Two new heuristics for the location set covering problem

Summary In this paper we present two new greedy-type heuristics for solving the location set covering problem. We compare our new pair of algorithms with the pair GH1 and GH2 [Vasko and Wilson (1986)] and show that they perform better for a selected set of test problems.     

Theoretical study of metal ligand aromatic cation–π interactions of [Co(NH3)6]3+ with benzene

In this work, density functional theory calculations on geometries and energies of all possible conformers of the [Co(NH₃)₆]³⁺–C₆H₆ cation–π complex are described. The calculations show that stationary points are several η₂ and the η₃ structures. The most stable η₃ structure has bonding energy, after basis set superposition error correction, of 32.18 kcal/mol. The energies of η₃ structures are similar; also, the energies of η₂ structures are similar while the difference in energy between η₃ and the η₂ structures is about 2 kcal/mol. This indicates a possibility for various orientations of the benzene ring with respect to interacting ligands in the case of metal ligand aromatic cation–π (MLACπ) interactions and a possibility for the existence of these interactions in different molecular systems. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Stereodifferentiation in the formation and decay of the encounter complex in bimolecular electron transfer with photoactivated acceptors

Experimental evidence has been obtained for the involvement of encounter complexes between both enantiomers of a pi,pi* triplet excited ketone and a chiral phenol or indole. Determination of the pre-equilibrium constants (K(EC)) and the intrinsic decay rate constants (kd) indicates a significant stereodifferentiation in both steps of the quenching process.     

Reactions of platinum(II) complexes with sulfur- and histidine-containing peptides: a model for selective platination of peptides and proteins

The reactions between two monofunctional platinum complexes [Pt(Me₄dien)Cl]⁺ (Me₄dien = 1,1,7,7-tetramethyl-diethylenetriamine) and [Pt(Et₄dien)Cl]⁺ (Et₄dien = 1,1,7,7-tetraethyldiethylenetriamine) and the peptides, N-acetylated L-methionyl-L-histidine (MeCO–Met–His) and glutathione (GSH), have been investigated by ¹H-n.m.r. spectroscopy and u.v.–vis. spectrophotometry. The reactions of the platinum(II) complexes with MeCO–Met–His were carried out at room temperature and at pH 3.0 and 7.0, whereas with GSH the reactions were studied only at pH 3.0. No binding of these two platinum complexes to the sulfur atom of methionine or to nitrogen atoms of histidine residue of MeCO–Met–His was observed during the first 24 h. When the reaction was followed further, after 24 h very slow binding of [Pt(Me₄dien)Cl]⁺ to the N3 nitrogen atom of imidazole was observed. Both platinum complexes react with the sulfur atom of the cysteine residue in GSH. Kinetic data show that GSH reacts twice as fast with [Pt(Me₄dien)Cl]⁺ than with [Pt(Et₄dien)Cl]⁺. Our findings indicate that sterically crowded platinum(II) complexes are only capable of reacting with the sulfhydryl group of the cysteine residue. This influences the design of new platinum(II) complexes for selective covalent modification of peptides and proteins.     

Nucleation of Polypropylene Crystallization with Gold Nanoparticles. Part 2: Relation between Particle Morphology and Nucleation Activity

The influence of gold nanoparticle morphology on nucleation of isotactic polypropylene (PP) crystallization was investigated. Previous experiments indicated certain nucleation activity of gold nanoparticles, varying with their size. In this work, eight types of gold micro/nanoparticles were used: vacuum-sputtered nanostructures (nanoparticles, nanoislands, and nanolayers), chemically prepared isometric gold nanocrystals (5, 20, and 100 nm diameters), and two types of gold microcrystals with well-developed crystal facets [with (100) and (111) facets, respectively]. To minimize the effect of particle agglomeration, we used our recently introduced sandwich method, in which the nucleating agent was deposited between thin PP films and the nucleation was evaluated by polarized light microscopy (PLM), X-ray scattering (WAXS), and differential scanning calorimetry (DSC). The nucleation activity of Au particles in PP was lower than it might be expected from the previous studies and depended on their morphology. The nucleation activity of Au microcrystals with well-developed facets was higher than the activity of non-faceted Au nanocrystals.     

Water-induced isomerism of salicylaldehyde and 2-acetylpyridine mono- and bis-(thiocarbohydrazones) improves the antioxidant activity: spectroscopic and DFT study

Structural Chemistry - Thiocarbohydrazones (TCHs) and structurally related molecules are versatile organic compounds which exert antioxidant, anticancer, and other beneficial health effects. The...     

Stability of mycophenolate mofetil in polypropylene 5% dextrose infusion bags and chemical compatibility associated with the use of the Equashield® closed‐system transfer device

Stability studies are necessary in healthcare settings as they facilitate fast, cost‐effective and efficient work related to batch manufacturing and availability of supplies. We studied the stability of 1–10 mg/mL mycophenolate mofetil (MMF) in polypropylene 5% dextrose infusion bags prepared from Cellcept^® and with a generic brand name (Micofenolato de Mofetilo Accord) at different storage temperatures. To ensure chemical compatibility during preparation, we also tested MMF sorption to the Equashield^® closed‐system drug transfer device used in this step. For this, a validated stability‐indicating high‐performance liquid chromatography method was developed for the quantification and identification of MMF in the infusion bags. The analytical selectivity of the assay was determined by subjecting an MMF sample to extreme values of pH, oxidative stress and heat conditions to force degradation. Protected from light, 1–10 mg/mL MMF in infusion polypropylene bags prepared from reconstituted Cellcept^® 500 mg or Accord 500 mg in 5% dextrose was stable for at least 35 days when stored at 2–8°C or between ?15 and ?25°C, and for 14 days when stored at 25°C. MMF loss owing to chemical sorption to the Equashield^® closed‐system drug transfer device set was negligible.     

Transition metal complexes with thiosemicarbazide-based ligands. Part LVI: Nickel(II) complex with 1,3-diphenylpyrazole-4-carboxaldehyde thiosemicarbazone and unusually deformed coordination geometry

Synthesis of a new nickel(II) complex, [Ni(Ph₂PzTSC-H)₂] with 1,3-diphenylpyrazole-4-carboxaldehyde thiosemicarbazone (Ph₂PzTSC), is described. The compounds have been characterized by elemental and thermal analysis, molar conductivity and spectral (UV–Vis, IR, ¹H NMR, and ¹³C NMR) measurements. In the case of complex the magnetic measurement has been also performed. Crystal and molecular structures of both the free ligand and the complex have been determined by single crystal X-ray analysis. It was found that the ligand coordinates in a bidentate NS fashion, in its deprotonated thioenolato form. The cis-square-planar geometry of the complex is significantly distorted tetrahedrally. The Cambridge Structural Database (CSD) study has been performed to obtain geometrical and structural informations on similar nickel(II) complexes in order to compare structural data.     

Stacking of Benzene with Metal Chelates: Calculated CCSD(T)/CBS Interaction Energies and Potential‐Energy Curves

Accurate values for the energies of stacking interactions of nickel‐ and copper‐based six‐membered chelate rings with benzene are calculated at the CCSD(T)/CBS level. The results show that calculations made at the ωB97xD/def2‐TZVP level are in excellent agreement with CCSD(T)/CBS values. The energies of [Cu(C₃H₃O₂)(HCO₂)] and [Ni(C₃H₃O₂)(HCO₂)] chelates stacking with benzene are ?6.39 and ?4.77 kcal mol^?1, respectively. Understanding these interactions might be important for materials with properties that are dependent on stacking interactions.