Single photon counting from individual nanocrystals in the infrared

Experimental restrictions imposed on the collection and detection of shortwave-infrared photons (SWIR) have impeded single molecule work on a large class of materials whose optical activity lies in the SWIR. Here we report the successful observation of room-temperature single nanocrystal photoluminescence at SWIR wavelengths using a highly efficient multielement superconducting nanowire single photon detector. We confirm that the photoluminescence from single lead sulfide nanocrystals is strongly antibunched, demonstrating the feasibility of performing sophisticated photon correlation experiments on individual weak SWIR emitters, and, more broadly, paving the way for sensitive measurements of spectral observables on infrared quantum systems that are incompatible with current detection techniques.     

Ferroelectric order in individual nanometre-scale crystals

Ferroelectricity in finite-dimensional systems continues to arouse interest, motivated by predictions of vortex polarization states and the utility of ferroelectric nanomaterials in memory devices, actuators and other applications. Critical to these areas of research are the nanoscale polarization structure and scaling limit of ferroelectric order, which are determined here in individual nanocrystals comprising a single ferroelectric domain. Maps of ferroelectric structural distortions obtained from aberration-corrected transmission electron microscopy, combined with holographic polarization imaging, indicate the persistence of a linearly ordered and monodomain polarization state at nanometre dimensions. Room-temperature polarization switching is demonstrated down to ~5?nm dimensions. Ferroelectric coherence is facilitated in part by control of particle morphology, which along with electrostatic boundary conditions is found to determine the spatial extent of cooperative ferroelectric distortions. This work points the way to multi-Tbit/in(2) memories and provides a glimpse of the structural and electrical manifestations of ferroelectricity down to its ultimate limits.     

Photocatalytic performance of nanocrystalline Bi5Ti3FeO15 layered perovskite under visible light

Nanocrystalline Bi5Ti3FeO15 layered perovskite exhibiting Aurivillius phase was synthesized by polymerized complex (PC) method and investigated for its physico-chemical as well as optical properties. The crystallization of Bi5Ti3FeO15 synthesized by PC method was found to occur in the temperature range of 800-1050 degress C, whereas the single crystalline Bi5Ti3FeO15 formed at 1030 degrees C by solid state reaction (SSR) method. The observation of highly pure phase and such lower crystallization temperature in Bi5Ti3FeO15 prepared by PC method, is in total contrast to that observed in Bi5Ti3FeO15 prepared by the conventional solid-state reaction (SSR) method. The band gap of nanocrystalline Bi5Ti3FeO15 determined from UV-Vis diffusion reflectance spectrometer was 2.38 eV (525 nm). The photocatalytic activity of Pt/Bi5Ti3FeO15 prepared by PC method was investigated with the photodecomposition of isopropyl alcohol (IPA) and hydrogen production from water-methanol mixed solution under visible light (lambda > or = 420 nm). The respective activities for PC sample were higher than that of Pt/Bi5Ti3FeO15 prepared by SSR as well as Pt/TiO(2-x)N(x).     

Modelling the dynamics of dengue real epidemics

In this work, we use a mathematical model for dengue transmission with the aim of analysing and comparing two dengue epidemics that occurred in Salvador, Brazil, in 1995-1996 and 2002. Using real data, we obtain the force of infection, Λ, and the basic reproductive number, R(0), for both epidemics. We also obtain the time evolution of the effective reproduction number, R(t), which results in a very suitable measure to compare the patterns of both epidemics. Based on the analysis of the behaviour of R(0) and R(t) in relation to the adult mosquito control parameter of the model, we show that the control applied only to the adult stage of the mosquito population is not sufficient to stop dengue transmission, emphasizing the importance of applying the control to the aquatic phase of the mosquito.     

Complex dynamics of life at different scales: from genomic to global environmental issues

This introduction to the Theme Issue, Complex dynamics of life at different scales: from genomic to global environmental issues, gives a short overview on why the ideas and concepts in complexity and nonlinearity are relevant to the understanding of life in its different manifestations. Also, it discusses how life phenomena can be thought of as composing different scales of organization. Finally, the articles in this thematic publication are briefly commented on in terms of their relevance in helping to understand the complexity of life systems.     

Pentafluorophenoxy boron subphthalocyanine as a fluorescent dopant emitter in organic light emitting diodes

A fluorinated phenoxy boron subphthalocyanine (BsubPc) is shown to function as a fluorescent dopant emitter in small molecule organic light emitting diodes (OLEDs). Narrow electroluminescence (EL) emission with a full width at half-maximum of ～30 nm was observed regardless of the host used, indicating that this narrow EL is intrinsic to the BsubPc molecule. A bathochromic shift and the growth of a new EL peak at higher wavelengths with increasing doping concentration were found to be a result of molecular aggregation. Excitation of BsubPc by direct charge trapping as well as Fo?rster resonant energy transfer were shown using different host molecules. A maximum efficiency of 1.5 cd/A was achieved for a 4,4'-N,N'-dicarbazole-biphenyl (CBP) host.     

The calculation of polar surface area from first principles: an application of quantum chemical topology to drug design

The calculation of polar surface areas (PSA) from the electron density using quantum chemical topology (QCT) and a newly developed algorithm to determine isodensity surface areas is described. PSA values were calculated from the atomic partitioning of B3LYP/6-311G* wavefunctions and the results described herein represent the first application of this new algorithm. PSA values were calculated for forty drugs and compared to the topological polar surface area (TPSA) and those calculated by the QikProp program. Oral bioavailabilities predicted from the QCT PSA values for a subset of twenty drugs (the Palm set) were similar to those predicted by the dynamic polar surface area (DPSA) and in general, are in agreement with the observed values. Overall, PSA values obtained from QCT were generally similar to the DPSA, TPSA, and QikProp values, though differences in fragment contributions were found, with nitrogen-bearing functional groups showing the largest variation between methods. Differences between methods showed how the calculation of the PSA is dependent on the method used and, therefore, judicious application of the upper limits used in the prediction of oral bioavailability is warranted. These results also indicate that, because of the differences in the way PSA values are calculated, values from the different methods should not be used interchangeably.     

Women and Smokers Have Elevated Urinary F2-Isoprostane Metabolites: A Novel Extraction and LC–MS Methodology

F(2)-Isoprostanes (F(2)-IsoPs), regio- and stereoisomers of prostaglandin F(2alpha) (PGF(2alpha)), and urinary F(2)-IsoP metabolites including 2,3-dinor-5,6-dihydro-8-iso-PGF(2alpha) [2,3-dinor-8-iso-PGF(1alpha) (2,3-dinor-F1)] and 2,3 dinor-8-iso-PGF(2alpha) (2,3-dinor-F2), have all been used as biomarkers of oxidative stress. A novel method was developed to measure these biomarkers using a single solid phase extraction (SPE) cartridge, separation by HPLC, and detection by negative mode selected reaction monitoring (SRM) mass spectrometry (MS), using authentic standards of PGF(2alpha); 8-iso-PGF(2alpha); 2,3-dinor-F1 and 2,3-dinor-F2 to identify specific chromatographic peaks. The method was validated in a population of healthy, college-aged nonsmokers (n = 6 M/8F) and smokers (n = 6 M/5F). Urinary F(2)-IsoP concentrations were approximately 0.2-1.5 microg/g creatinine, 2,3-dinor-F1 was approximately1-3 microg/g and 2,3-dinor-F2 was approximately 3-5 microg/g. Additional F(2)-IsoPs metabolites were identified using SRM. The sum of all urinary F(2)-IsoP metabolites was 50-100 microg/g creatinine indicating their greater abundance than F(2)-IsoPs. Women had higher F(2)-IsoP metabolite concentrations than did men (MANOVA, main effect P = 0.003); cigarette smokers had higher concentrations than did nonsmokers (main effect P = 0.036). For men or women, respectively, smokers had higher metabolite concentrations than did nonsmokers (P < 0.05). Thus, our method simultaneously allows measurement of urinary F(2)-IsoPs and their metabolites for the determination of oxidative stress.     

Synthesis and immunological properties of a tetrasaccharide portion of the B side chain of rhamnogalacturonan II (RG-II)

A highly convergent strategy was used for the synthesis of a tetrasaccharide [3-aminopropyl beta-L-arabinofuranosyl-(1-->3)-alpha-L-rhamnopyranosyl-(1-->2)-[alpha-L-rhamnopyranosyl-(1-->3)]-alpha-L-arabinopyranoside] portion of the B side chain of the plant cell-wall pectic polysaccharide rhamnogalacturonan II (RG-II). The terminal nonreducing beta-L-arabinofuranosyl residue of the target compound was installed by using an arabinofuranosyl donor that was protected with a 3,5-O-(di-tert-butylsilane) group to facilitate nucleophilic attack from the beta-face. The synthetic strategy also employed a chemoselective glycosylation of a trichloroacetimidate donor with a thioglycosyl acceptor; this gave a product that could be used immediately in a subsequent glycosylation. The reducing end of the tetrasaccharide contained an aminopropyl group to facilitate conjugation to keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA). Mice that were immunized with a KLH-tetrasaccharide conjugate produced antibodies that recognized RG-II isolated from Arabidopsis thaliana cell walls, but did not recognize RG-II obtained from red wine. Our data suggest that the arabinopyranosyl residue exists in the (4)C(1) conformation in the tetrasaccharide and in A. thaliana RG-II, whereas it has the (1)C(4) conformation in wine RG-II. It is proposed that differences in the conformation of side chain B might account for the ability of antibodies to discriminate between RG-II that was isolated from Arabidopsis and wine.