The Role of Low-Energy Electron Interactions in cis-Pt(CO)2Br2 Fragmentation

Abstract

Platinum coordination complexes have found wide applications as chemotherapeutic anticancer drugs in synchronous combination with radiation (chemoradiation) as well as precursors in focused electron beam induced deposition (FEBID) for nano-scale fabrication. In both applications, low-energy electrons (LEE) play an important role with regard to the fragmentation pathways. In the former case, the high-energy radiation applied creates an abundance of reactive photo- and secondary electrons that determine the reaction paths of the respective radiation sensitizers. In the latter case, low-energy secondary electrons determine the deposition chemistry. In this contribution, we present a combined experimental and theoretical study on the role of LEE interactions in the fragmentation of the Pt(II) coordination compound cis-PtBr2(CO)2. We discuss our results in conjunction with the widely used cancer therapeutic Pt(II) coordination compound cis-Pt(NH3)2Cl2 (cisplatin) and the carbonyl analog Pt(CO)2Cl2, and we show that efficient CO loss through dissociative electron attachment dominates the reactivity of these carbonyl complexes with low-energy electrons, while halogen loss through DEA dominates the reactivity of cis-Pt(NH3)2Cl2.

A combined gas-phase dissociative ionization, dissociative electron attachment and deposition study on the potential FEBID precursor [Au(CH3)2Cl]2

“…Most noticeably, platinum precursors Pt(CO) 2 X 2 (X = Cl, Br) have been studied with respect to FEBID and their low-energy electron interaction under a variety of different conditions. Those are the gas phase [ 59 , 61 ] in thin layers under non-steady state conditions [ 57 ], in comparative FEBID experiments under HV and UHV conditions [ 60 ], and with respect to post-deposition purification through electron exposure and through reductive halogen removal using atomic hydrogen [ 58 ]. In an early study by Spencer et al [ 57 ], 0.7 nm layers of Pt(CO) 2 Cl 2 were exposed to 500 eV electrons and desorbing ligands were monitored by mass spectrometry, while the development of the deposit was monitored using XPS.…”

Interaction of low-energy electrons with radiosensitizers

“…For previously discussed PtBr 2 and CDDP, the primary DEA channel is leading to the formation of halogen anion. Both carbonyls Pt(CO) 2 Br 2 230 and Pt(CO) 2 Cl 2 231 lose primary the CO ligands, despite the exothermicity of halogen anion formation channel. The provided explanation is based on the different orbitals available for electron attachment.…”

Nitro rotation tuned dissociative electron attachment upon targeted radiosensitizer 4-substituted Z bases

“…In addition, platinum drugs are proposed as radiosensitizers to preferentially enhance the formation of cluster damage to DNA, and the LEEs play a major role in the induction of such lesions. 15–17 However, it should be noted that the utilized exogenous compounds may perturb the native structures of DNA and result in other potential cytotoxicity. Scientists have made a lot of attempts to find appropriate compounds which can be utilized in clinical evaluation to provide a radiosensitivity response to the high-energy radiation after incorporation into DNA without altering gene expression prior to irradiation.…”