Röntgen-Kontrastmittel. 16. Mitteilung. Derivate von jodierten Benzoylamino-phenyl- und Benzoylamino-phenoxy-alkansäuren

A number of new [(3-amino-2,4,6-triiodo-benzoylamino)-phenyl- and -phenoxy]-alkanoic acids have been synthesized for evaluation as X-ray contrast agents. The toxicity, the bilitropism, and the urotropism of these compounds were determined.     

Structure and phase transitions of alkyl chains on mica

We use molecular dynamics as a tool to understand the structure and phase transitions [Osman, M. A.; et al. J. Phys. Chem. B 2000, 104, 4433-4439. Osman, M. A.; et al. J. Phys. Chem. B 2002, 106, 653-662] in alkylammonium micas. The consistent force field 91 is extended for accurate simulation of mica and related minerals. We investigate mica sheets with 12 octadecyltrimethylammonium (C(18)) ions or 12 dioctadecyldimethylammonium (2C(18)) ions, respectively, as single and layered structures at different temperatures with periodicity in the xy plane by NVT dynamics. The alkylammonium ions reside preferably above the cavities in the mica surface with an aluminum-rich boundary. The nitrogen atoms are 380-390 pm away from the superficial silicon-aluminum plane. With increasing temperature, rearrangements of C(18) ions on the mica surface are found, while 2C(18) ions remain tethered due to geometric restraints. We present basal-plane spacings in the duplicate structures, tilt angles of the alkyl chains, and gauche-trans ratios to analyze the chain conformation. Agreement with experimental data, where available, is quantitative. In C(18)-mica with less than 100% alkali-ion exchange, the disordered C(18) rods in the island structures [Hayes, W. A.; Schwartz, D. K. Langmuir 1998, 14, 5913-5917] break at 40 degrees C. At 60 degrees C, the headgroups of the C(18) alkyl chains rearrange on the mica surface, and the broken chain backbones assume a coillike structure. The C(18)-mica obtained on fast cooling of this phase is metastable due to slow reverse rearrangements of the headgroups. In 2C(18)-mica with 70-80% ion exchange, the alkali ions are interspersed between the alkyl chains, corresponding to a single phase on the surface. The observed phase transition at approximately 53 degrees C involves an increase of chain disorder (partial melting) of the 2C(18) ions without significant rearrangements on the mica surface. We propose a geometric parameter lambda for the saturation of the surface with alkyl chains, which determines the preferred self-assembly pattern, that is, islands, intermediate, or continuous. lambda allows the calculation of tilt angles in continuous layers on mica or other surfaces. The thermal decomposition seems to be a Hofmann elimination with mica as a base-template.     

An integral probe for capillary zone electrophoresis/continuous-flow fast atom bombardment mass spectrometry

An integral probe for capillary zone electrophoresis/continuous-flow fast atom bombardment mass spectrometry was constructed and operated in either the coaxial or liquid-junction interface mode. Results using these interfaces for the analyses of synthetic peptides are presented. The coaxial arrangement attains the best electrophoretic performance, generally providing a greater number of theoretical plates. However, in that the electrophoresis times are generally greater for the liquid-junction interface because there is no mechanical flow resulting from the source vacuum, the overall separation efficiency of the liquid-junction interface is equal to or greater than that of the coaxial interface. In addition, the liquid-junction interface is easier to set up and operate, and allows larger inner diameter capillaries to be used to achieve higher sample loads.     

Syntheses and X-Ray Structures for Model Compounds of a Pyrimidinediyl-Based Rigid-Rod Aromatic Polyamide

A variety of model compounds for the pyrimidinediyl-based rigid-rod polyamide poly[imino-(pyrimidine-2,5-diyl)-imino-tetraphthaloyl] (PPYMT) was prepared, in order to compare their conformations to several model compounds of the related, fully aromatic polymer poly(p-phenyleneterephthalamide) (PPTA). In particular, the structures of N-(2-pyrimidyl)benzamide (PYMB) and its complexed form bis[(N-pyrimidin-2-yl)benzamide]nickel(II) dichloride (NiPYMB) were determined by X-ray diffraction. The molecular packing in these crystals provides us with a model for the possible ‘cross-linking’ of PPYMT fibers. The structures of the trimer model compounds N,N′ -bis(2-pyrimidyl)terephthalamide (PYTA) and N,N′ -bis(benzoyl)-2,5-diaminopyrimidine (BDAP) yield information about the conformation of PPYMT chains and are compared to analogous model compounds of PPTA.     

Relationship between Molecular Properties and Conformation of Chiral Alkanes

Mixtures of the diastereomers of 2,2,3,5,6-pentamethylheptane were prepared in two ways, either starting with compounds of (3R)-configuration, or from compounds of (5R)-configuration. Comparison of the GC. and optical rotatory power of the fractions of these two mixtures permitted the unambiguous assignment of the absolute configuration and molar rotatory power to the various diastereomers ([M] = + 119.1° for the (3R, 5R)- and [M] = + 79.8° for the (3R, 5S)-diastereomer). The very high molar rotatory power which was expected on the basis of the conformational analysis carried out with a rotational-isomeric-3-states model is interpreted as arising from the molecular ‘conformational rigidity’, i.e. from the presence of only few conformers. Conformational properties of these compounds were computed using a new approach, which scans the whole space of each bond (2 π) in 5° steps and calculates the conformational energy based upon semiempirical potential functions. The conformational flexibility of each bond of the two diastereomers is evaluated in terms of the a priori probability density function of that bond. This allows us to analyze in detail how configurational differences affect conformational properties. The molar rotatory power of the two diastereomers as calculated with a new method recently developed in our group is in excellent agreement with experimental data. The molar rotatory power is analyzed in terms of the contribution of the single bonds.     

Synthesis and structure of UO2I2(OH2)2 x 4Et2O: first structurally characterized U(VI)-I bond and lightest missing member of the UO2X2 (X = halide) series

UO2I2(OH2)2.4Et2O has been synthesized and structurally characterized using X-ray diffraction. This thermally unstable species is the lightest missing member of the dioxouranium dihalide (UO2X2, X = F, Cl, Br, I)-containing series to be structurally characterized and is, to our knowledge, the first structurally characterized compound containing a U(VI)-I bond.