Adenosine transition metal complexes

Toropov et al.76-79 developed QSPR models for the complexes of nine alkaline-earth and transition metals with some amino acids, phosphate derivatives of adenosine, and heterocyclic compounds based on topological indices. Although the numbers of examples in the datasets were big enough, 11076 and 150,79 they involved only a few different ligands (17 and 25 molecules, respectively). The validation calculations were performed on the test sets containing the same ligands as in the training sets, which could explain the well observed performance of the predictions.7679... 

Most transition metal ions bind six ligand atoms. An important tetradentate ligand is adenosine triphosphate (ATP), which binds to divalent metal ions (such as Mg ", Mn ", Co ", and Ni " ) through four of their six coordination positions (Figure 13-2). The fifth and sixth positions are occupied by water molecules. The biologically active form of ATP is generally the Mg " complex. 

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... 

Association of the hydrophobic tails of membrane lipids leads, as depicted in Fig. 4.47a, to what Watkins [341] has described as polar discontinuities. Transition to the micellar state is considered to be essential to allow cell fusion to occur as the biomolecular leaflet is thermodynamically a stable system which would resist coalescence with similar structures. External influences can, however, induce phospholipid aggregation and can thus alter the permeability of cell membranes to water-soluble and oil-soluble species. Calcium ions, for example, induce inverse micelle formation in phospholipid systems [342]. Other metal ions also result in this transformation (Fig. 4.47b) addition of adenosine triphosphate (ATP) removes the metal and leads to a reversion to the normal micellar pattern. Maas and Coleman [343] have postulated that such transitions may have significance in nerve membrane operation. Metal-ATP-phospholipid complexes... 

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