Convenient synthesis of microspheres by self-assembly of random copolymers in supercritical carbon dioxide

A novel and convenient synthesis of microspheres was attained by molecular self-assembly of random copolymers in supercritical carbon dioxide. Poly{2-(perfluorooctyl)ethyl acrylate-ran-2-(dimethylamino)ethyl acrylate} random copolymers (P[POA-r-DAA]), with 7:3, 8:2, and 9:1 as the molar ratios of 2-(perfluorooctyl)ethyl acrylate (POA)/2-(dimethylamino)ethyl acrylate (DAA), were soluble in supercritical CO₂ and had their cloud points at about 75 bar higher than the critical pressure of CO₂. The CO₂ density at the cloud points decreased with an increase in temperature. Although the copolymers made a slight difference in the cloud point in the absence of perfluoroazelaic acid (PA), they made a marked difference in the presence of PA. The copolymer with a lower DAA content had a cloud point at lower CO₂ density. The scanning electron microscopy observation demonstrated that the copolymers produced microspheres in the presence of PA at 0.5 as PA/DAA in the heterogeneous state below the cloud points. The microspheres were unstable to pressure and changed to unspecific forms as a result of increasing the CO₂ pressure, although the microspheres were stable to temperature. The POA/DAA ratio in the copolymer had effect not only on the cloud point but also on the size of the microspheres. The copolymer with a lower DAA content formed smaller microspheres.     

Spin-frustrated (VO)36+-triangle-sandwiching octadecatungstates as a new class of molecular magnets

Spin-frustrated polyoxometalates, K(11)H[(VO)(3)(SbW(9)O(33))(2)].27H(2)O (1) and K(12)[(VO)(3)(BiW(9)O(33))(2)].29H(2)O (2), containing approximately equilateral and isosceles (VO)(3)(6+)-triangles (V(IV)...V(IV) separation of 5.4-5.5 A) sandwiched by two diamagnetic alpha-B nonatungstate ligands ([SbW(9)O(33)](9)(-) and [BiW(9)O(33)](9)(-)) with approximate D(3)(h) symmetry, are found to show magnetization jumps with distinct hysteresis for the S = (1)/(2) <--> S = (3)/(2) level crossing under fast sweeping pulsed magnetic fields (approximately 10(3) T/s) at T < or = 0.5 K. This unusual phenomenon is attributed to the theoretical prediction of half step magnetization, which is expected for an antiferromagnetic spin triangle with antisymmetrical Dzyaloshinky-Moriya interaction. The degeneracy of the S = (1)/(2) states for 1 is removed by slightly lower symmetry effects of triangular structure for 2. The calorimetry of 1 and 2 shows the heat capacity anomaly at 2 < or = T < or = 20 K which is associated with a thermal excitation from the S = (1)/(2) ground states to the S = (3)/(2) state at zero field. Zero-field splitting energies (5-7 K) between S = (1)/(2) and S = (3)/(2) states for 1 and 2, readily estimated by the level-crossing field for the magnetization, allow us to measure the hyperfine-structural 22 lines due to three equivalent I = (7)/(2) (51)V nuclei, the fine-structural triplet line of the S = (3)/(2) excited state, and the g anisotropy on the high-frequency ESR spectra. The spin-frustrated (VO)(3)(6+)-triangle for 1 and 2 is a good model of the magnetization between pure quantum states S = (1)/(2) and (3)/(2) and provides a new class of single-molecule magnets.     

Iridium complex-catalyzed reaction of 1,6-enynes: cycloaddition and cycloisomerization

[reaction: see text] 1,6-Enynes reacted with monoynes to give cyclohexadiene derivatives in the presence of a catalytic amount of [Ir(cod)Cl](2)/ligand. DPPE was most suitable for cycloaddition. Diastereoselective cycloaddition was also possible. In the absence of monoynes, 1,6-enynes cycloisomerized to (Z)-1-alkylidene-2-methylenecyclopentane derivatives. DPPF was most suitable for cycloisomerization. These results are the first examples of highly Z-selective cycloisomerization.     

Preparation of micelles with azo dye and UV absorbent at their cores or coronas using non-amphiphilic block copolymers

Micelles with azo dye and UV absorbent at their cores or coronas were prepared from non-amphiphilic random diblock copolymers by α,ω-diamine. Poly[4-(phenylazophenoxymethyl)styrene-ran-4-(2-hydroxybenzophenoxymethyl)styrene-ran-vinylphenol]-block-polystyrene (P(AS-r-HBS-r-VPh)-b-PSt) and poly(vinylphenol)-block-poly[4-(phenylazophenoxymethyl)styrene-ran-4-(2-hydroxybenzophenoxymethyl)styrene-ran-styrene] (PVPh-b-P(AS-r-HBS-r-St)) diblock copolymers were prepared by living radical polymerization mediated by 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl. The former copolymer had a molecular weight of Mn[P(AS-r-HBS-r-VPh)-b-PSt] = 10,000-b-250,000 by ¹H NMR and a molar ratio of AS:HBS:VPh = 0.01:0.01:0.98, while the latter had a molecular weight of Mn[PVPh-b-P(AS-r-HBS-r-St)] = 10,000-b-111,000 and a molar ratio of AS:HBS:St = 0.02:0.03:0.95. The copolymers showed no self-assembly in 1,4-dioxane because this solvent was non-selective to the copolymers. Dynamic light scattering demonstrated that the copolymers formed micelles in the solvent in the presence of α,ω-diamine. The hydrodynamic radii of the micelles slightly increased with the copolymer concentration decrease, while the aggregation numbers were almost independent of the copolymer concentration. It was found that P(AS-r-HBS-r-VPh)-b-PSt formed smaller micelles with a lower aggregation number than PVPh-b-P(AS-r-HBS-r-St) because of the steric hindrance of the AS and HBS units present at the micellar coronas.     

Photoinduced swing of a diarylethene thin broad sword shaped crystal: a study on the detailed mechanism

We report a swinging motion of photochromic thin broad sword shaped crystals upon continuous irradiation with UV light. By contrast in thick crystals, photosalient phenomena were observed. The bending and swinging mechanisms are in fact due to molecular size changes as well as phase transitions. The first slight bending away from the light source is due to photocyclization-induced surface expansion, and the second dramatic bending toward UV incidence is due to single-crystal-to-single-crystal (SCSC) phase transition from the original phase I to phase II_UV. Upon visible light irradiation, the crystal returned to phase I. A similar SCSC phase transition with a similar volume decrease occurred by lowering the temperature (phase III_temp). For both photoinduced and thermal SCSC phase transitions, the symmetry of the unit cell is lowered; in phase II_UV the twisting angle of disordered phenyl groups is different between two adjacent molecules, while in phase III_temp, the population of the phenyl rotamer is different between adjacent molecules. In the case of phase II_UV, we found thickness dependent photosalient phenomena. The thin broad sword shaped crystals with a 3 μm thickness showed no photosalient phenomena, whereas photoinduced SCSC phase transition occurred. In contrast, large crystals of several tens of μm thickness showed photosalient phenomena on the irradiated surface where SCSC phase transition occurred. The results indicated that the accumulated strain, between isomerized and non-isomerized layers, gave rise to the photosalient phenomenon.

We report a swinging motion of photochromic thin broad sword shaped crystals upon continuous irradiation with UV light.     

Ligand-Controlled Stereoselective Synthesis and Biological Activity of 2-Exomethylene Pseudo-glycoconjugates: Discovery of Mincle-Selective Ligands

Glycoconjugate analogues in which the sp³-hybridized C2 position of the carbohydrate structure (normally bearing a hydroxy group) is converted into a compact sp²-hybridized exomethylene group are expected to have unique biological activities. We established ligand-controlled Tsuji–Trost-type glycosylation methodology to directly prepare a variety of these 2-exomethylene pseudo-glycoconjugates, including glucosylceramide analogues, in an α- or β-selective manner. Glucocerebrosidase GBA1 cleaves these synthetic pseudo-β-glucosylceramides similarly to native glucosylceramides. The pseudo-glucosylceramides exhibit selective ligand activity towards macrophage-inducible C-type lectin (Mincle), but unlike native glucosylceramides, are inactive towards CD1d.     

Reduction-induced micellization of a diblock copolymer containing stable nitroxyl radicals

A novel micelle formation induced by reduction was attained using a diblock copolymer supporting 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). Poly(4-vinylbenzyloxy-TEMPO)-block-polystyrene (PVTEMPO-b-PSt) showed ultraviolet (UV) absorption at 467 nm as λ _max based on the TEMPO radicals. As the phenylhydrazine was added to the copolymer solution in benzene, the UV absorbance decreased. The decrease in the absorbance suggested that the TEMPO radicals were reduced to the colorless hydroxylamine by phenylhydrazine. The PVTEMPO-b-PSt copolymer showed no self-assembly in benzene due to the nonselective solvent. A light scattering study demonstrated that the scattering intensity of the copolymer increased with a decrease in the UV absorbance. The hydrodynamic diameter of the copolymer rapidly increased with the addition of phenylhydrazine and became almost steady over the molar ratio of phenylhydrazine to the VTEMPO unit of 0.2. It was found that the hydroxylamine in the micelles reverted to the TEMPO radicals by oxidation with oxygen.     

Effect of water on the interfacial structures of room-temperature ionic liquids

The interfacial structures of cyano-based room-temperature ionic liquids play a very important role in reducing friction. However, the presence of water impairs their tribological performance. The interfacial structures and friction forces of 1-ethyl-3-methylimidazolium dicyanamide, [EMIM][DCN], and the effect of water on these structures and forces were investigated using atomic force microscopy. In addition, the interaction of water and [EMIM][DCN] was evaluated using Fourier-transform infrared (FT-IR) spectroscopy. Multiple repulsive layers were observed in the [EMIM][DCN] solution. This solution showed low friction force because these repulsive layers worked as protective layers against friction. On the other hand, the specific repulsive layer characteristics of [EMIM][DCN] could not be observed in a [EMIM][DCN] + 2 wt% H₂O solution. FT-IR results indicated that the layer structure of [EMIM][DCN] was disturbed by the addition of H₂O. Therefore, the solution containing water exhibited a high friction force.     

Highly Emissive Diborylphenylene‐Containing Bis(phenylethynyl)benzenes: Structure–Photophysical Property Correlations and Fluoride Ion Sensing

A series of 2,5‐bis(dimesitylboryl)‐1,4‐bis(arylethynyl)benzenes 1 – 6 that contain various p‐substituents on the terminal benzene rings, including NPh₂ ( 1 ), OMe ( 2 ), Me ( 3 ), H ( 4 ), CF₃ ( 5 ), and CN ( 6 ) groups, were synthesized, and the effects of the p‐substituents on the absorption and fluorescence properties were investigated both in solution and in the solid state. Linear relationships were obtained not only between the Hammett σ_p⁺ constants of the p‐substituents and the absorption and fluorescence maxima, quantum yields, and excited‐state dynamics parameters in solution, but also between the σ_p⁺ constants and the fluorescence quantum yields in the solid state. An important finding extracted from these results is that the suppressed fluorescence quenching in the solid state is a common feature for the present laterally boryl‐substituted π‐conjugated skeletons. Hence, the diborylphenylene can serve as a useful core unit to develop highly emissive organic solids. In fact, most of the derivatives showed more intense emission in the solid state than in solution. In addition to these studies, the titration experiment of 1 by the addition of nBu₄NF was conducted, which showed the stepwise bindings of two fluoride ions with high association constants as well as a drastic change in the fluorescence spectra, while constantly maintaining high quantum yields (0.61–0.76), irrespective of the binding modes. This result also demonstrated the potential utility of the present molecules as an efficient fluorescent fluoride ion sensor.     

Thermodynamics and kinetics on micelle formation of a nonamphiphilic poly(vinylphenol)-<Emphasis Type="Italic">block</Emphasis>-polystyrene by α,ω-diamine

A poly(vinylphenol)-block-polystyrene diblock copolymer (PVPh-b-PSt) forms micelles in the presence of 1,4-butanediamine (BDA) in 1,4-dioxane, a nonselective solvent. The micellization proceeds through the formation of hydrogen bond cross-linking between the PVPh blocks via BDA, and the dissociation and reconstruction of the micelles is reversibly controlled by temperature. We explored the thermodynamics and kinetics on the micellization of the nonamphiphilic PVPh-b-PSt copolymer by BDA. Light scattering studies demonstrated that an equilibrium existed between the micelles and the unimers. The equilibrium constants were determined for the dissociation and the reconstruction of the micelles on the basis of variation in the aggregation number of the micelles. The equilibrium constant of the dissociation showed a good agreement with the reciprocal of the equilibrium constant of the reconstruction. Based on the equilibrium constants, the standard Gibbs energy, enthalpy, and entropy of the dissociation and reconstruction were estimated. The standard enthalpy was Δ H° = 30–40 kJ mol⁻¹ for the dissociation. The enthalpy of the reconstruction was obtained as a negative value, however, there was a negligible difference in the absolute values of Δ H° between the dissociation and the reconstruction. The rate constant of the micellization was ca. 10² times larger than the back reaction, and increased with a decrease in the temperature.