Chiral separations by host-guest complexation with cyclodextrin and crown ether in capillary zone electrophoresis

Summary Capillary zone electrophoresis using cyclodextrins and a chiral crown ether as buffer constituents was studied for the enantiomeric separation of drugs and amino acids. Based on results obtained from separation of racemic -amino acids both chiral selectors are compared with respect to resolution, efficiency and retention time. For (±)-Quinagolide effects of buffer composition and temperature are examined using -cyclodextrin as chiral agent. Optimum conditions were pH 2.5 at 30 mmol L^–1 -cyclodextrin. A linear dependence of retention on -cyclodextrin concentration allowed calculation of formation constants of the host-guest complexes. Buffer concentration and temperature also influence resolution. The application of a chiral crown ether to the separation of optical isomers in capillary zone electrophoresis is described for the first time. Chiral recognition of solutes depends on the formation of protonated alkyl amines and separation is attributed to the formation of diastereomeric host-guest complexes with different interactions for each enantiomer. The effects of crown ether concentration on resolution are presented.     

Inclusive ϕ production inK − p interactions at 110 GeV/c and search for structure in φ π−

Results on inclusive ? production inK ^? p interactions at 110 GeV/c are presented. The production cross section is found to be larger than in πp andpp interactions at similar energies, suggesting OZI allowed \(s\bar s\) fusion to be the dominant mechanism in ? production. Thex distributions of ? and \(\bar K^{*0} \) are found to be similar to each other over the entirex range suggesting an overall strangeness suppression factor of 0.20±0.04 in the sea to be the dominant source of the difference in the cross section for ? and \(\bar K^{*0} \) . There is no evidence of a narrowφπ ^? state around 2.1 GeV/c² as suggested byK ⁺ experiments, but there is some excess of events in the region 1.94?1.98 GeV/c² consistent with theF-meson mass as observed ine ⁺ e ^? experiments.     

High resolution mass spectrometric studies of some bicyclic γ-lactones

The mass spectra of three bicyclic γ-lactones have been studied, and the fragmentation pathways have been proposed with the aid of accurate mass measurements and metastable transitions. An unusually low [M ? CH₃] ion and the presence of an abundant [M ? C₅H₉] ion in the mass spectrum of dihydroactinidiolide were interpreted as a possible rearrangement involving a methyl migration. The eliminations of methyl radical, carbon monoxide and ketene are important processes in many cases.     

Cyclopeptid-Antibiotika aus Aspergillus-Arten. Struktur der Echinocandine C und D

Cyclopeptide antibiotics from Aspergillus species. Structure of echinocandins C and D The echinocandins B, C and D are antifungal antibiotics produced by a strain of Aspergillus rugulosus. All three metabolites are closely related representing cyclic oligopeptides composed of six amino acids and a linolic acid residue in an amide linkage. The complete structure of echinocandin B ( 1 ) has recently been established by X-ray analysis. Structural assignments to the new minor metabolites C and D have now been made by hydrolytic and oxidative cleavage reactions, formation of N-acyl-α-aminoethers as well as by chemical correlations and extensive NMR. examinations. Echinocandin C ( 2 ), C₅₂H₈₁N₇O₁₅, contains 3-hydroxyhomotyrosine in the place of 3, 4-dihydroxyhomotyrosine present in 1 . Echinocandin D ( 3 ), C₅₂H₈₁N₇O₁₃, differs in two amino acids: 3, 4-dihyroxyhomotyrosine and 4, 5-dihydroxyornithine, unusual units of 1 being replaced by 3-hydroxyhomotyrosine and ornithine.     

The agglomeration state of nanosecond laser-generated aerosol particles entering the ICP

Fundamental understanding of aerosol formation and particle transport are important aspects of understanding and improving laser-ablation ICP–MS. To obtain more information about particles entering the ICP, laser aerosols generated under different ablation conditions were collected on membrane filters. The particles and agglomerates were then visualised using scanning electron microscope (SEM) imaging. To determine variations between different sample matrices, opaque (USGS BCR-2G) and transparent (NIST SRM 610) glass, CaF₂, and brass (MBH B26) samples were ablated using two different laser wavelengths, 193 and 266 nm. This study showed that the condensed nano-particles (∼10 nm in diameter) formed by laser ablation reach the ICP as micron-sized agglomerates; this is apparent from filters which contain only a few well-separated particles and particle agglomerates. Ablation experiments on different metals and non-metals show that the structure of the agglomerates is matrix-dependent. Laser aerosols generated from silicates and metals form linear agglomerates whereas particle-agglomerates of ablated CaF₂ have cotton-like structures. Amongst other conditions, this study shows that the absorption characteristics of the sample and the laser wavelength determine the production of micron-sized spherical particles formed by liquid droplet ejection.