Proton-transfer and charge-transfer interactions between the antibiotic trimethoprim and several σ− and π−acceptors: A spectroscopic study

The σ−acceptor iodine and π−acceptors chloranil (CHL), chloranilic acid (CLA), and picric acid (PA) were complexed with the antibiotic trimethoprim (TMP) as the donor through transfer-type reactions. The spectroscopic properties and structural morphology of the resultant complexes were investigated in both their soluble and solid states; CHN elemental analysis, 1H NMR, 13C NMR, FT−IR, Raman, UV-visible spectroscopies, TEM, and SEM-EDX were used to determine these properties. This work highlights that TMP reacted with iodine and CHL via a CT interaction and with CLA and PA via a PT interaction to form stable solid complexes that ranged in color from yellow (TMP-PA), to violet (TMP-CLA), brown (TMP-CHL), and black (TMP-iodine). The 1:2 stoichiometry between TMP and iodine and 1:1 stoichiometry with the other acceptors was verified by elemental analysis and the spectrophotometric titration method. TEM revealed that the structural morphologies of the TMP complexes were markedly different ranging from spherical particles with the CHL and CLA acceptors to short rods with iodine acceptor to long tubes with the PA acceptor.