Gelation capability of cysteine-modified cyclo(L-Lys-L-Lys)s dominated by Fmoc and Trt protecting groups

A series of symmetrical peptidomimetics (3-8) based on cysteine-modified cyclo(L-Lys-L-Lys)s were synthesized, and their gelation capability in organic solvents was dominated by fluorenylmethyloxycarbonyl (Fmoc) and triphenylmethyl (Trt) protecting groups and the exchange of thiol-to-disulfide as well. The peptidomimetics holding Trt (3 and 4) showed no gel performance, while the Fmoc groups promoted 5 and 6 to give rise to thermo-reversible organogels in a number of organic solvents. The self-assembled fibrillar networks were distinctly evidenced in the organogels by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observations. Fourier transform infrared spectroscopy (FT-IR) and fluorescence analyses revealed that the hydrogen bonding and π-π stacking play as major driving forces for the self-assembly of these organogelators. A β-turn secondary structure was deduced for the organogel of 6 by virtue of X-ray diffraction, FT-IR and circular dichroism (CD) measurements, and an interdigitated bilayer structure was also presented.