Abstract
Formation of supramolecular aggregates such as micelles and vesicles is governed by hydrophobic and hydrophilic interaction as well as the geometric shapes of the aggregating molecules. Here we present an experiment for upper secondary chemistry class to show how structural properties of molecules such as fatty acids govern the shapes of aggregates. For fatty acids, the pH value controls whether micelles or vesicles are formed. Using a size exclusion column and the possibility to encase fluorescing dye molecules in vesicles, the properties of micelles and vesicles are explored and compared to typical micelle building surfactants from dish detergent and the vesicle building lecithin.
Highlights
Self-aggregation plays an important role in chemical and biological processes, typically governed by simple chemical driving forces, e.g. hydrophilic and/or hydrophobic interactions, hydrogen bonds and pi-pi stacking [1]
Aggregates determine phenomena such as structural conformation in proteins and DNA, reduction of surface tension due to surfactants and the formation of biologically relevant structures such as micelles, important for fat storage within cells, or vesicles, playing an essential role for substance transport in living organisms. Supramolecular aggregates such as micelles and vesicles are consistently important in research for e.g. reconstitution processes of proteins in biochemistry [2] or, in the case of vesicles, are subject of current research on biological transport phenomena [3]
While the formation of micelles is typically referred to regarding washing processes using surfactants from dish detergents or soap, vesicles are mentioned with regard to the synaptic transport of neurotransmitters [5] as consisting of phospholipids and to some extent sphingolipids
Summary
Self-aggregation plays an important role in chemical and biological processes, typically governed by simple chemical driving forces, e.g. hydrophilic and/or hydrophobic interactions, hydrogen bonds and pi-pi stacking [1]. Supramolecular aggregates of these molecules lead to micelles as schematically shown in A2 and A3 Lipids, such as phospholipids from e.g. lecithin, a main component of eukaryotic cellular membranes [6,7,8], typically have a larger headgroup and 2 alkyl chains, which resembles a more cylindrical structure as depicted B1. Aggregation of these molecules leads to bilayer structures such as vesicles, as presented in B2 and B3. Explanation: When dish detergent, lecithin and fatty acids are dissolved in the colored solution, aggregates with sizes in the nanometer range form based on the amphiphilic nature of the molecules.
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