Salt molecular dynamics

Sachs JN, Nanda H, Petrache HI, Woolf TB. (2004) Changes in phosphatidylcholine headgroup tilt and water order induced by monovalent salts Molecular dynamics simulations. Biophys J86 3772-3782. 

Woodcock L V 1971. Isothermal Molecular Dynamics Calculations for Liquid Salts. Chemical Phi, Letters 10 257-261. 

The concentration of salt in physiological systems is on the order of 150 mM, which corresponds to approximately 350 water molecules for each cation-anion pair. Eor this reason, investigations of salt effects in biological systems using detailed atomic models and molecular dynamic simulations become rapidly prohibitive, and mean-field treatments based on continuum electrostatics are advantageous. Such approximations, which were pioneered by Debye and Huckel [11], are valid at moderately low ionic concentration when core-core interactions between the mobile ions can be neglected. Briefly, the spatial density throughout the solvent is assumed to depend only on the local electrostatic poten-... 

In the case of molten salts, no obvious model based on statistical mechanics is available because the absence of solvent results in very strong pair correlation effects. It will be shown that the fundamental properties of these liquids can be described by quasi-chemical models or, alternatively, by computer simulation of molecular dynamics (MD). 

There is difficulty in defining the absolute mobilities of the constituent ions in a molten salt, since it does not contain fixed particles that could serve as a coordinate reference. Experimental means for measuring external transport numbers or external mobilities are scarce, although the zone electromigration method (layer method) and the improved Hittorf method may be used. In addition, external mobilities in molten salts cannot be easily calculated, even from molecular dynamics simulation. 

Molecular dynamics and Monte Carlo simulations have been extensively applied to molten salts since 1968 to study structure, thermodynamic properties, and dynamic properties from a microscopic viewpoint. Several review papers have been published on computer simulation of molten salts. " Since the Monte Carlo method cannot yield dynamic properties, MD methods have been used to calculate dynamic properties. 

Saboungi ML, Rahman A, Halley JW, Blander M (1988) Molecular-dynamics studies of complexing in binary molten-salts with polarizable anions - Max4. J Chem Phys 88(9) 5818—5823... 

Figure 1 (Plate 1). A molecular view of a small section of a flat lipid bilayer generated by molecular dynamics simulations. The bilayers are composed of l-stearoyl-2-docosa-hexaenoyl-5M-g]ycero-3-phosphatidylcholine lipids, i.e. the sn 1 chain is 18 C atoms long and the sn2 chain has 22 carbons, including six cis double bonds. The hydrophobic core is in the centre of the picture, and the hydrated head-group regions are both on top and bottom of the view graph. The head group is zwitterionic and no salt has been added. From [102], Reproduced by permission of the American Physical Society. Copyright (2003)...

Lin Y, Liao Q, Jin X. Molecular dynamics simulations of dendritic polyelectrolytes with flexible spacers in salt free solution. J Phys Chem B 2007 111 5819-5828. 

Protonated forms of the large-ring macrocycle [24]Ng02 (5) and related compounds have been shown to be active as synthetic phosphorylation catalysts in ATP synthesis. It is likely that in this case the substrate enters the macrocyclic cavity to some extent, or is enveloped by it. Evidence for this possibility comes from the crystal structure of the chloride salt of 5-6H (Figure 1) in which a chloride ion is enveloped within a cleft formed by the boat-shaped conformation of the macrocy-cle. The crystal structure of the nitrate salt of 5-4H has also recently been determined and the host again adopts a boat-like conformation as it interacts with the anion. The hydrochloride salt of the smaller [22]Ng binds two chloride anions above and below the host plane in a similar way to 1. Molecular dynamics simulations indicate that the pocket-like conformation for 5-6H is maintained in solution, although Cl NMR experiments demonstrate that halide ions are in rapid exchange between the complexed and solvated state. 

Solvent polarity is known to affect catalytic activity, yet consistent correlations between activity and solvent dielectric (e) have not been observed [12,102]. However, a striking correlation was found between the catalytic efficiency of salt-activated subtilisin Carlsberg and the mobility of water molecules (as determined using NMR relaxation techniques) associated with the enzyme in solvents of varying polarities (Figure 3.11) [103]. As the solvent polarity increased, the water mobility of the enzyme increased, yet the catalytic activity of the enzyme decreased. This is consistent with previous EPR and molecular dynamics (MD) studies, which indicated that enzyme flexibility increases with increasing solvent dielectric [104]. 

Molecular dynamic simulation, adsorption process, 965 Molten salt... 

Baaden, M., Bemy, F., Muzet, N., Troxler, L., Wipff, G. 2000. Interfacial features of assisted liquid-liquid extraction of uranyl and cesium salts A molecular dynamics investigation. In Calixarenes for Separation. Lumetta, G., Rogers, R., Gopalan, A. Eds. ACS Symposium Series 757, American Chemical Society, Washington, DC, pp. 71-85. 

In view of the studies [75] of aqueous NaCl solutions by using molecular-dynamics simulation, one may suggest that our models are applicable61 only at low salt concentrations Cm, for which the Kirkwood correlation factor g could be calculated from Eq. (414d), where the ionic contribution Ae on(0) is not involved. 

Subject areas for the Series include solutions of electrolytes, liquid mixtures, chemical equilibria in solution, acid-base equilibria, vapour-liquid equilibria, liquid-liquid equilibria, solid-liquid equilibria, equilibria in analytical chemistry, dissolution of gases in liquids, dissolution and precipitation, solubility in cryogenic solvents, molten salt systems, solubility measurement techniques, solid solutions, reactions within the solid phase, ion transport reactions away from the interface (i.e. in homogeneous, bulk systems), liquid crystalline systems, solutions of macrocyclic compounds (including macrocyclic electrolytes), polymer systems, molecular dynamic simulations, structural chemistry of liquids and solutions, predictive techniques for properties of solutions, complex and multi-component solutions applications, of solution chemistry to materials and metallurgy (oxide solutions, alloys, mattes etc.), medical aspects of solubility, and environmental issues involving solution phenomena and homogeneous component phenomena. 

Carrieri, A., Centeno, N.B., Rodrigo, J., Sanz, F., Carotti, A. Theoretical evidence of a salt bridge disruption as the initiating process for the a1(j-adrenergic receptor activation a molecular dynamics and docking study. Proteins 2001, 43, 382-394. 

A remarkable effect was observed for salt 28, as no 31P NMR signals could be obtained between —100 and +30 °C. According to theoretical calculations of the 31P NMR shift values and an inversion barrier, this effect is related to molecular dynamics <2003AGE2778>. Dynamic NMR spectroscopic evidence was established for a rapid 1,3-migrational exchange of the phosphorus atoms A and B within the four-membered ring of triphospha bicyclopentene 31 <1998CC1537>. 

This chapter attempts to review the microscopic mechanism of the dissolution and nucleation processes of crystals at a molecular level with the help of molecular dynamic (MD) simulations and, partly, of solution X-ray diffraction salts. Different procedures are outlined in what follows. 

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