Protein crystallography with the PILATUS 1M detector at the Swiss Light Source

The last few years have seen an increase in the demand of automation at synchrotron radiation facilities. The main driving forces behind this quest are the Structural Genomics Centers and related projects [1], with their need for large throughput of samples and an increasing number of relatively unskilled users with ever increasing demands.

In order to meet the needs of this diverse community, the structure determination process must be streamlined. A production pipeline for high volume determination of structures requires optimization and automation of current processes in use at synchrotron facilities. The ultimate goal is to arrive at a system that, with little more input than a sample, will provide the researcher with the final molecular structure.     

Ion‐exchange vs reversed‐phase chromatography for separation and determination of basic psychotropic drugs

Ion exchange chromatography, an alternative to reversed‐phase (RP) chromatography, is described in this paper. We aimed to obtain optimal conditions for the separation of basic drugs because silica‐based RP stationary phases show silanol effect and make the analysis of basic analytes hardly possible. The retention, separation selectivity, symmetry of peaks and system efficiency were examined in different eluent systems containing different types of buffers at acidic pH and with the addition of organic modifiers: methanol and acetonitrile. The obtained results reveal a large influence of the salt cation used for buffer preparation and the type of organic modifier on the retention behavior of the analytes. These results were also compared with those obtained on an XBridge C₁₈ column. The obtained results demonstrated that SCX stationary phases can be successfully used as alternatives to C₁₈ stationary phases in the separation of basic compounds. The most selective and efficient chromatographic systems were applied for the quantification of some psychotropic drugs in fortified human serum samples. Copyright © 2015 John Wiley & Sons, Ltd.     

Synoxazolidinones A and B: novel bioactive alkaloids from the ascidian Synoicum pulmonaria

Bioassay-guided fractionation of the sub-Arctic ascidian Synoicum pulmonaria collected off the Norwegian coast led to the isolation of a novel family of brominated guanidinium oxazolidinones named synoxazolidinones A and B (1 and 2). The backbone of the compounds contains a 4-oxazolidinone ring rarely seen in natural products. The structure of the compounds was determined by spectroscopic methods. The synoxazolidinones exhibited antibacterial and antifungal activities.     

Substituent effects on the electron affinities and ionization energies of tria-, penta-, and heptafulvenes: a computational investigation

The extent of substituent influence on the vertical electron affinities (EAs) and ionization energies (IEs) of 43 substituted tria-, penta-, and heptafulvenes was examined computationally at the OVGF/6-311G(d)//B3LYP/6-311G(d) level of theory and compared with those of tetracyanoquinodimethane (TCNQ) and tetrathiafulvalene (TTF) as representing strong electron-acceptor and -donor compounds, respectively. The substituents X at the exocyclic positions of the fulvenes were either NH(2), H, or CN, while the substituents Y at the ring positions were H, Cl, F, CN, or NH(2). The variations of the EAs and IEs were rationalized by qualitative arguments based on frontier orbital symmetries for the different fulvene classes with either X or Y being constant. The minimum and maximum values found for the calculated EAs of the tria-, penta-, and heptafulvenes were 0.51-2.05, 0.24-3.63, and 0.53-3.14 eV, respectively, and for the IEs 5.27-9.96, 7.07-10.31, and 6.35-10.59 eV, respectively. Two of the investigated fulvenes outperform TCNQ (calcd EA = 2.63 eV) and one outperforms TTF (calcd IE = 6.25 eV) with regard to acceptor and donor abilities, respectively. We also evaluated the properties of bis(fulvene)s, i.e., compounds composed of a donor-type heptafulvene fused with an acceptor-type pentafulvene, and it was revealed that these bis(fulvene)s can be designed so that the IE and EA of the two separate fulvene segments are retained, potentially allowing for the design of compact donor-acceptor dyads.     

Design of novel bilayer compounds of the CPO-8 type containing 1D channels

The reaction between Zn(NO3)2.6H2O and 5-aminoisophthalic acid (aip) in a mixture of diethylformamide (DEF) and ethanol resulted in [Zn(C8H5NO4)(C5H11NO)]n (CPO-8-DEF). This compound is composed of infinite 2D layers with tetrahedral Zn atoms and aip ligands in a triangular topology. The DEF molecules are bonded to Zn, and within each layer, the DEF molecules are oriented in the same direction, while in the subsequent layer, the DEF molecules are oriented in the opposite direction. By introduction of the pillaring ligands 4,4-bipyridine (BPY), 1,2-di-4-pyridylethylene (DPE), 1,2-di-4-pyridylethane (DPA), and 1,3-di-4-pyridylpropane (DPP) into mixtures of N,N'-dimethylformamide and water with Zn(NO3)2 and aip, we have successfully synthesized a series of related pillared bilayer compounds with the same common triangular Zn(aip) layer structural motif as that observed in CPO-8-DEF. The compounds are denoted as CPO-8-BPY ([Zn(C8H5NO4)(C10H8N2)(0.5)]n.3nH2O), CPO-8-DPE ([Zn(C8H5NO4)(C12H10N2)(0.5)]n.2.5nH2O), CPO-8-DPA ([Zn(C8H5NO4)(C12H12N2)(0.5)]n.2.5nH2O), and CPO-8-DPP ([Zn(C8H5NO4)(C13H14N2)(0.5)]n.3nH2O). In all cases, the pillars create spaces inside the bilayers that result in 1D channels running along the [010] directions with dimensions of 3.5 x 6.7 A(2). These channels contain water molecules that can be removed on heating to 150 degrees C, resulting in porous structures. The crystal structures of these porous high-temperature variants have been determined on the basis of powder X-ray diffraction data. All of the compounds show preferential adsorption of H2 over N2 at 77 K.     

Regularity Results for the Spherically Symmetric Einstein–Vlasov System

The spherically symmetric Einstein–Vlasov system is considered in Schwarzschild coordinates and in maximal-isotropic coordinates. An open problem is the issue of global existence for initial data without size restrictions. The main purpose of the present work is to propose a method of approach for general initial data, which improves the regularity of the terms that need to be estimated compared to previous methods. We prove that global existence holds outside the center in both these coordinate systems. In the Schwarzschild case we improve the bound on the momentum support obtained in Rein et al. (Commun Math Phys 168:467–478, 1995) for compact initial data. The improvement implies that we can admit non-compact data with both ingoing and outgoing matter. This extends one of the results in Andréasson and Rein (Math Proc Camb Phil Soc 149:173–188, 2010). In particular our method avoids the difficult task of treating the pointwise matter terms. Furthermore, we show that singularities never form in Schwarzschild time for ingoing matter as long as 3m ≤ r. This removes an additional assumption made in Andréasson (Indiana Univ Math J 56:523–552, 2007). Our result in maximal-isotropic coordinates is analogous to the result in Rendall (Banach Center Publ 41:35–68, 1997), but our method is different and it improves the regularity of the terms that need to be estimated for proving global existence in general.