One-electron reduction of 8-bromo-2-aminoadenosine in the aqueous phase: radiation chemical and DFT studies of the mechanism.
Two tautomeric forms of one-electron oxidized 2-aminoadenosine (2AA) have been produced by reactions of hydrated electrons (e aq-) with 8-bromo-2-aminoadenosine (8-Br-2AA) at natural pH, whereas only one tautomer is formed by oxidation of 2AA. Tailored experiments by pulse radiolysis and time-dependent DFT (TD-B3LYP/6-311G**//B1B95/6-31+G**) calculations allowed the definition of the reaction mechanism in some detail. The electron adducts of 8-Br-2AA protonated at C8 eject Br- and produce the two short-lived tautomers (8 and 9). The first observable species decays by first-order kinetics to produce the second intermediate, which is also obtained by oxidation of 2AA by SO4*-. The rate of tautomerization (k taut = 4.5 x 104 s-1) is strongly accelerated by phosphate and is retarded in D2O (kinetic isotope effect 7). B1B95/6-31+G** calculations showed that the tautomerization is a water-assisted process. In acidic or basic solutions, the "instantaneous" formation of one-electron oxidized 2AA or its deprotonated forms has been produced by reactions of e aq- with 8-Br-2AA. gamma-Radiolysis of 8-Br-2AA in aqueous solutions followed by product studies led to the formation of 2AA as a single product.
Kaloudis
Panagiotis
P
ISOF, Consiglio Nazionale delle Ricerche, Via P. Gobetti 101, 40129 Bologna, Italy.
D'Angelantonio
Mila
M
Guerra
Maurizio
M
Gimisis
Thanasis
T
Mulazzani
Quinto G
QG
Chatgilialoglu
Chryssostomos
C
D000143:Acids / Q000737:chemistry; D000241:Adenosine / Q000031:analogs & derivatives* / Q000737:chemistry; D000468:Alkalies / Q000737:chemistry; D004583:Electrons; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry; D007554:Isotopes; D008745:Methylation; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D012996:Solutions; D013237:Stereoisomerism; D014867:Water / Q000737:chemistry
C529545:8-bromo-2-aminoadenosine; D000143:Acids; D000468:Alkalies; D007477:Ions; D007554:Isotopes; D012996:Solutions; D014867:Water; D000241:Adenosine