Peroxodisulfate as a chemical initiator for methacrylate-ester monolithic columns for capillary electrochromatography

Organic monolithic stationary phases for CEC were synthesized in situ in fused-silica capillaries. Polymerization mixtures were composed of butyl methacrylate, ethylene dimethacrylate, and [2-(methacryloyloxy)ethyl]trimethyl ammonium chloride in the presence of a porogenic solvent, using ammonium peroxodisulfate as chemical initiator, and N,N,N',N'-tetramethylethylenediamine to activate the reaction. The influence of the amount of initiator, temperature, and composition of porogenic solvent on the physical and chromatographic properties of monolithic stationary phases has been investigated. A minimum plate height of 14.5 microm was obtained at 18 wt% of 1,4-butanediol in the polymerization mixture. The produced monolithic stationary phases exhibited a good repeatability and batch-to-batch and mixture-to-mixture reproducibility, with RSD values below 5.6% in the electrochromatographic parameters studied. A comparison with columns prepared by thermal initiation with alpha,alpha'-azobisisobutyronitrile (AIBN) was also performed. The most efficient column initiated with peroxodisulfate showed better efficiencies and selectivities than that prepared with AIBN at the same composition mixture.     

Local linear regression for functional predictor and scalar response

The aim of this work is to introduce a new nonparametric regression technique in the context of functional covariate and scalar response. We propose a local linear regression estimator and study its asymptotic behaviour. Its finite-sample performance is compared with a Nadayara-Watson type kernel regression estimator and with the linear regression estimator via a Monte Carlo study and the analysis of two real data sets. In all the scenarios considered, the local linear regression estimator performs better than the kernel one, in the sense that the mean squared prediction error is lower.     

Atomic force microscopy of mechanically trapped bacterial cells.

This article presents a study on the influence of the protocol used for immobilization of bacterial cells onto surfaces by mechanically trapping them into a filter. In this sense, the surface and structure of trapped cells are analyzed. Bacteria can be present solely or with extracellular polymeric substances (EPS). To test the behavior of the EPS layer duing the filtering process, different strains of a well-known EPS-producer bacteria (Staphylococcus epidermidis), which produce an extracellular matrix clearly visible in AFM images, have been used. Results show that this immobilization method can cause severe structural and mechanical deformation to the cell membrane. This altered mechanical state may possibly influence the parameters derived from AFM force curves (which are micro/nano-mechanical tests). Also, our results suggest that the EPS layer might move during the filtering process and could accumulate at the upper part of the cell, thus favoring distorted data of adhesion/pull-off forces as measured by an AFM tip, especially in the case of submicron-sized microbial cells such as bacteria.     

Evaluation of enantioselective binding of basic drugs to plasma by ACE

The present paper deals with the evaluation of the stereoselective binding of antihistamines (brompheniramine, chlorpheniramine, hydroxyzine, orphenadrine and phenindamine), phenothiazines (promethazine and trimeprazine) and a local anesthetic (bupivacaine) to human plasma proteins. Since all of them are drugs highly bound to proteins, a methodology to determine the bound fraction of each drug enantiomer was proposed. This methodology includes the incubation of samples containing plasma and racemic drug, ultrafiltration of the mixture and the chiral separation of enantiomers in the bound drug fraction using affinity EKC (AEKC)-partial filling technique and HSA as chiral selector. The results shown in this paper represent the first evidence of the enantioselective binding of some antihistamines such as brompheniramine, hydroxyzine, orphenadrine and phenindamine and the phenothiazines, promethazine and trimeprazine, to human plasma proteins. The binding of phenindamine to plasma presented the highest enantioselectivity (ES) (ES = 2.5) followed by trimeprazine (ES = 1.5) and promethazine (ES = 1.4).     

2-Methylimidazole palladium(II) complexes

Summary The preparation of two new tetracoordinated complexes of palladium(II) with 2-methylimidazole, 2-MeIm, and chloride as ligands is described.     

New protocol to obtain spirolides from Alexandrium ostenfeldii cultures with high recovery and purity

The aim of this work was to develop a method to purify large amounts of spirolide toxins from cultures of Alexandrium ostenfeldii. The dinoflagellates grew in batches under controlled conditions of salinity, light and temperature. Analysis of the cultures demonstrated the existence of neurotoxins associated with paralytic shellfish poisoning toxins and two spirolides, 13‐desmethyl spirolide C and 13,19‐didesmethyl spirolide C. The protocol designed presents several stages of extraction, separation between spirolides and paralytic shellfish poisoning toxins, and cleanup in solid‐phase extraction. Finally, the purification of spirolides was conducted by a preparative high‐performance liquid chromatography system coupled to a mass spectrometer detector. The purity and the amount of both toxins in each step was monitored by analytical liquid chromatographic–mass spectrometry. Large amounts of 13‐desMeC, 97% pure, and 13,19‐didesMeC, 99% pure, were obtained. A novel and efficient method to separate and purify spirolide toxins from large amounts of phytoplankton is provided. The protocol proposed shows, for the first time, a complete and detailed methodology to separate and purify spirolide toxins with high purity, recovery, repeatability and stability. Copyright © 2010 John Wiley & Sons, Ltd.     

A New 3,5‐Bisporphyrinylpyridine Derivative as a Fluorescent Ratiometric Probe for Zinc Ions

A new 3,5‐disubstituted pyridine with two porphyrin moieties was prepared through an efficient synthetic approach involving 2‐formyl‐5,10,15,20‐tetraphenylporphyrin ( 1 ), piperidine, and catalytic amounts of [La(OTf)₃]. 3,5‐Bis(5,10,15,20‐tetraphenylporphyrin‐2‐ylmethyl)pyridine ( 2 ) was fully characterized and its sensing ability towards Zn²⁺, Cu²⁺, Hg²⁺, Cd²⁺, and Ag⁺ was evaluated in solution by absorption and fluorescence spectroscopy and in gas phase by using matrix‐assisted laser desorption/ionization (MALDI)‐TOF mass spectrometry. Strong changes in the ground and excited state were detected in the case of the soft metal ions Zn²⁺, Cd²⁺, Hg²⁺, and Cu²⁺. A three‐metal‐per‐ligand molar ratio was obtained in all cases and a significant ratiometric behavior was observed in the presence of Zn²⁺ with the appearance of a new band at 608 nm, which can be assigned to a metal‐to‐ligand charge transfer. The system was able to quantify 79 ppb of Zn²⁺ and the theoretical calculations are in accordance with the stoichiometry observed in solution. The gas‐phase sensorial ability of compound 2 towards all metal ions was confirmed by using MALDI‐TOF MS and in solid state by using polymeric films of polymethylmethacrylate (PMMA) doped with ligand 2 . The results showed that compound 2 can be analytically used to develop new colorimetric molecular devices that are able to discriminate between Hg²⁺ and Zn²⁺ in solid phase. The crystal structure of Zn^II complex of 3,5‐bisporphyrinylpyridine was unequivocally elucidated by using single‐crystal X‐ray diffraction studies.     

From alkenylphosphane aminoallenylidene ruthenium(II) complexes to highly unsaturated ruthenaphosphabicycloheptene complexes

The alkenylaminoallenylidene complex [Ru(η⁵-C₉H₇){CCC(NEt₂)[C(Me)CPh₂]}{κ(P)-Ph₂PCH₂CHCH₂}(PPh₃)][PF₆] (2) has been prepared by the reaction of the allenylidene [Ru(η⁵-C₉H₇)(CCCPh₂){κ(P)-Ph₂PCH₂CHCH₂}(PPh₃)][PF₆] (1) with the ynamine MeCCNEt₂. The reaction proceeds regio- and stereoselectively, and the insertion of the ynamine takes place exclusively at the C_βC_γ bond of the unsaturated chain. The secondary allenylidene [Ru(η⁵-C₉H₇){CCC(H)[C(Me)CPh₂]}{κ(P)-Ph₂PCH₂CHCH₂}(PPh₃)][PF₆] (3) is obtained, in a one-pot synthesis, from the reaction of aminoallenylidene 2 with LiBHEt₃ and subsequent treatment with silica. Moreover, the addition of an excess of NaBH₄ to a solution of the complex 2 in THF at room temperature gives exclusively the alkynyl complex [Ru(η⁵-C₉H₇){CCCH₂[C(Me)CPh₂]}{κ(P)-Ph₂PCH₂CHCH₂}(PPh₃)] (5). The heating of a solution of allenylidene derivative 3 in THF at reflux gives regio- and diastereoselectively the cyclobutylidene complex [Ru(η⁵-C₉H₇) (PPh₃)][PF₆](4) through an intramolecular cycloaddition of the CC allyl and the C_αC_β bonds in the allenylidene complex 3. The structure of complex 4 has been determined by single crystal X-ray diffraction analysis.     

Environmentally friendly LC for the simultaneous determination of ascorbic acid and its derivatives in skin-whitening cosmetics

Ascorbic acid (AA), also known as vitamin C, is a very popular skin-whitening agent used in cosmetics. However, the use of AA (and also its sodium or magnesium salts) in cosmetic products is limited owing to its labile oxidative properties. In order to avoid its early degradation, different derivatives have been designed, such as ascorbyl phosphate (APH; as magnesium or sodium salts) and ascorbyl palmitate (AP), and more recently the ascorbyl glucoside (AG). Bearing in mind that all these chemicals in skin-whitening cosmetic products must be determined in order to control the efficacy of such products, this paper focuses on developing a wide-ranging LC analytical method able to determine the above-mentioned compounds simultaneously in cosmetic products. The chromatographic variables were studied and selected in order to achieve the total separation and subsequent determination of all the analytes involved. Thus, an octadecylsilica (C(18)) stationary phase and a mobile phase gradient of ethanol: 50 mM phosphate buffer at different pHs (containing 0.1 M NaCl) were used. Detection was carried out with a UV/visible spectrometry detector set at different wavelengths. The LOD ranged from 2 to 6 microg/mL depending on the analyte. The proposed method was validated by analysing a laboratory-made and six commercial skin-whitening cosmetic samples. The method allows any mixture of the four skin-whitening agents studied to be both separated at good resolution and determined without interferences from samples, and moreover it does not require the use of either highly toxic organic solvents or hazardous chemicals.     

Interfacial charge recombination between e(-)-TiO2 and the I(-)/I3(-) electrolyte in ruthenium heteroleptic complexes: dye molecular structure-open circuit voltage relationship

A series of heteroleptic ruthenium(II) polypyridyl complexes containing phenanthroline ligands have been designed, synthesized, and characterized. The spectroscopic and electrochemical properties of the complexes have been studied in solution and adsorbed onto semiconductor nanocrystalline metal oxide particles. The results show that for two of the ruthenium complexes, bearing electron-donating (-NH2) or electron-withdrawing (-NO2) groups, the presence of the redox-active I(-)/I3(-) electrolyte produces important changes in the interfacial charge transfer processes that limit the device performance. For example, those dyes enhanced the electron recombination reaction between the photoinjected electrons at TiO2 and the oxidized redox electrolyte. In an effort to understand the details of such striking observations, we have monitored the charge transfer reactions taking place at the different interfaces of the devices using time-resolved single photon counting, laser transient spectroscopy, and light-induced photovoltage measurements.