Synergistic Interactions of Sugars/Polyols and MonovalentSalts with Phospholipids Depend upon Sugar/Polyol Complexity and AnionIdentity.

We found that interactions of dipalmitoylphosphatidylcholine(DPPC) lipid monolayers with sugars are influenced by addition ofNaCl. This work is of general importance in understanding how sugar–lipid–saltinteractions impact biological systems. Using Langmuir isothermalcompressions, fluorescence microscopy, atomic force microscopy, andneutron reflectometry, we examined DPPC monolayers upon addition ofsugars/polyols and/or monovalent salts. Sugar–lipid interactionsin the presence of NaCl increased with increasing complexity of thesugar/polyol in the order glycerol ≪ glucose < trehalose.When the anion was altered in the series NaF, NaCl, and NaBr, onlyminor differences were observed. When comparing LiCl, NaCl, and KCl,sodium chloride had the greatest influence on glucose and trehaloseinteractions with DPPC. We propose that heterogeneity created by cationbinding allows for sugars to bind the lipid headgroups. While cationbinding increases in the order K+< Na+<Li+, lithium ions may also compete with glucose for bindingsites. Thus, both cooperative and competitive factors contribute tothe overall influence of salts on sugar–lipid interactions. [ABSTRACT FROM AUTHOR]