Bogdan Smyk

Spectroscopic investigation of the equilibria of the ionic forms of sinapic acid

The equilibria of the ionic forms of sinapic acid (SA) in Britton-Robinson buffer at pH 1.9–11.5 and 297 K were studied using spectrophotometry and spectrofluorimetry. Three ionic forms of SA were found. Equilibrium constants and pK values were calculated. The absorption and fluorescence spectra for all the ionic forms of SA were determined.

Spectroscopic manifestations of flavomononucleotide dimers in polyvinyl alcohol films.

Absorption and fluorescence spectra of flavomononucleotide (FMN) in polyvinyl alcohol films (PVA) over a very wide concentration range are investigated. The dimerization constant as well as the pure monomer and dimer spectra are calculated and the structural parameters of FMN dimer are established. Excitation wavelength and temperature dependencies of FMN/PVA fluorescence spectra for different FMN concentrations were carried out. These measurements together with those of absorption reveal that dimers are imperfect traps for excitation energy and that the energy transfer can occur both in forward and in reverse direction. Moreover, it was shown that the observed temperature changes in fluorescence spectra may be qualitatively explained by the effect of inhomogeneous broadening of FMN energy levels and by the presence of fluorescent dimers.

Fluorescence Study of Sinapic Acid Interaction with Bovine Serum Albumin and Egg Albumin

The mechanism of interaction of protein with compounds used for preparation of matrices for matrix-assisted laser desorption ionization–mass spectrometry (MALDI-MS) methods is unknown. This paper reports the investigation of this mechanism for sinapic acid and bovine serum albumin and egg albumin. To examine these interactions in water a fluorescence method was applied. Sinapic acid can exist in three different forms, depending on pH: undissociated and with one or two deprotonated groups. pKas of these states are: 4.47 for the COOH group and 9.21 for the OH group [1]. Therefore the interactions were examined at pH: 2.0, 6.4, and 10.5. The results show that sinapic acid at pH 10.5, being a bivalent anion, does not form any complex with these two proteins. At pH 2.0, sinapic acid, being undissociated, interacts weakly with egg albumin. Sinapic acid does not interact with bovine serum albumin at this pH. At pH 6.4, sinapic acid interacts only with bovine serum albumin. Parameters of the sinapic acid and bovine serum albumin complex were calculated based on the theory of multiple equlibria: the total number of binding sites, N = 15; the binding constant, K = 600 M−1; and the Hills coefficient, j = 0.97. These parameters indicate (but not definitively because a large saturation was not obtained) that this is a simple binding of sinapic acid to bovine serum albumin with the binding sites of the same type.

Steady-state and time-resolved fluorescence studies of stripped Borage oil.

In this study we explored the spectroscopic properties of Borage oil, particularly the use of fluorescence techniques to investigate the presence of conjugated fatty acids (CFAs). This research has important health and dietary applications. The absorption and fluorescence spectra of different CFAs and Borage oil in ethanol were measured. Time-domain fluorescence was employed to establish the life times of the samples. We found that Borage oil contains 1.2x10(-3) mol L(-1) of alpha-eleostearic acid or its isomer (i.e., a conjugated triene), 1.6x10(-4) mol L(-1) of cis-parinaric acid (i.e., a conjugated tetraene) and 1.1x10(-5) mol L(-1) of c-COPA (i.e., a conjugated pentaene). Because of the three-exponential fluorescence intensity decay for Borage oil, other fatty acids with a four conjugated double bond system could not be excluded.

Excitation Energy Transport in a Concentrated System of Flavomononucleotide in Polyvinyl Alcohol Films

Excitation energy transport mechanism of flavomononucleotide polyvinyl alcohol films is studied. Excitation wavelength and temperature dependences of fluorescence spectra and quantum yields for different concentrations of the dye are investigated. These measurements together with those of absorption reveal that dimers are imperfect traps for excitation energy and that the energy transfer can occur both in the forward and in the reverse direction. It was found that, contrary to liquid solutions, the dimerization constant of flavomononucleotide in polyvinyl alcohol films does not depend on temperature and that the irregularities observed can be explained by the temperature-dependent changes in the quantum yield of the monomer–dimer system and the effect of inhomogeneous orientation broadening of energy levels.

Ultraviolet Fluorescence of Cyanidin and Malvidin Glycosides in Aqueous Environment

Abstract The fluorescence of cyanidin 3‐glucoside (Cy 3‐glc), cyanidin 3,5‐diglucoside (Cy 3,5‐diglc) and malvidin 3,5‐diglucoside (Mv 3,5‐diglc) in binary solvents (water–methanol, 1∶1, v/v) and in water at pH 4–5.5 has been studied. The absorption spectra, steady‐state fluorescence spectra, and fluorescence excitation spectra have been measured. Fluorescence excitation was in the UV range at the absorption maxima of cyanidin and malvidin glycosides (λexc=220 nm) and at the characteristic absorption band of about λexc=280 nm. In the aqueous environment, Cy 3‐glc exhibits short‐wavelength fluorescence FSH at λmax fl=299 nm which was most effectively excited at 220 nm. Similar short‐wavelength fluorescence FSH was observed for Cy 3,5‐diglc (λmax fl=308 nm) and Mv 3,5‐diglc (λmax fl=293 nm) in a binary solvent system. We postulate that the observed short‐wavelength fluorescence FSH is related to the hemiacetal forms of the analyzed anthocyanin glycosides.

Singlet oxygen autoxidation of vegetable oils: Evidences for lack of synergy between β-carotene and tocopherols

The synergy between β-carotene and tocopherols--antioxidants protecting oils from oxidation, was analyzed in a model system. The model used stripped borage and evening primrose oils. A chlorophyll extract, β-carotene and one of the tocopherols were added together or separately to the oils. Oil oxidation was initiated by singlet oxygen that was produced by chlorophylls irradiated with the use of a xenon lamp equipped with the cut-off 600 nm filter. Experiments were carried out at two mole ratios of tocopherols to β-carotene, i.e. at 1:1 and 23:1. Analyses were performed using absorption and fluorescence spectra in the UV+Vis region. The results demonstrated an antagonistic action of the antioxidants. The protective effect of unsaturated fatty acids was significantly better in the case of β-carotene compared to the tocopherols. Furthermore, tocopherols were less effective in protecting the oils in the presence of β-carotene than without it.

Retinyl palmitate in water environment

Abstract The interaction between retinyl palmitate molecules and their environment in binary water- p -dioxane solvent (at different molar ratios of water to p -dioxane) was studied. The absorption, fluorescence emission and fluorescence excitation spectra were analysed. In this binary solvent, the interaction between retinyl palmitate molecules and environments of different polarity leads to the self-organization of retinyl palmitate. The possible consequences of the existence of self-organized structures for retinoid transport through the water phase are discussed.

Spectral properties of flavins in hydrophilic matrices

Abstract Absorption and emission properties, of flavins (riboflavin 5-phosphate (FMN), riboflavin and 10-formylmethylisoalloxazine) in hydrophilic matrices have been studied. The results were discussed in terms of a possible change of the isoalloxazine nucleus geometry. The angles between absorption transition moments and emission transition moment were estimated. It is suggested that FMN stabilized by PVA matrix can be treated as the energetically-well-isolated molecular system.

A new approach to the old problem: Inner filter effect type I and II in fluorescence

The fluorescence technique is very popular and has been used in many fields of research. It is simple in its assumptions but not very easy to use. One of the main problems is the inner filter effect (IF) I and II which takes place in the cuvette. IF type I is permanently present, but IF type II occurs only when absorption and fluorescence spectra overlap. To avoid IF type I, absorbencies in the cuvette should be smaller than 0.05, which is however very difficult to obtain in many experiments. In this work we propose a new method to solve these problems in the case of a Cary Eclipse fluorimeter, having horizontally-oriented slits, based on old equations developed in the middle of the last century. This method can be applied for other instruments, even these with vertically-oriented beams, because we share scripts written in MATLAB and GRAMS/AI environment. Calculations in our method enable specifying beam geometry parameters in the cuvette, which is necessary to obtain the correct shape and fluorescence intensity of emission and excitation spectra. Such a specific fluorescence intensity dependence on absorbance can, in many cases, afford possibilities to determine the quantum yield (QY) using slopes of the straight-lines, which was demonstrated with the use of Tryptophan (Trp), Tyrosine (Tyr), and Rhodamine B (RhB) solutions. For example, assuming that QY=0.14 for Tyr, the QY determined for RhB reached QY=0.71±0.05, although the measurement for Tyr and RhB was performed at a completely different spectral range.