Copper(II) and lead(II) complexes of 4,4′-bipyridine-<Emphasis Type="Italic">N,N</Emphasis>′-dioxide

Cu(II) and Pb(II) complexes of 4,4′-bipyridine-N,N′-dioxide have been prepared using a solvent-layering system. [Cu₂Cl₄(bpdo)₃(H₂O)₂] . 2(CH₃)₂SO (1) crystallises in P-1, a=8.731(2), b=8.943(2), c=14.408(3) ?, α=102.85(3), β=97.49(3), γ=109.77(3)°. The Cu(II) complex is a z-shaped discrete molecule with a DMSO molecule hydrogen bonded to the host through coordinated water molecule. Crystallisation of PbCl₂, PbBr₂ and PbI₂ with bpdo afforded isostructural 2D coordination polymers. [PbCl₂(bpdo)]_n is monoclinic, C2/c with a=16.3274(7), b=4.0708(1), c=18.6146(8) ?, β=93.73(1)°; [PbBr₂(bpdo)]_n is monoclinic, C2/c with a=16.403(3), b=4.2412(8), c=18.846(4) ?, β=92.59(3)° and [PbI₂(bpdo)]_n is monoclinic, C2/c with a=16.438(3), b=4.538(1), c=18.973(4) ?, β=91.04(3)°. The adjacent metal centres of these polymers are bridged by coordinated Cl⁻, Br⁻ or I⁻ anions as well as by bpdo ligands. These polymers possess no conventional hydrogen bonds.     

Scheduling jobs on heterogeneous processors

We consider the problem of schedulingn jobs nonpreemptively onm processors to minimize various weighted cost functions of job completion times. The time it takes processorj to process a job is distributed exponentially with rate parameter _j , independent of the other processors. Associated with jobi is a weightw _i . There are no precedence constraints and any job may be processed on any processor. Assume that _{1 2}...µ _m andw ₁w ₂...w _n . Then for certain weighted cost functions, the optimal policy is such that the processors can be partitioned into setsS ₁, ...,S _n+1 such that if the fastest available processor is in setS _i ,i=1, ...,n, then jobi should be assigned to it, and if it isS _n+1, it will never be used. After each assignment the jobs are renumbered (so that jobi+1 becomes jobi if jobi is assigned to a processor). The partitioning is independent of the job weights and the states (busy or idle) of the processors. The optimal policy can be determined in at most max {m, n} steps. If all the weights are identical, the optimal policy reduces to a simple threshold rule such that a job should be assigned to the fastest available processor, sayj, if there are more thanK _j jobs waiting.K _j will depend on ₁, ..., _j but not on _j+1, ...,µ _m . The optimal policy is also individually optimal in the sense that it minimizes the cost for each jobi subject to the constraint that processors will first be offered to the jobs in the order 1, 2, ...,n.We explicitly characterize the optimal policy for several specific examples of cost functions, such as weighted flow time, weighted discounted flowtime, and weighted number of tardy jobs.     

Solid-phase extraction–spectrophotometric determination of uranium(VI) in natural waters

A method for the extraction and determination of uranyl ion in natural waters using octadecyl bonded silica membrane disks modified with piroxicam and spectrophotometry with arsenazo(III) is proposed. The perconcentration step was studied with regard to experimental parameters such as amount of extractant, type and amount of eluent, pH, flow rates and tolerance limit of diverse ions on the recovery of uranyl ion. The limit of detection of the proposed method is 0.4 micro g L(-1) of uranyl. The method was applied to the recovery of uranyl from different water samples.     

A simple route to 6- and 7-fluoro-substituted naphthalene-1-carboxylic acids

A simple one-pot method for the synthesis of 6-fluoro- and 6,7-difluoro-1-naphthoic acid is described. 6-Fluoro-1-naphthoic acid can be converted into 7-fluoro-1-naphthoic acid in three straightforward steps.     

Geometric bases and topological equivalence

There are many algebraic and topological invariants associated to a singular point of a complex analytic function. The intent here is to discuss some of these invariants and the topological classification of singularities. Specifically, we establish that the topological type is determined by the Lefschetz vanishing cycles obtained by unfolding the singularity and certain local monodromy operators defined by Gabrielov. In Brieskorn's terminology singularities with the same geometric bases are topologically indistinguishable. Thus the higher invariants in the hierarchy of Brieskorn are necessary to understand the geometry of higher singularities. As a corollary to our main theorem, we obtain the result of Lê-Ramanujam which states that the topological type is constant in a oneparameter family of singularities with constant Milnor number.     

Delayed minocycline inhibits ischemia-activated matrix metalloproteinases 2 and 9 after experimental stroke

Background  

Matrix metalloproteinases 2 and 9 (MMP-2 and MMP-9) are increased in the brain after experimental ischemic stroke in rats. These two proteases are involved with the degradation of the basal lamina and loss of stability of the blood brain barrier that occurs after ischemia and that is associated with thrombolytic therapy in ischemic stroke. Minocycline is a lipophilic tetracycline and is neuroprotective in several models of brain injury. Minocycline inhibits inflammation, apoptosis and extracellular matrix degradation. In this study we investigated whether delayed minocycline inhibits brain MMPs activated by ischemia in a model of temporary occlusion in Wistar rats.     

Substituent electronic effects in chiral ligands for asymmetric catalysis

The majority of reports of ligand modification for catalysis have followed from systematic variation of the spatial demands of the catalyst. The focus of this review is to highlight selected major contributions to the area of substituent controlled electronic-tuning of some well known chiral ligands and the subsequent effect of these changes during asymmetric catalysis. The ligand types discussed include the salens, phosphites and phosphoramidites, ferrocene-containing ligands, oxazolines and axially chiral ligands. For each ligand type we attempt analyse the effect of systematic variation of electronics and note whether any improvements in catalyst activity and selectivity are obtained.