Total synthesis of the tropoloisoquinoline alkaloid pareitropone via alkynyliodonium salt chemistry and related studies

The first chemical synthesis of pareitropone, by a route featuring application of alkynyliodonium salt chemistry, is described. The key transform initiates with addition of an alkylidenecarbene, derived by intramolecular nucleophile addition to the alkynyliodonium moiety, to a proximal aromatic ring. This addition delivers a highly strained norcaradiene substructure that rapidly reorganizes to furnish the pareitropone skeleton.     

Excited-state proton transfer in chiral environments. 1. Chiral solvents

Excited-state proton transfer from the "super" photoacid 5,8-dicyano-2-naphthol to 2-butanol is faster in the enantiopure solvent than in its racemic form. The difference observed is discussed in terms of long-range order in homo- and heterodimers of 2-butanol.     

Temperature-controlled surface plasmon resonance in VO (2) nanorods

The optical properties of VO(2) nanoparticles formed in an amorphous SiO(2) host by stoichiometric ion implantation of vanadium and oxygen and thermal annealing have been determined and correlated with the particle size and morphology. The results show that that the temperature-controlled semiconductor-to-metal phase transition of the VO(2) nanophase precipitates turns on the classical surface plasmon resonance, with specific features that depend on the size and aspect ratio of the VO(2) particles. This effect improves the optical contrast between the metallic and semiconducting states in the near-IR region of the spectrum as a result of dielectric confinement that is due to the SiO(2) host. A fiber-optic application is demonstrated, as is the ability to control the characteristics of the phase transition by using ion implantation to dope the VO(2) nanoparticles with tungsten or titanium ions.     

A miniature pulser-preamplifier for ultrasonic transducers

In order to avoid difficulties experienced with conventional ultrasonic systems using several feet of shielded cable to connect transducer and electronics, a miniature pulser-preamplifier was developed to fit the transducer holder. Its characteristics proved superior to most devices in common use.     

The kinetics of radiation induced hydrogen abstraction by CCl3 radicals in the liquid phase: Cyclanes

The kinetics of gamma-radiation induced free radicals reactions in carbon tetrachloride solutions of cyclohexane, cyclooctane and cyclododecane were studied in the range of 27–190°C. The activation energies found were in the order c? C₆H₁₂ > c? C₁₂H₂₄ > c? C₈H₁₆, which was explained as due to their ring strain which has the same order. The following log k₁ was obtained using the known Arrhenius parameters for CCl₃ radical recombination:      

Photoconductivity in high purity,semiconducting CdF2

The photoconductivity spectra of high purity, semiconducting CdF₂, containing low concentrations of rare-earth donors, are interpreted in terms of a shallow trap 1260 ± 100 cm⁻¹ below the bottom of the conduction band and an excited bound state 1030 cm⁻¹ above the ground state.     

Heterogeneous in vivo MR images of soft tissue tumors: guide to gross specimen sampling.

Twelve soft tissue tumors preoperatively studied with magnetic resonance (MR) imaging contained areas of inhomogeneous intralesional signal intensity. The pathologist's selection of biopsy sites from gross specimens was based on specific MR images selected by a radiologist and depended on close cooperation between the radiologist and pathologist. The histopathology so sampled, further depended on the lesion's size, careful gross specimen orientation, discrete sampling, and a specially developed Grid Analysis technique. Our initial experience indicates that (1) histology may vary within different and often neighboring sites of a single soft tissue lesion; (2) that such variability is common in soft tissue tumors; (3) that histological variability within different sites of a single lesion influences signal heterogeneity; and (4) that although differing MR signal intensities per se are not tissue specific, MR may enhance the histopathological accuracy of pathologists who can be directed to particular gross specimen sites by magnetic resonance images. To our knowledge such a specific, detailed effort has not been made.     

Clustering on surfaces

In this review we summarize the current theoretical and experimental understanding of clustering phenomena on surfaces, with an emphasis on dynamical properties. The basic theoretical concepts to predict evolving cluster size distributions are presented, with extensions to less restrictive assumptions, such as including the influence of non-zero deposition rates. The discussion of experimental results to test these concepts is preceded by a brief introduction of the experimental techniques used in morphological cluster studies. Finally, two important physical surface quantities, surface diffusion coefficients and adatom binding energies, are used to demonstrate the impact of clustering in their understanding.     

Trapping effects in the luminescence of Zn2GeO4:Mn2+

Free carriers are created in this material under sub-band-gap excitation and the effects of these on the luminescence are studied. The slow rise of emission, long afterglow and infrared stimulability are explained with a model utilizing an empirical set of configuration coordinate curves. The rise and afterglow curves are fitted to solutions to a rate equation which is based on the postulation of only one kind of trapping center.