Ruthenium(salen)-catalyzed aerobic oxidative desymmetrization of meso-diols and its kinetics

Chiral (nitrosyl)ruthenium(salen) complexes were found to be efficient catalysts for aerobic oxidative desymmetrization of meso-diols under photoirradiation to give optically active lactols. The scope of the applicability of this reaction ranges widely from acyclic diols to mono-cyclic diols, although fine ligand-tuning of the ruthenium(salen) complexes was required to attain high enantioselectivity (up to 93% ee). In particular, the nature of the apical ligand was found to affect not only enantioselectivity but also kinetics of the desymmetrization reaction. Spectroscopic analysis of the oxidation disclosed that irradiation of visible light is indispensable not only for dissociation of the nitrosyl ligand but also for single electron transfer from the alcohol-bound ruthenium ion to dioxygen.     

Temperature dependence of three-body hydrophobic interactions: potential of mean force, enthalpy, entropy, heat capacity, and nonadditivity

Temperature-dependent three-body hydrophobic interactions are investigated by extensive constant-pressure simulations of methane-like nonpolar solutes in TIP4P model water at six temperatures. A multiple-body hydrophobic interaction is considered to be (i) additive, (ii) cooperative, or (iii) anti-cooperative if its potential of mean force (PMF) is (i) equal to, (ii) smaller than, or (iii) larger than the corresponding pairwise sum of two-methane PMFs. We found that three-methane hydrophobic interactions at the desolvation barrier are anti-cooperative at low to intermediate T, and vary from essentially additive to slightly cooperative at high T. Interactions at the contact minimum are slightly anti-cooperative over a wider temperature range. Enthalpy, entropy, and heat capacity are estimated from the computed PMFs. Contrary to the common expectation that burial of solvent-accessible nonpolar surface area always leads to a decrease in heat capacity, the present results show that the change in heat capacity upon three-methane association is significantly positive at the desolvation barrier and slightly positive at the contact minimum. This suggests that the heat capacity signature of a hydrophobic polymer need not vary uniformly nor monotonically with conformational compactness. Ramifications for protein folding are discussed.     

Label-free electronic detection of DNA-hybridization on nanogapped gold particle film

A label-free high-resolution DNA sensing technique using a nanogapped gold particle film is presented to acquire nucleotide polymorphism information, which can be read by electronic protocols.     

A new synthetic method for alpha-alkoxycarbonyl iminium salt and its reaction with nucleophiles

An iminium salt was easily prepared using the oxidation of amino ketene silyl acetal with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, and the subsequent nucleophilic addition to this iminium species proceeded efficiently to afford alpha-amino esters in good yields.     

Self-assembling structures of long-chain sugar-based amphiphiles influenced by the introduction of double bonds

Nine phenyl glucoside or galactoside amphiphiles possessing a saturated or unsaturated long alkyl-chain group as the self-assembling unit of a highly organized molecular architecture were synthesized. Their self-assembly properties were investigated by using energy-filtering TEM (EF-TEM), SEM, CD, XRD, and FT-IR techniques. Compound 2, possessing one cis double bond in the lipophilic portion, exhibited twisted helical fibers, which formed a bilayered structure with a 3.59 nm period, while 3 exhibited helical ribbons and left-handed nanotubular structures with 150-200 nm inner diameters and a wall thickness of approximately 20 nm. Very interestingly, 4, possessing three cis double bonds, exhibited a nanotubular structure with an inner diameter of approximately 70 nm and a d spacing value of 4.62 nm. On the other hand, 7, possessing two trans double bonds in the lipophilic region, exhibited crystal- or plate-like structures, which formed a bilayer structure with a d spacing value of 3.93 nm. These results indicate that the self-assembly properties are strongly dependent on the type of double bond. Furthermore, 8 and 9, with the galactopyranose moiety, revealed helical ribbon and well-defined double helical fiber structures, respectively. These findings support the view that the orientation of the intermolecular hydrogen-bonding interaction between the sugar moieties plays a critical role in producing the nanotubular structures. According to CD and powder XRD experiments, the relatively strong intermolecular hydrogen-bonding interaction of the glucopyranoside moiety in 3 and 4 provided a highly ordered chiral packing structure. Even though these compounds formed a weak hydrophobic interaction between lipophilic groups, it led to the formation of the nanotubular structure.     

A novel kinetic method for the speciation of cadmium in river water by micro solvent extraction with dithizone.

Cadmium species in river water were kinetically extracted with dithizone by varying the extraction time. The obtained extraction curve showed a three-stage stepwise profile that reflected the rate of the ligand substitution reaction between the dithizone and cadmium species. Corresponding to each stage, we divided these extracted cadmium species into three groups: "highly labile", "moderately labile" and "slowly labile" species.     

Proton polarization with p-terphenyl crystal by integrated solid effect on photoexcited triplet state

We have carried out the experiments for polarizing protons in single crystals of p-terphenyl doped with 0.1 mol% pentacene. The experiments have been performed in a magnetic field of 3 kG at room temperature or at 77 K. We obtained the polarization of 1.3% for protons in bulk at room temperature by using a pulsed dye-laser with the wavelength of 590 nm, the average power of 150 mW, and the repetition rate of 50 Hz. The polarization at 77 K reached 18% by irradiation with the dye-laser of 500 mW, 50 Hz and the same wavelength. The polarization of protons was measured by the neutron transmission method also. The result was consistent with that measured by the nuclear magnetic resonance.     

Gamow-teller strengths in proton-rich exotic nuclei deduced in the combined analysis of mirror transitions

Isospin symmetry is expected for the T(z)=+/-1-->0 isobaric analogous transitions in isobars with mass number A, where T(z) is the z component of isospin T. Assuming this symmetry, strengths of analogous Gamow-Teller (GT) transitions within A = 50 isobars were determined from a high energy-resolution study at 0 degrees in combination with the decay Q value and lifetime from the beta decay. This method can be applied to other pf-shell nuclei and can be used to study GT strengths of astrophysical interest.     

Measuring the thermal conductivity of a single carbon nanotube

Although the thermal properties of millimeter-sized carbon nanotube mats and packed carbon nanofibers have been readily measured, measurements for a single nanotube are extremely difficult. Here, we report a novel method that can reliably measure the thermal conductivity of a single carbon nanotube using a suspended sample-attached T-type nanosensor. Our experimental results show that the thermal conductivity of a carbon nanotube at room temperature increases as its diameter decreases, and exceeds 2000 W/mK for a diameter of 9.8 nm. The temperature dependence of the thermal conductivity for a carbon nanotube with a diameter of 16.1 nm appears to have an asymptote near 320 K. The present method is, in principle, applicable to any kind of a single nanofiber, nanowire, and even single-walled carbon nanotube.     

High pressure Raman study of bromine and iodine: soft phonon in the incommensurate phase

A new phase of solid bromine was discovered at a pressure region above 80 GPa by Raman scattering experiments with a diamond anvil high-pressure cell. This phase was found to be the same as the iodine phase V with an incommensurate structure [Nature (London) 423, 971 (2003)] which appears between the molecular phase I and the monatomic phase II. In the incommensurate phases of both bromine and iodine, Raman active soft modes were clearly found in the low frequency region. The data suggest that the monoatomic phase II occurs above 30 and 115 GPa for iodine and bromine, respectively.