Guanine–aspartic acid interactions probed with IR–UV resonance spectroscopy

Abstract

Double resonance spectroscopy of clusters of guanine with aspartic acid reveals geometries similar to patterns exhibited in DNA base pairs. In the spectral region of 32 800 cm⁻¹ to 35 500 cm⁻¹ we observe five isomers of guanine–aspartic acid clusters and assign their structures based on IR–UV hole-burning spectra and wave function theory calculations at the MP2/cc-pVDZ and MP2/cc-pVTZ levels. The calculations employed both harmonic and one-dimensional scan anharmonic approximations. Three of the isomers are similar, assigned to structures containing three hydrogen bonds and 9-enolguanine. We assign the fourth isomer to a structure containing a 9-keto tautomer of guanine and forming a triply bonded structure similar to a base pairing interaction. The fifth isomer dissociates with proton transfer upon excitation or ionization. This is the first set of experiments and high-level ab initio calculations of the isolated, microscopic interactions of an amino acid and a nucleobase, the building blocks of nucleic acids and proteins.