Abstract
Pulsed electron-electron double resonance (PELDOR, also known as DEER) has become a method of choice to measure distances in biomolecules. In this work we show how the performance of the method can be improved at high EPR frequencies (94 GHz) using variable dual frequency irradiation in a dual mode cavity in order to obtain enhanced resolution toward orientation selection. Dipolar evolution traces of a representative RNA duplex and an α-helical peptide were analysed in terms of possible bi-radical structures by considering the inherent ambiguity of symmetry-related solutions.
Highlights
Igor Tkach,a Soraya Pornsuwan,a Claudia Hobartner,b Falk Wachowius,b Snorri Th
In this work we show how the performance of the method can be improved at high electron paramagnetic resonance (EPR) frequencies (94 GHz) using variable dual frequency irradiation in a dual mode cavity in order to obtain enhanced resolution toward orientation selection
Dipolar evolution traces of a representative RNA duplex and an a-helical peptide were analysed in terms of possible bi-radical structures by considering the inherent ambiguity of symmetry-related solutions
Summary
Orientation selection in distance measurements between nitroxide spin labels at 94 GHz EPR with. A commercial W-band resonator (Bruker TeraFlex) was used that allows for a maximal separation of pump and detection frequencies of 56 MHz at 400 mW of available microwave power (Bruker Power Upgrade 2).[12] For the RNA duplex (Fig. 2b, left), the orientation selection at 94 GHz shows clear deformations of the Pake patterns, with the parallel component of the dipolar tensor (DJ) appearing at resonances close to gz in the EPR spectrum and maximal modulation depth observed between gx and gy This is qualitatively consistent with a distance vector interconnecting the labels that is almost parallel to the duplex stacking axis (Fig. 1). The operation was carried out for both possible positions of the label in the
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