ESI-FTICR investigation of triethylammonium ion-driven resorcin[4]arene dimer formation and structure

In the course of mass spectrometric measurements a self-assembled hydrogen bonded resorcinarene dimer was observed, the formation of which was driven by the binding of triethylammonium ion as a guest and as an ionic label.     

Quinoxaline N-oxides

It is found that 2,3-dimethylquinoxaline-l, 4-di-N-oxide reacts with formaldehyde only in the presence of alkaline reagents, and that independent of the amount of formaldehyde taken, 2-(-hydroxyethyl)-3-methyl- and 2, 3-bis ( -hydroxyethyl) quinoxaline-di-N-oxides are formed. Oxidation of quinoxaline derivatives of general formula VI gives the corresponding mono- and di-N-oxides.For Part X see [3].     

N-oxides of imidazo[4,5-b]quinoxalines and imidazo[4,5-b]pyrazines

The N-oxides and N,N-dioxides of methyl derivatives of imidazo[4,5-b]quinoxaline and imidazo[4,5-b]pyrazine were synthesized. The higher reactivity of the 2-methyl group in the N-oxides of 2-methylimidazo[4,5-b]quinoxaline as compared with the corresponding unoxidized derivatives was demonstrated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1266–1270, September, 1972.     

Silica-titania sol-gel hybrid materials: synthesis, characterization and potential application in solid phase extraction

The biphenilaminepropylsilica and biphenilaminepropylsilicatitania were synthesized by sol-gel method, in two steps: (a) biphenylamine reacts with chloropropyltrimethoxysilane and (b) the product of reaction was polycondensed with tetraethylorthosilicate (TEOS) or TEOS and titanium isopropoxide. The sol-gel materials were characterized using infrared spectroscopy and N₂ adsorption-desorption isotherms and they were employed as sorbents for carcinogenic N-containing compound retention, in aqueous solution, using the SPE technique. The N-containing compounds adsorption was influenced by the titania presence and the sorption process seems to happen in the pores with higher organic density.     

Spontaneous Resolution of an Electron‐Deficient Tetrahedral Fe4L4 cage

A highly electron‐deficient C₃‐symmetric tris(bipyridyl) ligand was prepared in four steps and used for the coordination of Fe(OTf)₂, thereby resulting in the homochiral assembly of a new family of robust tetrahedral M₄L₄ cages. This homochiral T‐symmetric cage containing a relatively large cavity of 330 ų is capable of encapsulating an anionic guest, as was determined by mass spectrometry, ¹⁹F NMR spectroscopy, and finally shown from its crystal structure. Moreover, crystallization of the cage from CH₃CN led to crystals containing both (ΔΔΔΔ and ΛΛΛΛ) enantiomers, while crystallization from CH₃OH resulted in crystals containing only the right‐handed (ΔΔΔΔ) cage. The difference in the crystal packing of the two crystal structures is discussed and a feasible explanation for the unique phenomenon among supramolecular cages—spontaneous resolution—is given.     

The use of ultrasound in the extraction of Ilex paraguariensis leaves: a comparison with maceration

The objective of this work is to discuss the main parameters that influence the sonication extraction of Ilex paraguariensis leaves. For this purpose, the extraction time, solvent polarity, solvent volume, sample mass and particle size were evaluated. Results showed that the main variable affecting the extraction process was the solvent polarity. Though in a less extent, temperature and extraction time also demonstrated to be important parameters, while the other variables did not present a significant influence on the extraction yield. The extracts at the optimized condition were compared with those obtained by maceration, in terms of mass yield and chemical composition. The major compounds identified in the extracts were caffeine and palmitic acid. Some saturated hydrocarbons such as fatty acids, fatty acid methyl esters, phytosterols, and theobromine were also identified in the fractions.     

Characterization and evaluation of the hydrolytic stability of trifluoroacetylated cellulose fibers

The controlled heterogeneous modification of cellulose fibers with trifluoroacetic anhydride was investigated. The characterization of the ensuing materials was performed by elemental analysis, FTIR spectroscopy, X-ray diffraction (XRD), thermogravimetry, and surface analysis (XPS, ToF-SIMS, and contact angles measurements). The trifluoroacetylation enhanced significantly the hydrophobic and lipophobic character of the fibers, whereas their thermal stability and cristallinity were only modestly affected by this treatment, except under the most severe conditions for the latter. Their hydrolytic stability to water vapour was also assessed as a function of the air humidity and shown to be lower than that of still liquid water in the case of a saturated atmosphere.     

Exploitation of bile acid transport systems in prodrug design

The enterohepatic circulation of bile acids is one of the most efficient recycling routes in the human body. It is a complex process involving numerous transport proteins, which serve to transport bile acids from the small intestine into portal circulation, from the portal circulation into the hepatocyte, from the hepatocyte into the bile, and from the gall bladder to the small intestine. The tremendous transport capacity and organ specificity of enterohepatic circulation combined with versatile derivatization possibilities, rigid steroidal backbone, enantiomeric purity, availability, and low cost have made bile acids attractive tools in designing pharmacological hybrid molecules and prodrugs with the view of improving intestinal absorption, increasing the metabolic stability of pharmaceuticals, specifically targeting drugs to organs involved in enterohepatic circulation, as well as sustaining therapeutically reasonable systemic concentrations of active agents. This article briefly describes bile acid transport proteins involved in enterohepatic circulation, summarizes the key factors affecting on the transport by these proteins, and reviews the use of bile acids and their derivatives in designing prodrugs capable of exploiting the bile acid transport system.     

(−)-Sparteine-Mediated Asymmetric Cyclocarbolithiation of Alkenes Combined with a Stereospecific retro-[1,4]-Brook Rearrangement

A novel domino-type reaction sequence consisting of an enantioselective intramolecular carbolithiation of 6-phenylhex-5-enyl carbamates and a highly stereospecific retro-[1,4]-Brook rearrangement is reported. The carbocycles are formed with high enantiomeric (er >98 : 2) and diastereoisomer ratios (dr >99 : 1) in good yields (47 – 60%). On the basis of the absolute configuration of the cyclization products, a stereoretentive mechanism is proposed for the retro-[1,4]-Brook rearrangement.     

Searching for and Quantifying Nonconvexity Regions of Functions*

Lithuanian Mathematical Journal - Convexity plays a prominent role in a number of areas, but practical considerations often lead to nonconvex functions. We suggest a method for determining regions...