Self-Inclusion Complexation of Electron-Accepting Guest into Electron-Donating Cyclic Host by Photoexcitation.

Self-inclusion complexes consisting of host-guest conjugates are one of the unique supramolecular structures because they form in-state and out-state depending on the external stimuli. Despite many reports of the stimuli-responsive self-inclusion complex formation, study of the structural relaxation from out-state to in-state by photoexcitation has been unexplored. Herein, we report that an electron-donating host and an electron-accepting guest conjugate exhibits the structural relaxation from out-state to in-state by photoexcitation. Formation of the in-state in the excited state resulted in exciplex emission along with the locally excited emission from the out-state. Moreover, this structural relaxation by photoexcitation was suppressed not only by temperature, but also by the presence of guest molecules, resulting in changes in the ratio of the dual emission intensities.

Molecular Motor-Driven Light-Controlled Logic-Gated K+ Channel for Cancer Cell Apoptosis.

Developing artificial ion transport systems, which process complicated information and step-wise regulate properties, is essential for deeply comprehending the subtle dynamic behaviors of natural channel proteins (NCPs). Here a photo-controlled logic-gated K+ channel based on single-chain random heteropolymers containing molecular motors, exhibiting multi-core processor-like properties to step-wise control ion transport is reported. Designed with oxygen, deoxygenation, and different wavelengths of light as input signals, complicated logical circuits comprising "YES", "AND", "OR" and "NOT" gate components are established. Implementing these logical circuits with K+ transport efficiencies as output signals, multiple state transitions including "ON", "Partially OFF" and "Totally OFF" in liposomes and cancer cells are realized, further causing step-wise anticancer treatments. Dramatic K+ efflux in the "ON" state (decrease by 50% within 7 min) significantly induces cancer cell apoptosis. This integrated logic-gated strategy will be expanded toward understanding the delicate mechanism underlying NCPs and treating cancer or other diseases is expected.

Silapillar[n]arenes: Their Enhanced Electronic Conjugation and Conformational Versatility.

During recent decades, methylene-bridged macrocyclic arenes have been widely used in supramolecular chemistry. However, their π-conjugations are very weak, as the methylene bridges disrupt the electronic communication between π orbitals of the aromatic units. Herein, we successfully synthesized a series of silapillar[n]arenes (n = 4, 6, and 8) using silylene bridging. These showed enhanced electronic conjugation compared with the parent pillar[n]arenes because of σ*-π* conjugation between σ* (Si-C) orbitals and π* orbitals of the benzenes. Owing to the longer Si-C bond compared with the C-C bond, silylene-bridging provides additional structural flexibility into the pillar[n]arene scaffolds; a strained silapillar[4]arene was formed, which is unavailable in the parent pillar[n]arenes because of the steric requirements. Furthermore, silapillar[n]arenes displayed interesting size-dependent structural and optical properties.

Combinatorial Screening of Water/Proton Permeation of Self-Assembled Pillar[5]arene Artificial Water Channel Libraries.

Artificial water channels (AWCs) that selectively transport water and reject ions through bilayer membranes have potential to act as synthetic Aquaporins (AQPs). AWCs can have a similar osmotic permeability, better stability, with simpler manufacture on a larger-scale and have higher functional density and surface permeability when inserted into the membrane. Here, we report the screening of combinatorial libraries of symmetrical and unsymmetrical rim-functionalized PAs A-D that are able to transport ca. 107 -108 water molecules/s/channel, which is within 1 order of magnitude of AQPs' and show total ion and proton rejection. Among the four channels, C and D are 3-4 times more water permeable than A and B when inserted in bilayer membranes. The binary combinations of A-D with different molar ratios could be expressed as an independent (linear ABA), a recessive (inhibition AB, AC, DB, ACA), or a dominant (amplification, DBD) behavior of the water net permeation events.

Diastereoselective Rotaxane Synthesis with Pillar[5]arenes via Co-crystallization and Solid-State Mechanochemical Processes.

Chiral rotaxanes have attracted much attention in recent decades for their unique chirality based on their interlocked structures. Thus, selective synthesis methods of chiral rotaxanes have been developed. The introduction of substituents with chiral centers to produce diastereomers is a powerful strategy for the construction of chiral rotaxanes. However, in case of a small energy difference between the diastereomers, diastereoselective synthesis is extremely difficult. Herein, we report a new diastereoselective rotaxane synthesis method using solid-phase diastereoselective [3]pseudorotaxane formation and mechanochemical solid-phase end-capping reactions of the [3]pseudorotaxanes. By co-crystallization of stereodynamic planar chiral pillar[5]arene with stereogenic carbons at both rims and axles with suitable end groups and lengths, the [3]pseudorotaxane with a high diastereomeric excess (ca. 92% de) was generated in the solid state because of higher effective molarity with aid by packing effects and significant energy differences between [3]pseudorotaxane diastereomers. In contrast, the de of the pillar[5]arene was low in solution (ca. 10% de) because of a small energy difference between diastereomers. Subsequent end-capping reactions of the polycrystalline [3]pseudorotaxane with high de in solvent-free conditions successfully yielded rotaxanes while maintaining the high de generated by the co-crystallization.

Alignment and Dynamic Inversion of Planar Chirality in Pillar[n]arenes.

Pillar[n]arenes are symmetrical macrocyclic compounds composed of benzene panels with para-methylene linkages. Each panel usually exhibits planar chirality and prefers chirality-aligned states. Because of this feature, pillar[n]arenes are attractive scaffolds for chiroptical materials that are easy to prepare and optically resolve and show intense circular dichroism (CD) signals. In addition, rotation of the panels endows the chirality of pillar[n]arenes with a dynamic nature. The chirality in tubular oligomers and supramolecular assemblies sometimes show time- and procedure-dependent alignment phenomena. Furthermore, the CD signals of some pillar[n]arenes respond to the addition of chiral guests when their dynamic chirality is coupled with host-guest properties. By using diastereomeric pillar[n]arenes with additional chiral structures, the response can also be caused by achiral guests and changes of the environment, providing molecular sensors.

Sequentially Controlled Recognition of Different Proteins Using Programmable Protein Imprinted Nanospheres.

Although protein imprinted materials with multiple templates are developed to selectively separate different proteins, it is difficult to achieve the programmed adsorption and separation of different proteins using one material, because the available protein imprinted materials are constructed through irreversible crosslinking and their structures are unprogrammable and non-reconstructive. Herein, a novel nanosphere (MS@PTL-g-PNIPAM) is designed, which not only is temperature and pH responsive but also can dynamically reversibly crosslink/de-crosslink under ultraviolet light of different wavelengths. With the help of the dynamically reversible photo-crosslinking, the nanospheres can be repeatedly programmed into protein imprinted nanospheres toward different target proteins. Moreover, the prepared imprinted nanospheres can easily achieve the controlled rebinding and release of target proteins, benefiting from the introduced temperature- and pH-responsive moieties. As a consequence, this study realizes the specific separation of different target proteins from protein mixture and the real bovine blood sequentially by programming one material. It is resource saving, time saving, recyclable, and it will provide convenience for protein imprinted materials to use in the blood purification, drug delivery, and virus detection.

Efficient synthesis and unit-selective π-extension of π-fused [4.3.3]propellane as a chiral building block.

A three-dimensional skeleton, π-fused [4.3.3]propellane, was constructed and derivatized by selective π-extension at the two naphthalene units. The obtained propellanes existed as stereoisomers different in spatial arrangement, one of which displayed a chiroptical response originating from through-space interactions between 5-azachrysenes in a skew position.

Dynamic-to-Static Planar Chirality Conversion in Pillar[5]arenes Regulated by Guest Solvents or Amplified by Crystallization.

Controlling dynamic chirality and memorizing the controlled chirality are important. Chirality memory has mainly been achieved using noncovalent interactions. However, in many cases, the memorized chirality arising from noncovalent interactions is erased by changing the conditions such as the solvent and temperature. In this study, the dynamic planar chirality of pillar[5]arenes was successfully converted into static planar chirality by introducing bulky groups through covalent bonds. Before introducing the bulky groups, pillar[5]arene with stereogenic carbon atoms at both rims existed as a pair of diastereomers, and thus showed planar chiral inversion that was dependent on the chain length of the guest solvent. The pS and pR forms, regulated by guest solvents, were both diastereomerically memorized by introducing bulky groups. Furthermore, the diastereomeric excess was amplified by crystallization of the pillar[5]arene. The subsequent introduction of bulky groups yielded pillar[5]arene with an excellent diastereomeric excess (95 % de).

Adaptive Planar Chirality of Pillar[5]arenes Invertible by n-Alkane Lengths.

Chirality of host molecules can be induced and/or inverted by the guest molecules. However, the adapting chirality of hosts to the length of n-alkanes remains a great challenge because n-alkanes are neutral, achiral, and linear molecules, resulting in a weak interaction with most compounds. Herein, we report a system with chirality adapted to n-alkane lengths, using a pillar[5]arene-based macrocyclic host, S-Br, which contains five stereogenic carbons and five terminal bromine atoms on each rim. The electron-rich cavity of S-Br could include n-alkanes and the planar-chiral isomers sensitively inverted in response to the lengths of the complexed n-alkanes. The inclusion of a short n-alkane such as n-pentane made S-Br more inclined to be in the pS-form, whereas the inclusion of long n-alkanes such as n-heptane made the pR-form more favorable. The difference in the stability of the isomers was supported by the crystal structures and the theoretical calculations. Furthermore, temperature drives the adaptive chirality of S-Br with n-alkanes. An n-alkane with middle length, n-hexane, showed the dominance of the pR-form of S-Br at a higher temperature, whereas the pS-form was shown at a lower temperature.

Functional thiolactone assisted imprinting cavities with abundant amines for strong binding of protein imprinted nanospheres.

In order to develop new protein imprinting polymerization methods and to prepare protein imprinted nanomaterials with high recognition, a novel protein imprinted strategy is developed in this study by using polyethyleneimine (PEI) for aminolysis of tailor-made thiolactone-based functional monomers and crosslinkers on amine-modified magnetic nanospheres in an aqueous medium. The prepared protein imprinted nanospheres can seize BSA templates in the imprinting polymerization process through multiple hydrogen bonds, and hydrophobic and electrostatic interactions. In addition, the aminolysis reaction also generates abundant amide bonds in the imprinting polymer network, which not only enhances the hydrogen bonding interactions between the imprinted nanospheres and BSA but also improves the stability of the imprinting cavities by increasing the rigidity of the polymer chains. Based on the above advantages, the protein imprinted nanospheres show excellent rebinding specificity for BSA, for which the rebinding capacity is up to 505 ± 15 mg g-1 and the imprinting factor is 4.09. The protein imprinted nanospheres exhibit fast adsorption kinetics, outstanding reusability, and can selectively separate BSA from a protein mixture and actual biological samples. The generality of this imprinted method is also verified. Thus, this study will provide a new idea for the design of protein imprinted materials with high recognition.

Real-time chirality transfer monitoring from statistically random to discrete homochiral nanotubes.

Real time monitoring of chirality transfer processes is necessary to better understand their kinetic properties. Herein, we monitor an ideal chirality transfer process from a statistically random distribution to a diastereomerically pure assembly in real time. The chirality transfer is based on discrete trimeric tubular assemblies of planar chiral pillar[5]arenes, achieving the construction of diastereomerically pure trimers of pillar[5]arenes through synergistic effect of ion pairing between a racemic rim-differentiated pillar[5]arene pentaacid bearing five benzoic acids on one rim and five alkyl chains on the other, and an optically resolved pillar[5]arene decaamine bearing ten amines. When the decaamine is mixed with the pentaacid, the decaamine is sandwiched by two pentaacids through ten ion pairs, initially producing a statistically random mixture of a homochiral trimer and two heterochiral trimers. The heterochiral trimers gradually dissociate and reassemble into the homochiral trimers after unit flipping of the pentaacid, leading to chirality transfer from the decaamine and producing diastereomerically pure trimers.

Ring -opening of polythiolactones to construct protein-imprinted nanospheres with high recognition and regulation capabilities.

Developing and preparing novel protein-imprinted nanomaterials with high recognition ability remains challenging because it is difficult to controllably and orderly design and arrange functional groups on the imprinted polymer layers of protein-imprinted nanomaterials to improve their protein identification. Herein, we present a new technology using rationally designed polythiolactone-decorated magnetic nanospheres as the precursor of multifunctionalized imprinted materials. Moreover, the strategy of ring-opening the polythiolactione layers using primary amines with terminal alcohols, acids and pyrrolidines introduces abundant recognition sites, which enhance the recognition for template proteins through multiple hydrogen-bonding and hydrophobic interactions. Thiols generated in situ by the ring-opening reaction provide sufficient crosslinking sites proximate to each recognition site for the formation of imprinting cavities, endowing the imprinted nanospheres with promising regulation capabilities. Based on the rational design, the imprinted nanospheres can be prepared conveniently and present tunable rebinding capacity and specificity for bovine serum albumin (BSA). The maximum saturated rebinding capacity of imprinted materials for BSA is up to 285 ± 15 mg g-1 and the highest imprinting factor reaches 5.79. The simple and versatile strategy demonstrated in this study shows promise for the design of other protein-imprinted materials with high recognition ability.

Room-Temperature Ring-Opening Polymerization of δ-Valerolactone and ϵ-Caprolactone Caused by Uptake into Porous Pillar[5]arene Crystals.

Confined space provides a reaction platform with altered reaction rate and selectivity compared with a homogeneous solution. In this work, porous phenolic pillar[5]arene crystals were used as a reaction space to promote and perturb equilibrium between lactones and their corresponding polyesters. Immersion of porous pillar[5]arene crystals in liquid lactones induced ring-opening polymerization of δ-valerolactone and ϵ-caprolactone at room temperature because the phenolic hydroxy groups have catalytic activity via hydrogen bonds and the pillar[5]arene cavities prefer linear guests. After the reaction, pillar[5]arene and polyesters formed pseudo-polyrotaxanes.

Discrete Macrocycles with Fixed Chirality and Two Distinct Sides: Dipole-Dependent Chiroptical Response.

Control of symmetry is fundamental in molecular design with aimed properties. Herein we report a set of chiroptical C5 -symmetric molecules with variable dipolar structures based on a rim-differentiated cylindrical macrocycle, pillar[5]arene. Incorporation of electron-withdrawing ester groups formed an explicit two-sided structure, leading to increase in response wavelength and luminescence efficiency. On the other hand, chiroptical measurement of separated enantiomers revealed that such a dipolar character diminished dissymmetry of the electronic transitions. By suppressing the dipole, the dissymmetry factor for luminescence was enhanced from 0.4×10-3 to 5.1×10-3 in a less dipolar methoxy-substituted molecule, which was larger than reported pillar[5]arene derivatives without C5 -symmetry around one order of magnitude.

CPL on/off control of an assembled system by water soluble macrocyclic chiral sources with planar chirality.

Herein, we report the synthesis and planar chiral properties of a pair of water-soluble cationic pillar[5]arenes with stereogenic carbons. Interestingly, although units of the molecules were rotatable, only one planar chiral diastereomer existed in water in both cases. As a new type of chiral source, these molecules transmitted chiral information from the planar chiral cavities to the assembly of a water-soluble extended π-conjugated compound, affording circularly polarized luminescence (CPL). The chirality transfer process and resulting CPL were extremely sensitive to the feed ratio of the chiral pillar[5]arenes owing to the combined action of their planar chirality, bulkiness, and strong binding properties. When a limited amount of chiral source was added, further assembly of the extended π-conjugated compound into helical fibers with CPL was triggered. Unexpectedly, larger amounts of chiral source destroyed the helical fiber assemblies, resulting in elimination of the chirality and CPL properties from the assembled structures.

Noncovalently bound and mechanically interlocked systems using pillar[n]arenes.

Pillar[n]arenes are pillar-shaped macrocyclic compounds owing to the methylene bridges linking the para-positions of the units. Owing to their unique pillar-shaped structures, these compounds exhibit various excellent properties compared with other cyclic host molecules, such as versatile functionality using various organic synthesis techniques, substituent-dependent solubility, cavity-size-dependent host-guest properties in organic media, and unit rotation along with planar chiral inversion. These advantages have enabled the high-yield synthesis and rational design of pillar[n]arene-based mechanically interlocked molecules (MIMs). In particular, new types of pillar[n]arene-based MIMs that can dynamically convert between interlocked and unlocked states through unit rotation have been produced. The highly symmetrical pillar-shaped structures of pillar[n]arenes result in simple NMR spectra, which are useful for studying the motion of pillar[n]arene wheels in MIMs and creating sophisticated MIMs with higher-order structures. The creation and application of polymeric MIMs based on pillar[n]arenes is also discussed.

State- and water repellency-controllable molecular glass of pillar[5]arenes with fluoroalkyl groups by guest vapors.

Molecular glasses are low-molecular-weight organic compounds that are stable in the amorphous state at room temperature. Herein, we report a state- and water repellency-controllable molecular glass by n-alkane guest vapors. We observed that a macrocyclic host compound pillar[5]arene with the C2F5 fluoroalkyl groups changes from the crystalline to the amorphous state (molecular glass) by heating above its melting point and then cooling to room temperature. The pillar[5]arene molecular glass shows reversible transitions between amorphous and crystalline states by uptake and release of the n-alkane guest vapors, respectively. Furthermore, the n-alkane guest vapor-induced reversible changes in the water contact angle were also observed: water contact angles increased and then reverted back to the original state by the uptake and release of the n-alkane guest vapors, respectively, along with the changes in the chemical structure and roughness on the surface of the molecular glass. The water repellency of the molecular glass could be controlled by tuning the uptake ratio of the n-alkane guest vapor.

Reversible "On/Off" Chiral Amplification of Pillar[5]arene Assemblies by Dual External Stimuli.

We report dual-stimuli, thermo- and photostimuli, responsive chiral assemblies, of planar-chiral pillar[5]arenes with azobenzene groups on their rims. The azobenzene-substituted planar-chiral pillar[5]arenes were synthesized by copper(I)-catalyzed alkyne-azide cycloaddition "click" reaction of azide-substituted planar-chiral pillar[5]arenes containing S or R stereogenic carbon atoms with an alkyne-substituted azobenzene. These decaazides with stereogenic carbons could act as starting points for a large library of planar-chiral pillar[5]arenes. Homeotropic alignment of azobenzenes, caused by the mesogenic property of the azobenzene groups, was induced by annealing a film of the azobenzene-substituted planar-chiral pillar[5]arenes. The alignment resulted in chiral propagation from the planar-chiral pillar[5]arene cores to the azobenzene area and caused significant chiral amplification consequently. These aligned chiral assemblies were collapsed by trans to cis photoisomerization of the azobenzene groups, resulting in chiral amplification off, and reconstructed by cis to trans thermo-isomerization, again turning on the chiral amplification.

Pre-regulation of the planar chirality of pillar[5]arenes for preparing discrete chiral nanotubes.

Regulating the chirality of macrocyclic host molecules and supramolecular assemblies is crucial because chirality often plays a role in governing the properties of these systems. Herein, we describe pillar[5]arene-based chiral nanotube formation via pre-regulation of the building blocks' chirality, which is different from frequently used post-regulation strategies. The planar chirality of rim-differentiated pillar[5]arenes is initially regulated by chiral awakening and further induction/inversion through stepwise achiral external stimuli. The pre-regulated chiral information is well stored in discrete nanotubes by interacting with a per-alkylamino-substituted pillar[5]arene. Such pre-regulation is more efficient than post-regulating the chirality of nanotubes.