Question #44980

In an aqueous buffer at 298 K (pH = 7.4), the lactam-lactim (keto-enol) tautomerization equilibrium constant ($K_{eq} = \frac{[\text{enol}]}{[\text{keto}]}$) for the nucleoside deoxyguanosine (dG) is $1.0 \times 10^{-4}$. Upon phosphorylation to form deoxyguanosine 5'-monophosphate (dGMP), the negatively charged phosphate group exerts a through-space field effect. This effect selectively stabilizes the keto tautomer to minimize repulsive dipole-dipole interactions, increasing the standard free energy of tautomerization ($\Delta G^\circ$) by exactly $5.706 \text{ kJ mol}^{-1}$.

Given $2.303 RT = 5.706 \text{ kJ mol}^{-1}$ at 298 K, determine the new tautomeric equilibrium constant ($K_{dGMP}$) for the nucleotide. Additionally, identify the Hydrogen-Bond Donor (D) / Acceptor (A) profile at the Watson-Crick face (reading positions C6, N1, and C2 respectively) for the specific tautomer that is \textit{destabilized} by this field effect.