Investigation of ibuprofen drug using mass spectrometry,thermal analyses,and semi-empirical molecular orbital calculation |
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Authors: | Mohamed A Zayed M F Hawash M A Fahmey Ali M M El-Gizouli |
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Institution: | (1) Chemistry Department, Faculty of Science, Cairo University, Giza, 12613, Egypt;(2) Nuclear Research Centre, Nuclear Physics Department, AEA, Cairo, 13759, Egypt |
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Abstract: | Ibuprofen (C15H18O2) is an anti-inflammatory drug. It is important to investigate its structure to know the active groups and weak bond responsible
for its medical activity. Consequently in the present study, ibuprofen was investigated by mass spectrometry (MS) and thermal
analyses (TAs) (TG/DTG and DTA), and confirmed by semi-empirical molecular orbital (MO) calculation using PM3 procedure, on
the neutral and positively charged forms of the drug. These calculations included bond order, bond length, and bond strain,
and charge distribution, heat of formation, and ionization energy. The mass spectra and thermal analysis fragmentation pathways
were proposed and compared to each other to select the most suitable scheme representing the correct fragmentation pathway
of the drug in both techniques. From the electron ionization (EI) mass spectra, the primary cleavage site of the charged molecule
is because of the rupture of COOH group (the lowest bond order) followed by propyl group loss. The TAs of the drug revealed
high response of the drug to the temperature variation with very fast rate. It decomposed in several sequential steps in the
temperature range 25–360 °C. The initial thermal decomposition is similar to that obtained by MS fragmentation of the first
rupture (COOH), then subsequent one of propyl loss, and finally of ethylene loss. These mass losses appear as endothermic
peaks required energy values of −214.83, −895.95, and −211.10 J g−1, respectively. The order of these losses is also related to the values of the MO calculation parameters. Therefore, the comparison
between MS and TA helps in the selection of the proper pathway representing the decomposition of this drug to give its metabolites
in in vivo system. This comparison is also successfully confirmed by MO calculations. |
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