Conformational, concomitant polymorphs of 4,4-diphenyl-2,5-cyclohexadienone: conformation and lattice energy compensation in the kinetic and thermodynamic forms

4,4-Diphenyl-2,5-cyclohexadienone (1) crystallized as four conformational polymorphs and a record number of 19 crystallographically independent molecules have been characterized by low-temperature X-ray diffraction: form A (P2(1), Z'=1), form B (P1, Z'=4), form C (P1, Z'=12), and form D (Pbca, Z'=2). We have now confirmed by variable-temperature powder X-ray diffraction that form A is the thermodynamic polymorph and B is the kinetic form of the enantiotropic system A-D. Differences in the packing of the molecules in these polymorphs result from different acidic C-H donors approaching the C=O acceptor in C-H...O chains and in synthons I-III, depending on the molecular conformation. The strength of the C-HO interaction in a particular structure correlates with the number of symmetry-independent conformations (Z') in that polymorph, that is, a short C-HO interaction leads to a high Z' value. Molecular conformation (Econf) and lattice energy (Ulatt) contributions compensate each other in crystal structures A, B, and D resulting in very similar total energies: Etotal of the stable form A=1.22 kcal mol(-1), the metastable form B=1.49 kcal mol(-1), and form D=1.98 kcal mol(-1). Disappeared polymorph C is postulated as a high-Z', high-energy precursor of kinetic form B. Thermodynamic form A matches with the third lowest energy frame based on the value of Ulatt determined in the crystal structure prediction (Cerius2, COMPASS) by full-body minimization. Re-ranking the calculated frames on consideration of both Econf (Spartan 04) and Ulatt energies gives a perfect match of frame #1 with stable structure A. Diphenylquinone 1 is an experimental benchmark used to validate accurate crystal structure energies of the kinetic and thermodynamic polymorphs separated by <0.3 kcal mol(-1) (approximately 1.3 kJ mol(-1)).     

Single Crystal Structure of Terfenadine Form I

Journal of Chemical Crystallography - Terfenadine, C32H41NO2, 1, contains an α,α-diphenyl-4-piperidinomethanol moiety, which is related to the H1-receptor blocking activity, facilitating...     

Augmentation of the step‐by‐step Energy‐Scanning EXAFS beamline BL‐09 to continuous‐scan EXAFS mode at INDUS‐2 SRS

An innovative scheme to carry out continuous‐scan X‐ray absorption spectroscopy (XAS) measurements similar to quick‐EXAFS mode at the Energy‐Scanning EXAFS beamline BL‐09 at INDUS‐2 synchrotron source (Indore, India), which is generally operated in step‐by‐step scanning mode, is presented. The continuous XAS mode has been implemented by adopting a continuous‐scan scheme of the double‐crystal monochromator and on‐the‐fly measurement of incident and transmitted intensities. This enabled a high signal‐to‐noise ratio to be maintained and the acquisition time was reduced to a few seconds from tens of minutes or hours. The quality of the spectra (signal‐to‐noise level, resolution and energy calibration) was checked by measuring and analysing XAS spectra of standard metal foils. To demonstrate the energy range covered in a single scan, a continuous‐mode XAS spectrum of copper nickel alloy covering both Cu and Ni K‐edges was recorded. The implementation of continuous‐scan XAS mode at BL‐09 would expand the use of this beamline in in situ time‐resolved XAS studies of various important systems of current technological importance. The feasibility of employing this mode of measurement for time‐resolved probing of reaction kinetics has been demonstrated by in situ XAS measurement on the growth of Ag nanoparticles from a solution phase.     

Binding of an Anti-inflammatory Drug Lornoxicam with Blood Proteins: Insights from Spectroscopic Investigations

The interaction between an anti-inflammatory drug, lornoxicam (LXM) and protein (human serum albumin and bovine serum albumin) was studied by spectroscopic techniques (Fluorescence, synchronous, FT-IR, UV-vis absorption and circular dichroism). The quenching mechanism of fluorescence of the protein by the drug was discussed. Based on the interaction studies carried out at different temperatures by spectrofluorometry, the binding constant and the number of binding sites for drug on protein have been evaluated. The nature of binding force operating between the drug and protein was proposed to be electrostatic and hydrophobic based on thermodynamic parameters. The distance r between the donor (protein) and acceptor (drug) was determined based on the Förster’s theory of non-radiation energy transfer and found to be 2.38 nm and 2.56 nm for LXM-BSA and LXM-HSA respectively. Displacement studies with different site probes revealed that the drug bound to the hydrophobic pocket located in sub domain IIA; that is to say, Trp-214 was near or within the binding site. Circular dichroism data of protein in the presence of drug revealed the decreased α-helicity and hence changes in secondary structure of protein. The effects of some common ions were also investigated.     

Recurrence of carboxylic acid-pyridine supramolecular synthon in the crystal structures of some pyrazinecarboxylic acids.

X-ray crystal structures of pyrazinic acid 1 and isomeric methylpyrazine carboxylic acids 2-4 are analyzed to examine the occurrence of carboxylic acid-pyridine supramolecular synthon V in these heterocyclic acids. Synthon V, assembled by (carboxyl)O-H...N(pyridine) and (pyridine)C-H...O(carbonyl) hydrogen bonds, controls self-assembly in the crystal structures of pyridine and pyrazine monocarboxylic acids. The recurrence of acid-pyridine heterodimer V compared to the more common acid-acid homodimer I in the crystal structures of pyridine and pyrazine monocarboxylic acids is explained by energy computations in the RHF 6-31G* basis set. Both the O-H.N and the C-H...O hydrogen bonds in synthon V result from activated acidic donor and basic acceptor atoms in 1-4. Pyrazine 2,3- and 2,5-dicarboxylic acids 10 and 11 crystallize as dihydrates with a (carboxyl)O-H...O(water) hydrogen bond in synthon VII, a recurring pattern in the diacid structures. In summary, the carboxylic acid group forms an O-H...N hydrogen bond in pyrazine monocarboxylic acids and an O-H...O hydrogen bond in pyrazine dicarboxylic acids. This structural analysis correlates molecular features with supramolecular synthons in pyridine and pyrazine carboxylic acids for future crystal engineering strategies.     

Chemical vapor deposition of metal borides: 6. The formation of neodymium boride thin film materials from polyhedral boron clusters and metal halides by chemical vapor deposition

The chemical vapor deposition (CVD) of crystalline thin films of neodymium hexaboride (NdB₆) was achieved using either nido ‐pentaborane(9) or nido ‐decaborane(14) with neodymium(III) chloride on different substrates. The highly crystalline NdB₆ films were formed at relatively moderate temperatures (835 °C, ca. 1 µm/h) and were characterized by scanning electron microscopy, X‐ray emission spectroscopy, X‐ray diffraction and glow discharge mass spectrometry. The NdB₆ polycrystalline films were found to be pure and uniform in composition in the bulk material. Depositions using CoCl₂, NdCl₃ and B₅H₉ as the CVD precursors resulted in the formation of a mixture of NdB₆ and CoB phases, rather than the ternary phase. Copyright © 2008 John Wiley & Sons, Ltd.     

X-ray study of some spinels containing gallium and manganese

The ternary oxides CrMnGaO₄, NiMnGaO₄, CuMnGaO₄ and ZnMnGaO₄, crystallize in the cubic spinel structure with lattice parametera=8.41±0.02 Å, 8.34±0.02 Å, 8.36±0.02 Å and 8.32±0.02 Å, respectively. The oxidation state of manganese in these spinels was determined x-ray spectroscopically. The site distribution was determined from the structural properties and calculated site preference energies of cations in the lattice. The ionic structures were found to be Ga³⁺ [Mn²⁺ Cr³⁺] O ₄ ^2? . Ga³⁺ [Cu²⁺ Mn³⁺] O ₄ ^2? , Mn²⁺ [Ga³⁺ Ni³⁺] O ₄ ^2? and Zn²⁺ [Mn³⁺ Ga³⁺] O ₄ ^2? .     

Electroluminescence in lead titanate single crystals

Electroluminescence in PbTiO₃ single crystals is studied with variation in applied electric field, frequency (20 Hz to 5 kHz) and temperature. The EL onset depends on the rate at which the dipole switches. Extremely sharp upward rising nature of the pulses of micro second duration suggest that there is a self maintained discharge in the dielectric due to secondaryγ _p mechanism. Frequency dependence of EL suggests that both the secondary mechanisms, viz. theγ _p andγ _i are active after the application of a high field and the critical field at which this occurs decreases with increase in the frequency of the applied voltage. Similarly the onset voltage decreases with increase in frequency. The temperature dependence of EL at the applied frequency of 50 Hz shows that the onset voltage is intimately connected with the coercive field of the crystal and it is minimum at the Curie point. The study suggests that EL occurs in the bulk and there is a breakdown in the dielectric due to an avalanche formation.     

[Tris(4‐tolyl)­methyl]­benzene

The crystal structure of the title compound, C₂₈H₂₆, in the monoclinic space group C2/c has a columnar packing arrangement with a 7.20 Å axis, a feature common to several tetra­phenyl­methanes.     

Density functional theory study of Te(CN)2, Te(CN)(NC), and Te(NC)2 and their isomerizations

The equilibrium structures of Te(CN)₂, Te(CN)(NC), and Te(NC)₂ and three isomerization reactions: Te(CN)₂ ? Te(CN)(NC), Te(CN)(NC) ? Te(NC)₂, and Te(CN)₂ ? Te(NC)₂ were studied in the gas-phase using density functional theory. Three functionals (B3LYP, BLYP, and BHLYP) were employed to characterize the low-lying electronic singlet and triplet TeC₂N₂ isomers. The basis sets for carbon and nitrogen used were of double-ζ plus polarization quality with additional s- and p-type diffuse functions, DZP++. For the tellurium atom, the LANL2DZ (ECP) basis set was used. The energetic ordering (kcal mol^?1) (B3LYP) including zero-point vibrational energy corrections for the singlet ground state isomers follows: Te(CN)₂ (0.0, global minimum) < Te(CN)(NC) (15.4) < Te(NC)₂ (29.8). Electrostatic potentials and average local ionization energies of the ground state Te(CN)₂, Te(CN)(NC), and Te(NC)₂ isomers provide some guidance as to sites for noncovalent and covalent interactions. Energetics such as the different forms of electron affinities, ionization energies, and singlet–triplet gaps were also reported. Further the theoretical rate constants for the isomerization reactions were evaluated using transition state theory. We predict that these isomers may crystallize in similar patterns, if stable, as does Se(CN)₂.