Structures of two novel monoterpene alkaloid glucosides from Lonicera Xylosteum L.

The structures of loxylostosidine A and B, two new sulfoxide - containing monoterpene alkaloid glucosides, are described.     

Kontinuierliche Konzentrationsbestimmung von Elektrolyten mit Hilfe der Oscillometrie

Zusammenfassung Die Messung der Elektrolytkonzentration in fließenden Lösungen, auch bei solchen, die Niederschläge oder Suspensionen enthalten, wird auf Grund der Veränderung des Dielektrikums einer Zelle, welche von einem elektrischen Hochfrequenzstrom durchflossen wird, durchgeführt. Auf diesem Wege ist die quantitative Bestimmung der Konzentration der gelösten Substanz oder die der durchlaufenden Menge beträchtlich vereinfacht und automatisiert. Dabei werden subjektive und Manipulationsfehler weitgehend ausgeschlossen. Die untersuchte Probe erleidet keinerlei Veränderungen.

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Summary The electrolyte concentration of flowing solutions and of suspensions or solutions containing precipitates can be measured by the variation of the dielectrics in a cell, which is coupled with a high-frequency circuit. By means of this method the quantitative determination of the concentration of solutions or the determination of the quantity of ions passed through the tube can be simplified. The method makes possible an automatization and it precludes the possibility of subjective and manipulation errors. During the measurement the sample remains unchanged.

     

Oligodeoxynucleotide analogues containing 3′-deoxy-3′-C-threo-hydroxymethylthymidine: Synthesis, hybridization properties and enzymatic stability

Novel Oligodeoxynucleotide analogues containing 3′-C-threo-methylene phosphodiester internucleoside linkages were synthesized on automated DNA-synthesizers using the phosphoramidite approach. The sugar modified phosphoramidite building block 5 was obtained by phosphitylation of 1-(2,3-dideoxy-5-O-(4,4′-dimethoxytrityl)-3-C-hydroxymethyl-β-D-threo-pentofuranosyl)thymine (4) which was synthesized in only three steps from 5′-O-(4,4′-dimethoxytrityl)thymidine (1). The hybridization properties and enzymatic stability of the oligonucleotide analogues were studied by UV experiments. 17-Mers having one or three modifications in the middle or two modifications in each end hybridized to DNA with moderate lowered affinity compared to unmodified 17-mers (ΔT_m 1–3°C per modification). Furthermore, the end-modified and all-modified oligonucleotides were stable towards snake venom phosphodiesterase.     

The crystal and molecular structure of the cycloadduct from an activated carbodiimide and methyl isothiocyanate

The crystal and molecular structures of the cycloadduct from isopropyl[α-(dimethylthio-carbamoyl)isopropyl]carbodiimide and methyl isothiocyanate were determined by single-crystal X-ray methods. The product was established to be 2-(1-isopropyl-3,5-dimethyl-4,6-dithioxo-hexahydro-1,3,5-triazine-2-ylidenamino)-N,N-dimethylthioisoburyramide, in which contrary to expectations based on hybridisation the heterocyclic ring adopts a boat conformation.     

Optical sensors for determination of heavy metal ions

A review is given on optical means for single shot testing (probing) as well as continuous monitoring (sensing) of heavy metal ions (HMs). Following an introduction into indicator based approaches, we discuss the types of indicator dyes and polymeric supports used, as well as existing sensing schemes for HMs. The wealth of information is compiled in the form of tables and critically reviewed. Notwithstanding the tremendous work performed so far, it is obvious that still severe limitations do exist in terms of selectivity, limits of detection, dynamic ranges, applicability to specific problems, and reversibility. On the other hand, such sensors have found — and will find — their application whenever rapid and cost-effective testing is required, where personnel is scarce or unskilled, and in field tests. Despite their limitations, the number of such sensors (and of irreversible probes) for HMs is likely to increase in future.     

Dimerer Zimtalkohol

Zusammenfassung Die Stammsubstanzen des Lignins gehören der Gruppe der p-Hydroxyzimtalkohole an. Sie werden durch wäßrige Mineralsäure polymerisiert. Um das Wesen dieser Reaktion kennenzulernen, wurde der Zimtalkohol selbst in verdünnter wäßriger Lösung der Wirkung von Säure ausgesetzt. Er bildet ein Dimeres der Konstitution VIII, die durch Abbau und Synthese bewiesen wurde. Es ist anzynehmen, daß die Polymerisation der p-Hydroxyzimtalkohole nacl, einem Schema verläuft, von dem die Dimerisation des Zimtalkohols die erste Stufe ist.Institut für die Chemie dei Holzes und der PolysaccharideKollegenA. Wacek in alter Freundschaft zum 60. Geburtstag gewidmet.K. Freudenberg.     

(Eta3-phenylallyl)(phosphanyloxazoline)palladium complexes: X-ray crystallographic studies,NMR investigations,and Ab initio/DFT calculations

All possible (eta(3)-allyl)palladium complexes (1-4) of the ligand (4S)-[2-(2'-diphenylphosphanyl)phenyl]-4,5-dihydro-4-(2-propyl)-oxazole (L 1) and eta(3)-allyl ligands with one to three phenyl substituents at the terminal allylic centers were synthesized and characterized by X-ray crystal structure analysis and, with respect to allylic isomers, by NMR investigations. Equilibrium geometries, electronic structures, and relative energies of isomeric complexes were computed by restricted Hartree-Fock (RHF) and density functional theory (DFT) calculations; experimentally determined isomer ratios could be reproduced. The results allowed important conclusions to be drawn regarding the mechanism of Pd-catalyzed asymmetric allylic substitutions.     

Quantum field theoretical methods in chemically bonded systems II

Summary Many-body perturbation theory is derived for chemical bonds. Paired quasiparticles represent the bonds. Products of the paired quasiparticles define a model Bardeen-Cooper-Schrieffer function. The pairing force is added as a model interaction to the self-consistent problem. The starting model is based on valency and adiabatic symmetry correlation. Symmetries are enforced by the model Hamiltonian. Perturbative corrections are expressed as ordinary Feynman diagrams. The number of diagrams needed is the same as for particle-hole theory.This work was supported in part by the U.S. Department of the Navy, Space and Naval Warfare Systems Command under Contract N00039-89-C-0001, and in part by NATO Research Grant 1861. It was presented, in part, at the A.C. Wahl Memorial Session, Molecular Spectroscopy Symposium, Columbus, Ohio, 1984; and Midwest Theoretical Chemistry Conference, Milwaukee, Wisconsin, 1985.     

Über das Anwachsen der Lösungen linearer Differentialgleichungen mit rationalen Koeffizienten in Winkelräumen

Let z=∞ be the only irregular singular point of the linear differential equation $$(D)w^{(n)} + P_{n - 1} (z)w^{(n - 1)} + \cdots + P_o (z)w = 0$$ with rational coefficients p_j(z). If w is a multivalent and irregular solution of (D), we define the index I(τr,W), τ ∈ (0,1), of a branch W of w in the plane cut along a half ray. If r→∞, I(τr,W) possesses a finite number of aymptotic directions being exactly the asymptotic directions of the points z with maximal possible modulus of W(z). It follows that each branch W is of mean type σ(W)=|d|/λ in each sector containing an asymptotic direction of I. The possible values of the order of growth λ=λ(W)<∞ and the constant d are given by the PUISEUX-diagram of (D).     

Conformations of the ten-membered ring in 5,10-secosteroids I. X-ray and NMR. Analysis of (E)-3 β-hydroxy-5,10-seco-1(10)-cholesten-5-one esters

X-ray structure determination of the p-bromobenzoate 2b of one of the (E/Z)-isomeric 3β-hydroxy-5,10-seco-1(10)-cholesten-5-ones confirmed the (E)-configuration proposed previously and showed the cyclodecenone ring to adopt an extended crown conformation of type A ₁ (Fig. 9). Analysis of the ¹H- and ¹³C-NMR. spectra of acetate 2a revealed that in solution the ten-membered ring of this steroid exists in at least two distinct forms, the predominant (about 85%) corresponding to the solid-state conformation of 2b (= A ₁), and the minor most likely to B ₂ (Fig. 9). From NMR. data the energy difference between the two species and the relevant activation energy were estimated. A number of conformational force field calculations using a simplified partial structural model was performed; but the computed energy differences between the various possible conformations do not reproduce the effective situation, neither in solution nor in the crystal lattice, indicating that additional effects such as the transannular interaction of the double bond with the carbonyl group may strongly influence the thermodynamic stability of the system. The conformations deduced were used to rationalize the stereochemical course of different chemical reactions of 2a .