Capillary zone electrophoresis of synthetic opioid and tachykinin peptides

Alkaloids of the Lauraceae

This chapter presents an overview of the chemistry and pharmacology of the alkaloids found in species of the Lauraceae family. The occurrence of alkaloids from Lauraceae species as well as their chemical structures is summarized in informative and easy-to-understand tables. Within the Lauraceae family, the genera Ocotea (195), Litsea (180), Cryptocarya (133), and Neolitsea (110) have led to the greater number of publications regarding alkaloids content. Valuable and comprehensive information about the structure of these alkaloids is provided. The alkaloids of the aporphine type, found in 22 of the 23 genera, represent the predominant group in this family. Many of the isolated alkaloids exhibit unique structures. From plants of this family, 22 different types of skeletons have been isolated, among them only the purine alkaloids are classified as pseudoalkaloids, and the types phenethylamines, phenethylcinnamides, and phthalidoisoquinoline are classified as protoalkaloids. The chapter is presented as a contribution for the scientific community, mainly to enable the search for alkaloids in species belonging to the Lauraceae family.

Preparative capillary zone electrophoresis using a dynamic coated wide-bore capillary

Preparative capillary zone electrophoresis separations of cytochrome c from bovine and horse heart are performed efficiently in a surfactant-coated capillary. The surfactant, dimethylditetradecylammonium bromide (2C(14)DAB), effectively eliminated protein adsorption from the capillary surface, such that symmetrical peaks with efficiencies of 0.7 million plates/m were observed in 50-microm id capillaries when low concentrations of protein were injected. At protein concentrations greater than 1 g/L, electromigration dispersion became the dominant source of band broadening and the peak shape distorted to triangular fronting. Matching of the mobility of the buffer co-ion to that of the cytochrome c resulted in dramatic improvements in the efficiency and peak shape. Using 100 mM bis(2-hydroxyethyl)imino-tris(hydroxymethyl)methane phosphate buffer at pH 7.0 with a 100-microm id capillary, the maximum sample loading capacity in a single run was 160 pmol (2.0 microg) of each protein.

Modelling migration behavior of peptide hormones in capillary electrophoresis-electrospray mass spectrometry

The applicability in capillary electrophoresis-electrospray mass spectrometry (CE-ESI-MS) of the classical semiempirical relationships between electrophoretic mobility and charge-to-mass ratio (me versus q/Malpha) has been investigated in order to describe the migration behavior of a series of bioactive peptide hormones. The influence upon the models of the separation electrolyte pH and the accuracy of the pK values of these compounds were studied first by capillary electrophoresis with ultraviolet detection (CE-UV). The classical polymer model, alpha = 1/2, resulted in slightly better correlations at any of the studied pH. Furthermore, a general linear equation can be adjusted combining all the experimental data pairs, which suggests that correlation in the whole pH range is independent of the ionic form of the studied peptide hormones. The plots of q/M1/2 against separation electrolyte pH were used to predict their electrophoretic separations, using the accurate pK values obtained in a previous work by CE-UV for charge calculations. A volatile separation electrolyte containing 50 mM of acetic acid and 50 mM of formic acid at pH 2.85 was selected for optimum CE-UV and CE-ESI-MS analysis of the peptide mixture. At this pH and taking into account the specific features of the coupling, the correlation using the classical polymer law was excellent and its parameters were similar to the ones of the general linear equation previously obtained by CE-UV. This confirmed the applicability in CE-ESI-MS of the semiempirical relationship originally established by CE-UV.

Reversed-phase electrochromatography of amino acids and peptides using porous polymer monoliths

Efficient and rapid separation of minute levels of amino acids and bioactive peptides is of significant importance in the emerging field of proteomics as well as in the clinical and pharmaceutical arena. We have developed novel UV-initiated acrylate-based porous polymer monoliths as stationary phases for capillary- and chip-electrochromatography of cationic, anionic, and neutral amino acids and peptides, followed by absorbance or laser-induced fluorescence detection. The rigid monoliths are cast-to-shape and are tunable for charge and hydrophobicity. For separations at low pH, monoliths containing quaternary amine moieties were used to achieve high electroosmotic flow, and for high pH separations monoliths with acidic sulfonic acid groups were employed. Efficient and reproducible separations of phenylthiohydantoin-labeled amino acids, native peptides, and amino acids and peptides labeled with naphthalene-2,3-dicarboxaldehyde (NDA) were achieved using both negatively- and positively-charged polymer monoliths in capillaries. Separation efficiencies in the range of 65,000-371,000 plates/m were obtained with capillary electrochromatography. Buffer composition and the degree of column hydrophobicity were studied systematically to optimize separations. The monoliths were also cast in the microchannels of glass chips and electrochromatographic separation followed by laser-induced fluorescence detection of three NDA-labeled bioactive peptides was obtained.

Determination of bisbenzylisoquinoline alkaloids by high-performance liquid chromatography (II)

After the earlier analysis of nine bisbenzylisoquinoline alkaloids with ion pair chromatography, seven other bisbenzylisoquinoline alkaloids were analyzed using gradient elution with an acetonitrile-phosphate buffer (pH 8.0) mixture, and UV detection. Four alkaloids were detected in the stem woods of a Lauraceous plant, Dehaasia triandra Merr. and their contents determined. LC-MS suggested that a major unknown compound in the plant was also a bisbenzylisoquinoline alkaloid.

Mass spectrometric analysis of neuropeptidergic systems in the human pituitary and cerebrospinal fluid

Neuropeptidergic systems have been studied in human tissues and fluids, which include the pituitary and lumbar cerebrospinal fluid, respectively. This paper reviews the qualitative and quantitative mass spectrometric analytical data obtained from three areas of study. Methionine enkephalin (ME) and beta-endorphin (BE) were quantified in the human pituitary by liquid secondary ion mass spectrometry (LSI MS)-tandem mass spectrometry. Corresponding stable isotope-incorporated synthetic peptide internal standards were used. Proenkephalin A and proopiomelanocortin produce ME and BE, respectively. The analysis of neuropeptides in macroadenomas demonstrated a decrease in both of those neuropeptidergic systems relative to controls. An analysis of prolactin-secreting microadenomas showed an increase in the proenkephalin A system. Mass spectrometry was also used to detect opioid peptide-containing proteins in the pituitary. Enzymes that process the precursors of proenkephalin A and tachykinin (substance P) neuropeptides were studied in human lumbar cerebrospinal fluid. Electrospray ionization mass spectrometry was used to characterize the molecular mass of each peptide product.

Strategies for capillary electrophoresis: method development and validation for pharmaceutical and biological applications

This review is in support of the development of selective, reproducible and validated capillary electrophoretis (CE) methods. Focusing on pharmaceutical and biological applications, the successful use of CE is demonstrated by more than 800 references, mainly from 1994 until 1998. Approximately 80 recent reviews have been catalogued. These articles sum up the existing strategies for method development in CE, especially in the search for generally accepted concepts, but also looking for new, promising reagents and ideas. General strategies for method development were derived not only with regard to selectivity and efficiency, but also with regard to precision, short analysis time, limit of detection, sample pretreatment requirements and validation. Standard buffer recipes, surfactants used in micellar electrokinetic capillary chromatography (MEKC), chiral selectors, useful buffer additives, polymeric separation media, electroosmotic flow (EOF) modifiers, dynamic and permanent coatings, actions to deal with complex matrices and aspects of validation are collected in 20 tables. Detailed schemes for the development of MEKC methods and chiral separations, for optimizing separation efficiency, means of troubleshooting, and other important information for key decisions during method development are given in 19 diagrams. Method development for peptide and protein separations, possibilities to influence the EOF and how to stabilize it, as well as indirect detection are considered in special sections.

Generation of tryptic maps of alpha- and beta-globin chains by capillary electrophoresis in isoelectric buffers

A novel method for generating peptide maps, following tryptic digests of proteins, is reported here: capillary zone electrophoresis in the presence of isoelectric buffers as the sole buffering species. A typical buffer composition comprises 50 mM aspartic acid (pH = pI = 2.77), 0.5% hydroxyethyl cellulose (added as a dynamic coating agent for preventing peptide adsorption to weakly ionized silanols), 5% trifluoroethanol and 1% zwitterionic detergent (CHAPS). With this buffer composition, a high-voltage gradient can be applied (typically 600 V/cm in 75 microns I.D. and 900 V/cm in 50 microns I.D. capillaries), thus drastically reducing the analysis times. The method is applied to the generation of peptide maps of alpha- and beta-globin chains from human adult hemoglobin. In the case of beta-peptides, at an operative pH of 2.77, which represents a cross-over point in the titration curve of peptides T2 and T9, the two analytes merge into a single peak. However it is shown that it is possible to change the pH of the zwitterionic buffer by adjusting its concentration in solution. In 30 mM Asp (pH 3.0) or 20 mM Asp (pH 3.1) resolution of these two peptides is fully restored. Isoelectric, amphoteric buffers thus seem to represent a novel, powerful buffer system able to offer high resolution and high selectivity.

Micellar electrokinetic chromatographic study of the interaction between enkephalin peptide analogs and charged micelles

The relative hydrophobicity/hydrophilicity of the pentapeptides leucine enkephalin (LE), methionine enkephalin (ME) and five analogs, differing in their uncharged side chain and/or chirality, was investigated by micellar electrokinetic capillary chromatography (MEKC) employing anionic and cationic surfactants. The effect of sodium dodecyl sulfate (SDS) concentration on peptide mobility was studied at pH 8.8, a value that is well above the peptide isoelectric point, to minimize electrostatic interaction with the anionic micelles. Similarly, the effect of cetyltrimethylammonium bromide (CTAB) cationic micelles on peptide migration was studied at pH 4.1. The migration order from MEKC experiments was compared to the peptide hydrophobicity calculated from reversed-phase HPLC-derived hydrophobicity coefficients. Although relative peptide hydrophobicity was, in general, positively correlated with effective electrophoretic mobility, a tryptophan-containing analog showed only weak interaction with micelles compared to the less hydrophobic peptides. The enkephalins studied were zwitterionic in character from pH 3 to 8, and their migration as a function of pH under MEKC conditions demonstrated that electrostatic forces were at least as important as hydrophobic interactions in pentapeptide-micelle complexation.

Optimization of the capillary zone electrophoresis loading limit and resolution of proteins, using triethylamine, ammonium formate and acidic pH

Capillary zone electrophoresis (CZE) of five model proteins (lysozyme, myoglobin, ribonuclease A, alpha-lactalbumin, and trypsinogen), using ammonium formate as the electrophoretic buffer and triethylamine (TEA) as a buffer additive at pH 2.5, was used for protein separation. The electrophoretic behavior of these proteins was examined with respect to various concentrations (10-40 mM) of TEA and of ammonium formate. Based on the experimental parameters of electrophoretic resolution, current, and peak separation time, an electrolyte (30 mM each of TEA and ammonium formate) was empirically derived as the optimum for scale-up separation. The loading limit for proteins, covering a wide range of injection volumes (60-990 nl) and amount of protein (1-21 pmol of each protein), was investigated on 75 and 100 microns I.D. untreated fused-silica capillaries. Protein adsorption (average < 15%) was experimentally determined using this volatile buffer system.

Measurement of bioactive neuropeptides using a chromatographic immunosensor cartridge

Neuropeptide modulation of host defenses is associated with a number of clinical conditions in which tissue injury is caused by a process termed neurogenic inflammation. Monitoring of neuropeptide activity during both disease episodes and therapy has proven difficult due to a lack of correlation between laboratory evaluations and disease activity. Although a number of assays are available for measuring the total neuropeptide content of tissue samples, few can measure the bioactive component which is the more physiologically accurate parameter. In an attempt to overcome this problem, a receptor-affinity chromatographic technique coupled with immunological detection has been developed for measuring three bioactive neuropeptides (substance P, vasoactive intestinal peptide, and calcitonin gene-related peptide) in tissue biopsy extracts. The technique involves isolation of the active neuropeptides via their ability to bind to immobilized receptors followed by measurement of the bound materials by a series of simultaneous immunoassays. The techniques compares favourably with results obtained using conventional bioassays and has the added advantage that multiple analytes can be measured in a single procedure.

Complete capillary electrophoretic separation of substance P and its metabolites at neutral pH using ionic run buffer additives

Substance P (SP), a bioactive peptide that is present in the extracellular fluid of the brain at picomolar concentrations, has been proposed to be a neurotransmitter and a neuromodulator in the central and peripheral nervous systems. This paper describes the development of analytical methodology for the separation of SP and its metabolites by capillary electrophoresis at neutral pH. Since SP is a cationic peptide, it tends to adsorb to silica surfaces. In this work, phytic acid was employed as a run buffer additive to eliminate the interaction of SP and its cationic N-terminus metabolites with ionized silanol groups. The separation of the C-terminus metabolites was then accomplished through the use of sulfobutyl ether beta-cyclodextrin, which imparted a negative charge to these otherwise neutral metabolites through complexation of the phenylalanine residue. The final separation buffer consisted of 150 mM boric acid, 15 mM phytic acid and 5 mM SBE(IV)beta-cyclodextrin at pH 7. Under these conditions, it was possible to separate SP from all eight of its reported metabolites.

Preparative capillary zone electrophoresis of synthetic peptides conversion of an autosampler into a fraction collector

Preparative capillary zone electrophoresis of three synthetic peptides was performed either manually or automatically by simple manipulations of a commercial electropherograph that is equipped only with an autosampler without any built-in fraction collection capability. Manual fraction collection was achieved by replacing the outlet (cathode) beaker with a microcentrifuge tube, and automatic fraction collection was accomplished by converting the electropherograph's autosampler into a fraction collector. The latter was easily achieved mainly by the use of an extension wire, which completed the electrical circuit and facilitated fraction collection either at a specified time or within fixed time intervals.

Capillary zone electrophoresis of two synthetic neuropeptides: examination of detectability and resolution as a function of peptide concentration and buffer concentration

The capillary zone electrophoretic behavior of substance P and methionine enkephalin, when the amount of peptide was increased at a constant injection volume, was examined using a 50-microns I.D. capillary. Peak-shape distortion (asymmetry) increased when the concentration of these two peptides exceeded 1% of the buffer concentration. Increasing the buffer concentration increased the peak height and decreased the peak width, leading to higher detectability and resolution, respectively. Peak area versus analyte concentration remained linear, even under the overloading conditions that distorted the peak shape.