Fluorotris(trifluoromethylsulfonyl)methane: synthesis, characterization and reactivity

The hitherto elusive title compound was synthesized and characterized with the aim to study its potential as a carbon-based (“CF-type”) electrophilic fluorination reagent. A detailed discussion of its structure, properties and reactivity is based on experimental studies as well as on molecular modeling.     

Wegner estimate for sparse and other generalized alloy type potentials

We prove a Wegner estimate for generalized alloy type models at negative energies (Theorems 8 and 13). The single site potential is assumed to be non-positive. The random potential does not need to be stationary with respect to translations from a lattice. Actually, the set of points to which the individual single site potentials are attached, needs only to satisfy a certain density condition. The distribution of the coupling constants is assumed to have a bounded density only in the energy region where we prove the Wegner estimate.     

Remarks on the Born approximation and the Factorization Method

In this paper, we compare the far-field operators for the full nonlinear inverse scattering problem with the Born approximation as its linearization. The Factorization Method shows that both operators share the same behavior with respect to illposedness of the inverse problem. The results are derived for acoustic and electromagnetic scattering problems and the corresponding problem in electrical impedance tomography.     

Intra-operative optical diagnostics with vibrational spectroscopy

Established methods for characterization of tissue and diagnostics, for example histochemistry, magnetic resonance imaging (MRI), X-ray tomography, or positron emission tomography (PET), are mostly not suitable for intra-operative use. However, there is a clear need for an intra-operative diagnostics especially to identify the borderline between normal and tumor tissue. Currently, vibrational spectroscopy techniques (both Raman and infrared) complement the standard methods for tissue diagnostics. Vibrational spectroscopy has the potential for intra-operative use, because it can provide a biochemically based profile of tissue in real time and without requiring additional contrast agents, which may perturb the tissue under investigation. In addition, no electric potential needs to be applied, and the measurements are not affected by electromagnetic fields. Currently, promising approaches include Raman fiber techniques and nonlinear Raman spectroscopy. Infrared spectroscopy is also being used to examine freshly resected tissue ex vivo in the operating theater. The immense volume of information contained in Raman and infrared spectra requires multivariate analysis to extract relevant information to distinguish different types of tissue. The promise and limitations of vibrational spectroscopy methods as intra-operative tools are surveyed in this review.     

Cytotoxic effect of some pentacyclic triterpenes and hemisynthetic derivatives of stigmasterol

Two different oxidation reactions (PCC and KMnO₄) of stigmasterol gave three products, stigmasta-4,22-dien-3-one (1a), stigmasta-4,22-diene-3,6-dione (1b), and 3-O-acetyl-5β,6β-epoxystigmast-22-ene-3-ol (1c). The cytotoxic activities of hemisynthetic compounds, stigmasterol, and four pentacyclic triterpens 2–5 previously isolated from cultivated and wild Triumfetta cordifolia and identified were investigated against human fibrosarcoma cell line (HT1080). Most of the drugs showed moderate cytotoxic activity. It was also notice that the triterpene skeleton had a range of number of OH functions in which activity was observed. Spectroscopic analyses (¹H and ¹³ C NMR) and mass were used to elucidate the structure of hemisynthetic compounds.     

2-Iodoxybenzoic acid--a simple oxidant with a dazzling array of potential applications

Since its discovery by Christoph Hartmann and Victor Meyer in 1893, 2-iodoxybenzoic acid (IBX) has emerged as a rather ubiquitous oxidant for organic synthesis. The past decade has seen the development of a large variety of applications that go far beyond the simple oxidation of alcohols. This Review is concerned with the synthetic potential of IBX, with particular emphasis on uncommon reactivity patterns and novel fields of application.     

Anderson localization and Lifshits tails for random surface potentials

We consider Schrödinger operators on L²(R^d) with a random potential concentrated near the surface R^d₁×{0}⊂R^d. We prove that the integrated density of states of such operators exhibits Lifshits tails near the bottom of the spectrum. From this and the multiscale analysis by Boutet de Monvel and Stollmann [Arch. Math. 80 (2003) 87-97] we infer Anderson localization (pure point spectrum and dynamical localization) for low energies. Our proof of Lifshits tails relies on spectral properties of Schrödinger operators with partially periodic potentials. In particular, we show that the lowest energy band of such operators is parabolic.