Au(iii)-aryl species have been unequivocally identified as reactive intermediates in oxidant-free C-O and C-N cross coupling catalysis. The crystal structures of cyclometalated neutral and cationic ...Au(iii) species are described and their key role in 2 electron-redox Au(i)/Au(iii) catalysis in C-O and C-N cross couplings is shown. Nucleophiles compatible with Au-catalyzed cross couplings include aromatic and aliphatic alcohols and amines, as well as water and amides.
Regio- and enantioselective hydroformylation of styrenes is attained upon embedding a chiral Rh complex in a nonchiral supramolecular cage formed from coordination-driven self-assembly of macrocyclic ...dipalladium complexes and tetracarboxylate zinc porphyrins. The resulting supramolecular catalyst converts styrene derivatives into aldehyde products with much higher chiral induction in comparison to the nonencapsulated Rh catalyst. Spectroscopic analysis shows that encapsulation does not change the electronic properties of the catalyst nor its first coordination sphere. Instead, enhanced enantioselectivity is rationalized by the modification of the second coordination sphere occurring upon catalyst inclusion inside the cage, being one of the few examples in achieving an enantioselective outcome via indirect through-space control of the chirality around the catalyst center. This effect resembles those taking place in enzymatic sites, where structural constraints imposed by the enzyme cavity can impart stereoselectivities that cannot be attained in bulk. These results are a showcase for the future development of asymmetric catalysis by using size-tunable supramolecular capsules.
Since fullerenes are available in macroscopic quantities from fullerene soot, large efforts have been geared toward designing efficient strategies to obtain highly pure fullerenes, which can be ...subsequently applied in multiple research fields. Here we present a supramolecular nanocage synthesized by metal-directed self-assembly, which encapsulates fullerenes of different sizes. Direct experimental evidence is provided for the 1:1 encapsulation of C60, C70, C76, C78 and C84, and solid state structures for the host-guest adducts with C60 and C70 have been obtained using X-ray synchrotron radiation. Furthermore, we design a washing-based strategy to exclusively extract pure C60 from a solid sample of cage charged with a mixture of fullerenes. These results showcase an attractive methodology to selectively extract C60 from fullerene mixtures, providing a platform to design tuned cages for selective extraction of higher fullerenes. The solid-phase fullerene encapsulation and liberation represent a twist in host-guest chemistry for molecular nanocage structures.
Shoots and roots are autotrophic and heterotrophic organs of plants with different physiological functions. Do they have different metabolomes? Do their metabolisms respond differently to ...environmental changes such as drought? We used metabolomics and elemental analyses to answer these questions. First, we show that shoots and roots have different metabolomes and nutrient and elemental stoichiometries. Second, we show that the shoot metabolome is much more variable among species and seasons than is the root metabolome. Third, we show that the metabolic response of shoots to drought contrasts with that of roots; shoots decrease their growth metabolism (lower concentrations of sugars, amino acids, nucleosides, N, P, and K), and roots increase it in a mirrored response. Shoots are metabolically deactivated during drought to reduce the consumption of water and nutrients, whereas roots are metabolically activated to enhance the uptake of water and nutrients, together buffering the effects of drought, at least at the short term.
Morphology and size controllable rhodium nanoparticles stabilized by a nitrogen‐rich polyoxyethylenated derivative have been prepared by reduction of RhCl3 with NaBH4 in water at room temperature and ...fully characterized. The flower‐like Rh NPs are effective and recyclable catalysts for the stereoselective hydrosilylation of challenging internal alkynes and diynes, affording the (E)‐vinylsilanes in quantitative yields for a wide range of substrates. The insolubility of the nanocatalyst in diethyl ether allows its easy separation and recycling.
The preparation of multifunctional chiral molecules can be greatly simplified by adopting a route via the sequential catalytic assembly of achiral building blocks. The catalytic aldol assembly of ...prebiotic compounds into stereodefined pentoses and hexoses is an as yet unmet challenge. Such a process would be of remarkable synthetic utility and highly significant with regard to the origin of life. Pursuing an expedient enzymatic approach, here we use engineered D-fructose-6-phosphate aldolase from Escherichia coli to prepare a series of three- to six-carbon aldoses by sequential one-pot additions of glycolaldehyde. Notably, the pertinent selection of the aldolase variant provides control of the sugar size. The stereochemical outcome of the addition was also altered to allow the synthesis of L-glucose and related derivatives. Such engineered biocatalysts may offer new routes for the straightforward synthesis of natural molecules and their analogues that circumvent the intricate enzymatic pathways forged by evolution.
Plants in natural environments are increasingly being subjected to a combination of abiotic stresses, such as drought and warming, in many regions. The effects of each stress and the combination of ...stresses on the functioning of shoots and roots have been studied extensively, but little is known about the simultaneous metabolome responses of the different organs of the plant to different stresses acting at once.
We studied the shift in metabolism and elemental composition of shoots and roots of two perennial grasses, Holcus lanatus and Alopecurus pratensis, in response to simultaneous drought and warming.
These species responded differently to individual and simultaneous stresses. These responses were even opposite in roots and shoots. In plants exposed to simultaneous drought and warming, terpenes, catechin and indole acetic acid accumulated in shoots, whereas amino acids, quinic acid, nitrogenous bases, the osmoprotectants choline and glycine betaine, and elements involved in growth (nitrogen, phosphorus and potassium) accumulated in roots. Under drought, warming further increased the allocation of primary metabolic activity to roots and changed the composition of secondary metabolites in shoots.
These results highlight the plasticity of plant metabolomes and stoichiometry, and the different complementary responses of shoots and roots to complex environmental conditions.
A new persistent organic free radical has been synthetized with Br atoms occupying the ortho‐ and para‐positions of a trityl core. After the isolation of its two propeller‐like atropisomers, Plus (P) ...and minus (M), their absolute configurations were assigned by a combination of theoretical and experimental data. Remarkably, no hints of racemization were observed up to 60 °C for more than two hours, due to the higher steric hindrance imposed by the bulky Br atoms. Therefore, when compared to its chlorinated homologue (t1/2=18 s at 60 °C), an outstanding stability against racemization was achieved. A circularly polarized luminescence (CPL) response of both enantiomers was detected. This free radical shows a satisfactory luminescent dissymmetry factor (|glum(592 nm)|≈0.7×10−3) despite its pure organic nature and low luminescence quantum yield (LQY). Improved organic magnetic CPL emitters derived from the reported structure can be envisaged thanks to the wide possibilities that Br atoms at para‐positions offer for further functionalization.
Get radical! An efficient circularly polarized luminescence emitter, based on a persistent trityl radical substituted with bulky bromine atoms at ortho‐ and para‐positions, is reported (see figure). In addition, this emitter has a high racemization barrier between its enantiomers.
A general review of novel NMR methods to measure heteronuclear long-range proton-carbon coupling constants ((n)JCH; n>1) in small molecules is made. NMR experiments are classified in terms of NMR ...pulse scheme and cross-peak nature. A discussion about simplicity, general applicability and accuracy for each particular NMR experiment is presented and exemplified. Important aspects such as the sign determination and measurement of very small coupling values involving protonated and non-protonated carbons as well as the complementarity between different experiments are also discussed. Finally, a compilation of applications in structural and conformational analysis of different types of molecules since 2000 is surveyed.
Palladium nanoparticles stabilized with tris‐imidazolium tetrafluoroborates catalyze the stereoselective hydrosilylation of internal alkynes in a dry inert atmosphere to give (E)‐vinylsilanes in ...excellent yields. In the presence of controlled amounts of water a transfer hydrogenation reaction takes place with the formation of (Z)‐alkenes or the corresponding alkanes.
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