bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐buffering capacity, hydrolytically stable, low‐pI isoelectric membranes for isoelectric trapping separations
Authors: Lalwani Sanjiv , Shave Evan , Vigh Gyula
Published: October 2004

Hydrolytically stable, low‐pI isoelectric membranes have been synthesized from low‐pI ampholytic components, poly(vinyl alcohol), and a bifunctional cross‐linker, glycerol‐1,3‐diglycidyl ether. The low‐pI ampholytic components used contain one amino group and at least two weakly acidic functional groups. The acidic functional groups are selected such that the pI value of the ampholytic component is determined by the pKa values of the acidic functional groups. When the concentration of the ampholytic component incorporated into the membrane is higher than a required minimum value, the pI of the membrane becomes independent of variations in the actual incorporation rate of the ampholytic compound. The new, low‐pI isoelectric membranes have been successfully used as anodic membranes in isoelectric trapping separations with pH < 1.5 anolytes and replaced the hydrolytically less stable polyacrylamide‐based isoelectric membranes. The new low‐pI isoelectric membranes have excellent mechanical stability, low electric resistance, good buffering capacity, and long life time, even when used with as much as 50 W power and current densities as high as 33 mA/cm2 during the isoelectric trapping separations.
Fundamental aspects of contactless conductivity detection for capillary electrophoresis. Part I: Frequency behavior and cell geometry
Authors: Kubáň Pavel , Hauser Peter C.
Published: October 2004

A better understanding of the characteristics of the axial contactless conductivity cell could be obtained by carefully studying the effect of the cell geometry on its frequency behavior. A good fit between theoretical and experimental results shows that the axial contactless conductometric detector can effectively be described by the simplest possible equivalent circuitry consisting of a capacitor, resistor, and a second capacitor. The cell constant is largely defined by the length of the gap between the electrodes. The effective electrode size is thus not related to the dimensions of the real electrodes but more closely to the cross‐sectional area of the internal diameter of the capillary. Typical experimental values of 20 MΩ and 0.1 pF were obtained for the resistance and capacitances, respectively, of a cell formed by a 2 mm gap between two 4 mm long electrodes fitted with a capillary of 50 μm ID. It could be shown that the diameter of the electrode is not critical and tight coupling of the electrodes to the outer wall of the capillary is not needed. The peak overshoot phenomenon, which has frequently been reported, is an artefact that can be minimized by optimizing the frequency for cell excitation. The frequency setting has to be optimized for each cell design, operational amplifier, electrolyte solution and capillary.
Fundamental aspects of contactless conductivity detection for capillary electrophoresis. Part II: Signal‐to‐noise ratio and stray capacitance
Authors: Kubáň Pavel , Hauser Peter C.
Published: October 2004

The signal‐to‐noise ratio of a contactless conductivity detector for capillary electrophoresis was examined for different cell arrangements and operating parameters. The best signal‐to‐noise ratios, and hence the best detection limits, are obtained for frequencies which give highest sensitivity. Comparative experiments for three different excitation voltages (20, 100, and 200 Vpp) showed that the best signal‐to‐noise ratios were achieved for the highest excitation voltage of 200 Vpp. Low conductivity of the background electrolyte solution is mandatory to obtain lowest noise levels, and also the improvement on applying high excitation voltages was best for the electrolyte solution with lowest conductivity. The diameter of the electrodes was found to have only a negligible effect, so that a tight fitting of the electrodes to the external diameter of the capillary is not necessary. A cell without shielding between the two electrodes showed significant direct coupling (stray capacitance) and lower signal‐to‐noise ratios for all experimental conditions used. A serious distortion of the peak shapes was also observed for this cell arrangement.
Haplotype studies support slippage as the mechanism of germline mutations in short tandem repeats
Authors: Klintschar Michael , Dauber Eva‐Maria , Ricci Ugo , Cerri Nicoletta , Immel Uta‐Dorothee , Kleiber Manfred , Mayr Wolfgang R.
Published: October 2004

Germline mutations of human short tandem repeat (STR) loci are expansions or contractions of repeat arrays which are not well understood in terms of the mechanism(s) underlying such mutations. Although polymerase slippage is generally accepted as a mechanism capable to explain most features of such mutations, it is still possible that unequal crossing over plays some role in those events, as most studies in humans could not exclude unequal crossing over (UCO). Crossing over can be studied by analyzing haplotypes using flanking markers. To check for UCO in mutations, we have analyzed 150 paternity cases for which more than the usual trio (mother, child, and father) were available for testing by analyzing 16 STR loci. In a total of 4900 parent‐child allele transfers four mutations were observed at different loci (D8S1179, D18S51, D21S11, and SE33/ACTBP2). To identify the mutated allele and to check for UCO, we typed at least four informative loci flanking the mutated locus and used the pedigree data to establish haplotypes. By doing so we were able to exclude UCO in each case. Moreover, we were able to identify the mutations as one‐repeat contractions/expansions. Our data thus support slippage as the mechanism of germline mutations in STRs.
Capillary electrophoretic separation of cationic constituents of imidazolium ionic liquids
Authors: Markuszewski Michał J. , Stepnowski Piotr , Marszałł Michał P.
Published: October 2004

A capillary electrophoretic method for resolving selected imidazolium ionic liquid cations is reported. The method, in which citric buffer is used as the running electrolyte, is simple and reproducible. The separation of a standard mixture is in linear accordance with the relative molecular mass (Mr) of solutes regardless of the type of substitution (alkyl or aryl). The theoretical prediction of compounds as yet not analyzed is therefore possible; however, cations with identical molecular masses are inseparable with this method. Nevertheless, the method's quantitative analytical performance was excellent. The paper also discusses the applicability of a method for tracking the photodegradation kinetics of an exemplary ionic liquid.
Capillary isoelectric focusing‐mass spectrometry for shotgun approach in proteomics
Authors: Storms Henricus F. , van der Heijden Robert , Tjaden Ubbo R. , van der Greef Jan
Published: October 2004

We report on capillary isoelectric focusing‐mass spectrometry (CIEF‐MS) of complex peptide mixtures in the absence of carrier ampholytes. Furthermore, the use of low concentrations of carrier ampholytes as mere spacers is investigated. Carrier ampholytes are complex mixtures of amphoteric compounds with high buffering capacity. Since all peptides are amphoteric compounds by themselves, the use of carrier ampholytes may be superfluous to establish a stable pH gradient in CIEF analysis of protein digests. Our research showed that when carrier ampholytes are omitted, the analyte ions are not focused at their isoelectric point. The analytes are charged, leading to electrophoretic mobility uncharacteristic for CIEF. The method was tested for a five‐protein‐mixture at 0.02 mg/mL per protein and 0.05 mg/mL per protein. At the lower concentration, the analytes were stacked during the focusing process in only a limited length of the capillary. Therefore, the higher concentration led to better separation efficiency. It was found that at low concentration (0.20%) the carrier ampholytes could work as spacers. Though it led to sensitivity losses of 15–45%, this was compensated by the higher separation efficiencies seen. The method was evaluated with an eight‐protein‐mixture, of which all could be identified after performing MS/MS.
Systematic multiplex polymerase chain reaction and reverse transcription‐polymerase chain reaction analyses of changes in copy number and expression of proto‐oncogenes and tumor suppressor genes in cancer tissues and cell lines
Authors: Yamamoto Miyako , Metoki Rikiya , Yamamoto Fumiichiro
Published: October 2004

Systematic multiplex reverse transcription‐polymerase chain reaction (SM RT‐PCR) is distinguishable from other multiplex RT‐PCR methods by (i) utilization of primers that amplify sequences that fall within a single exon of the genes, (ii) utilization of genomic DNA as a calibration standard, and (iii) optimized PCR conditions that allow amplification of bands of similar intensity using genomic DNA template. We previously developed the human experimental systems of 68 glycosyltransferase genes, 39 Hox genes, and 26 integrin subunit genes, and analyzed the expression of those genes in human adult tissues. Here we report the establishment of an SM RT‐PCR system of proto‐oncogenes and tumor suppressor genes and the analysis of gene expression in human cancer tissues and cell lines. We also demonstrate that the SM RT‐PCR system, which was developed for cDNA expression analysis, could also be used successfully for more exquisite analysis of copy number changes in genomic DNA. We observed a decrease in band intensity of HRAS, TP73, CDKN2A, and CDKN2B genes in most of the breast and prostate cancer cell lines examined. The decrease in copy number of HRAS proto‐oncogene leads us to suspect the presence of tumor suppressor genes in the vicinity of this gene on chromosome 11p15.5.
Importance of the counterion in optimization of a borate electrolyte system for analyses of anions in samples with complex matrices performed by capillary zone electrophoresis
Authors: Křivánková Ludmila , Březková Michaela , Gebauer Petr , Boček Petr
Published: October 2004

Borate buffers are common background electrolytes for analyses of anions in capillary zone electrophoresis. Usually, sodium borate at a given pH is used and this specification seems to be sufficient for a successful analysis. In this paper, we show that free migration of OH‐ may deteriorate the analysis of a typical anionic analysis of clinical samples due to uncontrolled migration of OH‐ throughout the systems of analyzed zones and may damage the stacking of anionic analytes of interest. We have proven that the use of ammonium borate may remedy the situation where the presence of ammonium may selectively stop the free migration of OH‐ ions, slow down their effective mobility and bring their safe behavior resulting in reproducible stacking of clinically important anions. Results of real analyses of human serum samples confirmed the proposed method and proved that substitution of sodium for ammonium in borate buffers offers reliable analyses of clinical samples having chloride as the bulk component. The experimental results given in this paper are supported also by computer simulation, which can not only support the positive results but also show the dynamics of the separation that is otherwise hidden to any detection possibilities.