Search

The electrochemical deposition and stripping of mercury on gold surfaces was investigated to assess whether gold electrodes would return to mercury-free states after stripping analyses. X-ray photoelectron spectroscopy studies demonstrate the presence of mercury on gold foil electrodes that have undergone controlled-potential deposition procedures in [Hg.sup.2+] solutions (10 nM-0.1 mM) followed by stripping and cleaning in mercury-free electrolyte. Results show that mercury is not completely removed electrochemically from the gold electrodes, even when the oxidizing potential is +2.5 V vs Ag/AgCl. Bulk electrolyses deposition and stripping procedures coupled with cold vapor atomic absorption spectroscopic analyses of solutions after deposition and stripping are also reported. Results suggest that the nature of the gold electrode is fundamentally altered by irreversible adsorption of mercury; that is, mercury is adsorbed during deposition and some of the mercury is retained even after stripping and cleaning. The implications and strategies for using stripping analysis and gold electrodes for the measurement of mercury under the experimental conditions employed in this study are discussed.

Remote, in situ sensors able to selectively detect mercury and other ionic contaminants, would provide many benefits in the monitoring of trace ion contaminants in industrial applications. The shear horizontal acoustic plate mode (SHAPM) device, is a method of detecting mercury in solution. The piezoelectric device, in combination with an electrochemical cell, offers increased sensitivity and reversibility.

A study was conducted to determine the stability and photochemistry of cis- and trans-Au2X2(dppee) (X = Cl (2), Br (3) and I (4)) by quantum theoretical methods. Findings from the ab initio calculations showed direct relationship between cis compounds and the softness of the ligand in aurophilic interactions and the stabilization of the first excited singlet state which led to a red shift and increased transition moment in contrast to the trans product. Moreover, the interactions were deemed instrumental to analyzing the photochemistry observed in gold compounds such as Au2X2 (dppee).

The extended X-ray absorption fine structure and luminescence spectroscopic studies of solid samples of neutral, dinuclear gold(I) complexes reveal gold(I)-gold(I) interactions. Luminescence is observed for all the neutral, dinuclear gold(I) complexes at room temperature in the solid state. A large distortion occurs in the excited state compared to the ground state.

The structure and bonding of dinuclear gold complexes are studied and the occurrence of gold(I)-gold(I) interactions correlated with ring size or rigidity of the complex. Intermolecular gold-gold interactions were observed in solid state structures of (Au2(p-tc)2(dpppn)) and (Au2(p-tc)2(dppb)), the two largest open chain molecules. Red shifts were evaluated as the result of gold-gold interactions and repulsive interactions between sulfur centered HOMO orbitals. Variable-temperature NMR studies showed equilibria bonding between intramolecular gold in some solutions of complexes.

Cloud-top pressure remote-sensing via reflected sunlight observations in the A band of oxygen absorption is attempted. The attenuation of reflected radiance by oxygen absorption above and within the cloud makes this difficult. Thus, cloud-top pressure and photon pathlength distribution within the cloud is retrieved simultaneously, and error induced by instrumental noise and thermal uncertainties are estimated. Spectral resolution and spectral channel number and placement affect such errors. However, accuracies of 5 hPa are possible under certain conditions.

The organometallic complex Co(CO)3L2 exhibits solvent-dependent spectral properties and substitution reactivity. This behavior can be attributed to the degree of unpaired electron delocalization that exists in the complex. Solvents of decreasing polarity facilitate the increase in the delocalization of the unpaired electron coming from the chelating phosphine to the Co(CO)3 fragment. This makes the organometallic complex more reactive in nonpolar solvents than in polar solvents.

The InterChemNet (ICN) project offers a Web-based platform to support instrumentation, curriculum delivery and evaluation of the effectiveness of laboratory curricula. It was conceived to overcome barriers to effective learning in large general chemistry classes by targeting the lab portion of the course.

A study on the targets and mechanisms of action of gold complexes to counter rheumathoid arthritis demonstrated that mild oxidation of gold-sulfur complexes produces gold clusters and disulfide by way of an electron-transfer mechanism that occurs with unexpected n values. These results suggest an oxidative reactivity for gold-sulfur centers that has not been previously recognized. Furthermore, the oxidative reactivity of gold-sulfur complexes suggests some exciting possibilities for the biochemistry of gold.

This paper examines the effects of demographic dynamics on the measured rates of economic growth. It develops a model of production with labor productivity that varies with age. Macroeconomic and demographic data are used to estimate the relative productivity of different age groups. A panel database of effective labor supply is constructed in order to reflect the changing age structure of the population. The historical measured growth rates are then deconstructed into effects of demographic dynamics and into 'real' growth rates, net of demographic effects. [JEL J11, J21, 047], The series of dinuclear gold(I) complexes, Au2X2(cis-dppee) (X=Cl, Br, I, p-SC6H4-CH3) exhibit unique photochemical reactivity and isomerize to the trans isomers, Au2X2 (trans-dppee), upon photolysis. It is significant that photochemical isomerization also takes place in the solid state. The dinuclear gold(I) complexes are investigated using cis- and trans-dppee ligands, Au2X2(cis-dppee) and Au2X2(trans-dppee) (X = Cl, Br, I, p-SC6H4CH3).

Primitive placental mammals include shrews and moles, comprising the Insectivora of some authors. Shrews, considered to be relatively basal among living mammals, have been shown to contain locomotor muscles lacking type I, slow oxidative myofibers. One rationale proposed for this is that these mammals are lightweight and do not support their bodies off of the substrate for long periods of time. The question remains as to whether or not the muscles have been constrained (to lack type I fibers) by phylogeny assuming that the condition is a synapomorphy within Insectivora and other basal mammals. Thus, the evolution of type I fibers might be associated with derived mammals in response to functional demands. We analyzed the muscle architecture and histochemical properties, as well as myosin heavy chain isoforms in star-nosed moles (Condylura cristata) as one example of a primitive group of mammals despite their unique locomotor morphology and natural history. A suite of muscles including teres major and pectoralis contained all type II fibers that were of uniformly small diameter but that expressed a range of glycolytic potential as assessed with alpha-GPD reactions. Screening against two type I myosin antibodies yielded negative results in shrew and mole muscle. While birds and reptiles appear to have muscles containing type I fibers, we are intrigued at the absence of these fatigue resistant myofibers in these basal mammals. We extend this analysis to include functional interpretation of the forelimb and hindlimb muscles of the star-nosed mole and comparison with the short-tailed shrew (Blarina brevicauda).

The lengths and diameters of avian limb bone elements increase rapidly throughout ontogeny. Allometric scaling patterns could act to increase material strength or the size of limb elements experiencing greater stresses as mass increases and/or different limbs are used in locomotion during ontogeny. In this investigation, four avian taxa (chickens, ducks, emu, and pigeons) with variable developmental periods and patterns of limb use throughout ontogeny were examined from in ovo to adulthood. In general, most bone elements across the four species exhibited positive allometry (L a D>1.0exp) Data collected on bone length and diameter revealed that the rate of bone development appears to correlate with limb use. For example, leg bone lengths and diameters of ducks increased more rapidly than bone elements of wing; whereas, pigeons and chicken leg and wing bone lengths grew more similarly. Finally, taxa with shorter developmental periods (pigeons vs ducks and chickens) may experience more constrained influences on growth patterns.