Effects and mechanisms of L-phenylalanine on growth of Microcystis aeruginosa

The effects and possible mechanisms of action of L- phenylalanine on the growth of Microcystis aeruginosa cells were explored by cell counting and flow cytometry assays. L- phenylalanine promoted the growth of Microcystis aeruginosa at concentrations between 0.078 and 0. 312 μg/mL, but inhibited growth at concentrations between 0. 625 and 20μg/mL in 24 h exposure. The dose-effect and time-course relationships between exposure to L-phenylalanine and growth inhibition of Microcystis aeruginosa were observed. The IC50 value of L-phenylalanine for growth inhibition of Microcystis aeruginosa was 6. 2 μg/mL （95% confidence interval was 0. 005 to 16. 76 μg/mL）. The membrane integrity of the cells showed significant variations after 24 h exposure to L-phenylalanine. Meanwhile, no effects on esterase activity of the cells were observed until after 48 h exposure to L-phenylalanine. In conclusion, L-phenylalanine has hormesis effects and algae control effects on Microcystis aeruginosa. The latter is closely related to alterations or disorders in the cell membrane and with variation of esterase activity in the cells.

Synthesis, Characterization and Antibacterial Properties of Rare Earth Complexes with L-Phenylalanine and o-Phenanthroline

New solid ternary complexes of rare earth with L-Phenylalanine （ L-Phe ） and o-Phenanthroline （Phen） were synthesized in ethyl alcohol solution. Their composition were characterized by elemental analysis, molar conductance, IR, Raman, UV-VIS, TG-DTA. The compositions of the complexes were confirmed to be RE （ Phe ）3Phen Cl3 · 3H2O （ RE = La^3＋, Ce^3＋, Pr^3＋, Nd^3＋, Sm^3＋, Eu^3＋, Er^3＋, Y^3＋）. The antibacterial activities testing indicates that all these solid ternary complexes have antibacterial ability against Escherich coli, Staphy lococcus aureus, Candida albican （MIC are about 65 × 10^-4%, 15 × 10^-3%, 4 × 10^-2%, respectively）.

Modified DIX model for ion-exchange equilibrium of L-phenylalanine on a strong cation-exchange resin

L-phenylalanine, one of the nine essential amino acids for the human body, is extensively used as an ingredient in food, pharmaceutical and nutrition industries. A suitable equilibrium model is required for purification of L-phenylalanine based on ion-exchange chromatography. In this work, the equilibrium uptake of L-phenylalanine on a strong acid-cation exchanger SH11 was investigated experimentally and theoretically. A modified Donnan ion-exchange （DIX） model, which takes the activiW into account, was established to predict the uptake of L-phenylalanine at various solution pH values. The model parameters including selectivity and mean activity coefficient in the resin phase are presented. The modified DIX model is in good agreement with the experimental data. The optimum operating pH value of 2.0, with the highest t-phenylalanine uptake on the resin, is predicted by the model. This basic information combined with the general mass transfer model will lay the foundation for the prediction of dynamic behavior of fixed bed separation process.

EFFECTS OF L-PHENYLALANINE ON THE RADIATION SYNTHESIS OF POLY(N,N'-METHYLENEBISACRYLAMIDE-co-4-VINYLPYRIDINE)(MICRO)GELS

The effects of L-phenylalanine （L-Phe） on the synthesis ofpoly（N,N＇-methylenebisacrylamide-co-4-vinylpyridine） （poly（Bis-co-4-VP）） （micro）gels by γ-ray irradiation were studied. The addition of L-Phe could not only decrease the gelation dose （Dg） of the synthesis obviously, but also transform the morphology of copolymer from microgel to gel. In addition, the swelling ability of the （micro）gels was also affected in the presence of L-Phe. The decrease of Dg was ascribed to the effect of pH, while the transformation of the morphology was ascribed to the effect of L-Phe on the stability of the poly（Bis-co-4-VP） microgel. Such an effect was confirmed further as compared with the effects of L-alanine, L-glutamic acid, L-arginine, sulfuric acid and aqueous ammonia.

Colorimetric Recognition of 3,4-Dihydroxy-D,L-phenylalanine with Tetrapeptide-modified Copper Nanoparticles as Chiral Nanozymes

The construct of artificial nanocatalyts by simulating natural enzymes and thereby bringing new properties for practical applications is still a challenging task to date.In this study,chiral tetrapeptide(L-phenylalanine-L-phenylalanine-L-cysteine-L-histidine)-engineered copper nanoparticles(FFCH@CuNPs)were fabricated as an artificial peroxidase(POD).More interestingly,the nano-catalysts exhibited chiral identification function.In comparison with other nanocatalysts like L-cysteine-,L-histidine-,chiral dipeptide(L-cysteine-L-histidine)-,or chiral tripeptide(L-phenylalanine-L-cysteine-L-histidine)-modified CuNPs,FFCH@CuNPs demonstrated higher POD-mimetic catalytic activity in the 3,3',5,5'-tetramethylbenzidine(TMB)-H_(2)O_(2) system and stronger enantioselectivity in the recognition of 3,4-dihydroxy-D,L-phenylalanine(D,L-DOPA)enantiomers.Considering the strength difference between the intermolecular hydrogen bonding and theπ-πinteractions,the principle behind the chiral discrimination of D,L-DOPA was explored.Furthermore,higher contents of surface Cu2+ions and hydroxyl radicals were found in the FFCH@CuNPs-D-DOPA-TMB-H_(2)O_(2) system than in the FFCH@CuNPs-L-DOPA-TMB-H_(2)O_(2) system.Based on these results,a protocol for distinguishing between D,L-DOPA enantiomers through colorimetric recognition was established.This study provides a new insight into the design and fabrication of oligopeptides@CuNPs-based chiral nanozymes with improved catalytic performance and features additional to those of natural enzymes.

Synthesis of novel copolymer:Poly(p-dioxanone-co-L-phenylalanine)

In order to expand the application of poly（p-dioxanone） or PPDO in biomedical area,a series of novel copolymers were synthesized successfully by one-step,melted copolymerization of p-dioxanone（PDO） and L-phenylalanine N-carboxyanhydride（L-Phe-NCA） monomers.With the in-feed molar ratio of L-PheNCA /PDO equal to 1/20,the conversions of the two kinds of monomers were calculated from 1H NMR. The average molecular weight and polydispersity of the copolymer increase with the increasing reaction time and catalyst concentration.However,the conversions of the two kinds of monomers did not change with the reaction conditions.A three-step mechanism is presented and proved by high resolution 1H NMR and IR spectrums.

Determination of L-phenylalanine by cucurbit[7]uril sensitized fluorescence quenching method

The determination method of L-phenylalartine （LPA） by fluorescence quenching was developed. The assay was based on the combination of the cucurbit[7]uril （CB [7]） with palmatine hydrochloride （PAL） reaction. In the presence of CB [7], the fluorescence of PAL was quenched by LPA which can be employed to detect LPA. Under the optimal conditions, a linear range 3.63 ×10^-8- 9.68 ×10^-6 mol/L and a detection limit 1.27 ×10^-8 mol/L of LPA were obtained. The relative standard deviation （R.S.D） was 1.8% obtained from a series of 11 standards each containing 6.05 ×10^-6 mol/L of LPA. This paper also discusses the mechanism of fluorescence indicator probe.

Computational Design and Fabrication of Enantioselective Recognition Sorbents for L-phenylalanine Benzyl Ester on Multiwalled Carbon Nanotubes Using Molecular Imprinting Technology

Computational strategies have been employed to investigate the influence of the nature of monomers and cross-linker in order to design three dimensional imprinted polymers with selective recognition sites for L-phenylalanine benzyl ester(L-PABE)molecule.Here,computational chemistry methods were applied to screen the molar quantity of functional monomers that interact with one mole of the template molecule.Effects of the nature of functional monomer,cross-linker,and molar ratio were determined computationally using density functional calculations with B3LYP functional and generic 6-31G basis set.Methacrylic acid(MAA)and ethylene glycol dimethacrylate(EGDMA)were used as the functional monomer and crosslinking agent,respectively.L-PABE imprinted polymer layered on multiwalled carbon nanotube(MWCNT)and conventional bulk MIP were synthesised and characterized as well.To investigate the influence of pre-organization of binding sites on the selectivity of L-PABE,respective non-imprinted polymers were also synthesised.MWCNT-MIPs and MIPs exhibited the highest adsorption capacity towards L-PABE.The synthesized polymers revealed characteristic adsorption features and selectivity towards L-PABE in comparison with those of its enantiomer analogues.

Preparation and Chiral Recognition of Thermosensitive Poly（N-isopropylacrylamide） Microgels Containing Modified L-Phenylalanine Groups

Thermosensitive poly[N-isopropylacrylamide（NIPAM）-co-N-acryloyl-L-phenylalanine ethyl ester （NALPE）] microgels were prepared by the free radical polymerization of NIPAM and chiral monomer, NALPE. Such microgels exhibited spherical shape and favorable monodispersity. Increasing the content of NALPE units would en- hance the average diameter, but decrease the thermosensitivity and volume-phase transition temperatures of the mi- crogels. Compared with PNIPAM microgels, the microgels containing NALPE units performed chiral recognozable capacities for D-phenylalanine and D-tartaric acid, and the enantioselectivity and adsorption capacity of the microgels improved with increasing the temperature and/or the content of NALPE units.

Synthesis of Protected Tetrapeptide, N-o-Ns-N(Me)-Val-N(Me)-Val-N(Me)-Val-N(Me)-Phe-O^tBu

The protected tetrapeptide, N-o-Ns-N （ Me ） -Val-N （ Me ） -Val-N （ Me ） -Val- N （ Me ） -Phe- OtBu, was prepared from L-valine and L-phenylalanine. Ted-butyl acetate and HClO4 were used to protect carbonyl group, o-nitrobenzenesulfonyl chloride and triethyl amine were used to protect amino group, and N-alkylation was finished with iodomethane. Then the protected amino acid was turned into acid chloride which was taken as coupling reagent. After 14 steps, such as protection, alkylation, deprotection and coupling, the protected tetrapeptide was obtained with a yield of 26.9%. The structures of intermediates and target compound were identified with NMR spectra and high resolution mass spectra.

Syntheses, Structures and Interactions with DNA of Two in situ Generated Palladium(Ⅱ) Complexes

Two new complexes [Pd（L-phe）2·2H2O] （1） and [Pd（4,4＇-dcbpy）（en）·H2O] （2） （L-phe = L-phenylalanine, 4,4＇-dcbpy = 2,2＇-bipyridyl-4,4＇-dicarboxylate, en = ethylenediamine） were synthesized and characterized. L-phenylalanine was in situ formed via the hydrolysis of N-（tert-butoxycarbonyl）-L-phenylalanine, and ethylenediamine came from the in situ reaction of piperazine （pip） under hydrothermal conditions. The single-crystal X-ray structure analyses reveal that the Pd（Ⅱ） ion constructs a square planer coordination geometry in complexes 1 and 2, respectively. Complex 1 extends into a 2D layered structure via H-bond interactions and complex 2 connects into a 3D network through hydrogen bonds and 7r-tr stacking interactions. The interactions of 1 and 2 with fish sperm DNA （FS-DNA） were examined via UV-Vis absorption spectra and fluorescence spectroscopy. The cleavage reaction for plasmid DNA has been assayed by agarose gel electrophoresis. The results indicate that two complexes interact with DNA and the insertion is the main binding mode.

Effect of Chloride Ions and Dissolved Oxygen on the Deactivation of Phenylalanine Ammonia-lyase

With the method of synthesizing the L-phenylalanine by trans-cinnamic acid and ammonia in the presence of phenylalanine ammonialyase (PAL) under high pH and high concentration of cinnamic acid, it is not favorable for the conversion because of the deactivation of the PAL.For this reason, it is important to find out the suita-