Settling time bounds forM/G/1 queues

This paper addresses the question of how long it takes for anM/G/1 queue, starting empty, to approach steady state. A coupling technique is used to derive bounds on the variation distance between the distribution of number in the system at timet and its stationary distribution. The bounds are valid for allt. This research was supported in part by a grant from the AT&T Foundation and NSF grant DCR-8351757.     

Cyclotrimerization of Benzobarrelene: Synthesis of New Isomeric Barrelene Architectures

The cyclotrimerization reaction of benzobarrelene derivatives was investigated. Dibromobenzobarrelene 10 was converted to the bromostannyl derivative 11 , which was used as the substrate of the cyclotrimerization reaction. Thus, reaction of 11 , with copper(I) thiophene‐2‐carboxylate (CuTC) gave a mixture of the isomeric cyclotrimers 5 and 6 and the dimers 12 and 13 , in addition to a trace of protodestannylated bromoalkene 14 (Scheme 2).     

High temperature bromination. Part 18: Bromination of benzonorbornadiene derivatives: Polybrominated benzonorbornenes and benzonorbornadienes

The low and high temperature bromination reactions of bromobenzonorbornadiene derivatives were studied and the possible role of a neighboring group in rearrangements was investigated. New polybrominated benzonorbornadiene and benzonorbornene derivatives were synthesized. All compounds were characterized properly using NMR spectroscopy.     

Findings of national proficiency test exercise for the determination of trace elements in edible mushroom reference material

This paper presents the results of the proficiency test exercise conducted in Pakistan for the determination of trace elements in mushroom reference material. Thirteen laboratories from different organizations of the country submitted trace elemental data on Al, As, Br, Ca, Cd, Ce, Cl, Co, Cr, Cs, Cu, Fe, Hg, K, Li, Mg, Mn, Na, P, Pb, Rb Sc, Si, Sm, Sr, Th, Zn. Results for Al, As, Br, Ca, Cd, Cl, Co, Cr, Cs, Cu, Fe, K, Mg, Mn, Na, Rb Sc, and Zn, in the mushroom material were reported by two or more participating laboratories and could be subjected to statistical evaluation. The original data of these trace elements was subjected to a computer program “Histo Version 2.1” provided by IAEA. The four outlier tests, i.e., Dixon, Grubbs, skewness and kurtosis were applied to the data sets. Consensus (overall) mean values, absolute standard deviation, relative standard deviation, standard error, median and range of values for these elements have been reported at a significance level of 0.05.     

Energetics of binding and protein unfolding upon amphiphilic drug complexation with a globular protein in different aqueous media

The interactions and complexation process of the structurally related amphiphilic phenothiazines promazine and triflupromazine hydrochlorides with horse myoglobin in aqueous buffered solutions of pH 2.5, 5.5 and 9.0 have been examined by zeta-potential, isothermal titration calorimetry (ITC), UV-vis spectroscopy and dynamic light-scattering techniques with the aim of analyzing the effect of hydrophobic and electrostatic forces, the alteration of protein conformation and the effect of substituents in the drug molecular structure on the binding mechanism and structure of the resulting complexes. The energetics and stoichiometry of the binding process was derived from ITC. The enthalpies of binding obtained are small and exothermic, and the Gibbs energies of binding are dominated by large increases in entropy consistent with hydrophobic interactions. Binding isotherms were obtained from microcalorimetric data by using a theoretical model based on the Langmuir isotherm. zeta-Potential data showed a reversal in the sign of the protein charge at pH 9.0 as a consequence of drug binding. Gibbs energies of drug binding per mole of drug were also derived from zeta-potential data. On the other hand, binding of the phenothiazines causes a conformational transition on protein structure which was followed as a function of drug concentration by using UV-vis spectroscopy. These data were analyzed to obtain the Gibbs energy of the transition in water (DeltaG(w)(degrees)) and in a hydrophobic environment (DeltaG(hc)(degrees)). Finally, the population distribution of the different species in solution and their size was analyzed through dynamic light scattering. The existence of an aggregation process of drug/protein complexes, mainly at pH 2.5, was observed. We think this is a consequence of the already expanded structure of the protein at this pH and the subsequent binding of drug molecules to the protein.     

A trinuclear nickel(II) enediolate complex: synthesis, characterization, and O2 reactivity

Using a new N(4)-donor chelate ligand having a mixture of hydrophobic phenyl and hydrogen-bond-donor appendages, a trinuclear nickel(II) complex of the doubly deprotonated form of 2-hydroxy-1,3-diphenylpropane-1,3-dione was isolated, characterized (X-ray crystallography, elemental analysis, UV-vis, (1)H NMR, FTIR, and magnetic moment measurement), and evaluated for O(2) reactivity. This complex, [(6-NA-6-Ph(2)TPANi)(2)(mu-PhC(O)C(O)C(O)Ph)(2)Ni](ClO(4))(2) (4), has two terminal pseudooctahedral Ni(II) centers supported by the tetradentate chelate ligand and a central square-planar Ni(II) ion ligated by oxygen atoms of two bridging enediolate ligands. In CH(3)CN, 4 exhibits a deep orange/brown color and lambda(max) = 463 nm (epsilon = 16 000 M(-1)cm(-1)). The room temperature magnetic moment of 4, determined by Evans method, is mu(eff) = 5.3(2) mu(B). This is consistent with the presence of two noninteracting high-spin Ni(II) centers, a diamagnetic central Ni(II) ion, and an overall quintet ground state. Exposure of a CH(3)CN solution of 4 to O(2) results in the rapid loss of the orange/brown color to give a green solution. The products identified from this reaction are [(kappa(3)-6-NA-6-Ph(2)TPA)Ni(O(2)Ph)(H(2)O)]ClO(4) (5), benzil [PhC(O)C(O)Ph], and CO. Identification of 5 was achieved via its independent synthesis and a comparison of its (1)H NMR and mass spectral features with those of the 6-NA-6-Ph(2)TPA-containing product generated upon reaction of 4 with O(2). The independently prepared sample of 5 was characterized by X-ray crystallography, elemental analysis, UV-vis, mass spectrometry, and FTIR. The O(2) reactivity of 4 has relevance to the active-site chemistry of Ni(II)-containing acireductone dioxygenase (Ni(II)ARD).     

Synthesis,Enzyme Inhibition,and Molecular Docking Studies of Hydrazones from Dichlorophenylacetic Acids

A series of hydrazones 5a–i were synthesized by the condensation of hydrazides derived from dichlorophenylacetic acids with different aromatic aldehydes and ketones. Their structures were confirmed by spectroscopic data and elemental analysis. Hydrazones 5a–i were evaluated for α‐glucosidase and urease inhibition activities. Five compounds exhibited potent α‐glucosidase inhibitory potential with IC₅₀ values 8.5 ± 0.3, 22.2 ± 0.78, 32.9 ± 1.5, 34 ± 2.4, and 170.6 ± 7.5 μM, respectively, which are many times better than that of the standard inhibitor acarbose (IC₅₀ = 840 ± 1.73 μM). Furthermore, molecular docking study was performed to explore the binding mode in the active sites of α‐glucosidase and urease enzymes.     

Synthesis of Some Novel Norbornene‐Fused Pyridazines as Potent Inhibitors of Carbonic Anhydrase and Acetylcholinesterase

The reaction of benzocyclic norbornene derivatives with tetrazines provided the 1,3‐dihydropyridazine derivatives as a single product. The dihydropyridazine derivatives have been dehydrogenated with phenyliodine bis(trifluoroacetate) to yield the corresponding pyridazines in a high yield. Two stable diazines, primary product of corresponding 1,4‐dihydropyridazine, were also isolated. Structures were then determined by ¹H‐NMR, and ¹³C‐NMR beside to elemental analyses. The novel pyridazine derivatives ( 8 , 9 ) efficiently inhibited the cytosolic human carbonic anhydrase isoenzymes I and II (hCA I and II). In addition, these novel pyridazine derivatives ( 8 , 9 ) were evaluated for their in vitro acetylcholinesterase inhibitory activity. Ligand–receptor interactions are tested using molecular docking simulations. Obtained docking scores are in good agreement with in vitro results.     

Synthesis, structure, and magnetic properties of valence ambiguous dinuclear antiferromagnetically coupled cobalt and ferromagnetically coupled iron complexes containing the chloranilate(2-) and the significantly stronger coupling chloranilate(*3-) radical trianion

Dinuclear [(TPyA)MII(CA2-)MII(TPyA)]2+ [TPyA=tris(2-pyridylmethyl)amine; CA2-=chloranilate dianion; M=Co (1(2+)), Fe (2(2+))] complexes have been prepared by the reaction of M(BF4)(2).6H2O, TPyA, H2CA, and triethylamine in MeOH solution. Their reduced forms [(TPyA)MII(CA*3-)MII(TPyA)]+ [M=Co(1+), Fe (2+)] have been synthesized by using cobaltocene, and oxidized forms of 1, [(TPyA)CoIII(CAn)CoIII(TPyA)]z+ [z=3, n=3- (1(3+)); z=4, n=2- (1(4+))], have been obtained by using FcBF4 and ThianBF4 (Fc=ferrocenium; Thian=thianthrinium), respectively. The dinuclear compound bridged chloranilates (CA2- or CA*3-) were isolated and characterized by X-ray crystallography, electrochemistry, magnetism, and EPR spectroscopy. Unlike the other redox products, valence ambiguous 13+ forms via a complex redox-induced valence electron rearrangement whereby the one-electron oxidation of the [CoIICA2-CoII]2+ core forms [CoIIICA*3-CoIII]3+, not the expected simple 1-e- transfer mixed-valent [CoIICA2-CoIII]3+ core. The M ions in 1 and 2 have a distorted octahedral geometry by coordination with four nitrogens of a TPyA, two oxygens of a chloranilate. Due to the interdimer offset face-to-face pi-pi and/or herringbone interactions, all complexes show extended 1-D and/or 2-D supramolecular structures. The existence of CA*3- in 1(3+) is confirmed from both solid-state magnetic and solution EPR data. Co-based 1n+ exhibit antiferromagnetic interactions [1(2+): g=2.24, J/kB=-0.65 K (-0.45 cm-1); 1+: g=2.36, J/kB=-75 K (52 cm-1)], while Fe-based 2n+ exhibit ferromagnetic interactions [2(2+): g=2.08, J/kB=1.0 K (0.70 cm-1); 2+: g=2.03, J/kB=28 K (19 cm-1)] [H=-2JS1.S2 for 12+ and 2(2+); H=-2J(S1.S2+S2.S3) for 1+ and 2+]. Thus, due to direct spin exchange CA*3- is a much strong spin coupling linkage than the superexchange spin-coupling pathway provided by CA2-.     

Acireductone dioxygenase- (ARD-) type reactivity of a nickel(II) complex having monoanionic coordination of a model substrate: product identification and comparisons to unreactive analogues

A mononuclear Ni(II) complex ([(6-Ph2TPA)Ni(PhC(O)C(OH)C(O)Ph)]ClO4 (1)), supported by the 6-Ph2TPA chelate ligand (6-Ph2TPA = N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine) and containing a cis-beta-keto-enolate ligand having a C2 hydroxyl substituent, undergoes reaction with O2 to produce a Ni(II) monobenzoate complex ([(6-Ph2TPA)Ni(O2CPh)]ClO4 (3)), CO, benzil (PhC(O)C(O)Ph), benzoic acid, and other minor unidentified phenyl-containing products. Complex 3 has been identified through independent synthesis and was characterized by X-ray crystallography, 1H NMR, FAB-MS, FTIR, and elemental analysis. A series of cis-beta-keto-enolate Ni(II) complexes supported by the 6-Ph2TPA ligand ([(6-Ph2TPA)Ni(PhC(O)CHC(O)Ph)]ClO4 (4), [(6-Ph2TPA)Ni(CH3C(O)CHC(O)CH3)]ClO4 (5), and [(6-Ph2TPA)Ni(PhC(O)CHC(O)C(O)Ph) (6)) have been prepared and characterized. While these complexes exhibit structural and/or spectroscopic similarity to 1, all are unreactive with O2. The results of this study are discussed in terms of relevance to Ni(II)-containing acireductone dioxygenase enzymes, as well as in the context of recently reported cofactor-free, quercetin, and beta-diketone dioxygenases.