Heterodyne-detected vibrational sum frequency generation spectroscopy

We present a new technique of broad-band heterodyne-detected sum frequency generation (HD-SFG) spectroscopy and demonstrate its high sensitivity allowing surface-selective measurements of vibrational spectra at submonolayer surface coverage, as low as a few percent of a monolayer. This was achieved without the help of surface enhancement phenomena, on a transparent dielectric substrate (water), and without introducing fluorescent labels, in fact, without utilizing any electronic resonances. Only the intrinsic vibrational transitions were employed for the detection of the analyte molecules (1-octanol). Unlike conventional (homodyne-detected) SFG spectroscopy, where the signal intensity decreases quadratically with decreasing surface coverage, in HD-SFG, the scaling is linear, and the signal is amplified by interference with a reference beam, significantly improving sensitivity and detection limits. At the same time, HD-SFG provides the phase as well as the amplitude of the signal and thus allows accurate subtraction of the non-resonant background--a common problem for surfaces with low concentrations of analyte molecules (i.e., weak resonant signals).     

A cost effective 100 Gbps hybrid MDM–OCDMA–FSO transmission system under atmospheric turbulences

FSO or free space optics is a familiar name used in a wide array of applications in the area of telecommunications. Due to its features of low maintenance cost and deployment time, most of the applications consider FSO as the alternative solution for appropriately replacing fiber optics. In this work, we have designed 100 Gbps FSO system by combining mode division multiplexing (MDM) and optical code multiple access scheme (OCDMA). Ten channels, each carrying 10 Gbps data, are transported over 8 km FSO link by using MDM of two Laguerre Gaussian modes and random diagonal codes. Moreover, the performance of proposed MDM–OCDMA–FSO system is also investigated under atmospheric turbulences.     

Rubbing-induced anisotropy of long alkyl side chains at polyimide surfaces

Molecular organization at polyimide surfaces used as alignment layers in liquid crystal displays was investigated using vibrational sum frequency generation (SFG) spectroscopy. We focus on the orientation of the long alkyl side groups at the polymer surface using polarization-selected SFG spectra of the CH(3)- and CH(2)-stretch modes of the side chain. Mechanical rubbing and baking, an accepted industrial procedure used to produce pretilt of the liquid crystal, was found to induce pronounced azimuthal anisotropy in the orientational distribution of the alkyl side chains. Orientational analysis of the SFG vibrational spectra in terms of the azimuthal and tilt angles (in and out of plane, respectively) of the alkyl side chains shows their preferential tilt along the rubbing direction, with the azimuthal distribution narrower for stronger rubbed polymer samples.     

Optimization of the catalytic activity of manganese dioxide (MnO2) nanoparticles for degradation of environmental pollutants

Research on Chemical Intermediates - A routine release of slow-degrading agrochemicals in the environment has resulted in their gradual accumulation posing a major threat both to the terrestrial...     

Performance estimation of 100 GB/s hybrid SACOCDMA-FSO-MDM system under atmospheric turbulences

Optical and Quantum Electronics - A D-shape elliptical stoma photonic crystal fiber (PCF) based on surface plasmon resonance is proposed and investigated with finite element method. The gold film...     

Novel chemiluminescent detection of chemical warfare simulant

A glow assay technology for the detection of a chemical warfare simulant is presented, which is based on modulating the peroxyoxalate chemiluminescence pathway by way of utilising an oximate super nucleophile that gives an "off-on" glow response.     

A review of chemical gradient systems for cell analysis

Microfluidic spatial and temporal gradient generators have played an important role in many biological assays such as in the analysis of wound healing, inflammation, and cancer metastasis. Chemical gradient systems can also be applied to other fields such as drug design, chemical synthesis, chemotaxis, etc. Microfluidic systems are particularly amenable to gradient formation, as the length scales used in chips enable fluid processes that cannot be conducted in bulk scale. In this review we discuss new microfluidic devices for gradient generation and applications of those systems in cell analysis.     

A colorimetric chemodosimeter for Pd(II): a method for detecting residual palladium in cross-coupling reactions

A colorimetric chemodosimeter (SQ1) for the detection of trace palladium salts in cross-coupling reactions mediated by palladium is described. Decolorization of SQ1 is affected by nucleophilic attack of ethanethiol in basic DMSO solutions. Thiol addition is determined to have an equilibrium constant (K_eq) of 2.9×10⁶ M⁻¹, with a large entropic and modest enthalpic driving force. This unusual result is attributed to solvent effects arising from a strong coordinative interaction between DMSO and the parent squaraine. Palladium detection is achieved through thiol scavenging from the SQ1-ethanethiol complex leading to a color ‘turn-on’ of the parent squaraine. It was found that untreated samples obtained directly from Suzuki couplings showed no response to the assay. However, treatment of the samples with aqueous nitric acid generates a uniform Pd(NO₃)₂ species, which gives an appropriate response. ‘Naked-eye’ detection of Pd(NO₃)₂ was estimated to be as low as 0.5 ppm in solution and instrument-based detection was tested as low as 100 ppb. The average error over the working range of the assay was determined to be 7%.     

Regioselective hydrolysis of myo-inositol 1,3,5-orthobenzoate via a 1,2-bridged 2'-phenyl-1',3'-dioxolan-2'-ylium ion provides a rapid route to the anticancer agent Ins(1,3,4,5,6)P5

Acid hydrolysis of myo-inositol 1,3,5-orthobenzoate leads regioselectively to 2-O-benzoyl-myo-inositol via a 1,2-bridged 2'-phenyl-1',3'-dioxolan-2'-ylium ion observed by 1H and 13C NMR spectroscopy, providing the precursor for a highly efficient route to the anticancer agent myo-inositol 1,3,4,5,6-pentakisphosphate.