Polyradical PROXYL/TEMPO-Derived Amides: Synthesis, Physicochemical Studies, DFT Calculations, and Antimicrobial...

Area of Science:

• Organic Chemistry
• Physical Chemistry
• Biochemistry

Background:

• Nitroxide radicals, such as PROXYL and TEMPO, are stable free radicals with diverse applications.
• Polynitroxide amides offer unique structural and electronic properties due to multiple radical centers.
• Understanding the relationship between structure, dynamics, and electrochemical properties is crucial for designing novel functional materials.

Purpose of the Study:

• Synthesize and characterize novel polynitroxide amides incorporating PROXYL and/or TEMPO units.
• Investigate the paramagnetic properties and intramolecular dynamics using Electron Paramagnetic Resonance (EPR) spectroscopy.
• Evaluate the electrochemical behavior and potential antimicrobial activities of the synthesized compounds.

Main Methods:

• Synthesis of polynitroxide amides with varying bridge structures.
• Electron Paramagnetic Resonance (EPR) spectroscopy for paramagnetic characterization and dynamic analysis.
• Low-temperature X- and Q-band EPR for spin-spin distance determination.
• Density Functional Theory (DFT) calculations for theoretical spin-spin distances.
• Cyclic voltammetry for electrochemical behavior assessment.
• Antimicrobial assays against bacteria, yeasts, and fungi.

Main Results:

• Successful synthesis of polynitroxide amides containing PROXYL and/or TEMPO moieties.
• EPR studies revealed detailed information on intramolecular motions, thermodynamics, and spin-exchange mechanisms.
• Spin-spin distances determined by EPR correlated well with DFT calculations.
• PROXYL-based biradicals exhibited reversible electrochemical behavior, while TEMPO-containing compounds showed reduced reversibility.
• Some nitroxide compounds demonstrated inhibitory activity against model microorganisms.

Conclusions:

• The synthesized polynitroxide amides possess distinct paramagnetic and electrochemical properties influenced by their structure.
• EPR spectroscopy is a powerful tool for probing dynamics and spin interactions in these systems.
• Electrochemical stability varies significantly between PROXYL and TEMPO based radicals.
• The compounds show potential for applications requiring stable radicals and exhibit preliminary antimicrobial effects.