RESUMEN
Introduction: Antimicrobial peptides (AMPs) play an important role in defending against the attack of pathogenic microorganisms. Among them, the proline-rich antibacterial peptides (PrAMPs) have been attracting close attention due to their simple structure, strong antibacterial activity, and low cell toxicity. OaBac5mini is an active fragment of the sheep-derived OaBac5 belonging to the PrAMPs family. Methods: In this study, the antibacterial activity of OaBac5mini was investigated by testing the MICs against different stains of E. coli and S. aureus as well as the time-kill curve. The bactericidal mechanism was explored by determining the effect of OaBac5mini on the cell membrane. The stability and biosafety were also evaluated. Results: The susceptibility test demonstrated that OaBac5mini showed potent antibacterial activity against the multidrug-resistant (MDR) E. coli isolates. It is noticeable that the absence of inner membrane protein SbmA in E. coli ATCC 25922 caused the MIC of OaBac5mini to increase 4-fold, implying OaBac5mini can enter into the cytoplasm via SbmA and plays its antibacterial activity. Moreover, the antibacterial activity of OaBac5mini against E. coli ATCC 25922 was not remarkably affected by the serum salts except for CaCl2 at a physiological concentration, pH, temperature, repeated freeze-thawing and proteases (trypsin < 20 µg/mL, pepsin or proteinase K). Time-kill curve analysis showed OaBac5mini at the concentration of 200 µg/mL (8 × MICs) could effectively kill E. coli ATCC 25922 after co-incubation for 12 h. In addition, OaBac5mini was not hemolytic against rabbit red blood cells and also was not cytotoxic to porcine small intestinal epithelial cells (IPEC-J2). Bioinformatic analysis indicated that OaBac5mini is a linear peptide with 8 net positive charges. Furthermore, OaBac5mini significantly increased the outer membrane permeability and impaired the inner membrane integrity and ultrastructure of E. coli ATCC25922. Conclusion: OaBac5mini is a stable and potent PrAMP that kills E. coli by two different modes of action - inhibiting intracellular target(s) and damaging cell membrane.
RESUMEN
The nonlinear governing equations on the coupling between electromechanical fields and charge carrier in a thermal equilibrium piezoelectric pn junction subjected to asymmetric mechanical loads are established in this article. Effect of mechanical loads on the basic physical parameters of a piezoelectric pn junction, such as potential barrier region width, contact potential difference, electric potential, and carrier concentrations are analyzed numerically. Results show that asymmetry compressive stresses exert more influence on the movement of the potential barrier region's boundary and the migration of carrier compare to asymmetry tensile stresses. It is also found that asymmetry compressive stresses lead to a pn junction with a thin potential barrier region which enhances the chance of carrier's passing through of potential barrier region. The obtained results are useful in reducing the disadvantage of capacitance on rectification characteristic and can be used to tune the I - V characteristic of the pn junction working with bias voltage.
RESUMEN
A model is proposed to study the diffusion of non-equilibrium minority carriers under the influence of a piezo potential and to calculate the corresponding current-voltage (I-V) characteristics of a piezoelectric p-n junction exposed to mechanical loading. An effective solution to describe this non-equilibrium process has been put forward including two concepts: the influence of prestress loading on p-n junctions in a quasi-electrostatic thermal equilibrium and the perturbation of small fields superposed on the obtained quasi-electrostatic solutions. A few useful results are obtained through this loaded p-n junction model. Under a forward-bias voltage, a tensile (compressive) loading raises (reduces) the potential barrier of the space charge zone (SCZ), i.e., produces an equivalent reverse- (forward-) electric voltage on the SCZ. When a piezoelectric p-n junction is exposed to a reverse-bias voltage, the current density monotonically decreases with increasing reverse voltage and gradually approaches saturation. A bigger tensile (compressive) loading produces a smaller (larger) saturation current density. The appearance of an equivalent voltage on the SCZ induced by prestress indicates that the performance of a p-n junction with the piezo effect can be effectively tuned and controlled by mechanical loadings. Meanwhile, numerical results show that a loading location closer to the SCZ produces a stronger effect on the I-V characteristics of a piezoelectric p-n junction, implying that the tuning effect of mechanical loadings depends on how much influence of the deformation-induced electric field can reach the SCZ. Furthermore, it is also found that the deformation-induced electric field becomes weak with increasing doping because the higher doping is corresponding to the stronger electric leakage. Thus, the higher mechanical tuning performance on higher doped piezoelectric p-n junctions requires the prestress loadings to be applied closer to the interface of p- and n-zone. This study on a non-equilibrium process of piezoelectric p-n junctions has significance for piezotronics.
RESUMEN
In piezoelectric semiconductors, electric fields drive carriers into motion/redistribution, and in turn the carrier motion/redistribution has an opposite effect on the electric field itself. Thus, carrier drift in a piezoelectric semiconducting structure is essentially nonlinear unless the induced fluctuation of carrier concentration is very small. In this paper, the nonlinear governing equation of carrier concentration was established by coupling both piezoelectric effect and semiconduction. A nonlinear carrier-drift effect on the performance of a ZnO nanogenerator was investigated in detail and it was elucidated that carrier motion/redistribution occurs in the ZnO nanowire (ZNW) cross section while there is no carrier motion in the axial direction. At the same time, we noted that the amplitude of boundary electric charge grows with increasing deformation, but the peaks of boundary electric charge do not appear at the cross-section endpoints. Thus, in order to effectively improve the performance of the ZNW nanogenerator, the effect of electrode configuration on the piezoelectric potential difference and output power was analyzed in detail. The electrode size for the optimal performance of a ZnO nanowire generator was proposed. This analysis that couples electromechanical fields and carrier concentration as a whole has some referential significance to piezotronics.