Yanhua Hou

Enhanced dielectric properties of PVDF-HFP/BaTiO3-nanowire composites induced by interfacial polarization and wire-shape

Polymer based composites with high dielectric constant were successfully fabricated using BaTiO3 nanowires with high aspect ratio as inorganic filler and PVDF-HFP as polymer matrix. PVDF-HFP/BaTiO3 nanoparticles composites were also prepared as a contrast. The BaTiO3 nanowires were synthesized via one-step hydrothermal method. The BaTiO3 nanowires and its two types of composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. For the composites, breakdown strength measurements, tensile tests and broadband dielectric spectroscopy analyses were also carried out. The results show that the two types of fillers are homogeneously dispersed in the matrix. The dielectric constant of composites filled by BaTiO3 nanowires is larger than that filled by BaTiO3 nanoparticles at the same content. Stronger interfacial polarization was found in PVDF-HFP/BaTiO3 nanowire composites. Two theoretical models were employed to predict the dielectric constants of composites, and the experimental data were consistent with the estimated trend. The enhanced dielectric properties of PVDF-HFP/BaTiO3 nanowire composites are attributed to the superior interfacial polarization and high aspect ratio of BaTiO3 nanowires.

Giant piezoelectric properties of BZT–0.5BCT thin films induced by nanodomain structure

Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BZT–0.5BCT) thin films were prepared from two ceramics targets, Ba(Zr0.2Ti0.8)O3 and (Ba0.7Ca0.3)TiO3, using dual-magnetron sputtering, and a LaNiO3 (LNO) seed layer was introduced between the film and Pt(111)/Ti/SiO2/Si substrates via a sol–gel technique. Domain structures were observed on the thin films by piezoelectric force microscopy (PFM), and then an autocorrelation function technique was applied to analyze the obtained PFM images. The mean sizes of the domains of the BZT–0.5BCT and (001)-oriented BZT–0.5BCT/LNO thin films are 69.2 nm and 151 nm at room temperature respectively. On the basis of our results, it is proven that the nanodomains have a large effect on the piezoelectricity of the thin films for MPB composition: the converse piezoelectric coefficient d33 is 258 pm V−1 for BZT–0.5BCT thin films and 122 pm V−1 for BZT–0.5BCT/LNO thin films. It is worth noting that not only the crystal orientation, but also the domain structures play critical roles in the piezoelectricity for the BZT–0.5BCT thin films. Furthermore, (001)-oriented BZT–0.5BCT/LNO thin films exhibit excellent dielectric properties and the dielectric constant (e ∼ 1046) is dramatically increased compared with the BZT–0.5BCT thin films (e ∼ 168). The C–V results indicate that both of the thin films are ferroelectric in nature.

Molecular cloning, expression and enzymatic characterization of glutathione S-transferase from Antarctic sea-ice bacteria Pseudoalteromonas sp. ANT506

A glutathione S-transferase (GST) gene from Antarctic sea-ice bacteria Pseudoalteromonas sp. ANT506 (namely PsGST), was cloned and expressed in Escherichia coli. The open reading frame of PsGST comprised 654 bp encoding a protein of 217 amino acids with a calculated molecular size of 24.3 kDa. The rPsGST possesses the conserved amino acid defining the binding sites of glutathione (G-site) and substrate binding pocket (H-site) in GST N_3 family. PsGST was expressed in E. coli and the recombinant PsGST (rPsGST) was purified by Ni-affinity chromatography with a high specific activity of 74.21 U/mg. The purified rPsGST showed maximum activity at 40 °C and exhibited 14.2% activity at 0 °C. It was completely inactivated at 50 °C for 40 min. These results indicated that rPsGST was a typical cold active GST with low thermostability. The enzyme was little affected by H2O2 and Triton X-100, and 50.2% of the remaining activity was detected in the presence of high salt concentrations (2M NaCl). The enzymatic Km values for CDNB and GSH was 0.22 mM and 1.01 mM, respectively. These specific enzyme properties may be related to the survival environment of Antarctic sea ice bacteria.

Self-polarization induced by lattice mismatch and defect dipole alignment in (001) BaTiO3/LaNiO3 polycrystalline film prepared by magnetron sputtering at low temperature

Upward self-polarization phenomenon was observed and studied in the highly (001)-oriented BaTiO3/LaNiO3 polycrystalline film, and the polycrystalline film was in situ prepared by radio frequency magnetron sputtering at 400 °C without post treatment. The low temperature crystallization and high orientation of BaTiO3 polycrystalline film may be caused by the better compatibility between BaTiO3 and LaNiO3. The upward self-polarization phenomena was characterized by piezoelectric force microscopy (PFM), and the coupling effects of low crystallization temperature, high (001) orientation, large compressive strain gradient and preferred orientation of defect dipoles are considered to be responsible for the upward self-polarization phenomena in the BaTiO3/LaNiO3 polycrystalline film during the cooling process, especially when ferroelectric domains nucleate and grow near 120 °C.

Cloning, expression and biochemical characterization of recombinant superoxide dismutase from Antarctic psychrophilic bacterium Pseudoalteromonas sp. ANT506.

In this study, a superoxide dismutase gene (PsSOD) from Pseudoalteromonas sp. ANT506 was cloned and over expressed in Escherichia coli. The PsSOD has an open reading frame of 582 bp with a putative product of 193 amino acid residue and an estimated molecular size of 21.4 kDa. His‐tagged PsSOD was subsequently purified 12.6‐fold by Ni‐affinity chromatography and the yield of 22.9%. The characterization of the purified rPsSOD exhibited maximum activity at 30 °C and pH 8.0. The enzyme exhibited 13.9% activity at 0 °C and had high‐thermo lability at higher than 50 °C. rPsSOD exhibited well capability to 2.5 M NaCl (62.4%). These results indicated that rPsSOD exhibited special catalytic properties.

Cloning, Expression, Purification, and Characterization of Glutaredoxin from Antarctic Sea-Ice Bacterium Pseudoalteromonas sp. AN178

Glutaredoxins (Grxs) are small ubiquitous redox enzymes that catalyze glutathione-dependent reactions to reduce protein disulfide. In this study, a full-length Grx gene (PsGrx) with 270 nucleotides was isolated from Antarctic sea-ice bacterium Pseudoalteromonas sp. AN178. It encoded deduced 89 amino acid residues with the molecular weight 9.8 kDa. Sequence analysis of the amino acid sequence revealed the catalytic motif CPYC. Recombinant PsGrx (rPsGrx) stably expressed in E. coli BL21 was purified to apparent homogeneity by Ni-affinity chromatography. rPsGrx exhibited optimal activity at 30°C and pH 8.0 and showed 25.5% of the activity at 0°C. It retained 65.0% of activity after incubation at 40°C for 20 min and still exhibited 37.0% activity in 1.0 M NaCl. These results indicated that rPsGrx was a typical cold active protein with low thermostability.

Highly sensitive and selective fluorescence detection of Hg(II) ions based on R-phycoerythrin from Porphyra yezoensis

R-Phycoerythrin (R-PE) is a kind of natural fluorescent protein from marine Porphyra yezoensis. A highly sensitive and selective fluorimetric method has been developed to detect Hg2+ ions utilizing R-PE as a fluorescent probe. R-PE could respond selectively to Hg2+ ions among a series of metal ions. The reaction mechanism was investigated through UV-vis, fluorescence microscope imaging and fluorescence measurements. It was demonstrated that the interaction between the R-PE fluorescent probe and Hg2+ ions would cause fluorescence quenching. Besides, there was a linear relationship between R-PE fluorescence intensities and Hg2+ concentrations. A novel method was thus explored to detect Hg2+ ions with high sensitivity, selectivity, and a broad linear range of 0.0010–25.0 μM, which could allow for Hg2+ ions down to 0.0130 μM with a relative standard deviation of about 1.60%. Additionally, the method was successfully applied to detect Hg2+ ions in diverse water samples, showing the appropriate rates of recovery between 92.0% and 108.0%. This highly sensitive and selective natural green fluorescent probe of R-PE should have huge potential applications for detecting Hg2+ ions in diverse environments.

Optimization of cold-adapted lysozyme production from the psychrophilic yeast Debaryomyces hansenii using statistical experimental methods.

UNLABELLED Statistical experimental designs were employed to optimize culture conditions for cold-adapted lysozyme production of a psychrophilic yeast Debaryomyces hansenii. In the first step of optimization using Plackett-Burman design (PBD), peptone, glucose, temperature, and NaCl were identified as significant variables that affected lysozyme production, the formula was further optimized using a four factor central composite design (CCD) to understand their interaction and to determine their optimal levels. A quadratic model was developed and validated. Compared to the initial level (18.8 U/mL), the maximum lysozyme production (65.8 U/mL) observed was approximately increased by 3.5-fold under the optimized conditions. PRACTICAL APPLICATION Cold-adapted lysozymes production was first optimized using statistical experimental methods. A 3.5-fold enhancement of microbial lysozyme was gained after optimization. Such an improved production will facilitate the application of microbial lysozyme. Thus, D. hansenii lysozyme may be a good and new resource for the industrial production of cold-adapted lysozymes.

A glutathione peroxidase from Antarctic psychrotrophic bacterium Pseudoalteromonas sp. ANT506: Cloning and heterologous expression of the gene and characterization of recombinant enzyme

ABSTRACT A glutathione peroxidase (GPx) gene, designated as PsGPx, was cloned from Antarctic psychrotrophic bacterium Pseudoalteromonas sp. ANT506 and expressed in Escherichia coli. The full-length PsGPx contained a 585-bp encoding 194 amino acids with predicted molecular masses of approx. 21.7 kDa. Multiple sequence alignments revealed that PsGPx belonged to the thioredoxin-like superfamily. PsGPx was heterologously overexpressed in E. coli, purified and characterized. The maximum catalytic temperature and pH value for recombinant PsGPx (rPsGPx) were 30°C and pH 9.0, respectively. rPsGPx retained 45% of the maximum activity at 0°C and exhibited high thermolability with a half-life of approx. 40 min at 40°C. In addition, the enzymatic activity of rPsGPx was still manifested under 3 M NaCl. The Km and Vmax values of the recombinant enzyme using GSH and H2O2 as substrates were 1.73 mM and 16.28 nmol/mL/min versus 2.46 mM and 21.50 nmol/mL/min, respectively.

A Novel Cold-Adapted Leucine Dehydrogenase from Antarctic Sea-Ice Bacterium Pseudoalteromonas sp. ANT178

l-tert-leucine and its derivatives are useful as pharmaceutical active ingredients, in which leucine dehydrogenase (LeuDH) is the key enzyme in their enzymatic conversions. In the present study, a novel cold-adapted LeuDH, psleudh, was cloned from psychrotrophic bacteria Pseudoalteromonas sp. ANT178, which was isolated from Antarctic sea-ice. Bioinformatics analysis of the gene psleudh showed that the gene was 1209 bp in length and coded for a 42.6 kDa protein containing 402 amino acids. PsLeuDH had conserved Phe binding site and NAD+ binding site, and belonged to a member of the Glu/Leu/Phe/Val dehydrogenase family. Homology modeling analysis results suggested that PsLeuDH exhibited more glycine residues, reduced proline residues, and arginine residues, which might be responsible for its catalytic efficiency at low temperature. The recombinant PsLeuDH (rPsLeuDH) was purified a major band with the high specific activity of 275.13 U/mg using a Ni-NTA affinity chromatography. The optimum temperature and pH for rPsLeuDH activity were 30 °C and pH 9.0, respectively. Importantly, rPsLeuDH retained at least 40% of its maximum activity even at 0 °C. Moreover, the activity of rPsLeuDH was the highest in the presence of 2.0 M NaCl. Substrate specificity and kinetic studies of rPsLeuDH demonstrated that l-leucine was the most suitable substrate, and the catalytic activity at low temperatures was ensured by maintaining a high kcat value. The results of the current study would provide insight into Antarctic sea-ice bacterium LeuDH, and the unique properties of rPsLeuDH make it a promising candidate as a biocatalyst in medical and pharmaceutical industries.