Modeling the electrophoretic behavior of quinolones in aqueous and hydroorganic media

Development of a background electrolyte for the determination of inorganic cations in high ionic strength samples by capillary electrophoresis with indirect UV-absorption detection

In this study, a background electrolyte capable to separate and quantify inorganic cations in high ionic strength samples by UV-absorption indirect detection was designed. In this regard, the four most abundant monovalent and divalent cations in earth crust (K⁺, Na⁺, Ca⁺², Mg⁺²) were selected as model compounds. A group of small carboxylic acids and, several toluidines and pyridines were evaluated as mild strength complexing agents and chromophoric probes, respectively. The optimized background electrolyte was composed of 200 mM 2,4,6-trimethylpyridine as the chromophoric probe, 250 mM lactic acid as the weak complexing agent and pH buffering reagent (adjusted to pH 4.5), and 5% v/v methanol as organic solvent modifier. Based on a minimum number of components, it provided outstanding separation performance in less than 4 min in a wide linear dynamic range (10 - 2500 µg·mL^-1). Performances were contrasted against a reference method based on conductometric detection. Furthermore, studies of separation efficiency and peak shape were carried out at different analyte concentrations in high electric conductivity solutions. The herein developed method demonstrated exceptional features in terms of limits of detection (~10 µg·mL^-1), resolution, speed of analysis, sensitivity and peak capacity in high electric conductivity samples. Moreover, the method was successfully applied to high ionic strength samples such as rock digest, sea water, soy sauce and isotonic drinks.

Modelling the electrophoretic migration behaviour of peptides and glycopeptides from glycoprotein digests in capillary electrophoresis-mass spectrometry

In this study, the classical semiempirical relationships between the electrophoretic mobility and the charge-to-mass ratio (me vs. q/M(α)) were used to model the migration behaviour of peptides and glycopeptides originated from the digestion of recombinant human erythropoietin (rhEPO), a biologically and therapeutically relevant glycoprotein. The Stoke's law (α=1/3), the classical polymer model (α=1/2) and the Offord's surface law (α=2/3) were evaluated to predict migration of peptides and glycopeptides, with and without sialic acids (SiA), in rhEPO digested with trypsin and trypsin-neuraminidase. The Stoke's law resulted in better correlations for the set of peptides used to evaluate the models, while glycopeptides fitted better with the classical polymer model. Once predicted migration times with both models, it was easy to simulate their separation electropherogram. Results were later validated predicting migration and simulating separation of a different set of rhEPO glycopeptides and also human transferrin (Tf) peptides and glycopeptides. The excellent agreement between the experimental and the simulated electropherograms with rhEPO and Tf digests confirmed the potential applicability of this simple strategy to predict, in general, the peptide-glycopeptide electrophoretic map of any digested glycoprotein.

Identification of bioactive peptides in hypoallergenic infant milk formulas by CE-TOF-MS assisted by semiempirical model of electromigration behavior

Biologically active peptides derived from complex bovine milk protein hydrolysates are of particular interest in food science and nutrition because they have been shown to play different physiological roles, providing benefits in human health. In this study, we used CE-TOF-MS for separation and identification of bioactive peptides in three hypoallergenic infant milk formulas. An appropriate sample cleanup using a citrate buffer with DTT and urea followed by SPE with Sep-Pack® C18 and StrataX™ cartridges allowed the detection of a large number of low molecular mass bioactive peptides. This preliminary identification was solely based on the measured experimental monoisotopic molecular mass values (M(exp)). Later, we evaluated the classical semiempirical relationships between electrophoretic mobility and charge-to-mass ratio (m(e) vs. q/M(α), α = 1/2 for the classical polymer model) to describe their migration behavior. The assistance of migration prediction proved to be useful to improve reliability of the identification, avoiding misinterpretations and solving some identity conflicts. After revision, the identity of 24, 30, and 38 bioactive peptides was confirmed in each of the three infant milk formulas. A significant number of these peptides were reported as inhibitors of angiotensin-converting enzyme, however, the presence of sequences with other biological activities such as antihypertensive, antithrombotic, hypocholesterolemic, immunomodulation, cytotoxicity, antioxidant, antimicrobial, antigenic, or opioid was also confirmed.

Determination of acidity constants and ionic mobilities of polyprotic peptide hormones by CZE

CZE has been applied to determination of thermodynamic acidity constants (pKa ) of ionogenic groups and actual ionic mobilities of polyprotic peptides-synthetic human and salmon gonadotropin-releasing hormones and their derivatives and fragments. First, the mixed acidity constants, pKa,imix, of ionogenic groups, and actual ionic mobilities, mi , of gonadotropin-releasing hormone peptides were determined by nonlinear regression analysis of pH dependence of their effective electrophoretic mobilities. The effective mobilities were measured by CZE in a series of BGEs within a broad pH range (1.80-12.10), at constant ionic strength (25 mM) and reference temperature (25°C). Second, the pKa,imix values were recalculated to thermodynamic pKa s using the Debye-Hückel theory. Thermodynamic pKa of carboxyl groups was estimated to be in the range of 2.5-3.3 for C-terminal amino acids of the above peptides, and 5.2 for glutamic acid in the middle of peptide chain; pKa of imidazolyl group of histidine residues was in the range of 5.7-6.8, pKa of N-terminal amino group of the peptide with free N-terminus was equal to 6.2, pKa of phenol group of tyrosine residues was in the range of 9.8-10.8, and pKa of guanidinyl group or arginine residues reached values 11.1-11.3, depending on the position of the residues in the peptide and on the amino acid sequence of the peptide. Absolute values of actual ionic mobilities of peptides with charge number ±2 were in the range (14.6-18.6) × 10(-9) m(2) V(-1) s(-1) , and ionic mobilities of peptides with charge number ±1 reached values (6.5-12.9) × 10(-9) m(2) V(-1) s(-1) .