SYNTHESIS AND GEL FORMATION OF AMPHIPHILIC SEMICARBAZONES CONTAINING SACCHARIDE UNITS

The synthesis of 4-alkyl-semicarbazones derived from reducing sugars a nd semicarbazides is presented as a convenient route for the preparati on of amphiphilic saccharides. This semicarbazone route allows to empl oy a large variety of reducing sugars as hydrophilic building block fo r saccharide tensides. The preparation of two series of amphiphiles ba sed on D-maltose with non-methylated and mono-N-methylated semicarbazo ne units is described. The n-alkyl chains were varied from n-octyl to n-hexadecyl. Various maltotriose derivatives have also been prepared. Critical micelle concentration (CMC) as well as critical gel concentra tion of the derivatives were studied in dependence of the n-alkyl chai n length. Both values decreased with increasing length of the n-alkyl chain. Self-organization of the gels was studied by transmission elect ron microscopy of freeze-fractured samples. Due to the supramolecular organization of the amphiphiles, the gels consisted of twisted rope-li ke molecular assemblies with the same helical twist sense. The helical pitch depended on the hydrophilic/lipophilic balance. In contrast to gels of n-alkylgluconamides, the gels were formed in dilute aqueous so lution and exhibited striking longevity without additional stabilizati on by surfactants. In the solid, the amphiphiles exhibited thermotropi c transitions to partially disordered mesophases.