Synthesis of proton‐ionizable acyclic,macrocyclic and macrobicyclic compounds containing one or two triazole groups

New acyclic, macrocyclic and macrobicyclic compounds containing one or two proton‐ionizable triazole groups are prepared and characterized. The series includes six podands, a macrocycle with one triazole and one pyridine unit in the ring, a bis‐triazolo macrocycle with four pentafluorobenzyl substitutents, and two bis(crown ethers) with a triazolo group connecting the two polyether rings. The solid‐state structure and solubility in supercritical carbon dioxide are determined for the bis‐triazolo macrocycle with pendant pentafluorobenzyl groups.     

Synthesis of dibenzo‐16‐crown‐5 compounds with pendant ester and ether groups

Structurally related dibenzo‐16‐crown‐5 lariat ethers with pendant ester and ether groups are prepared. Structural variations within the series of alkyl lariat ether esters include changes in the O‐alkyl group, attachment site and nature of the lipophilic group, and length of the spacer, which connects the ester group to the polyether framework. Also synthesized are bis(crown ether) diesters with two dibenzo‐16‐crown‐5 or two dicyclohexano‐16‐crown‐5 units and two ester groups connected to each other by a linker of varying length. Synthetic strategies for the preparation of these lariat ethers with pendant ester‐ and ether‐containing side arms are described.     

Detection of hydrogen at room temperature with catalyst-coated multiple ZnO nanorods

A variety of different metal catalyst coatings (Pt, Pd, Au, Ag, Ti and Ni) deposited on multiple ZnO nanorods have been compared for their effectiveness in enhancing sensitivity for detecting hydrogen at room temperature. Pt-coated nanorods show a relative response of up to 8% in room-temperature resistance upon exposure to a hydrogen concentration in N₂ of 500 ppm. This is a factor of two larger than that obtained with Pd and more than an order of magnitude larger than that achieved with the remaining metals. The power levels for these sensors were low, ∼0.4 mW for the responses noted above. Pt-coated ZnO nanorods easily detected hydrogen down to 100 ppm, with a relative response of 4% at this concentration after 10-min exposure. The nanorods show a return to their initial conductance upon switching back to a pure-air ambient with time constants of the order of a few minutes at room temperature. This slow response at room temperature is a drawback in some applications, but the sensors do offer low-power operation and ppm detection sensitivity. PACS 78.66.Hf; 73.61.Ga; 73.40.Qv     

Polarization anisotropy in vertical-cavity semiconductor optical amplifiers

The polarization-dependent gain (PDG) characteristics of a vertical-cavity semiconductor optical amplifier (VCSOA) are measured, and the case of the PDG is determined. It is often assumed that the polarization states of a VCSOA are degenerate because of the circular geometry of the device. This assumption is not true in practice, and it is found that VCSOAs possess a dominant linear polarization state and a small difference in frequency between polarization states. The difference in resonant frequencies causes the PDG of the VCSOA. Measurements of the polarization state show that the cause of the splitting is electro-optic birefringence.     

Free-space optical interconnection: A technology comparison of vertical-cavity surface-emitting lasers and multiple-quantum-well modulators

We evaluate current vertical-cavity surface-emitting laser (VCSEL) and multiple-quantum-well (MQW) modulator technologies for low-fanout system applications. Si-CMOS transimpedance receiver circuits are used in the comparison. The aggregate bandwidth per unit area is calculated from the bandwidth and the total on-chip power dissipation. The results indicate that the electrical power dissipation in the receiver circuits dominates at low operating frequencies. At high operating frequencies the receiver gain drops significantly, thus more electrical power is dissipated in the transmitter to provide more optical power to the receiver to satisfy the voltage requirement at the receiver output. In VCSEL based systems, the optical power is generated entirely on-chip. Thus, only VCSELs with low threshold current and low series resistance would be able to provide the same aggregate bandwidth as the MQW modulator based systems.     

Characterization of a polymer microlens fabricated by use of the hydrophobic effect

We report a means of fabricating hydrophilic domains in a hydrophobic background by lithographically patterning an adhesive hydrophobic layer. Polymer microlenses were fabricated on these substrates by use of a dip-coating technique. Various lens shapes (circular, elliptical, square) were fabricated on a variety of substrates (SiO(2), SiN, GaAs, InP, etc.), ranging in size from 2 to 500 microm in diameter, with fill factors of up to 90%. Plano-convex and double-convex lenses were fabricated, with f-numbers as low as 1.38 and 1.2, respectively. Optimum lens surfaces deviated from spherical by just +/-5 nm . The lenses are stable at room temperature and exhibit minimal degradation after 24 h at 105 degrees C. The transfer of these polymer lenses to an underlying substrate was also demonstrated.     

Synthesis and characterization of lipid-polymer hybrid nanoparticles with pH-triggered poly(ethylene glycol) shedding

Novel lipid-polymer hybrid nanoparticles are designed with a poly(ethylene glycol) (PEG) coating that is shed in response to a low pH trigger. This allows the nanoparticles to be stable during systemic circulation and at neutral pH, but destabilize and fuse with lipid membranes in acidic environments. The hybrid nanoparticles consist of a poly(lactic-co-glycolic acid) core with a lipid and lipid-PEG monolayer shell. To make the hybrid nanoparticles pH sensitive, a lipid-(succinate)-mPEG conjugate is synthesized to provide a hydrolyzable PEG stealth layer that is shed off the particle surface at low pH. The pH-sensitivity of the nanoparticles is tunable using the molar concentration of the lipid-(succinate)-mPEG incorporated in the lipid shell of the particles. Possible uses of these pH-sensitive nanoparticles include aggregating in acidic tumor microenvironments, escaping acidified endosomes, or aggregating in deep lung tissue for improved inhalation administration.     

Spectroscopic and structural properties of N-(acetamide) morpholinium bromide

A new crystal of N-(acetamide) morpholinium (NAM) bromide has been prepared in methanol at room temperature and characterized by single crystal X-ray analysis, elemental analysis, GS-MS, FTIR, NMR((1)H,(13)C, DEPTH and HETCOR). The N-(acetamide) morpholinium crystallizes in the orthorhombic crystal system, Pnma with unit cell a=12.798(9) ?, b=7.222(5) ?, c=9.244(5) ?, β=90.00, V=854.4(9) ?(3), Z=4. The X-ray structure determination revealed that there are strong inner and intermolecular hydrogen bonds in the crystal.