Benzoylguanidines as Anion-Responsive Systems

Area of Science:

• Supramolecular Chemistry
• Analytical Chemistry
• Computational Chemistry

Background:

• Benzoylguanidinium salts are investigated for their anion-sensing capabilities.
• Understanding proton transfer equilibria is crucial for designing chemical sensors.

Purpose of the Study:

• To synthesize and characterize benzoylguanidinium salts.
• To investigate their spectral responses to various anions.
• To model the electronic transitions responsible for spectral changes.

Main Methods:

• Synthesis of benzoylguanidinium salts.
• UV/Vis spectroscopy to monitor spectral changes upon anion addition.
• Potentiometric titration to determine pK_a values in acetonitrile and acetonitrile/water mixtures.
• Time-dependent Density Functional Theory (TD-DFT) calculations (CAM-B3LYP, PBE0) and CC2 calculations for spectral modeling.

Main Results:

• All synthesized compounds deprotonate in the presence of basic anions in acetonitrile.
• N¹ -benzoyl-N³ -(p-nitrophenyl) guanidinium chloride shows a distinct color change from colorless to yellow.
• Measured pK_a (BH⁺ ) values in acetonitrile range from 12-16, and 4-6 in acetonitrile/water mixtures.
• TD-DFT calculations with optimized long-range correction parameters (ω) successfully model experimental UV/Vis spectra, correlating spectral shifts with charge transfer character.

Conclusions:

• Benzoylguanidinium salts can act as effective anion sensors, indicated by spectral changes.
• The observed spectral properties are well-reproduced by computational modeling, particularly TD-DFT.
• The study provides insights into the electronic structure and proton transfer mechanisms of benzoylguanidinium systems.