1.10- Phenanthrolines metal complexes

Modified d metal complex systems involving photoactivated cleavage A- and A- tris(substituted 1,10-phenanthroline) metal complexes with chiral specificity. 

Researchers have also studied DNA-mediated electron transfer by using donor-acceptor pairs that bind DNA noncovalently (27-30). Early work in our laboratory used cationic tris(phenanthroline) metal complexes as donor-acceptor pairs (29, 30). These complexes, shown in Figure 1, associate with DNA through two modes, (i) intercalation and... 

Barton, J. K.,Tris (phenanthroline) metal complexes probes for DNA helicity,... 

In this chapter we first summarize the basics needed to consider the interactions of metal ions and complexes with nucleic acids. What are the structures of nucleic acids What is the basic repertoire of modes of association and chemical reactions that occur between coordination complexes and polynucleotides We then consider in some detail the interaction of a simple family of coordination complexes, the tris(phenanthroline) metal complexes, with DNA and RNA to illustrate the techniques, questions, and applications of metal/nucleic-acid chemistry that are currently being explored. In this section, the focus on tris(phenanthroline) complexes serves as a springboard to compare and contrast studies of other, more intricately designed transition-metal complexes (in the next section) with nucleic acids. Last we consider how Nature uses metal ions and complexes in carrying out nucleic-acid chemistry. Here the principles, techniques, and fundamental coordination chemistry of metals with nucleic acids provide the foundation for our current understanding of how these fascinating and complex bioinorganic systems may function. 

III. A CASE STUDY TRIS(PHENANTHROLINE) METAL COMPLEXES... 

Now we may examine in detail the interaction of one class of metal complexes with nucleic acids, how these complexes bind to polynucleotides, the techniques used to explore these binding interactions, and various applications of the complexes to probe biological structure and function. Tris(phenanthroline) metal complexes represent quite simple, well-defined examples of coordination complexes that associate with nucleic acids. Their examination should offer a useful illustration of the range of binding modes, reactivity, techniques for study, and applications that are currently being exploited and explored. In addition, we may contrast these interactions with those of other transition-metal complexes, both derivatives of the tris(phenanthroline) family and also some complexes that differ substantially in structure or reactivity. 

Tris(phenanthroline) complexes of ruthenium(II), cobalt(III), and rhodium(III) are octahedral, substitutionally inert complexes, and as a result of this coordina-tive saturation the complexes bind to double-helical DNA through a mixture of noncovalent interactions. Tris(phenanthroline) metal complexes bind to the double helix both by intercalation in the major groove and through hydrophobic association in the minor groove. " " Intercalation and minor groove-binding are, in fact, the two most common modes of noncovalent association of small molecules with nucleic acids. In addition, as with other small molecules, a nonspecific electrostatic interaction between the cationic complexes and the DNA polyanion serves to stabilize association. Overall binding of the tris(phenanthroline) complexes to DNA is moderate (log K = 4)." ... 

Many of the same techniques employed in studying the basic chemistry of coordination complexes can be be used in following the binding of transition-metal complexes to nucleic acids, but biochemical methods, with their often exquisite sensitivity, become valuable aids as well in delineating specific binding interactions. Tris(phenanthroline) metal complexes are particularly useful to illustrate this point, since here the metal center in the complex is selected in terms of the technique used for examination. 

The variety of studies conducted with tris(phenanthroline)metal complexes and DNA perhaps most easily illustrate this point (16). Tris(phenanthroline) complexes of ruthenium(II) and its derivatives possess an intense luminescent metal-to-ligand charge-transfer state that is... 

Ru(TMP)3] A distinctive characteristic of the A conformation is its shallow and wide minor-groove surface. Tris(phenanthroline)metal complexes bind to DNA both through intercalation in the major groove and through a surface-bound interaction in the minor groove (18-20) (see above). It is this surface-bound interaction that has been exploited in the construction of a complex, a derivative of tris(phenanthroline)ruthenium(II) that selectively targets A-form helical structures (30, 75). 

Technetium-99m coordination compounds are used very widely as noniavasive imaging tools (35) (see Imaging technology Radioactive tracers). Different coordination species concentrate ia different organs. Several of the [Tc O(chelate)2] types have been used. In fact, the large majority of nuclear medicine scans ia the United States are of technetium-99m complexes. Moreover, chiral transition-metal complexes have been used to probe nucleic acid stmcture (see Nucleic acids). For example, the two chiral isomers of tris(1,10-phenanthroline)mthenium (IT) [24162-09-2] (14) iateract differentiy with DNA. These compounds are enantioselective and provide an addition tool for DNA stmctural iaterpretation (36). 

The electronic spectra and optical activity of phenanthroline and dipyridyl metal complexes. S. F. Mason, Inorg. Chim. Acta, Rev., 1968, 2, 89-109 (84). 

Although the number of applications of olefin metathesis to transition metal complexes is small compared to the number of applications in organic synthesis, this field is becoming increasingly important. Spectacular examples are the double RCM reactions of copper phenanthroline complexes as a synthetic route to catenanes [113] or a recently reported approach to steric shielding of rhenium complex terminated sp-carbon chains [114]. 

What happens if we look at the K2 or Ki, values for didentate ligands In general, the Kj values show stability patterns which closely parallel those for K. However, the values are different. Figure 8-17 presents K, data for transition-metal complexes of 1,10-phenanthroline and 1,2-diaminoethane (Eq. 8.14). 

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