Amino Acids In Aqueous Solutions Research Articles

Water Activity in Aqueous Amino Acid Solutions Containing Ammonium Sulfate at 298.2 K

Water activity in aqueous solutions of dl-alanine, glycine, or l-serine, with ammonium sulfate, molality ranging from 0.5 to 5.0, have been measured at 298.2 K. The new experimental data was correlated using three different theoretical schemes such as Zdanovskii–-Stokes–Robinson, its extension, or the Clegg–Seinfeld–Brimblecombe approach, with global average absolute deviations in the calculation of the osmotic coefficient of 3.46 %, 0.93 % and 1.95 %, respectively. The extended Zdanovskii–Stokes–Robinson method also enabled the prediction of unsymmetric molal activity coefficients of the electrolyte, in fair agreement with the experimental values found from literature measured by an electrochemical method. It is evidenced the usefulness of the experimental ternary data measured to extend the capabilities of thermodynamic models to higher salt and amino acid concentrations.

DFT Study of the Effects of Halogen Anions on the Stability of Alanine Zwitterion

Alanine is the most abundant and important amino acid found in proteins, and is present on both the interior and exterior surface of proteins in contact with water. The structure of alanine has been studied both experimentally and theoretically by many researchers. Using a highpressure mass spectrometer (HPMS) and ab initio calculations, Wu et al. showed that certain organic ammonium ions are able to stabilize the zwitterionic structure of amino acids. Amino acids in aqueous solutions also exist in the zwitterionic form over a wide range of pH. However, they do not exist in the zwitterionic form in the gas phase. Zwitterions play an important role in variety of biological reactions. The electric fields of zwitterionic structures serve as the driving force that determines the activity of amino acids, peptides, and proteins. In particular, many drugs are present in their zwitterionic form and exhibit strong electrostatic interactions with protein receptors. Because of the instability of amino acid zwitterions in the gas phase, direct experimental evidence of their behavior is lacking; therefore, numerous attempts were made to stabilize gas-phase zwitterions. On the basis of ab initio calculations, Jensen et al. reported that two water molecules can stabilize the glycine zwitterion. Metalation and protonation also stabilize the amino acid zwitterions. Kass stabilized the zwitterionic glycine using oxalic and malonic dianions, which cannot exist independently in the gas phase. He also examined the utility of self-stabilized anionic species to stabilize amino acid zwitterionic structures. On the basis of this finding, and as continuation of our studies on organic radicals and alanine radical cations, we report the effects of halogen anions on the stability of the alanine zwitterion in this paper. All theoretical calculations on structures considered in this study were carried out with the Gaussian 09 series of programs. The relativistic effects play important roles in the Br and I elements, and accordingly their electrons near the nuclei are represented with the LanL2DZ basis set containing effective core potential (ECP). In accordance with ref 13, F and Cl elements were treated the same method as Br and I. DFT calculations were evaluated at the B3LYP level, and ab initio calculations were performed using the MP2 level of theory. Equilibrium geometries of each structures were fully optimized without any restriction on symmetries. Vibration frequencies were also calculated to confirm whether all the stationary points correspond to the true minima. The stationary structures were obtained by verifying if the harmonic frequencies for the local minimum were real. In this study, halogen anions (X = F−, Cl−, Br−, and I−) were used as the anionic stabilizer for zwitterionic alanine in the gas phase. Through interactions with binding sites of halogen anionic stabilizers (2X−), alanine zwitterions (AZW) can be stabilized and form AZW–2X− complexes. The dissociation energy (DE) of the AZW–2X− complexes were estimated using the following equation:

Bionanocomposite materials from layered double hydroxide/N-trimellitylimido-l-isoleucine hybrid and poly(vinyl alcohol)

Nanocomposites (NCs) of poly(vinyl alcohol) (PVA) with chiral-modified magnesium–aluminum-layered double hydroxides (LDHs) were prepared by solution intercalation method. A novel chiral organomodified LDH was synthesized from the coprecipitation reaction of the aluminum (III) nitrate nonahydrate, magnesium (II) nitrate hexahydrate, and bioactive N-trimellitylimido-l-isoleucine amino acid in aqueous solution via simple, fast, and green method under ultrasound irradiation for the first time. The morphology and structure of the obtained material are examined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), and field-emission SEM techniques. The TEM and XRD structure study revealed a coexistence of exfoliated and intercalated modified LDH in PVA matrix. The effects of modified LDH contents on the thermal property of PVA films were investigated by thermogravimetric analysis method, and the results show that by the addition of the modified LDH into the PVA causes an increase in the thermal decomposition temperatures of the novel NC materials.

Investigations on solute–solvent interactions of amino acids in aqueous solutions of sodium dihydrogen phosphate at different temperatures

The interactions of amino acids glycine, l-alanine and l-valine with sodium dihydrogen phosphate as a function of temperature have been investigated by the combination of volumetric and acoustic measurements. Densities and speeds of sound of amino acids in aqueous solutions of sodium dihydrogen phosphate have been measured at T = 288.15, 293.15, 298.15, 303.15 and 308.15 K and atmospheric pressure. The apparent molar volume (V ϕ ), the partial molar volume ( $$V_{\phi }^{0}$$ ) and standard partial molar volumes of transfer ( $$\Delta V_{\phi }^{0}$$ ) for amino acids from water to aqueous sodium dihydrogen phosphate solutions have been calculated from density data. Partial molar isentropic compression ( $$\kappa_{\phi ,s}$$ ) and partial molar isentropic compression of transfer ( $$\Delta \kappa_{\phi ,S}^{0}$$ ) have been calculated from speed of sound data. The pair and triplet interaction coefficients have been calculated from both the properties. The results have been explained based on competing patterns of interactions of co-solvents and the solute.

Dielectric spectra broadening as a signature for dipole-matrix interaction. IV. Water in amino acids solutions

In this paper, the fourth one of our series on the dielectric spectrum symmetrical broadening of water, we consider amino acid (AA) aqueous solutions. The developed 3D-trajectory is applied here to the variety of zwitterion amino acids representing both the hydrophobic and hydrophilic nature of their residues. The dipole moment of amino acids due to their zwitterion determines their interaction with the solvent and reflects mostly the dipole-matrix interactions described in our Paper I [E. Levy et al., J. Chem. Phys. 136, 114502 (2012)]. It is also shown that in the case of charged AAs at high concentrations, the shape of the 3D trajectory transforms to the pattern typical of the dipole-charge interactions that were described in our Paper III [A. Puzenko et al., J. Chem. Phys. 137, 194502 (2012)].

Stabilities of the Ternary Complexes of Copper(II) with Substituted 1,10-Phenanthrolines and Some Amino Acids in Aqueous Solution

In this study the binary and ternary complexes of copper(II) with substituted 1,10-phenanthrolines [s-phen: 1,10-phenanthroline (phen), 4,7-dimethyl-1,10-phenanthroline (dmphen) and 5-nitro-1,10-phenanthroline (nphen)] and l-amino acids [aa: l-phenylalanine (phe), l-tyrosine (tyr) and l-tryptophan (trp)] have been investigated using potentiometric methods in 0.1 mol·L−1 KCl aqueous ionic media at 298.2 K. The protonation constants of the ligands and the stability constants of the binary and ternary complexes of Cu(II) with the ligands were calculated from the potentiometric data using the “BEST” software package. It was inferred that the aromatic 1,10-phenanthrolines act as a primary ligand in the ternary complexes, while the oxygen and nitrogen donor-containing amino acids are secondary ligands. The observed values of Δlog10 K indicate that the ternary complexes are more stable than the binary ones, suggesting no interaction takes place between the ligands in the ternary complexes. The magnitudes of the measured stability constants of all of the ternary complexes are in the order [Cu(s-phen)(trp)]+ > [Cu(s-phen)(tyr)]+ > [Cu(s-phen)(phe)]+, which is identical to the sequence found for the binary complexes of Cu(II) with the amino acids. When the substituted 1,10-phenanthroline is changed, the stability constants of the ternary complexes decrease in the following order: [Cu(dmphen)(aa)]+ > [Cu(phen)(aa)]+ > [Cu(nphen)(aa)]+.

Solvation behaviour of biologically active compounds in aqueous solutions of antibacterial drug amoxicillin at different temperatures

The interactions of glycine (Gly), l-alanine (Ala), l-valine (Val) and l-Leucine (Leu) with drug amoxicillin (AMX) as a function of temperature have been investigated by combination of volumetric and acoustic measurements. Densities and speeds of sound of amino acids in aqueous solutions of amoxicillin have been measured at T=(305.15, 310.15 and 315.15)K and atmospheric pressure. The apparent molar volume (Vϕ), the partial molar volume (Vϕ0) and standard partial molar volumes of transfer (ΔVϕ0) for amino acids from water to aqueous amoxicillin solutions have been calculated from density data. Group contributions of amino acids to partial molar volume were determined. Partial molar isentropic compression (κϕ,s) and partial molar isentropic compression of transfer (Δκϕ,S0) have been calculated from speed of sound data. The pair and triplet interaction coefficient have been calculated from both the properties. The results have been explained based on competing patterns of interactions of co-solvents and the solute.

A fluorescence turn-on probe for the detection of thiol-containing amino acids in aqueous solution and bioimaging in cells

A turn-on fluorescent probe, based on a water-soluble terphenyl derivative, for the detection of cysteine and homocysteine is reported. The aldehyde groups in the probe play crucial roles in providing reaction with thiol groups in the amino acids, leading to a formation of thiazolidine (from cysteine) or thiazinane ring (from homocysteine). As a result, the new formation of such rings alters the electronic property of the conjugated system in the probe and results in emission enhancement. The probe in aqueous solution exhibits a remarkable increase in its quantum yield upon exposure to cysteine (up to 20-fold) and to homocysteine (up to 700-fold), while slight quenching is observed in the presence of glutathione. Moreover, an investigation on time-resolved fluorescence spectra of the probe in the presence of cysteine and homocysteine reveals potential discriminatory detection of cysteine and homocysteine. Bioimaging of the thiols in live HeLa cells was successfully applied.

Apparent molar volume, compressibility and viscometric studies of sodium dodecyl benzene sulfonate (SDBS) and dodecyltrimethylammonium bromide (DTAB) in aqueous amino acid solutions: A thermo-acoustic approach

Abstract In this paper, we examine density (d), ultrasonic velocity (u) and viscosity studies of SDBS and DTAB in water and in aqueous solutions of 0.01, 0.05, 0.10 mol kg−1 l -glutamine, l -histidine and l -methionine at T = 293.15, 298.15, 303.15, 308.15, 313.15 K. The apparent molar volume (ϕv) dependence on SDBS and DTAB concentration reflects the modification of water–water interactions described as hydrophobic hydration of the surfactant molecules in the presence of amino acid. The trends of apparent molar adiabatic compression (ϕk) values of DTAB with surfactant concentration appear reasonable to suggest that hydrophilic hydration of DTAB–amino acid complex occurs at low surfactant concentration region rendering it to be negative. The gradual increase in viscous relaxation time (τ) with rise in concentration of surfactant and decrease with temperature seem to be happen due to the structural relaxation processes occurring as a result of re-arrangement of molecules.

Studies on sodium dodecylsulfate in aqueous and in aqueous amino acid solutions: Volumetric and viscometric approaches

Physicochemical properties like density, ultrasound velocity and viscosity of aqueous solutions of glycine and SDS (sodium dodecylsulfate) in 0.1m aqueous glycine solution as a function of concentration at different temperatures ranging from 293.15K to 313.15K have been determined. These data have been used to calculate apparent molar volume, isentropic compressibility and viscosity B-coefficient values of the studied solutions. The viscosity coefficients A and B have been determined from the Jones–Dole equation. The limiting apparent molar volumes (ϕv0) and experimental slopes (Sv) derived from the Masson equations have been interpreted in terms of solute–solute and solute–solvent interactions. From the volumetric and viscometric data, the structural effect of SDS in glycine solution has been discussed. The change in free energy, enthalpy and entropy of activation were calculated using the Nightingale and Benck, and Eyring equations. Glycine in aqueous solution exhibits structure-breaking behaviour. The results were explained in terms of structure making and structure breaking properties.

Investigation on molecular interaction of amino acids in aqueous disodium hydrogen phosphate solutions with reference to volumetric and compressibility measurements

The interactions of amino acids glycine (Gly), l-alanine (Ala), and l-valine (Val) with disodium hydrogen phosphate (DSHP) as a function of temperature have been investigated by combination of volumetric and acoustic measurements. Densities (ρ) and speeds of sound (u) of amino acids in aqueous solutions of disodium hydrogen phosphate have been measured at T=(288.15, 293.15, 298.15, 303.15 and 308.15)K and atmospheric pressure. The apparent molar volume (Vϕ), the partial molar volume (Vϕ0) and standard partial molar volumes of transfer (ΔVϕ0) for amino acids from water to aqueous disodium hydrogen phosphate solutions have been calculated from density data. Partial molar adiabatic compressibility (κϕ,s) and partial molar adiabatic compressibility of transfer (Δκϕ,S0) have been calculated from speed of sound data. The pair (VAB,κAB) and triplet (VABB,κABB) interaction coefficient have been calculated from both the properties. The results have been explained based on competing patterns of interactions of co-solvents and the solute.

Study of the interactions of PAMAM-NH2 G4 dendrimer with selected natural amino acids in aqueous solutions

The interactions of PAMAM-NH2 G4 dendrimer with selected natural amino acids (Gly, Ala, Val, Leu, Ile, Phe, Ser, Thr, Met, Asn, Gln, Pro and Trp) in aqueous solutions were measured with the use of the techniques of calorimetric titration and dilution calorimetry. The results of calorimetric measurements show strong interactions between PAMAM-NH2 G4 dendrimer and amino acids with polar substituents. A macromolecule of PAMAM-NH2 G4 dendrimer can coordinate 20 to 40 molecules of amino acid.

Group-contribution to limiting partial molar isentropic compressions of small amphiphile molecules in water. The temperature effect

A simple additive scheme based on a multi-parametric least-squares fitting method is described and employed to estimate group-contributions to limiting partial molar isentropic compressions of small amphiphile molecules in water. To complement high quality literature data for aqueous solutions of aliphatic alcohols, alkoxyalcohols, amines, alkoxyamines, aminoalcohols, amino-acids and dipeptides, new accurate densities and ultrasound speeds have been experimentally determined for several very-dilute aqueous solutions of 2-(isopropylamino)ethanol, 2-butoxyethanol and 2-isobutoxyethanol at 5K intervals in the temperature range T=(283.15 to 303.15)K. Reliable limiting partial molar isentropic compressions for 31 amphiphiles in water at five fixed temperatures have been used to estimate group-contribution values and their associate uncertainties of the following eleven structural groups: CH3; CH2; CH; N; NH; NH2; CH2COCH2; CH2OH; CHOH; COOH; and CONH, at five different temperatures. The goodness of the fit of reconstituted against experimental values indicates that a consistent set of group-contribution values has been obtained and that their dependence on temperature deserves credit. These values and their sensibility to temperature changes have been analysed in terms of hydration processes in solution. Deviations of predicted from experimental values are found for molecules containing a vicinal diol group and dipeptides showing hindrance or enhancement of H-bond formation. These deviations for molecules not included in the basic set, are tentatively explained.

A colorimetric and fluorescent probe for thiols based on 1, 8-naphthalimide and its application for bioimaging

A new highly sensitive 1, 8-naphthalimide-based compound (probe 1) has been designed and synthesized. The colorimetric and fluorescent properties of probe 1 towards various amino acids were investigated in detail. Specific colorimetry and fluorescence response of probe 1 for thiols were found in PBS buffer solution, which can be deduced to a reaction of thio-promoted conjugate addition/cyclization sequence between probe 1 and thiols. The probe 1 can selectively recognize cysteine rather than other natural amino acids in aqueous solution with a rapid response time. Con-focal fluorescence imaging of cells for detecting thiols in vivo was carried out successfully.

Molecular Dynamics Simulations of Highly Crowded Amino Acid Solutions: Comparisons of Eight Different Force Field Combinations with Experiment and with Each Other

Although it is now commonly accepted that the highly crowded conditions encountered inside biological cells have the potential to significantly alter the thermodynamic properties of biomolecules, it is not known to what extent the thermodynamics of fundamental types of interactions such as salt bridges and hydrophobic interactions are strengthened or weakened by high biomolecular concentrations. As one way of addressing this question we have performed a series of all-atom explicit solvent molecular dynamics (MD) simulations to investigate the effect of increasing solute concentration on the behavior of four types of zwitterionic amino acids in aqueous solution. We have simulated systems containing glycine, valine, phenylalanine or asparagine at concentrations of 50, 100, 200 and 300 mg/ml. Each molecular system has been simulated for 1 μs in order to obtain statistically converged estimates of thermodynamic parameters, and each has been conducted with 8 different force fields and water models; the combined simulation time is 128 μs. The density, viscosity, and dielectric increments of the four amino acids calculated from the simulations have been compared to corresponding experimental measurements. While all of the force fields perform well at reproducing the density increments, discrepancies for the viscosity and dielectric increments raise questions both about the accuracy of the simulation force fields and, in certain cases, the experimental data. We also observe large differences between the various force fields' descriptions of the interaction thermodynamics of salt bridges and, surprisingly, these differences also lead to qualitatively different predictions of their dependences on solute concentration. For the aliphatic interactions of valine sidechains, fewer differences are observed between the force fields, but significant differences are again observed for aromatic interactions of phenylalanine sidechains. Taken together, the results highlight the potential power of using explicit-solvent simulation methods to understand behavior in concentrated systems but also hint at potential difficulties in using these methods to obtain consistent views of behavior in intracellular environments.

Absence of leucine in an essential amino acid supplement reduces activation of mTORC1 signalling following resistance exercise in young females

The purpose of the study was to investigate the specific effect of leucine on mTORC1 signalling and amino acid metabolism in connection with resistance exercise. Comparisons were made between ingestion of supplements with and without leucine. Eight young women performed leg press exercise on 2 occasions. In randomized order they received either an aqueous solution of essential amino acids with leucine (EAA) or without leucine (EAA-Leu), given as small boluses throughout the experiment. Muscle biopsies were taken after an overnight fast before exercise and 1 and 3 h postexercise and samples of blood were taken repeatedly during the experiment. Plasma and muscle concentrations of leucine rose 60%-140% (p < 0.05) with EAA and fell 35%-45% (p < 0.05) with the EAA-Leu supplement. In the EAA-trial, plasma and muscle levels of tyrosine (not present in the supplement) and the sum of the EAA were 15%-25% (p < 0.05) lower during recovery. Phosphorylation of mTOR and p70S6k was elevated to a larger extent following 1 h of recovery with leucine in the supplement (120% vs. 49% (p < 0.05) and 59- vs. 8-fold (p < 0.05) for EAA and EAA-Leu, respectively). The levels of MAFbx and MuRF-1 mRNA and of the corresponding proteins were not significantly altered after 3 h recovery from exercise. In conclusion, the presence of leucine in the supplement enhances the stimulatory effect on mTORC1 signalling and reduces the level of tyrosine and the sum of the EAA in muscle and plasma, suggesting a stimulation of protein synthesis and (or) inhibition of breakdown, leading to improvement in net protein balance.

Thermodynamic Study of RbF/CsF in Amino Acid Aqueous Solution Based on the Pitzer, Modified Pitzer, and Extended Debye–Hückel Models at 298.15 K by a Potentiometric Method

This article reports mean activity coefficients determined by the potentiometric method for RbF and CsF in alanine/proline/serine + water mixtures at 298.15 K. The experimental results were modeled by the Pitzer, modified Pitzer, and extended Debye–Huckel equations. The results showed that the three models fit the experimental data well and gave satisfactory results. The osmotic coefficients, excess Gibbs free energy, and corresponding parameters were also obtained.

Study of mixed micellar aqueous solutions of sodium dodecyl sulfate and amino acids

Thermodynamic properties of sodium dodecyl sulfate (SDS) in micellar aqueous solutions of L-serine and L-threonine were determined by fluorescence spectroscopy and dynamic light scattering techniques. The values of Gibbs free energy, enthalpy and entropy of the process of micelle formation were calculated using the critical micelle concentration and degree of dissociation. Changes in critical micelle concentration of SDS with the addition of amino acids were examined by both conductivity and pyrene I 1/I 3 ratio methods at different temperatures. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of SDS with amino acids. The aggregation behavior of SDS was explained in terms of structural changes in mixed solutions. The data on dynamic light scattering suggest that size of SDS micelles was influenced by the presence of amino acids.

Binary Diffusion Coefficients of Aqueous Phenylalanine, Tyrosine Isomers, and Aminobutyric Acids at Infinitesimal Concentration and Temperatures from (293.2 to 333.2) K

Mutual diffusion coefficients at infinitesimal concentration and atmospheric pressure were measured for binary aqueous solutions of four α-amino acids (2-amino-3-phenylpropanoic acid (phenylalanine), 2-amino-3-(4-hydroxyphenyl)-propanoic acid (p-tyrosine), 2-amino-3-(3-hydroxyphenyl)-propanoic acid (m-tyrosine), and 2-amino-3-(2-hydroxyphenyl)-propanoic acid (o-tyrosine)) at temperatures from (298.3 to 313.2) K and five aminobutyric acid isomers (2-aminobutanoic acid (α-aminobutyric acid), 2-amino-2-methylpropanoic acid (α-aminoisobutyric acid), 3-aminobutanoic acid (β-aminobutyric acid), 3-amino-2-methylpropanoic acid (β-aminoisobutyric acid), and 4-aminobutanoic acid (γ-aminobutyric acid)) at temperatures from (293.2 to 333.2) K. The diffusion coefficients for each of the amino acids were well-represented by a simple correlation as a function of temperature and solvent viscosity with two adjustable parameters determined for each solute. The two parameters determined for each amino acid in our present and previous studies were closely related to the molar volume of the amino acids at its normal boiling point. We proposed predictive correlations for the diffusion coefficients of aqueous amino acid solutions at infinitesimal concentrations and tested the accuracy of the predictions with the reference data for aqueous amino acids at 298.2 K.

Salting-in with a Salting-out Agent: Explaining the Cation Specific Effects on the Aqueous Solubility of Amino Acids

Although the understanding of ion specific effects on the aqueous solubilities of biomolecules is crucial for the development of many areas of biochemistry and life sciences, a consensual and well-supported molecular picture of the phenomena has not yet been established. Mostly, the influence of cations and the nature of the molecular interactions responsible for the reversal of the Hofmeister trend in aqueous solutions of amino acids and proteins are still defectively understood. Aiming at contributing to the understanding of the molecular-level mechanisms governing the cation specific effects on the aqueous solubilities of biocompounds, experimental solubility measurements and classical molecular dynamics simulations were performed for aqueous solutions of three amino acids (alanine, valine, and isoleucine), in the presence of a series of inorganic salts. The evidence gathered suggests that the mechanism by which salting-in inducing cations operate in aqueous solutions of amino acids is different from that of anions, and allows for a novel and consistent molecular description of the effect of the cation on the solubility based on specific interactions of the cations with the negatively charged moieties of the biomolecules.