Catalytic droplets

Subjects

Catalysis research has long focused on the structure and properties of reactive sites. Yet chemical reactivity is often governed just as strongly by the surrounding microenvironment, including local polarity, substrate partitioning and effective concentrations. Biomolecular droplets formed by liquid–liquid phase separation (Bio-LLPS) provide one such microenvironment and are considered compartmentalized reaction media for both chemical and biological contexts.

In this new system, however, the catalytic motif is built into the droplet itself. The researchers constructed droplets from a tripeptide, l-Pro-l-Phe-l-Phe bearing a C-terminal methyl ester (PFF-OMe), which spontaneously forms droplets in water by LLPS. The catalytic functionality of aldol chemistry, where the phenylalanine residues may help establish a hydrophobic interior, enables high local densities of catalytic groups, proline at the ends, in an easily extensible design. This PFF-OMe droplet is able to incorporate cyclohexane, probably owing to the hydrophobic environment inside the PFF-OMe droplets. This hydrophobic environment was demonstrated experimentally by both a spectroscopic assay using a solvatochromic dye and through hydrophobic fluorescent dye-selective incorporation into droplets. This supported the proposed model that the hydrophobic environment of the droplet contributes to the accumulation of reactive species. In addition, it suggests that modifying the internal conditions of the droplet could enable the selective accumulation of the desired species.

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