Witnessing differences without redundancies

We show that elements suffice to witness the differences of pairwise distinct sets, and provide sufficient conditions for an infinite family of pairwise distinct sets to have a minimal collection of elements witnessing the differences between any two of its members.

     

Oxidative Cyclization of Iodo Ketones. Synthesis of 6-Oxa-5alpha-pregnane-3,20-dione

The steroidal delta- and gamma-iodo ketones 1 and 9 were converted to the cyclic hemiketals 3 and 10, by oxidation to the iodoso derivatives with m-CPBA. Spontaneous cyclization of the latter intermediates to the corresponding oxocarbenium ions, followed by stereoselective addition of water, rendered the hemiketals. Depending on the reaction conditions, the five-membered oxocarbenium ion derived from the gamma-iodo ketone 9 may add H(2)O or m-CPBA to give either the hemiketal or a Baeyer-Villiger type product 12, while the oxocarbenium derived from 1 gives exclusively the hemiketal. When the reaction was carried out in dry methanol, methyl ketals were formed. Use of this methodology allowed us to synthesize 6-oxa-5alpha-pregnanes with and without functionalization at C-19.     

Detection and quantitation of sulfonylurea herbicides in soil at the ppb level by capillary electrophoresis

A multi-residue analytical method based on solid-phase extraction enrichment combined with capillary electrophoresis (CE), using micellar electrokinetic capillary chromatography, was developed to isolate, recover and quantitate three sulfonylurea herbicides (chlorsulfuron, chlorimuron and metasulfuron) from soil samples. Optimization for CE separation was achieved using an overlapping resolution map scheme. The recovery of each herbicide was >80% and the limit of detection was 10 ppb. The capability of CE in providing quantitative analysis of sulfonylureas in soil samples at the ppb level has been demonstrated.     

Titrimetric semimicro determination of reducing sugars in wines and liquors

Summary A semimicro modification of the method ofFehling-Causse-Bonnams is described for the determination of invert sugar in wines and liquors. A relative standard deviation of 4 parts per thousand is obtained by closely adhering to a standardized procedure which is also required for the attainment of accuracy.

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Zusammenfassung Ein Halbmikroverfahren der Methode vonFehling-Causse-Bonnams wird für die Bestimmung von Invertzucker in Wein und Likören beschrieben. Der relative mittlere Fehler konnte durch Konstanthaltung der Versuchsbedingungen auf 0,4% beschränkt werden, eine Maßregel, die für die Erzielung richtiger Ergebnisse erforderlich ist. Die zur Entfärbung verwendete Pflanzenkohle adsorbiert auch etwa 2% des reduzierenden Zuckers pro 50 mg Kohle und der dadurch bedingte Korrektionsfaktor muß durch Kontrollanalysen mit Invertzuckerlösungen bekannten Gehaltes für jede Kohlesorte bestimmt werden.

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Résumé On décrit un procédé semi-micro pour la méthode deFehling-Causse-Bonnams pour le dosage du sucre interverti dans le vin et les liqueurs. L'erreur relative moyenne a pu être limitée à 0,4% par maintien constant des conditions de l'expérience; cette mesure est nécessaire pour l'obtention de résultats corrects. Le charbon végétal utilisé pour décolorer adsorbe environ 2% de sucre réducteur pour 50 mg de charbon et le facteur de correction qui en résulte doit, dans les analyses de contrôle, être déterminé pour chaque qualité de charbon avec des solutions de sucre interverti de teneur connue.

     

Application of technetium and rhenium carbonyl chemistry to nuclear medicine. Preparation of [NEt4]2[TcCl3(CO)3] from [NBu4][TcO4] and structure of [NEt4][Tc2(μ-Cl)3(CO)6]; structures of the model complexes [NEt4][Re2(μ-OEt)2(μ-OAc)(CO)6] and [ReBr({-CH2S(CH2)2Cl}2)(CO)3]

Transition Metal Chemistry - A detailed investigation of the one-pot synthesis of [NEt4]2[MX3(CO)3] [M=Tc (1a) or Re (1b); X= Cl?, Br?] is presented. The intermediates...     

The development of solid-surface fluorescence characterization of polycyclic aromatic hydrocarbons for potential screening tests in environmental samples

This paper presents the characterization of polycyclic aromatic hydrocarbons (PAHs) in solid-surface fluorescence as the first step for obtaining new optical sensors for PAHs screening. The fluorescence properties of the EPA-PAHs (naphthalene, acenaphthene, acenaphthylene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, chrysene, benzo[a]anthracene, benzo[k]fluoranthene, benzo[b]fluoranthene, benzo[a]pyrene, indeno [1,2,3-cd]pyrene, benzo[g,h,i]perylene and dibenzo[a,h]anthracene) on five types of solid-surfaces were evaluated. The experimental variables (pH and percentage of organic solvent in samples) were studied, obtaining different possibilities for making individual sensors for some of these PAHs and the best conditions for developing sensors for PAH screening were also studied.     

Controlling multivalent interactions in triply-threaded two-component superbundles

We have investigated the (1)H NMR spectra, the absorption spectra, the fluorescence spectra and decays, and the electrochemical properties of i). a tritopic receptor in which three benzo[24]crown-8 macrorings are fused onto a triphenylene core, ii). a trifurcated trication wherein three dibenzylammonium ions are linked 1,3,5 to a central benzenoid core, and iii). their 1:1 adduct which constitutes a triply-threaded, two-component supramolecular bundle. X-Ray crystallography has established the precise geometry of this paucivalent recognition motif in the solid state. In addition to [N(+)-H...O] hydrogen bonding and [C-H...O] interactions between the NH(2) (+) centers on the three dibenzylammonium ion containing arms of the trication and the three crown ether rings in the tritopic receptor, there is a stabilizing [pi...pi] stacking interaction between the two aromatic cores. Mass spectrometry and (1)H NMR spectroscopy have confirmed the integrity of the 1:1 adduct beyond the solid state, provided the solvents are relatively apolar (e.g., chloroform and acetonitrile). The intense fluorescence emissions of the two recognition components are quenched upon association with the concomitant appearance of a lower energy, broad fluorescence band originating from the pi-pi stacking in the 1:1 adduct of the aromatic cores in the two matching components. Titration experiments, including Job plots, establish the 1:1 stoichiometry of the adduct, an observation which is also confirmed by electrochemical experiments. The electrochemical results show that, both in the tritopic receptor and in the superbundle itself, the first oxidation process is associated with the hexaalkoxytriphenylene core. The successive oxidation processes of the peripheral dioxybenzene units are affected by charge-transfer interactions in the tritopic receptor, whereas, in the superbundle, such units are not interacting. In acetonitrile solution, dethreading/rethreading of the 1:1 adduct can be controlled quantitatively by addition of base and acid. Dethreading and rethreading is also observed by (1)H NMR spectroscopy when dimethylsulfoxide is added to a solution of the 1:1 adduct in equal volumes of acetonitrile and chloroform. A trifurcated trication where methyl groups are located on the para positions of the three dibenzylammonium ions, which are linked 1,3,5 to the neutral benzenoid core, has been employed to demonstrate that dethreading of the 1:1 adduct involves doubly-threaded and singly-threaded species, that is, the paucivalent site is dismembered in a sequence of logical steps involving stable intermediates. This molecular recognition system is a rare example of a supramolecular entity based on a cooperative binding motif that can be switched on and off by chemical means.     

Adsorption equilibria of butyl- and amylbenzene on monolithic silica-based columns

The adsorption isotherms of butyl- and amylbenzene on silica monolithic columns were measured by frontal analysis. The external, internal and total porosities of these columns were determined by inverse size-exclusion chromatography. The adsorption isotherms are concave upward in the entire concentration range investigated. They were fitted to the anti-Langmuir model, an unusual model in liquid-solid and liquid-liquid phase equilibria. Band profiles under overloaded conditions were recorded. They were in good agreement with the profiles calculated using th,e lumped pore diffusion model of chromatography and these adsorption isotherms.     

Reaction of sulfenes with heterocyclic N,N-disubstituted α-aminomethyleneketones. XII. Synthesis of [1]benzothiepino[4,5-e][1,2]oxathiin derivatives

The 1,4-cycloaddition of sulfene to N,N-disubstituted (E)-4-aminomethylene-3,4-dihydro[1]benzothiepin-5(2H)-ones I occurred only in the case of aliphatic N,N-disubstitution to give in good yield 4-dialkylamino-3,4,5,6-tetrahydro[1]benzothiepino[4,5-e][1,2]oxathiin 2,2-dioxides, which are derivatives of the new heterocyclic system [1]benzothiepino[4,5-e][1,2]oxathiin. Also the reaction of I with chlorosulfene occurred only in the case of aliphatic N,N-disubstitution to afford chiefly trans-4-dialkylamino-3-chloro-3,4,5,6-tetrahydro-[1]benzothiepino[4,5-e][1,2]oxathiin 2,2-dioxides III in satisfactory yield. Adducts III were dehydrochlorinated with DBN to 4-dialkylamino-5,6-dihydro[1]benzothiepino[4,5-e][1,2]oxathiin 2,2-dioxides in good yield.