posted on 2024-02-08, 22:43authored byWangtao Zhao, Mei Gao, Liufen Kong, Shunfeng Yu, Chuanzhuang Zhao, Chongyi Chen
The low emission efficiency of clusteroluminogens restricts
their
practical applications in the fields of sensors and biological imaging.
In this work, the clusteroluminescence of ordered/disordered polypeptides
was observed, and the photoluminescence (PL) intensity of polypeptides
can be modulated by the chirality of amino acid residues. Polyglutamates
with different chiral compositions were synthesized, and the racemic
polypeptides exhibited a significantly higher PL intensity than the
enantiopure ones. This emission originates from the n–π*
transition between CO groups of polypeptides and is enhanced
by clusterization of polypeptides. CD and Fourier transform infrared
spectra demonstrated that the enantiopure and racemic polypeptides
form α-helix and random coil structures, respectively. The disordered
polypeptides can form more chain entanglements and interchain interactions
because of their high flexibility, leading to more clusterizations
and stronger PL intensity. The rigidity of ordered helical structures
restrains the chain entanglements, and the formation of intrachain
hydrogen bonds between amide groups of the backbone impairs the interchain
interaction between polypeptides, resulting in lower PL intensity.
The PL intensity of the polypeptides can also be manipulated by the
addition of urea or trifluoroacetic acid. Our study not only elucidates
the chirality/order-based structure–property relationship of
clusteroluminescence in peptide-based polymers but also offers implications
for the rational design of fluorescent peptides/proteins.