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

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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 32800 cm−1 to 35500 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.

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