XAS spectroelectrochemistry: reliable measurement of X‐ray absorption spectra from redox manipulated solutions at room temperature

The design and operation of a low‐volume spectroelectrochemical cell for X‐ray absorption spectroscopy (XAS) of solutions at room temperature is described. Fluorescence XAS measurements are obtained from samples contained in the void space of a 50 µL reticulated vitreous carbon (sponge) working electrode. Both rapid electrosynthesis and control of the effects of photoreduction are achieved by control over the flow properties of the solution through the working electrode, where a good balance between the rate of consumption of sample and the minimization of decomposition was obtained by pulsing the flow of the solution by 1–2 µL with duty cycle of ～3 s while maintaining a small net flow rate (26–100 µL h^?1). The performance of the cell in terms of control of the redox state of the sample and minimization of the effects of photoreduction was demonstrated by XAS measurements of aqueous solutions of the photosensitive Fe^III species, [Fe(C₂O₄)₃]^3?, together with that of the electrogenerated [Fe(C₂O₄)₃]^4? product. The current response from the cell during the collection of XAS spectra provides an independent measure of the stability of the sample of the measurement. The suitability of the approach for the study of small volumes of mM concentrations of protein samples was demonstrated by the measurement of the oxidized and electrochemically reduced forms of cytochrome c.     

Reevaluation of the kinetics of polynuclear mimics for manganese catalases

Considerable effort has been expended in order to understand the mechanism of manganese catalases and to develop functional mimics for these enzymes. For many years, the most efficient reactivity mimic was [MnIVsalpn(mu-O)]2 [H2salpn = 1,3-bis(salicylideneiminato)propane], a compound that cycles between the MnIV2 and MnIII2 oxidation levels instead of the MnII2 and MnIII2 oxidation states used by the enzyme, with kcat = 250 s(-1) and kcat/KM = 1000 M(-1) s(-1). Recently, a truly exceptional high value of kcat was reported for the complex [Mn(bpia)(mu-OAc)]22+ [bpia = bis(picolyl)(N-methylimidazol-2-yl)amine]. On the basis of a calculated kcat value of 1100 s(-1) and an efficiency kcat/KM of 34 000 M(-1) s(-1), this complex has been suggested to represent a significant breakthrough in catalytic efficiencies of manganese catalase mimics. However, a plot of ri/[cat]T vs [H2O2]0, where the saturation value approaches 1.5 s(-1), is inconsistent with the 1100 s(-1) value tabulated for kcat. Similar discrepancies are observed for two other families of manganese complexes containing either a Mn2(mu-OPh)22+ core and different substituted tripodal ligands or complexes of methyl and ethyl salicylimidate, with an Mn2(mu-OPh)24+ core. Reevaluation of the kinetic parameters for these three systems reveals that the originally reported values were overestimated by a factor of approximately 1000 for both kcat and kcat/KM. We discuss the origin of the discrepancy between the previously published kinetic parameters and the newly derived values. Furthermore, we provide a short analysis of the existing manganese catalase mimics in an effort to provide sound directions for future investigations in this field.     

Characteristics of X‐ray attenuation in electrospun bismuth oxide/polylactic acid nanofibre mats

The characteristics of the X‐ray attenuation in electrospun nano(n)‐ and micro(m)‐Bi₂O₃/polylactic acid (PLA) nanofibre mats with different Bi₂O₃ loadings were compared as a function of energy using mammography (i.e. tube voltages of 22–49 kV) and X‐ray absorption spectroscopy (XAS) (7–20 keV). Results indicate that X‐ray attenuation by electrospun n‐Bi₂O₃/PLA nanofibre mats is distinctly higher than that of m‐Bi₂O₃/PLA nanofibre mats at all energies investigated. In addition, with increasing filler loading (n‐Bi₂O₃ or m‐Bi₂O₃), the porosity of the nanofibre mats decreased, thus increasing the X‐ray attenuation, except for the sample containing 38 wt% Bi₂O₃ (the highest loading in the present study). The latter showed higher porosity, with some beads formed, thus resulting in a sudden decrease in the X‐ray attenuation.     

Partially informed noise traders

The single auction equilibrium of Kyle??s (1985) is studied, in which noise traders may be partially informed, or alternatively they can be manipulated. Unlike Kyle??s assumption that the quantity traded by the noise traders is independent of the asset value, we assume that the noise traders are able to correlate their trade with the true price. This has several implications for the equilibrium, one being that the informed trader??s expected profits decrease as the noise traders?? ability to correlate positively improve. In the limit, the noise traders do not lose on average, and the informed trader makes zero expected profits. When the correlation is negative, we interpret this as manipulation. In this case the insider makes the highest expected profits, and the informativeness of prices is at its minimum.     

Structures and Properties of Novel Mononuclear Iron(III) Complexes with Benzimidazole Containing Tripodal Tetradentate Ligands

The iron(III) complexes of the tripodal benzimidazole‐containing ligands tris(2‐benzimidazolylmethyl)amine (ntb), bis(2‐benzimidazolylmethyl)(2‐hydroxyethyl)‐amine (bbimae) and tris(5,6‐dimethyl‐2‐benzimidazolylmethyl)amine (me₂ntb) are structural and functional models for intradiol cleaving catechol dioxygenases. The complexes [Fe(ntb)Cl₂]Cl · 3 CH₃OH ( 1 ; P 1, a = 9.830(2) Å, b = 12.542(3) Å, c = 13.139(3) Å, α = 82.88(3)°, β = 73.45(3)°, γ = 85.53(3)°, V = 1539.2(6) ų; Z = 2) and [Fe(bbimae)Cl₂]Cl ( 2 ; P2₁/n, a = 7.461(2) Å, b = 18.994(5) Å, c = 14.515(4) Å, β = 98.22(2)°, V = 2035.8(9) ų, Z = 4) have been characterized by X‐ray crystallography and spectroscopic methods. In the octahedrally coordinated complexes two cis coordination sites – essential for catechol binding – are occupied by chloride ligands. The significant intradiol cleaving catechol dioxygenase activity of the model complexes was examined using 3,5‐di‐tert‐butylcatechol as a substrate.     

Polyimide aligned ferroelectric smectic C liquid crystals

27 alkyl-aromatic polyimides have been synthesized and tested as alignment layers for surface stabilized ferroelectric liquid crystals with a number of room temperature ferroelectric mixtures. The cone angles are used as a quantitative measure of the bistability obtained in these cells. The effect of the structure of the polyimides on the cone angles obtained and the stability of the alignment is discussed.