Mass spectroscopy of natural products. XXIII,Comparative positive and negative ion mass spectral studies of scapanin-type diterpenoidst

The mass spectral behaviour of 15 scapanin-type diterpenoids (8α,12-epoxylabdanes) was elucidated using accurate mass measurements and deuterium-labelled derivatives. The results obtained allow a localization of the functional groups in the diterpenoid system. Furthermore, the negative ion mass spectra of the scapanin-type diterpenoids are discussed and compared with the positive ion spectra.     

Structural Factors Affecting the Basicity of ω-Pyridylalkanols, ω-Pyridylalkanamides and ω-Pyridylalkylamines

The present paper describes the preparation by conventional methods (when not available commercially) and the pK_a-determination of the α-, β- and γ-isomers of pyridylethanamide, 3-pyridylpropanamide. 4-pyridylbutanamide, 5-pyridyl-pentanamide, pyridylmethanol, 2-pyridylethanol, 3-pyridylpropanol, 4-pyridyl-butanol, 5-pyridylpentanol, pyridylmethylamine, 2-pyridylethylamine, 3-pyridyl-propylamine, 4-pyridylbutylamine, and 5-pyridylpentylamine. While a field effect accounts for many variations in pK_a as a function of chain length, marked inductive effects are operative in some methyl and ethyl homologs. The pK_a-decreasing influence of an intramolecular H-bond is also apparent in some lower homologs belonging to the α-series.     

Low temperature electron transfer in strongly condensed phase

Electron transfer coupled to a collective vibronic degree of freedom is studied in strongly condensed phase and at lower temperatures where quantum fluctuations are essential. Based on an exact representation of the reduced density matrix of the electronic + reaction coordinate compound in terms of path integrals, recent findings on the overdamped limit in quantum dissipative systems are employed. This allows us to give a consistent generalization of the well-known Zusman equations to the quantum domain. Detailed conditions for the range of validity are specified. Using the Wigner transform these results are also extended to the quantum dynamics in full phase space. As an important application electronic transfer rates are derived that comprise adiabatic and nonadiabatic processes in the low temperature regime including nuclear tunneling. Accurate agreement with precise quantum Monte Carlo data is observed.     

über dilatometrische Titrationen

Zusammenfassung Mit Hilfe dilatometrischer Titrationen wurde die Protonierung von Säureanionen verfolgt. Die quantitative Auswertung der Titrationskurven erlaubt die genaue Ermittlung der Dissoziationskonstanten mittelstarker Säuren und deren maximalen Reaktionsvolumina. Als Beispiele werden die Protonierungstitrationen von CH₃COONa, HCOONa, BrCH₂COONa, ClCH₂COONa, Cl₂CHCOONa und Cl₃CCOONa mit HCl in wäßriger Lösung bei 20°C ausgewertet.Wit danken der Deutschen Forschungsgemeinschaft für die Unterstützung dieser Arbeit.     

Early stages of particle formation in precipitation reactions-quinacridone and boehmite as generic examples

For many products, such as nanoparticulate systems, particle formation by precipitation is an essential procedural step. To learn more about the processes involved in precipitation, we investigated particle formation during precipitation reactions by means of online and offline methods. As model systems we chose the catalyst boehmite and the organic pigment quinacridone. The reactants were mixed in a mixing device and led into a reaction tube. At the end of the tube, a free jet of the suspension was produced. By varying the length of the reaction tube the time between mixing the reactants and the moment of observation was varied. Thus a time resolution down to 10 ms from the beginning of the reaction was obtained. Small-angle X-ray scattering on the free jet yielded online information about the structural inhomogeneities within the reacting systems. Transmission electron microscopy patterns obtained from quenched samples, which were taken by shooting copper grids through the free jet into liquid nitrogen, provided complementary information about structural features. Immediately after mixture an emulsion-like structure develops indicating that classical nucleation theory does not apply in the present systems. This finding can be explained by assuming instantaneous reaction at the interfaces of the two reactants that meet in the mixing device. From this preliminary state primary particles form with a size in the nanometer range. The observations can be rationalized by considering the underlying hydrodynamics of turbulent mixing of the reactants.     

Automatische S?ulen-Chromatographie von Peptiden im Nanomolma?stab

Zusammenfassung Es werden Methoden zur automatischen Säulen-Chromatographie von Peptiden in Mengen von 10–200 nMol beschrieben. Die Ionenaustausch-Chromatographie erfolgt in 0,1×50 cm-Capillarsäulen an einem Polystyrol-Sulfonsäure-Kationenaustauscher oder an dem Anionenaustauscher QAE-Sephadex. Die Säulen werden mit geeigneten pH- und Salzgradienten mit einer Flußrate von 0,4 ml/h eluiert.Durch den automatisierten Nachweis mit 2,4,6-Trinitrobenzolsulfonsäure werden aus 10–50 nMol analytische Peptidmuster von Proteinen gewonnen. Zur präparativen Chromatographie an den gleichen Säulen werden die Peptide durch direkte Photometrie bei 280/289 nm bzw. bei 220 nm nachgewiesen.Die Entsalzung und weitere Auftrennung erfolgt durch Gelfiltration in 0,4×100 cm-Säulen mit Sephadex G 10-G 25. Als Beispiel wird die Isolierung zweier tryptophanhaltiger Peptide der Phosphoglyceratkinase aus Hefe demonstriert.

---

Automated column chromatography of peptides in the nanomole range

Methods are described for the chromatographic resolution of peptides at the 10–200 nanomole range. Separation is achieved on 0.1×50 cm capillary columns with a sulfonated polystyrene cation-exchanger or with the anion-exchanger QAE-Sephadex. The columns are eluted by suitable gradients of pH and salt at a flowrate of 0.4 ml per hour.By automatic detection with 2,4,6-trinitrobenzene-sulfonic acid peptide elution patterns are produced with 10–50 nanomoles. For preparative chromatography with the same columns, the peptides are detected by monitoring at 280/289 nm resp. 220 nm.The effluent samples from the columns are desalted and further fractionated by gel filtration (Sephadex G 10–G 25) on 0.4×100 cm columns. The isolation of two tryptophane-containing peptides from phosphoglycerate kinase from yeast is demonstrated.

---

---

Diese Veröffentlichung berichtet aus einem Forschungs-programm, das unter der Leitung von Herrn Prof. Dr. Dr. H.C. Th. Bücher mit Unterstützung der Deutschen Forschungsgemeinschaft und des Sonderforschungsbereichs 51 durchgeführt wird.     

The unimolecular dissociation of protonated phenyl ethers formed by chemical ionization

A series of phenyl ethers with cyclic and acyclic olefins has been observed to form proton-bound complexes on protonation under chemical ionization conditions with methane as the reagent gas. The competitive dissociations of these complexes have been studied by ion kinetic energy spectrometry and the measured branching ratios have been correlated with the relative stabilities of the product species.