Recognition of amino acids by functionalized calixarenes

The calixarenic receptors exhibit remarkable host-guest properties towards biologically relevant guests. Aspects of complex formation reactions between both native and derivatized amino acids, di-and tripeptides with calixarenic (chiral or not) receptors are summarized in this critical review. Thus, the discussions emphasize the parameters that affect the molecular binding selectivity and efficiency of functionalized calix[n]arenes towards these substrates. A brief survey on their application in separation of amino acids is also considered (123 references).     

Fluorescence probes for thiol-containing amino acids and peptides in aqueous solution

A new fluorescence probe is described using the "chemosensing ensemble" method. The probe shows high selectivity and sensitivity for thiol-containing amino acids and peptides, and can detect cysteine and homocysteine from healthy to abnormal levels under physiologically-relevant conditions.     

Photolysis (193 nm) of aliphatic amino acids in aqueous solution

An investigation of the photochemical properties of glycine, aspartic acid, valine, leucine and methionine was carried out using nanosecond 193 nm laser irradiation and high performance liquid chromatography analysis. The quantum yields of formation of hydrated electrons (Φ_e−) and decomposition of the substrate (Φ_d) were determined for the five aliphatic amino acids in neutral aqueous solution at room temperature. From the dependences of Φ_e− on the laser intensity it follows that the mechanism of photo-ionization is monophotonic (single step). The Φ_d values under Ar and in the presence of oxygen or N₂O are interpreted on the basis of photo-ionization as the dominant process for decomposition of methionine and a significant contribution from photo-ionization in the other cases. A comparison was made between the Φ_d values (in the presence of oxygen) using irradiation at 193 nm and those from previous measurements at 213 nm.     

Thermodynamics of mixed-ligand complexation of gadolinium ethylenediaminetetraacetate with amino acids in aqueous solution

Mixed-ligand complexation of GdEdta⁻ with glycinate, L-glutamate, DL-aspartate, iminodiacetate, and nitrilotriacetate anions in aqueous solutions at 298.15 K and the ionic strength I = 0.5 (KNO₃) was studied. The thermodynamic parameters (logK, Δ _r G, Δ _r H, Δ _r S) of these reactions were determined from calorimetric and pH-metric data. The most probable way of coordination of the amino acids in the heteroleptic complexes is discussed.     

Inhibition of corrosion of copper in nitric acid solution by four amino acids

Inhibition of corrosion of copper in 1M HNO₃ solution by four amino acids, proline (Pro), phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Try), has been studied by use of gravimetric and electrochemical polarization measurements. The results obtained the from two different techniques are comparable, and show that Tyr and Try act as good inhibitors of corrosion of copper in 1 mol L^?1 HNO₃. Correlation between inhibition efficiency and quantum chemical calculations, performed using semi empirical (AM1 and MNDO) and ab-initio methods, is discussed.     

Effect of basic amino acids on photoreaction of ketoprofen in phosphate buffer solution

Photoreaction of ketoprofen (KP), one of the widely used nonsteroidal anti-inflammatory drugs (NSAIDs), was studied with transient absorption spectroscopy in phosphate buffer solution (pH 7.4) in the presence of basic amino acids of histidine (His), lysine (Lys) and arginine (Arg). Deprotonated form of KP (KP(-)) excited with UV-light irradiation gave rise to carbanion through a decarboxylation reaction. It was found that carbanion abstracted a proton from the side chain of the protonated amino acids to yield 3-ethylbenzophenone ketyl biradical (EBPH); however, no reaction was observed with alanine. The relative yield of EBPH by the proton transfer reaction with His was ca. 40 times larger than that of the other two basic amino acids, suggesting that the proton-donating ability of His (protonated His) should be quite high. The information on the photoreaction mechanism of NSAIDs with basic amino acids was essential to understand primary reaction of excited NSAIDs in vivo causing photosensitization on human skin.     

Chemistry of unprotected amino acids in aqueous solution: direct bromination of aromatic amino acids with bromoisocyanuric acid sodium salt under strong acidic condition

Brominations of unprotected aromatic amino acids such as phenylalanine, tyrosine, and glycine, with bromoisocyanuric acid mono sodium salt (BICA-Na) were conducted in 60% aq. H(2)SO(4) at 0 degrees C to give a mixture of mono-brominated products in good yield. Unexpectedly, meta-bromophenylglycine was obtained as main product accompanied by ortho- and para-substituted products, while phenylalanine gave only ortho- and para-substituted products. Bromination of 2-phenylethylamine or benzylamine showed a tendency similar to the corresponding amino acids.     

Enthalpic characteristics of solution of amino acids and aliphatic dipeptides in aqueous solutions of KCl

The integral enthalpies of dissolution Δ_sol H ^m of L-α-serine and L-α-asparagine in mixtures of water with KCl were measured in electrolyte concentrations of up to 4 mol/kg at 298.15 K. The standard enthalpies of dissolution (Δ_sol H ^o) and transfer (Δ_tr H ^o) of amino acids from water to aqueous solutions of KCl were calculated. The enthalpic pair interaction coefficients h _xy of biomolecules with KCl were estimated within the McMillan-Mayer theory. The changing nature of the interaction between the components of the solution (depending on the structure of the dissolved biosubstance side substituents) is shown on the basis of data we obtained earlier for amino acids and dipeptides series. Estimates of the contributions from the electrostatic and other interactions of dipolar ions of amino acids and dipeptides with ions of electrolyte KCl in the enthalpic pair interaction coefficients h _xy are obtained using the Kirkwood approach.     

Time dependent density functional theory modeling of chiroptical properties of small amino acids in solution

Time dependent density functional theory (TDDFT) and the conductor-like screening model (COSMO) of solvation were used to model the specific rotation and optical rotatory dispersion (ORD) of alanine, proline and serine solutions. Zwitterionic, cationic and anionic forms of amino acids were investigated and the results compared with experimental literature data obtained in neutral, acidic and basic conditions, respectively. It was found that TDDFT consistently underestimated the electronic excitation energies of the molecules, leading to calculated optical rotations that are of the correct sign but somewhat larger in magnitude than those of experiment. An additional challenge was encountered in the modeling of serine, an amino acid with a strong tendency to form intramolecular hydrogen bonds. The model used overestimated the extent of such hydrogen bonding for the zwitterions while possibly underestimating such bonding for the cationic form. This effect on the calculated mole fractions of the different conformers had an impact on the specific rotation.     

Thermodynamic characteristics of solution and viscous flow of amino acids in water at 298.15 K

Thermodynamic and transport properties of aqueous solutions of 13 amino acids at 298.15 K are analyzed in relation to the structure of the side chains of the biomolecules on the basis of the newly obtained and published data. The standard enthalpies of solution (Δ_sol H ⁰), partial molar volumes (V _2,φ ⁰ ), and partial molar contributions to the molar Gibbs free energy of activation of the viscous flow (Δμ ₂ ^0≠ ) were determined for the amino acids in water. Correlation equations were suggested to describe the relationship between the enthalpy characteristics of hydration of amino acids, viscous flow parameters, and bulk properties of their aqueous solutions.     

Pulsed amperometric detection of underivatized amino acids using polypyrrole modified copper electrode in acidic solution

The successful pulsed amperometric detection of underivatized amino acids have been carried out in an acidic media on a polypyrrole (PPy) modified Cu electrode. The formation of PPy film doped with glutamate (glu) on a Cu electrode surface changes the mechanism of Cu dissolution. After application of multistep potential waveform, the PPy film was glu free due to the electro-reduction and overoxidation. High anodic potential polarization treatment yielded partially overoxidized PPy film as long as the Cu surface dissolution and amino acid permeation through the film was well controlled. This overoxidized PPy film acted as a charge and size exclusion barrier in order to improve the selectivity and stability of a Cu electrode. Various process parameters such as film modification time, detection and cleaning potential and pH of solution have been optimized to maximize the beneficial electrocatalytic properties of the electrode surface. At an optimized condition, detection limits for positively charged histidine and arginine are 19 and 22 pg respectively, whereas the neutral amino acids detected in amounts of 0.9–2.3 ng. Furthermore, the PPy coated Cu electrode response was long lived, stable and reproducible.     

Recognition of vinification technology through gas chromatographic data on enantiomeric purity of free amino acids

Analysis of D-amino acids in food, a matter of growing interest due to nutritional implications, has been used as a tool for food evaluation, detection of falsifications and as a genuinity parameter. The evolution of free D-amino acids in wines of a portuguese Vitis vinifera variety (Roupeiro white), bottled during the period 1978–1989 is studied by means of chiral high resolution gas chromatography. D-Ala, D-Val, D-Thr, D-Leu, D-Ser, D-Asx, D-Met, D-Phe, and D-Glx are present in most of the analyzed wines. It was not possible to correlate the evolution of the D/L ratio to the age of the wine. However, a clear correlation between enantiomer purity profiles and the vinification technique could be established. The results show that free D-amino acids may be used as markers for the biotechnological process used in vinification.Dedicated to Professor Dr. Dr. h.c. mult. J.F.K. Huber on the occasion of his 70th birthday     

Silicon amino acids

The existence and gas phase stability of silicon analogues of three natural amino acids (i.e., silicon glycine, silicon alanine, and silicon valine) belonging to the novel class of compounds termed silicon amino acids (SiAA) are investigated theoretically on the basis of ab initio QCISD/aug‐cc‐pVTZ and MP2/aug‐cc‐pVTZ calculations. All molecules studied (in their gas phase canonical forms) are structurally comparable to their proteinogenic counterparts (i.e., glycine, l ‐alanine, and l ‐valine) and capable of forming several structural isomers as such. These higher energy isomers are characterized by small relative energies (not exceeding 4 kcal mol⁻¹). The simulated IR spectra of the Si‐Gly, Si‐Ala, and Si‐Val global minima are also presented and discussed.     

Excitatory amino acids

Recent developments in the understanding of the molecular function of memory and other CNS-mediated processes have arisen from the multidisciplinary interplay of excitatory amino acid synthesis and medicinal chemistry, X-ray crystallographic structural protein analysis, molecular biology, pharmacology and physiology. This review seeks to place recent synthetic developments of EAA analogues in the wider pharmacological setting, illustrating the need for and importance of these compounds.     

Study of the behaviour of amino acids in aqueous solution by time-domain NMR and high-resolution NMR

The study of protein hydration by time-domain NMR is complicated by the great number of interactions involved, resulting from the presence of several amino acids and the possible modifications produced by the various structures. Moreover, a good comprehension of the molecular interactions of the simple amino acids in solution is essential to elucidate the mechanism of the biological functions of proteins. Measurements of transverse relaxation rates of the protons of water (R(2) = 1/T(2)) in aqueous solutions of amino acids such as L-glycine, L-asparagine, L-arginine and L-tryptophan were carried out in order to study the effects of chemical exchange and molecular diffusion on the amplitude of R(2). The values of R(2) measured by the Carr-Purcell-Meiboom-Gill (CPMG) sequence were studied while varying the solution pH and the parameters of the CPMG sequence. The dependence of R(2) on pH and tau (inter-pulse delay between the first and the second pulses of the CPMG sequence) is interpreted in terms of chemical exchange between the protons of water and those of the labile amino acid groups. This interpretation was confirmed by the analysis of the proton spectra acquired using a 300 MHz NMR spectrometer.     

Thermodynamics of mixed-ligand complex formation of copper(II) ethylenediaminetetraacetate with amino acids in solution

The mixed-ligand complex formation in the systems Cu²⁺–Edta^4?–L (L = His, Lys, Orn, Arg, Im) has been calorimetrically, pH-potentiometrically, and spectrophotometrically studied in aqueous solution at 298.15 K and the ionic strength of I = 0.5 (KNO₃). The thermodynamic parameters of formation of the CuEdtaL, CuEdtaHL, and (CuEdta)₂L complexes have been determined. The probable coordination mode for the complexone and the ancillary ligand in the mixed-ligand complexes was discussed.     

A cyclometalated palladium-azo complex as a differential chromogenic probe for amino acids in aqueous solution

Solutions of a cyclometalated palladium-azo complex exhibited differential UV-Vis absorption spectra in the presence of alpha-amino acids with different side chain groups.