Mechanistic study of photomediated triangular silver nanoprism growth

This article presents a mechanistic study of the photomediated growth of silver nanoprisms. The data show that the photochemical process is driven by silver redox cycles involving reduction of silver cations by citrate on the silver particle surface and oxidative dissolution of small silver particles by O2. Bis(p-sulfonatophenyl)phenylphosphine increases the solubility of the Ag(+) by complexing it and acts as a buffer to keep the concentration of Ag(+) at 20 microM. The silver particles serve as photocatalysts and, under plasmon excitation, facilitate Ag(+) reduction by citrate. Higher Ag(+) concentrations favor a competitive thermal process, which results in increased prism thickness.     

Molecular assembly of rubrene on a metal/metal oxide nanotemplate

We investigated the adsorption properties and self-assembly of rubrene molecules on the copper oxide nanotemplate formed by high-temperature exposure of Cu(110) to molecular oxygen. Using high-resolution scanning tunneling microscopy under ultrahigh-vacuum conditions, we observed a complex variety of self-assembled motifs, driven by competing effects such as the chemical affinity between the organic molecule and the surface, surface coverage, and spatial confinement of the rubrene molecules within the rows of the template.     

Diameters of 3-sphere quotients

Let G⊂O(4) act isometrically on S³. In this article we calculate a lower bound for the diameter of the quotient spaces S³/G. We find it to be , which is exactly the value of the lower bound for diameters of the spherical space forms. In the process, we are also able to find a lower bound for diameters for the spherical Aleksandrov spaces, Sn/G, of cohomogeneities 1 and 2, as well as for cohomogeneity 3 (with some restrictions on the group type). This leads us to conjecture that the diameter of Sn/G is increasing as the cohomogeneity of the group G increases.     

Purification of high-throughput organic synthesis libraries by counter-current chromatography

Experiments were performed to evaluate whether counter-current chromatography (CCC) could function as an alternative purification method to reversed-phase high-performance liquid chromatography (RP-HPLC) and normal-phase supercritical fluid chromatography (SFC). RP-HPLC and SFC are the routine methods currently used in our high-throughput purification (HTP) facility for the purification of high-throughput organic synthesis (HTOS) libraries and medicinal chemistry reaction mixtures. Pre-equilibration of the solvent mixture layers was not mandatory for effective chromatography when hexanes–ethyl acetate–methanol–water (HEMW) solvent mixtures were used. Key to the use of CCC for high-throughput applications is the ability to effectively select a solvent system appropriate to each library member. Pilot-scale CCC elution time was used to estimate a starting solvent ratio and RP-HPLC retention time was then used to adjust solvent ratios within a particular library. It was also found that dimethyl sulfoxide (DMSO) and DMSO–methanol were suitable as sample injection solvents when using the HEMW solvent systems.     

Nafion-CNT coated carbon-fiber microelectrodes for enhanced detection of adenosine

Adenosine is a neuromodulator that regulates neurotransmission. Adenosine can be monitored using fast-scan cyclic voltammetry at carbon-fiber microelectrodes and ATP is a possible interferent in vivo because the electroactive moiety, adenine, is the same for both molecules. In this study, we investigated carbon-fiber microelectrodes coated with Nafion and carbon nanotubes (CNTs) to enhance the sensitivity of adenosine and decrease interference by ATP. Electrodes coated in 0.05 mg mL(-1) CNTs in Nafion had a 4.2 ± 0.2 fold increase in current for adenosine, twice as large as for Nafion alone. Nafion-CNT electrodes were 6 times more sensitive to adenosine than ATP. The Nafion-CNT coating did not slow the temporal response of the electrode. Comparing different purine bases shows that the presence of an amine group enhances sensitivity and that purines with carbonyl groups, such as guanine and hypoxanthine, do not have as great an enhancement after Nafion-CNT coating. The ribose group provides additional sensitivity enhancement for adenosine over adenine. The Nafion-CNT modified electrodes exhibited significantly more current for adenosine than ATP in brain slices. Therefore, Nafion-CNT modified electrodes are useful for sensitive, selective detection of adenosine in biological samples.     

Entire solutions of first-order nonlinear partial differential equations

We show that any entire solution of an essentially nonlinear first-order partial differential equation in two variables must be linear.

     

The Zoo Connection: A Cooperative Project Between Formal and Informal Educational Institutions

This project was a cooperative effort between university faculty, elementary school teachers, and members of the Education Department at the Indianapolis Zoo. The purpose of this project was to develop, evaluate, and disseminate a set of fourteen K-6 science lessons that could be used in conjunction with field trips to the zoo. These lessons, titled The Zoo Connection, follow the Learning Cycle teaching model. In addition to following the model, the development of the lessons was based on the premise that teachers should focus on a specific science concept or set of related concepts when visiting a zoo. Workshop sessions were conducted to introduce teachers to the materials and to provide them with strategies for implementing the materials in their science instruction. An evaluation was conducted for each workshop session to determine teachers' perceptions of the materials and to determine whether they felt prepared to use them with their students. The materials were also field-tested in several elementary schools to assess their effectiveness for presenting science concepts to elementary school children. Results indicate that teachers felt the workshops adequately prepared them to use the materials and that the materials were effective for presenting science concepts.     

Polyvinylidene fluoride-co-chlorotrifluoroethylene and polyvinylidene fluoride-co-hexafluoropropylene nanofiber-coated polypropylene microporous battery separator membranes

Nanofiber-coated polypropylene (PP) separator membranes were prepared by coating a Celgard® microporous PP membrane with electrospun polyvinylidene fluoride-co-chlorotrifluoroethylene (PVDF-co-CTFE) and PVDF-co-CTFE/polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP) nanofibers. Three PVDF polymer solutions of varying compositions were used in the preparation of the nanofiber coatings. Two of the polymer solutions were PVDF-co-CTFE blends made using different types of PVDF-co-HFP copolymers. The PVDF-co-CTFE and PVDF-co-CTFE/PVDF-co-HFP blend nanofiber coatings have been found to have comparable adhesion to the PP microporous membrane substrate. The electrolyte uptakes and separator–electrode adhesion properties of nanofiber-coated membranes were evaluated. Both the electrolyte uptake and the separator–electrode adhesion were improved by the nanofiber coatings. The improvement in electrolyte update capacity is not only related to the gelation capability of the PVDF copolymer nanofibers, but also attributed to the increased porosity and capillary effect on nanofibrous structure of the electrospun nanofiber coatings. Enhancement of the separator–electrode adhesion was owing to the adhesion properties of the copolymer nanofiber coatings. Compared with the PVDF-co-CTFE/PVDF-co-HFP blend nanofiber coatings studied, the PVDF-co-CTFE coating was more effective in improving the electrolyte uptake and separator–electrode adhesion. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013