Medium-throughput pKa screening of pharmaceuticals by pressure-assisted capillary electrophoresis

Abstract

A fast screening method for the determination of the dissociation constants (pKa) of acidic, basic, and multivalent compounds was developed by using pressure-assisted capillary electrophoresis (PACE). External air pressure was applied to shorten the analysis time. The separation efficiency decreases as air pressure increases. However, it was found that air pressure does not affect the measurement of electrophoretic mobility and pKa significantly when it is less than 2 psi. The method was evaluated in terms of accuracy, precision, and ruggedness by using a set of 48 compounds with literature pKa values ranging from 2 to 10. The difference between the measured pKa values and literature values is less than 0.2 units. The throughput is approximately 20 compounds per day with a 12-point measurement ranging from pH 2.5 to 11. It was demonstrated that this method is applicable for pKa screening of pharmaceuticals with diverse chemical structures.

Determination of dissociation constants of folic acid, methotrexate, and other photolabile pteridines by pressure-assisted capillary electrophoresis

“…CZE was introduced as a tool for characterization of acid-base chemistry in 1991 [19]. Since then, over 60 papers have been published in this field [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] and the developments have recently been reviewed [25]. The determination of ionization constants by CE relies on registration of effective electrophoretic mobility (m eff ) in a series of BGE solutions with varying pH and constant ionic strength (I = Sz 2 i c i for all ions).…”

“…Early attempts to circumvent this problem used dynamic coating of the capillary inner wall with charged polymers [22], but this strategy proved to be unsuitable for routine pK a assessment of compounds of diverse charge type [25]. Significant progress has recently been achieved by pressure-assisted CE (PACE), in which a small, constant pressure (20-50 mbar) is applied simultaneously with the electrophoresis voltage to create a rapid bulk-flow at all pH values, extending thus the range of accessible pK a values [25][26][27][28][29][30][31][32][33]. This accelerates all pK a determinations of one analyte significantly, resulting in improved sample-throughputs up to 20 molecules/h by CE-iontrap-MS [31] or capillary-array electrophoresis [32].…”

“…(2) is independent of the ionic strength, the underlying standard state (y i = 1 for each species) being the hypothetical case of infinitely dilute solution. Since typically low ionic strengths are applied in electromigration methods, CE [20,24] and PACE [26,27,29,34] studies are devoted to determine pK th values. However, biological or environmental fluids are solutions of nonzero ionic strengths.…”

“…3). Previously, repeatabilities of 2-3% RSD were reported for PACE [27,30], and also when short-end injection was used [29].…”

Two star‐shaped tetranuclear Ru(II) complexes containing uncoordinated imidazole groups: synthesis, characterization, photophysical and pH sensing properties

“…5a), the MLCT band at 460 nm, the ligand H 4 L 1 centered intraligand π→π* transition band at 318 nm, and the 2,2′-bipyridine centered intraligand π→π* transition band at 285 nm are slightly decreasing in their intensities with one isosbestic point at 345 nm appearing. Several methods can be used to determine the pK a values (37)(38)(39)(40), for this work, the spectrophotometric method already reported in the literature for the analogous Ru(II) polypyridyl complexes was chosen (41). A plot of absorbance at 236 nm versus pH for complex [{Ru(bpy) 2 } 4 (μ 4 -H 4 L 1 )] 8+ is given in the inset of Fig.…”