Dielectric response and quasielastic light scattering on freely suspended films of the SmC * α phase in an external transverse electric field

A theoretical analysis of dynamic properties of freely suspended films of a SmC^* _α phase in an external electric field is performed within the ‘clock’ model, where the interactions up to nextnearest neighbours are considered. It is shown, that for an N-layer film, N amplitude and N phase fluctuation modes are present. The relaxation rates of the amplitude modes are in the MHz region, whereas the phase modes are typically in the kHz region. Magnitudes of the dielectric response and quasielastic light scattering cross-sections for individual modes are calculated as a function of an electric field applied along the smectic layers.     

Reply to the comment of pieranski and cladis on “the effect of an electric field on the selective reflection bands of liquid crystalline blue phases”

It is shown that in the cubic liquid crystalline blue phase I a given lattice orientation cannot be changed by electric fields up to 10⁴ V cm⁻¹ because of the high stiffness of the BPI structure.     

Probenecid and benzamide: DSC applied to the study of an “impossible” pharmaceutical system

Journal of Thermal Analysis and Calorimetry - The study of the binary system probenecid–benzamide is an excellent example of the power and the limits of thermal analysis applied to the...     

Simple kinetic method for distinguishing between homogeneous and heterogeneous mechanisms of catalysis,illustrated by the example of “ligand-free” Suzuki and Heck reactions of aryl iodides and aryl bromides

Using a simple method based on an analysis of the phase trajectories of competing reactions of several substrates, it has been established that the selectivity of catalytically active species in the Suzuki reaction of aryl bromides depends on the nature of the catalyst precursor. This indicates that there is a considerable contribution from heterogeneous catalysis. At the same time, in the reaction involving aryl iodides, when the catalyst concentration in the solution is much higher, the selectivity of the catalyst is precursor-independent, suggesting that homogeneous catalysis is dominant. In the Heck reaction of both aryl bromides and aryl iodides, pure homogeneous catalysis takes place.     

Exploring the interaction between “site-markers,aspirin and esterase-like activity” ternary systems on the human serum albumin: direct evidence for modulation of catalytic activity of the protein in different inhibition modes

Albumin which is the most abundant drug carrier protein in plasma controls the distribution aspect of drug pharmacokinetics. The aim of this study has been to elucidate the concurrent binding behavior of indomethacin/ibuprofen/heme to HSA under the effect of aspirin-mediated protein acetylation and also to explore the esterase-like catalytic property of the unmodified/modified proteins, as binary or ternary systems, by using various spectroscopic and molecular docking techniques. We found that aspirin-based modification of HSA affects the protein conformation as well as ligand binding at sites I–III. Decrease in pNPA-mediated esterase activity of HSA in different reversible inhibition modes, upon the protein–ligand interactions, was also documented, an issue that may receive considerable attention for computational prodrug design in near future.     

Chemistry, commentary, and community: discussion of “an examination of the vaporization enthalpies and vapor pressures of pyrazine, pyrimidine, pyridazine, and 1,3,5-triazine” by Lipkind and Chickos

Vaporization enthalpies for the isomeric diazines were discussed within the context of recent measurements and estimation techniques. It is suggested that pyridazine shows enigmatic behavior.

Comment on “the effect of reagent rotation on steric requirements of elementary exchange reactions” by H. Kornweitz,A. Persky and R.D. Levine

The conclusion that reagent rotation in O+HCl enhances reactivity at high impact parameter, but suppresses reactivity at low impact parameter has been examined. It is found instead that rotation enhances reactivity as effectively for low as for high impact parameter.     

Response on “Regulations in the field of residue and doping analysis should ensure a well-defined risk of a false positive declaration” by N. M. Faber

Dr. Faber provided support for a valuable methodology for the comparison of mass spectra. However, since many other factors are involved in the evaluation process before declaring a sample “positive”, i.e. reporting an adverse analytical finding, his conclusions on this subject are incorrect. In this paper a number of arguments are listed showing that Dr. Faber did not take all factors under consideration when making his claims. These factors involve parameters directly related to mass spectrometric criteria, but also to other equally important factors including sample preparation specificity, retention time (since in doping control mass spectrometry is used as part of a hyphenated technique), etc. These arguments clearly illustrate that the risks for a false positive declaration can not be calculated according to Dr. Faber’s proposed methodology. Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board and the Publisher.     

Photo-induced reduction of Cr<Superscript>6+</Superscript> by the hybrid systems “Cu<Superscript>II</Superscript> complex with Schiff base and TiO<Subscript>2</Subscript>”: dependence on irradiation wavelength

The synthesis of novel Cu^II complexes with a Schiff base obtained by condensation of salicylaldehyde and an l-aspartic acid ester are described. The physicochemical properties of the complexes were compared with those of related Cu^II complexes obtained earlier. All the complexes studied were characterized by elemental analysis as well as by IR, UV-Vis, and EPR spectroscopies. The activity of the complexes and their hybrid systems (HS) with TiO₂ in visible-light-driven photocatalysis in organic solvents was investigated. After irradiation with visible light, the complexes and corresponding HS reduce Cr⁶⁺ to Cr³⁺ more efficiently than bare TiO₂. To determine the molecular orbital compositions and energies and to explain the electronic spectra and redox properties of the systems studied, density functional calculations of the optimized structures of representative model complexes were performed.