Chiroptical switching and strong circularly polarized luminescence in peptide supramolecular assemblies

Abstract

Peptide-based materials offer unique advantages for constructing supramolecular chiral systems due to their bioactivity and intrinsic chirality. However, precise control over the expression, transfer, and amplification of chirality from the molecular to supramolecular level remains a significant challenge in developing high-performance chiral materials. In this study, we demonstrate that achiral anions regulate hydrogen bonding interactions in dipeptide assembly, leading to the formation of chiral microrolls composed of two-dimensional nanosheets. These microrolls exhibit pH-dependent chiroptical switching and intense circularly polarized luminescence with a dissymmetry factor (|g_lum|) of 0.062. Furthermore, the chiral ultraviolet emission from these microrolls enables enantioselective polymerization of diacetylene, offering potential applications in chiral catalysis. These findings enhance our understanding of chirality modulation in biomolecular assemblies and provide a pathway toward the development of high-performance chiral biomaterials.

Fig. 1. Construction of Fmoc-YK microbelts and Fmoc-YK/SO₄²⁻ microrolls through liquid-liquid phase separation (LLPS) process.

(a) Schematic representation of the microbelts and microrolls formation via LLPS and gel-to-crystal translation process; b formation process of gels via LLPS (scale bar: 500 nm); (c) TEM images of the aged Fmoc-YK microbelts (scale bar: 2 μm); (d, e) formation process of microrolls via LLPS (scale bar: 500 nm, 1 μm), yellow arrows indicating 2D nanosheets.; (f) PXRD, (g) SAED (scale bar: 2 nm⁻¹), and (h) FTIR spectra of Fmoc-YK nanofibers, microbelts and Fmoc-YK/SO₄²⁻ microrolls.

Fig. 2. Molecular packing of Fmoc-YK microbelts and Fmoc-YK/SO₄²⁻ microrolls.

a, b 2D molecular layer structure of microbelts and microrolls; (c) hydrogen bonding between amino and carboxyl groups in microbelts; (d) β-sheet structure of Fmoc-YK microbelts; (e) hydrogen bonding between SO₄²⁻ and various groups; (f) Fmoc groups arrangement in adjacent layers.

Fig. 3. Chiral properties of Fmoc-YK/SO₄²⁻ microrolls.

a Morphological evolution of microrolls (scale bar: 2 μm); (b) supercoiled arrangement of Fmoc-YK/SO₄²⁻ microrolls; (c) circularly polarized luminescence (CPL) value of Fmoc-YK/SO₄²⁻ microrolls and other Fmoc-YK assemblies with various anions; (d) the dissymmetric factor (g_lum) value of micobelts and microrolls (error bars, mean ± SD); (e) CPL, direct current (DC), (f) circular dichroism (CD) spectra and (g) SEM images of Fmoc-Y^LK^L/SO₄²⁻ and Fmoc-Y^DK^D/SO₄²⁻ microrolls (scale bar: 1 μm).

Fig. 4. pH-responsive chirality switchable properties of Fmoc-YK/SO₄²⁻ microrolls.

a pH-responsive morphology changes and underlying mechanism (scale bar: 2 μm); (b) CD spectra of microrolls and nanobelts; (c–e) cyclic CPL spectrum and g_lum (error bars, mean ± SD).

Fig. 5. Chiral transfer and chiral catalysis of Fmoc-YK/SO₄²⁻ microrolls.

a Schematic diagram of the energy and chiral transfer in Fmoc-YK/SO₄²⁻ microrolls upon doping with Thioflavin T (ThT); (b) normalized fluorescence (FL) spectrum of Fmoc-Y^LK^L/SO₄²⁻ microrolls and UV absorption (abs) spectrum of 0.1 mg/mL ThT solution (the shaded area indicating the overlap between the microrolls’ emission peak and ThT’s absorption peak); (c) FRET in Fmoc-Y^LK^L/SO₄²⁻ microrolls after doping with varying concentrations of ThT solution; (d–f) the CD spectra, CPL spectra, and g_lum of Fmoc-Y^LK^L/SO₄²⁻ and Fmoc-Y^DK^D/SO₄²⁻ microrolls after doping with 0.1 mg/mL ThT; (g) schematic setup for enantioselective photopolymerization of 2,4-heneicosadiynoic acid (HA); (h) CD spectra of poly(diacetylene) (PDA) films after exposing to CPL generated from the Fmoc-YK/SO₄²⁻ microrolls. The inset shows the photographs of HA and PDA films.