Ice formation in model biological membranes in the presence of cryoprotectors

Abstract

Ice formation in model biological membranes is studied by SAXS and WAXS in the presence of cryoprotectors: dimethyl sulfoxide and glycerol. Three types of phospholipid membranes: DPPC, DMPC, DSPC are chosen for the investigation as well-studied model biological membranes. A special cryostat is used for sample cooling from 14.1 o C to −55.4 o C. The ice formation is only detected by WAXS in binary phospholipid/water and ternary phospholipid/cryoprotector/water systems in the condition of excess solvent. Ice formation in a binary phospholipid/water system creates an abrupt decrease of the membrane repeat distance by ∆d, so-called ice-induced dehydration of intermembrane space. The value of ∆d decreases as the cryoprotector concentration increases. The formation of ice does not influence the membrane structure (∆d = 0) for cryoprotector mole fractions higher than 0.05. IntroductionDimethyl sulfoxide (DMSO) and glycerol are well-known cryoprotectors widely used in cryobiology for the conservation of biological tissues at low temperatures [1]. The main purpose of cryobiology is to find an "optimal" way for cooling biological systems to low temperatures (about the liquid nitrogen temperature), and prevent the crystallisation of water inside biological tissues. One of the problems is a longer time of freeze-induced dehydration (diffusion of water molecules from biological tissues through the membrane to the conserving solvent) than the time of ice formation [2]. The ice-induced dehydration of intermembrane space at the moment of water crystallization is observed by X-ray diffraction [3] and calorimetry [4] for binary phospholipid /water systems. In macromolecular crystallography the portion of X-ray diffraction experiments at cryogenic temperatures is exponentially increasing. In many cases, a dramatic reduction in radiation damage at low temperatures allows complete data sets to be collected from a single crystal. cryoprotectors make it possible to cool samples to low temperature and store them without damage in the crystal [5].In this article ice formation is investigated by small-and wide-angle X-ray scattering (SAXS and WAXS) in ternary phospholipid/cryoprotector/water systems. Three phospholipids are studied: dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC) and distearoylphosphatidylcholine (DSPC). DPPC, DMPC, and DSPC are taken as phospholipids with an equal polar heads and with the difference in the length of hydrocarbon chains. The reason why we use DMSO and glycerol is the fact of their different interactions with the membrane surface. Glycerol penetrates into the region of polar head groups and produces influence on the thickness of the membrane bilayer and the thickness of an intermembrane solvent [6]. DMSO molecules do not penetrate into the region of polar head groups and thus do not influence the membrane thickness [7,8]. DMSO molecules strongly interact with water molecules and form hydrogen bonds. Such interaction is more intensive than the interaction between DMSO a...

Water sorption–desorption in Nafion® membranes at low temperature, probed by micro X-ray diffraction

“…Water desorption in soft materials as a function of temperature, was already observed previously [34][35][36]. For example, some investigations on starch-based foods have identified the possibility of damage caused by sub-zero storage [36].…”

Molecular dynamics simulations of microstructure and mixing dynamics of cryoprotective solvents in water and in the presence of a lipid membrane

“…(For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) DMSO/DPPC/water systems [51][52][53][54]. In addition, the favorable location of DMSO at the interface has also been proposed by recent MD studies [30,31].…”

The interaction of single walled carbon nanotube (SWCNT) with phospholipids membrane: in point view of solvent effect

“…Dipalmitoylphosp hatidylcholine (DPPC) anddimyristoylphos phatidylcholine (DMPC) are taken as phospholipids with an equal polar heads and with the difference in the length of hydrocarbon chains 34,35 .These two molecules have saturated fatty acid tail groups [36][37][38][39] .…”