Structural basis for the phase switching of bisaminecopper(II) cations at the thermal limits of lattice stability

The structural grounds of the decrease of point and lattice symmetries coupled with switching of the exchange interaction in single crystals of a highly strained, coordinationally unsaturated bisdiaminecopper(II) cation are described. The combined magnetic susceptibility and X-ray diffraction results indicate that the interplay between the inherent vibronic instability and ligand-field strain imposed by moderately flexible, coordinationally shielding ligands enables effective switching of the pseudo-Jahn-Teller d9 centers between states with different exchange interaction in the low-temperature regime and valence orbital orientation and coordination geometry in the high-temperature regime. Within the low-temperature hysteresis region, the phase transition can also be induced by excitation of the ligand-to-metal charge-transfer bands, resulting in overall shrinkage of the lattice. The compound is a prototype of weakly electronically coupled one-dimensional Jahn-Teller systems, which can undergo phase transitions induced by light, in addition to heating, cooling, and change of pressure, and it represents a prospective basis for the design of switching materials capable of multimode external control.     

On the existence of zeros of monotone operators in reflexive Banach spaces

This paper is devoted to the investigation on the existence of zeros of monotone operators in reflexive Banach spaces. We first present a sufficient condition under which single-valued monotone operators have zeros. The obtained theorem includes a previous result as a special case. A necessary and sufficient condition for the existence of zeros of maximal monotone operators is presented.     

Feasibility study of low-power multiquantum-well vertical transmission optical amplifiers for optical interconnection

Performance of 0.98-μm InGaAs strained multiquantum-well Fabry-Perot vertical transmission optical amplifiers (MQW FP VTOAs) for optical inter-board connection is analyzed theoretically, and compared with those of GaAs MQW, GaAs bulk, and InGaAsP bulk VTOAs. A low-power operation of about 2 mA and a cascadability of several hundred boards are predicted for an InGaAs strained MQW FP VTOA.     

Significant increase of the barrier energy for magnetization reversal of a single-4f-ionic single-molecule magnet by a longitudinal contraction of the coordination space

Two-electron oxidation of [{Pc(OEt)8}2TbIII]- [Pc(OEt)8=dianion of 2,3,9,10,16,17,23,24-octaethoxyphthalocyanine], which leads to a longitudinal contraction of the coordination space of the single-4f-ionic single-molecule magnet (SMM), resulted in a significant increase of the magnetization-reversal barrier energy and a remarkable upward temperature shift of chi' peaks and chi'T drops. This is the first evidence that the dynamic magnetism of 4f SMMs can be controlled by a redox reaction on the ligand side without introducing any additional magnetic site or spin system.     

Synthesis of 6-O-Hexadecyl- and 6-O-Octylsucroses and Their Self-Assembling Properties Under Aqueous Conditions

This paper reports the synthesis and self-assembling properties of 6-O-hexadecyl- and 6-O-octylsucroses. Mono-etherification of 2,3,4,1′,3′,4′-hexa-O-benzylsucrose with the corresponding alkyl bromides predominantly took place at the glucose 6-position and the products were isolated by silica gel column chromatography. Benzyl groups in the isolated products were cleaved to yield the target derivatives. The SEM, TEM, XRD, and DLS results indicated that 6-O-alkylsucroses formed vesicle-type particles via formation of lamellar-like planes under aqueous conditions, which were further merged by fusion of the planes to construct larger aggregates. The self-assembling properties of the materials were different from those of the previously reported 6-O- and 6’-O-hexadecylsucroses mixture.     

Optical head with metal cladding in asymmetrical butted-grating structure for small thermal spot in laser-assisted magnetic recording

A planar near-field optical head with a high optical efficiency of 12.9% (3.2 times higher than that of our previous design) for laser-assisted magnetic recording is described. In this head, a slab-type waveguide with a narrow core is butt-coupled into a one-sided multilayer thin-film stack. Metal cladding is used in the core because of its high optical efficiency due to surface plasmon excitation. To keep production costs low, we use only two layers for the side part, which act as a two-index-step lens that couples light in the side part into a core of the central part. We optimized the parameters of this optical head and recording medium by means of an optical simulator using the finite-difference time-domain method and a thermal simulator. The calculated full width half maximum (FWHM) optical spot size on the recording medium is 24 × 47 nm² and the thermal spot size is 80 × 88 nm² (FWHM).     

An Atypical Arginine Dihydrolase Involved in the Biosynthesis of Cyclic Hexapeptide Longicatenamides

The incorporation of non-proteinogenic amino acids (NPAAs) enriches the structural diversity of nonribosomal peptides. Recently, four NPAA-containing cyclic hexapeptides, longicatenamides A−D, were isolated using a combined-culture strategy. Based on in silico analysis, we discovered their putative biosynthetic gene cluster (lon) and proposed a possible biosynthetic mechanism. Surprisingly, the lon22 gene encodes an atypical arginine dihydrolase, which can also catalyze the hydrolysis of citrulline to ornithine. Phylogenetic analysis showed that Lon22-like proteins form a novel clade that is separated from other guanidine-modifying enzymes. After rational design, the catalytic efficiencies of a Lon22 Y80F mutant for arginine and citrulline substrates were 2.31- and 4.70-fold that of the wild-type (WT), respectively. In addition, characterization of the Lon20-A4 adenylation domain suggested that it can incorporate both ornithine and lysine into the final products.     

Carrier Protein Mediated Formation of the Dihydropyridazinone Ring in Actinopyridazinone Biosynthesis

Heterocycles with nitrogen-nitrogen (N−N) bonds are privileged building blocks of synthetic drugs. They are also found in natural products, although the biosynthetic logic behind them is poorly understood. Actinopyridazinones produced by Streptomyces sp. MSD090630SC-05 possess unique dihydropyridazinone rings that have been studied as core nuclei in several approved synthetic therapeutics. Herein, we performed gene knockouts and in vitro biochemical experiments to elucidate the major steps in actinopyridazinone biosynthesis, including the unprecedented carrier protein mediated machinery for dihydropyridazinone formation.