Thermodynamics of Interactions Between Charged Surfactants and Ionic Poly(amino acids) by Isothermal Titration Calorimetry

Abstract

Interactions between charges play a role in protein stability and contribute to the energetics of binding between various charged ligands. Ionic surfactants are charged molecules, whose interactions with proteins are still rather poorly understood despite their wide applications. Here, we show by isothermal titration calorimetry that cationic alkylammonium surfactants bind to negatively charged polyaspartate and polyglutamate homopolymers stoichiometrically, i.e., one surfactant molecule per charged amino acid. Similarly, negatively charged alkyl sulfates (e.g., sodium dodecyl sulfate) and alkane sulfonates bind stoichiometrically to positively charged polylysine, polyornithine, and polyarginine homopolymers. In these reactions, the interacting counterparts form ion pairs and the resulting electrostatically neutral complex coprecipitates from solution. The enthalpies and heat capacities are determined for various pairs of ionic surfactants and charged amino acid homopolymers. These results show the energetic contributions of ionic headgroups and the CH2 group to surfactant interactions with proteins.

Revealing the Molecular-Level Interactions between Cationic Fluorinated Polymer Sorbents and the Major PFAS Pollutant PFOA

“…55,56 For polymers bearing cationic quaternary ammonium groups, endothermic events are observed for titration of PFOA into solutions of both PAO-F + (first injection) and PA+ (first three injections) (Figures 7, in red and gray), indicating the presence of an endothermic event arising from the electrostatic attraction between PFOA and the two cationic polymers. This is in line with the report by Skvarnavicíus et al, 57 who observed endothermic binding interactions by titrating cationic alkylamines surfactant solution into a solution containing anionic poly(amino acid)s with carboxyl groups.…”

Salt‐tolerant cation exchanger‐containing sulfate groups as a viable alternative for mixed‐mode type and heparin‐based affinity resins

“…Skvarnavicius [ 28 ] presented another experimental observation about the difference between sulfate and sulfonium groups. The authors measured the enthalpies by isothermal titration calorimetry of cationic poly(amino acid)s with negatively charged alkyl sulfates and alkane sulfonates.…”

“…[ 35 ] Even though, chromatography is the method of choice for plasma fractionation, there is still a need for optimization of the production processes for increased economic benefits and safety. [ 28 ] Biopolymers with sulfate‐based ligands, mostly Heparin Sepharose, are used in these polishing steps, especially for production of both recombinant and plasma derived clotting factor IX, and possible introduction of more stable and virus‐safe substitutions for this resin have been frequently discussed. [ 19,20,35,37 ]…”

A Review on Interactions between Amino Acids and Surfactants as Well as Their Impact on Corrosion Inhibition

“…As denaturation and unfolding of protein depend on the pH of the medium, , the micelle formation of surfactants is also affected by the pH of the solution. It has been observed that at low pH and concentration, the interactions between amino acids and surfactants are mainly electrostatic, and the interactions become hydrophobic with an increase in the concentration of surfactants. , Further, at low pH, amino acids become cationic, and at high pH, they behave as zwitterions/anionic . Numerous surfactants have been studied, and it has been shown that pH has no impact on aggregations. , However, amino acids are neutral when the pH is near to the isoelectric point.…”