title: Synthesis and acid-base properties of an imidazole-containing nucleotide analog, 1-(2'-deoxy-β-D-ribofuranosyl)imidazole 5'-monophosphate (dImMP(2-)).
abstract: 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(3)(2-) group by potentiometric pH titrations in aqueous solution. The micro acidity constants show that N(3) is somewhat more basic than PO(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 pK 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 (pk(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.
authors.affiliation: Institute of Inorganic and Analytical Chemistry, University of Münster, Corrensstrasse 28/30, D-48149 Münster.
authors.forename: Nicole
authors.initials: N
authors.lastname: Megger
authors.forename: Silke
authors.initials: S
authors.lastname: Johannsen
authors.forename: Jens
authors.initials: J
authors.lastname: Müller
authors.forename: Roland K O
authors.initials: RK
authors.lastname: Sigel
mesh_terms: D003854:Deoxyribonucleotides / Q000138:chemical synthesis / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000138:chemical synthesis / Q000737:chemistry*; D015394:Molecular Structure; D009711:Nucleotides / Q000737:chemistry*
chemical_list: D003854:Deoxyribonucleotides; D007093:Imidazoles; D009711:Nucleotides