Photochemistry of aqueous solutions of kynurenic acid and kynurenine yellow

Abstract

The photophysics and photochemistry of kynurenic acid (KNA) and kynurenine yellow (KNY) in neutral aqueous solutions were investigated using time-resolved optical spectroscopy. Both molecules have similar quinoline-like structures, the only difference being the absence of conjugation in the nitrogen containing cycle in KNY. The main channel of S 1 excited state decay in the case of partially-unconjugated KNY is the solvent assisted S 1 → S 0 radiationless transition via intermolecular hydrogen bonds (Φ IC = 0.96), whereas, in the case of fully-conjugated KNA, it is intersystem crossing to the triplet state (Φ T = 0.82). The major intermediate products of the singlet excited KNY deactivation are the triplet state (Φ T = 0.022) and, most probably, the enol form (Φ enol = 0.012), which decay with the formation of 2,3-dihydro-4-hydroxyquinoline and 4-hydroxyquinoline, respectively. The results obtained show that KNA and KNY, which are products of the decomposition of the UV filter kynurenine, are significantly more photoactive and less photostable than the parent molecule.

Antiradical capacity of ommochromes

“…Apparently, as the size of the molecule increases the electrons become more delocalized, excitation energy decreases and consequently λ max increases. The comparison of the theoretical results with available experimental values reported previously [18,26] indicates that theory and experiment concur well. The calculated λ max values are overestimated in comparison with the experimental data.…”

“…Results reported in the literature that refer to the antiradical properties of certain ommochromes are all experimental [20,21,23,26]. In order to elucidate the possible mechanisms and reactivity of these molecules, it is important to also investigate these ommochromes from a theoretical point of view.…”

“…The antiradical capacity of ommochromes is compared to previous results for carotenoids [11,12,15,16]. To compare with the experimental values [18,26] the UV/VIS spectra of neutral ommochromes are obtained, assuming that water is the solvent.…”

Bright Green Biofluorescence in Sharks Derives from Bromo-Kynurenine Metabolism

“…Similarly, compound 6 was found to have a blue wavelength emission, although it trailed into the green spectra with a peak emission of 484 nm. Non-brominated kynurenine yellow is known to exhibit bright green fluorescence with an emission maxima of ∼520 nm (Mizdrak et al., 2007, Zelentsova et al., 2013), whereas our experimental fluorescence spectrum of bromo-kynurenine yellow ( 8 ) obtained in methanol revealed a blue wavelength emission maximum of 472 nm (Figure 5H). Given the discrepancy, we further obtained fluorescence spectra of the compounds in a more biologically relevant phosphate buffered saline (PBS) system, and the compounds displayed significant shifts of their fluorescence spectra compared with those in methanol (Table 1 and Figure S20).…”

Detection, Quantification, and Total Synthesis of Novel 3-Hydroxykynurenine Glucoside–Derived Metabolites Present in Human Lenses

“…Additionally, along with 3OHKG-D being unstable, there is evidence that 3OHKG-Y is photochemically active, with Zelentsova et al 19 showing that the structurally similar kynurenine yellow is reactive upon UV irradiation. Thus, 3OHKG-W, 3OHKG-Y, and AHAG most likely do not function as significant UV filter compounds in the lens, but are intermediate products of 3OHKG decomposition.…”