Porphyrin-Supermoleküle, aufgebaut aus Porphyrin-Einheiten, die durch Spacer kovalent [1] oder koordinativ [2] miteinander verknüpft sind, entwickelten sich unter vorwiegend anwendungsorientierten Gesichtspunkten (Bausteine für elektronische und optische Funktionseinheiten, Sensoren, Photosynthese-Modelle usw.) zu einem aktuellen Forschungsthema in der Porphyrinchemie. In auffallendem Gegensatz zu solchen mittlerweile in großer struktureller Vielfalt synthetisierten Supermolekülen traten die nicht minder interessanten Di-und Oligoporphyrine mit direkter Kupplung (meso-meso, b-b, meso-b) erst in jüngster Zeit ins Blickfeld (Schema 1).Unter den bislang bekannten Diporphyrinen nimmt dasformal dem Biphenyl entsprechende -meso-meso-Diporphyrin 1 (n = 1) [3] eine Schlüsselstellung ein, denn es ist nicht nur Baustein der faszinierenden Stabmoleküle 1 (n > 1) von Osuka et al., [4] sondern ermöglicht oxidativ auch einen Zugang zu den mehrfach verknüpften Diporphyrinen 2 und 3.[5] meso-b-Diporphyrine, komplementär zu 1 aus Metalloporphyrinen durch elektrochemische Oxidation erhältlich, [6] eröffnen einen Zugang zu doppelt meso-b-verknüpften Diporphyrinen. [7,8] Einfach b-b-verknüpfte Diporphyrine kennt man zwar seit längerem, [9] doch wurden erst jetzt brauchbare Synthesen beschrieben.[10] Zu den vorgenannten Diporphyrinen gesellte sich schließlich das Diporphyrin 4, [11] in dem zwei Porphyrinmoleküle durch eine gemeinsame b-bPyrrolbindung verknüpft sind.Ein unseres Wissens bislang nicht realisierter Typ von Diporphyrinen sind die meso-Spirodiporphyrine, repräsen-tiert durch Spirodiporphyrin 5 und Spirodicorrol 6 (Schema 2; die Porphyrin-und Corrol-Einheiten in 5 bzw. 6 liegen jeweils als Isoformen vor). Als besonders interessanter Aspekt von 5 und 6 ist mit einer homokonjugativen Wechselwirkung zwischen den durch das tetragonale Spirozentrum separierten p-Systemen der beiden Molekülhälften zu rechnen, die als Spirokonjugation [12] bezeichnet wird. Wenngleich die Synthese von Spirodiporphyrinen als freie Liganden noch aussteht, können wir hier über den zweikernigen Nickelkomplex 13 des Spirodicorrols (als Hexadecaethylderivat), einen gegen Demetallierung außerordentlich stabilen Komplex, sowie über den zweikernigen Palladiumkomplex 17 eines ungewöhnlichen Spirodiporphyrins berichten.Es sei vorab eingeräumt, dass der Nickelkomplex 13 nicht Ergebnis einer gezielten Synthese ist, sondern im Verfolg der Chemie des "Figure-Eight"-Cyclooctapyrrols 7[13] als Produkt einer bislang nicht näher aufgeklärten Reaktionskaskade erhalten wurde. Das Cyclooctapyrrol 7 (Octaphyrin-(1.1.1.0.1.1.1.0)), das ein ganzes Spektrum von Metallkomplexen bildet, [14a]
Dedicated to Professor Ronald BreslowPorphyrin supermolecules constructed from multiple porphyrin moieties that are linked covalently [1] or coordinatively [2] by spacers have developed as an important line of research in porphyrin chemistry (with potential applications as electronic or optical functional units, sensors, and artificial photosynthetic devices). In contrast to these porphyrin supermolecules, the no less intriguing di-and oligoporphyrins devoid of spacers, that is, meso-meso-, b-b-or meso-b-linked porphyrins, have only recently attracted attention (Scheme 1).Among the diporphyrins of this type, the meso-mesodiporphyrin 1 (n = 1) [3]
In this DFT study, the mechanism of the copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) reaction is revisited in light of recent experimental findings that made significant contributions to unraveling this challenging and important reaction. The generally accepted binuclear mechanism was used as a framework to investigate two inquiries raised by new experiments. First, Fokin et al. have proposed ligand exchanges that can take place as possible alternative pathways to the generic path and in that way they have proved the binuclear nature of the CuAAC mechanism. In this study, the experimentally proposed ligand exchanges which deviate from the generic path were modeled with NHC as the ligand and the electronic nature of the mechanism was also investigated with the NBO analyses. The results in this study are compatible with the experimental proposals, since the ligand exchange and the generic pathways’ calculated energies are on the same order. Second, possible pathways for the formation of a recently isolated bis-copper triazolide intermediate were considered by DFT calculations to explain this mechanism thoroughly. It was shown that its formation is energetically highly unfavorable during the cycloaddition step, whereas it can be facile after the formation of the mononuclear triazolide. The calculations were performed at the M06-L/6-31+G(d,p) level with the LANL2TZ+ effective core potential for copper atoms.
The essential biological function of phosphodiesterase (PDE) type enzymes is to regulate the cytoplasmic levels of intracellular second messengers, 3′,5′-cyclic guanosine monophosphate (cGMP) and/or 3′,5′-cyclic adenosine monophosphate (cAMP). PDE targets have 11 isoenzymes. Of these enzymes, PDE5 has attracted a special attention over the years after its recognition as being the target enzyme in treating erectile dysfunction. Due to the amino acid sequence and the secondary structural similarity of PDE6 and PDE11 with the catalytic domain of PDE5, first-generation PDE5 inhibitors (i.e. sildenafil and vardenafil) are also competitive inhibitors of PDE6 and PDE11. Since the major challenge of designing novel PDE5 inhibitors is to decrease their cross-reactivity with PDE6 and PDE11, in this study, we attempt to identify potent tadalafil-like PDE5 inhibitors that have PDE5/PDE6 and PDE5/PDE11 selectivity. For this aim, the similarity-based virtual screening protocol is applied for the “clean drug-like subset of ZINC database” that contains more than 20 million small compounds. Moreover, molecular dynamics (MD) simulations of selected hits complexed with PDE5 and off-targets were performed in order to get insights for structural and dynamical behaviors of the selected molecules as selective PDE5 inhibitors. Since tadalafil blocks hERG1 K channels in concentration dependent manner, the cardiotoxicity prediction of the hit molecules was also tested. Results of this study can be useful for designing of novel, safe and selective PDE5 inhibitors.
ABSTRACT:Acrylates have gained importance because of their ease of conversion to high-molecular-weight polymers and their broad industrial use. Methyl methacrylate (MMA) is a well-known monomer for free radical polymerization, but its ␣-methyl substituent restricts the chemical modification of the monomer and therefore the properties of the resulting polymer. The presence of a heteroatom in the methyl group is known to increase the polymerizability of MMA. Methyl ␣-hydroxymethylacrylate (MHMA), methyl ␣-methoxymethylacrylate (MC 1 MA), methyl ␣-acetoxymethylacrylate (MAcMA) show even better conversions to high-molecular-weight polymers than MMA. In contrast, the polymerization rate is known to decrease as the methyl group is replaced by ethyl in ethyl ␣-hydroxymethylacrylate (EHMA) and t-butyl in t-butyl ␣-hydroxymethylacrylate (TBHMA). In this study, quantum mechanical tools (B3LYP/6-31G*) have been used in order to understand the mechanistic behavior of the free radical polymerization reactions of acrylates. The polymerization rates of MMA, MHMA, MC 1 MA, MAcMA, EHMA, TBHMA, MC 1 AN (␣-methoxymethyl acrylonitrile), and MC 1 AA (␣-methoxymethyl acrylic acid) have been evaluated and rationalized. Simple monomers such as allyl alcohol (AA) and allyl chloride (AC) have also been modeled for comparative purposes.
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