TEMPO-Mediated Oxidation of Pullulan and Influence of Ionic Strength and Linear Charge Density on the Dimensions of the Obtained Polyelectrolyte Chains

Abstract

The applied pH during the TEMPO-mediated (2,2,6,6-tetramethylpiperidine-1-oxyl) oxidation of the polysaccharide pullulan has a substantial influence on the molar mass distribution of the products. The least degradation was found in the pH range 9.2-9.7 and especially at higher pH, significant degradation occurs due to β-elimination. Four samples were prepared at pH 9.4 with different degrees of oxidation and the influence of the charge parameter ξ on the rms radius of gyration at various ionic strengths (Cs) was determined with size exclusion chromatography (SEC) using a multiangle laser light scattering (MALLS) detection system. Experimental values were compared to values obtained with the wormlike chain model for polyelectrolytes in combination with excluded-volume theory. The ionic strength-linear charge density dependence of the rms radius of gyration is quite accurately described, whereas the prediction of its absolute value is more problematic for lack of a quantitative description of solvent quality. However, very reasonable values for the rms radii of gyration are obtained using eq 15, originally derived as a scaling relation. Furthermore, it is shown that there is no discrepancy between the apparent persistence length, proportional to ξ/Cs 1/2 , and the real persistence length, proportional to ξ 2 /Cs, when excluded-volume effects are accounted for.

Oxidation and N‐Alkylation at the C‐6 Position of Galactomannan Extracted from Caesalpinia ferrea var. ferrea Seeds

“…[14] By NaBr/NaClO presence, the reagent TEMPO generates in situ the N-oxoammonium ion, responsible to primary alcohol oxidation in high conversion rate. [7,15] The proposed mechanism of modifications was based on previous reports in the literature. [8,13,15] Under alkaline conditions, after a hydrogen abstraction by bromide an alcoholic substrate and an N-oxoammonium ion combine through a nucleophilic addition followed by a cyclic elimination, generating acid groups at the end of reaction (Figure 3a).…”

“…[8,13,15] Under alkaline conditions, after a hydrogen abstraction by bromide an alcoholic substrate and an N-oxoammonium ion combine through a nucleophilic addition followed by a cyclic elimination, generating acid groups at the end of reaction (Figure 3a). [7,16] In the same conditions but without NaBr, the N-alkylation reaction was performed in two successive steps (Figure 3b). First, an OH -ion abstracts a hydrogen atom from the amine and the nitrogen receives a lone pair of electrons; then, during the formation of aldehydic groups on GM, the addition of the hydrophobic chain occurs by the reductive amination of dodecylamine via NCBH A number of 13 C signals in the NMR spectra of the derivatives ( Figure 5) were assigned and are shown in Table 2.…”

“…Chemical and/or enzymatic modifications of polysaccharides, in general, are useful for altering their physicochemicalfunctional properties for diversified applications, for example, certain types of derivatives can be used to improve drug-release specificity. [5] Nooy et al [6,7] described a derivatisation method via the selective oxidation of the primary alcohols found in polysaccharides using the 2,2,6,6-tetramethylpiperidine-1-oxyl reagent (TEMPO) in catalytic concentration and a hypochlorite/bromide system.…”

High Temperature TEMPO Oxidation in a Heterogeneous Reaction System: An Investigation of Reaction Kinetics, Pulp Properties, and Disintegration Behavior

“…The trends seen in the data for DP V are to be expected because a higher temperature and a higher dosage of sodium hypochlorite should result in more extensive degradation of the cellulose polymers. This behavior may, at least partly, be explained by β-elimination reactions that occur during TEMPO oxidation at alkaline conditions (de Nooy et al 1996;Fujisawa et al 2010). Some additional degradation in DP V had probably occurred during the analytical procedure, see experimental section.…”

Influences of Integrated Tempo-Mediated Oxidation and Recycling on the Properties of TMP Fibers

“…It is understood that cellulose chain scissions contribute to a loss of zero-span tensile strength that is often observed when fibers are recycled (Klungness et al 1982). The TEMPO-mediated oxidation also had an adverse impact on the zero span tensile strength due to the side reactions during TEMPO-mediated oxidation (Ma et al 2001), in particular the β-elimination of cellulose (De Nooy et al 1996;Potthast et al 2007), which was also evident when R 0 was compared with O-R 0, (Fig. 6).…”