Differential interaction of erythromycin with cytochromes P450 3A1/2 in the endoplasmic reticulum: a CO flash photolysis study

The kinetics of CO binding to cytochromes P450, measured by the flash photolysis technique, were used to probe the interaction of erythromycin with cytochromes P450 in rat liver microsomes. Addition of erythromycin generates substrate difference spectra using microsomes from rats treated with phenobarbital or dexamethasone but not from untreated rats, showing that it binds to P450s induced by these agents. In contrast, erythromycin and/or a monoclonal antibody to P450 3A1/2 accelerated CO binding to microsomes from rats treated with phenobarbital but had no effect on microsomes from untreated or dexamethasone-treated rats. Based on the differential amounts and inducibilities of the P450 3A1 and 3A2 forms in these microsomal samples, these results indicate that erythromycin increased the rate for P450 3A2 but not P450 3A1. The divergent effects of erythromycin on these P450s, which exhibit 89% sequence similarity, were consistent with a model of the P450 substrate binding site in which erythromycin forms a more rigid complex with P450 3A1 than P450 3A2. These results demonstrate the sensitivity of P450 conformation/dynamics to substrate binding, and show that CO binding kinetics can distinguish among closely related P450s in a microsomal environment.     

Tunable morphology from 2D to 3D in the formation of hierarchical architectures from a self-assembling dipeptide: thermal-induced morphological transition to 1D nanostructures

Construction of complex three-dimensional (3D) architectures through hierarchical self-assembly of peptide molecules has become an attractive approach of fabricating multifunctional advanced materials due to their various potential applications in bionanotechnology. This paper describes the tunable formation of flower-like 3D hierarchical architectures of intricate morphology from a simple self-assembling dipeptide phenylalanine–tyrosine with a facile preparative method by applying a range of voltages through a drop of peptide solution. The fine-tuning of voltages and their application time enable to produce morphological changes of the microstructures from 2D to 3D and also control their formation. The morphology has been characterized by the gradual change in the height-to-diameter ratio of the microstructures with change in the applied voltages. Moreover, these microstructures show significant thermal stability over a wide range of temperatures, whereas adequately high temperature promotes the morphological transformation of the microstructures into different types of ultrathin 1D nanostructures such as nanowires, nanofibrils, etc. Furthermore, we have suggested a possible growth model for the fabrication of unique hierarchical architectures through diffusion-limited aggregation mechanism.     

Tunable Reverse‐Biased Graphene/Silicon Heterojunction Schottky Diode Sensor

A new chemical sensor based on reverse‐biased graphene/Si heterojunction diode has been developed that exhibits extremely high bias‐dependent molecular detection sensitivity and low operating power. The device takes advantage of graphene's atomically thin nature, which enables molecular adsorption on its surface to directly alter graphene/Si interface barrier height, thus affecting the junction current exponentially when operated in reverse bias and resulting in ultrahigh sensitivity. By operating the device in reverse bias, the work function of graphene, and hence the barrier height at the graphene/Si heterointerface, can be controlled by the bias magnitude, leading to a wide tunability of the molecular detection sensitivity. Such sensitivity control is also possible by carefully selecting the graphene/Si heterojunction Schottky barrier height. Compared to a conventional graphene amperometric sensor fabricated on the same chip, the proposed sensor demonstrated 13 times higher sensitivity for NO₂ and 3 times higher for NH₃ in ambient conditions, while consuming ～500 times less power for same magnitude of applied voltage bias. The sensing mechanism based on heterojunction Schottky barrier height change has been confirmed using capacitance‐voltage measurements.     

Reduced trapping effects and improved electrical performance in buried-gate 4H-SiC MESFETs

Surface effects on the current instability of 4H-SiC MESFETs were studied by comparing different surface structures. The current instability phenomenon was illustrated by bias sweeping methods and current recovery time measurements. A reduction in the current instability was observed for gate-recessed and buried-gate devices compared to the nonrecessed and channel-recessed devices. In addition, the buried-gate devices were found to have higher current density and breakdown voltage compared to the gate-recessed devices, resulting from their shorter effective gate length and lower electric field distribution under the gate, respectively. With high saturation current, high breakdown voltage, and much reduced surface effects, the buried-gate structure is a candidate for high-power SiC MESFETs.     

Slow transients observed in AlGaN/GaN HFETs: effects of SiN/sub x/ passivation and UV illumination

Very slow drain current and surface potential transients have been observed in AlGaN/GaN heterostructure field effect transistors that are subjected to high bias stress. Simultaneous measurements of drain current and surface potential indicate that large change in surface potential after stress is responsible for the reduction in drain current in these devices. Measurements of surface potential profile from the gate edge toward the drain as a function of time indicate that surface potential changes occur mostly near the gate. It is proposed that the surface potential changes are caused by electrons which tunnel from the gate under high bias stress and get trapped at the surface states near the gate. Passivation of the surface with SiN/sub x/ reduces the transient magnitudes to a large extent. This correlates with a large improvement in microwave power performance in these devices after passivation. UV illumination of these devices totally eliminates the drain current and surface potential transients.     

Polymerization of Non-Drying Oils in Azeotropic Salt Bath

Groundnut and castor oils were passed through an azeotropic salt bath to yield heterogeneous masses. Both the oils yield acetone-soluble and -insoluble fractions. In both the cases acetone-insoluble fractions show the presence of benzenoid rings, ether linkages and oxiranes. The average molecular weights of acetone-soluble fractions vary from 901 to 936 in the case of groundnut oils and from 974 to 979 with castor oils. This shows that these oils are capable of polymerization by the present method.     

Design and self-assembly of a leucine-enkephalin analogue in different nanostructures: application of nanovesicles

An opioid (leucine-enkephalin) conformational analogue forms diverse nanostructures such as vesicles, tubes, and organogels through self-assembly. The nanovesicles encapsulate the natural hydrophobic drug curcumin and allow the controlled release through cation-generated porogens in membrane mimetic solvent.     

Influence of 4H-SiC semi-insulating substrate purity on SiC metal-semiconductor field-effect transistor performance

The performances of silicon carbide (SiC) metal-semiconductor field-effect transistors (MESFETs) fabricated on conventional V-doped semi-insulating substrates and new V-free semi-insulating substrates have been compared. The V-free 4H-SiC substrates were confirmed by secondary ion mass spectrometry (SIMS). X-ray topography revealed significantly fewer micropipes and low-angle boundaries in V-free semi-insulating substrates than in conventional V-compensated substrates. Deep-level transient spectroscopy (DLTS) indicated that the spectra signals observed in conventional V-doped substrates were either reduced or disappeared in V-free substrates. The intrinsic deep levels in V-free substrates to make semi-insulating properties were also observed in DLTS spectra. Under various DC and RF stresses, SiC MESFETs fabricated on new V-free semi-insulating substrates showed superior device performance and stability.     

Growth direction modulation and diameter-dependent mobility in InN nanowires

Diameter-dependent electrical properties of InN nanowires (NWs) grown by chemical vapor deposition have been investigated. The NWs exhibited interesting properties of coplanar deflection at specific angles, either spontaneously, or when induced by other NWs or lithographically patterned barriers. InN NW-based back-gated field effect transistors (FETs) showed excellent gate control and drain current saturation behaviors. Both NW conductance and carrier mobility calculated from the FET characteristics were found to increase regularly with a decrease in NW diameter. The observed mobility and conductivity variations have been modeled by considering NW surface and core conduction paths.