Oleksandr

Crystalline sponges (CS) used under a set of standard conditions have often failed to give viable N-containing nucleophilic compounds. Despite the high affinity of these nucleophiles to the binding sites of the CS, N-containing compounds considerably harm the coordination framework of the CS during the guest-soaking step. Herein, it is disclosed that these compounds are efficiently absorbed into the CS, without harming the host, under mild conditions (<4 °C, <2 μg) that normally do not work for common organic guests. Moreover, the use of ZnCl₂ as the metal component of CS significantly improved the tolerance and robustness of the host framework toward N-containing compounds. Out of 22 drug (or drug-like) N-containing compounds chosen from the WHO model list of essential medicines, we succeeded in analyzing 17 analytes with the modified protocols and/or by using the ZnCl₂-noded CS. This demonstrates that the CS method is now a practical tool for drug-discovery research in pharmaceutical industries.

Overcoming trypophobia: trapping N-containing compounds in crystalline sponges (CS) has been problematic because N-containing nucleophilic compounds considerably harm the host. This significant limitation was overcome by developing a new CS with much better tolerance and robustness toward such compounds. The hit rate of the CS method was raised to about 80 %.

We report on the fabrication of a rewritable and reprogrammable dual-photoresponsive liquid crystalline-based actuator containing an azomerocyanine dye that can be locally converted into the hydroxyazopyridinium form by acid treatment. Each dye absorbs at a different wavelength giving access to programmable actuators, the folding of which can be controlled by using different colors of light. The acidic patterning is reversible and allows the erasing and rewriting of patterns in the polymer film, giving access to reusable, adjustable soft actuators.

Bending patterns: Rewritable and reprogrammable actuators can be obtained by using the local activation of an initially chemically homogenous film. The locally activated material is exposed to UV light, which results in the precise folding of the actuator. By switching the wavelength, a different shape can be obtained. Furthermore, the pattern can be erased and a new one can be written, giving access to a multitude of actuated shapes.

The ultrasonic irradiation of aqueous solution is demonstrated to be a suitable source of initiating radicals for a controlled radical polymerization when conducted in the presence of a thiocarbonylthio-containing reversible addition–fragmentation chain transfer (RAFT) agent. This allows for a highly “green” method of externally regulated/controlled polymerization with a potentially broad scope for polymerizable monomers and/or polymer structures.

Make some noise: A sonochemically induced RAFT polymerization with efficient temporal control is demonstrated using high-frequency ultrasound. Unlike the low frequencies used in mechanically induced polymerizations the high frequency employed produces very little shear force, potentially avoiding chain-breaking “depolymerization” events.

A generic method is used for compartmentalization of supramolecular hydrogels by using water-in-water emulsions based on aqueous multi-phase systems (AMPS). By forming the low-molecular-weight hydrogel throughout all phases of all-aqueous emulsions, distinct, micro-compartmentalized materials were created. This structuring approach offers control over the composition of each type of the compartments by directing the partitioning of objects to be encapsulated. Moreover, this method allows for barrier-less, dynamic exchange of even large hydrophilic solutes (MW≈60 kDa) between separate aqueous compartments. These features are expected to find use in the fields of, for instance, micro-structured catalysts, templating, and tissue engineering.

Hydrogel compartments: A versatile approach is used to create aqueous microcompartments inside low-molecular-weight hydrogels using polymer phase separation. Distinct micrometer-sized domains are thus created with controlled composition and unrestricted exchange of even large polar solutes. The method may potentially find use for templating porous soft materials or in the fabrication of tissue engineering scaffolds.

The idea of anion-π catalysis is to stabilize anionic transition states by anion-π interactions on aromatic surfaces. For asymmetric anion-π catalysis, π-acidic surfaces have been surrounded with stereogenic centers. This manuscript introduces the first anion-π catalysts that operate with axial chirality. Bifunctional catalysts with tertiary amine bases next to π-acidic naphthalenediimide planes are equipped with a bulky aromatic substituent in the imide position to produce separable atropisomers. The addition of malonic acid half thioesters to enolate acceptors is used for evaluation. In the presence of a chiral axis, the selective acceleration of the disfavored but relevant enolate addition was much better than with point chirality, and enantioselectivity could be observed for the first time for this reaction with small-molecule anion-π catalysts. Enantioselectivity increased with the π acidity of the π surface, whereas the addition of stereogenic centers around the aromatic plane did not cause further improvements. These results identify axial chirality of the active aromatic plane generated by atropisomerism as an attractive strategy for asymmetric anion-π catalysis.

Chiral planes: To stabilize anionic transition states by anion-π interactions on aromatic surfaces stereoselectively, symmetry breaking of this active plane with axial chirality is more powerful than the accumulation of point chirality around the same active plane.

Current approaches to lowering the pH of basic media rely on the addition of a proton source. An alternative approach is described herein that involves the liquid–liquid extraction-based removal of cesium salts, specifically CsOH and Cs₂CO₃, from highly basic media. A multitopic ion-pair receptor (2) is used that can recognize and extract the hydroxide and carbonate anions as their cesium salts, as confirmed by ¹H NMR spectroscopic titrations, ICP-MS, single-crystal structural analyses, and theoretical calculations. A sharp increase in the pH and cesium concentrations in the receiving phase is observed when receptor 2 is employed as a carrier in U-tube experiments involving the transport of CsOH through an intervening chloroform layer. The pH of the source phase likewise decreases.

Less is less: Lowering pH by extraction. The elusive inorganic hydroxide and carbonate anions are captured in the form of their cesium salts by a metal-free multitopic ion-pair receptor consisting of a hemispherand-strapped calix[4]pyrrole. Direct liquid–liquid extraction and transport studies reveal that it is possible to lower the pH of a highly basic aqueous phase through the removal of the hydroxide anion instead of the addition of protons.

The dynamic exchange of enamines from secondary amines and enolizable aldehydes has been demonstrated in organic solvents. The enamine exchange with amines was efficiently catalyzed by Bi(OTf)₃ and Sc(OTf)₃ (2 mol %) and the equilibria (60 mm) could be attained within hours at room temperature. The formed dynamic covalent systems displayed high stabilities in basic environment with <2 % by-product formation within one week after complete equilibration. This study expands the scope of dynamic C−N bonds from imine chemistry to enamines, enabling further dynamic methodologies in exploration of this important class of structures in systems chemistry.

System Of A D(own)ynamic Enamine: The dynamic exchange of enamines from secondary amines and enolizable aldehydes can be efficiently catalyzed by Bi^III and Sc^III at room temperature. Dynamic enamine systems, stable under basic conditions, were formed in organic solvents with up to >300 times higher equilibration rates than the corresponding uncatalyzed reactions.