Discovery of 4-tert-butyl-2,6-dimethylphenylsulfur trifluoride as a deoxofluorinating agent with high thermal stability as well as unusual resistance to aqueous hydrolysis, and its diverse fluorination capabilities including deoxofluoro-arylsulfinylation with high stereoselectivity

Versatile, safe, shelf-stable, and easy-to-handle fluorinating agents are strongly desired in both academic and industrial arenas, since fluorinated compounds have attracted considerable interest in many areas, such as drug discovery, due to the unique effects of fluorine atoms when incorporated into molecules. This article describes the synthesis, properties, and reactivity of many substituted and thermally stable phenylsulfur trifluorides, in particular, 4-tert-butyl-2,6-dimethylphenylsulfur trifluoride (Fluolead, 1k), as a crystalline solid having surprisingly high stability on contact with water and superior utility as a deoxofluorinating agent compared to current reagents, such as DAST and its analogues. The roles of substituents on 1k in thermal and hydrolytic stability, fluorination reactivity, and the high-yield fluorination mechanism it undergoes have been clarified. In addition to fluorinations of alcohols, aldehydes, and enolizable ketones, 1k smoothly converts non-enolizable carbonyls to CF(2) groups, and carboxylic groups to CF(3) groups, in high yields. 1k also converts C(=S) and CH(3)SC(=S)O groups to CF(2) and CF(3)O groups, respectively, in high yields. In addition, 1k effects highly stereoselective deoxofluoro-arylsulfinylation of diols and amino alcohols to give fluoroalkyl arylsulfinates and arylsulfinamides, with complete inversion of configuration at fluorine and the simultaneous, selective formation of one conformational isomer at the sulfoxide sulfur atom. Considering the unique and diverse properties, relative safety, and ease of handling of 1k in addition to its convenient synthesis, it is expected to find considerable use as a novel fluorinating agent in both academic and industrial arenas.     

A binuclear Fe(III)Dy(III) single molecule magnet. Quantum effects and models

The binuclear [FeIII(bpca)(mu-bpca)Dy(NO3)4], having Single Molecule Magnet (SMM) properties, belonging to a series of isostructural FeIIILnIII complexes (Ln = Eu, Gd, Tb, Dy, Ho) and closely related FeIILnIII chain structures, was characterized in concise experimental and theoretical respects. The low temperature magnetization data showed hysteresis and tunneling. The anomalous temperature dependence of M?ssbauer spectra is related to the onset of magnetic order, consistent with the magnetization relaxation time scale resulting from AC susceptibility measurements. The advanced ab initio calculations (CASSCF and spin-orbit) revealed the interplay of ligand field, spin-orbit, and exchange effects and probed the effective Ising nature of the lowest states, involved in the SMM and tunneling effects.     

Study on the spin crossover transition and glass transition for Fe(II) complex film, [Fe(II)(H-triazole) 3 ]@Nafion, by means of M?ssbauer spectroscopy

[Fe(II)(H-trz)₃]@Nafion (trz = triazole) is a transparent spin crossover complex film, where the spin crossover transition between the low-spin (S = 0) and the high-spin (S = 2) states takes place between 225?K and 300?K. In this film, two doublets corresponding to the low-spin and high-spin states were observed in the ⁵⁷Fe M?ssbauer spectra, reflecting the spin crossover transition. From the analysis of ⁵⁷Fe M?ssbauer spectra, the Debye temperatures of the low-spin and high-spin sites were estimated at 185?K and 176?K, respectively, in the temperature range between 10?K and 150?K. In this film, the total intensity of the M?ssbauer spectra corresponding to the low-spin and high-spin sites drastically decreases above 200?K, reflecting the glass transition of Nafion, where the lattice vibration of [Fe(H-trz)₃] $_{\rm n}^{\,\,\rm 2n+}$ is softened just as in solution due to micro-Brown motion of the segment of Nafion polymer membrane.     

Enhancement of the fluorescence intensity of DNA intercalators using nano-imprinted 2-dimensional photonic crystal

We have fabricated polymer-based 2-dimensional photonic crystals that play a key role in enhancing the fluorescence of DNA intercalators. Highly ordered 2-dimensional photonic crystals possessing triangle-shaped and nm-sized hole arrays were fabricated on a 100 μm thick polymer film using nano-imprint lithography. Samples of double-stranded DNAs (sizes: 4361 and 48502 bp; concentration: 1 pM to 10 nM) were adsorbed on the surface of the 2-dimensional photonic crystal by electrostatic interactions and then treated with intercalators. It is found that the fluorescence intensity of the intercalator is enhanced by a factor of up to 10 compared to the enhancement in the absence of the 2-dimensional photonic crystal. Fluorescence intensity increases with increasing length and concentration of the DNAs. If the 2-dimensional photonic crystal is used as a Bragg reflection mirror, the enhancement of fluorescence intensity can be easily observed using a conventional spectrofluorometer. These results suggest that the printed photonic crystal offers a great potential for highly sensitive intercalator-based fluorescent detection of DNAs.

Acceleration of ammonium nitrite denitrification by freezing: determination of activation energy from the temperature of maximum reaction rate

A reaction of ammonium nitrite in ice was investigated. Upon freezing, some nitrite is oxidized by dissolved oxygen and some nitrite reacts with ammonium to produce nitrogen and water in a denitrification reaction. The former reaction was accelerated only during freezing, and the latter one was accelerated even after the whole sample was frozen. The denitrification reaction proceeded at very low concentration in ice, which were conditions under which the reaction would not proceed in solution. The nitrogen production increased linearly with increasing initial concentration of ammonium nitrite. The concentration factor in the unfrozen solution in ice was estimated to be 50.6 when the initial concentration was 0.5 mmol dm(-3), as obtained from comparison of reaction rates in solution and in ice. A new method for determination of the activation energy is proposed that gives a value of 53 to 61 kJ mol(-1) for denitrification. The reaction order of the denitrification process is also determined using our method, and it is concluded to follow third-order kinetics.     

Existence of limit cycles for coupled van der Pol equations

In this paper, we consider the existence of limit cycles of coupled van der Pol equations by using S¹-degree theory due to Dylawerski et al. (see Ann. Polon. Math. 62 (1991) 243).     

Nanosize effect on high-rate Li-ion intercalation in LiCoO2 electrode

Recently, battery technology has come to require a higher rate capability. The main difficulty in high-rate charge-discharge experiments is kinetic problems due to the slow diffusion of Li-ions in electrodes. Nanosizing is a popular way to achieve a higher surface area and shorter Li-ion diffusion length for fast diffusion. However, while various nanoelectrodes that provide excellent high-rate capability have been synthesized, a size-controlled synthesis and a systematic study of nanocrystalline LiCoO2 have not been carried out because of the difficulty in controlling the size. We have established the size-controlled synthesis of nanocrystalline LiCoO2 through a hydrothermal reaction and, for the first time, clarified the structural and electrochemical properties of this intercalation cathode material. Lattice expansion in nanocrystalline LiCoO2 was found from powder X-ray diffraction measurements and Raman spectroscopy. Electrochemical measurements and theoretical analyses on nanocrystalline LiCoO2 revealed that extreme size reduction below 15 nm was not favorable for most applications. An excellent high-rate capability (65% of the 1 C rate capability at 100 C) was observed in nanocrystalline LiCoO2 with an appropriate particle size of 17 nm.     

Enantioselective,Desymmetrizing, Bromolactonization Reactions of Symmetric Olefinic Dicarboxylic Acids

The results of studies leading to the development of enantioselective desymmetrizing, bromolactonization reactions of symmetric olefinic dicarboxylic acids, which are promoted by a C₃‐symmetric trisimidazoline catalyst, are described. These processes generated carboxylic‐acid‐containing bromolactones in moderately high enantiomeric excesses. The results of optimization studies showed that reactions in a mixed solvent system of toluene and acetone proceeded with the highest levels of enantioselectivity. NMR studies probing the interactions between the catalyst and dicarboxylic acid substrates, as well as the effect of acetone on the stereochemistry of the process, are also described.     

Texton-based super-resolution for achieving high spatiotemporal resolution in hybrid camera system

Many super-resolution methods have been proposed to enhance the spatial resolution of images by using iteration and multiple input images. In a previous paper, we proposed the example-based super-resolution method to enhance an image through pixel-based texton substitution to reduce the computational cost. In this method, however, we only considered the enhancement of a texture image. In this study, we modified this texton substitution method for a hybrid camera to reduce the required bandwidth of a high-resolution video camera. We applied our algorithm to pairs of high- and low-spatiotemporal-resolution videos, which were synthesized to simulate a hybrid camera. The result showed that the fine detail of the low-resolution video can be reproduced compared with bicubic interpolation and the required bandwidth could be reduced to about 1/5 in a video camera. It was also shown that the peak signal-to-noise ratios (PSNRs) of the images improved by about 6 dB in a trained frame and by 1.0–1.5 dB in a test frame, as determined by comparison with the processed image using bicubic interpolation, and the average PSNRs were higher than those obtained by the well-known Freeman’s patch-based super-resolution method. Compared with that of the Freeman’s patch-based super-resolution method, the computational time of our method was reduced to almost 1/10.