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J Phys Chem B. 2014 Feb 27;118(8):2274-83. doi: 10.1021/jp412273h. Epub 2014 Feb 11.

Thermoregulated formation and disintegration of cationic block copolymer vesicles: fluorescence resonance energy transfer study.

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Department of Chemistry, Indian Institute of Technology Kharagpur , West Bengal 721302, India.


Formation and disintegration of self-assembled nanostructures in response to external stimuli are important phenomena that have been widely explored for a variety of biomedical applications. In this contribution, we report the thermally triggered assembly of block copolymer molecules in aqueous solution to form vesicles (polymersomes) and their disassembly on reduction of temperature. A new thermoresponsive diblock copolymer of poly(N-isopropylacrylamide) poly((3-methacrylamidopropyl)trimethylammonium chloride) (PNIPA-b-PMAPTAC) was synthesized by reversible addition-fragmentation chain transfer technique. The solution properties and self-assembling behavior of the block copolymer molecules were studied by turbidimetry, temperature-dependent proton nuclear magnetic resonance, fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. Fluorescence resonance energy transfer studies between coumarin-153 (C-153, donor) and rhodamine 6G (R6G, acceptor) have been performed by steady-state and picosecond-resolved fluorescence spectroscopy to probe the structural and dynamic heterogeneity of the vesicles. The occurrence of efficient energy transfer was evident from the shortening of donor lifetime in the presence of the acceptor. The capability of the vesicles to encapsulate both hydrophobic and hydrophilic molecules and release them in response to decrease in temperature makes them potentially useful as drug delivery vehicles.


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