Vortex‐assisted liquid–liquid micro‐extraction and high‐performance liquid chromatography for a higher sensitivity methyl methacrylate determination in biological matrices

A vortex‐assisted liquid–liquid micro‐extraction coupled with high‐performance liquid chromatography, with UV–vis, is proposed to pre‐concentrate methyl methacrylate and to improve separation in biological matrices. The use of 1‐octanol as extracting phase, its volume, the need for a dispersant agent, the agitation conditions and the cooling time before phase separation were evaluated. In optimum conditions, enrichment factors of 20 (±0.5) and enrichment recovery of 99% were obtained. The straightforward association of this extraction process with the HPLC method, previously regulated by the International Organization for Standardization, afforded a detection limit of 122 ng/mL and a quantification limit of 370 ng/mL. The within‐batch precision, relative standard deviation, was 3% for a sample with 1.49 µg/mL and 4% for a sample with 13.4 µg/mL. The results showed a between batch‐precision of 21% for experiments performed on five different days, for a sample with a concentration of 1.10 µg/mL in methyl methacrylate. Copyright © 2013 John Wiley & Sons, Ltd.     

Dihalogenation of β-Keto Sulfides. Synthesis of α-Keto Methyl Esters and α-Keto S-Phenyl Thioesters

α-Keto esters and α-Keto S-Phenyl Thioesters are synthesized from β-keto sulfides by dihalogenation with sulfuryl chloride followed by solvolysis with methanol and acetone/water respectively.     

19F nuclear relaxation study of the fluorite system Pb0.84Bi0.16F2.16

Abstract

Measurements of the ¹⁹F nuclear relaxation times are reported for the fluorite-structured Pb_0.84Bi_0.16F_2.16 single crystal. The formation of clusters by thermal treatment, as revealed by changes in the fluorine T ₂ during temperature cycling, is discussed.     

Synthesis of gold nanoparticles using herbal Acorus calamus rhizome extract and coating on cotton fabric for antibacterial and UV blocking applications

Gold nanoparticles (AuNPs) have been synthesized by greener method using chloroauric acid as precursor and extract of Acorus calamus rhizome as reducing agent. Formation of AuNP was confirmed by the presence of Surface Plasmon Resonance (SPR) peak in UV–Visible spectral analysis. XRD and FT-IR spectral analyses were performed for characterization. SEM images show spherical morphology and HR-TEM images reveal nanosize of AuNPs. The AuNPs were then coated on cotton fabric by pad-dry-cure method and characterized by SEM with EDAX technique. The results reveal the deposition of AuNPs on the surface of cotton fabric. Uncoated cotton, neat extract coated cotton and extract containing AuNPs coated cotton fabrics were then tested for antibacterial activity against Gram positive (Staphylococcus aureus) and Gram negative (Escherichia coli) bacterial strains by AATCC 100 test method. It showed that the extract containing AuNPs coated cotton fabric had higher antibacterial activity than other test samples against E. coli. UV-DRS analysis performed on extract containing AuNPs coated cotton fabric showed improved UV-blocking property than uncoated cotton fabric and neat extract coated cotton fabric.     

Generalized exponential function and discrete growth models

Here we show that a particular one-parameter generalization of the exponential function is suitable to unify most of the popular one-species discrete population dynamic models into a simple formula. A physical interpretation is given to this new introduced parameter in the context of the continuous Richards model, which remains valid for the discrete case. From the discretization of the continuous Richards’ model (generalization of the Gompertz and Verhulst models), one obtains a generalized logistic map and we briefly study its properties. Notice, however that the physical interpretation for the introduced parameter persists valid for the discrete case. Next, we generalize the (scramble competition) θ-Ricker discrete model and analytically calculate the fixed points as well as their stabilities. In contrast to previous generalizations, from the generalized θ-Ricker model one is able to retrieve either scramble or contest models.     

A comparison of drug loading capacity of cellactose with two ad hoc processed lactose-cellulose direct compression excipients

This study compares the drug loading capacity of Cellactose and two excipients of similar composition and similar particle size, prepared by dry granulation and extrusion-spheronization respectively. The drugs evaluated were acetaminophen and furosemide. Acetaminophen did not significantly affect the flow properties of any of the excipients, whereas furosemide markedly worsened flow properties, eliminating the differences initially existing among the three excipients. For both drugs, tablet mechanical properties were clearly better with Cellactose than with the other excipients. Acetaminophen dissolution rate was very similar regardless of the excipient used, but furosemide dissolution rate was lower from Cellactose tablets than from tablets prepared with the other excipients. This important difference is discussed in terms of micropore structure, specific surface area, and wettability of tablets, and is attributable to the special structure of Cellactose particles.     

On the cogeneration of <Emphasis Type="Italic">t</Emphasis>-structures

Let C be a set of objects in a triangulated compactly generated category We denote by the smallest suspended subcategory closed under coproducts which contains C (the smallest cosuspended subcategory closed under products which contains C). We prove that if C is a set of compacts objects then is a t-structure in where T_C I is the dual of C with respect to an injective cogenerator I in the category Mod C. Moreover, we show that: C is a tilting set if and only if And, this is equivalent to T_CI is a cotilting object in Received: 28 March 2003     

Tameness on the boundary and Ahlfors’ measure conjecture

Let N be a complete hyperbolic 3-manifold that is an algebraic limit of geometrically finite hyperbolic 3-manifolds. We show N is homeomorphic to the interior of a compact 3-manifold, or tame, if one of the following conditions holds:1. N has non-empty conformal boundary,2. N is not homotopy equivalent to a compression body, or3. N is a strong limit of geometrically finite manifolds.The first case proves Ahlfors measure conjecture for Kleinian groups in the closure of the geometrically finite locus: given any algebraic limit of geometrically finite Kleinian groups, the limit set of is either of Lebesgue measure zero or all of . Thus, Ahlfors conjecture is reduced to the density conjecture of Bers, Sullivan, and Thurston.     

Study on thioridazine 5-sulfoxide epimerization and degradation by capillary electrophoresis

We present a method for the stereoselective analysis of thioridazine 5-sulfoxide (THD 5-SO) in human plasma based on liquid-liquid extraction with diethyl ether and chiral resolution of the stereoisomers by capillary electrophoresis using hydroxypropyl-beta-cyclodextrin and sulfated beta-cyclodextrin as chiral selectors. The method showed recovery rates of 85.5% for both THD 5-SO (slow-eluting, SE) enantiomers. The coefficients of variation observed in the precision studies, as well as the accuracy values, were below 10%. After validation, the method was used to study the stability and configurational changes of this THD metabolite. Our results showed that both enantiomers of THD 5-SO (SE) were stable under conditions of variation of temperatures (38 degrees C, 4 degrees C and -20 degrees C), pH (5.0, 7.0 and 8.5) and ionic strengths (0.2, 0.5 and 1.0 mol/L). The influence of light on the stability of the THD 5-SO (SE) stereoisomers was also studied using standard solutions prepared in methanol and an inversion in configuration was observed under UV light (254 and 366 nm).     

Deterministic and random partially self-avoiding walks in random media

Consider a set of N cities randomly distributed in the bulk of a hypercube with d dimensions. A walker, with memory μ, begins his route from a given city of this map and moves, at each discrete time step, to the nearest point, which has not been visited in the preceding μ steps. After reviewing the more interesting general results, we consider one-dimensional disordered media and show that the walker needs not to have full memory of its trajectory to explore the whole system, it suffices to have memory of order lnN/ln2.