Hexaruthenium carbonyl cluster complexes with basal edge-bridged square pyramidal metallic skeleton: efficient synthesis of 2-imidopyridine derivatives and determination of their reactive sites in carbonyl substitution reactions

The reactions of [Ru(3)(CO)(12)] with half equivalent of 2-amino-6-methylpyridine (H(2)ampy) or 2-aminopyridine (H(2)apy) in refluxing xylene give the hexanuclear products [Ru(6)(mu(3)-H)(2)(mu(5)-eta(2)-L)(mu-CO)(2)(CO)(14)] (L = ampy, 1; apy, 2). These reactions represent the first high-yield syntheses of hexanuclear complexes with a basal edge-bridged square pyramidal metallic skeleton. Five metal atoms of these complexes are bridged by the N-donor ligand in such a way that the edge-bridging metal atom is attached to the pyridine nitrogen, while the basal atoms of the square pyramid are capped by an imido fragment that arises from the activation of both N-H bonds of the NH(2) group. The reactive sites of these complexes in CO substitution reactions have been determined by studying the reactivity of 1 with triphenylphosphine. Two kinetically controlled monosubstitutions take place on the edge-bridging metal atom in positions cis to the pyridine nitrogen, leading to a mixture of two isomers of formula [Ru(6)(mu(3)-H)(2)(mu(5)-eta(2)-ampy)(mu-CO)(2)(CO)(13)(PPh(3))] (3 and 4). On heating at 80 degrees C, these monosubstituted isomers are transformed, via a dissociative pathway, into the product of thermodynamic control (5), which has the PPh(3) ligand on the apical Ru atom. The di- and trisubstituted derivatives [Ru(6)(mu(3)-H)(2)(mu(5)-eta(2)-ampy)(mu-CO)(2)(CO)(12)(PPh(3))(2)] (6) and [Ru(6)(mu(3)-H)(2)(mu(5)-eta(2)-ampy)(mu-CO)(2)(CO)(11)(PPh(3))(3)] (7) are stepwise formed from 3-5 and PPh(3). Compound 6 has the PPh(3) ligands on the edge-bridging and apical Ru atoms, and compound 7 has an additional PPh(3) ligand on an unbridged basal Ru atom. The compound [Ru(6)(mu(3)-H)(2)(mu(5)-eta(2)-ampy)(mu-CO)(2)(CO)(12)(mu-dppm)] (8), in which a basal and the apical Ru atoms are spanned by the dppm ligand, has been isolated from the reaction of 1 with bis(diphenylphosphino)methane.     

Studies on the synthesis of pentacyclic strychnos indole alkaloids. photocyclization of n-chloroacetyl-1,2,3,4,5,6-hexahydro-1,5-methanoazocino[4,3-b]indole derivatives

Photocyclization of 2-chloroacetyl-1,2,3,4,5,6-hexahydro-1, 5-methanoazocino[4,3-b]indole ($\text{5}$) takes place at the indole 4-position to give a 1 ,2 ,3 ,4 , 5 ,6-hexahydro-2 ,11-ethano-1 ,5-methanoazocino [4 , 3-6] indole system. Consequently, the method appears to be unsuitable for constructing the pyrrolidine ring of pentacyclic Strychnos indole alkaloids.     

Pyrylium-containing polymers as sensory materials for the colorimetric sensing of cyanide in water

A sensory polymeric material for the colorimetric sensing of cyanide in water has been developed based on the reactivity of this anion with the pyrylium cation.     

Size evolution of the vibrational predissociation process in Br2...Nen clusters: simulation and kinetic study

A hybrid quantum-classical simulation of the vibrational predissociation of Br2...Nen, (n = 2-11) clusters in the B electronic state is carried out. The time-evolution of the reactants, products, and intermediates is analyzed by a kinetic mechanism consisting of three elementary steps: direct vibrational predissociation (VP), intramolecular vibrational redistribution (IVR), and evaporative cooling (EC). The importance of intramolecular vibrational redistribution followed by evaporative cooling relative to direct vibrational predissociation is shown to increase rapidly with increasing cluster size. Final product state distributions reveal that only one or less Br2 stretching quantum per neon atom is required in order to achieve complete dissociation (n quanta for n < or = 9 and n - 1 for n = 10 and 11). The proportion of available energy going into translation is proposed as a parameter to study the statistical behavior of the Van der Waals clusters. It is shown to depend only on the number of remaining degrees of freedom, a characteristic of a statistical behavior, for n > or = 3.     

Screening and analytical confirmation of sulfonamide residues in milk by capillary electrophoresis-mass spectrometry

A new methodology is proposed to automate the monitoring of sulfonamide residues in milk samples. It combines a screening unit for the total amount of sulfonamide with capillary electrophoresis-mass spectrometry (CE-MS) equipment for processing the samples containing a detectable level of sulfonamide. The screening unit consists of continuous-flow system (CFS) to precipitate the proteins connected on-line to the CE-MS equipment, in which a common characteristic ion of all sulfonamides was monitored with the MS detector by flushing the sample through the capillary. The confirmatory method is based on the purification and preconcentration of sulfonamides in a CFS unit and posterior analysis by CE-MS. The sample treatment unit was also on-line connected to the CE-MS equipment. In order to increase sensitivity, the flow rate of the sheath liquid was diminished from 0.5 to 0.2 microL.min(-1) by increasing the content in water from 0 to 50% and the formic acid from 0.5 to 1.5% in this liquid and by applying an overimposed pressure of 5 mbar during the electrophoretic separation. The method allowed the analysis of 30 samples per hour.     

Design and synthesis of aromatic inhibitors of anthranilate synthase

Aromatic analogues of chorismate were synthesised as potential inhibitors of anthranilate synthase. Molecular modelling using GOLD2.1 showed that these analogues docked into the active site of Serratia marcescens anthranilate synthase in the same conformation as chorismate. Most compounds were found to be micromolar inhibitors of S. marcescens anthranilate synthase. The most potent analogue, 3-(1-carboxy-ethoxy)-4-hydroxybenzoate (K(I) 3 microM), included a lactyl ether side chain. This appears to be a good replacement for the enol-pyruvyl side chain of chorismate.     

Electrophoretic properties of complexes between DNA and the cationic surfactant cetyltrimethylammonium bromide

We use agarose gel electrophoresis to characterize how the monovalent catioinic surfactant cetyltrimethylammonium bromide (CTAB) compacts double-stranded DNA, which is detected as a reduction in electrophoretic DNA velocity. The velocity reaches a plateau at a ratio R = 1.8 of CTAB to DNA-phosphate charges, i.e., above the neutralization point, and the complexes retain a net negative charge at least up to R = 200. Condensation experiments on a mixture of two DNA sizes show that the complexes formed contain only one condensed DNA molecule each. These CTAB-DNA globules were further characterized by time-resolved measurements of their velocity inside the gel, which showed that CTAB does not dissociate during the migration but possibly upon entry into the gel. Using the Ogston-model for electrophoresis of spherical particles, the measured in-gel velocity of the globule is quantitatively consistent with CTAB having two opposite effects, reduction of both the electrophoretic charge and DNA coil size. In the case of CTAB the two effects nearly cancel, which can explain why opposite velocity shifts (globule faster than uncomplexed DNA) have been observed with some catioinic condensation agents. Dissociation of the complexes by addition of anionic surfactants was also studied. The DNA release from the globule was complete at a mixing ratio between anionic and cationic surfactants equal to 1, in agreement with equilibrium studies. Circular DNA retained its supercoiling, and this demonstrates a lack of DNA nicking in the compaction-release cycle which is important in DNA transfection and purification applications.     

Part I. epoxydes diterpeniques : synthese et reactivite d'epoxydes derives d'acides resiniques

Epoxidation of methyl esters of resin acids with the pimarane skeleton with p-nitroperbenzoic acid has permitted the isolation of epoxides of the intracyclic double bond. Allylic diterpenic alcohols were obtained by acid-catalysed isomerisation of diterpene epoxides, and the action of Collins reagent on these allylic alcohols has been studied.     

Synthesis of [13]-membered macrocyclic stevastelins via a transesterification reaction as the key step: total synthesis of stevastelin C3

A new synthesis of stevastelin C3 (3), a [13]-membered ring component of the stevastelin family, whose structure was recently revised, is reported. Initially, a macrolactonization approach was attempted to generate the [13]-membered macrolactone but this met with failure, so a translactonization reaction was tried to obtain the targeted stevastelin C3 (3) from the corresponding [15]-membered ring counterpart. Unfortunately, this strategy did not prove successful, and, consequently, we opted to undertake a transesterification reaction from 23, as a means to accommodate the requisite aminoacid moiety at the correct position, to obtain 24. From 24, and through intermediates 25-28, the acyclic precursor of the [13]-membered ring macrolactone, compound 30, was efficiently prepared. By utilizing the synthetic course developed by Chida, we took 30 forward and completed the total synthesis of stevastelin C3 (3).     

Determination of cadmium by electrothermal atomic absorption spectrometry after microwave-assisted digestion of animal tissues and sewage sludges

The determination of cadmium in different sample types has been carried out by electrothermal atomization atomic absorption spectrometry with D(2)-background correction using a unpyrocoated graphite tube, after pressurized microwave-assisted digestion. Five chemical modifiers [(NH(4))(2)HPO(4), Pd(NO)(3))(2), Ni(NO(3))(2), thiourea and Triton X-100] have been assayed and nickel nitrate has been found to be most effective for an accurate determination of cadmium in mussel tissue, pig kidney and sewage sludge. The characteristic mass of the method is of the order of 1 pg and the limit of detection is lower than 0.1 ng/ml.