INSIDE THE M₆L₄ CAGE

A small space.
A different
chemistry.

Six metal centres. Four ligands.
A cavity that recognises molecules—and reshapes what they can do.

Space-filling rendering of the M6L4 coordination cage, with its molecular surface surrounding an internal cavity — M₆L₄ A self-assembled molecular host

01 / RECOGNITION

The chemistry of fitting in.

The cage is a host; the molecule it binds is a guest. Recognition emerges from the fit between the guest, the cavity and the surrounding solvent.

A pocket in water

The cage’s hydrophobic interior can favour the uptake of organic guests from water. Open windows allow molecules to enter and leave.

II.

A complementary fit

Size, shape and noncovalent contacts determine how a guest is accommodated. When guests share the cavity, their interactions also matter.

III.

A constrained geometry

Inside, a molecule has fewer ways to move and fold. Confinement can stabilise unusual conformations and expose particular sites to reaction.

02 / MOLECULAR CONFINEMENT

Recognise. Fold. Transform.

Three views into the same family of cages. Three ways confinement changes molecular behaviour.

Orange terpenoid folded into a U-shaped conformation inside a grey coordination cage — Linear diterpenoid · U-shaped folding

FOLDING / 2019

A long molecule,
folded into place.

A flexible linear diterpenoid adopts a U-shaped conformation inside the cage. This arrangement shields internal carbon–carbon double bonds, enabling selective reaction at an exposed site.

Conformation controls accessibility.

Takezawa, Kanda, Nanjo & Fujita
Journal of the American Chemical Society 2019, 141, 5112–5115.Read the study →

An amide guest highlighted inside the coordination cage in a confined, twisted conformation — Aromatic amide · Conformational distortion

TWISTING / 2020

A subtle twist.
A change in reactivity.

Encapsulation stabilises a twisted amide conformation. Distorting the normally planar amide weakens its conjugation and accelerates hydrolysis.

Conformation changes chemical reactivity.

Takezawa, Shitozawa & Fujita
Nature Chemistry 2020, 12, 574–578.Read the study →

Calixarene guest highlighted in orange within the grey coordination cage — Calix[4]arene · Enforced conformation

SITE DIFFERENTIATION / 2023

A familiar ring.
A new distinction.

Confinement enforces a particular calix[4]arene conformation. The surrounding cage differentiates chemical sites, providing a route to selective functionalisation.

Conformation creates distinct chemical sites.

Iizuka, Takezawa & Fujita
Journal of the American Chemical Society 2023.Read the study →

03 / FROM RECOGNITION TO SEEING

Capture molecules.
Reveal their structures.

Binding a guest is only the beginning. To see it by X-ray diffraction, the host–guest complex must form a crystal in which the guest is sufficiently ordered.

Electrostatic assembly with “sticker” anions links cationic cages into crystalline materials. Controlling this assembly helps carry solution-state host–guest chemistry into the solid state—and opens the way to cage-based crystalline sponges.

He, Yu, Iizuka, Takezawa & Fujita
Nature Chemistry 2025Read the study →

Discover the method Explore the Collection

Four molecular structures shown as space-filling models within grey coordination cages — Capture molecules. Reveal their structures.

A small space.A different chemistry.