Orthosteric Control of Acidity Through Sulfate Binding in a Neutral Cyclo[8]pyrrole

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Chemical Sensing

Background:

• Binding events can modulate local environments, shifting acid-base equilibria.
• Synthetic systems that regulate proton activity via binding are desirable for chemical control.

Purpose of the Study:

• To design and synthesize a naphthalimide-fused cyclo[8]pyrrole analogue.
• To investigate anion recognition-induced shifts in protonation equilibria.
• To develop an anion-actuated acid switch.

Main Methods:

• Synthesis of a novel electron-deficient macrocycle.
• Characterization of its redox and acid-base properties in organic solvents.
• Investigation of anion binding effects on protonation equilibria using techniques like pKa measurements.

Main Results:

• The electron-deficient macrocycle prefers a neutral redox state and exhibits high Brønsted acidity.
• It retains anion recognition capabilities, including strong sulfate affinity.
• Sulfate binding increases the first pKa by approximately four units in DMSO, demonstrating an orthosteric acid switch.

Conclusions:

• A new synthetic system demonstrates anion-actuated control over protonation equilibria.
• This expands the design principles for switchable acidity beyond existing methods.
• The developed macrocycle serves as a functional anion-actuated acid switch.