The changes in cross-peak intensity observed going from G-quartet (Figure ) to G4 (Figure ) can be explained by the change in relative orientation of the guanine bases of a quartet. In the G-quartet, molecular planes of adjacent guanine bases intersect at an angle of 21 o . In the G4, this angle is altered to 19 o in the terminal quartets and 0 o in the central, planar quartet (Figure in Supplementary Information). These structural changes result in changes in the orientation of transition dipole moments, which account for the changes in intensity observed in cross-peaks across the spectrum.