Heteroacene-Based Amphiphile as a Molecular Scaffold for Bioimaging Probes

Abstract

The challenges faced with current fluorescence imaging agents have motivated us to study two nanostructures based on a hydrophobic dye, 6H-pyrrolo[3,2-b:4,5-b’]bis [1,4]benzothiazine (TRPZ). TRPZ is a heteroacene with a rigid, pi-conjugated structure, multiple reactive sites, and unique spectroscopic properties. Here we coupled TRPZ to a tert-butyl carbamate (BOC) protected 2,2-bis(hydroxymethyl)propanoic acid (bisMPA) dendron via azide-alkyne Huisgen cycloaddition. Deprotection of the protected amine groups on the dendron afforded a cationic terminated amphiphile, TRPZ-bisMPA. TRPZ-bisMPA was nanoprecipitated into water to obtain nanoparticles (NPs) with a hydrodynamic radius that was <150 nm. For comparison, TRPZ-PG was encapsulated in pluronic-F127 (Mw = 12 kD), a polymer surfactant to afford NPs almost twice as large as those formed by TRPZ-bisMPA. Size and stability studies confirm the suitability of the TRPZ-bisMPA NPs for biomedical applications. The photophysical properties of the TRPZ-bisMPA NPs show a quantum yield of 49%, a Stokes shift of 201 nm (0.72 eV) and a lifetime of 6.3 ns in water. Further evidence was provided by cell viability and cellular uptake studies confirming the low cytotoxicity of TRPZ-bisMPA NPs and their potential in bioimaging.

Heteroacene-Based Polymer with Fast-Switching Visible–Near Infrared Electrochromic Behavior

“…We hypothesize that the TRPZ-scaffold will facilitate higher mobility of holes when between two EDOT groups and be stabilized in the oxidized state. We speculate that the faster hole transfer rate results in a faster switching time of the electrochromic material. , Additionally, TRPZ is reported to show proaromaticity confirmed by computational calculations, which we believe can be used to maintain a stable oxidized state and prevent chemical degradation …”

“…31,32 Additionally, TRPZ is reported to show proaromaticity confirmed by computational calculations, which we believe can be used to maintain a stable oxidized state and prevent chemical degradation. 33 An ethyl hexyl group is placed on the core nitrogen atom of TRPZ for solubility. The terminal ends of the TRPZ core were coupled to the EDOT molecule through direct arylation to synthesize the monomer unit, TRPZ-EDOT.…”

The Multifaceted Opportunities Provided by the Pheomelanin-Inspired 1,4-Benzothiazine Chromophore: A Still-Undervalued Issue

“…In particular, the prepared nanoparticles exhibited a strong neon green fluorescence with an emission maximum at 695 nm, with a very large Stoke shift (201 nm) and a high quantum yield (49%) in water, which are both fundamental characteristics for bioimaging applications. They also exhibited promising cellular uptake properties, with very low cytotoxicity (Figure 9) [55]. A 1,4-benzothiazine ring fused with a coumarin moiety (PBC) has been, instead, exploited as a fluorescent probe for the bioimaging of cellular hypochlorite.…”