2-amino-4-nitroaniline, a known compound with unexpected properties

2-amino-4-nitroaniline crystallizes in a noncentrosymmetric space group, which gives it significant potential for second-order nonlinear optical properties (NLO) in the bulk. Crystallographic and linear-polarized IR-spectrocopic data in the solid state unambiguously confirm a quinoide-like structure in the ground state in contrast to UV and theoretical data, which indicate an aromatic one for the excited state. UV-vis spectral elucidations in solutions with different polarities indicate a significant charge-transfer band with shifts of up to 100 nm, corresponding to a large value for the molecular first hyperpolarizability. Calculations of the UV- and IR-spectroscopic properties confirm the stabilization of the quinoide-like structure in the ground state, as well as the theoretically predicted NLO properties at the molecular level and provide a value of beta(tot), which is some 3.6 times higher than the analogous parameter for p-nitroaniline, a classical compound with experimentally confirmed NLO properties.     

Spectroscopic and structural elucidation of L-tyrosine-containing dipeptides valyl-tyrosine and tyrosyl-alanine: solid-state IR-LD spectroscopy, quantum chemical calculations and vibrational analysis

L-Tyrosine-containing dipeptides valyl-tyrosine (H-Val-Tyr-OH) and tyrosyl-alanine (H-Tyr-Ala-OH) are characterized structurally by means of quantum chemical ab initio calculations and solid-state linear-dichroic infrared (IR-LD) spectroscopy. The IR-characteristic bands are assigned by application of reducing-difference procedure for polarized IR-spectra interpretation. Infrared data obtained are supported as well by the made vibrational analysis. The structures of both peptides are predicted on the basis of conformational analysis and structural information, obtained by the shown IR-spectroscopic tool.     

Tryptammonium (2S,3S)-hydrogentartrate monohydrate [Struct Chem (2008) 19:147–154]: redetermination at 110 K and re-refinement against room temperature data

The crystal structure of the title compound was incorrectly reported as a methanol solvate [Koleva et al. in Struct Chem 19:147–154, 2008] on the basis of room temperature X-ray diffraction data. We have now established the presence of a disordered water molecule rather than the methanol molecule using a low temperature data set collected at 110 K.     

Vibrational spectra and structure of benzil and its 18O- and d10-labelled derivatives: a quantum chemical and experimental study

Geometry and vibrational spectroscopic data of benzil-d0 benzil-d10 and benzil-18O calculated at various levels of theory (RHF/6-31G*, B3LYP/6-31G*, BLYP/6-31G*) are reported. The theoretical results are discussed mainly in terms of the comparisons with infrared (4000-100 cm(-1)) and Raman (4000-50 cm(-1)) spectral data. The calculated isotopic frequency shifts, induced by the 18O- and d10-labeling, are in a good agreement with the measured values. A complete vibrational assignment was made with the help of ab initio force field calculations. The data thus obtained were used for reassigning some vibrational frequencies. The results of the optimized molecular structure obtained on the basis of RHF and the DFT calculations are presented and compared with the experimental X-ray diffraction for the benzil-d0 single crystal. It turns out that the best structural parameters are predicted by the B3LYP/6-31G* method.     

A novel approach for enhancing metal ion separation using acoustic nebulisation

A novel technique for anionic surfactant assisted separation and preconcentration of metal cations was developed using ultrasound induced nebulization at MHz frequency. The ions of copper, zinc, cadmium, and calcium were used as model analytes. Analysis of the aerosol using flame atomic absorption spectrometry showed enrichment factors for the metal ions studied between 5 and 8, when dilute solutions containing sodium dodecylsulfate and the metal ions were nebulized. The mechanism of metal ion enrichment was explained based on surfactant adsorption and the droplet model for aerosol droplets. It was demonstrated that further increase in the enrichment factor could be achieved by increasing the ultrasound frequency, thus producing smaller droplets.     

The radioactivity and the chemical nature of additives as factors determining the photocatalytic activity of TiO2

Microcomposites consisting of TiO₂ and ThF₄ or UO₃ (0.5?C2% of the TiO₂ mass) are produced by sol-gel synthesis of TiO₂ in presence of the respective additives. X-ray diffraction study reveals small effect of the latter on TiO₂ phase composition and cell parameters and significant influence on the crystallite size and UV/Vis reflectance spectra. The photocatalytic tests in presence of TiO₂-ThF₄ microcomposites under UV and solar irradiation show a non-monotonic increase of the Malachite Green degradation rate constant with the increase of ThF₄-content. No changes in the photocatalytic activity are observed in the presence of UO₃ but the latter composites exhibit activity in darkness. The results are compared with previously reported data on the performance of TiO₂-ThO₂ photocatalyst with the same radioactivity and suggest that both radioactivity and the chemical nature of the dopants are responsible for the photocatalytic performance of TiO₂-based composites containing radioactive substances.      

Resolution enhancement for infrared rotatory dispersion spectra of induced cholesteric phases

For a solution of optically active compounds in liquid crystals, the infrared rotatory dispersion can be measured by Fourier transform spectroscopy. The results of a resolution enhancement by Fourier deconvolution and second derivative approach for the spectral features of the so-called A-Cotton effects are discussed. The experimental spectrum shown was recorded from a solution of cholesteryl oleyl carbonate in liquid crystal MBBA.