Precise Determination of 2‐Deoxy‐D‐Ribose Internal Energies after keV Proton Collisions

Abstract

The interaction of keV protons with building blocks of DNA is of particular biological relevance in view of the increasing number of facilities employing MeV proton irradiation for tumor treatment.[1] When ions traverse tissue and are decelerated to MeV and sub-MeV energies, the Bragg peak is reached. At ion energies in the Bragg peak region, the induced damage is highest due to maximum linear energy transfer and relative biological effectiveness. The volume selectivity given by the existence of a well-localized Bragg peak region renders proton therapy such a promising tool for cancer treatment. [2] Furthermore, biological consequences of irradiation with energetic protons from galactic cosmic rays and solar particle events are a limiting factor for human space exploration. This issue is of particular importance for future manned missions outside low earth orbit, for example, lunar or Mars missions. [3] It is well-known that biological radiation damage is the ultimate result of ionization and fragmentation of cellular DNA. To explore the molecular mechanisms underlying radiation-induced DNA damage, numerous recent studies focused on ionization and fragmentation of DNA building blocks upon irradiation with slow electrons, photons and ions. In their pioneering studies, Sanche and co-workers showed that low-energy (secondary) electrons can cause single-and doublestrand breaks of plasmid DNA. [4,5] Huels and coworkers investigated interactions of hyperthermal ions with DNA building blocks and concluded that heavy ions have the potential to induce particularly complex damage to DNA in the Bragg peak region. [6] Ionization and fragmentation of 2-deoxy-d-ribose (dR, C 5 H 10 O 4 ) molecules upon impact of keV and sub-keV ions has recently been investigated for isolated molecules [7] as well as for the condensed phase. [6] In both studies, almost complete disintegration of the molecule was observed and it was concluded that direct ion-induced DNA damage-for example in heavy ion or proton therapy of malignant tumors-may be dominated by deoxyribose fragmentation. Furthermore, Deng and coworkers have recently reported evidence for reactive scattering damage of 2-deoxy-d-ribose thin films by hyperthermal ions. [8,9] In the gas-phase studies, the mass spectrum of the fragment ions largely follows a power-law distribution with a characteristic exponent t of the order of 2, depending on the ion velocity, charge state and the atomic number of the impinging ion. From this, it was concluded that the fragmentation is to a large extent statistical. t was found to be an ideal parameter for the quantification of damage inflicted upon a molecule whose fragmentation yield is very close to 100 %, [7] but this quantification was purely phenomenological, since the fragmentation channels and the characteristic exponent could not be directly related to the amount of energy initially deposited into the deoxyribose molecules. In a study on MeV Si q + collisions with C 60 , Itoh et al. have already concluded that t carries information about the...

A VUV Photoionization and Ab Initio Determination of the Ionization Energy of a Gas-Phase Sugar (Deoxyribose)

“…2(B ionization, 4 VUV ionization, 13 and particle bombardment. 6 The mass fragments at m/z 70, 73, 88, 103, 116 and 117 amu have been observed under these conditions, but very little or no parent cation (m/z 134) has been observed in these earlier experiments. In a previous VUV photoionization study of deoxyribose, 13 the parent mass at m/z 134 was not detected, and there was extensive fragmentation, similar to a 70 eV electron ionization mass spectrum.…”

“…There is one report in the literature of a 10.5 eV ionization energy measured using electron ionization, 4 and a few theoretical calculations present numbers around this value. [5][6][7][8] This is a surprisingly high value for a molecule that contains oxygen in a ring structure. Similar molecules such as tetrahydrofuran have ionization energies much lower, and there is near perfect agreement between theory and experiment for that molecule.…”

Experimental andab initiostudy of the photofragmentation of DNA and RNA sugars

“…The pattern (18,29) is very weak, but the other one ascribed to the ion pair OH + 3 and CHO + is stronger. According to the proton impact study on 2-deoxy-D-ribose by Alvarado et al [20], the majority of OH + 3 s is ejected from the molecule and is not formed from residual gas. Cation OH + 3 is seen together with heavier ions than CHO + in the same study.…”

Ion‐Induced Fragmentation of Amino Acids: Effect of the Environment

“…[22,23] Only recently, the first studies of amino acid ionisation and fragmentation upon ion impact have emerged. Bari et al investigated the ion-induced fragmentation of several isolated amino acids: alanine isomers, [24] glycine and valine.…”