Differential partitioning of tRNAs between micellar and aqueous phases: a convenient gel filtration method for separation of tRNAs

Mechanism of signal suppression by anionic surfactants in capillary electrophoresis-electrospray ionization mass spectrometry

Micellar-mediated capillary electrophoresis (CE) is used for a wide variety of applications, including the separation of pharmaceuticals, environmental contaminants, illicit drugs, DNA fragments, and many other biological samples. The electrospray ionization interface is one of the most common CE-MS interfaces. Coupling micellar-mediated CE separations with MS detection combines two very powerful, widely applicable analytical techniques. Some types of surfactants strongly interfere with electrospray ionization mass spectrometric (ESI-MS) detection of analytes, and in many cases the ESI-MS analyte signals are completely quenched. Only a few reports have appeared that describe the ESI-MS detection of analytes in the presence of surfactants; however, the exact mechanism of ionization suppression has not yet been addressed. In this work, a modified aerosol ionic redistribution (AIR) model is presented that qualitatively explains the results of previous studies, including those using "polymeric surfactants". Analyte ionization suppression by surfactants appears to be caused by Coulombic interaction between oppositely charged solute and surfactant ions in the ESI-produced offspring droplets. It appears that the ability of surfactants to quench electrospray ionization is directly related to the surface activity and the charge of the surfactant. Also, highly surface active components tend to be enriched in ESI-produced offspring droplets. Analyte ion signals can be detected under conditions that lower the surface concentration of oppositely charged surfactant ions in aerosol droplets. The mechanistic information outlined here may be used to design micellar-mediated CE separations that allow detection of analyte ions by ESI-MS.

Chiral electrokinetic chromatography using dipeptide polymeric surfactants: present state of the art

Polymeric amino acid based surfactants have been recently employed as pseudostationary phases in capillary electrophoresis. These phases are effective for chiral separation of analytes in different charge states and hydrophobicities. This review paper focuses on polymeric dipeptide surfactants. The benefits of dipeptide over single amino acid micelle polymers are shown. Some aspects of dipeptide surfactants that are presented here includes the amino acid order, effect of number and position of chiral centers, and steric factors on enantiomeric separation of chiral compounds in different charge states. In addition, the preferential site of interaction of the chiral analyte using diastereomers of polymeric dipeptide surfactants is discussed.

The effects of a mixture of charged and neutral additives on analyte migration behavior in capillary electrophoresis

Multicomponent additives, such as derivatized cyclodextrins with various degrees of substitution, can be considered single-component additives as long as the fraction of each component remains constant. In this paper, equations are derived describing the effect of such additives on the migration behavior of analytes. These equations are used in the study of capillary electrophoresis (CE) systems with differentially charged cyclodextrins as additives. For weakly acidic analytes, the binding with highly negatively charged sulfobutyl ether beta-cyclodextrin (SBE-beta-CD) increases their negative electrophoretic mobility, while the binding with neutral hydroxypropyl-beta-cyclodextrin (HP-beta-CD) decreases their negative mobility. By obtaining the equilibrium constants and mobilities for each additive with each analyte (in this case, phenol, 2-naphthol and 1-naphthol), the migration behavior of these analytes in CE systems is quantitatively predicted at various concentrations of mixtures of the two additives. The properties of the contour lines in the binding isotherm surfaces of such CE systems are discussed.

Charge-shift electrophoretic behavior of T-2 toxin in agarose gels

We report the use of charge-shift electrophoresis to define the behavior of the trichothecene mycotoxin T-2 in aqueous solutions. We found that T-2 behaves in a hydrophobic manner and that this technique can be adapted for the separation of small hydrophobic molecules such as T-2 and cholesterol.

Partitioning of amino acids and nucleotides between water and micellar hexadecyltrimethylammonium halides. The prebiotic significance of cationic surfaces

Using quantitative gel filtration techniques partition coefficients, Kp-values, have been determined between aqueous cationic micellar hexadecyltrimethylammonium bromide, CTAB, and several biomonomer. Kp-values for 5'-adenylic acid, 5'-cytidylic acid, 5'-guanylic acid, 5'-uridylic acid and 5'-thymidylic acid are 1,400 +/- 150. Nucleotides bind to CTAB micelles effectively, but nonselectively. Conversely, the binding of tRNAs to micellar CTAB is selective. Kp-values for glutamic acid II, tyrosine and phenylalanine tRNAs (in 1.0MNaCl) are 520, 3,100 and 5,600, respectively. Kp-values for the binding of alanine, arginine, aspartic acid, glutamic acid, glycine, histidine, phenylalanine, serine, threonine and tryptophan to micellar CTAB are less than 8. Conversion of unitless Kp-values for the binding of amino acids, nucleotides and nucleosides to both anionic and cationic micelles, to K (in 1/g) values allows the comparison of clays and micelles as prebiotic concentrating media. Using correlations between surface densities of the biomonomers and their binding constants, it is shown that aqueous micelles (at pH = 8) are a better concentrating media than are clays.