Acetone hydration in supercritical water: C-NMR13 spectroscopy and Monte Carlo simulation

Abstract

The (13)C-NMR chemical shift of acetone delta((13)C[Double Bond]O) was measured in aqueous solution at high temperatures up to 400 degrees C and water densities of 0.10-0.60 g/cm(3) for the study of hydration structure in the supercritical conditions. The average number N(HB) of hydrogen bonds (HBs) between an acetone and solvent waters and the energy change DeltaE upon the HB formation were evaluated from the delta and its temperature dependence, respectively. At 400 degrees C, N(HB) is an increasing function of the water density, the increase being slower at higher water densities. The acetone-water HB formation is exothermic in supercritical water with larger negative DeltaE at lower water densities (-3.3 kcal/mol at 0.10 g/cm(3) and -0.3 kcal/mol at 0.60 g/cm(3)), in contrast to the positive DeltaE in ambient water (+0.078 kcal/mol at 4 degrees C). The corresponding Monte Carlo simulations were performed to calculate the radial and orientational distribution functions of waters around the acetone molecule. The density dependence of N(HB) calculated at 400 degrees C is in a qualitative agreement with the experimental results. In the supercritical conditions, the HB angle in a neighboring acetone-water pair is weakly influenced by the water density, because of the absence of collective HB structure. This is in sharp contrast to the hydration structure in ambient water, where the acetone-water HB formation is orientationally disturbed by the tetrahedral HB network formation among the surrounding waters.

The isotropic nuclear magnetic shielding constants of acetone in supercritical water: A sequential Monte Carlo/quantum mechanics study including solute polarization

“…However, they are both smaller than the experimental shift of 9 -11 ppm. 47 Comparison between the chemical shifts for other molecules obtained using different functionals have led to similar conclusions. 20,45,63 All the results to be obtained next will then use only the B3LYP/ 6-311 + +G͑2d ,2p͒ model.…”

“…However, from the data reported in Ref. 47, an experimentally inferred shift in ͑ 13 C͒, in changing from normal to supercritical condition, is estimated in the range of 9 -11 ppm. To make an appropriate comparison with available experimental results, we have computed the solvent effects on the shielding constants for both supercritical and normal conditions.…”

“…48 The structural properties of the hydration shell around acetone are very different from those under ambient conditions and there is a sensitive reduction in the average number of hydrogen bonds between acetone and water. MC simulation 48 and indirect experimental results 5,47 suggest that the number of hydrogen bonds for SCW in the near-critical regime is reduced to 30%-45% compared to NW. In the present work, we use the sequential Monte Carlo/quantum mechanics ͑S-MC/QM͒ methodology 37 to study the solvent effects on the nuclear magnetic shielding constants of acetone in water at both SC and normal conditions.…”

“…In the SC conditions, theoretical studies of the nuclear magnetic shielding constants are very scarce and this present work fills an important gap. On the experimental side, data on 13 C NMR chemical shifts of acetone in SC conditions have been presented by Takebayashi et al 47 The measurements of the 13 C NMR chemical shifts in solution are generally carried out with an external reference and a direct comparison with experimental results is difficult. However, from the data reported in Ref.…”

Properties of the Liquid–Vapor Interface of Acetone–Water Mixtures. A Computer Simulation and ITIM Analysis Study

“…1 Although numerous computer simulation studies of the bulk liquid phase of neat acetone [2][3][4][5][6] as well as of its mixtures with water [7][8][9][10][11][12][13][14][15][16][17][18] and other cosolvents, 9,[19][20][21][22][23][24][25] being sometimes in supercritical state 12,22 have been reported in the past decades, little is known about the behavior of acetone at interfaces. In fact, although the properties of the acetone molecules adsorbed at the surface of ice, 26,27 mixed acetone-water nanoclusters, 28 the liquid-vapor interface of neat acetone [29][30][31] and acetone-methanol mixtures of various compositions 32 have already been investigated by computer simulation methods several times, and the liquid-vapor interface of neat acetone 29,33 as well as of acetone-water mixtures 34,35 have also been studied, although scarcely, by surface sensitive experimental methods, we are not aware of any detailed computer simulation investigation of the liquidvapor interface of acetone-water mixtures.…”