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Mass Spectrometric Study of Some Fluoroquinolone Drugs Using Electron Ionization and Chemical Ionization Techniques in Combination with Semi-Empirical Calculations

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Mass Spectrometric Study of Some Fluoroquinolone Drugs Using Electron Ionization and Chemical Ionization Techniques in Combination with Semi-Empirical Calculations Benha University Faculty of Science Physics department MASS SPECTROMETRIC STUDY OF SOME FLUOROQUINOLONE DRUGS USING ELECTRON IONIZATION AND CHEMICAL IONIZATION TECHNIQUES IN COMBINATION WITH SEMI-EMPIRICAL CALCULATIONS. BY MAMOUN SARHAN MAHMOUD ABD EL KAREEM (M.Sc. PHYSICS) Atomic Energy Authority, Cairo, Egypt THESIS SUBMITTED FOR THE Ph.D. DEGREE (EXPERIMENTAL PHYSICS) From FACULITY OF SCIENCE BENHA UNIVERSITY Supervisors Prof. Dr. M. I. El-Zaiki Prof. Dr. Ezzat T.M.Selim Prof. of Nuclear Physics Atomic & Molecular Physics Division Physics Department Experimental Nuclear Physics Department Faculty of Science, (Benha University) Atomic Energy Authority. (Egypt) Prof. Dr. M.A.Rabbih Prof. Dr. A.M.Hassan Rezk Atomic & Molecular Physics Division National Center for Radiation Research Experimental Nuclear Physics Department and Technology Atomic Energy Authority. (Egypt) Atomic Energy Authority. (Egypt) 2013 Abbreviations and Acronyms EI Electron Ionization CI Chemical Ionization MO Molecular Orbital MNDO Modified Neglect of Diatomic Overlap TFC–MS/MS Turbulent Flow Chromatography/Tandem Mass Spectrometry SPE Solid-Phase Extraction FQ Fluoroquinolone SPME Solid-Phase Microextraction LC/MS/MS Liquid Chromatography–Tandem Mass Spectrometry IE Ionization Energy ΔHf Heats of Formation PA Proton Affinity AE Appearance Energy IP Ionization Potential GC/MS Gas Chromatograph/Mass Spectrometer RI Relative Intensity m/z Mass to Charge Ratio ACKNOWLEDGMENT This work was performed in the Molecular Physics Division of the Experimental Nuclear Physics Department, in cooperation with Radiation Chemistry Department, National Center for Radiation Research and Technology, Atomic Energy Authority, Cairo, Egypt. I wish to express my deepest thanks to Head of Experimental Nuclear Physics Department of the Egyptian Atomic Energy Authority and Head of Physics Department Faculty of Science, Benha University, for their encouragement interest. Special thanks to Professor Dr.M.E. El–Zeiki Faculty of Science, Benha University for continuous support and for encouragement interest during the course of this work. I would like to express my deepest thanks to Professor Dr. Ezzat T.M.Selim, Experimental Nuclear Physics Department of the Egyptian Atomic Energy Authority, for his great efforts in illuminating the discussion. I would like to express my gratitude and appreciation to Professor Dr. M.A.Rabbih Experimental Nuclear Physics Department of the Egyptian Atomic Energy Authority, for his great efforts for suggesting and supervising this work and also for his valuable guidance and illuminating discussions. I would like to express my gratitude and appreciation to Professor Dr. A.M.Hassan Rezk, Radiation Chemistry Department, National Center for Radiation Research and Technology, Atomic Energy Authority, for his great efforts in the mass spectrometric measurements and supervising this work. Abstract A mass spectrometer of the type QMS (SSQ710) is used to record the electron ionization mass spectra of some 6-fluoroquinolones molecules, namely: Norfloxacin, Pefloxacin, Ciprofloxacin and Levofloxacin.While the chemical ionization mass spectra of these compounds are recorded using Thermo Finnigan TRACE DSQ GC/MS system. In EI mass spectra, the relative intensities for the molecular ions [M]+• of the studied compounds and the prominent fragment ions are reported and discussed. Furthermore, fragmentation patterns for the four compounds have been suggested and discussed and +• + the most important fragmentation processes such as [M-CO2] , [M-C2H4N] and [M- + CO2-C2H4N] are investigated. On the other hand, the chemical ionization (CI) mass spectra of the compounds have been recorded using methane as the reagent gas. These spectra are discussed in terms of the structure of the compounds, with particular reference to their conventional electron ionization mass spectra. The protonated molecules [M+H]+ are more relatively intense than [M]+• ions in the recorded EI mass spectra indicating higher stability in the case of [M+H]+. Also, fragmentation patterns for the four compounds have been suggested and discussed (using chemical ionization technique) and the most important fragmentation processes +• + + such as [MH-CO2] , [MH-C2H4N] and [MH-H2O] are investigated. Using MNDO semi-empirical method for computation together with the experimental results gave valuable information about the heats of formation and ionization energies of the molecules. The effect of substituents on the geometry of the neutral and ionized molecules are reflected in the values of the ionization energy and heats of formation of +∙ neutral ∆Hf(M) and ionized ∆Hf(M) molecules. The calculated values for ionization energies of Norfloxacin, Pefloxacin, Ciprofloxacin and Levofloxacin are 8.1, 8, 8.8 and 8.3 eV, respectively. The calculated charge distributions at N1 and O12 in the qinolone ring of the studied molecules as well as the presence of a lone pair electrons at N1 and O12 atoms indicate that the ionization processes occur at these two atoms. The appearance +• + (AE) and activation energies of the fragment ions [M-CO2] and [M-C2H4N] are also calculated and discussed. It is noteworthy that all the presently calculated values of ionization, appearance and activation energies are not yet published. The MNDO method is also used to probe the protonation of the studied compounds. The calculated proton + affinities (PA's) together with ∆Hf [M+H] values at nitrogen (N1) and at oxygen (O12) atoms are calculated. These results give interesting features for the protonation sites. The protonation at oxygen (O12) site is more favored than that at nitrogen (N1) site. Furthermore, the calculated values of the heats of formation of neutral [M], ionized [M]+•, + protonated molecule [M+H] and PA's values are reported for the first time CONTENTS Page ABSTRACT і CHAPTER 1. INTRODUCTION AND AIM OF THE WORK 1.1 Introduction 1 1.2 Aim of the Work 5 CHAPTER 2 . THEORETICAL CONSIDERATIONS 2.1. Processes of Ionization and Dissociation by Electron Ionization 6 2.2. Frank - Condon Principle 9 2.3. Ionization Probability Near Thershold 9 2.4. Determination of Thermochemical Data 10 2.5. Stevenson's Rule 11 2.6. Characteristics of Mass Spectra 12 2.7. Simple Bond Cleavage Processes 12 2.8. Rearrangements Processes 13 2.9. Processes of Ionization and Dissociation by Chemical Ionization 13 2.10. Proton Affinity 14 2.11. Semiempirical quantum chemical methods and the predicting mass spectrometric fragmentations 15 CHAPTER 3. APPARATUS AND EXPERIMENTAL CONDITIONS 3.1. Apparatus 16 3.2. Materials 16 3.3. Experimental Conditions 17 CHAPTER 4 . RESULTS AND DISCUSSION 4.1. Results 18 4.1.1. Experimental Measurements 18 4.1.2. Computational Results 19 4.2. Discussion 20 4.2.1. Mass spectra of Norfloxacin using EI technique 25 4.2.2. Ionization processes of Norfloxacin using EI technique 29 4.2.3. Fragmentation of Norfloxacin using EI technique 31 4.2.4. Mass spectrum of Norfloxacin using CI technique 37 4.2.5. Chemical ionization, proton transfer 40 4.2.6. Fragmentation of Norfloxacin using CI technique 41 4.2.7. The proton affinity (PA) , heat of formation(∆Hf) and the charge distributions of Norfloxacin 43 4.3.1. Mass spectra of Pefloxacin under EI technique 45 4.3.2. Ionization Process of Pefloxacin using EI technique 49 4.3.3. Fragmentation of Pefloxacin using EI technique 51 4.3.4. Fragmentation of Pefloxacin using CI technique 55 4.3.5. The proton affinity (PA), heat of formation (∆Hf) and charge distributions of Pefloxacin 58 4.4.1. Mass spectra of Ciprofloxacin using EI technique 59 4.4.2.Ionization process of Ciprofloxacin using EI technique 63 4.4.3. Fragmentation of Ciprofloxacin using EI technique 65 4.4.4. Fragmentation of Ciprofloxacin using CI technique 70 4.4.5. The proton affinity (PA),heat of formation (∆Hf) and charge distributions of Ciprofloxacin 73 4.5.1. Mass spectra of Levofloxacin using EI technique 74 4.5.2. Ionization process of Levofloxacin using EI technique 78 4.5.3. Fragmentation of Levofloxacin using EI technique 80 4.5.4. Fragmentation of Levofloxacin using CI technique 83 4.5.5. The proton affinity (PA), heat of formation (∆Hf) and charge distributions of Levofloxacin 86 CHAPTER 5. CONCLUSIONS 87 REFRENCES 88 ARABIC SUMMARY List of Figures and Schemes figure Name Page Figure 1 Potential energy curves for a molecule M ionized to either a 7 nondissociative M+• or dissociative state F+ + N• . Path (a) represents the adiabatic transition while path (v) represents the vertical transition. Figure 2 Structure of fluoroquinolones 20 Figure 3 The structures of Norfloxacin , Pefloxacin , Ciprofloxacin 22 and Levofloxacin Figure 4 The numbering system of the 6-fluoroquinolone compounds 23 used in this study. Figure 5 The protonation sites at oxygen(O12) and nitrogen(N1) atoms 24 for 6-fluoroquinolone compounds Figure 6 The EI mass spectrum of Norfloxacin at 70 eV 26 Figure 7 The EI mass spectrum of Norfloxacin at 15 eV 27 Figure 8 The CI mass spectrum of Norfloxacin 38 Figure 9 The EI mass spectrum of Pefloxacin at 70 eV 46 Figure 10 The EI mass spectrum of Pefloxacin at 15 eV 47 Figure 11 The CI mass spectrum of Pefloxacin 57 Figure 12 The EI mass spectrum of Ciprofloxacin at 70 eV 60 Figure 13 The EI mass spectrum of Ciprofloxacin at 15 eV 61 Figure 14 The CI mass spectrum of Ciprofloxacin 72 Figure 15 The EI mass spectrum of Levofloxacin at 70 eV 75 Figure 16 The EI mass spectrum of Levofloxacin at 15 eV 76 Figure 17 The CI mass spectrum of Levofloxacin 85 Schemes Scheme 1 Main fragmentation pathways of Norfloxacin
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