Molecular mobility of sorbitol and maltitol: A ^13C NMR and molecular dynamics approach

Abstract

Molecular mobility in two similar organic glass formers, namely sorbitol and maltitol, is studied in order to understand their difference in the cross-over between α and β relaxations, far above their respective glass transition temperatures. In this goal, the individual mobility of each carbon atom of the 6 carbon chain present both in sorbitol and maltitol is studied by means of 13 C nuclear magnetic resonance and molecular dynamics simulations. Both techniques imply that the mobility of carbons located at the end of the 6 carbon chain is greater than that of any other carbon of this chain and that the difference in carbon mobility is greater within the sorbitol moiety of maltitol than in sorbitol. The relaxation time obtained by magnetic resonance for carbons at the end of the 6 carbon chain is related to the β relaxation time and the one of carbons in the middle of the chain is in relation with the value of the α relaxation time. This result may suggest that the merging between the α and β relaxation processes in both sugars would be related to the decrease of the differences in mobility between the atoms of 6 carbon chain.

Molecular dynamics studies of the conformation of sorbitol

“…More recently, Sixou et al . have shown that the C-1–H bond vectors in sorbitol reorient faster than the C-4–H bond vectors at T = 400 K, in agreement with 13 C NMR measurements 13,14. These workers concluded that the main contribution to the C-1–H reorientation is associated with local conformational transitions.…”

“…Several types of experimental data exist for comparison purposes. These include crystal structures for sorbitol,10–12,17 13 C NMR relaxation times for pure (neat) liquid sorbitol,13,14 and additional 1 C NMR data concerning the populations of conformers in aqueous solution 18–20…”

Local Mobility in Amorphous Pharmaceuticals—Characterization and Implications on Stability

“…116 The molecular dynamics in sorbitol and maltitol were compared using 13 C NMR in order to explain the differences in the crossover between the a-and the b-relaxations above their respective T g values. 117 Studies correlating chemical stability with local mobility have been carried out by Yoshioka et al 8,9,97 as described earlier.…”

Two-order-parameter model of the liquid–glass transition. III. Universal patterns of relaxations in glass-forming liquids

“…This seems to be supported by the existence of T cross above T g , or the Arrhenius behavior even above T g , for supercooled liquids (see, e.g., Refs. [91][92][93][94][95][96][97]) and also for plastic crystals [98]. However, the data analysis in the crossover region is not easy and further studies are necessary to settle this problem.…”