Self-Assembly Thermodynamics of pH-Responsive Amino-Acid-Based Polymers with a Nonionic Surfactant

Abstract

The behavior of pH-responsive polymers poly(N-methacryloyl-l-valine) (P1), poly(N-methacryloyl-l-phenylalanine) (P2), and poly(N-methacryloylglycyne-l-leucine) (P3) has been studied in the presence of the nonionic surfactant Brij98. The pure polymers phase-separate in an acidic medium with critical pHtr values of 3.7, 5.5, and 3.4, respectively. The addition of the surfactant prevents phase separation and promotes reorganization of polymer molecules. The nature of the interaction between polymer and surfactant depends on the amino acid structure in the side chain of the polymer. This effect was investigated by dynamic light scattering, isothermal titration calorimetry, electrophoretic measurements, small-angle neutron scattering, and infrared spectroscopy. Thermodynamic analysis revealed an endothermic association reaction in P1/Brij98 mixture, whereas a strong exothermic effect was observed for P2/Brij98 and P3/Brij98. Application of regular solution theory for the analysis of experimental enthalpograms indicated dominant hydrophobic interactions between P1 and Brij98 and specific interactions for the P2/Brij98 system. Electrophoretic and dynamic light scattering measurements support the applicability of the theory to these cases. The specific interactions can be ascribed to hydrogen bonds formed between the carboxylic groups of the polymer and the oligo(ethylene oxide) head groups of the surfactant. Thus, differences in polymer-surfactant interactions between P1 and P2 polymers result in different structures of polymer-surfactant complexes. Specifically, small-angle neutron scattering revealed pearl-necklace complexes and "core-shell" structures for P1/Brij98 and P2/Brij98 systems, respectively. These results may help in the design of new pH-responsive site-specific micellar drug delivery systems or pH-responsive membrane-disrupting agents.

Structure Tuning of Electrostatically Self‐Assembled Nanoparticles through pH: The Role of Charge Ratio

“…A versatile trigger to achieve structural control over the self‐assembled nanoparticles is pH; for instance, building blocks with pH‐dependent molecular structure can be used . Recently, we have introduced a concept of electrostatic self‐assembly relying on a general combination of interactions leading to the synthesis of well‐defined supramolecular nanoscale assemblies .…”

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particular with regard to newer concepts for self-assembly.A versatile trigger to achieve structural control over the self-assembled nanoparticles is pH; for instance, building blocks with pH-dependent molecular structure can be used. [12][13][14][15][16] Recently, we have introduced a concept of electrostatic self-assembly relying on a general combination of interactions leading to the synthesis of well-defined supramolecular nanoscale assemblies. [17] The process is based on the self-assembly of polyelectrolytes and organic counterions and results in electrostatically stabilized nanoparticles with sizes up to more than hundred nanometers.

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Structure Tuning of Electrostatically Self-Assembled Nanoparticles through pH

“…In addition, particles with triggerable size and shape are of special interest for drug delivery. For example, the circulation lifetime of intravenously administered nanoparticles has been demonstrated to depend on their dimension and shape. − Among others, pH variation is commonly used as a trigger for size and shape. − In this context, we have recently introduced the concept of electrostatic self-assembly for the formation of responsive supramolecular nanoscale assemblies. − The process is based on the interconnection of dendrimeric macroions and oppositely charged multivalent azo dyes under secondary interaction effects such as π–π stacking or geometric factors and leads to the formation of nanoparticles with sizes up to more than 100 nm. , The process relies on a general combination of interactions rather than on specific binding motifs. Choosing appropriate building blocks, switchable nanoparticles that respond to light and pH have been built. ,, An assembly with on–off switchability through pH is realized via protonation and deprotonation of the polyelectrolyte, that is, charging and uncharging the dendrimer macroions.…”

Dual Thermoresponsive Boc-Lysine-Based Acryl Polymer: RAFT Kinetics and Anti-Protein-Fouling of Its Zwitterionic Form

“…FTIR (cm −1 ) (Figure S2C): 3300, ν N−H (amide); 1692, ν CO (carbamate); 1657, ν CO (amide I); 1520, ν CO (amide II); 1394, ν C−N (amide). 1 H NMR (400 MHz, CD 3 OD, TMS) δ (ppm) (Figure S9): 1.42 (s, 9H, "h"), 4.0 (br s, 1H), 1.75 (br s, 2H, "g"), 1.61 (br s, 2H, "f"), 1.52 (br s, 2H, "d"), 3.0 (br s, 2H, "e"), 2.0 (br s, 2H, "a"), and 1.51 (br s, 1H, "b"). 13 C NMR (100 MHz, CD 3 OD, TMS) δ (ppm) (Figure S10): 23.1 (methylene, "f"), 28.2 (methyl, "l"), 28.7 (methylene, "e"), 30.7 (methylene, "g"), 40.3 (methylene, "d"), 55.5 (methyne, "h"), 80.8 (tertiary, "k"), 31.5 (methylene, "a"), 42.7 (methyne, "b"), 158.5 (carbamate, "j"), 177.3 (amide, "c"), and 178.6 (carboxyl, "i").…”