Jacek Kozioł

Characterization of Edible Oils Using Total Luminescence Spectroscopy

Total luminescence spectroscopy was used to characterise and differentiate edible oils and additionally, to control one of the major problems in the oil quality—the effect of thermal and photo-oxidation. We studied several vegetable oils available on the Polish market, including soybean, rapeseed, corn, sunflower, linseed and olive oils. Total luminescence spectroscopy measurements were performed using two different sample geometries: front-face for pure oil samples and right-angle for transparent samples, diluted in n-hexane. All the samples studied as n-hexane solutions exhibit an intense peak, which appears at 320 nm in emission and 290 nm in excitation, attributed to tocopherols. Some of the oils exhibit a second long-wavelength peak, appearing at 670 nm in emission and 405 nm in excitation, belonging to pigments of the chlorophyll group. Additional bands were present in the intermediate range of excitation and emission wavelengths; however, the compounds responsible for this emission were not identified. The front-face spectra for pure oils included chlorophyll peaks for most samples, and some additional peaks in the intermediate range, while the tocopherol peaks were comparatively less intense. The results presented demonstrate the capability of the total luminescence techniques to characterise and differentiate vegetable oil products, and additionally, to characterize the effect of thermal and photo-oxidation on such products. In the photo-oxidation experiments, special attention was paid to possible involvement of singlet oxygen. Experiments were done to monitor the highly specific O2 (1Δg) → O2(3Σ−) singlet oxygen emission at 1270 nm. Thus, total luminescence spectroscopy presents an interesting alternative to time-consuming and expensive techniques such as gas or liquid chromatography, mass spectrometry and other methods requiring wet chemistry steps.

Phototautomerism of 5-deazalumichrome (in the presence of acetic acid)

Abstract The phototautomerism of 5-deazalumichrome was studied in 1,2-dichloroethane in the presence of acetic acid. In comparison with 3-methyllumichrome, 5-deazalumichrome undergoes excited state proton transfer with higher efficiency, manifested by its fluorescence spectrum and lifetimes. The replacement of N-5 by carbon in the pyrazine ring of alloxazine restricts the electron density redistribution involved in the phototautomerism to the region of N-1:C-10a:N-10, and eliminates the competitive contribution of the rest of the conjugated double bond system. Semiempirical calculations confirm the experimental observations.

A new method of isolation of natural flavins using phenoltype resins.

It was shown that riboflavin (as lumiflavin and lumichrome) is sorbed by all resins with free phenolic groups, e.g. phenolsulphonic and phenolcarboxylic ion exchangers or a simple resin of resorcinol and formaldehyde. FMN and FAD, in aqueous solutions, passed through these columns without sorption, but can be retained in salt solutions, especially by a resorcinol resin. Flavins can be eluted from phenol resins by a mixture of water and acetone, propanol or dioxane and saturated aqueous solutions of urea with ethanol or cellosolve. The ability of phenol resins to form complexes with flavins can be used both for analytical and preparative purposes.

Spectral properties of riboflavin tetrabutyrate in the presence of hydrogen-bonding agents

Abstract The electronic spectra of riboflavin tetrabutyrate in solvents of different polarity change in the presence of trifluoroacetic acid and hexafluoroisopropanol as hydrogen-bonding agents. The characteristic red shift of the near-UV maximum, which indicates hydrogen bonding with trifluoroacetic acid, is larger in the absorption than in the excitation spectra suggesting the formation of non-fluorescent species. In the presence of 0.8 M trifluoroacetic acid, weakly fluorescent cationic forms of riboflavin tetrabutyrate are formed in 1,2-dichloroethane and acetonitrile. In the emission spectra a rapid decrease in intensity is observed. In the presence of 0.8 M hexafluoroisopropanol, the changes in the absorption, excitation and emission spectra reach the values observed in aqueous solution, thus indicating its usefulness as a hydrogen-bonding agent in media of low polarity. Plots of the shifts in the absorption and emission intensities vs. the concentration of the hydrogen-bonding agents and Stern-Volmer plots are non-linear in all cases, indicating the complex interaction patterns in the ground and excited states.

Molecular relaxation spectroscopy of lumichrome

Abstract Molecular relaxation spectroscopic experiments on lumichrome compounds dissolved in propylene glycol have resulted in the determination of dipolar relaxation times and the dipole moment difference in the ground and first excited singlet states. As for the closely flavin compounds, this difference was found to be small (approximately 1 D with a slightly dipole moment for the excited singlet). A close examination of the emission spectra obtained on main-band and red-edge excitation revealed that lumichrome can exist in different ground state solvent configurations probably arising from different hydrogen-bonded forms.