Bacterial Cadmium Sulfide Semiconductor Particles: An Assessment of their Photoactivity by EPR Spectroscopy

Abstract— The bacterium Klebsiella aerogenes produces extracellular particles of cadmium sulfide in the presence of cadmium ions. The photoactivity of these particles has been studied using electron paramagnetic resonance (EPR) spectroscopy. Bacterial samples containing these semiconductor particles were irradiated with visible light in the presence of a spin trap, either phenyl-tert-butylnitrone (PBN) or 5,5-dimethyl-l-pyrroline-N-oxid(eD MPO). The results obtained reveal that a number of radicals, both oxygen and carbon based, are generated. Bacterial samples grown in the absence of cadmium ions exhibit weak, irradiation-independent EPR signals. These bacterially produced radicals are quenched when CdS particles are present. The observation of light-induced radicals provides evidence that the bacterial CdS particles are photoactive, behaving in a similar manner to inorganic CdS particles, and therefore could be used to mediate photocatalytic reactions.     

Quantification of surface-bound proteins by fluorometric assay: Comparison with quartz crystal microbalance and amido black assay

Protein adsorption is of major and widespread interest, being useful in the fundamental understanding of biological processes at interfaces through to the development of new materials. A number of techniques are commonly used to study protein adhesion, but few are directly quantitative. Here we describe the use of Nano Orange, a fluorometric assay, to quantitatively assess the adsorption of bovine fibrinogen and albumin onto model hydrophilic (OH terminated) and hydrophobic (CH3 terminated) surfaces. Results obtained using this method allowed the calibration of previously unquantifiable data obtained on the same surfaces using quartz crystal microbalance measurements and an amido black protein assay. Both proteins were found to adsorb with higher affinity but with lower saturation levels onto hydrophobic surfaces. All three analytical techniques showed similar trends in binding strength and relative amounts adsorbed over a range of protein concentrations, although the fluorometric analysis was the only method to give absolute quantities of surface-bound protein. The versatility of the fluorometric assay was also probed by analyzing protein adsorption onto porous superhydrophobic and superhydrophilic surfaces. Results obtained using the assay in conjunction with these surfaces were surface chemistry dependent. Imbibition of water into the superhydrophilic coatings provided greater surface area for protein adsorption, although the protein surface density was less than that found on a comparable flat hydrophilic surface. Superhydrophobic surfaces prevented protein solution penetration. This paper demonstrates the potential of a fluorometric assay to be used as an external calibration for other techniques following protein adsorption processes or as a supplemental method to study protein adsorption. Differences in protein adsorption onto hydrophilic vs superhydrophilic and hydrophobic vs superhydrophobic surfaces are highlighted.     

Measurement of the absolute Raman cross section of the optical phonon in silicon

The absolute Raman cross section σ_RS of the first-order 519 cm⁻¹ optical phonon in silicon was measured using a small temperature-controlled blackbody for the signal calibration of the Raman system. Measurements were made with a 25-mil thick (001) silicon sample located in the focal plane of a 20-mm effective focal length (EFL) lens using 785-, 1064-, and 1535-nm CW pump lasers for the excitation of Raman scattering. The pump beam was polarized along the [100] axis of the silicon sample. Values of 1.0±0.2×10⁻²⁷, 3.6±0.7×10⁻²⁸, and 1.1±0.2×10⁻²⁹ cm² were determined for for 785-, 1064-, and 1535-nm excitation, respectively. The corresponding values of the Raman scattering efficiency S are 4.0±0.8×10⁻⁶, 1.4±0.3×10⁻⁶, and 4.4±0.8×10⁻⁸ cm⁻¹ sr⁻¹.The values of the Raman polarizability |d| for 785-, 1064-, and 1535-nm excitation are 4.4±0.4×10⁻¹⁵, 5.1±0.5×10⁻¹⁵, and 1.9±0.2×10⁻¹⁵ cm², respectively. The values of 4.4±0.4×10⁻¹⁵ and 5.1±0.5×10⁻¹⁵ cm² for |d| for 785- and 1064-nm excitation, respectively, are 1.3 and 2.0 times larger than the values of 3.5×10⁻¹⁵ and 2.5×10⁻¹⁵ cm² calculated by Wendel. The Raman polarizability |d| computed using the density functional theory in the long-wavelength limit is consistent with the general trend of the measured data and Wendel’s model.     

trans‐Dichloro(dimethyl sulfide‐κS)(pyridine‐κN)platinum(II)

The structure of the title compound, [PtCl₂(C₅H₅N)(C₂H₆S)], consists of discrete mol­ecules in which the Pt‐atom coordination is slightly distorted square planar. The Cl atoms are trans to each other, with a Cl—Pt—Cl angle of 176.60 (7)°. The pyridine ligand is rotated 64.5 (2)° from the Pt square plane and one of the Pt—Cl bonds essentially bisects the C—S—C angle of the di­methyl sulfide ligand. In the crystal structure, there are extensive weak C—H⋯Cl interactions, the shortest of which connects mol­ecules into centrosymmetric dimers. A comparison of the structural trans influence on Pt—S and Pt—­N distances for PtS(CH₃)₂ and Pt(pyridine) fragments, respectively, in square‐planar Pt^II complexes is presented.     

Measurement of the absolute Raman scattering cross section of the 1584‐cm−1 band of benzenethiol and the surface‐enhanced Raman scattering cross section enhancement factor for femtosecond laser‐nanostructured substrates

The absolute Raman scattering cross section (σ_RS) for the 1584‐cm⁻¹ band of benzenethiol at 897 nm (1.383 eV) has been measured to be 8.9 ± 1.8 × 10⁻³⁰ cm² using a 785‐nm pump laser. A temperature‐controlled, small‐cavity blackbody source was used to calibrate the signal output of the Raman spectrometer. We also measured the absolute surface‐enhanced Raman scattering cross section (σ_SERS) of benzenethiol adsorbed onto a silver‐coated, femtosecond laser‐nanostructured substrate. Using the measured values of 8.9 ± 1.8 × 10⁻³⁰ and 6.6 ± 1.3 × 10⁻²⁴ cm² for σ_RS and σ_SERS respectively, we calculate an average cross‐section enhancement factor (EF) of 0.8 ± 0.3 × 10⁶. Copyright © 2009 John Wiley & Sons, Ltd.     

An assessment of the sharpness of carotid artery tissue boundaries with acquisition voxel size and field strength

A measure of the sharpness of vessel wall interfaces in carotid artery MRI may be useful for assessing the conspicuity of the wall's features. An edge detection technique was used to measure the signal intensity gradients in 2D time-of-flight (2D-TOF) and double-inversion recovery black-blood (DIR-BB) carotid artery images of normal subjects that were acquired at 1.5 T with 0.55 x 0.55 x 2.0-mm (0.6 mm3) acquisition voxels and zero filled to reduce the in-plane reconstructed voxel size by one half in each dimension as well as with 0.27 x 0.27 x 2.0-mm (0.15 mm3) acquisition voxels and at 3.0 T with 0.27 x 0.27 x 2.0-mm (0.15 mm3) acquisition voxels using surface coils. The gradient intensities of the lumen-to-background interface varied closely with the contrast-to-noise ratio of the 2D-TOF imaging. For the DIR-BB imaging, in which higher spatial frequency artery structures are visible, the gradient intensities at the interfaces were higher than theoretically predicted at both field strengths with smaller acquisition voxels. The use of acquisition voxels smaller than those previously used at 1.5 T can improve the visualization of carotid artery structures at 1.5 and 3.0 T with surface coil reception.     

Tripyrrolylphosphine as a unique bridging ligand in the Rh6CO14(mu2-P(NC4H4)3) cluster: structure,bonding, fluxionality,thermodynamics, and kinetics studies

Tripyrrolylphosphine reacts with the cluster Rh6CO15(NCMe) to afford the disubstituted Rh6CO14(mu2)-P(NC4H4)3) derivative (2) via the Rh6CO15P(NC4H4)3 intermediate (1) with eta(1)-P coordination. In the solid state, 2 has the phosphine occupying a bridging position where it is bonded to two neighboring Rh atoms in the Rh(6) octahedron through the P-atom and an approximately tetrahedral alpha-carbon atom of one of the pyrrolyl rings. This can be described by the interaction of an electron pair, associated with a negative charge on one of the canonical forms of the NC(4)H(4) ring, with the adjacent Rh center. (1)H NMR spectra show that the solid-state structure is retained in solution, but the phosphine is not rigid, and three distinctive dynamic processes are observed. Each of these represents independent hindered rotation of inequivalent pyrrolyl rings about P-N bonds, the ring involved in the interaction with the Rh(6) skeleton displaying the highest activation barrier with deltaH = 15.8 +/- 0.1 kcal mol(-1) and deltaS = 1.4 +/- 0.3 cal K(-1) mol(-1). The assignment has been confirmed by 1H TOCSY and EXSY experiments, and a mechanism is proposed. The formation of 2 from 1 is reversible in the presence of CO, which is highly unusual for bridged clusters. The kinetics of the forward and reverse reactions have been studied, and the values of DeltaH degrees and DeltaS degrees for formation of 2 (+1.3 +/- 0.5 kcal mol(-1) and -9 +/- 2 cal K(-1) mol (-1), respectively) show that the Rh-C bond in the bridge is comparable in strength with the Rh-CO bond it replaces. The intrinsic entropy of 2 is exceptionally unfavorable, overcoming the favorable entropy caused by CO release, and this allows the reversibility of bridge formation. The reactions proceed via a reactive intermediate that may involve agostic bonding of the ring. The reverse reaction has an exceedingly unfavorable activation entropy that emphasizes the unique nature of 2.     

Errors as Multistable Response Options

Five simulations mimicked benchmark phenomena of intact and dyslexic word naming. Initially, an iterative map was tuned to simulate the frequency × consistency interaction in skilled naming. Subsequently, two model parameters were changed, in turn, to produce the regularization error of surface dyslexia (PINT pronounced to rhyme with /mint/), absent pseudoword (BINT) naming of phonological dyslexia (words are named correctly; pseudowords are not), the semantic error of deep dyslexia (BUSH named as /tree/), and a dissociation in picture naming of spoken versus written responses (the spoken response to a picture of a bush is /tree/, but the written response is BUSH). All errors, except absent pseudoword naming, were simulated as transcritical bifurcations.