In honour of N. Yngve Öhrn: surveying proton cancer therapy reactions with Öhrn's electron nuclear dynamics method. Aqueous clusters radiolysis and DNA-base damage by proton collisions

¹The authors warmly dedicate this SLEND investigation in honour of Professor N. Yngve Öhrn on the occasion of his 80th birthday celebration during the 54th Sanibel Symposium in St. Simons’ Island, Georgia, on February 16–21, 2014. Associate Professor Jorge A. Morales was a former chemistry PhD student under the mentorship of Professor Öhrn and Dr Ajith Perera took various quantum chemistry courses taught by Professor Öhrn during his chemistry PhD studies. Both Jorge and Ajith look back to those great times of their scientific formation under Yngve's guidance during the 1990s with a strong sense of gratitude toward him (and even with a sense of nostalgia). The authors are pleased to present to Professor Öhrn this birthday gift of fully mature SLEND developments that now venture to treat systems of biochemical interest.

Abstract

Proton cancer therapy (PCT) utilises high-energy H⁺ projectiles to cure cancer. PCT healing arises from its DNA damage in cancerous cells, which is mostly inflicted by the products from PCT water radiolysis reactions. While clinically established, a complete microscopic understanding of PCT remains elusive. To help in the microscopic elucidation of PCT, Professor Öhrn's simplest-level electron nuclear dynamics (SLEND) method is herein applied to H⁺ + (H₂O)_3–4 and H⁺ + DNA-bases at E_Lab = 1.0 keV. These are two types of computationally feasible prototypes to study water radiolysis reactions and H⁺-induced DNA damage, respectively. SLEND is a time-dependent, variational, non-adiabatic and direct-dynamics method that adopts a nuclear classical-mechanics description and an electronic single-determinantal wavefunction. Additionally, our SLEND + effective-core-potential method is herein employed to simulate some computationally demanding PCT reactions. Due to these attributes, SLEND proves appropriate for the simulation of various types of PCT reactions accurately and feasibly. H⁺ + (H₂O)_3–4 simulations reveal two main processes: H⁺ projectile scattering and the simultaneous formation of H and OH fragments; the latter process is quantified through total integrals cross sections. H⁺ + DNA-base simulations reveal atoms and groups displacements, ring openings and base-to-proton electron transfers as predominant damage processes.

Keywords:

• electron nuclear dynamics
• non-adiabatic dynamics
• proton cancer therapy
• water radiolysis
• DNA-base damage

Acknowledgements

The authors thank Mr. S. Hinds [Texas Tech University (TTU) chemistry undergraduate student] for his help with some H⁺ + (H₂O)_{3 − 4} simulations and Ms. A. Aguilar, Mr. B. Hernandez and Mr. Kevin Cassity (participants of the Summer Research Academy for Theoretical and Computational Chemistry in 2011, 2011 and 2012, respectively) for their help with some H⁺ + DNA-base simulations. All the present calculations have been performed at the TTU High Performance Computer Center (TTU HPCC), the TTU Chemistry Computer Cluster (TTU CCC) and the Texas Advanced Computing Center (TACC) at the University of Texas at Austin. The authors thank TTU HPCC and TACC for providing free computer time to run some of the present calculations.

Notes

¹ The authors warmly dedicate this SLEND investigation in honour of Professor N. Yngve Öhrn on the occasion of his 80th birthday celebration during the 54th Sanibel Symposium in St. Simons’ Island, Georgia, on February 16–21, 2014. Associate Professor Jorge A. Morales was a former chemistry PhD student under the mentorship of Professor Öhrn and Dr Ajith Perera took various quantum chemistry courses taught by Professor Öhrn during his chemistry PhD studies. Both Jorge and Ajith look back to those great times of their scientific formation under Yngve's guidance during the 1990s with a strong sense of gratitude toward him (and even with a sense of nostalgia). The authors are pleased to present to Professor Öhrn this birthday gift of fully mature SLEND developments that now venture to treat systems of biochemical interest.

Additional information

Funding

This work is partially supported by the National Science Foundation [grant number CHE-0645374 (CAREER) and grant number CHE-0840493] (to build the TTU CCC)], and the Robert A. Welch Foundation Grant [grant number D-1539].