Experimental setup for the determination of analytes contained in ultrasonically levitated drops

An automated technique for the determination of analytes in an ultrasonically levitated sample of 2 to 5 microL volume has been developed. Contactless dosing of reagents or solvents into an ultrasonically levitated drop was realized via piezoelectric micropumps. Drop size was continually controlled with a programmed CCD camera. A diode array spectrometer designed for the use with optical fibers was used for absorption and fluorescence measurements. Determinations via direct absorption measurements following the method of standard addition and acid-base titrations with an absorption indicator and a fluorescent indicator were carried out. The mean consumption of sodium hydroxide added via a piezoelectric micropump in five successive titrations with 18 nmol of sulfuric acid inside a levitated drop (indicator bromothymol blue) had a relative standard deviation of 0.7% and differed only by 0.2% from the expected value.     

Immobilizing a Fluorescent Dye Offers Potential to Investigate the Glass/Resin Interface

Silane coupling agents are commonly applied to glass fibers to promote fiber/resin adhesion and enhance durability in composite parts. In this study, a coupling agent multilayer on glass was doped with trace levels of the dimethylaminonitrostilbene (DMANS) fluorophore. The fluorophore was immobilized on the glass surface by tethering the molecule to a triethoxy silane coupling agent, creating the DMANS/silane coupling agent molecule (DMSCA). DMSCA was then diluted with commonly used coupling agents and grafted to a glass microscope coverslip to create a model composite interface. A 53-nm blue shift in fluorescence from the immobilized DMSCA can be followed during cure of an epoxy resin overlayer, giving this technique potential to monitor the properties of the fiber/resin interface during composite processing. Contact angle measurements on these coupling agent layers were similar in the presence or absence of the DMSCA molecule, suggesting that trace levels of the fluorescent probe did not affect the structure of the layer. The immobilized DMSCA molecule behaved similarly to the DMANS precursor in solution. Both showed longer wavelength fluorescence in more polar environments. Copyright 2000 Academic Press.     

(Z)-3-p-tolylsulfinylacrylonitrile as a chiral dienophile: diels-alder reactions with furan and acyclic dienes

The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles.     

Photothermal deflection measurement of effective gas diffusion coefficient of a porous medium

In this work, an effective gas diffusion coefficient of a porous medium was measured using photothermal deflection (PD) technique. An in-house made Loschmidt diffusion cell with a photothermal-deflection probe were employed to measure the effective gas diffusion coefficient of a gas diffusion layer (GDL) with a porosity ε ≈ 0.7. The concentration evolutions of CO₂ in O₂ with and without the GDL were measured, respectively, using a transverse normal PD technique. The concentration variations were used to deduce the gas diffusion coefficients in the presence and absence of the GDL by solving mass diffusion equations. The effective gas diffusion coefficient of the GDL was calculated from the diffusion coefficients using a model of an equivalent resistance to diffusion and found to be 4.39 × 10^-6 m²s^-1, demonstrating that PD technique can be employed to determine the effective gas diffusion coefficient of a porous medium.     

Solid-Phase Synthesis of a Monofunctional trans-a(2)Pt(II) Complex Tethered to a Single-Stranded Oligonucleotide

Cross-linking ability is possible with the oligonucleotide-tethered, monofunctional trans-Pt(II) complex shown. It was synthesized by a novel solid-phase approach comprising conjugation of immobilized tetrathymidylic acid with a trans-a(2)Pt(II) building unit, ammonolysis, and transformation of the resulting complex (R=1-N-cyclohexylmethylthyminate) into the chloro derivative (R=Cl). a=NH(2)CH(3), T=thymine.