Pressure-Induced Structural Transformations and Electronic Transitions in TeO2 Glass by Raman Spectroscopy.

TeO2 glass has been studied by Raman spectroscopy up to the record pressure of 70 GPa. The boson peak frequency ωb exhibits a decrease of the ∂ωb/∂P slope at 5-6 GPa and saturates above 30 GPa with a practically constant value up to 70 GPa. Experiment and theory indicate that pressures up to 20 GPa induce the transformation of single Te-O-Te bridges to double Te-O2-Te bridges, leading to a more compact structure, while Raman activity developing at higher pressures around 580 cm-1 signals the increase of Te coordination from 4- to 6-fold. Natural bond orbital analysis shows that double Te-O2-Te bridges favor the s → d transition and promote the increase of Te coordination through d2sp3 hybridization. This transition leads to the formation of TeO6 octahedra, in strict difference with crystalline TeO2 at the same pressure range, and to the development of a 3D network that freezes the medium range order.

Linker Functionalization Strategy for Water Adsorption in Metal-Organic Frameworks.

Water adsorption in metal-organic frameworks has gained a lot of scientific attention recently due to the potential to be used in adsorption-based water capture. Functionalization of their organic linkers can tune water adsorption properties by increasing the hydrophilicity, thus altering the shape of the water adsorption isotherms and the overall water uptake. In this work, a large set of functional groups is screened for their interaction with water using ab initio calculations. The functional groups with the highest water affinities form two hydrogen bonds with the water molecule, acting as H-bond donor and H-bond acceptor simultaneously. Notably, the highest binding energy was calculated to be -12.7 Kcal/mol for the -OSO3H group at the RI-MP2/def2-TZVPP-level of theory, which is three times larger than the reference value. Subsequently, the effect of the functionalization strategy on the water uptake is examined on a selected set of functionalized MOF-74-III by performing Monte Carlo simulations. It was found that the specific groups can increase the hydrophilicity of the MOF and enhance the water uptake with respect to the parent MOF-74-III for relative humidity (RH) values up to 30%. The saturation water uptake exceeded 800 cm3/cm3 for all candidates, classifying them among the top performing materials for water harvesting.

On the Absence of Doubly Bonded Te═O Groups in TeO2 Glass.

Tellurium oxide clusters (TeO2)6 were investigated through density functional theory to gain information on the structure of TeO2 glass. Among a large number of stable conformers studied, a cyclic, nonsymmetric structure was optimized without terminal Te═O double bonds. The dimer of this structure, (TeO2)12, gives calculated Raman and infrared spectra in very good agreement with the experimental ones, with its total pair distribution function being also in agreement with results of neutron and high-energy X-ray diffraction studies. The (TeO2)12 cluster consists mainly of TeO4 units connected by asymmetric and nearly symmetric Te-O-Te bridges as in γ-TeO2 and involves also edge-sharing through double-oxygen Te-O2-Te bridges as in the ß-TeO2 polymorph. The optimized cluster structure is slightly unstable compared to the calculated global minimum structure, suggesting a kinetically stable product similar to its corresponding experimental TeO2 glass.

Examining barbiturate scaffold for the synthesis of new agents with biological interest.

Aim: Barbiturates have a long history of being used as drugs presenting wide varieties of biological activities (antimicrobial, anti-urease and antioxidant). Reactive oxygen species are associated with inflammation implicated in cancer, atherosclerosis and autoimmune diseases. Multitarget agents represent a powerful approach to the therapy of complicated inflammatory diseases. Results: A novel series of barbiturates has been synthesized and evaluated in several in vitro assays. Compound 16b (lipoxygenases inhibitor, 55.0 µM) was found to be a cyclooxygenase-2 inhibitor (27.5 µM). Compound 8b was profiled as a drug-like candidate. Conclusion: The barbiturate core represents a new scaffold for lipoxygenases inhibition, and the undertaken derivatives show promise as multiple-target agents to combat inflammatory diseases.

Canonical orbital contributions to the magnetic fields induced by global and local diatropic and paratropic ring currents.

The induced magnetic field (IMF) of naphthalene, biphenyl, biphenylene, benzocyclobutadiene, and pentalene is dissected to contributions from the total π system, canonical π-molecular orbitals (CMO), and HOMO→π* excitations, to evaluate and interpret relative global and local diatropicity and paratropicity. Maps of the IMF of the total π system reveal its relative strength and topology that corresponds to global and local diatropic and paratropic ring currents. The total π magnetic response is determined by this of canonical HOMOs and particularly by paratropic contributions of rotational excitations from HOMOs to unoccupied π* orbitals. Low energy excitations and similar nodal structure of HOMO and π* induce strong paratropic fields that dominate on antiaromatic rings. High energy excitations and different nodal structures lead to weak paratropic contributions of canonical HOMOs, which are overwhelmed by diatropic response of lower energy canonical orbitals in aromatic rings. CMO-IMF analysis is found in agreement with ring current analysis. © 2017 Wiley Periodicals, Inc.

Boronic Acid Group: A Cumbersome False Negative Case in the Process of Drug Design.

Herein we present, an exhaustive docking analysis considering the case of autotaxin (ATX). HA155, a small molecule inhibitor of ATX, is co-crystallized. In order to further extract conclusions on the nature of the bond formed between the ligands and the amino acid residues of the active site, density functional theory (DFT) calculations were undertaken. However, docking does not provide reproducible results when screening boronic acid derivatives and their binding orientations to protein drug targets. Based on natural bond orbital (NBO) calculations, the formed bond between Ser/Thr residues is characterized more accurately as a polar covalent bond instead of a simple nonpolar covalent one. The presented results are acceptable and could be used in screening as an active negative filter for boron compounds. The hydroxyl groups of amino acids are bonded with the inhibitor's boron atom, converting its hybridization to sp³.

Study of Electron Delocalization in 1,2-, 1,3-, and 1,4-Azaborines Based on the Canonical Molecular Orbital Contributions to the Induced Magnetic Field and Polyelectron Population Analysis.

The electron delocalization in 1,2-azaborine, 1,3-azaborine, and 1,4-azaborine is studied using canonical molecular orbital contributions to the induced magnetic field (CMO-IMF) method and polyelectron population analysis (PEPA). Contour maps of the out-of-plane component of the induced magnetic field (Bz(ind)) of the π system show that the three azaborines, in contrast with borazine, sustain much of benzene's π-aromatic character. Among them, 1,3-azaborine exhibits the strongest π delocalization, while 1,4-azaborine is the weakest. Contour maps of Bz(ind) for individual π orbitals reveal that the differentiation of the magnetic response among the three isomers originates from the π-HOMO orbitals, whose magnetic response is governed by rotational allowed transitions to unoccupied orbitals. The low symmetry of azaborines enables a paratropic response from HOMO to unoccupied orbitals excitations, with their magnitude depending on the shape of interacting orbitals. 1,3-Azaborine presents negligible paratropic contributions to Bz(ind) from HOMO to unoccupied orbitals transitions, where 1,2- and 1,4-azaborine present substantial paratropic contributions, which lead to reduced diatropic response. Natural bond orbital (NBO) analysis employing PEPA shows that only the 1,3-azaborine contains π-electron fully delocalized resonance structures.

Application of density functional theory in combination with FTIR and DSC to characterise polymer drug interactions for the preparation of sustained release formulations between fluvastatin and carrageenans.

In the present study, ι- and λ-carrageenans were used as appropriate carriers for sustained release formulations of fluvastatin drug. From viscosity measurements, it was found that both carrageenans can give miscible blends with fluvastatin due to the interactions between the sulfate groups of carrageenans and hydroxyl groups of fluvastatin. This was predicted by computational analysis using density functional theory and proved by FTIR spectroscopy. These interactions, which are in higher intensity using ι-carrageenan, lead to the formation of complexes between polymeric matrices and fluvastatin drug. DSC experiments also confirmed that miscible blends between carrageenans and fluvastatin can be formed since in all concentrations only one glass transition temperature was recorded. Fluvastatin release depends on the drug content and in all formulations of λ-carrageenans containing 10, 25 and 50 wt% drug, almost sustained release profiles were observed. Fluvastatin/carrageenan complexes have lower dissolution profiles compared with physical mixtures. Polymer swelling seems to be the dominant drug release mechanism. Besides to neat ι- and λ-carrageenans, their blends can be also used as effective matrices for sustained release.

Interpretation of electron delocalization in benzene, cyclobutadiene, and borazine based on visualization of individual molecular orbital contributions to the induced magnetic field.

The magnetic response of the valence molecular orbitals (MOs) of benzene, cyclobutadiene, and borazine to an external magnetic field has been visualized by calculating the chemical shielding in two-dimensional grids of points on the molecular plane and on a plane perpendicular to it, using gauge-including atomic orbitals (GIAOs). The visualizations of canonical MO contributions to the induced magnetic field (CMO-IMF) provide a clear view of the spatial extension, the shape, and the magnitude of shielding and deshielding areas within the vicinity of the molecule, originating from the induced currents of each valence orbital. The results are used to investigate the delocalization of each valence MO and to evaluate its contribution to the aromatic character of systems under study. The differentiation of the total magnetic response among the three molecules originates exclusively from π-HOMO orbitals because the magnetic response of the subsets of the remaining MOs is found to be almost identical. Borazine is classified as nonaromatic as the four electrons that occupy the π-HOMO are found to be strongly localized on nitrogen centers. CMO-IMF can clarify the interpretation of various NICS indexes and can be applied for the investigation of various types of electron delocalization.

Copper(I) complexes of 1,10-phenanthroline and heterocyclic thioamides: an experimental and theoretical (DFT) investigation of the photophysical characteristics.

A series of luminescent mixed ligand complexes of copper(I) halides with 1,10-phenanthroline and the heterocyclic thioamides pyridine-2(1H)-thione (py2SH), pyrimidine-2(1H)-thione (pymtH), 4,6-dimethylpyrimidine-2(1H)-thione (dmpymtH), 1,4,5,6-tetrahydropyrimidine-2-thione (tHpymtH), 1,3-imidazolidine-2-thione (imtH(2)) and 4,5-diphenyl-2-oxazolethiol (dpoxtH) have been synthesized and characterized. The molecular structures of two representative compounds have been established by single-crystal X-ray diffraction. The mononuclear complexes feature the metal in a distorted tetrahedral environment surrounded by the two N atoms of the chelating 1,10-phenanthroline, the thione-S atom of the thioamide, and the halogen atom. The molecular structure, the electronic and photophysical properties and the energetics of the metal-ligand interactions for [CuI(phen)(py2SH)] have been studied by means of density functional calculations.

Theoretical study of hydrogen bond interactions of fluvastatin with ι-carrageenan and λ-carrageenan.

The binding of the reductase inhibitor drug fluvastatin, hydroxy-3-methylglutaryl coenzyme A, with the hydrophilic ι- or λ-carrageenan polymers, serving as potential controllers of the drug's release rate, have been studied at the density functional level of theory with the B3LYP exchange correlation functional. Three low energy conformers of fluvastatin have been calculated. The vibrational spectroscopic properties calculated for the most stable conformer were in satisfactory agreement with the experimental data. A series of hydrogen bonded complexes of the most stable conformer of fluvastatin anion with low molecular weight models of the polymers have been fully optimized. In almost all, intermolecular H-bonds are formed between the sulfate groups of ι- or λ-carrageenan and fluvastatin's hydroxyls, resulting in a red shift of the fluvastatin's O - H stretching vibrations. Cooperative intramolecular H-bonds within fluvastatin or ι-, λ-carrageenan are also present. The BSSE and ZPE corrected interaction energies were estimated in the range 281-318 kJ mol⁻¹ for ι-carrageenan - fluvastatin and 145-200 kJ mol⁻¹ for λ-carrageenan - fluvastatin complexes. The electron density (ρ (bcp)) and Laplacian (∇²ρ (bcp)) properties at critical points of the intermolecular hydrogen bonds, estimated by AIM (atoms in molecules) calculations, have a low and positive character (∇²ρ(bcp) > 0), consistent with the electrostatic character of the hydrogen bonds. The structural and energetic data observed, as well as the extent of the red shift of the fluvastatin's O - H stretching vibrations upon complex formation and the properties of electron density show a stronger binding of fluvastatin to ι- than to λ-carrageenan.