Abstract
Saccharides protect biostructures against adverse environmental conditions mainly by preventing large scale motions leading to unfolding. The efficiency of this molecular mechanism, which is higher in trehalose with respect to other sugars, strongly depends on hydration and sugar/protein ratio. Here we report an Infrared Spectroscopy study on dry amorphous matrices of the disaccharides trehalose, maltose, sucrose and lactose, and the trisaccharide raffinose. Samples with and without embedded protein (Myoglobin) are investigated at different sugar/protein ratios, and compared. To inspect matrix properties we analyse the Water Association Band (WAB), and carefully decompose it into sub-bands, since their relative population has been shown to effectively probe water structure and dynamics in different matrices. In this work the analysis is extended to investigate the structure of protein-sugar-water samples, for the first time. Results show that several classes of water molecules can be identified in the protein and sugar environment and that their relative population is dependent on the type of sugar and, most important, on the sugar/protein ratio. This gives relevant information on how the molecular interplay between residual waters, sugar and protein molecules affect the biopreserving properties of saccharides matrices.
Highlights
It is well known that saccharide glasses protect biomolecules from damages induced by dehydration or high temperatures
In this respect it has been shown that disaccharides can produce homogeneous glasses at any cooling rate, above a definite water/sugar mole ratio [8], which for trehalose, maltose and sucrose is in the same order as that reported for the perturbation of the hydrogen bond (HB) network by sugars [9,10]
Water plays a fundamental role in the modulation the matrix structure and dynamics and the protein-matrix coupling in amorphous saccharide matrices at low hydration
Summary
It is well known that saccharide glasses protect biomolecules from damages induced by dehydration or high temperatures. A peculiar mechanism based on its glass transition temperature (Tg ), higher with respect to its homologues sucrose and maltose [6,7], has been proposed In this respect it has been shown that disaccharides can produce homogeneous glasses at any cooling rate, above a definite water/sugar mole ratio [8], which for trehalose, maltose and sucrose is in the same order as that reported for the perturbation of the hydrogen bond (HB) network by sugars [9,10]. Measurements on other saccharides (dextran, inulin and raffinose) showed that a stable glassy state is not correlated with properties of the HB patterns [11,12,13] It has been shown how trehalose efficiency could arise from two factors, a strong hydrogen bonding capability and, at the same time, the ability to produce stable glassy structures in a wide hydration range [8,14,15]
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