Polynuclear lanthanide hydroxo complexes: new chemical precursors for coordination polymers.

The synthesis of hexanuclear lanthanide hydroxo complexes by controlled hydrolysis led to polymorphic compounds. The hexanuclear entities crystallize in four different ways that depend on the extent of their hydration. The four structures can be described as hexanuclear lanthanide entities with formula [Ln(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(6)(H(2)O)(12)](2+). Two additional NO(3)(-) ions intercalate between the hexanuclear entities in order to ensure the electroneutrality of the crystal structure. Some crystallization water molecules fill the intermolecular space. The three first families of compounds (1-3) exhibit crystal structures that have previously been reported. The fourth family of compounds (4) is described here for the first time. Its chemical formula is [Ln(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(6)(H(2)O)(12)](NO(3))(2).2H(2)O (Ln = Gd, Er, and Y). In this paper, the chemical and thermal stabilities of the hexanuclear lanthanide compounds are reported together with the magnetic properties of the Gd(III)-containing species. To use these entities as precursors for new materials, the substitution of the nitrato groups by chloride ions has been studied. Two byproduct compounds have so been obtained: The first (compound 5) is a nitrato/chloride hexanuclear compound of chemical formula [Er(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(6)(H(2)O)(12)](NO(3))Cl.2H(2)O. The second one (compound 6) is a polymeric compound in which the hexanuclear entities are linked by an unexpected and original N(2)O(4) bridge. Its chemical formula is [Er(6)(mu(6)-O)(mu(3)-OH)(8)(NO(3))(4)(H(2)O)(11)(OH)(ONONO(2))]Cl(3).2H(2)O. Its crystal structure can be described as the juxtaposition of chainlike molecular motifs. To the best of our knowledge, this is the first example of a coordination polymer synthesized from an isolated polylanthanide hydroxo complex.

HOROPLAN: computer-assisted nurse scheduling using constraint-based programming.

Nurse scheduling is a difficult and time consuming task. The schedule has to determine the day to day shift assignments of each nurse for a specified period of time in a way that satisfies the given requirements as much as possible, taking into account the wishes of nurses as closely as possible. This paper presents a constraint-based, artificial intelligence approach by describing a prototype implementation developed with the Charme language and the first results of its use in the Rouen University Hospital. Horoplan implements a non-cyclical constraint-based scheduling, using some heuristics. Four levels of constraints were defined to give a maximum of flexibility: French level (e.g. number of worked hours in a year), hospital level (e.g. specific day-off), department level (e.g. specific shift) and care unit level (e.g. specific pattern for week-ends). Some constraints must always be verified and can not be overruled and some constraints can be overruled at a certain cost. Rescheduling is possible at any time specially in case of an unscheduled absence.

SETH: an expert system for the management on acute drug poisoning in adults.

The aim of SETH is to give end-users specific advice concerning treatment and monitoring of adult drug poisoning. SETH is developed with an off the shelf expert system shell (KBMS) and runs on a microcomputer. Technical choices were done according to this analysis, financial considerations and portability. Currently, the database contains 1000 French drugs from 75 different toxicological classes. The SETH expert system simulates the expert reasoning, taking into account for each toxicological class delay, signs and dose. Two phases of evaluation were performed. The experimental implementation of Seth began in April 1992 in our Poison Control Centre. Since then, 1100 cases inputted by residents were analysed by SETH. The extension of the knowledge base to child poisoning began in March 1993.

Zonal high-performance affinity chromatography as a tool for protein interaction studies with special reference to the lipase-colipase complex.

The technique of zonal high-performance affinity chromatography applied to the lipase-colipase system (lipase B as eluted acceptor and colipase as silica-bonded ligand) gave qualitatively the same results as conventional affinity chromatography. The elution volume of the acceptor increases with decreasing load introduced at constant volume into the column of ligand-bonded silica. This led to the use of a mathematical treatment for calculating the dissociation constant (KD) of the lipase-colipase complex. The influence of some physical and chemical chromatographic parameters was studied. Increasing temperature and flow-rate reduced the affinity of lipase for colipase, whereas it was only slightly modified by increasing the ionic strength. The KD value was minimal and equal to 0.1 X 10(-6) M at pH 4.7 and 0.38 X 10(-6) M at pH 6.5, after correction for the flow-rate. The latter value is similar to that obtained by more conventional techniques. The absence of some marked KD modifications by ionic strength and the value of delta S for the complex association obtained by temperature studies suggest the intervention of mixed hydrophobic-ionic interactions in the formation of the lipase-colipase complex. Their respective importances are discussed.

Further results on lipase-colipase interactions studied by affinity chromatography.

Affinity chromatography of lipase on a colipase-coupled gel was studied in the present paper. The elution volume of the associable lipase increased when the loaded amount decreased. A KD value of 1.9 X 10(-6) M at pH 6.2 was thus deduced. A minimum value of 1.5 X 10(-6) M was obtained at pH 5.1-5.3. Mixed micelles associated with coupled colipase, but no modifications of lipase-colipase interactions took place when mixed micelles were added to the elution buffer. DMMA-modified coupled colipase failed to interact with lipase, owing to the specific orientation of the modified cofactor in the gel.