Atomic Theory Research Articles

On the Existence of Pnictogen Bonding Interactions in As(III) S-Adenosylmethionine Methyltransferase Enzymes.

As(III) S-adenosylmethionine methyltransferases, pivotal enzymes in arsenic metabolism, facilitate the methylation of arsenic up to three times. This process predominantly yields trivalent mono- and dimethylarsenite, with trimethylarsine forming in smaller amounts. While this enzyme acts as a detoxifier in microbial systems by altering As(III), in humans, it paradoxically generates more toxic and potentially carcinogenic methylated arsenic species. The strong affinity of As(III) for cysteine residues, forming As(III)-thiolate bonds, is exploited in medical treatments, notably in arsenic trioxide (Trisenox®), an FDA-approved drug for leukemia. The effectiveness of this drug is partly due to its interaction with cysteine residues, leading to the breakdown of key oncogenic fusion proteins. In this study, we extend the understanding of As(III)'s binding mechanisms, showing that, in addition to As(III)-S covalent bonds, noncovalent O⋅⋅⋅As pnictogen bonding plays a vital role. This interaction significantly contributes to the structural stability of the As(III) complexes. Our crystallographic analysis using the PDB database of As(III) S-adenosylmethionine methyltransferases, augmented by comprehensive theoretical studies including molecular electrostatic potential (MEP), quantum theory of atoms in molecules (QTAIM), and natural bond orbital (NBO) analysis, emphasizes the critical role of pnictogen bonding in these systems. We also undertake a detailed evaluation of the energy characteristics of these pnictogen bonds using various theoretical models. To our knowledge, this is the first time pnictogen bonds in As(III) derivatives have been reported in biological systems, marking a significant advancement in our understanding of arsenic's molecular interactions.

Bistriazolotriazole-tetramine: commendable energetic moiety and cation.

Various 7H,7'H-[6,6'-bi[1,2,4]triazolo[4,3-b][1,2,4]triazole]-3,3',7,7'-tetramine (A) based nitrogen-rich energetic salts were designed and their properties explored. All energetic salts possess relatively high nitrogen content (> 48%), positive heats of formation (> 429kJ/mol) and stability owing to a significant contribution from fused backbone. The cationic component shows a very high heat of formation (2516kJ/mol); therefore, it is highly suitable for enthalpy enhancement in new energetic salts. The cation was paired with the energetic anions nitrate (NO3-), perchlorate (ClO4-), dinitromethanide (CH(NO2)2-), trinitromethanide (C(NO2)3-), nitroamide (NHNO2-), and dinitroamide (N(NO2)2-) to improve oxygen balance and detonation performance. Designed salts show moderate detonation velocities (7.9-8.7 km/s) and pressures (23.8 - 33.1 GPa). The distribution of frontier molecular orbitals, molecular electrostatic surface potentials, QTAIM topological properties, and noncovalent interactions of designed salts were simulated to understand the electronic structures, charge distribution in molecules, hydrogen bonding, and other nonbond interactions. The predicted safety factor (SF) and impact sensitivity (H50) of designed salts suggest their insensitivity to mechanical stimuli. This work explored the 7H,7'H-[6,6'-bi[1,2,4]triazolo[4,3-b][1,2,4]triazole]-3,3',7,7'-tetramine as a suitable cationic component which could be promising and serve exemplarily in energetic materials. The optimization and energy calculations of all the designed compounds were carried out at the B3LYP/6-311 + + G(d,p) and M06-2X/def2-TZVPP levels, utilizing the Gaussian software package. The molecular surface electrostatic potential, quantum theory of atoms in molecules (QTAIM), reduced density gradient (RDG), and noncovalent interaction (NCI) analysis were performed by employing Multiwfn software. The EXPLO5 (v 7.01) thermochemical code and PILEM web application were used to predict the detonation properties.

A Charge-Charge Flux-Dipole Flux Analysis of Simple Molecular Systems with Halogen Bonds.

The presence of halogen bonds (R-X···B; R = substituent group, X = halogen, and B = Lewis base) provides quite amazing molecular systems for electronic structure investigations, presenting unique characteristics of fundamental relevance to supramolecular chemistry among other areas. Here, we use a double-hybrid approach from Density Functional Theory and triple-ζ basis sets augmented with diffuse functions (B2PLYP/def2-TZVPD) to deal with a large group of simple molecular systems containing halogen bonds (XBs), focusing on geometrical structures, binding energies, harmonic vibrational frequencies, and fundamental infrared intensities. Next, the electron densities and their variations on vibrations are carefully studied with the Quantum Theory of Atoms in Molecules (QTAIM) formalism and the charge-charge flux-dipole flux (CCFDF) model. We notice that the R-X stretching mode usually shows vibrational frequency decrements and infrared intensifications during the XB formation. Such features were also observed in hydrogen bonds, although the explanation for the band strengthening is different. Surprisingly, the most important contribution to these intensity increments due to complexation is now the interaction term between the charge flux and dipole flux (CF × DF). Thus, the use of atomic dipoles is mandatory to fully understand this phenomenon. In fact, the huge charge flux contributions to changes in dipole moment derivatives of R-X stretchings on halogen bonding are no longer accompanied by opposite variations of similar magnitudes in polarizations described by atomic dipole fluxes, which provided nearly unaltered values during the XB formation. Thus, the electronic charge flux direction change that takes place in complexes (from B to R) now reinforces dipole moment derivative terms from such atomic polarizations (mainly from the X atom). This intermolecular charge flux seems to be responsible for the unusual features noticed in the R-X stretching mode with the CCDDF/QTAIM model.

Theoretical Insights into Different Complexation Modes of Dioxovanadium(V) Compounds with Pyridoxal Semicarbazone/Thiosemicarbazone/S-Methyl-iso-thiosemicarbazone Ligands.

Vanadium complexes have gained considerable attention as biologically active compounds. In this contribution, three previously reported dioxovanadium(V) complexes with pyridoxal semicarbazone, thiosemicarbazone, and S-methyl-iso-thiosemicarbazone ligands are theoretically examined. The intermolecular stabilization interactions within crystallographic structures were investigated by Hirshfeld surface analysis. These experimental structures were optimized at the B3LYP-D3BJ/6-311++G(d,p)(H,C,N,O,S)/def2-TZVP(V) level of theory, and crystallographic and optimized bond lengths and angles were compared. High correlation coefficients and low mean absolute errors between these two data sets proved that the selected level of theory was appropriate for the description of the system. The changes in structures and stability were examined by adding explicit solvent molecules. The Quantum Theory of Atoms in Molecules (QTAIM) was employed to analyze the intramolecular interactions with special emphasis on the effect of substituents. A good correlation between electron density/Laplacian and interatomic distance was found. Through molecular docking simulations towards Bovine Serum Albumin (BSA), the binding affinity of complexes was further investigated. The spontaneity of binding in the active position of BSA was shown. Further experimental studies on this class of compounds are advised.

Cavitands based nanocapsule as smart and highly effective vehicle for 5-fluorouracil anti-cancer drug delivery: DFT insights

The nanomaterials have been widely investigated as drug delivery system for a variety of anticancer drugs to limit their adverse effects while transporting to the target site. In the current study, we report the cavitand-based nanocapsules as a drug delivery vehicle for nitrosourea (NU) and fluorouracil (FU) anti-cancer drugs. FU and NU drugs interact with the nanocapsules with the interaction energies in gas phase (solvent) −24.78 kcal/mol (–22.39 kcal/mol) and −21.58 kcal/mol (-20.45 kcal/mol), respectively. The results of Quantum theory of atoms in molecules (QTAIM) and noncovalent index (NCI) analyses indicate that the FU@Capsule and NU@Capsule complexes are mainly stabilized through hydrogen bonding and van der Waals interactions. Electron density difference (EDD) and natural bond order (NBO) analyses reveal that significant amount of charge is transferred from the nanocapsule to drug molecules. Frontier molecular orbital (FMO) analysis also reveals slight reduction in the energy gap. AIMDS analysis shows that cavitand capsules can efficiently carry the anti-cancerous drug to their target site without distorting complexes. The dipole moments and pH effect are studied to understand the drug release mechanism of considered anticancer drugs. The decrease in adsorption energy and increase in interaction distances indicate that anticancer drugs can easily be off-loaded from the carrier (nanocapsule) at the target site due to the low pH of cancerous cells compared to the normal cells. Therefore, cavitand nanocapsule can be employed as an excellent drug delivery carrier in smart targeted drug delivery.

On the role of water in antimony electrodeposition from choline chloride/ethylene glycol/water mixture

Through experimental research and theoretical calculation, it was investigated the effect of water and temperature on the electrodeposition of antimony (Sb) on a platinum (Pt) electrode. The plating solutions were prepared by the addition of 0.05 mol L–1 SbCl3 to the mixtures of choline chloride (ChCl), ethylene glycol (EG) and water (W) in the following molar ratio: 1ChCl:2EG (bath 1), 1ChCl:2EG:0.45 W (bath 2), and 1ChCl:2EG:1.62 W (bath 3). Furthermore, the Sb coatings were electrodeposited at 297 and 338 K. The surface morphologies and crystalline structures of Sb electrodeposits were analysed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. In addition, to understand the interactions of Sb3+ species with the other components of the plating solution, models were created and calculated using density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM). The results of the voltammetric behaviour of Sb3+ species indicated that the reduction potential was shifted towards more positive values with increasing water content on the electrolyte, indicating that the water catalyses the electrochemical reduction of the Sb3+ species. The values of the diffusion coefficients for the Sb3+ species were calculated by applying the Cottrell equation, which increased with the addition of water and temperature increment. The water content and temperature increase affect the surface morphologies of the Sb electrodeposited coatings, which is attributed to the improvement of Sb electrodeposition rate. Moreover, Sb electrodeposited coatings were successfully obtained without adding a complexing agent, indicating that the procedure adopted for the Sb electrodeposition is environmentally friendly. The XRD results revealed the pure phase Sb films. DFT simulations indicated that the Sb-Cl interaction is stronger, which suggests the formation of Sb-Cl complexes. Adding H2O molecules favours the electron affinity of the systems, and QTAIM results suggested that this additive decreased the electron density of Sb3+ ions.

Synthesis, crystal structure investigation and computational studies binding of (7S,8R)-7-acetyl-8-(4-chlorophenyl)-3-(ethylthio)-1,6-dimethyl-7,8-dihydroisoquinoline-4-carbonitrile with monoamine oxidase B

This work reports the preparation of a new dihydroisoquinoline derivative whose structure was characterized by IR, NMR (1H, 13C), MS and verified through single-crystal X-ray analysis. The mean planes of the acetyl and 4-chlorophenyl groups in the title molecule are nearly perpendicular to that of the pyridine ring. In the crystal, π-stacking and C—H···O hydrogen bond interactions involving the pyridine ring and the nitrile group of an adjacent molecule form the full 3-D structure. Hirshfeld surface (HS) analysis shows the topology of the molecules in the crystal packing. Fingerprint (FP) diagrams show the percentage contribution of several intermolecular interactions where H‧‧‧H interactions have a significant contribution (46%). The DFT study reveals a low HOMO-LUMO gap and significant charge transfer is indicated by the natural bonding orbitals (NBO) and frontier molecular orbital (FMO) analyses. Non-covalent interactions and bond characteristics were investigated using the quantum theory of atom in the molecule (QTAIM) and ELF analysis. FMO analysis was used to calculate the HOMO-LUMO energy gap and orbital energies. Using the DFT method, parameters such as global reactivity were calculated. Using the implicit solvent model, properties such as optical and nonlinear optical (NLO) were characterized in the solvent (water) phase and gas phase. The affinity of the title molecule for Monoamine Oxidase B was examined using molecular docking and molecular dynamics studies and these results showed good binding of the target molecule.

Extensive optical and DFT studies on novel AIE active fluorescent sensor for Colorimetric and fluorometric detection of nitrobenzene in Solid, solution and vapor phase

An electron rich isophthalamide based sensor IPA has been synthesized through a simple two-step reaction, containing noteworthy aggregation induced emission (AIE) properties. Considering the significant emission with λmax at 438 nm, sensor IPA has been employed for the sensing of nitrobenzene (NB) in solid, solution and vapor state with high sensitivity and selectivity. Sensor IPA showed noteworthy colorimetric and fluorometric quenching in fluorescence emission when exposed to NB. Small size of NB and involvement of photoinduced electron transfer (PET) lead to detection of NB down to 60 nM. IPA-NB interaction was studied through UV–Vis. spectroscopic studies along with fluorescence spectroscopy. Moreover, 1H and 13C NMR titration experiments provided additional support for determination of interaction type. Furthermore, by using density functional theory (DFT) calculations, thermodynamic stability was studied. Additionally, non-covalent interactions (NCI), frontier molecular orbitals (FMO), density of states (DOS), were investigated for providing further evidence of nitrobenzene sensing and its interaction with sensor. Natural bond orbital (NBO) analysis was carried out for charge transfer studies. Quantum theory of atom in molecule (QTAIM) and SAPT0 studies provided information about interaction points and binding energy. Additionally, IPA was investigated for NB sensing in real water samples, and its effective participation in solid state on-site detection as well as in solution phase was brought to light along with logic gate construction.

Investigating structural dynamics and sensing capabilities: Spectroscopic and DFT analysis of novel AIEE active deferasirox based organic sensor

A deferasirox based sensor DPA was rationally designed through single step amidation reaction. Sensor DPA exhibited aggregation induced emission enhancement (AIEE) property that was attributed to restriction in intramolecular rotation (RIR). Moreover, the sensor DPA displayed remarkable bathochromic shift (red-shift) of 110 nm in wavelength, ascribed to formation of J-aggregates. Furthermore, sensor DPA was employed for the selective and sensitive fluorescence based sensing of hazardous and carcinogenic nitrobenzene (NB). The sensor DPA successfully detected NB in solution through the quenching of emission intensity. The quenching of sensor fluorescence intensity was ascribed to photoinduced electron transfer (PET) mechanism. The sensing mechanism was investigated by 1H NMR titration experiment, Job's plot and density functional theory (DFT) calculations. Additionally, the existence of non-covalent interactions between sensor DPA and NB were examined by Bader's Quantum theory of atoms in molecules (QTAIM) and non-covalent interaction (NCI) analysis. Finally, sensor DPA was employed for the detection of volatile nitrobenzene in vapor phase.

Quantitative clustering and matching of conformers using average electron densities

This study presents a new approach of quantitatively clustering conformers of small molecules, such that conformers of the same group share similar electrostatic potential (ESP) maps. This helps expedite the drug design process as ESP maps guide the “key & lock” complementarity between a molecule and its receptor. The clustering is based on similarities in the average electron density (AED) of a group of interest within a molecule. AED values are computationally evaluated using the quantum theory of atoms in molecules (QTAIM). The AED tool was validated, separately, on 43 conformers of ibuprofen and 40 conformers of a tetrazole analogue of ibuprofen. The conformers were grouped based on their AED values using the K-means clustering method. It was found that conformers of the same group share similar ESP maps, with a remarkable accuracy exceeding 96%. In addition, using a drug design concept known as bioisosterism, it was found that the AED tool depicts similarities in the ESP maps of not only conformers of a single molecule, but also conformers of different molecules that share similar biological activities.

Experimental and theoretical Ritz–Rydberg analysis of the electronic structure of highly charged ions of lead and bismuth by optical spectroscopy

Intra-configuration fine-structure transitions in highly charged ions (HCIs) result in most cases from changes in the coupling of equivalent electrons. They are multipole forbidden to varying degrees and often occur within the optical range. In HCI with semi-filled nd and nf subshells, electrons can in principle couple to states which are energetically close but with very different total angular momenta, e.g. 0⩽J⩽10 . This gives rise to metastable states with very long lifetimes that exhibit particularly interesting clock transitions or, as in the case of orbital level crossings, acquire a considerable sensitivity to a possible variation of the fine-structure constant α. We investigate both experimentally and theoretically connecting the ground state and adjacent states of Pb XXII to Pb XXXIV and Bi X to Bi XV, respectively, covering complex couplings of electrons in the 4f and 5d shells. These and others such as nd and nf , which also contain equivalent electrons, are of interest for frequency metrology using quantum logic spectroscopy, for atomic structure and QED theory tests, and for the search for Dark Matter candidates. We infer their level structure, benchmark calculations from two different electronic structure codes, and lay the groundwork for inferring the wavelengths of forbidden transitions of higher multipolarity in the optical and VUV region.

Homologs of Thioacetone and Acetone in the Quantum Theory of Atoms in Molecules

Homologs of Thioacetone and Acetone in the Quantum Theory of Atoms in Molecules

Neoclassical Theory of Atoms

The "Neoclassical Theory of Atoms" challenges the dominance of quantum mechanics in explaining certain atomic phenomena. This work argues that a classical approach, utilizing electromagnetic Coulomb forces and Newtonian mechanics, can potentially account for discrete energy levels and spectral lines observed in hydrogen and helium atoms. It questions the necessity of invoking the seemingly counterintuitive aspects of quantum mechanics for these specific phenomena. By demonstrating the potential of a classical framework, this research aims to stimulate debate and exploration of alternative explanations within physics. This could potentially lead to a deeper understanding of the nature of reality and the limitations (or potential for expansion) of current physical theories.

Theoretical Study of Am(III) and Eu(III) Separation by a Bipyridyl Phosphate Ligand.

Actinide An(III) and lanthanide Ln(III) are known to exhibit similar chemical properties; thus, it is difficult to distinguish them in the separation of highly radioactive waste liquids. One potential method to efficiently separate actinides and lanthanides involves the design and development of phosphorus-oxygen-bonded ligands with solvent extraction separation. Here, a bipyridine phosphate ligand with two isopropyl and phosphate groups is introduced to selectively extract actinides. The electronic structure, bonding properties, thermodynamic behavior, and quantum theory of atoms in molecules (QTAIM) of Am(III) and Eu(III) complexes with the bipyridine phosphate ligands were analyzed by using density functional theory (DFT) calculations. The analysis demonstrates that the Am-N bond exhibits stronger covalent characteristics than the Eu-N bond, indicating that the bipyridine phosphate ligand had better selectivity for Am(III) than for Eu(III) in terms of binding affinity. The thermodynamic analysis established the complex [ML(NO3)2(H2O)2]+ as the most stable species during the complexation process. The results indicate great potential for utilizing the bipyridine phosphate ligand for the effective separation of An(III)/Ln(III) in spent fuel reprocessing experiments.

3-(2-pyridyl)-5-(4-chlorophenyl)-1,2,4-triazine as a ligand: Synthesis of three lead(II) complexes, a spectroscopic and structural study using experimental and theoretical methods

Three new Pb(II) complexes of the ligand 3-(2-pyridyl)-5-(4-chlorophenyl)-1,2,4-triazine (pcpt) and different anionic co-ligands (1: bromide, 2: iodide and 3: isothiocyanate) were synthesized and characterized by elemental (CHN) analysis, FT-IR and 1H NMR spectroscopy and single crystal X-ray diffraction (SC-XRD). Considering only strong primary coordination bonds, the Pb(II) centres in complexes 1 and 2 are holodirectionally and in 3 hemidirectionally coordinated by the organic pcpt ligands due to stereochemical inactivity (1, 2) and activity (3) of the lone electron pair. The primary coordination sphere in 3 is sterically suitable for establishing interactions at longer distances, where the Pb centre acts as Lewis acid. Thus, all the Pb centers participate in Pb⋅⋅⋅Cl tetrel interactions, which together with secondary interactions of the ligands extend the structures into 1D supramolecular assemblies. A Hirshfeld surface inspection, along with the natural bond analysis (NBO), quantum theory of atoms in molecules (ATAIM), molecular electrostatistic potential (MEP) surface, and theoretical vibrational analysis at B3LYP/Def2-TZVP level of theory were conducted for the sake of further investigation of the non-covalent interactions in complexes 1–3. An enrichment ratio is also calculated for the chemical species to determine the tendency of their interactions in the crystal packing. The theoretical values obtained from the DFT at B3LYP/Def2-TZVP level of theory ensure that the expected consequences match the experimental findings. The QTAIM calculations allow the estimation of the strength of the primary and secondary/tetrel interactions and to propose the theoretical criteria based on the |VBCP|/GBCP, HBCP/ρBCP, and DI parameters for distinguishing the interactions. The MEP calculations confirmed the presence of a σ-hole in the proximity of the PbII centers.

Conformational Preference of Lithium Polysulfide Clusters Li2Sx (x = 4-8) in Lithium-Sulfur Batteries.

Structures are of fundamental importance for diverse studies of lithium polysulfide clusters, which govern the performance of lithium-sulfur batteries. The ring-like geometries were regarded as the most stable structures, but their physical origin remains elusive. In this work, we systematically explored the minimal structures of Li2Sx (x = 4-8) clusters to uncover the driving force for their conformational preferences. All low-lying isomers were generated by performing global searches using the ABCluster program, and the ionic nature of the Li···S interactions was evidenced with the energy decomposition analysis based on the block-localized wave function (BLW-ED) approach and further confirmed with the quantum theory of atoms in molecule (QTAIM). By analysis of the contributions of various energy components to the relative stability with the references of the lowest-lying isomers, the controlling factor for isomer preferences was found to be the polarization interaction. Notably, although the electrostatic interaction dominates the binding energies, it contributes favorably to the relative stabilities of most isomers. The Li+···Li+ distance is identified as the key geometrical parameter that correlates with the strength of the polarization of the Sx2- fragment imposed by the Li+ cations. Further BLW-ED analyses reveal that the cooperativity of the Li+ cations primarily determines the relative strength of the polarization.

The interplay of motor adaptation and groupitizing in numerosity perception: Insights from visual motion adaptation and proprioceptive motor adaptation.

Groupitizing is a well-established strategy in numerosity perception that enhances speed and sensory precision. Building on the ATOM theory, Anobile proposed the sensorimotor numerosity system, which posits a strong link between number and action. Previous studies using motor adaptation technology have shown that high-frequency motor adaptation leads to underestimation of numerosity perception, while low-frequency adaptation leads to overestimation. However, the impact of motor adaptation on groupitizing, and whether visual motion adaptation produces similar effects, remain unclear. In this study, we investigate the persistence of the advantage of groupitizing after motor adaptation and explore the effects of visual motion adaptation. Surprisingly, our findings reveal that proprioceptive motor adaptation weakens the advantage of groupitizing, indicating a robust effect of motor adaptation even when groupitizing is employed. Moreover, we observe a bidirectional relationship, as groupitizing also weakens the adaptation effect. These results highlight the complex interplay between motor adaptation and groupitizing in numerosity perception. Furthermore, our study provides evidence that visual motion adaptation also has an adaptation effect, but does not fully replicate the effects of proprioceptive motor adaptation on groupitizing. In conclusion, our research underscores the importance of groupitizing as a valuable strategy in numerosity perception, and sheds light on the influence of motion adaptation on this strategy.

The adsorption mechanism of 5-fluorouracil on MnO2-based nanostructures by DFT calculation and experimental analysis

It is of great significance to explore the mechanism of drug molecules hiking on nanomaterials for targeted delivery. In this study, we evaluated the interaction potential of three manganese dioxide (MnO2) nanostructures with 5-fluorouracil (5-FU) using a density function theory (DFT) framework and dispersion correction (D3BJ) and conducted experimental verification. All possible adsorption modes and locations were predicted by electrostatic surface potential (ESP) and van der Waals force calculations. The charge transfer between molecular groups was estimated by electron density difference (EDD). The energy-favorable model of 5-FU interaction with distinct MnO2 crystals was investigated by using partial density of states (PDOS). Further, the quantum theory of atoms in molecules (QTAIM) calculation and independent gradient model based on Hirshfeld partition (IGMH) analysis were applied to reveal the interaction details. Our results suggest that 5-FU can be absorbed at different positions on the surface of MnO2, in which the O-adsorption mode is mainly dominated by hydrogen bond, while the Mn-adsorption mode is dominated by coordination interaction. Besides, the dispersion-dominated interaction cannot be ignored. DFT calculations show that MnO2 nanostructures are promising drug carriers, and β-MnO2 exhibits better adsorption behavior than the other two crystals. Experimental study showed that the 5-FU drug loading of β-MnO2 (28.82 %) was higher than that of α-MnO2 (16.72 %) and δ-MnO2 (21.69 %).

Study on separation of methanol and dimethyl carbonate azeotropic system with deep eutectic solvents

Dimethyl carbonate (DMC) is an important diesel and gasoline additive that is also a low-toxic and environmentally friendly chemical raw material. However, it will form an azeotrope with methanol (MeOH) during the actual chemical production process. Therefore, separating high-purity DMC from the azeotrope is of significance. In extractive distillation, deep eutectic solvents (DESs) have demonstrated superior separation performance as green extractants. This study calculated the σ-profiles of DMC, MeOH, and DESs by the COSMO-SAC model to examine the most appropriate DES for the MeOH and DMC separation. Eventually, DES1(1:2 choline chloride (ChCl): malonic acid (MA)), DES2(1:2 ChCl: urea), DES3(1:2 ChCl: glycerol (G)), DES4(1:2 ChCl: ethylene glycol (EG)), DES5(1:2 ChCl: pyruvic acid (PA)) were designated as preferred extractants. The vapor pressures of five DESs at different temperatures were determined using a thermogravimetric analyzer, while their critical properties, normal boiling points, and acentric factors were predicted. The vapor–liquid equilibrium (VLE) data measured for DMC + MeOH + DESs ternary systems at 101.3 kPa showed that the addition of 15 mol % of any of the five DESs could successfully break the azeotrope and DES2 achieved a higher degree of separation in the MeOH-DMC binary azeotrope compared to the other DESs evaluated. The binary interaction parameters between MeOH/DMC and DESs were calculated through the NRTL (Non-Random Two-Liquid) model, and the fitting results were found to be consistent with the experimental data. The mechanism of the MeOH-DMC separation by DES2 was elucidated through quantum chemical (QC) calculations. The improved independent gradient model (IGMH) and the theory of atoms in molecules (AIM) demonstrated that the stronger interaction between DES2 and MeOH molecules is the key for DES2 to break the azeotrope of the system.

Modeling the Interaction between the Isoniazid Anti-Tuberculosis Drug and Functionalized Carbon Nanotubes for Medical Applications: A Quantum Chemical Study

Introduction: The purpose of using nano-carriers for drugs delivery, such as nanotubes, was slow release of drug and reducing side effects of drugs. Drugs are very active due to their many functional groups. Therefore, reactivity of drug is reduced by being in nanotube field due to electronic resonance of drug with nanotube and it stays longer in body. The present study aimed to investigate the interaction of isoniazid with functionalized single-walled carbon nanotubes.
 Methods: In the present theoretical study, considering the importance of isoniazid as the first line of treatment for tuberculosis disease, the performance of carbon nanostructures for adsorption of isoniazid was evaluated using quantum computation. Using density functional theory at theoretical level of B3LYP/6-31G** structure of drug and f-SWCNT and nano-drug complexes were optimized.
 Results: Effect of adsorption on the electronic properties and stability of the nanotube was also examined. In this regard, for different configurations, the strength and nature of intermolecular interactions were evaluated by energy parameters and molecular orbitals. Based on the obtained results, a specific configuration displayed the most negative adsorption energy and enthalpy, establishing itself as the most stable structure among the various configurations.
 Conclusion: Results showed that the electron density of the HOMO (Highest Occupied Molecular Orbital) was localized on the nanotube, while the electron density of the LUMO (Lowest Unoccupied Molecular Orbital) was situated on the drug molecule. The energy gap between two molecular orbitals increased due to the adsorption process; changes lead to an increase in the electrical conductivity of the complex following adsorption. According to the natural bond orbitals, results, the isoniazid molecule and functionalized single-walled carbon nanotube act as both electron donor and acceptor in the complex. Analysis of the results obtained from quantum theory of atoms in molecules, showed the intermolecular interaction between the drug and the functional group of the nanotube has been established, the most important of which is the hydrogen bond. Finally, the findings showed that functionalized SWCNTs can be acted as a drug carrier for isoniazid anti-tuberculosis drug.