Hierarchical supramolecular platelets from hydrophobically-modified polysaccharides and α-cyclodextrin: Effect of hydrophobization and α-cyclodextrin concentration on platelet formation

Micro- and nano-platelets are a group of particles with typical flat surfaces and hexagonal shape. They are obtained by hierarchical self-assembly in water of alpha-cyclodextrin and polysaccharides hydrophobically-modified with alkyl chains. It is expected that the formation of well structured and cohesive platelets is driven by the interaction between alkyl chains grafted on polysaccharides and alpha-cyclodextrin. The objective of this investigation is to tune platelet formation by modifying these two parameters, independently on polysaccharide composition. A systematic study was conducted by varying polysaccharide type (dextran, pullulan, amylopectin), degree of substitution (DS: 0.1-5.6%) and alpha-cyclodextrin concentration (0-10 wt%) for a fixed concentration of polysaccharide esterified with palmitoyl groups (1 wt%). Characterizations include ATR-FTIR, elemental analysis, solid state C-13 NMR and transmission electron microscopy. Abundant and well-organized hexagonal platelets were obtained with high DS (4.2-5.6%) and a concentration of alpha-cyclodextrin higher than 2.5 wt%. Isothermal titration calorimetry revealed a sequential binding with a stoichiometry of 2 alpha-cyclodextrin molecules for 1 palmitoyl group grafted on dextran. This is the first report showing the possibility to control platelet formation by modifying DS and alpha-cyclodextrin concentration, independently on polysaccharide composition.