The rhodium-catalysed 1,2-addition of arylboronic acids to aldehydes and ketones with sulfonated S-Phos

The rhodium-catalysed 1,2-addition of arylboronic acids to aryl aldehydes has been accomplished in high yield using sulfonated S-Phos, a water-soluble biaryl phosphine ligand which allows for catalyst recycling. The catalytic protocol has also been successful in the challenging arylation of ketones.     

Evaluation of the UFXC32k photon‐counting detector for pump–probe experiments using synchrotron radiation

This paper presents the performance of a single‐photon‐counting hybrid pixel X‐ray detector with synchrotron radiation. The camera was evaluated with respect to time‐resolved experiments, namely pump–probe–probe experiments held at SOLEIL. The UFXC camera shows very good energy resolution of around 1.5 keV and allows the minimum threshold setting to be as low as 3 keV keeping the high‐count‐rate capabilities. Measurements of a synchrotron characteristic filling mode prove the proper separation of an isolated bunch of photons and the usability of the detector in time‐resolved experiments.     

Optical signatures of spin polarization of carriers in quantum dots

We predict theoretically the optical signatures of spin polarization of carriers in self-assembled quantum dots. The emission spectra are mapped out as a function of increasing electron spin polarization for a fixed number of electrons and holes. The spin-polarized spectra are determined using exact diagonalization techniques for up to 12 particles, corresponding to two lowest filled shells. We predict that the spin polarization leads to photon polarization, to redshifts of emission lines due to excess exchange interactions among the spin-polarized electrons, and to a complete breakup of emission lines for spin-polarized electronic shells.     

Thermodynamic properties of germanium/carbon microclusters

Theoretical studies on the Ge(n)C(m) (n=1,2; m=1-3) microclusters have been performed using the state of the art calculations. Several alternative structures of these clusters were studied to locate the lowest-energy isomers. It is observed that the structures of the complexes result from the competition between ionic Ge-C, conjugated covalent C-C, and metallic Ge-Ge bonds. The ionization of the molecules enhances the ionic character of the Ge-C bond and has significant structural consequences. Using theoretically determined partition functions, thermodynamic data are computed and experimental enthalpies are enhanced. The ab initio atomization energies of germanium carbides compare well with corrected experimental functions. The experimental appearance potentials are well reproduced by the theoretical ionization potentials.     

An extension of Günther’s volume comparison theorem

The aim of this note if to give an extension of a classical volume comparison theorem for Riemannian manifolds with sectional curvature bounded above (see Günther, P. Einige Sätze über das Volumenelement eines Riemannschen Raumes, Publ. Math. Debrecen 7, 78–93 (1960)). For the case of a n-dimensional simply connected complete Riemannian manifold with nonpositive sectional curvature our theorem states that the function tarea(S _t (p))/t ^n–2 is convex for every pM where S _t (p) denotes the sphere of radius t with center p. In view of area(S ₀ (p))=0, it is easy to see that our theorem implies the classical result. A similar result holds true for simply connected manifolds with sectional curvature bounded above by a negative constant.Research partially supported by Fondecyt Grant # 1000713 and by UTFSM Grant # 120023     

NO-bound myoglobin: structural diversity and dynamics of the NO ligand

We used femtosecond infrared polarization spectroscopy and density functional theory in a study on the key signaling molecule nitric oxide (NO) bound to myoglobin. Our results show that after photolysis, a substantial fraction of NO recombines within the first few picoseconds. We discovered that the diatomic ligand is severely tilted in the protein and present evidence that the Fe-NO moiety can sample a wide range of off-axis tilting and bending conformations.     

Polyoxometalate-catalysed epoxidation of 1-octene with hydrogen peroxide in microemulsions coupled with ultrafiltration

Epoxidation of 1-octene with hydrogen peroxide catalysed by amphiphilic salts of peroxo tungstophosphate [PO4[WO(O2)2]4]3- in water-in-oil microemulsions is an efficient and environmentally benign reaction which, coupled with ultrafiltration, shows the potential for continuous production of epoxides.     

An algorithm for the enumeration of spanning trees

Enumeration of spanning trees of an undirected graph is one of the graph problems that has received much attention in the literature. In this paper a new enumeration algorithm based on the idea of contractions of the graph is presented. The worst-case time complexity of the algorithm isO(n+m+nt) wheren is the number of vertices,m the number of edges, andt the number of spanning trees in the graph. The worst-case space complexity of the algorithm isO(n ²). Computational analysis indicates that the algorithm requires less computation time than any other of the previously best-known algorithms.