Properties with nucleobases, nucleosides

The coordination properties of the nucleobases have been reviewed by Houlton (40) and by Lippert (2). In a recent review, Lippert discussed the influence of the metal coordination on the piSTa of the nucleobases (41), which correlates with their coordination properties. While the coordination properties of nucleobases, nucleosides, and nucleotides have been extensively studied and reviewed, the number of articles dedicated to the coordination properties of nucleic acids is signihcantly smaller. DeRose et al. (42) recently published a systematic review of the site-specific interactions between both main group and transition metal ions with a broad range of nucleic acids from 10 bp DNA duplexes to 300 00 nucleotide RNA molecules as well as with some nucleobases, nucleosides, and nucleotides. They focused on results obtained primarily from X-ray crystallographic studies. Egli also presented information on the metal ion coordination to DNA in reviews dedicated to X-ray studies of nucleic acids (43, 44). Sletten and Fr0ystein (45) reviewed NMR studies of the interaction between nucleic acids and several late transition metal ions and Zn. Binding of metal complexes to DNA by n interactions has been reviewed by Dupureur and Barton (46). 

In contrast to the amino acid, peptide, and protein conjugates, where a number of different organometallic complexes were used for labeling, DNA derivatives are by and large limited to ferrocene. This is very likely due to the attractive electrochemical properties of ferrocene. Indeed, electrochemical DNA sensors are covered in more detail in Section 1.31.5.2. Two recent reviews cover the ferrocene conjugates with nucleobases, nucleosides and nucleotides,... 

The reaction of hydrated electrons formed by radiolysis with peroxydisulfate yields the sulfate radical anion SO4 which is a strong chemical oxidant (Eqx = 2.4 V/NHE) [50, 58]. The oxidation of both purine and pyrimidine nucleotides by S04 occurs with rate constants near the diffusion-controlled limit (2.1-4.1 x 10 M s ). Candeias and Steenken [58a] employed absorption spectroscopy to investigate acid-base properties of the guanosine cation radical formed by this technique. The cation radical has a pKa of 3.9, and is rapidly deprotonated at neutral pH to yield the neutral G(-H) . Both G+ and G(-H) have broad featureless absorption spectra with extinction coefffcients <2000 at wavelengths longer than 350 nm. This has hampered the use of transient absorption spectra to study their formation and decay. Candeias and Steenken [58b] have also studied the oxidation of di(deoxy)nucleoside phosphates which contain guanine and one of the other three nucleobases by SO4 , and observe only the formation of G+ under acidic conditions and G(-H) under neutral conditions. 

One of the most important aspects of 4-fluoro-6-methylbenzimidazole as a modified nucleobase is its strong stabilization of duplex DNA through a stacking effect. The stacking properties of 97 and other modified nucleosides can be measured by the dangling end thermal denaturation studies of DNA duplexes with self-complementary stands (dXCGC-... 

---