Asymmetric synthesis of 2H-azirines derived from phosphine oxides using solid-supported amines. Ring opening of azirines with carboxylic acids

A simple and efficient asymmetric synthesis of 2H-azirine-2-phosphine oxides 3 is described. The key step is a solid-phase bound achiral or chiral amine-mediated Neber reaction of beta-ketoxime tosylates derived from phosphine oxides 1. Reaction of 2H-azirines 3 and 11 with carboxylic acids 4 gives phosphorylated ketamides 5 and 12. Ring closure of ketamides 5 and 12 with triphenylphosphine and hexachloroethane in the presence of triethylamine leads to the formation of phosphorylated oxazoles 8 and 13.     

All-solid-state potentiometric sensors sensitive to nonionic surfactants based on ionophores containing ethoxylate units

Earlier work of potentiometric Ion-selective electrodes (ISEs) sensitive to nonionic surfactants of the polyethoxylate type is further extended. The ISEs constructed were all-solid-state sensors with plasticized PVC membranes. The sensing material was a tetraphenylborate salt of the barium complex with a polyethoxylate nonionic surfactant. As membrane component, the combinations of two polyethoxylates of the nonylphenoxy type, which differed in the number of oxyethylene units (5 or 12), and two different plasticizers, (o-nitrophenyloctyl ether and o-nitrophenylphenyl ether), were tested. The response of these electrodes to different nonionic surfactants and the interference effect of several species has been evaluated. For all the types of tested electrodes, the sensitivities shown were ca. 30.0 mV dec(-1) and the limit of detection, ca. 10(-5) M, when a nonylphenoxyde with 12 oxyethylene units was used as standard. The membrane with the best response characteristics was then applied in potentiometric titrations of this kind of surfactants in the presence of Ba(2+) ion and using tetraphenylborate as the titrant.     

Genomic clustering of the Trypanosoma cruzi nonlong terminal L1Tc retrotransposon with defined interspersed repeated DNA elements

We have analyzed the genomic distribution and organization of the long interspersed nucleotide element (LINE) L1Tc, a nonlong terminal repeat (LTR) retrotransposon of Trypanosoma cruzi. The results indicate that the L1Tc element is dispersed along the parasite genome and that in some regions it is organized in tandem repeats. The data allowed us to define the existence of short direct-repeated sequences flanking the genomic L1Tc elements. Relevant is the finding that the LINE L1Tc is located in genomic regions rich in short interspersed nucleotide elements (SINE)-like sequences. In particular, the L1Tc element is found associated to E13-related sequences, redefined in this work and renamed RS13Tc, and to a newly described RS1Tc sequence. The RS1Tc sequence is present, per haploid genome, in about 3,200 copies. Northern blot analysis showed that the RS1Tc is being transcribed into RNAs of different sizes. The analysis of the chromosomal distribution of these elements in various strains of T. cruzi suggested that this type of clustering might be a common feature of the genome of these parasites.     

Effects of Adsorbed Polyaniline on Redox Process on MoO3 Surface

The effects exhibited by adsorbed conducting polyaniline on the redox process on a molybdenum oxide surface were studied. Thermogravimetric results indicate a 4% polyaniline deposition. Cyclic voltammograms of the adsorbed polymer on MoO3 show that polyaniline exerts remarkable effects on the molybdenum blue oxidation-reduction process, with oxidation and reduction potentials of 0.33 and 0.18 V, respectively. This effect strongly enhances the electrode response, and can be used as an important tool in qualitative and/or quantitative determinations of molybdenum in solution as well as in any substrate. Copyright 1999 Academic Press.     

Stability study and determination of benzene- and naphthalenesulfonates following an on-line solid-phase extraction method using the new programmable field extraction system

Seven benzene- and naphthalenesulfonates (3-nitrobenzenesulfonate, 4-methylbenzenesulfonate, 1-hydroxy-4-naphthalenesulfonate, 1-amino-7-naphthalenesulfonate, 4-chlorobenzenesulfonate, 1-naphthalenesulfonate and 2-naphthalenesulfonate) were studied. A rapid method for quantifying aromatic sulfonated compounds from waste water samples was developed. This method consists in on-line in-field sampling and monitoring based on ion-pair solid-phase extraction with PLRP-S sorbent, using the new programmable field extraction system and ion-pair liquid chromatography with UV diode-array and electrospray mass spectrometry. Limits of detection for the studied compounds, using the SIM acquisition mode, ranged from 0.01 to 0.33 ng ml(-1). The influence of the aqueous matrix on the on-line SPE was checked by spiking ground and waste waters. Recoveries varied from 70 to 99% when 10 ml of water sample were enriched. The method was applied to the analysis of some environmental sewage samples. This study confirmed that high concentration levels of aromatic sulfonated compounds can be found in sewage samples. In addition, the stability of the seven studied sulfonated benzene and naphthalene compounds was investigated using on-line polymeric SPE pre-columns, based on the styrene-divinylbenzene polymer PLRP-S. Different storage conditions were tested to carry out the stability survey, which included storage at room temperature, at 4 degrees C and at -20 degrees C, during a period of up to 2 weeks. This study showed that the stability of aromatic sulfonic acids on disposable on-line SPE polymeric pre-columns is related to temperature and that the target compounds are more stable at lower temperatures.     

An evaluation of analytical techniques for determination of lead, cadmium, chromium, and mercury in food-packaging materials

Closed microwave digestion and a high-pressure asher have been evaluated for wet-oxidation and extraction of lead, cadmium, chromium, and mercury from a range of typical packaging materials used for food products. For the high-pressure asher a combination of nitric and sulfuric acids was efficient for destruction of a range of packaging materials; for polystyrene, however, nitric acid alone was more efficient. For microwave digestion, a reagent containing nitric acid, sulfuric acid, and hydrogen peroxide was used for all materials except polystyrene. Use of the high-pressure asher resulted in the highest recoveries of spiked lead (median 92%), cadmium (median 92%), chromium (median 97%), and mercury (median 83%). All samples were spiked before digestion with 40 microg L(-1) Cd, Cr, and Pb and 8 microg L(-1) Hg in solution. The use of indium as internal standard improved the accuracy of results from both ICP-MS and ICP-AES. Average recovery of the four elements from spiked packaging materials was 92 +/- 14% by ICP-MS and 87 +/- 15% (except for mercury) by ICP-AES. For mercury analysis by CVAAS, use of tin(II) chloride as reducing agent resulted in considerably better accuracy than use of sodium borohydride reagent.     

Synthesis of ynones by palladium-catalyzed acylation of terminal alkynes with acid chlorides

Phosphane-free oxime-derived palladacycle 2 is an efficient precatalyst for the copper-free acylation of terminal alkynes with different carboxylic acid chlorides in toluene in the presence of 3 equiv of TEA as base, giving the corresponding ynones in good yields. The coupling reaction can normally be performed under air or under inert atmosphere when very low catalyst loadings (10(-3) mol % Pd) (turnover numbers (TONs) up to 23,000, turnover frequencies (TOFs) up to 958 h(-1)) or sensitive carboxylic acid chlorides are used. In addition, Pd(OAc)(2) has been shown as an efficient catalyst for the ligandless process, although usually working under higher loading conditions. This new protocol allows one to perform the synthesis of ynones at 110 degrees C, at room temperature, or under microwave irradiation conditions.     

Analysis of polar hydrophilic aromatic sulfonates in waste water treatment plants by CE/MS and LC/MS

The present work describes the development and optimization of a capillary (zone) electrophoresis/mass spectrometric (CE/MS) analysis method for polar hydrophilic aromatic sulfonates (ASs). The compounds were detected by negative ion electrospray ionization (NIESI) and selected ion monitoring (SIM). In comparison with CE/UV, for CE/MS a lower-concentration volatile ammonium acetate buffer (5 mM) without organic modifier and a higher separation voltage were better suited for separation. Sensitivity of CE/MS was slightly better than for CF/UV, with the limit of detection (LOD) ranging between 0.1 and 0.4 mg l(-1). For verification of the CE/MS results, ASs were also analysed by ion-pair liquid chromatography/diode array UV detection coupled in series with electrospray mass spectrometry (IPC/DAD/ESI-MS). Real water samples of different waste water treatment plants (WWTPs) in Catalonia (NE Spain) were extracted by solid-phase extraction (SPE) with LiChrolut EN and analysed with CE/MS and LC/MS. ASs were found in influent and effluent water samples of the WWTPs in the microg l(-1) concentration range. LC/MS offered a higher separation efficiency and sensitivity than CE/MS. Therefore with LC/MS more compounds could be identified in the WWTPs. The persistency of the ASs was distinct: some compounds were well degraded during the water treatment process, while others were quite persistent.     

Preparation of RCM substrates for azepinoindole synthesis: reductive amination versus tetrahydro-γ-carboline formation

Treatment of N-(phenylsulfonyl)-2-vinyl-3-indolecarbaldehydes with primary aliphatic amines under mild reductive amination conditions leads to tetrahydro-γ-carbolines in high yield. The process can be suppressed by changing the protecting group at the indole nitrogen for a methoxymethyl group, thus allowing the preparation of RCM substrates for azepinoindole synthesis.