Evaluation of derivative normal pulse polarography for use in metal speciation studies

A simple inexpensive microcomputer-orientated approach for obtaining pseudo-derivative polarograms is demonstrated. The method, called derivative normal pulse polarography (d.n.p.p.), produces better signal-to-noise ratios, and therefore lower detection limits, than differential pulse polarography (d.p.p.). The foremost advantage of d.n.p.p. is its relative freedom from influences of homogeneous chemical kinetics which makes it an excellent method for metal speciation studies. Response curve shapes for Pb(II) between 2 × 10^-4 and 8 × 10^-4 M exhibit excellent agreement with theory. Titration of EDTA with 0.01 M Cu(II) and 0.01 M Cd(II) using d.n.p.p. for detection exhibited recoveries of 98.0 and 99.5%, respectively.     

Nanoscale tools to selectively destroy cancer cells

We present experimental data that demonstrate the potential of synthetic crown ether modified peptide nanostructures to act as selective and efficient chemotherapeutic agents that operate by attacking and destroying cell membranes.     

The determination of pesticidal and non-pesticidal organotin compounds in water matrices by in situ ethylation and gas chromatography with pulsed flame photometric detection

The concurrent determination of pesticidal and non-pesticidal organotin compounds in several water matrices, using a simultaneous in situ ethylation and liquid–liquid extraction followed by splitless injection mode capillary gas chromatography with pulsed flame photometric detection, is described. The speciation analysis of nine organotin compounds includes low molecular weight–low boiling (non-pesticidal) and high molecular weight–high boiling analytes (pesticidal) of significant environmental interest. The minimum time for sodium tetraethylborate alkylation, using mechanical agitation, is determined to be 15 min in order to ensure the complete derivatization of the entire list of analytes. The utilization of a “hot needle” and a rapid injection rate is shown to be an efficacious means to eliminate “mass” or “needle” discrimination when determining the mixture of organotin compounds. Method detection limits are calculated to be in the low ng L^{− 1} range. The final method is applied to various water samples; storm water from the Cincinnati area demonstrated low native levels of three of the organotin compounds.     

Korteweg–de vries zero dispersion limit: Through first breaking for cubic-like analytic initial data

The characteristic solution of the initial value problem for the Riemann invariant form of the Korteweg-de Vries modulation equations is obtained locally through first breaking in the case of initial data which is analytic near a cubic inflection point. Tsarev's (see [11]) system is used to define the solution implicitly in terms of the speeds of the generalized KdV modulation equations. These “higher flow” speeds satisfy the same derivative identities obtained by Levermore for the KdV flow (see [6]). Moreover, by explicitly constructing the Lax-Levermore (see [5]) minimizer the Tsarev solution is shown to be the unique solution of Whitham's equations corresponding to the KdV zero dispersion limit. Also the Tsarev system possesses at most one three-sheeted solution in a uniform neighborhood of the inflection point. Finally the explicit minimizer provides phase information for the Venakides' small dispersion KdV waveform through first breaking; see [12]. © 1993 John Wiley & Sons, Inc.     

An error analysis for the calculation of semiintegrals and semiderivatives by the RL algorithm

The numerical approximation of the semiintegral and semiderivative of a function f by the RL algorithm of Oldham and Spanier [1] is examined. An error analysis is given for the case when f has a continuous second derivative. The performance of the algorithm when applied to experimental data is also discussed. Numerical examples are presented to illustrate the theory.     

Large Isoperimetric Regions in Asymptotically Hyperbolic Manifolds

We show the existence of isoperimetric regions of sufficiently large volumes in general asymptotically hyperbolic three manifolds. Furthermore, we show that large coordinate spheres are uniquely isoperimetric in manifolds that are Schwarzschild–anti-deSitter at infinity. These results have important repercussions for our understanding of spacelike hypersurfaces in Lorentzian space-times which are asymptotic to null infinity. In fact, as an application of our results, we verify the asymptotically hyperbolic Penrose inequality in the special case of the existence of connected isoperimetric regions of all volumes.     

Synthesis of an anion-binding amino acid

We achieved the synthesis of a derivative of phenylalanine with a diazamacrocycle on its side chain by macrocyclization of a dichloride on l-DOPA. We also report its incorporation into peptide structures by solid phase peptide synthesis which will lead to the development of artificial anion channels.