Effects of Halide Anions on the Solution Behavior of Double Hydrophilic Carboxy-Sulfobetaine Block Copolymers

Abstract

The solution behavior of the double polybetaine block copolymer poly­(2-((2-(methacryloyloxy)­ethyl)­dimethylammonio)­acetate)-block-poly­(3-((2-(methacryloyloxy)­ethyl)­dimethylammonio)­propane-1-sulfonate (PGLBT-b-PSPE) in sodium halide aqueous solutions was investigated. In the presence of salt ions, the unimer-to-micelle transition of PGLBT-b-PSPE that originated by Coulombic attraction between PSPE motifs was suppressed and shifted to much lower temperatures. The transition was hindered more by increases in the salt concentration because of additional counterion binding on the ionized site of PGLBT-b-PSPE chains, which screens the dipole–dipole attractions. The specific ion effect was investigated on four different halides, Cl–, Br–, I–, and F–. Cl– and two chaotropes (Br– and I–) apparently prevented micelle formation, and the hindering effectiveness on the PSPE pairing followed the general Hofmeister series of anions: I– > Br– > Cl–. More chaotropic anions strongly maintained the polymer chains in a fully hydrated state when the same amount of salts was incorporated. However, F–, which is classified as a kosmotrope, only made a small contribution to lowering the transition point and led to abrupt transition without showing a gradual phase change prior to the transition. The variations of hydrodynamic radius and zeta potentials of unimers and micelles gave hints of the solvation state of salt-incorporated PGLBT-b-PSPEs in each state. These results suggest that chaotropic halides tend to exist in the vicinity of the diblock polybetaine chain surface and thus prominently influenced the thermoresponsive solution behavior, whereas kosmotropic F– prefers water molecules and causes minor changes in the PGLBT-b-PSPE aqueous solution.

Modulation of Double Zwitterionic Block Copolymer Aggregates by Zwitterion-Specific Interactions

“…The micellar assemblies dissociate by thermal activation because of the dissociation of the PSB3 chains which show upper critical solution temperature. Furthermore, the SB couple dissociation is promoted by the interaction with ions, and the efficiency depends on the ion species. − Although the PCB2- b -PSB4 diblock copolymers studied in this study consists of a PSB chain with longer CSL (the carbon number between the charges is 4), the aggregation behavior, impact of ions, and ion specificity in the dissociation of the micellar aggregates were almost consistent with PCB2- b -PSB3 (Figures S3 and S4). It should be noted that the temperature responsibility is diminished because of the enhanced association efficiency of PSB4, whereas the ion responsibility was promoted due to the charge separation with long hydrocarbon .…”

“…Matsuoka and co-workers reported systematic studies for the aggregation of double zwitterionic diblock copolymers composed of PCB2 and PSB with CSL of 3 (the carbon number between the charges is 3; PSB3) in aqueous solutions. − The PCB2- b -PSB3 block copolymers produce spherical core–shell micelles as shown in the shape factor ( R g / R h ) values. The micellar assemblies dissociate by thermal activation because of the dissociation of the PSB3 chains which show upper critical solution temperature.…”

“…The SB couples dissociate in aqueous electrolyte solutions due to the charge screening effect. Matsuoka and co-workers reported that block copolymers composed of PCB and PSB chains produce spherical core–shell micellar aggregates in salt-free water, while the micelles dissociate in response to temperature and salts. − We showed the lyotropic microphase separation in high concentration aqueous solutions of a block copolymer composed of poly­(2-[( N -2-methacryloyl­oxyethyl- N , N -dimethyl)­ammonio]­acetate) (PCB2) and poly­(3-[( N -2-methacryl­oyloxyethyl- N , N -dimethyl)­ammonio]­butane-1-sulfonate]) (PSB4) (PCB2- b -PSB4) and the polymer concentration-dependent morphology transition . Thus, the double zwitterionic block copolymers could be regarded as a new type of double hydrophilic block copolymers that produce ordered aggregates; however, the molecular mechanisms in the phase separation have not yet been elucidated.…”

Double hydrophilic block copolymers self-assemblies in biomedical applications

“…Temperature and pH have been largely exemplified in this work and are the two main parameters considered for triggering the change of macromolecular conformation in water, especially for drug delivery. However, ionic strength and the nature of the counter ions can also be considered, for example in the case of zwitterionic DHBCs [107] or of DHBCs exhibiting self-assembly upon addition of metal ions to form supramolecular hydrogels [108].…”

Thermo-Responsive Polyion Complex of Polysulfobetaine and a Cationic Surfactant in Water

“…Some of them exhibit pH-responsive [ 17 , 18 , 19 , 20 , 21 ] and thermo-responsive behaviors [ 22 , 23 , 24 , 25 , 26 , 27 ] and biocompatibility [ 28 , 29 , 30 ]. Especially, polysulfobetaines show upper critical solution temperature (UCST) behavior in water [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. UCST is the critical temperature above which the mixture solution is miscible, meaning that a single phase exists for all of the composition, and under critical temperatures, the solution becomes turbid because the solute cannot dissolve in solvent.…”