Quantum Chemical Study Research Articles

Green synthesis, spectroscopic investigation, quantum chemical and molecular docking studies of 3-methylisoxazolo [4,5-b]pyridine

The present work, synthesized molecular compound of MIP from carbinol extract of Hybanthus Enneaspermus by green synthesis method. The GC–MS analysis method has validated the molecular structure of MIP and revealed structural characteristics. FT-IR and UV-Visible spectra have been used to characterize the newly synthesized molecular molecule. DFT calculations employing the B3LYP/6-311++G(d,p) basis set are used to analyses the optimized molecular geometry and vibrational frequencies of the MIP compound. The Homo-Lumo energy gap of the MIP molecules is 5.4793 eV. The interaction (intra-inter, hydrogen bonding, and charge delocalization) of MIP molecules computed by NBO 3.1 program. TD-DFT was used to describe the electronic transition of ground state to excited state and compare with the recorded UV- Visible absorption spectra of MIP compounds. Molecular docking studies was interpreted and recorded the newly synthesis compound against 2YJR and IUSN receptor (lungs and kidney cancer).

Quantum chemical study on the catalytic debromination mechanism of brominated epoxy resins

The study employed Density Functional Theory (DFT) to investigate the catalytic debromination mechanism of brominated epoxy resins (BERs) by iron (Fe) and copper (Cu) catalysts. By introducing electric field (EF), intramolecular electron transfer and polarization effects on BERs debromination were explored and experimentally validated. Results indicated that the bond dissociation energy (BDE) of the C-Br bond was 312.27 kJ/mol without catalysis, while with Fe, Cu, and EF, it was 114.47 kJ/mol, 94.85 kJ/mol, and 292.59 kJ/mol, respectively, enhancing reactivity. EF parallel to the C-Br bond and oriented toward the C atom, altered electrostatic potential and dipole moment around C-Br bond, leading to 68.60% and 50.19% increment in electronic contribution difference and molecule polarity, respectively, thereby reducing the C-Br BDE. Fe and Cu facilitated electron transfers with BERs, inducing reactions between their negative electrostatic potentials and Br's positive potential, changing electron sharing, resulting in 19.87% and 12.11% increase in polarity, respectively, and further BDE reduction. Structural modifications by the EF and catalysts also intensified van der Waals forces with bromine atoms and decreased spatial hindrance, collectively making C-Br bond breakage easier. Experiments revealed the EF enhanced BERs' debromination efficiency but hindered Fe/Cu's catalysis at lower temperatures.

Single crystal X-ray diffraction analysis, spectroscopic measurement, quantum chemical studies, antimicrobial potency and molecular docking of a new [Co(NCS)4]2(C6H17N3)2·4H2O coordination compound based on piperazine-thiocyanate as co-ligand

A new cobalt (II) complex was synthesized and characterized by physicochemical evidences. According to crystallography study, the molecular structure consisting of anionic hybrid layer, while [C6H17N3]2+ cations, are mainly trapped onto successive between these latter, forming corrugated organic layers. This analysis suggests a distorted tetrahedral geometry around cobalt (II) having a CoN4 coordinating atmosphere. The crystal packing is stabilized by intra- and intermolecular hydrogen bonds. The vibrational properties were discussed by infrared spectroscopy to identify functional groups. Hirshfeld surface analysis and corresponding 2D fingerprint plots have been performed in order to elucidate short contacts resulting from the structural data. The new compound gave strong antimicrobial potential against the most treated microbial pathogens, with lysozyme and anti-biofilm activities. Molecular docking interactions between the complex and Salmonella enterica protein 4K6L forming conventional hydrogen bonds with amino acid residues LYS E:83 G:128, ARG C:90 and ASP E:87 with bond lengths of 2.35, 2.40 and 3.53 Å, respectively, and a binding affinity of -4.2 Kcal/mol. The complex [Co(NCS)4]2 (C6H17N3)2. 4H2O bonded with the protein 7EE6 with binding affinity of about -4.3 Kcal/mol forming conventional hydrogen bonds with amino acid residues LYS A:90, ASN B:90, ETH E:88, LYS G:242, ASN B:87 and GLU G:23 with bond lengths of 2.68, 2.82, 241, 2.65, 3.59 and 3.78 Å, respectively. From these results, despite not matching the docking performance of doxycycline and ciprofloxacin, the compound displayed considerable biological feasibility. Therefore, the study leaves space for experimental studies.

A Quantum Chemical Study of the Electrochemical Properties of a Series of Methanofullerenes

A Quantum Chemical Study of the Electrochemical Properties of a Series of Methanofullerenes

니코틴산에서 유래된 알칼로이드 분자에 대한 양자화학적 연구

A quantum chemical studies were conducted on nicotine, nornicotine, anabasine, arecholine, ricinine, cotinine, -nicotrine, anatabine and myosmine molecules, which are alkaloids derived from or related to nicotine acid, using ab initio methods. As a result, we have proposed a molecular electrostatic potential diagram in the form of a 3D mapped isosurface and a net charge of molecules, which predict or proposed a specific reaction site. The average electrodonating power obtained by the frontier energy of alkaloid molecules was 1.173171, which was larger than the average electroaccepting power of 0.599333. Protonation reactions at specific reaction sites predicted for alkaloid molecules showed that the changes in free energy and enthalpy ranged from -149.257 to -655.769 kJ/mol and -140.970 to -657.806 kJ/mol, respectively and were spontaneous and exothermic reactions. The data and methodology of the research results are expected to be useful for future research on alkaloids.

Improvement the formaldehyde sensing and detection through Pt-doped graphdiyne monolayer: Quantum chemical study

One of the commonly employed chemical feedstocks is formaldehyde (CH2O), which has diverse applications in many fields. However, CH2O might have detrimental effects on human because of its toxicity. Hence, it is of utmost significance to effectively monitor and detect CH2O. Within this piece of research, the adhesion attributes of the pristine graphdiyne (PGRD) and Pt-doped GRD (Pt@GRD) for CH2O were examined through DFT calculations. Moreover, the HOMO-LUMO energy levels, electrostatic potentials, energy band structures, adhesion structure parameters, and doping site optimizations of the Pt@GRD were investigated. Based on the results, doping the Pt atom the optimal site (CII) dramatically reduced the energy gap and substantially enhanced the electrical conductance. The PGRD was not suitable for the detection of CH2O with high sensitivity since it used mainly physisorption. However, there was a robust chemical adsorption between Pt@GRD and CH2O via the chemical reaction and hybridization of the Pt-d orbital with the molecular orbital of CH2O. The performance of Pt@GRD as a novel 2D material in detecting CH2O was extremely high. The current results can provide useful insights into developing future sensors for the detection of various gasses.

Synthesis of urea on the surface of interstellar water ice clusters. A quantum chemical study

Urea is a prebiotic molecule that has been detected in few sources of the interstellar medium (ISM) and in Murchison meteorite. Being stable against ultraviolet radiation and high-energy electron bombardment, urea is expected to be present in interstellar ices. Theoretical and experimental studies suggest that isocyanic acid (HNCO) and formamide (NH2CHO) are possible precursors of urea. However, uncertainties still exist regarding its formation routes. Previous computational works characterised urea formation in the gas phase or in presence of few water molecules by reaction of formamide with nitrogen-bearing species. In this work, we investigated the reaction of HNCO + NH3 on an 18 water molecules ice cluster model mimicking interstellar ice mantles by means of quantum chemical computations. We characterised different mechanisms involving both closed-shell and open-shell species at B3LYP-D3(BJ)/ma-def2-TZVP level of theory, in which the radical–radical H2NCO + NH2 coupling has been found to be the most favourable one due to being almost barrierless. In this path, the presence of the icy surfaces is crucial for acting as reactant concentrators/suppliers, as well as third bodies able to dissipate the energy liberated during the urea formation.

On the adsorption of arsenic on single-walled carbon nanotube and Fe-doped single-walled carbon nanotube: a quantum chemical study

On the adsorption of arsenic on single-walled carbon nanotube and Fe-doped single-walled carbon nanotube: a quantum chemical study

Quantum-chemical study of the stability of solvents with respect to strong organic bases

The possibility of theoretical calculation of the ionization constants of strong organic bases in dimethyl sulfoxide and hexametapole was studied by the DLPNO-CCSD (T) and DFT methods. By comparison with the experimental data available in the literature, it has been established that the error of such calculations lies within 1–2 pKa units. The stability of some ionizing solvents against strong organic bases is investigated, the mechanisms of decomposition of solvent molecules in strongly basic media are predicted, and the corresponding energy barriers are estimated. According to the calculations, among ionizing solvents, hexamethylphosphoramide has the highest resistance to superbases, being able to maintain pH > 50 at room temperature. At the same time, 1,3-dimethyl-2-imidazolidinone gradually decomposes under these conditions, while tetrahydrofuran and pivalonitrile are even less stable.

Quantum chemistry and metadynamics study of kinetic routes to alanine formation by CO or CO2 insertions in E- or Z-ethanimine isomers

Quantum chemistry and metadynamics study of kinetic routes to alanine formation by CO or CO2 insertions in E- or Z-ethanimine isomers

Stabilization of Cyclic C4 by Four Donor Ligands: A Theoretical Study of (L)4C4 (L = Carbene).

Quantum chemical studies using density functional theory were carried out for the (L)4C4 complexes with L = cAAC, DAC, NHC, SNHC, MIC1, and MIC2. The results show that the title complexes are highly stable with respect to dissociation, (L)4C4 → C4 + 4L. However, their stability with respect to (L)4C4 → 2(L)2C2 is crucial for the assessment of their experimental viability. The (L)4C4 complexes with L = cAAC and DAC dissociate exergonically at room temperature into two (L)2C2 units. In contrast, the other (L)4C4 complexes with L = NHC, SNHC, MIC1, and MIC2 are thermochemically stable with respect to dissociation, (L)4C4 → 2(L)2C2. The computed adiabatic ionization potentials of (L)4C4 complexes with L = NHC, MIC1, and MIC2 are lower than those for the cesium atom. Particularly, (MIC1)4C4 and (MIC2)4C4 will very easily lose electrons to form cationic complexes. The SNHC ligand is the best for the experimental realization of (L)4C4 complexes, followed by NHC. The bonding analysis using charge and energy decomposition methods suggests that the (L)3C4-CL bond can be best described as a typical electron-sharing double bond with a strong σ-bond and a weaker π-bond. Therefore, the core bonding pictures in the title complexes resemble a [4]radialene. Larger substituents at the carbene ligands enhance the stability of the complexes (L)4C4 against dissociation.

Formation of hydroxide anions in amorphous astrophysical ices and recombination with protons: a quantum chemical study

ABSTRACT Quantum chemical cluster calculations employing density functional theory and correlation consistent basis sets reveal the following pathways by which hydroxide anions (OH–) may form in amorphous astrophysical ices: (1) hydroxyl radicals (OH), which may arise in ice via ultraviolet photolysis, can capture electrons; (2) adsorbed hydrogen atoms can capture electrons to form H–, which reacts with water to yield H2 and OH–; (3) NaOH deposited on ice dissociates into Na+ and OH–; (4) NaH deposited on ice dissociates into Na+ and H–; H– then reacts with water to yield H2 and OH– as above. The IR spectrum of ice-bound OH– is presented, based on nine clusters containing up to 31H2O and 1–2 OH– anions. The interaction of OH– in ice with cations is also explored. Prior work shows that when HCO+ is deposited on pure amorphous water clusters, it reacts with H2O to form formic acid (HCOOH) and the hydronium (H3O+). When HCO+ is deposited on a cluster containing OH–, the reaction proceeds in almost the same manner, but the H3O+ and OH– charge centres migrate through the water network toward each other and tend to neutralize one another by forming H2O. This occurred in all but one of seven cases considered; migration occurred even when the oxygen atom attacked by HCO+ is over 10 Å from the oxygen atom in OH–. Cations and anions can interact in ice via pathways not present in the gas phase or incorporated in current models.

Quantum-Chemical Study of the Benzene Reaction with Fluorine

The reaction of benzene with fluorine atoms may be of interest as a source of phenyl and ipso-fluorocyclohexadienyl radicals or as a method for fluorobenzene gas phase synthesis. The structures and electronic energies of the equilibrium configurations and transition complexes of the C6H6F system are calculated in the density functional approximation. It was found that the interaction of benzene with atomic fluorine can proceed via two channels: hydrogen abstraction with the phenyl radical formation, and hydrogen substitution with the ipso-fluorocyclohexadienyl radical as primary product. Then the dissociation of the ipso-fluorocyclohexadienyl radical leads to creation of fluorobenzene and atomic hydrogen. The initiation of this reaction requires the activation energy near 27 kcal/mol, which indicates the low probability of this process, occurring at temperatures close to the standard (298 K). The calculations of the fluorocyclohexadienyl isomers and their cations also indicate that the formation of fluorobenzene as a product of secondary reactions is unlikely. The conclusions are confirmed by experimental data.

Physicochemical and quantum chemical studies of the thermal-oxidative aging resistance of bitumen modified with isocyanate-based reactive additive

The use of methylene diphenyl diisocyanate (MDI)-based additives to prepare isocyanate-modified bitumen (IMB) provides an effective solution for achieving energy savings and performance improvements. However, the thermal-oxidative aging properties of bitumen modified with isocyanate additive have not been well discussed, which limits the fundamental understanding of its durability-related performance. To promote the understanding of the aging mechanism of IMB, experimental investigations and quantum chemical calculations were conducted to investigate the aging properties of IMB. IMB samples were prepared and aged under controlled laboratory conditions. The evolutions of aging behaviors were examined through physical and chemical approaches. The role of noncovalent intermolecular interactions in delaying oxidation was interpreted through density functional theory (DFT)-based theoretical calculation. The results revealed that amide-related bonds can be generated due to the chemical interactions between isocyanate and bitumen compounds. Chemical reactions tend to reduce the potential sites for oxidative attacks, thereby inducing delayed oxidation of IMB. Consequently, lower chemical and rheological aging indexes can be observed in IMB, and chemical crosslinking can provide effective support for the elastic response after aging. In addition, the noncovalent interactions between isocyanate and bitumen molecules can result in a lower tendency towards oxidation, which provides a cooperative effect on the inhibition of aging. The findings of this study offer insights into the aging behaviors of IMB and provide references for the design of chemically modified bitumen.

Study of the interaction of the H<sub>2</sub>O-BF<sub>3</sub> complex catalyst with <i>p</i>-methylstyrene in toluene of stoichiometric composition 1:1:2 using the <i>ab initio</i> method

For the first time, a quantum-chemical study of the reaction of protonation of the monomer of cationic polymerization of p-methylstyrene in the presence of a complex catalyst boron fluoride – water in toluene with a stoichiometric composition of 1:1:2 was carried out by the ab initio method with the reaction coordinate RC1-H20. I t is shown that the value of the activation energy is 123 kJ/mol, and the thermal effect of the reaction is 86 kJ/mol. It has been proved that the interaction of the studied catalytic complex with p-methylstyrene in toluene of stoichiometric composition 1:1:2 is a coordinated process.

Insights into the geometrical parameters, charge distribution, and reactivity of Ca, Mg, Sr, and Bi complexes of piroxicam and meloxicam: A quantum chemical study

DFT studies have been used to calculate the geometrical parameters of optimized structures, along with the charge distribution and reactivity of the respective compounds. The gas-phase optimization of the recently synthesized Ca, Mg, Sr, and Bi complexes of piroxicam and meloxicam were carried out using B3LYP functional in the Gaussian program and 6-31G(d,p), LanL2DZ, and SDD basis set in a sequel. The charge distribution around metal atoms was analyzed using the same basis set. The reactivity descriptors were calculated from the frontier molecular orbitals (FMOs) energy calculations. The relationship between geometrical parameters, the dipole moment of the complexes, and the type of metal were established in this study. The charge analysis study dictated the less electron-back donation with the increased size of the metal atom. The theoretical calculations concluded that the studied complexes are soft, more polarizable, and prefer to act as electrophiles during chemical reactions with nucleophiles.

Hydration structure and dynamics, ultraviolet–visible and fluorescence spectra of caffeine in ambient liquid water. A combined classical molecular dynamics and quantum chemical study

The hydration structure and related dynamics of caffeine diluted in ambient liquid water have been extensively studied by performing classical molecular dynamics simulations, using our previously developed potential model of caffeine and the TIP4P/2005 water model. The results obtained have revealed that the first hydration shell of caffeine contains on average 56 water molecules. Hydrated caffeine forms in total 3 hydrogen bonds with its neighbor water molecules, with the Ocaffeine … Hwater hydrogen bonds exhibiting similar lifetimes with the ones corresponding to Owater … Hwater hydrogen bonds in liquid water. The self-diffusion coefficient of caffeine has been found to be four times lower than the corresponding value for water, being also in agreement with recent experimental measurements. The presence of water molecules inside the solvation shell of caffeine changes significantly their low-frequency intermolecular vibrations, as reflected on the calculated atomic velocity time correlation functions and corresponding spectral densities. Using the estimated average intermolecular structure of the first hydration shell of caffeine, the molecular cluster caffeine@W56 was optimized via quantum chemical calculations and subsequently the time-dependent density functional theory was used in order to predict the ultraviolet–visible and fluorescence spectra of hydrated caffeine. The results obtained are in agreement with recent experimental studies, which have proposed that such spectroscopic measurements can be used for the direct determination of alkaloids in aqueous extracts of natural products. In this framework, multi-scale molecular modelling providing accurate predictions of experimental data could also be a very useful tool, linking theoretical physical chemistry with analytical chemistry applications.

Optimization studies of expired mouthwash drugs on the corrosion of aluminum 7475 in 1 M hydrochloric acid: Gravimetrical, electrochemical, morphological and theoretical investigations

The aim of the present work is to study the corrosion inhibition of Al 7475 alloy by an expired mouthwash drug (EMWD) in a 1 M HCl solution. The corrosion rate was optimized by the Doehlert experimental design at various temperatures, concentrations of inhibitor, and rotational velocity. The corrosion behavior was investigated by mass loss, Tafel potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. SEM, MOMT, XRD, FT-IR spectrum, and drop wettability measurement were used in characterizations of EMWD and surface morphology. Optimum conditions for corrosion control of EMWD on aluminum were 44.12 °C, 141.71 mL/L of EMWD per liter of acid, and 234.89 rpm. Maximum corrosion inhibition efficiency was 84.717% at higher levels of temperature and inhibitor concentration. It is observed that EMWD follows the Langmuir Adsorption Isotherm with negative values of ΔGadso, proposing a stable spontaneous inhibition process. The inhibitor efficiency increased as the inhibitor concentration increased. Moreover, increasing the solution temperature and rotational velocity had an adverse influence on inhibitor efficiency. The results of mass loss were in good agreement with potentiodynamic polarization and EIS. Polarization diagrams revealed that the inhibitor acts as a mixed-type inhibitor. It could be concluded that response surface Doehlert design (RSDD) was adequately applicable in the optimization of corrosion inhibition process variables and that EMWD sufficiently inhibited the corrosion of the aluminum at the studied conditions. Simulation of the EMWD molecules adsorption on the metal surface by quantum chemical theoretical studies was a powerful tool for supporting experimental outcomes.

Development and Evaluation of an Efficient Second Order Non-Linear Optical Single Crystal – 2-(3-Aminopyridinium-1-yl)-3-Carboxy-Proponate Monohydrate

A slow evaporation solution approach was used to create high-quality single crystals of 2-(3-aminopyridinium-1-yl)-3-carboxyproponate monohydrate (3ACPM). The single crystal X-ray diffraction was used to determine the crystal system and lattice characteristics. Software called Krystal Shaper was used to mimic the morphology of the 3ACPM. To evaluate the optical transmittance, UV-vis spectral analysis was used. The Nd:YAG laser was used to assess the laser-induced surface damage threshold (LISDT) of 3ACPM single crystal. The presence of second harmonic generation (SHG) was evaluated using the Kurtz-Perry powder method. Full Text: PDF References Y. Zhang, H. Li, B. Xi, Y. Che,vJ. Zheng, "Growth and characterization of l-histidine nitrate single crystal, a promising semiorganic NLO material", Mater. Chem. Phys. 108, 192 (2008), CrossRef S. Draguta, M.S. Fonari, A.E. Masunov, J. Zazueta, S. Sullivan, M.Y. Antipin, T.V. Timofeeva, "New acentric materials constructed from aminopyridines and 4-nitrophenol", Cryst. Eng. Comm. 15, 4700 (2013) CrossRef G. Peramaiyan, R. Mohan Kumar, "Nonlinear optical and laser damage threshold studies of an ammonium p-toluenesulfonate crystal", Appl. Phys. A 119, 707 (2015), CrossRef G.M. Corrales, D. Morales-Morales,S. Hernandez-Ortega, J.J. Campos-Gaxiolaa, A. Cruz Enrıquez, "2-(3-Aminopyridinium-1-yl)-3-carboxypropanoate monohydrate", Acta Cryst. E68, o853 (2012), CrossRef S.K. Kurtz, T.T. Perry, "A Powder Technique for the Evaluation of Nonlinear Optical Materials", J. Appl. Phys. 39, 3798 (1968), CrossRef S. Panchapakesan, K. Subramani, B.Srinivasan, "Growth, characterization and quantum chemical studies of an organic single crystal: 3-Aminopyridine 4-Nitrophenol for opto-electronic applications", J. Mater. Sci: Mater. Electron. 28, 5754 (2017), CrossRef

Thermodynamic and Kinetic Characteristics of Molnupiravir Tautomers and Its Complexes with RNA Purine Bases as an Explanation of the Possible Mechanism of Action of This Novel Antiviral Medicine: A Quantum-Chemical Study.

The mechanism of action of molnupiravir, a novel antiviral drug, was analyzed from the point of view of its tautomerism by means of quantum-mechanical calculations. It was established that although the uracil-like tautomer Mu (3 kcal/mol in the water environment) is the most thermodynamically stable, in fact, it is the cytosine-like tautomer Mc that plays the main role. There are several reasons, as follows: (1) A large part of Mu exists as a more stable but inactive form Mu-m that is unable to pair with adenine. (2) The phosphorylated form of Mc is only 1 kcal/mol less stable than Mu in the water environment and thus is readily available for building into the RNA strand, where the Mu/Mc energy gap increases and the probability of Mc → Mu interconversion leading to C → U mutation is high. (3) The guanine-Mc complex has similar stability to guanine-cytosine, but the adenine-Mu complex has lower stability than adenine-uracil. Additionally, the guanine-Mc complex has a suboptimal distorted geometry that further facilitates the mutations. (4) The activation barrier for proton transfer leading to Mu-m interconversion into a cytosine-like tautomer is higher than for Mu, which makes the uracil-like form even less available. These facts confirm an intriguing experimental observation that molnupiravir competes mainly with cytosine and not uracil.