Development of a new high performance low pressure chromatographic system using a multisyringe burette coupled to a chromatographic monolithic column

A novel combination of high performance low pressure chromatography with multisyringe flow injection analysis is presented. This system comprises a multisyringe module, three low pressure solenoid valves, a monolithic Chromolith Flash RP-18e column and a diode array spectrophotometer. UV detection is carried out at 250 nm. AutoAnalysis software is used for instrumental control and automated data collection. The results obtained with multisyringe liquid chromatography (MSC) were compared with those obtained with a HPLC system using similar conditions. The chromatographic parameters were calculated from a mixture of anthracene and thiourea using a mobile phase containing acetonitrile-water (60:40) at a flow rate of 2 ml min⁻¹. The proposed MSC system has been successfully applied to the determination of amoxicillin, ampicillin and cephalexin using a mobile phase of sodium acetate buffer (pH 6.2, 0.1 mol l⁻¹)-methanol (90:10) at a flow rate of 2 ml min⁻¹. The low-cost, flexibility and simplicity of MSC should be highlighted.     

Phase behavior and surface tensions of amphiphilic fluorinated random copolymer aqueous solutions

Phase behavior and surface tension of aqueous solutions of fluorinated random copolymers [perfluoroalkylacrylate]–[poly(ethyleneoxide)methacrylate], [C_mRf-acrylate]-[EO_n-methacrylate] with fluroalkyl carbon number m = 8, 6, 4, 2 and number of ethyleneoxide unit, n = 9 and 4.5 were investigated as a function of composition and different combinations of m and n. Isotropic solutions are formed at lower temperatures over wide concentration range of copolymer but at higher temperature phase separation occurs. The cloud point of copolymer decreases with decreasing n as well as m, and also with decreasing the number of poly(ethyleneoxide)methacrylate chain per perfluorinatedalkylacrylate chain, suggesting that the copolymers become more hydrophobic on decreasing m and n. Equilibrium and dynamic surface tension measurements show that copolymers become increasingly surface active as m as well as n decrease but the adsorption at the air–water interface is very slow due to bulkiness of the molecules. No clear evidence of the formation of micellar aggregates could be obtained from surface tension–composition curves.     

Effectiveness of universal pre-enrichment broth for recovery of Salmonella from selected dairy foods

The relative efficiencies of 2 Bacteriological Analytical Manual (BAM) pre-enrichments, lactose broth (LAC) and brilliant green water (BGW), were compared with Universal Pre-enrichment (UP) broth for the recovery of individual Salmonella serovars from instant nonfat dry milk (NFDM), dry whole milk (DWM), lactic casein (LC), and liquid whole milk (LWM). BGW was compared with UP broth for the analysis of NFDM and DWM but not with the other 2 matrixes. LAC was compared with UP broth for the analysis of LC and LWM. UP broth was made both from a commercial dehydrated preparation (UPC) and from individual ingredients (UPI). Bulk quantities of the selected dairy foods were inoculated with Salmonella serovars at levels intended to produce fractionally positive results, where at least half of the test portions analyzed, with one of the methods being evaluated, would be shown to be Salmonella-positive. For NFDM, in 6 of 9 experiments, with 2 different Salmonella serovars, BGW was significantly more productive than either UPI or UPC broth (p < 0.05). Salmonella was recovered from 118 of 180 test portions with BGW, from 25 of 180 test portions with UPC, and from 14 of 180 test portions with UPI. For DWM, in 2 of 4 experiments, with 2 different Salmonella serovars, BGW was significantly more productive than either UPI or UPC broth (p < 0.05). Salmonella was recovered from 67 of 80 test portions with BGW, from 36 of 80 test portions with UPC, and from 37 of 80 test portions with UPI. For LWM, in 9 of 9 experiments, with 3 different Salmonella serovars, there were no significant differences among the broths. Salmonella was recovered from 120 of 180 test portions with LAC, from 135 of 180 test portions with UPC, and from 129 of 180 test portions with UPI. For LC, in 5 of 7 experiments, with 2 different Salmonella serovars, both UPI and UPC broth were significantly more productive than LAC (p < 0.05). Salmonella was recovered from 42 of 140 test portions with LAC, from 114 of 140 test portions with UPC, and from 114 of 140 test portions with UPI. In addition, overall results showed that UPC and UPI broths were equivalent for the recovery of Salmonella from the foods tested, without regard to their performance in comparison with either LAC or BGW.     

Structural, spectral, and magnetic properties of end-to-end di-mu-thiocyanato-bridged polymeric complexes of Ni(II) and Co(II). X-ray crystal structure of di-mu-thiocyanatobis(imidazole)nickel(II)

Thiocyanatonickel(II) and thiocyanatocobalt(II) complexes of the composition Ni(NCS)(2)(HIm)(2) (1) and Co(NCS)(2)(HIm)(2) (2), where HIm = imidazole, were prepared and studied. In particular, the crystal structure of Ni(NCS)(2)(HIm)(2) was determined by X-ray methods. This compound crystallizes in the monoclinic system, space group P2(1)/n, with a = 7.720(1) A, b = 5.557(1) A, c = 13.774(3) A, beta = 102.54(3) degrees, and Z = 2. Its structure consists of a one-dimensional polymeric chain in which nickel(II) ions are bridged by two thiocyanate groups bonding in an end-to-end fashion in a trans arrangement. The Ni...Ni distance is 5.557(1) A. The crystal packing is determined by the intermolecular hydrogen bonds and ring-stacking interactions. From their X-ray powder-diffraction patterns and IR spectra, the complexes 1 and 2 were found to be mutually isomorphous. The coordination compounds were identified and characterized using elemental analysis, magnetic measurements, and infrared and ligand-field spectra. Both complexes are first examples of ferromagnetically coupled one-dimensional polymeric compounds with double end-to-end thiocyanate bridges. The magnetic properties of the title compounds were investigated over the 1.9-290 K temperature range. The compounds exhibit long-range magnetic ordering with T(c) equal to 5.0 and 5.5 K for 1 and 2, respectively. Their isothermal magnetization was also studied. The magnetostructural properties of the nickel(II) compound obtained are discussed and compared to those of other double end-to-end thiocyanate-bridged nickel(II) complexes.     

Self-assembly of a hydrophobically modified naphthalene-labeled poly(acrylic acid) polyelectrolyte in water: organic solvent mixtures followed by steady-state and time-resolved fluorescence

The solution properties of two water-soluble polymers, poly(acrylic acid) (PAA), covalently labeled with the fluorescent hydrophobic dye naphthalene (Np), have been investigated in water:organic solvent mixtures. The naphthalene chromophores have been randomly attached, onto the polymer, with two different degrees of labeling. Fluorescence measurements (steady-state and time-resolved) have been used to follow the photophysical behavior of the polymers and consequently report on the self-association of the polymers in the mixed organic (methanol or dioxane):aqueous solutions. The emission spectra of the high-labeled Np PAA reveal the presence of monomer and excimer bands whereas with the low-labeled polymer only monomer emission is observed. The excitation spectra collected at the monomer and excimer emission bands show significant differences, depending on the water content of the mixture, which indicate the simultaneous presence of preformed and dynamic dimers as routes to excimer formation. The time-resolved data decay profiles of the high-labeled polymer in the mixtures were always triple exponential whereas in pure methanol and dioxane they follow biexponential laws. The data in the mixtures are consistent with two types of monomers and one excimer. Both monomers are able to give rise to excimer in the excited state, one type involving the movement of long distant Np chromophores and the other involving a local reorientation of adjacent Np chromophores. These correspond to different decay times: (1) a long which corresponds to the long distant approach of non-neighboring Np chromophores forming an excimer and (2) a short corresponding to the fast adjustment of two neighboring Np chromophores in order to have the adequate parallel geometry. An additional decay time corresponding to the excimer decay was found to be present at all wavelengths. All the decay times were dependent on the water content of the mixture. An estimation of the two excimer forming rate constants values is made for the mixed media considered in this work. On the whole, using both steady-state and time-resolved fluorescence parameters, and by comparing data for a polymer with a small number of hydrophobes with a more highly modified one, it is possible in great detail to demonstrate how association is controlled by solvent quality for the hydrophobes and by the distance between hydrophobes.     

Photodetachment spectrum of OHF-: three-dimensional study of the heavy-light-heavy resonances

In this work a simulation of the OHF(-) photodetachment spectrum is performed in a three-dimensional potential energy surface recently developed for OHF((3)A(")). The ground (2)A(') state potential of the anion is calculated in three dimensions based on accurate ab initio calculations and the reaction dynamics is studied using a wave packet method. The calculated spectrum shows a sequence of bands associated to vibrational HF(v) up to v=3. Each band is formed by a continuous spectrum and resonant structures. These resonances are associated to the OH-F channel well of the (3)A(") PES, in which fragmentation occurs through vibrational predissociation. Above the OH(v=0) threshold a new resonant pattern appears corresponding to heavy-light-heavy resonances. Special attention is paid to the assignment of these resonances because they mediate the reaction dynamics in the OH+F collision at low kinetic energies. The sequence of bands is in rather good agreement with that appearing in the experimental spectrum, especially at higher electron kinetic energies. At low kinetic energies, however, some other electronic states may contribute. The resonance structures might be washed out by the rotational average and the relatively low energy resolution of the experiment.     

Photochemical versus aluminium chloride-catalyzed fries rearrangement of aryl hydrogen succinates. synthesis of 2(3H)-furanones

Summary The photochemical and aluminium chloride-catalyzed Fries rearrangement of a series of aryl hydrogen succinates3 a–f to the corresponding 4-oxoacids1 a–f are compared. Both approaches are complementary: the photochemical process is more general and becomes the method of choice for the succinoylation of phenols supporting alkoxy or hydroxy substituents, while the classical rearrangement is superior in the presence of alkyl or halogen substituents. These results are applied to the preparation of the 2(3H)-furanones2 a–f.

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Photochemische und Aluminiumchlorid-katalysierte Friessche Umlagerung von Bernsteinsäuremonoarylestern. Synthese von 2(3H)-Furanonen

Zusammenfassung Die photochemische und AlCl₃-katalysierte Friessche Umlagerung einer Reihe von Bernsteinsäuremonoarylestern3 a–f zu den entsprechenden 4-Oxosäuren1 a–f werden verglichen. Beide Methoden ergänzen einander: Der photochemische Prozeß ist breiter anwendbar und wird bei Phenolen mit Alkoxy- oder Hydroxy-Substituenten bevorzugt, während die klassische Umlagerung in Gegenwart von Alkyl- oder Halogen-Substituenten vorteilhafter ist. Diese Ergebnisse werden für die Synthese der 2(3H)-Furanone2 a–f angewendet.

     

Characterization of proteins from Spirulina platensis microalga using capillary electrophoresis-ion trap-mass spectrometry and capillary electrophoresis-time of flight-mass spectrometry

In this work, a new capillary electrophoresis-mass spectrometry (CE-MS) procedure is developed to analyze proteins in Spirulina platensis microalgae. It is demonstrated that a fine optimization of several separation parameters is essential in order to achieve suitable CE-MS analysis of these proteins in natural extracts from microalgae. Namely, optimization of the composition of the separation buffer, electrospray conditions, and washing routine between runs are required in order to obtain reliable and reproducible CE-MS analyses of the main proteins found in this microalga (namely, allophycocyanin-alpha chain, allophycocyanin-beta, c-phycocyanin-alpha, and c-phycocyanin-beta). The relative molecular mass of these biopolymers is determined using two different MS instruments coupled to CE, i.e., CE-ion trap-MS and CE-time of flight-MS (CE-TOF-MS). A comparison between the results obtained with both instruments is carried out. The high resolution of the TOF-MS enables the distinction of small modifications in proteins and, thus, a more accurate mass determination. Interestingly, molecular mass values obtained by both CE-MS procedures agree very well while these experimental values are only in partial agreement with those theoretically expected (i.e., genetically derived masses). Some protein modifications due to amino acids exchange induced by nucleotide codon mutations are proposed to explain this difference.     

Preparation of α,n-dilithiotoluene equivalents. Synthesis of tamoxifen

The successive reaction of chlorobenzyl alcohols with n-butyllithium and lithium powder in the presence of a substoichiometric amount of 4,4′-di-tert-butylbiphenyl (DTBB) at −78°C yields the expected (lithiooxymethyl)phenyllithium derivative, which is trapped by reaction with different ketones. The subsequent arene-catalysed lithiation at 25°C permits the one-pot chemoselective lithiation of the primary benzyl alcoholate in the presence of a tertiary one. These new functionalised benzyllithium derivatives react with different electrophilic compounds, such as aldehydes, ketones and chlorotrimethylsilane, to give after hydrolysis the expected functionalised benzyl alcohols. Some of these alcohols are successfully transformed into mono- or di-olefins by acidic treatment. This whole strategy is applied to the preparation of anti-cancer drug tamoxifen.