Formal synthesis of angiogenesis inhibitor NM-3

We report the formal synthesis of angiogenesis inhibitor NM-3 (1) in six steps from either of the 2,4-dimethoxyhalobenzenes 13a,b or 3,5-dimethoxychlorobenzene (13c). The first key reaction is the regiospecific alkylation/rearrangement between the aryne derived from 13a-c with sodium diethylmalonate in THF to produce diester 11, which after hydrolysis and cyclization affords homophthalic anhydride 3. The second is the reaction of anhydride 3 with either ethyl 2-methylmalonate (28a), in the presence of 1,1'-carbonyldiimidazole, or ethyl-2-methylmalonyl chloride (28b) under basic conditions to afford key isocoumarin 27. The conversion of 27 constitutes a formal synthesis of NM-3.     

Synthesis of polyfluoroaryl [2.2] cyclophanes

New and improved syntheses of 4,5,7,8-tetrafluoro- and 4,5,7,8,12,13,15,16-octafluoro[2.2]paracyclophanes are described. The preparation of the new compound, 4,5,7,8-tetrafluoro[2.2]metaparacyclophane, is outlined.     

Observation of structure in the quasicontinuum of multiple-photon-excited C2 F5Cl

We report the observation of strong spectral structure in the dissociation yield of C₂ F₅Cl excited by two CO₂ lasers, as a function of the second, non-resonant laser, observed under molecular-beam conditions. This structure is associated with combination bands revealed by matrix-isolation spectroscopy.     

Front velocity dependence on vinyl ether and initiator concentration in radical-induced cationic frontal polymerization of epoxies

Formulations containing vinyl ethers and epoxy were successfully polymerized through a radical-induced cationic frontal polymerization mechanism, using an iodonium salt superacid generator with a peroxide thermal radical initiator and fumed silica as a filler. It was found that an increase of vinyl ether content resulted in higher front velocities for divinyl ethers in formulations with trimethylolpropane triglycidyl ether. However, increased hydroxymonovinyl ether either decreased the front velocity or suppressed frontal polymerization. The kinetic effects of the superacid generator and thermal radical initiator with varying vinyl ether content were also studied. It was observed that increasing concentrations of initiators increased the front velocity, with the system exhibiting higher sensitivity to the superacid generator concentration.     

Convenient Synthesis of Vinyldiazomethanes from α-Diazo-β-Keto Esters and Related Systems

A series of vinydiazomethanes were readily prepared by sodium borohydride reduction of a-diazo-p-ketoesters followed by phosphorus oxychloride induced dehydration of the resulting a-diazo-p-hydroxyesters.     

Approximating the ideal free distribution via reaction-diffusion-advection equations

We consider reaction-diffusion-advection models for spatially distributed populations that have a tendency to disperse up the gradient of fitness, where fitness is defined as a logistic local population growth rate. We show that in temporally constant but spatially varying environments such populations have equilibrium distributions that can approximate those that would be predicted by a version of the ideal free distribution incorporating population dynamics. The modeling approach shows that a dispersal mechanism based on local information about the environment and population density can approximate the ideal free distribution. The analysis suggests that such a dispersal mechanism may sometimes be advantageous because it allows populations to approximately track resource availability. The models are quasilinear parabolic equations with nonlinear boundary conditions.     

Plasmid DNA damage induced by helium atmospheric pressure plasma jet

Recently demonstrated ghost interference using correlated photons of different frequencies, has been theoretically analyzed. The calculation predicts an interesting nonlocal effect: the fringe width of the ghost interference depends not only on the wave-length of the photon involved, but also on the wavelength of the other photon with which it is entangled. This feature, arising because of different frequencies of the entangled photons, was hidden in the original ghost interference experiment. This prediction can be experimentally tested in a slightly modified version of the experiment.     

Envelope solitons in acoustically dispersive vitreous silica

Acoustic radiation-induced static strains, displacements, and stresses are manifested as rectified or 'dc' waveforms linked to the energy density of an acoustic wave or vibrational mode via the mode nonlinearity parameter of the material. An analytical model is developed for acoustically dispersive media that predicts the evolution of the energy density of an initial waveform into a series of energy solitons that generates a corresponding series of radiation-induced static strains (envelope solitons). The evolutionary characteristics of the envelope solitons are confirmed experimentally in Suprasil W1 vitreous silica. The value (- 11.9 ± 1.43) for the nonlinearity parameter, determined from displacement measurements of the envelope solitons via a capacitive transducer, is in good agreement with the value (- 11.6 ± 1.16) obtained independently from acoustic harmonic generation measurements. The agreement provides strong, quantitative evidence for the validity of the model.     

On the effects of nonlinear boundary conditions in diffusive logistic equations on bounded domains

We study a diffusive logistic equation with nonlinear boundary conditions. The equation arises as a model for a population that grows logistically inside a patch and crosses the patch boundary at a rate that depends on the population density. Specifically, the rate at which the population crosses the boundary is assumed to decrease as the density of the population increases. The model is motivated by empirical work on the Glanville fritillary butterfly. We derive local and global bifurcation results which show that the model can have multiple equilibria and in some parameter ranges can support Allee effects. The analysis leads to eigenvalue problems with nonstandard boundary conditions.     

Traditional vs. Retrospective Pretests for Measuring Science Teaching Efficacy Beliefs in Preservice Teachers

The difference in gain scores produced by traditional pretests and those produced by retrospective pretests when compared to posttest scores on the Science Teaching Efficacy Belief Instrument for preservice teachers was investigated in this study. Results indicated that gain scores using the traditional pretest produced significant improvement in one factor, but not in the other, which is congruent with most other results for this instrument found in the literature. However, gain scores produced by using retrospective pretests produced a greater magnitude of significance for the first factor, and also produced significant gains for the second factor. Follow‐up interviews with participants provided evidence for greater internal validity for the retrospective pretest. Findings support the notion that retrospective pretests may produce gain scores with greater validity and greater statistical power.