The Structure and Thermal Stability of 1,2-Dimethoxycarbonyl-3,3-dimethylcyclopropene

The X-ray crystal structure of 1,2-dimethoxycarbonyl-3,3-dimethylcyclopropene (1) is reported and the geometry is contrasted to that of cyclopropene (2) and 3,3-dimethylcyclopropene (3). Ab initio and density functional theory calculations were carried out in order to examine the conformational preference of the ester groups (i.e., s-cis vs. s-trans) and to probe the thermal stability of 1 via a model compound, 1-methoxycarbonyl-3-methylcyclopropene. Experimental activation parameters for the unimolecular isomerization were measured and compared to an analogous dibenzoylcyclopropene derivative.     

Highly sensitive detection of ATPase activity in native gels

Native electrophoresis is a powerful tool for the separation of intact protein complexes. By incubating such gels in a suitable reaction solution, specific enzyme activities can be screened comprehensively. The recent standard procedure for determination of ATP hydrolysis activity in blue or clear native gels is based on formation of a lead phosphate precipitate. The resulting white bands are challenging for detection and documentation of low activities. For the analysis of photosynthetic ATP synthases, the method has to be adapted to deregulate the inhibition of latent ATPase functions. Therefore, we introduced an incubation of gels in detergent solution, whereby taurodeoxycholate turned out to be the most efficient activator. In order to detect low ATPase activities, a short additional incubation step subsequent to the formation of lead phosphate is recommended. By adding ammonium sulfide, the white bands are converted into brownish‐black bands of lead sulfide. Our new procedure sustains the linear quantitation range of the original lead phosphate protocol and moreover expands the detection limit.     

Sulfur- and Selenium-Containing Compounds Potentially Exhibiting Al Ion Conductivity

We have created a set of crystalline model structures exhibiting straight lines of Al³⁺ connected to chalcogenides (O²⁻, S²⁻, and Se²⁻) connected to metal cations of varying valence (Sr²⁺, Y³⁺, Zr⁴⁺, Nb⁵⁺, and Mo⁶⁺). They were relaxed with density functional theory computations and analysed by Bader partitioning. As Al³⁺ ions are supposed to strongly interact with their atomic environment, we studied the electron density topology induced by higher-valent cations in the extended chemical neighbourhood of Al. In fact, we found a general decrease of ionic charges and an increasing displacement of the chalcogenides towards higher-valent ions for the heavier chalcogens. Therefore, we comprehensively screened S- and Se-containing compounds for candidates theoretically exhibiting low migration barriers for Al³⁺ ions by using Voronoi–Dirichlet partitioning and bond valence site energy calculations. The basis for this search is the Inorganic Crystal Structure Database. Indeed, we could extract six promising candidates with low Al³⁺ migration barriers. which are even lower than the barriers for any other element inside of these materials. This will encourage efforts towards preparing suitable Al³⁺ conductors.     

Asymmetric Catalysis in Liquid Confinement: Probing the Performance of Novel Chiral Rhodium–Diene Complexes in Microemulsions and Conventional Solvents

The role of liquid confinement on the asymmetric Rh catalysis was studied using the 1,2-addition of phenylboroxine ( 2 ) to N-tosylimine 1 in the presence of [RhCl(C₂H₄)₂]₂ and chiral diene ligands as benchmark reaction. To get access to Rh complexes of different polarity, enantiomerically pure C₂-symmetric p-substituted 3,6-diphenylbicyclo[3.3.0]octadienes 4 and diastereomerically enriched unsymmetric norbornadienes 5 and 6 carrying either the Evans or the SuperQuat auxiliary were synthesized. A microemulsion containing the equal amounts of H₂O/KOH and toluene/reactants was formulated using the hydrophilic sugar surfactant n-octyl β-d -glucopyranoside (C₈G₁) to mediate the miscibility between the nonpolar reactants and KOH, needed to activate the Rh–diene complex. Prominent features of this organized reaction medium are its temperature insensitivity as well as the presence of water and toluene-rich compartments with a domain size of 55 Å confirmed by small-angle X-ray scattering (SAXS). Although bicyclooctadiene ligands 4 a , b , e performed equally well under homogeneous and microemulsion conditions, ligands 4 c , d gave a different chemoselectivity. For norbornadienes 5 , 6 , however, microemulsions markedly improved conversion and enantioselectivity as well as reaction rate, as was confirmed by kinetic studies using ligand 5 b .     

3-T MR-guided brachytherapy for gynecologic malignancies

Gynecologic malignancies are a leading cause of death in women worldwide. Standard treatment for many primary and recurrent gynecologic cancer cases includes external-beam radiation followed by brachytherapy. Magnetic resonance (MR) imaging is beneficial in diagnostic evaluation, in mapping the tumor location to tailor radiation dose and in monitoring the tumor response to treatment. Initial studies of MR guidance in gynecologic brachytherapy demonstrate the ability to optimize tumor coverage and reduce radiation dose to normal tissues, resulting in improved outcomes for patients.     

Advances in vibrational configuration interaction theory - part 2: Fast screening of the correlation space

For larger molecules, the computational demands of configuration selective vibrational configuration interaction theory (cs-VCI) are usually dominated by the configuration selection process, which commonly is based on second order vibrational Møller-Plesset perturbation (VMP2) theory. Here we present two techniques, which lead to substantial accelerations of such calculations while retaining the desired high accuracy of the final results. The first one introduces the concept of configuration classes, which allows for a highly efficient exploitation of the analogs of the Slater-Condon rules in vibrational structure calculations with large correlation spaces. The second approach uses a VMP2 like vector for augmenting the targeted vibrational wavefunction within the selection of configurations and thus avoids any intermediate diagonalization steps. The underlying theory is outlined and benchmark calculations are provided for highly correlated vibrational states of several molecules.     

Physical aging of molecular glasses studied by a device allowing for rapid thermal equilibration

Aging to the equilibrium liquid state of organic glasses is studied. The glasses were prepared by cooling the liquid to temperatures just below the glass transition. Aging following a temperature jump was studied by measuring the dielectric loss at a fixed frequency using a microregulator in which temperature is controlled by means of a Peltier element. Compared to conventional equipment, the new device adds almost two orders of magnitude to the span of observable aging times. Data for the following five glass-forming liquids are presented: dibutyl phthalate, diethyl phthalate, 2,3-epoxy propyl-phenyl-ether, 5-polyphenyl-ether, and triphenyl phosphite. The aging data were analyzed using the Tool-Narayanaswamy formalism. The following features are found for all five liquids: (1) The liquid has an "internal clock," a fact that is established by showing that aging is controlled by the same material time that controls the dielectric properties. (2) There are no so-called expansion gaps between the long-time limits of the relaxation rates following up and down jumps to the same temperature. (3) At long times, the structural relaxation appears to follow a simple exponential decay. (4) For small temperature steps, the rate of the long-time exponential structural relaxation is identical to that of the long-time decay of the dipole autocorrelation function.     

Quantitative analysis of penicillins in porcine tissues, milk and animal feed using derivatisation with piperidine and stable isotope dilution liquid chromatography tandem mass spectrometry

Penicillins are used universally in both human and veterinary medicine. The European Union (EU) has established maximum residue levels (MRLs) for most ß-lactam antibiotics in milk and animal tissues and included them in the National Residue Monitoring Programs. In this study, a novel method is described for the determination and confirmation of eight penicillins in porcine tissues, milk and animal feed by liquid chromatography–tandem mass spectrometry (LC–MS/MS). To prevent degradation of penicillin residues during workup, a derivatisation procedure was developed, by which penicillins were converted to stable piperidine derivatives. Deuterated piperidine derivatives were synthesised for all relevant penicillins, enabling the use of isotope dilution for accurate quantification. Penicillin residues were derivatised in the crude extract with piperidine and isolated using solid-phase extraction. The penicillin piperidine derivatives were determined by LC–MS/MS. The method was validated at the current MRLs, which range from 25–300 µg kg^?1 in muscle and kidney to 4–30 µg kg^?1 in milk as well as at the target value of 100 µg kg^?1 chosen for animal feed, according to the EU requirements for a quantitative confirmatory method. Accuracy ranged from 94–113% (muscle), 83–111% (kidney) and 87–103% (milk) to 88–116% (animal feed). Intra-day precision (relative standard deviation (RSD)_r) ranged from 5–13% (muscle, n?=?18), 4–17% (kidney, n?=?7) and 5–18% (milk, n?=?7) to 11–32% (animal feed, n?=?18). Inter-day precision (RSD_RL, n?=?18) ranged from 6–23% (muscle) to 11–36% (animal feed). From the results, it was concluded that the method was fit for purpose at the target MRLs in animal tissue and target levels for animal feed.