Date of Award

8-2021

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Dr. Ekkehard Sinn

Second Advisor

Dr. Ramakrishna Guda

Third Advisor

Dr. Sherine Obare

Fourth Advisor

Dr. Massood Atashbar

Keywords

Synthesis, characterization, novel organic ligands

Abstract

Transition metal complexes of symmetrical and asymmetrical Schiff bases have played a significant role in the field of coordination, inorganic, and bioinorganic chemistry as models for biological, analytical, industrial, and pharmaceutical applications. Over recent years a great deal of interest has developed in new transition metal complexes of Schiff base ligand. The preparation of novel organic ligands is the most important step in the development of metal complexes that exhibit unique properties and novel reactivity. To highlight the presentation of this dissertation and to provide more detailed investigations, the dissertation was separated into six chapters according to the sequence of the work.

The first chapter gives an overview of Schiff bases and the coordination chemistry of different metal complexes focusing on Pt (II), Pt (IV), Cu (II), U (IV), and U (VI) ions with ligands and their geometric preferences.

The second chapter presents the synthesis and characterization of five new platinum based anticancer drugs. They have been categorized under three different types. The first type, chelate agents, is done by having starting materials together in water. The platinum center will react with the organic compound and the solvent to work as a leaving group. Bidentate ligands have two donor atoms, allowing them to bind to a central metal atom. The second type consists of Pt (IV)-based complexes, where two additional ligands essentially keep the drugs inactive until they reach target DNA. Platinum (IV) complexes are the six-coordinate (octahedral coordination geometry), and the two additional ligands allow for further tuning of the properties. The third type is π-bond binding, is a new and interesting field. The stability of the metal-olefin bond in platinum (II) complexes is related to the formal charge on the complex and has been the subject of studies in the past few years. The action occurs when the pi-acid alkene donates electron density to the platinum d-orbital from a π symmetry bonding orbital between the carbon atoms. Then, platinum donates electrons back from another filled d-orbital into the vacant π antibonding orbital.

The third chapter focuses on the synthesis and characterization of the novel Pt(II) and Pt(IV) complexes with derivatives of ciprofloxacin which is considered as an antibiotic that belongs to a class of drugs called fluoroquinolones. The novel design of these Pt-Cipro conjugates was based on the premise that attaching Cipro to cisplatin derivatives should result in simultaneous release inside the cell of two antiproliferative agents that act by different mechanisms on different cellular targets. Thus, the platinum conjugates could also serve to bring into the tumor cells, along with the free antitumor Pt(II) compound, also free Cipro in the amount that could make it possible to execute their biological function.

Chapter four presents the synthesis, characterization, and structural studies of different series of copper and uranium complexes of salicylaldehyde Schiff base derivatives with various organic diamine compounds. The Schiff bases act as neutral and bidentate ligands, which can attach to the metal through the azomethine nitrogen and furfural oxygens. These Schiff bases are prepared by reacting salicylaldehyde with organic diamines. In the case of most complexation reactions, highly colored precipitates were formed immediately. The complexes were found to have composition Cu (II)L and Cu (II)LUO2(NO2)2, where L is the organic ligand. This implies “mono” structures one metal + one H2L ligands, and “heterobimetallic” where the ligands hold two different metal atoms in close proximity.

Chapter five deals with another series of CuL complexes, UO2L complexes and CuL-UO2 heterobimetallic complexes of an hexadentate bicompartmental Schiff base ligand that their central coordination sites is composed of an imine-based N2O2 entity coordinating Cu (II) ions. The subsequent rearrangement of the ligand into a Ω-shape generates a second recognition site, O2O2, composed of four phenoxy groups, able to coordinate U(IV) ions. Our copper-based metalloligands (CuL), which act as interesting chelate ligands for the uptake of large cations, led us to explore their structural differences upon coordination to group 2 metal ions.

All ligands and the metal complexes were characterized by a combination of NMR spectroscopy, and mass spectrometry. Despite all our efforts, no crystals suitable for an X-ray crystallographic study, were obtained. The results of the spectroscopic studies revealed that the Schiff base ligands coordinated to metal ions through nitrogen atom in the platinum complexes as well as through the (>C=N) nitrogen and phenolic oxygen atoms in H2L ligands and through N2O2 and O2O2 in H4L ligands in copper and uranium complexes.

Finally, chapter six presents the future work and further investigation to support the results by studying the biological effects and using green chemistry to synthesize novel organic ligands which would be a unique method to stop using the organic solvents.

Access Setting

Dissertation-Open Access

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