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Ab initio calculations (HF, MP2, DFT for isolated and PCM for solvated molecules) were performed for cytisine (1) and its model compounds: N-methyl-2-pyridone (2) and piperidine (3). Among three heteroatomic functions (carbonyl oxygen, pyridone and piperidine nitrogens) considered as the possible sites of protonation in 1, surprisingly the carbonyl oxygen takes preferentially the proton in the gas phase whereas in water the piperidine nitrogen is firstly protonated. For model compounds, the piperidine nitrogen in 3 is more basic than the carbonyl oxygen in 2 in both, the gas phase and water.

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The aim of this study was to examine the oxidation of selected plant oils in concentrated beverage emulsions colored with natural β-carotene. Carotenoid preparations obtained from carrots were dissolved in cold-pressed linseed oil, refined canola oil, and refined palm olein. Oxidative stability of the lipids was examined with and without addition of the pigment to the oil/water (O/W) emulsion. Carotenoid/lipid hydro peroxide (LOOH) concentration was evaluated using two different methods: LOOH + Fe2+ reaction connected with a colored complex of ammonium thiocyanate determined with the help of a spectrophotometer, and LOOH determined with the help of a chemiluminometer. It was shown that oxidation rate of lipids in the O/W emulsions strongly depended on chemical composition of the lipid fraction (type of oil used). Presence of the carotenoid pigment increased the rate. Therefore, if a carotenoid-containing emulsion is to be stable, it should be based on oils of a high oxidative stability.