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Issue 8, 2009
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Xanthosine 5′-monophosphate (XMP). Acid–base and metal ion-binding properties of a chameleon-like nucleotide

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Abstract

The four acidity constants of threefold protonated xanthosine 5′-monophosphate, H3(XMP)+, reveal that in the physiological pH range around 7.5 (X  H·MP)3− strongly dominates and not XMP2− as commonly given in textbooks and often applied in research papers. Therefore, this nucleotide, which participates in many metabolic processes, should be addressed as xanthosinate 5′-monophosphate as is stated in this critical review. Micro acidity constant schemes allow quantification of intrinsic site basicities. In 9-methylxanthine nucleobase deprotonation occurs to more than 99% at (N3)H, whereas for xanthosine it is estimated that about 30% are (N1)H deprotonated and for (X  H·MP)3− it is suggested that (N1)H deprotonation is further favored, especially in macrochelates where the phosphate-coordinated M2+ interacts with N7. The formation degree of these macrochelates in the (X  H·MP·M) species of Co2+, Ni2+, Cu2+, Zn2+ or Cd2+ amounts to 90% or more. In the monoprotonated (M·X  H·MP·H)± complexes, M2+ is located at the N7/[(C6)O] unit as the primary binding site and it forms macrochelates with the P(O)2(OH) group to about 65% for nearly all metal ions considered (i.e., including Ba2+, Sr2+, Ca2+, Mg2+); this indicates outer-sphere binding to P(O)2(OH). Finally, a new method quantifying the chelate effect is applied to the M(X  H·MP) species, stabilities and structures of mixed-ligand complexes are considered, and the stability constants for several M(X  H·DP)2− and M(X  H·TP)3− complexes are estimated (112 references).

Graphical abstract: Xanthosine 5′-monophosphate (XMP). Acid–base and metal ion-binding properties of a chameleon-like nucleotide

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Publication details

The article was received on 04 Feb 2009 and first published on 22 Jun 2009


Article type: Critical Review
DOI: 10.1039/B902181G
Citation: Chem. Soc. Rev., 2009,38, 2465-2494
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    Xanthosine 5′-monophosphate (XMP). Acid–base and metal ion-binding properties of a chameleon-like nucleotide

    H. Sigel, B. P. Operschall and R. Griesser, Chem. Soc. Rev., 2009, 38, 2465
    DOI: 10.1039/B902181G

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