Self-assembly of chiral fluorescent nanoparticles based on water-soluble L-tryptophan derivatives of p-tert- butylthiacalix[4]arene

Abstract

New water-soluble tetra-substituted derivatives of p-tert-butylthiacalix[4]arene containing fragments of L-tryptophan in cone and 1,3-alternate conformations were obtained. It was shown that the resulting compounds form stable, positively charged aggregates of 86-134 nm in diameter in water at a concentration of 1 × 10^-4 M as confirmed by dynamic light scattering, scanning electron microscopy and transmission electron microscopy. It was established that these aggregates are fluorescently active and chiral. A distinctive feature of the compounds is the pronounced dependence of their spectral (emission and chiroptical) properties on the polarity of the solvent and the length of the linker between the macrocyclic and fluorophore parts of the molecule.

Keywords: fluorescence; nanoparticles; self-assembly; thiacalixarene; tryptophan.

Figure 1

Possible paths of the formation of supramolecular associates.

Scheme 1

Reagents and conditions: (i) SOCl₂, C₂H₅OH, (ii) BrCH₂COBr, NaHCO₃, C₆H₆/H₂O, (iii) 3, CH₃CN, reflux.

Figure 2

SEM images of self-associates based on thiacalix[4]arene: А) compound 8, B) compound 9, C) compound 10, D) compound 11 in water (1 × 10⁻⁴ М). Scale bar 1 µm.

Figure 3

A) Fluorescence spectra of compounds 8–11 in water (1 × 10⁻⁵ М), B) UV spectra of aqueous solutions of thiacalix[4]arenes 8–11 (1 × 10⁻⁵ М).

Figure 4

Fluorescence spectra of compounds 8–11 in methanol (1 × 10⁻⁵ М).

Figure 5

The CD spectra of the compounds 2 and 8–11 in water and methanol.