title: Deprotonated purine dissociation: experiments, computations, and astrobiological implications.
abstract: A central focus of astrobiology is the determination of abiotic formation routes to important biomolecules. The dissociation mechanisms of these molecules lend valuable insights into their synthesis pathways. Because of the detection of organic anions in the interstellar medium (ISM), it is imperative to study their role in these syntheses. This work aims to experimentally and computationally examine deprotonated adenine and guanine dissociation in an effort to illuminate potential anionic precursors to purine formation. Collision-induced dissociation (CID) products and their branching fractions are experimentally measured using an ion trap mass spectrometer. Deprotonated guanine dissociates primarily by deammoniation (97%) with minor losses of carbodiimide (HNCNH) and/or cyanamide (NH2CN), and isocyanic acid (HNCO). Deprotonated adenine fragments by loss of hydrogen cyanide and/or isocyanide (HCN/HNC; 90%) and carbodiimide (HNCNH) and/or cyanamide (NH2CN; 10%). Tandem mass spectrometry (MS(n)) experiments reveal that deprotonated guanine fragments lose additional HCN and CO, while deprotonated adenine fragments successively lose HNC and HCN. Every neutral fragment observed in this study has been detected in the ISM, highlighting the potential for nucleobases such as these to form in such environments. Lastly, the acidity of abundant fragment ions is experimentally bracketed. Theoretical calculations at the B3LYP/6-311++G(d,p) level of theory are performed to delineate the mechanisms of dissociation and analyze the energies of reactants, intermediates, transition states, and products of these CID processes.
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado , 215 UCB, Boulder, Colorado 80309, United States.
authors.forename: Callie A
authors.initials: CA
authors.lastname: Cole
authors.forename: Zhe-Chen
authors.initials: ZC
authors.lastname: Wang
authors.forename: Theodore P
authors.initials: TP
authors.lastname: Snow
authors.forename: Veronica M
authors.initials: VM
authors.lastname: Bierbaum
mesh_terms: D000225:Adenine / Q000737:chemistry; D000838:Anions / Q000737:chemistry; D002234:Carbodiimides / Q000737:chemistry; D003198:Computer Simulation; D003484:Cyanamide / Q000737:chemistry; D003485:Cyanates / Q000737:chemistry; D003486:Cyanides / Q000737:chemistry; D018559:Exobiology; D006147:Guanine / Q000737:chemistry; D006856:Hydrogen Cyanide / Q000737:chemistry; D008956:Models, Chemical; D015394:Molecular Structure; D011522:Protons; D011687:Purines / Q000737:chemistry*; D053719:Tandem Mass Spectrometry
chemical_list: D000838:Anions; D002234:Carbodiimides; D003485:Cyanates; D003486:Cyanides; D011522:Protons; D011687:Purines; D006856:Hydrogen Cyanide; D003484:Cyanamide; D006147:Guanine; D000225:Adenine; C005057:isocyanic acid; C030985:purine