Comparative Analysis of Fluorescence Emission in Myricetin, Kaempferol, and Quercetin Powders and Solutions.

Myricetin is a flavonol with high antioxidant properties. In this research, the fluorescence emission of myricetin powder and its solutions in different solvents were measured and analyzed by comparing with the results of calculations. Comparison of the calculated and measured characteristic wavelengths allowed the identification of all the spectral features in the fluorescence spectra of myricetin powder and solutions with different concentrations. The computation was based on modeling the process of the excited state intermolecular proton transfer, which predicts the formation of tautomeric forms of the flavonol molecule. Characteristic emission wavelengths were obtained using TDDFT/M06-2X/6-31++G(d,p). To understand the influence of the hydroxyl groups in the B-ring of the flavonol molecule on the emission spectrum, we also compared the fluorescence spectra of myricetin with those of kaempferol and quercetin. Moreover, based on the analysis of the changes in the shape of the FL spectra with the concentration of the solution, a criterion for the complete dissolution of the flavonol powders was established, which is important for bioavailability of flavonoids.

Experimental and Theoretical Study of Fluorescent Properties of Morin.

Morin (M) is one of the most widely distributed flavonoids with several beneficial effects on human health, and has the potential of being used as a possible treatment for COVID-19. To achieve a better understanding of the process of M dissolution, the fluorescent (FL) emission from M solutions prepared with different polar and nonpolar solvents (methanol, DMSO, and chloroform) was measured and compared with the FL emission from M powder and M crystals. In the FL spectra of the solutions with high M concentration, as well as in the spectra of M in solid state, two features, at 615 nm and 670 nm, were observed. As the solution concentration decreases, the maxima of FL spectra of the M solutions in all considered solvents shift to the blue side of the spectrum until reaching the value of 520 nm. To explain the experimental results, the TDDFT-M06-2X/6-31++G(d,p) method was used to determine the possible electronic transitions in the M molecule. The computations show that the FL emission in the spectral range of detection of our setup (405-800 nm) is related to the excited state intramolecular proton transfer (ESIPT). Comparison of the experimental data with the computations strongly suggests that in low-concentrated solutions, the FL emission is mostly due to electronic transitions in the keto OH3 form, whereas in aggregated states, the dominate contribution to the FL emission spectra is due to the transitions in keto OH5 form. Moreover, the time evolution of the M solutions FL spectra was observed, measured and explained for the first time.

The role of molecular structure of sugar-phosphate backbone and nucleic acid bases in the formation of single-stranded and double-stranded DNA structures.

Our previous DFT computations of deoxydinucleoside monophosphate complexes with Na(+)-ions (dDMPs) have demonstrated that the main characteristics of Watson-Crick (WC) right-handed duplex families are predefined in the local energy minima of dDMPs. In this work, we study the mechanisms of contribution of chemically monotonous sugar-phosphate backbone and the bases into the double helix irregularity. Geometry optimization of sugar-phosphate backbone produces energy minima matching the WC DNA conformations. Studying the conformational variability of dDMPs in response to sequence permutation, we found that simple replacement of bases in the previously fully optimized dDMPs, e.g. by constructing Pyr-Pur from Pur-Pyr, and Pur-Pyr from Pyr-Pur sequences, while retaining the backbone geometry, automatically produces the mutual base position characteristic of the target sequence. Based on that, we infer that the directionality and the preferable regions of the sugar-phosphate torsions, combined with the difference of purines from pyrimidines in ring shape, determines the sequence dependence of the structure of WC DNA. No such sequence dependence exists in dDMPs corresponding to other DNA conformations (e.g., Z-family and Hoogsteen duplexes). Unlike other duplexes, WC helix is unique by its ability to match the local energy minima of the free single strand to the preferable conformations of the duplex.

DFT study of B-like conformations of deoxydinucleoside monophosphates containing Gua and/or Cyt and their complexes with Na+ cation.

B-like minimum energy conformations of deoxydinucleoside monophosphate anions (dDMPs) containing Gua and/or Cyt and their Na+ complexes have been studied by the DFT PW91PW91/DZVP method. The optimized geometry of the dDMPs is in close agreement with experimental observations and the obtained minimum energy conformations are consistent with purine-purine, purine-pyrimidine, and pyrimidine-purine arrangements in crystals of B-DNA duplexes. All the studied systems are characterized by pyramidalization of the amino groups, which participate in the formation of unusual hydrogen bond between the carbonyl oxygen of the second base in the dGpdC, dCpdG dDMPs, and their Na+ complexes. In all the obtained structures the bases assume a nearly parallel disposition to each other and this effect is independent on the degree of their spatial superposition. From this it is concluded that the parallel disposition of the bases in the B-like single-stranded conformations is dictated by the sugar-phosphate backbone. Correspondingly, the base-base interactions attain a secondary role in the formation of these spatial structures. The formation of a weak C6-H6...O5' hydrogen bond between cytosine and the phosphate oxygen is reported, in agreement with experimental observations.