Synthesis of diblock copolymers with cellulose derivatives. 3. Cellulose derivatives carrying a single pyrene group at the reducing-end and fluorescent studies of their self-assembly systems in aqueous NaOH solutions

Novel cellobiose and cellulose (DP _n =ca. 30) derivatives, N-(1-pyrenebutyloyl)-4-O-(β-d-glucopyranosyl)-β-d-glucopyranosylamine (6), N-(15-(1-pyrenebutyloylamino)-pentadecanoyl)-4-O-(β-d-glucopyranosyl)-β-d-glucopyranosylamine (7), N-(1-pyrenebutyloyl)-β-cellulosylamine (13), N-(15-(1-pyrenebutyloylamino)-pentadecanoyl)-β-cellulosylamine (14) carrying a pyrene group as a single fluorescent probe at the reducing end, were prepared in order to investigate their self-assembly systems in solutions. The relative intensity of the excimer emission at ca. 480 nm due to dimerized pyrenes (intensity I _E) to the monomer emission at ca. 380 nm due to isolated pyrene (intensity I _M), i.e., I _E/I _M, was monitored in various solutions. In water/dimethyl sulfoxide (DMSO) mixed solvent (0–98%, v/v), the ratio I _E/I _M remained low (0.04) for compound 6 over the range of water concentrations, indicating that pyrenes at C-1 position of compound 6 were diffused. On the other hand, the ratio I _E/I _M increased (0.04–4.96) for compound 7 with the increase in water concentration, indicating that pyrenes at C-1 position were associated. In aqueous NaOH solutions (4.4–17.5%, w/w), compound 14 showed a large increase in the ratio I _E/I _M (0.84–8.14) with the increase in NaOH concentration, compared to compound 13 (0.06–0.41). It was found that the association of hydrophobic groups at the reducing-end of cellulose could be controlled by the hydrophilic–hydrophobic balance of compounds and the solvent polarity.     

Flavonol glycosides in leaves of two Diospyros species

Fourteen flavonol glycosides including two new compounds were isolated from the leaves of two Diospyros plants (D. cathayensis and D. rhombifolia). The structures of isolated compounds were determined by spectroscopic analysis. The scavenging activity of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical of the isolated compounds was also investigated.     

The simple solvent-free synthesis of 1H-quinazoline-2,4-diones using supercritical carbon dioxide and catalytic amount of base

Only supercritical carbon dioxide (scCO₂) as a reactant and a solvent, and catalytic amount of base (DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), DBN (1,5-diazabicyclo[4.3.0]non-5-ene), Dabco^® (1,4-diazabicyclo[2.2.2]octane), and triethylamine) afforded 1H-quinazoline-2,4-diones in good to excellent yields from 2-aminobenzonitriles. 6,7-Dimethoxy-1H-quinazoline-2,4-dione, which is a key intermediate of medicines (Prazosin, Bunazosin, and Doxazosin) was synthesized successfully in a 97% yield, using 0.1 equiv of DBU under scCO₂ (10 MPa) at 80 °C.     

Stereoregularity of poly(alkyl α-chloroacrylates) and mechanism of isotactic polymerization

The catalytic activity of the complexes prepared by the reaction of Grignard reagents with ketones, esters, and an epoxide as polymerization catalysts of methyl and ethyl α-chloroacrylates was investigated. The modifiers which gave isotactic polymers were α,β-unsaturated ketones such as benzalacetophenone, benzalacetone, dibenzalacetone, mesityl oxide, and methyl vinyl ketone, and α,β-unsaturated esters such as ethyl cinnamate, ethyl crotonate, and methyl acrylate. Catalysts with butyl ethyl ketone, propiophenone, and propylene oxide as modifiers produced atactic polymers but no isotactic polymers. It was revealed that the complex catalysts having a structure ? C?C? O? MgX (X is halogen) gave isotactic polymers. The mechanism of isotactic polymerization was discussed. In addition, for radical polymerization of ethyl α-chloroacrylate, enthalpy and entropy differences between isotactic and syndiotactic additions were calculated to give ΔH_i^* ? ΔH_s^* = 910 cal/mole and ΔS_i^* ? ΔS_s^* = 0.82 eu.     

Interaction of an organic cation with Gibbs monolayers of n-hexadecyl phosphate

Surface phase behavior of n-hexadecyl phosphate (n-HDP) and its mixture with L-arginine (L-arg), which behaves as L-argininium cation (L-arg(+)) in aqueous solution, at a molar ratio 2:3 in Gibbs adsorption layers has been studied by film balance, Brewster angle microscopy (BAM) and surface tensiometry at 20 degrees C. The monolayers of n-HDP show three phases that are gas (G), intermediate (I) and liquid condensed (LC), and two phase transitions. A first-order G-I phase transition that is followed by a second-order I-LC phase transition is found in these monolayers. Although the monolayers of the mixtures containing n-HDP and L-arg show three phases, the nature of the middle phase is different from that of the n-HDP monolayers. The three phases observed for the mixed systems are G, liquid expanded (LE) and LC phases. A first-order G-LE phase transition is found at a low surface pressure at > or =10 degrees C. This transition is followed by another first-order LE-LC phase transition at a certain higher surface pressure. The first-order nature of the phase transitions for both the systems is confirmed by the presence of plateaus in the pi-t curves, which are accompanied by two surface phases. A second-order phase transition in the monolayers of n-HDP is indicated by a gradual change in the surface morphology, from a uniformly bright isotropic to an anisotropic mosaic textured phase, which is accompanied by a continuous change in the surface pressure. The domains formed during the first-order phase transition in the adsorption layers of n-HDP are circular and remain unaffected by changing the temperature. Although the domains of an LE phase are circular, those of an LC phase at the latter transition are fractal in the mixed system. A further branching of the arms of the fractal domains is found to occur by an increase in the temperature. All the results are explained by considering salt formation between anion from n-HDP and L-arg(+).     

Fabrication of mesoporous Pt inside micrometer channels via “solvent-evaporation-mediated direct physical casting”

We have proposed a novel convenient pathway via solvent-evaporation-mediated direct physical casting (SEDPC) for the fabrication of mesoporous metals in a micrometer scale. We have presented the successful deposition of highly ordered mesoporous Pt into micrometer channels prepared by lithography. The direct observation by a high-resolution scanning microscope (HR-SEM) showed the formation of highly ordered 2D-hexagonal (p6mm) mesoporous metals onto such substrates. The cyclic voltammogram of the mesoporous Pt in sulfuric acid revealed a typical feature which can identify the clean Pt surface. Moreover, mesoporous Pt exhibits an effective reduction of dissolved dioxygen molecules. It is proved that mesoporous Pt deposited in a very confined area via the SEDPC method possesses electrocatalytic performance owing to Pt.     

An improved gravimetric method for determining oxygen in binary and ternary uranium oxides by addition of alkali or alkaline earth metal nitrate

A known amount of lithium or calcium nitrate solution is added to the sample powder which is then heated in air or oxygen. The oxygen in test samples of UO_2+x, Sr_0.1U_0.9O_{2 + x} and Sr_0.2U_0.5O_{2 + x} was determined with an estimated standard deviation of ± 0.002.     

Sub-micro-second time-resolved absorption spectroscopy of a polar carotenoid analogue, 2-(all-trans-retinylidene)indan-1,3-dione; formation of the dication by direct triplet-excited sensitization

Sub-micro-second time-resolved difference absorption spectra of a polar carotenoid analogue, 2-(all-trans-retinylidene)indan-1,3-dione (hereafter, we will call RetInd), were recorded in tetrahydrofuran at room temperature upon anthracene-sensitized triplet excitation. In addition to the typical Tn <-- T1 absorption spectrum of anthracene followed by that of RetInd, a novel transient species, which peaked at 670 nm, was detected. The lifetime and the population of the 670 nm species was not affected by the presence of oxygen but was quenched by the cation scavenger, triethylamine. Therefore, we have identified this species as a "cation". The transient 670 nm species was not generated by direct photoexcitation of RetInd in the absence of a triplet sensitizer. Therefore, this species was not generated via the T1 species of RetInd but rather via an "invisible state" of RetInd, which is generated by direct energy or electron transfer from T1 anthracene. This proposed pathway was confirmed by a singular-value decomposition followed by a global fitting analysis. The "cation" of RetInd shows vibrational structure in its absorption spectrum, and its lifetime was determined to be 15 micros. Chemical oxidation of RetInd in 2,2,2-trifluoroethanol (dichloromethane) produced a broad absorption band around 880 (1013) nm, which could be transformed into a shoulder around 640 (675) nm upon addition of increasing amounts of the oxidant, FeCl3. The former absorption band can be assigned to a radical cation, while the latter to a dication. Because of the spectral similarity, the 670 nm species can be assigned to the dication, and the "invisible state" is ascribed to the radical cation of RetInd. This is the first direct evidence for the production of a dication of a biological polyene moiety generated in non-halogenated solution following anthracene-sensitized excitation.     

A conductometric method for colloid titrations

A negative or positive colloid sample solution can be directly titrated, respectively, with a polycationic (poly-N, N-diallyldimethylammonium chloride) or polyanionic (potassium polyvinylsulfate) titrant to a conductometric end-point. With the conventional toluidine blue indicator method a positive colloid solution is titrated directly with a polyanionic titrant, but a negative colloid solution must be treated with an excess of a polycationic titrant, which is back-titrated with the polyanionic titrant. For positive colloid solutions, both indicator and conductometric methods are suitable; for negative colloids the conductometric method is preferable because of its constant titration vlues over a range of pH values.     

Molecular dynamics simulation of clustered DNA damage sites containing 8-oxoguanine and abasic site

Clustered DNA damage sites induced by ionizing radiation have been suggested to have serious consequences to organisms, such as cancer, due to their reduced probability to be repaired by the enzymatic repair machinery of the cell. Although experimental results have revealed that clustered DNA damage sites effectively retard the efficient function of repair enzymes, it remains unclear as to what particular factors influence this retardation. In this study, approaches based on molecular dynamics (MD) simulation have been applied to examine conformational changes and energetic properties of DNA molecules containing clustered damage sites consisting of two lesioned sites, namely 7,8-dihydro-8-oxoguanine (8-oxoG) and apurinic/apyrimidinic (AP) site, located within a few base pairs of each other. After 1 ns of MD simulation, one of the six DNA molecules containing a clustered damage site develops specific characteristic features: sharp bending at the lesioned site and weakening or complete loss of electrostatic interaction energy between 8-oxoG and bases located on the complementary strand. From these results it is suggested that these changes would make it difficult for the repair enzyme to bind to the lesions within the clustered damage site and thereby result in a reduction of its repair capacity.