The growing utility of semiconductor quantum dots (QDs) in biochemical and cellular research necessitates, in turn, continuous development of surface functionalizing ligands to optimize their performance for ever more challenging and diverse biological applications. Here, we describe a new class of multifunctional polymeric ligands as a stable, compact and high affinity alternative to multidentate thiolated molecules. The polymeric ligands are designed with a poly(acrylic acid) backbone where pyridines are used as anchoring groups that are not sensitive to degradation by air and light, along with short poly(ethylene glycol) (PEG) pendant groups which are coincorporated for aqueous solubility, biocompatibility and colloidal stability. The percentages of each of the latter functional groups are controlled during initial synthesis along with incorporation of carboxyl groups which serve as chemical handles for subsequent covalent modification of the QD surface. A detailed physicochemical characterization indicates that the multiple pyridine groups are efficiently bound on the QD surface since they provide for relatively small overall hydrodynamic sizes along with good colloidal stability and strong fluorescence over a wide pH range, under high salt concentration and in extremely dilute conditions at room temperature under room light over extended timeframes. Covalent conjugation of dyes and metal-affinity coordination with functional enzymes to the QD surfaces were also demonstrated. Biocompatibility and long-term stability of the pyridine polymer coated QDs were then confirmed in a battery of relevant assays including cellular delivery by both microinjection and peptide facilitated uptake along with intracellular single QD tracking studies and cytotoxicity testing. Cumulatively, these results suggest this QD functionalization strategy is a viable alternative that provides some desirable properties of both compact, discrete ligands and large amphiphilic polymers.

The Johari-Goldstein (JG) secondary relaxation, presumed to be universal, has never been seen in 1,4-polyisoprene (PI) by dielectric spectroscopy, despite very many measurements extending over the past half-century. By using a high-resolution capacitance bridge, we are able to show the existence of a secondary relaxation in PI that has the properties of the JG process. Measurements were also carried out at lower temperatures, which probe the dynamics of chain units "caged" by neighboring segments comprising the local structure. The caged dynamics precede by decades of time the JG relaxation and, from general physical principles, are also expected to be a property of all glass-forming materials. Collectively, the caged dynamics and JG relaxation serve as precursors to structural relaxation (i.e., the glass transition) and thus are of central importance to understanding vitrification. The present data show that the dynamics of caged PI repeat units are manifested as a nearly constant loss (NCL). This NCL has been found in other glass-formers, both molecular and polymeric, and its temperature dependence in PI is similar to that for other materials. The experimental results are consistent with the predictions from the coupling model.

End-linked polydimethysiloxane (PDMS) networks were prepared by end-linking vinylterminated PDMS chains with tetrafunctional silanes. Dielectric R-relaxation spectra, thermal expansivities, and the (rubbery) elastic modulus were measured for these materials. From the cross-link density at which marked changes occur in the segmental relaxation times and the TR-scaled temperature dependence (fragility), a characteristic length for the R-relaxation was determined. The result, 14 Å at TR, is quite close to the length scale associated with constraint of crystallization in similar PDMS networks. Cross-linking also affects the thermal expansion and elastic modulus, although these properties exhibit a smoother variation with cross-link density.

This study examined similarities and differences in study approaches reported by general chemistry students performing at different achievement levels. The study population consisted of freshmen enrolled in a required year-long general chemistry course at the U.S. Naval Academy. Students in the first and second semesters of the course were surveyed using a modified version of the published Approaches and Study Skills Inventory for Students (ASSIST) referred to as the M-ASSIST (Modified Approaches and Study Skills Inventory). Responses to items associated with using deep or surface approaches to studying were examined for students of three achievement levels (A/B, C, and D/F course grades) using both ANOVA and Structured Means Modeling to look for differences in study approaches between achievement levels. Results show that, with only 12 items, the M-ASSIST can be used to measure differences in reported use of deep and surface approaches by students in different achievement groups; that Structured Means Modeling can uncover significant differences that are not apparent with an ANOVA analysis of the same data; and that A/B and D/F students can be classified as reporting using either using primarily deep (A/B students) or primarily surface (D/F) study approaches. C students reported study approaches characteristic of both the A/B and D/F groups, leading to the interpretation that C students may be in an intermediate and possibly transitional state between the higher- and lower-grade groups. These results suggest a new understanding of C students as those who may not fully implement deep approaches to studying but, in general, demonstrate less reliance on surface approaches than lower-achieving students.

Interest in undergraduate student research has grown in response to initiatives from various professional societies and educational organizations. Participation in research changes student attitudes towards courses as they realize the utility and relevance of what they are learning. At the U.S. Naval Academy, the chemistry majors' curriculum was redesigned to require fourth-year projects of all the majors. The restructured laboratory curriculum is based on four semesters of integrated laboratory, a sequence organized around broad themes in chemistry such as separation and purification, synthesis, qualitative analysis, quantitative analysis, and so forth rather than traditional subdisciplines within chemistry. The integrated laboratory curriculum has facilitated the inclusion of a research or capstone experience for all the chemistry majors. The two tracks for the fourth-year chemistry majors to participate in projects are described. The development of these options, challenges with implementation, outcomes, and advice to other institutions are discussed. These changes required significant effort in redesigning the curriculum and the acceptance of undergraduate research as a culminating experience worthy of faculty and administrative support. However, the effort was justified as the number of chemistry majors has increased, students seem more satisfied with the major, interactions between students and faculty have increased, and research productivity seems to have been enhanced.