Implementation of chemometric methodology in ACE: Predictive investigation of protein–ligand binding

Optimization of capillary electrophoresis conditions for a glucagon competitive immunoassay using response surface methodology

The capillary electrophoresis (CE) conditions for a competitive immunoassay of glucagon were optimized for highest sensitivity of the immunoassay and resolution of the electrophoretic peaks using a Box-Behnken design. Injection time, voltage ramp time, and separation voltage were varied between three levels and two responses, bound-to-free (B/F) ratio of the immunoassay peaks and resolution between the peaks, were measured. Analysis of variance was applied to fit a predictive model, and a desirability function was used to simultaneously optimize both responses. A 10-s injection, 1.6-min ramp time, and a 22-kV separation voltage were the conditions found when high B/F was given more emphasis than high resolution. To test the model, calibration curves of a glucagon immunoassay were measured at the optimum and least optimum CE conditions. Optimal conditions increased the sensitivity of the immunoassay by 388% compared to the least optimum conditions while maintaining adequate resolution.

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

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 ((1)H NMR)]. Recently, there have been put forward several new methods that are particularly adaptable, use very small quantities of material, and 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 phasetransfer methods.

Chemometrical examination of active parameters and interactions in flow injection-capillary electrophoresis

The first detailed examination of flow injection-capillary electrophoresis (FI-CE) active parameters and their interactions via response surface methodology (RSM) is presented. Specifically, RSM in the form of a Box-Behnken design was implemented to effectively predict the significance of capillary length, voltage and injection volume on the optimization of an in-house built FI-CE analyzer. Initial studies were performed assessing peak height and peak shape of the model compound N,N-dimethylformamide. Optimum model conditions were then derived and used in the model separation of two small molecules, nicotinamide adenine dinucleotide, reduced form (NADH) and benzenesulfonamide. By implementing the RSM approach, detailed examination of active FI-CE parameters was possible, including the ability to reveal a significant interactive effect. This work is not only highly significant for advancing FI-CE developments, but instructive for investigators actively exploring other coupled analytical techniques and associated experimental parameters.

Affinity capillary electrophoretic DNA separation using PEG-oligodeoxyribonucleotide block copolymers: relationship between peak resolution and affinity strength

Capillary electrophoretic separation of chemically synthesized ssDNA and a single-base-substituted one (normal and mutant ssDNA, respectively) was demonstrated using a PEG-oligodeoxyribonucleotide block copolymer (PEG-b-ODN) as an affinity ligand. When the base sequence of PEG-b-ODN was designed to be complementary to part of normal ssDNA including the base-substituted site, the electrophoretic mobility of normal ssDNA significantly decreased whereas that of mutant ssDNA slightly changed. Resolution of the separation strongly depended on the ODN length of the copolymer, the capillary temperature, and the Mg2+ concentration in the running buffer, indicating that the retardation of migration of normal ssDNA was induced by the reversible hybridization with PEG-b-ODN. It was found that the dissociation constant (K(d)) of the duplex between normal ssDNA and the affinity probe ODN should be smaller than 10(-6) M to achieve the good peak separation. In addition, we calculated the mobility of the complex (mu(C)) between normal ssDNA and PEG-b-ODN using a two-state model. The base sequence of affinity probe ODN appropriate to achieve the sufficient resolution will be predicted on the basis of the mu(C) and K(d )values.

Response surface examination of the relationship between experimental conditions and product distribution in electrophoretically mediated microanalysis

This work presents the first known use of response surface methodology (RSM) in electrophoretically mediated microanalysis. This concept is demonstrated by examining the optimization of reaction conditions for the conversion of nicotinamide adenine dinucleotide to nicotinamide adenine dinucleotide, reduced form by glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) in the conversion of glucose-6-phosphate to 6-phosphogluconate. Experimental factors including voltage, enzyme concentration, and mixing time of reaction at the applied voltage were selected at three levels and tested in a Box-Behnken response surface design. Upon migration in a capillary under CE conditions, plugs of substrate and enzyme are injected separately in buffer and allowed to react at variable conditions. Extent of reaction and product ratios were subsequently determined by CE. The model predicted results are shown to be in good agreement (7.1% discrepancy difference) with experimental data. The use of chemometric RSM provides a direct relationship between electrophoretic conditions and product distribution of microscale reactions using CE, thereby offering a new and versatile approach to optimizing enzymatic experimental conditions.