The Evolution of a Web-Based Chemistry Learning Site

This paper discusses some of the various means of presenting Web-based chemistry tutorials and the relative effectiveness of each method. These methods utilize animated images, interactive question and answer tutorials, images with embedded links, and interactive multiple-choice questions with answers that attempt to explain why wrong selections are not correct.Presented at the ACS Division of Chemical Education sponsored symposium on web-assisted learning in chemistry at its 221st national meeting in San Diego, CA April 1–5, 2001.     

Dependence of magnetic ordering temperature of doped and undoped EuFe2As2 on hydrostatic pressure to 0.8 GPa

The ac susceptibility of single crystalline tetragonal EuFe₂As₂, EuFe₂As_1.4P_0.6, and EuFe_1.715Co_0.285As₂ has been measured over the temperature and hydrostatic (He-gas) pressure ranges 10–60 K and 0–0.8 GPa, respectively. For all three samples the magnetic ordering temperature (17–19 K) from the Eu sublattice increases linearly with pressure, presumably due to the enhanced exchange coupling between Eu-layers. No evidence for a superconducting transition was observed in the susceptibility for any sample over the measured temperature/pressure range.     

Material effects in ultra-short pulse laser drilling of metals

Although hole drilling using ultra-short laser pulses has been shown to produce holes of excellent quality, we have observed that during the evolution of the hole, the morphology of the hole bottom has a dependence on fluence, number of shots, and polarization. We describe the nature of this structure within the hole and under what conditions it is observed.     

Simulation of material removal efficiency with ultrashort laser pulses

Understanding physical processes accompanying ablation is necessary for the optimal use of ultrashort laser pulse (USLP) material processing. We describe the implementation of self-consistent electromagnetic propagation-energy absorption in our numerical models. We evaluate absorption as a function of the pulse duration, energy, angle of incidence and polarization. We formulate a measure of material removal and use it to estimate the effect of energy, pulselength and prepulses on material removal.     

Quantifying CFSE label decay in flow cytometry data

We developed a series of models for the label decay in cell proliferation assays when the intracellular dye carboxyfluorescein succinimidyl ester (CFSE) is used as a staining agent. Data collected from two healthy patients were used to validate the models and to compare the models with the Akiake Information Criteria. The distinguishing features of multiple decay rates in the data are readily characterized and explained via time dependent decay models such as the logistic and Gompertz models.     

Reviewing the use of chitosan and polydopamine for electrochemical sensing

Biopolymers possess highly favorable properties for electrochemical biosensing such as their inherent biocompatibility, inexpensive nature, and strong interfacial adhesion. In this mini-review, we will focus on chitosan and polydopamine, two of the most commonly used biopolymers, for electrochemical sensing applications. Chitosan is a polysaccharide that exhibits high chemical resistance, offers straightforward modification and cross-linking, and possesses antibacterial properties and mucoadhesion. Polydopamine has the benefit of universal adhesion, in addition to the ability to form self-assembled structures. We will demonstrate how the unique structural and electrochemical features of these biopolymers can be used in a range of electrochemical biosensing platforms.     

Metallic Free Carbon Nanotube Cluster Modified Screen Printed Electrodes for the Sensing of Nicotine in Artificial Saliva

We demonstrate that metallic free carbon nanotube cluster modified screen printed electrodes provide an advantageous sensing methodology for nicotine. The electrochemical oxidation of nicotine is possible at low potentials compared to other commercially available carbon electrodes. Using the carbon nanotube cluster modified screen printed electrodes a detection range of 10 to 1000 μM is possible with a limit of detection of 2 μM. The sensing protocol is shown to be viable in artificial saliva and is promising as a portable and rapid sensor for nicotine in oral fluid (saliva) in areas such as health/life insurance, instances where smoking is banned and also as a point of care test to help improve smoking quit rates.     

The Heterogeneity of Multiwalled and Single‐Walled Carbon Nanotubes: Iron Oxide Impurities Can Catalyze the Electrochemical Oxidation of Glucose

It is well established that the heterogeneity of carbon nanotubes must be determined before the origin of the electrochemical performance can be attributed. Recently it has been diligently reported that for the case of multiwalled carbon nanotube modified electrodes, copper oxide impurities are responsible for the electrochemical activity facilitating a nonenzymatic sensing strategy towards glucose. We have explored both commercially available multiwalled and single‐walled carbon nanotubes for the sensing of glucose and find that iron oxide impurities remaining from the fabrication process are the electroactive sites facilitating the nonenzymatic detection of glucose. Given that the multiwalled carbon nanotubes in this work are purchased from the same leading supplier as that used recently, discrepancies in the fabrication process exist which clearly has implications in the commercialization of electrochemical sensors based on multiwalled carbon nanotubes.     

The profound effect of fluorine substitution on the reactivity and regioselectivity of nucleophilic substitution reactions of strained heterocycles. A study of aziridine and its derivatives

Unlike the synthetically exploited oxiranes and thiiranes, aziridines that lack electron-withdrawing substituents, such as acyl or sulfonyl functionalities at nitrogen, are rather unreactive. As expected, three-membered aziridine 6 was calculated to be significantly more reactive than azetidine 7 in nucleophilic cleavage by ammonia, a typical nucleophile. The reactivity of 7 was about the same as that of an acyclic model compound, 8, when release of ring strain in the transition state was taken into account. Fluorine due to its similar size but vastly different electronegativity has been substituted for hydrogen as a means of modifying chemical properties for varied applications. In the present investigation, the effect of fluorine substitution at aziridine positions other than nitrogen was studied. Computations at the MP2(Full)/6-311++G(d,p)//MP2(Full)/6-31+G(d) level found a vast preference for attack by ammonia at the 3-position of 2-fluoroaziridine in the gas phase at 298 K. When release of ring strain was taken into account, this compound reacted more than 10(11) times faster than 6. The reaction rate with trans-2,3-difluoroaziridine was about twice that of 2-fluoroaziridine, while its diastereomer reacted with ammonia considerably slower. Acyclic fluorinated amine model compounds were employed to assess the generality of the effects produced by fluorine substitution. The results were rationalized by the energy contributions of strain energy releases, stabilization of the leaving group, and the relative electrostatic energies of the heterocycles in the transition states. The more reactive fluoroaziridines underwent nucleophilic attack at rates comparable to those of N-acetylaziridine.