Molecular Complexes of DDQ with Drugs: A Spectrophotometric Study

Spectrophotometric study of molecular complexes of DDQ (2,3-Dichloro-5,6-dicyano-1,4-benzoquinone) with six drugs viz., Ofloxacin, Trazadone, Losartan K, Irbesartan, Cisapride and Ramipril have been carried out. Each of the complex formed between DDQ as acceptor and drug as donor, in CHCl₃ exhibited charge transfer band/bands in the region where neither of the components have absorption. The λmax of each complex is characteristic of the donor drug. The ionization potentials of the drugs have been evaluated from the position of CT band. Each complex is found to have 1:1 composition as determined by Job's continuous variation method. The stability constants of CT complexes have been evaluated using Rose-Drago and Benesi-Hildebrand methods. The stability constants are correlated to the ionization potentials. Thermodynamic parameters of the complexes are estimated from the variation of log K with temperature by vant-Hoff method. The molar extinction eo-efficients (ε) are obtained from intersection points of Rose-Drago plots and intercept of BH plots. The oscillatory strengths (f) and transition dipole moments (D) have been evaluated from the values of ε and half-band widths of CT band.