Unusual magnetic resonance imaging of the head in manganese and ephedrone intoxication - a case report.

Manganese intoxication leads to the accumulation of manganese in the brain, mostly in the globus pallidus, which clinically manifests as a L-DOPA - resistant parkinsonian syndrome with specific symptoms, such as spastic-hypokinetic dysarthria and postural instability. A new kind of manganese poisoning associated with drug abuse has been reported in Eastern European countries. A CASE REPORT: We present an adult patient with neurological abnormalities secondary to manganese intoxication related to the abuse of psychoactive substances. High serum levels of manganese, hyperintense lesions on T1-weighted magnetic resonance imaging (MRI), and parkinsonism in this case confirmed the diagnosis. MRI results showed accumulation of manganese in the basal ganglia which caused an increased signal in this area of the brain on T1 weighted sequence. This is the second case reported with diffuse high signal intensity of the entire white matter due to manganese and ephedron neurointoxication. To the best of our knowledge, this is the first time such extensive pathological changes to cerebellar white matter, located near the fourth ventricle, have been described. CONCLUSIONS: We suggest that chronic exposure to manganese and ephedron damaged the white matter in the cerebral hemispheres and continued to affect the periventricular area of the fourth ventricle, causing continuous changes to the white matter.

Noncrystalline-to-crystalline transformations in Pt nanoparticles.

We show that the noncrystalline-to-crystalline transition of supported Pt nanoparticles (NPs) in the subnanometer to nanometer size range is statistical in nature, and strongly affected by particle size, support, and adsorbates (here we use H2). Unlike in the bulk, a noncrystalline phase exists and is stable in small NPs, reflecting a general mesoscopic feature. Observations of >3000 particles by high-resolution transmission electron microscopy show a noncrystalline-to-crystalline transition zone that is nonabrupt; there is a size regime where disordered and ordered NPs coexist. The NP size at which this transition occurs is strongly dependent on both the adsorbate and the support, and this effect is general for late 5d transition metals. All results are reconciled via a statistical description of particle-support-adsorbate interactions.

Short range order in bimetallic nanoalloys: an extended X-ray absorption fine structure study.

Partial coordination numbers measured by extended X-ray absorption fine structure (EXAFS) spectroscopy have been used for decades to resolve between different compositional motifs in bulk and nanoscale bimetallic alloys. Due to the ensemble-averaging nature of EXAFS, the values of the coordination numbers in nanoparticles cannot be simply interpreted in terms of the degree of alloying or segregation if the compositional distribution is broad. We demonstrate that a Cowley short range order parameter is an objective measure of either the segregation tendency (e.g., a core-shell type) or the degree of randomness (in homogeneous nanoalloys). This criterion can be used even in the case when the clusters are random but have broad compositional distributions. All cases are illustrated using the analyses of EXAFS data obtained in three different nanoscale bimetallic systems: Pt(core)-Pd(shell), Pd(core)-Pt(shell), and Pt-Pd random alloy.

Metastability and structural polymorphism in noble metals: the role of composition and metal atom coordination in mono- and bimetallic nanoclusters.

This study examines structural variations found in the atomic ordering of different transition metal nanoparticles synthesized via a common, kinetically controlled protocol: reduction of an aqueous solution of metal precursor salt(s) with NaBH4 at 273 K in the presence of a capping polymer ligand. These noble metal nanoparticles were characterized at the atomic scale using spherical aberration-corrected scanning transmission electron microscopy (C(s)-STEM). It was found for monometallic samples that the third row, face-centered-cubic (fcc), transition metal [(3M)-Ir, Pt, and Au] particles exhibited more coherently ordered geometries than their second row, fcc, transition metal [(2M)-Rh, Pd, and Ag] analogues. The former exhibit growth habits favoring crystalline phases with specific facet structures while the latter samples are dominated by more disordered atomic arrangements that include complex systems of facets and twinning. Atomic pair distribution function (PDF) measurements further confirmed these observations, establishing that the 3M clusters exhibit longer ranged ordering than their 2M counterparts. The assembly of intracolumn bimetallic nanoparticles (Au-Ag, Pt-Pd, and Ir-Rh) using the same experimental conditions showed a strong tendency for the 3M atoms to template long-ranged, crystalline growth of 2M metal atoms extending up to over 8 nm beyond the 3M core.

Influence of adsorbates on the electronic structure, bond strain, and thermal properties of an alumina-supported Pt catalyst.

We describe the results of an X-ray absorption spectroscopy (XAS) study of adsorbate and temperature-dependent alterations of the atomic level structure of a prototypical, noble metal hydrogenation and reforming catalyst: ∼1.0 nm Pt clusters supported on gamma alumina (Pt/γ-Al(2)O(3)). This work demonstrates that the metal-metal (M-M) bonding in these small clusters is responsive to the presence of adsorbates, exhibiting pronounced coverage-dependent strains in the clusters' M-M bonding, with concomitant modifications of their electronic structures. Hydrogen and CO adsorbates demonstrate coverage-dependent bonding that leads to relaxation of the M-M bond strains within the clusters. These influences are partially compensated, and variably mediated, by the temperature-dependent electronic perturbations that arise from cluster-support and adsorbate-support interactions. Taken together, the data reveal a strikingly fluxional system with implications for understanding the energetics of catalysis. We estimate that a 9.1 ± 1.1 kJ/mol strain exists for these clusters under H(2) and that this strain increases to 12.8 ± 1.7 kJ/mol under CO. This change in the energy of the particle is in addition to the different heats of adsorption for each gas (64 ± 3 and 126 ± 2 kJ/mol for H(2) and CO, respectively).

The atomic structural dynamics of γ-Al2O3 supported Ir-Pt nanocluster catalysts prepared from a bimetallic molecular precursor: a study using aberration-corrected electron microscopy and X-ray absorption spectroscopy.

This study describes a prototypical, bimetallic heterogeneous catalyst: compositionally well-defined Ir-Pt nanoclusters with sizes in the range of 1-2 nm supported on γ-Al(2)O(3). Deposition of the molecular bimetallic cluster [Ir(3)Pt(3)(µ-CO)(3)(CO)(3)(η-C(5)Me(5))(3)] on γ-Al(2)O(3), and its subsequent reduction with hydrogen, provides highly dispersed supported bimetallic Ir-Pt nanoparticles. Using spherical aberration-corrected scanning transmission electron microscopy (C(s)-STEM) and theoretical modeling of synchrotron-based X-ray absorption spectroscopy (XAS) measurements, our studies provide unambiguous structural assignments for this model catalytic system. The atomic resolution C(s)-STEM images reveal strong and specific lattice-directed strains in the clusters that follow local bonding configurations of the γ-Al(2)O(3) support. Combined nanobeam diffraction (NBD) and high-resolution transmission electron microscopy (HRTEM) data suggest the polycrystalline γ-Al(2)O(3) support material predominantly exposes (001) and (011) surface planes (ones commensurate with the zone axis orientations frequently exhibited by the bimetallic clusters). The data reveal that the supported bimetallic clusters exhibit complex patterns of structural dynamics, ones evidencing perturbations of an underlying oblate/hemispherical cuboctahedral cluster-core geometry with cores that are enriched in Ir (a result consistent with models based on surface energetics, which favor an ambient cluster termination by Pt) due to the dynamical responses of the M-M bonding to the specifics of the adsorbate and metal-support interactions. Taken together, the data demonstrate that strong temperature-dependent charge-transfer effects occur that are likely mediated variably by the cluster-support, cluster-adsorbate, and intermetallic bonding interactions.

Visualizing materials chemistry at atomic resolution.

Analytical electron microscopy--empowered by advances in electron optics and detectors--is poised to radically transform our understanding of the complex phenomena arising from atomic and electronic structure in materials chemistry. (To listen to a podcast about this article, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html.).

Structural characterization of Pt-Pd and Pd-Pt core-shell nanoclusters at atomic resolution.

We describe the results of a study at atomic resolution of the structures exhibited by polymer-capped monometallic and bimetallic Pt and Pd nanoclusters--models for nanoscale material electrocatalysts--as carried out using an aberration-corrected scanning transmission electron microscope (STEM). The coupling of sub-nanometer resolution with Z-contrast measurements provides unprecedented insights into the atomic structures and relative elemental speciation of Pt and Pd within these clusters. The work further defines the nature of deeply quenched states that prevent facile conversions of core-shell motifs to equilibrium alloys and the nature of nonidealities such as twinning (icosahedral cores) and atomic segregation that these structures can embed. The nature of the facet structure present in these model systems is revealed by theory directed modeling in which experimental intensity profiles obtained in Z-contrast measurements at atomic resolution are compared to simulated intensity profiles using theoretically predicted cluster geometries. These comparisons show close correspondences between experiment and model and highlight striking structural complexities in these systems that are compositionally sensitive and subject to amplification by subsequent cluster growth processes. The work demonstrates an empowering competency in nanomaterials research for STEM measurements carried out using aberration corrected microscopes, approaches that hold considerable promise for characterizing the structure of these and other important catalytic materials systems at the atomic scale.

The emergence of nonbulk properties in supported metal clusters: negative thermal expansion and atomic disorder in Pt nanoclusters supported on gamma-Al2O3.

The structural dynamics-cluster size and adsorbate-dependent thermal behaviors of the metal-metal (M-M) bond distances and interatomic order-of Pt nanoclusters supported on a gamma-Al(2)O(3) are described. Data from scanning transmission electron microscopy (STEM) and X-ray absorption spectroscopy (XAS) studies reveal that these materials possess a dramatically nonbulklike nature. Under an inert atmosphere small, subnanometer Pt/gamma-Al(2)O(3) clusters exhibit marked relaxations of the M-M bond distances, negative thermal expansion (NTE) with an average linear thermal expansion coefficient alpha = (-2.4 +/- 0.4) x 10(-5) K(-1), large static disorder and dynamical bond (interatomic) disorder that is poorly modeled within the constraints of classical theory. The data further demonstrate a significant temperature-dependence to the electronic structure of the Pt clusters, thereby suggesting the necessity of an active model to describe the cluster/support interactions mediating the cluster's dynamical structure. The quantitative dependences of these nonbulklike behaviors on cluster size (0.9 to 2.9 nm), ambient atmosphere (He, 4% H(2) in He or 20% O(2) in He) and support identity (gamma-Al(2)O(3) or carbon black) are systematically investigated. We show that the nonbulk structural, electronic and dynamical perturbations are most dramatically evidenced for the smallest clusters. The adsorption of hydrogen on the clusters leads to an increase of the Pt-Pt bondlengths (due to a lifting of the surface relaxation) and significant attenuation of the disorder present in the system. Oxidation of these same clusters has the opposite effect, leading to an increase in Pt-Pt bond strain and subsequent enhancement in nonbulklike thermal properties. The structural and electronic properties of Pt nanoclusters supported on carbon black contrast markedly with those of the Pt/gamma-Al(2)O(3) samples in that neither NTE nor comparable levels of atomic disorder are observed. The Pt/C nanoclusters do exhibit, however, both size- and adsorbate-induced trends in bond strain that are similar to those of their Pt/gamma-Al(2)O(3) analogues. Taken together, the data highlight the significant role that electronic effects--specifically charge exchange due to both metal-support and metal-adsorbate interactions--play in mediating the structural dynamics of supported nanoscale metal clusters that are broadly used as heterogeneous catalysts.

Intracorneal ring segments after laser in situ keratomileusis.

PURPOSE: To evaluate the safety and efficacy of intracorneal ring segments (ICRS) for correction of residual refractive error in patients previously operated with laser in situ keratomileusis (LASIK). METHODS: Thirteen postoperative LASIK eyes (eight patients) with residual myopic refractive error underwent implantation with INTACS (Keravision) intracorneal ring segments. Correction of the residual error was the first goal, but also improved best spectacle-corrected visual acuity was obtained by correcting residual irregular astigmatism. RESULTS: Mean spherical equivalent refraction improved from -3.25 to +0.75 D and mean uncorrected visual acuity improved from 0.2 to 0.6 after ICRS insertion. Best spectacle-corrected visual acuity remained stable or improved; no eyes lost lines of corrected visual acuity. In one of the 13 eyes, the intracorneal ring segments were removed because of progressive stromal melting. CONCLUSIONS: The use of corneal ring segments in selected eyes with residual myopic refractive errors after LASIK was safe and effective.