Rational Design of Chiral Nanostructures from Self-Assembly of a Ferrocene-Modified Dipeptide

We report a new paradigm for the
rational design of chiral nanostructures
that is based on the hierarchical self-assembly of a ferrocene (Fc)-modified
dipeptide, ferrocene-l-Phe-l-Phe-OH (Fc-FF). Compared
to other chiral self-assembling systems, Fc-FF is unique because of
its smaller size, biocompatibility, multiple functions (a redox center),
and environmental responsiveness. X-ray and spectroscopic analyses
showed that the incorporation of counterions during the hierarchical
self-assembly of Fc-FF changed the conformations of the secondary
structures from flat β sheets into twisted β sheets. This
approach enables chiral self-assembly and the formation of well-defined
chiral nanostructures composed of helical twisted β sheets.
We identified two elementary forms for the helical twist of the β
sheets, which allowed us to create a rich variety of rigid chiral
nanostructures over a wide range of scales. Furthermore, through subtle
modulations in the counterions, temperature, and solvent, we are able
to precisely control the helical pitch, diameter, and handedness of
the self-assembled chiral nanostructures. This unprecedented level
of control not only offers insights into how rationally designed chiral
nanostructures can be formed from simple molecular building blocks
but also is of significant practical value for the use in chiroptics,
templates, chiral sensing, and separations.