Determination of binding constants by affinity capillary electrophoresis, electrospray ionization mass spectrometry and phase-distribution methods

doi:10.1016/j.trac.2008.06.008

TrAC Trends in Analytical Chemistry

Volume 27, Issue 9, October 2008, Pages 738-748

https://doi.org/10.1016/j.trac.2008.06.008 Get rights and content

Abstract

Many methods for determining intermolecular interactions have been described in the literature in the past several decades. Chief among them are methods based on spectroscopic changes, particularly those based on absorption or nuclear magnetic resonance (NMR) [especially proton NMR (¹H NMR)]. Recently, there have been put forward several new methods that are particularly adaptable, use very small quantities of material, and that do not place severe requirements on the spectroscopic properties of the binding partners. This review covers new developments in affinity capillary electrophoresis, electrospray ionization mass spectrometry (ESI-MS) and phase-transfer methods.

Introduction

Non-covalent intermolecular associations are omnipresent in chemical and biochemical systems. Cyclodextrin-drug inclusion, and protein-drug, peptide-peptide, carbohydrate-drug and antigen-antibody binding are a few examples. Binding constants provide a fundamental measure of the affinity of a solute to a ligand; hence the determination of binding constants has been an important step in describing and understanding molecular interactions.

Many techniques have been developed to measure binding constants. They can be categorized into two groups: separation-based and non-separation-based methods [1].

Separation-based methods physically separate the free solute and the bound solute and evaluate their concentrations. Depending on how the separation is achieved, they can be further classified as heterogeneous or homogeneous. Chromatography [2], dialysis [3], ultrafiltration [4], surface-plasmon resonance (SPR) [5] are heterogeneous methods. The free solute is separated from the bound one on the surface of a solid substrate. Affinity capillary electrophoresis (ACE) [6], [7], [8], [9] and electrospray ionization mass spectrometry (ESI-MS) [10] are homogeneous methods. The separation occurs either in solution or in the gas phase.

Non-separation-based methods monitor the change in specific physicochemical properties of the solute or ligand upon complexation. This category includes: spectroscopy (e.g., ultraviolet-visible (UV-Vis) [11], [12], [13], infrared (IR) [14], fluorescence [13], [14], and nuclear magnetic resonance (NMR) [15]); electrochemical methods (e.g., conductimetry [15], potentiometry [16], and polarography [17]); phase-solubility [18] and hydrolysis kinetics [19], [20].

Connors [21] thoroughly reviewed many of the above methods 20 years ago, hence this selective review will emphasize ACE, ESI-MS, and phase-distribution methods recently.

Section snippets

Affinity capillary electrophoresis

ACE refers to the separation by CE of substances that participate in specific or non-specific affinity interactions during CE [22]. In the past two decades, ACE has been one of the most rapidly growing analytical techniques for studying a variety of non-covalent interactions and determining binding constants and stoichiometries.

There have been specialized and general reviews of ACE [6], [9], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38],

Electrospray ionization mass spectrometry

ESI-MS provides a soft ionization procedure that allows the transfer of weakly-bound complexes from solution to the gas phase for mass analysis, so it has frequently been used to study the binding behavior of a wide variety of non-covalent complexes [82], [83], [84]. Specificity, sensitivity, and speed are advantages of ESI-MS [85]. Moreover, ESI-MS can provide stoichiometric information of the complex directly and detect multiple components simultaneously.

Since one of the earliest reviews that

Phase-distribution methods

Phase-distribution methods monitor the dependence of the solute-distribution coefficient between two phases on the ligand concentration in one phase to determine the solute-ligand binding constant. Usually, one of the phases is aqueous and the other is organic. The binding equilibrium can be studied in either phase. This method has been applied to measure binding constants for the complex formation of caffeine/benzoic acid [18], solute/cyclodextrin [2], [96], [97], [98], [99], [100], [101],

Conclusions

Some general conclusions are warranted. All the methods described have the advantage of using very little material. The phase-distribution method, especially in its high-throughput form, is advantageous in many regards. Of the three methods described above, it is the least dependent on models for deriving information from data. The analytical method used for quantitation is not defined by the approach – any suitable method can be used. Under many circumstances, all three methods can function

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A potential problem with the use of a protein in the entire buffer is that this may generate a large background signal at the detector [56,57,62–64]. The partial filling technique can overcome this disadvantage by creating conditions in which the protein solution is not present as the analyte enters the detection window; however, this approach can also be more complex to perform and optimize than the use of a protein solution throughout the CE system [56,57,62,63]. Both AGP and albumins have been used in homogeneous methods for binding studies and chiral separations in ACE [64–67].
Affinity capillary electrophoresis (ACE) is a separation technique that combines a biologically-related binding agent with the separating power and efficiency of capillary electrophoresis. This review will examine several classes of binding agents that have been used in ACE and applications that have been described for the resulting methods in clinical or pharmaceutical analysis. Binding agents that will be considered are antibodies, aptamers, lectins, serum proteins, carbohydrates, and enzymes. This review will also describe the various formats in which each type of binding agent has been used in CE, including both homogeneous and heterogeneous methods. Specific areas of applications that will be considered are CE-based immunoassays, glycoprotein/glycan separations, chiral separations, and biointeraction studies. The general principles and formats of ACE for each of these applications will be examined, along with the potential advantages or limitations of these methods.
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Determination of binding constants by affinity capillary electrophoresis, electrospray ionization mass spectrometry and phase-distribution methods

Abstract

Introduction

Section snippets

Affinity capillary electrophoresis

Electrospray ionization mass spectrometry

Phase-distribution methods

Conclusions

Anal. Chim. Acta

J. Pharm. Sci.

J. Chromatogr., A

Eur. J. Pharm. Sci.

J. Pharm. Biomed. Anal.

Biorg. Med. Chem.

J. Pharm. Biomed. Anal.

J. Am. Pharm. Assoc. (1912-1977)

Int. J. Pharm.

J. Chromatogr., A

J. Chromatogr., A

Anal. Biochem.

J. Chromatogr., B

J. Chromatogr., A

J. Chromatogr., B

Curr. Opin. Biotechnol.

J. Chromatogr., A.

J. Chromatogr., B.

J. Chromatogr., A.

J. Chromatogr., A

J. Chromatogr., A

J. Chromatogr., B

J. Chromatogr.

Anal. Biochem.

Anal Biochem

Int. J. Mass Spectrom.

Int. J. Mass Spectrom.

Int. J. Mass Spectrom.

J. Am. Soc. Mass. Spectrom.

J. Am. Soc. Mass. Spectrom.

J. Colloid Interface Sci.

J. Colloid Interface Sci.

Anal. Chim. Acta

Ligand-Receptor Energetics: A Guide for the Perplexed

Chem. Pharm. Bull.

J. Chem. Eng. Jpn.

Anal. Biochem.

Electrophoresis

Electrophoresis

J. Am. Chem. Soc.

J. Incl. Phenom. Macrocycl. Chem.

Chirality

J. Chin. Chem. Soc.

Pharm. Sci.

Binding Constants

J. Mol. Recogn.

Electrophoresis

Electrophoresis

J. Chin. Chem. Soc.

Electrophoresis