Characterization of the Micelle Formed by a Hydrophobically Modified Pullulan in Aqueous Solution: Size Exclusion Chromatography

Abstract

Size exclusion chromatography equipped with a multi-angle, light-scattering online detector (SEC-MALS) measurements were carried out on a hydrophobically modified pullulan (PUL-OSA) with degrees of substitution (DS) of 0.14, 0.2, and 0.3 in 0.01 M aqueous NaCl to obtain the degree of polymerization (N0) dependence of the radius of gyration (⟨S2⟩1/2) for PUL-OSA in the aqueous NaCl. The result was consistent with the loose flower necklace model proposed in a previous study, and the increase in the chain size with introducing OSA groups was explained by the backbone stiffness of the loose flower necklace formed by PUL-OSA. For PUL-OSA samples with DS = 0.2 and 0.3, ⟨S2⟩1/2 obtained by SEC-MALS in a high N0 region deviated downward from ⟨S2⟩1/2 expected by the loose flower necklace model. This deviation came from a tiny amount of the aggregating component of PUL-OSA, taking a branched architecture composed of loose flower necklaces. Although the aggregating component of PUL-OSA was also detected by previous small angle X-ray scattering measurements, its conformation was revealed in this study by SEC-MALS.

Micellar structure of hydrophobically modified polysaccharides in aqueous solution

“…for micelles of a PUL-OSA sample with DS = 0.2, synthesized from a polydisperse PUL (c) sample. 22 While data points at N0 < 4000 almost obey the solid curve for PUL, being consistent with the SAXS results, 20 those at N0 < 4000 deviate downward from the curve, which may correspond to the higher aggregates of the PUL-OSA micelle detected also by SAXS. 20 Just like the g factor for branched polymers, we define the shrinking factors g′S for the radius of gyration and g′H for the hydrodynamic radius due to the micellization by the ratio of the radius of gyration (or the hydrodynamic radius) for the micelle to that for the linear chain with the same N0 as the micelle and DS = 0 in the same solvent condition.…”

“…Only recently, Kameyama et al 19 and Yang and Sato [20][21][22] investigated micellar structures of an amphiphilic amylose derivate (C12CMA) and hydrophobically modified pullulan, respectively.…”