Second-order Perturbation Energy Research Articles

Quantum computational, molecular structure, experimental spectra, and molecular docking studies on (S)-3-benzyl-5-(phenylselanyl)-6-(p-tolyl)-3,4-dihydropyran-2-one

The published molecule (S)-3-Benzyl-5-(phenylselanyl)-6-(p-tolyl)-3,4-dihydropyran-2-one (3B6PL) was selected for the identification of anticancer properties, and the computational calculations were employed using density function theory (DFT) with the B3LYP/6–311++G (d,p) basis set to validate the proposed molecular structure features by the theoretical computational calculations. Herein, the FT-IR, UV-800, 1H NMR, and 13C NMR analytical techniques were used for the characterization of the selected molecule. In FT-IR, the characteristic frequencies of the molecule were compared using an appropriate scaling factor (0.961) for the potential energy distribution (PED) and simulated spectra of 3B6PL. Moreover, UV-800 and NMR spectral data were validated using the NBO that was demonstrated to the charge transfer in the molecules and exhibits a prominent second-order perturbation energy, E(2) value is 309.85 kcal/mol. HOMO-LUMO, Molecular electrostatic potential (MEP) both find molecule's electrical properties, as well as its softness, hardness, and overall stability. To understand the reactive locations of the molecule, fukui functions have been employed. Moreover, the exceptional NLO (non-linear optical) characteristics of the molecule were demonstrated, and intermolecular interactions were evaluated using a Hirshfeld surface as well. On the contrary, the druglikeness of the molecule was evaluated under Lipinski's rule of five and ADME/T studies. In-silico analysis and molecular docking were also demonstrated for the anticancer potential of the proposed molecule against the kinase insert domain receptors of VEGFR and showed binding affinities of -6.3 kcal/mol for the VEGFR-ligand complex as a preliminary investigation. Therefore, this compound could be used for in-vitro and in-vivo analyses to find out its cytotoxicity and could also be derivatized to enhance its potent anticancer properties.

Combining Donor Strength and Oxidative Stability in Scorpionates: A Strongly Donating Fluorinated Mesoionic Tris(imidazol-5-ylidene)borate Ligand.

Strongly donating scorpionate ligands support the study of high-valent transition metal chemistry; however, their use is frequently limited by oxidative degradation. To address this concern, we report the synthesis of a tris(imidazol-5-ylidene)borate ligand featuring trifluoromethyl groups surrounding its coordination pocket. This ligand represents the first example of a chelating poly(imidazol-5-ylidene) mesoionic carbene ligand, a scaffold that is expected to be extremely donating. The {NiNO}10 complex of this ligand, as well as that of a previously reported strongly donating tris(imidazol-2-ylidene)borate, has been synthesized and characterized. This new ligand's strong donor properties, as measured by the υNO of its {NiNO}10 complex and natural bonding orbital second-order perturbative energy analysis, are at par with those of the well-studied alkyl-substituted tris(imidazol-2-ylidene)borates, which are known to effectively stabilize high-valent intermediates. The good donor properties of this ligand, despite the electron-withdrawing trifluoromethyl substituents, arise from the strongly donating imidazol-5-ylidene mesoionic carbene arms. These donor properties, when combined with the robustness of trifluoromethyl groups toward oxidative decomposition, suggest this ligand scaffold will be a useful platform in the study of oxidizing high-valent transition-metal species.

Exploring the potential of hydrophobic deep eutectic solvents for bioethanol separation using DFT and COSMO-RS model

Bioethanol has sparked significant interest as a promising energy source due to its green nature and sustainability. However, the separation of bioethanol presents considerable challenges. Deep eutectic solvents (DESs), as alternatives to conventional solvents, have shown efficient separation capabilities in various separation processes. However, selection of an ideal DES for a specific task always remains a challenge. In the present study, fifteen different hydrophobic DESs have been screened by employing COSMO-RS model. Three DESs (1,2-Decanediol: Thymol, Atropine: Thymol, and Lauric acid: Lidocaine) showing the best separation performance for ethanol from water were selected. DFT simulations have unveiled interaction mechanisms, emphasizing hydrogen bonding. Molecular electrostatic potential (MEP) analysis has identified the possible interaction sites for binding. Thermodynamic stabilities of the DES-ethanol complexes are elucidated through energy decomposition analysis (EDA) and second-order perturbation energies. Quantum theory of atoms in molecules (QTAIM) and interaction region indicator (IRI) analyses corroborate the existence of electrostatic interactions, predominantly in the form of hydrogen bonding, between ethanol and DESs. The significance of robust hydrogen bonding in driving ethanol separation is underscored through core-valence bifurcation (CVB) index analysis. The findings of this study yield a robust and practical methodology for choosing the most suitable DES, thereby enhancing the efficacy of ethanol separation from fermentation broths. This outcome offers a valuable and efficient approach that holds considerable promise for advancing the field of bioethanol production and refining processes.

Synthesis, characterization, pharmaceutical evaluation, molecular docking and DFT calculations of a novel drug (E)-5-bromo-3-(phenylimino) indolin-2-one

Herein, one-pot synthesis of (E)-5-bromo-3-(phenylimino)indolin-2-one (5BPI molecule), density function theory for validation of the synthesized molecule, and biological activities, have been reported. Anticancer activity of the synthesized (E)-5-bromo-3-(phenylimino)indolin-2-one compound from National Cancer Institute, USA, was evaluated. However, antimicrobial nature of the molecule against 1NCO, 7C2N, 3DRA, and 4YNU proteins was also demonstrated using molecular docking as a preliminary investigation that showed the binding with ligand possess very low binding affinity as −6.22, −6.51, −5.59, and −7.45 kcal/mol, respectively. Density Functional Theory was effectively used to analyse the stability of the molecular structure under optimized circumstances, for comparative studies involving experimental and theoretical data for the gas and solvent phases. According to this analysis, UV–Vis spectra, band gap energy, nonlinear optical properties, molecular electrostatic potential, electron localization function, localized orbital locator, and reduced density gradient were illustrated in different solvents. In addition, natural bond orbital analysis was conveyed to the largest second-order perturbation energy that corresponded to electron delocalization from the donor and acceptor interaction. As a consequence, it was clearly demonstrated by the compound's drug-likeness, ADMET characteristics, docked complexes' released energies, and anticancer activity that it may be employed as a lead molecule to treat different carcinomas after the more potent alterations in their skeleton prompted by chemical reactions.

Theoretical and Experimental Study of CO2 Absorption by N-2-ethylhexylethylenediaminium-TFS Type Protic Ionic Liquid

The CO2 absorption using the mixture of ethylenediaminium type protic ionic liquid [HEtHexen][TFS] and H2O with different molar ratio was investigated by the measurement of pH, density, viscosity and conductivity at 30°C. Meanwhile, we studied the hydrogen bonding between [HEtHexen][TFS] and CO2 using DFT calculation, the result of the interaction energy, vibration frequency and second-order perturbation energy, etc. shows that a weak or medium strength N-H···O type hydrogen bonding occurred between [HEtHexen][TFS] and nCO2 (n=1−4). The result of experimental and theoretical study indicates that one [HEtHexen][TFS] molecule absorbed a maximum of three molecules of CO2.

Insight with Crystallization, Quantum Computation, Hirshfeld, ELF/LOL and Molecular Docking of Syringic Acid Nicotinamide Cocrystal as Potent Mycobacterium Tuberculosis Inhibitor

Tuberculosis (TB) is a recurring and progressive illness with a high global death rate. MycobacteriumTB drug resistance is a serious impediment to allelopathy therapy. Contemplating combinatorial drug delivery (pharmaceutical cocrystal) as anti-TB medicines targeting Mycobacterium tuberculosis’s active site can be an alternative strategy. The syringic acid nicotinamide (SYNI) cocrystal was synthesized in this work through slow evaporation technique and was examined based on quantum chemical calculations, Hirshfeld analysis, electron localization analysis and molecular docking. The intended vibrational wavenumbers were allocated a PED value and related with experimental frequencies. The UV–Visible absorption spectra of the cocrystal in the liquid phase (ethanol) were revealed as [Formula: see text]* electronic transitions. The HOMO–LUMO values, band gap, molecular electrostatic potential and Mulliken atomic charge distribution of the molecule were evaluated to estimate its stability and molecular reactivity. The molecule’s second-order perturbation energy [Formula: see text] standards were determined by means of natural bond orbital analysis, and potential reactive site was assessed using local reactivity descriptors. Hirshfeld analysis revealed that H…H (44.9%), O…H/H…O (39.3%), C…H/H…C (6.1%), N…H/H…N (5.3%) and C…C (2.4%) have the major percentage contributions from the most significant interactions. The topological features of the SYNI cocrystal were assessed through electron localization function based on color gradient. The binding ability of SYNI cocrystal with the Mycobacterium tuberculosis associated proteins was evaluated through docking and their binding scores fall between the range of −9.1 kcal/mol and −10.8 kcal/mol, which confirms the better binding ability and makes SYNI cocrystal a potent medication against TB.

Ligand and Substituent Effect on Regium-π Bonding in Cu and Ag π-Conjugated Complexes: A Density Functional Study.

Density functional theory investigation of regium (Rg)-π bonding using the RgL-X model system, where Rg = Cu and Ag; L = CN, NO2, and OH; X = π-conjugated system (benzene, cyanobenzene, benzoic acid, pyridine, 2-methoxy aniline, 1,4-dimethoxy benzene, and cyclophane), has been performed. Conclusive evidence of the Rg-π bond has been provided by analysis of molecular electrostatic potential surfaces, Rg-π bond length, interaction energy (ΔE), second-order perturbation energy (E2), charge transfer (Δq), quantum theory of atom in molecules, and noncovalent interaction plots for 42 structural arrangements with varying ligands and the substituted aromatic ring. The Rg-π bond length in the optimized model systems varies from 2.03 to 2.12 Å in Cu complexes (1-21) and from 2.26 to 2.38 Å in Ag complexes (22-42) at the PBE0-D3 functional. While the ligand (L) attached to the Rg metal has a bargaining effect on the strength of the Rg-π bond (in the order of -OH > -CN = -NO2), the π-conjugated systems have a diminutive effect. Two X-ray crystal structures (CUCSOI and AHIDQU) having the Rg-π bond, accessed from Cambridge Crystallographic Data Centre (CCDC), are discussed here to signify the influence of Rg-π bonding on the crystal structure.

Investigating the potential of thiazolyl carbohydrazides derivatives as anti-Candida albicans agents: An intuition from molecular modelling, pharmacokinetic evaluation, and molecular docking analysis

With increasing incidences of antifungal resistance, biofilm formation, and its predilection for vulnerable populations, Candida albicans have been reported to cause a wide range of infections, from superficial skin irritations to life-threatening systemic diseases. Therefore, understanding and addressing the infections associated with Candida albicans has become an urgent imperative in the realm of global healthcare. As a result, this study employed DFT calculations at the DFT/ωB97XD/6–311++G (2d, 2p) level to optimize the geometric properties of two compounds: (Z)-N'-(4-(4-bromophenyl)-3-(4-fluorophenyl)thiazol-2(3H)-ylidene)-2-(thiophen-2-yl)thiazole-5-carbohydrazide (4-FBC) and (Z)-N'-(4-(4-bromophenyl)-3-(2-fluorophenyl)thiazol-2(3H)-ylidene)-2-(thiophen-2-yl)thiazole-5-carbohydrazide(2-FBC). Significantly, employing spectral analysis techniques such as FT-IR and NMR, the compounds were characterized and identified. Additionally, the compounds (4-FBC and 2-FBC) exhibited comparable reactivity and stability, with more promising reactivity potential in water than in the gas phase. The analysis of Molecular Electrostatic Potential (MESP) and the density of States (DOS) shed light on the electrical characteristics and intermolecular interactions occurring during chemical processes. Furthermore, the natural bond orbital (NBO) analysis provided insights into second-order perturbation energies and the presence of intense intermolecular interactions, as evident in the order of their increasing concentrated intermolecular interaction as thus: 4-FBC_gas (668.34 kcal/mol) > 4-FBC _water (563.98 kcal/mol) and 2-FBC _gas (978.64 Kcal/mol) > 2-FBC_water (696.46 Kcal/mol). The pharmacokinetics study indicated favorable intestinal absorption, low distribution, and cytotoxicity profiles, although 4-FBC required further optimization due to slower clearance, potential enzyme interactions, and immunotoxicity concerns. In addition, molecular docking analysis revealed robust binding affinities and the presence of significant conventional hydrogen bonds. The optimal binding positions (best pose) for the 4-FBC and 2-FBC complexes were determined to have binding affinities of -8.7, -8.4, -8.3 kcal/mol, and -8.6, -8.5, -8.3 kcal/mol, respectively, when interacting with 4YDE, 3DRA, and 1EAG. These findings provide strong evidence supporting the potential pharmacological suitability of 4-FBC and 2-FBC compounds as effective choices for inhibiting and treating Candida albicans.

Influence of anionic species on the molecular structure, nature of bonding, reactivity, and stability of ionic liquids-based on 1-butyl-3-methylimidazolium

The unique physicochemical properties of ionic liquids (ILs) have positioned them as a significant class of solvents, making them a subject of considerable interest. In this investigation, the experimental analysis involved solvothermal reflux techniques, while theoretical approaches utilized density functional theory (DFT) with the def2-SVP/ωB97XD computational approach to explore the electronic properties, reactivity, stability, and structural aspects of ILs based on the combinations of [BMIM]+ cation with [MeSO3]-, [BF4]-, [PF6]-, and [C2H3O2]- anions. The experimental and theoretical data exhibited good agreement, demonstrating that the choice of cation and anion greatly influences the stability of ILs. By employing Frontier molecular orbital analysis, the reactivity and stability of the studied ionic species were observed to follow the order of [BMIM]+[MeSO3]- > [BMIM]+[BF4]- > BMIM > [BMIM]+[PF6]- > [BMIM]+[C2H3O2]-, with corresponding energy gaps of 4.8474 > 3.1971 > 2.013 > 1.8830 and 1.3276 eV, respectively. The Natural Bond Orbital (NBO) analysis, encompassing second-order perturbation energy, revealed the strength of interactions within the investigated systems in the following order: [BMIM]+[PF6]- < [BMIM]+[MeSO3]- < [BMIM]+[BF4]- < [BMIM]+[C2H3O2]-. Topology analysis indicated a higher electron density (ρ(r)) value of 0.8966 a.u., indicating a denser distribution of electrons. Furthermore, the nature of bonding in the studied ion pairs displayed the following order: [BMIM]+[MeSO3]- > [BMIM]+[BF4]- > [BMIM]+[PF6]- > [BMIM]+[C2H3O2]-, signifying that [BMIM]+[MeSO3]- exhibited stronger interactions compared to the other combinations. The vibrational spectra and UV–vis results of the investigated ILs underscored the sensitivity of characteristic peaks in frequency and intensity to the specific cation–anion combination. These findings have the potential to guide experimental researchers in exploring the applications of the studied ionic species in diverse areas such as energy storage and catalysis.

Theoretical Study on CO&lt;sub&gt;2&lt;/sub&gt;/SO&lt;sub&gt;2&lt;/sub&gt; Absorption Using &lt;i&gt;N&lt;/i&gt;- Alkylethylenediaminium Protic Ionic Liquid

The protic ionic liquids (PILs) comprising with N-2-ethylhexylethylenediaminium cation (HEtHex+) and bis (trifluoromethanesulfonate) imide anion (TFSA-) forming [HEtHex][TFSA] which has two amines in the polar group and available to absorbs acid gases such as CO2 and SO2. In order to study the CO2/SO2 absorption mechanism of [HEtHex][TFSA], the stable configurations of [HEtHex][TFSA]-nCO2 (n=1, 2, 3, 4) and [HEtHex][TFSA]-nSO2 (n=1, 2, 4, 6) are investigated using the density functional theory at the M06-2X/6-311G (d, p) level, then the interaction energy, molecular vibration frequency, second-order perturbation energy, electron density and Laplace value are calculated and analysed for the most stable configurations. The results show that N–H...O type weak or medium hydrogen bonding are mainly formed between [HEtHex][TFSA] and CO2/SO2 molecules. The hydrogen bonding interaction is stronger for [HEtHex][TFSA]-nSO2 comparing with [HEtHex][TFSA]-nCO2 and increases with increasing the number of CO2/SO2 molecules.

A study of the valence photoelectron spectrum of uracil and mixed water-uracil clusters.

The valence ionization of uracil and mixed water-uracil clusters has been studied experimentally and by ab initio calculations. In both measurements, the spectrum onset shows a red shift with respect to the uracil molecule, with the mixed cluster characterized by peculiar features unexplained by the sum of independent contributions of the water or uracil aggregation. To interpret and assign all the contributions, we performed a series of multi-level calculations, starting from an exploration of several cluster structures using automated conformer-search algorithms based on a tight-binding approach. Ionization energies have been assessed on smaller clusters via a comparison between accurate wavefunction-based approaches and cost-effective DFT-based simulations, the latter of which were applied to clusters up to 12 uracil and 36 water molecules. The results confirm that (i) the bottom-up approach based on a multilevel method [Mattioli et al. Phys. Chem. Chem. Phys. 23, 1859 (2021)] to the structure of neutral clusters of unknown experimental composition converges to precise structure-property relationships and (ii) the coexistence of pure and mixed clusters in the water-uracil samples. A natural bond orbital (NBO) analysis performed on a subset of clusters highlighted the special role of H-bonds in the formation of the aggregates. The NBO analysis yields second-order perturbative energy between the H-bond donor and acceptor orbitals correlated with the calculated ionization energies. This sheds light on the role of the oxygen lone-pairs of the uracil CO group in the formation of strong H-bonds, with a stronger directionality in mixed clusters, giving a quantitative explanation for the formation of core-shell structures.

Experimental and computation studies of a Zn(II) coordination complex with isophthalic acid and benzimidazole as ligands

The complex [Zn(C7N2H6)2(C8O4H5)2] was synthesized by benzimidazole (bim), isophthalic acid (ipH2) and ZnCl2. The Zn2+is four coordinated and connected to two benzimidazoles and two isophthalic acids via monodentate coordination. The complex is a monomer which form a 3D network, through the π-π interactions and hydrogen bonds. In Hirshfeld surface analysis, the spots on the de and dnorm surfaces indicate the donor or acceptor of hydrogen bonds. The IR spectra, UV spectra, fluorescence property and TG analysis are researched. The IR data shown that the coordinated carboxyl group is in monodentate coordination mode. The fluorescent shown the maximum emission wavelength is 394 nm for the complex and it is probably due to the π-π* transition occurs when Zn2+ is ligated to the ligands. TG result demonstrated the final residue maybe ZnO. The molecular orbitals, bond order analysis, natural population analysis, second-order perturbation energy analysis, and AIM analysis were also performed.

Bonding nature, nucleophilic reactivity and electron excitation of NLO active 2,6 dichloroindophenol sodium salt (polar and non polar solvents) with topology analysis- bacterial pathogens study

2,6 Dichloroindophenol sodium salt was an aromatic compound evaluated by DFT through experimental and computation using various solvents used in solvation analysis investigation. FT-IR studies are used to identify the various functional groups, which are then compared with simulated spectra. The estimated vibrational wavenumbers were scaled using a suitable scaling factor after the optimized geometrical parameters were determined. The plotted FT-IR, FT-Raman; and UV–vis spectra are correlated with experimental calculations. Measured and computed spectra are found to be quite similar. NBO (Natural Bond Analysis) research explains how charges transferred occur in a molecule. NBO analysis indicates that the greatest second-order perturbation energy E(2) = 25.77 kcal/mol is associated with electron delocalization from the donor π (C13-C15) to π* (O4-C17) acceptor interaction. Local reactivity descriptor stipulates the molecule's reactive areas. The stability, hardness, and softness are studied by Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO). FMO (Frontier Molecular Orbital) divulge kinetic stabilization and reactivity of DCIP (2,6 Dichloroindophenol sodium salt). Reactive descriptors and molecular reactivity of DCIP were significantly changed by the solvents. The material under analysis has outstanding NLO (Non-linear Optical) properties. ELF (Electron Localization Function), LOL (Localised Orbital Locator) and RDG (Reduced Density Gradient) were performed and reported. Molecular docking is used to investigate specific biological data of DCIP. Two bacterial targets interact with a protein ligand. Whereas to ascertain the biological properties drug-likeness and ADMET were utilised. The outcome of the ADMET experiments showed that the structure under investigation possesses antibacterial properties. To test the substance's effectiveness against various bacterial strains, antibacterial tests were carried out.

Copper(I) iodide complex with 4-pyridinecarboxaldehyde ligand: Synthesis, spectroscopic characterisation, AIM and NCI analysis combined with molecular docking and antibacterial activity studies

In this article, we synthesized a [CuI(4-pyridinecarboxaldehyde)4] complex characterized by CHN analyses, FT-IR, UV-Vis, and DFT. The spectroscopic characteristics and biological activities of the synthesized complex were investigated using quantum mechanical methods using combined experimental and computational approaches. The orbital NBO and topological AIM approaches were used to investigate intermolecular interactions. According to the second-order perturbation energy analysis, the majority of the E(2) stabilization energies of of LP(N) → LP∗(Cu) are higher than those of LP(I) → LP∗(Cu), implying that the nitrogen atom in the complex is the main contributor to coordination. In addition, the biological activities of the title complex were investigated by using molecular docking analysis. In this investigation, the title Cu (I) complex was the most active molecule, with the maximum antibacterial activity against S. aureus and S. epidermidis infections that should be further clinically investigated due to its effective anti and anti-quorum sensing properties. The title complex showed good antiquorum-sensing activity when tested against C. violaceum ATCC 12472. Furthermore, in-silico molecular docking investigations corroborated the chemical activity correlations. The Cu (I) combination has a maximum dock score for some of the active chemicals.

Stochastic evaluation of four-component relativistic second-order many-body perturbation energies: A potentially quadratic-scaling correlation method.

A second-order many-body perturbation correction to the relativistic Dirac-Hartree-Fock energy is evaluated stochastically by integrating 13-dimensional products of four-component spinors and Coulomb potentials. The integration in the real space of electron coordinates is carried out by the Monte Carlo (MC) method with the Metropolis sampling, whereas the MC integration in the imaginary-time domain is performed by the inverse-cumulative distribution function method. The computational cost to reach a given relative statistical error for spatially compact but heavy molecules is observed to be no worse than cubic and possibly quadratic with the number of electrons or basis functions. This is a vast improvement over the quintic scaling of the conventional, deterministic second-order many-body perturbation method. The algorithm is also easily and efficiently parallelized with 92% strong scalability going from 64 to 4096 processors.

Density functional theory on ionic liquid as carbonate scale dissolver in petroleum pipelines

The carbonate scale is the common oilfield scale found in the petroleum pipeline, which will cause flow assurance problems. In the purpose to conquer this problem, the alternative approach is to use ionic liquids (ILs) particularly in dissolving carbonate scale. The main objective of this study is to determine the effective ILs to dissolve carbonate scale in petroleum pipelines, and to evaluate the effect of intermolecular interaction in ILs toward their properties such as dissolution capabilities. The density functional theory (DFT) calculation is used to investigate the intermolecular interaction of a series of different ion pair, namely cations and anions-based of ILs with carbonate ion. All the calculations are completed by Gaussian software at the hybrid Becke 3-Lee-Yang-Parr (B3LYP) level using the 6-311++G(d, p) basis set. The optimized structure of carbonate ion and ion pairs of ILs have been obtained from the calculation which was further complemented by harmonic vibrational frequency, binding energies, bond type, bond order, and natural bond orbital (NBO). The binding energy for the cation and anion-based ILs are obtained where the ammonium ion is −302.2627 kJ/mol and tetrafluoroborate ion is −562.9194 kJ/mol which depict to have the highest value compare to others. Both of them are made up of the single bond and are characterized as the polar covalent bond. The NBO analysis pointed out the higher second-order perturbation energy, E (2) for ammonium ion is at a lone pair, LP (1) N 9 to antibonding sigma, BD*(1) O 3H 6 while BF4 ion is at lone pair LP (3) F 2 to antibonding lone pair, LP*(1) Ca 6. The selective ILs, ammonium tetrafluoroborate shown the higher negative binding energy which is −371.93 kJ/mol having the same nature of bond type and bond order from the findings in cation and anion-based ILs.

Study of the alkyl-π interaction between methane and few substituted pyrimidine systems using DFT, AIM and NBO calculations

In the present study alkyl-π interactions between methane and the pyrimidine heterocyclic systems have been studied. Interaction energies were calculated using the B97D/def2-TZVPP level of theory. Energy decomposition analysis (EDA) using SAPT0/ jun-cc-pVTZ method revealed that the interaction energy is mainly dispersion and electrostatic with a minor contribution from induction energy. Non covalent index analysis was performed to visualize the interactions between the fragments of the studied complexes and atoms in molecule (AIM) study were done to investigate the bond critical points (BCP). The natural bond order (NBO) analyses were carried out to study the donor-acceptor orbitals and the second-order perturbation energies. Interaction energy, AIM study and NBO analysis revealed that the alkyl-π interactions involving the pyrimidine heterocyclic systems become stronger with the presence of various substituents on the pyrimidine ring.

Evidences for sulfur centered hydrogen bond with sulfur atoms as a donor in aromatic thiols and aliphatic thiols in aqueous solution

It has been more than a century since the discovery of hydrogen bond, but the knowledge about its impact on day to day life of people is getting enhanced even now. It has a pivotal role in the stabilization of various biomolecules and subsequent bioactivity. Sulfur centered hydrogen bond (SCHB), which is a weak interaction, has attracted the attention of many scientists in the last few decades. In this work, we report the nature of the SCHB between aliphatic/aromatic thiols and water. B3LYP-D3(BJ) with cc-pVTZ level was used for modeling the hydrogen bonded thiol-water complexes. Domain-based local pair natural orbitals coupled-cluster theory with single, double, and perturbative triple excitation DLPNO-CCSD(T) method was used for local energy decomposition analysis. QTAIM analysis helped to examine hydrogen bonds, weak non-covalent interactions, and the various electron density delocalization. Natural Bond Orbital (NBO) analysis explains the reason for the sulfur atom being the H-bond donor. Second-order perturbation energy from NBO findings supports the data obtained by LED and AIM calculations. Aromatic thiols form stronger hydrogen bonds than aliphatic thiols. The effect of substituents was also explored by studying aromatic systems with electron-withdrawing groups and donating groups. EDG substituted have more vital interaction, and EWG substituted thiols form stronger S-H···O hydrogen bond.

Second-order perturbative correlation energy functional in the ensemble density-functional theory

We derive the second-order approximation (PT2) to the ensemble correlation energy functional by applying the G\"{o}rling-Levy perturbation theory on the ensemble density-functional theory (EDFT). Its performance is checked by calculating excitation energies with the direct ensemble correction method in 1D model systems and 3D atoms using numerically exact Kohn-Sham orbitals and potentials. Comparing with the exchange-only approximation, the inclusion of the ensemble PT2 correlation improves the excitation energies in 1D model systems in most cases, including double excitations and charge-transfer excitations. However, the excitation energies for atoms are generally worse with PT2. We find that the failure of PT2 in atoms is due to the two contributions of an orbital-dependent functional to excitation energies being inconsistent in the calculations. We also analyze the convergence of PT2 excitation energies with respect to the number of unoccupied orbitals.

Quantum mechanical study on complexation phenomenon of pillar[5]arene towards neutral dicyanobutane

ABSTRACT Based on density functional theory calculations, we have addressed the electronic structure, binding and nature of non-covalent interactions between alkylated pillar[5]arene (P[5]A) and 1,4-dicyanobutane (DCB)-based host-guest macrocycles. Neutral 1,4-dicyanobutane-based alkylated DCB_ProP[5]A is found to show higher binding energy when compared to the other three host-guest macrocycles. These complexes are largely stabilised by non-covalent interactions, which are ascertained through NCI and QTAIM analyses. Furthermore, the second-order perturbation energy of NBO analysis show that LP (N) – σ*(C-H) interactions predominate in DCB_ProP[5]A complex. Particularly, alkyl substituents (-methyl, -ethyl and -propyl) are playing a vital role in stabilising the host-guest complexes. In summary, the present work not only exhibits an efficient strategy to build a new family of alkylated P[5]A inclusion complexes but also providing deeper understanding on various non-covalent interactions towards 1,4-dicyanobutane (DCB) guest molecules inside the host environment.