The DNA binding of the Delta Delta-, Delta Lambda- and Lambda Lambda-stereoisomers of [{Ru(Me(2)bpy)(2)}(2)(mu-bpm)](4+)

H-1 NMR spectroscopy has been used to study the dodecanucleotide binding of the rac (Delta Delta- and Lambda Lambda-) and meso (Delta Lambda stereoiso mers of the dinuclear species [{Ru(Me(2)bpy)(2)}(2) (mu -bpm)](4+) (Me(2)bp y = 4,4'-dimethyl-2,2'-bipyridine; bpm = 2,2'-bipyrimidine). The addition o f the Delta Delta- and Lambda Lambda -enantiomers to the dodecanucleotide d (CAATCCGGATTG)(2) induced different shifts for the resonances from each ena ntiomer. On binding, the meso diastereoisomer exhibited twice the number of resonances observed for the free metal complex, identified as two sets of resonances with shifts similar to those induced by the Delta Delta- and Lam bda Lambda -enantiomers of the rac form. In NOESY spectra of d( CAATCCGGATT G)(2) bound with each stereoisomer, NOE's from the metal complex were obser ved to the dodecanucleotide H1' and H4' protons, indicating that [{Ru(Me(2) bpy)(2)}(2)(mu -bpm)](4+) bound in the dodecanucleotide minor groove. The s trongest NOE's from the metal complex to d(CAATCCGGATTG)(2) were observed f or the Lambda Lambda -isomer. The observed pattern of intermolecular NOE's indicated that the Lambda Lambda -isomer bound at the central CC/GG site as well as at the terminal CA/GT sequence of the dodecanucleotide. By contras t, NOE data of the Lambda Lambda -isomer associated with a second dodecanuc leotide d(CAATCGCGATTG)(2) indicated that the Lambda Lambda -isomer bound a t the AAT/ATT sequence as well as at the terminal base pairs in this case. It is proposed that [{Ru(Me(2)bpy)(2)}(2) (mu -bpm)](4+) will only bind in the DNA minor groove: however, as the metal complex is not easily accommoda ted in the groove because of its size, it will only bind at sites where the minor groove is more open.