Melting Properties of Peptides and Their Solubility in Water. Part 2: Di- and Tripeptides Based on Glycine, Alanine, Leucine, Proline, and Serine

Abstract

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.

The melting properties of D-α-glucose, D-β-fructose, D-sucrose, D-α-galactose, and D-α-xylose and their solubility in water: A revision

“…Melting properties with FSC. Following the experimental FSC method established in our previous research and characterization of melting properties of amino acids and peptides [19][20][21][22], the saccharides D-α-glucose, D-β-fructose, D-sucrose, D-α-galactose, and D-α-xylose were characterized experimentally with Fast Scanning Calorimetry (FSC) with scanning rates from 2000 K•s −1 to 10,000 K•s −1 . The onset temperatures, T SL � 0i ( ) , from the melting peak in heating step #5 with respect to heating rates, β, were shown in Fig.…”

“…To our best knowledge, for disaccharides such as D-sucrose mutarotation cannot be observed. In this work, D-sucrose solubility was modeled as previously done for amino acids [19,20] and peptides [21,22]. The FSC melting enthalpy was adjusted to the solubility at T = 298.15 K with the experimentally obtained difference between solid and liquid state heat capacities and is still within the FSC uncertainty.…”

“…The specific melting enthalpy,Δh SL 0i , is determined from the slope of the sample mass dependency of ΔH SL 0i ; for details, see Fig. 4 and references [22,23,41]. In order to ensure good thermal contact between the sample and the sensor (3) surface and to minimize sublimation/evaporation, the sample can be covered with silicon oil before heating step #5.…”

“…Differential Scanning Calorimetry (DSC), due to chemical decomposition (degradation) [16].With the access to high scanning rates with Fast Scanning Calorimetry (FSC), thermodynamic properties such as melting properties can be directly measured, especially for biomolecules without decomposition [17,18]. Recently, an experimental FSC method has been developed for the successful determination of the melting properties of amino acids [19,20], peptides [21,22], nucleobases [23,24], bio-polymers [17,18] and low molecular mass pharmaceuticals [25].…”

Computer-aided solvent screening for the fractionation of wet microalgae biomass

“…Their water-solubility, however, strongly depends on their amino acid composition. 81 Single amino acids as building-blocks for proteins, on the contrary, can be modeled in much shorter time. Therefore, in this study, the four most abundant amino acids in P. tricornutum, namely glutamine, asparagine, alanine, and leucine were used to represent the protein fraction.…”