An X-ray diffraction study on concentrated aqueous calcium nitrate solutions at subzero temperatures

Смирнов, П. Р.; Yamagami, Motoyuki; Wakita, Hisanobu; Yamaguchi, Toshio

doi:10.1016/s0167-7322(97)00075-5

Cited by 50 publications

(56 citation statements)

References 35 publications

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“…35 Recent results from IRMPD spectroscopy of Ca 2+ (H 2 O) n with n up to 69 indicate a change in CN from 6 to 8 for clusters with 12 or more water molecules. 30 Many condensed-phase experiments and simulations support CN values for M ) Mg, Ca, and Ba of 6, 37 7 or 8, [37][38][39][40][41][42][43][44][45][46][47][48] and 9, 37,49-51 respectively. However, the range of reported CN values from condensed-phase studies is greater than those from gas-phase studies.…”

Section: Introductionmentioning

confidence: 99%

Hydration of Alkaline Earth Metal Dications: Effects of Metal Ion Size Determined Using Infrared Action Spectroscopy

et al. 2009

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Infrared laser action spectroscopy is used to characterize divalent Mg, Ca, and Ba ions solvated by discrete numbers of water molecules in the gas phase. The spectra of the hexahydrated ions are very similar and indicate that all six water molecules directly solvate the metal ion. The spectra of the heptahydrated ions indicate the presence of populations of structures that have a water molecule in the outer shell for all ions and an average coordination number (CN) for Ba that is higher than that for Ca or Mg. Comparisons between CN values obtained from M06 density functional and local MP2 theory indicate that the B3LYP density functional favors smaller CN values. The spectra of clusters containing at least 12 water molecules indicate that the relative abundance of single-acceptor water molecules for a given cluster size decreases with increasing metal ion size, indicating that tighter water binding to smaller metal ions disrupts the hydrogen bond network and results in fewer net hydrogen bonds. The spectra of the largest clusters (n = 32) are very similar, suggesting that intrinsic water properties are more important than ion-water interactions by that size, but subtle effects of Mg on surface water molecules are observed even for such large cluster sizes.

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Section: Introductionmentioning

confidence: 99%

Hydration of Alkaline Earth Metal Dications: Effects of Metal Ion Size Determined Using Infrared Action Spectroscopy

et al. 2009

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“…[2,3] The ability of calcium to coordinate multiple ligands (from six to eight oxygen atoms) with an asymmetric coordination shell enables it to cross-link different segments of a protein and induce large conformational changes. The great biochemical importance of the calcium ion has led to a number of studies to determine its hydration shell and its preferred coordination number in water.Experimental studies have used a variety of techniques, including X-ray diffraction (XRD), [4][5][6] extended X-ray absorption fine structure (EXAFS) spectroscopy, [7,8] and neutron diffraction [9,10] to elucidate the coordination of Ca 2 + ions in water. The range of coordination numbers (n C ) inferred by X-ray diffraction studies varies from six to eight, and is consistent with that reported in EXAFS experiments (8 [7] and 7.2 [8] ).…”

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confidence: 99%

A First‐Principles Molecular Dynamics Study of Calcium in Water

et al. 2005

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Herein, we report on Car-Parrinello [1] simulations of the divalent calcium ion in water, aimed at understanding the structure of the hydration shell and at comparing theoretical results with a series of recent experiments. We show some of the progress in the investigation of aqueous solutions brought about by the advent of ab initio molecular dynamics and highlight the importance of accessing subtle details of ion-water interactions from first principles.Calcium plays a vital role in many biological systems, including signal transduction, blood clotting, and cell division. In particular, calcium ions are known to interact strongly with proteins as they tend to bind well to both negatively charged (e.g. in aspartate and glutamate) and uncharged oxygens (e.g. in main-chain carbonyls). [2,3] The ability of calcium to coordinate multiple ligands (from six to eight oxygen atoms) with an asymmetric coordination shell enables it to cross-link different segments of a protein and induce large conformational changes. The great biochemical importance of the calcium ion has led to a number of studies to determine its hydration shell and its preferred coordination number in water.Experimental studies have used a variety of techniques, including X-ray diffraction (XRD), [4][5][6] extended X-ray absorption fine structure (EXAFS) spectroscopy, [7,8] and neutron diffraction [9,10] to elucidate the coordination of Ca 2 + ions in water. The range of coordination numbers (n C ) inferred by X-ray diffraction studies varies from six to eight, and is consistent with that reported in EXAFS experiments (8 [7] and 7.2 [8] ). A wider range of values (6 to 10) was found in early neutron diffraction studies, [9] depending on concentration, while a more recent measurement by Badyal et al. reports a value close to seven. [10] In addition to experimental measurements, many theoretical studies have been carried out to investigate the solvation of Ca 2 + ions in water and have also reported a wide range of coordination numbers. Most of the classical molecular dynamics (MD) [4,7,11] and quantum molecular (QM)/MM simulations [12,13] report n C values in the range of eight to ten; in general, n C appears to be highly sensitive to the choice of the ion-water potential used in the calculations.[11] Even ab initio MD simulations have so far obtained conflicting values for n C . For the structure of the first solvation shell Naor et al. found n C = 7 to 8 and a Ca 2 + -oxygen average distance (r Ca-O ) of 2.64 , [14] while Bakó et al. found n C = 6 and r Ca-O = 2.45 . [15] In view of the existing controversies, we have carried out extensive Car-Parrinello [1,16] simulations of Ca 2 + solvation in water, using both a rigid and a flexible water model, up to time scales of 40 ps. Our simulations show variations of coordination numbers from 6, 7 and 8 occurring over intervals of % 0.3 to 0.4 exchanges per picosecond, and yielding average coordination numbers of 6.2 and 7 for flexible and rigid water models, respectively. These results are consistent with ...

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“…However, from a combined x-ray and Raman spectroscopy investigation of Ca͑NO 3 ͒ 2 ·6H 2 O and Ca͑NO 3 ͒ 2 · 12H 2 O, 9 it has been proposed O an -Ca distances of 2.50 and 2.85 Å ͑see Fig. 4 9 and n O =6 in Ca͑NO 3 ͒ 2 · 4.1H 2 O. 8 The MD simulations suggest that such ambiguity in the models that are able to reproduce the experimental g͑r͒ might arise from the relatively broad distribution of the number of neighbors around the cations.…”

Section: Structurementioning

confidence: 99%

“…1,3 In this work, we are concerned with a prototype of these glass-forming liquids, namely, aqueous solution of calcium nitrate, Ca͑NO 3 ͒ 2 · nH 2 O, n = 4, 6, and 8, where n indicates concentration as the water to salt mole ratio. A large literature related to thermodynamics, 1,4,5 structural, [6][7][8][9][10] and dynamical properties 5,[11][12][13] investigated with many different techniques is available for Ca͑NO 3 ͒ 2 · nH 2 O. However, previous molecular dynamics ͑MD͒ simulations of aqueous solutions of nitrate salts have been reported mainly in the limit of dilute solution, [14][15][16][17] in which the most important issue is the equilibrium structure of the hydration shell around the ions.…”

Section: Introductionmentioning

confidence: 99%

Polarization effects in molecular dynamics simulations of glass-formers Ca(NO3)2⋅nH2O, n=4, 6, and 8

Ribeiro

2010

The Journal of Chemical Physics

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Monte Carlo simulation strategies for computing the wetting properties of fluids at geometrically rough surfaces J. Chem. Phys. 135, 184702 (2011) Semi-bottom-up coarse graining of water based on microscopic simulations J. Chem. Phys. 135, 184101 (2011) Hydrophobic interactions in presence of osmolytes urea and trimethylamine-N-oxide J. Chem. Phys. 135, 174501 (2011) Potential of mean force between identical charged nanoparticles immersed in a size-asymmetric monovalent electrolyte J. Chem. Phys. 135, 164705 (2011) Additional information on J. Chem. Phys. Thermodynamics, equilibrium structure, and dynamics of glass-forming liquids Ca͑NO 3 ͒ 2 · nH 2 O, n = 4, 6, and 8, have been investigated by molecular dynamics ͑MD͒ simulations. A polarizable model was considered for H 2 O and NO 3 − on the basis of previous fluctuating charge models for pure water and the molten salt 2Ca͑NO 3 ͒ 2 · 3KNO 3 . Similar thermodynamic properties have been obtained with nonpolarizable and polarizable models. The glass transition temperature, T g , estimated from MD simulations was dependent on polarization, in particular the dependence of T g with electrolyte concentration. Significant polarization effects on equilibrium structure were observed in cation-cation, cation-anion, and water-water structures. Polarization increases the diffusion coefficient of H 2 O, but does not change significantly the diffusion coefficients of ions. Viscosity decreases upon inclusion of polarization, but the conductivity calculated with the polarizable model is smaller than the nonpolarizable model because polarization enhances anion-cation interactions.

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An X-ray diffraction study on concentrated aqueous calcium nitrate solutions at subzero temperatures

Cited by 50 publications

References 35 publications

Hydration of Alkaline Earth Metal Dications: Effects of Metal Ion Size Determined Using Infrared Action Spectroscopy

Hydration of Alkaline Earth Metal Dications: Effects of Metal Ion Size Determined Using Infrared Action Spectroscopy

A First‐Principles Molecular Dynamics Study of Calcium in Water

Polarization effects in molecular dynamics simulations of glass-formers Ca(NO3)2⋅nH2O, n=4, 6, and 8

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