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Plants from the Garcinia genus have been used worldwide due to their therapeutic properties. Among the various metabolites isolated from this genus, 7-epi-clusianone, a tetraprenylated benzophenone, stands out for its wide range of identified biological activities. This benzophenone can exist in five tautomeric forms, although the benzene-d 6 and chloroform-d 3 solution nuclear magnetic resonance (NMR) spectra revealed only two tautomeric forms (B and C) in equilibrium, with concentration ratio depending on the solvent in which the spectrum was obtained. Calculated energy values suggested that tautomeric forms B and E would be prevalent in benzene-d 6 solution, in contrast to the experimental data. Considering this conflicting result, we employed the statistical DP4 + method based on 13 C and 1 H NMR chemical shift calculations, in the gas phase and in benzene-d 6 solution, to confirm that the B and C tautomeric forms of 7-epi-clusianone are the most prevalent in the experimental conditions., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Nonlinear optical materials have been investigated recently due to their potential technological applications in information storage and communications. In this context, semi-organic crystals can effectively combine the desired nonlinear optical properties of amino acids with the promising mechanical and thermal properties of inorganic materials. In this work, we have synthesized and characterized a semi-organic crystal of the amino acid L-histidine and hydrofluoric acid and investigated the chemical interactions between the organic and inorganic moieties. The crystal of L-histidine bis(fluoride) has been produced by slow solvent evaporation and characterized by X-ray diffraction (XRD) crystallography and thermogravimetric and differential thermal analyses. The XRD conducted using the Rietveld method shows that the unit cell is orthorhombic with the P2 1 2 1 2 space group and contains four L-histidine bis(fluoride) units. Both differential thermal analysis and temperature-dependent XRD show that the crystals are thermally stable up to 191°C and do not undergo phase transition. The computational Hirshfeld surface analysis of the crystal structure reveals the main intermolecular interactions. Density functional theory has been employed to calculate the ionic interaction energy and electrostatic potential maps and confirm the spontaneity of ionic association at 191°C. The combined experimental and computational results show that the thermal stability of the semi-organic L-histidine bis(fluoride) crystal makes it suitable for nonlinear optical applications in optical sensing and communication systems., (© 2022. © Her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources Canada 2022.)

The quantum theory of atoms in molecules (QTAIM) and density functional theory (DFT) calculations were employed to investigate the structure and tautomeric equilibrium of epiclusianone, a polyisoprenylated benzophenone with interesting biological activities. Two different exchange-correlation functionals were employed, namely ωB97x-D and M06-2x, including implicit solvent models (benzene and DMSO). Our results for the thermodynamic properties show that the isomer in which the H atom is bonded to the oxygen away from the benzene ring is the most stable tautomer form of the epiclusianone, thus confirming previous charge density analysis from X-ray diffraction data (Martins et al. J Braz Chem Soc 18(8):1515-1523, 22).

Calcium complexes with bidentate carbonyl ligands are important in biological systems, medicine and industry, where the concentration of Ca 2+ is controlled using chelating ligands. The exchange of two water molecules of [Ca(H 2 O) 6 ] 2+ for one bidentate monosubstituted and homo disubstituted dicarbonyl ligand was investigated using the B3LYP/6-311++G(d,p) method. The ligand substituents NH 2 , OCH 3 , OH, CH 3 , H, F, Cl, CN and NO 2 are functional groups with distinct electron-donating and -withdrawing effects that bond directly to the sp 2 C atom of the carbonyl group. The geometry, charge and energy characteristics of the complexes were analyzed to help understand the effects of substituents, spacer length and chelation. Coordination strength was quantified in terms of the enthalpy and free energy of the exchange reaction. The most negative enthalpies were calculated for the coordination of bidentate ligands containing three to five methylene group spacers between carbonyls. The chelate effect contribution was analyzed based on the thermochemistry. The electronic character of the substituent modulates the strength of binding to the metal cation, as ligands containing electron-donor substituents coordinate stronger than those with electron-acceptor substituents. This is reflected in the geometric (bond length and chelating angle), electronic (atomic charges) and energetic (components of the total interacting energy) characteristics of the complexes. Energy decomposition analysis (EDA)-an approach for partitioning of the energy into its chemical origins-shows that the electrostatic component of the coordination is predominant, and yields relevant contribution of the covalent term, especially for the electron-withdrawing substituted ligands. The chelate effect of the bidentate ligands was noticeable when compared with substitution by two monodentate ligands. Graphical abstract The affinity of 18 bidentate carbonyl ligands toward the [Ca(H 2 O) 4 ] 2+ cation is evaluated in terms of energetic, geometric and electronic parameters of the isolated ligands and the substituted aqua complexes. The electronic effects-inductive and mesomeric-intrinsic to the molecular structure of each ligand are found to modulate the strength of the metal-ligand interaction. The effects of polysubstitution, chelation and the length of the alkyl spacers between the anchor points of the ligand are also analyzed.

The structures and energies for the Huisgen 1,3-dipolar cycloaddition reactions of methyl and ethyl azides with some cyclooctynes and dibenzocyclooctynes were computed at the B3LYP/6-311++G(d,p) level. The activation strain model (ASM) and quantitative molecular orbital (MO) theory were used to investigate the reactivity and regiochemistry in these reactions. The energy decomposition analysis (EDA) was used to identify the intrinsic electronic factor that lead to the preferential formation of 1,7-regiochemistry products. The reactivity order agrees with formation of more synchronous transition states and lower distortion energies. For the reaction of N 3 Met with azacyclooctyne, the 1,7-regiochemistry preference is attributed to a lower FMO gap and a higher contribution of the polarization term of the interaction energy than for the 1,8-transition state. For the reaction with aza-dibenzocyclooctyne, the 1,7-preference is due to a lower strain energy and a more pronounced contribution of the exchange term of the interaction energy. Graphical Abstract In the reactions between methyl and ethyl azides with azacyclooctynes the regiochemistry is governed by the intrinsic electronic factors.

The affinity of the pentaaqua Mg(2+) cation for a set of para-substituted imino [HN = CHC₆H₄(R)] and thiocarbonyl [S = CHC₆H₄(R)] ligands (R = H, F, Cl, Br, OH, OCH₃, CH₃, CN, NH₂ and NO₂) was analyzed with DFT (B3LYP/6-31+G(d)) and semi-empirical (PM6-DH2) methods. The interaction enthalpy was calculated to quantify the affinity of the Mg(2+) cation for the ligands. Additionally, geometric and electronic parameters were correlated with the intensity of the metal-ligand interaction. The imino ligands have stronger interaction with the pentaaqua Mg(2+) cation than the thiocarbonyl derivatives. The electronic nature of the substituent is the main parameter that determines the interaction enthalpy. Ligands with electron donor substituents have more exothermic interaction enthalpies than those with electron withdrawing groups. The HSBA analysis showed that the interaction between the Mg(2+) cation and hard bases (imino ligands) is stronger than with soft bases (thiocarbonyl derivatives). The EDA analysis showed that the electrostatic, covalent and repulsion components of the interaction are the most affected by the substituent, whereas the dispersion and exchange components are almost constant.