Site-Specific Photo-oxidation of the Isolated Adenosine-5′-triphosphate Dianion Determined by Photoelectron Imaging

Abstract

Photoelectron imaging of the isolated adenosine-5´-triphosphate dianion excited to the 1 ππ* states reveals that electron emission is predominantly parallel to the polarization axis of the light and arises from subpicosecond electron tunneling through the repulsive Coulomb barrier (RCB). The computed RCB shows that the most probable electron emission site is on the amino group of adenine. This is consistent with the photoelectron imaging: excitation to the 1 ππ* states leads to an aligned ensemble distributed predominantly parallel to the long axis of adenine, the subsequent electron tunneling site is along this axis, and the negatively charged phosphate groups guide the outgoing electron mostly along this axis at long range. Imaging electron tunneling from polyanions combined with computational chemistry may offer a general route to probing the intrinsic photo-oxidation site and dynamics as well as overall structure of complex isolated species.

Photoelectron spectroscopy of the protoporphyrin IX dianion

“…Both direct detachment features exhibit a slight negative anisotropy (β 2 ≈ -0.4) as a result of the RCB guiding the outgoing electron. 30,31,[38][39][40][41][42][43][44][45] The tunnelling peak has β 2 ≈ -0.3, which is more unexpected. This finding suggests that tunnelling is competitive with the timescale of rotational dephasing of the molecule, which is likely on the order of several picoseconds due to the large size of the molecule.…”

Photoelectron Spectroscopy and Theoretical Investigations of Gaseous Doubly Deprotonated 2′-Deoxynucleoside 5′-Monophosphate Dianions

“…A more recent isomer-selected photoelectron spectroscopy study provided direct evidence of the existence of a plethora of isomers in oligonucleotide MCAs, in which one type of isomer has at least one deprotonated nucleobase and the lowest ionization sites in these oligonucleotide MCAs are all from bases . In addition to oligonucleotide MCAs, mononucleotides with a multiple-phosphate group chain, e.g., adenosine di- and triphosphate dianions [dADP-2H] 2– and [ATP-2H] 2– , respectively, were also observed and extensively studied. − Infrared photodissociation spectroscopy, PES, and theoretical calculations revealed that the two deprotonated sites are both from the phosphate group chain, on which the highest occupied molecular orbitals (HOMO) are located. , The intrinsic photo-oxidation from the adenine base site in [ATP-2H] 2– was recently characterized using base-specific two-photon resonance-enhanced photoelectron imaging spectroscopy . Photodissociation of adenosine 5′-diphosphate and triphosphate anions that arose from the adenine-centered π–π* excitation was investigated and compared in both anionic and dianionic charge states .…”

“…24,25 The intrinsic photo-oxidation from the adenine base site in [ATP-2H] 2− was recently characterized using base-specific twophoton resonance-enhanced photoelectron imaging spectroscopy. 26 Photodissociation of adenosine 5′-diphosphate and triphosphate anions that arose from the adenine-centered π−π* excitation was investigated and compared in both anionic and dianionic charge states. 27 Despite the aforementioned significant advances in gas-phase spectroscopy of nucleotide-related molecules, the smallest basic unit of DNA, mononucleotide in doubly deprotonated state [dNMP-2H] 2− , has remained elusive to date.…”

Intramolecular Photo-Oxidation as a Potential Source to Probe Biological Electron Damage: A Carboxylated Adenosine Analogue as Case Study

“…That population then decays on a 290 fs timescale by internal conversion leaving no excited state photoelectron signal beyond ~1 ps. The same population dynamics are also seen in bare adenine, 9-methyl-adenine, adenine oligonucleotides and adenine triphosphate dianions [ 42 , 44 , 45 , 46 , 47 ]. Hence, it is not wholly unsurprising that similar overall dynamics are observed in C-Ado − .…”

“…For background subtraction, as well as to increase PE signal, the PE images were collected with both the ion trap open and closed at ~1 Hz. A more detailed description of this procedure can be found here [ 46 ].…”