Poly(β-Amino acids). VI. Synthesis and conformational properties of poly[(r)-3-pyrrolidinecarboxylic acid]

Racemic and optically active 3-pyrrolidinecarboxylic acids (β-proline) were synthesized, and their polymers, poly[(RS)-β-proline] and poly[(R)-β-proline], were prepared by the polycondensation reaction of the p-nitrophenyl esters. Model compounds, N-cyclopentylcarboxylic acid pyrrolidide and N-cyclopentylcarbonyl-(R)-3-pyrrolidinecarboxylic acid pyrrolidide, were synthesized to elucidate the conformation of the polymer. The solution properties of poly[(R)-β-proline] and the model compounds were investigated by means of circular dichroism (CD) and NMR spectroscopy. The spectral patterns of the polymer and model compounds were similar in various solvents. Poly[(R)-β-proline] and poly[(RS)-β-proline] showed identical NMR spectra. These results suggest that poly[(R)-β-proline] may exist in a random conformation consisting of mixtures of cis and trans amide bonds. The conformational study of cyclopentanecarboxylic acid pyrrolidide by NMR spectroscopy with a shift reagent, Eu(fod)₃, in CDCl₃ implied that the plane containing the amide group bisects the cyclopentane ring. This suggests that each amide plane in the polymer in chloroform may also bisect the pyrrolidine ring.     

A Class of Asymmetric Gapped Hamiltonians on Quantum Spin Chains and its Characterization II

We give a characterization of the class of gapped Hamiltonians introduced in Part I (Ogata, A class of asymmetric gapped Hamiltonians on quantum spin chains and its classification I, 2015). The Hamiltonians in this class are given as MPS (Matrix product state) Hamiltonians. In Ogata (A class of asymmetric gapped Hamiltonians on quantum spin chains and its classification I, 2015), we list up properties of ground state structures of Hamiltonians in this class. In this Part II, we show the converse. Namely, if a (not necessarily MPS) Hamiltonian H satisfies five of the listed properties, there is a Hamiltonian H′ from the class by Ogata (A class of asymmetric gapped Hamiltonians on quantum spin chains and its classification I, 2015), satisfying the following: The ground state spaces of the two Hamiltonians on the infinite interval coincide. The spectral projections onto the ground state space of H on each finite intervals are approximated by that of H′ exponentially well, with respect to the interval size. The latter property has an application to the classification problem with open boundary conditions.     

A rhodamine-cyclen conjugate as a highly sensitive and selective fluorescent chemosensor for Hg(II)

A rhodamine-cyclen conjugate (1) behaves as a highly sensitive and selective fluorescent chemosensor for Hg(2+). The high emission selectivity is due to the formation of 1-Hg(2+) 1:2 complex leading to spirocycle opening of 1.     

Imaging of conformational changes of biotinylated triamide molecules covalently bonded to a carbon nanotube surface

A diamide molecule bearing a biotin terminus was bonded via an amide linkage to the surface of an aminated single-walled carbon nanotube and examined by a high-resolution transmission electron microscope. The still and movie images allowed us to study not only the conformation of the molecule but also its time evolution. An iterative sequence of modeling and simulation allowed us to assign one plausible conformation out of >10(8) possibilities. The images also provide direct support for the accepted wisdom that the curved regions of pristine carbon nanotubes are chemically reactive.     

Stable carbon, nitrogen, and oxygen isotope analysis as a potential tool for verifying geographical origin of beef

Stable isotope analysis of organic elements such as carbon and nitrogen has been employed as a powerful tool for provenance determination of food materials, because isotopic compositions of the materials reflect many factors in natural environment. In this study, we examined carbon, nitrogen, and oxygen isotope signatures of beef from Australia, Japan, and USA, in order to confirm the method as a potential tool for verifying geographical origin of beef commercially distributed in Japan. Defatted dry matter of beef from USA was characterized by higher carbon isotopic composition (-13.6 per thousand to -11.1 per thousand) than that from Japan (-19.6 per thousand to -17.0 per thousand) and Australia (-23.6 per thousand to -18.7 per thousand). That from Australia was characterized by higher oxygen isotopic composition (+15.0 per thousand to +19.4 per thousand) than that from Japan (+7.3 per thousand to +13.6 per thousand) and USA (+9.5 per thousand to +11.7 per thousand). The oxygen isotopic composition in Japanese beef showed a positive correlation with the isotopic composition of cattle drinking water, the difference in which is clearly latitude dependent. These results suggest that a comparison of carbon, nitrogen, and oxygen isotopic compositions is applicable as a potential tool to discriminate the provenance of beef not only between different countries (i.e. Australia, Japan, and USA) but also among different regions within Japan.     

Cytotoxic iridoid aldehydes from Taiwanese Viburnum luzonicum

Four new iridoid aldehydes bearing (E)- or (Z)-p-coumaroyl group, luzonial A (1), luzonial B (2), luzonidial A (3), and luzonidial B (4), were isolated from a methanol extract of the dried leaves of Viburnum luzonicum collected in Kaoshiung, Taiwan and their structures were elucidated by analysis of spectroscopic data. Compounds 1-3 exhibited moderate inhibitory activity against HeLa S3 cancer cells.     

Remote substituent effects upon the rearrangements of housane cation radicals

The rearrangement of a series of housane-derived cation radicals was investigated. Surprisingly, 2-aryl-substituted systems rearranged regioselectively and in a process whose selectivity proved to be independent of the electronic character of para substituents. The major reaction pathway is suggested to be the one that allows maximum delocalization, and allows it to be maintained for as long as possible. Bridging is invoked to account for the regio- and stereoselectivity. When a nonbridging trimethylsilylmethyl substituent is appended to C2, the regioselectivity is eroded entirely. B3LYP/6-31G(d) calculations corroborate the notion that bridging plays a role. While bridging ought to stabilize an intermediate by allowing delocalization of the charge/spin, there should be an accompanying entropic penalty. To determine the relative importance of enthalpic and entropic factors in determining the product selectivity, the rearrangement of the p-methoxyphenyl-substituted housane was investigated as a function of temperature. Enthalpic factors dominated over the entire temperature range that was explored. Overall, the results indicate that it is possible to influence the direction of migration in housane-derived cation radical rearrangements even when the regiochemical control unit is not directly appended to the migration terminus. This finding suggests that there may be other substituents that can be placed at C2 that could do the same, perhaps more efficiently.     

A systematic preparation of new contracted Gaussian-type orbital sets. V. From Na through Ca

Minimal compact contracted Gaussian basis sets are constructed for the atoms from Na to Ca. They give satisfactory valence shell orbital energies, although they are minimal-type basis sets. Split-type basis sets are also derived from the minimal Gaussian basis sets in order to enhance the flexibility of the basis sets for molecular calculations.     

Novel synthesis of 2,3-diarylbuta-1,3-dienes from 1,4-dimethoxybutyne-2

It was found that 2,3-diarylbuta-1,3-dienes were readily obtained in good to excellent yields through the S_N-2′ type substitution of 1,4-dimethoxybutyne-2 with aryl Grignard reagents in the presence of a copper(I) salt.     

Physical properties and structure of silk. V. Thermal behavior of silk fibroin in the random-coil conformation

The thermal behavior of films of amorphous silk fibroin in the random-coil conformation has been investigated in the temperature range 25–220°C by differential scanning calorimetry (DSC), thermal expansion, dynamic mechanical measurements, x-ray diffraction, and infrared spectroscopy. As the temperature is raised, water is lost up to about 100°C. Intramolecular and intermolecular hydrogen bonds are broken between 150 and 180°C. The glass transition is observed at 173°C by DSC. The random-coil→β-form transition accompanied by reformation of hydrogen bonds takes place above 180°C. Thermally induced crystallization to the β-form crystals starts at about 190°C.