Dynamics and structural changes of small water clusters on ionization

Despite utmost importance in understanding water ionization process, reliable theoretical results of structural changes and molecular dynamics (MD) of water clusters on ionization have hardly been reported yet. Here, we investigate the water cations [(H₂O)_{n = 2–6}⁺] with density functional theory (DFT), Möller–Plesset second‐order perturbation theory (MP2), and coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. The complete basis set limits of interaction energies at the CCSD(T) level are reported, and the geometrical structures, electronic properties, and infrared spectra are investigated. The characteristics of structures and spectra of the water cluster cations reflect the formation of the hydronium cation moiety (H₃O⁺) and the hydroxyl radical. Although most density functionals fail to predict reasonable energetics of the water cations, some functionals are found to be reliable, in reasonable agreement with high‐level ab initio results. To understand the ionization process of water clusters, DFT‐ and MP2‐based Born‐Oppenheimer MD (BOMD) simulations are performed on ionization. On ionization, the water clusters tend to have an Eigen‐like form with the hydronium cation instead of a Zundel‐like form, based on reliable BOMD simulations. For the vertically ionized water hexamer, the relatively stable (H₂O)₅⁺ (5sL4A) cluster tends to form with a detached water molecule (H₂O). © 2013 Wiley Periodicals, Inc.     

Quantitative analysis of propofol-glucuronide in hair as a marker for propofol abuse

The inappropriate or illegal use of propofol has recently come to the fore as a serious social issue in South Korea. Thus, in spite of its superior potency as a therapeutic drug, propofol was classified as a controlled drug under the purview of Narcotics Control Law in South Korea in February of 2011. Accordingly, the determination of propofol and/or its metabolites in biological specimens is required to prove ingestion. Therefore, to demonstrate chronic ingestion, a quantitative analytical method for propofol-glucuronide in hair was developed and validated using liquid chromatography-tandem mass spectrometry (LC-MS/MS). This method was applied to measure propofol-glucuronide in hair samples from 23 propofol abuse suspects and in both pigmented and nonpigmented hair from rats which had ingested propofol. Propofol-glucuronide in hair was extracted in methanol and then filtered and analyzed by LC-MS/MS with electrospray ionization in negative mode. The validation results of selectivity, matrix effect, recovery, linearity, precision and accuracy, and processed sample stability were satisfactory. The limit of detection was 20 pg/10 mg hair and the limit of quantification was 50 pg/10 mg hair. The concentration range of propofol-glucuronide in hair segments from 23 propofol abuse suspects was shown up to 1,410 pg/mg. The animal study demonstrated that the presence of melanin did not affect the deposition of propofol-glucuronide in hair. Thus, we propose propofol-glucuronide in hair as a marker for propofol abuse. This method will be very useful for monitoring the inappropriate use of propofol for both legal and public health aspects.     

Fabrication of UV detectors based on ZnO nanowires using silicon microchannel

Aligned ZnO nanowires were grown by metal organic chemical vapor deposition on patterned silicon substrate. The shape of nanostructures was greatly influenced by the micropatterned surface. The aspect ratio, packing fraction and the number density of nanowires on top surface are around 10, 0.8 and 10⁷ per mm², respectively, whereas the values are 20, 0.3 and 5×10⁷ per mm², respectively, towards the bottom of the cavity. XRD patterns suggest that the nanostructures have good crystallinity. High-resolution transmission electron microscopy confirmed the single-crystalline growth of the ZnO nanowires along the [0 0 0 1] direction. Photosensitivity of the nanowires, grown on both top and bottom surface of the microchannel, was observed. However, the nanowires grown on bottom surface have shown better UV response with base line recovery at dark condition.     

Effect of D-allose on prostate cancer cell lines: phospholipid profiling by nanoflow liquid chromatography-tandem mass spectrometry

d-Allose, a rare, naturally occurring monosaccharide, is known to exert anti-proliferative effects on cancer cells. The effects of d-allose on the cellular membranes of hormone-refractory prostate cancer cell line (DU145), hormone-sensitive prostate cancer cell line (LNCaP), and normal prostate epithelial cells (PrEC) were studied at the molecular level by phospholipid (PL) profiling using a shotgun lipidomic method. The molecular structures of 85 PL species including 23 phosphatidylcholines, 12 phosphatidylethanolamines (PEs), 11 phosphatidylserines (PSs), 16 phosphatidylinositols, 9 phosphatidic acids (PAs), and 14 phosphatidylglycerols (PGs) were identified by data-dependent collision-induced dissociation of nanoflow liquid chromatography–tandem mass spectrometry, and the PL amounts were quantified. The addition of d-allose to prostate cancer cell lines during their growth phases had negligible or decreased effects on the relative regulation of PL species, but several new PS molecules (two for DU145 and three for LNCaP) emerged. In contrast, experiments on the PrEC cell line revealed that some high abundant species (14:0/14:0-PE, 16:2/16:0-PG, and 20:6/18:1-PA) showed significant increases in concentration. These findings support a mechanism for the anti-proliferative effect of d-allose on prostate cancer cell lines that involves the induction of programmed cell death since PS molecules are known to induce apoptosis. Principal component analysis was carried out to examine differences in PL distributions among the three cell lines promoted by d-allose.     

Ligand topology effect on the reactivity of a mononuclear nonheme iron(IV)-oxo complex in oxygenation reactions

Mononuclear nonheme iron(IV)-oxo complexes with two different topologies, cis-α-[Fe(IV)(O)(BQCN)](2+) and cis-β-[Fe(IV)(O)(BQCN)](2+), were synthesized and characterized with various spectroscopic methods. The effect of ligand topology on the reactivities of nonheme iron(IV)-oxo complexes was investigated in C-H bond activation and oxygen atom-transfer reactions; cis-α-[Fe(IV)(O)(BQCN)](2+) was more reactive than cis-β-[Fe(IV)(O)(BQCN)](2+) in the oxidation reactions. The reactivity difference between the cis-α and cis-β isomers of [Fe(IV)(O)(BQCN)](2+) was rationalized with the Fe(IV/III) redox potentials of the iron(IV)-oxo complexes: the Fe(IV/III) redox potential of the cis-α isomer was 0.11 V higher than that of the cis-β isomer.     

Metal-organic frameworks based on unprecedented trinuclear and pentanuclear metal-tetrazole clusters as secondary building units

Solvothermal reactions of manganese(II) chloride tetrahydrate with a bis-tetrazole ligand, 2,6-di(1H-tetrazol-5-yl)naphthalene (H(2)NDT), in N,N'-dimethylformamide (DMF)/MeOH mixed solvent at two slightly different temperatures, 75 and 100 °C, led to two different metal-organic frameworks (MOFs), [Mn(II)(3)O(HNDT)(2)(NDT)(DMF)(3)] (1) and [Mn(II)(5)O(2)(HNDT)(2)(NDT)(2)(DMF)(8)] (2), with different net topologies. Single-crystal X-ray diffraction studies reveal that 1 is constructed from an unprecedented trinuclear building block, [Mn(II)(3)O(CN(4))(6)], as a 6-connected trigonal prismatic secondary building unit (SBU) of topological D(3h) site symmetry, and that the ligand in the HNDT(-1)/NDT(2-) deprotonation states is a linker, where two tetrazole (CN(4)) groups of the ligand are connected via a rigid naphthyl group. The tetrazole groups in 1 adopt a 1,2-μ-bridging mode with the manganese(II) ions to form a μ(3)-oxo trinuclear SBU. The trigonalprismatic SBU in 1 is connected to six neighboring SBUs to form a three-dimensional MOF of acs net topology. 2 is constructed from an unprecedented pentanuclear building block, [Mn(II)(5)O(2)(CN(4))(8)], as an 8-connected tetragonal prismatic SBU of topological D(4h) site symmetry. The tetrazole groups in 2 adopt monodentate, 1,2-μ- and 2,3-μ-bridging bidentate and 1,2,3-μ-bridging tridentate binding modes with the manganese(II) centers to form a bis-μ(3)-oxo pentanuclear SBU of local C(2) site symmetry. The tetragonal prismatic SBU in 2 is connected to eight neighboring SBUs to form a 3-D MOF of bcu net topology.     

Thickness dependence of the resistive switching behavior of nonvolatile memory device structures based on undoped ZnO films

The resistive switching behavior of Al/ZnO/Al layered memory device structures was investigated in connection with varying ZnO layer thickness and related changes in crystallinity and concentration of oxygen-related defects. It was observed that, with increasing thickness, the crystallinity of the ZnO layer was improved and the concentration of oxygen-related defects within the layer increased. While the device showed unipolar switching characteristics, the current-voltage hysteresis was dependent on the thickness of the ZnO layer. In particular, the set voltage gradually increased with increasing layer thickness in the high resistive state whereas the reset voltage remained almost constant in the low resistive state. The observed operation characteristics of the device structures in relation to the crystallinity and oxygen-related defect concentration of the ZnO layer suggest that extended defects such as grain boundaries and dislocations play important roles in determining device performances.     

Growth, modulation and photoresponse characteristics of vertically aligned ZnO nanowires

Vertically aligned, c-axis oriented zinc oxide (ZnO) nanowires were grown on Si substrate by metal organic chemical vapor deposition (MOCVD) technique, where sputtered aluminum nitride (AlN) film was used as an intermediate layer and thermally evaporated barium fluoride (BaF₂) film as a sacrificial layer. The aspect ratio and density of the nanowires were also varied using only Si microcavity without any interfacial or sacrificial layer. The UV detectors inside the microcavity have shown the higher on-off current ratio and fast photoresponse characteristics. The photoresponse characteristics were significantly varied with the aspect ratio and the density of nanowires.     

Bias temperature instability analysis on memory properties improved by hydrogen annealing treatment in Ti/HfOx /Pt capacitors

The influence of the hydrogen annealing treatment on the reliability of Ti/HfO_x /Pt capacitors is investigated by analyzing bias temperature instability (BTI). As compared to the N₂‐annealed sample, in the case of hydrogen‐annealed samples, both the set/reset voltages and currents are reduced from 6.5 V/–1.6 V to 3.8 V/–1.2 V and from 4 mA/170 nA to 800 µA/30 nA at 0.1 V, respectively. Of particular interest is the dramatic reduction in the set voltage variation from 3.3 V to 1.8 V. In addition, in BTI experiments, the current shift at the high resistance state (HRS) is reduced from 1.5 µA to 40 nA under a bias stress of –1 V/1000 s and from 40 µA to 0.5 µA under a temperature stress of 120 °C/1000 s. These results show that the hydrogen annealing treatment is very effective in improving the reliability of RRAM cells because it reduces the leakage current under bias temperature stress. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)