Spatially inhomogeneous enhancement of fluorescence by a monolayer of silver nanoparticles

Near-field scanning optical microscopy (NSOM) was applied to study the effect of a two-dimensional array of silver nanoparticles on the spatial distribution and magnitude of fluorescence signal enhancement for a monolayer of Rhodamine 6G (Rh6G). Twenty polyelectrolyte monolayers were deposited between the nanoparticles and the dye by a layer-by-layer deposition technique resulting in a 15-20 nm separation cushion, necessary to minimize the fluorescence signal quenching. The fluorescence signal in NSOM images was found to be distributed inhomogeneously as small (100-200 nm in diameter) fluorescent clusters with typically 5-30 times higher fluorescence intensities than a sample without nanoparticles. The position and relative intensity of the clusters was found to be dependent on the excitation wavelength, suggesting that the enhancement originates from the nanoparticle surface plasmon resonance.     

New “Gabriel” syntheses of amines

The Gabriel synthesis is generalized as monoalkylation of an ammonia or primary amine derivative with subsequent removal of the derivatizing group(s) from nitrogen. Two new derivatives for this purpose are introduced: phenacylsulfonamides and triflamides, with discussion of their generality and effectiveness.     

Restriction De La Cohomologie D’une Variété De Shimura à Ses Sous-variétés

Let G be a connected semisimple group over . Given a maximal compact subgroup K ⊂ G() such that X = G()/K is a Hermitian symmetric domain, and a convenient arithmetic subgroup Γ ⊂ G(), one constructs a (connected) Shimura variety S = S(Γ) = Γ\X. If H ⊂ G is a connected semisimple subgroup such that H() / K is maximal compact, then Y = H()/K is a Hermitian symmetric subdomain of X. For each g ∈ G() one can construct a connected Shimura variety S(H, g) = (H() ∩ g ⁻¹Γg)\Y and a natural holomorphic map j _g : S(H, g) → S induced by the map H() → G(), h → gh. Let us assume that G is anisotropic, which implies that S and S(H, g) are compact. Then, for each positive integer k, the map j _g induces a restriction map

Synthetic approaches to monofluoroalkenes

Monofluoroalkenes are an important fluorinated class of compounds with applications in medicinal chemistry, material sciences and organic chemistry. An overview of methods allowing synthetic access to these fluorinated building blocks is provided. In particular, this critical review, which covers publications up to October 2010, will be divided according to the substitution pattern of the monofluoroalkenes, i.e. di-, tri- or tetra-substituted. Within each group, the various synthetic approaches will be divided according to the reaction type (282 references).     

Importance of using highly pure internal standards for successful liquid chromatography/tandem mass spectrometric bioanalytical assays

Internal standards (IS) with similar physicochemical properties to the analyte provide multiple advantages in liquid chromatography/tandem mass spectrometric (LC/MS/MS) bioanalytical methods such as: reduction of the analysis run time, improvement in the intra‐injection reproducibility, impact reduction of matrix and ionization effects. However, it is important to evaluate the purity of the IS prior to their use. Indeed, a minor impurity in the IS may lead to an important issue during bioanalytical method development. Stable labelled internal standards are usually appropriate IS for bioanalysis. The use of oxycodone‐D3, ursodiol‐D5 and atovaquone‐D4 as internal standards in three different bioanalytical methods was evaluated. During oxycodone, oxymorphone and noroxycodone simultaneous quantification method development, oxymorphone was identified as a contaminant in oxycodone‐D3. Since the limit of quantification for oxymorphone was very low (10 pg/mL), the presence of an even low percentage of oxymorphone in oxycodone‐D3 leads to the change of the stable labelled IS for an analogue, ethylmorphine. 23‐Nordeoxycholic acid was preferred to ursodiol‐D5 as internal standard for the ursodiol, tauroursodiol and glycoursodiol simultaneous quantification method. Indeed, more than 7% of ursodiol was identified in the ursodiol‐D5 which could not be bypassed by decreasing the IS concentration without compromising the linearity. An atovaquone‐D4 reference standard revealed the non‐negligible presence of atovaquone‐D5 to atovaquone‐D8 that has a large impact on the method validation. Therefore, atovaquone‐D4 was sent for recertification since its isotopic purity was found to be much less than the isotopic purity mentioned on its certificate of analysis. Consequently, during bioanalytical method development, the purity of the IS should be scrutinized. Copyright © 2009 John Wiley & Sons, Ltd.     

Acyclic Complexes Related to Noncommutative Symmetric Functions

In this paper, we show how to endow the algebra of noncommutative symmetric functions with a natural structure of cochain complex which strongly relies on the combinatorics of ribbons, and we prove that the corresponding complexes are acyclic.