Structural Chemistry最新文献

In this study, we demonstrate that quantum-chemical calculations can be successfully employed in a priori estimation of the thermal properties of alkylammonium hydrogen sulfate protic ionic liquids (PILs) and show how these characteristics can be controlled by altering the cation structure. The geometries, charge distributions, energies of the highest occupied and lowest unoccupied molecular orbitals, proton affinities, and dipole moments of the ammonium cation and some of its alkyl derivatives are investigated by the dispersion-corrected density functional theory (DFT-D) method in the gas phase and in the dielectric medium applying the conductor-like polarizable continuum model. The correlations between the calculated characteristics of the single cations and the thermal properties of the alkylammonium hydrogen sulfates are analyzed. The findings indicate that the melting temperature of the specified PILs has a more pronounced correlation with the dipole moment of the cation while the decomposition temperature correlates well with the lowest unoccupied molecular orbital energy. These cation parameters are used to construct one-parameter models to evaluate the thermal properties of the PILs. The resultant data form the basis for designing new alkylammonium hydrogen sulfates. The experimental values of the melting and decomposition temperatures of the newly synthesized PIL, methylpropylammonium hydrogen sulfate, are found to be in exact agreement with the values calculated using the models.

Proteins/polypeptides are a large class of organic/biochemical/biomedical related molecules most simply and most generally described by the generic structure NH₂CH(R¹)CONHCH(R²)CONHCH(R³),,, NHCH(R^{some large number})COOH, or more properly as the corresponding zwitterion. In these species, R¹, R², R^{some large number} are arbitrarily chosen from a well-defined collection of some 20 affixed groups. The archetypal example is polyglycine, the related “shorter” glycine, diglycine … hexaglycine. For these species, all of these R groups are H and much of their understanding has come from calorimetric determinations of their enthalpies of formation, and more recently high-level quantum chemical calculations. In the current study, we ask the question given as the title of this paper “If polyglycine is the polymer, then what is the monomeric repeating unit)?” Three natural choices are given, − CH₂–CO–NH − , − NH–CH₂ − CO–, or − CH₂–NH–CO − . From the analysis of the energetics of the related dimer, 2,5-diketopierazine, we demonstrate that these choices are in fact equivalent.

Piroctone olamine, an antifungal agent used in anti-dandruff cosmetics, was studied to characterize its structure and physicochemical properties, along with its complex with 2-amino-1-ethanol. Using DFT methods, geometry optimization and calculations of thermodynamic, electronic, and reactivity parameters were performed. Spectroscopic techniques (FTIR, Raman, UV–Vis, and spectrofluorimetry) supported experimental data interpretation. Molecular docking and dynamics simulations revealed stable piroctone-protein interactions, indicating potential pharmacological relevance beyond antifungal activity. This research enhances understanding of 1-hydroxy-2-pyridinone derivatives and their broader therapeutic potential.

In a series of three chiral thioureas bearing a tetrahydronaphthyl fragment, none of the homochiral samples forms “true chiral” hydrogen-bonded motifs in the crystal. In all three cases, the addition of a second independent molecule to the cell is observed. In one case, a pseudosymmetric dimer was found in the crystal, and in the other two cases, a chain motif with alternation of independent molecules was found. The conformational transformations of the thiourea fragment are considered.

Zeolites are valued and extensively used industrially silicate materials with microporous framework structures containing uniform channels typically below 1 nm in diameter. The efforts to synthesize new frameworks and crystal forms revealed another exceptional trait of zeolites, namely, that for the same topology, 2 forms are possible: the standard extended 3D crystals and 2D materials composed of nanosheets with uniform thickness below approximately 3 nm. The latter can be converted to 3D frameworks by topotactic condensation, e.g., upon thermal treatment. They are named formally as layered zeolite precursors. So far, approximately 20 such precursors have been identified out of over 250 recognized 3D frameworks, but the number is gradually increasing (of both). Herein we analyze 2 recently reported structures designated ITQ-8 and PKU-22. ITQ-8 was described as related to zeolite levyne (LEV; zeolite structures are denoted with three letter codes) but its parent framework remained unrecognized. By analyzing structures in the online zeolite database, we identified SAS as the parent framework of ITQ-8, its formal precursor. The mentioned LEV topology is produced by joining the sas layers with additional single atoms, making it formally the so-called interlayer expanded zeolite form (IEZ). The layers of ITQ-8 and PKU-22 (parent structure stilbite, STI) are lacking in-plane mirror plane and produce different topologies by translation and mirror reflection operations. In addition to detailed presentation of the structures, we provide suggestions for experimental transformation of ITQ-8 and PKU-22 to the corresponding 3D frameworks.

Interaction of A(HSeO₃) [A = K, Rb, Cs, (NH₄)] and CdX₂ (X = Cl, Br) in aqueous solutions results in crystallization of multinary hydroselenite halides. The overwhelming majority of the products correspond to the ACd(HSeO₃)X₂ composition and crystallize in triclinic symmetry similarly to the recently reported ACu(HSeO₃)X₂. Yet, the only exception is KCd(HSeO₃)₂Br, which expands the chemistry of the “layered hydroselenite” A_n(H₂O)_m[M(HSeO₃)₂X_n] family (M = Cu, Co, Zn; n = 1, 2). Formation of the two possible stoichiometries of the metal hydroselenite halide frameworks, [M(HSeO₃)X₂]^– vs. [M(HSeO₃)₂X]^–, (M = Cu, Cd; X = Cl, Br) is likely to depend on both the synthesis conditions and the r(A⁺)/r(X^–) ratio. The potassium-free substructure of the triclinic ACd(HSeO₃)X₂ is represented by a planar net comprised of trans-CdO₂X₄ octahedra and hydroselenite anions. If the dimer of anions instead of the monomer is considered a secondary building unit (SBU), the net acquires a kagome net-like topology. The potassium-free substructure of monoclinic KCd(HSeO₃)₂Br is represented by planar nets, and upon considering SBU = (HSeO₃)₂ instead of (HSeO₃), one obtains a simple square net.

Geometric, electronic, and nonlinear optical features of a new class of excess electrons, i.e., alkaline earthides have been examined. The rational design principle involves inserting transition metals inside the 3⁶adz to serve as a source of excess electron for Mg metal doped on the outer face of the cage, i.e., M⁺(3⁶adz)Mg⁻ (where M⁺ is V to Zn). By using 3⁶adz as a complexant, eight different complexes are investigated. The electronic and thermodynamic stability of complexes is evaluated from their vertical ionization potential and interaction energies, respectively. The true alkaline earthide feature of the complexes is validated through natural bond orbital (NBO) charges, molecular electrostatic potential (MEP), and frontier molecular orbital (FMO) analysis. Further validity of the earthide feature of computed complexes is signified graphically through spectra of partial density of states (PDOS). Moreover, the HOMO–LUMO energy gap (H–L gaps) of all compounds are very small (2.40 to 5.51 eV), when compared with the H–L gap of pure cage, i.e., 8.50 eV. All these properties reward the complexes with quite small values of transition energies ranging from 0.79 to 1.19 eV which ultimately results in unusually enhanced hyperpolarizability up to 6.17 × 10⁵ au for Zn⁺(3⁶adz)Mg⁻ compound of the series. Furthermore, the hyperpolarizability projection over dipole moment is determined by calculating β_vec values. Additionally, the application of an external electric field (EEF) on the computed complexes increases the hyperpolarizability further. The notable enhancement of 1000-fold in hyperpolarizability has been seen for Cr⁺(3⁶adz)Mg⁻ compound after applying EEF, i.e., from 2.26 × 10⁴ au to 1.5 × 10⁷ au, when compounds are exposed to EEF of 1 × 10⁻³ au strength.

A self-consistent approach is proposed for the basis set extrapolation of Hartree–Fock (HF) energies. Similar to existing extrapolation techniques, our scheme is based on convergent basis set hierarchies such as correlation-consistent basis sets. However, unlike the former, which utilize two or more HF energies obtained in separate HF calculations, the present method approximates the complete basis set limit HF energy in a single self-consistent field calculation minimizing a simple energy functional. Our benchmark results demonstrate that the performance of the self-consistent extrapolation approach is very similar to that of the conventional ones. The major advantage of the self-consistent technique is that the variational nature of the extrapolated energy facilitates the evaluation of analytic derivatives.

Phosphorene has emerged as a promising drug carrier for anticancer applications. In this study, density functional theory (DFT) and MD were employed to investigate the adsorption of curcumin on pristine phosphorene, stone wales (SW) defected phosphorene, and B, N, and Si-doped phosphorene (both pristine and SW defective). The oxygen atom of curcumin preferentially interacts with the phosphorene carriers, exhibiting the highest BSSE-corrected adsorption energies observed for PhswB@C (− 0.240 eV) and PhB@C (− 0.223 eV). Doping and curcumin adsorption reduce the energy gap (Eg), with PhswB@Cand PhB@C exhibiting E_g values of 1.096 and 1.922 eV, respectively. Natural bond orbital (NBO) analysis indicates charge transfer from curcumin to the carrier, while electron localization function (ELF) analysis reveals subtle variations in electron density, particularly for PhB and PhswB. Density of states (DOS) analysis highlights significant electronic modifications upon complex formation. The QTAIM analysis confirms strong non-covalent interactions and high G(r)/V(r) ratios for PhB@C. Time-dependent DFT (TD-DFT) calculations reveal red and blue shifts in λmax within the visible and shortwave infrared (SWIR) regions. PhB and PhswB complexes exhibit high dipole moments, enhanced chemical reactivity, and greater softness. The molecular dynamical behavior of the PhB@C and PhswB@C complexes exhibits greater stability, high drug loading capacity, and controlled drug release. Thus, PhB and PhswB carriers are identified as most promising candidates for curcumin delivery in cancer therapy.