We studied the effects of isotopic substitution (namely, deuterium substitution in solvents and 15N substitution in a spin label) on improving the sensitivity of distance measurements based on double quantum coherence (DQC) electron paramagnetic resonance (EPR) using cardiac troponin C. Deuteration of solvents increased the phase memory time, T m, by a factor of only 1.7, whereas the DQC amplitude increased significantly at long pulse intervals. The two-pulse echo amplitude was 1.7 times larger for the 15N spin label than it was for the 14N label because of the limited bandwidth of the microwave pulses. In the case of DQC, the echo is 2.7 times greater for the 15N label than it is for the 14N label due to the accumulated effects of the finite bandwidth. The combination of the two isotopic substitutions is expected to increase the sensitivity by about a factor of 6 when measuring distances longer than 4-5 nm.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics