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Solvent Switchable Nanostructure and Function of a π-Amphiphile

Abstract

The manuscript reports solvent-tunable nanostructure of a π-amphiphile (NDI-PY) consisting of a naphthalene-diimide (NDI) chromophore connected to a non-ionic hydrophilic-wedge by a hydrazide linker and a pyridine group on the other arm. NDI-PY self-assembles in water as well as in tetra-chloroethylene (TCE) by H-bonding and π-stacking with almost identical critical aggregation concentration (~ 0.3 mM) and H values (-12.3 KJ mol-1 and -5.35 KJ mol-1 in water and TCE, respectively). However, it produces monolayer vesicles (Dh = 150-180 nm) in water with the pyridine groups displayed at the outer surface, while in TCE it generates a transparent gel with nanotubular (width ~ 50 nm, wall thickness of ~ 10 nm) morphology. Powder X-ray diffraction studies show a single sharp peak at the low angle (d = 19.3 Å, little shorter than the extended length of the molecule) in water suggesting monolayer membrane, while in TCE several sharp peaks appear with the d values maintaining a ratio of 1: 1/√3: 1/2: 1/√7: 1/3: 1/√12 indicating a 2D hexagonal lattice. Photoconductivity measurement reveals moderate electronic conduction in both cases. However it shows remarkable enhancement of the lifetime of the charge-carriers for the nanotubular structure compared to the vesicular morphology. On the other hand, the vesicles display antimicrobial activity selectively against Gram-positive S. aureus with a promising MICLB value of 29.4 µg/mL. In contrast, it does not lyse human red blood cells even at 2.5 mg/mL (HC50> 2.5mg/mL) implying high selectivity of the NDI-PY vesicles towards bacterial cells over mammalian cells. Display of the pyridine groups at the outer wall of the membrane enables molecular recognition by H-bonding with a carboxylic acid group and thereby facilitates uptake of the attached pyrene chromophores in the NDI-membrane by NDI-pyrene charge-transfer interaction. A Job’s plot reveals maximum uptake at 1:1 ratio of the NDI-PY / pyrene indicating all the pyridine groups are accessible at the vesicular surface.

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Publication details

The article was received on 26 Oct 2017, accepted on 05 Jan 2018 and first published on 09 Jan 2018


Article type: Paper
DOI: 10.1039/C7NR07989C
Citation: Nanoscale, 2018, Accepted Manuscript
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    Solvent Switchable Nanostructure and Function of a π-Amphiphile

    A. Sikder, J. Sarkar, T. Sakurai, S. Seki and S. Ghosh, Nanoscale, 2018, Accepted Manuscript , DOI: 10.1039/C7NR07989C

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