Spatially polarizing autocloned elements

A space-variant polarization converting element is introduced that utilizes an autocloning effect to produce high aspect ratio from birefringent gratings. This method utilizes a multilayer deposition process on a template to convert a linearly polarized incident beam to an azimuthally polarized output at a wavelength of 1.55 microm with more than 90% efficiency.     

Two Cu2 and Zn2 metallamacrocycles featuring a novel extended pi-conjugated carbazole bridge

Two neutral dinuclear metallamacrocycles, [Cu2(hbca)2].2CHCl3.2H2O (1) and [Zn2(hbca)2].7H2O (2), have been assembled from reactions of the new rigid carbazole-based ligand H2hbca [N,N'-bis(2-hydroxobenzylidene)-9H-carbazole-3,6-diamine] with copper(II) or zinc(II) acetate. The extended aromatic ligand spacer is responsible for intermetallic antiferromagnetic exchange, which is rationalized using the spin-polarization formalism with the help of density functional theory calculations.     

Polymerizable phospholipids: a novel class of biomaterials

Polymerizable phospholipids are organic monomers that are able to self-assemble into membranes. This is quite similar to the self assembly of naturally occurring lipid membranes found in biological systems. The polymerizable lipids can then be polymerized to stabilize these membranes. These stabilized structures have a number of different morphologies which offer a variety of technically attractive features. This article reviews the chemical and physical properties of these materials in terms of their technological applications.     

Azithromycin extraction from municipal wastewater and quantitation using liquid chromatography/mass spectrometry

Azithromycin is a broad spectrum antimicrobial agent that is approved in the United States for use in humans. Due to azithromycin's low rate of metabolism it is likely to be found in wastewater treatment plants, where its broad spectrum of antimicrobial activity could lead to development of resistance in bacteria. A liquid-liquid extraction using K2CO3 and methyl-t-butyl ether (MTBE) was used to extract azithromycin from 10 ml aliquots of wastewater. Liquid chromatography was performed using a Luna C18(2) (30 mm x 2.0 mm) column with a mass spectrometer friendly mobile phase containing 50:24:2:24 acetonitrile, methanol, tetrahydrofuran, and 0.04 M ammonium hydroxide. The mass spectrometer used an electrospray source with positive ionization and an ion trap detector. A linear standard curve from 5 to 200pg/ml was validated and used to quantitate azithromycin in wastewater.     

Insertion of a small peptide of six amino acids into the β7–β8 loop of the p51 subunit of HIV-1 reverse transcriptase perturbs the heterodimer and affects its activities

Background  

HIV-1 RT is a heterodimeric enzyme, comprising of the p66 and p51 subunits. Earlier, we have shown that the β7-β8 loop of p51 is a key structural element for RT dimerization (Pandey et al., Biochemistry 40: 9505, 2001). Deletion or alanine substitution of four amino acid residues of this loop in the p51 subunit severely impaired DNA binding and catalytic activities of the enzyme. To further examine the role of this loop in HIV-1 RT, we have increased its size such that the six amino acids loop sequences are repeated in tandem and examined its impact on the dimerization process and catalytic function of the enzyme.     

Fluorometric and isothermal titration calorimetric studies on binding interaction of a telechelic polymer with sodium alkyl sulfates of varying chain length

Steady-state fluorescence measurements and isothermal titration calorimetric experiments have been performed to study the interaction between a telechelic polymer, pyrene-end-capped poly(ethylene oxide) (PYPY), and sodium alkyl sulfate surfactants having decyl, dodecyl, and tetradecyl hydrocarbon tails. Fluorometric results suggest polymer-surfactant interaction in the very low range of polymer concentrations. The relative variation in the excimer to monomer pyrene emission intensities with varying surfactant concentration reveals that initial addition of surfactant favors intramolecular preassociation until the surfactant molecules start binding with the ethylene oxide (EO) chain. With the growing number of surfactant aggregates along the EO chain, the association becomes hindered due to the polyelectrolyte effect. The results from microcalorimetric titrations in the low concentration range of PYPY solution (approximately 10(-6) M) with alkyl sulfates suggest two kinds of surfactant-polymer interactions, one with the polymer hydrophobic end groups and the other with the ethylene oxide backbone. The overall polymer-surfactant interaction starts at a much lower surfactant concentration for the hydrophobically modified polymers compared to that in the case of unsubstituted poly(ethylene oxide) homopolymer. From the experiments critical aggregation concentration values and the second critical concentration where free micelles start forming have been determined. An endeavor has been made to unveil the mechanism underlying the corresponding associations of the surfactants with the polymer.     

5-Aminolevulinic acid-induced protoporphyrin-IX accumulation and associated phototoxicity in macrophages and oral cancer cell lines

Studies were carried out on 5-aminolevulinic acid (ALA)-induced protoporphyrin (PpIX) synthesis in mice peritoneal macrophages and two human oral squamous cell carcinoma (OSCC) cell lines NT8e and 4451. Cells were treated with 200 microg/ml ALA for 15 h and PpIX accumulation was monitored by spectrofluorometry and phototoxicity to red light (630+/-20 nm) was measured by MTT assay. PpIX accumulation was higher in macrophages as compared to OSCC cells under both normal serum concentration (10%) and conditions of serum depletion. The results on phototoxicity measurements correlated well with the levels of PpIX accumulation in both macrophages and cancer cells. While red light caused 20% phototoxicity in macrophages, no phototoxicity was seen in 4451 cells at 10% serum. Decrease in serum concentration to 5% and 1% led to higher phototoxicity corresponding to 40% and 70% in macrophages and 10% and 15% in 4451 cells. Similar results were obtained in NT8e cell line. Propidium iodide staining followed by fluorescence microscopic observations on photodynamically treated co-culture of murine or human macrophages and cancer cells showed selective damage to macrophages. These results suggest that in OSCC, macrophages would contribute more to tumor PpIX level than tumor cells themselves and PDT may lead to selective killing of macrophages at the site of treatment. Since macrophages are responsible for production and secretion of various tumor growth mediators, the effect of selective macrophage killing on the outcome of PDT would be significant.     

Unique asymmetric (CuII4) double-stranded helicate from a hexadentate piperazine-based ligand: ligand conformation isomerism upon coordination

In methanol, the reaction of Cu(ClO(4))(2).6H(2)O and a sterically constrained piperazine imine phenol ligand (H(2)L), in the presence of NEt(3), affords a novel tetranuclear copper(II) complex of formula [Cu(II)(4)(mu(3)-L)(2)(mu-OH)(2)(H(2)O)(2)](ClO(4))(2).H(2)O (1). The X-ray structure of this complex shows an elongated Cu(4) quasi-tetrahedron coordinated to two hexadentate chair-(e,a)-mu(3)-piperazine bridging ligands. Variable-temperature magnetic studies show an S(t) = 0 spin ground state resulting from antiferromagnetic interactions between Cu(II) ions within the complex.     

A linear-time algorithm for computing the voronoi diagram of a convex polygon

We present an algorithm for computing certain kinds of three-dimensional convex hulls in linear time. Using this algorithm, we show that the Voronoi diagram ofn sites in the plane can be computed in (n) time when these sites form the vertices of a convex polygon in, say, counterclockwise order. This settles an open problem in computational geometry. Our techniques can also be used to obtain linear-time algorithms for computing the furthest-site Voronoi diagram and the medial axis of a convex polygon and for deleting a site from a general planar Voronoi diagram.This research began while the first and fourth authors were visiting the Mathematical Sciences Research Institute in Berkeley, California. Work by the fourth author was supported in part by NSF Grant No. 8120790.     

Electron beam irradiated polyamide-6,6 films—II: mechanical and dynamic mechanical properties and water absorption behavior

Electron beam irradiation of poly(iminohexamethylene-iminoadipoyl) (Polyamide-6,6) films was carried out over a range of irradiation doses (20–500 kGy) in air. The mechanical properties were studied and the optimum radiation dose was 200 kGy, where the ultimate tensile stress (UTS), 10% modulus, elongation at break (EB) and toughness showed significant improvement over the unirradiated film. At a dose of 200 kGy, the UTS was improved by 19%, the 10% modulus by 9% and the EB by 200% over the control. The dynamic mechanical properties of the films were studied in the temperature region 303–473 K to observe the changes in the glass transition temperature (T_g) and loss tangent (tan δ) with radiation dose. The storage modulus of the film receiving a radiation dose of 200 kGy was higher than the unirradiated film. The water uptake characteristics of the Polyamide-6,6 films were investigated. The water uptake was less for the films that received a radiation dose of 200 and 500 kGy than the unirradiated film. The role of crystallinity, crosslinking and chain scission in affecting the tensile, dynamic mechanical and water absorption properties was discussed.