Spectrophotometric Determination of Niacin, Thiamine, Glibenclamide, Erythromycin and Para Amino Benzo Ic Acid Using 2, 3 – Dichloro – 5, 6 – Dicyano – 1, 4 – Benzoquinone.


A simple and sensitive spectrophotometric method is described for the assay of the drugs; niacin, glibenclamide, erythromycin, thiamine and 4-aminobenzoic acid. The method is based on charge transfer complexation (CT) reaction of niacin, glibenclamide, erythromycin, thiamine and 4-aminobenzoic acid as n-electron donors with 2,3- dichloro-5,6-dicyno-1,4-benzoquinone (DDQ) as л-electron acceptor in methanol.

Intensely coloured charge transfer complexes with niacin (reddish brown, lmax ;464 nm; εmax, 1.02×103 dm3 mol-1 cm-1 ) thiamine (reddish brown ,lmax ;474 nm; εmax, 1.08×103 dm3 mol-1 cm-1 ), glibenclamide (reddish brown , lmax ;474 nm; εmax,0.99×103 dm3 mol1 cm-1 ) erythromycin(reddish brown , lmax ;464 nm; εmax, 1.27×103 dm3 mol-1 cm-1 ) 4- aminobenzoic acid(reddish brown, lmax ;474nm; εmax, 1.06×103 dm3 mol-1 cm-1 ) all in a 1:1 stoichiometric ratio.

Condition for complete reactions and optimum stability of complexes were niacin (70 min, 60 OC) thiamine (25 min, 40 OC), glibenclamide (35 min, 40 OC), erythromycin (15 min, 60 OC) and 4-aminobenzoic acid (15 min, 60 OC) as absorbances of the complexes remained invariant within these conditions. Formation and stability of the complexes of niacin, thiamine, 4-aminobenzoic acid and erythromycin were optimum at pH 8. For glibenclamide pH 2.0 favoured optimum stability and formation.

The bands distinguished for the donors to donor-acceptor CT complexes displayed small changes in band intensities and frequency values in the IR spectra ,The –NH2 group vibration occurring at 3609 cm-1 shifted to 3610 cm-1 in thiamine, PABA (3222 cm-1 to 3183 cm-1 ), ѵ (N-H) occurring at 3331cm-1 shifted to 3371 cm-1 in glibenclamide, ѵ(C= N) occurring at 2936 cm-1 shifted to 2944 cm-1 in niacin, ѵ (CH3-N) occurring at 2948 cm-1 shifted to 2939 cm-1 in erythromycin. 


Acceptors are aromatic systems containing electron withdrawing substituents such as nitro, cyano and halogen groups (Foster, 1967). Electron donors are systems that are electron rich (Ajali and Chukwurah, 2001). The interaction between electron donor and electron acceptor results in formation of charge transfer complex (Ajali et al, 2008). The term charge transfer denotes a certain type of complex which results from interaction of an electron acceptor and an electron donor with the formation of weak bonds (Hassib and Issa, 1996). 

However, the nature of the interaction in a charge transfer complex is not a stable chemical bond and is much weaker than covalent forces. It is better characterized as a weak electron resonance. As a result, the excitation energy of this resonance occurs very frequently in the visible region of the electromagnetic spectrum. This produces the usually intense colour characteristic for these complexes. These optical absorption bands are often referred to as charge transfer bands.

Molecular interactions between electron donors and acceptors are generally associated with the formation of intensely coloured charge transfer complexes which absorb radiation in the visible region.Charge transfer (CT) complexes have been widely studied (Ezeanokete et al, 2013; Hala et al, 2013; Frag et al, 2011; Ramzin et al, 2012; Farha, 2013). Charge transfer complexes are known to take part in many chemical reactions like addition, substitution and condensation reactions (Van et al, 2006). 


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