Microfluidic synthesis of chitosan-based nanoparticles for fuel cell applications

A microfluidic platform is developed for the synthesis of monodisperse, 100 nm, chitosan based nanoparticles using nanogelation with ATP. The resulting nanoparticles tuned and enhanced transport and electrochemical properties of Nafion based nanocomposite membranes, which is highly favorable for fuel cell applications.     

Rheology of highly concentrated anionic surfactants

Surfactant solution flow behavior is of great importance to both the chemical and consumer product industries. Most studies on the flow behavior of surfactant solutions, however, have focused on the dilute regime. Seldom reported is rheology in the highly concentrated regime where typically these surfactants are processed and delivered. First, we present here the phase diagram for the ternary system: water and two anionic surfactants (sodium salt of lauric and oleic acid) at different temperatures. Then, we present both linear viscoelastic and steady shear flow results in the high (70 to 90%) surfactant regime. We find that high values of the shear modulus are directly dependent on the quantity of surfactant crystals and that the formation of a lamellar liquid crystal phase at 45°C affects both modulus and flow of the system. Lamellar crystals create a stiff network resulting in wall slip at large shear strain. Using serrated plates removes slip at the wall and we find a shear rate where microfractures localize in a preferential plane and the material flows. This behavior is reversible.     

The development and characterization of protein-based stationary phases for studying drug-protein and protein-protein interactions

Protein-based liquid chromatography stationary phases are used in bioaffinity chromatography for studying drug-protein interactions, the determination of binding affinities, competitive and allosteric interactions, as well as for studying protein-protein interactions. This review addresses the development and characterization of protein-based stationary phase, and the application of these phases using frontal and zonal chromatography techniques. The approach will be illustrated using immobilized heat shock protein 90α and the immobilized estrogen related receptor stationary phases. In addition, the review discusses the use of the protein-coated magnetic beads for ligand and protein fishing as well as for the identification of unknown ligands from cellular or botanical extracts.     

Sun Screen Microemulsions

Three sunscreen compounds, p-amino benzoic acid (PABA), octyl-di-methyl-p-amino benzoic acid (ODP), and 2-hydroxy-4-methyoxy-5-sulfobenzophenone (HMSB) were incorporated into a model microemulsion system stabilized by sodium dodecyl sulfate and pentanol.

The PABA acted as a hydrotrope supporting the stability of an oil-in-water microemulsion, while ODP had the opposite effect. HMSB, finally retained both the oil-in-water and the water-in-oil parts of the microemulsion system.     

Synthesis of an immobilized Bombyx mori pheromone-binding protein liquid chromatography stationary phase

The pheromone-binding protein from the silkworm moth, Bombyx mori (BmorPBP) has been covalently bonded to a liquid chromatographic stationary phase. The resulting column was evaluated using radiolabeled bombykol and the immobilized protein retained its ability to bind this ligand. The data also demonstrate that the BmorPBP column was able to distinguish between four compounds, and rank them in their relative order of affinity for the protein from highest to lowest: bombykol > bombykal > 1-hexadecanol > (Z,E)-5,7-dodecadien-1-ol, and that the immobilized BmorPBP retained its pH-dependent conformational mobility.The results of this study demonstrate that pheromone-binding protein from the silkworm moth, Bombyx mori and an odorant binding protein (OBP) obtained from the female mosquito Culex quinquefasciatoes have been immobilized on a silica support with retention of ligand-binding activity. The data indicate that proteins from non-mammalian organisms can be used to create liquid chromatography affinity columns.     

Identification of P-glycoprotein substrates using open tubular chromatography on an immobilized P-glycoprotein column: Comparison of chromatographic results with Caco-2 permeability

The Caco-2 cell monolayer model was used to classify 13 compounds as P-glycoprotein (Pgp) substrates or non-substrates. The apparent permeability coefficients (Papp) in the basal-to-apical direction (Papp_B-A) and in the apical-to-basal direction (Papp_A-B) were determined for each compound and a compound was designated as a Pgp substrate if Papp_B-A/Papp_A-B, the permeability ratio, exceeded 2.0. The same compounds were chromatographed on open tubular glass columns containing membranes from cell lines that either expressed Pgp (Pgp(+)-OT column) or did not express Pgp (Pgp(−)-OT column). The differential retentions in min, Δt values, of the compounds were determined using the following relationship Δt = t_(Pgp(+)-OT) − t_{(Pgp(−)-OT)}. A statistically significant correlation was observed between the Δt values and the permeability ratios, r² = 0.7749 (p = 0.0063), indicating that the differential chromatography approach could be used to quantitatively assess permeability ratios. The results also indicated that a Δt value ≥0.5 min was a reliable measure of a permeability ratios >2 and could be used as a rapid qualitative determination of whether a test compound was a Pgp substrate. The chromatographic study took 1 h to complete and a single pair of columns could be used to screen at least 150 compounds a week and 600 compounds during the 4-week lifetime of the columns.     

Lamellar liquid crystals of zwitterionic surfactants with hydrocarbon and polyisobutylene chains

Abstract

Surfactants from either polyisobutylene or alkylsuccinic anhydrides derivatized with diethanolamine in a 1:1 molar ratio with hydrocarbon and polyisobutylene chains of similar length formed lamellar liquid crystals in situ and also with added water. The repeat distance between layers was determined using low angle X-ray diffraction (LAXD), and the water penetration into the hydrocarbon space in the lamellar structure was calculated.

The results revealed a significantly increased repeat distance for the polyisobutylene chain surfactants compared to the alkyl analogues. The water penetration was significantly greater for a surfactant with a decyl chain compared to the one with a dodecyl chain and was intermediate for the polyisobutylene based surfactant.     

Acetylcholinesterase immobilized on modified magnetic beads as a tool for screening a compound library

Acetylcholinesterase (AChE) from Electrophorus electricus was immobilized on the surface of amino-modified magnetic beads (AChE-MB), and its activity evaluated by the quantification of acetylcholine hydrolysis. A reference mixture composed of AChE binders (galanthamine and a probe coumarin, K _i = 0.031 ± 0.010 μM) and non-binders (ketamine and propranolol) was used to probe the fishing assay. The performance of the bioconjugation assay was demonstrated with a library of 12 reference coumarins from which two ligands were directly identified by LC-MS/MS in a single assay, demonstrating the usefulness of this approach.

A bioconjugate-screening assay with AChE-modified magnetic beads was developed to direct identification of AChE binders, in mixtures, by LC-MS/MS. A reference mixture of twelve coumarins was used and, the two ligands were identified.

     

Development and characterization of an immobilized enzyme reactor (IMER) based on human glyceraldehyde-3-phosphate dehydrogenase for on-line enzymatic studies

Immobilized enzyme reactors (IMERs) for on-line enzymatic studies are useful tool to select specific inhibitors and may be used for direct determination of drug-receptor binding interactions and for the rapid on-line screening to identify specific inhibitors. This technique has been shown to increase the stability of enzymes. The enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) plays an important role in the life cycle of the Trypanosoma cruzi and it has become a key target in the drug discovery program for Chagas' disease. Crystallographic studies have indicated that there are significant inter-species differences in GAPDH activity and sensitivity. For example the active sites of GAPDH in T. cruzi and humans differ by a substitution of ASP(210) (T. cruzi) by Leu(194) in human. Based on this information we initiated the study to develop optimal conditions for the covalent immobilization of the human GAPDH enzyme on a modified capillary support (400 mm x 0.10 mm). The chromatographic separation of NAD from NADH was achieved using a RP-Spherex-diol-OH (10 cm x 0.46 cm, 10 microm, 100 A) column. By using multidimensional HPLC chromatography system it was possible to investigate the activity and kinetic parameters of the GAPDH-IMER. The values obtained for D-GA3P and NAD were K(m)=3.5+/-0.2 mM and 0.75+/-0.04 mM, respectively, and were compared with values obtained with the free enzyme. The activity of the immobilized GAPDH has been preserved for over 120 days.