Determination of Interparticle Forces by Colloidal Particle Scattering: A Simulation Study

Preflocculated ferric hydroxide flocs were subjected to either a simple shear flow or a two-dimensional straining flow, and their motion was optically observed. Digital image analysis was applied to extract information on orientation and deformation from the digitized frames. It was found that the simple shear flow led to a rotation of the flocs whose motion can be understood from the behavior of a solid ellipsoid. In the extensional flow, no continuous rotation occurred and flocs were broken apart along the axis of straining. The rupture forces estimated from an ellipsoid model were found to be in the range of 0.1 N/m(2). Copyright 2000 Academic Press.     

The ground stateM1 strength in40Ca

The M1 gamma decay strengths of the ground state transitions of the 1⁺,T=1 states of⁴⁰Ca at 9.86 MeV and 10.32 MeV have been measured using the reaction³⁹K(p,γ)⁴⁰Ca. The measured ground state gamma decay widths of these levels are 1.06±0.15 eV and 5.8±0.8 eV respectively. These relatively large M1 strengths can be explained by a shell model calculation incorporating excited core configurations.     

The 5v 3 bands of 18O enriched ozone: line positions of 16O16O18O, 16O18O16O, 16O18O18O and 18O16O18O

The four 5v ₃ bands of ¹⁸O enriched ozone have been observed and analysed for the first time. Two species (¹⁶O¹⁸O¹⁶O and ¹⁸O¹⁶O¹⁸O) belong to the C_2v symmetry group and two other (¹⁸O¹⁸O¹⁶O and ¹⁶O¹⁶O¹⁸O) to the C_s symmetry group. They have been recorded at a resolution of 0.008 cm^?1 with a pathlength of 32.16 m. Despite the very weak absorptions observed, almost 250 energy levels have been derived for each of the 4 species, with J ? 35 and K _a ? 13, and suitable sets of Hamiltonian parameters have been determined. For 3 species it has been necessary to account for the resonance between the (005) and (311) states to correctly reproduce the spectra observed. These resonances, anharmonic for C_2v, and hybrid (both anhar-monic and Coriolis) for C_s symmetry confirm the accidentally extremely strong coupling between the (005) and (311) states for ¹⁶O₃, due in that case to the very close distance between unperturbed energy levels. This work also confirms the excellent prediction of band centres of these four species derived from the recently determined isotopically invariant molecular potential function.     

The biosynthesis of quadrone and terrecyclic acid

Feedings of [1-¹³C]- and [1,2-¹³C₂]acetate Aspergillus terreus gave quadrone and terrecyclic acid which were analyzed by ¹³C NMR. The pattern of ¹³C-enrichments and couplings is consistent with the formation of 1 and 2 by cyclization of farnesyl pyrophosphate.     

Polymorphic forms of cilostazol

Two unique conformational polymorphic forms of the compound 6‐[4‐(1‐cyclo­hexyl‐1H‐tetrazol‐5‐yl)­butoxy]‐3,4‐di­hydro­quinolin‐2(1H)‐one (cilostazol), C₂₀H₂₇N₅O₂, have been discovered and characterized using single‐crystal X‐ray structural analysis. A third polymorph also exists, but acceptable crystals could not be obtained. Features of both reported polymorphic structures include a chair conformation of the cyclo­hexyl ring and puckering in the quinolinone ring. The major feature distinguishing the two polymorphic forms is a rotational twisting of the butoxy chain between the tetrazole and quinolinone rings. This difference in conformation influences the intermolecular forces, and hence the packing of the two mol­ecules during crystallization.     

The synthesis and structure of triphenylsiloxycyclotriphosphazenes

The triphenylsiloxy-substituted cyclotriphosphazenes, N₃P₃Cl₅OSiPh₃, gem-N₃P₃Cl₄(OSiPh₃)₂, N₃P₃(OSiPh₃)₆, and N₃P₃(OPh)₅OSiPh₃, have been prepared. The synthesis of gem-N₃P₃Cl₄(OSiPh₃)₂ involves the reaction of (NPCl₂)₃ with Ph₃SiONa to form the intermediates gem-N₃P₃Cl₄(OSiPh₃)₂(ONa) and gem-N₃P₃Cl₄(ONa)₂, which yield gem-N₃P₃Cl₄(OSiPh₃)₂ when treated with Ph₃SiCl. The compounds N₃P₃Cl₅OSiPh₃ and N₃P₃(OSiPh₃)₀ are formed by the condensation reactions of N₃P₃Cl₅OBuⁿ and N₃P₃(OBuⁿ)₆, respectively, with Ph₃SiCl. The compound N₃P₃(OPh)₅OSiPh₃ is synthesized by the reaction between N₃P₃(OPh)₅Cl and Et₃SiONa to first give the intermediate N₃P₃(OPh)₅ONa, which yields N₃P₃(OPh)₅OSiPh₃ when reacted with Ph₃SiCl. The structural characterization and properties of these compounds are discussed. The crystal and molecular structure of gem-N₃P₃Cl₄(OSiPh₃)₂ has been investigated by single-crystal X-ray diffraction techniques. The crystals are monoclinic with the space group P2₁/c with a = 16.850(8), b = 12.829(4), c = 18.505(15) Å, and β = 101.00(6)° with V = 3927 ų and Z = 4. © 1996 John Wiley & Sons, Inc.     

Enhancing the effectiveness of virtual screening by fusing nearest neighbor lists: a comparison of similarity coefficients

This paper evaluates the effectiveness of various similarity coefficients for 2D similarity searching when multiple bioactive target structures are available. Similarity searches using several different activity classes within the MDL Drug Data Report and the Dictionary of Natural Products databases are performed using BCI 2D fingerprints. Using data fusion techniques to combine the resulting nearest neighbor lists we obtain group recall results which, in many cases, are a considerable improvement on standard average recall values obtained for individual structures. It is shown that the degree of improvement can be related to the structural diversity of the activity class that is searched for, the best results being found for the most diverse groups. The group recall of active compounds using subsets of the class is also investigated: for highly self-similar activity classes, the group recall improvement saturates well before the full activity class size is reached. A rough correlation is found between the relative improvement using the group recall and the square of the number of unique compounds available in all of the merged lists. The Tanimoto coefficient is found unambiguously to be the best coefficient to use for the recovery of active compounds using multiple targets. Furthermore, when using the Tanimoto coefficient, the "MAX" fusion rule is found to be more effective than the "SUM" rule for the combination of similarity searches from multiple targets. The use of group recall can lead to improved enrichment in database searches and virtual screening.     

A Mössbauer effect study of Y(57Fe:Mn)12

The intermetallic compound, YMn₁₂, doped with 0.5at.%⁵⁷Fe has been investigated using the⁵⁷Fe Mössbauer resonance. The data show that the Fe impurities occupy preferentially the f-site at the expense of the i- and j-sites. Whereas the i- and j-sites are expected to carry identical local magnetic moments in the ordered state, low temperature hyperfine fields of 50.08(±0.05)T and 2.90(±0.03)T are measured for the i- and j-sites respectively. It is proposed that large transferred hyperfine fields are responsible for this disparity.