Structural insight into repeated-rhomboid coordination polymers from 4,4′-dithiodipyridine and zinc nitrate

Reaction of Zn(NO₃)₂·6H₂O with the bent bridging ligand 4,4′-dithiodipyridine (dtdp), showing axial chirality, in the presence of the chelating 1,10-phenanthroline (phen) ligand in ethanol yielded [{Zn(μ-dtdp)₂(H₂O)₂}(NO₃)₂·2C₂H₅OH·2H₂O] _n (1). In 1, Zn²⁺ ions are linked by two dtdp ligands of opposite chirality into a one-dimensional coordination polymer of the repeated-rhomboid type; the phen co-ligand was not encountered in the crystal. Pseudo-symmetry of the lattice is discussed for 1. Reaction of Zn(NO₃)₂·6H₂O and dtdp in an ethanol/water mixture in absence of phen led to the known repeated-rhomboid coordination polymer [{Zn(NO₃)(μ-dtdp)₂(H₂O)}NO₃·4H₂O] _n (2), the crystal structure of which was redetermined at 110 K. At low temperature, the nitrato-κO ligand in one axial position of Zn²⁺ was found to be non-disordered as distinct from the room temperature structure (Horikoshi and Mikuriya, Cryst Growth Des 5:223–230, 2005). The Zn²⁺ ions in 2 are joined by two dtdp ligands of the same chirality.     

Oxidative Catalysis by TAMLs: Obtaining Rate Constants for Non-Absorbing Targets by UV-Vis Spectroscopy

Understanding the catalysis of oxidative reactions by TAML activators of peroxides, i. e. iron(III) complexes of tetraamide macrocyclic ligands, advocated a spectrophotometric procedure for quantifying the catalytic activity of TAMLs for colorless targets (k_II′, M⁻¹ s⁻¹), which is incomparably more advantageous in terms of time, cost, energy, and ecology than NMR, HPLC, UPLC, GC-MS and other similar techniques. Dyes Orange II or Safranin O (S) are catalytically bleached by non-excessive amount of H₂O₂ in the presence of colorless substrates (S₁) according to the rate law: −d[S]/dt=k_Ik_II[H₂O₂][S][TAML]/(k_I[H₂O₂]+k_II[S]+k_II′[S₁]). The bleaching rate is thus a descending hyperbolic function of S₁ : v=ab/(b+[S₁]). Values of k_II′ found from a and b for phenol and propranolol with commonly used TAML [Fe^III{o,o′-C₆H₄(NCONMe₂CO)₂CMe₂}₂(OH₂)]⁺ are consistent with those for S₁ (phenol, propranolol) obtained directly by UPLC. The study sends vital messages to enzymologists and environmentalists.     

Formation of the shear-induced state in dilute cationic surfactant solutions

In cationic surfactant solutions a change of state occurs due to mechanical stresses. In the dilute regime of rodlike micelles the formation of a so-called Shear-Induced State (SIS) occurs above a critical shear rate. In this context dilute means that there is no sterical interaction between rodlike micelles, the solution is below the overlap concentration. Employing a mathematical model, it is shown that aggregation forces are weak compared to hydrodynamic forces. The mathematical formulation is based on a model of Israelachvili which describes the chemical potential of micelles. Hydrodynamic forces are calculated with a rigid-dumbbell model. SIS formation can be explained by the destruction of rodlike micelles.     

Experimental Characterization of Premixed Flame Instabilities of a Model Gas Turbine Burner

In recent years, the NO _x emissions of heavy duty gas turbine burners have been significantly reduced by introducing premixed combustion. These highly premixed burners are known to be prone to combustion oscillations. In this paper, investigations of a single model gas turbine burner are reported focusing on thermo-acoustic instabilities and their interaction with the periodic fluctuations of the velocity and pressure. Phase-locked optical measurement techniques such as LDA and LIF gave insight into the mechanisms.Detailed investigations of a gas turbine combustor rig revealed that the combustor as well as the air plenum oscillate in Helmholtz modes. These instabilities could be attributed to the phase lag of the pressure oscillations between the air plenum and the combustor, which causes an acceleration and deceleration of the air flow through the burner and, therefore, alternating patterns of fuel rich and lean bubbles. When these bubbles reach the reaction zone, density fluctuations are generated which in turn lead to velocity fluctuations and, hence, keep up the pressure oscillations.With increasing the equivalence ratio strong combustion oscillations could be identified at the same frequency. Similarly as with weak oscillations, Helmholtz mode pressure fluctuations are present but the resulting velocity fluctuations in the combustor can be described as a pumping motion of the flow. By the velocity fluctuations the swirl stabilization of the flame is disturbed. At the same time, the oscillating pressure inside the combustor reaches its minimum value. Shortly after the flame expands again, the pressure increases inside the combustor. This phenomenon which is triggered by the pressure oscillations inside the air plenum seems to be the basic mechanism of the flame instability and leads to a significant increase of the pressure amplitudes.     

Work function increase of transparent conductive electrodes by solution processed electron acceptor molecular monolayers

We show how the work function of transparent conductive oxide surfaces can be increased by more than 1 eV by solution-depositing strong electron acceptor monolayers comprising tetrafluoro-tetracyanoquinodimethane (F4TCNQ) or hexaazatriphenylene-hexacarbonitrile (HATCN). The effects of ambient atmosphere on the work function are investigated by comparing Kelvin probe measurements in air and ultraviolet photoelectron spectroscopy in ultrahigh vacuum. In this way, important technological issues related to the influence of ambient moisture on electrode properties are elucidated.