Figure 5. Simulation of the nano-MRI protocol carried out on a single rapamycin molecule (C₅₁H₇₉NO₁₃).

(a) Hydrogen and carbon substructure of the rapamycin molecule. Sampling was performed over 150 slices for each of 11 × 24 latitude and longitude orientations of B₀ with M_S=2000 measurements per slice and sequence length t=8 ms. (b,c) Extracted ¹H and ¹³C nuclear densities, respectively. The 3D density is represented through 50% and 75% contours that reveal subthreshold features. Atomic positions are identified corresponding to local maxima in the 3D density that are >90% or greater in relative terms (shown as crosses in (c,d)). The uncertainty in position (effective resolution) is estimated from the average of the (x,y,z) FWHM cross-sections of the 3D density peaks. Peaks closer to the probe (smaller z values) are narrower due to stronger gradient coupling to the probe, while isolated peaks are further localized due to a greater relative contrast in the numerical inversion procedure. (d) Reconstruction of the atomic positions and associated resolution (colour scales) are shown for ¹H (blue colour scale) and ¹³C (red colour scale). The sphere size corresponds to the average statistical deviation in comparison to the exact coordinates of Δr=0.5 Å (superimposed on the data is the exact skeletal structure from a.