Water in the hydration shell of cryoprotectants and their non-cryoprotecting structural analogues as observed by Raman-MCR spectroscopy

Abstract

Cryoprotectant preserves cellular integrity of biological entities at sub-zero temperatures via vitrification of cellular constituents. To shed light onto the molecular mechanism of cryoprotectant induced vitrification of water, we have selectively extracted the vibrational response of water at the immediate vicinity (hydration shell) of two prototype cryoprotectants (dimethyl sulfoxide (DMSO) and ethyleneglycol (EG)) and their non-cryoprotecting structural analogues (acetone and 1,4‑dioxane (DXN)), using Raman multivariate curve resolution (Raman-MCR) spectroscopy. It is observed that the hydrogen-bonding (H-bonding) of water in the hydration shell of the cryoprotectant is similar to that in bulk water; whereas that in the hydration shell of the non-cryoprotectant is weaker than that in bulk water. Thus, the H-bonding environment provided by a cryoprotectant to its neighboring water is very similar to the one, a water molecule provides to its neighboring water. As a result, aqueous cryoprotectant solution solidifies at sub-zero temperature along with the cryoprotecting molecules, leading to vitrification. Non-cryoprotectant on the other hand, because of its weaker interaction with water, gets excluded from the H-bond network, enabling the water to form ice.