The effect of π-stacking and H-bonding on ionization energies of a nucleobase: uracil dimer cation

Abstract

The electronic structure of the ionized pi-stacked and H-bonded uracil dimers as well as that of the monomer, is characterized by the equation-of-motion coupled-cluster method for ionization potentials (EOM-IP). Vertical ionization energies (IEs) for the 5 lowest states of the monomer and the 10 lowest states of the dimers are presented. Non-covalent interactions in the dimers reduce the lowest vertical IE by 0.34 and 0.13 eV in the pi-stacked and H-bonded dimers, respectively. The electronic spectra of the cations are also presented. The two dimer cations feature intense charge resonance bands at 0.52 and 0.11 eV, respectively. The position and intensity of the bands are sensitive to the dimer structures, for example, the geometric relaxation in the pi-stacked dimer blue-shifts the CR band by more than 1 eV and results in a threefold intensity increase. The results of the calculations are rationalized within the dimer molecular orbital - linear combination of fragment molecular orbitals (DMO-LCFMO) framework. The basis set effects and energy additivity schemes are also discussed.

Ionization of cytosine monomer and dimer studied by VUV photoionization and electronic structure calculations

“…Same-magnitude shifts of different sign for ionization from bonding/antibonding pairs of orbitals were observed in a variety of stacked dimers. 22,23,37 Thus, the deviation is likely to be due to the stronger perturbation of the orbitals introduced by hydrogen bonding.…”

“…As discussed in Refs. 22 and 23 , using computational methods that are capable of describing multiple interacting states of open-shell character is crucial for obtaining reliable results for the ionized systems, and EOM-IP-CC is one such approach. [24][25][26][27][28][29] There are no experimental reports for the IEs of the cytosine dimer.…”

The effect of microhydration on ionization energies of thymine

“…As part of our effort to understand the role played by different interactions of NABs with the environment [3][4][5][6][7][8], we recently characterized the effect of hydrogen-bonding and π-stacking on the ionized states of the gas-phase dimers of AA, TT, AT, and CC in a combined experimental and theoretical study [7,8]. We found that stacking and hydrogen-bonding can reduce the IEs by 0.4-1 eV via two distinct mechanisms: hole delocalization and electrostatic charge-dipole interactions.…”

Spectroscopic signatures of proton transfer dynamics in the water dimer cation

“…By comparing the spectra of the monomer and the dimer, one can quantify the effects of clustering on electronic states, such as shifts in ionization energies (see, for example, Refs. [13,42,43]). We compare the computed photoelectron spectrum of the dimer with the pseudo-photoelectron spectrum derived from photo efficiency measurements.…”