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Sample records for absorbed water molecules

  1. Dual band metamaterial perfect absorber based on artificial dielectric "molecules".

    PubMed

    Liu, Xiaoming; Lan, Chuwen; Li, Bo; Zhao, Qian; Zhou, Ji

    2016-01-01

    Dual band metamaterial perfect absorbers with two absorption bands are highly desirable because of their potential application areas such as detectors, transceiver system, and spectroscopic imagers. However, most of these dual band metamaterial absorbers proposed were based on resonances of metal patterns. Here, we numerically and experimentally demonstrate a dual band metamaterial perfect absorber composed of artificial dielectric "molecules" with high symmetry. The artificial dielectric "molecule" consists of four "atoms" of two different sizes corresponding to two absorption bands with near unity absorptivity. Numerical and experimental absorptivity verify that the dual-band metamaterial absorber is polarization insensitive and can operate in wide-angle incidence. PMID:27406699

  2. Y-shaped two-photon absorbing molecules with an imidazole-thiazole core

    NASA Technical Reports Server (NTRS)

    Feng, Ke; De Boni, Leonardo; Misoguti, Lino; Mendonca, C. R.; Meador, Michael; Hsu, Fu-Lian; Bu, Xiu R.

    2004-01-01

    Two new classes of two-photon absorbing Y-shaped molecules have been developed to possess an imidazole-thiazole core and a stilbene-type conjugation pathway with either nitro or sulfonyl as terminal electron-accepting group.

  3. Spectroscopic modeling of water molecule

    NASA Astrophysics Data System (ADS)

    Danylo, R. I.; Okhrimenko, B. A.

    2013-12-01

    This research is devoted to the vibrational spectroscopy inverse problem solution that gives a possibility to design a molecule and make conclusions about its geometry. The valence angle finding based on the usage of inverse spectral vibrational spectroscopy problem is a well-known task. 3N-matrix method was chosen to solve the proposed task. The usage of this method permits to make no assumptions about the molecule force field, besides it can be applied to molecules of matter in liquid state. Anharmonicity constants assessment is an important part of the valence angle finding. The reduction to zero vibrations is necessary because used matrix analytical expression were found in the harmonic approach. In order to find the single-valued inverse spectral problem of vibrational spectroscopy solution a shape parameter characterizing "mixing" of ω1 and ω2 vibrations forms must be found. The minimum of such a function Υ called a divergence parameter was found. This function characterizes method's accuracy. The valence angle assessment was reduced to the divergence parameter minimization. The β value concerning divergence parameter minimum was interpreted as the desired valence angle. The proposed method was applied for water molecule in liquid state: β = (88,8 ±1,7)° . The found angle fits the water molecule nearest surrounding tetrahedral model including hydrogen bond curvature in the first approximation.

  4. Water molecules orientation in surface layer

    NASA Astrophysics Data System (ADS)

    Klingo, V. V.

    2000-08-01

    The water molecules orientation has been investigated theoretically in the water surface layer. The surface molecule orientation is determined by the direction of a molecule dipole moment in relation to outward normal to the water surface. Entropy expressions of the superficial molecules in statistical meaning and from thermodynamical approach to a liquid surface tension have been found. The molecules share directed opposite to the outward normal that is hydrogen protons inside is equal 51.6%. 48.4% water molecules are directed along to surface outward normal that is by oxygen inside. A potential jump at the water surface layer amounts about 0.2 volts.

  5. Ultraviolet light absorbers having two different chromophors in the same molecule

    DOEpatents

    Vogl, O.; Li, S.

    1983-10-06

    This invention relates to novel ultraviolet light absorbers having two chromophors in the same molecule, and more particularly to benzotriazole substituted dihydroxybenzophenones and acetophenones. More particularly, this invention relates to 3,5-(di(2H-benzotriazole-2-yl))-2,4-dihydroxybenzophenone and 3,5-(di(2H-benzotriazole-2-yl))-2,4-dihydroxyacetophenone which are particularly useful as an ultraviolet light absorbers.

  6. Size-dependent fluorescence of bioaerosols: Mathematical model using fluorescing and absorbing molecules in bacteria

    SciTech Connect

    Hill, Steven C.; Williamson, Chatt C.; Doughty, David C.; Pan, Yong-Le; Santarpia, Joshua L.; Hill, Hanna H.

    2015-02-02

    This paper uses a mathematical model of fluorescent biological particles composed of bacteria and/or proteins (mostly as in Hill et al., 2013 [23]) to investigate the size-dependence of the total fluorescence emitted in all directions. The model applies to particles which have negligible reabsorption of fluorescence within the particle. The specific particles modeled here are composed of ovalbumin and of a generic Bacillus. The particles need not be spherical, and in some cases need not be homogeneous. However, the results calculated in this paper are for spherical homogeneous particles. Light absorbing and fluorescing molecules included in the model are amino acids, nucleic acids, and several coenzymes. Here the excitation wavelength is 266 nm. The emission range, 300 to 370 nm, encompasses the fluorescence of tryptophan. The fluorescence cross section (CF) is calculated and compared with one set of published measured values. We investigate power law (Ady) approximations to CF, where d is diameter, and A and y are parameters adjusted to fit the data, and examine how y varies with d and composition, including the fraction as water. The particle's fluorescence efficiency (QF=CF/geometric-cross-section) can be written for homogeneous particles as QabsRF, where Qabs is the absorption efficiency, and RF, the fraction of the absorbed light emitted as fluorescence, is independent of size and shape. When QF is plotted vs. mid or mi(mr-1)d, where m=mr+imi is the complex refractive index, the plots for different fractions of water in the particle tend to overlap.

  7. Size-dependent fluorescence of bioaerosols: Mathematical model using fluorescing and absorbing molecules in bacteria

    DOE PAGESBeta

    Hill, Steven C.; Williamson, Chatt C.; Doughty, David C.; Pan, Yong-Le; Santarpia, Joshua L.; Hill, Hanna H.

    2015-02-02

    This paper uses a mathematical model of fluorescent biological particles composed of bacteria and/or proteins (mostly as in Hill et al., 2013 [23]) to investigate the size-dependence of the total fluorescence emitted in all directions. The model applies to particles which have negligible reabsorption of fluorescence within the particle. The specific particles modeled here are composed of ovalbumin and of a generic Bacillus. The particles need not be spherical, and in some cases need not be homogeneous. However, the results calculated in this paper are for spherical homogeneous particles. Light absorbing and fluorescing molecules included in the model are aminomore » acids, nucleic acids, and several coenzymes. Here the excitation wavelength is 266 nm. The emission range, 300 to 370 nm, encompasses the fluorescence of tryptophan. The fluorescence cross section (CF) is calculated and compared with one set of published measured values. We investigate power law (Ady) approximations to CF, where d is diameter, and A and y are parameters adjusted to fit the data, and examine how y varies with d and composition, including the fraction as water. The particle's fluorescence efficiency (QF=CF/geometric-cross-section) can be written for homogeneous particles as QabsRF, where Qabs is the absorption efficiency, and RF, the fraction of the absorbed light emitted as fluorescence, is independent of size and shape. When QF is plotted vs. mid or mi(mr-1)d, where m=mr+imi is the complex refractive index, the plots for different fractions of water in the particle tend to overlap.« less

  8. Size-dependent fluorescence of bioaerosols: Mathematical model using fluorescing and absorbing molecules in bacteria

    NASA Astrophysics Data System (ADS)

    Hill, Steven C.; Williamson, Chatt C.; Doughty, David C.; Pan, Yong-Le; Santarpia, Joshua L.; Hill, Hanna H.

    2015-05-01

    This paper uses a mathematical model of fluorescent biological particles composed of bacteria and/or proteins (mostly as in Hill et al., 2013 [23]) to investigate the size-dependence of the total fluorescence emitted in all directions. The model applies to particles which have negligible reabsorption of fluorescence within the particle. The specific particles modeled here are composed of ovalbumin and of a generic Bacillus. The particles need not be spherical, and in some cases need not be homogeneous. However, the results calculated in this paper are for spherical homogeneous particles. Light absorbing and fluorescing molecules included in the model are amino acids, nucleic acids, and several coenzymes. Here the excitation wavelength is 266 nm. The emission range, 300 to 370 nm, encompasses the fluorescence of tryptophan. The fluorescence cross section (CF) is calculated and compared with one set of published measured values. We investigate power law (Ady) approximations to CF, where d is diameter, and A and y are parameters adjusted to fit the data, and examine how y varies with d and composition, including the fraction as water. The particle's fluorescence efficiency (QF=CF/geometric-cross-section) can be written for homogeneous particles as QabsRF, where Qabs is the absorption efficiency, and RF, the fraction of the absorbed light emitted as fluorescence, is independent of size and shape. When QF is plotted vs. mid or mi(mr-1)d, where m=mr+imi is the complex refractive index, the plots for different fractions of water in the particle tend to overlap.

  9. Fundamental research on oscillating water column wave power absorbers

    SciTech Connect

    Maeda, H.; Kato, W.; Kinoshita, T.; Masuda, K.

    1985-03-01

    An oscillating water column (OWC) wave power absorber is one of the most promising devices, as well as the Salter Duck and the Clam. This paper presents a simple prediction method, in which the equivalent floating body approximation is used, for absorbing wave power characteristics of an oscillating water column device. The effects of the compressibility of air and inertia of an air turbine and electric generator on absorbed wave power are obtained by using the equivalent electric circuit concept. Both the experimental and theoretical studies are carried out in this paper.

  10. Ultraviolet light absorbers having two different chromophors in the same molecule

    DOEpatents

    Vogl, Otto; Li, Shanjun

    1988-05-17

    Ultraviolet light absorbing compounds having two different chromophors in the same molecule, particularly the benzotriazole chromophor and either the dihydroxybenzophenone or dihydroxyacetophenone chromophor; specifically, the two compounds 3,5-[di(2H-benzotriazole-2-yl)]-2,4-dihydroxyacetophenone and 3,5-[di(2H-benzotriazole-2-yl)]2,4-dihydroxybenzophenone.

  11. Optimization of UV absorptivity of layered double hydroxide by intercalating organic UV-absorbent molecules.

    PubMed

    Mohsin, Sumaiyah Megat Nabil; Hussein, Mohd Zobir; Sarijo, Siti Halimah; Fakurazi, Sharida; Arulselvan, Palanisamy; Taufiq-Yap, Yun Hin

    2014-08-01

    Intercalation of Zn/Al layered double hydroxide (LDH) with benzophenone 9 (B9), a strong ultraviolet (UV) absorber, had been carried out by two different routes; co-precipitation and ion exchange method. Powder X-ray diffraction (PXRD) patterns of co-precipitated (ZB9C) and ion exchanged product (ZB91) showed basal spacing of 15.9 angstrom and 16.6 angstrom, respectively, as a result of the intercalation of B9 anions into the lamellae spaces of LDH. Intercalation was further confirmed by Fourier transform infrared spectra (FTIR), carbon, hydrogen, nitrogen and sulfur (CHNS) and thermogravimetric and differential thermogravimetric (TGA/DTG) studies. UV-vis absorption properties of the nanocomposite was investigated with diffuse reflectance UV-visible spectrometer and showed broader UV absorption range. Furthermore, stability of sunscreen molecules in LDH interlayer space was tested in deionized water, artificial sea water and skin pH condition to show slow deintercalation and high retention in host. Cytotoxicity study of the synthesized nanocomposites on human dermal fibroblast (HDF) cells shows no significant cytotoxicity after 24 h exposure for test concentrations up to 25 microg/mL. PMID:25016649

  12. Design of water molecule and its surrounding

    NASA Astrophysics Data System (ADS)

    Danylo, R. I.; Okhrimenko, B. A.; Yablochkova, K. S.

    2015-02-01

    Hydrogen bonds and their fluctuations are one of the factors that determine the unique properties of water [1]. Building models of formation and rupture of hydrogen bonds due to non-eigen vibrations of a molecule of water is to a large extent determined by the availability of accurate information on the geometric structure of the water molecule. Geometric parameters of the water molecule have been well studied for the gaseous state. This was aided by the possibility of an experimental study of the regularities in the rotational spectra of molecules. However, some questions about the geometry of the water molecule in the liquid state remain unanswered. For example, many sources state that the valence angle of the water molecule decreases during the transition into the liquid state [2]. Based on the experimental data of molecular vibration spectra in D2O and H2O molecules [3], the authors have estimated valence angle of water in the liquid state. Consequently, the value of the valence angle of water in liquid state was determined to be (89 +/-2)°. A question of determination of libration vibrations of water molecule, as well as the analysis of its consequent inversion doubling, based on the new information on the equilibrium angle of the water molecules in the liquid state, constitutes an interest and is discussed in the present paper.

  13. Metamaterial Absorber for Electromagnetic Waves in Periodic Water Droplets

    NASA Astrophysics Data System (ADS)

    Yoo, Young Joon; Ju, Sanghyun; Park, Sang Yoon; Ju Kim, Young; Bong, Jihye; Lim, Taekyung; Kim, Ki Won; Rhee, Joo Yull; Lee, Youngpak

    2015-09-01

    Perfect metamaterial absorber (PMA) can intercept electromagnetic wave harmful for body in Wi-Fi, cell phones and home appliances that we are daily using and provide stealth function that military fighter, tank and warship can avoid radar detection. We reported new concept of water droplet-based PMA absorbing perfectly electromagnetic wave with water, an eco-friendly material which is very plentiful on the earth. If arranging water droplets with particular height and diameter on material surface through the wettability of material surface, meta-properties absorbing electromagnetic wave perfectly in GHz wide-band were shown. It was possible to control absorption ratio and absorption wavelength band of electromagnetic wave according to the shape of water droplet-height and diameter- and apply to various flexible and/or transparent substrates such as plastic, glass and paper. In addition, this research examined how electromagnetic wave can be well absorbed in water droplets with low electrical conductivity unlike metal-based metamaterials inquiring highly electrical conductivity. Those results are judged to lead broad applications to variously civilian and military products in the future by providing perfect absorber of broadband in all products including transparent and bendable materials.

  14. Metamaterial Absorber for Electromagnetic Waves in Periodic Water Droplets.

    PubMed

    Yoo, Young Joon; Ju, Sanghyun; Park, Sang Yoon; Ju Kim, Young; Bong, Jihye; Lim, Taekyung; Kim, Ki Won; Rhee, Joo Yull; Lee, YoungPak

    2015-01-01

    Perfect metamaterial absorber (PMA) can intercept electromagnetic wave harmful for body in Wi-Fi, cell phones and home appliances that we are daily using and provide stealth function that military fighter, tank and warship can avoid radar detection. We reported new concept of water droplet-based PMA absorbing perfectly electromagnetic wave with water, an eco-friendly material which is very plentiful on the earth. If arranging water droplets with particular height and diameter on material surface through the wettability of material surface, meta-properties absorbing electromagnetic wave perfectly in GHz wide-band were shown. It was possible to control absorption ratio and absorption wavelength band of electromagnetic wave according to the shape of water droplet-height and diameter- and apply to various flexible and/or transparent substrates such as plastic, glass and paper. In addition, this research examined how electromagnetic wave can be well absorbed in water droplets with low electrical conductivity unlike metal-based metamaterials inquiring highly electrical conductivity. Those results are judged to lead broad applications to variously civilian and military products in the future by providing perfect absorber of broadband in all products including transparent and bendable materials. PMID:26354891

  15. Metamaterial Absorber for Electromagnetic Waves in Periodic Water Droplets

    PubMed Central

    Yoo, Young Joon; Ju, Sanghyun; Park, Sang Yoon; Ju Kim, Young; Bong, Jihye; Lim, Taekyung; Kim, Ki Won; Rhee, Joo Yull; Lee, YoungPak

    2015-01-01

    Perfect metamaterial absorber (PMA) can intercept electromagnetic wave harmful for body in Wi-Fi, cell phones and home appliances that we are daily using and provide stealth function that military fighter, tank and warship can avoid radar detection. We reported new concept of water droplet-based PMA absorbing perfectly electromagnetic wave with water, an eco-friendly material which is very plentiful on the earth. If arranging water droplets with particular height and diameter on material surface through the wettability of material surface, meta-properties absorbing electromagnetic wave perfectly in GHz wide-band were shown. It was possible to control absorption ratio and absorption wavelength band of electromagnetic wave according to the shape of water droplet–height and diameter– and apply to various flexible and/or transparent substrates such as plastic, glass and paper. In addition, this research examined how electromagnetic wave can be well absorbed in water droplets with low electrical conductivity unlike metal-based metamaterials inquiring highly electrical conductivity. Those results are judged to lead broad applications to variously civilian and military products in the future by providing perfect absorber of broadband in all products including transparent and bendable materials. PMID:26354891

  16. Ammonia-water bubble absorber with a plate heat exchanger

    SciTech Connect

    Kang, Y.T.; Kashiwagi, Takao; Christensen, R.N.

    1998-10-01

    The objectives of this paper are to develop a design model for a bubble absorber with plate heat exchangers and to evaluate the heat and mass transfer resistances within both liquid and bubble. Parametric analysis was performed to find optimum design conditions for the bubble absorber. An offset strip fin (OSF) is used to enhance heat transfer performance in the coolant region of a standard plate heat exchanger. It was found that the heat transfer resistance was dominant in the vapor region, while the mass transfer resistance was dominant in the liquid region. The mass transfer area was found to have more significant effect on the size of the bubble absorber than the heat transfer area. The direction of mass transfer was confirmed in the simulation of the countercurrent bubble absorber. The present design model predicts the water desorption process up to the length of 12.5 cm from the bottom of the bubble absorber. All geometric variables could be selected optimally for given thermal conditions by the design model developed in this paper. This is a significant contribution in designing the ammonia-water bubble absorber.

  17. Hybrid solar cells with ZnO-nanorods and dry processed small molecule absorber

    NASA Astrophysics Data System (ADS)

    Riedel, W.; Wiesner, S.; Greiner, D.; Hinrichs, V.; Rusu, M.; Lux-Steiner, M. Ch.

    2014-04-01

    We demonstrate hybrid solar cells with ZnO-nanorods (ZnO-NRs) prepared by a low temperature electrochemical method and small molecule organic absorber processed by dry organic vapor phase deposition. A homogeneous coverage of ZnO-NRs by the blend absorber consisting of zinc phthalocyanine (ZnPc) as donor and of fullerene C60 as acceptor is best realized when a thin C60 layer is first inserted at the ZnO-NR/ZnPc:C60 interface. ZnO-NR/C60/ZnPc:C60/MoO3/Ag solar cell devices with efficiencies of 2.8% under an illumination of 100 mW/cm2 at 25 °C are demonstrated.

  18. Modelling water molecules inside cyclic peptide nanotubes

    NASA Astrophysics Data System (ADS)

    Tiangtrong, Prangsai; Thamwattana, Ngamta; Baowan, Duangkamon

    2016-03-01

    Cyclic peptide nanotubes occur during the self-assembly process of cyclic peptides. Due to the ease of synthesis and ability to control the properties of outer surface and inner diameter by manipulating the functional side chains and the number of amino acids, cyclic peptide nanotubes have attracted much interest from many research areas. A potential application of peptide nanotubes is their use as artificial transmembrane channels for transporting ions, biomolecules and waters into cells. Here, we use the Lennard-Jones potential and a continuum approach to study the interaction of a water molecule in a cyclo[(- D-Ala- L-Ala)_4-] peptide nanotube. Assuming that each unit of a nanotube comprises an inner and an outer tube and that a water molecule is made up of a sphere of two hydrogen atoms uniformly distributed over its surface and a single oxygen atom at the centre, we determine analytically the interaction energy of the water molecule and the peptide nanotube. Using this energy, we find that, independent of the number of peptide units, the water molecule will be accepted inside the nanotube. Once inside the nanotube, we show that a water molecule prefers to be off-axis, closer to the surface of the inner nanotube. Furthermore, our study of two water molecules inside the peptide nanotube supports the finding that water molecules form an array of a 1-2-1-2 file inside peptide nanotubes. The theoretical study presented here can facilitate thorough understanding of the behaviour of water molecules inside peptide nanotubes for applications, such as artificial transmembrane channels.

  19. Direct absorbed dose to water determination based on water calorimetry in scanning proton beam delivery

    SciTech Connect

    Sarfehnia, A.; Clasie, B.; Chung, E.; Lu, H. M.; Flanz, J.; Cascio, E.; Engelsman, M.; Paganetti, H.; Seuntjens, J.

    2010-07-15

    Purpose: The aim of this manuscript is to describe the direct measurement of absolute absorbed dose to water in a scanned proton radiotherapy beam using a water calorimeter primary standard. Methods: The McGill water calorimeter, which has been validated in photon and electron beams as well as in HDR {sup 192}Ir brachytherapy, was used to measure the absorbed dose to water in double scattering and scanning proton irradiations. The measurements were made at the Massachusetts General Hospital proton radiotherapy facility. The correction factors in water calorimetry were numerically calculated and various parameters affecting their magnitude and uncertainty were studied. The absorbed dose to water was compared to that obtained using an Exradin T1 Chamber based on the IAEA TRS-398 protocol. Results: The overall 1-sigma uncertainty on absorbed dose to water amounts to 0.4% and 0.6% in scattered and scanned proton water calorimetry, respectively. This compares to an overall uncertainty of 1.9% for currently accepted IAEA TRS-398 reference absorbed dose measurement protocol. The absorbed dose from water calorimetry agrees with the results from TRS-398 well to within 1-sigma uncertainty. Conclusions: This work demonstrates that a primary absorbed dose standard based on water calorimetry is feasible in scattered and scanned proton beams.

  20. Water molecule conformation outside a metal surface

    NASA Astrophysics Data System (ADS)

    Flores, F.; Gabbay, I.; March, N. H.

    1981-05-01

    The effect of a metal surface on the conformation of a water molecule has been analyzed by discussing two independent effects: (i) the screening of the proton-proton repulsion, (ii) the interaction of the lone-pair orbitals with the surface. Both effects tend to increase the HOH angle. However, the interaction between the lone-pairs with the surface is the dominant effect for a water molecule approaching the surface. In particular, for a chemisorbed state this interaction is responsible for the major part of the molecule deformation. We have estimated that for H 2O chemisorbed on Ru, the HOH angle must increase from the free molecule value of 104.5° by 3.1 ± 0.5° in good agreement with the experimental evidence.

  1. Water-absorbing capacitor system for measuring relative humidity

    NASA Technical Reports Server (NTRS)

    Laue, Eric G. (Inventor)

    1987-01-01

    A method and apparatus using a known water-absorbent polymer as a capacitor which is operated at a dc voltage for measuring relative humidity is presented. When formed as a layer between porous electrically-conductive electrodes and operated in an RC oscillator circuit, the oscillator frequency varies inversely with the partial pressure of the moisture to be measured. In a preferred embodiment, the capacitor is formed from Nafion and is operated at a low dc voltage with a resistor as an RC circuit in an RC oscillator. At the low voltage, the leakage current is proper for oscillation over a satisfactory range. The frequency of oscillation varies in an essentially linear fashion with relative humidity which is represented by the moisture being absorbed into the Nafion. The oscillation frequency is detected by a frequency detector.

  2. Kevlar based nanofibrous particles as robust, effective and recyclable absorbents for water purification.

    PubMed

    Nie, Chuanxiong; Peng, Zihang; Yang, Ye; Cheng, Chong; Ma, Lang; Zhao, Changsheng

    2016-11-15

    Developing robust and recyclable absorbents for water purification is of great demand to control water pollution and to provide sustainable water resources. Herein, for the first time, we reported the fabrication of Kevlar nanofiber (KNF) based composite particles for water purification. Both the KNF and KNF-carbon nanotube composite particles can be produced in large-scale by automatic injection of casting solution into ethanol. The resulted nanofibrous particles showed high adsorption capacities towards various pollutants, including metal ions, phenylic compounds and various dyes. Meanwhile, the adsorption process towards dyes was found to fit well with the pseudo-second-order model, while the adsorption speed was controlled by intraparticle diffusion. Furthermore, the adsorption capacities of the nanofibrous particles could be easily recovered by washing with ethanol. In general, the KNF based particles integrate the advantages of easy production, robust and effective adsorption performances, as well as good recyclability, which can be used as robust absorbents to remove toxic molecules and forward the application of absorbents in water purification. PMID:27427892

  3. Direct MC conversion of absorbed dose to graphite to absorbed dose to water for 60Co radiation.

    PubMed

    Lye, J E; Butler, D J; Franich, R D; Harty, P D; Oliver, C P; Ramanathan, G; Webb, D V; Wright, T

    2013-06-01

    The ARPANSA calibration service for (60)Co gamma rays is based on a primary standard graphite calorimeter that measures absorbed dose to graphite. Measurements with the calorimeter are converted to the absorbed dose to water using the calculation of the ratio of the absorbed dose in the calorimeter to the absorbed dose in a water phantom. ARPANSA has recently changed the basis of this calculation from a photon fluence scaling method to a direct Monte Carlo (MC) calculation. The MC conversion uses an EGSnrc model of the cobalt source that has been validated against water tank and graphite phantom measurements, a step that is required to quantify uncertainties in the underlying interaction coefficients in the MC code. A comparison with the Bureau International des Poids et Mesures (BIPM) as part of the key comparison BIPM.RI(I)-K4 showed an agreement of 0.9973 (53). PMID:23152147

  4. The Dipole Polarizability of a Water Molecule in Liquid Water

    NASA Astrophysics Data System (ADS)

    Distasio, Robert; Maitra, Rahul

    The dipole polarizability, α, provides a measure of the tendency of a molecule or material to deform (or polarize) in the presence of an electric field. Within the framework of density functional theory (DFT), we present a hierarchy of first principles based approaches for computing α of a molecule located in the condensed phase. This hierarchy includes a successive treatment of both short-range (hybridization, Pauli exchange-repulsion, etc.) and long-range (Coulomb) electrodynamical response screening in the computation of α, while simultaneously accounting for the surrounding condensed-phase environment. Utilizing highly accurate liquid water configurations generated from van der Waals inclusive hybrid DFT based ab initio molecular dynamics, we computed α for a given water molecule in liquid water as a first application of this approach. Our findings will be compared and contrasted with α computed for an isolated gas-phase water molecule.

  5. An absorbed dose to water calorimeter for collimated radiation fields

    NASA Astrophysics Data System (ADS)

    Brede, H. J.; Hecker, O.; Hollnagel, R.

    2000-12-01

    A transportable calorimeter of compact design has been developed as a device for the absolute determination of the absorbed dose to water. The ease of operation of the calorimeter allows the application in clinical therapy beams of various energies, specifically for neutron, proton and heavy ion beams. The calorimeter requires collimated radiation fields with diameters lesser than 40 mm. The temperature rise caused by radiation is measured with a thermistor probe which is located in the centre of the calorimeter core. The calorimeter core consists of a cylindrical water-filled gilded aluminium can suspended by three thin nylon threads in a vacuum block in order to reduce the heat transfer by conduction. In addition, it operates at a temperature of 4°C, preventing heat transfer in water by convection. Heat transfer from the core to the surrounding by radiation is minimised by the use of two concentric temperature-controlled jackets, the inner jacket being operated at core temperature. A description of the mechanical and electrical design, of the construction and operation of the water calorimeter is given. In addition, calculations with a finite-element program code performed to determine correction factors for various radiation conditions are included.

  6. Clusters of mobile molecules in supercooled water

    NASA Astrophysics Data System (ADS)

    Giovambattista, Nicolas; Buldyrev, Sergey V.; Stanley, H. Eugene; Starr, Francis W.

    2005-07-01

    We study the spatially heterogeneous dynamics in water via molecular dynamics simulations using the extended simple point charge potential. We identify clusters formed by mobile molecules and study their properties. We find that these clusters grow in size and become more compact as temperature decreases. We analyze the probability density function of cluster size, and we study the cluster correlation length. We find that clusters appear to be characterized by a fractal dimension consistent with that of lattice animals. We relate the cluster size and correlation length to the configurational entropy, Sconf . We find that these quantities depend weakly on 1/Sconf . In particular, the linearity found between the cluster mass n* and 1/Sconf suggests that n* may be interpreted as the mass of the cooperatively rearranging regions that form the basis of the Adam-Gibbs approach to the dynamics of supercooled liquids. We study the motion of molecules within a cluster, and find that each molecule preferentially follows a neighboring molecule in the same cluster. Based on this finding we hypothesize that stringlike cooperative motion may be a general mechanism for molecular rearrangement of complex, as well as simple liquids. By mapping each equilibrium configuration onto its corresponding local potential energy minimum or inherent structure (IS), we are able to compare the mobile molecule clusters in the equilibrium system with the molecules forming the clusters identified in the transitions between IS. We find that (i) mobile molecule clusters obtained by comparing different system configurations and (ii) clusters obtained by comparing the corresponding IS are completely different for short time scales, but are the same on the longer time scales of diffusive motion.

  7. Dynamics of water molecules in glucose solutions.

    SciTech Connect

    Talon, C.; Smith, L. J.; Brady, J. W.; Copley, J. R. D.; Price, D. L.; Saboungi, M. L.; Materials Science Division; Centre de Recherche sur la Matiyre Divisye; Cornell Univ.; NIST; Centre de Recherche sur les Matyriaux y Haute Tempyrature

    2004-04-22

    The effects of the solution of glucose molecules on the dynamics of solvent water have been studied by quasielastic neutron scattering (QENS) measurements on solutions of selectively deuterated glucose in natural water. The data are fitted to two Lorentzians ascribed to pure translational and mixed translational and rotational character, respectively. The addition of the glucose to the water causes a substantial slowing down, by a factor 10 for the translational diffusion and 3-4 for the rotational motion at the highest concentration studied, 1:11 C{sub 6}H{sub 12}O{sub 6}:H{sub 2}O. The values obtained for water diffusion constants are consistent with previous QENS and NMR experiments on monosaccharide solutions but an order of magnitude higher than those derived from a recent molecular dynamics simulation.

  8. Absorbed dose to water reference dosimetry using solid phantoms in the context of absorbed-dose protocols

    SciTech Connect

    Seuntjens, Jan; Olivares, Marina; Evans, Michael; Podgorsak, Ervin

    2005-09-15

    For reasons of phantom material reproducibility, the absorbed dose protocols of the American Association of Physicists in Medicine (AAPM) (TG-51) and the International Atomic Energy Agency (IAEA) (TRS-398) have made the use of liquid water as a phantom material for reference dosimetry mandatory. In this work we provide a formal framework for the measurement of absorbed dose to water using ionization chambers calibrated in terms of absorbed dose to water but irradiated in solid phantoms. Such a framework is useful when there is a desire to put dose measurements using solid phantoms on an absolute basis. Putting solid phantom measurements on an absolute basis has distinct advantages in verification measurements and quality assurance. We introduce a phantom dose conversion factor that converts a measurement made in a solid phantom and analyzed using an absorbed dose calibration protocol into absorbed dose to water under reference conditions. We provide techniques to measure and calculate the dose transfer from solid phantom to water. For an Exradin A12 ionization chamber, we measured and calculated the phantom dose conversion factor for six Solid Water{sup TM} phantoms and for a single Lucite phantom for photon energies between {sup 60}Co and 18 MV photons. For Solid Water{sup TM} of certified grade, the difference between measured and calculated factors varied between 0.0% and 0.7% with the average dose conversion factor being low by 0.4% compared with the calculation whereas for Lucite, the agreement was within 0.2% for the one phantom examined. The composition of commercial plastic phantoms and their homogeneity may not always be reproducible and consistent with assumed composition. By comparing measured and calculated phantom conversion factors, our work provides methods to verify the consistency of a given plastic for the purpose of clinical reference dosimetry.

  9. Rotational motion of a single water molecule in a buckyball.

    PubMed

    Farimani, A Barati; Wu, Yanbin; Aluru, N R

    2013-11-01

    Encapsulation of a single water molecule in a buckyball (C60) can provide fundamental insights into the properties of water. Investigation of a single water molecule is feasible through its solitary confinement in C60. In this paper, we performed a detailed study of the properties and dynamics of a single water molecule in a buckyball using DFT and MD simulations. We report on the enhancement of rotational diffusion and entropy of a water molecule in C60, compared to a bulk water molecule. H2O@C60 has zero translational diffusion and terahertz revolution frequency. The harmonic, high amplitude rotation of a single water molecule in C60 is compared to stochastic behavior of bulk water molecules. The combination of large rotational and negligible translational motion of water in C60 creates new opportunities in nanotechnology applications. PMID:24061613

  10. Biodegradable water absorbent synthesized from bacterial poly(amino acid)s.

    PubMed

    Kunioka, Masao

    2004-03-15

    Biodegradable hydrogels prepared by gamma-irradiation from microbial poly(amino acid)s have been studied. pH-Sensitive hydrogels were prepared by the gamma-irradiation of poly(gamma-glutamic acid) (PGA) produced by Bacillus subtilis and poly(epsilon-lysine) (PL) produced by Streptomyces albulus in aqueous solutions. When the gamma-irradiation dose was 19 kGy or more, and the concentration of PGA in water was 2 wt.-% or more, transparent hydrogels could be produced. For the 19 kGy dose, the produced hydrogel was very weak, however, the specific water content (wt. of absorbed water/wt. of dry hydrogel) of this PGA hydrogel was approximately 3,500. The specific water content decreased to 200, increasing when the gamma-irradiation dose was over 100 kGy. Under acid conditions or upon the addition of electrolytes, the PGA hydrogels shrunk. The PGA hydrogel was pH-sensitive and the change in the volume of the hydrogel depended on the pH value outside the hydrogel in the swelling medium. This PGA hydrogel was hydrodegradable and biodegradable. A new novel purifier reagent (coagulant), made from the PGA hydrogels, for contaminated turbid water has been found and developed by Japanese companies. A very small amount of this coagulant (only 2 ppm in turbid water) with poly(aluminum chloride) can be used for the purification of turbid water. A PL aqueous solution also can change into a hydrogel by gamma-irradiation. The specific water content of the PL hydrogel ranged from 20 to 160 depending on the preparation conditions. Under acid conditions, the PL hydrogel swelled because of the ionic repulsion of the protonated amino groups in the PL molecules. The rate of enzymatic degradation of the respective PL hydrogels by a neutral protease was much faster than the rate of simple hydrolytic degradation. PMID:15468223

  11. Solar Inactivation of Enterococci and Escherichia coli in Natural Waters: Effects of Water Absorbance and Depth.

    PubMed

    Maraccini, Peter A; Mattioli, Mia Catharine M; Sassoubre, Lauren M; Cao, Yiping; Griffith, John F; Ervin, Jared S; Van De Werfhorst, Laurie C; Boehm, Alexandria B

    2016-05-17

    The decay of sewage-sourced Escherichia coli and enterococci was measured at multiple depths in a freshwater marsh, a brackish water lagoon, and a marine site, all located in California. The marine site had very clear water, while the waters from the marsh and lagoon contained colored dissolved organic matter that not only blocked light but also produced reactive oxygen species. First order decay rate constants of both enterococci and E. coli were between 1 and 2 d(-1) under low light conditions and as high as 6 d(-1) under high light conditions. First order decay rate constants were well correlated to the daily average UVB light intensity corrected for light screening incorporating water absorbance and depth, suggesting endogenous photoinactivation is a major pathway for bacterial decay. Additional laboratory experiments demonstrated the presence of colored dissolved organic matter in marsh water enhanced photoinactivation of a laboratory strain of Enterococcus faecalis, but depressed photoinactivation of sewage-sourced enterococci and E. coli after correcting for UVB light screening, suggesting that although the exogenous indirect photoinactivation mechanism may be active against Ent. faecalis, it is not for the sewage-source organisms. A simple linear regression model based on UVB light intensity appears to be a useful tool for predicting inactivation rate constants in natural waters of any depth and absorbance. PMID:27119980

  12. The large quadrupole of water molecules.

    PubMed

    Niu, Shuqiang; Tan, Ming-Liang; Ichiye, Toshiko

    2011-04-01

    Many quantum mechanical calculations indicate water molecules in the gas and liquid phase have much larger quadrupole moments than any of the common site models of water for computer simulations. Here, comparisons of multipoles from quantum mechanical∕molecular mechanical (QM∕MM) calculations at the MP2∕aug-cc-pVQZ level on a B3LYP∕aug-cc-pVQZ level geometry of a waterlike cluster and from various site models show that the increased square planar quadrupole can be attributed to the p-orbital character perpendicular to the molecular plane of the highest occupied molecular orbital as well as a slight shift of negative charge toward the hydrogens. The common site models do not account for the p-orbital type electron density and fitting partial charges of TIP4P- or TIP5P-type models to the QM∕MM dipole and quadrupole give unreasonable higher moments. Furthermore, six partial charge sites are necessary to account reasonably for the large quadrupole, and polarizable site models will not remedy the problem unless they account for the p-orbital in the gas phase since the QM calculations show it is present there too. On the other hand, multipole models by definition can use the correct multipoles and the electrostatic potential from the QM∕MM multipoles is much closer than that from the site models to the potential from the QM∕MM electron density. Finally, Monte Carlo simulations show that increasing the quadrupole in the soft-sticky dipole-quadrupole-octupole multipole model gives radial distribution functions that are in good agreement with experiment. PMID:21476758

  13. The Large Quadrupole of Water Molecules

    SciTech Connect

    Niu, Shuqiang; Tan, Ming-Liang; Ichiye, Toshhiko

    2011-04-07

    Many quantum mechanical calculations indicate water molecules in the gas and liquid phase have much larger quadrupole moments than any of the common site models of water for computer simulations. Here, comparisons of multipoles from quantum mechanical/molecular mechanical (QM/MM) calculations at the MP2/aug-cc-pVQZ level on a B3LYP/aug-cc-pVQZ level geometry of a waterlike cluster and from various site models show that the increased square planar quadrupole can be attributed to the p-orbital character perpendicular to the molecular plane of the highest occupied molecular orbital as well as a slight shift of negative charge toward the hydrogens. The common site models do not account for the p-orbital type electron density and fitting partial charges of TIP4P- or TIP5P-type models to the QM/MM dipole and quadrupole give unreasonable higher moments. Furthermore, six partial charge sites are necessary to account reasonably for the large quadrupole, and polarizable site models will not remedy the problem unless they account for the p-orbital in the gas phase since the QM calculations show it is present there too. On the other hand, multipole models by definition can use the correct multipoles and the electrostatic potential from the QM/MM multipoles is much closer than that from the site models to the potential from the QM/MM electron density. Finally, Monte Carlo simulations show that increasing the quadrupole in the soft-sticky dipole-quadrupole-octupole multipole model gives radial distribution functions that are in good agreement with experiment

  14. The large quadrupole of water molecules

    NASA Astrophysics Data System (ADS)

    Niu, Shuqiang; Tan, Ming-Liang; Ichiye, Toshiko

    2011-04-01

    Many quantum mechanical calculations indicate water molecules in the gas and liquid phase have much larger quadrupole moments than any of the common site models of water for computer simulations. Here, comparisons of multipoles from quantum mechanical/molecular mechanical (QM/MM) calculations at the MP2/aug-cc-pVQZ level on a B3LYP/aug-cc-pVQZ level geometry of a waterlike cluster and from various site models show that the increased square planar quadrupole can be attributed to the p-orbital character perpendicular to the molecular plane of the highest occupied molecular orbital as well as a slight shift of negative charge toward the hydrogens. The common site models do not account for the p-orbital type electron density and fitting partial charges of TIP4P- or TIP5P-type models to the QM/MM dipole and quadrupole give unreasonable higher moments. Furthermore, six partial charge sites are necessary to account reasonably for the large quadrupole, and polarizable site models will not remedy the problem unless they account for the p-orbital in the gas phase since the QM calculations show it is present there too. On the other hand, multipole models by definition can use the correct multipoles and the electrostatic potential from the QM/MM multipoles is much closer than that from the site models to the potential from the QM/MM electron density. Finally, Monte Carlo simulations show that increasing the quadrupole in the soft-sticky dipole-quadrupole-octupole multipole model gives radial distribution functions that are in good agreement with experiment.

  15. Waters of Hydration of Cupric Hydrates: A Comparison between Heating and Absorbance Methods

    ERIC Educational Resources Information Center

    Barlag, Rebecca; Nyasulu, Frazier

    2011-01-01

    The empirical formulas of four cupric hydrates are determined by measuring the absorbance in aqueous solution. The Beer-Lambert Law is verified by constructing a calibration curve of absorbance versus known Cu[superscript 2+](aq) concentration. A solution of the unknown hydrate is prepared by using 0.2-0.3 g of hydrate, and water is added such…

  16. Adsorption structure of water molecules on the Be(0001) surface

    SciTech Connect

    Yang, Yu; Li, Yanfang; Wang, Shuangxi; Zhang, Ping

    2014-06-07

    By using density functional theory calculations, we systematically investigate the adsorption of water molecules at different coverages on the Be(0001) surface. The coverage dependence of the prototype water structures and energetics for water adlayer growth are systematically studied. The structures, energetics, and electronic properties are calculated and compared with other available studies. Through our systematic investigations, we find that water molecules form clusters or chains on the Be(0001) surface at low coverages. When increasing the water coverage, water molecules tend to form a 2 × 2 hexagonal network on the Be(0001) surface.

  17. Molecules and metals in the distant universe: Sub-mm and optical spectroscopy of quasar absorbers

    NASA Astrophysics Data System (ADS)

    Morrison, Sean Stephen

    In order to gain a complete understanding of galaxy formation and evolution, knowledge of the atomic and molecular gas in the interstellar medium (ISM) is required. Absorption-line spectroscopy of quasars offer a powerful and luminosity independent probe of gas to high redshifts. The sub-Damped Lyman-alpha systems (sub-DLAs; 19.0 < log NHI < 20.3), and Damped Lyman-alpha systems (DLAs; 20.3 < log NHI), are the highest neutral hydrogen column density quasar absorbers contain most of the neutral gas available for star formation in the high-redshift Universe. This thesis presents photometric measurements of 10 quasars absorbers with redshifts 0.652 < zabs < 3.104 taken with the Spectral and Photometric Imaging Receiver (SPIRE) on Herschel. Of these 10 objects, 3 showed fluxes > 1 Jy. In addition spectra for 5 other quasars with DLAs (0.524 < zabs < 1.173) were taken with SPIRE and Heterodyne Instrument for the far-infrared (HIFI) on Herschel. These observations, in the far-IR and sub-mm bands, were optimized for detection of molecular lines of CO, 13CO, C 18O, H2O, HCO, and the forbidden transitions of [C II] and [N II]. Two targets, the DLA towards PKS0420-014 at z = 0.633 and the DLA towards AO0235+164 at z = 0.524, had a tentative detection of C18O, and another, the DLA towards TXS0827+243 at z = 0.52476, had a tentative detection of HCO. There were a number of other 3 sigma limits, with at least one limit for each of the 5 systems. In addition to the DLAs, 2 super-DLAs (with z = 2.5036 and z = 2.045) were observed using the echellette mode on Keck Echellette Spectrograph and Imager (ESI). These observations, in the optical and ultraviolet wavelengths, were optimized to detect metal lines. Both absorbers show remarkably similar metallicities of ~ -1.3 to ~ -1.4 dex and comparable, definitive depletion levels, as judged from [Fe/Zn] and [Ni/Zn]. One of the absorbers shows supersolar [S/Zn] and [Si/Zn]. Using potential detections of weak Ly-alpha emission at the

  18. Detection of Organic Compounds in Water by an Optical Absorbance Method

    PubMed Central

    Kim, Chihoon; Eom, Joo Beom; Jung, Soyoun; Ji, Taeksoo

    2016-01-01

    This paper proposes an optical method which allows determination of the organic compound concentration in water by measurement of the UV (ultraviolet) absorption at a wavelength of 250 nm~300 nm. The UV absorbance was analyzed by means of a multiple linear regression model for estimation of the total organic carbon contents in water, which showed a close correlation with the UV absorbance, demonstrating a high adjusted coefficient of determination, 0.997. The comparison of the TOC (total organic carbon) concentrations for real samples (tab water, sea, and river) calculated from the UV absorbance spectra, and those measured by a conventional TOC analyzer indicates that the higher the TOC value the better the agreement. This UV absorbance method can be easily configured for real-time monitoring water pollution, and built into a compact system applicable to industry areas. PMID:26742043

  19. Detection of Organic Compounds in Water by an Optical Absorbance Method.

    PubMed

    Kim, Chihoon; Eom, Joo Beom; Jung, Soyoun; Ji, Taeksoo

    2016-01-01

    This paper proposes an optical method which allows determination of the organic compound concentration in water by measurement of the UV (ultraviolet) absorption at a wavelength of 250 nm~300 nm. The UV absorbance was analyzed by means of a multiple linear regression model for estimation of the total organic carbon contents in water, which showed a close correlation with the UV absorbance, demonstrating a high adjusted coefficient of determination, 0.997. The comparison of the TOC (total organic carbon) concentrations for real samples (tab water, sea, and river) calculated from the UV absorbance spectra, and those measured by a conventional TOC analyzer indicates that the higher the TOC value the better the agreement. This UV absorbance method can be easily configured for real-time monitoring water pollution, and built into a compact system applicable to industry areas. PMID:26742043

  20. Longitudinal photoelectron momentum shifts induced by absorbing a single XUV photon in diatomic molecules

    NASA Astrophysics Data System (ADS)

    Lao, Di; He, Pei-Lun; He, Feng

    2016-06-01

    The photoelectron momentum shifts along the laser propagation are investigated by the time-dependent perturbation theory for diatomic molecules, such as H2+ , N2, and O2. Such longitudinal momentum shifts characterize the photon momentum sharing in atoms and molecules, and oscillate with respect to photon energies, presenting the double-slit interference structure. The atomic and molecular contributions are disentangled analytically, which gives an intuitive picture of how the double-slit interference structure is formed. Calculation results show that the longitudinal photoelectron momentum distribution depends on the internuclear distance, molecular orientation, and photon energy. The current laser technology is ready to verify these theoretical predictions.

  1. Absorbed dose to water: Standards and traceability for radiation oncology

    SciTech Connect

    Almond, P.R.

    1995-12-31

    Although the need for appropriate quantities and units for ionizing radiation has existed since shortly after discovery of X-rays, the quantities and units in general use today were not completely formalized until about 15 years ago. The development of appropriate national and international standards have also been ongoing. For many years the quantity, exposure, measured in units of roentgen was the national standard and they were also the quantity and units in which radiotherapy was described. With the introduction of megavoltage X-ray and electron-beam equipment and the adoption of the quantity {open_quotes}absorbed-dose{close_quotes} measured in units of rad (or gray) different approaches to calibrating these beams were needed. This was especially the case since the national standard in terms of exposure at a maximum photon energy for {sup 60}Co gamma rays was only available. Since the late 1960s various machine calibration protocols have been published. These protocols have to accommodate changes in modality, energy, quantities and units between the national standard and the user. Because of this, a new definition of traceability is proposed to accommodate the present system. By recording all intercomparisons and parameters used, an auditable calibration chain can be maintained. Even with the introduction of calibration protocols based upon national absorbed dose standards, the proposed traceability definition will still be needed.

  2. Reverse Mössbauer effect as a possible source of "hot" molecules absorbed in crystalline solids at low temperature.

    PubMed

    Demontis, Pierfranco; Suffritti, Giuseppe B

    2016-09-01

    As an attempt to explain some of the many anomalies and unresolved problems which have been reported about the dynamic behavior of particles and molecules absorbed in crystalline solids, the "reverse Mössbauer effect" (RME) is proposed. RME theory posits that a particle in non-equilibrium state with respect to a crystal (colliding with the crystal or absorbed in it, but set out of thermal equilibrium by some external cause) is scattered by the whole crystal with a momentum proportional to a vector representing a reciprocal lattice point. The scattering is expected to occur with a well-defined probability and the momentum transferable to the particle is expected to follow a predictable distribution. The RME theory, in practice, is an extension of the Bragg-von Laue scattering law to high-energy colliding particles, in general, and can be applied to any particle or molecule colliding with the surface of a crystalline solid or absorbed in it, but not in thermal equilibrium with the crystal lattice. We verified the RME theory by considering a well-defined unresolved problem. In an experimental study about methane adsorbed in the zeolite Na-ZSM-5 [H. Jobic, Chem. Phys. Lett. 170, 217 (1990)] reporting neutron inelastic-scattering spectra (recoiled bands) at 10 K, the translational kinetic energy of methane resulted to be much higher than equilibrium expected value, namely, about 85 K (or 7.3 meV). The author concluded that "the interpretation of this unusual behavior has yet to be found." In the present study, on the basis of the RME, an explanation of this behavior is put forward. PMID:27608992

  3. Immobilized chitosan as a selective absorbent for the nickel removal in water sample.

    PubMed

    Wu, Jian-Min; Wang, Yong-Yao

    2003-09-01

    Method for preparation of chitosan immobilized on silica gel (CTS-silica) was described. The CTS-silica was used as absorbent for the absorption of nickel in water. The results showed that this absorbent had relatively high selectivity and strong affinity to nickel. The maximum absorption capacity for nickel can reach 667 mg/g of chitosan. Factors that affect the absorption capacity, such as pH, ion strength and the presence of calcium, EDTA and the mechanism of absorption were discussed in detail. The absorbent can be regenerated with acid and reused for several times. The recovery rate for nickel can reach 99.99%. This absorbent filled in a column can be used in nickel removal from wastewater and drinking water. PMID:14562924

  4. Heavy-ion fragmentation studies in thick water absorbers

    NASA Technical Reports Server (NTRS)

    Shavers, M. R.; Miller, J.; Schimmerling, W.; Wilson, J. W.; Townsend, L. W.

    1993-01-01

    Proposed long-term space missions could expose crewmembers to significant fluxes of galactic cosmic radiation (GCR) particles and secondary particles created from nuclear collisions. An assessment of radiobiological risks is dependent upon an accurate description of the charged-particle radiation field inside the human body. As shield thickness increases and the incident ions are slowed, the production of secondary particles contributes an increasingly significant fraction of the total dose until eventually secondary particles become more important than the primary particles. The nuclear mean free path of the GCR ions (which usually have nuclear charge between 1 (protons) and 26 (iron), both inclusive) are comparable with thicknesses typical of spacecraft structures and the human body. Collisions in these media will create projectile and target fragments with charge less than that of the primary particle, and each interaction event can have a multiplicity of more than one emerging interaction product. Projectile fragments usually continue on with very nearly the velocity of the primary ion (the so-called straightahead approximation). Having sufficient energy, the fragments may collide with atomic nuclei in thick shields and create a second generation of fragments, and so on. Target fragments are emitted from a struck nucleus, usually with much lower energy than projectile fragments and nearly isotropically in the rest frame of the absorbing medium. The resulting spectrum of particles and their energy loss rates will be very different from that in the unshielded environment, will determine the radiobiological impact on exposed living tissues -- whether in space or in ground-based radiobiology experiments -- and will play an important role in radiation effects on microelectronics.

  5. Water absorbance and thermal properties of sulfated wheat gluten films

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Wheat gluten films of varying thicknesses formed at 30C to 70C were treated with cold sulfuric acid to produce sulfated gluten films. Chemical, thermal, thermal stability, and water uptake properties were characterized for neat and sulfated films. The sulfated gluten films were able ...

  6. Removal of fluorescence and ultraviolet absorbance of dissolved organic matter in reclaimed water by solar light.

    PubMed

    Wu, Qianyuan; Li, Chao; Wang, Wenlong; He, Tao; Hu, Hongying; Du, Ye; Wang, Ting

    2016-05-01

    Storing reclaimed water in lakes is a widely used method of accommodating changes in the consumption of reclaimed water during wastewater reclamation and reuse. Solar light serves as an important function in degrading pollutants during storage, and its effect on dissolved organic matter (DOM) was investigated in this study. Solar light significantly decreased the UV254 absorbance and fluorescence (FLU) intensity of reclaimed water. However, its effect on the dissolved organic carbon (DOC) value of reclaimed water was very limited. The decrease in the UV254 absorbance intensity and FLU excitation-emission matrix regional integration volume (FLU volume) of reclaimed water during solar light irradiation was fit with pseudo-first order reaction kinetics. The decrease of UV254 absorbance was much slower than that of the FLU volume. Ultraviolet light in solar light had a key role in decreasing the UV254 absorbance and FLU intensity during solar light irradiation. The light fluence-based removal kinetic constants of the UV254 and FLU intensity were independent of light intensity. The peaks of the UV254 absorbance and FLU intensity with an apparent molecular weight (AMW) of 100Da to 2000Da decreased after solar irradiation, whereas the DOC value of the major peaks did not significantly change. PMID:27155416

  7. Effect of water pressure on absorbency of hydroentangled greige cotton nonwoven fabrics

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A studied has been conducted to determine the effect of water pressure in a commercial-grade Fleissner MiniJet hydroentanglement system on the absorbency of greige (non-bleached) cotton lint-based nonwoven fabric. The study has shown that a water pressure of 125 Bar or higher on only two high-pressu...

  8. Clusterization of water molecules as deduced from statistical mechanical approach

    NASA Astrophysics Data System (ADS)

    Krasnoholovets, Volodymyr

    2004-12-01

    Using the methods of statistical mechanics we have shown that a homogeneous water network is unstable and spontaneously disintegrates to the nonhomogeneous state (i.e. peculiar clusters), which can be treated as an ordinary state of liquid water. The major peculiarity of the concept is that it separates the paired potential into two independent components—the attractive potential and the repulsive one, which in turn should feature a very different dependence on the distance from the particle (a water molecule in the present case). We choose the interaction potential as a combination of the ionic crystal potential and the vibratory potential associated with the elastic properties of the water system as a whole. The number ℵ of water molecules that enters a cluster is calculated as a function of several parameters, such as the dielectric constant, the mass of a water molecule, the distance between nearest molecules, and the vibrations of nearest molecules in their nodes. The number of H2O molecules that comprise a cluster is estimated as about ℵ ≈ 900, which agrees with the available experimental data.

  9. On the Several Molecules and Nanostructures of Water

    PubMed Central

    Whitney, Cynthia Kolb

    2012-01-01

    This paper investigates the water molecule from a variety of viewpoints. Water can involve different isotopes of Hydrogen and Oxygen, it can form differently shaped isomer molecules, and, when frozen, it occupies space differently than most other substances do. The tool for conducting the investigation of all this is called ‘Algebraic Chemistry’. This tool is a quantitative model for predicting the energy budget for all sorts of changes between different ionization states of atoms that are involved in chemical reactions and in changes of physical state. The model is based on consistent patterns seen in empirical data about ionization potentials, together with rational scaling laws that can interpolate and extrapolate for situations where no data are available. The results of the investigation of the water molecule include comments, both positive and negative, about technologies involving heavy water, poly water, Brown’s gas, and cold fusion. PMID:22312305

  10. On the several molecules and nanostructures of water.

    PubMed

    Whitney, Cynthia Kolb

    2012-01-01

    This paper investigates the water molecule from a variety of viewpoints. Water can involve different isotopes of Hydrogen and Oxygen, it can form differently shaped isomer molecules, and, when frozen, it occupies space differently than most other substances do. The tool for conducting the investigation of all this is called 'Algebraic Chemistry'. This tool is a quantitative model for predicting the energy budget for all sorts of changes between different ionization states of atoms that are involved in chemical reactions and in changes of physical state. The model is based on consistent patterns seen in empirical data about ionization potentials, together with rational scaling laws that can interpolate and extrapolate for situations where no data are available. The results of the investigation of the water molecule include comments, both positive and negative, about technologies involving heavy water, poly water, Brown's gas, and cold fusion. PMID:22312305

  11. Quantum Behavior of Water Molecules Confined to Nanocavities in Gemstones.

    PubMed

    Gorshunov, Boris P; Zhukova, Elena S; Torgashev, Victor I; Lebedev, Vladimir V; Shakurov, Gil'man S; Kremer, Reinhard K; Pestrjakov, Efim V; Thomas, Victor G; Fursenko, Dimitry A; Dressel, Martin

    2013-06-20

    When water is confined to nanocavities, its quantum mechanical behavior can be revealed by terahertz spectroscopy. We place H2O molecules in the nanopores of a beryl crystal lattice and observe a rich and highly anisotropic set of absorption lines in the terahertz spectral range. Two bands can be identified, which originate from translational and librational motions of the water molecule isolated within the cage; they correspond to the analogous broad bands in liquid water and ice. In the present case of well-defined and highly symmetric nanocavities, the observed fine structure can be explained by macroscopic tunneling of the H2O molecules within a six-fold potential caused by the interaction of the molecule with the cavity walls. PMID:26283245

  12. Effects of water molecules on photoluminescence from hierarchical peptide nanotubes and water probing capability.

    PubMed

    Wang, Minjie; Xiong, Shijie; Wu, Xinglong; Chu, Paul K

    2011-10-01

    Photoluminescence (PL) spectra reveal that deficiency of water molecules in the channel cores of bioinspired hierarchical diphenylalanine ( L -Phe- L -Phe, FF) peptide nanotubes (PNTs) not only modifies the bandgap of the subnanometer crystalline structure formed by the self-assembly process, but also induces a characteristic ultraviolet PL peak the position of which is linearly proportional to the number of water molecules in the PNTs. Addition or loss of water molecules gives rise to the UV PL redshift or blueshift. Density functional theory calculation also confirms that addition of water molecules to the PNTs causes splitting of the valence-band peak, which corresponds to the shift and splitting of the observed UV PL peak. Water molecules play an important role in the biological properties of FF PNTs and the results demonstrate that the PL spectra can be used to probe the number of water molecules bonded to the FF molecules. PMID:22049551

  13. Molecules to Materials for PEC Water Splitting

    SciTech Connect

    Neale, N. R.; Ruddy, D. A.; Lee, K.; Seabold, J. A.; Deutsch, T. G.; Dukovic, G.

    2013-01-01

    Advances in heterogeneous catalysis are driven by the formation of structure-property relationships at solid-liquid and solid-gaseous interfaces. The establishment of these relationships relies on cooperative research efforts on several fronts: prediction and analysis using high-level theoretical models, the development of new synthetic methods to prepare specific solid-state compositions and structures, new analytical methods to identify the active site and define interfacial properties, and mechanistic analysis of functioning catalysts. However, customized materials that allow for fine control of the interfacial properties at solid-liquid boundaries represent difficult synthetic targets. We have been investigating molecular synthons as precursors to advanced materials to address this challenge. In this presentation, we will discuss (1) the chemistry of molecular inorganic complexes, (2) their conversion to mixed-metal oxides, and (3) structure-property relationships of the resulting oxides relevant to PEC water splitting.

  14. Dynamics of Confined Water Molecules in Aqueous Salt Hydrates

    SciTech Connect

    Werhahn, Jasper C.; Pandelov, S.; Yoo, Soohaeng; Xantheas, Sotiris S.; Iglev, H.

    2011-04-01

    The unusual properties of water are largely dictated by the dynamics of the H bond network. A single water molecule has more H bonding sites than atoms, hence new experimental and theoretical investigations about this peculiar liquid have not ceased to appear. Confinement of water to nanodroplets or small molecular clusters drastically changes many of the liquid’s properties. Such confined water plays a major role in the solvation of macro molecules such as proteins and can even be essential to their properties. Despite the vast results available on bulk and confined water, discussions about the correlation between spectral and structural properties continue to this day. The fast relaxation of the OH stretching vibration in bulk water, and the variance of sample geometries in the experiments on confined water obfuscate definite interpretation of the spectroscopic results in terms of structural parameters. We present first time-resolved investigations on a new model system that is ideally suited to overcome many of the problems faced in spectroscopical investigation of the H bond network of water. Aqueous hydrates of inorganic salts provide water molecules in a crystal grid, that enables unambiguous correlations of spectroscopic and structural features. Furthermore, the confined water clusters are well isolated from each other in the crystal matrix, so different degrees of confinement can be achieved by selection of the appropriate salt.

  15. Theoretical study of impulsive orientation of asymmetric top water molecules

    NASA Astrophysics Data System (ADS)

    Rangan, Chitra; Senchuk, Andrew

    2008-05-01

    We theoretically study the orientation of a polar, asymmetric top molecule by a terahertz half-cycle pulse. This study is motivated by recent experimental results by C. Herne and P.H. Bucksbaum on the orientation of water molecule using terahertz half-cycle pulses. The half-cycle pulse is modelled as an impulse. The degree of orientation is calculated. Our aim is to characterize the calculated orientation curves in terms of rotational spectroscopy constants.

  16. Unprecedentedly rapid transport of single-file rolling water molecules

    NASA Astrophysics Data System (ADS)

    Qiu, Tong; Huang, Ji-Ping

    2015-10-01

    The realization of rapid and unidirectional single-file water-molecule flow in nanochannels has posed a challenge to date. Here, we report unprecedentedly rapid unidirectional single-file water-molecule flow under a translational terahertz electric field, which is obtained by developing a Debye doublerelaxation theory. In addition, we demonstrate that all the single-file molecules undergo both stable translation and rotation, behaving like high-speed train wheels moving along a railway track. Independent molecular dynamics simulations help to confirm these theoretical results. The mechanism involves the resonant relaxation dynamics of H and O atoms. Further, an experimental demonstration is suggested and discussed. This work has implications for the design of high-efficiency nanochannels or smaller nanomachines in the field of nanotechnology, and the findings also aid in the understanding and control of water flow across biological nanochannels in biology-related research.

  17. How Many Water Molecules Does it Take to Dissociate HCl?

    PubMed

    Vargas-Caamal, Alba; Cabellos, Jose Luis; Ortiz-Chi, Filiberto; Rzepa, Henry S; Restrepo, Albeiro; Merino, Gabriel

    2016-02-18

    The potential energy surfaces of the HCl(H2O)n (n is the number of water molecules) clusters are systematically explored using density functional theory and high-level ab initio computations. On the basis of electronic energies, the number of water molecules needed for HCl dissociation is four as reported by some experimental groups. However, this number is five owing to the inclusion of entropic factors. Wiberg bond indices are calculated and analyzed, and the results provide a quadratic correlation and classification of clusters according to the nondissociated, partially dissociated, and fully dissociated character of the H-Cl bond. Our computations show that if temperature is not controlled during the experiment, the values obtained for the dipole moment (or for any measurable property) are susceptible to change, providing a different picture of the number of water molecules needed for HCl dissociation in a nanoscopic droplet. PMID:26774026

  18. Transport behavior of water molecules through two-dimensional nanopores

    SciTech Connect

    Zhu, Chongqin; Li, Hui; Meng, Sheng

    2014-11-14

    Water transport through a two-dimensional nanoporous membrane has attracted increasing attention in recent years thanks to great demands in water purification and desalination applications. However, few studies have been reported on the microscopic mechanisms of water transport through structured nanopores, especially at the atomistic scale. Here we investigate the microstructure of water flow through two-dimensional model graphene membrane containing a variety of nanopores of different size by using molecular dynamics simulations. Our results clearly indicate that the continuum flow transits to discrete molecular flow patterns with decreasing pore sizes. While for pores with a diameter ≥15 Å water flux exhibits a linear dependence on the pore area, a nonlinear relationship between water flux and pore area has been identified for smaller pores. We attribute this deviation from linear behavior to the presence of discrete water flow, which is strongly influenced by the water-membrane interaction and hydrogen bonding between water molecules.

  19. Nano-porous-water Absorbents for Solid-absorbebt Heat Pump System

    NASA Astrophysics Data System (ADS)

    Mizota, Tadato; Nakayama, Noriaki

    Zeolite-water heat-pump system has been developed in these 25 years. Recently, an instant beer-cooling system has appeared by using the zeolite heat pump system as a commercial product. It takes so long time for the development since the first proposal. The most serious problem through the development has been of the ability of absorbents. Themaximum heat exchange capacity to date exceeds 1MJ•kg-1 for Mg89-A, which is comparable to the energy storage capacity of modern alkaline-ion batteries in weight-bases. But it needs high temperature heat sources more than 200°C for the activation. Absorbents useful at lower temperatures are thus desirable for effective use of various kinds of lower temperature heat sources Various nano-porous materials as well as zeolites now under investigation as candidates of heat-pump absorbents, such as silica-gels, allophane, imogolite, hydrotalcite, etc.

  20. New absorbed dose measurement with cylindrical water phantoms for multidetector CT.

    PubMed

    Ohno, Takeshi; Araki, Fujio; Onizuka, Ryota; Hioki, Kazunari; Tomiyama, Yuuki; Yamashita, Yusuke

    2015-06-01

    The aim of this study was to develop new dosimetry with cylindrical water phantoms for multidetector computed tomography (MDCT). The ionization measurement was performed with a Farmer ionization chamber at the center and four peripheral points in the body-type and head-type cylindrical water phantoms. The ionization was converted to the absorbed dose using a (60)Co absorbed-dose-to-water calibration factor and Monte Carlo (MC) -calculated correction factors. The correction factors were calculated from MDCT (Brilliance iCT, 64-slice, Philips Electronics) modeled with GMctdospp (IMPS, Germany) software based on the EGSnrc MC code. The spectrum of incident x-ray beams and the configuration of a bowtie filter for MDCT were determined so that calculated photon intensity attenuation curves for aluminum (Al) and calculated off-center ratio (OCR) profiles in air coincided with those measured. The MC-calculated doses were calibrated by the absorbed dose measured at the center in both cylindrical water phantoms. Calculated doses were compared with measured doses at four peripheral points and the center in the phantom for various beam pitches and beam collimations. The calibration factors and the uncertainty of the absorbed dose determined using this method were also compared with those obtained by CTDIair (CT dose index in air). Calculated Al half-value layers and OCRs in air were within 0.3% and 3% agreement with the measured values, respectively. Calculated doses at four peripheral points and the centers for various beam pitches and beam collimations were within 5% and 2% agreement with measured values, respectively. The MC-calibration factors by our method were 44-50% lower than values by CTDIair due to the overbeaming effect. However, the calibration factors for CTDIair agreed within 5% with those of our method after correction for the overbeaming effect. Our method makes it possible to directly measure the absorbed dose for MDCT and is more robust and accurate than the

  1. New absorbed dose measurement with cylindrical water phantoms for multidetector CT

    NASA Astrophysics Data System (ADS)

    Ohno, Takeshi; Araki, Fujio; Onizuka, Ryota; Hioki, Kazunari; Tomiyama, Yuuki; Yamashita, Yusuke

    2015-06-01

    The aim of this study was to develop new dosimetry with cylindrical water phantoms for multidetector computed tomography (MDCT). The ionization measurement was performed with a Farmer ionization chamber at the center and four peripheral points in the body-type and head-type cylindrical water phantoms. The ionization was converted to the absorbed dose using a 60Co absorbed-dose-to-water calibration factor and Monte Carlo (MC) -calculated correction factors. The correction factors were calculated from MDCT (Brilliance iCT, 64-slice, Philips Electronics) modeled with GMctdospp (IMPS, Germany) software based on the EGSnrc MC code. The spectrum of incident x-ray beams and the configuration of a bowtie filter for MDCT were determined so that calculated photon intensity attenuation curves for aluminum (Al) and calculated off-center ratio (OCR) profiles in air coincided with those measured. The MC-calculated doses were calibrated by the absorbed dose measured at the center in both cylindrical water phantoms. Calculated doses were compared with measured doses at four peripheral points and the center in the phantom for various beam pitches and beam collimations. The calibration factors and the uncertainty of the absorbed dose determined using this method were also compared with those obtained by CTDIair (CT dose index in air). Calculated Al half-value layers and OCRs in air were within 0.3% and 3% agreement with the measured values, respectively. Calculated doses at four peripheral points and the centers for various beam pitches and beam collimations were within 5% and 2% agreement with measured values, respectively. The MC-calibration factors by our method were 44-50% lower than values by CTDIair due to the overbeaming effect. However, the calibration factors for CTDIair agreed within 5% with those of our method after correction for the overbeaming effect. Our method makes it possible to directly measure the absorbed dose for MDCT and is more robust and accurate than the

  2. SPAM: A Simple Approach for Profiling Bound Water Molecules.

    PubMed

    Cui, Guanglei; Swails, Jason M; Manas, Eric S

    2013-12-10

    A method that identifies the hydration shell structure of proteins and estimates the relative free energies of water molecules within that hydration shell is described. The method, which we call "SPAM" (maps spelled in reverse), utilizes explicit solvent molecular dynamics (MD) simulations to capture discrete hydration sites at the water-protein interface and computes a local free energy measure from the distribution of interaction energies between water and the environment at a specific site. SPAM is able to provide a qualitative estimate of the thermodynamic profile of bound water molecules that correlates nicely with well-studied structure-activity relationships and observed binding "hot spots". This is demonstrated in retrospective analyses of HIV1 protease and hen egg white lysozyme, where the effects of water displacement and solvent binding have been studied extensively. The simplicity and effectiveness of SPAM allow for prospective application during the drug discovery process. PMID:26592287

  3. Structures of water molecules in carbon nanotubes under electric fields

    SciTech Connect

    Winarto,; Takaiwa, Daisuke; Yamamoto, Eiji; Yasuoka, Kenji

    2015-03-28

    Carbon nanotubes (CNTs) are promising for water transport through membranes and for use as nano-pumps. The development of CNT-based nanofluidic devices, however, requires a better understanding of the properties of water molecules in CNTs because they can be very different from those in the bulk. Using all-atom molecular dynamics simulations, we investigate the effect of axial electric fields on the structure of water molecules in CNTs having diameters ranging from (7,7) to (10,10). The water dipole moments were aligned parallel to the electric field, which increases the density of water inside the CNTs and forms ordered ice-like structures. The electric field induces the transition from liquid to ice nanotubes in a wide range of CNT diameters. Moreover, we found an increase in the lifetime of hydrogen bonds for water structures in the CNTs. Fast librational motion breaks some hydrogen bonds, but the molecular pairs do not separate and the hydrogen bonds reform. Thus, hydrogen bonds maintain the water structure in the CNTs, and the water molecules move collectively, decreasing the axial diffusion coefficient and permeation rate.

  4. Structures of water molecules in carbon nanotubes under electric fields

    NASA Astrophysics Data System (ADS)

    Winarto, Takaiwa, Daisuke; Yamamoto, Eiji; Yasuoka, Kenji

    2015-03-01

    Carbon nanotubes (CNTs) are promising for water transport through membranes and for use as nano-pumps. The development of CNT-based nanofluidic devices, however, requires a better understanding of the properties of water molecules in CNTs because they can be very different from those in the bulk. Using all-atom molecular dynamics simulations, we investigate the effect of axial electric fields on the structure of water molecules in CNTs having diameters ranging from (7,7) to (10,10). The water dipole moments were aligned parallel to the electric field, which increases the density of water inside the CNTs and forms ordered ice-like structures. The electric field induces the transition from liquid to ice nanotubes in a wide range of CNT diameters. Moreover, we found an increase in the lifetime of hydrogen bonds for water structures in the CNTs. Fast librational motion breaks some hydrogen bonds, but the molecular pairs do not separate and the hydrogen bonds reform. Thus, hydrogen bonds maintain the water structure in the CNTs, and the water molecules move collectively, decreasing the axial diffusion coefficient and permeation rate.

  5. [Investigation of membrane permeability of carp spermatozoa for water molecules].

    PubMed

    Pugovkin, A Iu; Kopeĭka, E F; Nardid, O A; Cherkashina, Ia O

    2014-01-01

    The fundamentals of a photometry method for determination of membrane permeability of some fish spermatozoa for water molecules are presented. Osmotic tolerance of carp spermatozoa membranes was studied using EPR-spectroscopy and photometric analysis methods. It was shown that carp spermatozoa look like the ideal osmometers in their reaction on media of different osmolarity. The value of membrane permeability of carp spermatozoa for water molecules was determined. Data obtained can be used in cryobiology for creating cryoprotective media and regimes of fish sperm cryopreservation. PMID:25715589

  6. Neural network consistent empirical physical formula construction for density functional theory based nonlinear vibrational absorbance and intensity of 6-choloronicotinic acid molecule

    NASA Astrophysics Data System (ADS)

    Yildiz, Nihat; Karabacak, Mehmet; Kurt, Mustafa; Akkoyun, Serkan

    2012-05-01

    Being directly related to the electric charge distributions in a molecule, the vibrational spectra intensities are both experimentally and theoretically important physical quantities. However, these intensities are inherently highly nonlinear and of complex pattern. Therefore, in particular for unknown detailed spatial molecular structures, it is difficult to make ab initio intensity calculations to compare with new experimental data. In this respect, we very recently initiated entirely novel layered feedforward neural network (LFNN) approach to construct empirical physical formulas (EPFs) for density functional theory (DFT) vibrational spectra of some molecules. In this paper, as a new and far improved contribution to our novel molecular vibrational spectra LFNN-EPF approach, we constructed LFFN-EPFs for absorbances and intensities of 6-choloronicotinic acid (6-CNA) molecule. The 6-CNA data, borrowed from our previous study, was entirely different and much larger than the vibrational intensity data of our formerly used LFNN-EPF molecules. In line with our another previous work which theoretically proved the LFNN relevance to EPFs, although the 6-CNA DFT absorbance and intensity were inherently highly nonlinear and sharply fluctuating in character, still the optimally constructed train set LFFN-EPFs very successfully fitted the absorbances and intensities. Moreover, test set (i.e. yet-to-be measured experimental data) LFNN-EPFs consistently and successfully predicted the absorbance and intensity data. This simply means that the physical law embedded in the 6-CNA vibrational data was successfully extracted by the LFNN-EPFs. In conclusion, these vibrational LFNN-EPFs are of explicit form. Therefore, by various suitable operations of mathematical analysis, they can be used to estimate the electronic charge distributions of the unknown molecule of the significant complexity. Additionally, these estimations can be combined with those of theoretical DFT atomic polar

  7. Nanotribological properties of water films adsorbing atop, and absorbing below, graphene layers supported by metal substrates

    NASA Astrophysics Data System (ADS)

    Liu, Zijian; Curtis, C. K.; Stine, R.; Sheehan, P.; Krim, J.

    The tribological properties of graphite, a common lubricant with known sensitivity to the presence of water, have been studied extensively at the macroscopic and microscopic scales. Although far less attention has been devoted to the tribological properties of graphene, it has been established that the tribological response to the presence of water is dissimilar from that of graphite. We report here a quartz crystal microbalance study of the nanotribological properties of water films adsorbed/absorbed on graphene layers prepared by either chemical decomposition on nickel(111) substrates or transfer of freestanding graphene layers to aluminum substrates. Sliding friction levels of the water films were also measured for metal surfaces in the absence of a graphene layer. We observe very high friction levels for water adsorbed atop graphene on Ni(111) and very low levels for water on aluminum. For the case of graphene/aluminum, the data indicate that the water is absorbing between the graphene layer and the aluminum. Dissipation levels moreover indicate the presence of an interstitial water increases sliding friction between the graphene and the aluminum substrate Work supported by NSF and NRL.

  8. Visualizing Water Molecules in Transmembrane Proteins Using Radiolytic Labeling Methods

    SciTech Connect

    Orban, T.; Gupta, S; Palczewski, K; Chance, M

    2010-01-01

    Essential to cells and their organelles, water is both shuttled to where it is needed and trapped within cellular compartments and structures. Moreover, ordered waters within protein structures often colocalize with strategically placed polar or charged groups critical for protein function, yet it is unclear if these ordered water molecules provide structural stabilization, mediate conformational changes in signaling, neutralize charged residues, or carry out a combination of all these functions. Structures of many integral membrane proteins, including G protein-coupled receptors (GPCRs), reveal the presence of ordered water molecules that may act like prosthetic groups in a manner quite unlike bulk water. Identification of 'ordered' waters within a crystalline protein structure requires sufficient occupancy of water to enable its detection in the protein's X-ray diffraction pattern, and thus, the observed waters likely represent a subset of tightly bound functional waters. In this review, we highlight recent studies that suggest the structures of ordered waters within GPCRs are as conserved (and thus as important) as conserved side chains. In addition, methods of radiolysis, coupled to structural mass spectrometry (protein footprinting), reveal dynamic changes in water structure that mediate transmembrane signaling. The idea of water as a prosthetic group mediating chemical reaction dynamics is not new in fields such as catalysis. However, the concept of water as a mediator of conformational dynamics in signaling is just emerging, because of advances in both crystallographic structure determination and new methods of protein footprinting. Although oil and water do not mix, understanding the roles of water is essential to understanding the function of membrane proteins.

  9. The Fricke dosimeter as an absorbed dose to water primary standard for Ir-192 brachytherapy

    NASA Astrophysics Data System (ADS)

    El Gamal, Islam; Cojocaru, Claudiu; Mainegra-Hing, Ernesto; McEwen, Malcolm

    2015-06-01

    The aim of this project was to develop an absorbed dose to water primary standard for Ir-192 brachytherapy based on the Fricke dosimeter. To achieve this within the framework of the existing TG-43 protocol, a determination of the absorbed dose to water at the reference position, D(r0,θ0), was undertaken. Prior to this investigation, the radiation chemical yield of the ferric ions (G-value) at the Ir-192 equivalent photon energy (0.380 MeV) was established by interpolating between G-values obtained for Co-60 and 250 kV x-rays. An irradiation geometry was developed with a cylindrical holder to contain the Fricke solution and allow irradiations in a water phantom to be conducted using a standard Nucletron microSelectron V2 HDR Ir-192 afterloader. Once the geometry and holder were optimized, the dose obtained with the Fricke system was compared to the standard method used in North America, based on air-kerma strength. Initial investigations focused on reproducible positioning of the ring-shaped holder for the Fricke solution with respect to the Ir-192 source and obtaining an acceptable type A uncertainty in the optical density measurements required to yield the absorbed dose. Source positioning was found to be reproducible to better than 0.3 mm, and a careful cleaning and control procedure reduced the variation in optical density reading due to contamination of the Fricke solution by the PMMA holder. It was found that fewer than 10 irradiations were required to yield a type A standard uncertainty of less than 0.5%. Correction factors to take account of the non-water components of the geometry and the volume averaging effect of the Fricke solution volume were obtained from Monte Carlo calculations. A sensitivity analysis showed that the dependence on the input data used (e.g. interaction cross-sections) was small with a type B uncertainty for these corrections estimated to be 0.2%. The combined standard uncertainty in the determination of absorbed dose to water

  10. The Fricke dosimeter as an absorbed dose to water primary standard for Ir-192 brachytherapy.

    PubMed

    El Gamal, Islam; Cojocaru, Claudiu; Mainegra-Hing, Ernesto; McEwen, Malcolm

    2015-06-01

    The aim of this project was to develop an absorbed dose to water primary standard for Ir-192 brachytherapy based on the Fricke dosimeter. To achieve this within the framework of the existing TG-43 protocol, a determination of the absorbed dose to water at the reference position, D(r0,θ0), was undertaken. Prior to this investigation, the radiation chemical yield of the ferric ions (G-value) at the Ir-192 equivalent photon energy (0.380 MeV) was established by interpolating between G-values obtained for Co-60 and 250 kV x-rays.An irradiation geometry was developed with a cylindrical holder to contain the Fricke solution and allow irradiations in a water phantom to be conducted using a standard Nucletron microSelectron V2 HDR Ir-192 afterloader. Once the geometry and holder were optimized, the dose obtained with the Fricke system was compared to the standard method used in North America, based on air-kerma strength.Initial investigations focused on reproducible positioning of the ring-shaped holder for the Fricke solution with respect to the Ir-192 source and obtaining an acceptable type A uncertainty in the optical density measurements required to yield the absorbed dose. Source positioning was found to be reproducible to better than 0.3 mm, and a careful cleaning and control procedure reduced the variation in optical density reading due to contamination of the Fricke solution by the PMMA holder. It was found that fewer than 10 irradiations were required to yield a type A standard uncertainty of less than 0.5%.Correction factors to take account of the non-water components of the geometry and the volume averaging effect of the Fricke solution volume were obtained from Monte Carlo calculations. A sensitivity analysis showed that the dependence on the input data used (e.g. interaction cross-sections) was small with a type B uncertainty for these corrections estimated to be 0.2%.The combined standard uncertainty in the determination of absorbed dose to water at

  11. Highly efficient water splitting by a dual-absorber tandem cell

    NASA Astrophysics Data System (ADS)

    Brillet, Jeremie; Yum, Jun-Ho; Cornuz, Maurin; Hisatomi, Takashi; Solarska, Renata; Augustynski, Jan; Graetzel, Michael; Sivula, Kevin

    2012-12-01

    Photoelectrochemical water-splitting devices, which use solar energy to convert water into hydrogen and oxygen, have been investigated for decades. Multijunction designs are most efficient, as they can absorb enough solar energy and provide sufficient free energy for water cleavage. However, a balance exists between device complexity, cost and efficiency. Water splitters fabricated using triple-junction amorphous silicon or III-V semiconductors have demonstrated reasonable efficiencies, but at high cost and high device complexity. Simpler approaches using oxide-based semiconductors in a dual-absorber tandem approach have reported solar-to-hydrogen (STH) conversion efficiencies only up to 0.3% (ref. 4). Here, we present a device based on an oxide photoanode and a dye-sensitized solar cell, which performs unassisted water splitting with an efficiency of up to 3.1% STH. The design relies on carefully selected redox mediators for the dye-sensitized solar cell and surface passivation techniques and catalysts for the oxide-based photoanodes.

  12. Hadronic chemistry applied to hydrogen and water molecules

    NASA Astrophysics Data System (ADS)

    Tangde, Vijay M.

    2012-09-01

    The decades of research of R M Santilli resulted into the formulation of iso-, geno- and hyper- mathematics [1, 2] that helped in understanding numerous diversified problems and removing inadequacies in most of the established and celebrated theories of 20th century physics and chemistry, for example, the theories of relativity, quantum mechanics (chemistry), astrophysics, particle physics, and so on. This involves the isotopic, genotopic, etc. lifting of Lie algebra that generated Lie admissible mathematics to properly describe irreversible processes. The studies on Hadronic m Mechanics based on Santilli's mathematics for the first time has removed the very fundamental limitations of quantum chemistry [3, 4] [2, 3, 4]. Herein, we review a Santilli-Shillady model[3, 4, 5] of hydrogen and water molecules characterized by a bond at short distances of the two valance electrons into a singlet quasi-particle state called isoelectronium for hydrogen molecule and two isoelctronia (one per H-O dimer) in case of water molecule. We especially emphasis on: the numerically exact representation of binding energies from unadulterated first axiomatic principle, the reduction of the hydrogen molecule to a restricted three body problem that admits exact analytic solutions and the reduction of computer time by at least a factor of 1000 folds due to a much faster convergent series.

  13. Development of a water calorimetry-based standard for absorbed dose to water in HDR {sup 192}Ir brachytherapy

    SciTech Connect

    Sarfehnia, Arman; Seuntjens, Jan

    2010-04-15

    Purpose: The aim of this article is to develop and evaluate a primary standard for HDR {sup 192}Ir brachytherapy based on 4 deg. C stagnant water calorimetry. Methods: The absolute absorbed dose to water was directly measured for several different Nucletron microSelectron {sup 192}Ir sources of air kerma strength ranging between 21 000 and 38 000 U and for source-to-detector separations ranging between 25 and 70 mm. The COMSOL MULTIPHYSICS software was used to accurately calculate the heat transport in a detailed model geometry. Through a coupling of the ''conduction and convection'' module with the ''Navier-Stokes incompressible fluid'' module in the software, both the conductive and convective effects were modeled. Results: A detailed uncertainty analysis resulted in an overall uncertainty in the absorbed dose of 1.90%(1{sigma}). However, this includes a 1.5% uncertainty associated with a nonlinear predrift correction which can be substantially reduced if sufficient time is provided for the system to come to a new equilibrium in between successive calorimetric runs, an opportunity not available to the authors in their clinical setting due to time constraints on the machine. An average normalized dose rate of 361{+-}7 {mu}Gy/(h U) at a source-to-detector separation of 55 mm was measured for the microSelectron {sup 192}Ir source based on water calorimetry. The measured absorbed dose per air kerma strength agreed to better than 0.8%(1{sigma}) with independent ionization chamber and EBT-1 Gafchromic film reference dosimetry as well as with the currently accepted AAPM TG-43 protocol measurements. Conclusions: This work paves the way toward a primary absorbed dose to water standard in {sup 192}Ir brachytherapy.

  14. Quantum behaviour of water molecule in gemstone: terahertz fingerprints

    NASA Astrophysics Data System (ADS)

    Zhukova, Elena S.; Gorshunov, Boris P.; Torgashev, Victor I.; Lebedev, Vladimir V.; Shakurov, Gil'man S.; Kremer, Reinhard K.; Pestrjakov, Efim V.; Thomas, Victor G.; Fursenko, Dimitry A.; Dressel, Martin

    2014-03-01

    We have shown that a weak interaction of a lone H2O molecule with the ''walls'' of nano-sized crystalline cage of gemstone (beryl) results in emergence of a rich set of molecular vibrational states. By analogy with translational and librational bands in liquid water and ice corresponding absorption bands are explained as due to translational (T) and librational (L) movements of the H2O molecule which is hydrogen bonded to the cage walls. In beryl crystal lattice, however, the six-fold symmetry of the cage brings about additional effect of splitting of the T and L bands into fine structure due to tunnelling within the six-well potential relief. The presented results will be of use for analysis of more complicated systems with confined water molecules like H2O chains in carbon nano-tubes, molecular clusters in e.g. zeolites, clays, silica gels and other natural or synthetic frameworks, as well as for interfacial water in biological systems.

  15. Insight into water molecules bonding on 4d metal surfaces

    NASA Astrophysics Data System (ADS)

    Carrasco, Javier; Michaelides, Angelos; Scheffler, Matthias

    2008-03-01

    Water-metal interactions are of capital importance to a wide variety of phenomena in materials science, catalysis, corrosion, electrochemistry, etc. Here we address the nature of the bond between water molecules and metal surfaces through a careful systematic study. Specifically, the bonding of isolated water molecules to a series of close-packed transition metal surfaces - Ru(0001), Rh(111), Pd(111) and Ag(111) - has been examined in detail with density functional theory (DFT). Aiming to understand the origin behind energetic and structural trends along the 4d series we employ a range of analysis tools, such as decomposition of the density of states, electron density differences, electronic reactivity function and inspection of individual Kohn-Sham orbitals. The results obtained allow us to rationalize the bonding between water and transition metal surfaces as a balance of covalent and electrostatic interactions. A frontier orbital scheme based on so-called two-center four-electron interactions between molecular orbitals of water and d band states of the surface proves incisive in understanding these systems.

  16. Interaction Of Water Molecules With SiC(001) Surfaces

    SciTech Connect

    Cicero, G; Catellani, A; Galli, G

    2004-08-10

    We have investigated the interaction of water molecules with the polar Si- and C- terminated surfaces of cubic Silicon Carbide by means of ab initio molecular dynamics simulations at finite temperature. Different water coverages were considered, from {1/4} to a complete monolayer. Irrespective of coverage, we find that water dissociates on the silicon terminated surfaces, leading to important changes in both its structural and electronic properties. On the contrary, the carbon terminated surface remains inert when exposed to water. We propose experiments to reveal the ionic and electronic structure of wet Si-terminated surfaces predicted by our calculations, which at full coverage are notably different from those of hydrated Si(001) substrates. Finally, we discuss the implications of our results for SiC surface functionalization.

  17. Pigmentation and Spectral Absorbance Signatures in Deep-Water Corals from the Trondheimsfjord, Norway

    PubMed Central

    Elde, Anette C.; Pettersen, Ragnhild; Bruheim, Per; Järnegren, Johanna; Johnsen, Geir

    2012-01-01

    The pigmentation and corresponding in vivo and in vitro absorption characteristics in three different deep-water coral species: white and orange Lophelia pertusa, Paragorgia arborea and Primnoa resedaeformis, collected from the Trondheimsfjord are described. Pigments were isolated and characterized by High-Performance Liquid Chromatography (HPLC) analysis and High-Performance Liquid Chromatography Time-Of-Flight Mass Spectrometer (LC-TOF MS). The main carotenoids identified for all three coral species were astaxanthin and a canthaxanthin-like carotenoid. Soft tissue and skeleton of orange L. pertusa contained 2 times more astaxanthin g−1 wet weight compared to white L. pertusa. White and orange L. pertusa were characterized with in vivo absorbance peaks at 409 and 473 nm, respectively. In vivo absorbance maxima for P. arborea and P. resedaeformis was typically at 475 nm. The shapes of the absorbance spectra (400–700 nm) were species-specific, indicated by in vivo, in vitro and the corresponding difference spectra. The results may provide important chemotaxonomic information for pigment when bonded to their proteins in vivo, bio-prospecting, and for in situ identification, mapping and monitoring of corals. PMID:22822381

  18. Anomalous water molecules and mechanistic effects of water nanotube clusters confined to molecular porous crystals.

    PubMed

    Tadokoro, Makoto; Ohhara, Takashi; Ohhata, Yuhki; Suda, Takaaki; Miyasato, Yuji; Yamada, Takeshi; Kikuchi, Tatsuya; Tanaka, Ichiro; Kurihara, Kazuo; Oguni, Masaharu; Nakasuji, Kazuhiro; Yamamuro, Osamu; Ryota, Kuroki

    2010-02-18

    The movement of water molecules in the limited space present within nanoscale regions, which is different from the molecular motion of bulk water, is significantly affected by strong interfacial interactions with the surrounding outer walls. Hence, most of the water molecules that are confined to nanochannel spaces having widths less than ca. 2 nm can generally be classified together as "structural water". Since the motions of such water molecules are limited by interfacial interactions with the outer wall, the nature of structural water, which is strongly influenced by the interactions, will have different characteristics from normal water. For our investigations on the characteristics of structural water, we have developed a nanoporous crystal with a diameter of ca. 1.6 nm; it was constructed from 1-D hydrophilic channels by self-organization of the designed molecules. A tubelike three-layered water cluster, called a water nanotube (WNT), is formed in each internal channel space and is regulated by H-bonds with the outer wall. The WNT undergoes a glass transition (T(g) = 107 K) and behaves as a liquid; it freezes at 234 K and changes into an icelike nanotube cluster. In this study, the structure of the WNT is investigated through neutron structure analysis, and it is observed to stabilize by a mechanistic anchor effect of structural water. Furthermore, from neutron-scattering experiments, it is seen that a few water molecules around the center of the WNT move approximately with the same diffusion constant as those in bulk water; however, the residence time and average jump length are longer, despite the restrictions imposed by the H-bonding with structural water. The behavior of mobile water within a WNT is investigated; this can be used to elucidate the mechanism for the effect of structural water on vital functions on the cell surface. PMID:20102158

  19. The spontaneous synchronized dance of pairs of water molecules

    SciTech Connect

    Roncaratti, Luiz F.; Cappelletti, David Pirani, Fernando

    2014-03-28

    Molecular beam scattering experiments have been performed to study the effect of long-range anisotropic forces on the collision dynamics of two small polar molecules. The main focus of this paper is on water, but also ammonia and hydrogen sulphide molecules have been investigated, and some results will be anticipated. The intermolecular distances mainly probed are of the order of 1 nm and therefore much larger than the molecular dimensions. In particular, we have found that the natural electric field gradient, generated by different spatial orientations of the permanent electric dipoles, is able to promote the transformation of free rotations into coupled pendular states, letting the molecular partners involved in the collision complex swinging to and fro around the field direction. This long-ranged concerted motion manifested itself as large increases of the magnitude of the total integral cross section. The experimental findings and the theoretical treatment developed to shed light on the details of the process suggest that the transformation from free rotations to pendular states depends on the rotational level of both molecules, on the impact parameter, on the relative collision velocity, on the dipole moment product and occurs in the time scale of picoseconds. The consequences of this intriguing phenomenon may be important for the interpretation and, in perspective, for the control of elementary chemical and biological processes, given by polar molecules, ions, and free radicals, occurring in several environments under various conditions.

  20. Sticking of Molecules on Nonporous Amorphous Water Ice

    NASA Astrophysics Data System (ADS)

    He, Jiao; Acharyya, Kinsuk; Vidali, Gianfranco

    2016-05-01

    Accurate modeling of physical and chemical processes in the interstellar medium (ISM) requires detailed knowledge of how atoms and molecules adsorb on dust grains. However, the sticking coefficient, a number between 0 and 1 that measures the first step in the interaction of a particle with a surface, is usually assumed in simulations of ISM environments to be either 0.5 or 1. Here we report on the determination of the sticking coefficient of H2, D2, N2, O2, CO, CH4, and CO2 on nonporous amorphous solid water. The sticking coefficient was measured over a wide range of surface temperatures using a highly collimated molecular beam. We showed that the standard way of measuring the sticking coefficient—the King–Wells method—leads to the underestimation of trapping events in which there is incomplete energy accommodation of the molecule on the surface. Surface scattering experiments with the use of a pulsed molecular beam are used instead to measure the sticking coefficient. Based on the values of the measured sticking coefficient, we suggest a useful general formula of the sticking coefficient as a function of grain temperature and molecule-surface binding energy. We use this formula in a simulation of ISM gas–grain chemistry to find the effect of sticking on the abundance of key molecules both on grains and in the gas phase.

  1. Resonance Raman spectra of organic molecules absorbed on inorganic semiconducting surfaces: Contribution from both localized intramolecular excitation and intermolecular charge transfer excitation

    SciTech Connect

    Ye, ChuanXiang; Zhao, Yi E-mail: liangwz@xmu.edu.cn; Liang, WanZhen E-mail: liangwz@xmu.edu.cn

    2015-10-21

    The time-dependent correlation function approach for the calculations of absorption and resonance Raman spectra (RRS) of organic molecules absorbed on semiconductor surfaces [Y. Zhao and W. Z. Liang, J. Chem. Phys. 135, 044108 (2011)] is extended to include the contribution of the intermolecular charge transfer (CT) excitation from the absorbers to the semiconducting nanoparticles. The results demonstrate that the bidirectionally interfacial CT significantly modifies the spectral line shapes. Although the intermolecular CT excitation makes the absorption spectra red shift slightly, it essentially changes the relative intensities of mode-specific RRS and causes the oscillation behavior of surface enhanced Raman spectra with respect to interfacial electronic couplings. Furthermore, the constructive and destructive interferences of RRS from the localized molecular excitation and CT excitation are observed with respect to the electronic coupling and the bottom position of conductor band. The interferences are determined by both excitation pathways and bidirectionally interfacial CT.

  2. High-harmonic generation in aligned water molecules

    NASA Astrophysics Data System (ADS)

    Wang, Song; Devin, Julien; Hoffmann, Matthias; Cryan, James; Kaldun, Andreas; Bucksbaum, Philip

    2016-05-01

    In recent years, the use of high harmonic generation (HHG) in aligned molecular vapors has become a powerful tool to study ultrafast dynamics of electronic and nuclear wave packets. In our new experimental setup, we are able to orient H2 O and D2 O molecules using a single cycle terahertz (THz) pulse. Aligning water is especially interesting as the highest occupied molecular orbital (HOMO) of water contains a node in the xz plane of the molecular frame, allowing us to perform HHG from second highest occupied molecular orbital (HOMO-1) only, by setting the polarization of the fundamental laser along the z-axis of the aligned water molecules. We are particularly interested in the HOMO-1 state, as there is fast motion of the H-O-H angle leading to sub-wavelength dynamics. On this poster we present our all-optical alignment setup where HHG and single-cycle THz generation take place in high-vacuum, where measurements with arbitrary polarization angles between the two are possible. In addition, we discuss the effects of the molecular orientation on HHG, including symmetry breaking that could produce even harmonics and isotope effects between H2 O and D2 O due to different vibrational energies. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division.

  3. Single ionization of water molecules in collisions with bare ions

    NASA Astrophysics Data System (ADS)

    Mondal, A.; Mandal, C. R.; Purkait, M.

    2016-04-01

    We present the double differential cross sections (DDCSs) for the direct ionization of water molecules by impact of fully stripped helium, carbon and oxygen atoms, respectively. In the present formalism, we have represented the wavefunction in the entrance channel as the product of a plane wave for the projectile and an accurate one-center-molecular wavefunction of the water molecule by Moccia (1964 J. Chem. Phys. 40 2186). In the exit channel, we have expressed the total wavefunction as the product of pair-wise Coulomb wavefunctions among the ejected electron, projectile ion and the residual target ion, respectively. The contributions of DDCSs for five different molecular orbitals of water to the spectrum of angular distributions have been analyzed for several electron emission energies. The present results for DDCSs are compared with existing experimental and theoretical findings. We find an overall good agreement between our calculated results and the experimental findings for electron emission cross sections. In addition, DDCS results for ionization from different orbitals at a few electron emission energies are given in tabular form.

  4. Electric Dipole Moments of Nanosolvated Acid Molecules in Water Clusters

    NASA Astrophysics Data System (ADS)

    Guggemos, Nicholas; Slavíček, Petr; Kresin, Vitaly V.

    2015-01-01

    The electric dipole moments of (H2O)nDCl (n =3 - 9 ) clusters have been measured by the beam-deflection method. Reflecting the (dynamical) charge distribution within the system, the dipole moment contributes information about the microscopic structure of nanoscale solvation. The addition of a DCl molecule to a water cluster results in a strongly enhanced susceptibility. There is evidence for a noticeable rise in the dipole moment occurring at n ≈5 - 6 . This size is consistent with predictions for the onset of ionic dissociation. Additionally, a molecular-dynamics model suggests that even with a nominally bound impurity an enhanced dipole moment can arise due to the thermal and zero-point motion of the proton and the water molecules. The experimental measurements and the calculations draw attention to the importance of fluctuations in defining the polarity of water-based nanoclusters and generally to the essential role played by motional effects in determining the response of fluxional nanoscale systems under realistic conditions.

  5. Ionization of water molecules by fast charged projectiles

    SciTech Connect

    Dubois, A.; Carniato, S.; Fainstein, P. D.; Hansen, J. P.

    2011-07-15

    Single-ionization cross sections of water molecules colliding with fast protons are calculated from lowest-order perturbation theory by taking all electrons and molecular orientations consistently into account. Explicit analytical formulas based on the peaking approximation are obtained for differential ionization cross sections with the partial contribution from the various electron orbitals accounted for. The results, which are in very good agreement with total and partial cross sections at high electron and projectile energies, display a strong variation on molecular orientation and molecular orbitals.

  6. “Nanofiltration” Enabled by Super-Absorbent Polymer Beads for Concentrating Microorganisms in Water Samples

    PubMed Central

    Xie, Xing; Bahnemann, Janina; Wang, Siwen; Yang, Yang; Hoffmann, Michael R.

    2016-01-01

    Detection and quantification of pathogens in water is critical for the protection of human health and for drinking water safety and security. When the pathogen concentrations are low, large sample volumes (several liters) are needed to achieve reliable quantitative results. However, most microbial identification methods utilize relatively small sample volumes. As a consequence, a concentration step is often required to detect pathogens in natural waters. Herein, we introduce a novel water sample concentration method based on superabsorbent polymer (SAP) beads. When SAP beads swell with water, small molecules can be sorbed within the beads, but larger particles are excluded and, thus, concentrated in the residual non-sorbed water. To illustrate this approach, millimeter-sized poly(acrylamide-co-itaconic acid) (P(AM-co-IA)) beads are synthesized and successfully applied to concentrate water samples containing two model microorganisms: Escherichia coli and bacteriophage MS2. Experimental results indicate that the size of the water channel within water swollen P(AM-co-IA) hydrogel beads is on the order of several nanometers. The millimeter size coupled with a negative surface charge of the beads are shown to be critical in order to achieve high levels of concentration. This new concentration procedure is very fast, effective, scalable, and low-cost with no need for complex instrumentation. PMID:26876979

  7. "Nanofiltration" Enabled by Super-Absorbent Polymer Beads for Concentrating Microorganisms in Water Samples.

    PubMed

    Xie, Xing; Bahnemann, Janina; Wang, Siwen; Yang, Yang; Hoffmann, Michael R

    2016-01-01

    Detection and quantification of pathogens in water is critical for the protection of human health and for drinking water safety and security. When the pathogen concentrations are low, large sample volumes (several liters) are needed to achieve reliable quantitative results. However, most microbial identification methods utilize relatively small sample volumes. As a consequence, a concentration step is often required to detect pathogens in natural waters. Herein, we introduce a novel water sample concentration method based on superabsorbent polymer (SAP) beads. When SAP beads swell with water, small molecules can be sorbed within the beads, but larger particles are excluded and, thus, concentrated in the residual non-sorbed water. To illustrate this approach, millimeter-sized poly(acrylamide-co-itaconic acid) (P(AM-co-IA)) beads are synthesized and successfully applied to concentrate water samples containing two model microorganisms: Escherichia coli and bacteriophage MS2. Experimental results indicate that the size of the water channel within water swollen P(AM-co-IA) hydrogel beads is on the order of several nanometers. The millimeter size coupled with a negative surface charge of the beads are shown to be critical in order to achieve high levels of concentration. This new concentration procedure is very fast, effective, scalable, and low-cost with no need for complex instrumentation. PMID:26876979

  8. “Nanofiltration” Enabled by Super-Absorbent Polymer Beads for Concentrating Microorganisms in Water Samples

    NASA Astrophysics Data System (ADS)

    Xie, Xing; Bahnemann, Janina; Wang, Siwen; Yang, Yang; Hoffmann, Michael R.

    2016-02-01

    Detection and quantification of pathogens in water is critical for the protection of human health and for drinking water safety and security. When the pathogen concentrations are low, large sample volumes (several liters) are needed to achieve reliable quantitative results. However, most microbial identification methods utilize relatively small sample volumes. As a consequence, a concentration step is often required to detect pathogens in natural waters. Herein, we introduce a novel water sample concentration method based on superabsorbent polymer (SAP) beads. When SAP beads swell with water, small molecules can be sorbed within the beads, but larger particles are excluded and, thus, concentrated in the residual non-sorbed water. To illustrate this approach, millimeter-sized poly(acrylamide-co-itaconic acid) (P(AM-co-IA)) beads are synthesized and successfully applied to concentrate water samples containing two model microorganisms: Escherichia coli and bacteriophage MS2. Experimental results indicate that the size of the water channel within water swollen P(AM-co-IA) hydrogel beads is on the order of several nanometers. The millimeter size coupled with a negative surface charge of the beads are shown to be critical in order to achieve high levels of concentration. This new concentration procedure is very fast, effective, scalable, and low-cost with no need for complex instrumentation.

  9. Water-molecule dissociation by proton and hydrogen impact

    NASA Astrophysics Data System (ADS)

    Luna, H.; de Barros, A. L. F.; Wyer, J. A.; Scully, S. W. J.; Lecointre, J.; Garcia, P. M. Y.; Sigaud, G. M.; Santos, A. C. F.; Senthil, V.; Shah, M. B.; Latimer, C. J.; Montenegro, E. C.

    2007-04-01

    Time-of-flight-based mass analysis of charged water fragments have been used to measure the dissociative and the nondissociative reaction pathways of water formed during collisions with 15to100keV and 500to3500keV H+ projectiles and with 8to100keV H0 projectiles. The fragmentation pathways resulting from the ionization and the electron capture collisions with the incident H+ and H0 projectiles, as well as collisions involving projectile electron loss by the incident H0 projectiles, were separately recorded by detecting the target product ions in coincidence with either the ejected target electrons or the charge-analyzed projectiles. The fragmentation profile shows that at high collision energies the ionization of water arises mainly through outer shell processes. At lower energies valence electron capture and ionization dominate and transfer ionization leads to substantially different fragmentation patterns. H0 and H+ projectiles are found to be equally efficient at ionizing the water molecule. These results are of particular interest to workers in astrophysics and those involved in cancer therapy with heavy particle ion beams.

  10. State of Water Molecules and Silanol Groups in Opal Minerals: a Near Infrared Spectroscopic Study of Opals from Slovakia

    NASA Astrophysics Data System (ADS)

    Bobon, Miroslav; Christy, Alfred A.; Kluvanec, Daniel; Illasova, L'udmila

    2011-06-01

    Recently near infrared spectroscopy in combination with double derivative technique has been effectively used by Christy [1] to differentiate between free silanol groups and hydrogen bonded silanol groups on silica gel. The method has given some insight into the type of functionalities and their location in silica gel samples. The inportant information in this respect comes from the overtones of the OH groups of water molecules hydrogen bonded to free silanol groups, and hydrogen bonded silanol groups absorbing in the region 5500- 5100 Cm-1 region. The approach was adapted to study the state of water and silanol functionalities and their locations in opals from Slovakia. Twenty opal samples classified into CT and A classes and one quartz sample were used in this work. The samples were crushed using a hydrolic press and powderised. Each sample was then subjected to evacuation process to remove surface adsorbed water at 200°C and the near infrared spectrum of the sample was measured using a Perkin Elmer NTS near infrared spectrometer equipped with a transflectance accessory. The detailed analysis of the sample was carried out using the second derivative profile of the spectrum. The samples were also heated to 750°C to study the state of water molecules in Opal minerals. The results indicate that the opal samples contain 1) surface adsorbed water 2) free and hydrogen bonded silanol groups on the surface 3) Trapped water in the bulk 4) free and hydrogen bonded silanol groups in the cavity surfaces in the bulk. A part of the water molecules found in the bulk of opal minerals are free molecules and the rest are found in hydrogen bonded state to free and hydrogen bonded silanol groups. [1] A. A. Christy, New insights into the surface functionalities and adsorption evolution of water molecules on silica gel surface: A study by second derivative Near Infrared Spectroscopy, Vib. Spectrosc. 54 (2010) 42-49.

  11. Quantum Tunneling of Water in Beryl: A New State of the Water Molecule

    NASA Astrophysics Data System (ADS)

    Kolesnikov, Alexander I.; Reiter, George F.; Choudhury, Narayani; Prisk, Timothy R.; Mamontov, Eugene; Podlesnyak, Andrey; Ehlers, George; Seel, Andrew G.; Wesolowski, David J.; Anovitz, Lawrence M.

    2016-04-01

    Using neutron scattering and ab initio simulations, we document the discovery of a new "quantum tunneling state" of the water molecule confined in 5 Å channels in the mineral beryl, characterized by extended proton and electron delocalization. We observed a number of peaks in the inelastic neutron scattering spectra that were uniquely assigned to water quantum tunneling. In addition, the water proton momentum distribution was measured with deep inelastic neutron scattering, which directly revealed coherent delocalization of the protons in the ground state.

  12. Measurements of absorbed heat flux and water-side heat transfer coefficient in water wall tubes

    NASA Astrophysics Data System (ADS)

    Taler, Jan; Taler, Dawid; Kowal, Andrzej

    2011-04-01

    The tubular type instrument (flux tube) was developed to identify boundary conditions in water wall tubes of steam boilers. The meter is constructed from a short length of eccentric tube containing four thermocouples on the fire side below the inner and outer surfaces of the tube. The fifth thermocouple is located at the rear of the tube on the casing side of the water-wall tube. The boundary conditions on the outer and inner surfaces of the water flux-tube are determined based on temperature measurements at the interior locations. Four K-type sheathed thermocouples of 1 mm in diameter, are inserted into holes, which are parallel to the tube axis. The non-linear least squares problem is solved numerically using the Levenberg-Marquardt method. The heat transfer conditions in adjacent boiler tubes have no impact on the temperature distribution in the flux tubes.

  13. Study of thermal effects and optical properties of an innovative absorber in integrated collector storage solar water heater

    NASA Astrophysics Data System (ADS)

    Taheri, Yaser; Alimardani, Kazem; Ziapour, Behrooz M.

    2015-10-01

    Solar passive water heaters are potential candidates for enhanced heat transfer. Solar water heaters with an integrated water tank and with the low temperature energy resource are used as the simplest and cheapest recipient devices of the solar energy for heating and supplying hot water in the buildings. The solar thermal performances of one primitive absorber were determined by using both the experimental and the simulation model of it. All materials applied for absorber such as the cover glass, the black colored sands and the V shaped galvanized plate were submerged into the water. The water storage tank was manufactured from galvanized sheet of 0.0015 m in thickness and the effective area of the collector was 0.67 m2. The absorber was installed on a compact solar water heater. The constructed flat-plate collectors were tested outdoors. However the simulation results showed that the absorbers operated near to the gray materials and all experimental results showed that the thermal efficiencies of the collector are over than 70 %.

  14. Searching for Water and Other Molecules with JWST

    NASA Astrophysics Data System (ADS)

    Valenti, Jeff

    2015-08-01

    The James Webb Space Telescope (JWST) will be a powerful tool for measuring water and other molecules in transiting exoplanets, warm circumstellar disks, brown dwarfs, and cool stars. In early 2019 the observatory is scheduled to begin science operations near the Sun-Earth L2 Lagrange point. The sunshield will allow the telescope and science instrument module to cool passively to approximately 40 K. The segmented primary mirror has 25 square meters of collecting area, giving the observatory unprecedented sensitivity in the infrared. JWST has four science instruments that cover wavelengths from 0.6 to 28 microns at spectral resolutions up to about R=3000. I will summarize relevant observatory constraints, instrument capabilities, and observing templates. I will illustrate practical issues with examples from the Science Operations Design Reference Mission. Finally, I will discuss the Cycle 1 proposal process, which begins in 2017.

  15. Experimental determination of the absorbed dose to water in a scanned proton beam using a water calorimeter and an ionization chamber

    NASA Astrophysics Data System (ADS)

    Gagnebin, Solange; Twerenbold, Damian; Pedroni, Eros; Meer, David; Zenklusen, Silvan; Bula, Christian

    2010-03-01

    The absorbed dose to water is the reference physical quantity for the energy absorbed in tissue when exposed to beams of ionizing radiation in radiotherapy. The SI unit of absorbed dose to water is the gray (Gy = 1 J/kg). Ionization chambers are used as the dosimeters of choice in the clinical environment because they show a high reproducibility and are easy to use. However, ionization chambers have to be calibrated in order to convert the measured electrical charge into absorbed dose to water. In addition, protocols require these conversion factors to be SI traceable to a primary standard of absorbed dose to water. We present experimental results where the ionization chamber used for the dosimetry for the scanned proton beam facility at PSI is compared with the direct determination of absorbed dose to water from the METAS primary standard water calorimeter. The agreement of 3.2% of the dose values measured by the two techniques are within their respective statistical uncertainties.

  16. A Feasibility Study of Fricke Dosimetry as an Absorbed Dose to Water Standard for 192Ir HDR Sources

    PubMed Central

    deAlmeida, Carlos Eduardo; Ochoa, Ricardo; de Lima, Marilene Coelho; David, Mariano Gazineu; Pires, Evandro Jesus; Peixoto, José Guilherme; Salata, Camila; Bernal, Mario Antônio

    2014-01-01

    High dose rate brachytherapy (HDR) using 192Ir sources is well accepted as an important treatment option and thus requires an accurate dosimetry standard. However, a dosimetry standard for the direct measurement of the absolute dose to water for this particular source type is currently not available. An improved standard for the absorbed dose to water based on Fricke dosimetry of HDR 192Ir brachytherapy sources is presented in this study. The main goal of this paper is to demonstrate the potential usefulness of the Fricke dosimetry technique for the standardization of the quantity absorbed dose to water for 192Ir sources. A molded, double-walled, spherical vessel for water containing the Fricke solution was constructed based on the Fricke system. The authors measured the absorbed dose to water and compared it with the doses calculated using the AAPM TG-43 report. The overall combined uncertainty associated with the measurements using Fricke dosimetry was 1.4% for k = 1, which is better than the uncertainties reported in previous studies. These results are promising; hence, the use of Fricke dosimetry to measure the absorbed dose to water as a standard for HDR 192Ir may be possible in the future. PMID:25521914

  17. From single molecules to water networks: Dynamics of water adsorption on Pt(111).

    PubMed

    Naderian, Maryam; Groß, Axel

    2016-09-01

    The adsorption dynamics of water on Pt(111) was studied using ab initio molecular dynamics simulations based on density functional theory calculations including dispersion corrections. Sticking probabilities were derived as a function of initial kinetic energy and water coverage. In addition, the energy distribution upon adsorption was monitored in order to analyze the energy dissipation process. We find that on the water pre-covered surface the sticking probability is enhanced because of the attractive water-water interaction and the additional effective energy dissipation channels to the adsorbed water molecules. The water structures forming directly after the adsorption on the pre-covered surfaces do not necessarily correspond to energy minimum structures. PMID:27609006

  18. Distribution of binding energies of a water molecule in the water liquid-vapor interface

    SciTech Connect

    Chempath, Shaji; Pratt, Lawrence R

    2008-01-01

    Distributions of binding energies of a water molecule in the water liquid-vapor interface are obtained on the basis of molecular simulation with the SPC/E model of water. These binding energies together with the observed interfacial density profile are used to test a minimally conditioned Gaussian quasi-chemical statistical thermodynamic theory. Binding energy distributions for water molecules in that interfacial region clearly exhibit a composite structure. A minimally conditioned Gaussian quasi-chemical model that is accurate for the free energy of bulk liquid water breaks down for water molecules in the liquid-vapor interfacial region. This breakdown is associated with the fact that this minimally conditioned Gaussian model would be inaccurate for the statistical thermodynamics of a dilute gas. Aggressive conditioning greatly improves the performance of that Gaussian quasi-chemical model. The analogy between the Gaussian quasi-chemical model and dielectric models of hydration free energies suggests that naive dielectric models without the conditioning features of quasi-chemical theory will be unreliable for these interfacial problems. Multi-Gaussian models that address the composite nature of the binding energy distributions observed in the interfacial region might provide a mechanism for correcting dielectric models for practical applications.

  19. Deep absorbing porphyrin small molecule for high-performance organic solar cells with very low energy losses.

    PubMed

    Gao, Ke; Li, Lisheng; Lai, Tianqi; Xiao, Liangang; Huang, Yuan; Huang, Fei; Peng, Junbiao; Cao, Yong; Liu, Feng; Russell, Thomas P; Janssen, René A J; Peng, Xiaobin

    2015-06-17

    We designed and synthesized the DPPEZnP-TEH molecule, with a porphyrin ring linked to two diketopyrrolopyrrole units by ethynylene bridges. The resulting material exhibits a very low energy band gap of 1.37 eV and a broad light absorption to 907 nm. An open-circuit voltage of 0.78 V was obtained in bulk heterojunction (BHJ) organic solar cells, showing a low energy loss of only 0.59 eV, which is the first report that small molecule solar cells show energy losses <0.6 eV. The optimized solar cells show remarkable external quantum efficiency, short circuit current, and power conversion efficiency up to 65%, 16.76 mA/cm(2), and 8.08%, respectively, which are the best values for BHJ solar cells with very low energy losses. Additionally, the morphology of DPPEZnP-TEH neat and blend films with PC61BM was studied thoroughly by grazing incidence X-ray diffraction, resonant soft X-ray scattering, and transmission electron microscopy under different fabrication conditions. PMID:26035342

  20. Effect of absorbents on water vapor transmission of free and applied polymer films.

    PubMed

    Amann, A H

    1976-04-01

    The influence of different types of absorbents on moisture transmission through free (cast films) and applied (coated tablets) polymer films was investigated. In free film studies, lubricated granulations were considered to be the absorbent. The compressed tablet was considered to be the absorbent in applied film studies. The results suggested that, using the same film formulation and film thickness in all cases, the polymer film reduced moisture absorption to the same degree, independent of the absorbent used, suggesting a constant moisture permeation. The results of the free film studies also simulated those of the applied films, allowing the correlation of the data. PMID:1271250

  1. [Estimation of absorbed dose of beta radiation into the critical tissues by a single injection of tritiated water].

    PubMed

    Tsuchiya, T; Norimura, T; Yamamoto, H; Hatakeyama, S; Dohi, S; Kunugita, N

    1988-12-01

    The biological effects of tritium in humans need to be clarified, because the chances of humans becoming exposed to tritium beta radiation may increase with the development of the nuclear fusion reactor. To evaluate the biological effects of tritium, it is necessary to estimate exactly the absorbed dose from the tritium beta rays in the tissue. In many reports, the absorbed dose of HTO in the tissues is estimated from the tritium content in body fluid and dose calculations are customarily based upon the water content of soft tissues, which is taken to be 0.7 to 0.8. However, these methods may not show the exact absorbed dose in the organs. In the present study, the radioactivity of the critical tissues was measured directly using a sample oxidizer and the absorbed dose was calculated from the radioactivity of tritium in the tissues. Details on the method for calculation of the absorbed dose in tissues of the mouse is shown in this report. The results suggest that the absorbed dose should be obtained from the radioactivity in the tissues. PMID:3212298

  2. Treatment of small-cell lung cancer xenografts with iodine-313-anti-neural cell adhesion molecule monoclonal antibody and evaluation of absorbed dose in tissue

    SciTech Connect

    Hosono, Makoto; Endo, Keigo; Hosono, Masako N.

    1994-02-01

    Human small-cell lung cancer (SCLC) is considered a feasible target for immunotherapy using a radiolabeled monoclonal antibody (Mab). A murine Mab, NE150 (IgG1), reacts with the neural cell adhesion molecule, which is identical to cluster 1 antigen of SCLC. To estimate their therapeutic effects, NE150 and an isotype-matched control Mab were labeled with {sup 131}I and administered intravenously as a single dose into athymic mice inoculated with a NCI-H69 SCLC xenograft. The absorbed dose in organs was also examined based upon a long-term biodistribution study of {sup 131}I-NE150. Tumors initial volume 563.4 {plus_minus} 223.5 mm{sup 3} treated with 11.1 MBq (300 {mu}Ci) of {sup 131}I-NE150 diminished and became invisible at days 30-33, demonstrating a 60-day mean growth delay to reach a tripled initial volume compared with sham-treated tumors. Cumulative absorbed doses were estimated to be 2310, 410, 500, 330, and 790 cGy for the tumor, liver, kidney, spleen and lung, respectively. Iodine-131-NE150 had potent therapeutic effects against SCLC transplants in athymic mice, however, careful assessment of the side effects, improvement of radioiodination and chimerization of the Mab might be necessary to achieve efficient targeting in clinical therapeutic applications. 25 refs., 2 figs., 3 tabs.

  3. Quantum Tunneling of Water in Beryl. A New State of the Water Molecule

    DOE PAGESBeta

    Kolesnikov, Alexander I.; Reiter, George F.; Choudhury, Narayani; Prisk, Timothy R.; Mamontov, Eugene; Podlesnyak, Andrey; Ehlers, George; Seel, Andrew G.; Wesolowski, David J.; Anovitz, Lawrence M.

    2016-04-22

    When using neutron scattering and ab initio simulations, we document the discovery of a new “quantum tunneling state” of the water molecule confined in 5 Å channels in the mineral beryl, characterized by extended proton and electron delocalization. We observed a number of peaks in the inelastic neutron scattering spectra that were uniquely assigned to water quantum tunneling. Additionally, the water proton momentum distribution was measured with deep inelastic neutron scattering, which directly revealed coherent delocalization of the protons in the ground state.

  4. Quantum Tunneling of Water in Beryl: A New State of the Water Molecule.

    PubMed

    Kolesnikov, Alexander I; Reiter, George F; Choudhury, Narayani; Prisk, Timothy R; Mamontov, Eugene; Podlesnyak, Andrey; Ehlers, George; Seel, Andrew G; Wesolowski, David J; Anovitz, Lawrence M

    2016-04-22

    Using neutron scattering and ab initio simulations, we document the discovery of a new "quantum tunneling state" of the water molecule confined in 5 Å channels in the mineral beryl, characterized by extended proton and electron delocalization. We observed a number of peaks in the inelastic neutron scattering spectra that were uniquely assigned to water quantum tunneling. In addition, the water proton momentum distribution was measured with deep inelastic neutron scattering, which directly revealed coherent delocalization of the protons in the ground state. PMID:27152824

  5. Disorder of Hydrofluorocarbon Molecules Entrapped in the Water Cages of Structure I Clathrate Hydrate.

    PubMed

    Takeya, Satoshi; Udachin, Konstantin A; Moudrakovski, Igor L; Ohmura, Ryo; Ripmeester, John A

    2016-05-23

    Water versus fluorine: Clathrate hydrates encaging hydrofluorocarbons as guests show both isotropic and anisotropic distributions within host water cages, depending on the number of fluorine atoms in the guest molecule; this is caused by changes in intermolecular interactions to host water molecules in the hydrates. PMID:27105807

  6. State of water molecules and silanol groups in opal minerals: a near infrared spectroscopic study of opals from Slovakia

    NASA Astrophysics Data System (ADS)

    Boboň, Miroslav; Christy, Alfred A.; Kluvanec, Daniel; Illášová, L'udmila

    2011-12-01

    Recently, near infrared spectroscopy in combination with double derivative technique has been effectively used by Christy (Vib Spectrosc 54:42-49, 2010) to study and differentiate between free and hydrogen bonded silanol groups on silica gel surface. The method has given some insight into the type of functionalities, their location in silica gel samples, and the way the water molecules bind onto the silanol groups. The important information in this respect comes from the overtones of the OH groups of water molecules hydrogen-bonded to free silanol groups, and hydrogen-bonded silanol groups absorbing in the region 5,500-5,100 cm-1. Chemically, opal minerals are hydrated silica and the same approach was adapted to study the state of water molecules, silanol functionalities, and their locations in opal samples from Slovakia. Twenty opal samples classified into CT and A classes and one quartz sample were used in this work. The samples were crushed using a hydraulic press and powderized. Each sample was then subjected to evacuation process to remove surface-adsorbed water at 200°C, and the near infrared spectrum of each sample was measured using a Perkin Elmer NTS FT-NIR spectrometer equipped with a transflectance accessory and a DTGS detector. The samples were also heated to 750°C to remove the hydrogen-bonded silanol groups on the surface to reveal their locality. Second derivative profiles of the near infrared reflectance spectra were obtained using the instrument's software and used in the detailed analysis of the samples. The analysis of the near infrared spectra and their second derivative profiles had the aim in finding relationships between the surface chemical structure and the classification of opal samples. The dry opal samples were also tested for their surface adsorption effectivity toward water molecules. The results indicate that the opal samples contain (1) surface-adsorbed water, (2) free and hydrogen-bonded silanol groups on the surface, (3) trapped

  7. Electron capture by bare ions on water molecules

    NASA Astrophysics Data System (ADS)

    Rivarola, Roberto; Montenegro, Pablo; Monti, Juan; Fojón, Omar

    2016-05-01

    Single electron capture from water molecules by impact of bare ions is theoretically investigated at intermediate and high collision energies. This reaction is of fundamental importance to determine the deposition of energy in biological matter irradiated with ion beams (hadrontherapy), dominating other ionizing processes of the target at low-intermediate impact velocities and giving principal contributions to the energetic region where electronic stopping power maximizes. The dynamics of the interaction between the aggregates is described within the one active-electron continuum distorted wave-eikonal initial state theory. The orbitals of the target in the ground state are represented using the approximate self-consistent complete neglect of differential orbitals (SC-CNDO) model. The contribution of different molecular orbitals on the partial cross sections to selected n-principal quantum number projectile states is discriminated as well as the collaboration of these n-states on total cross sections. The latter ones are dominated by capture to n=1 states at high enough energies decreasing their contribution as n increases.

  8. Method 415.3, Rev. 1.2: Determination of Total Organic Carbon and Specific UV Absorbance at 254 nm in Source Water and Drinking Water

    EPA Science Inventory

    This method provides procedures for the determination of total organic carbon (TOC), dissolved organic carbon (DOC), and UV absorption at 254 nm (UVA) in source waters and drinking waters. The DOC and UVA determinations are used in the calculation of the Specific UV Absorbance (S...

  9. A New HOM Water Cooled Absorber for the PEP-II B-factory Low Energy Ring

    SciTech Connect

    Weathersby, Stephen; Kosovsky, Michael; Kurita, Nadine; Novokhatski, Alexander; Seeman, John; /SLAC

    2006-09-05

    At high currents and small bunch lengths beam line components in the PEP-II B-factory experience RF induced heating from higher order RF modes (HOMs) produced by scattered intense beam fields. A design for a passive HOM water cooled absorber for the PEP-II low energy ring is presented. This device is situated near HOM producing beamline components such as collimators and provide HOM damping for dipole and quadrupole modes without impacting beam impedance. We optimized the impedance characteristics of the device through the evaluation of absorber effectiveness for specific modes using scattering parameter and wakefield analysis. Operational results are presented and agree very well with the predicted effectiveness.

  10. Metal oxide absorbents for regenerative carbon dioxide and water vapor removal for advanced portable life support systems

    NASA Technical Reports Server (NTRS)

    Hart, Joan M.; Borghese, Joseph B.; Chang, Craig H.; Stonesifer, Greg T.

    1991-01-01

    Recent studies of Allied Signal metal oxide based absorbents demonstrated that these absorbents offer a unique capability to regeneratively remove both metabolic carbon dioxide and water vapor from breathing air; previously, metal oxides were considered only for the removal of CO2. The concurrent removal of CO2 and H2O vapor can simplify the astronaut Portable Life Support System (PLSS) by combining the CO2 and humidity control functions into one regenerative component. The use of metal oxide absorbents for removal of both CO2 ad H2O vapor in the PLSS is the focus of an ongoing program. The full scale Metal Oxide Carbon dioxide and Humidity Remover (MOCHR) and regeneration unit is described.

  11. Study of water molecule decomposition in plasma by diode laser spectroscopy and optical actinometry methods

    NASA Astrophysics Data System (ADS)

    Bernatskiy, A. V.; Lagunov, V. V.; Ochkin, V. N.; Tskhai, S. N.

    2016-07-01

    The methods of diode laser radiation absorption at vibrational–rotational molecule transitions and optical actinometry with measurements of its electron emission spectra are used independently to study water molecule dissociation in glow discharge plasma in a mixture of water vapor and inert gases at reduced pressure. The methods yield close results. The dissociation reaches 98%.

  12. Key Role of Active-Site Water Molecules in Bacteriorhodopsin Proton-Transfer Reactions

    SciTech Connect

    Bondar, A.N.; Baudry, Jerome Y; Suhai, Sandor; Fischer, S.; Smith, Jeremy C

    2008-10-01

    The functional mechanism of the light-driven proton pump protein bacteriorhodopsin depends on the location of water molecules in the active site at various stages of the photocycle and on their roles in the proton-transfer steps. Here, free energy computations indicate that electrostatic interactions favor the presence of a cytoplasmic-side water molecule hydrogen bonding to the retinal Schiff base in the state preceding proton transfer from the retinal Schiff base to Asp85. However, the nonequilibrium nature of the pumping process means that the probability of occupancy of a water molecule in a given site depends both on the free energies of insertion of the water molecule in this and other sites during the preceding photocycle steps and on the kinetic accessibility of these sites on the time scale of the reaction steps. The presence of the cytoplasmic-side water molecule has a dramatic effect on the mechanism of proton transfer: the proton is channeled on the Thr89 side of the retinal, whereas the transfer on the Asp212 side is hindered. Reaction-path simulations and molecular dynamics simulations indicate that the presence of the cytoplasmic-side water molecule permits a low-energy bacteriorhodopsin conformer in which the water molecule bridges the twisted retinal Schiff base and the proton acceptor Asp85. From this low-energy conformer, proton transfer occurs via a concerted mechanism in which the water molecule participates as an intermediate proton carrier.

  13. Adsorption of Small Molecules at Water--Hexane and Water--Membrane Interfaces

    NASA Astrophysics Data System (ADS)

    Wilson, Michael A.

    1996-03-01

    The interaction of solutes with aqueous interfaces plays a significant role in a variety of physical processes, including general anesthesia and atmospheric chemistry. We present molecular dynamics results for the transfer of several small solutes across water liquid--vapor, water--hexane and water--GMO bilayer membrane interfaces. (A. Pohorille and M. A. Wilson, J. Chem. Phys. (in press, 1995).)^, (A. Pohorille, P. CIeplak, and M. A. Wilson, Chem. Phys. (in press, 1995).) The free energies of transferring small polar molecules across the interface exhibit fairly deep minima while those of nonpolar molecules do not. This is due to a balance between nonelectrostatic contributions --- primarily the work required to create a cavity large enough to accommodate the solute --- and the solute--solvent electrostatic interactions.^1 The surface excess of solute is calculated and compared with experimental results from the Gibbs adsorption isotherm. The interfacial solubilities correlate with measured anesthetic potencies of these compounds, implying that the binding sites for anesthetics are located near the water--membrane interface.

  14. Chemical reactions of water molecules on Ru(0001) induced by selective excitation of vibrational modes

    SciTech Connect

    Mugarza, Aitor; Shimizu, Tomoko K.; Ogletree, D. Frank; Salmeron, Miquel

    2009-05-07

    Tunneling electrons in a scanning tunneling microscope were used to excite specific vibrational quantum states of adsorbed water and hydroxyl molecules on a Ru(0 0 0 1) surface. The excited molecules relaxed by transfer of energy to lower energy modes, resulting in diffusion, dissociation, desorption, and surface-tip transfer processes. Diffusion of H{sub 2}O molecules could be induced by excitation of the O-H stretch vibration mode at 445 meV. Isolated molecules required excitation of one single quantum while molecules bonded to a C atom required at least two quanta. Dissociation of single H{sub 2}O molecules into H and OH required electron energies of 1 eV or higher while dissociation of OH required at least 2 eV electrons. In contrast, water molecules forming part of a cluster could be dissociated with electron energies of 0.5 eV.

  15. Infrared Spectra of Water Bending Bands of Propylene Oxide-Water Complexes: Sequential Solvation of a Chiral Molecule in Water

    NASA Astrophysics Data System (ADS)

    Liu, Xunchen; Xu, Yunjie

    2011-06-01

    Sequential solvation of propylene oxide (C3H6O), an prototypical chiral molecule, with water has been investigated using high resolution infrared spectroscopy and ab initio methods. In a number of low resolution studies, the vibrational and vibrational circular dichroism spectral features at the water bending vibration region had been shown to be highly sensitive to the water solvation structures around propylene oxide in aqueous solution. The current study aims to provide quantitative information about solvation of a chiral molecule with water molecules at the molecular level and to provide the experimental benchmarks for calculations of vibrational frequencies in these larger molecular complexes. The high resolution infrared spectra of the propylene oxide-water complexes have been measured using a pulsed jet infrared spectrometer equipped with a room temperature external cavity quantum cascade laser and an astigmatic multi-pass cell. At least 6 bands have been observed from 1650 to 1680 Cm-1. Based on the previous microwave spectroscopic studies, these bands have been assigned to the blue-shifted water bending (ν_2) vibration modes associated with both the syn- and anti- conformers of the binary (C3H6O-H2O) and ternary (C3H6O-(H2O)2) complexes. This report shows the power of high resolution infrared spectroscopy to study multi-conformers of relatively large organic molecule complexes produced in a jet expansion. M. Losada, P. Nguyen, and Y .Xu, J. Phys. Chem. A, 112, 5621, (2008) Z. Su, Q. Wen, and Y. Xu, J. Am. Chem. Soc., 128, 6755, (2006) Z. Su and Y. Xu, Angew. Chem. Int. Ed., 46, 6163, (2007)

  16. Specification of absorbed dose to water using model-based dose calculation algorithms for treatment planning in brachytherapy

    NASA Astrophysics Data System (ADS)

    Carlsson Tedgren, Åsa; Alm Carlsson, Gudrun

    2013-04-01

    Model-based dose calculation algorithms (MBDCAs), recently introduced in treatment planning systems (TPS) for brachytherapy, calculate tissue absorbed doses. In the TPS framework, doses have hereto been reported as dose to water and water may still be preferred as a dose specification medium. Dose to tissue medium Dmed then needs to be converted into dose to water in tissue Dw,med. Methods to calculate absorbed dose to differently sized water compartments/cavities inside tissue, infinitesimal (used for definition of absorbed dose), small, large or intermediate, are reviewed. Burlin theory is applied to estimate photon energies at which cavity sizes in the range 1 nm-10 mm can be considered small or large. Photon and electron energy spectra are calculated at 1 cm distance from the central axis in cylindrical phantoms of bone, muscle and adipose tissue for 20, 50, 300 keV photons and photons from 125I, 169Yb and 192Ir sources; ratios of mass-collision-stopping powers and mass energy absorption coefficients are calculated as applicable to convert Dmed into Dw,med for small and large cavities. Results show that 1-10 nm sized cavities are small at all investigated photon energies; 100 µm cavities are large only at photon energies <20 keV. A choice of an appropriate conversion coefficient Dw, med/Dmed is discussed in terms of the cavity size in relation to the size of important cellular targets. Free radicals from DNA bound water of nanometre dimensions contribute to DNA damage and cell killing and may be the most important water compartment in cells implying use of ratios of mass-collision-stopping powers for converting Dmed into Dw,med.

  17. Quasielastic neutron scattering from adsorbed water molecules on pyrogenic silica surfaces

    NASA Astrophysics Data System (ADS)

    Tumanov, A. A.; Zarko, V. I.

    1994-04-01

    Quasielastic neutron scattering (QNS) from hydrated samples of high dispersion (Aerosil) and of porous dioxide silicon was investigated. The broadening of the QNS peak analysis permits one to obtain the effective diffusion coefficient D of adsorbed water molecules. It was obtained that the D-value increases with silica hydration. The mean square displacement of the water molecules from equilibrium < x2> equals approximately 0.1 Å 2 and does not depend on the quantity of adsorbed water.

  18. Sonication-Aided Formation of Hollow Hybrid Nanoparticles as High-Efficiency Absorbents for Dissolved Toluene in Water.

    PubMed

    Huang, Ting; Xu, Liju; Wang, Chen; Yin, Zheng; Qiu, Dong

    2016-01-01

    A surfactant-free emulsion polymerization process was developed to produce hollow hybrid nanoparticles (HHNP thereafter). Ultrasonication was found not only to help the generation of nanosized monomer droplets but also to generate surface active species through mediating the hydrolysis of the monomer, 3-(methacryloyloxy) propyltrimethoxysilane (MPS), thus stabilizing the oil/water interface. The hollow structure was formed based on a soft template approach, where the partially hydrolyzed monomer served as emulsifier and polymerized at the interface to form a hybrid shell. These HHNPs were used to absorb dissolved toluene in water and it was found they could reduce the toluene level down to zero, a level hardly being achieved by other methods. Combined with their good colloidal stability in water, these HHNPs are very promising colloidal collectors for dissolved organic solvents, in order to generate high quality water from contaminated water. PMID:26467238

  19. Water disinfection: microbes versus molecules - an introduction of issues

    SciTech Connect

    Fowle, J.R. III, Kopfler, F.C.

    1986-11-01

    If the chemicals used to rid drinking water of disease-causing microbes are themselves potentially harmful, is drinking water safe. What trade-offs are acceptable with respect to microbial versus chemical water quality. This conference deals with current thinking about these topics. The subjects discussed reflect the evolution of thinking, both scientifically and socially, about how best to supply the public with safe, pure potable water. The goal of this paper is to introduce the issues associated with disinfectants and disinfectant by-products in water. This will be done by presenting a historical overview of the use of chemical disinfectants to purify drinking water and the subsequent awareness of potential health concerns. Historically, the major health issue associated with water has been the demonstrated role that water has played in spreading infectious disease. Waterborne infectious agents remain in the environment, and new ones emerge through evolution of humans and microorganisms and because of changing exposure patterns.

  20. Implication of crystal water molecules in inhibitor binding at ALR2 active site.

    PubMed

    Hymavati; Kumar, Vivek; Sobhia, M Elizabeth

    2012-01-01

    Water molecules play a crucial role in mediating the interaction between a ligand and a macromolecule. The solvent environment around such biomolecule controls their structure and plays important role in protein-ligand interactions. An understanding of the nature and role of these water molecules in the active site of a protein could greatly increase the efficiency of rational drug design approaches. We have performed the comparative crystal structure analysis of aldose reductase to understand the role of crystal water in protein-ligand interaction. Molecular dynamics simulation has shown the versatile nature of water molecules in bridge H bonding during interaction. Occupancy and life time of water molecules depend on the type of cocrystallized ligand present in the structure. The information may be useful in rational approach to customize the ligand, and thereby longer occupancy and life time for bridge H-bonding. PMID:22649481

  1. Use of a New Simltaneous Absorbance-Fluorescene Instrument to Monitor Hydraluic Fracture Mining Waste Water to Prevent Drinking Water Contamination

    NASA Astrophysics Data System (ADS)

    Gilmore, A. M.

    2013-05-01

    Recently, the issue of waste water effuse from oil and gas mining, especially that including hydraulic fracturing, has resurfaced on the news and the political atmosphere as an area of concern. One of the key concerns is drinking water contamination from the hydraulic fracturing chemicals and chemicals contained in the water introduced into the well at high-pressure and the flowback and produced water associate with the petroleum product extraction. The key to successfully meeting drinking water safety requirements lies in the drinking water treatment plant's ability to deal with often dramatic source-water variations in natural organic matter (NOM) content that can react during disinfection with high levels of chloride and bromide found in hydraulic facture waste water to form toxc disinfection by-products (DBPs). Importantly, the brominated DBP species are particularly dangerous. Whereas the regulated levels of NOM can roughly determined by measuring total organic carbon (TOC), often this parameter does not provide rapid or cost-effective qualitative or quantitative assessment of the various humic, fulvic and other aromatic NOM components associated with DBP formation. However, two main optical techniques namely UV absorbance and fluorescence excitation-emission mapping can be used for rapid assessment with precise identification of humic and fulvic components that cause DBPs. This study presents data from a new type of instrument which simultaneously measures the UV-VIS absorbance spectrum and EEM. The rapid absorbance-EEM is facilitated by a single system that is more than 100 time faster than conventional scanning absorbance and fluorescence optical benches. The new system can continuously collect EEMs and absorbance spectra at a rate often greater than 1 per min with the extra capacity to monitor the UV254 absorbance and fluorescence emission spectrum excited at 254 nm in 4 ms intervals (an equivalent scan rate of 5.5 million nm/min). The EEM spectral data is

  2. Direct measurement of absorbed dose to water in HDR {sup 192}Ir brachytherapy: Water calorimetry, ionization chamber, Gafchromic film, and TG-43

    SciTech Connect

    Sarfehnia, Arman; Kawrakow, Iwan; Seuntjens, Jan

    2010-04-15

    Purpose: Gafchromic film and ionometric calibration procedures for HDR {sup 192}Ir brachytherapy sources in terms of dose rate to water are presented and the experimental results are compared to the TG-43 protocol as well as with the absolute dose measurement results from a water calorimetry-based primary standard. Methods: EBT-1 Gafchromic films, an A1SL Exradin miniature Shonka thimble type chamber, and an SI HDR 1000 Plus well-type chamber (Standard Imaging, Inc., Middleton, WI) with an ADCL traceable S{sub k} calibration coefficient (following the AAPM TG-43 protocol) were used. The Farmer chamber and Gafchromic film measurements were performed directly in water. All results were compared to direct and absolute absorbed dose to water measurements from a 4 deg. C stagnant water calorimeter. Results: Based on water calorimetry, the authors measured the dose rate to water to be 361{+-}7 {mu}Gy/(h U) at a 55 mm source-to-detector separation. The dose rate normalized to air-kerma strength for all the techniques agree with the water calorimetry results to within 0.83%. The overall 1-sigma uncertainty on water calorimetry, ionization chamber, Gafchromic film, and TG-43 dose rate measurement amounts to 1.90%, 1.44%, 1.78%, and 2.50%, respectively. Conclusions: This work allows us to build a more realistic uncertainty estimate for absorbed dose to water determination using the TG-43 protocol. Furthermore, it provides the framework necessary for a shift from indirect HDR {sup 192}Ir brachytherapy dosimetry to a more accurate, direct, and absolute measurement of absorbed dose to water.

  3. Quantifying the Entropy of Binding for Water Molecules in Protein Cavities by Computing Correlations

    PubMed Central

    Huggins, David J.

    2015-01-01

    Protein structural analysis demonstrates that water molecules are commonly found in the internal cavities of proteins. Analysis of experimental data on the entropies of inorganic crystals suggests that the entropic cost of transferring such a water molecule to a protein cavity will not typically be greater than 7.0 cal/mol/K per water molecule, corresponding to a contribution of approximately +2.0 kcal/mol to the free energy. In this study, we employ the statistical mechanical method of inhomogeneous fluid solvation theory to quantify the enthalpic and entropic contributions of individual water molecules in 19 protein cavities across five different proteins. We utilize information theory to develop a rigorous estimate of the total two-particle entropy, yielding a complete framework to calculate hydration free energies. We show that predictions from inhomogeneous fluid solvation theory are in excellent agreement with predictions from free energy perturbation (FEP) and that these predictions are consistent with experimental estimates. However, the results suggest that water molecules in protein cavities containing charged residues may be subject to entropy changes that contribute more than +2.0 kcal/mol to the free energy. In all cases, these unfavorable entropy changes are predicted to be dominated by highly favorable enthalpy changes. These findings are relevant to the study of bridging water molecules at protein-protein interfaces as well as in complexes with cognate ligands and small-molecule inhibitors. PMID:25692597

  4. Fast transport of water molecules across carbon nanotubes induced by static electric fields

    NASA Astrophysics Data System (ADS)

    Zhang, Qi-Lin; Yang, Rong-Yao

    2016-01-01

    Water permeation across a single-walled carbon nanotube has been studied in the presence of static electric fields (SEFs) with different directions under hydrostatic pressures. With the angle between the SEF direction and tube axis increasing from 0∘ to 90∘, the water flux decreases gradually until almost vanishes, and the maximum value at 0∘ is approximately four times the case without SEFs. The phenomenon is attributed to the alignment of the polar water molecules along the SEF direction. We also show that water permeation properties are dependent on the field strength due mainly to thermal fluctuations of water molecules.

  5. Determination of the Absorbed Dose Rate to Water for the 18-mm Helmet of a Gamma Knife

    SciTech Connect

    Chung, Hyun-Tai; Park, Youngho; Hyun, Sangil; Choi, Yongsoo; Kim, Gi Hong; Kim, Dong Gyu; Chun, Kook Jin

    2011-04-01

    Purpose: To measure the absorbed dose rate to water of {sup 60}Co gamma rays of a Gamma Knife Model C using water-filled phantoms (WFP). Methods and Materials: Spherical WFP with an equivalent water depth of 5, 7, 8, and 9 cm were constructed. The dose rates at the center of an 18-mm helmet were measured in an 8-cm WFP (WFP-3) and two plastic phantoms. Two independent measurement systems were used: one was calibrated to an air kerma (Set I) and the other was calibrated to the absorbed dose to water (Set II). The dose rates of WFP-3 and the plastic phantoms were converted to dose rates for an 8-cm water depth using the attenuation coefficient and the equivalent water depths. Results: The dose rate measured at the center of WFP-3 using Set II was 2.2% and 1.0% higher than dose rates measured at the center of the two plastic phantoms. The measured effective attenuation coefficient of Gamma Knife photon beam in WFPs was 0.0621 cm{sup -1}. After attenuation correction, the difference between the dose rate at an 8-cm water depth measured in WFP-3 and dose rates in the plastic phantoms was smaller than the uncertainty of the measurements. Conclusions: Systematic errors related to the characteristics of the phantom materials in the dose rate measurement of a Gamma Knife need to be corrected for. Correction of the dose rate using an equivalent water depth and attenuation provided results that were more consistent.

  6. Shape of a water molecule as function of OH separation

    NASA Astrophysics Data System (ADS)

    Gabbay, I.; March, N. H.

    1980-02-01

    For small O-H separation the water molecule becomes linear. The Murrell-Sorbie potential energy surface affords a basis to study the shape of the molecule for larger OH separation. The possible relevance to H 2O outside a metal surface is discussed.

  7. The putative role of some conserved water molecules in the structure and function of human transthyretin.

    PubMed

    Banerjee, Avik; Dasgupta, Subrata; Mukhopadhyay, Bishnu P; Sekar, Kanagaraj

    2015-11-01

    Human transthyretin (hTTR) is a multifunctional protein that is involved in several neurodegenerative diseases. Besides the transportation of thyroxin and vitamin A, it is also involved in the proteolysis of apolipoprotein A1 and Aβ peptide. Extensive analyses of 32 high-resolution X-ray and neutron diffraction structures of hTTR followed by molecular-dynamics simulation studies using a set of 15 selected structures affirmed the presence of 44 conserved water molecules in its dimeric structure. They are found to play several important roles in the structure and function of the protein. Eight water molecules stabilize the dimeric structure through an extensive hydrogen-bonding network. The absence of some of these water molecules in highly acidic conditions (pH ≤ 4.0) severely affects the interfacial hydrogen-bond network, which may destabilize the native tetrameric structure, leading to its dissociation. Three pairs of conserved water molecules contribute to maintaining the geometry of the ligand-binding cavities. Some other water molecules control the orientation and dynamics of different structural elements of hTTR. This systematic study of the location, absence, networking and interactions of the conserved water molecules may shed some light on various structural and functional aspects of the protein. The present study may also provide some rational clues about the conserved water-mediated architecture and stability of hTTR. PMID:26527142

  8. Unraveling the Sc(3+) Hydration Geometry: The Strange Case of the Far-Coordinated Water Molecule.

    PubMed

    Migliorati, Valentina; D'Angelo, Paola

    2016-07-01

    The hydration structure and dynamics of Sc(3+) in aqueous solution have been investigated using a combined approach based on quantum mechanical (QM) calculations, molecular dynamics (MD) simulations, and extended X-ray absorption fine structure (EXAFS) spectroscopy. An effective Sc-water two-body potential has been generated from QM calculations and then used in the MD simulation of Sc(3+) in water, and the reliability of the entire procedure has been assessed by comparing the theoretical structural results with the EXAFS experimental data. The outstanding outcome of this work is that the Sc(3+) ion forms a well-defined capped square antiprism (SAP) complex in aqueous solution, where the eight water molecules closest to the ion are located at the vertexes of a SAP polyhedron, while the ninth water molecule occupying the capping position is unusually found at a very long distance from the ion. This far-coordinated water molecule possesses a degree of structure comparable with the other first shell molecules surrounding the ion at much shorter distances, and its presence gave us the unique opportunity to easily identify the geometry of the Sc(3+) coordination polyhedron. Despite very strong ion-water interactions, the Sc(3+) hydration shell is very labile, as the far-coordinated ligand allows first shell water molecules to easily exchange their positions both inside the solvation shell and with the rest of the solvent molecules. PMID:27300102

  9. High physisorption affinity of water molecules to the hydroxylated aluminum oxide (001) surface.

    PubMed

    Kittaka, Shigeharu; Yamaguchi, Keisuke; Takahara, Shuichi

    2012-02-15

    The adsorption mechanism of water on the hydroxylated (001) plane of α-Al(2)O(3) was studied by measuring adsorption isotherms and GCMC simulations. The experimental adsorption isotherms for three α-Al(2)O(3) samples from different sources are typical type II, in which adsorption starts sharply at low pressures, suggesting a high affinity of water to the Al(2)O(3) surface. Water molecules are adsorbed in two registered forms (bilayer structure). In the first form, water is registered at the center of three surface hydroxyl groups by directing a proton of the water. In the second form, a water molecule is adsorbed by bridging two of the first-layer water molecules through hydrogen bonding, by which a hexagonal ring network is constructed over the hydroxylated surface. The network domains are spread over the surface, and their size decreases as the temperature increases. The simulated adsorption isotherms present a characteristic two-dimensional (2D) phase diagram including a 2D critical point at 365K, which is higher than that on the hydroxylated Cr(2)O(3) surface (319 K). This fact substantiates the high affinity of water molecules to the α-Al(2)O(3) surfaces, which enhances the adsorbability originating from higher heat of adsorption. The higher affinity of water molecules to the α-Al(2)O(3) (001) plane is ascribed to the high compatibility of the crystal plane to form a hexagonal ring network of (001) plane of ice Ih. PMID:22178567

  10. Relaxation dynamics of surface-adsorbed water molecules in nanoporous silica probed by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Huang, Yu-Ru; Liu, Kao-Hsiang; Mou, Chung-Yuan; Sun, Chi-Kuang

    2015-08-01

    Relaxation dynamics of an exclusively adsorbed water molecule in mesoporous silica MCM-41-S was studied by using terahertz spectroscopy. With the temperature controlled from 0 to 50 °C, we observed strongly frequency- and temperature-dependent dielectric relaxation responses, implying that, unlike ice, surface-adsorbed water molecules retained flourishing picosecond dynamics. Based on the Debye relaxation model, a relaxation time constant was found to increase from 1.77 to 4.83 ps when the water molecule was cooled from 50 to 0 °C. An activation energy of ˜15 kJ/mol, which was in close agreement with a hydrogen-bonding energy, was further extracted from the Arrhenius analysis. Combined with previous molecular dynamics simulations, our results indicate that the reorientation relaxation originated from the "flip-flop" rotation of a three hydrogen-bonded surface-adsorbed water molecule.

  11. Asymmetric self-diffusion with orientation-dependence of water molecule in finite timescale

    NASA Astrophysics Data System (ADS)

    Wei, Xu; Sheng, Nan; Wan, RongZheng; Hu, GuoHui; Fang, HaiPing

    2016-07-01

    Self-diffusion of water has been investigated by molecular dynamics simulations. It was found that the preference of the direction in self-diffusion of water is orientation dependent in a finite time. For a time of ~100 ps, there are more possibilities for water molecules moving along the initial dipole orientation than in the opposite direction. This reveals that self-diffusion of water molecules is asymmetric in a finite time. We tested four water models and found that they all show similar asymmetric diffusion, indicating that asymmetric diffusion of water is intrinsic behavior rather than induced by the water model. These results are important for understanding and application of asymmetric diffusion in research fields such as biological water and confined water in small dimensions.

  12. Free energy barriers for escape of water molecules from protein hydration layer.

    PubMed

    Roy, Susmita; Bagchi, Biman

    2012-03-01

    Free energy barriers separating interfacial water molecules from the hydration layer at the surface of a protein to the bulk are obtained by using the umbrella sampling method of free energy calculation. We consider hydration layer of chicken villin head piece (HP-36) which has been studied extensively by molecular dynamics simulations. The free energy calculations reveal a strong sensitivity to the secondary structure. In particular, we find a region near the junction of first and second helix that contains a cluster of water molecules which are slow in motion, characterized by long residence times (of the order of 100 ps or more) and separated by a large free energy barrier from the bulk water. However, these "slow" water molecules constitute only about 5-10% of the total number of hydration layer water molecules. Nevertheless, they play an important role in stabilizing the protein conformation. Water molecules near the third helix (which is the important helix for biological function) are enthalpically least stable and exhibit the fastest dynamics. Interestingly, barrier height distributions of interfacial water are quite broad for water surrounding all the three helices (and the three coils), with the smallest barriers found for those near the helix-3. For the quasi-bound water molecules near the first and second helices, we use well-known Kramers' theory to estimate the residence time from the free energy surface, by estimating the friction along the reaction coordinate from the diffusion coefficient by using Einstein relation. The agreement found is satisfactory. We discuss the possible biological function of these slow, quasi-bound (but transient) water molecules on the surface. PMID:22288939

  13. The impact of microwave absorber and radome geometries on GNSS measurements of station coordinates and atmospheric water vapour

    NASA Astrophysics Data System (ADS)

    Ning, T.; Elgered, G.; Johansson, J. M.

    2011-01-01

    We have used microwave absorbing material in different geometries around ground-based Global Navigation Satellite System (GNSS) antennas in order to mitigate multipath effects on the estimates of station coordinates and atmospheric water vapour. The influence of a hemispheric radome - of the same type as in the Swedish GPS network SWEPOS - was also investigated. Two GNSS stations at the Onsala Space Observatory were used forming a 12 m baseline. GPS data from October 2008 to November 2009 were analyzed by the GIPSY/OASIS II software using the Precise Point Positioning (PPP) processing strategy for five different elevation cutoff angles from 5° to 25°. We found that the use of the absorbing material decreases the offset in the estimated vertical component of the baseline from ˜27 mm to ˜4 mm when the elevation cutoff angle varies from 5° to 20°. The horizontal components are much less affected. The corresponding offset in the estimates of the atmospheric Integrated Water Vapour (IWV) decreases from ˜1.6 kg/m2 to ˜0.3 kg/m2. Changes less than 5 mm in the offsets in the vertical component of the baseline are seen for all five elevation cutoff angle solutions when the antenna was covered by a hemispheric radome. Using the radome affects the IWV estimates less than 0.4 kg/m2 for all different solutions. IWV comparisons between a Water Vapour Radiometer (WVR) and the GPS data give consistent results.

  14. Laser photophoretic migration with periodic expansion-contraction motion of photo-absorbing microemulsion droplets in water.

    PubMed

    Tanaka, Makiko; Monjushiro, Hideaki; Watarai, Hitoshi

    2004-12-01

    When the water-in-oil (w/o) microemulsion droplets including the Co(III)-pyridylazo complex as the photo-absorber were irradiated with a continuous-wave Ar(+) ion laser (514.5 nm), we have observed unexpected phenomenon that photo-absorbing microemulsion droplets in water repeated the expansion and the sudden contraction during the laser photophoretic migration. The period of the expansion-contraction cycle was inversely proportional to both the concentration of the complex and the irradiated laser power and was independent of the initial size of the droplet. The mechanism of the periodic motion of the droplet was investigated by local temperature measurement and Raman microscope spectroscopy. It was suggested that the first step was the phase separation of the bicontinuous microemulsion droplet into the normal w/o microemulsion outer phase and the aqueous inner phase in the droplet, which was caused by the laser-induced temperature gradient inside the droplet. Subsequently, an expansion of the inner aqueous phase was induced by the percolation of the external water by thermo-osmosis, which was caused by the laser-induced temperature gradient between the inside and the outside of the microemulsion liquid membrane of the droplet. When the liquid membrane became thinner to a critical thickness, the inner aqueous phase was released and the droplet shrank into the original size. The proposed mechanism can give an account of the unique cyclical motion. PMID:15568826

  15. Mechanism of the typical relaxation process at low frequency based on dielectric measurements of water absorbed in porous titanium dioxide

    NASA Astrophysics Data System (ADS)

    Gao, Xin; Wang, Qiang; Sun, Gang; Li, Chenxi; Hu, Lin

    2016-02-01

    Dielectric spectroscopy is a valuable tool in physics, chemistry, biophysics, and materials science. However, there is still an argument about the typical relaxation process at low frequency, which is always masked by electrode polarization. Low-frequency dielectric measurements of water absorbed in porous titanium dioxide have been performed. The experimental results show that typical polarization at low frequency is caused by space-charge polarization. A model is proposed to explain the experimental results, which indicates that the electric field in the sample is close to 0. An effective circuit is given, and the calculation gives similar dielectric spectra to those measured in experiments, which confirms the physical model.

  16. Roles of water molecules in bacteria and viruses

    NASA Astrophysics Data System (ADS)

    Cox, C. S.

    1993-02-01

    In addition to water, microbes mainly comprise lipids, carbohydrates, proteins and nucleic acids. Their structure and function singularly and conjointly is affected by water activity. Desiccation leads to dramatic lipid phase changes whereas carbohydrates, proteins and nucleic acids initially suffer spontaneous, reversible low activation energy Maillard reactions forming products that more slowly re-arrange, cross-link etc. to give non-native states. While initial products spontaneously may reverse to native states by raising water activity, later products only do so through energy consumption and enzymatic activity eg. repair. Yet, native states of lipid membranes and associated enzymes are required to generate energy. Consequently, good reserves of high energy compounds (e.g. ATP) and of membrane stabilisers (e.g. trehalose) may be expected to enhance survival following drying and rehydration (e.g. anhydrobiotic organisms).

  17. Analytical model for three-dimensional Mercedes-Benz water molecules.

    PubMed

    Urbic, T

    2012-06-01

    We developed a statistical model which describes the thermal and volumetric properties of water-like molecules. A molecule is presented as a three-dimensional sphere with four hydrogen-bonding arms. Each water molecule interacts with its neighboring waters through a van der Waals interaction and an orientation-dependent hydrogen-bonding interaction. This model, which is largely analytical, is a variant of a model developed before for a two-dimensional Mercedes-Benz model of water. We explored properties such as molar volume, density, heat capacity, thermal expansion coefficient, and isothermal compressibility as a function of temperature and pressure. We found that the volumetric and thermal properties follow the same trends with temperature as in real water and are in good general agreement with Monte Carlo simulations, including the density anomaly, the minimum in the isothermal compressibility, and the decreased number of hydrogen bonds upon increasing the temperature. PMID:23005100

  18. Analytical model for three-dimensional Mercedes-Benz water molecules

    NASA Astrophysics Data System (ADS)

    Urbic, T.

    2012-06-01

    We developed a statistical model which describes the thermal and volumetric properties of water-like molecules. A molecule is presented as a three-dimensional sphere with four hydrogen-bonding arms. Each water molecule interacts with its neighboring waters through a van der Waals interaction and an orientation-dependent hydrogen-bonding interaction. This model, which is largely analytical, is a variant of a model developed before for a two-dimensional Mercedes-Benz model of water. We explored properties such as molar volume, density, heat capacity, thermal expansion coefficient, and isothermal compressibility as a function of temperature and pressure. We found that the volumetric and thermal properties follow the same trends with temperature as in real water and are in good general agreement with Monte Carlo simulations, including the density anomaly, the minimum in the isothermal compressibility, and the decreased number of hydrogen bonds upon increasing the temperature.

  19. Analytical model for three-dimensional Mercedes-Benz water molecules

    PubMed Central

    Urbic, T.

    2013-01-01

    We developed a statistical model which describes the thermal and volumetric properties of water-like molecules. A molecule is presented as a three-dimensional sphere with four hydrogen-bonding arms. Each water molecule interacts with its neighboring waters through a van der Waals interaction and an orientation-dependent hydrogen-bonding interaction. This model, which is largely analytical, is a variant of a model developed before for a two-dimensional Mercedes-Benz model of water. We explored properties such as molar volume, density, heat capacity, thermal expansion coefficient, and isothermal compressibility as a function of temperature and pressure. We found that the volumetric and thermal properties follow the same trends with temperature as in real water and are in good general agreement with Monte Carlo simulations, including the density anomaly, the minimum in the isothermal compressibility, and the decreased number of hydrogen bonds upon increasing the temperature. PMID:23005100

  20. An absorbed dose to water standard for HDR 192Ir brachytherapy sources based on water calorimetry: numerical and experimental proof-of-principle.

    PubMed

    Sarfehnia, Arman; Stewart, Kristin; Seuntjens, Jan

    2007-12-01

    Water calorimetry is an established technique for absorbed dose to water measurements in external beams. In this paper, the feasibility of direct absorbed dose measurements for high dose rate (HDR) iridium-192 (192Ir) sources using water calorimetry is established. Feasibility is determined primarily by a balance between the need to obtain sufficient signal to perform a reproducible measurement, the effect of heat loss on the measured signal, and the positioning uncertainty affecting the source-detector distance. The heat conduction pattern generated in water by the Nucletron microSelectron-HDR 192Ir brachytherapy source was simulated using COMSOL MULTIPHYSICS software. Source heating due to radiation self-absorption was calculated using EGSnrcMP. A heat-loss correction k(c) was calculated as the ratio of the temperature rise under ideal conditions to temperature rise under realistic conditions. The calorimeter setup used a parallel-plate calorimeter vessel of 79 mm diameter and 1.12 mm thick front and rear glass windows located 24 mm apart. Absorbed dose was measured with two sources with nominal air kerma strengths of 38 000 and 21 000 U, at source-detector separations ranging from 24.7 to 27.6 mm and irradiation times of 36.0 to 80.0 s. The preliminary measured dose rate per unit air kerma strength of (0.502 +/- 0.007) microGy/(s U) compares well with the TG-43 derived 0.505 microGy/(s U). This work shows that combined dose uncertainties of significantly less than 5% can be achieved with only modest modifications of current water calorimetry techniques and instruments. This work forms the basis of a potential future absolute dose to water standard for HDR 192Ir brachytherapy. PMID:18196821

  1. An absorbed dose to water standard for HDR {sup 192}Ir brachytherapy sources based on water calorimetry: Numerical and experimental proof-of-principle

    SciTech Connect

    Sarfehnia, Arman; Stewart, Kristin; Seuntjens, Jan

    2007-12-15

    Water calorimetry is an established technique for absorbed dose to water measurements in external beams. In this paper, the feasibility of direct absorbed dose measurements for high dose rate (HDR) iridium-192 ({sup 192}Ir) sources using water calorimetry is established. Feasibility is determined primarily by a balance between the need to obtain sufficient signal to perform a reproducible measurement, the effect of heat loss on the measured signal, and the positioning uncertainty affecting the source-detector distance. The heat conduction pattern generated in water by the Nucletron microSelectron-HDR {sup 192}Ir brachytherapy source was simulated using COMSOL MULTIPHYSICSTM software. Source heating due to radiation self-absorption was calculated using EGSnrcMP. A heat-loss correction k{sub c} was calculated as the ratio of the temperature rise under ideal conditions to temperature rise under realistic conditions. The calorimeter setup used a parallel-plate calorimeter vessel of 79 mm diameter and 1.12 mm thick front and rear glass windows located 24 mm apart. Absorbed dose was measured with two sources with nominal air kerma strengths of 38 000 and 21 000 U, at source-detector separations ranging from 24.7 to 27.6 mm and irradiation times of 36.0 to 80.0 s. The preliminary measured dose rate per unit air kerma strength of (0.502{+-}0.007) {mu}Gy/(s U) compares well with the TG-43 derived 0.505 {mu}Gy/(s U). This work shows that combined dose uncertainties of significantly less than 5% can be achieved with only modest modifications of current water calorimetry techniques and instruments. This work forms the basis of a potential future absolute dose to water standard for HDR {sup 192}Ir brachytherapy.

  2. Disulfuric acid dissociated by two water molecules: ab initio and density functional theory calculations.

    PubMed

    Kim, Seong Kyu; Lee, Han Myoung; Kim, Kwang S

    2015-11-21

    We have studied geometries, energies and vibrational spectra of disulfuric acid (H2S2O7) and its anion (HS2O7(-)) hydrated by a few water molecules, using density functional theory (M062X) and ab initio theory (SCS-MP2 and CCSD(T)). The most noteworthy result is found in H2S2O7(H2O)2 in which the lowest energy conformer shows deprotonated H2S2O7. Thus, H2S2O7 requires only two water molecules, the fewest number of water molecules for deprotonation among various hydrated monomeric acids reported so far. Even the second deprotonation of the first deprotonated species HS2O7(-) needs only four water molecules. The deprotonation is supported by vibration spectra, in which acid O-H stretching peaks disappear and specific three O-H stretching peaks for H3O(+) (eigen structure) appear. We have also kept track of variations in several geometrical parameters, atomic charges, and hybrid orbital characters upon addition of water. As the number of water molecules added increases, the S-O bond weakens in the case of H2S2O7, but strengthens in the case of HS2O7(-). It implies that the decomposition leading to H2SO4 and SO3 hardly occurs prior to the 2nd deprotonation at low temperatures. PMID:26400266

  3. Synthesis of novel fluorene-based two-photon absorbing molecules and their applications in optical data storage, microfabrication, and stimulated emission depletion

    NASA Astrophysics Data System (ADS)

    Yanez, Ciceron

    2009-12-01

    Two-photon absorption (2PA) has been used for a number of scientific and technological applications, exploiting the fact that the 2PA probability is directly proportional to the square of the incident light intensity (while one-photon absorption bears a linear relation to the incident light intensity). This intrinsic property of 2PA leads to 3D spatial localization, important in fields such as optical data storage, fluorescence microscopy, and 3D microfabrication. The spatial confinement that 2PA enables has been used to induce photochemical and photophysical events in increasingly smaller volumes and allowed nonlinear, 2PA-based, technologies to reach sub-diffraction limit resolutions. The primary focus of this dissertation is the development of novel, efficient 2PA, fluorene-based molecules to be used either as photoacid generators (PAGs) or fluorophores. A second aim is to develop more effective methods of synthesizing these compounds. As a third and final objective, the new molecules were used to develop a write-once-read many (WORM) optical data storage system, and stimulated emission depletion probes for bioimaging. In Chapter I, the microwave-assisted synthesis of triarylsulfonium salt photoacid generators (PAGs) from their diphenyliodonium counterparts is reported. The microwave-assisted synthesis of these novel sulfonium salts afforded reaction times 90 to 420 times faster than conventional thermal conditions, with photoacid quantum yields of new sulfonium PAGs ranging from 0.01 to 0.4. These PAGs were used to develop a fluorescence readout-based, nonlinear three-dimensional (3D) optical data storage system (Chapter II). In this system, writing was achieved by acid generation upon two-photon absorption (2PA) of a PAG (at 710 or 730 nm). Readout was then performed by interrogating two-photon absorbing dyes, after protonation, at 860 nm. Two-photon recording and readout of voxels was demonstrated in five and eight consecutive, crosstalk-free layers within a

  4. Auger spectrum of a water molecule after single and double core ionization

    SciTech Connect

    Inhester, L.; Burmeister, C. F.; Groenhof, G.; Grubmueller, H.

    2012-04-14

    The high intensity of free electron lasers opens up the possibility to perform single-shot molecule scattering experiments. However, even for small molecules, radiation damage induced by absorption of high intense x-ray radiation is not yet fully understood. One of the striking effects which occurs under intense x-ray illumination is the creation of double core ionized molecules in considerable quantity. To provide insight into this process, we have studied the dynamics of water molecules in single and double core ionized states by means of electronic transition rate calculations and ab initio molecular dynamics (MD) simulations. From the MD trajectories, photoionization and Auger transition rates were computed based on electronic continuum wavefunctions obtained by explicit integration of the coupled radial Schroedinger equations. These rates served to solve the master equations for the populations of the relevant electronic states. To account for the nuclear dynamics during the core hole lifetime, the calculated electron emission spectra for different molecular geometries were incoherently accumulated according to the obtained time-dependent populations, thus neglecting possible interference effects between different decay pathways. We find that, in contrast to the single core ionized water molecule, the nuclear dynamics for the double core ionized water molecule during the core hole lifetime leaves a clear fingerprint in the resulting electron emission spectra. The lifetime of the double core ionized water was found to be significantly shorter than half of the single core hole lifetime.

  5. Fast phase transition of water molecules in a defective carbon nanotube under an electric field

    NASA Astrophysics Data System (ADS)

    Meng, Xianwen; Huang, Jiping

    2016-02-01

    We utilize molecular dynamics simulations to study the effect of an electric field on the permeation of water molecules through a defective single-walled carbon nanotube (DSWCNT). Compared with a perfect single-walled carbon nanotube (PSWCNT), the behaviors of water molecules respond more quickly under the same electric field in a DSWCNT. Wet-dry phase transition of water molecules occurs when the electric field reaches 0.32 V/nm, which is much lower than the case of the PSWCNT. Besides, the critical electric field is affected by the number of defects. These results pave a way for designing fast wet-dry transition devices and provide a new insight into water permeation through a defective nanochannel.

  6. Water-absorbent polymer as a carrier for a discrete deposit of antisense oligodeoxynucleotides in the central nervous system.

    PubMed

    Bannai, M; Ichikawa, M; Nishimura, F; Nishihara, M; Takahashi, M

    1998-09-01

    One of the problems of introducing antisense oligodeoxynucleotides (ODN) into the central nervous system (CNS) is their rapid disappearance from the target site due to their dispersion and diffusion, which results in poor uptake and/or retention in cells (M. Morris, A.B. Lucion, Antisense oligonucleotides in the study of neuroendocrine systems, J. Neuroendocrinol. 7 (1995) 493-500; S. Ogawa, H.E. Brown, H.J. Okano, D.W. Pfaff, Cellular uptake of intracerebrally administrated oligodeoxynucleotides in mouse brain, Regul. Pept. 59 (1995) 143-149) [2,5]. Recently, we adapted a new method using water-absorbent polymer (WAP; internally cross-linked starch-grafted-polyacrylates) as a carrier for antisense ODN. The polymer forms a hydro-gel after absorbing water which is chemically and biologically inert. In these studies, the polymer (powder-form) is fully swollen by physiological saline containing antisense ODN (0.2 micromol/ml) to make 80-fold volume gel. Hydro-gel (1 microliter) is injected into the target site, and water solutes are assumed to be diffused stoichiometrically into CNS from the surface of the gel. Histological studies indicate that 24 h after the injection, antisense ODN (5'biotinylated-S-oligos of 15 mer) are distributed to within 800 micrometer from the edge of the area where the gel is located and then gradually disappear from this area within days, but still remain within 300-micrometer distance 7 days later. Antisense ODN are effectively incorporated by all the cell types examined, i.e., neurons, astrocytes and microglias, and suppress the synthesis of the target protein. This method can be adapted to slow delivery of antisense ODN and other water soluble substances into the CNS. PMID:9767125

  7. Vibrational states of a water molecule in a nano-cavity of beryl crystal lattice

    NASA Astrophysics Data System (ADS)

    Zhukova, Elena S.; Torgashev, Victor I.; Gorshunov, Boris P.; Lebedev, Vladimir V.; Shakurov, Gil'man S.; Kremer, Reinhard K.; Pestrjakov, Efim V.; Thomas, Victor G.; Fursenko, Dimitry A.; Prokhorov, Anatoly S.; Dressel, Martin

    2014-06-01

    Low-energy excitations of a single water molecule are studied when confined within a nano-size cavity formed by the ionic crystal lattice. Optical spectra are measured of manganese doped beryl single crystal Mn:Be3Al2Si6O18, that contains water molecules individually isolated in 0.51 nm diameter voids within the crystal lattice. Two types of orientation are distinguished: water-I molecules have their dipole moments aligned perpendicular to the c axis and dipole moments of water-II molecules are parallel to the c-axis. The optical conductivity σ(ν) and permittivity ɛ'(ν) spectra are recorded in terahertz and infrared ranges, at frequencies from several wavenumbers up to ν = 7000 cm-1, at temperatures 5-300 K and for two polarizations, when the electric vector E of the radiation is parallel and perpendicular to the c-axis. Comparative experiments on as-grown and on dehydrated samples allow to identify the spectra of σ(ν) and ɛ'(ν) caused exclusively by water molecules. In the infrared range, well-known internal modes ν1, ν2, and ν3 of the H2O molecule are observed for both polarizations, indicating the presence of water-I and water-II molecules in the crystal. Spectra recorded below 1000 cm-1 reveal a rich set of highly anisotropic features in the low-energy response of H2O molecule in a crystalline nano-cavity. While for E∥c only two absorption peaks are detected, at ˜90 cm-1 and ˜160 cm-1, several absorption bands are discovered for E⊥c, each consisting of narrower resonances. The bands are assigned to librational (400-500 cm-1) and translational (150-200 cm-1) vibrations of water-I molecule that is weakly coupled to the nano-cavity "walls." A model is presented that explains the "fine structure" of the bands by a splitting of the energy levels due to quantum tunneling between the minima in a six-well potential relief felt by a molecule within the cavity.

  8. Water and Small-Molecule Permeation of Dormant Bacillus subtilis Spores

    PubMed Central

    Cermak, Nathan; Feijó Delgado, Francisco; Setlow, Barbara; Setlow, Peter

    2015-01-01

    ABSTRACT We use a suspended microchannel resonator to characterize the water and small-molecule permeability of Bacillus subtilis spores based on spores' buoyant mass in different solutions. Consistent with previous results, we found that the spore coat is not a significant barrier to small molecules, and the extent to which small molecules may enter the spore is size dependent. We have developed a method to directly observe the exchange kinetics of intraspore water with deuterium oxide, and we applied this method to wild-type spores and a panel of congenic mutants with deficiencies in the assembly or structure of the coat. Compared to wild-type spores, which exchange in approximately 1 s, several coat mutant spores were found to have relatively high water permeability with exchange times below the ∼200-ms temporal resolution of our assay. In addition, we found that the water permeability of the spore correlates with the ability of spores to germinate with dodecylamine and with the ability of TbCl3 to inhibit germination with l-valine. These results suggest that the structure of the coat may be necessary for maintaining low water permeability. IMPORTANCE Spores of Bacillus species cause food spoilage and disease and are extremely resistant to standard decontamination methods. This hardiness is partly due to spores' extremely low permeability to chemicals, including water. We present a method to directly monitor the uptake of molecules into B. subtilis spores by weighing spores in fluid. The results demonstrate the exchange of core water with subsecond resolution and show a correlation between water permeability and the rate at which small molecules can initiate or inhibit germination in coat-damaged spores. The ability to directly measure the uptake of molecules in the context of spores with known structural or genetic deficiencies is expected to provide insight into the determinants of spores' extreme resistance. PMID:26483518

  9. First international comparison of primary absorbed dose to water standards in the medium-energy X-ray range

    NASA Astrophysics Data System (ADS)

    Büermann, Ludwig; Guerra, Antonio Stefano; Pimpinella, Maria; Pinto, Massimo; de Pooter, Jacco; de Prez, Leon; Jansen, Bartel; Denoziere, Marc; Rapp, Benjamin

    2016-01-01

    This report presents the results of the first international comparison of primary measurement standards of absorbed dose to water for the medium-energy X-ray range. Three of the participants (VSL, PTB, LNE-LNHB) used their existing water calorimeter based standards and one participant (ENEA) recently developed a new standard based on a water-graphite calorimeter. The participants calibrated three transfer chambers of the same type in terms of absorbed dose to water (NDw) and in addition in terms of air kerma (NK) using the CCRI radiation qualities in the range 100 kV to 250 kV. The additional NK values were intended to be used for a physical analysis of the ratios NDw/NK. All participants had previously participated in the BIPM.RI(I)-K3 key comparison of air kerma standards. Ratios of pairs of NMI's NK results of the current comparison were found to be consistent with the corresponding key comparison results within the expanded uncertainties of 0.6 % - 1 %. The NDw results were analysed in terms of the degrees of equivalence with the comparison reference values which were calculated for each beam quality as the weighted means of all results. The participant's results were consistent with the reference value within the expanded uncertainties. However, these expanded uncertainties varied significantly and ranged between about 1-1.8 % for the water calorimeter based standards and were estimated at 3.7 % for the water-graphite calorimeter. It was shown previously that the ratios NDw/NK for the type of ionization chamber used as transfer chamber in this comparison were very close (within less than 1 %) to the calculated values of (bar muen/ρ)w,ad, the mean values of the water-to-air ratio of the mass-energy-absorption coefficients at the depth d in water. Some of the participant's results deviated significantly from the expected behavior. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of

  10. Hydroxyl and water molecule orientations in trypsin: Comparison to molecular dynamics structures

    SciTech Connect

    McDowell, R.S.; Kossiakoff, A.A.

    1994-12-31

    A comparison is presented of experimentally observed hydroxyl and water hydrogens in trypsin determined from neutron density maps with the results of a 140ps molecular dynamics (MD) simulation. Experimental determination of hydrogen and deuterium atom positions in molecules as large as proteins is a unique capability of neutron diffraction. The comparison addresses the degree to which a standard force-field approach can adequately describe the local electrostatic and van der Waals forces that determine the orientations of these hydrogens. Neutron densities, derived from 2.1{Angstrom} D{sub 2}O-H{sub 2}O difference Fourier maps, provide a database of 27 well-ordered hydroxyl hydrogens. Most of the simulated hydroxyl orientations are within a standard deviation of the experimentally-observed positions, including several examples in which both the simulation and the neutron density indicate that a hydroxyl group is shifted from a {open_quote}standard{close_quote} rotamer. For the most highly ordered water molecules, the hydrogen distributions calculated from the trajectory were in good agreement with neutron density; simulated water molecules that displayed multiple hydrogen bonding networks had correspondingly broadened neutron density profiles. This comparison was facilitated by development of a method to construct a pseudo 2{Angstrom} density map based on the hydrogen atom distributions from the simulation. The degree of disorder of internal water molecules is shown to result primarily from the electrostatic environment surrounding that water molecule as opposed to the cavity size available to the molecule. A method is presented for comparing the discrete observations sampled in a dynamics trajectory with the time- averaged data obtained from X-ray or neutron diffraction studies. This method is particularly useful for statically-disordered water molecules, in which the average location assigned from a trajectory may represent a site of relatively low occupancy.

  11. Using LiF:Mg,Cu,P TLDs to estimate the absorbed dose to water in liquid water around an {sup 192}Ir brachytherapy source

    SciTech Connect

    Lucas, P. Avilés Aubineau-Lanièce, I.; Lourenço, V.; Vermesse, D.; Cutarella, D.

    2014-01-15

    Purpose: The absorbed dose to water is the fundamental reference quantity for brachytherapy treatment planning systems and thermoluminescence dosimeters (TLDs) have been recognized as the most validated detectors for measurement of such a dosimetric descriptor. The detector response in a wide energy spectrum as that of an{sup 192}Ir brachytherapy source as well as the specific measurement medium which surrounds the TLD need to be accounted for when estimating the absorbed dose. This paper develops a methodology based on highly sensitive LiF:Mg,Cu,P TLDs to directly estimate the absorbed dose to water in liquid water around a high dose rate {sup 192}Ir brachytherapy source. Methods: Different experimental designs in liquid water and air were constructed to study the response of LiF:Mg,Cu,P TLDs when irradiated in several standard photon beams of the LNE-LNHB (French national metrology laboratory for ionizing radiation). Measurement strategies and Monte Carlo techniques were developed to calibrate the LiF:Mg,Cu,P detectors in the energy interval characteristic of that found when TLDs are immersed in water around an{sup 192}Ir source. Finally, an experimental system was designed to irradiate TLDs at different angles between 1 and 11 cm away from an {sup 192}Ir source in liquid water. Monte Carlo simulations were performed to correct measured results to provide estimates of the absorbed dose to water in water around the {sup 192}Ir source. Results: The dose response dependence of LiF:Mg,Cu,P TLDs with the linear energy transfer of secondary electrons followed the same variations as those of published results. The calibration strategy which used TLDs in air exposed to a standard N-250 ISO x-ray beam and TLDs in water irradiated with a standard{sup 137}Cs beam provided an estimated mean uncertainty of 2.8% (k = 1) in the TLD calibration coefficient for irradiations by the {sup 192}Ir source in water. The 3D TLD measurements performed in liquid water were obtained with a

  12. Calcium polycarbophil, a water absorbing polymer, increases bowel movement and prevents sennoside-induced diarrhea in dogs.

    PubMed

    Saito, T; Yamada, T; Iwanaga, Y; Morikawa, K; Nagata, O; Kato, H; Mizumoto, A; Itoh, Z

    2000-07-01

    The effects of calcium polycarbophil (CP), a water-absorbing polymer, on bowel movement were examined in comparison with known laxatives and anti-diarrheal agents in dogs, a species that resembles humans for stool output. CP increased stool frequency, fecal water content and fecal weight in a dose-dependent manner, but did not induce diarrhea. Sennoside and carboxymethylcellulose sodium (CMC-Na) increased fecal water content and induced diarrhea at lower doses than that which enhanced stool frequency. Trimebutine decreased stool frequency, fecal weight and fecal water content, resulting in inhibition rather than stimulation of defecation. In sennoside-induced diarrhea, loperamide and CP improved stool consistency and this was accompanied by reduced fecal moisture and frequency of diarrhea. In contrast, CMC-Na aggravated stool consistency with increased fecal water content and frequency of diarrhea, and trimebutine had little noticeable effect apart from reducing fecal weight. Our results show that CP has both laxative and anti-diarrheal effects in dogs and differed from conventional laxatives and anti-diarrheal agents. CP may be a suitable agent for treatment of idiopathic constipation, secretory diarrhea and irritable bowel syndrome with alternating constipation and diarrhea and with either predominating in terms of less side effects such as diarrhea or constipation. PMID:10952069

  13. Improving protein-ligand docking with flexible interfacial water molecules using SWRosettaLigand.

    PubMed

    Li, Linqing; Xu, Weiwei; Lü, Qiang

    2015-11-01

    Computational protein-ligand docking is of great importance in drug discovery and design. Conformational changes greatly affect the results of protein-ligand docking, especially when water molecules take part in mediating protein ligand interactions or when large conformational changes are observed in the receptor backbone interface. We have developed an improved protocol, SWRosettaLigand, based on the RosettaLigand protocol. This approach incorporates the flexibility of interfacial water molecules and modeling of the interface of the receptor into the original RosettaLigand. In a coarse sampling step, SWRosettaLigand pre-optimizes the initial position of the water molecules, docks the ligand to the receptor with explicit water molecules, and minimizes the predicted structure with water molecules. The receptor backbone interface is treated as a loop and perturbed and refined by kinematic closure, or cyclic coordinate descent algorithm, with the presence of the ligand. In two cross-docking test sets, it was identified that for 8 out of 14, and 16 out of 22, test instances, the top-ranked structures by SWRosettaLigand achieved better accuracy than other protocols. PMID:26515196

  14. Water molecules inside protein structure affect binding of monosaccharides with HIV-1 antibody 2G12.

    PubMed

    Ueno-Noto, Kaori; Takano, Keiko

    2016-10-01

    Water molecules inside biomolecules constitute integral parts of their structure and participate in the functions of the proteins. Some of the X-ray crystallographic data are insufficient for analyzing a series of ligand-protein complexes in the same condition. We theoretically investigated antibody binding abilities of saccharide ligands and the effects of the inner water molecules of ligand-antibody complexes. Classical molecular dynamics and quantum chemical simulations using a model with possible water molecules inside the protein were performed with saccharide ligands and Human Immunodeficiency Virus 1 neutralizing antibody 2G12 complexes to estimate how inner water molecules of the protein affect the dynamics of the complexes as well as the ligand-antibody interaction. Our results indicate the fact that d-fructose's strong affinity to the antibody was partly due to the good retentiveness of solvent water molecules of the ligand and its stability of the ligand's conformation and relative position in the active site. © 2016 Wiley Periodicals, Inc. PMID:27388036

  15. Enhanced permeation of single-file water molecules across a noncylindrical nanochannel

    NASA Astrophysics Data System (ADS)

    Meng, X. W.; Huang, J. P.

    2013-07-01

    We utilize molecular dynamics simulations to study the effect of noncylindrical shapes of a nanochannel (which are inspired from the shape of real biological water nanochannels) on the permeation of single-file water molecules across the nanochannel. Compared with the cylindrical shape that has been tremendously adopted in the literature, the noncylindrical shapes play a crucial role in enhancing water permeation. Remarkably, the maximal enhancement ratio reaches a value of 6.28 (enhancement behavior). Meanwhile, the enhancement becomes saturated when the volume of the noncylindrical shape continues to increase (saturation behavior). The analysis of average diffusivity of water molecules helps to reveal the mechanism underlying the two behaviors whereas Poiseuille's law fails to explain them. These results pave a way for designing high-flow nanochannels and provide insight into water permeation across biological water nanochannels.

  16. Giant pumping of single-file water molecules in a carbon nanotube.

    PubMed

    Wang, Y; Zhao, Y J; Huang, J P

    2011-11-17

    Achieving a fast, unidirectional flow of single-file water molecules (UFSWM) across nanochannels is important for membrane-based water purification or seawater desalination. For this purpose, electro-osmosis methods are recognized as a very promising approach and have been extensively discussed in the literature. Utilizing molecular dynamics simulations, here we propose a design for pumping water molecules in a single-walled carbon nanotube in the presence of a linearly gradient electric (GE) field. Such a GE field is inspired by GE fields generated from charged ions located adjacent to biological membrane water nanochannels that can conduct water in and out of cells and can be experimentally achieved by using the charged tip of an atomic force microscope. As a result, the maximum speed of the UFSWM can be 1 or 2 orders of magnitude larger than that in a uniform electric (UE) field. Also, inverse transportation of water molecules does not exist in case of the GE field but can appear for the UE field. Thus, the GE field yields a much more efficient UFSWM than the UE field. The giant pumping ability as revealed is attributed to the nonzero net electrostatic force acting on each water molecule confined in the nanotube. These observations have significance for the design of nanoscale devices for readily achieving controllable UFSWM at high speed. PMID:21977917

  17. Formation of Organic Molecules and Water in Warm Disk Atmospheres

    NASA Astrophysics Data System (ADS)

    Najita, Joan R.; Ádámkovics, Máté; Glassgold, Alfred E.

    2011-12-01

    Observations from Spitzer and ground-based infrared spectroscopy reveal significant diversity in the molecular emission from the inner few AU of T Tauri disks. We explore theoretically the possible origin of this diversity by expanding on our earlier thermal-chemical model of disk atmospheres. We consider how variations in grain settling, X-ray irradiation, accretion-related mechanical heating, and the oxygen-to-carbon ratio can affect the thermal and chemical properties of the atmosphere at 0.25-40 AU. We find that these model parameters can account for many properties of the detected molecular emission. The column density of the warm (200-2000 K) molecular atmosphere is sensitive to grain settling and the efficiency of accretion-related heating, which may account, at least in part, for the large range in molecular emission fluxes that have been observed. The dependence of the atmospheric properties on the model parameters may also help to explain trends that have been reported in the literature between molecular emission strength and mid-infrared color, stellar accretion rate, and disk mass. We discuss whether some of the differences between our model results and the observations (e.g., for water) indicate a role for vertical transport and freezeout in the disk midplane. We also discuss how planetesimal formation in the outer disk (beyond the snowline) may imprint a chemical signature on the inner few AU of the disk and speculate on possible observational tracers of this process.

  18. Water-mediated influence of a crowded environment on internal vibrations of a protein molecule.

    PubMed

    Kuffel, Anna; Zielkiewicz, Jan

    2016-02-01

    The influence of crowding on the protein inner dynamics is examined by putting a single protein molecule close to one or two neighboring protein molecules. The presence of additional molecules influences the amplitudes of protein fluctuations. Also, a weak dynamical coupling of collective velocities of surface atoms of proteins separated by a layer of water is detected. The possible mechanisms of these phenomena are described. The cross-correlation function of the collective velocities of surface atoms of two proteins was decomposed into the Fourier series. The amplitude spectrum displays a peak at low frequencies. Also, the results of principal component analysis suggest that the close presence of an additional protein molecule influences the high-amplitude, low-frequency modes in the most prominent way. This part of the spectrum covers biologically important protein motions. The neighbor-induced changes in the inner dynamics of the protein may be connected with the changes in the velocity power spectrum of interfacial water. The additional protein molecule changes the properties of solvation water and in this way it can influence the dynamics of the second protein. It is suggested that this phenomenon may be described, at first approximation, by a damped oscillator driven by an external random force. This model was successfully applied to conformationally rigid Choristoneura fumiferana antifreeze protein molecules. PMID:26805932

  19. A graphite calorimeter for absolute measurements of absorbed dose to water: application in medium-energy x-ray filtered beams

    NASA Astrophysics Data System (ADS)

    Pinto, M.; Pimpinella, M.; Quini, M.; D'Arienzo, M.; Astefanoaei, I.; Loreti, S.; Guerra, A. S.

    2016-02-01

    The Italian National Institute of Ionizing Radiation Metrology (ENEA-INMRI) has designed and built a graphite calorimeter that, in a water phantom, has allowed the determination of the absorbed dose to water in medium-energy x-rays with generating voltages from 180 to 250 kV. The new standard is a miniaturized three-bodies calorimeter, with a disc-shaped core of 21 mm diameter and 2 mm thickness weighing 1.134 g, sealed in a PMMA waterproof envelope with air-evacuated gaps. The measured absorbed dose to graphite is converted into absorbed dose to water by means of an energy-dependent conversion factor obtained from Monte Carlo simulations. Heat-transfer correction factors were determined by FEM calculations. At a source-to-detector distance of 100 cm, a depth in water of 2 g cm-2, and at a dose rate of about 0.15 Gy min-1, results of calorimetric measurements of absorbed dose to water, D w, were compared to experimental determinations, D wK, obtained via an ionization chamber calibrated in terms of air kerma, according to established dosimetry protocols. The combined standard uncertainty of D w and D wK were estimated as 1.9% and 1.7%, respectively. The two absorbed dose to water determinations were in agreement within 1%, well below the stated measurement uncertainties. Advancements are in progress to extend the measurement capability of the new in-water-phantom graphite calorimeter to other filtered medium-energy x-ray qualities and to reduce the D w uncertainty to around 1%. The new calorimeter represents the first implementation of in-water-phantom graphite calorimetry in the kilovoltage range and, allowing independent determinations of D w, it will contribute to establish a robust system of absorbed dose to water primary standards for medium-energy x-ray beams.

  20. Rotation of water molecules in plastic phase at extreme conditions from first principles molecular dynamics method

    NASA Astrophysics Data System (ADS)

    Tasaka, Tomofumi; Tsumuraya, Kazuo

    2014-03-01

    Water has a variety of polymorphs in wide ranges of temperature and pressure. Ice VII phase transforms to ice X with increased pressure. However the ice VII transforms to a superionic phase at higher temperatures around 2000K and pressure 30GPa in which the protons migrate in the body centered cubic lattice of oxygens. The ice VII transforms into rotator phase (so called plastic phase at lower temperatures around 600K and 5 to 50GPa. The formation of the phase has been confirmed only with the empirical potentials, whereas the experimental confirmation has been postponed until now. The present study elucidates the mechanism of the rotation of the water molecules and the correlation between the molecules during the rotation with the first principles molecular dynamics method. The water molecules rotate around each oxygen atom to conserve the ice VII positions of the protons.

  1. Interaction of water molecules with hexagonal 2D systems. A DFT study

    NASA Astrophysics Data System (ADS)

    Rojas, Ángela; Rey, Rafael

    Over the years water sources have been contaminated with many chemical agents, becoming issues that affect health of the world population. The advances of the nanoscience and nanotechnology in the development new materials constitute an alternative for design molecular filters with great efficiencies and low cost for water treatment and purification. In the nanoscale, the process of filtration or separation of inorganic and organic pollutants from water requires to study interactions of these atoms or molecules with different nano-materials. Specifically, it is necessary to understand the role of these interactions in physical and chemical properties of the nano-materials. In this work, the main interest is to do a theoretical study of interaction between water molecules and 2D graphene-like systems, such as silicene (h-Si) or germanene (h-Ge). Using Density Functional Theory we calculate total energy curves as function of separation between of water molecules and 2D systems. Different spatial configurations of water molecules relative to 2D systems are considered. Structural relaxation effects and changes of electronic charge density also are reported. Universidad Nacional de Colombia.

  2. Note: Three wavelengths near-infrared spectroscopy system for compensating the light absorbance by water

    NASA Astrophysics Data System (ADS)

    Bhutta, M. Raheel; Hong, Keum-Shik; Kim, Beop-Min; Hong, Melissa Jiyoun; Kim, Yun-Hee; Lee, Se-Ho

    2014-02-01

    Given that approximately 80% of blood is water, we develop a wireless functional near-infrared spectroscopy system that detects not only the concentration changes of oxy- and deoxy-hemoglobin (HbO and HbR) during mental activity but also that of water (H2O). Additionally, it implements a water-absorption correction algorithm that improves the HbO and HbR signal strengths during an arithmetic task. The system comprises a microcontroller, an optical probe, tri-wavelength light emitting diodes, photodiodes, a WiFi communication module, and a battery. System functionality was tested by means of arithmetic-task experiments performed by healthy male subjects.

  3. Note: three wavelengths near-infrared spectroscopy system for compensating the light absorbance by water.

    PubMed

    Bhutta, M Raheel; Hong, Keum-Shik; Kim, Beop-Min; Hong, Melissa Jiyoun; Kim, Yun-Hee; Lee, Se-Ho

    2014-02-01

    Given that approximately 80% of blood is water, we develop a wireless functional near-infrared spectroscopy system that detects not only the concentration changes of oxy- and deoxy-hemoglobin (HbO and HbR) during mental activity but also that of water (H2O). Additionally, it implements a water-absorption correction algorithm that improves the HbO and HbR signal strengths during an arithmetic task. The system comprises a microcontroller, an optical probe, tri-wavelength light emitting diodes, photodiodes, a WiFi communication module, and a battery. System functionality was tested by means of arithmetic-task experiments performed by healthy male subjects. PMID:24593411

  4. High-performance size exclusion chromatography with a multi-wavelength absorbance detector study on dissolved organic matter characterisation along a water distribution system.

    PubMed

    Huang, Huiping; Sawade, Emma; Cook, David; Chow, Christopher W K; Drikas, Mary; Jin, Bo

    2016-06-01

    This study examined the associations between dissolved organic matter (DOM) characteristics and potential nitrification occurrence in the presence of chloramine along a drinking water distribution system. High-performance size exclusion chromatography (HPSEC) coupled with a multiple wavelength detector (200-280nm) was employed to characterise DOM by molecular weight distribution, bacterial activity was analysed using flow cytometry, and a package of simple analytical tools, such as dissolved organic carbon, absorbance at 254nm, nitrate, nitrite, ammonia and total disinfectant residual were also applied and their applicability to indicate water quality changes in distribution systems were also evaluated. Results showed that multi-wavelength HPSEC analysis was useful to provide information about DOM character while changes in molecule weight profiles at wavelengths less than 230nm were also able to be related to other water quality parameters. Correct selection of the UV wavelengths can be an important factor for providing appropriate indicators associated with different DOM compositions. DOM molecular weight in the range of 0.2-0.5kDa measured at 210nm correlated positively with oxidised nitrogen concentration (r=0.99), and the concentrations of active bacterial cells in the distribution system (r=0.85). Our study also showed that the changes of DOM character and bacterial cells were significant in those sampling points that had decreases in total disinfectant residual. HPSEC-UV measured at 210nm and flow cytometry can detect the changes of low molecular weight of DOM and bacterial levels, respectively, when nitrification occurred within the chloraminated distribution system. PMID:27266320

  5. Solvation of a probe molecule by fluid supercooled water in a hydrogel at 200 K.

    PubMed

    Santangelo, Maria Grazia; Levantino, Matteo; Cupane, Antonio; Jeschke, Gunnar

    2008-12-11

    By combining electron paramagnetic resonance (EPR) measurements on a nitroxide probe and differential scanning calorimetry (DSC), we demonstrate existence of liquid supercooled water in a silica hydrogel with high hydration level down to temperatures of at least 198 K. Besides the major fraction of liquid supercooled water, a minor fraction crystallizes at about 236 K during cooling and melts at 246 K during heating. The liquid domains are of sufficient size to solvate the nearly spherical paramagnetic probe molecule TEMPO with a diameter of about 6 A. Analysis of EPR spectra provides the rotational correlation time of the probe that is further used to compare the viscosity of the supercooled water with the one of bulk water. In the temperature interval investigated, the supercooled water behaves as a fragile liquid and eventually solidifies at 120 K to a glass that incorporates the probe molecules. PMID:19053683

  6. Water Impact Test and Simulation of a Composite Energy Absorbing Fuselage Section

    NASA Technical Reports Server (NTRS)

    Fasanella, Edwin L.; Jackson, Karen E.; Sparks, Chad; Sareen, Ashish

    2003-01-01

    In March 2002, a 25-ft/s vertical drop test of a composite fuselage section was conducted onto water. The purpose of the test was to obtain experimental data characterizing the structural response of the fuselage section during water impact for comparison with two previous drop tests that were performed onto a rigid surface and soft soil. For the drop test, the fuselage section was configured with ten 100-lb. lead masses, five per side, that were attached to seat rails mounted to the floor. The fuselage section was raised to a height of 10-ft. and dropped vertically into a 15-ft. diameter pool filled to a depth of 3.5-ft. with water. Approximately 70 channels of data were collected during the drop test at a 10-kHz sampling rate. The test data were used to validate crash simulations of the water impact that were developed using the nonlinear, explicit transient dynamic codes, MSC.Dytran and LS-DYNA. The fuselage structure was modeled using shell and solid elements with a Lagrangian mesh, and the water was modeled with both Eulerian and Lagrangian techniques. The fluid-structure interactions were executed using the fast general coupling in MSC.Dytran and the Arbitrary Lagrange-Euler (ALE) coupling in LS-DYNA. Additionally, the smooth particle hydrodynamics (SPH) meshless Lagrangian technique was used in LS-DYNA to represent the fluid. The simulation results were correlated with the test data to validate the modeling approach. Additional simulation studies were performed to determine how changes in mesh density, mesh uniformity, fluid viscosity, and failure strain influence the test-analysis correlation.

  7. Physicochemical controls on absorbed water film thickness in unsaturated geological media

    SciTech Connect

    Tokunaga, T.

    2011-06-14

    Adsorbed water films commonly coat mineral surfaces in unsaturated soils and rocks, reducing flow and transport rates. Therefore, it is important to understand how adsorbed film thickness depends on matric potential, surface chemistry, and solution chemistry. Here, the problem of adsorbed water film thickness is examined through combining capillary scaling with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Novel aspects of this analysis include determining capillary influences on film thicknesses, and incorporating solution chemistry-dependent electrostatic potential at air-water interfaces. Capillary analysis of monodisperse packings of spherical grains provided estimated ranges of matric potentials where adsorbed films are stable, and showed that pendular rings within drained porous media retain most of the 'residual' water except under very low matric potentials. Within drained pores, capillary contributions to thinning of adsorbed films on spherical grains are shown to be small, such that DLVO calculations for flat surfaces are suitable approximations. Hamaker constants of common soil minerals were obtained to determine ranges of the dispersion component to matric potential-dependent film thickness. The pressure component associated with electrical double layer forces was estimated using the compression and linear superposition approximations. The pH-dependent electrical double layer pressure component is the dominant contribution to film thicknesses at intermediate values of matric potential, especially in lower ionic strength solutions (< 10 mol m{sup -3}) on surfaces with higher magnitude electrostatic potentials (more negative than - 50 mV). Adsorbed water films are predicted to usually range in thickness from 1 to 20 nm in drained pores and fractures of unsaturated environments.

  8. Shear-stress-induced structural arrangement of water molecules in nanoscale Couette flow with slipping at wall boundary

    SciTech Connect

    Lin, Jau-Wen

    2014-08-07

    This study investigated the structuring of water molecules in a nanoscale Couette flow with the upper plate subjected to lateral forces with various magnitudes and water slipping against a metal wall. It was found that when the upper plate is subjected to a force, the water body deforms into a parallelepiped. Water molecules in the channel are then gradually arranged into lattice positions, creating a layered structure. The structural arrangement of water molecules is caused by the water molecules accommodating themselves to the increase in energy under the application of a lateral force on the moving plate. The ordering arrangement of water molecules increases the rotational degree of freedom, allowing the molecules to increase their Coulomb potential energy through polar rotation that accounts for the energy input through the upper plate. With a force continuously applied to the upper plate, the water molecules in contact with the upper plate move forward until slip between the water and upper plate occurs. The relation between the structural arrangement of water molecules, slip at the wall, and the shear force is studied. The relation between the slip and the locking/unlocking of water molecules to metal atoms is also studied.

  9. Dynamics of water molecules adsorbed by silica and resin SGK-7

    NASA Astrophysics Data System (ADS)

    Lisichkin, Yu. V.; Sakharova, L. A.; Tumanov, A. A.

    2014-01-01

    This paper has presented neutron spectroscopy data on the dynamics of light water molecules adsorbed in the cation exchanger (ion-exchange resin) SGK-7 and on the surface of aerosils (highly dispersed pyrogenic silica) with different levels of hydration. The measurements have been performed on a DIN-2PI spectrometer (Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research, Dubna, Russia). The characteristics of the diffusive and vibrational motions of adsorbed water molecules have been determined from the experimental neutron scattering spectra. The data obtained in the quasi-elastic neutron scattering region have been analyzed using a model accounting for the effects of restricted translational and rotational diffusion. The results have demonstrated a significant decrease in the diffusion mobility of adsorbed water molecules as compared to conventional (bulk) water. In particular, the self-diffusion coefficient decreases several times, and the diffusion rate is the lower, the smaller is the thickness of the hydration layer. The dependences of the intensity and half-width of the quasi-elastic scattering peak on the magnitude of the neutron momentum transfer q in the scattering process exhibit a nonmonotonic character. This indicates manifestation of the effects of restricted translational diffusion, rotational diffusion, and jump diffusion. The partial distributions of vibrational frequencies of hydrogen atoms of water molecules adsorbed by the cation exchanger and aerosils have been obtained from the inelastic neutron scattering data.

  10. Local lateral environment of the molecules at the surface of DMSO-water mixtures.

    PubMed

    Fábián, Balázs; Idrissi, Abdenacer; Marekha, Bogdan; Jedlovszky, Pál

    2016-10-12

    Molecular dynamics simulations of the liquid-vapour interface of dimethyl sulphoxide (DMSO)-water mixtures of 11 different compositions, including two neat systems are performed on the canonical (N, V, T) ensemble at 298 K. The molecules constituting the surface layer of these systems are selected by means of the identification of the truly interfacial molecules (ITIM) method, and their local lateral environment at the liquid surface is investigated by performing Voronoi analysis. The obtained results reveal that both molecules prefer to be in a mixed local environment, consisting of both kinds of molecules, at the liquid surface, and this preference is even stronger here than in the bulk liquid phase. Neat-like patches, in which a molecule is surrounded by like neighbours, are not found. However, vacancies that are surrounded solely by water molecules are observed at the liquid surface. Our results show that strongly hydrogen bonded DMSO·H2O complexes, known to exist in the bulk phase of these mixtures, are absent from the liquid surface. PMID:27506283

  11. Effect of UV-C radiation and vapor released from a water hyacinth root absorbent containing bergamot oil to control mold on storage of brown rice.

    PubMed

    Songsamoe, Sumethee; Matan, Narumol; Matan, Nirundorn

    2016-03-01

    The aims of this study were to develop absorbent material from a water hyacinth root containing bergamot oil and to improve its antifungal activity by using ultraviolet C (UV-C) against the growth of A. flavus on the brown rice. Process optimization was studied by the immersion of a water hyacinth root into a water and bergamot oil (300, 500 and 700 μl ml(-1)). The root (absorbent material) was dried at 50, 70, and 90 °C for 10 min. Then, ultraviolet C (UV-C) was used for enhancing the antifungal activity of bergamot oil for 10, 15, and 20 min. The shelf-life of the brown rice with the absorbent after incubation at 25 ° C with 100 % RH for 12 weeks was also investigated. A microscope and a Fourier transform infrared spectroscopy (FTIR) were used to find out possible mode of action. Results indicated that the absorbent material produced from the water hyacinth root containing bergamot oil at 500 μl ml(-1) in the water solution, dried at 70 ° C and UV for 15 min showed the highest antifungal activity in a vapor phase against A. flavus on the brown rice. A microscopy investigation confirmed that the water hyacinth root could absorb bergamot oil from an outside water solution into root cells. Limonene in vapor phase was shown to be a stronger inhibitor than essential oil after UV-C radiation and should be the key factor in boosting bergamot oil antifungal activity. A vapor phase of bergamot oil could be released and inhibit natural mold on the surface of the brown rice for up to 12 weeks; without the absorbent, mold covered the brown rice in only 4 weeks. PMID:27570269

  12. An ab initio molecular dynamics study on hydrogen bonds between water molecules

    NASA Astrophysics Data System (ADS)

    Pan, Zhang; Chen, Jing; Lü, Gang; Geng, Yi-Zhao; Zhang, Hui; Ji, Qing

    2012-04-01

    The quantitative estimation of the total interaction energy of a molecular system containing hydrogen bonds (H bonds) depends largely on how to identify H bonding. The conventional geometric criteria of H bonding are simple and convenient in application, but a certain amount of non-H bonding cases are also identified as H bonding. In order to investigate the wrong identification, we carry out a systematic calculation on the interaction energy of two water molecules at various orientation angles and distances using ab initio molecular dynamics method with the dispersion correction for the Becke-Lee-Yang-Parr (BLYP) functionals. It is shown that, at many orientation angles and distances, the interaction energies of the two water molecules exceed the energy criterion of the H bond, but they are still identified as H-bonded by the conventional "distance-angle" criteria. It is found that in these non-H bonding cases the wrong identification is mainly caused by short-range interaction between the two neighbouring water molecules. We thus propose that, in addition to the conventional distance and angle criteria of H bonding, the distance dHṡṡṡH between the two neighbouring hydrogen atoms of the two water molecules should also be taken as a criterion, and the distance rOṡṡṡH between the hydrogen atom of the H-bond donor molecule and the oxygen atom of the acceptor molecule should be restricted by a lower limit. When dHṡṡṡH and rOṡṡṡH are small (e.g., dHṡṡṡH < 2.0 Å and rOṡṡṡH < 1.62 Å), the repulsion between the two neighbouring atoms increases the total energy of the two water molecules dramatically and apparently weakens the binding of the water dimer. A statistical analysis and comparison of the numbers of the H bonds identified by using different criteria have been conducted on a Car-Parrinello ab initio molecular dynamics simulation with dispersion correction for a system of 64 water molecules at near-ambient temperature. They

  13. Lipid-absorbing Polymers

    NASA Technical Reports Server (NTRS)

    Marsh, H. E., Jr.; Wallace, C. J.

    1973-01-01

    The removal of bile acids and cholesterol by polymeric absorption is discussed in terms of micelle-polymer interaction. The results obtained with a polymer composed of 75 parts PEO and 25 parts PB plus curing ingredients show an absorption of 305 to 309%, based on original polymer weight. Particle size effects on absorption rate are analyzed. It is concluded that crosslinked polyethylene oxide polymers will absorb water, crosslinked polybutadiene polymers will absorb lipids; neither polymer will absorb appreciable amounts of lipids from micellar solutions of lipids in water.

  14. Multiple-layer Radiation Absorber

    NASA Astrophysics Data System (ADS)

    Baker, Robert M. L.; Baker, Bonnie Sue

    A structure is discussed for absorbing incident radiation, either electromagnetic (EM) or sound. Such a surface structure is needed, for example, in a highly sensitive high-frequency gravitational wave or HFGW detector such as the Li-Baker. The multi-layer absorber, which is discussed, is constructed with metamaterial [MM] layer or layers on top. This MM is configured for a specific EM or sound radiation frequency band, which absorbs incident EM or sound radiation without reflection. Below these top MM layers is a substrate of conventional EM-radiation absorbing or acoustical absorbing reflective material, such as an array of pyramidal foam absorbers. Incident radiation is partially absorbed by the MM layer or layers, and then it is more absorbed by the lower absorbing and reflecting substrate. The remaining reflected radiation is even further absorbed by the MM layers on its "way out_ so that essentially all of the incident radiation is absorbed _ a nearly perfect black-body absorber. In a HFGW detector a substrate, such as foam absorbers, may outgas into a high vacuum and reduce the capability of the vacuum-producing equipment, however, the layers above this lowest substrate will seal the absorbing and reflecting substrate from any external vacuum. The layers also serve to seal the absorbing material against air or water flow past the surfaces of aircraft, watercraft or submarines. Other applications for such a multiple-level radiation absorber include stealth aircraft, missiles and submarines.

  15. DFTr optimization and DFTr-MD studies of glucose, ten explicit water molecules enclosed by an implicit solvent, COSMO

    Technology Transfer Automated Retrieval System (TEKTRAN)

    DFTr optimization studies are carried out on alpha/beta-glucose surrounded by ten explicit water molecules and the glucose/water super-molecule completely enclosed by an implicit solvation model, COSMO. Twenty one starting configurations of the explicit waters were first optimized empirically with t...

  16. Chemically accurate energy barriers of small gas molecules moving through hexagonal water rings.

    PubMed

    Hjertenæs, Eirik; Trinh, Thuat T; Koch, Henrik

    2016-07-21

    We present chemically accurate potential energy curves of CH4, CO2 and H2 moving through hexagonal water rings, calculated by CCSD(T)/aug-cc-pVTZ with counterpoise correction. The barriers are extracted from a potential energy surface obtained by allowing the water ring to expand while the gas molecule diffuses through. State-of-the-art XC-functionals are evaluated against the CCSD(T) potential energy surface. PMID:27345929

  17. Water-Soluble NIR-Absorbing Rylene Chromophores for Selective Staining of Cellular Organelles.

    PubMed

    Kaloyanova, Stefka; Zagranyarski, Yulian; Ritz, Sandra; Hanulová, Mária; Koynov, Kaloian; Vonderheit, Andreas; Müllen, Klaus; Peneva, Kalina

    2016-03-01

    Biocompatible organic dyes emitting in the near-infrared are highly desirable in fluorescence imaging techniques. Herein we report a synthetic approach for building novel small peri-guanidine-fused naphthalene monoimide and perylene monoimide chromophores. The presented structures possess near-infrared absorption and emission, high photostability, and good water solubility. After a fast cellular uptake, they selectively stain mitochondria with a low background in live and fixed cells. They can be additionally modified in a one-step reaction with functional groups for covalent labeling of proteins. The low cytotoxicity allows a long time exposure of live cells to the dyes without the necessity of washing. Successful application in localization super-resolution microscopy was demonstrated in phosphate-buffered saline without any reducing or oxidizing additives. PMID:26891229

  18. Theoretical study of the decomposition of formamide in the presence of water molecules.

    PubMed

    Nguyen, Vinh Son; Orlando, Thomas M; Leszczynski, Jerzy; Nguyen, Minh Tho

    2013-03-28

    Formamide (NH2CHO, FM) has been considered an active key precursor in prebiotic chemistry on early Earth. Under certain conditions such as dry lagoons, FM can decompose to produce reactants that lead to formation of more complex biomolecules. Specifically, FM decomposition follows many reactive channels producing small molecules such as H2, CO, H2O, HCN, HNC, NH3, and HNCO with comparable energy barriers in the range of 73-82 kcal/mol. Due to the likely presence of water on prebiotic Earth and the intrinsic presence of water following FM decomposition, we explore the effects of water oligomers, (H2O)n with n = 1-3, on its dehydration, dehydrogenation, and decarbonylation reactions using quantum chemical computations. Geometries are optimized using MP2/aug-cc-pVxZ calculations (x = D,T), and relative energies are evaluated using coupled-cluster theory CCSD(T) with the aug-cc-pVxZ basis sets (x = D, T, Q). Where possible the coupled-cluster energies are extrapolated to the complete basis set limit (CBS). Water classically acts as an efficient bifunctional catalyst for decomposition. With the presence of one water molecule, the dehydration pathway leading to HCN is favored. When two and three water molecules are involved, dehydration remains energetically favored over other channels and attains an energy barrier of ~30 kcal/mol. PMID:23461351

  19. Size, separation, structural order, and mass density of molecules packing in water and ice

    PubMed Central

    Huang, Yongli; Zhang, Xi; Ma, Zengsheng; Li, Wen; Zhou, Yichun; Zhou, Ji; Zheng, Weitao; Sun, Chang Q.

    2013-01-01

    The structural symmetry and molecular separation in water and ice remain uncertain. We present herewith a solution to unifying the density, the structure order and symmetry, the size (H-O length dH), and the separation (dOO = dL + dH or the O:H length dL) of molecules packing in water and ice in terms of statistic mean. This solution reconciles: i) the dL and the dH symmetrization of the O:H-O bond in compressed ice, ii) the dOO relaxation of cooling water and ice and, iii) the dOO expansion of a dimer and between molecules at water surface. With any one of the dOO, the density ρ(g·cm−3), the dL, and the dH, as a known input, one can resolve the rest quantities using this solution that is probing conditions or methods independent. We clarified that: i) liquid water prefers statistically the mono-phase of tetrahedrally-coordinated structure with fluctuation, ii) the low-density phase (supersolid phase as it is strongly polarized with even lower density) exists only in regions consisting molecules with fewer than four neighbors and, iii) repulsion between electron pairs on adjacent oxygen atoms dictates the cooperative relaxation of the segmented O:H-O bond, which is responsible for the performance of water and ice. PMID:24141643

  20. Temperature dependence of the transport of single-file water molecules through a hydrophobic channel.

    PubMed

    Su, Jiaye; Yang, Keda

    2016-05-01

    Although great effort has been made on the transport properties of water molecules through nanometer channels, our understanding on the effect of some basic parameters are still rather poor. In this article, we use molecular dynamics simulations to study the temperature effect on the transport of single-file water molecules through a hydrophobic channel. Of particular interest is that the water flow and average translocation time both exhibit exponential relations with the temperature. Based on the continuous-time random-walk model and Arrhenius equation, we explore some new physical insights on these exponential behaviors. With the increase of temperature, the water dipoles flip more frequently, since the estimated flipping barrier is less than 2 kB T. Specifically, the flipping frequency also shows an exponential relation with the temperature. Furthermore, the water-water interaction and water occupancy demonstrate linear relations with the temperature, and the water density profiles along the channel axis can be slightly affected by the temperature. These results not only enhance our knowledge about the temperature effect on the single-file water transport, but also have potential implications for the design of controllable nanofluidic machines. © 2016 Wiley Periodicals, Inc. PMID:26777386

  1. The Dynamics, energetics and selectivity of water chain-containing aquapores created by the self-assembly of aquafoldamer molecules.

    PubMed

    Ma, Wenliang; Wang, Chunquan; Li, Juntong; Zhang, Kun; Lu, Yu-Jing; Huo, Yanping; Zeng, Huaqiang

    2015-11-21

    Through a series of crystallographic snapshots of water chain-containing aquapores formed from numerous one-dimensionally aligned aquafoldamer molecules 2, we demonstrated here (1) a preferential recognition of the water molecules over methanol molecules by the assembled cavity-containing aquapores with a selectivity factor of at least 17.7, (2) the dynamic nature of the water chains and the aquapores in response to varying external stimuli that exert the most influential impact on the aromatic π-π stacking in the aquapores and (3) the aquapores undergo a significant rearrangement in order to accommodate water, rather than methanol, molecules. PMID:26381358

  2. Seasonal variations in the light-absorbing properties of water-soluble and insoluble organic aerosols in Seoul, Korea

    NASA Astrophysics Data System (ADS)

    Kim, Hwajin; Kim, Jin Young; Jin, Hyoun Cher; Lee, Ji Yi; Lee, Se Pyo

    2016-03-01

    The spectral properties of light-absorbing organic aerosol extractions were investigated using 24-h average fine particulate matter (PM2.5) measurements from October 2012 to September 2013 in Seoul, Korea. The light-absorption spectra of water and methanol extracts exhibited strong evidence of brown carbon with Absorption Angstrom Exponent (AAE; fitted between 300 and 700 nm) ranges of 5.84-9.17 and 4.08-5.75, with averages of 7.23 ± 1.58 and 5.05 ± 0.67, respectively. The light absorption of both extracts at 365 nm (Abs365), which is typically used as a proxy for brown carbon (BrC), displayed strong seasonal variations and was well correlated with both water-soluble organic carbon (WSOC; r = 0.81) and organic carbon (OC; r = 0.85), indicating that both primary and secondary organics were sources of BrC in this region. Normalizing the Abs365 of water and methanol extracts to the mass of WSOC and OC yielded average solution mass absorption efficiency (MAE365) of 0.28-1.18 and 0.44-1.45 m2 g-1 C, respectively. MAE365 in Korea were in the same range or slightly lower than those in China, however, despite the same ranges, the seasonal variations were different, suggesting that the sources of light absorbers could be different. Combining the AAE, Abs365, and MAE365 of both extracts and a detailed chemical speciation of filter extracts identified the compounds responsible for the temporal variations of BrC in Korea. During summer, secondary organic aerosol (SOA), photochemically generated from anthropogenic emissions, was the major source; however, during winter, long range transported organics or transported BrC seem to be a source of BrC in Korea, a downwind site of China, where severe smog and BrC were observed during this season. Biomass burning was also an important source; however, unlike in previous studies, where it was identified as a major source during winter, here, it contributed during the whole year. Although many of its properties, sources, and potential

  3. Augmented Z scheme blueprint for efficient solar water splitting system using quaternary chalcogenide absorber material.

    PubMed

    Sarswat, Prashant K; Bhattacharyya, Dhiman; Free, Michael L; Misra, Mano

    2016-02-01

    Photoelectrochemical hydrogen (H2) production from water is a key method of addressing energy needs using an environmentally friendly approach. In the last two decades we have witnessed the evolution of many different expensive catalysts, photoelectrodes and related technologies, especially those involving precious metals and use of acidic or basic electrolytes for hydrogen production. Cu2ZnSnS4 (CZTS) is a relatively new candidate in the category of efficient photocathodes, due to its high absorption coefficient and near optimal energy band gap. In this paper, we demonstrate photoelectrochemical viability of CZTS in combination with other photoanodes such as TiO2, BiVO4, and WO3 for H2 production with the use of an electrolyte of near neutral pH, a single redox mediator, and insignificant potential biasing. A systematic study was performed to understand CZTS performance with each photoanode, band energetics of CZTS with other photoanodes, impedance behavior of each photoelectrode, and utility of a CZTS photocell in place of a CZTS photocathode. Our assessment indicates that a protected CZTS photocell performs well when used in a Z-scheme containing TiO2 nanotubular array-CZTS or nanocrystalline WO3-CZTS. Preliminary experiments indicated that apart from band energetics, porosity and effective surface area of the photoanodes play a crucial role in determining the photoelectrochemical performance of the system. PMID:26762553

  4. On Spectral Invariance of Single Scattering Albedo for Water Droplets and Ice Crystals at Weakly Absorbing Wavelengths

    NASA Technical Reports Server (NTRS)

    Marshak, Alexander; Knyazikhin, Yuri; Chiu, J. Christine; Wiscombe, Warren J.

    2012-01-01

    The single scattering albedo omega(sub O lambda) in atmospheric radiative transfer is the ratio of the scattering coefficient to the extinction coefficient. For cloud water droplets both the scattering and absorption coefficients, thus the single scattering albedo, are functions of wavelength lambda and droplet size r. This note shows that for water droplets at weakly absorbing wavelengths, the ratio omega(sub O lambda)(r)/omega(sub O lambda)(r (sub O)) of two single scattering albedo spectra is a linear function of omega(sub O lambda)(r). The slope and intercept of the linear function are wavelength independent and sum to unity. This relationship allows for a representation of any single scattering albedo spectrum omega(sub O lambda)(r) via one known spectrum omega(sub O lambda)(r (sub O)). We provide a simple physical explanation of the discovered relationship. Similar linear relationships were found for the single scattering albedo spectra of non-spherical ice crystals.

  5. Trapped water molecule in the charge separation of a bacterial reaction center.

    PubMed

    Ivashin, Nikolai; Larsson, Sven

    2008-09-25

    Low-frequency oscillations in the absorption spectrum at 1020 nm, connected to the primary charge separation process in Rhodobacter sphaeroides, have been shown by Yakovlev et al. to be caused by rotational motion of an interstitial water molecule called "water-A". The same water molecule was shown by Potter et al. to increase the rate of charge separation by a factor of 8. We have carried out geometry optimization of water-A and its nearest atoms in the protein pocket, using density functional theory (DFT). There are strong hydrogen bonds to the axial imidazol group of the B part of the special pair (P=PAPB) and to the keto carbonyl group of ring V of the accessory chlorophyll (BA). Rotation of water-A is thus impossible in the electronic ground state. We have tried to support our speculations on other possible mechanisms by calculations. The P(+)BA(-) charge transfer state is stabilized by proton transfer from water-A and simultaneous proton transfer from the axial group of PB to water-A. After double proton transfer the hydrogen bond to the keto group disappears whereby a possibility opens up for almost free water rotation. The results therefore would explain the 32 cm(-1) oscillation of Yakovlev et al. The proposed mechanism assumes, however, that the general assumption that the activation energy disappears in the primary charge separation of bacterial photosynthesis, holds also for this special case. PMID:18761433

  6. Trapping and desorption of complex organic molecules in water at 20 K

    NASA Astrophysics Data System (ADS)

    Burke, Daren J.; Puletti, Fabrizio; Woods, Paul M.; Viti, Serena; Slater, Ben; Brown, Wendy A.

    2015-10-01

    The formation, chemical, and thermal processing of complex organic molecules (COMs) is currently a topic of much interest in interstellar chemistry. The isomers glycolaldehyde, methyl formate, and acetic acid are particularly important because of their role as pre-biotic species. It is becoming increasingly clear that many COMs are formed within interstellar ices which are dominated by water. Hence, the interaction of these species with water ice is crucially important in dictating their behaviour. Here, we present the first detailed comparative study of the adsorption and thermal processing of glycolaldehyde, methyl formate, and acetic acid adsorbed on and in water ices at astrophysically relevant temperatures (20 K). We show that the functional group of the isomer dictates the strength of interaction with water ice, and hence the resulting desorption and trapping behaviour. Furthermore, the strength of this interaction directly affects the crystallization of water, which in turn affects the desorption behaviour. Our detailed coverage and composition dependent data allow us to categorize the desorption behaviour of the three isomers on the basis of the strength of intermolecular and intramolecular interactions, as well as the natural sublimation temperature of the molecule. This categorization is extended to other C, H, and O containing molecules in order to predict and describe the desorption behaviour of COMs from interstellar ices.

  7. Disintegration of water molecules in a steam-plasma torch powered by microwaves

    SciTech Connect

    Uhm, Han S.; Kim, Jong H.; Hong, Yong C.

    2007-07-15

    A pure steam torch is generated by making use of 2.45 GHz microwave. Steam from a steam generator enters the discharge tube as a swirl gas at a temperature higher than 150 deg. C. This steam becomes a working gas and produces a stable steam torch. The torch volume is almost linearly proportional to the microwave power. The temperature of the torch flame is measured by making use of optical spectroscopy and a thermocouple device. Two distinctive regions are exhibited, a bright, whitish region of a high-temperature zone and a reddish, dimmer region of a relatively low-temperature zone. The bright, whitish region is a typical torch based on plasma species and the reddish, dimmer region is hydrogen burning in oxygen. Study of water molecule disintegration and gas temperature effects on the molecular fraction characteristics in steam-plasma of a microwave plasma torch at the atmospheric pressure is carried out. An analytical investigation of water disintegration indicates that a substantial fraction of water molecules disintegrate and form other compounds at high temperatures in the steam-plasma torch. Emission profiles of the hydroxide radical and water molecules confirm the theoretical predictions of water disintegration in the torch.

  8. A systematic method for studying the spatial distribution of water molecules around nucleic acid bases.

    PubMed Central

    Schneider, B; Cohen, D M; Schleifer, L; Srinivasan, A R; Olson, W K; Berman, H M

    1993-01-01

    A new method to analyze the distribution of water molecules around the bases in DNA is presented. This method relies on the notion of a "hydrated building block," which represents the joint observed hydration around all bases of a particular type, in structures of a particular conformation type. The hydrated building blocks were constructed using atomic coordinates from 40 structures contained in the Nucleic Acid Database. Pseudoelectron densities were calculated for water molecules in each hydrated building block using standard crystallographic procedures. The electron densities were fitted to obtain "average building blocks," which represent bases with waters only at average or probable positions. Both types of building blocks were used to construct models of hydrated DNA oligomers. The essential features of the solvent structure around d(CGCGAATTCGCG)2 in the B form and d(CGCGCG)2 in the Z form were reproduced. Images FIGURE 4 FIGURE 5 PMID:8312469

  9. Monte Carlo simulation of several biologically relevant molecules and zwitterions in water

    NASA Astrophysics Data System (ADS)

    Patuwo, Michael Y.; Bettens, Ryan P. A.

    2012-02-01

    In this work, we study the hydration free energies of butane, zwitterionic alanine, valine, serine, threonine, and asparagine, and two neuraminidase inhibitors by means of Monte Carlo (MC) simulation. The solute molecule, represented in the form of distributed multipoles and modified 6-12 potential, was varied from a non-interacting 'ghost' molecule to its full potential functions in TIP4P water. Intermediate systems with soft-core solute-solvent interaction potentials are simulated separately and then subjected to Bennett's Acceptance ratio (BAR) for the free energy calculation. Hydration shells surrounding the solute particles were used to assess the quality of potential functions.

  10. Structure detection in a libration vibration spectrum of water molecules by methods of nonlinear optics

    SciTech Connect

    Babenko, V A; Sychev, Andrei A

    2012-09-30

    In exciting water possessing an enhanced optical strength by the radiation of a YAG : Nd{sup 3+} laser with 20-ps pulses, nonlinear scattering of light was detected in the frequency range of the optical second harmonic. A relationship was established of the signal of the nonlinear scattering with a stimulated Raman scattering (SRS) of the laser radiation in water. Near the SRS threshold, the structure was observed in the spectrum of nonlinear scattering, which is related to intermolecular libration vibrations of water molecules. (laser applications and other topics in quantum electronics)

  11. Water-inducing molecular self-assembly of amphiphilic molecules into nanofibers

    SciTech Connect

    Zhang, Weiguang; Zhao, Pusu; Song, Jie

    2011-12-15

    Graphical abstract: TPDP nanofibers with smooth surfaces can be obtained by reprecipitation method using ethanol as good solvent and water as poor solvent. In the self-assembly process, during the water adding to the amphiphilic molecules' saturated solution, the amphiphilic molecules firstly assembled into needle-like small rods. With an increase in the self-assembled time, a large number of the nanofibers are produced. The assembly behavior was revealed in the course of direct in situ monitoring of its growth with optical microscopy. Highlights: Black-Right-Pointing-Pointer 2,3,6,7-Tetramethoxy-9,10-di(4-pyridyl)-9,10-dihydroanthracen (TPDP) was synthesized. Black-Right-Pointing-Pointer TPDP nanofibers can be obtained by reprecipitation method. Black-Right-Pointing-Pointer The assembly behavior was revealed in situ monitoring with optical microscopy. -- Abstract: We present investigations on the microcosmic self-assembly process of new synthesized amphiphilic TPDP molecules. It can be seen that pure TPDP nanofibers with smooth surfaces can be obtained by reprecipitation method using ethanol as good solvent and water as poor solvent. In the self-assembly process, during the water adding to the amphiphilic molecules' saturated solution, the amphiphilic molecules firstly assembled into needle-like small rods. With an increase in the self-assembled time, a large number of the nanofibers are produced. The assembly behavior was revealed in the course of direct in situ monitoring of its growth with optical microscopy. Field emission scanning electron microscopy was adopted to characterize the morphologies of the products.

  12. Molecular mimicry of substrate oxygen atoms by water molecules in the beta-amylase active site.

    PubMed

    Pujadas, G; Palau, J

    2001-08-01

    Soybean beta-amylase (EC 3.2.1.2) has been crystallized both free and complexed with a variety of ligands. Four water molecules in the free-enzyme catalytic cleft form a multihydrogen-bond network with eight strategic residues involved in enzyme-ligand hydrogen bonds. We show here that the positions of these four water molecules are coincident with the positions of four potential oxygen atoms of the ligands within the complex. Some of these waters are displaced from the active site when the ligands bind to the enzyme. How many are displaced depends on the shape of the ligand. This means that when one of the four positions is not occupied by a ligand oxygen atom, the corresponding water remains. We studied the functional/structural role of these four waters and conclude that their presence means that the conformation of the eight side chains is fixed in all situations (free or complexed enzyme) and preserved from unwanted or forbidden conformational changes that could hamper the catalytic mechanism. The water structure at the active pocket of beta-amylase is therefore essential for providing the ligand recognition process with plasticity. It does not affect the protein active-site geometry and preserves the overall hydrogen-bonding network, irrespective of which ligand is bound to the enzyme. We also investigated whether other enzymes showed a similar role for water. Finally, we discuss the potential use of these results for predicting whether water molecules can mimic ligand atoms in the active center. PMID:11468361

  13. Single-molecule redox blinking of perylene diimide derivatives in water.

    PubMed

    Cordes, Thorben; Vogelsang, Jan; Anaya, Milena; Spagnuolo, Carla; Gietl, Andreas; Summerer, Wolfram; Herrmann, Andreas; Müllen, Klaus; Tinnefeld, Philip

    2010-02-24

    Dynamic developments in ultrasensitive and superresolution fluorescence microscopy call for improved fluorescence markers with increased photostability and new functionalities. We used single-molecule spectroscopy to study water-soluble perylene dicarboximide fluorophores (PDI), which were immobilized in aqueous buffer by attaching the fluorophore to DNA. Under these conditions bright fluorescence, comparable to that of single-molecule compatible organic fluorophores, is observed with homogeneous spectral and fluorescence decay time distributions. We additionally show how the fluorescence of the PDI can be controlled through photoinduced electron-transfer reactions by using different concentrations of reductants and oxidants, yielding either blinking or stable emission. We explain these properties by the redox potentials of PDI and the recently introduced ROXS (reducing and oxidizing system) concept. Finally, we evaluate how this fluorescence control of PDIs can be used for superresolution "Blink-Microscopy" in aqueous or organic media and more generally for single-molecule spectroscopy. PMID:20121094

  14. [Development of the 60Co gamma-ray standard field for therapy-level dosimeter calibration in terms of absorbed dose to water (N(D,w))].

    PubMed

    Fukumura, Akifumi; Mizuno, Hideyuki; Fukahori, Mai; Sakata, Suoh

    2012-01-01

    A primary standard for the absorbed dose rate to water in a 60Co gamma-ray field was established at National Metrology Institute of Japan (NMIJ) in fiscal year 2011. Then, a 60Co gamma-ray standard field for therapy-level dosimeter calibration in terms of absorbed dose to water was developed at National Institute of Radiological Sciences (NIRS) as a secondary standard dosimetry laboratory (SSDL). The results of an IAEA/WHO TLD SSDL audit demonstrated that there was good agreement between NIRS stated absorbed dose to water and IAEA measurements. The IAEA guide based on the ISO standard was used to estimate the relative expanded uncertainty of the calibration factor for a therapy-level Farmer type ionization chamber in terms of absorbed dose to water (N(D,w)) with the new field. The uncertainty of N(D,w) was estimated to be 1.1% (k = 2), which corresponds to approximately one third of the value determined in the existing air kerma field. The dissemination of traceability of the calibration factor determined in the new field is expected to diminish the uncertainty of dose delivered to patients significantly. PMID:24568023

  15. INTERSTELLAR ICES AS WITNESSES OF STAR FORMATION: SELECTIVE DEUTERATION OF WATER AND ORGANIC MOLECULES UNVEILED

    SciTech Connect

    Cazaux, S.; Spaans, M.; Caselli, P.

    2011-11-10

    Observations of star-forming environments revealed that the abundances of some deuterated interstellar molecules are markedly larger than the cosmic D/H ratio of 10{sup -5}. Possible reasons for this pointed to grain surface chemistry. However, organic molecules and water, which are both ice constituents, do not enjoy the same deuteration. For example, deuterated formaldehyde is very abundant in comets and star-forming regions, while deuterated water rarely is. In this paper, we explain this selective deuteration by following the formation of ices (using the rate equation method) in translucent clouds, as well as their evolution as the cloud collapses to form a star. Ices start with the deposition of gas-phase CO and O onto dust grains. While reaction of oxygen with atoms (H or D) or molecules (H{sub 2}) yields H{sub 2}O (HDO), CO only reacts with atoms (H and D) to form H{sub 2}CO (HDCO, D{sub 2}CO). As a result, the deuteration of formaldehyde is sensitive to the gas D/H ratio as the cloud undergoes gravitational collapse, while the deuteration of water strongly depends on the dust temperature at the time of ice formation. These results reproduce well the deuterium fractionation of formaldehyde observed in comets and star-forming regions and can explain the wide spread of deuterium fractionation of water observed in these environments.

  16. Bias-dependent local structure of water molecules at an electrochemical interface

    NASA Astrophysics Data System (ADS)

    Pedroza, Luana; Brandimarte, Pedro; Rocha, Alexandre R.; Fernandez-Serra, Marivi

    2015-03-01

    Following the need for new - and renewable - sources of energy worldwide, fuel cells using electrocatalysts can be thought of as a viable option. Understanding the local structure of water molecules at the interfaces of the metallic electrodes is a key problem. Notably the system is under an external potential bias, which makes the task of simulating this setup difficult. A first principle description of all components of the system is the most appropriate methodology in order to advance understanding of electrochemical processes. There, the metal is usually charged. To correctly compute the effect of an external bias potential applied to electrodes, we combine density functional theory (DFT) and non-equilibrium Green's functions methods (NEGF), with and without van der Waals interactions. In this work, we apply this methodology to study the electronic properties and forces of one water molecule and water monolayer at the interface of gold electrodes. We find that the water molecule has a different torque direction depending on the sign of the bias applied. We also show that it changes the position of the most stable configuration indicating that the external bias plays an important role in the structural properties of the interface. We acknowledge financial support from FAPESP.

  17. Theoretical and experimental investigation of the interactions between [emim]Ac and water molecules

    NASA Astrophysics Data System (ADS)

    Ding, Zhen-Dong; Chi, Zhen; Gu, Wen-Xiu; Gu, Sheng-Ming; Wang, Hai-Jun

    2012-05-01

    Density functional theory (DFT) calculations, atom in molecules (AIM) theory, natural bond orbital (NBO) analysis and infrared (IR) spectroscopy were performed to investigate the interactions between water molecules and ionic liquid 1-ethyl-3-methylimidazolium acetate ([emim]Ac). It was found that [emim]Ac interacts with water molecules mainly via H-bonds, and the anionic part of [emim]Ac plays a major role in the interaction with H2O. The energies of H-bonds were estimated from spectral shifts of hydroxy antisymmetric stretching vibration. Moreover, the experimental results also indicated that hydroxy of water mainly interacts with the COO- of [emim]Ac. Further studies indicated that the intensity of hydroxy stretching vibrations tend to be stronger with the increase of the concentration of water. In addition, the frequency of hydroxy stretching vibrations showed clearly red-shift, and the COO- vibrational frequency gradually shifted to the lower wavenumber region, which were indicative of extended hydrogen bonded network.

  18. Grand canonical Monte Carlo simulation of the adsorption isotherms of water molecules on model soot particles

    NASA Astrophysics Data System (ADS)

    Moulin, F.; Picaud, S.; Hoang, P. N. M.; Jedlovszky, P.

    2007-10-01

    The grand canonical Monte Carlo method is used to simulate the adsorption isotherms of water molecules on different types of model soot particles. The soot particles are modeled by graphite-type layers arranged in an onionlike structure that contains randomly distributed hydrophilic sites, such as OH and COOH groups. The calculated water adsorption isotherm at 298K exhibits different characteristic shapes depending both on the type and the location of the hydrophilic sites and also on the size of the pores inside the soot particle. The different shapes of the adsorption isotherms result from different ways of water aggregation in or/and around the soot particle. The present results show the very weak influence of the OH sites on the water adsorption process when compared to the COOH sites. The results of these simulations can help in interpreting the experimental isotherms of water adsorbed on aircraft soot.

  19. Anomalous and anisotropic nanoscale diffusion of hydration water molecules in fluid lipid membranes.

    PubMed

    Toppozini, Laura; Roosen-Runge, Felix; Bewley, Robert I; Dalgliesh, Robert M; Perring, Toby; Seydel, Tilo; Glyde, Henry R; García Sakai, Victoria; Rheinstädter, Maikel C

    2015-11-14

    We have studied nanoscale diffusion of membrane hydration water in fluid-phase lipid bilayers made of 1,2-dimyristoyl-3-phosphocholine (DMPC) using incoherent quasi-elastic neutron scattering. Dynamics were fit directly in the energy domain using the Fourier transform of a stretched exponential. By using large, 2-dimensional detectors, lateral motions of water molecules and motions perpendicular to the membranes could be studied simultaneously, resulting in 2-dimensional maps of relaxation time, τ, and stretching exponent, β. We present experimental evidence for anomalous (sub-diffusive) and anisotropic diffusion of membrane hydration water molecules over nanometer distances. By combining molecular dynamics and Brownian dynamics simulations, the potential microscopic origins for the anomaly and anisotropy of hydration water were investigated. Bulk water was found to show intrinsic sub-diffusive motion at time scales of several picoseconds, likely related to caging effects. In membrane hydration water, however, the anisotropy of confinement and local dynamical environments leads to an anisotropy of relaxation times and stretched exponents, indicative of anomalous dynamics. PMID:26338138

  20. Structure and dynamics of water and lipid molecules in charged anionic DMPG lipid bilayer membranes

    NASA Astrophysics Data System (ADS)

    Rønnest, A. K.; Peters, G. H.; Hansen, F. Y.; Taub, H.; Miskowiec, A.

    2016-04-01

    Molecular dynamics simulations have been used to investigate the influence of the valency of counter-ions on the structure of freestanding bilayer membranes of the anionic 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) lipid at 310 K and 1 atm. At this temperature, the membrane is in the fluid phase with a monovalent counter-ion and in the gel phase with a divalent counter-ion. The diffusion constant of water as a function of its depth in the membrane has been determined from mean-square-displacement calculations. Also, calculated incoherent quasielastic neutron scattering functions have been compared to experimental results and used to determine an average diffusion constant for all water molecules in the system. On extrapolating the diffusion constants inferred experimentally to a temperature of 310 K, reasonable agreement with the simulations is obtained. However, the experiments do not have the sensitivity to confirm the diffusion of a small component of water bound to the lipids as found in the simulations. In addition, the orientation of the dipole moment of the water molecules has been determined as a function of their depth in the membrane. Previous indirect estimates of the electrostatic potential within phospholipid membranes imply an enormous electric field of 108-109 V m-1, which is likely to have great significance in controlling the conformation of translocating membrane proteins and in the transfer of ions and molecules across the membrane. We have calculated the membrane potential for DMPG bilayers and found ˜1 V (˜2 ṡ 108 V m-1) when in the fluid phase with a monovalent counter-ion and ˜1.4 V (˜2.8 ṡ 108 V m-1) when in the gel phase with a divalent counter-ion. The number of water molecules for a fully hydrated DMPG membrane has been estimated to be 9.7 molecules per lipid in the gel phase and 17.5 molecules in the fluid phase, considerably smaller than inferred experimentally for 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine (DMPC

  1. A graphite calorimeter for absolute measurements of absorbed dose to water: application in medium-energy x-ray filtered beams.

    PubMed

    Pinto, M; Pimpinella, M; Quini, M; D'Arienzo, M; Astefanoaei, I; Loreti, S; Guerra, A S

    2016-02-21

    The Italian National Institute of Ionizing Radiation Metrology (ENEA-INMRI) has designed and built a graphite calorimeter that, in a water phantom, has allowed the determination of the absorbed dose to water in medium-energy x-rays with generating voltages from 180 to 250 kV. The new standard is a miniaturized three-bodies calorimeter, with a disc-shaped core of 21 mm diameter and 2 mm thickness weighing 1.134 g, sealed in a PMMA waterproof envelope with air-evacuated gaps. The measured absorbed dose to graphite is converted into absorbed dose to water by means of an energy-dependent conversion factor obtained from Monte Carlo simulations. Heat-transfer correction factors were determined by FEM calculations. At a source-to-detector distance of 100 cm, a depth in water of 2 g cm(-2), and at a dose rate of about 0.15 Gy min(-1), results of calorimetric measurements of absorbed dose to water, D(w), were compared to experimental determinations, D wK, obtained via an ionization chamber calibrated in terms of air kerma, according to established dosimetry protocols. The combined standard uncertainty of D(w) and D(wK) were estimated as 1.9% and 1.7%, respectively. The two absorbed dose to water determinations were in agreement within 1%, well below the stated measurement uncertainties. Advancements are in progress to extend the measurement capability of the new in-water-phantom graphite calorimeter to other filtered medium-energy x-ray qualities and to reduce the D(w) uncertainty to around 1%. The new calorimeter represents the first implementation of in-water-phantom graphite calorimetry in the kilovoltage range and, allowing independent determinations of D(w), it will contribute to establish a robust system of absorbed dose to water primary standards for medium-energy x-ray beams. PMID:26841127

  2. Chemical characteristics and light-absorbing property of water-soluble organic carbon in Beijing: Biomass burning contributions

    NASA Astrophysics Data System (ADS)

    Yan, Caiqing; Zheng, Mei; Sullivan, Amy P.; Bosch, Carme; Desyaterik, Yury; Andersson, August; Li, Xiaoying; Guo, Xiaoshuang; Zhou, Tian; Gustafsson, Örjan; Collett, Jeffrey L.

    2015-11-01

    Emissions from biomass burning contribute significantly to water-soluble organic carbon (WSOC) and light-absorbing organic carbon (brown carbon). Ambient atmospheric samples were collected at an urban site in Beijing during winter and summer, along with source samples from residential crop straw burning. Carbonaceous aerosol species, including organic carbon (OC), elemental carbon (EC), WSOC and multiple saccharides as well as water-soluble potassium (K+) in PM2.5 (fine particulate matter with size less than 2.5 μm) were measured. Chemical signatures of atmospheric aerosols in Beijing during winter and summer days with significant biomass burning influence were identified. Meanwhile, light absorption by WSOC was measured and quantitatively compared to EC at ground level. The results from this study indicated that levoglucosan exhibited consistently high concentrations (209 ± 145 ng m-3) in winter. Ratios of levoglucosan/mannosan (L/M) and levoglucosan/galacosan (L/G) indicated that residential biofuel use is an important source of biomass burning aerosol in winter in Beijing. Light absorption coefficient per unit ambient WSOC mass calculated at 365 nm is approximately 1.54 ± 0.16 m2 g-1 in winter and 0.73 ± 0.15 m2 g-1 in summer. Biomass burning derived WSOC accounted for 23 ± 7% and 16 ± 7% of total WSOC mass, and contributed to 17 ± 4% and 19 ± 5% of total WSOC light absorption in winter and summer, respectively. It is noteworthy that, up to 30% of total WSOC light absorption was attributed to biomass burning in significant biomass-burning-impacted summer day. Near-surface light absorption (over the range 300-400 nm) by WSOC was about ∼40% of that by EC in winter and ∼25% in summer.

  3. Versatile Small Molecule Motifs for Self-assembly in Water and Formation of Biofunctional Supramolecular Hydrogels

    PubMed Central

    Zhang, Ye; Kuang, Yi; Gao, Yuan; Xu, Bing

    2010-01-01

    This article introduces new structural motifs (referred as “samogen”) that serve as the building blocks of hydrogelators for molecular self-assembly in water to result in a series of supramolecular hydrogels. Using a compound that consists of two phenylalanine residues and a naphthyl group (also abbreviated as NapFF (1) in this text) as an example of the samogens, we demonstrated the ability of the samogens to convert bioactive molecules into molecular hydrogelators that self-assemble in water to result in nanofibers. By briefly summarizing the properties and applications (e.g., wound healing, drug delivery, controlling cell fate, typing bacteria, and catalysis) of these molecular hydrogelators derived from the samogens, we intend to illustrate the basic requirements and promises of the small molecule hydrogelators for applications in chemistry, materials science, and biomedicine. PMID:20608718

  4. Orientation and alignment effects in electron-induced ionization of a single oriented water molecule

    SciTech Connect

    Champion, C.; Rivarola, R. D.

    2010-10-15

    We here report a theoretical study about the orientation effect on the total ionization cross sections for a single oriented water molecule. The theoretical description of the ionization process is performed within the first Born framework with a collisional system including an initial state composed of a projectile and a water target molecule described by a plane wave and an accurate one-center molecular wave function, respectively, and a final state constituted by a slow ejected electron represented by a Coulomb wave and a scattered (fast) electron projectile described by a plane wave. Secondary electron energetic distributions as well as total cross sections are then compared for particular target configurations pointing out strong alignment and orientation effects on the description of the ionization process.

  5. Water molecule-enhanced CO{sub 2} insertion in lanthanide coordination polymers

    SciTech Connect

    Luo Liushan; Huang Xiaoyuan; Wang Ning; Wu Hongyan; Chen Wenbin; Feng Zihao; Zhu Huiping; Peng Xiaoling; Li Yongxian; Huang Ling; Yue Shantang; Liu Yingliang

    2009-08-15

    Two new lanthanide coordination polymers H{sub 2}N(CH{sub 3}){sub 2}.[Eu{sup III}{sub 2}(L{sub 1}){sub 3}(L{sub 2})] (1, L{sub 1}=isophthalic acid dianion, L{sub 2}=formic acid anion) and [La{sup III}(2,5-PDC)(L{sub 2})](2, 2,5-PDC=2,5-pyridinedicarboxylate dianion) were synthesized under solvothermal conditions. It is of interest that the formic ligand (L{sub 2}) is not contained in the stating materials, but arises from the water molecule-enhanced CO{sub 2} insertion during the solvothermal process. Both of the two compounds exhibit complicated three dimensional sandwich-like frameworks. - Graphical abstract: Two new lanthanide coordination polymers involving water molecule-enhanced CO{sub 2} insertion resulting in the formation of formic anion and dimethylammonium cation were synthesized under solvothermal conditions.

  6. Diagrammatic perturbation theory applied to the ground state of the water molecule

    NASA Technical Reports Server (NTRS)

    Silver, D. M.; Wilson, S.

    1977-01-01

    The diagrammatic many-body perturbation theory is applied to the ground state of the water molecule within the algebraic approximation. Using four different basis sets, the total energy, the equilibrium OH bond length, and the equilibrium HOH bond angle are examined. The latter is found to be a particularly sensitive test of the convergence of perturbation expansions. Certain third-order results, which incorporate all two-, three-, and four-body effects, show evidence of good convergence properties.

  7. Double ionization of single oriented water molecules by electron impact: Second-order Born description

    SciTech Connect

    Dal Cappello, C.; Champion, C.; Kada, I.; Mansouri, A.

    2011-06-15

    The double ionization of isolated water molecules fixed in space is investigated within a theoretical approach based on the second-order Born approximation. Electron angular distributions have been studied for specific kinematical conditions. The three usual mechanisms, the shake-off and the two two-step mechanisms, have been identified. A significant contribution of the two-step mechanism is clearly visible for some particular kinematics.

  8. Organic molecules and water in the planet formation region of young circumstellar disks.

    PubMed

    Carr, John S; Najita, Joan R

    2008-03-14

    The chemical composition of protoplanetary disks is expected to hold clues to the physical and chemical processes that influence the formation of planetary systems. However, characterizing the gas composition in the planet formation region of disks has been a challenge to date. We report here that the protoplanetary disk within 3 astronomical units of AA Tauri possesses a rich molecular emission spectrum in the mid-infrared, indicating a high abundance of simple organic molecules (HCN, C2H2, and CO2), water vapor, and OH. These results suggest that water is abundant throughout the inner disk and that the disk supports an active organic chemistry. PMID:18339932

  9. Infrared spectroscopy of water clusters co-adsorbed with hydrogen molecules on a sodium chloride film

    NASA Astrophysics Data System (ADS)

    Yamakawa, Koichiro; Fukutani, Katsuyuki

    2016-06-01

    Hydrogen gas containing a trace of water vapor was dosed on a vacuum-evaporated sodium chloride film at 13 K, and water clusters formed on the substrate were investigated by infrared absorption spectroscopy. Absorption bands due to (H2O)n clusters with n = 3-6 and an induced absorption band due to hydrogen were clearly observed. With increasing gas dosage, the intensities of the cluster bands increased linearly while the intensity of the hydrogen band was constant. This suggests that the water clusters were formed in two-dimensional matrices of hydrogen. We found that the water clusters did exist on the surface upon heating even after the hydrogen molecules had desorbed. A further rise of the substrate temperature up to 27 K yielded the formation of larger clusters, (H2O)n with n > 6 . We also discuss the origins of the two bands of the trimer in terms of pseudorotation and a metastable isomer.

  10. Experimental Evaluation of Proposed Small-Molecule Inhibitors of Water Channel Aquaporin-1.

    PubMed

    Esteva-Font, Cristina; Jin, Byung-Ju; Lee, Sujin; Phuan, Puay-Wah; Anderson, Marc O; Verkman, A S

    2016-06-01

    The aquaporin-1 (AQP1) water channel is a potentially important drug target, as AQP1 inhibition is predicted to have therapeutic action in edema, tumor growth, glaucoma, and other conditions. Here, we measured the AQP1 inhibition efficacy of 12 putative small-molecule AQP1 inhibitors reported in six recent studies, and one AQP1 activator. Osmotic water permeability was measured by stopped-flow light scattering in human and rat erythrocytes that natively express AQP1, in hemoglobin-free membrane vesicles from rat and human erythrocytes, and in plasma membrane vesicles isolated from AQP1-transfected Chinese hamster ovary cell cultures. As a positive control, 0.3 mM HgCl2 inhibited AQP1 water permeability by >95%. We found that none of the tested compounds at 50 µM significantly inhibited or increased AQP1 water permeability in these assays. Identification of AQP1 inhibitors remains an important priority. PMID:26993802

  11. WScore: A Flexible and Accurate Treatment of Explicit Water Molecules in Ligand-Receptor Docking.

    PubMed

    Murphy, Robert B; Repasky, Matthew P; Greenwood, Jeremy R; Tubert-Brohman, Ivan; Jerome, Steven; Annabhimoju, Ramakrishna; Boyles, Nicholas A; Schmitz, Christopher D; Abel, Robert; Farid, Ramy; Friesner, Richard A

    2016-05-12

    We have developed a new methodology for protein-ligand docking and scoring, WScore, incorporating a flexible description of explicit water molecules. The locations and thermodynamics of the waters are derived from a WaterMap molecular dynamics simulation. The water structure is employed to provide an atomic level description of ligand and protein desolvation. WScore also contains a detailed model for localized ligand and protein strain energy and integrates an MM-GBSA scoring component with these terms to assess delocalized strain of the complex. Ensemble docking is used to take into account induced fit effects on the receptor conformation, and protein reorganization free energies are assigned via fitting to experimental data. The performance of the method is evaluated for pose prediction, rank ordering of self-docked complexes, and enrichment in virtual screening, using a large data set of PDB complexes and compared with the Glide SP and Glide XP models; significant improvements are obtained. PMID:27054459

  12. Sound Absorbers

    NASA Astrophysics Data System (ADS)

    Fuchs, H. V.; Möser, M.

    Sound absorption indicates the transformation of sound energy into heat. It is, for instance, employed to design the acoustics in rooms. The noise emitted by machinery and plants shall be reduced before arriving at a workplace; auditoria such as lecture rooms or concert halls require a certain reverberation time. Such design goals are realised by installing absorbing components at the walls with well-defined absorption characteristics, which are adjusted for corresponding demands. Sound absorbers also play an important role in acoustic capsules, ducts and screens to avoid sound immission from noise intensive environments into the neighbourhood.

  13. Ultrafast Raman-induced Kerr-effect of water: Single molecule versus collective motions

    NASA Astrophysics Data System (ADS)

    Winkler, Kathrin; Lindner, Jörg; Bürsing, Helge; Vöhringer, Peter

    2000-09-01

    The ultrafast optical Kerr-response of water and heavy water has been measured at 1 bar in the temperature range between 273 and 373 K. The nuclear Kerr response of the liquid exhibits a pronounced double exponential decay on longer time scales after dephasing of impulsively perturbed acoustic modes is completed. The time constant, τ2, characterizing the slowly decaying exponential component of the Kerr-response function is in quantitative agreement with rotational diffusion time constants of the water molecules obtained form nuclear magnetic resonance (NMR) spin-lattice relaxation rates. A detailed comparison with THz time domain spectroscopy demonstrates that the reorientational dynamics responsible for the long time tail of the Kerr response are due to single molecule as opposed to collective effects. Furthermore, a good agreement between the single molecule rotational diffusion and the Stokes-Einstein-Debye equation is found in the temperature range of thermodynamic stability of the liquid. The time constant, τ1, characterizing the fast exponential component of the Kerr-response of water is found to be in qualitative agreement with central Lorentzian linewidths obtained from frequency-domain, depolarized Raman scattering experiments. The temperature dependence of τ2 does not follow an Arrhenius-type behavior, which was previously taken as evidence for thermally activated crossing of a librational barrier with concomitant hydrogen-bond breakage. Instead, the temperature dependence of the fast relaxation time constant can be represented adequately by the Speedy-Angell relation which has been shown to accurately describe a number of transport parameters and thermodynamic properties of water.

  14. Absorbed dose to water determination with ionization chamber dosimetry and calorimetry in restricted neutron, photon, proton and heavy-ion radiation fields.

    PubMed

    Brede, H J; Greif, K-D; Hecker, O; Heeg, P; Heese, J; Jones, D T L; Kluge, H; Schardt, D

    2006-08-01

    Absolute dose measurements with a transportable water calorimeter and ionization chambers were performed at a water depth of 20 mm in four different types of radiation fields, for a collimated (60)Co photon beam, for a collimated neutron beam with a fluence-averaged mean energy of 5.25 MeV, for collimated proton beams with mean energies of 36 MeV and 182 MeV at the measuring position, and for a (12)C ion beam in a scanned mode with an energy per atomic mass of 430 MeV u(-1). The ionization chambers actually used were calibrated in units of air kerma in the photon reference field of the PTB and in units of absorbed dose to water for a Farmer-type chamber at GSI. The absorbed dose to water inferred from calorimetry was compared with the dose derived from ionometry by applying the radiation-field-dependent parameters. For neutrons, the quantities of the ICRU Report 45, for protons the quantities of the ICRU Report 59 and for the (12)C ion beam, the recommended values of the International Atomic Energy Agency (IAEA) protocol (TRS 398) were applied. The mean values of the absolute absorbed dose to water obtained with these two independent methods agreed within the standard uncertainty (k = 1) of 1.8% for calorimetry and of 3.0% for ionometry for all types and energies of the radiation beams used in this comparison. PMID:16861773

  15. Absorbed dose-to-water protocol applied to synchrotron-generated x-rays at very high dose rates.

    PubMed

    Fournier, P; Crosbie, J C; Cornelius, I; Berkvens, P; Donzelli, M; Clavel, A H; Rosenfeld, A B; Petasecca, M; Lerch, M L F; Bräuer-Krisch, E

    2016-07-21

    Microbeam radiation therapy (MRT) is a new radiation treatment modality in the pre-clinical stage of development at the ID17 Biomedical Beamline of the European synchrotron radiation facility (ESRF) in Grenoble, France. MRT exploits the dose volume effect that is made possible through the spatial fractionation of the high dose rate synchrotron-generated x-ray beam into an array of microbeams. As an important step towards the development of a dosimetry protocol for MRT, we have applied the International Atomic Energy Agency's TRS 398 absorbed dose-to-water protocol to the synchrotron x-ray beam in the case of the broad beam irradiation geometry (i.e. prior to spatial fractionation into microbeams). The very high dose rates observed here mean the ion recombination correction factor, k s , is the most challenging to quantify of all the necessary corrections to apply for ionization chamber based absolute dosimetry. In the course of this study, we have developed a new method, the so called 'current ramping' method, to determine k s for the specific irradiation and filtering conditions typically utilized throughout the development of MRT. Using the new approach we deduced an ion recombination correction factor of 1.047 for the maximum ESRF storage ring current (200 mA) under typical beam spectral filtering conditions in MRT. MRT trials are currently underway with veterinary patients at the ESRF that require additional filtering, and we have estimated a correction factor of 1.025 for these filtration conditions for the same ESRF storage ring current. The protocol described herein provides reference dosimetry data for the associated Treatment Planning System utilized in the current veterinary trials and anticipated future human clinical trials. PMID:27366861

  16. Absorbed dose-to-water protocol applied to synchrotron-generated x-rays at very high dose rates

    NASA Astrophysics Data System (ADS)

    Fournier, P.; Crosbie, J. C.; Cornelius, I.; Berkvens, P.; Donzelli, M.; Clavel, A. H.; Rosenfeld, A. B.; Petasecca, M.; Lerch, M. L. F.; Bräuer-Krisch, E.

    2016-07-01

    Microbeam radiation therapy (MRT) is a new radiation treatment modality in the pre-clinical stage of development at the ID17 Biomedical Beamline of the European synchrotron radiation facility (ESRF) in Grenoble, France. MRT exploits the dose volume effect that is made possible through the spatial fractionation of the high dose rate synchrotron-generated x-ray beam into an array of microbeams. As an important step towards the development of a dosimetry protocol for MRT, we have applied the International Atomic Energy Agency’s TRS 398 absorbed dose-to-water protocol to the synchrotron x-ray beam in the case of the broad beam irradiation geometry (i.e. prior to spatial fractionation into microbeams). The very high dose rates observed here mean the ion recombination correction factor, k s , is the most challenging to quantify of all the necessary corrections to apply for ionization chamber based absolute dosimetry. In the course of this study, we have developed a new method, the so called ‘current ramping’ method, to determine k s for the specific irradiation and filtering conditions typically utilized throughout the development of MRT. Using the new approach we deduced an ion recombination correction factor of 1.047 for the maximum ESRF storage ring current (200 mA) under typical beam spectral filtering conditions in MRT. MRT trials are currently underway with veterinary patients at the ESRF that require additional filtering, and we have estimated a correction factor of 1.025 for these filtration conditions for the same ESRF storage ring current. The protocol described herein provides reference dosimetry data for the associated Treatment Planning System utilized in the current veterinary trials and anticipated future human clinical trials.

  17. Single-Molecule Imaging of DNAs with Sticky Ends at Water/Fused Silica Interface

    SciTech Connect

    Slavica Isailovic

    2005-12-17

    Total internal reflection fluorescence microscopy (TIRFM) was used to study intermolecular interactions of DNAs with unpaired (sticky) ends of different lengths at water/fused silica interface at the single-molecule level. Evanescent field residence time, linear velocity and adsorption/desorption frequency were measured in a microchannel for individual DNA molecules from T7, Lambda, and PSP3 phages at various pH values. The longest residence times and the highest adsorption/desorption frequencies at the constant flow at pH 5.5 were found for PSP3 DNA, followed by lower values for Lambda DNA, and the lowest values for T7 DNA. Since T7, Lambda, and PSP3 DNA molecules contain none, twelve and nineteen unpaired bases, respectively, it was concluded that the affinity of DNAs for the surface increases with the length of the sticky ends. This confirms that hydrophobic and hydrogen-bonding interactions between sticky ends and fused-silica surface are driving forces for DNA adsorption at the fused-silica surface. Described single-molecule methodology and results therein can be valuable for investigation of interactions in liquid chromatography, as well as for design of DNA hybridization sensors and drug delivery systems.

  18. SU-E-T-516: Measurement of the Absorbed Dose Rate in Water Under Reference Conditions in a CyberKnife Unit

    SciTech Connect

    Aragon-Martinez, N; Hernandez-Guzman, A; Gomez-Munoz, A; Massillon-JL, G

    2014-06-01

    Purpose: This paper aims to measure the absorbed-dose-rate in a CyberKnife unit reference-field (6cm diameter) using three ionization chambers (IC) following the new IAEA/AAPM formalism and Gafchromic film (MD-V3-55 and EBT3) protocol according to our work reported previously. Methods: The absorbed-dose-rates were measured at 90cm and 70cm SSD in a 10cmx10cm field and at 70cm SSD in a 5.4cmx5.4cm equivalent to 6cm diameter field using a linac Varian iX. All measurements were performed at 10cm depth in water. The correction factors that account for the difference between the IC response on the reference field and the CyberKnife reference field, k-(Q-msr,Q)^(f-msr,f-ref), were evaluated and Gafchromic film were calibrated using the results obtained above. Under the CyberKnife reference conditions, the factors were used to measure the absorbed-dose-rate with IC according to the new formalism and the calibrated film was irradiated in water. The film calibration curve was used to evaluate the absorbed-dose-rate in the CyberKnife unit. Results: Difference up to 2.56% is observed between dose-rate measured with IC in the reference 10cmx10cm field, depending where the chamber was calibrated, which was not reflected in the correction factor k-(Q-msr,Q)^(f-msr,f-ref ) where variations of ~0.15%-0.5% were obtained. Within measurements uncertainties, maximum difference of 1.8% on the absorbed-dose-rate in the CyberKnife reference field is observed between all IC and the films Conclusion: Absorbed-dose-rate to water was measured in a CyberKnife reference field with acceptable accuracy (combined uncertainties ~1.32%-1.73%, k=1) using three IC and films. The MD-V3-55 film as well as the new IAEA/AAPM formalism can be considered as a suitable dosimetric method to measure absorbed-dose-rate to water in small and non-standard CyberKnife fields used in clinical treatments However, the EBT3 film is not appropriated due to the high uncertainty provided (combined uncertainty ~9%, k=1

  19. Atomic force microscopy study of nitrogen molecule self-assembly at the HOPG-water interface

    NASA Astrophysics Data System (ADS)

    Lu, Yi-Hsien; Yang, Chih-Wen; Hwang, Ing-Shouh

    2014-06-01

    In this work, we investigated the evolution of the graphite-water interface in a nitrogen atmosphere by using frequency-modulation atomic force microscopy (FM-AFM). A highly ordered pyrolytic graphite (HOPG) sample was immersed in pre-degassed water and subsequently placed in the nitrogen environment. The dissolved nitrogen molecules diffused in water and self-assembled into ordered row-like structural domains at the interface. Nucleation and growth processes of the domains were observed. When the coverage of the ordered structure surpassed 50%, small clusters began to appear on the ordered structure. The number density of the clusters increases as the coverage of the ordered structures increases and these clusters may hop on the ordered structures. A model is proposed to explain the evolution of the nitrogen molecule self-assembly process at the interface. The observation of nitrogen clusters may shed light on the nature and nucleation of the so-called nanobubbles at hydrophobic-water interfaces.

  20. CVRQD ab initio ground-state adiabatic potential energy surfaces for the water molecule.

    PubMed

    Barletta, Paolo; Shirin, Sergei V; Zobov, Nikolai F; Polyansky, Oleg L; Tennyson, Jonathan; Valeev, Edward F; Császár, Attila G

    2006-11-28

    The high accuracy ab initio adiabatic potential energy surfaces (PESs) of the ground electronic state of the water molecule, determined originally by Polyansky et al. [Science 299, 539 (2003)] and called CVRQD, are extended and carefully characterized and analyzed. The CVRQD potential energy surfaces are obtained from extrapolation to the complete basis set of nearly full configuration interaction valence-only electronic structure computations, augmented by core, relativistic, quantum electrodynamics, and diagonal Born-Oppenheimer corrections. We also report ab initio calculations of several quantities characterizing the CVRQD PESs, including equilibrium and vibrationally averaged (0 K) structures, harmonic and anharmonic force fields, harmonic vibrational frequencies, vibrational fundamentals, and zero-point energies. They can be considered as the best ab initio estimates of these quantities available today. Results of first-principles computations on the rovibrational energy levels of several isotopologues of the water molecule are also presented, based on the CVRQD PESs and the use of variational nuclear motion calculations employing an exact kinetic energy operator given in orthogonal internal coordinates. The variational nuclear motion calculations also include a simplified treatment of nonadiabatic effects. This sophisticated procedure to compute rovibrational energy levels reproduces all the known rovibrational levels of the water isotopologues considered, H(2) (16)O, H(2) (17)O, H(2) (18)O, and D(2) (16)O, to better than 1 cm(-1) on average. Finally, prospects for further improvement of the ground-state adiabatic ab initio PESs of water are discussed. PMID:17144700

  1. Comparison between absorbed dose to water standards established by water calorimetry at the LNE-LNHB and by application of international air-kerma based protocols for kilovoltage medium energy x-rays

    NASA Astrophysics Data System (ADS)

    Perichon, N.; Rapp, B.; Denoziere, M.; Daures, J.; Ostrowsky, A.; Bordy, J.-M.

    2013-05-01

    Nowadays, the absorbed dose to water for kilovoltage x-ray beams is determined from standards in terms of air-kerma by application of international dosimetry protocols. New standards in terms of absorbed dose to water has just been established for these beams at the LNE-LNHB, using water calorimetry, at a depth of 2 cm in water in accordance with protocols. The aim of this study is to compare these new standards in terms of absorbed dose to water, to the dose values calculated from the application of four international protocols based on air-kerma standards (IAEA TRS-277, AAPM TG-61, IPEMB and NCS-10). The acceleration potentials of the six beams studied are between 80 and 300 kV with half-value layers between 3.01 mm of aluminum and 3.40 mm of copper. A difference between the two methods smaller than 2.1% was reported. The standard uncertainty of water calorimetry being below 0.8%, and the one associated with the values from protocols being around 2.5%, the results are in good agreement. The calibration coefficients of some ionization chambers in terms of absorbed dose to water, established by application of calorimetry and air-kerma based dosimetry protocols, were also compared. The best agreement with the calibration coefficients established by water calorimetry was found for those established with the AAPM TG-61 protocol.

  2. Vibrational spectra and molecular dynamics of hydrogen peroxide molecules at quartz/water interfaces

    NASA Astrophysics Data System (ADS)

    Lv, Ye-qing; Zheng, Shi-li; Wang, Shao-na; Yan, Wen-yi; Zhang, Yi; Du, Hao

    2016-06-01

    The influence of H2O2 on the water vibration at quartz interface was examined using sum-frequency generation (SFG) spectroscopy, and the effect of H2O2 concentration has been systematically studied. Further, the number density and radical distribution of water molecules, H2O2 molecules, and quartz surface silanol groups were calculated using molecular dynamics (MD) simulation to provide molecular level interpretation for the SFG spectra. It is concluded from this study that the hydrogen peroxide molecules prefers to donate H-bonds to the in-plane silanol groups rather than accepting H-bonds from out-of-plane silanol groups, as evidenced by the strengthening of the peak located at 3400 cm-1 assigned to "liquid-like" hydrogen-bonding network. The SFG results have been supported by the MD calculation results, which demonstrate that the relative intensity of the peak located at 3400 cm-1 to that of located at 3200 cm-1 increases monotonously with the increase in the number of hydrogen peroxide in the first hydration shell of silanol.

  3. Effects of a single water molecule on the OH + H2O2 reaction.

    PubMed

    Buszek, Robert J; Torrent-Sucarrat, Miquel; Anglada, Josep M; Francisco, Joseph S

    2012-06-21

    The effect of a single water molecule on the reaction between H(2)O(2) and HO has been investigated by employing MP2 and CCSD(T) theoretical approaches in connection with the aug-cc-PVDZ, aug-cc-PVTZ, and aug-cc-PVQZ basis sets and extrapolation to an ∞ basis set. The reaction without water has two elementary reaction paths that differ from each other in the orientation of the hydrogen atom of the hydroxyl radical moiety. Our computed rate constant, at 298 K, is 1.56 × 10(-12) cm(3) molecule(-1) s(-1), in excellent agreement with the suggested value by the NASA/JPL evaluation. The influence of water vapor has been investigated by considering either that H(2)O(2) first forms a complex with water that reacts with hydroxyl radical or that H(2)O(2) reacts with a previously formed H(2)O·OH complex. With the addition of water, the reaction mechanism becomes much more complex, yielding four different reaction paths. Two pathways do not undergo the oxidation reaction but an exchange reaction where there is an interchange between H(2)O(2)·H(2)O and H(2)O·OH complexes. The other two pathways oxidize H(2)O(2), with a computed total rate constant of 4.09 × 10(-12) cm(3) molecule(-1) s(-1) at 298 K, 2.6 times the value of the rate constant of the unassisted reaction. However, the true effect of water vapor requires taking into account the concentration of the prereactive bimolecular complex, namely, H(2)O(2)·H(2)O. With this consideration, water can actually slow down the oxidation of H(2)O(2) by OH between 1840 and 20.5 times in the 240-425 K temperature range. This is an example that demonstrates how water could be a catalyst in an atmospheric reaction in the laboratory but is slow under atmospheric conditions. PMID:22455374

  4. Influence of water on the mobility of small molecules dispersed in a polymeric system.

    PubMed

    Le Meste, M; Voilley, A; Colas, B

    1991-01-01

    The rotational mobility of paramagnetic solutes dispersed in partially hydrated macromolecules (proteins, polysaccharides, synthetic polymers) was measured using Electron Spin Resonance. A critical minimum amount of water was observed to be necessary for these molecules to reach a level of mobility of the same order as in dilute solutions. This amount of water depended on the size of the diffusing solute and on the microporosity of the macromolecule. Above this critical moisture range, a progressive increase of the proportion of mobile solute occurred over a hydration range determined by the size of the diffusing solute. At the same time, the rotational diffusivity of the mobile solute increased linearly with water content. The mobilization pattern of spin-labelled side chains of caseinates was observed to be similar to that of the solute. Results are discussed with reference to free volume theory. PMID:1660672

  5. Interactions of water, methanol and diethyl ether molecules with the surface of oxidized activated carbon

    NASA Astrophysics Data System (ADS)

    Salame, Issa I.; Bandosz, Teresa J.

    Two samples of oxidized activated carbon of wood origin were used as adsorbents of water, methanol, and diethyl ether. Structural and chemical characteristics of the samples' surfaces were obtained using adsorption of nitrogen and Boehm titration. The adsorption isotherms of water and methanol were measured using a volumetric apparatus whereas the adsorption of diethyl ether was studied by means of inverse gas chromatography at finite concentration. Then the isotherms at three different temperatures were used to calculate the isosteric heats of adsorption. The results showed that the strength of interaction depends on the porosity of the sample and its surface chemistry. The effect of surface chemistry and the presence of oxygenated groups are predominant in the case of water and the least important in the case of diethyl ether. This is the result of the chemical nature of the molecules, their sizes, and the relative strengths of the dispersive interactions in small pores in comparison with hydrogen bonding to surface functional groups.

  6. Single molecule force spectroscopy by AFM indicates helical structure of poly(ethylene-glycol) in water

    NASA Astrophysics Data System (ADS)

    Oesterhelt, F.; Rief, M.; Gaub, H. E.

    1999-03-01

    We elongated individual poly(ethylene-glycol) (PEG) molecules tethered at one end to an AFM cantilever. We observed the resistive force as a function of elongation in different solvents. In all cases the molecular response was found to be fully reversible and thus in thermodynamic equilibrium. In hexadecane the stretched PEG acts like an ideal entropy spring and can be well described as a freely jointed chain. In water we observed marked deviations in the transition region from entropic to enthalpic elasticity, indicating the deformation of a supra-structure within the polymer. An analysis based on elastically coupled Markovian two-level systems agrees well with recent ab initio calculations predicting that PEG in water forms a non-planar supra-structure which is stabilized by water bridges. We obtained a binding free energy of 3.0+/-0.3 kT.

  7. Shape-selective adsorption of aromatic molecules from water by tetramethylammonium-smectite

    USGS Publications Warehouse

    Lee, J.; Mortland, M.M.; Boyd, S.A.; Chiou, C.T.

    1989-01-01

    The adsorption of aromatic compounds by smectite exchanged with tetramethylammonium (TMA) has been studied. Aromatic compounds adsorbed by TMA-smectite are assumed to adopt a tilted orientation in a face-to-face arrangment with the TMA tetrahedra. The sorptive characteristics of TMA-smectite were influenced strongly by the presence of water. The dry TMA-smectite showed little selectivity in the uptake of benzen, toluene and xylene. In the presence of water, TMA-smectite showed a high degree of selectivity based on molecular size/shape, resulting in high uptake of benzene and progressively lower uptake of larger aromatic molecules. This selectivity appeared to result from the shrinkage of interlamellar cavities by water.

  8. Influence of the water molecules near surface of viral protein on virus activation process

    NASA Astrophysics Data System (ADS)

    Shepelenko, S. O.; Salnikov, A. S.; Rak, S. V.; Goncharova, E. P.; Ryzhikov, A. B.

    2009-06-01

    The infection of a cell with influenza virus comprises the stages of receptor binding to the cell membrane, endocytosis of virus particle, and fusion of the virus envelope and cell endosome membrane, which is determined by the conformational changes in hemagglutinin, a virus envelope protein, caused by pH decrease within the endosome. The pH value that induces conformation rearrangements of hemagglutinin molecule considerably varies for different influenza virus strains, first and foremost, due to the differences in amino acid structure of the corresponding proteins. The main goal of this study was to construct a model making it possible to assess the critical pH value characterizing the fusogenic activity of influenza virus hemagglutinin from the data on hemagglutinin structure and experimental verification of this model. Under this model, we assume that when the electrostatic force between interacting hemagglutinin molecules in the virus envelop exceeds a certain value, the hemagglutinin HA1 subunits are arranged so that they form a cavity sufficient for penetration of water molecules. This event leads to an irreversible hydration of the inner fragments of hemagglutinin molecule in a trimer and to the completion of conformational changes. The geometry of electrostatic field in hemagglutinin trimer was calculated taking into account the polarization effects near the interface of two dielectrics, aqueous medium and protein macromolecule. The critical pH values for the conformational changes in hemagglutinin were measured by the erythrocyte hemolysis induced by influenza virus particles when decreasing pH. The critical pH value conditionally separating the pH range into the regions with and without the conformational changes was calculated for several influenza virus H1N1 and H3N2 strains based on the data on the amino acid structure of the corresponding hemagglutinin molecules. Comparison of the theoretical and experimental values of critical pH values for

  9. 22 GHz water maser search in 37 nearby galaxies. Four new water megamasers in Seyfert 2 and OH maser/absorber galaxies

    NASA Astrophysics Data System (ADS)

    Wagner, J.

    2013-12-01

    Aims: We report four new 22 GHz H2O water masers found in a Green Bank Telescope search toward 37 nearby objects. Our goal was to find new maser galaxies, active galactic nucleus (AGN) disk masers, and objects where hydroxyl and water maser species coexist. Methods: We observed 37 sources within 250 Mpc that were selected by high X-ray luminosity (LX > 1040 W) and high absorbing column density (NH ≳ 1022 cm-2). Sources included dual or triple AGN and interacting systems. We also searched objects detected in hydroxyl (OH). A catalog of 4038 known H2O (non)detections was assembled to avoid unnecessary reobservations. The final selection consisted of 16 new sources, 13 nondetections to follow up with a factor 10 higher sensitivity, 10 OH masers and 1 deep OH absorber, of which 37 were observed. Results: Water megamasers were detected towards the Sy 2 galaxy 2MFGC 13581, towards the 6 GHz OH absorber NGC 4261 and towards the two 1.6 GHz OH maser sources IRAS 17526+3253 and IRAS 20550+1656. We set upper limits on 33 nondetections. The detection rate was 25% in OH galaxies and 11% overall. The mean sensitivity was 4 mJy over 24.4 kHz (0.31 km s-1) or between 0.1 L⊙ and 1.0 L⊙ rms for the distances covered by the source sample. Combined with other searches, a total of 95 objects have now been searched for both OH and H2O masers. Conclusions: The maser features in 2MFGC 13581 are typical of a sub-parsec accretion disk, whereas NGC 4261 likely has jet masers in a masing torus. The NGC 4261 galaxy (3C 270; dusty torus, twin jet) and its masers appear similar to NGC 1052, where continuum seed emission by a twin jet supports masers in the torus. Imaging with very long baseline interferometry is required to determine the masing regions in NGC 4261 and 2MFGC 13581. IRAS 17526+3253 has narrow 350 L⊙ systemic masers, and the tentative 5σ detection in IRAS 20550+1656 (II Zw 96) strongly resembles massive star formation kilomasers in NGC 2146. The latter two detections

  10. Dependence of Yb-169 absorbed dose energy correction factors on self-attenuation in source material and photon buildup in water

    SciTech Connect

    Medich, David C.; Munro, John J. III

    2010-05-15

    Purpose: Absorbed dose energy correction factors, used to convert the absorbed dose deposited in a LiF thermoluminescent dosimeter (TLD) into the clinically relevant absorbed dose to water, were obtained for both spherical volumetric sources and for the model 4140 HDR Yb-169 source. These correction factors have a strong energy dependence below 200 keV; therefore, spectral changes were quantified as Yb-169 photons traveled through both source material (Yb{sub 2}O{sub 3}) and water with the corresponding absorbed dose energy correction factors, f(r,{theta}), calculated as a function of location in a phantom. Methods: Using the MCNP5 Monte Carlo radiation transport simulation program, the Yb-169 spectrum emerging from spherical Yb{sub 2}O{sub 3} sources (density 6.9 g/cm{sup 3}) with radii between 0.2 and 0.9 mm were analyzed and their behavior compared against those for a point-source. The absorbed dose deposited to both LiF and H{sub 2}O materials was analyzed at phantom depths of 0.1-10 cm for each source radius and the absorbed dose energy correction factor calculated as the ratio of the absorbed dose to water to that of LiF. Absorbed dose energy correction factors for the Model 4140 Yb-169 HDR brachytherapy source similarly were obtained and compared against those calculated for the Model M-19 Ir-192 HDR source. Results: The Yb-169 average spectral energy, emerging from Yb{sub 2}O{sub 3} spherical sources 0.2-0.9 mm in radius, was observed to harden from 7% to 29%; as these photons traveled through the water phantom, the photon average energy softened by as much as 28% at a depth of 10 cm. Spectral softening was dependent on the measurement depth in the phantom. Energy correction factors were found to vary both as a function of source radius and phantom depth by as much as 10% for spherical Yb{sub 2}O{sub 3} sources. The Model 4140 Yb-169 energy correction factors depended on both phantom depth and reference angle and were found to vary by more than 10% between

  11. Determination of absorbed dose to water around a clinical HDR {sup 192}Ir source using LiF:Mg,Ti TLDs demonstrates an LET dependence of detector response

    SciTech Connect

    Carlsson Tedgren, Aasa; Elia, Rouba; Hedtjaern, Haakan; Olsson, Sara; Alm Carlsson, Gudrun

    2012-02-15

    Purpose: Experimental radiation dosimetry with thermoluminescent dosimeters (TLDs), calibrated in a {sup 60}Co or megavoltage (MV) photon beam, is recommended by AAPM TG-43U1for verification of Monte Carlo calculated absorbed doses around brachytherapy sources. However, it has been shown by Carlsson Tedgren et al.[Med. Phys. 38, 5539-5550 (2011)] that for TLDs of LiF:Mg,Ti, detector response was 4% higher in a {sup 137}Cs beam than in a {sup 60}Co one. The aim of this work was to investigate if similar over-response exists when measuring absorbed dose to water around {sup 192}Ir sources, using LiF:Mg,Ti dosimeters calibrated in a 6 MV photon beam. Methods: LiF dosimeters were calibrated to measure absorbed dose to water in a 6 MV photon beam and used to measure absorbed dose to water at distances of 3, 5, and 7 cm from a clinical high dose rate (HDR) {sup 192}Ir source in a polymethylmethacrylate (PMMA) phantom. Measured values were compared to values of absorbed dose to water calculated using a treatment planning system (TPS) including corrections for the difference in energy absorption properties between calibration quality and the quality in the users'{sup 192}Ir beam and for the use of a PMMA phantom instead of the water phantom underlying dose calculations in the TPS. Results: Measured absorbed doses to water around the {sup 192}Ir source were overestimated by 5% compared to those calculated by the TPS. Corresponding absorbed doses to water measured in a previous work with lithium formate electron paramagnetic resonance (EPR) dosimeters by Antonovic et al. [Med. Phys. 36, 2236-2247 (2009)], using the same irradiation setup and calibration procedure as in this work, were 2% lower than those calculated by the TPS. The results obtained in the measurements in this work and those obtained using the EPR lithium formate dosimeters were, within the expanded (k = 2) uncertainty, in agreement with the values derived by the TPS. The discrepancy between the results using

  12. Measurement of absorbed dose-to-water for an HDR {sup 192}Ir source with ionization chambers in a sandwich setup

    SciTech Connect

    Araki, Fujio; Kouno, Tomohiro; Ohno, Takeshi; Kakei, Kiyotaka; Yoshiyama, Fumiaki; Kawamura, Shinji

    2013-09-15

    Purpose: In this study, a dedicated device for ion chamber measurements of absorbed dose-to-water for a Nucletron microSelectron-v2 HDR {sup 192}Ir brachytherapy source is presented. The device uses two ionization chambers in a so-called sandwich assembly. Using this setup and by taking the average reading of the two chambers, any dose error due to difficulties in absolute positioning (centering) of the source in between the chambers is cancelled to first order. The method's accuracy was examined by comparing measurements with absorbed dose-to-water determination based on the AAPM TG-43 protocol.Methods: The optimal source-to-chamber distance (SCD) for {sup 192}Ir dosimetry was determined from ion chamber measurements in a water phantom. The {sup 192}Ir source was sandwiched between two Exradin A1SL chambers (0.057 cm{sup 3}) at the optimal SCD separation. The measured ionization was converted to the absorbed dose-to-water using a {sup 60}Co calibration factor and a Monte Carlo-calculated beam quality conversion factor, k{sub Q}, for {sup 60}Co to {sup 192}Ir. An uncertainty estimate of the proposed method was determined based on reproducibility of measurements at different institutions for the same type of source.Results: The optimal distance for the A1SL chamber measurements was determined to be 5 cm from the {sup 192}Ir source center, considering the depth dependency of k{sub Q} for {sup 60}Co to {sup 192}Ir and the chamber positioning. The absorbed dose to water measured at (5 cm, 90°) on the transverse axis was 1.3% lower than TG-43 values and its reproducibility and overall uncertainty were 0.8% and 1.7%, respectively. The measurement doses at anisotropic points agreed within 1.5% with TG-43 values.Conclusions: The ion chamber measurement of absorbed dose-to-water with a sandwich method for the {sup 192}Ir source provides a more accurate, direct, and reference dose compared to the dose-to-water determination based on air-kerma strength in the TG-43 protocol

  13. The Effect of Water Molecules on Mechanical Properties of Bamboo Microfibrils

    NASA Astrophysics Data System (ADS)

    Rahbar, Nima

    Bamboo fibers have higher strength-to-weight ratios than steel and concrete. The unique properties of bamboo fibers come from their natural composite structures that comprise mainly cellulose nanofibrils in a matrix of intertwined hemicellulose and lignin called lignin-carbohydrate complex (LCC). Here, we have utilized atomistic simulations to investigate the mechanical properties and mechanisms of interactions between these materials, in the presence of water molecules. Our results suggest that hemicellulose exhibits better mechanical properties and lignin shows greater tendency to adhere to cellulose nanofibrils. Consequently, the role of hemicellulose found to be enhancing the mechanical properties and lignin found to be providing the strength of bamboo fibers. The abundance of Hbonds in hemicellulose chains is responsible for improving the mechanical behavior of LCC. The strong van der Waals forces between lignin molecules and cellulose nanofibrils is responsible for higher adhesion energy between LCC/cellulose nanofibrils. We also found out that the amorphous regions of cellulose nanofibrils is the weakest interface in bamboo Microfibrils. In presence of water, the elastic modulus of lignin increases at low water content (less than 10 NSF CAREER Grant No. 1261284.

  14. Test conditions greatly influence permeation of water soluble molecules through the intestinal mucosa: need for standardisation.

    PubMed Central

    Peeters, M; Hiele, M; Ghoos, Y; Huysmans, V; Geboes, K; Vantrappen, G; Rutgeerts, P

    1994-01-01

    Permeability tests are widely used to investigate the pathogenesis of various gastrointestinal diseases including coeliac disease, infectious diarrhoea, and inflammatory bowel disease. In Crohn's disease they are used as activity parameters by some investigators. Lack of standardisation, however, makes it very difficult to compare data reported in different studies. The aim of this study was to gather permeation data in well controlled test conditions to standardise the methods. Nine healthy volunteers each received five consecutive permeability tests by mouth using polyethylene glycol-400 (PEG-400) and 51Cr-EDTA as probe molecules. The probes were dissolved in water, a glucose solution, a starch solution, a hyperosmolar lactulose-mannitol solution, and a liquid meal. A significantly decreased permeation for both probes was found when given with the hyperosmolar solution. The 51Cr-EDTA permeation was also decreased with water. The permeability index, 51Cr-EDTA/PEG-400, corrected for influencing factors, confirmed that the lactulose-mannitol solution and plain water yield lower values of macro-molecule permeation than starch, glucose or liquid meal. Hyperosmolarity was clearly accompanied by a decrease in permeability probably caused by reversed solvent drag. Interindividual variability of probe permeation and permeability index is very low with a standard liquid meal. It is proposed that for permeability studies a standard liquid meal is always used. PMID:7959195

  15. Test conditions greatly influence permeation of water soluble molecules through the intestinal mucosa: need for standardisation.

    PubMed

    Peeters, M; Hiele, M; Ghoos, Y; Huysmans, V; Geboes, K; Vantrappen, G; Rutgeerts, P

    1994-10-01

    Permeability tests are widely used to investigate the pathogenesis of various gastrointestinal diseases including coeliac disease, infectious diarrhoea, and inflammatory bowel disease. In Crohn's disease they are used as activity parameters by some investigators. Lack of standardisation, however, makes it very difficult to compare data reported in different studies. The aim of this study was to gather permeation data in well controlled test conditions to standardise the methods. Nine healthy volunteers each received five consecutive permeability tests by mouth using polyethylene glycol-400 (PEG-400) and 51Cr-EDTA as probe molecules. The probes were dissolved in water, a glucose solution, a starch solution, a hyperosmolar lactulose-mannitol solution, and a liquid meal. A significantly decreased permeation for both probes was found when given with the hyperosmolar solution. The 51Cr-EDTA permeation was also decreased with water. The permeability index, 51Cr-EDTA/PEG-400, corrected for influencing factors, confirmed that the lactulose-mannitol solution and plain water yield lower values of macro-molecule permeation than starch, glucose or liquid meal. Hyperosmolarity was clearly accompanied by a decrease in permeability probably caused by reversed solvent drag. Interindividual variability of probe permeation and permeability index is very low with a standard liquid meal. It is proposed that for permeability studies a standard liquid meal is always used. PMID:7959195

  16. Intramolecular cyclization of aspartic acid residues assisted by three water molecules: a density functional theory study

    NASA Astrophysics Data System (ADS)

    Takahashi, Ohgi; Kirikoshi, Ryota

    2014-01-01

    Aspartic acid (Asp) residues in peptides and proteins (l-Asp) are known to undergo spontaneous nonenzymatic reactions to form l-β-Asp, d-Asp, and d-β-Asp residues. The formation of these abnormal Asp residues in proteins may affect their three-dimensional structures and hence their properties and functions. Indeed, the reactions have been thought to contribute to aging and pathologies. Most of the above reactions of the l-Asp residues proceed via a cyclic succinimide intermediate. In this paper, a novel three-water-assisted mechanism is proposed for cyclization of an Asp residue (forming a gem-diol precursor of the succinimide) by the B3LYP/6-31 + G(d,p) density functional theory calculations carried out for an Asp-containing model compound (Ace-Asp-Nme, where Ace = acetyl and Nme = NHCH3). The three water molecules act as catalysts by mediating ‘long-range’ proton transfers. In the proposed mechanism, the amide group on the C-terminal side of the Asp residue is first converted to the tautomeric iminol form (iminolization). Then, reorientation of a water molecule and a conformational change occur successively, followed by the nucleophilic attack of the iminol nitrogen on the carboxyl carbon of the Asp side chain to form the gem-diol species. A satisfactory agreement was obtained between the calculated and experimental energetics.

  17. Long-term stability of liquid ionization chambers with regard to their qualification as local reference dosimeters for low dose-rate absorbed dose measurements in water.

    PubMed

    Bahar-Gogani, J; Grindborg, J E; Johansson, B E; Wickman, G

    2001-03-01

    The long-term sensitivity and calibration stability of liquid ionization chambers (LICs) has been studied at a local and a secondary standards dosimetry laboratory over a period of 3 years. The chambers were transported several times by mail between the two laboratories for measurements. The LICs used in this work are designed for absorbed dose measurements in the dose rate region of 0.1-100 mGy min(-1) and have a liquid layer thickness of 1 mm and a sensitive volume of 16.2 mm3. The liquids used as sensitive media in the chambers are mixtures of isooctane (C8H18) and tetramethylsilane (Si(CH3)4) in different proportions (about 2 to 1). Operating at a polarizing voltage of 300 V the leakage current of the chambers was stable and never exceeded 3% of the observable current at a dose rate of about 1 mGy min(-1). The volume sensitivity of the chambers was measured to be of the order of 10(-9) C Gy(-1) mm3. No systematic changes in the absorbed dose to water calibration was observed for any of the chambers during the test period (sigma < 0.2%). Variations in chamber dose response with small changes in the polarizing voltage as well as sensitivity changes with accumulated absorbed dose were also investigated. Measurements showed that the LIC response varies by 0.15% per 1% change in applied voltage around 300 V. No significant change could be observed in the LIC sensitivity after a single absorbed dose of 15 kGy. The results indicate that the LIC can be made to serve as a calibration transfer instrument and a reference detector for absorbed dose to water determinations providing good precision and long-term reproducibility. PMID:11277221

  18. Two-dimensional interlocked pentagonal bilayer ice: how do water molecules form a hydrogen bonding network?

    PubMed

    Zhu, Weiduo; Zhao, Wen-Hui; Wang, Lu; Yin, Di; Jia, Min; Yang, Jinlong; Zeng, Xiao Cheng; Yuan, Lan-Feng

    2016-06-01

    The plethora of ice structures observed both in bulk and under nanoscale confinement reflects the extraordinary ability of water molecules to form diverse forms of hydrogen bonding networks. An ideal hydrogen bonding network of water should satisfy three requirements: (1) four hydrogen bonds connected with every water molecule, (2) nearly linear hydrogen bonds, and (3) tetrahedral configuration for the four hydrogen bonds around an O atom. However, under nanoscale confinement, some of the three requirements have to be unmet, and the selection of the specific requirement(s) leads to different types of hydrogen bonding structures. According to molecular dynamics (MD) simulations for water confined between two smooth hydrophobic walls, we obtain a phase diagram of three two-dimensional (2D) crystalline structures and a bilayer liquid. A new 2D bilayer ice is found and named the interlocked pentagonal bilayer ice (IPBI), because its side view comprises interlocked pentagonal channels. The basic motif in the top view of IPBI is a large hexagon composed of four small pentagons, resembling the top view of a previously reported "coffin" bilayer ice [Johnston, et al., J. Chem. Phys., 2010, 133, 154516]. First-principles optimizations suggest that both bilayer ices are stable. However, there are fundamental differences between the two bilayer structures due to the difference in the selection among the three requirements. The IPBI sacrifices the linearity of hydrogen bonds to retain locally tetrahedral configurations of the hydrogen bonds, whereas the coffin structure does the opposite. The tradeoff between the conditions of an ideal hydrogen bonding network can serve as a generic guidance to understand the rich phase behaviors of nanoconfined water. PMID:27063210

  19. KEY COMPARISON: Comparison of the standards for absorbed dose to water of the ENEA-INMRI (Italy) and the BIPM for 60Co γ rays

    NASA Astrophysics Data System (ADS)

    Kessler, C.; Allisy-Roberts, P. J.; Burns, D. T.; Guerra, A. S.; Laitano, R. F.; Pimpinella, M.

    2010-01-01

    A comparison of the standards for absorbed dose to water of the Istituto Nazionale di Metrologia delle Radiazioni Ionizzanti of the Ente per le Nuove Tecnologie, l'Energia e l'Ambiente, Italy (ENEA-INMRI), and of the Bureau International des Poids et Mesures (BIPM) has been made in 60Co gamma radiation under the auspices of the key comparison BIPM.RI(I)-K4. The comparison result, based on the calibration coefficients for three transfer standards and expressed as a ratio of the ENEA and the BIPM standards for absorbed dose to water, is 0.9999 (0.0044). The present 2007 result replaces the earlier ENEA value in this key comparison. The degrees of equivalence between the ENEA and the other participants in this comparison have been calculated and the results are given in the form of a matrix for the ten national metrology institutes (NMIs) that have published results in this ongoing comparison for absorbed dose to water. A graphical presentation is also given. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI Section I, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

  20. Calculating Partition Coefficients of Small Molecules in Octanol/Water and Cyclohexane/Water.

    PubMed

    Bannan, Caitlin C; Calabró, Gaetano; Kyu, Daisy Y; Mobley, David L

    2016-08-01

    Partition coefficients describe how a solute is distributed between two immiscible solvents. They are used in drug design as a measure of a solute's hydrophobicity and a proxy for its membrane permeability. We calculate partition coefficients from transfer free energies using molecular dynamics simulations in explicit solvent. Setup is done by our new Solvation Toolkit which automates the process of creating input files for any combination of solutes and solvents for many popular molecular dynamics software packages. We calculate partition coefficients between octanol/water and cyclohexane/water with the Generalized AMBER Force Field (GAFF) and the Dielectric Corrected GAFF (GAFF-DC). With similar methods in the past we found a root-mean-squared error (RMSE) of 6.3 kJ/mol in hydration free energies which would correspond to an error of around 1.6 log units in partition coefficients if solvation free energies in both solvents were estimated with comparable accuracy. Here we find an overall RMSE of about 1.2 log units with both force fields. Results from GAFF and GAFF-DC seem to exhibit systematic biases in opposite directions for calculated cyclohexane/water partition coefficients. PMID:27434695

  1. Explicit Consideration of Water Molecules to Study Vibrational Circular DICHROÎSM of Monosaccharide's

    NASA Astrophysics Data System (ADS)

    Moussi, Sofiane; Ouamerali, Ourida

    2014-06-01

    Carbohydrates have multiples roles in biological systems. It has been found that the glycoside bond is fundamentally important in many aspects of chemistry and biology and forms the basis of carbohydrate chemistry. That means the stereochemical information, namely, glycosidic linkages α or β, gives an significant features of the carbohydrate glycosidation position of the glycosylic acceptor. For these reasons, much effort was made for the synthesis and analysis of the glycoside bond. Vibrational circular dichroism VCD has some advantages over conventional electronic circular dichroism (ECD) due to the applicability to all organic molecules and the reliability of ab initio quantum calculation. However, for a molecule with many chiral centers such as carbohydrates, determination of the absolute configuration tends to be difficult because the information from each stereochemical center is mixed and averaged over the spectrum. In the CH stretching region, only two VCD studies on carbohydrates have been reported and spectra--structure correlation, as determined for the glycoside band, remains to be investigated. T. Taniguchi and collaborators report that methyl glycosides exhibit a characteristic VCD peak, the sign of which solely reflects the C-1 absolute configuration. This work is a theoretical contribution to study the behaviour of VCD spectrum's of the monosaccharides when the water molecules are taken explicitly. This study is focused on six different monosaccharides in theirs absolute configuration R and S. We used the method of density functional theory DFT by means of the B3LYP hybrid functional and 6-31G * basis set.

  2. Interaction between water molecules and zinc sulfide nanoparticles studied by temperature-programmed desorption and molecular dynamics simulations.

    PubMed

    Zhang, Hengzhong; Rustad, James R; Banfield, Jillian F

    2007-06-14

    We have investigated the bonding of water molecules to the surfaces of ZnS nanoparticles (approximately 2-3 nm sphalerite) using temperature-programmed desorption (TPD). The activation energy for water desorption was derived as a function of the surface coverage through kinetic modeling of the experimental TPD curves. The binding energy of water equals the activation energy of desorption if it is assumed that the activation energy for adsorption is nearly zero. Molecular dynamics (MD) simulations of water adsorption on 3 and 5 nm sphalerite nanoparticles provided insights into the adsorption process and water binding at the atomic level. Water binds with the ZnS nanoparticle surface mainly via formation of Zn-O bonds. As compared with bulk ZnS crystals, ZnS nanoparticles can adsorb more water molecules per unit surface area due to the greatly increased curvature, which increases the distance between adjacent adsorbed molecules. Results from both TPD and MD show that the water binding energy increases with decreasing the water surface coverage. We attribute the increase in binding energy with decreasing surface water coverage to the increasing degree of surface under-coordination as removal of water molecules proceeds. MD also suggests that the water binding energy increases with decreasing particle size due to the further distance and hence lower interaction between adsorbed water molecules on highly curved smaller particle surfaces. Results also show that the binding energy, and thus the strength of interaction of water, is highest in isolated nanoparticles, lower in nanoparticle aggregates, and lowest in bulk crystals. Given that water binding is driven by surface energy reduction, we attribute the decreased binding energy for aggregated as compared to isolated particles to the decrease in surface energy that occurs as the result of inter-particle interactions. PMID:17518448

  3. Energy deposition model based on electron scattering cross section data from water molecules

    NASA Astrophysics Data System (ADS)

    Muñoz, A.; Oiler, J. C.; Blanco, F.; Gorfinkiel, J. D.; Limão-Vieira, P.; Maira-Vidal, A.; Borge, M. J. G.; Tengblad, O.; Huerga, C.; Téllez, M.; García, G.

    2008-10-01

    A complete set of electrons scattering cross sections by water molecules over a broad energy range, from the me V to the Me V ranges, is presented in this study. These data have been obtained by combining experiments and calculations and cover most relevant processes, both elastic and inelastic, which can take place in the considered energy range. A new Monte Carlo simulation programme has been developed using as input parameter these cross sectional data as well as experimental energy loss spectra. The simulation procedure has been applied to obtain electron tracks and energy deposition plots in water when irradiated by a Ru-106 plaque as those used for brachyteraphy of ocular tumours. Finally, the low energy electron tracks provided by the present model have been compared with those obtained with other codes available in the literature

  4. Dipole and quadrupole polarizabilities of the water molecule as a function of geometry.

    PubMed

    Loboda, Oleksandr; Ingrosso, Francesca; Ruiz-López, Manuel F; Reis, Heribert; Millot, Claude

    2016-09-01

    Dipolar, dipole-quadrupole and quadrupole-quadrupole static polarizabilities of the water molecule have been determined by ab initio calculations at coupled cluster level of theory with single, double and perturbative triple excitations CCSD(T) with an aug-cc-pVTZ basis set using a finite field and field-gradient method. The geometry dependence of polarizability tensor components has been explored and modeled by power series expansion in bond length and angle variations up to sum of powers equal to 4. The results provide a very detailed description of the static polarizability of water up to quadrupolar rank which can be used for the test and development of novel accurate polarizable interaction potentials for modeling aqueous solutions. © 2016 Wiley Periodicals, Inc. PMID:27354163

  5. Water and complex organic molecules in the warm inner regions of solar-type protostars

    NASA Astrophysics Data System (ADS)

    Coutens, A.; Jørgensen, J. K.; Persson, M. V.; Lykke, J. M.; Taquet, V.; van Dishoeck, E. F.; Vastel, C.; Wampfler, S. F.

    2015-12-01

    Water and complex organic molecules play an important role in the emergence of Life. They have been detected in different types of astrophysical environments (protostars, prestellar cores, outflows, protoplanetary disks, comets, etc). In particular, they show high abundances towards the warm inner regions of protostars, where the icy grain mantles thermally desorb. Can a part of the molecular content observed in these regions be preserved during the star formation process and incorporated into asteroids and comets, that can deliver it to planetary embryos through impacts? By comparison with cometary studies, interferometric observations of solar-type protostars can help to address this important question. We present recent results obtained with the Plateau de Bure interferometer about water deuteration, glycolaldehyde and ethylene glycol towards the low-mass protostar NGC 1333 IRAS2A.

  6. Measurement of absorbed dose to water around an electronic brachytherapy source. Comparison of two dosimetry systems: lithium formate EPR dosimeters and radiochromic EBT2 film

    NASA Astrophysics Data System (ADS)

    Adolfsson, Emelie; White, Shane; Landry, Guillaume; Lund, Eva; Gustafsson, Håkan; Verhaegen, Frank; Reniers, Brigitte; Carlsson Tedgren, Åsa; Alm Carlsson, Gudrun

    2015-05-01

    Interest in high dose rate (HDR) electronic brachytherapy operating at 50 kV is increasing. For quality assurance it is important to identify dosimetry systems that can measure the absorbed doses in absolute terms which is difficult in this energy region. In this work a comparison is made between two dosimetry systems, EPR lithium formate dosimeters and radiochromic EBT2 film. Both types of dosimeters were irradiated simultaneously in a PMMA phantom using the Axxent EBS. Absorbed dose to water was determined at distances of 10 mm, 30 mm and 50 mm from the EBS. Results were traceable to different primary standards as regards to absorbed dose to water (EPR) and air kerma (EBT2). Monte Carlo simulations were used in absolute terms as a third estimate of absorbed dose to water. Agreement within the estimated expanded (k = 2) uncertainties (5% (EPR), 7% (EBT2)) was found between the results at 30 mm and 50 mm from the x-ray source. The same result was obtained in 4 repetitions of irradiation, indicating high precision in the measurements with both systems. At all distances, agreement between EPR and Monte Carlo simulations was shown as was also the case for the film measurements at 30mm and 50mm. At 10mm the geometry for the film measurements caused too large uncertainty in measured values depending on the exact position (within sub-mm distances) of the EBS and the 10 mm film results were exculded from comparison. This work has demonstrated good performance of the lithium formate EPR dosimetry system in accordance with earlier experiments at higher photon energies (192Ir HDR brachytherapy). It was also highlighted that there might be issues regarding the energy dependence and intrinsic efficiency of the EBT2 film that need to be considered for measurements using low energy sources.

  7. Tuning dissociation using isoelectronically doped graphene and hexagonal boron nitride: Water and other small molecules

    NASA Astrophysics Data System (ADS)

    Al-Hamdani, Yasmine S.; Alfè, Dario; von Lilienfeld, O. Anatole; Michaelides, Angelos

    2016-04-01

    Novel uses for 2-dimensional materials like graphene and hexagonal boron nitride (h-BN) are being frequently discovered especially for membrane and catalysis applications. Still however, a great deal remains to be understood about the interaction of environmentally and industrially relevant molecules such as water with these materials. Taking inspiration from advances in hybridising graphene and h-BN, we explore using density functional theory, the dissociation of water, hydrogen, methane, and methanol on graphene, h-BN, and their isoelectronic doped counterparts: BN doped graphene and C doped h-BN. We find that doped surfaces are considerably more reactive than their pristine counterparts and by comparing the reactivity of several small molecules, we develop a general framework for dissociative adsorption. From this a particularly attractive consequence of isoelectronic doping emerges: substrates can be doped to enhance their reactivity specifically towards either polar or non-polar adsorbates. As such, these substrates are potentially viable candidates for selective catalysts and membranes, with the implication that a range of tuneable materials can be designed.

  8. Tuning dissociation using isoelectronically doped graphene and hexagonal boron nitride: Water and other small molecules.

    PubMed

    Al-Hamdani, Yasmine S; Alfè, Dario; von Lilienfeld, O Anatole; Michaelides, Angelos

    2016-04-21

    Novel uses for 2-dimensional materials like graphene and hexagonal boron nitride (h-BN) are being frequently discovered especially for membrane and catalysis applications. Still however, a great deal remains to be understood about the interaction of environmentally and industrially relevant molecules such as water with these materials. Taking inspiration from advances in hybridising graphene and h-BN, we explore using density functional theory, the dissociation of water, hydrogen, methane, and methanol on graphene, h-BN, and their isoelectronic doped counterparts: BN dopedgraphene and C doped h-BN. We find that dopedsurfaces are considerably more reactive than their pristine counterparts and by comparing the reactivity of several small molecules, we develop a general framework for dissociative adsorption. From this a particularly attractive consequence of isoelectronic doping emerges: substrates can be doped to enhance their reactivity specifically towards either polar or non-polar adsorbates. As such, these substrates are potentially viable candidates for selective catalysts and membranes, with the implication that a range of tuneable materials can be designed. PMID:27389233

  9. Conserved hydrogen bonds and water molecules in MDR HIV-1 protease substrate complexes

    SciTech Connect

    Liu, Zhigang; Wang, Yong; Yedidi, Ravikiran S.; Dewdney, Tamaria G.; Reiter, Samuel J.; Brunzelle, Joseph S.; Kovari, Iulia A.; Kovari, Ladislau C.

    2012-12-19

    Success of highly active antiretroviral therapy (HAART) in anti-HIV therapy is severely compromised by the rapidly developing drug resistance. HIV-1 protease inhibitors, part of HAART, are losing their potency and efficacy in inhibiting the target. Multi-drug resistant (MDR) 769 HIV-1 protease (resistant mutations at residues 10, 36, 46, 54, 62, 63, 71, 82, 84, 90) was selected for the present study to understand the binding to its natural substrates. The nine crystal structures of MDR769 HIV-1 protease substrate hepta-peptide complexes were analyzed in order to reveal the conserved structural elements for the purpose of drug design against MDR HIV-1 protease. Our structural studies demonstrated that highly conserved hydrogen bonds between the protease and substrate peptides, together with the conserved crystallographic water molecules, played a crucial role in the substrate recognition, substrate stabilization and protease stabilization. Additionally, the absence of the key flap-ligand bridging water molecule might imply a different catalytic mechanism of MDR769 HIV-1 protease compared to that of wild type (WT) HIV-1 protease.

  10. A water calorimeter for on-site absorbed dose to water calibrations in (60)Co and MV-photon beams including MRI incorporated treatment equipment.

    PubMed

    de Prez, Leon; de Pooter, Jacco; Jansen, Bartel; Aalbers, Tony

    2016-07-01

    In reference dosimetry the aim is to establish the absorbed dose to water, D w, under reference conditions. However, existing dosimetry protocols are not always applicable for rapidly emerging new treatment modalities. For primary standard dosimetry laboratories it is generally not feasible to acquire such modalities. Therefore it is strongly desired that D w measurements with primary standards can be performed on-site in clinical beams for the new treatment modalities in order to characterize and calibrate detectors. To serve this need, VSL has developed a new transportable water calorimeter serving as a primary D w standard for (60)Co and MV-photons including MRI incorporated treatment equipment. Special attention was paid to its operation in different beam geometries and beam modalities including the application in magnetic fields. The new calorimeter was validated in the VSL (60)Co beam and on-site in clinical MV-photon beams. Excellent agreement of 0.1% was achieved with previous (60)Co field calibrations, i.e. well within the uncertainty of the previous calorimeter, and with measurements performed in horizontal and vertical MV-photon beams. k Q factors, determined for two PTW 30013 ionization chambers, agreed very well with available literature data. The relative combined standard uncertainty (k  =  1) for D w measurements in (60)Co and MV-photons is 0.37%. Calibrations are carried out with a standard uncertainty of 0.42% and k Q -factors are determined with a relative standard uncertainty of 0.40%. PMID:27300589

  11. A water calorimeter for on-site absorbed dose to water calibrations in 60Co and MV-photon beams including MRI incorporated treatment equipment

    NASA Astrophysics Data System (ADS)

    de Prez, Leon; de Pooter, Jacco; Jansen, Bartel; Aalbers, Tony

    2016-07-01

    In reference dosimetry the aim is to establish the absorbed dose to water, D w, under reference conditions. However, existing dosimetry protocols are not always applicable for rapidly emerging new treatment modalities. For primary standard dosimetry laboratories it is generally not feasible to acquire such modalities. Therefore it is strongly desired that D w measurements with primary standards can be performed on-site in clinical beams for the new treatment modalities in order to characterize and calibrate detectors. To serve this need, VSL has developed a new transportable water calorimeter serving as a primary D w standard for 60Co and MV-photons including MRI incorporated treatment equipment. Special attention was paid to its operation in different beam geometries and beam modalities including the application in magnetic fields. The new calorimeter was validated in the VSL 60Co beam and on-site in clinical MV-photon beams. Excellent agreement of 0.1% was achieved with previous 60Co field calibrations, i.e. well within the uncertainty of the previous calorimeter, and with measurements performed in horizontal and vertical MV-photon beams. k Q factors, determined for two PTW 30013 ionization chambers, agreed very well with available literature data. The relative combined standard uncertainty (k  =  1) for D w measurements in 60Co and MV-photons is 0.37%. Calibrations are carried out with a standard uncertainty of 0.42% and k Q -factors are determined with a relative standard uncertainty of 0.40%.

  12. The binding energies of one and two water molecules to the first transition-row metal positive ions. II

    NASA Technical Reports Server (NTRS)

    Rosi, Marzio; Bauschlicher, Charles W., Jr.

    1990-01-01

    The present investigation of H2O's binding energy to transition-metal ions proceeds from the D(2h) structure and bends the two water molecules out of plane. The molecule is constrained to have C(2v) symmetry, so that each water molecule and metal ion lies on a plane. The ground states are bent only for Mn(H2O)2(+) and Zn(H2O)2(+), where only 4s4p hybridization is energetically favorable; 4s4p hybridization reduces repulsion.

  13. The effects of water molecules on the electronic and structural properties of peptide nanotubes.

    PubMed

    Andrade-Filho, T; Ferreira, Fabio Furlan; Alves, Wendel Andrade; Rocha, Alexandre Reily

    2013-05-28

    The self-assembly of short amino acid chains appears to be one of the most promising strategies for the fabrication of nanostructures. Their solubility in water and the possibility of chemical modification by targeting the amino or carboxyl terminus give peptide-based nanostructures several advantages over carbon nanotube nanostructures. However, because these systems are synthesized in aqueous solution, a deeper understanding is needed on the effects of water especially with respect to the electronic, structural and transport properties. In this work, the electronic properties of L-diphenylalanine nanotubes (FF-NTs) have been studied using the Self-Consistent Charge Density-Functional-based Tight-Binding method augmented with dispersion interaction. The presence of water molecules in the central hydrophilic channel and their interaction with the nanostructures are addressed. We demonstrate that the presence of water leads to significant changes in the electronic properties of these systems decreasing the band gap which can lead to an increase in the hopping probability and the conductivity. PMID:23588391

  14. Hydrodynamic and nonhydrodynamic contributions to the bimolecular collision rates of solute molecules in supercooled bulk water.

    PubMed

    Peric, Ida; Merunka, Dalibor; Bales, Barney L; Peric, Miroslav

    2014-06-26

    Bimolecular collision rate constants of a model solute are measured in water at T = 259-303 K, a range encompassing both normal and supercooled water. A stable, spherical nitroxide spin probe, perdeuterated 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl, is studied using electron paramagnetic resonance spectroscopy (EPR), taking advantage of the fact that the rotational correlation time, τ(R), the mean time between successive spin exchanges within a cage, τ(RE), and the long-time-averaged spin exchange rate constants, K(ex), of the same solute molecule may be measured independently. Thus, long- and short-time translational diffusion behavior may be inferred from K(ex) and τ(RE), respectively. In order to measure K(ex), the effects of dipole-dipole interactions (DD) on the EPR spectra must be separated, yielding as a bonus the DD broadening rate constants that are related to the dephasing rate constant due to DD, W(dd). We find that both K(ex) and W(dd) behave hydrodynamically; that is to say they vary monotonically with T/η or η/T, respectively, where η is the shear viscosity, as predicted by the Stokes-Einstein equation. The same is true of the self-diffusion of water. In contrast, τ(RE) does not follow hydrodynamic behavior, varying rather as a linear function of the density reaching a maximum at 276 ± 2 K near where water displays a maximum density. PMID:24874024

  15. Hydrodynamic and Nonhydrodynamic Contributions to the Bimolecular Collision Rates of Solute Molecules in Supercooled Bulk Water

    PubMed Central

    2015-01-01

    Bimolecular collision rate constants of a model solute are measured in water at T = 259–303 K, a range encompassing both normal and supercooled water. A stable, spherical nitroxide spin probe, perdeuterated 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl, is studied using electron paramagnetic resonance spectroscopy (EPR), taking advantage of the fact that the rotational correlation time, τR, the mean time between successive spin exchanges within a cage, τRE, and the long-time-averaged spin exchange rate constants, Kex, of the same solute molecule may be measured independently. Thus, long- and short-time translational diffusion behavior may be inferred from Kex and τRE, respectively. In order to measure Kex, the effects of dipole–dipole interactions (DD) on the EPR spectra must be separated, yielding as a bonus the DD broadening rate constants that are related to the dephasing rate constant due to DD, Wdd. We find that both Kex and Wdd behave hydrodynamically; that is to say they vary monotonically with T/η or η/T, respectively, where η is the shear viscosity, as predicted by the Stokes–Einstein equation. The same is true of the self-diffusion of water. In contrast, τRE does not follow hydrodynamic behavior, varying rather as a linear function of the density reaching a maximum at 276 ± 2 K near where water displays a maximum density. PMID:24874024

  16. ORGANIC MOLECULES AND WATER IN THE INNER DISKS OF T TAURI STARS

    SciTech Connect

    Carr, John S.; Najita, Joan R. E-mail: najita@noao.edu

    2011-06-01

    We report high signal-to-noise Spitzer Infrared Spectrograph spectra of a sample of 11 classical T Tauri stars. Molecular emission from rotational transitions of H{sub 2}O and OH and rovibrational bands of simple organic molecules (CO{sub 2}, HCN, C{sub 2}H{sub 2}) is common among the sources in the sample. The emission shows a range in both flux and line-to-continuum ratio for each molecule and in the flux ratios of different molecular species. The gas temperatures (200-800 K) and emitting areas we derive are consistent with the emission originating in a warm disk atmosphere in the inner planet formation region at radii <2 AU. The H{sub 2}O emission appears to form under a limited range of excitation conditions, as demonstrated by the similarity in relative strengths of H{sub 2}O features from star to star and the narrow range in derived temperature and column density. Emission from highly excited rotational levels of OH is present in all stars; the OH emission flux increases with the stellar accretion rate, and the OH/H{sub 2}O flux ratio shows a relatively small scatter. We interpret these results as evidence for OH production via FUV photodissociation of H{sub 2}O in the disk surface layers. No obvious explanation is found for the observed range in the relative emission strengths of different organic molecules or in their strength with respect to water. We put forward the possibility that these variations reflect a diversity in organic abundances due to star-to-star differences in the C/O ratio of the inner disk gas. Stars with the largest HCN/H{sub 2}O flux ratios in our sample have the largest disk masses. While larger samples are required to confirm this, we speculate that such a trend could result if higher mass disks are more efficient at planetesimal formation and sequestration of water in the outer disk, leading to enhanced C/O ratios and abundances of organic molecules in the inner disk. A comparison of our derived HCN-to-H{sub 2}O column density ratio

  17. Dynamic and Static Water Molecules Complement the TN16 Conformational Heterogeneity inside the Tubulin Cavity.

    PubMed

    Majumdar, Sarmistha; Maiti, Satyabrata; Ghosh Dastidar, Shubhra

    2016-01-19

    TN16 is one of the most promising inhibitors of α, β dimer of tubulin that occupies the cavity in the β-subunit located at the dimeric interface, known as the colchicine binding site. The experimentally determined structure of the complex (Protein Data Bank entry 3HKD) presents the conformation and position of the ligand based on the "best fit", keeping the controversy of other significant binding modes open for further investigation. Computation has already revealed that TN16 experiences fluctuations within the binding pocket, but the insight from that previous report was limited by the shorter windows of sampling and by the approximations on the surrounding environment by implicit solvation. This article reports that in most of the cases straightforward MMGBSA calculations of binding energy revealed a gradual loss of stabilization that was inconsistent with the structural observations, and thus, it indicated the lack of consideration of stabilizing factors with appropriate weightage. Consideration of the structurally packed water molecules in the space between the ligand and receptor successfully eliminated such discrepancies between the structure and stability, serving as the "litmus test" of the importance of explicit consideration of such structurally packed water in the calculations. Such consideration has further evidenced a quasi-degenerate character of the different binding modes of TN16 that has rationalized the observed intrinsic fluctuations of TN16 within the pocket, which is likely to be the most critical insight into its entropy-dominated binding. Quantum mechanical calculations have revealed a relay of electron density from TN16 to the protein via a water molecule in a concerted manner. PMID:26666704

  18. Vasoactive properties of CORM-3, a novel water-soluble carbon monoxide-releasing molecule.

    PubMed

    Foresti, Roberta; Hammad, Jehad; Clark, James E; Johnson, Tony R; Mann, Brian E; Friebe, Andreas; Green, Colin J; Motterlini, Roberto

    2004-06-01

    1 Carbon monoxide (CO), one of the end products of heme catabolism by heme oxygenase, possesses antihypertensive and vasodilatory characteristics. We have recently discovered that certain transition metal carbonyls are capable of releasing CO in biological fluids and modulate physiological functions via the delivery of CO. Because the initial compounds identified were not water soluble, we have synthesized new CO-releasing molecules that are chemically modified to allow solubility in water. The aim of this study was to assess the vasoactive properties of tricarbonylchloro(glycinato)ruthenium(II) (CORM-3) in vitro and in vivo. 2 CORM-3 produced a concentration-dependent relaxation in vessels precontracted with phenylephrine, exerting significant vasodilatation starting at concentrations of 25-50 microm. Inactive CORM-3, which does not release CO, did not affect vascular tone. 3 Blockers of ATP-dependent potassium channels (glibenclamide) or guanylate cyclase activity (ODQ) considerably reduced CORM-3-dependent relaxation, confirming that potassium channels activation and cGMP partly mediate the vasoactive properties of CO. In fact, increased levels of cGMP were detected in aortas following CORM-3 stimulation. 4 The in vitro and in vivo vasorelaxant activities of CORM-3 were further enhanced in the presence of YC-1, a benzylindazole derivative which is known to sensitize guanylate cyclase to activation by CO. Interestingly, inhibiting nitric oxide production or removing the endothelium significantly decreased vasodilatation by CORM-3, suggesting that factors produced by the endothelium influence CORM-3 vascular activities. 5 These results, together with our previous findings on the cardioprotective functions of CORM-3, indicate that this molecule is an excellent prototype of water-soluble CO carriers for studying the pharmacological and biological features of CO. PMID:15148243

  19. Vasoactive properties of CORM-3, a novel water-soluble carbon monoxide-releasing molecule

    PubMed Central

    Foresti, Roberta; Hammad, Jehad; Clark, James E; Johnson, Tony R; Mann, Brian E; Friebe, Andreas; Green, Colin J; Motterlini, Roberto

    2004-01-01

    Carbon monoxide (CO), one of the end products of heme catabolism by heme oxygenase, possesses antihypertensive and vasodilatory characteristics. We have recently discovered that certain transition metal carbonyls are capable of releasing CO in biological fluids and modulate physiological functions via the delivery of CO. Because the initial compounds identified were not water soluble, we have synthesized new CO-releasing molecules that are chemically modified to allow solubility in water. The aim of this study was to assess the vasoactive properties of tricarbonylchloro(glycinato)ruthenium(II) (CORM-3) in vitro and in vivo. CORM-3 produced a concentration-dependent relaxation in vessels precontracted with phenylephrine, exerting significant vasodilatation starting at concentrations of 25–50 μM. Inactive CORM-3, which does not release CO, did not affect vascular tone. Blockers of ATP-dependent potassium channels (glibenclamide) or guanylate cyclase activity (ODQ) considerably reduced CORM-3-dependent relaxation, confirming that potassium channels activation and cGMP partly mediate the vasoactive properties of CO. In fact, increased levels of cGMP were detected in aortas following CORM-3 stimulation. The in vitro and in vivo vasorelaxant activities of CORM-3 were further enhanced in the presence of YC-1, a benzylindazole derivative which is known to sensitize guanylate cyclase to activation by CO. Interestingly, inhibiting nitric oxide production or removing the endothelium significantly decreased vasodilatation by CORM-3, suggesting that factors produced by the endothelium influence CORM-3 vascular activities. These results, together with our previous findings on the cardioprotective functions of CORM-3, indicate that this molecule is an excellent prototype of water-soluble CO carriers for studying the pharmacological and biological features of CO. PMID:15148243

  20. Unintended consequences? Water molecules at biological and crystallographic protein-protein interfaces.

    PubMed

    Ahmed, Mostafa H; Habtemariam, Mesay; Safo, Martin K; Scarsdale, J Neel; Spyrakis, Francesca; Cozzini, Pietro; Mozzarelli, Andrea; Kellogg, Glen E

    2013-12-01

    The importance of protein-protein interactions (PPIs) is becoming increasingly appreciated, as these interactions lie at the core of virtually every biological process. Small molecule modulators that target PPIs are under exploration as new therapies. One of the greatest obstacles faced in crystallographically determining the 3D structures of proteins is coaxing the proteins to form "artificial" PPIs that lead to uniform crystals suitable for X-ray diffraction. This work compares interactions formed naturally, i.e., "biological", with those artificially formed under crystallization conditions or "non-biological". In particular, a detailed analysis of water molecules at the interfaces of high-resolution (≤2.30 Å) X-ray crystal structures of protein-protein complexes, where 140 are biological protein-protein complex structures and 112 include non-biological protein-protein interfaces, was carried out using modeling tools based on the HINT forcefield. Surprisingly few and relatively subtle differences were observed between the two types of interfaces: (i) non-biological interfaces are more polar than biological interfaces, yet there is better organized hydrogen bonding at the latter; (ii) biological associations rely more on water-mediated interactions with backbone atoms compared to non-biological associations; (iii) aromatic/planar residues play a larger role in biological associations with respect to water, and (iv) Lys has a particularly large role at non-biological interfaces. A support vector machines (SVMs) classifier using descriptors from this study was devised that was able to correctly classify 84% of the two interface types. PMID:24076743

  1. Orbiting Water Molecules Dance to Tune Of Galaxy's "Central Engine," Astronomers Say

    NASA Astrophysics Data System (ADS)

    2000-01-01

    A disk of water molecules orbiting a supermassive black hole at the core of a galaxy 60 million light-years away is "reverberating" in response to variations in the energy output from the galaxy's powerful "central engine" close to the black hole, astronomers say. The team of astronomers used the National Science Foundation's (NSF) Very Large Array (VLA) radio telescope in New Mexico and the 100-meter-diameter radio telescope of the Max Planck Institute for Radio Astronomy at Effelsberg, Germany, to observe the galaxy NGC 1068 in the constellation Cetus. They announced their findings today at the American Astronomical Society's meeting in Atlanta. The water molecules, in a disk some 5 light-years in diameter, are acting as a set of giant cosmic radio-wave amplifiers, called masers. Using energy radiated by the galaxy's "central engine," the molecules strengthen, or brighten, radio emission at a particular frequency as seen from Earth. "We have seen variations in the radio 'brightness' of these cosmic amplifiers that we believe were caused by variations in the energy output of the central engine," said Jack Gallimore, an astronomer at the National Radio Astronomy Observatory (NRAO) in Charlottesville, VA. "This could provide us with a valuable new tool for learning about the central engine itself," he added. Gallimore worked with Stefi Baum of the Space Telescope Science Institute in Baltimore, MD; Christian Henkel of the Max Planck Institute for Radio Astronomy in Bonn, Germany; Ian Glass of the South African Astronomical Observatory; Mark Claussen of the NRAO in Socorro, NM; and Almudena Prieto of the European Southern Observatory in Munich, Germany. "Our observations show that NGC 1068 is the second-known case of a giant disk of water molecules orbiting a supermassive black hole at a galaxy's core," Gallimore said. The first case was the galaxy NGC 4258 (Messier 106), whose disk of radio-amplifying water molecules was measured by the NSF's Very Long Baseline

  2. Rotations and vibrations of water molecule inside the fullerene cage: infrared study of H2O@C60

    NASA Astrophysics Data System (ADS)

    Room, Toomas; Shugai, A.; Nagel, U.; Mamone, S.; Krachmalnicoff, A.; Whitby, R. J.; Levitt, M. H.; Nishida, T.; Murata, Y.; Lei, Xuegong; Li, Yongjun; Turro, N. J.

    2015-03-01

    Water is the second molecule after hydrogen what has been trapped inside the cage of a C60 molecule by the molucular surgery method. We studied isolated water molecule isotopologs H2O, D2O, and HDO in the solid phase at cryogenic temperatures using IR spectroscopy. The water molecule rotation transitions were observed in the THz and vibration-rotation transitions in the mid-IR range. The slow conversion between para and ortho water allowed us to record the time evolution of spectra and to separate ortho and para absorption lines of water. The similarity of the rotation spectrum of caged water to water in the gas phase indicates that water is free to rotate in the C60 cage even at temperature as low as 3 K. However, spectral lines show a splitting of about 0.5 meV what is not compatible with the icosahedral symmetry of C60. Different models (e.g. crystal field effects in solid C60, C60 cage distortions) will be discussed. This work was supported by institutional research funding IUT23-3 of the Estonian Ministry of Education and Research.

  3. Adsorption of apolar molecules at the water liquid-vapor interface: A Monte Carlo simulations study of the water-n-octane system

    NASA Astrophysics Data System (ADS)

    Jedlovszky, Pál; Varga, Imre; Gilányi, Tibor

    2003-07-01

    The adsorption of n-octane at the water liquid-vapor interface has been investigated by Monte Carlo computer simulation. For this purpose, simulation of five different water-apolar interfacial systems have been performed, in which the number of n-octane molecules has been varied. The results clearly show that the apolar n-octane molecules are adsorbed from the vapor phase at the interface. The adsorption is driven by the weak attraction due to the dispersion forces acting between the water molecules and the methyl and methylene groups of the octanes. This weak attraction is, however, amplified by the fact that it is added up for the CH2 and CH3 groups belonging to the same molecule. Consistently, the n-octane molecules located closest to the aqueous phase are found to prefer all-trans conformation and parallel alignment with the plane of the interface. On the other hand, entropic effects become more important among the molecules of the outer part of the adsorption layer. Hence, the preferred orientation of these molecules is perpendicular to the interface, as they can be extended toward the less dense region of the apolar phase; and gauche dihedrals appear more frequently here than among the molecules located next to the aqueous phase.

  4. Anisotropic conductivity tensor imaging in MREIT using directional diffusion rate of water molecules

    NASA Astrophysics Data System (ADS)

    In Kwon, Oh; Jeong, Woo Chul; Sajib, Saurav Z. K.; Kim, Hyung Joong; Woo, Eung Je

    2014-06-01

    Magnetic resonance electrical impedance tomography (MREIT) is an emerging method to visualize electrical conductivity and/or current density images at low frequencies (below 1 KHz). Injecting currents into an imaging object, one component of the induced magnetic flux density is acquired using an MRI scanner for isotropic conductivity image reconstructions. Diffusion tensor MRI (DT-MRI) measures the intrinsic three-dimensional diffusion property of water molecules within a tissue. It characterizes the anisotropic water transport by the effective diffusion tensor. Combining the DT-MRI and MREIT techniques, we propose a novel direct method for absolute conductivity tensor image reconstructions based on a linear relationship between the water diffusion tensor and the electrical conductivity tensor. We first recover the projected current density, which is the best approximation of the internal current density one can obtain from the measured single component of the induced magnetic flux density. This enables us to estimate a scale factor between the diffusion tensor and the conductivity tensor. Combining these values at all pixels with the acquired diffusion tensor map, we can quantitatively recover the anisotropic conductivity tensor map. From numerical simulations and experimental verifications using a biological tissue phantom, we found that the new method overcomes the limitations of each method and successfully reconstructs both the direction and magnitude of the conductivity tensor for both the anisotropic and isotropic regions.

  5. The hydrolytic water molecule in trypsin, revealed by time-resolved Laue crystallography

    SciTech Connect

    Singer, P.T. ); Smalaas, A. ); Carty, R.P. ); Mangel, W.F.; Sweet, R.M. )

    1993-01-29

    Crystals of bovine trypsin were acylated at the reactive residue, serine 195, to form the transiently stable p-guanidinobenzoate. Hydrolysis of this species was triggered in the crystals by a jump in pH. The hydrolysis was monitored by three-dimensional Laue crystallography, resulting in three x-ray diffraction structures, all from the same crystal and each representing approximately 5 seconds of x-ray exposure. The structures were analyzed at a nominal resolution of 1.8 angstroms and were of sufficient quality to reproduce subtle features in the electron-density maps for each of the structures. Comparison of the structures before and after the pH jump reveals that a water molecule has positioned itself to attack the acyl group in the initial step of the hydrolysis of this transient intermediate. 12 refs., 3 figs., 2 tabs.

  6. Switching of the magnetocaloric effect of Mn(II) glycolate by water molecules.

    PubMed

    Chen, Yan-Cong; Guo, Fu-Sheng; Liu, Jun-Liang; Leng, Ji-Dong; Vrábel, Peter; Orendáč, Martin; Prokleška, Jan; Sechovský, Vladimír; Tong, Ming-Liang

    2014-03-10

    The transformation of Mn(II) glycolates (glc) between the three-dimensional coordination polymer [Mn(glc)2]n (1) and discrete mononuclear phase [Mn(glc)2 (H2O)2] (2) can be reversibly switched by water molecules, which dramatically change the magnetocaloric effect (MCE) of Mn(II) glycolates from the maximum of 6.9 J kg(-1)  K(-1) in 1 to 60.3 J kg(-1)  K(-1) in 2. This case example reveals that the effect of magnetic coupling on MCE plays a dominant role over that of other factors such as magnetic density for 3d-type magnetic refrigerants. PMID:24532426

  7. Computing the energy of a water molecule using multideterminants: A simple, efficient algorithm

    NASA Astrophysics Data System (ADS)

    Clark, Bryan K.; Morales, Miguel A.; McMinis, Jeremy; Kim, Jeongnim; Scuseria, Gustavo E.

    2011-12-01

    Quantum Monte Carlo (QMC) methods such as variational Monte Carlo and fixed node diffusion Monte Carlo depend heavily on the quality of the trial wave function. Although Slater-Jastrow wave functions are the most commonly used variational ansatz in electronic structure, more sophisticated wave functions are critical to ascertaining new physics. One such wave function is the multi-Slater-Jastrow wave function which consists of a Jastrow function multiplied by the sum of Slater determinants. In this paper we describe a method for working with these wave functions in QMC codes that is easy to implement, efficient both in computational speed as well as memory, and easily parallelized. The computational cost scales quadratically with particle number making this scaling no worse than the single determinant case and linear with the total number of excitations. Additionally, we implement this method and use it to compute the ground state energy of a water molecule.

  8. Computing the energy of a water molecule using multideterminants: a simple, efficient algorithm.

    PubMed

    Clark, Bryan K; Morales, Miguel A; McMinis, Jeremy; Kim, Jeongnim; Scuseria, Gustavo E

    2011-12-28

    Quantum Monte Carlo (QMC) methods such as variational Monte Carlo and fixed node diffusion Monte Carlo depend heavily on the quality of the trial wave function. Although Slater-Jastrow wave functions are the most commonly used variational ansatz in electronic structure, more sophisticated wave functions are critical to ascertaining new physics. One such wave function is the multi-Slater-Jastrow wave function which consists of a Jastrow function multiplied by the sum of Slater determinants. In this paper we describe a method for working with these wave functions in QMC codes that is easy to implement, efficient both in computational speed as well as memory, and easily parallelized. The computational cost scales quadratically with particle number making this scaling no worse than the single determinant case and linear with the total number of excitations. Additionally, we implement this method and use it to compute the ground state energy of a water molecule. PMID:22225142

  9. Measurements of the number density of water molecules in plasma by using a combined spectral-probe method

    NASA Astrophysics Data System (ADS)

    Bernatskiy, A. V.; Ochkin, V. N.; Afonin, O. N.; Antipenkov, A. B.

    2015-09-01

    A novel method for measuring the number density of water molecules in low-temperature plasma is developed. The absolute intensities of rotational lines of the (0,0) band of the OH( A 2Σ- X 2П) transition are used. Lines with sufficiently large rotational quantum numbers referring to the so-called "hot" group of molecules produced by electron-impact dissociative excitation of water molecules are chosen for measurements. The excitation rate of a process with a known cross section is determined by measuring the parameters of plasma electrons by means of the probe method. The measured number densities of molecules are compared with those in the initial plasma-forming mixture. The time evolution of the particle densities in plasma is investigated. The problems of the sensitivity and applicability of the absolute spectral method are considered.

  10. Measurements of the number density of water molecules in plasma by using a combined spectral−probe method

    SciTech Connect

    Bernatskiy, A. V. Ochkin, V. N.; Afonin, O. N.; Antipenkov, A. B.

    2015-09-15

    A novel method for measuring the number density of water molecules in low-temperature plasma is developed. The absolute intensities of rotational lines of the (0,0) band of the OH(A{sup 2}Σ–X{sup 2}Π) transition are used. Lines with sufficiently large rotational quantum numbers referring to the so-called “hot” group of molecules produced by electron-impact dissociative excitation of water molecules are chosen for measurements. The excitation rate of a process with a known cross section is determined by measuring the parameters of plasma electrons by means of the probe method. The measured number densities of molecules are compared with those in the initial plasma-forming mixture. The time evolution of the particle densities in plasma is investigated. The problems of the sensitivity and applicability of the absolute spectral method are considered.

  11. How small polar molecules protect membrane systems against osmotic stress: the urea-water-phospholipid system.

    PubMed

    Costa-Balogh, Fátima O; Wennerström, Håkan; Wadsö, Lars; Sparr, Emma

    2006-11-30

    We investigate how a small polar molecule, urea, can act to protect a phospholipid bilayer system against osmotic stress. Osmotic stress can be caused by a dry environment, by freezing, or by exposure to aqueous systems with high osmotic pressure due to solutes like in saline water. A large number of organisms regularly experience osmotic stress, and it is a common response to produce small polar molecules intracellularly. We have selected a ternary system of urea-water-dimyristoyl phosphatidylcholine (DMPC) as a model to investigate the molecular mechanism behind this protective effect, in this case, of urea, and we put special emphasis on the applications of urea in skin care products. Using differential scanning calorimetry, X-ray diffraction, and sorption microbalance measurements, we studied the phase behavior of lipid systems exposed to an excess of solvent of varying compositions, as well as lipid systems exposed to water at reduced relative humidities. From this, we have arrived at a rather detailed thermodynamic characterization. The basic findings are as follows: (i) In excess solvent, the thermally induced lipid phase transitions are only marginally dependent on the urea content, with the exception being that the P(beta) phase is not observed in the presence of urea. (ii) For lipid systems with limited access to solvent, the phase behavior is basically determined by the amount (volume) of solvent irrespective of the urea content. (iii) The presence of urea has the effect of retaining the liquid crystalline phase at relative humidities down to 64% (at 27 degrees C), whereas, in the absence of urea, the transition to the gel phase occurs already at a relative humidity of 94%. This demonstrates the protective effect of urea against osmotic stress. (iv) In skin care products, urea is referred to as a moisturizer, which we find slightly misleading as it replaces the water while keeping the physical properties unaltered. (v) In other systems, urea is known to

  12. DESCRIPTION OF THE TRITIUM-PRODUCING BURNABLE ABSORBER ROD FOR THE COMMERCIAL LIGHT WATER REACTOR TTQP-1-015 Rev 19

    SciTech Connect

    Burns, Kimberly A.; Love, Edward F.; Thornhill, Cheryl K.

    2012-02-01

    Tritium-producing burnable absorber rods (TPBARs) used in the U.S. Department of Energy’s Tritium Readiness Program are designed to produce tritium when placed in a Westinghouse or Framatome 17x17 fuel assembly and irradiated in a pressurized water reactor (PWR). This document provides an unclassified description of the current design baseline for the TPBARs. This design baseline is currently valid only for Watts Bar reactor production cores. A description of the Lead Use TPBARs will not be covered in the text of the document, but the applicable drawings, specifications and test plan will be included in the appropriate appendices.

  13. The local environment of the molecules in water-DMSO mixtures, as seen from computer simulations and Voronoi polyhedra analysis.

    PubMed

    Idrissi, Abdenacer; Marekha, B; Kiselev, M; Jedlovszky, Pál

    2015-02-01

    Molecular dynamics simulations of water-DMSO mixtures, containing 10, 20, 30, 40, 50, 60, 70, 80, and 90 mol% DMSO, respectively, have been performed on the isothermal-isobaric (N,p,T) ensemble at T = 298 K and at the pressure equal to the experimental vapor pressure at each mixture composition. In addition, simulations of the two neat systems have also been performed for reference. The potential models used in the simulations are known to excellently reproduce the mixing properties of these compounds. The simulation results have been analyzed in detail by means of the Voronoi polyhedra (VP) of the molecules. Distributions of the VP volume and the asphericity parameter as well as that of the radius of the spherical intermolecular voids have been calculated. Detailed analyses of these distributions have revealed that both molecules prefer to be in an environment consisting of both types of molecules, but the affinity of DMSO for mixing with water is clearly stronger than that of water for mixing with DMSO. As a consequence, the dilution of the two neat liquids by the other component has been found to follow different mechanisms: when DMSO is added to neat water small domains of neat-like water persist up to the equimolar composition, whereas no such domains are found when neat DMSO is diluted by water. The observed behaviour is also in line with the fact that the main thermodynamic driving force behind the full miscibility of water and DMSO is the energy change accompanying their mixing, and that the entropy change accompanying this mixing is negative in systems of low and positive in systems of high DMSO mole fractions. Finally, we have found a direct evidence for the existence of strong hydrogen bonded complexes formed by one DMSO and two water molecules, but it has also been shown that these complexes are in equilibrium with single (monomeric) water and DMSO molecules in the mixed systems. PMID:25533427

  14. Effect of nanotube-length on the transport properties of single-file water molecules: Transition from bidirectional to unidirectional

    NASA Astrophysics Data System (ADS)

    Su, Jiaye; Guo, Hongxia

    2011-06-01

    We use molecular dynamics (MD) simulations to study the transport of single-file water molecules through carbon nanotubes (CNTs) with various lengths in an electric field. Most importantly, we find that even the water dipoles inside the CNT are maintained along the field direction, a large amount of water molecules can still transport against the field direction for short CNTs, leading to a low unidirectional transport efficiency (η). As the CNT length increases, the efficiency η will increase remarkably, and achieves the maximum value of 1.0 at or exceeding a critical CNT length. Consequently, the transition from bidirectional to unidirectional transport is observed and is found to be relevant to thermal fluctuations of the two reservoirs, which is explored by the interaction between water molecules inside and outside the CNT. We also find that the water flow vs CNT length follows an exponential decay of f ˜ exp ( - L/L0), and the average translocation time of individual water molecules yields to a power law of τtrans ˜ Lυ, where L0 and ν are constant and slightly depend on the field strength. We further compare our results with the continuous-time random-walk (CTRW) model and find that the water flow can also be described by a power law of f ˜ L-μ modified from CTRW. Our results provide some new physical insights into the biased transport of single-file water molecules, which show the feasibility of using CNTs with any length to pump water in an electric field. The mechanism is important for designing efficient nanofluidic apparatuses.

  15. Transition energies of benzoquinone anions are immune to symmetry breaking by a single water molecule.

    PubMed

    Stockett, Mark H; Nielsen, Steen Brøndsted

    2016-03-14

    p-Benzoquinone is the prototypical member of the quinone class of molecules with a basic functionality relevant for the primary reactions of photosynthesis. As electronically excited quinone anions are formed in near-resonant electron transfer, key issues are how the local environment affects excited-state energy levels and deexcitation times. The former we address here with action spectroscopy of mass-selected bare radical anions (pBQ(-)) and one-water pBQ(-)·H2O complexes, isolated in vacuo. The complex represents a precursor for internal proton transfer to form the semiquinone free radical, the first chemical product in the light-driven electron transport chain. Both ions display bands in the visible and ultraviolet with, importantly, almost identical maxima. Despite localizing negative charge, thereby breaking the high orbital symmetries, water is surprisingly innocent. This finding implies that natural fluctuations in the quinone microenvironment cause only minor variations in excited-state energies and thus electron-transfer rates. Hence quinones are robust participants in electron transport. PMID:26490302

  16. A proactive role of water molecules in acceptor recognition by protein O-fucosyltransferase 2.

    PubMed

    Valero-González, Jessika; Leonhard-Melief, Christina; Lira-Navarrete, Erandi; Jiménez-Osés, Gonzalo; Hernández-Ruiz, Cristina; Pallarés, María Carmen; Yruela, Inmaculada; Vasudevan, Deepika; Lostao, Anabel; Corzana, Francisco; Takeuchi, Hideyuki; Haltiwanger, Robert S; Hurtado-Guerrero, Ramon

    2016-04-01

    Protein O-fucosyltransferase 2 (POFUT2) is an essential enzyme that fucosylates serine and threonine residues of folded thrombospondin type 1 repeats (TSRs). To date, the mechanism by which this enzyme recognizes very dissimilar TSRs has been unclear. By engineering a fusion protein, we report the crystal structure of Caenorhabditis elegans POFUT2 (CePOFUT2) in complex with GDP and human TSR1 that suggests an inverting mechanism for fucose transfer assisted by a catalytic base and shows that nearly half of the TSR1 is embraced by CePOFUT2. A small number of direct interactions and a large network of water molecules maintain the complex. Site-directed mutagenesis demonstrates that POFUT2 fucosylates threonine preferentially over serine and relies on folded TSRs containing the minimal consensus sequence C-X-X-S/T-C. Crystallographic and mutagenesis data, together with atomic-level simulations, uncover a binding mechanism by which POFUT2 promiscuously recognizes the structural fingerprint of poorly homologous TSRs through a dynamic network of water-mediated interactions. PMID:26854667

  17. Hyperfine coupling constants on inner-sphere water molecules of Gd(III)-based MRI contrast agents.

    PubMed

    Esteban-Gómez, David; de Blas, Andrés; Rodríguez-Blas, Teresa; Helm, Lothar; Platas-Iglesias, Carlos

    2012-11-12

    Herein we present a theoretical investigation of the hyperfine coupling constants (HFCCs) on the inner-sphere water molecules of [Gd(H(2)O)(8)](3+) and different Gd(III)-based magnetic resonance imaging contrast agents such as [Gd(DOTA)(H(2)O)](-), [Gd(DTPA)(H(2)O)](2-), [Gd(DTPA-BMA)(H(2)O)] and [Gd(HP-DO3A)(H(2)O)]. DFT calculations performed on the [Gd(H(2)O)(8)](3+) model system show that both hybrid-GGA functionals (BH&HLYP, B3PW91 and PBE1PBE) and the hybrid meta-GGA functional TPSSh provide (17)O HFCCs in close agreement with the experimental data. The use of all-electron relativistic approaches based on the DKH2 approximation and the use of relativistic effective core potentials (RECP) provide results of essentially the same quality. The accurate calculation of HFCCs on the [Gd(DOTA)(H(2)O)](-), [Gd(DTPA)(H(2)O)](2-), [Gd(DTPA-BMA)(H(2)O)] and [Gd(HP-DO3A)(H(2)O)] complexes requires an adequate description of solvent effects. This was achieved by using a mixed cluster/continuum approach that includes explicitly two second-sphere water molecules. The calculated isotropic (17)O HFCCs (A(iso)) fall within the range 0.40-0.56 MHz, and show deviations from the corresponding experimental values typically lower than 0.05 MHz. The A(iso) values are significantly affected by the distance between the oxygen atom of the coordinated water molecule and the Gd(III) ion, as well as by the orientation of the water molecule plane with respect to the Gd-O vector. (1)H HFCCs of coordinated water molecules and (17)O HFCCs of second-sphere water molecules take values close to zero. PMID:22927182

  18. SU-F-19A-02: Comparison of Absorbed Dose to Water Standards for HDR Ir-192 Brachytherapy Between the LCR, Brazil and NRC, Canada

    SciTech Connect

    Salata, C; David, M; Almeida, C de; El Gamal, I; Cojocaru, C; Mainegra-Hing, E; McEwen, M

    2014-06-15

    Purpose: To compare absorbed dose to water standards for HDR brachytherapy dosimetry developed by the Radiological Science Laboratory of Rio de Janeiro State University (LCR) and the National Research Council, Canada (NRC). Methods: The two institutions have separately developed absorbed dose standards based on the Fricke dosimetry system. There are important differences between the two standards, including: preparation and read-out of the Fricke solution, irradiation geometry of the Fricke holder in relation to the Ir-192 source, and determination of the G-value to be used at Ir-192 energies. All measurements for both standards were made directly at the NRC laboratory (i.e., no transfer instrument was used) using a single Ir-192 source (microSelectron v2). In addition, the NRC group has established a self-consistent method to determine the G-value for Ir-192, based on an interpolation between G-values obtained at Co-60 and 250kVp X-rays, and this measurement was repeated using the LCR Fricke solution to investigate possible systematic uncertainties. Results: G-values for Co-60 and 250 kVp x-rays, obtained using the LCR Fricke system, agreed with the NRC values within 0.5 % and 1 % respectively, indicating that the general assumption of universal G-values is appropriate in this case. The standard uncertainty in the determination of G for Ir-192 is estimated to be 0.6 %. For the comparison of absorbed dose measurements at the reference point for Ir-192 (1 cm depth in water, perpendicular to the seed long-axis), the ratio Dw(NRC)/Dw(LCR) was found to be 1.011 with a combined standard uncertainty of 1.7 %, k=1. Conclusion: The agreement in the absorbed dose to water values for the LCR and NRC systems is very encouraging. Combined with the lower uncertainty in this approach compared to the present air-kerma approach, these results reaffirm the use of Fricke solution as a potential primary standard for HDR Ir-192 brachytherapy.

  19. Key comparison BIPM.RI(I)-K6 of the standards for absorbed dose to water of the ARPANSA, Australia and the BIPM in accelerator photon beams

    NASA Astrophysics Data System (ADS)

    Picard, S.; Burns, D. T.; Roger, P.; Harty, P. D.; Ramanathan, G.; Lye, J. E.; Wright, T.; Butler, D. J.; Cole, A.; Oliver, C.; Webb, D. V.

    2014-01-01

    A comparison of the dosimetry for accelerator photon beams was carried out between the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) and the Bureau International des Poids et Mesures (BIPM) in September and October 2012. The comparison was based on the determination of absorbed dose to water for three radiation qualities at the ARPANSA. Following receipt of the provisional comparison results, the ARPANSA decided to verify the geometry of the jacket and calorimeter core. This resulted in a change in the conversion factors applied by the ARPANSA to convert from absorbed dose to graphite to absorbed dose to water which was implemented after the comparison. The results for the revised standard, reported as a ratio of the ARPANSA and the BIPM evaluations, are 0.9965 at 6 MV, 0.9924 at 10 MV and 0.9932 at 18 MV, with a combined standard uncertainty of 5.5 parts in 103, 6.0 parts in 103 and 5.9 parts in 103, respectively. This result is the fifth in the on-going BIPM.RI(I)-K6 series of comparisons, and the first to be based solely on graphite calorimetry. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

  20. AFM investigation of effect of absorbed water layer structure on growth mechanism of octadecyltrichlorosilane self-assembled monolayer on oxidized silicon

    NASA Astrophysics Data System (ADS)

    Li, Shaowei; Zheng, Yanjun; Chen, Changfeng

    2016-06-01

    The growth mechanism of an octadecyltrichlorosilane (OTS) self-assembled monolayer on a silicon oxide surface at various relative humidities has been investigated. Atomic force microscopy images show that excess water may actually hinder the nucleation and growth of OTS islands. A moderate amount of water is favorable for the nucleation and growth of OTS islands in the initial stage; however, the completion of the monolayer is very slow in the final stage. The growth of OTS islands on a low-water-content surface maintains a relatively constant speed and requires the least amount of time. The mobility of water molecules is thought to play an important role in the OTS monolayers, and a low-mobility water layer provides a steady condition for OTS monolayer growth.

  1. AFM investigation of effect of absorbed water layer structure on growth mechanism of octadecyltrichlorosilane self-assembled monolayer on oxidized silicon.

    PubMed

    Li, Shaowei; Zheng, Yanjun; Chen, Changfeng

    2016-06-28

    The growth mechanism of an octadecyltrichlorosilane (OTS) self-assembled monolayer on a silicon oxide surface at various relative humidities has been investigated. Atomic force microscopy images show that excess water may actually hinder the nucleation and growth of OTS islands. A moderate amount of water is favorable for the nucleation and growth of OTS islands in the initial stage; however, the completion of the monolayer is very slow in the final stage. The growth of OTS islands on a low-water-content surface maintains a relatively constant speed and requires the least amount of time. The mobility of water molecules is thought to play an important role in the OTS monolayers, and a low-mobility water layer provides a steady condition for OTS monolayer growth. PMID:27369535

  2. Optimization of water absorbing exopolysaccharide production on local cheap substrates by Bacillus strain CMG1403 using one variable at a time approach.

    PubMed

    Muhammadi; Afzal, Muhammad

    2014-01-01

    Optimum culture conditions, and carbon and nitrogen sources for production of water absorbing exopolysaccharide by Bacillus strain CMG1403 on local cheap substrates were determined using one variable at a time approach. Carbon source was found to be sole substrate for EPS biosynthesis in the presence of yeast extract that supported the growth only and hence, indirectly enhanced the EPS yield. Whereas, urea only coupled with carbon source could enhance the EPS production but no effect on growth. The maximum yield of EPS was obtained when Bacillus strain CMG1403 was grown statically in neutral minimal medium with 25% volumetric aeration at 30°C for 10 days. Under these optimum conditions, a maximum yield of 2.71±0.024, 3.82±0.005, 4.33±0.021, 4.73±0.021, 4.85±0.024, and 5.52±0.016 g/L culture medium was obtained with 20 g (sugar) of sweet whey, glucose, fructose, sucrose, cane molasses and sugar beet the most efficient one respectively as carbon sources. Thus, the present study showed that under optimum culture conditions, the local cheap substrates could be superior and efficient alternatives to synthetic carbon sources providing way for an economical production of water absorbing EPS by indigenous soil bacterium Bacillus strain CMG1403. PMID:24390837

  3. Key comparison BIPM.RI(I)-K4 of the absorbed dose to water standards of the PTB, Germany and the BIPM in 60Co gamma radiation

    NASA Astrophysics Data System (ADS)

    Kessler, C.; Burns, D. T.; Kapsch, R.-P.; Krauss, A.

    2016-01-01

    An indirect comparison has been made of the standards for absorbed dose to water in 60Co radiation of the Physikalisch-Technische Bundesanstalt, (PTB), Germany and of the Bureau International des Poids et Mesures (BIPM). The measurements at the BIPM were carried out in October 2015. The comparison result, based on the calibration coefficients for two transfer standards and evaluated as a ratio of the PTB and the BIPM standards for absorbed dose to water, is 0.9977 with a combined standard uncertainty of 3.8 × 10-3. The results are analysed and presented in terms of degrees of equivalence for entry in the BIPM key comparison database. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

  4. Absorbent Material

    NASA Technical Reports Server (NTRS)

    1985-01-01

    A superabsorbent fabric developed by Johnson Space Center and described in Tech Briefs was adapted by Honeywell and fabricated into special containment devices used on Navy "smart" torpedos. The superabsorbent fabric can sequester up to 400 times its own weight in water and protects the torpedo electronic controls from possible short circuiting by deepwater hull seepage.

  5. Water

    MedlinePlus

    ... Shopping Tips Food Safety Common Questions Learn More Water Printer-friendly It’s important for your body to have plenty of fluids each day. Water helps you digest food, absorb nutrients from food, ...

  6. Absorbent product to absorb fluids. [for collection of human wastes

    NASA Technical Reports Server (NTRS)

    Dawn, F. S.; Correale, J. V. (Inventor)

    1982-01-01

    A multi-layer absorbent product for use in contact with the skin to absorb fluids is discussed. The product utilizes a water pervious facing layer for contacting the skin, overlayed by a first fibrous wicking layer, the wicking layer preferably being of the one-way variety in which fluid or liquid is moved away from the facing layer. The product further includes a first container section defined by inner and outer layer of a water pervious wicking material between which is disposed a first absorbent mass. A second container section defined by inner and outer layers between which is disposed a second absorbent mass and a liquid impermeable/gas permeable layer. Spacesuit applications are discussed.

  7. A better energy allocation of absorbed light in photosystem II and less photooxidative damage contribute to acclimation of Arabidopsis thaliana young leaves to water deficit.

    PubMed

    Sperdouli, Ilektra; Moustakas, Michael

    2014-05-01

    Water deficit stress promotes excitation pressure and photooxidative damage due to an imbalance between light capture and energy use. Young leaves (YL) of Arabidopsis thaliana plants acclimate better to the onset of water deficit (OnsWD) than do mature leaves (ML). To obtain a better understanding of this differential response, we evaluated whether YL and ML of A. thaliana exposed to the OnsWD, mild water deficit (MiWD) and moderate water deficit (MoWD), show differences in their photosynthetic performance, and whether photosynthetic acclimation correlates with leaf developmental stage. Water deficit (WD) resulted in greater photooxidative damage in ML compared to YL, but the latter could not be protected under the OnsWD or MiWD, but only under MoWD. YL of A. thaliana with signs of photosynthetic acclimation under MoWD retained higher maximum quantum yield (Fv/Fm) and decreased reactive oxygen species (ROS) formation. YL under MoWD, show a reduced excitation pressure and a better balance between light capture and photochemical energy use, which contributed to their photoprotection, but only under low light intensity (LL, 130μmolphotonsm(-2)s(-1)) and not under high light (HL, 1200μmolphotonsm(-2)s(-1)). In conclusion, leaf developmental stage was correlated with photo-oxidative damage and a differential allocation of absorbed light energy in photosystem II (PSII) of Arabidopsis leaves under WD. PMID:24709149

  8. Two-dimensional description of surface-bounded exospheres with application to the migration of water molecules on the Moon

    NASA Astrophysics Data System (ADS)

    Schorghofer, Norbert

    2015-05-01

    On the Moon, water molecules and other volatiles are thought to migrate along ballistic trajectories. Here, this migration process is described in terms of a two-dimensional partial differential equation for the surface concentration, based on the probability distribution of thermal ballistic hops. A random-walk model, a corresponding diffusion coefficient, and a continuum description are provided. In other words, a surface-bounded exosphere is described purely in terms of quantities on the surface, which can provide computational and conceptual advantages. The derived continuum equation can be used to calculate the steady-state distribution of the surface concentration of volatile water molecules. An analytic steady-state solution is obtained for an equatorial ring; it reveals the width and mass of the pileup of molecules at the morning terminator.

  9. Single-molecule analysis of ultradilute solutions with guided streams of 1-{mu}m water droplets

    SciTech Connect

    Kung, C.; Barnes, M.D.; Lermer, N.; Whitten, W.B.; Ramsey, J.M.

    1999-03-01

    We describe instrumentation for real-time detection of single-molecule fluorescence in guided streams of 1-{mu}m (nominal) water droplets. In this technique, target molecules were confined to droplets whose volumes were comparable with illumination volumes in diffraction-limited fluorescence microscopy and guided to the waist of a cw probe laser with an electrostatic potential. Concentration detection limits for Rhodamine 6G in water were determined to be {approximately}1 fM, roughly 3 orders of magnitude lower than corresponding limits determined recently with diffraction-limited microscopy techniques for a chemical separation of similar dyes. In addition to its utility as a vehicle for probing single molecules, instrumentation for producing and focusing stable streams of 1{endash}2-{mu}m-diameter droplets may have other important analytical applications as well. {copyright} 1999 Optical Society of America

  10. Cardioprotective actions by a water-soluble carbon monoxide-releasing molecule.

    PubMed

    Clark, James E; Naughton, Patrick; Shurey, Sandra; Green, Colin J; Johnson, Tony R; Mann, Brian E; Foresti, Roberta; Motterlini, Roberto

    2003-07-25

    Carbon monoxide, which is generated in mammals during the degradation of heme by the enzyme heme oxygenase, is an important signaling mediator. Transition metal carbonyls have been recently shown to function as carbon monoxide-releasing molecules (CO-RMs) and to elicit distinct pharmacological activities in biological systems. In the present study, we report that a water-soluble form of CO-RM promotes cardioprotection in vitro and in vivo. Specifically, we found that tricarbonylchloro(glycinato)ruthenium(II) (CORM-3) is stable in water at acidic pH but in physiological buffers rapidly liberates CO in solution. Cardiac cells pretreated with CORM-3 (10 to 50 micromol/L) become more resistant to the damage caused by hypoxia-reoxygenation and oxidative stress. In addition, isolated hearts reperfused in the presence of CORM-3 (10 micromol/L) after an ischemic event displayed a significant recovery in myocardial performance and a marked and significant reduction in cardiac muscle damage and infarct size. The cardioprotective effects mediated by CORM-3 in cardiac cells and isolated hearts were totally abolished by 5-hydroxydecanoic acid, an inhibitor of mitochondrial ATP-dependent potassium channels. Predictably, cardioprotection is lost when CORM-3 is replaced by an inactive form (iCORM-3) that is incapable of liberating CO. Using a model of cardiac allograft rejection in mice, we also found that treatment of recipients with CORM-3 but not iCORM-3 considerably prolonged the survival rate of transplanted hearts. These data corroborate the notion that transition metal carbonyls could be used as carriers to deliver CO and highlight the bioactivity and potential therapeutic features of CO-RMs in the mitigation of cardiac dysfunction. The full text of this article is available online at http://www.circresaha.org. PMID:12842916

  11. Computing the energy of a water molecule using multideterminants: A simple, efficient algorithm

    SciTech Connect

    Clark, Bryan K.; Morales, Miguel A; Mcminis, Jeremy; Kim, Jeongnim; Scuseria, Gustavo E

    2011-01-01

    Quantum Monte Carlo (QMC) methods such as variational Monte Carlo and fixed node diffusion Monte Carlo depend heavily on the quality of the trial wave function. Although Slater-Jastrow wave functions are the most commonly used variational ansatz in electronic structure, more sophisticated wave functions are critical to ascertaining new physics. One such wave function is the multi-Slater- Jastrow wave function which consists of a Jastrow function multiplied by the sum of Slater deter- minants. In this paper we describe a method for working with these wave functions in QMC codes that is easy to implement, efficient both in computational speed as well as memory, and easily par- allelized. The computational cost scales quadratically with particle number making this scaling no worse than the single determinant case and linear with the total number of excitations. Addition- ally, we implement this method and use it to compute the ground state energy of a water molecule. 2011 American Institute of Physics. [doi:10.1063/1.3665391

  12. Association of Catechin Molecules in Water: Quantitative Binding Study and Complex Structure Analysis.

    PubMed

    Ujihara, Tomomi; Hayashi, Nobuyuki

    2016-01-22

    Associations between catechin molecules were investigated by (1)H NMR titration experiments. Eight green tea catechins formed self-assembled dimers in water, and gallate-type catechins had a greater tendency to self-associate than non-gallate-type catechins. All eight catechins also associated as 1:1 heterodimer complexes. Investigation of complex formation of epigallocatechin-3-O-gallate (EGCg) and epigallocatechin (EGC) with the other catechins showed that the affinity between EGCg and 2,3-trans-gallate-type catechins was remarkably high, and the binding affinity of EGCg for ECg was also rather strong. In contrast, the non-gallate-type catechin EGC exhibited generally low binding affinity for other catechins. Structural analyses of the complexes by ROESY experiments and density functional theory calculations demonstrated that the higher binding abilities of gallate-type catechins are due to providing multiple intermolecular interactions that remain effective in an aqueous environment, such as aromatic/aromatic or CH/π interactions. PMID:26720794

  13. Direct determination of the absorbed dose to water from 125I low dose-rate brachytherapy seeds using the new absorbed dose primary standard developed at ENEA-INMRI

    NASA Astrophysics Data System (ADS)

    Toni, M. P.; Pimpinella, M.; Pinto, M.; Quini, M.; Cappadozzi, G.; Silvestri, C.; Bottauscio, O.

    2012-10-01

    Low-intensity radioactive sources emitting low-energy photons are used in the clinic for low dose-rate brachytherapy treatments of tumours. The dosimetry of these sources is based on reference air kerma rate measurements. The absorbed dose rate to water at the reference depth d0 = 1 cm, \\dot {D}_{w,1\\,cm} , is then obtained by a conversion procedure with a large relative standard uncertainty of about 5%. This paper describes a primary standard developed at ENEA-INMRI to directly measure \\dot {D}_{w,1\\,cm} due to LDR sources. The standard is based on a large-angle and variable-volume ionization chamber, embedded in a graphite phantom and operating under ‘wall-less air chamber’ conditions. A set of correction and conversion factors, based on experiments and Monte Carlo simulations, are determined to obtain the value of Dw,1 cm from measurements of increment of ionization current with increasing chamber volume. The relative standard uncertainty on \\dot {D}_{w,1\\,cm} is 2.6%, which is appreciably lower than the current uncertainty. Characteristics of the standard, its associated uncertainty budget, and some experimental results are given for 125I BEBIG I25.S16.C brachytherapy seeds. Finally, results of the experimental determination of the dose-rate constant Λ1 cm, traceable to the Dw,1 cm and the low-energy air kerma ENEA-INMRI standards, are given. The relative standard uncertainty on Λ1 cm is 2.9%, appreciably lower than the typical uncertainty (4.8%) of the values available in the literature.

  14. About Some Of The Properties Of A Guest Molecule Confined In A Water Network, In Order To Form A Clathrate

    NASA Astrophysics Data System (ADS)

    Pérez, G. Bravo; Cruz-Torres, A.; Romero-Martínez, A.

    2008-03-01

    At conditions of high pressure and or low temperature, like a sea bottom from even 1 Km deep, hydrates formation may take place. Its presence is facilitated at the water/oil interface inside conducting oil pipelines. Once formed, the hydrates nucleate further to agglomerations, sticking to the inner surface of the tube. This represents a big problem to flow assurance. We present results contributing to a better understanding of the interaction of a guest molecule with a water cage confining it, that give rise to a hydrate formation. The hydrate structure, its formation energy, and the role that the H bond and its cooperative effect in the water network play in the electrostatic dipole moment of the hydrate, are presented. Molecular calculations using the HF/6-311g(d, p), B3LYP/6-311g(d, p), and B3LYP/6-311++g(d,p) methods, have been applied to compare three different hydrates, each one confining one, two CH4 molecules, and a CO2 molecule, requiring respectively n = 14, 35, and 15 water molecules for the confinement.

  15. Absorbent product and articles made therefrom

    NASA Technical Reports Server (NTRS)

    Dawn, F. S.; Correale, J. V. (Inventor)

    1982-01-01

    A multilayer absorbent product for use in contact with the skin to absorb fluids is described. The product has a water pervious facing layer for contacting the skin, and a first fibrous wicking layer overlaying the water pervious layer. A first container section is defined by inner and outer layers of a water pervious wicking material in between a first absorbent mass and a second container section defined by inner and outer layers of a water pervious wicking material between what is disposed a second absorbent mass, and a liquid impermeable/gas permeable layer overlaying the second fibrous wicking layer.

  16. Nonventing, Regenerable, Lightweight Heat Absorber

    NASA Technical Reports Server (NTRS)

    Izenson, Michael G.; Chen, Weibo

    2008-01-01

    A lightweight, regenerable heat absorber (RHA), developed for rejecting metabolic heat from a space suit, may also be useful on Earth for short-term cooling of heavy protective garments. Unlike prior space-suit-cooling systems, a system that includes this RHA does not vent water. The closed system contains water reservoirs, tubes through which water is circulated to absorb heat, an evaporator, and an absorber/radiator. The radiator includes a solution of LiCl contained in a porous material in titanium tubes. The evaporator cools water that circulates through a liquid-cooled garment. Water vapor produced in the evaporator enters the radiator tubes where it is absorbed into the LiCl solution, releasing heat. Much of the heat of absorption is rejected to the environment via the radiator. After use, the RHA is regenerated by heating it to a temperature of 100 C for about 2 hours to drive the absorbed water back to the evaporator. A system including a prototype of the RHA was found to be capable of maintaining a temperature of 20 C while removing heat at a rate of 200 W for 6 hours.

  17. Estimate of the Impact of Absorbing Aerosol Over Cloud on the MODIS Retrievals of Cloud Optical Thickness and Effective Radius Using Two Independent Retrievals of Liquid Water Path

    NASA Technical Reports Server (NTRS)

    Wilcox, Eric M.; Harshvardhan; Platnick, Steven

    2009-01-01

    Two independent satellite retrievals of cloud liquid water path (LWP) from the NASA Aqua satellite are used to diagnose the impact of absorbing biomass burning aerosol overlaying boundary-layer marine water clouds on the Moderate Resolution Imaging Spectrometer (MODIS) retrievals of cloud optical thickness (tau) and cloud droplet effective radius (r(sub e)). In the MODIS retrieval over oceans, cloud reflectance in the 0.86-micrometer and 2.13-micrometer bands is used to simultaneously retrieve tau and r(sub e). A low bias in the MODIS tau retrieval may result from reductions in the 0.86-micrometer reflectance, which is only very weakly absorbed by clouds, owing to absorption by aerosols in cases where biomass burning aerosols occur above water clouds. MODIS LWP, derived from the product of the retrieved tau and r(sub e), is compared with LWP ocean retrievals from the Advanced Microwave Scanning Radiometer-EOS (AMSR-E), determined from cloud microwave emission that is transparent to aerosols. For the coastal Atlantic southern African region investigated in this study, a systematic difference between AMSR-E and MODIS LWP retrievals is found for stratocumulus clouds over three biomass burning months in 2005 and 2006 that is consistent with above-cloud absorbing aerosols. Biomass burning aerosol is detected using the ultraviolet aerosol index from the Ozone Monitoring Instrument (OMI) on the Aura satellite. The LWP difference (AMSR-E minus MODIS) increases both with increasing tau and increasing OMI aerosol index. During the biomass burning season the mean LWP difference is 14 g per square meters, which is within the 15-20 g per square meter range of estimated uncertainties in instantaneous LWP retrievals. For samples with only low amounts of overlaying smoke (OMI AI less than or equal to 1) the difference is 9.4, suggesting that the impact of smoke aerosols on the mean MODIS LWP is 5.6 g per square meter. Only for scenes with OMI aerosol index greater than 2 does the

  18. Comparison of MCNPX and GEANT4 to Predict the Contribution of Non-elastic Nuclear Interactions to Absorbed Dose in Water, PMMA and A150

    NASA Astrophysics Data System (ADS)

    Shtejer, K.; Arruda-Neto, J. D. T.; Schulte, R.; Wroe, A.; Rodrigues, T. E.; de Menezes, M. O.; Moralles, M.; Guzmán, F.; Manso, M. V.

    2008-08-01

    Proton induced non-elastic nuclear reactions play an important role in the dose distribution of clinically used proton beams as they deposit dose of high biological effectiveness both within the primary beam path as well as outside the beam to untargeted tissues. Non-elastic nuclear reactions can be evaluated using transport codes based on the Monte Carlo method. In this work, we have utilized the Los Alamos code MCNPX and the CERN GEANT4 toolkit, which are currently the most widely used Monte Carlo programs for proton radiation transport simulations in medical physics, to study the contribution of non-elastic nuclear interactions to the absorbed dose of proton beams in the therapeutic energy range. The impact of different available theoretical models to address the nuclear reaction process was investigated. The contribution of secondary particles from non-elastic nuclear reactions was calculated in three materials relevant in radiotherapy applications: water, PMMA and A150. The results evidence that there are differences in the calculated contribution of the secondary particles heavier than protons to the absorbed dose, with different approaches to model the nuclear reactions. The MCNPX calculation give rise to a larger contribution of d, t, α3He to the total dose compared to the GEANT4 physical models chosen in this work.

  19. Comparison of MCNPX and GEANT4 to Predict the Contribution of Non-elastic Nuclear Interactions to Absorbed Dose in Water, PMMA and A150

    SciTech Connect

    Shtejer, K.; Arruda-Neto, J. D. T.; Rodrigues, T. E.; Schulte, R.; Wroe, A.; Menezes, M. O. de; Moralles, M.

    2008-08-11

    Proton induced non-elastic nuclear reactions play an important role in the dose distribution of clinically used proton beams as they deposit dose of high biological effectiveness both within the primary beam path as well as outside the beam to untargeted tissues. Non-elastic nuclear reactions can be evaluated using transport codes based on the Monte Carlo method. In this work, we have utilized the Los Alamos code MCNPX and the CERN GEANT4 toolkit, which are currently the most widely used Monte Carlo programs for proton radiation transport simulations in medical physics, to study the contribution of non-elastic nuclear interactions to the absorbed dose of proton beams in the therapeutic energy range. The impact of different available theoretical models to address the nuclear reaction process was investigated. The contribution of secondary particles from non-elastic nuclear reactions was calculated in three materials relevant in radiotherapy applications: water, PMMA and A150. The results evidence that there are differences in the calculated contribution of the secondary particles heavier than protons to the absorbed dose, with different approaches to model the nuclear reactions. The MCNPX calculation give rise to a larger contribution of d, t, {alpha}{sup 3}He to the total dose compared to the GEANT4 physical models chosen in this work.

  20. Formation of nitrogen- and sulfur-containing light-absorbing compounds accelerated by evaporation of water from secondary organic aerosols

    NASA Astrophysics Data System (ADS)

    Nguyen, Tran B.; Lee, Paula B.; Updyke, Katelyn M.; Bones, David L.; Laskin, Julia; Laskin, Alexander; Nizkorodov, Sergey A.

    2012-01-01

    Aqueous extracts of secondary organic aerosols (SOA) generated from the ozonolysis of d-limonene were subjected to dissolution, evaporation, and re-dissolution in the presence and absence of ammonium sulfate (AS). Evaporation with AS at pH 4-9 produced chromophores that were stable with respect to hydrolysis and had a distinctive absorption band at 500 nm. Evaporation accelerated the rate of chromophore formation by at least three orders of magnitude compared to the reaction in aqueous solution, which produced similar compounds. Absorption spectroscopy and high-resolution nanospray desorption electrospray ionization (nano-DESI) mass spectrometry experiments suggested that the molar fraction of the chromophores was small (<2%), and that they contained nitrogen atoms. Although the colored products represented only a small fraction of SOA, their large extinction coefficients (>105 L mol-1 cm-1 at 500 nm) increased the effective mass absorption coefficient of the residual organics in excess of 103 cm2 g-1 - a dramatic effect on the optical properties from minor constituents. Evaporation of SOA extracts in the absence of AS resulted in the production of colored compounds only when the SOA extract was acidified to pH ˜ 2 with sulfuric acid. These chromophores were produced by acid-catalyzed aldol condensation, followed by a conversion into organosulfates. The presence of organosulfates was confirmed by high resolution mass spectrometry experiments. Results of this study suggest that evaporation of cloud or fog droplets containing dissolved organics leads to significant modification of the molecular composition and serves as a potentially important source of light-absorbing compounds.

  1. Formation of Nitrogen- and Sulfur-Containing Light-Absorbing Compounds Accelerated by Evaporation of Water from Secondary Organic Aerosols

    SciTech Connect

    Nguyen, Tran B.; Lee, Paula B.; Updyke, Katelyn M.; Bones, David L.; Laskin, Julia; Laskin, Alexander; Nizkorodov, Sergey

    2012-01-14

    Aqueous extracts of secondary organic aerosols (SOA) generated from the ozonolysis of dlimonene were subjected to dissolution, evaporation, and re-dissolution in the presence and absence of ammonium sulfate (AS). Evaporation with AS at pH 4-9 produced chromophores that were stable with respect to hydrolysis and had a distinctive absorption band at 500 nm. Evaporation accelerated the rate of chromophore formation by at least three orders of magnitude compared to the reaction in aqueous solution, which produced similar compounds. Absorption spectroscopy and high-resolution nanospray desorption electrospray ionization (nano-DESI) mass spectrometry experiments suggested that the molar fraction of the chromophores was small (< 2%), and that they contained nitrogen atoms. Although the colored products represented only a small fraction of SOA, their large extinction coefficients (>10{sup 5} L mol{sup -1} cm{sup -1} at 500 nm) increased the effective mass absorption coefficient of the residual organics in excess of 10{sup 3} cm{sup 2} g{sup -1} - a dramatic effect on the optical properties from minor constituents. Evaporation of SOA extracts in the absence of AS resulted in the production of colored compounds only when the SOA extract was acidified to pH {approx} 2 with sulfuric acid. These chromophores were produced by acid-catalyzed aldol condensation, followed by a conversion into organosulfates. The presence of organosulfates was confirmed by high resolution mass spectrometry experiments. Results of this study suggest that evaporation of cloud or fog droplets containing dissolved organics leads to significant modification of the molecular composition and serves as a potentially important source of light-absorbing compounds.

  2. Extremely efficient and recyclable absorbents for oily pollutants enabled by ultrathin-layered functionalization.

    PubMed

    Wang, Qianqian; Wang, Hanghua; Xiong, Sen; Chen, Rizhi; Wang, Yong

    2014-11-12

    Oils and organic solvents that leak into water bodies must be promptly removed to avoid ecological disasters, for example, by selective absorption using oleophilic absorbents. However, it remains a challenge for the low-cost synthesis of efficient and recyclable absorbents for oily pollutants. By surface functionalization to inexpensive polyurethane (PU) foams, we synthesize oil absorbents exhibiting the highest absorption capacity and the best recyclability among all polymeric absorbents. The synthesis is enabled by atomic layer deposition of ∼5 nm-thick Al2O3 transition layer onto the skeleton surface of PU foams, followed by coupling a single-molecule layer of silanes to the Al2O3 layer. The sub-10 nm functionalization layer provides the PU foam an outstanding water-repelling and oil-absorbing functionality without compromising its high porosity and elasticity. The functionalized foam is able to quickly absorb oily pollutants spread on water surfaces or precipitated in water with a capacity more than 100 times its own weight. This ultrathin-layer-functionalization method is also applicable to renewable porous biomaterials, providing a sustainable solution for oil spills. Moreover, we propose devices than can continuously operate to efficiently collect oil spills from water surfaces based on the functionalized PU foam developed in this work. PMID:25315285

  3. Differential flexibility of the secondary structures of lysozyme and the structure and ordering of surrounding water molecules

    NASA Astrophysics Data System (ADS)

    Sinha, Sudipta Kumar; Bandyopadhyay, Sanjoy

    2011-03-01

    We have performed an atomistic molecular dynamics simulation of an aqueous solution of hen egg-white lysozyme at room temperature with explicit water molecules. Several analyses have been carried out to explore the differential flexibility of the secondary structural segments of the protein and the structure and ordering of water around them. It is found that the overall flexibility of the protein molecule is primarily controlled by few large-amplitude bistable motions exhibited by two coils; one connecting two α-helical segments in domain-1 and the other connecting a 310 helix and a β-sheet in domain-2 of the protein. The heterogeneous structuring of water around the segments of the protein has been found to depend on the degree of exposure of the segments to water. The ordering of water molecules around the protein segments and their tagged potential energies have been found to be anticorrelated with each other. Some of these findings can be verified by suitable experimental studies.

  4. Absorbing a Little Water: The Structural, Thermodynamic, and Kinetic Relationship between Pyrogallol and Its Tetarto-Hydrate.

    PubMed

    Braun, Doris E; Bhardwaj, Rajni M; Arlin, Jean-Baptiste; Florence, Alastair J; Kahlenberg, Volker; Griesser, Ulrich J; Tocher, Derek A; Price, Sarah L

    2013-09-01

    The anhydrate and the stoichiometric tetarto-hydrate of pyrogallol (0.25 mol water per mol pyrogallol) are both storage stable at ambient conditions, provided that they are phase pure, with the system being at equilibrium at a w (water activity) = 0.15 at 25 °C. Structures have been derived from single crystal and powder X-ray diffraction data for the anhydrate and hydrate, respectively. It is notable that the tetarto-hydrate forms a tetragonal structure with water in channels, a framework that although stabilized by water, is found as a higher energy structure on a computationally generated crystal energy landscape, which has the anhydrate crystal structure as the most stable form. Thus, a combination of slurry experiments, X-ray diffraction, spectroscopy, moisture (de)sorption, and thermo-analytical methods with the computationally generated crystal energy landscape and lattice energy calculations provides a consistent picture of the finely balanced hydration behavior of pyrogallol. In addition, two monotropically related dimethyl sulfoxide monosolvates were found in the accompanying solid form screen. PMID:24027438

  5. Label-Free Fluctuation Spectroscopy Based on Coherent Anti-Stokes Raman Scattering from Bulk Water Molecules.

    PubMed

    Rabasovic, M D; Sisamakis, E; Wennmalm, S; Widengren, J

    2016-04-01

    Nanoparticles (NPs) and molecules can be analyzed by inverse fluorescence correlation spectroscopy (iFCS) as they pass through an open detection volume, displacing fractions of the fluorescence-emitting solution in which they are dissolved. iFCS does not require the NPs or molecules to be labeled. However, fluorophores in μm-mm concentrations are needed for the solution signal. Here, we instead use coherent anti-Stokes Raman scattering (CARS) from plain water molecules as the signal from the solution. By this fully label-free approach, termed inverse CARS-based correlation spectroscopy (iCARS-CS), NPs that are a few tenths of nm in diameter and at pM concentrations can be analyzed, and their absolute volumes/concentrations can be determined. Likewise, lipid vesicles can be analyzed as they diffuse/flow through the detection volume by using CARS fluctuations from the surrounding water molecules. iCARS-CS could likely offer a broadly applicable, label-free characterization technique of, for example, NPs, small lipid exosomes, or microparticles in biomolecular diagnostics and screening, and can also utilize CARS signals from biologically relevant media other than water. PMID:26819085

  6. The Formation of Oxygen-Containing Molecules in Liquid Water Environments on the Surface of Titan (Invited)

    NASA Astrophysics Data System (ADS)

    Neish, C.

    2010-12-01

    Saturn’s moon Titan represents a unique locale for studying prebiotic chemistry. Reactions occurring in its thick nitrogen - methane atmosphere produce a wide variety of organic molecules. Observations by the Voyager spacecraft found evidence for six gas-phase hydrocarbons and three nitriles, along with an enveloping haze layer shrouding the surface of the moon (Hanel et al., 1981; Kunde et al., 1981; Maguire et al., 1981). More recently, the INMS instrument on the Cassini spacecraft has found evidence for organic molecules up to its mass limit of 100 Da at altitudes as high as 1200 km (Waite et al., 2005; Vuitton et al. 2007). Laboratory experiments that simulate the reactions occurring in Titan’s atmosphere produce many of the same organic molecules observed by Voyager and Cassini, along with organic precipitates known as tholins. Tholins have the general formula CxHyNz and are spectrally similar to Titan’s haze (Khare et al., 1984). Though interesting from the point of view of organic chemistry, the molecules found in Titan’s atmosphere stop short of addressing questions related to the origins of life. Oxygen - a key element for most known biological molecules - is generally lacking in Titan’s atmosphere. The most abundant oxygenated molecule, CO, is present at only ~50 ppm (de Kok et al., 2007). However, if Titan’s atmospheric organic molecules mix with water found in cryovolcanic lavas or impact melts, they may react to produce oxygen-containing, prebiotic species. In this paper, I will show that reactions between Titan tholins and low temperature aqueous solutions produce a wide variety of oxygen-containing species. These reactions display first-order kinetic behaviour with half-lives between 0.4 to 7 days at 273 K (in water) and between 0.3 and 14 days at 253 K (in 13 wt. % ammonia-water). Tholin hydrolysis is thus very fast compared to the freezing timescales of impact melts and volcanic sites on Titan, which take hundreds to thousands of years

  7. Extraction of Organic Molecules from Terrestrial Material: Quantitative Yields from Heat and Water Extractions

    NASA Technical Reports Server (NTRS)

    Beegle, L. W.; Abbey, W. A.; Tsapin, A. T.; Dragoi, D.; Kanik, I.

    2004-01-01

    In the robotic search for life on Mars, different proposed missions will analyze the chemical and biological signatures of life using different platforms. The analysis of samples via analytical instrumentation on the surface of Mars has thus far only been attempted by the two Viking missions. Robotic arms scooped relogith material into a pyrolysis oven attached to a GC/MS. No trace of organic material was found on any of the two different samples at either of the two different landing sites. This null result puts an upper limit on the amount of organics that might be present in Martian soil/rocks, although the level of detection for each individual molecular species is still debated. Determining the absolute limit of detection for each analytical instrument is essential so that null results can be understood. This includes investigating the trade off of using pyrolysis versus liquid solvent extraction to release organic materials (in terms of extraction efficiencies and the complexity of the sample extraction process.) Extraction of organics from field samples can be accomplished by a variety of methods such utilizing various solvents including HCl, pure water, supercritical fluid and Soxhelt extraction. Utilizing 6N HCl is one of the most commonly used method and frequently utilized for extraction of organics from meteorites but it is probably infeasible for robotic exploration due to difficulty of storage and transport. Extraction utilizing H2O is promising, but it could be less efficient than 6N HCl. Both supercritical fluid and Soxhelt extraction methods require bulky hardware and require complex steps, inappropriate for inclusion on rover spacecraft. This investigation reports the efficiencies of pyrolysis and solvent extraction methods for amino acids for different terrestrial samples. The samples studied here, initially created in aqueous environments, are sedimentary in nature. These particular samples were chosen because they possibly represent one of the

  8. Cold crystallisation behaviour of water molecules in ionic liquids as a screening method to evaluate biocompatibility of the hydrated ionic liquids.

    PubMed

    Fujita, Kyoko; Nikawa, Yohsuke; Ohno, Hiroyuki

    2013-04-21

    Hydrated ionic liquids, exhibiting cold crystallisation behaviour of water molecules in a certain range of water contents, successfully dissolved cytochrome c maintaining the original spin state of heme. PMID:23486783

  9. Reaction Kinetics of Water Molecules with Oxygen Vacancies on Rutile TiO2(110)

    SciTech Connect

    Petrik, Nikolay G.; Kimmel, Gregory A.

    2015-09-16

    The formation of bridging hydroxyls (OHb) via reactions of water molecules with oxygen vacancies (VO) on reduced TiO2(110) surfaces is studied using infrared reflection-absorption spectroscopy (IRAS), electron-stimulated desorption (ESD), and photon-stimulated desorption (PSD). Narrow IRAS peaks at 2737 cm-1 and 3711 cm-1 are observed for stretching vibrations of ODb and OHb on TiO2(110), respectively. IRAS measurements with s- and p-polarized light demonstrate that the bridging hydroxyls are oriented normal to the (110) surface. The IR peaks disappear after the sample is exposed to O2 or annealed in the temperature range of 400 – 600 K (correlating with the temperature at which pairs of OHb’s reform water and then desorb), which is consistent with their identification as bridging hydroxyls. We have studied the kinetics of water reacting with the vacancies by monitoring the formation of bridging hydroxyls (using IRAS) as a function of the annealing temperature for a small amount of water initially dosed on the TiO2(110) at low temperature. Separate experiments have also monitored the loss of water molecules (using water ESD) and vacancies (using the CO photooxidation reaction) due to the reactions of water molecules with the vacancies. All three techniques show that the reaction rate becomes appreciable for T > 150 K and that the reactions largely complete for T > 250 K. The temperature-dependent water-VO reaction kinetics are consistent with a Gaussian distribution of activation energies with Ea = 0.545 eV, ΔEa(FWHM) = 0.125 eV, and a “normal” prefactor, v = 1012 s-1. In contrast, a single activation energy with a physically reasonable prefactor does not fit the data well. Our experimental activation energy is close to theoretical estimates for the diffusion of water molecules along the Ti5c rows on the reduced TiO2

  10. Properties of Poloxamer Molecules and Poloxamer Micelles Dissolved in Water and Next to Lipid Bilayers: Results from Computer Simulations.

    PubMed

    Adhikari, Upendra; Goliaei, Ardeshir; Tsereteli, Levan; Berkowitz, Max L

    2016-07-01

    To study the properties of poloxamer molecules P85 and P188 and micelles containing these poloxamers in bulk water and also next to lipid bilayers, we performed coarse-grained molecular dynamics computer simulations. We used MARTINI force-field and adjusted Lennard-Jones nonbonded interaction strength parameters for poloxamer beads to take into account the presence of polarizable water. Simulations of systems containing poloxamer molecules or micelles solvated in bulk water showed that structural properties, such as radii of gyration of the molecules and micelles, agree with the ones inferred from experiments. We observed that P85 micelle is almost spherical in shape, whereas the P188 micelle is distorted from being spherical. Simulations containing systems with the water-lipid bilayer interface showed that hydrophilic blocks of poloxamers interact with lipid headgroups of the bilayer and remain at the interface, whereas hydrophobic blocks prefer to insert into the central hydrophobic region of the bilayer. Simulations containing poloxamer micelles next to lipid bilayer showed no permeation of these micelles into the bilayer. To study the "healing" properties of P188 poloxamer, we performed simulations on a system containing a P188 micelle next to "damaged" lipid bilayer containing a pore. We observed that hydrophobic chains of poloxamers got inserted into the bilayer through the pore region, ultimately closing the pore. PMID:26719970

  11. Adsorption of a water molecule on the MgO(100) surface as described by cluster and slab models.

    PubMed

    Karalti, Ozan; Alfè, Dario; Gillan, Michael J; Jordan, Kenneth D

    2012-06-01

    The interaction of a water molecule with the (100) surface of MgO as described by cluster models is studied using MP2, coupled MP2 (MP2C) and symmetry-adapted perturbation theory (SAPT) methods. In addition, diffusion Monte Carlo (DMC) results are presented for several slab models as well as for the smallest, 2X2 cluster model. For the 2X2 model it is found that the MP2C, DMC, and CCSD(T) methods give nearly the same potential energy curve for the water-cluster interaction, whereas the potential energy curve from the SAPT calculations differs slightly from those of the other methods. The interaction of the water molecule with the cluster models of the MgO(100) surface is weakened upon expanding the number of layers from one to two and also upon expanding the description of the layers from 2X2 to 4X4 to 6X6. The SAPT calculations reveal that both these expansions of the cluster model are accompanied by reductions in the magnitudes of the induction and dispersion constributions. The best estimate of the energy for binding an isolated water molecule to the surface obtained from the cluster model calculations is in good agreement with that obtained from the DMC calculations using a 2-layer slab model with periodic boundary conditions. PMID:22535216

  12. Discovery of earth abundant light absorbers for solar water splitting: Mn2V2O7 and beyond

    NASA Astrophysics Data System (ADS)

    Yan, Qimin; Newhouse, Pawl F.; Li, Guo; Yu, Jie; Chen, Wei; Persson, Kristin; Gregoire, John; Neaton, Jeffrey

    2015-03-01

    Utilizing a first-principles data driven discovery approach with high-throughput computations and machine learning techniques, we screen for transition metal oxide (TMO) compounds with low band gaps and optimal band edges for solar water splitting applications. Combining the computational screening with the high-throughput experimental synthesis efforts, we identify the complex oxide β-Mn2V2O7 as exhibiting a band gap and band edges that are near optimal for photocatalytic water splitting. Experiments, corroborated by theory, indicate that β-Mn2V2O7 has a near-direct band gap near 1.8 eV. Our calculations further reveal a valence band maximum composed of mixed O-p/Mn-d states, and a conduction band maximum of V d-character, leading to dipole-allowed direct transitions at the band edges. Photoelectrochemical measurements indicate appreciable photocurrent from Mn2V2O7 samples, corroborating our predictions. We further discuss design principles for guiding the discovery of more promising metal oxides with optimal band energetics for solar fuels applications. This work was supported by the DOE through the Materials Project and the Joint Center for Artificial Photosynthesis. Computational resources provided by NERSC.

  13. Dually cross-linked single network poly(acrylic acid) hydrogels with superior mechanical properties and water absorbency.

    PubMed

    Zhong, Ming; Liu, Yi-Tao; Liu, Xiao-Ying; Shi, Fu-Kuan; Zhang, Li-Qin; Zhu, Mei-Fang; Xie, Xu-Ming

    2016-06-28

    Poly(acrylic acid) (PAA) hydrogels with superior mechanical properties, based on a single network structure with dual cross-linking, are prepared by one-pot free radical polymerization. The network structure of the PAA hydrogels is composed of dual cross-linking: a dynamic and reversible ionic cross-linking among the PAA chains enabled by Fe(3+) ions, and a sparse covalent cross-linking enabled by a covalent cross-linker (Bis). Under deformation, the covalently cross-linked PAA chains remain intact to maintain their original configuration, while the Fe(3+)-enabled ionic cross-linking among the PAA chains is broken to dissipate energy and then recombined. It is found that the mechanical properties of the PAA hydrogels are significantly influenced by the contents of covalent cross-linkers, Fe(3+) ions and water, which can be adjusted within a substantial range and thus broaden the applications of the hydrogels. Meanwhile, the PAA hydrogels have excellent recoverability based on the dynamic and reversible ionic cross-linking enabled by Fe(3+) ions. Moreover, the swelling capacity of the PAA hydrogels is as high as 1800 times in deionized water due to the synergistic effects of ionic and covalent cross-linkings. The combination of balanced mechanical properties, efficient recoverability, high swelling capacity and facile preparation provides a new method to obtain high-performance hydrogels. PMID:27230478

  14. Optimisation of an integrated optical evanescent wave absorbance sensor for the determination of chlorinated hydrocarbons in water.

    PubMed

    Mayer, J; Bürck, J; Ache, H J

    1996-03-01

    The suitability of an integrated optical chemical sensor for the determination of highly volatile chlorinated hydrocarbons in aqueous solutions has been proven. The analytes are detected by NIR absorption spectrometry in the evanescent field of an integrated optical strip waveguide generated in a BGG31 (Schott, Germany) glass substrate, which is coated with a hydrophobic polymer superstrate as sensing layer. It has been shown that the sensitivity increases when the refractive index of the superstrate is increased from 1.333 up to 1.46. Different UV-cured polysiloxanes with low cross sensitivity to water have been prepared. Due to the good light transmission properties of the IO-sensors prepared by this method, quantitative measurements have been performed with the model system trichloroethene (TCE) in water. A detection limit of 22 ppm has been found and the sensor response times (t(90)-value) are between five and fourteen minutes for a coating thickness of around 30 microm. The sensor response is totally reversible. The analyte desorbes in air within 2 min. The enrichment of trichloroethene in the polysiloxane coating can be described by film diffusion through the aqueous boundary layer as rate determining step. PMID:15048399

  15. Extraction and Analysis of Strontium in Water Sample Using a Sr2+ Selective Polymer as the Absorbent Phase

    PubMed Central

    Ying, Rongjian

    2015-01-01

    A kind of Sr2+ selective resin was applied as an absorption phase to extract Sr2+ ion from an aqueous solution, and the amount of Sr2+ was determined using inductively coupled plasma optical emission spectrometer. Factors, including absorption time, temperature, stirring rate, salt-out effect, desorption, and the pH of the aqueous solution, were investigated to optimize the absorption efficiency of Sr2+. Foreign ions were examined to observe their effects on the absorption behavior of Sr2+. The optimum condition was absorption time at 20 min, pH of aqueous solution 7, temperature of 35°C, and 600 rpm stirring rate. A 10 mL solution of 0.1 mol/L HCl is used as the desorption agent. The linear range of Sr2+ concentrations from 50 to 1200 μg/L was investigated with the slope of 183 μg/L. The limit of detection was 21 μg/L with 4.23% relative standard deviation. The correlation coefficient was found to be 0.9947. Under the optimized conditions, the concentrations of Sr2+ in four water samples were detected by the developed method. We propose that this method effectively extracts strontium ion from environmental water samples. PMID:26640489

  16. Radical-Molecule Reaction C3H + H2O on Amorphous Water Ice: A Promising Route for Interstellar Propynal

    NASA Astrophysics Data System (ADS)

    Xie, Hong-bin; Shao, Chang-bin; Ding, Yi-hong

    2007-11-01

    Intriguing propynal (HCCCHO) has been attracting chemist's attention since 1955. However, to date, no satisfying conclusion concerning its formation mechanism in the interstellar medium (ISM) has been reached, although a variety of gas-reaction models, including ion-molecule, radical-molecule, and molecule-molecule, have been postulated. In this paper, we consider for the first time the gas-grain interaction model that involves heterogeneous reaction at the surface of dust grain or in the icy mantles to account for the propynal's formation. Based on the detailed density functional theory (DFT) and Gaussian-3 potential energy surface studies, we found that although the gaseous process C3H+H2O-->propynal+H must surmount a considerable entrance barrier (around 10 kcal mol-1), amorphous water ice can significantly catalyze the propynal's formation to be barrierless. So, this model should be a more reasonable one for propynal's formation in the low-temperature interstellar space. This result may also represent one rare case of the water-catalyzed reaction associated with a molecular radical in space. Future experimental studies are greatly desired to probe such interesting processes.

  17. A new water absorbable mechanical Epidermal skin equivalent: the combination of hydrophobic PDMS and hydrophilic PVA hydrogel.

    PubMed

    Morales-Hurtado, M; Zeng, X; Gonzalez-Rodriguez, P; Ten Elshof, J E; van der Heide, E

    2015-06-01

    Research on human skin interactions with healthcare and lifestyle products is a topic continuously attracting scientific studies over the past years. It is possible to evaluate skin mechanical properties based on human or animal experimentation, yet in addition to possible ethical issues, these samples are hard to obtain, expensive and give rise to highly variable results. Therefore, the design of a skin equivalent is essential. This paper describes the design and characterization of a new Epidermal Skin Equivalent (ESE). The material resembles the properties of epidermis and is a first approach to mimic the mechanical properties of the human skin structure, variable with the length scale. The ESE is based on a mixture of Polydimethyl Siloxane (PDMS) and Polyvinyl Alcohol (PVA) hydrogel cross-linked with Glutaraldehyde (GA). It was chemically characterized by XPS and FTIR measurements and its cross section was observed by macroscopy and cryoSEM. Confocal Microscope analysis on the surface of the ESE showed an arithmetic roughness (Ra) between 14-16 μm and contact angle (CA) values between 50-60°, both of which are close to the values of in vivo human skins reported in the literature. The Equilibrium Water Content (ECW) was around 33.8% and Thermo Gravimetric Analysis (TGA) confirmed the composition of the ESE samples. Moreover, the mechanical performance was determined by indentation tests and Dynamo Thermo Mechanical Analysis (DTMA) shear measurements. The indentation results were in good agreement with that of the target epidermis reported in the literature with an elastic modulus between 0.1-1.5 MPa and it showed dependency on the water content. According to the DTMA measurements, the ESE exhibits a viscoelastic behavior, with a shear modulus between 1-2.5MPa variable with temperature, frequency and the hydration of the samples. PMID:25840121

  18. How water molecules affect the catalytic activity of hydrolases - A XANES study of the local structures of peptide deformylase

    NASA Astrophysics Data System (ADS)

    Cui, Peixin; Wang, Yu; Chu, Wangsheng; Guo, Xiaoyun; Yang, Feifei; Yu, Meijuan; Zhao, Haifeng; Dong, Yuhui; Xie, Yaning; Gong, Weimin; Wu, Ziyu

    2014-12-01

    Peptide deformylase (PDF) is a prokaryotic enzyme that catalyzes the deformylation of nascent peptides generated during protein synthesis and water molecules play a key role in these hydrolases. Using X-ray absorption near edge spectroscopy (XANES) and ab initio calculations we accurately probe the local atomic environment of the metal ion binding in the active site of PDF at different pH values and with different metal ions. This new approach is an effective way to monitor existing correlations among functions and structural changes. We show for the first time that the enzymatic activity depends on pH values and metal ions via the bond length of the nearest coordinating water (Wat1) to the metal ion. Combining experimental and theoretical data we may claim that PDF exhibits an enhanced enzymatic activity only when the distance of the Wat1 molecule with the metal ion falls in the limited range from 2.15 to 2.55 Å.

  19. Molecular orientation effect on the differential cross sections for the electron-impact double ionization of oriented water molecules

    SciTech Connect

    Champion, C.; Dal Cappello, C.; Oubaziz, D.; Aouchiche, H.; Popov, Yu. V.

    2010-03-15

    Double ionization of isolated water molecules fixed in space is here investigated in a theoretical approach based on the first Born approximation. Secondary electron angular distributions are reported for particular (e,3e) kinematical conditions and compared in terms of shape and magnitude. Strong dependence of the fivefold differential cross sections on the molecular target orientation is clearly observed in (e,3-1e) as well as (e,3e) channels. Furthermore, for the major part of the kinematics considered, we identified the different mechanisms involved in the double ionization of water molecule, namely, the direct shake-off process as well as the two-step1 process. They are both discussed and analyzed with respect to the molecular target orientation.

  20. Observing the water molecule in macromolecules using infrared spectrometry: structure of the hydrogen bond network and hydration mechanism

    NASA Astrophysics Data System (ADS)

    Maréchal, Y.

    2004-08-01

    The power and precision of IR spectrometry, or IR quantitative spectroscopy, to observe water molecules embedded in macromolecules, is illustrated, taking as examples the determination of the structures of the hydrogen-bond network of a dried polysaccharide, hyaluronan, of a dried protein, bovine serum albumine, and of a dried polymer, a sulfonated polyimide. We also indicate how IR spectrometry conveys original and precise information from which their hydration mechanisms can be precisely determined in terms of chemical reactions.

  1. An Approach to Improve Intestinal Absorption of Poorly Absorbed Water-Insoluble Components via Niemann-Pick C1-Like 1.

    PubMed

    Takekawa, Yuto; Sato, Yuki; Yamaki, Yoshiaki; Imai, Mei; Noto, Kazuma; Sumi, Masato; Takekuma, Yoh; Iseki, Ken; Sugawara, Mitsuru

    2016-01-01

    Dietary and biliary cholesterol absorption contributes to the maintenance of tight control of cholesterol homeostasis. Cholesterol is present as mixed micelles formed by bile salts and phospholipids in the intestinal lumen. Recently, Niemann-Pick C1-Like 1 (NPC1L1) transporter was identified as being critical for cholesterol absorption. However, the uptake mechanism of an enveloped substrate of NPC1L1 in whole lipid emulsion particles remains unclear. In this study, we investigated the uptake mechanism of a substrate of NPC1L1 in lipid emulsion particles. We also investigated whether these particles containing cholesterol can improve the intestinal absorption of other lipophilic components via NPC1L1. The uptake of lysophosphatidylcholine (LPC)-4,4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-propionic acid saccinimidyl ester (BODIPY), a fluorescently labeled phospholipid, in lipid emulsion particles containing cholesterol (1 µM) was significantly increased compared to that without cholesterol in Caco-2 cells. On the other hand, its increased uptake was significantly inhibited by ezetimibe, a selective inhibitor of NPC1L1. These results suggested that not only cholesterol but also some components in lipid emulsion particles are taken up into enterocytes via NPC1L1. We also examined an approach to improve intestinal absorption of a poorly absorbed water-insoluble component, coenzyme Q10 (CoQ10), by this mechanism. The uptake of CoQ10 in lipid emulsion particles containing cholesterol was significantly increased compared to that without cholesterol. Its increased uptake was significantly inhibited by ezetimibe. Though it is still not clear whether CoQ10 is a substrate of NPC1L1, there is a potential for improvement of the absorption of poorly absorbed components by lipid emulsion particles containing cholesterol. PMID:26934923

  2. Velocity of a Molecule Evaporated from a Water Nanodroplet: Maxwell-Boltzmann Statistics versus Non-Ergodic Events.

    PubMed

    Abdoul-Carime, Hassan; Berthias, Francis; Feketeová, Linda; Marciante, Mathieu; Calvo, Florent; Forquet, Valérian; Chermette, Henry; Farizon, Bernadette; Farizon, Michel; Märk, Tilmann D

    2015-12-01

    The velocity of a molecule evaporated from a mass-selected protonated water nanodroplet is measured by velocity map imaging in combination with a recently developed mass spectrometry technique. The measured velocity distributions allow probing statistical energy redistribution in ultimately small water nanodroplets after ultrafast electronic excitation. As the droplet size increases, the velocity distribution rapidly approaches the behavior expected for macroscopic droplets. However, a distinct high-velocity contribution provides evidence of molecular evaporation before complete energy redistribution, corresponding to non-ergodic events. PMID:26473406

  3. Velocity of a Molecule Evaporated from a Water Nanodroplet: Maxwell–Boltzmann Statistics versus Non-Ergodic Events

    PubMed Central

    Abdoul-Carime, Hassan; Berthias, Francis; Feketeová, Linda; Marciante, Mathieu; Calvo, Florent; Forquet, Valérian; Chermette, Henry; Farizon, Bernadette; Farizon, Michel; Märk, Tilmann D

    2015-01-01

    The velocity of a molecule evaporated from a mass-selected protonated water nanodroplet is measured by velocity map imaging in combination with a recently developed mass spectrometry technique. The measured velocity distributions allow probing statistical energy redistribution in ultimately small water nanodroplets after ultrafast electronic excitation. As the droplet size increases, the velocity distribution rapidly approaches the behavior expected for macroscopic droplets. However, a distinct high-velocity contribution provides evidence of molecular evaporation before complete energy redistribution, corresponding to non-ergodic events. PMID:26473406

  4. Reduction of Local Stress Concentration on Nanosheet in Layered Nanoparticles with Water Molecules

    NASA Astrophysics Data System (ADS)

    Sato, Kiminori; Numata, Kazuomi; Fujimoto, Koichiro

    2014-01-01

    The local stress concentration on 2D nanosheets is investigated for saponite layered nanoparticles by means of X-ray diffraction (XRD) and positronium (Ps) annihilation spectroscopy. XRD experiments indicated that the layered structure for the mechanochemically milled sample is maintained in the presence of H2O molecules. Ps annihilation studies of self-assembly revealed that the 2D nanosheets are well in-plane ordered after uniaxial pressure compaction without H2O molecules due to the efficient propagation of stress concentration. The present results of both XRD and Ps lifetime spectroscopy clearly demonstrates that the stress concentration on the 2D nanosheets can be reduced in the presence of H2O molecules.

  5. METHOD 415.3 - MEASUREMENT OF TOTAL ORGANIC CARBON, DISSOLVED ORGANIC CARBON AND SPECIFIC UV ABSORBANCE AT 254 NM IN SOURCE WATER AND DRINKING WATER

    EPA Science Inventory

    2.0 SUMMARY OF METHOD

    2.1 In both TOC and DOC determinations, organic carbon in the water sample is oxidized to form carbon dioxide (CO2), which is then measured by a detection system. There are two different approaches for the oxidation of organic carbon in water sample...

  6. Effects of water molecules on the chemical stability of MAGeI3 perovskite explored from a theoretical viewpoint.

    PubMed

    Sun, Ping-Ping; Chi, Wei-Jie; Li, Ze-Sheng

    2016-09-21

    The stability of perovskite in humid environments is one of the biggest obstacles for its potential applications in light harvesting and electroluminescent displays. Understanding the detailed degradation mechanism of MAGeI3 in moisture is a critical way to explore the practicability of MAGeI3 perovskite. In this study, we report a quantitative and systematic investigation of MAGeI3 degradation processes by exploring the effects of H2O molecules on the structural and electronic properties of the most stable MAGeI3(101) surface under various simulated environmental conditions with different water coverage based on first-principles calculations. The results show that H2O molecules can easily diffuse into the inner side of the perovskite and gradually corrode the structure as the number of H2O molecules increases. As a result of the interactions between perovskite and H2O molecules, a hydrated intermediate will be generated as the first step in the degradation mechanism; the perovskite will further decompose to HI and GeI2. In terms of one MAGeI3 molecule, it will be dissociated completely to GeI2 as a result of hydrolysis reactions with a minimum of 4H2O molecules. In addition, the degradation of the perovskite will also affect the electronic structure, causing a decrease in optical absorption across the visible region of the spectrum and a distinct deformation change in the crystal structure of the material. These findings further illustrate the degradation of the hydrolysis process of MAGeI3 perovskite in humid environments, which should be helpful to inspire experimentalists to take action to prolong the lifetimes of perovskite solar cells to achieve high conversion efficiency in their applications. PMID:27539944

  7. TPX/TFTR Neutral Beam energy absorbers

    SciTech Connect

    Dahlgren, F.; Wright, K.; Kamperschroer, J.; Grisham, L.; Lontai, L.; Peters, C.; VonHalle, A.

    1993-11-01

    The present beam energy absorbing surfaces on the TFTR Neutral Beams such as Ion Dumps, Calorimeters, beam defining apertures, and scrapers, are simple water cooled copper plates which wee designed to absorb (via their thermal inertia) the incident beam power for two seconds with a five minute coal down interval between pulses. These components are not capable of absorbing the anticipated beam power loading for 1000 second TPX pulses and will have to be replaced with an actively cooled design. While several actively cooled energy absorbing designs were considered,, the hypervapotron elements currently being used on the JET beamlines were chosen due to their lower cooling water demands and reliable performance on JET.

  8. Control of water molecule aggregations in copper 1,4-cyclohexanedicarboxylate coordination polymers containing pyridyl-piperazine type ligands

    NASA Astrophysics Data System (ADS)

    Qiblawi, Sultan H.; LaDuca, Robert L.

    2014-01-01

    A series of layered divalent copper coordination polymers containing 1,4-cyclohexanedicarboxylate and long-spanning pyridyl-piperazine type ligands exhibits greatly different co-crystallized water molecule aggregations depending on the specific ligands used. Both [Cu(t-14cdc)(4-bpmp)]n (1, t-14cdc = trans-1,4-cyclohexanedicarboxylate, 4-bpmp = bis(4-pyridylmethyl)piperazine) and {[Cu(t-14cdc)(4-bpfp)(H2O)2]·6H2O}n (2, 4-bpfp = bis(4-pyridylformyl)piperazine) possess 2D (4,4) coordination polymer grids. However 1 lacks any co-crystallized water and has pinched grid apertures, while 2 manifests infinite water tapes with T6(2)4(2) classification and rectangular grid apertures. {[Cu2(c-14cdc)2(4-bpmp)]·2H2O}n (3, c-14cdc = cis-1,4-cyclohexanedicarboxylate) has [Cu2(c-14cdc)]2 ribbons with paddlewheel dimeric units linked into 2D slabs by 4-bpmp tethers, along with isolated water molecule pairs. In contrast, {[Cu2(c-14cdc)2(4-bpfp)]·10H2O}n (4) shows a very similar underlying coordination polymer topology but entrains unique decameric water molecule clusters. The minor product {[Cu2(c-14cdcH)2(t-1,4-cdc)(4-bpfp)2(H2O)2]·2H2O}n (5) was isolated along with 4; this compound underwent some in situ cis to trans cyclohexane-dicarboxylate ligand isomerization and exhibits a ladder polymer motif.

  9. Water-COOH Composite Structure with Enhanced Hydrophobicity Formed by Water Molecules Embedded into Carboxyl-Terminated Self-Assembled Monolayers.

    PubMed

    Guo, Pan; Tu, Yusong; Yang, Jinrong; Wang, Chunlei; Sheng, Nan; Fang, Haiping

    2015-10-30

    By combining molecular dynamics simulations and quantum mechanics calculations, we show the formation of a composite structure composed of embedded water molecules and the COOH matrix on carboxyl-terminated self-assembled monolayers (COOH SAMs) with appropriate packing densities. This composite structure with an integrated hydrogen bond network inside reduces the hydrogen bonds with the water above. This explains the seeming contradiction on the stability of the surface water on COOH SAMs observed in experiments. The existence of the composite structure at appropriate packing densities results in the two-step distribution of contact angles of water droplets on COOH SAMs, around 0° and 35°, which compares favorably to the experimental measurements of contact angles collected from forty research articles over the past 25 years. These findings provide a molecular-level understanding of water on surfaces (including surfaces on biomolecules) with hydrophilic functional groups. PMID:26565476

  10. Water-COOH Composite Structure with Enhanced Hydrophobicity Formed by Water Molecules Embedded into Carboxyl-Terminated Self-Assembled Monolayers

    NASA Astrophysics Data System (ADS)

    Guo, Pan; Tu, Yusong; Yang, Jinrong; Wang, Chunlei; Sheng, Nan; Fang, Haiping

    2015-10-01

    By combining molecular dynamics simulations and quantum mechanics calculations, we show the formation of a composite structure composed of embedded water molecules and the COOH matrix on carboxyl-terminated self-assembled monolayers (COOH SAMs) with appropriate packing densities. This composite structure with an integrated hydrogen bond network inside reduces the hydrogen bonds with the water above. This explains the seeming contradiction on the stability of the surface water on COOH SAMs observed in experiments. The existence of the composite structure at appropriate packing densities results in the two-step distribution of contact angles of water droplets on COOH SAMs, around 0° and 35°, which compares favorably to the experimental measurements of contact angles collected from forty research articles over the past 25 years. These findings provide a molecular-level understanding of water on surfaces (including surfaces on biomolecules) with hydrophilic functional groups.

  11. Ion condensation behavior and dynamics of water molecules surrounding the sodium poly(methacrylic acid) chain in water: a molecular dynamics study.

    PubMed

    Chung, Yung-Ting; Huang, Ching-I

    2012-03-28

    All-atom molecular dynamics simulations are used to study the condensation behavior of monovalent (Na(+)) and multivalent (Ca(2+)) salt counterions associated with the co-ions (Cl(-)) surrounding the charged poly(methacrylic acid) (PMAA) chain in water. The study is extended to the influences on chain conformation, local arrangement, and dynamics of water in the highly diluted aqueous solutions. We find that even when the salt ions are monovalent, they attract more than one charged monomer and act as a bridging agent within the chain, as the multivalent salt ions. In principle, the salt ions bridge between not only the "non-adjacent" but also the "adjacent" charged monomers, leading to a more coil-like and a locally stretched conformation, respectively. With an increase in the salt concentration, the amount of coiled-type condensed ions increase and reach a maximum when the chain conformation becomes the most collapsed; whereas, the stretched-type shows an opposite trend. Our results show that the attractive interactions through the condensed salt ions between the non-adjacent monomers are responsible for the conformational collapse. When the salt concentration increases high enough, a significant increase for the stretched-type condensed ions makes an expansion effect on the chain. These stretched-type salt ions, followed by the adsorption of the co-ions and water molecules, tend to form a multilayer organization outside surrounding the PMAA chain. Thus, the expansion degree of the chain conformation is greatly limited. When only the monovalent Na(+) ions are present in the solutions, water molecules are primarily adsorbed into either the condensed Na(+) ions or the COO(-) groups. These adsorbed water molecules form hydrogen bonds with each other and enhance the local bridging behavior associated with the Na(+) condensation on the resultant chain conformation. With an increase in the amount of multivalent Ca(2+) salt ions, more water molecules are bonded directly

  12. All-electron scalar relativistic calculation of water molecule adsorption onto small gold clusters.

    PubMed

    Kuang, Xiang-Jun; Wang, Xin-Qiang; Liu, Gao-Bin

    2011-08-01

    An all-electron scalar relativistic calculation was performed on Au( n )H(2)O (n = 1-13) clusters using density functional theory (DFT) with the generalized gradient approximation at PW91 level. The calculation results reveal that, after adsorption, the small gold cluster would like to bond with oxygen and the H(2)O molecule prefers to occupy the single fold coordination site. Reflecting the strong scalar relativistic effect, Au( n ) geometries are distorted slightly but still maintain a planar structure. The Au-Au bond is strengthened and the H-O bond is weakened, as manifested by the shortening of the Au-Au bond-length and the lengthening of the H-O bond-length. The H-O-H bond angle becomes slightly larger. The enhancement of reactivity of the H(2)O molecule is obvious. The Au-O bond-lengths, adsorption energies, VIPs, HLGs, HOMO (LUMO) energy levels, charge transfers and the highest vibrational frequencies of the Au-O mode for Au( n )H(2)O clusters exhibit an obvious odd-even oscillation. The most favorable adsorption between small gold clusters and the H(2)O molecule takes place when the H(2)O molecule is adsorbed onto an even-numbered Au( n ) cluster and becomes an Au( n )H(2)O cluster with an even number of valence electrons. The odd-even alteration of magnetic moments is observed in Au( n )H(2)O clusters and may serve as material with a tunable code capacity of "0" and "1" by adsorbing a H(2)O molecule onto an odd or even-numbered small gold cluster. PMID:21140279

  13. Nucleation of Mixed Nitric Acid-Water Ice Nanoparticles in Molecular Beams that Starts with a HNO3 Molecule.

    PubMed

    Lengyel, Jozef; Pysanenko, Andriy; Kočišek, Jaroslav; Poterya, Viktoriya; Pradzynski, Christoph C; Zeuch, Thomas; Slavíček, Petr; Fárník, Michal

    2012-11-01

    Mixed (HNO3)m(H2O)n clusters generated in supersonic expansion of nitric acid vapor are investigated in two different experiments, (1) time-of-flight mass spectrometry after electron ionization and (2) Na doping and photoionization. This combination of complementary methods reveals that only clusters containing at least one acid molecule are generated, that is, the acid molecule serves as the nucleation center in the expansion. The experiments also suggest that at least four water molecules are needed for HNO3 acidic dissociation. The clusters are undoubtedly generated, as proved by electron ionization; however, they are not detected by the Na doping due to a fast charge-transfer reaction between the Na atom and HNO3. This points to limitations of the Na doping recently advocated as a general method for atmospheric aerosol detection. On the other hand, the combination of the two methods introduces a tool for detecting molecules with sizable electron affinity in clusters. PMID:26296012

  14. Tailoring 1H spin dynamics in small molecules via supercooled water: a promising approach for metabolite identification and validation.

    PubMed

    Farooq, Hashim; Soong, Ronald; Courtier-Murias, Denis; Anklin, Clemens; Simpson, André

    2012-08-01

    Metabolic mixtures are often analyzed via NMR spectroscopy as it provides a metabolic profile without sample alteration in a noninvasive manner. These mixtures however tend to be very complex and demonstrate considerable spectral overlap resulting in assignments that are sometimes ambiguous given the range of current NMR methods available. De novo molecular identification in these mixtures is generally accomplished using chemical shift information and J-coupling based experiments to determine spin connectivity information, but these techniques fall short when a molecule of interest contains nonrelaying centers. A method is presented here that enhances intramolecular spatial interactions via supercooled water and uses the resulting spatial correlations to edit mixtures. This is accomplished by utilizing nuclear Overhauser effect spectroscopy (NOESY) at subzero temperatures in capillaries to enhance NOE and provide more complete spin systems. This technique is applied to a standard mixture of three known molecules in D(2)O with overlapping resonances and is further demonstrated to assign molecules in a worm tissue extract. The current method proves to be a powerful complement to existing methods such as total correlation spectroscopy (TOCSY) to expand the range of molecules that can be assigned in situ without physical separation of mixtures. PMID:22788933

  15. Fast rotational motion of water molecules increases ordering of hydrophobes in solutions and may cause hydrophobic chains to collapse

    NASA Astrophysics Data System (ADS)

    Mohorič, Tomaž; Bren, Urban; Vlachy, Vojko

    2015-12-01

    Using the molecular dynamics simulations with separate thermostats for translational and rotational degrees of freedom, we investigate the effects of water's rotational motion on the interaction among Lennard-Jones solutes. The situation with rotational temperature higher than the translational one (TR > TT) is mimicking the effects of microwaves on model solutions. Molecular dynamics simulations suggest that solutions of Lennard-Jones solutes become increasingly more structured with the rise in TR, while keeping the TT constant. This is evidenced by an increase of the first and the second peak of the solute-solute radial distribution function. In addition, the first peak moves toward slightly larger distances; the effect seems to be caused by the destabilization of water molecules in the first hydration shell around hydrophobic solutes. More evidence of strong effects of the rotationally excited water is provided by the simulations of short hydrophobic polymers, which upon an increase in TR assume more compact conformations. In these simulations, we see the re-distribution of water molecules, which escape from hydrophobic "pockets" to better solvate the solvent exposed monomers.

  16. Effects of water molecules on tribological behavior and property measurements in nano-indentation processes - a numerical analysis

    PubMed Central

    2013-01-01

    Nano/micro-manufacturing under wet condition is an important consideration for various tool-based processes such as indentation, scratching, and machining. The existence of liquids adds complexity to the system, changes the tool/work interfacial condition, and affects material behaviors. For indentation, it may also affect material property measurements. However, little effort has been made to study this challenging issue at nano- or atomistic scale. In this study, we tackle this challenge by investigating nano-indentation processes submerged in water using the molecular dynamics (MD) simulation approach. Compared with dry indentation in which no water molecules are present, the existence of water molecules causes the increase of indentation force in initial penetration, but the decrease of indentation force in full penetration. It also reduces the sticking phenomenon between the work and tool atoms during indenter retraction, such that the indentation geometry can be better retained. Meanwhile, nano-indentation under wet condition exhibits the indentation size effect, while dry nano-indentation exhibits the reverse indentation size effect. The existence of water leads to higher computed hardness values at low indentation loads and a smaller value of Young's modulus. In addition, the friction along the tool/work interface is significantly reduced under wet indentation. PMID:24044504

  17. Fast rotational motion of water molecules increases ordering of hydrophobes in solutions and may cause hydrophobic chains to collapse.

    PubMed

    Mohorič, Tomaž; Bren, Urban; Vlachy, Vojko

    2015-12-28

    Using the molecular dynamics simulations with separate thermostats for translational and rotational degrees of freedom, we investigate the effects of water's rotational motion on the interaction among Lennard-Jones solutes. The situation with rotational temperature higher than the translational one (TR > TT) is mimicking the effects of microwaves on model solutions. Molecular dynamics simulations suggest that solutions of Lennard-Jones solutes become increasingly more structured with the rise in TR, while keeping the TT constant. This is evidenced by an increase of the first and the second peak of the solute-solute radial distribution function. In addition, the first peak moves toward slightly larger distances; the effect seems to be caused by the destabilization of water molecules in the first hydration shell around hydrophobic solutes. More evidence of strong effects of the rotationally excited water is provided by the simulations of short hydrophobic polymers, which upon an increase in TR assume more compact conformations. In these simulations, we see the re-distribution of water molecules, which escape from hydrophobic "pockets" to better solvate the solvent exposed monomers. PMID:26723695

  18. SET7/9 Catalytic Mutants Reveal the Role of Active Site Water Molecules in Lysine Multiple Methylation

    SciTech Connect

    Del Rizzo, Paul A.; Couture, Jean-François; Dirk, Lynnette M.A.; Strunk, Bethany S.; Roiko, Marijo S.; Brunzelle, Joseph S.; Houtz, Robert L.; Trievel, Raymond C.

    2010-11-15

    SET domain lysine methyltransferases (KMTs) methylate specific lysine residues in histone and non-histone substrates. These enzymes also display product specificity by catalyzing distinct degrees of methylation of the lysine {epsilon}-amino group. To elucidate the molecular mechanism underlying this specificity, we have characterized the Y245A and Y305F mutants of the human KMT SET7/9 (also known as KMT7) that alter its product specificity from a monomethyltransferase to a di- and a trimethyltransferase, respectively. Crystal structures of these mutants in complex with peptides bearing unmodified, mono-, di-, and trimethylated lysines illustrate the roles of active site water molecules in aligning the lysine {epsilon}-amino group for methyl transfer with S-adenosylmethionine. Displacement or dissociation of these solvent molecules enlarges the diameter of the active site, accommodating the increasing size of the methylated {epsilon}-amino group during successive methyl transfer reactions. Together, these results furnish new insights into the roles of active site water molecules in modulating lysine multiple methylation by SET domain KMTs and provide the first molecular snapshots of the mono-, di-, and trimethyl transfer reactions catalyzed by these enzymes.

  19. Relationships between membrane water molecules and Patman equilibration kinetics at temperatures far above the phosphatidylcholine melting point.

    PubMed

    Vaughn, Alexandra R; Bell, Thomas A; Gibbons, Elizabeth; Askew, Caitlin; Franchino, Hannabeth; Hirsche, Kelsey; Kemsley, Linea; Melchor, Stephanie; Moulton, Emma; Schwab, Morgan; Nelson, Jennifer; Bell, John D

    2015-04-01

    The naphthalene-based fluorescent probes Patman and Laurdan detect bilayer polarity at the level of the phospholipid glycerol backbone. This polarity increases with temperature in the liquid-crystalline phase of phosphatidylcholines and was observed even 90°C above the melting temperature. This study explores mechanisms associated with this phenomenon. Measurements of probe anisotropy and experiments conducted at 1M NaCl or KCl (to reduce water permittivity) revealed that this effect represents interactions of water molecules with the probes without proportional increases in probe mobility. Furthermore, comparison of emission spectra to Monte Carlo simulations indicated that the increased polarity represents elevation in probe access to water molecules rather than increased mobility of relevant bilayer waters. Equilibration of these probes with the membrane involves at least two steps which were distinguished by the membrane microenvironment reported by the probe. The difference in those microenvironments also changed with temperature in the liquid-crystalline phase in that the equilibrium state was less polar than the initial environment detected by Patman at temperatures near the melting point, more polar at higher temperatures, and again less polar as temperature was raised further. Laurdan also displayed this level of complexity during equilibration, although the relationship to temperature differed quantitatively from that experienced by Patman. This kinetic approach provides a novel way to study in molecular detail basic principles of what happens to the membrane environment around an individual amphipathic molecule as it penetrates the bilayer. Moreover, it provides evidence of unexpected and interesting membrane behaviors far from the phase transition. PMID:25559316

  20. Density Functional Theory Study of the Complexation of the Uranyl Dication with Anionic Phosphate Ligands with and without Water Molecules

    SciTech Connect

    Jackson, Virgil E.; Gutowski, Keith E.; Dixon, David A.

    2013-08-01

    The structures, vibrational frequencies and energetics of anhydrous and hydrated complexes of UO2 2+ with the phosphate anions H2PO4 -, HPO4 2-, and PO4 3- were predicted at the density functional theory (DFT) and MP2 molecular orbital theory levels as isolated gas phase species and in aqueous solution by using self-consistent reaction field (SCRF) calculations with different solvation models. The geometries and vibrational frequencies of the major binding modes for these complexes are compared to experiment where possible and good agreement is found. The uranyl moiety is nonlinear in many of the complexes, and the coordination number (CN) 5 in the equatorial plane is the predominant binding motif. The phosphates are found to bind in both monodentate and bidentate binding modes depending on the charge and the number of water molecules. The SCRF calculations were done with a variety of approaches, and different SCRF approaches were found to be optimal for different reaction types. The acidities of HxPO4 3-x in HxPO4 3-x(H2O)4, x = 0-3 complexes were calculated with different SCRF models and compared to experiment. Phosphate anions can displace water molecules from the first solvation shell at the uranyl exothermically. The addition of water molecules can cause the bonding of H2PO4 - and HPO4 2- to change from bidentate to monodentate exothermically while maintaining CN 5. The addition of water can generate monodentate structures capable of cross-linking to other uranyl phosphates to form the types of structures found in the solid state. [UO2(HPO4)(H2O)3] is predicted to be a strong base in the gas phase and in aqueous solution. It is predicted to be a much weaker acid than H3PO4 in the gas phase and in solution.

  1. Subpicosecond energy transfer from a highly intense THz pulse to water: A computational study based on the TIP4P/2005 rigid-water-molecule model

    NASA Astrophysics Data System (ADS)

    Mishra, Pankaj Kr.; Vendrell, Oriol; Santra, Robin

    2016-03-01

    The dynamics of ultrafast energy transfer to water clusters and to bulk water by a highly intense, subcycle THz pulse of duration ≈150 fs is investigated in the context of force-field molecular dynamics simulations. We focus our attention on the mechanisms by which rotational and translational degrees of freedom of the water monomers gain energy from these subcycle pulses with an electric field amplitude of up to about 0.6 V/Å. It has been recently shown that pulses with these characteristics can be generated in the laboratory [C. Vicario, B. Monoszlai, and C. P. Hauri, Phys. Rev. Lett. 112, 213901 (2014), 10.1103/PhysRevLett.112.213901]. Through their permanent dipole moment, water molecules are acted upon by the electric field and forced off their preferred hydrogen-bond network conformation. This immediately sets them in motion with respect to one another as energy quickly transfers to their relative center of mass displacements. We find that, in the bulk, the operation of these mechanisms is strongly dependent on the initial temperature and density of the system. In low density systems, the equilibration between rotational and translational modes is slow due to the lack of collisions between monomers. As the initial density of the system approaches 1 g/cm3 , equilibration between rotational and translational modes after the pulse becomes more efficient. In turn, low temperatures hinder the direct energy transfer from the pulse to rotational motion owing to the resulting stiffness of the hydrogen bond network. For small clusters of just a few water molecules we find that fragmentation due to the interaction with the pulse is faster than equilibration between rotations and translations, meaning that the latter remain colder than the former after the pulse. In contrast, clusters with more than a few tens of water molecules already display energy gain dynamics similar to water in condensed phases owing to inertial confinement of the internal water molecules by

  2. Synthesis of oxocarbon-encapsulated gold nanoparticles with blue-shifted localized surface plasmon resonance by pulsed laser ablation in water with CO2 absorbers.

    PubMed

    Del Rosso, T; Rey, N A; Rosado, T; Landi, S; Larrude, D G; Romani, E C; Junior, F L Freire; Quinteiro, S M; Cremona, M; Aucelio, R Q; Margheri, G; Pandoli, O

    2016-06-24

    Colloidal suspensions of oxocarbon-encapsulated gold nanoparticles have been synthesized in a one-step procedure by pulsed-laser ablation (PLA) at 532 nm of a solid gold target placed in aqueous solution containing CO2 absorbers, but without any stabilizing agent. Multi-wavelength surface enhanced Raman spectroscopy allows the identification of adsorbed amorphous carbon and graphite, Au-carbonyl, Au coordinated CO2-derived bicarbonates/carbonates and hydroxyl groups around the AuNPs core. Scanning electron microscopy, energy dispersive x-ray analysis and high resolution transmission electron microscopy highlight the organic shell structure around the crystalline metal core. The stability of the colloidal solution of nanocomposites (NCs) seems to be driven by solvation forces and is achieved only in neutral or basic pH using monovalent hydroxide counter-ions (NaOH, KOH). The NCs are characterized by a blue shift of the localized surface plasmon resonance (LSPR) band typical of metal-ligand stabilization by terminal π-back bonding, attributed to a core charging effect caused by Au-carbonyls. Total organic carbon measurements detect the final content of organic carbon in the colloidal solution of NCs that is about six times higher than the value of the water solution used to perform PLA. The colloidal dispersions of NCs are stable for months and are applied as analytical probes in amino glycoside antibiotic LSPR based sensing. PMID:27171728

  3. Synthesis of oxocarbon-encapsulated gold nanoparticles with blue-shifted localized surface plasmon resonance by pulsed laser ablation in water with CO2 absorbers

    NASA Astrophysics Data System (ADS)

    Del Rosso, T.; Rey, N. A.; Rosado, T.; Landi, S.; Larrude, D. G.; Romani, E. C.; Freire Junior, F. L.; Quinteiro, S. M.; Cremona, M.; Aucelio, R. Q.; Margheri, G.; Pandoli, O.

    2016-06-01

    Colloidal suspensions of oxocarbon-encapsulated gold nanoparticles have been synthesized in a one-step procedure by pulsed-laser ablation (PLA) at 532 nm of a solid gold target placed in aqueous solution containing CO2 absorbers, but without any stabilizing agent. Multi-wavelength surface enhanced Raman spectroscopy allows the identification of adsorbed amorphous carbon and graphite, Au-carbonyl, Au coordinated CO2-derived bicarbonates/carbonates and hydroxyl groups around the AuNPs core. Scanning electron microscopy, energy dispersive x-ray analysis and high resolution transmission electron microscopy highlight the organic shell structure around the crystalline metal core. The stability of the colloidal solution of nanocomposites (NCs) seems to be driven by solvation forces and is achieved only in neutral or basic pH using monovalent hydroxide counter-ions (NaOH, KOH). The NCs are characterized by a blue shift of the localized surface plasmon resonance (LSPR) band typical of metal-ligand stabilization by terminal π-back bonding, attributed to a core charging effect caused by Au-carbonyls. Total organic carbon measurements detect the final content of organic carbon in the colloidal solution of NCs that is about six times higher than the value of the water solution used to perform PLA. The colloidal dispersions of NCs are stable for months and are applied as analytical probes in amino glycoside antibiotic LSPR based sensing.

  4. An aspartate and a water molecule mediate efficient acid-base catalysis in a tailored antibody pocket

    SciTech Connect

    Debler, Erik W.; Müller, Roger; Hilvert, Donald; Wilson, Ian A.

    2009-12-01

    Design of catalysts featuring multiple functional groups is a desirable, yet formidable goal. Antibody 13G5, which accelerates the cleavage of unactivated benzisoxazoles, is one of few artificial enzymes that harness an acid and a base to achieve efficient proton transfer. X-ray structures of the Fab-hapten complexes of wild-type 13G5 and active-site variants now afford detailed insights into its mechanism. The parent antibody preorganizes Asp{sup H35} and Glu{sup L34} to abstract a proton from substrate and to orient a water molecule for leaving group stabilization, respectively. Remodeling the environment of the hydrogen bond donor with a compensatory network of ordered waters, as seen in the Glu{sup L34} to alanine mutant, leads to an impressive 10{sup 9}-fold rate acceleration over the nonenzymatic reaction with acetate, illustrating the utility of buried water molecules in bifunctional catalysis. Generalization of these design principles may aid in creation of catalysts for other important chemical transformations.

  5. Binding site identification and role of permanent water molecule of PIM-3 kinase: A molecular dynamics study.

    PubMed

    Ul-Haq, Zaheer; Gul, Sana; Usmani, Saman; Wadood, Abdul; Khan, Waqasuddin

    2015-11-01

    The kinome is a protein kinase complement of the human genome, categorized as serine/threonine and tyrosine kinases. These kinases catalyze phosphorylation reaction by using ATP as phosphoryl donor. Proviral Integration Site for Moloney Murine Leukemia Virus (PIM) kinase encodes serine/threonine protein kinases that recognized as proto-oncogene, responsible for rapid growth of cancerous cells. It is implicated in cell survival and function via cell cycle progression and its metabolism. PIM-3, sub-member of PIM kinases is a proto-oncogene, its overexpression inhibits apoptosis, and results in progression of hepatocellular carcinoma. PIM-3 is considered as a promising drug target but attempts to develop its specific inhibitors is slowed down due to the lack of 3D structure by any experimental technique. In silico techniques generally facilitate scientist to explore hidden structural features in order to improve drug discovery. In the present study, homology modeling, molecular docking and MD simulation techniques were utilized to explore the structure and dynamics of PIM-3 kinase. Induction of water molecules during molecular docking simulation explored differences in the hinge region between PIM-1 and PIM-3 kinases that may be responsible for specificity. Furthermore, role of water molecules in the active site was also explored via radial distribution function (RDF) after a 10 ns molecular dynamics (MD) simulations. Generated RDF plots exhibited the importance of water for inhibitor binding through their bridging capability that links the ligand with binding site residues. PMID:26529487

  6. H-bonding networks of the distal residues and water molecules in the active site of Thermobifida fusca hemoglobin.

    PubMed

    Nicoletti, Francesco P; Droghetti, Enrica; Howes, Barry D; Bustamante, Juan P; Bonamore, Alessandra; Sciamanna, Natascia; Estrin, Darío A; Feis, Alessandro; Boffi, Alberto; Smulevich, Giulietta

    2013-09-01

    The ferric form of truncated hemoglobin II from Thermobifida fusca (Tf-trHb) and its triple mutant WG8F-YB10F-YCD1F at neutral and alkaline pH, and in the presence of CN(-) have been characterized by resonance Raman spectroscopy, electron paramagnetic resonance spectroscopy, and molecular dynamics simulations. Tf-trHb contains three polar residues in the distal site, namely TrpG8, TyrCD1 and TyrB10. Whereas TrpG8 can act as a potential hydrogen-bond donor, the tyrosines can act as donors or acceptors. Ligand binding in heme-containing proteins is determined by a number of factors, including the nature and conformation of the distal residues and their capability to stabilize the heme-bound ligand via hydrogen-bonding and electrostatic interactions. Since both the RR Fe-OH(-) and Fe-CN(-) frequencies are very sensitive to the distal environment, detailed information on structural variations has been obtained. The hydroxyl ligand binds only the WT protein giving rise to two different conformers. In form 1 the anion is stabilized by H-bonds with TrpG8, TyrCD1 and a water molecule, in turn H-bonded to TyrB10. In form 2, H-bonding with TyrCD1 is mediated by a water molecule. Unlike the OH(-) ligand, CN(-) binds both WT and the triple mutant giving rise to two forms with similar spectroscopic characteristics. The overall results clearly indicate that H-bonding interactions both with distal residues and water molecules are important structural determinants in the active site of Tf-trHb. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins. PMID:23467007

  7. Water-soluble carbon monoxide-releasing molecules: helping to elucidate the vascular activity of the 'silent killer'.

    PubMed

    Chatterjee, Prabal Kumar

    2004-06-01

    Carbon monoxide (CO) is formed during the degradation of haeme by haeme oxygenase (HO). As well as being an important signalling molecule and vasodilator, CO also possesses antihypertensive, anti-inflammatory and antiapoptotic qualities and protects against ischaemic tissue injury. Several approaches have been used to investigate the therapeutic potential of CO, ranging from direct administration of CO gas to the use of prodrugs, which generate CO upon metabolism. A novel approach involves the use of specific CO carriers, which will release measurable, controllable and effective amounts of CO into biological systems. Transitional metal carbonyls based around iron, manganese or ruthenium have recently been developed as CO-releasing molecules (CO-RMs) that, under appropriate conditions, will release CO. Such molecules have been shown to provide cardioprotection in both ex vivo and in vivo experiments. To date, CO-RMs have been largely incompatible with biological systems in that they are only soluble in organic solvents or have to be preactivated either by physical or chemical stimuli. However, the recent development of water-soluble CO-RMs has provided new opportunities to investigate the pharmacological and biological features of CO without such confounding influences. CORM-3, a novel water-soluble CO-RM, has recently been used to confirm the cardioprotective actions of CO. In this issue of British Journal of Pharmacology, Foresti and co-workers report that CORM-3 delivers CO, produces aortic vasodilation ex vivo and reduces blood pressure in vivo via modulation of the same cGMP and potassium channels utilised by endogenous and exogenous CO. These findings suggest that CORM-3 has the potential for use as a modulator of vascular function and hypertension. However, the use of water-soluble CO-RMs raises several questions of their own which will need to be addressed if CO-RMs are to be of future use therapeutically. PMID:15148242

  8. Water-soluble carbon monoxide-releasing molecules: helping to elucidate the vascular activity of the ‘silent killer'

    PubMed Central

    Chatterjee, Prabal Kumar

    2004-01-01

    Carbon monoxide (CO) is formed during the degradation of haeme by haeme oxygenase (HO). As well as being an important signalling molecule and vasodilator, CO also possesses antihypertensive, anti-inflammatory and antiapoptotic qualities and protects against ischaemic tissue injury. Several approaches have been used to investigate the therapeutic potential of CO, ranging from direct administration of CO gas to the use of prodrugs, which generate CO upon metabolism. A novel approach involves the use of specific CO carriers, which will release measurable, controllable and effective amounts of CO into biological systems. Transitional metal carbonyls based around iron, manganese or ruthenium have recently been developed as CO-releasing molecules (CO-RMs) that, under appropriate conditions, will release CO. Such molecules have been shown to provide cardioprotection in both ex vivo and in vivo experiments. To date, CO-RMs have been largely incompatible with biological systems in that they are only soluble in organic solvents or have to be preactivated either by physical or chemical stimuli. However, the recent development of water-soluble CO-RMs has provided new opportunities to investigate the pharmacological and biological features of CO without such confounding influences. CORM-3, a novel water-soluble CO-RM, has recently been used to confirm the cardioprotective actions of CO. In this issue of British Journal of Pharmacology, Foresti and co-workers report that CORM-3 delivers CO, produces aortic vasodilation ex vivo and reduces blood pressure in vivo via modulation of the same cGMP and potassium channels utilised by endogenous and exogenous CO. These findings suggest that CORM-3 has the potential for use as a modulator of vascular function and hypertension. However, the use of water-soluble CO-RMs raises several questions of their own which will need to be addressed if CO-RMs are to be of future use therapeutically. PMID:15148242

  9. DFT studies of carbohydrate solvation: II. MD-DFTr of a super-molecule complex of glucose, explicit waters, and an implicit solvent (COSMO)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    MD-DFTr studies are carried out on the super-molecule solvated complexes of glucose described in paper I. Included were ten explicit water molecules and an implicit solvation model, COSMO, superimposed upon the complex. Starting configurations were taken from DFTr optimized complexes resulting from ...

  10. Investigation of N-acyl homoserine lactone (AHL) molecule production in Gram-negative bacteria isolated from cooling tower water and biofilm samples.

    PubMed

    Haslan, Ezgi; Kimiran-Erdem, Ayten

    2013-09-01

    In this study, 99 Gram-negative rod bacteria were isolated from cooling tower water, and biofilm samples were examined for cell-to-cell signaling systems, N-acyl homoserine lactone (AHL) signal molecule types, and biofilm formation capacity. Four of 39 (10 %) strains isolated from water samples and 14 of 60 (23 %) strains isolated from biofilm samples were found to be producing a variety of AHL signal molecules. It was determined that the AHL signal molecule production ability and the biofilm formation capacity of sessile bacteria is higher than planktonic bacteria, and there was a statistically significant difference between the AHL signal molecule production of these two groups (p < 0.05). In addition, it was found that bacteria belonging to the same species isolated from cooling tower water and biofilm samples produced different types of AHL signal molecules and that there were different types of AHL signal molecules in an AHL extract of bacteria. In the present study, it was observed that different isolates of the same strains did not produce the same AHLs or did not produce AHL molecules, and bacteria known as AHL producers did not produce AHL. These findings suggest that detection of signal molecules in bacteria isolated from cooling towers may contribute to prevention of biofilm formation, elimination of communication among bacteria in water systems, and blockage of quorum-sensing controlled virulence of these bacteria. PMID:23250628

  11. Possible interstellar formation of glycine from the reaction of CH2=NH, CO and H2O: catalysis by extra water molecules through the hydrogen relay transport.

    PubMed

    Nhlabatsi, Zanele P; Bhasi, Priya; Sitha, Sanyasi

    2016-01-01

    "How the fundamental life elements are created in the interstellar medium (ISM)?" is one of the intriguing questions related to the genesis of life. Using computational calculations, we have discussed the reaction of CH2=NH, CO and H2O for the formation of glycine, the simplest life element. This reaction proceeds through a concerted mechanism with reasonably large barriers for the cases with one and two water molecules as reactants. For the two water case we found that the extra water molecule exhibits some catalytic role through the hydrogen transport relay effect and the barrier height is reduced substantially compared to the case with one water molecule. These two cases can be treated as ideal cases for the hot-core formation of the interstellar glycine. With an increasing number of water molecules as the reactants, we found that when the numbers of water molecules are three or more than three, the barrier height reduced so drastically that the transition states were more stable than the reactants. Such a situation gives a clear indication that with excess water molecules as the reactants, this reaction will be feasible even under the low temperature conditions existing in the cold interstellar clouds and the exothermic nature of the reaction will be the driving force. PMID:26616741

  12. Product distributions and rate constants for ion-molecule reactions in water, hydrogen sulfide, ammonia, and methane

    NASA Technical Reports Server (NTRS)

    Huntress, W. T., Jr.; Pinizzotto, R. F., Jr.

    1973-01-01

    The thermal energy, bimolecular ion-molecule reactions occurring in gaseous water, hydrogen sulfide, ammonia, and methane have been identified and their rate constants determined using ion cyclotron resonance methods. Absolute rate constants were determined for the disappearance of the primary ions by using the trapped ion method, and product distributions were determined for these reactions by using the cyclotron ejection method. Previous measurements are reviewed and compared with the results using the present methods. The relative rate constants for hydrogen-atom abstraction, proton transfer, and charge transfer are also determined for reactions of the parent ions.

  13. Double ionization of the water molecule: Influence of the target orientation on the secondary-electron angular distributions

    SciTech Connect

    Oubaziz, D.; Aouchiche, H.; Champion, C.

    2011-01-15

    Fivefold differential cross sections for electron-induced double ionization of isolated oriented water molecules are reported. The theoretical investigation is performed within the first Born approximation by describing the initial molecular state by means of single-center wave functions. The contributions of each final state to the double-ionization process, i.e., with target electrons ejected from similar and/or different molecular subshells, are studied and compared in terms of shape and magnitude. Furthermore, for the particular target orientations investigated, we identify clearly the signature of the main scenarios involved in (e,3e) reactions, namely, the shake-off and the two-step 1 mechanisms.

  14. Quantum-chemical study of the interactions between cyanide ions and water molecules

    SciTech Connect

    Baranovskii, V.I.; Fomicheva, V.P.; Ivanova, N.V.; Sizova, O.V.

    1986-05-01

    Nonempirical MO SCF calculations have been performed in the 4-31 G basis to examine the interactions of CN/sup -/ ions with H/sub 2/O molecules. The most stable geometrical configurations have been used in calculating the force constants of the C-N and hydrogen-bond stretching vibrations and of the deformation vibration for the H...N-C (H...C-N) angle. The frequencies of the corresponding vibrations have been determined. The results are compared with data obtained for the uncharged HCN x H/sub 2/O system.

  15. Effect of a Single Water Molecule on the Electronic Absorption by o- and p-Nitrophenolate: A Shift to the Red or to the Blue?

    PubMed

    Houmøller, Jørgen; Wanko, Marius; Rubio, Angel; Nielsen, Steen Brøndsted

    2015-11-25

    Many photoactive biomolecules are anions and exhibit ππ* optical transitions but with a degree of charge transfer (CT) character determined by the local environment. The phenolate moiety is a common structural motif among biochromophores and luminophores, and nitrophenolates are good model systems because the nitro substituent allows for CT-like transitions. Here we report gas-phase absorption spectra of o- and p-nitrophenolate·H2O complexes to decipher the effect of just one H2O and compare them with ab initio calculations of vertical excitation energies. The experimental band maximum is at 3.01 and 3.00 eV for ortho and para isomers, respectively, and is red-shifted by 0.10 and 0.13 eV relative to the bare ions, respectively. These shifts indicate that the transition has become more CT-like because of localization of negative charge on the phenolate oxygen, i.e., diminished delocalization of the negative excess charge. However, the transition bears less CT than that of m-nitrophenolate·H2O because this complex absorbs further to the red (2.56 eV). Our work emphasizes the importance of local perturbations: one water causes a larger shift than experienced in bulk for para isomer and almost the full shift for ortho isomer. Predicting microenvironmental effects in the boundary between CT and non-CT with high accuracy is nontrivial. However, in agreement with experiment, our calculations show a competition between the effects of electronic delocalization and electrostatic interaction with the solvent molecule. As a result, the excitation energy of ortho and para isomers is less sensitive to hydration than that of the meta isomer because donor and acceptor orbitals are only weakly coupled in the meta isomer. PMID:26549521

  16. Composition for absorbing hydrogen

    DOEpatents

    Heung, L.K.; Wicks, G.G.; Enz, G.L.

    1995-05-02

    A hydrogen absorbing composition is described. The composition comprises a porous glass matrix, made by a sol-gel process, having a hydrogen-absorbing material dispersed throughout the matrix. A sol, made from tetraethyl orthosilicate, is mixed with a hydrogen-absorbing material and solidified to form a porous glass matrix with the hydrogen-absorbing material dispersed uniformly throughout the matrix. The glass matrix has pores large enough to allow gases having hydrogen to pass through the matrix, yet small enough to hold the particles dispersed within the matrix so that the hydrogen-absorbing particles are not released during repeated hydrogen absorption/desorption cycles.

  17. Composition for absorbing hydrogen

    DOEpatents

    Heung, Leung K.; Wicks, George G.; Enz, Glenn L.

    1995-01-01

    A hydrogen absorbing composition. The composition comprises a porous glass matrix, made by a sol-gel process, having a hydrogen-absorbing material dispersed throughout the matrix. A sol, made from tetraethyl orthosilicate, is mixed with a hydrogen-absorbing material and solidified to form a porous glass matrix with the hydrogen-absorbing material dispersed uniformly throughout the matrix. The glass matrix has pores large enough to allow gases having hydrogen to pass through the matrix, yet small enough to hold the particles dispersed within the matrix so that the hydrogen-absorbing particles are not released during repeated hydrogen absorption/desorption cycles.

  18. Boltzmann equation analysis of electron-molecule collision cross sections in water vapor and ammonia

    SciTech Connect

    Yousfi, M.; Benabdessadok, M.D.

    1996-12-01

    Sets of electron-molecule collision cross sections for H{sub 2}O and NH{sub 3} have been determined from a classical technique of electron swarm parameter unfolding. This deconvolution method is based on a simplex algorithm using a powerful multiterm Boltzmann equation analysis established in the framework of the classical hydrodynamic approximation. It is well adapted for the simulation of the different classes of swarm experiments (i.e., time resolved, time of flight, and steady state experiments). The sets of collision cross sections that exist in the literature are reviewed and analyzed. Fitted sets of cross sections are determined for H{sub 2}O and NH{sub 3} which exhibit features characteristic of polar molecules such as high rotational excitation collision cross sections. The hydrodynamic swarm parameters (i.e., drift velocity, longitudinal and transverse diffusion coefficients, ionization and attachment coefficients) calculated from the fitted sets are in excellent agreement with the measured ones. These sets are finally used to calculate the transport and reaction coefficients needed for discharge modeling in two cases of typical gas mixtures for which experimental swarm data are very sparse or nonexistent (i.e., flue gas mixtures and gas mixtures for rf plasma surface treatment). {copyright} {ital 1996 American Institute of Physics.}

  19. Rotational dynamics of water molecules near biological surfaces with implications for nuclear quadrupole relaxation.

    PubMed

    Braun, Daniel; Schmollngruber, Michael; Steinhauser, Othmar

    2016-09-21

    Based on Molecular Dynamics simulations of two different systems, the protein ubiquitin dissolved in water and an AOT reverse micelle, we present a broad analysis of the single particle rotational dynamics of water. A comprehensive connection to NQR, which is a prominent experimental method in this field, is developed, based on a reformulation of its theoretical framework. Interpretation of experimental NQR results requires a model which usually assumes that the NQR experiences retardation only in the first hydration shell. Indeed, the present study shows that this first-shell model is correct. Moreover, previous experimental retardation factors are quantitatively reproduced. All of this is seemingly contradicted by results of other methods, e.g., dielectric spectroscopy, responsible for a long-standing debate in this field. Our detailed analysis shows that NQR omits important information contained in overall water dynamics, most notably, the retardation of the water dipole axis in the electric field exerted by a biological surface. PMID:27546227

  20. Size-dependent molecule-like to plasmonic transition in water-soluble glutathione stabilized gold nanomolecules

    NASA Astrophysics Data System (ADS)

    Kothalawala, Nuwan; Lee West, James, IV; Dass, Amala

    2013-12-01

    A size-dependent transition from molecule-like to plasmonic behaviour is demonstrated in the case of water soluble Au:SG nanomolecules. This was achieved using PAGE separation of smaller and larger nanomolecules, resulting in an unprecedented 26 bands, in a wide-range from 10's to 1000's of Au-atoms. PAGE separation of larger plasmonic nanomolecules is demonstrated for the first time. High resolution ESI-MS, with isotopic resolution, of smaller nanoparticles is reported, including the first time report of Au43(SG)26. This report will aid in the fundamental understanding of size-dependent properties of nanomolecules. The synthetic procedure employs a green approach with non-toxic chemicals and processes. The water solubility, non-toxicity and biocompatibility will lead to applications in biomedicine.A size-dependent transition from molecule-like to plasmonic behaviour is demonstrated in the case of water soluble Au:SG nanomolecules. This was achieved using PAGE separation of smaller and larger nanomolecules, resulting in an unprecedented 26 bands, in a wide-range from 10's to 1000's of Au-atoms. PAGE separation of larger plasmonic nanomolecules is demonstrated for the first time. High resolution ESI-MS, with isotopic resolution, of smaller nanoparticles is reported, including the first time report of Au43(SG)26. This report will aid in the fundamental understanding of size-dependent properties of nanomolecules. The synthetic procedure employs a green approach with non-toxic chemicals and processes. The water solubility, non-toxicity and biocompatibility will lead to applications in biomedicine. Electronic supplementary information (ESI) available: Detailed synthetic conditions, expanded MS, and optical spectra. This material is available free of charge via the Internet at http://pubs.acs.org. See DOI: 10.1039/c3nr03657j

  1. What interactions can distort the orientational distribution of interfacial water molecules as probed by second harmonic and sum frequency generation?

    NASA Astrophysics Data System (ADS)

    de Beer, Alex G. F.; Roke, Sylvie

    2016-07-01

    Aqueous interfaces are omnipresent in nature. Nonlinear optical methods such as second harmonic and sum frequency generation (SHG/SFG) are valuable techniques to access molecular level information from these interfaces. In the interpretation of SHG and SFG data for both scattering and reflection mode experiments, the relation between the second-order hyperpolarizability tensor β(2), a molecular property, and the surface second-order susceptibility (" separators=" χ(2), a surface averaged property, plays a central role. To correctly describe the molecular details of the interface, it needs to be determined how molecules are oriented, and what the influence is of interfacial electrostatic fields and H-bonding on the orientational distribution. Here, we revisit the relations between β(2) and χ(2) and show, by means of a Boltzmann average, that significant energy differences are needed to generate measurable changes in the molecular orientational distribution at the interface. In practice, H-bonding and surface pressure such as applied in a Langmuir trough can be strong enough to alter the shape of the orientational distribution function of water. In contrast, electrostatic fields, such as those present in the Stern layer, will not have a significant impact on the shape of the orientational distribution function of water molecules.

  2. Hydrogen-bonding changes of internal water molecules upon the actions of microbial rhodopsins studied by FTIR spectroscopy.

    PubMed

    Furutani, Yuji; Kandori, Hideki

    2014-05-01

    Microbial rhodopsins are classified into type-I rhodopsins, which utilize light energy to perform wide varieties of function, such as proton pumping, ion pumping, light sensing, cation channels, and so on. The crystal structures of several type-I rhodopsins were solved and the molecular mechanisms have been investigated based on the atomic structures. However, the crystal structures of proteins of interest are not always available and the basic architectures are sometimes quite similar, which obscures how the proteins achieve different functions. Stimulus-induced difference FTIR spectroscopy is a powerful tool to detect minute structural changes providing a clue for elucidating the molecular mechanisms. In this review, the studies on type-I rhodopsins from fungi and marine bacteria, whose crystal structures have not been solved yet, were summarized. Neurospora rhodopsin and Leptosphaeria rhodopsin found from Fungi have sequence similarity. The former has no proton pumping function, while the latter has. Proteorhodopsin is another example, whose proton pumping machinery is altered at alkaline and acidic conditions. We described how the structural changes of protein were different and how water molecules were involved in them. We reviewed the results on dynamics of the internal water molecules in pharaonis halorhodopsin as well. This article is part of a Special Issue entitled: Retinal Proteins - You can teach an old dog new tricks. PMID:24041645

  3. How water molecules affect the catalytic activity of hydrolases--a XANES study of the local structures of peptide deformylase.

    PubMed

    Cui, Peixin; Wang, Yu; Chu, Wangsheng; Guo, Xiaoyun; Yang, Feifei; Yu, Meijuan; Zhao, Haifeng; Dong, Yuhui; Xie, Yaning; Gong, Weimin; Wu, Ziyu

    2014-01-01

    Peptide deformylase (PDF) is a prokaryotic enzyme that catalyzes the deformylation of nascent peptides generated during protein synthesis and water molecules play a key role in these hydrolases. Using X-ray absorption near edge spectroscopy (XANES) and ab initio calculations we accurately probe the local atomic environment of the metal ion binding in the active site of PDF at different pH values and with different metal ions. This new approach is an effective way to monitor existing correlations among functions and structural changes. We show for the first time that the enzymatic activity depends on pH values and metal ions via the bond length of the nearest coordinating water (Wat1) to the metal ion. Combining experimental and theoretical data we may claim that PDF exhibits an enhanced enzymatic activity only when the distance of the Wat1 molecule with the metal ion falls in the limited range from 2.15 to 2.55 Å. PMID:25503313

  4. What interactions can distort the orientational distribution of interfacial water molecules as probed by second harmonic and sum frequency generation?

    PubMed

    de Beer, Alex G F; Roke, Sylvie

    2016-07-28

    Aqueous interfaces are omnipresent in nature. Nonlinear optical methods such as second harmonic and sum frequency generation (SHG/SFG) are valuable techniques to access molecular level information from these interfaces. In the interpretation of SHG and SFG data for both scattering and reflection mode experiments, the relation between the second-order hyperpolarizability tensor β(2), a molecular property, and the surface second-order susceptibility χ(2), a surface averaged property, plays a central role. To correctly describe the molecular details of the interface, it needs to be determined how molecules are oriented, and what the influence is of interfacial electrostatic fields and H-bonding on the orientational distribution. Here, we revisit the relations between β(2) and χ(2) and show, by means of a Boltzmann average, that significant energy differences are needed to generate measurable changes in the molecular orientational distribution at the interface. In practice, H-bonding and surface pressure such as applied in a Langmuir trough can be strong enough to alter the shape of the orientational distribution function of water. In contrast, electrostatic fields, such as those present in the Stern layer, will not have a significant impact on the shape of the orientational distribution function of water molecules. PMID:27475384

  5. Ligand uptake in Mycobacterium tuberculosis truncated hemoglobins is controlled by both internal tunnels and active site water molecules

    PubMed Central

    Davidge, Kelly S; Singh, Sandip; Bowman, Lesley AH; Tinajero-Trejo, Mariana; Carballal, Sebastián; Radi, Rafael; Poole, Robert K; Dikshit, Kanak; Estrin, Dario A; Marti, Marcelo A; Boechi, Leonardo

    2015-01-01

    Mycobacterium tuberculosis, the causative agent of human tuberculosis, has two proteins belonging to the truncated hemoglobin (trHb) family. Mt-trHbN presents well-defined internal hydrophobic tunnels that allow O 2 and •NO to migrate easily from the solvent to the active site, whereas Mt-trHbO possesses tunnels that are partially blocked by a few bulky residues, particularly a tryptophan at position G8. Differential ligand migration rates allow Mt-trHbN to detoxify •NO, a crucial step for pathogen survival once under attack by the immune system, much more efficiently than Mt-trHbO. In order to investigate the differences between these proteins, we performed experimental kinetic measurements, •NO decomposition, as well as molecular dynamics simulations of the wild type Mt-trHbN and two mutants, VG8F and VG8W. These mutations introduce modifications in both tunnel topologies and affect the incoming ligand capacity to displace retained water molecules at the active site. We found that a single mutation allows Mt-trHbN to acquire ligand migration rates comparable to those observed for Mt-trHbO, confirming that ligand migration is regulated by the internal tunnel architecture as well as by water molecules stabilized in the active site. PMID:26478812

  6. Ligand uptake in Mycobacterium tuberculosis truncated hemoglobins is controlled by both internal tunnels and active site water molecules.

    PubMed

    Boron, Ignacio; Bustamante, Juan Pablo; Davidge, Kelly S; Singh, Sandip; Bowman, Lesley Ah; Tinajero-Trejo, Mariana; Carballal, Sebastián; Radi, Rafael; Poole, Robert K; Dikshit, Kanak; Estrin, Dario A; Marti, Marcelo A; Boechi, Leonardo

    2015-01-01

    Mycobacterium tuberculosis, the causative agent of human tuberculosis, has two proteins belonging to the truncated hemoglobin (trHb) family. Mt-trHbN presents well-defined internal hydrophobic tunnels that allow O 2 and (•)NO to migrate easily from the solvent to the active site, whereas Mt-trHbO possesses tunnels that are partially blocked by a few bulky residues, particularly a tryptophan at position G8. Differential ligand migration rates allow Mt-trHbN to detoxify (•)NO, a crucial step for pathogen survival once under attack by the immune system, much more efficiently than Mt-trHbO. In order to investigate the differences between these proteins, we performed experimental kinetic measurements, (•)NO decomposition, as well as molecular dynamics simulations of the wild type Mt-trHbN and two mutants, VG8F and VG8W. These mutations introduce modifications in both tunnel topologies and affect the incoming ligand capacity to displace retained water molecules at the active site. We found that a single mutation allows Mt-trHbN to acquire ligand migration rates comparable to those observed for Mt-trHbO, confirming that ligand migration is regulated by the internal tunnel architecture as well as by water molecules stabilized in the active site. PMID:26478812

  7. Prototropic tautomerism of 4-Methyl 1,2,4-Triazole-3-Thione molecule in solvent water medium: DFT and Car-Parrinello molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Dutta, Bipan; De, Rina; Chowdhury, Joydeep

    2015-12-01

    The ground state prototropic tautomerism of 4-Methyl 1,2,4-Triazole-3-Thione molecule in solvent water medium has been investigated with the aid of DFT and Car-Parrinello molecular dynamics (CPMD) simulation studies. The CPMD simulations envisage the possibility of proton transfer reactions of the molecule through the solvent water medium. Probable proton transfer pathways have been predicted from the DFT calculations which are substantiated by the natural bond orbital analyses. The evolution and breaking of the concerned bonds of the molecule for different proton transfer reaction pathways are also estimated.

  8. Dynamics of molecules in a supercooled water nanoparticle during the ice accretion on the aircraft surface

    NASA Astrophysics Data System (ADS)

    Amelyushkin, I. A.; Stasenko, A. L.

    2015-06-01

    The principal aim of this work is to elaborate a robust physical model and the corresponding numerical code for prediction of the icing startup due to numerous water nanoparticles in the supercooled humid air. For this purpose, a scientified approach was used which is based not on the quantum-mechanics considerations but on the information about intermolecular potentials (especially, Lennard-Jones (LJ), etc.) tightly connected with the state equations of the corresponding specie (e. g., van der Waals for air and water and Mie-Grünaisen for circumfluent body). u In other words, the principal idea of this work is to adequately ascribe certain macroscopic characteristics of a water nanoparticle which may significantly differ from those indicated in physical reference books for bulk materials.

  9. Effect of anodizing voltage on the sorption of water molecules on porous alumina

    NASA Astrophysics Data System (ADS)

    Vrublevsky, I.; Chernyakova, K.; Bund, A.; Ispas, A.; Schmidt, U.

    2012-05-01

    The amount of water adsorbed on different centers on the surface of oxalic acid alumina films is a function of the anodizing voltage. It is decreased with increasing the anodizing voltage from 20 up to 50 V, came up to maximum value at 20-30 V and slightly increased at voltages above 50 V. Water adsorption by oxide films formed at voltages below 50 V can be due to the negative surface charge that is present on the alumina surface. The negative surface charge disappears in the films formed at voltages higher than 50 V, and thus, the water is adsorbed on aluminum ions in a tetrahedral and octahedral environment. The correlation between anodizing conditions of aluminum in oxalic acid and the structure and composition of anodic alumina was established by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), thermogravimetric and differential thermal analyses (TG/DTA).

  10. Mercedes–Benz water molecules near hydrophobic wall: Integral equation theories vs Monte Carlo simulations

    PubMed Central

    Urbic, T.; Holovko, M. F.

    2011-01-01

    Associative version of Henderson-Abraham-Barker theory is applied for the study of Mercedes–Benz model of water near hydrophobic surface. We calculated density profiles and adsorption coefficients using Percus-Yevick and soft mean spherical associative approximations. The results are compared with Monte Carlo simulation data. It is shown that at higher temperatures both approximations satisfactory reproduce the simulation data. For lower temperatures, soft mean spherical approximation gives good agreement at low and at high densities while in at mid range densities, the prediction is only qualitative. The formation of a depletion layer between water and hydrophobic surface was also demonstrated and studied. PMID:21992334

  11. Mercedes-Benz water molecules near hydrophobic wall: Integral equation theories vs Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Urbic, T.; Holovko, M. F.

    2011-10-01

    Associative version of Henderson-Abraham-Barker theory is applied for the study of Mercedes-Benz model of water near hydrophobic surface. We calculated density profiles and adsorption coefficients using Percus-Yevick and soft mean spherical associative approximations. The results are compared with Monte Carlo simulation data. It is shown that at higher temperatures both approximations satisfactory reproduce the simulation data. For lower temperatures, soft mean spherical approximation gives good agreement at low and at high densities while in at mid range densities, the prediction is only qualitative. The formation of a depletion layer between water and hydrophobic surface was also demonstrated and studied.

  12. Mercedes-Benz water molecules near hydrophobic wall: integral equation theories vs Monte Carlo simulations.

    PubMed

    Urbic, T; Holovko, M F

    2011-10-01

    Associative version of Henderson-Abraham-Barker theory is applied for the study of Mercedes-Benz model of water near hydrophobic surface. We calculated density profiles and adsorption coefficients using Percus-Yevick and soft mean spherical associative approximations. The results are compared with Monte Carlo simulation data. It is shown that at higher temperatures both approximations satisfactory reproduce the simulation data. For lower temperatures, soft mean spherical approximation gives good agreement at low and at high densities while in at mid range densities, the prediction is only qualitative. The formation of a depletion layer between water and hydrophobic surface was also demonstrated and studied. PMID:21992334

  13. Recombination time of an RF discharge plasma in the presence of water molecules

    SciTech Connect

    Protasevich, E.T.

    1986-05-01

    The authors show that the introduction of water vapor into an electrodeless rf discharge noticeably reduces the excitation temperature and substantially increases the recombination time of the plasma. An attempt is made to explain the physical processes associated with these phenomena.

  14. Hierarchical assembly of an achiral pi-conjugated molecule into a chiral nanotube through the air/water interface.

    PubMed

    Yao, Pingping; Wang, Haifeng; Chen, Penglei; Zhan, Xiaowei; Kuang, Xun; Zhu, Daoben; Liu, Minghua

    2009-06-16

    An achiral pi-conjugated fluorinated fused pyrazine derivative has been spread at the air/water interface, and its assembling property is investigated. It has been found that the compound, although without any long alkyl chain, could be spread as a floating film on water surface, the surface pressure of which can be compressed up to ca. 70 mN/m. An inflection point has been observed in the isotherm of the floating film on water surface. The atomic force microscope (AFM), scanning electron microscope (SEM) as well as the transmission electron microscope (TEM) observations revealed that the floating film first formed a multilayer structure and then was compressed into nanotubes after the inflection region as a result of the rolling of the ultrathin film. Interestingly, the rolled nanotubes show circular dichroism although the molecule itself is an achiral species, suggesting the chiral nanotube is predominantly produced on the water surface. The investigation provides an effective way to fabricate supramolecular-based organic chiral nanotubes through an interfacial supramolecular assembly process. PMID:19459675

  15. Structural and atoms-in-molecules analysis of hydrogen-bond network around nitroxides in liquid water.

    PubMed

    Houriez, Céline; Masella, Michel; Ferré, Nicolas

    2010-09-28

    In this study, we investigated the hydrogen-bond network patterns involving the NO moieties of five small nitroxides in liquid water by analyzing nanosecond scale molecular dynamics trajectories. To this end, we implemented two types of hydrogen-bond definitions, based on electronic structure, using Bader's atoms-in-molecules analysis and based on geometric criteria. In each definition framework, the nitroxide/water hydrogen-bond networks appear very variable from a nitroxide to another. Moreover, each definition clearly leads to a different picture of nitroxide hydration. For instance, the electronic structure-based definition predicts a number of hydrogen bonds around the nitroxide NO moiety usually larger than geometric structure-based ones. One particularly interesting result is that the strength of a nitroxide/water hydrogen bond does not depend on its linearity, leading us to question the relevance of geometric definition based on angular cutoffs to study this type of hydrogen bond. Moreover, none of the hydrogen-bond definitions we consider in the present study is able to quantitatively correlate the strength of nitroxide/water hydrogen-bond networks with the aqueous nitroxide spin properties. This clearly exhibits that the hydrogen-bonding concept is not reliable enough to draw quantitative conclusions concerning such properties. PMID:20886951

  16. Structural and atoms-in-molecules analysis of hydrogen-bond network around nitroxides in liquid water

    NASA Astrophysics Data System (ADS)

    Houriez, Céline; Masella, Michel; Ferré, Nicolas

    2010-09-01

    In this study, we investigated the hydrogen-bond network patterns involving the NO moieties of five small nitroxides in liquid water by analyzing nanosecond scale molecular dynamics trajectories. To this end, we implemented two types of hydrogen-bond definitions, based on electronic structure, using Bader's atoms-in-molecules analysis and based on geometric criteria. In each definition framework, the nitroxide/water hydrogen-bond networks appear very variable from a nitroxide to another. Moreover, each definition clearly leads to a different picture of nitroxide hydration. For instance, the electronic structure-based definition predicts a number of hydrogen bonds around the nitroxide NO moiety usually larger than geometric structure-based ones. One particularly interesting result is that the strength of a nitroxide/water hydrogen bond does not depend on its linearity, leading us to question the relevance of geometric definition based on angular cutoffs to study this type of hydrogen bond. Moreover, none of the hydrogen-bond definitions we consider in the present study is able to quantitatively correlate the strength of nitroxide/water hydrogen-bond networks with the aqueous nitroxide spin properties. This clearly exhibits that the hydrogen-bonding concept is not reliable enough to draw quantitative conclusions concerning such properties.

  17. Structure and energetics of model amphiphilic molecules at the water liquid-vapor interface - A molecular dynamics study

    NASA Technical Reports Server (NTRS)

    Pohorille, Andrew; Benjamin, Ilan

    1993-01-01

    A molecular dynamics study of adsorption of p-n-pentylphenol at infinite dilution at the water liquid-vapor interface is reported. The calculated free energy of adsorption is -8.8 +/- 0.7 kcal/mol, in good agreement with the experimental value of -7.3 kcal/mol. The transition between the interfacial region and the bulk solution is sharp and well-defined by energetic, conformational, and orientational criteria. At the water surface, the phenol head group is mostly immersed in aqueous solvent. The most frequent orientation of the hydrocarbon tail is parallel to the interface, due to dispersion interactions with the water surface. This arrangement of the phenol ring and the alkyl chain requires that the chain exhibits a kink. As the polar head group is being moved into the solvent, the chain length increases and the tail becomes increasingly aligned toward the surface normal, such that the nonpolar part of the molecule exposed to water is minimized. The same effect was achieved when phenol was replaced by a more polar head group, phenolate.

  18. Modelling Absorbent Phenomena of Absorbent Structure

    NASA Astrophysics Data System (ADS)

    Sayeb, S.; Ladhari, N.; Ben Hassen, M.; Sakli, F.

    Absorption, retention and strike through time, as evaluating criteria of absorbent structures quality were studied. Determination of influent parameters on these criteria were realized by using the design method of experimental sets. In this study, the studied parameters are: Super absorbent polymer (SAP)/fluff ratio, compression and the porosity of the non woven used as a cover stock. Absorption capacity and retention are mostly influenced by SAP/fluff ratio. However, strike through time is affected by compression. Thus, a modelling of these characteristics in function of the important parameter was established.

  19. Methods for absorbing neutrons

    DOEpatents

    Guillen, Donna P.; Longhurst, Glen R.; Porter, Douglas L.; Parry, James R.

    2012-07-24

    A conduction cooled neutron absorber may include a metal matrix composite that comprises a metal having a thermal neutron cross-section of at least about 50 barns and a metal having a thermal conductivity of at least about 1 W/cmK. Apparatus for providing a neutron flux having a high fast-to-thermal neutron ratio may include a source of neutrons that produces fast neutrons and thermal neutrons. A neutron absorber positioned adjacent the neutron source absorbs at least some of the thermal neutrons so that a region adjacent the neutron absorber has a fast-to-thermal neutron ratio of at least about 15. A coolant in thermal contact with the neutron absorber removes heat from the neutron absorber.

  20. Externally tuned vibration absorber

    DOEpatents

    Vincent, Ronald J.

    1987-09-22

    A vibration absorber unit or units are mounted on the exterior housing of a hydraulic drive system of the type that is powered from a pressure wave generated, e.g., by a Stirling engine. The hydraulic drive system employs a piston which is hydraulically driven to oscillate in a direction perpendicular to the axis of the hydraulic drive system. The vibration absorbers each include a spring or other resilient member having one side affixed to the housing and another side to which an absorber mass is affixed. In a preferred embodiment, a pair of vibration absorbers is employed, each absorber being formed of a pair of leaf spring assemblies, between which the absorber mass is suspended.

  1. Infrared photodissociation of a water molecule from a flexible molecule-H{sub 2}O complex: Rates and conformational product yields following XH stretch excitation

    SciTech Connect

    Clarkson, Jasper R.; Herbert, John M.; Zwier, Timothy S.

    2007-04-07

    Infrared-ultraviolet hole-burning and hole-filling spectroscopies have been used to study IR-induced dissociation of the tryptamine{center_dot}H{sub 2}O and tryptamine{center_dot}D{sub 2}O complexes. Upon complexation of a single water molecule, the seven conformational isomers of tryptamine collapse to a single structure that retains the same ethylamine side chain conformation present in the most highly populated conformer of tryptamine monomer. Infrared excitation of the tryptamine{center_dot}H{sub 2}O complex was carried out using a series of infrared absorptions spanning the range of 2470-3715 cm{sup -1}. The authors have determined the conformational product yield over this range and the dissociation rate near threshold, where it is slow enough to be measured by our methods. The observed threshold for dissociation occurred at 2872 cm{sup -1} in tryptamine{center_dot}H{sub 2}O and at 2869 cm{sup -1} in tryptamine{center_dot}D{sub 2}O, with no dissociation occurring on the time scale of the experiment ({approx}2 {mu}s) at 2745 cm{sup -1}. The dissociation time constants varied from {approx}200 ns for the 2869 cm{sup -1} band of tryptamine{center_dot}D{sub 2}O to {approx}25 ns for the 2872 cm{sup -1} band of tryptamine{center_dot}H{sub 2}O. This large isotope dependence is associated with a zero-point energy effect that increases the binding energy of the deuterated complex by {approx}190 cm{sup -1}, thereby reducing the excess energy available at the same excitation energy. At all higher energies, the dissociation lifetime was shorter than the pulse duration of our lasers (8 ns). At all wavelengths, the observed products in the presence of collisions are dominated by conformers A and B of tryptamine monomer, with small contributions from the other minor conformers. In addition, right at threshold (2869 cm{sup -1}), tryptamine{center_dot}D{sub 2}O dissociates exclusively to conformer A in the absence of collisions with helium, while both A and B conformational

  2. [DOTA-bis(amide)]lanthanide complexes: NMR evidence for differences in water-molecule exchange rates for coordination isomers.

    PubMed

    Zhang, S; Kovacs, Z; Burgess, S; Aime, S; Terreno, E; Sherry, A D

    2001-01-01

    Two derivatives of 1,4,7,10-tetraazacyclododecane with trans-acetate and trans-amide side-chain ligating groups have been prepared and their complexes with lanthanide cations examined by multinuclear NMR spectroscopy. These lanthanide complexes exist in aqueous solution as a mixture of slowly interconverting coordination isomers with 1H chemical shifts similar to those reported previously for the major (M) and minor (m) forms of the tetraacetate ([Ln(dota)]-) and tetraamide ([Ln(dtma)]3+) complexes. As in the [Ln(dota)]- and [Ln(dtma)]3+ complexes, the m/M ratio proved to be a sensitive function of lanthanide size and temperature. An analysis of 1H hyperfine shifts in spectra of the Yb3+ complexes revealed significant differences between the axial (D1) and non-axial (D2) components of the magnetic susceptibility tensor anisotropy in the m and M coordination isomers and the energetics of ring inversion and m <==> M isomerization as determined by two-dimensional exchange spectroscopy (EXSY). (17)O shift data for the Dy3+ complexes showed that both have one inner-sphere water molecule. A temperature-dependent (17)O NMR study of bulk water linewidths for solutions of the Gd3+ complexes provided direct evidence for differences in water exchange rates for the two coordination isomers. The bound-water lifetimes (tauM298) in the M and m isomers of the Gd3+ complexes ranged from 1.4-2.4 micros and 3-14 ns, respectively. This indicates that 1) the inner-sphere water lifetimes for the complexes with a single positive charge reported here are considerably shorter for both coordination isomers than the corresponding values for the [Gd(dtma)]3+ complex with three positive charges, and 2) the difference in water lifetimes for M and m isomers in these two series is magnified in the [Gd[dota-bis(amide)

  3. The reaction of clean Li surfaces with small molecules in ultrahigh vacuum. 2: Water

    SciTech Connect

    Zhuang, G.; Ross, P.N. Jr.; Kong, F.P.; McLarnon, F. |

    1998-01-01

    Reactions at the Li/H{sub 2}O interface were studied at 160 to 290 K in ultrahigh vacuum by a combination of spectroscopic ellipsometry and Auger electron spectroscopy. Ice multilayers, ca. 100 ML thick, were deposited on clean Li at 160 K. The evaporation rate of water at 160 K is sufficiently slow that the ice layer remains on the surface for about 1 h. After 10 min at 160 k, a pure LiOH layer ca. 70 {angstrom} thick is produced, and after 1 h there is evidence of a slow conversion to LiOH to Li{sub 2}O in the layer, probably at the Li/LiOH interface. Raising the temperature to 240 K results in desorption of the adsorbed water and conversion of all the LiOH to a porous (60% void) layer composed mostly of Li{sub 2}O (35%) with some metallic Li mixed in. Raising the temperature further to 290 K results in densification of the layer by both collapse of the voids and by diffusion of Li into the interstices of the Li{sub 2}O, increasing the Li content to 27% and shrinking the film thickness to 26 {angstrom}. Based on these results, a model for the behavior of small amounts of water in Li battery electrolyte is presented.

  4. Proposed photosynthesis method for producing hydrogen from dissociated water molecules using incident near-infrared light.

    PubMed

    Li, Xingxing; Li, Zhenyu; Yang, Jinlong

    2014-01-10

    Highly efficient solar energy utilization is very desirable in photocatalytic water splitting. However, until now, the infrared part of the solar spectrum, which constitutes almost half of the solar energy, has not been used, resulting in significant loss in the efficiency of solar energy utilization. Here, we propose a new mechanism for water splitting in which near-infrared light can be used to produce hydrogen. This ability is a result of the unique electronic structure of the photocatalyst, in which the valence band and conduction band are distributed on two opposite surfaces with a large electrostatic potential difference produced by the intrinsic dipole of the photocatalyst. This surface potential difference, acting as an auxiliary booster for photoexcited electrons, can effectively reduce the photocatalyst's band gap required for water splitting in the infrared region. Our electronic structure and optical property calculations on a surface-functionalized hexagonal boron-nitride bilayer confirm the existence of such photocatalysts and verify the reaction mechanism. PMID:24483934

  5. Ion hydration and associated defects in hydrogen bond network of water: Observation of reorientationally slow water molecules beyond first hydration shell in aqueous solutions of MgCl 2

    NASA Astrophysics Data System (ADS)

    Baul, Upayan; Vemparala, Satyavani

    2015-01-01

    Effects of the presence of ions, at moderate to high concentrations, on dynamical properties of water molecules are investigated through classical molecular dynamics simulations using two well-known nonpolarizable water models. Simulations reveal that the presence of magnesium chloride (MgCl2) induces perturbations in the hydrogen bond network of water leading to the formation of bulklike domains with ``defect sites'' on boundaries of such domains: water molecules at such defect sites have less number of hydrogen bonds than those in bulk water. Reorientational autocorrelation functions for dipole vectors of such defect water molecules are computed at different concentrations of ions and compared with system of pure water. Earlier experimental and simulation studies indicate significant differences in reorientational dynamics for water molecules in the first hydration shell of many dissolved ions. Results of this study suggest that defect water molecules, which are beyond the first hydration shells of ions, also experience significant slowing of reorientation times as a function of concentration in the case of MgCl2. However, addition of cesium chloride (CsCl) to water does not perturb the hydrogen bond network of water significantly even at higher concentrations. This difference in behavior between MgCl2 and CsCl is consistent with the well-known Hofmeister series.

  6. Comparison of the action spectra and relative DNA absorbance spectra of microorganisms: information important for the determination of germicidal fluence (UV dose) in an ultraviolet disinfection of water.

    PubMed

    Chen, Ren Zhuo; Craik, Stephen A; Bolton, James R

    2009-12-01

    The action spectra of Bacillus subtilis spores (ATCC6633) and Salmonella typhimurium LT2 were characterized using physical radiometry for irradiance measurements and a multiple target model to interpret the inactivation kinetics. The observed action spectrum of B. subtilis spores deviated significantly from the relative absorbance spectrum of the DNA purified from the spores, but matched quite well with the relative absorbance spectrum of decoated spores. The action spectrum of B. subtilis spores determined in this study was statistically different from those reported in previous studies. On the other hand, the action spectrum of S. typhimurium bacteria matched quite well with the relative absorbance spectrum of DNA extracted from vegetative cells, except in the region below 240nm. It is concluded that the common use of the relative DNA absorbance spectrum as a surrogate for the germicidal action spectrum can result in systematic errors when evaluating the performance of a polychromatic UV light reactors using bioassays. For example, if the weighted germicidal fluence (UV dose) calculated using the relative DNA absorbance spectrum as the germicidal weighting factor is found to be 40mJcm(-2) for a medium pressure lamp UV reactor, that calculated using the relative action spectrum of B. subtilis spores, as determined in this study, would be 66mJcm(-2). PMID:19762061

  7. Hydrogen isotope separation from water

    DOEpatents

    Jensen, R.J.

    1975-09-01

    A process for separating tritium from tritium-containing water or deuterium enrichment from water is described. The process involves selective, laser-induced two-photon excitation and photodissociation of those water molecules containing deuterium or tritium followed by immediate reaction of the photodissociation products with a scavenger gas which does not substantially absorb the laser light. The reaction products are then separated from the undissociated water. (auth)

  8. Photo-electrochemical Oxidation of Organic C1 Molecules over WO3 Films in Aqueous Electrolyte: Competition Between Water Oxidation and C1 Oxidation.

    PubMed

    Reichert, Robert; Zambrzycki, Christian; Jusys, Zenonas; Behm, R Jürgen

    2015-11-01

    To better understand organic-molecule-assisted photo-electrochemical water splitting, photo-electrochemistry and on-line mass spectrometry measurements are used to investigate the photo-electrochemical oxidation of the C1 molecules methanol, formaldehyde, and formic acid over WO3 film anodes in aqueous solution and its competition with O2 evolution from water oxidation O2 (+) and CO2 (+) ion currents show that water oxidation is strongly suppressed by the organic species. Photo-electro-oxidation of formic acid is dominated by formation of CO2 , whereas incomplete oxidation of formaldehyde and methanol prevails, with the selectivity for CO2 formation increasing with increasing potential and light intensity. The mechanistic implications for the photo-electro-oxidation of the organic molecules and its competition with water oxidation, which could be derived from this novel approach, are discussed. PMID:26382643

  9. Binding Energy of Molecules on Water Ice: Laboratory Measurements and Modeling

    NASA Astrophysics Data System (ADS)

    He, Jiao; Acharyya, Kinsuk; Vidali, Gianfranco

    2016-07-01

    We measured the binding energy of N2, CO, O2, CH4, and CO2 on non-porous (compact) amorphous solid water (np-ASW), of N2 and CO on porous ASW, and of NH3 on crystalline water ice. We were able to measure binding energies down to a fraction of 1% of a layer, thus making these measurements more appropriate for astrochemistry than the existing values. We found that CO2 forms clusters on the np-ASW surface even at very low coverages. The binding energies of N2, CO, O2, and CH4 decrease with coverage in the submonolayer regime. Their values at the low coverage limit are much higher than what is commonly used in gas-grain models. An empirical formula was used to describe the coverage dependence of the binding energies. We used the newly determined binding energy distributions in a simulation of gas-grain chemistry for cold cloud and hot-core models. We found that owing to the higher value of binding energy in the submonolayer regime, a fraction of all these ices remains for much longer and up to higher temperatures on the grain surface compared to the single value energies currently used in the astrochemical models.

  10. Confined Water Determines Transport Properties of Guest Molecules in Narrow Pores.

    PubMed

    Phan, Anh; Cole, David R; Weiß, R Gregor; Dzubiella, Joachim; Striolo, Alberto

    2016-08-23

    We computed the transport of methane through 1 nm wide slit-shaped pores carved out of solid substrates. Models for silica, magnesium oxide, and alumina were used as solid substrates. The pores were filled with water. The results show that the methane permeability through the hydrated pores is strongly dependent on the solid substrate. Detailed analysis of the simulated systems reveals that local properties of confined water, including its structure, and more importantly, evolution of solvation free energy and hydrogen bond structure are responsible for the pronounced differences observed. The simulations are extended to multicomponent systems representative of natural gas, containing methane, ethane, and H2S. The results show that all pores considered have high affinity for H2S, moderate affinity for methane, and low affinity for ethane. The H2S/methane transport selectivity through the hydrated alumina pore is comparable, or superior, to that reported for existing commercial membranes. A multiscale approach was then implemented to demonstrate that a Smoluchowski one-dimensional model is able to reproduce the molecular-level results for short pores when appropriate values for the local self-diffusion coefficients are used as input parameters. We propose that the model can be extended to predict methane transport through uniform hydrated pores of macroscopic length. When verified by experiments, our simulation results could have important implications in applications such as natural gas sweetening and predictions of methane migration through hydraulically fractured shale formations. PMID:27490280

  11. Theoretical investigation of hydrogen bonding between water and platinum(II): an atom in molecule (AIM) study

    NASA Astrophysics Data System (ADS)

    Li, Yan; Zhang, Guiqiu; Chen, Dezhan

    2012-02-01

    Recently, Rizzato et al. [Angew. Chem. Int. Ed. 49, 7440 (2010)] [1] reported a hydrogen-bonding-like interaction between a water molecule and a d8 metal ion (PtII) based on neutron diffraction, and provided the first crystallographic evidence for this interaction. We studied the hydrogen bonding of the O-H ... Pt interaction theoretically using atoms in molecule (AIM) and natural bond orbital analysis (NBO) in the crystallographic geometries. The method used density functional theory (DFT) with the hybrid B3LYP function. For platinum atoms, we used the Los Alamos National Laboratory 2-Double-Zeta (LANL2DZ) basis set, and for the other atoms we used 6-311++G(d,p) basis sets. Criteria based on a topological analysis of the electron density were used in order to characterize the nature of interactions in the complexes. The main purpose of the present work is to provide an answer to the following questions: Why can a filled d orbital of square-planar d8 metal ions such as platinum(II) also act as hydrogen-bond acceptors? Can a study based on the electron charge density answer this question? A good correlation between the density at the intermolecular bond critical point and the energy interaction was found. The interaction is mainly closed-shell and there is some charge transfer in this system.

  12. Open challenges in structure-based virtual screening: Receptor modeling, target flexibility consideration and active site water molecules description.

    PubMed

    Spyrakis, Francesca; Cavasotto, Claudio N

    2015-10-01

    Structure-based virtual screening is currently an established tool in drug lead discovery projects. Although in the last years the field saw an impressive progress in terms of algorithm development, computational performance, and retrospective and prospective applications in ligand identification, there are still long-standing challenges where further improvement is needed. In this review, we consider the conceptual frame, state-of-the-art and recent developments of three critical "structural" issues in structure-based drug lead discovery: the use of homology modeling to accurately model the binding site when no experimental structures are available, the necessity of accounting for the dynamics of intrinsically flexible systems as proteins, and the importance of considering active site water molecules in lead identification and optimization campaigns. PMID:26271444

  13. Rotationally resolved photoelectron spectroscopy of a triatomic molecule: Photoionization of the C (0.0.0) state of water

    SciTech Connect

    Glab, W.L.; Glynn, P.T.; Dehmer, P.M.; Dehmer, J.L.

    1996-05-01

    The authors have used a magnetic bottle photoelectron spectrometer to study the distribution of ion rotational states following photoionization of selected rotational states of the {tilde C}(0,0,0) state of water by 355 nm light. The spectrometer`s kinetic energy resolution of about 4 meV was sufficient to yield rotationally resolved time-of-flight photoelectron spectra. Comparison of the measured and calculated photoelectron spectra is encouraging and reveals unusual photoionization dynamics due to very nonatomic-like behavior in the photoionization continuum and to the presence of Cooper minima. This is the first time that such a test of photoionization theory for a polyatomic molecule at finite kinetic energy has been possible.

  14. Internal water molecules and H-bonding in biological macromolecules: a review of structural features with functional implications.

    PubMed Central

    Meyer, E.

    1992-01-01

    Conserved structural patterns of internal water molecules and/or H-bond chains were observed and are here correlated in this review, which then describes two functional properties: equilibration of hydrostatic pressure and proton transport. Available evidence in support of these hypotheses is presented, together with suggested experiments to test them. High-resolution crystal structures of a variety of proteins were studied with interactive computer graphics. Conserved H-bonding linkages may be used as a paradigm for a rationalization of proton transport in membranes. The concept of the "proton wire," which links buried active-site amino acids with the surface of the protein raises the more general question of the functional role of the various molecular components. PMID:1304887

  15. CO2 and C2H2 in cold nanodroplets of oxygenated organic molecules and water.

    PubMed

    Devlin, J Paul; Balcı, F Mine; Maşlakcı, Zafer; Uras-Aytemiz, Nevin

    2014-11-14

    Recent demonstrations of subsecond and microsecond timescales for formation of clathrate hydrate nanocrystals hint at future methods of control of environmental and industrial gases such as CO2 and methane. Combined results from cold-chamber and supersonic-nozzle [A. S. Bhabhe, "Experimental study of condensation and freezing in a supersonic nozzle," Ph.D. thesis (Ohio State University, 2012), Chap. 7] experiments indicate extremely rapid encagement of components of all-vapor pre-mixtures. The extreme rates are derived from (a) the all-vapor premixing of the gas-hydrate components and (b) catalytic activity of certain oxygenated organic large-cage guests. Premixing presents no obvious barrier to large-scale conditions of formation. Further, from sequential efforts of the groups of Trout and Buch, a credible defect-based model of the catalysis mechanism exists for guidance. Since the catalyst-generated defects are both mobile and abundant, it is often unnecessary for a high percentage of the cages to be occupied by a molecular catalyst. Droplets represent the liquid phase that bridges the premixed vapor and clathrate hydrate phases but few data exist for the droplets themselves. Here we describe a focused computational and FTIR spectroscopic effort to characterize the aerosol droplets of the all-vapor cold-chamber methodology. Computational data for CO2 and C2H2, hetero-dimerized with each of the organic catalysts and water, closely match spectroscopic redshift patterns in both magnitude and direction. Though vibrational frequency shifts are an order of magnitude greater for the acetylene stretch mode, both CO2 and C2H2 experience redshift values that increase from that for an 80% water-methanol solvent through the solvent series to approximately doubled values for tetrahydrofuran and trimethylene oxide (TMO) droplets. The TMO solvent properties extend to a 50 mol.% solution of CO2, more than an order of magnitude greater than for the water-methanol solvent mixture

  16. CO2 and C2H2 in cold nanodroplets of oxygenated organic molecules and water

    NASA Astrophysics Data System (ADS)

    Devlin, J. Paul; Balcı, F. Mine; Maşlakcı, Zafer; Uras-Aytemiz, Nevin

    2014-11-01

    Recent demonstrations of subsecond and microsecond timescales for formation of clathrate hydrate nanocrystals hint at future methods of control of environmental and industrial gases such as CO2 and methane. Combined results from cold-chamber and supersonic-nozzle [A. S. Bhabhe, "Experimental study of condensation and freezing in a supersonic nozzle," Ph.D. thesis (Ohio State University, 2012), Chap. 7] experiments indicate extremely rapid encagement of components of all-vapor pre-mixtures. The extreme rates are derived from (a) the all-vapor premixing of the gas-hydrate components and (b) catalytic activity of certain oxygenated organic large-cage guests. Premixing presents no obvious barrier to large-scale conditions of formation. Further, from sequential efforts of the groups of Trout and Buch, a credible defect-based model of the catalysis mechanism exists for guidance. Since the catalyst-generated defects are both mobile and abundant, it is often unnecessary for a high percentage of the cages to be occupied by a molecular catalyst. Droplets represent the liquid phase that bridges the premixed vapor and clathrate hydrate phases but few data exist for the droplets themselves. Here we describe a focused computational and FTIR spectroscopic effort to characterize the aerosol droplets of the all-vapor cold-chamber methodology. Computational data for CO2 and C2H2, hetero-dimerized with each of the organic catalysts and water, closely match spectroscopic redshift patterns in both magnitude and direction. Though vibrational frequency shifts are an order of magnitude greater for the acetylene stretch mode, both CO2 and C2H2 experience redshift values that increase from that for an 80% water-methanol solvent through the solvent series to approximately doubled values for tetrahydrofuran and trimethylene oxide (TMO) droplets. The TMO solvent properties extend to a 50 mol.% solution of CO2, more than an order of magnitude greater than for the water-methanol solvent mixture

  17. Advanced neutron absorber materials

    DOEpatents

    Branagan, Daniel J.; Smolik, Galen R.

    2000-01-01

    A neutron absorbing material and method utilizing rare earth elements such as gadolinium, europium and samarium to form metallic glasses and/or noble base nano/microcrystalline materials, the neutron absorbing material having a combination of superior neutron capture cross sections coupled with enhanced resistance to corrosion, oxidation and leaching.

  18. Increased Hydrogel Swelling Induced by Absorption of Small Molecules.

    PubMed

    Nam, Changwoo; Zimudzi, Tawanda J; Geise, Geoffrey M; Hickner, Michael A

    2016-06-01

    The water and small molecule uptake behavior of amphiphilic diacrylate terminated poly(dimethylsiloxane) (PDMSDA)/poly(ethylene glycol diacrylate) (PEGDA) cross-linked hydrogels were studied using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. These hydrogel networks absorbed more water as the PEGDA content of the network increased. In contrast to typical osmotic deswelling behavior that occurs when liquid water equilibrated hydrogels are immersed in small molecule solutions with water activities less than unity, water-swollen gels immersed in 2-acrylamido-2-methylpropanesulfonic acid (AMPS-H) solutions rapidly regained their water content within 4 min following an initial deswelling response. In situ ATR-FTIR analysis of the hydrogel film during the dynamic swelling experiment indicated that small molecule absorption into the gel played an important role in inducing gel reswelling in low water activity solutions. This aspect of polymer gel water uptake and interaction with small molecules is important for optimizing hydrogel coatings and hydrophilic polymer applications where there is an interaction between the internal chemical structure of the gel and electrolytes or other molecules in solution. PMID:27159118

  19. Ubiquitous Water-Soluble Molecules in Aquatic Plant Exudates Determine Specific Insect Attraction

    PubMed Central

    Sérandour, Julien; Reynaud, Stéphane; Willison, John; Patouraux, Joëlle; Gaude, Thierry; Ravanel, Patrick; Lempérière, Guy; Raveton, Muriel

    2008-01-01

    Plants produce semio-chemicals that directly influence insect attraction and/or repulsion. Generally, this attraction is closely associated with herbivory and has been studied mainly under atmospheric conditions. On the other hand, the relationship between aquatic plants and insects has been little studied. To determine whether the roots of aquatic macrophytes release attractive chemical mixtures into the water, we studied the behaviour of mosquito larvae using olfactory experiments with root exudates. After testing the attraction on Culex and Aedes mosquito larvae, we chose to work with Coquillettidia species, which have a complex behaviour in nature and need to be attached to plant roots in order to obtain oxygen. This relationship is non-destructive and can be described as commensal behaviour. Commonly found compounds seemed to be involved in insect attraction since root exudates from different plants were all attractive. Moreover, chemical analysis allowed us to identify a certain number of commonly found, highly water-soluble, low-molecular-weight compounds, several of which (glycerol, uracil, thymine, uridine, thymidine) were able to induce attraction when tested individually but at concentrations substantially higher than those found in nature. However, our principal findings demonstrated that these compounds appeared to act synergistically, since a mixture of these five compounds attracted larvae at natural concentrations (0.7 nM glycerol, <0.5 nM uracil, 0.6 nM thymine, 2.8 nM uridine, 86 nM thymidine), much lower than those found for each compound tested individually. These results provide strong evidence that a mixture of polyols (glycerol), pyrimidines (uracil, thymine), and nucleosides (uridine, thymidine) functions as an efficient attractive signal in nature for Coquillettidia larvae. We therefore show for the first time, that such commonly found compounds may play an important role in plant-insect relationships in aquatic eco-systems. PMID:18841203

  20. Multispectral metamaterial absorber.

    PubMed

    Grant, J; McCrindle, I J H; Li, C; Cumming, D R S

    2014-03-01

    We present the simulation, implementation, and measurement of a multispectral metamaterial absorber (MSMMA) and show that we can realize a simple absorber structure that operates in the mid-IR and terahertz (THz) bands. By embedding an IR metamaterial absorber layer into a standard THz metamaterial absorber stack, a narrowband resonance is induced at a wavelength of 4.3 μm. This resonance is in addition to the THz metamaterial absorption resonance at 109 μm (2.75 THz). We demonstrate the inherent scalability and versatility of our MSMMA by describing a second device whereby the MM-induced IR absorption peak frequency is tuned by varying the IR absorber geometry. Such a MSMMA could be coupled with a suitable sensor and formed into a focal plane array, enabling multispectral imaging. PMID:24690713

  1. Crystal Structure of Fatty Acid Amide Hydrolase Bound to the Carbamate Inhibitor URB597: Discovery of a Deacylating Water Molecule and Insight into Enzyme Inactivation

    SciTech Connect

    Mileni, Mauro; Kamtekar, Satwik; Wood, David C.; Benson, Timothy E.; Cravatt, Benjamin F.; Stevens, Raymond C.

    2010-08-12

    The endocannabinoid system regulates a wide range of physiological processes including pain, inflammation, and cognitive/emotional states. URB597 is one of the best characterized covalent inhibitors of the endocannabinoid-degrading enzyme fatty acid amide hydrolase (FAAH). Here, we report the structure of the FAAH-URB597 complex at 2.3 {angstrom} resolution. The structure provides insights into mechanistic details of enzyme inactivation and experimental evidence of a previously uncharacterized active site water molecule that likely is involved in substrate deacylation. This water molecule is part of an extensive hydrogen-bonding network and is coordinated indirectly to residues lining the cytosolic port of the enzyme. In order to corroborate our hypothesis concerning the role of this water molecule in FAAH's catalytic mechanism, we determined the structure of FAAH conjugated to a urea-based inhibitor, PF-3845, to a higher resolution (2.4 {angstrom}) than previously reported. The higher-resolution structure confirms the presence of the water molecule in a virtually identical location in the active site. Examination of the structures of serine hydrolases that are non-homologous to FAAH, such as elastase, trypsin, or chymotrypsin, shows a similarly positioned hydrolytic water molecule and suggests a functional convergence between the amidase signature enzymes and serine proteases.

  2. Dynamics of water around the complex structures formed between the KH domains of far upstream element binding protein and single-stranded DNA molecules

    SciTech Connect

    Chakraborty, Kaushik; Bandyopadhyay, Sanjoy

    2015-07-28

    Single-stranded DNA (ss-DNA) binding proteins specifically bind to the single-stranded regions of the DNA and protect it from premature annealing, thereby stabilizing the DNA structure. We have carried out atomistic molecular dynamics simulations of the aqueous solutions of two DNA binding K homology (KH) domains (KH3 and KH4) of the far upstream element binding protein complexed with two short ss-DNA segments. Attempts have been made to explore the influence of the formation of such complex structures on the microscopic dynamics and hydrogen bond properties of the interfacial water molecules. It is found that the water molecules involved in bridging the ss-DNA segments and the protein domains form a highly constrained thin layer with extremely retarded mobility. These water molecules play important roles in freezing the conformational oscillations of the ss-DNA oligomers and thereby forming rigid complex structures. Further, it is demonstrated that the effect of complexation on the slow long-time relaxations of hydrogen bonds at the interface is correlated with hindered motions of the surrounding water molecules. Importantly, it is observed that the highly restricted motions of the water molecules bridging the protein and the DNA components in the complexed forms originate from more frequent hydrogen bond reformations.

  3. Dynamics of water around the complex structures formed between the KH domains of far upstream element binding protein and single-stranded DNA molecules

    NASA Astrophysics Data System (ADS)

    Chakraborty, Kaushik; Bandyopadhyay, Sanjoy

    2015-07-01

    Single-stranded DNA (ss-DNA) binding proteins specifically bind to the single-stranded regions of the DNA and protect it from premature annealing, thereby stabilizing the DNA structure. We have carried out atomistic molecular dynamics simulations of the aqueous solutions of two DNA binding K homology (KH) domains (KH3 and KH4) of the far upstream element binding protein complexed with two short ss-DNA segments. Attempts have been made to explore the influence of the formation of such complex structures on the microscopic dynamics and hydrogen bond properties of the interfacial water molecules. It is found that the water molecules involved in bridging the ss-DNA segments and the protein domains form a highly constrained thin layer with extremely retarded mobility. These water molecules play important roles in freezing the conformational oscillations of the ss-DNA oligomers and thereby forming rigid complex structures. Further, it is demonstrated that the effect of complexation on the slow long-time relaxations of hydrogen bonds at the interface is correlated with hindered motions of the surrounding water molecules. Importantly, it is observed that the highly restricted motions of the water molecules bridging the protein and the DNA components in the complexed forms originate from more frequent hydrogen bond reformations.

  4. Water Splitting: Strongly Coupled Nafion Molecules and Ordered Porous CdS Networks for Enhanced Visible-Light Photoelectrochemical Hydrogen Evolution (Adv. Mater. 24/2016).

    PubMed

    Zheng, Xue-Li; Song, Ji-Peng; Ling, Tao; Hu, Zhen Peng; Yin, Peng-Fei; Davey, Kenneth; Du, Xi-Wen; Qiao, Shi-Zhang

    2016-06-01

    T. Ling, X.-W. Du, S. Z. Qiao, and co-workers report strongly coupled Nafion molecules and ordered-porous CdS networks for visible-light water splitting. The image conceptually shows how the three-dimensional ordered structure effectively harvests incoming light. As described on page 4935, the inorganic CdS skeleton is homogeneously passivated by the organic Nafion molecules to facilitate hydrogen generation. PMID:27311095

  5. Reflections on Small Molecule Manganese Models that Seek to Mimic Photosynthetic Water Oxidation Chemistry

    PubMed Central

    Mullins, Christopher S.

    2008-01-01

    Recent advances in the study of the Oxygen Evolving Complex (OEC) of Photosystem II (PSII) include structural information attained from several X-ray crystallographic (XRD) and spectroscopic (XANES and EXAFS) investigations. The possible structural features gleaned from these studies have enabled synthetic chemists to design more accurate model complexes, which in turn, offer better insight into the possible pathways used by PSII to drive photosynthetic water oxidation catalysis. Mononuclear model compounds have been used to advance the knowledge base regarding the physical properties and reactivity of high-valent (MnIV or MnV) complexes. Such investigations have been especially important in regard to the manganyl (MnIV=O or MnV≡O) species, as there are no reports, to date, of any structural characterized multinuclear model compounds that incorporate such a functionality. Dinuclear and trinuclear model compounds have also been thoroughly studied in attempts to draw further comparison to the physical properties observed in the natural system and to design systems of catalytic relevance. As the reactive center of the OEC has been shown to contain an oxo-Mn4Ca cluster, exact structural models necessitate a tetranuclear Mn core. The number of models that make use of Mn4 clusters has risen substantially in recent years, and these models have provided evidence to support and refute certain mechanistic proposals. Further work is needed to adequately address the rationale for Ca (and Cl) in the OEC and to determine the sequence of events that lead to O2 evolution. PMID:19081816

  6. Real Time Monitoring of Dissolved Organic Carbon Concentration and Disinfection By-Product Formation Potential in a Surface Water Treatment Plant with Simulaneous UV-VIS Absorbance and Fluorescence Excitation-Emission Mapping

    NASA Astrophysics Data System (ADS)

    Gilmore, A. M.

    2015-12-01

    This study describes a method based on simultaneous absorbance and fluorescence excitation-emission mapping for rapidly and accurately monitoring dissolved organic carbon concentration and disinfection by-product formation potential for surface water sourced drinking water treatment. The method enables real-time monitoring of the Dissolved Organic Carbon (DOC), absorbance at 254 nm (UVA), the Specific UV Absorbance (SUVA) as well as the Simulated Distribution System Trihalomethane (THM) Formation Potential (SDS-THMFP) for the source and treated water among other component parameters. The method primarily involves Parallel Factor Analysis (PARAFAC) decomposition of the high and lower molecular weight humic and fulvic organic component concentrations. The DOC calibration method involves calculating a single slope factor (with the intercept fixed at 0 mg/l) by linear regression for the UVA divided by the ratio of the high and low molecular weight component concentrations. This method thus corrects for the changes in the molecular weight component composition as a function of the source water composition and coagulation treatment effects. The SDS-THMFP calibration involves a multiple linear regression of the DOC, organic component ratio, chlorine residual, pH and alkalinity. Both the DOC and SDS-THMFP correlations over a period of 18 months exhibited adjusted correlation coefficients with r2 > 0.969. The parameters can be reported as a function of compliance rules associated with required % removals of DOC (as a function of alkalinity) and predicted maximum contaminant levels (MCL) of THMs. The single instrument method, which is compatible with continuous flow monitoring or grab sampling, provides a rapid (2-3 minute) and precise indicator of drinking water disinfectant treatability without the need for separate UV photometric and DOC meter measurements or independent THM determinations.

  7. Internal absorber solar collector

    DOEpatents

    Sletten, Carlyle J.; Herskovitz, Sheldon B.; Holt, F. S.; Sletten, E. J.

    1981-01-01

    Thin solar collecting panels are described made from arrays of small rod collectors consisting of a refracting dielectric rod lens with an absorber imbedded within it and a reflecting mirror coated on the back side of the dielectric rod. Non-tracking collector panels on vertical walls or roof tops receive approximately 90% of solar radiation within an acceptance zone 60.degree. in elevation angle by 120.degree. or more in the azimuth sectors with a collector concentration ratio of approximately 3.0. Miniaturized construction of the circular dielectric rods with internal absorbers reduces the weight per area of glass, plastic and metal used in the collector panels. No external parts or insulation are needed as heat losses are low due to partial vacuum or low conductivity gas surrounding heated portions of the collector. The miniature internal absorbers are generally made of solid copper with black selective surface and the collected solar heat is extracted at the collector ends by thermal conductivity along the absorber rods. Heat is removed from end fittings by use of liquid circulants. Several alternate constructions are provided for simplifying collector panel fabrication and for preventing the thermal expansion and contraction of the heated absorber or circulant tubes from damaging vacuum seals. In a modified version of the internal absorber collector, oil with temperature dependent viscosity is pumped through a segmented absorber which is now composed of closely spaced insulated metal tubes. In this way the circulant is automatically diverted through heated portions of the absorber giving higher collector concentration ratios than theoretically possible for an unsegmented absorber.

  8. The rates of exchange of water molecules from Al(III)-methylmalonate complexes: The effect of chelate ring size

    SciTech Connect

    Casey, W.H.; Phillips, B.L.; Nordin, J.P.; Sullivan, D.J.

    1998-08-01

    Rate coefficients are reported for exchange of hydration waters in the inner-coordination-sphere of Al(III)-methylmalonate complexes with bulk solution as determined via {sup 17}O-NMR. Surprisingly, water molecules in the thermodynamically less-stable complexes containing six-membered chelates are much more labile than those in five-membered oxalate-A(III) complexes. The surprising trend in reactivity is attributable either to differences in the Lewis basicities of oxygens in bidentate oxalate and methylmalonate ligands, or to rapid dissociation/reassociation of one of the acetate groups to the metal center. These results identify a useful case where trends in the apparent labilities of dissolved and presumed surface complexes deviate sharply. This deviation could be usefully exploited to probe surfaces if ligand-promoted dissolution rates could be compared at conditions where inner-sphere and outer-sphere chelate complexes could be distinguished spectroscopically. The authors expect inner-sphere oxalate to have a smaller labilizing effect than malonate or methylmalonate. A contrary result would indicate structural dissimilarity between complexes on the surface and in solution, or perhaps steric hindrance.

  9. Double differential distribution of electron emission in the ionization of water molecules by fast bare oxygen ions

    NASA Astrophysics Data System (ADS)

    Bhattacharjee, Shamik; Biswas, Shubhadeep; Bagdia, Chandan; Roychowdhury, Madhusree; Nandi, Saikat; Misra, Deepankar; Monti, J. M.; Tachino, C. A.; Rivarola, R. D.; Champion, C.; Tribedi, Lokesh C.

    2016-03-01

    The doubly differential distributions of low-energy electron emission in the ionization of water molecules under the impact of fast bare oxygen ions with energy of 48 MeV are measured. The measured data are compared with two quantum-mechanical models, i.e. the post and prior versions of the continuum distorted wave-eikonal initial state (CDW-EIS) approximation, and the first-order Born approximation with initial and final wavefunctions verifying correct boundary conditions (CB1). An overall excellent qualitative agreement is found between the data and the CDW-EIS models whereas the CB1 model showed substantial deviation. However, the detailed angular distributions display some discrepancies with both CDW-EIS models. The single differential and total cross-sections exhibit good agreement with the CDW-EIS models. The present detailed data set could also be used as an input for modeling highly charged ion induced radiation damage in living tissues, whose most abundant component is water. Similar measurements are also carried out for a projectile energy of 60 MeV. However, since the double differential cross-section data show similar results the details are not provided here, except for the total ionization cross-sections results.

  10. Theoretical predictions of the spectroscopic parameters in noble-gas molecules: HXeOH and its complex with water.

    PubMed

    Cukras, Janusz; Sadlej, Joanna

    2011-09-14

    We employ state-of-the-art methods and basis sets to study the effect of inserting the Xe atom into the water molecule and the water dimer on their NMR parameters. Our aim is to obtain predictions for the future experimental investigation of novel xenon complexes by NMR spectroscopy. Properties such as molecular structure and energetics have been studied by supermolecular approaches using HF, MP2, CCSD, CCSD(T) and MP4 methods. The bonding in HXeOH···H(2)O complexes has been analyzed by Symmetry-Adapted Perturbation Theory to provide the intricate insight into the nature of the interaction. We focus on vibrational spectra, NMR shielding and spin-spin coupling constants-experimental signals that reflect the electronic structures of the compounds. The parameters have been calculated at electron-correlated and Dirac-Hartree-Fock relativistic levels. This study has elucidated that the insertion of the Xe atom greatly modifies the NMR properties, including both the electron correlation and relativistic effects, the (129)Xe shielding constants decrease in HXeOH and HXeOH···H(2)O in comparison to Xe atom; the (17)O, as a neighbour of Xe, is deshielded too. The HXeOH···H(2)O complex in its most stable form is stabilized mainly by induction and dispersion energies. PMID:21804992

  11. Metal shearing energy absorber

    NASA Technical Reports Server (NTRS)

    Fay, R. J.; Wittrock, E. P. (Inventor)

    1973-01-01

    A metal shearing energy absorber is described. The absorber is composed of a flat thin strip of metal which is pulled through a slot in a cutter member of a metal, harder than the metal of the strip. The slot's length, in the direction perpendicular to the pull direction, is less than the strip's width so that as the strip is pulled through the slot, its edges are sheared off, thereby absorbing some of the pulling energy. In one embodiment the cutter member is a flat plate of steel, while in another embodiment the cutter member is U-shaped with the slot at its base.

  12. Modelling the spectroscopic behaviour of hot molecules

    NASA Astrophysics Data System (ADS)

    Tennyson, Jonathan

    2010-05-01

    At elevated temperatures the molecules absorb and emit light in a very complicated fashion which is hard to characterise on the basis of laboraroty measurement. Computed line lists of molecule transitions therefore provide a vital input for models of hot atmospheres. I will describe the calculation and use of such line lists including the BT2 water line list [1], which contains some 500 million distinct rotation-vibration transitions. This linelist proved crucial in the detection of water in extrasolar planet HD189733b and has been used extensively in atmospheric modelling. Illustrations will be given at the meeting. A new linelist for the ammonia molecule has just been completed [2] which shows that standard compilations for this molecule need to be improved. Progress on a more extensive linelist for hot ammonia and linelists for other molecules will be discussed at the meeting. [1] R.J. Barber, J. Tennyson, G.J. Harris and R.N. Tolchenov, Mon. Not. R. Astr. Soc., 368, 1087-1094 (2006) [2] S.N. Yurchenko, R.J. Barber, A. Yachmenev, W. Theil, P. Jensen and J. Tennyson, J. Phys. Chem. A, 113, 11845-11855 (2009).

  13. The dynamics of some metal-organic and organic molecules in water solution studied by molecular mechanical and molecular dynamical methods

    NASA Astrophysics Data System (ADS)

    Broo, Anders

    1993-07-01

    A force field is developed to reproduce geometries and vibration spectra of rutheniumhexaamine(III) and rutheniumhexamine(II) complexes. The force constants for ruthenium were then used in molecular dynamics simulation of a Ru 2+ ion, a Ru 3+ ion and Ru(NH 3) 5-pyrazine 2+ in water solution. Simulations of pyrazine and 1,3-dimethyluracile in water solution were also performed. A comparison of different ways of how to include solvation effects in quantum chemical calculations is discussed using the results from the simulations. The MD simulations show that the solvent surrounding a small charged ion, such as a Ru 2+ ion, have a pronounced shell structure and the first layer of solvent molecules is stable during a 61 ps simulation. For a metal-organic molecule as Ru(NH 3) 5-pyrazine the solvent shows shell structure, but the water molecules are exchanged frequently. In the relatively charge-symmetric pyrazine the solvent is not polarized around the molecule. In a molecule like 1,3-dimethyluracile, which is non-symmetric in the charge distribution, the water is strongly polarized.

  14. Uniform silica nanoparticles encapsulating two-photon absorbing fluorescent dye

    SciTech Connect

    Wu Weibing; Liu Chang; Wang Mingliang; Huang Wei; Zhou Shengrui; Jiang Wei; Sun Yueming; Cui Yiping; Xu Chunxinag

    2009-04-15

    We have prepared uniform silica nanoparticles (NPs) doped with a two-photon absorbing zwitterionic hemicyanine dye by reverse microemulsion method. Obvious solvatochromism on the absorption spectra of dye-doped NPs indicates that solvents can partly penetrate into the silica matrix and then affect the ground and excited state of dye molecules. For dye-doped NP suspensions, both one-photon and two-photon excited fluorescence are much stronger and recorded at shorter wavelength compared to those of free dye solutions with comparative overall dye concentration. This behavior is possibly attributed to the restricted twisted intramolecular charge transfer (TICT), which reduces fluorescence quenching when dye molecules are trapped in the silica matrix. Images from two-photon laser scanning fluorescence microscopy demonstrate that the dye-doped silica NPs can be actively uptaken by Hela cells with low cytotoxicity. - Graphical abstract: Water-soluble silica NPs doped with a two-photon absorbing zwitterionic hemicyanine dye were prepared. They were found of enhanced one-photon and two-photon excited fluorescence compared to free dye solutions. Images from two-photon laser scanning fluorescence microscopy demonstrate that the dye-doped silica NPs can be actively uptaken by Hela cells.

  15. Translational and rotational energy measurements of desorbed water molecules in their vibrational ground state following 157 nm irradiation of amorphous solid water

    NASA Astrophysics Data System (ADS)

    Hama, Tetsuya; Yokoyama, Masaaki; Yabushita, Akihiro; Kawasaki, Masahiro; Watanabe, Naoki

    2011-05-01

    Water ice is the major solid component in a variety of astrophysical environments, e.g., cold and dense molecular clouds. Photodesorption plays a dominant role in consuming ice in such cold regions. In this study, photodesorption of vibrationally ground-state H 2O( v = 0) from amorphous solid water has been investigated at 157 nm. Using a resonance-enhanced multiphoton ionization technique, the translational and rotational energy distributions of photodesorbed H 2O( v = 0) were measured, i.e., Boltzmann distributions at 1800 and 300 K, respectively. These energies are in good accordance with those predicted by classical molecular calculations for water photodesorption due to a kick-out mechanism following absorption of a single photon; hot H atom released by photodissociation of H 2O in ice transfers enough momentum to another H 2O molecule to kick it off the surface. Desorption of D 2O( v = 0) following 193 nm photoirradiation of a D 2O/H 2S mixed ice was investigated to provide further direct evidence for the operation of a kick-out mechanism. The other desorption mechanisms were also discussed in the context of possible photodesorption of vibrationally excited H 2O.

  16. Mixed-metal molecular complexes: Single-molecule nanomagnets and bioinorganic models of the water oxidizing complex of photosystem II

    NASA Astrophysics Data System (ADS)

    Mishra, Abhudaya

    2006-12-01

    The current burgeoning research in high nuclearity manganese-containing carboxylate clusters is primarily due to their relevance in areas as diverse as magnetic materials and bioinorganic chemistry. In the former, the ability of single molecules to retain, below a critical temperature (T B), their magnetization vector, resulting in the observation of bulk magnetization in the absence of a field and without long-range ordering of the spins, has termed such molecules as Single-Molecule Magnets (SMMs), or molecular nanomagnets. These molecules display superparamagnet like slow magnetization relaxation arising from the combination of a large molecular spin, S, and a large and negative magnetoanisotropy, D. Traditionally, these nanomagnets have been Mn containing species. An out of the box approach towards synthesizing SMMs is engineering mixed-metal Mn-containing compounds. An attractive choice towards this end is the use of Lanthanides (Ln), which possess both a high spin, S, and a large D. A family of related MnIII8Ce IV SMMs has been synthesized. However, the Ce ion of these complexes is diamagnetic (CeIV). Thus, further investigation has led to the isolation of a family of MnIII11Ln III4 complexes in which all but the Ln = Eu complex function as single-molecule nanomagnets. The mixed-metal synthetic effort has been extended to include actinides with the successful isolation of a Mn IV10ThIV6 complex, albeit this homovalent complex is not a SMM. In the bioinorganic research, the Water Oxidizing Complex (WOC) in Photosystem II (PS II) catalyzes the oxidation of H2O to O2 in green plants, algae and cyanobacteria. Recent crystal structures of the WOC confirm it to be a Mn4CaOx cluster with primarily carboxylate ligation. To date, various multinuclear Mn complexes have been synthesized as putative models of the WOC. On the contrary, there have been no synthetic MnCa(Sr) mixed-metal complexes. Thus, in this bioinorganic modeling research of the WOC, various synthetic

  17. Chemical interaction of water molecules with framework Al in acid zeolites: a periodic ab initio study on H-clinoptilolite.

    PubMed

    Valdiviés-Cruz, Karell; Lam, Anabel; Zicovich-Wilson, Claudio M

    2015-09-28

    Periodic quantum-chemistry methods as implemented in the CRYSTAL14 code were considered to analyse the interaction of acid clinoptilolite with water. Initially adsorbed molecules hydrolyse the Al-O bonds, giving rise to defective dealuminated materials. A suitable and representative periodic model of the partially disordered hydrated H-zeolite is the primitive cell (18 T sites) of a decahydrated trialuminated structure of HEU topology. The water distribution inside the material cavities was initially investigated. The model considered for further dealumination was the most stable one from those generated through a combined force field Monte Carlo and ab initio optimization strategy. Optimizations and energy estimations were made at the hybrid DFT level of theory (PBE0 functional) with an atomic basis set of VDZP quality. The energetics of the different pathways involved in the dealumination process was addressed by considering the Gibbs free energy with thermal and zero-point corrections through phonon analysis. It arises that hydrated models exhibit protonated water clusters stabilized by different kinds of H-bonds. The first Al extraction is slightly more energetically favourable from T3 than T2 sites, but at the same time the latter is more probable owing to its larger Al population. However, concerning the second dealumination step, it is more favourable removing the Al atom from both remaining sites after a starting abstraction from T2 rather than T3. These facts determine that the most probable overall pathways go through a first Al removal from T2. The agreement with experimental results is discussed. PMID:26299763

  18. "Smart" Electromechanical Shock Absorber

    NASA Technical Reports Server (NTRS)

    Stokes, Lebarian; Glenn, Dean C.; Carroll, Monty B.

    1989-01-01

    Shock-absorbing apparatus includes electromechanical actuator and digital feedback control circuitry rather than springs and hydraulic damping as in conventional shock absorbers. Device not subject to leakage and requires little or no maintenance. Attenuator parameters adjusted in response to sensory feedback and predictive algorithms to obtain desired damping characteristic. Device programmed to decelerate slowly approaching vehicle or other large object according to prescribed damping characteristic.

  19. Iron Chalcogenide Photovoltaic Absorbers

    SciTech Connect

    Yu, Liping; Lany, Stephan; Kykyneshi, Robert; Jieratum, Vorranutch; Ravichandran, Ram; Pelatt, Brian; Altschul, Emmeline; Platt, Heather A. S.; Wager, John F.; Keszler, Douglas A.; Zunger, Alex

    2011-08-10

    An integrated computational and experimental study of FeS₂ pyrite reveals that phase coexistence is an important factor limiting performance as a thin-film solar absorber. This phase coexistence is suppressed with the ternary materials Fe₂SiS₄ and Fe₂GeS₄, which also exhibit higher band gaps than FeS₂. Thus, the ternaries provide a new entry point for development of thin-film absorbers and high-efficiency photovoltaics.

  20. The Investigation of Property of Radiation and Absorbed of Infrared Lights of the Biological Tissues

    NASA Astrophysics Data System (ADS)

    Pang, Xiao-Feng; Deng, Bo; Xiao, He-Lan; Cai, Guo-Ping

    2010-04-01

    The properties of absorption of infrared light for collagen, hemoglobin, bivine serum albumen (BSA) protein molecules with α- helix structure and water in the living systems as well as the infrared transmission spectra for person’s skins and finger hands of human body in the region of 400-4000 cm-1 (i.e., wavelengths of 2-20 μm) have been collected and determined by using a Nicolet Nexus 670 FT-IR Spectrometer, a Perkin Elmer GX FT-IR spectrometer, an OMA (optical multichannel analysis) and an infrared probe systems, respectively. The experimental results obtained show that the protein molecules and water can all absorb the infrared lights in the ranges of 600-1900 cm-1 and 2900-3900 cm-l, but their properties of absorption are somewhat different due to distinctions of their structure and conformation and molecular weight. We know from the transmission spectra of person’s finger hands and skin that the infrared lights with wavelengths of 2 μm-7 μm can not only transmit over the person’s skin and finger hands, but also be absorbed by the above proteins and water in the living systems. Thus, we can conclude from this study that the human beings and animals can absorb the infrared lights with wavelengths of 2 μm-7 μm.

  1. Leaf absorbance and photosynthesis

    NASA Technical Reports Server (NTRS)

    Schurer, Kees

    1994-01-01

    The absorption spectrum of a leaf is often thought to contain some clues to the photosynthetic action spectrum of chlorophyll. Of course, absorption of photons is needed for photosynthesis, but the reverse, photosynthesis when there is absorption, is not necessarily true. As a check on the existence of absorption limits we measured spectra for a few different leaves. Two techniques for measuring absorption have been used, viz. the separate determination of the diffuse reflectance and the diffuse transmittance with the leaf at a port of an integrating sphere and the direct determination of the non-absorbed fraction with the leaf in the sphere. In a cross-check both methods yielded the same results for the absorption spectrum. The spectrum of a Fuchsia leaf, covering the short-wave region from 350 to 2500 nm, shows a high absorption in UV, blue and red, the well known dip in the green and a steep fall-off at 700 nm. Absorption drops to virtually zero in the near infrared, with subsequent absorptions, corresponding to the water absorption bands. In more detailed spectra, taken at 5 nm intervals with a 5 nm bandwidth, differences in chlorophyll content show in the different depths of the dip around 550 nm and in a small shift of the absorption edge at 700 nm. Spectra for Geranium (Pelargonium zonale) and Hibiscus (with a higher chlorophyll content) show that the upper limit for photosynthesis can not be much above 700 nm. No evidence, however, is to be seen of a lower limit for photosynthesis and, in fact, some experiments down to 300 nm still did not show a decrease of the absorption although it is well recognized that no photosynthesis results with 300 nm wavelengths.

  2. Thermodynamic properties of water molecules in the presence of cosolute depend on DNA structure: a study using grid inhomogeneous solvation theory.

    PubMed

    Nakano, Miki; Tateishi-Karimata, Hisae; Tanaka, Shigenori; Tama, Florence; Miyashita, Osamu; Nakano, Shu-Ichi; Sugimoto, Naoki

    2015-12-01

    In conditions that mimic those of the living cell, where various biomolecules and other components are present, DNA strands can adopt many structures in addition to the canonical B-form duplex. Previous studies in the presence of cosolutes that induce molecular crowding showed that thermal stabilities of DNA structures are associated with the properties of the water molecules around the DNAs. To understand how cosolutes, such as ethylene glycol, affect the thermal stability of DNA structures, we investigated the thermodynamic properties of water molecules around a hairpin duplex and a G-quadruplex using grid inhomogeneous solvation theory (GIST) with or without cosolutes. Our analysis indicated that (i) cosolutes increased the free energy of water molecules around DNA by disrupting water-water interactions, (ii) ethylene glycol more effectively disrupted water-water interactions around Watson-Crick base pairs than those around G-quartets or non-paired bases, (iii) due to the negative electrostatic potential there was a thicker hydration shell around G-quartets than around Watson-Crick-paired bases. Our findings suggest that the thermal stability of the hydration shell around DNAs is one factor that affects the thermal stabilities of DNA structures under the crowding conditions. PMID:26538600

  3. Tracking all-vapor instant gas-hydrate formation and guest molecule populations: a possible probe for molecules trapped in water nanodroplets.

    PubMed

    Uras-Aytemiz, Nevin; Cwiklik, Lukasz; Paul Devlin, J

    2012-11-28

    Quantitative Fourier-transform infrared spectra for low-temperature (160-200 K) aerosols of clathrate-hydrate nanoparticles that contain large-cage catalysts and small-cage nonpolar guests have been extended to a broad range of vapor compositions and sampling conditions. The data better reveal the stages by which room-temperature vapor mixtures, when cooled below ∼220 K, instantly generate aerosols with particles composed exclusively of the corresponding clathrate hydrates. In particular the quantitative data help relate the nature of the hydrates that form to the composition of the aqueous nanodroplets of the first stages of the rapid transition from the all-vapor mixture. The overall transition from an all-vapor mixture to "gas"-hydrate nanocrystals is a multistage one that has been characterized as homogeneous nucleation and growth of solution nanodroplets (∼240 K) followed by nucleation and growth of the gas-hydrate particles (∼220 K); all occurring within a subsecond that follows pulsing of the warm vapor into a sampling cold chamber. This may serve well as a general description of the instantaneous generation of the gas-hydrate aerosols, but closer consideration of the nature of the sampling method, in context with recent computation-based insights to (a) gas-hydrate nucleation stages∕rates and (b) the lifetimes of trapped small nonpolar molecules in cold aqueous nanodroplets, suggests a more complex multistage transition. The simulated lifetimes and extensive new quantitative infrared data significantly broaden the knowledge base in which the instantaneous transition from vapor to crystalline hydrate particles is viewed. The apparent need for a high occupancy of large-cage catalytic guest molecules currently limits the practical value of the all-vapor method. Only through greater clarity in the molecular-level description of the transition will the ultimate limits be defined. PMID:23206013

  4. Tracking all-vapor instant gas-hydrate formation and guest molecule populations: A possible probe for molecules trapped in water nanodroplets

    NASA Astrophysics Data System (ADS)

    Uras-Aytemiz, Nevin; Cwiklik, Lukasz; Paul Devlin, J.

    2012-11-01

    Quantitative Fourier-transform infrared spectra for low-temperature (160-200 K) aerosols of clathrate-hydrate nanoparticles that contain large-cage catalysts and small-cage nonpolar guests have been extended to a broad range of vapor compositions and sampling conditions. The data better reveal the stages by which room-temperature vapor mixtures, when cooled below ˜220 K, instantly generate aerosols with particles composed exclusively of the corresponding clathrate hydrates. In particular the quantitative data help relate the nature of the hydrates that form to the composition of the aqueous nanodroplets of the first stages of the rapid transition from the all-vapor mixture. The overall transition from an all-vapor mixture to "gas"-hydrate nanocrystals is a multistage one that has been characterized as homogeneous nucleation and growth of solution nanodroplets (˜240 K) followed by nucleation and growth of the gas-hydrate particles (˜220 K); all occurring within a subsecond that follows pulsing of the warm vapor into a sampling cold chamber. This may serve well as a general description of the instantaneous generation of the gas-hydrate aerosols, but closer consideration of the nature of the sampling method, in context with recent computation-based insights to (a) gas-hydrate nucleation stages/rates and (b) the lifetimes of trapped small nonpolar molecules in cold aqueous nanodroplets, suggests a more complex multistage transition. The simulated lifetimes and extensive new quantitative infrared data significantly broaden the knowledge base in which the instantaneous transition from vapor to crystalline hydrate particles is viewed. The apparent need for a high occupancy of large-cage catalytic guest molecules currently limits the practical value of the all-vapor method. Only through greater clarity in the molecular-level description of the transition will the ultimate limits be defined.

  5. 1H NMR detection of immobilized water molecules within a strong distal hydrogen-bonding network of substrate-bound human heme oxygenase-1.

    PubMed

    Syvitski, Ray T; Li, Yiming; Auclair, Karine; Ortiz De Montellano, Paul R; La Mar, Gerd N

    2002-12-01

    Solution 1H NMR is used to probe the environments of the donor protons of eight strong hydrogen bonds on the distal side of the heme substrate in the cyanide-inhibited, substrate-bound complex of human heme oxygenase, hHO. It is demonstrated that significant magnetization transfer from the bulk water signal to the eight labile protons does not result from chemical exchange, but from direct nuclear Overhauser effect due to the dipolar interaction of these labile protons with "ordered" water molecules. The enzyme labile proton to water proton distances are estimated at approximately 3 A. It is proposed that the role of the strong hydrogen-bonding network is to immobilize numerous water molecules which both stabilize the activated hydroperoxy species and funnel protons to the active site. PMID:12452690

  6. Maximizing T2-exchange in Dy3+DOTA-(amide)X chelates: Fine-tuning the water molecule exchange rate for enhanced T2 contrast in MRI

    PubMed Central

    Soesbe, Todd C.; Ratnakar, S. James; Milne, Mark; Zhang, Shanrong; Do, Quyen N.; Kovacs, Zoltan; Sherry, A. Dean

    2014-01-01

    Purpose The water molecule exchange rates in a series of DyDOTA-(amide)X chelates were fine-tuned to maximize the effects of T2-exchange line broadening and improve T2 contrast. Methods Four DyDOTA-(amide)X chelates having a variable number of glycinate side-arms were prepared and characterized as T2-exchange agents. The non-exchanging DyTETA chelate was also used to measure the bulk water T2 reduction due solely to T2*. The total transverse relaxivity (r2tot) at 22, 37, and 52 °C for each chelate was measured in vitro at 9.4 T (400 MHz) by fitting plots of total T2−1 versus concentration. The water molecule exchange rates for each complex were measured by fitting 17O line-width versus temperature data taken at 9.4 T (54.3 MHz). Results The measured transverse relaxivities due to water molecule exchange (r2ex) and bound water lifetimes (τM) were in excellent agreement with Swift-Connick theory, with DyDOTA-(gly)3 giving the largest r2ex = 11.8 s−1 mM−1 at 37 °C. Conclusion By fine-tuning the water molecule exchange rate at 37 °C, the transverse relaxivity has been increased by 2 to 30 times compared to previously studied Dy3+-based chelates. Polymerization or dendrimerization of the optimal chelate could yield a highly sensitive, molecule-sized T2 contrast agent for improved molecular imaging applications. PMID:24390729

  7. Mono/bimetallic water-stable lanthanide coordination polymers as luminescent probes for detecting cations, anions and organic solvent molecules.

    PubMed

    Wang, Huarui; Qin, Jianhua; Huang, Chao; Han, Yanbing; Xu, Wenjuan; Hou, Hongwei

    2016-08-01

    Eleven water-stable isostructural mono/bimetallic lanthanide coordination polymers (Ln-CPs) {[EuxTb1-x (HL)(H2O)3]·H2O}n (x = 1.0 (1), 0.9 (3), 0.8 (4), 0.7 (5), 0.6 (6), 0.4 (7), 0.3 (8), 0.2 (9), 0.1 (10), 0.05 (11), 0 (2), H4L = 5,5'-(1H-2,3,5-triazole-1,4-diyl)diisophthalic acid) with uncoordinated Lewis basic triazole sites within the pores were prepared. The Ln-CPs represented by 1 showed a rapid and drastic emission quenching induced by external Fe(3+) and Cr(3+) cations and CrO4(2-) and CO3(2-) anions in aqueous solution. In addition, because of the comparable emission intensities of Eu(3+) and Tb(3+) ions, bimetallic CP 8 can be used as a ratiometric luminescent sensor for organic solvent molecules. Moreover, the luminescent color of the 8 sensor in pyridine and in other guest solvents undergoes obvious changes that can be clearly distinguished by the naked eye. PMID:27443408

  8. Improved Estimation of Protein-Ligand Binding Free Energy by Using the Ligand-Entropy and Mobility of Water Molecules

    PubMed Central

    Fukunishi, Yoshifumi; Nakamura, Haruki

    2013-01-01

    We previously developed the direct interaction approximation (DIA) method to estimate the protein-ligand binding free energy (ΔG). The DIA method estimates the ΔG value based on the direct van der Waals and electrostatic interaction energies between the protein and the ligand. In the current study, the effect of the entropy of the ligand was introduced with protein dynamic properties by molecular dynamics simulations, and the interaction between each residue of the protein and the ligand was also weighted considering the hydration of each residue. The molecular dynamics simulation of the apo target protein gave the hydration effect of each residue, under the assumption that the residues, which strongly bind the water molecules, are important in the protein-ligand binding. These two effects improved the reliability of the DIA method. In fact, the parameters used in the DIA became independent of the target protein. The averaged error of ΔG estimation was 1.3 kcal/mol and the correlation coefficient between the experimental ΔG value and the calculated ΔG value was 0.75. PMID:24276169

  9. Interactions of carbon nanotubes with the nitromethane-water mixture governing selective adsorption of energetic molecules from aqueous solution.

    PubMed

    Liu, Yingzhe; Lai, Weipeng; Yu, Tao; Kang, Ying; Ge, Zhongxue

    2015-03-14

    The structure and dynamics of the nitromethane-water (NM-WT) binary mixture surrounding single walled carbon nanotubes (SWNTs) have been investigated by molecular dynamics simulations. The simulation trajectories show that the NM molecules can be selectively adsorbed both outside the surface and inside the cavity of SWNTs mainly dominated by van der Waals attractions because SWNTs have a higher binding affinity for NM than WT. The binding energies of SWNTs with NM and WT obtained from electronic structure calculations at the M06-2X/6-31+G* level are 15.31 and 5.51 kcal mol(-1), respectively. Compared with the SWNT exterior, the selective adsorption of NM is preferentially occurred in the SWNT interior due to the hydrophobic interactions and the dipole-dipole interactions, which induces the decrease of the hydrogen-bond number of NM with WT and ordered structures of NM with preferred intermolecular orientation in the SWNT cavity. Furthermore, the selective adsorption dynamics of NM from the aqueous solution is regardless of the chirality and radius of SWNTs. The SWNT radius plays a negligible role in the mass density distributions of NM outside the SWNTs, while the mass density of NM in the SWNT interior decreases gradually as the SWNT radius increases. The structural arrangements and intermolecular orientations of NM in the SWNT cavity are greatly dependent on the SWNT radius due to the size effect. PMID:25684688

  10. The role of water molecules in the binding of class I and II peptides to the SH3 domain of the Fyn tyrosine kinase.

    PubMed

    Camara-Artigas, Ana; Ortiz-Salmeron, Emilia; Andujar-Sánchez, Montserrrat; Bacarizo, Julio; Martin-Garcia, Jose Manuel

    2016-09-01

    Interactions of proline-rich motifs with SH3 domains are present in signal transduction and other important cell processes. Analysis of structural and thermodynamic data suggest a relevant role of water molecules in these protein-protein interactions. To determine whether or not the SH3 domain of the Fyn tyrosine kinase shows the same behaviour, the crystal structures of its complexes with two high-affinity synthetic peptides, VSL12 and APP12, which are class I and II peptides, respectively, have been solved. In the class I complexes two water molecules were found at the binding interface that were not present in the class II complexes. The structures suggest a role of these water molecules in facilitating conformational changes in the SH3 domain to allow the binding of the class I or II peptides. In the third binding pocket these changes modify the cation-π and salt-bridge interactions that determine the affinity of the binding. Comparison of the water molecules involved in the binding of the peptides with previous reported hydration spots suggests a different pattern for the SH3 domains of the Src tyrosine kinase family. PMID:27599862

  11. Dissecting the Influence of Protein Flexibility on the Location and Thermodynamic Profile of Explicit Water Molecules in Protein-Ligand Binding.

    PubMed

    Yang, Ying; Lill, Markus A

    2016-09-13

    Explicit water molecules in the binding site of proteins play a crucial role for protein-ligand association. Recent advances in computer-aided drug discovery methodology allow for an accurate prediction of the localized position and thermodynamic profile of water molecules (i.e., hydration sites) in the binding site. The underlying calculations are based on MD simulations of explicit water molecules in a restrained protein structure. However, the ligand-binding process is typically associated with protein conformational change that influences the position and thermodynamic properties of the hydration site. In this manuscript, we present the developments of two methods to incorporate the influence of protein conformational change on hydration sites either by following the conformational transition step-by-step (method I) or to match the hydration sites of the two transition end states using local coordinate systems (method II). Using these methods, we highlight the difference in the estimated protein desolvation free energy with and without inclusion of protein flexibility. To the best of our knowledge, this is the first study that explicitly studies the influence of protein conformational change on the position and thermodynamic profiles of water molecules and provides methodology to incorporate protein flexibility into the estimation of the desolvation free energy. PMID:27494046

  12. Determination of absorbed dose to water in reference conditions for radiotherapy kilovoltage x-rays between 10 and 300 kV: a comparison of the data in the IAEA, IPEMB, DIN and NCS dosimetry protocols

    NASA Astrophysics Data System (ADS)

    Peixoto, J. G. P.; Andreo, P.

    2000-03-01

    A comparison of four of the most commonly used dosimetry protocols for the determination of absorbed dose to water in therapeutic kilovoltage x-rays using an ionization chamber (IAEA TRS-277, IPEMB, DIN and NCS) has been carried out. Owing to the different energy ranges and HVLs recommended by each protocol, backscatter factors, water-to-air mass energy absorption coefficient ratios and perturbation correction factors have been recast to a common quality range that all protocols satisfy individually to make a comparison possible. The results of the comparison show that in the sometimes reduced quality range originally included by the different protocols, determinations of absorbed dose to water at all beam qualities agree to within ±1.0% with that obtained using the second edition of the IAEA TRS-277 code of practice (1997). The extrapolation of data to a common beam quality range practically preserves the agreement for all the protocols except for that issued by the NCS at the extremes of the range, where differences of up to 1.8% and 1.4% have been found for low and medium energies respectively. In all cases the DIN protocol yields very good agreement with TRS-277.

  13. Environmental swap energy and role of configurational entropy in transfer of small molecules from water into alkanes

    NASA Astrophysics Data System (ADS)

    Smejtek, Pavel; Word, Robert C.

    2004-01-01

    We studied the effect of segmented solvent molecules on the free energy of transfer of small molecules from water into alkanes (hexane, heptane, octane, decane, dodecane, tetradecane, and hexadecane). For these alkanes we measured partition coefficients of benzene, 3-methylindole (3MI), 2,3,4,6-tetrachlorophenol (TeCP), and 2,4,6-tribromophenol (TriBP) at 3, 11, 20, 3, and 47 °C. For 3MI, TeCP, and TriBP the dependence of free energy of transfer on length of alkane chains was found to be very different from that for benzene. In contrast to benzene, the energy of transfer for 3MI, TeCP, and TriBP was independent of the number of carbons in alkanes. To interpret data, we used the classic Flory-Huggins (FH) theory of concentrated polymer solutions for the alkane phase. For benzene, the measured dependence of energy of transfer on the number of carbons in alkanes agreed well with predictions based on FH model in which the size of alkane segments was obtained from the ratio of molar volumes of alkanes and the solute. We show that for benzene, the energy of transfer can be divided into two components, one called environmental swap energy (ESE), and one representing the contribution of configurational entropy of alkane chains. For 3MI, TeCP, and TriBP the contribution of configurational entropy was not measurable even though the magnitude of the effect predicted from the FH model for short chain alkanes was as much as 20 times greater than experimental uncertainties. From the temperature dependence of ESE we obtained enthalpy and entropy of transfer for benzene, 3MI, TeCP, and TriBP. Experimental results are discussed in terms of a thermodynamic cycle considering creation of cavity, insertion of solute, and activation of solute-medium attractive interactions. Our results suggest that correcting experimental free energy of transfer by Flory-Huggins configurational entropy term is not generally appropriate and cannot be applied indiscriminately.

  14. Unidirectional perfect absorber.

    PubMed

    Jin, L; Wang, P; Song, Z

    2016-01-01

    This study proposes a unidirectional perfect absorber (UPA), which we realized with a two-arm Aharonov-Bohm interferometer, that consists of a dissipative resonator side-coupled to a uniform resonator array. The UPA has reflection-less full absorption on one direction, and reflectionless full transmission on the other, with an appropriate magnetic flux and coupling, detuning, and loss of the side-coupled resonator. The magnetic flux controls the transmission, the left transmission is larger for magnetic flux less than one-half flux quantum; and the right transmission is larger for magnetic flux between one-half and one flux quantum. Besides, a perfect absorber (PA) can be realized based on the UPA, in which light waves from both sides, with arbitrary superposition of the ampli- tude and phase, are perfectly absorbed. The UPA is expected to be useful in the design of novel optical devices. PMID:27615125

  15. Effects of protonation state of Asp181 and position of active site water molecules on the conformation of PTP1B.

    PubMed

    Ozcan, Ahmet; Olmez, Elif Ozkirimli; Alakent, Burak

    2013-05-01

    In protein tyrosine phosphatase 1B (PTP1B), the flexible WPD loop adopts a closed conformation (WPDclosed ) in the active state of PTP1B, bringing the catalytic Asp181 close to the active site pocket, while WPD loop is in an open conformation (WPDopen ) in the inactive state. Previous studies showed that Asp181 may be protonated at physiological pH, and ordered water molecules exist in the active site. In the current study, molecular dynamics simulations are employed at different Asp181 protonation states and initial positions of active site water molecules, and compared with the existing crystallographic data of PTP1B. In WPDclosed conformation, the active site is found to maintain its conformation only in the protonated state of Asp181 in both free and liganded states, while Asp181 is likely to be deprotonated in WPDopen conformation. When the active site water molecule network that is a part of the free WPDclosed crystal structure is disrupted, intermediate WPD loop conformations, similar to that in the PTPRR crystal structure, are sampled in the MD simulations. In liganded PTP1B, one active site water molecule is found to be important for facilitating the orientation of Cys215 and the phosphate ion, thus may play a role in the reaction. In conclusion, conformational stability of WPD loop, and possibly catalytic activity of PTP1B, is significantly affected by the protonation state of Asp181 and position of active site water molecules, showing that these aspects should be taken into consideration both in MD simulations and inhibitor design. PMID:23239271

  16. Durability of Polymeric Glazing and Absorber Materials

    SciTech Connect

    Jorgensen, G.; Terwilliger, K.; Bingham, C.; Milbourne, M.

    2005-01-01

    The Solar Heating and Lighting Program has set the goal of reducing the cost of solar water heating systems by at least 50%. An attractive approach to such large cost reduction is to replace glass and metal parts with less-expensive, lighter-weight, more-integrated polymeric components. The key challenge with polymers is to maintain performance and assure requisite durability for extended lifetimes. The objective of this task is to quantify lifetimes through measurement of the optical and mechanical stability of candidate polymeric glazing and absorber materials. Polycarbonate sheet glazings, as proposed by two industry partners, have been tested for resistance to UV radiation with three complementary methods. Incorporation of a specific 2-mil thick UV-absorbing screening layer results in glazing lifetimes of at least 15 years; improved screens promise even longer lifetimes. Proposed absorber materials were tested for creep and embrittlement under high temperature, and appear adequate for planned ICS absorbers.

  17. Effect of plasticizers (water and glycerol) on the diffusion of a small molecule in iota-carrageenan biopolymer films for edible coating application.

    PubMed

    Karbowiak, Thomas; Hervet, Hubert; Léger, Liliane; Champion, Dominique; Debeaufort, Frédéric; Voilley, Andrée

    2006-06-01

    Translational diffusion of a fluorescein probe has been measured in iota-carrageenan edible films containing different amounts of glycerol (0, 15, 30, and 45%), using fluorescence recovery after photobleaching (FRAP) experiments. The effects of this plasticizer as well as the plasticizing effect of water on the diffusion of fluorescein have been studied in this edible coating mainly composed of natural biopolymer. Diffusion coefficients of about 10(-13) m2 s(-1) have been measured in these films for water activity (aw) lower than 0.7. Above this water content threshold, fluorescein translational diffusion coefficient increases up to 10(-12) m2 s(-1). Another interesting information obtained from FRAP experiments on this system is the ratio of the diffusing molecules which are immobilized in the carrageenan matrix at aw lower than 0.98. Moreover, films containing more than 30% glycerol (w/w carrageenan) present a huge increase of the diffusion coefficient of fluorescein at high water activity (about 2 orders of magnitude), this effect being less pronounced at low water activity. The increase of diffusion seems to be only related to the water content, and glycerol only acts through the enhancement of water adsorption. Therefore, in biopolymer films containing polyol plasticizers, the gain in mobility could be devoted to the effect of the ubiquitous plasticizing molecule, water, whose adsorption is increased by the plasticizer. PMID:16768427

  18. Thermodynamic properties of water molecules in the presence of cosolute depend on DNA structure: a study using grid inhomogeneous solvation theory

    PubMed Central

    Nakano, Miki; Tateishi-Karimata, Hisae; Tanaka, Shigenori; Tama, Florence; Miyashita, Osamu; Nakano, Shu-ichi; Sugimoto, Naoki

    2015-01-01

    In conditions that mimic those of the living cell, where various biomolecules and other components are present, DNA strands can adopt many structures in addition to the canonical B-form duplex. Previous studies in the presence of cosolutes that induce molecular crowding showed that thermal stabilities of DNA structures are associated with the properties of the water molecules around the DNAs. To understand how cosolutes, such as ethylene glycol, affect the thermal stability of DNA structures, we investigated the thermodynamic properties of water molecules around a hairpin duplex and a G-quadruplex using grid inhomogeneous solvation theory (GIST) with or without cosolutes. Our analysis indicated that (i) cosolutes increased the free energy of water molecules around DNA by disrupting water–water interactions, (ii) ethylene glycol more effectively disrupted water–water interactions around Watson–Crick base pairs than those around G-quartets or non-paired bases, (iii) due to the negative electrostatic potential there was a thicker hydration shell around G-quartets than around Watson–Crick-paired bases. Our findings suggest that the thermal stability of the hydration shell around DNAs is one factor that affects the thermal stabilities of DNA structures under the crowding conditions. PMID:26538600

  19. Photoinduced conversion of carbon dioxide and water molecules to methanol on the surface of molybdenum oxide MoO x ( x < 2)

    NASA Astrophysics Data System (ADS)

    Silaev, I. V.; Khubezhov, S. A.; Ramonova, A. G.; Grigorkina, G. S.; Kaloeva, A. G.; Demeev, Z. S.; Bliev, A. P.; Sekiba, D.; Ogura, S.; Fukutani, K.; Magkoev, T. T.

    2016-03-01

    X-ray and UV photoelectron spectroscopic data are used to demonstrate that, when pulsed laser light with a photon energy of 6.4 eV acts on the surface of nonstoichiometric molybdenum oxide MoO x ( x < 2), methanol is effectively formed from adsorbed molecules of carbon dioxide and water. The processes in which CO2 and H2O molecules are adsorbed on substrate surface defects and their bonds are activated, enhanced under the effect of photons, should be regarded as the key factors.

  20. PbnI4n+2(2n+2)- ribbons (n = 3, 5) as dimensional reductions of 2D perovskite layers in cystamine cation based hybrids, also incorporating iodine molecules or reversible guest water molecules.

    PubMed

    Louvain, Nicolas; Bi, Wenhua; Mercier, Nicolas; Buzaré, Jean-Yves; Legein, Christophe; Corbel, Gwenaël

    2007-03-01

    Pb(n)I(4n+2)((2n+2)-) (n = 3, 5) ribbons, which can be regarded as dimensional reductions of 2D perovskite layers, are stabilized by diprotonated cystamine cations in (NH(3)(CH(2))(2)SS(CH(2))(2)NH(3))(4)Pb(3)I(14),I(2) (1) and (NH(3)(CH(2))(2)SS(CH(2))(2)NH(3))(6)Pb(5)I(22).4H(2)O (2). Both 1 and 2 have interesting structural characteristics; it is unprecedented that the ribbons are linked via I(2) molecules incorporated in the lattice of 1, while tetrameric water clusters are trapped in the structure of 2. 2 undergoes a (reversible) water desorption process at 310 K leading to (NH(3)(CH(2))(2)SS(CH(2))(2)NH(3))(6)Pb(5)I(22).2H(2)O (3). The electrical behavior of 2 and 3 has been investigated in the ranges 293-310 K and 310-358 K respectively. Above 310 K, the electronic contribution remains constant while the ionic transference number tends towards unity showing almost pure ionic transport at 360 K (6 x 10(-7) S cm(-1) at 330 K) originating probably from the migration of protons through the hydrogen bonds connecting the water molecules to the cystamine counter cations. PMID:17308677

  1. Neutron Absorbing Alloys

    DOEpatents

    Mizia, Ronald E.; Shaber, Eric L.; DuPont, John N.; Robino, Charles V.; Williams, David B.

    2004-05-04

    The present invention is drawn to new classes of advanced neutron absorbing structural materials for use in spent nuclear fuel applications requiring structural strength, weldability, and long term corrosion resistance. Particularly, an austenitic stainless steel alloy containing gadolinium and less than 5% of a ferrite content is disclosed. Additionally, a nickel-based alloy containing gadolinium and greater than 50% nickel is also disclosed.

  2. Oxygen absorbers in food preservation: a review.

    PubMed

    Cichello, Simon Angelo

    2015-04-01

    The preservation of packaged food against oxidative degradation is essential to establish and improve food shelf life, customer acceptability, and increase food security. Oxygen absorbers have an important role in the removal of dissolved oxygen, preserving the colour, texture and aroma of different food products, and importantly inhibition of food spoilage microbes. Active packaging technology in food preservation has improved over decades mostly due to the sealing of foods in oxygen impermeable package material and the quality of oxygen absorber. Ferrous iron oxides are the most reliable and commonly used oxygen absorbers within the food industry. Oxygen absorbers have been transformed from sachets of dried iron-powder to simple self-adhesive patches to accommodate any custom size, capacity and application. Oxygen concentration can be effectively lowered to 100 ppm, with applications spanning a wide range of food products and beverages across the world (i.e. bread, meat, fish, fruit, and cheese). Newer molecules that preserve packaged food materials from all forms of degradation are being developed, however oxygen absorbers remain a staple product for the preservation of food and pharmaceutical products to reduce food wastage in developed nations and increased food security in the developing & third world. PMID:25829570

  3. Inorganics in Organics: Tracking down the Intrinsic Equilibriums between Organic Molecules and Trace Elements in Oceanic Waters

    NASA Astrophysics Data System (ADS)

    Lechtenfeld, O. J.; Koch, B. P.; Kattner, G.

    2010-12-01

    Recent developments in analytical instrumentation enable to describe biogeochemical processes in oceanic waters on a molecular level. This is the prerequisite to integrate biological and geochemical parameters and to develop chemical cycles on a global perspective. The state-of-the-art Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) applications for dissolved organic matter (DOM) focus mainly on carbon, hydrogen, oxygen and nitrogen isotopes. Implementation of sulfur and especially phosphorus in the molecular formula assignment has been questionable because of ambiguous calculated elemental formulas. On the other hand, many compounds bearing these elements are well known to occur in the dissolved state as part of the permanent recycling processes (e.g. phospholipids, phosphonates) but analytics of dissolved organic phosphorus (DOP) and sulfur (DOS) are often hampered by the large inorganic P and S pools. Even less is known about complexation characteristics of the DOM moieties. Although electrochemical methods provide some information about trace metal speciation, the high amount of organic molecules and its insufficient description as chemical functional classes prevent the assignment of trace metals to ligand classes. Nevertheless, it is undoubtful that a varying but extensive amount of transition metals is bond in form of organic complexes. Hyphenation of reversed phase high performance liquid chromatography (RP-HPLC) with high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) is a valuable tool to study these metal-organic interactions in a qualitative and quantitative approach. We established a desolvation method that allows direct transfer of high organic solvent loads into the plasma. Thus, in combination with internal standardization and external calibration, the investigation of a broad polarity scale was possible. This approach overcomes previous restrictions to non-organic solvent separation techniques like size

  4. The optical properties of molecules and chromogenic aggregates of xanthene dyes

    NASA Astrophysics Data System (ADS)

    Mikheev, Yu. A.; Guseva, L. N.; Ershov, Yu. A.

    2009-05-01

    The UV absorption spectra of rhodamine B and G molecules isolated from industrial dye samples were obtained. Two procedures were used. In one of them, rhodamine B molecules were displaced with water into a heptane layer from a solution of the dye in an alcohol-heptane mixture. The second procedure involved heating of the dye introduced into cellulose triacetate films. Individual rhodamine molecules (namely, dye cation-chlorine anion ion pairs) prepared by both methods did not absorb visible light. The spectra of individual rhodamine molecules coincided with the spectra of so-called pseudoleucobases of xanthene dyes reported in the literature. The conclusion was drawn that the chromaticity property in the series of xanthene dyes appeared because of the formation of supramolecular dimeric and larger aggregates, as was earlier established for triphenylmethane dyes (TPMDs) and copper phthalocyanine (CuPc). At the same time, individual xanthene dye molecules, like TPMD and CuPc molecules, are not chromogens.

  5. An FTIR study on the catalytic effect of water molecules on the reaction of CO successive hydrogenation at 3 and 10K

    NASA Astrophysics Data System (ADS)

    Pirim, C.; Krim, L.

    2011-05-01

    The ubiquitous presence of water and the relative high abundance of H2, H and CO molecules in the interstellar medium motivated numerous studies on their potential interaction. The reaction of successive hydrogenation of CO is of large interest in astrochemistry because of its implication in the formation of formaldehyde and methanol in interstellar grains and in comets. The catalytic effect of water on the successive hydrogenation of CO has been investigated by two methods. The first is the hydrogenation of a CO/H2O surface. The second is a co-injection of (CO/H2O) mixtures and H atoms. Both methods have been performed at 3 and 10 K. When the hydrogenation of a CO surface is performed at 3 K, no products are observed. In fact, the presence of solid hydrogen screens the hydrogenation process. However, when performed at 10 K, the experiment shows that water molecules increase the concentration of the H2CO and CH3OH species. At 3 and 10K, [(CO/H2O)+H] co-depositions confirm a subtantial impact on by-products formation. We show that water molecules increase the probability of reactive to encounter H atoms either physically, or chemically, by raising the number of chemical pathways. A coordinated theoretical study of the possible chemical pathways is currently under way.

  6. Changes in the hydrogen-bonding strength of internal water molecules and cysteine residues in the conductive state of channelrhodopsin-1

    NASA Astrophysics Data System (ADS)

    Lórenz-Fonfría, Víctor A.; Muders, Vera; Schlesinger, Ramona; Heberle, Joachim

    2014-12-01

    Water plays an essential role in the structure and function of proteins, particularly in the less understood class of membrane proteins. As the first of its kind, channelrhodopsin is a light-gated cation channel and paved the way for the new and vibrant field of optogenetics, where nerve cells are activated by light. Still, the molecular mechanism of channelrhodopsin is not understood. Here, we applied time-resolved FT-IR difference spectroscopy to channelrhodopsin-1 from Chlamydomonas augustae. It is shown that the (conductive) P2380 intermediate decays with τ ≈ 40 ms and 200 ms after pulsed excitation. The vibrational changes between the closed and the conductive states were analyzed in the X-H stretching region (X = O, S, N), comprising vibrational changes of water molecules, sulfhydryl groups of cysteine side chains and changes of the amide A of the protein backbone. The O-H stretching vibrations of "dangling" water molecules were detected in two different states of the protein using H218O exchange. Uncoupling experiments with a 1:1 mixture of H2O:D2O provided the natural uncoupled frequencies of the four O-H (and O-D) stretches of these water molecules, each with a very weakly hydrogen-bonded O-H group (3639 and 3628 cm-1) and with the other O-H group medium (3440 cm-1) to moderately strongly (3300 cm-1) hydrogen-bonded. Changes in amide A and thiol vibrations report on global and local changes, respectively, associated with the formation of the conductive state. Future studies will aim at assigning the respective cysteine group(s) and at localizing the "dangling" water molecules within the protein, providing a better understanding of their functional relevance in CaChR1.

  7. Changes in the hydrogen-bonding strength of internal water molecules and cysteine residues in the conductive state of channelrhodopsin-1.

    PubMed

    Lórenz-Fonfría, Víctor A; Muders, Vera; Schlesinger, Ramona; Heberle, Joachim

    2014-12-14

    Water plays an essential role in the structure and function of proteins, particularly in the less understood class of membrane proteins. As the first of its kind, channelrhodopsin is a light-gated cation channel and paved the way for the new and vibrant field of optogenetics, where nerve cells are activated by light. Still, the molecular mechanism of channelrhodopsin is not understood. Here, we applied time-resolved FT-IR difference spectroscopy to channelrhodopsin-1 from Chlamydomonas augustae. It is shown that the (conductive) P2(380) intermediate decays with τ ≈ 40 ms and 200 ms after pulsed excitation. The vibrational changes between the closed and the conductive states were analyzed in the X-H stretching region (X = O, S, N), comprising vibrational changes of water molecules, sulfhydryl groups of cysteine side chains and changes of the amide A of the protein backbone. The O-H stretching vibrations of "dangling" water molecules were detected in two different states of the protein using H2 (18)O exchange. Uncoupling experiments with a 1:1 mixture of H2O:D2O provided the natural uncoupled frequencies of the four O-H (and O-D) stretches of these water molecules, each with a very weakly hydrogen-bonded O-H group (3639 and 3628 cm(-1)) and with the other O-H group medium (3440 cm(-1)) to moderately strongly (3300 cm(-1)) hydrogen-bonded. Changes in amide A and thiol vibrations report on global and local changes, respectively, associated with the formation of the conductive state. Future studies will aim at assigning the respective cysteine group(s) and at localizing the "dangling" water molecules within the protein, providing a better understanding of their functional relevance in CaChR1. PMID:25494778

  8. The mobility of single-file water molecules is governed by the number of H-bonds they may form with channel-lining residues

    PubMed Central

    Horner, Andreas; Zocher, Florian; Preiner, Johannes; Ollinger, Nicole; Siligan, Christine; Akimov, Sergey A.; Pohl, Peter

    2015-01-01

    Channel geometry governs the unitary osmotic water channel permeability, pf, according to classical hydrodynamics. Yet, pf varies by several orders of magnitude for membrane channels with a constriction zone that is one water molecule in width and four to eight molecules in length. We show that both the pf of those channels and the diffusion coefficient of the single-file waters within them are determined by the number NH of residues in the channel wall that may form a hydrogen bond with the single-file waters. The logarithmic dependence of water diffusivity on NH is in line with the multiplicity of binding options at higher NH densities. We obtained high-precision pf values by (i) having measured the abundance of the reconstituted aquaporins in the vesicular membrane via fluorescence correlation spectroscopy and via high-speed atomic force microscopy, and (ii) having acquired the vesicular water efflux from scattered light intensities via our new adaptation of the Rayleigh-Gans-Debye equation. PMID:26167541

  9. Metasurface Broadband Solar Absorber

    DOE PAGESBeta

    Azad, Abul K.; Kort-Kamp, Wilton J. M.; Sykora, Milan; Weisse-Bernstein, Nina R.; Luk, Ting S.; Taylor, Antoinette J.; Dalvit, Diego A. R.; Chen, Hou-Tong

    2016-02-01

    Here, we demonstrate a broadband, polarization independent, wide-angle absorber based on a metallic metasurface architecture, which accomplishes greater than 90% absorptance in the visible and near-infrared range of the solar spectrum, and exhibits low absorptivity (emissivity) at mid- and far-infrared wavelengths. The complex unit cell of the metasurface solar absorber consists of eight pairs of gold nano-resonators that are separated from a gold ground plane by a thin silicon dioxide spacer. Moreover, our experimental measurements reveal high-performance absorption over a wide range of incidence angles for both s- and p-polarizations. We also investigate numerically the frequency-dependent field and current distributionsmore » to elucidate how the absorption occurs within the metasurface structure.« less

  10. Metasurface Broadband Solar Absorber

    PubMed Central

    Azad, Abul K.; Kort-Kamp, Wilton J. M.; Sykora, Milan; Weisse-Bernstein, Nina R.; Luk, Ting S.; Taylor, Antoinette J.; Dalvit, Diego A. R.; Chen, Hou-Tong

    2016-01-01

    We demonstrate a broadband, polarization independent, wide-angle absorber based on a metallic metasurface architecture, which accomplishes greater than 90% absorptance in the visible and near-infrared range of the solar spectrum, and exhibits low absorptivity (emissivity) at mid- and far-infrared wavelengths. The complex unit cell of the metasurface solar absorber consists of eight pairs of gold nano-resonators that are separated from a gold ground plane by a thin silicon dioxide spacer. Our experimental measurements reveal high-performance absorption over a wide range of incidence angles for both s- and p-polarizations. We also investigate numerically the frequency-dependent field and current distributions to elucidate how the absorption occurs within the metasurface structure. PMID:26828999

  11. Metasurface Broadband Solar Absorber

    NASA Astrophysics Data System (ADS)

    Azad, Abul K.; Kort-Kamp, Wilton J. M.; Sykora, Milan; Weisse-Bernstein, Nina R.; Luk, Ting S.; Taylor, Antoinette J.; Dalvit, Diego A. R.; Chen, Hou-Tong

    2016-02-01

    We demonstrate a broadband, polarization independent, wide-angle absorber based on a metallic metasurface architecture, which accomplishes greater than 90% absorptance in the visible and near-infrared range of the solar spectrum, and exhibits low absorptivity (emissivity) at mid- and far-infrared wavelengths. The complex unit cell of the metasurface solar absorber consists of eight pairs of gold nano-resonators that are separated from a gold ground plane by a thin silicon dioxide spacer. Our experimental measurements reveal high-performance absorption over a wide range of incidence angles for both s- and p-polarizations. We also investigate numerically the frequency-dependent field and current distributions to elucidate how the absorption occurs within the metasurface structure.

  12. Metasurface Broadband Solar Absorber.

    PubMed

    Azad, Abul K; Kort-Kamp, Wilton J M; Sykora, Milan; Weisse-Bernstein, Nina R; Luk, Ting S; Taylor, Antoinette J; Dalvit, Diego A R; Chen, Hou-Tong

    2016-01-01

    We demonstrate a broadband, polarization independent, wide-angle absorber based on a metallic metasurface architecture, which accomplishes greater than 90% absorptance in the visible and near-infrared range of the solar spectrum, and exhibits low absorptivity (emissivity) at mid- and far-infrared wavelengths. The complex unit cell of the metasurface solar absorber consists of eight pairs of gold nano-resonators that are separated from a gold ground plane by a thin silicon dioxide spacer. Our experimental measurements reveal high-performance absorption over a wide range of incidence angles for both s- and p-polarizations. We also investigate numerically the frequency-dependent field and current distributions to elucidate how the absorption occurs within the metasurface structure. PMID:26828999

  13. Ionized Absorbers in AGN

    NASA Astrophysics Data System (ADS)

    Mathur, S.

    1999-08-01

    As a part of this program, we observed three AGN:PKS2251 + 113, PG0043 = 039 and PLH909. Two objects show signatures of absorbtion in their UV spectra. Based on our earlier modeling of X-ray warm absorbents, we expected to observe X-ray observation in these objects. The third, PLH909, is known to have soft excess in EINSTEIN data. Attachment: "Exploratory ASCA observation of broad absorption line quasi-stellar objects".

  14. Ionized Absorbers in AGN

    NASA Technical Reports Server (NTRS)

    Mathur, S.

    1999-01-01

    As a part of this program, we observed three AGN:PKS2251 + 113, PG0043 = 039 and PLH909. Two objects show signatures of absorbtion in their UV spectra. Based on our earlier modeling of X-ray warm absorbents, we expected to observe X-ray observation in these objects. The third, PLH909, is known to have soft excess in EINSTEIN data. Attachment: "Exploratory ASCA observation of broad absorption line quasi-stellar objects".

  15. A structurally stable 3D supramolecular framework with 4.0% guest-accessible void spaces that are reversibly occupied by guest water molecules

    NASA Astrophysics Data System (ADS)

    Luo, Feng; Che, Yun-Xia; Zheng, Ji-min

    2008-02-01

    A new Cd(II)-Cu(II)-containing coordination compound, namely Cu(bpy)Cd(ip) 2(μ-OH 2) · (H 2O) 2 ( 1, bpy = 2,2 '-bipyridine, H 2ip = m-phthalic acid), has been synthesized hydrothermally by the reaction of CdCl 2, CuCl 2, bpy, and H 2ip. In 1, Cd(II) and Cu(II) ions are in turn connected by ip 2- ligands to generate the 2D (4, 4) nets. Further, these 2D sheets are linked together via π-π, C-H…O, and O-H…O contacts, thus resulting in the 3D supramolecular frameworks with the irregular 1D channels occupied by water molecules. Remarkably, the investigation by using IR, TG, and PXRD (powder X-ray diffraction) shows that the uptake and release of guest water molecules will not influence the structural integrity.

  16. Tuning the Redox Properties of a Nonheme Iron(III)-Peroxo Complex Binding Redox-Inactive Zinc Ions by Water Molecules

    SciTech Connect

    Lee, Yong-Min; Bang, Suhee; Yoon, Heejung; Bae, Seong Hee; Hong, Seungwoo; Cho, Kyung-Bin; Sarangi, Ritimukta; Fukuzumi, Shunichi; Nam, Wonwoo

    2015-06-19

    Here we report redox-inactive metal ions play important roles in tuning chemical properties of metal–oxygen intermediates. We describe the effect of water molecules on the redox properties of a nonheme iron(III)–peroxo complex binding redox-inactive metal ions. The coordination of two water molecules to a Zn2+ ion in (TMC)FeIII-(O2)-Zn(CF3SO3)2 (1-Zn2+) decreases the Lewis acidity of the Zn2+ ion, resulting in the decrease of the one-electron oxidation and reduction potentials of 1-Zn2+. This further changes the reactivities of 1-Zn2+ in oxidation and reduction reactions; no reaction occurred upon addition of an oxidant (e.g., cerium(IV) ammonium nitrate (CAN)) to 1-Zn2+, whereas 1-Zn2+ coordinating two water molecules, (TMC)FeIII-(O2)-Zn(CF3SO3)2-(OH2)2 [1-Zn2+-(OH2)2], releases the O2 unit in the oxidation reaction. In the reduction reactions, 1-Zn2+ was converted to its corresponding iron(IV)–oxo species upon addition of a reductant (e.g., a ferrocene derivative), whereas such a reaction occurred at a much slower rate in the case of 1-Zn2+-(OH2)2. Finally, the present results provide the first biomimetic example showing that water molecules at the active sites of metalloenzymes may participate in tuning the redox properties of metal–oxygen intermediates.

  17. Tuning the Redox Properties of a Nonheme Iron(III)-Peroxo Complex Binding Redox-Inactive Zinc Ions by Water Molecules

    DOE PAGESBeta

    Lee, Yong-Min; Bang, Suhee; Yoon, Heejung; Bae, Seong Hee; Hong, Seungwoo; Cho, Kyung-Bin; Sarangi, Ritimukta; Fukuzumi, Shunichi; Nam, Wonwoo

    2015-06-19

    Here we report redox-inactive metal ions play important roles in tuning chemical properties of metal–oxygen intermediates. We describe the effect of water molecules on the redox properties of a nonheme iron(III)–peroxo complex binding redox-inactive metal ions. The coordination of two water molecules to a Zn2+ ion in (TMC)FeIII-(O2)-Zn(CF3SO3)2 (1-Zn2+) decreases the Lewis acidity of the Zn2+ ion, resulting in the decrease of the one-electron oxidation and reduction potentials of 1-Zn2+. This further changes the reactivities of 1-Zn2+ in oxidation and reduction reactions; no reaction occurred upon addition of an oxidant (e.g., cerium(IV) ammonium nitrate (CAN)) to 1-Zn2+, whereas 1-Zn2+ coordinatingmore » two water molecules, (TMC)FeIII-(O2)-Zn(CF3SO3)2-(OH2)2 [1-Zn2+-(OH2)2], releases the O2 unit in the oxidation reaction. In the reduction reactions, 1-Zn2+ was converted to its corresponding iron(IV)–oxo species upon addition of a reductant (e.g., a ferrocene derivative), whereas such a reaction occurred at a much slower rate in the case of 1-Zn2+-(OH2)2. Finally, the present results provide the first biomimetic example showing that water molecules at the active sites of metalloenzymes may participate in tuning the redox properties of metal–oxygen intermediates.« less

  18. Tuning the Redox Properties of a Nonheme Iron(III)–Peroxo Complex Binding Redox-Inactive Zinc Ions by Water Molecules

    PubMed Central

    Lee, Yong-Min; Bang, Suhee; Yoon, Heejung; Bae, Seong Hee; Hong, Seungwoo; Cho, Kyung-Bin; Sarangi, Ritimukta; Fukuzumi, Shunichi; Nam, Wonwoo

    2015-01-01

    Redox-inactive metal ions play important roles in tuning chemical properties of metal–oxygen intermediates. Herein we report the effect of water molecules on the redox properties of a nonheme iron(III)–peroxo complex binding redox-inactive metal ions. The coordination of two water molecules to a Zn2+ ion in (TMC)FeIII-(O2)-Zn(CF3SO3)2 (1-Zn2+) decreases the Lewis acidity of the Zn2+ ion, resulting in the decrease of the one-electron oxidation and reduction potentials of 1-Zn2+. This further changes the reactivities of 1-Zn2+ in oxidation and reduction reactions; no reaction occurred upon addition of an oxidant (e.g., cerium(IV) ammonium nitrate (CAN)) to 1-Zn2+, whereas 1-Zn2+ coordinating two water molecules, (TMC)FeIII-(O2)-Zn(CF3SO3)2-(OH2)2 [1-Zn2+-(OH2)2], releases the O2 unit in the oxidation reaction. In the reduction reactions, 1-Zn2+ was converted to its corresponding iron(IV)–oxo species upon addition of a reductant (e.g., a ferrocene derivative), whereas such a reaction occurred at a much slower rate in the case of 1-Zn2+-(OH2)2. The present results provide the first biomimetic example showing that water molecules at the active sites of metalloenzymes may participate in tuning the redox properties of metal–oxygen intermediates. PMID:26096281

  19. WE-A-17A-01: Absorbed Dose Rate-To-Water at the Surface of a Beta-Emitting Planar Ophthalmic Applicator with a Planar, Windowless Extrapolation Chamber

    SciTech Connect

    Riley, A; Soares, C; Micka, J; Culberson, W; DeWerd, L

    2014-06-15

    Purpose: Currently there is no primary calibration standard for determining the absorbed dose rate-to-water at the surface of β-emitting concave ophthalmic applicators and plaques. Machining tolerances involved in the design of concave window extrapolation chambers are a limiting factor for development of such a standard. Use of a windowless extrapolation chamber avoids these window-machining tolerance issues. As a windowless extrapolation chamber has never been attempted, this work focuses on proof of principle measurements with a planar, windowless extrapolation chamber to verify the accuracy in comparison to initial calibration, which could be extended to the design of a hemispherical, windowless extrapolation chamber. Methods: The window of an extrapolation chamber defines the electrical field, aids in aligning the source parallel to the collector-guard assembly, and decreases the backscatter due to attenuation of lower electron energy. To create a uniform and parallel electric field in this research, the source was made common to the collector-guard assembly. A precise positioning protocol was designed to enhance the parallelism of the source and collector-guard assembly. Additionally, MCNP5 was used to determine a backscatter correction factor to apply to the calibration. With these issues addressed, the absorbed dose rate-to-water of a Tracerlab 90Sr planar ophthalmic applicator was determined using National Institute of Standards and Technology's (NIST) calibration formalism, and the results of five trials with this source were compared to measurements at NIST with a traditional extrapolation chamber. Results: The absorbed dose rate-to-water of the planar applicator was determined to be 0.473 Gy/s ±0.6%. Comparing these results to NIST's determination of 0.474 Gy/s yields a −0.6% difference. Conclusion: The feasibility of a planar, windowless extrapolation chamber has been demonstrated. A similar principle will be applied to developing a primary

  20. Structure of hydrated clusters of dibenzo-18-crown-6-ether in a supersonic jet--encapsulation of water molecules in the crown cavity.

    PubMed

    Kusaka, Ryoji; Inokuchi, Yoshiya; Ebata, Takayuki

    2008-11-01

    The structure of dibenzo-18-crown-6-ether (DB18C6) and its hydrated clusters has been investigated in a supersonic jet. Two conformers of bare DB18C6 and six hydrated clusters (DB18C6-(H(2)O)(n)) were identified by laser-induced fluorescence, fluorescence-detected UV-UV hole-burning and IR-UV double-resonance spectroscopy. The IR-UV double resonance spectra were compared with the IR spectra obtained by quantum chemical calculations at the B3LYP/6-31+G* level. The two conformers of bare DB18C6 are assigned to "boat" and "chair I" forms, respectively, among which the boat form is dominant. All the six DB18C6-(H(2)O)(n) clusters with n = 1-4 have a boat conformation in the DB18C6 part. The water molecules form a variety of hydration networks in the boat-DB18C6 cavity. In DB18C6-(H(2)O)(1), a water molecule forms the bidentate hydrogen bond with the O atoms adjacent to the benzene rings. In this cluster, the water molecule is preferentially hydrogen bonded from the bottom of boat-DB18C6. In the larger clusters, the hydration networks are developed on the basis of the DB18C6-(H(2)O)(1) cluster. PMID:18936847

  1. The effect on the lanthanide luminescence of structurally simple Eu(III) cyclen complexes upon deprotonation of metal bound water molecules and amide based pendant arms.

    PubMed

    Plush, Sally E; Clear, Naomi A; Leonard, Joseph P; Fanning, Ann-Marie; Gunnlaugsson, Thorfinnur

    2010-04-21

    A series of substituted 1,4,7,10-tetraazacylcododecane ligands 1-4, possessing sensitizing nitrobenzene or naphthalene antennae, as one of the amide pendant arms, and their complexes with europium(III) were synthesised. The protonation constants and the metal ion stability constants of two of these ligands were determined by potentiometric titration. The pK(a) of the water molecules coordinated to the complexed metal ion were determined by both luminescent and potentiometric measurements. The luminescence pH dependence of a further three Eu(III) complexes, 5-7, which lack any antennae, were also studied with the aim of gaining a better understanding of the role of the metal bound water molecules in the luminescence properties of such complexes upon direct excitation of the lanthanide ion. The results from these luminescent measurements demonstrate that the Eu(III) emission was significantly modulated as a function of pH for all the complexes, which we assigned to changes occurring in the coordination environment of the ion within the cyclen system, caused by deprotonation of metal bound water molecules and/or deprotonation of pendent amide arms. PMID:20354617

  2. Intercomparison of stratospheric water vapor observed by satellite experiments - Stratospheric Aerosol and Gas Experiment II versus Limb Infrared Monitor of the Stratosphere and Atmospheric Trace Molecule Spectroscopy

    NASA Technical Reports Server (NTRS)

    Chiou, E. W.; Mccormick, M. P.; Mcmaster, L. R.; Chu, W. P.; Larsen, J. C.; Rind, D.; Oltmans, S.

    1993-01-01

    A comparison is made of the stratospheric water vapor measurements made by the satellite sensors of the Stratospheric Aerosol and Gas Experiment II (SAGE II), the Nimbus-7 LIMS, and the Spacelab 3 Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment. It was found that, despite differences in the measurement techniques, sampling bias, and observational periods, the three experiments have disclosed a generally consistent pattern of stratospheric water vapor distribution. The only significant difference occurs at high southern altitudes in May below 18 km, where LIMS measurements were 2-3 ppmv greater than those of SAGE II and ATMOS.

  3. A new way to interpret perturbation-correlation moving-window two-dimensional correlation spectroscopy: probing the dynamic interaction of ionic liquid 1-ethyl-3-methylimidazolium acetate to absorb atmospheric water.

    PubMed

    Chen, Yu; Mu, Tiancheng

    2015-01-01

    A rule to interpret perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW2D) was developed. Compared with Morita's rule, this proposed rule retains the ability to obtain interval features (i.e., monotonicity, concavity, and convexity) and adds the function to quickly and accurately determine both tipping points (i.e., local extrema and inflection points). It could be described as follows: the local extrema and inflection point could be determined by the zero point with an opposite sign on its left and right side in ΠΦ (synchronous PCMW2D) and ΠΨ (asynchronous PCMW2D), respectively. Specifically, a negative left (right) side and a positive right (left) side of point indicates a local minimal (maximal) value. By using the rule to interpret ΠIR (PCMW2D infrared spectroscopy) of 1-ethyl-3-methyl-imidazolium acetate [EMIM][Ac]-atmospheric water (H2O) as a function of time, we found that the atmospheric water was absorbed only into the bulk of [EMIM][Ac] before 150 min by hydrogen-bonding interaction, only onto the surface of [EMIM][Ac] after 330 min by van der Waals force, and both to the bulk and surface of [EMIM][Ac] between 150 and 330 min by hydrogen-boding and van der Waals force simultaneously. The proportion of bulk water sorption and surface water sorption to [EMIM][Ac] was about 4 and 96%, respectively. PMID:25280060

  4. Absorber for terahertz radiation management

    DOEpatents

    Biallas, George Herman; Apeldoorn, Cornelis; Williams, Gwyn P.; Benson, Stephen V.; Shinn, Michelle D.; Heckman, John D.

    2015-12-08

    A method and apparatus for minimizing the degradation of power in a free electron laser (FEL) generating terahertz (THz) radiation. The method includes inserting an absorber ring in the FEL beam path for absorbing any irregular THz radiation and thus minimizes the degradation of downstream optics and the resulting degradation of the FEL output power. The absorber ring includes an upstream side, a downstream side, and a plurality of wedges spaced radially around the absorber ring. The wedges form a scallop-like feature on the innermost edges of the absorber ring that acts as an apodizer, stopping diffractive focusing of the THz radiation that is not intercepted by the absorber. Spacing between the scallop-like features and the shape of the features approximates the Bartlett apodization function. The absorber ring provides a smooth intensity distribution, rather than one that is peaked on-center, thereby eliminating minor distortion downstream of the absorber.

  5. Sensitivity study on the effects of hydrosol size and composition on linear polarization in absorbing and nonabsorbing clear and semi-turbid waters.

    PubMed

    Lerner, Amit; Shashar, Nadav; Haspel, Carynelisa

    2012-11-01

    A full Mie scattering subroutine is employed to calculate what we call the linear polarization phase function (LPPF; percent polarization and e-vector orientation of radiation as a function of scattering angle) that results from refraction of the direct solar beam from air into water followed by single scattering by spherical hydrosols. The separate effects of refraction at the air-water interface, hydrosol size, the real and imaginary parts of the hydrosol refractive index, and absorption by the surrounding medium (water) on the LPPF are investigated. All of the above factors are found to alter the LPPF, changing the value of the maximum percent polarization (P(max)), the location of P(max), the number of fluctuations in the LPPF, or the location of the neutral points (points of 0 percent polarization), though absorption by the surrounding medium is found to have only a minimal effect. The character and extent of the influence on the LPPF is found to depend on the scattering regime (Rayleigh, Mie, or geometric optics). We conclude that in calculating underwater polarization, it is important to take into consideration Mie scattering even in relatively clear waters. We also find a coupling between the partial polarization and the e-vector orientation, which suggests that for some polarization-based visual tasks, only one of these would suffice. Other implications for aquatic animal polarization vision are discussed. PMID:23201802

  6. Corrosion resistant neutron absorbing coatings

    SciTech Connect

    Choi, Jor-Shan; Farmer, Joseph C.; Lee, Chuck K.; Walker, Jeffrey; Russell, Paige; Kirkwood, Jon; Yang, Nancy; Champagne, Victor

    2012-05-29

    A method of forming a corrosion resistant neutron absorbing coating comprising the steps of spray or deposition or sputtering or welding processing to form a composite material made of a spray or deposition or sputtering or welding material, and a neutron absorbing material. Also a corrosion resistant neutron absorbing coating comprising a composite material made of a spray or deposition or sputtering or welding material, and a neutron absorbing material.

  7. Corrosion resistant neutron absorbing coatings

    SciTech Connect

    Choi, Jor-Shan; Farmer, Joseph C; Lee, Chuck K; Walker, Jeffrey; Russell, Paige; Kirkwood, Jon; Yang, Nancy; Champagne, Victor

    2013-11-12

    A method of forming a corrosion resistant neutron absorbing coating comprising the steps of spray or deposition or sputtering or welding processing to form a composite material made of a spray or deposition or sputtering or welding material, and a neutron absorbing material. Also a corrosion resistant neutron absorbing coating comprising a composite material made of a spray or deposition or sputtering or welding material, and a neutron absorbing material.

  8. Durability of Polymeric Glazing and Absorber Materials

    SciTech Connect

    Jorgensen, G.; Terwilliger, K.; Bingham, C.; Lindquist, C.; Milbourne, M.

    2005-11-01

    The Solar Heating and Lighting Program has set the goal of reducing the cost of solar water heating systems by at least 50%. An attractive approach to such large cost reduction is to replace glass and metal parts with less-expensive, lighter-weight, more-integrated polymeric components. The key challenge with polymers is to maintain performance and assure requisite durability for extended lifetimes. We have begun evaluation of several new UV-screened polycarbonate sheet glazing constructions. This has involved interactions with several major polymer industry companies to obtain improved candidate samples. Proposed absorber materials were tested for UV resistance, and appear adequate for unglazed ICS absorbers.

  9. Librational modes of the water molecules in barium and strontium halide monohydrates, MX 2 · 1H 2O (M = Ba, Sr; X = Cl, Br, I)

    NASA Astrophysics Data System (ADS)

    Lutz, H. D.; Christian, H.

    1983-09-01

    The IR and Raman spectra of the isotypic alkaline earth halide monohydrates, MX 2 · 1H 2O, with M = Sr, Ba and X = Cl, Br, I, and of deuterated samples are presented for the range 200-700 cm -1 and discussed in terms of normal modes, assignment, coupling, correlation with structure data, and temperature dependence of both the H 2O (D 2O) and the HDO librational modes. The normal modes of the out-of-plane librations of HDO molecules are of the wagging and twisting type rather than H and D out-of-plane vibrations [4], at least for water molecules with C2v or nearly C2v symmetry. Thus the observed H 2O/HDO isotopic shifts can be used as a criterion for assigning the H 2O librations. The librational modes of the halide monohydrates (with tetrahedrally coordinated water oxygen atoms) are found in the order ν Rγ ≫ ν Rt ≫ ν Rr. The intensities of the IR and Raman spectra are in the order Rγ ≫ Rr ≫ Rt (or ˜ Rt in the case of strongly distorted H 2O molecules) and Rt ≫ Rr ≫ Rγ, respectively. Correlations of the H 2O librational modes with structural or bonding data are restricted by frequency shifts due to vibrational coupling and by the fact that the oxygen and the hydrogen atoms of the water molecules are generally affected in a different manner by bond interactions. However, in the case of the twisting vibrations, there are clear correlations with both the size of the metal ions, i.e. increase of ν Rt with decreasing size, and the intermolecular bonding of the hydrogen atoms, as shown by the OH stretching frequencies, i.e. increase of ν Rt with decreasing ν OH.

  10. Solar radiation absorbing material

    DOEpatents

    Googin, John M.; Schmitt, Charles R.; Schreyer, James M.; Whitehead, Harlan D.

    1977-01-01

    Solar energy absorbing means in solar collectors are provided by a solar selective carbon surface. A solar selective carbon surface is a microporous carbon surface having pores within the range of 0.2 to 2 micrometers. Such a surface is provided in a microporous carbon article by controlling the pore size. A thermally conductive substrate is provided with a solar selective surface by adhering an array of carbon particles in a suitable binder to the substrate, a majority of said particles having diameters within the range of about 0.2-10 microns.

  11. Absorber for solar power.

    PubMed

    Powell, W R

    1974-10-01

    A simple, economical absorber utilizing a new principle of operation to achieve very low reradiation losses while generating temperatures limited by material properties of quartz is described. Its performance is analyzed and indicates approximately 90% thermal efficiency and 73% conversion efficiency for an earth based unit with moderately concentrated (~tenfold) sunlight incident. It is consequently compatible with the most economic of concentrator mirrors (stamped) or mirrors deployable in space. Space applications are particularly attractive, as temperatures significantly below 300 K are possible and permit even higher conversion efficiency. PMID:20134700

  12. Molecule nanoweaver

    DOEpatents

    Gerald, II; Rex E.; Klingler, Robert J.; Rathke, Jerome W.; Diaz, Rocio; Vukovic, Lela

    2009-03-10

    A method, apparatus, and system for constructing uniform macroscopic films with tailored geometric assemblies of molecules on the nanometer scale. The method, apparatus, and system include providing starting molecules of selected character, applying one or more force fields to the molecules to cause them to order and condense with NMR spectra and images being used to monitor progress in creating the desired geometrical assembly and functionality of molecules that comprise the films.

  13. Determination of absorbed dose in water at the reference point D(r{sub 0},{theta}{sub 0}) for an {sup 192}Ir HDR brachytherapy source using a Fricke system

    SciTech Connect

    Austerlitz, C.; Mota, H. C.; Sempau, J.; Benhabib, S. M.; Campos, D.; Allison, R.; Almeida, C. E. de; Zhu, D.; Sibata, C. H.

    2008-12-15

    A ring-shaped Fricke device was developed to measure the absolute dose on the transverse bisector of a {sup 192}Ir high dose rate (HDR) source at 1 cm from its center in water, D(r{sub 0},{theta}{sub 0}). It consists of a polymethylmethacrylate (PMMA) rod (axial axis) with a cylindrical cavity at its center to insert the {sup 192}Ir radioactive source. A ring cavity around the source with 1.5 mm thickness and 5 mm height is centered at 1 cm from the central axis of the source. This ring cavity is etched in a disk shaped base with 2.65 cm diameter and 0.90 cm thickness. The cavity has a wall around it 0.25 cm thick. This ring is filled with Fricke solution, sealed, and the whole assembly is immersed in water during irradiations. The device takes advantage of the cylindrical geometry to measure D(r{sub 0},{theta}{sub 0}). Irradiations were performed with a Nucletron microselectron HDR unit loaded with an {sup 192}Ir Alpha Omega radioactive source. A Spectronic 1001 spectrophotometer was used to measure the optical absorbance using a 1 mL quartz cuvette with 1.00 cm light pathlength. The PENELOPE Monte Carlo code (MC) was utilized to simulate the Fricke device and the {sup 192}Ir Alpha Omega source in detail to calculate the perturbation introduced by the PMMA material. A NIST traceable calibrated well type ionization chamber was used to determine the air-kerma strength, and a published dose-rate constant was used to determine the dose rate at the reference point. The time to deliver 30.00 Gy to the reference point was calculated. This absorbed dose was then compared to the absorbed dose measured by the Fricke solution. Based on MC simulation, the PMMA of the Fricke device increases the D(r{sub 0},{theta}{sub 0}) by 2.0%. Applying the corresponding correction factor, the D(r{sub 0},{theta}{sub 0}) value assessed with the Fricke device agrees within 2.0% with the expected value with a total combined uncertainty of 3.43%(k=1). The Fricke device provides a promising

  14. Optimization of ramified absorber networks doing desalination.

    PubMed

    Singleton, Martin S; Heiss, Gregor; Hübler, Alfred

    2011-01-01

    An iterated function system is used to generate fractal-like ramified graph networks of absorbers, which are optimized for desalination performance. The diffusion equation is solved for the boundary case of constant pressure difference at the absorbers and a constant ambient salt concentration far from the absorbers, while constraining both the total length of the network and the total area of the absorbers to be constant as functions of generation G. A linearized form of the solution was put in dimensionless form which depends only on a dimensionless membrane resistance, a dimensionless inverse svelteness ratio, and G. For each of the first nine generations G=2,…,10, the optimal graph shapes were obtained. Total water production rate increases parabolically as a function of generation, with a maximum at G=7. Total water production rate is shown to be approximately linearly related to the power consumed, for a fixed generation. Branching ratios which are optimal for desalination asymptote decreasingly to r=0.510 for large G, while branching angles which are optimal for desalination asymptote decreasingly to 1.17 radians. Asymmetric graphs were found to be less efficient for desalination than symmetric graphs. The geometry which is optimal for desalination does not depend strongly on the dimensionless parameters, but the optimal water production does. The optimal generation was found to increase with the inverse svelteness ratio. PMID:21405775

  15. Étude thermodynamique du polymère super absorbant X10 vis à vis de l'eau vapeur

    NASA Astrophysics Data System (ADS)

    Bakass, M.; Bellat, J. P.; Mokhlisse, A.; Bertrand, G.

    2004-12-01

    The organic polymers super absorbents present values of specific surface lower than 2m2/g. The isobars of adsorption of water vapor on studied polymer are of type III at ambient temperature with the hysterisis phenomena. For temperatures lower than ambient, the isobars become deformed because of an effect of chains. This type of polymer is characterized by a multi-layer adsorption which occurs before the full-course one is complete. During reactions of adsorption, the polymer undergoes rearrangement polymeric network which results from a co-operative diffusion of the water molecules and from a spacing of chain followed by an expansion of the polymeric network. Three types of water molecules adsorbed on polymer were identified: strongly dependent water, adsorbed water and the water only trapped between the macromolecular chains.

  16. Hydroxide absorption heat pumps with spray absorber

    SciTech Connect

    Summerer, F.; Alefeld, G.; Zeigler, F.; Riesch, P.

    1996-11-01

    The absorber is one of the most expensive components of an absorption heat pump or chiller, respectively. In order to reduce the cost of a heat exchanger, much effort is invested into searching for additives for heat transfer enhancement. Another way to reduce heat exchanger cost, especially for machines with low capacities, is to use an adiabatic spray absorber. The basic principles of the spray absorber is to perform heat and mass transfer separated from each other in two different components. In this way the heat can be rejected effectively in a liquid-liquid heat exchanger, whereas the mass transfer occurs subsequently in a simple vessel. The spray technique can not only save heat exchanger cost in conventional absorption systems working with water and lithium bromide, it also allows the use of quite different working fluids such as hydroxides, which have lower heat transfer coefficients in falling films. Moreover, the separated heat transfer can easily be performed in a liquid-to-air heat exchanger. Hence it is obvious to use hydroxides that allow for a high temperature lift for building an air-cooled chiller with spray absorber. In this presentation theoretical and experimental investigations of the spray absorber as well as the setup will be described. Finally, possible applications will be outlined.

  17. Liquid Cryogen Absorber for MICE

    SciTech Connect

    Baynham, D.E.; Bish, P.; Bradshaw, T.W.; Cummings, M.A.; Green,M.A.; Ishimoto, S.; Ivaniouchenkov, I.; Lau, W.; Yang, S.Q.; Zisman, M.S.

    2005-08-20

    The Muon Ionization Cooling Experiment (MICE) will test ionization cooling of muons. In order to have effective ionization cooling, one must use an absorber that is made from a low-z material. The most effective low z materials for ionization cooling are hydrogen, helium, lithium hydride, lithium and beryllium, in that order. In order to measure the effect of material on cooling, several absorber materials must be used. This report describes a liquid-hydrogen absorber that is within a pair of superconducting focusing solenoids. The absorber must also be suitable for use with liquid helium. The following absorber components are discussed in this report; the absorber body, its heat exchanger, the hydrogen system, and the hydrogen safety. Absorber cooling and the thin windows are not discussed here.

  18. Digital PCR using micropatterned superporous absorbent array chips.

    PubMed

    Wang, Yazhen; Southard, Kristopher M; Zeng, Yong

    2016-06-21

    Digital PCR (dPCR) is an emerging technology for genetic analysis and clinical diagnostics. To facilitate the widespread application of dPCR, here we developed a new micropatterned superporous absorbent array chip (μSAAC) which consists of an array of microwells packed with highly porous agarose microbeads. The packed beads construct a hierarchically porous microgel which confers superior water adsorption capacity to enable spontaneous filling of PDMS microwells for fluid compartmentalization without the need of sophisticated microfluidic equipment and operation expertise. Using large λ-DNA as the model template, we validated the μSAAC for stochastic partitioning and quantitative digital detection of DNA molecules. Furthermore, as a proof-of-concept, we conducted dPCR detection and single-molecule sequencing of a mutation prevalent in blood cancer, the chromosomal translocation t(14;18), demonstrating the feasibility of the μSAAC for analysis of disease-associated mutations. These experiments were carried out using the standard molecular biology techniques and instruments. Because of its low cost, ease of fabrication, and equipment-free liquid partitioning, the μSAAC is readily adaptable to general lab settings, which could significantly facilitate the widespread application of dPCR technology in basic research and clinical practice. PMID:27010726

  19. Synthesis of Strong Light Scattering Absorber of TiO₂-CMK-3/Ag for Photocatalytic Water Splitting under Visible Light Irradiation.

    PubMed

    Hung, Wei Hsuan; Lai, Sz Nian; Lo, An Ya

    2015-04-29

    The enhanced water splitting photocurrent has been observed through plasmonic mesoporous composite electrode TiO2-CMK-3/Ag under visible light irradiation. Strong light absorption achieved from the integrations of ordered mesoporous carbon (CMK-3) and silver plasmonic nanoparticles (NPs) layer in the TiO2, which significantly increased the effective optical depth of TiO2-CMK-3/Ag photoelectrode. The carbon-based CMK-3 also increased the surface wetting behavior and conductivity of the photoelectrodes, which resulted in a higher ion exchange rate and faster electron transport. The synthesis of high crystalline TiO2-CMK-3/Ag composite photocatalyst was verified by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Pronounced enhancement of light absorption of TiO2-CMK-3/Ag photoelectrode was confirmed by UV/vis spectrophotometers. Two orders of magnitude of the enhanced water splitting photocurrent were obtained in the TiO2-CMK-3/Ag composite photoelectrode with respect to TiO2 only. Finally, spatially resolved mapping photocurrents were also demonstrated in this study. PMID:25848834

  20. A hybrid mesoporous material functionalized by 1,8-naphthalimide-base receptor and the application as chemosensor and absorbent for Hg2+ in water.

    PubMed

    Meng, Qingtao; Zhang, Xiaolin; He, Cheng; Zhou, Peng; Su, Weiping; Duan, Chunying

    2011-03-15

    A novel hybrid material (SBA-P1) is prepared through the functionalization of mesoporous silica (SBA-15) with a 1,8-naphthalimide-based dye by sol-gel reaction. The characterization results of elemental analysis (EA), X-ray powder diffractometer (XRD) and spectroscopic methods demonstrate the fluorescence dye P1 is successfully grafted onto the inner surface of SBA-15 and the organized structure is preserved. SBA-P1 can detect Hg(2+) with high selectivity to Cu(2+), Zn(2+), Cd(2+), Pb(2+), Mn(2+), Ni(2+), Co(2+), Ag(+), Cr(3+), and Mg(2+), Ca(2+), Li(+), Na(+), K(+) in water and sensitivity to environmentally relevant mercury in complex natural samples. The quenching fluorescence detection is also reversible by treating with EDTA/base. Furthermore, its fluorescence intensity keeps stable in the physiologically relevant pH range. The extraction ability of SBA-P1 is also estimated by inductively coupled plasma source mass spectrometer (ICP), showing that approximately 90% of the Hg(2+) ion is extracted. These results imply that the hybrid material has potential application for sensing and removing of Hg(2+) ions in waste water and working as toxicide for acute mercury poisoning. PMID:21315897

  1. Dual reorientation relaxation routes of water molecules in oxyanion’s hydration shell: A molecular geometry perspective

    SciTech Connect

    Xie, Wen Jun; Yang, Yi Isaac; Gao, Yi Qin

    2015-12-14

    In this study, we examine how complex ions such as oxyanions influence the dynamic properties of water and whether differences exist between simple halide anions and oxyanions. Nitrate anion is taken as an example to investigate the hydration properties of oxyanions. Reorientation relaxation of its hydration water can occur through two different routes: water can either break its hydrogen bond with the nitrate to form one with another water or switch between two oxygen atoms of the same nitrate. The latter molecular mechanism increases the residence time of oxyanion’s hydration water and thus nitrate anion slows down the translational motion of neighbouring water. But it is also a “structure breaker” in that it accelerates the reorientation relaxation of hydration water. Such a result illustrates that differences do exist between the hydration of oxyanions and simple halide anions as a result of different molecular geometries. Furthermore, the rotation of the nitrate solute is coupled with the hydrogen bond rearrangement of its hydration water. The nitrate anion can either tilt along the axis perpendicularly to the plane or rotate in the plane. We find that the two reorientation relaxation routes of the hydration water lead to different relaxation dynamics in each of the two above movements of the nitrate solute. The current study suggests that molecular geometry could play an important role in solute hydration and dynamics.

  2. Estimation of Concentration and Bonding Environment of Water Dissolved in Common Solvents Using Near Infrared Absorptivity

    PubMed Central

    Dickens, Brian; Dickens, Sabine H.

    1999-01-01

    Integrated near infrared (NIR) absorbance has been used to determine the absorptivity of the υ2 + υ3 combination band of the asymmetric stretch (υ2) and the bending vibration (υ3) for water in several organic solvents. Absorptivity measured in this way is essentially constant across the absorption envelope and is found to be 336 L mol−1 cm−1 with a standard deviation of 4 L mol−1 cm−1 as estimated from a least squares fit of a straight line to data from water concentrations between 0.01 mol/L and 0.06 mol/L. Absorptivity measured from the peak maximum of the υ2 + υ3 combination band of water varies with the type of hydrogen bonding of the water molecule because the shape of the NIR absorption envelope changes with the hydrogen bonding. Because the integrated NIR absorptivity of the υ2 + υ3 combination band of water is essentially constant across the absorption envelope, the NIR absorption envelope reflects the distribution of hydrogen bonding of the water. The shape and location of the absorption envelope appear to be governed mostly by the number of hydrogen bonds from the water molecules to easily polarized atoms. Water that is a donor in hydrogen bonds to atoms which are not easily polarized (such as the oxygen of a typical carbonyl group) absorbs near 5240 cm−1 to 5260 cm−1. Water that donates one hydrogen bond to an easily polarized atom (such as a water molecule oxygen) absorbs near 5130 cm−1 to 5175 cm−1, and water that donates two hydrogen bonds to easily polarized atoms is estimated to absorb near 5000 cm−1 to 5020 cm−1. Water donating two hydrogen bonds to other water molecules may be said to be in a water-like environment. In no case does a small amount of water absorbed in a host material appear to have a water-like environment.

  3. Metamaterial electromagnetic wave absorbers.

    PubMed

    Watts, Claire M; Liu, Xianliang; Padilla, Willie J

    2012-06-19

    The advent of negative index materials has spawned extensive research into metamaterials over the past decade. Metamaterials are attractive not only for their exotic electromagnetic properties, but also their promise for applications. A particular branch-the metamaterial perfect absorber (MPA)-has garnered interest due to the fact that it can achieve unity absorptivity of electromagnetic waves. Since its first experimental demonstration in 2008, the MPA has progressed significantly with designs shown across the electromagnetic spectrum, from microwave to optical. In this Progress Report we give an overview of the field and discuss a selection of examples and related applications. The ability of the MPA to exhibit extreme performance flexibility will be discussed and the theory underlying their operation and limitations will be established. Insight is given into what we can expect from this rapidly expanding field and future challenges will be addressed. PMID:22627995

  4. Absorber coatings' degradation

    SciTech Connect

    Moore, S.W.

    1984-01-01

    This report is intended to document some of the Los Alamos efforts that have been carried out under the Department of Energy (DOE) Active Heating and Cooling Materials Reliability, Maintainability, and Exposure Testing program. Funding for these activities is obtained directly from DOE although they represent a variety of projects and coordination with other agencies. Major limitations to the use of solar energy are the uncertain reliability and lifetimes of solar systems. This program is aimed at determining material operating limitations, durabilities, and failure modes such that materials improvements can be made and lifetimes can be extended. Although many active and passive materials and systems are being studied at Los Alamos, this paper will concentrate on absorber coatings and degradation of these coatings.

  5. Optically absorbing nanoparticle mediated cell membrane permeabilization.

    PubMed

    Bhattacharyya, Kiran; Mehta, Smit; Viator, John

    2012-11-01

    Membrane permeabilization is imperative for gene and drug delivery systems, along with other cell manipulation methods, since the average eukaryotic cell membrane is not permeable to polar and large nonpolar molecules. Antibody conjugated optically absorbing gold nanospheres are targeted to the cell membrane of T47D breast cancer cell line and irradiated with 5 ns pulse, 20 Hz, 532 nm light to increase membrane permeability. Up to 90% permeabilization with less than 6% death is reported at radiant exposures up to 10 times lower than those of other comparable studies. PMID:23114334

  6. Site-specific vibrational spectral signatures of water molecules in the magic H3O+(H2O)20 and Cs+(H2O)20 clusters

    PubMed Central

    Fournier, Joseph A.; Wolke, Conrad T.; Johnson, Christopher J.; Johnson, Mark A.; Heine, Nadja; Gewinner, Sandy; Schöllkopf, Wieland; Esser, Tim K.; Fagiani, Matias R.; Knorke, Harald; Asmis, Knut R.

    2014-01-01

    Theoretical models of proton hydration with tens of water molecules indicate that the excess proton is embedded on the surface of clathrate-like cage structures with one or two water molecules in the interior. The evidence for these structures has been indirect, however, because the experimental spectra in the critical H-bonding region of the OH stretching vibrations have been too diffuse to provide band patterns that distinguish between candidate structures predicted theoretically. Here we exploit the slow cooling afforded by cryogenic ion trapping, along with isotopic substitution, to quench water clusters attached to the H3O+ and Cs+ ions into structures that yield well-resolved vibrational bands over the entire 215- to 3,800-cm−1 range. The magic H3O+(H2O)20 cluster yields particularly clear spectral signatures that can, with the aid of ab initio predictions, be traced to specific classes of network sites in the predicted pentagonal dodecahedron H-bonded cage with the hydronium ion residing on the surface. PMID:25489068

  7. Isolated monohydrates of a model peptide chain: effect of a first water molecule on the secondary structure of a capped phenylalanine.

    PubMed

    Biswal, Himansu S; Loquais, Yohan; Tardivel, Benjamin; Gloaguen, Eric; Mons, Michel

    2011-03-23

    The formation of monohydrates of capped phenylalanine model peptides, CH(3)-CO-Phe-NH(2) and CH(3)-CO-Phe-NH-CH(3), in a supersonic expansion has been investigated using laser spectroscopy and quantum chemistry methods. Conformational distributions of the monohydrates have been revealed by IR/UV double-resonance spectroscopy and their structures assigned by comparison with DFT-D calculations. A careful analysis of the final hydrate distribution together with a detailed theoretical investigation of the potential energy surface of the monohydrates demonstrates that solvation occurs from the conformational distribution of the isolated peptide monomers. The distribution of the monohydrates appears to be strongly dependent on both the initial monomer conformation (extended or folded backbone) and the solvation site initially occupied by the water molecule. The solvation processes taking place during the cooling can be categorized as follows: (a) solvation without significant structural changes of the peptide, (b) solvation inducing significant distortions of the backbone but retaining the secondary structure, and (c) solvation triggering backbone isomerizations, leading to a modification of the peptide secondary structure. It is observed that solvation by a single water molecule can fold a β-strand into a γ-turn structure (type c) or induce a significant opening of a γ-turn characterized by an elongated C(7) hydrogen bond (type b). These structural changes can be considered as a first step toward the polyproline II condensed-phase structure, illustrating the role played by the very first water molecule in the solvation process. PMID:21361380

  8. Use of near infrared correlation spectroscopy for quantitation of surface iron, absorbed water and stored electronic energy in a suite of Mars soil analog materials

    NASA Technical Reports Server (NTRS)

    Coyne, Lelia M.; Banin, Amos; Carle, Glenn; Orenberg, James; Scattergood, Thomas

    1989-01-01

    A number of questions concerning the surface mineralogy and the history of water on Mars remain unresolved using the Viking analyses and Earth-based telescopic data. Identification and quantitation of iron-bearing clays on Mars would elucidate these outstanding issues. Near infrared correlation analysis, a method typically applied to qualitative and quantitative analysis of individual constituents of multicomponent mixtures, is adapted here to selection of distinctive features of a small, highly homologous series of Fe/Ca-exchanged montmorillonites and several kalinites. Independently determined measures of surface iron, relative humidity and stored electronic energy were used as constituent data for linear regression of the constituent vs. reflectance data throughout the spectral region 0.68 to 2.5 micrometers. High correlations were found in appropriate regions for all three constituents, though that with stored energy is still considered tenuous. Quantitation was improved using 1st and 2nd derivative spectra. High resolution data over a broad spectral range would be required to quantitatively identify iron-bearing clays by remotely sensed reflectance.

  9. A chemometric-assisted method for the simultaneous determination of malachite green and crystal violet in water based on absorbance-pH data generated by a homemade pH gradient apparatus.

    PubMed

    Yu, Shuling; Yuan, Xuejie; Yang, Jing; Yuan, Jintao; Shi, Jiahua; Wang, Yali; Chen, Yuewen; Gao, Shufang

    2015-01-01

    An attractive method of generating second-order data was developed by a dropping technique to generate pH gradient simultaneously coupled with diode-array spectrophotometer scanning. A homemade apparatus designed for the pH gradient. The method and the homemade apparatus were used to simultaneously determine malachite green (MG) and crystal violet (CV) in water samples. The absorbance-pH second-order data of MG or CV were obtained from the spectra of MG or CV in a series of pH values of HCl-KCl solution. The second-order data of mixtures containing MG and CV that coexisted with interferents were analyzed using multidimensional partial least-squares with residual bilinearization. The method and homemade apparatus were used to simultaneously determine MG and CV in fish farming water samples and in river ones with satisfactory results. The presented method and the homemade apparatus could serve as an alternative tool to handle some analysis problems. PMID:26057094

  10. A Model of Ball Lightning as a Formation of Water Molecules Confining an Electric Charge and the Classical Theory of the Electron

    NASA Astrophysics Data System (ADS)

    Tennakone, K.

    2012-04-01

    Ball lightning or faintly luminous floating spheres with radii of the order of ten centimeters appearing transiently in air notably during stormy weather continue to remain an unresolved phenomenon. It is suggested that these objects are organized structures constituted of an electrically charged spherical thin shell of electro-frozen dipole oriented water molecules carrying an electric charge, balanced by the internal negative pressure and outward electrostatic stress. A model presented, resembling the classical theory of the electron with Poincare stresses explain almost all observed attributes of this phenomenon. The possibility of realizing macroscopic spherical surface charge distributions in the vacuum and their implication on the problem of electron are commented.

  11. [Dynamics of Irreversible Evaporation of a Water-Protein Droplet and a Problem of Structural and Dynamical Experiments with Single Molecules].

    PubMed

    Shaitan, K V; Armeev, G A; Shaytan, A K

    2016-01-01

    We discuss the effect of isothermal and adiabatic evaporation of water on the state of a water-protein droplet. The discussed problem is of current importance due to development of techniques to perform single molecule experiments using free electron lasers. In such structure-dynamic experiments the delivery of a sample into the X-ray beam is performed using the microdroplet injector. The time between the injection and delivery is in the order of microseconds. In this paper we developed a specialized variant of all-atom molecular dynamics simulations for the study of irreversible isothermal evaporation of the droplet. Using in silico experiments we determined the parameters of isothermal evaporation of the water-protein droplet with the sodium and chloride ions in the concentration range of 0.3 M at different temperatures. The energy of irreversible evaporation determined from in silico experiments at the initial stages of evaporation virtually coincides with the specific heat of evaporation for water. For the kinetics of irreversible adiabatic evaporation an exact analytical solution was obtained in the limit of high thermal conductivity of the droplet (or up to the droplet size of -100 Å). This analytical solution incorporates parameters that are determined using in silico. experiments on isothermal droplet evaporation. We show that the kinetics of adiabatic evaporation and cooling of the droplet scales with the droplet size. Our estimates of the water-protemi droplet. freezing rate in the adiabatic regime in a vacuum chamber show that additional techniques for stabilizing the temperature inside the droplet should be used in order to study the conformational transitions of the protein in single molecules. Isothermal and quasi-isothermal conditions are most suitable for studying the conformational transitions upon object functioning. However, in this case it is necessary to take into account the effects of dehydration and rapid increase of ionic strength in an

  12. Diagnostic beam absorber in Mu2e beam line

    SciTech Connect

    Rakhno, Igor; /Fermilab

    2011-03-01

    Star density, hadron flux, and residual dose distributions are calculated around the {mu}2e diagnostic beam absorber. Corresponding surface and ground water activation, and air activation are presented as well.

  13. Positron binding to molecules

    NASA Astrophysics Data System (ADS)

    Danielson, J. R.

    2011-05-01

    While there is theoretical evidence that positrons can bind to atoms, calculations for molecules are much less precise. Unfortunately, there have been no measurements of positron-atom binding, due primarily to the difficulty in forming positron-atom bound states in two-body collisions. In contrast, positrons attach to molecules via Feshbach resonances (VFR) in which a vibrational mode absorbs the excess energy. Using a high-resolution positron beam, this VFR process has been studied to measure binding energies for more than 40 molecules. New measurements will be described in two areas: positron binding to relatively simple molecules, for which theoretical calculations appear to be possible; and positron binding to molecules with large permanent dipole moments, which can be compared to analogous, weakly bound electron-molecule (negative-ion) states. Binding energies range from 75 meV for CS2 (no dipole moment) to 180 meV for acetonitrile (CH3CN). Other species studied include aldehydes and ketones, which have permanent dipole moments in the range 2.5 - 3.0 debye. The measured binding energies are surprisingly large (by a factor of 10 to 100) compared to those for the analogous negative ions, and these differences will be discussed. New theoretical calculations for positron-molecule binding are in progress, and a recent result for acetonitrile will be discussed. This ability to compare theory and experiment represents a significant step in attempts to understand positron binding to matter. In collaboration with A. C. L. Jones, J. J. Gosselin, and C. M. Surko, and supported by NSF grant PHY 07-55809.

  14. Electrochemically regenerable carbon dioxide absorber

    NASA Technical Reports Server (NTRS)

    Woods, R. R.; Marshall, R. D.; Schubert, F. H.; Heppner, D. B.

    1979-01-01

    Preliminary designs were generated for two electrochemically regenerable carbon dioxide absorber concepts. Initially, an electrochemically regenerable absorption bed concept was designed. This concept incorporated the required electrochemical regeneration components in the absorber design, permitting the absorbent to be regenerated within the absorption bed. This hardware was identified as the electrochemical absorber hardware. The second hardware concept separated the functional components of the regeneration and absorption process. This design approach minimized the extravehicular activity component volume by eliminating regeneration hardware components within the absorber. The electrochemical absorber hardware was extensively characterized for major operating parameters such as inlet carbon dioxide partial pressure, process air flow rate, operational pressure, inlet relative humidity, regeneration current density and absorption/regeneration cycle endurance testing.

  15. Liquid Hydrogen Absorber for MICE

    SciTech Connect

    Ishimoto, S.; Suzuki, S.; Yoshida, M.; Green, Michael A.; Kuno, Y.; Lau, Wing

    2010-05-30

    Liquid hydrogen absorbers for the Muon Ionization Cooling Experiment (MICE) have been developed, and the first absorber has been tested at KEK. In the preliminary test at KEK we have successfully filled the absorber with {approx}2 liters of liquid hydrogen. The measured hydrogen condensation speed was 2.5 liters/day at 1.0 bar. No hydrogen leakage to vacuum was found between 300 K and 20 K. The MICE experiment includes three AFC (absorber focusing coil) modules, each containing a 21 liter liquid hydrogen absorber made of aluminum. The AFC module has safety windows to separate its vacuum from that of neighboring modules. Liquid hydrogen is supplied from a cryocooler with cooling power 1.5 W at 4.2 K. The first absorber will be assembled in the AFC module and installed in MICE at RAL.

  16. Broadband patterned magnetic microwave absorber

    SciTech Connect

    Li, Wei; Wu, Tianlong; Wang, Wei; Guan, Jianguo; Zhai, Pengcheng

    2014-07-28

    It is a tough task to greatly improve the working bandwidth for the traditional flat microwave absorbers because of the restriction of available material parameters. In this work, a simple patterning method is proposed to drastically broaden the absorption bandwidth of a conventional magnetic absorber. As a demonstration, an ultra-broadband microwave absorber with more than 90% absorption in the frequency range of 4–40 GHz is designed and experimentally realized, which has a thin thickness of 3.7 mm and a light weight equivalent to a 2-mm-thick flat absorber. In such a patterned absorber, the broadband strong absorption is mainly originated from the simultaneous incorporation of multiple λ/4 resonances and edge diffraction effects. This work provides a facile route to greatly extend the microwave absorption bandwidth for the currently available absorbing materials.

  17. The binding energies of one and two water molecules to the first transition-row metal positive ions

    NASA Technical Reports Server (NTRS)

    Rosi, Marzio; Bauschlicher, Charles W., Jr.

    1989-01-01

    The bonding of water to the transition metal positive ions is electrostatic in origin. The electrostatic bonding is enhanced by a variety of mechanisms: mixing in 4p character, 4s-3d hybridization, and 4s promotion into the compact 3d orbital. The importance of these effects