Optical rotatory dispersion of water-soluble cellulose derivatives

Abstract

547.458.81 Dilute solutions of water-soluble cellulose esters and also solutions of model compounds -glucose and cellobiose -have been investigated. It has been shown that a definite influence on optical rotatory dispersion is exerted by the conformational difference of the pyranose rings of cellulose arising when the hydroxy groups in the macromolecule are partially replaced by functional groups of different natures.Optical activity characterizing features of the spatial structure of simple molecules was known even during the last century from the work of J. Biot, L. Pasteur, J. H. Van't-Hoff, A. M. Butlerov, and others. It is also known that features of the spatial structure of molecules determine various properties of a substance and play a major role in processes of synthesis.This question has been little studied as applied to cellulose and its derivatives. In the dissertation [1], which gathers together practically all the material on the optical activity of cellulose and celhilose acetate, there is no information on the connection of optical activity with the conditions of synthesis, the properties of the polymer, and the quality of the products. There are no clear ideas on the role of the functional groups of celhilose esters in the optical activities of their solutions.In order to elucidate the causes of the change in the optical activity of cellulose derivatives On the replacement of certain functional groups by others in the pyranose rings of the cellulose macromolecule, we have studied by the method of optical rotatory dispersion (ORD) dilute solutions of cellulose acetates (CAs) with different degrees of substitution, cellulose aminoacetate, and cellulose acetophthalate, and also solutions of model compounds -t~-ghicose and cellobiose.In this connection, we investigated solutions in acetic acid of CAs with various degrees of substitution obtained by the successive saponification of cellulose triacetate at temperatures of 59 and 20°C.The results of the optical rotatory dispersion investigations are given in Table 1, from which it can be seen that CAs with the same qualitative and quantitative compositions of the macromolecules can have negative or positive values of the ORD, depending on the conditions of synthesis. For solutions of CAs obtained at a low saponification temperature -20°C -a transition is observed from the negative to the positive region of optical rotatory dispersion. It can also be seen from Table 1 that the samples containing 54-56% of bound acetic acid obtained at 20°C were dextrorotatory, while those obtained at 59°C were levorotatory.In order to elucidate the factors causing CAs to change from levorotatory to dextrorotatory in the process of saponification, we studied model compounds of one functional composition -glucose and cellobiose -in acetic acid (Table 2). A difference in the optical activities of substances with one functional composition can be explained by a change in the conformational state of the pyranose rings and by rotational isomerism. However, rotational isomeris...

Spectral shifts in the properties of a periodic multilayered stack due to isotropic chiral layers

“…Our focus on spectroscopic shifts at the boundary of the visible and the ultraviolet regimes is in accord with the fact that the chirality of many isotropic materials is evident in both regimes. Examples include suspensions of poly-L-glutamic acid [25], solutions of glucose [26] and several derivatives of cellulose [27], and chiral barbituric acid [28]. Flooding a multilayered stack containing void regions alternating with metallic layers with isotropic chiral fluids is a way to dynamically blueshift the zero-crossing of Re ε .…”