bm6b00752_si_001.pdf (1.55 MB)
Design of Controllable Bio-Inspired Chiroptic Self-Assemblies
journal contribution
posted on 2016-07-26, 00:00 authored by Kai Tao, Guy Jacoby, Luba Burlaka, Roy Beck, Ehud GazitModulation of chiroptics, chiral
phenomena of the optical properties,
is pivotal in a variety of advanced applications, including chirality-specific
biosensing and photonic switches. One of the most effective methods
for achieving this control is assembly of the optical moieties into
chiral nanostructures. Lipopeptide self-assemblies have been extensively
employed as soft templates to organize composites into low-dimensional
superstructures due to their rigidity and ease of functionalization.
Therefore, an appealing approach is to provide chiroptical control
by using lipopeptide self-assemblies as templates to assemble chromophores.
Herein, two lipopeptidic molecules, namely, C14–FFK
and C14–FK, composed of phenylalanine and lysine
residues conjugated to a myristic acid chain, were custom-designed.
Spectroscopic and microscopic characterizations indicated that C14–FFK self-assembled to wide, slightly left-handed
nanoribbons, while C14–FK formed narrow, intensely
right-handed nanofibers. The different chirality was derived from
the distinct self-assembly driving forces, especially the molecular
bending dimensions. These superstructures presented an ideal capability
to serve as soft templates to assemble porphyrin (ZnTPyP) through
noncovalent electrostatic attractive interactions, or assemble the
phenolic groups through covalent conjugation to peptide backbones.
The distinct exciton coupling of the chromophores allowed their achiral
optics to become chiral, showing negative Cotton effect when templated
by nanoribbons and positive Cotton effect with nanofibers as templates.
Following replacement of the lipopeptides with their d-type
enantiomers, the handedness of the superstructures and the associated
chiroptics were reversed and presented “mirror” symmetric
CD signals to their l-type counterparts. These findings may
pave the way to the formation of morphologically and chioptically
controllable nanomaterials.