A Cationic Catechol Derivative Binds Anions in Competitive Aqueous Media

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Crystallography

Background:

• Simple isoquinolinium scaffolds can be synthesized.
• Natural products like pseudopalmatine can be co-isolated during synthesis optimization.
• Catechol motifs combined with positive charges can form potent anion receptors.

Purpose of the Study:

• To synthesize and characterize a simple dihydroxy isoquinolinium molecule (3+).
• To investigate the anion binding properties of compound 3+.
• To characterize unexpected zwitterionic products formed during anion metathesis.

Main Methods:

• Modification of a literature procedure for synthesis.
• Isolation and X-ray crystallography for characterization.
• Anion binding studies using techniques like NMR spectroscopy (implied by Ka values).
• X-ray crystallography for characterizing zwitterions.

Main Results:

• A simple dihydroxy isoquinolinium molecule (3+) was successfully prepared.
• Compound 3+ demonstrated potent sulfate binding (Ka > 10^4 M^-1 in specific solvent mixtures).
• Chloride binding was significantly weaker than sulfate binding.
• Unexpected zwitterions with tetrahedral boronate centers were formed and characterized by X-ray crystallography.
• Pseudopalmatine was isolated and characterized by X-ray crystallography for the first time.

Conclusions:

• The synthesized isoquinolinium molecule is a highly effective sulfate receptor.
• The molecule's reactivity with specific anions (BPh4-, BF4-) complicates anion binding studies but leads to novel zwitterionic structures.
• X-ray crystallography is crucial for characterizing both the target molecule, co-isolated natural products, and unexpected reaction products.