Two polymorphs of 5‐cyclohexyl‐5‐ethylbarbituric acid and their packing relationships with other barbiturates

Polymorph (Ia) (m.p. 474 K) of the title compound, C₁₂H₁₈N₂O₃, displays an N—H...O=C hydrogen‐bonded layer structure which contains R₆⁶(28) rings connecting six molecules, as well as R₂²(8) rings linking two molecules. The 3‐connected hydrogen‐bonded net resulting from these interactions has the hcb topology. Form (Ib) (m.p. 471 K) displays N—H...O=C hydrogen‐bonded looped chains in which neighbouring molecules are linked to one another by two different R₂²(8) rings. Polymorph (Ia) is isostructural with the previously reported form II of 5‐(2‐bromoallyl)‐5‐isopropylbarbituric acid (noctal) and polymorph (Ib) is isostructural with the known crystal structures of four other barbiturates.     

一个高度灵敏和高选择性铝离子比率探针的合成及应用

本文构建了一种基于3-苯丙噻唑基-2-羟基-5-甲基苯甲醛的荧光探针用于检测铝离子。该荧光探针能够灵敏、高选择性地检测铝离子,并显示出颜色和强烈的荧光变化双重响应。研究结果表明,该探针对铝离子表现出非常好的荧光增强效果,检测过程中其它金属离子不会对检测结果产生明显的干扰。其比率荧光强度(I490/I567)与铝离子的浓度(0~20μmol/L)之间具有良好的线性关系,检测限低至0.5μmol/L。由于具有高效的选择性,该探针可以用于检测污染河水中的铝离子含量。     

一种基于丹磺酰胺染料的高选择性汞(Ⅱ)离子荧光探针

对人类健康和社会环境而言,汞离子被认为是毒性最大的金属离子之一.本文设计、合成了一种新型基于丹磺酰胺染料的荧光探针,并研究了其对金属阳离子的识别性质.研究结果表明:该荧光探针在水溶液中,对汞离子具有高度的选择性和良好的灵敏度,且不受其它金属阳离子的干扰.该探针对汞离子的检测限可以达到2.1×10-8 mol/L.该探针极低的检测限和良好的水溶性表明其可用于活细胞中检测汞离子.生物成像实验证实该探针具有良好的细胞膜透性和生物相容性.     

基于黄酮的ESIPT型荧光探针检测三苯基膦

三苯基膦(PPh3)是一种重要的有机化合物,具有亲核性和还原性,已被广泛用于有机合成和有机金属化合物配位中。然而PPh3的过量使用不可避免地会引起环境的污染,并且对人体的健康也具有潜在威胁。因此我们迫切需要一种方便而高效的检测PPh3的方法。已有检测方法在便捷性和灵敏性等方面不如人意,而小分子荧光探针因其灵敏度高、选择性好、检测简单等优点受到广泛关注。受生物标记领域常用的无痕Staudinger连接反应的启发,本文设计合成了一个类似Staudinger连接反应,以能够具有固态发光性质的激发态分子内质子转移(ESIPT)特性的3-羟基黄酮荧光染料为母核,以邻叠氮苯乙酸酯为识别基团,用于检测PPh3的荧光增强型的探针分子。通过叠氮与PPh3反应,经过氮杂叶立德中间体,进行快速的分子内酰胺化,释放3-羟基黄酮染料并恢复荧光发射,从而实现在溶液中及滤纸上快速检测PPh3的目的。该探针在定量和定性检测PPh3方面具有潜在应用价值。     

Tuning the properties of a black TiO2-Ag visible light photocatalyst produced by a rapid one-pot chemical reduction

A highly efficient black TiO₂-Ag photocatalytic nanocomposite, active under both UV and visible light illumination, was synthesized by decorating the surface of 25 nm TiO₂ particles with Ag nanoparticles. The material was obtained via a rapid, one-pot, simple (surfactant and complexing agent free) chemical reduction method using silver nitrate and formaldehyde as a metal salt and reducing agent, respectively. The nanocomposite shows an increase of over 800% in the rate of photocatalytic methylene blue dye degradation, compared to commercial unmodified TiO_2, under UV-VIS illumination. Unlike pure TiO₂, the nanocomposite exhibits visible light activation, with a corresponding drop in optical reflectance from 100% to less than 10%. The photocatalytic properties were shown to be strongly enhanced by post-reduction annealing heat treatments in air, which were observed to decrease, rather than coarsen, silver particle size, and increase particle distribution. This, accompanied by a variation in the silver surface oxidation states, appear to dramatically affect the photocatalytic efficiency under both UV and visible light. This highly active photocatalyst could have wide ranging applications in water and air pollution remediation and solar fuel production.     

On the existence of free-surface azimuthal equatorial flows

This paper is concerned with the governing equations (together with the free boundary and the bottom boundary conditions) for an inviscid, incompressible fluid, written in spherical coordinates which are fixed at a point on the rotating Earth. For a special type of a steady flow moving only in the azimuthal direction, with no variation in this direction, we provide a functional-analytic study of the link between the pressure at the free surface of the ocean and the distortion of that surface.     

A General Mechanism of Photoconversion of Green‐to‐Red Fluorescent Proteins Based on Blue and Infrared Light Reduces Phototoxicity in Live‐Cell Single‐Molecule Imaging

Photoconversion of fluorescent proteins by blue and complementary near‐infrared light, termed primed conversion (PC), is a mechanism recently discovered for Dendra2. We demonstrate that controlling the conformation of arginine at residue 66 by threonine at residue 69 of fluorescent proteins from Anthozoan families (Dendra2, mMaple, Eos, mKikGR, pcDronpa protein families) represents a general route to facilitate PC. Mutations of alanine 159 or serine 173, which are known to influence chromophore flexibility and allow for reversible photoswitching, prevent PC. In addition, we report enhanced photoconversion for pcDronpa variants with asparagine 116. We demonstrate live‐cell single‐molecule imaging with reduced phototoxicity using PC and record trajectories of RNA polymerase in Escherichia coli cells.     

Detailed Evidence for an Unparalleled Interaction Mode between Calmodulin and Orai Proteins

Calmodulin (CaM) binds most of its targets by wrapping around an amphipathic α‐helix. The N‐terminus of Orai proteins contains a conserved CaM‐binding segment but the binding mechanism has been only partially characterized. Here, microscale thermophoresis (MST), surface plasmon resonance (SPR), and atomic force microscopy (AFM) were employed to study the binding equilibria, the kinetics, and the single‐molecule interaction forces involved in the binding of CaM to the conserved helical segments of Orai1 and Orai3. The results consistently indicated stepwise binding of two separate target peptides to the two lobes of CaM. An unparalleled high affinity was found when two Orai peptides were dimerized or immobilized at high lateral density, thereby mimicking the close proximity of the N‐termini in native Orai oligomers. The analogous experiments with smooth muscle myosin light chain kinase (smMLCK) showed only the expected 1:1 binding, confirming the validity of our methods.     

The Interstitial Carbon of the Nitrogenase FeMo Cofactor is Far Better Stabilized than Previously Assumed

The first quantum-mechanical calculations of all relevant potential constants in both the iron-molybdenum cofactor and the iron-vanadium cofactor of nitrogenase suggest that the carbide is bound to the center of the enzyme much more strongly than hitherto assumed. Previous studies seemed to indicate a dummy function of the interstitial carbon, with a weak force constant (ca. 0.32 N cm⁻¹). Our new investigations confirm a different picture: the central carbon atom binds the iron-sulfur cluster through six covalent C−Fe bonds. With a potential constant of more than 1.3 N cm⁻¹, the interstitial carbon also appears to be dynamically persistent. According to our investigations, the values for the elasticity within the iron-sulfur cluster have to be corrected too. These new details on the mechano-chemical properties of the FeMo cofactor will be important for elucidating the catalytic cycle of nitrogen fixation. By implementing our new algorithm in the freely available COMPLIANCE program, the dependence on the coordinates during the calculation of Hesse matrices is eliminated completely.     

A New kHz Velocity Map Ion/Electron Imaging Spectrometer for Femtosecond Time-Resolved Molecular Reaction Dynamics Studies

A new velocity map imaging spectrometer is constructed for molecular reaction dynamics studies using time-resolved photoelectron/ion spectroscopy method.By combining a kHz pulsed valve and an ICCD camera,this velocity map imaging spectrometer can be run at a repetition rate of 1 kHz,totally compatible with the fs Ti:Sapphire laser system,facilitating time-resolved studies in gas phase which are usually time-consuming.Time-resolved velocity map imaging study of NH₃ photodissociation at 200 nm was performed and the time-resolved total kinetic energy release spectrum of H+NH₂ products provides rich information about the dissociation dynamics of NH₃.These results show that this new apparatus is a powerful tool for investigating the molecular reaction dynamics using time-resolved methods.