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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Metal-catalysed hydroformylation is successfully combined with an organocatalysed stereoselective Mannich reaction in a tandem reaction sequence. This novel type of "tandem catalysis" allows access to complex molecular systems with high levels of enantioselectivity, using simple starting materials and an amino acid as the chiral catalyst.Keywords: hydroformylation; Mannich reaction; organocatalysis; tandem reactions Recent syntheses of natural and drug-like compounds have clearly revealed the advantages of combining several reactions into a tandem reaction sequence to provide complex molecules in a clean and efficient manner.[1] We and others have demonstrated that tandem reactions under hydroformylation conditions are a useful strategy for the synthesis of complex molecular systems.[2] More recent attention has been focused on "tandem catalysis" [3] where a metal catalyst works together with a chiral organocatalyst affording highly functionalised molecules with excellent levels of enantioselectivity.[4] Here we now report the first use of this methodology in sequential hydroformylation and asymmetric Mannich reactions. The proposed sequential transformation involves hydroformylation of an alkene mediated by a triphenyl phosphite-modified Rh catalyst and l-proline-catalysed enantioselective Mannich reaction of the aldehyde formed in situ, an aromatic amine and a ketone (Scheme 1). Like the related tandem hydroformylation/enantioselective aldol reactions, [4d,e] this process leads to the generation of up to four new adjacent stereogenic centres in the product, and clearly, when high levels of control are observed, these approaches are of considerable importance.The synthetic plan relied on finding optimal conditions for both hydroformylation and enantioselective Mannich reactions and then combining these reactions into a tandem sequence.The hydroformylation reactions were performed using the previously reported protocol.[4d] The catalyst was readily prepared in situ from [RhA C H T U N G T R E N N U N G (acac)(CO) 2 ] and an excess of triphenyl phosphite. Cyclic olefins were used as substrates in order to avoid the regioselectivity problems of hydroformylation reactions. The hydroformylation experiments were performed in acetone, since in subsequent Mannich reactions acetone will serve both as the enamine component and as solvent (Table 1). As shown in Table 1, excellent converScheme 1. Hydroformylation/enantioselective Mannich reactions.