Feller semigroups on R N

We present in a unified way, and in a purely analytic setting, some aspects of the theory of semigroups generated in the space of bounded continuous functions by second order elliptic operators with unbounded coefficients in R ^N , and the associated resolvent equation. Many examples are also presented.     

The enzymatic degradation of ultraviolet-irradiated deoxyribonucleic acid

Abstract— Double-stranded DNA, after u.v. irradiation, was degraded by the action of deoxy-ribonuclease and snake venom phosphodiesterase. In addition to mononucleotides a number of nuclease-resistant oligonucleotides, containing photochemically altered bases, could be detected and separated by column chromatography. The phosphorus contents indicated the existence of some photoproducts other than dimers of pyrimidines, especially within the trinucleotide fraction. Comparison of the DNase action on irradiated and on unirradiated DNA suggests that DNase is hindered from splitting the chain next to a photoproduct, tetra-nucleotides being the smallest and octanucleotides the most frequent degradation products bearing an altered base.     

A study of jets in electron positron annihilation into hadrons in the energy range 3.1 to 9.5 GeV

From an analysis of data taken with the detector PLUTO and the DORIS storage rings we have obtained evidence for jet structure in e⁺e^? annihilation with hadrons. Results for mean sphericity, mean thrust, the angular dependence of the jet axis and for 〈p_t〉 and 〈p_∥〉 with respect to the jet axis are presented. At 9.4 GeV we also discuss the angular dependence of the charged and neutral deposited energy with respect to the jet axis.     

Conformational landscape of meso-(1,3-dithian-2-yl)porphyrins

An investigation of the conformational landscape of 1,3-dithian-2-yl bearing porphyrins and the rotational behavior of the dithianyl substituents in meso position was carried out by variable-temperature (VT) NMR spectroscopy. Additionally, theoretical results for alternative conformations and energy barriers were obtained by molecular modeling. The study revealed different NH trans tautomers with regard to the orientation of the dithianyl ligands for the free base porphyrins 1-3. Relatively ruffled porphyrin core conformations were established for the transition states of the dithianyl rotation, resulting in a lower rotational energy barrier for the nickel(II) complex 4 compared to that of the free base systems. The data obtained and the first depiction of a rotational transition state for the rotation of bulky meso-alkyl substituents illustrate the close structural interplay between meso-alkyl substituents and the macrocycle conformation in porphyrins.     

Interplay of para- and diatropic ring currents [(anti)aromaticity] of macrocyclic rings subject to conformational influences,further annelation and hydrogenation of aromatic ring moieties

The spatial magnetic properties (Through Space NMR Shieldings—TSNMRS) of a variety of porphyrins, hemiporphyrazines and tetraoxo[8]circulenes have been computed, visualized as Iso-chemical Shielding Surfaces (ICSS) of various size and direction, and were examined subject to the interplay of present (para)-diatropic ring currents [(anti)aromaticity] and influences on the latter property originating from the macrocyclic ring conformation, further annelation and partial to complete hydrogenation of aromatic ring moieties. Caution seems to be indicated when concluding from a single NICS parameter to present (para)diatropic ring currents [(anti)aromaticity].     

Quantification of the (anti)aromaticity of fulvalenes subjected to pi-electron cross-delocalization

Fulvalenes 3-12 were theoretically studied at the ab initio level of theory. For the global minima structures, the occupation of the bonding (pi)C=C orbital of the interring C=C double bond obtained by NBO analysis quantitatively proves pi-electron cross-delocalization resulting in, at least partially, 2- or 6pi-electron aromaticity and 8pi-electron antiaromaticity for appropriate moieties. The cross-conjugation was quantified by the corresponding occupation numbers and lengths of the interring C=C double bonds, while the aromaticity or antiaromaticity due to cross-delocalization of the pi-electrons was visualized and quantified by through-space NMR shielding surfaces.     

Controlled Microsynthesis of Silica Particles in a Microfluidic Setup

We report on a novel microsynthesis method for easy controlling the size of silica micro- and nanoparticles. Colloids are synthesized in a microfluidic chamber by layer-wise adsorption of silica to precipitated nuclei. We prepare samples of spherical particles with different numbers of coatings and find that particles with less than 15 coating layers are uniform in size. Particles with more coatings are disperse. This finding is attributed to peptization of nanoparticles and independent growth of secondary nanoparticles. For all numbers of layers, the maximum particle size increases with the number of coatings.     

The COVID19-NMR Consortium: A Public Report on the Impact of this New Global Collaboration

The outbreak of COVID-19 in December 2019 required the formation of international consortia for a coordinated scientific effort to understand and combat the virus. In this Viewpoint Article, we discuss how the NMR community has gathered to investigate the genome and proteome of SARS-CoV-2 and tested them for binding to low-molecular-weight binders. External factors including extended lockdowns due to the global pandemic character of the viral infection triggered the transition from locally focused collaborative research conducted within individual research groups to digital exchange formats for immediate discussion of unpublished results and data analysis, sample sharing, and coordinated research between more than 50 groups from 18 countries simultaneously. We discuss key lessons that might pertain after the end of the pandemic and challenges that we need to address.