Journal
JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY
Volume 108, Issue 1, Pages 253-262Publisher
SPRINGER
DOI: 10.1007/s10973-011-1584-8
Keywords
Ciprofloxacin (CPF); Mass spectra (MS); Thermal analysis (TA); MO calculation; Structure reactivity relationship
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Ciprofloxacin (CPF, C17H18FN3O3) drug is used in the treatment of some bacterial infectious diseases. The drug was investigated using thermal analysis (TA) measurements (TG/DTG) and electron impact mass spectral (EI-MS) fragmentation at 70 eV techniques. Furthermore, the drug was characterized and investigated by other spectroscopic tools as IR, UV-Vis, H-1-, and C-13-NMR. Semi-empirical MO calculation using PM3 procedure has been carried out on neutral molecule and positively charged species. The calculations included, bond length, bond order, bond strain, partial charge distribution, ionization energy, and heat of formation (Delta H-f). The PM3 procedure provides a basis for fine distinction among sites of initial bond cleavage, which is crucial to the rationalization of subsequent fragmentation of the molecule. 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 of this drug. From EI-MS, the main primary cleavage site of the charged molecule is that due to C-COOH bond cleavage with H-rearrangement to skeleton and CO2 loss which can further decompose by piperazine loss. Thermal analysis of the neutral form of the drug reveals the high response of the drug to the temperature variation with very fast rate. Thermal decomposition has carried out in several sequential steps in the temperature range 40-650 degrees C. The initial thermal decomposition is similar to that obtained by mass spectrometric fragmentation (C-COOH fragment) but differ in that a rearrangement occurs by OH and CO loss. Therefore, comparison between MS and TA helps in selection the proper pathway representing the fragmentation of this drug. This comparison successfully confirmed by MO calculation. Finally, the effect of fluorine atom on the stability of the drug was discussed.
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