Resonating-valence-bond States and ferromagnetic correlations in the doped triangular Mott insulator

The two-dimensional t-J model on a triangular lattice is studied using high-temperature expansions. By studying the entropy and spin susceptibility, we find that the sign of the hopping integral t is very crucial. In the case of t>0, the peak of the spin susceptibility moves to the high-temperature region with hole doping, which indicates the appearance of the resonating-valence-bond state. In contrast, for t<0, the peak of the spin susceptibility disappears with hole doping and the entropy at low temperatures behaves as S=gammaT with large coefficient gamma, representing a large effective mass. This behavior is understood from the competition between Nagaoka's ferromagnetism and singlet formation.     

Spectroscopic studies on aquatic angiosperm

Reflectance, transmittance and absorbance spectra were observed of Hydrobryum japonicum, a kind of Aquatic angiosperm, over the wavelength range from 300 to 780 nm. Three remarkable peaks were observed at 380, 430, and at 680 nm in the absorbance curve, which were assigned to the two pigments flavonoid and chlorophyll. The functions of these pigments of making photosynthesis inevitable for the botanical activity and of protecting the plant from the heat given by the sunlight were discussed.     

Automatic analyzer for highly polar carboxylic acids based on fluorescence derivatization–liquid chromatography

A sensitive, versatile, and reproducible automatic analyzer for highly polar carboxylic acids based on a fluorescence derivatization–liquid chromatography (LC) method was developed. In this method, carboxylic acids were automatically and fluorescently derivatized with 4‐(N,N‐dimethylaminosulfonyl)‐7‐piperazino‐2,1,3‐benzoxadiazole (DBD‐PZ) in the presence of 4‐(4,6‐dimethoxy‐1,3,5‐triazin‐2‐yl)‐4‐methylmorpholinium chloride by adopting a pretreatment program installed in an LC autosampler. All of the DBD‐PZ‐carboxylic acid derivatives were separated on the ODS column within 30 min by gradient elution. The peak of DBD‐PZ did not interfere with the separation and the quantification of all the acids with the exception of lactic acid. From the LC‐MS/MS analysis, we confirmed that lactic acid was converted to an oxytriazinyl derivative, which was further modified with a dimethoxy triazine group of 4‐(4,6‐dimethoxy‐1,3,5‐triazin‐2‐yl)‐4‐methylmorpholinium chloride (DMT‐MM). We detected this oxytriazinyl derivative to quantify lactic acid. The detection limits (signal‐to‐noise ratio = 3) for the examined acids ranged from 0.19 to 1.1 µm , which correspond to 95–550 fmol per injection. The intra‐ and inter‐day precisions of typical, highly polar carboxylic acids were all <9.0%. The developed method was successfully applied to the comprehensive analysis of carboxylic acids in various samples, which included fruit juices, red wine and media from cultured tumor cells. Copyright © 2014 John Wiley & Sons, Ltd.     

7-β- and 10-β-Hydroxylated congeners of CAF-603; elucidation of absolute configuration of CAF-603 family,and their SAR studies in the anti-fungal activity

Novel 7-β- and 10-β-hydroxylated congeners of CAF-603 (4 and 5, respectively) were isolated from Trichoderma crassum. Relative configuration of 4 was determined by NOE experiments. Stereochemistry of 7-β-hydroxy group in 5 was established by a combination of vicinal ³J_H–H analyses and quantum chemical calculations. Absolute configurations of 4 and 5 were established by observing the Cotton effects of their bis(2-naphthoate) esters. T. crassum also produce known CAF-603 (1), 14-hydroxy and 8,9-β-epoxy derivatives (2 and 3, respectively). Present study first established the absolute configuration of CAF-603 family by taking their biosyntheses into account. Preliminary biological experiments revealed that the molecular target strictly recognizes the β-side of the cycloheptane ring.     

Efficient Light‐Harvesting Antennae Resulting from the Dense Organization of Dyes into DNA Junctions through d‐Threoninol

Herein we report the construction of efficient light‐harvesting antennae by hybridization of DNA oligonucleotides containing high densities of fluorophores into DNA junctions through d ‐threoninol. Six pyrene donors could be incorporated into each arm without self‐quenching. A perylene acceptor was located at the center of the junction. Antenna effects of a duplex and three‐ to eight‐way junctions were systematically compared. Six‐ and eight‐way junctions had the highest antenna effects, and their effective absorption coefficients were 8.5 times higher than that of perylene. Interestingly, even‐numbered junctions had higher efficiencies than odd‐numbered junctions. Nondenaturing gel analyses and fluorescence lifetime measurements demonstrated that the strong odd–even effects were derived from differences in the stability of junctions. The results presented will guide the design of efficient artificial photosynthetic systems.     

SnCl4-promoted rearrangement of 2,3-epoxy alcohol derivatives: stereochemical control of the reaction

The SnCl₄-promoted rearrangement of 2,2,3,3-tetrasubstituted-2,3-epoxy-1-alcohol derivatives proceeded in a regio- and stereo-controlled manner to selectively give two types of rearranged products from a single isomer by changing the protecting group of the alcohol.     

Stable molecular configuration in crystalline carboxylic acids

The stable (lower enthalpy) molecular configurations of propionic, butyric, Jeric and lauric acids in the crystalline state have been examined via their atom-atom potentials. It was found that the cis configuration is more stable than the trans configuration for propionic, butyric and valeric acids, and that the trans configuration is more stable than the cis configuration for lauric acid, in accord with a previous IR spectral analysis. The potential energy of benzoic acid was recalculated using the positions of atoms given by Speakman, and indicates that the A form is more stable than the B form, in agreement with the results of previous work.     

Photoinduced increase in vesicle size and role of photoresponsive malachite green leuconitrile derivative in vesicle fusion

The influence of photoirradiation on vesicles containing a Malachite Green leuconitrile derivative carrying a long alkyl chain, affording photogenerated amphiphilicity, was investigated. The photoresponsive Malachite Green leuconitrile derivative was embedded in the vesicle bilayer of two single-tailed amphiphiles with oppositely charged head groups consisting of cetyltrimethylammonium chloride (CTAC) and sodium octyl sulfate (SOS). Transmission electron microscopy, which was used for observing photoinduced structural change in the vesicles, demonstrated that photoirradiation of the vesicles containing the Malachite Green leuconitrile derivative increased the average size of the vesicle diameter from 116 to 243 nm in the [CTAC]/[SOS] = 0.48 system. The mechanism for vesicle enlargement was studied with fluorescent probe molecules. The photoinduced change in the vesicle size can be explained by the destabilization of the vesicle bilayer, which is perturbed by photogenerated amphiphilicity. In addition, it was shown that the fusion process arising from the destabilized bilayer contributed to the increase in vesicle size.     

Subdiffraction imaging through the selective donut-mode depletion of thermally stable photoswitchable fluorophores: numerical analysis and application to the fluorescent protein Dronpa

The fast and reversible on/off switching of the fluorescence emission of the GFP-like fluorescent protein Dronpa has attracted considerable interest for applications in subdiffraction imaging. In this paper we study the use of a donut-mode beam in combination with two more overlapping laser beams to increase the imaging resolution through selective switching to the nonfluorescent photoswitched state. We devise and run a series of numerical simulations to determine suitable photophysical parameters of prospective, thermally stable photoswitchable molecules, in terms of photoswitching quantum yields, fatigue resistance, and possible presence of transient nonfluorescent states. Many of our findings are applicable to other measurements that make use of donut beams, and these guidelines can be used in the synthesis and screening of novel photoswitchable compounds. We experimentally demonstrate the possibility of obtaining increased resolution by making use of the efficient and thermally stable Dronpa photoswitching, using equipment that is commonly available.     

Comprehensive separation of secondary metabolites in natural products by high-speed counter-current chromatography using a three-phase solvent system

High-speed counter-current chromatography (HSCCC) using the three-phase solvent system n-hexane-methyl acetate-acetonitrile-water at a volume ratio of 4:4:3:4 was applied to the comprehensive separation of secondary metabolites in several natural product extracts. A wide variety of secondary metabolites in each natural product was effectively extracted with the three-phase solvent system, and the filtered extract was directly submitted to the HSCCC separation using the same three-phase system. In the HSCCC profiles of crude natural drugs listed in the Japanese Pharmacopoeia, several physiologically active compounds were clearly separated from other components in the extracts. The HSCCC profiles of several tea products, each manufactured by a different process, clearly showed their compositional difference in main compounds such as catechins, caffeine, and pigments. These HSCCC profiles also provide useful information about hydrophobic diversity of whole components present in each natural product.