Photoinduced isothermal phase transitions of liquid-crystalline macrocyclic azobenzenes

Liquid-crystalline macrocyclic compounds, tethered by two or three azobenzenes bearing alkoxy side chains, exhibit isothermal phase transitions from liquid-crystal to isotropic as well as from crystal to isotropic phases upon light irradiation due to the drastic conformational change of their macrocyclic backbone.     

Phase behavior and rheology of oil-swollen micellar cubic phase and gel emulsions in nonionic surfactant systems

We have studied the phase behavior and rheological property of the cubic phase and related gel emulsions in water/nonionic/dodecane systems. In the phase behavior study, it is pointed out that the formation of the discontinuous cubic phase (I₁) is not common in all nonionic surfactant systems; however, a cubic phase (I₁) with oil-swollen micelles or a cubic phase microemulsion is found in the water/C₁₆EO₆/dodecane system, which can solubilize large amount of oil. It was also observed that water/C₁₆EO₆/dodecane system forms stable gel emulsion. In the rheological study we have found an anomalous behavior of the I₁ phase in the water/C₁₂EO₆/dodecane and the water/C₁₆EO₆/dodecane systems. In the water/C₁₂EO₆/dodecane system, the viscoelastic nature of the I₁ phase has been observed, which is shifted to the elastic nature with the addition of dodecane, whereas, highly elastic nature was observed in the water/C₁₆EO₆/dodecane system. In both the cases shear-thinning behavior were seen. The elastic modulus, G′ and complex viscosity, |η1| of the I₁ phase increase with the dodecane concentration in the water/C₁₂EO₆/dodecane system, whereas, decreasing trend have been observed in the water/C₁₆EO₆/dodecane system. This anomalous behavior is suggested due to the nonspherical shape of micelles or polydispersity of the micelles in the water/C₁₆EO₆/dodecane system. The rheological behavior of the O/I₁ gel emulsion was also studied in both the systems.     

Structural, magnetic, and electrochemical studies on lithium insertion materials LiNi1−xCoxO2 with 0≤x≤0.25

The structural, magnetic, and electrochemical properties of the LiNi_1−xCo_xO₂ samples with x= 0, 0.05, 0.1, and 0.25 have been investigated by powder X-ray diffraction analyses, magnetic susceptibility (χ) measurements, and electrochemical charge and discharge test in non-aqueous lithium cell. According to the structural analyses using a Rietveld method, the occupancy of the Ni ions in the Li layer was estimated to be below 0.01 for all the samples and was eventually independent of x. The temperature (T) dependence of χ⁻¹ obtained with the magnetic field H=10 kOe indicated that all the samples are a Curie-Weiss paramagnet down to . At low T, all the samples entered into a spin-glass-like phase below T_f. The magnitude of T_f was found to decrease almost linearly with x, as in the case for the x dependences of the lattice parameters of a_h- and c_h-axes, Weiss temperature, and effective magnetic moment. It is, therefore, found that the change of the magnetic properties with x is simply explained by a dilution effect due to the increase of the quantity of Co³⁺ ions. On the other hand, the electrochemical measurements demonstrated that the irreversible capacity at the initial cycle is drastically decreased by the small amount of Co ions. Furthermore, the discharge capacity (Q_dis) for the x=0.05 and 0.1 samples are larger than that for the x=0 sample; namely, Q_dis=180 mAh g⁻¹ for x=0, Q_dis=217 mAh g⁻¹ for x=0.05, and Q_dis=206 mAh g⁻¹ for x=0.1. Comparing with the past results, the amount of Ni ions in the Li layer is found to play a significant role for determining the magnetic and electrochemical properties of LiNi_1−xCo_xO₂.     

A comparison between the bond-strength-coordination number fluctuation model and the random walk model of viscosity

We have studied the temperature dependence of the viscosity of some polymeric materials by using both, the bond-strength-coordination number fluctuation model and the random walk model. The results reveal that both models show an excellent agreement with the experimental data. For the random walk model, two equations corresponding to two temperature regimes (low-T and high-T) separated by the critical temperature T _c, which is difficult to determine, are needed to describe the temperature dependence of the viscosity of a fragile system, whereas for the bond-strength-coordination number fluctuation model, a single equation with clear physical meaning describes the temperature dependence of the viscosity of both, the fragile and strong systems. We have also studied the relationship between the normalized temperature range of cooperativity and the fragility index. A theoretical expression for the relationship has been derived based on the bond-strength-coordination number fluctuation model. The comparison with the experimental data shows a good agreement, leading to the conclusion that the kinetic properties of glass forming liquids and the cooperativity of molecular relaxations are correlated.     

Folding pathways of human telomeric type-1 and type-2 G-quadruplex structures

We have investigated new folding pathways of human telomeric type-1 and type-2 G-quadruplex conformations via intermediate hairpin and triplex structures. The stabilization energies calculated by ab initio methods evidenced the formation of a hairpin structure with Hoogsteen GG base pairs. Further calculations revealed that the G-triplet is more stable than the hairpin conformation and equally stable when compared to the G-tetrad. This indicated the possibility of a triplex intermediate. The overall folding is facilitated by K(+) association in each step, as it decreases the electrostatic repulsion. The K(+) binding site was identified by molecular dynamics simulations. We then focused on the syn/anti arrangement and found that the anti conformation of deoxyguanosine is more stable than the syn conformation, which indicated that folding would increase the number of anti conformations. The K(+) binding to a hairpin near the second lateral TTA loop was found to be preferable, considering entropic effects. Stacking of G-tetrads with the same conformation (anti/anti or syn/syn) is more stable than mixed stacking (anti/syn and vice versa). These results suggest the formation of type-1 and type-2 G-quadruplex structures with the possibility of hairpin and triplex intermediates.     

Complex mixture analysis of organic compounds in green coffee bean extract by two‐dimensional NMR spectroscopy

A complex mixture analysis by one‐ and two‐dimensional nuclear magnetic resonance (NMR) spectroscopy was carried out for the first time for the identification and quantification of organic compounds in green coffee bean extract (GCBE). A combination of ¹H? ¹H DQF‐COSY, ¹H? ¹³C HSQC, and ¹H? ¹³C CT‐HMBC two‐dimensional sequences was used, and 16 compounds were identified. In particular, three isomers of caffeoylquinic acid were identified in the complex mixture without any separation. In addition, GCBE components were quantified by the integration of carbon signals by use of a relaxation reagent and an inverse‐gated decoupling method without a nuclear Overhauser effect. This NMR methodology provides detailed information about the kinds and amounts of GCBE components, and in our study, the chemical makeup of GCBE was clarified by the NMR results. Copyright © 2010 John Wiley & Sons, Ltd.     

Microstructure and mechanical properties of bacterial cellulose/chitosan porous scaffold

A family of polysaccharide based scaffold materials, bacterial cellulose/chitosan (BC/CTS) porous scaffolds with various weight ratios (from 20/80 to 60/40 w/w%) were prepared by freezing (−30 and −80 °C) and lyophilization of a mixture of microfibrillated BC suspension and chitosan solution. The microfibrillated BC (MFC) was subjected to 2,2,6,6-tetramethylpyperidine-1-oxyl radical (TEMPO)-mediated oxidation to introduce surface carboxyl groups before mixing. The integration of MFC within chitosan matrix was performed by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC)-mediated cross-linking. The covalent amide bond formation was determined by ATR-FTIR. Because of this covalent coupling, the scaffolds retain their original shapes during autoclave sterilization. The composite scaffolds are three-dimensional open pore microstructure with pore size ranging from 120 to 280 μm. The freezing temperature and mean pore size take less effect on scaffold mechanical properties. The compressive modulus and strength increased with increase in MFC content. The results show that the scaffolds of higher MFC content contribute to overall better mechanical properties.     

Liposomalization of hydroxyphenyl fluorescein as a reagent for detecting highly reactive oxygen species

It has been shown that lifestyle-related diseases and aging are related to reactive oxygen species (ROS), and many studies have reported on the direct detection of ROS. The topical fluorescence reagent 2,7-dichlorodihydrofluorescein (DCDHF) is used to measure oxidation. However, there are problems regarding its stability, and its similar sensitivity to ROS cannot be easily distinguished. In this study, we used hydroxyphenyl fluorescein (HPF), which is a novel fluorescence probe with high stability against light that undergoes specific reactions with highly ROS (hROS). We examined the specificity for hROS of HPF solution and liposomal HPF in different reactions. HPF containing high cholesterol liposomes (HC-H-lipo) maintained its ability to tolerate light scattering energy, dependent on the turbidity of this solution, but DCDHF did not. In the reaction with hydroxyl radicals, the fluorescein concentration in HC-H-lipo was increased compared with that in HPF solution. In contrast, in the reaction with peroxynitrite, HC-H-lipo was inhibited. It was confirmed that HC-H-lipo that reacted specifically with hydroxyl radicals was able to distinguishably detect hydroxyl radicals. It was regarded to be useful as an examination kit. Tissue disorder induced by sodium valproate (SV) was one of the prepared murine disease models. The reactivity ratio of HC-H-lipo with serum to that of HPF solution was markedly different between the normal group (30%) and SV group (70%). In conclusion, HC-H-lipo cannot only simply and directly detect ROS but can also selectively detect ROS type. This nanocarrier is expected to be used as a novel diagnosis method.     

Azobenzene‐Containing Block Copolymers as Light‐Induced Reworkable Adhesives: Effects of Molecular Weight,Composition, and Block Copolymer Architectures on the Adhesive Properties

We previously reported that ABA‐type triblock copolymers with azobenzene‐containing terminal blocks can be utilized as a light‐induced reworkable adhesive that enables repeatable bonding and debonding on demand. The reworkability was based on the photoisomerization of the azobenzene moiety and concomitant softening and hardening of the azo blocks. Our aim in this study is to investigate the effect of the composition, molecular weight, and block copolymer architectures on the reworkable adhesive properties. For this purpose, we prepared AB diblock, ABA triblock, and 4‐arm (AB)₄ star‐block copolymers consisting of polymethacrylates bearing an azobenzene moiety (A block) and 2‐ethylhexyl (B block) side chains and performed adhesion tests by using these block copolymers. As a result, among the ABA block copolymers with varied compositions and molecular weights, the ABA triblock copolymers with an azo block content of about 50 wt % and relatively low molecular weight could achieve an appropriate balance between high adhesion strength and low residual adhesion strength upon UV irradiation. Furthermore, the 4‐arm star‐block structure not only enhances the adhesion strength, but also maintains low residual adhesion strength when exposed to UV irradiation. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 806–813