Why is the N1–H stretch vibration frequency of guanine shifted upon dimerization to the red and the amino N–H stretch vibration frequency to the blue?
Abstract
Three isomers of the guanine dimer (K9K9-1, K9K7-1 and K7K7-1) possessing two N–H⋯OC H-bonds were investigated theoretically using the ab initio calculations at the HF/6-31G** level. Amino groups in these isomers were not directly involved in H-bonding. Besides the red shifts of the N–H stretch vibrations (supporting the H-bonded character of these contacts) an unexpected blue shift of