Molecular Modeling

Metal ions doped into merocyanine form of coumarin derivatives: nonlinear optical molecular switches Abstract In the present study, DFT calculations are carried out on domestically designed 7-methyl-2-phenyl-5’H-spiro[chromene-4,2′-chromeno[3,4-e][1,3]oxazin]-5′-one spiropyran and merocyanine derivatives to recognize alkali and alkaline earth metal ions. Detection of these metal ions can be attained by exploiting the variation of the second-order nonlinear optical properties. Merocyanine forms of these derivatives exhibit the ability to complex with different metal ions (Li+, Na+, K+, and Ca2+), which is associated with large contrasts in the hyper-Rayleigh scattering (HRS) response as a function of metal size and charge. Interestingly, in this study, Mero-Li+ shows significant nonlinear optical response with dynamic HRS first hyperpolarizability amounting to 7607 a.u., which is about nine times higher than its corresponding spiro form (846 a.u.) at the CAM-B3LYP/6-311G* level of theory. The present investigation clarifies the effect of metal nature on the enhancement of the first hyperpolarizability between the closed and open forms of the studied coumarin derivatives. Graphical abstract The coumarin-based compound 3 demonstrate the higher second-order NLO responses as a function of metal cation size and charges. Complexation of smaller alkali metal ions leads to the formation of stronger metal-ligand bonds, larger geometrical relaxations and significant enhancement of the HRS first hyperpolarizabilities. This present investigation elucidates the effect of metal nature on the enhancement of the first hyperpolarizability between the closed and open forms of studied coumarin derivatives

Theoretical investigation into the influence of molar ratio on mixture system: α , γ , δ -HMX molecules coexisting with β -HMX crystal Abstract Molecular dynamics (MD) simulation was conducted to research the effect of molar ratios for α/β-HMX, γ/β-HMX, and δ/β-HMX(octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) mixture systems on thermal stability, sensitivity, and mechanical properties of explosives, and the computing models were established by Materials Studio (MS). The binding energies, the maximum trigger bond length (LN–NO2), cohesive energy density as well as mechanical properties of the mixture systems and the pure β-HMX crystal were obtained and contrasted. The results demonstrate that the molar ratios have great influence on the binding capacity of molecules between α, γ, δ-HMX, and β-HMX in the mixture systems. The binding energies decrease with the increase of molecular molar ratio and have the maximum values at the 1:1 M ratio. The maximum trigger bond length does not change apparently after mixing, while the cohesive energy density (CED) increases as the molar ratio increases but are all smaller than the pure β-HMX crystal, demonstrating that the sensitivity of the mixture systems increases. The mechanical properties decrease after mixture, which illustrates that the mechanical properties of the pure crystal are superior to the mixture systems.

The nature of the T=T double bond (T = B, Al, Ga, In) in dialumene and its derivatives: topological study of the electron localization function (ELF) Abstract The local electronic structure of the Al=Al bond was studied in dialumene and derivatives of dialumene in which the Al atoms were substituted by B, Ga, or In atoms. DFT calculations were performed using the B3LYP, B3PW91, PBE0, M06-L, and M06-2X functionals. Topological analysis of the electron localization function described the covalent bonds mentioned above using the disynaptic basins Vi=1,2(B,B), Vi=1,2(Al,Al), V(Ga,Ga), and Vi=1,2(In,In). The basin populations were smaller than 4 e, as expected for a double bond: B=B 2.97 e, Al=Al 3.44–3.5 e, Ga=Ga 3.58 e, and In=In 3.86 e. The Al=Al, Ga=Ga, and In=In bonds were found to be intermediate in character between single and double bonds. Topological analysis of the ρ(r) field for dialumene showed a non-nuclear attractor along the Al=Al bond, with a pseudoatom basin population of 0.937 e. NBO analysis suggested that a double bond occurred only in the molecules containing Al, Ga, or In atoms. The character of the Ga=Ga bond was observed to be strongly dependent on the effective core potential used in the calculations.

First principles investigations of the structural, elastic, vibrational, and thermodynamic properties of TiMg 2 O 4 oxide spinels: cubic and tetragonal phases Abstract In the present study ab initio methology under density functional theory with generalized gradient approximation is used to study the structural, elastic, and vibrational properties of TiMg2O4 with cubic and tetragonal phases with space groups (Fd \( \overline{3} \) m) and P4_122, respectively. The present study shows that the studied compound TiMg2O4 is mechanically stable in both phases. Both phases have ductile nature and strong anisotropic properties, and it is also observed that the tetragonal phase has more anisotropic properties compared to the cubic phase. Obtained structural parameters are in good agreement with related literature.

Elucidating the origin of selectivity of [3 + 2]-cycloaddition reactions between thioketone and carbohydrate-derived nitrones by the DFT Abstract The mechanism and origin of selectivity for [3 + 2]-cycloaddition (32CA) reactions between thioketone and carbohydrate-derived nitrones in THF were investigated by using the density functional theory (DFT) at the M06-2X/6-311+G(d,p)//M06-2X/6-31+G(d,p) level of theory combined with the solvation SMD model. The calculated results revealed that the 32CA reactions proceed through the asynchronous one-step manner. For the chemoselectivity in thioketone, the C=S bond as a dipolarophile attacking three-atom-component (TAC) nitrone in reactivity was more preferential than the C=O bond. The theoretical results also confirmed the stereoselectivity of two 32CA reactions of thioketone with carbohydrate-derived nitrones with the anti-form product being more favored than the syn-form product, and the predicted anti/syn product ratios are in agreement with the experimental ones in literature. Furthermore, the analysis of the conceptual density functional theory reactivity indices showed that the 32CA reactions have polar character. Weak noncovalent interaction and Parr function analyses are used to reveal the origin of the stereoselectivity. Graphical abstract [3 + 2]-cycloaddition reactions between thioketone and carbohydrate-derived nitrones

Microhydration of caesium metaborate: structural and thermochemical properties of CsBO 2  +  n H 2 O ( n  = 1–4) aggregates Abstract The structures and thermodynamic properties of microhydrates of caesium metaborate (CsBO2) of nuclear safety interest are reported in this work. CsBO2 + n H2O (n = 1−4) molecular complexes were identified on the potential energy surface. The structures were optimized using the ωB97XD DFT method and the aug-cc-pVTZ basis set. Single-point energies were calculated at the CCSD(T)-F12a/awCVTZ and the ωB97XD/aug-cc-pVQZ levels of theory. The standard reaction enthalpies and the standard Gibbs free reaction energies were reported for all molecular complexes. The temperature dependence of ΔrG°(T) was evaluated for all studied structures over the temperature range 300–2000 K. Total hydration reactions were investigated. The results showed that the mono-hydrated form of CsBO2 exists only at temperatures lower than 720 K under standard conditions. The influence on the thermodynamic properties of the number of water molecules in the clusters was described, with successive dehydration from 720 to 480 K. In nuclear severe accident conditions, gaseous CsBO2 will remain unhydrated in the reactor coolant system.

Experimental and molecular modeling study of a novel arylsulfonamide chalcone Abstract Chalcones have been reported to present biological activities that are potentialized when a sulfonamide group is attached. A comprehensive structural study was performed for arylsulfonamide chalcone N-(2-(3–4-methoxyphenyl-propanoyl)-phenyl)-benzene-sulfonamide in order to describe its supramolecular arrangement and its physicochemical properties. The molecular packing arrangement was described by X-ray diffraction and Hirshfeld surfaces (HS). Theoretical calculations were performed using density functional theory (DFT), molecular electrostatic potential (MEP) mapping, ab initio Car-Parrinelo molecular dynamics (CPMD) and the quantum theory of atoms in molecules (QTAIM). The solid-state arrangement is stabilized by C– H⋯O and C–H⋯π interactions observed on HS and MEP map. The topological analysis was evaluated by QTAIM.

A comprehensive study on crystal structure of a novel sulfonamide-dihydroquinolinone through experimental and theoretical approaches Abstract Quinolinones and sulfonamides are moieties with biological potential that can be linked to form new hybrid compounds with improved potential. However, there are few hybrids of these molecules reported. In this sense, this work presents a structural description of a new sulfonamide-dihydroquinolinone (E)-2-(2-methoxyphenyl)-3-(3-nitrobenzylidene)-1-(phenylsulfonyl)-2,3 dihydroquinolin-4(1H)-one (DHQ). The molecular structure of DHQ was elucidated by X-ray diffraction, nuclear magnetic resonance and infrared spectroscopy, and both molecular packing and intermolecular interactions were analyzed by Hirshfeld surfaces and fingerprint maps. In addition, theoretical calculations on frontier orbitals, molecular electrostatic potential maps, and assignments were performed. The crystal packing of DHQ was found to be stabilized by a dimer through a weak C–H⋯O interaction along the c axis. Moreover, the structure is stabilized mainly by C–H⋯O and C–H⋯π interactions, since the interaction C25–H25⋯π contributes to a chain formation. The Hirshfeld normalized surface shows that the closest interactions are around the atoms linked to the dimer formation. The calculations indicate that DHQ possesses electrophilic sites near O atoms and depleted electrons around the H atoms. There is a band GAP of 3.29 eV between its frontier orbitals, which indicates that DHQ is more reactive than other analogues published.

Single-walled carbon nanotubes in tetrahydrofuran solution: microsolvation from first-principles calculations Abstract The molecular interactions between the commonly used solvent tetrahydrofuran (THF) and single-walled carbon nanotubes (SWCNT) are studied using density functional theory calculations and Car–Parrinello molecular dynamics simulations. The competitive interplay between THF–THF and THF–SWCNT interactions via C-H⋯O and C-H⋯π hydrogen bonds is analyzed in detail. The binding energies for different global and local energy minima configurations of THF monomers, dimers, trimers, and tetramers on SWCNT(10,0) were determined. The adsorbed species are analyzed in terms of their coordination to the surface via weak hydrogen bonds of the C-H⋯π type and in terms of their ability to form intermolecular C-H⋯O hydrogen bonds, which are responsible for the self-aggregation of THF molecules and a possible dimerization or tetramerization process. A special focus is put on the pseudorotation of the THF molecules at finite temperatures and on the formation of blue-shifting hydrogen bonds.

Rotaxane and pseudo-rotaxane molecules from molecular wires. Theoretical description Abstract Some rotaxane molecules were designed, and their electronic capabilities were studied by means of DFT calculations. The original molecular wire consists of an iron complex that comprises aromatic substituents that constitute linear chains, and this system is complemented by the addition of fullerene C60 unities at both extremes of the chain, which act as the stoppers of the chain. Another modification was to add a link that gives way to the mechanical bond; this link is a square molecule of bis-pyrydyl-pyridinium tetraion. An interesting effect was observed as a result of these modifications; the conductivity of the systems rises with the first substitution and even more with the second in such a way that the original semiconductor material changes to give a conductor one.