Noise-induced coherent switch

Taking the famous genetic toggle switch as an example, we numerically investigated the effect of noise on bistability. We found that extrinsic noise resulting from stochastic fluctuations in synthesis and degradation rates and from the environmental fluctuation in gene regulatory processes can induce coherent switch, and that there is an optimal noise intensity such that the noise not only can induce this switch, but also can amplify a weak input signal. In addition, we found that the intrinsic noise introduced through the Poisson τ-leap algorithm cannot induce such a switch.     

Photochemically and Thermally Driven Full‐Color Reflection in a Self‐Organized Helical Superstructure Enabled by a Halogen‐Bonded Chiral Molecular Switch

Supramolecular approaches toward the fabrication of functional materials and systems have been an enabling endeavor. Recently, halogen bonding has been harnessed as a promising supramolecular tool. Herein we report the synthesis and characterization of a novel halogen‐bonded light‐driven axially chiral molecular switch. The photoactive halogen‐bonded chiral switch is able to induce a self‐organized, tunable helical superstructure, that is, cholesteric liquid crystal (CLC), when doped into an achiral liquid crystal (LC) host. The halogen‐bonded switch as a chiral dopant has a high helical twisting power (HTP) and shows a large change of its HTP upon photoisomerization. This light‐driven dynamic modulation enables reversible selective reflection color tuning across the entire visible spectrum. The chiral switch also displays a temperature‐dependent HTP change that enables thermally driven red, green, and blue (RGB) reflection colors in the self‐organized helical superstructure.     

High-temperature dielectric switch and second harmonic generation integrated in a stimulus responsive material

Stimulus re s ponsive materials can provide a variety of desirable properties in one equipment unit,such as optoelectronic devices,data communications,actuators,memories,sensors and capacitors.However,it remains a large challenge to design such stimulus responsive materials,especially functional materials having both dielectric switch and second harmonic generation(SHG).Here,a new stimuli-responsive switchable material [(CH₃)₃N(CH₂)₂Cl]₂]Mn(SCN)₄(H₂O)₂] was discovered as a potential secondharmonic generation(SHG) dielectric switch.It is worth noting that it has SHG characteristics before and after undergoing reversible high-temperature phase transitions.In this work,we successfully refined the tetramethylammonium cation to obtain a quasi-spherical cation,which is tetramethylchloroethylamine(TMCEM) cation.By substituting H with a halogen,the increased steric hindrance of the molecular makes energy barrier increased,resulting in the reversible high-temperature phase transition.At the same time,the interactions of quasi-spherical cations and [Mn(SCN)₄(H₂O)₂]^2- anions affect a noncentrosymmetric structure to induce the SHG effect.These findings provide a new approach to design novel functional switch materials.     

A pH Switch for β-Sheet Protein Folding

Protein design advancements have led to biotechnological strategies based on more stable and more specific structures. Herein we present a 6-residue sequence (HPATGK) that acts as a stable structure-nucleating turn at physiological and higher pH but is notably unfavorable for chain direction reversal at low pH. When placed into the turn of a β-sheet, this leads to a pH switch of folding. Using a standard 3-stranded β-sheet model, the WW domain, it was found that the pH switch sequence insertion caused minimal change at pH 8 but a ca. 50 °C drop in the melting temperature (T_m) was observed at pH 2.5: ΔΔG_F ≥11.3 kJ mol⁻¹. Using the strategies demonstrated in this article, the redesign of β-sheets to contain a global, or local, pH-dependent conformational switch should be possible.     

四硫富瓦烯及其衍生物在分子开关领域的研究进展

四硫富瓦烯(TTF)及其衍生物由于具有特殊的结构和性质, 在分子开关、分子传感器、光信息存储和非线性光学等领域显示出诱人的应用前景. 综述了近几年TTF及其衍生物在分子开关领域的最新研究进展.     

高压变电站事故预警监测探讨-新型氟化氢气体在线监测仪的研制

通过监测六氟化硫（SF₆）气体的变化发现高压变电站系统中设备的异常. 气体绝缘开关设备（GIS）中的高压开关、电闸及其它各种设备因接触不良、电阻值增加、发热、融解、拉弧、连续拉弧等原因会造成设备短路. 因保护这些电器的SF₆气体不可能非常纯净,如存在H₂O. 在上述这些故障发生时变成催化条件,使SF₆与H₂O作用后生成氟化氢气体. 通过监测氟化氢气体的突发变化,可以预警GIS系统设备可能出现的故障.     

A High Contrast Tri‐state Fluorescent Switch: Properties and Applications

A high contrast tri‐state fluorescent switch (FSPTPE) with both emission color change and on/off switching is achieved in a single molecular system by fusing the aggregation‐induced emissive tetraphenylethene (TPE) with a molecular switch of spiropyran (SP). In contrast to most of the reported solid‐state fluorescent switches, FSPTPE only exists in the amorphous phase in the ring‐closed form owing to its highly asymmetric molecular geometry and weak intermolecular interactions, which leads to its grinding‐inert stable cyan emission in the solid state. Such an amorphous phase facilitates the fast response of FSPTPE to acidic gases and induces the structural transition from the ring‐closed form to ring‐open form, accompanied with the “Off” state of the fluorescence. The structural transition leads to a planar molecular conformation and high dipole moment, which further results in strong intermolecular interactions and good crystallinity, so when the acid is added together with a solvent, both the ring‐opening reaction and re‐crystallization can be triggered to result in an orange emissive state. The reversible control between any two of the three states (cyan/orange/dark) can be achieved with acid/base or mechanical force/solvent treatment. Because of the stable initial state and high color contrast (Δλ=120 nm for cyan/orange switch, dark state Φ_F<0.01 %), the fluorescent switch is very promising for applications such as displays, chemical or mechanical sensing, and anti‐counterfeiting.     

Investigating charge transport in molecular switches with neural networks

The control of charge transport on a polymer chain by impurity molecules working as switches is studied. Charge propagation is estimated using a backpropagation neural network approach. The supervised learning is accomplished using theoretical results in which the chain is modeled by a tight-binding Hamiltonian extended to include the effects of an external electric field. The charge transport through the sites that work like a switch is analyzed by the numerical integration of the equations of motion. For a donor–acceptor pair of impurities, we found that the chain offers a wide range of devices, from simple switches to perfect molecular rectifiers. The influence of the parameters of the molecules on the charge transport, the role of the length of separation between the sites where the impurity molecules bond, as well as the changes they must undergo to characterize each kind of molecular switch are determined. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1060–1066, 1999     

Small Janus dimer as electric field manipulated molecular clam switch and electric information storage unit

A small Janus molecular dimer, as external electric field (F_z) manipulated both a molecular clam switch and a novel electric information storage unit, is found by quantum chemical computations for the first time. The molecular clam switching is intriguing and reversible. A critical F_z value of 95 × 10⁻⁴ au causes a dramatically open change in conformation from Closed form to Open form. And a small reversed electric field of F_z = −10 × 10⁻⁴ au performs a close change from Open form to Closed form. In the switching process, owing to the existence of a great electric dipole moment (μ) contrast between 0 and 22.13 D, the molecular clam switch may serve as an electric information storage unit. Gratifyingly, the reading, writing, and erasing of binary information on the electric information storage unit are easy. And further calculations show that Janus graphene fragment dimer can also serve as a molecular clam switch. Thus, this work proposes a new molecular switch prototype in the invention of artificial molecular machines, and a novel electric information storage unit in the field of molecular electronics.     

随机扰动和周期信号对基因调控系统的影响

采用数值模拟方法,研究了生物信息学中人类遗传因子——基因的转录调控系统.研究表明:噪音对该系统的影响作用,体系可以出现内随机共振现象和噪音诱导的"开-关"过程;当周期信号加到系统上时,信号振幅和频率的改变能够使细胞信号产生更为丰富的动力学行为,如周期共振现象.     

Coherent Spin Transport Through a Six-Coordinate FeN6 Spin-Crossover Complex with Two Di erent Spin Con gurations

Due to the magnetic bistability, single-molecule spin-crossover (SCO) complexes have been considered to be the most promising building blocks for molecular spintronic devices. Here, we explore the SCO behavior and coherent spin transport properties of a six-coordinate FeN₆ complex with the low-spin (LS) and high-spin (HS) states by performing extensive first-principles calculations combined with non-equilibrium Green’s function technique. Theoretical results show that the LS?HS spin transition via changing the metal-ligand bond lengths can be realized by external stimuli, such as under light radiation in experiments. According to the calculated zero-bias transmission coefficients and density of states as well as the I-V curves under small bias voltages of FeN₆ SCO complex with the LS and HS states sandwiched between two Au electrodes, we find that the examined molecular junction can act as a molecular switch, tuning from the OFF (LS) state to the ON (HS) state. Moreover, the spin-down electrons govern the current of the HS molecular junction, and this observed perfect spin-filtering effect is not sensitive to the detailed anchoring structure. These theoretical findings highlight this examined six-coordinate FeN₆ SCO complex for potential applications in molecular spintronics.     

Coherent Resonance for Rate Oscillations During CO Oxidation on Pt(110) Surfaces: Interplay Between Internal and External Noise

Effects of noise on rate oscillations during CO oxidation on Pt(110) surface were investigated, both theo-retically and numerically, by focusing on the interplay of internal noise (IN) due to stochasticity in reaction events, and external noise (EN) resulting from parameter perturbation. The surface is divided into cells of variable size which are assumed to be well mixed, and we consider the behavior inside a single cell. At-tention is paid to parameter regions subthreshold of the deterministic Hopf bifurcation, where noise can induce stochastic oscillations, the signal-to-noise ratio (SNR) of which shows a maximum with the variation of noise intensity, known as coherent resonance (CR). By stochastic normal theory, we show that IN and EN contribute in a weighted additive way to an effective noise that lead to CR, such that SNR shows a ridge shape in the D-1/N plane, where D and 1/N measures the strength of EN and IN, respectively. It is shown that for too large IN (EN), CR behavior with EN (IN) no longer exists. Numerical simulations show good agreements with the theoretical results     

Influences of a periodic signal on a noisy synthetic gene network

The effects of noise and a periodic signal on a synthetic gene network have been investigated. By tuning the distance of a parameter from the Hopf bifurcation point, both implicit internal signal stochastic resonance and explicit internal signal stochastic resonance can be induced by noise. Furthermore, a switch process can also be elicited. When a periodic signal is coupled to the gene network, two interesting phenomena occur with the modulation of the frequency of the signal: the effect of noise amplifyin...     

Photo‐/Baso‐Chromisms and the Application of a Dual‐Addressable Molecular Switch

Two typical molecular switches of spiropyran (SP) and benzoxazine (OX) were fused by sharing an indole to achieve a new dual‐addressable molecular switch (SP‐OX‐NO₂). Through proper molecular modification with NO₂, the transformation from merocyanine (MC) to ring‐closed SP or ring‐closed OX can be controlled separately with visible light or base stimuli in solution, respectively, and these processes are verified by UV‐vis and NMR spectroscopy as well as control experiments. The cis‐merocyanine (cis‐MC) form is involved in the basochromic process in solution. DFT calculation suggests that the bidirectional switching property of the fused SP‐OX molecular switch can be controlled separately, when the OX isomer is more stable than the deprotonated SP isomer. Because of the significant color variations in solution, the simple dual‐addressable switch has been further successfully applied to construct a multicolor reversible display on paper.     

Synthesis and spectroscopic characterization of red-shifted spironaphthoxazine based optical switch probes

Spironaphthoxazine (NISO) is an efficient optical switch probe that has applications in high contrast detection of Förster resonance energy transfer (FRET) using optical lock-in detection (OLID). NISO exists in two distinct states, spiro (SP) and merocyanine (MC), that can be independently controlled by using alternate irradiation with near ultraviolet and visible light. Unfortunately, the SP-state of NISO has an absorption centered at 350 nm, which may lead to phototoxic effects when manipulating the probe within a living cell. To overcome this problem we introduce new, red-shifted amino-substituted NISO probes compared to NISO that undergo an efficient SP to MC transition in response to irradiation by using 405-nm light, which is less damaging to living cells. This study details the synthesis of amino-substituted NISO and their N-hydroxysuccinimide ester and maleimide derivatives and their use in generating covalent attached protein conjugates. This study also presents a characterization of the spectroscopic and optical switching properties of these red-shifted NISO probe in solution.     

A macrocycle/molecular-clip complex that functions as a quadruply controllable molecular switch

Herein, we report the synthesis of a molecular clip with TTF side-walls and its binding behavior towards electron-deficient guests, namely the formation of macrocycle/molecular-clip supramolecular complexes in solution. Four different sets of external stimuli--the K(+)/[2.2.2]cryptand, NH(4) (+)/Et(3)N and (p-BrPh)(3)NSbCl(6)/Zn pairs, and heating/cooling cycles-control the movement of this molecular switch between its threaded and unthreaded states and provide color changes that are observable by the naked eye. This macrocycle/molecular-clip complex system can be considered not only as a quadruple-use molecular switch, but can also be operated by three of these stimuli as a three-input molecular NOR-functioning logic gate that may be monitored by UV-visible spectroscopy.     

A Competitor-switched Electrochemical Sensor for Detection of DNA

A competitor‐switched electrochemical sensor based on a generic displacement strategy was designed for DNA detection. In this strategy, an unmodified single‐stranded DNA (cDNA) completely complementary to the target DNA served as the molecular recognition element, while a hairpin DNA (hDNA) labeled with a ferrocene (Fc) and a thiol group at its terminals served as both the competitor element and the probe. This electrochemical sensor was fabricated by self‐assembling a dsDNA onto a gold electrode surface. The dsDNA was pre‐formed through the hybridization of Fc‐labeled hDNA and cDNA with their part complementary sequences. Initially, the labeled ferrocene in the dsDNA was far from surface of the electrode, the electrochemical sensor exhibited a "switch‐off" mode due to unfavorable electron transfer of Fc label. However, in the presence of target DNA, cDNA was released from hDNA by target DNA, the hairpin‐open hDNA restored its original hairpin structure and the ferrocene approached onto the electrode surface, thus the electrochemical sensor exhibited a "switch‐on" mode accompanying with a change in the current response. The experimental results showed that as low as 4.4×10⁻¹⁰ mol/L target DNA could be distinguishingly detected, and this method had obvious advantages such as facile operation, low cost and reagentless procedure.     

Detection of Protein S‐Sulfhydration by a Tag‐Switch Technique

Protein S‐sulfhydration (forming ‐S‐SH adducts from cysteine residues) is a newly defined oxidative posttranslational modification and plays an important role in H₂S‐mediated signaling pathways. In this study we report the first selective, “tag‐switch” method which can directly label protein S‐sulfhydrated residues by forming stable thioether conjugates. Furthermore we demonstrate that H₂S alone cannot lead to S‐sulfhydration and that the two possible physiological mechanisms include reaction with protein sulfenic acids (P‐SOH) or the involvement of metal centers which would facilitate the oxidation of H₂S to HS^..     

Theoretical investigation on the spectroscopic properties of furylfulgide with different substituents and design of novel bis‐furylfulgimide photochromes

Density functional theory and time‐dependent density functional theory were employed to theoretically analyze the effect of different substituents on the spectroscopic properties of furylfulgide. The result shows that the absorption spectra of ring‐closed isomer which substituted by an electron‐donating group (NH₂) at the R₃‐position of furylfulgide has an evident bathochromic shift compared with the others. Due to the steric hindrance effect, the difference of absorption wavelength was evidently enlarged by introducing several representative electron‐withdrawing groups at the R₆‐position of furylfulgide. In addition, we also designed a series of novel dimers which combined two furylfulgimide monomers into one new molecule. The relevant frontier molecular orbitals, energy levels and absorption properties were analyzed in detail by the calculation of low‐lying excited states. Finally, taking BFF‐6 (bis‐furylfulgimide) for an example, we discussed the transformation mechanism of four stable isomers in the toluene solution. Our conclusions manifest that the asymmetrical BFF‐6 can act as a potential multifunctional molecular switch in consideration of its distinguishable absorption bands and reversible conversion process. We hope that this research will be beneficial to design more practical and efficient molecular switch for further applications.