Figure shows the calculated ratio spectrum for G4/G-quartet. This is compared with the experimentally measured ratio spectrum induced by the addition of 100 mM potassium ions (Figure ). Qualitatively, a number of key elements stand out as present in both calculated and measured spectra. Firstly, there is the pattern of a negative column at ~1600 cm-1 next to a lower-frequency positive column. Secondly there is the absence of such a pattern in the corresponding rows, due to the mode combination effects outlined in Figure . Thirdly, there is the general reduction in cross-peak intensities in both calculated and measured spectra. Based on these observations, we conclude that there is evidence to suggest that Myc2345 forms unstacked G-quartets in the absence of ions, and we depict in Figure how such a structure may look. In this model, on the addition of potassium ions, the G-quartets stack together to form a different structure presumed to be a G-quadruplex structure and based on the appearance of the two new coupling peaks, it is furthermore plausible that in such a structure, the guanine and/or thymine bases in the end caps of the DNA sequence couple to the stacked quartets.