Photoreconfigurable Supramolecular Nanotube

A photoreconfigurable bionanotube was developed by Mg²⁺-induced supramolecular polymerization using GroEL_SP, a mutant barrel-shaped chaperonin protein bearing multiple photochromic spiropyran (SP) units at its apical domains. Upon exposure to UV light, the nonionic SP units isomerize into ionic merocyanine (MC) to afford GroEL_MC, which is capable of polymerizing with MgCl₂. The resultant nanotube (NT) is stable as a result of multiple MC···Mg²⁺···MC bridges but readily breaks up into short NTs, including monomeric GroEL_SP, by the reverse (MC → SP) isomerization mediated by visible light. When this scission mixture is exposed to UV light, long NTs are reconfigured. A Förster resonance energy transfer (FRET) study revealed that NTs in the dark maintain their sequential integrity. However, when exposed to visible and UV light successively, the NTs lose their sequential memory as a result of intertubular reshuffling of the constituent GroEL_MC units

Crystalline Nanochannels with Pendant Azobenzene Groups: Steric or Polar Effects on Gas Adsorption and Diffusion?

An azobenzene-containing, zirconium-based metal–organic framework (^AzoMOF), upon irradiation with ultraviolet (UV) light at 365 ± 10 nm, underwent <i>trans</i>-to-<i>cis</i> isomerization of its azobenzene pendants to furnish the <i>cis</i>-isomer content of 21% (^AzoMOF^21%) in 30 min at the photostationary state and underwent backward isomerization into ^AzoMOF^1% upon either irradiation with visible light (420–480 nm) or heating. When the <i>cis</i>-isomer content increased, the diffusion rate and amount of CO₂ adsorbed into the nanochannels of ^AzoMOF decreased considerably. When erythrosine B, a polarity-probing guest, was used, it showed a red shift upon exposure of ^AzoMOF^20%⊃EB to visible light, indicating that the interior environment of ^AzoMOF turns less polar as the <i>trans</i>-isomer content becomes higher. In sharp contrast, the adsorption profiles of ^AzoMOF^15% and ^AzoMOF^1% for Ar having an analogous kinetic diameter to CO₂ but no quadrupole moment and a smaller polarizability were virtually identical to one another. Therefore, it is likely that CO₂ experiences a dominant effect of a polar effect rather than a steric effect in the crystalline nanochannels

Caged Molecular Glues as Photoactivatable Tags for Nuclear Translocation of Guests in Living Cells

We developed dendritic caged molecular glues (^CagedGlue-R) as tags for nucleus-targeted drug delivery, whose multiple guanidinium ion (Gu⁺) pendants are protected by an anionic photocleavable unit (butyrate-substituted nitroveratryloxycarbonyl; ^BANVOC). Negatively charged ^CagedGlue-R hardly binds to anionic biomolecules because of their electrostatic repulsion. However, upon exposure of ^CagedGlue-R to UV light or near-infrared (NIR) light, the ^BANVOC groups of ^CagedGlue-R are rapidly detached to yield an uncaged molecular glue (^UncagedGlue-R) that carries multiple Gu⁺ pendants. Because Gu⁺ forms a salt bridge with PO₄^–, ^UncagedGlue-R tightly adheres to anionic biomolecules such as DNA and phospholipids in cell membranes by a multivalent salt-bridge formation. When tagged with ^CagedGlue-R, guests can be taken up into living cells via endocytosis and hide in endosomes. However, when the ^CagedGlue-R tag is photochemically uncaged to form ^UncagedGlue-R, the guests escape from the endosome and migrate into the cytoplasm followed by the cell nucleus. We demonstrated that quantum dots (QDs) tagged with ^CagedGlue-R can be delivered efficiently to cell nuclei eventually by irradiation with light

Self-Sorting in the Formation of Metal–Organic Nanotubes: A Crucial Role of 2D Cooperative Interactions

A mixture of ferrocene-based tetratopic pyridyl ligands <b>FcL1</b> and <b>FcL2</b> undergoes self-sorting upon competitive coordination with AgBF₄, affording homomeric nanotubes <b>FcNT1</b> and <b>FcNT2</b> as a mixture. No mutual interference for the nanotubular growth occurred between <b>FcNT1</b> and <b>FcNT2</b> even when one of these ligands was used in large excess with respect to the other. 2D X-ray diffraction analysis of unidirectionally oriented nanotube samples, prepared by using the capillary technique, revealed that although <b>FcL1</b> as reported previously stacks helically in the resulting nanotube <b>FcNT1</b> <b>FcL2</b> prefers to stack with no discernible helical twist in <b>FcNT2</b>. Such a difference in their stacking geometries is most likely a major reason for why mixed-ligand metal–organic nanotubes are not constructed upon competitive coordination of <b>FcL1</b> and <b>FcL2</b> with AgBF₄

Friction-Mediated Dynamic Disordering of Phospholipid Membrane by Mechanical Motions of Photoresponsive Molecular Glue: Activation of Ion Permeation

A water-soluble photoresponsive molecular glue, Azo-¹⁸Glue, consisting of a photochromic azobenzene core and two adhesive dendritic wedges with a total of 18 peripheral guanidinium ion (Gu⁺) pendants tightly adheres to the surface of a phospholipid membrane, even in buffer, via a multivalent salt-bridge formation with phosphate anions. A photomechanical motion of adhering Azo-¹⁸Glue possibly gives rise to dynamic structural disordering of the phospholipid membrane and activates transmembrane ion permeation. In sharp contrast, no activation of ion permeation results when poorly adhesive Azo-⁶Glue carrying only six Gu⁺ pendants is used in place of Azo-¹⁸Glue

“Photochemical Surgery” of 1D Metal–Organic Frameworks with a Site-Selective Solubilization/Crystallization Strategy

One-dimensional (1D) hybrid MOFs are attractive if they consist of different MOF blocks with interconnected channels. However, the precision synthesis of such 1D multiblock MOFs with the desired block lengths and sequences remains a formidable challenge. Herein we propose the “photochemical surgery” method, which combines top-down and bottom-up approaches to enable the site-selective solubilization (removal)/crystallization (reconstruction) of 1D MOFs. We employed photoreactive MOFs, which were prepared by complexing either Cd2+ or Zn2+ with a mixture containing a photochromic bispyridyl ligand (PyDTEopen or PyDTZEopen) and an isophthalate (5-nitroisophthalate (nip2–) or 5-bromoisophthalate (bip2–)). These MOFs were obtained as high-aspect-ratio, needlelike, colorless crystals that bore 1D channels oriented parallel to the long needle axis. When photoreactive DTECdMOFNO2 ([Cd(nip)(PyDTEopen)(H2O)]n), for example, was immobilized at both ends with a metal alloy on a glass substrate and exposed to UV light through a photomask for 60 min in N,N-dimethylformamide/methanol (DMF/MeOH), the unmasked part was removed via solubilization to produce a 50 μm gap. The resulting specimen was immersed for 24 h at 25 °C in DMF/MeOH containing the necessary components for the construction of DTZECdMOFNO2 ([Cd(nip)(PyDTZEopen)(H2O)]n). Eventually, the gap was filled with DTZECdMOFNO2 to produce a triblock hybrid MOF (DTECdMOFNO2–​DTZECdMOFNO2–​DTECdMOFNO2). The result of a guest diffusion experiment confirmed that the newly formed DTZECdMOFNO2 block shared its 1D channels with the host DTECdMOFNO2 blocks. “Photochemical surgery” can be applied to synthesize 1D hybrid MOFs bearing unconventional sequences and morphologies, e.g., honeycomb- and inverted-honeycomb-patterned hybrids

“Photochemical Surgery” of 1D Metal–Organic Frameworks with a Site-Selective Solubilization/Crystallization Strategy

One-dimensional (1D) hybrid MOFs are attractive if they consist of different MOF blocks with interconnected channels. However, the precision synthesis of such 1D multiblock MOFs with the desired block lengths and sequences remains a formidable challenge. Herein we propose the “photochemical surgery” method, which combines top-down and bottom-up approaches to enable the site-selective solubilization (removal)/crystallization (reconstruction) of 1D MOFs. We employed photoreactive MOFs, which were prepared by complexing either Cd2+ or Zn2+ with a mixture containing a photochromic bispyridyl ligand (PyDTEopen or PyDTZEopen) and an isophthalate (5-nitroisophthalate (nip2–) or 5-bromoisophthalate (bip2–)). These MOFs were obtained as high-aspect-ratio, needlelike, colorless crystals that bore 1D channels oriented parallel to the long needle axis. When photoreactive DTECdMOFNO2 ([Cd(nip)(PyDTEopen)(H2O)]n), for example, was immobilized at both ends with a metal alloy on a glass substrate and exposed to UV light through a photomask for 60 min in N,N-dimethylformamide/methanol (DMF/MeOH), the unmasked part was removed via solubilization to produce a 50 μm gap. The resulting specimen was immersed for 24 h at 25 °C in DMF/MeOH containing the necessary components for the construction of DTZECdMOFNO2 ([Cd(nip)(PyDTZEopen)(H2O)]n). Eventually, the gap was filled with DTZECdMOFNO2 to produce a triblock hybrid MOF (DTECdMOFNO2–​DTZECdMOFNO2–​DTECdMOFNO2). The result of a guest diffusion experiment confirmed that the newly formed DTZECdMOFNO2 block shared its 1D channels with the host DTECdMOFNO2 blocks. “Photochemical surgery” can be applied to synthesize 1D hybrid MOFs bearing unconventional sequences and morphologies, e.g., honeycomb- and inverted-honeycomb-patterned hybrids

Helix Sense-Selective Supramolecular Polymerization Seeded by a One-Handed Helical Polymeric Assembly

Helix sense-selective supramolecular polymerization was achieved using a one-handed helical nanotubular polymeric assembly as a seed. First, bipyridine (BPY)-appended achiral hexabenzocoronene (^BPYHBC) was copolymerized noncovalently with chiral ^BPYHBC_<i>S</i> (or ^BPYHBC_<i>R</i>) at a molar ratio of 9:1, which, via the sergeants-and-soldiers effect, afforded a <i>P</i>-helical (or <i>M</i>-helical) nanotube, which was then treated with Cu²⁺ to transform into structurally robust ^(BPY)CuNT_(<i>P</i>) (or ^(BPY)CuNT_(<i>M</i>)) with a Cu²⁺/BPY coordination polymer shell. Helical seeds ^(BPY)CuNT_(<i>P</i>) and ^(BPY)CuNT_(<i>M</i>) brought about the controlled assembly of fluorinated chiral FHBC_<i>S</i> and FHBC_<i>R</i> as well as achiral FHBC to yield one-handed helical nanotubular supramolecular block copolymers, in which the helical senses of the newly formed block segments were solely determined by those of the helical seeds employed. Noteworthy, FHBC_<i>S</i> and FHBC_<i>R</i> alone without the helical seeds form ill-defined agglomerates. Attempted supramolecular polymerization of a racemic mixture of FHBC_<i>S</i> and FHBC_<i>R</i> from ^(BPY)CuNT_(<i>P</i>) (or ^(BPY)CuNT_(<i>M</i>)) resulted in its chiral separation, affording <i>P</i>-helical (or <i>M</i>-helical) diastereomeric block segments composed of FHBC_<i>S</i> and FHBC_<i>R</i> with different thermodynamic properties

Dynamic or Nondynamic? Helical Trajectory in Hexabenzocoronene Nanotubes Biased by a Detachable Chiral Auxiliary

When ether vapor was allowed to diffuse into a CH₂Cl₂ solution of an enantiomer of a hexa-<i>peri</i>-hexabenzocoronene (HBC) derivative carrying a chiral (BINAP)­Pt­(II)-appended coordination metallacycle (HBC^Py_{[(<i>R</i>)‑Pt]} or HBC^Py_{[(<i>S</i>)‑Pt]}), screw-sense-selective assembly took place to give optically active nanotubes (NT^Py_{[(<i>R</i>)‑Pt]} or NT^Py_{[(<i>S</i>)‑Pt]}) with helical chirality, which were enriched in either left-handed (<i>M</i>)-NT^Py_{[(<i>R</i>)‑Pt]} or right-handed (<i>P</i>)-NT^Py_{[(<i>S</i>)‑Pt]}, depending on the absolute configuration of the (BINAP)­Pt­(II) pendant. When MeOH was used instead of ether for the vapor-diffusion-induced assembly, nanocoils formed along with the nanotubes. As determined by scanning electron microscopy, the diastereomeric excess of the nanocoils was 60% (80:20 diastereomeric ratio). Removal of the (BINAP)­Pt­(II) pendants from NT^Py_{[(<i>R</i>)‑Pt]} or NT^Py_{[(<i>S</i>)‑Pt]} with ethylenediamine yielded metal-free nanotubes (NT^Py) that remained optically active even upon heating without any change in the circular dichroism spectral profile. No helical inversion took place when NT^Py derived from HBC^Py_{[(<i>R</i>)‑Pt]} or HBC^Py_{[(<i>S</i>)‑Pt]} was allowed to complex with (BINAP)­Pt­(II) with an absolute configuration opposite to the original one

Redox-Responsive Chiral Dopant for Quick Electrochemical Color Modulation of Cholesteric Liquid Crystal

Here, we report the first redox-active chiral dopant ^{<i><b>Fc</b></i>}<b>D</b>, which electrically alters its helical twisting power (HTP) for a cholesteric liquid crystalline (LC) medium and quickly changes the reflection color. ^{<i><b>Fc</b></i>}<b>D</b> is composed of an axially chiral binaphthyl unit in conjunction with a redox-active ferrocene unit. A cholesteric LC phase of 4′-pentyloxy-4-cyanobiphenyl, doped with ^{<i><b>Fc</b></i>}<b>D</b> (3.0 mol %), developed a blue reflection color. When nitrosyl tetrafluoroborate, a one-electron oxidant, was added to this cholesteric LC phase, ^{<i><b>Fc</b></i>}<b>D</b> was oxidized to decrease its original HTP value by 13%, so that a green reflection color was developed. In the presence of a supporting electrolyte, the reflection color was electrochemically modulated using a sandwich-type glass cell with indium tin oxide electrodes. In quick response to the applied voltage of +1.5 V, the reflection color changed from blue to green within 0.4 s. When 0 V was applied, the reflection color returned to its original blue color. The ^{<i><b>Fc</b></i>}<b>D</b>-doped cholesteric LC is characterized by its fastest electrochemical response and lowest operating voltage among those reported for electrically driven cholesteric LC devices