A theoretical evaluation on free radical scavenging activity of 3-styrylchromone derivatives: the DFT study

Characterization, DFT study and evaluation of antioxidant potentials of mycosporine-like amino acids (MAAs) in the cyanobacterium Anabaenopsis circularis HKAR-22

The physiological parameters such as growth, Chl a content, and photosynthetic performance of the experimental cyanobacterium Anabaenopsis circularis HKAR-22 were estimated to evaluate the cumulative effects of photosynthetically active radiation (PAR) and ultraviolet (UV) radiation. Maximum induction of UV-screening molecules, MAAs, was observed under the treatment condition of PAR + UV-A + UV-B (PAB) radiations. UV/VIS absorption spectroscopy and HPLC-PDA detection primarily confirmed the presence of MAA-shinorine (SN) having absorption maxima (λmax) at 332.3 nm and retention time (RT) of 1.47 min. For further validation of the presence of SN, HRMS, FTIR and NMR were utilized. UV-stress elevated the in vivo ROS scavenging and in vitro enzymatic antioxidant capabilities. SN exhibited substantial and concentration-dependent antioxidant capabilities which was determined utilizing 2,2-diphenyl-1-picryl-hydrazyl (DPPH), 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonate (ABTS), ferric reducing power (FRAP) and superoxide radical scavenging assay (SRSA). The density functional theory (DFT) method using B3LYP energy model and 6-311G++(d,p) basis set was implied to perform the quantum chemical calculation to systematically investigate the antioxidant nature of SN. The principal pathways involved in the antioxidant reactions along with the basic molecular descriptors affecting the antioxidant potentials of a compound were also studied. The results favor the potential of SN as an active ingredient to be used in cosmeceutical formulations.

Comparison of Cu3, Cu5, and Cu7 clusters as potential antioxidants: A theoretical quest

CONTEXT

Herein, we compare and contrast the dual roles of Cun clusters (n = 3, 5, and 7 atoms) in scavenging or generating RO• free radicals from ROH at the theoretical levels (where R = H, methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, and phenyl). This investigation is performed in water media to mimic the actual environment in the biological system. In the presence of the Cun clusters, bond dissociation energy (BDE) of RO-H and R-OH is reduced. This is clear evidence for the increased possibility of both the RO-H and R-OH bonds breakage and scavenging of RO• radicals. The nature of anchoring bonds responsible for the interaction of Cun clusters with ROH and RO• are interpreted using the quantum theory of atoms in molecules (QTAIM) and the natural bond orbital (NBO) analysis. The DFT results indicate that the O•⋅⋅⋅•Cu bond is stronger and has more covalent character in RO•⋅⋅⋅•Cun radical complexes than in ROH⋅⋅⋅•Cun. Therefore, the interactions of Cun clusters with RO• radicals (antioxidant) are more pronounced than their interactions with ROH non-radicals (pro-oxidant).

METHODS

The GAMESS software package was utilized in this paper. The B3LYP and M06 functions with the 6-311 +  + G(d,p), and LANL2DZ/SDD basis sets was used to perform the important geometrical parameters of RO•⋅⋅⋅•Cun and ROH⋅⋅⋅•Cun, binding energy (Eb), and bond dissociation energy (BDE).

Theoretical study on the radical scavenging activity of gallic acid

The global descriptors of the chemical activity: ionization potential IP, electron affinity EA, chemical potential μ, absolute electronegativity χ, molecular hardness η and softness S, electrophilicity index ω, electro-donating ω^-, electro-accepting ω⁺ powers as well as Ra and Rd indexes for gallic acid (GA) in the gas phase and water medium have been determined. To this aim, the HOMO and LUMO energies were calculated using the DFT method at the B3LYP, M06-2X, LC-ωPBE, BHandLYP, ωB97XD/cc-pVQZ theory levels using C-PCM, IEF-PCM and SMD solvation models, enabling more accurate descriptor calculations than those carried out so far. Quantum-chemical computations were also applied to investigate the GA structure and thermodynamic parameters characterizing its radical scavenging properties. To this aim, the full optimization of the neutral GA and its radical, cationic and anionic forms in vacuum and water medium has been performed, and then the bond dissociation enthalpy BDE, adiabatic ionization potential AIP, proton dissociation enthalpy PDE, proton affinity PA, electron transfer enthalpy ETE, gas phase acidity H_acidity and free Gibbs acidity G_acidity in water have been determined. The calculations revealed that GA in vacuum scavenges free radicals via hydrogen atom transfer (HAT), whereas in water (polar) medium by sequential proton loss electron transfer (SPLET). Analysis of the global activity descriptors of GA indicates that only B3LYP method combined with different solvation models satisfactory reproduces LUMO-HOMO energies and provides the smallest value of the total electron energy of GA. Among the parameters of chemical activity, the indexes Ra and Rd are the most independent of the computational method and the solvation model used. They can be recommended as a reliable source of information on the antioxidant activity of chemical compounds.

Current Trends in Computational Quantum Chemistry Studies on Antioxidant Radical Scavenging Activity

The antioxidative nature of chemicals is now routinely studied using computational quantum chemistry. Scientists are constantly proposing new approaches to investigate those methods, and the subject is evolving at a rapid pace. The goal of this review is to collect, consolidate, and present current trends in a clear, methodical, and reference-rich manner. This paper is divided into several sections, each of which corresponds to a different stage of elaborations: preliminary concerns, electronic structure analysis, and general reactivity (thermochemistry and kinetics). The sections are further subdivided based on methodologies used. Concluding remarks and future perspectives are presented based on the remaining elements.

Inhibition of Quorum-Sensing Regulator from Pseudomonas aeruginosa Using a Flavone Derivative

Quorum sensing (QS) is a cell-to-cell communication process that controls bacterial collective behaviors. The QS network regulates and coordinates bacterial virulence factor expression, antibiotic resistance and biofilm formation. Therefore, inhibition of the QS system is an effective strategy to suppress the bacterial virulence. Herein, we identify a phosphate ester derivative of chrysin as a potent QS inhibitor of the human pathogen Pseudomonas aeruginosa (P. aeruginosa) using a designed luciferase reporter assay. In vitro biochemical analysis shows that the chrysin derivative binds to the bacterial QS regulator LasR and abrogates its DNA-binding capability. In particular, the derivative exhibits higher anti-virulence activity compared to the parent molecule. All the results reveal the potential application of flavone derivative as an anti-virulence compound to combat the infectious diseases caused by P. aeruginosa.

A Comparative DFT Study on the Antioxidant Activity of some Novel 3-hydroxypyridine-4-one Derivatives

The current study on the antioxidant activity of Kojic acid and 3-hydroxypyridine-4-one derivatives was performed by implementation of density functional theory calculations with the B3LYP hybrid functional and the 6-311++ G** basis set in Polarizable Continuum Model. Compounds under evaluation were previously synthesized by our research group. The DPPH scavenging effect and IC 50 values of them in mM concentrations were evaluated. Subsequently, various electronic and energetic descriptors such as HOMO and LUMO energy gaps, bonding dissociation enthalpy of OH bond, ionization potential, electron affinity, hardness, and softness, NBOs and spin density of radical and neutral species were used to study antioxidant properties of investigated compounds. The computations detected two compounds, HP3 and HP4 , with significant antioxidant activity. Energetic descriptors indicated that SPLET mechanism is preferred over than other antioxidant mechanism and computational results were in accordance with the experimental results.

Theoretical investigations on the antioxidant potential of a non-phenolic compound thymoquinone: a DFT approach

Thymoquinone (TQ) is a natural compound present in black cumin which possesses potent antioxidant activity without having any phenolic hydroxyl group which is responsible for antioxidant activity. In the present study, computational calculation based on density functional theory (DFT) was executed to assess systematically the antioxidant behavior of this compound by considering geometrical characteristics, highest occupied molecular orbital - lowest unoccupied molecular orbital (HOMO-LUMO), and molecular electrostatic potential (MEP) surface. Thermochemical parameters correlated to the leading antioxidant mechanisms such as hydrogen atom transfer (HAT), single electron transfer-proton transfer (SETPT), and sequential proton loss electron transfer (SPLET) were studied in gas and water media. In addition, the changes of thermochemical parameters such as free energy change (∆G) and enthalpy change (∆H) were computed for hydrogen abstraction (HA) from TQ to hydroxyl radical in gas and water phases to investigate its free radical scavenging potency. The low and comparable values of bond dissociation enthalpy (BDE), proton dissociation enthalpy (PDE), ionization potential (IP), proton affinity (PA), and electron transfer enthalpy (ETE) revealed the antioxidant activity. The ∆G and ∆H also indicated apposite thermodynamic evidence in favor of antiradical capability of TQ. The attack of the free radical occurred preferentially at 3CH position of the molecule.

Screening possible drug molecules for Covid-19. The example of vanadium (III/IV/V) complex molecules with computational chemistry and molecular docking

We are still facing a Covid-19 pandemic these days and after the aggressively infection control measures taken by the governments in the whole world, there is a need of a rapid pharmaceutical solution in order to control this crisis. The computer aided chemistry and molecular docking is a rapid tool for drug screening and investigation. Moreover, more metal-based drugs are tested daily by research institutes for their antiviral activity. Here, we make use of theoretical studies on previously published biological active complex molecules of vanadium as an example of evaluating possible drug candidates before entering the laboratory. We used DFT calculation studies for structural elucidation and optimization of the molecules and molecular docking studies on several Covid-19 related proteins. Our findings suggest that drug discovery should always be computer -aided. Additionally, it is found that Vtocdea and VXn molecules are seem to be good candidates for further studies as antiviral agents.