Application of Pluronic copolymer liquid crystals for the capillary electrophoretic separation of collagen type I cyanogen bromide fragments

A review of electrophoretic separations in temperature-responsive Pluronic thermal gels

Gel electrophoresis is a ubiquitous bioanalytical technique used in research laboratories to validate protein and nucleic acid samples. Polyacrylamide and agarose have been the gold standard gel materials for decades, but an alternative class of polymer has emerged with potentially superior performance. Pluronic thermal gels are water-soluble polymers that possess the unique ability to undergo a change in viscosity in response to changing temperature. Thermal gels can reversibly convert between low-viscosity liquids and high-viscosity solid gels using temperature as an adjustable parameter. The properties of thermal gels provide unmatched flexibility as a dynamic separations matrix to measure analytes ranging from small molecules to cells. This review article describes the physical and chemical properties of Pluronic thermal gels to provide a fundamental overview of polymer behavior. The performance of thermal gels is then reviewed to highlight their applications as a gel matrix for electrokinetic separations in capillary, microfluidic, and slab gel formats. The use of dynamic temperature-responsive gels in bioanalytical separations is an underexplored area of research but one that holds exciting potential to achieve performance unattainable with conventional static polymers.

Pluronic F-127 as the buffer additive in capillary entangled polymer electrophoresis: some fundamental aspects

Polymeric macromolecules of well-designed structures and specific properties open promising directions in the capillary entangled polymer electrophoresis. Pluronic F-127, as a thermoassociating polymer, possesses some unique properties that can be utilized in capillary entangled polymer electrophoresis of amino acids, peptides and proteins. In this study, we studied properties of Pluronic F-127 polymer as an additive to BGE for the separation of peptides and proteins. The influence of the thermoassociation on separation selectivity was studied. The addition of Pluronic caused severe instabilities of the electrical current and the signal of the UV detector. This study reveals remarkable positive effect of a low pressure applied to the inlet buffer vial during the analysis, which apparently stabilizes the electrical current and the detector signal. The effect of hydrodynamic flow induced by the pressure applied on the separation efficiency was studied and the significance of this effect was discussed. Pluronic F-127, as a representative of synthetic macromolecules, was compared with dextran, as a representative of natural polymers, in terms of separation power, selectivity and repeatability of migration times.

Swelling of ionic and nonionic surfactant micelles by high pressure gases

The influence of different solvent environments on the size, shape, and characteristics of surfactant micelles of Pluronic F127 and CTAB was investigated by small-angle neutron scattering (SANS). SANS experiments were undertaken on dilute micellar surfactant solutions of F127 and CTAB that between them were exposed to liquid and supercritical carbon dioxide, liquid propane, ethane, and heptane under various pressures and temperatures. Swelling of the surfactant micelles could be directly related to the solubility of the solvents within the micelles, especially within their cores. Carbon dioxide produced the largest swelling of the Pluronic F127 micelles, compared to propane and ethane, which mirrors the solubility of the gases in the PPO core of the micelles. Conversely, the extent of swelling of the cores of CTAB micelles was greater with propane compared to carbon dioxide, which again relates to the solubility of the solvents in the alkane core of the CTAB micelles.

Nanostructured polymer matrix for oligonucleotide separation

A nanostructured copolymer matrix has successfully separated oligonucleotides with high resolution by CE using a very short separation channel which simulates the real microchip condition for the first time. The triblock copolymer, E(45)B(14)E(45) (B20-5000) with E, B, and subscript denoting oxyethylene, oxybutylene, and segment length, respectively, has a unique temperature-dependent viscosity-adjustable property and a dynamic coating ability in 1xTBE buffer (89 mM Tris, 89 mM boric acid, 2 mM EDTA in Milli-Q water). The B-block is hydrophilic at low temperatures, e.g., 4 degrees C, and the polymer solution has a very low viscosity of about 100 cP in a 32.5% w/v solution. At room temperatures, the B-block becomes hydrophobic due to a breakdown of hydrogen bonds between B-blocks and water, and the polymer matrix forms a body-centered cubic structure at high concentrations. Oligonucleotide sizing markers ranging from 8 to 32 base could be successfully separated with one-base resolution in a 1.5 cm long separation channel by E(45)B(14)E(45) in its gel-like state.

Capillary electromigration methods for the study of collagen

This review paper gives an overview of capillary electromigration methods used in the analysis of collagen. Analyses of the parent chains as well as of the bromcyane and collagenase fragments of collagens are presented. Methods include capillary zone electrophoresis, capillary gel electrophoresis, micellar electrokinetic chromatography as well as combinations of HPLC and capillary electrophoresis, and capillary electrophoresis with mass spectrometry.

Capillary electrophoresis of peptides and proteins with plug of Pluronic gel

Electromigration capillary methods are promising techniques in proteomics and they are still under research. We used a partial filling approach, i.e. a combination of gel and non-gel separation mechanisms in a single dimension. We tried using an interesting gel, Pluronic F 127, which can be considered as a surfactant capable of self-association both with isotropic and anisotropic gels. The Pluronic was inserted inside the capillary as a plug at the start of the capillary, and it provided separation at the first time. Separation by this gel was achieved according to molecular weight and/or hydrophobicity. The applicability of this method was demonstrated in the separation of real samples-peptides arising from collagen after CNBr or collagenase cleavage and albumin after trypsin cleavage (peptide mapping). Some peptides and proteins were selectively retained by the Pluronic gel. These interactions with the gel did not depended on their molecular weight alone, but they probably depend on a combination of both principles. It was confirmed that capillary electrophoresis with Pluronic plug can give us another new separation option, complementary to free solution capillary electrophoresis. The CE method presented here, consisting of a partial filling approach with combine gel and non-gel separation mechanisms seemed to be a promising method for the separation of complex mixtures of peptides.

Matrices for capillary gel electrophoresis—a brief overview of uncommon gels

This article gives an overview of uncommon replaceable matrices (gels) for capillary gel electrophoresis. This electrophoretic technique is useful mainly for the separation and analysis of biopolymers-nucleic acids and their fragments, and proteins/peptides. Commonly used gels are not reviewed. Those mentioned and discussed here are gels containing saccharides, newly developed acrylamide-based gels and thermoadjustable viscosity polymers, namely triblock copolymers and grafted polyacrylamide.

Quantitative measurement of collagen methylation by capillary electrophoresis

Collagen methylation has been exploited in various applications involving living cells. We have observed correlation between the collagen methylation with the rate of cell proliferation in three-dimensional (3-D) microenvironment. To quantify the degree of collagen methylation, we have developed a capillary zone electrophoresis method. Using a polyvinyl alcohol-coated fused-silica capillary and UV detection at 200 nm, we have optimized pH and separated the native collagen into three major bands in phosphate buffer (50 mM, pH 2.5) with 0.05% hydroxypropylmethylcellulose. Under these conditions, the methylated collagens were separated into four major bands, which changed with different methylation reaction conditions. We propose an index to quantify the degree of collagen methylation that also correlates with their effects on cell proliferation.

Application of capillaries with minimized electroosmotic flow to the electrokinetic study of acidic drug-beta-oleoyl-gamma-palmitoyl-L-alpha-phosphatidyl choline liposome interactions

Interaction of a model set of common drugs varying widely in their polarity as well as in their chemical structure (salicylic acid, acetylsalicylic acid, ketoprofen, phenytoin and propranolol) with beta-oleoyl-gamma-palmitoyl-L-alpha-phosphatidyl choline (POPC) liposomes was investigated by means of capillary electrophoresis. Two phosphate buffers differing in their pH (50 mM, pH 7.5 and 9.2) were used both for liposome reconstitution and as background electrolytes for capillary electrophoresis using capillaries with minimised electroosmotic flow (EOF). The liposomes showed practically no electrophoretic mobility and formed a stable plug in the capillary. At alkaline pH (9.2), the polyimide coated capillary exhibited residual endoosmotic flow (the EOF marker appeared before the detection window around 40 min as compared to 2.2 min in the untreated capillary; attempts to reveal endoosmotic flow at pH 7.5 were unsuccessful). The concentration of the mixture of the test compounds was 50 microg/ml (except for ketoprofen concentration of which was 5 microg/ml due to the lower solubility of the drug), i.e. large enough to exceed the binding capacity of the injected liposome plug at least at the neutral pH (7.5) which consequently resulted in two regions in the electropherogram, namely that which contained the unbound species and that corresponding to the liposome (lipid)-bound fraction. On the other hand in runs done at high pH of the background electrolyte (9.2) the whole amount injected interacted with the liposomes. Acidic drugs and phenytoin were run with negative polarity at the injection site. It was documented that both at pH 7.5 and 9.2 the investigated solutes interacted with POPC liposomes, though at pH 7.5 the equilibrium between the bound and unbound drugs was in favor of the unbound species. On the contrary, at pH 9.2 binding was considerably stronger and only the liposome bound fraction was seen upon electrophoresis. The well-known instability of phenytoin at room temperature resulted in the formation of an acidic hydrolytic product which was strongly bound to liposomes at the higher pH value. While no binding of phenytoin could be established at pH 7.5, at pH 9.2 this compound was degraded (hydrolyzed) and its degradation product was clearly bound to liposomes. It has to be emphasized that binding experiments must be done separately for acidic/neutral and basic drugs; binding of acidic/neutral drugs must be done at reversed polarity, while in order to reveal binding of basic drugs, positive polarity at the injection site must be used.

Capillary electrophoresis of proteins 1999-2001

This review article with 223 references describes recent developments in capillary electrophoresis (CE) of proteins and covers papers published during last two years, from the previous review (V. Dolnik, Electrophoresis 1999, 20, 3106-3115) through Spring 2001. It describes the topics related to CE of proteins including modeling of the electrophoretic properties of proteins, sample pretreatment, wall coatings, improving selectivity, detection, special electrophoretic techniques, and applications.

Capillary electrophoretic separation of proteins and peptides using Pluronic liquid crystals and surface-modified capillaries

Separation of model mixtures of peptides/proteins carried out in a hydrophilically coated capillary in 10 mmol/l Tris and 75 mmol/l phosphate buffer containing 7.5% (w/w) Pluronic F127 copolymer (apparent pH 2.9) revealed that the separation is predominantly driven by the charge/mass ratio with little or no sieving effect. Using a coated capillary helped to remove current fluctuations that are observed in the fused-silica capillaries in the presence of the Pluronic copolymer. With peptides bearing distinct positive charge (polylysine of Mr around 3300) molecular sieving helps more detailed separation of individual species. Polyamino acids carrying negative charge can be brought to the detector window in the reversed polarity mode, however, no detailed separation of the individual species involved was observed under the conditions used. With a naturally occurring mixture of collagen fragments released by CNBr treatment of the protein the sequence of emerging peptides (positive polarity mode) with no relation to the rel. mol. mass could be revealed. It is concluded that separation of proteins/peptides in the presence of Pluronic in the background electrolyte occur on the charge/mass ratio basis with molecular sieving effects acting as a secondary partition mechanism.

Advanced separation methods for collagen parent alpha-chains, their polymers and fragments

Current techniques used for collagen alpha-chains and their CNBr fragments are reviewed. Ion exchange, gel permeation, reversed-phase and affinity chromatography are discussed mainly from the preparative aspects as these are both the techniques of choice to remove biological matrix contaminants always present in collagen preparations and techniques routinely used for preparative purposes. Among electromigration procedures gel electrophoresis is widely used both for intact collagen alpha-chains and their fragments. Recently this technique was applied also for miniaturised preparations. Immunoblotting techniques serve more specific detection of otherwise hard to distinguish different collagen polypeptide chains. Capillary electromigration techniques brought recently new aspects of understanding the behaviour of collagen proteins upon different separation modes and seem to represent a smart perspective for better quantitation of individual collagen species.