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An immunochromatographic assay (ICA) based on surface-enhanced Raman scattering (SERS) for ultrasensitive and quantitative detection of florfenicol (FF) in food samples was developed. Au nanocubers (AuNCs) with long wavelength absorption were synthesised, characterised and used as the substrate in SERS-ICA. Immunoprobe was prepared by linking Raman reporter and the antibody against FF on AuNCs. The SERS-ICA was completed in 15 min. By measuring the Raman intensities on T lines, quantitative detection of FF was achieved. The IC50 and limit of detection (LOD) of the assay for FF were 0.027 ng mL−1 and 0.12 pg mL−1, respectively. The cross-reactivity (CR) of the assay with thiamphenicol, chloramphenicol and other four drugs were examined. The recoveries of FF in spiked samples were 88.5% ∼ 102.4% with RSD of 2.3% ∼ 7.4%. It was proven that SERS-ICA was able to rapidly detect FF in food samples with high sensitivity, accuracy and precision.

An immunochromatographic assay (ICA) based on surface-enhanced Raman scattering (SERS) for ultrasensitive and quantitative detection of florfenicol (FF) in food samples was developed. Au nanocubers (AuNCs) with long wavelength absorption were synthesised, characterised and used as the substrate in SERS-ICA. Immunoprobe was prepared by linking Raman reporter and the antibody against FF on AuNCs. The SERS-ICA was completed in 15 min. By measuring the Raman intensities on T lines, quantitative detection of FF was achieved. The IC50 and limit of detection (LOD) of the assay for FF were 0.027 ng mL−1 and 0.12 pg mL−1, respectively. The cross-reactivity (CR) of the assay with thiamphenicol, chloramphenicol and other four drugs were examined. The recoveries of FF in spiked samples were 88.5% ∼ 102.4% with RSD of 2.3% ∼ 7.4%. It was proven that SERS-ICA was able to rapidly detect FF in food samples with high sensitivity, accuracy and precision. [ABSTRACT FROM AUTHOR]

Raman intensities in molecular spectra are usually computed within double harmonic approximation. This procedure relies on treating a vibrating molecule as a collection of harmonic oscillators and on the assumption that polarisability tensor invariants display linear variations around the molecular equilibrium geometry. This methodology, originally formulated by Placzek, constitutes the theoretical foundation for computing Raman intensities in standard quantum chemistry packages. However, the two assumptions underlying double harmonic approximation have not been sufficiently tested. In this work, we employed exact anharmonic ro-vibrational wave functions and distance-dependent polarisability invariants together with their harmonic approximants to investigate the discrepancies in Raman intensities of the fundamental transitions in 12 diatomic molecules, caused by double harmonic approximation. We found that: (i) the errors in total Raman intensities were between −8.2% and +9.5%, (ii) the largest discrepancy was observed for F2, where the polarisability invariants could not be adequately modelled by their linear approximants, and (iii) quantum chemical methods fail to predict reliable polarisability invariants at non-equilibrium molecular geometries; the associated errors in Raman intensities are huge and completely overshadow the shortcomings of double harmonic approximation. We communicate here an urgent need for developing accurate methods capable of computing reliable polarisabilities also at distorted geometries. [ABSTRACT FROM AUTHOR]

The structural and dielectric properties of lead zirconium titanate (PZT) (52:48) ceramic prepared from different synthesis route are discussed in this paper. The PZT green powders were synthesised via three different routes: ceramic, combustion and co-precipitation. The x-ray diffraction (XRD) patterns confirm the pure tetragonal phase formation of PZT for all the different routes adopted by us. Scanning electron microscopy (SEM) micrographs show the surface morphology vary and also grain sizes of PZT prepared from three different routes change from nano to micron size. The Raman intensities were obtained with slight variation in peak intensities and also with slight variations in wave-numbers for all the three PZT samples prepared using different routes. These slightly varied wave-numbers for all the three present samples are however in close proximity with the Raman vibrational modes pertinent for PZT as seen in the literature. The dielectric constant variation with temperature measured for three different powders also shows a considerable change in transition temperature. The structural and dielectric variations are co-related to explain the variations in transition temperature.

Raman spectroscopy is a standard and powerful investigation technique for minerals, and garnet is one of the most observed and visible minerals, undoubtfully important both as a witness of our planet's evolution and as a main component in many high-tech applications. This paper presents the Raman spectrum of grossular, the calcium-aluminium end-member of garnets (Ca 3Al 2Si 3 O12), as computed by using an ab initio quantum-mechanical approach, an all-electron Gaussian-type basis set and the hybrid B3LYP functional. The wavenumbers of the 25 Raman active modes are in excellent agreement with the available experimental measurements, with the mean absolute difference being between 5 and 8 cm − 1. The apparent disagreement between a few experimental vs calculated data can be easily justified through the analysis of the corresponding calculated peak intensities, which is very low in all of these cases. The intensities of the Raman active modes of grossular were calculated here for the first time, thanks to a recent implementation by some of the present authors that allow for accurate predictions of the Raman spectra of minerals. To the authors' knowledge, there are no tabulated data sets for Raman intensities of grossular, although qualitative information can be extracted from the published spectra. This study can then be considered as an accurate reference data set for grossular, other than a clear evidence that quantum-mechanical simulation is an actual tool to predict spectroscopic properties of minerals. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The accurate harmonic vibration frequencies together with the infrared (IR) and Raman intensities of the most stable conformers of AlO and AlO molecules have been calculated by the density functional theory (DFT) method with B3LYP exchange-correlation potential and using a set of the augmented correlated consistent basis sets up to quintuple order. The anharmonic vibration frequencies of the non-linear AlO molecule have also been calculated. The obtained equilibrium geometrical parameters, harmonic and anharmonic vibration frequencies along with the IR and Raman intensities good converge to their limits with increasing the size of the used basis set. A comparison of the calculated harmonic and anharmonic vibrational frequencies with the available experimental ones points out that the small differences between the calculated harmonic and experimental frequencies can be further substantially reduced when calculations of the anharmonic vibrational frequencies will be available for all types of molecular geometries. [ABSTRACT FROM AUTHOR]

Abstract: Raman intensities and frequencies of 2,4,6-trinitrotoluene have been calculated using B3LYP/6-31+G**, 6-311+G** and Sadlej’s medium-sized polarized basis sets (Sadlej pVTZ). Transitions in the region were assigned. These assignments were facilitated by performing a normal mode analysis using a combination of localized and delocalized coordinates. Comparisons of the uniform scaled frequencies with the experimentally available results showed an average absolute deviation of . The relative Raman intensities calculated using 6-311+G** and Sadlej pVTZ polarized basis sets were found to be in very good agreement with the experimentally measured Raman intensities. One of the major advantages of using these basis sets is the removal of degeneracies found for the C–H stretching, C–H in-plane bending, ring breathing and methyl deformation modes, when 6-31+G** and 6-311+G** basis are used. The removal of these degeneracies clearly shows an improvement in the agreement between calculated and experimental frequencies. The geometry of 2,4,6-trinitrotoluene was calculated at B3LYP/6-31+G**, 6-311+G**, Sadlej pVTZ and MP2/6-31G* methods. Two lower energy structures A and B were computed and the global minimum structure was found to be the structure A in both methods. [Copyright &y& Elsevier]

Abstract: This study concentrates on the temperature dependence of the Raman intensities for the lattice modes in ammonium halides (NH4Cl and NH4Br) close to phase transitions. We predict their intensities using the results of a shell model for the Raman polarizability within the framework of an Ising pseudospin–phonon coupled model. From our observed Raman intensities of those phonon modes studied here, we extract the values of the critical exponent for the order parameter in these crystalline systems. The exponent values indicate that the Raman intensities show a logarithmic divergence at higher pressures in NH4Cl, whereas they predict a λ-type phase transition at zero pressure in NH4Br. [Copyright &y& Elsevier]

Abstract: The bond polarizabilities of pyrimidine are elucidated from the Raman intensities excited at 632.8nm by an algorithm proposed by Wu et al. [B. Tian, G. Wu, G. Liu, J. Chem. Phys. 87 (1987) 7300]. The contrast between the bond polarizabilities and the bond electronic densities by RHF/6-31G* calculation shows that, in the excited virtual state, the electrons of the C–N bond which is connected to the C–C bond tend to spread to the most spacious C–H bond, its adjacent C–N bond and possibly, the C–C bond in this nonresonant process. [Copyright &y& Elsevier]

Abstract: The Raman intensities of trans-stilbene (tSB) in the lowest singlet excited (S1) state is derived from quantum chemical calculations by the CIS method and compared with the transient Raman spectra observed under resonant and off-resonant conditions. The calculated Raman intensities of tSB in the S1 state are useful to some extent for assigning the observed Raman bands. However, some discrepancies are found between the calculated and observed Raman intensities. The reason for such discrepancies is discussed. [Copyright &y& Elsevier]

Abstract: 4-Thiocarbamoylpyridine is the parent compound of ethionamide. It is an important and efficacious drug in the treatment of multidrug-resistant tuberculosis. The molecular structure, natural atomic charges, vibrational frequencies, infrared and Raman intensities and theoretical vibrational spectra were calculated for 4-thiocarbamoylpyridine monomer and a pair of molecules linked by the intermolecular N–H⋯Npy hydrogen bond. The theoretical studies were performed using the B3LYP density functional method with the 6-311G(d,p) basis set. The FT-infrared and FT-Raman spectra of the title compound in the solid state have been measured. The theoretically predicted Raman spectra show good overall agreement with experiment. The detailed interpretation of the vibrational spectra has been made on the basis of the calculated potential energy distribution (PED). The presented vibrational assignment can be used in the further spectroscopic study of thioamides. [Copyright &y& Elsevier]

Abstract: The molecular structure, vibrational frequencies, infrared intensities and Raman scattering activities of carboplatin were calculated by the modified mPW1PW91 (mPW) density functional model using several basis sets. The results from natural bond orbital (NBO) analysis have provided new insights into platinum–ligand bonding, the hybridization of atoms and the electronic structure of the title molecule. The FT-Raman and FT-infrared spectra have been measured for carboplatin in the solid state. The theoretical Raman spectrum predicted by the mPW method shows very good agreement with experiment. In particular, the frequencies and Raman intensities of the platinum–ligand vibrations are very well predicted at the mPW/LanL2DZ level of theory. The detailed interpretation of the vibrational spectra has been made on the basis of the calculated potential energy distribution, PED. The characteristic ‘marker’ bands of carboplatin are discussed. The reported vibrational assignment can be used for further spectroscopic studies of new anticancer drugs, which are structurally similar to carboplatin. [Copyright &y& Elsevier]

Density functional calculations, using B3LPY/6-31G(d) methods, have been used to investigate the conformations and vibrational (Raman) spectra of three short-chain fatty acid methyl esters (FAMEs) with the formula CnH2nO2 (n=3–5). In all three FAMEs, the lowest energy conformer has a simple ‘all-trans’ structure but there are other conformers, with different torsions about the backbone, which lie reasonably close in energy to the global minimum. One result of this is that the solid samples we studied do not appear to consist entirely of the lowest energy conformer. Indeed, to account for the ‘extra’ bands that were observed in the Raman data but were not predicted for the all-trans conformer, it was necessary to add-in contributions from other conformers before a complete set of vibrational assignments could be made. Provided this was done, the agreement between experimental Raman frequencies and 6-31G(d) values (after scaling) was excellent, RSD=12.6 cm−1. However, the agreement between predicted and observed intensities was much less satisfactory. To confirm the validity of the approach followed by the 6-31G(d) basis set, we used a larger basis set, Sadlej pVTZ, and found that these calculations gave accurate Raman intensities and simulated spectra (summed from two different conformers) that were in quantitative agreement with experiment. In addition, the unscaled Sadlej pVTZ, and the scaled 6-31G(d) calculations gave the same vibrational mode assignments for all bands in the experimental data.This work provides the foundation for calculations on longer-chain FAMEs (which are closer to those found as triglycerides in edible fats and oils) because it shows that scaled 6-31G(d) calculations give equally accurate frequency predictions, and the same vibrational mode assignments, as the much more CPU-expensive Sadlej pVTZ basis set calculations. [Copyright &y& Elsevier]

A time-dependent quantum mechanical (TDQM) method of wavepacket propagation in computing resonance Raman intensities for polyatomic systems, has been developed and demonstrated by applying it to cis-stilbene and trans-azobenzene. In the case of the former, Raman excitation profiles (REPs) for the various vibrational modes have also been computed. It is observed that the calculated absorption spectrum and the REPs compare very well with the experimental results. A comparison of these results with those of the often semiclassical approach reveals that the TDQM method can be used to study polyatomic systems with as much ease as the semiclassical wavepacket method. [ABSTRACT FROM AUTHOR]