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C–H Stretch for Probing Kinetics of Self-Assembly into Macromolecular Chiral Structures at Interfaces by Chiral Sum Frequency Generation Spectroscopy
journal contribution
posted on 2013-03-26, 00:00 authored by Zhuguang Wang, Li Fu, Elsa C. Y. YanSelf-assembly
of molecules into chiral macromolecular and supramolecular
structures at interfaces is important in various fields, such as biomedicine,
polymer sciences, material sciences, and supramolecular chemistry.
However, probing the kinetics at interfaces remains challenging because
it requires a real-time method that has selectivity to both interface
and chirality. Here, we introduce an in situ approach
of using the C–H stretch as a vibrational probe detected by
chiral sum frequency generation spectroscopy (cSFG). We showed that
the C–H stretch cSFG signals of an amphiphilic peptide (LK7β) can reveal the kinetics of its self-assembly into
chiral β-sheet structures at the air–water interface.
The cSFG experiments in conjunction with measurements of surface pressure
allow us to propose a mechanism of the self-assembly process, which
involves an immediate adsorption of disordered structures followed
by a lag phase before the self-assembly into chiral antiparallel β-sheet
structures. Our method of using the C–H stretch signals implies
a general application of cSFG to study the self-assembly of bioactive,
simple organic, and polymeric molecules into chiral macromolecular
and supramolecular structures at interfaces, which will be useful
in tackling problems, such as protein aggregation, rational design
of functional materials, and fabrication of molecular devices.