Theoretical insight into the unexpected initial (3 + 2) cycloaddition reaction of mesitonitrile oxide with 1, 4-diazepine derivatives: A computational study.

1,4-Diazepine as an active drug component underlies the potency of most psychotic, anticancer, anticonvulsant, and antibacterial drugs in the market and is, therefore crucial in chemotherapeutic treatment in biomedicine. Proper functionalization of this moiety can afford even more potent drugs. As a result of their therapeutic significance, this study aims at precisely giving a comprehensive computational insight into the unexpected initial reactivity of 1,4-diazepine derivatives and mesitonitrile oxide. The initial reaction between mesitonitrile oxide and 1,4-diazepine derivatives proceeds via a (3 + 2) cycloaddition reaction which leads to the formation of a cycloadduct where the mesitonitrile oxide unexpectedly adds across the imine functionality at the expense of the potential olefinic carbon-carbon double bond. Calculations at the density functional theory (DFT) M06/6-311G (d, p) level of theory indicate that the initial (3 + 2) cycloaddition reaction of mesitonitrile oxide (1,3-dipole) and 1,4-diazepine derivatives (dipolarophile) in all cases proceeds to form the cycloadduct where the 1,3-dipole adds preferentially to the imine functionality at the expense of the potential olefinic carbon-carbon double bond. In light of the parent reaction, the most kinetically favored cycloadductP3A had a rate constant of 5.1 × 106 M-1s-1, which is about 12 manifolds faster than the next competing stereoisomer P1A with a rate constant of 4.1 × 105 M-1s-1 and about 1024 faster than the most favored cycloadduct P3B with a rate constant of 7.2 × 10-19 M-1s-1 in the unfavored pathway (Path B). Irrespective of the electronic and steric nature of the electron-donating (EDG) and electron-withdrawing (EWG) substituents placed on the dipolarophile, the selectivities of the reaction were maintained. Rationalization of the potential energy surface depicts that the 1,3-dipole adds across the dipolarophile via an asynchronous concerted mechanism. Rationalization of the HOMO-LUMO energies of the mesitonitrile oxide (1,3-dipole) and the 1,4-diazepine derivatives (dipolarophile) depict that the EDG-substituted dipolarophile react as nucleophiles, whereas the dipole reacts as an electrophile. Conversely, the HOMO-LUMO interaction between the EWG-substituted dipolarophile indicates that the EWG-substituted dipolarophile react as electrophiles, whereas the dipole reacts as a nucleophile. The electrophilic parr function at various reactive sites of the dipolarophile shows that the 1,3-dipole preferentially adds across the local centers with the largest electrophilic NBO or Mulliken spin densities which is consistent with the energetic trend observed. The reactivity of the 1,4-diazepine derivatives and the mesitonitrile oxide showed poor stereoselectivity.

Evaluation of phytochemical, proximate, antioxidant, and anti-nutrient properties of Corchorus olitorius, Solanum macrocarpon and Amaranthus cruentus in Ghana.

INTRODUCTION: In Ghana, Corchorus olitorius, Solanum macrocarpon and Amaranthus cruentus are green leafy vegetables that are customarily eaten together with a starchy staple food. The present study aimed at assessing the ethanolic leaf extract of C. olitorius, S. macrocarpon and A. cruentus for antioxidant capacity, phytochemical property, nutritional and anti-nutrient content. METHOD: Phytochemical constituent and proximate analysis were determined using standard protocols. The DPPH scavenging activity was used to determine the antioxidant activity of the ethanolic leaf extracts from the three vegetables. The antinutrients phytate and oxalate were determined by titrimetric methods of analysis. RESULTS: Pytochemical screening revealed the presence of tannins and flavonoids in C. olitorius, S. macrocarpon and A. cruentus. Alkaloids and saponins were present in C. olitorius and S. macrocarpon but not in A. cruentus. Terpenoids, steroids, carotenoids and coumarins were absent in all the three vegetables. Proximate analysis revealed varying levels of moisture, fat, protein, ash, crude fibre and carbohydrates in the three leafy vegetables. The DPPH scavenging showed 86.71%, 71.72% and 38.86% activity for S. macrocarpon, C. olitorius and A. cruentus respectively. The antinutrient results revealed an oxalate level of 2.7 ± 0.13% for C. olitorius, 6.43 ± 0.06% for A. cruentus and 12.32 ± 0.13% for S. macrocarpon. For levels of phytates, our results revealed a 3.084 ± 0.54%, 1.14 ± 0.26% and 1.71 ± 0.27% for C. olitorius, A. cruentus and S. macrocarpon, respectively. CONCLUSION: The current study has shown that C. olitorius, A. cruentus and S. macrocarpon possess important phytochemicals, nutrients and significant antioxidant activity, suggesting a potential of these vegetables against diverse disease, if eaten by humans.

Exploring the peri- and stereo- selectivities of the cycloaddition reaction of 2-(2- dimethylaminovinyl)-1-benzopyran-4-one with N-phenylmaleimide (NPM) and dimethylacetylenedicarboxylate (DMAD) - A DFT study.

The [4 + 2] cycloaddition reactions of 2-styrylchromones have been predominantly described as one of the efficient methods for the synthesis of xanthones-a prominent class of tricyclic molecules that occur widely in nature. These xanthones are well known for their pharmacological activities especially their role as anti-cancer agents in the medicinal world. In this study, the mechanistic insight into the unusual (peri- and stereo-) selectivities of the reaction of 2-(2-dimethylaminovinyl)-1-benzopyran-4-one (A1) with N-phenylmaleimide (NPM) and dimethylacetylenedicarboxylate (DMAD) has been studied using density functional theory (DFT) at the M06-2X/6-311G (d, p) level of theory. The reaction of A1 and NPM in dimethylformamide (DMF) is periselective towards the initial formation of a [4 + 2] cycloadduct and stereoselectively in an exo fashion with an activation energy of 6.8kcalmol-1 and a rate constant of 6.43×107s-1 which occurs about 878 million times faster than the closest competing pathway for the initial [2 + 2] cycloaddition fashion with an activation energy of 19.0kcalmol-1 and a rate constant of 7.32×10-2s-1. For the substituent effect on the reaction, the reaction selectivity is still maintained where the exo intermediate remains the most kinetically favored cycloadduct. However, the magnitude of the barriers increases slightly with a margin of about 0.1-4.8kcalmol for the electron-donating groups (EDGs) in the order; strong EDGs (OH < NH2 < OCH3) < weak EDGs (

Theoretical studies on the reaction mechanisms of the oxidation of tetramethylethylene using MO3Cl (M=Mn, Tc and Re).

A theoretical study on the reaction mechanisms of the addition of transition metal oxo complexes of the type MO3Cl (M = Mn, Tc, and Re) to tetramethylethylene (TME) is presented. Theoretical calculations using B3LYP/LACVP* and M06/LACVP* (LACVP* is a combination of the 6-31G(d) basis set along with LANL2DZ pseudopotentials on the metallic centres) were performed and the results are discussed within the framework of reaction energetics. The nature of the stability of the reaction mechanisms was equivalent for both theories. However, the M06/LACVP* simulations generally had slightly lower energies and shorter bond lengths compared to the B3LYP/LACVP* computations. Furthermore, it was observed that the reaction does not proceed via the stepwise reaction mechanism due to kinetic and thermodynamic instabilities. Epoxidation was also found to occur via the [2 + 2] concerted reaction mechanism for the MO3Cl (M = Tc and Re) whereas the permanganyl chloride complex epoxidizes TME via the [2 + 1] concerted reaction mechanism on the singlet potential energy surface (PES). Dioxylation was observed to proceed via the [3 + 2] route for the addition of MO3Cl (M = Tc and Re) and TME. Results indicate that all reaction surfaces were unselective except for the permanganyl chloride catalyzed surface which leads to the formation of epoxides exclusively. Changes in temperatures from 298.15 K to 373.15 K, resulted in kinetically and thermodynamically unstable reaction pathways as the activation and reaction energies increased generally. On the singlet PES, the rate constant calculations showed that the [3 + 2] catalyzed surface reaction mechanism leading to dioxylation was faster than the [2 + 2] mechanism in cases where plausible. Theoretical values from the global reactivity parameters, namely the chemical hardness, chemical potential, electrophilic and nucleophilic indices, are in good correlation with the DFT activation and reaction energies at both levels of theories. Thus, as the electrophilic nature of the metal decreases from Mn to Re, so do the activation and reaction energies increase from Mn to Re, indicating that the higher the electrophilicity of the metal centre, the more spontaneous the oxidation reaction.

Boosting the photocatalytic H2 evolution activity of type-II g-GaN/Sc2CO2 van der Waals heterostructure using applied biaxial strain and external electric field.

Two-dimensional (2D) van der Waals (vdW) heterostructures are a new class of materials with highly tunable bandgap transition type, bandgap energy and band alignment. Herein, we have designed a novel 2D g-GaN/Sc2CO2 heterostructure as a potential solar-driven photocatalyst for the water splitting process and investigate its catalytic stability, interfacial interactions, and optical and electronic properties, as well as the effects of applying an electric field and biaxial strain using first-principles calculation. The calculated lattice mismatch and binding energy showed that g-GaN and Sc2CO2 are in contact and may form a stable vdW heterostructure. Ab initio molecular dynamics and phonon dispersion simulations show thermal and dynamic stability. g-GaN/Sc2CO2 has an indirect bandgap energy with appropriate type-II band alignment relative to the water redox potentials. Meanwhile, the interfacial charge transfer from g-GaN to Sc2CO2 can effectively separate electron-hole pairs. Moreover, a potential drop of 3.78 eV is observed across the interface, inducing a built-in electric field pointing from g-GaN to Sc2CO2. The heterostructure shows improved visible-light optical absorption compared to the isolated g-GaN and Sc2CO2 monolayers. Our study demonstrates that tunable electronic and structural properties can be realised in the g-GaN/Sc2CO2 heterostructure by varying the electric field and biaxial strain. In particular, the compressive strain and negative electric field are more effective for promoting hydrogen production performance. Since it is challenging to tune the electric field and biaxial strain experimentally, our research provides strategies to boost the performance of MXene-based heterojunction photocatalysts in solar harvesting and optoelectronic devices.

A DFT study on the reaction mechanisms of the oxidation of ethylene mediated by technetium and manganese oxo complexes.

The oxidation of ethylene catalyzed by manganese and technetium oxo complexes of the type MO3L (M = Tc, Mn, and L = O-, Cl-, F-, OH-, Br-, I-) on both singlet and triplet potential energy surfaces (PESs) have been studied. All molecular structures were stable on the singlet PES except for the formation of the dioxylate intermediate for the MnO3L (L = O-, Cl-, F-, OH-, Br-, I-) catalyzed pathway. Frontier molecular orbital calculations showed that electrons flow from the HOMO of ethylene into the LUMO of the metal-oxo complex for all complexes studied except for MO3L (M = Tc, Mn, and L = O-) where the vice versa occurs. In the reaction of both TcO3L and MnO3L (L = O-, Cl-, F-, OH-, Br-, I-) with ethylene, it was observed that the formation of the dioxylate intermediate along the [3 + 2] addition pathway on the singlet reaction surface is both kinetically and thermodynamically favorable over its formation via the [2 + 2] pathway. Furthermore, it was observed that TcO4- and MnO4- catalyzed pathways exclusively form diols on the singlet PES. The formation of epoxides on the singlet surface is kinetically favorable through the [2 + 1] and [2 + 2] channel for the MnO3L (L = F-, Cl-, Br-, I-, OH-) and TcO3L (L = F-, Cl-, Br-, I-, OH-) catalyzed surfaces respectively. In all cases, the TcO3L complexes were found to be polar compared to the MnO3L complexes. The MnO4- (singlet) and MnO3F (singlet) are the best catalysts for the exclusive formation of the diols and epoxides respectively.

A review on the computational studies of the reaction mechanisms of CO2 conversion on pure and bimetals of late 3d metals.

Despite series of experimental studies that reveal unique activities of late 3d transition metals and their role in microorganisms known for CO2 conversion, these surfaces are not industrially viable yet. An insight into the elementary steps of surface catalytic processes is crucial for effective surface modification and design. The mechanisms of CO2 transformation into CO, through the reverse water gas shift and methane reforming, are being studied. Mechanisms of CO2 methanation is also being explored by the Sabatier reaction into methane. This review covers both experimental and theoretical studies into the mechanisms of CO2 reduction into CO and methane, on single metals and bimetals of late 3d transition metals, i.e. Fe, Co, Ni, Cu and Zn. This paper highlights progress and gaps still existing in our knowledge of the reaction mechanisms. These mechanistic studies reveal CO2 activation and reduction mechanisms are specific to both composition and surface facet. Surfaces with least CO2 binding potential are seen to favour CO and O binding and provide higher barriers to dissociation. No direct correlation has been seen between binding strength of CO2 and its degree of activation. Hydrogen-assisted dissociation is seen to be generally favoured kinetically on Cu and Ni surfaces over direct dissociation except on the Ni (211) surface. Methane production on Cu and Ni surfaces is seen to occur via the non-formate pathway. Hydrogenation reactions have focused on Cu and Ni, and more needs to be done on other surfaces, i.e. Co, Fe and Zn.

Mechanisms of ethyne oxidation catalyzed by LMnO3 (L = O-, Cl, NPH3, CH3, and Cp): a density functional theory study.

The mechanisms of LMnO3 (L = O-, Cl, NPH3, CH3, and Cp)-catalyzed oxidation of ethyne has been studied on the singlet and triplet hypersurfaces at the M06/6-311G(d) level of theory. For the first step, the [3 + 2] pathways to the formation of the metalla-2,5-dioxol-3-ene intermediate are kinetically and thermodynamically the most favored pathways in all the complexes studied; it is favored over the [2 + 2] addition pathways to the metallaoxetene intermediate. The formation of the oxirene precursor that could give the oxirene the reported key intermediates in the ozonolysis of alkynes would most likely result from the oxidation of ethyne by MnO3Cl on the triplet potential energy surface (PES). [3 + 2] versus [2 + 1] addition of MnO3Cl with ethyne at the M06/6-311G(d) level of theory.

Permanganyl chloride-mediated oxidation of tetramethylethylene: A density functional theory study.

The mechanisms of the oxidation of tetramethylethylene (TME) by permanganyl chloride (MnO3Cl) have been explored on the singlet and triplet potential energy surfaces at the B3LYP LANL2DZ/6-31G (d) level of theory. The results show that the pathway leading to the formation of the five-membered dioxylate through concerted [3 + 2] addition is favored kinetically and thermodynamically over the three other possible pathways, namely the [2 + 2] addition via the transient metallaoxetane intermediate, epoxidation, and hydrogen transfer pathways. The epoxide precursor that on hydrolysis would yield the epoxide product will most likely arise from a stepwise path through the intermediacy of an organometallic intermediate. This pathway affords the product that is more stable (thermodynamically favorable). However, kinetically, both the stepwise and the concerted [2 + 1] addition pathways leading to the epoxide precursors are very competitive (activation barrier difference of <0.7 kcal/mol).

Ab initio investigation of O2 adsorption on Ca-doped LaMnO3 cathodes in solid oxide fuel cells.

We present a Hubbard-corrected density functional theory (DFT+U) study of the adsorption and reduction reactions of oxygen on the pure and 25% Ca-doped LaMnO3 (LCM25) {100} and {110} surfaces. The effect of oxygen vacancies on the adsorption characteristics and energetics has also been investigated. Our results show that the O2 adsorption/reduction process occurs through the formation of superoxide and peroxide intermediates, with the Mn sites found to be generally more active than the La sites. The LCM25{110} surface is found to be more efficient for O2 reduction than the LCM25{100} surface due to its stronger adsorption of O2, with the superoxide and peroxide intermediates shown to be energetically more favorable at the Mn sites than at the Ca sites. Moreover, oxygen vacancy defect sites on both the {100} and {110} surfaces are shown to be more efficient for O2 reduction, as reflected in the higher adsorption energies calculated on the defective surfaces compared to the perfect surfaces. We show from Löwdin population analysis that the O2 adsorption on the pure and 25% Ca-doped LaMnO3 surfaces is characterized by charge transfer from the interacting surface species into the adsorbed oxygen πg orbital, which results in weakening of the O-O bonds and its subsequent reduction. The elongated O-O bonds were confirmed via vibrational frequency analysis.

A computational study of the addition of ReO3L (L = Cl(-), CH3, OCH3 and Cp) to ethenone.

The periselectivity and chemoselectivity of the addition of transition metal oxides of the type ReO3L (L = Cl, CH3, OCH3 and Cp) to ethenone have been explored at the MO6 and B3LYP/LACVP* levels of theory. The activation barriers and reaction energies for the stepwise and concerted addition pathways involving multiple spin states have been computed. In the reaction of ReO3L (L = Cl(-), OCH3, CH3 and Cp) with ethenone, the concerted [2 + 2] addition of the metal oxide across the C=C and C=O double bond to form either metalla-2-oxetane-3-one or metalla-2,4-dioxolane is the most kinetically favored over the formation of metalla-2,5-dioxolane-3-one from the direct [3 + 2] addition pathway. The trends in activation and reaction energies for the formation of metalla-2-oxetane-3-one and metalla-2,4-dioxolane are Cp < Cl(-) < OCH3 < CH3 and Cp < OCH3 < CH3 < Cl(-) and for the reaction energies are Cp < OCH3 < Cl(-) < CH3 and Cp < CH3 < OCH3 < Cl CH3. The concerted [3 + 2] addition of the metal oxide across the C=C double of the ethenone to form species metalla-2,5-dioxolane-3-one is thermodynamically the most favored for the ligand L = Cp. The direct [2 + 2] addition pathways leading to the formations of metalla-2-oxetane-3-one and metalla-2,4-dioxolane is thermodynamically the most favored for the ligands L = OCH3 and Cl(-). The difference between the calculated [2 + 2] activation barriers for the addition of the metal oxide LReO3 across the C=C and C=O functionalities of ethenone are small except for the case of L = Cl(-) and OCH3. The rearrangement of the metalla-2-oxetane-3-one-metalla-2,5-dioxolane-3-one even though feasible, are unfavorable due to high activation energies of their rate-determining steps. For the rearrangement of the metalla-2-oxetane-3-one to metalla-2,5-dioxolane-3-one, the trends in activation barriers is found to follow the order OCH3 < Cl(-) < CH3 < Cp. The trends in the activation energies for the most favorable [2 + 2] addition pathways for the LReO3-ethenone system is CH3 > CH3O(-) > Cl(-) > Cp. For the analogous ethylene-LReO3 system, the trends in activation and reaction energies for the most favorable [3 + 2] addition pathway is CH3 > CH3O(-) > Cl(-) > Cp [10]. Even though the most favored pathway in the ethylene-LReO3 system is the [3 + 2] addition pathway and that on the LReO3-ethenone is the [2 + 2] addition pathway, the trends in the activation energies for both pathways are the same, i.e. CH3 > CH3O(-) > Cl(-) > Cp. However, the trends in reaction energies are quite different due to different product stabilities. The formation of the acetic acid precursor through the direct addition pathways was unsuccessful for all the ligands studied. The formation of the acetic acid precursor through the cyclization of the metalla-2-oxetane-3-one is only possible for the ligands L = Cl(-), CH3 whiles for the cyclization of metalla-2-oxetane-4-one to the acetic acid precursor is only possible for the ligand L = CH3. Although there are spin-crossover reaction observed for the ligands L = Cl(-), CH3 and CH3O(-), the reactions occurring on the single surfaces have been found to occur with lower energies than their spin-crossover counterparts.

A theoretical study of the mechanisms of oxidation of ethylene by manganese oxo complexes.

The mechanisms of oxidation of ethylene by manganese-oxo complexes of the type MnO3L (L = O(-), Cl, CH3, OCH3, Cp, NPH3) have been explored on the singlet, doublet, triplet and quartet potential energy surfaces at the B3LYP/LACVP* level of theory and the results discussed and compared with those of the technetium and rhenium oxo complexes we reported earlier, thereby drawing group trends in the reactions of this important class of oxidation catalysts. In the reactions of MnO3L (L = O(-), Cl(-), CH3, OCH3, Cp, NPH3) with ethylene, it was found that the formation of the dioxylate intermediate along the concerted [3 + 2] addition pathway on the singlet potential energy is favored kinetically and thermodynamically over its formation by a two-step process via the metallaoxetane by [2 + 2] addition. The activation barriers for the formation of the dioxylate and the product stabilities on the singlet PES for the ligands studied are found to follow the order: NPH3 < Cl(-) < CH3O(-) < Cp < O(-) < CH3. On the doublet PES, the activation barriers for the formation of the dioxylate intermediate for the ligands are found to follow the order: CH3O(-) < Cl(-) < Cp < CH3 while the order of product stabilities is: Cl(-) < CH3O(-) < Cp < CH3. The order of dioxylate product stabilities on the triplet surface for the ligands studied is: Cl(-) < CH3O(-) < Cp < CH3 < NPH3 < O(-) and the order on the quartet surface is O(-) < Cp < CH3 < NPH3 < Cl(-) < CH3O(-). The re-arrangement of the metallaoxetane intermediate to the dioxylate is not a feasible reaction for all the ligands studied. Of the group VII B metal oxo complexes studied, MnO4(-) and MnO3(OCH3) appear to be the best catalysts for the exclusive formation of the dioxylate intermediate, MnO3(OCH3) being better so on both kinetic and thermodynamic grounds. The best epoxidation catalyst for the Mn complexes is MnO3Cl; the formation of the epoxide precursor will not result from the reaction of LMnO3 (L = O(-), Cp) with ethylene on any of the surfaces studied. The trends observed for the oxidation reactions of the Mn complexes with ethylene compare closely with those reported by us for the ReO3L and TcO3L (L = O(-), Cl, CH3, OCH3, Cp, NPH3) complexes, but there is far greater similarity between the Re and Tc complexes than between Mn and either of the other two. There does not appear to be any singlet-triplet or doublet-quartet spin-crossover in any of the pathways studied.

A density functional theory study of the mechanisms of oxidation of ethylene by rhenium oxide complexes.

The oxo complexes of group VII B are of great interest for their potential toward epoxidation and dihydroxylation. In this work, the mechanisms of oxidation of ethylene by rhenium-oxo complexes of the type LReO3 (L = O(-), Cl, CH3, OCH3, Cp, NPH3) have been explored at the B3LYP/LACVP* level of theory. The activation barriers and reaction energies for the stepwise and concerted addition pathways involving multiple spin states have been computed. In the reaction of LReO3 (L = O(-), Cl, CH3, OCH3, Cp, NPH3) with ethylene, it was found that the concerted [3 + 2] addition pathway on the singlet potential energy surfaces leading to the formation of a dioxylate intermediate is favored over the [2 + 2] addition pathway leading to the formation of a metallaoxetane intermediate and its re-arrangement to form the dioxylate. The activation barrier for the formation of the dioxylate on the singlet PES for the ligands studied is found to follow the order O(-) > CH3 > NPH3 > CH3O(-) > Cl(-) > Cp and the reaction energies follow the order CH3 > O(-) > NPH3 > CH3O(-) > Cl(-) > Cp. On the doublet PES, the [2 + 2] addition leading to the formation the metallaoxetane intermediate is favored over dioxylate formation for the ligands L = CH3, CH3O(-), Cl(-). The activation barriers for the formation of the metallaoxetane intermediate are found to increase for the ligands in the order CH3 < Cl(-) < CH3O(-) while the reaction energies follow the order Cl(-) < CH3O(-) < CH3. The subsequent re-arrangement of the metallaoxetane intermediate to the dioxylate is only feasible in the case of ReO3(OCH3). Of all the complexes studied, the best dioxylating catalyst is ReO3Cp (singlet surface); the best epoxidation catalyst is ReO3Cl (singlet surface); and the best metallaoxetane formation catalyst is ReO3(NPH3) (triplet surface).