Solute-solvent Combinations Research Articles

Optical Rotation Predictions for Rigid Chiral Solute-Achiral Solvent 1:1 Complexes with the PCM Model

We computed specific optical rotations (ORs) in solution for forty-two solute–solvent combinations, involving seventeen chiral solutes and eight achiral solvents, using cam-B3LYP/aug-cc-PVTZ. Explicit solvent effects were considered by calculating Boltzmann-averaged ORs from multiple conformers of a 1:1 solute–solvent complex, with additional implicit solvation. The PCM solvation model correctly predicted OR signs for all combinations, while the “1:1 complex plus PCM“ schemes misjudged it in two cases. Norbornenone in cyclohexane displayed the largest absolute deviation, indicating an inadequate description of the cam-B3LYP functional’s delocalized electronic structure. Incorrect OR signs for fenchone in methanol with the ”1:1 complex plus PCM“ schemes underscored the limitations of our simplistic scheme, which incorporates explicit effects by averaging one-to-one interactions between solute and solvent. Considering computational costs, the ”1:1 complex plus PCM“ scheme may not be the optimal choice for our test set, as the PCM model alone suffices for accurate specific OR calculations in solution.

Ambiguities in solvation free energies from cluster-continuum quasichemical theory: lithium cation in protic and aprotic solvents.

Gibbs free energies for Li+ solvation in water, methanol, acetonitrile, DMSO, dimethylacetamide, dimethoxyethane, dimethylformamide, gamma-butyrolactone, pyridine, and sulfolane have been calculated using the cluster-continuum quasichemical theory. With n independent solvent molecules S initial state forming the "monomer" thermodynamic cycle, Li+ solvation free energies are found to be on average 14 kcal mol-1 more positive compared to those from the "cluster" thermodynamic cycle where the initial state is the cluster Sn. We ascribe the inconsistency between the "monomer" and "cluster" cycles mainly to the incorrectly predicted solvation free energies of solvent clusters Sn from the SMD and CPCM continuum solvation models, which is in line with the earlier study of Bryantsev et al., J. Phys. Chem. B, 2008, 112, 9709-9719. When experimental-based solvation free energies of individual solvent molecules and solvent clusters are employed, the "monomer" and "cluster" cycles result in identical numbers. The best overall agreement with experimental-based "bulk" scale lithium cation solvation free energies was obtained for the "monomer" scale, and we recommend this set of values. We expect that further progress in the field is possible if (i) consensus on the accuracy of experimental reference values is achieved; (ii) the most recent continuum solvation models are properly parameterized for all solute-solvent combinations and become widely accessible for testing.

Impact of varying preparation methods of colloidal suspensions on droplet desiccation patterns on hydrophobic and hydrophilic substrates

The patterns left by desiccating droplets of colloidal solutions form an integral part of a gamut of applications in technology, medicine and fundamental science. While almost all attention is reserved for understanding flow dynamics of drying droplets and the resulting dried droplet pattern with respect to variation of a host of parameters, there is almost a total absence of any discussion on the importance of the ‘mixing methods’ of solute and solvent during solution preparation. We demonstrate in this work, that desiccation patterns of colloidal solutions show an amazing variation in details, depending on the manner of solution preparation. The variation is achieved by simple mechanical treatment, namely magnetic stirring and ultrasonication, and for different stirring times. The suitable explanation of the striking variation in the dried droplets on both hydrophilic and hydrophobic substrates lead us to propose that the stirring time corresponding to a particular method adopted for solution preparation, results in varying degrees of paring of aggregates. We establish that a homogeneous colloidal solution can only be achieved by mixing for a minimum time t std , that is a function of a particular mixing procedure and a given solute-solvent combination. The prepared solution may then be used in different applications to obtain faithful standard results.

Diffusion of Polymethylene Chain Molecules in Nonpolar Solvents.

The translational diffusion constants, D, for solutes with polymethylene chains are compared with the predictions of a hydrodynamic bead model based on Kirkwood-Riseman theory. The solute-solvent combinations include (a) n-alkanes in n-alkanes; (b) n-alkanes in benzene, toluene, tetralin, decalin, and CCl4; (c) 1-alkenes in n-alkanes; (d) 1-phenylalkanes in n-alkanes; and (e) 1-phenylalkanes in isocetane (2,2,4,4,6,8,8-heptamethylnonane), pristane (2,6,10,14-tetramethylpentadecane), and squalane (2,6,10,15,19,23-hexamethyltetracosane). The bead model gives good overall agreement with an average difference of less than 3% between 207 experimental and calculated diffusion constants that include published data as well as new D values determined for 1-alkenes and 1-phenylalkanes using capillary flow techniques. The calculated values are obtained using chain element (bead) radii that decrease as the solvent viscosity increases. The bead model's results are comparable to those obtained using cylinder and lollipop diffusion for many of the same solute-solvent systems; the three models are compared and discussed. The results for the 1-alkenes and n-alkanes in the n-alkanes are the first from a Kirkwood-Riseman analysis in a homologous series of solvents.

Solubility determination of raloxifene hydrochloride in ten pure solvents at various temperatures: Thermodynamics-based analysis and solute–solvent interactions

The purpose of the present study was to determine the solubility of raloxifene hydrochloride (RHCl) in ten solvents: water, ethanol, isopropyl alcohol (IPA), ethylene glycol (EG), propylene glycol (PG), polyethylene glycol-400 (PEG-400), Transcutol, 1-butanol, dimethyl sulfoxide (DMSO), and ethyl acetate (EA) at temperatures of 298.2–323.2 K and a pressure of 0.1 MPa. The solubility data obtained was fitted upon “Apelblat and Van't Hoff” equations. The maximum mole fraction solubility of RHCl was obtained in DMSO (5.02 × 10−2 at 323.2 K), followed by PEG-400 (5.92 × 10−3 at 323.2 K), EA (3.11 × 10−3 at 323.2 K), Transcutol (1.22 × 10−3 at 323.2 K), PG (2.19 × 10−4 at 323.2 K), 1-butanol (1.96 × 10−4 at 323.2 K), IPA (1.47 × 10−4 at 323.2 K), ethanol (7.90 × 10−5 at 323.2 K), EG (6.65 × 10−5 at 323.2 K), and water (3.60 × 10−5 at 323.2 K). Similar fashions were noticed at each studied temperature. The higher solubility of RHCl in DMSO, PEG-400, EA, and Transcutol was possibly referable to their lower polarity in comparison with water. The molecular interactions between the solute and solvent molecules were estimated by calculating parameters like activity coefficients, and more prominent solute–solvent molecular interactions were noted for RHCl–DMSO, RHCl–EA, and RHCl–PEG-400 in comparison with the other solute–solvent combinations. The outcomes of the “apparent thermodynamic analysis” showed that the dissolution of RHCl was “endothermic, spontaneous and entropy-driven” in all investigated solvents. The obtained solubility data of RHCl in commonly used solvents could be useful in the purification, recrystallization, and dosage form design of the drug.

Solubility, molecular interactions and mixing thermodynamic properties of piperine in various pure solvents at different temperatures

In this study, the solubility, molecular interactions and mixing thermodynamic properties of a poorly water soluble bioactive compound piperine in twelve different pure solvents namely “water, methanol, ethanol, isopropyl alcohol (IPA), ethylene glycol (EG), propylene glycol (PG), 1-butanol, 2-butanol, ethyl acetate (EA), dimethyl sulfoxide (DMSO), polyethylene glycol-400 (PEG-400) and 2-(2-ethoxyethoxy) ethanol [Transcutol®]” were evaluated. The solubility of piperine was determined at temperatures “T=298.2K to 318.2K” and pressure “p=0.1MPa”. The experimental solubility values of piperine were determined using a static equilibrium method by high-performance liquid chromatography at 254nm. The solubility data of piperine obtained in this study was regressed using “van't Hoff and Apelblat models” with root mean square deviation values of <5.0%. The solubilities of piperine in mole fraction were obtained maximum in Transcutol (9.17×10−2) followed by PEG-400 (7.88×10−2), DMSO (3.59×10−3), 2-butanol (2.25×10−2), 1-butanol (2.20×10−2), IPA (1.82×10−2), EA (1.54×10−2), PG (1.47×10−2), ethanol (1.34×10−2), methanol (7.91×10−3), EG (6.70×10−3) and water (1.52×10−5) at “T=318.2K”. Based on the results of activity coefficient, the solute-solvent interaction was seen maximum in piperine-Transcutol and piperine-PEG-400 in comparison with other solute-solvent combination studied. Mixing thermodynamic properties of piperine were determined by activity coefficient model and results indicated spontaneous and entropy-driven dissolution of piperine in most of the pure solvents studied.

Solubility measurement, thermodynamics and molecular interactions of flufenamic acid in different neat solvents

The solubility data of poorly soluble anti-inflammatory drug flufenamic acid (FFA) are scarce in literature. Therefore, in the current study, the solubility of FFA in eleven different neat solvents including “water, methanol, ethanol, isopropanol (IPA), ethylene glycol (EG), propylene glycol (PG), 1-butanol, 2-butanol, dimethyl sulfoxide (DMSO), polyethylene glycol-400 (PEG-400) and Transcutol®” was measured and correlated at temperatures “T=298.2K to 318.2K” and pressure “p=0.1MPa”. The solubilities of FFA in mole fraction were measured using a static equilibrium method and correlated with “van't Hoff and Apelblat equations”. The mole fraction solubilities of FFA were obtained maximum in DMSO (2.86×10−1), followed by Transcutol (2.78×10−1), 2-butanol (1.79×10−1), 1-butanol (1.77×10−1), IPA (1.44×10−1), ethanol (1.12×10−1), methanol (6.29×10−2), PEG-400 (6.16×10−2), EG (1.20×10−2), PG (1.81×10−2) and water (1.60×10−6) at “T=318.2K” and similar trends were also recorded at each temperature studied. Activity coefficients were also calculated in order to evaluate the molecular interactions between solute and solvent molecules and results showed higher solute-solvent molecular interactions in FFA-DMSO, FFA-Transcutol, FFA-2-butanol, FFA-1-butanol, FFA-IPA and FFA-ethanol in comparison with other solute-solvent combinations. “Apparent thermodynamic analysis” showed an “endothermic and entropy-driven dissolution” of FFA in all neat solvents studied.

Stable colloids in molten inorganic salts.

A colloidal solution is a homogeneous dispersion of particles or droplets of one phase (solute) in a second, typically liquid, phase (solvent). Colloids are ubiquitous in biological, chemical and technological processes, homogenizing highly dissimilar constituents. To stabilize a colloidal system against coalescence and aggregation, the surface of each solute particle is engineered to impose repulsive forces strong enough to overpower van der Waals attraction and keep the particles separated from each other. Electrostatic stabilization of charged solutes works well in solvents with high dielectric constants, such as water (dielectric constant of 80). In contrast, colloidal stabilization in solvents with low polarity, such as hexane (dielectric constant of about 2), can be achieved by decorating the surface of each particle of the solute with molecules (surfactants) containing flexible, brush-like chains. Here we report a class of colloidal systems in which solute particles (including metals, semiconductors and magnetic materials) form stable colloids in various molten inorganic salts. The stability of such colloids cannot be explained by traditional electrostatic and steric mechanisms. Screening of many solute-solvent combinations shows that colloidal stability can be traced to the strength of chemical bonding at the solute-solvent interface. Theoretical analysis and molecular dynamics modelling suggest that a layer of surface-bound solvent ions produces long-ranged charge-density oscillations in the molten salt around solute particles, preventing their aggregation. Colloids composed of inorganic particles in inorganic melts offer opportunities for introducing colloidal techniques to solid-state science and engineering applications.

Understanding temperature-induced primary nucleation in dual impinging jet mixers

The discovery that crystal nuclei can be generated by combining hot and cold saturated solutions in a dual-impinging-jet (DIJ) mixer motivates the theoretical analysis in this article. Nucleation is shown to be facilitated in solute–solvent systems that have much higher energy transfer than mass transfer rates near the impingement plane between the two jets. One- and two-dimensional spatial distributions of velocity, temperature, concentration, and supersaturation provide an improved understanding of primary nucleation in cooling DIJ mixers. In the most important spatial region for characterization of nucleation, the two-dimensional fields are shown to be very close to analytical solutions derived from a one-dimensional approximation of the energy and molar balances. This simplification enables the derivation of design criteria that facilitates assessment of whether any particular solute–solvent combination will nucleate crystals in a cooling DIJ mixer, based on the physicochemical properties of the system. These criteria could save time and material by avoiding or reducing trial-and-error experiments, which is helpful at the early stage of pharmaceutical process development.

Profiles of temperature, concentration and supersaturation within atomized droplets during flash-crystallization

Flash-crystallization is a suspension crystallization process to produce small, fine crystals (L50,3= 20–90μm) of substances which are well soluble. A hot and undersaturated solution is atomized into a low vacuum. The small droplets generated partially evaporate and cool down until thermal and mechanical equilibrium is reached. Consequently, they are highly supersaturated in a controlled manner and, thus, enable high nucleation rates. Experiments show that only certain solute–solvent combinations exhibit the high nucleation rates required and, thus, are suitable for flash-crystallization. We show that this observation is not caused solely by the buildup rate of supersaturation, but also by nucleation and growth kinetics. This is concluded by a comparison between the time of flight τf of the droplets in the crystallizer and the buildup time τb needed for the evolution of temperature and concentration profiles inside each droplet. The buildup time of supersaturation τb is negligibly short compared to the time of flight of the droplet. Thus, the driving force for nucleation and growth rate is present during virtually the entire time of flight, and therefore, slow nucleation and growth kinetics are the reason for the behavior observed. The model proposed is in good agreement with data measured.

Experimental screening method for flash-crystallization

Flash-crystallization is a process to produce small, fine crystals (L50,3=30–90μm) from solutions of substances which are well soluble. Such substances tend to crystallize readily at low supersaturations to rather coarse size ranges above 200μm (Mersmann and Kind, 1988). For such substances, the feasibility of the flash-crystallization process has been well examined on a laboratory scale and on a pilot plant scale. It is ready to be transferred to production scale. However, not all combinations of solute and solvent can be flash-crystallized. Nucleation and growth kinetics must allow for the fast formation of crystals. Here, we introduce an experimental screening method for a fast but reliable determination of the general suitability of any so far untested solute–solvent combination for the flash-crystallization process. It is found that the particle size of the product and residual supersaturation after flash-crystallization are key indicators for a successful nucleation in the droplets. Offline investigation of atomized droplets shows that one droplet carries approximately one nucleus and crystal. Additionally, this allows us to estimate the median particle size of so far untested solute–solvent combinations. They are in good agreement with measured particle sizes.

Dipolar solute rotation in ionic liquids, electrolyte solutions and common polar solvents: Emergence of universality

Here we develop a molecular theory attempting to answer the long-standing questions regarding the decoupling of dielectric friction from dipolar solute rotation in various liquid systems: ionic liquids, electrolyte solutions and polar solvents. Using both experimental and model solvent structure factors, we show insignificant dielectric friction and provide microscopic explanation for the experimentally observed domination of hydrodynamics in solute rotation in these media. Our analyses lead to a macro–micro relation indicating a quasi-universality in solute rotation for a wide variety of solute–solvent combinations. We demonstrate that both the quasi-universality and the domination of hydrodynamics originate from packing at liquid-like density.

Estimation of retention factor of cesium in sodium pool under fuel pin failure scenario in SFR

Abstract Radioactive source term in argon (Ar) cover gas region of the primary vessel due to cesium (Cs) leaked from the failed fuel pins into the primary coolant of Sodium cooled Fast Reactor (SFR) depends on its thermodynamic and kinetic behavior with the coolant sodium. Evaluation of this source term requires detailed knowledge on the distribution of Cs between large volume of the liquid sodium, and the inert Ar cover gas. Solute–solvent combination like liquid Cs and sodium, with relative volatility greater than unity, is an important system to be analyzed in the context of SFR safety. Distribution of Cs between Ar cover gas and liquid sodium pool is complicated by the imposition of temperature difference across the cover gas region and its resultant enrichment of the more volatile solute. An analytical model has been developed to obtain the geometry dependent Retention Factor (RF) of Cs in the sodium pool as a function of the height of cover gas, initial mass inventory of Cs, the temperature difference across the cover gas region (between the sodium pool surface and top roof bottom plate) for an infinite dilute solution of Cs in the sodium pool. The model predicted results are validated with available experimental results in the literature and found that they are fairly in good agreement. In the infinite dilute solution (IDS) regime sodium pool is having the retention capacity to keep the Cs from being released into the argon cover gas region.

Probing solvation decay length in order to characterize hydrophobicity-induced bead–bead attractive interactions in polymer chains

In this paper, we quantitatively demonstrate that exponentially decaying attractive potentials can effectively mimic strong hydrophobic interactions between monomer units of a polymer chain dissolved in aqueous solvent. Classical approaches to modeling hydrophobic solvation interactions are based on invariant attractive length scales. However, we demonstrate here that the solvation interaction decay length may need to be posed as a function of the relative separation distances and the sizes of the interacting species (or beads or monomers) to replicate the necessary physical interactions. As an illustrative example, we derive a universal scaling relationship for a given solute-solvent combination between the solvation decay length, the bead radius, and the distance between the interacting beads. With our formalism, the hydrophobic component of the net attractive interaction between monomer units can be synergistically accounted for within the unified framework of a simple exponentially decaying potential law, where the characteristic decay length incorporates the distinctive and critical physical features of the underlying interaction. The present formalism, even in a mesoscopic computational framework, is capable of incorporating the essential physics of the appropriate solute-size dependence and solvent-interaction dependence in the hydrophobic force estimation, without explicitly resolving the underlying molecular level details.

Mathematical correlations for describing solute transfer into functionalized alkane solvents containing hydroxyl, ether, ester or ketone solvents

Gas-to-liquid and water-to-liquid partition coefficients have been compiled for more than 2800 different solute–solvent combinations. Solutes considered include acyclic monofunctional alkanols, dialkyl ethers, alkyl alkanoates and alkanones, as well difunctional alkoxyalcohols. Both sets of partition coefficients were analyzed using the Abraham solvation parameter model with fragment-specific equation coefficients. The derived equations correlated the experimental gas-to-alcohol and water-to-alcohol partition coefficient data to within 0.15 and 0.16 log units, respectively. The fragment-specific equation coefficients that have been calculated for the CH 3, CH 2, CH, C, OH, O, C(O)O and C O fragment groups can be combined to yield expressions capable of predicting the partition coefficients of solutes in other anhydrous alkanol, dialkyl ether, alkyl alkanolate, alkanone and alkoxyalkanol solvents.

EPR Study of Rotational Diffusion in Viscous Ionic Liquids: Analysis by a Fractional Stokes–Einstein–Debye Law

Abstract Rotational correlation time (τc) of nitroxide radical solute was determined in ionic liquids by utilizing CW EPR spectroscopy. The experimental values of τc determined in viscous ionic liquids disagree with the values calculated according to Stokes–Einstein–Debye (SED) equation. A fractional SED law was examined for these solute–solvent combinations.

Solute-Solvent Chiral Interactions: Non-Symmetrical Effects of Enantiomers and Conformers on Right- and Left-Handed Cholesterics

Abstract Effective helical twisting powers of a number of enantiomers and achiral conformers were measured in highly twisted cholesteric phases varying in both chemical composition and macroscopic chirality. In certain solute-solvent combinations, and particularly in steroidal solvents, pronounced non-symmetric effects of enantiomers and conformers were observed on right- and left-handed cholesterics. Achiral rod-like solutes, which can exist in different conformations, were found to behave as though they have a left-handed helical twisting power in both right- and left-handed short pitch steroidal cholesterics. All effects can be interpreted as being due to specific short range molecule-molecule interactions. No evidence was found that the macroscopic chirality of a cholesteric medium can influence the conformation of an achiral solute.

The effect of polymer solution composition and film-forming procedure on aromatic polyamide membrane skin layer structure

Linear polymer phase inversion membrane casting solutions are composed of suspensions of relatively spherical polymer macromolecules. Estimates of macromolecule dimensions can be calculated, dependent on the type and concentration of the components in each particular solution. Membrane skin layer formation may be considered as interpenetration or partial coalescence and subsequent crystallization of solution surface macromolecules. The surface morphology of asymmetric membranes can be characterized by assuming a porous structure. With knowledge of the surface porous structure, membrane performance can be predicted for most solute—solvent combinations and operating conditions. It is assumed that all permeate transport through a membrane skin layer occurs between surface paracrystalline macromolecules. Macromolecule to pore radius comparisons can then be used to determine the effect of the casting composition and/or membrane-making procedure on the disposition and subsequent degree of interpenetration of surface macromolecules. Relationships between the casting composition/membrane-making procedure and interstitial coagulation may be used for membrane design considerations. This method of analysis is shown to be useful in examining reverse osmosis (RO) and ultrafiltration (UF) aromatic polyamide films.

On the infrared spectroscopy of SiF4 and SF6 in Ar clusters: Location of the solute

We have measured the infrared photodissociation spectra of argon clusters containing SiF4, as a function of the cluster size n (for n≤ 103) using molecular beam laser spectroscopy. The clusters were produced by both the conventional seeded expansion of a dilute mixture and by a ‘‘pickup’’ method where, upon colliding with it, the chromophore sticks to the surface of a cluster made in a neat solvent expansion. Furthermore, the spectra of small SF6/Arn clusters (n≤50) have been remeasured with the improved resolution resulting from the use of two line and tunable isotopic CO2 lasers. These data, together with previously published data on SF6/Ar, indicate a remarkably different behavior for these two solute–solvent combinations. The preferred ‘‘site’’ for SiF4 is at the surface of Ar clusters of all sizes, regardless of how the molecule is introduced to the cluster, while appreciable amounts of SF6 reside at the surface only when the cluster is large and the impurity is deposited onto the cluster surface. The behavior of SiF4 and SF6, together with the analogous behavior of other polyatomic chromophores, the IR spectra of which have been measured and reported previously [D. J. Levandier, M. Mengel, R. Pursel, J. McCombie, and G. Scoles, Z. Phys. D 10, 337 (1988); D. J. Levandier, S. Goyal, J. McCombie, B. Pate, and G. Scoles, J. Chem. Soc. Faraday Trans. 86, 2361 (1990)], can be rationalized in terms of molecular dynamics simulations of similar systems which are presented in the paper by Perera and Amar [L. Perera and F. G. Amar, J. Chem. Phys. 93, 4884 (1990)]. The combination of the theoretical and experimental results confirm the usefulness of infrared photodissociation spectroscopy for the study of the structure of clusters and suggest that assuming any particular location for an impurity in a cluster in the absence of experimental evidence or, at least, a dynamics calculation, can easily lead to wrong conclusions.

The effect of temperature and concentration on the electric field gradient in binary indium alloys

The concentration and temperature dependence of the quadrupole hyperfine interaction of111Cd in InTl (hcp),InPb (fct),InTl (fct) andInCd (fct and fcc) alloys were studied using the perturbed angular correlation technique. The change in the observed quadrupole interaction frequency with concentration can be described by a linear dependence on the axial ratioc/a in all cases. In the alloys with identical crystal structures the strength of thec/a dependence is independent of the solute, in contrast to the strength of the concentration dependence. In all cases where no phase transition occurs, the change in the electric field gradient with temperature follows the empirical relationVzz(T)=Vzz(0) · (1−B·T3/2), where the coefficientB depends on the lattice structure, on the solute-solvent combination and on the concentration. The phase transitions ofInCd alloys at 293 K could clearly be seen as discontinuities in the temperature curves. A similar series of discontinuities observed around 116 K suggests the existence of a cubic low temperature phase.