A Calorimetric and Spectroscopic Study of the Interactions Between Model Lipid Membrane Bilayers and Simple Sugars

Abstract

It is well known that various organisms, such as the tardigrade, naturally use carbohydrates, particularly disaccharides, to help preserve their cell structural and functional integrity during freezing or dehydration. There have been many different studies that have focused on investigating how certain sugars may help to preserve the structural and functional integrity of biological cells throughout such extreme conditions. These studies have used lipids as a simple and effective alternative to studying how small molecules, such as disaccharides, interact with model lipid membrane bilayers. Lipid bilayers, also known as liposomes, have classically been used to study and better understand the structure of membrane bilayers since their phase behavior is very well understood. Therefore, liposomes are often used to investigate how small molecules interact with membrane bilayers, and how these interactions translate into physical, structural, and potential biological changes. Differential scanning calorimetry (DSC) and infrared spectroscopy were used to examine the thermotropic phase behavior of model liposome membranes in the presence of either sucrose or sucralose. The data indicates that membranes are dehydrated and form an interdigitated layer in the presence of sucralose, but not in the presence of sucrose. We hypothesize that this behavior is due to the different hydrophobic properties of the sugars and that sucralose may penetrate the bilayer whereas sucrose will not. Additionally, at higher concentrations of sucralose the data suggests that sucralose may hydrogen bond to the polar head groups, particularly to the phosphate region of the lipid molecule, in an effort to stabilize the membrane bilayer and Van de Waals forces upon interdigitation. This study demonstrates that sucralose has a significant effect on the phase behavior of liposomes, and its usefulness as a possible cryoprotecting agent for the preservation of biological cells and tissues is of great interest and needs to be comprehensively investigated.