Mechanism of the condensation reaction between 1-aryl- and heteroaryl-1,4-dihydro-3(2H)-isoquinolinones and aldehydes

4-Benzylidene-1-phenyl-1,4-dihydro-3(2H)-isoquinolinone, the intermediary product of the carbonyl condensation reaction between 1-phenyl-1,4-dihydro-3(2H)-isoquinolinone and benzaldehyde, rearranges in the presence of an equivalent quantity of sodium hydride into 4-benzyl-1-phenyl-3(2H)-isoquinolinone. As the possibility of the migration of the hydrogen at C-1 in the form of a proton or a hydrogen atom (radical reaction) was excluded, the mechanism of the rearrangement could be depicted as an intermolecular hydride anion migration. In case of the 1-(4-pyridyl)- and 1-(3-pyridyl)-1,4-dihydro-3(2H)-isoquinolinones, however, the rearrangement can be carried out also in polyphosphoric acid and in this case a proton loss-proton gain mechanism was proved.     

Complexometric titrations controlled by anodic-stripping methods-I Voltammetric stripping

Anodic-stripping voltammetry is used to perform automatic complexometric titrations of metal ions, with high precision. The stripping peaks are converted into corresponding titrant volume increments which are added consecutively during stripping. In analysis of samples containing about 1 mmole, each of lead, indium and gallium, relative standard deviations of 0.008-0.03% were attained.     

Preparative Separation and Analysis of Complex Mixtures of Leucomycins and Desmycarosyl Leucomycins Using HPLC and Mass Spectrometry

Composition and hydrolysis products of a biotechnical available complex of macrolides were analyzed by HPLC and ESI-CID-MSⁿ. Major components are leucomycin-type antibiotics (leucomycins A₁ (5), A₇ (3), A₉ (2), 9-desoxy-9-oxo-turimycin H₃ (4) and niddamycin B (6). Hydrolysis of the complex mixture yielded 9-, 13-isoforocidins (7, 8, 9, 11) and 9-oxo-forocidin (10). A preparative separation procedure was elaborated furnishing compounds 3 - 11 for semisynthetic experiments.Prof. Dr. Udo Gräfe deceased on 14.2.2003. For obituarity see: Schlegel B (2003) J Peptide Sci 9: 661–661.     

Almost constant sequences and well-distribution in compact groups

We study the properties of sequences (c _n ) in a compact groupG such that (x _n ) being (weakly) well-distributed implies (c _n x _n ) being (weakly) well-distributed and give a complete characterisation in terms of almost constant sequences as well as a generalisation to non-compact locally compact groups.     

Electronic detection of the enzymatic degradation of starch

[reaction: see text] The enzymatic degradation of starch can be monitored electronically using single-walled carbon nanotubes (SWNTs) as semiconducting probes in field-effect transistors (FETs). Incubation of these devices in aqueous buffer solutions of amyloglucosidase (AMG) results in the removal of the starch from both the silicon surfaces and the side walls of the SWNTs in the FETs, as evidenced by direct imaging and electronic measurements.     

One-electron versus electron-electron interaction contributions to the spin-spin coupling mechanism in nuclear magnetic resonance spectroscopy: analysis of basic electronic effects

For the first time, the nuclear magnetic resonance (NMR) spin-spin coupling mechanism is decomposed into one-electron and electron-electron interaction contributions to demonstrate that spin-information transport between different orbitals is not exclusively an electron-exchange phenomenon. This is done using coupled perturbed density-functional theory in conjunction with the recently developed J-OC-PSP [=J-OC-OC-PSP: Decomposition of J into orbital contributions using orbital currents and partial spin polarization)] method. One-orbital contributions comprise Ramsey response and self-exchange effects and the two-orbital contributions describe first-order delocalization and steric exchange. The two-orbital effects can be characterized as external orbital, echo, and spin transport contributions. A relationship of these electronic effects to zeroth-order orbital theory is demonstrated and their sign and magnitude predicted using simple models and graphical representations of first order orbitals. In the case of methane the two NMR spin-spin coupling constants result from totally different Fermi contact coupling mechanisms. (1)J(C,H) is the result of the Ramsey response and the self-exchange of the bond orbital diminished by external first-order delocalization external one-orbital effects whereas (2)J(H,H) spin-spin coupling is almost exclusively mitigated by a two-orbital steric exchange effect. From this analysis, a series of prediction can be made how geometrical deformations, electron lone pairs, and substituent effects lead to a change in the values of (1)J(C,H) and (2)J(H,H), respectively, for hydrocarbons.     

Analysis of cyanobacterial toxins (anatoxin-a, cylindrospermopsin, microcystin-LR) by capillary electrophoresis

Capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) were applied to the simultaneous separation of cyanobacterial toxins (anatoxin-a, microcystin-LR, cylindrospermopsin). The analytical performance data of both methods, optimized for the three toxins, were similar with a precision of migration times smaller than 0.8 RSD% and a detection limit in the range of 1-4 microg/mL, using spectrophotometric detection at 230 nm. Both methods were applied to an analysis of cyanotoxins in water bloom samples and crude cyanobacterial extracts. The results obtained indicate that, for complex matrices, the sequential application of CZE and MEKC is necessary. It is recommended to use both CE techniques for the analysis of the same sample in order to confirm the results by an orthogonal approach.     

Single-isomer sulfated alpha-cyclodextrins for capillary electrophoresis. Part 2. Hexakis(6-O-sulfo)-alpha-cyclodextrin: synthesis, analytical characterization, and initial screening tests

The second member of the family of single-isomer sulfated alpha-cyclodextrins, the sodium salt of hexakis(6-O-sulfo)-alpha-cyclodextrin (HxS), has been synthesized, analytically characterized, and used as the resolving agent for the capillary electrophoretic separation of the enantiomers of nonionic, weak-acid and weak-base analytes present in our initial screening kit. HxS interacted less strongly with many of the analytes tested than the larger-ring analogs, heptakis(6-O-sulfo)-beta-cyclodextrin (HS) and octakis(6-O-sulfo)-gamma-cyclodextrin (OS). For some of the analytes, the separation selectivities obtained with HxS were complementary to those observed with hexakis(2,3-di-O-acetyl-6-O-sulfo)-alpha-cyclodextrin (HxDAS), HS, and OS. For all analytes, the effective mobilities and separation selectivities as a function of the background electrolyte concentration of HxS followed the trends that were found for HxDAS, HS, and OS.