Total assignment of the proton and carbon NMR spectra of the alkaloid quindoline — utilization of HMQC-TOCSY to indirectly establish protonated carbon-protonated carbon connectivities

The reisolation of the indoloquinoline alkaloid quindoline (also known as norcryptolepine) from Cryptolepis sanguinolenta is reported. The structure was unequivocally confirmed by two-dimensional nmr methods; the proton and carbon spectra were assigned for the first time. Because of congestion in the proton spectrum HMQC-TOCSY was used as an alternative to the more familiar COSY experiment. In addition to establishing proton-proton connectivities, HMQC-TOCSY affords the added benefit of providing, in an indirect sense, connectivity information between protonated carbons.     

Calculation of the entropy of random coil polymers with the hypothetical scanning Monte Carlo method

Hypothetical scanning Monte Carlo (HSMC) is a method for calculating the absolute entropy S and free energy F from a given MC trajectory developed recently and applied to liquid argon, TIP3P water, and peptides. In this paper HSMC is extended to random coil polymers by applying it to self-avoiding walks on a square lattice--a simple but difficult model due to strong excluded volume interactions. With HSMC the probability of a given chain is obtained as a product of transition probabilities calculated for each bond by MC simulations and a counting formula. This probability is exact in the sense that it is based on all the interactions of the system and the only approximation is due to finite sampling. The method provides rigorous upper and lower bounds for F, which can be obtained from a very small sample and even from a single chain conformation. HSMC is independent of existing techniques and thus constitutes an independent research tool. The HSMC results are compared to those obtained by other methods, and its application to complex lattice chain models is discussed; we emphasize its ability to treat any type of boundary conditions for which a reference state (with known free energy) might be difficult to define for a thermodynamic integration process. Finally, we stress that the capability of HSMC to extract the absolute entropy from a given sample is important for studying relaxation processes, such as protein folding.     

Preparation of crown compounds containing allyloxymethyl or butenyl groups for attachment to silica gel or containing long chain lipophilic groups for use in liquid membrane systems

Several new macrocyclic polyether ligands have been prepared for use in the separation of metal ions from aqueous solutions. Four of the crown ethers reported contain 1,2,4-triazole or 4-pyridone protonionizable subcyclic units and lipophilic groups. The remaining crown ethers are not proton-ionizable but contain alkene groups and were prepared for attachment to silica gel. The crowns were prepared by reacting the appropriate glycols with the appropriate ditosylates or dichloride in the case of the 1,2,4-triazole subcyclic unit. The crowns with proton-ionizable and lipophilic substituents were tested in liquid membrane transport systems and some of the crowns with alloxymethyl or butenyl substituents were attached to silica gel. The log K values for the interaction of these silica gel-bound macrocycles with certain metal ions were nearly the same (± 10%) as those for the association of the unbound macrocycles with the same metal ions.     

Selective determination of iron by fluorescence quenching of a naturally occurring pigment

A fluorescent pigment produced by Pseudomonas fluorescens is isolated and partially characterized. It is verified that the pigment reacts with iron(III) and iron(II0 with respective conditional formation constants of 1.1 × 10²⁴ and 5.3 × 10²³ at pH 8 and that the reaction results in quenching of the pigment fluorescence. The quenching effect permits the measurement of iron with a detection limit of 5 × 10^?9 M (0.3 μg 1^?1). Examination of 21 common constituents in water as potential interferents for the iron measurement indicates that a combination buffer solution can be used to mask those that deleteriously affect the measurement. The general accuracy of the procedure is confirmed with reference water samples.     

Langevin equation for the parametric oscillator: a model for ion confinement in a radio frequency trap

We have calculated 〈x ²〉 and 〈v ²〉 for an ion in a rf trap being cooled by a stochastic force. The results agree with earlier work (using a Fokker-Planck equation) as long as there is white noise. However, there is an appreciable reduction for both quantities, if non-Markovian processes are included.     

Empirical regularities of atomic ionization potentials

Regularities of the averaged ionization potentials for atoms and ions containing up to 18 electrons are studied in detail. It is shown that a two-variable function constructed from the averaged ionization potentials for each subshell is linear with respect to the degree of ionization q and the occupancy k of the s^k or p^k subshell. One linearity includes previous findings as a special case, and the other introduces a new regularity for atomic ionization potentials. Existing atomic ionization potentials and electron affinities are analyzed employing the regularities, and improved values of these quantities as well as term and fine structure separations in negative ions are derived.     

X=Y-ZH systems as potential 1,3-dipoles. Part 61: Metal exchanged zeolites, silver(I) oxide, Ni(II) and Cu(I) complexes as catalysts for 1,3-dipolar cycloaddition reactions of imines generating proline derivatives

A range of regio- and stereo-selective 1,3-dipolar reactions of imines of α-amino esters, generating polysubstituted prolines, catalysed by silver(I) exchanged zeolites or silver(I) supported on titania, both in combination with DBU, are described. The use of a catalytic amount of silver(I) oxide, Ni(II) complexes and cuprous iodide as catalysts for the cycloaddition reactions are also disclosed.     

Über organogermaniumtrisulfinsäureester und versuche zur darstellung von tetrasulfinsäureestern des germaniums

The trisulfinic esters of germanium RGe(O₂SR′)₃ (R = R′ = CH₃; R = C₆H₅, R′ = CH₃, C₂H₅), which are sensitive to hydrolysis and temperature, are obtained by reaction of the corresponding trichlorides RGeCl₃ with anhydrous silver sulfinates. Aromatic trisulfinic esters as well as tetrasulfinic esters of germanium could not be obtained because of steric reasons. The esters, in which the RSO₂^?-residues are linked to germanium via oxygen, are investigated on the basis of their ¹H NMR, mass, IR and Raman spectra.     

Data evaluation in combined gas chromatography—infrared spectroscopy—mass spectrometry

The technique of gas chromatography—infrared spectroscopy—mass spectrometry (g.c./i.r./m.s.) has great potential m qualitative and quantitative analysis. The utility of g.c./i.r./m.s. is presently limited by the lack of methods for reduction of the large amounts of data produced from complex mixtures. Approaches to qualitative and quantitative data evaluation which take into account differences in instrumental configuration are presented.