Electron-Spin Relaxation of Triarylmethyl Radicals in Glassy Trehalose

Abstract

Trehalose was recently proposed as a promising immobilizer of biomolecules for room-temperature electron paramagnetic resonance (EPR) structural studies. The most crucial parameter in these investigations is electron-spin relaxation (namely, phase memory time T_m). Recently, triarylmethyl (TAM) spin labels attached to DNA in trehalose were found to have the longest T_m at room temperature as compared to the existing spin labels and immobilizers. Therefore, in this work, we investigated TAM radicals in trehalose including Finland trityl (H36 form), perdeuterated Finland trityl (D36 form), and a deuterated version of OX063. The temperature dependence of electron-spin relaxation time of these radicals immobilized in trehalose was measured at X-band frequency, and possible mechanisms of relaxation were considered. OX063D in glassy trehalose has longer T_m up to 200 K as compared to Finland trityl, but at higher temperatures, OX063D is inferior in its relaxation properties, and the deuterated form of Finland trityl is preferable for pulse dipolar EPR spectroscopy experiments at 298 K. The influence of various deuterations (TAM or trehalose) on the observed relaxation times was studied, being controlled by the electron-spin-echo envelope modulation at room temperature.