Nonionic polysaccharides as calibration standards for aqueous size exclusion chromatography

Wanted: scalable tracers for diffusion measurements

Scalable tracers are potentially a useful tool to examine diffusion mechanisms and to predict diffusion coefficients, particularly for hindered diffusion in complex, heterogeneous, or crowded systems. Scalable tracers are defined as a series of tracers varying in size but with the same shape, structure, surface chemistry, deformability, and diffusion mechanism. Both chemical homology and constant dynamics are required. In particular, branching must not vary with size, and there must be no transition between ordinary diffusion and reptation. Measurements using scalable tracers yield the mean diffusion coefficient as a function of size alone; measurements using nonscalable tracers yield the variation due to differences in the other properties. Candidate scalable tracers are discussed for two-dimensional (2D) diffusion in membranes and three-dimensional diffusion in aqueous solutions. Correlations to predict the mean diffusion coefficient of globular biomolecules from molecular mass are reviewed briefly. Specific suggestions for the 3D case include the use of synthetic dendrimers or random hyperbranched polymers instead of dextran and the use of core-shell quantum dots. Another useful tool would be a series of scalable tracers varying in deformability alone, prepared by varying the density of crosslinking in a polymer to make say "reinforced Ficoll" or "reinforced hyperbranched polyglycerol."

Characterization of pore structure of a strong anion-exchange membrane adsorbent under different buffer and salt concentration conditions

The quantitative characterization of pore structure of Sartobind Q, a strongly basic membrane anion exchanger that is formed by cross-linked cellulose support and a hydrogel layer on its pore surface, was made combining the results obtained by several experimental techniques: liquid impregnation, batch size-exclusion, inverse size-exclusion chromatography, and permeability. Mercury intrusion and nitrogen sorption porosimetry were carried out for a dry cellulose support membrane in order to get additional information for building a model of the bimodal pore structure. The model incorporated the distribution of the total pore volume between transport and gel-layer pores and the partitioning of solutes of different molecular weights was expressed through the cylindrical pore model for the transport pores and random plane model for the gel layer. The effect of composition of liquid phase on the pore structure was investigated in redistilled water, phosphate and Tris-HCl buffers containing up to 1M NaCl. Evident differences in the bimodal pore structure were observed here when both the specific volume and size of the hydrogel layer pores significantly decreased with the ionic strength of liquid phase.

Characterization of the molecular mass distribution of pullulans by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry using 2,5-dihydroxybenzoic acid butylamine (DHBB) as liquid matrix

The performances of several matrices were investigated for the accurate determination of the molecular mass distributions of pullulans by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The ionic liquid matrix (ILM) 2,5-dihydroxybenzoic acid butylamine (DHBB) gave better and more reliable results than the crystalline matrices 2,5-dihydroxybenzoic acid (DHB) and 2,4,6-trihydroxyacetophenone (THAP). With the ILM it was possible to obtain spectra of pullulans up to more than 100 kDa, the highest molar mass reported thus far. Owing to the known advantages of liquid matrices providing better spot-to-spot reproducibility, an almost noise-free spectrum and constant baselines were obtained when working under optimized conditions. In particular, the extent of in-source fragmentation occurring with this group of fragile polymers was considerably and decisively reduced. Thus, a more reliable representation of the true oligomer and polymer distributions is experimentally attainable, especially for distributions with small polydispersity values. The maximum error in the measured distribution associated with fragmentation was estimated by model calculations describing the changes in the polymer distribution upon different probabilities of fragmentation events. These simulation results indicated that the data obtained by MALDI-TOFMS using the liquid DHBB matrix were of high reliability. In particular, the average value of the distributions, M(w), and the polydispersity were obtained with predicted uncertainties of between 3 and 15% depending on the width of the distribution and the mass of the polymers.

Quantitative characterization of pore structure of cellulose gels with or without bound protein ligand

Structural properties of cellulose gels Perloza MT, materials designed for the preparation of chromatographic adsorbents and immobilized biocatalysts, having a different content of polymer were investigated using a batch solute exclusion method. A homologous set of dextrans with a wide range of molecular weights was used to probe the pore accessibility of the gel particles. It was found that all gels possessed a bimodal pore structure where macropores were fully accessible to all dextrans whereas the solute partitioning depending on the molecule size occurred in the micropores of the swollen polymer network. The macropore and micropore fractions of the gels were estimated from the masses of total water and water accessible to the largest solute. The macropore fraction decreased with the gel polymer content. It was 0.57 at the gel containing 8% of polymer but only 0.22 at the gel with 38% of polymer. The micropore fraction varied from 0.38 to 0.47. The mass of accessible water for each solute was used to calculate the particle and gel-phase partition coefficients. The dependence of the latter quantity on the solute hydrodynamic radius was successfully fitted with the Ogston model. Bovine serum albumin that was used as a model protein ligand blocked almost all gel-phase pores of the gel with the highest polymer content whereas it little affected the accessibility of other materials.

Size-exclusion chromatography-a review of calibration methodologies

Recent developments are reviewed in size exclusion chromatographic calibration methodologies, including direct calibration by using narrow and broad polymer standards and various instrumental methods (nuclear magnetic resonance, mass spectrometry, light scattering) as well as universal calibration with and without viscometry detectors, for simple and complex polymers.

Nonperturbing fluorescent labeling of polysaccharides

A fluorescent labeling procedure, which does not perturb macromolecular conformations, was employed to bind a rhodamine derivative to the reducing end of several water-soluble polysaccharides by reductive amination in the presence of sodium cyanoborohydride. Fluorescence correlation spectroscopy, atomic force microscopy, and size exclusion chromatography were used to demonstrate that the conformations of the polysaccharides schizophyllan, polygalacturonic acid (PGUA), succinoglycan, and several dextrans were maintained following the labeling procedure.

In situ preparation of beta-D-1-O-hydroxylamino carbohydrate polymers mediated by galactose oxidase

[reaction: see text] Galactose oxidase produced a C-6 aldehyde in various terminal-containing galactose hydroxylamines for the simultaneous in situ generation of an A-B type condensation for the construction of unique oxime polymers. Molecular weights of the corresponding polymers were determined to be in the range of 4200-8900 g/mol, respectively. This indicates that approximately 20-25 sugar units were incorporated in these unique polymers.