Synthesis and Reactions of Some New Pyrrolylfuro[2,3‐d]Pyrimidines and Pyrrolopyrazinofuropyrimidines

5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities.     

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.     

On the Discrete Hardy Inequality

Necessary and sufficient conditions for the boundedness of thediscrete Hardy operator of the form , from to when 0 < q < 1 <p , is given.     

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.     

Structural,optical and electrical properties of undoped and Si-doped AlxGa1−xN thin films on Si (1 1 1) substrate grown by PA-MBE

We have studied the structural properties of undoped and Si-doped Al_xGa_1?xN/GaN/AlN on Si (1 1 1) substrate prepared by plasma-assisted molecular beam epitaxy (PA-MBE) using high-resolution X-ray diffraction (HR-XRD) and atomic force microscopy (AFM). In comparison with undoped AlGaN, the roughness and dislocation density on the surface of the AlGaN layer decrease with Si doping. Full width half maximum (FWHM) of the undoped and Si-doped samples were equal to 0.69° and 0.52°, respectively. This indicates that the Si doping improves the crystalline quality of the Al_xGa_1?xN layer compared with the undoped one. Raman scattering measurement reveals that the optical phonon modes of A₁(LO) and E₂(H) of the AlGaN show a one-mode and two-modes behavior, respectively. The Fourier-transform infrared reflectance (FTIR) investigation confirms the one-mode (two-mode) behavior of the LO (TO) phonon in our samples. This is in good agreement with Raman measurement. Finally, the barrier height (Φ_B) of undoped and Si-doped Al_xGa_1?xN samples was found to be 0.86 and 0.74 eV, respectively.     

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.     

Studies on photoinduced effects in pulse-electrodeposited Ag/Hg-1212/CdSe hetero-nanostructures

Metal/superconductor/semiconductor (Ag/Hg-1212/CdSe) hetero-nanostructures have been fabricated using pulse-electrodeposition technique and are characterized by X-ray diffraction (XRD), full-width at half-maximum (FWHM) and scanning electron microscopy (SEM) studies. The junction capacitance of Ag/Hg-1212, Hg-1212/CdSe and Ag/Hg-1212/CdSe heterojunctions is measured in dark and under laser irradiation at room temperature. The nature of the junction formed and built-in-junction potentials were determined. The increase in carrier concentration across the junction due to photo-irradiation has been observed.