M06-2X Functionals Research Articles

Unimolecular isomerizations of C6H6•+ radical cations: a computational study.

Eighteen concerted isomerization reactions of various C6H6•+ radical cation (RC) species are studied and found to proceed via well-defined transition states, whose relative positions along the reaction pathway generally agree with Hammond's postulate. From the barrier heights, the rate coefficients of these reactions are estimated by using transition state theory, and the activation energies are computed. Through combination among themselves, these 18 isomerizations yielded 15 multi-step conversion routes of various C6H6•+ species to the lowest energy benzene radical cation isomer 1, which routes are compared. Use is made of DFT with the B3LYP and M06-2X functionals, along with the CBS-QB3 approach to arrive at better energies. From the barrier heights for each of the concerted reactions, canonical transition state theory was applied to evaluate rate coefficients k over the temperature range 200-500K. The Arrhenius activation energies were computed using the plot of ln k vs. 1/T.

Gas Phase Proton Affinities of Proline-Containing Peptides. 1: ProGly, ProAla, ProVal, ProLeu, ProIle, and ProPro

The gas-phase proton affinities (PA) for a series of proline-containing dipeptides have been measured in an ESI triple quadrupole instrument using the extended kinetic method. Proton affinities of ProGly (1), ProAla (2), ProVal (3), ProLeu (4), ProIle (5), and ProPro (6) were determined to be 969.6 ±7.8, 990.4 ± 7.7, 987.6 ± 7.9, 982.8 ± 8.0, 988.8 ± 10.1, and 996.5 ± 12.2 kJ/mol, respectively. Predictions for the proton affinities for 1-6 were also obtained through isodesmic calculations at the B3LYP/6-311++G(d,p)//B3LYP/6-31+G(d) level of theory. The predicted proton affinities for 1 and 6 of 966.9 and 991.0 kJ/mol are in agreement with the experimental value. However, the predicted proton affinities for 2-5 of 973.5, 975.9, 975.7, and 975.9 are between 8 and 15 kJ/mol lower than the experimental values. Additional calculations with a larger basis set (B3LYP/6-311++G(2df,2p), inclusion of dispersion (B3LYP-D3/6-311++G(d,p)), switching to second order perturbation theory (MP2/6-31++G(d,p) and MP2/6-311++G(2df,2p), or switching density functional (M06-2x/6-311++G(d,p) and M06-2x/6-311++G(2df,2p) show only modest changes in derived thermochemistry lending support to the original calculations. We recommend using the experimental proton affinities for ProGly and ProPro and using the calculated values for ProAla, ProVal, ProLeu, and ProIle with the experimental proton affinities as upper limits.

Synthesis and study of nonlinear optical properties of an enaminone derived from dibenzoylmethane and N,N-diethylaminoaniline

The compound, (Z)-3-((4-(diethylamino)phenyl)amino)-1,3-diphenylprop-2-en-1-one, is synthesized by the reaction of dibenzoylmethane and 4-N,N-diethylaniline. The relative stabilities of the possible tautomers of the molecule are studied via the DFT B3LYP-D3BJ, CAM-B3LYP, M062X, and ωB97XD functionals in conjunction with the 6-311++G(d,p) basis set. The results showed that the enaminone tautomer with the intramolecularly hydrogen bonded chelated ring is the most stable. This is further confirmed by the Car–Parrinello MD calculations in the gas phase as well as the NCI analysis. The electronic spectrum is calculated by the TD DFT B3LYP/c-pVDZ level in ethanol, and the hole–electron analysis is carried out for the interpretation of the bands, which revealed that the longest one at 430 nm is of charge transfer origin while the others are of local transition origin. Atoms-in-molecules calculations in several media and levels of theory predicted that the ρBCP at the hydrogen bond in the gas phase to be 0.03791–0.04255 e/a0 3 which is a characteristic of a medium strong hydrogen bond. Researchers investigated the enaminone’s nonlinear optical (NLO) characteristics when it was exposed to a low power (<1 Watt), single fundamental transverse mode laser beam at 473 nm. By using diffraction patterns (DPs) and Z-scan methods, we calculated the nonlinear refractive index (NLRI) of the enaminone up to 4.597 × 10−11 m2 W−1 using DPs. The resulting DPs are numerically investigated using the Fraunhofer (F.) approximation and the Fresnel-Kirchhoff (F.K.) diffraction integral, showing excellent agreement with experimental findings. We successfully explored all-optical switching (AOS) in enaminone using two laser beams.

DFT study of difluoro & trifluoro bi-cyclohexane based dimer for application in electronic and optical devices

This investigation outlines a comprehensive analysis of the electronic and optical characteristics of difluoro and trifluoro bi-cyclohexane-based dimers in different conformations, specifically focusing on two distinct molecules: 4-(2,2,-difluorocyclopropyl)-4′-propyl-1,1′-bi(cyclohexane) and 4-propyl-4′-(1,2,2,-trifluorocyclopropyl)-1,1′-bi(cyclohexane). Utilizing Density Functional Theory (DFT) with advanced functionals M06-2X and B3LYP paired with a 6-311G(d,p) basis set, this study probes the interaction energy, orbital behaviors, and non-linear optical (NLO) properties across two primary molecular orientations such that in-plane and stacked.Our findings reveal that both configurations exhibit remarkable non-linear optical properties as evidenced by significant change in values of polarizability and hyperpolarizability, with the latter suggesting enhanced suitability for NLO applications. This study also ventures into frontier molecular orbital analysis, offering predictive insights into the chemical reactivity and charge transfer phenomena intrinsic to these molecular systems.

Tipping point to explain melamine’s non-planarity or otherwise. Can quasi-molecules be “seen” in the parent molecule?

The structure of melamine is optimized both at the DFT level with B3LYP and M06-2X functionals using AVTZ basis sets, and at ab initio level using DF-CCSD(T)/VDZ. Predicted planar with DFT when adding the zero-point-energy correction, it is a planar but distorted hexagonal triazine ring with three pyramidal amino groups at the coupled-cluster level. The potential energy surface of melanine is then expected to be rather flat near equilibrium. Both its planarity at the saddle point and non-planarity at equilibrium are deciphered, and pinpointed the role played by the embedded CNH2 quasi-molecules (tiles).

Electrochemical stability of low viscosity ion-pair electrolytes: Structure and interaction in quaternary ammonium-based Ionic liquid containing bis(trifluoromethylsulfonyl)imide anion and analogue

Quaternary ammonium-based ionic liquids (QAIL) consist of an aliphatic cation and possess characteristic properties different from those of aromatic (like imidazolium) with extensive cited applications. The redox stability of QA cations has attractively nominated them to achieve static and dynamic electrochemical phenomena. Herein, we investigated the influence of various anions (bis(fluorosulfonyl)imide [FSI]− and bis(trifluoromethylsulfonyl)imide [NTf2]−) on the structure, electronic, and electrochemical properties of low-viscosity ILs comprising QA cation (triethylpentyl ammonium [N2225]+) by employing highly versatile empirical exchange-correlation functional M06–2X in the context of density functional theory (DFT). The electronic structure, cation-anion interaction energy, dipole moment, cation-anion charge transfer, cathodic and anodic potential boundaries, electrochemical window (ECW), and density of state (DOS) were calculated and discussed. Liquid state studied by polarizable continuum model (PCM). The thermodynamics cycle method, an alternative to HOMO/LUMO method, was used to predict ECW's more realistic. ECWs for [N2225][FSI] ≥ [N2225][NTf2] were found to be wider than the experimental imidazolium counterpart by about two volts. [FSI]− anion is overwhelmingly involved in charge transfer with the cation compared to [NTf2]−. The more redox-stable [N2225][FSI] IL is expected to have less corrosive effects with metal electrodes because the anion (1) cis conformer takes a particular orientation relative to the cation, (2) has a higher charge transfer, and (3) F's atoms have a higher occupation number than [N2225][NTf2] IL. Therefore, these results provide insight for further investigation to expand the electrochemical application of redox-stable aliphatic QAILs involving the two targeted anions.

Predicting decomposition temperatures and carbonization feasibility of heterocycles with their decomposition mechanism

Pyrolysis of heterocyclic compounds such as Meldrum’s acid (MA) derivatives has been studied with focus on two key mechanisms analysing their energy barrier diagrams using the hybrid density functional theory method M06-2X. The feasibility of these decomposition reactions was calculated specifically for MA, monomethyl Meldrum’s acid (MMA), dimethyl Meldrum’s acid (DMMA), methylene Meldrum’s acid (MeMA) and (dimethylamino)methylene Meldrum’s acid (DMAMeMA), based on previous experimental analysis. The barrier to initial decomposition products (ketene or substituted ketenes with CO2 and acetone) were found to be endothermic requiring activation energies (∼180 – 230 kJ/mol) at decomposition temperatures of 280, 299, 301, 503 and 414 K respectively. Transition state theory calculations show MeMA and DMAMeMA are thermally more stable than other derivatives with low values for the rate constants and high energy barriers to produce initial decomposition products, suggesting they can produce fine carbon materials during carbonization. DMMA is found the best option for obtaining heteroatoms-doped carbon material formation.

Design amino acids Schiff base ligands and their Cu(II) and Zn(II) complexes as potent anticancer agent on human lung carcinoma, efficient CT-DNA binder, antibacterial and mesomorphic properties

A new mesogenic amino acid Schiff base ligands of the type Potassium (E)-4-((4-(hexadecyloxy)-2-hydroxybenzylidene)amino)butanoate (HL1) and Potassium (E)-6-((4-(hexadecyloxy)-2-hydroxybenzylidene)amino)hexanoate (HL2) and their copper(II) and zinc(II) complexes have been successfully synthesized and characterized by various elemental analyses, UV–visible, FT-IR, 1HNMR , 13CNMR , ESI-MS and thermogravimetric analysis (TGA). Both the ligands were found to exhibit mesophase with multiple textures as revealed from the polarizing optical microscope (POM) and differential scanning calorimetry (DSC). The metal complexes were found to exhibit efficient CT-DNA interaction and antibacterial activity against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli). The complexes were assessed for their in-vitro anticancer efficacy against A549 cell line and findings indicate notable cytotoxicity effect which is comparable to that of standard drug, cisplatin. The Density Functional Theory (DFT) study of the compounds was carried out by using LanL2DZ and 6–31 G (d, p) basis set with meta-hybrid Truhlar's functional M06–2X in order to obtain the optimized geometry.

Evaluation of DFT methods for predicting geometries and NMR spectra of Bi(III) dithiocarbamate complexes with antitumor properties.

Bismuth complexes with dithiocarbamate ligands have attracted attention because of their biological applications, such as antimicrobial, antileishmanial, and anticancer properties. These complexes have high cytotoxic activity against cancer cells, being more active than the standard drugs cisplatin, doxorubicin, and tamoxifen. In the present study, we investigated the ability of some DFT methods to reproduce the geometries and NMR spectra of the Bi(III) dithiocarbamate complexes, selected based on their proven antitumor activity. Our investigation revealed that the M06-L/def2-TZVP/ECP/CPCM method presented good accuracy in predicting geometries, while the TPSSh/def2-SVP/ECP/CPCM method proved effective in analyzing the 13C NMR spectra of these molecules. In general, all examined methods exhibited comparable performance in predicting 1H NMR signals. Calculations were performed with the Gaussian 09 program using the def2-SVP and def2-TZVP basis sets, employing relativistic effective core potential (ECP) for Bi and using the CPCM solvent model. The exchange-correlation functionals BP86, PBE, OLYP, M06-L, B3LYP, B3LYP-D3, M06-2X, TPSSh, CAM-B3LYP, and ωB97XD were used in the study. Geometry optimizations were started from crystallographic structures available at the Cambridge Structural Database. The theoretical results were compared with experimental data using the mean root-mean-square deviation (RMSD), mean absolute deviations (MAD), and linear correlation coefficient (R2).

Insights on molecular modeling and supramolecular arrangement of bilastine polymorphs.

The advancement in the development of second-generation drugs in the field of antihistamines represents a significant milestone in the management of allergic diseases, targeting the effects of histamine. The efficacy of bilastine in treating allergic disorders has sparked interest in investigating its polymorphism, a crucial property that impacts quality, safety, and effectiveness as per regulatory guidelines. This study examines the polymorphism of bilastine, focusing on two crystalline forms labeled as Form I and Form II. Utilizing advanced analytical techniques, the research explores the structural characteristics and molecular interactions within these forms. Geometric parameters, such as bond lengths, bond angles, and torsion angles, are examined to comprehend molecular conformations and crystal packing arrangements. Hydrogen bonding, covalent bonds, and van der Waals forces contribute to the unique supramolecular arrangements in these forms.This study provides a significant contribution to understanding bilastine's polymorphism, offering critical insights to researchers and regulatory bodies to ensure the quality, efficacy, and safety of antihistamine products. The molecular conformation of two bilastine forms was obtained through DFT with the exchange-correlation functional M06-2X and the 6-311 + + G(d,p) basis set, and the results were compared with the experimental X-ray. The atomic coordinates were obtained directly from the crystalline structures, and charge transfer was also investigated using frontier molecular orbitals (HOMO and LUMO), and MEP map in order to evaluate the energies associated with charge transfers and regions of high electron affinity. The geometric and topological parameters and intermolecular interactions in the crystals were analyzed using Hirshfeld Surface.

Theoretical Study on the Regioselectivity of Leapfrog B18 and B30 Boron Sheets in Electrophilic and Nucleophilic Reactions Using DFT-Based Reactivity Indices.

A combined computational and interpretational DFT study is performed to investigate the regioselectivity of B18 and B30 leapfrog boron sheets upon reaction with XH3-type electrophiles and nucleophiles (X = N, P, As, B, Al). The M062X, B3LYP, and B3LYP-D3 functionals are used combined with the 6-31+G(d,p) basis. The molecular electrostatic potential (MEP), Fukui functions, and the dual descriptor are employed to predict the local reactivity of B18 and B30. Our results reveal that both clusters are hard and prefer to react with hard bases and acids, such as NH3 and BH3. Further, these leapfrog B6n clusters can play the role of catalysts as they break B-H and Al-H bonds of BH3 and AlH3 in s-BH3-B6n and s-AlH3-B6n complexes, respectively. Leapfrog B6n-XH3 complexes (X = B and Al) can be considered as an interaction between two electron-deficient systems. Therefore, the chemical reactivity between these systems cannot be interpreted in terms of the Hard-Soft-Acid-Base principle.

Theoretical Study on the Mechanisms and Kinetics of Atmospheric Oxidation of Tetrafluoropropyne and Its Analogues.

Tetrafluoropropyne (C3F4) is a potential dielectric in various electrical insulating equipment to replace the most potent industrial greenhouse gas, sulfur hexafluoride. Atmospheric oxidation of C3F4 by OH radicals in the presence of molecular O2 has been investigated theoretically in order to clarify the lifetime and degradation products at mechanistic and kinetic aspects. Energetic minimum-energy pathways for the C3F4 + OH/O2 reactions were calculated in detail using various theoretical methods including density functional M06-2X and CCSD for geometries, CBS-QB3, CCSD(T), and multireference RS2 with extrapolation to the complete basis-set limit for energies. It has been demonstrated that the C3F4 + OH reaction takes place via the bifurcated C-O addition/elimination routes leading to CF3C(OH)═CF and CF3C═C(OH)F radical adducts, where the latter is more preferable in view of the difference in barrier heights (1.3 vs 0.3 kcal/mol), followed by H-migration, HF-elimination, and C-C and C-F bond fission. The atmospheric lifetime of C3F4 was estimated to be about 13 days, which is indicative of a very short-lived substance in the atmosphere. Further degradation of the energy-rich C3F4OH* intermediates by O2 takes place spontaneously in view of the successive barrier-free and highly exothermic pathways, producing a variety of fluorinated acids, anhydrides, biacetyls, and regenerating OH radicals. For comparison, the reactions of C3H4, CF3CCH, and CH3CCF with OH radicals were examined to clarify the F-substitution effect. It is revealed that the reactivity of fluoropropynes could be either reduced by CF3 or enhanced by atomic F attached to the acetylenic carbon. The present work provides a fundamental understanding of the reactions of fluoroalkynes with OH/O2. The use of C3F4 as a promising eco-friendly gaseous dielectric alternative to SF6 has been supported.

Ab Initio and Kinetic Modeling of β-d-Xylopyranose under Fast Pyrolysis Conditions.

Lignocellulosic biomass is an abundant renewable resource that can be upgraded to chemical and fuel products through a range of thermal conversion processes. Fast pyrolysis is a promising technology that uses high temperatures and fast heating rates to convert lignocellulose into bio-oils in high yields in the absence of oxygen. Hemicellulose is one of the three major components of lignocellulosic biomass and is a highly branched heteropolymer structure made of pentose, hexose sugars, and sugar acids. In this study, β-d-xylopyranose is proposed as a model structural motif for the essential chemical structure of hemicellulose. The gas-phase pyrolytic reactivity of β-d-xylopyranose is thoroughly investigated using computational strategies rooted in quantum chemistry. In particular, its thermal degradation potential energy surfaces are computed employing Minnesota global hybrid functional M06-2X in conjunction with the 6-311++G(d,p) Pople basis set. Electronic energies are further refined by performing DLPNO-CCSD(T)-F12 single-point calculations on top of M06-2X geometries using the cc-pVTZ-F12 basis set. Conformational analysis for minima and transition states is performed with state-of-the-art semiempirical quantum chemical methods coupled with metadynamics simulations. Key thermodynamic quantities (free energies, barrier heights, enthalpies of formation, and heat capacities) are computed. Rate coefficients for the initial steps of thermal decomposition are computed by means of reaction rate theory. For the first time, a detailed elementary reaction kinetic model for β-d-xylopyranose is developed by utilizing the thermodynamic and kinetic information acquired from the aforementioned calculations. This model specifically targets the initial stages of β-d-xylopyranose pyrolysis in the high-pressure limit, aiming to gain a deeper understanding of its reaction kinetics. This approach establishes a systematic strategy for exploring reactive pathways, evaluating competing parallel reactions, and selectively accepting or discarding pathways based on the analysis. The findings suggest that acyclic d-xylose plays a significant role as an intermediary in the production of key pyrolytic compounds during the pyrolysis of xylose. These compounds include furfural, anhydro-d-xylopyranose, glycolaldehyde, and dihydrofuran-3(2H)-one.

Antiparasitic activity, DNA/BSA binding interaction, molecular docking and DFT studies of mesogenic l-leucine based Schiff base and its derivatize Cu(II) and Zn(II) complexes

A new copper(II) and zinc(II) complexes derived from smectogenic l-leucine methyl ester Schiff base ligand have been successfully synthesized and characterized by various techniques. The ligand is found to exhibit SmA mesophase but Cu(II) and Zn(II) complexes do not. The biological importances of the compounds are evaluated using photophysical techniques to comprehend the binding interaction with biomolecules viz., CT-DNA and BSA. The compounds were assessed for their in-vitro anti-parasitic efficacy against Leishmania donovani by MTT assay. Notably, all the compounds exhibited IC50 in the range of 31.29 to 57.01 (μM). Molecular docking was performed in order to establish the nature of binding ability of the compounds with CT-DNA. The computational studies indicate that the CuL2 has the maximum DNA interaction as revealed from libDock score. The Density Functional Theory (DFT) study was performed in order to ascertain the optimized geometry of the compounds using LanL2DZ and 6–31 G (d, p) basis set with meta-hybrid Truhlar's functional M06–2X.

An Assessment of Dispersion-Corrected DFT Methods for Modeling Nonbonded Interactions in Protein Kinase Inhibitor Complexes.

Accurate modeling of nonbonded interactions between protein kinases and their small molecule inhibitors is essential for structure-based drug design. Quantum chemical methods such as density functional theory (DFT) hold significant promise for quantifying the strengths of these key protein-ligand interactions. However, the accuracy of DFT methods can vary substantially depending on the choice of exchange-correlation functionals and associated basis sets. In this study, a comprehensive benchmarking of nine widely used DFT methods was carried out to identify an optimal approach for quantitative modeling of nonbonded interactions, balancing both accuracy and computational efficiency. From a database of 2139 kinase-inhibitor crystal structures, a diverse library of 49 nonbonded interaction motifs was extracted, encompassing CH-π, π-π stacking, cation-π, hydrogen bonding, and salt bridge interactions. The strengths of nonbonded interaction energies for all 49 motifs were calculated at the advanced CCSD(T)/CBS level of theory, which serve as references for a systematic benchmarking of BLYP, TPSS, B97, ωB97X, B3LYP, M062X, PW6B95, B2PLYP, and PWPB95 functionals with D3BJ dispersion correction alongside def2-SVP, def2-TZVP, and def2-QZVP basis sets. The RI, RIJK, and RIJCOSX approximations were used for selected functionals. It was found that the B3LYP/def2-TZVP and RIJK RI-B2PLYP/def2-QZVP methods delivered the best combination of accuracy and computational efficiency, making them well-suited for efficient modeling of nonbonded interactions responsible for molecular recognition of protein kinase inhibitors in their targets.

New Cap-Holed AlP, GaP, and InP Nanotubes.

The structural, vibrational, and electronic properties of new inorganic X-phosphide nanotubes (ch-XPNT), with X = Al, Ga, or In and chirality of (5,5), are investigated. These new NTs display cap-hole ends, with the cap-hole features induced by the nonpassivated ends. Studies are based on density functional theory (DFT) using the M06-2X, PBE, and B3LYP functionals together with the LanL2DZ basis set. All nanostructures have been relaxed by minimizing the total energy, assuming a nonmagnetic nature and a total neutral charge. Note that the cap-hole NTs are terminated by a 10-atom ring, which in turn favors the geometrical ordering and yields stable structures. The (5,5) ch-XPNT are highly electrophilic and nonpolar, in addition to having high solvation energy values. Let us remark that solvation energies are produced by the intermolecular forces that involve the induced dipoles. Structural and vibrational results show that the X-P bonds are single bonds. Finally, results suggest that the inorganic nanotubes are structurally stable with semiconductor features, which means that their functionalization may yield interesting future applications.

Big data benchmarking: how do DFT methods across the rungs of Jacob's ladder perform for a dataset of 122k CCSD(T) total atomization energies?

Total atomization energies (TAEs) are a central quantity in density functional theory (DFT) benchmark studies. However, so far TAE databases obtained from experiment or high-level ab initio wavefunction theory included up to hundreds of TAEs. Here, we use the GDB-9 database of 133k CCSD(T) TAEs generated by Curtiss and co-workers [B. Narayanan, P. C. Redfern, R. S. Assary and L. A. Curtiss, Chem. Sci., 2019, 10, 7449] to evaluate the performance of 14 representative DFT methods across the rungs of Jacob's ladder (namely, PBE, BLYP, B97-D, M06-L, τ-HCTH, PBE0, B3LYP, B3PW91, ωB97X-D, τ-HCTHh, PW6B95, M06, M06-2X, and MN15). We first use the A25[PBE] diagnostic for nondynamical correlation to eliminate systems that potentially include significant multireference effects, for which the CCSD(T) TAEs might not be sufficiently reliable. The resulting database (denoted by GDB9-nonMR) includes 122k species. Of the considered functionals, B3LYP attains the best performance relative to the G4(MP2) reference TAEs, with a mean absolute deviation (MAD) of 4.09 kcal mol-1. This first-generation hybrid functional, in which the three mixing coefficients were fitted against a small set of TAEs, is one of the few functionals that are not systematically biased towards overestimating the G4(MP2) TAEs, as demonstrated by a mean-signed deviation (MSD) of 0.45 kcal mol-1. The relatively good performance of B3LYP is followed by the heavily parameterized M06-L meta-GGA functional, which attains a MAD of 6.24 kcal mol-1. The PW6B95, M06, M06-2X, and MN15 functionals tend to systematically overestimate the G4(MP2) TAEs and attain MADs ranging between 18.69 (M06) and 28.54 (MN15) kcal mol-1. However, PW6B95 and M06-2X exhibit particularly narrow error distributions. Thus, scaling their TAEs by an empirical scaling factor reduces their MADs to merely 3.38 (PW6B95) and 2.85 (M06-2X) kcal mol-1. Empirical dispersion corrections (e.g., D3 and D4) are attractive, and therefore, their inclusion worsens the performance of methods that systematically overestimate the TAEs.

Structure and dynamics of liquid water from ab initio simulations: adding Minnesota density functionals to Jacob's ladder.

The accurate representation of the structural and dynamical properties of water is essential for simulating the unique behavior of this ubiquitous solvent. Here we assess the current status of describing liquid water using ab initio molecular dynamics, with a special focus on the performance of all the later generation Minnesota functionals. Findings are contextualized within the current knowledge on DFT for describing bulk water under ambient conditions and compared to experimental data. We find that, contrary to the prevalent idea that local and semilocal functionals overstructure water and underestimate dynamical properties, M06-L, revM06-L, and M11-L understructure water, while MN12-L and MN15-L overdistance water molecules due to weak cohesive effects. This can be attributed to a weakening of the hydrogen bond network, which leads to dynamical fingerprints that are over fast. While most of the hybrid Minnesota functionals (M06, M08-HX, M08-SO, M11, MN12-SX, and MN15) also yield understructured water, their dynamical properties generally improve over their semilocal counterparts. It emerges that exact exchange is a crucial component for accurately describing hydrogen bonds, which ultimately leads to corrections in both the dynamical and structural properties. However, an excessive amount of exact exchange strengthens hydrogen bonds and causes overstructuring and slow dynamics (M06-HF). As a compromise, M06-2X is the best performing Minnesota functional for water, and its D3 corrected variant shows very good structural agreement. From previous studies considering nuclear quantum effects (NQEs), the hybrid revPBE0-D3, and the rung-5 RPA (RPA@PBE) have been identified as the only two approximations that closely agree with experiments. Our results suggest that the M06-2X(-D3) functionals have the potential to further improve the reproduction of experimental properties when incorporating NQEs through path integral approaches. This work provides further proof that accurate modeling of water interactions requires the inclusion of both exact exchange and balanced (non-local) correlation, highlighting the need for higher rungs on Jacob's ladder to achieve predictive simulations of complex biological systems in aqueous environments.

Nonlinear optical and spectroscopic properties, thermal analysis, and hemolytic capacity evaluation of quinoline-1,3-benzodioxole chalcone.

This article describes the synthesis, characterization (1H NMR, 13C NMR, FT-IR, HRMS and XRD), UV-Vis absorption and fluorescence spectra, theoretical analysis, evaluation of nonlinear optical properties (NLO), thermal analysis and determination of the hemolytic capacity of the compound (E)-N-(4-(3-(benzo[d][1,3]dioxol-5-yl)acryloyl)phenyl)quinoline-3-carboxamide (5). Radiological findings showed that compound 5 crystallized in space group Pca21. Furthermore, theoretical DFT studies performed with the B3LYP and M062X functionals showed good agreement with the experimental results and provided valuable information on the molecular and electronic structure, reactivity, polarizability, and kinematic stability of the compound. Besides, compound 5 did not show any hemolytic effect on human erythrocytes and exhibited strong NLO properties. The TG and DTA thermograms of quinoline-chalcone (5) revealed a multi-step thermal decomposition process with a total mass loss of 83.2%, including water content loss. The DTA curves exhibited endothermic peaks corresponding to decomposition steps, melting point, and thermochemical transition. Additionally, exothermic peaks in the DTA thermograms align with significant mass loss, confirming the compound's melting point and water content, as validated by X-ray diffraction analysis. These results contribute to the advancement of research on compounds with NLO properties and offer a promising avenue for the development of substances potentially applicable to optical devices in the biomedical field.

Effects of solvents on structure and energy of 6-amino-2-mercapto-3H-pyrimidin-4-one: A computational study

6-amino-2-mercapto-3H-pyrimidin-4-one (AMP) is a π-conjugated organic molecule extensively used as a semiconductor in many optoelectronic devices. The computational hybrid meta-generalized gradient Minnesota M06-2x, ωB97XD, and B3LYP functionals in conjunction with the correlation consistent polarized valence triplet zeta (cc-pVTZ) basis set and the moderate composite CBS-QB3 procedure were used with the aid of the Gaussian 09 program and the kinetic and statistical thermodynamical package (KiSThelP) in the temperature range 250–400 K to investigate the behavior of AMP in the gas phase, and in different polar (water, ethanol), and non-polar (dimethyl sulfoxide (DMSO), acetone)) solvents. Non-linear optical (NLO) characteristics and quantum chemical parameters were examined. Natural bond orbital analysis (NBO) was used to characterize the charge transfer of the electron density in the investigated compounds. The quality of the methods used was inspected and compared to give accurate results. The stability of AMP can be returned to the hyper conjugative interactions that leading to its nonlinear optical activity. Also, the charge delocalization was analyzed using natural bond orbital technique. The molecular electrostatic potential surfaces (MEPS) plots have been generated. The rate coefficients of tautomerization processes (kuni, in s−1) were calculated from the transition state theory (TST) and unimolecular Rice-Ramsperger-Kassel-Marcus (RRKM) methods. The results indicate comparable chemical rates obtained from TST and RRKM. In addition, positive temperature dependencies were located for all channels and a high dominance of transferring H-atom from the external N-atom to the S-atom (R3 reaction) during the applied temperature range which can return to its lower activation energy. This study is the first stone in studying AMP under different conditions such as the atmosphere, combustion conditions and as a nano catalyst.