RESUMEN
In the present work, the photoinduced charge-transfer (CT) behavior of 7-phenyl-6H-pyrido[1,2-a:3,4-b']diindole-6,13(12H)-dione (HCB) as a function of solvent polarity is reported by UV-vis absorption, steady-state and time-resolved fluorescence, and quantum chemical calculations. Calculated excited state energies of HCB at the B3PW91/6-31+G* level in vacuo and in solvents fulfill the energy requirements for singlet fission, which is the most promising path for the generation of highly efficient solar cells. The calculated potential energy curve for the compound reveals that the keto form is the predominant form in the ground state. Large bathochromic shifts in fluorescence with decreasing trends of quantum yield and lifetime indicate the occurrence of intramolecular CT from the indole bicycle to the indolinone moiety of HCB in highly polar solvents. The observed quenching of HCB fluorescence in different solvents without altering the spectral shape upon addition of a donor, triethylamine, is attributed to intermolecular CT, and it was examined in terms of the Stern-Volmer kinetics. The thermodynamics of photoinduced CT processes in HCB was analyzed using the measured photophysical data and cyclic voltammetric redox potentials via the Rehm-Weller equation. Analyses with the semiclassical Marcus theory suggest that both the CT processes fall under the Marcus normal region.
RESUMEN
Alpha-lipoic acid is an organic, sulfate-based compound produced by plants, humans, and animals. As a potent antioxidant and a natural dithiol compound, it performs a crucial role in mitochondrial bioenergetic reactions. A healthy human body, on the other hand, can synthesize enough α-lipoic acid to scavenge reactive oxygen species and increase endogenous antioxidants; however, the amount of α-lipoic acid inside the body decreases significantly with age, resulting in endothelial dysfunction. Molecular orbital energy and spin density analysis indicate that the sulfhydryl (-SH) group of molecules has the greatest electron donating activity, which would be responsible for the antioxidant potential and free radical scavenging activity. α-Lipoic acid acts as a chelating agent for metal ions, a quenching agent for reactive oxygen species, and a reducing agent for the oxidized form of glutathione and vitamins C and E. α-Lipoic acid enantiomers and its reduced form have antioxidant, cognitive, cardiovascular, detoxifying, anti-aging, dietary supplement, anti-cancer, neuroprotective, antimicrobial, and anti-inflammatory properties. α-Lipoic acid has cytotoxic and antiproliferative effects on several cancers, including polycystic ovarian syndrome. It also has usefulness in the context of female and male infertility. Although α-lipoic acid has numerous clinical applications, the majority of them stem from its antioxidant properties; however, its bioavailability in its pure form is low (approximately 30%). However, nanoformulations have shown promise in this regard. The proton affinity and electron donating activity, as a redox-active agent, would be responsible for the antioxidant potential and free radical scavenging activity of the molecule. This review discusses the most recent clinical data on α-lipoic acid in the prevention, management, and treatment of a variety of diseases, including coronavirus disease 2019. Based on current evidence, the preclinical and clinical potential of this molecule is discussed. Supplementary Information: The online version contains supplementary material available at 10.1007/s43450-023-00370-1.
