Dissociative Electron Transfer Research Articles

Low-lying Negative Ion States Probed in Potassium - Ethanol Collisions.

Dissociative electron transfer in collisions between neutral potassium atoms and neutral ethanol molecules yields mainly OH-, followed by C2H5O-, O-, CH3 - and CH2 -. The dynamics of negative ions have been investigated by recording time-of-flight mass spectra in a wide range of collision energies from 17.5 to 350 eV in the lab frame, where the branching ratios show a relevant energy dependence for low/intermediate collision energies. The dominant fragmentation channel in the whole energy range investigated has been assigned to the hydroxyl anion in contrast to oxygen anion from dissociative electron attachment (DEA) experiments. This result shows the relevant role of the electron donor in the vicinity of the temporary negative ion formed allowing access to reactions which are not thermodynamically attained in DEA experiments. The electronic state spectroscopy of such negative ions, was obtained from potassium cation energy loss spectra in the forward scattering direction at 205 eV impact energy, showing a prevalent Feshbach resonance at 9.36±0.10 eV with character, while a less pronounced contribution assigned to a shape resonance has been obtained at 3.16±0.10 eV. Quantum chemical calculations for the lowest-lying unoccupied molecular orbitals in the presence of a potassium atom have been performed to support the experimental findings.

Dissociative Electron Transfer to N‐(Arylthio)phthalimides: Factors Affecting the Formation and Dissociation of Radical Anions

AbstractA series of chemically and biologically relevant N‐(arylthio)phthalimides is synthesized and its electrochemical reduction investigated. The results of the electrochemical study are analysed through application of Savéant's dissociative electron transfer theory and with the assistance of theoretical calculations. Reduction of all investigated N‐(arylthio)phthalimides leads to the corresponding radical anions, followed by the ejection of the phthalimide anion resulting from the dissociation of the N−S chemical bond. This stepwise electron transfer mechanism is evidenced by the electrochemical data which allow determination of the standard reduction potentials of all compounds. In the formation of the N‐(arylthio)phthalimide radical anions, the theoretical calculations show that the incoming electron, is hosted by the phthalimidyl group indicating a homolytic dissociation mechanism. The dissociation rate constants of the radical anions are deduced and show that upon changing the substituent from the MeO, to Me, H, F, Cl and Br the dissociation becomes faster. A good correlation with the Hammett substituent constants is also obtained. Application of Savéant's theory through determination of the associated driving force and the intrinsic barrier energies help rationalize the observed results and show that the change in the dissociation rate constant depends mainly on the standard reduction potential of the parent compounds.

Electrochemical Oxidation of Aliphatic Carboxylates: Kinetics, Thermodynamics, Mechanism, and the Role of Hydrogen Bonding

AbstractThe oxidation of tetra‐n‐butylammonium acetate, propionate, and pivalate was studied in rigorously anhydrous acetonitrile by conventional linear sweep and convolution voltammetry (LSV and ConV, respectively). The results suggest oxidation occurs via a concerted dissociative electron transfer pathway (RCO2−→R⋅+CO2+e−). The addition of water lowers the intrinsic barrier, signaling a possible change in mechanism to stepwise dissociative electron transfer. In rigorously dry acetonitrile, the oxidation potentials of CH3CO2− (0.60±0.09), CH3CH2CO2−, (0.47±0.05) and (CH3)3CCO2− (0.40±0.04 V vs. Ag/AgNO3 (CH3CN, 0.1 M)) are reported. These values parallel the stabilities of the resulting free radicals, consistent with a possible concerted pathway, although differential solvation of the carboxylate anions cannot be completely excluded as a contributor to this trend.

Theoretical exploration of the antioxidant activity of honokiol and magnolol

The radical scavenging mechanism of two bio-active compounds from Magnolia officinalis namely, honokiol and magnolol was explored on thermodynamic grounds employing density functional theory using M06-2X/6-311+G** level. Three different possible mechanisms such as HAT, SET-PT and SPLET were scrutinized with the help of their respective molecular descriptors such as bond dissociation enthalpy (BDE), ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA) and electron transfer enthalpy (ETE). Whereas the HAT mechanism was found to be the most thermodynamically favored mechanism of the radical scavenging activity in gas phase, SPLET mechanism was found to be favored in polar solvent. Rate calculations additionally suggests a faster reaction in the case of conformation-2 of magnolol with intra-molecular H bonding. Our thermodynamic results and kinetic calculation predicts magnolol and honokiol as potent peroxyl radical scavengers. Moreover, the role of internal H bonding in tuning the high reactivity of one of the magnolol conformations is well established in our study.

Structure and fragmentation chemistry of the peptide radical cations of glycylphenylalanylglycine (GFG).

Herein, we explore the generation and characterization of the radical cations of glycylphenylalanylglycine, or [GFG]•+, formed via dissociative electron-transfer reaction from the tripeptide to copper(II) within a ternary complex. A comprehensive investigation employing isotopic labeling, infrared multiple-photon dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations elucidated the details and energetics in formation of the peptide radical cations as well as their dissociation products. Unlike conventional aromatic-containing peptide radical cations that primarily form canonical π-radicals, our findings reveal that 75% of the population of the experimentally produced [GFG]•+ precursors are [GFα•G]+, where the radical resides on the middle α-carbon of the phenylalanyl residue. This unexpected isomeric ion has an enthalpy of 6.8 kcal/mol above the global minimum, which has an N-terminal captodative structure, [Gα•FG]+, comprising 25% of the population. The [b₂-H]•+ product ions are also present in a ratio of 75/25 from [GFα•G]+/ [Gα•FG]+, the results of which are obtained from matches between the IRMPD action spectrum and predicted IR absorption spectra of the [b₂-H]•+ candidate structures, as well as from IRMPD isomer population analyses.

Noncatalytic Reductive Deiodination of Thyroid Hormones. Electrochemistry and Quantum Chemical Calculations

AbstractNoncatalytic processes may occur spontaneously leading often to undesired products. Electrochemical measurements provide data for thermodynamic calculations. Cyclic voltammetry of thyroxine (T4) and 3,3’,5‐triiodothyronine (T3) in N,N‐dimethylformamide (DMF) and alkaline aqueous solutions of pH 10–14 on glassy carbon electrodes yielded the values of redox potentials for the reduction leading to deiodination of those thyroid hormones under noncatalytic conditions. The first step of T4 deiodination occurs in DMF at −1.93 V vs. Fc+/Fc and for T3 at −1.95 V, which was confirmed by quantum‐chemical calculations at DFT and DLPNO‐CCSD(T) levels. In alkaline aqueous solutions, owing to poor solubility of these compounds, it was possible to determine only approximate values equal to −1.6 to −1.7 V vs. Ag/AgCl for the first step of deiodination. The reduction potentials do not depend on pH under these conditions. As shown by calculations, further steps exhibit very close reduction potentials. The radicals formed as products of concerted dissociative electron transfer to T4 and T3 are relatively kinetically stable which leads to side reactions initiated by radicals in uncatalyzed deiodination processes.

A novel fluorescent sensor with an overtone peak reference for highly sensitive detection of mercury (II) ions and hydrogen sulfide: Mechanisms and applications in environmental monitoring and bioanalysis

The present study introduces a novel fluorescent sensor with an overtone peak reference designed for the detection of mercury (Ⅱ) ions (Hg2+) and hydrogen sulfide (H2S). The study proposes two novel response mechanisms that hinges on the synergistic effect of cation exchange dissociation (CED) and photo-induced electron transfer (PET). This sensor exhibits a remarkable detection limit of 2.9 nM for Hg2+. Additionally, the sensor reacts with H2S to generate nickel sulfide (NiS) semiconductor nanoparticles, which amplify the fluorescence signal and enable a detection limit of 3.1 nM for H2S. The detection limit for H2S is further improved to 29.1 pM through the surface functionalization of the nanomaterial with pyridine groups (increasing reactivity) and chelation of gold nanoparticles (AuNPs), which enhances the sensor's specificity. This improvement is primarily due to the surface plasmon resonance (SPR) of AuNPs and their affinity for H2S. The single-emission strategy can yield skewed results due to environmental changes, whereas the overtone peak reference strategy enhances result accuracy and reliability by detecting environmental interference through reference emission peaks. In another observation, the low-toxicity dihydropyrene-bipyridine nanorods (TPP-BPY) has been successfully utilized for both endogenous and exogenous H2S detection in vivo using a mouse model. The successful development of TPP-BPY is expected to provide an effective tool for studying the role of H2S in biomedical systems.

Photoredox Annulation of Polycyclic Aromatic Hydrocarbons.

The rise of interest in using polycyclic aromatic hydrocarbons (PAHs) and molecular graphenoids in optoelectronics has recently stimulated the growth of modern synthetic methodologies giving access to intramolecular aryl-aryl couplings. Here, we show that a radical-based annulation protocol allows expansion of the planarization approaches to prepare functionalized molecular graphenoids. The enabler of this reaction is peri-xanthenoxanthene, the photocatalyst which undergoes photoinduced single electron transfer with an ortho-oligoarylenyl precursor bearing electron-withdrawing and nucleofuge groups. Dissociative electron transfer enables the formation of persistent aryl radical intermediates, the latter undergoing intramolecular C-C bond formation, allowing the planarization reaction to occur. The reaction conditions are mild and compatible with various electron-withdrawing and -donating substituents on the aryl rings as well as heterocycles and PAHs. The method could be applied to induce double annulation reactions, allowing the synthesis of π-extended scaffolds with different edge peripheries.

Long‐Life, High‐Rate Rechargeable Lithium Batteries Based on Soluble Bis(2‐pyrimidyl) Disulfide Cathode

AbstractOrganosulfides are promising candidates as cathode materials for the development of electric vehicles and energy storage systems due to their low‐cost and high capacity properties. However, they generally suffer from slow kinetics because of the large rearrangement of S−S bonds and structural degradation upon cycling in batteries. In this paper, we reveal that soluble bis(2‐pyrimidyl) disulfide (Pym2S2) can be a high‐rate cathode material for rechargeable lithium batteries. Benefiting from the superdelocalization of pyrimidyl group, the extra electrons prefer to be localized on the π* (pyrimidyl group) than σ* (S−S bond) molecular orbitals initially, generating the anion‐like intermedia of [Pym2S2]2− and thus decreasing the dissociation energy of the S−S bond. It makes the intrinsic energy barrier of dissociative electron transfer depleted, therefore the lithium half cell exhibits 2000 cycles at 5 C. This study provides a distinct pathway for the design of high‐rate, long‐cycle‐life organic cathode materials.

Long-Life, High-Rate Rechargeable Lithium Batteries Based on Soluble Bis(2-pyrimidyl) Disulfide Cathode.

Organosulfides are promising candidates as cathode materials for the development of electric vehicles and energy storage systems due to their low-cost and high capacity properties. However, they generally suffer from slow kinetics because of the large rearrangement of S-S bonds and structural degradation upon cycling in batteries. In this paper, we reveal that soluble bis(2-pyrimidyl) disulfide (Pym2 S2 ) can be a high-rate cathode material for rechargeable lithium batteries. Benefiting from the superdelocalization of pyrimidyl group, the extra electrons prefer to be localized on the π* (pyrimidyl group) than σ* (S-S bond) molecular orbitals initially, generating the anion-like intermedia of [Pym2 S2 ]2- and thus decreasing the dissociation energy of the S-S bond. It makes the intrinsic energy barrier of dissociative electron transfer depleted, therefore the lithium half cell exhibits 2000 cycles at 5 C. This study provides a distinct pathway for the design of high-rate, long-cycle-life organic cathode materials.

Formulation of the cosmic ray–driven electron-induced reaction mechanism for quantitative understanding of global ozone depletion

This paper formulates the cosmic ray-driven electron-induced reaction as a universal mechanism to provide a quantitative understanding of global ozone depletion. Based on a proposed electrostatic bonding mechanism for charge-induced adsorption of molecules on surfaces and on the measured dissociative electron transfer (DET) cross sections of ozone-depleting substances (ODSs) adsorbed on ice, an analytical equation is derived to give atmospheric chlorine atom concentration: [Formula: see text] where Φe is the prehydrated electron (epre-) flux produced by cosmic ray ionization on atmospheric particle surfaces, [Formula: see text] is the surface coverage of an ODS, and ki is the ODS's effective DET coefficient that is the product of the DET cross section, the lifetimes of surface-trapped epre- and Cl-, and the particle surface area density. With concentrations of ODSs as the sole variable, our calculated results of time-series ozone depletion rates in global regions in the 1960s, 1980s, and 2000s show generally good agreement with observations, particularly with ground-based ozonesonde data and satellite-measured data over Antarctica and with satellite data in a narrow altitude band at 13 to 20 km of the tropics. Good agreements with satellite data in the Arctic and midlatitudes are also found. A previously unreported effect of denitrification on ozone loss is found and expressed quantitatively. But this equation overestimates tropospheric ozone loss at northern midlatitudes and the Arctic, likely due to increased ozone production by the halogen chemistry in polluted regions. The results render confidence in applying the equation to achieve a quantitative understanding of global ozone depletion.

Dissociative electron transfer mechanism and application in the electrocatalytic activation of organic halides

The electrochemical dehalogenation of organic halides has been a widely investigated topic in primis for fundamental investigations of dissociative electron transfer (DET) and as a green way for the electrosynthesis of organic compounds and environmental remediation. The main drawback associated with the electrochemical activation of C-X is the very negative potentials required, and this is particularly true in the case of organic chlorides, which represent the most investigated ensemble among organic molecules containing a leaving group. This has boosted over the last decades the research of electrode materials that are active toward C–X bond breaking, and without any doubt, Ag possesses extraordinary electrocatalytic properties, so far unsurpassed by any other electrode material. In this paper, we will attempt to brush up on important concepts related to DET in organic halides, while also evaluating recent developments in terms of electrode materials used in electrosynthesis based on organic halides and RX degradation processes.

Comparative study of the antioxidant capability of EDTA and Irganox

Oxidative stress makes it difficult to preserve food and negatively affect the applicability of polymeric packaging. It is typically caused by an excess of free radicals, and it is dangerous to human health, resulting in the onset and development of diseases. The antioxidant ability and activity of ethylenediaminetetraacetic acid (EDTA) and Irganox (Irg) as synthetic antioxidant additives were studied. Three different antioxidant mechanisms were considered and compared by calculating bond dissociation enthalpy (BDE), ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA), and electron transfer enthalpy (ETE) values. Two density functional theory (DFT) methods were used, M05-2X and M06-2X with the 6–311++G(2d,2p) basis set in gas phase. Both additives can be used to protect pre-processed food products and polymeric packaging from oxidative stress related material deterioration. By comparing the two studied compounds, it was found that EDTA has a higher antioxidant potential than Irganox. To the best of our knowledge several studies have been carried out to understand the antioxidant potential of various natural and synthetic species, but EDTA and Irganox were not compared and investigated before. These additives can be used to protect pre-processed food products and polymeric packaging and prevent material deterioration caused by oxidative stress.

Hydrogen-Induced Defective Crystalline Carbon Nitride with Enhanced Bidirectional Charge Migration for Persulfate Photoactivation

A feasible way to overcome the moderate photoactivity of carbon nitride is by decreasing the carrier diffusion distance and increasing the intralayer active sites by synthesizing defective crystalline carbon nitride. However, the additive-free synthesis of this type of structure remains a great challenge, due to the trade-off between crystallinity control and defect modulation. Herein, we demonstrate the hydrogen-assisted synthesis of ultrathin carbon nitride nanosheets with efficient exciton dissociation and fast electron transfer. Experimental and theoretical investigations indicate that hydrogen not only facilitates intermolecular cross-linking for crystallization but also generates abundant nitrogen vacancies among non-hydrogen-bonded tri-s-triazine units for charge transportation. The simultaneous modulation of interlayer and intralayer interactions contributes to the efficient bidirectional charge transfer during photocatalytic reactions. The synergy of defective crystalline carbon nitride and persulfate oxidants results in a striking performance for contaminant degradation, with 9.2- and 18.4-times higher activity than separate photocatalysis and persulfate photoactivated by bulk g-C3N4, respectively. This work not only provides a facile approach to synthesizing defective crystalline carbon nitride without employing any extrinsic additives but also opens up a new avenue to improve the efficiency of metal-free photocatalysts by bidirectional charge modulation.

Understanding molecular and electrochemical charge transfer: theory and computations.

Electron, proton, and proton-coupled electron transfer (PCET) are crucial elementary processes in chemistry, electrochemistry, and biology. We provide here a gentle overview of retrospective and currently developing theoretical formalisms of chemical, electrochemical and biological molecular charge transfer processes, with examples of how to bridge electron, proton, and PCET theory with experimental data. We offer first a theoretical minimum of molecular electron, proton, and PCET processes in homogeneous solution and at electrochemical interfaces. We illustrate next the use of the theory both for simple electron transfer processes, and for processes that involve molecular reorganization beyond the simplest harmonic approximation, with dissociative electron transfer and inclusion of all charge transfer parameters. A core example is the electrochemical reduction of the S2O82- anion. This is followed by discussion of core elements of proton and PCET processes and the electrochemical dihydrogen evolution reaction on different metal, semiconductor, and semimetal (say graphene) electrode surfaces. Other further focus is on stochastic chemical rate theory, and how this concept can rationalize highly non-traditional behaviour of charge transfer processes in mixed solvents. As a second major area we address ("long-range") chemical and electrochemical electron transfer through molecular frameworks using notions of superexchange and hopping. Single-molecule and single-entity electrochemistry are based on electrochemical scanning probe microscopies. (In operando) scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) are particularly emphasized, with theoretical notions and new molecular electrochemical phenomena in the confined tunnelling gap. Single-molecule surface structure and electron transfer dynamics are illustrated by self-assembled thiol molecular monolayers and by more complex redox target molecules. This discussion also extends single-molecule electrochemistry to bioelectrochemistry of complex redox metalloproteins and metalloenzymes. Our third major area involves computational overviews of molecular and electronic structure of the electrochemical interface, with new computational challenges. These relate to solvent dynamics in bulk and confined space (say carbon nanostructures), electrocatalysis, metallic and semiconductor nanoparticles, d-band metals, carbon nanostructures, spin catalysis and "spintronics", and "hot" electrons. Further perspectives relate to metal-organic frameworks, chiral surfaces, and spintronics.

Density Functional Theory Study on Antioxidant Activity of Three Polyphenols.

In recent years, research on the antioxidant activity of natural antioxidants has become more and more popular. Polyphenols are a large number of natural antioxidants in plants. This paper selected three common polyphenols to study their antioxidant activity based on quantum chemistry theory. This experiment hopes to provide a theoretical basis for the further development of polyphenol health food with strong antioxidant activity. Three polyphenols resveratrol, liquiritigenin, and isoliquiritigenin were optimized at the level of B3lyp/6-311G (d, p), and the single point energy was calculated with B3lyp/6-311 + + G (2d, 2p). The phenol hydroxyl bond dissociation enthalpy (BDE), ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA), and electron transfer enthalpy (ETE) were calculated in different phase states study the antioxidant mechanism. Draw the frontier molecular orbital and conduct dynamic simulation analysis scavenging · OH and · OOH to explore the most possible active sites in different phenolic hydroxyl sites. The bond length, dihedral angle, BDE, IP, PDE, PA and ETE were compared to speculate the antioxidant activity: Resveratrol > isoliquiritigenin > liquiritigenin. By analyzing the frontier molecular orbital and dynamic simulation results, it is speculated that the phenolic hydroxyl groups at C4', C4', and C4 are the most likely active sites of resveratrol, liquiritigenin, and isoliquiritigenin, respectively. In different phase states, the three compounds showed the same antioxidant activity, and the phenolic hydroxyl activities of the three compounds were different at different sites.

Two Theorems and Important Insight on How the Preferred Mechanism of Free Radical Scavenging Cannot Be Settled. Comment on Pandithavidana, D.R.; Jayawardana, S.B. Comparative Study of Antioxidant Potential of Selected Dietary Vitamins; Computational Insights. Molecules 2019, 24, 1646.

Totally ignoring that the five enthalpies of reaction-bond dissociation enthalpy (BDE), adiabatic ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA), and electron transfer enthalpy (ETE)-characterizing the three free radical scavenging mechanisms-direct hydrogen atom transfer (HAT), sequential electron transfer proton transfer (SET-PT), and stepwise proton loss electron transfer (SPLET)-are not independent of each other, a recent publication on the antioxidant activity of dietary vitamins compared various vitamins and "found" different quantities, which should be strictly equal by virtue of energy conservation. Aiming to clarify this point, as well as to avoid such mistakes in future studies and to unravel errors in the previous literature, in the present paper we formulate two theorems that any sound results on antioxidation should obey. The first theorem states that the sums of the enthalpies characterizing the individual steps of SET-PT and SPLET are equal: IP+PDE = PA+ETE (=H2). This is a mathematical identity emerging from the fact that both the reactants and the final products of SET-PT and SPLET are chemically identical. The second theorem, which is also a mathematical identity, states that H2 - BDE = IPH > 0, where IPH is the ionization potential of the H-atom in the medium (e.g., gas or solvent) considered. Due to their general character, these theorems may/should serve as necessary sanity tests for any results on antioxidant activity, whatever the method employed in their derivation. From a more general perspective, they should represent a serious word of caution regarding attempts to assign the preferred free radical scavenging pathway based merely on thermochemical descriptors.

Critical analysis of radical scavenging properties of atorvastatin in methanol recently estimated via density functional theory

In this communication we draw attention on serious flaws that plague recently reported antioxidant properties of atorvastatin (ATV) in methanol. First and foremost, we emphasize that the O-H bond dissociation energies (BDE) of about 400kcal/mol previously reported are completely wrong. Further, we present results refuting the previous claim that the proton affinity (PA) of ATV is smaller than that of the ascorbic acid. That unfounded claim relies on incorrect data for PA’s ascorbic acid (which we correct here) circulated in the literature. Further, we correct the values of the chemical reactivity indices (e.g., chemical hardness, electrophilicity index, electroaccepting and electrodonating powers), which were inadequately estimated previously via Kohn–Sham HOMO and LUMO energies. Finally, our updated values for O-H bond dissociation enthalpy (BDE = 91.4kcal/mol) and electron transfer enthalpy (ETE = 105.7kcal/mol) tentatively suggest that direct H-atom transfer (HAT) and sequential proton loss electron transfer (SPLET) may coexist.

Antioxidant Potential of Santowhite as Synthetic and Ascorbic Acid as Natural Polymer Additives.

A wide variety of additives are used to improve specific characteristics of the final polymeric product. Antioxidant additives (AAs) can prevent oxidative stress and thus the damage of polymeric materials. In this work, the antioxidant potential and thus the applicability of Santowhite (SW) as synthetic and ascorbic acid (Asc) as natural AAs were explored by using computational tools. Two density functional theory (DFT) methods, M05-2X and M06-2X, have been applied in combination with the 6-311++G(2d,2p) basis set in gas phase. Three antioxidant mechanisms have been considered: hydrogen atom transfer (HAT), single electron transfer-proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET). Bond dissociation enthalpy (BDE), ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA), and electron transfer enthalpy (ETE) have been computed for each potential hydrogen donor site. The results indicate that the antioxidant potential of Asc is higher than SW. Furthermore, some of the C-H bonds, depending on their position in the structures, are potent radical scavengers, but O-H groups are more prone to donate H-atoms to free radicals. Nonetheless, both additives can be potentially applied to safeguard common polymers and prohibit oxidative stress-induced material deterioration.

Fisetin and Robinetin antiradical activity under solvent effect: density functional theory study

The structural and antioxidant activity of two flavonols, namely, Fisetin and Robinetin, have been investigated employing the density functional theory (DFT) using B3LYP functional and 6-311++G (d, p) basis set. The calculations were performed in the gas phase and under the solvent effect of water, dimethylsulfoxide (DMSO), methanol, and benzene. The Hydrogen-Atom Transfer (HAT), single Electron Transfer Followed by Proton Transfer (SET-PT), and sequential Proton Loss Electron Transfer (SPLET) mechanisms were investigated to rationalize the radical scavenging capacities and to identify the favored antioxidant mechanism. Hence, the bond dissociation enthalpies (BDE) ionization potential (IP), IE, proton dissociation enthalpy (PDE), proton affinity (PA), and electron Transfer enthalpy (ETE) related to each mechanism were reported and discussed in function of the solvent effect. For both flavonols, the results showed that 4'-OH hydroxyl is the preferred active site following the trend 4'-OH > 3'-OH > 3-OH > (5'-OH) > 7-OH. Besides, the HAT mechanism is energetically the most favored pathway. The energetically favored solvents follow the trends water > DMSO > benzene > methanol and benzene > DMSO > methanol > water, for Fisetin and Robinetin, respectively.