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Projekt Druckansicht

Quantenchemische Untersuchungen von Lanthanoid(III) und Actinoid(III) Texaphyrin-Komplexen sowie von deren medizinischen und technischen Anwendungen

Antragstellerin Dr. Xiaoyan Cao
Fachliche Zuordnung Theoretische Chemie: Elektronenstruktur, Dynamik, Simulation
Pharmazie
Theoretische Chemie: Moleküle, Materialien, Oberflächen
Förderung Förderung von 2014 bis 2020
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 259799661
 
Erstellungsjahr 2019

Zusammenfassung der Projektergebnisse

The objectives of the project, i.e., theoretical studies on the reaction mechanism of the oxidation of ascorbate (anion of L-ascorbic acid AscH2, vitamin C) catalyzed by lanthanide(III) texaphyrin complexes, were reached. AscH2 is found to be the energetically lowest species in aqueous solution, whereas the monoanion ascorbate AscH− is the most abundant one near pH=7. Asc2- was found to be the preferred reducing agent for autoxidation and oxidation. For lanthanide(III) texaphyrin complexes it was found that the first water coordination sphere contains six strongly bounded water molecules, resulting in [Ln-Motex(H2O)6]2+ (Ln=La, Gd, Lu) complexes with side chains folded by hydrogen bonds with the solvent molecules. La3+ was found to be bound directly to three water molecules, whereas only two water molecules were coordinated to Gd3+ and Lu3+. The obtained reduction potentials relative to Ag/AgCl in DMSO solution at the B3LYP level, i.e., -0.40, -0.29 and - 0.34 V for [Ln-Motex(H2O)6]2+ with Ln = La, Gd and Lu, respectively, are in reasonable agreement with the experimental (Ag/AgCl reference, 0.1 M TBAP) values of -0.294 V and -0.237 V for [Gd-Motex]2+ and [Lu-Motex]2+, respectively. Moreover the pure GGA functional BP86 was found to perform quite well and significantly better than the B3LYP hybrid functional in the calculations of the UV-vis spectrum compared to experimental data. In agreement with the experimental findings there are four absorption peaks (λmax) at the BP86 level shown in the calculated UV-vis spectrum of [Ln- Motex(H2O)6]2+ (Ln=La, Gd, Lu) in the wavelength region λ>300 nm. For the medically important Q-like band the calculated λmax agree quite well with the experimental data, i.e., the disagreement is only up to 5 nm. From lanthanum to lutetium the absorption peak in the Q-like band was shifted from red to blue (∆=11nm), which is only 4 nm lower than the experimental findings (∆=15 nm). For NADPH by modelling the solvent effects with an explicit treatment of 100 water molecules in combination with the COSMO model for bulk hydration effects a more extended geometry was found comparing to the free NADPH in the gas phase. Under aerobic conditions the oxidation of NADPH with Gd-Tex2+ , i.e., NADPH + ½ 3O2 + Gd-Tex2+ → NADP+ + Gd-Tex+ + ½ H2O2, can proceed spontaneously since the obtained negative ∆G (the changes of the Gibbs free energy in the reaction) values imply that the oxidation of NADPH by Gd-Tex2+ is exothermic. It has been shown that in aqueous solution the Motex-UO22+ over Ln3+. Since the safety of Ln-Motex2+ in vivo has been proven, Motex- might be used as chelating agent for UO22+ poisoning.

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