Cabohydrate stereoisomerschemistry self-assemble into affects the supramolecular fibers with different assemblyhelicityof Short short aromatic carbohydrate amphiphiles based supramolecular structures: stereochemistry effect on the assembly

Molecular self-assembly (MSA) is abundant in living systems where the same building blocks, e.g. amino acids, carbohydrates and nucleotides, are used to assemble diverse, highly specific and functional biologics. Among these building blocks, carbohydrates are distinguished by their potential to display a huge number of ligand structures in molecular recognition systems due to the number of available regio- and stereoisomers for each monosaccharide[MOU1] . In biological systems, these isomers interact with aromatic amino-acids from proteins via CH-p interactions, thus, contributing to key biological processes such as protein folding and receptor binding.

In an attempt to mimic this diversity and to understand better the information that they code, we synthesized three carbohydrate amphiphiles from the stereoisomers glucosamine (GlcN), galactosamine (GalN) and mannosamine (ManN) by N-functionalization with fluorenylmethoxycarbonyl (Fmoc). The Fmoc-derivatives were suspended in water and heated (75-80°C) until complete solubilization and then cooled at different rates (i.e. different energy inputs). Fmoc-ManN was insoluble at these conditions and thus, was excluded from the following studies.³

We confirmed the formation of nanofibres by CH-p interactions (fluorescence spectroscopy, signal at 450-480 nm). The helicity of the formed fibers was dependent on the cooling rate and on the carbohydrate stereochemistry. Fibers with positive signal in the circular dichroism (CD) spectra were generated from either Fmoc-GalN or Fmoc-GlcN at fast cooling rate, i.e. 40° C/min. Interestingly, at slow cooling rate (5° C/min), there was an inversion of the CD signal for Fmoc-GalN. Moreover, the nucleation and growing of the fibres were also influenced by the stereochemistry: Fmoc-GalN form less but longer fibres while more but shorter fibres were observed for Fmoc-GlcN. Also, we observed formation of spherulites whose size is bigger in the case of Fmoc-GalN. These differences influenced the viscoelastic properties and the stability of the hydrogels generated from the nanofibers. The sol-gel transition occurs within the temperature range between 35-55°C and the hydrogels prepared from Fmoc-GlcN have higher storage modulus than their Fmoc-GalN counterparts. Our results demonstrate that a short sequence (monosaccharide) carbohydrate can code and transfer information as a function of their stereochemistry. We also demonstrated that the energy input can alter the coded/transferred information, which is very important for biological systems.