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

Bush, Matthew F.; O’Brien, Jeremy T.; Prell, James S.; Wu, Chun‐Chieh; Saykally, Richard J.; Williams, Evan R.

doi:10.1021/ja901011x

Cited by 72 publications

(98 citation statements)

References 70 publications

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“…We have confirmed through a temperature study that this peak is due to a free OH bond and not involved in hydrogen bonding (SI Appendix). A free OH of interfacial water molecules with their oxygens interacting with Mg 2þ or with the Mg 2þ solvation shell likely contributes to this band (18). A peak in this spectral region was also observed by others and assigned to the symmetric stretch of the decoupled free OH and donor-bonded OH of three-coordinate water molecules (16) and weakly hydrogen-bonded water molecules (19).…”

Section: Resultssupporting

confidence: 69%

Surface organization of aqueous MgCl ₂ and application to atmospheric marine aerosol chemistry

Casillas-Ituarte

Callahan

Tang

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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Inorganic salts in marine aerosols play an active role in atmospheric chemistry, particularly in coastal urban regions. The study of the interactions of these ions with water molecules at the aqueous surface helps to elucidate the role of inorganic cations and anions in atmospheric processes. We present surface vibrational sum frequency generation (SFG) spectroscopic and molecular dynamics (MD) studies of aqueous MgCl 2 surfaces as models of marine aerosol. Spectroscopy results reveal that the disturbance of the hydrogen bonding environment of the air/aqueous interface is dependent on the MgCl 2 concentration. At low concentrations (<1 M) minor changes are observed. At concentrations above 1 M the hydrogen bonding environment is highly perturbed. The 2.1 M intermediate concentration solution shows the largest SFG response relative to the other solutions including concentrations as high as 4.7 M. The enhancement of SFG signal observed for the 2.1 M solution is attributed to a larger SFG-active interfacial region and more strongly oriented water molecules relative to other concentrations. MD simulations reveal concentration dependent compression of stratified layers of ions and water orientation differences at higher concentrations. SFG and MD studies of the dangling OH of the surface water reveal that the topmost water layer is affected structurally at high concentrations (>3.1 M). Finally, the MgCl 2 concentration effect on a fatty acid coated aqueous surface was investigated and SFG spectra reveal that deprotonation of the carboxylic acid of atmospherically relevant palmitic acid (PA) is accompanied by binding of the Mg 2þ to the PA headgroup. magnesium chloride | fatty acid | air/aqueous interface | sum frequency spectroscopy | molecular dynamics I norganic salts present in marine boundary layer (MBL) aerosol originate from turbulent wave action at the surface of the ocean (1). These aerosols, typically of the micron size range and smaller, travel over continental regions by being entrained in the air mass in which they were created, and have been detected more than 900 km inland (2). Aerosols play a key role in the modification of global climate through their effect on cloud condensation nuclei prevalence, radiative balance, and level of precipitation (3). Aerosol composition and size have also been correlated to thunderstorm severity (4). Alkali metals (Na, K, Li, and Rb), alkaline earth metals (Mg, Ca), and ammonium (NH þ 4 ) make up the majority of cationic species, and halides (F, Cl, Br, and I) and oxidized sulfur and nitrogen ions make up the majority of inorganic anionic species found in MBL aerosol (5, 6). While calcium and magnesium are the most prevalent divalent cations in seawater and MBL aerosols, chloride anion is the dominant halide species (5). Although recent cloud drop measurements in the MBL show that calcium concentrations are about four times higher than magnesium concentrations, (6) the small size and high charge density of Mg 2þ gives rise to a strongly hydrated complex in aqueous solut...

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Section: Resultssupporting

confidence: 69%

Surface organization of aqueous MgCl ₂ and application to atmospheric marine aerosol chemistry

Casillas-Ituarte

Callahan

Tang

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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“…[13,14] From these experimental studies, the bond dissociation energies (BDEs) for Mg 2 + (H 2 O) x , for x = 6-14 and x = 5-10, were determined, which leaves theoretical calculations to solve the bond energies for the remaining inner-shell complexes (x = 1-4). [16] This study revealed that 6 water molecules bind directly to magnesium and that even with 32 water ligands, effects of the metal persist in influencing the structure of the outermost water molecules, which is in contrast to analogous complexes of the larger calcium and barium dications. [15] This group also investigated Mg 2 + (H 2 O) x complexes in which x = 6-32 by infrared multiple photon dissociation (IRMPD) action spectroscopy in the OH stretching region (2800-3800 cm À1 ) in a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer.…”

Section: Introductionmentioning

confidence: 88%

Threshold Collision‐Induced Dissociation of Hydrated Magnesium: Experimental and Theoretical Investigation of the Binding Energies for Mg²⁺(H₂O)_x Complexes (x=2–10)

Carl

Armentrout

2012

ChemPhysChem

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The sequential bond energies of Mg(2+)(H2O)x complexes, in which x=2-10, are measured by threshold collision-induced dissociation in a guided ion beam tandem mass spectrometer. From an electrospray ionization source that produces an initial distribution of Mg(2+)(H2O)x complexes in which x=7-10, complexes down to x=3 are formed by using an in-source fragmentation technique. Complexes smaller than Mg(2+)(H2O)3 cannot be formed in this source because charge separation into MgOH(+)(H2O) and H3O(+) is a lower-energy pathway than simple water loss from Mg(2+)(H2O)3. The kinetic energy dependent cross sections for dissociation of Mg(2+)(H2O)x complexes, in which x=3-10, are examined over a wide energy range to monitor all dissociation products and are modeled to obtain 0 and 298 K binding energies. Analysis of both primary and secondary water molecule losses from each sized complex provides thermochemistry for the sequential hydration energies of Mg(2+) for x=2-10 and the first experimental values for x=2-4. Additionally, the thermodynamic onsets leading to the charge-separation products from Mg(2+)(H2O)3 and Mg(2+)(H2O)4 are determined for the first time. Our experimental results for x=3-7 agree well with quantum chemical calculations performed here and previously calculated binding enthalpies, as well as previous measurements for x=6. The present values for x=7-10 are slightly lower than previous experimental results and theory, but within experimental uncertainties.

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“…In aqueous solution, the most stable hydration states for Ca 2+ are CWT = 6, 7, consistent with experimental hydration number. 38,39 The most stable bound state for Ca 2+ is at (CWT = 2, CLP = 4), where the total coordination number is 6. Other stable bound states are at CLP = 3, 4, 5 with total coordination number of 4 ∼ 6, which are 2 ∼ 4 kcal/mol higher than the global minimum (see Table 1).…”

Section: 37mentioning

confidence: 99%

Specific Ion Binding at Phospholipid Membrane Surfaces

Yang

Calero

Bonomi

et al. 2015

J. Chem. Theory Comput.

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Metal cations are ubiquitous components in biological environments and play an important role in regulating cellular functioning and membrane properties. By applying metadynamics simulations, we have performed systematic free-energy calculations of Na + , K + , Ca 2+ , and Mg 2+ bound to phospholipid membrane surfaces for the first time. The free-energy landscapes unveil specific binding behaviors of metal cations on phospholipid membranes. Na + and K + are more likely to stay in the aqueous solution, and can easily bind to a few lipid oxygens by overcoming low free-energy barriers. Ca 2+ is most stable when bound to four lipid oxygens of the membranes, rather than being * To whom correspondence should be addressed † Technical University of Catalonia-Barcelona Tech ‡ Boston University ¶ University of Cambridge 1 hydrated in the aqueous solution. Mg 2+ is tightly hydrated, and can hardly lose a hydration water and bind directly to the membranes. When bound to the membranes, the cations' most favorable total coordination numbers with water and lipid oxygens are the same as their corresponding hydration numbers in aqueous solution, indicating a competition between ion binding to water and lipids. The binding specificity of metal cations on membranes is then highly correlated with the hydration free-energy and the size of the hydration shell.

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

Cited by 72 publications

References 70 publications

Surface organization of aqueous MgCl ₂ and application to atmospheric marine aerosol chemistry

Surface organization of aqueous MgCl ₂ and application to atmospheric marine aerosol chemistry

Threshold Collision‐Induced Dissociation of Hydrated Magnesium: Experimental and Theoretical Investigation of the Binding Energies for Mg²⁺(H₂O)_x Complexes (x=2–10)

Specific Ion Binding at Phospholipid Membrane Surfaces

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

Cited by 72 publications

References 70 publications

Surface organization of aqueous MgCl 2 and application to atmospheric marine aerosol chemistry

Surface organization of aqueous MgCl 2 and application to atmospheric marine aerosol chemistry

Threshold Collision‐Induced Dissociation of Hydrated Magnesium: Experimental and Theoretical Investigation of the Binding Energies for Mg2+(H2O)x Complexes (x=2–10)

Specific Ion Binding at Phospholipid Membrane Surfaces

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Surface organization of aqueous MgCl ₂ and application to atmospheric marine aerosol chemistry

Surface organization of aqueous MgCl ₂ and application to atmospheric marine aerosol chemistry

Threshold Collision‐Induced Dissociation of Hydrated Magnesium: Experimental and Theoretical Investigation of the Binding Energies for Mg²⁺(H₂O)_x Complexes (x=2–10)