Triarylmethyl Radicals: EPR Study of ¹³C Hyperfine Coupling Constants

Area of Science:

• Chemistry
• Spectroscopy
• Biophysics

Background:

• Triarylmethyl (TAM) radicals are vital spin labels in Electron Paramagnetic Resonance (EPR) spectroscopy and spin probes for *in vivo* oxymetry.
• Their narrow EPR lines and slow spin relaxation at physiological temperatures are advantageous for pulsed dipolar EPR methods in biomolecular distance measurements.

Purpose of the Study:

• To synthesize a diverse series of TAM radicals and their deuterated analogs.
• To characterize their spectroscopic parameters, including novel ¹³C hyperfine constants.
• To demonstrate the utility of these TAMs for distance measurements using Pulsed Electron Double Resonance (PELDOR).

Main Methods:

• Synthesis of a large series of triarylmethyl (TAM) radicals and their deuterated analogues.
• Spectroscopic characterization, including determination of ¹³C hyperfine constants.
• Application of Pulsed Electron Double Resonance (PELDOR/DEER) for distance measurements at room temperature.

Main Results:

• A comprehensive series of TAM radicals and deuterated analogues were synthesized and characterized.
• ¹³C hyperfine constants were obtained for the first time, showing negligible dependence on solvent and substituent variations.
• Successful room-temperature distance measurements were achieved using natural abundance ¹³C signals via PELDOR.

Conclusions:

• The synthesized TAM radicals exhibit favorable properties for EPR spectroscopy and imaging.
• ¹³C hyperfine constants are robust, simplifying their use in various environments.
• PELDOR measurements using natural abundance ¹³C signals offer a viable method for room-temperature distance determination in biomolecules.