ISSN:
1075-4261
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Physics
Notes:
Gas-phase ionization potentials (IPs) were theoretically evaluated for anionic 2′-deoxyadenosine 5′-phosphate (5′ dAMP-) and for 5′-dAMP- in water-counterion clusters with Na+. Two classes of clusters were examined. One contains Na+ associated with the phosphate group of 5′-dAMP- and five water molecules (cluster A). The second contains Na+ associated with the adenine N7 atom of 5′-dAMP-, and five or six water molecules (clusters B and C). Gas-phase IPs of isolated 5′-dAMP-, and of 5′-dAMP- in clusters containing Na+ and water molecules, obtained from ab initio self-consistent field (SCF) molecular orbital calculations were corrected by employing gas-phase ultraviolet photoelectron data on the model compounds 9-methyladenine and 3-hydroxytetrahydrofuran together with results from second-order Möller-Plesset and post-SCF configuration interaction calculations on the model anion H2PO-4. For gas-phase clusters, the electrostatic interaction of Na+ causes the lowest-energy base, sugar, and phosphate IPs to be significantly larger (1.7-3.9 eV) than the corresponding IPs of isolated 5′-dAMP-. For gas-phase clusters, the counterion location also strongly influences the IPs. In a cluster containing Na+ bound to phosphate (cluster A), the IPs of the lowest-energy base, sugar, and phosphate orbitals are 8.42, 9.14, and 9.12 eV, respectively. In a cluster containing Na+ bound to N7 of adenine (cluster B), the ordering of IPs is different and the lowest-energy base sugar and phosphate IPs are 9.46, 9.69, and 8.08 eV. Gibbs free energies associated with ionization in aqueous solution [ΔGioniz (solution)] were obtained by adding the difference (ΔΔGhyd) between the hydration energies of 5′-dAMP- or of the 5′-dAMP- clusters, before and after ionization, to the corrected gas-phase IPs. ΔGioniz (solution) ≈ IP + ΔΔGhyd. Differences between corresponding values of ΔGioniz (solution) for ionization from 5′-dAMP- versus 5′-dAMP- in clusters are smaller than differences between gas-phase IPs. © 1997 John Wiley & Sons, Inc. Biospect 3: 1-16, 1997
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
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