Naphthyl methacrylate-phenylene diacrylate-based monolithic column for reversed-phase capillary electrochromatography via hydrophobic and π interactions

A neutral naphthyl methacrylate-phenylene diacrylate-based monolith (NPM) was introduced for RP-CEC of various neutral and charged solute probes via hydrophobic and π interactions. The NPM column was prepared by the in situ polymerization of naphthyl methacrylate as the functional monomer and 1,4-phenylene diacrylate (PDA) as the crosslinker in a ternary porogenic solvent containing cyclohexanol, dodecanol and water. The NPM column exhibited cathodal EOF despite the fact that it was devoid of any fixed charges. NPM exhibited stronger EOF than its counterpart naphthyl methacrylate monolith (NMM) made from the in situ polymerization of naphthyl methacrylate and trimethylolpropane trimethacrylate (TRIM). As for NMM, it is believed that the EOF arises from the adsorption of mobile phase ions onto the monolith surface. The higher EOF exhibited by NPM may be attributed to the acrylate nature of PDA as compared to the methacrylate nature of TRIM, and therefore PDA has a higher binding capacity for mobile phase ions due to its higher polarity than TRIM. The adsorption of mobile phase ions together with the additional π interactions offered by the aromatic rings of the NPM matrix modulated solute retention and separation selectivity. The applications of NPM were demonstrated by the separation of a wide range of small and large solutes including peptides, tryptic peptide maps and proteins.     

Determination of the ionization constants of weak electrolytes by capillary zone electrophoresis

Capillary zone electrophoresis in untreated fused silica capillaries has proved suitable for the determination of the ionization constants of weak electrolytes. Several fundamental equations relating the electrophoretic mobilities of ionized solutes to hydronium ion concentrations in the running electrolyte have been verified experimentally. The observed dependence of the electrophoretic mobilities of weak bases and ampholytes on the pH of the electrolyte showed good agreement with predicted behavior. The pK_a values calculated from electrophoretic mobility data obtained by capillary zone electrophoresis were reasonably close to those reported in the literature.     

Capillary electrochromatography with monolithic silica columns. V. Study of the electrochromatographic behaviors of polar compounds on monolithic silica having surface bound cyano functionalities

In this report, a novel polar monolithic capillary column is described for normal phase CEC (NP-CEC) of representative polar compounds including mono- and oligosaccharides, peptides, and basic drugs. The polar monolithic column, which was described in detail in the preceding paper, consisted of silica-based monolith bonded with 1H-imidazole-4,5-dicarbonitrile (IDCN) and is denoted as 2CN-OH-Monolith. Various retention parameters for neutral polar solutes (e.g., mono- and oligosaccharides) and charged polar solutes (e.g., peptides and basic drugs) were evaluated over a wide-range of elution conditions. These retention parameters yielded quantitative assessment for the polar interactions between the model solutes and the stationary phase under investigation as well as the effect of electromigration of charged solutes on their overall migration in NP-CEC. Furthermore, this investigation demonstrated that despite the possibility of achieving isocratic separation in NP-CEC for widely differing polar species, multistep-gradient elution in NP-CEC is preferred to bring about the rapid separation of a large number of polar species in a single run.     

Chromatographic properties of zirconia-based stationary phases for ion exchange chromatography having surface bound cationic functions

A series of non-porous, microspherical zirconia-based stationary phases with surface bound cationic functions have been introduced and evaluated in ion exchange chromatography of proteins and small acidic solutes. Different surface modification procedures were evaluated in the covalent attachment of weak, strong or hybrid anion exchange moieties on the surface of non-porous zirconia micropar-ticles. N,N-Diethylaminoethanol (DEAE) was used as the weak anion exchange ligand while glycidyltrimethylammonium chloride, which was covalently attached to poly(vinyl alcohol) layer (PVAN) on the zirconia surface, constituted the strong anion exchange moiety. Partially quaternarized poly(ethyleneimine) hydroxyethylated (PEI) was used as the hybrid type of anion exchange coating. DEAE-zir-conia microparticles acted as purely cation exchange stationary phases toward basic proteins indicating the predominance of electron donor-electron acceptor interaction (EDA) with surface exposed zirconium sites as well as cation exchange mechanism via electrostatic interaction with unreacted and unshielded hydroxyl groups. PVAN-zirconia stationary phase exhibited anion exchange chromatographic properties toward acidic proteins, but EDA interaction has stayed as an important contributor to solute retention despite the presence of a relatively thick layer of poly(vinyl alcohol) on the surface of the zirconia particles. The modification of zirconia surface with partially quaternarized PEI proved to be the most effective approach to minimize Lewis acidic metallic properties of the support. In fact, PEI-zirconia stationary phase operated as an anion exchanger toward acidic proteins and other small acidic solutes.     

Micro-high-performance liquid chromatography platform for the depletion of high-abundance proteins and subsequent on-line concentration/capturing of medium and low-abundance proteins from serum. Application to profiling of protein expression in healthy and osteoarthritis sera by 2-D gel electrophoresis

In this investigation, an integrated microcolumn-based fluidic platform for the simultaneous depletion of high-abundance proteins and the subsequent on-line concentration/capturing of medium- and low-abundance proteins from human serum has been introduced. The platform consists of on-line coupling of tandem affinity micorcolumns to an RP microcolumn to achieve first the depletion of high-abundance proteins by the tandem affinity microcolumns followed by the concentration and capturing of medium- and low-abundance proteins by the RP microcolumn. The tandem affinity microcolumns are based on macroporous monoliths characterized by their relatively high permeability in pressure-driven flow while the RP microcolumn is packed with polymeric particles with an average particle diameter of 20 microm giving rise to a very little back pressure, thus allowing fast flow velocity across the coupled columns format and consequently short processing time of serum samples prior to analysis by 2-DE. The microcolumn-based fluidic platform was applied to serum samples from osteoarthritis (OA) donors before and after soy protein (SP) supplementation, and from healthy donors, and the resulting depleted serum samples from high-abundance proteins were profiled for protein expression by 2-DE. In general, the protein expression was lower in serum of the same OA patient after soy treatment than before soy treatment. Several proteins were down-regulated after soy treatment with transthyretin being the most affected by the SP supplementation. In addition, with respect to serum from healthy donors, the sera from OA patients showed difference in proteins expression.     

Reduction of protein concentration range difference followed by multicolumn fractionation prior to 2-DE and LC-MS/MS profiling of serum proteins

This article is concerned with the reduction of protein concentration range differences by the peptide beads library technology (ProteoMiner? or "equalizer" technology), which in principle allows the enrichment of proteins to the same concentration level (i.e. protein equalizer) regardless of the original protein abundance in a given biological fluid such as human serum, which is the subject of our investigation. After the equalization step, the captured proteins from human serum were fractionated on a series of tandem monolithic columns with surface-bound iminodiacetic acid ligands to which three different metal ions, namely, Zn2+, Ni2+ and Cu2+ were immobilized to yield the so-called immobilized metal affinity chromatography columns. These three monolithic columns were connected to a reversed-phase column packed with polystyrene divinyl benzene beads. Aliquots taken from the four collected fractions from the four tandem columns were subsequently fractionated by 2-DE. Also, aliquots from the four collected fractions were tryptically digested and analyzed by LC-MS/MS. The strategy of subsequent fractionation on the four tandem columns after equalization allowed the identification of more proteins than simply using the equalization by ProteoMiner? . The equalizer technology was compared to the immuno-subtraction approach. While the ProteoMiner? technology is superior in terms of the overall number of captured proteins, it only complements the immuno-subtraction approach since the latter can capture the proteins that were not captured by the former.     

No slip boundary effects in non-Darcian mixed convection from a vertical wall in saturated porous media. Analytical solution

An analytical study is made for wall effects in non-Darcy mixed convection from vertical impermeable surfaces embedded in a saturated porous medium. The governing equations are transformed into a dimensionless form by non-similar transformation to cover both forced and natural convection dominated regimes. Two different dimensionless parameters that measure the strength of mixed convection were found in both regimes. The parameters of forced convection dominated regime can be related to those of natural convection dominated regime. An approximate analytical solution for the governing equations was obtained. Temperature and velocity profiles for both regimes are presented. Received on 9 September 1997     

The Effects of Generalized Reciprocal Exchange on the Resilience of Social Networks: An Example from the Prehispanic Mesa Verde Region

The initial version of the model used in this study, Village 1.0, was implemented by Tim Kohler and a team of developers mostly from Washington State University. The original model addressed environmental constraints only and did not attempt to model social interaction. In a recent paper we employed Cultural Algorithms as a framework in which to add selected social considerations. In this paper we extend our previous model by adding the ability of agents to perform symmetrically initiated or asymmetrically initiated generalized reciprocal exchange. We have developed a state model for agents' knowledge and, given agents' different responses based on this knowledge. Experiments have shown that the network structure of the systems without reciprocity was the simplest but least resilient. As we allowed agents more opportunities to exchange resources we produced more complex network structures, larger populations, and more resilient systems. Furthermore, allowing the agents to buffer their requests by using a finite state model improved the relative resilience of these larger systems. Introducing reciprocity that can be triggered by both requestors and donors produced the largest number of successful donations. This represents the synergy produced by using the information from two complementary situations within the network. Thus, the network has more information with which it can work and tended to be more resilient than otherwise.     

Classification of Cylindrically Symmetric Static Spacetimes According to Their Ricci Collineations

A complete classification of cylindrically symmetric static Lorentzian manifolds according to their Ricci collineations (RCs) is provided. The Lie algebras of RCs for the non-degenerate Ricci tensor have dimensions 3 to 10, excluding 8 and 9. For the degenerate tensor the algebra is mostly but not always infinite dimensional; there are cases of 10-, 5-, 4- and 3-dimensional algebras. The RCs are compared with the Killing vectors (KVs) and homothetic motions (HMs). The (non-linear) constraints corresponding to the Lie algebras are solved to construct examples which include some exact solutions admitting proper RCs. Their physical interpretation is given. The classification of plane symmetric static spacetimes emerges as a special case of this classification when the cylinder is unfolded.