Photolabile thymidine cleavable with a 532 nanometer laser

The synthesis and characterization of a novel 3′ p-hydroxyphenacyl-caged thymidine bearing a 5′ N,N-diisopropylcyanoethylphosphoramidite is presented representing a new methodology for the photoregulation of PCR and gene expression. Solid phase oligonucleotide synthesis affords a primer blocked at the 3′ position, which could function as a phototrigger for polymerase activity. The caging group exhibits quantitative photolysis in 15 s using a 532 nm green hand laser.     

Single-step biofriendly synthesis of surface modifiable, near-spherical gold nanoparticles for applications in biological detection and catalysis

There is an increased interest in understanding the toxicity and rational design of gold nanoparticles (GNPs) for biomedical applications in recent years. Such efforts warrant reliable, viable, and biofriendly synthetic methodology for GNPs with homogeneous sizes and shapes, particularly sizes above 30 nm, which is currently challenging. In the present study, an environmentally benign, biofriendly, single-step/single-phase synthetic method using dextrose as a reducing and capping agent in a buffered aqueous solution at moderate temperature is introduced. The resulting GNPs are near-spherical, stable, catalytically active, place exchangeable, and water-soluble within the size range of 10-120 nm. The added advantage of the biologically friendly reaction medium employed in this new synthetic approach provides a method for the direct embedment/integration of GNPs into biological systems such as the E. coli bacterium without additional capping ligand or surface modification processes.     

Insertion mechanism of a poly(ethylene oxide)-poly(butylene oxide) block copolymer into a DPPC monolayer

Interactions between amphiphilic block copolymers and lipids are of medical interest for applications such as drug delivery and the restoration of damaged cell membranes. A series of monodisperse poly(ethylene oxide)-poly(butylene oxide) (EOBO) block copolymers were obtained with two ratios of hydrophilic/hydrophobic block lengths. We have explored the surface activity of EOBO at a clean interface and under 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayers as a simple cell membrane model. At the same subphase concentration, EOBO achieved higher equilibrium surface pressures under DPPC compared to a bare interface, and the surface activity was improved with longer poly(butylene oxide) blocks. Further investigation of the DPPC/EOBO monolayers showed that combined films exhibited similar surface rheology compared to pure DPPC at the same surface pressures. DPPC/EOBO phase separation was observed in fluorescently doped monolayers, and within the liquid-expanded liquid-condensed coexistence region for DPPC, EOBO did not drastically alter the liquid-condensed domain shapes. Grazing incidence X-ray diffraction (GIXD) and X-ray reflectivity (XRR) quantitatively confirmed that the lattice spacings and tilt of DPPC in lipid-rich regions of the monolayer were nearly equivalent to those of a pure DPPC monolayer at the same surface pressures.     

On the advantages of hydrocarbon radical stabilization energies based on R-H bond dissociation energies

Hydrocarbon radical stabilization energy (RSE) estimates based on the differences in R-H vs CH(3)-H bond dissociation energies have inherent advantages over RSEs based on R-CH(3) vs CH(3)-CH(3), as well as R-R vs CH(3)-CH(3) comparisons, since the R-CH(3) and R-R reference systems are prone to unbalanced contaminating intramolecular interactions involving the R groups. When the effects of steric crowding, branching, protobranching, conjugation, and hyperconjugation are taken into account, R-CH(3) and R-R based RSE values are nearly identical to R-H RSEs. Corrections for electronegativity differences between H and R are not needed to achieve agreement.     

Synthesis of diaryl ketones via a phosphine-free Fukuyama reaction

The synthesis of unsymmetrical diaryl ketones via the Fukuyama coupling of thioesters and organozinc reagents is described. Typically, the synthesis of diaryl ketones using this methodology provides low yields. The simple complex, Pd(dba)(2), was found to convert a variety of aryl thioesters to diaryl ketones in good yields.     

Uniformity study of wafer-scale InP-to-silicon hybrid integration

β-SiC nanowires were synthesized by a simple carbothermal reduction of carbonaceous silica xerogel. The morphology and structure of the nanowires were investigated by X-ray diffraction, scanning electron microscope and transmission electron microscopy. The results showed that the nanowires were hexagonal prism-shaped hierarchical nanostructures. The typical stacking faults and twin defects of SiC nanowires were also observed. Band-gap characterization and photoluminescence properties of SiC nanowires were investigated by UV-vis absorption spectroscopy and fluorescence photometry, respectively. The results showed the SiC nanowire was an indirect transition semiconductor and the band gap energy for the SiC nanowires was 2.85 eV. The photoluminescence peak value at 470 nm (2.64 eV) originating from the SiC nanowires was a little higher than the value of band-gap energy.     

Reduced basis catalogs for gravitational wave templates

We introduce a reduced basis approach as a new paradigm for modeling, representing and searching for gravitational waves. We construct waveform catalogs for nonspinning compact binary coalescences, and we find that for accuracies of 99% and 99.999% the method generates a factor of about 10-10(5) fewer templates than standard placement methods. The continuum of gravitational waves can be represented by a finite and comparatively compact basis. The method is robust under variations in the noise of detectors, implying that only a single catalog needs to be generated.     

Effect of multiphoton absorption and free carriers in slow-light photonic crystal waveguides

We examine the effects of multiphoton absorption, free carriers, and disorder-induced linear scattering in slow-light photonic crystal waveguides. We derive an analytic formulation for self-phase modulation including the group velocity scaling of the nonlinear phase shift in materials limited by three-photon absorption as a representative nonlinear process. We investigate the role of free carriers and derive an approximate critical intensity at which these effects begin to strongly modify the optical field. This critical intensity is employed to determine an optimal group index for the self-phase modulation in the slow-light devices. These observations are confirmed with numerical modeling.     

Dimers of Nineteen‐Electron Sandwich Compounds: Crystal and Electronic Structures,and Comparison of Reducing Strengths

The dimers of some Group 8 metal cyclopentadienyl/arene complexes and Group 9 metallocenes can be handled in air, yet are strongly reducing, making them useful n‐dopants in organic electronics. In this work, the X‐ray molecular structures are shown to resemble those of Group 8 metal cyclopentadienyl/pentadienyl or Group 9 metal cyclopentadienyl/diene model compounds. Compared to those of the model compounds, the DFT HOMOs of the dimers are significantly destabilized by interactions between the metal and the central C?C σ‐bonding orbital, accounting for the facile oxidation of the dimers. The lengths of these C?C bonds (X‐ray or DFT) do not correlate with DFT dissociation energies, the latter depending strongly on the monomer stabilities. Ru and Ir monomers are more reducing than their Fe and Rh analogues, but the corresponding dimers also exhibit much higher dissociation energies, so the estimated monomer cation/neutral dimer potentials are, with the exception of that of [RhCp₂]₂, rather similar (?1.97 to ?2.15 V vs. FeCp₂^+/0 in THF). The consequences of the variations in bond strength and redox potentials for the reactivity of the dimers are discussed.