Amino Acids In Aqueous Media Research Articles

Selective Recognition of Aromatic Amino Acids by a Molecular Cleft in Water

AbstractThe development of water‐soluble hosts for the selective recognition of aromatic amino acids is highly desirable and may serve as a tool to facilitate drug discovery and enable fabrication of sensors for point‐of‐care monitoring in the context of phenylketonuria disease. This paper presents the synthesis and characterization of a water‐soluble molecular cleft which is demonstrated to selectively bind aromatic amino acid guests over other amino acids in aqueous medium, favoring ʟ‐Trp over ʟ‐Phe and ʟ‐Tyr by a factor of approximately five. Host/guest‐interaction forces were studied by 1H‐NMR titrations complemented by fluorescence titrations and isothermal titration calorimetry. The here presented results provide a starting point for future optimizations in our efforts to selectively identify and quantify individual aromatic amino acids in aqueous medium.

Degradation of poly(conjugated ester)s using a conjugate substitution reaction with various amines and amino acids in aqueous media

Degradation of poly(conjugated ester)s using a conjugate substitution reaction with various amines and amino acids in aqueous media

Aryl Crown Ethers Based on d‐Glucose Scaffold – Highly Selective Receptors of Amino Acid Ester Hydrochlorides

AbstractAmino acids are important biomolecules with a broad scope of applications in chemical and biological sciences. Their functions and properties depend on their absolute configuration. Therefore, methods for chiral recognition and separation of amino acids are highly sought after. For the purposes of diagnostic and medicinal applications chiral recognition of amino acids in water is particularly relevant. However synthetic receptors for enantioselective binding of amino acids in aqueous media are rare. Recently we reported a d‐glucose‐based crown ether for chiral recognition of amino acid esters in water. We achieved enantioselectivities towards amino acids with hydrophobic sidechains which were among the highest ever reported for a small molecule receptor. The binding affinities were however moderate. Herein we disclose analogs of that receptor, containing aryl functionalities in the crown ether fragment. The new receptors show considerably improved binding affinities for amino acid ester hydrochlorides in water, while retaining high enantio‐ or chemoselectivities.

Water-Soluble Single-Benzene Chromophores: Excited State Dynamics and Fluorescence Detection.

Two water-soluble single-benzene-based chromophores, 2,5-di(azetidine-1-yl)-tereph- thalic acid (DAPA) and its disodium carboxylate (DAP-Na), were conveniently obtained. Both chromophores preserved moderate quantum yields in a wide range of polar and protonic solvents. Spectroscopic studies demonstrated that DAPA exhibited red luminescence as well as large Stokes shift (>200 nm) in aqueous solutions. Femtosecond transient absorption spectra illustrated quadrupolar DAPA usually involved the formation of an intramolecular charge transfer state. Its Frank–Condon state could be rapidly relaxed to a slight symmetry-breaking state upon light excitation following the solvent relaxation, then the slight charge separation may occur and the charge localization became partially asymmetrical in polar environments. Density functional theory (DFT) calculation results were supported well with the experimental measurements. Unique pH-dependent fluorescent properties endows the two chromophores with rapid, highly selective, and sensitive responses to the amino acids in aqueous media. In detail, DAPA served as a fluorescence turn-on probe with a detection limit (DL) of 0.50 μM for Arg and with that of 0.41 μM for Lys. In contrast, DAP-Na featured bright green luminescence and showed fluorescence turn-off responses to Asp and Glu with the DLs of 0.12 μM and 0.16 μM, respectively. Meanwhile, these two simple-structure probes exhibited strong anti-interference ability towards other natural amino acids and realized visual identification of specific analytes. The present work helps to understand the photophysic–structure relationship of these kinds of compounds and render their fluorescent detection applications.

Kinetic Studies of the Interaction of Pr(III) with some amino acids in Aqueous Medium using pH meter: Evaluation of Pre- exponential Factor and Activation Energy

Kinetic studies of the Complexation of Pr(III) with some amino acids (L-Aspartic acid, L-Histidine and L-Valine) in aqueous solvents were carried out at different temperatures (room temperature and higher temperatures) using pH meter. Different thermodynamic parameters (ΔEa, ΔSº, ΔGº and ΔHº) of the Complexation have been evaluated. It was found that the value of pH increases with time which shows that the rate of the reaction of Pr (III) with different amino acids in aqueous medium increases with time.

Interaction of the nitrogen-containing carbon backbone polymers with essential α-amino acids.

The aim of this work is to research the interactions of water-soluble nitrogen-containing copolymers with essential amino acids in aqueous media. For this, poly(N-vinylformamide-co-N-vinylimidazole) and poly(N-vinylcaprolactam-co-N-vinylimidazole) random copolymers were synthesized by free radical polymerization. The products obtained are characterized by GPC, DLS, and FTIR. The copolymers have a narrow molecular weight distribution and low dispersity. The interactions of the obtained copolymers with histidine, proline, arginine, leucine, phenylalanine, and methionine were researched by UV spectroscopy, FTIR, and TEM. It was found that conjugation of the copolymers with amino acids correlates with the copolymer composition and hydrodynamic radius Rh, and depends on the pH of the medium and amino acid structures. It is shown that chloride anion presence in the polymer-amino acid-water systems affects the mechanism of their interactions. The research shows that the synthesized copolymers can be used for the creation of effective eco-friendly amino acid extraction systems or matrices for enzyme immobilization.

Determining the Diastereoselectivity of the Formation of Dipeptidonucleotides by NMR Spectroscopy.

Proteins are composed of l‐amino acids, but nucleic acids and most oligosaccharides contain d‐sugars as building blocks. It is interesting to ask whether this is a coincidence or a consequence of the functional interplay of these biomolecules. One reaction that provides an opportunity to study this interplay is the formation of phosphoramidate‐linked peptido RNA from amino acids and ribonucleotides in aqueous condensation buffer. Here we report how the diastereoselectivity of the first peptide coupling of the peptido RNA pathway can be determined in situ by NMR spectroscopy. When a racemic mixture of an amino acid ester was allowed to react with an 5′‐aminoacidyl nucleotide, diastereomeric ratios of up to 72 : 28 of the resulting dipeptido nucleotides were found by integration of 31P‐ or 1H‐NMR peaks. The highest diastereomeric excess was found for the homochiral coupling product d‐Ser‐d‐Trp, phosphoramidate‐linked to adenosine 5′‐monophosphate with its d‐ribose ring. When control reactions with an N‐acetyl amino acid and valine methyl ester were run in organic solvent, the diastereoselectivity was found to be lower, with diastereomeric ratios≤62 : 38. The results from the exploratory study thus indicate that the ribonucleotide residue not only facilitates the coupling of lipophilic amino acids in aqueous medium but also the formation of a homochiral dipeptide. The methodology described here may be used to search for other stereoselective reactions that shed light on the origin of homochirality.

Silver oxide nano-colloid based selective colorimetric sensor for the recognition of cystine in aqueous solution

ABSTRACTSodium alginate modified Ag2O (SA@Ag2O) nano-colloid is synthesised and studied colorimetric response towards eight selected amino acids in aqueous medium at room temperature. The synthesised SA@Ag2O nano-colloid showed a surface plasmon band at 469 nm. Distinctive colour change of the dark brown colloid to colourless is observed in the case of Cystine. Among the eight amino acids studied such as D-L- Aspartic acid, L-Glutamic acid, Glycine, Alanine, D-L Methionine, L-Cysteine, L-Cystine and L-Tyrosine. L-Cystine stands out by completely decolorising the brown colloid which can be detected by the ‘naked-eye’. This sensor selectively detects Cystine. To understand the sensing mechanism, the amino acid treated SA@Ag2O colloids were characterised by UV, XRD, FTIR and TEM analysis. This approach offers several advantages such as simplicity, low cost and high sensitivity.

Microscopic investigation on empirical force-field model dependent structure and dynamical properties of amino acids in aqueous medium

Microscopic investigation on empirical force-field model dependent structure and dynamical properties of amino acids in aqueous medium

Evidences for complexations of β-cyclodextrin with some amino acids by 1H NMR, surface tension, volumetric investigations and XRD

Inclusion Composites between β-cyclodextrin and amino acids (viz., l-Methionine, l-Proline and l-Glutamine) are established in aqueous medium. Such complexation of amino acids in aqueous medium without using any organic solvent provides great ideas in different industries. The complexes are characterized by 1H NMR which proves the formation of inclusion complex. The interactions of β-CD with amino acids are analyzed by means of surface tension and density. Contributions of different groups of the guest molecules to the limiting apparent molar volume are determined. Additionally, the stoichiometry of the inclusion complexes is also determined to be 1:1 in all the three cases. The solid inclusion complex formations of β-CD with amino acids are confirmed by PXRD analysis.

A novel fluorescence turn-on probe based on diketopyrrolopyrrole-nitroolefin conjugate for highly selective detection of glutathione over cysteine and homocysteine

A new fluorescent probe, nitroolefin functionalized diketopyrrolopyrrole (DPP-NO2) was designed and synthesized as a highly sensitive and selective probe for detecting glutathione (GSH) over cysteine (Cys), homocysteine (Hcy) and other amino acids in aqueous media. The probe is a non-fluorescent compound. On being mixed with GSH in buffered THF/PBS (v/v=3:2) solution at pH 7.2, the probe exhibited the yellow-green emission at 548nm and a 2000-fold enhancement in fluorescence intensity, along with a 26nm hypsochromic shift from 515nm to 489nm in the absorption spectra. This probe was very sensitive and displayed a linear fluorescence off–on response to GSH with fluorometric detection limit of 6.14×10−8M. What’s more, through the fluorescence turn-on signal response to GSH, the probe was successfully utilized for monitoring GSH in living cells.

Thermodynamic study of N-acetyl glycine in aqueous tetraethylammonium iodide solutions in the temperature interval (288.15 to 308.15) K: Volumetric and acoustic study

Knowledge of thermodynamic properties of substituted amino acids in aqueous medium can provide valuable information regarding the stabilisation mechanism of proteins. In this study, we report the density and ultrasonic speeds of N-acetyl glycine in (0.03, 0.05, 0.1, 0.15 and 0.2)mol⋅kg−1 aqueous solutions of tetraethylammonium iodide (TEAI) at temperatures (288.15, 293.15, 298.15, 303.15 and 308.15)K and at pressures 101kPa. From these results, the apparent molar volume and acoustical parameters, coefficient of isentropic compression, molal hydration number and apparent molar isentropic compression have been evaluated. The partial molar volume, partial molar isentropic compression, and their corresponding transfer functions were calculated. These results were used to interpret the type of interactions occurring in the ternary mixtures using the co-sphere overlap model. The pair and triplet interaction coefficients have been calculated from both the properties. The concentration and temperature dependence of (solute+solute) and (solute+solvent) interactions in the present study was also discussed. The partial molar volumes were used to obtain the partial molar isobaric expansibilities for N-acetyl glycine to examine the temperature dependence of such interactions. The structure-making/breaking ability of N-acetyl glycine has also been discussed in terms of the sign of ∂CP,∅0∂PT.

Mechanistic aspects of ligand substitution on cis-diaqua-chloro-tris-(dimethyl sulfoxide)-ruthenium(II) complex by some amino acids in aqueous medium

Mechanistic aspects of ligand substitution on cis-diaqua-chloro-tris-(dimethyl sulfoxide)-ruthenium(II) complex by some amino acids in aqueous medium

Fluorescent calix[4]arene chemosensor for acidic and basic amino acids in pure aqueous media

A fluorescent calix[4]arene chemosensor 2 displays high sensitivity toward acidic and basic amino acids in aqueous media through multiple H-bond interactions.

Mechanistic aspects of ligand substitution on [(H2O)(tap)2RuORu(tap)2(H2O)]2+ ion {tap = 2-(m-tolylazo)pyridine} by some amino acids in aqueous medium at physiological pH

The interaction of the title complex with selected amino acids such as glycine (L1H), l-valine (L2H), and l-leucine (L3H) has been studied spectrophotometrically in aqueous medium as a function of [substrate complex], [ligand], and temperature. The reaction has been monitored at 600 nm, where the spectral difference between the reactant and product is maximum. At pH 7.4, the reaction has been found to proceed via two distinct consecutive steps, i.e., it shows a nonlinear dependence on the concentration of ligands: The first process is [ligand] dependent, but the second step is [ligand] independent. The rate constants for the processes are k1∼10−3 s−1 and k2∼10−4 s −1. The activation parameters were calculated from Eyring plots. Based on the kinetic and activation parameters, an associative interchange mechanism is proposed for the interaction processes. From the temperature dependence of the outer sphere association equilibrium constant, the thermodynamic parameters were also calculated, which gives a negative Δ Go value for both the steps at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex. The product of the reaction has been characterized with the help of conductance measurement, IR, NMR, and ESI-mass spectroscopic analysis. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 612–623, 2012

Thermodynamic Study of Some Amino Acids, 2-Aminopropanoic Acid, 2-Amino-3-methylbutanoic Acid, 2-Amino-4-methylpentanoic Acid, and 2-Amino-3-phenylpropanoic Acid in Aqueous Saccharide Solutions at Different Temperatures: Volumetric and Ultrasonic Study

Knowledge of thermodynamic properties of amino acids in aqueous medium can provide valuable information about the stabilization mechanism of proteins. In this study, we report the density and speed of sound of some amino acids (2-aminopropanoic acid, 2-amino-3-methylbutanoic acid, 2-amino-4-methylpentanoic acid, and 2-amino-3-phenylpropanoic acid) in aqueous fructose, d-(+)-cellobiose, and d-melezitose solutions (0.1 mol·kg−1) at (293.15, 298.15, 303.15, and 308.15) K. From these data, the apparent molar volume and apparent molar adiabatic compressibility have been evaluated. The partial molar volume, partial molar adiabatic compressibility, and their corresponding transfer functions were calculated. These results were used to interpret the type of interactions occurring in the ternary mixtures using the cosphere overlap model. The concentration and temperature dependence of solute−solute and solute−solvent interactions in the present study was also discussed.

An efficient and expeditious Fmoc protection of amines and amino acids in aqueous media

A new and environmentally friendly Fmoc protection of a variety of aliphatic and aromatic amines, amino acids, amino alcohols and amino phenols is reported in aqueous media under mild and catalyst-free conditions. The reaction proved to be chemoselective in presence of ambident nucleophiles.

On the synthesis of N-maleoyl amino acids in aqueous media: cautionary tales for the unwary traveller

The high cost or protracted syntheses associated with N-maleoyl amino acid derivatives coupled with a considerable demand from both the life and physical sciences has spurred the search for facile, low-cost routes to these compounds. Herein, we demonstrate that a recently published method purporting to deliver N-maleoyl amino acids by cyclization of maleamic acids in water, instead results in a hydrolysis product, namely the corresponding hemi-maleate salt.

ChemInform Abstract: Investigations on Photochemical Linking of Steroids with Amino Acids: Irradiation of α,β-Unsaturated Steroidal Ketones in the Presence of Amino Acids in Aqueous Medium.

ChemInform Abstract: Investigations on Photochemical Linking of Steroids with Amino Acids: Irradiation of α,β-Unsaturated Steroidal Ketones in the Presence of Amino Acids in Aqueous Medium.

In vitro condensation of amino acids in aqueous media: A synthesis driven by catalytic carbon monoxide oxidation

A novel mechanism is proposed for amino acid condensations to oligopeptides in aqueous media. The palladium-catalyzed condensation appears to proceed through a mechanism involving the Pd(0)/Pd(II) redox cycle. The reaction requires the use of carbon monoxide and an oxidant, and it is proposed that the oxidation of carbon monoxide to carbon dioxide drives the otherwise thermodynamically uphill condensation. The reaction occurs for several amino acids including glycine, alanine, β-alanine, and 5-aminopentanoic acid. Competition studies between glycine and alanine reveal steric effects on product formation. Dipeptides are the predominant condensation products, though some longer chains, containing up to 4 amino acids, can be observed. First-order plots for dipeptide appearance show an inverse, secondary, isotope effect consistent with the rate determining carboxylic-carbamic anhydride formation.