The observation of viscous waves in a He I film

The transverse acoustic impedance of a ⁴He film has been measured at 3.11 K and 20.5 MHz and shows the occurence of standing shear waves in the film. This is in good agreement with calculations using transmission line theory and gives a new method of measuring the thickness of liquid films.     

The transverse acoustic impedance of an inhomogeneous viscous fluid

The transverse acoustic impedance Z of a fluid can be determined from measurements of the complex reflection coefficient of a transverse ultrasonic wave incident on a plane solid/fluid interface. Inhomogeneities in the fluid close to the solid surface may have a significant effect on the measured values of Z. We have derived the Riccati equation which determines Z in an inhomogeneous viscous fluid, using transmission line theory. This equation was integrated numerically to obtain the impedance of viscous films and for inhomogeneities due to healing lengths and van der Waals forces near the solid/fluid interface. The results show that the measurement of both the real and imaginary parts of Z can be a powerful technique for investigating any inhomogeneities which occur on a length scale comparable with the viscous penetration depth in the fluid.     

Validation of different commercially available cholinesterases for pesticide toxicity test

A systematic study of different commercially available cholinesterases (AChEs from electric eel, human erythrocytes, bovine erythrocytes and BuChE from horse serum) for the FIA determination of some frequently used organophosphate (paraoxon, oxydemeton-methyl, triazophos, diazionon) and carbamate (carbofuran, propoxur) pesticides was carried out. Responses of the previously developed photothermal FIA system were found to be dependent on the origin of cholinesterases and properties of tested pesticides. The highest sensitivity was obtained with electric eel AChE and the lowest sensitivity with horse serum BuChE. The LOD values for investigated pesticides correlate with acute toxicities expressed as LD50 (oral, rat). The presented FIA system could serve as an alternative screening test to evaluate the toxicity of different environmental samples, new cholinesterase inhibiting pesticides or other products (e.g. nerve gases).     

Determination of arsenic in seafood by electrothermal atomic absorption spectrometry after microwave digestion: NMKL collaborative study

Eight laboratories participated in an interlaboratory method performance (collaborative) study of a method for the determination of arsenic in foodstuffs of marine origin by electrothermal atomic absorption spectrometry after wet digestion using a microwave oven technique. The study was preceded by a practice round of familiarization samples. The method was tested on 8 materials (cod roe, krill, blue mussel, saithe, scampi, cod fillet, shrimp, and cod extract) ranging in As content from 2 to 75 mg/kg. The materials were sent to participants in the study as blind duplicates, and the participants were asked to perform single determinations on each sample. Repeatability relative standard deviations (RSDr) for As ranged from 6.8 to 17.4%. Reproducibility relative standard deviations (RSDR) ranged from 7.6 to 24%. The highest RSDR value was found for the sample with the highest concentration of As.     

A new flowing afterglow-guided ion beam tandem mass spectrometer. Applications to the thermochemistry of polyiodide ions

A new flowing afterglow-guided ion beam tandem mass spectrometer has been constructed. The tandem mass spectrometer has a linear quadrupole-octopole-quadrupole geometry. The apparatus has been successfully tested for the measurement of reaction rates and endothermic reaction thresholds. The new instrument has been used to determine 0 K bond strengths in two polyiodide ions: D(I₂?I^?)=126±6 kJ/mol and D(I₂?I ₃ ^? )=49±6 kJ/mol. These values compare well to recent computational results. Electron affinity (EA)(I₃)=4.15±0.12 eV can be derived from this work and values in the literature.     

Highly effective electrochemical anion sensing based on oxoporphyrinogen

The effect of anion binding on the oxidation potential of an anion receptor, N₂₁,N₂₃-dibenzyl-5,10,15,20-(3,5-di-t-butyl-4-oxo-cyclohexa-2,5-dienylidene)porphyrinogen, 1 in o-dichlorobenzene is reported. The anion binding site of 1, at its inner pyrrolic amine hydrogens, is an integral part of the highly conjugated macrocycle, thus predicting larger potential shifts upon anion binding. Accordingly, cathodic shifts up to 600 mV are observed upon anion binding and such potential shifts correlate well with the anion binding constants.     

1-Azathioxanthone Appended Lanthanide(III) DO3A Complexes That Luminesce Following Excitation at 405 nm**

Since the pioneering report by Selvin, we have been fascinated by the potential of using lanthanide luminescence in bioimaging. The uniquely narrow emission lines and long luminescence lifetimes both provide the potential for background free images together with full certainty of probe localization. General use of lanthanide based bioimaging was first challenged by low brightness, and later by the need of UV (<405 nm) excitation sources not present in commercial microscopes. Here, we designed three lanthanide-based imaging probes based on a known motif to investigate the limitations of 405 nm excitation. These were synthesized, characterized, investigated on dedicated as well as commercial microscopes, and the photophysics was explored in detail. It was proven without doubt that the lanthanide complexes enter the cells and luminesce internally. Even so, no lanthanide luminescence were recovered on the commercial microscopes. Thus, we returned to the photophysical properties that afforded the conclusion that – despite the advances in light sources and photodetectors – we need new designs that can give us brighter lanthanide complexes before bioimaging with lanthanide luminescence becomes something that is readily done.     

A new mechanism for ozonolysis of unsaturated organics on solids: phosphocholines on NaCl as a model for sea salt particles

The ozonolysis of an approximately one monolayer film of 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (OPPC) on NaCl was followed in real time using diffuse reflection infrared Fourier transform spectrometry (DRIFTS) at 23 degrees C. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry and Auger electron spectroscopy were used to confirm the identification of the products. Ozone concentrations ranged from 1.7 x 10(12) to 7.0 x 10(13) molecules cm(-3) (70 ppb to 2.8 ppm). Upon exposure to O3, there was a loss of C[double bond, length as m-dash]C accompanied by the formation of a strong band at approximately 1110 cm(-1) due to the formation of a stable secondary ozonide (1,2,4-trioxolane, SOZ). The yield of the SOZ was smaller when the reaction was carried out in the presence of water vapor at concentrations corresponding to relative humidities between 2 and 25%. The dependencies of the rate of SOZ formation on the concentrations of ozone and water vapor are consistent with the initial formation of a primary ozonide (1,2,3-trioxolane, POZ) that can react with O3 or H2O in competition with its thermal decomposition to a Criegee intermediate and aldehyde. Estimates were obtained for the rate constants for the POZ thermal decomposition and for its reactions with O3 and H2O, as well as for the initial reaction of O3 with OPPC. The SOZ decomposed upon photolysis in the actinic region generating aldehydes, carboxylic acids and anhydrides. These studies show that the primary ozonide has a sufficiently long lifetime when formed on a solid substrate that direct reactions with O3 and H2O can compete with its thermal decomposition. In dry polluted atmospheres, ozone-alkene reactions may lead in part to the formation of stable secondary ozonides whose chemistry, photochemistry and toxicity should be taken into account in models of such regions.