Convenient method for the kinetic resolution of β-aminoalcohols

A variety of easily removable protecting groups were tested in the kinetic resolution of N-protected β-aminoalcohols using chiral catalysts derived from N-4′-pyridinyl--methyl proline. The trifluoroacetyl group was the most promising protecting group as it gave the highest selectivities with all alcohols tested and can easily be removed without loss of enantiomeric excess. This strategy constitutes a convenient method for the kinetic resolution of β-aminoalcohols.     

Flux confinement for a class of effective Lagrangians

Confinement properties recently proved in the leading logarithm model are shown to be generally truc for a wide class of effective Lagrangians. These include nonexistence of isolated quarks, confining static potential between \(q\bar q\) pair and flux confinement within a characteristic acting as a free boundary. A new variational principle is formulated.     

Structural and chemical characterization of monofluoro-substituted oligo(phenylene-ethynylene) thiolate self-assembled monolayers on gold

Monolayers of oligo(phenylene-ethynylene) (OPE) molecules have exhibited promise in molecular electronic test structures. This paper discusses films formed from a novel molecule within this class, 2-fluoro-4-phenylethynyl-1-[(4-acetylthio)phenylethynyl]benzene (F-OPE). The conditions of self-assembled monolayer (SAM) formation were systematically altered to fabricate reproducible high-quality molecular monolayers from the acetate-protected F-OPE molecule. Detailed characterization of the F-OPE monolayers was performed by using an array of surface probes, including reflection absorbance infrared spectroscopy (RAIRS), contact angle (CA) measurements, spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and atomic force microscopy (AFM). XPS and RAIRS established that the SAM formed without removal of the F substituent and without oxidation of the thiol. The monolayer thickness, determined from SE and AFM based nanolithography, was consistent with the formation of a densely packed monolayer. The valence electronic structure of the SAM was consistent with an aromatic structure shifted by the electron-withdrawing fluorine substituent and intermolecular coupling within an oriented array of molecules.     

Stereoselective Synthesis of (+)-Peperomin C

The stereoselective synthesis of peperomin C is reported. The key steps include the stereoselective alkylation of the substituted diphenylmethyl group to the r-butyrolactone ring and transformation of the carbonyl group to the other side in the butyrolactone ring by reduction of the lactone carbonyl followed by degradative oxidation.     

Nanometer-scale optical imaging of epitaxially grown GaN and InN islands using apertureless near-field microscopy

Nanometer-scale chemical imaging of epitaxially grown gallium nitride (GaN) and indium nitride (InN) islands is performed using scattering-type apertureless near-field scanning optical microscopy (ANSOM). The scattering of 633 nm laser radiation is modulated by an oscillating metallic probe, and the scattered radiation is detected by homodyne amplification, followed by high-harmonic demodulation, yielding optical near-field scattering maps with a spatial resolution better than 30 nm. The image contrast between InN and GaN, and the tip-sample distance dependence, can be qualitatively explained by a simple dipole-coupling model. The ANSOM images of InN and GaN also show structures that are absent in the topographic counterpart, and these substructures are explained by the variations of the local dielectric environment of InN and GaN.     

Synthesis of diverse macrocyclic peptidomimetics utilizing ring-closing metathesis and solid-phase synthesis

The synthesis of a range of highly functionalized peptidomimetic macrocycles has been accomplished using ring-closing metathesis and enyne tandem cross-metathesis-ring-closing metathesis reactions. This approach gives access to rigidified macrocycles modeled on the structures of cyclic peptides and designed to be biologically stable. The potential for peripheral functionalization of these templates has been demonstrated using Diels-Alder reactions, palladium(0) coupling reactions, and amide formation both in the solution phase and using polymer-supported syntheses.     

Does string theory predict an open universe?

It has been claimed that the string landscape predicts an open universe, with negative curvature. The prediction is a consequence of a large number of metastable string vacua, and the properties of the Coleman–De Luccia instanton which describes vacuum tunneling. We examine the robustness of this claim, which is of particular importance since it seems to be one of string theory's few claims to falsifiability. We find that, due to subleading tunneling processes, the prediction is sensitive to unknown properties of the landscape. Under plausible assumptions, universes like ours are as likely to be closed as open.