Raman Spectral Studies of the Effects of Solutes and Pressure on Water Structure

Abstract

to 171.67.34.69. Redistribution subject to AIP license or copyright; see http://jcp.aip.org/about/rights_and_permissions 768 HUNTER, DAVENPORT, AND SETTEponents. Although Pinkerton and Bauer have already shown that molecules of high reaction rate greatly alter the absorption when added to molecules of low reaction rate, our results in the relaxation region show that the result is a mutual one. A.Raman spectra excited by 4880-A argon-ion-Iaser radiation and recorded photoelectrically have been obtained from a series of ternary aqueous solutions by back scattering and by 90° scattering using Cary and Jarrell-Ash double monochromators, respectively. The OD stretching region of HDO (and D 2 0), 2300-2800 cm-I, and the OH stretching region of H 20 plus HDO, ~2800-3800 cm-I, were examined for the following solutes: ((C.H,).NCI, and (15) Xe. (See Addendum for other solutes.) In addition, Raman spectra were obtained from HDO in H20 at pressures from 1 to 3790 bar at 25°C, and from a 5.0M solution of NaCIO. in HDO and H 20 at pressures of 690 and 3450 bar at 25°C. Several pronounced intensity maxima were observed in the OD and OH stretching regions for salts of extremely strong acids, (1)-(4), and some qualitative correlations with the strengths of the corresponding acids were found for (1)-(10). Solutes (1)-(11) were also found to act as structure breakers in water, but (12) was found to enhance structure, and some hydrogen bonding was found for (13). Further, no significant spectral effects were noted for (15) when the Xe concentration of the molten clathrate hydrate was 0.8M at 70°C and 1720 bar. For (14), however, an intense low-frequency OD stretching component was observed near 2483 cm-I • The (C 4 H,).N+ cation is the first found to produce pronounced effects in the OD and OH stretching regions, and the 2483 cm-I OD stretching component appears to arise from a marked structure-making effect. The effect of pressure on the OD stretching contour of HDO in H 20 was observed to be small. Only a slight decrease in the frequency of the nonhydrogen-bonded component centered near 2660 cm-I was uncovered to pressures of 3790 bar, and no significant pressure effect was observed for the NaCIO. solution to 3450 bar. The highpressure spectra indicate that pressure is not very effective in breaking the hydrogen bonds in water, and the filling of holes as the result of a redistribution of angles and distances in the hydrogen-bonded network is suggested as a more important effect.

Molecular states of water in room temperature ionic liquidsElectronic Supplementary Information available. See http://www.rsc.org/suppdata/cp/b1/b106900d/

“…Two bands at 3640 and 3590 cm -1 in the Raman spectrum of water with added NaPF 6 have been previously observed. 24 However, the presence of the second band has been assigned to "electrostatic interactions", while Scherer 21 has suggested that the appearance of these bands can be explained by the formation of two weak H-bonds of water molecules with the two anions of the added salt. An analogous spectral picture has been reported for the weakly interacting water involving both its protons in the case of water absorbed into polymers where the interaction with the basic sites of the opposite polymer chains was possible.…”

Hydration and Lyotropic Melting of Amphiphilic Molecules: A Thermodynamic Study Using Humidity Titration Calorimetry

“…. H-O units (37). The conformation of the C-C-N(CH 3 ) 3 fragment of DTAB in the crystalline state is trans as revealed by the strong absorption band near 920 cm Ϫ1 (not shown).…”

“…11a). This effect can be interpreted in terms of the partial breakdown of the water structure (37). Note that hydrogen bond formation between water and the N ϩ (CH 3 ) 3 site cannot occur.…”

Consequence of Solubility Alteration by Salt Effect on Dissolution Enhancement and Biological Response of a Solid Dispersion of an Experimental Antianginal Drug

“…Therefore, cations and anions might exert their influence independently upon the solubility phenomenon (cf. [8][9][10][11]. The authors point out that the salts of 'salting-out cations' can lose their capacity to induce solubility changes when the anions are 'water structure breakers', such as P , SCN',C104 '.…”