Dual-direction Gires-Tournois etalon based on a single complex fiber Bragg grating

We propose and demonstrate a single fiber Bragg grating-based Gires-Tournois (GT) etalon, which is realized by applying a complex apodization profile on a linearly chirped fiber Bragg grating. Such a GT etalon not only has a simplified fabrication procedure but also can operate in dual directions.     

Dendritic structures of poly(ethylene glycol) on silicon nitride and gold surfaces

A hydrophilic silicon nitride surface was grafted with poly(ethylene glycol) monomethyl ether (average formula weight of 5000 Da) in a one-step protocol. The domains of stable dendritic structures of self-assembled monolayer islands on a silicon nitride surface were observed with atomic force microscopy. The moduli of elasticity of these dendritic structures in air and in KCl aqueous solution were compared. The value of the Young's modulus of these structures is reduced by more than 3 orders of magnitude, from approximately 12 GPa measured in air to approximately 5 MPa in KCl solution. This dramatic reduction in elasticity was attributed to the swelling of the dendritic structures in aqueous solution, which was verified by the increased film thickness. These dendritic structures were not stable in the aqueous environment and could be removed by soaking in water for 22 h because of the hydrolysis of the silicate bonds. This fact was confirmed by the reduction of the C1s signal in the X-ray photoelectron spectroscopy experiments. These morphologies are not unique to silicon nitride substrate; similar features were also observed for thiolated poly(ethylene glycol) monomethyl ether molecules absorbed on a gold surface.     

Efficient preparation and improved sensitivity of molecularly imprinted polymers using room temperature ionic liquids

Synthesis of trans-aconitic acid molecularly imprinted polymers in [bmim][BF4] and [bmim][PF6] under photochemical (5 degrees C, AIBN) and thermal (60 degrees C, AIBN) conditions gave polymer micro-spheres (<200 nm), under bulk and precipitation polymerisation conditions, and higher selectivity indices (100% improvement) relative to the more traditional precipitation polymerisation (CH3CN, high solvent volumes) approach.     

Development of sequential injection-lab-at-valve (SI-LAV) micro-extraction instrumentation for the spectrophotometric determination of an anionic surfactant.

The development of instrumentation for sequential injection analysis with a "lab-at-valve" (SIA-LAV) micro-extraction system is presented. The extractive determination of an anionic surfactant using methylene blue was selected as a model. Sample, reagents and organic solvent were sequentially aspirated into an extraction coil connected to the center of a selection valve, where extraction took place by flow reversal. The aqueous and organic phases were separated in a LAV unit attached to one port of the valve. The LAV unit situated a fiber-optic spectrophotometer to monitor the absorbance change of the extract product in the organic phase. The developed SIA-LAV system offers an alternative micro-total analysis system for automated micro-extraction.     

Approaches to crystallization from ionic liquids: complex solvents-complex results, or, a strategy for controlled formation of new supramolecular architectures?

There are now more than 1200 papers a year describing research results using the 'neoteric' solvents, known as ionic liquids (ILs). If ILs are such highly studied solvents, why has there been so comparatively little research in their use in crystallization? Here we explore this question and discuss possible strategies for utilization of the mundane and the unique aspects of ILs for novel crystallization strategies including crystallization of high and low melting solids using thermal shifts; "solvothermal" techniques; slow diffusion; electrocrystallization; and use of a co-solvent. The results presented here and those appearing in the literature indicate both the complex nature of these solvents and their promise in delivering unique solvation, metal ion coordination numbers, coordination polymer motifs, and metal-anion interactions, to name but a few. These complex, but fascinating, results and the promise of much more intimate control over crystallization processes will drive a growing interest in using ILs as crystallization solvents.     

Conformational behavior of simple furanosides studied by optical rotation

Experimental and theoretical specific optical rotations (OR) of anhydro, epithio, and epiminoderivatives of methyl tetrofuranosides in chloroform solutions have been compared and used as a tool for exploring their conformational behavior. The potential energy surfaces of these saccharides with reduced flexibility were examined with the density functional theory and the MP2 and CCSD(T) wavefunctions methods. Theoretical ORs were obtained by Boltzmann averaging of values calculated for local minima. Resultant rotations could be used to assess the quality of the DFT and MP2 relative conformer energies. OR values calculated for equilibrium geometries in vacuum were significantly improved when the solvent was accounted for by a polarizable continuum model and first and diagonal second OR derivatives were used for an anharmonic vibrational averaging. The DFT used as a default method reproduced the experimental data fairly well. A modified B3LYP functional containing 70% of HF exchange further improved the results. Because of the strong dependence of OR on the conformation, not only the absolute configuration could be determined, but also the conformational populations were estimated. Likewise, the predicted dependence of OR on the light wavelength well agreed with experiment. The increasing precision of the contemporary computational methods thus makes it possible to relate the specific rotation to more detailed features in molecular structure. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

Oxygen evolution on Ru1 − x Ni x O2 − y nanocrystalline electrodes

Nanocrystalline Ru_1 − x Ni _x O_2 − y with 0.02 < x < 0.30 were prepared by a sol–gel approach at temperatures between 300 and 600 °C. XRD patterns of the prepared materials indicate a single-phase character conforming to a tetragonal syngony. All prepared materials are sufficiently stable in acid media and show activity towards oxygen evolution. The activity towards oxygen evolution reaction of the materials with constant chemical composition decreases with increasing particle size. The increasing Ni content enhances the electrocatalytic activity in a stepwise manner with abrupt changes for materials containing approximately 5% or 15% of the cationic sites substituted by Ni.     

Identification of β-carotene in an evaporitic matrix—evaluation of Raman spectroscopic analysis for astrobiological research on Mars

Since evaporitic rocks on the Martian surface could (or still can) serve as potential habitats for microbial life on Mars, there is a reasonable possibility that these rocks may sustain molecular remnants as evidence for the presence of extinct or extant living organisms on Mars and that β-carotene could be a suitable biomarker. In this paper, Raman microspectrometry was tested as a nondestructive method of determining the lowest detectable β-carotene content in experimentally prepared evaporitic matrices—namely, gypsum, halite and epsomite. Two excitation wavelengths were compared—514.5 nm, because of the resonance Raman enhancement in the carotenoid analysis, and 785 nm, as a more universal wavelength now much used in the detection of biomolecules terrestrially. Mixtures were measured directly as well as with a laser beam penetrating the crystals of gypsum and epsomite. We have obtained β-carotene signals at the 0.1 to 10 mg kg⁻¹ level—the number of registered β-carotene Raman bands differed depending on the particular mineral matrix and the excitation wavelength. Concentrations of β-carotene of about one order of magnitude higher were identified when analysed through single crystals of gypsum and epsomite, respectively.     

Comparing the effects of reverberation and of noise on speech recognition in simulated electric-acoustic listening

Cochlear implant users report difficulty understanding speech in both noisy and reverberant environments. Electric-acoustic stimulation (EAS) is known to improve speech intelligibility in noise. However, little is known about the potential benefits of EAS in reverberation, or about how such benefits relate to those observed in noise. The present study used EAS simulations to examine these questions. Sentences were convolved with impulse responses from a model of a room whose estimated reverberation times were varied from 0 to 1 sec. These reverberated stimuli were then vocoded to simulate electric stimulation, or presented as a combination of vocoder plus low-pass filtered speech to simulate EAS. Monaural sentence recognition scores were measured in two conditions: reverberated speech and speech in a reverberated noise. The long-term spectrum and amplitude modulations of the noise were equated to the reverberant energy, allowing a comparison of the effects of the interferer (speech vs noise). Results indicate that, at least in simulation, (1) EAS provides significant benefit in reverberation; (2) the benefits of EAS in reverberation may be underestimated by those in a comparable noise; and (3) the EAS benefit in reverberation likely arises from partially preserved cues in this background accessible via the low-frequency acoustic component.     

Rhodamine B-based “turn-on” fluorescent and colorimetric chemosensors for highly sensitive and selective detection of mercury (II) ions

Two novel macromolecules based on 2-[3-(2-aminoethylsulfanyl)propylsulfanyl]ethanamine covalently bound to one and two units of rhodamine-B moieties, 1 and 2, were prepared and utilized as fluoroionophores and chromophores for the optical detection of Hg²⁺ ions. The sensors were readily prepared by a conventional two-step synthesis. Especially, sensor 1 exhibits high sensitivity and selective OFF–ON fluorescence enhancement and chromogenic change upon binding to Hg²⁺, which served as a “naked-eye” indicator by a noticeable color change of the solution (from colorless to pink–red color). 1 is shown to discriminate various competing metal ions, particularly Ag⁺ and Cu²⁺, as well as Cd²⁺, Na⁺, Li⁺, K⁺, Ba²⁺, Co²⁺, Ni²⁺, Mg²⁺, Mn²⁺ and Al³⁺, with a detection limit of 10 ppb.