Synthesis, structure and magnetic properties of nanocrystalline YMnO3

Nanocrystalline YMnO(3) has been prepared by wet chemical synthesis routes to obtain crystallites with sizes from 20 nm to bulk material. The crystal structure of hexagonal YMnO(3) nanocrystallites smaller than 80 nm deviates from bulk material in terms of unit cell distortion and unit cell volume. The ferrielectric displacements of Y(3+) cations along the polar c-axis decays progressively with decreasing size below 100 nm. Indications of weak ferromagnetism in the form of a narrow hysteresis loop and enhanced magnetic susceptibility below 43 K in 20 nm YMnO(3) nanoparticles is attributed to extrinsic effects. Low-temperature annealing of the 20 nm crystallites in an oxidizing atmosphere removed all traces of ferromagnetism, showing that this is not a size-induced property. Finally, formation of the competing metastable orthorhombic phase and the thermodynamically stable hexagonal phase is discussed with respect to oxidizing or reducing conditions during synthesis.     

Novel affinity ligands for chromatography using combinatorial chemistry

Spatially addressable combinatorial libraries were synthesized by solution phase chemistry and screened for binding to human serum albumin. Members of arylidene diamide libraries were among the best hits found, having submicromolar binding affinities. The results were analyzed by the frequency with which particular substituents appeared among the most potent compounds. After immobilization of the ligands either through the oxazolone or the amine substituent, characterization by surface plasmon resonance showed that ibuprofen affected the binding kinetics, but phenylbutazone did not. It is therefore likely that these compounds bind to Site 2 in sub domain IIIA of human serum albumin (HSA).     

Impurity diffusion of (141)Pr in LaMnO(3), LaCoO(3) and LaFeO(3) materials

The impurity diffusion of Pr(3+) in dense polycrystalline LaMnO(3), LaCoO(3) and LaFeO(3) was studied at 1373-1673 K in air in order to investigate cation diffusion in these materials. Cation distribution profiles were measured by secondary-ion mass spectrometry and it was found that penetration profiles of Pr(3+) had two distinct regions with different slopes. The first, shallow region was used to evaluate the bulk diffusion coefficients. The activation energies for bulk diffusion of Pr(3+) in LaMnO(3), LaCoO(3) and LaFeO(3) were 126 +/- 6, 334 +/- 68 and 258 +/- 75 kJ mol(-1), respectively, which are significantly lower than previously predicted by atomistic simulations. The bulk diffusion of Pr(3+) in LaMnO(3) was enhanced compared to LaCoO(3) and LaFeO(3) due to higher concentrations of intrinsic point defects in LaMnO(3), especially La site vacancies. Grain-boundary diffusion coefficients of Pr(3+) in LaCoO(3) and LaFeO(3) materials were evaluated according to the Whipple-Le Claire equation. Activation energies for grain-boundary diffusion of Pr(3+) in LaCoO(3) and LaFeO(3) materials were 264 +/- 41 kJ mol(-1) and 290 +/- 36 kJ mol(-1) respectively. Finally, a correlation between activation energies for cation diffusion in bulk and along grain boundaries in pure and substituted LaBO(3) materials (B = Cr, Fe, Co) is discussed.     

Modified 6‐Aza Uridines: Highly Emissive pH‐Sensitive Fluorescent Nucleosides

Optimized facile syntheses and highly desirable spectroscopic properties of two isomorphic fluorescent pyrimidines, comprising a 1,2,4‐triazine motif conjugated to a thiophene ( 1 a ) or a furan ( 1 b ), are described. Although structurally related to their 5‐modified uridine counterparts, these modified 6‐aza‐uridines reveal dramatically improved fluorescence properties and a remarkable sensitivity to polarity and pH changes. The thiophene derivative 1 a has an absorption maximum around 335 nm, which upon excitation yields visible emission with a polarity‐sensitive maximum and fluorescence quantum yield ranging from 415 nm (Φ=0.8) to 455 nm (Φ=0.2) in dioxane and water, respectively. Nucleoside 1 a also displays susceptibility to acidity. Correlating emission intensity and solution pH yields a pK_a value of 6.7–6.9, reasonably close to physiological pH values. The results illustrate that highly sought‐after fluorescence features (brightness and responsiveness) are not necessarily the trait of large fluorophores alone, but can be observed with probes that meet stringent isomorphic design criteria.     

Synthesis of Monodisperse Silicon Quantum Dots Through a K-Naphthalide Reduction Route

Si quantum dots (Si q-dots) with a size below ~5?nm have great potential in electronics and photovoltaics and are candidate materials for down conversion of light due to their strong photoluminescence (PL) properties. Proper control of size and size distribution as well as the surface characteristics of the Si q-dots are critical for applications in order to control the PL response. Here we report on the synthesis of Si q-dots by a chemical route using potassium-naphthalide as a reducing agent. A narrow size distribution of the Si q-dots, with size in the range from 3 to 30?nm, was achieved by controlling the concentration of the reduction agent, the concentration of silicon tetrachloride (SiCl₄) precursor, temperature and the reaction time. The crystallinity and the narrow size distribution of Si q-dots were demonstrated by electron microscopy and electron diffraction. The optical absorption and PL response in the blue region of the visible spectrum is reported for 3.1?±?0.6?nm octanoxy capped Si q-dots and 4.2?±?1.4?nm methoxy capped Si q-dots in 1,2-dimethoxyethane solution. A quantum efficiency of (1.63?±?0.16)?×?10^?3% was detected for the octanoxy terminated Si q-dots.     

Modeling of coupling mechanisms and frequency separation in double disk resonators

We present modeling expressions for the coupling mechanisms in vertically stacked disk resonators. Using lumped modeling techniques, analytic expressions for coupling mechanisms in a stack of two disks are derived. The modeling results are compared to those of high-fidelity finite element analyses and show that the analytic expressions derived can be used to predict frequency separation between radial extensional modes. The established model is useful for gaining insight into parameter sensitivity when designing a stacked double disk resonator.     

Extended ethidium bromide analogue as a triple helix intercalator: synthesis, photophysical properties and nucleic acids binding

Ethidium bromide has been extended by fusing an additional aromatic ring resulting in a larger intercalator with increased affinity for poly r(A) x r(U), poly d(A) x d(T) and triple helices when compared to the parent heterocycle.     

Microfluidic sorting system based on optical waveguide integration and diode laser bar trapping

Effective methods for manipulating, isolating and sorting cells and particles are essential for the development of microfluidic-based life science research and diagnostic platforms. We demonstrate an integrated optical platform for cell and particle sorting in microfluidic structures. Fluorescent-dyed particles are excited using an integrated optical waveguide network within micro-channels. A diode-bar optical trapping scheme guides the particles across the waveguide/micro-channel structures and selectively sorts particles based upon their fluorescent signature. This integrated detection and separation approach streamlines microfluidic cell sorting and minimizes the optical and feedback complexity commonly associated with extant platforms.