Yellow-to-blue frequency upconversion in Pr-doped aluminium fluoride glasses

Rare-earth-doped fluoride glasses are attractive materials for photonics, since they combine a transmission region from ultraviolet to infrared and low vibrational cut-off energy. We report on the spectroscopic properties of aluminium fluorophosphate glasses doped with 0.1, 0.6, 1, 3 and 10 mol% Pr³⁺. Yellow-to-blue upconversion was observed upon pulsed and continuous-wave (CW) excitation at 575 nm. The temporal evolution of the upconverted fluorescence is characterised by rise and decay times depending on Pr³⁺ concentration. The upconversion intensity has a quadratic dependence on incident pump power, indicating a two-step process. The upconversion emission is described in the framework of a two-ion energy transfer mechanism. Emission in the second telecom window (1.3 μm) was measured upon excitation at 976 nm.     

Simultaneous Detection of Tyrosine and Structure-Specific Intrinsic Fluorescence in the Fibrillation of Alzheimer's Associated Peptides

Understanding of the structural changes during their aggregation and interaction is a prerequisite for establishing the precise clinical relevance of human islet amyloid polypeptide (hIAPP) (involved in Type-II Diabetes Mellitus) in the treatment of Alzheimer's disease stemmed from beta-amyloid (Aβ). Herein, we show that the steady-state emission spectra obtained from photoluminescence (PL) simultaneously capture both the tyrosine derivative (tyrosinate) and the structure-specific intrinsic fluorescence during the aggregation of Aβ and hIAPP. We observe multiple peaks in the emission spectra which exist for structure-specific intrinsic fluorescence, and use the second derivative UV-Vis spectra and the shift in the tyrosine peak as a quantitative measure of the dissimilitude in the electronic states and the fibril growth. We further applied these techniques to detect the static electric field (0, 40, 120, 200 V/cm) induced promotion and inhibition of fibrillation in Aβ, hIAPP and their electric field dependent role in the fibrillation of Aβ : hIAPP(1 : 1). The results were corroborated by field-emission scanning electron microscopy (FESEM), and the determinations of secondary structures by Fourier transform infrared spectroscopy (FTIR). The results indicate that the emission spectrum can be used as a sensor to detect the presence of fibrils; hence for screening potential inhibitors of amyloid fibrillation.     

Ultrafast Dynamics of the Transoid-cis Isomer Formed in Photochromic Reaction from 3H-Naphthopyran

Recent efforts in designing new 3H-naphthopyran derivatives have been focused on efficient coloration process with a short fading time of the colored transoid-cis TC isomer. It is desirable to avoid photoisomerization of TC leading to transoid-trans TT isomers in the photoreaction. Long lifetime of TT can hamper fast applications such as dynamic holographic materials and molecular actuators, the residual color is one of the serious issues for photochromic lenses. Herein we characterize the photophysical and photochemical channels of TC excited state deactivation competing with the unwanted TC → TT isomerization process. Transient absorption spectroscopy reveals a very short lifetime of the singlet excited TC (≈0.8 ps) and its deactivation channels as S₁→S₀ internal conversion (major), intersystem crossing S₁→T₁, pyran ring formation, photoenolization and TC → TT isomerization. Computations support the S₁→S₀ and T₁→S₀ channels as responsible for photostabilization of the TC form.     

Quantum calculation of thermal effect in quantum‐dot cellular automata

We present a theoretical study of thermal effect in quantum‐dot cellular automata (QCA). An extended Hubbard‐type model for the Hamiltonian of the QCA arrays, and canonical distribution were used to obtain thermal average of polarization for the QCA cells. A full‐basis quantum method has been used for the calculation of response function for a two‐ and a three‐cell array system. Each cell is composed of four dots located at the corners of the cells. Results show that the nonlinear behavior of the response function functions decay with the temperature as well as with the number of cells in the array. © 2005 Wiley Periodicals, Inc. Complexity 10: 73–78, 2005     

Development of a High-Fibre Multigrain Bar Technology with the Addition of Curly Kale

The aim of this study was to find the effect of kale and dietary fibre (DF) on the physicochemical properties, nutritional value and sensory quality of multigrain bars. A recipe of multigrain bars was prepared with the addition of fresh kale (20% and 30%) and DF preparations (apple, blackcurrant, chokeberry and hibiscus). The bars were baked at 180 °C for 20 min. These snack bars, based on pumpkin seeds, sunflower seeds, flaxseed and wholegrain oatmeal, are a high-calorie product (302–367 kcal/100 g). However, the composition of the bars encourages consumption. In addition to the ability to quickly satisfy hunger, such bars are rich in many natural ingredients that are considered pro-health (high fibre content (9.1–11.6 g/100 g), protein (11.2–14.3 g/100 g), fat (17.0–21.1 g/100 g, including unsaturated fatty acids), carbohydrates (20.5–24.0 g/100 g), as well as vitamins, minerals and a large number of substances from the antioxidant group. The addition of kale caused a significant increase of water content, but reduction in the value of all texture parameters (TPA profiles) as well as calorific values. The content of polyphenols was strongly and positively correlated with the antioxidant activity (r = 0.92). In the bars with 30% addition of kale (422 mg GA/100 g d.m.), the content of polyphenols was significantly higher than based ones (334 mg GA/100 g d.m.). Bars with the addition of the DF were characterized by a higher antioxidant activity, and the content of carotenoids, chlorophyll A and B and polyphenols. High sensory quality was demonstrated for all (from 4.8 to 7.1 on a 10-point scale). The addition of fibre preparations was also related to technological aspects and allows to create attractive bars without additional chemicals.     

Tandem regioselective synthesis of tetrazoles and related heterocycles using iodine

A one-pot, tandem process has been developed for the synthesis of a library of tetrazoles from aryl isothiocyanates. Condensation of aryl isothiocyanates with ammonia, and aryl amines (R-NH(2)) provided mono, 1,3-disubstituted symmetrical and unsymmetrical thioureas, which on desulfurization with molecular iodine (I(2)) led to formation of the corresponding heterocumulene (cyanamides or carbodiimides). The in situ generated heterocumulene on subsequent treatment with sodium azide at room temperature gave corresponding tetrazoles. The product regioselectivity for unsymmetrical 1,3-disubstituted thioureas was found to be correlated with the basicities (pK(a)'s) of the parent amines attached to the thiourea. Aryl-sec-alkyl unsymmetrical thioureas gave thioamido guanidino products rather than the 5-aminotetrazoles produced by HgCl(2) mediation of the reaction. Bis-thioureas derived from aryl isothiocyanates and hydrazine gave thiadiazoles exclusively.     

Conformational study of a single molecule of poly para phenylene ethynylenes in dilute solutions

The conformation of single molecules of dialkyl poly para phenylene ethynylenes (PPEs), electro-active polymers, is studied in solutions using molecular dynamics simulations. The conformation of conjugated polymers affects their electro-optical properties and therefore is critical to their current and potential uses, though only limited theoretical knowledge is available regarding the factors that control their configuration. The present study investigates the affects of molecular parameters including molecular weight of the polymer and chemical structure of the side chains of PPEs in different solvents on the conformation of the polymers. The PPEs are modeled atomistically where the solvents are modeled both implicitly and explicitly. The study finds that PPEs assume extended configuration which is affected by the length of the polymer backbone and the nature and length of substituting side chains. While the polymer remains extended, local dynamics is retained and no long range correlations are observed within the backbone. The results are compared with scattering experiments.     

Simultaneous Detection of Ascorbic Acid and Hydrogen Peroxide by Flow‐Injection Analysis with a Thin Layer Dual‐Electrode Detector

Based on preliminary voltammetric investigations at unmodified and modified electrodes in aqueous solutions buffered at different pHs, a profitable thin layer dual‐electrode detector was developed for the selective and simultaneous determination of ascorbic acid (AA) and hydrogen peroxide present in the same samples. It consists of a small thickness (0.1 mm) cell, used as a detector for a flow injection system, in which a glassy carbon (GC) and a polyeugenol coated Pt electrode are encased. The GC electrode is selective for AA, thanks to the potential applied (0.3 V vs. Ag/AgCl,Cl^?_sat), while H₂O₂ alone can be oxidized at the Pt electrode (0.75 V), thanks to the size selectivity and electrostatic screen properties displayed by the polyeugenol coating layer which prevents oxidation of ascorbate anions. Repeatable sharp peaks (±4.5 %) were detected for both analytes over wide linear ranges (0.005–1.000 mM) and detection limits of about 10^?6 M (176 ppb) and 5×10^?7 M (16 ppb) were inferred for AA and H₂O₂ respectively. This flow injection approach was applied to the analysis of some orange‐taste soft drinks, used as prototype real samples, spiked with controlled amounts of both analytes, thus inferring good recoveries which pointed out that deviations never exceeding 5 % affected the relevant accuracy.     

Noninvasive monitoring of photocatalytic degradation of X‐ray contrast media using Raman spectrometry

The photocatalytic degradation of the X‐ray contrast agents iohexol and diatrizoate are monitored by in situ Raman spectrometry measurements in aqueous solution with a TiO₂ photocatalyst. Spectral features and changes are interpreted with the use of density functional theory calculations. While we observe similar results to those published previously, significant changes seen in the Raman spectrum allow us to better identify the mechanisms without the need for deductive approaches or complicated sample preparation. Diatrizoate spectra are consistent with hydroxyl radical attack leading to the loss of CO₂. Iohexol is more difficult to interpret, representing a current challenge to the use of Raman spectrometry for real‐time monitoring of photocatalytic degradation experiments. We explore internal standards that can be added to gauge overall degradation rates to some extent. Potential extensions of the work are described, particularly in terms of increased rate of data acquisition and more general application. Copyright © 2013 John Wiley & Sons, Ltd.