Temperature Scanning FTIR Analysis of Hydrogen Bonding States of Various Saccharides in Amorphous Matrixes below and above Their Glass Transition Temperatures

Abstract

Temperature scanning Fourier transform infrared, TS-FTIR, spectroscopy of various amorphous sugar matrixes was conducted to investigate the relationship between the glass transition temperature, T(g), of an amorphous sugar matrix and the nature of the hydrogen bonds in the matrix. An amorphous sugar matrix was prepared by air-drying an aqueous solution of sugar, and the degree of formation of hydrogen bonds in the matrix was evaluated at different temperatures using the peak positions of the IR band corresponding to the O-H stretching vibration at around 3400 cm(-1). The T(g) value increased with increasing peak position of the O-H stretching vibration at T(g) and were correlated reasonably well with the magnitude of the peak shift by the temperature increase (from 25 degrees C) to the T(g) value. This demonstrates that the amorphous sugar matrix, in which the segments are fixed by fewer hydrogen bonds, has a higher thermal resistance. The glycosidic linkage largely contributes to the restriction of the segments, pyranose ring, rather than a hydrogen bond. As the degree of polymerization of pyranose rings increases, the degree of hydrogen bond formation needed to hold the matrix in a fixed position decreases. However, the magnitude of the restriction of pyranose rings by a glycosidic linkage changes depending on the type: the restrictions imposed by alpha-1,1 and -1,6 glycosidic linkages are the tightest and most flexible of all of the types of glycosidic linkages, respectively.

Temperature scanning FTIR analysis of secondary structures of proteins embedded in amorphous sugar matrix

“…The temperature-scanning FTIR analyses of amorphous sugar samples 12,23 have demonstrated that increasing temperature decreases the degree of hydrogen-bond formation between sugar molecules, which abruptly becomes significant at the T g . Similar events may occur for sugar-protein hydrogen bonds.…”

“…12,13 In brief, a BaF 2 disc, with a dehydrated sugar-protein mixture, was placed in a SpectraTech Heated Cell (Shelton, CT) and then heated at a rate of 1.08C/min from room temperature (25 AE 58C) to more than 1508C. The sample temperature was monitored and controlled using an ES100P digital controller (OMRON Co., Kyoto, Japan) that had been calibrated using a previously prepared calibration plot.…”

“…The sample temperature was monitored and controlled using an ES100P digital controller (OMRON Co., Kyoto, Japan) that had been calibrated using a previously prepared calibration plot. 12 During heating, IR spectra of the sample were collected at appropriate intervals using a Nicolet Magna 560 FTIR (Nicolet, Madison, WI). For each IR spectrum, 64 scans were conducted over the range of 650-4000 cm À1 with a resolution of 2 cm…”

“…12,13,23 Namely, peak positions of the IR band due to O-H stretching vibration of sugar-protein mixtures were read from the IR spectra obtained at different temperatures and plotted against the corresponding temperatures. It has been well documented that the IR peak position increases linearly with increasing temperature, and at approximately the T g value, the slope of the increase in the peak position abruptly becomes larger.…”

“…In this study, we conducted a temperaturescanning Fourier transform infrared (TS-FTIR) spectroscopic analysis 12 of proteins embedded in an amorphous sugar solid using a temperaturecontrolled FTIR spectrometer. Five types of proteins and three types of sugars were studied.…”