X-ray quality geometries of geodesic polyarenes from theoretical calculations: what levels of theory are reliable?

[structure: see text] Computational methods for calculating molecular geometries have not been well calibrated heretofore against X-ray data for bowl-shaped polycyclic aromatic hydrocarbons (PAHs). The analysis presented here capitalizes on a rare opportunity provided by corannulene to account explicitly for molecular distortions from crystal packing forces. Within the error limits of an extensive X-ray data set, B3LYP/6-31G* calculations were found to correctly reproduce all of the experimental bond distances and bond angles. The reliability and shortcomings of geometry calculations at other levels of theory are enumerated.     

Effect of dehydration on sulfate coordination and speciation at the Fe-(hydr)oxide-water interface: a molecular orbital/density functional theory and Fourier transform infrared spectroscopic investigation

The effect of dehydration on the coordination and speciation of sulfate at the Fe-(hydr)oxide-H2O interface was investigated using molecular orbital/density functional theory (MO/DFT) and Fourier transform infrared (FTIR) spectroscopy. IR frequency calculations were performed at the UB3LYP/6-31+G(d) level of theory for potential sulfate (bidentate bridging, monodentate, and H-bonded) and bisulfate (bidentate bridging and monodentate) surface complexes. MO/DFT calculated IR frequencies were compared to available IR literature results and attenuated total reflectance (ATR) FTIR spectra collected in our laboratory of sulfate adsorbed at the hematite-H2O interface. IR frequency calculations performed using the larger 6-311+G(d,p) basis set resulted in minor frequency shifts that did not dramatically alter the agreement with experiment. This investigation proposes that sulfate undergoes a speciation change as a function of surface dehydration. A generalized model for the speciation change is proposed as follows. (1) At the Fe-(hydr)oxide-H2O interface, sulfate adsorbs as a bidentate bridging or monodentate surface complex under most experimental conditions. (2) Upon surface dehydration, sulfate changes speciation to form bidentate bridging and/or monodentate bisulfate. However, surface dehydration does not yield 100% speciation change but leads to a mixture of sulfate and bisulfate. (3) The speciation change is reversible as a function of rehydration. The reversibility of the sulfate-bisulfate speciation change is chiefly determined by the local hydration environment of the O-H bond in bisulfate. Under dehydrated conditions, the O-H bond length is approximately 0.98 A. The bond length substantially increases (bond strength decreases) to approximately 1.03 A when the initial H-bond network is re-established through hydration, likely leading to deprotonation upon full mineral surface hydration.     

General Synthesis of Secondary Alkylamines by Reductive Alkylation of Nitriles by Aldehydes and Ketones

The development of C−N bond formation reactions is highly desirable due to their importance in biology and chemistry. Recent progress in 3d metal catalysis is indicative of unique selectivity patterns that may permit solving challenges of chemical synthesis. We report here on a catalytic C−N bond formation reaction—the reductive alkylation of nitriles. Aldehydes or ketones and nitriles, all abundantly available and low-cost starting materials, undergo a reductive coupling to form secondary alkylamines and inexpensive hydrogen is used as the reducing agent. The reaction has a very broad scope and many functional groups, including hydrogenation-sensitive examples, are tolerated. We developed a novel cobalt catalyst, which is nanostructured, reusable, and easy to handle. The key seems the earth-abundant metal in combination with a porous support material, N-doped SiC, synthesized from acrylonitrile and a commercially available polycarbosilane.     

Radiotracers for Bone Marrow Infection Imaging

Introduction: Radiotracers are widely used in medical imaging, using techniques of gamma-camera imaging (scintigraphy and SPECT) or positron emission tomography (PET). In bone marrow infection, there is no single routine test available that can detect infection with sufficiently high diagnostic accuracy. Here, we review radiotracers used for imaging of bone marrow infection, also known as osteomyelitis, with a focus on why these molecules are relevant for the task, based on their physiological uptake mechanisms. The review comprises [⁶⁷Ga]Ga-citrate, radiolabelled leukocytes, radiolabelled nanocolloids (bone marrow) and radiolabelled phosphonates (bone structure), and [¹⁸F]FDG as established radiotracers for bone marrow infection imaging. Tracers that are under development or testing for this purpose include [⁶⁸Ga]Ga-citrate, [¹⁸F]FDG, [¹⁸F]FDS and other non-glucose sugar analogues, [¹⁵O]water, [¹¹C]methionine, [¹¹C]donepezil, [^99mTc]Tc-IL-8, [⁶⁸Ga]Ga-Siglec-9, phage-display selected peptides, and the antimicrobial peptide [^99mTc]Tc-UBI_29-41 or [⁶⁸Ga]Ga-NOTA-UBI_29-41. Conclusion: Molecular radiotracers allow studies of physiological processes such as infection. None of the reviewed molecules are ideal for the imaging of infections, whether bone marrow or otherwise, but each can give information about a separate aspect such as physiology or biochemistry. Knowledge of uptake mechanisms, pitfalls, and challenges is useful in both the use and development of medically relevant radioactive tracers.     

Weighted holomorphic spaces with trivial closed range multiplication operators

We deal with the space consisting of those analytic functions on the unit disc such that , with . We determine the critical rate of decay of such that the pointwise multiplication operator , and analytic, has closed range in only in the trivial case that is the product of an invertible function in and a finite Blaschke product.

     

Untersuchungen zur Entmischungskinetik von AlZnMg-Legierungen mittels isothermer E-Modul-Messungen

Isothermal investigations of the time dependence of Young's modulus (Y) of some Al-Zn (2.4, 3.0 and 6.0 at.%)-Mg(x) alloys have shown that already in the early stage of decomposition a maximum and a minimum of Y appears. The mean radius r_LG of the Guinier-Preston zones (GPZ) is in this stage of decomposition less than 10 Å and with that much lower than this ones (r_LG ∼ 33 Å) measured in the minimum of Y detected by other authors in Al-Zn alloys. Therefore this minimum of Y in the Al-Zn alloys and those extremes occurring during the initial decomposition of Al-Zn-Mg investigated in this work should be caused by different reasons. The initial increase of Y should be mainly caused by the capture of Mg atoms by the dislocation decreasing the mobility of dislocations. The maximum and the falling off of Y should be due to the lattice distortions caused by the clustering processes. The migration energies obtained by analyzing the maximum of Y can be explained assuming that in the initial decomposition process the clusters are mainly formed by the migration of ZnV pairs whereas the Mg atoms act essentially as traps for vacancies.     

Polymerization of ethylene with new diimine complexes of late transition metals

Three pyridylimine based complexes of Ni^II and Co^II were reacted with methylaluminoxane (MAO) and tested as catalysts in ethylene polymerization. The two nickel catalysts produced mainly methyl branched polymers with good to moderate activity, while the cobalt compound showed only marginal activity. Reaction conditions strongly affect the polymer properties, such as molecular weight, melting temperature, degree of branching, and chain end unsaturation type.