Low energy electron diffraction from Na(110) and Na2O(111) surfaces

Surfaces ofNa(110) are grown, investigated and oxidised to give Na₂O(111) surfaces. LEED spectra are taken for these surfaces and compared with theory to determine the surface composition of sodium oxide: the surface terminates the crystal in an integral number of electrically neutral NaONa sandwiches, with a bulk-like inter layer spacing. The effective Debye temperature for the Na(110) surface was found to be 107 K.     

Study of the oxidative half‐reaction catalyzed by a non‐heme ferrous catalytic center by means of structural and computational methodologies

Deacetoxycephalosporin C synthase (DAOCS) is a mononuclear ferrous enzyme that catalyzes the expansion of the five‐membered thiazolidine ring of the penicillin nucleus into the six‐membered dihydrothiazine ring of the cephalosporins. In the first half‐reaction with dioxygen and 2‐oxoglutarate, a reactive iron–oxygen species is produced that can subsequently react with the penicillin substrate to yield the cephalosporin. We describe quantum mechanical calculations of the first part of the reaction based on the high‐resolution structures of the active site of DAOCS and its complexes with ligands. These studies are aimed at understanding how the reactive species can be produced and contained in the active site of the enzyme. The results demonstrate the priming of the active site by the co‐substrate for oxygen binding and hint to the presence of a stable iron–peroxo intermediate in equilibrium with a more reactive ferryl species and the formation of CO₂ as a leaving group by decarboxylation of 2‐oxoglutarate. A conclusion from these studies is that substitution of CO₂ by the penicillin substrate triggers the oxidation reaction in a booby‐trap‐like mechanism. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

A DFT exploration of the enantioselective rearrangement of cyclohexene oxide to cyclohexenol

In this paper, we present computational results for the (1S,3R,4R)-3-(pyrrolidinyl)-methyl-2-azabicyclo[2.2.1]heptane mediated rearrangement of cyclohexene oxide. The results nicely explain the differences in enantioselectivities between catalytic and stoichiometric mode between different ligands, and provides a rational for the identification of non-stereospecific background reactions as the major cause of decreased enantioselectivity in catalytic reactions for sterically hindered diamines.     

Acrylamide: update on selected research activities conducted by the European food and drink industry

This paper reviews the progress made by the European food and drink industry (CIAA) on acrylamide with regard to analytical methods, mechanisms of formation, and mitigation research in the major food categories. It is an update on the first CIAA review paper, "A Review of Acrylamide: An Industry Perspective on Research, Analysis, Formation and Control." Initial difficulties with the establishment of reliable analytical methods, in most cases, have now been overcome, but challenges remain in terms of the need to develop simple and rapid test methods and certified reference materials. Many trials have been conducted under laboratory and experimental conditions in a variety of foods, and a number of possible measures have been identified to relatively lower the amounts of acrylamide in food. Promising applications were studied in reconstituted potato models by addition of amino acids or use of asparaginase. In bakery wares, predictive models have been established to determine the role of ammonium carbonate and invert sugar in acrylamide formation. Studies in several commercial foods showed that acrylamide is not stable over time in roasted and ground coffee. Some progress in relatively lowering acrylamide in certain food categories has been achieved, but at this stage can only be considered marginal. Any options that are chosen to reduce acrylamide in commercial products must be technologically feasible and must not adversely affect the quality and safety of the final product.     

Antiferroelectric behavior in a liquid crystalline polymer

Electro-optic and polarization reversal measurements were performed on a side-chain polymer exhibiting a chiral smectic phase. Based on the observed electro-optic and current responses, we discuss the possibility of an antiferroelectric structure in the polymer. In order to establish a model for the observed behavior, a detailed comparison with the properties of the low molar mass antiferroelectric substance MHPOBC was made. The birefringence modulation in the chiral smectic polymer, originating from the field-induced antiferroelectric-to-ferroelectric transition, is analyzed for the case of a randomly oriented sample. The result shows that the coincidence of birefringence modulation and polarization current peaks is strong evidence for the existence of antiferroelectric order in the smectic layers. Such coincidence was observed both for MHPOBC and the chiral side-chain polyacrylate.     

Size-dependent carbon monoxide adsorption on neutral gold clusters

We report on experiments probing the reactivity of neutral Au(n) clusters, n = 9-68, with carbon monoxide. The gold clusters are produced in a pulsed laser vaporization cluster source, operated at room temperature (RT) or at liquid-nitrogen temperature (LNT), pass through a low-pressure reaction cell containing CO gas, and are subsequently laser ionized. The reaction probabilities are determined by recording mass abundance spectra with time-of-flight mass spectrometry. The main observations are a strong temperature dependence and a remarkable size dependence. Upon cooling of the cluster source to LNT, the reactivity increases substantially. At LNT, the reaction probabilities for Au(n) with the first CO molecule are about a factor 10 higher than at RT. Moreover, adsorption of two, three, and even four CO molecules is observed, in contrast to RT clusters which at most adsorb one CO molecule. This temperature dependence is related to the lifetime of the cluster-molecule complexes, being much longer for cold clusters. The observed striking size dependence is similar at both temperatures and is discussed in terms of the electronic structure effects.     

Changes in mobile phase ion distribution when combining pressurized flow and electric field

The distribution of ions in a capillary with both pressurized flow and an electric field has been studied. We have earlier reported that the overall concentration of ions increase in a capillary with high electric field and a pressurized flow. Now we describe how the ions are distributed in the capillary both along the capillary length and in the radial direction as a result of the parabolic flow profile. We have combined current measurements with finite element techniques in order to get better understanding of the system. We have found that the concentration of the ions that because of the electric mobility moves towards the flow primarily increases at the beginning of the electric field and close to the capillary wall. In view of the results we have proposed an alterative explanation of earlier published results concerning voltage-induced variation in capacity factors.     

Electron energy loss spectroscopy of liquid glycerol

The inelastic scattering of low energy electrons from liquid glycerol has been studied. For the first time, electron energy loss spectra of liquids are sufficiently well resolved to permit the identification of vibrations corresponding to individual bonds, namely the C–H and O–H stretching vibrations in glycerol. The angular distribution of the specular peak is very broad, indicating the absence of long-range order at the surface of the liquid. The measurement of the loss signals as a function of the primary electron energy suggests a hybrid mechanism of excitation. The excitation mechanism for the O–H vibration has a stronger impact character as compared to the C–H vibration. A negative ion resonance of glycerol is found at a primary energy of 8 eV. The signal intensities measured as a function of the specular angle of the electron beam appear to be influenced by the angular dependence of the dipole and impact scattering cross-section and a possible preferred orientation of the C–H and O–H groups at the surface of the liquid.