Melting of saturated fatty acid zinc soaps

The melting of alkyl chains in the saturated fatty acid zinc soaps of different chain lengths, Zn(C(n)H(2n+1)COO)(2); n = 11, 13, 15, and 17, have been investigated by powder X-ray diffraction, differential scanning calorimetry, and vibrational spectroscopy. These compounds have a layer structure with the alkyl chains arranged as tilted bilayers and with all methylene chains adopting a planar, all-trans conformation at room temperature. The saturated fatty acid zinc soaps exhibit a single reversible melting transition with the associated enthalpy change varying linearly with alkyl chain length, but surprisingly, the melting temperature remaining constant. Melting is associated with changes in the conformation of the alkyl chains and in the nature of coordination of the fatty acid to zinc. By monitoring features in the infrared spectra that are characteristic of the global conformation of the alkyl chains, a quantitative relation between conformational disorder and melting is established. It is found that, irrespective of the alkyl chain length, melting occurs when 30% of the chains in the soap are disordered. These results highlight the universal nature of the melting of saturated fatty acid zinc soaps and provide a simple explanation for the observed phenomena.     

Tunable Molecular Logic Gates Designed for Imaging Released Neurotransmitters

Tunable dual‐analyte fluorescent molecular logic gates (ExoSensors) were designed for the purpose of imaging select vesicular primary‐amine neurotransmitters that are released from secretory vesicles upon exocytosis. ExoSensors are based on the coumarin‐3‐aldehyde scaffold and rely on both neurotransmitter binding and the change in environmental pH associated with exocytosis to afford a unique turn‐on fluorescence output. A pH‐functionality was directly integrated into the fluorophore π‐system of the scaffold, thereby allowing for an enhanced fluorescence output upon the release of labeled neurotransmitters. By altering the pH‐sensitive unit with various electron‐donating and ‐withdrawing sulfonamide substituents, we identified a correlation between the pK_a of the pH‐sensitive group and the fluorescence output from the activated fluorophore. In doing so, we achieved a twelvefold fluorescence enhancement upon evaluating the ExoSensors under conditions that mimic exocytosis. ExoSensors are aptly suited to serve as molecular imaging tools that allow for the direct visualization of only the neurotransmitters that are released from secretory vesicles upon exocytosis.     

Facile preparation of the oxetane-nucleosides

Efficient and practical large scale synthesis of suitably protected 1',2'-oxetane locked purine and pyrimidine nucleosides for incorporation in oligo-DNA or -RNA by solid-phase synthesis is reported. A high regio and stereoselectivity with preferential formation of the beta-anomer in the glycosylation reaction, using the Vorbrüggen procedure, was achieved by a convergent synthetic procedure with orthogonal protection strategy using either 1,2-di-O-acetyl-3,4-O-isopropylidene-6-O-(4-toluoyl)-d-psicofuranose or 2-O-acetyl-6-O-benzyl-1,3,4-tri-O-(4-toluoyl)-d-psicofuranose as the glycosyl donor.     

Hydrocarbon type analysis by thin-layer chromatography with flame-ionization detection: vacuum gas oils, heavy feeds, and hydroprocessed products

Thin-layer chromatography with flame-ionization detection (TLC-FID) provides quantitative hydrocarbon type data as well as distribution of aromatics by ring number. This method has been applied to obtain amounts of saturates, aromatics, and polars in heavy oil distillates such as light vacuum gas oils and heavy vacuum gas oils derived from different crude sources. TLC-FID chromatograms and resultant quantitative hydrocarbon type data show that these distillates vary markedly in aromatic contents and aromatic ring types. Similar observations are made with several fluid catalytic cracking feeds. Effects of process parameters such as operating pressure and temperature on hydroconversion of aromatics and polars from a heavy oil are assessed by TLC-FID. It has been demonstrated that there is a preferential reduction of higher polycyclic aromatic hydrocarbons and polars with an increase of both hydrogen partial pressure and reactor temperature.     

Spectra of K3Mn(CN)6

The polarised optical spectra of single crystal of K₃Mn(CN)₆ is reported at liquid nitrogen temperature. A new system of transition is located along with its hot components which is verified by temperature variation studies. The crystal field parameters to reproduce the bands are given.