The Correlations Between TCA-Glyoxalate Metabolite and Antibiotic Production of <Emphasis Type="Italic">Streptomyces</Emphasis> sp. M4018 Grown in Glycerol,Glucose, and Starch Mediums

The alterations of organic acids citrate, α-ketoglutarate, succinate, fumarate, malate production together with isocitrate lyase activity as a glyoxalate shunt enzyme, and antibiotic production of Streptomyces sp M4018 were investigated in relation to changes in the glucose, glycerol and starch concentrations (5–20 g/L) after identification as a strain of Streptomyces hiroshimensis based on phenotypic and genotypic characteristics. The highest intracellular citrate and α-ketoglutarate levels in 20 g/l of glucose, glycerol, and starch mediums were 399.47 ± 4.78, 426.93 ± 6.40, 355.84 ± 5.38 ppm and 444.81 ± 5.12, 192.96 ± 2.26, 115.20 ± 2.87 ppm, respectively. The highest succinate, malate, and fumarate levels were also determined in 20 g/l of glucose medium as 548.9 ± 11.21, 596.15 ± 8.26, and 406.42 ± 6.59 ppm and the levels were significantly higher than the levels in glycerol and starch. Extracellular organic acid levels measured also showed significant correlation with carbon source concentrations by showing negative correlation with pH levels of the growth medium. The antibiotic production of Streptomyces sp. M4018 was also higher in glucose medium as was the case also for organic acids when compared with glycerol. On the other hand, there is no production in starch.     

Production of Recombinant Porcine Interferon alpha Using PHB–Intein-Mediated Protein Purification Strategy

Interferons (IFNs) are involved in the pathogenesis and recovery of viral and other infectious diseases. Recombinant IFNs have been used as anti-infectious agents exhibiting a broad range of antiviral and immunomodulatory properties in both human and domestic animals. In this report, we describe a highly efficient and economical approach to purify porcine IFN alpha (PoIFNα) using polyhydroxybutyrate (PHB) as the affinity carrier and intein for self-cleaving removal of the affinity tag. Additionally, the conditions of protein expression and purification have been optimized. Our results suggested that culture medium containing 1.62% (w/v) of sodium lactate dramatically increases the accumulation of PHB binding protein in Escherichia coli cells. High yields of recombinant PoIFNα (30–35 mg/L, 97% purity by high-performance liquid chromatography) were obtained using intein-mediated self-cleaving conditions using a cleavage-inducing buffer with a pH of 6.5 at 20 °C for 24–36 h. The antiviral activity of the recovered recombinant PoIFNα was up to 1.4 × 10⁶ IU/mg of protein ascertained using recombinant human IFNα1 as a standard. This report also demonstrates that large-scale production of intein-mediated purification of highly pure and active recombinant PoIFNα is feasible for the purposes of experimental studies, veterinary clinic therapeutics, and swine infectious disease control.     

A neutral polysaccharide from <Emphasis Type="Italic">Glycyrrhiza inflata</Emphasis>

A neutral polysaccharide Gi-A1 was isolated from the roots of Glycyrrhiza inflata Bat. It had a molecular mass of over 2000 kDa and showed [α]_D²⁰ + 81.4° (c 1.05, H₂O). Acid hydrolysis and methylation analysis indicated that Gi-A1 was mainly composed of α-D-glucose, α-L-arabinose, and α-D-galactose with a molar ratio of 8.0:1.8:1.0. It can significantly stimulate spleen cell proliferation in vitro (P < 0.01). Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 13–14, January–February, 2009.     

Optimization of <Emphasis Type="Italic">α</Emphasis>-Terpineol Production by the Biotransformation of <Emphasis Type="Italic">R</Emphasis>-(+)-Limonene and (−)-β-Pinene

The main objective of this work is to present the optimization of the biotransformation of R-(+)-limonene and (−)-β-pinene aiming at the production of α-terpineol by strains of fungal and yeasts previously isolated by our research group using the methodology of experimental design. New optimized experimental data on α-terpineol production by the biotransformation of R-(+)-limonene and (−)-β-pinene using newly isolated microorganisms are reported in this work. Conversion of about 1,700 mg/L was achieved when R-(+)-limonene was used as substrate and the newly isolated strain 05.01.35 as microorganism at the central point of the experimental design, corresponding to a substrate concentration of 1.75%, mass of inoculum of 2 g, and substrate to ethanol volume ratio of 1:1. The same experimental condition led to higher conversions when (−)-β-pinene was used as substrates and the strains coded as 04.05.08 and 01.04.03 as microorganism. Here, conversions of about 770 mg/L were achieved.     

Cell membrane chromatography competitive binding analysis for characterization of α<Subscript>1A</Subscript> adrenoreceptor binding interactions

A new high α_1A adrenoreceptor (α_1AAR) expression cell membrane chromatography (CMC) method was developed for characterization of α_1AAR binding interactions. HEK293 α_1A cell line, which expresses stably high levels of α_1AAR, was used to prepare the stationary phase in the CMC model. The HEK293 α_1A/CMC-offline-HPLC system was applied to specifically recognize the ligands which interact with the α_1AAR, and the dissociation equilibrium constants (K _D) obtained from the model were (1.87 ± 0.13) × 10⁻⁶ M for tamsulosin, (2.86 ± 0.20) × 10⁻⁶ M for 5-methylurapidil, (3.01 ± 0.19) × 10⁻⁶ M for doxazosin, (3.44 ± 0.19) × 10⁻⁶ M for terazosin, (3.50 ± 0.21) × 10⁻⁶ M for alfuzosin, and (7.57 ± 0.31) × 10⁻⁶ M for phentolamine, respectively. The competitive binding study between tamsulosin and terazosin indicated that the two drugs interacted at the common binding site of α_1AAR. However, that was not the case between tamsulosin and oxymetazoline. The results had a positive correlation with those from radioligand binding assay and indicated that the CMC method combined modified competitive binding could be a quick and efficient way for characterizing the drug–receptor interactions.     

Separation and quantitative determination of 6α-hydroxycortisol and 6β-hydroxycortisol in human urine by high-performance liquid chromatography with ultraviolet absorption detection

The present study developed an high-performance liquid chromatography (HPLC) method for the simultaneous determination of urinary metabolites of endogenous cortisol, 6α-hydroxycortisol (6α-OHF) and 6β-hydroxycortisol (6β-OHF), in human urine, using 6α-hydroxycorticosterone as internal standard. 6α-OHF and 6β-OHF were extracted from urine with ethyl acetate by using a Sep-Pak C₁₈ plus cartridge. Separation of the stereoisomers was achieved on a reversed-phase hybrid column by a gradient elution of (A) 0.05 M KH₂PO₄–0.01 M CH₃COOH (pH 3.77) and (B) 0.05 M KH₂PO₄–0.01 M CH₃COOH/acetonitrile (2:3, v/v). 6α-OHF and 6β-OHF were well separated on an XTerra MS C₁₈ 5 μm column using two types of stepwise gradient elution program (programs 2 and 3). Resolutions of 6α-OHF and 6β-OHF were Rs = 4.41 for program 2 and Rs = 4.60 for program 3. The analysis was performed within 23~26 min, monitored by UV absorbance at 239 nm. The lower limits of detection of 6α-OHF and 6β-OHF were 0.80 ng per injection (s/n = ca. 8), and the lower limits of quantification were 5.02 ng/ml for 6α-OHF and 41.08 ng/ml for 6β-OHF, respectively. The within-day reproducibilities in the amounts of 6α-OHF and 6β-OHF determined were in good agreement with the actual amounts added, the relative errors being −5.37% and −3.73% (gradient 2) and −5.69% and −3.96% (gradient 3) for both 6α-OHF and 6β-OHF, respectively. The inter-assay precisions (RSDs) for 6α-OHF and 6β-OHF were less than 1.99% (gradient 2) and 2.61% (gradient 3), respectively. The present HPLC method was applied to the measurement of 6α-OHF and 6β-OHF in urine to evaluate the time courses of 6α-hydroxylation and 6β-hydroxylation clearances of cortisol during 40 days for phenotyping CYP3A in a healthy subject.     

Banana Peel: A Potential Substrate for Laccase Production by <Emphasis Type="Italic">Aspergillus fumigatus</Emphasis> VkJ2.4.5 in Solid-State Fermentation

In solid-state fermentation, among various solid supports evaluated, banana peel was found to be an ideal support and resulted into higher levels of laccase (6281.4 ± 63.60 U l⁻¹) along with notable levels of manganese peroxidase production (1339.0 ± 131.23 U l⁻¹) by Aspergillus fumigatus VkJ2.4.5. Maximum levels of laccase was achieved under derived conditions consisting of 80% of moisture level, 6 days of incubation period, 6% inoculum level, and an aeration level of 2.5 l min⁻¹. A column-tray bioreactor was designed to scale up and economize the enzyme production in three successive cycles of fermentation using the same fungal biomass. Thermal and pH stability profiles revealed that enzyme was stable up to 50°C and at varying pH range from 5–9 for up to 2 h. The apparent molecular weight of laccase was found to be 34 ± 1 kDa. MALDI-TOF/TOF analysis of the protein showed significant homology with maximum identity of 67% to other laccases reported in database.     

Accelerated sample treatment for screening of banned doping substances by GC–MS: ultrasonication versus microwave energy

A comparison between ultrasonication and microwave irradiation as tools to achieve a rapid sample treatment for the analysis of banned doping substances in human urine by means of gas chromatography–mass spectrometry (GC–MS) was performed. The following variables were studied and optimised: (i) time of treatment, (ii) temperature, (iii) microwave power and (iv) ultrasonic amplitude. The results were evaluated and compared with those achieved by the routine method used in the World Anti-Doping Agency (WADA) accredited Antidoping Laboratory of Rome. Only under the effect of the ultrasonic field was it possible to enhance the enzymatic hydrolysis reaction rate of conjugated compounds. Similar reaction yield to the routine method was achieved after 10 min for most compounds. Under microwave irradiation, denaturation of the enzyme occurs for high microwave power. The use of both ultrasonic or microwave energy to improve the reaction rate of the derivatisation of the target compounds with trimethyliodosilane/methyl-N-trimethylsilyltrifluoroacetamide (TMSI/MSTFA/NH₄I/2-mercaptoethanol) was also evaluated. To test the use of the two systems in the acceleration of the reaction with TMSI, a pool of 55 banned substances and/or their metabolites were used. After 3 min of ultrasonication, 34 of the 55 compounds had recoveries similar to those obtained with the classic procedure that lasts for 30 min (Student’s t test, n = 5), 18 increased to higher silylation yields, and for the compounds 13β,17α-diethyl-3α,17β-dihydroxy-5α-gonane (norboletone metabolite 1), metoprolol and metipranolol the same results were obtained increasing the ultrasonication time to 5 min. Similar results were obtained after 3 min of microwave irradiation at 1,200 W. In this case, 30 of the 55 compounds had recoveries similar to the classic procedure (Student’s t test, n = 5) whilst 18 had higher silylation yields. For the compounds 3α-hydroxy-1α-methyl-5α-androstan-17-one (mesterolone metabolite 1), 17α-ethyl-5β-estrane-3α,17β,21-triol (norethandrolone metabolite 1), epioxandrolone, 4-chloro-6β,17β-dihydroxy-17α-methyl-1,4-androstadien-3-one (chlormetandienone metabolite 1), carphedon, esmolol and bambuterol the same results were obtained after 5 min under microwave irradiation.     

LC–MS–MS determination of ibuprofen, 2-hydroxyibuprofen enantiomers,and carboxyibuprofen stereoisomers for application in biotransformation studies employing endophytic fungi

The purpose of this study was the development and validation of an LC–MS–MS method for simultaneous analysis of ibuprofen (IBP), 2-hydroxyibuprofen (2-OH-IBP) enantiomers, and carboxyibuprofen (COOH-IBP) stereoisomers in fungi culture medium, to investigate the ability of some endophytic fungi to biotransform the chiral drug IBP into its metabolites. Resolution of IBP and the stereoisomers of its main metabolites was achieved by use of a Chiralpak AS-H column (150 × 4.6 mm, 5 μm particle size), column temperature 8 °C, and the mobile phase hexane–isopropanol–trifluoroacetic acid (95: 5: 0.1, v/v) at a flow rate of 1.2 mL min⁻¹. Post-column infusion with 10 mmol L⁻¹ ammonium acetate in methanol at a flow rate of 0.3 mL min⁻¹ was performed to enhance MS detection (positive electrospray ionization). Liquid–liquid extraction was used for sample preparation with hexane–ethyl acetate (1:1, v/v) as extraction solvent. Linearity was obtained in the range 0.1–20 μg mL⁻¹ for IBP, 0.05–7.5 μg mL⁻¹ for each 2-OH-IBP enantiomer, and 0.025–5.0 μg mL⁻¹ for each COOH-IBP stereoisomer (r ≥ 0.99). The coefficients of variation and relative errors obtained in precision and accuracy studies (within-day and between-day) were below 15%. The stability studies showed that the samples were stable (p > 0.05) during freeze and thaw cycles, short-term exposure to room temperature, storage at −20 °C, and biotransformation conditions. Among the six fungi studied, only the strains Nigrospora sphaerica (SS67) and Chaetomium globosum (VR10) biotransformed IBP enantioselectively, with greater formation of the metabolite (+)-(S)-2-OH-IBP. Formation of the COOH-IBP stereoisomers, which involves hydroxylation at C3 and further oxidation to form the carboxyl group, was not observed.     

MALDI-TOF/TOF CID study of poly(α-methylstyrene) fragmentation reactions

MALDI-TOF/TOF CID experiments are reported for hydroxylated poly(α-methylstyrene) precursor ions (PAMS: m/z 1,445.9 (n = 10), 2,036.3 (n = 15), 2,626.7 (n = 20), 3,217.1 (n = 25), and 3,807.5 (n = 30), where the number of repeat units n corresponds to the oligomer mass numbers). The influences of structure, molecular weight, and kinetic energy on degradation mechanisms were examined to test the generality of our multi-chain fragmentation model developed for polystyrene. Our results indicate that poly(α-methylstyrene) free radicals are formed initially through multiple chain breaks and subsequently undergo a variety of depolymerization reactions to yield predominantly monomer and dimer species; the intensity of each species depends on the effective kinetic energy selected for the CID process. Each depolymerization mechanism is presented in detail with experimental and computational data to justify/rationalize the process and its kinetic energy dependence. These processes show the complex interrelationships between the various pathways along with preferred production of tertiary radicals, which suppresses the appearance of primary radicals. Additionally, Py-GC/MS experimental data are presented to allow a comparison of the multimolecular free radical reactions in pyrolysis with the unimolecular fragmentation reactions of MS/MS. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effect of cooling rate on the crystal/mesophase polymorphism of polyamide 6

The solidification of the quiescent polyamide 6 (PA 6) melt has been analyzed as a function of the cooling rate in a wide range between 1.67 × 10⁻² and close to 2 × 10² K s⁻¹, by means of differential scanning calorimetry at a low cooling rate of up to about 1 K s⁻¹, and by the recording of continuous cooling curves and time-resolved X-ray diffraction on cooling at a higher rate. The performed experiments allowed for the first time to establish the relationship between the cooling rate, the crystallization temperature, and the X-ray structure of PA 6. The exclusive formation of monoclinic α-crystals is only detected if the crystallization temperature is higher than about 430 K or if the cooling rate is slower than about 5 K s⁻¹, respectively. The formation of α-crystals is increasingly replaced by the development of mesophase with increasing cooling rate, accompanied with a decrease of the temperature of crystallization/ordering. Finally, completely amorphous samples were obtained on cooling faster than about 10² K s⁻¹. The continuous decrease of the temperature of crystallization with increasing cooling rate, regardless of the specific structure formed, precludes a primary effect of the nucleation mechanism on the α-crystal/mesophase polymorphism of PA 6. A preliminary discussion of the effect of molar mass of PA 6 on the cooling rate-dependent polymorphism is also included.     

Scale up and Application of Biosurfactant from <Emphasis Type="Italic">Bacillus subtilis</Emphasis> in Enhanced Oil Recovery

There is a lack of fundamental knowledge about the scale up of biosurfactant production. In order to develop suitable technology of commercialization, carrying out tests in shake flasks and bioreactors was essential. A reactor with integrated foam collector was designed for biosurfactant production using Bacillus subtilis isolated from agricultural soil. The yield of biosurfactant on biomass (Y _p/x), biosurfactant on sucrose (Y _p/s), and the volumetric production rate (Y) for shake flask were obtained about 0.45 g g⁻¹, 0.18 g g⁻¹, and 0.03 g l⁻¹ h⁻¹, respectively. The best condition for bioreactor was 300 rpm and 1.5 vvm, giving Y _x/s, Y _p/x, Y _p/s, and Y of 0.42 g g⁻¹, 0.595 g g⁻¹, 0.25 g g⁻¹, and 0.057 g l⁻¹ h⁻¹, respectively. The biosurfactant maximum production, 2.5 g l⁻¹, was reached in 44 h of growth, which was 28% better than the shake flask. The obtained volumetric oxygen transfer coefficient (K _L a) values at optimum conditions in the shake flask and the bioreactor were found to be around 0.01 and 0.0117 s⁻¹, respectively. Comparison of K _L a values at optimum conditions shows that biosurfactant production scaling up from shake flask to bioreactor can be done with K _L a as scale up criterion very accurately. Nearly 8% of original oil in place was recovered using this biosurfactant after water flooding in the sand pack.     

Boronic acid-facilitated α-hydroxy-carboxylate anion transfer at liquid/liquid electrode systems: the EICrev mechanism

The transfer of the α-hydroxy-carboxylates of glycolic, lactic, mandelic and gluconic acid from the aqueous electrolyte phase into an organic 4-(3-phenylpropyl)-pyridine (PPP) phase is studied at a triple-phase boundary electrode system. The tetraphenylporphyrinato complex MnTPP dissolved in PPP is employed to drive the anion transfer reaction and naphthalene-2-boronic acid (NBA) is employed as a facilitator. In the absence of a facilitator, the ability of α-hydroxy-carboxylates to transfer into the organic phase improves, consistent with hydrophobicity considerations giving relative transfer potentials (for aqueous 0.1 M solution) of gluconate>glycolate>lactate>mandelate. In the presence of NBA, a shift of the reversible transfer potential to more negative values is indicating fast reversible binding (the mechanism for the electrode process is EIC_rev) and the binding constants are determined as K _glycolate = 2 M⁻¹, K _mandelate = 60 M⁻¹, K _lactate = 130 M⁻¹ and K _gluconate = 2,000 M⁻¹. The surprisingly strong interaction for gluconate is rationalised based on secondary interactions between the gluconate anion and NBA.     

Suitability of ultra-high performance liquid chromatography for the determination of fat-soluble nutritional status (vitamins A, E, D, and individual carotenoids)

Our aim was to assess the suitability of ultra-high performance liquid chromatography (UHPLC) for the simultaneous determination of biomarkers of vitamins A (retinol, retinyl esters), E (α- and γ-tocopherol), D (25-OH-vitamin D), and the major carotenoids in human serum to be used in clinical practice. UHPLC analysis was performed on HSS T3 column (2.1 × 100 mm; 1.8 μm) using gradient elution and UV–VIS detection. The system allows the simultaneous determination of retinol, retinyl palmitate, 25-OH-vitamin D, α- and γ-tocopherol, lutein plus zeaxanthin, α-carotene, β-carotene, α- and β-cryptoxanthin and lycopene. The method showed a good linearity over the physiological range with an adequate accuracy in samples from quality control programs. Suitability of the method in clinical practice was tested by analyzing samples (n = 286) from patients. In conclusion, UHPLC constitutes a reliable approach for nutrient/biomarker profiling allowing the rapid, simultaneous and low-cost determination of vitamins A, E, and D (including vitamers and ester forms) and the major carotenoids in clinical practice.     

Electrochemical methods for simultaneous determination of trace amounts of dopamine and uric acid using a carbon paste electrode incorporated with multi-wall carbon nanotubes and modified with α-cyclodextrine

In this work, we investigate the electrochemical activity of dopamine (DA) and uric acid (UA) using both a bare and a modified carbon paste electrode as the working electrode, with a platinum wire as the counter electrode and a silver/silver chloride (Ag/AgCl) as the reference electrode. The modified carbon paste electrode consists of multi-walled carbon nanotubes (>95%) treated with α-cyclodextrine, resulting in an electrode that exhibits a significant catalytic effect toward the electro-chemical oxidation of DA in a 0.2-M Britton–Robinson buffer solution (pH 5.0). The peak current increases linearly with the DA concentration within the molar concentration ranges of 2.0 × 10⁻⁶ to 5.0 × 10⁻⁵ M and 5.0 × 10⁻⁵ to 1.9 × 10⁻⁴ M. The detection limit (signal to noise >3) for DA was found to be 1.34 × 10⁻⁷ M, respectively. In this work, voltammetric methods such as cyclic voltammetry, chronoamperometry, chronocuolometry, differential pulse and square wave voltammetry, and linear sweep and hydrodynamic voltammetry were used. Cyclic voltammetry was used to investigate the redox properties of the modified electrode at various scan rates. The diffusion coefficient (D, cm² s⁻¹ = 3.05 × 10⁻⁵) and the kinetic parameters such as the electron transfer coefficient (α = 0.51) and the rate constant (k, cm³ mol⁻¹ s⁻¹ = 1.8 × 10³) for DA were determined using electrochemical approaches. By using differential pulse voltammetry for simultaneous measurements, we obtained two peaks for DA and UA in the same solution, with the peak separation approximately 136 mV. The average recovery was measured at 102.45% for DA injection.     

Integration of spore-based genetically engineered whole-cell sensing systems into portable centrifugal microfluidic platforms

Bacterial whole-cell biosensing systems provide important information about the bioavailable amount of target analytes. They are characterized by high sensitivity and specificity/selectivity along with rapid response times and amenability to miniaturization as well as high-throughput analysis. Accordingly, they have been employed in various environmental and clinical applications. The use of spore-based sensing systems offers the unique advantage of long-term preservation of the sensing cells by taking advantage of the environmental resistance and ruggedness of bacterial spores. In this work, we have incorporated spore-based whole-cell sensing systems into centrifugal compact disk (CD) microfluidic platforms in order to develop a portable sensing system, which should enable the use of these hardy sensors for fast on-field analysis of compounds of interest. For that, we have employed two spore-based sensing systems for the detection of arsenite and zinc, respectively, and evaluated their analytical performance in the miniaturized microfluidic format. Furthermore, we have tested environmental and clinical samples on the CD microfluidic platforms using the spore-based sensors. Germination of spores and quantitative response to the analyte could be obtained in 2.5–3 h, depending on the sensing system, with detection limits of 1 × 10⁻⁷ M for arsenite and 1 × 10⁻⁶ M for zinc in both serum and fresh water samples. Incorporation of spore-based whole-cell biosensing systems on microfluidic platforms enabled the rapid and sensitive detection of the analytes and is expected to facilitate the on-site use of such sensing systems.     

Production of Lipids Containing High Levels of Docosahexaenoic Acid by a Newly Isolated Microalga, <Emphasis Type="Italic">Aurantiochytrium</Emphasis> sp. KRS101

In the present study, a novel oleaginous Thraustochytrid containing a high content of docosahexaenoic acid (DHA) was isolated from a mangrove ecosystem in Malaysia. The strain identified as an Aurantiochytrium sp. by 18S rRNA sequencing and named KRS101 used various carbon and nitrogen sources, indicating metabolic versatility. Optimal culture conditions, thus maximizing cell growth, and high levels of lipid and DHA production, were attained using glucose (60 g l⁻¹) as carbon source, corn steep solid (10 g l⁻¹) as nitrogen source, and sea salt (15 g l⁻¹). The highest biomass, lipid, and DHA production of KRS101 upon fed-batch fermentation were 50.2 g l⁻¹ (16.7 g l⁻¹ day⁻¹), 21.8 g l⁻¹ (44% DCW), and 8.8 g l⁻¹ (40% TFA), respectively. Similar values were obtained when a cheap substrate like molasses, rather than glucose, was used as the carbon source (DCW of 52.44 g l⁻¹, lipid and DHA levels of 20.2 and 8.83 g l⁻¹, respectively), indicating that production of microbial oils containing high levels of DHA can be produced economically when the novel strain is used.     

Microbial Production of Propionic Acid with <Emphasis Type="Italic">Propionibacterium freudenreichii</Emphasis> Using an Anion Exchanger-Based In Situ Product Recovery (ISPR) Process with Direct and Indirect Contact of Cells

The recovery of an inhibiting product from a bioreactor soon after its formation is an important issue in industrial bioprocess development. In the present study, the potential of the anion exchanger-based in situ product recovery (ISPR) technique for the biocatalytic production of propionic acid was discussed. The focus of the current work was the selection of a suitable configuration of metabolically active cells for application in propionic acid production. Accumulation of propionic acid in fermentation broth caused feedback inhibition of the growth and biotransformation activity of Propionibacterium freudenreichii CICC 10019. Relevant product inhibition kinetics was discussed, and the results showed that keeping the aqueous propionic acid concentration below 10.02 g L⁻¹ was an essential prerequisite for ISPR process. A batch study, in which three ISPR configuration mode designs were compared, was conducted. The comparison indicated that employing an external direct mode had significant advantages over other modes in terms of increased productivity and product yield, with a corresponding decrease in the number of downstream processing steps, as well as in substrate consumption. The fed-batch culture using an external direct mode for the continuous accumulation of propionic acid resulted in a cumulative propionic acid concentration of 62.5 g L⁻¹, with a corresponding product yield of 0.78 g propionic acid/g glucose.     

Oxidation pathways and kinetics of morphine in acidic and neutral media on the aluminum electrode covered by metallic palladium and modified by Prussian blue

This paper describes the use of an aluminum electrode covered by metallic palladium and modified by Prussian blue prepared by a simple and rapid electroless method for the electro-oxidation of morphine. Two different pathways for electro-oxidation of morphine at various pH ranges were suggested. Also, some thermodynamic and kinetic parameters such as the number of electrons involved in the rate determining step, n _α , transfer coefficient α, and the total electrons (n) involved in morphine oxidation at the time scale of the cyclic voltammetric technique, the catalytic rate constant of the electrochemical process k, and diffusion coefficient of morphine D were determined. The mean values obtained are 0.5, 0.5, 1, 26.8 M^-1 s^-1 and 3.1 × 10⁻⁵ cm² s⁻¹, respectively.     

Voltammetric sensor for nitrite determination based on its electrocatalytic reduction at the surface of p-duroquinone modified carbon paste electrode

A p-duroquinone (tetramethyl-p-benzoquinone) modified carbon paste electrode (DMCPE) was employed to study the electrocatalytic reduction of nitrite in aqueous solutions using cyclic voltammetry (CV), double potential-step chronoamperometry, and differential pulse voltammetry (DPV). It has found that under an optimum condition (pH 1.00), the reduction of nitrite at the surface of DMCPE occurs at a potential of about 660 mV less negative than that of an unmodified carbon paste electrode (CPE). The catalytic rate constant, k′_h, based on Andrieux and Saveant theoretical model was calculated as for scan rate 10 mV s^-1. Also, the apparent diffusion coefficient, D _app, was found as 2.5 × 10^–10 and 3.61 × 10^–5 cm² s^-1 for p-duroquinone in carbon paste matrix and nitrite in aqueous buffered solution, respectively. The values for αn_α were estimated to be −0.65 and −0.19 for the reduction of nitrite at the surface of DMCPE and CPE, respectively. The electrocatalytic reduction peak currents showed a linear dependence on the nitrite concentration, and a linear analytical curve was obtained in the ranges of 5.0 × 10^–5 M to 8.0 × 10^–3 M and 6.0 × 10^–6 M to 8.0 × 10^–4 M of nitrite concentration with CV and DPV methods, respectively. The detection limits (2σ) were determined as 2.5 × 10^–5 M and 4.3 × 10^–6 M by CV and DPV methods. This method was also applied as a simple, selective and precise method for determination of nitrite in real samples (the weak liquor from the wood and paper factory of Mazandaran province in Iran) by using a standard addition method.