Characterization of heat-assisted magnetic probe recording on CoNi/Pt multilayers

A method of heat-assisted magnetic recording (HAMR) potentially suitable for probe-based storage systems is characterized. In this work, field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. Pulse voltages of 2–7 V were applied to a CoNi/Pt multilayered film fabricated on either bare silicon or oxidized silicon substrates. Different types of Ir/Pt and W STM tips were used in the experiment. The results show that thermally recorded magnetic marks are formed with a nearly uniform mark size of 170 nm on the film fabricated on bare silicon substrate when the pulse voltage is above a threshold voltage. The mark size becomes 260 nm when they are written on the identical film fabricated on an oxidized silicon substrate. The threshold voltage depends on the material work function of the tip, with W having a threshold voltage about 1 V lower than Pt. A synthesized model, which contains the calculation of the emission current, the simulation of heat transfer during heating, and the study of magnetic domain formation, was introduced to explain experimental results. The simulation agrees well with the experiments.     

The phase study of the TlVS system and the properties of TlV6S8 and TlV5S8 phases

The ternary phase diagram of the TlVS system was investigated using samples quenched from 400°C, especially in the neighborhood of TlV₆S₈ and TlV₅S₈ phases. The TlV₆S₈ phase (Tl_xV₆S_y) exists between 0.75 < x < 1.00 and 7.55 < y < 7.90, and the TlV₅S₈ phase (Tl_x′V₅S_y′) between 0.70 < x′ < 1.00 and 7.54 < y′ < 7.98. A new ternary phase with the nominal composition of TlV₂S₄ was found in addition to the three known ternary phases. The entirely deintercalated V₆S_7.8 with the framework structure was obtained by using 1 N AlCl₃ + 0.01 N FeCl₃ aqueous solution, while the lower phase limit of the TlV₅S₈ phase was Tl_0.33V₅S₈ consistent with the earlier work. The electrical resistivity and the magnetic susceptibility measurements show that these compounds are expected to be weakly magnetic itinerant-electron systems.     

Reactions of 2-Pyridyl Substituted Phosphine Oxides and Phosphonium Salts with Organometallic Reagents and in Aqueous Media

Phosphine oxides bearing two or three 2-pyridyl groups react with organometallic reagents affording 2,2′-bipyridyl, 2-substituted pyridines and pyridine in good yields. Phosphonium salts and phosphine oxides, bearing at least two 2-pyridyl or substituted 2-pyridyl groups also give the corresponding 2,2′-bipyridyls and pyridines upon treatment with acid or neutral solvents such as water and alcohols in substantial yields. The 2,2′-bipyridyls are considered to be formed by ligand coupling within the pentacoordinated phosphorus intermediate formed incipiently during the reaction.     

Synthetic studies on β-lactam antibiotics. Part 16. synthesis of 1-carba-2-penem-3-carboxylic acid esters from penicillins utilizing a carbon-carbon coupling reaction

Allylazetidinones $\text{9}$, $\text{10}$, prepared by coupling of allylcoppers $\text{8}$ with chloroazetidinones $\text{6}$, $\text{7}$, were converted into carbapenem esters $\text{16}$, $\text{28}$–$\text{31}$ using an Emmons-Horner reaction to introduce the 6-side chain and an intramolecular Wittig reaction to form the carbapenem ring system.     

Atomic force microscopy study of surface morphology change in spinel LiMn2O4: Possibility of direct observation of Jahn-Teller instability

Surface morphology in 3.5 × 3.5 μm² area of spinel LiMn₂O₄, which is a typical cathode material for Li ion secondary batteries, is studied using an atomic force microscopy (AFM) with a conductive probe. Negative bias voltage is applied to the probe to attract Li⁺ ions toward LiMn₂O₄ surface during the AFM observation. Before applying the voltage (0 V), the whole LiMn₂O₄ surface is covered with scale-shaped grains. Under the negative voltage of 5.5 V, electric current abruptly increases, indicating Li⁺ ionic conduction. Simultaneously, part of the scale-shaped grains expand and flatten. Jahn-Teller phase transition, which is induced by the repulsive interaction between the Mn-e_g and O-2p electrons in Li accumulated layer, is proposed as a possible origin of these results.     

Chemical synthesis and application of C-terminally 5-carboxyfluorescein-labelled thymopentin as a fluorescent probe for thymopoietin receptor.

Thymopentin (TP5) is a synthetic pentapeptide fragment, which corresponds to position 32 - 36 of thymic polypeptide thymopoietin. Thymopoietin and TP5 display a variety of biological functions, including phenotypic differentiation of T cells and the regulation of immune systems. Previous chemical modification experiments suggested that there was an absolute requirement for N-terminal amino acids to maintain the biological activity of TP5. On the basis of this structure-activity relationship, we designed and synthesized the C-terminally 5-carboxyfluorescein-coupled TP5 (TP5-FAM) as a fluorescent probe for thymopoietin receptor. TP5-FAM could bind to the membrane of human lymphoid cell lines, MOLT-4 cells, in which the thymopoietin receptor is expressed. The binding is specific and saturable (K(d) = 33 microM). TP5 and human splenopentin are nearly equipotent inhibitors of TP5-FAM binding to the thymopoietin receptor, but porcine secretin did not show any significant inhibition of TP5-FAM binding to MOLT-4 cells. Thus, TP5-FAM is suggested to be a potent and biologically active ligand that would be useful for studying the binding and functional characteristics of the human thymopoietin receptor.     

Isoflavonoids from Belamcanda chinensis

Four new isoflavonoids were isolated along with six known related compounds from a rhizome of Belamcanda chinensis (Iridaceae), and their structures were characterized as 6'-O-p-hydroxybenzoyliridin, 6'-O-vanilloyliridin, 5,6,7,3'-tetrahydroxy-4'-methoxyisoflavone and 2,3-dihydroirigenin, respectively, on the basis of spectroscopic methods and chemical evidence.     

Photoreactivity of amino acids: tryptophan-induced photochemical events via reactive oxygen species generation.

Tryptophan (Trp), an aromatic amino acid, is a constituent of peptides/proteins and is also a precursor of serotonin, kynurenine derivatives, and nicotinamide adenine dinucleotides. There have been a number of reports on photochemical reactions involving peptides/proteins which contain Trp that showed significant photodegradation, dimerization, and photoionization. The photochemical properties of Trp have not been fully elucidated, and this would provide novel insight into the handling of Trp-containing peptides/proteins. Consequently, we have been trying to evaluate the photochemical properties of Trp, as well as other essential amino acids, focusing on their photosensitivity, photodegradation, and their ability to induce lipid peroxidation. Among all the essential amino acids tested, Trp exhibited the maximal level of superoxide anion generation under 18 h of light exposure (30000 lux). UV spectral analysis of Trp suggested the absorbability of UVA/B light, and exposure of Trp, in both solid and solution states, to UVA/B light resulted in significant photodegradation (t(0.5): 18 h) and gradual color changes. In addition, photoirradiated Trp generated lipoperoxidant, a causative agent of photoirritation, and this might be associated with ROS generation.     

Rational electronic tuning of CBS catalyst for highly enantioselective borane reduction of trifluoroacetophenone

α,α,α-Trifluoroacetophenone (2), which is susceptible to noncatalytic reduction by BH(3), could be reduced to chiral alcohol up to 90% ee by using electronically tuned-CBS catalyst (1) with BH(3). The enantioselectivities highly correlated with the differential orbital energies between 1-BH(3) adduct and 2, which were calculated by DFT method.