Guy Muller

Analysis of a complex polysaccharide (gum arabic) by multi-angle laser light scattering coupled on-line to size exclusion chromatography and flow field flow fractionation

The heterogeneous polysaccharide gum arabic has been characterized using size exclusion chromatography (SEC) and flow field flow fractionation (F4) coupled on-line to multi-angle laser light scattering (MALLS). Two distinct populations have been shown. About 80% of the material consist of highly branched arabinogalactan (AG) units. The rest is mainly composed of heterogeneous arabinogalactan–protein complex (AGP) of high molecular weight. The F4/MALLS method is shown to allow the complete analysis of gum arabic whereas SEC gave only partial information. From light-scattering-based radii of gyration (Rg) and F4-based hydrodynamic radii (Rh) we found that the ratio Rg/Rh is near 0.8 for AGP. This value is reasonably consistent with a globular conformation and gives further evidence in favour of the “wattle blossom model” proposed by Connolly et al.

Residual solvent effect on the permeation properties of fluorinated polyimide films

The main aim of this study was to determine how the residual solvent remaining after fabrication affected the gas permeation properties of 6FDA–mPDA polyimide films. For this purpose, films were made by spreading solutions of polyimide from different solvents on glass plates, then treated at 200°C for different periods of time. The films obtained were characterized by differential scanning calorimetry, thermogravimetry and permeametry. Permeation parameters (D, P, S) of the films towards N2 and CO2 were determined at 35°C. They were found to be dependent on the residual solvent in the films. Whatever the solvent, the difference in behaviour was found to decrease as the amount of solvent became smaller and to increase with the molar volume of the solvent. Solvents with high molar volumes left an imprint in the material during thermal treatment.

Salt dependence of the conformation of a single-stranded xanthan

Abstract A highly pyruvated single-stranded xanthan sample was studied by low angle light scattering and low shear viscosity in a salinity range (10 −5 M-1 M NaCl) where xanthan can exist in both ordered and disordered forms as shown by optical rotation. No aggregates have been observed in solutions prepared by direct dilution of the fermentation borth, but it was found that molecular associations can result from the polymer drying process used. No molecular weight change has been detected during the salt-induced conformational transition which is thus shown to be an intramolecular process. The salinity dependence of xanthan conformation is analysed on the basis of Yamakawas theory for a wormlike chain model with a total persistence length comprising a structural part, which is found to assume different values depending on the nature of the secondary structure (ordered or not), and an electrostatic part which is dependent on the ionic strength.

About the native and renatured conformation of xanthan exopolysaccharide

Abstract Low-angle laser light scattering (LALLS), size exclusion chromatography coupled with multi-angle light scattering (s.e.c./MALLS), low shear intrinsic viscosity and circular dichroism measurements were performed for elucidating the size and conformation changes associated with the temperature-induced denaturation and renaturation of native xanthan in different salt conditions (0.01 M and 0.1 M). Upon heating, at temperatures above the order—disorder transition temperature (Tm) the denaturation of the native ordered conformation occurs with a reduction of Mw by a factor of roughly two therefore indicating a double strand conformation for the native form. The molecular weight has been found invariant after renaturation on cooling that favours the hypothesis that the restoration of the ordered form of xanthan takes place through the same molecule. The most probable conformation for the renatured form of xanthan is that of an antiparallel double stranded structure consisting of one such chain folded as a hairpin loop.

Associative behaviour of hydrophobically modified carboxymethylpullulan derivatives

Hydrophobically modified carboxymethylpullulan (HMCMP) samples were obtained by reaction of small amounts of C16 alkylamine on carboxylic groups of the corresponding polyacid. The molar contents of alkyl chains ranged from 1.3 to 6.8% with respect to the anhydroglucose units (AGU) and the degree of substitution (DS) of carboxylic groups varied from 0.76 to 0.84. Solution properties of the sodium salt of HMCMPs were studied mainly by viscometric and size-exclusion chromatography/light-scattering methods. The low-shear viscosity of modified pullulans in 0.1 M NaCl solutions drastically increases with the hydrophobic content and polymer concentrations and the 6.8% modified sample has a quite pseudoplastic behaviour. These data showed that the polymers aggregated intermolecularly and displayed a compact globular structure in dilute solution. Furthermore, addition of NaCl or ethanol induced a decrease in viscosity although the molecular weights remained approximately constant. These results are consistent with a collapse of the polysaccharide aggregates.

Solution properties of gum exudates from Sterculia urens (Karaya gum)

Abstract Dilute solution properties of Karaya gum from Sterculia urens were studied using size-exclusion chromatography, static and dynamic light scattering and viscosity experiments in 0·1 m aq. NaCl. Solubility in water was found to be strongly dependent on the degree of acetylation. The native acetylated Karaya gum assumes a rather compact and branched conformation in aqueous solution, as evidenced by the low values of power-law exponents. In contrast, the fully deacetylated Karaya gum assumes a more expanded conformation and behaves as a random coil.

Salt-induced extension and dissociation of a native double-stranded xanthan

Abstract This study shows that xanthan molecules at room temperature may assume at least three different conformations in 0.1 m NaCl aqueous solutions in which the local structure is ordered: (1) the native compact double helix, (2) the extended double helix, and (3) the extended single helix. Experiments including viscosity, low-angle light scattering and optical rotation measurements have been carried out with a fully pyruvated and fully acetylated native laboratory sample supplied as fermentation broth. Two major conformation changes of the native double helix which were found irreversible in our experimental conditions can be induced by treatments at low ionic strength. After treatment in 10−4 m NaCl, xanthan is still a double helix in 10−1 m NaCl, but the backbone of each strand has been extended. After the sample has been in 10−5 m NaCl, the double helix has been dissociated and a single helix sample is obtained. Thus, the denaturing of xanthan is a two-step process. The first step consists of the extension of the two chains inside the double helix, and the second is a dissociation of the native double strand.

Aggregation of amphiphilic pullulan derivatives evidenced by on-line flow field flow fractionation/multi-angle laser light scattering.

Size-exclusion chromatography (SEC) is a useful steric separation technique for the analysis of water-soluble polysaccharides in aqueous solution. However, in the case of amphiphilic derivatives, the usefulness is limited because of interactions between hydrophobic segments and the stationary phase. Alkyl-bearing pullulans differing from the extent and the length of alkyl groups were characterized using flow-field flow fractionation with on-line coupling multi-angle laser light scattering (F4/MALLS). Comparison of SEC and F4 is presented and the interest of F4 in the field of amphiphilic derivatives is demonstrated.

Associative pullulan gels and their interaction with biological active substances.

This paper studies the synthesis and properties of anionic and/or amphiphilic pullulan microparticles crosslinked with epichlorohydrine or with sodium trimethaphosphate. The polysaccharide gels were physicochemically characterized and their interaction with enzymes (lysozyme) was studied with the aim to appreciate the performances for separation/purification/immobilization of the enzymes or controlled release drug systems.

Adsorption of cellulose derivatives onto montmorillonite: a SEC–MALLS study of molar masses influence

Abstract Adsorption properties of two commercial neutral cellulose derivatives: hydroxyethylcellulose (HEC) and hydrophobically modified hydroxyethylcellulose (HMHEC) onto montmorillonite were investigated in pure water and in salt solution. Regardless of the polymer, the adsorption onto clay is always larger in pure water than in salt solutions. In other respects, adsorption of the associative HMHEC is always slightly enhanced in comparison with its parent HEC. For both polymers, only simple layer type of adsorption is evidenced (Scatchard linearisation). Finally, a SEC–MALLS study conducted with HEC has shown that adsorption on clay occurs preferentially for the lower molar masses. The adsorbed amount of HEC on clay is larger for the lower molar masses.