Dielectric Studies on Mobility of the Glycosidic Linkage in Seven Disaccharides

Abstract

Isobaric dielectric relaxation measurements were performed on seven chosen disaccharides. For five of them, i.e., sucrose, maltose, trehalose, lactulose, and leucrose, we were able to observe the temperature evolution of the structural relaxation process. In the case of the other disaccharides studied (lactose and cellobiose), it was impossible to obtain such information because of the large contribution of the dc conductivity and polarization of the capacitor plates to the imaginary and real part of the complex permittivity, respectively. On the other hand, in the glassy state, two secondary relaxations have been identified in the dielectric spectra of all investigated carbohydrates. The faster one (gamma) is a common characteristic feature of the entire sugar family (mono-, di-, oligo-, and polysaccharide). The molecular origin of this process is still not unambiguously identified but is expected to involve intramolecular degrees of freedom as inferred from insensitivity of its relaxation time to pressure found in some monosaccharides (fructose and ribose). The slower one (labeled beta) was recently identified to be intermolecular in origin (i.e., a Johari-Goldstein (JG) beta-relaxation), involving twisting motion of the monosugar rings around the glycosidic bond. The activation energies and dielectric strengths for the beta-relaxation determined herein provide us valuable information about the flexibility of the glycosidic bond and the mobility of this particular linkage in the disaccharides studied. In turn, this information is essential for the control of the diffusivity of drugs or water entrapped in the sugar matrix.

Comment on “Study of dielectric relaxations of anhydrous trehalose and maltose glasses” [J. Chem. Phys. 134, 014508 (2011)]

“…Four relaxation processes were identified in dielectric spectra of both the saccharides. The slower one was identified as a structural relaxation process; the next one, not observed by the others, was assigned as Johari-Goldstein (JG) β-relaxation, while the last two secondary modes were of the same nature as found by Kaminski et al 2 Kwon et al 1 demonstrated that both in trehalose and maltose it is possible to follow dynamics of structural relaxation process even in the vicinity of the glass transition temperature. From the dielectric loss spectra presented in Figs.…”

“…At this place, it should be also explained why this process was visible in loss spectra of trehalose and maltose shown by Kwon et al, 1 while it is absent in dielectric spectra reported by Kaminski et al 2 and De Gusseme et al 4 To address this question, we would like to refer the readers to papers by Paluch et al 7 and Richert 9, 10 who showed that the Debye-like process can be generated in loss spectra as a result of using blocking electrode technique. As discussed in Refs.…”

“…4 by Kaminski et al 2 and that obtained by Kwon et al 1 and constructed the relaxation map, as shown in Fig. 1.…”

Dielectric relaxation of aqueous solutions of maltotriose

“…On the other hand, β-modes for both solutions have similar dependences below T g . Simple carbohydrate solutions show a relatively large peak in the dielectric relaxation curve derived from the large dipole moment of the hydroxy group [6][7][8][9][10][11]. As the water content is higher, the dielectric strengths for α-mode and β-mode become larger, indicating that the water molecules are contributed to these relaxation modes.…”

“…However, the investigations for the molecular motions have not been so developed compared with other biopolymers, such as proteins, because of their less ordered structures, except fundamental saccharides, such as glucose, sucrose and so on [6][7][8][9][10][11]. Most of polysaccharides exist in biological systems, where the systems contain abundant water molecules as a solvent.…”