The Purification and Characterization of Lipases from <Emphasis Type="Italic">Lasiodiplodia theobromae</Emphasis>, and Their Immobilization and Use for Biodiesel Production from Coconut Oil

The coconut kernel-associated fungus, Lasiodiplodia theobromae VBE1, was grown on coconut cake with added coconut oil as lipase inducer under solid-state fermentation conditions. The extracellular-produced lipases were purified and resulted in two enzymes: lipase A (68,000 Da)—purified 25.41-fold, recovery of 47.1%—and lipase B (32,000 Da)—purified 18.47-fold, recovery of 8.2%. Both lipases showed optimal activity at pH 8.0 and 35 °C, were activated by Ca²⁺, exhibited highest specificity towards coconut oil and p-nitrophenyl palmitate, and were stable in iso-octane and hexane. Ethanol supported higher lipase activity than methanol, and n-butanol inactivated both lipases. Crude lipase immobilized by entrapment within 4% (w/v) calcium alginate beads was more stable than the crude-free lipase preparation within the range pH 2.5–10.0 and 20–80 °C. The immobilized lipase preparation was used to catalyze the transesterification/methanolysis of coconut oil to biodiesel (fatty acyl methyl esters (FAMEs)) and was quantified by gas chromatography. The principal FAMEs were laurate (46.1%), myristate (22.3%), palmitate (9.9%), and oleate (7.2%), with minor amounts of caprylate, caprate, and stearate also present. The FAME profile was comparatively similar to NaOH-mediated transesterified biodiesel from coconut oil, but distinctly different to petroleum-derived diesel. This study concluded that Lasiodiplodia theobromae VBE1 lipases have potential for biodiesel production from coconut oil.     

Preparation of Biodiesel with Liquid Synergetic Lipases from Rapeseed Oil Deodorizer Distillate

To reduce industrial production cost, cheap and easily available rapeseed oil deodorizer distillates were used as feedstock to prepare biodiesel in this study. As a result, liquid forms of Candida rugosa lipase and Rhizopus oryzae lipase (ROL) were functioned as new and effective catalysts with biodiesel yield of 92.63% for 30 h and 94.36% for 9 h, respectively. Furthermore, the synergetic effect between the two lipases was employed to enhance biodiesel yield with a result of 98.16% in 6 h under optimized conditions via response surface methodology. The obtained conversion rate surpassed both yields of the individual two lipases and markedly shortened the reaction time. The resultant optimal conditions were ROL ratio 0.84, water content 46 wt% (w/w), reaction temperature 34 °C, and reaction time 6 h.     

Production and Biotechnological Application of Extracellular Alkalophilic Lipase from Marine Macroalga-Associated <Emphasis Type="Italic">Shewanella algae</Emphasis> to Produce Enriched C<Subscript>20-22</Subscript><Emphasis Type="Italic">n</Emphasis>-3 Polyunsaturated Fatty Acid Concentrate

An extracellular alkalophilic lipase was partially purified from heterotrophic Shewanella algae (KX 272637) associated with marine macroalgae Padina gymnospora. The enzyme possessed a molecular mass of 20 kD, and was purified 60-fold with a specific activity of 36.33 U/mg. The enzyme exhibited V_max and K_m of 1000 mM/mg/min and 157 mM, respectively, with an optimum activity at 55 °C and pH 10.0. The catalytic activity of the enzyme was improved by Ca²⁺ and Mg²⁺ ions, and the enzyme showed a good tolerance towards organic solvents, such as methanol, isopropanol, and ethanol. The purified lipase hydrolyzed the refined liver oil from leafscale gulper shark Centrophorus squamosus, yielding a total C_20-22 n-3 PUFA concentration of 34.99% with EPA + DHA accounting the major share (34% TFA), after 3 h of hydrolysis. This study recognized the industrial applicability of the thermostable and alkalophilic lipase from marine macroalga-associated bacterium Shewanella algae to produce enriched C_20-22 n-3 polyunsaturated fatty acid concentrate.     

A comparison of energy changes accompanying growth processes by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Calculations are made using the equations Δ_r G = Δ_r H ? TΔ_r S and Δ_r X = Δ_r H ? Δ_r Q where Δ_r X represents the free energy change when the exchange of absorbed thermal energy with the environment is represented by Δ_r Q. The symbol Q has traditionally represented absorbed heat. However, here it is used specifically to represent the enthalpy listed in tabulations of thermodynamic properties as (H _T  ? H ₀) at T = 298.15 K, the reason being that for a given substance TS equals 2.0 Q for solid substances, with the difference being greater for liquids, and especially gases. Since Δ_r H can be measured, and is tangibly the same no matter what thermodynamics are used to describe a reaction equation, a change in the absorbed heat of a biochemical growth process system as represented by either Δ_r Q or TΔ_r S would be expected to result in a different calculated value for the free energy change. Calculations of changes in thermodynamic properties are made which accompany anabolism; the formation of anabolic, organic by-products; catabolism; metabolism; and their respective non-conservative reactions; for the growth of Saccharomyces cerevisiae using four growth process systems. The result is that there is only about a 1% difference in the average quantity of free energy conserved during growth using either Eq. 1 or 2. This is because although values of TΔ_r S and Δ_r Q can be markedly different when compared to one another, these differences are small when compared to the value for Δ_r G or Δ_r X.     

Saw-sedge <Emphasis Type="Italic">Cladium mariscus</Emphasis> as a functional low-cost adsorbent for effective removal of 2,4-dichlorophenoxyacetic acid from aqueous systems

For the first time in the published literature, a study is described concerning the use of the saw-sedge Cladium mariscus (C. mariscus) for adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous systems. Among the experiments carried out, the elemental composition of C. mariscus was determined (C = 48.0 %, H = 7.1 %, N = 0.95 %, S = 0.4 %), FTIR spectroscopic analysis was performed to confirm the chemical structure of the adsorbent, and porous structure parameters were measured: BET surface area (A _BET  = 0.6 m²/g), total pore volume (V _p  = 0.001 cm³/g) and average pore size (S _p  = 6.6 nm). It was shown that the effectiveness of removal of 2,4-D from aqueous systems using C. mariscus depends on parameters of the process: contact time, system pH, mass of sorbent, and temperature. Maximum adsorption was attained for a solution at pH = 3. Further increase in the alkalinity of the tested systems led to a reduction in the effectiveness of the process. The kinetic of adsorption of 2,4-D by C. mariscus was also determined, and thermodynamic aspects were investigated. The experimental data obtained correspond to a pseudo-second-order kinetic model of type 1. Additionally the negative values obtained for ΔHº indicate that the process is exothermic, and the negative values of ΔGº show it to be spontaneous. As the temperature of the system increases the spontaneity of adsorption is reduced, in accordance with the exothermic nature of the process.     

Efficient <Emphasis Type="Italic">Candida rugosa</Emphasis> lipase immobilization on Maghnite clay and application for the production of (<Emphasis Type="Italic">1R</Emphasis>)-(−)-Menthyl acetate

This work focused on the identification of natural, economical, and efficient supports for immobilization of Candida rugosa lipase (CRL) to catalyze the resolution of (±)-menthol. To this purpose, CRL has been immobilized on natural montmorillonite from Algeria (Maghnite-H), ion-exchange resins (Amberjet^®1200-H and Amberjet^®4200-Cl), and diatomaceous earth (Celite^®545). After a preliminary screening of supports, the immobilization of CRL led to a markedly improved enantioselectivity. Excellent enantioselectivity (E ≥ 134) was achieved by the four supported lipases (E = 68 for free enzyme). Compared to the three other supports tested, higher enantioselectivity was observed with Maghnite-H used as immobilization matrix. In this work, the effects of solvent, reaction time, and temperature, on the conversion as well as on enantioselectivity were investigated. The maximum of conversion (% C = 43%) with high enantiomeric excess of products (eep > 99) was obtained when the reaction is catalyzed by CRL immobilized on Maghnite-H at 30 °C for 24 h, and using toluene as selected solvent. Immobilized CRL on Maghnite-H exhibited good thermostability over a wide temperature range (30–90 °C) compared to the free one. These results suggest that CRL immobilized on Maghnite-H has good potential as biocatalyst for the production of (1R)-(?)-menthyl acetate.     

Binding interaction and conformational changes of human serum albumin with ranitidine studied by spectroscopic and time-resolved fluorescence methods

This study was designed to examine the interaction of histamine H₂-receptor antagonist drug ranitidine (RTN) with human serum albumin by multi-spectroscopic methods. The experimental results showed the involvement of dynamic quenching mechanism which was further confirmed by lifetime spectral studies. The binding constants (K _a) at three temperatures (288, 298, and 308 K) were 2.058 ± 0.020, 4.160 ± 0.010 and 6.801 ± 0.011 × 10⁴ dm³ mol^?1, respectively, and the number of binding sites (m) were 1.169, respectively; thermodynamic parameters ΔH ⁰ (44.152 ± 0.047 kJ mol^?1), ΔG ⁰ (?26.214 ± 0.040 kJ mol^?1), and ΔS ⁰ (236.130 ± 0.025 J K^?1 mol^?1) were calculated. The distance r between donor and acceptor was obtained (r = 3.40 nm) according to the Förster theory of non-radiative energy transfer. Synchronous fluorescence, CD, AFM and 3D fluorescence spectral results revealed the changes in secondary structure of the protein upon interaction with RTN. A molecular modeling study further confirmed the binding mode obtained by the experimental studies.     

Thermodynamics of Viscous Flow of <Emphasis Type="Italic">tert</Emphasis>-Butanol with Butylamines: UNIFAC–VISCO,Grunberg–Nissan and McAllister Three Body Interaction Models for Viscosity Prediction and Quantum Chemical (DFT) Calculations

Thermodynamic activation parameters, enthalpies (ΔH ^?), entropies (ΔS ^?) and Gibbs energies (ΔG ^?) for viscous flow of the systems tert-butanol (TB)+n-butylamine (NBA), TB+di-n-butylamine (DBA) and TB+tri-n-butylamine (TBA) have been calculated from measured density and viscosity data at temperatures ranging from 303.l5 to 323.15 K over the composition range 0 ≤ x ₂ ≤ 1, where x ₂ is the mole fraction of TB. For all systems, the corresponding excess properties ΔH ^?E, ΔS ^?E and ΔG ^?E have been determined, which are negative in the whole range of composition. The observed negative excess activation properties have been accounted for in terms of dispersive forces and H-bonding. The derived properties are well represented by fourth degree polynomial equations whereas the excess properties could be fitted to third degree Redlich–Kister polynomial equations. Furthermore, the viscosities have been predicted by using the UNIFAC–VISCO model, Grunberg–Nissan model and McAllister three-body interaction model. The UNIFAC–VISCO model and Grunberg–Nissan model do not show good agreement with the experimental data, whereas the McAllister three-body interaction model shows excellent agreement for all three systems, with small average absolute percent deviations (AAD% = 0.6–2.3). The DFT-B3LYP method with the 6-311 G (d, p) basis set has been employed for the optimization of the geometry and calculation of the total energies of the pure compounds and their binary complexes.     

Volumetric,Viscometric and Speed of Sound Studies of Binary Mixtures of <Emphasis Type="Italic">Tert</Emphasis>-butyl Acetate with Fluorobenzene,Chlorobenzene and Bromobenzene at (298.15 and 308.15) K and at Atmospheric Pressure 0.087 MPa

Volumetric, viscometric and speed of sound studies of binary mixtures of tert-butyl acetate with fluorobenzene, chlorobenzene and bromobenzene have been made over the entire range of composition, at (298.15 and 308.15) K and at atmospheric pressure (p?=?0.089 MPa). From the experimental values of density, viscosity, and speed of sound, the excess molar volumes V^E, deviations in viscosity ?η and deviation in isentropic compressibility ΔK _S have been calculated. The V^E and ΔK _S values are negative while the ?η the values are positive over the entire composition range for the binary mixtures. The derived parameters have been fitted with the Redlich–Kister polynomial equation. The interaction parameters of McAllister model are used to correlate the experimental values of density, viscosity and speed of sound.     

Purification and characterization of an extracellular lipolytic enzyme from the fermented fish-originated halotolerant bacterium, <Emphasis Type="Italic">Virgibacillus alimentarius</Emphasis> LBU20907

A halotolerant Virgibacillus alimentarius LBU20907 isolated from fermented fish (Budu) was found to be an efficient producer of extracellular halophilic lipase enzyme. The enzyme was purified 5.99-fold with a 0.15% final yield to homogeneity by ammonium sulfate precipitation, followed by dialysis, Toyopearl DEAE-650 M ion exchange chromatography, Toyopearl butyl-650 M hydrophobic interaction chromatography, and Toyopearl-HW 55 F gel filtration chromatography. SDS-PAGE of purified lipase exhibited a homogenous single band with a very high molecular weight of 100 kDa. The properties of purified lipase revealed maximum activity at pH 7.0 and 40 °C. It was also highly stable in a pH range of 6.0–7.0, retaining more than 90% activity for 24 h. It was stable at the temperature of 30–50 °C and maintained more than 80% activity for 16 h. The purified lipase performing the maximal activity in the presence of 20.0% NaCl indicated halophilic enzyme properties. Its lipolytic activity was highest against p-nitrophenyl palmitate. The lipase activity was found to be enhanced in hexane. The enzyme activity was stimulated in the presence of Zn²⁺, Ca²⁺, Mg²⁺, and Sr²⁺; while, it was completely inhibited by Ba²⁺ and Co²⁺. The enzyme had a K _m and V _max of 108.0 mg and 79.1 U mL^?1, respectively.     

Modelling of proton and metal exchange in the alginate biopolymer

Acid–base behaviour of a commercial sodium alginate extracted from brown seaweed (Macrocystis pyrifera) has been investigated at different ionic strengths (0.1≤I/mol l^?1≤1.0) and in different supporting electrolytes (Et₄NI, NaCl, KCl, LiCl, NaCl+MgCl₂), with the aim of examining the influence of ionic medium on the proton-binding capacity and of quantifying the strength of interaction with light metal ions in the perspective of speciation studies in natural aqueous systems. Potentiometric ([H⁺]-glass electrode) and titration calorimetric data were expressed as a function of the dissociation degree (α) using different models (Henderson–Hasselbalch modified, Högfeldt three parameters and linear equations). The dependence on ionic strength of the protonation constants was taken into account by a modified specific interaction theory model. Differences among different media were explained in terms of the interaction between polyanion and metal cations of the supporting electrolytes. Quantitative information on the proton-binding capacity, together with the stabilities of different species formed, is reported. Protonation thermodynamic parameters, at α=0.5, are log K ^H=3.686±0.005, ΔG ⁰=?21.04±0.03 kJ mol^?1, ΔH ⁰=4.8±0.2 kJ mol^?1 and TΔS ⁰=35.7±0.3 kJ mol^?1, at infinite dilution. Protonation enthalpies indicate that the main contribution to proton binding arises from the entropy term. A strict correlation between ΔG and TΔS was found, TΔS=?9.5–1.73 ΔG. Results are reported in light of building up a chemical complexation model of general validity to explain the binding ability of naturally occurring polycarboxylate polymers and biopolymers. Speciation profiles of alginate in the presence of sodium and magnesium ions, naturally occurring cations in natural waters, are also reported.     

A Calcium-Ion-Stabilized Lipase from <Emphasis Type="Italic">Pseudomonas stutzeri</Emphasis> ZS04 and its Application in Resolution of Chiral Aryl Alcohols

An extracellular organic solvent-tolerant lipase-producing bacterium was isolated from oil-contaminated soil samples and was identified taxonomically as Pseudomonas stutzeri, from which the lipase was purified and exhibited maximal activity at temperature of 50 °C and pH of 9.0. Meanwhile, the lipase was stable below or at 30 °C and over an alkaline pH range (7.5–11.0). Ca²⁺ could significantly improve the lipase thermal stability which prompts a promising application in biocatalysis through convenient medium engineering. The lipase demonstrated striking features such as distinct stability to the most tested hydrophilic and hydrophobic solvents (25 %, v/v), and DMSO could activate the lipase dramatically. In the enzyme-catalyzed resolution, lipase ZS04 manifested excellent enantioselective esterification toward the (R)-1-(4-methoxyphenyl)-ethanol (MOPE), a crucial chiral intermediate in pharmaceuticals as well as in other analogs with strict substrate specificity and theoretical highest conversion yield. This strong advantage over other related schemes made lipase ZS04 a promising biocatalyst in organic synthesis and pharmaceutical applications.     

Viscosities and Surface Tensions of Phenetole with <Emphasis Type="Italic">N</Emphasis>-Methyl-2-pyrrolidone, <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dimethylformamide and Tetrahydrofuran Binary Systems at Three Temperatures

Viscosities, η, and surface tensions, σ, of binary systems of phenetole (ethoxy benzene or ethyl phenyl ether) with N-methyl-2-pyrrolidone, N,N-dimethylformamide or with tetrahydrofuran were measured over the entire mole fraction range and at (298, 303 and 308) K. The experimental data was used to compute the deviations in viscosity, Δη, and surface tension, Δσ. Values of the excess Gibbs energy of activation G*^E, surface entropy S _σ and surface enthalpy H _σ were calculated. Viscosity data of the binary systems were calculated using the Grunberg and Nissan and the three-body and four-body McAllister correlations. The Redlich–Kister method was used for evaluation of coefficients and standard deviations for Δη, Δσ and G*^E. The results were interpreted in terms of the probable effect of molecular interactions between components as well as polarity.     

Synthesis,crystal structure and fungicidal activity of 1-(4-chlorophenyl)-2-(5-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-4-phenyl-4H-1,2,4-triazol-3-ylthio)ethanone

A novel bis-heterocyclic compound was synthesized and characterized. The crystal structure of the title compound (C₂₂H₂₀ClN₅OS, Mr = 437.94) has been determined by single-crystal X-ray diffraction. The crystal is of triclinic, space group P-1 with a = 8.646 (2), b = 9.148 (3), c = 14.540 (4) Å, α = 94.422 (4), β = 98.500 (4), γ = 102.823 (4)°, V = 1101.8 (5) Å³, Z = 2, F(000) = 312, Dc = 1.320 g/cm³, μ = 0.2900 mm^?1, the final R ₁ = 0.041000 and wR ₂ = 0.1160 for 2675 observed reflections with I > 2σ(I). A total of 5623 reflections were collected, of which 3866 were independent (R _int = 0.019000). The fungicidal activity of title compound was determined, the results showed the title compound displayed moderate fungicidal activity against G. zeae Petch, Phytophthora infestans (Mont.) de Bary, Botryosphaeria berengeriana f. sp. piricola (Nose) koganezawa et Sakuma, Fusarium oxysporum f.sp. cucumerinum, and Cercospora arachidicola.     

Production of <Emphasis Type="Italic">R</Emphasis>-Mandelic Acid Using Nitrilase from Recombinant <Emphasis Type="Italic">E. coli</Emphasis> Cells Immobilized with Tris(Hydroxymethyl)Phosphine

Recombinant Escherichia coli cells harboring nitrilase from Alcaligenes faecalis were immobilized using tris(hydroxymethyl)phosphine (THP) as the coupling agent. The optimal pH and temperature of the THP-immobilized cells were determined at pH 8.0 and 55 °C. The half-lives of THP-immobilized cells measured at 35, 40, and 50 °C were 1800, 965, and 163 h, respectively. The concentration of R-mandelic acid (R-MA) reached 358 mM after merely 1-h conversion by the immobilized cells with 500 mM R,S-mandelonitrile (R,S-MN), affording the highest productivity of 1307 g L^?1 day^?1 and the space-time productivity of 143.2 mmol L^?1 h^?1 g^?1. The immobilized cells with granular shape were successfully recycled for 60 batches using 100 mM R,S-MN as substrate at 40 °C with 64% of relative activity, suggesting that the immobilized E. coli cells obtained in this study are promising for the production of R-MA.     

Efficient Regioselective Synthesis of the Crotonyl Polydatin Prodrug by <Emphasis Type="Italic">Thermomyces lanuginosus</Emphasis> Lipase: a Kinetics Study in Eco-friendly 2-Methyltetrahydrofuran

Bio-based solvents have recently been discussed as sustainable green and promising alternatives to conventional organic media for enzymatic processes. In this paper, highly regioselective synthesis of the 6″-O-crotonyl-polydatin catalyzed by Thermomyces lanuginosus lipase (TLL) in biomass-derived 2-methyltetrahydrofuran (2-MeTHF) was successfully performed for the first time. The results indicated that TLL lipase displayed significantly improved catalytic performance in 2-MeTHF than in other traditional solvents. Under the optimal conditions, the initial reaction rate, 6″-regioselectivity, and maximum substrate conversion were as high as 12.38 mM h^?1, 100 %, and 100 %, respectively. Moreover, further investigations on the operational stability, kinetic parameters like V _max, K _m, V _max/K _m, and E _a revealed that 2-MeTHF exhibited excellent biocompatibility and rendered the greener process of the enzymatic acylation.     

Enzymatic Hydrolysis of Black Liquor Xylan by a Novel Xylose-Tolerant,Thermostable β-Xylosidase from a Tropical Strain of <Emphasis Type="Italic">Aureobasidium pullulans</Emphasis> CBS 135684

From three cell-associated β-xylosidases produced by Aureobasidium pullulans CBS 135684, the principal enzyme was enriched to apparent homogeneity and found to be active at high temperatures (60–70 °C) over a pH range of 5–9 with a specific activity of 163.3 units (U) mg^?1. The enzyme was thermostable, retaining over 80% of its initial activity after a 12-h incubation at 60 °C, with half-lives of 38, 22, and 10 h at 60, 65, and 70 °C, respectively. Moreover, it was tolerant to xylose inhibition with a K _i value of 18 mM. The K _m and V _max values against p-nitrophenyl-β-d-xylopyranoside were 5.57 ± 0.27 mM and 137.0 ± 4.8 μmol min^?1 mg^?1 protein, respectively. When combining this β-xylosidase with xylanase from the same A. pullulans strain, the rate of black liquor xylan hydrolysis was significantly improved by up to 1.6-fold. The maximum xylose yield (0.812 ± 0.015 g g^?1 dry weight) was obtained from a reaction mixture containing 10% (w/v) black liquor xylan, 6 U g^?1 β-xylosidase and 16 U g^?1 xylanase after incubation for 4 h at 70 °C and pH 6.0.     

Measurement and Calculation the Excess Molar Properties of Binary Mixtures Containing Isobutanol, 1-Amino-2-Propanol,and 1-Propanol at Temperatures of (293.15 to 333.15) K

Densities, ρ, and viscosities, η, of pure isobutanol, 1-amino-2-propanol, and 1-propanol, along with their binary mixtures of {x ₁isobutanol + x ₂1-propanol}, {x ₁1-amino-2-propanol + x ₂1-propanol}, and {x ₁1-amino-2-propanol + x ₂isobutanol} were measured over the entire composition range and at temperatures (293.15–333.15) K at ambient pressure (81.5 kPa). Excess molar properties such as the excess molar volume, V _m ^E , partial molar volumes, \( \bar{V}_{1} \) and \( \bar{V}_{2} \), excess partial molar volumes, \( \bar{V}_{1}^{\text{E}} \) and \( \bar{V}_{2}^{\text{E}} \), thermal expansion coefficient, α, excess thermal expansion coefficient, α ^E, viscosity deviation, Δη, and the excess Gibbs energy of activation, ?G ^E*, for the binary mixtures were calculated from the experimental values of densities and viscosities. The excess values of the binary mixtures are negative in the entire composition range and at all temperatures, and increase with increasing temperature. Viscosity deviations, Δη, are negative over the entire composition range and decrease with increasing temperature. The viscosities of the mixtures were correlated by the models of McAllister, Heric, Hind, Katti, and Nissan. The obtained data were correlated by Redlich–Kister equation and the fitting parameters and standard deviations were determined.     

Synthesis and characterization of Sr<Subscript>0.75</Subscript>Y<Subscript>0.25</Subscript>Co<Subscript>0.9</Subscript>Ru<Subscript>0.1</Subscript>O<Subscript>3−<Emphasis Type="Italic">δ</Emphasis></Subscript> perovskite as a solid oxide fuel cell cathode material

The oxygen-deficient Sr_0.75Y_0.25Co_0.9Ru_0.1O_3?δ (SYCR) cathode is systematically evaluated for the application of solid oxide fuel cells. X-ray diffraction analysis indicates that SYCR presents a tetragonal structure with space group of I4/mmm (139). In the measured high oxygen partial pressure (pO₂) region (0.01–0.21 atm), the conductivity increases with increasing pO₂ because of the oxygen vacancy annihilation and hole creation, relating to a general p-type semiconducting mechanism. To get an insight into the rate-limiting step of SYCR cathode, behaviors of individual polarization resistance (R ₁ and R ₂) are investigated in different pO₂. The obtained fitting results reveal that R ₁ is nearly independent on the pO₂, while R ₂ presents a (pO₂)^?0.5 dependence. At 800 °C, SYCR cathode exhibits an R _p value of 0.14 Ω cm², moreover, when using the wet hydrogen (～ 3% H₂O) as fuel and ambient air as oxidant, the maximum power density of single cell Ni-YSZ (yttria-stabilized zirconia)|YSZ|SYCR reaches 452.9 W cm^?2.     

Spectroscopic Studies on the Interaction of Vitamin C with Bovine Serum Albumin

The mechanism of binding of vitamin C (VC) with bovine serum albumin (BSA) was investigated by spectroscopic methods under simulated physiological conditions. VC effectively quenched the intrinsic fluorescence of BSA. The binding constants K _A, and the number of binding sites, n, and corresponding thermodynamic parameters ΔG ^Θ , ΔH ^Θ and ΔS ^Θ between VC and BSA were calculated at different temperatures. The primary binding pattern between VC and BSA was interpreted as being a hydrophobic interaction. The interaction between VC and BSA occurs through static quenching and the effect of VC on the conformation of BSA was also analyzed using synchronous fluorescence spectroscopy. The average binding distance, r, between the donor (BSA) and acceptor (VC) was determined based on Förster’s theory and was found to be 3.65 nm. The effects of common ions on the binding constant of VC-BSA were also examined.