Ruthenium ions distance between

Ruthenium tris-2,2 -bipyridine complexes are known to play an active role as photochemical redox agents in the solar energy conversion The corresponding amphiphilic complex 96 does not polymerize, presumably due to sterical reasons. The Ru ions are octahedrally coordinated by the three 2,2 -bipyridine ligands, which causes a very bulky size of the head group. As a consequence, the distances between adjacent diyne units likely become too large for a solid-state 1,4-addition... 

This general approach has, however, serious limitations. The position of the site for attack (and therefore the electron transfer distance involved) is very conjectural. In addition, the vexing possibility, which we have encountered several times, of a dead-end mechanism (Sec. 1.6.4) is always present. One way to circumvent this difficulty, is to bind a metal complex to the protein at a specific site, with a known (usually crystallographic) relationship to the metal site. The strategy then is to create a metastable state, which can only be alleviated by a discernable electron transfer between the labelled and natural site. It is important to establish that the modification does not radically alter the structure of the protein. A favorite technique is to attach (NH3)5Ru to a histidine imidazole near the surface of a protein. Exposure of this modified protein to a deficiency of a powerful reducing agent, will give a eon-current (partial) reduction of the ruthenium(III) and the site metal ion e.g. iron(III) heme in cytochrome c... 

Heavier metal ions and metal complexes can find sites on nitrogen atoms of the nucleic acid bases. Examples are the platinum complex cisplatin and the DNA-cleaving antibiotic neocarzinostatin (Box 5-B). Can metals interact with the n electrons of stacked DNA bases A surprising result has been reported for intercalating complexes of ruthenium (Ru) and rhodium (Rh). Apparent transfer of electrons between Ru (II) and Rh (III) over distances in excess of 4.0 nm, presumably through the stacked bases, has been observed,181 as has electron transfer from other ions.181a Stacked bases are apparently semiconductors.182... 

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