High‐sensitivity spectrofluorimetric determination of tiopronin based on inhibition of hemoglobin

A highly sensitive and simple spectrofluorimetric method for the determination of tiopronin based on its inhibitory effect on the hemoglobin‐catalyzed reaction of H₂O₂ and l ‐tyrosine was developed. The concentration of tiopronin is linear with decreased fluorescence (ΔF) of the system under the optimal experimental conditions. The calibration graph is linear in the range 1.23 × 10^?8 to 3.06 × 10^?5 mol L^?1 with a detection limit of 6.13 × 10^?9 mol L^?1. The relative standard deviation was 4.38% for 11 determinations of 6.13 × 10^?6 mol L^?1. This method can be used for the determination of tiopronin in pharmaceuticals with satisfactory results. Copyright © 2010 John Wiley & Sons, Ltd.     

The molecular structure and solution conformation of an acidic heteropolysaccharide from Auricularia auricula-judae

A water soluble acidic heteropolysaccharide named WAF was isolated from Auricularia auricula‐judae by extracting with 0.9% NaCl solution. By using gas chromatography, gas chromatography‐mass spectrometry, and NMR, its chemical structure was determined to be composed of a backbone of α‐(1→3)‐linked D ‐mannopyranose residues with pendant side groups of β‐D ‐xylose, β‐D ‐glucose, or β‐D ‐glucuronic acid at position O6 or O2. Six fractions prepared from WAF with a weight‐average molecular mass (M_w) between 5.9 × 10⁴ and 64.7 × 10⁴ g/mol were characterized with laser light scattering and viscometry in 0.1M NaCl at 25°C. The dependence of intrinsic viscosity ([η]) and radius of gyration (R_g) on M_w for this polysaccharide were found to be [η] = 1.79 × 10^?3M_w^0.96 cm³ g^?1 and R_g = 6.99 × 10^?2 M_w^0.54 nm. The molar mass per unit contour length (M_L) and the persistence length (L_p) were estimated to be 1124 nm^?1 and 11 nm, respectively. The WAF exhibited a semirigid character typical of linear polysaccharides. Molecular modeling was then used to predict the ordered and disordered states of WAF; the simulated M_L and L_p were however much smaller than the experimental values. Taken altogether, the results suggested that WAF formed a duplex in solution. © 2010 Wiley Periodicals, Inc. Biopolymers 95: 217–227, 2011.     

Evaluation of substrate promiscuity of an L‐carbamoyl amino acid amidohydrolase from Geobacillus stearothermophilus CECT43

N‐carbamoyl‐amino‐acid amidohydrolase (also known as N‐carbamoylase) is the stereospecific enzyme responsible for the chirality of the D ‐ or L ‐amino acid obtained in the “Hydantoinase Process.” This process is based on the dynamic kinetic resolution of D ,L ‐5‐monosubstituted hydantoins. In this work, we have demonstrated the capability of a recombinant L ‐N‐carbamoylase from the thermophilic bacterium Geobacillus stearothermophilus CECT43 (BsLcar) to hydrolyze N‐acetyl and N‐formyl‐L ‐amino acids as well as the known N‐carbamoyl‐L ‐amino acids, thus proving its substrate promiscuity. BsLcar showed faster hydrolysis for N‐formyl‐L ‐amino acids than for N‐carbamoyl and N‐acetyl‐L ‐derivatives, with a catalytic efficiency (k_cat/K_m) of 8.58 × 10⁵, 1.83 × 10⁴, and 1.78 × 10³ (s^?1 M^?1), respectively, for the three precursors of L ‐methionine. Optimum reaction conditions for BsLcar, using the three N‐substituted‐L ‐methionine substrates, were 65°C and pH 7.5. In all three cases, the metal ions Co²⁺, Mn²⁺, and Ni²⁺ greatly enhanced BsLcar activity, whereas metal‐chelating agents inhibited it, showing that BsLcar is a metalloenzyme. The Co²⁺‐dependent activity profile of the enzyme showed no detectable inhibition at high metal ion concentrations. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Perturbation of the tris(2,2′‐bipyridine) ruthenium(II)‐catalyzed Belousov–Zhabotinsky oscillating chemiluminescence reaction by l‐cysteine and its application

Perturbation of the tris(2,2′‐bipyridine)ruthenium(II) [Ru(bpy)₃²⁺]‐catalyzed Belousov–Zhabotinsky (BZ) oscillating chemiluminescence (CL) reaction induced by l ‐cysteine was observed in the closed system. It was found that the CL intensity was decreased in the presence of l ‐cysteine. Meanwhile, oscillation period and oscillating induction period were prolonged. The sufficient reproducible induction period was used as parameter for the analytical application of oscillating CL reaction. Under the optimum conditions, the changes in the oscillating CL induction period were linearly proportional to the concentration of l ‐cysteine in the range from 8.0 × 10^?7 to 5.0 × 10^?5 mol L^?1 (r = 0.997) with a detection limit of 4.3 × 10^?7 mol L^?1. The possible mechanism of l ‐cysteine perturbation on the oscillating CL reaction was also discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Stopped‐flow chemiluminescence determination of the anticancer drug capecitabine: Application in pharmaceutical analysis and drug‐delivery systems

Capecitabine is a chemotherapeutic agent used for the treatment of patients with metastatic cancers. This study aimed at determining the drug capecitabine in a simple chemiluminescence (CL) system of acidic potassium permanganate using the stopped‐flow injection technique. Statistical methods were used to detect optimum conditions. The method showed two linear calibration ranges from 6.7 × 10^?6 to 6.7 × 10^?5 mol L^?1 and from 6.7 × 10^?5 to 2.7 × 10^?3 mol L^?1 with a detection limit of 1.5 × 10^?6 mol L^?1. Chitosan‐modified magnetic nanoparticles were studied in the drug‐delivery experiments. According to the pH sensitivity of chitosan and low pH values in tumour cells, the chitosan‐coated magnetic nanoparticles could provide a good targeting drug‐delivery system to tumour sites. To evaluate the applicability of the method, the capecitabine‐loaded magnetic chitosan nanoparticles were synthesized with two different cross‐linkers; loading and releasing rates of the drug were investigated using the proposed CL method and an ultraviolet–visible light spectrophotometric method (absorption at 305 nm). The results showed a good correlation between the two methods, and it was found that the synthesized chitosan‐modified magnetic nanoparticles could be used for pH‐dependent release of capecitabine in cancer cells. Moreover, determination of capecitabine in tablets and synthetic samples was performed.     

S‐perindopril assay using a potentiometric,enantioselective membrane electrode

A potentiometric, enantioselective membrane electrode based on graphite paste (graphite powder and paraffin oil) has been constructed. The graphite paste is impregnated with a 10⁻³ mol/L 2‐hydroxy‐3‐trimethylammoniopropyl‐β‐cyclodextrin (as chloride salt) solution. The potentiometric, enantioselective membrane electrode can be used reliably for enantiopurity tests of S‐perindopril using a chronopotentiometric (zero current) technique, in the 10⁻⁵–10⁻² mol/L concentration range (detection limit 5 × 10⁻⁶ mol/L), with an average recovery of 99.58% (RSD = 0.33%). The enantioselectivity was determined over R‐perindopril and d ‐proline. The response characteristics of the enantioselective, potentiometric membrane electrode were also determined for R‐perindopril. It was shown that l ‐proline is the main interfering compound. The surface of the electrode can be regenerated simply by polishing, obtaining a fresh surface ready to be used in a new assay. Chirality 11:631–634, 1999. © 1999 Wiley‐Liss, Inc.     

Electrophoresis–chemiluminescence detection of phenols catalyzed by hemin

Based on the catalytic activity of hemin, an efficient biocatalyst, an indirect capillary electrophoresis–chemiluminescence (CE‐CL) detection method for phenols using a hemin–luminol–hydrogen peroxide system was developed. Through a series of static injection experiments, hemin was found to perform best in a neutral solution rather than an acidic or alkaline medium. Although halide ions such as Br^? and F^? could further enhance the CL signal catalyzed by hemin, it is difficult to apply these conditions to this CE‐CL detection system because of the self‐polymerization of hemin, as it hinders the CE process. The addition of concentrated ammonium hydroxide to an aqueous/dimethyl sulfoxide solution of hemin–luminol afforded a stable CE‐CL baseline. The indirect CE‐CL detection of five phenols using this method gave the following limits of detections: 4.8 × 10^?8 mol/L (o‐sec‐butylphenol), 4.9 × 10^?8 mol/L (o‐cresol), 5.4 × 10^?8 mol/L (m‐cresol), 5.3 × 10^?8 mol/L (2,4‐dichlorophenol) and 7.1 × 10^?8 mol/L (phenol). Copyright © 2013 John Wiley & Sons, Ltd.     

Controlled feeding of hydrogen peroxide as oxygen source improves production of 5-ketofructose From L-sorbose using engineered pyranose 2-oxidase from Peniophora gigantea

5‐Keto‐D ‐fructose is a useful starting material for the synthesis of pyrrolidine iminosugars. It can be prepared by regioselective oxidation of L ‐sorbose using pyranose 2‐oxidase (P2Ox) and O₂ as a cosubstrate. As the solubility of O₂ in aqueous solution is low and the affinity of P2Ox for O₂ is poor, we developed a new and efficient process for the production of 5‐keto‐D ‐fructose based on engineered P2Ox from Peniophora gigantea and in situ generation of O₂ from H₂O₂ with catalase. This kind of oxygen supply required efficient mixing of the bioreactor which was achieved by controlled feeding of H₂O₂ close to the impeller tip where energy dissipation rate is highest. Thus bubbling, known to affect enzyme stability, was largely avoided, and the process could be run up to 145% oxygen super‐saturation which speeds‐up P2Ox activity. Under these conditions quantitative oxidation of 180 g L^?1 L ‐sorbose to 5‐keto‐D ‐fructose could be achieved within 4 h, resulting in a threefold higher overall productivity of the process compared to a process using gaseous oxygen supply. In addition, in situ generation of O₂ from H₂O₂ lowered the oxygen demand of the process by a factor of 100 compared to gaseous oxygen supply. Biotechnol. Bioeng. 2012; 109: 2941–2945. © 2012 Wiley Periodicals, Inc.     

A novel method for sensing of methimazole using gold nanoparticle‐catalyzed chemiluminescent reaction

Based on the inhibition effect of methimazole (MMI) on the reaction of luminol–H₂O₂ catalyzed by gold nanoparticles, a novel chemiluminescence (CL) method was developed for the determination of MMI. Under the optimum conditions, the relative CL intensity was linearly related to MMI concentration in the range from 5.0 × 10^?8 to 5.0 × 10^?5 mol L^?1. The detection limit was 1.6 × 10^?8 mol L^?1 (S/N = 3), and the RSD for 6.0 × 10^?6 mol L^?1 MMI was 4.83 (n = 11). This method has high sensitivity, wide linear range, inexpensive instrumentation and has been applied to detect MMI in pharmaceutical tablets and pig serum samples. Furthermore, a possible reaction mechanism is discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

A highly efficient and selective turn‐on fluorescent sensor for Hg2+, Ag+ and Ag nanoparticles based on a coumarin dithioate derivative

Based on chelation‐enhanced fluorescence, a new fluorescent coumarin derivative probe 3(1‐(7‐hydroxy‐4‐methylcoumarin)ethylidene)hydrazinecarbodithioate for Hg²⁺, Ag⁺ and Ag nanoparticles is reported. Fluorescent probe acts as a rapid and highly selective “off–on” fluorescent probe and fluorescence enhancement by factors 5 to12 times was observed upon selective complexation with Hg²⁺, Ag⁺ and Ag nanoparticles. The molar ratio plots indicated the formation of 1:1 complexes between Hg²⁺ and Ag⁺ with the probe. The linear response range covers a concentration range 0.1 × 10^–5–1.9 × 10^–5 mol/L, 0.1 × 10^–5–2.3 × 10^–5 mol/L and 0.146 × 10^–12–2.63 × 10^–12 mol/L for Hg²⁺, Ag⁺ and Ag nanoparticles, respectively. The interference effect of some anions and cations was also tested. Copyright © 2013 John Wiley & Sons, Ltd.     

Sensitive determination of enoxacin in pharmaceutical formulations by its quench effect on the fluorescence of glutathione‐capped CdTe quantum dots

A sensitive and simple method for the determination of enoxacin (ENX) was developed based on the fluorescence quenching effect of ENX for glutathione (GSH)‐capped CdTe quantum dots (QDs). Under optimum conditions, a good linear relationship was obtained from 4.333 × 10^?9 mol?L^?1 to 1.4 × 10^?5 mol?L^?1 with a correlation coefficient (R) of 0.9987, and the detection limit (3σ/K) was 1.313 × 10^?9 mol?L^?1. The corresponding mechanism has been proposed on the basis of electron transfer supported by ultraviolet–visible (UV) light absorption, fluorescence spectroscopy, and the measurement of fluorescence lifetime. The method has been applied to the determination of ENX in pharmaceutical formulations (enoxacin gluconate injections and commercial tablets) with satisfactory results. The proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrochemiluminescence detection of methamphetamine based on a Ru(bpy)32+‐doped silica nanoparticles/Nafion composite film modified electrode

An electrochemiluminescence (ECL) approach for methamphetamine determination was developed based on a glassy carbon electrode modified with a Ru(bpy)₃²⁺‐doped silica nanoparticles/Nafion composite film. The monodispersed nanoparticles, which were about 50 nm in size, were synthesized using the water‐in‐oil microemulsion method. The ECL results revealed that Ru(bpy)₃²⁺ doped in silica nanoparticles retained its original photo‐ and electrochemical properties. The ECL intensity was found to be proportional to methamphetamine concentration over the range from 1.0 × 10^?7 to 1.0 × 10^?5 mol L^?1, and the detection limit was found to be 2.6 × 10^?8 mol L^?1. The proposed ECL approach was used to analyze the methamphetamine content in drugs. Copyright © 2009 John Wiley & Sons, Ltd.     

Fluorescence sensing of nitric oxide in aqueous solution by triethanolamine‐modified CdSe quantum dots

The water‐soluble luminescent CdSe quantum dots were prepared by ligand exchange with triethanolamine (TEA). Oxygen can reversibly enhance the fluorescence of the synthesized quantum dots (TEA‐CdSe‐QDs) in aqueous solution. Nitric oxide radical (NO) can react easily with dissolved oxygen in water and was found to have a significant quenching effect on the fluorescence of the TEA‐CdSe‐QDs. The fluorescence responses were concentration‐dependent and can be well described by the typical Stern–Volmer equation. A good linear relationship (R² = 0.9963) was observed over the range 5.92 × 10^?7 to 1.85 × 10^?5 mol/L nitric oxide. Above this concentration was a second linear region ranging from 2.12 × 10^?5 to 1.12 × 10^?4 mol/L NO with a gentler slope. The detection limit, calculated following the 3σ IUPAC criteria, was 3.02 × 10^?7 mol/L. The interference effect of some common interferents such as nitrite (NO₂^?), nitrate (NO₃^?), glucose and l ‐ascorbic acid on the detection of NO was negligible for the proposed system, demonstrating the potential utility of this probe for the detection of NO in biological systems. The possible mechanism was also discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Spectroscopic study of the interaction between adenosine disodium triphosphate and gatifloxacin–Al3+ complex and its analytical application

A new and sensitive spectrofluorimetric method has been proposed to determine trace amount of adenosine disodium triphosphate (ATP). The method is based on the fluorimetric interaction between gatifloxacin (GFLX)–aluminium (III) (Al³⁺) complex and ATP and studied using UV‐visible and fluorescence spectroscopy. Weak luminescence spectra of Al³⁺ were enhanced after complexation with GFLX at 423 nm upon excitation at 272 nm due to energy transfer from the ligand to the Al³⁺ ion. It was observed that the FL emission spectrum of GFLX–Al³⁺ was enhanced significantly by the addition of ATP. Under the optimal conditions, the enhancement of FL intensity at 423 nm was responded linearly with the concentration of ATP in the range 1.3 × 10^–10 – 1.0 × 10^–8 mol L^–1 with correlation coefficient (r) of 0.9981. The limit of detection (LOD) was found to be 1.1 × 10^–11 mol L^–1 for ATP with the standard deviation (RSD) of 1.21% for five repeated measurement of 2.3 × 10^–8 mol L^–1 ATP. The presented method is simple, sensitive, free from coexisting interferents and can be applied successfully to determine ATP in the real samples. Copyright © 2015 John Wiley & Sons, Ltd.     

A novel phosphorescence sensor for Co2+ ion based on Mn‐doped ZnS quantum dots

N‐acetyl‐l ‐cysteine‐capped Mn‐doped ZnS quantum dots (QDs) were prepared by hydrothermal methods. It could emit phosphorescence at 583 nm with the excitation wavelength at 315 nm. The phosphorescence intensity of QDs could be quenched dramatically by increasing the concentration of Co²⁺ ion. The novel phosphorescence sensor based on N‐acetyl‐l ‐cysteine‐capped QDs was developed for detecting Co²⁺ ion with a linear dynamic range of 1.25 × 10^–6–3.25 × 10^–5 m . The limit of detection and RSD were 6.0 × 10^–8 m and 2.3%, respectively. Interference experiments showed excellent selectivity over numerous cations such as alkali, alkaline earth and transitional metal ions. The possible quenching mechanism was also examined by phosphorescence decays. The proposed phosphorescence method was further applied to the trace determination of Co²⁺ ion in tap and pond water samples with recoveries of 97.75–103.32%. Copyright © 2013 John Wiley & Sons, Ltd.     

Metabolism in 1,3‐propanediol fed‐batch fermentation by a D‐lactate deficient mutant of Klebsiella pneumoniae

Klebsiella pneumoniae HR526, a new isolated 1,3‐propanediol (1,3‐PD) producer, exhibited great productivity. However, the accumulation of lactate in the late‐exponential phase remained an obstacle of 1,3‐PD industrial scale production. Hereby, mutants lacking D ‐lactate pathway were constructed by knocking out the ldhA gene encoding fermentative D ‐lactate dehydrogenase (LDH) of HR526. The mutant K. pneumoniae LDH526 with the lowest LDH activity was studied in aerobic fed‐batch fermentation. In experiments using pure glycerol as feedstock, the 1,3‐PD concentrations, conversion, and productivity increased from 95.39 g L^?1, 0.48 and 1.98 g L^?1 h^?1 to 102. 06 g L^?1, 0.52 mol mol^?1 and 2.13 g L^?1 h^?1, respectively. The diol (1,3‐PD and 2,3‐butanediol) conversion increased from 0.55 mol mol^?1 to a maximum of 0.65 mol mol^?1. Lactate would not accumulate until 1,3‐PD exceeded 84 g L^?1, and the final lactate concentration decreased dramatically from more than 40 g L^?1 to <3 g L^?1. Enzymic measurements showed LDH activity decreased by 89–98% during fed‐batch fermentation, and other related enzyme activities were not affected. NADH/NAD⁺ enhanced more than 50% in the late‐exponential phase as the D ‐lactate pathway was cut off, which might be the main reason for the change of final metabolites concentrations. The ability to utilize crude glycerol from biodiesel process and great genetic stability demonstrated that K. pnemoniae LDH526 was valuable for 1,3‐PD industrial production. Biotechnol. Bioeng. 2009; 104: 965–972. © 2009 Wiley Periodicals, Inc.     

The behaviors of metal ions in the CdTe quantum dots–H2O2 chemiluminescence reaction and its sensing application

The behaviors of 15 kinds of metal ions in the thiol‐capped CdTe quantum dots (QDs)–H₂O₂ chemiluminescence (CL) reaction were investigated in detail. The results showed that Ag⁺, Cu²⁺ and Hg²⁺ could inhibit CdTe QDs and H₂O₂ CL reaction. A novel CL method for the selective determination of Ag⁺, Cu²⁺ and Hg²⁺ was developed, based on their inhibition of the reaction of CdTe QDs and H₂O₂. Under the optimal conditions, good linear relationships were realized between the CL intensity and the logarithm of concentrations of Ag⁺, Cu²⁺ and Hg²⁺. The linear ranges were from 2.0 × 10^?6 to 5.0 × 10^?8 mol L^?1 for Ag⁺, from 5.0 × 10^?6 to 7.0 × 10^?8 mol L^?1 for Cu²⁺ and from 2.0 × 10^?5 to 1.0 × 10^?7 mol L^?1 for Hg²⁺, respectively. The limits of detection (S/N = 3) were 3.0 × 10^?8, 4.0 × 10^?8 and 6.7 × 10^?8 mol L^?1 for Ag⁺, Cu²⁺ and Hg²⁺, respectively. A possible mechanism for the inhibition of CdTe QDs and H₂O₂ CL reaction was also discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Terbium‐sensitized fluorescence method for the determination of deferasirox in biological fluids and tablet formulation

A novel, rapid and sensitive spectroflurimetric method was developed and validated for the determination of deferasirox in urine, serum and tablet samples based on sensitization of terbium fluorescence. The excitation and emission wavelengths were 328 and 545 nm, respectively. The optimum conditions for the determination of deferasirox were investigated considering the effects of various parameters. The method was quantitatively evaluated in terms of linearity, recovery, reproducibility and limit of detection. Under the optimal conditions, the fluorescence intensities were linear with the concentration of deferasirox in the range of 5 × 10^?9 to 5×10^?6 mol L^?1, with a detection limit of 1.5 × 10^?9 mol L^?1 and a relative standard deviation of 1.1–2.3%. Linearity, reproducibility, recovery and limit of detection made the method suitable for determination of deferasirox in urine, serum and tablets samples. Copyright © 2010 John Wiley & Sons, Ltd.     

Cupric oxide nanoparticles‐enhanced chemiluminescence method for measurement of β‐lactam antibiotics

A simple, sensitive cupric oxide nanoparticles (CuO NPs) enhanced chemiluminescence (CL) method was developed for the measurement of β‐lactam antibiotics, including amoxicillin and cefazolin sodium. The method was based on suppression of the CuO NPs–luminol–H₂O₂ CL reaction by β‐lactam antibiotics. Experimental parameters that influenced the inhibitory effect of the antibiotic drugs on the CL system, such as NaOH (mol/L), luminol (µmol/L), H₂O₂ (mol/L) and CuO NPs (mg/L) concentrations, were optimized. Calibration graphs were linear and had dynamic ranges of 1.0 × 10^–6 to 8.0 × 10^–6 mol/L and 3.0 × 10^–5 to 5.0 × 10^–3 mol/L for amoxicillin and cefazolin sodium, respectively, with corresponding detection limits of 7.9 × 10^–7 mol/L and 1.8 × 10^–5 mol/L. The relative standard deviations of five replicate measurements of 5.0 × 10^–6 amoxicillin and 5 × 10^–4 cefazolin sodium were 5.43 and 5.01%, respectively. The synthesized CuO NPs were characterized by X‐ray diffraction (XRD) and transmission electronmicroscopy (TEM). The developed approach was exploited successfully to measure antibiotics in pharmaceutical preparations. Copyright © 2014 John Wiley & Sons, Ltd.     

Chemiluminescence sensor for sulfonylurea herbicide using molecular imprinted microspheres as recognition element

Uniform molecular imprinting microspheres were prepared using precipitation polymerization with thifensulfuron‐methyl (TFM) as template, acrylamide as functional monomer and ethylene glycol dimethacrylate as cross‐linker. TFM could be selectively adsorbed on the molecularly imprinted polymers (MIPs) matrix through the hydrogen bonding interaction and the adsorbed TFM could be sensed by its strikingly enhancing effect on the weak chemiluminescence (CL) reaction between luminol and hydrogen peroxide. On this basis, a novel CL sensor for the determination of TFM using MIPs as recognition elements was established. The logarithm of net CL intensity (ΔI) is linearly proportional to the logarithm of TFM concentration (C) in the range from 1.0 × 10^?9 to 5.0 × 10^?5 mol L^?1 with a detection limit of 8.3 × 10^?10 mol L^?1 (3σ). The results demonstrated that the MIP–CL sensor was reversible and reusable and that it could strikingly improve the selectivity and sensitivity of CL analysis. Furthermore, it is suggested that the CL enhancement of luminol–H₂O₂ by TFM might be ascribed to the enhancement effect of CO₂, which came from TFM hydrolysis in basic medium. Copyright © 2010 John Wiley & Sons, Ltd.