Mechanistic studies of nickel(II) alkyl agostic cations and alkyl ethylene complexes: investigations of chain propagation and isomerization in (alpha-diimine)Ni(II)-catalyzed ethylene polymerization

The synthesis of a series of (alpha-diimine)NiR(2) (R = Et, (n)Pr) complexes via Grignard alkylation of the corresponding (alpha-diimine)NiBr(2) precursors is presented. Protonation of these species by the oxonium acid [H(OEt(2))(2)](+)[BAr'(4)](-) at low temperatures yields cationic Ni(II) beta-agostic alkyl complexes which model relevant intermediates present in nickel-catalyzed olefin polymerization reactions. The highly dynamic nature of these agostic alkyl cations is quantitatively addressed using NMR line broadening techniques. Trapping of these complexes with ethylene provides cationic Ni alkyl ethylene species, which are used to determine rates of ethylene insertion into primary and secondary carbon centers. The Ni agostic alkyl cations are also trapped by CH(3)CN and Me(2)S to yield Ni(R)(L)(+) (L = CH(3)CN, Me(2)S) complexes, and the dynamic behavior of these species in the presence of varied [L] is discussed. The kinetic data obtained from these experiments are used to present an overall picture of the ethylene polymerization mechanism for (alpha-diimine)Ni catalysts, including effects of reaction temperature and ethylene pressure on catalyst activity, polyethylene branching, and polymer architecture. Detailed comparisons of these systems to the previously presented analogous palladium catalysts are made.     

The dynamics of impacting water droplets on alkanethiol self-assembled monolayers with co-adsorbed CH3 and CO2H terminal groups

The impact of water droplets (diameter 3.6 mm) at a fixed Weber number of 59 on solid surfaces with precisely tailored surface wettabilities was studied experimentally using a high-speed imaging camera at 2500 frames per second. Solid surface wettability was varied using four fractional mixtures of self-assembled monolayers of 1-octadecanethiol and 16-mercaptohexadecanoic acid. The surfaces so obtained are characterized for contact angle and chemical functionality using the axisymmetric drop shape analysis profile (ADSA-P) technique and Fourier transform infrared spectroscopy (FT-IR). Our results correlate the wetting effects of the impacting droplets with the surface energy and contact angle measurements of the tailored surfaces. Literature models for the maximum spreading diameter are employed and compared with those from our experiments. An equation is also proposed for the maximum spreading diameter which makes use of the correct contact angles and results in the least error among the models considered. As a consequence of Young's equation, the correct contact angles to be used for droplet impact dynamics should be the corresponding advancing angles on a smooth substrate of interest. We also conclude that accurate examination of literature models requires careful experimentation on impact dynamic data on well-prepared and characterized surfaces such as those presented here.     

HMDS/KI a simple,a cheap and efficient catalyst for the one-pot synthesis of N-functionalized pyrimidines

The syntheses of N-Alkylpyrimidine derivatives by reacting pyrimidin-2,4-diones with appropriate alkyl halide under microwave irradiation at 400?W were compared to the conventional synthesis route. These methodologies are regioselective and compatible with numerous substrates and furnish the corresponding N-alkylpyrimidines in good yields using a cheap catalyst HMDS/KI in MeCN. A comparison study between these two different modes of heating was investigated.     

Do we know the mass of a black hole? Mass of some cosmological black hole models

Using a cosmological black hole model proposed recently, we have calculated the quasi-local mass of a collapsing structure within a cosmological setting due to different definitions put forward in the last decades to see how similar or different they are. It has been shown that the mass within the horizon follows the familiar Brown–York behavior. It increases, however, outside the horizon again after a short decrease, in contrast to the Schwarzschild case. Further away, near the void, outside the collapsed region, and where the density reaches the background minimum, all the mass definitions roughly coincide. They differ, however, substantially far from it. Generically, we are faced with three different Brown–York mass maxima: near the horizon, around the void between the overdensity region and the background, and another at cosmological distances corresponding to the cosmological horizon. While the latter two maxima are always present, the horizon mass maxima is absent before the onset of the central singularity.     

Synthesis of oxo-Phosphoranylidene Aminobenzoic Acid Derivatives by a Multicomponent Reaction

2-Aminobenzoic acids or 4-aminobenzoic acid react with dimethyl acetylenedicarboxylate/triphenylphosphine in less than 20 min at 15–25°C to produce new organic phosphorus compounds in good to excellent yields. The conversion occurs with selective N- over O-alkylation of the amino group and isolation of the products is accomplished simply by filtration.     

Fabrication of an Electrochemical L‐Cysteine Sensor Based on Graphene Nanosheets Decorated Manganese Oxide Nanocomposite Modified Glassy Carbon Electrode

The graphene nanosheets/manganese oxide nanoparticles modified glassy carbon electrode (GC/GNSs/MnOx) was simply prepared by casting a thin film of GNSs on the GC electrode surface, followed by performing electrodeposition of MnOx at applied constant potential. The GC/GNSs/MnOx modified electrode shows high catalytic activity toward oxidation of L ‐cysteine. Hydrodynamic amperometry determination of L ‐cysteine gave linear responses over a concentration range up to 120 µM with a detection limit of 75 nM and sensitivity of 27 nA µM^?1. The GC/GNSs/MnOx electrode appears to be a highly efficient platform for the development of sensitive, stable and reproducible L ‐cysteine electrochemical sensors.     

Highly Sensitive and Selective Amperometric Detection of Periodate at Glassy Carbon Electrode Modified with a Cyclometalated Iridium(III) Complex and Single‐Wall Carbon Nanotubes

Single‐wall carbon nanotubes (SWCNTs) were used as an immobilization matrix to incorporate [Ir(ppy)₂(phen‐dione)](PF₆) complex onto a glassy carbon electrode for the study of electrocatalytic reduction of periodate ion. Detailed preliminary electrochemical data for the Ir(III)‐complex in acetonitrile solution and for the modified GCE/SWCNTs/[Ir(ppy)₂(phen‐dione)](PF₆)/CGE are presented. The modified electrode was applied to selective amperometric detection of periodate through its electrocatalytic reduction to iodide at 0.200 V and pH 2.0. The use of amperometry resulted in two calibration plots over the concentration ranges of 1‐20 μM and 20‐450 μM, with a detection limit of 0.6 μM and sensitivity of 198 nA μM^?1.     

Polycaprolactone solution–based ink for designing microfluidic channels on paper via 3D printing platform for biosensing application

This work reports a novel fabrication technique for development of channels on paper‐based microfluidic devices using the syringe module of a 3D printing syringe–based system. In this study, printing using polycaprolactone (PCL)‐based ink (Mw 70 000‐90 000) was employed for the generation of functional hydrophobic barriers on Whatman qualitative filter paper grade 1 (approximate thickness of 180 μm and pore diameter of 11 μm), which would effectively channelize fluid flow to multiple assay zones dedicated for different analyte detection on a microfluidic paper‐based analytical device (μPAD). The standardization studies reveal that a functional hydrophilic channel for sample conduction fabricated using the reported technique can be as narrow as 460.7 ± 20 μm and a functional hydrophobic barrier can be of any width with a lower limit of about 982.2 ± 142.75 μm when a minimum number of two layers of the ink is extruded onto paper. A comparison with the hydrodynamic model established for writing with ink is used to explain the width of the line printed by this system. A fluid flow analysis through a single channel system was also carried out to establish its conformity with the Washburn model, which governs the fluid flow in two‐dimensional μPAD. The presented fabrication technique proves to be a robust strategy that effectively taps the advantages of this 3D printing technique in the production of μPADs with enhanced speed and reproducibility.     

Critical dimensions for strings,bags,...

Consider extendedd-dimensional objects such as strings (d=1), membranes (d=2), ... It is argued that their quantum theories cannot be consistent in space-times of dimension exceeding the critical valueD=2+24/d (orD=2+8/d in the supersymmetric case). This rules out consistent theories for objects extended in more than 5 (3 in the supersymmetric case) space-like dimensions.