Anion-π Interactions in Supramolecular Chemistry

Anion-π interactions represent a distinct class of non-covalent forces in which electron-deficient aromatic systems engage attractively with negatively charged species. Once considered counter-intuitive due to presumed repulsion between negative charge and π-electron clouds, these interactions have emerged as powerful tools for molecular recognition, transport and catalysis within supramolecular assemblies. At their core, anion-π contacts rely on the combination of quadrupolar electrostatics, induced polarisation and dispersion forces to stabilise anionic guests on π-acidic surfaces. Such surfaces are often constructed from electron-poor aromatics bearing strong electron-withdrawing substituents, which enhance the positive quadrupole moment above and below the aromatic plane.

In supramolecular chemistry, anion-π motifs have been incorporated into receptors for selective anion binding, artificial ion channels for controlled transport and catalytic platforms for the stabilisation of anionic transition states. Molecular foldamers and micellar aggregates decorated with π-acidic units have demonstrated remarkable rates and selectivities in aqueous media, while discrete macrocyclic hosts exploit anion-π complementarity to achieve high-fidelity recognition of halides and oxoanions. Cooperativity with other weak forces, such as hydrogen bonding or π-π stacking, often amplifies affinity and specificity, yielding ternary assemblies with emergent functions. Beyond synthetic systems, statistical surveys of protein and nucleic acid structures have revealed that anion-π interactions contribute to enzyme active-site architecture, epigenetic regulation and protein-folding landscapes.

Global significance arises from the ability to harness anion-π interactions for green chemistry and advanced materials. Catalytic processes that stabilise charged intermediates on π-acidic surfaces offer routes to diastereo- and enantioselective transformations without reliance on metal centres. In materials science, integration of anion-π motifs into polymeric frameworks and crystalline networks enables controlled ion conduction, selective sensing and self-healing properties. The modularity of these interactions fosters rational design strategies across disciplines, bridging fundamental studies and practical applications in environmental remediation, pharmaceutical development and electronic devices.

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Anion-π Interactions in Supramolecular Chemistry publication trend

The graph below shows the total number of articles in anion-π interactions in supramolecular chemistry across all publications each year (not limited to Nature Index journals).

Technical terms

Anion-π interaction: Attractive non-covalent contact between an anion and an electron-deficient aromatic π-system, driven by electrostatic quadrupoles, polarisation and dispersion.

π-acidic surface: An aromatic framework rendered electron-poor through substituents or ring modification, creating regions of positive quadrupole for binding anions.

Supramolecular catalysis: Accelerated chemical transformation mediated by organised assemblies of molecules held together by non-covalent interactions.

Autocatalysis: Self-amplifying reaction mechanism in which product formation enhances its own rate, often via templating or activation on a catalytic surface.

References

1. Anion‐(π)n‐π Catalytic Micelles. Angewandte Chemie International Edition (2023).
2. The Origin of Anion−π Autocatalysis. JACS Au (2023).
3. A thorough anion–π interaction study in biomolecules: on the importance of cooperativity effects. Chemical Science (2016).
4. Experimental investigation of anion–π interactions – applications and biochemical relevance. Chemical Communications (2016).