalkene were also accomplished.     

Chiral [2.2.2] dienes as ligands for Rh(I) in conjugate additions of boronic acids to a wide range of acceptors

[reaction: see text] We document a series of investigations that led to new substituted [2.2.2]-diene ligands which display high selectivity in Rh(I)-catalyzed conjugate addition reactions to substrates not previously examined with diene ligands. Moreover, we disclose an unexpected, interesting effect that results from the introduction of a third C=C onto the ligand scaffold (cf. 1).