posted on 2012-10-30, 00:00authored byHai Cao, Quanzi Yuan, Xuefeng Zhu, Ya-Pu Zhao, Minghua Liu
The organogel formation and self-assembly of a glycine-based
achiral
molecule were investigated. It has been found that the compound could
gel organic solvents either at a lower temperature with lower concentration
or at room temperature with higher concentration, which showed different
self-assembled nanostructures. At a low temperature of −15
°C, the compound self-assembled into fibrous structures, whereas
it formed distinctive flat microbelts at room temperature. When the
organogel with nanofibers formed at −15 °C was brought
into an ambient condition, chiral twist nanostructures were immediately
evolved, which subsequently transferred to a giant microbelt through
a hierarchical dendritic twist with the time. Although the compound
is achiral, it formed chiral twist with both left- and right-handed
twist structures simultaneously. When a trace analogical chiral trigger, l-alanine or d-alanine derivative, was added, a complete
homochiral dendritic twist was obtained. Interestingly, a reverse
process, i.e. the transformation of the microbelts into twists, could
occur upon dilution of the organogel with microbelt structure. During
the dilution, both left- and right-handed chiral twists could be formed
again. Interestingly, the same branch from the microbelt formed the
twist with the same handedness. A combination of the density functional
theory (DFT), molecular mechanics (MM), and molecular dynamics (MD)
simulations demonstrates that the temperature-induced twisting of
the bilayer is responsible for the morphological transformation and
evolution of the dendrite twist. This research sheds new light on
the hierarchical transformation of the chiral structures from achiral
molecules via controlled self-assembly.