Crystal structures of trans-di-chlorido-tetra-kis-[1-(2,6-diiso-propyl-phen-yl)-1H-imidazole-κN (3)]iron(II), trans-di-bromido-tetra-kis-[1-(2,6-diiso-propyl-phen-yl)-1H-imidazole-κN (3)]iron(II) and trans-di-bromido-tetra-kis-[1-(2,6-diiso-propyl-phen-yl)-1H-imidazole-κN (3)]iron(II) diethyl ether disolvate.

The title compounds, [FeCl2(C15H20N2)4], (I), [FeBr2(C15H20N2)4], (II), and [FeBr2(C15H20N2)4]·2C4H10O, (IIb), respectively, all have triclinic symmetry, with (I) and (II) being isotypic. The Fe(II) atoms in each of the structures are located on an inversion center. They have octa-hedral FeX 2N4 (X = Cl and Br, respectively) coordination spheres with the Fe(II) atom coordinated by two halide ions in a trans arrangement and by the tertiary N atom of four aryl-imidazole ligands [1-(2,6-diiso-propyl-phen-yl)-1H-imidazole] in the equatorial plane. In the two independent ligands, the benzene and imidazole rings are almost normal to one another, with dihedral angles of 88.19 (15) and 79.26 (14)° in (I), 87.0 (3) and 79.2 (3)° in (II), and 84.71 (11) and 80.58 (13)° in (IIb). The imidazole rings of the two independent ligand mol-ecules are inclined to one another by 70.04 (15), 69.3 (3) and 61.55 (12)° in (I), (II) and (IIb), respectively, while the benzene rings are inclined to one another by 82.83 (13), 83.0 (2) and 88.16 (12)°, respectively. The various dihedral angles involving (IIb) differ slightly from those in (I) and (II), probably due to the close proximity of the diethyl ether solvent mol-ecule. There are a number of C-H⋯halide hydrogen bonds in each mol-ecule involving the CH groups of the imidazole units. In the structures of compounds (I) and (II), mol-ecules are linked via pairs of C-H⋯halogen hydrogen bonds, forming chains along the a axis that enclose R 2 (2)(12) ring motifs. The chains are linked by C-H⋯π inter-actions, forming sheets parallel to (001). In the structure of compound (IIb), mol-ecules are linked via pairs of C-H⋯halogen hydrogen bonds, forming chains along the b axis, and the diethyl ether solvent mol-ecules are attached to the chains via C-H⋯O hydrogen bonds. The chains are linked by C-H⋯π inter-actions, forming sheets parallel to (001). In (I) and (II), the methyl groups of an isopropyl group are disordered over two positions [occupancy ratio = 0.727 (13):0.273 (13) and 0.5:0.5, respectively]. In (IIb), one of the ethyl groups of the diethyl ether solvent mol-ecule is disordered over two positions (occupancy ratio = 0.5:0.5).

Theoretical study of the stacking behavior of selected polycondensed aromatic hydrocarbons with various symmetries.

Stacked dimers of four polycondensed aromatic hydrocarbons, with structures varying from high to reduced symmetries, have been calculated with dispersion-corrected density functional theory. The configurations of the stacked dimers are readily classified by two in-plane displacements and a relative rotation. The potential energy surface in these three coordinates was calculated with rigid monomers and appears to be slightly flat. Full geometry optimization was performed for selected low-energy structures, resulting in an energy ranking of a series of conformations whose geometries were characterized in considerable detail. The dissociation energy values reveal a clear preference for the symmetrical disk-shaped and triangular structures to dimerize into two in-plane-displaced arrangements, whereas the less symmetrical trapezoidal structures show a tendency to stack in displaced antiparallel over parallel arrangements. According to methodical checks, the key computational results, namely, the shape of the potential energy surface and the geometrical structures and energy ranking of dimer conformations, are essentially insensitive to computational assumptions such as the atomic orbital basis set and density functional chosen. This is shown in particular for the basis set superposition error, which, for the selected level of theory [B97-D3(BJ)/TZV(d,p)] was estimated by the counterpoise correction procedure to be in the narrow range between 7% and 8% of the uncorrected dissociation energies.

Yeast sphingolipids do not need to contain very long chain fatty acids.

Synthesis of VLCFAs (very long chain fatty acids) and biosynthesis of DHS (dihydrosphingosine) both are of vital importance for Saccharomyces cerevisiae. The bulk of VLCFAs and DHS are used for ceramide synthesis by the Lag1p (longevity-assurance gene 1)/Lac1p (longevity-assurance gene cognate 1)/Lip1p (Lag1p/Lac1p interacting protein) ceramide synthase. LAG1 and LAC1 are redundant but LIP1 is essential. Here we show that 4Delta (lag1Deltalac1Deltaypc1Deltaydc1Delta) cells devoid of all known endogenous ceramide synthesis pathways are unviable but can be rescued by the expression of Lass5, a mouse LAG1 homologue. Ceramide synthase activity of 4Delta.Lass5 cells only utilizes C16 and C18 fatty acids and does not require the help of Lip1p, an essential cofactor of Lag1p/Lac1p. HPLC-electrospray ionization-MS/MS analysis demonstrated that in IPCs (inositolphosphorylceramides) of 4Delta.Lass5, the very long chain fatty acids (C26 and C24) account for <1% instead of the normal >97%. Notwithstanding, IPCs incorporated into glycosylphosphatidylinositol anchors of 4Delta.Lass5 show normal mobility on TLC and the ceramide- and raft-dependent traffic of Gas1p (glycophospholipid-anchored surface protein) from endoplasmic reticulum to Golgi remains almost normal. Moreover, the biosynthesis of C24:0 fatty acids remains essential. Thus, C(24:0) and dihydrosphingosine are both necessary for survival of yeast cells even if they utilize C16 and C18 fatty acids for sphingolipid biosynthesis.

Self-aggregated perfluoroalkylated hexa-peri-hexabenzocoronene fibers observed by cryo-SEM and fluorescence spectroscopy.

The self-assembled architectures in solution of a new HBC derivative bearing perfluoroalkylated side chains were investigated by optical excitation and emission spectroscopy and correlated to cryo-SEM, a new technique in organic chemistry.

Chemical Nucleation of Diamond Films.

With the large differences in surface energy between film and substrate in combination with the low sticking coefficient of hydrocarbon radicals, nanocrystalline diamond growth on foreign substrates typically results in poor nucleation densities. A seeding technique is therefore required to realize pinhole-free and thin coalesced films. In this work, a chemical nucleation method for growth of diamond on nondiamond substrates based on 2,2-divinyladamantane is shown. After treating with the carbon-containing DVA, the chemically treated wafers were exposed to low-power-density plasma, known as the incubation phase, to facilitate the formation of diamond nucleation sites followed by a high-power-density growth regime to produce coalesced films. The resulting films demonstrate high crystallinity, whereas the Raman spectra suggest high-quality diamond with low sp2 content.

Synthesis of Arylamine Tribenzopentaphenes and Investigation of their Hole Mobility.

We report the versatile synthesis of two tribenzo[fj,ij,rst]pentaphene (TBP) derivatives bearing two diarylamine substituents attached at the opposite ends of the aromatic core. Field effect transistor (FET) devices of the bis-diarylamine-TBP compounds were fabricated using spin coating under different concentrations, spin speed, and solvent conditions. Emission spectra and surface investigation by atomic force microscopy (AFM) reveal the formation of aggregates induced by the strong π-π stacking of the aromatic core leading to island features, and thus, unexpected low hole mobilities. The synthetic strategy we show herein, however, offers the possibility to decorate the TBP core structure with various charge-carrier peripheral groups and optimized alkyl chains, which should improve the crystalline property of their thin films upon deposition, leading consequently to a better hole transport mobility.

Thermoreversible photocyclization of a pyrazolotriazole to a triazasemibullvalene: a novel electrocyclic reaction.

The photochemistry of the pyrazolo[1,2-a]benzotriazole 1b and its dimethyl derivative 1c was studied in argon matrices at 12 K and in solution at 190 K. On irradiation at 365 nm, 1b and 1e undergo ring closure to yield the triazasemibullvalenes 2b and 2c, respectively, which were identified unambiguously by NMR and IR spectroscopy. This novel type of cyclization is reversed on warming or by irradiation at 313 nm. Quantum chemical calculations serve to model the observed IR and UV spectra and to rationalize the mechanism of the photocyclization and its thermal back-reaction.