Partition Coefficients Of Amino Acids Research Articles

Partitioning of amino acids in the novel biphasic systems based on environmentally friendly ethyl lactate

For the first time, we report on the performance of biphasic system composed of ethyl lactate, water and inorganic salt (K3PO4, K2HPO4 and K2CO3) for the separation of amino acids (L-phenylalanine, L-tryptophan and L-tyrosine) from their aqueous solutions. Cloud points (solubility curve) and tie-lines for three ternary (ethyl la ctate + water + inorganic salt) systems at 298.2 K and 313.2 K at atmospheric pressure were determined. For certain composition range, these mixture exhibit biphasic systems – top and bottom phases rich in ethyl lactate and salt, respectively. Partition coefficients of amino acids and their extraction efficiencies, as essential parameters for design of any separation process, were measured at two temperatures – 298.2 K and 313.2 K. The maximum values of partition coefficients were observed for the system containing K3PO4: 3.5, 3.7 and 11.9 for L-phenylalanine at 313.2 K, L-tyrosine at 298.2 K and L-tryptophan at 313.2 K, respectively. The obtained results clearly showed that the biphasic systems based on ethyl lactate are suitable for the efficient and sustainable recovery of amino acids from solutions with water.

Amadori products formation in emulsified systems

The formation of Amadori products (APs) is the key step determining the development of the Maillard reaction (MR). The information on the chemical behaviour of the reaction between amino acids and reducing sugars in emulsions during thermal treatments is scanty and mainly focused on volatile compounds. The aim of this work was to investigate the formation of APs from glucose and two amino acids with different partition coefficients (phenylalanine and leucine) in emulsions. Two submicron oil-in-water (O/W) emulsions consisting of water, tricaprylin and Tween 20 were prepared, thermally treated and the formation of fructose-phenylalanine (Fru-Phe) and fructose-leucine (Fru-Leu) was monitored by mass spectrometry. The concentration of Fru-Phe in submicron emulsions was similar to that in water, while Fru-Leu was reduced up to 47% in the emulsions. These data indicated that partition coefficient of amino acids, determining the reactants location, can substantially influence the MR and the final quality of foods.

Modeling the partitioning of amino acids in aqueous two phase systems

A new model to obtain fast prediction of partition coefficients in polymer/polymer aqueous two phase systems (ATPSs) is presented, using amino acids as test systems. In particular, the partitioning behavior of eleven amino acids (glycine, alanine, leucine, phenylalanine, lysine, arginine, histidine, aspartic acid, glutamic acid, glutamine and serine) has been studied in 6 polymer/polymer ATPSs, formed by different pairs of nonionic polymers, including polyethylene glycol (PEG), Dextran, Ucon and Ficoll at 0.15M NaCl in 0.01M sodium phosphate buffer. The partition coefficients of the amino acids in the different ATPSs under study showed linear correlations as described by the Collander equation. Based on continuum electrostatics (CE), a semi-empirical model was developed to study the partitioning behavior in ATPSs. The approach employs a thermodynamic cycle where the electrostatic and nonpolar contributions to the free energy of partition are assumed to be additive. Three systems were chosen for the modeling studies: PEG-Dextran, PEG-Ficoll and Ficoll-Dextran. In general, the model was found to correctly predict the preferred phase for the studied amino acids, and, except for the charged ones, a good quantitative correlation of the calculated and experimental partition free energies was also obtained (e.g., with RMSE values of 150Jmol−1 for PEG-Ficoll). The model performance could be improved by grouping amino acids according to their electrostatic properties, resulting in very good quantitative partition coefficient predictions (e.g., RMSE values for nonpolar amino acids of 29, 16 and 0.4Jmol−1 for PEG-Dextran, PEG-Ficoll and Ficoll-Dextran system, respectively). The good performance of the proposed model in predicting partition coefficients of amino acids, the building blocks of proteins, offers a good prospect to its application to protein molecules and complexes.

Partitioning behavior of amino acids in aqueous two-phase systems formed by imidazolium ionic liquid and dipotassium hydrogen phosphate

Partition coefficients of amino acids, including glycine, alanine, 2-aminobutyric acid, valine, leucine, threonine, methinoine, tryptophan and tyrosine, in [Cnmim]Br (n=4, 6, 8)+K2HPO4 aqueous two-phase systems (ATPSs) have been determined, and the relative hydrophobicity of the equilibrium phases in the ionic liquids-based aqueous two-phase systems has been characterized by the Gibbs energies of transfer for methylene group from the bottom salt-rich phase to the top ionic liquid-rich phase. Based on these results, factors affecting the partitioning behavior of the amino acids have been investigated. It is shown that partition coefficients of the amino acids increase with the increase of hydrophobicity of the amino acids and the ionic liquids, solution pH value, tie-line length of the ATPSs and temperature of the systems. The possible driving forces and the thermodynamic parameters for the partitioning of amino acids in the ionic liquids-based ATPSs have also been discussed.

Partitioning of acidic, basic and neutral amino acids into imidazolium-based ionic liquids

In this paper, partitioning behaviors of typical neutral (Alanine), acidic (Glutamic acid) and basic (Lysine) amino acids into imidazolium-based ionic liquids [C(4)mim][PF(6)], [C(6)mim][PF(6)], [C(8)mim][PF(6)], [C(6)mim][BF(4)] and [C(8)mim][BF(4)] as extracting solvents were examined. [C(6)mim][BF(4)] showed the best efficiency for partitioning of amino acids. The partition coefficients of amino acids in ionic liquids were found to depend strongly on pH of the aqueous solution, amino acid and ionic liquid chemical structures. Different chemical forms of amino acids in aqueous solutions were pH dependent, so the pH value of the aqueous phase was a determining factor for extraction of amino acids into ionic liquid phase. Both water content of ionic liquids and charge densities of their anionic and cationic parts were important factors for partitioning of cationic and anionic forms of amino acids into ionic liquid phase. Extracted amino acids were back extracted into phosphate buffer solutions adjusted on appropriate pH values. The results showed that ionic liquids could be used as suitable modifiers on the stationary phase of an HPLC column for efficient separation of acidic, basic, and neutral amino acids.

Investigation of Amino Acid Partitioning in Aqueous Two-Phase Systems Containing Polyethylene Glycol and Inorganic Salts

The partitioning behavior of three amino acids, l-tryptophan, l-phenylalanine, and l-tyrosine, has been studied in aqueous two-phase systems of polyethylene glycol (PEG6000) + salts + H2O at 298.15 K. The salts used were magnesium sulfate, sodium sulfate, and ammonium sulfate. The effects of tie line length, salt, and side chain structure on the partition coefficients of amino acids have been studied. The results showed that increasing amino acid hydrophobicity and tie line length led to a corresponding increase of the partition coefficients. In addition, we also showed that the partition coefficients of the amino acids in the systems containing Na2SO4 are also significantly greater than the other two salts. The experimental data are correlated using a modified virial-type model. Comparisons between model and experimental data reveal a good agreement.

A united-residue force field for off-lattice protein-structure simulations. I. Functional forms and parameters of long-range side-chain interaction potentials from protein crystal data

A two-stage procedure for the determination of a united-residue potential designed for protein simulations is outlined. In the first stage, the long-range and local-interaction energy terms of the total energy of a polypeptide chain are determined by analyzing protein-crystal data and averaging the all-atom energy surfaces. In the second stage (described in the accompanying article), the relative weights of the energy terms are optimized so as to locate the native structures of selected test proteins as the lowest energy structures. The goal of the work in the present study is to parameterize physically reasonable functional forms of the potentials of mean force for side-chain interactions. The potentials are of both radial and anisotropic type. Radial potentials include the Lennard-Jones and the shifted Lennard-Jones potential (with the shift parameter independent of orientation). To treat the angular dependence of side-chain interactions, three functional forms of the potential that were designed previously to describe anisotropic systems are evaluated: Berne-Pechukas (dilated Lennard-Jones); Gay-Berne (shifted Lennard-Jones with orientation-dependent shift parameters); and Gay-Berne-Vorobjev (the same as the preceding one, but with one more set of variable parameters). These functional forms were used to parameterize, within a short-distance range, the potentials of mean force for side-chain pair interactions that are related by the Boltzmann principle to the pair correlation functions determined from protein-crystal data. Parameter determination was formulated as a generalized nonlinear least-squares problem with the target function being the weighted sum of squares of the differences between calculated and “experimental” (i.e., estimated from protein-crystal data) angular, radial-angular, and radial pair correlation functions, as well as contact free energies. A set of 195 high-resolution nonhomologous structures from the Protein Data Bank was used to calculate the “experimental” values. The contact free energies were scaled by the slope of the correlation line between side-chain hydrophobicities, calculated from the contact free energies, and those determined by Fauchere and Pliska from the partition coefficients of amino acids between water and n-octanol. The methylene group served to define the reference contact free energy corresponding to that between the glycine methylene groups of backbone residues. Statistical analysis of the goodness of fit revealed that the Gay-Berne-Vorobjev anisotropic potential fits best to the experimental radial and angular correlation functions and contact free energies and therefore represents the free-energy surface of side-chain-side-chain interactions most accurately. Thus, its choice for simulations of protein structure is probably the most appropriate. However, the use of simpler functional forms is recommended, if the speed of computations is an issue. © 1997 by John Wiley & Sons, Inc. J Comput Chem 18: 849–873, 1997

Measurement and correlation of partition coefficients of amino acids in dextran+poly(ethylene glycol)+water aqueous two-phase systems.

The partition coefficients of three amino acids (tryptophan, tyrosine and threonine) in various dextran+polyethylene+water aqueous two-phase systems were measured. The partition coefficients of six amino acids (glycine, phenylalanine, isoleucine, tryptophan, tyrosine and threonine), obtained in a previous and the present studies, were correlated by using the osmotic virial equation. The partition coefficients of amino acids were predicted successfully by using a hydrophilic group-parameters introduced in this study.

Phase behavior of α-amino acids in multicomponent aqueous alkanol solutions

A model describing the partitioning behavior of α-amino acids in systems containing water and partially miscible alkanols is presented. It incorporates a relationship expressing the solubilities of amino acids in miscible aqueous alkanol solutions and makes use of the phase behavior of the solute-free solvent system and the solubilities of amino acids in the pure solvent components. The solubilities of several amino acids in aqueous ethanol and isomeric propanol solutions and their partition coefficients in the 1-butanol + water system were taken from the literature and could succescfully be described with a single, amino acid specific, ternary interaction parameter. It is demonstrated that this parameter is related to well-established hydrophobicity scales for amino acid side-chain moieties. Without additional parameters the partition coefficients of amino acids in 1-octanol/water were predicted from the model and compare well with literature values. The extension of the model to multicomponent solvent systems is straight-forward and was demonstrated for the case of the ternary solvent system water + ethanol + 1-butanol.

A method to predict the transdermal permeability of amino acids and dipeptides through porcine skin

The penetration of various amino acids and dipeptides through porcine skin was measured in vitro in this work to examine the effect of lipophilicity and molecular weight of the compounds on the permeability of passive diffusion. Experimental results indicated that the effect of lipophilicity is a more dominant factor than the molecular weight. An equation was also developed to accurately predict the permeability of amino acids and dipeptides based on the lipophilicity of penetrants as follows: log K p = −2.73+0.38ln K−0.036(ln K) 2 with R 2 of 0.85 for the regression, where K, the lipophilicity, is represented by the partition coefficients of amino acids and dipeptides between the PEG/Na 2SO 4 aqueous two-phase system. In particular, the successful prediction of partition coefficients of dipeptides by Chen's method was used to further predict the dipeptides' permeability for transdermal delivery. The experimental results were deemed satisfactory.

A Model to Predict the Partition Coefficients of Amino Acids in PEG/Salt Aqueous Two-Phase Systems

Abstract A mathematical model incorporating both the influence of pH and solute hydrophobicity is presented to describe the partitioning of charged compounds in aqueous two-phase systems. The model is applied to the partitioning of amino acids in PEG/potassium phosphate aqueous two-phase systems in which the pH lies between 6.1 and 11.9. The model predicts the minimum in the partition coefficient of several amino acids which is observed in phase systems of intermediate pH.

Salt effect on partition coefficient of glycine, L-valine, and L-phenyl alanine in n-octanol-water system

The n-octanol-water partition coefficient is an important property to measure the hydrophobicity of organic compounds, which has been demonstrated to be a parameter in studying the conformation of biomolecules in aqueous solutions. The hydrophobic parameters of the amino acid side chains of peptides have been evaluated from the n-octanol-water partition coefficients of amino acids. For biological systems, electrolytes play an important role on thermodynamic properties. Numerous measurements of the partition coefficients of amino acids in the n-octanol-water system have been already made but without any salt effect. In this study, we investigated the salt effect on the n-octanol-water partition coefficients of glycine, L-valine, and L-phenyl alanine with the use of a generator column. The electrolytes used were LiCl, NaCl, and Na 2SO4.

A Correlation for Predicting Partition Coefficients in Aqueous Two-Phase Systems

Abstract Partition coefficients of amino acids and peptides are examined in poly(ethylene glycol)/magnesium sulfate systems. A correlation is proposed which relates the logarithm of the partition coefficient to the solute hydrophobicity and to the concentration difference between the phases of one of the phase-forming components. Partitioning data for several neutral amino acids were used to calculate individual amino acid residue hydrophobicities. These hydrophobicities were then used successfully to predict the partition coefficients of peptides in the same phase systems. The predicted and observed partition coefficients are compared for several peptides composed of two to four amino acid residues.

Calculation of solvation interaction energies for protein adsorption on polymer surfaces

Of the interactions that govern protein adsorption on polymer surfaces, solvation interactions (repulsive hydration and attractive hydrophobic interactions) are thought to be among the most important. The solvation interactions in protein adsorption, however, have not been dealt with in theoretical calculation of the adsorption energy owing to the difficulties in modelling such interactions. We have evaluated the solvation interaction energies using the fragment constant method of calculating the partition coefficients of amino acids. The fundamental assumption of this approach is that the partition coefficients of amino acids between water and organic solvent phases are related to the free energies of transfer from bulk water to the polymer surface. The X-ray crystallographic protein structures of lysozyme, trypsin, immunoglobulin Fab, and hemoglobin from the Brookhaven Protein Data Bank were used. The model polymer surfaces were polystyrene, polypropylene, polyethylene, poly(hydroxyethyl methacrylate) [poly(HEMA)], and poly(vinyl alcohol). All possible adsorption orientations of the proteins were simulated to study the effect of protein orientation on the solvation interactions. Protein adsorption on either hydrophobic or hydrophilic polymer surfaces was examined by considering the sum of solvation and other interaction energies. The results showed that the contribution of the solvation interaction to the total protein adsorption energy was significant. The average solvation interaction energy ranged from -259.1 to -74.1 kJ/mol for the four proteins on the hydrophobic polymer surfaces, such as polystyrene, polypropylene, and polyethylene. On the other hand, the average solvation interaction energies on hydrophilic surfaces such as poly(HEMA) and poly(vinyl alcohol) were larger than zero. This indicates that repulsive hydration interactions are in effect for protein adsorption on hydrophilic polymer surfaces. The total interaction energies of the proteins with hydrophobic surfaces were always lower than those with more hydrophilic surfaces. This trend is in agreement with the experimental observations in the literature. This study suggests that consideration of the solvation interaction energies is necessary for accurate calculation of the protein adsorption energies.

Amino acids in AOT reversed micelles. 1. Determination of interfacial partition coefficients using the phase-transfer method

The solubilization of amino acids in AOT reversed micelles using the phase-equilibrium method is analyzed in terms of a simple solubilization model allowing the partition coefficients of amino acids between water and the reversed micellar interfaces to be deduced by using only bulk concentration measurements. The partition coefficient is mostly influenced by those factors that affect the interfacial properties (surface pressure and bending moment) of the microemulsion droplets, namely, the organic solvent used and the type and concentration of cations in the system

Partition coefficients of amino acids and hydrophobic parameters π of their side-chains as measured by thin-layer chromatography

Partition coefficients in n-octanol—water have been determined for the naturally occurring and some synthetic α-amino acids using thin-layer chromatography in different solvent systems. Both literature and newly measured values of partition coefficients in n-octanol—water have been used as reference values. The relationship between R F values and partition coefficients ( P) has been established. Hansch hydrophobic parameters π have been evaluated for the side-chains. Fragmental group contributions to the overall π-value have also been evaluated. In this way P and π values of any non-listed amino acid become easily accessible either by thin-layer chromatography or by computation.

Coefficients de partage d’aminoacides, nucléobases, nucléosides et nucléotides dans un système solvant salin

Summary Partition coefficients of amino acids, nucleobases, nucleosides and nucleotides in a saline solvent system The behaviour of sixty-four nucleic compounds (bases, nucleosides, nucleoside-mono-, -di-, and -tri-phosphates) and eighteen amino acids was studied in a “saline solvent system” used for counter-current distribution of transfer ribonucleic acid, based on 1.50 M potassium phosphate pH 7.0, 2-methoxyethanol and 2-butoxyethanol. From the values of partition isotherms and partition coefficients K , measured in standard conditions at 20° and for 20% 2-butoxyethanol, it can be concluded that: (1) thiolation of bases decreases K , (2) phosphorylation of nucleosides accounts for negative, but additive effect on K , and (3) aliphatic lengthening of amino acids residues, N-alkylation, O-methylation, halogenation, C → N intracyclic substitution of bases, ribose → 3′-deoxyribose transformation increase K . The effect of these base or nucleoside substitutions is discussed and related to the mobility of tRNA separated by counter-current distribution.

Chromatography of amino acids belonging to homologous series

Because of the regularities that exist in the solubilities and partition coefficients of amino acids, members of homologous series produce spots in two-dimensional chromatograms of their mixtures which fall on smooth curves. This fact can profitably be used for the analysis of chromatograms of protein hydrolysates and especially as a source of suggestions concerning the character of substances producing unusual spots. Results from analyses of hydrolysates of E. coli are cited as an example.