Effect of some amino acids and peptides on silicic acid polymerization

The polymerization of silicic acid in aqueous solutions at different pH was followed by the colorimetric molybdosilicate method. The role of four amino acids (serine, lysine, proline and aspartic acid) and the corresponding homopeptides was studied. All four amino acids behave the same way and favor the condensation of silicic acid. Peptides exhibit a stronger catalytic effect than amino acids but they appear to behave in very different ways depending on the nature of side-groups and pH. Poly-lysine and poly-proline for instance lead to the precipitation of solid phases containing both silica and peptides. The role of these biomolecules on the polymerization of silicic acid is discussed in terms of electrostatic interactions, hydrogen bonds and solubility.     

Effect of certain chemical compounds on secondary metabolites of Penicillium janthinellum and P. duclauxii

The secondary metabolites of Penicillium janthinellum and P. duclauxii were affected by different concentrations of cadmium nitrate, sodium chloride, and sucrose. The fungal culture characteristics including mycelial fresh and dry weight, colony diameter, colony spore mass and reverse color, number of spores, and secondary metabolites were affected as well. Cyclopenin, carlosic acid, erythroskyrin, kojic acid, and patulin were produced by P. janthinellum on cadmium nitrate-free medium. However, cyclopenin, carlosic acid, frequentin, and islandicin were produced at 100 ppm, and cyclopenin at 500 ppm. On the other hand, the secondary metabolites produced by P. duclauxii were 9 on cadmium nitrate-free medium, 7 on medium containing 100 and 500 ppm of cadmium nitrate, and 4 at 1000 ppm cadmium nitrate concentration. Secondary metabolite brevianamide A was produced in the presence and absence of cadmium nitrate. The duclauxin, patulin, terrestic acid, and xanthomegin were produced only on cadmium nitrate-free medium. However, mycophenolic acid was produced only on cadmium nitrate-containing medium. The kojic acid was produced by P. janthinellum at 0.0%, 0.5%, 1.0%, 2.0%, 3.0%, and 5.0% concentrations of sodium chloride. The carlosic acid, erythroskyrin, and patulin were produced only at 0.0% and 1.0%. While carolic acid and islandicin were produced at 1%, 2%, and 3% and frequentin was produced only at 2% and 3%. On the other hand, 8 secondary metabolites were produced by P. duclauxii at 0.0%, 0.5%, 1.0%, and 2.0% concentration of sodium chloride and only 4 were produced at 3%. The secondary metabolites produced by P. janthinellum were 7 at 10% and 20%, 6 at 30%, and 2 only at 40% concentrations of sucrose. However, 8 secondary metabolites were produced by P. duclauxii at 10%, 20%, 30% and 3 at 40% concentrations of sucrose.     

Patterns of cation binding to the aromatic amino acid R groups in Trp,Tyr, and Phe

Previous joint experimental and theoretical work demonstrates that typically soluble peptides will be rendered insoluble in the presence of saturated sodium ions in aqueous solution due to disruption of cation-π interactions between Trp and Lys. The present work utilizes quantum chemical methods including density functional theory, symmetry-adapted perturbation theory, and even coupled cluster theory to determine the strengths of cation-π interactions for the aromatic R groups of Trp, Tyr, and Phe (approximated as skatole, methyl phenol, and toluene) with both alkali and alkaline-Earth atomic cations and electron-accepting R groups from Lys, Arg, and His approximated as methyl ammonium, guanidinium, and imidazolium cations. This work shows that sodium ion is still the most likely disrupter of peptide folding built upon cation-π interactions, since Trp, Tyr, and Phe all bind more strongly to sodium ion than to any of the polyatomic cations. Additionally, the atomic cation complex binding energies decrease with an increase in partial charge on the atomic cation in the complex. However, as the average partial charge increases in the interacting hydrogen atoms in the polyatomic cations, the binding energy increases. The disruption of such peptide–peptide cation-π interactions is certainly relevant for peptide design in β-sheets or β-hairpin structures, but it could also have implications for astrobiology.     

Separation of amino acid and peptide stereoisomers by nonionic micelle-mediated capillary electrophoresis after chiral derivatization

Enantiomers of amino acids and peptides were derivatized with a fluorescent chiral reagent, 4-(3-isothiocyanatopyrrolidin-1-yl)-7-nitro-2,1,3-benzoxadiazole [R-(−)- or S-(+)-NBD-PyNCS] and the resulting diastereomeric derivatives separated by capillary electrophoresis (CE). The CE running buffer consisted of 25 mM acetate buffer (pH 4) and 10 mM of the nonionic surfactant Triton X-100. The excitation maximum of NBD-PyNCS at 480 nm matches the major Ar-ion emission line at 488 nm allowing sensitive laser-induced fluorescence detection with limits of detection around 50 nM.

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-Proline and

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-aspartate spiked (at 10⁻⁴ M and 10⁻⁵ M concentrations, respectively) into complex biological matrices (rabbit serum and homogenate of Aplysia californica buccal ganglion) are detected without matrix interferences. This method has also been applied to the determination of

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- and

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-amino acid residues in peptides after acid hydrolysis. Results from the chiral analysis of the naturally-occurring peptide, gramicidin D, are shown.     

TLC separation of some biologically important amino acids on pyridinium tungstoarsenate impregnated layers

Summary A satisfactory TLC separation scheme for 15 important amino acids on silica gel layers impregnated with pyridinium tungstoarsenate using isoamyl alcohol-wateracetic acid (605030) as the solvent system has been worked out. It is found that the Martin relationship is obeyed by similarly constituted amino acids. A plot of R_M vs the concentration of pyridinium ion released shows a scatter suggesting that, besides exchange properties, other factors also strongly influence the movement of amino acids.     

Antifungal activities of amino acid ester functional pyrazolyl compounds against Fusarium oxysporum f.sp. albedinis and Saccharomyces cerevisiae yeast

Series of functional multidendate ligands based on pyrazole and amino acid derivatives were prepared in good and excellent yields (75–5%) by condensation of one equivalent of amino acid ester hydrochloride substrates with two equivalents of (3,5-dimethyl-1H–pyrazol-1-yl)methanol. These tridentate functionalized compounds and their starting materials were screened for their antifungal activities against Fusarium oxysporum f.sp. albedinis and the yeast of Saccharomyces cerevisiae. Considerable activities were recorded with respect to the two studied microorganisms.     

Synthesis of α,α-disubstituted amino acids based on tandem reaction of dehydroamino acid derivatives

The formation of all-substituted sp³-hybridized carbon-center was investigated via tandem reaction of dehydroamino acid derivatives. The diethylzinc-promoted reaction of dehydroamino acid derivatives with acid anhydride or π-allyl palladium complex proceeded smoothly to afford α,α-disubstituted amino acids via a radical and anionic carbon-carbon bond-forming processes. The tandem reductive reaction of N-phthaloyl dehydroalanine also proceeded effectively by using Bu₃SnH and Pd(PPh₃)₄.     

Structure and behaviour of the free radicals generated in gamma irradiated amino acid and iminodiacetic acid derivatives

An EPR study has been carried out to investigate the structure and behaviour of the free radical formed γ-irradiated l-alaninamide hydrochloride, dl-glutamic acid monohydrate and N-(2-carboxyethyl) iminodiacetic acid powders at room temperature. The observed paramagnetic species have been attributed to the CH(3)?HCONH(2), HOOCCH(2)CH(2)?HCOOH and HOOCCH(2)CH(2)N?HCH(2)(COOH)(2) radicals, respectively. Some spectroscopic properties and suggestions concerning possible structure of the radicals were also discussed in this study.     

Enantioseparation of various amino acid derivatives on a quinine based chiral anion-exchange selector at variable temperature conditions. Influence of structural parameters of the analytes on the apparent retention and enantioseparation characteristics

The influence of temperature on the performance of an enantioselective anion-exchange type chiral selector (SO) was systematically investigated. The resolution of the enantiomers of 23 N-acylated amino acids (selectands, SAs) on a covalently immobilized quinine tert.-butylcarbamate chiral stationary phase (CSP) was studied under linear chromatographic conditions over a temperature range of 0–85 °C with hydro–organic buffers (pH_a 6.0) as mobile phases. The apparent enantioseparation factors increased considerably at low column temperatures, indicating that enthalpic contributions are the dominating thermodynamic driving force for chiral recognition for all investigated SAs. Retention factors gave non-linear van’t Hoff plots, while the corresponding apparent enantioseparation factors showed linear van’t Hoff behavior. Correlations between magnitude and sign of the relative thermodynamic parameters of enantioselective adsorption (ΔΔG, ΔΔH and ΔΔS) and specific structural features of the analytes, i.e., steric and electronic nature of the various side chains and the N-acyl groups, are discussed with the aim to rationalize their possible contributions to the overall chiral recognition.     

Identification of unusual (modified and non-encoded) amino acid residues in peptides by combinations of high-performance liquid chromatography and high-performance capillary electrophoresis with matrix-assisted laser desorption ionization time-of-flight mass spectrometry

The techniques for micro-level analysis of some widespread unusual amino acids (phosphorylated and hydroxylated ones) as well as of some genetically non-encoded amino acids were developed for their subsequent identification in the peptide and protein amino acid sequence by narrow-bore column high-performance liquid chromatography (10 pmol of the sample), high-performance capillary electrophoresis (1–10 pmol), matrix-assisted laser desorption ionization time-of-flight mass spectrometry (1–10 pmol), and automatic protein gas phase sequencing (1–50 pmol).     

Quantitative analysis of 17 amino acids in tobacco leaves using an amino acid analyzer and chemometric resolution

A method was developed for quantifying 17 amino acids in tobacco leaves by using an A300 amino acid analyzer and chemometric resolution. In the method, amino acids were eluted by the buffer solution on an ion‐exchange column. After reacting with ninhydrin, the derivatives of amino acids were detected by ultraviolet detection. Most amino acids are separated by the elution program. However, five peaks of the derivatives are still overlapping. A non‐negative immune algorithm was employed to extract the profiles of the derivatives from the overlapping signals, and then peak areas were adopted for quantitative analysis of the amino acids. The method was validated by the determination of amino acids in tobacco leaves. The relative standard deviations (n = 5) are all less than 2.54% and the recoveries of the spiked samples are in a range of 94.62–108.21%. The feasibility of the method was proved by analyzing the 17 amino acids in 30 tobacco leaf samples.     

One-pot labeling-based capillary zone electrophoresis for separation of amino acid mixture and assay of biofluids

A fast, simple and cost-effective one-pot labeling strategy coupled with capillary zone electrophoresis was developed for the complete separation of amino acid mixture. The strategy includes two steps of reactions: Cyanuric chloride was made to react first with 7-amino-1,3-naphthalenedisulfonic acid monopotassium salt at 0 °C for 10 min, and then with amino acids at 55 °C for 6 min. The resulted products, after diluted with water, were injected into capillary zone electrophoresis system for separation. Using a running buffer of 20 mM sodium tetraborate decahydrate at pH 10.1, nineteen amino acids were efficiently separated in 25 min, with relative standard deviation of 0.36–1.6% and 0.96–2.1% (within and between days, respectively) for migration time and 0.030–1.6% and 0.22–2.4% (within and between days, respectively) for peak area. The proposed method has been successfully applied to the determination of free amino acids in biofluids, including human serum, urine, and saliva. The linearity of quantification was over two orders of magnitude for most amino acids, with a correlation coefficient larger than 0.999. The average recovery, determined by spiking a known amount of amino acid standards into real samples, was in a range from 91.6% to 105.9%. This method can be a noninvasive means since it could directly assay the urine and saliva samples.     

Continuous and gradient TLC development of 4-dimethylaminoazobenzene-4′-sulfonyl amino acid derivatives

Thin-layer gradient elution chromatography is a convenient technique for separation of very complicated mixtures; in some cases the gradient technique can be replaced by continuous development. The two techniques are compared in practice by using them to separate a mixture of dabsyl derivatives of amino acids.     

Spectral and thermal study of the ternary complexes of nickel with sulfasalazine and some amino acids

The ternary complexes of Ni(II) with sulfasalazine (H(3)SS) as a primary ligand and alanine (ala), aspartic acid (asp), histidene (hist), methionine (meth) and serine (ser) amino acids as secondary ligands have been synthesized. Characterization of the complexes was based on elemental analyses, IR, UV-vis, mass spectra, magnetic moment and thermal analysis (TG). The isolated complexes were found to have the general formula [M(HSS)(AA)]4H(2)O (AA=ala, asp, hist, meth, or ser amino acid) where nickel is tetra-coordinated. The thermal stability of the complexes was studied and the weight losses for the decomposition of the complexes were calculated and correlated with the mass fragmentation pattern. In most cases, the amino acid moiety is removed along with the Schiff base moiety leaving NiO as a metallic residue. The metallic residue was confirmed by powder XRD measurements.     

Effect of halides on the TLC resolution of amino acids below their isoelectric points

TLC of a fifteen component mixture of amino acids has been carried out in two ways; firstly, the amino acids were treated with halides below their isoelectric points and chromatographed on plain silica plates, and secondly the amino acids in their cationic forms were chromatographed on silica plates impregnated with halides, keeping the same solvent system. The resolution is considered to be affected by hydrophobic interactions between silica gel and amino acid molecule and by the polarity and the flow of the mobile phase. The method provides resolution of 10–11 amino acids from the fifteen component mixture.     

Fluorescent cyclodextrins bearing metal binding sites and their use for chemo- and enantioselective sensing of amino acid derivatives

Ditopic receptors based on cyclodextrins bearing a metal binding site were used as enantioselective fluorescence sensors, which were able to generate different responses in the presence of d- or l-amino acids. The performances of the selectors as a function of their structure were evaluated, and the same analysis was extended to other analytes. In this work, this approach is used for the enantiomers of a series of amino acid derivatives and in particular of 2-aminocaprolactam. The results showed that the ability of these sensors to perform enantiomeric analysis can be extended to other analytes of interest in organic synthesis such as amino acid amides and α-aminolactams.     

Complementary routes to both enantiomers of pipecolic acid and 4,5-dihydroxypipecolic acid derivatives

Complementary new routes to both enantiomers of N-protected pipecolic acid and the corresponding 4,5-dihydroxylated derivatives are developed, which involve stereo-divergent allylation of a chiral N-allylimine and ring-closing metathesis as key steps.     

Preparation of multiwall carbon nanotubes film modified electrode and its application to simultaneous determination of oxidizable amino acids in ion chromatography

A multiwall carbon nanotubes (MWNTs) film modified electrode was prepared and used as an amperometric sensor for the simultaneous determination of oxidizable amino acids including cysteine, tryptophane and tyrosine. The electrochemical behaviors of these amino acids at this modified electrode were studied by cyclic voltammetry (CV). The results indicated that the MWNTs chemically modified electrode (CME) exhibited efficient electrocatalytic activity towards the oxidation of these amino acids with relatively high sensitivity, stability and long-life. Following separation by ion chromatography (IC) with 2.0×10⁻³ mol l⁻¹ citric acid buffer solution (pH 6.5) as eluent, cysteine, tryptophane and tyrosine could be determined by the MWNTs CME successfully. Under the optimal conditions, the detection limits were 7.0×10⁻⁷ mol l⁻¹ for cysteine, 2.0×10⁻⁷ mol l⁻¹ for tryptophane and 3.5×10⁻⁷ mol l⁻¹ for tyrosine at the signal-to-noise of 3, respectively. The method was applied successfully to the determination of these substances in plasma.