Ligand-Receptor Interactions of : A View from Charge Density Study and QM/MM Calculations.

The nature and strength of interactions for an anti-HIV drug, , were studied in a pure crystal form of the drug and the ligand-receptor complexes. High-resolution single-crystal X-ray diffraction studies of the tetragonal polymorph allowed the drug's experimental charge density distribution in the solid state to be obtained. The QM/MM calculations were performed for a simplified model of the complex with deoxycytidine kinase (two complexes with different binding modes) to reconstruct the theoretical charge density distribution.

Octahedra-Tilted Control of Displacement Disorder and Dielectric Relaxation in Mn-Doped SrTiO Single Crystals.

Strontium titanate SrTiO (STO) is a canonical example of a quantum paraelectric, and its doping with manganese ions unlocks its potential as a quantum multiferroic candidate. However, to date, the specifics of incorporation of the manganese ion into the perovskite lattice and its impact on structure-property relationships are debatable questions. Herein, using high-precision X-ray diffraction of a Mn (2 atom %)-doped STO single crystal, clear fingerprints of the displacement disorder of Mn cations in the perovskite B-sublattice are observed.

Energetic [1,2,5]oxadiazolo [2,3-]pyrimidin-8-ium Perchlorates: Synthesis and Characterization.

A convenient method to access the above perchlorates has been developed, based on the cyclocondensation of 3-aminofurazans with 1,3-diketones in the presence of HClO. All compounds were fully characterized by multinuclear NMR spectroscopy and X-ray crystal structure determinations. Initial safety testing (impact and friction sensitivity) and thermal stability measurements (DSC/DTA) were also carried out.

Real-Space Interpretation of Interatomic Charge Transfer and Electron Exchange Effects by Combining Static and Kinetic Potentials and Associated Vector Fields.

Intricate behaviour of one-electron potentials from the Euler equation for electron density and corresponding gradient force fields in crystals was studied. Channels of locally enhanced kinetic potential and corresponding saddle Lagrange points were found between chemically bonded atoms. Superposition of electrostatic and kinetic potentials and electron density allowed partitioning any molecules and crystals into atomic - and potential-based -basins; -basins explicitly account for the electron exchange effect, which is missed for -ones.

Orbital-Free Quantum Crystallographic View on Noncovalent Bonding: Insights into Hydrogen Bonds, π⋅⋅⋅π and Reverse Electron Lone Pair⋅⋅⋅π Interactions.

A detailed analysis of a complete set of the local potentials that appear in the Euler equation for electron density is carried out for noncovalent interactions in the crystal of a uracil derivative using experimental X-ray charge density. The interplay between the quantum theory of atoms in molecules and crystals and the local potentials and corresponding inner-crystal electronic forces of electrostatic and kinetic origin is explored. Partitioning of crystal space into atomic basins and atomic-like potential basins led us to the definite description of interatomic interaction and charge transfer.

Solving the enigma of weak fluorine contacts in the solid state: a periodic DFT study of fluorinated organic crystals.

The nature and strength of weak interactions with organic fluorine in the solid state are revealed by periodic density functional theory (periodic DFT) calculations coupled with experimental data on the structure and sublimation thermodynamics of crystalline organofluorine compounds. To minimize other intermolecular interactions, several sets of crystals of perfluorinated and partially fluorinated organic molecules are considered. This allows us to establish the theoretical levels providing an adequate description of the metric and electron-density parameters of the C-F⋯F-C interactions and the sublimation enthalpy of crystalline perfluorinated compounds.

Quantum pressure focusing in solids: a reconstruction from experimental electron density.

Here an approach is presented for reconstructing the distribution of electronic internal quantum pressure in the electronic continuum of solids from the experimental electron density. Using the formalism of the density functional theory, the spatial inner-crystal map of the quantum pressure is obtained. The results are visualized via the indicator of quantum pressure focusing (IQPF) which reveals the regions where the pressure is concentrated or depleted due to quantum effects.

Why are reactions of 2- and 8-thioquinoline derivatives with iodine different?

The crystal structures of 1,2-dihydro-1,1'-bi[thiazolo[3,2-a]quinoline]-10a,10a'-diium diiodide hemihydrate, CHNS·2I·0.5HO, and 1,2-dihydro-1,1'-bi[thiazolo[3,2-a]quinoline]-10a,10a'-diium iodide triiodide, CHNS·I·I, obtained during the reaction of 1,4-bis(quinolin-2-ylsulfanyl)but-2-yne (2TQB) with iodine, have been determined at 120 K. The crystalline products contain the dication as a result of the reaction proceeding along the iodocyclization pathway.

Polar Order and Frustrated Antiferromagnetism in Perovskite Pb2MnWO6 Single Crystals.

Single crystals of the multiferroic double-perovskite Pb2MnWO6 have been synthesized and their structural, thermal, magnetic and dielectric properties studied in detail. Pure perovskite-phase formation and stoichiometric chemical composition of the as-grown crystals are confirmed by X-ray single-crystal and powder diffraction techniques as well as energy-dispersive X-ray and inductively coupled plasma mass spectrometry. Detailed structural analyses reveal that the crystals experience a structural phase transition from the cubic space group (s.

Characterization of bonding in cesium uranyl chloride: topological analysis of the experimental charge density.

The topological analysis of the charge density distribution in Cs(2)UO(2)Cl(4) obtained from an accurate X-ray diffraction experiment at 20K is reported. Details of the techniques applied during data collection and data refinement are discussed. A split Hansen-Coppens multipole model for uranium and cesium atoms has been used to describe the charge density features associated with valence electrons and core deformations.

Importance of the consideration of anharmonic motion in charge-density studies: a comparison of variable-temperature studies on two explosives, RDX and HMX.

Extremely accurate X-ray data were obtained for the explosive RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) at three different temperatures (20, 120 and 298 K). Collected reflections were integrated using the latest version of the program VIIPP which uses separate Kα(1)/Kα(2) contributions to the profile fitting during integration. For each temperature both anharmonic and harmonic descriptions of the atomic thermal motion were utilized in the model refinements along with the multipole expansion of the electron density.

Quantifying steric effect with experimental electron density.

Using experimental electron densities, the recent effort of quantifying steric effect within the framework of density functional theory is continued. In this work, steric potential, steric field, and steric charge distributions are systematically examines for diamond and boron nitride crystals. Bader's zero-flux condition has been employed to discuss the atomic contributions of these quantities.

17Alpha-estradiol x 1/2 H2O: super-structural ordering, electronic properties, chemical bonding, and biological activity in comparison with other estrogens.

The biological function of steroidal estrogens is related to their electronic properties. An experimental charge density study has been carried out on 17alpha-estradiol and compared to similar studies on more potent estrogens. High accuracy X-ray data were measured with a Rigaku rotating anode diffractometer equipped with an R-Axis Rapid curved image plate detector at 20 K.

The experimental and theoretical QTAIMC study of the atomic and molecular interactions in dinitrogen tetroxide.

The atomic and molecular interactions in a crystal of dinitrogen tetraoxide, alpha-N2O4, have been studied in terms of the quantum topological theory of molecular structure using high-resolution, low-temperature X-ray diffraction data. The experimental electron density and electrostatic potential have been reconstructed with the Hansen-Coppens multipole model. In addition, the three-dimensional periodic electron density of crystalline alpha-N2O4 has been calculated at the B3LYP/cc-pVDZ level of theory with and without the geometry optimization.

The δ-phase of SrTeO(3) at 780 K.

As part of a structural investigation of strontium tellurate(IV) (STO), SrTeO(3), with particular emphasis on the crystal chemistry and phase transitions, the structure of the δ-phase has been determined at 780 K using a single-crystal analysis. Both structural and non-linear optical measurements indicate that STO undergoes a γ→δ second-order ferroelectric phase transition at 633 K from the C2 (γ) to the C2/m (δ) modification. Systematic differences between the similar γ- and δ-phase structures were determined and it was found that this phase transformation can be described by a displacive mechanism.

α-Lead tellurite from single-crystal data.

The crystal structure of the title compound, α-PbTeO(3) (PTO), has been reported previously by Mariolacos [Anz. Oesterr. Akad.

Chemical bonding and intermolecular interactions in energetic materials: 1,3,4-trinitro-7,8-diazapentalene.

The electron density and related properties of the red-colored energetic material 1,3,4-trinitro-7,8-diazapentalene (space group Pca2(1)) have been determined from a low-temperature [90.0 (1) K] X-ray diffraction experiment. Intensity data were measured with a 2 K CCD Bruker diffractometer using Ag Kalpha radiation.

Determination of covalent bond orders and atomic valence indices using topological features of the experimental electron density.

We present an approach for the determination of covalent bond orders from the experimental electron density and its derivatives at the bond critical points. An application of this method to a series of organic compounds has shown that it provides a bonding quantification that is in reasonable agreement with that obtained by orbital theory. The 'experimental' atomic valence indices are also defined and their significance for the characterization of chemical problems is discussed.

Atoms-in-molecules study of intra- and intermolecular bonding in the pentaerythritol tetranitrate crystal.

Chemical bonding in the pentaerythritol tetranitrate crystal based on the experimental electron density obtained from X-ray diffraction data at 100 K and theoretical calculations at the experimental molecular geometry have been analyzed in terms of the Quantum Theory of Atoms in Molecules. Features of the intra- and intermolecular bond critical points and the oxygen atom lone-pair locations are discussed. Numerous intermolecular bonding interactions, including O.

Chemical bonding in pentaerythritol at very low temperature or at high pressure: an experimental and theoretical study.

Chemical bonding in the pentaerythritol crystal based on the experimental electron density at 15 (1) K, and theoretical calculations at the experimental molecular geometries obtained at room and low (15 K) temperatures have been analyzed and compared in terms of the topological analysis. Topological electron-density features corresponding to the high-pressure (1.15 GPa) geometry are also reported.

Atomic interactions in ethylenebis(1-indenyl)zirconium dichloride as derived by experimental electron density analysis.

A topological analysis of the experimental electron density in racemic ethylenebis(1-indenyl)zirconium dichloride, C20H16Cl2Zr, measured at 100 (1) K, has been performed. The atomic charges calculated by the numerical integration of the electron density over the zero-flux atomic basins demonstrate the charge transfer of 2.25 e from the Zr atom to the two indenyl ligands (0.

Synthesis and molecular structure of new acyclic analogues of nucleotides with a 1,2-alkadienic skeleton.

Reaction of 1-chloro-4-(diethoxyphosphonyl)alka-2,3-dienes 14,15 with purine and pyrimidine heterocyclic bases in the presence of cesium carbonate afforded new acyclic analogues of nucleotides containing a 1,2-alkadienic skeleton 18-23. Dealkylation of 18-23 furnished phosphonic acids 2a-f. In contrast, alkylation reaction with 1-chloro-4-(diethoxyphosphonyl)octa-2,3-diene 16 led to Z- and E-1,3-alkadienic phosphonates 25a,b and 26a,b.

Characterizing the oxygen-oxygen interaction in the dinitramide anion.

Atomic interactions between oxygen atoms have been analyzed in terms of the Theory of Atoms in Molecules for the biguanidium dinitramide and biguanidium bis-dinitramide crystals. The electron density has been derived from X-ray diffraction data obtained at 90 K, and the potential energy density has been calculated using the density functional approach. Bond critical points have been found on the O(1).

Reactivity of trans-[PtX(2)(ketoxime)(2)] Complexes toward m-Chloroperoxybenzoic Acid: An Efficient Route to Coordinated Nitrosoalkanes and Solvent Dependence of the Reaction.

The platinum(II) compounds trans-[PtX(2)(RR'C=NOH)(2)] [X = Cl, R = R' = Me, RR' = (CH(2))(4), (CH(2))(5); X = Br, R = R' = Me] react with m-chloroperoxybenzoic acid (MCPBA) in dimethylformamide to give the platinum(II) complexes [PtX(2){N(=O)CRR'ONCRR'}] containing coordinated nitrosoalkane ligands. The complexes [PtX(2){N(=O)CRR'ONCRR'}] were characterized by elemental analysis, EI-MS, IR, electronic absorption, and (1)H NMR spectroscopy; X-ray structure analysis was performed for [PtCl(2){N(=O)CC(5)H(10)ONCC(5)H(10)}]. The latter compound crystallizes in the triclinic P&onemacr; space group with a = 9.