Enantioseparation of chiral N-imidazole derivatives by electrokinetic chromatography using highly sulfated cyclodextrins: mechanism of enantioselective recognition

Baseline separation of ten new substituted [1-(imidazo-1-yl)-1-phenylmethyl)] benzothiazolinone and benzoxazolinone derivatives, with one chiral center, was achieved by CD-EKC using highly sulfated CDs (alpha, beta, gamma highly S-CDs) as chiral selectors. The influence of the type and concentration of the chiral selectors on the enantioseparations was investigated. The highly S-CDs exhibit a very high enantioselectivity power since they allow excellent enantiomeric resolutions compared to those obtained with the neutral CDs. The enantiomers were resolved with analysis times inferior to 2.5 min and resolution factors R(s) of 3.73, 3.90, 1.40, and 4.35 for compounds 1, 2, 3, and 5, respectively, using 25 mM phosphate buffer at pH 2.5 containing either highly S-alpha-CD, highly S-beta-CD, and highly S-gamma-CD (3 or 4% w/v) at 298 K, with an applied field of 0.30 kV/cm. The determination of the enantiomer migration order for the various analytes and the study of the analyte structure-enantioseparation relationships display the high contribution of the interactions between the analytes phenyl ring and the CDs to the enantiorecognition process. The thermodynamic study of the analyte-CD affinities permits us to improve our knowledge about the enantioseparation mechanism.     

Chiral separation of N-imidazole derivatives, aromatase inhibitors, by cyclodextrin-capillary zone electrophoresis. Mechanism of enantioselective recognition

Baseline separation of ten new, substituted [1-(imidazo-1-yl)-1-phenylmethyl)] benzothiazolinone and benzoxazolinone derivatives with one chiral center was achieved using cyclodextrin-capillary zone electrophoresis (CD-CZE). A method for the enantiomeric resolution of these compounds was developed using neutral CDs (native alpha-, beta-, gamma-CDs or alpha-, beta-, gamma-hydroxypropyl (HP)-CDs) as chiral selectors. Operational parameters including the nature and concentration of the chiral selectors, pH, ionic strength, organic modifiers, temperature, and applied voltage were investigated. The use of neutral CDs provides enantiomeric resolution by inclusion of compounds in the CD cavity. The HP-alpha-CD and HP-beta-CD were found to be the most effective complexing agents and allowed efficient enantiomeric resolutions. Optimal separation of N-imidazole derivatives was obtained using 50 mM phosphate buffer at pH 2.5 containing either HP-alpha-CD or HP-beta-CD (7.5-12.5 mM) at 25 degrees C, with an applied field of 0.50 kV.cm(-1) giving resolution factors Rs superior to 1.70 with migration times of the second enantiomer less than 13 min. The same enantiomer migration order observed for all molecules can be related to a close interaction mechanism with CDs. The influence of structural features of the solutes on Rs and tm was studied. The lipophilic character (log kw) of the solutes and the apparent and averaged association constants of inclusion complexes for four compounds with the six different CDs led us to rationalize the enantioseparation mechanisms. The conclusions were corroborated with reversed-phase high-performance liquid chromatography (HPLC) on chiral stationary phases (CSPs) based on CDs.     

Straightforward route for anchoring a glucosyl moiety onto nucleophilic species: reaction of amines and alcohols with carboxymethyl 3,4,6-tri-O-acetyl-alpha-D-glucopyranoside 2-O-lactone

The base-catalyzed reaction of carboxymethyl 3,4,6-tri-O-acetyl-alpha-D-glucopyranoside 2-O-lactone (prepared from isomaltulose) with amino acids and fatty amines under basic catalysis gave a series of new pseudoglucopeptides, nonionic amphiphiles, and polymerizable derivatives. The same reaction applied to alcohols provided the corresponding 2-(alpha-D-glucopyranosyloxy)acetyl esters with either basic or acidic catalysts.     

Chiral Resolution of the Enantiomers of New Aromatase Inhibitors by Liquid Chromatography on Amylose Stationary Phases

Analytical HPLC methods for derivatized amylose chiral stationary phases were developed for the direct enantioseparation of substituted [1-(imidazo-1-yl)-1-phenylmethyl)] benzothiazolinone and benzoxazolinone derivatives with one stereogenic center. These analogues of fadrozole constitute new potent nonsteroidal inhibitors of aromatase (P450 arom.). The separations were made using normal phase methodology with mobile phase consisting of n-hexane-alcohol (ethanol, 1-propanol or 2-propanol) in various proportions, and a silica-based amylose tris-3,5-dimethylphenylcarbamate (Chiralpak AD), or tris-(S)-1-phenylethylcarbamate (Chiralpak AS). The effects of concentration of various aliphatic alcohols in the mobile phase were studied. Baseline separation (R_s > 1.5) was easily obtained in all cases, ethanol being often the more interesting modifier. The effects of structural features of the solutes along with the temperature of the column on the discrimination between the enantiomers were examined for different mobile phase compositions.     

New Fluorescent Sensors Based on 1<Emphasis Type="Italic">H</Emphasis>-pyrazolo[3,4-<Emphasis Type="Italic">b</Emphasis>]quinoline Skeleton

Novel fluorescing dyes 1,3,4-triphenyl-6-(1,4,7,10-tetraoxa-13-aza-cyclopentadec-13-ylmethyl)-1H-pyrazolo[3,4-b]quinoline (K1) and 2-[(2-hydroxyethyl)-(1,3,4-triphenyl-1H-pyrazolo[3,4-b]quinolin-6-ylmethyl)-amino]ethanol (L1) have been synthesized and investigated by the means of steady state and time-resolved fluorescence techniques. These compounds act as sensors for the fluorescence detection of small inorganic cations (lithium, sodium, barium, magnesium and calcium) in solvents of different polarities (THF and acetonitrile). The mechanism, which allows application of these compounds as sensors, is an electron transfer from the electro-donative part of molecule to the acceptor part (fluorophore), which is retarded upon complexation of the electro-donative part by inorganic cations. We found that crown ether-containing compound is very sensitive to the addition of any investigated ions but amino alcohol-containing one exhibits better selectivity to the addition of two-valued cations. Two kinds of the complexes (LM⁺ and L₂M⁺) were found in the investigated systems. In addition, the dyes may be used as fluorescence indicators in solvents of lower polarity like tetrahydrofuran.     

A general method for convergent synthesis of functionalized exo-glycals based on halogenation and Suzuki cross-coupling of 1-exo-methylene sugars

Functionalized exo-glycals can be readily obtained by palladium catalyzed Suzuki cross-coupling of halo-exo-glycals with boronic acids.     

Exploring Reversible Quenching of Fluorescence from a Pyrazolo[3,4‐b]quinoline Derivative by Protonation

Pyrazolo[3,4‐b]quinoline derivatives are reported to be highly efficient organic fluorescent materials suitable for applications in light‐emitting devices. Although their fluorescence remains stable in organic solvents or in aqueous solution even in the presence of H₂O, halide salts (LiCl), alkali (NaOH) and weak acid (acetic acid), it suffers an efficient quenching process in the presence of protic acid (HCl) in aqueous or ethanolic solution. This quenching process is accompanied by a change in the UV spectrum, but it is reversible and can be fully recovered. Both steady‐state and transient fluorescence spectra of 1‐phenyl‐3,4‐dimethyl‐1H‐pyrazolo‐[3,4‐b]quinoline (PAQ5) during quenching are measured and analyzed. It is found that a combined dynamic and static quenching mechanism is responsible for the quenching processes. The ground‐state proton‐transfer complex [PAQ5 ??? H⁺] is responsible for static quenching. It changes linearly with proton concentration [H⁺] with a bimolecular association constant K_S=1.95 M ^?1 controlled by the equilibrium dissociation of HCl in ethanol. A dynamic quenching constant K_D=22.4 M ^?1 is obtained by fitting to the Stern–Volmer equation, with a bimolecular dynamic quenching rate constant k_d=1.03×10⁹ s^?1 M ^?1 under ambient conditions. A change in electron distribution is simulated and explains the experiment results.     

Star-burst 1H-pyrazolo[3,4-b]quinoline as chromophore for light-emitting diodes and photovoltaic devices

The current–voltage and electroluminescent features of a novel star-burst 1H-pyrazolo[3,4-b]quinoline chromophore show that it has potential applications as a material for light-emitting diodes. The electroluminescence covers the white light spectral range from 420 nm up to 610 nm and achieves maximal value about 18 Cd/m² at biased voltage 23 V. The photovoltaic efficiency achieved was equal to about 0.08%.     

Influence of dipole moments on light-emitting features of cardo-type 1H-pyrazolo[3,4-b]quinolines

Several 1H-pyrazolo[3,4-b]quinoline derivatives were synthesized from 9,9′-di(p-aminophenyl)fluorene as possible dye chromophore for the organic light-emitting diodes. All the compounds exhibit strong fluorescence in solution and in solid state as well. The maximally achieved brightness was 65 Cd/m² and spectral range of electroluminescence (EL) covers the wavelength ranges from 420 up to 470 nm. The prepared compounds were used as dye luminophores in poly(N-vinylcarbazole) (PVK) matrix for single-layer EL light-emitting device. Principal goal of the work consists in an establishment of a possibility to operate by their light-emitting features (spectral positions of emitting lines, efficiency of electroluminescence, brightness, etc.) by appropriate changes of state dipole moments of the particular chromophore determined by semi-empirical quantum chemical calculations. The principal physical mechanism of such effects is explained within dipole-dipole interactions between the dye chromophores and PVK polymer chains.     

Sweeping total reflection X-ray fluorescence optimisation to monitor the metallic contamination into IC manufacturing

Among the methods available on the market today to control as metallic contamination in integrated circuit manufacturing, Sweeping Total reflection X-ray Fluorescence mode appears a very good method, providing fast and entire wafer mapping. With the goal of a pertinent use of Sweeping Total reflection X-ray Fluorescence in advanced Integrated Circuit manufacturing this work discusses how acceptable levels of contamination specified by the production (low levels to be detected) can be taken into account.