Density functional calculations of electronic g-tensors for semiquinone radical anions. The role of hydrogen bonding and substituent effects

A recently developed density functional approach has been used to carry out a systematic computational study of electronic g-tensors for a series of 1,4-semiquinone radical anions. Good agreement with high-field EPR data in frozen 2-propanol is achieved only after taking into account the significant reduction of g-tensor anisotropy caused by hydrogen bonding to solvent molecules. The comparison of various model systems for the first solvation shell suggests two hydrogen bonds from 2-propanol molecules to each of the carbonyl groups of the radical anions, and one additional hydrogen bond to each of the methoxy groups in ubiquinone systems. 2-Propanol makes stronger hydrogen bonds than water and thus influences g-tensor anisotropy more strongly. Substituent effects at the semiquinone are reproduced quantitatively by the calculations. The g-tensor anisotropy is influenced significantly by the conformations of methyl and methoxy substituents, with opposite contributions. Analyses and interpretations of the interrelations between structure, bonding, and spectroscopic data are provided. The relevance of the computational results for the EPR spectroscopy of semiquinone radical anions in photosynthetic reaction centers is discussed.     

Determination of the quantum yields of the photochromism of spiropyrans with two chromene fragments

Conclusions The quantum yields of the photochromism of spiropyrans with two chromene functions have been determined. The combining of nitrochromene and benzochromene fragments in a single molecule results in an increase in the quantum yields of the photochromism of the benzochromene part of the molecules.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 773–776, April, 1988.We thank P. P. Levin for carrying out the measurements by the method of laser photolysis and A. S. Kholmanskii for determining the extinction coefficients of a number of compounds.     

Effect of mechanical activation on the thermal stability of polytetrafluoroethylene powder

It was found that processing in a planetary activator leading to amorphization of the structure of polytetrafluoroethylene powder was not accompanied by a noticeable decrease in its thermal stability. It was established that the temperature at the onset of melting drops slightly, the melting rate increases, and the enthalpy of the endoeffect declines noticeably heating.     

Zur Stabilitätsfrage Rotierender Elastischer Stäbe

Ohne ZusammenfassungDie nachstehende Arbeit bildet eine namentlich nach der variationstheoretischen Seite hin orientierte Weiterentwickelung einer von der philosophischen Fakultät der Friedrich-Wilhelm-Universität Berlin genehmigten Doktor-Dissertation (Referenten: Prof. Dr. R. v. Mises, Geheimrat Prof. Dr. M. Planck.)     

5d–4f luminescence of Ce3+, Gd3+ and Lu3+ in LiCaAlF6

The emission and excitation spectra as well as decay kinetics of luminescence due to 5d–4f transitions in Ce³⁺, Gd³⁺ and Lu³⁺ ions doped into LiCaAlF₆ crystals have been analyzed with high spectral and time resolution using synchrotron radiation for excitation. The rich fine structure originating from electronic origins of transitions and their phonon replica has been well resolved and identified. Experimental data are compared with the spectra simulated in the framework of the semiphenomenological models of the crystal field and the crystal lattice dynamics.     

Investigation of the influence of high-risk human papillomavirus on the biochemical composition of cervical cancer cells using vibrational spectroscopy

The main aetiology of cervical cancer is infection with high-risk human papillomavirus (HPV). Cervical cancer is almost 100% curable if detected in the early stages. Thus, information about the presence and levels of HPV in patient samples has high clinical value. As current screening methods, such as the Pap smear test, are highly subjective and in many cases show low sensitivity and specificity, new supportive techniques are desirable to improve the quality of cervical cancer screening. In this study, vibrational spectroscopic techniques (Raman and Fourier Transform Infra Red absorption) have been applied to the investigation of four cervical cancer cell lines: HPV negative C33A, HPV-18 positive HeLa with 20-50 integrated HPV copies per cell, HPV-16 positive SiHa with 1-2 integrated HPV strands per cell and HPV-16 positive CaSki containing 60-600 integrated HPV copies per cell. Results show that vibrational spectroscopic techniques can discriminate between the cell lines and elucidate cellular differences originating from proteins, nucleic acids and lipids. Similarities between C33A and SiHa cells were exhibited in the Raman and infrared spectra and were confirmed by Principal Component Analysis (PCA). Analysis of the biochemical composition of the investigated cells, with the aid of PCA, showed a clear discrimination between the C33A-SiHa group and HeLa and CaSki cell lines indicating the potential of vibrational spectroscopic techniques as a support to current methods for cervical cancer screening.     

On continuous relaxation spectrum. Method of calculation

A method of continuous relaxation spectrum calculations based on the Mellin integral transform has been proposed. It was demonstrated that the equivalent results were obtained regardless an experimental viscoelastic function used a base for calculations. It proves the correctness of the proposed method. The obtained relaxation spectrum provides right predictions in calculation of different viscoelastic functions for various polymeric materials regardless their relaxation state.     

The role of interdroplet interaction in the physics of highly concentrated emulsions

The osmotic pressure and shear modulus of highly concentrated emulsions were modelled by considering both interfacial energy and interdroplet interaction. This was performed for two- and three-dimensional cases and by optimization and approximation methods of predicting film thickness. The results show that even a small source of interaction can result in non-superimposition of scaled osmotic pressure and shear modulus by Laplace pressure for different droplet sizes, and also significant deviation from the models which consider interfacial interaction as the sole source of energy. The model was used to explain the reciprocal squared diameter dependency of elastic modulus: an interaction similar to the van der Waals type can be responsible for this observation. The model can also be used to analyze the interdroplet interactions in highly concentrated emulsions.     

Approximation of entropy on hyperbolic sets for one-dimensional maps and their multidimensional perturbations

We consider piecewise monotone (not necessarily, strictly) piecewise C ² maps on the interval with positive topological entropy. For such a map f we prove that its topological entropy h _top(f) can be approximated (with any required accuracy) by restriction on a compact strictly f-invariant hyperbolic set disjoint from some neighborhood of prescribed set consisting of periodic attractors, nonhyperbolic intervals and endpoints of monotonicity intervals. By using this result we are able to generalize main theorem from [1] on chaotic behavior of multidimensional perturbations of solutions for difference equations which depend on two variables at nonperturbed value of parameter.