Brush-like copolymer as a physically adsorbed coating for protein separation by capillary electrophoresis

In situ growth of dual-responsive polymer as coating for open tubular capillary electrochromatographic separation of epimedins

Recently, open tubular capillary electrochromatography (OT-CEC) has captured considerable interest; its efficient separation capability hinges on the interactions between analytes and polymer coatings. However, in situ growth of stimuli-responsive polymers as coatings has been rarely studied and is crucial for expanding the OT-CEC technique and its application. Herein, following poly(styrene-maleicanhydride) (PSM) chemically bonded onto the inner surface of the capillary, a dual pH/temperature stimuli-responsive block copolymer, P(SMN-COOH), was prepared by in situ polymerizing poly(N-isopropylacrylamide) carboxylic acid terminated [P(N-COOH)] in PSM. An OT-CEC protocol was first explored using the coated capillary for epimedins separation. As a proof of concept, the developed OT-CEC system facilitated hydrogen bonding and tuning the hydrophilic/hydrophobic interactions between the test analytes and the P(SMN-COOH) coating by varying buffer pH and environmental temperature. Four epimedins with similar chemical structures were baseline separated under 40 °C at pH 10.0, exhibiting dramatical improvement in separation efficiency in comparison to its performance under 25 °C at pH 4.0. In addition, the coated capillary showed good repeatability and reusability with relative standard deviations for migration time and peak area between 0.7 and 1.7% and between 2.9 and 4.6%, respectively, and no significant changes after six runs. This work introduces a paradigm for efficient OT-CEC separation of herbal medicines through adjusting the interactions between analytes and smart polymer coatings, addressing polymer coating design and OT-CEC challenges.

Open tubular capillary electrochromatography with dual-responsive polymer as coating for separation of chromones

Fabricating polymeric coatings that are responsive to multiple/dual stimuli is crucial and remains a major challenge in the development of highly efficient open tubular capillary electrochromatography (OT-CEC). In this study, a pH and temperature-responsive block copolymer, poly(styrene-maleic anhydride 2-dimethylamino ethyl methacrylate), P(St-MAn-DMAEMA), was designed and synthesized. Using P(St-MAn-DMAEMA) as the coating, an OT-CEC protocol was constructed for the analysis of chromones. The morphology and hydrophobicity-hydrophilicity of the polymeric coating could change via varying the environmental conditions, affecting the separation efficiency of OT-CEC. Interestingly, the best performance of OT-CEC was achieved at pH 9.7 and 45 °C via tuning the interactions between the coating and the analytes. Additionally, the proposed OT-CEC method exhibited a good linear range for the detection of the three test chromones from 10.0 to 100.0 μM, with all correlation coefficients (R2) >0.997. The coatings also had good stability and reusability. This work provides an approach for the preparation of new multiple-stimuli-responsive polymeric coatings for the establishment of OT-CEC systems.

Analysis of proteins and chiral drugs based on vancomycin covalent capillary electrophoretic coating

Vancomycin is an amphoteric glycopeptide molecule, and its group diversity and chiral active sites provide a potential basis for its application in chromatographic analysis. In this article, using photosensitive diazo resin (DR) as the coupling agent, vancomycin is modified on the inner wall of the capillary to construct a capillary coating separation system. The highlight of the coated capillary is that it has both anti-protein adsorption and chiral separation properties. Compared with the bare capillary or non-covalently bonded DR/vancomycin-coated capillary, it can not only achieve the separation of four mixed proteins of lysozyme (Lys), bovine serum albumin (BSA), myoglobin (Mb), and ribonuclease A (RNase A), but also shows excellent performance in chiral drugs. The coated capillary effectively solves the problems of low efficiency of the separation column and high sample loss and provides ideas for the development of coated capillaries in the future.

Metal cation control of electroosmotic flow magnitude in phospholipid-coated capillaries

CZE has become widespread for the separation and analysis of biomolecules such as proteins and peptides, due to factors such as, the speed of the separations, low sample volume, and high resolution associated with the technique. However, the separation of biomolecules by CZE does present a significant challenge due to the electrostatic attraction and adsorption of cationic, or cation containing, biomolecules to the capillary surface. To that end numerous methods have been developed to passivate, or protect the surface, in order to prevent the adsorption of analytes. Yet, in the process of protecting the capillary surface, the potential for further modification of the EOF, a factor crucial to effective analyte resolution, is greatly diminished. In seeking to overcome this limitation we have explored the potential of incorporating a range of metal cations into a phospholipid bilayer capillary coating. It has previously been established that the inclusion of calcium into the separation buffer with a phospholipid coating will reverse the EOF in the capillary. Here, we present our investigation of a broader range of metal cations included in the separation buffer (Ca(2+) , Mg(2+) , Co(2+) , Ni(2+) , Sr(2+) , Ba(2+) , and Ce(3+) ) revealing that the choice of metal cation can drastically influence the EOF, with observed values between -3.80 × 10(-4) and -5.74 × 10(-5) cm(2) /V·s.

A novel diazoresin/poly(N-vinyl aminobutyric acid) covalent capillary coating for the analysis of proteins by capillary electrophoresis

A novel method for the preparation of covalently linked capillary coatings of poly(N-vinyl aminobutyric acid) (PVAA) obtained from hydrolyzed polyvinylpyrrolidone was demonstrated using photosensitive diazoresin (DR) as a coupling agent. A layer-by-layer self-assembled film of DR and PVAA based on ionic bonding was first fabricated on the inner wall of capillary, then ionic bonding was converted into covalent bonding after treatment with UV light through a unique photochemical reaction of DR. The covalently bonded coatings suppressed protein adsorption on the inner surface of the capillary, and thus a baseline separation of lysozyme, cytochrome c, BSA, amyloglucosidase, and myoglobin was achieved using CE. Compared with bare capillary or noncovalently bonded DR/PVAA coatings, the covalently linked DR/PVAA capillary coatings not only improved the CE separation performance for proteins, but also exhibited good stability and repeatability. Due to the replacement of the highly toxic and moisture-sensitive silane coupling agent by DR in the covalent coating preparation, this method may provide a green and easy way to make covalently coated capillaries for CE.

Recent developments in capillary and microchip electroseparations of peptides (2011-2013)

The review presents a comprehensive survey of recent developments and applications of capillary and microchip electroseparation methods (zone electrophoresis, ITP, IEF, affinity electrophoresis, EKC, and electrochromatography) for analysis, isolation, purification, and physicochemical and biochemical characterization of peptides. Advances in the investigation of electromigration properties of peptides, in the methodology of their analysis, including sample preseparation, preconcentration and derivatization, adsorption suppression and EOF control, as well as in detection of peptides, are presented. New developments in particular CE and CEC modes are reported and several types of their applications to peptide analysis are described: conventional qualitative and quantitative analysis, determination in complex (bio)matrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid, sequence and chiral analysis, and peptide mapping of proteins. Some micropreparative peptide separations are shown and capabilities of CE and CEC techniques to provide relevant physicochemical characteristics of peptides are demonstrated.

Capillary electrophoresis/mass spectrometry relevant to pharmaceutical and biotechnological applications

Advanced analytical techniques play a crucial role in the pharmaceutical and biotechnological field. In this context, capillary electrophoresis/mass spectrometry (CE/MS) has attracted attention due to efficient and selective separation in combination with powerful detection allowing identification and detailed characterization. Method developments and applications of CE/MS have been focused on questions not easily accessible by liquid chromatography/mass spectrometry (LC/MS) as the analysis of intact proteins, carbohydrates, and various small molecules, including peptides. Here, recent approaches and applications of CE/MS relevant to (bio)pharmaceuticals are reviewed and discussed to show actual developments and future prospects. Based on other reviews on related subjects covering large parts of previous works, the paper is focused on general ideas and contributions of the last 2 years; for the analysis of glycans, the period is extended back to 2006.