Hyun-Joung Kwon

Study of dielectric relaxations of anhydrous trehalose and maltose glasses.

We investigated the frequency dependent dielectric relaxation behaviors of anhydrous trehalose and maltose glasses in the temperature range which covers a supercooled and glassy states. In addition to the α-, Johari-Goldstein (JG) β-, and γ-relaxations in a typical glass forming system, we observed an extra relaxation process between JG β- and γ-relaxations in the dielectric loss spectra. We found that the unknown extra relaxation is a unique property of disaccharide which might originate from the intramolecular motion of flexible glycosidic bond. We also found that the temperature dependence of the JG β-relaxation time changes at 0.95T(g) and it might be universal.

Temperature dependent vibrational modes of glycosidic bond in disaccharide sugars.

We studied the temperature dependent vibrational modes of the glycosidic bond in trehalose, sucrose, and maltose at wavenumbers ranging from 1000 to 1200 cm(-1). We found that the slope of temperature dependent Raman shifts of the glycosidic bond in trehalose and sucrose changed at temperatures around 120 degrees C, indicating a bond length or a bond angle (dihedral and torsional angles) change. However, we did not observe any slope change in maltose because the melting temperature of maltose is very close to 120 degrees C. We also found, at temperatures below 120 degrees C, that Raman shifts of the vibrational modes of the glycosidic bond in trehalose showed the strongest temperature dependence among the three disaccharides.

Nano‐Particle Size Measurement by Photon Correlation Spectroscopy and Dielectric Loss Spectroscopy

The size of nano‐particle was measured by using photon correlation spectroscopy and dielectric loss spectroscopy methods. The size was estimated from the relaxation time of colloidal particles by using the Stock‐Einstein relation. The results obtained from two different methods were in good agreements indicating that compare to the conventional scanning probe microscopy method, the photon correlation spectroscopy and dielectric loss spectroscopy are more convenient methods to measure the particle size.

The Liquid Glass Transition in Sugars and Sugar Mixtures

The liquid‐glass transition in sugars and sugar mixtures was studied with calorimetry, Brillouin scattering, and dielectric spectroscopy. Sugars are particular interest among other glass forming materials because sugars are main constitution of the biological system and sugar glasses play an important role in preservation and protection of biological cells. We studied a number of sugars and sugar mixtures including glucose, galactose, sucrose, maltose, trehalose, glucose/sucrose, sucrose/trehalose, using calorimetry (DTA and DSC), Brillouin scattering, and dielectric spectroscopy. We found the following: (1) Brillouin scattering technique can be used to determine the glass transition temperature. (2) In sugar mixtures, the volume compression effect from the molecule size and shape played an important role in the glass transition temperature. (3) The origin of the secondary relaxation in glucose‐water mixtures maybe relate to the rotation‐translation coupling constant in the schematic mode coupling theory.

Relaxation processes in disaccharide sugar glasses

We represented relaxation processes of disaccharide sugars (anhydrous trehalose and maltose) in supercooled and glassy states by using several spectroscopy techniques which include a broadband dielectric loss spectroscopy, photon correlation spectroscopy and X-ray diffraction (Retvield analysis) methods which are powerful tools to measure the dynamics in glass forming materials. In a dielectric loss spectroscopy study, we found that anhydrous trehalose and maltose glasses have an extra relaxation process besides α-, JG β- and γ-relaxations which could be related to a unique property of glycoside bond in disaccharides. In photon correlation spectroscopy study, we found an interesting compressed exponential relaxation at temperatures above 140°C. The q−1 dependence of its relaxation time corresponds to an ultraslow ballistic motion due to the local structure rearrangements. In the same temperature range, we found the glycosidic bond structure changes in trehalose molecule from the Raman and the Retvield X-r...

A Study of the Secondary Relaxation in Galactose‐Water Mixtures

We studied the secondary relaxation in galactose‐water mixtures by analyzing the dielectric loss spectra with two different fitting methods. The first method was the free fit without any constraint and the second method was the fit with the coupling relation in coupling model (CM) [1, 2, 3]. The behavior of the secondary relaxation process were very similar to that of the secondary relaxation process with changing the rotational‐traslational (RT) coupling constant in the schematic mode coupling theory (MCT) [4, 5]. The secondary relaxation times (τJG) obtained by the constrained fit contain a large uncertainty and were consistent with τsec within the experimental errors. We also found that the fitting quality of free fit was better.

Effects of Disaccharide Sugars on Dynamics of Water Molecules: Dynamic Light Scattering and Dielectric Loss Spectroscopy Studies

We studied the effects of disaccharide sugars (trehalose, sucrose, and maltose) on the dynamics of water molecules in sugar‐water mixtures. We measured the acoustic phonons in sugar‐water mixtures with different sugar contents by using a Sandercock Tandem 6‐pass Febry‐Petor interferometer and found that the Brillouin peak positions shifted to higher frequencies as the sugar concentration increased. We also measured the dielectric loss of hydrogen bonds in water molecules in sugar‐water mixtures by using a Network analyzer with different sugar contents. The loss peak position in the dielectric loss spectra moved to lower frequencies as the sugar contents increased. The trehalose‐water mixture showed the largest Brillouin peak shift and relaxation time change with increasing sugar content among three disaccharides indicating that the effect of trehalose on the dynamics of water molecules is the strongest. This unique property of trehalose sugar might be the origin of the superior bio‐protection ability of t...

A Study of α‐Relaxations in Trehalose Super Cooled Liquids

We measured the α‐relaxations in trehalose super cooled liquids by using photon correlation spectroscopy (PCS). The α‐relaxations of trehalose super cooled liquids showed a crossover from stretched to compressed‐exponential relaxations as the temperature increased [1]. From the Raman scattering measurements, we found that the unusual compressed‐exponential relaxation in trehalose super cooled liquids may be caused by the change of glycosidic linkage structure in trehalose molecule.

Dehydration Processes of Sugar Glasses and Crystals

The dehydration processes of sugar glasses and sugar crystals were studied by using Thermogravimetry — Differential Thermal Analysis method. We used three monosaccharide sugars (fructose, galactose, and glucose) and three disaccharide sugars (sucrose, maltose and trehalose). It was found that a trehalose showed different dehydration process compared to the other sugars. The amount of mass reductions in sugar glasses is larger than that in sugar crystals. However, in the case of trehalose, the amount of mass reduction in trehalose glasses is smaller than that in trehalose crystals. It seems to be possible that this unique dehydration property of trehalose glasses maybe relate to the cell protection ability during an anhydrobiosis process.