Synthesis and Structure of [4.5.5.5]Fenestranes ( = tetracyclo[5.4.1.04, 12.09, 12]dodecanes)

The preparation and the X-ray structure analysis of cis, trans, cis, cis-10-hydroxy-[4.5.5.5]fenestrane-1-methanol ( 8b ) is reported. The measured bond angles and bond lengths of the central C(C)₄ fragment are better reproduced by calculations with the AM 1 than by the MNDO method.     

Ab initio calculations on small hydrides including electron correlation

A method of calculating directly approximate natural orbitals in the electron pair approximation is applied to the ground state of the BeH₂ molecule, which is not known from experiment. The question of optimum localization of the electron pairs for asymmetric nuclear configuration receives particular attention. The interpair correlation energy is estimated. The physical properties of the molecule are predicted and experimental conditions are indicated under which it should be observed.

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Zusammenfassung Die Methode zur direkten Berechnung genäherter natürlicher Orbitale in der Elektronenpaar-näherung wird auf den Grundzustand des vom Experiment her unbekannten BeH₂-Moleküls angewandt. Die Frage der optimalen Lokalisierung der Elektronenpaare für asymmetrische Anordnung der Kerne findet besonderes Interesse. Die Interpaar-Korrelationsenergie wird abgeschätzt. Die vorausgesagten physikalischen Eigenschaften dieses Moleküls sind in einer Tabelle zusammengestellt. Bedingungen, unter denen das Molekül experimentell beobachtet werden sollte, werden angegeben.

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Résumé La méthode basée sur le calcul direct des orbitales naturelles approchées est appliquée á l'étude de l'état fondamental de la molécule BeH₂ qui est inconnu du point de vue expérimental. La question de la localisation optimale des paires d'électrons pour des configurations asymmétriques des noyaux est discutée en détail. La corrélation interpaires est estimée. On prédit les propriétés physiques de la molécule et on indique les conditions qui devraient permettre de l'observer.

     

Synthesis and Structure of Functionalized Cyclododecadiynes and -dienes

The cyclododecadiynes 3b–d, 8b–d , and 10b–c with functionalities in two propargylic positions, as well as the monofunctionalized diyne 13b have been prepared from simple open-chain building blocks. In the DMPU ( = N,N'-dimethylpropyleneurea)-assisted ring-closing alkylation of 1,7-diynes, the twelve-membered ring compounds have been prepared in yields of 16–55%. The preparation of the diene-diyne 15 and the cyclododeca-5,11-diyne-1,4-dione 18 are described.     

Dextran fatty acid esters as polymeric surfactants with low hemolytic activity

Practically all low molecular weight surfactants show hemolytic activities. Aside of this serious disadvantage almost all low molecular weight solubilizers cause considerable side effects, particularly during or after parenteral application. Polymeric surfactants, however, usually show no or only very little hemolytic effects. They therefore are supposed not to be able to penetrate neither into cellular or erythrocyte walls nor into phospholipid bilayers, resp., similar bilayer membranes due to their large molecular size. Therefore no decay of biological bilayers should be expected with polymeric surfactants. The only pharmaceutically widely used polymeric surfactants are at the moment polyoxyethylene-polyoxypropylene block copolymers (poloxamers (INN), Pluronicsr̀ and Pluriolsr̀). Unfortunately they have only poor solubility capacities. In order to find better solubilizing polymeric surfactants, some water soluble dextran fatty acid esters (Ref. 1) were synthesized and tested with respect to their solubilisation capacity and hemolytic activity. Usually the hemolytic activity is tested by standard methods using purified animal or human erythrocyte suspensions. As erythrocytes also contain a relatively high amount of lactose dehydrogenase (LDH), we studied the suitability of the highly sensitive, and in the medical diagnostic well known LDH test, as a supplemental hemolytic determination method (Ref. 2). The advantage of this test is, that there is no need of the time consuming purification and standardization as it is required with the erythrocytes' suspension. It can be performed with original blood and without costly preparations at all. The synthesized dextran fatty acid esters proved themselves as very little hemolytic and, compared with the polyoxyethylene-polyoxypropylene block copolymers, they show improved solubilisation capacities.     

Structures and energetics of small lead cluster ions

By a combination of gas phase ion mobility measurements and relativistic density functional theory calculations with inclusion of spin-orbit coupling, we assign structures of lead cluster cations and anions in the range between 4 and 15 atoms. We find a planar rhombus for the tetramer, a trigonal bipyramid for the pentamer, and a pentagonal bipyramid for the heptamer, independent of charge state. For the hexamer, the cation and anion structures differ: we find an octahedron for the anion while the cation consists of fused tetrahedra. For the octamer, we find in both cases structures based on the pentagonal bipyramid motif plus adatom. For the larger clusters investigated we always find different structures for cations and anions. For example, Pb(12)(-) is confirmed to be a hollow icosahedron while Pb(12)(+) is a truncated filled icosahedron. Pb(13)(+) is a filled icosahedron but Pb(13)(-) is a hollow icosahedron with the additional atom capping a face. In order to get experimental information on the relative stabilities, we investigated the collision induced dissociation mass spectra for the different cluster sizes and charge states, and observe a strong correlation with the calculated fragmentation energies. Up to n = 13 the main fragmentation channel is atom loss; for the larger cluster sizes we observe fission into two large fragments. This channel is dominant for larger anions, less pronounced but clearly present for the cations.     

Computation of the complexation energies of BH3NH3 and BH3PH3

Extended basis set computations on SCF and CEPA level were performed for BH₃NH₃ and BH₃PH₃ to determine the complexation energy ΔE and the equilibrium distance r(BX) between the “heavy” atoms. Our CEPA results (SCF in parentheses): ΔE(BH₃NH) = ?27(?21.3) kcal/mol, ΔE(BH₃PH₃) = ?17(?11.8) kcal/mol, r(BN) = 1.65(1.68) Å, r(BP) = 1.95(1.99) Å indicate a marked influence of electron correlation on these properties.     

The Radical Anions and Trianions of 1,8-Diphenylnaphthalene and of Some of its Derivatives Containing a Cyclophane Substructure

The radical anions of 1,8-diphenylnaphthalene ( 1 ) and its decadeuterio-(D₁₀- 1 ) and dimethyl-( 2 ) derivatives, as well as those of [2.0.0] (1,4)benzeno(1,8)naphthaleno(1,4)benzenophane ( 3 ) and its olefinic analogue ( 4 ) have been studied by ESR and ENDOR spectroscopy, At a variance with a previous report, the spin population in \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {2}^{-\kern-4pt {.}} $\end{document} is to a great extent localized in the naphthalene moiety. A similar spin distribution is found for \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {3}^{-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {4}^{-\kern-4pt {.}} $\end{document}. The ground conformations of \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document}-\documentclass{article}\pagestyle{empty}\begin{document}$ \rm {4}^{-\kern-4pt {.}} $\end{document} are chiral of C₂ symmetry. For \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document}, an energy barrier between these conformations and the angle of twist about the bonds linking the naphthalene moiety with the phenyl substituents were estimated as ca. 50 kJ/mol and ca. 45°, respectively. The radical trianions of 1 , D₁₀- 1 , and 2 , have also been characterized by their hyperfine data. In \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{3-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {2}^{3-\kern-4pt {.}} $\end{document}, the bulk of the spin population resides in the two benzene rings so that these radical trianions can be regarded as the radical anions of ‘open-chain cyclophanes’ with a fused naphthalene π-system bearing almost two negative charges. The main features of the spin distribution in both \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{3-\kern-4pt {.}} $\end{document} are correctly predicted by an HMO model of 1 .     

Auxiliary basis sets for main row atoms and transition metals and their use to approximate Coulomb potentials

We present auxilliary basis sets for the atoms H to At – excluding the Lanthanides – optimized for an efficient treatment of molecular electronic Coulomb interactions. For atoms beyond Kr our approach is based on effective core potentials to describe core electrons. The approximate representation of the electron density in terms of the auxilliary basis has virtually no effect on computed structures and affects the energy by less than 10⁻⁴ a.u. per atom. Efficiency is demonstrated in applications for molecules with up to 300 atoms and 2500 basis functions. Received: 17 December 1996 / Accepted: 8 May 1997