# Decoding the Principles Governing Molecular Cage Precipitation of Aliphatic and Perfluoroalkyl Acids (PFAAs)

## TL;DR

This study investigates how molecular cages remove pollutants and finds that lipophilicity, not fluorination, determines their effectiveness.

## Contribution

The study reveals that lipophilicity governs cage precipitation, challenging assumptions about fluorinated surfactant selectivity.

## Key findings

- Molecular cages do not inherently prefer fluorinated over aliphatic surfactants.
- Lipophilicity is the main factor controlling surfactant precipitation by molecular cages.
- Surfactants in mixtures can be selectively isolated based on their lipophilicity.

## Abstract

Perfluoroalkyl acids (PFAAs) are surfactants that rank
among the
most persistent and hazardous anthropogenic pollutants. Molecular
cages have emerged as promising remediation agents, enabling the straightforward
isolation and purification of PFAAs through selective binding and
precipitation. However, critical gaps remain regarding (i) the degree
of genuine selectivity for PFAAs over structurally analogous aliphatic
surfactants, (ii) the structural features that govern cage–surfactant
precipitation, and (iii) cage performance in mixed-surfactant systems.
The absence of systematic investigations has impeded the rational
design of cages with targeted selectivity and a limited understanding
of their behavior in chemically complex environments. Herein, using
one of the most efficient cages reported for PFAA removal, we address
these questions and demonstrate that molecular cages do not intrinsically
discriminate between fluorinated and aliphatic surfactants; instead,
lipophilicity is the primary parameter controlling precipitation.
Moreover, we show that surfactants in mixtures can be selectively
isolated in an ordered fashion according to their lipophilicity.