Vectorization of a classical trajectory code on a floating point systems,Inc. Model 164 attached processor

A triatomic classical trajectory code has been modified by extensive vectorization of the algorithms to achieve much improved performance on an FPS 164 attached processor. Extensive timings on both the FPS 164 and a VAX 11/780 with floating point accelerator are presented as a function of the number of trajectories simultaneously run. The timing tests involve a potential energy surface of the LEPS variety and trajectories with 1000 time steps. The results indicate that vectorization results in timing improvements on both the VAX and the FPS. For larger numbers of trajectories run simultaneously, up to a factor of 25 improvement in speed occurs between VAX and FPS vectorized code.     

α,ω-Diisocyanatocarbodiimides, -Polycarbodiimides,and Their Derivatives

Research in the field of low-molecular weight, oligomeric and polymeric α,ω-diisocyanatocarbodiimides and -polycarbodiimides has been fruitful, not only in connection with these compounds themselves, but also—as so often happens in chemistry—with quite different problems. Novel synthetic methods, discoveries concerning the properties of low-molecular weight carbodiimides and phosphane imide derivatives, as well as results on the fragmentation reactions of four-membered heterocyclic compounds containing oxygen, phosphorus, and nitrogen, and a better understanding of the diisocyanate polyaddition process are among the many by-products of this research. The “high- and low-temperature formation” of polycarbodiimides and the homogeneous and heterogeneous catalysis of this process are described, and the fundamental importance of four-membered ring fragmentation mechanisms resulting in the formation of phosphane imide derivatives is outlined. Interesting building blocks for the diisocyanate polyaddition and polycondensation processes can be synthesized by many derivatization reactions of oligomeric and high-molecular weight polycarbodiimides and polyuretonimines. The in situ production of polycarbodiimides via matrix reactions in flexible polyurethane foams leads to a cellular arrangement of the material due to the pronounced symmetrical growth processes. Combination-foams with increased carbonation tendencies are formed in this way. Attention is drawn to several industrial applications of α,ω-diisocyanatopolycarbodiimides, of high-molecular weight cross-linked polyuretonimines, and of polycarbodiimide foams.     

Stabilization of p-block organoelement terminal hydroxides, thiols, and selenols requires newer synthetic strategies

Metal hydroxides represent a very interesting and highly useful class of compounds that have been known to chemists for a very long time. While alkali and alkaline earth metal hydroxides (s‐block) are commonplace chemicals in terms of their abundance and their use in a chemical laboratory as bases, the interest in Brønsted acidic molecular terminal hydroxides of p‐block elements, such as aluminum and silicon, has been of recent origin, with respect to the variety of applications these compounds can offer both in materials science and catalysis. Moreover, these systems are environmentally friendly, relative to the metal halides, owing to their ‐OH functionality (resembling that of water). Design and conceptualization of the corresponding terminal thiols, selenols, and tellurols (M? SH, M? SeH, and M? TeH) offer even more challenging problems to synthetic inorganic chemists. This concept summarizes some of the recent strategies developed to stabilize these otherwise very unstable species. The successful preparation of a number of silicon trihydroxides a few years back resulted in the generation of several model compounds for metal–silicates. The recent synthesis of unusual aluminum compounds such as RAl(OH)₂, RAl(SH)₂, and RAl(SeH)₂ with terminal EH (E=O, Se, or Se) groups is likely to change the ways in which some of the well‐known catalytic conversions are being carried out. The need for very flexible and innovative synthetic strategies to achieve these unusual compounds is emphasized in this concept.     

New pressure-density-temperature measurements and new rational equations for the saturated liquid and vapour densities of oxygen

The results of pressure, density, temperature (p, ?, T) measurements in the temperature range from 65 K to 300 K, for pressures up to 7.2 MPa, and for densities from 0.3 mol dm^?3 to 39 mol dm^?3, are presented for pure oxygen. Using the experimental results, new values for the densities of saturated liquid and vapour are evaluated. To check the accuracy of these results, corresponding sets reported in the literature are critically analysed to determine the most reliable p, ?, T set for oxygen. Finally, new equations for the densities of saturated liquid and vapour are developed using a statistical procedure.     

Recent applications of the ring-oven technique : A brief review

The ring-oven technique is a special type of spot analysis. In this review, papers published since 1976 are discussed. The aspects dealt with include developments in the technique and its use, the identification and determination of inorganic ions, organic substances, enzymatic analysis, applications to air and water samples, and combinations with other techniques.     

Darstellung und Kristallstruktur von Cs2Sb4S7

Preparation and Crystal Structure of Cs₂Sb₄S₇ The first thioantimonite of Cesium has been synthesized and its crystal structure determined. The substance crystallizes monoclinic with spacegroup P2₁/_c. The lattice constants are a = 1111.2(5) pm, b = 1227.1(5) pm, c = 1163.7(5) pm and ß = 97.60(5)°. There are four formula units in the unit cell. Sb–S chains are formed by trigonal SbS₃ pyramids and ψ-trigonal SbS₄ bipyramids.     

Fused lactones as a route to functionalized 1-substituted indoles

Indole lactones 8 and 14 were synthesized as a means of functionalizing the 1-isopropyl substituent of the indole nucleus. Lactone 8 , upon reduction with diisobutylaluminum hydride, produces lactol 9 which behaves like a masked hydroxy aldehyde and undergoes a Horner-Emmons reaction with triethyl phosphonoacteate to give α,β-unsaturated ester 3 which possesses a hydroxyl group on the 1-isopropyl moiety.     

TreeDock: a tool for protein docking based on minimizing van der Waals energies

Predicting protein-protein and protein-ligand docking remains one of the challenging topics of structural biology. The main problems are (i) to reliably estimate the binding free energies of docked states, (ii) to enumerate possible docking orientations at a high resolution, and (iii) to consider mobility of the docking surfaces and structural rearrangements upon interaction. Here we present a novel algorithm, TreeDock, that addresses the enumeration problem in a rigid-body docking search. By representing molecules as multidimensional binary search trees and by exploring a sufficient number of docking orientations such that two chosen atoms, one from each molecule, are always in contact, TreeDock is able to explore all clash-free orientations at very fine resolution in a reasonable amount of time. Due to the speed of the program, many contact pairs can be examined to search partial or complete surface areas. The deterministic systematic search of TreeDock is in contrast to most other docking programs that use stochastic searches such as Monte Carlo or simulated annealing methods. At this point, we have used the Lennard-Jones potential as the only scoring function and show that this can predict the correct docked conformation for a number of protein-protein and protein-ligand complexes. The program is most powerful if some information is known about the location of binding faces from NMR chemical-shift perturbation studies, orientation information from residual dipolar coupling, or mutational screening. The approach has the potential to include docking-site mobility by performing molecular dynamics or other randomization methods of the docking site and docking families to families of structures. The performance of the algorithm is demonstrated by docking three complexes of immunoglobulin superfamily domains, CD2 to CD58, the V(alpha) domain of a T-cell receptor to its V(beta) domain, and a T-cell receptor to a pMHC complex as well as a small molecule inhibitor to a phosphatase.     

Tautomerism and stereochemistry of hypericin: Force field,NMR, and X-ray crystallographic investigations

Summary Stereochemistry and tautomerism of hypericin, pseudohypericin, and several of their partial structure models were investigated using an MM2 derived force field method. Besides the propeller type conformer, which was also found by the X-ray crystallographic study, the complicated energy hypersurface was shown to contain a novel double-butterfly conformer of similar stability. The upper limit interconversion barrier between these conformers and their enantiomers was found to be in the order of 115 kJ/mol.¹H-NMR experiments suggested a lower limit interconversion barrier of at least 80 kJ/mol. From the ten tautomers possible in principle, the 7,14-species was derived to be the most stable one by at least 48 kJ/mol.

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Tautomerie und Stereochemie von Hypericin: Untersuchungen mit Hilfe der Kraftfeld-Methodik, NMR-Spektroskopie und Röntgenstrukturanalyse

Zusammenfassung Die Stereochemie von Hypericin, Pseudohypericin und einigen seiner Partialstrukturmodelle wurde mit Hilfe einer von MM2 abgeleiteten Kraftfeldmethodik untersucht. In der komplizierten Energiehyperfläche wurde neben dem auch durch Röntgenstrukturanalyse gefundenen Propeller-Konformeren ein neues Doppelschmetterling-Konformer ähnlicher Stabilität aufgefunden. Die obere Grenze für die Interkonversionsbarrieren zwischen diesen Konformeren und ihren Enantiomeren sind in der Größenordnung von 115 kJ/mol. Aus¹H-NMR-Experimenten konnte eine untere Grenze von wenigstens 80 kJ/mol abgeleitet werden. Es wurde gefunden, daß von den zehn prinzipiell möglichen Tautomeren die 7,14-Spezies die um wenigstens 48 kJ/mol stabilste ist.