Density Functional Theory Quantum Research Articles

Tailoring body center tetragonal allotropes Cx (x = 8, 12, 16, 20) with C(sp3) and hybrid C(sp3)/C(sp2): Crystal chemistry and ab initio investigations of the physical properties

Based on literature tetragonal ths topology C8 characterized by trigonal C(sp2), selective insertions of carbon induce large structural changes leading to C(sp3) C12 with dia topology after geometry optimizations to ground state structure using calculations within the quantum density functional theory DFT. Further crystal engineering operated on C12 lead to complete the series with novel C16 and C20. Such allotropes respectively characterized by ene (C=C) and propadiene (C=C=C) -like units beside C4 tetrahedra reveal hybrid C(sp3)/C(sp2) with complex stc topology. Alike ths C8, all three allotropes (C12, C16, and C20) identified in high symmetry I41/amd (No. 141) space group are cohesive with larger magnitude for C12 than for ths C8 and close energies for C16 and C20. Mechanical properties show diamond-like Vickers hardness HV for C12 (HV = 95 GPa) and smaller magnitudes for mixed C(sp3)/C(sp2) C16 (HV = 26 GPa) and C20 (HV = 47 GPa), noting that C8 with C(sp2) was found with the largest compressibility with HV = 19 GPa. Dynamically, all allotropes are stable from positive phonon acoustic and optic frequencies with the largest frequency magnitudes for C16 and C20 corresponding to CC and C=C=C vibrations respectively. Thermodynamically, the temperature changes of the specific heat CV show close agreement with diamond experimental values for C12 and larger magnitudes for the three other allotropes. Electronic band structure analyses reveal conductive C8 and C16, insulating C12 with a large band gap close to diamond's and semi-conducting C20 with small band gap.

Novel Superhard Tetragonal Hybrid sp3/sp2 Carbon Allotropes Cx (x = 5, 6, 7): Crystal Chemistry and Ab Initio Studies

Novel superhard tetragonal carbon allotropes C5, C6, and C7, characterized by the presence of sp3- and sp2-like carbon sites, have been predicted from crystal chemistry and extensively studied by quantum density functional theory (DFT) calculations. All new allotropes were found to be cohesive, with crystal densities and cohesive energies decreasing along the C5-C6-C7 series due to the greater openness of the structures resulting from the presence of C=C ethene and C=C=C propadiene subunits, and they were mechanically stable, with positive sets of elastic constants. The Vickers hardness evaluated by different models qualifies all allotropes as superhard, with Hv values ranging from 90 GPa for C5 to 79 GPa for C7. Phonon band structures confirm that the new allotropes are also dynamically stable. The electronic band structures reveal their metallic-like behavior due to the presence of sp2-hybridized carbon.

Development of an Elementary Reaction-Based Kinetic Model to Predict the Aqueous-Phase Fate of Organic Compounds Induced by Reactive Free Radicals.

ConspectusAqueous-phase free radicals such as reactive oxygen, halogen, and nitrogen species play important roles in the fate of organic compounds in the aqueous-phase advanced water treatment processes and natural aquatic environments under sunlight irradiation. Predicting the fate of organic compounds in aqueous-phase advanced water treatment processes and natural aquatic environments necessitates understanding the kinetics and reaction mechanisms of initial reactions of free radicals with structurally diverse organic compounds and other reactions. Researchers developed conventional predictive models based on experimentally measured transformation products and determined reaction rate constants by fitting with the time-dependent concentration profiles of species due to difficulties in their measurements of unstable intermediates. However, the empirical treatment of lumped reaction mechanisms had a model prediction limitation with respect to the specific parent compound's fate. We use ab initio and density functional theory quantum chemical computations, numerical solutions of ordinary differential equations, and validation of the outcomes of the model with experiments. Sensitivity analysis of reaction rate constants and concentration profiles enables us to identify an important elementary reaction in formating the transformation product. Such predictive elementary reaction-based kinetics models can be used to screen organic compounds in water and predict their potentially toxic transformation products for a specific experimental investigation.Over the past decade, we determined linear free energy relationships (LFERs) that bridge the kinetic and thermochemical properties of reactive oxygen species such as hydroxyl radicals (HO•), peroxyl radicals (ROO•), and singlet oxygen (1O2); reactive halogen species such as chlorine radicals (Cl•) and bromine radicals (Br•); reactive nitrogen species (NO2•); and carbonate radicals (CO3•-). We used literature-reported experimental rate constants as kinetic information. We considered the theoretically calculated aqueous-phase free energy of activation or reaction to be a kinetic or a thermochemical property, and obtained via validated ab initio or density functional theory-based quantum chemical computations using explicit and implicit solvation models. We determined rate-determining reaction mechanisms involved in reactions by observing robust LFERs. The general accuracy of LFERs to predict aqueous-phase rate constants was within a difference of a factor of 2-5 from experimental values.We developed elementary reaction-based kinetic models and predicted the fate of acetone induced by HO• in an advanced water treatment process and methionine by photochemically produced reactive intermediates in sunlit fresh waters. We provided mechanistic insight into peroxyl radical reaction mechanisms and critical roles in the degradation of acetone and the formation of transformation products. We highlighted different roles of triplet excited states of two surrogate CDOMs, 1O2, and HO•, in methionine degradation. Predicted transformation products were compared to those obtained via benchtop experiments to validate our elementary reaction-based kinetic models. Predicting the reactivities of reactive halogen and nitrogen species implicates our understanding of the formation of potentially toxic halogen- and nitrogen-containing transformation products during water treatment processes and in natural aquatic environments.

Novel Approach for Predicting Vertical Electron Attachment Energies in Bulk-Solvated Molecules.

When low-energy electrons interact with molecules, they can give rise to transient anion states commonly known as resonances. These states are formed through vertical electron attachment processes and have the potential to induce various forms of DNA lesions, including base damage, single- and double-strand breaks, cross-links, and clustered lesions that are challenging to repair. So far, most experimental and theoretical studies have investigated the formation of resonances of (bio)molecules in the gas phase or in microsolvated environments. Since cellular environments are mainly composed of water molecules, it is crucial to understand how bulk water affects the resonances of (bio)molecules. Given the existing gap in studies on resonances of bulk-solvated molecules, we propose a novel theoretical-computational approach to address this void. Our approach combines the multibasis-set (time-dependent-)density functional theory and self-consistent sequential quantum mechanics/molecular mechanics polarizable electrostatic embedding methods. We apply this combined methodology to predict the vertical electron attachment energies of 1-methyl-5-nitroimidazole (1M5NI), a well-known radiosensitizer model, in bulk water. In addition, we analyze the rapid mutual polarization between the resonances (both shape- and core-excited) of 1M5NI and the surrounding bulk water environment. For comparison, we also studied the isolated and microsolvated 1M5NI. Overall, while the polarization of the environment is clearly sensitive to the solute charge, causing a significant impact on the vertical electron affinity and consequently on the attachment electron energies, it does not have a significant impact on the excitation energies of the anion.

Construction of an Au/g-C3N4/GO/Au substrate by a layer-by-layer assembly approach for surface-enhanced Raman spectroscopy

In this work, an Au/g-C3N4/GO/Au hybrid nanofilm for surface-enhanced Raman scattering (SERS) substrate application was prepared by a facile layer-by-layer assembly technique using nanosheet-structured graphitic carbon nitride (g-C3N4), graphene oxide (GO) and 40 nm-gold nanoparticles (Au NPs). The effects of composition, assembly sequence and assembly cycles on the SERS performance were optimized to achieve the SERS-active substrate. The detection limit of Au/g-C3N4/GO/Au substrate for crystal violet and rhodamine 6 G probe molecules reached as high as 10−8 M, with good stability and uniformity. Its further application in food colorants detection (erythrosine, carmine and temptation red) had successfully met the national food safety standards and the quantitative detection for erythrosine and temptation red had also been established. Based on finite-difference time-domain element simulation and density functional theory quantum chemical calculation, the mechanism of the SERS effect of the substrate was unveiled, which is attributed to the combination of electromagnetic enhancement effect of Au nanoparticle aggregates and chemical enhancement effect of GO and g-C3N4. Notably, water droplet evaporation induced Raman enhancement was observed on the Au/g-C3N4/GO/Au substrate. This can be ascribed to the inhomogeneous evaporation of the droplet that promotes the enrichment of the probe molecules into the center of the droplet. This novel enhancement strategy provides a new idea for further improving detection sensitivity of SERS substrate materials.

Sites and Zones of Maximum Reactivity of the most Stable Structure of the Receptor-binding Domain of Wild-type SARS-CoV-2 Spike Protein: A Quantum Density Functional Theory Study

Today, it is well known that Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has four types of proteins within its structure, between them the spike protein (S). The infection mechanism is carried out by the entry of the virus into the human host cell through the S protein, which strongly interacts with the human cell receptor angiotensin-converting enzyme 2 (ACE2). In this work, we propose an atomic model of the Receptor Binding Domain (RBD) of the S spike protein of the wild-type SARS-CoV-2 virus. The molecular structure of the model was composed of 50 amino acids that were chemically bonded, starting with Leucine and ending with one amino acid Tyrosine. The novelty of our work lies in the importance of knowing the sites and zones of maximum reactivity of the RBD from the fundamental levels of quantum mechanics considering the atomic structure of matter. For this, the local and global reactivity indices of the RBD were calculated, such as frontier orbitals, Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO), Fukui indices, chemical potential, chemical hardness, electrophilicity index; with this, it will be possible to know what type of molecules are more likely to interact with the RBD structure, and in this way, new knowledge will be generated at the quantum, atomic and molecular level to inhibit the virulent effects of wild-type SARS-CoV-2. Finally, in order to identify the functional groups within the most stable structure and thereby verify the future reactions that can be carried out between the RBD structure and biomolecules, the Infrared (IR) absorption spectrum was calculated. For this work, we used Material Studio v6.0 which uses the density functional theory (DFT) implemented in its DMol3 computational code. The IR spectrum was obtained using the Spartan ‘94 computer code. One novelty would be that we found nine amino acids more that could make the RBD and ACE2 binding further the already known. Thus, the Mulliken charge distribution indicates that the highest concentrations of positive and negative charge are found in the zones 477S, 478T, 484E, and 501N amino acids letting ionic or Van der Waals possible interactions with other structures.

Green Enzymatic Synthesis of Geranyl Butyrate: Process Optimization and Mechanistic Insights.

Flavor esters are organic compounds widely used in the food industry to enhance the aroma and taste of products. However, most chemical processes for the production of these flavoring compounds use toxic organic solvents. Some organic solvents derived from petroleum can leave behind residual traces in food products, which may raise concerns about potential health risks and contamination. In this study, we employ Eversa Transform 2.0, a commercial lipase derived from the lipase from Thermomyces lanuginosus, to produce geranyl butyrate in aqueous media. The chemical process was optimized using the Taguchi method, and a conversion of 93% was obtained at the optimal reaction conditions of: 1:5 molar ratio (v/v), 15% biocatalyst load (w/w), at 50 °C, in 6 h. Classic (molecular dynamics) and quantum (density functional theory) simulations unveiled amino acid residues involved in the stabilization of the enzyme-substrate complex. Detailed QM/MM mechanistic studies identified the nucleophilic attack of the deacylation reaction as the rate-limiting step of the entire mechanism, which has a free energy barrier of 14.0 kcal/mol.

Towards atomistic modelling of solid Pb-O formation and dissolution in liquid lead coolant: Interatomic potential development

Microscopic description of solid Pb-O formation and dissolution in liquid lead coolant is important for the modelling of fast neutron reactors. For this purpose, in this work we develop interatomic potential models for lead melt with dissolved oxygen. Potentials fitting is based on ab initio density functional theory (DFT) calculations and quantum molecular dynamics. Two different potential models are trained on the DFT data using the force-matching method: a computationally cheap embedded atom method (EAM) potential and a computationally expensive machine-learned moment tensor potential (MTP) that allows reproducing DFT data very accurately. The potentials are further validated to reproduce the properties of lead melt and the coordination of oxygen atoms in molten lead. The diffusion coefficient for oxygen in molten lead is calculated and compared with the available experimental data. We analyse how these interatomic potential models describe the crystal structure of the solid lead oxide to consider PbO nucleation and dissolution in molten lead. We extensively discuss the arising problems with the description of long-range electrostatic interactions. The possibility of matching the experimental data on the oxygen solubility limit by tuning the EAM potential is shown.

Yttrium‐ and nitrogen‐doped NiCo phosphide nanosheets for high‐efficiency water electrolysis

AbstractEngineering high‐performance and low‐cost bifunctional catalysts for H2 (hydrogen evolution reaction [HER]) and O2 (oxygen evolution reaction [OER]) evolution under industrial electrocatalytic conditions remains challenging. Here, for the first time, we use the stronger electronegativity of a rare‐Earth yttrium ion (Y3+) to induce in situ NiCo‐layered double‐hydroxide nanosheets from NiCo foam (NCF) treated by a dielectric barrier discharge plasma NCF (PNCF), and then obtain nitrogen‐doped YNiCo phosphide (N‐YNiCoP/PNCF) after the phosphating process using radiofrequency plasma in nitrogen. The obtained N‐YNiCoP/PNCF has a large specific surface area, rich heterointerfaces, and an optimized electronic structure, inducing high electrocatalytic activity in HER (331 mV vs. 2000 mA cm−2) and OER (464 mV vs. 2000 mA cm−2) reactions in 1 M KOH electrolyte. X‐ray absorption spectroscopy and density functional theory quantum chemistry calculations reveal that the coordination number of CoNi decreased with the incorporation of Y atoms, which induce much shorter bonds of Ni and Co ions and promote long‐term stability of N‐YNiCoP in HER and OER under the simulated industrial conditions. Meanwhile, the CoN‐YP5 heterointerface formed by plasma N‐doping is the active center for overall water splitting. This work expands the applications of rare‐Earth elements in engineering bifunctional electrocatalysts and provides a new avenue for designing high‐performance transition‐metal‐based catalysts in the renewable energy field.

A molecular insight into the development of sensitive glucometers along with DFT investigation of glucose adsorption by a beryllium oxide particle

A molecular insight into the sensitive glucometers along with examining the adsorption of glucose (GLU) with the assistance of a representative beryllium-oxide (BeO)-particle (BOP) was provided in this work. Quantum density functional theory (DFT) calculations were performed for optimizing the models and obtaining their required information. The results indicated the possibility of formations of six interacting configurations of GLU@BOP complexes, I - VI, with the existence of H⋯O and O⋯Be interactions from GLU to BOP, with a detected mode of non-classical hydrogen bond in two of the complexes. The results of interaction strengths and frontier molecular orbitals variations indicated possibilities of formations of reasonable complexes. The existence of non-covalent physical interactions helped approach a recovery time for employing the BOP in a re-adsorption process besides indicating different conductance levels. Consequently, the models of GLU@BOP complexes were found suitable for working in a sensitive adoption of GLU for developing sensitive glucometers.

High-Pressure Phases of Boron Pnictides BX (X = As, Sb, Bi) with Quartz Topology from First Principles

The superdense hexagonal boron pnictides BX (X = As, Sb, Bi), whose structures are formed by distorted tetrahedra and characterized by a quartz-derived (qtz) topology, have been predicted from first principles as potential high-pressure phases. From full geometry structure relaxation and ground state energy calculations based on quantum density functional theory (DFT), qtz BX was found to be mechanically (elastic constants) and dynamically (phonons) stable. From the energy–volume equations of state, at high but experimentally accessible pressures, qtz boron pnictides were found to be more energetically favorable than corresponding cubic zinc–blende phases with diamond-like (dia) topology. According to the electronic band structures, the zinc–blende BX have larger band gaps than the qtz phases, which can be attributed to the higher covalence of the latter. A metallic behavior is only observed for qtz BBi, which is related to the dynamic instability as it follows from the phonon band structure.

Carbon Nanohoops: Multiple Molecular Templates for Exploring Spectroscopic, Electronic, and Thermoelectric Properties.

A combination of density functional theory (DFT) methods and quantum transport theory (QTT) has been used to investigate the spectroscopic, electronic, and thermoelectric properties of carbon nanohoop molecules with different molecular templates. The connectivity type, along with inherent strain, impacts the transport behavior and creates a destructive quantum interference (DQI), which proves itself to be a powerful strategy to enhance the thermoelectric properties of these molecules, making them promising candidates for thermoelectric applications.

Revisiting Dynamic Processes and Relaxation Mechanisms in a Heterocyclic Glass-Former: Direct Observation of a Transient State.

Despite decades of studies, a clear understanding of near-Tg phenomena remains challenging for glass-forming systems. This review delves into the intricate molecular dynamics of the small, heterocyclic thioether, 6-methyl-2,3-dihydro-1,4-benzodithiine (MeBzS2), with a particular focus on its near-Tg cold crystallization and relaxation mechanisms. Investigating isothermal crystallization kinetics at various temperatures reveals a significant interplay between its molecular dynamics and recrystallization from a supercooled liquid. We also identify two independent interconversion paths between energetically privileged conformers, characterized by strained transition states. We demonstrate that these spatial transformations induce substantial alterations in the dipole moment orientation and magnitude. Our investigation also extends to the complex salt PdCl2(MeBzS2), where we observe the transient conformers directly, revealing a direct relationship between their abundance and the local or macroscopic electric field. The initially energetically privileged isomers in an undisturbed system become less favored in the presence of an external electric field or ions, resulting even in an unexpected inversion of states. Consequently, we confirm the intramolecular character of secondary relaxation in MeBzS2 and its mechanism related to conformational changes within the heterocyclic ring. The research is based on the combination of broadband dielectric spectroscopy, X-ray diffraction, and quantum density functional theory calculations.

Atomic ordered doping leads to enhanced sensitivity of phosgene gas detection in graphene nanoribbon: a quantum DFT approach

We explore a novel sensor for detection of phosgene gas by graphene derivatives such as pristine and doped graphene nanoribbons via first principles calculations. The interaction of phosgene molecule with various edge and center doped configurations of boron, phosphorus and boron-phosphorus co-doped armchair graphene nanoribbon (AGNR) and zigzag graphene nanoribbon (ZGNR) is investigated through density functional theory (DFT). P-doped systems showcase chemisorption, displaying enhanced sensitivity to phosgene detection as reflected by a more negative adsorption energy values, accompanied by a prominent charge transfer due to the doping. Regardless of nanoribbon geometry, the binding energies of P-doped systems exhibit notable uniformity within the range of −8.01 eV to −8.49 eV, however the adsorption energies in ZGNR are significantly lower than those observed in AGNR. Due to much higher(lower) electron-donating (accepting) capacity of phosphorous(boron) atoms in comparison to ‘C’ atom, substitutional doping with ‘P’ or ‘B’ atoms in AGNR has signifiant impact on the structural, electronic and adsorption properties of the nanoribbons. We observe that phosphorus doped configurations (edge/center) effectively interact with phosgene molecule with higher adsorption that corresponds to the chemisorption phenomenon. The strongest adsorption energy (−8.83 eV) is obtained for P doped configurations, followed by that for B+P co-doped AGNR (−4.23 eV). These results suggest significantly stronger adsorption of phosgene gas on P doped AGNR than on any other systems reported so far. Band structure analysis estimates that by phosphorus doping, changes in the band gap is significant and it also shows prominent changes in the band structures. Isosurface electronic charge density plots identify that the transfer of charge takes place from graphene system to phosgene molecule. Thus, significant variation in adsorption and electronic properties of P doped AGNR reveal that these geometries immensely promote the detection of phosgene gas, and may be considered as promising chemical sensor for phosgene removal.

Monophasic coamorphous sulpiride: a leap in physicochemical attributes and dual inhibition of GlyT1 and P-glycoprotein, supported by experimental and computational insights

Study aimed to design and development of a supramolecular formulation of sulpiride (SUL) to enhance its solubility, dissolution and permeability by targeting a novel GlyT1 inhibition mechanism. SUL is commonly used to treat gastric and duodenal ulcers, migraine, anti-emetic, anti-depressive and anti-dyspeptic conditions. Additionally, Naringin (NARI) was incorporated as a co-former to enhance the drug’s intestinal permeability by targeting P-glycoprotein (P-gp) efflux inhibition. NARI, a flavonoid has diverse biological activities, including anti-apoptotic, anti-oxidant, and anti-inflammatory properties. This study aims to design and develop a supramolecular formulation of SUL with NARI to enhance its solubility, dissolution, and permeability by targeting a novel GlyT1 inhibition mechanism, extensive experimental characterization was performed using solid-state experimental techniques in conjunction with a computational approach. This approach included quantum mechanics-based molecular dynamics (MD) simulation and density functional theory (DFT) studies to investigate intermolecular interactions, phase transformation and various electronic structure-based properties. The findings of the miscibility study, radial distribution function (RDF) analysis, quantitative simulations of hydrogen/π–π bond interactions and geometry optimization aided in comprehending the coamorphization aspects of SUL-NARI Supramolecular systems. Molecular docking and MD simulation were performed for detailed binding affinity assessment and target validation. The solubility, dissolution and ex-vivo permeability studies demonstrated significant improvements with 31.88-fold, 9.13-fold and 1.83-fold increments, respectively. Furthermore, biological assessments revealed superior neuroprotective effects in the SUL-NARI coamorphous system compared to pure SUL. In conclusion, this study highlights the advantages of a drug-nutraceutical supramolecular formulation for improving the solubility and permeability of SUL, targeting novel schizophrenia treatment approaches through combined computational and experimental analyses. Communicated by Ramaswamy H. Sarma

Theoretical investigations on electronic structure and optoelectronic properties of vinyl fused monomeric and oligomeric benzimidazole derivatives using DFT and TDDFT techniques.

The present work encompasses the theoretical investigation of 14 benzimidazole-based (seven vinyl fused monomeric benzimidazole (VFMBI) and seven vinyl fused oligomeric benzimidazole (VFOBI)) derivatives using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) techniques. The effects of electron donor and acceptor groups on the electronic structure such as HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energies, HOMO-LUMO energy gap, ionization potentials (IPs), electron affinities (EAs), internal reorganization energies of holes and electrons (λh/e), and excited state properties have been explored in the present work. In addition, natural bond orbital (NBO) analysis of these compounds has been investigated to reveal the typical stabilization interactions in these molecules. Hence, the aim of the present work is to explore the electronic structures and optoelectronic properties of the title molecules on the basis of the DFT quantum chemical calculations and to make an idea on the parameters influencing the optoelectronic efficiency toward a better understanding of the structure-property relationships. Moreover, the calculated results reveal the suitable optoelectronic properties of benzimidazole oligomer derivatives using theoretical techniques. Of the investigated molecules, 4_MABIMCY and 4_MABIOCY show potential optoelectronic properties and can be used as a potential charge transport material due to their narrow band gap, high hyperpolarizability, low ionization potential, and high electron affinity. The larger λab and λem values favor the system to be used as a potential optoelectronic material with better optical properties. All quantum chemical calculations were carried out using Gaussian09 theoretical chemistry code. Ground state calculations were made using the B3LYP/6-31+G(d,p) method. All excited state calculations had been computed using TDB3P86/6-311++(d,p). The initial structure for excited state calculations was optimized using the AM1 semi-empirical method.

Preparation and characterization of activated carbon from pine bark biomass for malachite green removal

ABSTRACT Using agricultural waste to prepare biomass materials to remove pollutants has become a research hotspot with the rise of the circular economy. This paper focused on the removal of Malachite Green (MG) as a cationic dye from an aqueous solution using adsorbents (ACBP1 and ACBP2) chemically activated from pine bark (PB) and phosphoric acid (H3PO4) as activated agent. Samples Characterisation was carried out by X-ray diffraction (XRD), Scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS), Fourier transform infrared spectroscopy (FTIR) and Zeta potential measurement. The MG adsorption study was carried out under the variation of several parameters such as pH, adsorbent dosage, contact time and medium temperature. The adsorption experimental capabilities of ACPB1 and ACPB2 for MG dye were 150.18 and 148.16 mg/g, respectively. The data fit the nonlinear equation of the Pseudo-first-order kinetic model for the two adsorbents ACBP1 and ACBP2 with correlation coefficients of 0.998 and 0.997, respectively, indicating that chemisorption controls adsorption. Temperature was found to have a slight impact on adsorption performance, with ACPB1 demonstrating a removal capacity of 184.510 mg/g at 25°C to 186.670 mg/g at 55°C. In addition, a theoretical study was performed using the Density Functional Theory (DFT) quantum calculation method to examine the interactions of reactive sites of the best adsorbent ACPB1 and the cationic dye MG. The theoretical results revealed that the – OH and – COOH groups of ACPB1 were involved in adsorption. The comparative investigation between the experimental and the theoretical results concluded that the ACPB1 adsorbent has a potential removal against the cationic MG dye.

Nucleation mechanism of gas-phase InGaN nanoparticles

The nucleation mechanism of nanoparticles during the growth of InGaN by metal–organic chemical vapor deposition was investigated using density functional theory quantum chemical calculations to explore molecules that are most likely to become the cores of nanoparticles. On the basis of previous research on the nucleation mechanism of nanoparticles in the III-V system, several possible nucleation pathways are proposed for gas-phase InGaN nanoparticles, focusing on the cross-reaction between In and Ga. The possibility of forming different cross-reaction products is also discussed. Among the several reaction pathways examined, the possibilities of generating several cross-reaction products with similar configurations (i.e., [MMGaNHDMInNH2]2 and [MMInNHDMGaNH2]2, [MMGaNHDMInNH2]3 and [MMInNHDMGaNH2]3) were similar; the self-polymerization of [MMXNH]n was most likely to occur, and [MMInNH]4 and [MMInNH]6 were most likely to become the core of nanoparticles.

Photolytic splitting of homodimeric quinone-derived oxetanes studied by ultrafast transient absorption spectroscopy and quantum chemistry.

The photoinduced cycloreversion of oxetane derivatives is of considerable biological interest since these compounds are involved in the photochemical formation and repair of the highly mutagenic pyrimidine (6-4) pyrimidone DNA photoproducts ((6-4)PPs). Previous reports have dealt with the photoreactivity of heterodimeric oxetanes composed mainly of benzophenone (BP) and thymine (Thy) or uracil (Ura) derivatives. However, these models are far from the non-isolable Thy〈º〉Thy dimers, which are the real precursors of (6-4)PPs. Thus, we have synthesized two chemically stable homodimeric oxetanes through the Paternò-Büchi reaction between two identical enone units, i.e. 1,4-benzoquinone (BQ) and 1,4-naphthoquinone (NQ), that led to formation of BQ-Ox and NQ-Ox, respectively. Their photoreactivity has been studied by means of steady-state photolysis and transient absorption spectroscopy from the femtosecond to the microsecond time scale. Thus, photolysis of BQ-Ox and NQ-Ox led to formation of the monomeric BQ or NQ, respectively, through ring opening in a "non-adiabatic" process. Accordingly, the transient absorption spectra of the triplet excited quinones (3BQ* and 3NQ*) were not observed as a result of direct photolysis of the quinone-derived oxetanes. In the case of NQ-Ox, a minor signal corresponding to 3NQ* was detected; its formation was ascribed to minor photodegradation of the oxetane during acquisitions of the spectra during the laser experiments. These results are supported by computational analyses based on density functional theory and multiconfigurational quantum chemistry (CASSCF/CASPT2); here, an accessible conical intersection between the ground and excited singlet states has been characterized as the main structure leading to deactivation of excited BQ-Ox or NQ-Ox. This behavior contrasts with those previously observed for heterodimeric thymine-derived oxetanes, where a certain degree of ring opening into the excited triplet state is observed.

Multiscale Modeling of Aqueous Electric Double Layers.

From the stability of colloidal suspensions to the charging of electrodes, electric double layers play a pivotal role in aqueous systems. The interactions between interfaces, water molecules, ions and other solutes making up the electrical double layer span length scales from Ångströms to micrometers and are notoriously complex. Therefore, explaining experimental observations in terms of the double layer's molecular structure has been a long-standing challenge in physical chemistry, yet recent advances in simulations techniques and computational power have led to tremendous progress. In particular, the past decades have seen the development of a multiscale theoretical framework based on the combination of quantum density functional theory, force-field based simulations and continuum theory. In this Review, we discuss these theoretical developments and make quantitative comparisons to experimental results from, among other techniques, sum-frequency generation, atomic-force microscopy, and electrokinetics. Starting from the vapor/water interface, we treat a range of qualitatively different types of surfaces, varying from soft to solid, from hydrophilic to hydrophobic, and from charged to uncharged.