Investigation of water absorption in clay-reinforced polypropylene nanocomposites

The behaviour of polypropylene nanocomposites containing different amounts of commercial nanoclay upon exposure to distilled water and sea water at different temperatures was investigated and compared with that of neat polypropylene. In the initial stages, the weight gain (moisture absorption) follows Fick's second law, but at longer times deviations are observed owing to physical degradation and in some cases a loss of mass. Distilled water diffuses more rapidly than sea water. As the nanoclay content increases, both the rate of moisture absorption and the maximum moisture content increase, owing to the hydrophilic nature of the nanoclay and the added compatibilizing agent. Although the moisture absorption decreases the flexural properties of both the nanocomposites and neat PP, because the unexposed (as-moulded) nanocomposites are significantly superior to the neat PP they remain so even after prolonged exposure.     

Designer variable repeat length polypeptides as scaffolds for surface immobilization of quantum dots

We demonstrate the use of a series of engineered, variable-length de novo polypeptides to discretely immobilize luminescent semiconductor nanocrystals or quantum dots (QDs) onto functional surfaces. The polypeptides express N-terminal dicysteine and C-terminal hexahistidine residues that flank a variable number (1, 3, 5, 7, 14, 21, 28, or 35) of core beta-strand repeats, with tyrosine, glutamic acid, histidine, and lysine residues located at the turns. Polypeptides have molecular weights ranging from 4 to 83 kDa and retain a rigid structure based on the antiparallel beta-sheet motif. We first use a series of dye-labeled polypeptides to test and characterize their self-assembly onto hydrophilic CdSe-ZnS QDs using fluorescence resonance energy transfer (FRET). Results indicate that peptides maintain their beta-sheet conformation after self-assembly onto the QD surfaces, regardless of their length. We then immobilize biotinylated derivatives of these polypeptides on a NeutrAvidin-functionalized substrate and use them to capture QDs via specific interactions between the peptides' polyhistidine residues and the nanocrystal surface. We found that each of the polypeptides was able to efficiently capture QDs, with a clear correlation between the density of the surface-tethered peptide and the capacity for nanocrystal capture. The versatility of this capture strategy is highlighted by the creation of a variety of one- and two-dimensional polypeptide-QD structures as well as a self-assembled surface-immobilized FRET-based nutrient sensor.     

Demicompactness Results for Strongly Continuous Semigroups,Generators and Resolvents

Let \((U(t))_ {t\ge 0}\) be a strongly continuous semigroup of bounded linear operators on a Banach space X and B be a bounded operator on X. In this paper, we develop some aspects of the theory of semigroup for which U(t)B (respectively, BU(t), BU(t)B) is demicompact for some (respectively, every) \(t>0\). In addition, we study the demicompactness of similar, subspace and product semigroups. We also investigate the demicompactness of the resolvent. We close this paper by giving some conditions guaranteeing the demicompactness of a generator of a strongly continuous semigroup in a Hilbert space.     

Syntheses, structures, and photophysical properties of mono- and dinuclear sulfur-rich gold(I) complexes

The dinuclear gold complexes [{Au(PPh 3)} 2(mu- dmid)] ( 1) ( dmid = 1,3-dithiole-2-one-4,5-dithiolate) and [{Au(PPh 3)} 2(mu- dddt)] ( 2) ( dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate) were synthesized and characterized by X-ray crystallography. Both complexes exhibit intramolecular aurophilic interactions with Au...Au distances of 3.1984(10) A for 1 and 3.1295(11) A for 2. A self-assembly reaction between 4,5-bis(2-hydroxyethylthio)-1,3-dithiole-2-thione ( (HOCH 2 CH 2 ) 2 dmit) and [AuCl(tht)] affords the complex [AuCl{ (HOCH 2 CH 2 ) 2 dmit}] 2 ( 4), which possesses an antiparallel dimeric arrangement resulting from a short aurophilic contact of 3.078(6) A. This motif is extended into two dimensions due to intra- and intermolecular hydrogen bonds via the hydroxyethyl groups, giving rise to a supramolecular network. Three compounds were investigated for their rich photophysical properties at 298 and 77 K in 2-MeTHF and in the solid state; [Au 2(mu- dmid)(PPh 3) 2] ( 1), [Au 2(mu- dddt)(PPh 3) 2] ( 2), and [AuCl{( HOCH 2 CH 2 ) 2 dmit}] ( 4). 1 exhibits relatively long-lived LMCT (ligand-to-metal charge transfer) emissions at 298 K in solution (370 nm; tau e approximately 17 ns, where M is a single gold not interacting with the other gold atom; i.e., the fluxional C-SAuPPh 3 units are away from each other) and in the solid state (410 nm; tau e approximately 70 mus). At 77 K, a new emission band is observed at 685 nm (tau e = 132 mus) and assigned to a LMCT emission where M is representative for two gold atoms interacting together consistent with the presence of Au...Au contacts as found in the crystal structure. In solution at 77 K, the LMCT emission is also red-shifted to 550 nm (tau e approximately 139 mus). It is believed to be associated to a given rotamer. 2 also exhibits LMCT emissions at 380 nm at 298 K in solution and at 470 nm in the solid state. 4 exhibits X/MLCT emission (halide/metal to ligand charge transfer) where M is a dimer in the solid state with obvious Au...Au interactions, resulting in red-shifted emission band, and is a monomer in solution in the 10 (-5) M concentration (i.e., no Au...Au interactions) resulting in blue-shifted luminescence. Both fluorescence and phosphorescence are observed for 4.     

Effectiveness of dairy treated wastewater and different irrigation systems on the growth,biomass and fruiting of a Tunisian olive orchard (Olea europaea L., cv Chemlali)

Abstract

The effectiveness of dairy treated wastewater (TWW) was evaluated, in comparison with tap water (TW), on a Tunisian olive orchard (Olea europea, cv Chemlali), irrigated manually (MI) and by surface dripping (SDI). To this purpose, tree growth, biomass and fruiting were monthly tested for a one-year period. Similar trunk diameters, nodes/tree, root lengths were obtained, independently of source and system of irrigation. Also, comparable tree length and leaf area, shoots/tree and biomass, were observed between TWW and TW plants. However, such parameters improved under SDI rather than MI. Fruiting occurred only in TWW and TW trees treated by MI. Concerning growth, biomass and fruiting, TWW represented a valid alternative source for the irrigation of olive orchard, especially in Tunisia, already facing the freshwater scarcity. Monitoring of soil, TWW, fruits and oil will be required to validate the use of such effluent for olive orchard irrigation.     

Surface-immobilized self-assembled protein-based quantum dot nanoassemblies

Luminescent semiconductor quantum dot (QD)-based optical biosensors have the potential to overcome many of the limitations associated with using conventional organic dyes for biodetection. We have previously demonstrated a hybrid QD-protein-based fluorescence resonance energy transfer (FRET) sensor. Although the QD acted as an energy donor and a protein scaffold in the sensor, recognition and specificity were derived from the proteins. Transitioning this hybrid prototype sensor into flow cells and integrated devices will require a surface-immobilization strategy that allows the QD-based sensor to sample the environment and still maintain a distinct protein-covered QD architecture. We demonstrate a self-assembled strategy designed to accomplish this. Using glass slides coated with a monolayer of neutravidin (NA) as the template, QDs with maltose binding protein (MBP) and avidin coordinated to their surface were attached to the glass slides in discrete patterns using an intermediary bridge of biotinylated MBP or antibody linkers. Control of the surface location and concentration of the QD-protein-based structures is demonstrated. The utility of this self-assembly strategy is further demonstrated by assembling a QD-protein structure that allows the QDs to engage in FRET with a dye located on the surface-covering protein.     

Delivering quantum dots into cells: strategies,progress and remaining issues

The use of semiconductor quantum dots (QDs) in biological sensing and labeling continues to grow with each year. Current and projected applications include use as fluorescent labels for cellular labeling, intracellular sensors, deep-tissue and tumor imaging agents, sensitizers for photodynamic therapy, and more recently interest has been sparked in using them as vectors for studying nanoparticle-mediated drug delivery. Many of these applications will ultimately require the QDs to undergo targeted intracellular delivery, not only to specific cells, but also to a variety of subcellular compartments and organelles. It is apparent that this issue will be critical in determining the efficacy of using QDs, and indeed a variety of other nanoparticles, for these types of applications. In this review, we provide an overview of the current methods for delivering QDs into cells. Methods that are covered include facilitated techniques such as those that utilize specific peptide sequences or polymer delivery reagents and active methods such as electroporation and microinjection. We critically examine the benefits and liabilities of each strategy and illustrate them with selected examples from the literature. Several important related issues such as QD size and surface coating, methods for QD biofunctionalization, cellular physiology and toxicity are also discussed. Finally, we conclude by providing a perspective of how this field can be expected to develop in the future.     

Solution-phase single quantum dot fluorescence resonance energy transfer

We present a single particle fluorescence resonance energy transfer (spFRET) study of freely diffusing self-assembled quantum dot (QD) bioconjugate sensors, composed of CdSe-ZnS core-shell QD donors surrounded by dye-labeled protein acceptors. We first show that there is direct correlation between single particle and ensemble FRET measurements in terms of derived FRET efficiencies and donor-acceptor separation distances. We also find that, in addition to increased sensitivity, spFRET provides information about FRET efficiency distributions which can be used to resolve distinct sensor subpopulations. We use this capacity to gain information about the distribution in the valence of self-assembled QD-protein conjugates and show that this distribution follows Poisson statistics. We then apply spFRET to characterize heterogeneity in single sensor interactions with the substrate/target and show that such heterogeneity varies with the target concentration. The binding constant derived from spFRET is consistent with ensemble measurements.