Indene and pseudoazulene discotic liquid crystals: a synthetic and structural study

Several new liquid-crystalline indene and pseudoazulene systems are reported. These molecules give rise to either columnar hexagonal mesophases and/or columnar plastic phases. The unique nature of these compounds stems from their non-classical discotic structure. Although the molecules have rigid aromatic cores, they lack terminal tails and instead the polarizable atoms (S, halogens) or polar groups (CN, CO) act as unusual soft parts. On the basis of many structurally related materials, we conclude that for this type of compound molecular stacking in the solid state is a prerequisite for the appearance of a columnar mesophase, although other intermolecular interactions within the layers are also important in establishing liquid-crystalline order. The behavior reported for these mesomorphic molecules opens up new possibilities in the search for related molecular interactions that might be useful for the construction of supramolecular architectures with particular properties.     

Correction: Direct synthesis of the organic and Ge free Al containing BOG zeolite (ITQ-47) and its application for transformation of biomass derived molecules

Aluminosilicate boggsite (Si/Al-BOG) has been hydrothermally synthesized without adding organic structure-directing agents (OSDAs) in the synthesis gel using the borosilicogermanium ITQ-47 (Si/B-ITQ-47) zeolite as seeds. The introduction of the costly and environmentally less benign phosphazene organic structure-directing agent is not required to grow the zeolite. Physicochemical characterization experiments show that Si/Al-BOG has good crystallinity, high surface area, tetrahedral Al³⁺ species, and acid sites. In order to test the catalytic performance of the zeolite, the synthesis of l,l-lactide from l-lactic acid was performed. Si/Al-BOG exhibits 88.2% conversion of l-lactic acid and 83.8% l,l-lactide selectivity, which are better than those of other zeolites studied up to now.

Aluminosilicate boggsite (Si/Al-BOG) has been hydrothermally synthesized without adding organic structure-directing agents (OSDAs) in the synthesis gel using the borosilicogermanium ITQ-47 (Si/B-ITQ-47) zeolite as seeds.     

The rate of homolysis of adducts of peroxynitrite to the C=O double bond.

Nucleophilic addition of the peroxynitrite anion, ONOO(-), to the two prototypical carbonyl compounds, acetaldehyde and acetone, was investigated in the pH interval 7.4-14. The process is initiated by fast equilibration between the reactants and the corresponding tetrahedral adduct anion, the equilibrium being strongly shifted to the reactant side. The adduct anion also undergoes fast protonation by water and added buffers. Consequently, the rate of the bimolecular reaction between ONOO(-) and the carbonyl is strongly dependent on the pH and on the concentration of the buffer. The pK(a) of the carbonyl-ONOO adduct was estimated to be approximately 11.8 and approximately 12.3 for acetone and acetaldehyde, respectively. It is shown that both the anionic and the neutral adducts suffer fast homolysis along the weak O-O bond to yield free alkoxyl and nitrogen dioxide radicals. The yield of free radicals was determined to be about 15% with both carbonyl compounds at low and high pH, while the remainder collapses to molecular products in the solvent cage. The rate constants for the homolysis of the adducts vary from ca. 3 x 10(5) to ca. 5 x 10(6) s(-1), suggesting that they cannot act as oxidants in biological systems. This small variation around a mean value of about 10(6) s(-1) suggests that the O-O bond in the adduct is rather insensitive to its protonation state and to the nature of its carbonyl precursor. An overall reaction scheme was proposed, and all the corresponding rate constants were evaluated. Finally, thermokinetic considerations were employed to argue that the formation of dioxirane as an intermediate in the reaction of ONOO(-) with acetone is an unlikely process.     

Synthesis, structure, and spectroscopy of phenylacetylenylene rods incorporating meso-substituted dipyrrin ligands

The synthesis, structure, and spectroscopic characterization of a series of phenylacetylenylene rodlike molecules containing dipyrromethene (dipyrrin) ligands are described. The combination of the phenylacetylenylene groups with the porphyrinogenic dipyrrin moieties results in a rich absorption spectroscopy for these compounds, although the fluorescence of the phenylacetylenylene moiety is quenched by presence of the dipyrrin chelator. The Cu(2+) and Fe(3+) complexes of these ligands have been prepared and three of these compounds have been structurally characterized by using single-crystal X-ray diffraction. Unlike other octahedral metal-dipyrrin complexes described to date, one of the iron complexes demonstrates ideal threefold symmetry in the solid-state. The elongated structure and high symmetry of these complexes suggests the use of these meso-substituted phenylacetylenylene ligands as an interesting class of extended, branched molecules for the construction of supramolecular architectures.     

Templating and selection in the formation of macrocycles containing [[P(micro-NtBu)(2)](micro-NH)](n) frameworks: observation of halide ion coordination

Amination of [ClP(micro-NtBu)](2) (1) using NH(3) in THF gives the cyclophospha(III)zane dimer [H(2)NP(micro-NtBu)](2) (2), in good yield. (31)P NMR spectroscopic studies of the reaction of 1 with 2 in THF/Et(3)N show that almost quantitative formation of the cyclic tetramer [[P(micro-NtBu)](2)(micro-NH)](4) (3) occurs. The remarkable selectivity of this reaction can (in part) be attributed to pre-organisation of 1 and 2, which prefer cis arrangements in the solid state and solution. The macrocycle 3 can be isolated in yields of 58-67 % using various reaction scales. The isolation of the major by-product of the reaction (ca. 0.5-1 % of samples of 3), the pentameric, host-guest complex [[P(micro-NtBu)(2)](2)(micro-NH)](5)(HCl).2 THF] (4.2 THF), gives a strong indication of the mechanism involved. In situ (31)P NMR spectroscopic studies support a stepwise condensation mechanism in which Cl(-) ions play an important role in templating and selection of 3 and 4. Amplification of the pentameric arrangement occurs in the presence of excess LiX (X=Cl, Br, I). In addition, the cyclisation reaction is solvent- and anion-dependent. The X-ray structures of 2 and 4.2 THF are reported.     

(CuBr)3P4Se4: A Low Symmetric Variant of the (CuI)3P4Se4 Structure Type

Bright orange (CuBr)₃P₄Se₄ is obtained from the reaction of CuBr, P, and Se in stoichiometric amounts (CuBr : P : Se = 3 : 4 : 4). The composition and the crystal structure of the compound were determined from single crystal X‐ray diffraction data. Lattice constants are a = 33.627(2) Å, b = 6.402(1) Å, c = 19.059(1) Å, β = 90.19(3) °, V = 4103.2(3) ų, and Z = 12. The compound crystallizes in a structure that is related to (CuI)₃P₄Se₄. Cages of β‐P₄Se₄ are stacked along the b‐axis and are separated by columns of copper(I) bromide. However, the coordination of the β‐P₄Se₄ cage molecules to the copper atoms in the CuBr columns in (CuBr)₃P₄Se₄ is quite different from (CuI)₃P₄Se₄. The monoclinic compound (space group: P2₁, no. 4) has an almost orthorhombic metric in combination with a threefold superstructure in [100]. Structural aspects of (CuBr)₃P₄Se₄ are discussed with respect to the heavier homologue (CuI)₃P₄Se₄.     

Porous MoS2 synthesized by ultrasonic spray pyrolysis

The hydrodesulfurization (HDS) activity of molybdenum sulfide-based catalysts is localized to the edges of this layered solid and is, therefore, highly dependent on the technique used to prepare the material. Here, ultrasonic spray pyrolysis (USP) was used to synthesize porous, nanostructured MoS2. Low surface area powders, not useful for catalysis, are generally produced by USP. This work shows that when combined with a dissolvable template, USP is capable of producing high surface area materials. An aqueous solution of ammonium tetrathiomolybdate and colloidal silica was nebulized and pyrolyzed to give a MoS2/SiO2 composite material. Leaching with HF removed the sacrificial SiO2, resulting in a highly porous MoS2 network with surface areas as high as 250 m2/g. Cobalt-promoted MoS2 networks were also synthesized. The thiophene HDS activities of these materials were substantially higher than those of unsupported MoS2 and RuS2 standards, illustrating the enhanced dispersion of the HDS active phase achieved by this synthetic technique.     

Vilsmeier formylation of 5,10,15-triphenylcorrole: expected and unusual products

5,10,15-Triphenylcorrole (1) reacts with the Vilsmeier reagent (POCl(3)/DMF) to give the corresponding 3-formyl derivative 3 as the major product. The regioselectivity of the reaction was proven by X-ray crystallography and only traces of the 2-formyl isomer were observed. A more polar product is also observed and this compound becomes the major product when an excess of DMF is used for the preparation of the Vilsmeier reagent, while the formation of the 3-formyl isomer is almost completely suppressed. X-ray crystallography allowed us to identify this compound as the fully substituted N-ethane bridged derivative 4, formed from the attack of the Vilsmeier reagent at the inner core of the macrocycle. This compound is unique among porphyrinoid macrocycles, and further confirms the peculiarity of corrole chemistry.     

SIAmate-a compact and modular sequential injection analysis controller

A number of sequential injection analysis (SIA) measurement methods have been developed during the last years. Almost all have been used in laboratory conditions with good results, but very few have been implemented as on-line methods, applied to non-stop measurements, producing immediate results for process control. The transfer of an SIA system from laboratory to an industrial facility [J. Ruzicka, Anal. Chim. Acta 261 (1992) 3] requires a whole new range of details to be taken into account. Some SIA platform related topics will be discussed. There are numerous ways of building an SIA system that meets the needs of the industry. One alternative, SIAmate, is presented.