Supporting Information. for. Influence of Cononsolvency on the. Aggregation of Tertiary Butyl Alcohol in. Methanol-Water Mixtures

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1 Supporting Information for Influence of Cononsolvency on the Aggregation of Tertiary Butyl Alcohol in Methanol-Water Mixtures Kenji Mochizuki,, Shannon R. Pattenaude, and Dor Ben-Amotz Research Institute for Interdisciplinary Science, Okayama university, Okayama 7-853, Japan Department of Chemistry, Purdue University, West Lafayette, Indiana 4797, United States S1

2 Computational details Potentials of mean force and the Kirkwood-Buff integrals We used GROMACS to obtain the computational results. The potentials of mean force (PMFs), described in Fig. S1, were computed from a set of umbrella sampling simulations with the weighted histogram analysis method. 2 We estimated the PMFs for a pair of tertiary butyl alcohol (TBA) molecules dissolved in methanol(meoh)/water mixtures as a function of the distance (r) between the centers of mass at 293 K and.1 MPa. The total number of solvent molecules was 2, and the mole fraction of MeOH (x m ) was varied from. (pure water) to 1. (pure MeOH) with intervals of.2. For each x m, a series of molecular dynamics (MD) simulations for 26 windows was performed with different harmonic-restraint potentials, V (r) = k(r d ) 2, where the force constant k is 2 kcal/mol/nm 2 and the equilibrium distance (d ) is.35,.4,...,1.6 nm. For each window an equilibration MD simulation in the canonical (NV T ) ensemble of 5 ps was followed by a 1 ns MD simulation in the isothermal-isobaric (N P T ) ensemble for obtaining an equilibrium distribution of r in the window. The resulting distribution is proportional to 4πr 2 g(r), and so the PMF was obtained after removing the entropic contribution k B T ln(4πr 2 ) with k B being the Boltzmann factor. An average of PMFs at distances from to 1.6 nm was chosen as the baseline, where two solute molecules are considered to be isolated. The distance r dependence of the Kirkwood-Buff integral between a pair of TBA molecules is computed from the corresponding PMF w(r) via r [e w(r)/k BT 1] 4πr 2 dr. The Kirkwood- Buff integral represents the magnitude of TBA-TBA interaction over a range of intermolecular distances. In order to estimate multi-body effects 3 5 of TBA on the PMFs, we performed MD simulations for approximately.6 M TBA solutions with varying x m. Table S1 shows the number of water, MeOH and TBA molecules at each x m. The production NP T MD run at each x m was 1 ns. The radial distribution functions g(r) between the centers of mass of S2

3 TBA molecules are first computed. Then, the PMFs in Fig S3 are obtained from the identity w(r) = k B T ln[g(r)]. MD simulations The time step of the MD simulations was 2. fs. The pressure of.1 MPa and the temperature of 293 K were controlled by the Parrinello Rahman barostat 6 and the Nosé-Hoover thermostat, 7,8 respectively, whereas the Berendsen algorithm 9 was used for the equilibration runs. Periodic boundary conditions were applied for the cubic simulation box. Force fields We considered two different sets of force fields; (i) the TraPPE-UA model 1,11 for TBA and MeOH, the TIP4P/25 model 12 for water, and the HH-Alkane model 13 for the alkane-water oxygen cross interactions. The TIP4P/25 model provides one of the best descriptions of the bulk liquid density and the excess chemical potential of simple molecules. 14 The HH-Alkane model accurately reproduces the thermodynamic properties of hydrophobic hydration of alkanes. 13 (ii) the GROMOS 53A6 model 15 for TBA and MeOH, and SPC/E water model. 16 This combination has been used to investigate the phase behavior of aqueous solutions of TBA 17 as well as other small molecules The LJ parameters for cross-interactions, except the HH-Alkane model mentioned above, were given by the Lorentz-Berthelot combination rules; ϵ ij = ϵ ii ϵ jj and σ ij = (σ ii + σ jj )/2. The intermolecular interactions were truncated at nm. The long-range Coulombic interactions were evaluated using the particle-mesh Ewald algorithm, 21 and dispersion corrections were implemented for the energy and pressure evaluations. S3

4 Preferential binding coefficients To obtain the preferential binding coefficients (Γ) in Fig. 3A and Fig. S7, we performed NP T -MD simulations of 1 ns each for two monomers and separately for one dimer of TBA molecules dissolved in MeOH/water mixtures of x m =.2,.4,.6 and.8, using umbrella samplings with d=1.6 nm and.6 nm, respectively. The same trajectories were used to obtain the results in Fig. 3B, 3C and 4. Experimental details Methanol (MeOH, 99.9 %, OmniSolv), methyl-d3 alcohol (MeOH-d3, 99.8 atom % D, CDN Isotopes), tert-butanol (TBA, 99.5 %, Sigma-Aldrich) and tert-butyl-d9 Alcohol (TBA-d9, 99.2 atom % D, CDN Isotopes) were used without further purification. Aqueous solutions were prepared using ultra pure water (Milli-Q UF Plus, 18.2 MΩ-cm resistance, Millipore). Raman spectra were collected at 2. C using a temperature controlled spectroscopic cell holder (LC6, Quantum Northwest), and a home-built Raman instrument utilizing a nm argon-ion excitation laser with a power of 15 mw at the sample as previously described. 22,23 Two or four spectra, each with an integration time of.1 s and a total scan time of 5 minutes, were collected for each solution. The Raman multivariate curve resolution (Raman-MCR) analyses of the measured solution spectra were performed using the selfmodeling curve resolution (SMCR) algorithm. 22,24,25 S4

5 Table S1: Number of water, MeOH and TBA molecules at each methanol mole fraction (x m ) for approximately.6 M TBA solutions. x m water MeOH TBA A 2 B Potential of mean force (kj/mol) x m r (nm) Figure S1: Potentials of mean force between the centers of mass of TBA molecules in MeOH/water mixtures with x m varying from. to 1.. Two different sets of force fields were considered; (A) TraPPE+TIP4P/25+HH-Alkane and (B) GROMOS 53A6+SPC/E. The arrows indicate the TBA-TBA contact distance located at the PMF minima, which are described in Fig. 1A as a function of x m. S5

6 Kirkwood-Buff integral (nm 3 ) A x m B r (nm) Figure S2: The Kirkwood-Buff integrals between a pair of TBA molecules in MeOH/water mixtures with x m varying from. to 1., obtained using (A)TraPPE+TIP4P/25+HH- Alkane and (B) GROMOS 53A6+SPC/E.The results clearly indicate that the TBA-TBA intermolecular interaction is most enhanced at x m = A 2 B Potential of mean force (kj/mol) x m r (nm) Figure S3: Potentials of mean force between the centers of mass of TBA molecules in MeOH/water mixtures with x m varying from. to 1., obtained from approximately.6 M TBA solutions. Two different sets of force fields were considered; (A) TraPPE+TIP4P/25+HH-Alkane and (B) GROMOS 53A6+SPC/E. The x m dependence of the PMF minimum exhibits a qualitatively same trend as observed in Fig. S1. S6

7 A C-D stretch [TBA].1M.2M.3M.4M.6M solvent B O-H stretch x m =.2 2 C D x m =.4 Normalized Intensity E F G H x m =.6 x m =.8 2 I x m = Raman shift (cm -1 ) Figure S4: Pure solvent spectra (dashed curves) are compared with TBA SC spectra, normalized to the same TBA C-H area, showing the (A, C, E, G, I) C-D and (B, D, F, H) O-H vibrational bands. Solutions contained TBA concentrations of.1 M (red),.2 M (orange),.3 M (green),.4 M (sky blue), and.6 M (blue) in MeOH-d3/water solvent with (A & B) x m =.2, (C & D).4, (E & F).6, (G & H).8, and (I) 1.. S7

8 Asymmetric CH stretch peak Symmetric CH stretch peak Raman shift (cm -1 ) Mole fraction of MeOH x m Figure S5: Frequency shifts of the symmetric and asymmetric CH stretch peaks of TBA, 26 plotted as a function of x m.the dashed straight lines are drawn connecting the two data points at x m =.2 and A 2 B Solvation Shell Depletion (%) x m = Concentration of TBA (M) Figure S6: Comparison of solvation shell depletion percentages of (A) SC CD (2-24 cm 1 ) and (B) SC OH ( cm 1 ) regions, obtained from Raman-SMCR of TBA in MeOH-d3/water mixtures with x m varying. to 1. (TBA-d9 in the case of x m =.). Solid lines are linear fits to the data points at each x m S8

9 Preferential binding coefficient Γ Dimer Monomer.6 12 A B C D r (nm) Figure S7: The preferential binding coefficients (Γ) for the TBA dimer and monomer as a function of the cut-off distance r at (A) x m =.2, (B).4, (C).6 and (D).8. The intermolecular distance (d) of TBA molecules is constrained at.6 nm (a dimer) and 1.6 nm (two monomers). The force field is G53A6 + SPC/E S9

10 References (1) H.J.C.Berendsen,; van der Spoel, D.; van Drunen, R. Comp. Phys. Comm. 1995, 91, (2) Hub, J. S.; de Groot, B. L.; van der Spoel, D. J. Chem. Theory Comp. 21, 6, (3) Czaplewski, C.; Liwo, A.; Ripoll, D. R.; Scheraga, H. A. J. Phys. Chem. B 25, 19, (4) Matsumoto, M. J. Phys. Chem. Lett. 21, 1, (5) Mochizuki, K.; Sumi, T.; Koga, K. Sci. Rep. 216, 6, (6) Parrinello, M.; Rahman, A. J. Appl. Phys. 1981, 52, (7) Nosé, S. Mol. Phys. 1984, 52, (8) W.G.Hoover, Phys. Rev. A 1985, 31, (9) Berendsen, H. J. C.; Postma, J. P. M.; van Gunsteren, W. F.; DiNola, A.; Haak, J. R. J. Chem. Phys. 1984, 81, (1) Martin, M. G.; Siepmann, J. I. J. Phys. Chem. B 1998, 12, (11) Martin, M. G.; Siepmann, J. I. J. Phys. Chem. B 1999, 13, (12) Abascal, J. L. F.; Vega, C. J. Chem. Phys. 25, 123, (13) Ashbaugh, H. S.; Liu, L.; Surampudi, L. N. J. Chem. Phys. 211, 135, (14) Ashbaugh, H. S.; Collett, N. J.; Hatch, H. W.; Staton, J. A. J. Chem. Phys. 21, 132, S1

11 (15) Oostenbrink, C.; Villa, A.; Mark, A. E.; van Gunsteren, W. F. J. Comput. Chem. 24, 25, (16) Berendsen, H. J. C.; Grigera, J. R.; Straatsma, T. P. J. Phys. Chem. 1987, 91, (17) Gupta, R.; Patey, G. N. J. Chem. Phys. 212, 137, (18) Gupta, R.; Patey, G. N. J. Phys. Chem. B 211, 115, (19) Gupta, R.; Patey, G. N. J. Mol. Liq. 213, 177, (2) Gupta, R.; Patey, G. N. J. Chem. Phys. 214, 141, (21) T.Darden,; D.York,; L.Pedersen, J. Chem. Phys. 1993, 98, 189. (22) Davis, J. G.; Gierszal, K. P.; Wang, P.; Ben-Amotz, D. Nature 212, 491, (23) Davis, J. G.; Rankin, B. M.; Gierszal, K. P.; Ben-Amotz, D. Nat. Chem. 213, 5, (24) Lawton, W. H.; Sylvestre, E. A. Technometrics 1971, 13, (25) Fega, K. R.; Wilcox, D. S.; Ben-Amotz, D. Appl. Spectrosc. 212, 66, (26) Wilcox, D. S.; Rankin, B. M.; Ben-Amotz, D. Faraday Discuss. 213, 167, S11

Supporting Information

Supporting Information Structure and Dynamics of Uranyl(VI) and Plutonyl(VI) Cations in Ionic Liquid/Water Mixtures via Molecular Dynamics Simulations Katie A. Maerzke, George S. Goff, Wolfgang H. Runde,