Browsing by Author "Yu, Peng"

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    Characterization and application of a periplasmic protein releasing system for extracellular recombinant protein production in Escherichia coli
    (1993) Yu, Peng; San, Ka-Yiu
    Escherichia coli is commonly used as a host in the production of high value therapeutic proteins. However, one major drawback associated with E. coli being a host is the intracellular location of product proteins. As a result, mechanical cell disruption is commonly employed in biotechnology industry for protein release. Unfortunately, mechanical disintegration always contaminates the target protein with other cellular substances. On the other hand, progress in the study of protein translocation across membrane often allows the transport of proteins from the cytoplasm to the periplasm. However, the outer membrane still presents a barrier for their extracellular release. The objective of this work is to bridge the gap between protein translocation and extracellular protein release. The main focus is to characterize a periplasmic protein release system and to apply the system to different processes for extracellular protein production. Bacteriocin Release Protein (BRP) and glycine were the two systems studied using a-amylase as the model protein. Both agents were shown to be effective in periplasmic protein release. When used alone in a batch fermentor, BRP released 41% of the periplasmic a-amylase extracellularly without causing substantial cell lysis. Similarly, glycine achieved a 45% protein release. Synergistic combination of BRP and glycine resulted in further increase in a-amylase release. At an optimal combination, 78% of a-amylase was released. Application of the release system for continuous extracellular protein production was successful. A maximum productivity of 8.3 units/ml/hr was obtained, of which one third was in the extracellular broth. Mathematical simulation suggested that higher expression levels of a-amylase at slower growth rates is mainly due to a higher plasmid copy number. Incorporation of hollow fiber cartridges into a chemostat process allowed continuous production of cell-free proteins as well as retention of recombinant cells. At an optimal dilution rate, 42% of a-amylase was produced in a cell-free form. Substitution of the Amp$\sp{\rm r}$ gene in pBR322-amy with a Km$\sp{\rm r}$ gene in an attempt to improve the performance of the release system resulted in a higher accumulation of a-amylase in the cytoplasm. The observation demonstrated that antibiotic markers are important parameters in a-amylase translocation and distribution.
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    Metallic 1T-TiS2 nanodots anchored on a 2D graphitic C3N4 nanosheet nanostructure with high electron transfer capability for enhanced photocatalytic performance
    (Royal Society of Chemistry, 2017) Liu, Yang; She, Xiaojie; Zhang, Xiaoni; Liang, Chenglu; Wu, Jingjie; Yu, Peng; Nakanishi, Yusuke; Xie, Banghu; Xu, Hui; Ajayan, Pulickel M.; Yang, Wei
    Photocatalysis is one of the most promising technologies for solar energy conversion. With the development of photocatalysis technology, the creation of low-dimensional structure photocatalysts with improved properties becomes more and more important. Metallic 1T-TiS2 nanodots with a low-dimensional structure were introduced into environmentally friendly two-dimensional g-C3N4 (2D-C3N4) nanosheets by a solvothermal method. It was found that the ultrathin TiS2 nanodots were uniformly anchored on the surface of the 2D-C3N4. The effective suppression of electron–hole recombination was realized due to the addition of the intrinsic metallic property of 1T-TiS2 in the prepared nanocomposite. The 5 wt% TiS2/2D-C3N4 nanocomposite exhibited the best photocatalytic performance and the degradation rate towards RhB was ca. 95% in 70 min, which showed an improvement of ca. 30% in comparison with 2D-C3N4. The results indicate that the obtained TiS2/2D-C3N4 nanocomposite is a promising photocatalyst for practical applications.
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    Room-temperature ferroelectricity in CuInP2S6 ultrathin flakes
    (Springer Nature, 2016) Liu, Fucai; You, Lu; Seyler, Kyle L.; Li, Xiaobao; Yu, Peng; Lin, Junhao; Wang, Xuewen; Zhou, Jiadong; Wang, Hong; He, Haiyong; Pantelides, Sokrates T.; Zhou, Wu; Sharma, Pradeep; Xu, Xiaodong; Ajayan, Pulickel M.; Wang, Junling; Liu, Zheng
    Two-dimensional (2D) materials have emerged as promising candidates for various optoelectronic applications based on their diverse electronic properties, ranging from insulating to superconducting. However, cooperative phenomena such as ferroelectricity in the 2D limit have not been well explored. Here, we report room-temperature ferroelectricity in 2D CuInP2S6 (CIPS) with a transition temperature of ~320 K. Switchable polarization is observed in thin CIPS of ~4 nm. To demonstrate the potential of this 2D ferroelectric material, we prepare a van der Waals (vdW) ferroelectric diode formed by CIPS/Si heterostructure, which shows good memory behaviour with on/off ratio of ~100. The addition of ferroelectricity to the 2D family opens up possibilities for numerous novel applications, including sensors, actuators, non-volatile memory devices, and various vdW heterostructures based on 2D ferroelectricity.