Chain mobility of pectin in aqueous solutions studied by the fluorescence depolarization method conducive

The chain mobility of pectin, an anionic polysaccharide containing a carboxyl group in each of its monosaccharide units, in aqueous solutions has been examined by the fluorescence depolarization method. Carboxyl groups of pectin were covalently labeled in part with anthryl groups as the fluorescent probe, and the rotational relaxation time of the probe was estimated as the measure of the mobility of the pectin chain. The activation energy could be estimated from the temperature dependence of the relaxation time and was found to be 1.5 kcal/mol, suggesting the stiff nature of this anionic polysaccharide chain. It is noteworthy that the addition of NaCl to aqueous solutions of up to I M does not affect the chain mobility of pectin. The pH dependence of the chain mobility for pectin is clearly different from that for gellan, an anionic polysaccharide containing a carboxyl group in four monosaccharide units. It is proposed that the intramolecular electrostatic repulsions of anionic polysaccharides have two opposing effects with respect to chain mobility: the long-range effect, which increases the degree of chain expansion, enhances the chain motion, and the short-range effect, which acts as the steric hindrance for the conformational transition, decreases the chain mobility.