Synthesis of the floresolide B hydroquinone lactone core using ring-closing metathesis

The hydroquinone lactone core of the floresolides was synthesized through a ring-closing metathesis (RCM) approach. Optimal RCM efficiency was obtained at higher reaction concentration. An unexpected Lewis acid-promoted rearrangement of the hydroquinone and other observations relevant to on-going total synthesis efforts are discussed.     

Supramolecular engineering of intrinsic and extrinsic porosity in covalent organic cages

Control over pore size, shape, and connectivity in synthetic porous materials is important in applications such as separation, storage, and catalysis. Crystalline organic cage molecules can exhibit permanent porosity, but there are few synthetic methods to control the crystal packing and hence the pore connectivity. Typically, porosity is either 'intrinsic' (within the molecules) or 'extrinsic' (between the molecules)--but not both. We report a supramolecular approach to the assembly of porous organic cages which involves bulky directing groups that frustrate the crystal packing. This generates, in a synthetically designed fashion, additional 'extrinsic' porosity between the intrinsically porous cage units. One of the molecular crystals exhibits an apparent Brunauer-Emmett-Teller surface area of 854 m(2) g(-1), which is higher than that of unfunctionalized cages of the same dimensions. Moreover, connectivity between pores, and hence guest uptakes, can be modulated by the introduction of halogen bonding motifs in the cage modules. This suggests a broader approach to the supramolecular engineering of porosity in molecular organic crystals.     

Understanding STM images and EELS spectra of oxides with strongly correlated electrons: a comparison of nickel and uranium oxides

Using a theoretical approach combining the local spin density approximation (LSDA) of density functional theory and the Hubbard U term (LSDA + U), we analyse the connection between the experimentally observed electron energy loss spectra and elevated temperature scanning tunnelling images of surfaces of semiconducting nickel monoxide NiO and uranium dioxide UO2. We show that a combination of electron energy loss spectroscopy, atomic-resolution tunnelling imaging and first-principles ab initio calculations provides a powerful tool for studying electronic and structural properties of surfaces of transition metal and actinide oxides.     

Adsorption von Gasen

Ohne Zusammenfassung     

N@C60-porphyrin: a dyad of two radical centers

Dyads of endohedral nitrogen fullerene and porphyrin have been synthesized. In the two-radical-center dyad, the copper(II) tetraphenylporphyrin suppressed the electron spin resonance (ESR) signal of N@C(60) through intramolecular dipolar coupling with a strength of 27.0 MHz. Demetalation of the metalloporphyrin moiety of the dyad, which effectively turned the two-radical-center dyad into a single-radical-center dyad, recovered 82% of the ESR signal of N@C(60). Such mechanism of switching a spin state on and off could find use in molecular spintronics applications.     

Some explicit badly approximable pairs

I consider the Diophantine approximation problem of sup-norm simultaneous rational approximation with common denominator of a pair of irrational numbers, and compute explicitly some pairs with large approximation constant. One of these pairs is the most badly approximable pair yet computed.