Redox Behavior of Neptunium(V) in Tributyl Phosphate and <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dihexyl Octanamide Extractants Dissolved in <Emphasis Type="Italic">n</Emphasis>-Dodecane

Spectrophotometric investigations have been carried out on the disproportionation of Np(V) to form Np(IV) and Np(VI) in 1.1 mol⋅L⁻¹ solutions of tributyl phosphate (TBP) and in N,N-dihexyl octanamide (DHOA) in n-dodecane medium. The Np(V) was found to coordinate with Np(IV) in 1.1 mol⋅L⁻¹ TBP solution in n-dodecane to form a mixed valence “cation–cation” complex by bonding through an axial oxo group on Np(V). By contrast, this interaction was less prominent in the case of 1.1 mol⋅L⁻¹ DHOA solutions. The effect of 1-octanol, added as phase modifier, on the disproportionation behavior of Np(V) was also investigated. An attempt was made to calculate the disproportionation/reduction rate constants for Np(V) under the conditions of these studies. Absorbance measurements on the Np stripped from organic phases revealed the occurrence of Np(V) in the aqueous phase.     

Precipitation polymerization of <Emphasis Type="Italic">N-tert</Emphasis>-butylacrylamide in water producing monodisperse polymer particles

The precipitation polymerizations of N-tert-butylacrylamide (NtBAM) in water are demonstrated; for example, the polymerization with potassium peroxodisulfate using a 15 g L⁻¹ (118 mmol L⁻¹) concentration of NtBAM in the feed ([NtBAM]₀) was performed at 70 °C for 12 h, quantitatively producing poly(N-tert-butylacrylamide) particles with a number-average diameter (d _n) of 203 nm and a coefficient of variation (C _v) of 4.7%. The particle sizes were controlled in the d _ns range between 75 and 494 nm by changing the monomer feeds or adding an electrolyte such as NaCl. The solid contents in the resulting aqueous latex solutions ranged from 0.1 to 1.5%, whereas it increased to 4.8% by applying a “shot-growth” technique. The polymerization in water under a somewhat unique condition is described, which was started from a heterogeneous system due to the presence of significantly large amounts of monomers ([NtBAM]₀ = 50 g L⁻¹). This also provided monodisperse latexes with the d _n of 370 nm in 96% yield, in which the solid content reached 4.9%.     

Thermodynamic characteristics of the complexation between Pb<Superscript>2+</Superscript> and <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Bis(carboxymethyl)aspartic acid in aqueous solution

The enthalpies of complexation between N,N-bis(carboxymethyl)aspartic acid (H₄Y) and the Pb²⁺ ion at 298.15 K were determined from calorimetric data for a wide range of the ionic strengths (KNO₃). The thermodynamic characteristics ΔH, ΔG, and ΔS, of formation of the complexes PbHY⁻ and PbY²⁻ were calculated for zero and fixed ionic strengths. The results obtained were interpreted.     

Enhanced Production of <Emphasis Type="SmallCaps">l</Emphasis>-Arginine by Expression of <Emphasis Type="Italic">Vitreoscilla</Emphasis> Hemoglobin Using a Novel Expression System in <Emphasis Type="Italic">Corynebacterium crenatum</Emphasis>

Corynebacterium crenatum SYPA 5-5 is an aerobic and industrial l-arginine producer. It was proved that the Corynebacterium glutamicum/Escherichia coli shuttle vector pJC1 could be extended in C. crenatum efficiently when using the chloramphenicol acetyltransferase gene (cat) as a reporter under the control of promoter tac. The expression system was applied to over-express the gene vgb coding Vitreoscilla hemoglobin (VHb) to further increase the dissolved oxygen in C. crenatum. As a result, the recombinant C. crenatum containing the pJC-tac-vgb plasmid expressed VHb at a level of 3.4 nmol g⁻¹, and the oxygen uptake rates reached 0.25 mg A₅₆₂⁻¹ h⁻¹ which enhanced 38.8% compared to the wild-type strain. Thus, the final l-arginine concentration of the batch fermentation reached a high level of 35.9 g L⁻¹, and the biomass was largely increased to 6.45 g L⁻¹, which were 17.3% and 10.5% higher than those obtained by the wild-type strain, respectively. To our knowledge, this is the first report that the efficient expression system was constructed to introduce vgb gene increasing the oxygen and energy supply for l-arginine production in C. crenatum, which supplies a good strategy for the improvement of amino acid products.     

1,3,5,7-Tetramethyl-8-(<Emphasis Type="Italic">N</Emphasis>-hydroxysuccinimidyl butyric ester)difluoroboradiaza-<Emphasis Type="Italic">s</Emphasis>-indacene as a new fluorescent labeling reagent for HPLC determination of amino acid neurotransmitters in the cerebral cortex of mice

1,3,5,7-Tetramethyl-8-(N-hydroxysuccinimidyl butyric ester)difluoroboradiaza-s-indacene (TMBB-Su), a new BODIPY-based fluorescent probe, was designed and synthesized for the labeling of amino compounds. It was used as a pre-column derivatizing reagent for determination of amino acid neurotransmitters by high-performance liquid chromatography (HPLC). The fluorescence quantum yield in acetonitrile increased from 0.84 to 0.95 when it reacted with amino acid neurotransmitters. Derivatization of TMBB-Su with seven amino acid neurotransmitters was completed within 30 min at 25 °C in 24.0 mmol L⁻¹ pH 7.8 boric acid buffer. The separation was performed on a C₁₈ column with methanol–water–buffer 55:35:10 (v/v) as mobile phase (buffer: 0.10 mol L⁻¹ H₃Cit–0.10 mol L⁻¹ NaOH). Interference from the other concomitant amino acids was eliminated successfully by means of pH gradient elution. With fluorescence detection at 494 and 504 nm for excitation and emission, respectively, the limits of detection (signal-to-noise ratio = 3) were from 2.1 to 12.0 nmol L⁻¹. The proposed method has been used to determine amino acid neurotransmitters in the cerebral cortex of mice with cerebral ischemia at the convalescence stage with satisfactory recoveries varying from 94.9 to 105.2%.     

Conversion of Isoeugenol to Vanillin by <Emphasis Type="Italic">Psychrobacter</Emphasis> sp. Strain CSW4

To screen strains of halotolerant or halophile bacteria which are able to convert isoeugenol to vanillin, 36 different strains of bacteria isolated from the salty environments in Iran were investigated. During growth on isoeugenol, a moderately halotolerant Gram-negative coccobacil showed capability of converting isoeugenol to vanillin. Based on morphological, physiological, and phylogenetic studies, strain CSW4 was classified as a bacterium belonging to the genus Psychrobacter. The bioconversion products were confirmed by thin-layer chromatography, high-performance liquid chromatography, and spectral data obtained from UV/Vis spectroscopy, FTIR, and mass-spectroscopy. Using growing cells, vanillin reached its maximum level of 88.18 mg L⁻¹ after 24 h of reaction time in the presence of 1 g L⁻¹ isoeugenol, resulting in a molar yield of 10.2%. The use of resting cells led to the optimal yield of vanillin (16.4%) which was obtained after 18-h reaction using 1 g L⁻¹ isoeugenol and 3.1 g of dry weight of cells per liter harvested at the end of the exponential growth phase. To improve vanillin yield, the effect of substrate concentration on vanillin production under resting cells conditions was also investigated. Using 10 g L⁻¹ isoeugenol, the maximal vanillin concentration (1.28 g L⁻¹) was achieved after a 48-h reaction, without further optimization. The present study brings the first evidence for biotransformation of isoeugenol to vanillin in the genus Psychrobacter.     

Culture of Microalgae <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis> in Wastewater for Biomass Feedstock Production

The objective of this research was to develop large-scale technologies to produce oil-rich algal biomass from wastewater. The experiments were conducted using Erlenmeyer flasks and biocoil photobioreactor. Chlamydomonas reinhardtii was grown in artificial media and wastewaters taken from three different stages of the treatment process, namely, influent, effluent, and centrate. Each of wastewaters contained different levels of nutrients. The specific growth rate of C. reinhardtii in different cultures was monitored over a period of 10 days. The biomass yield of microalgae and associated nitrogen and phosphorous removal were evaluated. Effects of CO₂ and pH on the growth were also studied. The level of nutrients greatly influenced algae growth. High levels of nutrients seem to inhibit algae growth in the beginning, but provided sustained growth to a high degree. The studies have shown that the optimal pH for C. reinhardtii is in the range of 7.5. An injection of air and a moderate amount of CO₂ promoted algae growth. However, too much CO₂ inhibited algae growth due to a significant decrease in pH. The experimental results showed that algal dry biomass yield reached a maximum of 2.0 g L⁻¹ day⁻¹ in the biocoil. The oil content of microalgae of C. reinhardtii was 25.25% (w/w) in dry biomass weight. In the biocoil, 55.8 mg nitrogen and 17.4 mg phosphorus per liter per day were effectively removed from the centrate wastewater. Ferric chloride was found to be an effective flocculent that helps the algae settle for easy harvest and separation from the culture media.     

Study on mechanism for oxidation of <Emphasis Type="Italic">N,N</Emphasis>-dimethylhydroxylamine by nitrous acid

The oxidation of N,N-dimethylhydroxylamine (DMHAN) by nitrous acid is investigated in perchloric acid and nitric acid medium, respectively. The effects of H⁺, DMHAN, ionic strength and temperature on the reaction are studied. The rate equation in perchloric acid medium has been determined to be −d[HNO₂]/dt = k[DMHAN][HNO₂], where k = 12.8 ± 1.0 (mol/L)⁻¹ min⁻¹ when the temperature is 18.5 °C and the ionic strength is 0.73 mol/L with an activation energy about 41.5 kJ mol⁻¹. The reaction becomes complicated when it is performed in nitric acid medium. When the molarity of HNO₃ is higher than 1.0 mol/L, nitrous acid will be produced via the reaction between nitric acid and DMHAN. The reaction products are analyzed and the reaction mechanism is discussed in this paper.     

Effect of Constant Glucose Feeding on the Production of Exopolysaccharides by <Emphasis Type="Italic">Tremella fuciformis</Emphasis> Spores

A fed-batch culture system with constant feeding (glucose 80 g L⁻¹, 0.25 ml min⁻¹) was used to study the influence of glucose on cell dry weight and exopolysaccharides production from submerged Tremella fuciformis spores in a 5-L stirred-tank bioreactor. The results showed that high levels of cell mass (9.80 g L⁻¹) and exopolysaccharides production (3.12 g L⁻¹) in fed-batch fermentation were obtained after 1 h of feeding, where the specific growth rate (μ) and exopolysaccharides yield on substrate consumed (YP/S) were 0.267 d⁻¹ and 0.14 g g⁻¹. Unlike batch fermentation, maximal cell mass and exopolysaccharides production merely reached 7.11 and 2.08 g L⁻¹; the specific growth rate (μ) and exopolysaccharides yield on substrate consumed (YP/S) were 0.194 d⁻¹ and 0.093 g g⁻¹, respectively. It is concluded that the synthesis of exopolysaccharides can be promoted effectively when feeding glucose at a late exponential phase.     

<Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-Butylcalix[8]arene loaded silica gel for preconcentration of uranium(VI) via solid phase extraction

This paper reports silica gel loaded with p-tert-butylcalix[8]arene as a new solid phase extractor for determination of trace level of uranium. Effective extraction conditions were optimized in column methods prior to determination by spectrophotometry using arsenazo(III). The results showed that U(VI) ions can be sorbed at pH 6 in a mini-column and quantitative recovery of U(VI) (>95–98%) was achieved by stripping 0.4 mol L⁻¹ HCl. The sorption capacity of the functionalized sorbent is 0.072 mmol uranium(VI) g⁻¹ modified silica gel. The relative standard deviation and detection limit were 1.2% (n = 10) for 1 μg uranium(VI) mL⁻¹ solution and 0.038 μg L⁻¹, respectively. The method was employed to the preconcentration of U(VI) ions from spiked ground water samples.     

Regioselective Reaction of <Emphasis Type="Italic">N</Emphasis><Superscript>1</Superscript>-Benzyl-<Emphasis Type="Italic">N</Emphasis><Superscript>2</Superscript>-(4-nitrophenyl)ethanediamide and Acetylenic Esters

Summary. The regioselective reaction of N¹-benzyl-N²-(4-nitrophenyl)ethanediamide with dialkyl acetylenedicarboxylates or alkyl propiolates in the presence of triphenylphosphine leads to dialkyl 4-benzylamino-1-(4-nitrophenyl)-5-oxo-2,5-dihydro-1H-pyrrole-2,3-dicarboxylates or alkyl 4-benzylamino-1-(4-nitrophenyl)-2-oxo-5-pyrrolidinecarboxylates in good yields.     

Molecular properties of the copolymers of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diallyl-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylammonium chloride and maleic acid

The hydrodynamic and conformational properties of molecules of poly(N,N-diallyl-N,N-dimethylammonium chloride) and N,N-diallyl-N,N-dimethylammonium chloride-maleic acid copolymers of different compositions in solutions with various ionic-strength and pH values, as well as of the polyelectrolyte complex based on the copolymer with dodecyl sulfate anions in chloroform, are studied. For poly(N,N-diallyl-N,N-dimethylammonium chloride) molecules in a 1 M NaCl solution, the Kuhn segment length and the hydrodynamic diameter of the chain are estimated as A = 3.9 nm and d = 0.48 nm, respectively. In acidic solutions with pH 3.5, the copolymers demonstrate behavior typical for polyelectrolytes. In an alkaline solution with pH 13, when 1 M NaCl is added to the solution of the copolymer containing 29 mol % maleic acid units, there is an antipolyelectrolyte effect that manifests itself as an increase in the intrinsic viscosity of the copolymer and in the hydrodynamic radius of its molecules. It is found that an increase in the fraction of maleic acid units in the copolymer from 12 to 42 mol % brings about a reduction in the equilibrium rigidity of its macromolecules from 4.1 to 2.2 nm. The equilibrium rigidity of polyelectrolyte-complex molecules is higher than that of initial copolymer molecules owing to steric interactions arising between the aliphatic chains of dodecyl sulfate anions. In an electric field, the molecules of the complex are oriented owing to the induced dipole moment resulting from the displacement of dodecyl sulfate anions along the chain contour.     

Heat capacities and thermodynamic properties of (<Emphasis Type="Italic">S</Emphasis>)-<Emphasis Type="Italic">tert</Emphasis>-butyl 1-phenylethylcarbamate

An N-tert-butyloxycarbonylated organic synthesis intermediate, (S)-tert-butyl 1-phenylethylcarbamate, was prepared and investigated by means of differential scanning calorimetry (DSC) and thermogravimetry (TG). The molar heat capacities of (S)-tert-butyl 1-phenylethylcarbamate were precisely determined by means of adiabatic calorimetry over the temperature range of 80-380 K. There was a solid–liquid phase transition exhibited during the heating process with the melting point of 359.53 K. The molar enthalpy and entropy of this transition were determined to be 29.73 kJ mol⁻¹ and 82.68 J K⁻¹ mol⁻¹ based on the experimental C _p–T curve, respectively. The thermodynamic functions, [H_T⁰ - H_298.15⁰ H_{T}^{0} - H_{298.15}^{0} ] and [S_T⁰ - S_298.15⁰ S_{T}^{0} - S_{298.15}^{0} ], were calculated from the heat capacity data in the temperature range of 80–380 K with an interval of 5 K. TG experiment showed that the pyrolysis of the compound was started at the temperature of 385 K and terminated at 510 K within one step.     

Kinetic and mechanistic studies on the substitution of aqua ligands from <Emphasis Type="Italic">cis</Emphasis>-diaqua-<Emphasis Type="Italic">bis</Emphasis>-(bypyridyl)-ruthenium(II) ion by vic-dioximes

Kinetics of aqua ligand substitution from cis-[Ru(bpy)₂(H₂O)₂]²⁺ by three vicinal dioximes, namely dimethylglyoxime (L¹H), 1,2-cyclohexane dionedioxime (L²H) and α-furil dioxime (L³H) have been studied spectrophotometrically in the 45–60 °C temperature range. The rate constants increase with increasing dioxime concentration and approach a limiting condition. We propose the following rate law for the reaction in the 3.5–5.5 pH range: where k ₂ is the interchange rate constant from outer sphere to inner sphere complex and K _E is the outer sphere association equilibrium constant. Activation parameters were calculated from the Eyring plots for all three systems: ΔH ^≠ = 59.2 ± 8.8, 63.1 ± 6.8 and 69.7 ± 8.5 kJ mol⁻¹, ΔS ^≠ = −122 ± 27, −117 ± 21 and −99 ± 26 J K⁻¹ mol⁻¹ for L¹H, L²H and L³H, respectively. An associative interchange mechanism is proposed for the substitution process. Thermodynamic parameters calculated from the temperature dependence of the outer sphere association equilibrium constants give negative ΔG ⁰ values for all the systems studied at all the temperatures (ΔH ⁰ = 30.05 ± 2.5, 18.9 ± 1.1 and 11.8 ± 0.2 kJ mol⁻¹; ΔS ⁰ = 123 ± 8, 94 ± 3 and 74 ± 1 J K⁻¹ mol⁻¹ for L¹H, L²H and L³H, respectively), which also support our proposition.     

Mechanistic aspects of ligand substitution on <Emphasis Type="Italic">cis</Emphasis>-diaqua(<Emphasis Type="Italic">cis</Emphasis>-1,2-diaminocyclohexane)platinum(II) by Glycine-<Emphasis Type="SmallCaps">l</Emphasis>-Leucine

The kinetics of the interaction of glycine-l-leucine (Glyleu) with cis-[Pt(cis-dach)(OH₂)₂]²⁺ (dach = 1,2-diaminocyclohexane) has been studied spectrophotometrically as a function of [cis-[Pt(cis-dach)(OH₂)₂]²⁺], [Glyleu] and temperature at pH 4.0, where the complex exists predominantly as the diaqua species and Glyleu as a zwitterion. The substitution reaction shows two consecutive steps: the first is the ligand-assisted anation and the second is the chelation step. The activation parameters for both the steps were evaluated using Eyring’s equation. The low ∆H₁^≠ (51.9 ± 2.8 kJmol⁻¹) and large negative value of ∆S₁^≠ (−152 ± 8 JK⁻¹mol⁻¹) as well as ∆H₂^≠ (54.4 ± 1.7 kJmol⁻¹) and ∆S₂^≠ (−162 ± 5 JK⁻¹mol⁻¹) indicate an associative mode of activation for both the aqua ligand substitution processes.     

PVA-Hydrogel Entrapped <Emphasis Type="Italic">Candida Guilliermondii</Emphasis> for Xylitol Production from Sugarcane Hemicellulose Hydrolysate

Viable cells of Candida guilliermondii were immobilized by inclusion into polyvinyl alcohol (PVA) hydrogel using the freezing–thawing method. Entrapment experiments were planned according to a 2³ full factorial design, using the PVA concentration (80, 100, and 120 g L⁻¹), the freezing temperature (−10, −15, and −20 °C), and the number of freezing-thawing cycles (one, three, and five) as the independent variables, integrated with three additional tests to estimate the errors. The effectiveness of the immobilization procedure was checked in Erlenmeyer flasks as the pellet capability to catalyze the xylose-to-xylitol bioconversion of a medium based on sugarcane bagasse hemicellulosic hydrolysate. To this purpose, the yield of xylitol on consumed xylose, xylitol volumetric productivity, and cell retention yield were selected as the response variables. Cell pellets were then used to perform the same bioconversion in a stirred tank reactor operated at 400 rpm, 30 °C, and 1.04 vvm air flowrate. At the end of fermentation, a maximum xylitol concentration of 28.7 g L⁻¹, a xylitol yield on consumed xylose of 0.49 g g⁻¹ and a xylitol volumetric productivity of 0.24 g L⁻¹ h⁻¹ were obtained.     

The application of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylhydroxylamine as reductant for the separation of plutonium from uranium

Both single stage and multi-stages experiments on stripping plutonium with N,N-dimethylhydroxylamine (DMHAN) as reductant with methylhydrozine (MMH) as supporting reductant were carried out. The effect of contact time, temperature, acidity, concentration of DMHAN on back-extraction rate of plutonium was investigated in the single stage experiment. The results demonstrated that the reaction of stripping Pu(IV) in the organic phase (30% TBP–kerosene) 1BF solutions by DMHAN exhibits excellent stripping efficiency. Under the given conditions, the back-extraction rate of plutonium reaches 90% within 2 min. Higher temperature, lower acidity and the increased concentration of DMHAN benifit the stripping reaction. The concentration profile of HNO₃, uranium and plutonium were determined in a multi-stages mixer-settler after the steady state of the back-extraction, and the multi-stages results show that the plutonium can be separated effectively from uranium. The recovery of plutonium and uranium reach 99.995% or over 99.99% respectively. The separation factor of U from Pu (SF_Pu/U) is about 2 × 10⁴.     

Determination of epoxides by high-performance liquid chromatography following derivatization with <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diethyldithiocarbamate

A reversed-phase, high-performance liquid chromatography (RP-HPLC) method that allows quantitation of low levels of epoxides has been described. The method involved derivatization of epoxides using 100- to 1,000-fold excess N,N-diethyldithiocarbamate (DTC) at 60 °C for 20 min at neutral pH. The unreacted DTC was then decomposed to CS₂ and diethyl amine by acidification of the reaction mixture to pH 2 using orthophosphoric acid. The first two steps could be performed in the same reaction vessel by sequential addition of reagents. In the final step, an aliquot (20 μL) of the derivatized sample was analyzed for the presence of stable esters of DTC by RP-HPLC using a Supelcosil LC-18-S (150 × 4.6-mm) column and a mobile phase consisting of 40% (v/v) acetonitrile in water at a flow of 1 mL min⁻¹. Using UV detection at 278 nm, the epoxides gave linear responses in the concentration range of 0.25 to 50 μM. The method is robust, and as low as 5 pmol of the analyte could be successfully detected and quantified with recoveries of ≥94%. Following a minimal pretreatment such as ultrafiltration (molecular weight cutoff 5,000 Da), the method is suitable for analysis of epoxides in complex physiological fluids (e.g., fetal bovine serum). The method has been rigorously evaluated and adapted in our laboratory for routine analysis and determination of stability of epoxides of 1,3-butadiene and other alkenes added to cell cultures.     

Thermochemical study on ternary complex of dysprosium <Emphasis Type="Italic">m</Emphasis>-nitrobenzoic acid with <Emphasis Type="Italic">o</Emphasis>-phenanthroline

A ternary binuclear complex of dysprosium chloride hexahydrate with m-nitrobenzoic acid and 1,10-phenanthroline, [Dy(m-NBA)₃phen]₂·4H₂O (m-NBA: m-nitrobenzoate; phen: 1,10-phenanthroline) was synthesized. The dissolution enthalpies of [2phen·H₂O(s)], [6m-HNBA(s)], [2DyCl₃·6H₂O(s)], and [Dy(m-NBA)₃phen]₂·4H₂O(s) in the calorimetric solvent (V_DMSO:V_MeOH = 3:2) were determined by the solution–reaction isoperibol calorimeter at 298.15 K to be \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [2phen·H₂O(s), 298.15 K] = 21.7367 ± 0.3150 kJ·mol⁻¹, \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [6m-HNBA(s), 298.15 K] = 15.3635 ± 0.2235 kJ·mol⁻¹, \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [2DyCl₃·6H₂O(s), 298.15 K] = −203.5331 ± 0.2200 kJ·mol⁻¹, and \Updelta_\texts H_\textm^q \Updelta_{\text{s}} H_{\text{m}}^{\theta } [[Dy(m-NBA)₃phen]₂·4H₂O(s), 298.15 K] = 53.5965 ± 0.2367 kJ·mol⁻¹, respectively. The enthalpy change of the reaction was determined to be \Updelta_\textr H_\textm^q = 3 6 9. 4 9 ±0. 5 6   \textkJ·\textmol ^{- 1} . \Updelta_{\text{r}} H_{\text{m}}^{\theta } = 3 6 9. 4 9 \pm 0. 5 6 \;{\text{kJ}}\cdot {\text{mol}}^{ - 1} . According to the above results and the relevant data in the literature, through Hess’ law, the standard molar enthalpy of formation of [Dy(m-NBA)₃phen]₂·4H₂O(s) was estimated to be \Updelta_\textf H_\textm^q \Updelta_{\text{f}} H_{\text{m}}^{\theta } [[Dy(m-NBA)₃phen]₂·4H₂O(s), 298.15 K] = −5525 ± 6 kJ·mol⁻¹.     

High Level Expression of an Acid-Stable Phytase from <Emphasis Type="Italic">Citrobacter freundii</Emphasis> in <Emphasis Type="Italic">Pichia pastoris</Emphasis>

To obtain a high level expression of phytase with favorable characteristics, a codon-optimized phytase gene from Citrobacter freundii was synthesized and transferred into Pichia pastoris. Small-scale expression experiments and activity assays were used to screen positive colonies. After purified by Ni²⁺–NTA agarose affinity column, the characterizations of the recombinant phytase were determined. The recombinant phytase (r-phyC) had two distinct pH optima at 2.5 and 4.5 and an optimal temperature at 50 °C. It retained more than 80% activity after being incubated under various buffer (pH 1.5–8.0) at 37 °C for 1 h. The specific activity, Km, and Vmax values of r-phyC for sodium phytate were 2,072 ± 18 U mg⁻¹, 0.52 ± 0.04 mM, and 2,380 ± 84 U mg⁻¹ min⁻¹, respectively. The enzyme activity was significantly improved by 1 mM of K⁺, Ca²⁺, and Mg²⁺. These characteristics contribute to its potential application in feed industry.