NMR spectroscopic determination of enantiomers via their triphenyltin derivatives: A new application of chiral solvating agents

A method is described for the NMR determination of the enantiomeric composition of chiral carboxylic acids and alcohols using their triphenyltin derivatives together with the chiral solvating agents quinine hydrochloride and phenylethylamine.     

Synthesis of stable analogues of thiamine di- and triphosphate as tools for probing a new phosphorylation pathway

Thiamine (vitamin B1) is an essential nutritional factor metabolized inside the body in its mono-, di-, and triphosphate forms. Although the action of thiamine and thiamine diphosphate have been intensely investigated, many questions remain unanswered and the role of thiamine triphosphate is still especially unknown. To probe recent hypotheses on the implication of thiamine triphosphate in a new phosphorylation pathway involving synaptic proteins, we synthesized a series of thiamine di- and triphosphate analogues that are resistant to both enzymatic and chemical hydrolyses. The key step in the preparation of the title compounds is the coupling of thiamine propyl disulfide with adequately protected methylenebis-phosphonic acid, the corresponding triphosphate analogue, and difluoromethylenebisphosphonic acid.     

What a difference ancillary thienyl makes: unexpected additional stabilization of the diruthenium(III,II) but not the diosmium(III,II) mixed-valent state in tetrazine ligand-bridged complexes

The Ru(2)(III,II) mixed-valent state is strongly stabilized in [(bpy)(2)Ru(mu-bttz)Ru(bpy)(2)](5+) (3(5+), bttz = 3,6-bis(2-thienyl)-1,2,4,5-tetrazine, as evident from lowered oxidation potentials and isolability, a strongly increased comproportionation constant K(c) = 10(16.6), and a high-energy intervalence charge transfer band at 10100 cm(-1). Curiously, no such effects were observed for the diosmium(III,II) analogue, whereas the related systems [(bpy)(2)M(mu-bmptz)M(bpy)(2)](5+), bmptz = 3,6-bis(4-methyl-2-pyridyl)-1,2,4,5-tetrazine, exhibit conventional behavior, i.e., a slightly higher K(c) value of the Os(2)(III,II) analogue. EPR signals were observed at 4 K for 3(5+) but not for the other mixed-valent species, and high-frequency (285 GHz) EPR was employed to study the diruthenium(II) radical complexes 2(3+) and 3(3+).     

Covalent Structures of Phosphorus: A Comprehensive Theoretical Study

Starting from earlier work by Baudler we introduce a chemical heuristic for the systematic deduction and classification of covalent partial structures of phosphorus in polycyclic phosphanes, phosphorus-rich polycyclic phosphides, and allotropes of phosphorus except the black forms. This approach is used to direct ab initio techniques (which also confirm the rules) in the quest for as yet unknown forms of molecular or macromolecular phosphorus. Based on calculated stabilities of systematically generated structural alternatives we rationalize the stabilities of Hittorf's phosphorus and of molecular P₄, confirm the possible existence of at least one other crystalline allotropic form of phosphorus, and provide insight into the probable structure of amorphous red phosphorus. In total, the combined approach of chemical heuristics and large scale ab initio calculations presented in this work supplies a coherent chemical understanding of covalent polyphosphorus structures.     

Tetraalkylammonium bromides in methanol: Small angle neutron scattering and vapor pressure measurements

Vapor pressure measurements and small angle scattering (SANS) experiments are reported and discussed for bispiperidinium (BP) bromide and n-tetrapentylammonium bromide solutions in methanol at 25°C. The BP⁺ ion which may be considered as a tetraalkylammonium (TAA) ion with pairwise connected alkyl chains, is used for the study of the effects due to flexible TAA alkyl chains. SANS intensities are calibrated with the help of the precise osmotic coefficients from the vapor pressure measurements.     

A polycationic dendrimer as noncovalent support for anionic organometallic complexes

Polycationic dendrimer 1 forms a well-defined, stoichiometric assembly with eight anionic metal complexes; this assembly is successfully applied as a Lewis acidic catalyst which performs comparably to the unsupported metal complex.     

Determination of carnitine and acylcarnitines in urine by high-performance liquid chromatography-electrospray ionization ion trap tandem mass spectrometry

A high-performance liquid chromatography-mass spectrometry method has been developed for the simultaneous determination of native carnitine and eight acylcarnitines in urine. The procedure uses a solid-phase extraction on a cation-exchange column and the separation is performed without derivatization within 17 min on a reversed-phase C8 column in the presence of a volatile ion-pairing reagent. The detector was an ion trap mass spectrometer and quantification was carried out in the MS-MS mode. Validation was done for aqueous standards at ranges between 0.75 and 200 micromol/l, depending on the compound. Carnitine was quantified in urine and comparison with a radioenzymatic assay gave a satisfactory correlation (R2 = 0.981). The assay could be successfully applied to the diagnostic of pathological acylcarnitines profile of metabolic disorders in urines of patients suffering from different organic acidurias.     

On a New Formulation of the Real-Time Propagator

The development of theoretical tools for the study of dynamical phenomena of many-particle systems on the quantum level is a fundamental challenge since many decades. A lot of efforts have been invested on Feynman's path integral approach, however, no computationally tractable method for investigating realistic systems could be developed up to now. In this paper we propose an alternative representation of the real-time many-body evolution operator formulated within the framework of the auxiliary field formalism. Our goal is to derive a new auxiliary field functional integral representation, in which the large oscillations of the functional integrand are reduced, in order to render the auxiliary field approach more attractive for real-time computation. This objective is attained using a generalized version of the method of Gaussian equivalent representation of Efimov and Ganbold [Phys. Stat. Sol. 168 (1991) 165], which eliminates the low-order fluctuations of the auxiliary field from the interaction functional.