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. 2018 Apr 2;9(19):4392-4401.
doi: 10.1039/c8sc00068a. eCollection 2018 May 21.

An addressable packing parameter approach for reversibly tuning the assembly of oligo(aniline)-based supra-amphiphiles

Wei Lyu  1   2 , Maha Alotaibi  1   3 , O Alexander Bell  1 , Kazuyoshi Watanabe  1 , Robert Harniman  1 , Benjamin M Mills  1 , Annela M Seddon  4   5 , Sarah E Rogers  6 , Stephen M King  6 , Wei Yan  2 , Charl F J Faul  1
Affiliations

An addressable packing parameter approach for reversibly tuning the assembly of oligo(aniline)-based supra-amphiphiles

Wei Lyu et al. Chem Sci. .

Abstract

We present a newly developed approach to non-covalently address the packing parameter of an electroactive amphiphile. The pH-responsive reversible switching of a tetra(aniline)-based cationic amphiphile, TANI-pentyl trimethylammonium bromide (TANI-PTAB), between self-assembled vesicles and nanowires by acid/base chemistry in aqueous solution is used to exemplify this approach. Trifluoroacetic acid (TFA) was selected as a prototypical acid to form emeraldine salt (ES) state (TANI(TFA)2-PTAB) vesicles for this new class of small-molecule supramolecular amphiphiles. UV-vis-NIR spectroscopy, transmission electron microscopy (TEM), tapping-mode atomic force microscopy (AFM), and fluorescence spectroscopy were used to investigate the reversible structural transformation from vesicles to nanowires. We show that utilising different protonic acid-dopants for TANI-PTAB can regulate the packing parameter, and thus the final self-assembled structures, in a predictable fashion. We envisage potential application of this concept as smart and switchable delivery systems.

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Figures

Scheme 1
Scheme 1. Schematic showing the unique reversible doping/de-doping properties of the TANI-based electroactive amphiphile TANI-PTAB. Tail volume, and thus the packing parameter, can be changed through the use of different dopants.
Fig. 1
Fig. 1. (a) Normalized UV-vis-NIR spectra of EB TANI-PTAB and TFA-doped ES TANI(TFA)2-PTAB samples. (b) TEM image of a 4 mM TANI(TFA)2-PTAB sample (stained with 1% uranyl acetate). (c) Number distribution of object sizes by DLS for a 4 mM TANI(TFA)2-PTAB solution. Scale bar: 200 nm.
Fig. 2
Fig. 2. (a) AFM image of 2 mM TANI(TFA)2-PTAB sample on a mica surface. (b) The corresponding diameter and height distributions counted from 317 particles. (c) AFM image of two typical vesicles, (d) the corresponding 3D image with the Z-ratio increased by a factor of 3 for clarity and (e) their cross-sectional height profile. (f) A proposed scheme showing the possible molecular packing model for the self-assembled vesicles.
Fig. 3
Fig. 3. (a) UV-vis-NIR spectra of TANI(TFA)2-PTAB sample, NaOH de-doped sample and TFA re-doped sample. (b) Control with the addition of NaCl to ES TANI(TFA)2-PTAB. Scale bar: 500 nm.
Fig. 4
Fig. 4. TEM images (stained with 1% uranyl acetate) of (a) TANI(TFA)2-PTAB (1 mM) after standing 1 day, (b) NaOH-de-doped TANI-PTAB after 1 day, (c) the same sample as (b) after 1 week, and (d) TANI(TFA)2-PTAB (0.92 mM) obtained by treating the same sample as (b, c) with TFA, after standing 1 week. Inset photographs (c and d) of the samples showing the gel–sol transition. Scale bars: 200 nm.
Scheme 2
Scheme 2. Schematic showing the proposed doping/de-doping responsive self-assembly behaviour of TANI(TFA)2-PTAB in aqueous solution.
Fig. 5
Fig. 5. TEM images (1 mM solutions, stained with 1% uranyl acetate) of (a) TANI(HCl)2-PTAB, (b) TANI(HNO3)2-PTAB, (c) TANI(TFA)2-PTAB, (d) TANI(DCA)2-PTAB, (e) TANI(AcOH)2-PTAB and (f) TANI(BINPO4H)2-PTAB, with corresponding dopant molecular structures inset. Scale bars: 200 nm.
Scheme 3
Scheme 3. Scheme showing the relationship between packing parameter and the obtained nanostructures using different dopants for our TANI-PTAB system.
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