Systematic studies on structural parameters for nanotubular assembly of hexa-peri-hexabenzocoronenes

Thirteen different hexa-peri-hexabenzocoronenes (HBCs) I-III were newly synthesized, and their self-assembling behaviors were investigated. Taking into account also the reported behaviors of amphiphilic HBCs, some structural parameters of HBC essential for the tubular assembly were revealed. Points to highlight include (1) the importance of two phenyl groups attached to one side of the HBC unit, (2) essential roles of long paraffinic side chains on the other side of the phenyl groups, and (3) no necessity of hydrophilic oligo(ethylene glycol) side chains. The hierarchical nanotubular structure, rendered by virtue of a synchrotron radiation technique, was virtually identical to our previous proposal, where the nanotubes are composed of helically coiled bilayer tapes with a tilting angle of approximately 45 degrees. Each tape consists of pi-stacked HBC units, where the inner and outer HBC layers are connected by interdigitation of paraffinic side chains. The coiled structure is most likely caused by a steric congestion of the phenyl groups attached to the HBC unit, whose tilting direction may determine the handedness of the helically chiral nanotube.     

Pressure response of three-dimensional cyanide-bridged bimetallic magnets

Effects of pressure on the structures and magnetic properties of three types of 3-D cyanide-bridged bimetallic coordination polymer magnets, MnIICrIII ferrimagnet [Mn(en)]3[Cr(CN)6]2.4H2O (1; en = ethylenediamine), NiIICrIII ferromagnet [Ni(dipn)]3[Cr(CN)6]2.3H2O (2; dipn = N,N-di(3-aminopropyl)amine), and NiIIFeIII ferromagnet [Ni(dipn)]2[Ni(dipn)(H2O)][Fe(CN)6]2.11H2O (3), were systematically examined under hydrostatic pressure up to 19.8 GPa using a piston-cylinder-type pressure cell and a diamond anvil cell. The ferrimagnet 1 showed the reversible crystalline-to-amorphous-like phase change, and the magnetic phase transition temperature (TC) was reversibly changed from 69 K at 0 GPa to 126 K at 4.7 GPa. At higher pressure, the net magnetization was suppressed with increasing pressure, and the magnetic state at 19.8 GPa was assumed to be paramagnetic. The initial ferrimagnetic phase of 1 was not recovered after releasing the pressure from 19.8 GPa. The magnetic phase of 2 was reversibly converted between ferromagnetic and paramagnetic-like phase in the range 0 相似文献   

Lateral phase separation in cholesterol/diheptadecanoylphosphatidylcholine binary bilayer membrane

We investigated the phase behavior of cholesterol/diheptadecanoylphosphatidylcholine (C17:0-PC) binary bilayer membrane as a function of the cholesterol composition (X(ch)) by fluorescence spectroscopy using 6-propionyl-2-(dimethylamino)naphthalene (Prodan) and differential scanning calorimetry (DSC). The fluorescence spectra showed that the wavelength at the maximum intensity (lambda(max)) changed depending on the bilayer state: ca. 440 nm for the lamellar gel ( [Formula: see text] or L(beta)) and the liquid ordered (L(o)) phases and ca. 490 nm for the liquid-crystalline (L(alpha)) phase. The transition temperatures were determined from the temperature dependence of lambda(max) and endothermic peaks of the DSC thermograms. Both measurements showed that the pre- and main transition disappear around X(ch)=0.05 and 0.30, respectively. The constructed temperature-X(ch) phase diagram resembled a typical phase diagram for a eutectic binary mixture containing a peritectic point. The presence of a peritectic point at X(ch)=0.15 suggested that a complex of cholesterol and C17:0-PC is stoichiometrically formed in the gel phase. Consideration based on the hexagonal lattice model revealed that the compositions of 0.05 and 0.15 correspond to the bilayer states where cholesterol molecules are regularly distributed in different ways. The former is nearly equal to the composition for the membrane occupied entirely with Units (1:18), composed of a cholesterol and 18 surrounding C17:0-PC molecules within the next-next nearest neighbor sites. The latter is represented by a Unit (1:6), including a cholesterol and 6 surrounding C17:0-PC molecules. Further, the disappearance of the main transition at X(ch)=0.30 indicates that the pure L(o) phase can exist in X(ch)>0.30. The eutectic behavior observed in the phase diagram was explainable in terms of phase separation between two different types of regions with different types of regular distributions of cholesterol.     

Supramolecular enantiodifferentiating photoisomerization of cyclooctene with modified beta-cyclodextrins: critical control by a host structure

Enantiodifferentiating photoisomerization of (Z)-cyclooctene included and sensitized by m-methoxybenzoyl-beta-cyclodextrin gave chiral (E)-isomers in up to 46% enantiomeric excess, which is the highest value ever reported for supramolecular photochirogenesis with analogous hosts, thus demonstrating the crucial role of the sensitizer-spacer moiety in supramolecular photochirogenic systems.     

Photocyclization reaction of a diarylmaleimide derivative in polar solvents

Photochromism of a symmetric diarylmaleimide derivative, having two thiophene rings (1), and a non-symmetric derivative having a S,S-dioxide thiophene ring and a thiophene ring (2) as the aryl moieties, was studied in various solvents. The photocyclization quantum yield of gradually decreased with increasing the solvent polarity and the reaction was not observed in polar solvents, such as ethanol and acetonitrile; on the other hand, such a strong solvent dependence of the photocyclization reaction was not observed for ; the different behavior is attributed to the weaker electron donating ability of the S,S-dioxide thiophene ring.     

Solid state structures and photophysical properties of (trimethylsilyl)methyl-substituted anthracenes and pyrenes

(Trimethylsilyl)methyl groups incorporated at 9- and 9,10-positions of anthracenes and at 1,3,6,8-positions of pyrenes were found to orient perpendicular to the aromatic frameworks in their crystals and induce red-shift of UV absorption and fluorescence spectra and enhancement of fluorescence quantum yields as compared with the parent hydrocarbons.     

Determination of Solvent‐Trapped Products Obtained by Photolysis of Aryl Azides in 2,2,2‐Trifluoroethanol

A series of nonfluorinated and fluorinated aryl azides with varied functionality patterns were irradiated in 2,2,2‐trifluoroethanol with either a high‐pressure or a low‐pressure mercury lamp. Interestingly, one of the major products in these reactions was the result of the recombination of anilino and alkyl radicals to form the corresponding hemiaminal compounds. The structure of the recombination products was assigned unambiguously after proton/deuterium exchange experiments followed by MS and MS/MS analysis.     

Rhodium‐Catalyzed Oxidative Coupling between Salicylaldehydes and Internal Alkynes with C?H Bond Cleavage To Produce 2,3‐Disubstituted Chromones

A direct oxidative coupling of salicylaldehydes with internal alkynes proceeds efficiently with cleavage of the aldehyde C? H bond to produce the corresponding chromone derivatives. A rhodium catalyst in combination with a cyclopentadiene ligand and a copper oxidant promote this straightforward annulation reaction. Solid‐state luminescence was observed for certain chromone products.