Nanostructured magnetic cuprate cluster: synthesis,structure, UV-Vis spectroscopy,and magnetic properties of a new copper(II) arsenate NaCuAsO4 containing discrete [Cu4O16]24- clusters

Crystals of copper(II) arsenate NaCuAsO(4) were grown by conventional high-temperature, solid-state methods in molten-salt media. The compounds were characterized by single crystal X-ray diffraction, UV-vis spectroscopy, and magnetic susceptibility measurements. NaCuAsO(4) crystallizes in a monoclinic lattice with a = 6.002 (1) A, b = 10.853 (2) A, c = 10.373 (2) A, beta = 91.50 (3) degrees, and V = 675.4(2) A(3); P2(1)/c (No. 14); Z = 8. The newly isolated sodium copper(II) arsenate reveals a pseudo-one-dimensional channel structure where the sodium cations reside. The extended framework contains nanostructured [Cu(4)O(16)](24-) magnetic clusters that are interlinked by closed-shell, nonmagnetic AsO(4)(3-) oxy anions via sharing vertex oxygen atoms of the CuO(5) and AsO(4) polyhedral units. Each [Cu(4)O(16)](24-) cluster consists of four CuO(5) square pyramidal units in a chair configuration centered by a center of inversion. The two crystallographically independent Cu(2+) cations adopt the [4 + 1] CuO(5) Jahn-Teller distortion giving rise to an intense d-d transition in UV-vis absorption spectra. The magnetic susceptibility measurements reveal that the title compound is antiferromagnetic. At high temperatures, the data follows a pure Curie law, suggesting noninteracting spins, but with a rapid suppression of the effective spin below T = 70 K. At low temperature, the susceptibility collapses, indicating spin gap formation as the magnetic-cluster material settles into the lowest energy magnetic singlet state. The current work in the exploratory synthesis of oxy compounds containing nanostructured transition-metal-oxide magnetic clusters leads to new materials for experimental and theoretical developments of magnetic models.     

Self-sensitized photooxygenation of 3,4-dialkoxyfurans to vitamin C or its derivatives

Self-sensitized photooxygenation of 3,4-dialkoxyfurans 3a-d with molecular oxygen and UV- or sunlight at room temperature gave vitamin C derivatives 2a-d in good to excellent yields. Furan 3c, having photodegradable protecting groups, was also photooxygenated to give L-ascorbic acid (1) in a "one-pot" reaction. Furthermore, a novel photolytic transformation was developed for deuteration of furan 3b at the C-2 position with D(2)O to give furan 3d in 95% yield. Toxicity of furans 3a-c and butenolides 2a-c against human embryonic cell, murine embryo fibroblasts, normal fibroblasts, HeLa, and Vero cell lines in the presence of oxygen and indirect solar light was found to be much less than those of the antipsoriasis drugs anthralin and 8-methoxypsoralen.     

Effect of trapped electrons in ultrathin SiO2 on the two-state inversion capacitance at varied frequencies of metal-oxide-semiconductor capacitor

Two-state inversion capacitances of a metal-oxide-semiconductor capacitor (MOSCAP) at varied AC frequencies after negative/positive constant voltage stress (negative/positive CVS) treatments are investigated. When the device was biased into inversion, a low/high inversion-capacitance state (set state/reset state) was achieved after the negative/positive CVS treatments with/without a few trapped electrons in the ultrathin SiO₂ layer. The inversion capacitances of set states were frequency independent, whereas those of reset states increased with the decreasing frequencies. It is different from the general characteristics of an MOSCAP whose inversion capacitances disperse at low frequencies. For this observed finding of the two-state inversion capacitances at varied frequencies, a mechanism of trapped-electrons-induced screening effect on the inversion electrons is proposed. The number of the trapped electrons in the SiO₂ layer affects the number of the inversion electrons, and thus dominates the values of the inversion capacitances. Besides, simulation curves of the inversion capacitances of set states are demonstrated. They are fitted well with the experimental data utilizing the mechanism we proposed. This work investigates further into the influence of the trapped electrons in the ultrathin SiO₂ layer on the inversion capacitance response.     

Hexamethyldisilathiane in Novel Chemical Transformations: Concept of “Counterattack Reagent”

Abstract

Deliberate design on utilization of each moiety in the “counterattack reagent,” Me₃SiSSiMe₃, allows it to accomplish multistep chemical transformations in one flask.     

Decreased surface tension of water by hard-x-ray irradiation

We discovered that intense irradiation by hard-x-ray strongly decreases the effects of natural surface tension of water in droplets and capillary tubes. The effect was revealed by direct experimental observations with phase contrast microradiology. A model based on ionization and surface charging explains this so far undetected phenomenon. The effect can impact the results of many experimental techniques based on x rays. This is an example of the largely unexplored effects that can be produced by extreme intense x-ray irradiation-an important issue due to current development of x-ray free-electron-lasers with unprecedented brilliance.