Synthesis and AcidBase Properties of an Imidazole‐Containing Nucleotide Analog, 1‐(2′‐Deoxy‐ β ‐ D ‐ribofuranosyl)imidazole 5′‐Monophosphate (dImMP 2− )

Deletion of the substituted pyrimidine ring in purine‐2′‐deoxynucleoside 5′‐monophosphates leads to the artificial nucleotide analog dImMP 2− . This analog can be incorporated into DNA to yield, upon addition of Ag + ions, a molecular wire. Here, we measured the acidity constants of H 2 (dImMP) ± having one proton at N(3) and one at the PO $\rm{{_{3}^{2-}}}$ group by potentiometric pH titrations in aqueous solution. The micro acidity constants show that N(3) is somewhat more basic than PO $\rm{{_{3}^{2-}}}$ and, consequently, the (H⋅ dImMP) − tautomer with the proton at N(3) dominates to ca. 75%. The calculated micro acidity constants are confirmed by 31 P‐ and 1 H‐NMR chemical shifts. The assembled data allow many quantitative comparisons, e.g. , the N(3)‐protonated and thus positively charged imidazole residue facilitates deprotonation of the P(O) 2 (OH) − group by 0.3 p K units. Information on the intrinsic site basicities also allows predictions about metal‐ion binding; e.g. , Mg 2+ and Mn 2+ will primarily coordinate to the phosphate group, whereas Ni 2+ and Cu 2+ will preferably bind to N(3). Macrochelate formation for these metal ions is also predicted. The micro acidity constant for N(3)H + deprotonation in the (H ⋅ dImMP⋅H) ± species (p k a  6.46) and the M n + ‐binding properties are of relevance for understanding the behavior of dImMP units present in DNA hairpins and metalated duplexes.