Volumetric,Acoustic and Transport Properties of Metformin Hydrochloride Drug in Aqueous <Emphasis Type="SmallCaps">d</Emphasis>-Glucose Solutions at <Emphasis Type="Italic">T</Emphasis> = (298.15–318.15) K

Apparent molar volumes, apparent molar adiabatic compressibilities and viscosity B-coefficients for metformin hydrochloride in aqueous d-glucose solutions were determined from solution densities, sound velocities and viscosities measured at T = (298.15–318.15) K and at pressure p = 101 kPa as a function of the metformin hydrochloride concentrations. The standard partial molar volumes (\( \phi_{V}^{0} \)) and slopes (\( S_{V}^{*} \)) obtained from the Masson equation were interpreted in terms of solute–solvent and solute–solute interactions, respectively. Solution viscosities were analyzed using the Jones–Dole equation and the viscosity A and B coefficients discussed in terms of solute–solute and solute–solvent interactions, respectively. Adiabatic compressibility (\( \beta_{s} \)) and apparent molar adiabatic compressibility (\( \phi_{\kappa }^{{}} \)), limiting apparent molar adiabatic compressibility (\( \phi_{\kappa }^{0} \)) and experimental slopes (\( S_{\kappa }^{*} \)) were determined from sound velocity data. The standard volume of transfer (\( \Delta_{t} \phi_{V}^{0} \)), viscosity B-coefficients of transfer (\( \Delta_{t} B \)) and limiting apparent molar adiabatic compressibility of transfer (\( \Delta_{t} \phi_{\kappa }^{0} \)) of metformin hydrochloride from water to aqueous glucose solutions were derived to understand various interactions in the ternary solutions. The activation parameters of viscous flow for the studied solutions were calculated using transition state theory. Hepler’s coefficient \( (d\phi /dT)_{p} \) indicated the structure making ability of metformin hydrochloride in the ternary solutions.     

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.     

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.     

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.     

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

     

<Emphasis Type="SmallCaps">d</Emphasis>(−)-Lactic Acid Production by <Emphasis Type="Italic">Leuconostoc mesenteroides</Emphasis> B512 Using Different Carbon and Nitrogen Sources

Sugar concentration from sugarcane juice and yeast autolysate increased lactic acid production more than the other agro-industrial substrates tested. The concentrations of these two components were further optimized using the Plackett–Burman design and response surface method. A second-order polynomial regression model estimated that a maximal lactic acid production of 66.11 g/L would be obtained when the optimal values of sugar and yeast autolysate were 116.9 and 44.25 g/L, respectively. To validate the optimization of the medium composition, studies were carried out using the optimized conditions to confirm the result of the response surface analysis. After 48 h, lactic acid production using the shake-flask method was at 60.2 g/L.     

Computer models of eutectic-type <Emphasis Type="Italic">T</Emphasis>–<Emphasis Type="Italic">x</Emphasis>–<Emphasis Type="Italic">y</Emphasis> diagrams with allotropy

Using the eutectic-type T–x–y diagram as an example, it can be represented the analysis of its geometrical construction dependence on the temperature of a component two polymorphous modifications which participate in mono- and invariant metatectic and invariant eutectic (eutectoid) transformations above or below (and within) binary eutectics temperature intervals and below a ternary eutectic temperature. Computer models for considered phase diagrams have been designed. Such models help to solve applied tasks like visualization, isopleths and isothermal sections decoding, mass balances calculation and evaluation of phase and conglomerate concentration in microstructure.     

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.     

The Partial Molar Isothermal Compressions of the Nucleosides Adenosine,Cytidine, and Uridine in Aqueous Solution at <Emphasis Type="Italic">T</Emphasis> = (288.15 and 313.15) K

Sound speeds have been measured for aqueous solutions of the nucleosides adenosine, cytidine, and uridine at T = (288.15 and 313.15) K and at ambient pressure. The partial molar isentropic compressions at infinite dilution, \( K_{S,2}^{\text{o}} \), were derived from the speed of sound data. The partial molar heat capacities at infinite dilution, \( C_{p,2}^{\text{o}} \), for the three nucleosides at T = (288.15 and 313.15) K were also determined. These \( K_{S,2}^{\text{o}} \) and \( C_{p,2}^{\text{o}} \) results, along with partial molar isobaric expansions at infinite dilution, \( E_{2}^{\text{o}} = \, (\partial V_{2}^{\text{o}} /\partial T)_{p} \), that were derived using data from the literature, were used to evaluate the partial molar isothermal compressions at infinite dilution, \( K_{T,2}^{\text{o}} \{ K_{T,2}^{\text{o}} = - \, (\partial V_{2}^{\text{o}} /\partial p)_{T} \} \), for the nucleosides. The \( K_{T,2}^{\text{o}} \) results were rationalized in terms of nucleoside hydration and its temperature dependence.     

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.     

Thermal properties and interpartical interactions of <Emphasis Type="SmallCaps">l</Emphasis>-proline,glycine, and <Emphasis Type="SmallCaps">l</Emphasis>-alanine in aqueous urea solutions at 288–318 K

The enthalpies of solution of l-proline have been measured in aqueous urea solutions at 0–6 mol urea kg⁻¹ water at 288.15, 298.15, 308.15, and 318.15 K by the calorimetric method. The two-parameter relation connecting the values of solution enthalpies of proline with urea concentration and temperature has been obtained. The enthalpy and heat capacity parameters of pair interaction of l-proline with urea in water have been computed. Using the thermodynamic relations, the temperature changes of reduced enthalpy, and also the change of entropy and reduced Gibbs energy of solution of l-proline in aqueous solutions of urea at the temperature rise from 288 to 318 K have been determined. Their comparison with the data for glycine and l-alanine has been carried out. It has been shown that the entropy–enthalpy compensation (Barclay–Butler rule) takes place for dissolution and transfer processes.     

<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.     

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.     

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.     

Modification of poly(vinyl alcohol) membrane via blending with poly(<Emphasis Type="Italic">γ</Emphasis>-benzyl <Emphasis Type="SmallCaps">l</Emphasis>-glutamate)-<Emphasis Type="Italic">block</Emphasis>-poly(ethylene glycol) copolymer

A series of poly(vinyl alcohol) (PVA)/poly(γ-benzyl l-glutamate)-block-poly(ethylene glycol) (PBLG-b-PEG) blend membranes with different PVA/PBLG-b-PEG mole ratios were prepared by pervaporation. Structure and morphologies of PVA/PBLG-b-PEG blend membranes were investigated using Fourier transformation infrared spectroscopy (FTIR), and atomic force microscopy (AFM). Mechanical and chemical properties of PVA/PBLG-b-PEG blend membrane were studied by tensile testing and other physical methods. It was revealed that the introduction of PBLG-b-PEG copolymer has significant effect on the properties of a PVA membrane.     

Optimization of Affinity Chromatography of Pepsins on Iodinated <Emphasis Type="SmallCaps">l</Emphasis>-Tyrosine–Sepharose

Iodinated l-tyrosine–Sepharose was used as an affinity sorbent for the separation of porcine and human pepsins. The optimized conditions for pepsin adsorption as well as enzyme desorption were investigated. The following basic characteristics of the prepared affinity sorbent were determined: the recovery of the loaded enzyme, capacity of the affinity sorbent, concentration range of the linear dependence of bound pepsin on the applied enzyme, and the reproducibility of the experiments. The method described here cannot only be used for pepsin separation but also for analytical purposes.     

<Emphasis Type="Italic">I</Emphasis>–<Emphasis Type="Italic">V</Emphasis>–<Emphasis Type="Italic">T</Emphasis> analysing an inhomogeneous Au/Poly(4-vinyl phenol)/p-Si structure with a double Gaussian distribution of barrier heights

In this study, the current–voltage (I–V) characteristics of Au/Poly(4-vinyl phenol)/p-Si structures have been measured over a wide temperature range (100–300 K). These structures have been analyzed according to thermionic emission (TE) theory, as a result of which an abnormal decrease occurred in the zero-bias barrier height (f_b0 \phi_{b0} ) and an increase in the ideality factor (n) was observed with temperature decrease and nonlinearity in the activation energy plot. By assuming a Gaussian distribution (GD) of barrier heights of the Au/Poly(4-vinyl phenol)/p-Si structures, barrier inhomogeneities are believed to responsible for this behavior. Evidence is given for the existence of a double GD with mean barrier heights ([`(f)]<sub>b0</sub> \bar{\phi }_{b0} ) of 1.042 and 0.623 eV, standard deviations of 0.138 and 0.081 V, and ideality factors 2.76 and 7.26, which remain effective in the temperature ranges of 180–300 and 100–160 K, respectively. As a result, without using the temperature coefficient of the barrier height, the modified ln(I <sub>o</sub> /T <sup>2</sup>) − q <sup>2</sup> σ <sub>o</sub> <sup>2</sup>/2(kT)<sup>2</sup> vs. q/kT plot gives [`(f)]_b0 \bar{\phi }_{b0} values and Richardson constants (A ^* ) as 1.036 and 0.623 eV, and 36.20 and 19.99 A/cm² K², respectively. The effective Richardson constant value of 36.20 A/cm² K² is very similar to the theoretical value of 32 A/cm²K² for p-Si. Consequently, the temperature dependence of the forward bias I–V characteristics of Au/Poly(4-vinyl phenol)//p-Si (MIS) structure could be attributed to the thermionic emission (TE) mechanism with double GD of the barrier heights.