Unique Similarity of the Asymmetric Trehalose Solid-State Hydration and the Diluted Aqueous-Solution Hydration Søren B. Engelsen ² and Serge Pe ´ rez* ,‡ Department of Dairy and Food Science, Food Technology, The Royal Veterinary and Agricultural UniVersity, RolighedsVej 30, DK-1958 Frederiksberg C, Denmark, and Centre de Recherches sur les Macromole ´ cules Ve ´ ge ´ tales, CNRS, BP 53X, 38041 Grenoble ce ´ dex, France. Affiliated with the UniVersite ´ Joseph Fourier at Grenoble ReceiVed: March 13, 2000; In Final Form: July 6, 2000 The structural and dynamical features of the hydration of the disaccharide R,R-trehalose have been derived from a 2.5 ns molecular dynamics with an explicit representation of the water molecules. The study aims at establishing a comprehensive understanding of the hydration pattern of trehalose and comparing such features with those displayed by sucrose. The homonuclear and heteronuclear coupling constants, the overall molecular tumbling time, and self-diffusion coefficient of the trehalose in aqueous solutions were established from the molecular dynamics simulations and compare well with experimental data. While the calculated translational diffusion of trehalose is very similar to that of sucrose, the calculated rotational diffusion is much slower. The presence of water in the simulation induces significant changes in the mean potential acting on trehalose. It generates an asymmetric mean structure between the two glucose rings, in the otherwise symmetrical trehalose. The analysis of the hydration characteristics provides an average molecular hydration number of 7.8 water molecules in the first hydration shell which is close to that derived experimentally from viscosity and apparent molar volume. Average and maximum residence times for water molecules around the trehalose solute were also characterized. The analysis revealed that the water molecules around the O-2 hydroxyl groups were the most resident and that the water molecules around the acetalic oxygens in the “central cavity” of trehalose were particular mobile. 2D radial pair distributions were calculated to analyze the solute surroundings for localized water densities, e.g., bridging water molecules between the two pyranose rings. This analysis revealed no strong first hydration shell interactions, as found in the case of sucrose, but revealed that the water molecules of the dihydrate solid-state structure are largely capable of satisfying the “hydration requirements” of the solute. Introduction Mushroom sugar or R,R-trehalose is the only naturally occurring out of three isomeric trehalose forms, and has a hydration characteristic, which displays extremely interesting features. It has been found to be the key substance produced by many cryptobionts in both the plant and animal kingdoms including desert insects, brine shrimp embryo, baker’s yeast, spores of certain fungi, and a few varieties of plant seeds. Survival of anhydrobiosis and cryptobiosis by many of these organisms was in the early 1980s found to be correlated with the presence of trehalose by Crowe and co-workers. 1,2 Since then, with research mainly driven by the potential interests in medical protein stability and food preservation, trehalose has been subjected to a large number of physical, chemical, and biological functional studies. The major results obtained are the following: (i) the ability of trehalose to protect and reversibly restitute proteins and bio-membranes from dehydration including the freeze-drying cycles; 3,4 (ii) that the trehalose-water system possesses a significantly higher glass-transition temperature than other related disaccharides, also called the trehalose anomaly; 5 (iii) the ability to retain and preserve volatile flavors and aromas in trehalose-dried foodstuff; 6 (iv) and most recently the ability of trehalose to preserve mammalian cells during freezing and drying. 7 While the detailed X-ray crystal structure of R,R-trehalose dihydrate was reported as early as in 1972 8,9 and the low- temperature anhydrous structure in 1985, 10 they provided no clues to explain the structural mechanism(s) responsible for the unique functional properties of trehalose. To elucidate these mechanisms trehalose has been subjected to a number of experimental and theoretical studies including solid-state infra- red 11,12 and NMR 13,14 studies of dehydrated lipid bilayers in the presence of trehalose. In solution state, trehalose has been studied by NMR 15 and optical rotation. 16 However, only very recently has trehalose been studied by NMR using [1- 13 C]- labeled trehalose to avoid the problems for characterization of the solution conformation caused by its C 2 molecular sym- metry. 17 Trehalose has also been subjected to molecular modeling studies as a complementary method to decipher some of its the structural features. In a vacuum, the detailed structure of trehalose has been investigated by Tvaroska and Vaclavik 18 using the MM2CARB force field; it has been followed up by a study by Dowd et al. 19 using the MM3 force field. Trehalose interactions with lipids have also been investigated using molecular modeling by Rudolph et al. 20 However, with the aim * Author to whom correspondence should be addressed. Tel: 33-476- 03-76-30. Fax: 33-476-03-76-29. E-mail: perez@cermav.cnrs.fr. ² The Royal Veterinary and Agricultural University. ‡ Centre de Recherches sur les Macromole ´cules Ve ´ge ´tales, CNRS. 9301 J. Phys. Chem. B 2000, 104, 9301-9311 10.1021/jp000943i CCC: $19.00 © 2000 American Chemical Society Published on Web 09/08/2000