A new look at rotational and vibrational excitation in the scattering of Li+ from N2 and CO at energies between 4 and 17 eV

New experimental time-of-flight distributions are reported for Li⁺-N₂ and Li²-CO at two center-of-mass energies of about 8 and 16 eV and large scattering angles θ_lab ? 120°. The Li⁺-N₂ spectra show two widely spaced maxima, whereas the Li⁺-CO spectra show two and sometimes three maxima. The results are consistent with the model of rotational rainbows, and have also been analyzed in terms of an impulsive model involving collisions with the individual atoms of the molecules with energy-dependent masses. Classical trajectories for a simple model potential reveal only small contributions from vibrational excitation.     

An examination of some active organometallic substances for ion-selective electrodes

Examinations of a number of possible electroactive substances for use in both liquid membrane and solid-state ion-selective electrodes were carried out. Liquid membrane electrodes incorporating organometallic salts of lead and thallium were considered as constituents of sulphate, chromate, carbonate and nitrate responsive sensors. No practically useful device was, however, found. Several electrically semiconducting metal-phthalocyanines, metal-tetracyanoethylene (TCNE) polymers and metal-coordination polymers were also synthesized and investigated with solid-state electrode constructional techniques. Metal-phthalocyanine electrodes were found to be responsive to anions rather than to cations and some anion selectivity was observed. Metal-TCNE polymer electrodes showed response to metal ions identical with those contained in the polymer, and some good selectivities, operational activity ranges and response times were found. Electrodes made from coordination polymers incorporating copper showed a limited response to copper ions whilst inclusion of cadmium and iron(III) in the polymer matrix produced an electrode with anion reponse and slight anion selectivity.     

PENETRATION POTENCY OF TOPICAL APPLIED δ-AMINOLEVULINIC ACID FOR PHOTODYNAMIC THERAPY OF BASAL CELL CARCINOMA *

Abstract Penetration potency of δ-aminolevulinic acid (ALA) was studied by examining fluorescence of endogenous protoporphyrin IX in different histological types of basal cell carcinoma. Ten basal cell carcinomas were coated with an ointment containing 10% ALA prior to excision; five served as controls. Tumors were excised either 4 h or 12 h after application of ALA using a modified Mohs’micrographic surgical technique. Horizontal sections were cut from deep dermis to tumor surface and examined under a fluorescence microscope. After 4 h of application, only skin appendages demonstrated fluorescence typical of protoporphyrin IX. After 12 h, fluorescence was detectable in tumor cells in deep dermis. The five controls revealed no fluorescence at any site. These results may confirm the high penetration potential of topically applied ALA and its usefulness in photodynamic therapy. For tumors penetrating to deep dermis, an application time of more than 4 h seems necessary, at least when hydrophilic solvents for ALA are used.     

Electronic effects steer the mechanism of asymmetric hydrogenations of unfunctionalized aryl-substituted alkenes

Density functional theory (PBE and B3LYP) was used to study asymmetric hydrogenations of alkenes catalyzed by an iridium imidazolylidine oxazoline complex. The calculation predicts that the alkene preferentially coordinates to the site trans to the carbene. The coordinated alkene then reacts first with the H2 ligand, then with the hydride to form alkane. Finally, the alkane is released by equilibrating with extrinsic H2 and alkene. Enantioface selectivities for hydrogenations of trisubstituted alkenes seem to be driven primarily by steric interactions with the adamantyl part of the ligand; only the smallest substituents can adopt a site close to it. Application of this theoretical model leads to correct predictions regarding the experimentally observed sense and magnitude of the enantioselectivities.     

A convenient protocol for selective cleavage of 2-hydroxy acid amides. Application to semisynthesis of the cyclic heptapeptide aza HUN-7293

A two-step protocol for the first chemoselective cleavage of 2-hydroxy acid amides has been developed. Mesylation of the model substrate 2-(hydroxypropionylamino)-4-methylpentanoic acid methyl ester (11) followed by treatment with N-ethylthiourea (13) allows cleavage of 2-hydroxy acid amides under smooth conditions. Successful application of this methodology to the open-chain transesterification product 15 (methylester) of the cyclic heptadepsipeptide HUN-7293, a potent inhibitor of inducible cell adhesion molecule expression, delivered the corresponding hexapeptide 18 with unprotected N-terminus in 70-75% yield. This result demonstrates that the protocol developed even works in the presence of an ester and several methylated and unmethylated amide bonds. Finally, a sequence of ligation of methyl D-dehydroglutaminate (20) to the C-terminus of the saponification product 21, followed by the degradation protocol and ring closure, allowed chemical "point mutation" at the DGCN site affording the aza analogue of HUN-7293 (24) in 15% overall yield. To the best of our knowledge this is the first report on chemoselective cleavage of 2-hydroxy acid amides.     

Synthesis and cross-coupling reactions of substituted 5-triflyloxyindoles

N-arylsulfonyl quinone monoimines undergo smooth cycloadditions in a [4+2] sense to yield the expected cycloadducts. The crude cycloadducts, when subjected to a short series of simple transformations, produce synthetically useful quantities of 5-triflyloxyindoles in excellent overall yields. Such compounds are excellent participants in cross-coupling chemistry.     

Rhodium-catalyzed reductive aldol reactions using aldehydes as the stoichiometric reductants

Chelated acyl rhodium hydrides, generated from the addition of [Rh(dppe)]ClO4 to beta-sulfide-substituted aldehydes, can function as the stoichiometric reductants in reductive aldol processes. Unsaturated nitriles, esters, and ketones can be used as enolate equivalents, and a variety of simple alpha- and beta-substituted aldehydes can be employed. The use of a second, more electrophilic, aldehyde allows three-component reactions to be performed.     

A recycling technique for the chromatographic separation of enantiomers and diastereomers on triacetylcellulose

A simple and inexpensive equipment for the optical resolution of enantiomers (and separation of diastereomers) on triacetylcellulose in ethanol at elevated pressure is described. It involves a closed circuit of solvent (pump—column—detector—pump) allowing a continuous chromatography up to 16 cycles without stopping the flow or handling fractions.This useful and versatile method permitting also the determination of enantiomeric purities is illustrated by several examples of centro-, axial- and planarchiral arenes and metallocenes.Herrn Prof. Dr.U. Schmidt, Stuttgart, zum 60. Geburtstag gewidmet.     

Fluordiazadiphosphetidine, 3. Mitt.: Die thermische Behandlung von 2,2,2,4,4,4-Hexafluoro-1,3-dimethyl-1,3,2,4-diazadiphosphetidin unter Druck in Gegenwart von Phosphor(V)fluorid und Alkalimetallfluoriden

Prolonged heating of (CH₃NPF₃)₂ in a sealed tube at 120°C yields (CH₃N)₄P₃F₇ and PF₅. Under the experimental conditions these compounds react to (CH₃N)₄P₃F₆ ⁺PF₆ ^–. Reaction of (CH₃NPF₃)₂ in the presence of PF₅ leads to a marked decrease in the formation of the ionic compound. The influence of the fluoride donating saltsMF (M=Li, Na, K, Cs) is investigated.

---

---

Mit 1 Abbildung

---

Früher: Alkyliminophosphorsäuretrihalogenide, 1. und 2. Mitt.     

Analysis of cyanobacterial toxins by hydrophilic interaction liquid chromatography-mass spectrometry

The combination of hydrophilic interaction liquid chromatography with electrospray mass spectrometry (HILIC-MS) has been investigated as a tool for the analysis of assorted toxins produced by cyanobacteria. Toxins examined included saxitoxin and its various analogues (1-18), anatoxin-a (ATX-a, 19), cylindrospermopsin (CYN, 20), deoxycylindrospermopsin (doCYN, 21), and microcystins-LR (22) and -RR (23). The saxitoxins could be unequivocally detected in one isocratic analysis using a TSK gel Amide-80 column eluted with 65% B, where eluent A is water and B is a 95% acetonitrile/water solution, both containing 2.0 mM ammonium formate and 3.6 mM formic acid. The analysis of ATX-a, CYN and doCYN required 75% B isocratic. Simultaneous determination of 1-21 was also possible by using gradient elution. HILIC proved to be suitable for the analysis of microcystins, but peak shape was not symmetric and it was concluded that these compounds are best analysed using existing reversed-phase methods. The HILIC-MS method was applied to the analysis of field and cultured samples of Anabaena circinalis and Cylindrospermopsis raciborskii. In general, the method proved quite robust with similar results obtained in two different laboratories using different instrumentation.