Hydrophobic Interaction Capillary Electrochromatography of Protein Mutants. Use of Lipid-Based Liquid Crystalline Nanoparticles as Pseudostationary Phase

Self-assembled and covalently linked capillary coating of diazoresin and cyclodextrin-derived dendrimer for analysis of proteins by capillary electrophoresis

Self-assembled and covalently linked capillary coatings of cyclodextrin-derived (CD) dendrimer were prepared using photosensitive diazoresin (DR) as a coupling agent. Layer by layer (LBL) self-assembled DR/CD-dendrimer coatings based on ionic bonding was fabricated first on the inner surface of capillary, and subsequently converted into covalent bonding after treatment with UV light through a unique photochemistry reaction of DR. Protein adsorption on the inner surface of capillary was suppressed by the DR/CD-dendrimer coating, and thus a baseline separation of lysozyme (Lys), myoglobin (Mb), bovine serum albumin (BSA) and ribonuclease A (RNase A) was achieved using capillary electrophoresis (CE). Compared with the bare capillary, the DR/CD-dendrimer covalently linked capillary coatings showed excellent protein separation performance with good stability and repeatability. Because of the replacement of highly toxic and moisture sensitive silane coupling agent by DR in the covalent coating preparation, this method may provide an environmentally friendly and simple way to prepare the covalently coated capillaries for CE.

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.

RAFT polymerized nanoparticles: influences of shell and core chemistries on performance for electrokinetic chromatography

The performance and solvation characteristics of two novel latex nanoparticle (NP) pseudo-stationary phases (PSPs) for EKC are determined and compared to those of previously reported micellar, polymeric, and NP materials. The new NPs have shells composed of strongly acidic poly(AMPS) as opposed to the poly(acrylic acid) shell of the prior NP, and have varied hydrophobic core chemistry of either poly(butyl acrylate) or poly(ethyl acrylate). The NPs poly(AMPS) shell shows only minor changes in mobility and selectivity between pH 4.9 and 9.4, allowing adjustment of pH to influence and optimize separation performance. All of the NP phases have significantly different solvation characteristics and selectivity relative to SDS micelles. The selectivity and solvent character are similar for NPs with poly(butyl acrylate) cores and different shells, but vary significantly between NPs with poly(butyl acrylate) versus poly(ethyl acrylate) cores. NPs with poly(butyl acrylate) cores are among the least cohesive PSPs reported to date, while the NP with poly(ethyl acrylate) core is among the most cohesive. The results demonstrate that PSPs with unique selectivity can be generated by altering the chemistry of the hydrophobic core.

Fast surface acoustic wave-matrix-assisted laser desorption ionization mass spectrometry of cell response from islets of Langerhans

A desire for higher speed and performance in molecular profiling analysis at a reduced cost is driving a trend in miniaturization and simplification of procedures. Here we report the use of a surface acoustic wave (SAW) atomizer for fast sample handling in matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) peptide and protein profiling of Islets of Langerhans, for future type 2 diabetes (T2D) studies. Here the SAW atomizer was used for ultrasound (acoustic) extraction of insulin and other peptide hormones released from freshly prepared islets, stimulated directly on a membrane. A high energy propagating SAW atomizes the membrane-bound liquid into approximately 2 μm diameter droplets, rich in cell-released molecules. Besides acting as a sample carrier, the membrane provides a purification step by entrapping cell clusters and other impurities within its fibers. A new SAW-based sample-matrix deposition method for MALDI MS was developed and characterized by a strong insulin signal, and a limit of detection (LOD) lower than 100 amol was achieved. Our results support previous work reporting the SAW atomizer as a fast and inexpensive tool for ultrasound, membrane-based sample extraction. When interfaced with MALDI MS, the SAW atomizer constitutes a valuable tool for rapid cell studies. Other biomedical applications of SAW-MALDI MS are currently being developed, aiming at fast profiling of biofluids. The membrane sampling is a simplistic and noninvasive collection method of limited volume biofluids such as the gingival fluid and the tearfilm.

Novel covalently coated diazoresin/polyvinyl alcohol capillary column for the analysis of proteins by capillary electrophoresis

A novel method for the preparation of covalently linked capillary coatings of PVA was demonstrated using photosensitive diazoresin (DR) as coupling agents. Layer-by-layer self-assembly film of DR and PVA based on hydrogen bonding was first fabricated on the inner wall of capillary, then the hydrogen bonding was converted into covalent bonding after treatment with UV light through the unique photochemistry reaction of DR. The covalently bonded coatings suppressed basic protein adsorption on the inner surface of capillary, and thus a baseline separation of lysozyme, cytochrome c and BSA was achieved using CE. Compared with bare capillary or noncovalently bonded DR/PVA coatings, the covalently linked DR/PVA capillary coatings not only improved the CE separation performance for proteins, but also exhibited good stability and repeatability. Due to the replacement of 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 the covalently coated capillaries for CE.

Thermodynamics of antimicrobial peptide JCpep8 binding to living Staphylococcus aureus as a pseudo-stationary phase in capillary electrochromatography and consequences for antimicrobial activity

To understand the details of the permeation pathways of antimicrobial peptide JCpep8, the antimicrobial processes were investigated step by step in this paper. First, the characterization of the initial binding process was explored by introducing the living Staphylococcus aureus cells (LSACs) into electrophoretic buffer used as pseudo-stationary phase in capillary electrochromatography (CEC), and the thermodynamic parameters were determined. The binding constants at 298, 303, and 309 K were 7.40 × 10¹¹, 1.43 × 10¹², and 2.6 × 10¹² M⁻¹, respectively, which indicated the evident interaction between JCpep8 and LSACs. This binding process was spontaneous. Both the electrostatic force and hydrophobic effect play major roles in this binding process. Second, antibacterial activity kinetics and outer membrane and inner membrane disruption assays were investigated. Data indicated that JCpep8 killed microbes principally by breaking their cell wall and membrane, followed by cell lysis. The results were confirmed by Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). In summary, JCpep8 kills microbes mainly by wall-/membrane-targeting pore-forming mechanisms.

Anionic functionalized gold nanoparticle continuous full filling separations: importance of sample concentration

Electrically driven separations which contain nanoparticles offer detection and separation advantages but are often difficult to reproduce. To address possible sources of separation inconsistencies, anionic functionalized gold nanoparticles are thoroughly characterized and subsequently included in continuous full filling capillary electrophoresis separations of varying concentrations of three small molecules. Citrate stabilized gold nanospheres are functionalized with 11-mercaptoundecanoic acid, 6-mercaptohexanoic acid, or thioctic acid self-assembled monolayers (SAMs) and characterized using dynamic light scattering, extinction spectroscopy, zeta potential, and X-ray photoelectron spectroscopy prior to use in capillary electrophoresis. Several important trends are noted. First, the stability of these anionic nanoparticles in the capillary improves with increased ligand packing density as indicated by a ratio of absorbance collected at 520 to 600 nm. Second, increasing nanoparticle concentration from 0 to 2 nM (0-0.002(5)%, w/w) minimally impacts analyte migration times; however, when higher nanoparticle concentrations are included within the capillary, nanoparticle aggregation occurs which induces separation inconsistencies. Third, analyte peak areas are most significantly impacted as their concentration decreases. These trends are attributed to both sample enrichment and electrostatic interactions between the anionic carboxylic acid functionalized gold nanoparticles and sample. These important findings suggest that sample concentration-induced conductivity differences between the sample matrix and separation buffer as well as SAM packing density are important parameters to both characterize and consider when nanoparticles are used during continuous full filling separations and their subsequent use to enhance spectroscopic signals to improve in-capillary analyte detection limits.

Electrokinetic chromatography and mass spectrometric detection using latex nanoparticles as a pseudostationary phase

The utility of novel latex nanoparticles as pseudostationary phases for electrokinetic chromatography with UV and mass spectrometric detection is demonstrated. The nanoparticles are synthesized using ab initio RAFT (reversible addition-fragmentation chain transfer) in emulsion polymerization, which yields small (63 nm) particles with a narrow size distribution, a hydrophobic core, and an ionic shell. The nanoparticles are shown to provide efficient and selective separations, with retention and separation selectivity dominated by hydrophobic interactions. The nanoparticles are highly retentive, such that they are effective at relatively low concentrations. Addition of the nanoparticles to the background electrolyte at these concentrations has a minor effect on the noise with UV detection, no measurable effect on the separation current, and minor effects on analyte ionization efficiency during electrospray ionization. The nanoparticles do not cause fouling or degradation of the electrospray-mass spectrometer interface even after several weeks of use. The combination of online sample preconcentration via sweeping and selective mass spectrometric detection yields low detection limits (10-16 ppb), particularly for more hydrophobic compounds.

Electrophoretic and electrochromatographic separation of proteins in capillaries: an update covering 2007-2009

This review article covers 3-year period from 2007 to 2009 and is a continuation of the review article by V. Dolnik, [Electrophoresis 2008, 29, 143-156]. This article with 125 references describes recent developments in CE and CEC of proteins in capillary format and does not cover the developments of CE and CEC in microchip format, since Tran et al. review the microchip subject in this special issue. The present review article has four major topics including (i) the separation media, (ii) multidimensional separations, (iii) detection, and (iv) applications.