Cooperativity between cation, OH or Lewis acids, OH interactions and H-bonds or van der Waals forces

Kammer, T.; Luck, W. A. P.

doi:10.1051/jcp/1993901643

Cited by 9 publications

(4 citation statements)

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“…Nevertheless, such an acidity is lower than that of the HY zeolites, for instance ( H 0 = −9) . By analogy with the results reported elsewhere in liquid phase, all these features can be interpreted as a cooperative effect of the cation on the coordinated water molecule. Previous studies of complexes of water (HOD) in solution with electron acceptors of different strength, from SbCl 3 to AlCl 3 , show that Brønsted acidity is created by water coordination.…”

Section: Resultssupporting

confidence: 76%

Investigation of Acid Sites in a Zeotypic Giant Pores Chromium(III) Carboxylate

et al. 2006

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A study of the zeotypic giant pores chromium(III) tricarboxylate Cr(III)3OF(x)(OH)(1-x)(H2O)2 x {C6H3-(CO2)3}2 x nH2O (MIL-100) has been performed. First, its thermal behavior, studied by X-ray thermodiffractometry and infrared spectroscopy, indicates that the departure of water occurs without any pore contraction and no loss in crystallinity, which confirms the robustness of the framework. In a second step, IR spectroscopy has shown the presence of three distinct types of hydroxy groups depending on the outgassing conditions; first, at high temperatures (573 K), only Cr-OH groups with a medium Brønsted acidity are present; at lower temperatures, two types of Cr-H2O terminal groups are observed; and at room temperature, their relatively high Brønsted acidity allows them to combine with H-bonded water molecules. Finally, a CO sorption study has revealed that at least three Lewis acid sites are present in MIL-100 and that fluorine atoms are located on a terminal position on the trimers of octahedra. A first result of grafting of methanol molecules acting as basic organic molecules on the chromium sites has also been shown, opening the way for a postsynthesis functionalization of MIL-100.

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Section: Resultssupporting

confidence: 76%

Investigation of Acid Sites in a Zeotypic Giant Pores Chromium(III) Carboxylate

et al. 2006

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“…The strong electrostatic interactions between water molecules and protons can induce cooperativity, a phenomenon in which water molecules with strong hydrogen bonds can induce stronger hydrogen bonding in the adjacent water molecules (that are hydrogen bonded to other water molecules). Although the hydrogen-bonding strength weakens as the connectivity number increases, the cooperativity of water molecules can be significant when strong hydrogen bonding is present. , The electric field produced by charge separation can also induce stronger cooperative tetrahedral OH stretching, increase the transition strength of the vibrations of interfacial water molecules, cause greater water dipole alignment along the surface normal, and/or increase the interfacial depth that the VSF probes. Previous SF studies of acidic solutions attribute the increased intensity to an enhanced electric field boosting the SF response …”

Section: Resultsmentioning

confidence: 99%

Spectroscopic Studies of Solvated Hydrogen and Hydroxide Ions at Aqueous Surfaces

2006

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Measuring the molecular properties of the surface of acidic and basic aqueous solutions is essential to understanding a wide range of important biological, chemical, and environmental processes on our planet. In the present studies, vibrational sum-frequency spectroscopy (VSFS) is employed in combination with isotopic dilution experiments at the vapor/water interface to elucidate the interfacial water structure as the pH is varied with HCl and NaOH. In acidic solutions, solvated proton species are seen throughout the interfacial region, and they alter the hydrogen bonding between water molecules in ways that reflect their depth in the interfacial region. At the higher frequencies of the OH stretch region, there is spectral evidence for solvated proton species residing in the topmost layers of the interfacial region. As reported in previous VSF studies, more strongly bound solvated proton species are observed at lower OH stretching frequencies. The solvated proton species that have stronger hydrogen bonding are similar in structure to those found in bulk acid solutions and likely reside somewhat deeper in the interfacial region. There is also evidence of OH stretching from solvated protons and relatively strong hydrogen bonding in the solvation sphere that is similar to other solvated ions. In contrast, water molecules solvating OH(-) ions show relatively weak hydrogen bonding and significantly less interfacial order. VSF spectra are acquired under multiple polarizations to provide crucial information for the interpretation of the spectra and for the determination of interfacial structure.

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“…K+ (radius, 1.38 A), which is a chaotrope (water-structure breaker) as judged by thermodynamic (10,11,14), transport (12,13), viscosity (25), NMR (26), infrared spectroscopy (27), and neutron diffraction (16) (10,11,14), transport (12,13), viscosity (25), infrared spectroscopy (27), and x-ray diffraction (16) data, when chromatographed as the Cl-salt is eluted in the position expected for Cl-(which adsorbs weakly to the nonpolar surface of Sephadex G-10), thus confirming that the effect of Na+ on water structure is small and demonstrating that the anion dominates the chromatographic behavior of the neutral salt. Li+ (radius, 0.74 A), in contrast, which is a polar kosmotrope as judged by thermodynamic (10,11,14), transport (12,13), viscosity (25), infrared spectroscopy (27), and neutron diffraction (16) data and has a substantial effect on water structure for a monovalent cation, does not adsorb to the nonpolar surface of Sephadex G-10. The neutral salt LiCl has an apparent molecular weight slightly larger than its anhydrous molecular weight, indicating that Li+ flows through the column with some water molecules attached.…”

Section: Methodsmentioning

confidence: 99%

Sticky ions in biological systems.

Collins

1995

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

337

284

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Continuum electrostatics utilizes a macroscopic dielectric constant to characterize the ability of a medium to attenuate an electric field and has been developed to a level of great sophistication in application to biological systems (1-3). But even apart from its neglect of microscopic detail and the incorporation of a number of questionable assumptions-for example, that the free energy of solvation will be the same for anions and cations of the same size and absolute charge (2)-there is a realization that continuum electrostatics gives an incomplete accounting of the forces acting on ions in aqueous solution. As a result, in calculating the free energy of processes in aqueous solution, terms must be added which reflect the cohesive force of water resulting from the strong interactions between water molecules (1, 4). This cohesive force of water may be expressed by using the macroscopic concept of a surface tension, which tends to minimize the water-exposed surface area of dissolved species or interfacial surfaces. This opposes the repulsive "image force" between an ion in a region of high dielectric constant and the surface of a nearby region of lower dielectric constant which results from the preference of the electric field of the ion to remain in the region of high dielectric constant (5-9). The image repulsion of a partially hydrated monovalent ion of radius 1.6 A in direct contact with a nonpolar surface is about kT relative to the bulk solution (5) and decreases with increasing ion size. The surfaceThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. tension "pushing" a nonpolar sphere of this size onto a nonpolar surface is of comparable magnitude, and the surface tension effect inereases with increasing sphere size (1, 4). These considerations suggest that monovalent ions of about 1.6 A and larger should adsorb to nonpolar surfaces independent of any attractive forces between the ion and the nonpolar surface, whereas those smaller than about 1.6 A should be repelled from nonpolar surfaces. Similar predictions can be made from a microscopic perspective by comparing the entropy of water molecules near monovalent ions to that of water molecules in bulk solution as determined by thermodynamic (10,11,14) and transport (12, 13) data or dynamic measures such as NMR (15). Fig. 1 plots the entropy of water near monovalent ions as calculated from the entropy of hydration of the ion (from dissolving the ion in water) versus the ionic radius of the ion (11). A negative AS,, (upper portion of Fig. 1) indicates tightly bound water that is less mobile than bulk water, whereas a positive AS,, (lower portion of Fig. 1) indicates loosely held water that is more mobile than bulk water. Increasing ion size (decreasing ion charge density) is associated with increasing mobility of nearby water molecules. If this mobile, loosely held water is immediately adjacent...

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Cooperativity between cation, OH or Lewis acids, OH interactions and H-bonds or van der Waals forces

Cited by 9 publications

References 0 publications

Investigation of Acid Sites in a Zeotypic Giant Pores Chromium(III) Carboxylate

Investigation of Acid Sites in a Zeotypic Giant Pores Chromium(III) Carboxylate

Spectroscopic Studies of Solvated Hydrogen and Hydroxide Ions at Aqueous Surfaces

Sticky ions in biological systems.

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