Diastereoselective spiroannulation of phenolic substrates: synthesis of (+/-)-2-tert-butyl-6-methoxy-1-oxaspiro[4,5]deca-6,9-diene-8-one

The synthesis of a new spiroether is described. The title compound is obtained as a diastereomeric mixture in 45% yield.     

Laser-induced flourescence spectra of YAG-laser vaporized Se2

Rotationally resolved, laser-induced fluorescence spectra of Se₂, cooled to near liquid-N₂ temperature after YAG-laser vaporization of selenium, have been observed. Molecular constants have been obtained for a new O_u state of Se₂. It, along with a l_u component, likely derives from a ³N_u state which has previously been identified as responsible for perturbations of B³Σ^?_uSe₂     

Laser-induced fluorescence spectrum of matrix-isolated C6H8+

A laser-induced fluorescence excitation and resolved emission spectrum of the radical cation of 1,3,5-hexatriene has been observed in a Ne matrix. Analysis of these spectra yield vibrational frequencies for both the ground $\text{X}\text{?}{}^2\text{A}{}_{\mathrm{u}}$ and excited $\text{A}\text{?}{}^2\text{B}{}_{\mathrm{g}}$ states of the ion. Observations are reported concerning the photoionization process, emission quantum yield, and ion fragmentation. Matrix site effects and production in the gas phase are also discussed.     

Spectroscopic and picosedond time-resolved studies of vibrational relaxation in naphthazarine in solid neon

Very extensive vibrationally unrelaxed florescence is observed following dye-laser excitation of single vibronic levels of naphthazarine. The rates and pathways of its vibrational relaxation are examined by means of picosecond emission spectroscopy. Analysis of its vibrational and electronic spectra establishes a C_2v symmetry for free naphthazarine.     

Cavity resonant mode in a metal film perforated with two-dimensional triangular lattice hole arrays

The transmission property of metallic films with two-dimensional hole arrays is studied experimentally and numerically. For a triangular lattice subwavelength hole array in a 150 nm thick Ag film, both cavity resonance and planar surface modes are identified as the sources of enhanced optical transmissions. Semi-analytical models are developed for calculating the dispersion relation of the cavity resonant mode. They agree well with the experimental results and full-wave numerical calculations. Strong interaction between the cavity resonant mode and surface modes is also observed.     

Magnetic iron oxide nanoparticles for biorecognition: evaluation of surface coverage and activity

Modifying the surfaces of magnetic nanoparticles (MNPs) by the covalent attachment of biomolecules will enable their implementation as contrast agents for magnetic resonance imaging or as media for magnetically assisted bioseparations. In this paper we report both the surface coverage and the activity of IgG antibodies on MNPs. The antibodies were immobilized on gamma-Fe2O3 nanoparticles by conventional methods using aminopropyltriethoxy silane and subsequent activation by glutaraldehyde. Novel fluorescence methods were used to provide a quantitative evaluation of this well-known approach. Our results show that surface coverage can be stoichiometrically adjusted with saturated surface coverage occurring at approximately 36% of the theoretical limit. The saturated surface coverage corresponds to 34 antibody molecules bound to an average-sized MNP (32 nm diameter). We also show that the immobilized antibodies retain approximately 50% of their binding capacity at surface-saturated levels.     

On MTL's First Decade

Three experiments used multiple methods—open-ended assessments, multiple-choice questionnaires, and interviews—to investigate the hypothesis that the development of students' understanding of the concept of real variable in algebra may be influenced in fundamental ways by their initial concept of number, which seems to be organized around the notion of natural number. In the first two experiments 91 secondary school students (ranging in age from 12.5 to 14.5 years) were asked to indicate numbers that could or could not be used to substitute literal symbols in algebraic expressions. The results showed that there was a strong tendency on the part of the students to interpret literal symbols to stand for natural numbers and a related tendency to consider the phenomenal sign of the algebraic expressions as their “real” sign. Similar findings were obtained in a third, individual interview study, conducted with tenth grade students. The results were interpreted to support the interpretation that there is a systematic natural number bias on students' substitutions of literal symbols in algebra.     

An infrared,Raman, and single-crystal x-ray study of cesium hexafluorophosphate

CsPF₆:M,=277.87, cubic,Fm3m-O _h ⁵, witha 8.228(5) Å,V 557(1) ų,Z=4,D _x =3.31 Mg m^–3, X(MoK)=0.7107 Å,(MoK)=6.85 mm^–1 F(000)=496,R=0.0327 for 114 reflections. The PF₆ ion exhibits orientational disorder; infrared and Raman spectra show that its point symmetry is lower thanm3m-O _h , in agreement with the equilibrium atomic positions found in the X-ray study. The rule of mutual exclusion is not obeyed in the spectra of CsPF₆; this can be explained if the disorder also involves a small shift of the P atom away fromm3m-O _h site symmetry. Such an effect could not be modelled in the X-ray study. The deviation from octahedral symmetry of PF₆ is small and, from a consideration of the vibrational spectra of the MPF₆ series, it is concluded that both the reorientational and other motions such as librational and torsional oscillations contribute toward the breadth of some vibrational modes.