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.     

Luminescence study on Mn,Ni co‐doped zinc sulfide nanocrystals

Zinc sulfide (ZnS) doped with transition metal has been used as phosphor for various optoelectronic applications. In the present report, ZnS:Mn doped and ZnS:Mn,Ni co‐doped were prepared using chemical co‐precipitation method using polyvinyl pyrolidone as a surfactant. The structural studies were carried out using an X‐ray diffraction technique; optical studies have been performed using ultraviolet–visible light absorption and photoluminescence (PL) spectroscopy. The presences of functional groups were confirmed using Fourier transform infrared spectroscopy. The X‐ray diffraction study and Reitveld analysis confirms the formation of cubic phase with crystalline size 2–3 nm for undoped and doped ZnS nanoparticles. A novel and enhanced luminescence characteristic have been observed in PL spectra. The luminescence intensity of Mn,Ni co‐doped ZnS in the blue region is much higher of that of ZnS. The PL results indicate that the doping of Ni creates shallow trap states or luminescence centres in the forbidden energy gap, which quenches the Mn states emission. Concentration quenching has been observed in Mn‐doped ZnS nanoparticles. From CIE coordinates, it is seen that the yellow and blue light emission of ZnS:Mn,Ni co‐doped nanophosphor may be a promising candidate for display devices and phosphor converted light‐emitting diode applications.     

Influence of thiol capping on the photoluminescence properties of L‐cysteine‐, mercaptoethanol‐ and mercaptopropionic acid‐capped ZnS nanoparticles

Mercaptoethanol (ME), mercaptopropionic acid (MPA) and L‐cysteine (L‐Cys) having ‐SH functional groups were used as surface passivating agents for the wet chemical synthesis of ZnS nanoparticles. The effect of the thiol group on the optical and photoluminescence (PL) properties of ZnS nanoparticles was studied. L‐Cysteine‐capped ZnS nanoparticles showed the highest PL intensity among the studied capping agents, with a PL emission peak at 455 nm. The PL intensity was found to be dependent on the concentration of Zn²⁺ and S^2– precursors. The effect of buffer on the PL intensity of L‐Cys‐capped ZnS nanoparticles was also studied. UV/Vis spectra showed blue shifting of the absorption edge. Copyright © 2015 John Wiley & Sons, Ltd.     

Tuneable luminescence properties of EDTA‐assisted ZnS:Mn nanocrystals from a yellow‐orange to a red emission band

Luminescence technology has been improved with the help of semiconductor nanoparticles that possess novel optical and electrical properties compared with their bulk counterpart. The aim of this study was to design semiconductor nanocrystals in their pure (ZnS) or doped form (ZnS:Mn) with different concentrations of Mn²⁺ ions by a wet chemical route stabilized by ethylenediamine tetra‐acetic acid (EDTA) and to evaluate their luminescence properties. The nanocrystals were characterized by physicochemical techniques such as X‐ray diffraction (XRD), High‐resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SEAD), EDS, and ultraviolet (UV)–visible light and photoluminescence (PL) studies. These results showed the presence of cubic phase and spherically shaped nanocrystals. A blue shift with respect to their bulk counterpart was observed. PL emission spectra were observed with a fixed blue peak and the yellow‐orange bands were red shifted towards the red region under the same excitation wavelength. The orange‐red bands were attributed to the radiation transition of electrons in 3d5 unfilled shells of Mn²⁺ ions [⁴T₁(⁴G)‐⁶A₁(⁶S)]; the ZnS matrix varied with Mn²⁺ concentration. Shift and increase in the intensity of the PL and absorption bands were observed with increase in Mn content. The study showed that Mn²⁺‐doped ZnS nanocrystal emission bands can be tuned from the yellow‐orange to the red regions under a controlled synthesis process and could be used as promising luminescent emitters in the biology field upon functionalization with suitable materials. Further studies on construction with various other materials will be useful for practical applications.     

Nucleation temperature‐controlled synthesis and in vitro toxicity evaluation of l‐cysteine‐capped Mn:ZnS quantum dots for intracellular imaging

Quantum dots (QDs), one of the fastest developing and most exciting fluorescent materials, have attracted increasing interest in bioimaging and biomedical applications. The long‐term stability and emission in the visible region of QDs have proved their applicability as a significant fluorophore in cell labelling. In this study, an attempt has been made to explore the efficacy of l ‐cysteine as a capping agent for Mn‐doped ZnS QD for intracellular imaging. A room temperature nucleation strategy was adopted to prepare non‐toxic, water‐dispersible and biocompatible Mn:ZnS QDs. Aqueous and room temperature QDs with l ‐cysteine as a capping agent were found to be non‐toxic even at a concentration of 1500 µg/mL and have wide applications in intracellular imaging. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of capping agent concentration on thermoluminescence and photoluminescence of copper‐doped zinc sulfide nanoparticles

Copper‐doped zinc sulfide (ZnS:Cu) nanoparticles with varying concentrations of capping agent were prepared using a chemical route technique. These particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy and X‐ray diffraction (XRD). Optical absorption studies showed that the absorption edge shifted towards the blue region as the concentration of the capping agent increased. Using effective mass approximation, calculation of the nanoparticle size indicated that effective band gap energy increases with decreasing particle size. The thermoluminescence (TL) properties of sodium hexameta phosphate (SHMP)‐passivated ZnS:Cu nanoparticles were investigated after UV irradiation at room temperature. The TL glow curve of capped ZnS:Cu showed variations in TL peak position and intensity with the change in capping agent concentration. The photoluminescence (PL) spectra of ZnS:Cu nanoparticles excited at 254 nm exhibited a broad green emission band peaking around 510 nm, which confirmed the characteristic feature of Zn²⁺ as well as Cu²⁺ ions as the luminescent centres in the lattice. The PL spectra of ZnS:Cu nanoparticles with increasing capping agent concentrations revealed that the emission becomes more intense and shifted towards shorter wavelengths as the sizes of the samples were reduced. Copyright © 2014 John Wiley & Sons, Ltd.     

Development of an optical sensor for chlortetracycline detection based on the fluorescence quenching of l‐tryptophan

A simple and selective spectrofluorimetric method for the detection of chlortetracycline (CTC) was studied. In pH 7.4 buffer medium l ‐tryptophan (l ‐Trp), applied as the fluorescence probe, interacted with CTC resulting in fluorescence quenching of the probe. CTC was detected with maximum excitation and emission wavelengths at λ_ex/λ_em = 275/350 nm. Notably, quenching of fluorescence intensities was positively proportional to the CTC concentration over the range of 0.65–30 μmol L^?1 and the limit of detection was 0.2 μmol L^?1. Effect of temperature shown in Stern?Volmer plots, absorption spectra and fluorescence lifetime determination, indicated that fluorescence quenching of l ‐Trp by CTC was mainly by static quenching. The proposed study used practical samples analysis satisfactorily.     

Thermoluminescence of mercaptoethanol‐capped ZnS:Mn nanoparticles

The thermoluminescence (TL) of nanoparticles has become a matter of keen interest in recent times but is rarely reported. This article reports the synthesis of ZnS:Mn nanocrystals using a chemical route, with mercaptoethanol (ME) as the capping agent. The particle sizes for the nanocrystals were measured by X‐ray diffraction (XRD) and also by studying transmission electron microscopy (TEM) patterns. The particle sizes of the synthesized samples were found to be between 1 and 3 nm. For samples with different concentrations of the capping agent, it was found that the TL intensity of the ZnS:Mn nanoparticles increased as the particle size decreased. A shift in the peak position of the TL glow curve was also seen with decreasing particle size. The TL intensity was found to be maximal for samples with 1.2% of Mn. A change in the peak position was not found for samples with different concentrations of Mn. The half‐width glow peak curve method was used to determine the trap‐depth. The frequency factor of the synthesized samples was also calculated. The stability of the charge carriers in the traps increases with decreasing nanoparticle size. The higher stability may be attributed to the higher surface/volume ratio and also to the increase in the trap‐depth with decreasing particle size. Copyright © 2014 John Wiley & Sons, Ltd.     

Far‐red light enhances photochemical efficiency in a wavelength‐dependent manner

Linear electron transport depends on balanced excitation of photosystem I and II. Far‐red light preferentially excites photosystem I (PSI) and can enhance the photosynthetic efficiency when combined with light that over‐excites photosystem II (PSII). The efficiency of different wavelengths of far‐red light exciting PSI was quantified by measuring the change in quantum yield of PSII (Φ_PSII) of lettuce (Lactuca sativa) under red/blue light with narrowband far‐red light added (from 678 to 752 nm, obtained using laser diodes). The Φ_PSII of lettuce increased with increasing wavelengths of added light from 678 to 703 nm, indicating longer wavelengths within this region are increasingly used more efficiently by PSI than by PSII. Adding 721 nm light resulted in similar Φ_PSII as adding 703 nm light, but Φ_PSII tended to decrease as wavelength increased from 721 to 731 nm, likely due to decreasing absorptance and low photon energy. Adding 752 nm light did not affect Φ_PSII. Leaf chlorophyll fluorescence light response measurements showed lettuce had higher Φ_PSII under halogen light (rich in far‐red) than under red/blue light (which over‐excites PSII). Far‐red light is more photosynthetically active than commonly believed, because of its synergistic interaction with light of shorter wavelengths.     

Chromatographic profiles of tryptophan and kynurenine enantiomers derivatized with (S)‐4‐(3‐isothiocyanatopyrrolidin‐1‐yl)‐7‐(N,N‐dimethylaminosulfonyl)‐2,1,3‐benzoxadiazole using LC–MS/MS on a triazole‐bonded column

d ‐ and l ‐Tryptophan (Trp) and d ‐ and l ‐kynurenine (KYN) were derivatized with a chiral reagent, (S )‐4‐(3‐isothiocyanatopyrrolidin‐1‐yl)‐7‐(N,N‐dimethylaminosulfonyl)‐2,1,3‐benzoxadiazole (DBD‐PyNCS), and were separated enantiomerically by high‐performance liquid chromatography (HPLC) equipped with a triazole‐bonded column (Cosmosil HILIC) using tandem mass spectrometric (MS/MS) detection. Effects of column temperature, salt (HCO₂NH₄) concentration, and pH of the mobile phase in the enantiomeric separation, followed by MS detection of (S )‐DBD‐PyNCS‐d ,l ‐Trp and ‐d ,l ‐KYN, were investigated. The mobile phase consisting of CH₃CN/10 mM ammonium formate in H₂O (pH 5.0) (90/10) with a column temperature of 50–60 °C gave satisfactory resolution (R s) and mass‐spectrometric detection. The enantiomeric separation of d ,l ‐Trp and d ,l ‐KYN produced R s values of 2.22 and 2.13, and separation factors (α) of 1.08 and 1.08, for the Trp and KYN enantiomers, respectively. The proposed LC–MS/MS method provided excellent detection sensitivity of both enantiomers of Trp and KYN (5.1–19 nM).     

Eu2+‐induced enhancement of defect luminescence of ZnS

The Eu²⁺‐induced enhancement of defect luminescence of ZnS was studied in this work. While photoluminescence (PL) spectra exhibited 460 nm and 520 nm emissions in both ZnS and ZnS:Eu nanophosphors, different excitation characteristics were shown in their photoluminescence excitation (PLE) spectra. In ZnS nanophosphors, there was no excitation signal in the PLE spectra at the excitation wavelength λ_ex > 337 nm (the bandgap energy 3.68 eV of ZnS); while in ZnS:Eu nanophosphors, two excitation bands appeared that were centered at 365 nm and 410 nm. Compared with ZnS nanophosphors, the 520 nm emission in the PL spectra was relatively enhanced in ZnS:Eu nanophosphors and, furthermore, in ZnS:Eu nanophosphors the 460 nm and 520 nm emissions increased more than 10 times in intensity. The reasons for these differences were analyzed. It is believed that the absorption of Eu²⁺ intra‐ion transition and subsequent energy transfer to sulfur vacancy, led to the relative enhancement of the 520 nm emission in ZnS:Eu nanophosphors. In addition, more importantly, Eu²⁺ acceptor‐bound excitons are formed in ZnS:Eu nanophosphors and their excited levels serve as the intermediate state of electronic relaxation, which decreases non‐radiative electronic relaxation and thus increases the intensity of the 460 nm and 520 nm emission dramatically. In summary, the results in this work indicate a new mechanism for the enhancement of defect luminescence of ZnS in Eu²⁺‐doped ZnS nanophosphors. Copyright © 2016 John Wiley & Sons, Ltd.     

A novel colorimetric assay of β‐D‐glucans in basidiomycete strains by alcian blue dye in a 96‐well microtiter plate

Basidiomycete strains synthesize several types of β‐d ‐glucans, which play a major role in the medicinal properties of mushrooms. Therefore, the specific quantification of these β‐d ‐glucans in mushroom strains is of great biochemical importance. Because published assay methods for these β‐d ‐glucans present some disadvantages, a novel colorimetric assay method for β‐d ‐glucan with alcian blue dye was developed. The complex formation was detected by following the decrease in absorbance in the range of 620 nm and by hypsochromic shift from 620 to 606 nm (～14 nm) in UV‐Vis spectrophotometer. Analysis of variance was used for optimization of the slope of the calibration curve by using the assay mixture containing 0.017% (w/v) alcian blue in 2% (v/v) acetic acid at pH 3.0. The high‐throughput colorimetric assay method on microtiter plates was used for quantification of β‐d ‐glucans in the range of 0–0.8 μg, with a slope of 44.15 × 10^?2 and a limit of detection of 0.017 μg/well. Recovery experiments were carried out by using a sample of Hericium erinaceus, which exhibited a recovery of 95.8% for β‐1,3‐d ‐glucan. The present assay method exhibited a 10‐fold higher sensitivity and a 59‐fold lower limit of detection compared with the published method with congo red. β‐d ‐glucans of several mushrooms strains were isolated from fruiting bodies and mycelia, and they were quantified by this assay method. This assay method is fast, specific, simple, and it can be used to quantify β‐d ‐glucans from other biological sources. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 31:1526–1535, 2015     

Chemiluminescence behaviour of CdTe–potassium permanganate enhanced by sodium hexametaphosphate and sensitized sensing of l‐ascorbic acid

A highly sensitive flow‐injection chemiluminescence (FIA‐CL) method based on the CdTe nanocrystals and potassium permanganate chemiluminescence system was developed for the determination of l ‐ascorbic acid. It was found that sodium hexametaphosphate (SP), as an enhancer, could increase the chemiluminescence (CL) emission from the redox reaction of CdTe quantum dots with potassium permanganate in near‐neutral pH conditions. l ‐Ascorbic acid is suggested as a sensitive enhancer for use in the above energy‐transfer excitation process. Under optimal conditions, the calibration graph of emission intensity against logarithmic l ‐ascorbic acid concentration was linear in the range 1.0 × 10^?9–5.0 × 10^?6 mol/L, with a correlation coefficient of 0.9969 and relative standard deviation (RSD) of 2.3% (n = 7) at 5.0 × 10^?7 mol/L. The method was successfully used to determine l ‐ascorbic acid in vitamin C tablets. The possible mechanism of the chemiluminescence in the system is also discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Luminescence study of monodispersed ZnS nanoparticles

Monodispersed ZnS nanoparticles have been successfully synthesized by a chemical precipitation method in an air atmosphere using polyvinylpyrrolidone (PVP) and sodium hexametaphosphate (SHMP) as surfactants. The synthesized nanoparticles were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FT‐IR), UV–Vis optical absorption and photoluminescence (PL) spectra. Prepared surfactants capped ZnS nanoparticles are highly homogeneous and well dispersed. Optical absorption spectra showed a strong blue shift from the uncapped particles due to the quantum confinement effect. The capped ZnS emission intensity is enhanced than more the uncapped particles. The size of the synthesized particles is around 4–6.5 nm range. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis,effect of capping agents and optical properties of manganese‐doped zinc sulphide nanoparticles

Mn²⁺‐doped ZnS nanoparticles have been successfully synthesized by a chemical precipitation method, using non‐ionic surfactants such as PMMA and PEG. The particles were prepared in an air atmosphere at 80°C. X‐ray diffraction (XRD), transmission electron microscopy (TEM), UV‐visible and photoluminescence (PL) studies were used to investigate the effect of the capping agent on the size, morphology and optical properties of the ZnS–Mn²⁺ nanoparticles. Enhanced PL was observed from the surfactant‐capped ZnS–Mn²⁺ nanoparticles. The PL spectra showed a broad blue emission band in the range 460–445 nm and a Mn²⁺‐related yellow‐orange emission band in the range 581–583 nm. Copyright © 2012 John Wiley & Sons, Ltd.     

Crystallographic and mutational analyses of cystathionine β‐synthase in the H2S‐synthetic gene cluster in Lactobacillus plantarum

Cystathionine β‐synthase (CBS) catalyzes the formation of l ‐cystathionine from l ‐serine and l ‐homocysteine. The resulting l ‐cystathionine is decomposed into l ‐cysteine, ammonia, and α‐ketobutylic acid by cystathionine γ‐lyase (CGL). This reverse transsulfuration pathway, which is catalyzed by both enzymes, mainly occurs in eukaryotic cells. The eukaryotic CBS and CGL have recently been recognized as major physiological enzymes for the generation of hydrogen sulfide (H₂S). In some bacteria, including the plant‐derived lactic acid bacterium Lactobacillus plantarum, the CBS‐ and CGL‐encoding genes form a cluster in their genomes. Inactivation of these enzymes has been reported to suppress H₂S production in bacteria; interestingly, it has been shown that H₂S suppression increases their susceptibility to various antibiotics. In the present study, we characterized the enzymatic properties of the L. plantarum CBS, whose amino acid sequence displays a similarity with those of O‐acetyl‐l ‐serine sulfhydrylase (OASS) that catalyzes the generation of l ‐cysteine from O‐acetyl‐l ‐serine (l ‐OAS) and H₂S. The L. plantarum CBS shows l ‐OAS‐ and l ‐cysteine‐dependent CBS activities together with OASS activity. Especially, it catalyzes the formation of H₂S in the presence of l ‐cysteine and l ‐homocysteine, together with the formation of l ‐cystathionine. The high affinity toward l ‐cysteine as a first substrate and tendency to use l ‐homocysteine as a second substrate might be associated with its enzymatic ability to generate H₂S. Crystallographic and mutational analyses of CBS indicate that the Ala70 and Glu223 residues at the substrate binding pocket are important for the H₂S‐generating activity.     

Screening of l‐histidine‐based ligands to modify monolithic supports and selectively purify the supercoiled plasmid DNA isoform

The growing demand of pharmaceutical‐grade plasmid DNA (pDNA) suitable for biotherapeutic applications fostered the development of new purification strategies. The surface plasmon resonance technique was employed for a fast binding screening of l ‐histidine and its derivatives, 1‐benzyl‐l ‐histidine and 1‐methyl‐l ‐histidine, as potential ligands for the biorecognition of three plasmids with different sizes (6.05, 8.70, and 14 kbp). The binding analysis was performed with different isoforms of each plasmid (supercoiled, open circular, and linear) separately. The results revealed that the overall affinity of plasmids to l ‐histidine and its derivatives was high (K_D > 10⁻⁸ M), and the highest affinity was found for human papillomavirus 16 E6/E7 (K_D = 1.1 × 10⁻¹⁰ M and K_D = 3.34 × 10⁻¹⁰ M for open circular and linear plasmid isoforms, respectively). l ‐Histidine and 1‐benzyl‐l ‐histidine were immobilized on monolithic matrices. Chromatographic studies of l ‐histidine and 1‐benzyl‐l ‐histidine monoliths were also performed with the aforementioned samples. In general, the supercoiled isoform had strong interactions with both supports. The separation of plasmid isoforms was achieved by decreasing the ammonium sulfate concentration in the eluent, in both supports, but a lower salt concentration was required in the 1‐benzyl‐l ‐histidine monolith because of stronger interactions promoted with pDNA. The efficiency of plasmid isoforms separation remained unchanged with flow rate variations. The binding capacity for pDNA achieved with the l ‐histidine monolith was 29‐fold higher than that obtained with conventional l ‐histidine agarose. Overall, the combination of either l ‐histidine or its derivatives with monolithic supports can be a promising strategy to purify the supercoiled isoform from different plasmids with suitable purity degree for pharmaceutical applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Precolumn o‐Phthalaldehyde‐N‐acetyl‐L‐cysteine Derivatization Followed by RP‐HPLC Separation and Fluorescence Detection of Sitagliptin Enantiomers in Rat Plasma

An indirect reversed‐phase high‐performance liquid chromatographic separation and fluorescence detection of sitagliptin enantiomers in rat plasma was developed and validated. Deproteinized rat plasma containing racemic sitagliptin was derivatized with o‐phthalaldehyde and N‐acetyl‐L‐cysteine under alkaline conditions, converted to diastereomers, and separated on a Lichrospher 100 RP‐18e column using 20 mM phosphate buffer and methanol (45:55 v/v) as a mobile phase under isocratic mode of elution at a flow rate of 1.0 mL/min. Fluorescence detection was performed at 330 and 450 nm as excitation and emission wavelengths, respectively. The method was linear in the range of 50–5000 ng/ mL for both enantiomers. The intra‐ and interday accuracy and precision were within the predefined limits of ≤15% at all concentrations. The method was successfully applied to a pharmacokinetic study of sitagliptin after 5 mg/kg oral administration to Wistar rats. Robustness of the method was evaluated using design of experiments. Chirality 25:883–889, 2013. © 2013 Wiley Periodicals, Inc.     

Hydrolytic properties of a thermostable α‐l‐arabinofuranosidase from Caldicellulosiruptor saccharolyticus

Aims: To characterize of a thermostable recombinant α‐l ‐arabinofuranosidase from Caldicellulosiruptor saccharolyticus for the hydrolysis of arabino‐oligosaccharides to l ‐arabinose. Methods and Results: A recombinant α‐l ‐arabinofuranosidase from C. saccharolyticus was purified by heat treatment and Hi‐Trap anion exchange chromatography with a specific activity of 28·2 U mg^?1. The native enzyme was a 58‐kDa octamer with a molecular mass of 460 kDa, as measured by gel filtration. The catalytic residues and consensus sequences of the glycoside hydrolase 51 family of α‐l ‐arabinofuranosidases were completely conserved in α‐l ‐arabinofuranosidase from C. saccharolyticus. The maximum enzyme activity was observed at pH 5·5 and 80°C with a half‐life of 49 h at 75°C. Among aryl‐glycoside substrates, the enzyme displayed activity only for p‐nitrophenyl‐α‐l ‐arabinofuranoside [maximum k_cat/K_m of 220 m(mol l^?1)^?1 s^?1] and p‐nitrophenyl‐α‐l ‐arabinopyranoside. This substrate specificity differs from those of other α‐l ‐arabinofuranosidases. In a 1 mmol l^?1 solution of each sugar, arabino‐oligosaccharides with 2–5 monomer units were completely hydrolysed to l ‐arabinose within 13 h in the presence of 30 U ml^?1 of enzyme at 75°C. Conclusions: The novel substrate specificity and hydrolytic properties for arabino‐oligosaccharides of α‐l ‐arabinofuranosidase from C. saccharolyticus demonstrate the potential in the commercial production of l ‐arabinose in concert with endoarabinanase and/or xylanase. Significance and Impact of the Study: The findings of this work contribute to the knowledge of hydrolytic properties for arabino‐oligosaccharides performed by thermostable α‐l ‐arabinofuranosidase.     

A cold‐adapted leucine dehydrogenase from marine bacterium Alcanivorax dieselolei: Characterization and l‐tert‐leucine production

l ‐tert‐leucine, an intermediate in the synthesis of several chiral drugs, is mainly produced by bioconversion, in which leucine dehydrogenase (LeuDH) is the key enzyme. A novel leudh was obtained from the marine bacterium Alcanivorax dieselolei B‐5(T) by PCR. The gene encoded a novel cold‐adapted LeuDH that showed low similarity (less than 50%) to any known proteins; the highest similarity (42.6%) was found for LeuDH from Bacillus cereus. The cold‐adapted LeuDH showed optimal activity at 30℃ and pH 6.5, and was identified to be extremely cold‐adaptive, retaining over 90% activity in the temperature range of 0–37℃. The enzyme exhibited better stability in weak alkali environment (pH 6.0–8.5) than Thermoactinomyces intermedius LeuDH. The best substrate concentration was established, and LeuDH conversion rate in catalyzing trimethylpyruvic acid to l ‐tert‐leucine was 54.6%. The cold activity and its ability to produce l ‐tert‐leucine with excellent performance of enantiomers of choice make it a promising biocatalyst for industrial application under extreme conditions.