Characterization of ethyl chloroformate derivative of <Emphasis Type="Italic">β</Emphasis>-methylamino-<Emphasis Type="SmallCaps">l</Emphasis>-alanine

Beta-methylamino-L-alanine (BMAA) is a neurotoxic amino acid that can be produced by cyanobacteria in aqueous environments. To analyze this compound by gas chromatography/mass spectrometry (GC/MS), BMAA must be derivatized to a nonpolar, volatile compound. This can be accomplished by reacting BMAA with ethyl chloroformate. While carrying out electron ionization (EI) mass spectrometric analysis on the (13)C-labeled derivative, it was discovered that the formation of an ion with a peak at m/z 245.12 is the result of [CH(3)CH(2)O.] loss from the amino groups resulting from alpha-cleavage. This differs from previous reports that attributed this peak to alpha-cleavage of the carboxylic ester portion of the BMAA derivative. This finding is important for understanding BMAA derivative mass spectrometric fragmentation patterns and ultimately to properly identifying and quantifying BMAA. Fragmentation pathways for the formation of other major peaks observed in the EI mass spectra are also proposed.     

Thermal behavior and polymorphism in medium–high temperature range of the sulfur containing amino acids <Emphasis Type="SmallCaps">l</Emphasis>-cysteine and <Emphasis Type="SmallCaps">l</Emphasis>-cystine

A thermophysical study of the sulfur containing amino acids l-cysteine and l-cystine has been carried out by differential scanning calorimetry (DSC). Heat capacities of both compounds were measured in the temperature interval from T = 268 K to near their respective melting temperatures. DSC and variable temperature powder X-ray diffraction analysis (PXRD) gave evidence for a solid–solid phase transition close to the melting point only in the l-cysteine sample. DSC experiments show that this solid–solid transition is not reversible in the temperature interval T = 235–485 K and presents a behavior depending on heating temperature, time, and rate. This behavior is also supported by variable-temperature PXRD. The patterns for the commercial samples, at room temperature, are consistent with those simulated for the orthorhombic and hexagonal polymorphic forms from the single-crystal X-ray analysis.     

Physical properties of aqueous solutions of potassium <Emphasis Type="SmallCaps">l</Emphasis>-prolinate from 298.15 to 343.15 K at atmospheric pressure

In this paper, experimental physical properties such as density, refractive index, and viscosity of aqueous potassium l-prolinate (KPr) as a solvent for CO₂ capture were investigated. Different concentrations of aqueous KPr in terms of mass fractions (0.05, 0.10, 0.20, 0.30, and 0.40) were studied over a temperature range 298.15–343.15 K. The obtained results showed that all physical properties increase with increasing the concentration of the solution (isothermally), and decrease as the solution temperature rises for any given concentration. The experimental data of density, refractive index, and viscosity were correlated using empirical correlations as a function of both, temperature and concentration. Coefficient of thermal expansion and activation energy were calculated from the experimental density and viscosity data, respectively, in the same temperature range. Thermal expansion coefficient slightly increases with increase in the temperature and concentration, while activation energy increases with the rise in concentration of amino acid salt.     

Interactions between several <Emphasis Type="SmallCaps">l</Emphasis>-α-amino acids and potassium chloride in aqueous solutions at 298.15 K

The enthalpies of solution of l-α-aminobutyric acid, l-α-valine, l-α-leucine, l-α-isoleucine, and l-α-cysteine have been measured in aqueous potassium chloride solutions at 298.15 K. From the obtained experimental results the standard dissolution enthalpies of amino acids in aqueous KCl solutions have been determined. These data were used to calculate the heterogeneous enthalpic pair interaction coefficients based on McMillan–Mayer’s theory. These values were interpreted in the terms of the hydrophobic or hydrophilic effects of the side chains of amino acids on their interactions with dissociated potassium chloride in water.     

Preparation of optical active aliphatic <Emphasis Type="Italic">α</Emphasis>-amino acid from fatty acid: synthesis of <Emphasis Type="SmallCaps">l</Emphasis>-norvaline and <Emphasis Type="SmallCaps">d</Emphasis>-norvaline

A new synthesis of l-norvaline is described. Using valeric acid as the raw material, α-brominevaleryl chloride was achieved by acyl chlorination and α-position bromination in one-pot with the yield of 84.7%. The yields of the following ammoniation of α-brominevaleryl chloride and resolution of dl-norvaline were 88.7% and 26.7%, respectively. d-Norvaline was also obtained in a similar method from the waste resolution solution. Other optical active amino acids, valine, α-aminobutyric acid and alanine were also synthesized in similar ways.     

“On-water” organic synthesis: <Emphasis Type="SmallCaps">l</Emphasis>-proline catalyzed synthesis of pyrimidine-2,4-dione-, benzo[<Emphasis Type="Italic">g</Emphasis>]- and dihydropyrano[2,3-<Emphasis Type="Italic">g</Emphasis>]chromene derivatives in aqueous media

In this work, functionalized pyrimidine-2,4-dione-, benzo[g]-, and dihydropyrano[2,3-g]chromene derivatives have been synthesized via a Michael addition of 2-hydroxy-1,4-naphthoquinone or 2,5-dihydroxy-1,4-benzoquinone to the Knoevenagel condensation product of an aldehyde with Meldrum’s acid, dimedone or barbituric acid in the presence of a catalytic amount of l-proline under refluxing conditions in water in good to excellent yields.     

Metal-Chelate Affinity Precipitation with Thermo-Responsive Polymer for Purification of <Emphasis Type="Italic">ε</Emphasis>-Poly-<Emphasis Type="SmallCaps">l</Emphasis>-Lysine

ε-Poly-l-lysine (ε-PL) is a natural preservative for food processing industry. A thermo-responsive polymer, attached with Cu²⁺ or Ni²⁺, was prepared for metal-chelate affinity precipitation for purification of ε-PL. The low critical solution temperatures (LCSTs) of these polymers were close to the room temperature (31.0–35.0 °C). The optimal adsorption conditions were as follows: pH 4.0, 0 mol/L NaCl, ligand density 75.00 μmol/g, and 120 min. The ligand Cu²⁺ showed a stronger affinity interaction with ε-PL and the highest adsorption amount reached 251.93 mg/g polymer. The elution recovery of ε-PL could be 98.42% with 0.50 mol/L imidazole (pH = 8.0) as the eluent. The method could purify ε-PL from fermentation broth and the final product was proved as electrophoretic pure by SDS-PAGE. Moreover, these affinity polymers could be recycled after the purification of ε-PL and the recoveries were above 95.00%.

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Graphical Abstract Scheme for affinity precipitation of ε-PL

     

Kinetics of arenesulfonylation of glycine, <Emphasis Type="Italic">D,L</Emphasis>-α-alanine,and <Emphasis Type="Italic">D,L</Emphasis>-valine in water-organic media

Kinetics of arenesulfonylation of glycine, D,L-α-alanine, and D,L-valine with 3-nitrobenzenesulfonyl chloride were studied in solvent systems water-1,4-dioxane and water-2-propanol at water content 40 wt % and at different temperatures (298–313 ?). The effective values of activation parameters of the reaction were calculated. The kinetic characteristics of the studied reactions were compared with the corresponding data for glycine, alanine, and valine in reaction with benzoyl chloride in aqueous dioxane.     

Directed Aminomethylation of Pyrrole,Indole, and Carbazole with <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N′</Emphasis>,<Emphasis Type="Italic">N′</Emphasis>-Tetramethylmethanediamine

Catalytic aminomethylation of pyrrole and indole with N,N,N′,N′-tetramethylmethanediamine in the presence of 5 mol % of ZrOCl₂·8H₂O proceeds selectively at the positions 2, 5 of pyrrole and 1, 3 of indole. Carbazole under the same conditions affords 3-formyl-9-aminomethyl derivative. The reaction in the presence of 5 mol % of K₂CO₃ occurs as monoaminomethylation: for pyrrole at the position 2, for indole at the position 3, and for carbazole at the nitrogen atom of the substrate. Water-soluble 1,1′-(1H-pyrrole-2,5-diyl)bis(N,N-dimethylmethanamine) exhibits a fungistatic activity with respect to phytopathogenic fungi Rhizoctonia solani.     

Properties of poly(<Emphasis Type="Italic">γ</Emphasis>-benzyl <Emphasis Type="SmallCaps">l</Emphasis>-glutamate) membrane modified by polyurethane containing carboxyl group

A series of poly(γ-benzyl l-glutamate) (PBLG)/polyurethane (PU) containing carboxyl group blend membranes was prepared by casting the polymer blend solution in dimethylformamide (DMF). The surface morphology of the PBLG/PU blend membranes was investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Thermal, mechanical, and chemical properties of PBLG/PU blend membranes were studied by differential scanning calorimetry (DSC), tensile tests and other physical methods. It was revealed that the introduction of PU could exert outstanding effects on the morphology and the properties of PBLG membrane.     

Alkyl <Emphasis Type="Italic">β</Emphasis>-<Emphasis Type="SmallCaps">d</Emphasis>-cellulosides: non-reducing cellulose mimics

Non-reducing cellulose mimics, termed alkyl β-d-cellulosides, were successfully prepared by two efficient multi-step syntheses starting from commercially available microcrystalline cellulose or cellulose triacetate. Introduction of the alkoxy moiety and degradation of the cellulose backbone was carried out in the presence of a Lewis acid, on one hand. On the other hand, cellulose hydrolysis mediated by mineral acids was combined with β-glycosidation performed in the presence of silver salts. The samples obtained possess a number-average degree of polymerization from 5 to 25, determined by size-exclusion chromatography, elemental analyses, NMR spectroscopy, and MALDI-TOF mass spectrometry. Samples in multi-gram quantities were available. Selective formation of a β-glycosidic bond between the C-1 atom of the reducing end group and alkoxy moieties was confirmed by a combination of 2D NMR spectroscopic and MALDI-TOF MS techniques. Due to the blocking of the aldehyde function, the cellulosides described are very useful mimics for the investigation of polysaccharide interactions with other complex molecules such as proteins or to determine polymer properties in solution or in solid state.     

Novel <Emphasis Type="Italic">β</Emphasis>-<Emphasis Type="Italic">N</Emphasis>-acetylglucosaminidases from <Emphasis Type="Italic">Vibrio harveyi 650</Emphasis>: Cloning,expression, enzymatic properties,and subsite identification

Background  

Since chitin is a highly abundant natural biopolymer, many attempts have been made to convert this insoluble polysaccharide into commercially valuable products using chitinases and β-N-acetylglucosaminidases (GlcNAcases). We have previously reported the structure and function of chitinase A from Vibrio harveyi 650. This study t reports the identification of two GlcNAcases from the same organism and their detailed functional characterization.     

Factors influencing aggregation behavior of poly(<Emphasis Type="Italic">γ</Emphasis>-benzyl <Emphasis Type="SmallCaps">l</Emphasis>-glutamate)-<Emphasis Type="Italic">graft</Emphasis>-poly(ethylene glycol) copolymer in mixed solvents

Poly(γ-benzyl l-glutamate)-graft-poly(ethylene glycol) (PBLG-graft-PEG) copolymer was synthesized by the ester exchange reaction of PBLG homopolymer with mPEG. Aggregation behavior of the PBLG-graft-PEG copolymer in mixtures of ethanol and chloroform was investigated by transmission electron microscopy (TEM), dynamic light scattering (DLS), and viscometry. Effects of the polymer solution concentration, grafting degree, test temperature, and chloroform content on the morphology, average particle diameter, and critical micelle concentration (CMC) of the micelles formed by the PBLG-graft-PEG copolymer in the mixed solvents were mainly studied. It was revealed that the PBLG-graft-PEG copolymer can self-assemble into polymeric micelles with a core-shell structure in various shapes depending on the preparation conditions.     

Thermophysical properties of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimеthylacetamide mixtures with <Emphasis Type="Italic">n</Emphasis>-butanol

The refraction, dielectric, viscosity, density, data of the binary mixtures of N,N-dimethylacetamide (DMA) with n-butanol at 308.15 and 313.15 K. The measured parameters used to obtain derived properties like Bruggeman factor, molar refraction and excess static dielectric constant, excess inverse relaxation time, excess molar volume and excess viscosity, excess molar refraction. The variation in magnitude with composition and temperature of these quantities has been used to discuss the type, strength and nature of binary interactions. Results confirm that there are strong hydrogen-bond interactions between unlike molecules of DMA+ n-butanol mixtures and that 1: 1 complexes are formed and strength of intermolecular interaction increases with temperature.     

Synthesis of a Fucosylated Trisaccharide Via Transglycosylation by α-<Emphasis Type="SmallCaps">l</Emphasis>-Fucosidase from <Emphasis Type="Italic">Thermotoga maritima</Emphasis>

Fucosylated oligosaccharides, such as 2′-fucosyllactose in human milk, have important biological functions such as prebiotics and preventing infection. In this work, the effect of an acceptor substrate (lactose) and the donor substrate 4-nitrophenyl-α-l-fucopyranoside (pNP-Fuc) on the synthesis of a fucosylated trisaccharide was studied in a transglycosylation reaction using α-l-fucosidase from Thermotoga maritima. Conducting a matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), it was demonstrated that synthesized oligosaccharide corresponded to a fucosylated trisaccharide, and high-performance liquid chromatography (HPLC) of the hydrolyzed compound confirmed it was fucosyllactose. As the concentration of the acceptor substrate increased, the concentration and synthesis rate of the fucosylated trisaccharide also increased, and the highest concentration obtained was 0.883 mM (25.2% yield) when using the higher initial lactose concentration (584 mM). Furthermore, the lower donor/acceptor ratio had the highest synthesis, so at the molar ratio of 0.001, a concentration of 0.286 mM was obtained (32.5% yield).     

Genome Shuffling Enhanced ε-Poly-<Emphasis Type="SmallCaps">l</Emphasis>-Lysine Production by Improving Glucose Tolerance of <Emphasis Type="Italic">Streptomyces graminearus</Emphasis>

The productivity of ε-poly-l-lysine (ε-PL) in currently reported wild-type strains is low. Here we improved glucose tolerance of a Streptomyces graminearus strain LS-B1 by genome shuffling while simultaneously enhancing the ε-PL productivity. The starting population was generated by ultraviolet irradiation and nitrosoguanidine mutagenesis and then subjected for recursive protoplast fusion. The positive colonies from library, created by fusing the inactivated protoplasts were screened on agar plates containing different concentrations of glucose. Characterization of all recombinants and wild-type strain in shake-flask fermentation indicated the compatibility of two phenotypes of glucose tolerance and ε-PL yield enhancement. The best performing recombinant, F3-4, was isolated after three rounds of genome shuffling, whose ε-PL production was about 88% higher than that of the parent strain. In batch fermentation test, the ε-PL concentration was obtained as 2.4 g/L by F3-4 compared with 1.6 g/L of wild type. Fed-batch fermentation by F3-4 was carried out and the ε-PL production accumulated to 13.5 g/L when initial glucose concentration was improved from 50 to 85 g/L. Enzyme activities of hexokinase, pyruvate kinase, and citrate synthase revealed that the glycolytic pathway and tricarboxylic acid circle way in F3-4 were more active than those in wild type, which was a possible reason for enhanced ε-PL production.     

<Emphasis Type="Italic">N</Emphasis>′-tetrazolylmethoxyl derivatives of <Emphasis Type="Italic">N</Emphasis>-methyldiazene <Emphasis Type="Italic">N</Emphasis>-oxides

A preparation method was developed for previously unknown tetrazole derivatives containing in the 1, 2, and/or 5 positions of the tetrazole ring N-methyldiazene-N-oxide-N′-oxymethyl groups.     

Isothermal Titration Calorimetry and Theoretical Studies on Host-guest Interaction of Ibuprofen with <Emphasis Type="Bold">α</Emphasis>-, <Emphasis Type="Bold">β</Emphasis>- and <Emphasis Type="Bold">γ</Emphasis>-Cyclodextrin

Thermodynamic parameters for formation of the inclusion complexes of α-, β- and γ-cyclodextrin (α-, β- and γ-CD) with ibuprofen (BF) in Tris-HCl buffer solutions (pH=7.0) have been determined by isothermal titration calorimetry (ITC) with nanowatt sensitivity, and the inclusion structures have been investigated by using ¹H-NMR spectra at 298.15 K. A theoretical study on the inclusion processes between BF and CDs has been performed with the B3LYP/6-31G*//PM3 method in order to investigate the formation mechanism of the inclusion complexes. An analysis of the thermodynamic data indicates that the stoichiometries of α-, β- and γ-CD with BF are all 1:1 and formation of the inclusion complexes α-CD⋅BF and β-CD⋅BF are driven by enthalpy and entropy, whereas formation of γ-CD⋅BF is an entropy driven process. The ¹H-NMR spectra provide clear evidence for the inclusion phenomenon, and show that the isobutyl group and aromatic ring of the guest molecule are trapped inside the cavity of the CDs. Theoretical calculations suggest that the complex formed by the BF molecule entering into the cavity of the CD molecule from the wide side is more stable than that from the narrow side.