Molecular spectroscopy and electro-optical effect of I52 liquid crystal molecules studied under the influence of an external electric field (THz): a theoretical approach.

In the present work, we have calculated the electro-optical effect of the I52 (4-Ethyl-2-fluoro-4'-[2-(4-pentyl-cyclohexyl)-ethyl]-biphenyl) liquid crystal (LC) molecules under the influence of an external electric field in the THz frequency region. The electro-optical calculation has been performed with the help of a theoretical model which is developed for the organic compounds (liquid crystal), and also suitable for the terahertz (THz) device application. The theoretical model gives the electro-optical properties and correlates with experimental evidence. The birefringence, order parameter, refractive index, dipolar strength, and HOMO-LUMO of the I52 molecules have been calculated theoretically. By increasing the electric field on the molecules, the order parameter and birefringence show positive as well as negative values. The I52 LC molecule behaves as an insulator due to having a large bandgap (5.08 eV).

A Systematic Account on Aromatic Hydroxylation by a Cytochrome P450 Model Compound I: A Low-Pressure Mass Spectrometry and Computational Study.

Cytochrome P450 enzymes are heme-containing mono-oxygenases that mainly react through oxygen-atom transfer. Specific features of substrate and oxidant that determine the reaction rate constant for oxygen atom transfer are still poorly understood and therefore, we did a systematic gas-phase study on reactions by iron(IV)-oxo porphyrin cation radical structures with arenes. We present herein the first results obtained by using Fourier transform-ion cyclotron resonance mass spectrometry and provide rate constants and product distributions for the assayed reactions. Product distributions and kinetic isotope effect studies implicate a rate-determining aromatic hydroxylation reaction that correlates with the ionization energy of the substrate and no evidence of aliphatic hydroxylation products is observed. To further understand the details of the reaction mechanism, a computational study on a model complex was performed. These studies confirm the experimental hypothesis of dominant aromatic over aliphatic hydroxylation and show that the lack of an axial ligand affects the aliphatic pathways. Moreover, a two-parabola valence bond model is used to rationalize the rate constant and identify key properties of the oxidant and substrate that drive the reaction. In particular, the work shows that aromatic hydroxylation rates correlate with the ionization energy of the substrate as well as with the electron affinity of the oxidant.

Deformylation Reaction by a Nonheme Manganese(III)-Peroxo Complex via Initial Hydrogen-Atom Abstraction.

Metal-peroxo intermediates are key species in the catalytic cycles of nonheme metalloenzymes, but their chemical properties and reactivity patterns are still poorly understood. The synthesis and characterization of a manganese(III)-peroxo complex with a pentadentate bispidine ligand system and its reactivity with aldehydes was studied. Manganese(III)-peroxo can react through hydrogen-atom abstraction reactions instead of the commonly proposed nucleophilic addition reaction. Evidence of the mechanism comes from experiments which identify a primary kinetic isotope effect of 5.4 for the deformylation reaction. Computational modeling supports the established mechanism and identifies the origin of the reactivity preference of hydrogen-atom abstraction over nucleophilic addition.