Integrating Service Learning into the College Chemistry Curriculum

The specular-reflectance technique has been used to develop an experiment for an undergraduate instrumental course that demonstrates the ability of Fourier transform IR spectroscopy to routinely procure vibrational spectra of thin films of polymethylmethacrylate on reflective copper discs. The experiment introduces students to the specular-reflectance technique and its selection rules, then demonstrates how they reveal the orientational constraint of adsorbed molecules within a thin film. Suggestions are included on how to expand the experiment to demonstrate the relationships between film thickness and the amount of light absorbed.     

DESIGN AND CHARACTERIZATION OF SEVELAMER HYDROCHLORIDE: A NOVEL PHOSPHATE-BINDING PHARMACEUTICAL

ABSTRACT

Sevelamer hydrochloride (polyallylamine crosslinked with epichlorohydrin) is a polymeric hydrogel that has been developed as an oral pharmaceutical to prevent the absorption of dietary phosphate by kidney dialysis patients. It has been found to bind to phosphate in vitro, and to do so more effectively than a wide range of other cationic polymers. It shows a preference for phosphate over other intestinal anions, such as chloride and bicarbonate. The preference for phosphate is believed to be due to its dianion character, and may also involve hydrogen bonding. The absorption of phosphate in vitro is rapid (less than a minute) relative to the time of passage of such a drug through the small intestine (hours). It has also been found to prevent the absorption of dietary phosphate in vivo and in humans, and is presently awaiting FDA approval.     

Reactions of Podophyllotoxin with DDQ

Introduction 2, 3-Dichloro-5, 6-dicyanobenzoquinone (DDQ) can react with lignans of the mono- arylidene-butyrolactone1, aryltetralin2, dibenzylbutane3 and aryltetralin-butyrolactone4,5 series. We have studied the reactions of this reagent with podophyllotoxin 1, which is a well-known natural product on account of its long history of use in folk medicine and the biological activity of its many derivatives6. In particular, derivatives of 4-demethyl epipodophyllotoxin are used in cancer chemo…     

DIFFUSION AND BIFURCATION PROBLEMS IN SINGULARLY PERTURBED DOMAINS

ABSTRACT. Diffusion problems under singular perturbations of the domain or the boundary conditions are analyzed. The first problem that we consider is the diffusion of a material from a domain that is nearly impermeable, having only several small patches on the boundary where the material can slowly leak out. The second problem that is studied is the diffusion of a material that originates from some localized regions in a two or three‐dimensional domain. Steady‐state solutions and the long‐time behavior of solutions are analyzed in detail. Finally, the analysis is extended to determine the change in bifurcation values associated with nonlinear diffusion equations under singular perturbations of the domain. The results are then applied to a model in resource management.     

Boundedness and Existence of Periodic Solutions of Quasi-linear Systems

Systems of the form x' = A (t, x)x+B(t, x) are considered, andresults are obtained concerning boundedness and periodicityby using corresponding information from linear systems of theform x' = A (t, f(t))x+B(t, f(t)).]Here f(t) belongs to theclosed ball of a suitable Banach space.     

The onset of thermal runaway in partially insulated or cooled reactors

The conditions for the onset of thermal runaway in partiallyinsulated or cooled reactors are investigated. The temperaturein the reactor is taken to satisfy a nonlinear elliptic equationand the reaction is modelled by an Arrhenius heat generationterm with finite activation energy. To determine the onset ofthermal runaway, the method of matched asymptotic expansionsis used to derive expressions for the critical Frank-Kamenetskiiparameter _c() for reactors containing either a small coolingrod or having a small cooling patch on their boundary. The theoryused to determine _c() is an extension of the results of Wardand Keller (1991). These previous results of Ward and Kellerare also extended to the case of finite activation energiesby using a numerical scheme to evaluate the coefficients inthe asymptotic results for _c(). In some special cases, the asymptoticexpansions for _c() are compared with numerical results for _c(),and clear agreement is found.     

PHOTOPHYSICAL AND PHOTOBIOLOGICAL PROPERTIES OF DIPORPHYRIN ETHERS

Spectral properties of several diporphyrin ethers were assessed in different solvents and after accumulation by leukemia L1210 cells in vitro. To facilitate studies in a variety of solvents, both tetramethylesters of the diporphyrin ethers and free acids were employed. For comparison, studies on the corresponding porphyrin monomers were also carried out. The joining of two porphyrins by an ether linkage had several consequences. We observed a blue shift in the Soret band of the ethers, but not of the corresponding simple porphyrins, in protic solvents. This phenomenon is likely related to ether aggregation under conditions which promote H-bonding. The presence of an ether linkage was associated with enhanced fluorescence at 630-640 nm and decreased fluorescence lifetimes and yields, especially in protic solvents. The ether linkage was unaffected by intracellular enzymes, but porphyrin esters were readily hydrolyzed upon accumulation by L1210 cells. The joining of two hematoporphyrin molecules by an ether linkage promoted dye accumulation by L1210 cells. In contrast, accumulation of mesoporphyrin and protoporphyrin was thereby retarded.     

Drift-dominated current flow in forward-biased semiconductor devices

The drift-diffusion equations of semiconductor physics, allowingfor field-dependent drift velocities, are analysed by the methodof matched asymptotic expansions for one-dimensional PN andPNPN forward-biased structures. The analysis is relevant todescribing the structure of the solutions to the drift-diffusionequations for large electric fields when drift velocity saturationeffects become significant. In this high-field limit, the boundarylayer structure for the solutions to the drift-diffusion equationsis seen to differ substantially from that near equilibrium.In particular, boundary layers for the carrier concentrationscan occur near the contacts. The asymptotic solutions and thecurrent-voltage relations, constructed in the high-field limit,are found to agree well with direct numerical solutions to thedrift-diffusion equations.