Solvent control of optical resolution of 2-amino-1-phenylethanol using dehydroabietic acid

The optical resolution of 2-amino-1-phenylethanol (2-APE) by the solvent switch method was investigated using dehydroabietic acid (DAA), a natural chiral acid obtained as one of the main components of disproportionated rosin. The solvent dependency of optical rotation measurements of 2-APE, DAA and the diastereomeric salts suggested solvent control of optical resolution. Both (R)- and (S)-2-APE were resolved, as the first success for aminoalcohols, only by changing the resolving solvents: (S)-2-APE was obtained in high optical purity by a single crystallization operation with polar solvents (epsilon > 50), whereas the efficiency was lower for (R)-2-APE using less polar solvents (20 < epsilon < 40). The results were compared and discussed with reference to the crystal structures of the diastereomeric salts.     

Improvement of <Superscript>137</Superscript>Cs analysis in small volume seawater samples using the Ogoya underground facility

¹³⁷Cs in seawater is one of the most powerful tracers of water motion. Large volumes of samples have been required for determination of ¹³⁷Cs in seawater. This paper describes improvement of separation and purification processes of ¹³⁷Cs in seawater, which includes purification of ¹³⁷Cs using hexachloroplatinic acid in addition to ammonium phosphomolybdate (AMP) precipitation. As a result, we succeeded the ¹³⁷Cs determination in seawater with a smaller sample volume of 10 liter by using ultra-low background gamma-spectrometry in the Ogoya underground facility. ¹³⁷Cs detection limit was about 0.1 mBq (counting time: 10⁶ s). This method is applied to determine ¹³⁷Cs in small samples of the South Pacific deep waters.     

pH-Dependent catalytic activity and chemoselectivity in transfer hydrogenation catalyzed by iridium complex with 4,4'-dihydroxy-2,2'-bipyridine

Transfer hydrogenation catalyzed by an iridium catalyst with 4,4'-dihydroxy-2,2'-bipyridine (DHBP) in an aqueous formate solution exhibits highly pH-dependent catalytic activity and chemoselectivity. The substantial change in the activity is due to the electronic effect based on the acid-base equilibrium of the phenolic hydroxyl group of DHBP. Under basic conditions, high turnover frequency values of the DHBP complex, which can be more than 1000 times the value of the unsubstituted analogue, are obtained (up to 81 000 h(-1) at 80 degrees C). In addition, the DHBP catalyst exhibits pH-dependent chemoselectivity for alpha,beta-unsaturated carbonyl compounds. Selective reduction of the C=C bond of enone with high activity are observed under basic conditions. The ketone moieties can be reduced with satisfactory activity under acidic conditions. In particular, pH-selective chemoselectivity of the C=O versus C=C bond reduction was observed in the transfer hydrogenation of cinnamaldehyde.     

Adsorption of Janus particles to curved interfaces

We investigate the adsorption of a spherical Janus particle to a spherically curved liquid-liquid interface. We show that the equilibrium contact angle is determined by the geometry of the particle, its wettability, and also the interfacial curvature. In contrast with a homogeneous particle, there is a preferred interfacial curvature (spontaneous curvature) due to the Janus particle when the particle satisfies certain conditions.     

Adsorption and decomposition of formic acid (DCOOD) on NiO(111) and Ni(111) surfaces probed by SFG

Received: 20 September 1998 / Revised version: 3 November 1998     

Synthesis and thermal properties of cellulose-based polycaprolactones

Cellulose-based polycaprolactone (CAPCL) sheets were prepared from cellulose acetate (CA) and ϵ-caprolactone (CL). Thermal properties of the obtained CAPCL's were studied by differential scanning calorimetry (DSC), thermogravimetry (TG) and TG-Fourier transform infrared spectrometry (TG-FTIR). The glass transition temperatures (T_g 's) of CAPCL decreased with increasing CL/OH ratio, until CL/OH ratio reached 15 and then increased above that ratio. Melting of CAPCL was observed when CL/OH ratio was over 10. The thermal degradation temperatures (T_d 's) of CAPCL increased from ca. 350 °C to 390 °C with increasing CL/OH ratio. The results obtained by TG-FTIR analysis of CAPCL showed that gases with OH, CH, C=O, C-O-C groups evolved by thermal degradation.     

Halorhodopsin from natronomonas pharaonis forms a trimer even in the presence of a detergent, dodecyl-beta-D-maltoside

Halorhodopsin (HR) is a transmembrane seven-helix retinal protein, and acts as an inward light-driven Cl⁻ pump. HR from Natronomonas pharaonis (NpHR) can be expressed in Escherichia coli inner membrane in large quantities. Here, we showed that NpHR forms the trimer structure even in the presence of 0.1% (2 m m ) to 1% (20 m m ) dodecyl-β- d -maltoside (DDM), whose concentrations are much higher than the critical micelle concentration (0.17 m m ). This conclusion was drawn from the following observations. (1) NpHR in the DDM solution showed an exciton-coupling circular dichroism (CD) spectrum. (2) From the elution volume of gel filtration, the molecular mass of the NpHR–DDM complex was estimated. After evaluation of the mass of the bound DDM molecules, the mass of NpHR calculated was approximately equal to that of the trimer. (3) The cross-linked NpHR by glutaraldehyde gave the SDS-PAGE corresponding to the trimer. Mass spectra of these samples also support the notion of the trimer. Using the membrane fractions expressing NpHR ( Escherichia coli and Halobacterium salinarum ), CD spectra showed exciton-coupling, which suggests strongly the trimer structure in the cell membrane.     

Self-assembly of photochromic diarylethenes with amphiphilic side chains: reversible thermal and photochemical control

Diarylethene derivatives with hexaethylene glycol side chains were synthesized and their self-assembling and photochromic reactivity were investigated. The diarylethenes showed photochromism in organic solvents and even in water. The aqueous solution of the compounds turned turbid quickly upon heating. The clouding behavior was investigated using 1H NMR spectroscopy, dynamic light scattering, and absorption spectroscopy. It was revealed that, in the aqueous solution, the compounds self-assembled into aggregates, and the aggregates were loosened by raising the temperature. The cloud-point temperature of the closed-ring isomer was 5-7 degrees C lower than that of the open-ring isomer. When asymmetric methyl groups were introduced in the amphiphilic side chains, induced circular dichroism (ICD) was observed upon irradiation with UV light in water. This ICD was explained by the difference in the self-assembling behavior between the open- and the closed-ring isomers. It was suggested that the closed-ring isomers assembled into a chiral nanostructure.     

Optical properties of six isomers of three dimensionally delocalized <Emphasis Type="Italic">π</Emphasis>-conjugated carbon nanocage

First-principles GW+Bethe-Salpeter method employing all-electron mixed basis approach is applied to hydrocarbon molecules consisting of 78–198 atoms and its theoretical accuracy and performance are evaluated. Based on the confirmed accuracy/reliability of our method, we simulated the UV–vis absorption spectra of previously reported six possible isomers [E. Kayahara et al., Nat. Chem. 4, 2694 (2013)]. We also attempted to identify the most stable isomers of recently synthesized ball-shaped carbon nanocages by taking into account available experimental spectra. The best agreement with the experiment is found for the most unstable isomer, labelled as T. Our simulation strongly suggests that the external experimental conditions such as solution and finite temperature affect stability.     

Electrochemically active cross-linking reaction for fluorescent labeling of aliphatic alkenes

Although cross-linking reactions serve as a valuable tool for the integration of two or more functionalities or properties, the application of electrochemical synthesis to cross-linking reactions is restricted due to the difficulty of mass transfer. Thus, the primary purpose of this research is to explore electrochemical cross-linking systems to construct a fluorescent probe, triggered by the formation of a covalent linkage. The second purpose is to apply the probe to insoluble targets. Towards these goals, a combination of electrochemically active phenol derivatives and aliphatic alkenes were employed to form polycyclic compounds. Several of the dihydrobenzofuran derivatives formed through [3+2] cyclization reactions exhibited fluorescence. Furthermore, this approach allowed the effective modification of alkene-modified silica gel with electrochemically active species, which enables the construction of fluorescent probes that are triggered by C-C bond formation.