Synthesis and characterization of a new family of bi-, tri-, tetra-, and pentanuclear ferric complexes

Nine members of a new family of polynuclear ferric complexes have been synthesized and characterized. The reaction of Fe(O(2)CMe)(2) with polydentate Schiff base proligands (H(2)L) derived from salicylidene-2-ethanolamine, followed in some cases by reaction with carboxylic acids, has afforded new complexes of general formulas [Fe(2)(pic)(2)(L)(2)] (where pic(-) is the anion of 2-picolinic acid), [Fe(3)(O(2)CMe)(3)(L)(3)], [Fe(4)(OR)(2)(O(2)CMe)(2)(L)(4)], and [Fe(5)O(OH)(O(2)CR)(4)(L)(4)]. The tri-, tetra-, and pentanuclear complexes all possess unusual structures and novel core topologies. M?ssbauer spectroscopy confirms the presence of high-spin ferric centers in the tri- and pentanuclear complexes. Variable-temperature magnetic measurements suggest spin ground states of S = 0, 1/2, 0, and 5/2 for the bi-, tri-, tetra-, and pentanuclear complexes, respectively. Fits of the magnetic susceptibility data have provided the magnitude of the exclusively antiferromagnetic exchange interactions. In addition, an easy-axis-type magnetic anisotropy has been observed for the pentanuclear complexes, with D values of approximately -0.4 cm(-)(1) determined from modeling the low-temperature magnetization data. A low-temperature micro-SQUID study of one of the pentanuclear complexes reveals magnetization hysteresis at nonzero field. This is attributed to an anisotropy-induced energy barrier to magnetization reversal that is of molecular origin. Finally, an inelastic neutron scattering study of one of the trinuclear complexes has revealed that the magnetic behavior arises from two distinct species.     

Synthesis and spectroscopic characterization of a new family of Ni(4) spin clusters

A new family of tetranuclear Ni complexes [Ni(4)(ROH)(4)L(4)] (H(2)L = salicylidene-2-ethanolamine; R = Me (1) or Et (2)) has been synthesized and studied. Complexes 1 and 2 possess a [Ni(4)O(4)] core comprising a distorted cubane arrangement. Magnetic susceptibility and inelastic neutron scattering studies indicate a combination of ferromagnetic and antiferromagnetic pairwise exchange interactions between the four Ni(II) centers, resulting in an S = 4 spin ground state. Magnetization measurements reveal an easy-axis-type magnetic anisotropy with D approximately -0.93 cm(-)(1) for both complexes. Despite the large magnetic anisotropy, no slow relaxation of the magnetization is observed down to 40 mK. To determine the origin of the low-temperature magnetic behavior, the magnetic anisotropy of complex 1 was probed in detail using inelastic neutron scattering and frequency domain magnetic resonance spectroscopy. The spectroscopic studies confirm the easy-axis-type anisotropy and indicate strong transverse interactions. These lead to rapid quantum tunneling of the magnetization, explaining the unexpected absence of slow magnetization relaxation for complex 1.     

Single-molecule magnets: novel Mn(8) and Mn(9) carboxylate clusters containing an unusual pentadentate ligand derived from pyridine-2,6-dimethanol

The reactions of the Mn(III)(3) and Mn(II)Mn(III)(2) complexes [Mn(3)O(O(2)CEt)(6)(py)(3)][ClO(4)] and [Mn(3)O(O(2)CEt)(6)(py)(3)] with pyridine-2,6-dimethanol (pdmH(2)) afford the mixed-valence Mn(II)(6)Mn(III)(2) octanuclear complex [Mn(8)O(2)(py)(4)(O(2)CEt)(8)(L)(2)][ClO(4)](2) (1) and the Mn(II)(7)Mn(III)(2) enneanuclear complex [Mn(9)(O(2)CEt)(12)(pdm)(pdmH)(2)(L)(2)] (2), respectively. Both compounds contain a novel pentadentate ligand, the dianion of (6-hydroxymethylpyridin-2-yl)-(6-hydroxymethylpyridin-2-ylmethoxy)methanol (LH(2)), which is the hemiacetal formed in situ from the Mn-assisted oxidation of pdmH(2). Complex 1 crystallizes in the monoclinic space group P2(1)/n with the following cell parameters at -160 degrees C: a = 16.6942(5) A, b = 13.8473(4) A, c = 20.0766(6) A, beta = 99.880(1) degrees, V = 4572.27 A(3), and Z = 2, R (R(w)) = 4.78 (5.25). Complex 2.0.2MeCN crystallizes in the triclinic space group Ponemacr; with the following cell parameters at -157 degrees C: a = 12.1312(4) A, b = 18.8481(6) A, c = 23.2600(7) A, alpha = 78.6887(8) degrees, beta = 77.9596(8) degrees, gamma = 82.3176(8) degrees, V = 5076.45 A(3), and Z = 2, R (R(w)) = 4.12 (4.03). Both complexes are new structural types comprising distorted-cubane units linked together, albeit in two very different ways. In addition, complex 2 features three distinct binding modes for the chelating ligands derived from deprotonated pdmH(2). Complexes 1 and 2 were characterized by variable-temperature ac and dc magnetic susceptibility measurements and found to possess spin ground states of 0 and 11/2, respectively. Least-squares fitting of the reduced magnetization data gave S = 11/2, g = 2.0, and D = -0.11 cm(-1) for complex 2, where D is the axial zero-field splitting parameter. Direct current magnetization versus field studies on 2 at <1 K show hysteresis behavior at <0.3 K, establishing 2 as a new single-molecule magnet. Magnetization decay measurements gave an effective barrier to magnetization relaxation of U(eff) = 3.1 cm(-1) = 4.5 K.     

At-line bioprocess monitoring by immunoassay with rotationally controlled serial siphoning and integrated supercritical angle fluorescence optics

In this paper we report a centrifugal microfluidic “lab-on-a-disc” system for at-line monitoring of human immunoglobulin G (hIgG) in a typical bioprocess environment. The novelty of this device is the combination of a heterogeneous sandwich immunoassay on a serial siphon-enabled microfluidic disc with automated sequential reagent delivery and surface-confined supercritical angle fluorescence (SAF)-based detection. The device, which is compact, easy-to-use and inexpensive, enables rapid detection of hIgG from a bioprocess sample. This was achieved with, an injection moulded SAF lens that was functionalized with aminopropyltriethoxysilane (APTES) using plasma enhanced chemical vapour deposition (PECVD) for the immobilization of protein A, and a hybrid integration with a microfluidic disc substrate. Advanced flow control, including the time-sequenced release of on-board liquid reagents, was implemented by serial siphoning with ancillary capillary stops. The concentration of surfactant in each assay reagent was optimized to ensure proper functioning of the siphon-based flow control. The entire automated microfluidic assay process is completed in less than 30 min. The developed prototype system was used to accurately measure industrial bioprocess samples that contained 10 mg mL⁻¹ of hIgG.     

Engineering Short Peptide Sequences for Uranyl Binding

Peptides are interesting tools to rationalize uranyl–protein interactions, which are relevant to uranium toxicity in vivo. Structured cyclic peptide scaffolds were chosen as promising candidates to coordinate uranyl thanks to four amino acid side chains pre‐oriented towards the dioxo cation equatorial plane. The binding of uranyl by a series of decapeptides has been investigated with complementary analytical and spectroscopic methods to determine the key parameters for the formation of stable uranyl–peptide complexes. The molar ellipticity of the uranyl complex at 195 nm is directly correlated to its stability, which demonstrates that the β‐sheet structure is optimal for high stability in the peptide series. Cyclodecapeptides with four glutamate residues exhibit the highest affinities for uranyl with log K_C=8.0–8.4 and, therefore, appear as good starting points for the design of high‐affinity uranyl‐chelating peptides.     

Quantitative analysis of WC grain shape in sintered WC-Co cemented carbides

The morphology of WC grains is examined by ab initio calculations, and by transmission electron microscopy in a WC-Co cemented carbide. Two compositions are studied to determine the effect of carbon chemical potential on the shape development. The WC grains are found to be truncated triangles, and the grain morphology is adequately reproduced by the ab initio calculations. The energy difference between the two types of grain facets is shown to be due to the formation of stronger bonds with more covalent character between low coordinated W and Co atoms at one type of facet.     

The effect of rate of stimulation on perception of spectral shape by cochlear implantees

The effect of rate of stimulation on spectral shape perception was measured in six users of the Nucleus CI24 cochlear implant. Three spectral shapes were created by using three profiles of current across seven electrode positions. Each current profile was replicated in three stimuli that interleaved stimulus pulses across the seven electrodes with cycle rates (rate per electrode) of 450, 900, and 1800 Hz. The stimulus space resulting from a multidimensional scaling experiment showed a clear dimension related to the rate of stimulation that was orthogonal to the dimension related to the spectral shapes. A second experiment was performed with the same subjects to investigate whether the perceptual dimension related to rate in Experiment 1 could be attributed to different perceptual flatness of the profiles at different rates. In Experiment 2, the rate of stimulation was fixed at 900 Hz and three profiles were created for each spectral shape that differed in flatness. This experiment did not, however, result in an independent perceptual dimension related to the flatness of the profile. In conclusion, rate of stimulation provided an independent perceptual dimension in the multiple-electrode stimuli, in spite of the rates being not discriminable or barely discriminable in single-electrode stimulation.     

Blends of carbon blacks and multiwall carbon nanotubes as reinforcing fillers for hydrocarbon rubbers

The reinforcement of a styrene‐butadiene rubber (SBR) by single fillers—carbon black (CB) or multiwall carbon nanotubes (MWNTs)—or by mixtures of CB and MWNTs, is investigated. The morphologies, mechanical and electrical properties of the composites, are analyzed. A significant improvement in the tensile properties is observed for samples containing a dual phase. Using atomic force (AFM) and transmission electron (TEM) microscopies, we demonstrate that the double loading improves the dispersion of the nanotubes in SBR. Electrical measurements show lower resistivity and a lower percolation threshhold for composites containing blends of fillers, which provides further evidence of better dispersion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 46: 1939–1951, 2008     

Precursor memory effect determining structural properties of sulfated zirconia

Properties of two catalysts tailored in the laboratory conditions by sulfation of commercial Zr-hydroxide and Zr-hydroxide of nitrate origin were compared with those of commercial SO₄-Zr-hydroxide. Equally thermally treated samples in the temperature interval 500–700°C, and having the same amount of sulfur, show different properties indicating memory effect of their solid parent materials. The catalyst obtained by sulfation of commercial Zr-hydroxide differs in amount of residual sulfates upon calcination from other two catalysts. The instability of sulfates in the previous case might be connected to the lowest surface area values of catalyst and the highest fraction of monoclinic phase observed at all applied calcination temperatures.     

Demonstration of a surface plasmon-coupled emission (SPCE)-based immunoassay in the absence of a spacer layer

The technique of surface plasmon-coupled emission (SPCE) involves the coupling of light which is emitted from a fluorophore into the surface plasmon of an adjacent thin metal film, giving rise to highly directional emission. We have combined the advantages of SPCE with the high light collection efficiency of supercritical angle fluorescence by carrying out an immunoassay on a paraboloid array biochip in the absence of the conventional SPCE spacer layer normally used to minimize metal quenching of the fluorescence. In this work, we have successfully demonstrated an SPCE-based assay by utilizing the protein assay layer as the spacer layer. A novel 3 × 3 injection molded polymer biochip with paraboloid elements was used. The paraboloid elements served to enhance the light collection efficiency while the top surface was coated with a gold layer to use excitation of surface plasmons and detection of SPCE emission. Theoretical modeling of the gold-protein layer structure showed that the surface plasmon resonance angles were located in the detection range of the paraboloid biochip. The polarization dependence of SPCE emission was also demonstrated. Finally, a human IgG sandwich immunoassay was carried out which exhibited a limit of detection of ~10 ng/ml using 3σ. The results demonstrate the potential of the SPCE-based paraboloid array biochip as a novel platform for high-throughput analysis of biomolecular interactions.