Inter and Intrastrand Vibrational Coupling in DNA Studied with Heterodyned 2D-IR Spectroscopy

Heterodyned 2D-IR, frequency resolved photon echo, and pump−probe spectroscopies were collected to study the couplings and anharmonicities of cytidine and guanosine bases in DNA. Cytidine and guanosine anharmonicities were measured to be 9 and 14 cm-1, respectively. Strong cross-peaks were observed between the guanosine (G) and cytosine (C) carbonyl stretches in the 2D-IR spectra of the self-complementary oligonucleotide dG5C5 (5‘-GGGGGCCCCC-3‘). The spectra are interpreted in terms of inter- and intrastrand couplings between the carbonyl modes, and an excitonic Hamiltonian, based on transition dipole coupling, was used to fit the 2D-IR spectra. The accuracy of this model is discussed in light of observed couplings to the ring modes.