Phenylsulfonyl ene-allenes as efficient precursors to bicyclic systems via intramolecular [2 + 2]-cycloaddition reactions

Various phenylsulfonyl allene derivatives were prepared with double bonds tethered either to the alpha-position or the gamma-position of the allene. These substrates underwent a highly regio- and stereospecific thermal [2 + 2]-cycloaddition across the nonactivated cumulene double bond, forming distal cycloadducts (i.e., 57) in the case of alpha-tethered allenes and proximal adducts (i.e., 25) in the case of gamma-tethered allenes. The mechanistic rationale for the observed stereospecificity involves initial diradical formation, followed by a rapid ring closure to the more stable cis-fused ring system. The tether may be equipped with heteroatoms, allowing for the formation of fused heterocycles (e.g., 61), and the cycloaddition can be facilitated by the introduction of sterically bulky groups and/or by conformational rigidity to the tether. Other modes of cyclization were observed in the presence of sodium benzenesulfinate or Lewis acids, in which cases polar mechanisms prevail. The chemoselectivity is reversed for [4 + 2]-cycloadditions, which prefer instead to engage the vinyl sulfone moiety, independent of whether the tether is attached to the alpha- or gamma-position of the allene.     

Direct selective detection of genomic DNA from coliform using a fiber optic biosensor

Fiber optic biosensors operated in a total internal reflection format were prepared based on covalent immobilization of 25mer lacZ single-stranded nucleic acid probe. Genomic DNA from Escherichia coli was extracted and then sheared by sonication to prepare fragments of approximately 300mer length. Other targets included a 25mer fully complementary lacZ sequence, 100mer polymerase chain reaction (PCR) products containing the lacZ sequence at various locations, and non-complementary DNA including genomic samples from salmon sperm. Non-selective adsorption of non-complementary oligonucleotides (ncDNA) was found to occur at a significantly faster rate than hybridization of complementary oligomers (cDNA) in all cases. The presence of ncDNA oligonucleotides did not inhibit selective interactions between immobilized DNA and cDNA in solution. The presence of high concentrations of non-complementary genomic DNA had little effect on extent or speed of hybridization of complementary oligonucleotides. Detection of genomic fragments containing the lacZ sequence was possible in as little as 20 s by observation of the steady-state fluorescence intensity increase or by time-dependent rate of fluorescence intensity changes.     

Characterization of Molecular Weight Distributions by the Standard Deviation

The standard deviation [sgrave] is known to be an absolute measure of Gaussian (G) distributions, because it (or multiples of it) always determines a constant fraction of the material. However, this is not true for distribution functions other than Gaussian. The weight fractions corresponding to weight standard deviations (±[sgrave]_w) of Schulz-Flory distributions depend on the polymolecularity index xw/xn, approaching a limiting value of W(x_w ± [sgrave]_w) = 86.5 for x_w/x_n →∞. The use of weight standard deviations is meaningless for generalized logarithmic normal (LN) distributions if x_w/x_n 52. The weight fractions W(X_n ± [sgrave]_n) around the number-average degree of polymerization of G and LN distributions first go through a maximum before decreasing with increasing x_w/x_n. The weight fractions W(x_n ± [sgrave]_n) decrease steadily with higher x_w/x_n.     

Surface-strain measurements on a hemispherical shell using holographic interferometry

A method is presented for using real-time fringe counting and double-exposure single-hologram interferometry to measure surface strain on pressurized hemispherical shells. An aluminum shell is employed for experimental verification of these techniques. Surface-strain variations caused by a defect in the aluminum wall are detected and measured. Strain-gage arrays are used for comparison of experimental results. Bendix Kansas City Division is a prime contractor to the Atomic Energy Commission.     

Thermodynamic study of a liquid crystal as a liquid phase in gas-liquid chromatography. II. A cholesteric liquid crystal.

Gas-liquid chromatography is utilized for the determination of thermodynamic solution parameters for various organic solutes at infinite dilution in the meso- and isotropic phases of cholesteryl palmitate. The thermodynamic data and trends in values of the activity coefficients for the solutes are discussed in relation to their structure and to the orientations of the liquid crystal.