Pressure Cell Assisted Solution Characterization of Polysaccharides. 1. Guar Gum

Abstract

To reduce time-dependent aggregation phenomena and achieve true "molecular" solution, the "pressure cell" solubilization method of Vorwerg and co-workers was applied to solutions of guar galactomannans (three samples of different molecular weights), using various heating, time, and pressure profiles. Physicochemical characterization of the guar samples before and after pressure cell treatment included measurements of intrinsic viscosity [eta] by capillary viscometry and M(w) and radius of gyration from size exclusion chromatography coupled to multiangle laser light scattering (SEC/MALLS). Heating the guar solutions (100-160 degrees C) without pressurization produced chain degradation with [eta] and M(w) values being reduced significantly, whereas this effect was reduced substantially for samples subject to initial pressurization ( approximately 5-10 bar). The constants in the Mark-Houwink-Sakurada equation, relating [eta] and M(w) were established and the characteristic ratio C(infinity) and chain persistence length L(p) were calculated using both the Burchard-Stockmayer-Fixman (BSF) method for flexible and semiflexible chains and the Hearst method more appropriate for stiffened chains. Definitive conclusions can now be drawn on the flexibility of the guar chain backbone, with L(p) approximately 4 nm from the BSF plot, in good agreement with previously published work using such geometric methods. This contrasts with the higher values obtained from extrapolation of data for polyelectrolytes with a similar backbone geometry, such as sodium carboxymethyl cellulose, to "infinite" ionic strength.

Global hydrodynamic analysis of the molecular flexibility of galactomannans

“…We can see that the persistence lengths ( Table 2) of ~ 8 -9 nm which is in good agreement with the results from the Hearst, Bohdanecky and Yamakawa-Fujii approaches in our previous analysis (Picout et al, 2001;2002;Patel et al, 2006) and with computer modelled data for hypothetical galactomannan molecules of ~ 8 -12 nm (Petkowitz, Reicher & Mazeau, 1998). ranging from blue (∆ = 0.13) to red (∆ = 1.00).…”

“…ranging from blue (∆ = 0.13) to red (∆ = 1.00). We can see that persistence lengths (Table 3) are in the range 7 -10 nm and in good agreement with those calculated when the mass per unit length was fixed and with the results from the Hearst, Bohdanecky and Yamakawa-Fujii approaches in our previous analyses (Picout et al, 2001;2002;Patel et al, 2006) and with the computer modelled data of Petkowitz et al (1998).…”

“…Whilst giving extra confidence in the values for the persistence length obtained the global method has not given results too different from the intrinsic viscosity and sedimentation coefficient data that had previously been used independently (Picout et al, 2001;2002;Patel et al, 2006). The combined analysis method Multi-HYDFIT (Ortega & García de la Torre, 2007) has been shown to give unbiased estimates for both, the persistence length, L p and mass unit length, M L .…”

“…It therefore provides objective criteria for whether, or not, a particular data set of experimental data ([η] versus M w for example) is consistent with the other data. We have therefore decided to interpret further our previous data (Picout et al, 2001;Picout et al, 2002;Patel et al, 2006) in the light of this new approach.…”

On hydrodynamic methods for the analysis of the sizes and shapes of polysaccharides in dilute solution: A short review

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