Self‐Assembly of Chiral Propeller‐like Supermolecules with Unusual “Sergeants‐and‐Soldiers” and “Majority‐Rules” Effects

Chiral amplification is an interesting phenomenon in supramolecular chemistry mainly observed in complicated systems in which cooperative effect dominate. Herein, chiral, supramolecular, propeller‐like architectures have been constructed through coassembly of an achiral disk‐shaped molecule and chiral amino acid derivatives driven by intermolecular hydrogen bonding. Both the “sergeants‐and‐soldiers” principle and “majority‐rules” effect are applicable in these discrete four‐component supermolecules, which are the simplest supramolecular system ever reported that exhibit chiral amplification.     

An “All‐Green” Catalytic Cycle of Aqueous Photoionization

Hydrated electrons are highly aggressive species that can force chemical transformations of otherwise unreactive molecules such as the reductive detoxification of halogenated organic compounds. We present the first example of the sustainable production of hydrated electrons through a homogeneous catalytic cycle driven entirely by green light (532 nm, coinciding with the maximum of the terrestrial solar spectrum). The catalyst is a metal complex serving as a “container” for a radical anion. This active center is generated from a ligand through quenching by a sacrificial electron donor, is shielded by the complex such that it stores the energy of the photon for much longer than a free radical anion could, and is finally ionized by another photon to regenerate the ligand and recover the starting complex quantitatively. The sacrificial donor can be a bioavailable reagent such as ascorbic acid.     

“On‐Water,” Microwave‐Assisted,Pd‐Catalyzed Synthesis of Indoles from Imines and o‐Difunctionalized Arenes

Regioselectively substituted indoles are prepared by a Pd‐catalyzed C? C/C? N bond‐forming sequence from imines and o‐dihaloarenes or o‐haloarene sulfonates. The heterogeneous reaction as a suspension in water and under microwave heating offers important advantages in comparison with the conventional reaction in an organic solvent, among them, operational simplicity, the employment of KOH solutions instead of alkoxides, and a dramatic reduction of reaction times.     

“Click”‐Triggered Self‐Healing Graphene Nanocomposites

Strategies to compensate material fatigue are among the most challenging issues, being most prominently addressed by the use of nano‐ and microscaled fillers, or via new chemical concepts such as self‐healing materials. A capsule‐based self‐healing material is reported, where the adverse effect of reduced tensile strength due to the embedded capsules is counterbalanced by a graphene‐based filler, the latter additionally acting as a catalyst for the self‐healing reaction. The concept is based on “click”‐based chemistry, a universal methodology to efficiently link components at ambient reaction conditions, thus generating a “reactive glue” at the cracked site. A capsule‐based healing system via a graphene‐based Cu₂O (TRGO‐Cu₂O‐filler) is used, acting as both the catalytic species for crosslinking and the required reinforcement agent within the material, in turn compensating the reduction in tensile strength exerted by the embedded capsules. Room‐temperature self‐healing within 48 h is achieved, with the investigated specimen containing TRGO‐Cu₂O demonstrating significantly faster self‐healing compared to homogeneous (Cu(PPh₃)₃F, Cu(PPh₃)₃Br), and heterogeneous (Cu/C) copper(I) catalysts.

     

One‐Step Formation of “Chain‐Armor”‐Stabilized DNA Nanostructures

DNA‐based self‐assembled nanostructures are widely used to position organic and inorganic objects with nanoscale precision. A particular promising application of DNA structures is their usage as programmable carrier systems for targeted drug delivery. To provide DNA‐based templates that are robust against degradation at elevated temperatures, low ion concentrations, adverse pH conditions, and DNases, we built 6‐helix DNA tile tubes consisting of 24 oligonucleotides carrying alkyne groups on their 3′‐ends and azides on their 5′‐ends. By a mild click reaction, the two ends of selected oligonucleotides were covalently connected to form rings and interlocked DNA single strands, so‐called DNA catenanes. Strikingly, the structures stayed topologically intact in pure water and even after precipitation from EtOH. The structures even withstood a temperature of 95 °C when all of the 24 strands were chemically interlocked.     

Stimuli‐Responsive Cycloaurated “OFF‐ON” Switchable Anion Transporters

Anion transporters have shown potential application as anti‐cancer agents that function by disrupting homeostasis and triggering cell death. In this research article we report switchable anion transport by gold complexes of anion transporters that are “switched on” in situ in the presence of the reducing agent GSH by decomplexation of gold. GSH is found in higher concentrations in tumors than in healthy tissue and hence this approach offers a strategy to target these systems to tumors.     

An “Ingredients” Approach to Functional Self‐Synthesizing Materials: A Metal‐Ion‐Selective,Multi‐Responsive,Self‐Assembled Hydrogel

New methodology for making novel materials is highly desirable. Here, an “ingredients” approach to functional self‐assembled hydrogels was developed. By designing a building block to contain the right ingredients, a multi‐responsive, self‐assembled hydrogel was obtained through a process of template‐induced self‐synthesis in a dynamic combinatorial library. The system can be switched between gel and solution by light, redox reactions, pH, temperature, mechanical energy and sequestration or addition of Mg^II salt.     

A Family of “Click” Nucleosides for Metal‐Mediated Base Pairing: Unravelling the Principles of Highly Stabilizing Metal‐Mediated Base Pairs

A family of artificial nucleosides has been developed by applying the Cu^I‐catalyzed Huisgen 1,3‐dipolar cycloaddition. Starting from 2‐deoxy‐β‐D ‐glycosyl azide as a common precursor, three bidentate nucleosides have been synthesized. The 1,2,3‐triazole involved in all three nucleobases is complemented by 1,2,4‐triazole ( TriTri ), pyrazole ( TriPyr ), or pyridine ( TriPy ). Molecular structures of two metal complexes indicate that metal‐mediated base pairs of TriPyr may not be fully planar. An investigation of DNA oligonucleotide duplexes comprising the new “click” nucleosides showed that they can bind Ag^I to form metal‐mediated base pairs. In particular the mispair formed from TriPy and the previously established imidazole nucleoside is significantly stabilized in the presence of Ag^I. A comparison of different oligonucleotide sequences allowed the determination of general factors involved in the stabilization of nucleic acids duplexes with metal‐mediated base pairs.     

A Perylene Bisimide Cyclophane as a “Turn‐On” and “Turn‐Off” Fluorescence Probe

A rigid, covalently linked perylene‐3,4:9,10‐tetracarboxylic acid bisimide (PBI) cyclophane was synthesized by imidization of a bay‐substituted perylene bisanhydride with p‐xylylenediamine. The interchromophoric distance of approximately 6.5 Å establishes an ideal rigid cavity for the encapsulation of large aromatic compounds such as perylene and anthracene with binding constants up to 4.6×10⁴ M ^?1 (in CHCl₃). For electron‐poor guest molecules, the complexation process is accompanied by a significantly increased fluorescence, whereas the emission intensity is dramatically quenched by more electron‐rich guests because of the formation of charge‐transfer complexes. Furthermore, the influence of the PBI core twist on the binding constant results in a remarkable selectivity towards more flexible aromatic guest molecules.     

An Allosteric Receptor by Simultaneous “Casting” and “Molding” in a Dynamic Combinatorial Library

Allosteric synthetic receptors are difficult to access by design. Herein we report a dynamic combinatorial strategy towards such systems based on the simultaneous use of two different templates. Through a process of simultaneous casting (the assembly of a library member around a template) and molding (the assembly of a library member inside the binding pocket of a template), a Russian‐doll‐like termolecular complex was obtained with remarkable selectivity. Analysis of the stepwise formation of the complex indicates that binding of the two partners by the central macrocycle exhibits significant positive cooperativity. Such allosteric systems represent hubs that may have considerable potential in systems chemistry.     

Synthesis of dendrimers through divergent iterative thio‐bromo “Click” chemistry

The development of a novel nucleophilic thio‐bromo “Click” reaction, specifically base‐mediated thioetherification of thioglycerol with α‐bromoesters, is reported. Combination of this thio‐bromo click reaction with subsequent acylation with 2‐bromopropionyl bromide provides an iterative two‐step divergent growth approach to the synthesis of a new class of poly(thioglycerol‐2‐propionate) (PTP) dendrimers. This approach is demonstrated in the rapid preparation of four generation (G1–G4) of PTP dendrimers with high‐structural fidelity. The isolated G1–G4 bromide‐terminated dendrimers can be used directly as dendritic macroinitiators for the synthesis of star‐polymers via SET‐LRP. Additionally, the intermediate hydroxy‐terminated dendrimers are analogs of other water‐soluble polyester and polyether dendrimers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3931–3939, 2009     

Carbocatalysis: The State of “Metal‐Free” Catalysis

The rise in global demand for crucial chemical compounds has driven immense research in the fundamental science of catalysis. Graphene and its derivatives (chemically modified graphene, CMGs) have recently emerged as a new class of heterogeneous catalyst that promises economically viable and greener routes to these compounds. Although CMGs possess unique catalytic properties, the actual active sites are often points of discussion. Current minimal understanding on the possible effects of metallic impurities on the electrocatalytic performances of these CMGs calls forth the need to raise awareness on possible metallic impurities misrepresenting the actual chemical catalytic performances of the CMGs. This Minireview highlights the latest advances in the application of CMGs as catalysts, with an emphasis on the possible effects of metallic impurities on CMG catalysis.     

Using “Threading Followed by Shrinking” to Synthesize Highly Stable Dialkylammonium‐Ion‐Based Rotaxanes

Herein, we report a “threading followed by shrinking” approach for the synthesis of rotaxanes by using an “oxygen‐deficient” macrocycle that contained two arylmethyl sulfone units and the dumbbell‐shaped salt bis(3,5‐dimethylbenzyl)ammonium tetrakis(3,5‐trifluoromethylphenyl)borate as the host and guest components, respectively. The extrusion of SO₂ from both of the arylmethyl sulfone units of the macrocyclic component in the corresponding [2]pseudorotaxane resulted in a [2]rotaxane that was sufficiently stable to maintain its molecular integrity in CD₃SOCD₃ at 393 K for at least 5 h.     

Thio‐bromo “Click,” post‐polymerization strategy for functionalizing ring opening metathesis polymerization (ROMP)‐derived materials

The use of a thio‐bromo click strategy as an efficient postpolymerization tool is described. Norbornene derivatives bearing an α‐bromo ester could be polymerized using Grubbs 2^nd generation initiator to provide α‐bromo ester‐containing homo‐and block copolymers that could be efficiently functionalized through reactions with various thiols. A one‐pot strategy was also used, in which up to four different thiols were reacted simultaneously. This chemistry could also be used as an efficient cross‐linking strategy to form ROMP‐based gels as well as a tool for terminal functionalization of polypropylene‐based oligomers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 179–185     

PVC‐Based Ion‐Selective Electrodes with Enhanced Biocompatibility by Surface Modification with “Click” Chemistry

We report here on plasticized ion‐selective poly(vinyl chloride) membranes with increased biocompatibility by means of a copper(I)‐catalyzed azide‐alkyne cycloaddition (‘click chemistry’) on the surface of finished membranes. We aimed for increasing the hydrophilicity of the surface and the application of NO releasing molecules. Employing the first principle, sodium selective membranes based on azide‐substituted PVC were modified with different length poly(ethylene glycol) (PEG) chains. For the second, cysteine groups were used as a nitrous oxide releasing substance. Surface modification was confirmed by Electrochemical Impedance Spectroscopy (EIS). Potentiometric measurements in undiluted whole blood showed an increased sensor stability in comparison to unmodified PVC. Membrane surfaces after 18 h contact with blood were analyzed with Scanning Electron Microscopy (SEM) and revealed a reduced level of blood cell adsorption on membranes modified with tetraethylene glycol (TEG) and PEGs. In contrast, cysteine modified membranes did not exhibit improved fouling resistance, suggesting that nitric oxide release by itself is not a sufficiently efficient mechanism.