Study of local atomic and electronic structure of titanium-containing forsterite based on analysis of X-ray absorption spectra

The local atomic structure of titanium-containing forsterite is investigated based on analysis of X-ray absorption near-edge structure (XANES) spectra. The Ti K-XANES spectra of the mineral under study are calculated for several possible structural models. Theoretical analysis of the X-ray absorption spectra is performed based on the full-potential finite-difference method. The local geometry of the titanium environment is determined by comparing the experimental Ti K-XANES spectrum with the theoretical spectra calculated for different structural models. The structural model where titanium atoms substitute for silicon ones is found to be most likely for titanium-containing forsterite. The calculated partial densities of electron states of titanium near the bottom of the conduction band of titanium-containing forsterite are analyzed.     

Evidence for a one-electron mechanistic regime in dirhodium-catalyzed intermolecular C-H amination

Swift and energy efficient conversion of chemical feedstocks to pharmaceuticals and agrochemicals requires the development of new methods to add nitrogen functionality to unfunctionalized organic substrates. Dirhodium-catalyzed insertion of nitrene species into C-H bonds is a promising new method, the main drawback of which is the currently limited understanding of the catalytic mechanism. Herein, cyclic voltammetry and controlled potential electrolysis measurements have enabled us to solve many of the mechanistic mysteries of intermolecular C-H amination catalyzed by [Rh(2)(esp)(2)] (esp=α,α,α',α'-tetramethyl-1,3-benzenedipropanoate). The primary result is that, in addition to a simple nitrene-transfer mechanism that dominates the early stages of the reaction, another mechanism is available that relies on sequential proton-coupled electron transfer steps. Whereas the nitrene-transfer mechanism requires the use of expensive, atom-inefficient oxidants, we show that simple one-electron oxidants such as Ce(4+) may be used to achieve catalytic C-H amination via the one-electron mechanistic regime.     

Interaction between phases in the liquid–gas system

This work analyzes the equilibrium between a liquid and a gas over this liquid separated by an interface. Various gas forms exist inside the liquid: dissolved gas molecules attached to solvent molecules, free gas molecules, and gaseous bubbles. Thermodynamic equilibrium is maintained between two phases; the first phase is the liquid containing dissolved and free molecules, and the second phase is the gas over the liquid and bubbles inside it. Kinetics of gas transition between the internal and external gas proceeds through bubbles and includes the processes of bubbles floating up and bubble growth as a result of association due to the Smoluchowski mechanism. Evolution of a gas in the liquid is considered using the example of oxygen in water, and numerical parameters of this system are given. In the regime under consideration for an oxygen–water system, transport of oxygen into the surrounding air proceeds through micron-size bubbles with lifetimes of hours. This regime is realized if the total number of oxygen molecules in water is small compared with the numbers of solvated and free molecules in the liquid.