Charge transfer complexes of atenololdrug with some dihydrxyanthraquinone and dihydroxybenzoquinone derivatives:Molecular structures, spectral, and quantitative studies.

Atenolol (ATN) is -blocker medication widely used in the clinic to treat hypertension. In this study, complexation of ATN with three different acceptors, namely alizarin (AZ), alizarin red S (AZR), and 2,5-dihydroxy-p-benzoquinone (DHBQ) was investigated spectrophotometrically. It was found that ATN formed charge transfer (CT) complexes with AZ, AZR, and DHBQ in MeOH. The CT reaction conditions between ATN and each acceptor were comprehensively investigated. Moreover, the formation constants and other related spectrophysical parameters were determined. The stoichiometry of 1:1 ratio was established for all studied complexes in MeOH using different methods. The optical band gap (Eg), which corresponds to the minimum energy required for the transition, was calculated by the optical absorption method. The values of Eg were found to be 2.02, 2.07, and 2.25 eV for the [ATN-AZ], [ATN-AZR], and [ATN-DHBQ] complexes, respectively. Solid complexes of ATN with these acceptors were effectively prepared and isolated. New bands in the FTIR spectra of the complexes were detected as a result of complexation. Additionally, the appearance of signals corresponding to the reactants in 1H NMR spectra of the products confirmed the formation of ATN complexes. In addition to the CT reactions between ATN and each acceptor, both FTIR and 1H NMR analyses suggested the existence of proton transfer reactions. Based on the fast complexation of ATN with the studied acceptors in MeOH, three direct, simple, and sensitive spectrophotometric methods were developed for the quantitative determination of ATN in its pure form and in pharmaceutical formulations. Validation studies confirmed the remarkable accuracy and precision of the developed methods without any interference from tablet excipients.