Amino Acids In Aqueous Solutions Research Articles

Thermodynamic modeling of amino acid solutions: A new perspective on CPA EOS

Abstract The Cubic Plus Association (CPA) equation of state is applied to simultaneously calculate various thermodynamic properties of single aqueous solutions containing amino acids. Likewise, with a new perspective on CPA model, the highly dependency of amino acid solubility on the prevailing pH value is investigated bringing up dissociation/association equilibria. Hence, pure component parameters of 24 organic amino acids are fitted to density, solute activity coefficient, and water activity of their aqueous solutions at ambient conditions, and solely one temperature independent binary interaction parameter is used for each system. Also, two new equations are presented according to optimized parameters of amino acids. To prove the proficiency of applied models, solubility of aqueous solutions is predicted in binary systems at different temperatures and pH values taking into account the dissociation/association equilibria. Subsequently, the optimized parameters of CPA model are applied to reproduce the literature data for various thermodynamic properties including density and solute activity coefficient at other temperatures which range till 333 K. In addition, the effect of pressure on liquid density is checked, and the liquid density of mixed aqueous solutions containing two amino acids is evaluated. Eventually, it can be comprehended that not only the water activity and activity coefficients of aqueous amino acid solutions, but also liquid density and solubility of single solutions are reasonably calculated by CPA EOS over a wide range of temperatures and solute concentration applying dissociation/association equilibria.

Volumetric and viscometric properties of aqueous solutions of sodium amino acids at T = (293.15 to 333.15) K

The densities and viscosities of aqueous solutions of sodium glycinate, sodium l-alaninate, sodium l-valinate, sodium l-threoninate and sodium l-argininate were measured at T = (293.15 to 333.15) K under the atmospheric pressure. The effects of temperature and concentration on the densities and viscosities of binary solutions were investigated. The volumetric and viscometric properties such as the apparent molar volume (Vφ), the limiting partial molar volume (Vφ0), the viscosity B-coefficient (B) and the activation energy for viscous flow (Ea) were calculated by the experimental density and viscosity data and analyzed based on the molecular structure and intermolecular interaction. Moreover, the group contribution method was utilized to study the limiting partial molar volume (Vφ0), and the contributions of the end group (-NH2,-COONa), CH- group, CH2- group, CH3- group, OH- group and CNHNHNH2- group to the limiting partial molar volume (Vφ0) were obtained. The results show that all these groups have positive contributions to the limiting partial molar volume (Vφ0).

A luminescent turn-up metal-organic framework sensor for tryptophan based on singlet-singlet Förster energy transfer.

A water stable metal-organic framework, ZJU-108, was designed and successfully synthesized as a luminescent turn-up sensor, and it can discriminate tryptophan from other natural amino acids in aqueous solution. Because of the apparent lower singlet level of tryptophan compared with other amino acids, the singlet-singlet Förster energy transfer mechanism was applied to design a luminescent sensor. As a result, a selective MOF sensor for tryptophan was realized by choosing the ligand with the appropriate singlet energy level. As expected, ZJU-108 shows an excellent luminescence enhancement response to tryptophan over other natural amino acids with a detection limit of 42.9 nM. This work presents a new insight for designing turn-up MOF sensors and demonstrates the potential of ZJU-108 as a luminescent probe for the detection of tryptophan.

Investigation of Volumetric and Acoustic Properties of Procainamide Hydrochloride in Aqueous Binary and (Water + Amino Acid) Ternary Mixtures at Different Temperatures

For effective drug design and development, an integrated process utilizing all available information from structural, thermodynamic, and biological studies plays a very important role. To understand the energy basis of molecular interactions utilizing various thermodynamic methods, volumetric and acoustic studies are vital early in the development process of any drug toward an optimal energy interaction profile while retaining a good pharmacological assay. In this article, we are reporting the data of densities (ρ) and speeds of sound (u) of an antiarrhythmic agent, namely, procainamide hydrochloride in an aqueous binary and aqueous solution of amino acids, i.e., l-alanine and l-valine at T = (298.15, 308.15 and 318.15) K. Different thermodynamic parameters such as the apparent molar volume (Vϕ) of the solute, the isentropic compressibility (κs) of the solution, and the apparent molar isentropic compressibility (κϕ) of procainamide hydrochloride in water and aqueous solutions of l-alanine and l-valine have been computed using the density and speed of sound data at different temperatures. The limiting apparent molar volume (Vϕ0) of solute and the limiting apparent molar compressibility (κϕ0) of solute in binary and ternary aqueous solutions have been obtained by extrapolating the plots. The results have been interpreted in light of the competing solute–solute and solute–solvent interactions.

A molecular rotor based ratiometric sensor for basic amino acids

The inevitable importance of basic amino acids, arginine and lysine, in human health and metabolism demands construction of efficient sensor systems for them. However, there are only limited reports on the ‘ratiometric’ detection of basic amino acids which is further restricted by the use of chemically complex sensor molecules, which impedes their prospect for practical applications. Herein, we report a ratiometric sensor system build on simple mechanism of disassociation of novel emissive Thioflavin-T H-aggregates from heparin surface, when subjected to interaction with basic amino acids. The strong and selective electrostatic and hydrogen bonding interaction of basic amino acids with heparin leads to large alteration in photophysical attributes of heparin bound Thioflavin-T, which forms a highly sensitive sensor platform for detection of basic amino acids in aqueous solution. These selective interactions between basic amino acids and heparin allow our sensor system to discriminate arginine and lysine from other amino acids. This unique mechanism of dissociation of Thioflavin-T aggregates from heparin surface provides ratiometric response on both fluorimetric and colorimetric outputs for detection of arginine and lysine, and thus it holds a significant advantage over other developed sensor systems which are restricted to single wavelength detection. Apart from the sensitivity and selectivity, our system also provides the advantage of simplicity, dual mode of sensing, and more importantly, it employs an inexpensive commercially available probe molecule, which is a significant advantage over other developed sensor systems that uses tedious synthesis protocol for the employed probe in the detection scheme, an impediment for practical applications. Additionally, our sensor system also shows response in complex biological media of serum samples.

A water-stable lanthanide metal-organic framework for fluorimetric detection of ferric ions and tryptophan

The preparation of a highly water stable and porous lanthanide metal-organic framework (MOF) nanoparticles (denoted SUMOF-7II; SU refers to Stockholm University) is described. SUMOF-7II was synthesized starting from the tritopic linker of 2,4,6-tri-p-carboxyphenyl pyridine (H3L2) and La(III) as metal clusters. SUMOF-7II forms a stable dispersion and displays high fluorescence emission with small variation over the pH range of 6 to 12. Its fluorescence is selectively quenched by Fe(III) ions compared to other metal ions. The intensity of the fluorescene emission drops drops linearly in 16.6–167 μM Fe(III) concentration range, and Stern-Volmer plots are linear. The limit of detection (LOD) is 16.6 μM (at an S/N ratio of >3). This indicator probe can also be used for selective detection of tryptophan among several amino acids. Compared to the free linker H3L2, SUMOF-7II offers improved sensitivity and selectivity of the investigated species.Graphical abstractA water-stable porous lanthanide metal-organic framework SUMOF-7II (La) has shown to be an excellent probe for the detection of ferric ions among other metal ions, and tryptophan among other amino acids in aqueous solution. The new probe displays high and stable fluorescence signal in a wide pH range (6–12).

Drop coating deposition Raman spectroscopy of proteinogenic amino acids compared with their solution and crystalline state

The Raman spectra of 20 proteinogenic amino acids were recorded in the solution, glass phase (as drop coating deposition Raman (DCDR) samples) and crystalline forms in the wide spectral range of 200–3200cm−1. The most apparent spectral differences between the Raman spectra of the crystalline forms, glass phases and aqueous solutions of amino acids were briefly discussed and described in the frame of published works. The possible density dependencies of spectral bands were noted. In some cases, a strong influence of the sample density, as well as of the organization of the water envelope, was observed. The most apparent changes were observed for Ser and Thr. Nevertheless, for the majority of amino acids, the DCDR sample form is an intermediate between the solution and crystalline forms. In contrast, aromatic amino acids have only a small sensitivity to the form of the sample. Our reference set of Raman spectra is useful for revealing discrepancies between the SERS and solid/solution spectra of amino acids. We also found that some previously published Raman spectra of polycrystalline samples resemble glassy state rather than crystalline spectra. Therefore, this reference set of spectra will find application in every branch of Raman spectroscopy where the spectra of biomolecules are collected from coatings.

Concentration Measurement of Amino Acid in Aqueous Solution by Quantitative 1H NMR Spectroscopy with Internal Standard Method.

We describe a procedure to determine concentrations of amino acid standard solutions by quantitative NMR spectroscopy using an internal standard. The measurement samples were prepared by solvent exchange to remove any intense solvent signal in the 1H NMR spectra. The method was demonstrated on valine aqueous solutions of different concentrations. The accuracy of the measured concentrations that fell well within the range of the expanded uncertainty is also discussed. All of the results are in good agreement with the preparation values. We believe that this approach should be useful to determine the concentrations of standard solutions whose solute components are difficult to weigh because of extremely small amount or hygroscopicity.

A chemosensor selection for the fluorescence identification of tryptophan (Trp) amino acids in aqueous solutions with nanomolar detection

A new disulfide-based, imine-linked fluorescent receptor 1 has been synthesized for the highly selective gratitude of tryptophan (Trp) among the all amino acids investigated in aqueous solutions via synergistic effects of intermolecular hydrogen bonding and electrostatic interactions. The photophysical properties of the receptor 1 were evaluated by UV/Vis absorption and fluorescence spectroscopic methods. Receptor 1 selectively recognized tryptophan (Trp) amino acid in DMSO/water with a detection limit down to 47.6nM. The mechanism of binding was fully validated by computational studies. The theoretical calculations revealed the role of π-π stacking as well as hydrogen bonding in binding of tryptophan with receptor.

Thermodynamics of Hydrophobic Amino Acids in Solution: A Combined Experimental-Computational Study.

We present a joint experimental–computational study to quantitatively describe the thermodynamics of hydrophobic leucine amino acids in aqueous solution. X-ray scattering data were acquired at a series of solute and salt concentrations to effectively measure interleucine interactions, indicating that a major scattering peak is observed consistently at q = 0.83 Å–1. Atomistic molecular dynamics simulations were then performed and compared with the scattering data, achieving high consistency at both small and wider scattering angles (q = 0–1.5 Å–1). This experimental–computational consistence enables a first glimpse of the leucine–leucine interacting landscape, where two leucine molecules are aligned mostly in a parallel fashion, as opposed to antiparallel, but also allows us to derive effective leucine–leucine interactions in solution. Collectively, this combined approach of employing experimental scattering and molecular simulation enables quantitative characterization of effective intermolecular interactions of hydrophobic amino acids, critical for protein function and dynamics such as protein folding.

Mode specific THz spectra of solvated amino acids using the AMOEBA polarizable force field.

We have used the AMOEBA model to simulate the THz spectra of two zwitterionic amino acids in aqueous solution, which is compared to the results on these same systems using ab initio molecular dynamics (AIMD) simulations. Overall we find that the polarizable force field shows promising agreement with AIMD data for both glycine and valine in water. This includes the THz spectral assignments and the mode-specific spectral decomposition into intramolecular solute motions as well as distinct solute-water cross-correlation modes some of which cannot be captured by non-polarizable force fields that rely on fixed partial charges. This bodes well for future studies for simulating and decomposing the THz spectra for larger solutes such as proteins or polymers for which AIMD studies are presently intractable. Furthermore, we believe that the current study on rather simple aqueous solutions offers a way to systematically investigate the importance of charge transfer, nuclear quantum effects, and the validity of computationally practical density functionals, all of which are needed to fully quantitatively capture complex dynamical motions in the condensed phase.

Methane hydrate-liquid-vapour-equilibrium phase condition measurements in the presence of natural amino acids

This work reports the thermodynamic effect of five amino acids on methane hydrate phase boundary. The studied amino acids are glycine, alanine, proline, serine and arginine. To effectively investigate the impact of selected amino acids on methane hydrates formation, the methane hydrate-liquid-vapour-equilibrium (HLwVE) curve is measured in amino acids aqueous solutions. Experiments are performed at concentration range of 5–20 wt% by employing the isochoric T-cycle method in a sapphire hydrate cell reactor at pressures and temperatures range of 3.86–9.98 MPa and 276.50–286.00 K, respectively. Results suggests that, all studied amino acid inhibits methane hydrate formation. Glycine showed the highest inhibition effect with an average depression temperature of 1.78 K at 10 wt%. The impact of inhibition is due to amino acids hydrogen bonding energies, confirmed via COSMO-RS predictions and side group alkyl chain. The inhibition impact of glycine is found to be in the range of some ionic liquid (OH-EMIM-Cl) and slightly higher than ethylene glycol (a conventional thermodynamic hydrate inhibitor) at 10 wt%. The methane hydrate dissociation enthalpies in the presence of amino acids are calculated using Clausius–Clapeyron equation, which suggests that, amino acids do not take part in methane hydrate cage occupation during hydrate formation.

An In Silico study of TiO2 nanoparticles interaction with twenty standard amino acids in aqueous solution.

Titanium dioxide (TiO2) is probably one of the most widely used nanomaterials, and its extensive exposure may result in potentially adverse biological effects. Yet, the underlying mechanisms of interaction involving TiO2 NPs and macromolecules, e.g., proteins, are still not well understood. Here, we perform all-atom molecular dynamics simulations to investigate the interactions between TiO2 NPs and the twenty standard amino acids in aqueous solution exploiting a newly developed TiO2 force field. We found that charged amino acids play a dominant role during the process of binding to the TiO2 surface, with both basic and acidic residues overwhelmingly preferred over the non-charged counterparts. By calculating the Potential Mean Force, we showed that Arg is prone to direct binding onto the NP surface, while Lys needs to overcome a ~2 kT free energy barrier. On the other hand, acidic residues tend to form “water bridges” between their sidechains and TiO2 surface, thus displaying an indirect binding. Moreover, the overall preferred positions and configurations of different residues are highly dependent on properties of the first and second solvation water. These molecular insights learned from this work might help with a better understanding of the interactions between biomolecules and nanomaterials.

Solvation behaviour of some amino acids in aqueous solutions of an antibiotic drug streptomycin sulfate at different temperatures: Volumetric, acoustic and viscometric approach

The volumetric, acoustic and viscometric approach has been used for investigating the interactions of l-serine, l-threonine and l-leucine in aqueous solutions of an antimycobacterial drug, namely, streptomycin sulfate, over a temperature range of (305.15, 310.15 and 315.15) K at atmospheric pressure. The apparent molar volume, Vϕ, limiting apparent molar volume, V0ϕ, the slope, Sv, partial molar volume of transfer, V0ϕ, tr, limiting apparent molar expansivity, E0ϕ, and Hepler's constant, (∂2V0ϕ/∂T2)P, have been calculated from density data. The apparent molar isentropic compression, Kϕ,s, limiting apparent molar isentropic compression, K0ϕ,s, its slope, Sk, and partial molar isentropic compression of transfer, K0ϕ,s,tr, have been calculated from speed of sound data. The compression data is also used for calculating the number of water molecules hydrated, nH, to the amino acids. The viscosity data has been used to determine relative viscosity ηr, viscosity B-coefficients, temperature derivative of B-coefficients, dB/dT and viscosity B-coefficients of transfer, Btr. Solvation behaviour, of amino acids has also been computed. The calculated parameters have been discussed in terms of various solute–solute and solute–solvent interactions prevailing in these solutions. Further, a detailed insight into the physicochemical interactions, e.g., ion-hydrophilic and hydrophilic–hydrophilic interactions in the amino acids in conjunction with the drug along with the structure-making/structure-breaking tendency has been retrieved through the perusal of these calculated parameters.

Spectroscopic Study of Interactions of Metal Complexes, Metal Salts and Amino Acids with Anionic Surfactant Sodium Dodecyl Sulphate (SDS) Using Surfactant-Solute-PAN Dye Ternary Systems

The study of micellar behavior of SDS in presence of additives such as metal (Fe, Cu, Co, Zn) phendione complexes, calcium salts and amino acids in aqueous solutions in surfactant-solute-1-(2-pyridylazo)-2-naphthol(PAN) dye ternary systems were carried out by measuring the absorbance of PAN at 470 nm. The complexes [Fe(phendione)3](ClO4)2·2H2O, [Co(phendione)3](ClO4)2·3H2O, and [Cu(phendione)2] (ClO4)2·2H2O, decreased the CMC value of SDS from 8 mM to 0.70 mM, 0.40 mM, and 1.0 mM, respectively. In presence of calcium salts (CaCl2, CaF2, calcium acetate, calcium oxalate·H2O) the CMC of SDS decreased. The study of interaction of amino acids with anionic surfactant SDS provides important information about protein-surfactant and peptide-surfactant interaction in aqueous environment. In the present study glycine, L-alanine, L-valine, L-histidine, L-leucine, L-lysine have been used as additives in SDS aqueous solution which also decreased the CMC of SDS. The thermodynamic parameters for each series were obtained from absorbance versus concentration curves. Among the series more negative values for ?G0mic of SDS are observed for the metal complexes. Amino acids series as well as metal salts show similar negative values for ?G0mic of SDS. Negative values of ?G0mic indicated that the process of micellization is thermodynamically favorable.

ChemInform Abstract: Ruthenium‐Catalyzed Hydrogenation of Aromatic Amino Acids in Aqueous Solution.

AbstractL‐phenylalanine and L‐phenylglycine are converted exclusively into the corresponding L‐cyclohexyl amino acids with retention of chirality and excellent selectivity.

Conductometric analysis of 1-butyl-3-methylimidazolium ibuprofenate as an active pharmaceutical ingredient ionic liquid (API-IL) in the aqueous amino acids solutions

In this work, electrical conductivities of the active pharmaceutical ingredient in ionic liquid form (API-IL), 1-butyl-3-methylimidazolium ibuprofenate, [BMIM][Ibu] in water and in the aqueous solutions of amino acids, glycine and l-alanine have been measured at T=(288.15–318.15)K. The calculated molar conductivity data were analyzed by two famous conductivity models, low concentration Chemical Model (lcCM) and Fernandez-Prini (FP). The results show that the FP equation is more appropriate for analysis of the molar conductivity data because the calculated parameters are not highly influenced by the initial guess values of the parameters. Using these models, the limiting molar conductivities (Λ0), ion association constants (KA) and standard Gibbs energy (ΔGA0) for the ion association process of the API-IL have been calculated. The values of Λ0 and KA decrease as the concentration of amino acid increase. This trend may be attributed to low mobility of the ions with large radii produced during the solvation of the ions by zwitterions of the amino acids. The values of Λ0 and KA also increase from glycine to l-alanine solutions. The ions of [BMIM][Ibu] are more solvated by (COO−/NH3+) zwitterionic centers of glycine rather than l-alanine. The more negative values of ΔGA0 for [BMIM][Ibu] in l-alanine rather than glycine solutions indicates that more spontaneously and more feasibility of the ion association process in this amino acid.

An EPR and voltammetric study of simple and mixed copper(II) complexes with l- or d-glutamate and l-arginate in aqueous solution

EPR CW measurements at room and low temperature have been carried out on the systems containing 63copper(II) nitrate, l-Arg and l-or d-Glu or dl- racemic mixtures of both amino acids in aqueous solution or in mixed solvents. For these copper(II) bis and ternary complexes, RT EPR spectra revealed that mixtures of cis and trans conformers are really present in aqueous solution. In most cases, for these systems, the cis conformer is more abundant at the lowest temperature (275K). Increasing gradually the temperature from 275K to 305K the cis/trans ratio tends towards the trans conformer. This latter is less abundant in the case of [Cu(l-Glu)2], because of the possible interaction of negative side chain carboxylate anions with the water molecules axially bound, and for [Cu(l-Arg)(d-Glu)], probably owing to a possible electrostatic interaction between the two opposite charged side chains which are on the same side of the CuN2O2 coordination plane. Low temperature frozen solution EPR spectra run on these systems show the presence of only one absorbing specie thus giving reason to the stabilization of one conformer over the other, in particular, the cis conformer. There are no evident differences in the anisotropic Spin Hamiltonian parameters derived from the frozen EPR solution spectra of these systems, which are characterized by a tetragonally elongated octahedral stereochemistry. SWV measurements confirmed the EPR spectroscopic data, actually giving rise to the observation of slightly asymmetrical peaks, which revealed two near formal redox potentials assigned to the two conformers.

Density and Viscosity Study of Interactions of Some Amino Acids in Aqueous Solutions of Sodium Benzoate

The density (ρ) and viscosity (η) of three amino acids, glycine, l-alanine, and l-valine, have been determined as a function of amino acid concentration in aqueous solutions of 0.1011, 0.3088, and 0.5245 mol·kg–1 sodium benzoate at temperatures 303.15, 308.15, and 313.15 K. Apparent molar volumes (Vϕ), limiting values of apparent molar volumes (V0ϕ), and transfer volumes (ΔtV0ϕ) have been calculated from the density data. The viscosity data could be fit to the Jones–Dole equation, and B coefficients and variation of B with temperature dB/dT were obtained at different concentrations and temperatures. Free energies of activation of the solvent (Δμ10≠) and solute (Δμ20≠) were also calculated by application of the Eyring transition-state theory. The obtained thermophysical data have been interpreted in terms of the structure of the amino acids and their interactions with the sodium benzoate solution.

Solubility of glycine and DL-nor-valine in aqueous solutions of NaNO3 and KNO3 and measurements of transfer thermodynamics

The solubility and solvation thermodynamics of the amino acids in aqueous solutions are related to their biochemical and biophysical actions in human physiology. This makes such studies to be highly relevant for academia, health and industry. In the present work solubilities of glycine and DL-nor-valine were measured under different experimental conditions by an analytical gravimetric method in aqueous NaNO3 and KNO3 solutions and the results were employed as an input in theoretical solvation investigations. Thermodynamic parameters like standard transfers Gibbs energies and entropies and other important physicochemical parameters such as molar volume, density, dipole moment, mixed solvent diameter, etc., of the experimental solutions were evaluated at 298.15K and compared with earlier values. Finally the above mentioned parameters were used to conclude ΔGt,ch0(i) i.e. chemical effects of the transfer Gibbs energies and ΤΔSt,ch0(i) i.e. chemical effects of the transfer entropy. Different factors such as nature of solute and solvent, interactions between solute and solvents, etc., which are influencing the solvation of glycine and DL-nor-valine were also characterized by different physical and analytical techniques.