The impact of π-π stacking interactions on photo-physical properties of hydroxyanthraquinones.

The impact of π-π stacking interactions on photo-physical properties of hydroxyanthraquinone (HA) has been investigated using the density functional (DFT) and time-dependent density functional theory (TD-DFT) calculations in the gas phase and solution media. The vertical transition is characterized with strong HOMO-LUMO transition in the complexes. The intramolecular hydrogen bond (IHB) made in the HA and π-π complexes is strengthened after S0 â†’ S1 excitation, such that the proton transfers is facilitated in the first excited state. The complexes exhibit an exothermic excited state intramolecular proton transfer (ESIPT) in the solution media, which is a barrierless process for some complexes. The π-π stacking interaction affects the absorption and emission bands of HA, and provides a large Stokes shift. This indicates the desirable fluorescence properties of π-π complexes, which are cross-validated by geometries, potential energy curve scannings, electronic and vibrational spectra, and frontier molecular orbital analyses.

Analysis of medicinal and therapeutic potential of Withania somnifera derivatives against COVID-19.

Apart from chemical and allopathic drugs, several medicinal plants contain phytochemicals that are potentially useful to counter the COVID-19 pandemic. Withania somnifera (Ashwagandha), which has a good effect on some viral infections, can be considered as a candidate against the virus. In the present study, thirty-nine natural compounds of Ashwagandha were investigated in terms of their binding to the important drug targets to treat the COVID-19. Although the molecular docking calculations reveal the binding affinities of the compounds to Mpro, TMPRSS2, NSP15, PLpro, Spike RBD + ACE2, RdRp and NSP12 as targets in controlling the coronavirus enzymes, Withanoside II is expected to be the most effective compound due to the high affinity in binding with many of considered targets. Furthermore, the Withanoside III, IV, V, X, and XI have favorable binding affinities as ligands with respect to the MM/GBSA calculations. The molecular dynamics simulations MD explore a stable hydrogen bond network between ligands and the active sites residues. Also, the dynamic fluctuations of the binding site residues verify their tight binding to ligands. Moreover, the stability of ligand-protein complexes is approved by the RMSD ranges lower than 0.5 Å in equilibration zone for all mentioned complexes. The TMPRSS2-Withanolide Q and Mpro-Withanoside IV complexes are the most stable pairs using the MM/GBSA calculations and MD simulation.Communicated by Ramaswamy H. Sarma.

TMPRSS2 receptor in terms of human relative proteins and Mpro and NSP15 receptors on coronavirus itself target are the effective target for inhibitory effects of Withania somnifera compounds.The highest binding affinity is related for WithanolideD, WithanolideQ, WithanosideIV, WithanosideIII, WithanosideV, WithanosideII, and 2,3-Didehydrosomnifericin ligands on the Spike RBD + ACE2, TMPRSS2, Mpro, PLpro, RdRp, NSP15, and NSP12 receptors, respectively.Withanolide compounds on human related proteins targets and Withanoside structures on coronavirus itself receptors have the highest inhibitory potential.Withanoside II ligand is expected to be the most effective compound due to the high affinity to bind to many considered targets.The stability of ligand-protein complexes is approved by the RMSD ranges lower than 0.5 Å in equilibration zone for WithanolideQ-TMPRSS2 and WithanosideIV-Mpro complexes.

The radical cationic repair pathway of cyclobutane pyrimidine dimer: the effect of sugar-phosphate backbone.

Radical cationic repair process of cis-syn thymine dimer has been investigated when (1) sugar-phosphate backbones were substituted by hydrogen atoms, (2) phosphate group was substituted by two hydrogen atoms each on a sugar ring and (3) sugar-phosphate backbone was taken into account. The effect of the interactions between N1 and N1' lone pairs and the C6-C6' antibonding orbital are the most important evidences for the cleavage of the C6-C6' bond in the first step of radical cationic repair mechanism in the absence of the sugar-phosphate backbone. The impact of the N1 and N1' lone pairs on the C6-C6' bond cleavage decreases and the energy barrier of the cleavage of that bond significantly increases in the presence of the deoxynucleoside sugars and the sugar-phosphate backbone.