Simultaneous measurement of the maximum oscillation amplitude and the transient decay time constant of the QCM reveals stiffness changes of the adlayer

Interpretation of adsorption kinetics measured with a quartz crystal microbalance (QCM) can be difficult for adlayers undergoing modification of their mechanical properties. We have studied the behavior of the oscillation amplitude, A₀, and the decay time constant, , of quartz during adsorption of proteins and cells, by use of a home-made QCM. We are able to measure simultaneously the frequency, f, the dissipation factor, D, the maximum amplitude, A₀, and the transient decay time constant, , every 300 ms in liquid, gaseous, or vacuum environments. This analysis enables adsorption and modification of liquid/mass properties to be distinguished. Moreover the surface coverage and the stiffness of the adlayer can be estimated. These improvements promise to increase the appeal of QCM methodology for any applications measuring intimate contact of a dynamic material with a solid surface.     

Exploring structural effects of levoglucosenone derived chiral auxiliaries in asymmetric Diels-Alder cycloadditions

New chiral auxiliaries derived from levoglucosenone were developed in a simple and efficient way and evaluated as chiral inductors in asymmetric Diels-Alder reactions between the corresponding acrylate derivatives and cyclopentadiene. The results showed an important influence of the absolute configuration of the C(2) center of the auxiliary on the level of stereoinduction obtained.     

Singlet oxygen generation via two-photon excited FRET

A new approach to two-photon excited photodynamic therapy has been developed. A dendritic array of eight donor chromophores capable of two-photon absorption (TPA) was covalently attached to a central porphyrin acceptor. Steady-state fluorescence measurements demonstrated that the donor chromophores transfer excited-state energy to the porphyrin with 97% efficiency. Two-photon excitation of the donor chromophores at 780 nm resulted in a dramatic increase in porphyrin fluorescence relative to a porphyrin model compound. Enhanced singlet oxygen luminescence was observed from oxygen-saturated solutions of the target compound under two-photon excitation conditions.     

Carbo‐biphenyls and Carbo‐terphenyls: Oligo(phenylene ethynylene) Ring Carbo‐mers

Ring carbo‐mers of oligo(phenylene ethynylene)s (OPEn, n=0–2), made of C₂‐catenated C₁₈ carbo‐benzene rings, have been synthesized and characterized by NMR and UV‐vis spectroscopy, crystallography and voltammetry. Analyses of crystal and DFT‐optimized structures show that the C₁₈ rings preserve their individual aromatic character according to structural and magnetic criteria (NICS indices). Carbo‐terphenyls (n=2) are reversibly reduced at ca. ?0.42 V/SCE, i.e. 0.41 V more readily than the corresponding carbo‐benzene (?0.83 V/SCE), thus revealing efficient inter‐ring π‐conjugation. An accurate linear fit of E_1/2^red1 vs. the DFT LUMO energy suggests a notably higher value (?0.30 V/SCE) for a carbo‐quaterphenyl congener (n=3). Increase with n of the effective π‐conjugation is also evidenced by a red shift of two of the three main visible light absorption bands, all being assigned to TDDFT‐calculated excited states, one of them restricting to a HOMO→LUMO main one‐electron transition.     

Determination of methylmercury in natural waters by headspace gas chromatography with microwave-induced plasma detection after preconcentration on a resin containing dithiocarbamate groups

A method for the determination of methylmercury at ng l^?1 levels in natural waters is described. Methylmercury present in a sample is first preconcentrated on a column of a resin containing dithiocarbamate groups and eluted quantitatively with acidic thiourea solution. Methylmercury in the effluent is then converted to the iodide by addition of sulphuric acid and iodoacetic acid and determined by headspace gas chromatography with microwave-induced plasma detection. The adsorption properties of the resin are discussed.     

Syntheses of β‐C(1→3)‐Glucopyranosides of 2‐ and 4‐Deoxy‐D‐hexoses

The Oshima? Nozaki (Et₂AlI) condensation of isolevoglucosenone ( 4 ) with 2,6‐anhydro‐3,4,5,7‐tetra‐O‐benzyl‐D ‐glycero‐D ‐gulo‐heptose ( 5 ) gave an enone 6 that was converted with high stereoselectivity to 3‐C‐[(1R)‐2,6‐anhydro‐D ‐glycero‐D ‐gulo‐heptitol‐1‐C‐yl]‐2,3‐dideoxy‐D ‐arabino‐hexose ( 1 ; 1 : 1 mixture of α‐ and β‐D ‐pyranose), and to 3‐C‐[(1R)‐2,6‐anhydro‐D ‐glycero‐D ‐gulo‐heptitol‐1‐C‐yl]‐2,3‐dideoxy‐D ‐lyxo‐hexose ( 2 ; 2.7 : 1.4 : 1.0 : 1.4 mixture of α‐D ‐furanose, β‐D ‐furanose, α‐D ‐pyranose, and β‐D ‐pyranose). The Oshima? Nozaki (Et₂AlI) condensation of levoglucosenone ( 17 ) with aldehyde 5 gave an enone 18 that was converted with high stereoselectivity to 3‐C‐[(1R)‐2,6‐anhydro‐D ‐glycero‐D ‐gulo‐heptitol‐1‐C‐yl]‐3,4‐dideoxy‐α‐D ‐arabino‐hexopyranose ( 3 ; single anomer).     

The new international reference system for pure α- and pure β-emitting radionuclides and some electron capture decaying radionuclides by liquid scintillation counting

Journal of Radioanalytical and Nuclear Chemistry - The Bureau International des Poids et Mesures (BIPM) is developing, with the support of national metrology institutes, an extension to the...     

Modulation of the Sorption Characteristics for an H-bonded porous Architecture by Varying the Chemical Functionalization of the Channel Walls

Five isostructural microporous supramolecular architectures prepared by H-bonded assembly between the hexa-anionic complex [Zr₂(Ox)₇]⁶⁻ (Ox=oxalate, (C₂O₄)²⁻) and tripodal cations (H₃-TripCH₂-R)³⁺ with R=H, CH₃, OH and OBn (Bn=CH₂Ph) are reported. The possibility to obtain the same structure using a mixture of tripodal cations with different R group (R=OH and R=CH₃) has also been successfully explored, providing a unique example of three-component H-bonded porous framework. The resulting SPA-1(R) materials feature 1D pores decorated by R groups, with apparent pore diameters ranging from 3.0 to 8.5 Å. Influence of R groups on the sorption properties of these materials is evidenced through CO₂ and H₂O vapor sorption/desorption experiments, as well as with I₂ capture/release experiments in liquid media. This study is one of the first to demonstrate the possibility of tuning the porosity and exerting precise control over the chemical functionalization of the pores in a given H-bonded structure, without modifying the topology of the reference structure, and thus finely adjusting the sorption characteristics of the material.