Zn2+ -Schiff’s base Complex as an “On-Off-On” Molecular Switch and a Fluorescence Probe for the Cu2+ and Ag+ ions

The present study presents a thorough theoretical analysis of the electronic structure and conformational preference of the Schiff’s base ligand N,N-bis(2-hydroxybenzilidene)-2,4,6-trimethyl benzene-1,3-diamine (H2L) and its metal complexes with Zn2+, Cu2+ and Ag+ ions. The study aims to investigate the behavior of H2L and the binuclear Zn2+ complex (1), as fluorescent probes for the detection of metal ions (Zn2+, Cu2+ and Ag+) using Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TDDFT). The six conformers of the H2L ligand were optimized using B3LYP/6-311++G** level of theory, while the L-2-metal complexes were optimized by applying B3LYP functional with LANL2DZ/6-311++G** mixed basis set. The gas-phase and solvated Enol-cis isomer (E-cis) was found to be the most stable species. The absorption spectra of E-cis isomer and its metal complexes were simulated using B3LYP, CAM-B3LYP, M06-2X and ωB97X functionals with a 6-311++G** basis set for C, O, N and H atoms and LANL2DZ basis set for the metal ions (Zn2+, Cu2+ and Ag+). The computational results of B3LYP functional were in excellent agreement with the experimental ones. Hence, it has been adopted for performing the emission calculations. The results indicated that, the metal complex (1) can act as a fluorescent chemosensor, for the detection of Ag+ and Cu2+ ions through the mechanism of the Intermolecular Charge Transfer (ICT) and as a molecular switch “On-Off-On” via the replacement of Cu2+ by Ag+ ions, as proved experimentally.

Energy and Reactivity Profile and Proton Affinity Analysis of Rimegepant with Special Reference to its Potential Activity against SARS-Cov-2 Virus Proteins using Molecular Dynamics

Rimegepant is a new medicine developed for the management of chronic headache due to migraine. This manuscript is an attempt to study the various structural, physical and chemical properties of the molecules. The molecule was optimised using B3LYP functional with 6-311G+(2d,p) basis set. Excited state properties of the compound were studied using CAM-B3LYP functional with same basis sets using IEFPCM model in methanol for the implicit solvent atmosphere. The various electronic descriptors helped to identify the reactivity behaviour and stability. The compound is found to possess good nonlinear optical properties in gas phase. The various intramolecular electronic delocalisations and non-covalent interactions were analysed and explained. As the compound contain several heterocyclic nitrogen atoms, they have potential proton abstraction features, which was analysed energetically. The most important result from this study is from the molecular docking analysis which indicates that rimegepant binds irreversibly with three established SARS-CoV-2 proteins with ID 6LU7, 6M03 and 6W63 with docking scores − 9.2988, -8.3629 and − 9.5421 kcal/mol respectively. Further assessment of docked complexes with molecular dynamics simulations revealed that hydrophobic interactions, water bridges and π – π interactions play a signification role in stabilising the ligand within the binding region of respective proteins. MMGBSA free energies further demonstrated that rimegepant is more stable when complexed with 6LU7 among the selected PDB models. As the pharmacology and pharmacokinetics of this molecule are already established, rimegepant can be considered as an ideal candidate with potential for use in the treatment of COVID patients after clinical studies.

Raman Spectra of SF6 Decomposed Characteristic Products Based on Density Functional Theory

SF6 decomposition product analysis is one of the most convenient and efficient methods to diagnose the potential faults of SF6 insulated electric equipment in the early stage. Based on SF6 decomposition characteristic gas analysis, the operation state of SF6 insulated power equipment can be judged by on-line monitoring, so as to ensure its normal operation. Raman spectrum analysis technology can realize the nondestructive detection of gas samples with a single wavelength laser. It has excellent applicability and high efficiency for the detection of SF6 decomposition characteristic components. In this paper, molecular configurations of CF4, CO, H2S, SO2 were obtained by B3LYP functional that based on density functional theory (DFT), and the Raman frequency and intensity characteristics were calculated by 6-31G (2df, p) basis group. The results were compared with National Institute of Standards and Technology (NIST) standard frequencies and it was found that the optimized configuration has no virtual frequency. The characteristic peaks of CO, CF4, SO2 and H2S that were identified by Raman spectrum are respectively 2221.11, 908.97, 1175.24 and 2688.82 cm-1, which are basically consistent with the corresponding NIST standard values. This study not only shows that the Raman spectrum of SF6 decomposition products calculated by B3LYP functional function is reliable, but provides a reference for the quantitative detection of SF6 decomposition products based on Raman spectrum.

Hydration and Proton Transfer Processes in Sulfonated Nata De Coco Membrane with Density Functional Theory

Direct Methanol Fuel Cells (DMFCs) is one of the most promising alternative energy resources to meet human energy needs. DMFCs is fuel cells that use polymer membranes as the electrolytes to transfer the protons from anode to cathode. The characteristics of those two types of membranes in ion exchange capacity (IEC) and degree of swelling (swelling) have shown a very important role of water in the proton transfer. However, the mechanism of interaction between the repeating units of the polymer with water molecules has not been studied in depth. Computational methods can be used to study such interactions as well as the transfer of protons. To examine the transfer of protons in the membrane, studies of computing via electronic structure calculations, geometry optimization, interaction inter/intra molecular, as well as the hydration process and transfer of protons in the sulfonated nata-de-coco membranes (NDCS) has been conducted in this work. All calculations were performed using DFT with B3LYP functional and basis set 6-311G(d). The repeating units of the membranes were optimized (n=1,2,...,5), to obtain the structure with minimum energy. The optimized structure was then interacted with one water molecule in the same position to study the effect of chain length on its interaction strength with water molecules. The thermodynamic and proton dissociation parameters was calculated by adding n water molecules (n=1,2, …,10) to determine the hydration process and the proton transfer on the membranes. The calculations showed that for interactions with water, the polymer structure in NDCS can be represented/modeled by two repeating units. Therefore, the hydration process and transfer of protons in the membranes were studied by adding n water molecules gradually into the two repeating units. The results showed that the proton dissociation process in NDCS membrane started with the addition of two molecules of water. The presence of water molecules promoted the proton dissociation in the -SO3H groups to form SO3- and H3O+ ions, which further formed Zundel ions and Eigen ions. The energy profile of proton transfer showed that the barrier energy was 58.13 kcal/mol for NDCS-5(H2O). Its thermodynamic parameters, the calculation showed that the interaction energy (ΔE), the enthalpy change (ΔH) and the Gibbs free energy (ΔG) to its interaction with n water molecules (n=1,2,…,10) in NDCS are getting more negative. This indicated that the interaction with water molecule is stronger. So, based on these results, it can be concluded that the computational calculations using DFT method at B3LYP functional and 6-311G(d) basis set can be used to describe the process of hydration and proton transfer in the interactions in the polymer electrolyte membrane (NDCS membrane)

The NV−....N+ charged pair in Diamond: a Quantum-Mechanical investigation

The NV−....N+ charged pair in diamond has been investigated by using a Gaussian-type basis set, the B3LYP functional, the supercell scheme and the CRYSTAL code. It turns out that: i)...

Dipole moments of conjugated donor–acceptor substituted systems: calculations vs. experiments

B3LYP functional can reproduce the experimental dipole moments of conjugated organic molecules with high accuracy.

DFT study of Anti Sars-Cov-2 EIDD-1931 and EIDD-2801 molecular structures

Scientists around the world are joining efforts in the study of the current SARS-CoV-2 virus and the Covid-19 disease. As a result, several compounds have been studied for the treatment of SARS-CoV-2, among them there are N4-hydroxycytidine prodrug (NHC; EIDD-1931), and EIDD-2801, that have shown antiviral activity against SARS-CoV-2. We have studied the structural and electronic properties of these molecules using B3LYP functional and aug-cc-pVDZ basis set.

Implementação dos parâmetros da quitosana no campo de força OPLS-AA para simulações da quitosana por dinâmica molecular

In this work, the molecular dynamics of the finite biopolymer of chitosan in the force field OPLS-AA was made. DFT calculations for structural optimization were performed in the ORCA program with the B3LYP functional and 6-31G base function. The partial atomic charges of Chitosan were obtained by the RESP methodology. The molecular structure of chitosan was structurally evaluated in terms of RMSD and ring overlap. A comparison between the chitosan parameters in OPLS-AA and GROMOS53a6 force-field indicated that in OPLS-AA energy and structural stability are achieved more quickly. The results obtained are in accordance with reports in the literature for this molecule in the GROMOS53A6 force field.

First-Principles Investigations of Magnetic Anisotropy and Spin-Crossover Behavior of Fe(III)-TBP Complexes

<div>With the ongoing efforts to obtain mononuclear 3d-transition metal complexes that manifest slow relaxation of magnetization and hence, can behave as single molecule magnets (SMMs), we have modelled 14 novel Fe(III) complexes out of which nine behave as potential SMMs. These complexes possess large zero-field splitting (ZFS)</div><div>parameter D in the range of -40 to -60 cm^-1. The first-principles investigation of the ground-spin state applying density functional theory (DFT) and wave-function based</div><div>multi-configurations methods e.g. SA-CASSCF/NEVPT2 are found to be quite consistent except for few delicate cases with near degenerate spin-states. In such cases, the</div><div>hybrid B3LYP functional is found to be biased towards high-spin (HS) state. Altering the percentage of exact exchange admixed in B3LYP functional leads to intermediate spin</div><div>(IS) ground state consistent with the multireference calculations. The origin of large zero field splitting (ZFS) in the Fe(III)-based trigonal bipyramidal (TBP) complexes</div><div>is investigated and the D-values are further tuned by varying the axial ligands with group XV elements (N, P and As) and equatorial halide ligands from F, Cl, Br and I. Furthermore, a number of complexes are identified with very small Gibbs free energy values indicating the possible spin-crossover phenomenon between the bi-stable spin-states.</div>

First-Principles Investigations of Magnetic Anisotropy and Spin-Crossover Behavior of Fe(III)-TBP Complexes

<div>With the ongoing efforts to obtain mononuclear 3d-transition metal complexes that manifest slow relaxation of magnetization and hence, can behave as single molecule magnets (SMMs), we have modelled 14 novel Fe(III) complexes out of which nine behave as potential SMMs. These complexes possess large zero-field splitting (ZFS)</div><div>parameter D in the range of -40 to -60 cm^-1. The first-principles investigation of the ground-spin state applying density functional theory (DFT) and wave-function based</div><div>multi-configurations methods e.g. SA-CASSCF/NEVPT2 are found to be quite consistent except for few delicate cases with near degenerate spin-states. In such cases, the</div><div>hybrid B3LYP functional is found to be biased towards high-spin (HS) state. Altering the percentage of exact exchange admixed in B3LYP functional leads to intermediate spin</div><div>(IS) ground state consistent with the multireference calculations. The origin of large zero field splitting (ZFS) in the Fe(III)-based trigonal bipyramidal (TBP) complexes</div><div>is investigated and the D-values are further tuned by varying the axial ligands with group XV elements (N, P and As) and equatorial halide ligands from F, Cl, Br and I. Furthermore, a number of complexes are identified with very small Gibbs free energy values indicating the possible spin-crossover phenomenon between the bi-stable spin-states.</div>