LAUSR

Abstract Drugs which are capable of targeting sequence specific DNA constitute a novel approach to chemotherapy and have been exploited in detail in recent years. In this context, the synthetic minor groove binder Hoechst 33258 has been in focus due to its ability to specifically bind double helical DNA. A theoretical study of the structure, stability and properties of the tautomers and rotamers of Hoechst 33258 in two different dielectric media, viz. gas phase and aqueous solution would be useful in this respect. Besides these studies, the electronic, vibrational, 1 H NMR and 13 C NMR spectra are also investigated in detail in this work. These are also compared with the experimental spectra. The results indicate that in the gas phase, in all these rotamers, while the three aromatic rings prefer the same plane, the piperazinyl ring projects out of plane. The degree of non-planarity of the central bond increases in aqueous medium. The molecule retains its aqueous state conformation on binding to DNA. Bond length, bond order and NBO analyses suggest an enhanced degree of conjugation in the bonds connecting the three aromatic rings.