Etude thermometrique de la formation des complexes citriques et tartriques des lanthanides

Thermometric measurements make it possible to detect all citrate and tartrate complexes of lanthanides on only one enthalpogram. A suitable gradient of pH must be chosen in order to allow the successive formation of the complexes.     

An autonomous programmable system for Mössbauer spectroscopy, accessed by a PC program

A low cost, stand alone microprocessed equipment for data acquisition and driver control, designed under the requirements of Mössbauer spectroscopy is described. It has a functional mode as pulse analyzer (PHA) and a second mode as a multichannel analyzer (MCA) while it generates waveforms -- triangular, sawtooth and sinusoidal -- between 2 and 40 Hz, buffered up to a capacity of 750 mA for velocity transducer (DRIVER) management, with PID signal synthesizer and error minimization circuits. Its resolution is variable, between 2 and 1024 channels. The system has CMOS technology of integration, Z-80--74HC, with a 4.9152 MHz crystal time based; its dead time is of 0.61 μs and its minimum dwell time is of 32 μs. Data are continuously kept in memory and can be transferred, under a managing program request, via RS-232c protocol at 9600 BAUD -- to a PC computer for its analysis and display. The program written for a PC is able to distinguish up to 8 different spectrometers by means of an identity number assigned to each unit. Therefore, the serial input may be multiplexed in order to attend all the systems, that can work simultaneously.     

Anticanonical models of ruled surfaces

Summary One investigates the properties of the so-called anticanonical model of a ruled non-rational surfaceX with the anticanonical dimension 2 (see theorem 2 below). In such a way one gets a ?non-rational? analogue of a result of F. Sakai (see [12], and also theorem 1 below). As an application of these two theorems one characterizes the normal projective surfacesY overC with the property that there is a positive integerr such that—rK _Y is an ample Cartier divisor, whereK _y is a canonical (Weil) divisor ofY (see corollary 8 below).

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Riassunto Si studiano i modelli anticanonici delle superficie rigate non-razionali di dimensione anticanonica 2 (teorema 2). Si trova un risultato simile a quello di F. Sakai (teorema 1). Come applicazione si dà una caratterizzazione delle superficie proiettive normaliY sul campoC tali che un multiplo—rK _Y, conr>0, è un divisore di Cartier ampio, doveK _y è un divisore (di Weil) canonico (Corollario 8).

     

Chromones from Licania arianeae (Chrysobalanaceae)

The phytochemical studies of the leaves of Licania arianeae Prance (Crysobalanaceae) have led to the identification of ten new chromones, four 5,7-dihydroxy-2-alkylchromones, four 5,7-dihydroxy-6-chloro-2-alkylchromones and two 5,7-dihydroxy-6,8-dichloro-2-alkylchromones. The structures were established from IR, NMR and FAB-MS spectra data including 2D NMR experiments of natural substances and of the methyl derivatives.     

Thermal properties of ferromagnetic clusters

The magnetic moments and heat capacities of small iron, cobalt and nickel clusters in a molecular beam have been measured as a function of their size and temperature. The magnetic moment of nickel and cobalt clusters decreases with increasing size and with increasing temperature, slowly converging to the bulk magnetization curve as the cluster size increases. Heat capacity measurement of the clusters in the beam reveals that the magnetic contribution to the heat capacity is well approximated using mean field concepts, combined with measured magnetic properties. In contrast, iron clusters show anomalies, both in the magnetic moments as well as in the heat capacities. We speculate that these effects reflect a sensitivity of the magnetic order on structure as in bulk iron.     

Heterodisubstituted ferrocene derivatives; β-lactamic antibiotics

The influence of the ferrocenyl residue on the antimicrobial activity of β-lactamic antibiotics was studied and the reaction conditions fixed for the formation of 1,1′-ferrocenyldicarboxamidopenicillanic (IX) and 1,1′-ferrocenyldicarboxamidocephalosporanic acid (Xa and Xb). The products were characterized as both acids IX and sodium salts X by IR and UV spectra as well as by thin-layer chromatography. The compounds IX and X show antimicrobial activity towards some Gram positive germs.     

17O nuclear magnetic resonance:mutual effect between two β oxygen atoms and α,β double bond effect on 17O chemical shift

Natural abundance ¹⁷ONMR spectra of acetals, ketals and 1,3-dioxolane derivatives have been measured. The mutual effect between oxygen atoms on ¹⁷O chemical shift is studied. The variations are tentatively explained in terms of changes in the conformation of the compounds. The ¹⁷O chemical shifts of unsaturated ethers were also studied. The ¹⁷O deshielding is found to be related to the β carbon shielding.