We report the melting properties of amino acids for the first time and highlight the usefulness of such data to predict material properties such as aqueous solubility of amino acids.

Carbon dioxide (CO 2 ) solubility in aqueous electrolyte solutions is of special interest for carbon capture and storage and for biochemical processes, particularly at moderate to high temperatures, pressures, and electrolyte concentrations. Unfortunately, experimental determination at such conditions is rather laborious. Therefore, the ionbased model ePC-SAFT was used in this work to model the CO 2 solubility in such systems over a broad range of conditions. The mixtures under investigation were the basis system CO 2 + water and higher systems containing either NaCl, KCl, MgCl 2 , CaCl 2 , NaNO 3 , KNO 3 , Mg(NO 3 ) 2 , or NaHCO 3 . In the pH range considered in this work (pH < 7), CO 2 dissociation reactions were found to be negligible; thus, only physical interactions were considered. Assuming induced association for CO 2 , binary interaction parameters between CO 2 −water and CO 2 − ion species were determined by fitting to literature data. For this purpose, different literature data sets were compared, and only the most reliable data were used to estimate the binary parameters. ePC-SAFT was found to be able to accurately model the CO 2 solubility in water as well as in aqueous systems containing electrolytes over a broad range of temperatures, pressures, and salt concentrations.

Salt solubility in organic solvents is of particular interest in industry, for example, for carbon capture and storage or utilization processes, battery technology, or biotechnology. Electrolyte thermodynamic models have been developed to reduce the experimental effort for the design of an electrolyte toward desired properties, for example, high solubility in an organic solvent. In this work, the solubility of nine salts (NaCl, KCl, CsCl, NaHCO 3 , KHCO 3 , CsHCO 3 , Na 2 CO 3 , K 2 CO 3 , and Cs 2 CO 3 ) in the organic solvents methanol, ethanol, and N-methyl-2pyrrolidone (NMP) was studied at temperatures between 288.15 and 348.15 K. These systems were chosen since the largest amount of experimental data points were available in order to ensure a broad set of data for high modeling accuracy. Experimental solubility data were collected from literature, and missing data were measured in this work by both ion-chromatography analysis and the all-gravimetric method. The thermodynamic solubility product K SP of the salts was determined at 298.15 K and 1 bar. These K SP values do NOT depend on the solvent; that is, once known, they can be used to predict the solubility in any solvent or solvent mixture. K SP requires that the solid form of the precipitating salt be the same in different organic solvents. Therefore, powder X-ray diffractometer measurements were carried out to investigate possible hydrate formation or solvate formation, and Karl Fischer measurements were used to validate the absence of water. The equation of state ePC-SAFT was applied to model salt solubility in organic solvents by accounting for concentration-dependent dielectric constants within Debye−Huckel theory and Born theory. The required K SP values of the salts were determined using experimental literature data on the salt solubility in water together with the corresponding mean ionic activity coefficients (MIACs) at saturation. The availability of K SP and the predicted MIACs allowed modeling of the salt solubility in organic solvents in excellent agreement with experimental data. Furthermore, solvent-specific analysis and ion-specific analysis revealed a non-intuitive behavior of salt solubility in the organic solvents. One example is that ionspecific effects of salt solubility in alcohols are not valid in other organic solvents such as NMP. Furthermore, in contrast to aqueous solutions, salt solubility in organic solvents does not depend linearly on the cation size. Thus, experimental rules of thumb cannot be applied, and the experimental effort to screen salt solubility in organic solvents can only be significantly reduced by theoretical approaches such as ePC-SAFT.

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In downstream processes for peptides, crystallization is still used as the state-of-the-art separation step for which the knowledge about the solubility of each single compound is mandatory. Since the determination of experimental temperature-dependent solubility data is time-consuming and expensive, modeling solubility based on physical properties such as melting properties is highly desired. Unfortunately, the direct determination of melting properties for biomolecules using conventional differential scanning calorimetry is not possible due to the decomposition of the peptides before their melting. In this work, fast scanning calorimetry (FSC) with heating rates up to 20,000 K s–1 was applied to measure the melting properties of 22 peptides with focus on isomeric dipeptides and tripeptides based on glycine, l-alanine, l-leucine, l-proline, and l-serine. The experimental determination of the aqueous solubility of these peptides was performed using the photometric method (UV/Vis spectrometer) and the gravimetric method of supersaturated solutions. Additionally, the pH value and the crystal structure of peptides were determined in order to ensure the neutral species in solution and to exclude crystal structure changes in the solid phase. The experimental FSC-measured melting properties were used as input data in the thermodynamic modeling framework PC-SAFT to model the peptide solubility in water. The PC-SAFT pure-component parameters of the peptides were determined following a weighted joint-parameter method introduced in this work. This approach allows determining the pure-component parameters of a peptide by joining the pure-component parameters of the parent amino acids. The binary interactions parameter between peptide and water was fitted to solubility-independent properties such as osmotic coefficients and mixture densities of aqueous peptide solutions. The modeled peptide solubility was in good agreement with the experimental solubility.

Proton activity, which is usually expressed as pH value, is among the most important properties in the design of chemical and biochemical processes as it determines the dissociation of species...