Coassembly of Poly(ethylene glycol)-<i>block</i>-Poly(glutamate sodium) and Gemini Surfactants with Different Spacer Lengths
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Abstract
The coassembly of poly(ethylene glycol)-<i>b</i>-poly(glutamate
sodium) copolymer (PEG<sub>113</sub>-PGlu<sub>100</sub>) with cationic
gemini surfactants alkanediyl-α,ω-bis-(dodecyldimethylammonium
bromide) [C<sub>12</sub>H<sub>25</sub>(CH<sub>3</sub>)<sub>2</sub>N(CH<sub>2</sub>)<sub><i>S</i></sub>N(CH<sub>3</sub>)<sub>2</sub>C<sub>12</sub>H<sub>25</sub>]Br<sub>2</sub> (designated as
C<sub>12</sub>C<sub><i>S</i></sub>C<sub>12</sub>Br<sub>2</sub>, <i>S</i> = 3, 6, and 12) have been studied by isothermal
titration microcalorimetry, cryogenic transmission electron microscopy,
circular dichroism, small-angle X-ray scattering, zeta potential,
and size measurement. It has been shown that the electrostatic interaction
of C<sub>12</sub>C<sub><i>S</i></sub>C<sub>12</sub>Br<sub>2</sub> with the anionic carboxylate groups of PEG<sub>113</sub>-PGlu<sub>100</sub> leads to complexation, and the C<sub>12</sub>C<sub><i>S</i></sub>C<sub>12</sub>Br<sub>2</sub>/PEG<sub>113</sub>-PGlu<sub>100</sub> complexes are soluble even at the electroneutral point.
The complexes display the feature of superamphiphiles and assemble
into ordered nanosheets with a sandwich-like packing. The gemini molecules
which were already bound with PGlu chains associate through hydrophobic
interaction and constitute the middle part of the nanosheets, whereas
the top and bottom of the nanosheets are hydrophilic PEG chains. The
size and morphology of the nanosheets are affected by the spacer length
of the gemini surfactants. The average sizes of the aggregates at
the electroneutral point are 81, 68, and 90 nm for C<sub>12</sub>C<sub>3</sub>C<sub>12</sub>Br<sub>2</sub>/PEG<sub>113</sub>-PGlu<sub>100</sub>, C<sub>12</sub>C<sub>6</sub>C<sub>12</sub>Br<sub>2</sub>/PEG<sub>113</sub>-PGlu<sub>100</sub>, and C<sub>12</sub>C<sub>12</sub>C<sub>12</sub>Br<sub>2</sub>/PEG<sub>113</sub>-PGlu<sub>100</sub>, respectively.
Both C<sub>12</sub>C<sub>3</sub>C<sub>12</sub>Br<sub>2</sub>/PEG<sub>113</sub>-PGlu<sub>100</sub> and C<sub>12</sub>C<sub>12</sub>C<sub>12</sub>Br<sub>2</sub>/PEG<sub>113</sub>-PGlu<sub>100</sub> mainly
generate hexagonal nanosheets, while the C<sub>12</sub>C<sub>6</sub>C<sub>12</sub>Br<sub>2</sub>/PEG<sub>113</sub>-PGlu<sub>100</sub> system only induces round nanosheets
