Optical rotation calculated with time-dependent density functional theory: the OR45 benchmark

Time-dependent density functional theory (TDDFT) computations are performed for 42 organic molecules and three transition metal complexes, with experimental molar optical rotations ranging from 2 to 2 × 10(4) deg cm(2) dmol(-1). The performances of the global hybrid functionals B3LYP, PBE0, and BHLYP, and of the range-separated functionals CAM-B3LYP and LC-PBE0 (the latter being fully long-range corrected), are investigated. The performance of different basis sets is studied. When compared to liquid-phase experimental data, the range-separated functionals do, on average, not perform better than B3LYP and PBE0. Median relative deviations between calculations and experiment range from 25 to 29%. A basis set recently proposed for optical rotation calculations (LPol-ds) on average does not give improved results compared to aug-cc-pVDZ in TDDFT calculations with B3LYP. Individual cases are discussed in some detail, among them norbornenone for which the LC-PBE0 functional produced an optical rotation that is close to available data from coupled-cluster calculations, but significantly smaller in magnitude than the liquid-phase experimental value. Range-separated functionals and BHLYP perform well for helicenes and helicene derivatives. Metal complexes pose a challenge to first-principles calculations of optical rotation.     

High-sensitivity detection using isotachophoresis with variable cross-section geometry

We present a theoretical and experimental study on increasing the sensitivity of ITP assays by varying channel cross-section. We present a simple, unsteady, diffusion-free model for plateau mode ITP in channels with axially varying cross-section. Our model takes into account detailed chemical equilibrium calculations and handles arbitrary variations in channel cross-section. We have validated our model with numerical simulations of a more comprehensive model of ITP. We show that using strongly convergent channels can lead to a large increase in sensitivity and simultaneous reduction in assay time, compared to uniform cross-section channels. We have validated our theoretical predictions with detailed experiments by varying channel geometry and analyte concentrations. We show the effectiveness of using strongly convergent channels by demonstrating indirect fluorescence detection with a sensitivity of 100 nM. We also present simple analytical relations for dependence of zone length and assay time on geometric parameters of strongly convergent channels. Our theoretical analysis and experimental validations provide useful guidelines on optimizing chip geometry for maximum sensitivity under constraints of required assay time, chip area and power supply.     

Dual optical sensor for oxygen and temperature based on the combination of time domain and frequency domain techniques

In measuring specific conditions in the real world, there are many situations where both the oxygen concentration and the temperature have to be determined simultaneously. Here we describe a dual optical sensor for oxygen and temperature that can be adapted for different applications. The measurement principle of this sensor is based on the luminescence decay times of the oxygen-sensitive ruthenium complex tris-4,7-diphenyl-1,10-phenanthroline ruthenium(III) [Rudpp] and the temperature-sensitive europium complex tris(dibenzoylmethane) mono(5-amino-1,10-phenanthroline)europium(III) [Eudatp]. The excitation and emission spectra of the two luminophores overlap significantly and cannot be discriminated in the conventional way using band pass filters or other optical components. However, by applying both the frequency and time domain techniques, we can separate the signals from the individual decay time of the complexes. The europium complex is entrapped in a poly(methyl methacrylate) (PMMA) layer and the ruthenium complex is physically adsorbed on silica gel and incorporated in a silicone layer. The two layers are attached to each other by a double sided silicone based tape. The europium sensing film was found to be temperature-sensitive between 10 and 70 °C and the ruthenium oxygen-sensitive layer can reliably measure between 0 and 21% oxygen.     

Validated stability indicating LC method for carprofen: characterization of degradation products by MS

A simple, sensitive, and selective stability indicating high performance liquid chromatographic method has been developed and validated for quantitative analysis of carprofen (CPF) in presence of its degradation products. All degradation products in acid hydrolysis and photolysis were separated, identified by mass spectroscopic method and probable structures were elucidated. The forced degradation studies were performed on a bulk sample of CPF by using various methods like 0.1 M hydrochloric acid, 0.1 M sodium hydroxide, 0.33% hydrogen peroxide (H(2)O), heating at 60°C and exposure to UV light at 254 nm. A 5 μm particle octa desyl silane (ODS) column (150 mm × 4.6 mm) was used with acetonitrile-ammonium acetate (100 mM, pH-6.7) 40:60 (v/v) as a mobile phase at flow rate of 1.2 mL/min. Column oven temperature was maintained at 30°C and quantitation was achieved at 239 nm on the basis of peak area. The linear range and correlation coefficient (r(2)) was found 0.5-60 μg/mL and 0.9999 respectively. The limit of detection (LOD) and limit of quantitation (LOQ) were obtained 0.066 μg/mL and 0.20 μg/mL respectively . The proposed method was found to be suitable and accurate for quantitative analysis, stability study and characterisation of degradation product of CPF.     

Efficient adiabatic wavelength conversion in Gires-Tournois resonators

We compare theoretically the performance capabilities of Fabry-Perot and Gires-Tournois resonators when used for adiabatic wavelength conversion. It is shown that the Gires-Tournois device will exhibit superior performance and is able to convert the wavelength of optical pulses with >74% efficiency while nearly preserving their temporal duration.     

Reduction of Escherichia coli O157:H7 on beef surfaces using low-voltage direct electric current and the impact on sensory properties

Low-voltage direct current was applied to beef, inoculated with Escherichia coli O157:H7 on the surface covered with a thin film of 0.15 M NaCl solution. Experiments were conducted with 15, 30, and 45 mA/cm² currents; 1, 10 and 100 kHz frequencies; 30, 50 and 70% duty cycles, and 2, 8 and 16 min treatment durations. Increase in current intensity, frequency, duty cycle, and treatment duration increased the % reduction of E. coli. A maximum reduction of 98.9% was achieved. Sensory color analysis showed significant differences between treated and untreated beef. The maximum temperature rise of NaCl solution was 31.9 °C.     

Fluorimetric Study on the Interaction between Norfloxacin and Proflavine Hemisulphate

The interaction between Norfloxacin (NF) and Proflavine hemisulphate (PF) was investigated by spectroscopic tools like UV–VIS absorption and Fluorescence spectroscopy. It was proved that fluorescence quenching of NF by PF is due to the formation of NF-PF complex which was supported by UV–VIS absorption study. The study of thermodynamic parameters suggested that the key interacting forces are hydrogen bond and van der Waal’s interactions and the binding interaction was spontaneous. The distance r between NF and PF was obtained according to the Förster’s theory of non-radiative energy transfer. The fluorescence quenching mechanism was applied to estimate PF directly from pharmaceutical samples.     

Ultrasonic studies on lyotropic liquid crystal CTAB in heavy water

Ultrasonic absorption and velocity measurements have been made on cetyl trimethyl ammonium bromide (CTAB) solution in heavy water. Velocity measurements have been made of CTAB concentration at 25°C and a frequency of 2.0?MHz. Absorption measurements have been made in the frequency range of 5.0–55.0?MHz for various CTAB concentration. The results of these measurements indicate micelle formation. Absorption measurements show the existence of a single relaxation frequency. A detailed analysis of the data has been presented. Theoretical and experimental relaxation frequencies are approximately the same.     

50 MeV Li3+ ion irradiation effect on structural, electrical, and dielectric properties of PVA-based nanocomposite polymer electrolytes

Nanocomposite polymer electrolyte thin films of polyvinyl alcohol (PVA)-orthophosphoric acid (H₃PO₄)-Al₂O₃ have been prepared by solution cast technique. Films are irradiated with 50 MeV Li³⁺ ions having four different fluences viz. 5?×?10¹⁰, 1?×?10¹¹, 5?×?10¹¹, and 1?×?10¹² ions/cm². The effect of irradiation on polymeric samples has been studied and characterized. X-ray diffraction spectra reveal that percent degree of crystallinity of samples decrease with ion fluences. Glass transition and melting temperatures have been also decreased as observed in differential scanning calorimetry. A possible complexation/interaction has been shown by Fourier transform infrared spectroscopy. Temperature-dependent ionic conductivity shows an Arrhenius behavior before and after glass transition temperature. It is observed that ionic conductivity increases with ion fluences and after a critical fluence, it starts to decrease. Maximum ionic conductivity of ～2.3?×?10^?5 S/cm owing to minimum activation energy of ～0.012 eV has been observed for irradiated electrolyte sample at fluence of 5?×?10¹¹ ions/cm². The dielectric constant and dielectric loss also increase with ion fluences while they decrease with frequency. Transference number of ions shows that the samples are of purely ionic in nature before and after ion irradiation.     

Tunable Bidirectional Electroosmotic Flow for Diffusion‐Based Separations

We present a new concept for on‐chip separation that leverages bidirectional flow, to tune the dispersion regime of molecules and particles. The system can be configured so that low diffusivity species experience a ballistic transport regime and are advected through the chamber, whereas high diffusivity species experience a diffusion dominated regime with zero average velocity and are retained in the chamber. We detail the means of achieving bidirectional electroosmotic flow using an array of alternating current (AC) field‐effect electrodes, experimentally demonstrate the separation of particles and antibodies from dyes, and present a theoretical analysis of the system, providing engineering guidelines for its design and operation.