Adenine transition metal complexes

According to Elving and coworkers ", adenine is rather strongly adsorbed at the mercury electrode at potentials between -0.200 and -0.700 V reaching a maximum at -0.40 to -0.45 V. This is not in the range of potential at which reduction has been observed to occur " so presumably is not an issue in the electrochemistry of the free molecule. However, it does overlap the potential range in which electron transfer to and from the central metal would be expected to occur in transition metal complexes. 

By far the greatest attention has been to the complexing of the transition metal ions, often with surprising results. Thus, Cu11 can be shown to bind to N-7 of the adenine moiety of ATP and yet it can considerably enhance the hydrolytic cleavage of the phosphate bonds under the same conditions. Earlier suggestions were that chelate formation occurred via the N-7 and phosphate O... 

ELECTROCHEMISTRY AND SPECTROELECTROCHEMISTRY OF ADENINE AND ADENOSINE COMPLEXES WITH 3d TRANSITION METALS... 

In this work, well-defined complexes of biologically important 3d transition metals (Cu(II), Fe(III), Fe(II), and Ni(II)) with either neutral or monodeprotonated anionic adenine or adenosine, synthesized and characterized 5 as described previously, have been used as a model system to study the effects of the interaction of transition metals with purine and purine nucleoside components of nucleic acids on redox properties of the system. The structures of the complexes is simpler than that of nucleic acids and facilitates evaluation of the electrochemical results. The non-phosphorylated monomeric units are suitable model ligands as the use of nucleotides offers complicating factors associated with phosphate due to self-association and self-complexation and preference for the PO4 moiety as the site for complexation. ... 

As shown in Figure la, adenine has five potential binding sites, all of which have been reported as having been used in coordination to transition metal ions in various adenine metal complexes. The anionic adenine in the complexes used in this study is deprotonated at the N-9 site (Figure la). Adenosine has the four potential binding sites shown in Figure lb. 

Complexes of 3d transition metals with adenine (Ad) and/or the mono-deprotonated anion (Ad-) or adenosine (Ado) were prepared by refluxing a mixture of Ad or Ado with the appropriate hydrate metal perchlorate dissolved in triethylorthoformate and ethanol. Both the syntheses 3 and characterization , have been described previously. Hydrated metal perchlorates, adenine, and adenosine used in electrochemical experiments were used as received from Aldrich. All electrochemical experiments were performed in dimethyl sulfoxide (Me2S0) (Aldrich) containing 0.1 M tetra-butylammonium perchlorate (TBAP) (Eastman Kodak). Me2S0 was purified by fractional crystallization using a method similar to that described for purification of pyridine s. s recrystallized and dried in vacuo... 

Electrochemistry and Spectroelectrochemistry of Adenine and Adenosine Complexes with 3d Transition Metals... 

A novel class of nucleic acid mimics has been described which possess two ethylenediamine moieties for intermolecular metal co-ordination (25). In the presence of Zn + ions and template DNA, the analogues (25) form relatively stable structures, stabilised by the co-ordination of adjacent chelating moieties with zinc ions. It was shown that with an oligothymidine template and the adenine derivative of (25) that a 2 1 complex was formed, which showed a biphasic melting transition. Short RNA duplexes (3-4 bp) are considerably stabilised if both termini of the duplexes are bridged by non-nucleotidic linkers. For example, the pairing of rGAA with rUUC in such a cyclic system exhibits a Tm of 36°C in IM salt solution. 

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