Małgorzata Insińska-Rak

Simultaneous analysis of riboflavin and aromatic amino acids in beer using fluorescence and multivariate calibration methods

The study demonstrates an application of the front-face fluorescence spectroscopy combined with multivariate regression methods to the analysis of fluorescent beer components. Partial least-squares regressions (PLS1, PLS2, and N-way PLS) were utilized to develop calibration models between synchronous fluorescence spectra and excitation-emission matrices of beers, on one hand, and analytical concentrations of riboflavin and aromatic amino acids, on the other hand. The best results were obtained in the analysis of excitation-emission matrices using the N-way PLS2 method. The respective correlation coefficients, and the values of the root mean-square error of cross-validation (RMSECV), expressed as percentages of the respective mean analytic concentrations, were: 0.963 and 14% for riboflavin, 0.974 and 4% for tryptophan, 0.980 and 4% for tyrosine, and 0.982 and 19% for phenylalanine.

Riboflavin Interactions with Oxygen—A Survey from the Photochemical Perspective

In this short review we provide some insights to the main processes that riboflavin is involved in upon absorption of a photon. We describe riboflavin properties in its interactions with oxygen, comparing them to the properties of some other singlet oxygen sensitizers. Data are provided on riboflavin photosensitizing properties in vivo and in vitro, and its properties as an endogenous singlet oxygen sensitizer are discussed. We additionally report flavin catalytic role in organic synthesis and photochemical reactivity in solutions of riboflavin and some of its derivatives.

Spectroscopy and photophysics of flavin-related compounds: 3-benzyl-lumiflavin.

Molecular structure, spectroscopic and photophysical data for the singlet state of 3-benzyl-lumiflavin in different solvents are presented. Theoretical studies concerning singlet–singlet and triplet–triplet excitation energies were carried out using time-dependent density functional theory (TD-DFT) calculations. These predictions are in good agreement with the experimental results, which reflect the solvent interactions. All the observable singlet–singlet transitions have π–π* character. The title compound appears to be an efficient sensitizer of the production of singlet oxygen (ϕΔ = 0.53). The crystal structure of 3-benzyl-lumiflavin is also presented, along with its solid-state photophysical data.

Photochemistry of riboflavin derivatives in methanolic solutions.

Light-induced degradation of the riboflavin derivatives is reported, including 5-deaza-riboflavin, iso-6,7-riboflavin, 3-methyl-tetra-acetyl-riboflavin (3MeTARF), and 3-benzyl-lumiflavin. The studied compounds undergo photolytic processes with considerable quantum yields in methanolic solutions (φ ≈ 10(-3)-10(-4) mol einst(-1)). Photolysis in anaerobic conditions is more efficient than that in the presence of oxygen. Experiments show that triplet excited state of flavin molecules is involved in the reactions. The main photoproducts are the respective alloxazinic and isoalloxazinic derivatives of the substrates. 3MeTARF reveals higher photostability than riboflavin. The values of photodegradation quantum yields were estimated for the four studied derivatives.

Spectral and photophysical properties of some imidazo[1,2-a]purine derivatives related to acyclovir

Abstract Spectral and photophysical properties of 3,9-dihydro-3-[(2-hydroxyethoxy)methyl]-6-phenyl-9-oxo-imidazo[1,2-a]purine 7b (congener of acyclovir) and its three substituted derivatives 7a, c and 8a in organic solvents and in aqueous buffer solutions have been determined. Compound 7c has an ester group in the para position of the phenyl ring, compounds 7a and 8a are derivatives of 7b with a methyl group attached to imidazole N(5) or pyrimidine N(4) ring of the tricyclic skeleton, respectively. Experimental study has been supplemented with theoretical calculations of the singlet electronic transition energies and oscillator strengths by the time dependent density functional theory (TD-DFT). Combination of experimental and computational results have indicated that compounds 7b and c having mobile hydrogen exist in the ground state in a single N(5)H tautomeric form. The lowest excited S1 state of all compounds investigated has the π, π∗ configuration. The spectral and photophysical properties of 7a–c are similar. The fluorescence behaviour of the compounds depends on the solvent polarity and pH of the aqueous medium in the range of pH: 0–4 and 6–12. The pH dependence is a consequence of the protonation of the molecules (pKa=2.2 for 7a and pKa=2.0 for 7b and c) and their deprotonation in the ground state (pKa=8.0 and 8.2 for 7b and c, respectively). The absorption and fluorescence properties of the ionic forms have been determined. In contrast to 7a–c, the spectral and photophysical properties of 8a are not significantly influenced by the solvent polarity and they are independent on pH of aqueous solution within 4–12 range.