Amino Acids In Aqueous Solutions Research Articles

Optical sensor based on liquid crystals for detecting the amino acids concentration in aqueous solutions

In the article, we have studied the influence of amino acids in aqueous solutions on the spectral characteristics of cholesteric-nematic mixtures. We used cholesterol-nematic mixtures (BLO62 + 5CB) as an active element of optical sensors for the detection of amino acids (serine, l-histidine, valine) in aqueous solutions. It enabled to use this active medium for amino acid optical sensors.

Terahertz polarization and chirality sensing for amino acid solution based on chiral metasurface sensor

The detection and identification of chiral materials, especially chiral biochemical samples, have a wide range of applications. Terahertz (THz) sensing has obvious advantages in online real-time non-contact and label-free biochemical detection, but it is difficult to detect the chiral solution samples. Herein, we propose a new THz sensing method based on THz reflective time-domain polarization spectroscopy (RTDPS) system and a chiral metasurface sensor. The chiral enantiomers of three kinds of amino acids aqueous solution were measured by this sensing method, which improves sensitivity and detection accuracy for amino acid aqueous solutions compared with the traditional THz resonance sensing. The sensing accuracies of the different amino acid samples are all in the order of 10−5 ∼ 10−4 g/mL, and the minimum value reaches 1 × 10-5 g/mL. Moreover, the D- and L- enantiomers with the same concentration can be distinguished by the significant difference in THz polarization parameters at the characteristic frequency. This method is not only suitable for amino acid aqueous solutions, but also other chiral biochemical solutions. Therefore, THz polarization spectroscopy and chiral metasurface sensor have great potential for high-sensitive quantitative detection and chirality identification in the analysis of biochemical materials.

532‐nm‐excited hyper‐Raman spectroscopy of amino acids

AbstractThis paper reports the hyper‐Raman (HR) spectra of the 20 amino acids in aqueous solution in the range of 400–1,800 cm−1 with an excitation wavelength of 532 nm. A remarkable common feature in the nonresonance HR spectra is the large intensity of the HR bands of the COO− group. Whereas the peak position is mostly identical between the HR and Raman spectra, the intensity pattern is not. We discuss the similarities and dissimilarities between the pattern of the two spectra of each amino acid and give possible assignments to each HR band by comparing them with those of the corresponding Raman band. This study offers a reference for the HR spectra of the amino acids as the basic building block of proteins. It helps interpret the HR spectra of proteins and peptides.

Investigation of the thermodynamic and compressibility properties of antihypertensive drug Hydralazine hydrochloride in aqueous and aqueous amino acids solutions at various temperatures

In present communication we report experimental density and speed of sound data for the antihypertensive drug Hydralazine hydrochloride in water and 0.05 mol.kg−1 L-alanine and L-valine aqueous solutions at temperatures 293.15, 298.15, 303.15, 308.15 and 313.15 K within the molality range of 0.06–0.15 mol.kg−1. By using the experimental density and speed of sound data and appropriate equations, we calculate the parameter like apparent molar volume of solute(Vϕ), limiting apparent molar volume of solute (Vϕ0), apparent molar expansivity(Eϕ), isobaric expansivity coefficient (α), limiting apparent molar expansivity(Eϕ0), isentropic compressibility(Ks), apparent molar isentropic compressibility of solute(KS, ϕ) apparent molar isentropic compressibility at the infinite dilutions(KS, ϕ0), and hydration number(nh). The limiting apparent molar volume of solute has been used to obtain transfer parameter for Hydralazine hydrochloride. The hydration behavior for the experimental studied drug in the different mediums has been understood by computing the hydration number.

Charge Regulation of Natural Amino Acids in Aqueous Solutions

The aim of this work is to develop a predictive model to describe the electrostatic behavior of 20 natural amino acids under diverse solution conditions. A coarse-grained model is proposed to accou...

An extensive thermodynamic study on amino acids aqueous solutions and their CO2 solubility by taking into account dipolar and quadrupolar contributions

Amino acids are significant biological components that in water form predominant species named zwitterions. They are highly dipolar molecules with negative and positive charges. Aqueous solutions of amino acids have numerous practical applications where knowing their thermodynamic behavior is essential to model, design, and optimize processes concerned with them. Although, dipole-dipole interactions play important roles in aqueous solution of amino acids, dipole-quadrupole and quadrupole-quadrupole ones make significant contributions when considering the solubility a highly quadrupolar component such as carbon dioxide in aqueous solution of amino acids, i.e., CO2 capture by an amino acid aqueous solution. According to the literature, there is still room to apply a more simple and effective thermodynamic model considering dipole-dipole interactions for water + amino acid systems where this work did so by applying Cubic-Plus-Polar (CPP) Equation of State (EoS). Moreover, water + amino acid + carbon dioxide systems were thermodynamically modeled by taking into account dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole contributions which such investigation has not yet been carried out in the literature. The predictive capability of the proposed model were extensively examined by evaluating the model-calculated data of activity coefficient, osmotic coefficient, density, and water activity of numerous aqueous solutions of amino acids including glycine, alanine, α-aminobutyric acid, valine, serine, proline, threonine, leucine, cysteine, methionine, glutamic acid, histidine, and arginine at various temperatures. The osmotic coefficient of water + valine + alanine and water + valine + glycine systems were also predicted by CPP EoS. The solubility of CO2 in aqueous solution of methionine was finally calculated by the proposed model over a wide range of pressure. The quantitative and qualitative results provided by CPP EoS verified its reliability in all studied situations.

Synergistic effects of amino acids in clathrates hydrates: Gas capture and storage applications

This study reports enhanced carbon dioxide capture and storage, using gas hydrate-based technology, in the presence of low-dose (0.5 wt%) amino acids (AAs). The aqueous solutions, with l-methionine (l-met) and l-phenylalanine (l-phe), showed higher affinity in CH4 hydrate formation. However, the affinity for CO2 hydrates is high in l-met and very low in l-phe systems. Further, the hydrate conversion is high in the l-met solution in CO2+CH4 gas mixtures. However, it decreased dramatically in l-phe solutions, incredibly if the feed gas rich in CO2 (> 75 mol%). Higher hydrate conversion (~ 4–6 times) for CO2 and CO2+CH4 is observed upon using mixed AA aqueous solutions. Faster and efficient conversion is a consequence of the cooperative effects.

Detection of some amino acids with modulation-doped and surface-nanoengineered GaAs Schottky P-I-N diodes

Most current techniques for analyzing amino acids require substantial instrumentation and significant sample preprocessing. In this study, we designed, fabricated, and tested a scalable diode-based microdevice that allows for direct sensing of amino acids. The device is based on modulation-doped GaAs heterostructure with a Schottky contact on one side. The relatively high mobility and relatively small dielectric constant of GaAs are naturally helpful in this problem. We also paid attention to a proper etching procedure allowing for substantial modification of the surface properties, thereby further boosting the sensing performance. Transport data (I-V, differential conductance) are presented for three qualitatively different classes of amino acids (i.e., nonpolar with aliphatic R-group, polar uncharged R-group, and charged R-group) with glycine, cysteine, and histidine as specific examples, respectively. The conductance for the GaAs-amino acid interface measured using a scanning tunneling microscope (STM) was previously reported to have distinct spectral features. In this paper, we show that measuring the differential conductance of a GaAs diode, whose surface is in direct contact with an aqueous solution of amino acid, is a simple methodology to access useful information, previously available only through sophisticated and equipment-demanding STM and molecular electronics approaches. Density functional theory calculations were used to examine which adsorption processes were likely responsible for the observed surface conductance modification. Last, in future and ongoing work, we illustrate how it might be possible to employ standard multivariate data analysis techniques to reliably identify distinct (95%) single amino acid specific features in near-ambient differential conductance data.

Insight into intermolecular interactions and hydration properties of biologically active amino acids in aqueous solutions of cefepime: volumetric, compressibility and viscometric studies

The measurement of density, speed of sound and viscosity of an amino acid and its dipeptide i.e., glycine and glycylglycine in aqueous solution of antibiotic drug cefepime has been carried out at various temperatures. The density and speed of sound data has been used to obtain partial molar volume partial molar expansion coefficient second derivative hydration number (), isentropic compressibility partial molar isentropic compressibility partial molar volume of transfer and partial molar isentropic compressibility of transfer The viscosity data have been used to calculate the viscosity B–coefficients, its temperature derivative dB/dT, viscosity B–coefficient of transfer () and various thermodynamic parameters of activation of viscous flow i.e., and for amino acid/peptide in cefepime solutions. The dependence of these parameters upon concentration and temperature clearly suggests the role of amino acid/peptide and cefepime in solute-solvent interactions. The obtained results have been explained on the basis of competing pattern of interactions between the co-solute and solute in the studied ternary system in order to deduce important information regarding drug-amino acid/peptide interactions.

Mechanism of lithiation of amino acids in aqueous solutions: A laser desorption/ionization-time-of- flight mass spectrometry and theoretical study

Mono- and di-lithiation of small amino acids (AA) including alanine, proline, histidine and arginine were studied by laser desorption/ionization-time of flight (TOF) mass spectrometry. The mass spectra showed that two adduct cations of amino acids [AA + Li]+ and [AA+2Li-H]+ are formed. The relative intensities of the [AA + Li]+ and [AA+2Li-H]+ peaks in mass spectrum depend on the nature of side chain of the amino acids and the pH of the solution containing AA and lithium salt. In basic solution, the [AA+2Li-H]+ peak was more intense than that of [AA + Li]+ and a reverse trend was observed in the acidic solution. Furthermore, it was found that the di-lithiation of arginine and histidine takes place more favorably than alanine and proline which was attributed to presence of strong basic sites in the side chains of the formers. The theoretical calculations showed that attachment of the first Li+ cation to amino acids enhances their acidity so that [AA + Li]+ is more easily releases it proton compared to AA. Hence, Li+ attachment, basicity of the side chain of AA, and solution pH influence the formation of [AA+2Li-H]+.

Gluconate‐Stabilized Silver Nanoparticles as pH Dependent Dual‐Nanosensor for Quantitative Evaluation of Methionine and Cysteine

AbstractSilver nanoparticles (AgNPs) based naked‐eye and spectrophotometric dual‐nanosensor for two most important biothiols: methionine and cysteine would be highly useful for an analyst. We have explored potential use of gluconate‐stabilized AgNPs (Glu‐AgNPs) for such unique purpose. Simply, aggregation of Glu‐AgNPs by the analyte, methionine/cysteine technique was adopted. Gluconate ions make the AgNPs anionic in nature. The anionic Glu‐AgNPs, as a pH‐ dependent nanosensor are selective to sensing methionine and cysteine over other amino acids in aqueous solution. By tuning pH of the particles’ solution we have at different demonstrated that the equilibria components of methionine/cysteine at different pH may play guiding roles in aggregating the particles, consequently in selectivity and sensitivity of the nanosensor. The LOL, LOQ, and LOD for methionine are 42, 9.89 and 2.97 μM, and for cysteine are 1.4, 0.49 and 0.14 μM, respectively. The interactions of cysteine (Kasso, 3.07x105 M−1) with the anionic Glu‐AgNPs are greater than that of methionine (Kasso, 1.635x104 M−1). Overall, the recovery results from the real samples: urine, blood serum and aCsF are excellent, which may make the developed nanosensor attractive to an analyst.

The temperature of maximum density for amino acid aqueous solutions. An experimental and molecular dynamics study

The temperature of maximum density (TMD) for aqueous solutions of seven amino acids has been experimentally determined by means of density measurements versus temperature. The selected amino acids have been arginine, cysteine, glutamic acid, glutamine, lysine, methionine, and threonine. The TMD dependence against composition has been obtained from the experimental data and characterized through the Despretz constant. All amino acids induce a depression in the TMD as compared with that of pure water. If the mole fraction is selected as composition variable, a clear dependence against amino acid molar mass is observed, which disappears when TMDs are represented versus mass fraction; almost all data shrink onto a single straight line. It must be pointed out that the TMD depressions for all studied amino acids are quite larger than those previously observed for proteins. This suggests that TMDs for proteins cannot be explained as a simple, additive result of its constituents, and, therefore complex cooperative phenomena seem to take place. The partial molar volume at infinite dilution has been obtained from density data, and a consistency test between its temperature dependence and that of temperature of maximum density versus composition has been performed, obtaining satisfactory results. A molecular dynamics study for all the studied systems has been also carried out. Amino acids have been modeled through the OPLS-AA force field, whereas the TIP4P/2005 model was used for water. The temperature of maximum density and partial molar volume have been calculated from the simulated density, and the results are compared with experimental data. Although the agreement is only fair, similar qualitative trends were obtained. The simulated Despretz constants are smaller than the experimental ones, a result that was already previously observed for methanol aqueous solutions. A structural analysis of water molecules in solution along the MD trajectories showed no enhancement of ice-like structures in complete agreement with the TMD decrease with concentration.

Thermodynamic modeling of clathrate hydrate stability conditions in the presence of amino acid aqueous solution

The drawbacks of using chemical compounds in the oil and gas industries necessitate applying green and environmentally friendly compounds. Amino acids can be considered as a fantastic remedy to the regular widely used organic hydrate inhibitors in the gas pipelines and facilities. In the present work, hydrate stability conditions of various hydrate formers including methane, CO2, and natural gas in the attendance of a variety of amino acids (Glycine, Alanine, Serine, Valine, Proline, Arginine, Threonine, Asparagine, Phenylalanine and Histidine) aqueous solutions were theoretically studied. Two distinct approaches are considered: The van der Waals-Platteeuw (vdW-P) theory-based approach in which the activity coefficient parameters of the amino acids are available and the modified Pieroen model proposed by Dickens and Quinby-Hunt in which no information is available for the activity coefficient parameters of the amino acids. The vdW-P theory-based approach applies the solid solution theory in which, the UNIQUAC activity coefficient model is employed to calculate the water activity in the liquid/aqueous phase and the Peng-Robinson equation of state (EoS) is applied for calculation of the vapor/gas phase fugacity. The Dickens and Quinby-Hunt model preforms the cryoscopic method and relates the liquid water-hydrate-vapor/gas curve to the ice-water curve. The average absolute deviation (AAD) for the hydrate dissociation temperatures for all 333 reported hydrate dissociation data points is about 0.22 K, which is satisfactory.

A near-IR Fluorescent Probe for Enantioselective Recognition of Amino Acids in Aqueous Solution.

A novel BINOL-based near-IR fluorescent probe was designed and synthesized by incorporating a rhodamine-like dye. In the presence of Zn(II), this compound was found to exhibit highly enantioselective fluorescence enhancement at λemi > 730 nm and λexc = 690 nm when treated with 14 common amino acids in aqueous solution. An enantioselective fluorescence enhancement ratio up to 163 was observed. The mechanism of the fluorescence response of this probe was investigated by various spectroscopic methods.

Thermo-acoustic properties of maltose in aqueous amino acids system

Abstract Sweetness behavior of a carbohydrate namely maltose was studied in the presence of amino acids (L-alanine and L-arginine) in terms of volumetric and acoustic properties of their solutions. Density (ρ) and ultrasonic velocity (μ) of maltose in different concentrations of amino acids solutions were measured at temperatures 293.15 K, 303.15 K and 313.15 K. Calculated volumetric and acoustic parameters such as apparent molar compressibility, specific molar volume and expansibility factor etc. were explored in terms of molecular interactions present in carbohydrate-amino acid solutions. Obtained results of transfer volume of maltose from aqueous to amino acid systems indicated the presence of ion-ion, ion-polar and hydrophobic–hydrophobic interactions in solutions, which was also confirmed from obtained positive values of apparent molar volume and negative values of apparent molar isentropic compressibility. Calculated value of apparent specific volumes i.e. 0.618 cm3g−1 lies in the range of 0.51 cm3g−1 to 0.71cm3g−1 for sweetness response indicated the sweetness behavior of maltose in aqueous amino acids solutions.

Study to reconnoiter solvation consequences of l-arginine/l-histidine and sodium salicylate in aqueous environment probed by physicochemical approach in the temperature range (293.15–318.15) K

Abstract The densities, ρ, ultrasonic speeds, u and viscosities, η of l-arginine and l-histidine in aqueous-sodium salicylate (1% and 2% sodium salicylate in water, w/w) solvents were measured at temperatures (293.15, 298.15, 303.15, 308.15, 313.15 and 318.15) K and at atmospheric pressure in seven different concentrations. The experimental density data have been used to calculate the apparent molar volume, Vϕ, limiting apparent molar volume, Vϕ° and transfer volume, Vϕ, tr°. Likewise from the ultrasonic speed data, different thermo-acoustical parameters, such as apparent molar compressibility, Ks,ϕ, limiting apparent molar compressibility, Ks, ϕ° and transfer compressibility, Ks, ϕ, tr° have been evaluated. The viscosity data have been used to determine Falkenhagen Coefficient, A, Jones-Dole coefficient, B, free energy of activation of viscous flow per mole of solvent, Δμ1°# and solute, Δμ2°#, entropies, ΔS°# and enthalpies, ΔH°# of activation of viscous flow. These parameters have been discussed in light of solute-solute and solute-solvent interactions prevailing in these solutions and their variations are revealed to get the basic picture of the molecular interactions occurring in the systems studied. The negative values of dB/dT favour structure making behavior of amino acids in aqueous solutions of sodium salicylate. The free energy parameters indicate the formation of transition state in the presence of amino acids.

Computational analysis of amino acids\u2019 adhesion to the graphene surface

The mechanisms of cellular growth have attracted scientists’ attention for a long time, leading to recent efforts in establishing cellular growth on specific functionalized substrates. In order to fully understand the supported cellular growth mechanisms, one needs first to comprehend how individual amino acids interact with the substrate material as cells are known to attach to surfaces through specific proteins designed to improve adhesion. In this study, we have considered graphene as a candidate material for support-assisted cellular growth and simulated the interaction of all 20 naturally occurring amino acids deposited on graphene. Investigations utilized classical molecular dynamics (MD) for amino acids in aqueous solution and in vacuo, in tandem with quantum chemical calculations. The MD simulations were carried out for classical and polarizable CHARMM force fields. The simulations performed with the polarizable force field confirmed that adhesion of amino acids to the graphene surface may be significantly enhanced due to the polarization forces, which was further supported by quantum chemical calculations. The performed analysis thus revealed the role of polarization on amino acids’ adhesion to the graphene surface.Graphical abstract

Volumetric, acoustic and infrared spectroscopic study of amino acids in aqueous solutions of pyrrolidinium based ionic liquid, 1–butyl–1–methyl pyrrolidinium bromide

The effect of ionic liquid, 1–butyl–1–methyl pyrrolidinium bromide [C4C1Pyrr]Br on the thermodynamic properties of glycine, L–alanine and L–valine in aqueous solution was studied at the temperature range of 288.15–308.15 K and experimental pressure of p = 0.1 MPa by density, ultrasonic speed and FTIR spectroscopic techniques. Apparent molar volumes, standard partial molar volumes, standard partial molar volumes of transfer and hydration number are evaluated using density data. Side chain contributions and temperature dependence of partial molar volume have been calculated. Apparent molar isentropic compression, standard partial molar isentropic compression, standard partial molar isentropic compression of transfer and hydration number have been calculated using ultrasonic speed data. Fourier transform infrared (FTIR) spectral studies have also have been carried out for the present mixture. These volumetric, acoustic and spectroscopic studies can help to understand the mixing effects and other complex biological processes between amino acids and ionic liquid aqueous solution.

PH-stimulus response dye-cucurbituril sensor for amino acids in aqueous solution.

The host-guest inclusion complexes that comprise an inverted cucurbit[7]uril (iQ[7]) and a quinoline derivative, 4-(4-dimethylaminostyryl) quinoline (DSQ) at different pHs were exploited as multiple supramolecular sensors to sense l-α-amino acids. DSQ complexation inside iQ[7] at different pHs leads to increased fluorescence and formation of different-colored iQ[7]-DSQ complexes. The enhanced fluorescence of DSQ after iQ[7] encapsulation may be attributed to limited dimethylamine rotation and the formation of a twisted internal charge transfer (TICT) state. The DSQ@iQ[7] sensors have different affinities for l-α-amino acids at different pHs. Therefore, we propose a pH-stimulus response supramolecular sensor for the discrimination of structurally similar l-α-amino acids in aqueous solution.

Electrochemiluminescence analysis of tryptophan in aqueous solutions based on its reaction with tetraphenylborate anions.

The emission of electrogenerated chemiluminescence (ECL) is observed upon the oxidation of fluorescent aromatic amino acid tryptophan in aqueous solutions at a glassy carbon electrode in the presence of a sodium tetraphenylborate co-reactant in a broad pH range. The emission is particularly strong when potential pulses are applied to the electrode. The ECL intensity is proportional to the concentration of amino acid and allows its determination in the concentration range of 0.3 μM-0.3 mM with high selectivity in the presence of other amino acids. The results of studies suggest that the indole ring of tryptophan is responsible for the observed ECL emission.