Single or double hydrogen atom transfer in the reaction of metal – Associated phenolic acids with •OH radical: DFT study

Solvation energies of the ferrous ion in water and in ammonia at various temperatures

CONTEXT

The solvation of metal ions is crucial to understanding relevant properties in physics, chemistry, or biology. Therefore, we present solvation enthalpies and solvation free energies of the ferrous ion in water and ammonia. Our results agree well with the experimental reports for the hydration free energy and hydration enthalpy. We obtained [Formula: see text] kJ mol[Formula: see text] for the hydration free energy and [Formula: see text] kJ mol[Formula: see text] for the hydration enthalpy of ferrous ion in water at room temperature. At ambient temperature, we obtained [Formula: see text] kJ mol[Formula: see text] as the [Formula: see text] ammoniation free energy and [Formula: see text] kJ mol[Formula: see text] for the ammoniation enthalpy. In addition, the free energy of solvation is deeply affected when the temperature increases. This pattern can be attributed to the rise of entropy when the temperature rises. Besides, the temperature does not affect the ammoniation enthalpies and the hydration enthalpy of the [Formula: see text] ion.

METHOD

All the geometry optimizations are performed at the MP2 methods associated with the 6-31++g(d,p) basis set of Pople. solvated phase structures of [Formula: see text] ion in water or in ammonia are performed using the PCM model. The [Formula: see text] program suite was used to perform all the calculations. The program TEMPO was also used to evaluate the temperature sensitivity of the different obtained geometries.

Use of vinasse and coffee waste as chelating agent of photo-Fenton landfill leachate treatment

This research studies the use of vinasse (VS) coming from Pisco and caffeic acid (Caa) from solid coffee waste as chelating agents of this process, to carry out a photo-Fenton process using UVc lamps of 254-nm wavelength for 60 min, at the natural pH of the landfill leachate (8.9). Without the chelating agent, there was a removal of UV 254 and COD of 54.2% and 54.7%, respectively, when the photo-Fenton reaction was carried out at pH 3; at pH 6, the removal of UV 254 and COD was 13.1% and 39.2%, respectively, and at pH 8.9, the elimination of UV 254 and COD was 10.8% and 16.1%, respectively. When Caa was used in the landfill leachate (LL) for the photo-catalytic processes carried out at pH 8.9, a removal of 24.1%, 43.0%, and 47.4% of UV 254 was obtained using 5 mg/L, 50 mg/L, and 100 mg/L of Caa. The removal of UV 254 was 27.3%, 30.7%, and 36.3% using 5 mg/L, 50 mg/L, and 100 mg/L of VS, respectively, and the removal of COD was 32.2%, 35.4%, and 39.2% using 5 mg/L, 50 mg/L, and 100 mg/L of VS, respectively. When Caa was used in the LL at pH 8.9, the concentration of total Fe went from 37.5 to 33.2, from 40.2 to 36.8, and from 45.2 to 42.1, using 5 mg/L, 50 mg/L, and 100 mg/L of caffeic acid, respectively. Using VS in the LL at pH 8.9, the concentration of total Fe along the run went from 35.1 to 32.2, from 39.4 to 34.8, and from 42.1 to 40.2, using 5 mg/L, 50 mg/L, and 100 mg/L of VS, respectively. As a result of these processes, it was noted that the use of Caa and VS increases the solubility of Fe at a higher pH.

Antioxidant activity of delphinidin and pelargonidin: Theory and practice

The quantum chemical density functional theory and in vitro chemical-based antioxidant assays were used to research the reaction mechanism of delphinidin/pelargonidin with free radicals including superoxide anion radicals (O₂ ^- ∙) and hydroperoxide radicals (OOH∙). The geometric configuration, bond dissociation energy, PCM (polarizable continuum model) solvent model reaction enthalpy changes were studied to explain the transition states, and the reaction enthalpy change value was calculated to determine the active site. From the results of spatial configuration, delphinidin showed a stronger conjugation effect than that of pelargonidin. The dihedral angle between the three rings of delphinidin was almost 180°, and the angle between the B and C rings was only -2.81868°. Both coplanar and antioxidant activity of delphinidin was better than pelargonidin. The consequences of reaction enthalpy change in PCM were consistent with the bond dissociation energy. The phenolic hydroxyl bond dissociation energy of delphinidin was slightly smaller than that of pelargonidin. Moreover, the C4' site of delphinidin and the C3 site of pelargonidin were the active sites for scavenging free radicals. The free radical scavenging ability of delphinidin was marginally higher than that of pelargonidin. On the other hand, in vitro antioxidant results proved the scavenging ability of delphinidin and pelargonidin on superoxide anions, DPPH, and ABTS^∙+ free radicals. It was shown that the chemical-based antioxidant activity was consistent with the theoretical calculation results, with delphinidin showing greater antioxidant activity. These results could explain the antioxidant mechanism of delphinidin/pelargonidin in scavenging free radicals from chemical reactions. PRACTICAL APPLICATIONS: This manuscript explained the antioxidant mechanism of delphinidin/pelargonidin in scavenging free radicals through the analysis of the geometric configuration of delphinidin/pelargonidin and the theoretical calculation of the reaction transition state. It could also speculate on the possible reaction sites, and provide a basis for judging how to efficiently select antioxidants with great antioxidant activity.

Theoretical study of the impact of metal complexation on the reactivity properties of Curcumin and its diacetylated derivative as antioxidant agents

The chemical behavior of Curcumin and its derivatives as antioxidant and metal chelator has become the subject of intense experimental research. In this work, a theoretical study was conducted with the aim to investigate whether the acetylation of the aromatic group in Curcumin, which makes it more lipophilic, will alter its biological activities. Also, we selected from the literature metal complexes of Curcumin and its diacetylated derivative with Ga(III) and In(III), in order to discriminate the molecular active sites of the investigated molecules in which the oxidative process occurs and to obtain information about their antioxidation mechanisms. The geometrical structures and electronic properties of these compounds have been obtained using the density functional theory (DFT) method, known for its accurate results. As our other objective is to understand the factors driving biological behavior of all the studied compounds as well as the impact of the metal complexation of Curcumin and its diacetylated derivative, we provided here evidences to explain experimental observations from a molecular reactivity perspective.

A DFT Study of Structural and Bonding Properties of Complexes Obtained from First-Row Transition Metal Chelation by 3-Alkyl-4-phenylacetylamino-4,5-dihydro-1H-1,2,4-triazol-5-one and Its Derivatives

Density functional calculations were used to explore the complexation of 3-alkyl-4-phenylacetylamino-4,5-dihydro-1h-1,2,4-triazol-5-one (ADPHT) derivatives by first-row transition metal cations. Neutral ADPHT ligand and mono deprotonated ligands have been used. Geometry optimizations have been performed in gas-phase and solution-phase (water, benzene, and N,N-dimethylformamide (DMF)) with B3LYP/Mixed I (LanL2DZ for metal atom and 6-31+G(d,p) for C, N, O, and H atoms) and with B3LYP/Mixed II (6-31G(d) for metal atom and 6-31+G(d,p) for C, N, O, and H atoms) especially in the gas-phase. Single points have also been carried out at CCSD(T) level. The B3LYP/Mixed I method was used to calculate thermodynamic energies (energies, enthalpies, and Gibb energies) of the formation of the complexes analyzed. The B3LYP/Mixed I complexation energies in the gas phase are therefore compared to those obtained using B3LYP/Mixed II and CCSD(T) calculations. Our results pointed out that the deprotonation of the ligand increases the binding affinity independently of the metal cation used. The topological parameters yielded from Quantum Theory of Atom in Molecules (QTAIM) indicate that metal-ligand bonds are partly covalent. The significant reduction of the proton affinity (PA) observed when passing from ligands to complexes in gas-phase confirms the notable enhancement of antioxidant activities of neutral ligands.

Quantum Chemical Investigation on the Antioxidant Activity of Neutral and Anionic Forms of Juglone: Metal Chelation and Its Effect on Radical Scavenging Activity

The chelation ability of divalent Mg, Ca, Fe, Co, Ni, Cu, Zn, and monovalent Cu ions by neutral and anionic forms of juglone has been investigated at DFT/B3LYP/6-31+G(d,p) level of theory in gas and aqueous phases. It is noteworthy that only the 1 : 1 stoichiometry was considered herein. The effects of these metals on the radical scavenging activity of neutral juglone were evaluated via the usual descriptors of hydrogen atom transfer. According to our results, metal chelation by the two forms of juglone was spontaneous and exothermic in both media. Based on the binding energies, Cu(II) ion showed the highest affinity for the ligands. QTAIM analyses identified the metal-ligand bonds as intermediate type interactions in all the chelates, except those of Ca and Mg. It was also found that the chelates were better radical scavengers than the ligands. In the gas phase, the scavenging activity of the compounds was found to be governed by direct hydrogen atom transfer, the Co(II) chelate being the most reactive. In the aqueous phase also, the sequential proton loss electron transfer was preferred by all the molecules, while the Cu(II) chelates were the most reactive.

Structural and Antioxidant Properties of Compounds Obtained from Fe2+ Chelation by Juglone and Two of Its Derivatives: DFT, QTAIM, and NBO Studies

The chelating ability of juglone and two of its derivatives towards Fe²⁺ion and the antioxidant activity (AOA) of the resulting chelates and complexes (in the presence of H₂O and CH₃OH as ligands) in gas phase is reported via bond dissociation enthalpy, ionization potential, proton dissociation enthalpy, proton affinity, and electron transfer enthalpy. The DFT/B3LYP level of theory associated with the 6-31+G(d,p) and 6-31G(d) Pople-style basis sets on the atoms of the ligands and the central Fe(II), respectively, was used. Negative chelation free energies obtained revealed that juglone derivatives possessing the O-H substituent (L₂) have the greatest ability to chelate Fe²⁺ ion. Apart from 1B, thermodynamic descriptors of the AOA showed that the direct hydrogen atom transfer is the preferred mechanism of the studied molecules. NBO analysis showed that the Fe-ligand bonds are all formed through metal to ligand charge transfer. QTAIM studies revealed that among all the Fe-ligand bonds, the O₁-Fe bond of 1A is purely covalent. The aforementioned results show that the ligands can be used to fight against Fe(II) toxicity, thus preserving human health, and fight against the deterioration of industrial products. In addition, most of the complexes studied have shown a better AOA than their corresponding ligands.

DFT study of the effect of solvent on the H-atom transfer involved in the scavenging of the free radicals (·)HO2 and (·)O2(-) by caffeic acid phenethyl ester and some of its derivatives

H-atom transfer from caffeic acid phenethyl ester (CAPE), MBC (3-methyl-2-butenyl caffeate), BC (benzoic caffeate), P3HC (phenethyl-3-hydroxycinnamate), and P4HC (phenethyl-4-hydroxycinnamate) to the selected free radicals (·)HO2 and (·)O2(-) was studied. Such a transfer can proceed in three different ways: concerted proton-coupled electron transfer (CPCET), electron transfer followed by proton transfer (ET-PT), and proton transfer followed by electron transfer (PT-ET). The latter pathway is sometimes competitive with SPLET (sequential proton loss electron transfer) in polar media. Analyzing the thermodynamic descriptors of the reactions of CAPE and its derivatives with co-reactive species-in particular, the free energies of reactions, the activation barrier to the CPCET mechanism, and their rate constants-appears to be the most realistic method of investigating the H-atom transfers of interest. These analyses were performed via DFT calculations, which agree well with the data acquired from experimental studies (IC50) and from CBS calculations. The CPCM solvation model was used throughout the work, while the SMD model-employed as a reference-was used only for CAPE. The main conclusion drawn from the analysis was that SPLET is the mechanism that governs the reaction of phenolic acids with (·)HO2, while PT-ET governs the reaction of phenols with (·)O2(-). In kinetic investigations of the CPCET process, the rate constant decreases as the solvent polarity increases, so the reaction velocity slows down.

Theoretical and experimental investigation of the semiquinone forms of protocatechuic acid. The effect of manganese

Ten oxidized, oxygenated and dimeric forms of protocatechuic acid (PCA, 3,4-dihydroxybenzoic acid, 3,4-DHBA) have been studied using DFT calculations (at the B3LYP/TZVP level of theory) and their structural and spectroscopic parameters (electronic transitions, NMR resonances) have been calculated. Combination with experimental results (under anaerobic or aerobic environment) determines the conditions for the existence of protonated, fully deprotonate and/or oxygenated semiquinones of PCA. Several energy optimized conformers containing manganese-(PCA-semiquinones) and water or/and peroxo-groups have been drawn (species 11-16) and their structural and spectroscopic properties have been calculated at the same level of theory. Experimental parallel to the theoretical results provide evidence for the existence of Mn(II)- and Mn(III)-[PCA-semiquinone] as well the conditions of dioxygen activation. Two of the blue solids (17 and 18) isolated from these solutions, have been characterized. Elemental analyzes, TGA, IR and ESR spectra support the formulation Mn(2)(PCA)(2)(O(2))(OH)(2)(AcO)(ClO(4))(2)(H(2)O)(3) (17), and Mn(2)(PCA)(2)(O(2))(2)(OH)(2)(AcO)H(2)O (18). Their ESR spectra, in solution (blue solutions), are almost identical and indicative of Mn(IV) existence. From the whole investigation, the activation of dioxygen by the PCA, its relocation on manganese and the oxidation of the metal ion have been provided.