Sample matrix influence on the choice of background electrolyte for the analysis of bases with capillary zone electrophoresis

Low levels of impurities need to be determined in drugs. Consequently, if UV detection is used, a large sample amount must be loaded and as narrow peaks as possible obtained. The sample matrix and the stability of the samples as well as the peak resolution should be considered when the electrolyte is chosen. In this study the influence of the sample matrix composition with varying background electrolytes on the peak appearance of model mixtures loaded in large amounts was investigated. A robust electrolyte for analysis of bases in a sample with varying pH was found to consist of a buffering co-ion and a buffering counter-ion (the pH was approximately 4.2 in the electrolyte). If a minor component has higher mobility than the macrocomponent and the co-ion, better peak shape can be obtained if, for instance, enough sodium chloride is added to the sample, i.e., sample self-stacking is exploited. The effect of addition of organic modifiers, isopropanol or acetonitrile, was examined and good linearity and precision have been shown for impurities in the concentration range tested, approximately 0.03 to 5 mol% of the main component, in model mixtures.     

Mehrkernige Kobaltkomplexe. II. Herstellung und Struktur von [(tren) (NH3)Co(O2)Co(NH3) (tren)](SCN)4 · 2H2O

Polynuclear Cobalt Complexes. II. Preparation and Structure of [(tren) (NH₃)Co(O₂)Co(NH₃) (tren)](SCN)₄ · 2H₂O The title compound is obtained on oxygenation of [Co(tren)(H₂O)₂]²⁺ in 6M aqueous ammonia or by ligand exchange starting from [(NH₃)₅Co(O₂)Co(NH₃)₅]-(NO₃)₄. An X-ray structure determination was made. The substance forms monoclinic crystals, space group P2₁/c, lattice constants a=10,135, b=8,473, c=19,484 Å, β=108,58°, with two formula units in the cell. The final R is 0,066. The binuclear cation has a center of symmetry, so the Co? O? O? Co unit is planar; the Co? O? O angle is 111,5°. The tertiary nitrogen atoms of both chelate groups are cis to the O₂ bridge, as found in doubly bridged [(tren)Co(O₂,OH)Co(tren)](ClO₄)₃ · 3H₂O. On acidification in solution, the singly bridged cation [(tren) (NH₃)CoO₂Co(NH₃)(tren)]⁴⁺ (a) loses the bound O₂ completely. But unlike the doubly bridged cation b , the rate of dissociation of a is independent of pH (Fig. 5). At higher pH (8–10) bridging a→b (Fig. 2) occurs. Both reactions must have the same rate determining step, the first order rate constants being of the order of 2 · 10^?3 s^?1 (25°, 0,35M KCl).     

Mehrkernige Kobaltkomplexe. III. Über meso-[(en)2Co(OH)2Co(en)2] (NO3)4

Polynuclear Cobalt Complexes. III. On meso-[(en)₂Co(OH)₂Co(en)₂] (NO₃)₄ The structure of the title compound has been determined by X-ray analysis and refined to R = 0,060. The crystals are monoclinic, space group very probably C2/m, with cell dimensions a = 16,113(3), b = 10,946(2), c = 7,193(2) Å, β = 113,22(2)° and Z = 2. The configuration of the cation is ΔΛ IR. and UV./VIS. spectroscopic data are given.     

Morse-type index theory for flows and periodic solutions for Hamiltonian Equations

An index theory for flows is presented which extends the classical Morse theory for gradient flows on compact manifolds. The theory is used to prove a Morse-type existence statement for periodic solutions of a time-dependent (periodic in time) and asymptotically linear Hamiltonian equation.     

Synthesis and Biological Evaluation of the Antimicrobial Natural Product Lipoxazolidinone A

Natural products have historically been a major source of antibiotics and therefore novel scaffolds are constantly of interest. The lipoxazolidinone family of marine natural products, with an unusual 4‐oxazolidinone heterocycle at their core, represents a new scaffold for antimicrobial discovery; however, questions regarding their mechanism of action and high lipophilicity have likely slowed follow‐up studies. Herein, we report the first synthesis of lipoxazolidinone A, 15 structural analogues to explore its active pharmacophore, and initial resistance and mechanism of action studies. These results suggest that 4‐oxazolidinones are valuable scaffolds for antimicrobial development and reveal simplified lead compounds for further optimization.     

Influence of strain on growth mode and electro-optical properties of high-brightness InGaN-LEDs on SiC

We present a detailed study, on the influence of buffer strain on the MOVPE crystal growth mode in the QW active layer of high-brightness InGaN LEDs on SiC substrate. While highly strained buffers are related to InGaN QWs with homogeneous In-distribution, low In-concentration and reduced quantum efficiency, buffers with reduced strain are shown to induce InGaN-QW growth with a dot-like In-distribution, locally high In-concentration and good quantum efficiency. Using an optimised buffer technology, we developed extremely bright InGaN QW-LEDs with a brightness of more than 7 mW (at 460 nm and 20 mA) in a 5 mm radial lamp, good wavelength stability, low forward voltage, high ESD-stability and low ageing.     

Direct and Converse Results on Weighted Simultaneous Approximation by the Method of Operators of Baskakov-Durrmeyer Type

We consider the n- th. operators of Baskakov-Durrmeyer type, which result from the classical Baskakov-type operators with weights p _nk, if the values f(k/n) are replaced by the integral terms \((n - c)\int_{I} p_{nk} (t) f(t) dt \) , where I denotes the corresponding interval which depends on the parameter c. For integrable functions the rate of weighted simultaneous approximation will be related to the Ditzian-Totik modulus of smoothness.     

Evaluation of generic chiral liquid chromatography screens for pharmaceutical analysis

Two different automated generic liquid chromatography screens for the separation of chiral compounds of pharmaceutical interest have been evaluated. The test set comprised 53 chemically diverse chiral compounds involving 55 enantiomeric pairs from the pharmaceutical industry (i.e. starting materials, synthetic intermediates and drug substances). The first screen utilised four polysaccharide-based columns with five mobile phases and showed enantioselectivity for 87% of the test compounds. The second screen employed three macrocyclic glycopeptide columns with two mobile phases and showed enantioselectivity for 65% of the test compounds. Merging of the two screening procedures resulted in an enantioselectivity for 96% of the chiral compounds. It is anticipated that the systematic use of the automated chiral HPLC screens described in this report will substantially reduce the necessary time for method development of pharmaceutically related chiral analytical methods.     

Structural characterization,thermal investigation,and liquid crystalline behavior of 4-[(4-chlorobenzyl)oxy]-3,4′-dichloroazobenzene

Using the Williamson method, a new dye 4-[(4-chlorobenzyl)oxy]-3,4′-dichloroazobenzene (CODA) with liquid crystalline properties was synthesized. The structure and the thermal behavior of CODA were investigated by means of nuclear magnetic resonance, X-ray diffraction, differential scanning calorimetry, and light polarized optical microscopy techniques. The thermophysical processes were monitored by heating–cooling cycles, but the formation of liquid crystal phases were exhibited only for small values of the cooling rates. For the first heating–cooling cycle, the melting and the solidification processes, thus the characteristic temperatures, are shifted to higher values when compared to the following cycles.