Oligosaccharides Self-Assemble and Show Intrinsic Optical Properties.

Yang Yu,Dongyoon Kim,Soeun Gim,Peter H Seeberger,Martina Delbianco,Ehud Gazit,Zohar A Arnon

doi:10.1021/jacs.8b11882

Abstract

Self-assembling peptides and oligonucleotides have given rise to synthetic materials with several applications in nanotechnology. Aggregation of synthetic oligosaccharides into well-defined architectures has not been reported even though natural polysaccharides, such as cellulose and chitin, are key structural components of biomaterials. Here, we report that six synthetic oligosaccharides, ranging from dimers to hexamers, self-assemble into nanostructures of varying morphologies and emit within the visible spectrum in an excitation-dependent manner. Well-defined differences in chain length, monomer modification, and aggregation methods yield glycomaterials with distinct shapes and properties. The excitation-dependent fluorescence in a broad range within the visible spectrum illustrates their potential for use in optical devices and imaging applications. We anticipate that our systematic approach of studying well-defined synthetic oligosaccharides will form the foundation of our understanding of carbohydrate interactions in nature.

Highlights

Simple peptides[1] and nucleic acids[2] can spontaneously selfassemble to form defined supramolecular patterns
Three dimers (1−3) as well as one additional hexasaccharide (6) were prepared to probe the influence of chain length, linkage, and modification on self-assembly (Figure 1A)
These particles exist in solution, as confirmed by cryo-SEM of 2-D (Figure S1) and dynamic light scattering (DLS) measurements (Figure S2)

Summary

■ INTRODUCTION

Simple peptides[1] and nucleic acids[2] can spontaneously selfassemble to form defined supramolecular patterns. Direct injection of water into a glycan solution in HFIP (fast solvent switch) results in faster mixing, higher oligosaccharide concentration, and altered self-assembly behavior (Figure 2A, g−l).[17] Needle-like structures were found for 2-S-HFIP (5−10 μm length, 10−50 nm height, and 100−500 nm width, Figure 2A, h, and Figure S3) and a spheroidal architecture (1−2 μm diameter) for the hexamer 5-S-HFIP analogue (Figure 2A, k). We believe that this phenomenon is the result of the formation of supramolecular chromophores within the material, as previously observed for self-assembled peptides, nucleic acids, and amino acids.[17,21] An extended π-conjugation system and/or charge delocalization through a dense hydrogen-bonding network are generally responsible for this behavior.21b. This red edge excitation shift (REES) is a common phenomenon observed in graphene oxide,21c ionic liquids,21d and highly ordered assemblies,[17] suggesting potential applications of self-assembling oligosaccharides for optical devices, semiconductors, and nanotechnology.1d,17,21a,b

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES