Emission Turn‐On and Solubility Turn‐Off in Conjugated Polymers: One‐ and Two‐Photon‐Induced Removal of Fluorescence‐Quenching Solubilizing Groups

The synthesis of highly efficient two‐photon uncaging groups and their potential use in functional conjugated polymers for post‐polymerization modification are reported. Careful structural design of the employed nitrophenethyl caging groups allows to efficiently induce bond scission by a two‐photon process through a combination of exceptionally high two‐photon absorption cross‐sections and high reaction quantum yields. Furthermore, π‐conjugated polyfluorenes are functionalized with these photocleavable side groups and it is possible to alter their emission properties and solubility behavior by simple light irradiation. Cleavage of side groups leads to a turn‐on of the fluorescence while solubility of the π‐conjugated materials is drastically reduced.

     

Rapid Determination of Free Amino Acids in Milk by Microchip Electrophoresis Coupled with Laser‐induced Fluorescence Detection

A simple and sensitive method for determination of free amino acids in milk by microchip electrophoresis (MCE) coupled with laser‐induced fluorescence (LIF) detection was developed. Seven kinds of standard amino acids were derivated with sulfoindocyanine succinimidyl ester (Cy5) and then perfectly measured by MCE‐LIF within 150 s. The parameters of MCE separation were carefully investigated to obtain the optimal conditions: 100 mmol·L^?1 sodium borate solution (pH 10.0) as running buffer solution, 0.8 kV as injection voltage, 2.2 kV as separation voltage etc. The linear range of the detection of amino acids was from 0.01 µmol·L^?1 to 1.0 µmol·L^?1 and the detection limit was as low as about 1.0 nmol·L^?1. This MCE‐LIF method was applied to the measurements of free amino acids in actual milk samples and satisfactory experimental results were achieved.     

Matrix Effect of Alkali and Alkaline Earth Metal Halides on Fluorescence Quantum Yield of Indium in Laser‐Induced Fluorescence Flame Spectrometry

As interfered with by alkali and alkaline earth metal halides added as the matrix in an acetylene/air flame, the fluorescence quantum yield of In as the analyte in a laser‐induced fluorescence (LIF) flame spectrometry has been thoroughly characterized. The fluorescence quantum yield is determined by a ratio of F to A, where F is the measured fluorescence of In and A is the difference between the absorption signals recorded for the analyte and the blank solutions. The normalized fluorescence signal is treated to prevent deviations due to variations of the atomization efficiency under the conditions with and without the matrix added. The fluorescence quantum yield is measured to be almost independent of the matrix concentration up to 500 ppm (μg/mL) studied, under conditions of either optical unsaturation or saturation. By considering a quenching effect induced by electron‐atom collisions, the calculated fluorescence quantum yields are consistent with our observations.     

Simultaneous Determination of Levodopa and Its Metabolite in Human Blood by Capillary Electrophoresis with Laser‐induced Fluorescence Detection

A rapid, sensitive and reproducible method is described for the analysis of levodopa and its metabolite dopamine (DA) in human blood. The influence of carbidopa as the inhibitor againist the decarboxylase activity on the metabolism has been also studied. After derivatization in a dark pulsator for 12 h at room temperature, the fluorescein isothiocyanate (FITC) derivative of levodopa and other components were separated by capillary zone electrophoresis (CZE) within 13 min and detected with laser-induced fluorescence (LIF). Under the optimum analysis conditions, the linear range is 3.0×10^－8—4.0×10^－6 mol/L and 1.0×10^－8—2.0×10^－6 mol/L for levodopa and DA, respectively. The detection limits of levodopa and DA were 7.8×10^－9 mol/L (39.0 amol) and 3.1×10^－9 mol/L (15.5 amol), respectively. The method was successfully applied to monitoring the levodopa and DA in human blood after one took tablets orally.     

Control over Electrochemical Water Oxidation Catalysis by Preorganization of Molecular Ruthenium Catalysts in Self‐Assembled Nanospheres

Oxygen formation through water oxidation catalysis is a key reaction in the context of fuel generation from renewable energies. The number of homogeneous catalysts that catalyze water oxidation at high rate with low overpotential is limited. Ruthenium complexes can be particularly active, especially if they facilitate a dinuclear pathway for oxygen bond formation step. A supramolecular encapsulation strategy is reported that involves preorganization of dilute solutions (10^?5 m ) of ruthenium complexes to yield high local catalyst concentrations (up to 0.54 m ). The preorganization strategy enhances the water oxidation rate by two‐orders of magnitude to 125 s^?1, as it facilitates the diffusion‐controlled rate‐limiting dinuclear coupling step. Moreover, it modulates reaction rates, enabling comprehensive elucidation of electrocatalytic reaction mechanisms.     

IR Laser‐Induced Degradation of Poly(vinyl acetate): Novel Thermal Reactions in Solid Polymers

Summary: Pulsed‐IR laser‐induced decomposition of poly(vinyl acetate) (PVAC) differs remarkably from its conventional pyrolysis, which results in the formation of acetic acid and non‐polar carbonaceous residue. In contrast, the products in the former case are (i) vinyl acetate (low energy channel), (ii) products of cleavage in the acetate group, and (iii) an ablatively deposited polar polymeric film containing roughly half of the acetoxy groups initially present.

Schematic of the different routes of poly(vinyl acetate) degradation.     

Cooperative Catalysis of Noncompatible Catalysts through Compartmentalization: Wacker Oxidation and Enzymatic Reduction in a One‐Pot Process in Aqueous Media

A Wacker oxidation using CuCl/PdCl₂ as a catalyst system was successfully combined with an enzymatic ketone reduction to convert styrene enantioselectively into 1‐phenylethanol in a one‐pot process, although the two reactions conducted in aqueous media are not compatible due to enzyme deactivation by Cu ions. The one‐pot feasibility was achieved via compartmentalization of the reactions. Conducting the Wacker oxidation in the interior of a polydimethylsiloxane thimble enables diffusion of only the organic substrate and product into the exterior where the biotransformation takes place. Thus, the Cu ions detrimental to the enzyme are withheld from the reaction media of the biotransformation. In this one‐pot process, which formally corresponds to an asymmetric hydration of alkenes, a range of 1‐arylethanols were formed with high conversions and 98–99 % ee. In addition, the catalyst system of the Wacker oxidation was recycled 15 times without significant decrease in conversion.     

Reactivity Towards Europium(III) of the Radiolysis Products of the Ionic Liquid 1‐Methyl‐3‐butyl‐1H‐imidazolium Bis[(trifluoromethyl)sulfonyl]amide (C4‐mimTf2N) and Effect of Water: A TRLFS (Time‐Resolved Laser‐Induced Fluorescence Spectroscopy) Preliminary Study

The effect of laser irradiation at λ_exc 266 nm onto the fluorescence characteristics of Eu^III in solution of the ionic liquid 1‐methyl‐3‐butyl‐1H‐imidazolium bis[(trifluoromethyl)sulfonyl]amide (C₄‐mimTf₂N) was examined for various amounts of H₂O added. Stable radiolytic products that were generated at very low doses (in the range of 4 kGy) were very reactive with Eu^III and led to the appearance of a new europium luminescent species that was characterized by lifetime, relative intensity, and emission spectrum. Although the lifetime and the intensity depended on the H₂O content, the emission spectrum was not influenced by H₂O. It was shown that large amounts of H₂O, although not preventing radiolysis of C₄‐mimTf₂N, inhibited the complexation with Eu^III.     

Hydrophobic Modification of Pd/SiO2@Single‐Site Mesoporous Silicas by Triethoxyfluorosilane: Enhanced Catalytic Activity and Selectivity for One‐Pot Oxidation

To enhance the catalytic activity in a selective one‐pot oxidation using in‐situ generated H₂O₂, a hydrophobically modified core–shell catalyst was synthesized by means of a simple silylation reaction using the fluorine‐containing silylation agent triethoxyfluorosilane (TEFS, SiF(OEt)₃). The catalyst consisted of a Pd‐supported silica nanosphere and a mesoporous silica shell containing isolated Ti^IV and F ions bonded with silicon (Si?F bond). Structural analyses using XRD and N₂ adsorption–desorption suggested that the mesoporous structure and large surface area of the mesoporous shells were retained even after the modification. During the one‐pot oxidation of sulfide, catalytic activity was enhanced significantly by increasing the amount of fluorine in the shell. A hydrophobic surface enhanced adsorption of the hydrophobic reactant into the mesopore, while the less hydrophobic oxygenated products efficiently diffused into the outside of the shell, which improved the catalytic activity and selectivity. In addition, the present methodology can be used to enhance the catalytic activity and selectivity in the one‐pot oxidation of cyclohexane by using an Fe‐based core–shell catalytic system.     

富氧条件下Co/ZSM-5催化剂对C3H8选择还原NOx的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C₃H₈选择性催化还原NO_x性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co³⁺和Co²⁺物种,也有孔内的Co²⁺离子。富氧条件下Co/ZSM-5催化剂上C₃H₈选择性催化还原NO_x的活性主要与ZSM-5载体孔外表面分散的CoO_x物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoO_x物种中钴离子可还原能力增强,C₃H₈选择性催化还原NO_x的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NO_x的转化率和催化剂比速率（k）的下降。孔外表面Co₃O₄晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C₃H₈的氧化燃烧,使C₃H₈选择性催化还原NO_x的活性降低。     

富氧条件下Co/ZSM-5催化剂对C_3H_8选择还原NO_x的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C3H8选择性催化还原NOx性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co3+和Co2+物种,也有孔内的Co2+离子。富氧条件下Co/ZSM-5催化剂上C3H8选择性催化还原NOx的活性主要与ZSM-5载体孔外表面分散的CoOx物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoOx物种中钴离子可还原能力增强,C3H8选择性催化还原NOx的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NOx的转化率和催化剂比速率(k)的下降。孔外表面Co3O4晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C3H8的氧化燃烧,使C3H8选择性催化还原NOx的活性降低。     

Understanding the Solvent Effect on the Catalytic Oxidation of 1,4‐Butanediol in Methanol over Au/TiO2 Catalyst: NMR Diffusion and Relaxation Studies

The effect of water on the catalytic oxidation of 1,4‐butanediol in methanol over Au/TiO₂ has been investigated by catalytic reaction studies and NMR diffusion and relaxation studies. The addition of water to the dry catalytic system led to a decrease of both conversion and selectivity towards dimethyl succinate. Pulsed‐field gradient (PFG)‐NMR spectroscopy was used to assess the effect of water addition on the effective self‐diffusivity of the reactant within the catalyst. NMR relaxation studies were also carried out to probe the strength of surface interaction of the reactant in the absence and presence of water. PFG‐NMR studies revealed that the addition of water to the initial system, although increasing the dilution of the system, leads to a significant decrease of effective diffusion rate of the reactant within the catalyst. From T₁ and T₂ relaxation measurements it was possible to infer the strength of surface interaction of the reactant with the catalyst surface. The addition of water was found to inhibit the adsorption of the reactant over the catalyst surface, with the T₁/T₂ ratio of 1,4‐butanediol decreasing significantly when water was added. The results overall suggest that both the decrease of diffusion rate and adsorption strength of the reactant within the catalyst, due to water addition, limits the access of reactant molecules to the catalytic sites, which results in a decrease of reaction rate and conversion.     

Reducing the Cost and Preserving the Reactivity in Noble‐Metal‐Based Catalysts: Oxidation of CO by Pt and Al–Pt Alloy Clusters Supported on Graphene

The oxidation mechanisms of CO to CO₂ on graphene‐supported Pt and Pt‐Al alloy clusters are elucidated by reactive dynamical simulations. The general mechanism evidenced is a Langmuir–Hinshelwood (LH) pathway in which O₂ is adsorbed on the cluster prior to the CO oxidation. The adsorbed O₂ dissociates into two atomic oxygen atoms thus promoting the CO oxidation. Auxiliary simulations on alloy clusters in which other metals (Al, Co, Cr, Cu, Fe, Ni) replace a Pt atom have pointed to the aluminum doped cluster as a special case. In the nanoalloy, the reaction mechanism for CO oxidation is still a LH pathway with an activation barrier sufficiently low to be overcome at room temperature, thus preserving the catalyst efficiency. This provides a generalizable strategy for the design of efficient, yet sustainable, Pt‐based catalysts at reduced cost.