Adaptive local grid refinement algorithms for finite-element collocation

An adaptive grid refinement procedure allows accurate solutions to advection-dominated, time-dependent flows using finite-element collocation. The technique relies on a data structure that is readily amenable to parallel computing. The paper discusses computational aspects of the method.     

Methodology for the preparation of C1-monoalkylated 1,2-dihydro[C70)] derivatives: formation of the "other" regioisomer

Deprotonation of 1,2-C(70)H(2) with TBAOH, followed by alkylation with methyl bromoacetate, results in formation of a C1-monoalkylated 1,2-dihydro-C(70) derivative. The position of the alkyl group (C1) was established by NMR spectroscopy and comparison with literature spectra of C2-monoalkylated analogs. Presumably, C1-alkylation is the major process due to selective deprotonation of 1,2-C(70)H(2) at C1. Substitution of benzyl bromide for methyl bromoacetate results in rapid dialkylation, unless the amount of base is carefully controlled, in which case C1-monobenzylation is the major process. This methodology for alkylation at C1 is complimentary to methods for the C2-monoalkylation of C(70) with Zn and methyl bromoacetate.     

Design,synthesis, and evaluation of 6-carboxyalkyl and 6-phosphonoxyalkyl derivatives of 7-oxo-8-ribitylaminolumazines as inhibitors of riboflavin synthase and lumazine synthase

A series of 6-carboxyalkyl and 6-phosphonoxyalkyl derivatives of 7-oxo-8-D-ribityllumazine were synthesized as inhibitors of both Escherichia coli riboflavin synthase and Bacillus subtilis lumazine synthase. The compounds were designed to bind to both the ribitylpurine binding site and the phosphate binding site of lumazine synthase. In the carboxyalkyl series, maximum activity against both enzymes was observed with the 3'-carboxypropyl compound 22. Lengthening or shortening the chain linking the carboxyl group to the lumazine by one carbon resulted in decreased activity. In the phosphonoxyalkyl series, the 3'-phosphonoxypropyl compound 33 was more potent than the 4'-phosphonoxybutyl derivative 39 against lumazine synthase, but it was less potent against riboflavin synthase. Molecular modeling suggested that the terminal carboxyl group of 6-(3'-carboxypropyl)-7-oxo-8-D-ribityllumazine (22) may bind to the side chains of Arg127 and Lys135 of the enzyme. A hypothetical molecular model was also constructed for the binding of 6-(2'-carboxyethyl)-7-oxolumazine (15) in the active site of E. coli riboflavin synthase, which demonstrated that the active site could readily accommodate two molecules of the inhibitor.     

Synthesis of spiro-fused (C5)-isoxazolino-(C4)-pyrazolones (1-oxa-2,7,8-triazaspiro[4,4]-2,8-dien-6-ones) via 1,3-dipolar cycloaddition and cycloelimination

An efficient and selective method for the synthesis of spiro-fused (C5)-isoxazolino-(C4)-pyrazolones (C) is reported. The process consists of utilizing the Baylis-Hillman reaction-or a quicker, stepwise MAC procedure-to give I followed by 1,3-dipolar cycloaddition and Swern oxidation to give beta-ketoesters H, which were condensed with hydrazine derivatives to provide hydrazones that underwent cycloelimination. These novel spiro-fused (C5)-isoxazolino-(C4)-pyrazolones were confirmed by spectroscopic analysis as well as single-crystal X-ray of 5. We also concluded that all condensations/cycloeliminations, except with hydrazine itself, were more effective with catalysts or higher reaction temperatures. For example, TiCl(4) was an efficient catalyst for hydrazone formation and cycloelimination with methylhydrazine, while phenyl-, benzyl-, and (4-methoxyphenyl)hydrazine reacted effectively without catalyst in refluxing xylene.     

Energetics of the Preyssler anion's molecular orbitals: quantifying the effect of the encapsulated-cation's charge

The ground state electronic properties of metal-exchanged Preyssler heteropolyoxoanions [M(n+)P(5)W(30)O(110)](n-15), in which the encapsulated M(n+) ions are the spherical, diamagnetic ions Na(+), Ca(2+), Sr(2+), Y(3+), La(3+) and Th(4+), are studied using a combination of electrochemical, optical, and NMR experiments. We have designed experiments that focus on the influence of the charge (n) of the encapsulated cations, which themselves have no redox response, and its effect upon the W-O framework MOs. As n increases, the cluster anions accept electrons into their LUMOs with increasing ease, and their lowest-energy LMCT bands reveal a corresponding blue shift, which is indicative of an increase of the LUMO-HOMO energy splitting with increasing n. (183)W NMR spectra are used to identify the atomic origin of the LUMO states, which are shown to be composed primarily of orbitals from the ring of 5 W atoms near M(n+). The cation charge correlates directly and linearly with the half-wave potentials of the first redox couples, the LMCT band energies, and the W chemical shifts. We have combined this suite of experimental results to construct an energy level diagram of the frontier MOs for the Preyssler cluster anions. In so doing, we provide a fundamental perspective that is not otherwise available on the cation's role with specific regard to the electronic behavior of the W-O orbitals. These results are expected to provide benchmarking information as theorists begin to study these large POM systems.     

Evaluation of an Economical Sunlamp that Emits a Near Solar UV Power Spectrum for Conducting Photoimmunological and Sunscreen Immune Protection Studies

Expense and inconvenience have restricted the use of the filtered xenon are lamp (solar simulator) as a UV source for conducting large-scale animal studies. Because sunscreen immunoprotective levels are significantly affected by the UV power spectrum of the source it is imperative that a solar simulating source be used for accurate measurements of sunscreen protection levels that are relevant to human UV exposures from sunlight. However, relatively inexpensive sunlamps, e. g. the UVA-340, that emit a UV power spectrum similar to that of a solar simulator are available. Unlike FS-type UVB sunlamps, which have a significant amount of effective immunosuppressive nonsolar UV energy at wavelengths below 295 nm, the immunosuppression effectiveness spectrum of UVA-340 sunlamps was nearly identical to that of a solar simulator. The purpose of this study was to evaluate this sunlamp for conducting photoimmunological and sunscreen immune protection studies. Groups of C3H mice were exposed to a range of UVA-340 sunlamp doses (0.25 KJ/m² to 20.0 KJ/m²) to establish a dose-response curve and determine the minimum immune suppression dose (MISD) for induction of local-type suppression of contact hypersensitivity (CH). The MISD, defined as the lowest UV dose given to produce ～50% suppression of the CH response in mice, was determined to be 1.0 kJ/m² for UVA-340 sunlamps. Immune protection tests on four marketed sunscreen lotions (sun protection factors [SPF] 4, 8, 15 and 30) were then conducted with UVA-340 sunlamps using MISD as the endpoint. The immune protection factors for these sunscreens were equivalent to the level of protection predicated by their labeled SPF. These results are similar to those we have previously obtained using a solar simulator. We conclude from these data that the immunosuppressive effects of UVA-340 sunlamps are similar to those of a solar simulator; however, further studies are needed to determine if UVA-340, or similar, sunlamps are a viable alternative to the solar simulator for conducting large-scale animal experiments that require a relevant UV solar spectrum.     

Synthesis of the ladybug alkaloids (±)-propyleine and (±)-isopropyleine. Modification of the published structure of propyleine

The total syntheses of the ladybug alkaloids (±)-propyleine and (±)-isopropyleine are described. Evidence that the alkaloid propyleine is actually a rapidly interconverting mixture of propyleine and a previously unknown isomer isopropyleine is presented.     

A novel anthracenyl tagged protecting group for "phase-switching" applications in parallel synthesis

A new "phase-switching" protecting group 1 that facilitates the parallel synthesis of carboxylic acids, esters, and carboxamides is described. Its use permits chemistries to be performed in solution, which may be conveniently monitored with conventional analytical techniques, followed by subsequent immobilization onto a solid-phase support to aid compound purification. Carboxylic acids, esters, and carboxamides are then cleaved from the solid support following activation of the "safety-catch" and treatment with the desired nucleophile.     

Effects of deformability, uneven surface charge distributions, and multipole moments on biocolloid electrophoretic migration

Liposomes have been widely used as cellular and bioparticle mimics due to their lipid bilayer structure and relative ease of production and manipulation. Such biocolloids are frequently characterized by capillary electrophoresis (CE), which promises a wealth of information about such properties as surface charge, composition, and rigidity. The applicability of this information is somewhat limited, however, since it is interpreted with colloidal theories that do not account for the unique properties of biocolloids. In this work, the effects of deformability, mobile surface charges, intrinsic polarizability, and uneven surface charge distributions are incorporated into colloidal theories in order to better model the electrophoretic behaviors of liposomes.