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.     

Electronic structures of the boron cage molecules B4H4, B4Cl4 and B4F4

Ab initio calculations have been performed on B₄H₄, B₄Cl₄ and B₄F₄ in order to aid our understanding of the bonding in these compounds, which is presumably based on a tetrahedral boron cage. This cage has only 8 electrons and so is less than that expected on the basis of the usual framework electron counting rules. Basis sets with polarisation functions were used at the SCF, CI and CPF levels of theory to confirm that the T _d structures are indeed more stable than the D _4h ones. Davidson-Roby population analyses were able to show that many factors, including 3-centre 2-electron bonding and backbonding from the ligand to the boron cage, are of importance in determining the relative stability of the three compounds, of which B₄Cl₄ is the only one that has yet been observed experimentally.     

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.     

Millimeter/submillimeter nonlinear spectroscopy

The techniques of coherent transient spectroscopy have been successfully applied to the microwave and optical regions of the spectrum, but lack of suitable sources has prevented convenient extension to the millimeter/submillimeter region where several strong molecular transitions occur. Analysis of the experimental requirements and theory for such experiments considering several molecules including H₂O and CH₃Cl indicates how such experiments can be performed employing recently developed oscillators with increased power.     

Structures of tin cluster cations Sn3(+) to Sn15(+)

We employ a combination of ion mobility measurements and an unbiased systematic structure search with density functional theory methods to study structure and energetics of gas phase tin cluster cations, Sn(n)(+), in the range of n = 3-15. For Sn(13)(+) we also carry out trapped ion electron diffraction measurements to ascertain the results obtained by the other procedures. The structures for the smaller systems are most easily described by idealized point group symmetries, although they are all Jahn-Teller distorted: D(3h) (trigonal bipyramid), D(4h) (octahedron), D(5h) (pentagonal bipyramid) for n = 5, 6, and 7. For the larger systems we find capped D(5h) for Sn(8)(+) and Sn(9)(+), D(3h) (tricapped trigonal prism) and D(4d) (bicapped squared antiprism) plus adatoms for n = 10, 11, 14, and 15. A centered icosahedron with a peripheral atom removed is the dominant motif in Sn(12)(+). For Sn(13)(+) the calculations predict a family of virtually isoenergetic isomers, an icosahedron and slightly distorted icosahedra, which are about 0.25 eV below two C(1) structures. The experiments indicate the presence of two structures, one from the I(h) family and a prolate C(1) isomer based on fused deltahedral moieties.     

Compact diode-pumped 1.1 kW Yb:YAG Innoslab femtosecond amplifier

We demonstrate a compact diode-pumped Yb:KGW femtosecond oscillator-Yb:YAG Innoslab amplifier master oscillator power amplifier (MOPA) with nearly transform-limited 636 fs pulses at 620 W average output power, 20 MHz repetition rate, and beam quality of M(x)(2) = 1.43 and M(y)(2) = 1.35. By cascading two amplifiers, we attain an average output power of 1.1 kW, a peak power of 80 MW, and a 615 fs pulse width in a single linearly polarized beam. The power-scalable MOPA is operated at room temperature, and no chirped-pulse amplification technique is used.     

Small clusters of aluminum and tin: highly correlated calculations and validation of density functional procedures

We present results of molecular electronic structure treatments of multireference configuration interaction (MRCI) type for clusters Al(n) and Sn(n) in the range up to n = 4, and of coupled cluster singles and doubles with perturbative triples corrections (CCSD(T)) type in the range up to n = 10. Basis sets of quadruple zeta size are employed, computed energy differences, such as cohesive energies, E(coh), or dissociation energies for the removal of a single atom, D(e), differ from the complete basis set limit by only a few 0.01 eV. MRCI and CCSD(T) results are then compared to those obtained from density functional theory (DFT) treatments, which show that all computational procedures agree with the general features of D(e) and E(coh). The best agreement of DFT with CCSD(T) is found for the meta-GGA (generalized gradient approximation) TPSS (Tao, Perdew, Staroverov, Scuseria) for which D(e) differs from CCSD(T) by at most 0.15 eV for Al(n) and 0.21 eV for Sn(n). The GGA PBE (Perdew, Burke, Ernzerhof) is slightly poorer with maximum deviations of 0.23 and 0.24 eV, whereas hybrid functionals are not competitive with GGA and meta-GGA functionals. A general conclusion is that errors of D(e) and/or energy differences of isomers computed with DFT procedures may easily reach 0.2 eV and errors for cohesive energies E(coh) 0.1 eV.     

Planarization of Tetracoordinate Carbon Atom. Synthesis of 13-oxa-14-oxo-pentacyclo [5.5.2.1.04,15010,15]pentadecane,a bridged ‘tetraquinacane’ preliminary communication

Structural aspects of planoid deformation of tetracoordinate carbon atom, particularly those in annulenes with central carbon atom are discussed. [12] Annulene 11 with central carbon atom is proposed as compound with strong planoid deformation around the internal carbon centre. The synthesis of a saturated precursor 15 is described.