Alteration in DNA binding pattern of conformationally locked NC(O)N system: A spectroscopic investigation

The binding mode of a conformationally locked NC(O)N planar system with deoxyribonucleic acid (DNA) is investigated using various spectroscopic and enzymatic assays. Compound 1 and its four different salts (comp. 2–5) were prepared for this purpose. They showed certain changes in their respective DNA-compound complex at ground state and excited state as measured by UV–vis and fluorescence emission spectra. The Stern-Volmer quenching constant (KSV) for the neutral species (1) is found 8545 M−1, whereas, for its salts 2, 3, 4 and 5 the quenching constants were 33510 M−1, 11352 M−1, 19693 M−1 and 27270 M−1 respectively. Nevertheless, the binding constant values remain comparable in neutral and salt forms except for 5. To elucidate the reason we took their CD spectra and ran a topoisomerase I (Topo I) assay. These experimental data revel the fact that compound 1 (neutral form) binds at the minor groove of DNA, whereas, its salt (2) has an extended intercalating property.

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