Mimic of the Green Fluorescent Protein β‑Barrel: Photophysics and Dynamics of Confined Chromophores Defined by a Rigid Porous Scaffold

Chromophores
with a benzylidene imidazolidinone core define the
emission profile of commonly used biomarkers such as the green fluorescent
protein (GFP) and its analogues. In this communication, artificially
engineered porous scaffolds have been shown to mimic the protein β-barrel
structure, maintaining green fluorescence response and conformational
rigidity of GFP-like chromophores. In particular, we demonstrated
that the emission maximum in our artificial scaffolds is similar to
those observed in the spectra of the natural GFP-based systems. To
correlate the fluorescence response with a structure and perform a
comprehensive analysis of the prepared photoluminescent scaffolds, 13C cross-polarization magic angle spinning solid-state (CP-MAS)
NMR spectroscopy, powder and single-crystal X-ray diffraction, and
time-resolved fluorescence spectroscopy were employed. Quadrupolar
spin–echo solid-state 2H NMR spectroscopy, in combination
with theoretical calculations, was implemented to probe low-frequency
vibrational dynamics of the confined chromophores, demonstrating conformational
restrictions imposed on the coordinatively trapped chromophores. Because
of possible tunability of the introduced scaffolds, these studies
could foreshadow utilization of the presented approach toward directing
a fluorescence response in artificial GFP mimics, modulating a protein
microenvironment, and controlling nonradiative pathways through chromophore
dynamics.