Abstract
Organic phosphates and phosphonates are present in a number of cellular components that can be damaged by exposure to ionizing radiation. This work reports femtosecond time-resolved mass spectrometry (FTRMS) studies of three organic phosphonate radical cations that model the DNA sugar-phosphate backbone: dimethyl methylphosphonate (DMMP), diethyl methylphosphonate (DEMP), and diisopropyl methylphosphonate (DIMP). Upon ionization, each molecular radical cation exhibits unique oscillatory dynamics in its ion yields resulting from coherent vibrational excitation. DMMP has particularly well-resolved 45 fs ( cm) oscillations with a weak feature at 610–650 cm, while DIMP exhibits bimodal oscillations with a period of ∼55 fs and two frequency features at and 670–720 cm. In contrast, the oscillations in DEMP decay too rapidly for effective resolution. The low- and high-frequency oscillations in DMMP and DIMP are assigned to coherent excitation of the symmetric O–P–O bend and P–C stretch, respectively. The observation of the same ionization-induced coherently excited vibrations in related molecules suggests a possible common excitation pathway in ionized organophosphorus compounds of biological relevance, while the distinct oscillatory dynamics in each molecule points to the potential use of FTRMS to distinguish among fragment ions produced by related molecules.
Highlights
Organic phosphates and phosphonates comprise important cellular components including the DNA backbone, lipid membranes, and post-translationally modified proteins
Due to the importance of understanding the dynamics and chemical mechanisms leading to DNA damage upon one-electron oxidation of the sugar-phosphate backbone, many experimental techniques have been applied for this purpose
We present femtosecond time-resolved mass spectrometry (FTRMS) results on dimethyl methylphosphonate (DMMP), diethyl methylphosphonate (DEMP), and diisopropyl methylphosphonate (DIMP) (Section 2.1) indicating that coherent vibrational motion is excited upon electron removal to form the respective radical cations
Summary
Organic phosphates and phosphonates comprise important cellular components including the DNA backbone, lipid membranes, and post-translationally modified proteins. Due to the importance of understanding the dynamics and chemical mechanisms leading to DNA damage upon one-electron oxidation of the sugar-phosphate backbone, many experimental techniques have been applied for this purpose. Experiments conducted at cryogenic temperatures have identified the structures of sugar radicals formed by one-electron phosphate oxidation in γ-irradiated DNA [2]. Mass spectrometry is widely used to characterize the products of radiation-induced DNA damage including modified sugars and bases [5]. While these studies provide significant insight into how one-electron oxidation of the sugar-phosphate backbone
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