Spectroscopic studies on the interaction of cimetidine drug with biologically significant σ- and π-acceptors

Spectroscopic studies revealed that the interaction of cimetidine drug with electron acceptors iodine and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) resulted through the initial formation of ionic intermediate to charge transfer (CT) complex. The CT-complexes of the interactions have been characterized using UV–vis, 1H NMR, FT-IR and GC–MS techniques. The formation of triiodide ion, I3−, is further confirmed by the observation of the characteristic bands in the far IR spectrum for non-linear I3− ion with Cs symmetry at 156 and 131 cm−1 assigned to νas(I–I) and νs(I–I) of the I–I bond and at 73 cm−1 due to bending δ(I3−). The rate of formation of the CT-complexes has been measured and discussed as a function of relative permittivity of solvent and temperature. The influence of relative permittivity of the medium on the rate indicated that the intermediate is more polar than the reactants and this observation was further supported by spectral studies. Based on the spectroscopic results plausible mechanisms for the interaction of the drug with the chosen acceptors were proposed and discussed and the point of attachment of the multifunctional cimetidine drug with these acceptors during the formation of CT-complex has been established.