Square Planar Metal Complexes with Cyclopeptide and Porphyrin-Based Ligands

  • Metal-directed self-assembly with metals such as Pd(II) and Pt(II), that prefer a square planar coordination geometry, has been showing remarkable potential to construct supramolecular architectures such as helices, tubes, locks and cages. Some of these complexes have also been shown to assemble by means of metal-metal interactions and, more remarkably, the luminescent properties of certain complexes can also be used for sensing. For instance, Pt(II) and Pd(II) complexes display strong phosphorescence which is strongly reduced in the presence of oxygen. The work developed for this thesis is divided into three main chapters dealing with the different properties of Pd(II) and Pt(II) metal complexes. Chapter I was mainly developed at Technische Universität Kaiserslautern with a short partnership with the Kekulé-Institut für Organische Chemie und Biochemie at the Universität Bonn and addressed the construction of coordination macrocycles and cages from suitable Pd(II) sources and cyclopeptide-derived ligands. Cyclopeptide derived hollow coordination compounds were obtained through Pd(II)-directed self-assembly. Specifically, the treatment of the pyridine containing cyclopeptides CP1 and CP2 with [Pd(en)(NO3)2] afforded the metallamacrocycle CP12Pd2 and the cage CP22Pd3. These products were characterized by means of NMR spectroscopy and mass spectrometry. The reaction between CP1 and [Pd(CH3CN)4](BF4)2] afforded, according to ESI-MS and NMR measurements, a complex with the composition CP16Pd3 and the smaller cage CP14Pd2. Binding studies indicated that CP12Pd2 incorporated different dicarboxylates, sodium 1,3- benzenedisulfonate (BDS), and sodium 2,6-naphthalenedisulfonate (NDS) into its cavity. In the case of BDS a 1:1 complex was formed that had a log Ka of 4.8 ± 0.2 in D2O/CD3OD, 1:1 (v/v). In the case of NDS, binding was slow on the NMR time-scale and involved the binding of two guest molecules as confirmed by a crystal structure of the complex. Based on these first examples of Pd(II)-containing cyclopeptide-derived coordination compounds, future work should focus on the design of molecular architectures that can, for example, be used as receptors for biorelevant guests. In Chapter II, the aggregation abilities and photophysical properties of Pt(II) complexes bearing tridentate-azolate-based ligands and cyclopeptides with peripheral pyridyl moieties were investigated. This project was the result of a short-term secondment developed at the Institut de Science et d'Ingénierie Supramoléculaires in Strasbourg. Efforts were made at creating luminescent cyclopeptide-derived Pt(II) complexes by coordinating CP1 or CP2 to suitable Pt(II)-containing precursors. The coordination of both peptides to a known Pt(II) complex afforded insoluble products that could not be characterized further. To circumvent these solubility issues, the synthesis of the analogous cyclopeptide complexes containing more polar ligands was attempted. Although mass spectrometry provided evidence for the formation of the target complexes PtDeg-CP1 and PtDeg-CP2 in the crude reaction mixtures, the products could not be isolated in pure form. The impure samples of PtDeg-CP1 and PtDegCP2 both exhibited orange emission. Further work is necessary to improve the preparation of such complexes. Only then can the characterization of their photophysical properties and self-assembling behavior be addressed. Chapter III was the result of a project executed at Micronit Micro Technologies B.V. in Enschede, in which a microfluidic device with oxygen sensing abilities was produced from nanoparticles containing Pt(II)-porphyrins. To this end, microfluidic devices containing the Pt(II) complex PtTPTBPF incorporated in different polymeric matrices were prepared and their oxygen sensing abilities characterized. It was shown that chips containing the Pt(II) complex incorporated into OXNANO nanoparticles were highly sensitive to oxygen, easy to fabricate, and allowed reliable oxygen quantification. Chips made by using other polymeric matrices such as PDMS, Elastosil®E43 or polystyrene were less suitable for the measurements. The OXNANO-containing chips furthermore allowed measuring the oxygen consumption of HUVEC cells in a biological assay even in repeated measurements. Future studies should now involve using these chips for monitoring in real time small scale biological processes.

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Author:Lígia Margarida Marques Mesquita
Advisor:Stefan Kubik
Document Type:Doctoral Thesis
Language of publication:English
Publication Date:2021/12/13
Year of Publication:2021
Publishing Institute:Technische Universität Kaiserslautern
Granting Institute:Technische Universität Kaiserslautern
Acceptance Date of the Thesis:2021/12/03
Date of the Publication (Server):2021/12/14
Number of page:IX, 263
Faculties / Organisational entities:Fachbereich Chemie
DDC-Cassification:5 Naturwissenschaften und Mathematik / 540 Chemie
Licence (German):Creative Commons 4.0 - Namensnennung, nicht kommerziell, keine Bearbeitung (CC BY-NC-ND 4.0)