CLIP: similarity searching of 3D databases using clique detection

This paper describes a program for 3D similarity searching, called CLIP (for Candidate Ligand Identification Program), that uses the Bron-Kerbosch clique detection algorithm to find those structures in a file that have large structures in common with a target structure. Structures are characterized by the geometric arrangement of pharmacophore points and the similarity between two structures calculated using modifications of the Simpson and Tanimoto association coefficients. This modification takes into account the fact that a distance tolerance is required to ensure that pairs of interatomic distances can be regarded as equivalent during the clique-construction stage of the matching algorithm. Experiments with HIV assay data demonstrate the effectiveness and the efficiency of this approach to virtual screening.     

Reaction of oxalyl and malonyl chloride with 1,1-dimethyl-2-substituted hydrazides

Recently we reported the reaction of 1,1-dimethyl-4-substituted semicarbazides with phosgene to occur with formation of several new heterocyclic ring systems. Here we report the reaction of several semicarbazides, thiosemicarbazides and related acyl substituted hydrazides with oxalyl chloride and malonyl chloride. These reactions occur with the formation of heterocyclic products which are oxadiazolinones, imidazolidinetriones, 2-thioxoimidazolindine-4,5-diones, and 2-thioxo-1,3-diazine-4,6-diones (2-thioxopyrimidine-4,6-diones).     

Structure and magnetism of a spin ladder system: (C5H9NH3)2CuBr4

The crystal structure of bis(cyclopentylammonium)tetrabromocuprate(II) has been determined at room temperature and at -70 degrees C. The room temperature structure is orthorhombic, space group Pn2(1)a, with a = 12.092(6) A, b = 8.134(4) A, and c = 18.698(10) A. The low temperature structure is also orthorhombic, space group Pna2(1), with a = 24.111(5) A, b = 8.089(2) A, and c = 18.448(4) A. DSC studies reveal the presence of a weak endotherm at -13 degrees C. The structures of the two phases are very similar, differing only in the relative orientations of the cyclopentyl rings of the organic cations and slight displacements of the anionic tetrahedra. The CuBr(4)(2)(-) anions in the low temperature phase are arranged to define a spin ladder system through Cu-Br.Br-Cu two-halide exchange pathways. Magnetic susceptibility data have been analyzed and yield antiferromagnetic exchange strengths 2J(rail)/k = -11.6 K and 2J(rung)/k = -5.5 K with a singlet-triplet gap energy Delta/k(B) = 2.3 K. This is the first report of a spin ladder with a stronger interaction along the axis of the ladder than along the rungs.     

Preparation and Characterization of Electroactive Biopolymers

Biopolymers have the potential for use as a matrix for applications such as controlled release devices, environmentally sensitive membranes, mimic materials and energetic applications. Renewable resources (such as starch) can be utilized as polymer matrices for electroactive materials that are sensitive to their environment. Natural polymers are generally more environmentally-friendly and biocompatible than existing synthetic products. Thermoplastic starch is naturally insulative; however, the chemical, electrical, and mechanical properties of the biopolymer matrix can be tailored for specific functionality in a continuous process utilizing reactive extrusion. Conductance can be measured in the solid state by a direct-current resistance method. Ion-conducting materials, produced by doping thermoplastic starch and biopolymers with metal halides, have 5 orders of magnitude greater conductance than native materials. There is a correlation between polymer mobility and conductance. Plant or microbial biopolymers with ionic functional groups have shown promise for higher levels of conductance. The conductance approaches the level of synthetic polymer electrolytes.     

Chaotic Expansion of Elements of the Universal Enveloping Algebra of a Lie Algebra Associated with a Quantum Stochastic Calculus

The functional Ito formula, in the form df() = f( + d ) –f(),is formulated and proved in the context of a Lie algebra L associatedwith a quantum (non-commutative) stochastic calculus. Here fis an element of the universal enveloping algebra U of L, andf() + d() – f() is given a meaning using the coproductstructure of U even though the individual terms of this expressionhave no meaning. The Ito formula is equivalent to a chaoticexpansion formula for f() which is found explicitly. 1991 MathematicsSubject Classification: primary 81S25; secondary 60H05; tertiary18B25.     

Graph-theoretic techniques for macromolecular docking

We propose a solution to the problem of docking two macromolecules. We represent each of two proteins as a set of potential hydrogen bond donors and acceptors and use a clique-detection algorithm to find maximally complementary sets of donor/acceptor pairs. Preliminary results are presented which demonstrate the feasibility of the method.     

Uniqueness for second order nonlinear boundary value problems with applications to almost periodic solutions

Summary The problem of uniqueness of bounded solutions for various nonlinear boundary value problems is considered. Results for problems with an unbounded interval are obtained. The results obtained for the uniqueness of bounded solutions on the interval (−∞, ∞) are applied to the problem of proving the existence of almost periodic solutions. Entrata in Redazione il 4 aprile 1968.     

Evidence for current-flow anomalies in the irradiated 2D electron system at small magnetic fields

We report experimental transport results in 2D electron systems exposed to dipole radiation up to 20 GHz. Magnetoresistance oscillations occur as seen with higher frequency radiation; however, minima here can be seen to extend to negative biases, and zeros are not observed persistently around sample perimeters. Under radiation, voltages are generated from internal to external contacts in the absence of applied driving currents. These findings may be consistent with theoretical pictures of current instabilities due to local negative resistivities.     

Experimental demonstration of Fermi surface effects at filling factor 5/2

Using small wavelength surface acoustic waves (SAW) on ultrahigh mobility heterostructures, Fermi surface properties are detected at 5/2 filling factor at temperatures higher than those at which the quantum Hall state forms. An enhanced conductivity is observed at 5/2 by employing sub-0.5-microm SAW, indicating a quasiparticle mean-free path substantially smaller than that in the lowest Landau level. These findings are consistent with the presence of a filled Fermi sea of composite fermions, which may pair at lower temperatures to form the 5/2 ground state.