Density Functional Theory Computational Studies Research Articles

Complete Degradation of Gaseous Methanol over Pt/FeOx Catalysts by Normal Temperature Catalytic Ozonation.

Normal temperature catalytic ozonation (NTCO) is a promising yet challenging method for the removal of volatile organic compounds (VOCs) because of limited activity of the catalysts at ambient temperature. Here, we report a series of Pt/FeOx catalysts prepared by the co-precipitation method for NTCO of gaseous methanol. All samples were found to be active and among them, the Pt/FeOx-400 (calcined at 400 °C) catalyst with a Pt cluster loading of 0.2% exhibited the highest activity, able to completely convert methanol into CO2 and H2O at 30 °C. Extensive experimental research suggested that the superior catalytic activity could be attributed to the highly dispersed Pt clusters and an appropriate molar ratio of Pt0/Pt2+. Furthermore, electron paramagnetic resonance and density functional theory computational studies revealed the mechanism that the Pt/FeOx-400 catalyst could activate O3 and water effectively to produce hydroxyl radicals responsible for the catalytic oxidation of methanol. The findings of this work may foster the development of technologies for normal temperature abatement of VOCs with low energy consumption.

Characterization of β-turns by electronic circular dichroism spectroscopy: a coupled molecular dynamics and time-dependent density functional theory computational study.

Electronic circular dichroism is one of the most used spectroscopic techniques for peptide and protein structural characterization. However, while valuable experimental spectra exist for α-helix, β-sheet and random coil secondary structures, previous studies showed important discrepancies for β-turns, limiting their use as a reference for structural studies. In this paper, we simulated circular dichroism spectra for the best-characterized β-turns in peptides, namely types I, II, I' and II'. In particular, by combining classical molecular dynamics simulations and state-of-the-art quantum time-dependent density functional theory (with the polarizable embedding multiscale model) computations, two common electronic circular dichroism patterns were found for couples of β-turn types (namely, type I/type II' and type II/type I'), at first for a minimal di-peptide model (Ace-Ala-Ala-NHMe), but also for all sequences tested with non-aromatic residues in the central positions. On the other hand, as expected, aromatic substitution causes important perturbations to the previously found ECD patterns. Finally, by applying suitable approximations, these patterns were subsequently rationalized based on the exciton chirality rule. All these results provide useful predictions and pave the way for a possible experimental characterization of β-turns based on circular dichroism spectroscopy.

The synthesis of polyaspartic acid derivative PASP-Im and investigation of its scale inhibition performance and mechanism in industrial circulating water.

A polyaspartic acid derivative (PASP-Im) as a novel scale inhibitor was synthesized by a simple green synthesis route with polysuccinimide and iminodiacetic acid as the starting materials. The as-synthesized PASP-Im was characterized via nuclear magnetic resonance spectroscopy (1H-NMR) and Fourier transform infrared spectrometry (FT-IR), and its scale inhibition performance was evaluated by a static scale inhibition method. Moreover, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and density functional theory computational studies were conducted to explore the scale inhibition mechanism of PASP-Im. The findings indicate that the as-synthesized PASP-Im exhibits better antiscale performance against the CaCO3 deposits than the unmodified PASP because of the introduction of iminodiacetic acid group. It also can change the crystallization path of calcium carbonate from stable calcite to vaterite that is dispersible in water, thereby resulting in great changes in the morphology of the CaCO3 scale. Furthermore, the O and N atoms in the negatively charged functional groups (such as –NH2 and –COOH) of PASP-Im can interact with calcium ions to block the active growth point of CaCO3 crystals, which also accounts for the excellent antiscale performance of PASP-Im. With new insights into the synergy between the functional groups of the antiscale molecule and scale-forming ions, this approach would be helpful towards the development of novel high-performance anti-scaling macromolecules.

Mononuclear Cr(III), Mn (II), and Fe(III) complexes derived from new ONO symmetrical flexible hydrazone: synthesis, spectral characterization, optical band gap and DFT computational study

New mononuclear Mn (II), Cr (III) and Fe (III) complexes of flexible symmetrical 2-(2-(2-hydroxy-3-methoxybenzylidene) hydrazinyl)-2-oxo-N-(pyridine-2-yl) acetamid (H4MPA) were isolated and characterized. IR spectra proved that the hydrazone coordinates as ONO dibasic or monobasic in keto and enol forms. The density functional theory (DFT) based quantum chemical calculations were accomplished at B3LYP/6-level of theory. Muilikan atomic charge in a companion with global and local reactivities and various energitic values have been calculated at the selected atoms, and the reactive sites have been assigned on the surface of the molecules through molecular electrostatic potential (MEP) map. The stability of all compounds was examined by TGA and DrTGA and the associated kinetic parameters were determined. Also, the optical band gap values were evaluated and found to be comparable with those obtained by DFT suggesting the possibility of using the title compounds in solar cells.

Urease inhibition studies of six Ni(II), Co(II) and Cu(II) complexes with two sexidentate N2O4-donor bis-Schiff base ligands: An experimental and DFT computational study

Six novel complexes, [Ni(C36H34N2O10)]·2.25CH3OH·0.5C4H10O (1), [Co(C36H34N2O10)] (2), [Cu(C36H34N2O10)]·2CH3OH (3), [Ni(C36H32N2O8Cl2)]·2CH3OH (4), [Co(C36H32N2O8Cl2)]·4CH3OH (5) and [Cu(C36H32N2O8Cl2)]·2CH3OH (6) with two sexidentate N2O4-donor bis-Schiff base ligands (C36H34N2O10 = 1,2-bis(2-methoxy-6-formylphenoxy)ethane-l-tyrosine; C36H32N2O8Cl2 = 1,2-bis(2-methoxy-6-formylphenoxy)ethane-l-4-chlorophenylalanine) have been synthesized and structurally characterized. Theoretical calculation of the six complexes was carried out by density functional theory (DFT) Becke's three-parameter hybrid (B3LYP) method employing the 6-3lG basis set, indicating that the calculation results are in accordance with experimental results. Moreover, the inhibitory activities of complexes 1–6 were tested in vitro against jack bean urease. At the same time, molecular docking was investigated to determine the probable binding mode. The experimental values and docking simulation exhibited that complexes 3 and 6 showed strong inhibitory activity (IC50 = 10.36 ± 1.13, 15.63 ± 3.04 μM) compared with the positive reference acetohydroxamic acid (IC50 = 26.99 ± 1.43 μM). Their structure-inhibitory activity relationship was further discussed from the perspective of molecular docking and theoretical calculation.

Fluorene‐Functionalized, Dendrimer‐Modified SBA‐15: Detection of Iron(III) and Mercury (II) in Aqueous Media and Logic Gate Studies

AbstractA novel silica‐based fluorescent sensor, (S‐DPP), was prepared via grafting of dimethyl 3,3′‐(propylazanediyl)(1Z,1′Z)‐bis(N‐(9H‐fluoren‐2‐yl)propanimidate) (DPP), onto the pore walls of SBA‐15 channels. DPP was prepared by growing of dendrimer (G= 0.5) onto the amino functionalized surface of SBA‐15, followed by anchoring of 2‐aminflourene via imine condensation. Synthesized materials were characterized using FT‐IR, PXRD, SEM, TEM, BET and TGA techniques. Fluorescence properties of the sensor were investigated in aqueous solution towards various metal ions. The signal quenching of sensor at λ=380 nm is based on complex formation between the S‐DPP and Fe3+ or Hg2+ ions, leading to the inhibition of reverse intramolecular charge transitions at the probe and appearance of new transitions at Mn+—S‐DPP complex. Furthermore, the limit of detection of both ions were calculated as 2.4 × 10−8 M and 6.3 × 10−8 M, respectively. A reversibility in fluorescence behavior of the probe was found in the presence of Cl−, and was demonstrated a circuit logic system with the Fe3+, Hg2+ and Cl− ions. Finally, density functional theory (DFT) and time‐dependent density functional theory (TDDFT) computational studies were performed in order to obtain a detailed electronic description of the quenching mechanism by Hg2+ and Fe3+ as well as studying the structure and bonding in the complexes.

A DFT computational study of the mechanism of super-high oxygen evolution potential of W doped SnO2 anodes

W doped SnO2 anodes are shown to exhibit a super-high oxygen evolution potential (OEP) of 2.5 V (vs SHE) based on Density Functional Theory (DFT). Calculation of the free energy of oxygen evolution reactions (OER) provided a deep understanding of the mechanism for such high OEP. Typical four-step associative process was used to investigate the OER on (110) surface of W doped SnO2. The analysis of OER indicated that the free energy difference ΔG4 of the third proton-transfer on the (110) W–SnO2 with W on the surface layer contributed to the super-high oxygen evolution potential. Cyclic voltammetric measurements on W doped SnO2 prepared on Ti substrates showed an OEP of 2.6 V (vs SHE) in good agreement with the calculations.

Dearomative [4 + 2] Cycloaddition of Pyridine via Energy-Transfer Catalysis

In this issue of Chem, Glorius and coworkers report the first photocatalytic dearomative cycloaddition of pyridine with alkene. High-value isoquinuclidines could be easily assembled from N-cinamoyl picolinamides under mild and operationally simple conditions.

Molecular dynamic simulation and DFT computational studies on the adsorption performances of methylene blue in aqueous solutions by orange peel-modified phosphoric acid

Adsorptive removal of methylene blue dye (MB) from aqueous medium using orange peels treated with phosphoric acid (OP-H 3 PO 4 ) was examined. The OP-H 3 PO 4 was characterized using Fourier transform Infra-red spectroscopy, X-ray diffraction, scanning electron microscopy, Energy Dispersive X-ray Spectroscopy, and thermogravimetric analysis. The effect of different process parameters, namely contact time, initial dye concentration, initial solutions pH, and temperature effect were examined. Equilibrium experimental data were fitted by Langmuir, Freundlich, Redlich-Peterson (R-P) and Sips isotherm models. For the two-parameter models, the data fitted well with the Langmuir isotherm model suggesting a monolayer adsorption of the dye onto the homogeneous adsorbent surface. However, regarding the three-parameter models, for the whole temperature range, both the sips and the Redlich-Peterson models showed high correlation factors, indicating that calculated data were close to those found experimentally and suggesting that MB adsorption occurs on both homogeneous and heterogeneous surfaces of OP-H 3 PO 4 The present study revealed that OP-H 3 PO 4 is an effective and efficient adsorbent for the removal of basic dyes from aqueous solution. In addition, quantum chemical calculations realized with density functional theory (DFT) method were successfully considered to correlate the experimental results. Moreover, the molecular dynamics simulations (MDS) were used to simulate the interactions between the MB molecule and the OP-H 3 PO 4 (110) surface, indicating that the MB molecule adsorbs onto the OP-H 3 PO 4 (110) surface in a nearby horizontal position. • High adsorption potential of OP-H3PO4, about 307.63 mg/g at 25 °C. • Adsorption kinetics shows that the pseudo-second-order model was the most reliable to describe experimental data. • The equilibrium data indicates that both Sips and Langmuir models could represent the MB uptake onto OP-H 3 PO 4. • The results of the ionic strength effect showed that the competition between the MB dye and the Na + ions led to a decrease in the amount adsorbed.

Flexible Metal-Organic Frameworks for Light-Switchable CO2 Sorption Using an Auxiliary Ligand Strategy.

We report the synthesis and characterization of two photoactive metal-organic frameworks (MOFs), TCM-14 and TCM-15. The compounds were synthesized by incorporating 4,4'-azopyridine auxiliary ligands into pto-type scaffolds that are composed of dinuclear copper(II) "paddle-wheel"-based secondary building units and flexible, acetylene-extended, tritopic benzoate linkers. Room temperature CO2 sorption of the MOFs was studied, and UV-light irradiation is shown to result in reduced CO2 adsorption under static conditions. TCM-15 reveals a dynamic response leading to an instant desorption of up to 20% of CO2 upon incidence of UV light because of the occurrence of nonperiodic structural changes. Physicochemical and computational density functional theory studies were carried out to gain insight into the mechanism of the interaction of light with the frameworks.

Structure, DFT Calculations, and Magnetic Characterization of Coordination Polymers of Bridged Dicyanamido-Metal(II) Complexes

Three coordination polymers of metal(II)-dicyanamido (dca) complexes with 4-methoxypyridine-N-oxide (4-MOP-NO); namely, catena-[Co(µ1,5-dca)2(4-MOP-NO)2] (1), catena-[Mn(µ1,5-dca)2(4-MOP-NO)2] (2), catena-[Cd(µ1,5-dca)2(4-MOP-NO)2] (3), and the mononuclear [Cu(κ1dca)2(4-MOP-NO)2] (4), were synthesized in this research. The complexes were analyzed by single crystal X-ray diffraction as well as spectroscopic methods (UV/vis, IR). The polymeric 1-D chains in complexes 1–3 were achieved by the doubly µ1,5-bridging dca ligands and the O-donor atoms of two axial 4-MOP-NO molecules in trans configuration around the distorted M(II) octahedral. On the other hand, the two “trans-axial” pyridine-N-oxide molecules in complexes 2 and 3 display opposite orientation (s-trans). The DFT (density functional theory) computational studies on the complexes 1–3 were consistent with the experimentally observed crystal structures. Compounds 1 and 2 display weak antiferromagnetic coupling between metal ions (J = −10.8 for 1 and −0.35 for 2).

Polymeric-Based Epoxy Cured with a Polyaminoamide as an Anticorrosive Coating for Aluminum 2024-T3 Surface: Experimental Studies Supported by Computational Modeling

The present research focused on a coating formulation for aluminum surface 2024-T3 to protect it from corrosion. The formulation consisted of a polymeric epoxy resin-coated bisphenol A diglycidyl ether (DGEBA) cured with a polymeric polyaminoamide. The coated aluminum 2024-T3 was tested in a harsh environment of electrolyte solution (3 wt% NaCl solution) to simulate the harsh marine environment. The coated sample was evaluated by Electrochemical Impedance Spectroscopy (EIS). Under these conditions, a very high impedance (Z) value was obtained; even after exposure for a period longer than 4392 h, the performance was still acceptable. Surface morphological study of metallic specimens before and after exposures to the simulated marine environment (3 wt% NaCl) was carried out using scanning electron microscopy (SEM). The results indicate that the DGEBA-polyaminoamide (DGEBAAA) performed as an excellent barrier for Al surface. The results were combined by several modeling approaches involving molecular dynamics simulation (MD), Monte Carlo methods (MC), and the electronic density functional theory (DFT) computations to explore the adhesion forces between the DGEBAAA and the aluminum surface. The computational MD, MC, and DFT studies were executed in aqueous media. Computational results further evidenced the stronger DGEBA-aminoamide adhesion onto the aluminum 2024-T3 even in a wet environment.

Synthesis of Indenes by Tandem Gold(I)-Catalyzed Claisen Rearrangement/Hydroarylation Reaction of Propargyl Vinyl Ethers.

The tandem gold(I)-catalyzed propargyl Claisen rearrangement/hydroarylation reaction of suitable propargyl vinyl ethers, followed by in situ reduction of the resulting carbonyl group, provides functionalized indenes in good to excellent yields. The reaction occurs at room temperature in dichloromethane in the presence of 3 mol % [IPrAuCl]/AgBF4 as the best catalytic system. Instead, cyclization of the allene intermediate either does not take place or is very slow with phosphine ligands. A variety of substituents and functional groups present on the substrate are tolerated. The effect of the aryl ring substituents and the results of a density functional theory computational study suggest that the final hydroarylation is the rate-determining step of this cascade process. Further in situ chain elongation, prior final work up of the tandem process, can be carried out by Wittig olefination of the aldehyde functionality, thus incrementing the diversity of the products obtained.

Multiresponsive Tetradentate Phosphorescent Metal Complexes as Highly Sensitive and Robust Luminescent Oxygen Sensors: Pd(II) Versus Pt(II) and 1,2,3-Triazolyl Versus 1,2,4-Triazolyl.

Two Pd(II) complexes based on tetradentate chelate ligands with either a 1,2,4-triazolyl (Pd1) or 1,2,3-triazolyl (Pd2) unit were synthesized, and their structure-property relationships were studied. Both Pd1 and Pd2 are rare bright deep blue Pd(II) phosphors with contrasting properties. Pd1 displays stimuli-responsive luminescence in response to UV irradiation, concentration, or temperature change, which is ascribed to the facile switching of monomer to excimer emission. In contrast, a similar stimuli-responsive luminescence was not observed for Pd2. Crystal structures and time-dependent density functional theory computational studies established that the excimer formation of Pd1 is caused by electronically favored intermolecular π-π interactions and less steric protection of the Pd core because of the position of its alkyl chains, compared to Pd2. In solution, the excimer emission of Pd1 shows a much greater sensitivity toward oxygen than the monomer emission with a very large Stern-Volmer constant ( Ksv) that is more than twice that of the monomer emission. Both Pd(II) complexes are found to be outstanding oxygen sensors in ethyl cellulose films with superior sensitivity ( Ksvapp = 0.228-0.346 Torr-1) over their Pt(II) equivalents ( Ksvapp = 0.00674-0.0110 Torr-1), owing to their long phosphorescence decay lifetimes. Furthermore, Pd1 shows an excellent photostability, compared to the Pt(II) analogue, making it one of the best and highly robust oxygen sensors based on cyclometalated metal complexes.

Quo vadis niobium? Divergent coordination behavior of early-transition metals towards MOF-5.

Treatment of MOF-5 with NbCl4(THF)2 in acetonitrile leads to incorporation of Nb(iv) centers in a fashion that diverges from the established cation metathesis reactivity of this iconic material. A combination of X-ray absorption spectroscopy analysis and reactivity studies altogether supported by density functional theory computational studies document an unprecedented binding mode for the Zn4O(O2C-)6 secondary building units (SBUs), which in Nb(iv)-MOF-5 function as κ 2-chelating ligands for NbCl4 moieties, with no exchange of Zn2+ observed. This unusual reactivity expands the portfolio of post-synthetic modification techniques available for MOFs, exemplified here by MOF-5, and underscores the diverse coordination environments offered by this and potentially other MOFs towards heterometal species.

Computational density functional theory study on the selective conversion of CO2 to formate on homogeneously and heterogeneously mixed CuFeO2 and CuO surfaces

This study examines the reaction pathways for the selective conversion of CO2 to formate on the surface of mixed CuFeO2 and CuO (CFO) by employing density functional theory (DFT) calculation of the reaction energy and activation energy barrier. Two different systems were employed to model the CFO structure: homogeneous structures (HMS) of uniformly mixed 40% CuFeO2 (012) and 60% CuO (111), and a heterogeneous structure (HTS) created with CuO (111) clusters intermittently supported on the CuFeO2 (012) surface. The monodentate and bidentate oxygen coordinations (OCO2) in possible CO2 adsorption configurations were investigated for the preferential reduction of CO2 to formate on the surface Cu sites constrained by dense electron density. In the OCO2-monodentate configuration, the reaction energy and activation barrier for formate formation using PBE + D3 were −0.41 eV and 0.28 eV, respectively, for the HTS and −0.69 eV and 0.72 eV, respectively, for the HMS. In the OCO2-bidentate configuration, the corresponding values were −0.58 eV and 0.53 eV, respectively, for the HTS and −1.17 eV and 0.54 eV, respectively, for the HMS. Consequently, the conversion of CO2 to formate in the OCO2-monodentate mode was kinetically more advantageous in the HTS. This result indicated that the heterogeneity of the CFO structure, as well as the CO2 adsorption configuration, would change the rate-limiting energy barrier through the reaction coordinates, ultimately supporting the selective conversion of CO2 on HTS.

Computational DFT study on nickel symmetric bis(thiosemicarbazone) complexes: Electronic absorption and redox potentials

This work deals with the performance of density functional theory (DFT) for evaluating one-electron reduction potentials and UV–Vis spectra of nickel complexes containing symmetric bis(thiosemicarbazones). Nine DFT calculation methods in combination with the polarisable continuum solvation model (PCM) were applied to calculate one-electron redox potentials (Ecalc) of nickel complexes. The best predicted results were gained by B3PW91/6-311++G(2df,2p)//B3LYP/6-31+G(d) level of theory in DMF. The results revealed that the most important effective thermodynamic factor is the solvation factor. Although the contribution of the electron attachment (EA) energy is more than ΔΔsolvG° and ΔΔεgeom for NiL1, NiL2, NiL3, and NiL4, ΔΔsolvG° and ΔΔεgeom play important roles in redox potentials. The calculated reduction potentials reproduce the tendency in experimental data. The derived error was in the region of −0.342 to −0.051 V. Reduction potentials have correlation with the energy of the frontier molecular orbitals LUMO/HOMO. According to the Natural Population Analysis (NPA), the geometries of nickel complexes remain distorted square planar, after reduction.

Aminobenzylated 4-Nitrophenols as Antibacterial Agents Obtained from 5-Nitrosalicylaldehyde through a Petasis Borono-Mannich Reaction.

Multidrug-resistant bacteria are one of the current biggest threats to public health and are responsible for most nosocomial infections. Herein, we report the efficient and facile synthesis of antibacterial agents aminoalkylphenols, derived from 5-nitrosalicyladehyde and prepared through a Petasis borono–Mannich multicomponent reaction. Minimum inhibitory concentrations (MICs) as low as 1.23 μM for a chlorine derivative were determined for multidrug-resistant Gram-positive bacteria, namely, Staphylococcus aureus and Enterococcus faecalis, two of the main pathogens responsible for infections in a hospital environment. The most promising antibacterial agents were further tested against eight strains of four Gram-positive species in order to elucidate their antibacterial broadness. In vitro cytotoxicity assays of the most active aminoalkylphenol revealed considerably lower toxicity against mammalian cells, as concentrations one order of magnitude higher than the determined MICs were required to induce human keratinocyte cell death. The phenol moiety was verified to be important in deeming the antibacterial properties of the analyzed compounds, although no correlation between such properties and their antioxidant activity was observed. A density functional theory computational study substantiated the ability of aminoalkylphenols to serve as precursors of ortho-quinone methides.

Assessment of the chitosan-functionalized graphene oxide as a carrier for loading thioguanine, an antitumor drug and effect of urea on adsorption process: Combination of DFT computational and molecular dynamics simulation studies

In this study, the interaction thioguanine (TG) anticancer drug with the functionalized graphene oxide (GO) nanosheet surface is theoretically studied in both gas phase and separately in physiological media using the density functional theory (DFT) calculations. DFT calculations indicated the adsorption and solvation energies are negative for f-GONS/TG complexes which propose the adsorption process of TG molecule onto the f-GONS surface is possible from the energetic viewpoint. QTAIM calculations confirm the nature of partially covalent-partially electrostatic between drug and nanosheet. These results are sorely relevant that an approach for loading of TG molecule is the chemical modification of GO using covalent functionalization which can serve as a nanocarrier to load drug molecules. Moreover, to understand the effect of urea on the nature of the interaction between TG and f-GONS, molecular dynamics (MD) simulation was employed. The results indicated that in the presence of urea the adsorption process gets affected and leads to instability of system, while the affinity of the TG for adsorption onto GO surface is increased in pure water.Communicated by Ramaswamy H. Sarma

Synthesis, Crystal Structure, UV-Vis Adsorption Properties, Photoelectric Behavior, and DFT Computational Study of All-Inorganic and Lead-Free Copper Halide Salt K2Cu2Cl6.

In this study, all-inorganic copper halide salt K2Cu2Cl6 single-crystal and thin films were prepared. The single-crystal diffraction data belonged to the monoclinic K2Cu2Cl6 (space group = P2(1)/C, unit cell parameters of a = 4.0340 Å, b = 13.7987 Å, c = 8.7445 Å, α = 90.000, β = 97.123, and γ = 90.000). As far as we know, this is the first study of the copper halide salt K2Cu2Cl6 for optoelectronic applications. The band gap of K2Cu2Cl6 is calculated to be approximately 1.85 eV. A low-cost photodetector based on the K2Cu2Cl6 thin film was efficient under different monochromatic light from 330 to 390 nm with different chopping frequencies (1.33–30 Hz). Density functional theory (DFT) computational results indicate that the valence bands (VBs) and conduction bands (CBs) are shifted up in energy using the orbital-dependent correction to the DFT energy. Partial density of states reveals that the VBs and narrow CBs are derived from the hybrid orbitals of Cu2+ 3d and Cl– p, respectively.