Universal method for determining electrolyte temperatures in capillary electrophoresis

Vanadium(IV) and vanadium(V) complexation by succinic acid studied by affinity capillary electrophoresis. Simultaneous injection of two analytes in equilibrium studies

The interaction of V(IV) and V(V) with succinic acid was investigated by affinity capillary electrophoresis (ACE) in aqueous acid solutions at pH values 1.5, 2.0 and 2.4, and different ligand concentrations. V(IV) and V(V) form protonated complexes with succinic acid ligand at this pH range. The logarithms of the stability constants, measured at 0.1 mol L^-1 (NaClO₄/HClO₄) ionic strength and 25 °C, are logβ₁₁₁=7.4 ± 0.2 and logβ₁₂₂=14.1 ± 0.5 for V(IV), and logβ₁₁₁=7.3 ± 0.1 for V(V), respectively. The stability constant values, extrapolated to zero ionic strength with the Davies equation, are logβ°₁₁₁=8.3 ± 0.2 and logβ°₁₂₂=15.6 ± 0.5 for V(IV) and logβ°₁₁₁=7.9 ± 0.1 for V(V). The application of ACE to the simultaneous equilibria of V(IV) and V(V) (injection of two analytes) was also attempted. When the results were compared with those obtained when introducing only one analyte in the capillary, using the traditional version of the method, similar stability constants and precision are obtained. The possibility of studying two analytes simultaneously decreases the time needed for the determination of the constants; this feature is especially valuable when working with hazardous materials or when only small quantities of ligand are available.

Moment theory for the analytical determination of rate constants for solute permeation at the interface of spherical molecular aggregates

Moment equations were developed on the basis of the Einstein equation for diffusion and the random walk model to analytically determine the rate constant for the interfacial solute permeation from a bulk solvent into molecular aggregates (k_in ) and the inverse rate constant from the molecular aggregates to the bulk solvent (k_out ). The moment equations were in good agreement with those derived in a different manner. To demonstrate their effectiveness in one concrete example, the moment equations were used to analytically determine the values of k_in and k_out of three electrically neutral solutes, i.e. resorcinol, phenol, and nitrobenzene, from the first absolute (μ_1A ) and second central (μ_2C ) moments of their elution peaks, as measured by electrokinetic chromatography (EKC), in which the sodium dodecyl sulfate (SDS) micelles were used as a pseudostationary phase. The values of k_in and k_out should be determined with no chemical modifications and no physical action with the molecular aggregates because they are dynamic systems formed through weak interactions between the components. The moment analysis of the elution peak profiles measured by EKC is effective to unambiguously determine k_in , k_out , and the partition equilibrium constant (k_in /k_out ) under appropriate experimental conditions.

Heat dissipation in slab gel electrophoresis: The effect of embedded TiO2 nanoparticles on the thermal profiles

Despite the fast development of novel and high-resolution electrophoresis techniques such as capillary-based methods and microfluidic devices, the slab gel electrophoresis is still a popular method for the separation of biomolecules in medicine and biology. It is a low cost and simple method and offers high throughput. However, this technique is limited to low voltages leading to slow separations. Producing the heat during the electrophoresis known as Joule heating inevitably leads to a rise in the gel temperature. For the first time, this work offers a whole gel temperature measurement by using a thermal camera which presents accurate temperature profiles in the gel with a resolution of more than 10 pixel/mm² and a precision of 0.1 °C. Titania, TiO₂, nanoparticles (NPs) were embedded into the polyacrylamide (PA) gel to improve the electrophoretic separation of proteins. By embedding 0.025% w/v TiO₂ NPs, heat dissipation increases by 16.5% at applied voltage of 200 V compared with that of PA gel with no embedded TiO₂ NPs. The thermal images showed that the composite gel was 2.5 °C in average cooler than PA gel after 15 min of electrophoresis run at 200 V. The maximum separation voltage increased by 30 V in the composite PA/TiO₂ gel compared with the pure PA gel. Moreover, the average number of theoretical plates over the 10 protein peaks, as a criterion of separation performance, increased by about 63% at 180 V when TiO₂ NPs were included into the gel.

Ideal-filter capillary electrophoresis: A highly efficient partitioning method for selection of protein binders from oligonucleotide libraries

Selection of affinity ligands for protein targets from oligonucleotide libraries currently involves multiple rounds of alternating steps of partitioning of protein-bound oligonucleotides (binders) from protein-unbound oligonucleotides (nonbinders). We have recently introduced ideal-filter capillary electrophoresis (IFCE) for binder selection in a single step of partitioning. In IFCE, protein-binder complexes and nonbinders move inside the capillary in the opposite directions, and the efficiency of their partitioning reaches 10⁹ , i.e., only one of a billion molecules of nonbinders leaks through IFCE while all binders pass through. The condition of IFCE can be satisfied when the magnitude of the mobility of EOF is smaller than that of the protein-binder complexes and larger than that of nonbinders. The efficiency of partitioning in IFCE is 10 million times higher than those of solid-phase-based methods of partitioning typically used in selection of affinity ligands for protein targets from oligonucleotide libraries. Here, we provide additional details on our justification for IFCE development. We elaborate on electrophoretic aspects of the method and define the theoretical range of EOF mobilities that support IFCE. Based on these theoretical results, we identify an experimental range of background electrolyte's ionic strength that supports IFCE. We also extend our interpretation of the results and discuss in-depth IFCE's prospective in practical applications and fundamental studies.

Complexation of An(vi) with succinic acid in aqueous acid solutions: uranyl vs. plutonyl

Due to stronger electrostatic interaction in a uranyl–succinate system, complex species of U(vi) with succinate are more stable than the ones of Pu(vi).

Enhancing effectiveness of capillary electrophoresis as an analytical tool in the supramolecular acidity modification

A strategic modification of acidity (pK_a values) by the non-covalent host-guest interactions is one of the most promising concepts in current supramolecular chemistry. This work is aimed at enhancing the effectiveness of capillary electrophoresis (CE) in determination of pK_a shifts caused by such interactions and their thermal dependencies crucial in a deep thermodynamic description. We show how to (i) minimize the systematic errors related to Joule heating, (ii) minimize the influence of a voltage ramp time, (iii) speed up pK_a shift identification and estimation, (iv) interpret thermal effects related to two overlapped dynamic equilibria, and (v) determine pK_a shifts by an alternative spectrophotometric method (CE-DAD). The proposed solutions were implemented to examine the supramolecular pK_a shifts of several coumarin derivatives, caused by a variety of structurally different cyclodextrins. It was revealed that a specific host substitution pattern determines the magnitude of apparent pK_a shifts. Accordingly, heptakis(2,6-di-O-methyl)-β-cyclodextrin induces the much stronger shifts than both non-methylated-β-cyclodextrin and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin applied at the same concentration. We also show that insofar as the complexation of 4-hydroxycoumarin and its derivative (coumatetralyl) are similarly exothermic, the thermal effects accompanying the deprotonation process are remarkably different for both molecules. The pK_a shift induced by complexation with calixarene was also for the first time determined by a CE method. These observations throw a new light on the background of acidity modification and confirm the applicability of CE as an analytical tool.

Seven Approaches to Elimination of the Inherent Systematic Errors in Determination of Electrophoretic Mobility by Capillary Electrophoresis

Electrophoretic mobility is a basic parameter that describes the electromigration of an ionized particle, which is used in many fields of analytical and physicochemical science. Its determination by capillary electrophoresis (CE), using a routine method, is intrinsically affected by the generation of Joule heating, entailing a drop in viscosity and possible alteration of the degree of ionization, and also by other commonly overlooked effects: axial electric field distortion and voltage ramping. The objective of this work was to provide the first theoretical overview and experimental comparison of all accessible methods that could be used to prevent these sources of inaccuracy. We have discussed seven independent approaches: (i) extrapolation of mobility to the zero power, (ii) initial buffer resistance-based correction, (iii) rational cooling adjustment, (iv) elimination of the nonthermostated capillary part, (v) inter/extrapolation to the nominal temperature, (vi) internal standard-based correction, and (vii) simple recalculation based on the temperature rise. Two methodologies (v and vi) have been proposed for the first time. Furthermore, we have shown how some approaches can be further developed, obtaining several novel and more sophisticated methods, which are also included in the comparison. Our investigation will help researchers to choose the optimal approach. We have also demonstrated for the first time how to measure the independent impact of four different effects. The outcomes reveal the compensatory character of some phenomena and explain the highly diverse and unpredictable magnitude of the total errors. The use of a correction method seems crucial for ensuring the high reliability of CE-based analyses.

Analysis of DNA in Phosphate Buffered Saline Using Kinetic Capillary Electrophoresis

Kinetic capillary electrophoresis (KCE) methods are useful in the study of kinetics and equilibrium properties of interactions between DNA and its binding partners (ligands). KCE experiments are typically performed in a narrow set of "conventional" low-conductivity run buffers while DNA-ligand interactions in biological systems occur in physiological fluids, characterized by high ionic strengths. The nature and ionic strength of the buffer, in which DNA-ligand interaction occurs, can significantly influence the binding. Therefore, KCE experiments meant to study such interactions would greatly benefit if they could be performed in physiological buffers, such as phosphate buffered saline (PBS). No previous KCE studies of DNA used PBS as the run buffer. Here, we test the feasibility of using PBS as a KCE run buffer for analysis of DNA and show that its usage under standard KCE conditions renders DNA undetectable. We uncover the causes of this previously unreported detrimental effect and come up with a modification of KCE which allows one to overcome it. We apply the modified KCE method to an experimental model of a platelet-derived growth factor (PDGF) protein and its DNA aptamer, which was selected in PBS, and show that the results obtained in PBS run buffer are much closer to previously reported values than those which were obtained with a conventional low-conductivity capillary electrophoresis (CE) buffer.

Study of deoxyribonucleic acid-ligand interactions by partial filling affinity capillary electrophoresis

In this work, a new partial filling affinity capillary electrophoresis (PF-ACE) method has been developed and applied to investigation of non-covalent molecular interactions between double stranded DNA oligonucleotide (Dickerson dodecamer) and classical DNA intercalator ligand-ethidiumbromide (EtBr) or oligophenylene derivatives-based potential new type of DNA ligands. Binding constants of DNA-ligand complexes were determined from the dependence of migration time changes of DNA oligomer (applied as analyte) on the length of ligand zones introduced beforehand as plugs of various lengths (0-75mm with 12.5mm step) in hydroxypropylcellulose coated fused silica capillary of 50/375μm I.D./O.D. and 400/300mm total/effective length. PF-ACE experiments were performed in two background electrolytes, Tris-borate, pH 8.0, ionic strength 14.3mM (BGE1), and sodium phosphate, pH 7.5, ionic strength 133mM (BGE2). Binding constants of DNA-EtBr complex (ca 15300L/mol in the BGE1 and 4200L/mol in the BGE2) were found to be significantly higher than those of DNA complexes with oligophenylene derivatives (ca 2200-3600L/mol in the BGE1 and 1600-2300L/mol in the BGE2).

Electrophoresis of a charge-regulated zwitterionic particle: influence of temperature and bulk salt concentration

The influence of temperature on the electrophoretic behavior of a charge-regulated zwitterionic particle is investigated by considering a spherical SiO(2) particle in a relatively dilute aqueous NaCl solution of concentration C(NaCl) with its pH adjusted by NaOH and HCl as an example. A complete mobility-pH-temperature plot and a mobility-C(NaCl)-temperature plot are prepared for pH, C(NaCl), and temperature ranging from 3 to 9.5, 10(-4) to 10(-2) M, and 293 to 308 K, respectively, for the first time, and empirical correlation relationships are developed. These provide necessary information for both interpreting experimental data and designing electrophoresis devices, where the variation in the temperature can be a factor. In general, the absolute value of the particle mobility increases with T, and that value has a local maximum as pH varies.

Slow-dissociation and slow-recombination assumptions in nonequilibrium capillary electrophoresis of equilibrium mixtures

Nonequilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) is a kinetic affinity method with both analytical and preparative applications. NECEEM requires that the dissociation of the complexes be negligible in its first phase and the recombination of the dissociated complexes be negligible in its second phase. Here, we introduce a method, which facilitates easy examination of whether or not these requirements are satisfied. We derived expressions for two parameters, termed the slow-dissociation parameter (SDP) and slow-recombination parameter (SRP), which can be used to assess the assumptions. Both parameters should be much less than 1 for the assumptions to be satisfied. We calculated the two parameters for new and previously published NECEEM experiments and found that the assumptions were satisfied in all of them. Finally, we discuss changes to NECEEM conditions that should be done if the assumptions are found not to be satisfied. The SDP/SRP assessment helps to easily validate the results of NECEEM-based analyses and thus makes the NECEEM method more robust.