Interactions du Cu(II), du Hg(II) et du Pt(II) avec les formes monomères et dimères de la thymine, de la thymidine et de l'acide orotique

The intrinsic acid-base properties of the hexa-2'-deoxynucleoside pentaphosphate, d(ApGpGpCpCpT) [=(A1∙G2∙G3∙C4∙C5∙T6)=(HNPP)⁵⁻] have been determined by ¹H NMR shift experiments. The pKa values of the individual sites of the adenosine (A), guanosine (G), cytidine (C), and thymidine (T) residues were measured in water under single-strand conditions (i.e., 10% D₂O, 47 °C, I=0.1 M, NaClO₄). These results quantify the release of H⁺ from the two (N7)H⁺ (G∙G), the two (N3)H⁺ (C∙C), and the (N1)H⁺ (A) units, as well as from the two (N1)H (G∙G) and the (N3)H (T) sites. Based on measurements with 2'-deoxynucleosides at 25 °C and 47 °C, they were transferred to pKa values valid in water at 25 °C and I=0.1 M. Intramolecular stacks between the nucleobases A1 and G2 as well as most likely also between G2 and G3 are formed. For HNPP three pKa clusters occur, that is those encompassing the pKa values of 2.44, 2.97, and 3.71 of G2(N7)H⁺, G3(N7)H⁺, and A1(N1)H⁺, respectively, with overlapping buffer regions. The tautomer populations were estimated, giving for the release of a single proton from five-fold protonated H₅(HNPP)(±) , the tautomers (G2)N7, (G3)N7, and (A1)N1 with formation degrees of about 74, 22, and 4%, respectively. Tautomer distributions reveal pathways for proton-donating as well as for proton-accepting reactions both being expected to be fast and to occur practically at no "cost". The eight pKa values for H₅(HNPP)(±) are compared with data for nucleosides and nucleotides, revealing that the nucleoside residues are in part affected very differently by their neighbors. In addition, the intrinsic acidity constants for the RNA derivative r(A1∙G2∙G3∙C4∙C5∙U6), where U=uridine, were calculated. Finally, the effect of metal ions on the pKa values of nucleobase sites is briefly discussed because in this way deprotonation reactions can easily be shifted to the physiological pH range.

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Metal complexes of thymidine — a study of binary and ternary systems with bivalent and trivalent metal ions in solution

Reddy

Keerthi

Adharani

1989

Proc. Indian Acad. Sci. (Chem. Sci.)

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The interaction of bivalent I-Cu(II), Ni(II), Zn(II), Co(II), Mg(II), Ca(II)] and trivalent I-La(III), Pr(III), Nd(III), Sm(III), Gd(llI), Dy(IIl)] metal ions with thymidine both in binary and ternary systems have been investigated by potentiometric pH measurements at 35~ and 0-10 M (KNO2) ionic strength. The secondary ligands used in this investigation were glycine, histidine, histamine, o-phenanthroline and a, ~,'-bipyridyl. The various stability constants pertaining to the above interactions were computed and compared. The influence of pH on the concentrations of several species present in aqueous solution, has been assessed. The effects of (i) charge on the metal ions, and (ii) the presence of a methyl group on the pyrimidine ring, on the stabilities of complexes have been assessed. A comparison with the corresponding constants of uridine has been made. Thymidine forms more stable complexes than uridine.Keywords. Metal complexes of thymidine; binary and ternary systems; bivalent and trivalent metal ions.

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Interactions du Cu(II), du Hg(II) et du Pt(II) avec les formes monomères et dimères de la thymine, de la thymidine et de l'acide orotique

Cited by 6 publications

References 10 publications

Vibrational analysis and spectra of orotic acid

Vibrational analysis and spectra of orotic acid

Intrinsic Acid–Base Properties of a Hexa‐2′‐deoxynucleoside Pentaphosphate, d(ApGpGpCpCpT): Neighboring Effects and Isomeric Equilibria

Metal complexes of thymidine — a study of binary and ternary systems with bivalent and trivalent metal ions in solution

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