Measurement of monomolecular binding constants of neutral phenols into the beta-cyclodextrin by continuous frontal analysis in capillary and microchip electrophoresis via a competitive assay

Study of interactions between carboxylated core shell magnetic nanoparticles and polymyxin B by capillary electrophoresis with inductively coupled plasma mass spectrometry

In this work, interactions of carboxylated core shell magnetic nanoparticles with polymyxin B sulfate were studied by connecting capillary electrophoresis with inductively coupled plasma mass spectrometry. The interaction was probed by affinity mode of capillary electrophoresis with 25 mM phosphate buffer at physiological pH. ⁵⁴Fe, ⁵⁶Fe, ⁵⁷Fe, ³⁴S, and ¹²C isotopes were used to monitor the migration of an electroosmotic flow marker and the interaction of the nanoparticles with polymyxin B. The analysis of interaction data showed two distinct interaction regions, one with low polymyxin B concentration, the second with high polymyxin B concentration. These regions differed in the strength of the interaction, 1.49 × 10⁷ M^-1 and 1.60 × 10⁴ M^-1, and in the stoichiometry of 0.7 and 3.5, respectively. These differences can be explained by the decrease of electrostatic repulsion between nanoparticles caused by polymyxin B. This is also in agreement with the nanoparticles peak shapes: sharp for low polymyxin B concentrations and broad for high polymyxin B concentrations.

Detailed NMR investigation of cyclodextrin-perfluorinated surfactant interactions in aqueous media

Perfluorochemicals (PFCs) are contaminants of serious concern because of their toxicological properties, widespread presence in drinking water sources, and incredible stability in the environment. To assess the potential application of α-, β-, and γ-cyclodextrins for PFC remediation, we investigated their complexation with linear fluorinated carboxylic acids, sulfonates, and a sulfonamide with carbon backbones ranging from C4-C9. ¹⁹F Nuclear Magnetic Resonance (NMR) spectroscopy studies demonstrated β-CD formed the strongest complexes with these PFCs. The polar head group had a modest influence, but for PFCs with backbones longer than six carbons, strong association constants are observed for 1:1 (K_1:1∼10⁵M^-1) and 2:1 (K_2:1∼10³M^-1) β-CD:PFC complexes. Excess β-CD can be used to complex 99.5% of the longer chain PFCs. Competition studies with adamantane-carboxylic acid and phenol confirmed the nature and persistence of the β-CD:PFC complex. Detailed analyses of the individual NMR chemical shifts and Job plots indicate the favored positions of the β-CD along the PFC chain. Solution pH, ionic strength, and the presence of humic acid have modest influence on the β-CD:PFC complexes. The strong encapsulation of PFCs by β-CD under a variety of water quality conditions demonstrates the tremendous potential of CD-based materials for the environmental remediation of PFCs.

Nano-capillary electrophoresis for environmental analysis

Many analytical techniques have been used to monitor environmental pollutants. But most techniques are not capable to detect pollutants at nanogram levels. Hence, under such conditions, absence of pollutants is often assumed, whereas pollutants are in fact present at low but undetectable concentrations. Detection at low levels may be done by nano-capillary electrophoresis, also named microchip electrophoresis. Here, we review the analysis of pollutants by nano-capillary electrophoresis. We present instrumentations, applications, optimizations and separation mechanisms. We discuss the analysis of metal ions, pesticides, polycyclic aromatic hydrocarbons, explosives, viruses, bacteria and other contaminants. Detectors include ultraviolet-visible, fluorescent, conductivity, atomic absorption spectroscopy, refractive index, atomic fluorescence spectrometry, atomic emission spectroscopy, inductively coupled plasma, inductively coupled plasma-mass spectrometry, mass spectrometry, time-of-flight mass spectrometry and nuclear magnetic resonance. Detection limits ranged from nanogram to picogram levels.

Determination of binding parameters between lysozyme and its aptamer by frontal analysis continuous microchip electrophoresis (FACMCE)

An original and simple methodology based on microchip electrophoresis (MCE) in a continuous frontal analysis mode (named frontal analysis continuous microchip electrophoresis, FACMCE) was developed for the simultaneous determination of the binding parameters, i.e. ligand-site dissociation constant (k(d)) and number of binding sites on the substrate (n). This simultaneous determination was exemplified with the interaction between an aptamer and its target. The selected target is a strongly basic protein, lysozyme, as its quantification is of great interest due to its antimicrobial and allergenic properties. A glass microdevice equipped with a fluorescence detection system was coated with hydroxypropylcellulose, reducing the electroosmotic flow and adsorption onto the channel walls. This microdevice allowed the continuous electrokinetic injection of a mixture of fluorescently labelled aptamer and non-labelled lysozyme. By determining the concentration of the free fluorescently labelled aptamer thanks to its corresponding plateau height, mathematical linearization methods allowed to determine a k(d) value of 48.4±8.0 nM, consistent with reported results (31 nM), while the average number of binding sites n on lysozyme, never determined before, was 0.16±0.03. These results seem to indicate that the buffer nature and the SELEX process should influence the number and affinity of the binding sites. In parallel it has been shown that the binding between lysozyme and its aptamer presents two sites of different binding affinities.

Microchip capillary electrophoresis for frontal analysis of free bilirubin and study of its interaction with human serum albumin

To meet the need for bedside monitoring of free bilirubin for neonates under critical conditions, a microfluidic chip was fabricated and tested for its coupling with CE/frontal analysis (FA) to determine free bilirubin and study of its binding interaction with HSA, which regulated its concentration in plasma. The poly(methyl methacrylate) (PMMA) multichannel chip was fabricated by CO2 laser ablation and bonded with a fused-silica separation capillary for CE/FA separation with UV detection. The chip was designed to allow a complete assay of four electrophoretic runs using preconditioned channels to speed up the determination of free bilirubin and to deliver quick results for bedside monitoring. Under optimized conditions, the linear working range for free bilirubin was from 10 to 200 micromol with RSDs from 2.1 to 5.0% for n=3, and the LOD at 9 micromol for S/N=3. From a binding study between bilirubin and HSA under FA condition, the second binding constant for bilirubin-HSA was determined as 1.07x10(5) L/mol and the number of binding sites per HSA as 3.46. The results enabled the calculation of free bilirubin for jaundiced infants based on the clinically significant level of total bilirubin, producing a range of 118.3-119.4 micromol/L. The developed method is shown to meet the clinical requirement with additional margin of protection to detect the early rising level of free bilirubin prior to jaundice condition. The low-cost microchip CE/FA device is shown to produce quick results with high potential to deliver a suitable bed-side monitoring method for bilirubin management in neonates.

Electrophoretic affinity measurements on microchip. Determination of binding affinities between diketopiperazine receptors and peptide ligands

ACE on a microchip (MC-ACE) is introduced as a fast and reliable method to determine binding affinities. It is based on monitoring the change in the ionic mobility of a receptor upon binding to a ligand, or vice versa. The method is complementary to other standard methods for binding affinity determinations, like isothermal titration calorimetry (ITC), NMR, UV-Vis spectroscopy, etc. and allows for affinity studies of weak to strong binding interactions. The method is attractive since it principally allows for the analysis of the binding affinity of multiple receptors to a given ligand and requires comparatively small quantities of the binding partners (particularly in comparison to affinity measurements on capillary). We demonstrate the applicability of MC-ACE for the determination of the binding affinities between acid-rich diketopiperazine receptors and basic tripeptides in aqueous solution.

Studying drug–plasma protein interactions by two-injector microchip electrophoresis frontal analysis

We developed a simple, rapid, and sensitive two-injector microchip electrophoresis frontal analysis (MCE-FA) method for studying drug-plasma protein interactions. In this method, large volumes of a reference sample and drug-plasma protein mixture were simultaneously introduced into the respective sections of the microchannel through the separated injectors and then electrophoresed. Since the reference sample did not meet with the interacting species during migration, it could be used as an external standard. The interaction between heparin and HSA was quantitatively characterized as a model system. The binding constant was found to be (1.53 +/- 0.01) x 10(4) M(-1).

Bioanalytical interaction studies executed by preincubation affinity capillary electrophoresis

The versatility of CE is beneficial for the study of many types of molecular interactions, because different experimental designs can be made to suit the characteristics of a particular interaction. A very versatile starting point is the preequilibration type of affinity CE that has been used extensively for characterizing biomolecular interactions in the last 15 years. We review this field here and include a comprehensive overview of the existing preincubation ACE modes including their advantages and limitations as well as the methodological developments and applications within the bioanalytical field.