pH-Sensitive surfactants from lysine: assessment of their cytotoxicity and environmental behavior

The toxicity and environmental behavior of new pH-sensitive surfactants from lysine are presented. Three different chemical structures are studied: surfactants with one amino acid and one alkyl chain, surfactants with two amino acids on the polar head and one alkyl chain, and gemini surfactants. The pH sensitivity of these compounds can be tuned by modifying their chemical structures. Cytotoxicity has been evaluated using erythrocytes and fibroblast cells. The toxic effects against these cells depend on the hydrophobicity of the molecules as well as their cationic charge density. The effect of hydrophobicity and cationic charge density on toxicity is different for each type of cells. For erythrocytes, the toxicity increases as hydrophobicity and charge density increases. Nevertheless, for fibroblasts cationic charge density affects cytotoxicity in the opposite way: the higher charge density, the lower the toxicity. The effect of the pH on hemolysis has been evaluated in detail. The aquatic toxicity was established using Daphnia magna . All surfactants yielded EC(50) values considerably higher than that reported for cationic surfactants based on quaternary ammonium groups. Finally, their biodegradability was evaluated using the CO(2) headspace test (ISO 14593). These lysine derivatives showed high levels of biodegradation under aerobic conditions and can be classified as "readily biodegradable compounds".     

Structural pairwise comparisons of HLM stability of phenyl derivatives: Introduction of the Pfizer metabolism index (PMI) and metabolism-lipophilicity efficiency (MLE)

Data mining by pairwise comparison of over 150,000 human liver microsome (HLM) intrinsic clearance values stored within the internal Pfizer database has been performed by an automated tool. Systematic probability tables of specific structural changes on the intrinsic clearance of phenyl derivatives have been generated. From these data two new parameters, the Pfizer Metabolism Index (PMI) and Metabolism-Lipophilicity Efficiency (MLE) are introduced for each fragment. The findings are applied to a Topliss style analysis that focuses on metabolic stability.     

Purification and Partial Characterization of an Exo-polygalacturonase from Paecilomyces variotii Liquid Cultures

An extracellular polygalacturonase (PG) produced from Paecilomyces variotii was purified to homogeneity through two chromatography steps using DEAE-Fractogel and Sephadex G-100. The molecular weight of P. variotii PG was 77,300 Da by gel filtration and SDS-PAGE. PG had isoelectric point of 4.37 and optimum pH 4.0. PG was very stable from pH 3.0 to 6.0. The extent of hydrolysis of different pectins by the purified enzyme was decreased with an increase in the degree of esterification. PG had no activity toward non-pectic polysaccharides. The apparent K _m and V _max values for hydrolyzing sodium polypectate were 1.84 mg/mL and 432 μmol/min/mg, respectively. PG was found to have temperature optimum at 65 °C and was totally stable at 45 °C for 90 min. Half-life at 55 °C was 50.6 min. Almost all the examined metal cations showed partial inhibitory effects under enzymatic activity, except for Na⁺¹, K⁺¹, and Co⁺² (1 mM) and Cu⁺² (1 and 10 mM).     

Real time culture and analysis of embryo metabolism using a microfluidic device with deformation based actuation

We report a computerized microfluidic real time embryo culture and assay device that can perform automated periodic analyses of embryo metabolism. This automated program uses a modified "gated injection" scheme (sample injection, reagent mixing, enzyme reaction of 15 min incubation, and sample detection) to sequentially measure fluorescence from sample, reference, and background (without any analyte) every hour. Measurements assessed with reference solutions demonstrated the stability of these microfluidic measurements over a 24 h period. Furthermore, this system was able to measure time dependent nutrient consumption by single or multiple (10) live mouse blastocyst-stage embryos with pmol h(-1) sensitivity. Mechanical deformation-based microfluidic actuation created by computerized movement of Braille pins enables automated fluid pumping and valving sequences without unwanted gravity-driven backflow or exposure to electrical fields as would be required in electrokinetic schemes. The convenient, non-invasive, and automated nature of these assays open the way for the development of integrated microfluidic platforms for practical single embryo culture and real time biochemical analysis to assess embryo viability and select embryos with the greatest implantation potential, thus improving success in clinical assisted reproductive technology laboratories.     

Optical and structural characterization of SrZr0,1Ti0,9O3

In this work, the ceramic compound SrTi_0.90Zr_0,1O₃ (SZT) was synthesized by the citrate method. This solid showed a 12 nm crystallite size, reflecting the high degree of crystallinity obtained by this synthesis route. Differential and gravimetric thermal analysis showed that the solid was formed from 520 °C; the chemical composition was determined by ICP–AES4, giving a stoichiometry corresponding to the SrTi_0.90Zr_0.10O₃ formula, and proved to be compatible with the X-ray diffraction data, refined by the Rietveld method. The morphology was explored by means of SEM and TEM, finding a homogenous particles distribution, arranged in lumps, susceptible to density changes by sintering between 1000 °C and 1200 °C. The photoluminescence (PL) spectrum shows a band between 470 nm and 520 nm, corresponding to the Ti and Zr ions 3d electronic transition. The SZT crystal structure is tetragonal with space group I4/mcm, number (140).     

New supported liquid membrane-capillary electrophoresis in-line arrangement for direct selective analysis of complex samples

An in-line coupling of a micro-membrane extraction unit, based on supported liquid membrane, with commercially available capillary electrophoresis equipment is described. A main characteristic of this micro-membrane device, made from a simple Eppendorf tube, is that it permits the application of voltage in the acceptor solution to be applied during the extraction process. This has been shown as an alternative to enhance sensitivity, as the analytical signal achieved by applying 10 kV for 20 min was similar to that obtained without the application of voltage and with extraction time of 60 min. In addition, the design has been made permitting both in-line hydrodynamic and electrokinetic sample introduction into the electrophoretic capillary. The analytical potential of the proposed system has been demonstrated by the direct determination of nitroimidazoles from pig liver tissue. The high efficiency of the proposed system allowed the extraction and the determination of the analytes to be performed from a simple tissue homogenate obtained in water. The precision of the analysis of spiked samples, expressed in terms of relative standard deviation, was better than 4.8%.     

Calculation of the force between surfaces coated with grafted molecules by molecular simulation

We discuss the calculation of the force between surfaces coated with anchored molecules. This force is related to the pressure and can therefore be calculated by the usual means: either by summing over all surface-particle forces or from the virial. However, we argue that the grafting of the molecule must be included by means of a restraining potential-otherwise, nonphysical results can be obtained, such as the appearance of a net force even when the particles are spaced very far away. Bond-stretching potentials are also required if the virial is employed.     

Radiative corrections to the Higgs potential in the LH model

In this work we compute the radiative corrections to the Higgs mass and the Higgs quartic couplings coming from the Higgs sector itself and the scalar fields φ in the Littlest Higgs (LH) model. The restrictions that the new contributions set on the parameter space of the models are also discussed. Finally, this work, together with our three previous papers, complete our program addressed to compute the relevant contributions to the Higgs low-energy effective potential in the LH model and the analysis of their phenomenological consequences.     

A new, practical and efficient sulfone-mediated synthesis of trifluoromethyl ketones from alkyl and alkenyl bromides

We report herein a new and efficient method to prepare trifluoromethyl ketones from the corresponding bromides through sulfones in good yields.     

Synthesis and crosslinking of vinyl‐terminated biphenyl and naphthalene liquid‐crystalline poly(epichlorohydrin) derivatives: Effect of nonmesogenic nonvinylic units on the mesogenic properties

Two series of vinyl‐terminated side‐chain liquid‐crystalline polyethers containing ethylene oxide or glycidyl aromatic carboxylates as spacers were synthesized. The mesogenic cores were 4,4′‐biphenyl or 2,6‐naphthalene moieties. The polymers were synthesized by chemically modifying poly(epichlorohydrin) or poly(epichlorohydrin)‐poly(ethylene oxide) with the corresponding mesogenic carboxylic acids or with mixtures of these acids and the nonmesogenic non‐crosslinkable analogous 4‐biphenyl‐ and 2‐naphthalenecarboxylic acids. In most cases the degree of modification achieved was higher than 90%. The polymers were characterized by chlorine analysis, IR, and ¹H and ¹³C NMR spectroscopies; viscosimetry; size exclusion chromatography; multi‐angle laser light scattering; and thermogravimetric analysis. The liquid‐crystal behavior, shown by most polymers, was examined by differential scanning calorimetry, polarized optical microscopy (POM), and X‐ray diffraction on mechanically oriented samples. The crosslinking of most polymers was done by peroxide‐type initiators that led to liquid‐crystal thermosets or elastomers. The freezing of the mesophase organization on the crosslinked materials was confirmed by POM and X‐ray diffraction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3893–3908, 2002