Gas phase intramolecular proton transfer in cationized glycine and chlorine substituted derivatives (M-Gly, M = Na+, Mg2+, Cu+, Ni+, and Cu2+): existence of Zwitterionic structures?

The intramolecular proton transfer in cationized glycine and chlorine substituted derivatives with M = Na+, Mg2+, Ni+, Cu+, and Cu2+ has been studied with the three parameter B3LYP density functional method. The coordination of metal cations to the oxygens of the carboxylic group of glycine stabilizes the zwitterionic structure. For all monocations the intramolecular proton transfer occurs readily with small energy barriers (1-2 kcalmol(-1)). For the dication Mg2+ and Cu2+ systems, the zwitterionic structure becomes very stable. However, whereas for Mg2+, the proton transfer process takes place spontaneously, for Cu2+ the reaction occurs with an important energy barrier. The substitution of the hydrogens of the amino group by chlorine atoms decreases the basicity of nitrogen, which destabilizes the zwitterionic structure. For monosubstituted glycine complexed with Na+, the zwitterionic structure still exists as a minimum, but for disubstituted glycine no minimum appears for this structure. In contrast, for Mg2+ complexed to mono- and disubstituted glycine, the zwitterionic structure remains the only minimum, since the enhanced electrostatic interaction with the dication overcomes the destabilizing effect of the chlorine atoms.     

Synthesis and crystal structure of [(η3-C3H5)(CO)2Mo(μ-S2CPCy3)-Mo(η3-CH2CMeCH2)(CO)2]

A novel dimolybdenum complex [(³-C₃H₅)(CO)₂Mo(-S₂CPCy₃)Mo(³-CH₂CMeCH₂)(CO)₂], obtained by reacting the [(CO)₂(³-C₃H₅)Mo(-S₂CPCy₃)Mo(CO)₃]^– anion with an excess of ClCH₂CMe=CH₂, has been characterized by i.r., ³¹P{¹H}, ¹H- and ¹³C-n.m.r. spectroscopy and by elemental analysis. The crystal structure of the complex, determined by X-ray diffraction, shows a definite preference for the central carbon of the S₂CPCy₃ bridge to bind to the Mo(2) atom coordinated by ³-2-methylallyl, rather than the Mo(1) atom attached to unsubstituted ³-allyl ligand.     

Barreleneiridium(I) complexes. Crystal structures of [Ir(Me3TFB)(η6-C6H4Me2)]ClO4 and [Ir(TFB)(η5-PhNPh2)]BF4·CH2Cl2 (TFB = tetrafluorobenzobarrelene)

A new series of cationic areneiridium(I) complexes of formula [Ir(barrelene)(arene)]⁺ or [Ir(barrelene)(PhNRPh)]⁺ (R= Ph or H) have been synthesized from neutral iridium complexes of the type [IrY(barrelene)]_x (barrelene = Me₃TFB, Y = Cl or OMe (x = 2), Y = acac (x = 1); barrelene = TFB, Y = OMe (x = 2), Y = acac (x = 1)). The crystal structures of [Ir(Me₃TFB)(1,4-C₆H₄Me₂)]ClO₄ and [Ir(TFB)(PhNPh₂)]BF₄·CH₂Cl₂ have been determined by X-ray diffraction. They crystallize in the space groups Pbca and Pna2₁ respectively with lattice constants of 17.6947(11), 15.8072(10), 16.0019(11) Å and 9.8059(2), 20.8097(9), 14.3367(4) Å. Final R factors were 0.063 and 0.042 for the observed data. Both complexes show a staggered arrangement between the arene and the TFB moieties and deviation from planarity of the coordinated arene ligands. In the second complex the IrC and NC distances, the CNC angle, the type of arene puckering, and the spectroscopic data indicate a distortion of the coordinated arene towards a η⁵-coordinated iminocyclohexadienyl form.     

Analysis of99Tc atmospheric samples

The analysis of⁹⁹Tc was carried out in filter, peat and rainwater samples. A solvent extraction technique was used to separate Tc from them, where tributylphosphate was the extracting agent. Radiochemical yield was obtained by using^99mTc as an internal tracer. A typical value of 60% was found for it. However, problems encountered in its determination are discussed in the text. Additionally, rainwater samples were analyzed for¹³⁷Cs. This was adsorbed in ammonium phosphomolibdate. Radiochemical yield was obtained by using¹³⁴Cs as an internal tracer.Work partially supported under Contract CAICYT No. 2849/83.     

Extraction-spectrophotometric determination of iron with 2-(2′-benzothiazolylazo)-4,6-dimethylphenol

An extraction-spectrophotometric method for the determination of trace amounts of iron based on its extraction into chloroform with 2-(2-benzothiazolylazo)-4,6-dimethylphenol (BTADMP) from a pH 6.5 medium has been developed. The extracted 12 FeBTADMP complex species allow the determination of 4–30gmg of iron (=3.92×10⁴1·mol^–1·cm^–1 at 790 nm). The method is highly selective and has been applied to the determination of iron in polymineral-polyvitamin pharmaceutical products.     

Sensitive determination of probenecid in urine samples by reversed-phase liquid chromatography and UV-visible detection using solid-phase extraction techniques for sample clean-up

Summary This study describes a rapid method for the determination of probenecid in human urine by liquid chromatography with UV detection at 254 nm, after clean-up through a C8 solid-phase extraction column. Liquid chromatography was carried out on a C18-bonded phase using an acetonitrile-acetate buffer (pH=4) gradient elution. Ethacrynic acid was used as internal standard. The system has been applied to the determination of probenecid in the 0.10–100.0 g/ml concentration range; the limit of detection was 5 ng/mL.     

Salt Stress Proteins Identified by a Functional Approach in Yeast

We have performed functional genomics of salt stress by overexpression of gene libraries in yeast and selection for salt tolerance. Thirty halotolerance genes were isolated from yeast, Arabidopsis, and sugar beet. The results indicate that Na⁺ transport (uptake, efflux, and compartmentation), sulfate activation, RNA processing, and protein synthesis are crucial for salt tolerance.     

A study of the electrospray ionisation and ion-trap fragmentation of [M - H](-) ions of new 3,5-disubstituted tetrahydro-2H-1,3,5-thiadiazin-2-thiones

The electrospray ionisation (ESI) in negative mode of the pharmacologically significant 3,5-disubstituted tetrahydro-2H-1,3,5-thiadiazin-2-thiones, and their subsequent fragmentations using an ion-trap mass spectrometer, have been investigated. Experiments on sequential product ion fragmentations (MS(n)) were performed in order to elucidate the degradation pathways for these compounds. The data presented show that the fragmentation of the even-electron [M - H](-) ions could proceed through an internal nucleophilic substitution displacement. Decarboxylation and extrusion of carbon disulfide are other fragmentations observed.     

Ring-closing metathesis of chiral allylamines. Enantioselective synthesis of (2S,3R,4S)-3,4-dihydroxyproline

The ring-closing metathesis (RCM) of two types of unsaturated chiral allylamines III, easily available from enantiomerically enriched epoxy alcohols, has been studied. Fully protected allylamines IIIa [(1)R = CH(2)-(CH(2))(n)()-CH=CH(2); (2)R = Boc; (3)R = PMB] have been prepared from unsaturated epoxy alcohols, whereas bis-allylamines IIIb ((1)R = Ph, (2)R = allyl,(3)R = Boc or PMB) have been prepared from 2,3-epoxy-3-phenylpropanol. Both types have been subjected to RCM to provide either cyclic allylamine I or II. The synthetic potential of these intermediates has been demonstrated by the enantioselective synthesis of (2S,3R,4S)-3,4-dihydroxyproline.