Ribose Photochemistry in Space: Non-adiabatic Reaction Pathways

Ribose is a key biomolecule in the context of the RNA world hypothesis and prebiotic chemistry, yet the photochemistry of carbohydrates remains significantly less explored than that of amino acids or nucleobases. In this work, a theoretical investigation of the excited-state dynamics of β-D-ribopyranose following ultraviolet (UV) excitation using non-adiabatic molecular dynamics simulations is presented.

Several electronic structure approaches of different accuracy and computational cost were employed and compared, including CASSCF, MRSF-TDDFT, and OM2/MRCISD. To enable simulations with the MRSF-TDDFT method, a new interface between the ABIN molecular dynamics package and the OpenQP electronic structure program was developed. The suitability of the individual methods for non-adiabatic dynamics simulations of sugar-like systems was critically evaluated.

The simulations provide insight into the low-lying excited states of ribose, the topology of the relevant potential energy surfaces, and the dominant relaxation pathways following UV excitation. The excited-state dynamics reveal ultrafast relaxation to the ground state accompanied by competing photochemical processes, including pyranose ring opening, bond dissociation, and return to the initial closed-ring structure.

These findings suggest that β-D-ribopyranose can efficiently dissipate absorbed UV energy under the investigated conditions, accompanied by competing reactive and non-reactive relaxation pathways. This work contributes to the understanding of saccharide photochemistry under extraterrestrial conditions and provides a comparison of electronic structure methods for non-adiabatic molecular dynamics simulations of biologically relevant carbohydrate molecules.