DFT Study on the Spin States of Polyaniline-3d Transition-Metal (Sc-Zn) Composites and Their Sensing Application to Detect Chemical Warfare Agents.

Organic-inorganic composite materials, combining polymers with transition metal (TM) atoms based on PAni and 3d TMs, have been designed and investigated in various spin states by performing density functional calculations. These designed composites were analyzed for their stability in different spin states as well as for their calculated electronic properties, including binding energies, frontier molecular orbitals, and dipole moments. Additionally, 3D isosurfaces and 2D scattered plots of reduced density gradient as a function of (sign λ2)ρ provide insights into the noncovalent interactions between the composite units. The most stable Mn@PAni composite has been assessed as a sensing material for chemical warfare blood agents (HCN, NCCl, NCBr, NCCN, and AsH3) using density functional-based calculations. The reduced band gap and significant red/blue shift in the UV-vis spectra obtained through TDDFT calculations underline the selectivity and efficiency of the Mn@PAni composite toward different analytes.

Ligand and Substituent Effect on Regium-π Bonding in Cu and Ag π-Conjugated Complexes: A Density Functional Study.

Density functional theory investigation of regium (Rg)-π bonding using the RgL-X model system, where Rg = Cu and Ag; L = CN, NO2, and OH; X = π-conjugated system (benzene, cyanobenzene, benzoic acid, pyridine, 2-methoxy aniline, 1,4-dimethoxy benzene, and cyclophane), has been performed. Conclusive evidence of the Rg-π bond has been provided by analysis of molecular electrostatic potential surfaces, Rg-π bond length, interaction energy (ΔE), second-order perturbation energy (E2), charge transfer (Δq), quantum theory of atom in molecules, and noncovalent interaction plots for 42 structural arrangements with varying ligands and the substituted aromatic ring. The Rg-π bond length in the optimized model systems varies from 2.03 to 2.12 Å in Cu complexes (1-21) and from 2.26 to 2.38 Å in Ag complexes (22-42) at the PBE0-D3 functional. While the ligand (L) attached to the Rg metal has a bargaining effect on the strength of the Rg-π bond (in the order of -OH > -CN = -NO2), the π-conjugated systems have a diminutive effect. Two X-ray crystal structures (CUCSOI and AHIDQU) having the Rg-π bond, accessed from Cambridge Crystallographic Data Centre (CCDC), are discussed here to signify the influence of Rg-π bonding on the crystal structure.

Encapsulation of heavy metal ions via adsorption using cellulose/ZnO composite: First principles approach.

The primary goal of the current research is to describe an effective and eco-friendly adsorbent for the removal of aquatic micropollutants. The design of the cellulose-modified zinc oxide (ZnO) nanocomposite was successfully carried out by density functional calculations. The proposed structures of the constituent and composite materials were confirmed using formation energy (Ef), frontier orbitals, band gaps (Egap), density of state (DOS) plots, natural bond orbitals (NBO), and UV-Vis spectral analysis. The cellulose/(ZnO)12 composite was further used for the adsorption of different heavy metal ions such as Hg(II), Pb(II), Cd(II), Ni(II), and As(III) through calculation of electronic and optical properties. The values of the adsorption energy (Eads) show that the As(III) interacted better with the composite in both phases, i.e., gas (-806.98 kcal/mol) and aqueous (-491.66 kcal/mol). The analysis of frontier molecular orbital data exhibited a decrease in the Egap of composite@metal ion complexes. The high negative value of the solvation energies (ΔEsol) indicates the suitability of composite@metal ions in an aqueous environment. The nature of interactions between metal ions and the composite unit is analyzed by noncovalent interactions (NCI) and the quantum theory of atoms in molecules (QTAIM). The theoretical results of the present study show the feasibility of the cellulose/(ZnO)12 composite for the removal of heavy metal ions and provide useful information to experimentalists to treat contaminated water.

Properties of Naked Silver Clusters with Up to 100 Atoms as Found with Embedded-Atom and Density-Functional Calculations.

The structural and energetic properties of small silver clusters Agn with n = 2-100 atoms are reported. For n = 2-100 the embedded atom model for the calculation of the total energy of a given structure in combination with the basin-hopping search strategy for an unbiased structure optimization has been used to identify the energies and structures of the three energetically lowest-lying isomers. These optimized structures for n = 2-11 were subsequently studied further through density-functional-theory calculations. These calculations provide additional information on the electronic properties of the clusters that is lacking in the embedded-atom calculations. Thereby, also quantities related to the catalytic performance of the clusters are studied. The calculated properties in comparison to other available theoretical and experimental data show a good agreement. Previously unidentified magic (i.e., particularly stable) clusters have been found for n>80. In order to obtain a more detailed understanding of the structural properties of the clusters, various descriptors are used. Thereby, the silver clusters are compared to other noble metals and show some similarities to both copper and nickel systems, and also growth patterns have been identified. All vibrational frequencies of all the clusters have been calculated for the first time, and here we focus on the highest and lowest frequencies. Structural effects on the calculated frequencies were considered.

Photodegradation of dye using Polythiophene/ZnO nanocomposite: A computational approach.

Incorporating nanostructured photocatalysts in polymers is a strategic way to obtain novel water purification systems. Here, we present density functional theory (DFT) study of Polythiophene/Zinc oxide (PTh/ZnO) nanocomposite with high photocatalytic performance and stability which exhibits superior degradation of alizarine dye under the visible light condition with interaction energy of -149.55 kcal/mol between conducting polymer (PTh) and metal oxide, with PTh sponsoring more number of electrons to the conduction band of ZnO. The electrical and optical properties of optimized geometries of PTh/ZnO nanocomposite were studied by frontier molecular orbital analysis, natural bond orbital (NBO) charge simulation, natural electronic configuration, and UV-vis absorption spectra. The modulation of the energy band gap (∽ 2.60 eV) and exciton binding energy (∽ 0.36 eV) causes visible light absorption and hence enhances the photodegradation activity of PTh/ZnO. NBO analysis evidences the electron accepting behavior of ZnO in the composites as it withdraws electron cloud density of about 0.14e from the polymer unit.

Cooperative Effect of Noncovalent Interactions on Tetrel Bonding in Halogenated Silanes.

Tetrel bond, a weak noncovalent interaction between the σ-hole of a Group IV element (silicon in our case) and the cloud of an electronegative element (oxygen in our case) is the focus of this work. The percentage strengthening of tetrel bond has been investigated by optimizing 16 binary complexes of halogenated silane and water of general formula SiXn H4-n -H2 O and 16 ternary complexes, of general formula NaX-SiXn H4-n -H2 O, where X=F, Cl, Br and I and n=1, 2, 3 and 4 at various levels of theory defined within the formalism of density functional theory (DFT). With the addition of NaX, tetrel bond between Si and O in SiXn H4-n -H2 O gets strengthened up to 49 %, owing to cooperativity effect exerted by hydrogen bonding between X and H in the ternary complex NaX-SiXn H4-n -H2 O. In the series of complexes studied here, overall stabilization due to cooperativity lies between 10 kJ/mol to 170 kJ/mol. This large extent of reinforcement due to cooperativity has never been showcased before. The exceptional stabilization and reinforcement owe its genesis to the transformation of the ternary complex into a cluster orchestrated by the H-bonding in most of the cases and covalent bonding in few of the cases.

Kinetics and Thermodynamics of CO Oxidation by (TiO2)6.

Molecular level insights into the mechanism and thermodynamics of CO oxidation by a (TiO2)6 cluster have been obtained through density functional calculations. Thereby, in this study, as an example, two different structural isomers of (TiO2)6 are considered with the purpose of understanding the interplay between local structure and activity for the CO oxidation reaction. Active sites in the two isomeric forms were identified on the basis of global and local reactivity descriptors. For the oxidation of CO to CO2, the study considered both sequential and simultaneous adsorption of CO and O2 on (TiO2)6 cluster through the ER and LH mechanisms, respectively. Three different pathways were obtained for CO oxidation by (TiO2)6 cluster, and the mechanistic route of each pathway were identified by locating the transition-state and intermediate structures. The effect of temperature on the rate of the reaction was investigated within the harmonic approximation. The structure-dependent activity of the cluster was rationalized through reactivity descriptors and analysis of the frontier orbitals.

First Principle Studies to Tailor Graphene Through Synergistic Effect as a Highly Efficient Electrocatalyst for Oxygen Evolution Reaction.

The Oxygen Evolution Reaction (OER) is one of the major roadblocks for electrocatalytic oxidation of water (water splitting) and for designing efficient metal-air batteries. Herein, we present a comprehensive study to design graphene based efficient electrocatalyst, modified by doping with main group elements Al, Si, P, S and co-doping with B and N, for OER using DFT computations. Four elementary steps in the OER reaction have been traced, free energy change for each elementary step was calculated considering thermodynamic corrections. Out of all the doped models, S doped graphene shows maximum efficiency that was further enhanced by adjusting the concentration of codopants B and N around the active dopant site. Our results show that synergy between codopants B and N and dopant S atom leads to high electrocatalytic efficiency of modified graphene towards OER and brings down the overpotential to as low as 0.44 V.

Mononuclear Pseudostannatranes Possessing Unsymmetrical [4.4.3.01,5]Tridecane Cage: Experimental and Theoretical Aspects of Reverse Kocheshkov Reaction in Phenyl Pseudostannatrane.

The synthetic protocols, structural aspects, and spectroscopic aspects of mononuclear pseudostannatranes possessing a [4.4.3.01,5]tridecane cage have been reported. A tripodal ligand N(CH2CH2OH){CH2(2-t-Bu-4-Me-C6H2OH)}2 (H3L) having unsymmetrical arms was reacted with n-butyltrichlorostannane, phenyltrichlorostannane, and tin tetrachloride under different solvent systems to obtain pseudostannatranes (1-3). The reaction of n-butyltrichlorostannane and the ligand in CH3OH/Na/THF yielded an aqua complex of pseudostannatrane [LSnBu(H2O)] (1a), which was crystallized as its acetone solvate (i.e 1a·Me2CO). However, the same reactants yielded methanol complex [LSnBu(CH3OH)] (1b) when the reaction was carried out in the NaOCH3/C2H5OH system. Similarly, the reaction of phenyltrichlorostannane and the ligand under these solvent systems yielded pseudostannatranes, i.e., an aqua complex [LSnPh(H2O)] (2a) and a methanol complex [LSnPh(CH3OH)] (2b) (where 2a was crystallized as 2a·Me2CO). The reaction of tin tetrachloride and the ligand in the Et3N/THF system resulted in the formation of pseudostannatrane [LHSnCl2] (3). A similar product was isolated as its triethylamine solvate (3·NEt3) due to the disproportion reaction when PhSnCl3 was reacted with the ligand in the Et3N/C6H5CH3 system, which demonstrates the first report on the reverse Kocheshkov reaction in pseudostannatranes. The experimental findings on the formation of 3·NEt3 due to the reverse Kocheshkov reaction have been corroborated with 119Sn NMR spectroscopy and density functional calculations that provide insightful information about the underlying details of the reaction route.

Conceptual DFT and TDDFT study on electronic structure and reactivity of pure and sulfur doped (CrO3)n (n = 1-10) clusters.

Different isomers of (CrO3)n (n = 1-10) cluster units have been investigated using Density functional approach. Their stability and reactivity has been analyzed by plotting chemical potential and HOMO-LUMO gap as a function of cluster size. The CrO3, (CrO3)6 and (CrO3)9 are identified as the most reactive species. Reactivity of each atomic site in the cluster has been interpreted using local reactivity descriptors called Fukui Function plots. The clusters have been doped with sulfur by adding it as substitutional impurity, effect of sulfur doping has been understood by analyzing excitation energies and absorption wavelengths using time dependent-DFT(TDDFT) at CAM-B3LYP level of theory.

Qualitative as well as quantitative analysis of interactions present in chlorine and bromine substituted aromatic organic crystals: A DFT linked Crystal Explorer study.

The effect of noncovalent interactions in shaping a crystal structure is explored qualitatively as well as quantitatively in a DFT linked Crystal Explorer (CE) study of nine different Chlorine and Bromine substituted benzene derivatives. The qualitative approach to analyze interactions is based on Hirshfeld surface that locates electronic charge distribution on the surface, quantitative estimation is obtained by linking DFT computations withCE.In the halogen substituted benzene derivatives considered here, in addition to conventional hydrogen and halogen bonding other interactions such as those between Chlorine-Hydrogen, Bromine-Hydrogen, Bromine-Oxygen have been deciphered. The molecular crystal structure of a variety of halogen substituted aromatic molecules has been rationalized and attributed to specific interactions.

Mechanistic details of amino acid catalyzed two-component Mannich reaction: experimental study backed by density functional calculations.

The role of pH-dependent ionic structures of L-amino acids in catalysis has been investigated for the two-component Mannich reactions between dimethyl malonate (DMM)/ethyl acetoacetate (EAA) and imines. As catalysts, L-amino acids performed well, even better than corresponding base catalysts and provided the ß-amino carbonyl compounds in very high yields. Density functional calculations were used to gain the mechanistic insight of the reaction. High catalytic efficiency of amino acids was attributed to the facile formation of carbanion intermediate through barrierless transition state TS1 (- 19.43 kcal/mol) and then its stabilization owing to carbanion interaction with protonated amino acid.

Understanding structure-activity relation in VxOy clusters of varied stoichiometry and sizes through conceptual density functional approach.

Computations have been performed on VxOy clusters (with x = 1-8, y = 1-21) to explore their structure, stability, and reactivity based on local and global reactivity descriptors defined within the formalism of density functional theory (DFT). The vertical and adiabatic ionization energies and electron affinities are in accordance with Franck-Condon principle and suggest that the VxOy clusters are more likely to be electron acceptors than donors. The structure and reactivity of VxOy clusters delicately depend on their oxygen content and environment. Distinct active sites have been identified for each cluster species on the basis of coordination, symmetry, and charge distribution. The propensity of all the reactive sites towards an approaching electrophile and/or nucleophile has been studied using local reactivity descriptor. In oxygen-poor clusters, the vanadium atoms are more prone to nucleophilic attack. With an increase in oxygen concentration, the coordination number of vanadium increases and reaches four-fold, the site for nucleophilic attack shifts to terminal oxygens. We conclude that of all the stoichiometries, the stable VxOy clusters have the (VO3)a(V2O5)b formula unit. The localization of positive charge density in cubic cage structure of V8O20 successfully traps halide ions (F-, Cl-, and Br-). In view of increasing use of metal oxide clusters in heterogeneous catalysis, the understanding of structure-activity relationship in vanadium oxides' clusters provided in the current study is highly desirable.

Single-Atom Catalysis Using Chromium Embedded in Divacant Graphene for Conversion of Dinitrogen to Ammonia.

Reduction of dinitrogen to ammonia under ambient conditions is a long-standing challenge. The few metal-based catalysts proposed have conspicuous disadvantages such as high cost, high energy consumption, and being hazardous to the environment. Single-atom catalysis has emerged as a new frontier in heterogeneous catalysis and metal atoms atomically dispersed on supports receive more and more attention owing to rapid advances in synthetic methodologies and computational modeling. Herein, we propose metal atoms embedded in divacant graphene as a catalyst for N2 fixation based on density functional calculations. We systematically investigate the potential of using transition metal like Cr, Mn, Fe, Mo and Ru as catalysts and our study reveals that Cr embedded in graphene exhibit good catalytic activity for N2 fixation. The synergy between the metal atoms and graphene surface provides a stable support to the metal center that has a high spin density to promote adsorption of N2 and activation of its N≡N triple bond. Our study deciphers the mechanism of conversion of N2 to ammonia following two possible reaction pathways, distal and enzymatic routes, via sequential protonation and reduction of activated N2 . The study provides a rational framework for conversion of dinitrogen to ammonia using single atom catalyst.

A QM/MM study on ethene and benzene oxidation using silica-supported chromium trioxide.

Oxidation of ethene and benzene by chromium oxide (CrO3) supported on silica (SiO2) was investigated by employing hybrid quantum mechanics/molecular mechanics (QM/MM) model calculations. Various mechanistic possibilities, such as C-H or C=C bond activation of hydrocarbons, were investigated in detail for the reaction of ethene and benzene with CrO3 grafted on a silica surface. While activation of the C-H bond leads to the formation of alcohol, epoxide is obtained via C=C bond activation. The complete reaction routes for the formation of each product were traced and found to be exothermic. Thermochemical analysis were performed to predict temperature conditions for the reaction to be feasible in a forward direction. The study provides conclusive evidence to aid experimentalists for further research on oxidation of hydrocarbons using silica-supported metal oxides. Graphical abstract Oxidation of ethene and benzene using silica-supported chromium trioxide.

Functionalized magnetic nanomaterials for rapid and effective adsorptive removal of fluoroquinolones: Comprehensive experimental cum computational investigations.

Alarming growth of pharmaceutical residues in aquatic environment has elevated concerns about their potential impact on human health. Taking cognizance of this, the present study is focussed on the coating of cobalt ferrite nanoparticles with different functionalities and to use them as adsorbents for pharmaceutical waste. The thickness of the coating was analysed using Small angle X-ray scattering technique. Thorough study of the isotherms and kinetics were performed suggesting monolayer adsorption and pseudo kinetic order model, respectively. To get an insight of the interactions liable for adsorption of fluoroquinolones over the functionalized magnetic nanoparticles computational studies were undertaken. The results demonstrated substantial evidence proposing remarkable potential of these nanostructures as adsorbents for different pollutants with an additional advantage of stability and facile recoverability with a view to treat wastewater.

Nucleotide conjugated (ZnO)3 cluster: Interaction and optical characteristics using TDDFT.

Binding of four DNA nucleotide units with (ZnO)3 cluster in an aqueous phase has been investigated using density functional theory (DFT) and time dependent-density functional theory (TDDFT) method and the stability order for (ZnO)3-nucleobases/sugar/phosphate systems is predicted as phosphate > C > A > S > T ∼ G. The order of binding energy for (ZnO)3-nucleotide hybrid systems is observed to be (ZnO)3 + nuc-C ˃ (ZnO)3 + nuc-A ˃ (ZnO)3 + nuc-G ˃ (ZnO)3 + nuc-T. The binding of nucleotide units with the cluster has been explained on the basis of molecular electrostatic potential (MEP) plots, hydrogen bonding, glycosidic torsion angles, density of state (DOS) plots. The photophysical properties of (ZnO)3-nucleotide complexes have been studied using TDDFT approach. Among all (ZnO)3-nucleotide complexes, the absorption spectra of (ZnO)3 + nuc-A and (ZnO)3 + nuc-C complexes are seen to undergo red shift with respect to their bare nucleotide units that would be useful in the optical sensing of the respective nucleotides of DNA. It is interesting to note that binding of the nucleotide unit with the cluster makes it fluorescent, the study reports the fluorescence activity of (ZnO)3 + nuc-T complex.

Correction to: Removal of fluoroquinolone from aqueous solution using graphene oxide: experimental and computational elucidation.

Unfortunately, the original version of this article contains a mistake. The figures no. 10, 11, 12 and 13 in the original version of the article should be replaced by the figures shown in this paper.

Removal of fluoroquinolone from aqueous solution using graphene oxide: experimental and computational elucidation.

The environmental risks of antibiotics have attracted increasing research attention due to their prevalence and persistence in the aquatic environment. In this study, oxygen functionalized graphene, namely, graphene oxide (GO), was synthesized by modified Hummer's and Offeman's method and used as potential effective absorbent for the removal of fluoroquinolones (FQs), i.e., ciprofloxacin (CIP), norfloxacin (NOR), and ofloxacin (OFL), from aqueous solution. The as-synthesized GO was characterized by Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and high-resolution transmission electron microscopy (HRTEM). Out of various factors that were taken to consideration while studying the adsorption process, it was found that pH of antibiotic solution is more crucial than the other experimental parameters such as initial antibiotic concentration, contact time, and adsorbent dosage and has significant impact on FQ adsorption via the GO adsorbent. The maximum removal of FQ was observed at pH 7 for CIP and NOR, while adsorption was maximum at pH 4 for OFL. Experimental data best fitted to the pseudo-second-order model as compared to the pseudo-first-order kinetic adsorption model. Best fitting of the equilibrium experimental data to Langmuir isotherm compared to Freundlich isotherm models established that FQ adsorbs over the GO in monolayer manner. Density functional theory (DFT) calculations performed at B3LYP/6-31G(d) level of theory in order to elucidate the thermodynamic feasibility of adsorption process and nature of interactions of antibiotic molecules with the GO adsorbent. Graphical abstract ᅟ.

Dispersion corrected density functional study of CO oxidation on pristine/functionalized/doped graphene surfaces in aqueous phase.

The catalytic oxidation of CO by molecular oxygen (O2) over graphene, epoxy functionalized graphene and sulphur doped graphene surface is investigated theoretically by employing dispersion corrected Density Functional Theory. The adsorption of O2 and CO molecules over the pristine, functionalized and doped graphene surface has been compared. The channel for oxidation of CO to CO2 is elucidated in detail in the presence of aqueous solvent. Computations suggest that catalytic cycle of CO oxidation is initiated through the ER-mechanism, with the formation of a carbonate intermediate, the second pre-adsorbed CO reacts with the carbonate intermediate through LH-mechanism whereby, two CO2 molecules are released and adsorption surface becomes available for the subsequent reaction. The activation barrier for CO oxidation is considerably lowered in the case of oxidation over functionalized 12.45kcal/mol and doped 14.52kcal/mol graphene surface in comparison to the observed barrier of 23.98kcal/mol for the pristine graphene.