Terms Of Molar Mass Research Articles

Analysis of calcium salt of carboxymethyl cellulose: size distributions of parent carboxymethyl cellulose by size-exclusion chromatography with dual light-scattering and refractometric detection

Generally, the insoluble calcium salt of carboxymethyl cellulose can be quantitatively transformed in a batch process into its sodium form using chelating resin Lewatit TP-208. The resulting sodium carboxymethyl cellulose, having a fairly low degree of substitution close to 0.6, was analysed using size exclusion chromatography with multiangle light scattering/refractometric detection. Commercial samples of sodium carboxymethyl cellulose having degree of substitution 0.7 and 1.2 were used to highlight the relation between the degree of substitution and the presence of aggregated structures. It was found that all calcium/sodium transformed carboxymethyl cellulose samples contain a significant amount of macrogel particles larger than 5 μm which can be removed by centrifugation or filtration. Centrifuged and filtered samples were then shown to contain significant amounts of smaller aggregated structures (fringed micelles) which were found also in sodium carboxymethyl cellulose reference samples where their amount was inversely proportional to their degree of substitution. Because size exclusion chromatography separates macromolecules according to their hydrodynamic volume, linear and aggregated structures having the same hydrodynamic volume, but entirely different molar mass, are eluted together and a significant heterogeneity in terms of molar mass at a fixed elution volume is found especially at lower sample elution volumes. Hence, molar mass distributions become undefined. Fortunately, the elution was found to be homogeneous in terms of experimentally accessible radii of gyration and reliable size distributions could be evaluated.

Activity and process stability of purified green pepper (Capsicum annuum) pectin methylesterase.

Pectin methylesterase (PME) from green bell peppers (Capsicum annuum) was extracted and purified by affinity chromatography on a CNBr-Sepharose-PMEI column. A single protein peak with pectin methylesterase activity was observed. For the pepper PME, a biochemical characterization in terms of molar mass (MM), isoelectric points (pI), and kinetic parameters for activity and thermostability was performed. The optimum pH for PME activity at 22 degrees C was 7.5, and its optimum temperature at neutral pH was between 52.5 and 55.0 degrees C. The purified pepper PME required the presence of 0.13 M NaCl for optimum activity. Isothermal inactivation of purified pepper PME in 20 mM Tris buffer (pH 7.5) could be described by a fractional conversion model for lower temperatures (55-57 degrees C) and a biphasic model for higher temperatures (58-70 degrees C). The enzyme showed a stable behavior toward high-pressure/temperature treatments.

Partial purification, characterization, and thermal and high-pressure inactivation of pectin methylesterase from carrots (Daucus carrota L.).

Pectin methylesterase (PME) from carrots (Daucus carrota L.) was extracted and purified by affinity chromatography on a CNBr-Sepharose 4B-PME inhibitor column. A single protein and PME activity peak was obtained. A biochemical characterization in terms of molar mass (MM), isoelectric points (pI), and kinetic parameters of carrot PME was performed. In a second step, the thermal and high-pressure stability of the enzyme was studied. Isothermal and combined isothermal-isobaric inactivation of purified carrot PME could be described by a fractional-conversion model.

Purification, characterization, thermal, and high-pressure inactivation of pectin methylesterase from bananas (cv Cavendish).

Pectin methylesterase (PME) was extracted from bananas (cv Cavendish) and purified by affinity chromatography on a CNBr-Sepharose-PME inhibitor (PMEI) column. A single protein and PME activity peak was obtained. For banana PME, a biochemical characterization in terms of molar mass (MM), pI, and kinetic parameters was performed. In a second step, the thermal and high-pressure stability of the enzyme was studied. Isothermal inactivation of purified banana PME could be described by a first-order kinetic model in a temperature range of 65 degrees to 72.5 degrees C, whereas its isobaric-isothermal inactivation followed a fractional-conversion model. Banana PME was found to be more thermally stable compared with PMEs extracted from orange, tomato, and apple.

Determination of the structural parameters of aqueous polymer solutions in the molecular, partially aggregated, and particulate states by means of FFFF/MALLS

Flow field-flow fractionation (FFFF) has a separation range from ≈104 to 1012 g mol−1 in terms of molar mass and only requires that the sample be soluble (or dispersable) in some carrier liquid. By coupling this technique with a multiangle laser light-scattering photometer (MALLS), it becomes possible to obtain the absolute distributions of the molar mass and radii of gyration in addition to the distribution of the hydrodynamic radii. The required information on the polymer shape and solution structure can then be derived from these data. The coupling of FFFF/MALLS has proven to be a powerful method for characterizing aqueous systems; one of the reasons for this was the introduction of a circulating cross flow. The scope for applying this new analytical technique is illustrated by means of homogeneously dissolved polymer molecules (dextran), cationic polyelectrolytes (poly-diallyldimethylammonium chloride), particulate systems (latices, albumin, and tobacco mosaic virus), and solutions containing partially aggregated molecules (pectin solutions) within a molar mass range from MW=8×104 g mol−1 to MW=2×107 g mol−1. © 1998 John Wiley & Sons, Inc. J Micro Sep 10: 51–56, 1998