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. 2019 Jul 25:7:518.
doi: 10.3389/fchem.2019.00518. eCollection 2019.

Tunable Self-Assembled Nanostructures of Electroactive PEGylated Tetra(Aniline) Based ABA Triblock Structures in Aqueous Medium

Irrum Mushtaq  1 , Zareen Akhter  1 , Faiz Ullah Shah  2
Affiliations

Tunable Self-Assembled Nanostructures of Electroactive PEGylated Tetra(Aniline) Based ABA Triblock Structures in Aqueous Medium

Irrum Mushtaq et al. Front Chem. .

Abstract

PEGylated tetra(aniline) ABA triblock structure PEG-TANI-PEG (2) consisting of tetra(aniline) (TANI) and polyethylene glycol (PEG) was synthesized by coupling the tosylated-PEG to boc-protected NH2/NH2 TANI (1) through a simple nucleophilic substitution reaction. Deprotection of 2 resulted in a leucoemeraldine base state of TANI (2-LEB), which was oxidized to stable emeraldine base (2-EB) state. 2-EB was doped with 1 M HCl to emeraldine salt (2-ES) state. FTIR, 1H and 13C NMR and UV-Vis-NIR spectroscopy, and MS (ESI) was used for structural characterization. The synthesized triblock structure exhibited good electroactivity as confirmed by CV and UV-Vis-NIR spectroscopy. Self-assembling of the triblock structure in aqueous medium was assessed by DLS, TEM, and SEM. Spherical aggregates were observed with variable sizes depicting the effect of concentration and oxidation of 2-LEB. Further, the aggregates showed acid/base sensitivity as evaluated by doping and dedoping of 2-EB with 1 M HCl and 1 M NH4OH, respectively. Future applications in drug delivery and sensors are envisaged for such tunable self-assembled nanostructures in aqueous media.

Keywords: PEGylation; aqueous self-assembly; redox activity; triblock nanostructures; tunable self-assembled structures.

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Figures

Scheme 1
Scheme 1
Synthesis of (a) tosylated-PEG, (b) ABA type triblock structures containing secondary amine (NH) linkage (2), (c) deprotection, (d) oxidation and (e) doping.
Figure 1
Figure 1
FTIR spectra of (a) 1 (bottom trace), (b) 2 (middle trace), and (c) 2-LEB (top trace). The spectra are shifted along the direction of intensity for clarity.
Figure 2
Figure 2
1H NMR spectra of (A) 2, and (B) 2-LEB in CDCl3.
Figure 3
Figure 3
UV-Vis-NIR spectra: (A) 1-LEB (1) and 2-LEB (2), (B) 2-LEB (1), 2-EB (2) and 2-ES, doped with 1M HCl (3), and (C) Cyclic voltammogram of 2-EB at different scan rates in 1M H2SO4 as an electrolyte.
Figure 4
Figure 4
TEM images of 2-LEB at different concentrations; (a) 0.2 mg/mL, (b) 1 mg/mL, (c) 5 mg/mL and DLS analysis of 2-LEB; (d) Auto-correlation function (ACF), (e) particle size distribution at different concentrations shown as insert in (d).
Figure 5
Figure 5
TEM image (a) and particle size distribution (b) of 0.2 mg/ml aqueous solution of 2-EB.
Figure 6
Figure 6
Self-assembly of doped/dedoped 2-EB. (a) TEM image of 2-ES doped with 1M HCl, (b) SEM image of 2-ES, (c) particle size distribution curve of 2-ES, (d) UV-Vis spectra of doped and dedoped 2-EB, (e) TEM image of 2-ES dedoped with 1 M NH4OH.
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