Nucleosides self-association

Dependence of tt complex binding constants upon nucleoside ionization potentials for ( ) uridine, ( ) thymidine, (A) cytidine, (o) adenosine, (O) guanosine, and (A) N,N,-dimethyladenosine. Panel A shows association constants for the binding of nucleosides to riboflavin. Panel B shows association constants for the self association of nucleosides. (Reproduced from Ref. 82. Copyright 1981, American Chemical Society.)... 

Cyclic Dimer Configurations. In 8-bromoinosine [BRINOSlOj the inosine residues are self-associated (Fig. 17.8 a). This is a rare example of self-association in the crystal structures of the nucleosides. Surprisingly, in uridine [BEURID10] (Fig. 17.8b) the CH- 0=C hydrogen bond plays the same role as the NH 0=C interaction in 8-bromoinosine. 

In inosine, the NH2 at C(2) on guanine is removed, thereby reducing the hydrogen-bonding capability by a donor group with two functional hydrogens. 8-Bromoinosine is a rare example where the self-association of the purine residues occurs in the crystal structure of a nucleoside. 

Wth the introduction of the electron-withdrawing ribose moiety, nucleosides have a greater tendency for self-association through stacking than their corresponding purine or pyrimidine base. This effect will be reflected in an increase in retention behavior of nucleosides over that of corresponding bases at any mobile-phase pH. 

Figure 9 Lipophilic nucleosides G 5 and isoG 6 self-associate in the presence of cations to give hydrogen-bonded G4-quartets or isoG -pentamers. The relative orientation of the nucleoside s hydrogen bond donor and acceptor groups determines assembly size (Adapted from ref 3 with permission).

Nucleoside 5-triphosphates self-association, acid-base, and metal ion-binding properties 05CSR875. 

It is obvious that the conformations, which these compounds can acquire in aqueous solution are of prime importance to their biological activity, and thus water should be the solvent of choice. However, the investigation of aqueous solutions of the purine(p)nueleosides by NNR techniques has two very severe experimental limitations First, ma of the nucleosides are only very sparingly soluble in neutral water at room temperature. Second, the aqueous solutions of these compounds do show pronounced self association at the concentrations necessary for NHR-experiments (A) and this association renders the application of proton-T and NOE studies to the quantitative determination of conformations nearly impossible, since it is very difficult to separate intromolecular effects from the contributions of nei bouring molecules. 

On the other hand, DNA-modified mercury electrodes can be prepared easily by immersing a hanging mercury drop electrode or a mercury film electrode into a drop of the DNA solution. This approach requires less amount of DNA for analysis [51-53]. DNA bases and nucleosides are strongly adsorbed at mercury electrodes. Nucleosides possess an extraordinary ability of self-association (two-dimensional condensation) at the surface of mercury electrodes and can form monomolecular compact films. At high positive potentials, all DNA bases can react with mercury electrodes, forming sparingly soluble compounds. 

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. ... 

---