Quinoxaline N-oxides

The reactions of 2-methyl- and 2, 3-dimethylquinoxalines and their N-oxides with C₆H₅CHO, p-O₂NC₆H₄CHO, and p-CH₃OC₆H₄CHO, have been investigated. It is shown that the 1, 4-di-N-oxides of 2-methyl- and 2, 3-dimethylquinoxaline do not undergo condensation with aromatic aldehydes when heated in the presence of acids, but that in the presence of strongly basic reagents they readily, without heating, undergo an aldol-type reaction, to give the corresponding carbinols. Under those conditions the di-N-oxide of 2, 3-dimethylquinoxaline and C₆H₅CHO or p-CH₃OC₆H₄CHO gives only monocarbinols, whereas p-O₂NC₆H₄CHO reacts with both methyl groups. Under the action of concentrated H₂SO₄ these carbinols give the corresponding styryls. The di-N-oxides of -methyl derivatives of quinoxaline react with aromatic aldehydes more readily than the N-oxides of - and -methylpyridines and quinolines. Views are put forward regarding the relationships between reactivities of - and -methyl derivatives of heterocyclic N-oxides and their abilities to undergo polarization in two opposite directions.     

Novel Porphyrin-Cholic Acid Conjugates as Receptors for Biologically Important Anions

A series of novel receptors showing high binding affinity in aqueous media for biologically important anions are reported. These naturally chromophoric porphyrin-based receptors contain cholic acids connected via quaternary alkyl ammonium amido linkages.     

Structure Effect of Imidazolium-Based Dicationic Ionic Liquids on Claisen Rearrangement

A large group of imidazolium-based dicationic ionic liquids (DILs) has been prepared in good yields. Thermal stability of all DILs has been determined. The effects of the reaction time, cation, imidazolium C₂–H acidity, and anion on the Claisen rearrangement of allyl phenyl ether have been investigated. Type of anion and the presence of the acidic C₂–H bond in the imidazolium moieties have proven to be essential for this reaction. The simple procedure and the possibility of avoiding the use catalysts and volatile organic solvents make this synthetic method environmentally benign and adaptable for large-scale applications.     

Time-resolved fluorescence spectroscopy reveals functional differences of cationic polymer-DNA complexes

Cationic polymers bind DNA and form compacted nanoparticulates (i.e., polyplexes). Polyplexes augment DNA delivery into the cells as a nonviral method of gene therapy. DNA packing and release are the key factors in polyplex-mediated gene delivery, but they are poorly understood due to the lack of physical methods of investigation. We used time-resolved fluorescence spectroscopy to study poly(ethylenimine) (PEI) and poly(L-lysine) (PLL) polyplexes. Analysis of fluorescence lifetimes and time-resolved spectra revealed that DNA exists in several different states in PEI polyplexes and only in one tightly bound state in PLL polyplexes. The observed difference in the nature of the polyplexes may explain why PEI releases DNA more easily than PLL even though both polycations condense DNA effectively. The present method utilizing time-resolved fluorescence spectroscopy gives information on the specific interactions between DNA and the cationic polymers in the polyplexes. This kind of information is very important in the development of biologically effective nonviral systems for DNA delivery.     

Lecithin organogels used as bioactive compounds carriers. A microdomain properties investigation

Organogels were obtained by adding small amounts of water to a solution of lecithin in organic solvents. Either isooctane or isopropyl palmitate and isopropyl myristate were used as the continuous organic phase of the gels. EPR spectroscopy using both DSA membrane-sensitive and lipophilic spin probes was applied to define the dynamic structure of the surfactant monolayer and the continuous oil phase of lecithin organogels. It was found that by increasing the water quantity, an increase of the polar head area per lecithin molecule was induced, and as a consequence the total interface expanded. It was found that the use of esters as organic solvents induced a decrease of the size of the dispersed structures. The interconnection of the aqueous microdomains and their dynamics were monitored by both static and time-resolved fluorescence quenching spectroscopy using Ru(bipy)32+ as fluorophore and Fe(CN)63- as quencher. It was found that the rates of inter- and/or intra-micellar exchange of water molecules were very slow because they appeared quite immobilized close to the lecithin polar heads. According to the results of the dynamic studies, appropriate organogels were formulated and used to incorporate model bioactive compounds with medicinal or cosmetic interest such as caffeine and theophylline. When these systems were tested for trans-membrane diffusion, they showed a 24 h permeation of 20% and 35%, respectively.     

Comprehensive Two-Dimensional Gas Chromatography–Mass Spectrometry Analysis of Exhaled Breath Compounds after Whole Grain Diets

Exhaled breath is a potential noninvasive matrix to give new information about metabolic effects of diets. In this pilot study, non-targeted analysis of exhaled breath volatile organic compounds (VOCs) was made by comprehensive two-dimensional gas chromatography–mass spectrometry (GCxGC-MS) to explore compounds relating to whole grain (WG) diets. Nine healthy subjects participated in the dietary intervention with parallel crossover design, consisting of two high-fiber diets containing whole grain rye bread (WGR) or whole grain wheat bread (WGW) and 1-week control diets with refined wheat bread (WW) before both diet periods. Large interindividual differences were detected in the VOC composition. About 260 VOCs were detected from exhaled breath samples, in which 40 of the compounds were present in more than half of the samples. Various derivatives of benzoic acid and phenolic compounds, as well as some furanones existed in exhaled breath samples only after the WG diets, making them interesting compounds to study further.     

Measuring H-bonding in supramolecular complexes by gas phase ion-molecule reactions

H/D and guest-exchange ion-molecule reactions have been used as a new tool to elucidate the operation of multiple hydrogen bonding in gas-phase complexes formed between phosphonate cavitands and ethyl-substituted ammonium ions.