A World Wide Web-service to aid the development of AMBER parameters using analogy to standard parameters.

A World-Wide Web service has been constructed to assist the development of force field parameters extending the AMBER force fields. This service extracts parameters from the standard AMBER force field parameter databases. From a Web-based interface the user can choose between bond, angle and torsional parameters with certain constraints on element and/or atom hybridization. The software constructed for the purpose of finding appropriate parameters will locate standard AMBER force field parameters matching the user specification. For bond and angle parameters a scatter plot of the reference values against force constants is provided. This service has been produced to assist in extraction and evaluation of parameters that may be useful for molecules other than proteins and nucleic acids.     

T2-weighted breathold imaging of the liver: a quantitative and qualitative comparison of fast spin echo and half Fourier single shot fast spin echo imaging

The imaging characteristics of two EPI-hybrid breath-hold sequences, T2-weighted fast spin-echo [FSE, effective echo time (TE_eff) 138ms] and half Fourier single shot turbo spin-echo (HASTE, TE_eff 60 ms), were compared in hepatic imaging. A total of 111 patients with suspected hepatic disease were studied at 1.5 Tesla using a body phase-array coil. The signal-to-noise (S/N) and contrast-to-noise (C/N) ratios for organs and lesions were calculated and quantitatively compared. Organ delineation, visualization of anatomical structures and pathological lesions, artifacts, and total image quality were qualitatively assessed and statistically compared. The final diagnoses were metastases from colorectal, breast, and pancreatic cancer in 23/111, hepatocellular carcinoma in 15/111, cysts in 19/111, hemangiomas in 9/111, several other lesions in 7/111, and no lesions in 38/111 of the cases. A total of 139 lesion in 73% of the patients were seen while 85% of the lesions were at least 1.5 cm in size. Regarding S/Ns HASTE was significantly (P<0.03) superior to FSE with only minor (P>0.05) differences in C/Ns between the two sequences for anatomical and pathological structures. HASTE demonstrated in almost all (97.3%) of the cases no artifacts, while on fast SE imaging moderate to minor artifacts were present in 23.5–51.7% of the cases. The overall image quality and diagnostic confidence was rated significantly higher (good 43.2%, excellent 53.2%) for HASTE than for fast SE imaging (good 44.8%, excellent 17.6%). Providing comparable C/Ns for anatomical and pathological structures, breatheld HASTE imaging proved to be superior to fast SE in T2-weighted imaging of the upper abdomen regarding general image quality, and, with adequate technical prerequisites, may be a suitable substitute of fast T2-imaging techniques.     

Reliability and interruption cost prediction using time-dependent failure rates and interruption costs

The main idea presented and discussed in this paper is a model reproducing a time-dependent component failure rate pattern similar to the observed pattern recorded in failure statistics. This pattern includes all types of failures, caused by the weather or by technical and human aspects. Failure causes and mechanisms are not modelled explicitly and the observed pattern is assumed to be representative for the analysis period ahead. Being able to predict and time-tag component failures, the time-dependent variables of load, repair time and customer-specific interruption costs can be adequately combined to calculate annual reliability indices and interruption costs. This fact also permits us to apply an analytical model which will produce expectation values comparable with average values in a Monte Carlo simulation. © 1998 John Wiley & Sons, Ltd.     

Einfluß der Faserbehandlung auf das Feuchteverhalten von glasfaserverstärkten Epoxidharzen

The strength of glass fiber reinforced epoxy resins can be significantly reduced under exposure to moisture. Besides other factors, the interface between fiber and matrix plays an important role. It is responsible for a proper load transfer between fibers and matrix by coupling effects and significantly affects the moisture behavior of the composite. In the present study, glass fibers were treated with different sizes under defined conditions and embedded in three epoxy matrix systems. The composites were exposed to different moisture conditions. The change of the shear and impact behavior due to moisture was determined. It will be shown that the composites with coupling agent treated fibers are significantly more resistant to moisture than composites with poor fiber/matrix adhesion. Furthermore, it will be shown that also the binder plays an important role if the material is subjected to moisture.     

Iminiumsalze in quantitativen Gas/Festköper- und Festkörper/Festkörper-Reaktionen

Iminium Salts in Quantitative Gas/Solid and Solid/Solid Reactions Iminium salts that are highly susceptible to hydrolysis are quantitatively prepared and reacted in the solid state without solvents or liquid phases. Atomic force microscopy AFM helps in elucidating the mechanism of these still unusual gas-solid and solid-solid syntheses by recording surface topographies of reacting crystals of L-histidine (10) and triphenylverdazyl (15) . Various imines add gaseous HCl or HBr to form stable iminium halides (1, 3, 4, 5, 11) even if frozen liquids of very weak heterocyclic bases are treated at low temperatures. Another way for quantitative yields of iminium salt hydrates (6) starts with solid primary ammonium halides and gaseous acetone. o-Phenylenediamines (7) give quantitatively 1,5-benzodiazepines (9) by solid state cyclization of bis-iminium salt intermediates (8) . Crystalline nitroxyls (12) and triphenylverdazyl (15) undergo stoichiometric one-electron transfer with gaseous NO₂ or XeF₂ to give nitrosonium (14) and azonium salts (17) . The solid state chlorination of tetramethylthiuramdisulfide (18) or dimethylthiocarbamoylchloride (20) yields phosgene dimethyliminiumchloride (Viehe salt 21 ) in quantitative yield. Solid Viehe salt is quantitatively treated with gaseous Cl₂ to give the trichloride 19 and solid SbCl₅ or PCl₅ to produce the hexachloroantimoniates (22) , -phosphates (23) . Solid brenzcatechol (24) , mercaptobenzimidazole (27) , p-nitroaniline (30) , N-methylbenzothiazolone-2-hydrazone (34) and acetophenone (41) are treated with 21 to give the corresponding chloroiminium salts (25, 28, 31, 35, 43) . p-Toluenesulfonamide (37) and 22 give the chloroiminium salt 38 . These quantitative solid-solid reactions are most easily run in ball mills with cooling device. The “waste-free” techniques achieve exclusion of moisture in an elegant way. The preparative use of the versatile products with nucleophiles is indicated. The three-step solid-state mechanisms are discussed.     

Asymmetric Hydrogenation of Amino Acid Precursors promoted by a new type of cholesterol amphiphiles: Investigation of aggregation behaviour and stereoselective effects

Reaction of 2-hydroxyethanesulfonic acid sodium salt, 3-hydroxypropanesulfonic acid sodium salt or 2-aminoethanesulfonic acid sodium salt with cholest-5-en-3β-ol-3-chloroformate yields the chiral amphiphilic compounds 2-(cholest-5-en-3β)oxy-carbonyloxy-ethanesulfonic acid sodium salt 1 , 2-(cholest-5-en-3β)oxy-carbonyloxy-propanesulfonic acid sodium salt 2 and 2-(cholest-5-en-3β)oxy-carbonylaminoethanesulfonic acid sodium salt 3 , respectively. Another chiral amphiphile 2-(cholest-5-en-3β)oxy-carbonylethanesulfonic acid sodium salt 4 was synthesized by treating cholest-5-en-3β-ol with sulfopropionic acid anhydride. The surfactants form vesicles in aqueous solutions, as shown by electron microscopy. Stepwise destruction of these vesicles by addition of ethanol or methanol was proved by Circular Dichroism (CD) measurements. Especially compound 3 shows pronounced induced CD effects with the achiral dye 3,6-diamino-acridine-sulfate (proflavine). The synthesized chiral amphiphiles were used in the asymmetric hydrogenation reaction of methyl (Z)-α-acetamidocinnamate. In the case of an achiral rhodium complex as catalyst the prepared surfactants 1, 2 , and 4 are able to provide an enantiomer excess by themselves. The best ee-value reached was 8.5% methyl (R)-N-acetylphenyl-alaninate in connection with compound 4 .