Browsing by Author "Filippou, Vasileios"

Filter results by typing the first few letters
Now showing 1 - 6 of 6
  • Thumbnail Image
    ItemOpen Access
    Das Elektronentransferverhalten von Campherchinonimin-Liganden koordiniert an Ruthenium, Rhenium und Kupfer
    (2017) Filippou, Vasileios; Kaim, Wolfgang (Prof. Dr.)
    Ausgangspunkt für meine Dissertation war das bisher nicht untersuchte Koordinations- und Redoxverhalten von Campherchinoniminen. Diese Ligandenklasse hat zwei potenzielle Donorzentren, die zu einer zweizähnigen Metallkoordination befähigt sind. Weiterhin sollte das O=C-C=N-Fragment schrittweise zwei Ein-Elektronen-Reduktionen eingehen können, wofür in der Literatur allerdings keine Beispiele zu finden sind. Im Fokus der Untersuchungen stand daher das Elektronentransferverhalten dieser Ligandenklasse. Das methodische Vorgehen zur Untersuchung dieser Fragestellung kann in drei Teilbereiche eingeteilt werden: (i) Die organische und anorganische Synthese und Isolierung neuer Koordinationsverbindungen von Campherchinonimin-Derivaten mit den Metallen Kupfer, Rhenium und Ruthenium, (ii) die Charakterisieung dieser Verbindungen, darunter CHN-Elementaranalyse, Massenspektrometrie, Kristallstrukturanalyse, Cyclovoltammetrie, 1H-NMR-, EPR-, IR-, UV-Vis-NIR-Spektroskopie sowie Spektroelektrochemie und (iii) die Analyse dieser Messdaten, wobei hier quantenchemische Methoden (DFT) und Vergleiche mit bereits literaturbekannten ähnlichen Systemen zum Einsatz kommen. Die Ergebnisse liefern Einblicke in die Bindungssituation und das Elektronentransferverhalten dieser Ligandenklasse. Es werden elektronische Zustände für die nicht-triviale Wechselwirkung von redoxaktiven Liganden und Metallen auf Grundlage der experimentellen und DFT-unterstützten Ergebnisse diskutiert.
  • Thumbnail Image
    ItemOpen Access
    Homodinuclear complexes of [Cu(dppf)]+ or [Ru(bpy)2]2+ with 1,4‐Bis(camphorquinoneimino)benzene (bcqb) as a redox‐active bridging ligand
    (2021) Filippou, Vasileios; Bubrin, Martina; Fiedler, Jan; Kaim, Wolfgang
    The product μ‐bcqb from the reaction between p‐phenylenediamine and two equivalents of camphorquinone has been used as a potentially conjugated molecular bridge between two complex fragments [Cu(dppf)]+, dppf=1,1‘‐bis(diphenylphosphino)ferrocene, to yield 12+, and between two [Ru(bpy)2]2+ moieties, resulting in 24+. The molecular structure of 1(BF4)2 shows an intramolecular Cu-Cu distance of 8.04 Å and a torsionally twisted conformation of the bridge, while cyclic voltammetry, EPR, IR and UV‐vis‐NIR spectroelectrochemistry reveal two closely spaced one‐electron reductions and a ferrocene‐based two‐electron oxidation. Compound 2(PF6)4 exhibits at least three one‐electron reduction waves and one 2e‐oxidation, the former attributed to μ‐bcqb and the latter assigned to metal‐based processes showing no evidence for a Ru-Ru mixed‐valent intermediate. However, intra‐ligand based mixed valency with intense LLIVCT absorptions in the near infrared was observed for the metal coordinated μ‐bcqb.- and μ‐bcqb.3- bridges. The two examples 1n+ and 2n+ illustrate that a combination of physical methods is advantageous to analyze and define the correct electronic structures in complexes involving several metal centers and noninnocent ligand components.
  • Thumbnail Image
    ItemOpen Access
    Intramolecular charge transfer in ruthenium complexes [Ru(acac)2(ciq)] with ambidentate camphoriminoquinone (ciq) ligands
    (2021) Filippou, Vasileios; Blickle, Svenja; Bubrin, Martina; Kaim, Wolfgang
    Reaction of [Ru(acac)2(MeCN)2], acac−=acetylacetonate, with N‐phenylcamphoriminoquinone (pciq) or the new N‐(2‐thiomethylphenyl)‐camphoriminoquinone (tciq) produces complexes [Ru(acac)2(pciq)] and [Ru(acac)2(tciq)] with N,O or N,S coordination and E or Z configuration at the C=N bond, respectively. Oxidation state assignments in comparison with classical iminoquinone ligands are based on structural data in connection with DFT calculations. Reversible oxidation yields complex ions [RuIII(acac)2(pciq)]+ and [RuIII(acac)2(tciq)]+ as characterized by EPR, IR and UV‐vis‐NIR spectroelectrochemistry.
  • Thumbnail Image
    ItemOpen Access
    PESIN conjugates for multimodal imaging : can multimerization compensate charge influences on cell binding properties? : a case study
    (2021) Hübner, Ralph; Paretzki, Alexa; von Kiedrowski, Valeska; Maspero, Marco; Cheng, Xia; Davarci, Güllü; Braun, Diana; Damerow, Helen; Judmann, Benedikt; Filippou, Vasileios; Dallanoce, Clelia; Schirrmacher, Ralf; Wängler, Björn; Wängler, Carmen
    Recently, anionic charges were found to negatively influence the in vitro gastrin-releasing peptide receptor (GRPR) binding parameters of dually radioisotope and fluorescent dye labeled GRPR-specific peptide dimers. From this, the question arose if this adverse impact on in vitro GRP receptor affinities could be mitigated by a higher valency of peptide multimerization. For this purpose, we designed two different hybrid multimodal imaging units (MIUs), comprising either one or two click chemistry-compatible functional groups and reacted them with PESIN (PEG3-BBN7-14, PEG = polyethylene glycol) dimers to obtain a dually labeled peptide homodimer or homotetramer. Using this approach, other dually labeled peptide monomers, dimers, and tetramers can also be obtained, and the chelator and fluorescent dye can be adapted to specific requirements. The MIUs, as well as their peptidic conjugates, were evaluated in terms of their photophysical properties, radiolabeling efficiency with 68Ga and 64Cu, hydrophilicity, and achievable GRP receptor affinities. Here, the hydrophilicity and the GRP receptor binding affinities were found to be especially strongly influenced by the number of negative charges and peptide copies, showing logD (1-octanol-water-distribution coefficient) and IC50 (half maximal inhibitory concentration) values of -2.2 ± 0.1 and 59.1 ± 1.5 nM for the homodimer, and -1.9 ± 0.1 and 99.8 ± 3.2 nM for the homotetramer, respectively. From the obtained data, it can be concluded that the adverse influence of negatively charged building blocks on the in vitro GRP receptor binding properties of dually labeled PESIN multimers can, at least partly, be compensated for by the number of introduced peptide binding motives and the used molecular design.
  • Thumbnail Image
    ItemOpen Access
    Structural and oxidation state alternatives in platinum and palladium complexes of a redox‐active amidinato ligand
    (2021) Ehret, Fabian; Filippou, Vasileios; Blickle, Svenja; Bubrin, Martina; Záliš, Stanislav; Kaim, Wolfgang
    Reaction of [Pt(DMSO)2Cl2] or [Pd(MeCN)2Cl2] with the electron‐rich LH=N,N’‐bis(4‐dimethylaminophenyl)ethanimidamide yielded mononuclear [PtL2] (1) but dinuclear [Pd2L4] (2), a paddle‐wheel complex. The neutral compounds were characterized through experiments (crystal structures, electrochemistry, UV‐vis‐NIR spectroscopy, magnetic resonance) and TD‐DFT calculations as metal(II) species with noninnocent ligands L-. The reversibly accessible cations [PtL2]+ and [Pd2L4]+ were also studied, the latter as [Pd2L4][B{3,5‐(CF3)2C6H3}4] single crystals. Experimental and computational investigations were directed at the elucidation of the electronic structures, establishing the correct oxidation states within the alternatives [PtII(L-)2] or [Pt.(L )2], [PtII(L0.5-)2]+ or [PtIII(L-)2]+, [(PdII)2(μ‐L−)4] or [(Pd1.5)2(μ‐L0.75-)4], and [(Pd2.5)2(μ‐L-)4]+ or [(PdII)2(μ‐L0.75-)4]+. In each case, the first alternative was shown to be most appropriate. Remarkable results include the preference of platinum for mononuclear planar [PtL2] with an N‐Pt‐N bite angle of 62.8(2)° in contrast to [Pd2L4], and the dimetal (Pd24+→Pd25+) instead of ligand (L-→L ) oxidation of the dinuclear palladium compound.
  • Thumbnail Image
    ItemOpen Access
    Tetrazine chelate ligands bridging two [Ru(acac)2] fragments : mixed valency and radical complex formation
    (2022) Kaim, Wolfgang; Löw, Isabell; Ringenberg, Mark R.; Schwederski, Brigitte; Filippou, Vasileios; Fiedler, Jan
    Using bis(3‐methyl‐2‐pyridyl)‐1,2,4,5‐tetrazine 1, 3‐(2‐pyrimidyl)‐6‐methyl‐1,2,4,5‐tetrazine 2 and bis(2‐pyrimidyl)‐1,2,4,5‐tetrazine=bmtz as ligands, the complexes 3=[Ru(acac)2(1)], 4={[Ru(acac)2]2(1)], 5={[Ru(acac)2]2(bmtz)], and 6={[Ru(acac)2]2(2)] were prepared and identified by structure analysis of crystallized material. The one‐electron oxidized form 6(PF6) was also studied structurally, suggesting a Class II mixed‐valent situation. The neutral dinuclear systems exhibit two reversible oxidation processes with comproportionation constants 109.2