Interproton coupling over dual vicinal and homoallylic paths in 4-membered rings

A study is presented of cis and trans H? H coupling over dual vicinal (H? C? C? H) and homoallylic/interbenzylic/interbenzylic (H? C? C?C? C? H) paths in the series of molecules cyclobutene and benzocyclobutanes, and a series of dihydrocyclobutacenaphthylenes. Both the experimental and calculated molecular orbital results for these molecules increase in magnitude as the π-bond order of the homoallylic (interbenzylic) path decreases. These trends appear to be consistent only with homoallylic (interbenzylic) coupling contributions of negative sign. At least qualitatively, these trends can be rationalized in terms of the increase in positive contributions associated with the π→π* transitions as the energy denominators decrease in the series.     

Convergent syntheses of [Sn7{C6H3-2,6-(C6H3-2,6-iPr2)2}21: a cluster with a rare pentagonal bipyramidal motif

Two complementary synthetic routes to a pentagonal bipyramidal Sn7 cluster, Sn7Aryl2 (Aryl = terphenyl ligand), are reported.     

Plasma surface modification and characterization of POSS-based nanocomposite polymeric thin films

The effect of a remote oxygen plasma on nanocomposite hybrid polymer thin films of poly[(propylmethacryl-heptaisobutyl-polyhedral oligomeric silsequioxane)-co-(methylmethacrylate)] (POSS-MA) has been examined by advancing contact angle, X-ray photoelectron spectroscopy (XPS), and variable-angle spectroscopic ellipsometry (VASE). Exposure to a 25 W remote oxygen-containing plasma was found to convert the surface of POSS-MA films from hydrophobic to hydrophilic within 20 s. The exposure time needed for this conversion to occur decreased as the O2/N2 ratio in the plasma environment increased, indicating a positive correlation between the hydrophilicity and the presence of oxygen in the plasma. Local bonding information inferred from high-resolution XPS data showed that the isobutyl bonding to the POSS moiety is replaced with oxygen as a result of plasma exposure. Finally, VASE data demonstrates that increasing the weight percent of POSS in the copolymer significantly impedes the oxygen plasma degradation of POSS-MA films. On the basis of these results, a model is presented in which the oxygen plasma removes isobutyl groups from the POSS cages and leaves a SiO2-like surface that is correspondingly more hydrophilic than the surface of the untreated samples and is more resistant to oxidation by the plasma. The ability to modify surfaces in this manner may impact the utility of this material for biomedical applications such as microfluidic devices in which the ability to control surface chemistry is critical.     

Organo-soluble porphyrin mixed monolayer-protected gold nanorods with intercalated fullerenes

Organo-soluble porphyrin mixed monolayer-protected gold nanorods were synthesized and characterized. The resulting gold nanorods encapsulated by both porphyrin thiol and alkyl thiol on their entire surface with strong covalent Au-S linkages were very stable in organic solvents without aggregation or decomposition and exhibited unique optical properties different from their corresponding spherical ones. Alkyl thiol acts as a stabilizer not only to fill up the potential space on gold nanorod surface between bulky porphyrin molecules but also to provide space for further insertion of C(60) molecules forming a stable C(60)-porphyrin-gold nanorod hybrid nanostructure.     

Plasmonic enhancement of the two photon absorption cross section of an organic chromophore using polyelectrolyte-coated gold nanorods

The effect of plasmonic enhancement on the two-photon absorption cross section of organic chromophores attached to polyelectrolyte-coated gold nanorods was investigated. The magnitudes of such enhancements were confirmed using single and two photon excitations of the chromophore molecules bound to polyelectrolyte-coated gold nanorods. By synthesizing two-, four-, six-, and eight-polyelectrolyte layer coated nanorods of a particular aspect ratio, the distance dependence of the evanescent electromagnetic field on molecular two-photon absorption was observed. Enhancements of 40-fold were observed for the chromophores nearest to the surface.     

An efficient catalytic method for the Friedländer annulation mediated by peptide coupling agent propylphosphonic anhydride (T3P®)

We have demonstrated the utilization of T3P, a mild and low toxic peptide coupling agent, as a promoter and water scavenger in the Friedländer annulation, and thus introduced a highly efficient catalytic process to access carbocyclic and heterocyclic fused quinolines under microwave irradiation or a conventional heating technique. The reaction conditions are sufficiently mild to tolerate the acid and base sensitive functional groups that can serve as levers for further extension of the quinoline products.     

Organo-soluble chiral thiol-monolayer-protected gold nanorods

Here, we report the synthesis and characterization of organo-soluble chiral thiol-monolayer-protected gold nanorods. The resulting gold nanorods respectively covered with two opposite enantiomers via the strong covalent Au-S linkage were found to not only be stable in both organic media and solid state, but also show optical activity. Their circular dichroism (CD) spectra exhibited a mirror image relationship, indicating that enantiomeric thiol surfactant on gold surface can produce the corresponding enantiomeric gold nanorods. The densely packed azobenzene thiol monolayer on gold surface exhibited a photoresponsive behavior upon irradiation with 254 nm light instead of 365 nm light, which was found to have an effect on plasmonic absorption of gold nanorods.     

Iodobenzene Dichloride II - An Efficient Reagent for Deoximation

Reaction of Aromatic and Aralkyl ketoximes with iodobenzene dichloride leads to the formation of corresponding ketones in good yields in a single pot reaction.