Fast directed motion of "fakir" droplets

In this Letter, we report on the motion of water droplets on surfaces decorated with molecular gradients comprising semifluorinated (SF) organosilanes. SF molecular gradients deposited on flat silica substrates facilitate faster motion of water droplets relative to the specimens covered with an analogous hydrocarbon gradient. Further increase in the drop speed is achieved by advancing it along porous substrates coated with the SF wettability gradients. The results of our experiments are in quantitative agreement with a simple scaling theory that describes the faster liquid motion in terms of reduced friction at the liquid/substrate interface.     

Chiral recognition in NMR spectroscopy using crown ethers and their ytterbium(III) complexes

Chiral crown ethers 1 and 5 are useful enantiomeric discriminating agents in ¹H NMR spectroscopy for neutral and protonated primary amines, amino acids, and amino alcohols. The presence of the carboxylic acid groups in 1 and 5 provide sites at which ytterbium(III) can bind. Adding ytterbium(III) nitrate to crown–substrate mixtures in methanol-d₄ causes shifts in the spectra of substrates and often enhances the chiral discrimination in the ¹H NMR spectrum. The enhancement in enantiomeric discrimination that occurs in the presence of ytterbium(III) allows lower concentrations of the crown ether to be used in chiral recognition studies. Several amide derivatives of 1 were prepared and evaluated as chiral NMR discriminating agents, although except for 1e, these were less effective than 1.     

A study of the epoxidation of 6-deoxyhex-5-enopyranosides. 1,5-Dicarbonyl derivatives and novel synthetic routes to D-xylo-hexos-5-ulose and D-lyxo-hexos-5-ulose

The work described deals with the isolation and characterization of epoxides from 6-deoxyhex-5-enopyranosides and preliminary exploration of their synthetic potential. Prolonged epoxidation reaction times led to their hydrolysis in situ and gave novel protected D-hexos-5-ulose derivatives (sugar 1,5-dicarbonyls). Some reactions of the hexos-5-uloses were studied, and in some cases septanoside (seven-membered-ring saccharide) derivatives were isolated. Novel routes to D-xylo-hexos-5-ulose and D-lyxo-hexos-5-ulose, of interest as intermediates in the synthesis and biosynthesis of inositols and aza sugars, are also described. The structures of the epoxides and novel hexos-5-uloses were established by NMR and X-ray crystallographic methods.     

Comparative study of anionic and radical cyclization for the preparation of 1,3-dimethylindans: highly stereoselective preparation of cis-1,3-disubstituted indans via intramolecular carbolithiation

[reaction: see text] The preparation of 1,3-dimethylindans from 4-(2-bromophenyl)-1-pentene (1) and 2-(2-iodo-1-methylethyl)styrene (2) substrates via radical-mediated cyclization and intramolecular carbolithiation has been investigated. Although cyclization of the radical derived from either substrate proceeds with modest selectivity for the cis-isomer, as does cycloisomerization of the aryllithium derived from substrate 1 (cis/trans approximately 2), intramolecular cyclization of the alkyllithium derived from substrate 2 is a highly cis-selective process (cis/trans = 12).     

The complete matter sector in a three-generation compactification

We consider a Calabi-Yau compactification paradigm with three light generations and anR-symmetry. From a special form of the Tian-Yau manifold, we also construct a new three-generation model with markedly different phenomenology. Thecomplete spectrum of all light matter fields is obtained in a universal way and moreover in a physically suitable basis, allowing a straightforward analysis of all their couplings. Here we discuss all the renormalizable Yukawa couplings. This computation can equally well be repeated for all compactification models based on Calabi-Yau complete intersections in products of homogeneous spaces.     

Latent low-coordinate titanium imides supported by a sterically encumbering beta-diketiminate ligand

Addition of an equal molar quantity of R- (R = Me, SiMe3) to complex (Nacnac)Ti=NAr(OTf) (Nacnac- =[ArNC(tBu)]2CH, Ar = 2,6-iPr2C6H3) forms the imido alkyl (Nacnac)Ti=NAr(R), which can be readily protonated to afford [(Nacnac)Ti=NAr(L)]+ (L = THF, Et2O, eta1-C6H5NMe2), or treated with B(C6F5)3 to afford the zwitterion (Nacnac)Ti=NAr(micro-CH3)B(C6F5)3.     

An evaluation of atmospheric pressure ionization techniques for the analysis of N-Methyl carbamate pesticides by liquid chromatography mass spectrometry

Atmospheric pressure ionization (API) techniques are evaluated for the mass spectral analysis of N-methyl carbamate pesticides. Atmospheric pressure chemical ionization (APCI) using a heated nebulizer interface provided both protonated molecules and abundant, characteristic fragment ions. With ion spray (ISP; pneumatically assisted electrospray ionization), which utilizes a milder “ion evaporation” process, primarily protonated molecules were obtained, although fragment ions similar to those observed in APCI could be induced by variation of the API orifice voltage. Product ion spectra of ISP-derived protonated molecules, generated by tandem mass spectrometry using collision-induced dissociation, are also presented. The APCI and ISP spectra of the carbamates are compared to those obtained with a thermospray interface and also to their electron ionization and methane CI spectra obtained with a particle beam interface. For all four interfaces, combined liquid chromatography mass spectrometry methods using conventional (4.6 mm i.d.) columns are described for the separation and detection of pesticide mixtures. These methods are applied to the confirmatory analysis of three representative carbamate pesticides, spiked at the 0.1-ppm level in green peppers. For those carbamates amenable to gas chromatography mass spectrometry, comparative results are presented.     

Intermolecular C-H bond activation promoted by a titanium alkylidyne

The transient titanium alkylidyne complex (PNP)TiCtBu (PNP = N-[2-P(CHMe2)2-4-methylphenyl]2-), prepared from alpha-hydrogen abstraction of the corresponding alkylidene-alkyl species (PNP)Ti=CHtBu(CH2tBu), can readily undergo intermolecular 1,2-addition of C-H bonds of benzene and SiMe4. Synthesis and reactivity, isotopic labeling, kinetics, and theoretical studies strongly favor an alkylidyne pathway and the alpha-H abstraction step to be the rate-determining step.