Here, we report spectrophotometric method for the determination of gabapentin through charge transfer complexes with σ and π acceptors and also with dye stuffs. The method involves ion-pair complex formation of gabapentin with ninhydrin, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, tetracyanoethylene, methyl orange and picric acid. The optimum conditions for the reactions and validation of described procedure have been studied. Resulting complexes absorb at 580, 315, 340, 464 and 342 nm in the Beer's law range of 2-22, 32-80, 40-360, 12-96 and 15-135 µg mL-1 with correlation coefficient greater than 0.998 in each case respectively. The proposed method was applied successfully for the determination of gabapentin in pharmaceutical formulations. Satisfactory recovery values suggest that the method is reliable for the determination of gabapentin in pharmaceutical formulations without interference of excipients. In addition, the spectral characteristics including oscillator's strength, dipole moment, ionization potential, energy of complexes, resonance energy and also the thermodynamic parameters i.e. association constant and Gibb's free energy changes have been determined. Benesi-Hildebrand plots for each complex have been constructed. Further, solid charge transfer complexes of gabapentin were synthesized and characterized by IR spectroscopy.

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