Potentiometric determination of stepwise stability constants of vanadium, molybdenum and tungsten chelates formed with asparagine and glutamine

The metal chelates of V(IV), Mo(VI) and W(VI) formed with asparagine and glutamine have been studied potentiometrically. Stepwise stability constants in O.1M sodium perchlorate at 25 degrees C are reported as follows. Asparagine chelates--log K(1)K(2) 14.50 and log K(3) 4.04 for V, log K(1) 8.06, log K(2) 7.29 and log K(3) 3.45 for Mo, and log K(1) 5.84, log K(2) 5.11 and log K(3) 3.30 for W. Glutamine chelates--log K(1)K(2) 14.45, and log K(3) 4.07 for V, log K(1) 7.90, log K(2) 6.93, and log K(3) 3.35 for Mo, and log K(1) 5.76, log K(2) 5.09 and log K(3) 3.20 for W.     

Potentiometric determination of stepwise stability constants of zirconium, thorium and uranium chelates of asparagine and glutamine

The metal chelates of Zr(IV), Th(IV) and U(VI) with asparagine and glutamine have been studied potentiometrically. Stepwise stability constants in 0.1 M sodium perchlorate at 25 degrees are as follows. Asparaginate chelates-log K(1) 8.80, log K(2) 6.25 for Zr, log K(1) 6.79, log K(2) 6.16 for U, log K(1) 8.28, log K(2) 7.77 and log K(3) 7.72 for Th. Glutaminate chelates-log K(1) 8.75, log K(2) 6.10 for Zr, log K(1) 6.63, log K(2) 6.22 for U, log K(1) 8.30, log K(2) 7.61 and log K(3) 7.55 for Th.     

Potentiometric determination of stepwise stability constants of zirconium and thorium chelates formed with aspartic and glutamic acids

The metal chelates of Zr(IV) and Th(IV) with aspartic and glutamic acids have been studied potentiometrically. Stepwise stability constants in 0.1 M sodium perchlorate at 25 degrees are reported as: aspartate chelates-log K(1) 9.70, log K(2) 6.85, and log K(3) 3.50 for Zr, and log k(1) 9.23, log K(2) 8.57, log K(3) 4.55 and log K(4) 3.87 for Th; glutamate chelates-log K(1) 9.60, log K(2) 6.40 and log K(3) 3.32 for Zr and log K(1) 9.11, log K(2) 8.52, log K(3) 4.18 and log K(4) 3.62 for Th.     

Cell-based fluorescence screen for K+ channels and transporters using an extracellular triazacryptand-based K+ sensor

K+ channels and K+-coupled membrane transporters are important targets for drug discovery. We previously developed a triazacryptand (TAC)-based K+ sensor, TAC-Red, and demonstrated its utility to image K+ waves in mouse brain in vivo (Padmawar et al. Nat. Methods. 2005, 2, 825-827). Here, we synthesized a green-fluorescing dextran conjugate of TAC-bodipy ("TAC-Limedex") for use as an extracellular K+ sensor and demonstrated its utility in measuring K+ transport across cell membranes. TAC-Limedex fluorescence increased by 50% with increasing [K+] from 0 to 2 mM and was insensitive to [Na+], [Cl-], or pH. K+ efflux from cells was quantified from increasing extracellular TAC-Limedex fluorescence following cell immersion in K+-free buffer. In HT-29 cells, K+ efflux was 2.0 +/- 0.1 micromol/cm2/s, increasing 8-fold following K+ channel activation by ATP; the increase in K+ efflux was inhibited by a K+ channel blocker or by preventing cytoplasmic calcium elevation. Electroneutral K+/Cl- cotransport was demonstrated in SiHa cells, in which K+ efflux was increased 3-fold by hypotonic challenge; the increase in K+ efflux was fully inhibited by a K+/Cl- transport blocker. K+ efflux measurements were adapted to a commercial fluorescence platereader for automated screening. The fluorescence-based K+ transport assay largely replaces assays requiring radioactive rubidium and is suitable for high-throughput identification of K+ transport modulators.     

Multi-temperature synchrotron PXRD and physical properties study of half-Heusler TiCoSb

Phase pure samples of the half-Heusler material TiCoSb were synthesised and investigated. Multi-temperature synchrotron powder X-ray diffraction (PXRD) data measured between 90 and 1000 K in atmospheric air confirm the phase purity, but they also reveal a decomposition reaction starting at around 750 K. This affects the high temperature properties since TiCoSb is semiconducting, whereas CoSb is metallic. Between 90 K and 300 K the linear thermal expansion coefficient is estimated to be 10.5 × 10(-6) K(-1), while it is 8.49 10(-6) K(-1) between 550 K and 1000 K. A fit of a Debye model to the Atomic Displacement Parameters obtained from Rietveld refinement of the PXRD data gives a Debye temperature of 395(4) K. The heat capacity was measured between 2 K and 300 K and a Debye temperature of 375(5) K was obtained from modelling of the data. Coming from low temperatures the electrical resistivity shows a metallic to semiconducting transition at 113 K. A relatively high Seebeck coefficient of ～-250 μV K(-1) was found at 400 K, but the substantial thermal conductivity (～10 W mK(-1) at 400 K) leads to a moderate thermoelectric figure of merit of 0.025 at 400 K.     

生物质混煤燃烧过程中钾的迁移转化规律

通过将稻秆和褐煤混燃，研究了燃烧温度以及生物质掺混比例对于混燃过程中K的释放、灰样中K的赋存形式以及矿物质变化的影响。研究表明，燃烧温度对于混合燃料中K的释放影响显著。在600-750℃时，随着温度升高，水溶性K和醋酸铵溶性K大量释放到气相，使得K的释放速率较快；而当温度在750-850℃时，水溶性K和醋酸铵溶性K开始大量地转化为其他形式的K而被固定在灰样中，使得K的释放速率变得缓慢；当温度高于850℃时，随着温度升高，盐酸溶性K的分解导致K释放速率重新增大。通过XRD分析发现，灰样中水溶性K主要以KCl的形式存在，K₂SO₄的生成同时受到原料中K的含量和S/Cl比值两个因素的共同影响，原料中K的含量越高，且S/Cl比值越大，越会促进K₂SO₄的生成。同时也发现生物质和煤混燃时存在协同作用，煤中Al、Si等元素会和生物质中的K反应生成碱性硅铝酸盐，从而导致更多K留在灰烬中。     

Vapour—liquid equilibria in binary systems formed by N-Methylpyrrolidone with hydrocarbons and hydroxyl derivatives

The vapour—liquid equilibria (VLE) determined by an ebulliometric total pressure method under isothermal conditions for binary systems formed by N-methylpyrrolidone with hexane (333.25 and 343.15 K), dodecane (393.25 K), cyclohexane (333.25 and 354.15 K), methyl-cyclohexane (354.15 and 373.25 K), benzene (333.25 and 354.15 K), toluene (362.15 and 383.35 K), propylbenzene (352.15 and 373.75 K), butylbenzene (352.15 and 373.75 K), propanol-1 (354.15 K), hexanol-1 (351.75 and 393.35 K) and at 393.55 K for cyclohexanol, 4-methylphenol and 2,4-dimethylphenol are reported. The vapour pressures of the pure substances are given. The least squares analysis of VLE data by means of the Redlich-Kister equation is given.     

A new high-pressure vapour–liquid equilibrium apparatus

A new variable volume static type high-pressure VLE apparatus has been designed, constructed, and tested on a number of systems. The apparatus has an operating temperature range from 250 K to 393 K and pressure range from absolute vacuum up to 120 bar. The stainless steel equilibrium cell has sapphire viewing windows and a novel liquid sampling technique utilizing gas chromatographic sampling valves which permit phase sampling without disturbance to the equilibrium condition. The apparatus was tested by measuring VLE isotherms for some binary systems, viz., carbon dioxide + toluene at 283.25 K, 311.15 K, 353.15 K and 391.45 K; carbon dioxide + methanol at 263.15 K, 273.15 K, 313.15 K, 363.15 K and 373.15 K; and propane + 1-propanol at 323.15 K, 378.15 K and 393.15 K. Satisfactory modeling was obtained of the measured VLE data and thermodynamic consistency tests showed the data to be not inconsistent.     

Cu2S-EuS phase diagram

In the Cu₂S-EuS system, a eutectic is formed between Cu₂S- and EuS-based solid solutions (ss) at (1069 ± 2) K, 24.5 mol % EuS. EuS dissolves 7.0 (at 1770 K), 5.0 (1170 K), and 3.0 (770 K) mol % Cu₂S. A ??-Cu₂S-based ss is of the open type, has an extent (mol %) of 15.5 (at 1069 K), 7.5 (970 K), 4.5 (770 K), 2.5 (520 K), and 1.5 (379 K) EuS, and melts incongruently at 1186 K, 7.0 mol % EuS. ??-Cu₂S at 379 K dissolves 6.5 mol % EuS; ??-Cu₂S at (1186 ± 3) K dissolves 3.5 mol % EuS.     

Direct detection of potassium cations bound to G-quadruplex structures by solid-state 39K NMR at 19.6 T

We report solid-state 39K NMR detection of the K+ ions bound to three G-quadruplex structures formed by self-assembly of 5'-tert-butyl-dimethylsilyl-2',3'-O-isopropylidene guanosine, guanosine, and guanosine 5'-monophosphate. The 39K NMR spectra clearly show different spectral signatures for K+ ions inside the G-quadruplex channel and for K+ ions bound to the phosphate groups. Solid-state 39K NMR spectra for hydrated K salts of adenosine 2'-monophosphate and adenosine 5'-diphosphate are also reported.     

Self-assembly of short peptide amphiphiles: the cooperative effect of hydrophobic interaction and hydrogen bonding

The interplay between hydrogen bonding, hydrophobic interaction and the molecular geometry of amino acid side-chains is crucial to the development of nanostructures of short peptide amphiphiles. An important step towards developing their practical use is to understand how different amino acid side-chains tune hydrophobic interaction and hydrogen bonding and how this process leads to the control of the size and shape of the nanostructures. In this study, we have designed and synthesized three sets of short amphiphilic peptides (I(3)K, LI(2)K and L(3)K; L(3)K, L(4)K and L(5)K; I(3)K, I(4)K and I(5)K) and investigated how I and L affected their self-assembly in aqueous solution. The results have demonstrated a strong tendency of I groups to promote the growth of β-sheet hydrogen bonding and the subsequent formation of nanofibrillar shapes. All I(m)K (m = 3-5) peptides assembled into nanofibers with consistent β-sheet conformation, whereas the nanofiber diameters decreased as m increased due to geometrical constraint in peptide chain packing. In contrast, L groups had a weak tendency to promote β-sheet structuring and their hydrophobicity became dominant and resulted in globular micelles in L(3)K assembly. However, increase in the number of hydrophobic sequences to L(5)K induced β-sheet conformation due to the cooperative hydrophobic effect and the consequent formation of long nanofibers. The assembly of L(4)K was, therefore, intermediate between L(3)K and L(5)K, similar to the case of LI(2)K within the set of L(3)K, LI(2)K and I(3)K, with a steady transition from the dominance of hydrophobic interaction to hydrogen bonding. Thus, changes in hydrophobic length and swapping of L and I can alter the size and shape of the self-assembled nanostructures from these simple peptide amphiphiles.     

Defective histone H3K27 trimethylation modification in embryos derived from heated mouse sperm

The mouse sperm genome is resistant to in vitro heat treatment, and embryos derived from heated sperm can support full-term embryonic development, but the blastocyst rate and implantation rate are lower compared to embryos derived from fresh sperm. In the present study, the patterns of DNA methylation, histone H4K12 (ACH4K12) acetylation, H3K9 trimethylation (H3K9-TriM), and H3K27 trimethylation (H3K27-TriM) in preimplantation embryos derived from 65 °C-heated sperm were investigated. Although no evident changes in global DNA methylation, histone H4K12 (ACH4K12) acetylation, and H3K9 trimethylation (H3K9-TriM) were found, significantly lower levels of H3K27-TriM, which was thought to be one of the reasons for low efficiency of mouse cloning, were found in the inner cell mass of heated-sperm derived blastocysts. Thus, defective modification of H3K27-TriM might contribute to compromised development of embryos derived from heated sperm.     

Cation exchange at the mineral-water interface: H3O+/K+ competition at the surface of nano-muscovite

This article describes a (39)K nuclear magnetic resonance (NMR) spectroscopic study of K (+) displacement at the muscovite/water interface as a function of aqueous phase pH. (39)K NMR spectra and T 2 relaxation data for nanocrystalline muscovite wet with a solid/solution weight ratio of 1 at pH 1, 3, and 5.5 show substantial liquid-like K (+) only at pH 1. At pH 3 and 5.5, all K (+) appears to be associated with muscovite as inner- or outer-sphere complexes, indicating that H 3O (+) does not displace basal surface K (+) beyond the (39)K detection limit under these conditions. In our pH 1 mixture, only approximately 1/3 of the initial basal surface K (+) population is located more than 3-4 A from the surface. (29)Si and (27)Al MAS NMR spectra and SEM images show no evidence of dissolution during the (39)K experiments, consistent with the liquid-like (39)K fraction originating from displaced basal surface K (+). Assuming no muscovite dissolution or interlayer exchange, the K (+)/H 3O (+) ratio relevant to the solution/surface exchange equilibrium is controlled by the total amount of K (+) on the surface and H 3O (+) in solution (K (+) surf/H 3O (+) aq). These parameters, in turn, depend on the basal surface area, solution pH, and the solid/solution ratio. The results here are consistent with significant displacement of surface K (+) only under conditions where the initial K (+) surf/H 3O (+) aq ratio is less than approximately 1. Computational molecular models of the muscovite/water interface should account for both K (+) and H 3O (+) in the near-surface region.     

一种新的钾试剂和低浓度钾离子的高效富集剂

本文报导一种新的钾试剂和低浓度钾离子的高效富集剂: 1,2,4,5-苯四酚-四乙酸。叙述了它的合成方法, 并研究了它对多种体系中低浓度钾离子的化学行为, 初步探讨了其捕钾机理, 作为高选择性的钾试剂, 可用于多种体系包括海水及卤水等复杂水盐体系中钾离子的分析, 富集与分离。     

重铬酸钾晶体低温热容及热力学性质的研究

用精密自动绝热量热计测定了重铬酸钾晶体在100～390 K温区内的摩尔热容.实验结果表明在研究温度区间内重铬酸钾无相变和其它热反常现象发生,但其热容在不同的温度范围表现出不同的变化趋势.在100 K≤ T ≤ 275 K和350 K≤ T ≤390 K区间内,其热容随温度的升高明显增大,在275 K≤ T ≤350 K区间,其热容约为定值.将重铬酸钾摩尔热容实验值Cp,m(J•K－1•mol－1)拟合成温度T的多项式方程,在100 K≤ T ≤275 K,为Cp,m=0.0050T2－1.0320T＋125.22； 275 K≤ T ≤ 350 K,为Cp,m=209.37； 350 K≤ T ≤390 K,为Cp,m= 0.0266T2－18.823T＋3542.3.根据热力学函数关系式,从热容值计算出了298.15 K～ 400 K温区范围内每隔5 K的热力学函数值.     

Nanoporous block copolymer micelle/micelle multilayer films with dual optical properties

We introduce a novel and versatile approach for preparing self-assembled nanoporous multilayered films with tunable optical properties. Protonated polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and anionic polystyrene-block-poly(acrylic acid) (PS-b-PAA) block copolymer micelles (BCM) were used as building blocks for the layer-by-layer assembly of BCM multilayer films. BCM film growth is governed by electrostatic and hydrogen-bonding interactions between the opposite BCMs. Both film porosity and film thickness are dependent upon the charge density of the micelles, with the porosity of the film controlled by the solution pH and the molecular weight (M(w)) of the constituents. PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K) films prepared at pH 4 (for PS(7K)-b-P4VP(28K)) and pH 6 (for PS(2K)-b-PAA(8K)) are highly nanoporous and antireflective. In contrast, PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K) films assembled at pH 4/4 show a relatively dense surface morphology due to the decreased charge density of PS(2K)-b-PAA(8K). Films formed from BCMs with increased PS block and decreased hydrophilic block (P4VP or PAA) size (e.g., PS(36K)-b-P4VP(12K)/PS(16K)-b-PAA(4K) at pH 4/4) were also nanoporous. This is attributed to a decrease in interdigitation between the adjacent corona shells of the low M(w) BCMs, thus creating more void space between the micelles. Multilayer films with antireflective and photochromic properties were obtained by incorporating a water-insoluble photochromic dye (spiropyran) into the hydrophobic PS core of the BCMs assembled in the films. The optical properties of these films can be modulated by UV irradiation to selectively and reversibly control the transmission of light. Light transmission of higher than 99% was observed with accompanying photochromism in the (PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K)) multilayer films assembled at pH 4/6. Our approach highlights the potential to incorporate a range of materials, ranging from conventional hydrophilic materials with specific interactions to hydrophobic compounds, into the assembled BCMs to yield multifunctional nanoporous films.     

高效热管传热工质的热力学研究

用精密绝热量热法测量了高效热管传热工质在78～320 K温区内的热容.结果表明，在78.41～245.19 K， Cp/(J•K－1•g－1)=0.5369T＋0.07279.在274.08～318.51 K， Cp/(J•K－1•g－1)=3.403±0.020.在245～274 K， 高效热管传热工质发生固液相变.其相变温度、相变焓和相变熵分别是271.21 K、353.6 J•g－1，和1.304 J•K－1•g－1.根据热容与温度的定量关系和热力学函数之间的关系，得到了以标准温度298.15 K为基准的高效热管传热工质的热力学函数.     

Benchmark database of barrier heights for heavy atom transfer, nucleophilic substitution, association, and unimolecular reactions and its use to test theoretical methods

A benchmark database of forward and reverse barrier heights for 19 non-hydrogen-transfer reactions has been developed by using Weizmann 1 calculations, and 29 DFT methods and 6 ab initio wave-function theory (WFT) methods have been tested against the new database as well as against an older database for hydrogen atom transfer reactions. Among the tested hybrid DFT methods without kinetic energy density, MPW1K is the most accurate model for calculations of barrier heights. Among the tested hybrid meta DFT methods, BB1K and MPWB1K are the two most accurate models for the calculations of barrier heights. Overall, the results show that BB1K and MPWB1K are the two best DFT methods for calculating barrier heights, followed in order by MPW1K, MPWKCIS1K, B1B95, MPW1B95, BH and HLYP, B97-2, mPW1PW91, and B98. The popular B3LYP method has a mean unsigned error four times larger than that of BB1K. Of the methods tested, QCISD(T) is the best ab initio WFT method for barrier height calculations, and QCISD is second best, but QCISD is outperformed by the BB1K, MPWB1K, MPWKCIS1K, and MPW1K methods.     

库水硼镁石2MgO.3B2O3.15H2O的65-310K间的比热测定及其热力学性质的计算

用真空绝热量热计测定了库水硼镁石2MgO.3B2O3.15H2O在65-310K间的比热.根据Debye-Einsein函数组合式, 计算了0-65K间的比热, 其误差为0.4%.在65-310K范围内, 每隔5K, 计算了熵、焓和自由能函数.