A bifunctional probe for Al3+ and Zn2+ based on diarylethene with an ethylimidazo[2,1-b]thiazole-6-hydrazide unit

A new diarylethene with ethylimidazo[2,1-b]thiazole-6-hydrazide unit was synthesized, and its photochromic and fluorescent behaviors have been systematically investigated by the stimulation of lights and metal ions in methanol. This new diarylethene exhibited high selectivity and sensitivity toward Al³⁺ and Zn²⁺. The addition of Al³⁺ and Zn²⁺ displayed excellent colorimetric response behaviour with the concomitant color change from colorless to yellow, which could be easily observed by the naked eye. Upon addition of Al³⁺, the fluorescence intensity was enhanced by 180–fold and the emission peak of 1O–Al³⁺ blue-shifted by 15?nm accompanied with a color change from colorless to bright blue. In contrast, when stimulated with Zn²⁺, its fluorescence intensity was enhanced by 35–fold and the emission peak of 1O–Zn²⁺ red-shifted by 16?nm with an evident color change from black to bright green. The LOD for Al³⁺ and Zn²⁺ were determined to be 2.97?×?10^?9?mol?L^?1 and 5.98?×?10^?9?mol?L^?1, respectively. Moreover, a logic circuit was constructed with the fluorescence intensity as the output signal responding to the light and chemical species as the inputs.     

3D Carbon Foam Supported Edge-Rich N-Doped MoS2 Nanoflakes for Enhanced Electrocatalytic Hydrogen Evolution

Molybdenum disulfide (MoS₂) is one of the most promising alternatives to the Pt-based electrocatalysts for the hydrogen evolution reaction (HER). However, its performance is currently limited by insufficient active edge sites and poor electron transport. Hence, enormous efforts have been devoted to constructing more active edge sites and improving conductivity to obtain enhanced electrocatalytic performance. Herein, the 3D carbon foam (denoted as CF) supported edge-rich N-doped MoS₂ nanoflakes were successfully fabricated by using the commercially available polyurethane foam (PU) as the 3D substrate and PMo₁₂O₄₀³⁻ clusters (denoted as PMo₁₂) as the Mo source through redox polymerization, followed by sulfurization. Owing to the uniform distribution of nanoscale Mo sources and 3D carbon foam substrate, the as-prepared MoS₂-CF composite possessed well-exposed active edge sites and enhanced electrical conductivity. Systematic investigation demonstrated that the MoS₂-CF composite showed high HER performance with a low overpotential of 92 mV in 1.0 m KOH and 155 mV in 0.5 m H₂SO₄ at a current density of 10 mA cm⁻². This work offers a new pathway for the rational design of MoS₂-based HER electrocatalysts.     

GSH and H2O2 Co-Activatable Mitochondria-Targeted Photodynamic Therapy under Normoxia and Hypoxia

Currently, photosensitizers (PSs) that are microenvironment responsive and hypoxia active are scarcely available and urgently desired for antitumor photodynamic therapy (PDT). Presented herein is the design of a redox stimuli activatable metal-free photosensitizer (aPS), also functioning as a pre-photosensitizer as it is converted to a PS by the mutual presence of glutathione (GSH) and hydrogen peroxide (H₂O₂) with high specificity on a basis of domino reactions on the benzothiadiazole ring. Superior to traditional PSs, the activated aPS contributed to efficient generation of reactive oxygen species including singlet oxygen and superoxide ion through both type 1 and type 2 pathways, alleviating the aerobic requirement for PDT. Equipped with a triphenylphosphine ligand for mitochondria targeting, ^mito aPS showed excellent phototoxicity to tumor cells with low light fluence under both normoxic and hypoxic conditions, after activation by intracellular GSH and H₂O₂. The ^mito aPS was also compatible to near infrared PDT with two photon excitation (800 nm) for extensive bioapplications.     

喜树碱与胰蛋白酶的相互作用

喜树碱(camptothecin,CPT)是从珙桐科乔木喜树中分离得到的一类重要抗癌药物,对动物肿瘤及白血病均有明显的抑制作用[1]。CPT分子为五环结构,含有一个吡咯[3,4-b]喹啉环,一个共轭吡啶环和一个α-羟基六元内脂环[2]。CPT通过嵌合抑制DNA拓扑异构酶Ⅰ的活性,对卵巢癌、结肠直肠癌     

A three-channel microfluidic device for generating static linear gradients and its application to the quantitative analysis of bacterial chemotaxis

We have developed a prototype three-channel microfluidic chip that is capable of generating a linear concentration gradient within a microfluidic channel and is useful in the study of bacterial chemotaxis. The linear chemical gradient is established by diffusing a chemical through a porous membrane located in the side wall of the channel and can be established without through-flow in the channel where cells reside. As a result, movement of the cells in the center channel is caused solely by the cells chemotactic response and not by variations in fluid flow. The advantages of this microfluidic chemical linear gradient generator are (i) its ability to produce a static chemical gradient, (ii) its rapid implementation, and (iii) its potential for highly parallel sample processing. Using this device, wildtype Escherichia coli strain RP437 was observed to move towards an attractant (e.g., l-asparate) and away from a repellent (e.g., glycerol) while derivatives of RP437 that were incapable of motility or chemotaxis showed no bias of the bacteria's distribution. Additionally, the degree of chemotaxis could be easily quantified using this assay in conjunction with fluorescence imaging techniques, allowing for estimation of the chemotactic partition coefficient (CPC) and the chemotactic migration coefficient (CMC). Finally, using this approach we demonstrate that E. coli deficient in autoinducer-2-mediated quorum sensing respond to the chemoattractant l-aspartate in a manner that is indistinguishable from wildtype cells suggesting that chemotaxis is insulated from this mode of cell-cell communication.     

氧原子在Pt(s)-[n(111)×(100)]型台阶面上的吸附和振动

应用原子和表面簇合物相互作用的5-参数Morse势(简称5-MP)方法系统地研究了氧-铂台阶面体系.理论结果表明:在Pt(s)-[n(111)×(100)]型台阶面上，氧原子吸附在台阶下的四重位，对应稳定吸附态β2；平台上靠近四重位的三重吸附态被湮灭，其它三重位对应吸附态β1；而且平台的长度对四重吸附态有影响.     

Interplay of mechanical and binding properties of Fibronectin type I

Fibronectins (FNs) are a major component of the extracellular matrix (ECM), and provide important binding sites for a variety of ligands outside and on the surface of the cell. Similar to other ECM proteins, FNs are consistently subject to mechanical stress in the ECM. Therefore, it is important to study their structure and binding properties under mechanical stress and understand how their binding and mechanical properties might affect each other. Although certain FN modules have been extensively investigated, no simulation studies have been reported for the FN type I (Fn1) domains, despite their prominent role in binding of various protein modules to FN polymers in the ECM. Using equilibrium and steered molecular dynamics simulations, we have studied mechanical properties of Fn1 modules in the presence or the absence of a specific FN-binding peptide (FnBP). We have also investigated how the binding of the FnBP peptide to Fn1 might be affected by tensile force. Despite the presence of disulfide bonds within individual Fn1 modules that are presumed to prevent their extension, it is found that significant internal structural changes within individual modules are induced by the forces applied in our simulations. These internal structural changes result in significant variations in the accessibility of different residues of the Fn1 modules, which affect their exposure, and, thus, the binding properties of the Fn1 modules. Binding of the FnBP appears to reduce the flexibility of the linker region connecting individual Fn1 modules (exhibited in the form of reduced fluctuation and motion of the linker region), both with regard to bending and stretching motions, and hence stabilizes the inter-domain configuration under force. Under large tensile forces, the FnBP peptide unbinds from Fn1. The results suggest that Fn1 modules in FN polymers do contribute to the overall extension caused by force-induced stretching of the polymer in the ECM, and that binding properties of Fn1 modules can be affected by mechanically induced internal protein conformational changes in spite of the presence of disulfide bonds which were presumed to completely abolish the capacity of Fn1 modules to undergo extension in response to external forces.     

Fractional coverage of defects in self-assembled thiol monolayers on gold

Au electrodes are alkylated by self-assembled organic monolayers of octadecanethiol from alcohol solution. The electron tunnelling resistance of a monolayer-coated gold electrode has been investigated by ac impedance. The relation between the fractional coverage of different defects and the corresponding film thickness at these ‘collapsed’ sites has been deduced from electron tunnelling theory. By using the concepts of average film thickness at defect (d_a) and average fractional coverage of defect (θ_a), we have obtained the θ_ad_a plot. The influence of the apparent standard rate constant on the shape of the θ_ad_a plot has been discussed. In our experiments, Fe(CN)₆^3−/4− is used as a redox probe to study the θ_ad_a plot of an octadecanethiol monolayer. The θ_a versus d_a plot indicates that the defects with d_a<6 methylene groups and θ_a<0.1 can increase the apparent standard rate constant from 1.9×10⁻¹⁰ cm s⁻¹, which is the theoretical value calculated from electron tunnelling theory, to 2.9×10⁻⁷ cm s⁻¹. The average thickness of the whole monolayer (ATWM), which is obtained from the θ_a versus d_a plot and which can indicate the blocking property of the monolayer, is 11 methylene groups.     

Selective light-triggered chemiluminescence between fluorescent dyes and luminol, and its analytical application

We report herein a novel chemiluminescence (CL) phenomenon triggered by light irradiation when a fluorescent dye, for example hematoporphyrin, fluorescein, eosin, or methylene blue is present in the luminol solution. A possible mechanism is proposed for the photoinduced chemiluminescence (PICL) reaction. Compared with reported methods for CL triggering, for example flow-injection, static reagent injection, and the electrochemical technique, the proposed in-situ PICL method presented has three advantages. First, the method is more selective, because the PICL signal of the target fluorescent dyes is initiated by excitation at a selective wavelength only. Second, the space and time resolution of the PICL method are better. Last, and most important, compared with injecting a reagent or inserting a electrode into the CL system to initiate the CL reaction, with the in-situ PICL method there is no physical interference with the target detecting system. All these advantages of the PICL method indicate it has many potential applications in the analytical sciences. The proposed method was applied to analysis of urine containing adrenaline. The linear range for adrenaline is 2.0?×?10^?10–1.0?×?10^?7 g mL^?1 and the detection limit is 6.0?×?10^?11 g mL^?1.