Cromoglycate mesogen forms isodesmic assemblies promoted by peptides and induces aggregation of a range of proteins

Disodium cromoglycate (5'DSCG) belongs to a class of nonamphiphilic molecules that form nematic chromonic liquid crystals in aqueous solutions. As the concentration increases, it is believed that the molecules first form isodesmic assemblies in water, which further align to form liquid crystal phases. However, the reports on isodesmic assemblies of 5'DSCG have been scarce. Herein, we show that the presence of peptides can promote the isodesmic assembly of 5'DSCG over a broad range of concentrations before reaching the liquid crystal phase. The presence of peptides can lower the 5'DSCG concentration in the aqueous solution to ∼1.5 wt% (from 11-12 wt%, forming a nematic liquid crystal phase) for isodesmic assembly formation. This result indicates a demixing between 5'DSCG and peptides in aqueous solution. We further explored this demixing mechanism to precipitate a wide range of proteins, namely, lectin A, esterase, lipase, bovine serum albumin, trypsin, and a pilin protein from bacterium Pseudomonas aeruginosa. We found that 5'DSCG caused the aggregation of all these proteins except trypsin. These results, along with past findings, suggest that 5'DSCG isodesmic assemblies have the potential to assist in protein purification and crystallization.