Turn-off Switch Research Articles

Eu3+ functionalized Gd-BTC: Turn-off fluorescent switch for selectively detecting acetone and Fe3+

The detection of Fe3+ ions and acetone in aqueous solution is an important issue in human health and environmental monitoring. In this work, the novel lanthanide metal organic framework (Eu@Gd-BTC-x, x = 0.01, 0.03, 0.05 and 0.07) with excellent luminescence property and stability has been synthesized through in-situ functional Eu3+ ions to partially substitute the metal sites (Gd3+) of Gd-BTC. The luminescent detection experiment revealed that the Eu@Gd-BTC-0.03 exhibited a unique concentration quenching effect to Fe3+ and acetone in water, the results also proved the Eu@Gd-BTC-0.03 had excellent selectivity for Fe3+ among a series of metal ions in aqueous solution with a low detection limit of 6.8 × 10−6 M and high linear fit. Besides, the luminescent selective quenching mechanism of the Eu@Gd-BTC-0.03 is attributed to the energy absorption competition between the luminescence center (Eu3+) and the acetone or Fe3+ ions. Consequently, the Eu@Gd-BTC-0.03 would be employed as a potential luminescent sensor for detecting Fe3+ ions in the future.

Turn-off fluorene-based chemosensor switch to Fe3+: Spectroscopic study, merit parameters, theoretical calculations, and its application in Brazilian ethanol fuel

Development of a new chemosensor is challenging, because it has to deliver sensitiveness, selectiveness, reproducibility, robustness, and the least number of interfering analytes. In this sense coordination chemistry can offer an attractive approach to the problem. Diethyl 2-(9-fluorenyl) malonate (DEFM) was found to be an efficient fluorosensor for Fe3+ ions in ethanolic solutions, showing fluorescence quenching of 99% in the concentration range of 0.1–1.0 μmol L−1, and most importantly, with no effect of interfering ions. Theoretical calculations supported photoelectron transfer (PET) mechanism to explain the fluorescence suppression observed. The method passed several analytical tests and showed the limit of detection and the limit of quantification at 15.56 and 51.85 nmol L−1, respectively. The sensor passed a series of analytical tests and proved to be an attractive low-cost approach for Fe3+ quantification in ethanol fuel.

Dynamic control of the distribution of carbon flux between cell growth and butyrate biosynthesis in Escherichia coli.

Microbial cell factories offer an economic and environmentally friendly method for the biosynthesis of acetyl-CoA-derived chemicals. However, the static control of carbon flux can cause direct and indirect competition for acetyl-CoA between cell growth and chemical biosynthesis, limiting the efficiency of microbial cell factories. Herein, recombinase-based genetic circuits were developed to achieve the optimal distribution of acetyl-CoA between cell growth and butyrate biosynthesis. First, three dynamic devices-a turn-on switch, a turn-off switch, and a recombinase-based inverter (RBI)-were constructed based on Bxb1 recombinase. Then, the turn-on switch was used to dynamically control the butyrate biosynthetic pathway, which directly improved the consumption of acetyl-CoA. Next, the turn-off switch was applied to dynamically control cell growth, which indirectly enhanced the supply of acetyl-CoA. Finally, an RBI was adopted for the dynamic dual control of the distribution of acetyl-CoA between cell growth and butyrate biosynthesis. The final butyrate production rate was increased to 34 g/L, with a productivity of 0.405 g/L/h. The strategy described herein will pave the way for the development of high-performance microbial cell factories for the production of other desirable chemicals. KEY POINTS: • Competition for acetyl-CoA between cell growth and synthesis limits productivity. • Recombinase-based genetic circuits were developed to dynamic control of acetyl-CoA. • Optimal distribution of acetyl-CoA between cell growth and synthesis was achieved.

Rewiring carbon flux in Escherichia coli using a bifunctional molecular switch

The unbalanced distribution of carbon flux in microbial cell factories can lead to inefficient production and poor cell growth. Uncoupling cell growth and chemical synthesis can therefore improve microbial cell factory efficiency. Such uncoupling, which requires precise manipulation of carbon fluxes, can be achieved by up-regulating or down-regulating the expression of enzymes of various pathways. In this study, a dynamic turn-off switch (dTFS) and a dynamic turn-on switch (dTNS) were constructed using growth phase-dependent promoters and degrons. By combining the dTFS and dTNS, a bifunctional molecular switch that could orthogonally regulate two target proteins was introduced. This bifunctional molecular switch was used to uncouple cell growth from shikimic acid and D-glucaric acid synthesis, resulting in the production of 14.33 g/L shikimic acid and the highest reported productivity of D-glucaric acid (0.0325 g/L/h) in Escherichia coli MG1655. This proved that the bifunctional molecular switch could rewire carbon fluxes by controlling target protein abundance.

A Multi-component All-DNA Biosensing System Controlled by a DNAzyme.

We report on a programmable all-DNA biosensing system that centers on the use of a 4-way junction (4WJ) to transduce a DNAzyme reaction into an amplified signal output. A target acts as a primary input to activate an RNA-cleaving DNAzyme, which then cleaves an RNA-containing DNA substrate that is designed to be a component of a 4WJ. The formation of the 4WJ controls the release of a DNA output that becomes an input to initiate catalytic hairpin assembly (CHA), which produces a second DNA output that controls assembly of a split G-quadruplex as a fluorescence signal generator. The 4WJ can be configured to produce either a turn-off or turn-on switch to control the degree of CHA, allowing target concentration to be determined in a quantitative manner. We demonstrate this approach by creating a sensor for E. coli that could detect as low as 50 E. coli cells mL-1 within 85 min and offers an amplified bacterial detection method that does not require a protein enzyme.

A selective and sensitive fluorescent probe for bilirubin in human serum based on europium(III) post-functionalized Zr(IV)-Based MOFs

In the present study, a kind of Eu(III) post-functionalized Zr(IV)-based metal-organic framework (UiO-66(COOH)2, Zr-MOF: Eu3+) was synthesized and utilized as an independently luminescent probe for sensing bilirubin (BR) in human serum, a biomarker of jaundice hepatitis. It can be served as a turn-off fluorescent switch for BR because its red emission from Eu3+ can be easily quenched by BR through a fluorescent resonant energy transfer (FRET) process between BR and its ligands, and as a result, BR is recognized successfully. Particularly, Zr-MOF: Eu3+ has shown many appealing properties, such as high sensitivity, quick response (less than 1 min), broad response window (0–15 μM), and excellent selectivity. Most importantly, a kind of portable test paper based on Zr-MOF: Eu3+ probe has been developed for directly assessing the level of BR in real human serum and further diagnosing bilirubin-related diseases via visually observing the luminescent color variation.

Live-Cell Imaging of Protein Degradation Utilizing Designed Protein-Tag Mutant and Fluorescent Probe with Turn-Off Switch.

Protein degradation plays various roles in cellular homeostasis and signal transduction. Real-time monitoring of the degradation process not only contributes to the elucidation of relevant biological phenomena but also offers a powerful tool for drug discoveries targeting protein degradation. Fluorescent protein labeling with a protein tag and a synthetic fluorescent probe is a powerful technique that enables the direct visualization of proteins of interest in living cells. Although a variety of protein tags and their labeling probes have been reported, techniques for the visualization of protein degradation in living cells remain limited. In order to overcome this limitation, we herein employed a PYP-tag labeling probe with a fluorescence turn-off switch that enables the imaging of protein degradation. Furthermore, we performed a structure-based design of a PYP-tag to stabilize a complex formed by the probe and the protein tag for long-term live-cell imaging. We successfully applied this technique to live-cell imaging of the degradation process of Regnase-1 in response to immunostimulation.

An adjustable dual-emission fluorescent metal-organic framework: Effective detection of multiple metal ions, nitro-based molecules and DMA.

A novel multifunctional Pb(II)-based MOF, [Pb1.5(DBPT)]2·(DMA)3(H2O)4 (1), with excellent chemical stability, was successfully assembled by connecting {Pb2O10} unit with a multi-topic polycarboxylate ligand of 3-(3,5-dicarboxylphenyl)-5-(4-carboxylphenyl)-1-H-1,2,4-triazole (H3DBPT). It exhibits dual fluorescence emissions at 380 nm (λex = 280 nm) and 540 nm (λex = 380 nm), respectively. Through the adjustable dual fluorescence emissions, it could act as a turn-off and turn-on switch for detecting N,N-dimethylacetamide (DMA) molecule. Moreover, Fe3+ ions exert luminescence quenching role on compound 1 at both excitation lengths in water, among which the quenching at λex = 280 nm is of high sensitivity (KSV = 1.2 × 105), and the quenching at λex = 380 nm is of wide-range. The sensing for metal ions of In3+, Zr4+, and Al3+ is also effective at λex = 280 nm, with the KSV constants of 1.6 × 105, 1.6 × 105, and 4.3 × 104, respectively. More importantly, a series of nitroaromatic compounds (TNP, 2,4,6-trinitrophenol; 4-NA, 4-nitroaniline; NB, nitrobenzene) and nitro-based drugs (MNZ, metronidazole; DMZ, dimetridazole) could be detected at both excitation lengths, demonstrating the advantage of broad range response of fluorescence sensing. Thanks to the excellent chemical stability and unusual dual emission luminescence properties for chemical detection of various metal ions, nitro-based molecules and DMA solvent, the Pb-based MOF reported in this work is, therefore, a very promising multi-response sensor.

Functional Molecular System of Bis(pyrazolyl)pyridine Derivatives: Photophysics, Spectroscopy, Computation, and Ion Sensing.

A new series of conjugated donor−π–acceptor type of 2,6-bis(pyrazolyl)pyridine derivatives (compounds IK-(3–9)) have been synthesized via Horner–Wadsworth–Emmons (HWE) reaction, starting from a common phosphonate precursor and diverse donor aromatic aldehydes and characterized by routine spectral analysis including elemental analysis. Compound IK-2, one of the starting precursors, and molecule IK-3, the first member of the donor−π–acceptor series, are additionally characterized by single-crystal X-ray structure determination. Compounds IK-2 and IK-3 are crystallized in P1̅ (triclinic) and P21/c (monoclinic) space groups, respectively. The absorption maxima in the electronic spectra of the title compounds shift mainly due to intramolecular charge transfer (ICT) between different donor (dibutyl and cyclic pyrrolidine) groups and the acceptor moiety [2,6-bis(pyrazolyl) pyridine]. Solution-state emission spectral studies of all these compounds show large solvent sensitive behavior with significant amounts of Stokes shifts. The large solvent dependence of the emission indicates that the excited state is stabilized in more polar solvents due to the ICT. All chromophores exhibit solid-state fluorescence behavior except compound IK-7. The role of the position and nature of the donor functionalities in the conjugated backbone of overall donor moiety of compounds IK-(3–9), on the electronic absorption properties of the title chromophores has been demonstrated, which has further been corroborated by density functional theory (DFT) and time-dependent DFT (TDDFT) computational studies. The emission spectral results of compounds IK-3, IK-5, and IK-7 have also been supported by the DFT and TDDFT calculations. A fluorescence lifetime study on this series also shows that the excited states are stabilized in more polar solvents. Finally, one of the chromophores (chromophore IK-4) in the title series has been shown to act as a selective molecular sensor (turn-off switch) for the Cu(II) ion.

Effect of intermediate capacitance on slow‐scale instability of Cuk power factor correction converter operating in discontinuous capacitor voltage mode

Due to features of near-unity power factor, soft turn-off switching and low switch current stress, Cuk power factor correction (PFC) converter operating in discontinuous capacitor voltage mode (DCVM) has attracted much attention. However, it is found that with the increase of intermediate capacitance, slow-scale instability occurs in voltage mode control (VMC) DCVM Cuk PFC converter. In this study, a simplified model for VMC DCVM Cuk PFC converter is established, upon which the effect of intermediate capacitance on the slow-scale instability and the corresponding bifurcation behaviours are studied by using harmonic balance method and Floquet theory. Furthermore, the stability boundaries in terms of the intermediate capacitance under different load resistance and input voltage are given, which is helpful for parameter design of VMC DCVM Cuk PFC converter. Finally, numerical simulations and experimental results are provided to verify the analysis results.

Self-monitoring of driving speed

In-vehicle data recorders (IVDR) have been found to facilitate safe driving and are highly valuable in accident analysis. Nevertheless, it is not easy to convince drivers to use them. Part of the difficulty is related to the “Big Brother” concern: installing IVDR impairs the drivers' privacy. The “Big Brother” concern can be mitigated by adding a turn-off switch to the IVDR. However, this addition comes at the expense of increasing speed variability between drivers, which is known to impair safety. The current experimental study examines the significance of this negative effect of a turn-off switch under two experimental settings representing different incentive structures: small and large fines for speeding. 199 students were asked to participate in a computerized speeding dilemma task, where they could control the speed of their “car” using “brake” and “speed” buttons, corresponding to automatic car foot pedals. The participants in two experimental conditions had IVDR installed in their “cars”, and were told that they could turn it off at any time. Driving with active IVDR implied some probability of “fines” for speeding, and the two experimental groups differed with respect to the fine’s magnitude, small or large. The results indicate that the option to use IVDR reduced speeding and speed variance. In addition, the results indicate that the reduction of speed variability was maximal in the small fine group. These results suggest that using IVDR with gentle fines and with a turn-off option maintains the positive effect of IVDR, addresses the “Big Brother” concern, and does not increase speed variance.

A cost effective voltage sag compensator for distribution system

In a large power system voltage sag is considered to be the most common and critical power quality (PQ) issue. With the advent of power-semiconductor devices many PQ devices came into existence. Dynamic voltage restorer (DVR) and distribution static compensator (D-STATCOM) are normally employed as voltage sag mitigation devices. This paper presents a low cost alternative for voltage sag compensation. The proposed device does not require any energy storage device and has only one gate turn-off switch per phase for pulse width modulation, unlike DVR and D-STATCOM that employ DC-to-AC converter topology. Simulation analysis of three phase compensator is performed in MATLAB/Simulink environment and the total harmonic distortion of load voltage when the compensator is functioning during disturbance condition is within the acceptable limits.

Membrane-Bound Steel Factor Induces More Persistent Tyrosine Kinase Activation and Longer Life Span of c-kit Gene-Encoded Protein Than Its Soluble Form

Alternative splicing of exon 6 results in the production of two isoforms of Steel factor (SLF): the membrane-bound and soluble forms. To investigate differences in the kinetics of c-kit tyrosine kinase activated by these two isoforms, we used a stromal cell line (SI/SI4) established from SI/SI homozygous murine embryo fetal liver and its stable transfectants containing either hSCF248 cDNA (including exon 6; secreted form) or hSCF220 cDNA (lacking exon 6; membrane-bound form) as the source of each isoform. Interaction of factor dependent myeloid cell line MO7e with stromal cells producing either isoform resulted in activated c-kit tyrosine kinase and induction of the same series of tyrosine phosphorylated cellular proteins in MO7e cells. However, SI4-h220 (membrane-bound form) induced more persistent activation of c-kit kinase than SI4-h248 (soluble form) did. Flow cytometric analysis and pulse-chase studies using [35S]methionine showed that SI4-h248 induced rapid downmodulation of cell-surface c-kit expression and its protein degradation in MO7e cells, whereas SI4-h220 induced more prolonged life span of c-kit protein. Addition of soluble recombinant human SLF to SI4-h220 cultures enhanced reduction of cell-surface c-kit expression and its protein degradation. Because the kinetics of c-kit inactivation strikingly fits with the protein degradation rates of c-kit under the conditions described above, rapid proteolysis of c-kit protein induced by soluble SLF stimulation may function as a "turn-off switch" for activated c-kit kinase.

A Cost Effective Short Circuit Proof Light Dimmer

Power in conventional light dimmer circuits is controlled by TRIACS. They require a serial inductor for EMI filtering and a fuse to protect them against overload and short circuit.This paper describes a soft dimmer based on the use of an IGBT as a turn-off controllable switch. This allows to control the current switching slope, cancelling by the way, the serial inductor and its associated acoustical noise.

The GTO — a new power switch

The gate turn-off switch (GTO) offers unique operational advantages for certain applications. This article describes the development, characteristics and design of the GTO

Thyristor Semiconductor Components Today

Recent progress in semiconductor controlled rectifier components (the major type of thyristor) will be reviewed. As a result of advances in dynamic characteristics, SCRs are now applicable to equipments operating under severe transient conditions and at frequencies ranging into the ultrasonic spectrum. A number of other types of thyristors have been developed for special control and static power conversion applications. Among the devices described are the 4-layer diode, the light-activated SCR, the gate turn-off switch, the silicon controlled switch, and both the diode and the triode bidirectional thyristors. While lagging behind the SCR in acceptance, these newer types of thyristors can be expected to have an equally profound impact on the power conversion and control fields.