Drago Kočar

Degradation of pullulans of narrow molecular weight distribution—the role of aldehydes in the oxidation of polysaccharides

Degradation of pullulan samples of narrow molecular weight distribution was studied in O2 and N2 atmosphere at 180 °C and in air at 80 °C, 65% RH. At higher temperatures, size exclusion chromatographic analyses provided evidence for non-random degradation and formation of cross-links, a phenomenon depending on the concentration of carbonyl groups. Initial degradation rates in oxidative and inert environments were comparable, while at longer reaction times extensive cross-linking was typical of degradation in oxygen. At 80 °C, in a moderately alkaline environment, the degradation remains random, as demonstrated by the mono-modal distributions of molecular weights. Furthermore, there was no evidence of cross-linking. Correlations between the concentration of aldehyde end-groups in the pullulan samples, rates of degradation and the content of peroxides after a pre-oxidation treatment, as determined by the use of chemiluminometry, were demonstrated. This leads to the conclusion that aldehyde groups, via the peroxide intermediates, have the decisive influence on the rates of oxidative degradation of polysaccharides.

Copper Dissolution in Ammonia Solutions: Identification of the Mechanism at Low Overpotentials

Corrosion of copper in ammonia solutions is significantly affected by a large number of parameters such as the concentration of ammonia, pH, temperature, concentration of Cu 2+ , the presence/absence of dissolved oxygen, the chemical nature, and the concentration of the anion but also by selected corrosion products, in particular, Cu + , various adsorbed intermediates, and finally passive films. In the present work we try to elucidate the corrosion of copper in a wide potential window [from ―1.4 to 0 vs mercury/mercurous sulfate electrode (MSE)] and in a broad range of concentrations of various species (0.2-3.5 mol/L NH 3 , 0-0.1 mol/L Cu 2+ , pH 10-12.5). Then, we focus on the first peak occurring within ―1.0 to ―0.6 V vs MSE with the aim to explain the underlying mechanism. We show that the reaction order of the dissolution reaction with respect to ammonia is 2. We further show that using conventional electrochemical methods in combination with an optical method (scanning electron microscopy), a two-step (electrochemical-chemical) reaction yielding Cu 2 O is identified as the most likely passivation mechanism, consistent with previous assumptions by other authors. Finally, we confirm this mechanism by performing impedance analysis at various experimental conditions.

Parallel synthesis of 7-heteroaryl-pyrazolo[1,5-a]pyrimidine-3-carboxamides

A simple and practical four-step protocol for the parallel synthesis of 7-heteroaryl-pyrazolo[1,5-

Evaluation of a method for treatment of iron gall ink corrosion on paper

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Rapid identification of atypical tetracyclines using tandem mass spectrometric fragmentation patterns

a]pyrimidine-3-carboxamides was developed. The synthesis starts with transformation of commercially available 2-acetylpyridine and acetylpyrazine with

Photo-induced degradation of cellulose

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