Very-high-resolution tandem Fabry-Perot etalon cylindrical beam volume hologram spectrometer for diffuse source spectroscopy

We demonstrate a compact and slitless spectrometer with high resolution formed by cascading a Fabry-Perot etalon (FPE) and a cylindrical beam volume hologram (CBVH). The most significant advantage of this combined spectrometer is that we can independently encode spectral information of a diffuse beam in a 2D plane. Also, we show that in this slitless configuration we can simultaneously benefit from the advantages of both elements: the high resolution of the FPE and the large spectral range of the CBVH. Here, we report on the experimental demonstration of a spectrometer with better than 0.2 nm resolution.     

Catecholthioether derivatives: preliminary study of in-vitro antimicrobial and antioxidant activities

In this research, synthesis, antimicrobial and antioxidant activities of a series of catecholthioethers having benzoxazole and tetrazole moieties are described. Antimicrobial activity was evaluated by minimum inhibitory concentration (MIC) assay. The synthesized compounds were tested in vitro against three Gram-positive bacteria including Staphylococcus aureus (clinical isolated), Staphylococcus aureus ATCC 25922, Enterococcus faecium (clinical isolated), and two Gram-negative bacteria including Klebsiella pneumoniae (clinical isolated) and Pseudomonas aeruginosa 27853 and the yeast Candida albicans in comparison with control drugs. Microbiological results indicated that the synthesized compounds possessed a broad spectrum of activity against the tested microorganisms at MIC values between 4-256 μg/ml. This shows compounds having tetrazole moiety were the most active against Gram-negative strains, whereas compounds having benzoxazole moiety were more active against Gram-positive ones. Also both of them showed significant antifungal activity against Candida albicans and had lower activity than the compared control drugs (Sulfamethoxazole and Fluconazole). The antioxidant activity was assessed using two methods, including, 1,1-biphenyl-2-picrylhydrazyl (DPPH) radical scavenging, and reducing power assays. Some of the catecholthioether derivatives showed antioxidant activity more than Trolox and butylated hydroxyanisole (BHA) as reference antioxidants.     

Label-free flow cytometry using multiplex coherent anti-Stokes Raman scattering (MCARS) for the analysis of biological specimens

We present the first demonstration, to our knowledge, of a label-free flow cytometer for the analysis of biological specimens using multiplex coherent anti-Stokes Raman scattering (MCARS) and elastic scatter measurements. The MCARS system probes the Raman vibrational energy levels and the elastic scatter provides morphological information. We demonstrate these capabilities by probing a culture of Saccharomyces cerevisiae at 100 spectra/s and constructing a background-free Raman reconstruction using a Kramers-Kronig relation. A theoretical analysis shows that this system could operate at speeds of 10 kHz with appropriate hardware; thus facilitating integration into commercial flow cytometers or use as a high-speed, stand-alone device.     

Inhomogeneous charge transfer within monolayer zinc phthalocyanine absorbed on TiO2(110)

The d-orbital contribution from the transition metal centers of phthalocyanine brings difficulties to understand the role of the organic ligands and their molecular frontier orbitals when it adsorbs on oxide surfaces. Here we use zinc phthalocyanine (ZnPc)/TiO(2)(110) as a model system where the zinc d-orbitals are located deep below the organic orbitals leaving room for a detailed study of the interaction between the organic ligand and the substrate. A charge depletion from the highest occupied molecular orbital is observed, and a consequent shift of N1s and C1s to higher binding energy in photoelectron spectroscopy (PES). A detailed comparison of peak shifts in PES and near-edge X-ray absorption fine structure spectroscopy illustrates a slightly uneven charge distribution within the molecular plane and an inhomogeneous charge transfer screening between the center and periphery of the organic ligand: faster in the periphery and slower at the center, which is different from other metal phthalocyanine, e.g., FePc/TiO(2). Our results indicate that the metal center can substantially influence the electronic properties of the organic ligand at the interface by introducing an additional charge transfer channel to the inner molecular part.     

Azimuthal-order variations of surface-roughness-induced mode splitting and scattering loss in high-Q microdisk resonators

We report an experimental observation of strong variations of quality factor and mode splitting among whispering-gallery modes with the same radial order and different azimuthal orders in a scattering-limited microdisk resonator. A theoretical analysis based on the statistical properties of the surface roughness reveals that mode splittings for different azimuthal orders are uncorrelated, and variations of mode splitting and quality factor among the same radial mode family are possible. Simulation results agree well with the experimental observations.     

Effect of the dielectric constant of the surrounding medium and the substrate on the surface plasmon resonance spectrum and sensitivity factors of highly symmetric systems: silver nanocubes

Silver nanocubes (AgNCs), 60 nm, have four extinction surface plasmon resonance (SPR) peaks. The finite difference time domain (FDTD) simulation method is used to assign the absorption and scattering peaks and also to calculate the plasmon field intensity for AgNCs. Because AgNCs have a highly symmetric cubic shape, there is a uniform distribution of the plasmon field around them, and they are thus sensitive to asymmetric dielectric perturbations. When the dielectric medium around a nanoparticle is changed anisotropically, either by placing the particle on a substrate or by coating it asymmetrically with a solvent, the plasmon field is distorted, and the plasmonic absorption and scattering spectra could shift differently. For the 60 nm AgNC, we found that the scattering resonance peak shifted more than the absorption peak. This changes the extinction bandwidth of these overlapping absorption and scattering bands, and consequently the figure of merit of the nanoparticle, as a localized SPR sensor, no longer has a constant value.     

Modified Borohydride Agents1a-d Methyltriphenylphosphonium Tetrahydroborate; MePh3P+BH4 − as a Selective and An Efficient Reducing Agent

Abstract

MePh₃P⁺BH₄ ^? is able to reduce aldehydes and ketones to their corresponding alcohols in CH₂Cl₂. Aldehydes are reduced with high selectivity in the presence of ketones. α,β-Unsaturated carbonyl compounds undergo 1,2-reduction and produce their corresponding allylic alcohols in high yields. Carboxylic acid chlorides are also converted to their alcohols with high yields.     

Wet silica-supported permanganate for the cleavage of semicarbazones and phenylhydrazones under solvent-free conditions

Wet silica-supported potassium permanganate was used as an inexpensive and efficient reagent for conversion of semicarbazones and phenylhydrazones to the corresponding carbonyl compounds under solid-state conditions.