Determination of the most stable structures of selected hydroxypyrones and their cations and anions

Review on the Use of Kojic Acid—A Skin-Lightening Ingredient

This article reviews the use of Kojic Acid (KA) as a skin-lightening ingredient in the cosmetics industry. In 1907, Saito discovered KA, a natural product; it has since become one of the most investigated skin-lightening agents. This paper highlights the findings of the research conducted on this agent. It has been found that KA has certain disadvantages, and researchers have attempted to mitigate these disadvantages by designing new equivalents of KA that are more efficient in tyrosinase inhibition. These equivalents are also safe to use and have improved properties and solubility. The Cosmeceutical Ingredient Review (CIR) indicates that this ingredient can be safely used at a concentration not higher than 1% due to its cytotoxicity. Other scientific data also support its safety at a concentration of 2% or less. It was shown to be helpful in the treatment of hyper pigmentary disorders, such as freckles, age spots, post-inflammatory hyperpigmentation, and melasma, which has been proven clinically.

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.

Molecular modification approach on kojic acid derivatives as antioxidants related to ascorbic acid

A hypothetical study by using molecular modeling for antioxidant capacity of kojic acid derivatives was performed using quantum chemistry calculations by DFT/B3LYP/6-311++G(3d,2p). Four modification approaches were considered namely simplification, functional modifications, ring regioisomerism, and hydroxylation. Molecular orbitals, single-electron transfers, hydrogen atom transfers, and spin density distributions were used for antioxidant prediction. In accordance with HOMO, LUMO, Gap, ionization potential, bond dissociation energy, and stabilization energy, the molecular simplifications of kojic acid show that enol moiety is more important for antioxidant capacity than alcohol group. Few molecular modifications on alcohol or enol position were more potent than kojic acid. The π conjugation system among ether, alkene, and hydroxyl moieties can be involved on resonance effects of better compounds. A different performance was observed on alcohol molecular modifications when compared to enol position. All lactone derivatives were more potent than kojic acid on both mechanisms, and their hydroxylated derivatives were more potent than ascorbic acid. In conclusion, the ring regioisomers and its hydroxylated derivatives have better antioxidant capacity than kojic acid. Graphical Abstract The theoretical study using molecular modeling for antioxidant capacity prediction of kojic acid was more related to enol moiety than alcohol. The regioisomerism and hybrid derivatives show that the lactone derivatives increase antioxidant capacity more than the pyrone derivatives.

Solvent Effects on the Symmetric and Asymmetric SN2 Reactions in the Acetonitrile Solution: A Reaction Density Functional Theory Study

Bimolecular nucleophilic substitution (S_N2) reactions are of great importance in chemistry and biochemistry due to their capability of constructing functional groups. In this work, we investigate the solvent effect on the free energy profiles of symmetric and asymmetric S_N2 reactions in the acetonitrile solution using the proposed reaction density functional theory (RxDFT) method. This multiscale method utilizes quantum density functional theory for calculating intrinsic reaction free energy coupled with classical density functional theory for addressing solvation contribution. We find that the presence of acetonitrile brings both the polarization effect and solvation effect on the reaction pathways. For the eight selected symmetric S_N2 reactions, the predicated reaction pathways agree well with the results from the direct and thermodynamic cycle (TC) methods with the SMD-M062X solvation model. In addition, the polarization effect reduces the free energy barriers by about 6 kcal/mol, while the solvation effect increases the barriers by about 18 kcal/mol. For the four selected asymmetric S_N2 reactions, the predicted reaction pathways agree well with the results from the Monte Carlo simulations and experiments. The polarization effect and the solvation effect mutually reduce the free energy barriers, and the solvation effect plays a dominant role.