Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

Centrosymmetric lie algebras and boost-dilations

We define the Lie algebrac(n) of centrosymmetric matrices. It generates a noncompact and nonsemisimple local Lie group with the unusual property that expc(n) c(n). The group contains an invariant subgroup of Lorentz boost/ dilation transformations. Forn even, these form a subgroup of the conformal group of the Lorentzian metric with signature (– + – + – +).     

A dynamic edge covering and scheduling problem: complexity results and approximation algorithms

We consider a new dynamic edge covering and scheduling problem that focuses on assigning resources to nodes in a network to minimize the amount of time required to process all edges in it. Resources need to be co-located at the endpoints of an edge for it to be processed and, therefore, this problem contains both edge covering and scheduling decisions. These new problems have motivating applications in traffic systems and military intelligence operations. We provide complexity results for the dynamic edge covering and scheduling problem over different types of networks. We then show that existing approximation algorithms for parallel machine scheduling problems can be leveraged to provide approximation algorithms for this new class of problems over certain types of networks.     

An algorithm for calculating atomic D states with explicitly correlated gaussian functions

An algorithm for the variational calculation of atomic D states employing n-electron explicitly correlated gaussians is developed and implemented. The algorithm includes formulas for the first derivatives of the hamiltonian and overlap matrix elements determined with respect to the gaussian nonlinear exponential parameters. The derivatives are used to form the energy gradient which is employed in the variational energy minimization. The algorithm is tested in the calculations of the two lowest D states of the lithium and beryllium atoms. For the lowest D state of Li the present result is lower than the best previously reported result.     

Probabilistic value pricing

In this paper we consider the class of probabilistic value pricing mechanisms for cost allocation problems, which are related to probabilistic values for finite games with transferable utility. We characterize probabilistic value pricing axiomatically, as well as several related pricing mechanisms, including semivalue pricing (symmetric pricing without cost sharing), quasivalue pricing (cost sharing pricing without symmetry), and weighted Shapley value pricing. We also describe a class of problems in which (symmetric) Shapley value pricing coincides with Aumann-Shapley pricing, and a class of problems for which every quasivalue pricing mechanism is supportable.     

Fluorodienes. V. Copolymerization of 1,1,4,4-tetrafluoro-1,3-butadiene with oxygen and nitric oxide

1,1,4,4-Tetrafluoro-1,3-butadiene reacts with oxygen to form a polyperoxide containing 1.0–1.1 peroxide groups for each diene unit. This polymer behaves like a typical peroxide. It explodes violently when heated to 120°C. or when subjected to shock, and it initiates polymerization of vinyl monomers at temperatures of 90°C. or higher. The tetrafluorobutadiene also copolymerizes with nitric oxide to give a highly crosslinked polymer containing three molecules of diene for each two molecules of nitric oxide.     

Polymers containing polyhedral borane rings I. Condensation polymers

The preparation and properties of a unique new class of polymers containing polyhedral borane cages as part of the backbone polymer chain are described. The synthesis of polyamides, polyesters, polyureas, and polyurethanes proceeds from suitably chosen B₁₀ and B₁₂ polyhedral borane dicarbonyls, diols, and diisocyanates by typical condensation polymer techniques. Each complementary monomer may be a borane compound, but more often higher molecular weight products are provided when one monomer is a conventional organic reagent such as an aromatic diisocyanate. The polyamides prepared from 1, 12-B₁₂H₁₀(CO)₂ and organic diamines were crystalline and soluble, but molecular weight were limited because the amidation reaction was reversible and/or the amide linkage could be split by nucleophilic attack by some solvents. The polyurethanes prepared from Na₂B₁₂H₁₀(OH)₂ and aromatic diisocyanates were high molecular weight and relatively more stable. Clear, colorless, tough films were prepared. These polymers were soluble in many polar solvents and exhibited typical polyelectrolyte behavior.     

Condensation polymers from 1,2,5-thiadiazole-3,4-dicarboxylic acid

A series of polyamides was prepared by interfacial polymerization of diamines with 1,2,5-thiadiazole-3,4-dicarbonyl chloride. Polyamides from secondary cycloaliphatic diamines and aromatic diamines have high softening points, high glass transition temperatures, and good thermal stability. Secondary amines, in particular cycloaliphatic secondary amines, form very high molecular weight polyamides. The polyamide from trans-2,5-dimethylpiperazine and 1,2,5-thiadiazole-3,4-dicarbonyl chloride is soluble in chloroform and 1,1,2-trichloroethane and has been cast into films and spun into fibers from those solvents. Fibers of this polymer are strong and have very high work recovery from small strains. In addition, these fibers show good retention of strength and work recovery over a range of temperatures and humidities.     

Polymerization of Fluorothiocarbonyl Compounds

Recently it was shown that the C[dbnd]S group in fluorothiocarbonyl compounds readily undergoes addition polymerization. This review describes polymers obtainable from such compounds as CF₂[dbnd]S, CF₃CF[dbnd]S, ClCF₂CF[dbnd]S, HCFClCF[dbnd]S, and hexafluorothioacetone. The polymerization of CF₂[dbnd]S is readily brought about in anionic systems at low temperatures, giving a high-molecular-weight poly(thiocarbonyl fluoride) with a number-average molecular weight in the range of 300,000 to 400,000. It is believed that the major portion of this polymer is composed of chains of CF₃–-S—(—CF₂S—)_n–CF[dbnd]S. Poly(thiocarbonyl fluoride) is a highly resilient elastomer in the amorphous form but suffers the disadvantage of slow crystallization at temperatures below 35°C and concomitant loss of rubbery properties. Above 175°C it depolymerizes. Fluorothioacyl fluorides also undergo anionic polymerization, but the products are logy elastomers. Copolymers of fluorothioacyl fluorides with CF₂[dbnd]S have better thermal stability but poorer resilience than poly(thiocarbonyl fluoride). Hexafluorothioacetone has been polymerized at—110°C to give a white elastomer that slowly depolymerizes at room temperature to regenerate monomer. Thiocarbonyl fluoride is also susceptible to free-radical polymerization, and in free-radical systems it copolymerizes with conventional vinyl monomers, giving a wide variety of new elastomeric products.