Plasmons in Pb nanowire arrays on Si(557): Between one and two dimensions

The plasmon dispersion in arrays of nanowires of Pb close to an average Pb coverage of one monolayer was determined on the Si(557) surface using electron energy loss spectroscopy with both high energy and momentum resolution. While we find purely one-dimensional (1D) plasmon losses at a Pb concentration of 1.31 monolayers (ML), measured with respect to the Si(111) surface concentration, the 1.2 and 1.4 ML coverages exhibit wavelength-dependent transitions from 1D to anisotropic 2D properties. However, due to the high anisotropy in the system at all coverages, the dispersion curves exhibit 1D characteristics in both directions. This behavior seems to be related to the Pb-induced refacetting of the Si(557) surface, which depends on Pb coverage. It changes both effective system sizes and coupling strength between miniterraces. © 2011 American Physical Society.Ministry of Education, Culture, Sports, Science, and Technology, Japa

Conformation of Oligocholate Foldamers with 4-Aminobutyroyl Spacers

Extended oligocholates with 4-aminobutyroyl groups in between the cholate units were labeled with a naphthyl and a dansyl at the chain ends. Fluorescence resonance energy transfer (FRET) from the naphthyl to the dansyl was observed in 2:1 hexane/ethyl acetate (EA) containing a few percent of methanol. An increase of methanol in the solvent caused unfolding of the extended oligocholates, diminishing the energy-transfer efficiency. The 4-aminobutyroyl spacers strongly influenced the conformation of the oligocholates. Whereas the parent oligocholates (with no spacing groups in between the cholates) require at least five cholate groups to fold cooperatively, the 4-aminobutyroyl-spaced oligocholates could do so in more competitive solvents with as few as three or four cholates

Spacer-Dependent Folding and Aggregation of Oligocholates in SDS Micelles

Insertion of flexible, 4-aminobutyroyl spacers in between the cholate repeat units had been found previously to enhance the folding of cholate oligomers in homogeneous solution (Zhao, Y. J. Org. Chem. 2009, 74, 834−843). The opposite effect was observed when the oligomers were solubilized in aqueous solutions of sodium dodecyl sulfate (SDS). The spacers enabled formation of tight aggregates of the oligocholates in SDS solutions when the surfactant was below its critical micelle concentration (CMC). Above the CMC, SDS micelles formed and dissociated the oligocholate aggregates. The parent oligocholates (without spacers in between the repeat units) also aggregated when they were too short to fold (e.g., dimer). The longer tetramer and hexamer preferred to fold, as their rigid, awkwardly shaped backbones prevented tight packing needed in the formation of stable aggregates. Folding was favored both below and above the CMC of SDS and was enhanced by an increase in the chain length

Optimal returns for the enterprises.

Digitally enabled higher education involves the in-depth use of new-generation digital technology, which has subverted and innovated the traditional teaching mode, driven the development of high-quality teaching and learning, and improved teachers’ teaching experience, and increased efficiency. Based on ecosystem theory, this paper constructs a higher education ecosystem with the government, enterprises, and universities as the core participating subjects. It considers the participating subjects’ effort level and the ecosystem’s overall benefits under the three scenarios of noncooperative research and development (R&D), cost sharing, and cooperative R&D. The results show that (1) the service innovation effort level of the three parties increases with increasing human resource level and technology maturity, and the government’s benefit decreases with increasing cost of fulfilling social responsibility. (2) The government’s cost subsidies to universities and enterprises can enhance the service innovation level of both parties and increase the optimal returns of the three parties and the ecosystem as a whole. (3) In the cooperative R&D game scenario, the effort level of the three parties and the total ecosystem returns are greater than those in the noncollaborative R&D scenario, and after determining the subsidy coefficients of the government, Pareto optimality of the three parties and the ecosystem as a whole can be achieved. The conclusions of this study can aid in understanding the dynamic evolution mechanism of digitally enabled higher education and provide a realistic decision-making reference for higher education ecosystem managers.</div

Synergistic Hydrolysis of Cellulose by a Blend of Cellulase-Mimicking Polymeric Nanoparticle Catalysts

Enzyme-like catalysts by design have been a long sought-after goal of chemists but difficult to realize due to the challenges in the construction of multifunctionalized active sites with accurately positioned catalytic groups for complex substrates. Hydrolysis of cellulose is a key step in biomass utilization and requires multiple enzymes to work in concert to overcome the difficulty associated with hydrolyzing the recalcitrant substrate. We here report methods to construct synthetic versions of these enzymes through covalent molecular imprinting and strategic postmodification of the imprinted sites. The synthetic catalysts cleave a cellulose chain endolytically at multiple positions or exolytically from the nonreducing end by one or three glucose units at a time, all using the dicarboxylic acid motif found in natural cellulases. By mimicking the endocellulase, exocellulase, and β-glucosidase, the synthetic catalysts hydrolyze cellulose in a synergistic manner, with an activity at 90 °C in pH 6.5 buffer more than doubled that of Aspergillus niger cellulase at pH 5 and 37 °C and 44% of that of a commercial cellulase blend (from Novozyme). As robust cross-linked polymeric nanoparticles, the synthetic catalysts showed little changes in activity after preheating at 90 °C for 3 days and could be reused, maintaining 76% of activity after 10 reaction cycles

Comparison of overall higher education ecosystem benefits under the three models.

Comparison of overall higher education ecosystem benefits under the three models.</p

Optimal return for governments.

Digitally enabled higher education involves the in-depth use of new-generation digital technology, which has subverted and innovated the traditional teaching mode, driven the development of high-quality teaching and learning, and improved teachers’ teaching experience, and increased efficiency. Based on ecosystem theory, this paper constructs a higher education ecosystem with the government, enterprises, and universities as the core participating subjects. It considers the participating subjects’ effort level and the ecosystem’s overall benefits under the three scenarios of noncooperative research and development (R&D), cost sharing, and cooperative R&D. The results show that (1) the service innovation effort level of the three parties increases with increasing human resource level and technology maturity, and the government’s benefit decreases with increasing cost of fulfilling social responsibility. (2) The government’s cost subsidies to universities and enterprises can enhance the service innovation level of both parties and increase the optimal returns of the three parties and the ecosystem as a whole. (3) In the cooperative R&D game scenario, the effort level of the three parties and the total ecosystem returns are greater than those in the noncollaborative R&D scenario, and after determining the subsidy coefficients of the government, Pareto optimality of the three parties and the ecosystem as a whole can be achieved. The conclusions of this study can aid in understanding the dynamic evolution mechanism of digitally enabled higher education and provide a realistic decision-making reference for higher education ecosystem managers.</div

Detection of Hg²⁺ in Aqueous Solutions with a Foldamer-Based Fluorescent Sensor Modulated by Surfactant Micelles

A hybrid foldamer constructed from six cholate units and two methionines was labeled with a DANSYL (DNS) group. The foldamer was solubilized by surfactant micelles to allow its usage as a fluorescent sensor for mercury ions present in the micromolar range in aqueous solutions. Its sensitivity was largely independent of the concentration of nonionic surfactants but was strongly influenced by both the nature and the concentration of ionic surfactants

Translocation of Hydrophilic Molecules across Lipid Bilayers by Salt-Bridged Oligocholates

Macrocyclic oligocholates were found in a previous work (Cho, H.; Widanapathirana, L.; Zhao, Y. J. Am. Chem. Soc. 2011, 133, 141−147) to stack on top of one another in lipid membranes to form nanopores. Pore formation was driven by a strong tendency of the water molecules in the interior of the amphiphilic macrocycles to aggregate in a nonpolar environment. In this work, cholate oligomers terminated with guanidinium and carboxylate groups were found to cause efflux of hydrophilic molecules such as glucose, maltotriose, and carboxyfluorescein (CF) from POPC/POPG liposomes. The cholate trimer outperformed other oligomers in the transport. Lipid-mixing assays and dynamic light scattering ruled out fusion as the cause of leakage. The strong dependence on chain length argues against random intermolecular aggregates as the active transporters. The efflux of glucose triggered by these compounds increased significantly when the bilayers contained 30 mol % cholesterol. Hill analysis suggested that the active transporter consisted of four molecules. The oligocholates were proposed to fold into “noncovalent macrocycles” by the guanidinium−carboxylate salt bridge and stack on top of one another to form similar transmembrane pores as their covalent counterparts

Facile Preparation of Organic Nanoparticles by Interfacial Cross-Linking of Reverse Micelles and Template Synthesis of Subnanometer Au−Pt Nanoparticles

A single- and a double-tailed cationic surfactant with the triallylammonium headgroup formed reverse micelles (RMs) in heptane/chloroform containing a small amount of water. The reverse micelles were cross-linked at the interface upon UV irradiation in the presence of a water-soluble dithiol cross-linker and a photoinitiator. The resulting interfacially cross-linked reverse micelles (ICRMs) of the single-tailed surfactant aggregated in a solvent-dependent fashion, whereas those of the double-tailed were identical in size as the corresponding RMs. The ICRMs could extract anionic metal salts, such as AuCl4− and PtCl62−, from water into the organic phase. Au and Pt metal nanoparticles were produced upon reduction of metal salts. The covalent nature of the ICRMs made the template synthesis highly predictable, with the size of the metal particles controlled by the amount of the metal salt and the method of reduction. Nanoalloys were obtained by combining two metal precursors in the same reaction. Reduction of the ICRM-entrapped aurate also occurred without any external reducing agents, and the gold nanoparticles differed dramatically from those obtained through sodium borohydride reduction. The same template allowed the preparation of luminescent Au4, Au8, and Au13−Au23 clusters, as well as gold nanoparticles several nanometers in size, simply by using different amounts of gold precursor and reducing conditions