A recyclable bifunctional acid-base organocatalyst with ionic liquid character. The role of site separation and spatial configuration on different condensation reactions

A series of bifunctional organic catalysts containing acid and basic sites with ionic liquid characteristics have been prepared and their catalytic activity and reaction coordinate for aldol and Knoevenagel condensations have been compared. While the only factor controlling catalyst activity for the Knoevenagel condensation was the distance between the acid and base sites, the spatial orientation of the organocatalyst is also key to achieve high activity and selectivity in the Claisen-Schmidt condensation. Mechanistic studies based on theoretical DFT calculations show that the acid-base bifunctional organocatalyst follows a mechanism inspired in natural aldolases for the synthesis of trans-chalcones, being able to produce a large variety of these compounds of industrial interest. The combination of the acid-base pairs within the proper geometry and the ionic liquid nature makes this catalyst active, selective and recyclable.     

Determination of nanostructure of liposomes containing two model drugs by X‐ray scattering from a synchrotron source

Small‐angle X‐ray scattering has been employed to study how the introduction of paracetamol and acetylsalicylic acid into a liposome bilayer system affects the system's nanostructure. An X‐ray scattering model, developed for multilamellar liposome systems [Pabst et al. (2000), Phys. Rev. E, 62 , 4000–4009], has been used to fit the experimental data and to extract information on how structural parameters, such as the number and thickness of the bilayers of the liposomes, thickness of the water layer in between the bilayers, size and volume of the head and tail groups, are affected by the drugs and their concentration. Even though the experimental data reveal a complicated picture of the drug–bilayer interaction, they clearly show a correlation between nanostructure, drug and concentration in some aspects. The localization of the drugs in the bilayers is discussed.     

Zur reaktion von organophosphinen mit chalkogenen und ithalogenen: Rasche übertragung von tellur und jod zwischen phosphinen

Nucleophilic attack of tertiary phosphines at tellurium in R₃PTe and at iodine in R₃PI⁺ is indicated by rapid Te (or I⁺) transfer reactions in the systems R₃PTe PR₃ and R₃PI⁺/PR₃ (R = (CH₃)₃C, (CH₃)₂N). Linear intermediates of the type R₃PYPR3 (Y = Te, I⁺) are proposed.     

Realization of a near-perfect antireflection coating for silicon solar energy utilization

To harness the full spectrum of solar energy, Fresnel reflection at the surface of a solar cell must be eliminated over the entire solar spectrum and at all angles. Here, we show that a multilayer nanostructure having a graded-index profile, as predicted by theory [J. Opt. Soc. Am. 66, 515 (1976); Appl. Opt. 46, 6533 (2007)], can accomplish a near-perfect transmission of all-color of sunlight. An ultralow total reflectance of 1%-6% has been achieved over a broad spectrum, lambda = 400 to 1600 nm, and a wide range of angles of incidence, theta = 0 degrees-60 degrees . The measured angle- and wavelength-averaged total reflectance of 3.79% is the smallest ever reported in the literature, to our knowledge.