Gas-phase basicities of histidine and lysine and their selected di- and tripeptides

The gas-phase basicities (GB) of histidine, lysine, and di- and triglycyl peptides containing either one histidine or one lysine residue have been determined. In all, 12 compounds were examined in a Fourier transform ion cyclotron resonance mass spectrometer. The GBs of the biomolecules were evaluated by proton transfer reactions employing a range of reference compounds with varying gas-phase basicities. In addition, the GBs were determined by using the kinetic method of collision-induced dissociation on a proton-bound dimer containing the peptide and a reference compound. The GBs of histidine and lysine were both found to be 220.8 kcal/mol via proton transfer reactions. The kinetic method experiments, including dissociation of a proton-bound dimer containing both histidine and lysine, also suggest equivalent GBs for these amino acids. However, the small peptides containing lysine are generally more basic than the corresponding histidine-containing peptides. For the peptides, the data suggest that the protonation site is on the basic side chain functional group of the histidine or lysine residues. The GBs of the di- and tripeptides are dependent upon the location of the basic residue. For example, the GBs of the tripeptides glycylglycyl-l-lysine (GlyGlyLys) and l-lysylglycylglycine (LysGlyGly) were both determined to be 230.7 kcal/mol while a GB of kcal/mol was obtained for glycyl-l-lysylglycine (GlyLysGly). A similar GB trend is seen with the histidine-containing tripeptides. Generally, the GBs obtained by using the kinetic method are slightly higher than those obtained by deprotonation reactions; however, the trends in relative GB values are essentially the same with the two techniques.     

Biomimetic synthesis of calcium carbonate with different morphologies under the direction of different amino acids

Using three different amino acids (AAs) as organic matrices, including the highly nonpolar hydrophobic l-valine, the positively charged l-arginine and the less polar uncharged l-serine, calcium carbonate (CaCO₃) with different morphologies and polymorphs were synthesized by a facile gas diffusion reaction based on biomimetic strategy. Compared with the control cubic calcite obtained in the absence of AAs, the product from l-valine was cubic calcite aggregates assembled by nano-platelets. The product from l-arginine was spherical vaterite aggregates assembled by spherical nanoparticles. The product from l-serine was the mixture of cubic calcite and spherical vaterite. The structures and properties of the side chains of the AAs exerted the significant effects on the nucleation and growth of the CaCO₃. The formation mechanisms of the CaCO₃ in the presence of AAs are preliminarily discussed. The results suggest that the polymorphs and morphologies of the inorganic nanomaterials might be easily adjusted through the careful selection of the organic matrices.     

Partial Molar Volumes of l-Serine and l-Threonine in Aqueous Ammonium Sulfate Solutions at (278.15, 288.15, 298.15, and 308.15) K

In this study, the partial molar volumes of l-serine and l-threonine in aqueous solutions of ammonium sulfate at (0.0, 0.1, 0.3, 0.7, and 1.0) mol·kg^?1 are reported between 278.15 and 308.15 K. Transfer volumes and hydration numbers were obtained, which are larger in l-serine than in l-threonine. Dehydration of the amino acids is observed, rising with the temperature and salt molality. The data suggest that interactions between ions and charged/hydrophilic groups are predominant, and by applying the McMillan and Mayer formalism, it was concluded that they are mainly pair wise. The combination of the data presented in this study with solubility and molecular dynamics data suggests a stronger interaction of the ammonium cation with the zwitterionic centers of the amino acids when compared to the interactions of those centers with the sulfate anion.     

Conductometric and fluorescence probe investigations of molecular interactions between dodecyltrimethylammonium bromide and dipeptides

The effect of five dipeptides (glycylglycine, glycyl-l-valine, glycyl-l-leucine, glycyl-l-glutamine, and l-alanyl-l-glutamine) on the micellar properties of catonic surfactant dodecyltrimethylammonium bromide (DTAB) has been investigated by electrical conductivity and fluorescence spectroscopy. From the conductivity data, the critical micellar concentration (c _cmc), counterion binding constant (β), and thermodynamic parameters of micellization (ΔG _m ^o , ΔH _m ^o and ΔS _m ^o ) have been calculated. The effect of dipeptides on the micellar properties of DTAB depends upon their nature and concentration as well as on temperature and has been used to study the interactions present in the micellar systems. Enthalpy–entropy compensation effect has also been observed. The pyrene fluorescence spectra were used as an index for the estimation of micropolarity of micellar produced by the interaction of DTAB with dipeptides and the aggregation behavior of DTAB. Comparison on the interactions between different types of surfactants and dipeptide showed that the order of the strength for these interactions is TX-100?相似文献   

Volumetric Properties of l-Alanine and l-Serine in Aqueous N,N-Dimethylformamide Solutions at 298.15 K

The densities of l-alanine and l-serine in aqueous solutions of N,N-dimethylformamide (DMF) have been measured at 298.15 K with an Anton Paar Model 55 densimeter. Apparent molar volumes $ (V_{\phi } ) $ ( V ? ) , standard partial molar volumes $ (V_{\phi }^{0} ) $ ( V ? 0 ) , standard partial molar volumes of transfer $ (\Updelta_{\text{tr}} V_{\phi }^{0} ) $ ( Δ tr V ? 0 ) and hydration numbers have been determined for the amino acids. The $ \Updelta_{\text{tr}} V_{\phi }^{0} $ Δ tr V ? 0 values of l-serine are positive which suggest that hydrophilic–hydrophilic interactions between l-serine and DMF are predominant. The –CH₃ group of l-alanine has much more influence on the volumetric properties and the $ \Updelta_{\text{tr}} V_{\phi }^{0} $ Δ tr V ? 0 have smaller negative values. The results have been interpreted in terms of the cosphere overlap model.     

Effect of Cofactor Folate on the Growth of Corynebacterium glutamicum SYPS-062 and l-Serine Accumulation

The direct fermentative production of l-serine from sugar has attracted increasing attention. Corynebacterium glutamicum SYPS-062 can directly convert sugar to l-serine. In this study, the effects of exogenous and endogenous regulation of cofactor folate on C. glutamicum SYPS-062 growth and l-serine accumulation were investigated. For exogenous regulation, the inhibitor (sulfamethoxazole) or precursor (p-aminobenzoate) of folate biosynthesis was added to the medium, respectively. For endogenous regulation, the gene (pabAB) that encodes the key enzyme of folate biosynthesis was knocked out or overexpressed to obtain the recombinant C. glutamicum SYPS-062 ΔpabAB and SYPS-062(pJC-tac-pabAB), respectively. The results indicated that decreased levels of cofactor folate supported l-serine accumulation, whereas increased levels of cofactor folate aided in cell growth of C. glutamicum SYPS-062. Thus, this study not only elucidated the role of folate in C. glutamicum SYPS-062 growth and l-serine accumulation, but also provided a novel and convenient approach to regulate folate biosynthesis in C. glutamicum.     

Arenesulfonylation of dl-serine, l-proline, l-threonine, and dl-methionine in systems 1,4-dioxane—water and propan-2-ol—water

Kinetics of interaction of dl-serine, l-proline, l-threonine, and dl-methionine with 3-nitrobenzenesulfonyl chloride in water (40%)—1,4-dioxane and water (40%)—isopropanol mixed solvents was studied spectrophotometrically at 298 K. The main reactive form of α-amino acids is shown to be anionic. Under conditions of arenesulfonylation, the basicity of α-amino acids is crucial in determining the reaction rate. Arenesulfonylation rate constants are 20—50 times lower than the constants of N-acylation of the same α-amino acids with benzoyl chloride and 10⁴–10⁵ times higher than the rate constants of their reactions with benzoic acid 4-nitrophenyl ester.     

Application of Hydrazino Dinitrophenyl-Amino Acids as Chiral Derivatizing Reagents for Liquid Chromatographic Enantioresolution of Carbonyl Compounds

A new series of chiral derivatizing reagents (CDRs) consisting of five hydrazino dinitrophenyl (HDNP)-amino acids (CDR 1?C5) was prepared by a two-step synthesis procedure starting from 1,5-difluoro-2,4-dinitrobenzene (DFDNB). In the first step, five fluoro-dinitrophenyl (FDNP)-reagents, namely FDNP-l-Leu, FDNP-l-Val, FDNP-l-Phe, FDNP-l-Ala and FDNP-d-Phg were synthesized by substituting one of the fluorine atoms in DFDNB moiety with amino acids l-Leu, l-Val, l-Phe, l-Ala and d-Phg, respectively. In the following step, the remaining fluorine atom of the FDNP reagents was substituted with hydrazine hydrate to obtain five HDNP reagents (i.e. CDR 1?C5; HDNP-l-Leu, HDNP-l-Val, HDNP-l-Phe, HDNP-l-Ala and HDNP-d-Phg). These five CDRs were used for synthesis of diastereomers of six racemic carbonyl compounds which were resolved by high-performance liquid chromatography using C18 column and gradient eluting mixture of acetonitrile or methanol with triethylammonium phosphate buffer with UV detection at 348 nm. Microwave irradiation was used for synthesis of both the CDRs and the diastereomers. The newly synthesized CDRs were observed to be superior in comparison to their counterparts having amino acid amides as chiral auxiliaries in terms of cost effectiveness and providing better resolution of diastereomers. The method was validated for limit of detection, linearity, accuracy and precision.     

Specific features of the reaction of l-cysteine with pyridoxal and N-pyridoxylidene-β-alanine

The mechanisms of condensation of l-cysteine, l-methionine, and l-serine with pyridoxal and of transaldimination of N-pyridoxylidene-??-alanine with l-cysteine were studied by the kinetic method. Unlike methionine and serine, the condensation of cysteine with pyridoxal and transaldimination with Npyridoxylidene-??-alanine involves intermediate formation of stable product having a thiazolidine ring. Its structure was determined by elemental analysis, UV, and IR spectroscopy, and quantum-chemical calculations. The thiazolidine fragment in the pyridoxal condensation product with l-cysteine is turned through an angle of ??90° with respect to the pyridine ring plane due to mutual repulsion of the negatively charged oxygen atom in the ortho position of the pyridine ring and sulfur and nitrogen atoms in the thiazolidine ring.     

The pivotal role of copper(II) in the enantiorecognition of tryptophan and histidine by gold nanoparticles

Stereoselective amino acid analysis has increasingly moved into the scope of interest of the scientific community. In this work, we report a study on the chiral recognition of d,l-Trp and d,l-His using l-Cys-capped gold nanoparticles (AuNPs) and copper(II) ion. In the l-Cys-capped AuNPs, the thiol group of the amino acid interacts with AuNPs through the formation of Au–S bond, whereas the α-amino and α-carboxyl groups of the surface-confined cysteine can coordinate the copper(II) ion, which in turn, binds the l- or d-amino acid present in solution forming diastereoisomeric complexes. The resulting systems have been characterized by UV–Vis spectra and dynamic light scattering measurements, obtaining different results for l- and d-Trp, as well as for l- and d-His. The knowledge of the solution equilibria of the investigated systems allowed us to accurately calculate in advance the concentrations of the species present in solution and to optimize the system performances, highlighting the pivotal role of copper(II) ion in the enantiodiscrimination processes.     

Thermodynamic and structural aspects of the interaction of l-histidine with urea and dimethylformamide in water

The solubility of l-histidine in water and aqueous solutions of dimethylformamide (DMF) at 25°C was determined. The thermal effects of solution of l-histidine in aqueous solutions of urea and DMF were measured. The standard enthalpies, free energies, and entropies of solution and transfer of the amino acid from water to aqueous solutions of amides were calculated. It was shown that the interaction of l-histidine with urea is attractive, and that with DMF, repulsive, with the change in the free energy determined by the enthalpy term in both cases. The enthalpy-entropy compensation taking place to a certain extent in the interaction of l-histidine and l-phenylalanine with amide was revealed. This effect is the most pronounced in the interaction of predominantly hydrophobic DMF and l-phenylalanine.     

Comparison of ordered mesoporous materials sorption properties towards amino acids

The adsorption of amino acids such as l-phenylalanine and l-histidine was carried out on a series of mesoporous carbons obtained with the use ordered silicas KIT-6, SBA-16, SBA-15 as templates and furfuryl alcohol as carbon precursor. Small angle XRD analysis confirmed the ordered mesoporous structures of all materials obtained. They were also characterised by well-developed surface areas and high pore volumes. Adsorption behaviour of amino acids on ordered mesoporous carbons was investigated in potassium phosphate buffer solutions with adjustable l-phenylalanine and l-histidine concentration, ion strength, and pH. The highest sorption capacity towards the amino acids were observed at pH close to the isoelectric point of l-phenylalanine (pI = 5.48) and l-histidine (pI = 7.59). Electrostatic, hydrophobic and steric interactions had very strong effect on the adsorption of amino acids on mesoporous carbons. The amount of l-phenylalanine and l-histidine adsorbed decreased in the following sequence: C_KIT-6 > C_SBA-16 > C_SBA-15 that was strongly related to their structure, surface areas and average pore diameters.     

Study of the interaction between ethanol and natural amino acids containing ionic side groups in water at T = 298.15 K

The enthalpies of solution of l-α-aspartic acid, l-α-glutamic acid, l-α-arginine, l-α-lysine, and l-α-histidine have been measured in aqueous ethanol solutions at 298.15 K. From the obtained experimental results, the standard enthalpies of solution of amino acids in water–ethanol solutions have been determined. These data were used to calculate the heterogeneous enthalpic pair interaction coefficients based on McMillan–Mayer’s formalism. These values were interpreted in the terms of the ionic or no polar effect of the side chains of l-α-amino acids on their interactions with a molecule of ethanol in water.     

Study on the intermolecular complexation behavior between p-sulfonatocalix[4]arene with l-tyrosine

The formation of the complexation behavior of host molecules water-soluble p-sulfonatocalix[4]arene (p-SCX4) with l-tyrosine (l-Tyr) guest molecule has been studied by spectrophotometric including fluorescence and nuclear magnetic resonance (NMR) spectroscopy. Experimental conditions including concentration of p-SCX4 and medium acidity were investigated in detail. The results showed that p-SCX4 forms 1:1 complexes with l-Tyr in water. Their stability constant determined by spectrofluorometric titration is 15761 L mol. Moreover, to obtain information about the binding mechanism of the interaction, ¹H NMR studies were carried out showing that the water-soluble p-SCX4 was found to be able to complex the aromatic l-Tyr, and the part of benzene ring of amino acid penetrated into the hydrophobic cavity of calix[4]arene and charged aliphatic chain of l-Tyr stick out of the cavity. In addition, the thermodynamic parameters for the complexation of p-SCX4 with l-Tyr were determined through Van’t Hoff analysis. The obtained data further confirmed the binding mode of p-SCX4 with l-Tyr. The related mechanism is proposed to explain the complexation processes.     

Thermal study of l-alanine, l-threonine, and taurine crystals related to hydrogen bonding

In this study l-alanine, l-threonine, and taurine crystals were characterized through dilatometric technique and thermogravimetric and differential thermal analysis. The dilatometric analysis shows that the thermal expansion of the crystals is correlated with the strengths of local hydrogen bonding in the amino acid structures at room temperature. Thermogravimetric analysis and differential thermal analysis of the l-alanine, taurine, and l-threonine crystals have been performed at high temperatures. No clear correlation between the hydrogen bonding strengths and endothermic peak positions was observed.     

Protonation Equilibria of Some Selected α-Amino Acids in DMSO–Water Mixture and Their Cu(II)-Complexes

The protonation constants of some α-amino acids (glycine (Gly), l-alanine (Ala), l-valine (Val), l-serine (Ser), l-leucine (Leu) and l-isoleucine (Ile)) were studied in water and DMSO–water solution mixtures containing 30, 50 and 70 vol-% DMSO; in addition the complex formation equilibria of their copper(II) complexes were studied by potentiometric technique using a combined pH electrode system calibrated in concentration units of the hydrogen ion at 25 ± 0.1 °C under a nitrogen atmosphere, and at an ionic strength of 0.10 mol·dm^?3 NaNO₃. The protonation constants and the overall stability constants of copper(II) complexes were influenced by changes in solvent composition, and their variations are discussed in terms of solvent and structural properties.     

Enhancing Production of l-Serine by Increasing the glyA Gene Expression in Methylobacterium sp. MB200

Microbial fermentation using methylotrophic bacteria is one of the most promising methods for l-serine production. Here we describe the metabolic engineering of a Methylobacterium strain to increase the production of l-serine. The glyA gene, encoding serine hydroxymethyltransferase (SHMT), was isolated from the genomic DNA of Methylobacterium sp. MB200, using a DNA fragment encoding Methylobacterium extorquens AM1 SHMT as a probe, and inserted into the vector pLAFR3. The resulting construct was transformed into Methylobacterium sp. MB200 using triparental mating. The genetic-engineered strain, designated as Methylobacterium sp. MB202, was shown to produce 11.4?±?0.6 mg/ml serine in resting cell reactions from 30 mg/ml wet cells, 20 mg/ml glycine, and 70 mg/ml methanol in 2 days, representing a 4.4-fold increase from that of the wild strain. The results demonstrated the potential for improving l-serine production by manipulating the glyA in bacteria and should facilitate the production of l-serine using Methylobacterium sp. strains.     

The yjjN of E. coli codes for an l-galactonate dehydrogenase and can be used for quantification of l-galactonate and l-gulonate

Escherichia coli is able to utilize l-galactonate as a sole carbon source. A metabolic pathway for l-galactonate catabolism is described in E. coli, and it is known to be interconnected with d-galacturonate metabolism. The corresponding gene encoding the first enzyme in the l-galactonate pathway, l-galactonate-5-dehydrogenase, was suggested to be yjjN. However, l-galactonate dehydrogenase activity was never demonstrated with the yjjN gene product. Here, we show that YjjN is indeed an l-galactonate dehydrogenase having activity also for l-gulonate. The K _m and k _cat for l-galactonate were 19.5?±?0.6 mM and 0.51?±?0.03 s^?1, respectively. In addition, YjjN was applied for a quantitative detection of the both of these substances in a coupled assay. The detection limits for l-galactonate and l-gulonate were 1.65 and 10 μM, respectively.     

Exploiting thermodynamic data to optimize the enantioseparation of underivatized amino acids in ligand exchange capillary electrophoresis

Stereoselective amino acid analysis has increasingly moved into the scope of interest of the scientific community. In this work, we report a study on the chiral separation of underivatized d,l-His by ligand exchange capillary electrophoresis (LECE), utilizing accurate ex ante calculations. This has been obtained by the addition to the background electrolytes (BGE) of NaClO₄ which renders the separations “all in solution processes”, allowing to accurately calculate in advance the concentrations of the species present in solution and to optimize the system performances. To this aim, the formation of ternary complexes of Cu²⁺ ion and l-lysine (l-Lys) or l-ornithine (l-Orn) with l- and d-histidine (His), and histamine (Hm) have been studied by potentiometry and calorimetry at 25 °C and with 0.1 mol dm^?3 (KNO₃) in aqueous solution. The ternary species [Cu(L)(l-His)H]⁺ and [Cu(L)(d-His)H]⁺ (where L?=?l-Lys or l-Orn) show a slight but still detectable stereoselectivity, and the determination of ΔH° and ΔS° values allowed the understanding of the factors which determine this phenomenon. The stereoselectivity showed by the protonated ternary species has been exploited to chirally separate d,l-His in LECE, by using the binary complexes of copper(II) with l-Lys or l-Orn as background electrolytes added with the appropriate amounts of NaClO₄.