Controlled redistribution of vibrational population by few-cycle strong-field laser pulses

The use of strong-field (i.e. intensities in excess of 10(13) Wcm(-2)) few-cycle ultrafast (durations of 10 femtoseconds or less) laser pulses to create, manipulate and image vibrational wavepackets is investigated. Quasi-classical modelling of the initial superposition through tunnel ionization, wavepacket modification by nonadiabatically altering the nuclear environment via the transition dipole and the Stark effect, and measuring the control outcome by fragmenting the molecule is detailed. The influence of the laser intensity on strong-field ultrafast wavepacket control is discussed in detail: by modifying the distribution of laser intensities imaged, we show that focal conditions can be created that give preference to this three-pulse technique above processes induced by the pulses alone. An experimental demonstration is presented, and the nuclear dynamics inferred by the quasi-classical model discussed. Finally, we present the results of a systematic investigation of a dual-control pulse scheme, indicating that single vibrational states should be observable with high fidelity, and the populated state defined by varying the arrival time of the two control pulses. The relevance of such strong-field coherent control methods to the manipulation of electron localization and attosecond science is discussed.

The unique palladium-centered pentagonal antiprismatic cationic bismuth cluster: a comparison of related metal-centered 10-vertex pnictogen cluster structures by density functional theory

Structures for the metal-centered 10-vertex pnictogen clusters M@Pn(10)(4+) (M = Ni, Pd, Pt; Pn = As, Sb, Bi) based on polyhedra with 3-fold, 4-fold, and 5-fold symmetry have been studied by density functional theory. Among these nine M/Pn combinations, only Pd@Bi(10)(4+) and Pt@Bi(10)(4+) are predicted to have the D(5d) pentagonal antiprism as the lowest energy structure in accord with experimental observation of this cluster in the ternary halide Bi(14)PdBr(10) as well as the prediction of the Wade-Mingos rules for these arachno systems. The lowest energy structures for the arsenic and antimony clusters M@Pn(10)(4+) (Pn = As, Sb) and Ni@Bi(10)(4+) are predicted to have structures derived from a tetracapped trigonal prism that has been severely distorted for M@As(10)(4+) (M = Pd, Pt). The volumes of the As(10) polyhedra other than the pentagonal prism are too small to contain interstitial palladium or platinum atoms so that major distortions are predicted for such clusters leading to partial opening of the polyhedron.

Temporal and spatial patterns of contaminants in Lake Erie watersnakes (Nerodia sipedon insularum) before and after the round goby (Apollonia melanostomus) invasion

Temporal and spatial trends in contaminant concentrations were assessed in Lake Erie watersnakes, a threatened (USA)/endangered (Canada) species restricted to western Lake Erie. Temporal changes in plasma contaminant levels were determined in 1990 and 2003, and spatial patterns in 2003 at 12 sites, throughout the species' range. During this period, the watersnakes' diet changed from fish (75%) and amphibians (25%) that avoid zebra mussels, to round gobies (95%) that feed extensively on zebra mussels. Temporal trends indicate that watersnakes on Pelee and North Bass Islands showed a marginal increase in hexachlorobenzene levels, and a significant decline in dieldrin, oxychlordane, and heptachlor epoxide, likely reflecting declines in aerial deposition and clearing of local vineyards. The contaminants with the greatest burdens, sum PCBs and p,p'-DDE, remained stable in the snakes, consistent with trends in other local biota, suggesting that although the dietary switch to round gobies meant consumption of a more contaminated diet, their diet remained at the same trophic position. We suggest that the watersnakes' PCB and p,p'-DDE temporal patterns reflect the lack of change in sediment concentrations with minimal influence from their dietary switch. Similar to top avian predators, PCBs, p,p'-DDE, and technical chlordane, are most prevalent in watersnakes; this ranking remains unchanged. In 2003, the watersnakes demonstrated significant spatial differences in concentrations of p,p'-DDE, dieldrin, technical chlordane and its metabolites. Their 2003 concentrations of p,p'-DDE, and to a lesser extent PCBs, exceed the recommended interim no-observable effects levels on watersnake embryonic survival. Further investigations are required to determine if these higher levels of PCBs, p,p'-DDE, and technical chlordane, affect reproductive and physiological parameters of the Lake Erie watersnake. Until concentrations of sediment contaminants decline in western Lake Erie, these endangered/threatened watersnakes will continue to be exposed to higher concentrations of persistent organic pollutants.

Oblate deltahedra in dimetallaboranes: geometry and chemical bonding

A new series of nonspherical and very oblate deltahedra, conveniently called the oblatocloso deltahedra, is found in dimetallaboranes among which the dirhenaboranes Cp2Re2B(n-2)H(n-2) (8 <or= n <or= 12) are the prototypes. The D(6h) hexagonal bipyramid is the first member of this series (n = 8). However, the higher members of the series are not bipyramids but are derivable from them by a number of diamond-square-diamond processes. A viable model for the skeletal bonding in the oblatocloso dimetallaboranes can be developed if the two metal vertices, typically degree 6 or 7 vertices, are assumed each to contribute five internal orbitals rather than the three internal orbitals assumed by the Wade-Mingos rules. This leads to 2n + 4 actual skeletal electrons for an n vertex oblatocloso dimetallaborane rather than the Wadean 2n - 4 skeletal electrons. The surface bonding of an n vertex oblatocloso dimetallaborane then consists of n three-center two-electron bonds similar to that in corresponding isocloso metallaboranes thereby leaving four orbitals and four electrons for a metal-metal double bond inside the deltahedron. Removal of one or two boron vertices from oblatocloso deltahedra leads to oblatonido and oblatoarachno dimetallaboranes, respectively, having the same number of skeletal electrons as the oblatocloso deltahedra from which they are derived.

Density Functional Theory Study of 10-Atom Germanium Clusters: Effect of Electron Count on Cluster Geometry

Density functional theory (DFT) at the hybrid B3LYP level has been applied to Ge10z germanium clusters (z = -6, -4, -2, 0, +2, +4, +6) starting from 12 different initial configurations. The D4d 4,4-bicapped square antiprism found experimentally in B10H102- and other 10-vertex clusters with 22 skeletal electrons is calculated for the isoelectronic Ge102- to be the global minimum by more than 15 kcal/mol. The global minima found for electron-rich clusters Ge104- and Ge106- are not those known experimentally. However, experimentally known structures for nido-B10H14 and the pentagonal antiprism of arachno-Pd@Bi104+ are found at higher but potentially accessible energies for Ge104- and Ge106-. The global minimum for Ge10 is the C3v 3,4,4,4-tetracapped trigonal prism predicted by the Wade-Mingos rules and found experimentally in isoelectronic Ni@Ga1010-. However, only slightly above this global minimum for Ge10 (+3.3 kcal/mol) is the likewise C3v isocloso 10-vertex deltahedron found in metallaboranes such as (eta6-arene)RuB9H9 derivatives. Structures found for more electron-poor clusters Ge102+ and Ge104+ include various capped octahedra and pentagonal bipyramids. This study predicts a number of 10-vertex cluster structures that have not yet been realized experimentally but would be interesting targets for future synthetic 10-vertex cluster chemistry using vertex units isolobal with the germanium vertices used in this work.

Gorging on gobies: beneficial effects of alien prey on a threatened vertebrate

Invasive species often have rapid and far-reaching negative impacts on populations and ecological communities. These effects are most common when invasive species have few competitors or predators. Although higher level carnivores do consume invasive species, quantitative effects of new and abundant food sources on predators have rarely been documented and, as a consequence, potentially positive effects of invasive species may be under appreciated. We investigated the effects of the invasive round goby (Neogobius melanostomus (Pallas, 1814)) on diet composition, growth rate, and body size of the Lake Erie Water Snake (Nerodia sipedon insularum (Conant and Clay, 1937)), which is threatened in the USA and endangered in Ontario, Canada. Water Snakes have shifted their diet, and round gobies now constitute >92% of prey consumed. This shift in diet has occurred in just one or two Water Snake generations, yet has resulted in more rapid growth and attainment of larger body size in Water Snakes. These positive effects may reduce predation, speed reproductive maturity, increase offspring production, and fuel population growth of this threatened species.

Density Functional Study of 8- and 11-Vertex Polyhedral Borane Structures: Comparison with Bare Germanium Clusters

Density functional theory (DFT) at the hybrid B3LYP level has been applied to the polyhedral boranes B(n)H(n)(z) (n = 8 and 11, z = -2, -4, and -6) for comparison with isoelectronic germanium clusters Ge(n)(z). The energy differences between the global minima and other higher energy borane structures are much larger relative to the case of the corresponding bare germanium clusters. Furthermore, for both B(8)H(8)(2-) and B(11)H(11)(2-), the lowest energy computed structures are the corresponding experimentally observed most spherical deltahedra predicted by the Wade-Mingos rules, namely the D(2)(d) bisdisphenoid and the C(2)(v) edge-coalesced icosahedron, respectively. Only in the case of B(8)H(8)(2-) is there a second structure close (+2.6 kcal/mol) to the D(2)(d) bisdisphenoid global minimum, namely the C(2)(v) bicapped trigonal prism corresponding to the "square" intermediate in a single diamond-square-diamond process that can lead to the experimentally observed room temperature fluxionality of B(8)H(8)(2-). Stable borane structures with 3-fold symmetry (e.g., D(3)(h), C(3)(v), etc.) are not found for boranes with 8- and 11-vertices, in contrast to the corresponding germanium clusters where stable structures derived from the D(3)(d) bicapped octahedron and D(3)(h) pentacapped trigonal prism are found for the 8- and 11-vertex systems, respectively. The lowest energy structures found for the electron-rich boranes B(8)H(8)(4-) and B(11)H(11)(4-) are nido polyhedra derived from a closo deltahedron by removal of a relatively high degree vertex, as predicted by the Wade-Mingos rules. They relate to isoelectronic species found experimentally, e.g., B(8)H(12) and R(4)C(4)B(4)H(4) for B(8)H(8)(4-) and C(2)B(9)H(11)(2-) for B(11)H(11)(4-). Three structures were found for B(11)H(11)(6-) with arachno type geometry having two open faces in accord with the Wade-Mingos rules.

Density Functional Theory Study of 11-Atom Germanium Clusters: Effect of Electron Count on Cluster Geometry

Density functional theory (DFT) at the hybrid B3LYP level has been applied to the germanium clusters Ge(11)(z) (z = -6, -4, -2, 0, +2, +4, +6) starting from eight different initial configurations. The global minimum within the Ge(11)(2-) set is an elongated pentacapped trigonal prism distorted from D(3)(h) to C(2v) symmetry. However, the much more spherical edge-coalesced icosahedron, also of C(2v) symmetry, expected by the Wade-Mingos rules for a 2n + 2 skeletal electron system and found experimentally in B(11)H(11)(2-) and isoelectronic carboranes, is of only slightly higher energy (+5.2 kcal/mol). Even more elongated D(3)(h) pentacapped trigonal prisms are the global minima for the electron-rich structures Ge(11)(4-) and Ge(11)(6-). For Ge(11)(4-) the C(5v) 5-capped pentagonal antiprism analogous to the dicarbollide ligand C(2)B(9)H(11)(2-) is of significantly higher energy (approximately 28 kcal/mol) than the D(3h) global minimum. The C(2v) edge-coalesced icosahedron is also the global minimum for the electron-poor Ge(11) similar to its occurrence in experimentally known 11-vertex "isocloso" metallaboranes of the type (eta(6)-arene)RuB(10)H(10). The lowest energy polyhedral structures computed for the more hypoelectronic Ge(11)(4+) and Ge(11)(6+) clusters are very similar to those found experimentally for the isoelectronic ions E(11)(7-) (E = Ga, In, Tl) and Tl(9)Au(2)(9-) in intermetallics in the case of Ge(11)(4+) and Ge(11)(6+), respectively. These DFT studies predict an interesting D(5h) centered pentagonal prismatic structure for Ge(11)(2+) and isoelectronic metal clusters.

Density functional theory study of eight-atom germanium clusters: effect of electron count on cluster geometry

Density functional theory (DFT) at the hybrid B3LYP level has been applied to the germanium clusters Ge8z(z=-6, -4, -2, 0, +2, +4) using nine initial geometries. For Ge8(2-) the D2d bisdisphenoid structure predicted by the Wade-Mingos rules is not computed to be the global minimum but instead lies 3.9 kcal mol-1 above the Td tetracapped tetrahedron global minimum predicted to exhibit spherical aromaticity. The hyperelectronic clusters Ge(8)4- and Ge8(6-) have nido B8H12 and square antiprism structures, respectively, as global minima in accord with the Wade-Mingos rules and experimental data on E(8)2+(E=Sb, Bi) cations. Hypoelectronic eight-vertex clusters isoelectronic and isolobal with Ge8, Ge8(2+) and Ge(8)4+ are not known experimentally. Their computed structures include smaller polyhedra having one or more capped triangular faces as well as more open non-polyhedral structures.

Cyclopentadienyl Ruthenium, Rhodium, and Iridium Vertices in Metallaboranes: Geometry and Chemical Bonding

Most cyclopentadienylmetallaboranes containing the vertex units CpM (M = Co, Rh, Ir; Cp = eta(5)-cyclopentadienyl ring, mainly eta(5)-Me(5)C(5)) and CpRu donating two and one skeletal electrons, respectively, have structures closely related to binary boranes or borane anions. Smaller clusters of this type, such as metallaborane analogues of arachno-B(4)H(10) (e.g., (CpIr)(2)B(2)H(8)), nido-B(5)H(9) (e.g., (CpRh)(2)B(3)H(7) and (CpRu)(2)B(3)H(9)), arachno-B(5)H(11) (e.g., CpIrB(4)H(10)), B(6)H(6)(2)(-) (e.g., (CpCo)(4)B(2)H(4)), nido-B(6)H(10) (e.g., CpIrB(5)H(9) and (CpRu)(2)B(4)H(10)), and arachno-B(6)H(12) (e.g., (CpIr)(2)B(4)H(10)), have the same skeletal electron counts as those of the corresponding boranes. However, such clusters with eight or more vertices, such as metallaborane analogues of B(8)H(8)(2)(-) (e.g., (CpCo)(4)B(4)H(4)), arachno-B(8)H(14) (e.g., (CpRu)(2)B(6)H(12)), and nido-B(10)H(14) (e.g., (CpRu)(2)B(8)H(12)), have two skeletal electrons less than those of the corresponding metal-free boranes, analogous to the skeletal electron counts of isocloso boranes relative to those of metal-free deltahedral boranes. Some metallaboranes have structures not analogous to metal-free boranes but instead analogous to metal carbonyl clusters such as 3-capped square pyramidal (CpRu)(2)B(4)H(8) and (CpRu)(3)B(3)H(8) analogous to H(2)Os(6)(CO)(16) and capped octahedral (CpRh)(3)B(4)H(4) analogous to Os(7)(CO)(21). In the metallaborane structures closely related to metal-free boranes, the favored degrees of BH and CpM vertices appear to be 5 and 6, respectively.

Density Functional Theory Study of Nine-Atom Germanium Clusters: Effect of Electron Count on Cluster Geometry

Density functional theory (DFT) at the hybrid B3LYP level has been applied to the germanium clusters Ge(9)(z) clusters (z = -6, -4, -3, -2, 0, +2, and +4) starting from three different initial configurations. Double-zeta quality LANL2DZ basis functions extended by adding one set of polarization (d) and one set of diffuse (p) functions were used. The global minimum for Ge(9)(2)(-) is the tricapped trigonal prism expected by Wade's rules for a 2n + 2 skeletal electron structure. An elongated tricapped trigonal prism is the global minimum for Ge(9)(4)(-) similar to the experimentally found structure for the isoelectronic Bi(9)(5+). However, the capped square antiprism predicted by Wade's rules for a 2n + 4 skeletal electron structure is only 0.21 kcal/mol above this global minimum indicating that these two nine-vertex polyhedra have very similar energies in this system. Tricapped trigonal prismatic structures are found for both singlet and triplet Ge(9)(6)(-), with the latter being lower in energy by 3.66 kcal/mol and far less distorted. The global minimum for the hypoelectronic Ge(9) is a bicapped pentagonal bipyramid. However, a second structure for Ge(9) only 4.54 kcal/mol above this global minimum is the C(2)(v)() flattened tricapped trigonal prism structure found experimentally for the isoelectronic Tl(9)(9)(-). For the even more hypoelectronic Ge(9)(2+), the lowest energy structure consists of an octahedron fused to two trigonal bipyramids. For Ge(9)(4+), the global minimum is an oblate (squashed) pentagonal bipyramid with two pendant Ge vertices.

Defective vertices in arachno borane networks

Triangulated boron networks can be described in terms of the deviation of their local vertex environments from the degree 5 vertices found in ideal icosahedra. Vertices of degrees other than 5 or equivalent are considered to be defective vertices. This method, which was previously applied to deltahedral borane anions B(n)H(n)(2-) and nido-B(n)H(n+4) boranes, has now been applied to arachno boranes of the types B(n)H(n+6) and B(n)H(n+5)(-) (4 < or = n < or = 10). The known structures of the neutral arachno boranes B(4)H(10), B(8)H(14), and n-B(9)H(15) consist of triangulated boron networks with no defective vertices in accord with their higher stabilities relative to other neutral arachno boranes. In other structures of known arachno boranes, there are relatively small numbers of defective vertices, and these are isolated as far as possible from each other.

Flattening of rhodium vertices in mixed rhodium-nickel carbonyl clusters: relationships to borane and zintl ion structures

The flattened deltahedra and related polyhedra found in hypoelectronic bare group 13 metal cluster anions are also found in some anionic mixed rhodium-nickel carbonyl clusters. In all cases the rhodium vertices rather than the nickel vertices are involved in the flattening process so that the rhodium vertices contribute four internal orbitals and the nickel vertices three internal orbitals to the skeletal bonding of the cluster. Thus, the 11-vertex cluster Rh(5)Ni(6)(CO)(21)(3-) has a D(3h) triflattened pentacapped trigonal prismatic structure similar to that found in the In(11)(7-) anion of the intermetallic K(8)In(11). Similarly the polyhedra in the 11-vertex cluster RhNi(10)(CO)(19)(3-) and the 9-vertex cluster Rh(3)Ni(6)(CO)(17)(3-) are both derived from a 10-vertex isocloso polyhedron by capping (for RhNi(10)(CO)(19)(3-)) or vertex removal (for Rh(3)Ni(6)(CO)(17)(3-)) followed by flattening all of the rhodium vertices. A D(3h) icosahedron with flattened rhodium vertices is found in the 12-vertex cluster Rh(3)Ni(9)(CO)(22)(3-).

Defective vertices in closo- and nido-borane polyhedra

Boron polyhedra can be described in terms of the deviation of their local vertex environments from the degree 5 vertices found in ideal icosahedra. Vertices of degrees other than 5 can be considered to be defective vertices. The most favorable structures for borane polyhedra are those in which the defective vertices are isolated as much as possible, similar to the Frank-Kasper polyhedra found in metal alloy structures. Using this criterion, the 9- and 10-vertex borane deltahedra are seen to be more favorable than the other nonicosahedral deltahedra in the boranes B(n)H(n)(2-) (6 < or = n < or = 12) in accord with experimental observations. Extension of such ideas to neutral boron hydrides of the type B(n)H(n+4) accounts for the relatively high stability of B(10)H(14), the formation of metal complexes of B(6)H(10), and the stability of B(18)H(22). In addition, the borane B(12)H(16) is predicted to form stable transition-metal complexes.

Binuclear homoleptic copper carbonyls Cu(2)(CO)(x) (x = 1-6): remarkable structures contrasting metal-metal multiple bonding with low-dimensional copper bonding manifolds

Binuclear homoleptic copper carbonyls Cu(2)(CO)(x) (x = 1-6) have been studied using four different density functional theory methods (DFT) in conjunction with a basis set of extended double-zeta plus polarization quality, labeled as DZP. For each homoleptic binuclear copper carbonyl compound, several stationary point structures are presented, and these structures are characterized in terms of their geometries, thermochemistry, and vibrational frequencies. The optimal unsaturated Cu(2)(CO)(x) (x = 1-6) structures are generated by joining 18-electron tetrahedral, 16-electron trigonal, 14-electron linear copper carbonyl building blocks, and/or bare copper atoms with copper-copper single bonds rather than by joining 18-electron copper carbonyl units with multiple copper-copper bonds. For Cu(2)(CO)(6) the eclipsed and staggered ethane-like structure are virtually degenerate and lie significantly lower in energy than other possible structures. The eclipsed Cu-Cu single bond distance is predicted to be 2.61 A, while that for the staggered structure is 2.65 A. The lowest energy structure for Cu(2)(CO)(5) is the eclipsed ethyl radical-like structure, with r(e)(Cu-Cu) = 2.51 A. The staggered ethyl radical-like structure lies only 0.1 kcal/mol higher in energy, with a Cu-Cu distance shorter by only approximately 0.001 A. For Cu(2)(CO)(4) a methylcarbene-like structure is predicted to lie lowest, with Cu-Cu distance 2.40 A. However, twisted and planar ethylene-like structure lie only 3-5 kcal/mol higher. For Cu(2)(CO)(3) a surprising methylcarbyne-like structure with r(e)(Cu-Cu) = 2.38 A is predicted to lie lowest with all four DFT methods. However, a classical vinyl radical-like lies only 2-4 kcal/mol higher. For Cu(2)(CO)(2) theory predicts a vinylidene-like structure with r(e)(Cu-Cu) = 2.34 A to be essentially degenerate with cis and trans bent acetylene structures with copper-copper distances 2.33 A. Finally, and consistent with earlier theoretical studies, the linear end on Cu-Cu-CO structure with r(e)(Cu-Cu) = 2.27 A is the predicted global minimum for Cu(2)(CO).

Nonhanded chirality in octahedral metal complexes

Chiral molecules can either be handed (i.e., "shoes") or nonhanded ("potatoes"). The only chiral ligand partition for tetrahedral metal complexes (or for a tetrahedral carbon atom such as that found in amino acids and other chiral biological molecules) is the fully unsymmetrical degree 6 partition (1(4)), which leads to handed metal complexes of the type MABCD with a lowest-degree chirality polynomial consisting of the product of all six possible linear factors of the type (s(i)-s(j)) where 1 < or = i,j < or = 4. The lowest-degree chiral ligand partitions for octahedral metal complexes are the degree 6 partitions (31(3)) and (2(3)) leading to handed chiral metal complexes of the types fac-MA(3)BCD and cis-MA(2)B(2)C(2). The form of the lowest-degree chirality polynomial for the (31(3)) chiral ligand partition of the octahedron resembles that of the (1(4)) chiral ligand partition of the tetrahedron, likewise with four different ligands. However, the form of the lowest-degree chirality polynomial for the (2(3)) chiral ligand partition of the octahedron corresponds to the square of the chirality polynomial of the (1(3)) chiral ligand partition of the polarized triangle, which likewise has three different ligands. Ligand partitions for octahedral metal complexes such as (2(2)1(2)), (21(4)), and (1(6)), which are less symmetrical than the lowest-degree chiral ligand partitions (31(3)) and (2(3)), lead to chiral octahedral metal complexes which are nonhanded. In such complexes, pairs of enantiomers can be interconverted by simple ligand interchanges without ever going through an achiral intermediate.

Transition to home care after stroke: depression, physical health, and adaptive processes in support persons

A longitudinal design was used to examine adaptation in primary support persons (PSP) of stroke survivors during the transition from hospitalization (T1) to home care (T2). The major purposes of the study were (a) to examine changes in depression, physical health, and contextual and coping factors from hospitalization of the stroke survivor through the first 6-10 weeks of home care; and (b) to identify predictors of depression. Data (N = 136) were collected on depression, physical health, background, survivor illness, and social environmental variables; appraisal of impact; social support resources; and coping skills. Reduction in mean PSP depression was significant at T2, but the change in physical health was not significant. Significant changes occurred in survivor function, family functioning, and three of six coping skills. Hierarchical multiple regression analyses were used to predict depression. T1 variables accounted for 29% of the variance in T1 PSP depression, with gender and appraisal of impact the strongest of seven predictors. T1 depression, T2 health, family functioning, and avoidance coping were the strongest of seven predictors, explaining 50% of the variance in T2 depression. Findings highlight the importance of maintaining caregiver health and preventing depression and identify variables to target for the reduction of PSP depression.

Three-dimensional aromaticity in polyhedral boranes and related molecules

Chemical bonding models based on graph theory or tensor surface harmonic theory demonstrate the analogy between the aromaticity in two-dimensional planar polygonal hydrocarbons such as benzene and that in three-dimensional deltahedral borane anions of the type BnHn2- (6 < or = n < or = 12). Such models are supported both by diverse computational studies and experimental determinations of electron density distribution. Related methods can be used to study the chemical bonding in the boron polyhedra found in other structures including neutral binary boron hydrides, metallaboranes, various allotropes of elemental boron, and boron-rich solid-state metal borides.

Aromaticity in transition metal oxide structures

The concept of aromaticity is useful for understanding the properties of some polyoxometalates containing transition metals such as vanadium, molybdenum, and tungsten having structures based on metal macropolygons and macropolyhedra with M-O-M edges. Thus, the aromatic macrocuboctahedral Keggin ions readily undergo one-electron reductions to highly colored mixed-valence "blues" (e.g., molybdenum blue), whereas the macroicosahedral Silverton ions, M(IV)Mo12O42(8-) (M(IV) = Ce, Th, U), which, like cyclohexane, do not have vertex valence orbitals available for delocalization, do not undergo analogous reduction reactions. A macrohexagon of d1 vanadium(IV) atoms as V-O-V units has been imbedded into an electronically inactive borate matrix in the ion [V6B20O50H8](8-). The small beta unit for the V-O-V interactions in this V6 macrohexagon leads to an unprecedented example of high spin aromaticity with a paramagnetism corresponding to four unpaired electrons per V6 unit in contrast to benzene, which is diamagnetic and hence exhibits low spin aromaticity. The M-O-M interactions in these aromatic metal oxides are closely related to the Cu-O-Cu interactions in the high critical temperature superconducting copper oxides which are essential to the electron transport in these systems.

Some Examples of Unusual Skeletal Bonding Topologies in Metallaboranes Containing Two or Three Early Transition Metal Vertices

The metallaboranes (CpM)(2)B(n)H(n+4) (M = Cr, Mo, W; n = 4, 5; Cp = eta(5)-C(5)H(5), eta(5)-C(5)Me(5)), (CpW)(2)B(7)H(9), (CpRe)(2)B(7)H(7), and (CpW)(3)B(8)H(9) have the 2v or 2v + 2 skeletal electrons for closo or isocloso deltahedra (v = number of polyhedral vertices) if the early transition metal vertices are assumed to contribute four or more internal orbitals rather than the usual three internal orbitals for BH vertices. The polyhedra for the metallaboranes (CpM)(2)B(n)H(n+4) (M = Cr, Mo, W; n = 4, 5) are derived from (n + 1)-gonal bipyramids by removal of an equatorial vertex. The deltahedra for the larger metallaboranes (CpW)(2)B(7)H(9), (CpRe)(2)B(7)H(7), and (CpW)(3)B(8)H(9) are derived from the corresponding B(n)H(n)(2)(-) deltahedra (n = 9 and 11 in these cases) by sufficient diamond-square-diamond processes to provide vertices of degrees > or = 6 for each of the CpM vertices. Reasonable skeletal bonding topologies in accord with the availability of skeletal electrons and orbitals consist of surface 2c-2e and 3c-2e bonds supplemented by metal-metal bonding through the center of the polyhedron.

Delayed onset of hemidystonia and hemiballismus following head injury: a clinicopathological correlation. Case report

The authors report the case of a young man who suffered multiple injuries in a motor vehicle accident, the most significant of which arose in the brain, creating an unusual clinical syndrome. After experiencing an initial coma for several days, the patient was found to have a right-sided homonymous hemianopsia and a right hemiparesis, which was more marked at the shoulder and was accompanied by preservation of finger movement. Dystonic movements appeared 2 months later and progressed, along with increased spasticity on volition, to severe uncontrolled arm movements at 2 years postinjury. This motor disorder continued to worsen during the following 6 years prior to the patient's death. At autopsy, the left side of the brain was observed to have marked atrophy of the optic tract, a partial lesion of the posterior portion of the medial segment of the globus pallidus (GP), and a reduction in the size of the internal capsule at the level of the GP, suggesting impaired circulation to these areas at the time of injury. The isolated lesion of the internal segment of the GP was the presumed cause of the dystonia, acting through an alteration in thalamic inhibition. The atrophic subthalamic nucleus was the probable cause of the hemiballismus. The authors speculate that this and other delayed and progressive features of this case were the result of an active, but disordered, adaptive process that failed to compensate and, instead, caused even greater problems than the original injury.

Chemical applications of topology and group theory. 34. Structure and bonding in titanocarbohedrene cages

Chemical bonding models are developed for the titanocarbohedrenes Ti14C13 and Ti8C12 by assuming that the Ti atoms use a six-orbital sd5 manifold and there is no direct Ti...Ti bonding. In the 3 x 3 x 3 cubic structure of Ti14C13, the 8 Ti atoms at the vertices of the cube are divided into two tetrahedral sets, one Ti(III) set and one Ti(IV) set, and the 6 Ti atoms at the midpoints of the cube faces exhibit square planar TiC4 coordination with two perpendicular three-center four-electron bonds. The energetically unfavorable Th dodecahedral structure for Ti8C12 has 8 equivalent Ti(III) atoms and C2(4-) units derived from the complete deprotonation of ethylene. In the more energetically favorable Td tetracapped tetrahedral structure for Ti8C12, the C2 units are formally dianions and the 8 Ti atoms are partitioned into inner tetrahedra (Ti(i)) bonded to the C2 units through three-center Ti-C2 bonds and outer tetrahedra (Ti degrees) bonded to the C2 units through two-center Ti-C bonds. The Ti atoms in one of the Ti4 tetrahedra are Ti(0) and those in the other Ti4 tetrahedron are Ti(III). Among the two such possibilities, the lower energy form has the (Ti0)o4(Ti(III))i4 configuration, corresponding to dicarbene C2 ligands with two unpaired electrons in the carbon-carbon pi-bonding similar to the multiple bond in triplet O2. This contrasts with the opposite (Ti(III)o4(Ti0)i4 configuration in the higher energy form of Th-Ti8C12, corresponding to ethynediyl ligands with full C...C triple bonds and unpaired electrons in the C sp hybrid orbitals for sigma-bonding to Ti.

Motor neuron presentation of an ulnar neuropathy and Riche-Cannieu anastomosis

A Riche (7)-Cannieu (2) anastomosis (ulnar-to-median anastomosis in the hand) in the setting of an ulnar or median nerve lesion can produce confusing clinical and electrodiagnostic findings. We report a patient with a deep branch ulnar neuropathy complicated by a Riche-Cannieu anastomosis. His clinical presentation led to an initial diagnosis of motor neuron disease. Extensive electrophysiologic studies clarified the extent of the Riche-Cannieu anastomosis and the ulnar neuropathy.

A (13)C NMR double-labeling method to quantitate local myocardial O(2) consumption using frozen tissue samples

Measurement of local myocardial O(2) consumption (VO(2)) has been problematic but is needed to investigate the heterogeneity of aerobic metabolism. The goal of the present investigation was to develop a method to measure local VO(2) using small frozen myocardial samples, suitable for determining VO(2) profiles. In 26 isolated rabbit hearts, 1.5 mmol/l [2-(13)C]acetate was infused for 4 min, followed by 1.5 min of [1,2-(13)C]acetate. The left ventricular (LV) free wall was then quickly frozen. High-resolution (13)C-NMR spectra were measured from extracts taken from 2- to 3-mm thick transmural layer samples. The multiplet intensities of glutamate were analyzed with a computer model allowing simultaneous estimation of the absolute flux through the tricarboxylic acid cycle and the fractional contribution of acetate to acetyl CoA formation from which local VO(2) was calculated. The (13)C-derived VO(2) in the LV free wall was linearly related to "gold standard" VO(2) from coronary venous O(2) electrode measurements in the same region (r = 0.932, n = 22, P < 0.0001, slope 1.05) for control and lowered metabolic rates. The ratio of subendocardial to subepicardial VO(2) was 1.52 +/- 0.19 (SE, significantly >1, P < 0.025). Local myocardial VO(2) can now be quantitated with this new (13)C method to determine profiles of aerobic energy metabolism.