Mikrochemie

Ohne Zusammenfassung     

Model for mercury photosensitized hydrogen abstraction from alkanes

Mercury photosensitized hydrogen abstraction from alkanes is studied theoretically. A simple model based on the energy transfer to an electronic state of the alkane is shown to yield satisfactory agreement with the available experimental data.     

The effect of LH wave on the peripheral plasma of TM-1-MH tokamak

The work is devoted to the study of the LH wave effect on the peripheral plasma of the TM-1-MH tokamak. The observed enhancement of the ion saturated current in the limiter shadow is interpreted as heating of the peripheral ions by absorption of decay waves generated in this region due to the nonlinear wave-plasma interaction.     

The mechanism of enzymatic and biomimetic oxidations of aromatic sulfides and sulfoxides

Biomimetic and enzymatic oxidations of benzyl sulfides and sulfoxides lead to products (sulfoxides or sulfones) different from those obtained with bona fide electron transfer oxidations (products of C---H and/or C---S bond cleavage), which suggests the operation of an oxygen transfer mechanism.     

RhIAr/AuIAr′ Transmetalation: A Case of Group Exchange Pivoting on the Formation of M−M′ Bonds through Oxidative Insertion

By combining kinetic experiments, theoretical calculations, and microkinetic modeling, we show that Pf/Rf (C₆F₅/C₆Cl₂F₃) exchange between [AuPf(AsPh₃)] and trans‐[RhRf(CO)(AsPh₃)₂] does not occur by typical concerted Pf/Rf transmetalation via electron‐deficient double bridges. Instead, it involves asymmetric oxidative insertion of the Rh^I complex into the (Ph₃As)Au?Pf bond to produce a [(Ph₃As)Au?RhPfRf(CO)(AsPh₃)₂] intermediate, followed by isomerization and reductive elimination of [AuRf(AsPh₃)]. Interesting differences were found between the LAu?Ar asymmetric oxidative insertion and the classical oxidative addition process of H₂ to Vaska complexes.     

Single-shot extreme ultraviolet laser imaging of nanostructures with wavelength resolution

We have demonstrated near-wavelength resolution microscopy in the extreme ultraviolet. Images of 50 nm diameter nanotubes were obtained with a single ~1 ns duration pulse from a desktop-size 46.9 nm laser. We measured the modulation transfer function of the microscope for three different numerical aperture zone plate objectives, demonstrating that 54 nm half-period structures can be resolved. The combination of near-wavelength spatial resolution and high temporal resolution opens myriad opportunities in imaging, such as the ability to directly investigate dynamics of nanoscale structures.     

A higher-order parametric nonlinear reduced-order model for imperfect structures using Neumann expansion

Nonlinear Dynamics - We present an enhanced version of the parametric nonlinear reduced-order model for shape imperfections in structural dynamics we studied in a previous work. In this model, the...     

Structure and properties of licochalcone A-human serum albumin complexes in solution: a spectroscopic, photophysical and computational approach to understand drug-protein interaction

In the present contribution we address the study of the interaction of a flavonoid-derivative licochalcone A (LA) with human serum albumin (HSA). The application of circular dichroism, UV-Vis absorption, fluorescence and laser flash photolysis combined with molecular mechanics, molecular dynamics and quantum mechanical calculations of rotational strength afforded a clear picture of the modes of association of the LA neutral molecule to HSA, evidencing specific interactions with protein amino acids and their photophysical consequences. The drug is primarily associated in subdomain IIA where a strong interaction with Trp214 is established. At least two different positions of LA with respect to tryptophan are possible, one with the phenolic ring of the drug facing the aromatic ring of Trp214 and the other with the methoxyphenolic ring of LA in proximity to Trp214. In both cases LA is at ca. 4 angstroms from Trp214. This vicinity does not affect much the S1 singlet state deactivation of the bound drug, which exhibits a slightly higher fluorescence quantum yield and fluorescence lifetime on the order of that of the free molecule. The LA triplet lifetime appears to be somewhat shortened in this site. The secondary binding site is in subdomain IIIA. Here, the carbonyl group of LA experiences a strong H-bond with the OH-phenolic substituent of Tyr411. This interaction reduces substantially the LA molecular degrees of freedom, thereby determining a decrease of both radiative and nonradiative rate constants for decay of the singlet. The overall rigidity of the structure causes a lengthening of the triplet lifetime.