A covering lemma for rectangles in

We prove a covering lemma for rectangles in which has connections to a problem of Zygmund and its solution in three dimensions by Cordoba.

     

Co(thd)2: a superior catalyst for aerobic epoxidation and hydroperoxysilylation of unactivated alkenes: application to the synthesis of spiro-1,2,4-trioxanes

Bis(2,2,6,6-tetramethyl-3,5-heptanedionato)cobalt(II) (Co(thd)₂), a β-diketonate prepared in a simple one-step procedure, is an excellent catalyst for aerobic epoxidation and Mukaiyama-Isayama hydroperoxysilylation of unactivated alkenes. For hydroperoxysilylation, Co(thd)₂ is superior to Co(acac)₂ and can catalyse oxidation of cyclic alkenes in excellent yield. Chiral β-diketonate or keto iminato catalysts failed to catalyse this reaction in an enantioselective manner and a free radical mechanism consistent with this observation is proposed. Hydroperoxysilylation of cyclohex-1-enylmethanol by Co(thd)₂ followed by addition of a ketone/TsOH provides a simple one-pot procedure for the synthesis of spiro-1,2,4-trioxane antimalarials.     

Spectral tuning of shortwave-sensitive visual pigments in vertebrates

Of the four classes of vertebrate cone visual pigments, the shortwave-sensitive SWS1 class shows some of the largest shifts in lambda(max), with values ranging in different species from 390-435 nm in the violet region of the spectrum to < 360 nm in the ultraviolet. Phylogenetic evidence indicates that the ancestral pigment most probably had a lambda(max) in the UV and that shifts between violet and UV have occurred many times during evolution. In violet-sensitive (VS) pigments, the Schiff base is protonated whereas in UV-sensitive (UVS) pigments, it is almost certainly unprotonated. The generation of VS pigments in amphibia, birds and mammals from ancestral UVS pigments must involve therefore the stabilization of protonation. Similarly, stabilization must be lost in the evolution of avian UVS pigments from a VS ancestral pigment. The key residues in the opsin protein for these shifts are at sites 86 and 90, both adjacent to the Schiff base and the counterion at Glu113. In this review, the various molecular mechanisms for the UV and violet shifts in the different vertebrate groups are presented and the changes in the opsin protein that are responsible for the spectral shifts are discussed in the context of the structural model of bovine rhodopsin.     

Molecular assembly of rubrene on a metal/metal oxide nanotemplate

We investigated the adsorption properties and self-assembly of rubrene molecules on the copper oxide nanotemplate formed by high-temperature exposure of Cu(110) to molecular oxygen. Using high-resolution scanning tunneling microscopy under ultrahigh-vacuum conditions, we observed a complex variety of self-assembled motifs, driven by competing effects such as the chemical affinity between the organic molecule and the surface, surface coverage, and spatial confinement of the rubrene molecules within the rows of the template.     

Synthesis of (2-chlorophenyl)(phenyl)methanones and 2-(2-chlorophenyl)-1-phenylethanones by Friedel-Crafts acylation of 2-chlorobenzoic acids and 2-(2-chlorophenyl)acetic acids using microwave heating

Several 2-(2-chlorophenyl)-1-phenylethanones and (2-chlorophenyl)(phenyl)methanones were prepared by the Friedel-Crafts acylation reaction of 2-(2-chlorophenyl) acetic acids and 2-chlorocarboxylic acids, respectively, in the presence of cyanuric chloride, pyridine, and AlCl₃ or FeCl₃ using microwave heating. The yields of the ketones were significantly higher than those obtained using conventional heating. In addition, similar reactions carried out with the less inexpensive and less toxic FeCl₃ gave titled ketones in comparable yields. Interestingly, the FeCl₃ catalyzed reactions gave pure ketones (no chromatographic purification required), whereas the AlCl₃ catalyzed reaction gave impure product that required chromatographic purification.     

Reveal E. coli 2.0 method for detection of Escherichia coli O157:H7 in raw beef

Reveal E. coli 2.0 is a new lateral-flow immunodiagnostic test for detection of E. coli O157:H7 and O157:NM in raw beef trim and ground beef. Compared with the original Reveal E. coli O157:H7 assay, the new test utilizes a unique antibody combination resulting in improved test specificity. The device architecture and test procedure have also been modified, and a single enrichment protocol was developed which allows the test to be performed at any point during an enrichment period of 12 to 20 h. Results of inclusivity and exclusivity testing showed that the test is specific for E. coli serotypes O157:H7 and O157:NM, with the exception of two strains of O157:H38 and one strain of O157:H43 which produced positive reactions. In internal and independent laboratory trials comparing the Reveal 2.0 method to the U.S. Department of Agriculture-Food Safety and Inspection Service reference culture procedure for detection of E. coli O157:H7 in 65 and 375 g raw beef trim and ground beef samples, there were no statistically significant differences in method performance with the exception of a single internal trial with 375 g ground beef samples in which the Reveal method produced significantly more positive results. There were no unconfirmed positive results by the Reveal assay, for specificity of 100%. Results of ruggedness testing showed that the Reveal test produces accurate results even with substantial deviation in sample volume or device incubation time or temperature. However, addition of the promoter reagent to the test sample prior to introducing the test device is essential to proper test performance.