Yeonweon Choi

Calix[4]arene-based fluorescent probe and the adsorption capacity of its electrospun nanofibrous film for the cesium cation as an adsorbent

Abstract Calix[4]arene-based cation receptor 1 has been synthesised by following a multi-step synthetic procedure. The fluorescence properties of 1 upon the addition of various metal ions were investigated by fluorescence spectroscopy. As a result, it was revealed that 1 displayed dramatic quenching effect upon the exposure to Cs+. In contrast, no significant quenching effects were observed upon the addition of other metal ions such as Li+, Na+, K+, Mg2+, Ca2+, Sr2+, Ag+, Zn2+ and Ni2+. Compound 1 was also found by Job plot to form a 1:1 complex with Cs+. In addition, we also prepared 1-embedded electrospun nanofibrous film (NF-1) as an adsorbent for Cs+. NF-1 is proved to adsorb Cs+ effectively from an aqueous solution, indicating that it would be usefully utilised as an adsorbent to remove Cs+.

Unusual fluorescence and sol–gel transition properties of a pyridine-based polymeric gel formed via the hydrazone reaction

A polymeric gel via the hydrazone reaction was prepared. A remarkable fluorescence attributed to the aggregation-induced emission (AIE) effect occurred via a gelation process, which was not seen in its sol state. The fluorescence intensity of the polymeric gel was dependent on the concentration of HCl. Furthermore, the gel underwent a sol–gel transition at ca. 140 °C. This property is uniquely different in comparison with general polymeric gels.

Self-Assembled Coumarin Nanoparticle in Aqueous Solution as Selective Mitochondrial-Targeting Drug Delivery System

The development of specifically targeted nanoparticles for subcellular organelles modified with a low-molecular-weight organic compound as drug nanocarriers can bring about wide applications in cancer therapy. However, their utility has been hampered by low selectivity, poor biodistribution, and limited efficiency. Herein, we report the aggregation behavior of a triphenylphosphonium-appended coumarin probe (TPP-C) in an aqueous solution and its applications as a mitochondria-targeting probe, and drug delivery carrier, which is a rare example for a low molecular-weight organic compound. The TPP-C formed homogeneous nanoparticles with small diameters in water as well as in mixtures of organic solvents and water. In pure water, the homogeneous nanoparticles induced J-aggregation, whereas in mixed solvents, the homogeneous nanoparticles induced H-aggregation. The luminescence intensities of nanoparticles originated from the aggregation-induced emission (AIE) effect in pure water and also in mixtures of organic solvents and water. These findings indicate that the AIE effect of TPP-C was dependent on the solvent. More interestingly, the TPP-C nanoparticles selectively accumulated in mitochondria. The TPP-C nanoparticles alone exhibited noncytotoxicity toward cancer cells. However, with the encapsulation of the anticancer drug doxorubicin (DOX) into the TPP-C nanoparticles, the DOX was efficiently delivered to the mitochondria. These results indicated that the proposed system demonstrates promise as a platform for future clinical medication, particularly for specific suborganelle-targeted drug delivery systems for cancer therapy.

Bis(naphthol)-based fluorescent chemoprobe for cesium cation and its immobilisation on silica nanoparticle as a high selective adsorbent

Abstract A bis(naphthol)-based cation receptor 1 has been synthesised by three steps of synthetic procedure. The spectroscopic properties of 1 upon addition of various metal ions were investigated by UV–vis absorption and fluorescence spectroscopy. As a result, the absorption of 1 was linearly decreased as a function of concentration of added Cs+. Also, 1 exhibited dramatic fluorescence quenching effect upon exposure to caesium cation. Contrastively, no significant quenching effect was observed upon addition of other metal ions such as Na+, K+, Rb+, Mg2+, Ca2+, Sr2+, Ba2+, Ni2+ and Zn2+. It was found that 1 formed a 1:1 complex with Cs+ by Job’s plot. Furthermore, we also prepared 1-functionalised silica nanoparticle (SiO2-1) as an adsorbent for Cs+. SiO2-1 showed a great capacity for selective removal of caesium ion from aqueous solution as well as from tap water. Thus, it is potentially useful for the detection and removal of caesium cation from environmental and biological fluids polluted by nuclear radiation and nuclear waste.

Selective detection of Hg2+ using fluorescent rhodamine-functionalized Fe3O4 nanoparticles

Novel hybrid nanomagnets functionalized with a rhodamine derivative were prepared, and their spectroscopic behavior in the selective detection and removal of Hg2+ was investigated. Selective sensing of mercury ions was followed by a structural transformation of the rhodamine motif to a highly conjugated xanthene moiety, causing a ca. 5.3-fold fluorescence enhancement. Moreover, the selective detection and removal of Hg2+ by the hybrid nanomagnets in the presence of other metal ions were confirmed by fluorescence spectroscopy. These findings provide a promising new method for the detection and removal of Hg2+ from environmental pollutants.

Origin of Both Right- and Left-Handed Helicities in a Supramolecular Gel with and without Ni2+ at the Supramolecular Level

We demonstrate the different origins of helical directions in polymeric gels derived from a hydrazone reaction in the absence and presence of Ni2+. The right-handed helicity of polymeric gels without Ni2+ originates from the enantiomeric d-form alanine moiety embedded in the building block. However, the right-handed helicity is inverted to a left-handed helicity upon the addition of Ni2+, indicating that added Ni2+ greatly affects the conformation of the polymeric gel by overcoming the influence of the enantiomer embedded in the building block on the helicity at the supramolecular level. More interestingly, the ratio of the right-toleft-handed helical fibers varies with the concentration of Ni2+, which converts from 100% right-handed helical fiber to 90% left-handed helical fiber. In the presence of Ni2+, both right- and left-handed helical fibers coexist at the supramolecular level. Some fibers also exhibit both right- and left-handed helicities in a single fiber.

Retracted Article: Spatially resolved mechanical properties of photo-responsive azobenzene-based supramolecular gels

The viscoelastic and stiffness properties of azobenzene-based supramolecular gels have been investigated by rheometry and AFM. Interestingly, the viscoelastic properties of cis-isomers were 8–10 fold enhanced in comparison to the trans-isomer, which was a unique phenomenon. More interestingly, Youngs modulus of gels increased linearly with time of UV irradiation. The stiffness of gels was finely controlled in the spatial micro-scale environment. The improved mechanical strength was attributed to electrostatic interaction with the production of radicals of the gelators.

Reversible cyanovinylcarbazole-based polymer gel via photo-cross-linking reaction

Abstract A polymeric gel was prepared from a bis(3-cyanovinylcarbazole)-based derivative and a thymine-bearing calix[4]arene derivative via photo-cross-linking between 3-cyanovinylcarbazole and thymine groups by irradiation with 365 nm UV light, a novel and facile method to obtain a soft material. Values for storage and loss moduli of the bis(3-cyanovinylcarbazole)-based derivative and the thymine-bearing calix[4]arene derivative gradually increased during photoirradiation. This gel was transformed back to the solution state by decomposition of the polymer network to the monomers via irradiation with 312 nm UV light.

Correction: A crown-ether-based moldable supramolecular gel with unusual mechanical properties and controllable electrical conductivity prepared by cation-mediated cross-linking

Typical supramolecular gels do not exhibit electrical conductivity because of the wide band gaps present in the low-conjugation gelator molecules and the long distances between them, which arise because of the large amount of solvent within gel networks. Consequently, the practical applications of supramolecular gels are largely limited. Herein, a strategy for significantly enhancing the mechanical, electrical, and vibrational isolation properties of supramolecular gels derived from low-molecular-weight building blocks, which involves the incorporation of Cs+ ions, is described. High-elasticity supramolecular gels produced from the hydrazone reaction between calix[4]arene- and 18-crown-6-ether-based building blocks are mechanically strong and can be molded into free-standing objects. By controlling the concentration of Cs+ in the supramolecular gels, their mechanical and electrical properties can be tuned. The supramolecular gels exhibit 34-fold and 62-fold enhanced storage and loss moduli, respectively, upon addition of Cs+ ions. Furthermore, the electrical conductivities of the supramolecular gels proportionally increase with the amount of Cs+ ions in the gel network. These dramatic enhancements are due to the sandwich complex formation between the 18-crown-6 moieties and Cs+ ions. Also, the supramolecular gels reveal effective vibration-isolation abilities. It is believed that this strategy presents new possibilities for developing soft materials with unique functions.

Non-peptidic guanidinium-functionalized silica nanoparticles as selective mitochondria-targeting drug nanocarriers

We report on the design and fabrication of a Fe3O4 core-mesoporous silica nanoparticle shell (Fe3O4@MSNs)-based mitochondria-targeting drug nanocarrier. A guanidinium derivative (GA) was conjugated onto the Fe3O4@MSNs as the mitochondria-targeting ligand. The fabrication of the Fe3O4@MSNs and their functionalization with GA were carried out by the sol-gel polymerization of alkoxysilane groups. Doxorubicin (DOX), an anti-cancer drug, was loaded into the pores of a GA-attached Fe3O4@MSNs due to both its anti-cancer properties and to allow for the fluorescent visualization of the nanocarriers. The selective and efficient mitochondria-targeting ability of a DOX-loaded GA-Fe3O4@MSNs (DOX/GA-Fe3O4@MSNs) was demonstrated by a co-localization study, transmission electron microscopy, and a fluorometric analysis on isolated mitochondria. It was found that the DOX/GA-Fe3O4@MSNs selectively accumulated into mitochondria within only five minutes; to the best of our knowledge, this is the shortest accumulation time reported for mitochondria targeting systems. Moreover, 2.6 times higher amount of DOX was accumulated in mitochondria by DOX/GA-Fe3O4@MSNs than by DOX/TPP-Fe3O4@MSNs. A cell viability assay indicated that the DOX/GA-Fe3O4@MSNs have high cytotoxicity to cancer cells, whereas the GA-Fe3O4@MSNs without DOX are non-cytotoxic; this indicates that the DOX/GA-Fe3O4@MSNs have great potential for use as biocompatible and effective mitochondria-targeting nanocarriers for cancer therapy.