High Critical Temperature above Tg May Contribute to the Stability of Biological Systems

Abstract

In this study, we characterized the molecular mobility around T(g) in sugars, poly-L-lysine and dry desiccation-tolerant biological systems, using ST-EPR, (1)H-NMR, and FTIR spectroscopy, to understand the nature and composition of biological glasses. Two distinct changes in the temperature dependence of the rotational correlation time (tau(R)) of the spin probe 3-carboxy-proxyl or the second moment (M(2)) were measured in sugars and poly-L-lysine. With heating, the first change was associated with the melting of the glassy state (T(g)). The second change (T(c)), at which tau(R) abruptly decreased over several orders of magnitude, was found to correspond with the so-called cross-over temperature, where the dynamics changed from solid-like to liquid-like. The temperature interval between T(g) and T(c) increased in the order of sucrose < trehalose < raffinose </= staychose < poly-L-lysine < biological tissues, from 17 to >50 degrees C, implying that the stability above T(g) improved in the same order. These differences in temperature-dependent mobilities above T(g) suggest that proteins rather than sugars play an important role in the intracellular glass formation. The exceptionally high T(c) of intracellular glasses is expected to provide excellent long-term stability to dry organisms, maintaining a slow molecular motion in the cytoplasm even at temperatures far above T(g).

Analysis of Molecular or Ion Mobility in Glassy and Rubbery Foods by Electric and Proton-NMR Measurements

“…The dependency of M 2 on temperature showed typically one or two transition temperatures where the M 2 decrease became steeper, reflecting motional changes in the immobile component. The lower of these 2 transitions was assigned by Hemminga and co-workers (Buitink et al, 2000) to the onset of significant molecular mobility associated with the glass transition temperature (T g ). The second transition temperature referred to as the critical temperature (T c ) was associated with the crossover from solid-like to liquid-like dynamics where the material first begins to show properties of a viscous liquid (Rössler et al, 1994).…”

“…Component 3 was obtained only under conditions of high temperature and/or high water content, typically well into the rubbery state. In order to monitor the mobility of the immobile protons, the second moment was calculated (Van den Dries et al, 1998;Buitink et al, 2000):…”

Preservative Effect of Polyols on the Stability of Biocatalysts during Short-term Dehydration Stress

“…Recently, the up-regulation of HSP expression, as well as increases in the levels of protective osmolytes such as trehalose and glycerol, was also found to reduce dehydration-induced stress (Benoit et al, 2010). Since proteins have a considerable effect on the molecular properties of sugar glasses (Slade and Levine, 1991;Bell and Hageman, 1996;Buitink et al, 2000), it seems likely that HSP also has an effect on macromolecular stability in concert with polyhydroxyl compounds in the cytoplasm in a desiccated state. However, little is known about the interplay between HSP and protective osmolytes.…”

Hurdle Technology in Food Preservation

“…change in slope between above and below the critical ratio) at T/T g equal to 1, if glass transition concept is valid or X w /X b equal to 1, if water activity concept is valid. Buitink et al (2000) measured molecular mobility by ST-EPR and 1 H-NMR, and observed two distinct changes: first one minor shift just close to T g and second abrupt decrease due to solid-like to liquid-like defined as T c . In the case of sugars, T c was observed at 17-35 °C higher than T g and for biological materials it was more than 50 °C.…”