Impact of defects on the surface chemistry of ZnO(0001 macro)-O

Scanning tunneling microscopy and core level photoelectron spectroscopy measurements have been used to investigate the morphology of ZnO(0001 macro)-O, and its reactivity with carbon monoxide and carbon dioxide, as a function of surface preparation. Real space images of the surface indicate that increasing the substrate anneal temperature during preparation significantly reduces the surface step density. Surface defect concentration is also monitored by employing formic acid as a chemical probe, which is shown to adsorb dissociatively (HCOOH --> [HCOO](-) + H(+)) only on zinc cations at step edges. Carbon 1s X-ray photoelectron spectra show that carbon monoxide and carbon dioxide both react to form surface carbonate species. Spectra, recorded both as a function of surface preparation and following coadsorption, demonstrate that the carbonate formed from either reactant molecule is located at oxygen vacancies at step edges, evidencing the significant role that defects can play in the surface chemistry of ZnO(0001 macro)-O.     

Graschromatographie der Isomeren Pyridin-2- und-4-carbons?ure-n-butylester

Zusammenfassung Die Trennung der Isomere Pyridin-4- und -2-carbonsäure-n-butyl-ester gelingt durch Gaschromatographie an Hochvakuum-Fett Apiezon-L auf Celite C22 bei 230°C.

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Summary Separation of the isomers pyridine-4- and -2-carbonic acid n-butyl ester can be achieved by gas chromatography with a column containing high-cavuum grease Apiezon-L on Celite C22 at 230° C.

     

A comparison among different instrumental approaches for bromide analysis in foodstuffs digested by a suitably modified microwave procedure

Cathodic stripping voltammetry (CSV), ion-chromatography (IC) and spectrophotometry (SP) have been tested as instrumental approaches alternative to inductively coupled plasma mass spectrometry (ICP-MS) for the determination of inorganic bromide residues in foodstuffs fumigated with brominated pesticides and digested by a suitably improved microwave procedure proposed previously. They were chosen in view of the fact that the relevant instrumentation is less expensive than that required for ICP-MS and more frequently available in analytical laboratories designed for routine food control. These approaches were compared with one another, as well as with the ICP-MS method previously adopted, not only with regard to their performance, but also in terms of the interferences caused by the composition of final samples coming from the microwave digestion procedure. The results found pointed out unambiguously that IC turns out to be well suited for replacing ICP-MS, thanks to its consistency with the composition of digested samples and its good sensitivity which allows a quite low detection limit for bromides (0.2 mg kg⁻¹) to be achieved. Conversely, CSV and SP performance appears to be significantly affected by interferences caused by the presence in digested samples of chlorides and ammonium ions, respectively.     

A remark on some degenerate elliptic problems

We prove existence of bounded weak solutions to a quasilinear degenerate elliptic equation in divergence form.

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Sunto Dimostriamo l'esistenza di soluzioni deboli limitate per una equazione ellittica, quasilineare, degenere, in forma di divergenza.

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We acknowledge the support of MURST (60%, 40%) and GNAFA-CNR.     

3-Carboxylate-Substituted Isoindolinones in K2CO3-Catalyzed Michael Reactions

Activated 3-substituted isoindolinones have proved to be efficient nucleophiles in K₂CO₃-catalyzed Michael reactions of several types of electron-deficient olefins. Moreover, tricyclic pyrrolizidines have been conveniently synthesized via a modification of the described general protocol as a consequence of a cascade Michael/cyclization reaction of unsaturated aldehydes.     

A modified electrode for the electrochemical detection of biogenic amines and their amino acid precursors separated by microchip capillary electrophoresis

The use of a mixed-valent ruthenium oxide/hexacyanoruthenate polymeric film electrochemically deposited onto glassy carbon electrodes is proposed here for the detection of biogenic amines and their amino acid precursors, following their separation by microchip capillary electrophoresis. The ability of this ruthenium coating to electrocatalyze the oxidation of aliphatic and heterocyclic amines, as well as their amino acid precursors, was checked by using ethanolamine, tryptamine and tryptophane as prototype compounds and adopting a 25 mM sulphuric acid as the electrolyte in the detection cell, where a constant potential of 1.05 V versus Ag/AgCl, 3 M KCl was applied to the modified working electrode. Optimization of parameters affecting both detection and separation steps led to satisfactory separations when performed by using a 20 mM phosphate running buffer (pH 2.5) and applying a high voltage of 2.5 kV both in the separation and in the electrokinetic injection (duration 4 s). The recorded peaks were characterized by good repeatability (RSD ≤ 3.6%), high sensitivity and a wide linear range. Detection limits of 23 μM (1.4 mg/L), 27 μM (4.3 mg/L) and 34 μM (6.8 mg/L) were inferred for ethanolamine, tryptamine and tryptophane, respectively. The approach proposed here was also applied for the analysis of some double malt dark beers spiked with a controlled amount of the analytes considered.     

Photosystem II fluorescence lifetime imaging in avocado leaves: contributions of the lutein-epoxide and violaxanthin cycles to fluorescence quenching

Lifetime-resolved imaging measurements of chlorophyll a fluorescence were made on leaves of avocado plants to study whether rapidly reversible ΔpH-dependent (transthylakoid H(+) concentration gradient) thermal energy dissipation (qE) and slowly reversible ΔpH-independent fluorescence quenching (qI) are modulated by lutein-epoxide and violaxanthin cycles operating in parallel. Under normal conditions (without inhibitors), analysis of the chlorophyll a fluorescence lifetime data revealed two major lifetime pools (1.5 and 0.5 ns) for photosystem II during the ΔpH build-up under illumination. Formation of the 0.5-ns pool upon illumination was correlated with dark-retention of antheraxanthin and photo-converted lutein in leaves. Interconversion between the 1.5- and 0.5-ns lifetime pools took place during the slow part of the chlorophyll a fluorescence transient: first from 1.5 ns to 0.5 ns in the P-to-S phase, then back from 0.5 ns to 1.5 ns in the S-to-M phase. When linear electron transport and the resulting ΔpH build-up were inhibited by treatment with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), the major fluorescence intensity was due to a 2.2-ns lifetime pool with a minor faster contribution of approximately 0.7 ns. In the presence of DCMU, neither the intensity nor the lifetimes of fluorescence were affected by antheraxanthin and photo-converted lutein. Thus, we conclude that both antheraxanthin and photo-converted lutein are able to enhance ΔpH-dependent qE processes that are associated with the 0.5-ns lifetime pool. However, unlike zeaxanthin, retention of antheraxanthin and photo-converted lutein may not by itself stabilize quenching or cause qI.     

Multipole expansions of the electrostatic molecular potential

Multipole expansions of the electrostatic molecular potential up to the hexadecapole terms are examined for H₂O, NH₃ and C₂H₄NH. A reasonable approximation to get unexpensive first order representations of the electrostatic potential for regions outside the van der Waals volume is found.     

Diagnostic potential of autofluorescence for an assisted intraoperative delineation of glioblastoma resection margins

The intrinsic autofluorescence properties of biological tissues can be affected by the occurrence of histological and biochemical alterations induced by pathological processes. In this study the potential of autofluorescence to distinguish tumor from normal tissues was investigated with the view of a real-time diagnostic application in neurosurgery to delineate glioblastoma resection margins. The autofluorescence properties of nonneoplastic and neoplastic tissues were analyzed on tissue sections and homogenates by means of a microspectrofluorometer, and directly on patients affected by glioblastoma multiforme, during surgery, with a fiber-optic probe. Scan-microspectrofluorometric analysis on tissue sections evidenced a reduction of emission intensity and a broadening of the main emission band, along with a redshift of the peak position, from peritumoral nonneoplastic to neoplastic tissues. Differences in both spectral shape and signal amplitude were found in patients when the glioblastoma lesion autofluorescence was compared with those of cortex and white matter taken as healthy tissues. Both biochemical composition and histological organization contribute to modify the autofluorescence emission of neoplastic, with respect to nonneoplastic, brain tissues. The differences found in the in vivo analysis confirm the prospects for improving the efficacy of tumor resection margin delineation in neurosurgery.