Synthesis, Characterization, and Application of a Highly Hydrophilic Triarylmethyl Radical for Biomedical EPR

Abstract

Stable tetrathiatriarylmethyl radicals have significantly contributed to the recent progress in biomedical electron paramagnetic resonance (EPR) due to their unmatched stability in biological media and long relaxation times. However, the lipophilic core of the most commonly used structure (Finland trityl) is responsible for its interaction with plasma biomacromolecules, such as albumin, and self-aggregation at high concentrations and/or low pH. While Finland trityl is generally considered inert toward many reactive radical species, we report that sulfite anion radical efficiently substitutes the three carboxyl moieties of Finland trityl with a high rate constant of 3.53 × 108 M–1 s–1, leading to a trisulfonated Finland trityl radical. This newly synthesized highly hydrophilic trityl radical shows an ultranarrow linewidth (ΔB pp = 24 mG), a lower affinity for albumin than Finland trityl, and a high aqueous solubility even at acidic pH. Therefore, this new tetrathiatriarylmethyl radical can be considered as a superior spin probe in comparison to the widely used Finland trityl. One of its potential applications was demonstrated by in vivo mapping oxygen in a mouse model of breast cancer. Moreover, we showed that one of the three sulfo groups can be easily substituted with S-, N-, and P-nucleophiles, opening access to various monofunctionalized sulfonated trityl radicals.

Perspectives for polychlorinated trityl radicals

“…It uses oxygen-sensing spin probes whose EPR lines are broadened by molecular oxygen. 127 It is even possible to perform in vivo oxygen mapping in animals, 128,129 or to use two techniques at the same time such as dissolution dynamic nuclear polarization and Overhauser-enhanced magnetic resonance imaging (OMRI) for Trityl organic radicals can be used as spin labels to measure distances in biomacromolecules. Using pulsed dipolar EPR spectroscopy (PDS) in conjunction with sitedirected spin labelling (SDSL) techniques, these species have enabled distances measurements to be performed in DNA and proteins for structural biology studies.…”

Synthesis and Redox Properties of Water-Soluble Asymmetric Trityl Radicals

“…A similar result has been recently reported for a hydrophilic trityl radical dFT-(SO 3 ) 3 whose EPR signal intensity does not show any noticeable decrease in the mixture of GSH and Asc. 34 Complete inhibition of the reaction of CT-03 with GSH by Asc (500 μM) is most likely due to the high reactivity (k 2 = 2.7 × 10 5 M −1 s −1 ) 49 of Asc with O 2…”

“…Moreover, trityl-based spin labels exhibit great application potentials in room temperature and in-cell distance measurements of proteins and nucleic acids by pulsed EPR dipolar spectroscopy. − We have also synthesized various trityl-nitroxide biradicals which are excellent polarizing agents for high-field DNP − and can also be used to measure total redox status . Considering the wide applications of trityl radicals, various synthetic methods have also been developed for asymmetric − and hydrophilic − derivatives.…”

Dynamic Electron Paramagnetic Resonance Imaging: Modern Technique for Biodistribution and Pharmacokinetic Imaging

“…Of course, it is possible to function and administer the marker with a drug or other selected substance, obtaining precise information about the dynamics of its influence and outflow. This type of experiment is possible in future research …”

“…This type of experiment is possible in future research. 48 We believe that hundreds of different drugs can be investigated as long as it correlates with the spin probe. Some drugs could be investigated after conjugation with a spin probe.…”