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| - Role of the Central Metal Ion and Ligand Charge in the DNABinding and Modification by Metallosalen Complexes
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| - Several metal complexes of three different functionalized salenderivatives have been synthesized.The salens differ in terms of the electrostatic character and thelocation of the charges. The interactionsof such complexes with DNA were first investigated in detail byUV−vis absorption titrimetry. Itappears that the DNA binding by most of these compounds is primarilydue to a combination ofelectrostatic and other modes of interactions. The meltingtemperatures of DNA in the presence ofvarious metal complexes were higher than that of the pure DNA. Thepresence of additional chargeon the central metal ion core in the complex, however, alters thenature of binding. Bis-cationic salencomplexes containing central Ni(II) or Mn(III) were found toinduce DNA strand scission, especiallyin the presence of co-oxidant as revealed by plasmid DNA cleavage assayand also on the basis of theautoradiogram obtained from their respective high-resolution sequencinggels. Modest base selectivitywas observed in the DNA cleavage reactions. Comparisons of thelinearized and supercoiled forms ofDNA in the metal complex-mediated cleavage reactions reveal that thesupercoiled forms are moresusceptible to DNA scission. Under suitable conditions, the DNAcleavage reactions can be inducedeither by preformed metal complexes or by in situcomplexation of the ligand in the presence of theappropriate metal ion. Also revealed was the fact that theanalogous complexes containing Cu(II) orCr(III) did not effect any DNA strand scission under comparableconditions. Salens with pendantnegative charges on either side of the precursor salicylaldehyde orethylenediamine fragments didnot bind with DNA. Similarly, metallosalen complexes with netanionic character also failed to induceany DNA modification activities.
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