The influence of iodide ions on the radiative and radiationless decay of the triplet state of aromatic hydrocarbons

An analysis of the influence of I^? ions on radiative and radiationless transitions from the lowest triplet state of aromatic hydrocarbons is presented. The distance dependence in the external heavy atom effects and the dependence of the enhancement of the T₁→S₀ radiative transition on the triplet energy is discussed in terms of perturbation theory.     

Surface-enhanced Raman scattering: a new optical probe in molecular biophysics and biomedicine

Sensitive and detailed molecular structural information plays an increasing role in molecular biophysics and molecular medicine. Therefore, vibrational spectroscopic techniques, such as Raman scattering, which provide high structural information content are of growing interest in biophysical and biomedical research. Raman spectroscopy can be revolutionized when the inelastic scattering process takes place in the very close vicinity of metal nanostructures. Under these conditions, strongly increased Raman signals can be obtained due to resonances between optical fields and the collective oscillations of the free electrons in the metal. This effect of surface-enhanced Raman scattering (SERS) allows us to push vibrational spectroscopy to new limits in detection sensitivity, lateral resolution, and molecular structural selectivity. This opens up exciting perspectives also in molecular biospectroscopy. This article highlights three directions where SERS can offer interesting new capabilities. This includes SERS as a technique for detecting and tracking a single molecule, a SERS-based nanosensor for probing the chemical composition and the pH value in a live cell, and the effect of so-called surface-enhanced Raman optical activity, which provides information on the chiral organization of molecules on surfaces.     

Synthesis of nucleoside-amino acid conjugates containing boranephosphate, boranephosphorothioate and boranephosphoramidate linkages

Conjugates of 3^′-azido-2^′,3^′-dideoxythymidine (AZT) and 2^′,3^′-didehydro-2^′,3^′-dideoxythymidine (D4T) with the hydroxyl group of tyrosine containing boranephosphate and boranephosphorothioate moieties were prepared via the oxathiaphospholane and dithiaphospholane methodology as a mixture of P-diastereomers. Their structures were confirmed by MS analysis and ¹H, ³¹P NMR spectroscopy. It has been shown that the boranephosphorothioate linkage is unstable under acidic conditions. The first nucleoside-alanine conjugates connected through a boranephosphoramidate linkage were also obtained.     

CO Extrusion in Homogeneous Gold Catalysis: Reactivity of Gold Acyl Species Generated through Water Addition to Gold Vinylidenes

Herein, we describe a new gold‐catalyzed decarbonylative indene synthesis. Synergistic σ,π‐activation of diyne substrates leads to gold vinylidene intermediates, which upon addition of water are transformed into gold acyl species, a type of organogold compound hitherto only scarcely reported. The latter are shown to undergo extrusion of CO, an elementary step completely unknown for homogeneous gold catalysis. By tuning the electronic and steric properties of the starting diyne systems, this new reactivity could be exploited for the synthesis of indene derivatives in high yields.     

Mass spectrometry and molecular modeling studies on the inclusion complexes between alendronate and β-cyclodextrin

Complexation of alendronate sodium (AlnNa) with β-cyclodextrin (β-CD) was studied by means of ESI-mass spectrometry. The experimental results show that stable 1:1 inclusion complexes between selected bisphosphonates and β-CD were formed. In addition, complexes with different stoichiometry were observed. DFT/B3LYP calculations were performed to elucidate the different inclusion behavior between alendronate and β-CD. Molecular modeling showed that the inclusion complex of Aln-β-CD where the two phosphonate groups bound to the central carbon atom of bisphosphonate were inserted into the cavity of β-CD from its “top” side was thermodynamically more favorable than when they were inserted from its “bottom” side; the complexation energy was ?74.05 versus ?60.85 kcal/mol. The calculations indicated that the formation of conventional hydrogen bonds was the main factor for non-covalent β-CD:Aln complex formation and stabilization in the gas phase.     

Epoxide hydrolase-catalyzed enantioselective synthesis of chiral 1,2-diols via desymmetrization of meso-epoxides. lzhao@diversa.com

The discovery, from nature, of a diverse set of microbial epoxide hydrolases is reported. The utility of a library of epoxide hydrolases in the synthesis of chiral 1,2-diols via desymmetrization of a wide range of meso-epoxides, including cyclic as well as acyclic alkyl- and aryl-substituted substrates, is demonstrated. The chiral (R,R)-diols were furnished with high ee's and yields. The discovery of the first microbial epoxide hydrolases providing access to complementary (S,S)-diols is also described.     

Validation of the Method of Selected Polychlorinated Biphenyls Determination in Human Milk Samples

A method for determination of trace concentrations of individual PCB congeners in human milk was validated. The analytical procedure included the following steps: acetone : hexane extraction, clean-up of extracts with concentrated sulfuric acid and solid phase extraction (SPE) on Florisil. The identification and quantification of analytes in purified extracts were carried out by high-resolution gas chromatography (HRGC) with electron capture detection (ECD) and/or with low-resolution mass spectrometry (LRMS). Recoveries of 14 PCB congeners from spiked cow milk samples, based on HRGC-ECD were between 87.3 and 93.6%. The precision of analyte determination was established as close to or less than 10%. The detection limits ranged between 0.14 and 0.26 ng/g fat and the quantification limits between 0.57 and 0.86 ng/g fat. The method was linear and characterized by good correlation coefficients (>0.99) for most of the compounds studied. The quality of the method under validation was verified by the analysis of Standard Reference Material (CRM-450) and interlaboratory exercise.