Effects of amide side chains on nanoassembly formation and gelation of Fmoc–valine conjugates

• Self assembly and gelation of four new Fmoc–valine amide conjugates were studied.
• Secondary structural studies revealed the presence of mixed alpha helices and beta sheets.
• Thermal studies indicated gel–gel transitions in all cases.
• The materials may be applicable for drug delivery or as tissue engineering scaffolds.

In this work, we have examined the formation of nanoassemblies by self-assembly process using amide derivatives of Fmoc–valine (fluorenylmethyloxycarbonyl-protected valine). The derivatives were synthesized by combining Fmoc–Val with four different linkers (diphenyl amine; hexadecylamine; N1,N4,N9-tris-Boc-spermine and N1,N4-bis-Boc-spermidine). The materials were allowed to self-assemble into nanoassemblies and their growth and gelation were probed at varying pH values. Secondary structural analysis was carried out using FTIR and CD spectroscopy to shed light into the mechanistic aspects of formation of the assemblies. The morphologies and thermal properties were studied by transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) respectively. Wettability studies using contact angle measurements were carried to examine the hydrophobicity changes of the assemblies due to incorporation of the various amide derivatives. Our results indicate that while stacking interactions between the FMOC moieties played a vital role in the self-assembly process and gelation behavior in all cases, the morphologies were also influenced by the chain length and functionalities of the linkers utilized. The assemblies showed mixed conformations of both alpha-helices and beta-sheets. The materials formed may have a wide range of potential applications from drug delivery to development of tissue engineering scaffolds.

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