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Title: Preferential Solvation in Urea Solutions at Different Concentrations: Properties from Simulation Studies

Abstract

We performed molecular dynamics simulations of urea solutions at different concentrations with two urea models (OPLS and KBFF) to examine the structures responsible for the thermodynamic solution properties. Our simulation results showed that hydrogen-bonding properties such as the average number of hydrogen bonds and their lifetime distributions were nearly constant at all concentrations between infinite dilution and the solubility limit. This implies that the characterization of urea-water solutions in the molarity concentration scale as nearly ideal is a result of facile local hydrogen bonding rather than a global property. Thus, urea concentration does not influence the local propensity for hydrogen bonds, only how they are satisfied. By comparison, the KBFF model of urea donated fewer hydrogen bonds than OPLS. We found that the KBFF urea model in TIP3P water better reproduced the experimental density and diffusion constant data. Preferential solvation analysis showed that there were weak urea-urea and water-water associations in OPLS solution at short distances, but there were no strong associations. We divided urea molecules into large, medium, and small clusters to examine fluctuation properties and found that any particular urea molecule did not stay in the same cluster for a long time. We found neither persistent nor largemore » clusters.« less

Authors:
;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1012312
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the American Chemical Society, 111(19):5233-5242; Journal Volume: 111; Journal Issue: 19
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; BONDING; DIFFUSION; DILUTION; FLUCTUATIONS; HYDROGEN; LIFETIME; SIMULATION; SOLUBILITY; SOLVATION; THERMODYNAMICS; UREA; WATER; Environmental Molecular Sciences Laboratory

Citation Formats

Kokubo, Hironori, and Pettitt, Bernard M. Preferential Solvation in Urea Solutions at Different Concentrations: Properties from Simulation Studies. United States: N. p., 2007. Web. doi:10.1021/jp067659x.
Kokubo, Hironori, & Pettitt, Bernard M. Preferential Solvation in Urea Solutions at Different Concentrations: Properties from Simulation Studies. United States. doi:10.1021/jp067659x.
Kokubo, Hironori, and Pettitt, Bernard M. Sat . "Preferential Solvation in Urea Solutions at Different Concentrations: Properties from Simulation Studies". United States. doi:10.1021/jp067659x.
@article{osti_1012312,
title = {Preferential Solvation in Urea Solutions at Different Concentrations: Properties from Simulation Studies},
author = {Kokubo, Hironori and Pettitt, Bernard M.},
abstractNote = {We performed molecular dynamics simulations of urea solutions at different concentrations with two urea models (OPLS and KBFF) to examine the structures responsible for the thermodynamic solution properties. Our simulation results showed that hydrogen-bonding properties such as the average number of hydrogen bonds and their lifetime distributions were nearly constant at all concentrations between infinite dilution and the solubility limit. This implies that the characterization of urea-water solutions in the molarity concentration scale as nearly ideal is a result of facile local hydrogen bonding rather than a global property. Thus, urea concentration does not influence the local propensity for hydrogen bonds, only how they are satisfied. By comparison, the KBFF model of urea donated fewer hydrogen bonds than OPLS. We found that the KBFF urea model in TIP3P water better reproduced the experimental density and diffusion constant data. Preferential solvation analysis showed that there were weak urea-urea and water-water associations in OPLS solution at short distances, but there were no strong associations. We divided urea molecules into large, medium, and small clusters to examine fluctuation properties and found that any particular urea molecule did not stay in the same cluster for a long time. We found neither persistent nor large clusters.},
doi = {10.1021/jp067659x},
journal = {Journal of the American Chemical Society, 111(19):5233-5242},
number = 19,
volume = 111,
place = {United States},
year = {Sat Apr 21 00:00:00 EDT 2007},
month = {Sat Apr 21 00:00:00 EDT 2007}
}
  • The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. We performed molecular dynamics simulations of urea solutions at different concentrations with two urea models (OPLS and KBFF) to examine the structures responsible for the thermodynamic solution properties. Our simulation results showed that hydrogen-bonding properties such as the average number of hydrogen bonds and their lifetime distributions were nearly constant at all concentrations between infinite dilution and the solubility limit.more » This implies that the characterization of urea-water solutions in the molarity concentration scale as nearly ideal is a result of facile local hydrogen bonding rather than a global property. Thus, urea concentration does not influence the local propensity for hydrogen bonds, only how they are satisfied. By comparison, the KBFF model of urea donated fewer hydrogen bonds than OPLS. We found that the KBFF urea model in TIP3P water better reproduced the experimental density and diffusion constant data. Preferential solvation analysis showed that there were weak urea-urea and water-water associations in OPLS solution at short distances, but there were no strong associations. We divided urea molecules into large, medium, and small clusters to examine fluctuation properties and found that any particular urea molecule did not stay in the same cluster for a long time. We found neither persistent nor large clusters.« less
  • Frozen solutions of silver perchlorate exposed to /sup 60/Co ..gamma.. irradiation at 4 K form silver atoms by reaction of radiation-produced electrons with the silver ion. At 4 K the silver atoms are initially produced in a nonequilibrium or presolvated state, and upon brief warming to 77 K the first solvation shell geometry changes to produce an equilibrium or solvated silver atom. The presolvated and solvated silver atoms in water and ethanol matrices are characterized by different isotropic hyperfine couplings and line widths measured by electron spin resonance. We have investigated silver atoms in water-ethanol mixtures to search for preferentialmore » solvation effects. From 0 to 13 mol % ethanol the presolvated silver atom formed at 4 K exhibits parameters characteristic of a water environment. At 13 mol % the parameters suddenly change to those characteristic of an ethanol environment. This suggests that the original silver ion undergoes a drastic change in its first solvation shell at 13 mol % ethanol. This dramatic change appears to corrleate with the minimum in the excess enthalpy of mixing of ethanol and water vs ethanol mole percent. Further solvation changes occur on thermal annealing the silver atoms at 77 K.« less
  • The form of Raoult's law is modified to express the activity of water (a(H/sub 2/O)) for aqueous electrolyte solutions by the mole fraction of a free (nonsolvating) solvent structural unit raised to the reciprocal power of the solvent structural constant. Relatively close agreement with experiment is obtained for a(H/sub 2/O) of aqueous sodium chloride solutions up to 300/sup 0/C and nearly saturated concentrations, and of other aqueous electrolyte solutions at 25/sup 0/C. In an example for aqueous-organic systems, a(H/sub 2/O) for urea solutions at 25/sup 0/C is described with an average deviation of 0.09% for molalities from 0 to 20mmore » (54.6 wt%) by using the necessary (universal) structural constant and a single solvation parameter.« less