Unknown

Dataset Information

0

The guanine cation radical: investigation of deprotonation states by ESR and DFT.


ABSTRACT: This work reports ESR studies that identify the favored site of deprotonation of the guanine cation radical (G*+) in an aqueous medium at 77 K. Using ESR and UV-visible spectroscopy, one-electron oxidized guanine is investigated in frozen aqueous D2O solutions of 2'-deoxyguanosine (dGuo) at low temperatures at various pHs at which the guanine cation radical, G*+ (pH 3-5), singly deprotonated species, G(-H)* (pH 7-9), and doubly deprotonated species, G(-2H)*- (pH > 11), are found. C-8-deuteration of dGuo to give 8-D-dGuo removes the major proton hyperfine coupling at C-8. This isolates the anisotropic nitrogen couplings for each of the three species and aids our analyses. These anisotropic nitrogen couplings were assigned to specific nitrogen sites by use of 15N-substituted derivatives at N1, N2, and N3 atoms in dGuo. Both ESR and UV-visible spectra are reported for each of the species: G*+, G(-H)*, and G(-2H)*-. The experimental anisotropic ESR hyperfine couplings are compared to those obtained from DFT calculations for the various tautomers of G(-H)*. Using the B3LYP/6-31G(d) method, the geometries and energies of G*+ and its singly deprotonated state in its two tautomeric forms, G(N1-H)* and G(N2-H)*, were investigated. In a nonhydrated state, G(N2-H)* is found to be more stable than G(N1-H)*, but on hydration with seven water molecules G(N1-H)* is found to be more stable than G(N2-H)*. The theoretically calculated hyperfine coupling constants (HFCCs) of G*+, G(N1-H)*, and G(-2H)*- match the experimentally observed HFCCs best on hydration with seven or more waters. For G(-2H)*-, the hyperfine coupling constant (HFCC) at the exocyclic nitrogen atom (N2) is especially sensitive to the number of hydrating water molecules; good agreement with experiment is not obtained until nine or 10 waters of hydration are included.

SUBMITTER: Adhikary A 

PROVIDER: S-EPMC2526163 | biostudies-literature | 2006 Nov

REPOSITORIES: biostudies-literature

altmetric image

Publications

The guanine cation radical: investigation of deprotonation states by ESR and DFT.

Adhikary Amitava A   Kumar Anil A   Becker David D   Sevilla Michael D MD  

The journal of physical chemistry. B 20061101 47


This work reports ESR studies that identify the favored site of deprotonation of the guanine cation radical (G*+) in an aqueous medium at 77 K. Using ESR and UV-visible spectroscopy, one-electron oxidized guanine is investigated in frozen aqueous D2O solutions of 2'-deoxyguanosine (dGuo) at low temperatures at various pHs at which the guanine cation radical, G*+ (pH 3-5), singly deprotonated species, G(-H)* (pH 7-9), and doubly deprotonated species, G(-2H)*- (pH > 11), are found. C-8-deuteration  ...[more]

Similar Datasets

| S-EPMC4590776 | biostudies-literature
| S-EPMC2526165 | biostudies-literature
| S-EPMC4213299 | biostudies-literature
| S-EPMC3240735 | biostudies-literature
| S-EPMC7139295 | biostudies-literature
| S-EPMC5618257 | biostudies-literature
| S-EPMC7450633 | biostudies-literature
| S-EPMC2740929 | biostudies-literature
| S-EPMC11318630 | biostudies-literature
| S-EPMC4266391 | biostudies-literature