Mark Maroncelli | The Pennsylvania State University (original) (raw)
Papers by Mark Maroncelli
![Research paper thumbnail of 2-Cyano-3-(2,3,6,7-tetrahydro-1 H ,5 H -benzo[ ij ]quinolizin-9-yl)prop-2-enoic acid dimethyl sulfoxide monosolvate](https://attachments.academia-assets.com/75997196/thumbnails/1.jpg)
](Acta Crystallographica Section E Structure Reports Online, 2012
In dimethyl sulfoxide solvated 9-(2-carboxy-2-cyanovinyl)julolidine, C 16 H 16 N 2 O 2 ÁC 2 H 6 O... more In dimethyl sulfoxide solvated 9-(2-carboxy-2-cyanovinyl)julolidine, C 16 H 16 N 2 O 2 ÁC 2 H 6 OS, the essentially planar-CH (CN)-CO 2 H substituent (r.m.s. deviation = 0.014 Å) is almost coplanar with respect to the benzene ring, the dihedral angle between the two planes being 0.48 (2). The conformations of the fused, non-aromatic rings were found to be halfchair. In the crystal, the acid molecule forms a hydrogen bond to the O atom of the solvent molecule. The acid molecule is disordered over two positions with respect to the methylene C atoms in a 1:1 ratio. The crystal studied was found to be a racemic twin. Related literature For the synthesis of 9-(2-carboxy-2-cyanovinyl)julolidine, commonly known as CCVJ, see: Rumble et al. (2012). For a related molecule, see: Liang et al. (2009). For fluorescent-rotor probe studies of CCVJ, see:
The Journal of Physical Chemistry B
The Journal of Physical Chemistry
... (Refemng to Figure 2, AvaH measures the vertical displacement of the absorption regression li... more ... (Refemng to Figure 2, AvaH measures the vertical displacement of the absorption regression line from the respective 1-propanol point, and similarly for AyeH.) Under the assumption ... time P probe solute (v),bS (I&, #em N -&bs -Sem AS AYabs Avem AAv AvaH AyeH ~(0) - Y(-) ...
The Journal of Physical Chemistry B, Dec 22, 2011
Steady-state and picosecond time-resolved emission spectroscopy are used to monitor the bimolecul... more Steady-state and picosecond time-resolved emission spectroscopy are used to monitor the bimolecular electron transfer reaction between the electron acceptor 9,10-dicyanoanthracene in its S(1) state and the donor N,N-dimethylaniline in a variety of ionic liquids and several conventional solvents. Detailed study of this quenching reaction was undertaken in order to better understand why rates reported for similar diffusion-limited reactions in ionic liquids sometimes appear much higher than expected given the viscous nature of these liquids. Consistent with previous studies, Stern-Volmer analyses of steady-state and lifetime data provide effective quenching rate constants k(q), which are often 10-100-fold larger than simple predictions for diffusion-limited rate constants k(D) in ionic liquids. Similar departures from k(D) are also observed in conventional organic solvents having comparably high viscosities, indicating that this behavior is not unique to ionic liquids. A more complete analysis of the quenching data using a model combining approximate solution of the spherically symmetric diffusion equation with a Marcus-type description of electron transfer reveals the reasons for frequent observation of k(q) ≫ k(D). The primary cause is that the high viscosities typical of ionic liquids emphasize the transient component of diffusion-limited reactions, which renders the interpretation of rate constants derived from Stern-Volmer analyses ambiguous. Using a more appropriate description of the quenching process enables satisfactory fits of data in both ionic liquid and conventional solvents using a single set of physically reasonable electron transfer parameters. Doing so requires diffusion coefficients in ionic liquids to exceed hydrodynamic predictions by significant factors, typically in the range of 3-10. Direct, NMR measurements of solute diffusion confirm this enhanced diffusion in ionic liquids.
The Journal of Physical Chemistry B, 1999
Monte Carlo simulations of the pyridinium N-phenolate dye "betaine-30" in 12 solvents (20 solvent... more Monte Carlo simulations of the pyridinium N-phenolate dye "betaine-30" in 12 solvents (20 solvent representations) were performed in order to explore the molecular basis of the E T (30) scale of solvent polarity. Ab initio (HF/6-31G*) and semiempirical (AM1 and INDO/S) electronic structure calculations were used to determine the geometry and charge distribution of betaine-30 in its S 0 and S 1 states. The solvent effect on the betaine absorption spectrum was assumed to derive from electrostatic interactions between the effective charge distributions of solvent molecules and the charge shift brought about by the S 0 f S 1 transition. Two models for this charge shift, one obtained from INDO/S calculations and the other an idealized two-site model, were used for the spectral calculations. Good agreement between simulated and observed ∆E T shifts (E T (30) values measured relative to the nonpolar standard tetramethylsilane) was found for both charge-shift models. In water and other hydroxylic solvents, the O atom of the betaine solute was observed to form moderately strong hydrogen bonds to between one and two solvent molecules. The contribution of these specifically coordinated molecules to the ∆E T shift was found to be large, (30-60%) and comparable to experimental estimates. Additional simulations of acetonitrile and methanol in equilibrium with the S 1 state of betaine-30 were used to determine reorganization energies in these solvents and to decide the extent to which the solvent response to the S 0 T S 1 transition conforms to linear response predictions. In both solvents, the spectral distributions observed in the S 0 state simulations were ∼15% narrower than those in the S 1 simulations, indicating only a relatively small departure from linear behavior. Reorganization energies were also estimated for a number of other solvents and compared to values reported in previous experimental and theoretical studies.
The Journal of Physical Chemistry B, 2013
The dynamic Stokes shift of coumarin 153, measured with a combination of broad-band fluorescence ... more The dynamic Stokes shift of coumarin 153, measured with a combination of broad-band fluorescence upconversion (80 fs resolution) and time-correlated single photon counting (to 20 ns), is used to determine the complete solvation response of 21 imidazolium, pyrrolidinium, and assorted other ionic liquids. The response functions so obtained show a clearly bimodal character consisting of a subpicosecond component, which accounts for 10-40% of the response, and a much slower component relaxing over a broad range of times. The times associated with the fast component correlate with ion mass, confirming its origins in inertial solvent motions. Consistent with many previous studies, the slower component is correlated to solvent viscosity, indicating that its origins lie in diffusive, structural reorganization of the solvent. Comparisons of observed response functions to the predictions of a simple dielectric continuum model show that, as in dipolar solvents, solvation and dielectric relaxation involve closely related molecular dynamics. However, in contrast to dipolar solvents, dielectric continuum predictions systematically underestimate solvation times by factors of at least 2-4.
The Journal of Physical Chemistry A, 1997
... MP Heitz and M. Maroncelli*. Department of Chemistry, The Pennsylvania State University, 152 ... more ... MP Heitz and M. Maroncelli*. Department of Chemistry, The Pennsylvania State University, 152 Davey Lab, University Park, Pennsylvania 16802. J. Phys. Chem. A , 1997, 101 (33), pp 58525868. DOI: 10.1021/jp971096v. Publication ...
The Journal of Physical Chemistry Letters, 2013
It was shown recently that a simple dielectric continuum model predicts the integral solvation ti... more It was shown recently that a simple dielectric continuum model predicts the integral solvation time of a dipolar solute ⟨τsolv⟩ to be inversely proportional to the electrical conductivity σ0 of an ionic solvent or solution. In this Letter, we provide a more general derivation of this connection and show that available data on coumarin 153 (C153) in ionic liquids generally support this prediction. The relationship between solvation time and conductivity can be expressed by ln(⟨τsolv⟩/ps) = 4.37 - 0.92 ln (σ0/S m(-1)) in 34 common ionic liquids.
The Journal of Chemical Physics, 1993
ABSTRACT
The Journal of Chemical Physics, 2000
Simulations of the time-dependent friction controlling rotational, translational, and vibrational... more Simulations of the time-dependent friction controlling rotational, translational, and vibrational motions of dipolar diatomic solutes in acetonitrile and methanol have been used to examine the nature of ``dielectric'' friction. The way in which electrical interactions increase the friction beyond that present in nonpolar systems is found to be rather different than what is anticipated by most theories of dielectric friction. Long-range electrostatic forces do not simply add an independent contribution to the friction due to short-ranged or ``mechanical'' sources (modeled here in terms of Lennard-Jones forces). Rather, the electrical and Lennard-Jones contributions are found to be strongly anticorrelated and not separable in any useful way. For some purposes, the mechanism by which electrical interactions increase friction is better viewed as a static electrostriction effect: electrical forces cause a subtle increase in atomic density in the solute's first solvation shell, which increases the amplitude of the force fluctuations derived from the Lennard-Jones interactions, i.e., the mechanical friction. However, electrical interactions also modify the dynamics of the friction, typically adding a long-time tail, which significantly increases the integral friction. Both of these effects must be included in a correct description of friction in the presence of polar interactions.
The Journal of Chemical Physics, 2006
Computer simulations are used to study solvation free energies and solubilities in supercritical ... more Computer simulations are used to study solvation free energies and solubilities in supercritical solvents. Solvation free energies are calculated using the particle insertion method. The equilibrium solvent configurations required for these calculations are based on molecular dynamics simulations employing model solvent potentials previously tuned to reproduce liquid-vapor coexistence properties of the fluids Xe, C(2)H(6), CO(2), and CHF(3). Solutes are represented by all-atom potentials based on ab initio calculations and the OPLS-AA parameter set. Without any tuning of the intermolecular potentials, such calculations are found to reproduce the solvation free energies of a variety of typical solid solutes with an average accuracy of +/-2 kJmol. Further calculations on simple model solutes are also used to explore general aspects of solvation free energies in supercritical solvents. Comparisons of solutes in Lennard-Jones and hard-sphere representations of Xe show that solvation free energies and thus solubilities are not significantly influenced by solvent density fluctuations near the critical point. The solvation enthalpy and entropy do couple to these fluctuations and diverge similarly to solute partial molar volumes. Solvation free energies are also found to be little affected by the local density augmentation characteristic of the compressible regime. In contrast to solute-solvent interaction energies, which often provide a direct measure of local solvent densities, solvation free energies are remarkably insensitive to the presence of local density augmentation.
Faraday Discussions, 2012
The complete solvation response of coumarin 153 (C153) has been determined over the range 10(-13)... more The complete solvation response of coumarin 153 (C153) has been determined over the range 10(-13)-10(-8) s in a variety of ionic liquids by combining femtosecond broad-band fluorescence upconversion and picosecond time-correlated single photon counting measurements. These data are used together with recently reported dielectric data in eight ionic liquids to test the accuracy of a simple continuum model for predicting solvation dynamics. In most cases the features of the solvation response functions predicted by the dielectric continuum model are similar to the measured dynamics of C153. The predicted dynamics are, however, systematically faster than those observed, on average by a factor of 3-5. Computer simulations of a model solute/ionic liquid system also exhibit the same relationship between dielectric predictions and observed dynamics. The simulations point to spatial dispersion of the polarization response as an important contributor to the over-prediction of solvation rates in ionic liquids.
Chemical Physics Letters, 1999
Equilibrium and nonequilibrium solvation properties as measured by the Stokes shift of coumarin 1... more Equilibrium and nonequilibrium solvation properties as measured by the Stokes shift of coumarin 153 are reported for a series of acetonitrilerpropylene carbonate binary mixtures at room temperature. Steady-state spectroscopy shows that the solvent reorganization energy is independent of composition in this mixture. Solvation and rotational times vary nearly tenfold between the pure solvent limits, in a manner that is correlated to bulk solution viscosity. The wide range of solvation times together with the constant solvent reorganization energy should render this binary system useful for investigating dynamical solvent effects on charge-transfer processes.
Annual Review of Physical Chemistry, 2011
Ionic liquids are subjects of intense current interest within the physical chemistry community. A... more Ionic liquids are subjects of intense current interest within the physical chemistry community. A great deal of progress has been made in just the past five years toward identifying the factors that cause these salts to have low melting points and other useful properties. Supramolecular structure and organization have emerged as important and complicated topics that may be key to
The Journal of Physical Chemistry B, 2016
Table of Contents: 1. Simulation methodology used for benzene simulations in [Im41][BF4]. 2. Fig.... more Table of Contents: 1. Simulation methodology used for benzene simulations in [Im41][BF4]. 2. Fig. SI-1: Correlation between rotation times of benzene in ionic liquids and average ion volumes. 15. Fig. SI-12: Relative mean squared torques on charge-modified benzene solutes in ILM2 (350 K).
The Journal of Physical Chemistry B, 2013
Diffusion coefficients of a variety of dilute solutes in the series of 1-alkyl-1-methylpyrrolidin... more Diffusion coefficients of a variety of dilute solutes in the series of 1-alkyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imides ([Prn1][Tf2N], n = 3, 4, 6, 8, and 10), trihexyltetracedecylphosphonium bis(trifluoromethanesulfonyl)imide [P14,666][Tf2N], and assorted imidazolium ionic liquids are measured using pulsed field gradient (1)H NMR. These data, combined with available literature data, are used to try to uncover the solute and solvent characteristics most important in determining tracer diffusion rates. Discussion is framed in terms of departures from simple hydrodynamic predictions for translational friction using the ratio ζobs/ζSE, where ζobs is the observed friction, determined from the measured diffusion coefficient D via ζobs = kBT/D, and ζSE = 6πηR is the Stokes friction on a sphere of radius R (determined from the solute van der Waals volume) in a solvent with viscosity η. In the case of neutral solutes, the primary determinant of whether hydrodynamic predictions are accurate is the relative size of solute versus solvent molecules. A single correlation, albeit with considerable scatter, is found between ζobs/ζSE and the ratio of solute-to-solvent van der Waals volumes, ζobs/ζSE = {1 + a(VU/VV)(-p)}, with constants a = 1.93 and p = 1.88. In the case of small solutes, the observed friction is over 100-fold smaller than predictions of hydrodynamic models. The dipole moment of the solute has little effect on the friction, whereas solute charge has a marked effect. For monovalent solutes of size comparable to or smaller than the solvent ions, the observed friction is comparable to or even greater than what is predicted by hydrodynamics. These general trends are shown to be quite similar to what is observed for tracer diffusion in conventional solvents.
The Journal of Physical Chemistry B, 2013
Diffusion coefficients of a variety of dilute solutes in the series of 1-alkyl-1-methylpyrrolidin... more Diffusion coefficients of a variety of dilute solutes in the series of 1-alkyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imides ([Prn1][Tf2N], n = 3, 4, 6, 8, and 10), trihexyltetracedecylphosphonium bis(trifluoromethanesulfonyl)imide [P14,666][Tf2N], and assorted imidazolium ionic liquids are measured using pulsed field gradient (1)H NMR. These data, combined with available literature data, are used to try to uncover the solute and solvent characteristics most important in determining tracer diffusion rates. Discussion is framed in terms of departures from simple hydrodynamic predictions for translational friction using the ratio ζobs/ζSE, where ζobs is the observed friction, determined from the measured diffusion coefficient D via ζobs = kBT/D, and ζSE = 6πηR is the Stokes friction on a sphere of radius R (determined from the solute van der Waals volume) in a solvent with viscosity η. In the case of neutral solutes, the primary determinant of whether hydrodynamic predictions are accurate is the relative size of solute versus solvent molecules. A single correlation, albeit with considerable scatter, is found between ζobs/ζSE and the ratio of solute-to-solvent van der Waals volumes, ζobs/ζSE = {1 + a(VU/VV)(-p)}, with constants a = 1.93 and p = 1.88. In the case of small solutes, the observed friction is over 100-fold smaller than predictions of hydrodynamic models. The dipole moment of the solute has little effect on the friction, whereas solute charge has a marked effect. For monovalent solutes of size comparable to or smaller than the solvent ions, the observed friction is comparable to or even greater than what is predicted by hydrodynamics. These general trends are shown to be quite similar to what is observed for tracer diffusion in conventional solvents.
Acta Crystallographica Section E Structure Reports Online, 2012
In dimethyl sulfoxide solvated 9-(2-carboxy-2-cyanovinyl)julolidine, C 16 H 16 N 2 O 2 ÁC 2 H 6 O... more In dimethyl sulfoxide solvated 9-(2-carboxy-2-cyanovinyl)julolidine, C 16 H 16 N 2 O 2 ÁC 2 H 6 OS, the essentially planar-CH (CN)-CO 2 H substituent (r.m.s. deviation = 0.014 Å) is almost coplanar with respect to the benzene ring, the dihedral angle between the two planes being 0.48 (2). The conformations of the fused, non-aromatic rings were found to be halfchair. In the crystal, the acid molecule forms a hydrogen bond to the O atom of the solvent molecule. The acid molecule is disordered over two positions with respect to the methylene C atoms in a 1:1 ratio. The crystal studied was found to be a racemic twin. Related literature For the synthesis of 9-(2-carboxy-2-cyanovinyl)julolidine, commonly known as CCVJ, see: Rumble et al. (2012). For a related molecule, see: Liang et al. (2009). For fluorescent-rotor probe studies of CCVJ, see:
The Journal of Physical Chemistry B
The Journal of Physical Chemistry
... (Refemng to Figure 2, AvaH measures the vertical displacement of the absorption regression li... more ... (Refemng to Figure 2, AvaH measures the vertical displacement of the absorption regression line from the respective 1-propanol point, and similarly for AyeH.) Under the assumption ... time P probe solute (v),bS (I&, #em N -&bs -Sem AS AYabs Avem AAv AvaH AyeH ~(0) - Y(-) ...
The Journal of Physical Chemistry B, Dec 22, 2011
Steady-state and picosecond time-resolved emission spectroscopy are used to monitor the bimolecul... more Steady-state and picosecond time-resolved emission spectroscopy are used to monitor the bimolecular electron transfer reaction between the electron acceptor 9,10-dicyanoanthracene in its S(1) state and the donor N,N-dimethylaniline in a variety of ionic liquids and several conventional solvents. Detailed study of this quenching reaction was undertaken in order to better understand why rates reported for similar diffusion-limited reactions in ionic liquids sometimes appear much higher than expected given the viscous nature of these liquids. Consistent with previous studies, Stern-Volmer analyses of steady-state and lifetime data provide effective quenching rate constants k(q), which are often 10-100-fold larger than simple predictions for diffusion-limited rate constants k(D) in ionic liquids. Similar departures from k(D) are also observed in conventional organic solvents having comparably high viscosities, indicating that this behavior is not unique to ionic liquids. A more complete analysis of the quenching data using a model combining approximate solution of the spherically symmetric diffusion equation with a Marcus-type description of electron transfer reveals the reasons for frequent observation of k(q) ≫ k(D). The primary cause is that the high viscosities typical of ionic liquids emphasize the transient component of diffusion-limited reactions, which renders the interpretation of rate constants derived from Stern-Volmer analyses ambiguous. Using a more appropriate description of the quenching process enables satisfactory fits of data in both ionic liquid and conventional solvents using a single set of physically reasonable electron transfer parameters. Doing so requires diffusion coefficients in ionic liquids to exceed hydrodynamic predictions by significant factors, typically in the range of 3-10. Direct, NMR measurements of solute diffusion confirm this enhanced diffusion in ionic liquids.
The Journal of Physical Chemistry B, 1999
Monte Carlo simulations of the pyridinium N-phenolate dye "betaine-30" in 12 solvents (20 solvent... more Monte Carlo simulations of the pyridinium N-phenolate dye "betaine-30" in 12 solvents (20 solvent representations) were performed in order to explore the molecular basis of the E T (30) scale of solvent polarity. Ab initio (HF/6-31G*) and semiempirical (AM1 and INDO/S) electronic structure calculations were used to determine the geometry and charge distribution of betaine-30 in its S 0 and S 1 states. The solvent effect on the betaine absorption spectrum was assumed to derive from electrostatic interactions between the effective charge distributions of solvent molecules and the charge shift brought about by the S 0 f S 1 transition. Two models for this charge shift, one obtained from INDO/S calculations and the other an idealized two-site model, were used for the spectral calculations. Good agreement between simulated and observed ∆E T shifts (E T (30) values measured relative to the nonpolar standard tetramethylsilane) was found for both charge-shift models. In water and other hydroxylic solvents, the O atom of the betaine solute was observed to form moderately strong hydrogen bonds to between one and two solvent molecules. The contribution of these specifically coordinated molecules to the ∆E T shift was found to be large, (30-60%) and comparable to experimental estimates. Additional simulations of acetonitrile and methanol in equilibrium with the S 1 state of betaine-30 were used to determine reorganization energies in these solvents and to decide the extent to which the solvent response to the S 0 T S 1 transition conforms to linear response predictions. In both solvents, the spectral distributions observed in the S 0 state simulations were ∼15% narrower than those in the S 1 simulations, indicating only a relatively small departure from linear behavior. Reorganization energies were also estimated for a number of other solvents and compared to values reported in previous experimental and theoretical studies.
The Journal of Physical Chemistry B, 2013
The dynamic Stokes shift of coumarin 153, measured with a combination of broad-band fluorescence ... more The dynamic Stokes shift of coumarin 153, measured with a combination of broad-band fluorescence upconversion (80 fs resolution) and time-correlated single photon counting (to 20 ns), is used to determine the complete solvation response of 21 imidazolium, pyrrolidinium, and assorted other ionic liquids. The response functions so obtained show a clearly bimodal character consisting of a subpicosecond component, which accounts for 10-40% of the response, and a much slower component relaxing over a broad range of times. The times associated with the fast component correlate with ion mass, confirming its origins in inertial solvent motions. Consistent with many previous studies, the slower component is correlated to solvent viscosity, indicating that its origins lie in diffusive, structural reorganization of the solvent. Comparisons of observed response functions to the predictions of a simple dielectric continuum model show that, as in dipolar solvents, solvation and dielectric relaxation involve closely related molecular dynamics. However, in contrast to dipolar solvents, dielectric continuum predictions systematically underestimate solvation times by factors of at least 2-4.
The Journal of Physical Chemistry A, 1997
... MP Heitz and M. Maroncelli*. Department of Chemistry, The Pennsylvania State University, 152 ... more ... MP Heitz and M. Maroncelli*. Department of Chemistry, The Pennsylvania State University, 152 Davey Lab, University Park, Pennsylvania 16802. J. Phys. Chem. A , 1997, 101 (33), pp 58525868. DOI: 10.1021/jp971096v. Publication ...
The Journal of Physical Chemistry Letters, 2013
It was shown recently that a simple dielectric continuum model predicts the integral solvation ti... more It was shown recently that a simple dielectric continuum model predicts the integral solvation time of a dipolar solute ⟨τsolv⟩ to be inversely proportional to the electrical conductivity σ0 of an ionic solvent or solution. In this Letter, we provide a more general derivation of this connection and show that available data on coumarin 153 (C153) in ionic liquids generally support this prediction. The relationship between solvation time and conductivity can be expressed by ln(⟨τsolv⟩/ps) = 4.37 - 0.92 ln (σ0/S m(-1)) in 34 common ionic liquids.
The Journal of Chemical Physics, 1993
ABSTRACT
The Journal of Chemical Physics, 2000
Simulations of the time-dependent friction controlling rotational, translational, and vibrational... more Simulations of the time-dependent friction controlling rotational, translational, and vibrational motions of dipolar diatomic solutes in acetonitrile and methanol have been used to examine the nature of ``dielectric'' friction. The way in which electrical interactions increase the friction beyond that present in nonpolar systems is found to be rather different than what is anticipated by most theories of dielectric friction. Long-range electrostatic forces do not simply add an independent contribution to the friction due to short-ranged or ``mechanical'' sources (modeled here in terms of Lennard-Jones forces). Rather, the electrical and Lennard-Jones contributions are found to be strongly anticorrelated and not separable in any useful way. For some purposes, the mechanism by which electrical interactions increase friction is better viewed as a static electrostriction effect: electrical forces cause a subtle increase in atomic density in the solute's first solvation shell, which increases the amplitude of the force fluctuations derived from the Lennard-Jones interactions, i.e., the mechanical friction. However, electrical interactions also modify the dynamics of the friction, typically adding a long-time tail, which significantly increases the integral friction. Both of these effects must be included in a correct description of friction in the presence of polar interactions.
The Journal of Chemical Physics, 2006
Computer simulations are used to study solvation free energies and solubilities in supercritical ... more Computer simulations are used to study solvation free energies and solubilities in supercritical solvents. Solvation free energies are calculated using the particle insertion method. The equilibrium solvent configurations required for these calculations are based on molecular dynamics simulations employing model solvent potentials previously tuned to reproduce liquid-vapor coexistence properties of the fluids Xe, C(2)H(6), CO(2), and CHF(3). Solutes are represented by all-atom potentials based on ab initio calculations and the OPLS-AA parameter set. Without any tuning of the intermolecular potentials, such calculations are found to reproduce the solvation free energies of a variety of typical solid solutes with an average accuracy of +/-2 kJmol. Further calculations on simple model solutes are also used to explore general aspects of solvation free energies in supercritical solvents. Comparisons of solutes in Lennard-Jones and hard-sphere representations of Xe show that solvation free energies and thus solubilities are not significantly influenced by solvent density fluctuations near the critical point. The solvation enthalpy and entropy do couple to these fluctuations and diverge similarly to solute partial molar volumes. Solvation free energies are also found to be little affected by the local density augmentation characteristic of the compressible regime. In contrast to solute-solvent interaction energies, which often provide a direct measure of local solvent densities, solvation free energies are remarkably insensitive to the presence of local density augmentation.
Faraday Discussions, 2012
The complete solvation response of coumarin 153 (C153) has been determined over the range 10(-13)... more The complete solvation response of coumarin 153 (C153) has been determined over the range 10(-13)-10(-8) s in a variety of ionic liquids by combining femtosecond broad-band fluorescence upconversion and picosecond time-correlated single photon counting measurements. These data are used together with recently reported dielectric data in eight ionic liquids to test the accuracy of a simple continuum model for predicting solvation dynamics. In most cases the features of the solvation response functions predicted by the dielectric continuum model are similar to the measured dynamics of C153. The predicted dynamics are, however, systematically faster than those observed, on average by a factor of 3-5. Computer simulations of a model solute/ionic liquid system also exhibit the same relationship between dielectric predictions and observed dynamics. The simulations point to spatial dispersion of the polarization response as an important contributor to the over-prediction of solvation rates in ionic liquids.
Chemical Physics Letters, 1999
Equilibrium and nonequilibrium solvation properties as measured by the Stokes shift of coumarin 1... more Equilibrium and nonequilibrium solvation properties as measured by the Stokes shift of coumarin 153 are reported for a series of acetonitrilerpropylene carbonate binary mixtures at room temperature. Steady-state spectroscopy shows that the solvent reorganization energy is independent of composition in this mixture. Solvation and rotational times vary nearly tenfold between the pure solvent limits, in a manner that is correlated to bulk solution viscosity. The wide range of solvation times together with the constant solvent reorganization energy should render this binary system useful for investigating dynamical solvent effects on charge-transfer processes.
Annual Review of Physical Chemistry, 2011
Ionic liquids are subjects of intense current interest within the physical chemistry community. A... more Ionic liquids are subjects of intense current interest within the physical chemistry community. A great deal of progress has been made in just the past five years toward identifying the factors that cause these salts to have low melting points and other useful properties. Supramolecular structure and organization have emerged as important and complicated topics that may be key to
The Journal of Physical Chemistry B, 2016
Table of Contents: 1. Simulation methodology used for benzene simulations in [Im41][BF4]. 2. Fig.... more Table of Contents: 1. Simulation methodology used for benzene simulations in [Im41][BF4]. 2. Fig. SI-1: Correlation between rotation times of benzene in ionic liquids and average ion volumes. 15. Fig. SI-12: Relative mean squared torques on charge-modified benzene solutes in ILM2 (350 K).
The Journal of Physical Chemistry B, 2013
Diffusion coefficients of a variety of dilute solutes in the series of 1-alkyl-1-methylpyrrolidin... more Diffusion coefficients of a variety of dilute solutes in the series of 1-alkyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imides ([Prn1][Tf2N], n = 3, 4, 6, 8, and 10), trihexyltetracedecylphosphonium bis(trifluoromethanesulfonyl)imide [P14,666][Tf2N], and assorted imidazolium ionic liquids are measured using pulsed field gradient (1)H NMR. These data, combined with available literature data, are used to try to uncover the solute and solvent characteristics most important in determining tracer diffusion rates. Discussion is framed in terms of departures from simple hydrodynamic predictions for translational friction using the ratio ζobs/ζSE, where ζobs is the observed friction, determined from the measured diffusion coefficient D via ζobs = kBT/D, and ζSE = 6πηR is the Stokes friction on a sphere of radius R (determined from the solute van der Waals volume) in a solvent with viscosity η. In the case of neutral solutes, the primary determinant of whether hydrodynamic predictions are accurate is the relative size of solute versus solvent molecules. A single correlation, albeit with considerable scatter, is found between ζobs/ζSE and the ratio of solute-to-solvent van der Waals volumes, ζobs/ζSE = {1 + a(VU/VV)(-p)}, with constants a = 1.93 and p = 1.88. In the case of small solutes, the observed friction is over 100-fold smaller than predictions of hydrodynamic models. The dipole moment of the solute has little effect on the friction, whereas solute charge has a marked effect. For monovalent solutes of size comparable to or smaller than the solvent ions, the observed friction is comparable to or even greater than what is predicted by hydrodynamics. These general trends are shown to be quite similar to what is observed for tracer diffusion in conventional solvents.
The Journal of Physical Chemistry B, 2013
Diffusion coefficients of a variety of dilute solutes in the series of 1-alkyl-1-methylpyrrolidin... more Diffusion coefficients of a variety of dilute solutes in the series of 1-alkyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imides ([Prn1][Tf2N], n = 3, 4, 6, 8, and 10), trihexyltetracedecylphosphonium bis(trifluoromethanesulfonyl)imide [P14,666][Tf2N], and assorted imidazolium ionic liquids are measured using pulsed field gradient (1)H NMR. These data, combined with available literature data, are used to try to uncover the solute and solvent characteristics most important in determining tracer diffusion rates. Discussion is framed in terms of departures from simple hydrodynamic predictions for translational friction using the ratio ζobs/ζSE, where ζobs is the observed friction, determined from the measured diffusion coefficient D via ζobs = kBT/D, and ζSE = 6πηR is the Stokes friction on a sphere of radius R (determined from the solute van der Waals volume) in a solvent with viscosity η. In the case of neutral solutes, the primary determinant of whether hydrodynamic predictions are accurate is the relative size of solute versus solvent molecules. A single correlation, albeit with considerable scatter, is found between ζobs/ζSE and the ratio of solute-to-solvent van der Waals volumes, ζobs/ζSE = {1 + a(VU/VV)(-p)}, with constants a = 1.93 and p = 1.88. In the case of small solutes, the observed friction is over 100-fold smaller than predictions of hydrodynamic models. The dipole moment of the solute has little effect on the friction, whereas solute charge has a marked effect. For monovalent solutes of size comparable to or smaller than the solvent ions, the observed friction is comparable to or even greater than what is predicted by hydrodynamics. These general trends are shown to be quite similar to what is observed for tracer diffusion in conventional solvents.