1,721,089 research outputs found
Synthetic studies on biologically active natural compounds. Part I: Stereospecific transformation of uvidin a into (−)-cinnamodial
No full textREACTIONS OF ACETYLENES WITH NOBLE-METAL CARBONYL HALIDES .8. MULTINUCLEAR NMR-STUDIES ON PLATINUM ALKENYL COMPLEXES
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Synthesis and X-ray powder diffraction characterization of tetra- and hexa-imidazole complexes of magnesium(II)
No full textX-ray powder diffraction data for two ionic salts contg. imidazole (Him) complexes of the magnesium(II) ion, [Mg(Him)4(H2O)2]Cl2 and [Mg(Him)6](NO3)2, are reported. Their crystal and mol. structures were detd. by simulated annealing and full-profile Rietveld refinement methods. [Mg(Him)4(H2O)2]Cl2 was found to crystallize in the monoclinic system with space group C2/c, a=12.3980(3) A, b=11.0234(2) A, c=14.4691(3) A, and =107.024(1). [Mg(Him)6](NO3)2 crystallizes in the trigonal R-3 space group with a=b=12.4631(4) A and c=14.9449(6) A. Both species contain centrosym. complexes, and Mg is octahedrally coordinated by six imidazoles, as in [Mg(Him)6](NO3)2, or by four imidazoles and two water mols., as in [Mg(Him)4(H2O)2]Cl2. Addnl. analytic, thermogravimetric, calorimetric, and spectroscopic characterizations were also performed
Large-scale Integrated Academic Portals
No full textThe increasing availability of fixed/wireless network connectivity and the integration of telecommunication systems and the Internet create novel opportunities for users who can benefit from anytime anywhere access to a growing amount of Internet/Intranet Web information. In particular, university communities clearly perceive the potential benefits of widespread availability of Web-based services, which should satisfy heterogeneous requirements from different classes of users, e.g., students, teachers, administrative and technical staffs.
However, university Web sites are typically populated by autonomous institutions (faculties, departments, research groups, ...) that desire to maintain an independent control over data content. Consequently, data from different sites of the same university are usually organized in different ways, by rarely reflecting a common standard for data presentation, representation, and communication; such a plethora of heterogeneous academic/educational information poses novel management and technological challenges. On the one hand, the lack of a centralized entry point for service delivery and information retrieval creates difficulties for users, forced to browse many links before reaching the desired contents. On the other hand, the lack of a standard for data classification and presentation obstacles service/data integration and interoperability.
The academic community of the University of Bologna, the oldest university in the western world, had to face the above technological and management challenges emerging in large scale organizations. In fact, Bologna university community groups many academic and administrative institutions, willing to share common standards of data presentation/communication even though maintaining their autonomy in data management.
These challenges have been faced by designing and implementing an integrated academic/educational Web Portal (UniBo) (The Web Portal, 2005). The UniBo project focuses on two main goals: first, to impose the University of Bologna as a single entry point for transmitting social-cultural knowledge through novel communication channels, such as fixed and wireless networks; second, to organize and customize the heterogeneous data provided by different institutions to easily satisfy the requirements of various user targets (different views for students, teachers, and administrative staff). In the following, we present the peculiar aspects of the UniBo project, by pointing out the motivations of the technological choices made and the crucial challenges of activity reorganization deriving from developing such a large-scale Web Portal. In particular, the contribution underlines the relevance of implementing an integrated technological platform that not only enables common technological, graphic, and usability standards, but also permits the access to shared application services and to university databases about staff, students, teaching activities, and research projects
Reactions of acetylenes with noble-metal carbonyl halides II. Insertions into the chloro-platinum bond
No full textThe reaction of dichlorodicarbonylplatinum with ROOCCCCOOR (R = CH3, C2H5) in benzene and toluene gives carbonylchloro(1,2-trans-dicarboalkoxy-2-chloroethenyl)platinum compounds by insertion of the active acetylene molecule into the PtCl bond. These chelated stable square-planar vinyl derivatives react with neutral donor ligands to give simple σ-alkenyl derivatives: [Pt(CO)Cl(ROOCCC(Cl)COOR)L] (L = C5H5N, CH3C5H4N), [PtCl(ROOCCC(Cl)COOR)L2] (L = PPh3, PCH3Ph2), and [PtCl(ROOCCC(Cl)COOR)(LL)] (LL = DPE, bipy, Me2bipy). The anionic species [cis-Pt(CO)X2(ROOCCC(Cl)COOR)]- have been isolated as PPN salts by treating the vinyl complexes with Cl-, I- or SCN-. The stereochemistry has been elucidated from spectroscopic data (IR and 1H NMR)
CONFORMATIONAL STUDIES AND STEREOCHEMICAL ASSIGNMENTS OF THE LACTARANE SESQUITERPENES FUROSCROBICULIN-D AND BLENNIN-D
No full textTwo lactarane, sesquiterpenes, furoscrobiculin D and blennin D, previously isolated from the mushrooms Lactarius scrobiculatus and Lactarius blennius, respectively, have been submitted to conformational analysis by molecular mechanics. The results of the molecular modeling were related to the observed 1H NMR data and allowed to assign stereostructure 4 to furoscrobiculin D, correcting the previous assignment 1, and stereostructure 5 to blennin D, confirming the previous assignment
High-yield syntheses of [Rh7(CO)16]3- and [Rh14(CO)25]4- working in ethylene glycol solution under 1atm of CO.
No full textThe anionic rhodium carbonyl clusters [Rh7(CO)16]3- and [Rh14(CO)25]4- can be easily prepd. by a new simple and high yield one-pot synthesis starting from RhCl3nH2O dissolved in ethylene glycol and involving two steps: (i) treatment of RhCl3nH2O under 1 atm of CO at 50 C to give [Rh(CO)2Cl2]-; (ii) addn. of a base (CH3CO2Na or Na2CO3) followed by reductive carbonylation under 1 atm of CO at an adequate temp. (50 C for [Rh7(CO)16]3-; 150 C for [Rh14(CO)25]4-). These new syntheses are more convenient than those previously reported, esp. since such clusters are not accessible via silica surface-mediated reactions. This different behavior is due to the particular stabilization on the silica surface and under 1 atm of CO of an anionic carbonyl cluster, called A, which does not allow the formation of a higher nuclearity carbonyl cluster, called B, which was shown to be the key-intermediate in the synthesis of [Rh14(CO)25]4- working in ethylene glycol soln. Although it was not possible to isolate crystals of A and B suitable for X-ray structural detn., a combination of cyclovoltammetry, one of the few examples so far available of the use of this technique for anionic rhodium carbonyl clusters, IR spectroscopy and elemental analyses suggest that A and B are probably the never reported [Rh7(CO)14]- and [Rh15(CO)28]3- clusters, resp. In particular the tentative formulation of the two clusters was carried out by a non-conventional method based on the existence of a linear correlation between carbonyl frequencies of the main band and the [(charge/Rh atoms)/CO no.] ratio
Reactions of acetylenes with noble-metal carbonyl halides .3. chemical and structural studies of sigma-alkenyl complexes of platinum(II)
No full textThe reaction of [Pt(CO)Cl(ROOCCC(Cl)COOR)] and of the anions [cisPt(CO)Cl2(ROOCCC(Cl)COOR)]- (R = Me or Et) with primary and secondary alcohols (MeOH, EtOH, n-PrOH, i-PrOH, allyl-OH) gives rise to specific alcoholysis of the γ-alkoxy group. The specificity is interpreted in terms of the interaction of the β-carboalkoxy group with platinum. The crystal structure of (PPN)[cis-Pt(CO)Cl2(EtOOCCC(Cl)COOPr-i)] has been solved by X-ray analysis
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