A New Calamenene Sesquiterpene Glycoside from the Bark of Thespesia populnea

Chemistry of Natural Compounds - One new calamenene sesquiterpene glycoside, (1R,2R,3S,4S)-4-isopropyl-1,6-dimethyl-1,2,3,4- tetrahydronaphthalene-2,7-diol 3-O-β-D-glucopyranoside (1), along...     

A no-go theorem for halting a universal quantum computer

A very brief introduction to quantum computing with an emphasis on the distinction between universal quantum computers and quantum networks. We then prove that, under very general and desirable assumptions, it is not possible to check for halting a universal quantum computer without losing the quantum computation.     

One-pot synthesis of a novel magnetic activated carbon/clay composite for removal of heavy metals from aqueous solution

Abstract

In the present work, a novel composite consisting of magnetite, activated carbon from spent coffee grounds and natural clay (MACCC) was prepared by a one-pot synthesis method via a simultaneous activation and magnetization processes. Various techniques (XRD, FTIR, SEM, TEM, EDX, BET) were utilized to characterize the synthesized composite before utilizing it as an adsorbent for removal of Cu(II), Ni(II) and Pb(II) ions from aqueous solutions. Conditions for removal of heavy metals were thoroughly optimized as 25?°C, pH of 5.5, adsorbent dosage of 2?g L^?1, and a contact time of 60?min. Three models of pseudo first-, second-order and intraparticle diffusion as well as three models of Langmuir, Freundlich, and Temkin were used to analyze kinetics and isotherms of the adsorption process. Thermodynamics was discussed completely. Regeneration and recyclability of the adsorbent were also evaluated. Based on the analysis of experimental results, a possible adsorption mechanism of heavy metals onto the synthesized composite was proposed. The maximum capacities caculated from Langmuir model followed the order of Pb(II) > Cu(II) > Ni(II) as 143.56, 96.16 and 84.86?mg·g^?1, respectively. The overall results indicated that MACCC is a potential adsorbent for removal of toxic Pb(II), Cu(II) and Ni(II) ions from wastewater due to simple preparation, high removal efficiency and good recyclability.     

Analysis of inorganic cations in biological samples by the combination of micro-electrodialysis and capillary electrophoresis with capacitively coupled contactless conductivity detection

Micro-electrodialysis (μED) and CE were combined for rapid pretreatment and subsequent determination of inorganic cations in biological samples. Combination of μED with CE greatly improved the analytical performance of the latter as the adsorption of high molecular weight compounds present in real samples on the inner capillary wall was eliminated. Fifty microliter of 80-fold diluted human body fluids such as plasma, serum and whole blood was used in the donor compartment of the μED system requiring less than 1?μL of the original body fluid per analysis. Inorganic cations that migrated through a cellulose acetate dialysis membrane with molecular weight cut-off value of 500?Da were collected in the acceptor solution and were then analyzed using CE-C?D. Baseline separation of inorganic cations was achieved in a BGE solution consisting of 12.5?mM maleic acid, 15?mM L-arginine and 3?mM 18-crown-6 at pH 5.5. Repeatability of the CE-C?D method was better than 0.5% and 2.5% for migration times and peak areas, respectively; limits of detection of all inorganic cations in the presence of 2?mM excess of Na(+) were around 1?μM and calibration curves were linear with correlation coefficients better than 0.998. Repeatability of the sample pretreatment procedure was calculated for six independent electrodialysis runs of artificial and real samples and was better than 11.8%. Recovery values between 96.3 and 110% were achieved for optimized electrodialysis conditions of standard solutions and real samples; lifetime of the dialysis membranes for pretreatment of real samples was estimated to 100 runs.     

N-phosphonio formamidine derivatives: Synthesis,characterization, X-ray crystal structures,and deprotonation reactions

A simple and efficient method for the preparation of N-phosphonio formamidine derivatives of the general formula [R”₂N?C(H)=N?P(R’)R₂]⁺X^? is described. The data recorded in solution and the single crystal X-ray studies revealed that these compounds are best described by the combination of the two mesomeric N-phosphonio formamidine [R”₂N?C(H)=N?P(R’)R₂]⁺ and iminium phosphazene [R”₂N=C(H)?N=P(R’)R₂]⁺ forms. Formamidine phosphorus ylides ⁱPr₂N?C(H)=N?P(CH₂)R₂ were prepared after addition of ^tBuLi at –78 °C from the corresponding N-phosphonio compounds. [(PhCN)₂Pd(Cl)₂] was reacted with ⁱPr₂N?C(H)=N?P(CH₂)ⁱPr₂ to form the dimeric complex [(ⁱPr₂N?C(H)=N?P(CH₂)ⁱPr₂)Pd(Cl)(μ-Cl)]₂ which was structurally characterized by X-ray analysis. The deprotonation reactions conducted on [ⁱPr₂N?C(H)=N?PPh₃]⁺X^? occurred via an intramolecular rearrangement to give the cyanamide compound ⁱPr₂N?C≡N and PPh₃; transient formation of the amino-phosphazene-carbene ⁱPr₂N?C?N=PPh₃ was not observed.     

Loan and nonloan flows in the Australian interbank network

High-value transactions between banks in Australia are settled in the Reserve Bank Information and Transfer System (RITS) administered by the Reserve Bank of Australia. RITS operates on a real-time gross settlement (RTGS) basis and settles payments and transfers sourced from the SWIFT payment delivery system, the Austraclear securities settlement system, and the interbank transactions entered directly into RITS. In this paper, we analyse a dataset received from the Reserve Bank of Australia that includes all interbank transactions settled in RITS on an RTGS basis during five consecutive weekdays from 19 February 2007 inclusive, a week of relatively quiescent market conditions. The source, destination, and value of each transaction are known, which allows us to separate overnight loans from other transactions (nonloans) and reconstruct monetary flows between banks for every day in our sample. We conduct a novel analysis of the flow stability and examine the connection between loan and nonloan flows. Our aim is to understand the underlying causal mechanism connecting loan and nonloan flows. We find that the imbalances in the banks’ exchange settlement funds resulting from the daily flows of nonloan transactions are almost exactly counterbalanced by the flows of overnight loans. The correlation coefficient between loan and nonloan imbalances is about −0.9 on most days. Some flows that persist over two consecutive days can be highly variable, but overall the flows are moderately stable in value. The nonloan network is characterised by a large fraction of persistent flows, whereas only half of the flows persist over any two consecutive days in the loan network. Moreover, we observe an unusual degree of coherence between persistent loan flow values on Tuesday and Wednesday. We probe static topological properties of the Australian interbank network and find them consistent with those observed in other countries.     

Trace determination of perchlorate using electromembrane extraction and capillary electrophoresis with capacitively coupled contactless conductivity detection

Electromembrane extraction (EME) and CE with capacitively coupled contactless conductivity detection (CE‐C⁴D) was applied to rapid and sensitive determination of perchlorate in drinking water and environmental samples. Porous polypropylene hollow fiber impregnated with 1‐heptanol acted as a supported liquid membrane (SLM) and perchlorate was transported and preconcentrated in the fiber lumen on application of electric field. High selectivity of perchlorate determination and its baseline separation from major inorganic anions was achieved in CE‐C⁴D using background electrolyte solution consisting of 7.5 mM L ‐histidine and 40 mM acetic acid at pH 4.1. The analytical method showed excellent parameters in terms of reproducibility; RSD values for migration times and peak areas at a spiked concentration of 15 μg/L of perchlorate (US EPA recommended limit for drinking water) were below 0.2 and 8.7%, respectively, in all examined water samples. Linear calibration curves were obtained for perchlorate in the concentration range 1–100 μg/L (r²≥0.999) with limits of detection at 1 μg/L for tap water and at 0.25–0.35 μg/L for environmental and bottled potable water samples. Recoveries at 15 μg/L of perchlorate were between 95.9 and 106.7% with minimum and maximum recovery values for snow and bottled potable water samples, respectively.