Hydration IndexA Better Parameter for Explaining Small Molecule Hydration in Inhibition of Ice Recrystallization

Abstract

Several simple mono- and disaccharides have been assessed for their ability to inhibit ice recrystallization. Two carbohydrates were found to be effective recrystallization inhibitors. D-galactose (1) was the best monosaccharide and D-melibiose (5) was the most active disaccharide. The ability of each carbohydrate to inhibit ice growth was correlated to its respective hydration number reported in the literature. A hydration number reflects the number of tightly bound water molecules to the carbohydrate and is a function of carbohydrate stereochemistry. It was discovered that using the absolute hydration number of a carbohydrate does not allow one to accurately predict its ability to inhibit ice recrystallization. Consequently, we have defined a hydration index in which the hydration number is divided by the molar volume of the carbohydrate. This new parameter not only takes into account the number of water molecules tightly bound to a carbohydrate but also the size or volume of a particular solute and ultimately the concentration of hydrated water molecules. The hydration index of both mono- and disaccharides correlates well with experimentally measured RI activity. C-Linked derivatives of the monosaccharides appear to have RI activity comparable to that of their O-linked saccharides but a more thorough investigation is required. The relationship between carbohydrate concentration and RI activity was shown to be noncolligative and a 0.022 M solution of D-galactose (1) and C-linked galactose derivative (10) inhibited recrystallization as well as a 3% DMSO solution. The carbohydrates examined in this study did not possess any thermal hysteresis activity (selective depression of freezing point relative to melting point) or dynamic ice shaping. As such, we propose that they are inhibiting recrystallization at the interface between bulk water and the quasi liquid layer (a semiordered interface between ice and bulk water) by disrupting the preordering of water.

Synthetic polymers enable non-vitreous cellular cryopreservation by reducing ice crystal growth during thawing

“…Ben et al have developed a series of short glycopeptides that have specific IRI activity at very low concentrations. These analogues have been showed to be more synthetically accessible, biocompatible with human embryonic liver (WRL-68) cells and shown marginal benefits when added into standard cryopreservation solutions 28,29 . These peptides have also been shown to be readily internalized, making their post-thaw removal non-trivial.…”

Design and Synthesis of Antifreeze Glycoproteins and Mimics

“…[85] Further modulation of the properties of these mimics could be delivered by increasing the hydrophobicity of the backbone through the preparation of the corresponding Xaa-Ala-Ala/Xaa-Val-Val mimics. The strong correlation between the hydration index and RI activity also suggests that glycoconjugates of melibiose, which was measured as containing the highest hydration index, [83] can deliver even more potent compounds. Finally, the ability to predict whether a designed molecule is likely to exhibit antifreeze activity would be extremely useful.…”

“…In order to further fine-tune the RI activity, the hydration index was developed as a general method aimed at assessing the degree of hydration of carbohydrates. [83] The hydration index was shown to correlate well with RI activity for a range of mono-and disaccharides, with the C-linked derivatives of the monosaccharides having comparable activity to the corresponding O-linked monosaccharides.…”

Small molecule ice recrystallization inhibitors enable freezing of human red blood cells with reduced glycerol concentrations

“…b-PMP-Glc (6) also exhibited comparable IRI activity to a 220 mM solution of sucrose, which is a common ingredient of many cryopreservation solutions 28 . Our laboratory has previously correlated IRI activity to carbohydrate hydration and reported that glycoconjugates containing highly hydrated monosaccharides (such as D-galactose) were more IRI active than those containing less hydrated monosaccharides (D-glucose and D-mannose) 23,43 . This trend was also observed in small molecules where the non-ionic pyranose-based surfactants containing a highly hydrated D-galactose head group (b-Octyl-Gal, 1, Fig.…”

“…This is the first example where a glucopyranose derivative is significantly more IRI active than a galactopyranose derivative. It was also surprising that both b-PMP-Gal (5) and b-PMP-Man (7) exhibited identical IRI activities despite the difference in hydration between these two pyranose residues 23,43,44 . Unfortunately, hydration numbers or molar compressibilities of 5-7 have not been reported in the literature, thus a correlation between the hydration characteristics of these compounds and their IRI activity is not possible at this time.…”