A World Beyond Hydrogen Bonds?—Chalcogen–Chalcogen Interactions Yielding Tubular Structures

It is shown that tubular structures arise in the solid state through close chalcogen-chalcogen (X...X) contacts. As examples a variety of cyclic systems containing sulfur and selenium centers is presented. Common to all of them are close contacts between the chalcogen centers of neighboring stacks giving rise to a zigzag or ladder-type arrangement. In the case of cyclic systems of ring size 24-33 the resulting tubes are able to include hydrocarbons as guest molecules. For 2,7-ditelluraocta-3,5-diyne (17) the close contacts between the tellurium centers of the acyclic C(2) symmetric building blocks generate a helical arrangement in which n-hexane was included. The favored X...X contacts can be traced back to np(X)-sigma*(X[bond]C) interactions.     

Small‐Molecule Stabilization of Protein–Protein Interactions: An Underestimated Concept in Drug Discovery?

The modulation of protein-protein interactions (PPIs) has been recognized as one of the most challenging tasks in drug discovery. While their systematic development has long been considered as intractable, this view has changed over the last years, with the first drug candidates undergoing clinical studies. To date, the vast majority of PPI modulators are interaction inhibitors. However, in many biological contexts a prolonged lifespan of a PPI might be desirable, calling for the complementary approach of PPI stabilization. In fact, nature offers impressive examples of this concept and some PPI-stabilizing natural products have already found application as important drugs. Moreover, directed small-molecule stabilization has recently been demonstrated. Therefore, it is time to take a closer look at the constructive side of modulating PPIs.     

One Decade of Microwave‐Assisted Polymerizations: Quo vadis?

The application of microwave irradiation in polymer syntheses and modifications is of continuously growing interest and has received significant international interest since the beginning of the millennium. Preceded by a review that was published 6 years ago, the present paper summarizes the most recent trends in this research area. Radical as well as step‐growth and ring‐opening polymerizations will be addressed; furthermore, the evolution from microwave‐assisted polymerizations to microwave‐assisted material fabrication will be described on the examples of polymeranalogous reactions, polymer/metal composites and bio‐based materials.

     

Is Electrostatics Sufficient to Describe Hydrogen‐Bonding Interactions?

The stability and geometry of a hydrogen‐bonded dimer is traditionally attributed mainly to the central moiety A?H???B, and is often discussed only in terms of electrostatic interactions. The influence of substituents and of interactions other than electrostatic ones on the stability and geometry of hydrogen‐bonded complexes has seldom been addressed. An analysis of the interaction energy in the water dimer and several alcohol dimers—performed in the present work by using symmetry‐adapted perturbation theory—shows that the size and shape of substituents strongly influence the stabilization of hydrogen‐bonded complexes. The larger and bulkier the substituents are, the more important the attractive dispersion interaction is, which eventually becomes of the same magnitude as the total stabilization energy. Electrostatics alone are a poor predictor of the hydrogen‐bond stability trends in the sequence of dimers investigated, and in fact, dispersion interactions predict these trends better.     

Upconverting‐Nanoparticle‐Assisted Photochemistry Induced by Low‐Intensity Near‐Infrared Light: How Low Can We Go?

Upconverting nanoparticles (UCNPs) convert near‐infrared (NIR) light into UV or visible light that can trigger photoreactions of photosensitive compounds. In this paper, we demonstrate how to reduce the intensity of NIR light for UCNP‐assisted photochemistry. We synthesized two types of UCNPs with different emission bands and five photosensitive compounds with different absorption bands. A λ=974 nm laser was used to induce photoreactions in all of the investigated photosensitive compounds in the presence of the UCNPs. The excitation thresholds of the photoreactions induced by λ=974 nm light were measured. The lowest threshold was 0.5 W cm^?2, which is lower than the maximum permissible exposure of skin (0.726 W cm^?2). We demonstrate that low‐intensity NIR light can induce photoreactions after passing through a piece of tissue without damaging the tissue. Our results indicate that the threshold for UCNP‐ assisted photochemistry can be reduced by using highly photosensitive compounds that absorb upconverted visible light. Low excitation intensity in UCNP‐assisted photochemistry is important for biomedical applications because it minimizes the overheating problems of NIR light and causes less photodamage to biomaterials.     

Intramolecular Methylacridan–Methylacridinium Complexes with a Phenanthrene‐4,5‐diyl or Related Skeleton: Geometry–Property Relationships in Isolable C?H Bridged Carbocations

Bridging the gap : Snapshots of 1,6‐H‐shift precursors indicate that a narrower C? H???C⁺ separation (D in the ORTEP diagram) in the title complexes induces faster degenerate rearrangement of 1 ⁺. A contact distance of less than 2.7 Å is necessary to realize the organic three‐center two‐electron bond of [C? H? C]⁺, as indicated by extrapolation of the X‐ray data.

     

Aldehyde‐Assisted Ruthenium(II)‐Catalyzed C?H Oxygenations

Versatile ruthenium(II) complexes allow for site‐selective C H oxygenations with weakly‐coordinating aldehydes. The challenging C H functionalizations proceed with high chemoselectivity by rate‐determining C H metalation. The new method features an ample substrate scope, which sets the stage for the step‐economical preparation of various bioactive heterocycles.     

Palladium‐Catalyzed Intramolecular C?H Difluoroalkylation: Synthesis of Substituted 3,3‐Difluoro‐2‐oxindoles

The synthesis of 3,3‐difluoro‐2‐oxindoles through a robust and efficient palladium‐catalyzed C H difluoroalkylation is described. This process generates a broad range of difluorooxindoles from readily prepared starting materials. The use of BrettPhos as the ligand was crucial for high efficiency. Preliminary mechanistic studies suggest that oxidative addition is the rate‐determining step for this process.     

Aromatic Homologation by Non‐Chelate‐Assisted RhIII‐Catalyzed C?H Functionalization of Arenes with Alkynes

Larger condensed arenes are of interest owing to their electro‐ and photochemical properties. An efficient synthesis is the catalyzed aromatic annulation of a smaller arene with two alkyne molecules. Besides difunctionalized starting materials, directed C H functionalization can be used for such aromatic homologation. However, thus far the requirement of either pre‐functionalized substrates or suitable directing groups were limiting this approach. Herein, we describe a rhodium(III)‐catalyzed method allowing the use of completely unbiased arenes and internal alkynes. The reaction works best with copper(II) 2‐ethylhexanoate and decabromodiphenyl ether as the oxidant combination. This aromatic annulation tolerates a variety of functional groups and delivers homologated condensed arenes. Aside from simple benzenes, naphthalenes and higher condensed arenes provide access to highly substituted and highly soluble acenes structures having important electronic and photophysical properties.     

Diketopyrrolopyrrole?Thiophene‐Based Acceptor–Donor–Acceptor Conjugated Materials for High‐Performance Field‐Effect Transistors

We report the synthesis, morphology, and field‐effect‐transistor (FET) characteristics of new acceptor–donor–acceptor conjugated materials that consist of diketopyrrolopyrrole (DPP) acceptor groups and one of four different thiophene moieties, that is, dithiophene (2T), thieno[3,2‐b]‐thiophene (TT), dithieno[3,2‐b:2′,3′‐d]‐thiophene (DTT), and 5,5′′′‐di‐(2‐ethylhexyl)‐[2,3′;5′,2′′;4′′,2′′′]quaterthiophene (4T). The optical band gaps of the as‐prepared materials are smaller than 1.7 eV, which is attributed to the strong intramolecular charge transfer and the backbone coplanarity of the thiophene moieties. The order of both crystallinity and FET mobility (×10^?2–×10^?4 cm² V^?1 s^?1) is TT2DPP > 4T2DPP > 2T2DPP >DTT2DP, which differ in the structure of the π‐conjugated cores and core symmetry. Well‐ordered intermolecular chain packing was confirmed by the GIXD and AFM results. In particular, the FET hole mobility of TT2DPP was further improved to 0.1 cm² V^?1 s^?1, which was attributed to the well‐interconnected structure through solution‐shearing. These experimental results suggest the potential applications of the new DPP? thiophene? DPP conjugated materials for organic electronic devices.     

Ruthenium–Porphyrin‐Catalyzed Diastereoselective Intramolecular Alkyl Carbene Insertion into C?H Bonds of Alkyl Diazomethanes Generated In Situ from N‐Tosylhydrazones

With a ruthenium–porphyrin catalyst, alkyl diazomethanes generated in situ from N‐tosylhydrazones efficiently underwent intramolecular C(sp³) H insertion of an alkyl carbene to give substituted tetrahydrofurans and pyrrolidines in up to 99 % yield and with up to 99:1 cis selectivity. The reaction displays good tolerance of many functionalities, and the procedure is simple without the need for slow addition with a syringe pump. From a synthetic point of view, the C H insertion of N‐tosylhydrazones can be viewed as reductive coupling between a CO bond and a C H bond to form a new C C bond, since N‐tosylhydrazones can be readily prepared from carbonyl compounds. This reaction was successfully applied in a concise synthesis of (±)‐pseudoheliotridane.     

Do Intrinsically Disordered Proteins Possess High Specificity in Protein–Protein Interactions?

Specific protein–protein interactions are critical to cellular function. Structural flexibility and disorder‐to‐order transitions upon binding enable intrinsically disordered proteins (IDPs) to overcome steric restrictions and form complementary binding interfaces, and thus, IDPs are widely considered to have high specificity and low affinity for molecular recognition. However, flexibility may also enable IDPs to form complementary binding interfaces with misbinding partners, resulting in a great number of nonspecific interactions. Consequently, it is questionable whether IDPs really possess high specificity. In this work, we investigated this question from a thermodynamic viewpoint. We collected mutant thermodynamic data for 35 ordered protein complexes and 43 disordered protein complexes. We found that the enthalpy–entropy compensation for disordered protein complexes was more complete than that for ordered protein complexes. We further simulated the binding processes of ordered and disordered protein complexes under mutations. Simulation data confirmed the observation of experimental data analyses and further revealed that disordered protein complexes possessed smaller changes in binding free energy than ordered protein complexes under the same mutation perturbations. Therefore, interactions of IDPs are more malleable than those of ordered proteins due to their structural flexibility in the complex. Our results provide new clues for exploring the relationship between protein flexibility, adaptability, and specificity.