Cell transport via electromigration in polymer-based microfluidic devices

Electrokinetic transport of Escherichia coli and Saccharomyces cerevisiae (baker's yeast) cells was evaluated in microfluidic devices fabricated in pristine and UV-modified poly(methyl methacrylate)(PMMA) and polycarbonate (PC). Chip-to-chip reproducibility of the cell's apparent mobilities (micro(app)) varied slightly with a RSD of approximately 10%. The highest micro(app) for baker's yeast cells was observed in UV-modified PC with 0.5 mM PBS (pH = 7.4), and the lowest was measured in pristine PMMA with 20 mM PBS (pH = 7.4). Baker's yeast in all devices migrated toward the cathode because of their smaller electrophoretic mobility compared to the EOF. In 0.5 mM and 1 mM PBS, E. coli cells migrated toward the anode in all cases, opposite to the direction of the EOF due to their larger electrophoretic mobility. E. coli cells in 20 mM PBS migrated toward the cathode, which indicated that the electrophoretic mobility of E. coli cells decreased at higher ionic strengths. Observed differential migrations of E. coli and baker's yeast cells in appropriately prepared polymer microchips were used as the basis for selective introduction into microfluidic devices of only one type of cell. As a working model, experiments were performed with E. coli and RBCs (red blood cells). RBCs migrated toward the cathode in pristine PMMA with 1 mM and 20 mM PBS (pH = 7.4), opposite to the direction of the E. coli cells. By judicious choice of the buffer concentration in which the cell suspension was prepared and the polymer material, RBCs or E. coli cells were selectively introduced into the microdevice, which was monitored via laser backscatter signals.     

DSC study of linolenic acid autoxidation inhibited by BHT,dehydrozingerone and olivetol

Non-isothermal oxidation of linolenic acid (LNA) in bulk phase was monitored by differential scanning calorimetry. The kinetic parameters E _a, Z and k (activation energies, pre-exponential factors, and rate constants, respectively) were calculated by Ozawa-Flynn-Wall method for the first detectable exothermic effect of uninhibited LNA oxidation. The kinetic parameters were also calculated for LNA oxidation inhibited by 2,6-di-tert-butyl-4-methylphenol (BHT), and two natural compounds, 1,3-dihydroxy-5-pentylbenzene (olivetol), and 4-(4’-hydroxy-3’-methoxyphenyl)-3-buten-2-one (DHZ, dehydrozingerone) at various concentrations. For oxidation processes at 25, 90 and 180°C the plots of logk values vs. concentration of phenolic compounds indicated that optimal concentration of inhibitor determined for one particular temperature cannot be extrapolated to other temperatures.     

Characteristics of glucose electrode with enzyme immobilised on nylon net

Glucose oxidase was immobilised on nylon net by the method of O-alkylation using dimethyl sulfate and lysine as a spacer. The influence of alkylation conditions on the characteristics of the resulting glucose electrode was evaluated. The best electrode was then tested under batch and flow conditions, respectively. The influence of pH and temperature on electrode response were examined. The glucose oxidase immobilised on nylon net seemed to be inhibited by glucose in alkaline pH and at higher temperatures. Moreover, the shape of the electrode signal after addition of glucose was unusual. Glucose oxidase immobilised on nylon net was unstable and lost its activity rather quickly, especially when stored dry in the refrigerator. Also the operational stability of the electrode in the flow system was rather poor. Received: 26 February 1998 / Revised: 22 May 1998 / Accepted: 29 June 1998     

Characteristics of glucose electrode with enzyme immobilised on nylon net

Glucose oxidase was immobilised on nylon net by the method of O-alkylation using dimethyl sulfate and lysine as a spacer. The influence of alkylation conditions on the characteristics of the resulting glucose electrode was evaluated. The best electrode was then tested under batch and flow conditions, respectively. The influence of pH and temperature on electrode response were examined. The glucose oxidase immobilised on nylon net seemed to be inhibited by glucose in alkaline pH and at higher temperatures. Moreover, the shape of the electrode signal after addition of glucose was unusual. Glucose oxidase immobilised on nylon net was unstable and lost its activity rather quickly, especially when stored dry in the refrigerator. Also the operational stability of the electrode in the flow system was rather poor.     

Structural Balance of Opinions

The concept of Heider balance, usually applied to interpersonal relations, is generalized here to opinions gathered in surveys. At first, we compare four algorithms, which drive a matrix dataset to a balanced state. The criterion is that the final state obtained with an algorithm should be as close as possible to the initial state. The result is that deterministic differential equations work better than their Monte Carlo counterparts. Next, we apply the winning algorithms to the matrix of correlations between opinions gathered in American states between 1974 and 1998. The results are interpreted in terms of the classic comfort hypothesis (E. Babbie, 2007).     

Extraction and determination of hexavalent chromium in soil samples

A procedure for the extraction of Cr(VI) from solid soil-like samples was presented in which the complexing properties of diethylenetriaminepentaacetic acid (DTPA) were exploited to extract insoluble compounds of Cr(VI). A concentration of DTPA in an ammonium sulphate/ammonium hydroxide buffer equal to 0.02 mol l⁻¹ was chosen. The conditions of extraction of insoluble Cr(VI) from solid samples were optimised using soil certified reference material spiked with known concentration of insoluble Cr(VI) added as PbCrO₄. The extracts were analysed by adsorptive stripping voltammetry. Validation of the proposed procedure of extraction was carried out by analysis of certified reference material (CRM) 545 and comparison of the results obtained using the proposed and other methods of extraction in the course of analysis of natural soil samples.     

Synthesis and reactivity of bis(cycloamidinium-2-yl)alkane bromide tribromides,brominating agents and tectons for molecular engineering

Bis(cycloamidine-2-yl)alkanes easily form bromide tribromide salts in the reduction-oxidation processes with bromine. Bis(tetrahydroimidazolium-2-yl)ethane and bis(hexahydropyrimidinium-2-yl)-ethane bromide tribromides are such new convenient brominating agents for aromatic amides in chemo- and regioselective electrophilic substitutions and α-bromination reactions. Correspondence: Katarzyna Ostrowska, Department of Organic Chemistry, Jagiellonian University, R. Ingardena 3, PL-30060 Kraków, Poland.     

Pulse radiolysis of 9-anthrylmethylammonium cation in aqueous solution

The reaction of hydrated electron with 9-anthrylmethylammonium cation to form the respective anthracene radical anion in aqueous solution has been studied by the method of pulse radiolysis. The rate constant of the reaction of with is reported. It is demonstrated that the anthracene radical anion is unstable and undergoes further reactions. The spectra of transient intermediates, leading to the final reduction products, are presented.     

1′-Carbopalladated-4-ferrocenyl-1,3-oxazolines as catalysts for Heck reactions: Further evidence in support of the Pd(0)/Pd(II) mechanism

1′-Carbopalladated complexes derived from 4-ferrocenyl-1,3-oxazolines are reported in this paper as efficient catalysts for the Heck coupling of iodo- and bromoarenes with alkenes. Experimental evidence points out strongly towards the involvement of a Pd(0)/Pd(II) catalytic cycle in the mechanism of the reaction. For the first time, the disassembly of the carbopalladated complex via coupling with the olefin in a non-catalytic Heck reaction has been demonstrated to be the origin of the release of Pd(0) from the palladacycle carrier.