Influence of Ring Contraction on the Electronic Structure of Nickel Tetrapyrrole Complexes: Corrole vs Porphyrin

The influence of the contracted corrole macrocycle, in comparison to the larger porphyrin macrocycle, on the electronic structure of nickel was studied with X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Synthesis and in situ characterization of the Ni complexes of octaethylporphyrin (NiOEP) and hexaethyldimethylcorrole (NiHEDMC) were performed in ultra-high vacuum. XPS and NEXAFS spectra reveal a +2 oxidation state and a low-spin d8 electron configuration of Ni in both complexes, despite the formal trianionic nature of the corrole ligand. UPS, in combination with density functional theory (DFT) calculations, support the electronic structure of a Ni(II) corrole with a π-radical character of the ligand. The NEXAFS spectra also reveal differences in the valence electronic structure, which are attributed to the size mismatch between the small Ni(II) center and the larger central cavity of NiOEP. Analysis of the gas-phase structures shows that the Ni−N bonds in NiOEP are 4%–6% longer than those in NiHEDMC, even when NiOEP adopts a ruffled conformation. The individual interactions that constitute the Ni−ligand bond are altogether stronger in the corrole complex, according to bonding analysis within the energy decomposition analysis and the natural orbitals for chemical valence theory (EDA-NOCV)

Lösungsstrategien zur Verminderung von Einträgen von urbanem Plastik in limnische Systeme - PLASTRAT - Synthesebericht

Der Einsatz von Plastik gehört zu den großen Errungenschaften unserer Zeit. Die Nutzung von Plastik in unseren verschiedenen Lebensbereichen ermöglicht uns heute Vieles. Dabei setzen wir Plastik oft ein, ohne dass uns dies bewusst ist. Wieviel „virtuelles Plastik“ war allein notwendig, um diesen Synthesebericht zu erstellen? Wieviel Plastik benötigen Sie gerade, um diesen Synthesebericht zu lesen? Wie so oft, so hat auch der Einsatz von Plastik zwei Seiten: den positiven Errungenschaften stehen negative Auswirkungen gegenüber, vor allem nach der Nutzung von Plastik. Im Fokus stehen hierbei Fragestellungen der Toxikologie sowie der Abfallverwertung. Im Gegensatz zu vielen anderen Stoffen, mit denen wir täglich in Berührung sind, hat Plastik die Eigenschaft, dass sich kleinste Partikel bilden. So ist es nicht verwunderlich, dass sich mittlerweile in allen Umweltmedien Mikroplastikpartikel finden lassen. Die Idee von PLASTRAT war es, in einem interdisziplinären Team Ansätze für die Verminderung von Einträgen von Plastik in Gewässer zu untersuchen. Dabei standen über den Ansatz der systemischen Risikoanalyse die unterschiedlichen Sektoren im Fokus, angefangen von der Erzeugung, über die Nutzung bis hin zu den Eintragspfaden und die toxikologische Bewertung. Der Synthesebericht fasst die Ergebnisse von PLASTRAT zusammen. Vor allem zeigt der Synthesebericht die großen Herausforderungen sowie Lösungsansätze zum Thema Mikroplastik auf. Dabei wird auch deutlich, dass wir bei vielen Fragestellungen zum Umgang mit Plastik erst am Anfang stehen. Die ersten Ideen zu PLASTRAT entstanden 2016. In den vergangenen fünf Jahren stand das Thema Plastik im Fokus von Öffentlichkeit und Presse. In dieser Zeit gab es bereits wichtige Veränderungen beim Einsatz von Plastik bei diversen Produkten, beispielsweise durch die Substitution durch alternative Materialien. Dies zeigt deutlich, dass eine Bewusstseinsveränderung stattgefunden hat, die sich sicherlich in der Zukunft fortsetzten wird. Die Arbeiten und Diskussionen im Projektteam von PLASTRAT waren spannend. In vielen Projektbesprechungen wurde an den Forschungsfragestellungen gearbeitet und nach Lösungen gesucht. Es gab einen intensiven persönlichen Austausch mit allen am Projekt beteiligten Personen, so dass uns die seit 2020 geltenden Einschränkungen durch die Corona-Pandemie nicht immer leichtgefallen sind. Wir möchten uns bei allen bedanken, die bei PLASTRAT mitgewirkt haben. Allen Lesern des Syntheseberichts wünschen wir viele Freude beim Lesen und hoffen, dass wir Ihnen einen Impuls für den zukünftigen Umgang mit (Mikro-)Plastik geben können

Factors Influencing the Survival Rate of Teeth and Implants in Patients after Tumor Therapy to the Head and Neck Region—Part 2: Implant Survival

During prosthetic rehabilitation after tumor therapy (TT) in the head and neck region, the dentist must assess whether the prognosis of the remaining teeth is sufficiently good or whether implants should be used to anchor dentures. Thus, the aim of the present study was to compare the survival rate of teeth and implants after TT and to evaluate factors potentially influencing implant survival. One hundred fifteen patients (male: 70.3%; mean age: 63.2 ± 12.4 years) having received dental treatment before and after TT at the Martin Luther University Halle-Wittenberg were enrolled in the study. Clinical examination including assessment of dental status and stimulated salivary flow rate was performed. Information about disease progression and therapy was retrieved from medical records. After TT, from a total of 1262 teeth, 27.2% had to be extracted. Of 308 implants inserted after TT, 7.0% were lost. Teeth exhibited lower 5-year survival probability (76.8%) than implants (89.9%; p = 0.001). The risk of loss (RL) of implants increased with age, nicotine use, intraoral defects, and RCT. Radiotherapy did not independently increase the RL. Thus, implants seem to be a reliable treatment option in case of progressive tooth decay after TT, particularly after RT

UV aged epoxy coatings ̶ Ecotoxicological effects and released compounds

Organic coatings can guarantee long-term protection of steel structures due to causing a physical barrier against water and oxygen. Because of their mechanical properties and resistances to heat and chemicals, epoxy resin-based coatings are widely used for corrosion protection. Despite of the aromatic backbone and the resulting susceptibility to UV degradation, epoxy resins are frequently used as binding agent in top layers of anti-corrosion coating systems. Consequently, these organic polymers are directly exposed to sunlight and thus UV radiation. The present study was designed to investigate if toxic effects of epoxy resin-based-coatings are changed by UV-A irradiation. For this purpose, two epoxide-based top coatings were examined with and without UV aging for their bacterial toxicity and estrogenicity. In addition, chemical analyses were performed to identify released compounds as well as photolytic degradation products and to assign toxic effects to individual substances. UV-A irradiation of epoxy resin based top coatings resulted in an overall decrease of acute and specific ecotoxicological effects but as well to the formation of toxic transformation products. Both, in leachates of untreated and UV-A irradiated coatings, 4tBP was identified as the main driver of estrogenicity and toxicity to luminescent bacteria. BPA and structural analogs contributing to estrogenic effects in leachates were formed by UV-A irradiation. The combination of HPTLC coupled bioassays and LC-MS analyses supported the identification of bioactive compounds in terms of an effect-directed analysis. The present findings indicate that epoxide-based coatings are less suitable for the application as top coatings and more UV stable coatings like aliphatic polyurethanes should be preferred

Synthesis and Reactivity of Sterically Encumbered Diazaferrocenes

Bulky pyrrolyl ligands have been used for the synthesis of diazaferrocenes, which have been characterized by various spectroscopic techniques, including X-ray diffraction for <i>rac</i>-[{η⁵-2,3,5-(Me₃C)₃C₄HN}₂Fe]. Chemical oxidation of diazaferrocenes to the corresponding diazaferrocenium cations has been accomplished with AgSbF₆. In addition, EPR and Mössbauer spectroscopic, electrochemical, and density function theory (DFT) studies have provided a more detailed understanding of the electronic structures of these complexes

Synthesis and Characterization of N<i>-</i>Donor-Functionalized Enantiomerically Pure Pentadienyl Ligands Derived from (1<i>R</i>)‑(−)-Myrtenal

A series of enantiomerically pure −SiMe₂NR₂ (R = Me, Et) substituted pentadienyl ligands were prepared starting from the natural product (1<i>R</i>)-(−)-myrtenal. Deprotonation with a Schlosser superbase yields the corresponding potassium salts, which were characterized by various spectroscopic techniques. In solution these neutral N-donor-substituted pentadienyl systems predominantly adopt a <i>U</i> conformation, but in two cases the rare <i>S</i> conformation was also observed as a minor component in solution. Addition of 18-crown-6 allowed the molecular structures of two of these potassium pentadienyls to be determined by X-ray diffraction. Interestingly, η⁵ and κ<i>N</i> coordination of the pentadienyl system to the [K­(18-crown-6)]⁺ cation was observed. Furthermore, these ligand systems also coordinate to transition metals and form an open titanocene, open vanadocenes, open chromocenes, and half-open trozircenes with [TiCl₃(thf)₃], [VCl₃(thf)₃], CrCl₂, and [(η⁷-C₇H₇)­ZrCl­(tmeda)], respectively. These complexes were characterized by elemental analyses and various spectroscopic techniques. However, no coordination of the pendant −SiMe₂NR₂ group to the metal centers was observed. In addition, significant steric crowding in these open metallocenes prevents the formation of isolable CO or PMe₃ adducts. This was further corroborated by EPR studies on an open vandadocene, which showed that no adduct formation occurs at ambient temperature in solution, but a weak PMe₃ adduct was detected at 26 K

Chemical and toxicological assessment of leachates from UV-degraded plastic materials using in-vitro bioassays

The broad use of plastics and the persistence of the material results in plastic residues being found practically everywhere in the environment. If plastics remain in the (aquatic) environment, natural weathering leads to degradation processes and compounds may leach from plastic into the environment. To investigate the impact of degradation process on toxicity of leachates, different types of UV irradiation (UV-C, UV-A/B) were used to simulate weathering processes of different plastic material containing virgin as well as recyclate material and biodegradable polymers. The leached substances were investigated toxicologically using in-vitro bioassays. Cytotoxicity was determined by the MTT-assay, genotoxicity by using the p53-CALUX and Umu-assay, and estrogenic effects by the ERα-CALUX. Genotoxic as well as estrogenic effects were detected in different samples depending on the material and the irradiation type. In four leachates of 12 plastic species estrogenic effects were detected above the recommended safety level of 0.4 ng 17β-estradiol equivalents/L for surface water samples. In the p53-CALUX and in the Umu-assay leachates from three and two, respectively, of 12 plastic species were found to be genotoxic. The results of the chemical analysis show that plastic material releases a variety of known and unknown substances especially under UV radiation, leading to a complex mixture with potentially harmful effects. In order to investigate these aspects further and to be able to give recommendations for the use of additives in plastics, further effect-related investigations are advisable

Synthesis and Electronic Ground-State Properties of Pyrrolyl-Based Iron Pincer Complexes: Revisited

The pyrrolyl-based iron pincer compounds [(^<i>t</i>BuPNP)­FeCl] (<b>1</b>), [(^<i>t</i>BuPNP)­FeN₂] (<b>2</b>), and [(^<i>t</i>BuPNP)­Fe­(CO)₂] (<b>3</b>) were prepared and structurally characterized. In addition, their electronic ground states were probed by various techniques including solid-state magnetic susceptibility and zero-field ⁵⁷Fe Mössbauer and X-band electron paramagnetic resonance spectroscopy. While the iron­(II) starting material <b>1</b> adopts an intermediate-spin (<i>S</i> = 1) state, the iron­(I) reduction products <b>2</b> and <b>3</b> exhibit a low-spin (<i>S</i> = ¹/₂) ground state. Consistent with an intermediate-spin configuration for <b>1</b>, the zero-field ⁵⁷Fe Mössbauer spectrum shows a characteristically large quadrupole splitting (Δ<i>E</i>_Q ≈ 3.7 mm s^–1), and the solid-state magnetic susceptibility data show pronounced zero-field splitting (|<i>D</i>| ≈ 37 cm^–1). The effective magnetic moments observed for the iron­(I) species <b>2</b> and <b>3</b> are larger than expected from the spin-only value and indicate an incompletely quenched orbital angular momentum and the presence of spin–orbit coupling in the ground state. The experimental findings are complemented by density functional theory computations, which are in good agreement with the experimental data. Most notably, these calculations reveal a low-lying (<i>S</i> = 2) excited state for complex <b>1</b>; furthermore, the computed Mössbauer parameters for all complexes studied herein are in excellent agreement with the experimental findings

Synthesis and Electronic Ground-State Properties of Pyrrolyl-Based Iron Pincer Complexes: Revisited

The pyrrolyl-based iron pincer compounds [(^<i>t</i>BuPNP)­FeCl] (<b>1</b>), [(^<i>t</i>BuPNP)­FeN₂] (<b>2</b>), and [(^<i>t</i>BuPNP)­Fe­(CO)₂] (<b>3</b>) were prepared and structurally characterized. In addition, their electronic ground states were probed by various techniques including solid-state magnetic susceptibility and zero-field ⁵⁷Fe Mössbauer and X-band electron paramagnetic resonance spectroscopy. While the iron­(II) starting material <b>1</b> adopts an intermediate-spin (<i>S</i> = 1) state, the iron­(I) reduction products <b>2</b> and <b>3</b> exhibit a low-spin (<i>S</i> = ¹/₂) ground state. Consistent with an intermediate-spin configuration for <b>1</b>, the zero-field ⁵⁷Fe Mössbauer spectrum shows a characteristically large quadrupole splitting (Δ<i>E</i>_Q ≈ 3.7 mm s^–1), and the solid-state magnetic susceptibility data show pronounced zero-field splitting (|<i>D</i>| ≈ 37 cm^–1). The effective magnetic moments observed for the iron­(I) species <b>2</b> and <b>3</b> are larger than expected from the spin-only value and indicate an incompletely quenched orbital angular momentum and the presence of spin–orbit coupling in the ground state. The experimental findings are complemented by density functional theory computations, which are in good agreement with the experimental data. Most notably, these calculations reveal a low-lying (<i>S</i> = 2) excited state for complex <b>1</b>; furthermore, the computed Mössbauer parameters for all complexes studied herein are in excellent agreement with the experimental findings