Formation, manipulation, and elasticity measurement of a nanometric column of water molecules

Nanometer-sized columns of condensed water molecules are formed by an atomic-resolution force microscope operated in ambient conditions. An unusual stepwise decrease of the force gradient associated with the ultrathin water bridge in the tip-substrate gap is observed during its stretch, exhibiting regularity in step heights (approximately 0.5 N/m) and plateau lengths (approximately 1 nm). Such "quantized" elasticity is indicative of an atomic-scale stick slip at the tip-water interface. A thermodynamic-instability-induced rupture of the water meniscus (5 nm long and 2.6 nm wide) is also found. This work opens a high-resolution study of the structure and interface dynamics of a nanometric aqueous column.     

Electrical conductances of sodium bromide and sodium tetraphenylborate in 2-ethoxyethanol + water mixtures at 308.15, 313.15, 318.15 and 323.15 K

The electrical conductances of the solutions of sodium bromide (NaBr) and sodium tetraphenylborate (NaBPh₄) in 2-ethoxyethanol + water mixed solvent media containing 0.25, 0.50 and 0.75 mass fractions of 2-ethoxyethanol (w₁) have been reported at 308.15, 313.15, 318.15, and 323.15 K. The conductance data have been analyzed by the 1978 Fuoss conductance–concentration equation in terms of the limiting molar conductance (Λ⁰), the association constant (K_A) and the association diameter (R). Of the two electrolytes investigated here, sodium bromide exists essentially in the form of free ions in aqueous 2-ethoxyethanol solutions over the entire temperature range investigated. However, slight ionic association was observed for sodium tetraphenylborate—the extent of which increases with increasing amount of 2-ethoxyethanol in the present mixed solvent media. The solvations of the bromide ion and of the sodium ion were found to be gradually weakened as the 2-ethoxyethanol content of the medium increases. Furthermore, the limiting molar conductivity values of the two electrolytes increase as the temperature increases in all 2-ethoxyethanol + water mixtures which have been described by polynomial equations.     

Spectral characteristics of water clusters in the interaction with ozone molecules and bromide ions

The molecular dynamics method is used to study the interaction of the (Br⁻) _i (H₂O)_{50 − i} clusters in a medium of water vapor with ozone molecules. The clusters absorb O₃ molecules and retain them, along with Br⁻ ions, for a 25-ps-long calculation procedure. The presence of bromide ions results in significant increases in the values of the real and imaginary parts of the relative permittivity. The addition of bromide ions causes a significant increase in the integrated IR radiation absorption intensities and in the radiant power emitted by the clusters. The addition of Br⁻ ions only slightly affects the intensity of the Raman spectra until the number of Br⁻ reaches six, when a dramatic decrease of the integrated intensity of this spectrum occurs. Bromide ions absorbed by water clusters produce a much more lasting impact on the ozone molecules trapped by the cluster than chlorine ions do, all other things being equal.     

Study of ion–solvent interactions and activation energy of LiBr in DMSO,H<Subscript>2</Subscript>O and DMSO–H<Subscript>2</Subscript>O mixtures at various temperatures

The Jones–Dole B coefficients of the electrolyte Lithium bromide (LiBr), reference salts tetra butyl ammonium tetra phenyl borate (BU₄NBPh₄), tetra butyl ammonium bromide (BU₄NBr), and potassium chloride (KCl) in dimethylsulfoxide (DMSO), water, and DMSO–water mixtures were obtained at different temperatures range from 25 to 45 °C For this, the relative viscosities were measured for Lithium bromide (LiBr) and reference salts in DMSO, water, and DMSO–water mixtures at above-mentioned temperatures. The B coefficients of these electrolytes were behaved as structure makers in DMSO, while in H₂O and DMSO–H₂O mixtures, the B-coefficient values were less positive showing the weak structure-making effect. Ionic viscosity B coefficients allow us to assess the behavior of ions in the solvent mixtures. In this study it was observed that all the values of ionic B coefficient of (Li⁺) were positive and small showing the weak structure-making effects. It was also observed that Br⁻ ions maintain negative B coefficient values in all DMSO–H₂O mixtures, except in 60% DMSO mole fraction. From this it can be concluded that Br⁻ ion behaved as a structure breaker in water and in all DMSO–H₂O mixtures except in 60% DMSO mole fraction mixtures. The low B _± values of alkali metal ions and Br⁻ ions in water are due to the breakdown of the tetrahedral structural of water and the formation of strongly structured solvated ion. It is also observed that the values of the energy of activation of the flow for LiBr are greater in DMSO–water mixtures and in pure water than in DMSO. This may be due the presence of a network of hydrogen bonds which cause the hindrance in the flow of the solution of LiBr in DMSO–water mixtures and in pure water than in DMSO.     

真空、低能离子注入对人宫颈癌（HeLa）细胞中 p53及c-fos mRNA的表达影响

在具有高效护水功能石蜡油的保护下进行了人宫颈癌细胞(HeLa细胞)的低能离子注入及真空处理, 用荧光定量PCR的方法分别研究了真空和30 keV N+的不同注入剂量下, 细胞中p53基因和c-fos基因的mRNA表达变化。 结果表明, 上述两个基因的表达与真空及低能离子注入之间存在着剂量关系。     

Viscosity of interfacial water

The effective shear viscosity and frequency-dependent dynamic oscillatory shear spectra of water containing monovalent or divalent ions (ionic strength 25 mM), confined between mica crystals at 1-2 water molecules thickness, oscillated with twist angle with the period expected for the pseudohexagonal surface lattice. The effective viscosity varied by orders of magnitude as the twist angle was changed. Confinement appeared to imprint lateral spatial correlation on the ultrathin liquid, the more so the better the confining lattices were aligned, but the oft-proposed "ice structure" was not observed dynamically.     

Protein hydration and location of water molecules in oxidized horse heart cytochrome c by (1)H NMR

The hydration properties of the oxidized form of horse heart cytochrome c have been studied by (1)H NMR spectroscopy. Two-dimensional, homonuclear ePHOGSY-NOESY experiments are used to map water-protein interactions. The detected NOEs reveal interactions between nonexchangeable protein protons and both water protons and labile protein protons which exchange with water protons. Among the many water molecules apparent in the X-ray structure, three have been identified with a residence time longer than 300 ps. One of them is located inside the distal heme cavity, in the deepest part of a hydration pathway extending toward the surface. The identification of hydrophilic regions and detection of three long-lived water molecules settles some ambiguities and provides a better representation of the water-protein interactions in oxidized cytochrome c.     

Sonochemistry of antitumor quinones in argon-saturated aqueous solutions: enhanced ferricytochrome c reduction

Sonolysis of argon-saturated aqueous antitumor quinone solutions resulted in an enhancement in ferricytochrome c (Cyt c) reduction. Partial inhibition of these reduction enhancements by addition of superoxide dismutase evidences the production of superoxide ions. No correlation between quinone hydrophobicity or redox potential is observed in the extent of Cyt c reduction. The semiquinone of the parent quinone as well as other quinone-derived reductants are proposed as the electron shuttle intermediates which reduce Cyt c.     

Isentropic compressibility, effective pressure, classical sound absorption and shear relaxation time of aqueous lithium bromide, sodium bromide and potassium bromide solutions

Densities, speeds of sound and viscosities of aqueous lithium bromide, sodium bromide and potassium bromide solutions were measured as functions of concentration (0.0085≤m (mol kg⁻¹)≤14.06) and temperature (273.15≤T(K)≤323.15). Allied properties like isentropic compressibilities, effective pressure, classical sound absorption and shear relaxation time were calculated by using the measured data. The interaction in these three bromide solutions vary in the order of NaBr>KBr>LiBr. The primary hydration shells are saturated at 10.8, 5.1 and 5.8 mol kg⁻¹ with 5.1, 10.9 and 9.6 number of water molecules in the primary hydration shell of lithium bromide, sodium bromide and potassium bromide solutions respectively. The cationic environment is found to influence the hydration phenomena of the anion.

The non-Arrhenius temperature dependence of shear relaxation time were analysed by using the Vogel-Tammann-Fulcher (VTF) equation. The concentration dependence of shear relaxation time is different in these three bromide solutions. Such an effect is attributed to the competitive effects of hydrogen bonding, structure forming/breaking effect of ions and the formation of ion pairs.     

On autoionization and pH of liquid water

The ionization constant of water K_w (or pH) is currently determined on the proton conductivity σ₀ which is measured at frequencies lower than 10⁷ Hz. We develop the idea that the high frequency conductivity σ_∞ (~10¹¹ Hz), rather than σ₀ represents a net proton dynamics in water. We count the concentration c of the H₃O⁺ and OH^– ions from σ_∞ to find c to be not dependent on temperature. We conclude that spontaneous ionization of H₂O molecules is not essential in water electrodynamics; the common K_w reflects the thermoactivation of the H₃O⁺ and OH^– ions from the potential of their interaction; the lifetime of a target water molecule does not exceed parts of nanosecond.     

Observation of a near-threshold enhancement in the e+e- -->Lambda+_(c)Lambda-_(c) cross section using initial-state radiation

We report a measurement of the exclusive e+ e- -->Lambda+_(c)Lambda-_(c) cross section as a function of center-of-mass energy near the Lambda+_(c)Lambda-_(c) threshold. A clear peak with a significance of 8.2sigma is observed in the Lambda+_(c)Lambda-_(c) invariant mass distribution just above threshold. With an assumption of a resonance origin for the observed peak, a mass and width of M=[4634 (+8)_(-7)(stat)(+5)_(-8)(syst)] MeV/c(2) and Gamma_(tot)=[92 (+40)_(-24)(stat)(+10)_(-21)(syst)] MeV are determined. The analysis is based on a study of events with initial-state-radiation photons in a data sample collected with the Belle detector at the Upsilon(4S) resonance and nearby continuum with an integrated luminosity of 695 fb(-1) at the KEKB asymmetric-energy e+ e- collider.     

Doping dependent evolution of magnetism and superconductivity in Eu(1-x)K(x)Fe2As2 (x = 0-1) and temperature dependence of the lower critical field H(c1)

We have synthesized polycrystalline samples of Eu(1-x)K(x)Fe2As2 (x = 0-1) and carried out systematic characterization using x-ray diffraction, ac and dc magnetic susceptibility, and electrical resistivity measurements. A clear signature of the coexistence of a superconducting transition (T(c) = 5.5 K) with spin density wave (SDW) ordering is observed in our underdoped sample with x = 0.15. The SDW transition disappears completely for the x = 0.3 sample and superconductivity arises below 20 K. The superconducting transition temperature Tc increases with increase in the K content and a maximum Tc = 33 K is reached for x = 0.5, beyond which it decreases again. The doping dependent Tx phase diagram is extracted from the magnetic and electrical transport data. It is found that magnetic ordering of Eu moments coexists with the superconductivity up to x = 0.6. The isothermal magnetization data taken at 2 K for the doped samples suggest the 2+ valence state of the Eu ions. We also present the temperature dependence of the lower critical field H(c1) of the superconducting polycrystalline samples. The values of H(c1)(0) obtained for x = 0.3, 0.5, and 0.7 after taking the demagnetization factor into account are 202, 330, and 212 Oe, respectively. The London penetration depth λ(T) calculated from the lower critical field does not show exponential dependence at low temperature, as would be expected for a fully gapped clean s-wave superconductor. In contrast, it shows a T2 power law feature up to T = 0.3Tc, as observed in Ba(1-x)K(x)Fe2As2 and BaFe(2-x)Co(x)As2.     

Diffusion of ions in supercritical water: Dependence on ion size and solvent density and roles of voids and necks

We have performed molecular dynamics simulations of alkali metal (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and halide (F⁻, Cl⁻, Br⁻, I⁻) ions in supercritical water at 673 K. The calculations were done for water at three different densities of 1.0, 0.7 and 0.35 g cm⁻³ to investigate the effects of solute size on the diffusion of ions in supercritical water. On increase of ion size, we observe a maximum for diffusion of ions in supercritical water of higher densities (1.0 and 0.7 g cm⁻³). However, no such maximum is found for ion diffusion in the supercritical water of low density (0.35 g cm⁻³) or for diffusion of neutral solutes at all densities. These results are analyzed in terms of passage through voids and necks present in supercritical water. Correlations of the observed diffusion behavior with the sizes of ions and voids present in the systems are discussed.     

Microscopic dynamics in water and ionic aqueous solutions: velocity cross-correlations

The microscopic momentum transfer between distinct particles in water and ionic aqueous solutions has been investigated by molecular dynamics simulation. The time correlation functions between the initial velocity of a central molecule and later velocities of molecules within different coordination shells were calculated for liquid water. Special attention was paid to the influence of the intermolecular hydrogen bonds on the exchange of momentum among water molecules and on the power spectra of the velocity autocorrelation functions. The velocity cross-correlations between ions in an aqueous NaCl solution also were calculated. It was observed that the difference between the results for the Na⁺ and Cl^? ions are associated mainly with the different sizes of the ions.     

Measurements of the mass and width of the eta(c) meson and of an eta(c)(2S) candidate

The mass m(eta(c)) and total width Gamma(eta(c))(tot) of the eta(c) meson have been measured in two-photon interactions at the SLAC e(+)e(-) asymmetric B Factory with the BABAR detector. With a sample of approximately 2500 reconstructed eta(c)-->K(0)(S)K+/-pi(-/+) decays in 88 fb(-1) of data, the results are m(eta(c))=2982.5+/-1.1(stat)+/-0.9(syst) MeV/c(2) and Gamma(eta(c))(tot)=34.3+/-2.3(stat)+/-0.9(syst) MeV/c(2). Using the same decay mode, a second resonance with 112+/-24 events is observed with a mass of 3630.8+/-3.4(stat)+/-1.0(syst) MeV/c(2) and width of 17.0+/-8.3(stat)+/-2.5(syst) MeV/c(2). This observation is consistent with expectations for the eta(c)(2S) state.     

Spectrum of OH-stretching vibrations of water in a “floating” water bridge

The axial distribution (over the cross section) of the spectra of the OH-stretching band of water in a water bridge is investigated using the Raman scattering method. It is found that the axial structure of the bridge is inhomogeneous: the core at the center of the bridge contains a larger amount of water with an ??icelike?? structure and a presumably larger number of H⁺ ions, while the outer layer probably consists of water with a larger number of OH^? ions.     

Sonochemical formation of nitrate and nitrite in water

The formation of nitrite and nitrate ions in water under irradiation with 900 kHz ultrasound was studied as a function of time, temperature and gas (oxygen/nitrogen) composition. The rate decreases as temperature increases, and is below the detection limit when there is no O2 gas present. The absolute rate of formation of NOx- ions obtained (about 30 x 10(-9) mol min-1 W-1) agrees well with previous similar studies. The differences in the NO2-/NO3- ratio found between various studies can be satisfactorily explained though a mechanism where HNO2 and HNO3 are formed in the gas phase of the imploding cavity, and then dissolve in the water and dissociate to ions. The NO2- species is initially substantially favoured, as considerably more NO is formed than NO2. Thermodynamic calculations indicate that at the 'hot spot' temperature of about 5000 K believed to be present, there would very large amounts of NO and OH radicals present, and at such high temperatures, thermodynamics would be a good approximation of the situation, since the rates of reactions would be very rapid. The reaction needs O2 in order to proceed to a significant degree; no NOx- was detected in the absence of oxygen gas.     

Experimental investigation of the two-photon widths of the chi(c0) and the chi(c2) mesons

Using 12.7 fb(-1) of data collected with the CLEO detector at CESR, we observed two-photon production of the cc states chi(c0) and chi(c2) in their decay to pi(+)pi(-)pi(+)pi(-). We measured gamma(gammagamma)(chi(c))xB(chi(c)-->pi(+)pi(-)pi(+)pi(-)) to be 75+/-13(stat)+/-8(syst) eV for the chi(c0) and 6.4+/-1.8(stat)+/-0.8(syst) eV for the chi(c2), implying gamma(gammagamma)(chi(c0)) = 3.76+/-0.65(stat)+/-0.41(syst)+/-1.69(br) keV and gamma(gammagamma)(chi(c2)) = 0.53+/-0.15(stat)+/-0.06(syst)+/-0.22(br) keV. Also, cancellation of dominant experimental and theoretical uncertainties permits a precise comparison of gamma(gammagamma)(chi(c0))/gamma(gammagamma)(chi(c2)), evaluated to be 7.4+/-2.4(stat)+/-0.5(syst)+/-0.9(br), with QCD-based predictions.     

The effect of clustering of VO2+ ions in sub- and supercritical water. An in situ EPR study

Temperature variations of the EPR spectra of VO²⁺ ions in sub- and supercritical water under isothermal and temperature gradient conditions are investigated using an in situ EPR. Broadening of the hyperfine structure at increasing temperature and the appearance of an unresolved broad low-intensity line (ΔH _pp ≈ 300 Oe) in the supercritical state are observed in the absence of temperature gradients, indicating an increase of exchange interaction between VO²⁺ ions in supercritical water. An exchange-narrowed anisotropic absorption line is observed under the temperature-gradient conditions in the subcritical water near the transition to a supercritical state. The shape of this line is close to that observed in the solid salt VOSO₄ · 3H₂O. It is shown that in situ EPR allows us to investigate the effects of changing the local environment of paramagnetic ions, which precedes the well-known process of clustering and formation of amorphous oxide particles in sub- and supercritical conditions.