Bile Salt Anion Sorption by Polymeric Resins: Comparison of a Functionalized Polyacrylamide Resin with Cholestyramine

Cholestyramine and a cross-linked polyacrylamide resin with lateral alkyl quaternary ammonium groups (QPDA12) were used to study their ability to bind several bile salt anions (including the cholate, glycocholate, taurocholate, and chenodeoxycholate), individually and competitively, from phosphate buffer solutions at room temperature. The latter resin showed high affinities for all the bile salt anions examined, while cholestyramine exhibited a high affinity only for the more hydrophobic chenodeoxycholate. However, for the binding with cholestyramine, cooperative effects were more pronounced, leading to the enhancement of sorption at higher concentrations. The Langmuir equation and its modified versions were used in the interpretation of both individual and competitive binding of bile salts. The data from competitive binding studies indicated that the presence of the tightly bound chenodeoxycholate did not significantly diminish the ability of QPDA12 resin to bind cholate. However, for cholestyramine, the sorption of chenodeoxycholate increased the relative binding affinity for the more hydrophilic cholate, revealing a novel "cooperative" effect involving different bile salt anions. The latter results suggest that the observed higher affinity of QPDA12 is brought about predominantly through the hydrophobic interactions with the pendant alkyl groups rather than with the resin backbone. Copyright 2000 Academic Press.     

Control of nano-micrometric twist and helical ribbon formation with gemini-oligoalanine via interpeptidic beta-sheet structure formation

Confinement of anionic oligo-alanine peptides at the surfaces of cationic membrane by ionic interaction can induce their secondary structure formation; such organized peptides reciprocally transfer their chirality to membranes with non-chiral amphiphiles and their supramolecular chiral structures can be tuned both by peptides and amphiphiles structures.     

Dirac-bracket structure in multidimensional mode conversion

The intersection of two (2n − 1)-dimensional dispersion manifolds D_a and D_b in the 2n-dimensional ray phase space P yields a (2n − 2)-dimensional conversion manifold M≡D_a∩D_b that naturally possesses a Dirac-bracket structure that is inherited from the canonical Poisson bracket on ray phase space. The canonical symplectic two-form Ω ≡ Ω_∥ + Ω_⊥, defined on the 2n-dimensional tangent plane T_z0P≡T_z0M⊕(T_z0M)_⊥, can thus be decomposed into the Dirac two-form Ω_∥ on the (2n − 2)-dimensional tangent plane T_z0M at a conversion point z₀∈M, and the symplectic two-form Ω_⊥ on its orthogonal 2-dimensional complement (T_z0M)_⊥. These two symplectic two-forms are introduced in our analysis of multidimensional mode conversion, where their respective geometrical roles are defined. We note that since the Dirac-bracket structure Ω_∥ vanishes identically when n = 1, it represents a new structure in multidimensional (n > 1) mode conversion theory.     

Estimating Measurement Uncertainty on Stress-Strain Curves from SHPB

Split Hopkinson Pressure Bar tests are commonly used to determine material stress-strain relationship at high deformation rates. Obtaining this relationship is dependant both on certain assumptions and substantial post-processing of the data recorded during the test. Measurement uncertainty rarely appears on the resulting curves. This article introduces a simple method of estimating the measurement uncertainty associated with SHPB tests.     

Monodisperse hydrogel microspheres by forced droplet formation in aqueous two-phase systems

This paper presents a method to form micron-sized droplets in an aqueous two-phase system (ATPS) and to subsequently polymerize the droplets to produce hydrogel beads. Owing to the low interfacial tension in ATPS, droplets do not easily form spontaneously. We enforce the formation of drops by perturbing an otherwise stable jet that forms at the junction where the two aqueous streams meet. This is done by actuating a piezo-electric bending disc integrated in our device. The influence of forcing amplitude and frequency on jet breakup is described and related to the size of monodisperse droplets with a diameter in the range between 30 and 60 μm. Rapid on-chip polymerization of derivatized dextran inside the droplets created monodisperse hydrogel particles. This work shows how droplet-based microfluidics can be used in all-aqueous, surfactant-free, organic-solvent-free biocompatible two-phase environment.