Proton Transfer Accompanied by the Oxidation of Adenosine

Abstract

Despite numerous experimental and theoretical studies, the proton transfer accompanying the oxidation of 2'-deoxyadenosine 5'-monophosphate 2'-deoxyadenosine 5'monophosphate (5'-dAMP, A)i ss till under debate. To address this issue, we have investigated the oxidation of A in acidic and neutral solutions by using transient absorption (TA) and time-resolved resonance Raman( TR 3 )s pectroscopic methods in combination with pulse radiolysis. The steadystate Raman signal of A was significantly affected by the solution pH, but not by the concentration of adenosine (2-50 mm). More specifically,t he A in acidic and neutral solutions exists in its protonated (AH + (N1 + H + )) and neutral( A) forms, respectively.O nthe one hand, the TA spectral changes observed at neutral pH revealed that the radical cation (AC + )g enerated by pulse radiolysis is rapidly converted into AC(N6ÀH) through the loss of an imino protonf rom N6. In contrast, at acidic pH (< 4), AHC 2 + (N1 + H + )g enerated by pulse radiolysis of AH + (N1 + H + )d oes not undergo the deprotonationp rocess owing to the pK a value of AHC 2 + (N1 + H + ), whichi sh igher than the solutionp H. Furthermore, the resultsp resented in this study have demonstrated that A, AH + (N1 + H + ), and their radical species exist as monomers in the concentrationr ange of 2-50 mm.C ompared with the Ramanb ands of AH + (N1 + H + ), the TR 3 bandso fAHC 2 + (N1 + H + )a re significantly down-shifted, indicatingadecrease in the bond order of the pyrimidine and imidazole rings due to the resonance structure of AHC 2 + (N1 + H + ). Meanwhile, AC(N6ÀH) does not show aR aman band corresponding to the pyrimidine + NH 2 scissoring vibration due to diprotonation at the N6 position. These resultss upport the final products generated by the oxidation of adenosine in acidic and neutrals olutions being AHC 2 + (N1 + H + )a nd AC(N6ÀH), respectively.

UV–vis Photodissociation Action Spectroscopy Reveals Cytosine–Guanine Hydrogen Transfer in DNA Tetranucleotide Cation Radicals upon One-Electron Reduction

“…Among those, reactions involving electron transfer along the DNA double strand have been investigated most frequently by experiments that focused on the kinetics and downstream analysis of radical products formed by reactions with solvent or other components in the reaction mixture. − In contrast to electron transfer, proton transfer between an ionized and neutral nucleobase has been considered to occur in guanine–cytosine (G–C) and adenine–thymine (A–T) Watson–Crick pairs. Experimental studies of oligonucleotides tagged with oxidizable groups have revealed rapid deprotonation of guanine cation radicals. , Proton transfer between base pairs has been investigated in solution − and studied in silico by density functional theory (DFT) calculations to indicate the proton recipient position. − In a gas-phase study of the G–C cation radical complex, O’Hair and co-workers have utilized infrared multiphoton dissociation action spectroscopy to assign the ion structure as resulting from a proton transfer between the nucleobases . However, there have been few reports addressing the possibility of proton transfer along the DNA strand in cation radicals …”

Electrochemical Detection of Adrenaline and Hydrogen Peroxide on Carbon Nanotube Electrodes

“…A likely mechanism of adrenaline oxidation is the loss of an electron followed by rapid deprotonation. An intermediate radical is formed which loses a further electron to form the quinone product (32). (Figure 2B) compares the experimental results with theory.…”

Coupling Pulse Radiolysis with Nanosecond Time-Resolved Step-Scan Fourier Transform Infrared Spectroscopy: Broadband Mid-Infrared Detection of Radiolytically Generated Transients

“…Indeed, there are a number of notable examples of the application of time-resolved resonance Raman spectroscopy to pulse radiolysis from groups in the United States [6][7][8][9] and Japan. [10][11][12][13] However, we have focused on coupling the complementary technique of time-resolved infrared (TRIR) spectroscopy with pulse radiolysis, that is, PR-TRIR. While there were some early examples of PR-TRIR on gas-phase samples, 14,15 in 2010 we reported 16 the first application of nanosecond TRIR spectroscopy to the pulse radiolysis of liquid samples at our 9 MeV Laser Electron Accelerator Facility (LEAF), 17 which is part of the Accelerator Center for Energy Research (ACER) in the Chemistry Division at Brookhaven National Laboratory (BNL).…”