Size Exclusion Chromatography-multiangle Light Scattering Research Articles

Branched Poly(phenylacetylene)

Characterization of poly(phenylacetylene) (PPA) samples produced using Rh(I) complexes featuring hemilabile phosphine ligands by size exclusion chromatography, multiangle light scattering (SEC-MALS), or asymmetric flow field flow fractionation (A4F)-MALS has revealed that some of these PPA samples contain a mixture of linear and branched polymer. The occurrence and extent of branching is dependent on both catalyst structure and polymerization conditions. The levels of branching are consistent with either terminal branching through copolymerization of macromonomer or chain transfer to polymer, where the branched species are less reactive toward further polymerization than the linear chains. The MM dependence of B, the number of branches per molecule, or λ, the number of branches per 1000 repeat units, suggests that the latter explanation may be correct, but further work is needed.

Cross-linking of β-casein by Trichoderma reesei tyrosinase and Streptoverticillium mobaraense transglutaminase followed by SEC–MALLS

Enzymatic modification of proteins, in order to produce functional materials such as hydrogels, adhesives and films via cross-linked networks or scaffolds of proteins, is a constantly evolving technology to create tailored micro- and nanostructured materials for food, cosmetic, and medical applications. For the successful utilization of oxidoreductases or transferases such as tyrosinases and transglutaminases, respectively, it is crucial to understand the action of these enzymes on protein substrates. In this study, cross-linking of the milk protein β-casein by Trichoderma reesei tyrosinase (TrTyr) was studied using size-exclusion chromatography (SEC) equipped with multi-angle light scattering (MALLS) and ultraviolet/visible (UV/Vis) detectors in order to determine the molecular mass (MM), radius of gyration ( R G) and degree of polymerization (DP) of the reaction products. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to detect early polymerization states. The widely used S treptoverticillium mobaraense transglutaminase (Tgase) was used for comparison to tyrosinase from T. reesei. The results showed that cross-linking of β-casein by these two different types of enzymes resulted in the formation of polymerized reaction products with MM ranging from 500 to 1700 kg mol −1 depending on the enzyme dosage and incubation time. The DP varied from 21 to 71, respectively. In the case of TrTyr the polymerized reaction products were slightly colored, and formation of the covalent cross-linking of β-casein could be monitored by UV/Vis as a function of incubation time.

Room-Temperature Bonding for Plastic High-Pressure Microfluidic Chips

A generic method for the rapid, reproducible, and robust bonding of microfluidic chips fabricated from plastics has been developed and optimized. One of the bonding surfaces is exposed to solvent vapor prior to bringing the mating parts into contact and applying a load. Nanoindentation measurements performed by atomic force microscopy show that a reversible material softening occurs upon exposure to solvent vapor. Subsequent exposure of the bonded chip to UV light then strengthens the bond between mating parts and increases the burst pressure by 50% due to partial cross-linking and chain scission reactions as measured by size exclusion chromatography-multiangle light scattering (SEC-MALS). Performing all steps of this procedure at room temperature eliminates channel distortion observed during thermal bonding and affords channels with highly uniform cross-sectional dimensions. Our technique enables chips resistant to pressures as high as 34.6 MPa.

Preparation of cationic comb-type copolymer having guanidino moieties and its interaction with DNAs

In order to evaluatet effects of different cationic moieties, such as primary amino and guanidino groups, on interactions between DNAs and cationic comb-type copolymers, comb-type copolymers having guanidino groups were prepared. The copolymers (GPLL-g-Dex) were obtained by guanidination of poly(L-lysine)-graft-dextran copolymers (PLL-g-Dex) using 1-guanyl3,5-dimethylpyrazole nitrate under weak basic conditions. The resulting copolymers were characterized using NMR spectroscopy and size-exclusion chromatography-multiangle light scattering (SECMALS). The primary amino groups of the PLL backbones were thoroughly replaced with guanidino ones without any detectable side reactions, including fragmentation of PLL or Dex chains. The interactions of GPLL-g-Dex and PLL-g-Dex with DNAs were assessed by UV-melting curve measurements. These copolymers diversly affected the melting behavior of double-stranded DNA (dsDNA). GPLL-g-Dex has a lower ability to increase the T m of dsDNA than PLL-g-Dex and also exhibits a higher affinity for dsDNA. The results suggest that the stability of dsDNA may be affected not only by ionic interaction between the copolymers and DNAs, but also by other modes of interactions, such as hydrogen-bondinginteractions.

Aspects of the structural integrity of chondroitin sulphate after laser irradiation

The effects of laser irradiation on molecular mass and conformation of pure chondroitin sulphate dissolved in phosphate buffered saline (PBS) were investigated using size exclusion chromatography/multi-angle light scattering (SEC/MALS) and sedimentation velocity in the analytical ultracentrifuge. In addition, cartilage pieces immersed in buffer were irradiated with a laser in order to study whether cartilage components may diffuse away from the matrix and into the surrounding aqueous medium as a result of laser treatment. Size exclusion chromatography/multi-angle light scattering and sedimentation velocity measurements showed that (a) laser irradiation decreases the molecular mass of chondroitin sulphate and (b) laser irradiation of cartilage induces diffusion of macromolecules into the medium.

Conformational change and aggregation of κ-carrageenan studied by flow field-flow fractionation and multiangle light scattering

The relatively novel combination of flow field-flow fractionation (FFF) and multiangle light scattering (MALS) was employed to study a nondegraded κ-carrageenan in different 0.1M salt solutions. The applicability of the technique was tested, and the effects of salt type and salt composition on the molar mass and radius of gyration were studied. A conformational ordering was induced at room temperature by switching the solvent from 0.1M NaCl (coil form) to 0.1M NaI (helix form). An approximate doubling of the average molar mass and an increase in radius of gyration was then observed, in agreement with results obtained previously using size exclusion chromatography–MALS. This increase in size was attributed to conformational ordering and to the formation of double helices. Severe aggregation was observed above 40% CsI in the 0.1M mixed salt solution of CsI and NaI. This was ascribed to the association of helices into large aggregates. For these large associates, having molar masses of several millions, a reversal of the elution order in flow FFF was detected. © 1998 John Wiley & Sons, Inc. Biopoly 45: 85–96 1998