Synthesis and characterization of polyimides containing heterocyclic units

Five new polyimides containing phenoxaphosphine as well as dibenzothiophene, phenoxathiin, and thianthrene units have been synthesized from 10-phenylphenoxaphosphine-2,3,7,8-tetracarboxylic dianhydride-10-oxide and heterocyclic diamines by the cyclopolycondensation method. These polyimides had inherent viscosities in the 0.75–1.10 dL/g range in conc. H₂SO₄ at 30°C. All the polymers were characterized by elemental analysis, density, solubility, crystallinity, IR spectra, and thermal methods.     

The determination of a carbamate insecticide in soil samples by differential pulse polarography

Differential pulse polarography is shown to be a simple and potentially useful method for monitoring the degradation of a carbamate insecticide (Bendiocarb; 2,3-isopropyli-denedioxyphenyl-N-methylcarbamate) in soil samples. Only extraction from the soil sample with dichloromethane and evaporation of the extract is needed prior to polarography. Calibration plots were linear over the range 10–50 mg l^?1 at ?0.94 V vs. Ag/AgCl in an acetate buffer of pH 5.0. There is no apparent interference from hydrolysis products or soil components.     

Optimal nonuniform wavebanding in WDM mesh networks

Grouping together a set of consecutive wavelengths in a WDM network and switching them together as a single waveband could achieve savings in switching costs of an optical cross-connect. This technique is known as waveband switching. While previous work has focused on either uniform band sizes or nonuniform band sizes considering a single node or ring networks, in this paper we focus on optimizing the number of wavebands and their sizes for mesh topologies. We formulate a problem of optimizing the number of wavebands in a mesh network for a given set of lightpaths. The objective of the band minimization problem is to minimize the number of nonuniform wavebands in the network while satisfying the traffic requests. We formulate an integer linear program and propose efficient heuristics. Simulation results are presented to demonstrate the effectiveness of the proposed approaches under static traffic case. Our results show that the number of switching elements can be reduced by a large amount using waveband switching compared to wavelength switching. We also apply the proposed waveband strategy to the dynamic stochastic traffic case and evaluate the network performance in terms of blocking probability through numerical simulations.     

Assembly of bionanostructures onto beta-cyclodextrin molecular printboards for antibody recognition and lymphocyte cell counting

The assembly of complex bionanostructures onto beta-cyclodextrin (betaCD) monolayers has been investigated with the aims of antibody recognition and cell adhesion. The formation of these assemblies relies on host-guest, protein-ligand, and protein-protein interactions. The buildup of a structure consisting of a divalent bis(adamantyl)-biotin linker, streptavidin (SAv), biotinylated protein A (bt-PA), and an Fc fragment of a human immunoglobin G (IgG-Fc) was studied with surface plasmon resonance (SPR) spectroscopy. Patterns of this bionanostructure were obtained via microcontact printing of the divalent linker at the molecular printboard, followed by the subsequent attachment of the proteins. Fluorescence microscopy showed that the buildup of these bionanostructures on the betaCD monolayers is highly specific. On the basis of these results, bionanostructures were made in which whole antibodies (ABs) were used instead of the IgG-Fc. These ABs were bound to the SAv layer via biotinylated protein G (bt-PG) or via a biotinylated AB. These constructions yielded specifically bound ABs with a less than maximal density, as shown by SPR spectroscopy and atomic force microscopy (AFM). Finally, the immobilization of ABs to the molecular printboard was used to create platforms for lymphocyte cell count purposes. Monoclonal ABs (MABs) were attached to the SAv layer using bt-PG, an engineered biotin functionality, or through nonspecific adsorption. The binding specificity of the immobilized cells was the highest on the buildup made from bt-PG, which is attributed to an optimized orientation of the antibodies. An approximately linear relationship between the numbers of seeded cells and counted cells was demonstrated, rendering the platform potentially suitable for lymphocyte cell counting.     

Nanometer arrays of functional light harvesting antenna complexes by nanoimprint lithography and host-guest interactions

We show an approach based on a combination of site-directed mutagenesis, NIL and multivalent host-guest interactions for the realization of engineered ordered functional arrays of purified components of the photosynthetic system, the membrane-bound LH2 complex. In addition to micrometer-scale patterned structures, we demonstrated the use of nanometer-scale hard NIL stamps to generate functional protein arrays approaching molecular dimensions.     

Fabrication and Visualization of Metal‐Ion Patterns on Glass by Dip‐Pen Nanolithography

Fluorescent self‐assembled monolayers (SAMs) are used as dip‐pen nanolithography (DPN) substrates for the fabrication of patterns of Ca²⁺ and Cu²⁺ ions. The driving force for the transfer of these ions from an atomic force microscopy (AFM) tip to the surface is their complexation to organic ligands on the monolayer. By means of fluorescent surfaces, the patterns can be visualized under a fluorescence microscope. We use a custom‐built atomic force fluorescence microscope (AFFM), a combination of atomic force and confocal fluorescence microscopes, to deposit the metal ions onto the sensing SAMs by DPN and to subsequently visualize modulations of fluorescence intensity in a sequential write–read mode.     

Spectral Versatility of Single Reef Coral Fluorescent Proteins Detected by Spectrally‐Resolved Single Molecule Spectroscopy

We use spectrally‐resolved room temperature single molecule spectroscopy to yield insights into the occurrence and dynamics of spectral forms of single tetramers of DsRed and its variants DsRed2, Fluorescent Timer, DsRed_N42H and AG4. The red‐emitting chromophore in DsRed and all studied variants readily converts into a high quantum efficiency super‐red emitting form. We propose the existence of two super‐red forms of different quantum efficiencies. The observed emission from the green‐emitting chromophore is consistent with bulk spectroscopy. We further observe distinct new spectral forms from each variant, which we attribute to a photoinduced chemical reaction leading to a truncated form of the red‐emitting chromophore analogous to the chromophore in the visible fluorescent protein zFP538. Our results have implications for the accurate interpretation of biological and biochemical processes illuminated by fluorescent proteins as well as for choosing appropriate experimental configurations.     

Multiple conformational states in crystals and in solution in alphagamma hybrid peptides. Fragility of the C12 helix in short sequences

The conformational properties of foldamers generated from alphagamma hybrid peptide sequences have been probed in the model sequence Boc-Aib-Gpn-Aib-Gpn-NHMe. The choice of alpha-aminoisobutyryl (Aib) and gabapentin (Gpn) residues greatly restricts sterically accessible conformational space. This model sequence was anticipated to be a short segment of the alphagamma C12 helix, stabilized by three successive 4-->1 hydrogen bonds, corresponding to a backbone-expanded analogue of the alpha polypeptide 3(10)-helix. Unexpectedly, three distinct crystalline polymorphs were characterized in the solid state by X-ray diffraction. In one form, two successive C12 hydrogen bonds were obtained at the N-terminus, while a novel C17 hydrogen-bonded gamma alpha gamma turn was observed at the C-terminus. In the other two polymorphs, isolated C9 and C7 hydrogen-bonded turns were observed at Gpn (2) and Gpn (4). Isolated C12 and C9 turns were also crystallographically established in the peptides Boc-Aib-Gpn-Aib-OMe and Boc-Gpn-Aib-NHMe, respectively. Selective line broadening of NH resonances and the observation of medium range NH(i) <--> NH(i+2) NOEs established the presence of conformational heterogeneity for the tetrapeptide in CDCl3 solution. The NMR results are consistent with the limited population of the continuous C12 helix conformation. Lengthening of the (alphagamma) n sequences in the nonapeptides Boc-Aib-Gpn-Aib-Gpn-Aib-Gpn-Aib-Gpn-Xxx (Xxx = Aib, Leu) resulted in the observation of all of the sequential NOEs characteristic of an alphagamma C12 helix. These results establish that conformational fragility is manifested in short hybrid alphagamma sequences despite the choice of conformationally constrained residues, while stable helices are formed on chain extension.     

Alkaloids and saponins in dietary supplements of blue cohosh (Caulophyllum thalictroides)

Preparations of blue cohosh (Caulophyllum thalictroides) have been used traditionally by Native Americans for medicinal purposes. Dietary supplements containing dried roots or extracts of blue cohosh rhizomes are available as dietary supplements. The safety and efficacy of these preparations have not been systematically evaluated. Recent studies indicate that ingestion of specific alkaloids in blue cohosh preparations can produce birth defects and neonatal heart failure. Blue cohosh also contains saponins, which may be responsible for uterine-stimulating effects. We determined the amounts of major alkaloids and saponins in preparations of blue cohosh by high-performance liquid chromatography (HPLC). Alkaloids and saponins were monitored with a photodiode array detector and an evaporative light-scattering detector, respectively. Profiles were compared with those of authenticated blue cohosh root extracts. Identities of the alkaloids and saponins were confirmed by HPLC/mass spectrometry and nuclear magnetic resonance spectrometry. Calculations based on the results of analyses of dietary supplements showed that maximum daily intake of alkaloids and saponins will vary with the form (e.g., root, liquid extract) and doses recommended in product labeling. Intakes may vary from < 1 to 75 mg/day for alkaloids and from about 9 to 420 mg/day for saponins.