Chemische synthese verzweigter Polysaccharide, 8. Vergleichende struckturuntersuchungen an amylose‐ und Cellulosederivaten mit verschiedenen Substituenten an C‐6 durch optische Rotationsdispersion und circular‐dichroismus

Abstract

AbstractCarbanilated and tritylated derivatives of amylose and cellulose previously studied by light scattering were further characterized by measurement of optical rotatory dispersion (ORD) and circular dichroism (CD). No anomalous ORD and only a weak CD was found for 6‐tritylamylose in 1,4‐dioxane, indicating a widely unordered structure which is in accordance with the low viscosity of the compound. In comparison with the other carbanilated derivatives having substituents in C‐6 position, i.e. trityl‐, carbanilyl‐ or glucosyl groups, 2,3‐dicarbanilylamylose is distinguished by an especially high Cotton effect. This result suggests a helical chain,— clearly visible by excition splitting—, that may adopt a more regular orientation in case of free C‐6 hydroxyl groups, whereas trityl‐, carbanilyl‐, and glucosyl groups almost equally will contribute to a lower state of orientation. Conversely in the cellulose derivatives a clear steric dependence on the size of the C‐6 substituent was found. The increase of the Cotton effect observed for the bulky trityl group may arise from the β(1 → 4) linkage that causes an alternating or syndiotactic like structure in cellulose, which is more sensitive to restrictions of the free rotation due to steric effect. In addition, viscosity and optical rotation in NMP and 1,4‐dioxane were measured in the range of 20 to 70°C. An unusual behaviour is observed for 6‐trityl‐2,3‐dicarbanilylamylose in NMP indicating a conformation transition near 45°C, and is discussed in connection with the findings from light scattering measurements.