Etude conformationnelle des formes ouvertes d'un spiropyranne benzothiazolinique

The results of the conformational study of a benzothiazolinic dimethinmérocyanine (open form) are described. Variations of electron π energy (Pariser-Parr-Pople method) and of non bonding energy are considered.All possible conformations have been investigated and the results of computations give evidence for a twisted structure, confirming a previous study taking account of σ and π electrons (Extended Huckel method).     

Synthesis, reactivity, and ligand properties of a stable alkyl carbene

Stable tert-butyl diisopropylamino carbene is more nucleophilic but also more electrophilic than diamino carbenes; it undergoes cyclopropanation reactions and easily binds to metal fragments.     

A micro co-precipitation technique for use in X-ray fluorescence analysis

An apparatus and a procedure are described for the preconcentration of nanogram amounts of trace elements. Co-precipitation and pressure filtration confine the precipitate to a 1.27 mm diameter spot on a filter membrane. Trace elements in the 10-100 ng range are collected reproducibly and detected with high sensitivity by X-ray fluorescence, by use of a milliprobe instrument. Advantages of the technique for quantitative applications are discussed.     

Molar heat capacity of a vitreous solid electrolyte: Ag7I4AsO4

Vitreous solid electrolytes occupy an interesting position between crystalline solid electrolytes and molten salts. In the present work, measurements of the molar heat capacity of vitreous Ag₇I₄AsO₄ indicate that the anion sublattice may become progressively disordered in a reversible manner at temperatures well below the glass-liquid transition temperature. The effect of this on the silver ion mobility is briefly discussed.     

Toward improving the chemistry of N-acyliminium ions: nucleophilic substitution reactions of pyrrolidinone derivatives with trialkylsilyl nucleophiles catalyzed by triisopropylsilyltrifluoromethane sulfonate (TIPSOTf)

[reaction: see text] Nucleophilic substitution reactions of racemic and chiral 5-acetoxy-, 5-ethoxy-, and 5-methoxypyrrolidin-2-ones by silicon-based nucleophiles were efficiently catalyzed by TIPSOTf. This process was found to be general and accommodates a broad range of substrate-nucleophile combinations.     

Contrasting effects of exterior and interior hydrophobic moieties in the complexation of amino acid functionalized gold clusters with alpha-chymotrypsin

[chemical structure: see text]. A series of L-amino acid functionalized gold nanoparticles with oligo(ethylene glycol) (OEG) tethers of varying length are prepared. These studies show that the hydrophobic side chains of amino acids facilitate the structural retention of alpha-chymotrypsin (ChT) but the interior alkyl chains promote its denaturation. An 80-fold range of denaturation rate constants were obtained for ChT in the presence of various nanoparticles. Thus, the tunable denaturation of protein could be achieved by rational combination of amino acid side chains and OEG tethers.     

An artificial siderophore for the detection of iron(III)

An artificial siderophore in the form of a squaraine dye (1) has been synthesized. The bidentate ligand chelates to Fe(III) between the deprotonated hydroxyl group on the ortho position of the ring adjacent to the carbonyl group of the cyclobutadiene ring. The optical response is due to a subtle geometry change of 1 on chelation to Fe(III). This artificial siderophore forms a 2 ratio 1 ligand ratio metal complex, as indicated by a sigmoidal isotherm (K(a)= 10(7) M(-1)). The optical response on the addition of Fe(III) is observed at low concentrations in comparison to other metal salts. The X-ray crystal structure and calculated structures of dye (1) are also included, and will be discussed.