Designing and modulating the local structure of metal sites is the key to gain the unique selectivity and high activity of single metal site catalysts. Herein, we report strain engineering of curved single atomic iron-nitrogen sites to boost electrocatalytic activity. First, a helical carbon structure with abundant high-curvature surface is realized by carbonization of helical polypyrrole that is templated from self-assembled chiral surfactants. The high-curvature surface introduces compressive strain on the supported FeÀN 4 sites. Consequently, the curved FeÀN 4 sites with 1.5 % compressed FeÀN bonds exhibit downshifted d-band center than the planar sites. Such a change can weaken the bonding strength between the oxygenated intermediates and metal sites, resulting a much smaller energy barrier for oxygen reduction. Catalytic tests further demonstrate that a kinetic current density of 7.922 mA cm À2 at 0.9 V vs. RHE is obtained in alkaline media for curved Fe À N 4 sites, which is 31 times higher than that for planar ones. Our findings shed light on modulating the local three-dimensional structure of single metal sites and boosting the catalytic activity via strain engineering.

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Localized surface plasmon resonance (LSPR) is essentially a collective oscillation of free electrons in nanostructured metals. Interband excitation may also produce conduction-band electrons above the Fermi level. However, a question here is whether these excited electrons can take part in plasmonic oscillation. To answer this question, femtosecond pump-probe measurements on gold nanoparticles were performed using interband excitation, where the pump pulse produced a large amount of electrons in the sp-conduction band and left holes in the d-band. Probing by transient absorption spectroscopy, we resolved an induced LSPR feature located at a red-shifted spectrum. This feature cannot be observed for a pumping photon energy lower than the threshold for interband transition. The commonly observed red-shift or broadening of LSPR spectrum due to electron-electron and electron-phonon scattering under strong optical excitation can be ruled out for understanding this feature by a comparison between the plasmonic dynamics at a pump above and below the interband-transition threshold. In particular, a “holding” time of about 1 ps was resolved for the interband-excitation-induced electrons to relax to the LSPR oscillation.

In this work, a single-well electromembrane extraction (EME) device was developed based on a thin (100μm) and flat porous membrane of polypropylene supporting a liquid membrane. The new EME device was operated with a relatively large acceptor solution volume to promote a high recovery. Using this EME device, exhaustive extraction of the basic drugs quetiapine, citalopram, amitriptyline, methadone and sertraline was investigated from both acidified water samples and human plasma. The volume of acceptor solution, extraction time, and extraction voltage were found to be important factors for obtaining exhaustive extraction. 2-Nitrophenyl octyl ether was selected as the optimal organic solvent for the supported liquid membrane. From spiked acidified water samples (600μl), EME was carried out with 600μl of 20mM HCOOH as acceptor solution for 15min and with an extraction voltage of 250V. Under these conditions, extraction recoveries were in the range 89-112%. From human plasma samples (600μl), EME was carried out with 600μl of 20mM HCOOH as acceptor solution for 30min and with an extraction voltage of 300V. Under these conditions, extraction recoveries were in the range of 83-105%. When combined with LC-MS, the new EME device provided linearity in the range 10-1000ng/ml for all analytes (R(2)>0.990). The repeatability at low (10ng/ml), medium (100ng/ml), and high (1000ng/ml) concentration level for all five analytes were less than 10% (RSD). The limits of quantification (S/N=10) were found to be in the range 0.7-6.4ng/ml.

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In this work, a simple breath figure method was proposed to directly fabricate large-area and ordered honeycomb structures on commercial PMMA substrates or PS Petri dishes without the use of an external polymer solution. The obtained honeycomb structure is indeed part of the substrate, providing the honeycomb layer with enough mechanical stability. The breath figure method in this work for the synthesis of honeycomb structure is extremely simple with scale-up capability to large-area production, which offers new insights into surface engineering with great potential in commercial technologies. For example, using the honeycomb-patterned Petri dishes prepared via this method, cells can be easily separated into divided aggregation, which favors understanding of naturally occurring networks in higher organisms and cell-cell and cell-matrix interactions, and the therapeutic control of genetic circuits.

AbstractElectromembrane extraction (EME) was invented in 2006 as a miniaturized sample preparation technique for the separation of ionized species from aqueous samples. This concept has been investigated in different areas of analytical chemistry by different research groups worldwide since the introduction. Under the influence of an electrical field, EME is based on electrokinetic migration of the analytes through a supported liquid membrane (SLM), which is an organic solvent immobilized in the pores of the polymeric membrane, and into the acceptor solution. Up to date, close to 150 research articles with focus on EME have been published. The current review summarizes the performance of EME with different organic solvents and discusses several criteria for efficient solvents in EME. In addition, the authors highlight their personal perspective about the most promising organic solvents for EME and have indicated that more fundamental work is required to investigate and discover new organic solvents for EME.

This work describes the preparation and investigation of molecularly imprinted polymer (MIP) microgel (MG) stabilized Pickering emulsions (PEs) for their ability to catalyze the formation of disulfide bonds in peptides at the O/W interface. The MIP MGs were synthesized via precipitation polymerization and a programmed initiator change strategy. The MIP MGs were characterized using DLS analysis, SEM measurement, and optical microscopy analysis. The dry and wet MIP MGs showed a hydrodynamic diameter of 100 and 280 nm, respectively. A template rebinding experiment showed that the MIP MGs bound over two times more template (24 mg g) compared to the uptake displayed by a nonimprinted reference polymer (NIP) MG (10 mg g) at saturation. Using the MIP MGs as stabilizers, catalytic oxidation systems were prepared by emulsifying the oil phase and water phase in the presence of different oxidizing agents. During the cyclization, the isolation of the thiol precursors and the oxidizing reagents nonselectively decreased the formation of the byproducts, while the imprinted cavities on the MIP MGs selectively promoted the intramolecular cyclization of peptides. When I was used as the oxidizing agent, the MIP-PE-I system showed a product yield of 50%, corresponding to a nearly 2-fold increase compared to that of the nonimprinted polymer NIP-PE-I system (26%). We believe the interfacial catalysis system presented in this work may offer significant benefits in synthetic peptide chemistry by raising productivity while suppressing the formation of byproducts.