In contrast, BPEI binding (Figure ) results in complex changes in the DNA bands between ∼ 1300 -1500 cm -1 , which generally increase in intensity as a function of N/P ratio. In addition, pronounced intensity decreases for both the 1222 cm -1 and 1680 cm -1 DNA bands are observed as the N/P ratio increases. However, unlike LPEI, binding of BPEI to DNA does not result in a frequency shift of the PO - 2 asymmetric stretching band at 1222 cm -1 .