Dynamic,Bioresponsive Hydrogels via Changes in DNA Aptamer Conformation

DNA aptamers are integrated into synthetic hydrogel networks with the aim of creating hydrogels that undergo volume changes when exposed to target molecules. Specifically, single‐stranded DNA aptamers in cDNA‐bound, extended state are incorporated into hydrogel networks as cross‐links, so that the nanoscale conformational change of DNA aptamers upon binding to target molecules will induce macroscopic volume decreases of hydrogels. Hydrogels incorporating adenosine triphosphate (ATP)–binding aptamers undergo controllable volume decreases of up to 40.3 ± 4.6% when exposed to ATP, depending on the concentration of DNA aptamers incorporated in the hydrogel network, temperature, and target molecule concentration. Importantly, this approach can be generalized to aptamer sequences with distinct binding targets, as demonstrated here that hydrogels incorporating an insulin‐binding aptamer undergo volume changes in response to soluble insulin. This work provides an example of bioinspired hydrogels that undergo macroscopic volume changes that stem from conformational shifts in resident DNA‐based cross‐links.     

Benzin

Ohne Zusammenfassung     

Batch mode reinforcement learning based on the synthesis of artificial trajectories

In this paper, we consider the batch mode reinforcement learning setting, where the central problem is to learn from a sample of trajectories a policy that satisfies or optimizes a performance criterion. We focus on the continuous state space case for which usual resolution schemes rely on function approximators either to represent the underlying control problem or to represent its value function. As an alternative to the use of function approximators, we rely on the synthesis of “artificial trajectories” from the given sample of trajectories, and show that this idea opens new avenues for designing and analyzing algorithms for batch mode reinforcement learning.     

Blue LED Irradiation of Iodonium Ylides Gives Diradical Intermediates for Efficient Metal‐free Cyclopropanation with Alkenes

A facile and highly chemoselective synthesis of doubly activated cyclopropanes is reported where mixtures of alkenes and β‐dicarbonyl‐derived iodonium ylides are irradiated with light from blue LEDs. This metal‐free synthesis gives cyclopropanes in yields up to 96 %, is operative with cyclic and acyclic ylides, and proceeds with a variety of electronically‐diverse alkenes. Computational analysis explains the high selectivity observed, which derives from exclusive HOMO to LUMO excitation, instead of free carbene generation. The procedure is operationally simple, uses no photocatalyst, and provides access in one step to important building blocks for complex molecule synthesis.     

Denitrogenative Hydrotrifluoromethylation of Benzaldehyde Hydrazones: Synthesis of (2,2,2-Trifluoroethyl)arenes

Reacting hydrazones of arylaldehydes with Togni's CF₃-benziodoxolone reagent, in the presence of potassium hydroxide and cesium fluoride, induces a denitrogenative hydrotrifluoromethylation event to produce (2,2,2-trifluoroethyl)arenes. This novel reaction was tolerant to many electronically-diverse functional groups and substitution patterns, as well as naphthyl- and heteroaryl-derived substrates. Advantages of this process include the easy access to hydrazone precursors on a large scale, speed and operational simplicity, and being transition metal-free.     

The role of organic electron donors in the initiation of BHAS base-induced coupling reactions between haloarenes and arenes

Coupling reactions between haloarenes and arenes(including heteroarenes) that are conducted without added transition metals but in the presence of KOtBu or Na OtBu, have been a topic of great interest since their discovery in 2008. Diverse organic structures act as additives that assist these reactions. These additives are converted into organic electron donors by the butoxide base and this leads to initiation of the coupling reactions, which proceed by radical chain mechanisms. This review provides an overview of the initiation stages of these reactions.     

Modelling Slight Compressibility for Hyperelastic Anisotropic Materials

In order to avoid the numerical difficulties in locally enforcing the incompressibility constraint using the displacement formulation of the Finite Element Method, slight compressibility is typically assumed when simulating the mechanical response of nonlinearly elastic materials. The current standard method of accounting for slight compressibility of hyperelastic materials assumes an additive decomposition of the strain-energy function into a volumetric and an isochoric part. A new proof is given to show that this is equivalent to assuming that the hydrostatic stress is a function of the volume change only and that uniform dilatation is a possible solution to the hydrostatic stress boundary value problem, with therefore no anisotropic contribution to the mechanical response. An alternative formulation of slight compressibility is proposed, one that does not suffer from this defect. This new model generalises the standard model by including a mixed term in the volume change and isochoric response. Specific models of slight compressibility are given for isotropic, transversely isotropic and orthotropic materials.     

Highly Efficient Triplet Photosensitizers: A Systematic Approach to the Application of IrIII Complexes containing Extended Phenanthrolines

A series of Ir^III complexes, based on 1,10‐phenanthroline featuring aryl acetylene chromophores, were prepared and investigated as triplet photosensitizers. The complexes were synthesized by Sonogashira cross‐coupling reactions using a “chemistry‐on‐the‐complex” method. The absorption properties and luminescence lifetimes were successfully tuned by controlling the number and type of light‐harvesting group. Intense UV/Vis absorption was observed for the Ir^III complexes with two light‐harvesting groups at the 3‐ and 8‐positions of the phenanthroline. The asymmetric Ir^III complex (with a triphenylamine (TPA) and a pyrene moiety attached) exhibited the longest lifetime. Red emission was observed for all the complexes in deaerated solutions at room temperature. Their emission at low temperature (77 K) and nanosecond time‐resolved transient difference absorption spectra revealed the origin of their triplet excited states. The singlet‐oxygen (¹O₂) sensitization and triplet‐triplet annihilation (TTA)‐based upconversion were explored. Highly efficient TTA upconversion (Φ_UC=28.1 %) and ¹O₂ sensitization (Φ_Δ=97.0 %) were achieved for the asymmetric Ir^III complex, which showed intense absorption in the visible region (λ_abs=482 nm, ?=50900 m ^?1 cm^?1) and had a long‐lived triplet excited state (53.3 μs at RT).     

Synthesis and Structure of the Alkoxido-Titanium Pentamolybdate (nBu4N)3[(iPrO)TiMo5O18]: An Entry into Systematic TiMo5 Reactivity

The alkoxido-titanium pentamolybdate [(ⁱPrO)TiMo₅O₁₈]³⁻ (1) has been obtained as its tetrabutylammonium (TBA) salt by hydrolysis of a mixture containing (TBA)₂[Mo₂O₇], (TBA)₄[Mo₈O₂₆] and Ti(OⁱPr)₄ in MeCN and has been characterised by ¹H, ¹³C, ¹⁷O, ⁴⁹Ti and ⁹⁵Mo NMR and FTIR spectroscopy, electrospray ionisation mass spectrometry, elemental microanalysis and single-crystal X-ray crystallography. The Lindqvist-type structure is derived from [Mo₆O₁₉]²⁻ by replacement of {Mo=O}⁴⁺ by {(ⁱPrO)Ti}³⁺ and shows bond alternation in the TiMo₃O₄ rings, with average bond distances of 1.956(8) ? for Ti–O(Mo), 1.832(7) ? for Mo–O(Ti), 1.943(7) ? for Mo_eq–O(Mo_ax) and 1.910(6) ? for Mo_ax–O(Mo_eq), while the increase in charge results in a decrease in ¹⁷O NMR chemical shift for terminal Mo=O groups from δ 933 for [Mo₆O₁₉]²⁻ to δ 875 and 857 for 1 and a shift in ν_Mo=O from 951 cm⁻¹ for [Mo₆O₁₉]²⁻ to 930 cm⁻¹ for 1. The main peaks in the negative-ion electrospray ionisation mass spectrum of (TBA)₃ 1 could be assigned to ion aggregates containing 1 or fragments derived from 1, including {(TBA)₂[(ⁱPrO)TiMo₅O₁₈]}⁻, {(TBA)[(ⁱPrO)TiMo₅O₁₈]}²⁻, {(ⁱPrO)TiMo₂O₈}⁻, {TiMo₅O₁₈}²⁻, {TiMo₄O₁₅}²⁻ and {Mo₃O₁₀}²⁻.