An occurrence of two different guanine carbonyl modes giving rise to what is normally a corresponding row and column of cross-peaks is impossible to reconcile with the spectroscopy of an isolated guanine base (Figure in Supplementary Information). The calculated EVV 2DIR spectra and the associated vibrational analysis do, however, exhibit a comparable behaviour for the structures involving coupled guanine bases as in a G-quartet (Figure ) or a G4 (Figure ). The reason for this is that the roughly symmetric G-quartet structure gives rise to multiple combinations of guanine stretch modes in a manner analogous to simple exciton coupling. Although many different guanine carbonyl centric modes contribute to the column of cross-peaks, four in the case of the G-quartet and 12 in the case of the G4 pictured in Figure , the coupling strength of the cross-peaks associated with each carbonyl mode differ and one mode has much stronger couplings than the others. Interestingly, the dominating carbonyl stretch mode in the row of cross-peaks, is not the same mode that dominates the corresponding column of cross-peaks. Thus, in these calculated spectra, the rows and columns actually originate from different combinations of guanine motions. While the relative difference between the central frequency of the dominating row and column are different and opposite in sign between the experimental and our calculated spectra, this observation can be taken as support for the notion that the observation of differing guanine stretch modes in the rows and columns of the EVV 2DIR spectrum of Myc2345 in the absence of ions, can be due to the presence of a pre-existing structure involving coupled guanine bases. In effect, EVV 2DIR picks out differences in oscillator strength between the onequantum states of the G-quartet, with one being excited first in the row and another in the corresponding column. As the 'excitonic' interactions of the original isolated guanine motions, can result in one quantum transitions of different oscillator strength when they combine 'excitonically', then one can have the situation where one state dominates the column whilst another dominates the row.