Enthalpy of formation of americium sesquioxide; systematics of actinide sesquioxide thermochemistry

The enthalpy of formation of hexagonal Am/sub 2/O/sub 3/ at 298.15 K has been determined to be -1690.4 +- 7.9 kj mol/sup -1/ by solution microcalorimetry. Systematic comparison of the measured enthalpies of formation of hexagonal Pu/sub 2/O/sub 3/ and Am/sub 2/O/sub 3/, monoclinic Cm/sub 2/O/sub 3/, and all lanthanide sesquioxides has been utilized to develop a predictive understanding of stability relationships among all actinide sesquioxides and other actinide species

Automatischer Aufbau von Wissensbanken durch Wissensakquisition aus Texten

SIGLETIB: RO 3459(1988,4) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Untersuchung der in Wassergefaehrdungsklassen 0 und 1 eingestuften Stoffe hinsichtlich ihrer Bodengefaehrdung

SIGLEAvailable from TIB Hannover: RN 8908(98-002) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekUmweltbundesamt, Berlin (Germany); Bundesministerium fuer Umwelt, Naturschutz und Reaktorsicherheit, Bonn (Germany)DEGerman

Impact of the ceramide subspecies on the nanostructure of stratum corneum lipids using neutron scattering and molecular dynamics simulations. Part I impact of CER[NS]

For this study mixtures based on the ceramides [NS] NS non hydroxy sphingosine and [AP] AP amp; 945; hy droxy phytosphingosine in a 2 1 and 1 2 ratio, together with cholesterol and lignoceric acid, were investigated. These mixtures are modelling the uppermost skin layer, the stratum corneum. Neutron diffraction, utilizing specifically deuterated ceramide molecules, was used to obtain a maximum amount of experimental detail. Highly detailed molecular dynamics simulations were used to generate even more information from the ex perimental data. It was possible to observe a single lamellar phase for both systems. They had a lamellar repeat distance of 5.43 0.05 nm for the [NS] [AP] 2 1 and a slightly shorter one of 5.34 0.05 nm for the 1 2 system. The structure and water content was uninfluenced by excess humidity. Both the experimental and simulation data indicated slightly tilted ceramides, with their C24 chains overlapping in the lamellar mid plane. This arrange ment is well comparable to systems investigated before. The structure of both systems, except for the differing repeat distance, looks similar at first. However, on a smaller scale there were various distinct differences, de monstrating only low redundancy between the different ceramide species, despite only minor chemical differ ences. The mainly ceramide [AP] determined 1 2 system has a slightly smaller repeat distance. This is a result of a tighter arrangement of the lipids chain along the bilayer normal and increased overlapping of the long chains in the lamellar middle. For the CER[NS] some novel features could be shown, despite it being the overall most investigated ceramide. These include the low adaptability to changed lateral interactions, leading to an in creased chain opening. This effect could explain its low miscibility with other lipids. The investigated model systems allows it to directly compare results from the literature which have used ceramide [NS] to the most recent studies using the phytosphingosine ceramides such as ceramide [AP

Influence of a Novel Dimeric Ceramide Molecule on the Nanostructure and Thermotropic Phase Behavior of a Stratum Corneum Model Mixture

The stratum corneum SC is the outermost layer of the skin and is composed of a multilayered assembly of mostly ceramids Cer , free fatty acids, cholesterol Chol , and cholesterol sulfate Chol S . Because of the tight packing of these lipids, the SC features unique barrier properties defending the skin from environmental influences. Under pathological conditions, where the skin barrier function is compromised, topical application of molecules that rigidify the SC may lead to a restored barrier function. To this end, molecules are required that incorporate into the SC and bring back the original rigidity of the skin barrier. Here, we investigated the influence of a novel dimeric ceramide dim Cer molecule designed to feature a long, rigid hydrocarbon chain ideally suited to forming an orthorhombic lipid phase. The influence of this molecules on the thermotropic phase behavior of a SC mixture consisting of Cer[AP18] 55 wt , cholesterol Chol, 25 wt , steric acid SA, 15 wt , and cholesterol sulfate Chol S, 5 wt was studied using a combination of neutron diffraction and 2H NMR spectroscopy. These methods provide detailed insights into the packing properties of the lipids in the SC model mixture. Dim Cer remains in an all trans state of the membrane spanning lipid chain at all investigated temperatures, but the influence on the phase behavior of the other lipids in the mixture is marginal. Biophysical experiments are complemented by permeability measurements in model membranes and human skin. The latter, however, indicates that dim Cer only partially provides the desired effect on membrane permeability, necessitating further optimization of its structure for medical application