Density Functional Theoretical Calculations Research Articles

Experimental and theoretical investigations on chalcones containing pyrene

Three chalcone derivatives featuring pyrene chromophore are designed, synthesised and studied for their thermal, photophysical and electrochemical properties. They exhibited a maximum absorption peak ranging from 414 nm to 421 nm and emission in cyan region. A chalcone containing nitro substituent displayed intramolecular charge transfer than a similar compound containing methoxy group. Excited lifetime analysis reveals the biexponential decay with two lifetime components. Solvatochromism of the chalcones revealed the effect of auxochrome in the intramolecular charge transfer. All the chalcones exhibited aggregation induced blue-shifted emission due to the restricted rotation and H-aggregation. The density functional theoretical calculation results further confirmed the charge transfer characteristic of the compounds.

Conformational Selectivity of Merocyanine on Nanostructured Silver Films: Surface Enhanced Resonance Raman Scattering (SERRS) and Density Functional Theoretical (DFT) Study.

In this study, detailed structural and vibrational analysis of merocyanine has been investigated using Raman, surface enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS). The Raman, SERS and SERRS studies aided by density functional theoretical (DFT) calculations clearly established the prevalence of the trans- and cis-conformers of the protonated form of merocyanine (MCH+) in solid and acetonitrile solution. The binding characteristics of merocyanine adsorbed on nanostructured silver-coated films (SCFs) were investigated using excitation-dependent SERS, concentration-dependent SERRS and DFT studies. The conformers of merocyanine involved in the surface adsorption processes were recognized. The prominent marker bands observed at 1538 (ethylenic C=C stretch) and 1133 cm−1 (pyridinium C-N stretch) in the Raman spectrum of merocyanine in acetonitrile shifted to 1540 and 1126 cm−1, respectively on the nanostructured SCFs. The shift in the marker bands is associated with either the preferential binding of selective conformer or change in resonance equilibrium between the benzenoid and quinoid forms. The excitation wavelength dependent SERS spectrum infers that in addition to the major contribution from the electromagnetic enhancement, chemical (resonance) effect leads to the amplification of the 1540 cm−1 band. The concentration-dependent SERRS study showed maximum enhancement for the nanostructured SCFs functionalized with 1 μM concentration of merocyanine, indicative of monolayer coverage. For lower concentrations of merocyanine, the SERRS signal intensity reduced without any alteration in the peak positions. The SERRS study thus, revealed sub-nanomolar (0.1 nM) sensing of merocyanine using nanostructured SCFs with the analytical enhancement factor (AEF) of ∼ 1010 for the 1126 cm−1 and 1540 cm−1 Raman bands for MC concentration of 0.1 nM. In this study, combination of SERRS and DFT have clearly established the predominance of trans-MCH+ on the nanostructured silver surface with minor contribution from cis-MCH+, which remain exclusively bound to the surface via the phenoxyl ring O atom. This conformational surface selectivity of geometrical isomers of merocyanine using nanostructured surfaces can be further explored for energy efficient and economical separation of geometrical isomers.

Dicyanomethylene-4H-pyran based Schiff base for turn on NIR fluorescence sensing of Fe3+, Al3+ and Cr3+ and its application in molecular logic gate

A novel Schiff base derivative HMA containing dicyanomethylene-4H-pyran unit was designed and synthesized. It can be used to detect Fe3+, Al3+, Cr3+ accompanied with near-infrared (NIR) fluorescence enhancement. Fluorescence experiments show that it has a large Stokes shift (λex = 480 nm, λem = 670 nm), low detection limit and large binding constant. The interaction between HMA and Fe3+, Al3+, Cr3+ was investigated by NMR, FT-IR, as well as density functional theoretical calculations. It shows that the emission of HMA experiences an excited state intramolecular proton transfer (ESIPT) process, while the addition of Fe3+, Al3+ and Cr3+causes their coordination, increases the rigidity of HMA and enhances the fluorescence. Additionally, the reversible experiment was carried out by adding F− ion. For Al3+ and Cr3+, the corresponding solutions can return to their original state but not for Fe3+. On the basis of the reversible experiment, a molecular logic gate was designed with Al3+/Cr3+ and F− as input and the fluorescence signal at 670 nm of HMA as output.

Opening up a Radical Cross-Coupling Etherification Path by a Defect-Rich Cu/ZrO2 Catalyst for a High-Value Transformation of HMF

In this work, a radical coupling path was opened up for the construction of C–O bonds in the reduction–etherification of 5-hydroxymethylfurfural (HMF) by designing the unpaired electron defect-rich catalyst Cu/ZrO2. A decent 2,5-bis(isopropoxymethyl)furan (BPMF) yield (86.3%) was obtained under the absence of H2 and external pressure. A radical quenching experiment proved that the etherification process, which is the key step for achieving BPMF, indeed belongs to a radical-related route. Subsequently, a series of in situ FTIR, radical capture experiment, and electron spin density analyses were used to elucidate the formation of key radical intermediates at the molecular level in which the O–H dissociation of 2.5-dihydroxymethylfuran and C–O dissociation of isopropanol occurred on the zirconium-vacancy-adjacent lattice oxygen atom (VZr–O–) and oxygen vacancy (VO) sites, respectively. Furthermore, we revealed the induction mechanism of the alkoxy radical intermediate at the electronic level and the electron structure cycle process of the unpaired electron VZr–O– sites via a combination of density functional theoretical calculations and isotope labeling. More importantly, the calculation result from Gaussian showed that radical intermediates do not occur in a chain reaction with unactivated molecules; thus, the optimal path of radical cross-coupling to produce BPMF was clarified. The findings reported by this article reveal the role of unpaired electron defects in opening up a radical coupling path and thus broaden the downstream production of the high-value transformation of HMF. Furthermore, this study could provide a reference for the construction of C–O bonds in other heterogeneous reaction systems.

Morphology controlled synthesis of Fe and Mn co-doped In2O3 nanocubes and their Dopant-Atom effects on electronic structure and magnetic properties

Fe and Mn co-doped In2O3 single-phase cubic crystal structure nanocubes of uniform size and control over dopant concentration (In1.96Fe0.02Mn0.02O3, In1.94Fe0.02Mn0.04O3, In1.92Fe0.02Mn0.06O3 and In1.90Fe0.02Mn0.08O3) and microstructure were prepared using the hydrothermal-annealing technique. On a wider vision, we systematically investigated the influence of Fe and Mn co-doping in In2O3 through complementary experimental techniques and density functional theoretical (DFT) calculations to reveal the physical mechanisms involved in the origin of observed ferromagnetism. DFT calculations demonstrated that the substitution of surface indium atom by iron (FeIn) leads to impurity states on the top of In2O3 valence band maximum (VBM). Conversely, incorporation of interstitial (Mni) impurities in the host matrix without oxygen vacancies (VO) slightly shifts the top of the valence band and incorporation of interstitial Mn-impurity in the In2O3 (111) surface with oxygen vacancy does not provide noticeable changes in the electronic structure of the defective surface. High-resolution transmission electron microscopy measurements showed the formation of regular nanocubes in shape with 36.9–37.6 nm in average edge length. X-ray photoelectron spectroscopy investigations revealed that valence state of Fe mostly as Fe2+ and Fe3+ and Mn2+ for Mn atom in the In1.96Fe0.02Mn0.02O3, In1.94Fe0.02Mn0.04O3, In1.92Fe0.02Mn0.06O3 and In1.90Fe0.02Mn0.08O3. Magnetic studies exhibited room temperature ferromagnetism (RTFM) in the investigated samples with the high coercivity and saturation magnetization of 145.48 Oe and 0.023 emu/g, respectively for the In1.94Fe0.02Mn0.04O3. The origin of observed RTFM was described based on the bound magnetic polaron (BMP) model mechanism. DFT investigations demonstrated the clusters of impurities (FeIn-nMni) robust magnetic interactions within the cluster and between the clusters. Interestingly, only FeIn-nMni clusters contribute ferromagnetism observed in the investigated co-doped systems. Therefore, increasing the concentration of defects leads to the improvement of ferromagnetism. The comprehensive experimental and DFT investigations present new evidence to the observed ferromagnetism and electronic structure of Fe,Mn co-doped In2O3 nanocubes.

Ion Chemistry of Carbon Dioxide in Nonthermal Reaction with Molecular Hydrogen.

The exothermic hydrogen transfer from H2 to CO2·+ leading to H and HCO2+ is investigated in a combined experimental and theoretical work. The experimental mass/charge ratios of the ionic product (HCO2+) and the ionic reactant (CO2·+) are recorded as a function of the photoionization energy of the synchrotron radiation. Theoretical density functional calculations and variational transition state theory are employed and adapted to analyze the energetic and the kinetics of the reaction, which turns out to be barrierless and with nonthermal rate coefficients controlled by nonstatistical processes. This study aims to understand the mechanisms and energetics that drive the reactivity of the elementary reaction of CO2·+ with H2 in different processes.

First principles study of SnX2 (X = S, Se) and Janus SnSSe monolayer for thermoelectric applications

Tin-based chalcogenides are of increasing interest for thermoelectric applications owing to their low-cost, earth-abundant, and environmentally friendly nature. This is especially true for 2D materials, in which breaking of the structural symmetry plays a crucial role in tuning the electronic properties. 2D materials present a unique opportunity to manipulate the electronic and thermal properties by transforming a monolayer into a Janus monolayer. In the present work, we have investigated the thermoelectric properties of hexagonal SnS2, SnSe2 monolayer, and Janus SnSSe monolayer. Density functional theoretical calculations points out the hexagonal Janus SnSSe monolayer as a potential high-performing thermoelectric material. Results for the Janus SnSSe monolayer show an ultra-low thermal conductivity originating from the low group velocity of the low-lying optical modes, leading to superior zT values of 0.5 and 3 at 300 K and 700 K for the p-type doping, respectively.

Efficient separation of strontium ions from aqueous solution by dibenzo-18-crown-6 functionalized resin: Static and dynamic adsorption studies with computational DFT insights

The separation and utilization of radiotoxic 90Sr from liquid nuclear waste streams generated in the nuclear fuel reprocessing is highly desirable and challenging. Herein, we studied dibenzo-18-cown-6 functionalized chloromethyl-polystyrene (CMPS-DB18C6) resin which displays an excellent affinity toward Sr2+ion adsorption from aqueous solution. Adsorption behaviors were investigated as a function of solution pH, contact time, Sr2+ion concentration, temperature and presence of other metal ions. The prepared grafted resin exhibits high adsorption capacity of 141.37 mg/g at pH 6 with good selectivity in the presence of interfering coexisting ions such as Li+, Na+, Mg2+and Ca2+ions.The adsorption kinetics and isotherm were well fitted by the pseudo second order and Langmuir model, respectively. The adsorption efficiency was seen to be reduced with temperature. The regeneration of the used CMPS-DB18C6 resin was accomplished by 0.5 M HNO3acid and regenerated resin was reused up to four cycles with modest change in the adsorption capacity. The breakthrough curve analysis using a fixed-bed column showed 99.6% adsorber performance with bed capacity of 147.56 mg/g and 1.38 mbar pressure drop across the adsorber bed. The adsorbent showed good radiation stability as seen from the almost constant strontium distribution coefficient up to 500 kGy radiation dose. Further, the high adsorption and selectivity of Sr2+ ion was complimented using complexation Gibbs free energy by performing density functional theoretical calculations. The present work might provide an easy and efficient adsorptive removal process for the separation Sr2+ ions from radioactive waste stream for environmental remediation.

Cyclic Peptide Protomer Detection in the Gas Phase: Impact on CCS Measurement and Fragmentation Patterns.

With the recent improvements in ion mobility resolution, it is now possible to separate small protomeric tautomers, called protomers. In larger molecules above 1000 Da such as peptides, a few studies suggest that protomers do exist as well and may contribute to their gas-phase conformational heterogeneity. In this work, we observed a CCS distribution that can be explained by the presence of protomers of surfactin, a small lipopeptide with no basic site. Following preliminary density functional theoretical calculations, several protonation sites in the gas phase were energetically favorable in positive ionization mode. Experimentally, at least three near-resolved IM peaks were observed in positive ionization mode, while only one was detected in negative ionization mode. These results were in good agreement with the DFT predictions. CID breakdown curve analysis after IM separation showed different inflection points (CE50) suggesting that different intramolecular interactions were implied in the stabilization of the structures of surfactin. The fragment ratio observed after collision-induced fragmentation was also different, suggesting different ring-opening localizations. All these observations support the presence of protomers on the cyclic peptide moieties of the surfactin. These data strongly suggest that protomeric tautomerism can still be observed on molecules above 1000 Da if the IM resolving power is sufficient. It also supports that the proton localization involves a change in the 3D structure that can affect the experimental CCS and the fragmentation channels of such peptides.

Arylpyrazole Schiff base: Synthesis and selective recognition of Cu2+

A series of novel arylpyrazole Schiff bases were designed and synthesized, and their structures were characterized by 1H NMR, 13C NMR, FT-IR, and elemental analysis. The UV-absorption and fluorescence emission spectra of arylpyrazole Schiff bases have investigated in pure DMF solution. The ion recognition experiment showed that both A1 and C1 could selectively recognize Cu2+ with two different ion recognize mechanisms: compound C1 coordinated with Cu2+ to form copper complexes, while A1 would take an oxidation cyclization reaction to generate compound 1,3,4-oxadiazole (A1–1) after coordinating with Cu2+. Density functional theoretical calculations were also used to explain the recognition mechanisms.

Optimizing quasi-solid-state sodium storage performance of Na3V2(PO4)2F2.5O0.5 cathode by structural design plus nitrogen doping

Sodium vanadium fluorophosphate has been extensively explored for the cathode of sodium ion batteries (SIBs), which is known for its high voltage platform, three-dimensional framework structure and minor volume deformation. However, low intrinsic electronic conductivity restricts its practical charge/discharge performances. Accelerating the electron/ion transport process of sodium vanadium fluorophosphate is the vital point to realize high performances of SIBs. Herein, a well-designed nitrogen doped three-dimensional (3D) nanosheet flower-like Na3V2(PO4)2F2.5O0.5 composite (N-NVPFO) is proposed by optimizing nanostructure plus heteroatom doping. The 3D flower-like structure of N-NVPFO provides a great deal of active sites and guarantees the structure stability. In addition, the N-doping in Na3V2(PO4)2F2.5O0.5 bulk phase could enhance the intrinsic electronic conductivity by narrowing the energy gap, which is confirmed through the density functional theoretical (DFT) calculation. The N-NVPFO electrode delivers excellent rate capability (84 mAh g−1 at 10C) and long cycling life (86% capacity retention up to 2000 cycles). Furthermore, the quasi-solid-state SIBs using NaTi2(PO4)3 anode also exhibits good electrochemical performances.

Growing ZnIn2S4 nanosheets on FeWO4 flowers with p-n heterojunction structure for efficient photocatalytic H2 production

Constructing heterojunction structure can efficiently accelerate the separation and transfer of charge carriers and improve the photoactivity. Herein, a high-performance FeWO4/ZnIn2S4 composite with abundant and tight 2D/2D hetero-interfaces was rational designed and prepared. ZnIn2S4 nanosheets as hydrogen evolution species uniformly grow on the surface of FeWO4 flower, constructing a unique face-to-face hierarchical architecture. A maximum H2 production rate of 3531.2 μmol h−1 g−1 was obtained at the optimal mass ratio of FeWO4 to ZnIn2S4, which was 35 times higher than pure ZnIn2S4. Based on the experimental results and the Density Functional Theoretical calculation results, a possible p-n heterojunction mechanism and the transfer route of photoinduced charges toward the improved H2 production were proposed. The p-n heterojunction between FeWO4 and ZnIn2S4 nanosheets plays a key role in enhancing photocatalytic H2 production activity. Moreover, the intimate interface between two components and the preferable hydrophilic property favors the improved H2 evolution rate.

Phase Transitions and Amorphization of M2AgF4 (M = Na, K, Rb) Compounds at High Pressure

We report the results of high-pressure Raman spectroscopy studies of alkali metal fluoroargentates (M2AgF4, where M = Na, K, Rb) combined with theoretical and X-ray diffraction studies for the K member of the series. Theoretical density functional calculations predict two structural phase transitions for K2AgF4: one from low-pressure monoclinic P21/c (beta) phase to intermediate-pressure tetragonal I42d structure at 6 GPa, and another to high-pressure triclinic P1 phase at 58 GPa. However, Raman spectroscopy and X-ray diffraction data indicate that both polymorphic forms of K2AgF4, as well as two other fluoroargentate phases studied here, undergo amorphization at pressures as low as several GPa.

Modulating the Electronic Structure of FeCo Nanoparticles in N-Doped Mesoporous Carbon for Efficient Oxygen Reduction Reaction.

The development of highly efficient and stable oxygen reduction electrocatalysts and revealing their underlying catalytic mechanism are crucial in expanding the applications of metal‐air batteries. Herein, an excellent FeCo alloy nanoparticles (NPs)‐decorated N‐doped mesoporous carbon electrocatalyst (FeCo/NC) for oxygen reduction reaction, prepared through the pyrolysis of a dual metal containing metal‐organic framework composite scaffold is reported. Benefiting from the highly exposed bimetal active sites and the carefully designed structure, the Fe0.25Co0.75/NC‐800 catalyst exhibits a promising electrocatalytic activity and a superior durability, better than those of the state‐of‐the‐art catalysts. Suggested by both the X‐ray absorption fine structures and the density functional theoretical calculation, the outstanding catalytic performance is originated from the synergistic effects of the bimetallic loading in NC catalysts, where the electronic modulation of the Co active sites from the nearby Fe species leads to an optimized binding strength for reaction intermediates. This work demonstrates a class of highly active nonprecious metals electrocatalysts and provides valuable insights into investigating the structure–performance relationship of transition metal‐based alloy catalysts.

The Synergy of La2O3 Nanoparticles and Graphene for Advanced Li‐S Batteries

AbstractAs a promising alternative for next‐generation energy storge devices, lithium‐sulfur batteries suffer from polysulfide shuttle and the inherent slow kinetics under long‐ term operating and high mass loading which mainly cause by the absence of available immobilizer and conversion mediators. Herein, La2O3 nanoparticles anchored on graphene composite is designed and demonstrates a high‐performance sulfur immobilizer and conversion promoter. Benefiting from the composite, the corresponding Li−S batteries display good cycling stability (capacity fading rate 0.051 % per cycle after 500 cycles), high initial specific capacity (1423.7 mA h g−1 at 0.2 A g−1), and excellent cycling performance at high sulfur loading (5.03 mg cm−2). The results of experiments and density functional theoretical (DFT) calculations revealed that the La2O3 nanoparticles is a desirable separator modification material that can effectively tuning the absorption and conversion interactions with polysulfides through S−La and Li−O chemical bonds.

Experimental and density functional theoretical modeling of triazole pesticides extraction by Ti2C nanosheets as a sorbent in dispersive solid phase extraction method before HPLC-MS/MS analysis

In this research, a convenient, fast, and green dispersive solid phase extraction procedure based on Ti2C nanosheets was developed for effectively enrichment of some triazole pesticides prior to high performance liquid chromatography-tandem mass spectrometry. Characterization of the etching sorbent was carried out in details. Adsorption and desorption steps have been optimized in detail to obtain efficient phase separation and reliable analytical results. Under optimized conditions, the presented method exhibited a wide working range (0.52–1000 ng mL−1), low detection limits (0.03–0.30 ng mL−1) and acceptable extraction recoveries (70–75%). The introduced method precision was checked by calculating intra and inter-day relative standard deviations for three different concentrations of triazole pesticides. The matrix effect was investigated by the recovery study. Following validation studies, the presented method was successfully applied to the extraction and determination of the studied triazole pesticides from fruit juice samples. The adsorption mechanism was supported by theoretical studies. The interactions between the studied pesticides and Ti2C nanosheets were investigated with the help of density functional theoretical calculations. The calculations supported the obtained experimental results.

Interactions of N-hydroxyamphetamine with an iron porphyrin: A unique intramolecular H-bond probed by DFT calculations

Hydroxylamine (NH2OH) and its N-substituted derivatives (RNHOH) are important biological intermediates in the global N cycle. Heme plays a central role in the binding and activation of these hydroxylamines. We report the crystal structures of N-hydroxyamphetamine (AmphNHOH) in complex with Fe and Co heme models. We demonstrate a previously unrecognized internal H-bond interaction between a hydroxylamine RNHO–H group and a porphyrin N-atom. We utilize density functional theoretical (DFT) calculations to show that the conformations with the internal H-bond represent global minima along the potential energy surfaces for both the Fe and Co heme models. A natural bond orbital (NBO) analysis reveals a donor π (porN=C) to acceptor σ* (O-H) interaction of 3.04 kcal/mol for Fe, accounting for 11% of the total heme–AmphNHOH interaction energy. Our DFT calculations with the parent Fe–NH2OH suggests that the presence of internal H-bonds between hydroxylamine (R/H)NHOH moieties and heme N-atoms may be more common than previously recognized.

Superlithiophilic N, S-codoped carbon on Ni foam as a stable 3D host for dendrite-free Li metal anodes

The commercialization of Li metal anodes (LMAs) has long been obstructed by potential safety concerns and infinite volume changes arising from the inevitable lithium dendrites growth. Herein, we decorate a 3D porous Ni foam with nitrogen, sulfur-codoped carbon (NSC@Ni) through an interfacial polymerization strategy. It can be demonstrated that the synergetic effect of N and S co-doping can significantly improve the lithiophilicity of both pyrrolic and pyridinic N (in N, S-codoped carbon) according to density functional theoretical calculations. Benefitting from the lithiophilic heteroatom doping, the 3D NSC@Ni skeleton can realize a flat and dendrite-free Li deposition. As a result, the NSC@Ni electrode displays a high Coulombic efficiency of ≈98.59% at 2 mA cm−2 with 4 mA h cm−2 for over 153 cycles. And a stable cycle for 780 h at 1 mA cm−2 with 1 mA h cm−2 in NSC@Ni-Li symmetric cell can be realized. Impressively, a full cell assembled with LiFePO4 cathode shows outstanding rate performance and cycling stability at 1 C (300 cycles and capacity retention of 80.74%).

Vibrational spectra and molecular docking studies of bergapten isolated from Melicopedenhamii leaves as anti-breast cancer agents

This paper highlights the notable bioactivity and pharmaceutical significance of the natural furocoumarin viz. Bergapten (BG), extracted from the medicinal plant Melicopedenhamii. The equilibrium geometry, chemical reactivity and Natural Bond Orbital analysis to understand the charge transfer interactions of BG have been carried out aided by density functional theoretical calculations at the B3LYP/6–311++G(d,p) level. Vibrational spectral analysis of the extracted Bergapten, brings to light the vibrational wavenumbers and intensities of the compound. The analysis of the electron density of HOMO and LUMO gives an idea of the delocalization in the molecule and the low value of the energy gap aids in electron transport and thereby bioactivity of the molecule. Molecular docking studies which reveal the best binding sites with target proteins, particularly its inhibiting activity against carcinoma type proteins, manifest Bergapten as a promising agent for breast cancer therapy.

Sensing mechanism of acetone adsorption on charged ZnO and ZnSe surfaces: Insights from DFT calculations

Acetone sensing is meaningful for human health, food safety and animal safety. In this work, the sensing mechanism of acetone adsorption on charged II-VI semiconductor (ZnO and ZnSe) is systematically investigated by density functional theoretical calculations. It is found that compared with charged ZnO surfaces, charged ZnSe surfaces possess stronger acetone adsorption strength. Both positive and negative surface charges could enhance acetone sensing of ZnO surface while only negative surface charges could enhance acetone sensing on ZnSe surface. The appropriate charge states of ZnO or ZnSe are of significance to realize fast recovery. Because acetone desorption process could be endothermic with added energy under some charge states. Additionally, the acetone selectivity of sensing surface could be controlled by surface charge states. Moreover, acetone sensing could be effectively improved by the synergistic effect of surface charge states and ZnSe/ZnO heterostructures. Our results extend the knowledge into the acetone sensing mechanisms induced by surface charge states.