Chiral Recognition of Deoxyoligonucleotides by .DELTA.- and .LAMBDA.-Tris(ethylenediamine)cobalt(III)

59Co NMR and CD measurements show for both stereoisomers of Co(en)3(3+) a similar trend in the sequence dependence of DNA recognition, as was reported previously for Co(NH3)6(3+). In particular, specific binding is evident to DNA molecules possessing runs of two or more same-strand guanine residues. The binding of either isomer to such sequences induces structural transitions toward A-DNA characteristics. Such measurements also show significant differences between the two stereoisomers in terms of how they recognize specific duplex DNA sequences. delta-Co(en)3(3+) binds more tightly than lambda-Co(en)3(3+) to right-handed, guanine-rich DNA, whereas lambda-Co(en)3(3+) binds more tightly than delta-Co(en)3(3+) to left-handed DNA. The two stereoisomers bind in an indistinguishable manner to AT-rich DNA.