Andreas Dölle

Molecular structure, reorientational dynamics, and intermolecular interactions in the neat ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate

Results on the molecular and liquid structure and the reorientational dynamics are reported for the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]). In quantum-chemical calculations for [BMIM][PF6] in the gas phase, hydrogen bonding between the proton at carbon 2 in the aromatic ring and the fluorine atoms of the hexafluorophosphate anion was found. From the analysis of 13C relaxation data, the reorientational motions were evaluated, and the Vogel-Fulcher-Tammann and Arrhenius activation energies for the overall and internal reorientational motions, respectively, of the different 13C-1H vectors are given as well as correlation times at 300 K. By performing molecular dynamics (MD) simulations, pair distribution functions between moieties in the cation and the phosphorous atom in the anion were determined. The pair distribution function for the proton at carbon 2 exhibits a particular sharp and strong maximum indicating a strong interaction with the anion. The quantum-chemical calculations, the motional parameters, and the results from the MD simulations support the existence of hydrogen bonding and the formation of ion pairs in the ionic liquid.

N-2-(Azol-1(2)-yl)ethyliminodiacetic acids: a novel series of Gd(III) chelators as T2 relaxation agents for magnetic resonance imaging

The synthesis, physicochemical properties, and toxicological implications of a novel series of N-2-(azol-1(2)-yl)ethyliminodiacetic acids, useful as contrast agents for magnetic resonance imaging are reported. Compounds were prepared by alkylation of methyl iminodiacetate with N-2-bromoethylazoles and subsequent hydrolysis. Stability constants of the corresponding Gd(III) complexes and T1 and T2 relaxivities were determined and interpreted in terms of optimized geometries obtained by semiempirical PM3 calculations. Compounds show increased T2 relaxivity and decreased toxicity in vitro as compared to EDTA-Gd(III) complexes.

Metabolism of D‐ and L‐[13C]alanine in rat liver detected by 1H and 13C NMR spectroscopy in vivo and in vitro

Alanine is the major amino acid utilized by the liver for gluconeogenesis under normal conditions. The metabolism of alanine in rat liver was investigated by means of 1H and 13C NMR spectroscopic studies in vivo and in vitro after infusion of L‐ and D‐alanine labelled with 13C at the carboxyl and methyl group into normal, fasted rats. Valuable information about different metabolic pathways of alanine in rat liver and their regulation under the conditions of gluconeogenesis were obtained. The enrichment of the alanine pool by the infusate was estimated to be 11% for L‐alanine and 70% for D‐alanine. After infusion of labelled D‐alanines, the metabolic pathway via D‐amino acid oxidase was observed. The labelled alanines entered the tricarboxylic acid cycle mainly via pyruvate carboxylase; the ratio of pyruvate dehydrogenase activity to that of pyruvate carboxylase is about 28%. The ratio of flux from phosphoenolpyruvate (PEP) through phosphoenolpyruvate kinase as compared with the flux from PEP to glucose was approximately 42%. From the labelling pattern of glucose it was concluded that the pentose phosphate cycle was active under the experimental conditions.

Reduction of the isolated double bond in bis(N-alkenylbenzimidazole)Pd(II) complexes with KBH4

Abstract Palladium(II)-promoted vicinal diamination of N -alkenylbenzimidazoles has been investigated. Dichlorobis(1-(alkenyl)benzimidazole)palladium(II) complexes were identified as initial reaction products which proved to be rather inert to the subsequent oxidative diamination required in the process. Instead, they were readily reduced by KBH 4 to give the corresponding 1-alkylbenzazoles as the main reaction products. The crystal structure of the isolated complex trans -dichlorobis(1-(3-butenyl)benzimidazole)palladium(II) was determined by X-ray diffraction analysis.

Molecular dynamics of hydantoins and barbiturates assessed by 1H, 13C and 15N relaxation data

The molecular dynamics of hydantoin,5,5-dimethylhydantoin,5,5-diphenylhydantoin, barbituric acid and 5-ethyl-5-phenylbarbituric acid in solution are determined to investigate the molecular basis for the activity of these neuroactive drugs. From dipolar 13C and 15N spin-lattice relaxation times the correlation times for the rotational dynamics of specific bond vectors are evaluated. Conclusions can be drawn concerning the anisotropy of the overall molecular rotational motion and the internal rotations of molecular segments. The translational molecular diffusion coefficients are obtained from self diffusion measurements by the pulsed gradients method. The observed differences in the dynamics as well as structural differences may account for the variation in the neuroactivity of the studied compounds.

Structure, Molecular Dynamics, and Host-Guest Inter-Actions of a Water-Soluble Calix[4]Arene

The influence of host-guest interactions between water-soluble p-sulfonatocalix[4] arene and various tetraalkylammonium cations on the molecular reorientational motions was studied in aqueous solutions by measurement of 13C and 14N NMR relaxation data.