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Water equilibrium

Aidan T Brown, Wilson C K Poon, Christian Holm, Joost de Graaf
Polar solvents like water support the bulk dissociation of themselves and their solutes into ions, and the re-association of these ions into neutral molecules in a dynamic equilibrium, e.g., H2O2 ⇌ H(+) + HO2(-). Using continuum theory, we study the influence of these association-dissociation reactions on the self-propulsion of colloids driven by surface chemical reactions (chemical swimmers). We find that association-dissociation reactions should have a strong influence on swimmers' behaviour, and therefore should be included in future modelling...
January 18, 2017: Soft Matter
Chao Wang, Yipin Duan, Nicole S Zacharia, Bryan D Vogt
Composite hydrogels containing graphene oxide (GO) offer advantageous mechanical properties, but tuning these properties generally requires the synthesis of new hydrogels or if the hydrogel is thermally responsive, utilization of a chemistry determined temperature window. Here, we demonstrate a simple route to generate a family of GO-based hydrogels from aqueous solution based assembly of GO with polycationic poly(ethylenimine), PEI, without any secondary chemical crosslinking. Tuning the ratio of GO : PEI during the assembly produces a family of hydrogels that responds to mechanical compression by irreversibly altering their equilibrium water content and mechanical properties in a controllable manner...
January 18, 2017: Soft Matter
Miguel A Soler, José Zúñiga, Alberto Requena, Adolfo Bastida
Despite the increasing evidence that conformational transitions in peptides and proteins are driven by specific vibrational energy pathways along the molecule, the current experimental techniques of analysis do as yet not allow to study these biophysical processes in terms of anisotropic energy flows. Computational methods offer a complementary approach to obtain a more detailed understanding of the vibrational and conformational dynamics of these systems. Accordingly, in this work we investigate jointly the vibrational energy distribution and the conformational dynamics of trialanine peptide in water solution at room temperature by applying the Instantaneous Normal Mode analysis to the results derived from equilibrium molecular dynamics simulations...
January 18, 2017: Physical Chemistry Chemical Physics: PCCP
Rossend Rey, James T Hynes
In previous installments it has been shown how a detailed analysis of energy fluxes induced by electronic excitation of a solute can provide a quantitative understanding of the dominant molecular energy flow channels characterizing solvation---and in particular, hydration--- relaxation dynamics. Here this work and power approach is complemented with a detailed characterization of the changes induced by such energy fluxes. We first examine the water solvent's spatial and orientational distributions and the assorted energy fluxes in the various hydration shells of the solute to provide a molecular picture of the relaxation...
January 17, 2017: Journal of Physical Chemistry. B
Thuy T Bui, Andreia Alves, Anna Palm-Cousins, Stefan Voorspoels, Adrian Covaci, Ian T Cousins
There is a lack of knowledge regarding uptake of phthalate esters (PEs) and other chemicals into the human nail plate and thus, clarity concerning the suitability of human nails as a valid alternative matrix for monitoring long-term exposure. In particular, the relative importance of internal uptake of phthalate metabolites (from e.g. blood) compared to external uptake pathways is unknown. This study provides first insights into the partitioning of phthalate-metabolites between blood and nail using pharmacokinetic (PK) modelling and biomonitoring data from a Norwegian cohort...
January 11, 2017: Environment International
Shu-Xin Zhang, Xin-Sheng Chai, Ran Jiang
This work reports on a method for the determination of residual acrylic acid (AA) in the superabsorbent polymers for hygiene products by headspace analysis. It was based on water extraction for the polymer sample at a room temperature for 50min. Then, the AA in the extractant reacted with bicarbonate solution in a closed headspace sample vial, from which the carbon dioxide generated from the reaction (within 20min at 70°C) was detected by gas chromatography (GC). It was found that there is adsorption partition equilibrium of AA between solid-liquid phases...
January 10, 2017: Journal of Chromatography. A
M Arshadi, F Mousavinia, M K Abdolmaleki, M J Amiri, A Khalafi-Nezhad
A polar nano-dendritic adsorbent containing amine groups (SAPAMAA) was synthesized onto the nanoparticles of SiO2Al2O3 and its uptake of salicylic acid (SA) from the synthetic and real water was investigated. The synthesized nanomaterials were fully studied by nuclear magnetic resonance spectrum ((1)H NMR and (13)C NMR), Fourier transform infrared spectroscopy (FT-IR), zeta potential (ζ), inductively coupled plasma atomic emission spectroscopy (ICP-AES), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) and elemental analysis...
January 9, 2017: Journal of Colloid and Interface Science
Shalini Rajput, Lok P Singh, Charles U Pittman, Dinesh Mohan
Superparamagnetic maghemite (γ-Fe2O3) nanoparticles of controllable morphology were successfully synthesized using a flame spray pyrolysis (FSP) technique. Their physico-chemical properties, size, morphology, and surface chemistries were determined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), selected area electron diffraction patterns (SAED), SEM-EDX, scanning electron microscopy (SEM), and pHZPC(6.3). Elemental contents before and after adsorption were identified using energy dispersive X-ray fluorescence (ED-XRF), energy dispersive X-ray analysis (EDX) and elemental mapping...
November 27, 2016: Journal of Colloid and Interface Science
Radhakrishnan Gnanasambandam, Chiranjib Ghatak, Anthony Yasmann, Kazuhisa Nishizawa, Frederick Sachs, Alexey S Ladokhin, Sergei I Sukharev, Thomas M Suchyna
GsMTx4 is a spider venom peptide that inhibits cationic mechanosensitive channels (MSCs). It has six lysine residues that have been proposed to affect membrane binding. We synthesized six analogs with single lysine-to-glutamate substitutions and tested them against Piezo1 channels in outside-out patches and independently measured lipid binding. Four analogs had ∼20% lower efficacy than the wild-type (WT) peptide. The equilibrium constants calculated from the rates of inhibition and washout did not correlate with the changes in inhibition...
January 10, 2017: Biophysical Journal
Dennis C Prieve, Benjamin A Yezer, Aditya S Khair, Paul J Sides, James W Schneider
After presenting a brief historical overview of the classic contributions of Faraday, Arrhenius, Kohlrausch, Bjerrum, Debye, Hückel and Onsager to understanding the conductivity of true electrolytes in aqueous solutions, we present an in-depth review of the 1933 work of Fuoss & Kraus who explored the effect of the solvent on electrolyte dissociation equilibria in either polar or nonpolar media. Their theory predicts that the equilibrium constant for dissociation decays exponentially with the ratio of the Bjerrum length λB to the ion-pair size a...
November 19, 2016: Advances in Colloid and Interface Science
Jovan Kamcev, Donald R Paul, Gerald S Manning, Benny D Freeman
This study presents a framework for predicting salt permeability coefficients in ion exchange membranes in contact with an aqueous salt solution. The model, based on the solution-diffusion mechanism, was tested using experimental salt permeability data for a series of commercial ion exchange membranes. Equilibrium salt partition coefficients were calculated using a thermodynamic framework (i.e., Donnan theory), incorporating Manning's counter-ion condensation theory to calculate ion activity coefficients in the membrane phase and the Pitzer model to calculate ion activity coefficients in the solution phase...
January 10, 2017: ACS Applied Materials & Interfaces
Jeremy S Bril, Kathryn Langenfeld, Craig L Just, Scott N Spak, Teresa J Newton
A freshwater "mussel mortality threshold" was explored as a function of porewater ammonium (NH4(+)) concentration, mussel biomass, and total nitrogen (N) utilizing a numerical model calibrated with data from mesocosms with and without mussels. A mortality threshold of 2 mg-N L(-1) porewater NH4(+) was selected based on a study that estimated 100% mortality of juvenile Lampsilis mussels exposed to 1.9 mg-N L(-1) NH4(+) in equilibrium with 0.18 mg-N L(-1) NH3. At the highest simulated mussel biomass (560 g m(-2)) and the lowest simulated influent water "food" concentration (0...
2017: PeerJ
Tuanny S Frantz, Nauro Silveira, Maurízio S Quadro, Robson Andreazza, Amauri A Barcelos, Tito R S Cadaval, Luiz A A Pinto
Adsorption of copper ions onto chitosan films was studied, and the matrix effect was evaluated using a synthetic solution and a real effluent from closed copper mine. Chitosan films were prepared by casting technique and characterized. The adsorption study was carried out by equilibrium isotherms, thermodynamics, and kinetics. The thermodynamic parameters indicated that the copper adsorption onto chitosan film was favorable, spontaneous, and exothermic, suggesting an increased randomness at the solid/solution interface...
January 7, 2017: Environmental Science and Pollution Research International
A Bénarouche, L Sams, C Bourlieu, V Vié, V Point, J F Cavalier, F Carrière
The access to kinetic parameters of lipolytic enzyme adsorption onto lipids is essential for a better understanding of the overall catalytic process carried out by these interfacial enzymes. Gastric lipase, for instance, shows an apparent optimum activity on triglycerides (TAG) at acidic pH, which is controlled by its pH-dependent adsorption at lipid-water interfaces. Since gastric lipase acts on TAG droplets covered by phospholipids, but does not hydrolyze these lipids, phospholipid monolayers spread at the air-water interfaces can be used as biomimetic interfaces to study lipase adsorption and penetration through the phospholipid layer, independently from the catalytic activity...
2017: Methods in Enzymology
Yu-Ming Mindy Huang, Mark Anthony V Raymundo, Wei Chen, Chia-En A Chang
Equilibrium constants, together with kinetic rate constants of binding, are key factors in the efficacy and safety of drug compounds, informing drug design. However, the association pathways of protein-ligand binding, which contribute to their kinetic behaviors, are little understood. In this work, we used unbiased all-atom molecular dynamics (MD) simulations with an explicit solvent model to study the association processes of protein-ligand binding. Using the protein-ligand systems of HIV protease (HIVp)-xk263 and HIVp-ritonavir as cases, we observed that ligand association is a multi-step process involving diffusion, localization, and conformational rearrangements of the protein, ligand and water molecules...
January 6, 2017: Biochemistry
M Zhang, Z Xiao, J Zou, T Chen, N Yue
PURPOSE: This study is aiming to identify the smallest field size for which a treatment planning system (TPS) can accurately calculate the relative dose distribution. The finding would be used as a guideline to choose the smallest proton field for clinical treatment. METHODS: Mevion S250™ double scattering proton delivery system and Eclipse™ TPS (Varian) with pencil beam convolution (PBC) dose algorithm were used in this study. Square sized fields of 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, and 10 cm were planned on a cubical water phantom with iso-center placed at 10 cm depth...
June 2016: Medical Physics
N Neba, N Mensah-Brown, T Howlin, S Howard, H Saleh
PURPOSE: To determine the effect on machine output calibration, following the TG-51 protocol, as the water temperature increasingly deviates from Standard temperature (22°C) METHODS: A water tank was set up according to TG-51 protocol. Two sets of measurements were taken and the pressure recorded. The measurements consisted of readings at different temperatures. In the first set, P(ion), P(pol), and P(elec) were assumed constant while they were accounted for in the second. The outputs were normalized to that at 22°C...
June 2016: Medical Physics
K Cline, M Obeidat, S Stathakis, C Kabat, M Markovic, N Papanikolaou, K Rasmussen, A Gutierrez, C Ha, S Lee, E Shim, N Kirby
PURPOSE: Radiotherapy treatment is specified by radiation dose prescriptions, but biological DNA damage actually controls treatment effectiveness. It is impractical to directly measure dose in the clinic, so we measure quantities, such as collected charge, and calculate the relationship to dose. At small fields, such as those in stereotactic radiosurgery (SRS), charged-particle equilibrium (CPE) breaks down and the accuracy of the measurement for delivered dose decreases. By measuring DNA double-strand breaks (DSB) directly, we believe treatment accuracy could improve by providing a more meaningful measurement...
June 2016: Medical Physics
S Stathakis, D Defoor, D Saenz, N Kirby, P Mavroidis, N Papanikolaou
PURPOSE: Stereotactic radiosurgery (SRS) outcomes are related to the delivered dose to the target and to surrounding tissue. We have commissioned a Monte Carlo based dose calculation algorithm to recalculated the delivered dose planned using pencil beam calculation dose engine. METHODS: Twenty consecutive previously treated patients have been selected for this study. All plans were generated using the iPlan treatment planning system (TPS) and calculated using the pencil beam algorithm...
June 2016: Medical Physics
Z Huang, W Jiang, B Stuart, S Leu, T Liu, Y Feng
PURPOSE: Since electrons are easily scattered, the virtual source position for electrons is expected to locate below the x-ray target of Medical Linacs. However, the effective SSD method yields the electron virtual position above the x-ray target for some applicators for some energy in Siemens Linacs. In this study, we propose to use IC Profiler (Sun Nuclear) for evaluating the electron virtual source position for the standard electron applicators for various electron energies. METHODS: The profile measurements for various nominal source-to-detector distances (SDDs) of 100-115 cm were carried out for electron beam energies of 6-18 MeV...
June 2016: Medical Physics
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