Fig. 3.

a, b Maximum signal-to-noise ratio measured for peaks in the individual 3D cubes (indirect domains ω₁ × ω₂ × ω₃) in each point of directly detected dimension (ω₄). The plots show the ratio of the most intense spectral point (absolute value) to the noise level in the corresponding 3D cube (c, d). Assuming that cross-peaks do not overlap in the 4D spectrum these plots reflect the overall sensitivity of experiment. Considerable sensitivity advantage of the aliphatic-to-aromatic (a, c) over aromatic-to-aliphatic (b, d) NOESY is apparent. Noise levels (c, d) in the 3D cubes for each point of directly detected dimension were measured as the median of absolute values of all spectral intensities. From the uniformity of noise level across directly detected dimension one can conclude that advanced procedures for NUS artifact suppression are not beneficial in this case, and that the both experiments are sensitivity-limited. The scale was cut for intense water resonance (at 4.68 ppm)