Quantum Theory Of Atoms In Molecules Research Articles

The nature of halogen bonding: insights from interacting quantum atoms and source function studies.

A detailed study of the X...N (X = I, Br) halogen bonds in complexes formed by an extended set of substituted pyridines with D-X molecules (D = X, CN) is reported here. The nature of these interactions has been investigated at different (MP2 and DFT) levels of theory through Bader's quantum theory of atoms in molecules (QTAIM) and Pendás' interacting quantum atoms (IQA) scheme, focusing on the role of the local environment (i.e. the substituent on the pyridine ring and the halogenated residue) on the halogen bond features. We found that the exchange-correlation energy represents a substantial contribution to the IQA total energy, in some cases comparable to (I2 complexes) or even dominating (ICN complexes) the electrostatic term. Meaningful information is provided by the source function, indicating that the major contribution to the electron density at the bond critical point of the X...N interaction is derived from the halogen atom, while a much lower contribution comes from the nitrogen atom, which acts as either source or sink for electron density. A relevant contribution from distal atoms, including the various electron-donor and electron-withdrawing substituents in different positions of the pyridine ring, is also determined, highlighting the non-local character of the electron density. The existence of possible relationships between binding energies, interaction energies according to IQA, and QTAIM descriptors such as delocalization indices and source function, has been inspected. In general, good correlations are only found when the local environment, external to the directly involved halogen and nitrogen atoms, plays a minor role in the interaction.

Computational insight into the formation of cation-π/cation-lone pair complexes between 3d-metal (II) ions and furan.

Cation-π and cation-lone pair interactions between 3d-metal (II) ions [Fe(II), Co(II), Ni(II) and Cu(II)] and furan are explored in the formation of 1:1 and 1:2 type complexes. Both cation-π (IEgas = -192.27 to -312.65 kcal mol-1) and cation-lone pair (IEgas = -163.13 to -271.76 kcal mol-1) interactions are reasonably strong and lead to the formation of stable 1:1 and 1:2 type complexes in gas phase. The complexes are also stable in solvent phase, but their stability is reduced significantly in presence of solvent dielectrics, especially in ethanol, DMSO and water. Formation of the complexes is thermodynamically favourable (exothermic and spontaneous). Charge transfer (Δq = 0.62 to 1.92 e-), Laplacian of electron density (∇2ρ = 0.1435 to 0.6628 au) and total electron energy density (H(r) = -0.0019 to -0.0436 au) analysis have argued in favour of partial ionic and partial covalent character of the interactions. Density functional theory (DFT) is exclusively used for the study. Polarizable continuum model (PCM) is used to perform solvent phase study. Natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM) and non-covalent interaction (NCI) analyses are performed for understanding other aspects of complex formation.

Synthesis, Antibacterial, and Antibiofilm Activities of Imidazo[2,1-b]Thiazole Chalcone Derivatives: In Vitro and In Silico Studies.

In recent years, imidazothiazole-chalcone conjugates have emerged as notable pharmacophores with potential applications in discovering biologically active compounds. This study focuses on synthesizing novel imidazo[2,1-b]thiazole chalcone derivatives through a facile and conventional process adhering to several principles of green chemistry, facilitating scalable production. The synthesized compounds underwent comprehensive spectroscopic analysis, including 1H NMR, 13C NMR, LC-MS, and FT-infrared (IR) techniques. Theoretical FT-IR and NMR analysis, frontier molecular orbitals (FMOs), and global reactivity descriptors were calculated and interpreted. Furthermore, molecular electrostatic potential (MEP) surface, Mulliken atomic charge, electron localization function (ELF), localized orbital locator (LOL), and quantum theory of atoms in molecules (QTAIM) were analyzed. The newly synthesized compounds were screened in vitro for their antibacterial and antibiofilm activities. In addition, computational docking studies were performed to gain further insights into molecular interactions and found to support the results.

Chemical Bond Overlap Descriptors From Multiconfiguration Wavefunctions.

The chemical bond is a fundamental concept in chemistry, and various models and descriptors have evolved since the advent of quantum mechanics. This study extends the overlap density and its topological descriptors (OP/TOP) to multiconfigurational wavefunctions. We discuss a comparative analysis of OP/TOP descriptors using CASSCF and DCD-CAS(2) wavefunctions for a diverse range of molecular systems, including X-O bonds in X-OH (XH, Li, Na, H2B, H3C, H2N, HO, F) and Li-X' (XF, Cl, and Br). Results show that OP/TOP aligns with bonding models like the quantum theory of atoms in molecules (QTAIM) and local vibrational modes theory, revealing insights such as overlap densities shifting towards the more electronegative atom in polar bonds. The Li-F dissociation profile using OP/TOP descriptors demonstrated sensitivity to ionic/neutral inversion during Li-F dissociation, highlighting their potential for elucidating complex bond phenomena and offering new avenues for understanding multiconfigurational chemical bond dynamics.

Stacking interactions in stabilizing supramolecular assembly of M[9C]2M complexes: dynamic stability with remarkable nonlinear optical features.

Continual attempts have been made to discover excellent nonlinear optical (NLO) materials. Here, we investigate the role of stacking interactions and van der Waals forces in the designed parallel stacked complexes M[9C]2M (where M = Li, Na, K, Be, Mg, and Ca) using various quantum chemical and molecular dynamics methods. The thermodynamic stability of the present complexes is also revealed by the computed interaction energy, enthalpy of formation, and Gibbs free energy of formation (ΔGf). Molecular dynamics simulations were performed at room temperature to determine the stability of the dimer formation and their complexes. Alkali metals act as a more prominent source of excess electrons at long-range interaction distances. Charge decomposition analysis (CDA) and natural bonding orbital (NBO) analyses suggest excellent charge transfer in the alkalide complexes. In this series, Li[9C]2Li exhibits an excellent hyperpolarizability response up to 2.3 × 106 a.u., while Ca[9C]2Ca performs well in alkaline-earth metal complexes. The NLO response is mostly influenced by the alkalide and earthide characteristics. Dynamic NLO features were computed at externally applied frequencies. Scattering first hyperpolarizability (βHRS) and its associated components were also measured. The effect of solvents on hyperpolarizability is also considered. The quantum theory of atoms in molecules (QTAIM) and NCI are employed to investigate the bonding nature and vdW forces in addition to stacking interactions. TD-DFT and vibrational studies are also performed. We aim for this research to pave the way for the innovative strategies in designing supramolecular assemblies tailored for NLO applications.

Nanoring interactions with bio-relevant molecule: A quantum chemical approach to C18 and B9N9 systems.

This study investigates the interaction of a synthetic bio-relevant molecule with C18 and B9N9 nanorings, exploring their potential applications in sensing and drug delivery. Employing Density Functional Theory (DFT) at the ωB97XD level with the 6-31G(d,p) basis set, we computed the adsorption and electronic properties of the resulting nanocomplexes. A total of ten distinct configurations were identified for the interactions, with adsorption energies ranging from -6.75 to -12.62kcal/mol for the C18@target molecule and -9.01 to -18.46kcal/mol for the B9N9@target molecule. Notably, alterations in the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) upon interaction suggest an enhancement in electrical conductivity. The effect of aqueous media was also examined, revealing an increase of approximately 2.0 Debye in the dipole moments of the most stable nanocomplexes. Additional analyses, including reduced density gradient (RDG), UV-Vis spectroscopy, and Quantum Theory of Atoms in Molecules (QTAIM), were conducted in both gas and aqueous phases. Our findings indicate that C18 and B9N9 nanorings exhibit significant promise as candidates for drug delivery and sensing applications, particularly due to their enhanced electronic properties upon interaction with the bio-relevant molecule.

ESTUDO COMPUTACIONAL DA INFLUÊNCIA DE CO2 NO EMPILHAMENTO-π DE MONÔMEROS DE CORONENO SUBSTITUÍDOS COM ENXOFRE

COMPUTATIONAL STUDY OF THE INFLUENCE OF CO2 ON THE π-STACKING OF SULFUR-SUBSTITUTED CORONENE MONOMERS. Asphaltenes are complex molecules with a tendency to aggregate. This property can be an issue for the oil industry due to CO2 reinjection into reservoirs to mitigate these gas emissions. The present theoretical study aimed to study the CO2 interaction with no-substitute and substituted coronene as an asphaltene model compound at CAM-B3LYP-D3/6-311G(d,p) level. The electronic properties were evaluated using harmonic oscillator model of aromaticity (HOMA), quantum theory of atoms in molecules (QTAIM), and reduced density gradient (RDG) methods. The results showed that the coronene’s functionalization by a sulfur atom changes the coronene’s electronic structure. However, functionalization does not change the type of interactions between the monomers, as they remain predominantly van der Waals interactions. CO2 interaction with substituted coronene barely changed due to the presence of sulfur atoms. However, in dimers, the position of the heteroatom directly influences the interaction with CO2, although it is insufficient to change the interaction’s magnitude. For this reason, our results indicate that the sulfur heteroatom in asphaltenes should be addressed. However, new studies must be conducted by increasing the number of substituents, CO2 numbers, and the model size.

Smart drug delivery: a DFT study of C24 fullerene and doped analogs for pyrazinamide.

The potential applicability of the C24 nanocage and its boron nitride-doped analogs (C18B3N3 and C12B6N6) as pyrazinamide (PA) carriers was investigated using density functional theory. Geometry optimization and energy calculations were performed using the B3LYP functional and 6-31G(d) basis set. Besides, dispersion-corrected interaction energies were calculated at CAM (Coulomb attenuated method)-B3LYP/6-31G(d,p) and M06-2X/6-31G(d,p) levels of theory. The adsorption energy (E ads), enthalpy (ΔH), and Gibbs free energy (ΔG) values for C24-PA, C18B3N3-PA, and C12B6N6-PA structures were calculated. The molecular descriptors such as electrophilicity (ω), chemical potential (μ), chemical hardness (η) and chemical softness (S) of compounds were investigated. Natural bond orbital (NBO) analysis confirms the charge transfer from the drug molecule to nanocarriers upon adsorption. Based on the quantum theory of atoms in molecules (QTAIM), the nature of interactions in the complexes was determined. These findings suggest that C24 and its doped analogs are promising candidates for smart drug delivery systems and PA sensing applications, offering significant potential for advancements in targeted tuberculosis treatment.

Chiral recognition of amino acids through homochiral metallacycle [ZnCl2L]2.

Chiral recognition holds tremendous significance in both life science and chemistry. The ability to differentiate between enantiomers is crucial because one enantiomer typically holds greater biological relevance while its counterpart is often not only unnecessary but also potentially harmful. In this regard, homochiral metallacycle [ZnCl2L]2 is used in this study to understand and differentiate between the R and S enantiomers of amino acids (alanine, proline, serine, and valine). The electronic, geometric, and thermodynamic stabilities of the amino acid enantiomers inside the metallacycle are determined through various analyses. The greater interaction energy (Eint) is obtained for the ser@metallacycle complexes i.e., -33.03 and -30.75 kcal mol-1, respectively for the S and R enantiomers. The highest chiral discrimination energy of 3.11 kcal mol-1 is achieved for ala@metallacycle complexes. Regarding the electronic properties, the frontier molecular orbital (FMO) analysis indicates that the energy gap decreases after complexation, which is confirmed through density of states (DOS) analysis. Moreover, natural bond orbital (NBO) analysis determines the amount and direction of charge transfer i.e., from metallacycle towards amino acids. The maximum NBO charge transfer is observed for S-pro@metallacycle complex i.e., -0.291 |e|. Electron density difference (EDD) analysis further proves the direction of charge transfer. Noncovalent interaction index (NCI) and quantum theory of atoms in molecules (QTAIM) analyses demonstrate that the noncovalent interactions present between the host and guest are the weak van der Waals forces and hydrogen bonding. The results of NCI and QTAIM analyses for all the complexes are in alignment with those of the interaction energy (Eint) and chiral discrimination energy (Echir) analyses, i.e., significantly greater non-bonding interactions are observed for the complexes with greater Echir, i.e., for ala@metallacycle. Overall, our analyses demonstrate the excellent chiral discrimination ability of metallacycle towards chiral molecules, i.e., for enantiomers of amino acids through host-guest supramolecular chemistry.

Experimental, Theoretical, and In Silico Studies of Potential CDC7 Kinase Inhibitors.

In this work, we present the synthesis, solid-state characterization, and in silico studies of two pyrazole derivatives: 5-(2-methylphenoxy)-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde (I) and 5-(4-methylphenoxy)-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde (II). The molecular crystal properties, in terms of intermolecular hydrogen bonds and other weak interactions, are analyzed using single crystal X-ray diffraction. The Hirshfeld surfaces computational method is used to quantify the intermolecular interactions, density functional theory for theoretical structural optimization, and its comparison with the experimental structure and in-silico studies using docking and molecular dynamics studies of I and II with CDC7-kinase. In addition, the quantum theory of atoms in molecules (QTAIM) approach is applied to calculate the topological properties of electron density and the Laplacian of electron density of the chemical bonds of both molecules. Compounds I and II crystallize in a monoclinic crystal system, and molecules are connected via C-H···O intermolecular hydrogen bonds. Hirshfeld surfaces analysis revealed that the H···H type intercontact contributes more toward the crystal packing. DFT-optimized structures show a perfect overlay with the experimental structures. The in silico results show that both I (-41.50 kcal/mol) and II (-44.53 kcal/mol) exhibit strong binding free energies as ligands binding to the active sites of the CDC7-kinase. The most significant contributions for ligand and protein binding in both compounds are dominated by van der Waals interactions.

Adsorption and Sensing Performance of Transition Metal Decorated Graphene Quantum Dots for AsH3, NH3, PH3, and H2S.

We have conducted a systematic study employing density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) to explore the gas sensing capabilities of nitrogen-doped single vacancy graphene quantum dots (SV/3N) decorated with transition metals (TM = Mn, Co, Cu). We have studied the interactions between TM@SV/3N and four different target gases (AsH3, NH3, PH3, and H2S) through the computation of adsorption energies, charge transfer, noncovalent interaction, density of states, band gap, and work function for 12 distinct adsorption systems. Our comprehensive analysis included an in-depth assessment of sensors' stability, sensitivity, selectivity, and reusability for practical applications. Our findings indicate that the Co@SV/3N surface strongly interacts with PH3, with the highest adsorption energy (-1.15 eV). It shows remarkable sensitivity and selectivity toward PH3, making it a promising candidate for PH3 gas sensing applications. Similarly, Mn@SV/3N exhibits high sensitivity and selectivity toward NH3, positioning it as a suitable candidate for NH3 gas sensing applications. We believe this study will provide valuable theoretical guidance for developing TM@SV/3N-based gas sensors.

Interaction of CO, CO2, CSO, H2O, N2O, NO, NO2, O2, ONH, and SO2 gases onto BNNT(m,n)_x, (m = 3, 5, 7; n = 0, 3, 5, 7; x = 3-9).

This research investigates two critical areas, providing valuable insights into the properties and interactions of boron nitride nanotubes (BNNTs). Initially, a variety of BNNT structures (BNNT(m,n)_x, where m = 3, 5, 7; n = 0, 3, 5, 7; x = 3-9) with different lengths and diameters are explored to understand their electronic properties. The study then examines the interactions between these nanotubes and several gases (CO, CO2, CSO, H2O, N2O, NO, NO2, O2, ONH, and SO2) to identify the most stable molecular configurations using the bee colony algorithm for global optimization. The primary findings highlight the impact of nanotube diameter on these properties. It was observed that smaller diameters result in a larger energy gap due to increased quantum confinement. Significant charge transfer, especially with CO, was detected, affecting the electronic structure of the nanotubes. The study highlighted that BNNTs exhibit the strongest adsorption tendencies for NO₂, O₂, and SO₂. These findings underscore the critical roles of nanotube diameter and charge transfer in sensor applications and demonstrate the comprehensive utility of various analytical methods in understanding BNNT-gas interaction mechanisms. The research employs a comprehensive computational framework based on density functional theory (DFT). Various DFT methods, such as PBE0, B3LYP(GD3BJ), CAM-B3LYP, HSE06i, M06-2X, and ωB97XD functionals, are utilized along with the Def2tzvp basis set for the calculations. Structural optimizations are performed to ensure accuracy, and modifications to the energy gaps are analyzed using conceptual DFT. Additionally, Total Density of States (TDOS) analyses are conducted. Charge transfer mechanisms are investigated through Natural Bond Orbital (NBO) analysis. The interactions between gases and nanotubes are characterized at critical points using the Quantum Theory of Atoms in Molecules (QTAIM) framework.

Insights Into the Uranium Phosphine Bonds in [UCp3(PR3)]: A Combined Molecular Orbital, QTAIM and EDA‐NOCV Study

AbstractA series of ten uranium(III) complexes with cyclopentadienyl and monodentate phosphine ligands [UCp3(PR3)] with R=Me, Et, nPr, iPr, tBu, Ph, Cy, F and CF3 was investigated using density functional theory calculations. The ligand dissociation energies were calculated, as well as bonding analysis of the uranium‐phosphorus bond performed, using molecular orbitals, bond orders, quantum theory of atom in molecules (QTAIM) analysis and energy decomposition analysis with natural orbitals for chemical valence (EDA‐NOCV). It was found that the bond orders correlate well with the U−P bond lengths and phosphine cone angles, indicating a large influence of phosphine sterics on the bond properties. All bonding analyses show partial covalent character of the U−P bond, which is most pronounced for PF3 and least for PtBu3. π‐Backbonding was found for the most π‐acidic phosphine ligands. No good correlation was found between the ligand dissociation energies and bond metrics.

Controlled tuning of HOMO and LUMO levels in supramolecular nano-Saturn complexes.

Optoelectronics usually deals with the fabrication of devices that can interconvert light and electrical energy using semiconductors. The modification of electronic properties is crucial in the field of optoelectronics. The tuning of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and their energy gaps is of paramount interest in this domain. Herein, three nano-Saturn supramolecular complex systems are designed, i.e., Al12N12@S-belt, Mg12O12@S-belt, and B12P12@S-belt, using S-belt as the host and Al12N12, Mg12O12, and B12P12 nanocages as guests. The high interaction energies ranging from -22.03 to -63.64 kcal mol-1 for the complexes demonstrate the stability of these host-guest complexes. Frontier molecular orbital (FMO) analysis shows that the HOMO of the complexes originates from the HOMO of the host, and the LUMO of the complexes originate entirely from the LUMO of the guests. The partial density of states (PDOS) analysis is in corroboration with FMO, which provides graphical illustration of the origin of HOMO and LUMO levels and the energy gaps. The shift in the electron density upon complexation is demonstrated by the natural bond orbital (NBO) charge analysis. For the Al12N12@S-belt and B12P12@S-belt complexes, the direction of electron density shift is towards the guest species, as indicated by the overall negative charge on encapsulated Al12N12 and B12P12. For the Mg12O12@S-belt complex, the overall NBO charge is positive, elaborating the direction of overall shift of electronic density towards the S-belt. Electron density difference (EDD) analysis verifies and corroborates with these findings. Noncovalent interaction index (NCI) and quantum theory of atoms in molecules (QTAIM) analyses signify that the complexes are stabilized via van der Waals interactions. Absorption analysis explains that all the complexes absorb in the ultraviolet (UV) region. Overall, this study explains the formation of stable host-guest supramolecular nano-Saturn complexes along with the controlled tuning of HOMO and LUMO levels over the host and guests, respectively.

Efficient and green separation of phenolics by halogen free deep eutectic solvents

To deeply investigate the mechanism of deep eutectic solvents (DES) separation of phenolics from coal tar, three halogen free DESs were synthesized by using L-carnitine as the hydrogen bonding acceptor (HBA) combined with triethanolamine, ethylene glycol and formic acid as the hydrogen bonding donor (HBD). The effects of the mass ratio of these three DESs to phenol, extraction temperature, extraction time and other parameters on the extraction efficiency were investigated. Among them, DES3 synthesized by L-carnitine and formic acid exhibits a high extraction efficiency of 97.1 % and a low neutral oil entrained efficiency of 14 %. The microscopic interaction mechanism between DESs and phenol/toluene was investigated through quantum chemical calculations based on density functional theory. The results demonstrated that DES3 interacts with phenol through strong hydrogen bonding and van der Waals forces, as evidenced by an interaction energy of −62.24 kJ/mol, substantially higher than that with toluene (−37.61 kJ/mol). A variety of methods, including electrostatic potential (ESP) analysis, independent gradient model based on Hirshfeld partition (IGMH) analysis, and quantum theory of atoms in molecules (QTAIM) analysis, were used to further confirmed that DES3 has a stronger affinity and selectivity for phenol, laying a solid theoretical foundation for its application as an efficient and recyclable industrial extractant.

Effect of pH on azobenzene-4,4'-dicarboxylate/α-CD complex formation. Synthesis, kinetic study and molecular modeling simulations

The current study focuses on the molecular behavior of the azobenzene-4,4'-dicarboxylate/α-CD pseudorotaxane and how it is affected by changes in pH. A combination of experimental measurements and molecular simulations were used, including different computational calculations, to evaluate the kinetic and thermodynamic aspects of the formation of this mechanically bound architecture. The research involved determining the formation rate constants for these complexes at different pH values and conducting a comprehensive kinetic study. Additionally, the binding affinity and complexation reaction was analyzed using free energy profiles derived from umbrella sampling in molecular dynamics simulations. To gain a better understanding of the energetic and structural aspects of the complexes, hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) calculations were employed. The intermolecular interactions that stabilize the pseudorotaxanes were characterized using quantum theory of atoms in molecules (QTAIM) and Molecular Electrostatic Potentials (MEPs)

Unconventional C-Hlg···H-C (Hlg = Cl, Br, and I) Interactions Involving Organic Halides: A Theoretical Study.

In this study, unconventional C-Hlg···H-C (Hlg = Cl, Br, and I) interactions involving sp, sp2, and sp3 organic halides were investigated at the RI-MP2/aug-cc-pVQZ level of theory. Energy Decomposition Analyses (EDA) and Natural Bonding Orbital (NBO) studies showed that these intermolecular contacts are mainly supported by orbital and dispersion contributions, which counteracted the unfavorable/slightly favorable electrostatics due to the halogen-hydrogen σ-hole facing. In addition, the Bader's Quantum Theory of Atoms in Molecules (QTAIM) and the Noncovalent Interaction plot (NCIplot) visual index methodologies were used to further characterize the interactions discussed herein. We expect that the results reported herein will be useful in the fields of supramolecular chemistry, crystal engineering, and rational drug design, where the fine tuning of noncovalent interactions is crucial to achieve molecular recognition or a specific solid-state architecture.

Mechanistic insight into the catalytic activities of metallic sites on nitrogen-doped graphene quantum dots for CO2 hydrogenation

The origin of selectivity and activity of the CO2 hydrogenation reaction on single-atom catalysts composed of three adjacent 3d transition metals (Fe, Co, and Ni) supported on N-doped graphene quantum dots were systematically investigated and compared using density functional theory (DFT) calculations, natural bond orbital (NBO), and quantum theory of atoms in molecules (QTAIM) analysis. This study reveals that π-backbonding between the metal and CO2* does not occur and [CO2]δ+ species drive the reaction. The CO2* reacts with H2 via the Eley-Rideal (ER) mechanism by using the synergistic effects of the N site. The higher the partial positive charge on the C atom, the lower the Ea of the reaction. Subsequently, a tautomerization reaction, which is facilitated by hydrogen bonding, occurs and hydrogen is transferred to HCOO* resulting in the formation of CHOOH*. This study shows the selective formation of formic acid from CO2 is accessible on these SACs and Fe-SAC is the best one between these three catalysts. Although CO2 is more inert than formic acid the H2 molecule reacts with the adsorbed formic acid more difficult than the adsorbed CO2. It is because the hydrogenation of formic acid causes C-H bond formation resulting in failure of the coordinated O atom's octet and the unstable H2COOH* is formed. This step is the rate-determining step of HOCH2OH formation from CO2, with Ea of 1.94, 2.03, and 2.23 eV for Fe, Co, and Ni, respectively. Finally, the system undergoes another tautomerization reaction resulting in the formation of HOCH2OH (formaldehyde monohydrate).

Probing the hybridized triazole-chalcones: an in-depth investigations of molecular structure journey towards antibacterial potential against DNA gyrase

The present study delves into the comprehensive structural investigations of the six Chalcone derivatives (4A–F), each featuring the 1, 2, 3 triazole linkages. The work commences with the synthesis by employing a multifaceted approach to unravel its molecular properties and potential biological significance. Single crystal X-ray diffraction technique was used to determine the precise 3D structure of the grown single crystals of 4D and 4F. The crystal structure exhibited significant investigations on intermolecular interactions, particularly hydrogen bonding, π–π stacking, Van der Waals forces and other intra-intermolecular interactions contributing to the molecular assembly. Density Functional Theory (DFT) was employed using the B3LYP functional and 6-311++ G (d, p) basis set to explore compound’s electronic structure and physicochemical properties. Quantum theory of atoms in molecule (QTAIM) and non-covalent interactions (NCI) analysis provided insights into the topology of the compounds. Further the biological assessments were performed to know the antimicrobial properties of the compounds against both gram-negative and gram-positive bacteria. The research also culminated the evaluation of the drug-likeness of the compounds, drawing upon ADME-T predictions. Further, in silico molecular docking and dynamics simulation analysis were conducted to anticipate the most favorable binding configuration of the derivatives within the active site cavity of the Type II topoisomerase DNA gyrase receptors. In vitro antimicrobial study was also performed and it demonstrated notable results. Overall, this extensive study offers a deep study into the structural intricacies of these compounds, providing insights for chemical and biological evaluations, particularly in the context of bacterial enzyme inhibition.

The Analysis of Electron Densities: From Basics to Emergent Applications.

The electron density determines all properties of a system of nuclei and electrons. It is both computable and observable. Its topology allows gaining insight into the mechanisms of bonding and other phenomena in a way that is complementary to and beyond that available from the molecular orbital picture and the formal oxidation state (FOS) formalism. The ability to derive mechanistic insight from electron density is also important with methods where orbitals are not available, such as orbital-free density functional theory (OF-DFT). While density topology-based analyses such as QTAIM (quantum theory of atoms-in-molecules) have been widely used, novel, vector-based techniques recently emerged such as next-generation (NG) QTAIM. Density-dependent quantities are also actively used in machine learning (ML)-based methods, in particular, for ML DFT functional development, including machine-learnt kinetic energy functionals. We review QTAIM and its recent extensions such as NG-QTAIM and localization-delocalization matrices (LDM) and their uses in the analysis of bonding, conformations, mechanisms of redox reactions excitations, as well as ultrafast phenomena. We review recent research showing that direct density analysis can circumvent certain pitfalls of the FOS formalism, in particular in the description of anionic redox, and of the widely used (spherically) projected density of states analysis. We discuss uses of density-based quantities for the construction of DFT functionals and prospects of applications of analyses of density topology to get mechanistic insight with OF-DFT and recently developed time-dependent OF-DFT.