Mode of action of intercalators: a theoretical study.

Mode of action of some intercalators has been theoretically investigated on the basis of quantum mechanical perturbation method. Energies of H-bond interaction between drug chromophore and base pairs have been calculated in all possible orientations. The stacking energy has also been calculated with the base pairs. The effect of these interactions on specific recognition has also been discussed. On the basis of these studies, a model for the interaction of these drugs has been proposed. This explains the relative activities of acridine intercalators and satisfies the experimental observations.

A theoretical study of acriflavin-DNA binding.

A theoretical study of binding behaviour of acriflavin, a well-known mutagen, with DNA base pairs such as AT, GC, TA and CG has been performed using CNDO/2 method to compute net atomic charges and dipoles located at various centres in acriflavine as well as base pairs. Acriflavine-DNA base pair interactions have been evaluated using second order perturbation method with multicentered multipole approximation. Only minimum energy configurations have been reported. Results have been discussed with a view to obtain a comparative behaviour of other similar dyes like proflavine and acridine orange.

Stacking interactions between demethylated ellipticines and DNA base pairs--a quantum mechanical study.

A study of the binding behaviour of ellipticine compounds, derivatives of pyrido (4-3b) carbazole, has been carried out to elucidate the relationship between the drug-activity and demethylation of ellipticine. An all valence electron method (CNDO/2) has been employed to compute molecular charge distribution corresponding to various atomic centres of ellipticines and DNA base pairs. Using these atomic charges and dipoles, intermolecular interaction energy has been calculated with the help of second order perturbation theory and multicentered-multipole expansion technique. A comparative analysis of the binding patterns for nor-5,11-dimethyl-ellipticine and nor-11-methyl-ellipticine has been presented vis-a-vis ellipticine. Attempt has been made to correlate interaction energy studies with demethylation of ellipticine and the possible binding patterns.

Interaction energy studies on pyrazolopyrimidine nucleoside antibiotics —A theoretical study: Oxoformycin Β.

The biological activity of oxoformycin Β has been exafned on the basis of the model developed for the incorporation of nucleoside analogues during transcription. Claverie's simplified formula has been employed for intermolecular interaction energy calculation. The pairing energy of oxoformycin Β base with complementary bases as well as the association energy with nucleic acid base pairs have been calculated. The results are compared with those of similar computation with normal bases. In addition to the in-plane interaction the vertical interaction energy between the analogue and the normal bases has been computed to specify the particular position of the analogue in the chain. On the basis of the model an attempt has been made to explain the mechanism of the biological action of oxoformycin Β and to compare the biological activity of pyrazolopyrimidine nucleoside analogues.

Quantum mechanical studies on the activity of anticancerous drug—Ellipticine.

Ellipticine compounds, derivatives of pyrido-(4-3b) carbazole are used in the human cancer therapy. Most of these drugs interact directly with DNA molecule. CNDO method, alongwith second order perturbation theory and multicentered-multipole approxiation have been used to compute intermolecular interaction energies of ellipticine with DNA ase pairs (GC and AT) in both normal and inverted cases. An attempt has been made to correlate the drug-nucleic acid interactions for ellipticine to locate site of drug action and binding pattern on the basis of intermolecular forces.