Detlef Stöckigt

A Method for High‐Throughput Screening of Enantioselective Catalysts

About 1000 catalytic or stoichiometric asymmetric reactions of racemic compounds or prochiral substrates bearing enantiotopic groups can be analyzed per day. In this highly efficient method the enantioselectivity is determined by electrospray ionization mass spectrometry using isotopically labeled substrates. The picture shows the mass spectrum of the mixture obtained upon hydrolysis of 1 to afford the pseudo-enantiomeric products 2 and 3.

Eine Methode zum High-Throughput-Screening von enantioselektiven Katalysatoren

Etwa 1000 katalytische oder stochiometrische asymmetrische Reaktionen racemischer Verbindungen oder prochiraler Substrate mit enantiotopen Gruppen konnen durch Verwendung von ESI-MS und isotopenmarkierten Substraten an nur einem Tag bestimmt werden. Gezeigt ist das Massenspektrum der Mischung, die bei der Hydrolyse von 1 erhalten wird, bei der die pseudo-enantiomeren Produkte 2 und 3 entstehen.

General approach for the analysis of various alkaloid classes using capillary electrophoresis and capillary electrophoresis-mass spectrometry

Abstract The analysis of various alkaloid classes employing capillary electrophoresis (CE) and on-line combined CE-mass spectrometry (CE-MS) is described. A CE method is presented for the analysis of alkaloids without derivatisation or purification. The separation of four different groups of alkaloids consisting of monoterpenoid indole alkaloids, protoberberines/benzophenanthridines, β-carboline alkaloids, and isoquinolines from poppy by free zone capillary electrophoresis has been obtained using a 1:1 mixture of 100 mmol 1 −1 ammonium acetate (pH 3.1) and acetonitrile. The influence of alkaloid structure on the electrophoretic mobility is discussed. The CE-MS reconstructed total ion current (RIC) of the indole- and the opium-type standard alkaloids shows a decreased signal-to-noise ratio compared to CE using only UV detection. As expected the single-ion traces (or individual mass traces) of the [M+H] + ions show higher signal-to-noise ratios than the RIC. The electrospray MS data of the alkaloids are dominated by the protonated molecules and the Na + -, and K + -adducts. They display the typical pattern resulting from cluster formation or doubly charged species.

High-performance liquid chromatographic, capillary electrophoretic and capillary electrophoretic-electrospray ionisation mass spectrometric analysis of selected alkaloid groups

Systems for efficient separation of selected alkaloid groups by high performance liquid chromatography (HPLC), capillary electrophoresis (CE) and capillary electrophoresis coupled with electrospray ionisation mass spectrometry (CE-ESI-MS) are described. The optimized HPLC system was applied for the separation of 23 standard indole alkaloids as well as for qualitative and quantitative analyses of crude alkaloid extracts of Rauvolfia serpentina X Rhazya stricta hybrid cell cultures. The developed conditions for CE analysis proved to be efficient for separation of mixtures of standard indole and beta-carboline alkaloids. The described buffer system is also applicable in the combination of CE with electrospray ionisation mass spectrometry. This analytical technique allowed the separation and identification of components of standard indole alkaloid mixture as well as crude extracts of R. serpentina roots, R. serpentina cell suspension cultures and cortex of Aspidosperma quebracho-blanco. The influence of buffer composition and analyte structures on separation is discussed.

Separation and Identification of Basic Dendrimers Using Capillary Electrophoresis On‐line Coupled to a Sector Mass Spectrometer

The on-line coupling of capillary electrophoresis (CE) with a sector mass spectrometer via an electrospray ionization (ESI) source has been used to separate and identify polydisperse dendrimeric diaminobutane (DAB)-based polynitriles. A sample of the corresponding second generation has been analysed and revealed to be a complex mixture of the product, DAB-dendr-(CN)8 accompanied by several by-products. The capillary electrophoresis/mass spectrometry (CE/MS) data, including the reconstructed-ion current, the mass spectra and the UV-trace, provided fast and detailed information concerning the heterogeneity of the sample. The respective ESI mass spectra are dominated by the [M+H]+, [2M+H]+ and/or [M+2H]2+ peaks. The mass resolution of the sector mass spectrometer requiring m/Δm=2000, easily allowed signals of doubly charged ions to be assigned. CE/MS proved to be a promising tool with regard to the efficient analysis of basic dendrimers.

Analysis of basic pharmaceuticals by capillary electrophoresis in coated capillaries and on-line mass spectrometric detection

Basic pharmaceuticals were separated using capillary electrophoresis (CE) and positively identified with the aid of an on-line coupled sectorfield mass spectrometer (MS). The coupling device consisted of a modified electrospray (ES) ion source with coaxial sheath liquid. The adaptation of the CE-conditions for the particular needs of ES-MS is discussed in brief. Applying volatile buffers of low ionic strength and using uncoated capillaries in CE causes limited sample loadability, poor peak shapes and decreases resolution. The separation performance can be significantly improved if the capillaries are coated with poly(ethylene glycol) (PEG) or poly(vinyl alcohol) (PVA). As extracted from the reconstructed ion current of the mass spectra, the baselineseparated signals of structurally very similar compounds can be achieved. Signals due to the protonated and Na+-attached molecules have been observed. Nozzle-skimmer dissociation may be a versatile tool for additional molecular structure information.

Application of density functional theory /Hartree-Fock hybrid methods. Geometries and bond dissociation energies of Al+ complexes

Abstract A mixture of Hartree-Fock exchange and density functional theory exchange-correlation treatment has been applied to determine the geometry and bond dissociation energies (BDEs) of cationic Al+-X complexes (X = CH3, NH3, H2O, OH, HF, HCN, HNC, CO, CN, CH2O, CO2, N2, O2, and F2). By using the local spin density approximation and the ‘Becke-3-Lee-Young-Parr’ functionals each combined with three different basis sets (i.e. 6–31 G(d, p), 6–311 + G(d, p), and 6–311 + + G(3df, 2p)), the present findings (i) show good agreement with experimental and theoretical results of Moller-Plesset, configuration interaction and Gaussian-2 (G2) calculations on BDE and geometry, (ii) yield predictions of as yet experimentally and theoretically unknown species, (iii) recommend the combination of the B3LYP /6–311 + G(d, p) method for the geometry optimization and the B3LYP /6–311 + + G(3df, 2p)/ /BB3LYP /6–311 + G(d, p) level to yield a sufficiently accurate description of the energetics of cationic aluminum complexes within a short time, and therefore (iv) support the successful application of DFT methods towards metal-ion complexes.

Synthesis, structure and characterization of zinc(II), copper(II), zinc(II) barium(II) and copper(II) barium(II) complexes of macrocyclic heteronucleating ligands based on isothiosemicarbazide

Abstract The linear polyether dialdehydes (2-hydroxybenzaldehyde-3-yl)-O-(CH 2 CH 2 O) n -(3-yl-2-hydroxybenzaldehyde), where n = 3 ( 1 ), 4 (2), react with S -methylisothiosemicarbazide hydroiodide (or hydrochloride) in the presence of Ba(CF 3 SO 3 ) 2 and zinc(II) acetate and/or copper(II) acetate in methanol/THF to give [ZnBaL 1 l(CF 3 SO 3 )(CH 3 OH)] 2 ·0.5H 2 O ( 5 ). [CuBaL 1 (CF 3 SO 3 ) 2 ] 2 ( 8 ) and [CuBaL 2 (CF 3 SO 3 ) 2 ] 2 ( 10 ). Treatment of 5 with AgCF 3 SO 3 in methanol and subsequent recrystallization from ethanol results in loss of I − to give [ZnBal 1 (CF 3 SO 3 ) 2 (H 2 O)] 2 ( 6 ). Removal of the Ba 2− from 6,8 and 10 by using an aqueous solution of guanidinium sulfate affords ZnL 1 ·H 2 O ( 7 ), CuL 1 ·2H 2 O ( 9 ) and CuL 2 ·2H 2 O ( 11 ). The molecular structure of 5 has been determined by X-ray crystallography. Crystal data for 5 : monoclinic, P2 1 /c,a=9.331(1), b=15.293(2), c=25.940(2) A , β=97.94(1)°, Z=2 . Electronic and NMR spectra, the magnetic behavior, ESR and mass spectra, and the electrochemistry of the new compounds are discussed.

Analysis of Rauwolfia Alkaloids Employing Capillary Electrophoresis-Mass Spectrometry

Abstract Capillary electrophoresis-mass spectrometry (CE-MS) was applied to analyse extracts of roots and cell suspension cultures from Rauwolfia serpentina. Most of the alkaloids known to be present in the respective plant material have been resolved via CE and assigned according to their electrospray mass spectra.