Interactions of two homologues of cationic surface active ionic liquids with sodium carboxymethylcellulose in aqueous solution

In the preceding paper of this series, we studied the interactions of copolymers with the ionic liquids, 1-alkyl-3-methylimidazolium bromide (C _n mimBr, n?=?8, 10, 12, 14, 16) and N-alkyl-N-methylpyrrolidinium bromide (C _n MPB, n?=?12, 14, 16). An obvious difference was detected between the interaction mechanism and the alkyl chain length of the surfactant. In the present study, we performed a systematic study on the interaction of sodium carboxymethylcellulose (NaCMC) with ionic liquids in aqueous solution by isothermal titration microcalorimetry (ITC), conductivity, turbidity, and dynamic light scattering (DLS) measurements. The existence of electrostatic attraction between NaCMC and ILs could increase the complexity of these systems. The results show that the monomers of C₈mimBr can bind to the NaCMC chains and form free surfactant micelles in the solution, while no micelle-like C₈mimBr/NaCMC cluster is detected. For other surfactants, the formation of surfactant/NaCMC clusters in the solution is driven by electrostatic and hydrophobic interactions, which could be divided into two types. One type is the polymer-induced surfactant/NaCMC complexes that form in the solution for the surfactant of C _n mimBr (n?=?10, 12, 14) or C _n MPB (n?=?12, 14). The other type is that the surfactant-induced surfactant/NaCMC complexes come into being for the surfactant of C₁₆mimBr or C₁₆MPB. Finally, the different modes of complex formation proposed have a good interpretation of the experiment results, unraveling the details of the effect of surfactant alkyl chain length and headgroup on the surfactant–NaCMC interactions.     

Interaction between PEO-PPO-PEO copolymers and a hexapeptide in aqueous solutions

Interaction between PEO-PPO-PEO copolymers and a hexapeptide, growth hormone releasing peptide-6 (GHRP-6), was investigated by NMR to study the potential use of the copolymers in peptide drug delivery. (1)H NMR and nuclear Overhauser effect spectroscopy (NOESY) measurements determined that PO methyl protons interacted with methyl protons of the Ala moiety, aromatic protons of the Trp moiety, and some of the Phe aromatic protons. The Lys moiety and part of the Phe moiety entered the hydrophilic EO environment via hydrogen bonding. PEO-PPO-PEO copolymers and the peptide formed a complex in 1:1 stoichiometry. Binding constants between copolymers and GHRP-6 were determined, and it was indicated that the copolymers containing more EO and PO units will lead to greater affinity with the peptide. Isothermal titration calorimetry (ITC) measurements confirmed the results of NMR experiments. This study indicates that PEO-PPO-PEO copolymers have great potential in delivering peptide drugs.     

Room temperature sphere-to-rod growth and gelation of PEO-PPO-PEO triblock copolymers in aqueous salt solutions

The effects of NaCl and KF on the sphere-to-rod micellar growth behavior of triblock copolymers having two different compositions, (EO)20(PO)70(EO)20 (P123) and (EO)26(PO)40(EO)26 (P85), have been studied by dynamic light scattering (DLS), small angle neutron scattering (SANS) and dilute solution viscometry. NaCl can effectively tune the sphere-to-rod growth temperature of the micelles of both these copolymers and induce micellar growth down to the room temperature and below. The growth behavior is found to be dependent on the composition of the copolymer as P123 being more hydrophobic shows the room temperature growth in the presence of ethanol at significantly lesser NaCl concentration than the less hydrophobic copolymer P85. DLS studies depict for the first time the growth driven transition of the copolymer solutions from dilute to semi-dilute regime as a function of copolymer and salt concentrations. KF can also induce room temperature growth of the P123 micelles at lesser salt concentration than NaCl but it fails to induce any such growth of the P85 micelles. A pseudo-binary temperature-concentration phase diagram on 15% copolymer solutions shows the variation of the sphere-to-rod transition temperature and the cloud point of the copolymer solutions as a function of salt concentration.     

Effect of ionic liquids on the aggregation behavior of PEO-PPO-PEO block copolymers in aqueous solution

Effect of 1-butyl-3-methyl-imidazolium bromide (BmimBr) on the aggregation behavior of PEO-PPO-PEO Pluronic P104 aqueous solution was studied by Fourier transform infrared (FTIR) spectroscopy, freeze fracture transmission electron microscopy (FF-TEM), dynamic light scattering (DLS), and NMR spectroscopy. When the BmimBr concentration was below 1.232 mol/L, the critical micelle temperature (CMT) of Pluronic P104 remained constant, while the size of micelles increased with increasing the BmimBr concentration; above this concentration, the CMT of Pluronic P104 decreased abruptly, and bigger clusters of BmimBr were formed. The selective nuclear Overhauser effect (NOE) spectrum indicates that the PO block of the P104 interacts with the butyl group of the Bmim+ cation by hydrophobic interaction. It suggests that when the concentration of BmimBr is below 1.232 mol/L, there are P104 micelles in the aqueous solution with BmimBr embedding to the micellar core, while above this concentration, P104 micelles and BmimBr clusters coexist in the system.     

Effects of cationic head groups of ionic liquid on micellization in aqueous solution of PEO-PPO-PEO triblock copolymer

The interaction of ionic liquids (ILs) with non-ionic triblock copolymer, Pluronic® P123 in aqueous solutions has been investigated using DLS, surface tension, and viscosity measurements. The addition of ILs increased the Critical Micelle Concentration (CMC) of P123, which appears to be logistic. As the added IL enhances the solubility of PPO moiety (and PEO), which makes them to behave like a more hydrophilic block copolymer that would be micellized at high copolymer concentration. The DLS data is in good agreement to the results observed from surface tension measurements. Viscosity results show the propensity in micellar size reduction upon addition of ILs, and hence, intrinsic viscosity decreases as compared to pure P123 aqueous solution. The results are studied and discussed as a function of cationic head groups of N-octyl-pyridinium/imidazolium chloride based ILs.     

Temperature-induced self-assembly of triple-responsive triblock copolymers in aqueous solutions

A series of triple-thermoresponsive triblock copolymers from poly(N-n-propylacrylamide) (PNPAM, A), poly(methoxydiethylene glycol acrylate) (PMDEGA, B), and poly(N-ethylacrylamide) (PNEAM, C) was synthesized by sequential reversible addition-fragmentation chain transfer polymerizations. Polymers of differing block sequences, ABC, BAC, and ACB, with increasing phase transition temperatures in the order A < B < C were prepared. Their aggregation behavior in dilute aqueous solution was investigated using dynamic light scattering, turbidimetry, and NMR spectroscopy. The self-organization of such polymers was found to dependent strongly on the block sequence. While polymers with a terminal low-LCST (lower critical solution temperature) block undergo aggregation above the first phase transition temperature at 20-25 °C, triblock copolymers with the low-LCST block in the middle show aggregation only above the second phase transition. The collapse of the middle block is not sufficient to induce aggregation but produces instead stable, unimolecular micelles with a collapsed middle block, as supported by NMR and fluorescence probe data. Continued heating of all copolymers led to two additional thermal transitions at 40-55 and 70-80 °C, which could be correlated to the phase transitions of the B and C blocks, respectively. All polymers show a high tendency for cluster formation, once aggregation is induced. The carrier abilities of the triple responsive triblock copolymers for hydrophobic agents were probed with the solvatochromic fluorescence dye Nile Red. With passing through the first thermal transition, the block copolymers are capable of solubilizing Nile Red. In the case of block copolymers with sequences ABC or ACB, which bear the low-LCST block at one terminus, notable amounts of dye are solubilized already at this stage. In contrast, the hydrophobic probe is much less efficiently incorporated by the BAC triblock copolymer, which forms unimolecular micelles. Only after the collapse of the B block, when reaching the second phase transition at about 45 °C, does aggregation occur and solubilization becomes efficient. In the case of ABC and ACB polymers, the hydrophobic probe seems to partition between the originally collapsed A chains and the additional hydrophobic chains formed after the collapse of the less hydrophobic B block.     

Surface adsorption and micelle formation of surface active ionic liquids in aqueous solution

Aqueous solutions of three kinds of surface active ionic liquids composed of the 1-alkyl-3-methylimidazolium cation have been investigated by means of surface tension and electrical conductivity measurements at room temperature (298 K). The surface tension measurements provided a series of parameters, including critical micelle concentration (cmc), surface tension at the cmc (gammacmc), adsorption efficiency (pC20), and effectiveness of surface tension reduction (Picmc). In addition, with application of the Gibbs adsorption isotherm, maximum surface excess concentration (Gammamax) and minimum surface area/molecule (Amin) at the air-water interface were estimated. The effect of sodium halides, NaCl, NaBr, and NaI, on the surface activity was also investigated. It was found that both the pC20 and the Picmc were rather larger than those reported for traditional ionic surfactants and the cmc values were somewhat lower than those for typical cationic surfactants, alkyltrimethylammonium bromides, and comparable to typical anionic surfactants, sodium alkyl sulfates. These results demonstrate that the surface activity of long-chained imidazolium IL is somewhat superior to that of conventional ionic surfactants.     

Salt induced micellization of very hydrophilic PEO-PPO-PEO block copolymers in aqueous solutions

Symmetrical poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, triblock copolymers with 80% polyethylene oxide (PEO, the hydrophilic end blocks) and polypropylene oxide (PPO, the hydrophobic middle block) usually remain as molecularly dissolved at ambient temperature even at fairly high-concentrations (2 wt.% or more). However, the micellization is induced at lower concentration/temperature in the presence of salts. The results on salt induced micellization from four such hydrophilic copolymers Pluronic^® F38, F68, F88 and F108 obtained from several independent techniques are described. FTIR and fluorescence results provide essentially identical critical micelle temperatures (CMTs) showing marked decrease with increase in PPO molecular weight and in the presence of salt. These copolymers were weakly surface active and did not show a clear break point in surface tension concentration plot typical of surfactants. While addition of salt decreases the cloud point, no significant micelle growth was observed even at temperature close to cloud point (CP). Marked increased in solubilization of an oil dye was observed in presence of KCl. Different methods showed good agreement in temperature/salt-induced micellization of these hydrophilic copolymers.     

Adsorption of PEO-PPO-PEO triblock copolymers with end-capped cationic chains of poly(2-dimethylaminoethyl methacrylate)

We study the adsorption of a symmetric triblock copolymer of ethylene oxide, EO, and propylene oxide, PO, end-capped with quarternized poly(2-dimethylaminoethyl methacrylate), DMAEMA (DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24)). Light scattering and tensiometry are used to measure the relative size of the associated structures and surface excess at the air-liquid interface. The adsorbed amount, the amount of coupled water, and the viscoelasticity of the adsorbed polymer layer are measured on hydrophobic and hydrophilic surfaces (polypropylene, cellulose, and silica) by using quartz crystal microgravimetry (QCM) and surface plasmon resonance (SPR) at different ionic strengths and temperatures. The results of the experiments are compared with those obtained after adsorption of the uncharged precursor copolymer, without the cationic end-caps (EO(132)PO(50)EO(132)). DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) possesses higher affinity with the negatively charged silica and cellulose surfaces while the uncharged copolymer adsorbs to a larger extent on polypropylene surfaces. In this latter case, adsorption increases with increasing solution ionic strength and temperature. Adsorption of EO(132)PO(50)EO(132) on silica surfaces has little effect on the water contact angle (WCA), while adsorption of DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) increases the WCA of silica to 32°, indicating a large density of exposed PPO blocks upon adsorption. After adsorption of EO(132)PO(50)EO(132) and DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) on PP, the WCA is reduced by ≈14° and ≈28°, respectively, due to the exposed hydrophilic EO and highly water-soluble DMAEMA segments on the surfaces. The extent of surface coverage at saturation at the polypropylene/liquid interfaces (≈31 and 40 nm(2)/molecule obtained by QCM and SPR, respectively) is much lower, as expected, when compared with results obtained at the air/liquid interface, where a tighter packing is observed. The percentage of water coupled to the adsorbed cationic polymer decreases with solution ionic strength. Overall, these observations are ascribed to the effects of electrostatic screening, polymer hydrodynamic size, and solvency.     

Aggregation behavior of aqueous solutions of ionic liquids

The aggregation behavior in aqueous solutions of three ionic liquids based on the 1-alkyl-3-methylimidazolium cation has been investigated by means of surface tension, conductivity, and small-angle neutron scattering (SANS) measurements. From analysis of the SANS data, models for the shapes and sizes of aggregates have been proposed: the short-chain 1-butyl-3-methylimidazolium tetrafluoroborate [C4mim] [BF4] system can be best modeled by treating it as a dispersion of polydisperse spherical aggregates that form above a critical aggregation concentration, whereas the 1-octyl-3-methylimidazolium iodide, [C8mim] [I], solutions can be modeled as a system of regularly sized near-spherical charged micelles that form above a critical micelle concentration. Solutions of 1-octyl-3-methylimidazolium chloride, [C8mim]-[Cl], display weak long-range ordering of possibly disklike particles culminating in the formation of structures with distinct long-range order at higher concentrations.     

Effects of Hofmeister anions on the aggregation behavior of PEO-PPO-PEO triblock copolymers

The effects of a series of Hofmeister anions on the phase behaviors of a poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer were investigated with an automated melting point system. Well hydrated anions and poorly hydrated anions interacted with the polymer differently and further affected the phase transition of the polymer. Poorly hydrated anions worked through changing the interfacial tension at the polymer/aqueous interface and in enhancing the polymer hydration by ion binding. The phase transition of the polymer in the presence of well hydrated anions correlated directly to the hydration entropy of the anions. As a consequence, the polymer showed a two-step phase transition in solutions containing poorly hydrated anions while displayed a single-step phase transition in the presence of well hydrated anions. The mechanisms of how ions interact with the polymer and further modulate its phase behaviors were discussed.     

The solubilisation behaviour of some dichloroalkanes in aqueous solutions of PEO-PPO-PEO triblock copolymers: a dynamic light scattering, fluorescence spectroscopy, and SANS study

The aggregation behaviour of PEO-PPO-PEO triblock copolymers in water and in water + chlorinated additive mixtures was studied by means of fluorescence spectroscopy, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). The copolymers were chosen such as to investigate the effects of molecular architecture (L35 and 10R5) and molecular weight by keeping constant the hydrophilic/hydrophobic balance (F88 and F108). 1,2-Dichloroethane was used as a prototype of water basins contaminants. The hydrodynamic radius of the block copolymer aggregates (R(h,M)) and the intensity ratio of pyrene of the first and the third vibrational band (I(1)/I(3)) were determined as a function of temperature (10-45 degrees C) and concentration. The copolymer architecture essentially does not affect R(h,M) in the entire range of temperature and concentration investigated. At a given temperature, increasing macromolecular size leads to a decrease of R(h,M). With rising temperature R(h,M) also decreases. According to the DLS results, the I(1)/I(3) change with temperature clearly detects the aggregation only for F88 and F108. The presence of 1,2-dichloroethane, at concentrations close to its solubility in water, does not lead to changes in the distribution of hydrodynamic radii for L35 and 10R5. Larger quantities of additive induce the formation of quite polydisperse mixed aggregates for L35 and of networks for 10R5. In the case of F88 and F108, low concentrations of additive lead to formation of mixed aggregates with smaller R(h,M). The SANS results corroborate the DLS and fluorescence findings proving enhancement of the copolymer aggregation through the presence of 1,2-dichloroethane. The DLS findings combined with those from the fluorescence spectroscopy provide some insight into the site of solubilisation of the additive in the aggregates.     

Mechanisms of micellization and rheology of PEO-PPO-PEO triblock copolymers with various architectures

Micelle formation was followed by micro-DSC and rheology for aqueous solutions of two copolymers of PEO-PPO-PEO, the Pluronic F127 (from BASF) and the EG56 (from PolymerExpert), a branched copolymer built with three chains of F127 type. It is shown that micellization is endothermic and that, for both polymers, the enthalpy of formation/melting is proportional to total concentration. The rheology of the solutions was carefully analyzed, before gelation for F127, and it reveals firstly the progressive changes of solubility of the unimers (decease of relative solution viscosity), followed by micelle formation over a 10 degrees C range. In this range, the micelle concentration dependence on temperature was deduced from enthalpy measurements and the corresponding volume fractions were derived. Viscosity was interpreted within the framework of well-known theories for hard sphere suspensions (Krieger-Dougherty or Quemada) based on an analogy between micelles and nanosized hairy grain suspensions. The gel state is achieved due to formation of the colloidal crystal. For EG56, the rheology is quite different; as the aggregation increases with temperature, a progression is observed from Newtonian to visco-elastic liquid. The characteristic frequency, defined by the relation G(') = G('), for EG56 varies with temperature and the corresponding times increase by two orders of magnitude according to an Arrhenius law. The frequency dependence of G(') and G(') at different temperatures can be superposed with a horizontal shift factor and a small amplitude adjustment. There is no elastic solid formation in this case. The "gelation" of these two copolymers is compared to the physical gelation of cold-set gels (gelatin).     

1H NMR spectroscopic investigations on the micellization and gelation of PEO-PPO-PEO block copolymers in aqueous solutions

The effects of temperature, polymer composition, and concentration on the micellization and gelation properties of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers in aqueous solutions were investigated by 1H NMR spectroscopy. It was found that the temperature-dependent behavior of PPO blocks, observed as changes in chemical shift, half-height width, and integral value, could be attributed as an intrinsic tool to characterize the transition states during unimer to micelle formation. The 1H NMR spectral analysis revealed that the hydrophobic part, PPO, of the Pluronic polymers plays a more significant role in the temperature-induced micellization, whereas the transitional behavior of Pluronic polymer, i.e., from micellization to liquid crystals formation, resulted in the drastic broadening of the spectral signals for the PEO, indicating that the PEO segments play a more significant role in the crystallization process. It was also observed that the temperature-dependent changes in the half-height width of the PEO -CH2- signal are sensitive to the liquid crystalline phase formation, which could be attributed to the close packing of spherical micelles at high polymer concentrations or temperatures.     

Block copolymer micelle shuttles with tunable transfer temperatures between ionic liquids and aqueous solutions

Four poly((1,2-butadiene)- block-ethylene oxide) (PB-PEO) diblock copolymers were shown to self-assemble into micelles with PB cores and PEO coronas (including spheres, cylinders, and vesicles) in the ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). All four systems exhibited the "micelle shuttle" (He, Y.; Lodge, T. P. J. Am. Chem. Soc. 2006, 128, 12666-12667), whereby PB-PEO micelles transferred, reversibly and with preservation of micelle structure, from an aqueous phase at room temperature to a hydrophobic ionic liquid at high temperature. The micelle size (both mean and distribution) depends on whether it was initially dissolved in water or in the ionic liquid, but the initial micelle structures in the ionic liquid were shown by dynamic light scattering to be preserved during the transfer and persist essentially unchanged for months in both the ionic liquid and water. The transfer was shown to be driven by the deteriorating solvent quality of water for PEO at high temperature, while the ionic liquid remains a good solvent. The transfer temperature could be tuned by adding ionic or nonionic additives to the aqueous phase to change the solvent quality of water for PEO, and by using ionic liquids with different polarity.     

Thermodynamics of dilute aqueous solutions of imidazolium based ionic liquids

Experimental measurements of density ρ, speed of sound u, and viscosity η of aqueous solutions of various 1-alkyl-3-methylimidazolium based ionic liquid (IL) solutions have been performed in dilute concentration regime at 298.15 K to get insight into hydration behaviour of ILs. The investigated ILs are based on 1-alkyl-3-methylimidazolium cation, [C_nmim] having $[{\text{BF}}_4{]}^{-}$, [Cl]^?, $[{\text{C}}_1{\text{OSO}}_3{]}^{-}$, and $[{\text{C}}_8{\text{OSO}}_3{]}^{-}$ as anions where n = 4 or 8. Several thermodynamic parameters like apparent molar volume φ_V, isentropic compressibility β_s, and viscosity B-coefficients have been derived from experimental data. Limiting value of apparent molar volume has been discussed in terms of intrinsic molar volume (V_int) molar electrostriction volume (V_elec), molar disordered (V_dis), and cage volume (V_cage). Viscosity B-coefficients have been used to quantify the kosmotropic or chaotropic nature of ILs. Hydration number of ILs obtained using elctrostriction volume, isentropic compressibility, viscosity, and differential scanning calorimetry have been found to be comparative within the experimental error. The hydrophobic hydration has found to play an important role in hydration of ILs as compared to hydration due to hydrogen bonding and electrostriction. Limiting molar properties, hydration numbers, and B-coefficients have been discussed in terms of alkyl chain length of cation or nature of anion.     

Interaction of cationic surfactant and anionic polyelectrolytes in mixed aqueous solutions

Surfactant–polymer interactions in aqueous solutions have been studied using dynamic surface tension, polyelectrolyte titration, nephelometric turbidity, and dynamic light scattering. For the preparation of complexes, a technical cationic surfactant was used in combination with two poly(maleic acid-co-polymers) of similar structure but different hydrophobicity. The dynamic surface tensions of mixed solutions as functions of surfactant concentration at constant polyelectrolyte content, as well as changes in the surface activity due to the influence of polyanion at constant surfactant concentration are discussed in terms of a complex or aggregate formation in the bulk phase. The interaction of the surfactant with poly(maleic acid-alt-propene) (P-MS-P) and poly(maleic acid-alt--methylstyrene) (P-MS-MeSty), respectively, is strong in both cases and results in the formation of nanoparticles with properties depending on the composition of the corresponding mixture.     

Small-angle X-ray scattering, light scattering, and NMR study of PEO-PPO-PEO triblock copolymer/cationic surfactant complexes in aqueous solution

The formation of triblock copolymer/surfactant complexes upon mixing a nonionic Pluronic polymer (PEO-PPO-PEO) with a cationic surfactant, hexadecyltrimethylammonium chloride (CTAC), has been studied in dilute aqueous solutions using small-angle X-ray scattering, static and dynamic light scattering, and self-diffusion NMR. The studied copolymer (denoted P123, EO(20)PO(68)EO(20)) forms micelles with a radius of 10 nm and a molecular weight of 7.5 x 10(5), composed of a hydrophobic PPO-rich core of radius 4 nm and a water swollen PEO corona. The P123/CTAC system has been investigated between 1 and 5 wt % P123 and with varying surfactant concentration up to approximately 170 mM CTAC (or a molar ratio n(CTAC)/n(P123) = 19.3). When CTAC is mixed with micellar P123 solutions, two different types of complexes are observed at various CTAC concentrations. At low molar ratios (>/=0.5) a "P123 micelle-CTAC" complex is obtained as the CTAC monomers associate noncooperatively with the P123 micelle, forming a spherical complex. Here, an increased interaction between the complexes with increasing CTAC concentration is observed. The interaction has been investigated by determining the structure factor obtained by using the generalized indirect Fourier transformation (GIFT) method. The interaction between the P123 micelle-CTAC complexes was modeled using the Percus-Yevick closure. For the low molar ratios a small decrease in the apparent molecular weight of the complex was obtained, whereas the major effect was the increase in electrostatic repulsion between the complexes. Between molar ratios 1.9 and 9 two coexisting complexes were found, one P123 micelle-CTAC complex and one "CTAC-P123" complex. The latter one consists of one or a few P123 unimers and a few CTAC monomers. As the CTAC concentration increases above a molar ratio of 9, the P123 micelles are broken up and only the CTAC-P123 complex that is slightly smaller than a CTAC micelle exists. The interaction between the P123/CTAC complexes was modeled with the hypernetted-chain closure using a Yukawa type potential in the GIFT analysis, due to the stronger electrostatic repulsion.     

Thermochemistry of the dissolution and association of ionic liquids in aqueous and acetonitrile solutions

The enthalpies of dissolution for three ionic liquids in water and acetonitrile in the field of dilute solutions at 298.15 K are measured in a hermetic highly sensitive calorimeter equipped with an isothermal shell, along with the enthalpies of dilution for aqueous and acetonitrile solutions of the same compounds in moving from three different concentrations to ones that are approximately the same. The enthalpies and constants of the ionic association of such liquids as electrolytes in solutions are calculated, along with their standard enthalpies of dissolution in water and acetonitrile.