Squaramide macrocycles that prefer sulfate in water

Meta-linked squaramide macrocycles bind SO42− so tightly in wet DMSO that NMR cannot measure Ka, and they still select sulfate in 50% water.

Keep what you just learned

Save these 11 cards to your NoteFren library. Your first review starts right away, and each card links back to the study it came from.

What new receptors were made?

A family of squaramide-based macrocycles that can be functionalized for solubility.

Which anion do the meta-MSQs prefer, even in 50% water?

Sulfate (SO42−).

How tight is sulfate binding for 1 and 2 in wet DMSO?

Ka > 10^4 M−1, too high to measure accurately by NMR.

How does 2 differ from 1 in selectivity?

2 is highly sulfate-selective; 1 also binds H2PO4− and AcO− strongly.

What crystal geometry does 1·SO42− adopt?

A 1:1 bowl-like cone reminiscent of a calixarene.

Why is sulfate hard to bind in water?

Its hydration energy is −1090 kJ mol−1.

What Ka does Nature’s sulfate-binding protein achieve?

8.3 × 10^6 M−1 between pH 5 and 9.

Does 6 beat the protein at sulfate vs chromate?

Authors say 6 discriminates sulfate from chromate better than the sulfate-binding protein.

What binding stoichiometry fits the NMR titrations?

A 1:1 model in Hyperquad (Job plots agree).

Suggested applications if selectivity holds?

Nuclear-waste sulfate extraction and plasma sulfate detection.

What hydrogen-bond donors line the cavity?

Squaramide NH groups (four contacts to sulfate oxygens in the crystal).