Electronic Structure-activity Relationship Research Articles

Unraveling volcano trend in OER of metal–organic frameworks with asymmetric configuration through energy band engineering

Local symmetry breaking of catalysts has emerged as an effective strategy for finely tuning oxygen evolution reaction (OER) activity, yet the fundamental comprehension regarding asymmetric structure-activity relationships remains limited. Here, we propose the energy band engineering to bridge the correlation between established asymmetric electronic structure and adsorption/desorption ability of reaction intermediates within metal-organic frameworks (MOFs). The deliberate synthesis of CoM-MOFs (M=Cu, Ni, and Fe) with distinct coordination microenvironments enables the customization of asymmetric Co-O-M electronic structure. A volcano-shaped relationship can be revealed between calculated OER overpotential and average d‐band center (Ed) energy level for both active Co sites and substituted M. The CoFe-MOF, located close to the summit, showcases the balanced reaction intermediate behavior and thus for enhanced OER activity. This work presents a promising approach to thoroughly understand asymmetric electronic structure-activity relationships from the perspective of energy band engineering and further guide the discovery of high-efficiency MOF-based OER catalysts.

Accelerating σ-Bond Metathesis at Sn(II) Centers.

Molecular main-group hydride catalysts are attractive as cheap and Earth-abundant alternatives to transition-metal analogues. In the case of the latter, specific steric and electronic tuning of the metal center through ligand choice has enabled the iterative and rational development of superior catalysts. Analogously, a deeper understanding of electronic structure-activity relationships for molecular main-group hydrides should facilitate the development of superior main-group hydride catalysts. Herein, we report a modular Sn-Ni bimetallic system in which we systematically vary the ancillary ligand on Ni, which, in turn, tunes the Sn center. This tuning is probed using Sn L1 XAS as a measure of electron density at the Sn center. We demonstrate that increased electron density at Sn centers accelerates the rate of σ-bond metathesis, and we employ this understanding to develop a highly active Sn-based catalyst for the hydroboration of CO2 using pinacolborane. Additionally, we demonstrate that engineering London dispersion interactions within the secondary coordination sphere of Sn allows for further rate acceleration. These results show that the electronics of main-group catalysts can be controlled without the competing effects of geometry perturbations and that this manifests in substantial reactivity differences.

Solar driven CO2 hydrogenation on transition metal doped Zn12O12 cluster.

Photocatalytic hydrogenation of carbon dioxide (CO2) to produce value-added chemicals and fuel products is a critical routine to solve environmental issues. However, developing photocatalysts composed of earth-abundant, economic, and environmental-friendly elements is desired and challenging. Metal oxide clusters of subnanometer size have prominent advantages for photocatalysis due to their natural resistance to oxidation as well as tunable electronic and optical properties. Here, we exploit 3d transition metal substitutionally doped Zn12O12 clusters for CO2 hydrogenation under ultraviolet light. By comprehensive ab initio calculations, the effect of the dopant element on the catalytic behavior of Zn12O12 clusters is clearly revealed. The high activity for CO2 hydrogenation originates from the distinct electronic states and charge transfer from transition metal dopants. The key parameters governing the activity and selectivity, including the d orbital center of TM dopants and the energy level of the highest occupied molecular orbital for the doped Zn12O12 clusters, are thoroughly analyzed to establish an explicit electronic structure-activity relationship. These results provide valuable guidelines not only for tailoring the catalytic performance of subnanometer metal oxide clusters at atomic precision but also for rationally designing non-precious metal photocatalysts for CO2 hydrogenation.

Molecular Functionalization of NiO Nanocatalyst for Enhanced Water Oxidation by Electronic Structure Engineering.

Tuning the local environment of nanomaterial‐based catalysts has emerged as an effective approach to optimize their oxygen evolution reaction (OER) performance, yet the controlled electronic modulation around surface active sites remains a great challenge. Herein, directed electronic modulation of NiO nanoparticles was achieved by simple surface molecular modification with small organic molecules. By adjusting the electronic properties of modifying molecules, the local electronic structure was rationally tailored and a close electronic structure‐activity relationship was discovered: the increasing electron‐withdrawing modification readily decreased the electron density around surface Ni sites, accelerating the reaction kinetics and improving OER activity, and vice versa. Detailed investigation by operando Raman spectroelectrochemistry revealed that the electron‐withdrawing modification facilitates the charge‐transfer kinetics, stimulates the catalyst reconstruction, and promotes abundant high‐valent γ‐NiOOH reactive species generation. The NiO−C6F5 catalyst, with the optimized electronic environment, exhibited superior performance towards water oxidation. This work provides a well‐designed and effective approach for heterogeneous catalyst fabrication under the molecular level.

The role of intramolecular H-bonds predominant effects in myricetin higher antioxidant activity

Flavonoid antioxidants play essential roles in the prevention of damage caused by free radicals, which is concerned in many chemical and biological processes. The structural electronic properties of myricetin (Myc) and six respective radicals such as total electronic energies, bond dissociation enthalpy magnitudes (BDEs), intramolecular H–bonds strength and charges density distributions have been computed using density functional theory approach with B3P86 level. The important Myc molecular characteristics, the antioxidant activities, electronic structure–activity relationships, OH numbers and positions–activity relationships as well as radical scavenging mechanisms were discussed. The sequential active OH groups for H atom abstraction was predicted as 4′-OH>3′-OH≈5′-OH>3-OH>7-OH>5-OH that concomitant with B-ring>pyrone C-ring>A-ring activity in Myc structure. The vital role of intramolecular H-bonds was comprehensively monitored for the stabilization of B-ring radicals (4′-O, 3′-O, 5′-O), that lead to the highest activity of 4′-OH, 3′-OH, 5′-OH in B-ring. Also, the electrons delocalization among A, B and C-ring (increasing co-planarity) play second possible role for easy H atom donation. The number of three ortho-phenolic OH groups and radical stabilization by the strength of intramolecular H-bonds make B-ring to be very active and excellent to react with free radicals among three-rings in Myc structures. Our findings may be useful to elucidate the radical scavenging mechanism of other flavonoid antioxidants for the aim to design novel antioxidants.

Electrocatalysis of Perovskites: The Influence of Carbon on the Oxygen Evolution Activity

Single and double perovskite oxides have been reported to be amongst the most active electrocatalysts for the oxygen evolution reaction (OER) in alkaline electrolyte. Although a detailed study of the bulk electronic structure-activity relationship towards oxygen evolution on these oxides has been reported, the influence of carbon on the behavior of these oxides as OER catalysts is not yet clearly understood. In the present work we study the influence of functionalized acetylene black (ABf) carbon in the electrode composition on the OER activity for perovskite oxides using the thin-film rotating disk electrode technique. It was found that the addition of ABf significantly enhances the OER activity of the single perovskite oxides, namely Ba0.5Sr0.5Co0.8Fe0.2O3-δ, (BSCF) and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF). The activity of the double perovskite oxide, (Pr0.5Ba0.5)CoO3-δ (PBCO), was relatively unaffected by the addition of ABf in the electrode. Ex situ impedance spectroscopy measurements at room temperature showed that BSCF powder displayed a lower resistivity compared to PBCO with LSCF displaying the highest resistivity of the three materials. These results therefore suggest that the ABf present can more than simply improve the conductive pathway in the perovskite/carbon composite electrodes but can also significantly enhance the electrocatalytic activity of selected perovskites towards the OER.

Quantitative Structure-Activity Relationship Analysis of Antimalarial Compound of Mangostin Derivatives Using Regression Linear Approach

Quantitative electronic structure-activity relationship (QSAR) analysis of a series of mangostin derivatives as antiplasmodial compounds have been conducted using atomic net charges (q), dipole moment (μ) ELUMO, EHOMO, polarizability (α), log P and massa molecular as the descriptors. The descriptors were obtained from computational chemistry method using semi-empirical PM3. Antiplasmodial activities were taken as the activity of the drugs against chloroquine-resistant plasmodiumfalciparum FCR3 strain and are presented as the value of ln (1/IC50) where IC50 is an effective concentration inhibiting 50 % of the parasite growth. The best model of QSAR model was determined by multiple linear regression method and giving equation of QSAR: ln 1/IC50 = -189.029-(752.054) qC5 + (1249.672)qO6 + (3134.359) qC9 + (1174.323) qC10 + (329.121)qC13 - (1.409)µ + (75.214) ELUMO - (23.683) ELUMO - (2.156) α- (3.372) log P + (0.309) MM. The equation was significant on the 95 % level with statistical parameters: n = 15; r = 0.951; r 2 = 0.905; SE = 1.326498; Fcalc/Ftable = 1.029 and gave the PRESS = 5.650972. Its means that there were only a relatively few deviations between the experimental and theoretical data of antimalarial activity.

QUANTITAVE STRUCTURE-ACTIVITY RELATIONSHIP ANALYSIS (QSAR) OF ANTIMALARIAL 1,10-PHENANTHROLINE DERIVATIVES COMPOUNDS

Quantitative Electronic Structure-Activity Relationship (QSAR) analysis of a series of 1,10-phenanthroline derivatives as antiplasmodial compounds have been conducted using atomic net charges (q), dipole moment (μ) ELUMO, EHOMO, polarizability (α) and log P as the descriptors. The descriptors were obtained from computational chemistry method using semi-empirical PM3. Antiplasmodial activities were taken as the activity of the drugs against chloroquine-resistant Plasmodium falciparum FCR3 strain and are presented as the value of ln (1/IC50) where IC50 is an effective concentration inhibiting 50% of the parasite growth. The best model of QSAR model was determine by multiple linear regression method and giving equation of QSAR: ln 1/IC50 = 3.732 + (5.098) qC5 + (7.051) qC7 + (36.696) qC9 + (41.467) qC11 -(135.497) qC12 + (0.332) μ - (0.170) α + (0.757) log P. The equation was significant on the 95% level with statistical parameters: n=16; r=0.987; r2= 0.975; SE=0.317; Fcalc/Ftable = 15.337 and gave the PRESS=0.707. Its means that there were only a relatively few deviations between the experimental and theoretical data of antimalarial activity. Keywords: QSAR, antimalarial, semi-empirical method, 1,10-phenanthroline.

A Computer-Based Structure-Activity Relationship Method for Predicting the Toxic Effects of Organic Chemicals from Onedimensional Representations of their Molecular Structures.

A computer-based method is presented for the analysis and interpretation of structural formulae characterising chemical molecules. This method was developed to enable a computer to identify substructures of chemical molecules that are relevant in the context of specific toxicological questions. The new computer-based structure-examination method was used to develop the "structure" parts of several electronic structure-activity relationship models (SAR models) for analysing and interpreting the structural formula of a chemical from its one dimensional representation, by applying recursive principles and identifying partial isomorphic graphs. The structure-examination method is designed as part of an open-endpoint procedure to be used in expert systems, and could be applied in the construction of SAR models for almost all toxicological endpoints. The system was satisfactorily tested by identifying substructures relevant to severely damaging effects on skin and eyes.

Theoretical evidence of the existence of a diazafulvene intermediate in the reaction pathway of imidazoleglycerol phosphate dehydratase: design of a novel and potent heterocycle structure for the inhibitor on the basis of the electronic structure-activity relationship study

The reaction mechanism of imidazoleglycerol phosphate dehydratase has not yet been clearly revealed. Structural comparison between inhibitors and the substrate IGP implicates that the reaction involves a diazafulvene intermediate. Here, we present evidence to support this hypothesis by investigating the electronic structure-enzyme inhibitory activity relationship on inhibitors with different heterocycles using 6-31G** level theory of the ab initio molecular orbital method. The calculation results showed that potent inhibitors can be distinguished from weak ones by the atomic charge density and by the energy levels of the highest occupied lone-pair orbital on the nitrogen atoms in the heterocycles. Furthermore, very good correlations ( r 2=0.8–0.9) were found between the charge density on the nitrogen atom and the inhibitory activity. It was also revealed that the diazafulvene is electronically similar to the potent inhibitors. Thus, these results strongly suggest the existence of the diazafulvene as an intermediate possessing tight-binding affinity to the enzyme. Based on the electronic structural similarity between the potent inhibitors and the proposed intermediate, a novel heterocycle was designed and predicted its inhibitory activity prior to the synthesis. Then, activity of synthesized inhibitors showed excellent agreement with this prediction. Hence, from the theoretical studies and experimental results, we conclude to obtain evidence of the hypothesis that the enzyme reaction proceeds via the diazafulvene intermediate.

Electronic structure-activity relationship for derivatives of propenone. Communication II. 2-cinnamoylbenzimidazoles and 2-(β-benzoylvinyl)-1-methylbenzimidazoles

Our systematic investigations of some regularities of the electronic structure-activity relationship (ESAR) in a series of chalcone derivatives and the corresponding heterocyclic analogs substantiated the structural characteristics that determine the antioxidant, antiallergic, antiinflammatory, and other types of activity [1, 2]. In earlier communications we described the results of antiallergic activity studies [1] and the analysis of ESAR for derivatives of 4-carboxyvinylenechalcones and 3-einnamoylcoumarins [3]. As a continuation of these studies, we considered it reasonable to obtain heterocyclic analogs of chalcone, in which one of the aromatic rings was replaced by the benzimidazole fragment. Benzimidazole derivatives are known to process more than 25 types of pharmacological action, including antiallergic [4] and immunomodulating activity (dibazole). We synthesized two types of benzimidazole analogs, 2cinnamoylbenzimidazoles and 2-(13-benzoylvinyl)-l-methylbenzimidazoles (see Table I). Compounds I a n were synthesized by condensation of 2-acetylbenzimidazole with aromatic aldehydes in the presence of a basic or acidic catalyst; compounds I I a n were synthesized by the reaction of 2-formyl-l-methylbenzimidazole with corresponding acetophenones. Biological testing of the compounds obtained revealed pronounced antiallergic and sedative activities (AA and SA, respectively) as well as moderate hypotensive and antihemorrhagic activities. The outlined conclusions [3] about the decisive contribution of electronic parameters of the ct,IB-unsaturated carbonyl fragment to the biological activity of chalcone and coumarin derivatives served as a basis for the search for ESAR in a series of synthesized benzimidazole analogs of chalcone.

Quantitative electronic structure-activity relationship (QESAR) of natural cytotoxic compounds: maytansinoids, quassinoids and cucurbitacins

A relationship between the electronic structure of the maytansinoids, quassinoids and cucurbitacins and their biological activities (cytotoxicity, antitumor activity) was established on the basis of semiempirical SCF-MO calculations, using multiple linear regression analysis as a framework. Based on this relationship, the pharmacophore could be evaluated, and some novel derivatives were designed.

Electronic structure-activity relationships (ESAR) for derivatives of propenone. Part 1. 4-carboxyvinylenechalcones and 3-cinnamoylcoumarins

Electronic structure-activity relationships (ESAR) for derivatives of propenone. Part 1. 4-carboxyvinylenechalcones and 3-cinnamoylcoumarins

Quantum Pharmacological Analysis of Structure-Activity Relationships for Mefloquine Antimalarial Drugs

Linear models for quantitative electronic structure-activity relationships (QSAR) of mefloquine-type antimalarial drugs have been evaluated on the basis of CNDO/2 molecular orbital calculations. The results indicate that mefloquines could interact via two active sites in a similar mechanism, as proposed for primaquine and chloroquine drugs.

A quantitative aspect of charge-transfer phenomenon in the biological activity of hallucinogens, local anesthetics and nicotinic agents

The qualitative electronic structure-activity relationships, that had led some workers to suggest that hallucinogens, local anesthetics, and nicotinic agents exert their biological effect through the formation of charge-transfer complexes with the receptors, are tested statistically. The statistical test is found to support the suggestion along with the observation that in addition to the charge-transfer mechanism, a secondary binding is also involved in the activity of nicotinic agents.