Spectrophotometric and FT-IR studies of interaction of narcotic drugs (morphine, codeine and thebaine) with acceptors (HQ, BQ, NQ, PA, o-Chlo, DNB), their thermodynamics and determination of the vertical ionization potentials of the drugs

摘要

Morphine, codeine and thebaine formed charge transfer complexes with acceptors like hydroquinone, bcnzo-quinone, naphthaquinone, picric acid, chloranil and dinitrobenzene as evidenced from the shifting of absorption maxima and change in optical densities in the UV regions. The evidence of complex formation was observed from the optical densities of the complex in the visible region when DA and where D and A do not absorb. The evidence of complex formation was also adduced from FT-IR measurements for morphine + naphthaquinone, codeine + naphthaquinone and thebaine + naphthaquinone complexes. The formations of CT complexes with those acceptors are confirmed from the plots of hv_(CT) against I_D~V (vertical ionization potential) of the drugs. From the values CT transition energies, the vertical ionization potentials (I_D~V) of morphine, codeine and thebaine were estimated to be 7.228 ± 0.396, 7.236 ± 0.399 and 7.233 ± 0.405 eV respectively. The almost equal values are due to structural similarities of the drugs. The degrees of overlap in the ground state of the complexes were also calculated. The association constants and thermodynamics of the complexes (e.g. ΔG~0, ΔH~0 and ΔS~R) were determined spectrophotometrically from the o.d measurements at 298, 303, 306 and 310 K using D and A in stoichiometric ratios, a condition necessary for the accurate determination of the association constants. The complexes are fairly stable.