EasySpin forum

We have been trying to analyze the hyperfine coupling to an exchangeable proton in a protein complex using 2H-HYSCORE. To aid our analysis, we have measured CW spectra in H2O and D2O to compare the line broadening due to the exchangeable proton(s). These CW spectra have been fit with estfit, with Hstrains for D2O of [46.3, 50.1, 48.4], whereas H2O was [50.4, 55.4, and 56.9]. I believe the units are MHz. Thus the change in Hstrain is ~[4, 5, 8.5]. As I understand it, this change in Hstrain should be equal to n4.51A(2H), where n is the number of coupled protons/deuterons and A(2H) is the deuterium hyperfine coupling. Based on this, we would expect the maximum 2H HF coupling to be ~+-[1,1,2], and if there are two exchangeable protons the coupling would be even smaller.

Strangely, however, the span of our deuterium HYSCORE measurements suggests A(2H) = ~[-3,-3,6] rather than [-1,-1,2]. Given how far off this is, we suspect this might be due to incorrect assumptions about units or some error in our math. Any help in this analysis will be appreciated.

I am not familiar with the n4.51A(2H) expression. What you could do is to simulate two CW spectra (using identical HStrain in both), one without deuterons, and one with deuterons. Then, you can look at the simulated broadening and see how it compares to the A(2H) use for the simulation.