Donor-Acceptor Couples of Metal and Metal Oxides with Enriched Ni3+ Active Sites for Oxygen Evolution.

Exploiting precious-metal-free and high-activity oxygen evolution reaction (OER) electrocatalysts has been in great demands toward many energy storage and conversion processes, for example, carbon dioxide reduction, metal-air batteries, and water splitting. In this study, the simple solid-state method is employed for coupling Ni (electron donors) with lower-Fermi-level MoO2 or WOx (electron acceptors) into donor-acceptor ensembles with well-designed interfaces as robust electrocatalysts for OER. The resulting Ni/MoO2 and Ni/WOx electrocatalysts exhibit smaller overpotentials of 287 and 333 mV at 10 mA cm-2 as well as smaller Tafel slopes of 51 and 65 mV/dec, respectively, with respect to the single Ni, MoO2, WOx, and even the benchmark RuO2 in 1 M KOH. Specially, on account of a higher Fermi level of Ni in comparison with MoO2 and WOx, their strong electronic interaction results in directional interfacial electron transfer and increases the hole density over Ni, dramatically enriching the population of high-valence Ni3+ active sites and decreasing the Fermi level of Ni. The existence of Ni3+ can strengthen the chemisorption of OH-, and the downshift of the Ni Fermi level can significantly expedite migration of electrons toward the surface of catalysts during OER, thus synergistically boosting the OER catalytic performance. Furthermore, the inner Ni/MoO2 and Ni/WOx heterostructures and the electrochemically induced surface layers of oxides/hydroxides collectively boost the OER kinetics. This study highlights the importance of designing highly efficient OER electrocatalysts with high-valence active species (Ni3+) and better matched energy levels induced by the work function difference through interfacial engineering.

Fabrication of ultramicroporous triphenylamine-based polyaminal networks for low-pressure carbon dioxide capture.

Three triphenylamine-based polyaminal networks (TMPs) with monodispersed ultramicropore (about 0.54 nm) and abundant doped-nitrogen (up to 42.88 wt%) are successfully prepared through the direct polycondensation of triphenylamine-based aldehydes with melamine. The synergistic effects of uniform ultramicropore and rich CO2-philic polar sites endow TMPs with exceptional CO2 sorption capacity and selectivity over N2 and CH4. For example, the CO2 uptakes of TMPs can reach 15.7 wt% (273 K) and 11.2 wt% (298 K) at 1 bar. Especially, at a low pressure of 0.15 bar, TMP-3 simultaneously exhibits excellent CO2 sorption capacity of 4.16 wt% (∼1 mmol g-1, 298 K), high adsorption selectivities of CO2/N2 (61.9, 298 K) and CO2/CH4 (7.8, 298 K) and good cycle reusability, which are superior to most of the microporous polymers. In addition, the porous properties of TMPs could be effectively tuned by varying the amount of substitution formyl. This facile preparation method and excellent CO2 adsorption properties enable TMPs to possess promising application potential in CO2 capture and separation from low-concentration gas mixtures.

Confined Complexation Reaction of Metal Ions with a Lipophilic Surfactant at the Water/Air Interface: A New Understanding Based on Surface Experiments and Molecular Dynamics Simulations.

Understanding the fundamentals of confined chemical reaction was an important subject in various heterogeneous physicochemical processes. Here, we investigated the orientation behavior of an amphiphilic ligand, the tri- n-octylphosphine oxide (TOPO), in a compressed monolayer at the air/water interface and its impact on the complexation reactivity of TOPO molecules with chromate ions at the interface. The analysis of sum frequency generation and polarization modulation infrared reflection absorption spectroscopy experiments combined with surface pressure measurements reveals a significant dependence of the adsorption rate and saturated concentration of chromate ions on the orientation of TOPO molecules during the increase of the surface pressure. In parallel, the analysis of molecular dynamics simulations indicates that the interaction energy between TOPO molecules and chromate ions is strongly sensitive to the orientation of TOPO molecules confined at the water/air interface. The present work provides a novel insight into the unique chemical reactivity of molecules in a confined microenvironment, and it provides a basis for further progresses in improving chemical reactivity and selectivity of molecules in a confined environment by regulating confinement of molecules.

Aptamer and PNIPAAm co-conjugated nanoparticles regulate activity of enzyme with different temperature.

In this paper, we described a temperature responsive nano-system that can regulate activity of enzyme with different temperature. Temperature responsive polymer poly(N-isopropylacrylamide) (PNIPAAm), with low critical solution temperature of 32°C, was synthesized with thiol modification. PNIPAAm and thrombin aptamer were co-functionalized on the surface of gold nanoparticles for effective regulation of thrombin activity with different temperature. On the one hand, we studied the thermal responsive properties of this inhibitor via UV-visible spectroscopy. On the other hand, we investigated the regulation of thrombin activity by this platform with different temperature. The PNIPAAm chains could extend and shrink with different temperature, which suggested that PNIPAAm on the surface of gold nanoparticles could regulate interaction between thrombin and aptamer according to temperature changing. At 25°C, PNIPAAm was hydrophilic extended state, which blocked the interaction between thrombin and aptamer on the surface of gold nanoparticles, therefore thrombin activity had no change. On the contrary, at 37°C, PNIPAAm transformed from hydrophilic extended state to hydrophobic shrank state, allowing the aptamer to capture thrombin, inhibiting the activity of thrombin. More interestingly, this regulation was reverse to normal condition, where 37°C was always the optimum reaction temperature for most of human enzymes. This system we prepared was opposite, which was capable of inhibiting the thrombin activity at 37°C. Furthermore, this was the first report of regulation of thrombin activity using this temperature responsive platform.

Reversible regulation of thrombin adsorption and desorption based on photoresponsive-aptamer modified gold nanoparticles.

In the protein separation, adsorption and desorption of target protein have been using different buffer condition. Different buffer will change the structure and activity of target protein in some cases. This work describes the use of different wavelength light for remote regulation of adsorption and desorption of target protein in the same buffer solutions. A dynamic system that captured and released protein in response to light is reported. Matrix gold nanoparticles and light-responsive affinity ligand comprising thrombin aptamer (APT15), polyethylene glycol linker, and azobenzene-modified complementary sequence were used. UV light induced a trans-cis isomerization of the azobenzene that destabilized the duplex of aptamer and azobenzene-modified complementary sequence, resulting in thrombin binding to aptamer sequence. Visible light irradiation resulted in DNA duplex rehybridization and thrombin released. Our work demonstrates that different light wavelengths effectively regulated the adsorption and desorption of thrombin in the same buffer, and this system also can capture and release prothrombin from plasma with different wavelength light. Furthermore, this method can be widely applied to a variety of different protein separation process.

Bare magnetic nanoparticles as fluorescence quenchers for detection of thrombin.

Rapid and sensitive detection of thrombin has very important significance in clinical diagnosis. In this work, bare magnetic iron oxide nanoparticles (magnetic nanoparticles) without any modification were used as fluorescence quenchers. In the absence of thrombin, a fluorescent dye (CY3) labeled thrombin aptamer (named CY3-aptamer) was adsorbed on the surface of magnetic nanoparticles through interaction between a phosphate backbone of the CY3-aptamer and hydroxyl groups on the bare magnetic nanoparticles in binding solution, leading to fluorescence quenching. Once thrombin was introduced, the CY3-aptamer formed a G-quartet structure and combined with thrombin, which resulted in the CY3-aptamer being separated from the magnetic nanoparticles and restoration of fluorescence. This proposed assay took advantage of binding affinity between the CY3-aptamer and thrombin for specificity, and bare magnetic nanoparticles for fluorescence quenching. The fluorescence signal had a good linear relationship with thrombin concentration in the range of 1-60 nM, and the limit of detection for thrombin was estimated as low as 0.5 nM. Furthermore, this method could be applied for other target detection using the corresponding fluorescence labeled aptamer.

Expression and purification of an antitumor-analgesic peptide from the venom of Mesobuthus martensii Karsch by small ubiquitin-related modifier fusion in Escherichia coli.

To prevent protein aggregation, some proteins are usually expressed as fusion proteins from which target proteins can be released by proteolytic or chemical reagents. In this report, small ubiquitin-related modifier (SUMO) linked with a hexa-histidine tag was used as a fusion partner for the antitumor-analgesic peptide from the venom of Buthus martensii (Karsch) scorpion (AGAP). The optimal expression level of the soluble fusion protein, SUMO-AGAP, was up to 40% of the total cellular protein. The fusion protein was purified by Ni-NTA affinity chromatography and cleaved by a SUMO-specific protease (Ulp1) to obtain the recombinant AGAP (rAGAP), which was further purified by Ni-NTA affinity chromatography. The purified final product was >95% pure by SDS-PAGE stained with Coomassie brilliant blue R-250. Mass spectroscopic analysis indicated the protein to be 7142.63 Dalton, which equaled the theoretically expected mass. N-terminal sequencing of rAGAP showed the sequence corresponded to the native protein. MTT assay indicated the rAGAP could significantly inhibit the proliferation of Jurkat and Hut 78 T lymphoma cell lines. The further writhing experiment showed that the rAGAP had an intensive analgesic effect. The expression strategy presented in this study allows convenient high yield and easy purification of the rAGAP with native sequences.

Molecular cloning, expression, and bioactivity of dove B lymphocyte stimulator (doBAFF).

B cell activating factor (BAFF) belonging to the tumor necrosis factor (TNF) family is a novel member of the tumor necrosis factor ligand family and plays an important role in B lymphocyte maturation and survival. cDNA of dove B lymphocyte stimulator (doBAFF) was amplified from total RNA of dove spleen by RT-PCR (reverse transcription PCR). The open reading frame of doBAFF consists 867 bases encoding a protein of 288 amino acids. Sequence comparison indicated the amino acid sequence of doBAFF showed high identity to hBAFF (50.66%) and cBAFF (91.32%). The result of RT-PCR showed that doBAFF was highly expressed in the spleen and bursa of fabricius. To enhance the soluble expression of doBAFF in Escherichia coli, we fused the extracellular region of doBAFF gene with a small ubiquitin-related modifier gene (SUMO) by over-lap PCR. The resulting fused protein SUMO-sdoBAFF was highly expressed in DE3(BL21) with a molecular weight of 35kDa. The fusion protein was purified by Ni-NTA affinity chromatography and cleaved by a SUMO-specific protease, Ulp1. The sdoBAFF protein was further purified by Ni-NTA affinity chromatography. In vitro, the MTT assays indicated that the purified doBAFF as well as SUMO-sdoBAFF proteins were able to promote bursa lymphocyte survival in dose-dependent manner.