Proton Magnetic Resonance Studies on Polysaccharide Derivatives

Abstract

Proton magnetic resonance studies on synthetic polymers such as polystyrene, PVC, poly-K-methylstyrene are generally complicated by the broad signals of the individual protons. The line broadening arises mainly from conformative and configurative factors, and in the case of copolymers from composition factors. Once a degree of polymerization of 20 has been exceeded, the 1H-NMR spectra of these polymers remain almost unchanged and differ considerably from the spectra of the monomers.The acetyl and benzoyl derivatives of polysaccharides exhibit a quite different behavior. We have conducted measurements on a large number of different tri-0-acetyl-and tri-0-benzoylpolysaccharides having degrees of polymerization from about 30 to 3000 (molecular weights ranging from 9000 to 900000) in CDCI3 with the aid of a 220 MHz spectrometer. shows the IH-NMR spectrum of a 2,3,6-tri-O-acetylcellulose having a degree of polymerization of ca. 200 (mol. wt. ca. 60000).The signals of all seven ring protons are seen individually between 6 = 3.5 and 5 ppm alongside the separate signals belonging to the three methyl groups of the acyl substituents in positions 2, 3, and 6. The width of the lines is only about double that occurring in the monosubstituted monosaccharide. The signals can therefore be assigned to the various ring protons by means of the spin-spin coupling constants, and the configuration of the substituents and the nature of the glycosidic bond between the monomers can be determined unequivocally. The coupling constant Jlz = 8 Hz corresponds t o an axial-axial coupling between H(1) and H (2). i.e. H (1) is in an axial position; it therefore follows that the monomer units are joined by @-glycosidic linkages. The configuration of the monomer units corresponds to that of glucose since, according to the magnitude of the coupling constants, the protons on C-2, C-3, and C-4 are axial. The spectrum is thus in accord with the generally recognized structure of cellulose.We also hope to be able to assign the signals of the acetylsubstituents in order that we may use this method, e.g., to elucidate the structure of partially acetylated celluloses possessing industrial interest.As a second example we shall give the 220-MHz spectrum of 2,3,6-tri-0-acetylamyIose having a degree of polymerization of CCI. 100 (mol. wt. cu. 30000) together with assignments (see Figure is only about 3 Hz. This value, which was deduced from the splitting of the H(l) signal, corresponds to a coupling between axial and equatorial protons. Since the magnitude of the coupling constant Jz3 reveals that the proton on C-2 is in the axial position, H(1) must b e equatorial. The magnitudes of the other coupling constants indicate that the protons on C-3 and C-4 are axial. The methyl signals of the three 0-acetyl groups occur separately as in tri-0-acetylcellulose; the signals have not yet been assigned. Thus the structure hitherto assumed for amylose -a-gtycosidicalIy linked glucose unitsis confirmed by the 1H-NMR spectrum.We obtained IH-NMR spectra showing the same e...

Cellulose alkyl ester/vinyl polymer blends: effects of butyryl substitution and intramolecular copolymer composition on the miscibility

“…After a reaction time-period of 5 -25 h, the product CB was precipitated in deionized water and then washed with distilled water, methanol, and ethanol to remove thoroughly residual DMAc, LiCl, and other reagents. Six samples of CB were prepared to have mutually different degrees of butyryl substitution; the DS values were 2.11, 2.41, 2.54, 2.67, 2.85, and 2.94, determined by 1 H NMR measurements (Friebolin et al 1969;Ho et al 1972).…”

Biosynthèse de cellulose bacterienne à partir de glucose sélectivement deuterié en position 6: Étude par RMN

“…En effet, dans 1~ spcctre B 250 MHz tous les protons du cycle sont s&par& et peuvent dtre do&s approximativement par simple intigration. Leur identification a CtC faite par Friebolin et Kcilich [9] qui cependant n'ont pas dktermirk les protons 6 pro-R et 6 pro-S. L'exptkience de biosynthke rCalis@e g partir de glucose monodeutCriC nous a permis une identification non ambiguti de ces deux protons (voir plus loin).…”

Determination of Distribution of Sodium Sulfate Group in Glucopyranose Units of Sodium Cellulose Sulfate by 13C and 1H Nuclear Magnetic Resonance Analysis

“…Peak assignment was performed by a mutual comparison of a peak areas, and a comparison of the spectrum with that of cellulose acetate. 5 The proton signal at the C3 position, which was sulfated, appears at the lowest magnetic field strength (4.97 ppm). Side band from HOD may be included to a small degree in peaks 3 and 1.…”