Hydroxyethyl Cellulose Solutions Research Articles

Simultaneous determination of maltose and glucose using a screen-printed electrode system

A screen-printed sensor system consisting of a glucose oxidase (GOD) electrode and an amyloglucosidase/glucose oxidase (A/G) electrode was constructed to determine maltose and glucose simultaneously in a mixture. Sensor construction was optimised so that it contained 20 units of GOD/40 units of amyloglucosidase and 0.2 mM 1,1′-ferrocenedimethanol. These components were deposited onto a screen-printed carbon electrode and an outer membrane was printed from 3.5% hydroxyethyl cellulose (HEC) solution. The optimum pH was 4.8. The linear range of the system was up to 40 mM glucose or 20 mmol/L maltose with coefficients of variation (CVs) ranging from 3.5% to 5.29%. The results obtained by using the enzyme electrode system agreed well with those obtained by the Fehling titration method. When stored dry, especially at 4°C, the enzyme electrodes showed good stability over four months.

Band broadening during dc and field inversion capillary electrophoresis of lambda DNA in dilute hydroxyethylcellulose solutions.

Capillary electrophoresis of lambda double-stranded (ds) DNA (48.5 kbp) in dilute hydroxyethylcellulose (HEC) solutions shows band spreading that cannot be explained by diffusion alone. Dispersion and asymmetry factors of lambda ds-DNA bands were measured as functions of capillary length, HEC concentration and field strength. Band spreading and asymmetry can be explained by a recently developed model in which the dominant contribution is assumed to be dispersion in DNA-HEC disentanglement times. Bandwidth reduction using square-wave field inversion was also investigated. It is proposed that correlation of DNA motion is the source of band narrowing during field inversion.

Association of Ethyl(hydroxyethyl)cellulose Solutions

Ethyl(hydroxyethyl)cellulose (EHEC) forms true molecular solutions in 10 mM aqueous solution NaCl at concentrations equal or less than 0.1%. Less hydrophilic EHEC forms true molecular solution also in methanol/10 mM aqueous NaCl (1:1, v/v) mixture. An associative clustering was observed in this solvent mixture in the case of a more hydrophilic EHEC derivative. The amount and size of clusters increased with EHEC sample concentration. Repulsive forces related to some minute charge of EHEC, evidenced by ion-exclusion chromatography in the absence of salt in the methanol/water (1:1, v/v) mobile phase, became operative in clustering solution without salt; both the amount and size of clusters decreased. EHEC contains a low amount of particle impurities. The light-scattering signal related to these impurities may be misinterpreted as an aggregation when the solutions are not properly filtered.

Influence of Surface Aging on the Drainage of Foam Films Stabilized by Aqueous Solutions of Ethyl Hydroxyethyl Cellulose

The drainage times of microscopic horizontal foam films stabilized by dilute aqueous solutions of ethyl hydroxyethyl cellulose (EHEC) was shown to be dependent on the aging effects (configuration changes of the adsorbed macromolecules) occurring in the freshly created air/solution interface. At low polymer concentration (5 ppm), the films drained fairly rapidly from thicknesses of about 400 to 300 nm with drainage times about 5 to 6 times greater than theoretical values calculated using the Reynolds equation. However, at higher polymer concentrations (100 ppm) at extended surface aging (15−180 min) the film drainage times were shown to increase drastically giving values 50 times greater than theoretical values. Although these aging effects could not be directly related to surface tension data, diffusion coefficients were calculated from interfacial tension profiles using classical diffusion theory. As the concentration of polymer increased, the diffusion coefficients were shown to decrease and were considerably smaller than previously reported experimentally values determined in bulk solution by NMR. This difference between experimental and theoretical results endorsed a kinetic rather than a diffusion or mass transport model for the transfer of EHEC molecules to the interface. The increase in drainage times with extended aging times could be explained by the gradual formation of a steric energy barrier caused by configuration changes of the adsorbed polymer. This probably involved the progressive extension of the EHEC tails into the aqueous phase increasing the disjoining pressure, decreasing the drainage rate, and producing thick stable films.

Microviscosity in Clusters of Ethyl Hydroxyethyl Cellulose and Sodium Dodecyl Sulfate Formed in Dilute Aqueous Solutions As Determined with Fluorescence Probe Techniques

The microviscosity has been measured in dilute aqueous solutions of ethyl hydroxyethyl cellulose (EHEC) and sodium dodecyl sulfate (SDS) by utilizing three steady-state fluorescence probe techniques: intramolecular excimer formation by 1,3-di(1-pyrenyl)propane (P3P), fluorescence depolarization of perylene, and intramolecular rotational relaxation about bonds with (p-(dimethylamino)benzylidene)malononitrile (BMN). Results obtained by the three techniques are compared. They all detect qualitatively the same behavior with a well-developed maximum in microviscosity and rigidity of the EHEC/SDS clusters formed at a surfactant concentration close to or slightly higher than the critical surfactant concentration where adsorption to the polymer starts. The EHEC/SDS clusters have, independent of composition, higher microviscosities than ordinary SDS micelles. The microviscosity is also compared with other EHEC/SDS/water system features such as the bulk viscosity, the actual adsorption isotherm, the average aggreg...

Capillary electrophoresis of supercoiled and linear DNA in dilute hydroxyethyl cellulose solution.

Capillary electrophoresis in dilute hydroxyethyl cellulose is shown to separate supercoiled DNA in the size range 2000-16,000 base pairs. The plasmids migrate more slowly than linear ds-DNA of the same sizes. Plasmid bandwidths are larger than observed for ds-DNA, allowing identification of the type of DNA by bandwidth. The differing dependence of mobility on chain length can be explained by assuming that a plasmid migrates as an elastic rod, while ds-DNA migrates as a wormlike chain.

Capillary Electrophoretic Separation of DNA Restriction Fragments in Mixtures of Low- and High-Molecular-Weight Hydroxyethylcellulose

Previous studies (Barron et al., 1993, 1994) have shown that dilute aqueous solutions of hydroxyethylcellulose (HEC) polymers provide an excellent alternative to gel-based DNA separation media for capillary electrophoresis (CE) of DNA restriction fragments (72−23 130 base pairs). DNA separation by CE in HEC solutions is strongly influenced by the average HEC molecular weight as well as by the HEC concentration in the electrophoresis buffer. Here we describe a systematic investigation of the effects of a mixture of low- and high-molecular weight HEC polymers, over a range of concentrations, to form a DNA separation medium with a broad range of polymer chain lengths. Our results show that, relative to separation media containing solely low-molecular-weight or high-molecular-weight HEC polymers, the mixed polymer solutions provide superior separation over the DNA size range of interest, while providing a five-fold viscosity reduction. The addition of a very small amount of high-molecular-weight HEC to a solution of low-molecular-weight HEC leads to a significant improvement in the separation of larger DNA fragments (>603 base pairs), while retaining resolution of smaller DNA fragments. The consequences of these results on the proposed mechanism of DNA separation in un-cross-linked polymer solutions are discussed.

The effects of polymer properties on DNA separations by capillary electrophoresis in uncross-linked polymer solutions.

Low-viscosity, aqueous solutions of hydrophilic linear polymers have been shown to be useful for the separation of DNA restriction fragments by capillary electrophoresis (CE). However, the choice of polymer type, size, and concentration remains largely empirical, because the mechanism of high-field electrophoretic DNA separations in polymer solutions is not well understood. To assist in elucidating the mechanism of DNA separation, we experimentally investigated the effects of polymer properties such as stiffness (persistence length), average molecular mass, polydispersity, and hydrophilicity on the separation of DNA ranging from 72 bp to 23 kbp. This was accomplished by comparing the results of DNA separations obtained by counter-migration CE in dilute and semidilute solutions of linear polyacrylamide (PAA), hydroxyethyl-cellulose (HEC), and hydroxypropylcellulose (HPC) polymers of several different average molecular masses.

Gels from modified hydroxyethyl cellulose and ionic surfactants

Abstract The macroscopic properties of aqueous solutions of hydroxyethyl cellulose (HEC) and of modified HEC samples which carry cationic groups (cat-HEC) or a cationic and hydrophobic group (cat-HMHEC) and their interactions with ionic surfactants (SDS and STS) are investigated by rheological, electric birefringence and surface tension measurements. The gel formation of the surfactant free polymer solutions strongly depends on the polymer concentration and the constitution of the polymer. HEC forms thermoreversible gels for T c 3 wt%. HEC does not interact with ionic surfactants. The 1 wt% viscoelastic solutions of cat-HEC and cat-HMHEC can be transformed into physically crosslinked gels by the addition of oppositely charged surfactants. The polymer solutions are first transparent and show an increase in viscosity and elasticity with increasing surfactant concentration (pre-precipitation area). For higher surfactant concentrations associative phase separation occurs because of charge neutralization and then a second single phase area is observed. In this post-precipitation area the viscosity continuously decreases by further addition of surfactants. The concentration dependence of the gel state formed by cat-HMHEC and STS is strongly affected by the history of the complexes: A 1 wt% polymer-STS-gel retains a yield stress value when diluted down to 0.7 wt% polymer concentration while the addition of STS to the 0.7 wt% polymer solution does not result in a gel state. Network formation is also observed for the hydrophobic polyelectrolytes by the addition of anionic surfactants below the critical overlap concentration of the surfactant free cat-HMHEC solutions.

Dynamics of T2 DNA during electrophoresis in entangled and ultradilute hydroxyethyl cellulose solutions

Dynamics of T2 DNA during electrophoresis in entangled and ultradilute hydroxyethyl cellulose solutions

Dynamics of T2 DNA during electrophoresis in entangled and ultradilute hydroxyethyl cellulose solutions

Dynamics of T2 DNA during electrophoresis in entangled and ultradilute hydroxyethyl cellulose solutions

Analysis of internucleosomal DNA fragmentation in apoptotic thymocytes by dynamic sieving capillary electrophoresis

The analysis, by slab gel electrophoresis, of internucleosomal DNA cleavage or laddering, characteristic of apoptosis in many cell systems, is labour intensive, difficult to automate and best only semi-quantitative. In this report we show that CE, using dilute solutions of hydroxyethylcellulose as a replaceable sieving matrix, can be applied to the relatively rapid analysis of DNA laddering in whole digests of apoptotic rat thymocytes. Also, using the sensitivity of laser-induced fluorescence detection and the highly sensitive nucleic acid stain YO-PRO-1, the CE method reported here can use 1000–2000 fold fewer cells than needed for traditional slab gel methods.

Comparison of the extensional and shear viscosity characteristics of aqueous hydroxyethyl cellulose solutions

The extensional viscosity characteristics of aqueous solutions of varying concentrations of three samples of hydroxyethylcellulose (HEC) of differing molecular masses have been determined using a commercially available opposed jet extensional rheometer. The results have been compared to the shear flow characteristics of the solutions and the Trouton ratio, T R , of the various systems calculated. For all polymer solutions studied, T R was found to approach the predicted Newtonian value of 3 at low extensional strain rates. This observation was taken as a strong indication that the opposed jet rheometer was producing reliable extensional viscosity data. At higher strain rates, T R generally increased with increasing strain rate and, for any given sample, with increasing polymer concentration thereafter. All HEC solutions studied were found to exhibit strain-thinning behavior in extensional flow and shear-thinning behavior in shear flow, with the most pronounced effects being observed with the highest molecular mass sample (M v ∼4.5×10 5 g/mol). The relative degrees of strain and shear thinning exhibited by the various HEC solutions have been quantified using the power law analysis. For the two samples of lowest molecular mass (M v ∼6.5×10 4 and ∼1.9×10 5 g/mol) the value of a power law index, n, in both extensional and shear flow, was close to unity. For all solutions of the sample of highest molecular mass, the value of n in extensional flow was significantly higher than that observed in shear flow. Regions of apparent strain thickening were observed for a few of the lowest viscosity solutions, but these observations were attributed to the onset of significant inertial effects rather than any coil-stretch transition phenomena

DNA conformational dynamics in polymer solutions above and below the entanglement limit

Video microscopy of nucleic acids (DNA) undergoing electrophoresis in hydroxyethyl cellulose (HEC) sieving buffers demonstrates previously unobserved shape-changing interactions between DNA and HEC molecules. We provide the first visual demonstration of entanglement between DNA and one or several discrete HEC molecules, which has been postulated to occur in ultradilute polymer solutions. Typically, nucleic acids appear to become entangled with HEC at a single region only, in both dilute and fully entangled HEC solutions. Fluctuations of the center of mass velocity of a DNA molecule and its correlation with conformation are revealed from analyses of the image data. These observations account for the success of recently reported rapid, high-resolution dc and pulsed-field capillary electrophoretic separations of nucleic acids in ultradilute hydroxyethyl cellulose solutions and hydroxyethyl cellulose/poly(ethylene oxide) solutions.

Rapid pulsed field capillary electrophoretic separation of megabase nucleic acids.

Pulsed field capillary electrophoresis in ultradilute solutions of sieving polymers has been used to separate nucleic acid fragments as long as 1.6 million base pairs. Hydroxyethyl cellulose solutions are used for separations in the size range 8000-50,000 base pairs. Longer chain nucleic acids are separated in mixed hydroxyethyl cellulose/poly(ethylene oxide) solutions. Separations are rapid (12-13 min).

High-Sensitivity Capillary Electrophoresis of Double-Stranded DNA Fragments Using Monomeric and Dimeric Fluorescent Intercalating Dyes

Fluorescence-detected capillary electrophoresis separations of phi X174/HaeIII DNA restriction fragments have been performed using monomeric and dimeric intercalating dyes. Replaceable hydroxyethyl cellulose solutions were used as the separation medium. Confocal fluorescence detection was performed following 488-nm laser excitation. The limits of DNA detection for on-column staining with monomeric dyes (ethidium bromide, two propidium dye derivatives, oxazole yellow, thiazole orange, and a polycationic thiazole orange derivative) were determined. The thiazole orange dyes provide the most sensitive detection with limiting sensitivities of 2-4 amol of DNA base pairs per band, and detection of the 603-bp fragment was successful, injecting from phi X174/HaeIII samples containing only 1-2 fg of this fragment per microliter. Separations of preformed DNA-dimeric dye complexes were also performed. The breadth of the bands observed in separations of preformed DNA-dimeric dye complexes is due to the presence of DNA fragments with different numbers of bound dye molecules that can be resolved as closely spaced subbands in many of our separations. The quality of these DNA-dye complex separations can be dramatically improved by performing the electrophoresis with 9-aminoacridine (9AA) in the column and running buffers. The optimum concentrations of 9AA for the separation of complexes preformed with the dimeric dyes TOTO, EthD, TOTAB, and YOYO were determined to be 100, 1, 1, and 0.5 microM, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of viscosity on product distribution of fast competitive chemical reactions

AbstractThe objective of this study was to determine the influence of viscosity on micromixing in turbulent flow. It was first necessary to find a suitable viscosity‐raising additive. HEC (hydroxyethyl cellulose) proved to be better than previously studied additives [sorbitol and carboxymethylcellulose (CMC)]. In concentrations up to 1 wt‐%, HEC solutions are almost Newtonian with viscosities independent of pH over the range 2 to 10. HEC had no effect on the reaction rate constants and the spectrophotometric analysis of the fast, competing reactions used – the diazo coupling between 1‐naphthol and diazotized sulphanilic acid. The viscosity can then be raised by around an order of magnitude by adding less than 1 wt‐% HEC to this reaction system.Diazo couplings were conducted in a 20 1 semi‐batch tank reactor stirred by a Rushton turbine at two viscosity levels (0.9 and 6.2 mPa s). Long feed times ensured that micromixing was controlling. More bisazo dye was formed in the more viscous solution, all other conditions being unchanged, indicating more intense segregation and slower micromixing.This was also shown by visualizing the extent of neutralisation zones, with more spreading and slower micromixing being observed in viscous solution. Higher turbine speeds reduced this spreading. One feed point near and one far from the turbine were employed: the strong inhomogeneity of the turbulence led to smaller amounts of bisazo dye when the feed was added to the turbine suction, irrespective of the viscosity. All results agreed with the trends predicted by the engulfment model of micromixing. Its simplest form assigns an average energy dissipation rate to the reaction zone: the values obtained are of similar magnitude to those measured by physical techniques and were related to the spreading of the reaction zone.

Numerical Analysis of Power Consumption and Mixing Time for a Pseudoplastic Liquid in Geometrically Similar Stirred Vessels with Several Kinds of Plate-type Impellers.

A numerical analysis method of estimating power consumption for a pseudoplastic liquid in stirred vessels fitted with various plate impellers is first presented in terms of the energy dissipation distribution in the vessels. The pseudoplastic liquid used was a 1.2 wt.% aqueous solution of hydroxyethyl cellulose. Good agreement between numerically analysed results and experimental data of power consumption in a model vessel of 0.2 m diameter with various impellers and in a vessel of 0.4 m diameter with a paddle impeller proved the method to be sufficiently reliable. Subsequently, the same analysis and mixing analysis were numerically performed for geometrically similar large-scale vessels of 0.4, 0.6 and 0.8 m diameters. It was ascertained from these analyses that the relation between the scale-up ratio and the power consumption, mixing time, and mixing energy can be quantitatively estimated by a numerical analysis of stirred vessels with various types of stirring impellers for a pseudoplastic liquid.

High-Speed Parallel Separation of DNA Restriction Fragments Using Capillary Array Electrophoresis

A new method for performing high-speed, high-throughput sizing of DNA has been developed. Samples containing DNA restriction fragments between 70 and 10,000 base pairs in length are electrophoretically separated using capillary arrays in ∼20 min and detected with high sensitivity using a fluorescence detection system. The separations of ΦX174/HaeIII fragments are performed on an array of seven 100-μm i.d., 350-μm o.d. capillaries using replaceable hydroxyethyl-cellulose solutions as the sieving medium. The fragments are fluorescently labeled using ethidium bromide in the running buffer and detected with a laser-excited, confocal-fluorescence scanner. The limit of detection is ∼1 pg of DNA per band and separations can be detected injecting DNA samples as dilute as 0.1 ng/μl. Samples were electrokinetically injected from a cassette of microcentrifuge tubes using a format that will facilitate the application of capillary electrophoresis to separations in molecular biology. The feasibility of extending this technique to lower DNA concentrations and to ∼100 capillary arrays is discussed.

Capillary electrophoresis of DNA in uncross-linked polymer solutions

We have used dilute and semi-dilute uncross-linked hydroxyethyl cellulose (HEC) solutions as separation matrices for capillary electrophoresis of DNA restriction fragments. In these experiments, we investigated the effects of HEC molecular weight and concentration on resolution, attempting to relate these parameters to the polymer entanglement threshold concentration. The entanglement thresholds of seven molecular weight fractions of hxdroxyethyl cellulose were determined from viscosity-concentration data; the entanglement threshold was found to scale as N −1.2, where N = number of HEC monomers. This finding is not in agreement with classical scaling arguments. We present a relationship to predict the observed entanglement threshold of HEC in solution as a function of number average molecular weight. It was found that excellent separation of ΦX174/ HaeIII DNA restriction fragments (72–1353 base pairs) by capillary electrophoresis in HEC solutions can be achieved significantly below the entanglement threshold, depending on DNA size and HEC molecular weight. The mechanism of separation in these uncross-linked polymer solutions must therefore be reexamined. Our experiments show that the entanglement threshold is a useful parameter in predicting a range of HEC concentrations which will separate certain DNA fragments for a given HEC molecular weight. However, the presence of a fully entangled network is not a prerequisite for separation.