Fig. 7
Comparison of 14N couplings in HYSCORE spectra of SMPs and AOX-SMPs at 40 K. X-band spectra (a and b) were recorded at g = 2.006 with a four-pulse sequence (π/2–τ–π/2–t1–π–t2–π/2–τ–echo) with π/2 = 16 ns, π = 16 ns, τ = 116 ns, shot repetition time 2 ms. The intensity of the stimulated echo (c) was normalised to the intensity of the cross peaks at [4.1, 1.6] MHz. Simulations (d) were calculated as a single 14N nucleus coupled to a single electron spin, with parameters Aiso = 0.54 MHz, T = − 0.2 MHz, κ = 0.425 MHz, η = 0.18 MHz (see Eq. 3 for calculation of quadrupole coupling parameters). Antidiagonal lines are given for the 14N Larmor frequency. Very similar data as in a were recorded for AOX-SMPs in the presence of carboxin (Additional file 5, Figure S5); the data shown here are for SMPs because of their higher signal to noise ratio. No strongly coupled 14N nuclei were detected in the (−,+) quadrant; for the entire (+,+) quadrant (including the 1H region), see Figures S6 and S7 in Additional files 7 and 8, respectively