Amylose optical rotation in some mixed solvent systems

Abstract

AbstractThis paper extends a previous study in which a discontinuity in the specific rotation of open chain α‐l,4‐linked glucopyranosides in the water–dimethyl sulfoxide (H2O–DMSO) system was attributed to a symmetry change about a polymer chain segment. Optical rotation of amylose, cyclohexamylose, methyl β‐maltoside, and dextran was measured in the following mixed solvent systems: formamide–dimethyl sulfoxide (F‐DMSO), ethylenediamine–dimethyl sulfoxide (E–DMSO), and hexamethylphosphoramide–dimethyl sulfoxide (HMPA–DMSO). Refractive index measurements were used in an attempt to detect hydrogen bonding between solvent components. The specific rotation of amylose corrected for variation in refractive index (CSR), as a function of solvent composition, showed a discontinuity at solvent compositions corresponding to about 1 mole F to 2 moles DMSO and to 1 mole E to at least 8 moles DMSO. A discontinuity in the CSR function of amylose in the H2O‐DMSO mixed solvent that occurs at 25°C is not observed at 70°C. The CSR function of methyl‐β‐maltoside exhibits a discontinuity in solvent composition corresponding to mole ratios between 2F–DMSO and 3F–DMSO. Present results indicate that an amylose chain segment may undergo a symmetry change in solvent compositions corresponding to mole ratios between F–DMSO and F–2DMSO. Our CSR measurements of amylose and model compounds in E–DMSO and HMPA–DMSO do not permit us to distinguish between possible changes in amylose chain segment symmetry and solvent interactions that could affect symmetry properties of the glucopyranose ring.