Attractive in theory and confirmed to exist, anion-pi interactions have never really been seen at work. To catch them in action, we prepared a collection of monomeric, cyclic and rod-shaped naphthalenediimide transporters. Their ability to exert anion-pi interactions was demonstrated by electrospray tandem mass spectrometry in combination with theoretical calculations. To relate this structural evidence to transport activity in bilayer membranes, affinity and selectivity sequences were recorded. pi-acidification and active-site decrowding increased binding, transport and chloride > bromide > iodide selectivity, and supramolecular organization inverted acetate > nitrate to nitrate > acetate selectivity. We conclude that anion-pi interactions on monomeric surfaces are ideal for chloride recognition, whereas their supramolecular enhancement by pi,pi-interactions appears perfect to target nitrate. Chloride transporters are relevant to treat channelopathies, and nitrate sensors to monitor cellular signaling and cardiovascular diseases. A big impact on organocatalysis can be expected from the stabilization of anionic transition states on chiral pi-acidic surfaces.
Matching matters when building supramolecular n/p‐heterojunction photosystems on solid supports that excel with efficient photocurrent generation, important critical thickness, smooth surfaces, and flawless responsiveness to functional probes for the existence of operational intra‐ and interlayer recognition motifs.
A new class of sugar-oxasteroid-quinone hybrid molecules has been designed and synthesized involving an efficient enyne metathesis/Diels-Alder reaction strategy.
A concise and highly enantioselective route has been developed for the synthesis of angucyclinone-type natural products. Utilizing this strategy, total syntheses of five natural products YM-181741, (+)-ochromycinone, (+)-rubiginone B2, (-)-tetrangomycin, and MM-47755 have been accomplished in 22%, 23%, 19%, 18%, and 12% overall yields, respectively. Our approach for the synthesis of these natural products having the benz[a]anthraquinone skeleton is based on a sequential intramolecular enyne metathesis, intermolecular Diels-Alder reaction (DAR), and aromatization. The intramolecular enyne metathesis reaction was employed for the synthesis of enantiopure 1,3-dienes in excellent yields. Furthermore, the synthesis of YM-181741 as well as structurally similar angucyclinones such as (+)-ochromycinone and (+)-rubiginone B2 was achieved via asymmetric enolate alkylation of an oxazolidinone in excellent de. The related angucyclinones (-)-tetrangomycin and MM-47755, bearing a labile tertiary alcohol, were synthesized via Sharpless asymmetric epoxidation of a known allylic alcohol followed by opening the epoxide with Red-Al. The introduction of oxygen functionality at C-1 in all these natural products was accomplished by photooxygenation under a positive pressure of oxygen.
The objective of this study was to synthesize multichromophoric donor-acceptor systems with non-halogenated red (RO) naphthalenediimides (NDIs) attached along p-oligophenyl (POP) and oligophenylethynyl (OPE) scaffolds, and to evaluate their usefulness for zipper assembly of artificial photosystems. Compared to halogenated red NDIs (RCl, RBr), the HOMO of RO is 0.2 eV higher and the HOMO/LUMO gap 0.1 eV smaller, the latter introducing a shade of pink. Consistent with higher HOMO levels, RO zippers generate less photocurrent than RBr zippers in their respective action spectra. RO zippers are less sensitive to topological mismatch than RBr zippers and thus more robust and broadly applicable. Transient absorption measurements reveal efficient electron transfer from excited OPE donors to RO acceptors and less efficient hole injection from excited RO donors into OPE acceptors. Both processes demonstrate compatibility with OMARG-SHJ photosystems (supramolecular n/p-heterojunctions with oriented multicolored antiparallel redox gradients). Decreasing hole transfer with decreasing HOMO energy differences further demonstrates that SHJ-type hole injection disappears gradually (rather than abruptly). Losses in photonic energy during this process can thus be minimized by optoelectronic finetuning, but eventual gains in open circuit voltages risk coming with complementary losses in short circuit current
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