Thermodynamic properties of aqueous organic mixtures near the critical demixing: Cases of 2,6-dimethylpyridine and of 2-isobutoxyethanol

Phase diagrams, volumes and heat capacities of aqueous mixtures of 2,6-dimethylpyridine (2,6-L) and 2-isobutoxyethanol (iBE) and activities of 2,6-L in aqueous mixtures were measured in the monophasic region near the lower critical solution temperature (LCST). With 2,6-L some measurement were also made just above the LCST. From the temperature dependence of these data, partial molar relative enthalpies (2,6-L), expansibilities and the temperature derivative of heat capacities were calculated and show that iBE undergoes a microphase transition at low concentration which is not related to the phase separation. On the other hand, the properties of 2,6-L in the water-rich region at temperatures well below the LCST indicates that this solute has only a slight tendency to associate. The heat capacities of 2,6-L show an important increase near the LCST. Such changes are not observed for iBE and other alkoxyethanols and amines since these systems already exist in the form of microphases; the partial molar properties of iBE near the LCST are nearly equal to the molar values of the pure liquid, and the changes in thermodynamic properties corresponding to the macroscopic phase transition, are therefore too small to be measured by the present techniques.     

New chiral cyclooctatriene-based polycyclic architectures

The synthesis and properties of new chiral polycyclic architectures that display both helicity and a saddle-type shape are described. The enantiomers have been separated, and their absolute configuration was determined by VCD and ECD. The unprecedented molecular architecture is based on a cyclooctatriene core surrounded by an association of benzo[c]fluorene and ortho-phenylene units.     

Thermal investigation of heavy crude oil by simultaneous TG–DSC–FTIR and EDXRF

Present study investigates thermal behavior of two heavy crude oils with different °API values by simultaneous thermogravimetry–differential scanning calorimetry–fourier transform infrared spectroscopy (TG–DSC–FTIR), and an evaluation of the chemical element levels present in the oils’ ashes was done by energy dispersive X-ray fluorescence spectrometry. TG and DSC curves were obtained for two samples in nitrogen atmosphere. Among all inorganic components evaluated, the highest concentration in the two oils was SO₃. Thus this study may contribute to a better understanding of the thermal behavior of heavy crude oils and their composition.     

Effect of Membrane Preparation Methods on the Release of Theophylline through CA Membranes at In-Vitro Conditions

In this study the effect of the membrane preparation methods on the release of theophylline through cellulose acetate (CA) membranes was studied at in vitro conditions. CA/acetone binary and CA/acetone/water ternary systems were used as casting solutions and poly(ethylene glycol) (PEG) was used as the pore forming, plasticizing agent in the study. Membranes were characterized by FTIR, SEM, and DSC analysis. It was determined that pH, temperature and drug concentration affected the release of theophylline. A decrease in pH, increase in temperature and drug concentration increased the permeated amount of theophylline through the membranes. In addition, receiver solution circulation at a capillary blood rate increased the permeation of theophylline. As a result of the study, it was concluded that the release of theophylline could be controlled for a prolonged period of time and modified CA membranes prepared in the study could be as an advisable membrane material for potential release of theophylline at transdermal conditions.     

Synthesis and characteristics of a nonaggregating tris(tetrathiafulvaleno)dodecadehydro[18]annulene

A new tris(tetrathiafulvaleno)dodecadehydro[18]annulene with six peripheral n-hexyl substituents was prepared by oxidative Glaser-Hay cyclization of a corresponding diethynylated tetrathiafulvalene (TTF) precursor. The electronic properties of the neutral and oxidized species were studied by both UV/Vis absorption spectroscopy and electrochemistry. From these studies, it transpires that the strongly violet-colored macrocycle does not aggregate in solution to any significant degree, which was confirmed by (1)H NMR spectroscopy. This reluctance towards aggregation contrasts that observed for related TTF-annulenes containing other peripheral substitutents. Oxidation of the TTF-annulene occurs in two three-electron steps as inferred from both the peak amplitudes and the spectroelectrochemical study. We find that the tris(TTF)-fused dehydro[18]annulene is more difficult to oxidize (by +0.20 V) than the silyl-protected diethynylated mono-TTF precursor. In contrast, the first vertical ionization energy calculated at the B3 LYP/6-311+G(2d,p) level for the parent tris(TTF)-fused dehydro[18]annulene devoid of peripheral hexyl substituents is in fact lower (by 0.44 eV). Moreover, the surface morphology of 1 d drop-cast on a mica substrate was investigated by atomic force microscopy (AFM). Crystalline domains with slightly different orientations were observed. The thickness of individual layers seen in the crystalline domains and the thickness of a monolayer obtained from a very dilute solution were determined to 1.8-1.9 nm. This thickness corresponds to the diameter of the macrocycle and the layers seen in the film are apparently formed when the molecules stack in the horizontal direction relative to the substrate.     

The Antiepileptic Lamotrigine and Its Analogues: Comparative Theoretical Electronic Properties

Electronic properties of lamotrigine (LTG) and two analogues (A1 and A2) are compared through MOPAC-AM1 calculations. Two stable conformers of LTG are calculated to exist in agreement with X-ray crystallography. In the three compounds and the two conformers for each of them, the more favorable protonation sites are N₂ and N₄; these should then be the sites appropriate for interaction with a receptor, and group valence reinforces the supposition. The molecular electrostatic potentials show that a region between the two chlorine atoms in LTG could be the site for an electrostatic interaction with a corresponding site in the receptor. The fluorine atom in A1 would play an equivalent role. A simple model for LTG-receptor interaction is proposed.     

Simple but Precise Engineering of Functional Nanocapsules through Nanoprecipitation

A general, rapid, and undemanding method to generate at will functional oil‐filled nanocapsules through nanoprecipitation is reported. On the basis of polymer and hexadecane/water/acetone phase diagrams, the composition can be set so that polymer chains preferentially stick at the interface of the oil droplets to create nanocapsules. The nanocapsules can be decorated with biorelevant molecules (biotin, fluorescent tags, metal nanoparticles) within the shell and loaded with hydrophobic molecules in a simple one‐pot procedure.     

Improved Purification of C60 and Formation of σ- and π-Homoaromatic methano-bridged fullerenes by reaction with alkyl diazoacetates

A rapid and inexpensive method for the large-scale purification of C₆₀ is the simple filtration of the toluenesoluble extract of commercial fullerene soot through a short plug of charcoal/silica gel with toluene as the eluent. Reactions of C₆₀ with ethyl and tert-butyl diazoacetates in refluxing toluene lead to the formation of the (alkoxycarbonyl)methylene-bridged isomers 1a – 3a and 1b – 3b , respectively, which can be equilibrated, upon further heating, into the single compounds 1a and 1b , respectively. Isomers 1a / b possess the methano bridge at the 6–6 ring junction, whereas structures 2a / b and 3a / b are bridged at the 6–5 junction. A dramatic influence of local and π-ring current anisotropic effects of the fullerene sphere on the NMR chemical shifts of the methine protons in the bridge is observed: the chemical shifts of the protons located over a pentagon ring in 2a / b and over a hexagon ring in 3a / b differ by Δδ = 3.47 and 3.45 ppm, respectively. The analysis of the ¹³C-NMR chemical shifts of the bridgehead C-atoms and the ¹J(C,H) coupling constants for the methano-bridge atoms reveals conclusively that the 6-5-ring-bridged structures 2a / 2b and 3a / 3b are π-homoaromatic (‘open’ transannular bond) and the 6-6-ring-bridged structures 1a / b are π-homoaromatic (‘closed’ transannular bond). The electronic absorption spectra show that π-homoconjugation in 2a / b and 3a / b represents a much smaller electronic perturbation of the original C₆₀ chromophore than σ-homoconjugation in 1a / b . The results of this study demonstrate an impressive linkage between the chemistry of methano-bridged annulenes and methano-bridged fullerenes.     

Untersuchung von Seifen

Ohne Zusammenfassung