Fundamental Molecular Design for Precise Control of Thermoresponsiveness of Organic Polymers by Using Ternary Systems

The de novo design of thermosensitive polymers in solution has been achieved by using the addition of small organic molecules (or “effectors”). Hydrogen bonding as an attractive polymer–polymer or polymer–effector interaction substantially dominates the responsivity, causing facile switching between LCST-type and UCST-type phase transitions, control of the transition temperature, and further coincidence of the two transitions. Small molecules having a high affinity for the polymer induce UCST-type phase behavior, whereas those having a low affinity for the polymer showed LCST-type phase behavior

Disassembly Control of Saccharide-Based Amphiphiles Driven by Electrostatic Repulsion

According to the design of disassembly using electrostatic repulsion, novel amphiphiles consisting of a lipophilic ion part and a hydrophilic saccharide part were synthesized via the facile copper-catalyzed click reaction, and their molecular assemblies in water and chloroform were studied. The amphiphiles exhibited a molecular orientation opposite to that of the conventional amphiphiles in each case. ζ Potential measurements indicated that the lipophilic ion part is exposed outside in chloroform. The size of a solvophobic part in the amphiphiles dominates the size of an assembling structure; that is, in water, these amphiphiles tethering different lengths of the saccharide part exhibited almost identical assembling size, whereas in chloroform, the size depends on the length of the saccharide part in the amphiphiles

Ionic Polymers Act as Polyelectrolytes in Nonpolar Media

Polyelectrolytes are ubiquitous materials, and their unique properties originate from dissociation of ionic groups to the small number of macromolecular ions and the large number of small counterions. They have been exploited only in water or high-dielectric media and scarcely in nonpolar ones (ε < 10). Herein, we demonstrate that poly­(octadecyl acrylate) bearing tetraalkylammonium tetraarylborate as ionic groups behaves as a polyelectrolyte in the common nonpolar organic solvents such as chloroform, THF, and 1,2-dichloroethane. Conductivity measurement, DOSY NMR spectroscopy, and viscosity measurements clearly indicate that they form the extended conformation in them. This result emphasizes that the ionic polymers bearing suitable ion pairs ionizable in the given media act as polyelectrolytes. Various characteristic properties and processes of polyelectrolytes should be realized in nonpolar media by designing ion pairs and polymer chains in the ionic polymers. Moreover, our results imply that electrostatic interaction is readily available as a long-range repulsive force even in the nonpolar media

Organic Reaction as a Stimulus for Polymer Phase Separation

Molecular design of stimuli-sensitive polymers has been attracting considerable interest of chemists because of their latent ability to achieve smart materials. Heat, light, pH, and chemicals have been often utilized as a stimuli-inducing polymer phase transition from solution to aggregation and vice versa. In this report, as a new trigger for lower critical solution temperature (LCST)-type polymer phase transition, we introduce organic reaction of small organic molecules, not to the polymer chain itself. The addition of the reactant for the “effector”, which can interact with the polymer chain for increasing the compatibility of the polymer chain with the media, caused a polymer phase separation, due to reduction of the solvation ability of the effector to the polymer chain. In other words, decrease of the “effector” concentration induced the polymer phase separation. Within our knowledge, this is the first report to connect a polymer phase separation with organic reaction dynamics. This process will be the first step for the development of artificial allosteric enzyme mimics from a combination of a simple synthetic polymer and a product or reactant in organic reactions

Stimuli-Responsive Fluorescence of AIE Elastomer Based on PDMS and Tetraphenylethene

We synthesized a tetravinyl AIE luminogen based on tetraphenylethene (<b>TPE-CL</b>), followed by its reaction with H-terminated PDMS via hydrosilylation to construct AIE elastomers. NMR and IR spectroscopy studies showed facile progress of the preparative reaction. The obtained sample strips represented typical elastomeric behavior revealed by tensile test, while the mechanical properties were varied by the chain length of employed PDMS. The homogeneous distribution of <b>TPE-CL</b> in an elastomer was confirmed by UV–vis absorption spectra variation upon increase of <b>TPE-CL</b> content. The elastomers exhibited stimuli-sensitive fluorescence against organic solvents and temperature, and the responsiveness was found to be reversible. These characteristics are clearly derived from AIE property of <b>TPE-CL</b>, which is sensitive to intramolecular rotation

Transformation of Metal–Organic Framework to Polymer Gel by Cross-Linking the Organic Ligands Preorganized in Metal–Organic Framework

Until now, seamless fusion of metal–organic frameworks (MOFs) and covalently cross-linked polymer gels (PG) at molecular level has been extremely rare, since these two matters have been regarded as opposite, that is, hard versus soft. In this report, we demonstrate transformation of cubic MOF crystals to PG via inner cross-linking of the organic linkers in the void space of MOF, followed by decomposition of the metal coordination. The obtained PG behaved as a polyelectrolyte gel, indicating the high content of ionic groups inside. Metal ions were well adsorbed in the PG due to its densely packed carboxylate groups. A chimera-type hybrid material consisting of MOF and PG was obtained by partial hydrolysis of resulting cross-linked MOF. The shape of resulting PG network well reflected the crystal structure of MOF employed as a template. Our results will connect the two different network materials that have been ever studied in the two different fields to provide new soft and hard hybrid materials, and the unique copolymerization in the large void space of the MOF will open a new horizon toward “ideal network polymers” never prepared before now

Twist of CC Bond Plays a Crucial Role in the Quenching of AIE-Active Tetraphenylethene Derivatives in Solution

Aggregation-induced emission (AIE) has emerged as a new class of attractive photoluminescence behavior. Understanding the precise mechanism of the AIE phenomenon will lead to the rational molecular design of novel molecules with AIE properties (AIEgens). In this work, we selected disubstituted derivatives of tetraphenylethene (TPE), a well-known archetypal AIEgen, as the model compounds to elucidate the AIE mechanism. As the result of photochemical experiments and quantum chemical computations, π-bond twist (π twist), including <i>E</i>–<i>Z</i> isomerization (EZI), was found to be the major factor for quenching the photoexcited state of TPE derivatives in the solution state, differently from the well-accepted propeller-like rotation of the side phenyl groups in earlier research. In photochemical experiments, the prepared TPE derivatives exhibited EZI in the solution state upon photoirradiation, and a negative correlation was observed between this isomerization and the AIE phenomenon. The theoretical computations verified the crucial role of π twist triggered by photoirradiation in the solution state, rather than intramolecular rotation. In the crystal state, π twist was efficiently suppressed by the surrounding molecules. Our results will support the realization of novel smart AIEgens that can respond to various external stimuli

Stable and Functional Gold Nanorod Composites with a Metal–Organic Framework Crystalline Shell

Practical and functional surface-enhanced Raman scattering (SERS)-active nanomaterials working in solution require a protecting shell. In this study, we demonstrate the fabrication of gold nanorods coated by metal–organic frameworks of several hundred nanometers in size, which is one kind of crystalline porous materials, as s suspension-based SERS sensor. The composites also showed enough stability and reproducibility for detection of the guest molecules

Biomolecular Motor Modulates Mechanical Property of Microtubule

The microtubule (MT) is the stiffest cytoskeletal filamentous protein that takes part in a wide range of cellular activities where its mechanical property plays a crucially significant role. How a single biological entity plays multiple roles in cell has been a mystery for long time. Over the recent years, it has been known that modulation of the mechanical property of MT by different cellular agents is the key to performing manifold in vivo activities by MT. Studying the mechanical property of MT thus has been a prerequisite in understanding how MT plays such diversified in vivo roles. However, the anisotropic structure of MT has been an impediment in obtaining a precise description of the mechanical property of MT along its longitudinal and lateral directions that requires employment of distinct experimental approach and has not been demonstrated yet. In this work, we have developed an experimental system that enabled us to investigate the effect of tensile stress on MT. By using our newly developed system, (1) we have determined the Young’s modulus of MT considering its deformation under applied tensile stress and (2) a new role of MT associated motor protein kinesin in modulating the mechanical property of MT was revealed for the first time. Decrease in Young’s modulus of MT with the increase in interaction with kinesin suggests that kinesin has a softening effect on MT and thereby can modulate the rigidity of MT. This work will be an aid in understanding the modulation of mechanical property of MTs by MT associated proteins and might also help obtain a clear insight of the endurance and mechanical instability of MTs under applied stress

Motility of Microtubules on the Inner Surface of Water-in-Oil Emulsion Droplets

Water-in-oil emulsion systems have recently attracted much attention in various fields. However, functionalization of water-in-oil emulsion systems, which is required for expanding their applications in industries and research, has been challenging. We now demonstrate the functionalization of a water-in-oil emulsion system by anchoring a target protein molecule. A microtubule (MT)-associated motor protein kinesin-1 was successfully anchored to the inner surface of water-in-oil emulsion droplets by employing the specific interaction of nickel–nitrilotriacetic acid–histidine tag. The MTs exhibited a gliding motion on the kinesin-functionalized inner surface of the emulsion droplets, which confirmed the success of the functionalization of the water-in-oil emulsion system. This result would be beneficial in exploring the roles of biomolecular motor systems in the cellular events that take place at the cell membrane and might also contribute to expanding the nanotechnological applications of biomolecular motors and water-in-oil emulsion systems in the future