Potential biomedicinal applications of graphene oxide (GO), for example, as a carrier of biomolecules or a reagent for photothermal therapy and biosensing, are limited by its cytotoxicity and mutagenicity. It is believed that these properties are at least partially caused by GO-induced oxidative stress in cells. However, it is not known which chemical fragments of GO are responsible for this unfavorable effect. We generated four GOs containing variable redox-active groups on the surface, including Mn(2+), C-centered radicals, and endoperoxides (EPs). A comparison of the abilities of these materials to generate reactive oxygen species in human cervical cancer cells revealed that EPs play a crucial role in GO-induced oxidative stress. These data could be applied to the rational design of biocompatible nontoxic GOs for biomedical applications.
Starting from the optically pure [6]helicene-like alcohol (P,3S)-3-methyl-4-(4-methylphenyl)-1, 3,6,7-tetrahydrobenzo-[c]benzo [5,6]phenanthro [4,3-e]oxepin-14-ol, four helical phosphites were prepared from the corresponding chlorophosphites. These ligands containing parent or substituted 1,3,2-dioxaphospholan-2-yl or dibenzo [d,f][1,3,2]dioxaphosphepin-6-yl moieties were applied to the asymmetric hydroformylation of terminal alkenes catalyzed by Rh(acac)(CO) 2 and the asymmetric allylic amination of cinnamyl-type carbonates catalyzed by [Ir(cod)Cl] 2 . The helical phosphite containing the dibenzo [d,f][1,3,2]dioxaphosphepin-6-yl group was most successful in the asymmetric hydroformylation of
The role of the helicity of small molecules in enantioselective catalysis, molecular recognition, self-assembly, material science, biology, and nanoscience is much less understood than that of point-, axial-, or planar-chiral molecules. To uncover the envisaged potential of helically chiral polyaromatics represented by iconic helicenes, their availability in an optically pure form through asymmetric synthesis is urgently needed. We provide a solution to this problem present since the birth of helicene chemistry in 1956 by developing a general synthetic methodology for the preparation of uniformly enantiopure fully aromatic [5]-, [6]-, and [7]helicenes and their functionalized derivatives. [2 + 2 + 2] Cycloisomerization of chiral triynes combined with asymmetric transformation of the first kind (ultimately controlled by the 1,3-allylic-type strain) is central to this endeavor. The point-to-helical chirality transfer utilizing a traceless chiral auxiliary features a remarkable resistance to diverse structural perturbations.
A cobalt-mediated [2+2+2] cycloisomerisation of ynedinitriles to helical pyridazines in good to high yields was developed. The construction of the pyridazine nucleus from one alkyne and two nitrile units is proposed to follow either a conventional organometallic mechanism or to be triggered by a single-electron transfer from a Co(II) species. Various [5]-, [6]- and [7]helicene pyridazines were prepared.
Potentielle biomedizinische Anwendungen von Graphenoxid (GO), z. B. als Träger von Biomolekülen, Reagentien für die photothermische Therapie oder Biosensoren, werden durch die Zytotoxizität und Mutagenität dieses Materials eingeschränkt. Es wird davon ausgegangen, dass diese Eigenschaften zumindest zum Teil auf eine von GO verursachte Erhöhung des oxidativen Stresses in Zellen zurückzuführen ist. Es ist jedoch nicht bekannt, auf welchen chemischen Fragmenten dieser ungünstige Effekt beruht. In dieser Arbeit wurden vier GOs entwickelt, welche verschiedene redoxaktive Gruppen wie Mn2+, C‐zentrierte Radikale sowie Endoperoxide (EPs) auf der Oberfläche besitzen. Der Vergleich der Fähigkeit der Materialien, reaktive Sauerstoffspezies in humanen Gebärmutterhalskrebszellen zu generieren, zeigt, dass EPs eine entscheidende Rolle im GO‐induzierten oxidativen Stress spielen. Diese Ergebnisse können für die gezielte Entwicklung von biokompatiblem und nicht‐toxischem GO für biomedizinische Anwendungen verwendet werden.
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