Radical copolymerization of novel trifluorovinyl ethers with ethyl vinyl ether and vinyl acetate: Estimating reactivity ratios and understanding reactivity behavior of the propagating radical

Two novel trifluorovinyl ether (TFVE) monomers were copolymerized with either ethyl vinyl ether (EVE) or vinyl acetate (VAc) in a redox‐initiated aqueous emulsion: 1‐(2‐phenoxyethoxy)‐1,2,2‐trifluoroethene (Ph‐TFVE) and 1‐[2‐(2‐ethoxyethoxy)ethoxy]‐1,2,2‐trifluoroethene (Et‐TFVE). Previous studies demonstrated a propensity for radical hydrogen abstraction from the oligoether pendant group during the homopolymerization of Et‐TFVE with continued propagation of the resulting radical, thereby providing the rationale to investigate the copolymerization of our new TFVEs with EVE or VAc. Reactivity ratios were estimated using the error‐in‐variables model from a series of bulk free radical copolymerizations of Ph‐TFVE with EVE or VAc. The reactivity ratios were r_Ph‐TFVE = 0.25 ± 0.07, r_EVE = 0.016 ± 0.04; r_Ph‐TFVE = 0.034 ± 0.04, r_VAc =0.89 ±0.08. Partial hydrolysis of polymers containing VAc to vinyl alcohol (VA) resulted in two terpolymers: poly(Ph‐TFVE‐co‐VAc‐co‐VA) and poly(Et‐TFVE‐co‐VAc‐co‐VA), respectively. We investigated the possibility of hydrogen abstraction from VAc during polymerization by comparing the molar mass before and after hydrolysis. Abstraction from VAc was not apparent during polymerization; however, abstraction from the oligoether pendant group of Et‐TFVE was again evident and was more significant for those copolymers having a greater fraction of Et‐TFVE in the monomer feed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1344–1354, 2000     

SERS-based plasmonic nanobiosensing in single living cells

In this paper, we describe the development and application of a pH-sensitive plasmonics-active fiber-optic nanoprobe suitable for intracellular bioanalysis in single living human cells using surface-enhanced Raman scattering (SERS) detection. The effectiveness and usefulness of SERS-based fiber-optic nanoprobes are illustrated by measurements of intracellular pH in HMEC-15/hTERT immortalized “normal” human mammary epithelial cells and PC-3 human prostate cancer cells. The results indicate that fiber-optic nanoprobe insertion and interrogation provide a sensitive and selective means to monitor cellular microenvironments at the single cell level.     

A practical approach to the synthesis of 2,4-disubstituted oxazoles from amino acids

[reaction: see text] A new sequence for the synthesis of various 2,4-disubstituted oxazoles from alpha-amino acids is reported. The method is shown to be general and incorporates the reagent combination, triphenylphosphine/hexachloroethane, for cyclodehydration of intermediate alpha-acylamino aldehydes. Implementation of this reagent system for the conversion of alpha-acylamino ketones to oxazoles is briefly investigated.     

Insight into the electrochemical reduction of CO2 on gold via surface-enhanced Raman spectroscopy and N-containing additives

Journal of Solid State Electrochemistry - Due to increasing levels of greenhouse gases in the atmosphere, increased attention has been given to minimizing their emissions and reducing current...     

Influence of Ti addition on boehmite-derived aluminum silicate aerogels: structure and properties

Aluminosilicate aerogels offer potential for extremely low thermal conductivities at temperatures greater than 900?°C, beyond where silica aerogels reach their upper temperature use limits. Aerogels have been synthesized at two Al:Si ratios, a 3Al:1Si mullite composition, and an 8Al:1Si alumina rich composition. Boehmite (AlOOH) is used as the Al source, and tetraethoxysilane as the Si precursor. The influence of Ti as a ternary constituent, introduced through the addition of titanium isopropoxide in the sol?Cgel synthesis, on aerogel morphology and thermal properties is evaluated. Four different boehmite precursor powders are evaluated. Morphology, surface area and pore size, and thermal transformation vary with the crystallite size of the starting boehmite powder, as does incorporation of titanium and evolution of Ti-containing crystalline phases. The addition of Ti influences sol viscosity, gelation time, surface area and pore size distribution, as well as phase formation on heat treatment.     

Ordering surfaces on the nanoscale: implications for protein adsorption

Monolayer-protected metal nanoparticles (MPMNs) are a newly discovered class of nanoparticles with an ordered, striped domain structure that can be readily manipulated by altering the ratio of the hydrophobic to hydrophilic ligands. This property makes them uniquely suited to systematic studies of the role of nanostructuring on biomolecule adsorption, a phenomenon of paramount importance in biomaterials design. In this work, we examine the interaction of the simple, globular protein cytochrome C (Cyt C) with MPMN surfaces using experimental protein assays and computational molecular dynamics simulations. Experimental assays revealed that adsorption of Cyt C generally increased with increasing surface polar ligand content, indicative of the dominance of hydrophilic interactions in Cyt C-MPMN binding. Protein-surface adsorption enthalpies calculated from computational simulations employing rigid-backbone coarse-grained Cyt C and MPMN models indicate a monotonic increase in adsorption enthalpy with respect to MPMN surface polarity. These results are in qualitative agreement with experimental results and suggest that Cyt C does not undergo significant structural disruption upon adsorption to MPMN surfaces. Coarse-grained and atomistic simulations furthermore elucidated the important role of lysine in facilitating Cyt C adsorption to MPMN surfaces. The amphipathic character of the lysine side chain enables it to form close contacts with both polar and nonpolar surface ligands simultaneously, rendering it especially important for interactions with surfaces composed of adjacent nanoscale chemical domains. The importance of these structural characteristics of lysine suggests that proteins may be engineered to specifically interact with nanomaterials by targeted incorporation of unnatural amino acids possessing dual affinity to differing chemical motifs.     

Gender,Prior Academic Performance and Beliefs as Predictors of Attitudes Toward Biology Laboratory Experiences

The purpose of this study was to investigate the relationships between gender, prior academic performance, beliefs and student attitudes toward biology laboratory experiences. The sample consisted of 294 students from 10th, 11th and 12th grades enrolled in a Catholic high school in a major metropolitan area in the Southeast. Two 11-item scales were created; one to measure student attitudes toward biology laboratory experiences, and the other to measure student beliefs about the benefits of biology laboratory. A three-way analysis of variance (gender × prior academic performance × beliefs) was conducted with the attitudes toward biology used as the dependent variable. Gender had a significant effect on attitudes, with females reporting more positive attitudes toward biology laboratory than males. Prior academic experience was also a significant predictor of attitudes; students who received lower GPAs in previous science courses reported more positive attitudes toward biology laboratory than students with higher GPAs. Based on previous research this finding was surprising; however, it appears that lower achieving students may perceive that there is a higher benefit from “hands on” laboratory experiences than high achieving students. The data also indicated that beliefs had the strongest correlations with attitudes; students who believed laboratory experiences were beneficial had more positive attitudes. The implications for research, theory and practice are also presented.     

Controlling Proton Delivery through Catalyst Structural Dynamics

The fastest synthetic molecular catalysts for H₂ production and oxidation emulate components of the active site of hydrogenases. The critical role of controlled structural dynamics is recognized for many enzymes, including hydrogenases, but is largely neglected in designing synthetic catalysts. Our results demonstrate the impact of controlling structural dynamics on H₂ production rates for [Ni(P^Ph₂N^C6H4R₂)₂]²⁺ catalysts (R=n‐hexyl, n‐decyl, n‐tetradecyl, n‐octadecyl, phenyl, or cyclohexyl). The turnover frequencies correlate inversely with the rates of chair–boat ring inversion of the ligand, since this dynamic process governs protonation at either catalytically productive or non‐productive sites. These results demonstrate that the dynamic processes involved in proton delivery can be controlled through modification of the outer coordination sphere, in a manner similar to the role of the protein architecture in many enzymes. As a design parameter, controlling structural dynamics can increase H₂ production rates by three orders of magnitude with a minimal increase in overpotential.